[PATCH 0/2] block layer filter and block device snapshot module

[PATCH 0/2] block layer filter and block device snapshot module

[Sergei Shtepa]

Hello everyone! Requesting for your comments and suggestions.

# blk-filter

Block layer filter allows to intercept BIO requests to a block device.

Interception is performed at the very beginning of the BIO request
processing, and therefore does not affect the operation of the request
processing queue. This also makes it possible to intercept requests from
a specific block device, rather than from the entire disk.

The logic of the submit_bio function has been changed - since the
function execution results are not processed anywhere (except for swap
and direct-io) the function won't return a value anymore.

Now the submit_bio_direct() function is called whenever the result of
the blk_qc_t function is required. submit_bio_direct() is not
intercepted by the block layer filter. This is logical for swap and
direct-io.

Block layer filter allows you to enable and disable the filter driver on
the fly. When a new block device is added, the filter driver can start
filtering this device. When you delete a device, the filter can remove
its own filter.

The idea of multiple altitudes had to be abandoned in order to simplify
implementation and make it more reliable. Different filter drivers can
work simultaneously, but each on its own block device.

# blk-snap

We propose a new kernel module - blk-snap. This module implements
snapshot and changed block tracking functionality. It is intended to
create backup copies of any block devices without usage of device mapper.
Snapshots are temporary and are destroyed after the backup process has
finished. Changed block tracking allows for incremental and differential
backup copies.

blk-snap uses block layer filter. Block layer filter provides a callback
to intercept bio-requests. If a block device disappears for whatever
reason, send a synchronous request to remove the device from filtering.

blk-snap kernel module is a product of a deep refactoring of the
out-of-tree kernel veeamsnap kernel module
(https://github.com/veeam/veeamsnap/):
* all conditional compilation branches that served for the purpose of
  compatibility with older kernels have been removed;
* linux kernel code style has been applied;
* blk-snap mostly takes advantage of the existing kernel code instead of
  reinventing the wheel;
* all redundant code (such as persistent cbt and snapstore collector)
  has been removed.

Several important things are still have to be done:
* refactor the module interface for interaction with a user-space code -
  it is already clear that the implementation of some calls can be
  improved.

Your feedback would be greatly appreciated!

Sergei Shtepa (2):
  Block layer filter - second version
  blk-snap - snapshots and change-tracking for block devices

 block/Kconfig                               |  11 +
 block/Makefile                              |   1 +
 block/blk-core.c                            |  52 +-
 block/blk-filter-internal.h                 |  29 +
 block/blk-filter.c                          | 286 ++++++
 block/partitions/core.c                     |  14 +-
 drivers/block/Kconfig                       |   2 +
 drivers/block/Makefile                      |   1 +
 drivers/block/blk-snap/Kconfig              |  24 +
 drivers/block/blk-snap/Makefile             |  28 +
 drivers/block/blk-snap/big_buffer.c         | 193 ++++
 drivers/block/blk-snap/big_buffer.h         |  24 +
 drivers/block/blk-snap/blk-snap-ctl.h       | 190 ++++
 drivers/block/blk-snap/blk_deferred.c       | 566 +++++++++++
 drivers/block/blk-snap/blk_deferred.h       |  67 ++
 drivers/block/blk-snap/blk_descr_file.c     |  82 ++
 drivers/block/blk-snap/blk_descr_file.h     |  26 +
 drivers/block/blk-snap/blk_descr_mem.c      |  66 ++
 drivers/block/blk-snap/blk_descr_mem.h      |  14 +
 drivers/block/blk-snap/blk_descr_multidev.c |  86 ++
 drivers/block/blk-snap/blk_descr_multidev.h |  25 +
 drivers/block/blk-snap/blk_descr_pool.c     | 190 ++++
 drivers/block/blk-snap/blk_descr_pool.h     |  38 +
 drivers/block/blk-snap/blk_redirect.c       | 507 ++++++++++
 drivers/block/blk-snap/blk_redirect.h       |  73 ++
 drivers/block/blk-snap/blk_util.c           |  33 +
 drivers/block/blk-snap/blk_util.h           |  33 +
 drivers/block/blk-snap/cbt_map.c            | 210 +++++
 drivers/block/blk-snap/cbt_map.h            |  62 ++
 drivers/block/blk-snap/common.h             |  31 +
 drivers/block/blk-snap/ctrl_fops.c          | 691 ++++++++++++++
 drivers/block/blk-snap/ctrl_fops.h          |  19 +
 drivers/block/blk-snap/ctrl_pipe.c          | 562 +++++++++++
 drivers/block/blk-snap/ctrl_pipe.h          |  34 +
 drivers/block/blk-snap/ctrl_sysfs.c         |  73 ++
 drivers/block/blk-snap/ctrl_sysfs.h         |   5 +
 drivers/block/blk-snap/defer_io.c           | 397 ++++++++
 drivers/block/blk-snap/defer_io.h           |  39 +
 drivers/block/blk-snap/main.c               |  82 ++
 drivers/block/blk-snap/params.c             |  58 ++
 drivers/block/blk-snap/params.h             |  29 +
 drivers/block/blk-snap/rangevector.c        |  85 ++
 drivers/block/blk-snap/rangevector.h        |  31 +
 drivers/block/blk-snap/snapimage.c          | 982 ++++++++++++++++++++
 drivers/block/blk-snap/snapimage.h          |  16 +
 drivers/block/blk-snap/snapshot.c           | 225 +++++
 drivers/block/blk-snap/snapshot.h           |  17 +
 drivers/block/blk-snap/snapstore.c          | 929 ++++++++++++++++++
 drivers/block/blk-snap/snapstore.h          |  68 ++
 drivers/block/blk-snap/snapstore_device.c   | 532 +++++++++++
 drivers/block/blk-snap/snapstore_device.h   |  63 ++
 drivers/block/blk-snap/snapstore_file.c     |  52 ++
 drivers/block/blk-snap/snapstore_file.h     |  15 +
 drivers/block/blk-snap/snapstore_mem.c      |  91 ++
 drivers/block/blk-snap/snapstore_mem.h      |  20 +
 drivers/block/blk-snap/snapstore_multidev.c | 118 +++
 drivers/block/blk-snap/snapstore_multidev.h |  22 +
 drivers/block/blk-snap/tracker.c            | 449 +++++++++
 drivers/block/blk-snap/tracker.h            |  38 +
 drivers/block/blk-snap/tracking.c           | 270 ++++++
 drivers/block/blk-snap/tracking.h           |  13 +
 drivers/block/blk-snap/version.h            |   7 +
 fs/block_dev.c                              |   6 +-
 fs/direct-io.c                              |   2 +-
 fs/iomap/direct-io.c                        |   2 +-
 include/linux/bio.h                         |   4 +-
 include/linux/blk-filter.h                  |  76 ++
 include/linux/genhd.h                       |   8 +-
 kernel/power/swap.c                         |   2 +-
 mm/page_io.c                                |   4 +-
 70 files changed, 9074 insertions(+), 26 deletions(-)
 create mode 100644 block/blk-filter-internal.h
 create mode 100644 block/blk-filter.c
 create mode 100644 drivers/block/blk-snap/Kconfig
 create mode 100644 drivers/block/blk-snap/Makefile
 create mode 100644 drivers/block/blk-snap/big_buffer.c
 create mode 100644 drivers/block/blk-snap/big_buffer.h
 create mode 100644 drivers/block/blk-snap/blk-snap-ctl.h
 create mode 100644 drivers/block/blk-snap/blk_deferred.c
 create mode 100644 drivers/block/blk-snap/blk_deferred.h
 create mode 100644 drivers/block/blk-snap/blk_descr_file.c
 create mode 100644 drivers/block/blk-snap/blk_descr_file.h
 create mode 100644 drivers/block/blk-snap/blk_descr_mem.c
 create mode 100644 drivers/block/blk-snap/blk_descr_mem.h
 create mode 100644 drivers/block/blk-snap/blk_descr_multidev.c
 create mode 100644 drivers/block/blk-snap/blk_descr_multidev.h
 create mode 100644 drivers/block/blk-snap/blk_descr_pool.c
 create mode 100644 drivers/block/blk-snap/blk_descr_pool.h
 create mode 100644 drivers/block/blk-snap/blk_redirect.c
 create mode 100644 drivers/block/blk-snap/blk_redirect.h
 create mode 100644 drivers/block/blk-snap/blk_util.c
 create mode 100644 drivers/block/blk-snap/blk_util.h
 create mode 100644 drivers/block/blk-snap/cbt_map.c
 create mode 100644 drivers/block/blk-snap/cbt_map.h
 create mode 100644 drivers/block/blk-snap/common.h
 create mode 100644 drivers/block/blk-snap/ctrl_fops.c
 create mode 100644 drivers/block/blk-snap/ctrl_fops.h
 create mode 100644 drivers/block/blk-snap/ctrl_pipe.c
 create mode 100644 drivers/block/blk-snap/ctrl_pipe.h
 create mode 100644 drivers/block/blk-snap/ctrl_sysfs.c
 create mode 100644 drivers/block/blk-snap/ctrl_sysfs.h
 create mode 100644 drivers/block/blk-snap/defer_io.c
 create mode 100644 drivers/block/blk-snap/defer_io.h
 create mode 100644 drivers/block/blk-snap/main.c
 create mode 100644 drivers/block/blk-snap/params.c
 create mode 100644 drivers/block/blk-snap/params.h
 create mode 100644 drivers/block/blk-snap/rangevector.c
 create mode 100644 drivers/block/blk-snap/rangevector.h
 create mode 100644 drivers/block/blk-snap/snapimage.c
 create mode 100644 drivers/block/blk-snap/snapimage.h
 create mode 100644 drivers/block/blk-snap/snapshot.c
 create mode 100644 drivers/block/blk-snap/snapshot.h
 create mode 100644 drivers/block/blk-snap/snapstore.c
 create mode 100644 drivers/block/blk-snap/snapstore.h
 create mode 100644 drivers/block/blk-snap/snapstore_device.c
 create mode 100644 drivers/block/blk-snap/snapstore_device.h
 create mode 100644 drivers/block/blk-snap/snapstore_file.c
 create mode 100644 drivers/block/blk-snap/snapstore_file.h
 create mode 100644 drivers/block/blk-snap/snapstore_mem.c
 create mode 100644 drivers/block/blk-snap/snapstore_mem.h
 create mode 100644 drivers/block/blk-snap/snapstore_multidev.c
 create mode 100644 drivers/block/blk-snap/snapstore_multidev.h
 create mode 100644 drivers/block/blk-snap/tracker.c
 create mode 100644 drivers/block/blk-snap/tracker.h
 create mode 100644 drivers/block/blk-snap/tracking.c
 create mode 100644 drivers/block/blk-snap/tracking.h
 create mode 100644 drivers/block/blk-snap/version.h
 create mode 100644 include/linux/blk-filter.h

--
2.20.1

[PATCH 1/2] Block layer filter - second version

[Sergei Shtepa]

Signed-off-by: Sergei Shtepa <sergei.shtepa@veeam.com>
---
 block/Kconfig               |  11 ++
 block/Makefile              |   1 +
 block/blk-core.c            |  52 +++++--
 block/blk-filter-internal.h |  29 ++++
 block/blk-filter.c          | 286 ++++++++++++++++++++++++++++++++++++
 block/partitions/core.c     |  14 +-
 fs/block_dev.c              |   6 +-
 fs/direct-io.c              |   2 +-
 fs/iomap/direct-io.c        |   2 +-
 include/linux/bio.h         |   4 +-
 include/linux/blk-filter.h  |  76 ++++++++++
 include/linux/genhd.h       |   8 +-
 kernel/power/swap.c         |   2 +-
 mm/page_io.c                |   4 +-
 14 files changed, 471 insertions(+), 26 deletions(-)
 create mode 100644 block/blk-filter-internal.h
 create mode 100644 block/blk-filter.c
 create mode 100644 include/linux/blk-filter.h

diff --git a/block/Kconfig b/block/Kconfig
index bbad5e8bbffe..a308801b4376 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -204,6 +204,17 @@ config BLK_INLINE_ENCRYPTION_FALLBACK
 	  by falling back to the kernel crypto API when inline
 	  encryption hardware is not present.
 
+config BLK_FILTER
+	bool "Enable support for block layer filters"
+	default y
+	depends on MODULES
+	help
+	  Enabling this lets third-party kernel modules intercept
+	  bio requests for any block device. This allows them to implement
+	  changed block tracking and snapshots without any reconfiguration of
+	  the existing setup. For example, this option allows snapshotting of
+	  a block device without adding it to LVM.
+
 menu "Partition Types"
 
 source "block/partitions/Kconfig"
diff --git a/block/Makefile b/block/Makefile
index 8d841f5f986f..b8ee50b8e031 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -38,3 +38,4 @@ obj-$(CONFIG_BLK_SED_OPAL)	+= sed-opal.o
 obj-$(CONFIG_BLK_PM)		+= blk-pm.o
 obj-$(CONFIG_BLK_INLINE_ENCRYPTION)	+= keyslot-manager.o blk-crypto.o
 obj-$(CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK)	+= blk-crypto-fallback.o
+obj-$(CONFIG_BLK_FILTER)	+= blk-filter.o
diff --git a/block/blk-core.c b/block/blk-core.c
index 10c08ac50697..cc06402af695 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1216,23 +1216,20 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
 EXPORT_SYMBOL(submit_bio_noacct);
 
 /**
- * submit_bio - submit a bio to the block device layer for I/O
- * @bio: The &struct bio which describes the I/O
- *
- * submit_bio() is used to submit I/O requests to block devices.  It is passed a
- * fully set up &struct bio that describes the I/O that needs to be done.  The
- * bio will be send to the device described by the bi_disk and bi_partno fields.
+ * submit_bio_direct - submit a bio to the block device layer for I/O
+ * bypass filter.
+ * @bio:  The bio describing the location in memory and on the device.
  *
- * The success/failure status of the request, along with notification of
- * completion, is delivered asynchronously through the ->bi_end_io() callback
- * in @bio.  The bio must NOT be touched by thecaller until ->bi_end_io() has
- * been called.
+ * Description:
+ *    This is a version of submit_bio() that shall only be used for I/O
+ *    that cannot be intercepted by block layer filters.
+ *    All file systems and other upper level users of the block layer
+ *    should use submit_bio() instead.
+ *    Use this function to access the swap partition and directly access
+ *    the block device file.
  */
-blk_qc_t submit_bio(struct bio *bio)
+blk_qc_t submit_bio_direct(struct bio *bio)
 {
-	if (blkcg_punt_bio_submit(bio))
-		return BLK_QC_T_NONE;
-
 	/*
 	 * If it's a regular read/write or a barrier with data attached,
 	 * go through the normal accounting stuff before submission.
@@ -1282,8 +1279,35 @@ blk_qc_t submit_bio(struct bio *bio)
 
 	return submit_bio_noacct(bio);
 }
+EXPORT_SYMBOL(submit_bio_direct);
+
+/**
+ * submit_bio - submit a bio to the block device layer for I/O
+ * @bio: The &struct bio which describes the I/O
+ *
+ * submit_bio() is used to submit I/O requests to block devices.  It is passed a
+ * fully set up &struct bio that describes the I/O that needs to be done.  The
+ * bio will be send to the device described by the bi_disk and bi_partno fields.
+ *
+ * The success/failure status of the request, along with notification of
+ * completion, is delivered asynchronously through the ->bi_end_io() callback
+ * in @bio.  The bio must NOT be touched by thecaller until ->bi_end_io() has
+ * been called.
+ */
+void submit_bio(struct bio *bio)
+{
+	if (blkcg_punt_bio_submit(bio))
+		return;
+
+#ifdef CONFIG_BLK_FILTER
+	blk_filter_submit_bio(bio);
+#else
+	submit_bio_direct(bio);
+#endif
+}
 EXPORT_SYMBOL(submit_bio);
 
+
 /**
  * blk_cloned_rq_check_limits - Helper function to check a cloned request
  *                              for the new queue limits
diff --git a/block/blk-filter-internal.h b/block/blk-filter-internal.h
new file mode 100644
index 000000000000..d456a09f50db
--- /dev/null
+++ b/block/blk-filter-internal.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ *
+ * Block device filters internal declarations
+ */
+
+#ifndef BLK_FILTER_INTERNAL_H
+#define BLK_FILTER_INTERNAL_H
+
+#ifdef CONFIG_BLK_FILTER
+#include <linux/blk-filter.h>
+
+void blk_filter_part_add(struct hd_struct *part, dev_t devt);
+
+void blk_filter_part_del(struct hd_struct *part);
+
+#else /* CONFIG_BLK_FILTER */
+
+
+static inline void blk_filter_part_add(struct hd_struct *part, dev_t devt)
+{ };
+
+static inline void blk_filter_part_del(struct hd_struct *part)
+{ };
+
+#endif /* CONFIG_BLK_FILTER */
+
+#endif
diff --git a/block/blk-filter.c b/block/blk-filter.c
new file mode 100644
index 000000000000..f6de16c45a16
--- /dev/null
+++ b/block/blk-filter.c
@@ -0,0 +1,286 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/genhd.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include "blk-filter-internal.h"
+#include <linux/rwsem.h>
+
+
+LIST_HEAD(filters);
+DECLARE_RWSEM(filters_lock);
+
+static void blk_filter_release(struct kref *kref)
+{
+	struct blk_filter *flt = container_of(kref, struct blk_filter, kref);
+
+	kfree(flt);
+}
+
+static inline void blk_filter_get(struct blk_filter *flt)
+{
+	kref_get(&flt->kref);
+}
+
+static inline void blk_filter_put(struct blk_filter *flt)
+{
+	kref_put(&flt->kref, blk_filter_release);
+}
+
+
+/**
+ * blk_filter_part_add() - Notify filters when a new partition is added.
+ * @part: The partition for new block device.
+ * @devt: Device id for new block device.
+ *
+ * Description:
+ *    When the block device is appears in the system, call the filter
+ *    callback to notify that the block device appears.
+ */
+void blk_filter_part_add(struct hd_struct *part, dev_t devt)
+{
+	down_read(&filters_lock);
+	if (!list_empty(&filters)) {
+		struct list_head *_list_head;
+
+		list_for_each(_list_head, &filters) {
+			void *filter_data;
+			bool attached = false;
+			struct blk_filter *flt;
+
+			flt = list_entry(_list_head, struct blk_filter, link);
+
+			attached = flt->ops->part_add(devt, &filter_data);
+			if (attached) {
+				blk_filter_get(flt);
+				part->filter = flt;
+				part->filter_data = filter_data;
+				break;
+			}
+		}
+	}
+	up_read(&filters_lock);
+}
+
+/**
+ * blk_filter_part_del() - Notify filters when the partition is deleted.
+ * @part: The partition of block device.
+ *
+ * Description:
+ *    When the block device is destroying and the partition is releasing,
+ *    call the filter callback to notify that the block device will be
+ *    deleted.
+ */
+void blk_filter_part_del(struct hd_struct *part)
+{
+	struct blk_filter *flt = part->filter;
+
+	if (!flt)
+		return;
+
+	flt->ops->part_del(part->filter_data);
+
+	part->filter_data = NULL;
+	part->filter = NULL;
+	blk_filter_put(flt);
+}
+
+
+/**
+ * blk_filter_submit_bio() - Send new bio to filters for processing.
+ * @bio: The new bio for block I/O layer.
+ *
+ * Description:
+ *    This function is an implementation of block layer filter
+ *    interception. If the filter is attached to this block device,
+ *    then bio will be redirected to the filter kernel module.
+ */
+void blk_filter_submit_bio(struct bio *bio)
+{
+	bool intercepted = false;
+	struct hd_struct *part;
+
+	bio_get(bio);
+
+	part = disk_get_part(bio->bi_disk, bio->bi_partno);
+	if (unlikely(!part)) {
+		bio->bi_status = BLK_STS_IOERR;
+		bio_endio(bio);
+
+		bio_put(bio);
+		return;
+	}
+
+	down_read(&part->filter_rw_lockup);
+
+	if (part->filter)
+		intercepted = part->filter->ops->filter_bio(bio, part->filter_data);
+
+	up_read(&part->filter_rw_lockup);
+
+	if (!intercepted)
+		submit_bio_direct(bio);
+
+	disk_put_part(part);
+
+	bio_put(bio);
+}
+EXPORT_SYMBOL(blk_filter_submit_bio);
+
+/**
+ * blk_filter_register() - Register block layer filter.
+ * @ops: New filter callbacks.
+ *
+ * Return:
+ *     Filter ID, a pointer to the service structure of the filter.
+ *
+ * Description:
+ *    Create new filter structure.
+ *    Use blk_filter_attach to attach devices to filter.
+ */
+void *blk_filter_register(struct blk_filter_ops *ops)
+{
+	struct blk_filter *flt;
+
+	flt = kzalloc(sizeof(struct blk_filter), GFP_KERNEL);
+	if (!flt)
+		return NULL;
+
+	kref_init(&flt->kref);
+	flt->ops = ops;
+
+	down_write(&filters_lock);
+	list_add_tail(&flt->link, &filters);
+	up_write(&filters_lock);
+
+	return flt;
+}
+EXPORT_SYMBOL(blk_filter_register);
+
+/**
+ * blk_filter_unregister() - Unregister block layer filter.
+ * @filter: filter identifier.
+ *
+ * Description:
+ *    Before call blk_filter_unregister() and unload filter module all
+ *    partitions MUST be detached. Otherwise, the system will have a
+ *    filter with non-existent interception functions.
+ */
+void blk_filter_unregister(void *filter)
+{
+	struct blk_filter *flt = filter;
+
+	down_write(&filters_lock);
+	list_del(&flt->link);
+	up_write(&filters_lock);
+
+	blk_filter_put(flt);
+}
+EXPORT_SYMBOL(blk_filter_unregister);
+
+/**
+ * blk_filter_attach() - Attach block layer filter.
+ * @devt: The block device identification number.
+ * @filter: Filter identifier.
+ * @filter_data: Specific filters data for this device.
+ *
+ * Return:
+ *    Return code.
+ *    -ENODEV - cannot find this device, it is OK if the device does not exist yet.
+ *    -EALREADY - this device is already attached to this filter.
+ *    -EBUSY - this device is already attached to the another filter.
+ *
+ * Description:
+ *    Attach the device to the block layer filter.
+ *    Only one filter can be attached to a single device.
+ */
+int blk_filter_attach(dev_t devt, void *filter, void *filter_data)
+{
+	int ret = 0;
+	struct blk_filter *flt = filter;
+	struct block_device *blk_dev;
+
+
+	blk_dev = bdget(devt);
+	if (!blk_dev)
+		return -ENODEV;
+
+	blk_filter_freeze(blk_dev);
+
+	if (blk_dev->bd_part->filter) {
+		if (blk_dev->bd_part->filter == flt)
+			ret = -EALREADY;
+		else
+			ret = -EBUSY;
+	} else {
+		blk_filter_get(flt);
+		blk_dev->bd_part->filter = flt;
+		blk_dev->bd_part->filter_data = filter_data;
+	}
+
+	blk_filter_thaw(blk_dev);
+
+	bdput(blk_dev);
+
+	return ret;
+}
+EXPORT_SYMBOL(blk_filter_attach);
+
+/**
+ * blk_filter_detach() - Detach block layer filter.
+ * @devt: The block device identification number.
+ *
+ * Description:
+ *    Detach the device from the block layer filter.
+ *    Do not forget detach all devices before calling the
+ *    blk_filter_unregister() function and unload the module!
+ */
+void blk_filter_detach(dev_t devt)
+{
+	struct blk_filter *flt;
+	struct block_device *blk_dev;
+
+	blk_dev = bdget(devt);
+	if (!blk_dev)
+		return;
+
+	blk_filter_freeze(blk_dev);
+
+	flt = blk_dev->bd_part->filter;
+	if (flt) {
+		blk_dev->bd_part->filter_data = NULL;
+		blk_dev->bd_part->filter = NULL;
+		blk_filter_put(flt);
+	}
+
+	blk_filter_thaw(blk_dev);
+
+	bdput(blk_dev);
+}
+EXPORT_SYMBOL(blk_filter_detach);
+
+/**
+ * blk_filter_freeze() - Lock bio submitting.
+ * @bdev: The block device pointer.
+ *
+ * Description:
+ *    Stop bio processing.
+ */
+void blk_filter_freeze(struct block_device *bdev)
+{
+	down_write(&bdev->bd_part->filter_rw_lockup);
+}
+EXPORT_SYMBOL(blk_filter_freeze);
+
+/**
+ * blk_filter_thaw() - Unlock bio submitting.
+ * @bdev: The block device pointer.
+ *
+ * Description:
+ *    Resume bio processing.
+ */
+void blk_filter_thaw(struct block_device *bdev)
+{
+	up_write(&bdev->bd_part->filter_rw_lockup);
+}
+EXPORT_SYMBOL(blk_filter_thaw);
diff --git a/block/partitions/core.c b/block/partitions/core.c
index 722406b841df..6b845e98b9a1 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -11,6 +11,7 @@
 #include <linux/blktrace_api.h>
 #include <linux/raid/detect.h>
 #include "check.h"
+#include "../blk-filter-internal.h"
 
 static int (*check_part[])(struct parsed_partitions *) = {
 	/*
@@ -320,9 +321,11 @@ int hd_ref_init(struct hd_struct *part)
  */
 void delete_partition(struct gendisk *disk, struct hd_struct *part)
 {
-	struct disk_part_tbl *ptbl =
-		rcu_dereference_protected(disk->part_tbl, 1);
+	struct disk_part_tbl *ptbl;
+
+	blk_filter_part_del(part);
 
+	ptbl = rcu_dereference_protected(disk->part_tbl, 1);
 	/*
 	 * ->part_tbl is referenced in this part's release handler, so
 	 *  we have to hold the disk device
@@ -412,6 +415,9 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
 	p->nr_sects = len;
 	p->partno = partno;
 	p->policy = get_disk_ro(disk);
+#ifdef CONFIG_BLK_FILTER
+	init_rwsem(&p->filter_rw_lockup);
+#endif
 
 	if (info) {
 		struct partition_meta_info *pinfo;
@@ -469,6 +475,9 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
 	/* everything is up and running, commence */
 	rcu_assign_pointer(ptbl->part[partno], p);
 
+	/*inform filter about a new partition*/
+	blk_filter_part_add(p, devt);
+
 	/* suppress uevent if the disk suppresses it */
 	if (!dev_get_uevent_suppress(ddev))
 		kobject_uevent(&pdev->kobj, KOBJ_ADD);
@@ -552,6 +561,7 @@ int bdev_del_partition(struct block_device *bdev, int partno)
 		goto out_unlock;
 
 	sync_blockdev(bdevp);
+
 	invalidate_bdev(bdevp);
 
 	delete_partition(bdev->bd_disk, part);
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 8ae833e00443..431eae17fd8f 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -237,7 +237,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
 	if (iocb->ki_flags & IOCB_HIPRI)
 		bio_set_polled(&bio, iocb);
 
-	qc = submit_bio(&bio);
+	qc = submit_bio_direct(&bio);
 	for (;;) {
 		set_current_state(TASK_UNINTERRUPTIBLE);
 		if (!READ_ONCE(bio.bi_private))
@@ -400,7 +400,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
 				polled = true;
 			}
 
-			qc = submit_bio(bio);
+			qc = submit_bio_direct(bio);
 
 			if (polled)
 				WRITE_ONCE(iocb->ki_cookie, qc);
@@ -421,7 +421,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
 			atomic_inc(&dio->ref);
 		}
 
-		submit_bio(bio);
+		submit_bio_direct(bio);
 		bio = bio_alloc(GFP_KERNEL, nr_pages);
 	}
 
diff --git a/fs/direct-io.c b/fs/direct-io.c
index 183299892465..d9bb1b6f6814 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -459,7 +459,7 @@ static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
 		sdio->submit_io(bio, dio->inode, sdio->logical_offset_in_bio);
 		dio->bio_cookie = BLK_QC_T_NONE;
 	} else
-		dio->bio_cookie = submit_bio(bio);
+		dio->bio_cookie = submit_bio_direct(bio);
 
 	sdio->bio = NULL;
 	sdio->boundary = 0;
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index c1aafb2ab990..e05f20ce8b5f 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -73,7 +73,7 @@ static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap,
 				file_inode(dio->iocb->ki_filp),
 				iomap, bio, pos);
 	else
-		dio->submit.cookie = submit_bio(bio);
+		dio->submit.cookie = submit_bio_direct(bio);
 }
 
 static ssize_t iomap_dio_complete(struct iomap_dio *dio)
diff --git a/include/linux/bio.h b/include/linux/bio.h
index c6d765382926..5b0a32697207 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -10,6 +10,7 @@
 #include <linux/ioprio.h>
 /* struct bio, bio_vec and BIO_* flags are defined in blk_types.h */
 #include <linux/blk_types.h>
+#include <linux/blk-filter.h>
 
 #define BIO_DEBUG
 
@@ -411,7 +412,8 @@ static inline struct bio *bio_kmalloc(gfp_t gfp_mask, unsigned int nr_iovecs)
 	return bio_alloc_bioset(gfp_mask, nr_iovecs, NULL);
 }
 
-extern blk_qc_t submit_bio(struct bio *);
+extern blk_qc_t submit_bio_direct(struct bio *bio);
+extern void submit_bio(struct bio *bio);
 
 extern void bio_endio(struct bio *);
 
diff --git a/include/linux/blk-filter.h b/include/linux/blk-filter.h
new file mode 100644
index 000000000000..f3e79e5b4586
--- /dev/null
+++ b/include/linux/blk-filter.h
@@ -0,0 +1,76 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * API declarations for kernel modules utilizing block device filters
+ */
+
+#ifndef BLK_FILTER_H
+#define BLK_FILTER_H
+
+#ifdef CONFIG_BLK_FILTER
+#include <linux/kref.h>
+
+struct blk_filter_ops {
+	/*
+	 * Intercept bio callback.
+	 *
+	 * Returns true if the request was intercepted and placed in the
+	 * queue for processing. Otherwise submit_bio_direct() calling
+	 * needed.
+	 */
+	bool (*filter_bio)(struct bio *bio, void *filter_data);
+
+	/*
+	 * Callback to a request to add block device to the filter.
+	 *
+	 * Returns true if the block device will be filtered.
+	 * p_filter_data gets a pointer to data that is unique to
+	 * this device.
+	 */
+	bool (*part_add)(dev_t devt, void **p_filter_data);
+
+	/*
+	 * Callback to remove block device from the filter.
+	 */
+	void (*part_del)(void *filter_data);
+};
+
+struct blk_filter {
+	struct list_head link;
+	struct kref kref;
+	struct blk_filter_ops *ops;
+};
+
+/*
+ * Register/unregister device to filter
+ */
+void *blk_filter_register(struct blk_filter_ops *ops);
+
+void blk_filter_unregister(void *filter);
+
+/*
+ * Attach/detach device to filter
+ */
+int blk_filter_attach(dev_t devt, void *filter, void *filter_data);
+
+void blk_filter_detach(dev_t devt);
+
+/*
+ * For a consistent state of the file system use the freeze_bdev/thaw_bdav.
+ * But in addition, to ensure that the filter is not in the state of
+ * intercepting the next BIO, you need to call black_filter_freeze/blk_filter_thaw.
+ * This is especially actual if there is no file system on the disk.
+ */
+
+void blk_filter_freeze(struct block_device *bdev);
+
+void blk_filter_thaw(struct block_device *bdev);
+
+/*
+ * Filters intercept function
+ */
+void blk_filter_submit_bio(struct bio *bio);
+
+#endif /* CONFIG_BLK_FILTER */
+
+#endif
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 4ab853461dff..514fab6b947e 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -4,7 +4,7 @@
 
 /*
  * 	genhd.h Copyright (C) 1992 Drew Eckhardt
- *	Generic hard disk header file by  
+ *	Generic hard disk header file by
  * 		Drew Eckhardt
  *
  *		<drew@colorado.edu>
@@ -75,6 +75,12 @@ struct hd_struct {
 	int make_it_fail;
 #endif
 	struct rcu_work rcu_work;
+
+#ifdef CONFIG_BLK_FILTER
+	struct rw_semaphore filter_rw_lockup; /* for freezing block device*/
+	struct blk_filter *filter; /* block layer filter*/
+	void *filter_data; /*specific for each block device filters data*/
+#endif
 };
 
 /**
diff --git a/kernel/power/swap.c b/kernel/power/swap.c
index 01e2858b5fe3..5287346b87a1 100644
--- a/kernel/power/swap.c
+++ b/kernel/power/swap.c
@@ -283,7 +283,7 @@ static int hib_submit_io(int op, int op_flags, pgoff_t page_off, void *addr,
 		bio->bi_end_io = hib_end_io;
 		bio->bi_private = hb;
 		atomic_inc(&hb->count);
-		submit_bio(bio);
+		submit_bio_direct(bio);
 	} else {
 		error = submit_bio_wait(bio);
 		bio_put(bio);
diff --git a/mm/page_io.c b/mm/page_io.c
index e485a6e8a6cd..4540426400b3 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -362,7 +362,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
 	count_swpout_vm_event(page);
 	set_page_writeback(page);
 	unlock_page(page);
-	submit_bio(bio);
+	submit_bio_direct(bio);
 out:
 	return ret;
 }
@@ -434,7 +434,7 @@ int swap_readpage(struct page *page, bool synchronous)
 	}
 	count_vm_event(PSWPIN);
 	bio_get(bio);
-	qc = submit_bio(bio);
+	qc = submit_bio_direct(bio);
 	while (synchronous) {
 		set_current_state(TASK_UNINTERRUPTIBLE);
 		if (!READ_ONCE(bio->bi_private))
-- 
2.20.1

Re: [PATCH 1/2] Block layer filter - second version

[Johannes Thumshirn]

On 21/10/2020 11:04, Sergei Shtepa wrote:
> +	help
> +	  Enabling this lets third-party kernel modules intercept
> +	  bio requests for any block device. This allows them to implement

The "third-party kernel modules" part sounds a bit worrisome to me. Especially
as this functionality is based on EXPORT_SYMBOL()s without the GPL suffix.

I read it as a "allow a proprietary module to mess with bios", which is a big 
no-no to me.

Not providing any sort of changelog doesn't help much either.

Thanks,
	Johannes

Re: [PATCH 1/2] Block layer filter - second version

[Sergei Shtepa]

The 10/21/2020 12:14, Johannes Thumshirn wrote:
> On 21/10/2020 11:04, Sergei Shtepa wrote:
> > +	help
> > +	  Enabling this lets third-party kernel modules intercept
> > +	  bio requests for any block device. This allows them to implement
> 
> The "third-party kernel modules" part sounds a bit worrisome to me. Especially
> as this functionality is based on EXPORT_SYMBOL()s without the GPL suffix.
> 
> I read it as a "allow a proprietary module to mess with bios", which is a big 
> no-no to me.
> 
> Not providing any sort of changelog doesn't help much either.
> 
> Thanks,
> 	Johannes
> 

I think the words "third-party" are is not necessary.
In my opinion, creating proprietary kernel modules for Linux is an empty idea.

EXPORT_SYMBOL() -> EXPORT_SYMBOL_GPL() - no problem.

-- 
Sergei Shtepa
Veeam Software developer.

Re: [PATCH 1/2] Block layer filter - second version

[Damien Le Moal]

On 2020/10/21 18:04, Sergei Shtepa wrote:
> Signed-off-by: Sergei Shtepa <sergei.shtepa@veeam.com>
> ---
>  block/Kconfig               |  11 ++
>  block/Makefile              |   1 +
>  block/blk-core.c            |  52 +++++--
>  block/blk-filter-internal.h |  29 ++++
>  block/blk-filter.c          | 286 ++++++++++++++++++++++++++++++++++++
>  block/partitions/core.c     |  14 +-
>  fs/block_dev.c              |   6 +-
>  fs/direct-io.c              |   2 +-
>  fs/iomap/direct-io.c        |   2 +-
>  include/linux/bio.h         |   4 +-
>  include/linux/blk-filter.h  |  76 ++++++++++
>  include/linux/genhd.h       |   8 +-
>  kernel/power/swap.c         |   2 +-
>  mm/page_io.c                |   4 +-
>  14 files changed, 471 insertions(+), 26 deletions(-)
>  create mode 100644 block/blk-filter-internal.h
>  create mode 100644 block/blk-filter.c
>  create mode 100644 include/linux/blk-filter.h
> 
> diff --git a/block/Kconfig b/block/Kconfig
> index bbad5e8bbffe..a308801b4376 100644
> --- a/block/Kconfig
> +++ b/block/Kconfig
> @@ -204,6 +204,17 @@ config BLK_INLINE_ENCRYPTION_FALLBACK
>  	  by falling back to the kernel crypto API when inline
>  	  encryption hardware is not present.
>  
> +config BLK_FILTER
> +	bool "Enable support for block layer filters"
> +	default y
> +	depends on MODULES
> +	help
> +	  Enabling this lets third-party kernel modules intercept
> +	  bio requests for any block device. This allows them to implement
> +	  changed block tracking and snapshots without any reconfiguration of
> +	  the existing setup. For example, this option allows snapshotting of
> +	  a block device without adding it to LVM.
> +
>  menu "Partition Types"
>  
>  source "block/partitions/Kconfig"
> diff --git a/block/Makefile b/block/Makefile
> index 8d841f5f986f..b8ee50b8e031 100644
> --- a/block/Makefile
> +++ b/block/Makefile
> @@ -38,3 +38,4 @@ obj-$(CONFIG_BLK_SED_OPAL)	+= sed-opal.o
>  obj-$(CONFIG_BLK_PM)		+= blk-pm.o
>  obj-$(CONFIG_BLK_INLINE_ENCRYPTION)	+= keyslot-manager.o blk-crypto.o
>  obj-$(CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK)	+= blk-crypto-fallback.o
> +obj-$(CONFIG_BLK_FILTER)	+= blk-filter.o
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 10c08ac50697..cc06402af695 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1216,23 +1216,20 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
>  EXPORT_SYMBOL(submit_bio_noacct);

Probably best to have this as its own patch last in the series.

>  
>  /**
> - * submit_bio - submit a bio to the block device layer for I/O
> - * @bio: The &struct bio which describes the I/O
> - *
> - * submit_bio() is used to submit I/O requests to block devices.  It is passed a
> - * fully set up &struct bio that describes the I/O that needs to be done.  The
> - * bio will be send to the device described by the bi_disk and bi_partno fields.
> + * submit_bio_direct - submit a bio to the block device layer for I/O
> + * bypass filter.
> + * @bio:  The bio describing the location in memory and on the device.
>   *
> - * The success/failure status of the request, along with notification of
> - * completion, is delivered asynchronously through the ->bi_end_io() callback
> - * in @bio.  The bio must NOT be touched by thecaller until ->bi_end_io() has
> - * been called.
> + * Description:
> + *    This is a version of submit_bio() that shall only be used for I/O
> + *    that cannot be intercepted by block layer filters.
> + *    All file systems and other upper level users of the block layer
> + *    should use submit_bio() instead.
> + *    Use this function to access the swap partition and directly access
> + *    the block device file.
>   */
> -blk_qc_t submit_bio(struct bio *bio)
> +blk_qc_t submit_bio_direct(struct bio *bio)
>  {
> -	if (blkcg_punt_bio_submit(bio))
> -		return BLK_QC_T_NONE;
> -
>  	/*
>  	 * If it's a regular read/write or a barrier with data attached,
>  	 * go through the normal accounting stuff before submission.
> @@ -1282,8 +1279,35 @@ blk_qc_t submit_bio(struct bio *bio)
>  
>  	return submit_bio_noacct(bio);
>  }
> +EXPORT_SYMBOL(submit_bio_direct);

EXPORT_SYMBOL_GPL

> +
> +/**
> + * submit_bio - submit a bio to the block device layer for I/O
> + * @bio: The &struct bio which describes the I/O
> + *
> + * submit_bio() is used to submit I/O requests to block devices.  It is passed a
> + * fully set up &struct bio that describes the I/O that needs to be done.  The
> + * bio will be send to the device described by the bi_disk and bi_partno fields.
> + *
> + * The success/failure status of the request, along with notification of
> + * completion, is delivered asynchronously through the ->bi_end_io() callback
> + * in @bio.  The bio must NOT be touched by thecaller until ->bi_end_io() has
> + * been called.
> + */
> +void submit_bio(struct bio *bio)
> +{
> +	if (blkcg_punt_bio_submit(bio))
> +		return;
> +
> +#ifdef CONFIG_BLK_FILTER> +	blk_filter_submit_bio(bio);
> +#else
> +	submit_bio_direct(bio);
> +#endif


	if (IS_ENABLED(CONFIG_BLK_FILTER))
		blk_filter_submit_bio(bio);
	else
		submit_bio_direct(bio);

is much cleaner...


> +}
>  EXPORT_SYMBOL(submit_bio);
>  
> +
>  /**
>   * blk_cloned_rq_check_limits - Helper function to check a cloned request
>   *                              for the new queue limits


The remaining should probably be a different patch before the above change.

> diff --git a/block/blk-filter-internal.h b/block/blk-filter-internal.h
> new file mode 100644
> index 000000000000..d456a09f50db
> --- /dev/null
> +++ b/block/blk-filter-internal.h
> @@ -0,0 +1,29 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + *
> + * Block device filters internal declarations
> + */
> +
> +#ifndef BLK_FILTER_INTERNAL_H
> +#define BLK_FILTER_INTERNAL_H
> +
> +#ifdef CONFIG_BLK_FILTER
> +#include <linux/blk-filter.h>
> +
> +void blk_filter_part_add(struct hd_struct *part, dev_t devt);
> +
> +void blk_filter_part_del(struct hd_struct *part);
> +
> +#else /* CONFIG_BLK_FILTER */
> +
> +

double blank line

> +static inline void blk_filter_part_add(struct hd_struct *part, dev_t devt)
> +{ };
> +
> +static inline void blk_filter_part_del(struct hd_struct *part)
> +{ };
> +
> +#endif /* CONFIG_BLK_FILTER */
> +
> +#endif
> diff --git a/block/blk-filter.c b/block/blk-filter.c
> new file mode 100644
> index 000000000000..f6de16c45a16
> --- /dev/null
> +++ b/block/blk-filter.c
> @@ -0,0 +1,286 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/genhd.h>
> +#include <linux/bio.h>
> +#include <linux/blkdev.h>
> +#include "blk-filter-internal.h"
> +#include <linux/rwsem.h>
> +
> +

Again here

> +LIST_HEAD(filters);
> +DECLARE_RWSEM(filters_lock);
> +
> +static void blk_filter_release(struct kref *kref)
> +{
> +	struct blk_filter *flt = container_of(kref, struct blk_filter, kref);
> +
> +	kfree(flt);
> +}
> +
> +static inline void blk_filter_get(struct blk_filter *flt)
> +{
> +	kref_get(&flt->kref);
> +}
> +
> +static inline void blk_filter_put(struct blk_filter *flt)
> +{
> +	kref_put(&flt->kref, blk_filter_release);
> +}
> +
> +
> +/**
> + * blk_filter_part_add() - Notify filters when a new partition is added.
> + * @part: The partition for new block device.
> + * @devt: Device id for new block device.
> + *
> + * Description:
> + *    When the block device is appears in the system, call the filter
> + *    callback to notify that the block device appears.
> + */
> +void blk_filter_part_add(struct hd_struct *part, dev_t devt)
> +{
> +	down_read(&filters_lock);
> +	if (!list_empty(&filters)) {
> +		struct list_head *_list_head;
> +
> +		list_for_each(_list_head, &filters) {
> +			void *filter_data;
> +			bool attached = false;
> +			struct blk_filter *flt;
> +
> +			flt = list_entry(_list_head, struct blk_filter, link);
> +
> +			attached = flt->ops->part_add(devt, &filter_data);
> +			if (attached) {
> +				blk_filter_get(flt);
> +				part->filter = flt;
> +				part->filter_data = filter_data;
> +				break;
> +			}
> +		}
> +	}
> +	up_read(&filters_lock);
> +}
> +
> +/**
> + * blk_filter_part_del() - Notify filters when the partition is deleted.
> + * @part: The partition of block device.
> + *
> + * Description:
> + *    When the block device is destroying and the partition is releasing,
> + *    call the filter callback to notify that the block device will be
> + *    deleted.
> + */
> +void blk_filter_part_del(struct hd_struct *part)
> +{
> +	struct blk_filter *flt = part->filter;
> +
> +	if (!flt)
> +		return;
> +
> +	flt->ops->part_del(part->filter_data);
> +
> +	part->filter_data = NULL;
> +	part->filter = NULL;
> +	blk_filter_put(flt);
> +}
> +
> +
> +/**
> + * blk_filter_submit_bio() - Send new bio to filters for processing.
> + * @bio: The new bio for block I/O layer.
> + *
> + * Description:
> + *    This function is an implementation of block layer filter
> + *    interception. If the filter is attached to this block device,
> + *    then bio will be redirected to the filter kernel module.
> + */
> +void blk_filter_submit_bio(struct bio *bio)
> +{
> +	bool intercepted = false;
> +	struct hd_struct *part;
> +
> +	bio_get(bio);
> +
> +	part = disk_get_part(bio->bi_disk, bio->bi_partno);
> +	if (unlikely(!part)) {
> +		bio->bi_status = BLK_STS_IOERR;
> +		bio_endio(bio);
> +
> +		bio_put(bio);
> +		return;
> +	}
> +
> +	down_read(&part->filter_rw_lockup);
> +
> +	if (part->filter)
> +		intercepted = part->filter->ops->filter_bio(bio, part->filter_data);
> +
> +	up_read(&part->filter_rw_lockup);
> +
> +	if (!intercepted)
> +		submit_bio_direct(bio);
> +
> +	disk_put_part(part);
> +
> +	bio_put(bio);
> +}
> +EXPORT_SYMBOL(blk_filter_submit_bio);
> +
> +/**
> + * blk_filter_register() - Register block layer filter.
> + * @ops: New filter callbacks.
> + *
> + * Return:
> + *     Filter ID, a pointer to the service structure of the filter.
> + *
> + * Description:
> + *    Create new filter structure.
> + *    Use blk_filter_attach to attach devices to filter.
> + */
> +void *blk_filter_register(struct blk_filter_ops *ops)
> +{
> +	struct blk_filter *flt;
> +
> +	flt = kzalloc(sizeof(struct blk_filter), GFP_KERNEL);
> +	if (!flt)
> +		return NULL;
> +
> +	kref_init(&flt->kref);
> +	flt->ops = ops;
> +
> +	down_write(&filters_lock);
> +	list_add_tail(&flt->link, &filters);
> +	up_write(&filters_lock);
> +
> +	return flt;
> +}
> +EXPORT_SYMBOL(blk_filter_register);
> +
> +/**
> + * blk_filter_unregister() - Unregister block layer filter.
> + * @filter: filter identifier.
> + *
> + * Description:
> + *    Before call blk_filter_unregister() and unload filter module all
> + *    partitions MUST be detached. Otherwise, the system will have a
> + *    filter with non-existent interception functions.
> + */
> +void blk_filter_unregister(void *filter)
> +{
> +	struct blk_filter *flt = filter;
> +
> +	down_write(&filters_lock);
> +	list_del(&flt->link);
> +	up_write(&filters_lock);
> +
> +	blk_filter_put(flt);
> +}
> +EXPORT_SYMBOL(blk_filter_unregister);
> +
> +/**
> + * blk_filter_attach() - Attach block layer filter.
> + * @devt: The block device identification number.
> + * @filter: Filter identifier.
> + * @filter_data: Specific filters data for this device.
> + *
> + * Return:
> + *    Return code.
> + *    -ENODEV - cannot find this device, it is OK if the device does not exist yet.
> + *    -EALREADY - this device is already attached to this filter.
> + *    -EBUSY - this device is already attached to the another filter.
> + *
> + * Description:
> + *    Attach the device to the block layer filter.
> + *    Only one filter can be attached to a single device.
> + */
> +int blk_filter_attach(dev_t devt, void *filter, void *filter_data)
> +{
> +	int ret = 0;
> +	struct blk_filter *flt = filter;
> +	struct block_device *blk_dev;
> +
> +
> +	blk_dev = bdget(devt);
> +	if (!blk_dev)
> +		return -ENODEV;
> +
> +	blk_filter_freeze(blk_dev);
> +
> +	if (blk_dev->bd_part->filter) {
> +		if (blk_dev->bd_part->filter == flt)
> +			ret = -EALREADY;
> +		else
> +			ret = -EBUSY;
> +	} else {
> +		blk_filter_get(flt);
> +		blk_dev->bd_part->filter = flt;
> +		blk_dev->bd_part->filter_data = filter_data;
> +	}
> +
> +	blk_filter_thaw(blk_dev);
> +
> +	bdput(blk_dev);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(blk_filter_attach);
> +
> +/**
> + * blk_filter_detach() - Detach block layer filter.
> + * @devt: The block device identification number.
> + *
> + * Description:
> + *    Detach the device from the block layer filter.
> + *    Do not forget detach all devices before calling the
> + *    blk_filter_unregister() function and unload the module!
> + */
> +void blk_filter_detach(dev_t devt)
> +{
> +	struct blk_filter *flt;
> +	struct block_device *blk_dev;
> +
> +	blk_dev = bdget(devt);
> +	if (!blk_dev)
> +		return;
> +
> +	blk_filter_freeze(blk_dev);
> +
> +	flt = blk_dev->bd_part->filter;
> +	if (flt) {
> +		blk_dev->bd_part->filter_data = NULL;
> +		blk_dev->bd_part->filter = NULL;
> +		blk_filter_put(flt);
> +	}
> +
> +	blk_filter_thaw(blk_dev);
> +
> +	bdput(blk_dev);
> +}
> +EXPORT_SYMBOL(blk_filter_detach);

All the EXPORT_SYMBOL should probably be EXPORT_SYMBOL_GPL.

> +
> +/**
> + * blk_filter_freeze() - Lock bio submitting.
> + * @bdev: The block device pointer.
> + *
> + * Description:
> + *    Stop bio processing.
> + */
> +void blk_filter_freeze(struct block_device *bdev)
> +{
> +	down_write(&bdev->bd_part->filter_rw_lockup);
> +}
> +EXPORT_SYMBOL(blk_filter_freeze);
> +
> +/**
> + * blk_filter_thaw() - Unlock bio submitting.
> + * @bdev: The block device pointer.
> + *
> + * Description:
> + *    Resume bio processing.
> + */
> +void blk_filter_thaw(struct block_device *bdev)
> +{
> +	up_write(&bdev->bd_part->filter_rw_lockup);
> +}
> +EXPORT_SYMBOL(blk_filter_thaw);
> diff --git a/block/partitions/core.c b/block/partitions/core.c
> index 722406b841df..6b845e98b9a1 100644
> --- a/block/partitions/core.c
> +++ b/block/partitions/core.c
> @@ -11,6 +11,7 @@
>  #include <linux/blktrace_api.h>
>  #include <linux/raid/detect.h>
>  #include "check.h"
> +#include "../blk-filter-internal.h"
>  
>  static int (*check_part[])(struct parsed_partitions *) = {
>  	/*
> @@ -320,9 +321,11 @@ int hd_ref_init(struct hd_struct *part)
>   */
>  void delete_partition(struct gendisk *disk, struct hd_struct *part)
>  {
> -	struct disk_part_tbl *ptbl =
> -		rcu_dereference_protected(disk->part_tbl, 1);
> +	struct disk_part_tbl *ptbl;
> +
> +	blk_filter_part_del(part);
>  
> +	ptbl = rcu_dereference_protected(disk->part_tbl, 1);
>  	/*
>  	 * ->part_tbl is referenced in this part's release handler, so
>  	 *  we have to hold the disk device
> @@ -412,6 +415,9 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
>  	p->nr_sects = len;
>  	p->partno = partno;
>  	p->policy = get_disk_ro(disk);
> +#ifdef CONFIG_BLK_FILTER
> +	init_rwsem(&p->filter_rw_lockup);
> +#endif
>  
>  	if (info) {
>  		struct partition_meta_info *pinfo;
> @@ -469,6 +475,9 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
>  	/* everything is up and running, commence */
>  	rcu_assign_pointer(ptbl->part[partno], p);
>  
> +	/*inform filter about a new partition*/
> +	blk_filter_part_add(p, devt);
> +
>  	/* suppress uevent if the disk suppresses it */
>  	if (!dev_get_uevent_suppress(ddev))
>  		kobject_uevent(&pdev->kobj, KOBJ_ADD);
> @@ -552,6 +561,7 @@ int bdev_del_partition(struct block_device *bdev, int partno)
>  		goto out_unlock;
>  
>  	sync_blockdev(bdevp);
> +
>  	invalidate_bdev(bdevp);
>  
>  	delete_partition(bdev->bd_disk, part);
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 8ae833e00443..431eae17fd8f 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -237,7 +237,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
>  	if (iocb->ki_flags & IOCB_HIPRI)
>  		bio_set_polled(&bio, iocb);
>  
> -	qc = submit_bio(&bio);
> +	qc = submit_bio_direct(&bio);
>  	for (;;) {
>  		set_current_state(TASK_UNINTERRUPTIBLE);
>  		if (!READ_ONCE(bio.bi_private))
> @@ -400,7 +400,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>  				polled = true;
>  			}
>  
> -			qc = submit_bio(bio);
> +			qc = submit_bio_direct(bio);
>  
>  			if (polled)
>  				WRITE_ONCE(iocb->ki_cookie, qc);
> @@ -421,7 +421,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>  			atomic_inc(&dio->ref);
>  		}
>  
> -		submit_bio(bio);
> +		submit_bio_direct(bio);
>  		bio = bio_alloc(GFP_KERNEL, nr_pages);
>  	}
>  
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 183299892465..d9bb1b6f6814 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -459,7 +459,7 @@ static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
>  		sdio->submit_io(bio, dio->inode, sdio->logical_offset_in_bio);
>  		dio->bio_cookie = BLK_QC_T_NONE;
>  	} else
> -		dio->bio_cookie = submit_bio(bio);
> +		dio->bio_cookie = submit_bio_direct(bio);

All these changes are unnecessary if you reverse things: submit_bio() is kept as
the direct version (as today) and you use a "submit_bio_filtered()" where needed.

>  
>  	sdio->bio = NULL;
>  	sdio->boundary = 0;
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index c1aafb2ab990..e05f20ce8b5f 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -73,7 +73,7 @@ static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap,
>  				file_inode(dio->iocb->ki_filp),
>  				iomap, bio, pos);
>  	else
> -		dio->submit.cookie = submit_bio(bio);
> +		dio->submit.cookie = submit_bio_direct(bio);
>  }
>  
>  static ssize_t iomap_dio_complete(struct iomap_dio *dio)
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index c6d765382926..5b0a32697207 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -10,6 +10,7 @@
>  #include <linux/ioprio.h>
>  /* struct bio, bio_vec and BIO_* flags are defined in blk_types.h */
>  #include <linux/blk_types.h>
> +#include <linux/blk-filter.h>
>  
>  #define BIO_DEBUG
>  
> @@ -411,7 +412,8 @@ static inline struct bio *bio_kmalloc(gfp_t gfp_mask, unsigned int nr_iovecs)
>  	return bio_alloc_bioset(gfp_mask, nr_iovecs, NULL);
>  }
>  
> -extern blk_qc_t submit_bio(struct bio *);
> +extern blk_qc_t submit_bio_direct(struct bio *bio);
> +extern void submit_bio(struct bio *bio);
>  
>  extern void bio_endio(struct bio *);
>  
> diff --git a/include/linux/blk-filter.h b/include/linux/blk-filter.h
> new file mode 100644
> index 000000000000..f3e79e5b4586
> --- /dev/null
> +++ b/include/linux/blk-filter.h
> @@ -0,0 +1,76 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * API declarations for kernel modules utilizing block device filters
> + */
> +
> +#ifndef BLK_FILTER_H
> +#define BLK_FILTER_H
> +
> +#ifdef CONFIG_BLK_FILTER
> +#include <linux/kref.h>
> +
> +struct blk_filter_ops {
> +	/*
> +	 * Intercept bio callback.
> +	 *
> +	 * Returns true if the request was intercepted and placed in the
> +	 * queue for processing. Otherwise submit_bio_direct() calling
> +	 * needed.
> +	 */
> +	bool (*filter_bio)(struct bio *bio, void *filter_data);
> +
> +	/*
> +	 * Callback to a request to add block device to the filter.
> +	 *
> +	 * Returns true if the block device will be filtered.
> +	 * p_filter_data gets a pointer to data that is unique to
> +	 * this device.
> +	 */
> +	bool (*part_add)(dev_t devt, void **p_filter_data);
> +
> +	/*
> +	 * Callback to remove block device from the filter.
> +	 */
> +	void (*part_del)(void *filter_data);
> +};
> +
> +struct blk_filter {
> +	struct list_head link;
> +	struct kref kref;
> +	struct blk_filter_ops *ops;
> +};
> +
> +/*
> + * Register/unregister device to filter
> + */
> +void *blk_filter_register(struct blk_filter_ops *ops);
> +
> +void blk_filter_unregister(void *filter);
> +
> +/*
> + * Attach/detach device to filter
> + */
> +int blk_filter_attach(dev_t devt, void *filter, void *filter_data);
> +
> +void blk_filter_detach(dev_t devt);
> +
> +/*
> + * For a consistent state of the file system use the freeze_bdev/thaw_bdav.
> + * But in addition, to ensure that the filter is not in the state of
> + * intercepting the next BIO, you need to call black_filter_freeze/blk_filter_thaw.
> + * This is especially actual if there is no file system on the disk.
> + */
> +
> +void blk_filter_freeze(struct block_device *bdev);
> +
> +void blk_filter_thaw(struct block_device *bdev);
> +
> +/*
> + * Filters intercept function
> + */
> +void blk_filter_submit_bio(struct bio *bio);
> +
> +#endif /* CONFIG_BLK_FILTER */
> +
> +#endif
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index 4ab853461dff..514fab6b947e 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -4,7 +4,7 @@
>  
>  /*
>   * 	genhd.h Copyright (C) 1992 Drew Eckhardt
> - *	Generic hard disk header file by  
> + *	Generic hard disk header file by
>   * 		Drew Eckhardt
>   *
>   *		<drew@colorado.edu>
> @@ -75,6 +75,12 @@ struct hd_struct {
>  	int make_it_fail;
>  #endif
>  	struct rcu_work rcu_work;
> +
> +#ifdef CONFIG_BLK_FILTER
> +	struct rw_semaphore filter_rw_lockup; /* for freezing block device*/
> +	struct blk_filter *filter; /* block layer filter*/
> +	void *filter_data; /*specific for each block device filters data*/
> +#endif
>  };
>  
>  /**
> diff --git a/kernel/power/swap.c b/kernel/power/swap.c
> index 01e2858b5fe3..5287346b87a1 100644
> --- a/kernel/power/swap.c
> +++ b/kernel/power/swap.c
> @@ -283,7 +283,7 @@ static int hib_submit_io(int op, int op_flags, pgoff_t page_off, void *addr,
>  		bio->bi_end_io = hib_end_io;
>  		bio->bi_private = hb;
>  		atomic_inc(&hb->count);
> -		submit_bio(bio);
> +		submit_bio_direct(bio);
>  	} else {
>  		error = submit_bio_wait(bio);
>  		bio_put(bio);
> diff --git a/mm/page_io.c b/mm/page_io.c
> index e485a6e8a6cd..4540426400b3 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -362,7 +362,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
>  	count_swpout_vm_event(page);
>  	set_page_writeback(page);
>  	unlock_page(page);
> -	submit_bio(bio);
> +	submit_bio_direct(bio);
>  out:
>  	return ret;
>  }
> @@ -434,7 +434,7 @@ int swap_readpage(struct page *page, bool synchronous)
>  	}
>  	count_vm_event(PSWPIN);
>  	bio_get(bio);
> -	qc = submit_bio(bio);
> +	qc = submit_bio_direct(bio);
>  	while (synchronous) {
>  		set_current_state(TASK_UNINTERRUPTIBLE);
>  		if (!READ_ONCE(bio->bi_private))
> 

Separate into multiple patches: one that introduces the filter functions/ops
code and another that changes the block layer where needed.


-- 
Damien Le Moal
Western Digital Research

Re: [PATCH 1/2] Block layer filter - second version

[Sergei Shtepa]

EXPORT_SYMBOL_GPL - ok.

#ifdef CONFIG_BLK_FILTER or IS_ENABLED() - It's a matter of habit.

> double blank line
Ok, I did.
Looks like a candidate for ./scripts/checkpatch.pl.

> Separate into multiple patches: one that introduces the filter
> functions/ops code and another that changes the block layer where needed.

I'll think about it. Personally, it seems to me that this separation
does not make it easier to understand the code. 
It is important for me to know immediately where the function is called,
and this determines its behavior.

-- 
Sergei Shtepa
Veeam Software developer.

Re: [PATCH 1/2] Block layer filter - second version

[Matthew Wilcox]

On Wed, Oct 21, 2020 at 09:21:36AM +0000, Damien Le Moal wrote:
> > + * submit_bio_direct - submit a bio to the block device layer for I/O
> > + * bypass filter.
> > + * @bio:  The bio describing the location in memory and on the device.
> >   *
> > + * Description:

You don't need this line.

> > + *    This is a version of submit_bio() that shall only be used for I/O
> > + *    that cannot be intercepted by block layer filters.
> > + *    All file systems and other upper level users of the block layer
> > + *    should use submit_bio() instead.
> > + *    Use this function to access the swap partition and directly access
> > + *    the block device file.

I don't understand why O_DIRECT gets to bypass the block filter.  Nor do
I understand why anybody would place a block filter on the swap device.
But if somebody did place a filter on the swap device, why should swap
be able to bypass the filter?

Re: [PATCH 1/2] Block layer filter - second version

[Sergei Shtepa]

The 10/21/2020 14:44, Matthew Wilcox wrote:
> On Wed, Oct 21, 2020 at 09:21:36AM +0000, Damien Le Moal wrote:
> > > + * submit_bio_direct - submit a bio to the block device layer for I/O
> > > + * bypass filter.
> > > + * @bio:  The bio describing the location in memory and on the device.
> > >   *
> > > + * Description:
> 
> You don't need this line.
> 
> > > + *    This is a version of submit_bio() that shall only be used for I/O
> > > + *    that cannot be intercepted by block layer filters.
> > > + *    All file systems and other upper level users of the block layer
> > > + *    should use submit_bio() instead.
> > > + *    Use this function to access the swap partition and directly access
> > > + *    the block device file.
> 
> I don't understand why O_DIRECT gets to bypass the block filter.  Nor do
> I understand why anybody would place a block filter on the swap device.
> But if somebody did place a filter on the swap device, why should swap
> be able to bypass the filter?
> 

I am very happy to hear such a question. You are really trying to
understand the algorithm.

Yes, intercepting the swap partition is absurd. But we can't guarantee
that the filter won't intercept swap.

Swap operation is related to the memory allocation logic. If a swap on
the block device are accessed during memory allocation from filter,
a deadlock occurs. We can allow filters to occasionally shoot off their
feet, especially under high load. But I think it's better not to do it.

"directly access" - it is not O_DIRECT. This means (I think) direct
reading from the device file, like "dd if=/dev/sda1".
As for intercepting direct reading, I don't know how to do the right thing.

The problem here is that in fs/block_dev.c in function __blkdev_direct_IO()
uses the qc - value returned by the submit_bio() function.
This value is used below when calling 
blk_poll(bdev_get_queue(dev), qc, true).
The filter cannot return a meaningful value of the blk_qc_t type when
intercepting a request, because at that time it does not know which queue
the request will fall into.

If function submit_bio() will always return BLK_QC_T_NONE - I think the
algorithm of the __blk dev_direct_IO() will not work correctly.
If we need to intercept direct access to a block device, we need to at
least redo the __blkdev_direct_IO function, getting rid of blk_pool.
I'm not sure it's necessary yet.

-- 
Sergei Shtepa
Veeam Software developer.

Re: [PATCH 1/2] Block layer filter - second version

[Matthew Wilcox]

On Wed, Oct 21, 2020 at 03:55:55PM +0300, Sergei Shtepa wrote:
> The 10/21/2020 14:44, Matthew Wilcox wrote:
> > I don't understand why O_DIRECT gets to bypass the block filter.  Nor do
> > I understand why anybody would place a block filter on the swap device.
> > But if somebody did place a filter on the swap device, why should swap
> > be able to bypass the filter?
> 
> Yes, intercepting the swap partition is absurd. But we can't guarantee
> that the filter won't intercept swap.
> 
> Swap operation is related to the memory allocation logic. If a swap on
> the block device are accessed during memory allocation from filter,
> a deadlock occurs. We can allow filters to occasionally shoot off their
> feet, especially under high load. But I think it's better not to do it.

We already have logic to prevent this in Linux.  Filters need to
call memalloc_noio_save() while they might cause swap to happen and
memalloc_noio_restore() once it's safe for them to cause swap again.

> "directly access" - it is not O_DIRECT. This means (I think) direct
> reading from the device file, like "dd if=/dev/sda1".
> As for intercepting direct reading, I don't know how to do the right thing.
> 
> The problem here is that in fs/block_dev.c in function __blkdev_direct_IO()
> uses the qc - value returned by the submit_bio() function.
> This value is used below when calling 
> blk_poll(bdev_get_queue(dev), qc, true).
> The filter cannot return a meaningful value of the blk_qc_t type when
> intercepting a request, because at that time it does not know which queue
> the request will fall into.
> 
> If function submit_bio() will always return BLK_QC_T_NONE - I think the
> algorithm of the __blk dev_direct_IO() will not work correctly.
> If we need to intercept direct access to a block device, we need to at
> least redo the __blkdev_direct_IO function, getting rid of blk_pool.
> I'm not sure it's necessary yet.

This isn't part of the block layer that I'm familiar with, so I can't
help solve this problem, but allowing O_DIRECT to bypass the block filter
is a hole that needs to be fixed before these patches can be considered.

Re: [PATCH 1/2] Block layer filter - second version

[Sergei Shtepa]

The 10/21/2020 16:07, Matthew Wilcox wrote:
> On Wed, Oct 21, 2020 at 03:55:55PM +0300, Sergei Shtepa wrote:
> > The 10/21/2020 14:44, Matthew Wilcox wrote:
> > > I don't understand why O_DIRECT gets to bypass the block filter.  Nor do
> > > I understand why anybody would place a block filter on the swap device.
> > > But if somebody did place a filter on the swap device, why should swap
> > > be able to bypass the filter?
> > 
> > Yes, intercepting the swap partition is absurd. But we can't guarantee
> > that the filter won't intercept swap.
> > 
> > Swap operation is related to the memory allocation logic. If a swap on
> > the block device are accessed during memory allocation from filter,
> > a deadlock occurs. We can allow filters to occasionally shoot off their
> > feet, especially under high load. But I think it's better not to do it.
> 
> We already have logic to prevent this in Linux.  Filters need to
> call memalloc_noio_save() while they might cause swap to happen and
> memalloc_noio_restore() once it's safe for them to cause swap again.

Yes, I looked at this function, it can really be useful for the filter.
Then I don't need to enter the submit_bio_direct() function and the wait
loop associated with the queue polling function blk_mq_poll() will have
to be rewritten.

> 
> > "directly access" - it is not O_DIRECT. This means (I think) direct
> > reading from the device file, like "dd if=/dev/sda1".
> > As for intercepting direct reading, I don't know how to do the right thing.
> > 
> > The problem here is that in fs/block_dev.c in function __blkdev_direct_IO()
> > uses the qc - value returned by the submit_bio() function.
> > This value is used below when calling 
> > blk_poll(bdev_get_queue(dev), qc, true).
> > The filter cannot return a meaningful value of the blk_qc_t type when
> > intercepting a request, because at that time it does not know which queue
> > the request will fall into.
> > 
> > If function submit_bio() will always return BLK_QC_T_NONE - I think the
> > algorithm of the __blk dev_direct_IO() will not work correctly.
> > If we need to intercept direct access to a block device, we need to at
> > least redo the __blkdev_direct_IO function, getting rid of blk_pool.
> > I'm not sure it's necessary yet.
> 
> This isn't part of the block layer that I'm familiar with, so I can't
> help solve this problem, but allowing O_DIRECT to bypass the block filter
> is a hole that needs to be fixed before these patches can be considered.

I think there is no such problem, but I will check, of course.

-- 
Sergei Shtepa
Veeam Software developer.

Re: [PATCH 1/2] Block layer filter - second version

[Randy Dunlap]

On 10/21/20 2:04 AM, Sergei Shtepa wrote:
> diff --git a/block/Kconfig b/block/Kconfig
> index bbad5e8bbffe..a308801b4376 100644
> --- a/block/Kconfig
> +++ b/block/Kconfig
> @@ -204,6 +204,17 @@ config BLK_INLINE_ENCRYPTION_FALLBACK
>  	  by falling back to the kernel crypto API when inline
>  	  encryption hardware is not present.
>  
> +config BLK_FILTER
> +	bool "Enable support for block layer filters"
> +	default y

Drop the default y. We don't add modules to a default build without
some tough justification.

> +	depends on MODULES
> +	help
> +	  Enabling this lets third-party kernel modules intercept

	                lets loadable kernel modules intercept

> +	  bio requests for any block device. This allows them to implement
> +	  changed block tracking and snapshots without any reconfiguration of
> +	  the existing setup. For example, this option allows snapshotting of
> +	  a block device without adding it to LVM.


-- 
~Randy

Re: [PATCH 1/2] Block layer filter - second version

[Greg KH]

On Wed, Oct 21, 2020 at 12:04:08PM +0300, Sergei Shtepa wrote:
> Signed-off-by: Sergei Shtepa <sergei.shtepa@veeam.com>

I know I don't take patches without any changelog text.

Maybe some maintainers are more lax...

Also, "second version" doesn't belong in the subject line, the
documentation shows how to properly version patch series, please do
that.

thanks,

greg k-h

> ---
>  block/Kconfig               |  11 ++
>  block/Makefile              |   1 +
>  block/blk-core.c            |  52 +++++--
>  block/blk-filter-internal.h |  29 ++++
>  block/blk-filter.c          | 286 ++++++++++++++++++++++++++++++++++++
>  block/partitions/core.c     |  14 +-
>  fs/block_dev.c              |   6 +-
>  fs/direct-io.c              |   2 +-
>  fs/iomap/direct-io.c        |   2 +-
>  include/linux/bio.h         |   4 +-
>  include/linux/blk-filter.h  |  76 ++++++++++
>  include/linux/genhd.h       |   8 +-
>  kernel/power/swap.c         |   2 +-
>  mm/page_io.c                |   4 +-
>  14 files changed, 471 insertions(+), 26 deletions(-)
>  create mode 100644 block/blk-filter-internal.h
>  create mode 100644 block/blk-filter.c
>  create mode 100644 include/linux/blk-filter.h
> 
> diff --git a/block/Kconfig b/block/Kconfig
> index bbad5e8bbffe..a308801b4376 100644
> --- a/block/Kconfig
> +++ b/block/Kconfig
> @@ -204,6 +204,17 @@ config BLK_INLINE_ENCRYPTION_FALLBACK
>  	  by falling back to the kernel crypto API when inline
>  	  encryption hardware is not present.
>  
> +config BLK_FILTER
> +	bool "Enable support for block layer filters"
> +	default y
> +	depends on MODULES
> +	help
> +	  Enabling this lets third-party kernel modules intercept
> +	  bio requests for any block device. This allows them to implement
> +	  changed block tracking and snapshots without any reconfiguration of
> +	  the existing setup. For example, this option allows snapshotting of
> +	  a block device without adding it to LVM.
> +
>  menu "Partition Types"
>  
>  source "block/partitions/Kconfig"
> diff --git a/block/Makefile b/block/Makefile
> index 8d841f5f986f..b8ee50b8e031 100644
> --- a/block/Makefile
> +++ b/block/Makefile
> @@ -38,3 +38,4 @@ obj-$(CONFIG_BLK_SED_OPAL)	+= sed-opal.o
>  obj-$(CONFIG_BLK_PM)		+= blk-pm.o
>  obj-$(CONFIG_BLK_INLINE_ENCRYPTION)	+= keyslot-manager.o blk-crypto.o
>  obj-$(CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK)	+= blk-crypto-fallback.o
> +obj-$(CONFIG_BLK_FILTER)	+= blk-filter.o
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 10c08ac50697..cc06402af695 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1216,23 +1216,20 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
>  EXPORT_SYMBOL(submit_bio_noacct);
>  
>  /**
> - * submit_bio - submit a bio to the block device layer for I/O
> - * @bio: The &struct bio which describes the I/O
> - *
> - * submit_bio() is used to submit I/O requests to block devices.  It is passed a
> - * fully set up &struct bio that describes the I/O that needs to be done.  The
> - * bio will be send to the device described by the bi_disk and bi_partno fields.
> + * submit_bio_direct - submit a bio to the block device layer for I/O
> + * bypass filter.
> + * @bio:  The bio describing the location in memory and on the device.
>   *
> - * The success/failure status of the request, along with notification of
> - * completion, is delivered asynchronously through the ->bi_end_io() callback
> - * in @bio.  The bio must NOT be touched by thecaller until ->bi_end_io() has
> - * been called.
> + * Description:
> + *    This is a version of submit_bio() that shall only be used for I/O
> + *    that cannot be intercepted by block layer filters.
> + *    All file systems and other upper level users of the block layer
> + *    should use submit_bio() instead.
> + *    Use this function to access the swap partition and directly access
> + *    the block device file.
>   */
> -blk_qc_t submit_bio(struct bio *bio)
> +blk_qc_t submit_bio_direct(struct bio *bio)
>  {
> -	if (blkcg_punt_bio_submit(bio))
> -		return BLK_QC_T_NONE;
> -
>  	/*
>  	 * If it's a regular read/write or a barrier with data attached,
>  	 * go through the normal accounting stuff before submission.
> @@ -1282,8 +1279,35 @@ blk_qc_t submit_bio(struct bio *bio)
>  
>  	return submit_bio_noacct(bio);
>  }
> +EXPORT_SYMBOL(submit_bio_direct);
> +
> +/**
> + * submit_bio - submit a bio to the block device layer for I/O
> + * @bio: The &struct bio which describes the I/O
> + *
> + * submit_bio() is used to submit I/O requests to block devices.  It is passed a
> + * fully set up &struct bio that describes the I/O that needs to be done.  The
> + * bio will be send to the device described by the bi_disk and bi_partno fields.
> + *
> + * The success/failure status of the request, along with notification of
> + * completion, is delivered asynchronously through the ->bi_end_io() callback
> + * in @bio.  The bio must NOT be touched by thecaller until ->bi_end_io() has
> + * been called.
> + */
> +void submit_bio(struct bio *bio)
> +{
> +	if (blkcg_punt_bio_submit(bio))
> +		return;
> +
> +#ifdef CONFIG_BLK_FILTER
> +	blk_filter_submit_bio(bio);
> +#else
> +	submit_bio_direct(bio);
> +#endif
> +}
>  EXPORT_SYMBOL(submit_bio);
>  
> +
>  /**
>   * blk_cloned_rq_check_limits - Helper function to check a cloned request
>   *                              for the new queue limits
> diff --git a/block/blk-filter-internal.h b/block/blk-filter-internal.h
> new file mode 100644
> index 000000000000..d456a09f50db
> --- /dev/null
> +++ b/block/blk-filter-internal.h
> @@ -0,0 +1,29 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + *
> + * Block device filters internal declarations
> + */
> +
> +#ifndef BLK_FILTER_INTERNAL_H
> +#define BLK_FILTER_INTERNAL_H
> +
> +#ifdef CONFIG_BLK_FILTER
> +#include <linux/blk-filter.h>
> +
> +void blk_filter_part_add(struct hd_struct *part, dev_t devt);
> +
> +void blk_filter_part_del(struct hd_struct *part);
> +
> +#else /* CONFIG_BLK_FILTER */
> +
> +
> +static inline void blk_filter_part_add(struct hd_struct *part, dev_t devt)
> +{ };
> +
> +static inline void blk_filter_part_del(struct hd_struct *part)
> +{ };
> +
> +#endif /* CONFIG_BLK_FILTER */
> +
> +#endif
> diff --git a/block/blk-filter.c b/block/blk-filter.c
> new file mode 100644
> index 000000000000..f6de16c45a16
> --- /dev/null
> +++ b/block/blk-filter.c
> @@ -0,0 +1,286 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/genhd.h>
> +#include <linux/bio.h>
> +#include <linux/blkdev.h>
> +#include "blk-filter-internal.h"
> +#include <linux/rwsem.h>
> +
> +
> +LIST_HEAD(filters);
> +DECLARE_RWSEM(filters_lock);
> +
> +static void blk_filter_release(struct kref *kref)
> +{
> +	struct blk_filter *flt = container_of(kref, struct blk_filter, kref);
> +
> +	kfree(flt);
> +}
> +
> +static inline void blk_filter_get(struct blk_filter *flt)
> +{
> +	kref_get(&flt->kref);
> +}
> +
> +static inline void blk_filter_put(struct blk_filter *flt)
> +{
> +	kref_put(&flt->kref, blk_filter_release);
> +}
> +
> +
> +/**
> + * blk_filter_part_add() - Notify filters when a new partition is added.
> + * @part: The partition for new block device.
> + * @devt: Device id for new block device.
> + *
> + * Description:
> + *    When the block device is appears in the system, call the filter
> + *    callback to notify that the block device appears.
> + */
> +void blk_filter_part_add(struct hd_struct *part, dev_t devt)
> +{
> +	down_read(&filters_lock);
> +	if (!list_empty(&filters)) {
> +		struct list_head *_list_head;
> +
> +		list_for_each(_list_head, &filters) {
> +			void *filter_data;
> +			bool attached = false;
> +			struct blk_filter *flt;
> +
> +			flt = list_entry(_list_head, struct blk_filter, link);
> +
> +			attached = flt->ops->part_add(devt, &filter_data);
> +			if (attached) {
> +				blk_filter_get(flt);
> +				part->filter = flt;
> +				part->filter_data = filter_data;
> +				break;
> +			}
> +		}
> +	}
> +	up_read(&filters_lock);
> +}
> +
> +/**
> + * blk_filter_part_del() - Notify filters when the partition is deleted.
> + * @part: The partition of block device.
> + *
> + * Description:
> + *    When the block device is destroying and the partition is releasing,
> + *    call the filter callback to notify that the block device will be
> + *    deleted.
> + */
> +void blk_filter_part_del(struct hd_struct *part)
> +{
> +	struct blk_filter *flt = part->filter;
> +
> +	if (!flt)
> +		return;
> +
> +	flt->ops->part_del(part->filter_data);
> +
> +	part->filter_data = NULL;
> +	part->filter = NULL;
> +	blk_filter_put(flt);
> +}
> +
> +
> +/**
> + * blk_filter_submit_bio() - Send new bio to filters for processing.
> + * @bio: The new bio for block I/O layer.
> + *
> + * Description:
> + *    This function is an implementation of block layer filter
> + *    interception. If the filter is attached to this block device,
> + *    then bio will be redirected to the filter kernel module.
> + */
> +void blk_filter_submit_bio(struct bio *bio)
> +{
> +	bool intercepted = false;
> +	struct hd_struct *part;
> +
> +	bio_get(bio);
> +
> +	part = disk_get_part(bio->bi_disk, bio->bi_partno);
> +	if (unlikely(!part)) {
> +		bio->bi_status = BLK_STS_IOERR;
> +		bio_endio(bio);
> +
> +		bio_put(bio);
> +		return;
> +	}
> +
> +	down_read(&part->filter_rw_lockup);
> +
> +	if (part->filter)
> +		intercepted = part->filter->ops->filter_bio(bio, part->filter_data);
> +
> +	up_read(&part->filter_rw_lockup);
> +
> +	if (!intercepted)
> +		submit_bio_direct(bio);
> +
> +	disk_put_part(part);
> +
> +	bio_put(bio);
> +}
> +EXPORT_SYMBOL(blk_filter_submit_bio);
> +
> +/**
> + * blk_filter_register() - Register block layer filter.
> + * @ops: New filter callbacks.
> + *
> + * Return:
> + *     Filter ID, a pointer to the service structure of the filter.
> + *
> + * Description:
> + *    Create new filter structure.
> + *    Use blk_filter_attach to attach devices to filter.
> + */
> +void *blk_filter_register(struct blk_filter_ops *ops)
> +{
> +	struct blk_filter *flt;
> +
> +	flt = kzalloc(sizeof(struct blk_filter), GFP_KERNEL);
> +	if (!flt)
> +		return NULL;
> +
> +	kref_init(&flt->kref);
> +	flt->ops = ops;
> +
> +	down_write(&filters_lock);
> +	list_add_tail(&flt->link, &filters);
> +	up_write(&filters_lock);
> +
> +	return flt;
> +}
> +EXPORT_SYMBOL(blk_filter_register);
> +
> +/**
> + * blk_filter_unregister() - Unregister block layer filter.
> + * @filter: filter identifier.
> + *
> + * Description:
> + *    Before call blk_filter_unregister() and unload filter module all
> + *    partitions MUST be detached. Otherwise, the system will have a
> + *    filter with non-existent interception functions.
> + */
> +void blk_filter_unregister(void *filter)
> +{
> +	struct blk_filter *flt = filter;
> +
> +	down_write(&filters_lock);
> +	list_del(&flt->link);
> +	up_write(&filters_lock);
> +
> +	blk_filter_put(flt);
> +}
> +EXPORT_SYMBOL(blk_filter_unregister);
> +
> +/**
> + * blk_filter_attach() - Attach block layer filter.
> + * @devt: The block device identification number.
> + * @filter: Filter identifier.
> + * @filter_data: Specific filters data for this device.
> + *
> + * Return:
> + *    Return code.
> + *    -ENODEV - cannot find this device, it is OK if the device does not exist yet.
> + *    -EALREADY - this device is already attached to this filter.
> + *    -EBUSY - this device is already attached to the another filter.
> + *
> + * Description:
> + *    Attach the device to the block layer filter.
> + *    Only one filter can be attached to a single device.
> + */
> +int blk_filter_attach(dev_t devt, void *filter, void *filter_data)
> +{
> +	int ret = 0;
> +	struct blk_filter *flt = filter;
> +	struct block_device *blk_dev;
> +
> +
> +	blk_dev = bdget(devt);
> +	if (!blk_dev)
> +		return -ENODEV;
> +
> +	blk_filter_freeze(blk_dev);
> +
> +	if (blk_dev->bd_part->filter) {
> +		if (blk_dev->bd_part->filter == flt)
> +			ret = -EALREADY;
> +		else
> +			ret = -EBUSY;
> +	} else {
> +		blk_filter_get(flt);
> +		blk_dev->bd_part->filter = flt;
> +		blk_dev->bd_part->filter_data = filter_data;
> +	}
> +
> +	blk_filter_thaw(blk_dev);
> +
> +	bdput(blk_dev);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(blk_filter_attach);
> +
> +/**
> + * blk_filter_detach() - Detach block layer filter.
> + * @devt: The block device identification number.
> + *
> + * Description:
> + *    Detach the device from the block layer filter.
> + *    Do not forget detach all devices before calling the
> + *    blk_filter_unregister() function and unload the module!
> + */
> +void blk_filter_detach(dev_t devt)
> +{
> +	struct blk_filter *flt;
> +	struct block_device *blk_dev;
> +
> +	blk_dev = bdget(devt);
> +	if (!blk_dev)
> +		return;
> +
> +	blk_filter_freeze(blk_dev);
> +
> +	flt = blk_dev->bd_part->filter;
> +	if (flt) {
> +		blk_dev->bd_part->filter_data = NULL;
> +		blk_dev->bd_part->filter = NULL;
> +		blk_filter_put(flt);
> +	}
> +
> +	blk_filter_thaw(blk_dev);
> +
> +	bdput(blk_dev);
> +}
> +EXPORT_SYMBOL(blk_filter_detach);
> +
> +/**
> + * blk_filter_freeze() - Lock bio submitting.
> + * @bdev: The block device pointer.
> + *
> + * Description:
> + *    Stop bio processing.
> + */
> +void blk_filter_freeze(struct block_device *bdev)
> +{
> +	down_write(&bdev->bd_part->filter_rw_lockup);
> +}
> +EXPORT_SYMBOL(blk_filter_freeze);
> +
> +/**
> + * blk_filter_thaw() - Unlock bio submitting.
> + * @bdev: The block device pointer.
> + *
> + * Description:
> + *    Resume bio processing.
> + */
> +void blk_filter_thaw(struct block_device *bdev)
> +{
> +	up_write(&bdev->bd_part->filter_rw_lockup);
> +}
> +EXPORT_SYMBOL(blk_filter_thaw);
> diff --git a/block/partitions/core.c b/block/partitions/core.c
> index 722406b841df..6b845e98b9a1 100644
> --- a/block/partitions/core.c
> +++ b/block/partitions/core.c
> @@ -11,6 +11,7 @@
>  #include <linux/blktrace_api.h>
>  #include <linux/raid/detect.h>
>  #include "check.h"
> +#include "../blk-filter-internal.h"
>  
>  static int (*check_part[])(struct parsed_partitions *) = {
>  	/*
> @@ -320,9 +321,11 @@ int hd_ref_init(struct hd_struct *part)
>   */
>  void delete_partition(struct gendisk *disk, struct hd_struct *part)
>  {
> -	struct disk_part_tbl *ptbl =
> -		rcu_dereference_protected(disk->part_tbl, 1);
> +	struct disk_part_tbl *ptbl;
> +
> +	blk_filter_part_del(part);
>  
> +	ptbl = rcu_dereference_protected(disk->part_tbl, 1);
>  	/*
>  	 * ->part_tbl is referenced in this part's release handler, so
>  	 *  we have to hold the disk device
> @@ -412,6 +415,9 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
>  	p->nr_sects = len;
>  	p->partno = partno;
>  	p->policy = get_disk_ro(disk);
> +#ifdef CONFIG_BLK_FILTER
> +	init_rwsem(&p->filter_rw_lockup);
> +#endif
>  
>  	if (info) {
>  		struct partition_meta_info *pinfo;
> @@ -469,6 +475,9 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
>  	/* everything is up and running, commence */
>  	rcu_assign_pointer(ptbl->part[partno], p);
>  
> +	/*inform filter about a new partition*/
> +	blk_filter_part_add(p, devt);
> +
>  	/* suppress uevent if the disk suppresses it */
>  	if (!dev_get_uevent_suppress(ddev))
>  		kobject_uevent(&pdev->kobj, KOBJ_ADD);
> @@ -552,6 +561,7 @@ int bdev_del_partition(struct block_device *bdev, int partno)
>  		goto out_unlock;
>  
>  	sync_blockdev(bdevp);
> +
>  	invalidate_bdev(bdevp);
>  
>  	delete_partition(bdev->bd_disk, part);
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 8ae833e00443..431eae17fd8f 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -237,7 +237,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
>  	if (iocb->ki_flags & IOCB_HIPRI)
>  		bio_set_polled(&bio, iocb);
>  
> -	qc = submit_bio(&bio);
> +	qc = submit_bio_direct(&bio);
>  	for (;;) {
>  		set_current_state(TASK_UNINTERRUPTIBLE);
>  		if (!READ_ONCE(bio.bi_private))
> @@ -400,7 +400,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>  				polled = true;
>  			}
>  
> -			qc = submit_bio(bio);
> +			qc = submit_bio_direct(bio);
>  
>  			if (polled)
>  				WRITE_ONCE(iocb->ki_cookie, qc);
> @@ -421,7 +421,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>  			atomic_inc(&dio->ref);
>  		}
>  
> -		submit_bio(bio);
> +		submit_bio_direct(bio);
>  		bio = bio_alloc(GFP_KERNEL, nr_pages);
>  	}
>  
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 183299892465..d9bb1b6f6814 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -459,7 +459,7 @@ static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
>  		sdio->submit_io(bio, dio->inode, sdio->logical_offset_in_bio);
>  		dio->bio_cookie = BLK_QC_T_NONE;
>  	} else
> -		dio->bio_cookie = submit_bio(bio);
> +		dio->bio_cookie = submit_bio_direct(bio);
>  
>  	sdio->bio = NULL;
>  	sdio->boundary = 0;
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index c1aafb2ab990..e05f20ce8b5f 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -73,7 +73,7 @@ static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap,
>  				file_inode(dio->iocb->ki_filp),
>  				iomap, bio, pos);
>  	else
> -		dio->submit.cookie = submit_bio(bio);
> +		dio->submit.cookie = submit_bio_direct(bio);
>  }
>  
>  static ssize_t iomap_dio_complete(struct iomap_dio *dio)
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index c6d765382926..5b0a32697207 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -10,6 +10,7 @@
>  #include <linux/ioprio.h>
>  /* struct bio, bio_vec and BIO_* flags are defined in blk_types.h */
>  #include <linux/blk_types.h>
> +#include <linux/blk-filter.h>
>  
>  #define BIO_DEBUG
>  
> @@ -411,7 +412,8 @@ static inline struct bio *bio_kmalloc(gfp_t gfp_mask, unsigned int nr_iovecs)
>  	return bio_alloc_bioset(gfp_mask, nr_iovecs, NULL);
>  }
>  
> -extern blk_qc_t submit_bio(struct bio *);
> +extern blk_qc_t submit_bio_direct(struct bio *bio);
> +extern void submit_bio(struct bio *bio);
>  
>  extern void bio_endio(struct bio *);
>  
> diff --git a/include/linux/blk-filter.h b/include/linux/blk-filter.h
> new file mode 100644
> index 000000000000..f3e79e5b4586
> --- /dev/null
> +++ b/include/linux/blk-filter.h
> @@ -0,0 +1,76 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * API declarations for kernel modules utilizing block device filters
> + */
> +
> +#ifndef BLK_FILTER_H
> +#define BLK_FILTER_H
> +
> +#ifdef CONFIG_BLK_FILTER
> +#include <linux/kref.h>
> +
> +struct blk_filter_ops {
> +	/*
> +	 * Intercept bio callback.
> +	 *
> +	 * Returns true if the request was intercepted and placed in the
> +	 * queue for processing. Otherwise submit_bio_direct() calling
> +	 * needed.
> +	 */
> +	bool (*filter_bio)(struct bio *bio, void *filter_data);
> +
> +	/*
> +	 * Callback to a request to add block device to the filter.
> +	 *
> +	 * Returns true if the block device will be filtered.
> +	 * p_filter_data gets a pointer to data that is unique to
> +	 * this device.
> +	 */
> +	bool (*part_add)(dev_t devt, void **p_filter_data);
> +
> +	/*
> +	 * Callback to remove block device from the filter.
> +	 */
> +	void (*part_del)(void *filter_data);
> +};
> +
> +struct blk_filter {
> +	struct list_head link;
> +	struct kref kref;
> +	struct blk_filter_ops *ops;
> +};
> +
> +/*
> + * Register/unregister device to filter
> + */
> +void *blk_filter_register(struct blk_filter_ops *ops);
> +
> +void blk_filter_unregister(void *filter);
> +
> +/*
> + * Attach/detach device to filter
> + */
> +int blk_filter_attach(dev_t devt, void *filter, void *filter_data);
> +
> +void blk_filter_detach(dev_t devt);
> +
> +/*
> + * For a consistent state of the file system use the freeze_bdev/thaw_bdav.
> + * But in addition, to ensure that the filter is not in the state of
> + * intercepting the next BIO, you need to call black_filter_freeze/blk_filter_thaw.
> + * This is especially actual if there is no file system on the disk.
> + */
> +
> +void blk_filter_freeze(struct block_device *bdev);
> +
> +void blk_filter_thaw(struct block_device *bdev);
> +
> +/*
> + * Filters intercept function
> + */
> +void blk_filter_submit_bio(struct bio *bio);
> +
> +#endif /* CONFIG_BLK_FILTER */
> +
> +#endif
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index 4ab853461dff..514fab6b947e 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -4,7 +4,7 @@
>  
>  /*
>   * 	genhd.h Copyright (C) 1992 Drew Eckhardt
> - *	Generic hard disk header file by  
> + *	Generic hard disk header file by
>   * 		Drew Eckhardt
>   *
>   *		<drew@colorado.edu>
> @@ -75,6 +75,12 @@ struct hd_struct {
>  	int make_it_fail;
>  #endif
>  	struct rcu_work rcu_work;
> +
> +#ifdef CONFIG_BLK_FILTER
> +	struct rw_semaphore filter_rw_lockup; /* for freezing block device*/
> +	struct blk_filter *filter; /* block layer filter*/
> +	void *filter_data; /*specific for each block device filters data*/
> +#endif
>  };
>  
>  /**
> diff --git a/kernel/power/swap.c b/kernel/power/swap.c
> index 01e2858b5fe3..5287346b87a1 100644
> --- a/kernel/power/swap.c
> +++ b/kernel/power/swap.c
> @@ -283,7 +283,7 @@ static int hib_submit_io(int op, int op_flags, pgoff_t page_off, void *addr,
>  		bio->bi_end_io = hib_end_io;
>  		bio->bi_private = hb;
>  		atomic_inc(&hb->count);
> -		submit_bio(bio);
> +		submit_bio_direct(bio);
>  	} else {
>  		error = submit_bio_wait(bio);
>  		bio_put(bio);
> diff --git a/mm/page_io.c b/mm/page_io.c
> index e485a6e8a6cd..4540426400b3 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -362,7 +362,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
>  	count_swpout_vm_event(page);
>  	set_page_writeback(page);
>  	unlock_page(page);
> -	submit_bio(bio);
> +	submit_bio_direct(bio);
>  out:
>  	return ret;
>  }
> @@ -434,7 +434,7 @@ int swap_readpage(struct page *page, bool synchronous)
>  	}
>  	count_vm_event(PSWPIN);
>  	bio_get(bio);
> -	qc = submit_bio(bio);
> +	qc = submit_bio_direct(bio);
>  	while (synchronous) {
>  		set_current_state(TASK_UNINTERRUPTIBLE);
>  		if (!READ_ONCE(bio->bi_private))
> -- 
> 2.20.1
> 

[PATCH 2/2] blk-snap - snapshots and change-tracking for block devices

[Sergei Shtepa]

Signed-off-by: Sergei Shtepa <sergei.shtepa@veeam.com>
---
 drivers/block/Kconfig                       |   2 +
 drivers/block/Makefile                      |   1 +
 drivers/block/blk-snap/Kconfig              |  24 +
 drivers/block/blk-snap/Makefile             |  28 +
 drivers/block/blk-snap/big_buffer.c         | 193 ++++
 drivers/block/blk-snap/big_buffer.h         |  24 +
 drivers/block/blk-snap/blk-snap-ctl.h       | 190 ++++
 drivers/block/blk-snap/blk_deferred.c       | 566 +++++++++++
 drivers/block/blk-snap/blk_deferred.h       |  67 ++
 drivers/block/blk-snap/blk_descr_file.c     |  82 ++
 drivers/block/blk-snap/blk_descr_file.h     |  26 +
 drivers/block/blk-snap/blk_descr_mem.c      |  66 ++
 drivers/block/blk-snap/blk_descr_mem.h      |  14 +
 drivers/block/blk-snap/blk_descr_multidev.c |  86 ++
 drivers/block/blk-snap/blk_descr_multidev.h |  25 +
 drivers/block/blk-snap/blk_descr_pool.c     | 190 ++++
 drivers/block/blk-snap/blk_descr_pool.h     |  38 +
 drivers/block/blk-snap/blk_redirect.c       | 507 ++++++++++
 drivers/block/blk-snap/blk_redirect.h       |  73 ++
 drivers/block/blk-snap/blk_util.c           |  33 +
 drivers/block/blk-snap/blk_util.h           |  33 +
 drivers/block/blk-snap/cbt_map.c            | 210 +++++
 drivers/block/blk-snap/cbt_map.h            |  62 ++
 drivers/block/blk-snap/common.h             |  31 +
 drivers/block/blk-snap/ctrl_fops.c          | 691 ++++++++++++++
 drivers/block/blk-snap/ctrl_fops.h          |  19 +
 drivers/block/blk-snap/ctrl_pipe.c          | 562 +++++++++++
 drivers/block/blk-snap/ctrl_pipe.h          |  34 +
 drivers/block/blk-snap/ctrl_sysfs.c         |  73 ++
 drivers/block/blk-snap/ctrl_sysfs.h         |   5 +
 drivers/block/blk-snap/defer_io.c           | 397 ++++++++
 drivers/block/blk-snap/defer_io.h           |  39 +
 drivers/block/blk-snap/main.c               |  82 ++
 drivers/block/blk-snap/params.c             |  58 ++
 drivers/block/blk-snap/params.h             |  29 +
 drivers/block/blk-snap/rangevector.c        |  85 ++
 drivers/block/blk-snap/rangevector.h        |  31 +
 drivers/block/blk-snap/snapimage.c          | 982 ++++++++++++++++++++
 drivers/block/blk-snap/snapimage.h          |  16 +
 drivers/block/blk-snap/snapshot.c           | 225 +++++
 drivers/block/blk-snap/snapshot.h           |  17 +
 drivers/block/blk-snap/snapstore.c          | 929 ++++++++++++++++++
 drivers/block/blk-snap/snapstore.h          |  68 ++
 drivers/block/blk-snap/snapstore_device.c   | 532 +++++++++++
 drivers/block/blk-snap/snapstore_device.h   |  63 ++
 drivers/block/blk-snap/snapstore_file.c     |  52 ++
 drivers/block/blk-snap/snapstore_file.h     |  15 +
 drivers/block/blk-snap/snapstore_mem.c      |  91 ++
 drivers/block/blk-snap/snapstore_mem.h      |  20 +
 drivers/block/blk-snap/snapstore_multidev.c | 118 +++
 drivers/block/blk-snap/snapstore_multidev.h |  22 +
 drivers/block/blk-snap/tracker.c            | 449 +++++++++
 drivers/block/blk-snap/tracker.h            |  38 +
 drivers/block/blk-snap/tracking.c           | 270 ++++++
 drivers/block/blk-snap/tracking.h           |  13 +
 drivers/block/blk-snap/version.h            |   7 +
 56 files changed, 8603 insertions(+)
 create mode 100644 drivers/block/blk-snap/Kconfig
 create mode 100644 drivers/block/blk-snap/Makefile
 create mode 100644 drivers/block/blk-snap/big_buffer.c
 create mode 100644 drivers/block/blk-snap/big_buffer.h
 create mode 100644 drivers/block/blk-snap/blk-snap-ctl.h
 create mode 100644 drivers/block/blk-snap/blk_deferred.c
 create mode 100644 drivers/block/blk-snap/blk_deferred.h
 create mode 100644 drivers/block/blk-snap/blk_descr_file.c
 create mode 100644 drivers/block/blk-snap/blk_descr_file.h
 create mode 100644 drivers/block/blk-snap/blk_descr_mem.c
 create mode 100644 drivers/block/blk-snap/blk_descr_mem.h
 create mode 100644 drivers/block/blk-snap/blk_descr_multidev.c
 create mode 100644 drivers/block/blk-snap/blk_descr_multidev.h
 create mode 100644 drivers/block/blk-snap/blk_descr_pool.c
 create mode 100644 drivers/block/blk-snap/blk_descr_pool.h
 create mode 100644 drivers/block/blk-snap/blk_redirect.c
 create mode 100644 drivers/block/blk-snap/blk_redirect.h
 create mode 100644 drivers/block/blk-snap/blk_util.c
 create mode 100644 drivers/block/blk-snap/blk_util.h
 create mode 100644 drivers/block/blk-snap/cbt_map.c
 create mode 100644 drivers/block/blk-snap/cbt_map.h
 create mode 100644 drivers/block/blk-snap/common.h
 create mode 100644 drivers/block/blk-snap/ctrl_fops.c
 create mode 100644 drivers/block/blk-snap/ctrl_fops.h
 create mode 100644 drivers/block/blk-snap/ctrl_pipe.c
 create mode 100644 drivers/block/blk-snap/ctrl_pipe.h
 create mode 100644 drivers/block/blk-snap/ctrl_sysfs.c
 create mode 100644 drivers/block/blk-snap/ctrl_sysfs.h
 create mode 100644 drivers/block/blk-snap/defer_io.c
 create mode 100644 drivers/block/blk-snap/defer_io.h
 create mode 100644 drivers/block/blk-snap/main.c
 create mode 100644 drivers/block/blk-snap/params.c
 create mode 100644 drivers/block/blk-snap/params.h
 create mode 100644 drivers/block/blk-snap/rangevector.c
 create mode 100644 drivers/block/blk-snap/rangevector.h
 create mode 100644 drivers/block/blk-snap/snapimage.c
 create mode 100644 drivers/block/blk-snap/snapimage.h
 create mode 100644 drivers/block/blk-snap/snapshot.c
 create mode 100644 drivers/block/blk-snap/snapshot.h
 create mode 100644 drivers/block/blk-snap/snapstore.c
 create mode 100644 drivers/block/blk-snap/snapstore.h
 create mode 100644 drivers/block/blk-snap/snapstore_device.c
 create mode 100644 drivers/block/blk-snap/snapstore_device.h
 create mode 100644 drivers/block/blk-snap/snapstore_file.c
 create mode 100644 drivers/block/blk-snap/snapstore_file.h
 create mode 100644 drivers/block/blk-snap/snapstore_mem.c
 create mode 100644 drivers/block/blk-snap/snapstore_mem.h
 create mode 100644 drivers/block/blk-snap/snapstore_multidev.c
 create mode 100644 drivers/block/blk-snap/snapstore_multidev.h
 create mode 100644 drivers/block/blk-snap/tracker.c
 create mode 100644 drivers/block/blk-snap/tracker.h
 create mode 100644 drivers/block/blk-snap/tracking.c
 create mode 100644 drivers/block/blk-snap/tracking.h
 create mode 100644 drivers/block/blk-snap/version.h

diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index ecceaaa1a66f..c53ef661110f 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -460,4 +460,6 @@ config BLK_DEV_RSXX
 
 source "drivers/block/rnbd/Kconfig"
 
+source "drivers/block/blk-snap/Kconfig"
+
 endif # BLK_DEV
diff --git a/drivers/block/Makefile b/drivers/block/Makefile
index e1f63117ee94..312000598944 100644
--- a/drivers/block/Makefile
+++ b/drivers/block/Makefile
@@ -40,6 +40,7 @@ obj-$(CONFIG_BLK_DEV_PCIESSD_MTIP32XX)	+= mtip32xx/
 obj-$(CONFIG_BLK_DEV_RSXX) += rsxx/
 obj-$(CONFIG_ZRAM) += zram/
 obj-$(CONFIG_BLK_DEV_RNBD)	+= rnbd/
+obj-$(CONFIG_BLK_SNAP)	+= blk-snap/
 
 obj-$(CONFIG_BLK_DEV_NULL_BLK)	+= null_blk.o
 null_blk-objs	:= null_blk_main.o
diff --git a/drivers/block/blk-snap/Kconfig b/drivers/block/blk-snap/Kconfig
new file mode 100644
index 000000000000..7a2db99a80dd
--- /dev/null
+++ b/drivers/block/blk-snap/Kconfig
@@ -0,0 +1,24 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# blk-snap block io layer filter module configuration
+#
+#
+#select BLK_FILTER
+
+config BLK_SNAP
+	tristate "Block device snapshot filter"
+	depends on BLK_FILTER
+	help
+
+	  Allow to create snapshots and track block changes for a block
+	  devices. Designed for creating backups for any block devices
+	  (without device mapper). Snapshots are temporary and are released
+	  then backup is completed. Change block tracking allows you to
+	  create incremental or differential backups.
+
+config BLK_SNAP_SNAPSTORE_MULTIDEV
+	bool "Multi device snapstore configuration support"
+	depends on BLK_SNAP
+	help
+
+	  Allow to create snapstore on multiple block devices.
diff --git a/drivers/block/blk-snap/Makefile b/drivers/block/blk-snap/Makefile
new file mode 100644
index 000000000000..1d628e8e1862
--- /dev/null
+++ b/drivers/block/blk-snap/Makefile
@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: GPL-2.0
+blk-snap-y += blk_deferred.o
+blk-snap-y += blk_descr_file.o
+blk-snap-y += blk_descr_mem.o
+blk-snap-y += blk_descr_multidev.o
+blk-snap-y += blk_descr_pool.o
+blk-snap-y += blk_redirect.o
+blk-snap-y += blk_util.o
+blk-snap-y += cbt_map.o
+blk-snap-y += ctrl_fops.o
+blk-snap-y += ctrl_pipe.o
+blk-snap-y += ctrl_sysfs.o
+blk-snap-y += defer_io.o
+blk-snap-y += main.o
+blk-snap-y += params.o
+blk-snap-y += big_buffer.o
+blk-snap-y += rangevector.o
+blk-snap-y += snapimage.o
+blk-snap-y += snapshot.o
+blk-snap-y += snapstore.o
+blk-snap-y += snapstore_device.o
+blk-snap-y += snapstore_file.o
+blk-snap-y += snapstore_mem.o
+blk-snap-y += snapstore_multidev.o
+blk-snap-y += tracker.o
+blk-snap-y += tracking.o
+
+obj-$(CONFIG_BLK_SNAP)	 += blk-snap.o
diff --git a/drivers/block/blk-snap/big_buffer.c b/drivers/block/blk-snap/big_buffer.c
new file mode 100644
index 000000000000..c0a75255a807
--- /dev/null
+++ b/drivers/block/blk-snap/big_buffer.c
@@ -0,0 +1,193 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "common.h"
+#include <linux/mm.h>
+#include "big_buffer.h"
+
+static inline size_t page_count_calc(size_t buffer_size)
+{
+	size_t page_count = buffer_size / PAGE_SIZE;
+
+	if (buffer_size & (PAGE_SIZE - 1))
+		page_count += 1;
+	return page_count;
+}
+
+struct big_buffer *big_buffer_alloc(size_t buffer_size, int gfp_opt)
+{
+	int res = SUCCESS;
+	struct big_buffer *bbuff;
+	size_t count;
+	size_t inx;
+
+	count = page_count_calc(buffer_size);
+
+	bbuff = kzalloc(sizeof(struct big_buffer) + count * sizeof(void *), gfp_opt);
+	if (bbuff == NULL)
+		return NULL;
+
+	bbuff->pg_cnt = count;
+	for (inx = 0; inx < bbuff->pg_cnt; ++inx) {
+		struct page *pg = alloc_page(gfp_opt);
+
+		if (!pg) {
+			res = -ENOMEM;
+			break;
+		}
+		bbuff->pg[inx] = page_address(pg);
+	}
+
+	if (res != SUCCESS) {
+		big_buffer_free(bbuff);
+		return NULL;
+	}
+
+	return bbuff;
+}
+
+void big_buffer_free(struct big_buffer *bbuff)
+{
+	size_t inx;
+	size_t count = bbuff->pg_cnt;
+
+	if (bbuff == NULL)
+		return;
+
+	for (inx = 0; inx < count; ++inx)
+		if (bbuff->pg[inx] != NULL)
+			free_page((unsigned long)bbuff->pg[inx]);
+
+	kfree(bbuff);
+}
+
+size_t big_buffer_copy_to_user(char __user *dst_user, size_t offset, struct big_buffer *bbuff,
+			       size_t length)
+{
+	size_t left_data_length;
+	int page_inx = offset / PAGE_SIZE;
+	size_t processed_len = 0;
+	size_t unordered = offset & (PAGE_SIZE - 1);
+
+	if (unordered != 0) { //first
+		size_t page_len = min_t(size_t, (PAGE_SIZE - unordered), length);
+
+		left_data_length = copy_to_user(dst_user + processed_len,
+						bbuff->pg[page_inx] + unordered, page_len);
+		if (left_data_length != 0) {
+			pr_err("Failed to copy data from big_buffer to user buffer\n");
+			return processed_len;
+		}
+
+		++page_inx;
+		processed_len += page_len;
+	}
+
+	while ((processed_len < length) && (page_inx < bbuff->pg_cnt)) {
+		size_t page_len = min_t(size_t, PAGE_SIZE, (length - processed_len));
+
+		left_data_length =
+			copy_to_user(dst_user + processed_len, bbuff->pg[page_inx], page_len);
+		if (left_data_length != 0) {
+			pr_err("Failed to copy data from big_buffer to user buffer\n");
+			break;
+		}
+
+		++page_inx;
+		processed_len += page_len;
+	}
+
+	return processed_len;
+}
+
+size_t big_buffer_copy_from_user(const char __user *src_user, size_t offset,
+				 struct big_buffer *bbuff, size_t length)
+{
+	size_t left_data_length;
+	int page_inx = offset / PAGE_SIZE;
+	size_t processed_len = 0;
+	size_t unordered = offset & (PAGE_SIZE - 1);
+
+	if (unordered != 0) { //first
+		size_t page_len = min_t(size_t, (PAGE_SIZE - unordered), length);
+
+		left_data_length = copy_from_user(bbuff->pg[page_inx] + unordered,
+						  src_user + processed_len, page_len);
+		if (left_data_length != 0) {
+			pr_err("Failed to copy data from user buffer to big_buffer\n");
+			return processed_len;
+		}
+
+		++page_inx;
+		processed_len += page_len;
+	}
+
+	while ((processed_len < length) && (page_inx < bbuff->pg_cnt)) {
+		size_t page_len = min_t(size_t, PAGE_SIZE, (length - processed_len));
+
+		left_data_length =
+			copy_from_user(bbuff->pg[page_inx], src_user + processed_len, page_len);
+		if (left_data_length != 0) {
+			pr_err("Failed to copy data from user buffer to big_buffer\n");
+			break;
+		}
+
+		++page_inx;
+		processed_len += page_len;
+	}
+
+	return processed_len;
+}
+
+void *big_buffer_get_element(struct big_buffer *bbuff, size_t index, size_t sizeof_element)
+{
+	size_t elements_in_page = PAGE_SIZE / sizeof_element;
+	size_t pg_inx = index / elements_in_page;
+	size_t pg_ofs = (index - (pg_inx * elements_in_page)) * sizeof_element;
+
+	if (pg_inx >= bbuff->pg_cnt)
+		return NULL;
+
+	return bbuff->pg[pg_inx] + pg_ofs;
+}
+
+void big_buffer_memset(struct big_buffer *bbuff, int value)
+{
+	size_t inx;
+
+	for (inx = 0; inx < bbuff->pg_cnt; ++inx)
+		memset(bbuff->pg[inx], value, PAGE_SIZE);
+}
+
+void big_buffer_memcpy(struct big_buffer *dst, struct big_buffer *src)
+{
+	size_t inx;
+	size_t count = min_t(size_t, dst->pg_cnt, src->pg_cnt);
+
+	for (inx = 0; inx < count; ++inx)
+		memcpy(dst->pg[inx], src->pg[inx], PAGE_SIZE);
+}
+
+int big_buffer_byte_get(struct big_buffer *bbuff, size_t inx, u8 *value)
+{
+	size_t page_inx = inx >> PAGE_SHIFT;
+	size_t byte_pos = inx & (PAGE_SIZE - 1);
+
+	if (page_inx >= bbuff->pg_cnt)
+		return -ENODATA;
+
+	*value = bbuff->pg[page_inx][byte_pos];
+
+	return SUCCESS;
+}
+
+int big_buffer_byte_set(struct big_buffer *bbuff, size_t inx, u8 value)
+{
+	size_t page_inx = inx >> PAGE_SHIFT;
+	size_t byte_pos = inx & (PAGE_SIZE - 1);
+
+	if (page_inx >= bbuff->pg_cnt)
+		return -ENODATA;
+
+	bbuff->pg[page_inx][byte_pos] = value;
+
+	return SUCCESS;
+}
diff --git a/drivers/block/blk-snap/big_buffer.h b/drivers/block/blk-snap/big_buffer.h
new file mode 100644
index 000000000000..f38ab5288b05
--- /dev/null
+++ b/drivers/block/blk-snap/big_buffer.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+struct big_buffer {
+	size_t pg_cnt;
+	u8 *pg[0];
+};
+
+struct big_buffer *big_buffer_alloc(size_t count, int gfp_opt);
+void big_buffer_free(struct big_buffer *bbuff);
+
+size_t big_buffer_copy_to_user(char __user *dst_user_buffer, size_t offset,
+			       struct big_buffer *bbuff, size_t length);
+size_t big_buffer_copy_from_user(const char __user *src_user_buffer, size_t offset,
+				 struct big_buffer *bbuff, size_t length);
+
+void *big_buffer_get_element(struct big_buffer *bbuff, size_t index, size_t sizeof_element);
+
+void big_buffer_memset(struct big_buffer *bbuff, int value);
+void big_buffer_memcpy(struct big_buffer *dst, struct big_buffer *src);
+
+//byte access
+int big_buffer_byte_get(struct big_buffer *bbuff, size_t inx, u8 *value);
+int big_buffer_byte_set(struct big_buffer *bbuff, size_t inx, u8 value);
diff --git a/drivers/block/blk-snap/blk-snap-ctl.h b/drivers/block/blk-snap/blk-snap-ctl.h
new file mode 100644
index 000000000000..4ffd836836b1
--- /dev/null
+++ b/drivers/block/blk-snap/blk-snap-ctl.h
@@ -0,0 +1,190 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+#define MODULE_NAME "blk-snap"
+#define SNAP_IMAGE_NAME "blk-snap-image"
+
+#define SUCCESS 0
+
+#define MAX_TRACKING_DEVICE_COUNT 256
+
+#define BLK_SNAP 'V'
+
+#pragma pack(push, 1)
+//////////////////////////////////////////////////////////////////////////
+// version
+
+#define BLK_SNAP_COMPATIBILITY_SNAPSTORE 0x0000000000000001ull /* rudiment */
+//#define BLK_SNAP_COMPATIBILITY_BTRFS	 0x0000000000000002ull /* rudiment */
+#define BLK_SNAP_COMPATIBILITY_MULTIDEV 0x0000000000000004ull
+
+struct ioctl_compatibility_flags_s {
+	unsigned long long flags;
+};
+#define IOCTL_COMPATIBILITY_FLAGS _IOW(BLK_SNAP, 0, struct ioctl_compatibility_flags_s)
+
+struct ioctl_getversion_s {
+	unsigned short major;
+	unsigned short minor;
+	unsigned short revision;
+	unsigned short build;
+};
+#define IOCTL_GETVERSION _IOW(BLK_SNAP, 1, struct ioctl_getversion_s)
+
+//////////////////////////////////////////////////////////////////////////
+// tracking
+struct ioctl_dev_id_s {
+	int major;
+	int minor;
+};
+#define IOCTL_TRACKING_ADD _IOW(BLK_SNAP, 2, struct ioctl_dev_id_s)
+
+#define IOCTL_TRACKING_REMOVE _IOW(BLK_SNAP, 3, struct ioctl_dev_id_s)
+
+struct cbt_info_s {
+	struct ioctl_dev_id_s dev_id;
+	unsigned long long dev_capacity;
+	unsigned int cbt_map_size;
+	unsigned char snap_number;
+	unsigned char generationId[16];
+};
+struct ioctl_tracking_collect_s {
+	unsigned int count;
+	union {
+		struct cbt_info_s *p_cbt_info;
+		unsigned long long ull_cbt_info;
+	};
+};
+#define IOCTL_TRACKING_COLLECT _IOW(BLK_SNAP, 4, struct ioctl_tracking_collect_s)
+
+#define IOCTL_TRACKING_BLOCK_SIZE _IOW(BLK_SNAP, 5, unsigned int)
+
+struct ioctl_tracking_read_cbt_bitmap_s {
+	struct ioctl_dev_id_s dev_id;
+	unsigned int offset;
+	unsigned int length;
+	union {
+		unsigned char *buff;
+		unsigned long long ull_buff;
+	};
+};
+#define IOCTL_TRACKING_READ_CBT_BITMAP _IOR(BLK_SNAP, 6, struct ioctl_tracking_read_cbt_bitmap_s)
+
+struct block_range_s {
+	unsigned long long ofs; //sectors
+	unsigned long long cnt; //sectors
+};
+
+struct ioctl_tracking_mark_dirty_blocks_s {
+	struct ioctl_dev_id_s image_dev_id;
+	unsigned int count;
+	union {
+		struct block_range_s *p_dirty_blocks;
+		unsigned long long ull_dirty_blocks;
+	};
+};
+#define IOCTL_TRACKING_MARK_DIRTY_BLOCKS                                                           \
+	_IOR(BLK_SNAP, 7, struct ioctl_tracking_mark_dirty_blocks_s)
+//////////////////////////////////////////////////////////////////////////
+// snapshot
+
+struct ioctl_snapshot_create_s {
+	unsigned long long snapshot_id;
+	unsigned int count;
+	union {
+		struct ioctl_dev_id_s *p_dev_id;
+		unsigned long long ull_dev_id;
+	};
+};
+#define IOCTL_SNAPSHOT_CREATE _IOW(BLK_SNAP, 0x10, struct ioctl_snapshot_create_s)
+
+#define IOCTL_SNAPSHOT_DESTROY _IOR(BLK_SNAP, 0x11, unsigned long long)
+
+struct ioctl_snapshot_errno_s {
+	struct ioctl_dev_id_s dev_id;
+	int err_code;
+};
+#define IOCTL_SNAPSHOT_ERRNO _IOW(BLK_SNAP, 0x12, struct ioctl_snapshot_errno_s)
+
+struct ioctl_range_s {
+	unsigned long long left;
+	unsigned long long right;
+};
+
+//////////////////////////////////////////////////////////////////////////
+// snapstore
+struct ioctl_snapstore_create_s {
+	unsigned char id[16];
+	struct ioctl_dev_id_s snapstore_dev_id;
+	unsigned int count;
+	union {
+		struct ioctl_dev_id_s *p_dev_id;
+		unsigned long long ull_dev_id;
+	};
+};
+#define IOCTL_SNAPSTORE_CREATE _IOR(BLK_SNAP, 0x28, struct ioctl_snapstore_create_s)
+
+struct ioctl_snapstore_file_add_s {
+	unsigned char id[16];
+	unsigned int range_count;
+	union {
+		struct ioctl_range_s *ranges;
+		unsigned long long ull_ranges;
+	};
+};
+#define IOCTL_SNAPSTORE_FILE _IOR(BLK_SNAP, 0x29, struct ioctl_snapstore_file_add_s)
+
+struct ioctl_snapstore_memory_limit_s {
+	unsigned char id[16];
+	unsigned long long size;
+};
+#define IOCTL_SNAPSTORE_MEMORY _IOR(BLK_SNAP, 0x2A, struct ioctl_snapstore_memory_limit_s)
+
+struct ioctl_snapstore_cleanup_s {
+	unsigned char id[16];
+	unsigned long long filled_bytes;
+};
+#define IOCTL_SNAPSTORE_CLEANUP _IOW(BLK_SNAP, 0x2B, struct ioctl_snapstore_cleanup_s)
+
+struct ioctl_snapstore_file_add_multidev_s {
+	unsigned char id[16];
+	struct ioctl_dev_id_s dev_id;
+	unsigned int range_count;
+	union {
+		struct ioctl_range_s *ranges;
+		unsigned long long ull_ranges;
+	};
+};
+#define IOCTL_SNAPSTORE_FILE_MULTIDEV                                                              \
+	_IOR(BLK_SNAP, 0x2C, struct ioctl_snapstore_file_add_multidev_s)
+//////////////////////////////////////////////////////////////////////////
+// collect snapshot images
+
+struct image_info_s {
+	struct ioctl_dev_id_s original_dev_id;
+	struct ioctl_dev_id_s snapshot_dev_id;
+};
+
+struct ioctl_collect_snapshot_images_s {
+	int count; //
+	union {
+		struct image_info_s *p_image_info;
+		unsigned long long ull_image_info;
+	};
+};
+#define IOCTL_COLLECT_SNAPSHOT_IMAGES _IOW(BLK_SNAP, 0x30, struct ioctl_collect_snapshot_images_s)
+
+#pragma pack(pop)
+
+// commands for character device interface
+#define BLK_SNAP_CHARCMD_UNDEFINED 0x00
+#define BLK_SNAP_CHARCMD_ACKNOWLEDGE 0x01
+#define BLK_SNAP_CHARCMD_INVALID 0xFF
+// to module commands
+#define BLK_SNAP_CHARCMD_INITIATE 0x21
+#define BLK_SNAP_CHARCMD_NEXT_PORTION 0x22
+#define BLK_SNAP_CHARCMD_NEXT_PORTION_MULTIDEV 0x23
+// from module commands
+#define BLK_SNAP_CHARCMD_HALFFILL 0x41
+#define BLK_SNAP_CHARCMD_OVERFLOW 0x42
+#define BLK_SNAP_CHARCMD_TERMINATE 0x43
diff --git a/drivers/block/blk-snap/blk_deferred.c b/drivers/block/blk-snap/blk_deferred.c
new file mode 100644
index 000000000000..1d0b7d2c4d71
--- /dev/null
+++ b/drivers/block/blk-snap/blk_deferred.c
@@ -0,0 +1,566 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-deferred"
+#include "common.h"
+
+#include "blk_deferred.h"
+#include "blk_util.h"
+#include "snapstore.h"
+#include "params.h"
+
+struct bio_set blk_deferred_bioset = { 0 };
+
+struct dio_bio_complete {
+	struct blk_deferred_request *dio_req;
+	sector_t bio_sect_len;
+};
+
+struct dio_deadlocked_list {
+	struct list_head link;
+
+	struct blk_deferred_request *dio_req;
+};
+
+LIST_HEAD(dio_deadlocked_list);
+DEFINE_RWLOCK(dio_deadlocked_list_lock);
+
+atomic64_t dio_alloc_count = ATOMIC64_INIT(0);
+atomic64_t dio_free_count = ATOMIC64_INIT(0);
+
+void blk_deferred_done(void)
+{
+	struct dio_deadlocked_list *dio_locked;
+
+	do {
+		dio_locked = NULL;
+
+		write_lock(&dio_deadlocked_list_lock);
+		if (!list_empty(&dio_deadlocked_list)) {
+			dio_locked = list_entry(dio_deadlocked_list.next,
+						struct dio_deadlocked_list, link);
+
+			list_del(&dio_locked->link);
+		}
+		write_unlock(&dio_deadlocked_list_lock);
+
+		if (dio_locked) {
+			if (dio_locked->dio_req->sect_len ==
+			    atomic64_read(&dio_locked->dio_req->sect_processed))
+				blk_deferred_request_free(dio_locked->dio_req);
+			else
+				pr_err("Locked defer IO is still in memory\n");
+
+			kfree(dio_locked);
+		}
+	} while (dio_locked);
+}
+
+void blk_deferred_request_deadlocked(struct blk_deferred_request *dio_req)
+{
+	struct dio_deadlocked_list *dio_locked =
+		kzalloc(sizeof(struct dio_deadlocked_list), GFP_KERNEL);
+
+	dio_locked->dio_req = dio_req;
+
+	write_lock(&dio_deadlocked_list_lock);
+	list_add_tail(&dio_locked->link, &dio_deadlocked_list);
+	write_unlock(&dio_deadlocked_list_lock);
+
+	pr_warn("Deadlock with defer IO\n");
+}
+
+void blk_deferred_free(struct blk_deferred_io *dio)
+{
+	size_t inx = 0;
+
+	if (dio->page_array != NULL) {
+		while (dio->page_array[inx] != NULL) {
+			__free_page(dio->page_array[inx]);
+			dio->page_array[inx] = NULL;
+
+			++inx;
+		}
+
+		kfree(dio->page_array);
+		dio->page_array = NULL;
+	}
+	kfree(dio);
+}
+
+struct blk_deferred_io *blk_deferred_alloc(unsigned long block_index,
+					   union blk_descr_unify blk_descr)
+{
+	size_t inx;
+	size_t page_count;
+	struct blk_deferred_io *dio = kmalloc(sizeof(struct blk_deferred_io), GFP_NOIO);
+
+	if (dio == NULL)
+		return NULL;
+
+	INIT_LIST_HEAD(&dio->link);
+
+	dio->blk_descr = blk_descr;
+	dio->blk_index = block_index;
+
+	dio->sect.ofs = block_index << snapstore_block_shift();
+	dio->sect.cnt = snapstore_block_size();
+
+	page_count = snapstore_block_size() / (PAGE_SIZE / SECTOR_SIZE);
+	/*
+	 * empty pointer on the end
+	 */
+	dio->page_array = kzalloc((page_count + 1) * sizeof(struct page *), GFP_NOIO);
+	if (dio->page_array == NULL) {
+		blk_deferred_free(dio);
+		return NULL;
+	}
+
+	for (inx = 0; inx < page_count; inx++) {
+		dio->page_array[inx] = alloc_page(GFP_NOIO);
+		if (dio->page_array[inx] == NULL) {
+			pr_err("Failed to allocate page\n");
+			blk_deferred_free(dio);
+			return NULL;
+		}
+	}
+
+	return dio;
+}
+
+int blk_deferred_bioset_create(void)
+{
+	return bioset_init(&blk_deferred_bioset, 64, sizeof(struct dio_bio_complete),
+			   BIOSET_NEED_BVECS | BIOSET_NEED_RESCUER);
+}
+
+void blk_deferred_bioset_free(void)
+{
+	bioset_exit(&blk_deferred_bioset);
+}
+
+struct bio *_blk_deferred_bio_alloc(int nr_iovecs)
+{
+	struct bio *new_bio = bio_alloc_bioset(GFP_NOIO, nr_iovecs, &blk_deferred_bioset);
+
+	if (new_bio == NULL)
+		return NULL;
+
+	new_bio->bi_end_io = blk_deferred_bio_endio;
+	new_bio->bi_private = ((void *)new_bio) - sizeof(struct dio_bio_complete);
+
+	return new_bio;
+}
+
+static void blk_deferred_complete(struct blk_deferred_request *dio_req, sector_t portion_sect_cnt,
+				  int result)
+{
+	atomic64_add(portion_sect_cnt, &dio_req->sect_processed);
+
+	if (dio_req->sect_len == atomic64_read(&dio_req->sect_processed))
+		complete(&dio_req->complete);
+
+	if (result != SUCCESS) {
+		dio_req->result = result;
+		pr_err("Failed to process defer IO request. errno=%d\n", result);
+	}
+}
+
+void blk_deferred_bio_endio(struct bio *bio)
+{
+	int local_err;
+	struct dio_bio_complete *complete_param = (struct dio_bio_complete *)bio->bi_private;
+
+	if (complete_param == NULL) {
+		//bio already complete
+	} else {
+		if (bio->bi_status != BLK_STS_OK)
+			local_err = -EIO;
+		else
+			local_err = SUCCESS;
+
+		blk_deferred_complete(complete_param->dio_req, complete_param->bio_sect_len,
+				      local_err);
+		bio->bi_private = NULL;
+	}
+
+	bio_put(bio);
+}
+
+static inline size_t _page_count_calculate(sector_t size_sector)
+{
+	size_t page_count = size_sector / (PAGE_SIZE / SECTOR_SIZE);
+
+	if (unlikely(size_sector & ((PAGE_SIZE / SECTOR_SIZE) - 1)))
+		page_count += 1;
+
+	return page_count;
+}
+
+sector_t _blk_deferred_submit_pages(struct block_device *blk_dev,
+				    struct blk_deferred_request *dio_req, int direction,
+				    sector_t arr_ofs, struct page **page_array, sector_t ofs_sector,
+				    sector_t size_sector)
+{
+	struct bio *bio = NULL;
+	int nr_iovecs;
+	int page_inx = arr_ofs >> (PAGE_SHIFT - SECTOR_SHIFT);
+	sector_t process_sect = 0;
+
+	nr_iovecs = _page_count_calculate(size_sector);
+
+	while (NULL == (bio = _blk_deferred_bio_alloc(nr_iovecs))) {
+		size_sector = (size_sector >> 1) & ~((PAGE_SIZE / SECTOR_SIZE) - 1);
+		if (size_sector == 0)
+			return 0;
+
+		nr_iovecs = _page_count_calculate(size_sector);
+	}
+
+	bio_set_dev(bio, blk_dev);
+
+	if (direction == READ)
+		bio_set_op_attrs(bio, REQ_OP_READ, 0);
+	else
+		bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
+
+	bio->bi_iter.bi_sector = ofs_sector;
+
+	{ //add first
+		sector_t unordered = arr_ofs & ((PAGE_SIZE / SECTOR_SIZE) - 1);
+		sector_t bvec_len_sect =
+			min_t(sector_t, ((PAGE_SIZE / SECTOR_SIZE) - unordered), size_sector);
+		struct page *page = page_array[page_inx];
+		unsigned int len = (unsigned int)from_sectors(bvec_len_sect);
+		unsigned int offset = (unsigned int)from_sectors(unordered);
+
+		if (unlikely(page == NULL)) {
+			pr_err("NULL found in page array");
+			bio_put(bio);
+			return 0;
+		}
+		if (unlikely(bio_add_page(bio, page, len, offset) != len)) {
+			bio_put(bio);
+			return 0;
+		}
+		++page_inx;
+		process_sect += bvec_len_sect;
+	}
+
+	while (process_sect < size_sector) {
+		sector_t bvec_len_sect =
+			min_t(sector_t, (PAGE_SIZE / SECTOR_SIZE), (size_sector - process_sect));
+		struct page *page = page_array[page_inx];
+		unsigned int len = (unsigned int)from_sectors(bvec_len_sect);
+
+
+		if (unlikely(page == NULL)) {
+			pr_err("NULL found in page array");
+			break;
+		}
+		if (unlikely(bio_add_page(bio, page, len, 0) != len))
+			break;
+
+		++page_inx;
+		process_sect += bvec_len_sect;
+	}
+
+	((struct dio_bio_complete *)bio->bi_private)->dio_req = dio_req;
+	((struct dio_bio_complete *)bio->bi_private)->bio_sect_len = process_sect;
+
+	submit_bio_direct(bio);
+
+	return process_sect;
+}
+
+sector_t blk_deferred_submit_pages(struct block_device *blk_dev,
+				   struct blk_deferred_request *dio_req, int direction,
+				   sector_t arr_ofs, struct page **page_array, sector_t ofs_sector,
+				   sector_t size_sector)
+{
+	sector_t process_sect = 0;
+
+	do {
+		sector_t portion_sect = _blk_deferred_submit_pages(
+			blk_dev, dio_req, direction, arr_ofs + process_sect, page_array,
+			ofs_sector + process_sect, size_sector - process_sect);
+		if (portion_sect == 0) {
+			pr_err("Failed to submit defer IO pages. Only [%lld] sectors processed\n",
+			       process_sect);
+			break;
+		}
+		process_sect += portion_sect;
+	} while (process_sect < size_sector);
+
+	return process_sect;
+}
+
+struct blk_deferred_request *blk_deferred_request_new(void)
+{
+	struct blk_deferred_request *dio_req = NULL;
+
+	dio_req = kzalloc(sizeof(struct blk_deferred_request), GFP_NOIO);
+	if (dio_req == NULL)
+		return NULL;
+
+	INIT_LIST_HEAD(&dio_req->dios);
+
+	dio_req->result = SUCCESS;
+	atomic64_set(&dio_req->sect_processed, 0);
+	dio_req->sect_len = 0;
+	init_completion(&dio_req->complete);
+
+	return dio_req;
+}
+
+bool blk_deferred_request_already_added(struct blk_deferred_request *dio_req,
+					unsigned long block_index)
+{
+	bool result = false;
+	struct list_head *_list_head;
+
+	if (list_empty(&dio_req->dios))
+		return result;
+
+	list_for_each(_list_head, &dio_req->dios) {
+		struct blk_deferred_io *dio = list_entry(_list_head, struct blk_deferred_io, link);
+
+		if (dio->blk_index == block_index) {
+			result = true;
+			break;
+		}
+	}
+
+	return result;
+}
+
+int blk_deferred_request_add(struct blk_deferred_request *dio_req, struct blk_deferred_io *dio)
+{
+	list_add_tail(&dio->link, &dio_req->dios);
+	dio_req->sect_len += dio->sect.cnt;
+
+	return SUCCESS;
+}
+
+void blk_deferred_request_free(struct blk_deferred_request *dio_req)
+{
+	if (dio_req != NULL) {
+		while (!list_empty(&dio_req->dios)) {
+			struct blk_deferred_io *dio =
+				list_entry(dio_req->dios.next, struct blk_deferred_io, link);
+
+			list_del(&dio->link);
+
+			blk_deferred_free(dio);
+		}
+		kfree(dio_req);
+	}
+}
+
+void blk_deferred_request_waiting_skip(struct blk_deferred_request *dio_req)
+{
+	init_completion(&dio_req->complete);
+	atomic64_set(&dio_req->sect_processed, 0);
+}
+
+int blk_deferred_request_wait(struct blk_deferred_request *dio_req)
+{
+	u64 start_jiffies = get_jiffies_64();
+	u64 current_jiffies;
+
+	while (wait_for_completion_timeout(&dio_req->complete, (HZ * 1)) == 0) {
+		current_jiffies = get_jiffies_64();
+		if (jiffies_to_msecs(current_jiffies - start_jiffies) > 60 * 1000) {
+			pr_warn("Defer IO request timeout\n");
+			return -EDEADLK;
+		}
+	}
+
+	return dio_req->result;
+}
+
+int blk_deferred_request_read_original(struct block_device *original_blk_dev,
+				       struct blk_deferred_request *dio_copy_req)
+{
+	int res = -ENODATA;
+	struct list_head *_list_head;
+
+	blk_deferred_request_waiting_skip(dio_copy_req);
+
+	if (list_empty(&dio_copy_req->dios))
+		return res;
+
+	list_for_each(_list_head, &dio_copy_req->dios) {
+		struct blk_deferred_io *dio = list_entry(_list_head, struct blk_deferred_io, link);
+
+		sector_t ofs = dio->sect.ofs;
+		sector_t cnt = dio->sect.cnt;
+
+		if (cnt != blk_deferred_submit_pages(original_blk_dev, dio_copy_req, READ, 0,
+						     dio->page_array, ofs, cnt)) {
+			pr_err("Failed to submit reading defer IO request. offset=%lld\n",
+			       dio->sect.ofs);
+			res = -EIO;
+			break;
+		}
+		res = SUCCESS;
+	}
+
+	if (res == SUCCESS)
+		res = blk_deferred_request_wait(dio_copy_req);
+
+	return res;
+}
+
+
+static int _store_file(struct block_device *blk_dev, struct blk_deferred_request *dio_copy_req,
+		       struct blk_descr_file *blk_descr, struct page **page_array)
+{
+	struct list_head *_rangelist_head;
+	sector_t page_array_ofs = 0;
+
+	if (unlikely(list_empty(&blk_descr->rangelist))) {
+		pr_err("Invalid block descriptor");
+		return -EINVAL;
+	}
+	list_for_each(_rangelist_head, &blk_descr->rangelist) {
+		struct blk_range_link *range_link;
+		sector_t process_sect;
+
+		range_link = list_entry(_rangelist_head, struct blk_range_link, link);
+		process_sect = blk_deferred_submit_pages(blk_dev, dio_copy_req, WRITE,
+							 page_array_ofs, page_array,
+							 range_link->rg.ofs, range_link->rg.cnt);
+		if (range_link->rg.cnt != process_sect) {
+			pr_err("Failed to submit defer IO request for storing\n");
+			return -EIO;
+		}
+		page_array_ofs += range_link->rg.cnt;
+	}
+	return SUCCESS;
+}
+
+int blk_deferred_request_store_file(struct block_device *blk_dev,
+				    struct blk_deferred_request *dio_copy_req)
+{
+	struct list_head *_dio_list_head;
+
+	blk_deferred_request_waiting_skip(dio_copy_req);
+
+	if (unlikely(list_empty(&dio_copy_req->dios))) {
+		pr_err("Invalid deferred io request");
+		return -EINVAL;
+	}
+	list_for_each(_dio_list_head, &dio_copy_req->dios) {
+		int res;
+		struct blk_deferred_io *dio;
+
+		dio = list_entry(_dio_list_head, struct blk_deferred_io, link);
+		res = _store_file(blk_dev, dio_copy_req, dio->blk_descr.file, dio->page_array);
+		if (res != SUCCESS)
+			return res;
+	}
+
+	return blk_deferred_request_wait(dio_copy_req);
+}
+
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+
+static int _store_multidev(struct blk_deferred_request *dio_copy_req,
+			   struct blk_descr_multidev *blk_descr, struct page **page_array)
+{
+	struct list_head *_ranges_list_head;
+	sector_t page_array_ofs = 0;
+
+	if (unlikely(list_empty(&blk_descr->rangelist))) {
+		pr_err("Invalid block descriptor");
+		return -EINVAL;
+	}
+	list_for_each(_ranges_list_head, &blk_descr->rangelist) {
+		sector_t process_sect;
+		struct blk_range_link_ex *range_link;
+
+		range_link = list_entry(_ranges_list_head, struct blk_range_link_ex, link);
+		process_sect = blk_deferred_submit_pages(range_link->blk_dev, dio_copy_req, WRITE,
+							 page_array_ofs, page_array,
+							 range_link->rg.ofs, range_link->rg.cnt);
+		if (range_link->rg.cnt != process_sect) {
+			pr_err("Failed to submit defer IO request for storing\n");
+			return -EIO;
+		}
+
+		page_array_ofs += range_link->rg.cnt;
+	}
+
+	return SUCCESS;
+}
+
+int blk_deferred_request_store_multidev(struct blk_deferred_request *dio_copy_req)
+{
+	struct list_head *_dio_list_head;
+
+	blk_deferred_request_waiting_skip(dio_copy_req);
+
+	if (unlikely(list_empty(&dio_copy_req->dios))) {
+		pr_err("Invalid deferred io request");
+		return -EINVAL;
+	}
+	list_for_each(_dio_list_head, &dio_copy_req->dios) {
+		int res;
+		struct blk_deferred_io *dio;
+
+		dio = list_entry(_dio_list_head, struct blk_deferred_io, link);
+		res = _store_multidev(dio_copy_req, dio->blk_descr.multidev, dio->page_array);
+		if (res != SUCCESS)
+			return res;
+	}
+
+	return blk_deferred_request_wait(dio_copy_req);
+}
+#endif
+
+static size_t _store_pages(void *dst, struct page **page_array, size_t length)
+{
+	size_t page_inx = 0;
+	size_t processed_len = 0;
+
+	while ((processed_len < length) && (page_array[page_inx] != NULL)) {
+		void *src;
+		size_t page_len = min_t(size_t, PAGE_SIZE, (length - processed_len));
+
+		src = page_address(page_array[page_inx]);
+		memcpy(dst + processed_len, src, page_len);
+
+		++page_inx;
+		processed_len += page_len;
+	}
+
+	return processed_len;
+}
+
+int blk_deferred_request_store_mem(struct blk_deferred_request *dio_copy_req)
+{
+	int res = SUCCESS;
+	sector_t processed = 0;
+
+	if (!list_empty(&dio_copy_req->dios)) {
+		struct list_head *_list_head;
+
+		list_for_each(_list_head, &dio_copy_req->dios) {
+			size_t length;
+			size_t portion;
+			struct blk_deferred_io *dio;
+
+			dio = list_entry(_list_head, struct blk_deferred_io, link);
+			length = snapstore_block_size() * SECTOR_SIZE;
+
+			portion = _store_pages(dio->blk_descr.mem->buff, dio->page_array, length);
+			if (unlikely(portion != length)) {
+				res = -EIO;
+				break;
+			}
+			processed += (sector_t)to_sectors(portion);
+		}
+	}
+
+	blk_deferred_complete(dio_copy_req, processed, res);
+	return res;
+}
diff --git a/drivers/block/blk-snap/blk_deferred.h b/drivers/block/blk-snap/blk_deferred.h
new file mode 100644
index 000000000000..3c516a835c25
--- /dev/null
+++ b/drivers/block/blk-snap/blk_deferred.h
@@ -0,0 +1,67 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+#include "blk_descr_file.h"
+#include "blk_descr_mem.h"
+#include "blk_descr_multidev.h"
+
+#define DEFER_IO_DIO_REQUEST_LENGTH 250
+#define DEFER_IO_DIO_REQUEST_SECTORS_COUNT (10 * 1024 * 1024 / SECTOR_SIZE)
+
+struct blk_deferred_io {
+	struct list_head link;
+
+	unsigned long blk_index;
+	union blk_descr_unify blk_descr;
+
+	struct blk_range sect;
+
+	struct page **page_array; //null pointer on tail
+};
+
+struct blk_deferred_request {
+	struct completion complete;
+	sector_t sect_len;
+	atomic64_t sect_processed;
+	int result;
+
+	struct list_head dios;
+};
+
+void blk_deferred_done(void);
+
+struct blk_deferred_io *blk_deferred_alloc(unsigned long block_index,
+					   union blk_descr_unify blk_descr);
+void blk_deferred_free(struct blk_deferred_io *dio);
+
+void blk_deferred_bio_endio(struct bio *bio);
+
+sector_t blk_deferred_submit_pages(struct block_device *blk_dev,
+				   struct blk_deferred_request *dio_req, int direction,
+				   sector_t arr_ofs, struct page **page_array, sector_t ofs_sector,
+				   sector_t size_sector);
+
+struct blk_deferred_request *blk_deferred_request_new(void);
+
+bool blk_deferred_request_already_added(struct blk_deferred_request *dio_req,
+					unsigned long block_index);
+
+int blk_deferred_request_add(struct blk_deferred_request *dio_req, struct blk_deferred_io *dio);
+void blk_deferred_request_free(struct blk_deferred_request *dio_req);
+void blk_deferred_request_deadlocked(struct blk_deferred_request *dio_req);
+
+void blk_deferred_request_waiting_skip(struct blk_deferred_request *dio_req);
+int blk_deferred_request_wait(struct blk_deferred_request *dio_req);
+
+int blk_deferred_bioset_create(void);
+void blk_deferred_bioset_free(void);
+
+int blk_deferred_request_read_original(struct block_device *original_blk_dev,
+				       struct blk_deferred_request *dio_copy_req);
+
+int blk_deferred_request_store_file(struct block_device *blk_dev,
+				    struct blk_deferred_request *dio_copy_req);
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+int blk_deferred_request_store_multidev(struct blk_deferred_request *dio_copy_req);
+#endif
+int blk_deferred_request_store_mem(struct blk_deferred_request *dio_copy_req);
diff --git a/drivers/block/blk-snap/blk_descr_file.c b/drivers/block/blk-snap/blk_descr_file.c
new file mode 100644
index 000000000000..fca298d35744
--- /dev/null
+++ b/drivers/block/blk-snap/blk_descr_file.c
@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-blk_descr"
+#include "common.h"
+
+#include "blk_descr_file.h"
+
+static inline void list_assign(struct list_head *dst, struct list_head *src)
+{
+	dst->next = src->next;
+	dst->prev = src->prev;
+
+	src->next->prev = dst;
+	src->prev->next = dst;
+}
+
+static inline void blk_descr_file_init(struct blk_descr_file *blk_descr,
+				       struct list_head *rangelist)
+{
+	list_assign(&blk_descr->rangelist, rangelist);
+}
+
+static inline void blk_descr_file_done(struct blk_descr_file *blk_descr)
+{
+	struct blk_range_link *range_link;
+
+	while (!list_empty(&blk_descr->rangelist)) {
+		range_link = list_entry(blk_descr->rangelist.next, struct blk_range_link, link);
+
+		list_del(&range_link->link);
+		kfree(range_link);
+	}
+}
+
+void blk_descr_file_pool_init(struct blk_descr_pool *pool)
+{
+	blk_descr_pool_init(pool, 0);
+}
+
+void _blk_descr_file_cleanup(void *descr_array, size_t count)
+{
+	size_t inx;
+	struct blk_descr_file *file_blocks = descr_array;
+
+	for (inx = 0; inx < count; ++inx)
+		blk_descr_file_done(file_blocks + inx);
+}
+
+void blk_descr_file_pool_done(struct blk_descr_pool *pool)
+{
+	blk_descr_pool_done(pool, _blk_descr_file_cleanup);
+}
+
+static union blk_descr_unify _blk_descr_file_allocate(void *descr_array, size_t index, void *arg)
+{
+	union blk_descr_unify blk_descr;
+	struct blk_descr_file *file_blocks = descr_array;
+
+	blk_descr.file = &file_blocks[index];
+
+	blk_descr_file_init(blk_descr.file, (struct list_head *)arg);
+
+	return blk_descr;
+}
+
+int blk_descr_file_pool_add(struct blk_descr_pool *pool, struct list_head *rangelist)
+{
+	union blk_descr_unify blk_descr;
+
+	blk_descr = blk_descr_pool_alloc(pool, sizeof(struct blk_descr_file),
+					 _blk_descr_file_allocate, (void *)rangelist);
+	if (blk_descr.ptr == NULL) {
+		pr_err("Failed to allocate block descriptor\n");
+		return -ENOMEM;
+	}
+
+	return SUCCESS;
+}
+
+union blk_descr_unify blk_descr_file_pool_take(struct blk_descr_pool *pool)
+{
+	return blk_descr_pool_take(pool, sizeof(struct blk_descr_file));
+}
diff --git a/drivers/block/blk-snap/blk_descr_file.h b/drivers/block/blk-snap/blk_descr_file.h
new file mode 100644
index 000000000000..0e9a5e3efdea
--- /dev/null
+++ b/drivers/block/blk-snap/blk_descr_file.h
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+#include "blk_descr_pool.h"
+
+struct blk_descr_file {
+	struct list_head rangelist;
+};
+
+struct blk_range_link {
+	struct list_head link;
+	struct blk_range rg;
+};
+
+void blk_descr_file_pool_init(struct blk_descr_pool *pool);
+void blk_descr_file_pool_done(struct blk_descr_pool *pool);
+
+/*
+ * allocate new empty block in pool
+ */
+int blk_descr_file_pool_add(struct blk_descr_pool *pool, struct list_head *rangelist);
+
+/*
+ * take empty block from pool
+ */
+union blk_descr_unify blk_descr_file_pool_take(struct blk_descr_pool *pool);
diff --git a/drivers/block/blk-snap/blk_descr_mem.c b/drivers/block/blk-snap/blk_descr_mem.c
new file mode 100644
index 000000000000..cd326ac150b6
--- /dev/null
+++ b/drivers/block/blk-snap/blk_descr_mem.c
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-blk_descr"
+#include "common.h"
+#include "blk_descr_mem.h"
+
+#define SECTION "blk_descr "
+
+static inline void blk_descr_mem_init(struct blk_descr_mem *blk_descr, void *ptr)
+{
+	blk_descr->buff = ptr;
+}
+
+static inline void blk_descr_mem_done(struct blk_descr_mem *blk_descr)
+{
+	blk_descr->buff = NULL;
+}
+
+void blk_descr_mem_pool_init(struct blk_descr_pool *pool, size_t available_blocks)
+{
+	blk_descr_pool_init(pool, available_blocks);
+}
+
+void blk_descr_mem_cleanup(void *descr_array, size_t count)
+{
+	size_t inx;
+	struct blk_descr_mem *mem_blocks = descr_array;
+
+	for (inx = 0; inx < count; ++inx)
+		blk_descr_mem_done(mem_blocks + inx);
+}
+
+void blk_descr_mem_pool_done(struct blk_descr_pool *pool)
+{
+	blk_descr_pool_done(pool, blk_descr_mem_cleanup);
+}
+
+static union blk_descr_unify blk_descr_mem_alloc(void *descr_array, size_t index, void *arg)
+{
+	union blk_descr_unify blk_descr;
+	struct blk_descr_mem *mem_blocks = descr_array;
+
+	blk_descr.mem = &mem_blocks[index];
+
+	blk_descr_mem_init(blk_descr.mem, (void *)arg);
+
+	return blk_descr;
+}
+
+int blk_descr_mem_pool_add(struct blk_descr_pool *pool, void *buffer)
+{
+	union blk_descr_unify blk_descr;
+
+	blk_descr = blk_descr_pool_alloc(pool, sizeof(struct blk_descr_mem),
+					 blk_descr_mem_alloc, buffer);
+	if (blk_descr.ptr == NULL) {
+		pr_err("Failed to allocate block descriptor\n");
+		return -ENOMEM;
+	}
+
+	return SUCCESS;
+}
+
+union blk_descr_unify blk_descr_mem_pool_take(struct blk_descr_pool *pool)
+{
+	return blk_descr_pool_take(pool, sizeof(struct blk_descr_mem));
+}
diff --git a/drivers/block/blk-snap/blk_descr_mem.h b/drivers/block/blk-snap/blk_descr_mem.h
new file mode 100644
index 000000000000..43e8de76c07c
--- /dev/null
+++ b/drivers/block/blk-snap/blk_descr_mem.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+#include "blk_descr_pool.h"
+
+struct blk_descr_mem {
+	void *buff; //pointer to snapstore block in memory
+};
+
+void blk_descr_mem_pool_init(struct blk_descr_pool *pool, size_t available_blocks);
+void blk_descr_mem_pool_done(struct blk_descr_pool *pool);
+
+int blk_descr_mem_pool_add(struct blk_descr_pool *pool, void *buffer);
+union blk_descr_unify blk_descr_mem_pool_take(struct blk_descr_pool *pool);
diff --git a/drivers/block/blk-snap/blk_descr_multidev.c b/drivers/block/blk-snap/blk_descr_multidev.c
new file mode 100644
index 000000000000..cf5e0ed6f781
--- /dev/null
+++ b/drivers/block/blk-snap/blk_descr_multidev.c
@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-blk_descr"
+#include "common.h"
+
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+#include "blk_descr_multidev.h"
+
+static inline void list_assign(struct list_head *dst, struct list_head *src)
+{
+	dst->next = src->next;
+	dst->prev = src->prev;
+
+	src->next->prev = dst;
+	src->prev->next = dst;
+}
+
+static inline void blk_descr_multidev_init(struct blk_descr_multidev *blk_descr,
+					   struct list_head *rangelist)
+{
+	list_assign(&blk_descr->rangelist, rangelist);
+}
+
+static inline void blk_descr_multidev_done(struct blk_descr_multidev *blk_descr)
+{
+	struct blk_range_link_ex *rangelist;
+
+	while (!list_empty(&blk_descr->rangelist)) {
+		rangelist = list_entry(blk_descr->rangelist.next,
+				       struct blk_range_link_ex, link);
+
+		list_del(&rangelist->link);
+		kfree(rangelist);
+	}
+}
+
+void blk_descr_multidev_pool_init(struct blk_descr_pool *pool)
+{
+	blk_descr_pool_init(pool, 0);
+}
+
+static void blk_descr_multidev_cleanup(void *descr_array, size_t count)
+{
+	size_t inx;
+	struct blk_descr_multidev *descr_multidev = descr_array;
+
+	for (inx = 0; inx < count; ++inx)
+		blk_descr_multidev_done(descr_multidev + inx);
+}
+
+void blk_descr_multidev_pool_done(struct blk_descr_pool *pool)
+{
+	blk_descr_pool_done(pool, blk_descr_multidev_cleanup);
+}
+
+static union blk_descr_unify blk_descr_multidev_allocate(void *descr_array, size_t index, void *arg)
+{
+	union blk_descr_unify blk_descr;
+	struct blk_descr_multidev *multidev_blocks = descr_array;
+
+	blk_descr.multidev = &multidev_blocks[index];
+
+	blk_descr_multidev_init(blk_descr.multidev, (struct list_head *)arg);
+
+	return blk_descr;
+}
+
+int blk_descr_multidev_pool_add(struct blk_descr_pool *pool, struct list_head *rangelist)
+{
+	union blk_descr_unify blk_descr;
+
+	blk_descr = blk_descr_pool_alloc(pool, sizeof(struct blk_descr_multidev),
+					 blk_descr_multidev_allocate, (void *)rangelist);
+	if (blk_descr.ptr == NULL) {
+		pr_err("Failed to allocate block descriptor\n");
+		return -ENOMEM;
+	}
+
+	return SUCCESS;
+}
+
+union blk_descr_unify blk_descr_multidev_pool_take(struct blk_descr_pool *pool)
+{
+	return blk_descr_pool_take(pool, sizeof(struct blk_descr_multidev));
+}
+
+#endif //CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
diff --git a/drivers/block/blk-snap/blk_descr_multidev.h b/drivers/block/blk-snap/blk_descr_multidev.h
new file mode 100644
index 000000000000..0145b0d78b10
--- /dev/null
+++ b/drivers/block/blk-snap/blk_descr_multidev.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+
+#include "blk_descr_pool.h"
+
+struct blk_descr_multidev {
+	struct list_head rangelist;
+};
+
+struct blk_range_link_ex {
+	struct list_head link;
+	struct blk_range rg;
+	struct block_device *blk_dev;
+};
+
+void blk_descr_multidev_pool_init(struct blk_descr_pool *pool);
+void blk_descr_multidev_pool_done(struct blk_descr_pool *pool);
+
+int blk_descr_multidev_pool_add(struct blk_descr_pool *pool,
+				struct list_head *rangelist); //allocate new empty block
+union blk_descr_unify blk_descr_multidev_pool_take(struct blk_descr_pool *pool); //take empty
+
+#endif //CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
diff --git a/drivers/block/blk-snap/blk_descr_pool.c b/drivers/block/blk-snap/blk_descr_pool.c
new file mode 100644
index 000000000000..b1fe2ba9c2d0
--- /dev/null
+++ b/drivers/block/blk-snap/blk_descr_pool.c
@@ -0,0 +1,190 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-blk_descr"
+#include "common.h"
+#include "blk_descr_pool.h"
+#include "params.h"
+
+struct pool_el {
+	struct list_head link;
+
+	size_t used_cnt; // used blocks
+	size_t capacity; // blocks array capacity
+
+	u8 descr_array[0];
+};
+
+static void *kmalloc_huge(size_t max_size, size_t min_size, gfp_t flags, size_t *p_allocated_size)
+{
+	void *ptr = NULL;
+
+	do {
+		ptr = kmalloc(max_size, flags | __GFP_NOWARN | __GFP_RETRY_MAYFAIL);
+
+		if (ptr != NULL) {
+			*p_allocated_size = max_size;
+			return ptr;
+		}
+		pr_err("Failed to allocate buffer size=%zu\n", max_size);
+		max_size = max_size >> 1;
+	} while (max_size >= min_size);
+
+	pr_err("Failed to allocate buffer.");
+	return NULL;
+}
+
+static struct pool_el *pool_el_alloc(size_t blk_descr_size)
+{
+	size_t el_size;
+	struct pool_el *el;
+
+	el = kmalloc_huge(8 * PAGE_SIZE, PAGE_SIZE, GFP_NOIO, &el_size);
+	if (el == NULL)
+		return NULL;
+
+	el->capacity = (el_size - sizeof(struct pool_el)) / blk_descr_size;
+	el->used_cnt = 0;
+
+	INIT_LIST_HEAD(&el->link);
+
+	return el;
+}
+
+static void _pool_el_free(struct pool_el *el)
+{
+	if (el != NULL)
+		kfree(el);
+}
+
+void blk_descr_pool_init(struct blk_descr_pool *pool, size_t available_blocks)
+{
+	mutex_init(&pool->lock);
+
+	INIT_LIST_HEAD(&pool->head);
+
+	pool->blocks_cnt = 0;
+
+	pool->total_cnt = available_blocks;
+	pool->take_cnt = 0;
+}
+
+void blk_descr_pool_done(struct blk_descr_pool *pool,
+			 void (*blocks_cleanup_cb)(void *descr_array, size_t count))
+{
+	mutex_lock(&pool->lock);
+	while (!list_empty(&pool->head)) {
+		struct pool_el *el;
+
+		el = list_entry(pool->head.next, struct pool_el, link);
+		if (el == NULL)
+			break;
+
+		list_del(&el->link);
+		--pool->blocks_cnt;
+
+		pool->total_cnt -= el->used_cnt;
+
+		blocks_cleanup_cb(el->descr_array, el->used_cnt);
+
+		_pool_el_free(el);
+	}
+	mutex_unlock(&pool->lock);
+}
+
+union blk_descr_unify blk_descr_pool_alloc(
+	struct blk_descr_pool *pool, size_t blk_descr_size,
+	union blk_descr_unify (*block_alloc_cb)(void *descr_array, size_t index, void *arg),
+	void *arg)
+{
+	union blk_descr_unify blk_descr = { NULL };
+
+	mutex_lock(&pool->lock);
+	do {
+		struct pool_el *el = NULL;
+
+		if (!list_empty(&pool->head)) {
+			el = list_entry(pool->head.prev, struct pool_el, link);
+			if (el->used_cnt == el->capacity)
+				el = NULL;
+		}
+
+		if (el == NULL) {
+			el = pool_el_alloc(blk_descr_size);
+			if (el == NULL)
+				break;
+
+			list_add_tail(&el->link, &pool->head);
+
+			++pool->blocks_cnt;
+		}
+
+		blk_descr = block_alloc_cb(el->descr_array, el->used_cnt, arg);
+
+		++el->used_cnt;
+		++pool->total_cnt;
+
+	} while (false);
+	mutex_unlock(&pool->lock);
+
+	return blk_descr;
+}
+
+static union blk_descr_unify __blk_descr_pool_at(struct blk_descr_pool *pool, size_t blk_descr_size,
+						 size_t index)
+{
+	union blk_descr_unify bkl_descr = { NULL };
+	size_t curr_inx = 0;
+	struct pool_el *el;
+	struct list_head *_list_head;
+
+	if (list_empty(&(pool)->head))
+		return bkl_descr;
+
+	list_for_each(_list_head, &(pool)->head) {
+		el = list_entry(_list_head, struct pool_el, link);
+
+		if ((index >= curr_inx) && (index < (curr_inx + el->used_cnt))) {
+			bkl_descr.ptr = el->descr_array + (index - curr_inx) * blk_descr_size;
+			break;
+		}
+		curr_inx += el->used_cnt;
+	}
+
+	return bkl_descr;
+}
+
+union blk_descr_unify blk_descr_pool_take(struct blk_descr_pool *pool, size_t blk_descr_size)
+{
+	union blk_descr_unify result = { NULL };
+
+	mutex_lock(&pool->lock);
+	do {
+		if (pool->take_cnt >= pool->total_cnt) {
+			pr_err("Unable to get block descriptor: ");
+			pr_err("not enough descriptors, already took %zu, total %zu\n",
+			       pool->take_cnt, pool->total_cnt);
+			break;
+		}
+
+		result = __blk_descr_pool_at(pool, blk_descr_size, pool->take_cnt);
+		if (result.ptr == NULL) {
+			pr_err("Unable to get block descriptor: ");
+			pr_err("not enough descriptors, already took %zu, total %zu\n",
+			       pool->take_cnt, pool->total_cnt);
+			break;
+		}
+
+		++pool->take_cnt;
+	} while (false);
+	mutex_unlock(&pool->lock);
+	return result;
+}
+
+bool blk_descr_pool_check_halffill(struct blk_descr_pool *pool, sector_t empty_limit,
+				   sector_t *fill_status)
+{
+	size_t empty_blocks = (pool->total_cnt - pool->take_cnt);
+
+	*fill_status = (sector_t)(pool->take_cnt) << snapstore_block_shift();
+
+	return (empty_blocks < (size_t)(empty_limit >> snapstore_block_shift()));
+}
diff --git a/drivers/block/blk-snap/blk_descr_pool.h b/drivers/block/blk-snap/blk_descr_pool.h
new file mode 100644
index 000000000000..32f8b8c4103e
--- /dev/null
+++ b/drivers/block/blk-snap/blk_descr_pool.h
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+struct blk_descr_mem;
+struct blk_descr_file;
+struct blk_descr_multidev;
+
+union blk_descr_unify {
+	void *ptr;
+	struct blk_descr_mem *mem;
+	struct blk_descr_file *file;
+	struct blk_descr_multidev *multidev;
+};
+
+struct blk_descr_pool {
+	struct list_head head;
+	struct mutex lock;
+
+	size_t blocks_cnt; // count of struct pool_el
+
+	size_t total_cnt;  // total count of block descriptors
+	size_t take_cnt;   // take count of block descriptors
+};
+
+void blk_descr_pool_init(struct blk_descr_pool *pool, size_t available_blocks);
+
+void blk_descr_pool_done(struct blk_descr_pool *pool,
+			 void (*blocks_cleanup_cb)(void *descr_array, size_t count));
+
+union blk_descr_unify blk_descr_pool_alloc(
+	struct blk_descr_pool *pool, size_t blk_descr_size,
+	union blk_descr_unify (*block_alloc_cb)(void *descr_array, size_t index, void *arg),
+	void *arg);
+
+union blk_descr_unify blk_descr_pool_take(struct blk_descr_pool *pool, size_t blk_descr_size);
+
+bool blk_descr_pool_check_halffill(struct blk_descr_pool *pool, sector_t empty_limit,
+				   sector_t *fill_status);
diff --git a/drivers/block/blk-snap/blk_redirect.c b/drivers/block/blk-snap/blk_redirect.c
new file mode 100644
index 000000000000..4c28a8cb4275
--- /dev/null
+++ b/drivers/block/blk-snap/blk_redirect.c
@@ -0,0 +1,507 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-redirect"
+#include "common.h"
+#include "blk_util.h"
+#include "blk_redirect.h"
+
+#define bio_vec_sectors(bv) (bv.bv_len >> SECTOR_SHIFT)
+
+struct bio_set blk_redirect_bioset = { 0 };
+
+int blk_redirect_bioset_create(void)
+{
+	return bioset_init(&blk_redirect_bioset, 64, 0, BIOSET_NEED_BVECS | BIOSET_NEED_RESCUER);
+}
+
+void blk_redirect_bioset_free(void)
+{
+	bioset_exit(&blk_redirect_bioset);
+}
+
+void blk_redirect_bio_endio(struct bio *bb)
+{
+	struct blk_redirect_bio *rq_redir = (struct blk_redirect_bio *)bb->bi_private;
+
+	if (rq_redir != NULL) {
+		int err = SUCCESS;
+
+		if (bb->bi_status != BLK_STS_OK)
+			err = -EIO;
+
+		if (err != SUCCESS) {
+			pr_err("Failed to process redirect IO request. errno=%d\n", 0 - err);
+
+			if (rq_redir->err == SUCCESS)
+				rq_redir->err = err;
+		}
+
+		if (atomic64_dec_and_test(&rq_redir->bio_count))
+			blk_redirect_complete(rq_redir, rq_redir->err);
+	}
+	bio_put(bb);
+}
+
+struct bio *_blk_dev_redirect_bio_alloc(int nr_iovecs, void *bi_private)
+{
+	struct bio *new_bio;
+
+	new_bio = bio_alloc_bioset(GFP_NOIO, nr_iovecs, &blk_redirect_bioset);
+	if (new_bio == NULL)
+		return NULL;
+
+	new_bio->bi_end_io = blk_redirect_bio_endio;
+	new_bio->bi_private = bi_private;
+
+	return new_bio;
+}
+
+struct blk_redirect_bio_list *_redirect_bio_allocate_list(struct bio *new_bio)
+{
+	struct blk_redirect_bio_list *next;
+
+	next = kzalloc(sizeof(struct blk_redirect_bio_list), GFP_NOIO);
+	if (next == NULL)
+		return NULL;
+
+	next->next = NULL;
+	next->this = new_bio;
+
+	return next;
+}
+
+int bio_endio_list_push(struct blk_redirect_bio *rq_redir, struct bio *new_bio)
+{
+	struct blk_redirect_bio_list *head;
+
+	if (rq_redir->bio_list_head == NULL) {
+		//list is empty, add first bio
+		rq_redir->bio_list_head = _redirect_bio_allocate_list(new_bio);
+		if (rq_redir->bio_list_head == NULL)
+			return -ENOMEM;
+		return SUCCESS;
+	}
+
+	// seek end of list
+	head = rq_redir->bio_list_head;
+	while (head->next != NULL)
+		head = head->next;
+
+	//append new bio to the end of list
+	head->next = _redirect_bio_allocate_list(new_bio);
+	if (head->next == NULL)
+		return -ENOMEM;
+
+	return SUCCESS;
+}
+
+void bio_endio_list_cleanup(struct blk_redirect_bio_list *curr)
+{
+	while (curr != NULL) {
+		struct blk_redirect_bio_list *next;
+
+		next = curr->next;
+		kfree(curr);
+		curr = next;
+	}
+}
+
+static unsigned int get_max_sect(struct block_device *blk_dev)
+{
+	struct request_queue *q = bdev_get_queue(blk_dev);
+
+	return min((unsigned int)(BIO_MAX_PAGES << (PAGE_SHIFT - SECTOR_SHIFT)),
+		   q->limits.max_sectors);
+}
+
+static int _blk_dev_redirect_part_fast(struct blk_redirect_bio *rq_redir, int direction,
+				       struct block_device *blk_dev, sector_t target_pos,
+				       sector_t rq_ofs, sector_t rq_count)
+{
+	__label__ _fail_out;
+	__label__ _reprocess_bv;
+
+	int res = SUCCESS;
+
+	struct bio_vec bvec;
+	struct bvec_iter iter;
+
+	struct bio *new_bio = NULL;
+
+	sector_t sect_ofs = 0;
+	sector_t processed_sectors = 0;
+	int nr_iovecs;
+	struct blk_redirect_bio_list *bio_endio_rec;
+
+	nr_iovecs = get_max_sect(blk_dev) >> (PAGE_SHIFT - SECTOR_SHIFT);
+
+	bio_for_each_segment(bvec, rq_redir->bio, iter) {
+		sector_t bvec_ofs;
+		sector_t bvec_sectors;
+
+		unsigned int len;
+		unsigned int offset;
+
+		if ((sect_ofs + bio_vec_sectors(bvec)) <= rq_ofs) {
+			sect_ofs += bio_vec_sectors(bvec);
+			continue;
+		}
+		if (sect_ofs >= (rq_ofs + rq_count))
+			break;
+
+		bvec_ofs = 0;
+		if (sect_ofs < rq_ofs)
+			bvec_ofs = rq_ofs - sect_ofs;
+
+		bvec_sectors = bio_vec_sectors(bvec) - bvec_ofs;
+		if (bvec_sectors > (rq_count - processed_sectors))
+			bvec_sectors = rq_count - processed_sectors;
+
+		if (bvec_sectors == 0) {
+			res = -EIO;
+			goto _fail_out;
+		}
+
+_reprocess_bv:
+		if (new_bio == NULL) {
+			new_bio = _blk_dev_redirect_bio_alloc(nr_iovecs, rq_redir);
+			while (new_bio == NULL) {
+				pr_err("Unable to allocate new bio for redirect IO.\n");
+				res = -ENOMEM;
+				goto _fail_out;
+			}
+
+			bio_set_dev(new_bio, blk_dev);
+
+			if (direction == READ)
+				bio_set_op_attrs(new_bio, REQ_OP_READ, 0);
+
+			if (direction == WRITE)
+				bio_set_op_attrs(new_bio, REQ_OP_WRITE, 0);
+
+			new_bio->bi_iter.bi_sector = target_pos + processed_sectors;
+		}
+
+		len = (unsigned int)from_sectors(bvec_sectors);
+		offset = bvec.bv_offset + (unsigned int)from_sectors(bvec_ofs);
+		if (unlikely(bio_add_page(new_bio, bvec.bv_page, len, offset) != len)) {
+			if (bio_sectors(new_bio) == 0) {
+				res = -EIO;
+				goto _fail_out;
+			}
+
+			res = bio_endio_list_push(rq_redir, new_bio);
+			if (res != SUCCESS) {
+				pr_err("Failed to add bio into bio_endio_list\n");
+				goto _fail_out;
+			}
+
+			atomic64_inc(&rq_redir->bio_count);
+			new_bio = NULL;
+
+			goto _reprocess_bv;
+		}
+		processed_sectors += bvec_sectors;
+
+		sect_ofs += bio_vec_sectors(bvec);
+	}
+
+	if (new_bio != NULL) {
+		res = bio_endio_list_push(rq_redir, new_bio);
+		if (res != SUCCESS) {
+			pr_err("Failed to add bio into bio_endio_list\n");
+			goto _fail_out;
+		}
+
+		atomic64_inc(&rq_redir->bio_count);
+		new_bio = NULL;
+	}
+
+	return SUCCESS;
+
+_fail_out:
+	bio_endio_rec = rq_redir->bio_list_head;
+	while (bio_endio_rec != NULL) {
+		if (bio_endio_rec->this != NULL)
+			bio_put(bio_endio_rec->this);
+
+		bio_endio_rec = bio_endio_rec->next;
+	}
+
+	bio_endio_list_cleanup(bio_endio_rec);
+
+	pr_err("Failed to process part of redirect IO request. rq_ofs=%lld, rq_count=%lld\n",
+	       rq_ofs, rq_count);
+	return res;
+}
+
+int blk_dev_redirect_part(struct blk_redirect_bio *rq_redir, int direction,
+			  struct block_device *blk_dev, sector_t target_pos, sector_t rq_ofs,
+			  sector_t rq_count)
+{
+	struct request_queue *q = bdev_get_queue(blk_dev);
+	sector_t logical_block_size_mask =
+		(sector_t)((q->limits.logical_block_size >> SECTOR_SHIFT) - 1);
+
+	if (likely(logical_block_size_mask == 0))
+		return _blk_dev_redirect_part_fast(rq_redir, direction, blk_dev, target_pos, rq_ofs,
+						   rq_count);
+
+	if (likely((0 == (target_pos & logical_block_size_mask)) &&
+		   (0 == (rq_count & logical_block_size_mask))))
+		return _blk_dev_redirect_part_fast(rq_redir, direction, blk_dev, target_pos, rq_ofs,
+						   rq_count);
+
+	return -EFAULT;
+}
+
+void blk_dev_redirect_submit(struct blk_redirect_bio *rq_redir)
+{
+	struct blk_redirect_bio_list *head;
+	struct blk_redirect_bio_list *curr;
+
+	head = curr = rq_redir->bio_list_head;
+	rq_redir->bio_list_head = NULL;
+
+	while (curr != NULL) {
+		submit_bio_direct(curr->this);
+
+		curr = curr->next;
+	}
+
+	bio_endio_list_cleanup(head);
+}
+
+int blk_dev_redirect_memcpy_part(struct blk_redirect_bio *rq_redir, int direction, void *buff,
+				 sector_t rq_ofs, sector_t rq_count)
+{
+	struct bio_vec bvec;
+	struct bvec_iter iter;
+
+	sector_t sect_ofs = 0;
+	sector_t processed_sectors = 0;
+
+	bio_for_each_segment(bvec, rq_redir->bio, iter) {
+		void *mem;
+		sector_t bvec_ofs;
+		sector_t bvec_sectors;
+
+		if ((sect_ofs + bio_vec_sectors(bvec)) <= rq_ofs) {
+			sect_ofs += bio_vec_sectors(bvec);
+			continue;
+		}
+
+		if (sect_ofs >= (rq_ofs + rq_count))
+			break;
+
+		bvec_ofs = 0;
+		if (sect_ofs < rq_ofs)
+			bvec_ofs = rq_ofs - sect_ofs;
+
+		bvec_sectors = bio_vec_sectors(bvec) - bvec_ofs;
+		if (bvec_sectors > (rq_count - processed_sectors))
+			bvec_sectors = rq_count - processed_sectors;
+
+		mem = kmap_atomic(bvec.bv_page);
+		if (direction == READ) {
+			memcpy(mem + bvec.bv_offset + (unsigned int)from_sectors(bvec_ofs),
+			       buff + (unsigned int)from_sectors(processed_sectors),
+			       (unsigned int)from_sectors(bvec_sectors));
+		} else {
+			memcpy(buff + (unsigned int)from_sectors(processed_sectors),
+			       mem + bvec.bv_offset + (unsigned int)from_sectors(bvec_ofs),
+			       (unsigned int)from_sectors(bvec_sectors));
+		}
+		kunmap_atomic(mem);
+
+		processed_sectors += bvec_sectors;
+
+		sect_ofs += bio_vec_sectors(bvec);
+	}
+
+	return SUCCESS;
+}
+
+int blk_dev_redirect_zeroed_part(struct blk_redirect_bio *rq_redir, sector_t rq_ofs,
+				 sector_t rq_count)
+{
+	struct bio_vec bvec;
+	struct bvec_iter iter;
+
+	sector_t sect_ofs = 0;
+	sector_t processed_sectors = 0;
+
+	bio_for_each_segment(bvec, rq_redir->bio, iter) {
+		void *mem;
+		sector_t bvec_ofs;
+		sector_t bvec_sectors;
+
+		if ((sect_ofs + bio_vec_sectors(bvec)) <= rq_ofs) {
+			sect_ofs += bio_vec_sectors(bvec);
+			continue;
+		}
+
+		if (sect_ofs >= (rq_ofs + rq_count))
+			break;
+
+		bvec_ofs = 0;
+		if (sect_ofs < rq_ofs)
+			bvec_ofs = rq_ofs - sect_ofs;
+
+		bvec_sectors = bio_vec_sectors(bvec) - bvec_ofs;
+		if (bvec_sectors > (rq_count - processed_sectors))
+			bvec_sectors = rq_count - processed_sectors;
+
+		mem = kmap_atomic(bvec.bv_page);
+		memset(mem + bvec.bv_offset + (unsigned int)from_sectors(bvec_ofs), 0,
+		       (unsigned int)from_sectors(bvec_sectors));
+		kunmap_atomic(mem);
+
+		processed_sectors += bvec_sectors;
+
+		sect_ofs += bio_vec_sectors(bvec);
+	}
+
+	return SUCCESS;
+}
+
+int blk_dev_redirect_read_zeroed(struct blk_redirect_bio *rq_redir, struct block_device *blk_dev,
+				 sector_t rq_pos, sector_t blk_ofs_start, sector_t blk_ofs_count,
+				 struct rangevector *zero_sectors)
+{
+	int res = SUCCESS;
+	struct blk_range_tree_node *range_node;
+
+	sector_t ofs = 0;
+
+	sector_t from = rq_pos + blk_ofs_start;
+	sector_t to = rq_pos + blk_ofs_start + blk_ofs_count - 1;
+
+	down_read(&zero_sectors->lock);
+	range_node = blk_range_rb_iter_first(&zero_sectors->root, from, to);
+	while (range_node) {
+		struct blk_range *zero_range = &range_node->range;
+		sector_t current_portion;
+
+		if (zero_range->ofs > rq_pos + blk_ofs_start + ofs) {
+			sector_t pre_zero_cnt = zero_range->ofs - (rq_pos + blk_ofs_start + ofs);
+
+			res = blk_dev_redirect_part(rq_redir, READ, blk_dev,
+						    rq_pos + blk_ofs_start + ofs,
+						    blk_ofs_start + ofs, pre_zero_cnt);
+			if (res != SUCCESS)
+				break;
+
+			ofs += pre_zero_cnt;
+		}
+
+		current_portion = min_t(sector_t, zero_range->cnt, blk_ofs_count - ofs);
+
+		res = blk_dev_redirect_zeroed_part(rq_redir, blk_ofs_start + ofs, current_portion);
+		if (res != SUCCESS)
+			break;
+
+		ofs += current_portion;
+
+		range_node = blk_range_rb_iter_next(range_node, from, to);
+	}
+	up_read(&zero_sectors->lock);
+
+	if (res == SUCCESS)
+		if ((blk_ofs_count - ofs) > 0)
+			res = blk_dev_redirect_part(rq_redir, READ, blk_dev,
+						    rq_pos + blk_ofs_start + ofs,
+						    blk_ofs_start + ofs, blk_ofs_count - ofs);
+
+	return res;
+}
+void blk_redirect_complete(struct blk_redirect_bio *rq_redir, int res)
+{
+	rq_redir->complete_cb(rq_redir->complete_param, rq_redir->bio, res);
+	redirect_bio_queue_free(rq_redir);
+}
+
+void redirect_bio_queue_init(struct redirect_bio_queue *queue)
+{
+	INIT_LIST_HEAD(&queue->list);
+
+	spin_lock_init(&queue->lock);
+
+	atomic_set(&queue->in_queue_cnt, 0);
+	atomic_set(&queue->alloc_cnt, 0);
+
+	atomic_set(&queue->active_state, true);
+}
+
+struct blk_redirect_bio *redirect_bio_queue_new(struct redirect_bio_queue *queue)
+{
+	struct blk_redirect_bio *rq_redir = kzalloc(sizeof(struct blk_redirect_bio), GFP_NOIO);
+
+	if (rq_redir == NULL)
+		return NULL;
+
+	atomic_inc(&queue->alloc_cnt);
+
+	INIT_LIST_HEAD(&rq_redir->link);
+	rq_redir->queue = queue;
+
+	return rq_redir;
+}
+
+void redirect_bio_queue_free(struct blk_redirect_bio *rq_redir)
+{
+	if (rq_redir) {
+		if (rq_redir->queue)
+			atomic_dec(&rq_redir->queue->alloc_cnt);
+
+		kfree(rq_redir);
+	}
+}
+
+int redirect_bio_queue_push_back(struct redirect_bio_queue *queue,
+				 struct blk_redirect_bio *rq_redir)
+{
+	int res = SUCCESS;
+
+	spin_lock(&queue->lock);
+
+	if (atomic_read(&queue->active_state)) {
+		INIT_LIST_HEAD(&rq_redir->link);
+		list_add_tail(&rq_redir->link, &queue->list);
+		atomic_inc(&queue->in_queue_cnt);
+	} else
+		res = -EACCES;
+
+	spin_unlock(&queue->lock);
+	return res;
+}
+
+struct blk_redirect_bio *redirect_bio_queue_get_first(struct redirect_bio_queue *queue)
+{
+	struct blk_redirect_bio *rq_redir = NULL;
+
+	spin_lock(&queue->lock);
+
+	if (!list_empty(&queue->list)) {
+		rq_redir = list_entry(queue->list.next, struct blk_redirect_bio, link);
+		list_del(&rq_redir->link);
+		atomic_dec(&queue->in_queue_cnt);
+	}
+
+	spin_unlock(&queue->lock);
+
+	return rq_redir;
+}
+
+bool redirect_bio_queue_active(struct redirect_bio_queue *queue, bool state)
+{
+	bool prev_state;
+
+	spin_lock(&queue->lock);
+
+	prev_state = atomic_read(&queue->active_state);
+	atomic_set(&queue->active_state, state);
+
+	spin_unlock(&queue->lock);
+
+	return prev_state;
+}
diff --git a/drivers/block/blk-snap/blk_redirect.h b/drivers/block/blk-snap/blk_redirect.h
new file mode 100644
index 000000000000..aae23e78ebe2
--- /dev/null
+++ b/drivers/block/blk-snap/blk_redirect.h
@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+#include "rangevector.h"
+
+int blk_redirect_bioset_create(void);
+void blk_redirect_bioset_free(void);
+
+void blk_redirect_bio_endio(struct bio *bb);
+
+struct blk_redirect_bio_list {
+	struct blk_redirect_bio_list *next;
+	struct bio *this;
+};
+
+struct redirect_bio_queue {
+	struct list_head list;
+	spinlock_t lock;
+
+	atomic_t active_state;
+	atomic_t in_queue_cnt;
+	atomic_t alloc_cnt;
+};
+
+struct blk_redirect_bio {
+	struct list_head link;
+	struct redirect_bio_queue *queue;
+
+	struct bio *bio;
+	int err;
+	struct blk_redirect_bio_list *bio_list_head; //list of created bios
+	atomic64_t bio_count;
+
+	void *complete_param;
+	void (*complete_cb)(void *complete_param, struct bio *rq, int err);
+};
+
+int blk_dev_redirect_part(struct blk_redirect_bio *rq_redir, int direction,
+			  struct block_device *blk_dev, sector_t target_pos, sector_t rq_ofs,
+			  sector_t rq_count);
+
+void blk_dev_redirect_submit(struct blk_redirect_bio *rq_redir);
+
+int blk_dev_redirect_memcpy_part(struct blk_redirect_bio *rq_redir, int direction, void *src_buff,
+				 sector_t rq_ofs, sector_t rq_count);
+
+int blk_dev_redirect_zeroed_part(struct blk_redirect_bio *rq_redir, sector_t rq_ofs,
+				 sector_t rq_count);
+
+int blk_dev_redirect_read_zeroed(struct blk_redirect_bio *rq_redir, struct block_device *blk_dev,
+				 sector_t rq_pos, sector_t blk_ofs_start, sector_t blk_ofs_count,
+				 struct rangevector *zero_sectors);
+
+void blk_redirect_complete(struct blk_redirect_bio *rq_redir, int res);
+
+void redirect_bio_queue_init(struct redirect_bio_queue *queue);
+
+struct blk_redirect_bio *redirect_bio_queue_new(struct redirect_bio_queue *queue);
+
+void redirect_bio_queue_free(struct blk_redirect_bio *rq_redir);
+
+int redirect_bio_queue_push_back(struct redirect_bio_queue *queue,
+				 struct blk_redirect_bio *rq_redir);
+
+struct blk_redirect_bio *redirect_bio_queue_get_first(struct redirect_bio_queue *queue);
+
+bool redirect_bio_queue_active(struct redirect_bio_queue *queue, bool state);
+
+#define redirect_bio_queue_empty(queue) (atomic_read(&(queue).in_queue_cnt) == 0)
+
+#define redirect_bio_queue_unactive(queue)                                                         \
+	((atomic_read(&((queue).active_state)) == false) &&                                        \
+	 (atomic_read(&((queue).alloc_cnt)) == 0))
diff --git a/drivers/block/blk-snap/blk_util.c b/drivers/block/blk-snap/blk_util.c
new file mode 100644
index 000000000000..57db70b86516
--- /dev/null
+++ b/drivers/block/blk-snap/blk_util.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "common.h"
+#include "blk_util.h"
+
+int blk_dev_open(dev_t dev_id, struct block_device **p_blk_dev)
+{
+	int result = SUCCESS;
+	struct block_device *blk_dev;
+	int refCount;
+
+	blk_dev = bdget(dev_id);
+	if (blk_dev == NULL) {
+		pr_err("Unable to open device [%d:%d]: bdget return NULL\n", MAJOR(dev_id),
+		       MINOR(dev_id));
+		return -ENODEV;
+	}
+
+	refCount = blkdev_get(blk_dev, FMODE_READ | FMODE_WRITE, NULL);
+	if (refCount < 0) {
+		pr_err("Unable to open device [%d:%d]: blkdev_get return error code %d\n",
+		       MAJOR(dev_id), MINOR(dev_id), 0 - refCount);
+		result = refCount;
+	}
+
+	if (result == SUCCESS)
+		*p_blk_dev = blk_dev;
+	return result;
+}
+
+void blk_dev_close(struct block_device *blk_dev)
+{
+	blkdev_put(blk_dev, FMODE_READ);
+}
diff --git a/drivers/block/blk-snap/blk_util.h b/drivers/block/blk-snap/blk_util.h
new file mode 100644
index 000000000000..0776f2faa668
--- /dev/null
+++ b/drivers/block/blk-snap/blk_util.h
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+int blk_dev_open(dev_t dev_id, struct block_device **p_blk_dev);
+void blk_dev_close(struct block_device *blk_dev);
+
+/*
+ * this function was copied from block/blk.h
+ */
+static inline sector_t part_nr_sects_read(struct hd_struct *part)
+{
+#if (BITS_PER_LONG == 32) && defined(CONFIG_SMP)
+	sector_t nr_sects;
+	unsigned int seq;
+
+	do {
+		seq = read_seqcount_begin(&part->nr_sects_seq);
+		nr_sects = part->nr_sects;
+	} while (read_seqcount_retry(&part->nr_sects_seq, seq));
+
+	return nr_sects;
+#elif (BITS_PER_LONG == 32) && defined(CONFIG_PREEMPTION)
+	sector_t nr_sects;
+
+	preempt_disable();
+	nr_sects = part->nr_sects;
+	preempt_enable();
+
+	return nr_sects;
+#else
+	return part->nr_sects;
+#endif
+}
diff --git a/drivers/block/blk-snap/cbt_map.c b/drivers/block/blk-snap/cbt_map.c
new file mode 100644
index 000000000000..e913069d1a57
--- /dev/null
+++ b/drivers/block/blk-snap/cbt_map.c
@@ -0,0 +1,210 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-cbt_map"
+#include "common.h"
+#include "cbt_map.h"
+
+int cbt_map_allocate(struct cbt_map *cbt_map, unsigned int cbt_sect_in_block_degree,
+		     sector_t device_capacity)
+{
+	sector_t size_mod;
+
+	cbt_map->sect_in_block_degree = cbt_sect_in_block_degree;
+	cbt_map->device_capacity = device_capacity;
+	cbt_map->map_size = (device_capacity >> (sector_t)cbt_sect_in_block_degree);
+
+	pr_info("Allocate CBT map of %zu\n", cbt_map->map_size);
+
+	size_mod = (device_capacity & ((sector_t)(1 << cbt_sect_in_block_degree) - 1));
+	if (size_mod)
+		cbt_map->map_size++;
+
+	cbt_map->read_map = big_buffer_alloc(cbt_map->map_size, GFP_KERNEL);
+	if (cbt_map->read_map != NULL)
+		big_buffer_memset(cbt_map->read_map, 0);
+
+	cbt_map->write_map = big_buffer_alloc(cbt_map->map_size, GFP_KERNEL);
+	if (cbt_map->write_map != NULL)
+		big_buffer_memset(cbt_map->write_map, 0);
+
+	if ((cbt_map->read_map == NULL) || (cbt_map->write_map == NULL)) {
+		pr_err("Cannot allocate CBT map. map_size=%zu\n", cbt_map->map_size);
+		return -ENOMEM;
+	}
+
+	cbt_map->snap_number_previous = 0;
+	cbt_map->snap_number_active = 1;
+	generate_random_uuid(cbt_map->generationId.b);
+	cbt_map->active = true;
+
+	cbt_map->state_changed_sectors = 0;
+	cbt_map->state_dirty_sectors = 0;
+
+	return SUCCESS;
+}
+
+void cbt_map_deallocate(struct cbt_map *cbt_map)
+{
+	if (cbt_map->read_map != NULL) {
+		big_buffer_free(cbt_map->read_map);
+		cbt_map->read_map = NULL;
+	}
+
+	if (cbt_map->write_map != NULL) {
+		big_buffer_free(cbt_map->write_map);
+		cbt_map->write_map = NULL;
+	}
+
+	cbt_map->active = false;
+}
+
+static void cbt_map_destroy(struct cbt_map *cbt_map)
+{
+	pr_info("CBT map destroy\n");
+	if (cbt_map != NULL) {
+		cbt_map_deallocate(cbt_map);
+
+		kfree(cbt_map);
+	}
+}
+
+struct cbt_map *cbt_map_create(unsigned int cbt_sect_in_block_degree, sector_t device_capacity)
+{
+	struct cbt_map *cbt_map = NULL;
+
+	pr_info("CBT map create\n");
+
+	cbt_map = kzalloc(sizeof(struct cbt_map), GFP_KERNEL);
+	if (cbt_map == NULL)
+		return NULL;
+
+	if (cbt_map_allocate(cbt_map, cbt_sect_in_block_degree, device_capacity) != SUCCESS) {
+		cbt_map_destroy(cbt_map);
+		return NULL;
+	}
+
+	spin_lock_init(&cbt_map->locker);
+	init_rwsem(&cbt_map->rw_lock);
+	kref_init(&cbt_map->refcount);
+
+	return cbt_map;
+}
+
+void cbt_map_destroy_cb(struct kref *kref)
+{
+	cbt_map_destroy(container_of(kref, struct cbt_map, refcount));
+}
+
+struct cbt_map *cbt_map_get_resource(struct cbt_map *cbt_map)
+{
+	if (cbt_map)
+		kref_get(&cbt_map->refcount);
+
+	return cbt_map;
+}
+
+void cbt_map_put_resource(struct cbt_map *cbt_map)
+{
+	if (cbt_map)
+		kref_put(&cbt_map->refcount, cbt_map_destroy_cb);
+}
+
+void cbt_map_switch(struct cbt_map *cbt_map)
+{
+	pr_info("CBT map switch\n");
+	spin_lock(&cbt_map->locker);
+
+	big_buffer_memcpy(cbt_map->read_map, cbt_map->write_map);
+
+	cbt_map->snap_number_previous = cbt_map->snap_number_active;
+	++cbt_map->snap_number_active;
+	if (cbt_map->snap_number_active == 256) {
+		cbt_map->snap_number_active = 1;
+
+		big_buffer_memset(cbt_map->write_map, 0);
+
+		generate_random_uuid(cbt_map->generationId.b);
+
+		pr_info("CBT reset\n");
+	}
+	spin_unlock(&cbt_map->locker);
+}
+
+int _cbt_map_set(struct cbt_map *cbt_map, sector_t sector_start, sector_t sector_cnt,
+		 u8 snap_number, struct big_buffer *map)
+{
+	int res = SUCCESS;
+	size_t cbt_block;
+	size_t cbt_block_first = (size_t)(sector_start >> cbt_map->sect_in_block_degree);
+	size_t cbt_block_last = (size_t)((sector_start + sector_cnt - 1) >>
+					 cbt_map->sect_in_block_degree); //inclusive
+
+	for (cbt_block = cbt_block_first; cbt_block <= cbt_block_last; ++cbt_block) {
+		if (cbt_block < cbt_map->map_size) {
+			u8 num;
+
+			res = big_buffer_byte_get(map, cbt_block, &num);
+			if (res == SUCCESS)
+				if (num < snap_number)
+					res = big_buffer_byte_set(map, cbt_block, snap_number);
+		} else
+			res = -EINVAL;
+
+		if (res != SUCCESS) {
+			pr_err("Block index is too large. #%zu was demanded, map size %zu\n",
+			       cbt_block, cbt_map->map_size);
+			break;
+		}
+	}
+	return res;
+}
+
+int cbt_map_set(struct cbt_map *cbt_map, sector_t sector_start, sector_t sector_cnt)
+{
+	int res = SUCCESS;
+
+	spin_lock(&cbt_map->locker);
+
+	res = _cbt_map_set(cbt_map, sector_start, sector_cnt, (u8)cbt_map->snap_number_active,
+			   cbt_map->write_map);
+	cbt_map->state_changed_sectors += sector_cnt;
+
+	spin_unlock(&cbt_map->locker);
+	return res;
+}
+
+int cbt_map_set_both(struct cbt_map *cbt_map, sector_t sector_start, sector_t sector_cnt)
+{
+	int res = SUCCESS;
+
+	spin_lock(&cbt_map->locker);
+
+	res = _cbt_map_set(cbt_map, sector_start, sector_cnt,
+			   (u8)cbt_map->snap_number_active, cbt_map->write_map);
+	if (res == SUCCESS)
+		res = _cbt_map_set(cbt_map, sector_start, sector_cnt,
+				   (u8)cbt_map->snap_number_previous, cbt_map->read_map);
+	cbt_map->state_dirty_sectors += sector_cnt;
+
+	spin_unlock(&cbt_map->locker);
+	return res;
+}
+
+size_t cbt_map_read_to_user(struct cbt_map *cbt_map, void __user *user_buff, size_t offset,
+			    size_t size)
+{
+	size_t readed = 0;
+	size_t left_size;
+	size_t real_size = min((cbt_map->map_size - offset), size);
+
+	left_size = real_size -
+		    big_buffer_copy_to_user(user_buff, offset, cbt_map->read_map, real_size);
+
+	if (left_size == 0)
+		readed = real_size;
+	else {
+		pr_err("Not all CBT data was read. Left [%zu] bytes\n", left_size);
+		readed = real_size - left_size;
+	}
+
+	return readed;
+}
diff --git a/drivers/block/blk-snap/cbt_map.h b/drivers/block/blk-snap/cbt_map.h
new file mode 100644
index 000000000000..cb52b09531fe
--- /dev/null
+++ b/drivers/block/blk-snap/cbt_map.h
@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+#include "big_buffer.h"
+#include <linux/kref.h>
+#include <linux/uuid.h>
+
+struct cbt_map {
+	struct kref refcount;
+
+	spinlock_t locker;
+
+	size_t sect_in_block_degree;
+	sector_t device_capacity;
+	size_t map_size;
+
+	struct big_buffer *read_map;
+	struct big_buffer *write_map;
+
+	unsigned long snap_number_active;
+	unsigned long snap_number_previous;
+	uuid_t generationId;
+
+	bool active;
+
+	struct rw_semaphore rw_lock;
+
+	sector_t state_changed_sectors;
+	sector_t state_dirty_sectors;
+};
+
+struct cbt_map *cbt_map_create(unsigned int cbt_sect_in_block_degree, sector_t device_capacity);
+
+struct cbt_map *cbt_map_get_resource(struct cbt_map *cbt_map);
+void cbt_map_put_resource(struct cbt_map *cbt_map);
+
+void cbt_map_switch(struct cbt_map *cbt_map);
+int cbt_map_set(struct cbt_map *cbt_map, sector_t sector_start, sector_t sector_cnt);
+int cbt_map_set_both(struct cbt_map *cbt_map, sector_t sector_start, sector_t sector_cnt);
+
+size_t cbt_map_read_to_user(struct cbt_map *cbt_map, void __user *user_buffer, size_t offset,
+			    size_t size);
+
+static inline void cbt_map_read_lock(struct cbt_map *cbt_map)
+{
+	down_read(&cbt_map->rw_lock);
+};
+
+static inline void cbt_map_read_unlock(struct cbt_map *cbt_map)
+{
+	up_read(&cbt_map->rw_lock);
+};
+
+static inline void cbt_map_write_lock(struct cbt_map *cbt_map)
+{
+	down_write(&cbt_map->rw_lock);
+};
+
+static inline void cbt_map_write_unlock(struct cbt_map *cbt_map)
+{
+	up_write(&cbt_map->rw_lock);
+};
diff --git a/drivers/block/blk-snap/common.h b/drivers/block/blk-snap/common.h
new file mode 100644
index 000000000000..bbd5e98ab2a6
--- /dev/null
+++ b/drivers/block/blk-snap/common.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+#ifndef BLK_SNAP_SECTION
+#define BLK_SNAP_SECTION ""
+#endif
+#define pr_fmt(fmt) KBUILD_MODNAME BLK_SNAP_SECTION ": " fmt
+
+#include <linux/version.h> /*rudiment - needed for using KERNEL_VERSION */
+
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/mutex.h>
+#include <linux/rwsem.h>
+#include <linux/spinlock.h>
+#include <linux/slab.h>
+#include <linux/list.h>
+#include <linux/atomic.h>
+#include <linux/blkdev.h>
+
+#define from_sectors(_sectors) (_sectors << SECTOR_SHIFT)
+#define to_sectors(_byte_size) (_byte_size >> SECTOR_SHIFT)
+
+struct blk_range {
+	sector_t ofs;
+	blkcnt_t cnt;
+};
+
+#ifndef SUCCESS
+#define SUCCESS 0
+#endif
diff --git a/drivers/block/blk-snap/ctrl_fops.c b/drivers/block/blk-snap/ctrl_fops.c
new file mode 100644
index 000000000000..b7b18539ee96
--- /dev/null
+++ b/drivers/block/blk-snap/ctrl_fops.c
@@ -0,0 +1,691 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-ctrl"
+#include "common.h"
+#include "blk-snap-ctl.h"
+#include "ctrl_fops.h"
+#include "version.h"
+#include "tracking.h"
+#include "snapshot.h"
+#include "snapstore.h"
+#include "snapimage.h"
+#include "tracker.h"
+#include "blk_deferred.h"
+#include "big_buffer.h"
+#include "params.h"
+
+#include <linux/module.h>
+#include <linux/poll.h>
+#include <linux/uaccess.h>
+
+int blk_snap_major; //zero by default
+
+const struct file_operations ctrl_fops = { .owner = THIS_MODULE,
+					   .read = ctrl_read,
+					   .write = ctrl_write,
+					   .open = ctrl_open,
+					   .release = ctrl_release,
+					   .poll = ctrl_poll,
+					   .unlocked_ioctl = ctrl_unlocked_ioctl };
+
+atomic_t dev_open_cnt = ATOMIC_INIT(0);
+
+const struct ioctl_getversion_s version = { .major = FILEVER_MAJOR,
+					    .minor = FILEVER_MINOR,
+					    .revision = FILEVER_REVISION,
+					    .build = 0 };
+
+int get_blk_snap_major(void)
+{
+	return blk_snap_major;
+}
+
+int ctrl_init(void)
+{
+	int ret;
+
+	ret = register_chrdev(0, MODULE_NAME, &ctrl_fops);
+	if (ret < 0) {
+		pr_err("Failed to register a character device. errno=%d\n", blk_snap_major);
+		return ret;
+	}
+
+	blk_snap_major = ret;
+	pr_info("Module major [%d]\n", blk_snap_major);
+	return SUCCESS;
+}
+
+void ctrl_done(void)
+{
+	unregister_chrdev(blk_snap_major, MODULE_NAME);
+	ctrl_pipe_done();
+}
+
+ssize_t ctrl_read(struct file *fl, char __user *buffer, size_t length, loff_t *offset)
+{
+	ssize_t bytes_read = 0;
+	struct ctrl_pipe *pipe = (struct ctrl_pipe *)fl->private_data;
+
+	if (pipe == NULL) {
+		pr_err("Unable to read from pipe: invalid pipe pointer\n");
+		return -EINVAL;
+	}
+
+	bytes_read = ctrl_pipe_read(pipe, buffer, length);
+	if (bytes_read == 0)
+		if (fl->f_flags & O_NONBLOCK)
+			bytes_read = -EAGAIN;
+
+	return bytes_read;
+}
+
+ssize_t ctrl_write(struct file *fl, const char __user *buffer, size_t length, loff_t *offset)
+{
+	struct ctrl_pipe *pipe = (struct ctrl_pipe *)fl->private_data;
+
+	if (pipe == NULL) {
+		pr_err("Unable to write into pipe: invalid pipe pointer\n");
+		return -EINVAL;
+	}
+
+	return ctrl_pipe_write(pipe, buffer, length);
+}
+
+unsigned int ctrl_poll(struct file *fl, struct poll_table_struct *wait)
+{
+	struct ctrl_pipe *pipe = (struct ctrl_pipe *)fl->private_data;
+
+	if (pipe == NULL) {
+		pr_err("Unable to poll pipe: invalid pipe pointer\n");
+		return -EINVAL;
+	}
+
+	return ctrl_pipe_poll(pipe);
+}
+
+int ctrl_open(struct inode *inode, struct file *fl)
+{
+	fl->f_pos = 0;
+
+	if (false == try_module_get(THIS_MODULE))
+		return -EINVAL;
+
+	fl->private_data = (void *)ctrl_pipe_new();
+	if (fl->private_data == NULL) {
+		pr_err("Failed to open ctrl file\n");
+		return -ENOMEM;
+	}
+
+	atomic_inc(&dev_open_cnt);
+
+	return SUCCESS;
+}
+
+int ctrl_release(struct inode *inode, struct file *fl)
+{
+	int result = SUCCESS;
+
+	if (atomic_read(&dev_open_cnt) > 0) {
+		module_put(THIS_MODULE);
+		ctrl_pipe_put_resource((struct ctrl_pipe *)fl->private_data);
+
+		atomic_dec(&dev_open_cnt);
+	} else {
+		pr_err("Unable to close ctrl file: the file is already closed\n");
+		result = -EALREADY;
+	}
+
+	return result;
+}
+
+int ioctl_compatibility_flags(unsigned long arg)
+{
+	unsigned long len;
+	struct ioctl_compatibility_flags_s param;
+
+	param.flags = 0;
+	param.flags |= BLK_SNAP_COMPATIBILITY_SNAPSTORE;
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+	param.flags |= BLK_SNAP_COMPATIBILITY_MULTIDEV;
+#endif
+	len = copy_to_user((void *)arg, &param, sizeof(struct ioctl_compatibility_flags_s));
+	if (len != 0) {
+		pr_err("Unable to get compatibility flags: invalid user buffer\n");
+		return -EINVAL;
+	}
+
+	return SUCCESS;
+}
+
+int ioctl_get_version(unsigned long arg)
+{
+	unsigned long len;
+
+	pr_info("Get version\n");
+
+	len = copy_to_user((void *)arg, &version, sizeof(struct ioctl_getversion_s));
+	if (len != 0) {
+		pr_err("Unable to get version: invalid user buffer\n");
+		return -ENODATA;
+	}
+
+	return SUCCESS;
+}
+
+int ioctl_tracking_add(unsigned long arg)
+{
+	unsigned long len;
+	struct ioctl_dev_id_s dev;
+
+	len = copy_from_user(&dev, (void *)arg, sizeof(struct ioctl_dev_id_s));
+	if (len != 0) {
+		pr_err("Unable to add device under tracking: invalid user buffer\n");
+		return -ENODATA;
+	}
+
+	return tracking_add(MKDEV(dev.major, dev.minor), 0ull);
+}
+
+int ioctl_tracking_remove(unsigned long arg)
+{
+	struct ioctl_dev_id_s dev;
+
+	if (copy_from_user(&dev, (void *)arg, sizeof(struct ioctl_dev_id_s)) != 0) {
+		pr_err("Unable to remove device from tracking: invalid user buffer\n");
+		return -ENODATA;
+	}
+	return tracking_remove(MKDEV(dev.major, dev.minor));
+	;
+}
+
+int ioctl_tracking_collect(unsigned long arg)
+{
+	unsigned long len;
+	int res;
+	struct ioctl_tracking_collect_s get;
+
+	pr_info("Collecting tracking devices:\n");
+
+	len = copy_from_user(&get, (void *)arg, sizeof(struct ioctl_tracking_collect_s));
+	if (len  != 0) {
+		pr_err("Unable to collect tracking devices: invalid user buffer\n");
+		return -ENODATA;
+	}
+
+	if (get.p_cbt_info == NULL) {
+		res = tracking_collect(0x7FFFffff, NULL, &get.count);
+		if (res == SUCCESS) {
+			len = copy_to_user((void *)arg, (void *)&get,
+					   sizeof(struct ioctl_tracking_collect_s));
+			if (len != 0) {
+				pr_err("Unable to collect tracking devices: invalid user buffer for arguments\n");
+				res = -ENODATA;
+			}
+		} else {
+			pr_err("Failed to execute tracking_collect. errno=%d\n", res);
+		}
+	} else {
+		struct cbt_info_s *p_cbt_info = NULL;
+
+		p_cbt_info = kcalloc(get.count, sizeof(struct cbt_info_s), GFP_KERNEL);
+		if (p_cbt_info == NULL)
+			return -ENOMEM;
+
+		do {
+			res = tracking_collect(get.count, p_cbt_info, &get.count);
+			if (res != SUCCESS) {
+				pr_err("Failed to execute tracking_collect. errno=%d\n", res);
+				break;
+			}
+			len = copy_to_user(get.p_cbt_info, p_cbt_info,
+					      get.count * sizeof(struct cbt_info_s));
+			if (len != 0) {
+				pr_err("Unable to collect tracking devices: invalid user buffer for CBT info\n");
+				res = -ENODATA;
+				break;
+			}
+
+			len = copy_to_user((void *)arg, (void *)&get,
+					   sizeof(struct ioctl_tracking_collect_s));
+			if (len != 0) {
+				pr_err("Unable to collect tracking devices: invalid user buffer for arguments\n");
+				res = -ENODATA;
+				break;
+			}
+
+		} while (false);
+
+		kfree(p_cbt_info);
+		p_cbt_info = NULL;
+	}
+	return res;
+}
+
+int ioctl_tracking_block_size(unsigned long arg)
+{
+	unsigned long len;
+	unsigned int blk_sz = change_tracking_block_size();
+
+	len = copy_to_user((void *)arg, &blk_sz, sizeof(unsigned int));
+	if (len != 0) {
+		pr_err("Unable to get tracking block size: invalid user buffer for arguments\n");
+		return -ENODATA;
+	}
+	return SUCCESS;
+}
+
+int ioctl_tracking_read_cbt_map(unsigned long arg)
+{
+	dev_t dev_id;
+	unsigned long len;
+	struct ioctl_tracking_read_cbt_bitmap_s readbitmap;
+
+	len = copy_from_user(&readbitmap, (void *)arg,
+				sizeof(struct ioctl_tracking_read_cbt_bitmap_s));
+	if (len != 0) {
+		pr_err("Unable to read CBT map: invalid user buffer\n");
+		return -ENODATA;
+	}
+
+	dev_id = MKDEV(readbitmap.dev_id.major, readbitmap.dev_id.minor);
+	return tracking_read_cbt_bitmap(dev_id, readbitmap.offset, readbitmap.length,
+					(void *)readbitmap.buff);
+}
+
+int ioctl_tracking_mark_dirty_blocks(unsigned long arg)
+{
+	unsigned long len;
+	struct ioctl_tracking_mark_dirty_blocks_s param;
+	struct block_range_s *p_dirty_blocks;
+	size_t buffer_size;
+	int result = SUCCESS;
+
+	len = copy_from_user(&param, (void *)arg,
+			     sizeof(struct ioctl_tracking_mark_dirty_blocks_s));
+	if (len != 0) {
+		pr_err("Unable to mark dirty blocks: invalid user buffer\n");
+		return -ENODATA;
+	}
+
+	buffer_size = param.count * sizeof(struct block_range_s);
+	p_dirty_blocks = kzalloc(buffer_size, GFP_KERNEL);
+	if (p_dirty_blocks == NULL) {
+		pr_err("Unable to mark dirty blocks: cannot allocate [%zu] bytes\n", buffer_size);
+		return -ENOMEM;
+	}
+
+	do {
+		dev_t image_dev_id;
+
+		len = copy_from_user(p_dirty_blocks, (void *)param.p_dirty_blocks, buffer_size);
+		if (len != 0) {
+			pr_err("Unable to mark dirty blocks: invalid user buffer\n");
+			result = -ENODATA;
+			break;
+		}
+
+		image_dev_id = MKDEV(param.image_dev_id.major, param.image_dev_id.minor);
+		result = snapimage_mark_dirty_blocks(image_dev_id, p_dirty_blocks, param.count);
+	} while (false);
+	kfree(p_dirty_blocks);
+
+	return result;
+}
+
+int ioctl_snapshot_create(unsigned long arg)
+{
+	unsigned long len;
+	size_t dev_id_buffer_size;
+	int status;
+	struct ioctl_snapshot_create_s param;
+	struct ioctl_dev_id_s *pk_dev_id = NULL;
+
+	len = copy_from_user(&param, (void *)arg, sizeof(struct ioctl_snapshot_create_s));
+	if (len != 0) {
+		pr_err("Unable to create snapshot: invalid user buffer\n");
+		return -ENODATA;
+	}
+
+	dev_id_buffer_size = sizeof(struct ioctl_dev_id_s) * param.count;
+	pk_dev_id = kzalloc(dev_id_buffer_size, GFP_KERNEL);
+	if (pk_dev_id == NULL) {
+		pr_err("Unable to create snapshot: cannot allocate [%zu] bytes\n",
+		       dev_id_buffer_size);
+		return -ENOMEM;
+	}
+
+	do {
+		size_t dev_buffer_size;
+		dev_t *p_dev = NULL;
+		int inx = 0;
+
+		len = copy_from_user(pk_dev_id, (void *)param.p_dev_id,
+				     param.count * sizeof(struct ioctl_dev_id_s));
+		if (len != 0) {
+			pr_err("Unable to create snapshot: invalid user buffer for parameters\n");
+			status = -ENODATA;
+			break;
+		}
+
+		dev_buffer_size = sizeof(dev_t) * param.count;
+		p_dev = kzalloc(dev_buffer_size, GFP_KERNEL);
+		if (p_dev == NULL) {
+			pr_err("Unable to create snapshot: cannot allocate [%zu] bytes\n",
+			       dev_buffer_size);
+			status = -ENOMEM;
+			break;
+		}
+
+		for (inx = 0; inx < param.count; ++inx)
+			p_dev[inx] = MKDEV(pk_dev_id[inx].major, pk_dev_id[inx].minor);
+
+		status = snapshot_create(p_dev, param.count, &param.snapshot_id);
+
+		kfree(p_dev);
+		p_dev = NULL;
+
+	} while (false);
+	kfree(pk_dev_id);
+	pk_dev_id = NULL;
+
+	if (status == SUCCESS) {
+		len = copy_to_user((void *)arg, &param, sizeof(struct ioctl_snapshot_create_s));
+		if (len != 0) {
+			pr_err("Unable to create snapshot: invalid user buffer\n");
+			status = -ENODATA;
+		}
+	}
+
+	return status;
+}
+
+int ioctl_snapshot_destroy(unsigned long arg)
+{
+	unsigned long len;
+	unsigned long long param;
+
+	len = copy_from_user(&param, (void *)arg, sizeof(unsigned long long));
+	if (len != 0) {
+		pr_err("Unable to destroy snapshot: invalid user buffer\n");
+		return -ENODATA;
+	}
+
+	return snapshot_destroy(param);
+}
+
+static inline dev_t _snapstore_dev(struct ioctl_dev_id_s *dev_id)
+{
+	if ((dev_id->major == 0) && (dev_id->minor == 0))
+		return 0; //memory snapstore
+
+	if ((dev_id->major == -1) && (dev_id->minor == -1))
+		return 0xFFFFffff; //multidevice snapstore
+
+	return MKDEV(dev_id->major, dev_id->minor);
+}
+
+int ioctl_snapstore_create(unsigned long arg)
+{
+	unsigned long len;
+	int res = SUCCESS;
+	struct ioctl_snapstore_create_s param;
+	size_t inx = 0;
+	dev_t *dev_id_set = NULL;
+
+	len = copy_from_user(&param, (void *)arg, sizeof(struct ioctl_snapstore_create_s));
+	if (len != 0) {
+		pr_err("Unable to create snapstore: invalid user buffer\n");
+		return -EINVAL;
+	}
+
+	dev_id_set = kcalloc(param.count, sizeof(dev_t), GFP_KERNEL);
+	if (dev_id_set == NULL)
+		return -ENOMEM;
+
+	for (inx = 0; inx < param.count; ++inx) {
+		struct ioctl_dev_id_s dev_id;
+
+		len = copy_from_user(&dev_id, param.p_dev_id + inx, sizeof(struct ioctl_dev_id_s));
+		if (len != 0) {
+			pr_err("Unable to create snapstore: ");
+			pr_err("invalid user buffer for parameters\n");
+
+			res = -ENODATA;
+			break;
+		}
+
+		dev_id_set[inx] = MKDEV(dev_id.major, dev_id.minor);
+	}
+
+	if (res == SUCCESS)
+		res = snapstore_create((uuid_t *)param.id, _snapstore_dev(&param.snapstore_dev_id),
+				       dev_id_set, (size_t)param.count);
+
+	kfree(dev_id_set);
+
+	return res;
+}
+
+int ioctl_snapstore_file(unsigned long arg)
+{
+	unsigned long len;
+	int res = SUCCESS;
+	struct ioctl_snapstore_file_add_s param;
+	struct big_buffer *ranges = NULL;
+	size_t ranges_buffer_size;
+
+	len = copy_from_user(&param, (void *)arg, sizeof(struct ioctl_snapstore_file_add_s));
+	if (len != 0) {
+		pr_err("Unable to add file to snapstore: invalid user buffer\n");
+		return -EINVAL;
+	}
+
+	ranges_buffer_size = sizeof(struct ioctl_range_s) * param.range_count;
+
+	ranges = big_buffer_alloc(ranges_buffer_size, GFP_KERNEL);
+	if (ranges == NULL) {
+		pr_err("Unable to add file to snapstore: cannot allocate [%zu] bytes\n",
+		       ranges_buffer_size);
+		return -ENOMEM;
+	}
+
+	if (big_buffer_copy_from_user((void *)param.ranges, 0, ranges, ranges_buffer_size)
+		!= ranges_buffer_size) {
+
+		pr_err("Unable to add file to snapstore: invalid user buffer for parameters\n");
+		res = -ENODATA;
+	} else
+		res = snapstore_add_file((uuid_t *)(param.id), ranges, (size_t)param.range_count);
+
+	big_buffer_free(ranges);
+
+	return res;
+}
+
+int ioctl_snapstore_memory(unsigned long arg)
+{
+	unsigned long len;
+	int res = SUCCESS;
+	struct ioctl_snapstore_memory_limit_s param;
+
+	len = copy_from_user(&param, (void *)arg, sizeof(struct ioctl_snapstore_memory_limit_s));
+	if (len != 0) {
+		pr_err("Unable to add memory block to snapstore: invalid user buffer\n");
+		return -EINVAL;
+	}
+
+	res = snapstore_add_memory((uuid_t *)param.id, param.size);
+
+	return res;
+}
+int ioctl_snapstore_cleanup(unsigned long arg)
+{
+	unsigned long len;
+	int res = SUCCESS;
+	struct ioctl_snapstore_cleanup_s param;
+
+	len = copy_from_user(&param, (void *)arg, sizeof(struct ioctl_snapstore_cleanup_s));
+	if (len != 0) {
+		pr_err("Unable to perform snapstore cleanup: invalid user buffer\n");
+		return -EINVAL;
+	}
+
+	pr_info("Cleanup snapstore %pUB\n", (uuid_t *)param.id);
+	res = snapstore_cleanup((uuid_t *)param.id, &param.filled_bytes);
+
+	if (res == SUCCESS) {
+		if (0 !=
+		    copy_to_user((void *)arg, &param, sizeof(struct ioctl_snapstore_cleanup_s))) {
+			pr_err("Unable to perform snapstore cleanup: invalid user buffer\n");
+			res = -ENODATA;
+		}
+	}
+
+	return res;
+}
+
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+int ioctl_snapstore_file_multidev(unsigned long arg)
+{
+	unsigned long len;
+	int res = SUCCESS;
+	struct ioctl_snapstore_file_add_multidev_s param;
+	struct big_buffer *ranges = NULL; //struct ioctl_range_s* ranges = NULL;
+	size_t ranges_buffer_size;
+
+	len = copy_from_user(&param, (void *)arg,
+				sizeof(struct ioctl_snapstore_file_add_multidev_s));
+	if (len != 0) {
+		pr_err("Unable to add file to multidev snapstore: invalid user buffer\n");
+		return -EINVAL;
+	}
+
+	ranges_buffer_size = sizeof(struct ioctl_range_s) * param.range_count;
+
+	ranges = big_buffer_alloc(ranges_buffer_size, GFP_KERNEL);
+	if (ranges == NULL) {
+		pr_err("Unable to add file to multidev snapstore: cannot allocate [%zu] bytes\n",
+		       ranges_buffer_size);
+		return -ENOMEM;
+	}
+
+	do {
+		uuid_t *id = (uuid_t *)(param.id);
+		dev_t snapstore_device = MKDEV(param.dev_id.major, param.dev_id.minor);
+		size_t ranges_cnt = (size_t)param.range_count;
+
+		if (ranges_buffer_size != big_buffer_copy_from_user((void *)param.ranges, 0, ranges,
+								    ranges_buffer_size)) {
+			pr_err("Unable to add file to snapstore: invalid user buffer for parameters\n");
+			res = -ENODATA;
+			break;
+		}
+
+		res = snapstore_add_multidev(id, snapstore_device, ranges, ranges_cnt);
+	} while (false);
+	big_buffer_free(ranges);
+
+	return res;
+}
+
+#endif
+//////////////////////////////////////////////////////////////////////////
+
+/*
+ * Snapshot get errno for device
+ */
+int ioctl_snapshot_errno(unsigned long arg)
+{
+	unsigned long len;
+	int res;
+	struct ioctl_snapshot_errno_s param;
+
+	len = copy_from_user(&param, (void *)arg, sizeof(struct ioctl_dev_id_s));
+	if (len != 0) {
+		pr_err("Unable failed to get snapstore error code: invalid user buffer\n");
+		return -EINVAL;
+	}
+
+	res = snapstore_device_errno(MKDEV(param.dev_id.major, param.dev_id.minor),
+				     &param.err_code);
+
+	if (res != SUCCESS)
+		return res;
+
+	len = copy_to_user((void *)arg, &param, sizeof(struct ioctl_snapshot_errno_s));
+	if (len != 0) {
+		pr_err("Unable to get snapstore error code: invalid user buffer\n");
+		return -EINVAL;
+	}
+
+	return SUCCESS;
+}
+
+int ioctl_collect_snapimages(unsigned long arg)
+{
+	unsigned long len;
+	int status = SUCCESS;
+	struct ioctl_collect_snapshot_images_s param;
+
+	len = copy_from_user(&param, (void *)arg, sizeof(struct ioctl_collect_snapshot_images_s));
+	if (len != 0) {
+		pr_err("Unable to collect snapshot images: invalid user buffer\n");
+		return -ENODATA;
+	}
+
+	status = snapimage_collect_images(param.count, param.p_image_info, &param.count);
+
+	len = copy_to_user((void *)arg, &param, sizeof(struct ioctl_collect_snapshot_images_s));
+	if (len != 0) {
+		pr_err("Unable to collect snapshot images: invalid user buffer\n");
+		return -ENODATA;
+	}
+
+	return status;
+}
+
+struct blk_snap_ioctl_table {
+	unsigned int cmd;
+	int (*fn)(unsigned long arg);
+};
+
+static struct blk_snap_ioctl_table blk_snap_ioctl_table[] = {
+	{ (IOCTL_COMPATIBILITY_FLAGS), ioctl_compatibility_flags },
+	{ (IOCTL_GETVERSION), ioctl_get_version },
+
+	{ (IOCTL_TRACKING_ADD), ioctl_tracking_add },
+	{ (IOCTL_TRACKING_REMOVE), ioctl_tracking_remove },
+	{ (IOCTL_TRACKING_COLLECT), ioctl_tracking_collect },
+	{ (IOCTL_TRACKING_BLOCK_SIZE), ioctl_tracking_block_size },
+	{ (IOCTL_TRACKING_READ_CBT_BITMAP), ioctl_tracking_read_cbt_map },
+	{ (IOCTL_TRACKING_MARK_DIRTY_BLOCKS), ioctl_tracking_mark_dirty_blocks },
+
+	{ (IOCTL_SNAPSHOT_CREATE), ioctl_snapshot_create },
+	{ (IOCTL_SNAPSHOT_DESTROY), ioctl_snapshot_destroy },
+	{ (IOCTL_SNAPSHOT_ERRNO), ioctl_snapshot_errno },
+
+	{ (IOCTL_SNAPSTORE_CREATE), ioctl_snapstore_create },
+	{ (IOCTL_SNAPSTORE_FILE), ioctl_snapstore_file },
+	{ (IOCTL_SNAPSTORE_MEMORY), ioctl_snapstore_memory },
+	{ (IOCTL_SNAPSTORE_CLEANUP), ioctl_snapstore_cleanup },
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+	{ (IOCTL_SNAPSTORE_FILE_MULTIDEV), ioctl_snapstore_file_multidev },
+#endif
+	{ (IOCTL_COLLECT_SNAPSHOT_IMAGES), ioctl_collect_snapimages },
+	{ 0, NULL }
+};
+
+long ctrl_unlocked_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+{
+	long status = -ENOTTY;
+	size_t inx = 0;
+
+	while (blk_snap_ioctl_table[inx].cmd != 0) {
+		if (blk_snap_ioctl_table[inx].cmd == cmd) {
+			status = blk_snap_ioctl_table[inx].fn(arg);
+			break;
+		}
+		++inx;
+	}
+
+	return status;
+}
diff --git a/drivers/block/blk-snap/ctrl_fops.h b/drivers/block/blk-snap/ctrl_fops.h
new file mode 100644
index 000000000000..98072b61aa96
--- /dev/null
+++ b/drivers/block/blk-snap/ctrl_fops.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+#include <linux/fs.h>
+
+int get_blk_snap_major(void);
+
+int ctrl_init(void);
+void ctrl_done(void);
+
+int ctrl_open(struct inode *inode, struct file *file);
+int ctrl_release(struct inode *inode, struct file *file);
+
+ssize_t ctrl_read(struct file *filp, char __user *buffer, size_t length, loff_t *offset);
+ssize_t ctrl_write(struct file *filp, const char __user *buffer, size_t length, loff_t *offset);
+
+unsigned int ctrl_poll(struct file *filp, struct poll_table_struct *wait);
+
+long ctrl_unlocked_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
diff --git a/drivers/block/blk-snap/ctrl_pipe.c b/drivers/block/blk-snap/ctrl_pipe.c
new file mode 100644
index 000000000000..73cfbca93487
--- /dev/null
+++ b/drivers/block/blk-snap/ctrl_pipe.c
@@ -0,0 +1,562 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-ctrl"
+#include "common.h"
+#include "ctrl_pipe.h"
+#include "version.h"
+#include "blk-snap-ctl.h"
+#include "snapstore.h"
+#include "big_buffer.h"
+
+#include <linux/poll.h>
+#include <linux/uuid.h>
+
+#define CMD_TO_USER_FIFO_SIZE 1024
+
+LIST_HEAD(ctl_pipes);
+DECLARE_RWSEM(ctl_pipes_lock);
+
+
+static void ctrl_pipe_push_request(struct ctrl_pipe *pipe, unsigned int *cmd, size_t cmd_len)
+{
+	kfifo_in_spinlocked(&pipe->cmd_to_user, cmd, (cmd_len * sizeof(unsigned int)),
+			    &pipe->cmd_to_user_lock);
+
+	wake_up(&pipe->readq);
+}
+
+static void ctrl_pipe_request_acknowledge(struct ctrl_pipe *pipe, unsigned int result)
+{
+	unsigned int cmd[2];
+
+	cmd[0] = BLK_SNAP_CHARCMD_ACKNOWLEDGE;
+	cmd[1] = result;
+
+	ctrl_pipe_push_request(pipe, cmd, 2);
+}
+
+static inline dev_t _snapstore_dev(struct ioctl_dev_id_s *dev_id)
+{
+	if ((dev_id->major == 0) && (dev_id->minor == 0))
+		return 0; //memory snapstore
+
+	if ((dev_id->major == -1) && (dev_id->minor == -1))
+		return 0xFFFFffff; //multidevice snapstore
+
+	return MKDEV(dev_id->major, dev_id->minor);
+}
+
+static ssize_t ctrl_pipe_command_initiate(struct ctrl_pipe *pipe, const char __user *buffer,
+					  size_t length)
+{
+	unsigned long len;
+	int result = SUCCESS;
+	ssize_t processed = 0;
+	char *kernel_buffer;
+
+	kernel_buffer = kmalloc(length, GFP_KERNEL);
+	if (kernel_buffer == NULL)
+		return -ENOMEM;
+
+	len = copy_from_user(kernel_buffer, buffer, length);
+	if (len != 0) {
+		kfree(kernel_buffer);
+		pr_err("Unable to write to pipe: invalid user buffer\n");
+		return -EINVAL;
+	}
+
+	do {
+		u64 stretch_empty_limit;
+		unsigned int dev_id_list_length;
+		uuid_t *unique_id;
+		struct ioctl_dev_id_s *snapstore_dev_id;
+		struct ioctl_dev_id_s *dev_id_list;
+
+		//get snapstore uuid
+		if ((length - processed) < 16) {
+			pr_err("Unable to get snapstore uuid: invalid ctrl pipe initiate command. length=%zu\n",
+			       length);
+			break;
+		}
+		unique_id = (uuid_t *)(kernel_buffer + processed);
+		processed += 16;
+
+		//get snapstore empty limit
+		if ((length - processed) < sizeof(u64)) {
+			pr_err("Unable to get stretch snapstore limit: invalid ctrl pipe initiate command. length=%zu\n",
+			       length);
+			break;
+		}
+		stretch_empty_limit = *(u64 *)(kernel_buffer + processed);
+		processed += sizeof(u64);
+
+		//get snapstore device id
+		if ((length - processed) < sizeof(struct ioctl_dev_id_s)) {
+			pr_err("Unable to get snapstore device id: invalid ctrl pipe initiate command. length=%zu\n",
+			       length);
+			break;
+		}
+		snapstore_dev_id = (struct ioctl_dev_id_s *)(kernel_buffer + processed);
+		processed += sizeof(struct ioctl_dev_id_s);
+
+		//get device id list length
+		if ((length - processed) < 4) {
+			pr_err("Unable to get device id list length: ivalid ctrl pipe initiate command. length=%zu\n",
+			       length);
+			break;
+		}
+		dev_id_list_length = *(unsigned int *)(kernel_buffer + processed);
+		processed += sizeof(unsigned int);
+
+		//get devices id list
+		if ((length - processed) < (dev_id_list_length * sizeof(struct ioctl_dev_id_s))) {
+			pr_err("Unable to get all devices from device id list: invalid ctrl pipe initiate command. length=%zu\n",
+			       length);
+			break;
+		}
+		dev_id_list = (struct ioctl_dev_id_s *)(kernel_buffer + processed);
+		processed += (dev_id_list_length * sizeof(struct ioctl_dev_id_s));
+
+		{
+			size_t inx;
+			dev_t *dev_set;
+			size_t dev_id_set_length = (size_t)dev_id_list_length;
+
+			dev_set = kcalloc(dev_id_set_length, sizeof(dev_t), GFP_KERNEL);
+			if (dev_set == NULL) {
+				result = -ENOMEM;
+				break;
+			}
+
+			for (inx = 0; inx < dev_id_set_length; ++inx)
+				dev_set[inx] =
+					MKDEV(dev_id_list[inx].major, dev_id_list[inx].minor);
+
+			result = snapstore_create(unique_id, _snapstore_dev(snapstore_dev_id),
+						  dev_set, dev_id_set_length);
+			kfree(dev_set);
+			if (result != SUCCESS) {
+				pr_err("Failed to create snapstore\n");
+				break;
+			}
+
+			result = snapstore_stretch_initiate(
+				unique_id, pipe, (sector_t)to_sectors(stretch_empty_limit));
+			if (result != SUCCESS) {
+				pr_err("Failed to initiate stretch snapstore %pUB\n", unique_id);
+				break;
+			}
+		}
+	} while (false);
+	kfree(kernel_buffer);
+	ctrl_pipe_request_acknowledge(pipe, result);
+
+	if (result == SUCCESS)
+		return processed;
+	return result;
+}
+
+static ssize_t ctrl_pipe_command_next_portion(struct ctrl_pipe *pipe, const char __user *buffer,
+					      size_t length)
+{
+	unsigned long len;
+	int result = SUCCESS;
+	ssize_t processed = 0;
+	struct big_buffer *ranges = NULL;
+
+	do {
+		uuid_t unique_id;
+		unsigned int ranges_length;
+		size_t ranges_buffer_size;
+
+		//get snapstore id
+		if ((length - processed) < 16) {
+			pr_err("Unable to get snapstore id: ");
+			pr_err("invalid ctrl pipe next portion command. length=%zu\n",
+			       length);
+			break;
+		}
+		len = copy_from_user(&unique_id, buffer + processed, sizeof(uuid_t));
+		if (len != 0) {
+			pr_err("Unable to write to pipe: invalid user buffer\n");
+			processed = -EINVAL;
+			break;
+		}
+		processed += 16;
+
+		//get ranges length
+		if ((length - processed) < 4) {
+			pr_err("Unable to get device id list length: ");
+			pr_err("invalid ctrl pipe next portion command. length=%zu\n",
+			       length);
+			break;
+		}
+		len = copy_from_user(&ranges_length, buffer + processed, sizeof(unsigned int));
+		if (len != 0) {
+			pr_err("Unable to write to pipe: invalid user buffer\n");
+			processed = -EINVAL;
+			break;
+		}
+		processed += sizeof(unsigned int);
+
+		ranges_buffer_size = ranges_length * sizeof(struct ioctl_range_s);
+
+		// ranges
+		if ((length - processed) < (ranges_buffer_size)) {
+			pr_err("Unable to get all ranges: ");
+			pr_err("invalid ctrl pipe next portion command. length=%zu\n",
+			       length);
+			break;
+		}
+		ranges = big_buffer_alloc(ranges_buffer_size, GFP_KERNEL);
+		if (ranges == NULL) {
+			pr_err("Unable to allocate page array buffer: ");
+			pr_err("failed to process next portion command\n");
+			processed = -ENOMEM;
+			break;
+		}
+		if (ranges_buffer_size !=
+		    big_buffer_copy_from_user(buffer + processed, 0, ranges, ranges_buffer_size)) {
+			pr_err("Unable to process next portion command: ");
+			pr_err("invalid user buffer for parameters\n");
+			processed = -EINVAL;
+			break;
+		}
+		processed += ranges_buffer_size;
+
+		{
+			result = snapstore_add_file(&unique_id, ranges, ranges_length);
+
+			if (result != SUCCESS) {
+				pr_err("Failed to add file to snapstore\n");
+				result = -ENODEV;
+				break;
+			}
+		}
+	} while (false);
+	if (ranges)
+		big_buffer_free(ranges);
+
+	if (result == SUCCESS)
+		return processed;
+	return result;
+}
+
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+static ssize_t ctrl_pipe_command_next_portion_multidev(struct ctrl_pipe *pipe,
+						       const char __user *buffer, size_t length)
+{
+	unsigned long len;
+	int result = SUCCESS;
+	ssize_t processed = 0;
+	struct big_buffer *ranges = NULL;
+
+	do {
+		uuid_t unique_id;
+		int snapstore_major;
+		int snapstore_minor;
+		unsigned int ranges_length;
+		size_t ranges_buffer_size;
+
+		//get snapstore id
+		if ((length - processed) < 16) {
+			pr_err("Unable to get snapstore id: ");
+			pr_err("invalid ctrl pipe next portion command. length=%zu\n",
+			       length);
+			break;
+		}
+		len = copy_from_user(&unique_id, buffer + processed, sizeof(uuid_t));
+		if (len != 0) {
+			pr_err("Unable to write to pipe: invalid user buffer\n");
+			processed = -EINVAL;
+			break;
+		}
+		processed += 16;
+
+		//get device id
+		if ((length - processed) < 8) {
+			pr_err("Unable to get device id list length: ");
+			pr_err("invalid ctrl pipe next portion command. length=%zu\n", length);
+			break;
+		}
+		len = copy_from_user(&snapstore_major, buffer + processed, sizeof(unsigned int));
+		if (len != 0) {
+			pr_err("Unable to write to pipe: invalid user buffer\n");
+			processed = -EINVAL;
+			break;
+		}
+		processed += sizeof(unsigned int);
+
+		len = copy_from_user(&snapstore_minor, buffer + processed, sizeof(unsigned int));
+		if (len != 0) {
+			pr_err("Unable to write to pipe: invalid user buffer\n");
+			processed = -EINVAL;
+			break;
+		}
+		processed += sizeof(unsigned int);
+
+		//get ranges length
+		if ((length - processed) < 4) {
+			pr_err("Unable to get device id list length: ");
+			pr_err("invalid ctrl pipe next portion command. length=%zu\n",
+			       length);
+			break;
+		}
+		len = copy_from_user(&ranges_length, buffer + processed, sizeof(unsigned int));
+		if (len != 0) {
+			pr_err("Unable to write to pipe: invalid user buffer\n");
+			processed = -EINVAL;
+			break;
+		}
+		processed += sizeof(unsigned int);
+
+		ranges_buffer_size = ranges_length * sizeof(struct ioctl_range_s);
+
+		// ranges
+		if ((length - processed) < (ranges_buffer_size)) {
+			pr_err("Unable to get all ranges: ");
+			pr_err("invalid ctrl pipe next portion command.  length=%zu\n",
+			       length);
+			break;
+		}
+		ranges = big_buffer_alloc(ranges_buffer_size, GFP_KERNEL);
+		if (ranges == NULL) {
+			pr_err("Unable to process next portion command: ");
+			pr_err("failed to allocate page array buffer\n");
+			processed = -ENOMEM;
+			break;
+		}
+		if (ranges_buffer_size !=
+		    big_buffer_copy_from_user(buffer + processed, 0, ranges, ranges_buffer_size)) {
+			pr_err("Unable to process next portion command: ");
+			pr_err("invalid user buffer from parameters\n");
+			processed = -EINVAL;
+			break;
+		}
+		processed += ranges_buffer_size;
+
+		{
+			result = snapstore_add_multidev(&unique_id,
+							MKDEV(snapstore_major, snapstore_minor),
+							ranges, ranges_length);
+
+			if (result != SUCCESS) {
+				pr_err("Failed to add file to snapstore\n");
+				result = -ENODEV;
+				break;
+			}
+		}
+	} while (false);
+	if (ranges)
+		big_buffer_free(ranges);
+
+	if (result == SUCCESS)
+		return processed;
+
+	return result;
+}
+#endif
+
+static void ctrl_pipe_release_cb(struct kref *kref)
+{
+	struct ctrl_pipe *pipe = container_of(kref, struct ctrl_pipe, refcount);
+
+	down_write(&ctl_pipes_lock);
+	list_del(&pipe->link);
+	up_write(&ctl_pipes_lock);
+
+	kfifo_free(&pipe->cmd_to_user);
+
+	kfree(pipe);
+}
+
+struct ctrl_pipe *ctrl_pipe_get_resource(struct ctrl_pipe *pipe)
+{
+	if (pipe)
+		kref_get(&pipe->refcount);
+
+	return pipe;
+}
+
+void ctrl_pipe_put_resource(struct ctrl_pipe *pipe)
+{
+	if (pipe)
+		kref_put(&pipe->refcount, ctrl_pipe_release_cb);
+}
+
+void ctrl_pipe_done(void)
+{
+	bool is_empty;
+
+	pr_info("Ctrl pipes - done\n");
+
+	down_write(&ctl_pipes_lock);
+	is_empty = list_empty(&ctl_pipes);
+	up_write(&ctl_pipes_lock);
+
+	if (!is_empty)
+		pr_err("Unable to perform ctrl pipes cleanup: container is not empty\n");
+}
+
+struct ctrl_pipe *ctrl_pipe_new(void)
+{
+	int ret;
+	struct ctrl_pipe *pipe;
+
+	pipe = kzalloc(sizeof(struct ctrl_pipe), GFP_KERNEL);
+	if (pipe == NULL)
+		return NULL;
+
+	INIT_LIST_HEAD(&pipe->link);
+
+	ret = kfifo_alloc(&pipe->cmd_to_user, CMD_TO_USER_FIFO_SIZE, GFP_KERNEL);
+	if (ret) {
+		pr_err("Failed to allocate fifo. errno=%d.\n", ret);
+		kfree(pipe);
+		return NULL;
+	}
+	spin_lock_init(&pipe->cmd_to_user_lock);
+
+	kref_init(&pipe->refcount);
+
+	init_waitqueue_head(&pipe->readq);
+
+	down_write(&ctl_pipes_lock);
+	list_add_tail(&pipe->link, &ctl_pipes);
+	up_write(&ctl_pipes_lock);
+
+	return pipe;
+}
+
+ssize_t ctrl_pipe_read(struct ctrl_pipe *pipe, char __user *buffer, size_t length)
+{
+	int ret;
+	unsigned int processed = 0;
+
+	if (kfifo_is_empty_spinlocked(&pipe->cmd_to_user, &pipe->cmd_to_user_lock)) {
+		//nothing to read
+		ret = wait_event_interruptible(pipe->readq,
+					       !kfifo_is_empty_spinlocked(&pipe->cmd_to_user,
+									&pipe->cmd_to_user_lock));
+		if (ret) {
+			pr_err("Unable to wait for pipe read queue: interrupt signal was received\n");
+			return -ERESTARTSYS;
+		}
+	}
+
+	ret = kfifo_to_user(&pipe->cmd_to_user, buffer, length, &processed);
+	if (ret) {
+		pr_err("Failed to read command from ctrl pipe\n");
+		return ret;
+	}
+
+	return (ssize_t)processed;
+}
+
+ssize_t ctrl_pipe_write(struct ctrl_pipe *pipe, const char __user *buffer, size_t length)
+{
+	ssize_t processed = 0;
+
+	do {
+		unsigned long len;
+		unsigned int command;
+
+		if ((length - processed) < 4) {
+			pr_err("Unable to write command to ctrl pipe: invalid command length=%zu\n",
+			       length);
+			break;
+		}
+		len = copy_from_user(&command, buffer + processed, sizeof(unsigned int));
+		if (len != 0) {
+			pr_err("Unable to write to pipe: invalid user buffer\n");
+			processed = -EINVAL;
+			break;
+		}
+		processed += sizeof(unsigned int);
+		//+4
+		switch (command) {
+		case BLK_SNAP_CHARCMD_INITIATE: {
+			ssize_t res = ctrl_pipe_command_initiate(pipe, buffer + processed,
+								 length - processed);
+			if (res >= 0)
+				processed += res;
+			else
+				processed = res;
+		} break;
+		case BLK_SNAP_CHARCMD_NEXT_PORTION: {
+			ssize_t res = ctrl_pipe_command_next_portion(pipe, buffer + processed,
+								     length - processed);
+			if (res >= 0)
+				processed += res;
+			else
+				processed = res;
+		} break;
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+		case BLK_SNAP_CHARCMD_NEXT_PORTION_MULTIDEV: {
+			ssize_t res = ctrl_pipe_command_next_portion_multidev(
+				pipe, buffer + processed, length - processed);
+			if (res >= 0)
+				processed += res;
+			else
+				processed = res;
+		} break;
+#endif
+		default:
+			pr_err("Ctrl pipe write error: invalid command [0x%x] received\n", command);
+			break;
+		}
+	} while (false);
+	return processed;
+}
+
+unsigned int ctrl_pipe_poll(struct ctrl_pipe *pipe)
+{
+	unsigned int mask = 0;
+
+	if (!kfifo_is_empty_spinlocked(&pipe->cmd_to_user, &pipe->cmd_to_user_lock))
+		mask |= (POLLIN | POLLRDNORM); /* readable */
+
+	mask |= (POLLOUT | POLLWRNORM); /* writable */
+
+	return mask;
+}
+
+void ctrl_pipe_request_halffill(struct ctrl_pipe *pipe, unsigned long long filled_status)
+{
+	unsigned int cmd[3];
+
+	pr_info("Snapstore is half-full\n");
+
+	cmd[0] = (unsigned int)BLK_SNAP_CHARCMD_HALFFILL;
+	cmd[1] = (unsigned int)(filled_status & 0xFFFFffff); //lo
+	cmd[2] = (unsigned int)(filled_status >> 32);
+
+	ctrl_pipe_push_request(pipe, cmd, 3);
+}
+
+void ctrl_pipe_request_overflow(struct ctrl_pipe *pipe, unsigned int error_code,
+				unsigned long long filled_status)
+{
+	unsigned int cmd[4];
+
+	pr_info("Snapstore overflow\n");
+
+	cmd[0] = (unsigned int)BLK_SNAP_CHARCMD_OVERFLOW;
+	cmd[1] = error_code;
+	cmd[2] = (unsigned int)(filled_status & 0xFFFFffff); //lo
+	cmd[3] = (unsigned int)(filled_status >> 32);
+
+	ctrl_pipe_push_request(pipe, cmd, 4);
+}
+
+void ctrl_pipe_request_terminate(struct ctrl_pipe *pipe, unsigned long long filled_status)
+{
+	unsigned int cmd[3];
+
+	pr_info("Snapstore termination\n");
+
+	cmd[0] = (unsigned int)BLK_SNAP_CHARCMD_TERMINATE;
+	cmd[1] = (unsigned int)(filled_status & 0xFFFFffff); //lo
+	cmd[2] = (unsigned int)(filled_status >> 32);
+
+	ctrl_pipe_push_request(pipe, cmd, 3);
+}
diff --git a/drivers/block/blk-snap/ctrl_pipe.h b/drivers/block/blk-snap/ctrl_pipe.h
new file mode 100644
index 000000000000..1aa1099eec25
--- /dev/null
+++ b/drivers/block/blk-snap/ctrl_pipe.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+#include <linux/kref.h>
+#include <linux/wait.h>
+#include <linux/kfifo.h>
+
+struct ctrl_pipe {
+	struct list_head link;
+
+	struct kref refcount;
+
+	wait_queue_head_t readq;
+
+	struct kfifo cmd_to_user;
+	spinlock_t cmd_to_user_lock;
+};
+
+struct ctrl_pipe *ctrl_pipe_get_resource(struct ctrl_pipe *pipe);
+void ctrl_pipe_put_resource(struct ctrl_pipe *pipe);
+
+void ctrl_pipe_done(void);
+
+struct ctrl_pipe *ctrl_pipe_new(void);
+
+ssize_t ctrl_pipe_read(struct ctrl_pipe *pipe, char __user *buffer, size_t length);
+ssize_t ctrl_pipe_write(struct ctrl_pipe *pipe, const char __user *buffer, size_t length);
+
+unsigned int ctrl_pipe_poll(struct ctrl_pipe *pipe);
+
+void ctrl_pipe_request_halffill(struct ctrl_pipe *pipe, unsigned long long filled_status);
+void ctrl_pipe_request_overflow(struct ctrl_pipe *pipe, unsigned int error_code,
+				unsigned long long filled_status);
+void ctrl_pipe_request_terminate(struct ctrl_pipe *pipe, unsigned long long filled_status);
diff --git a/drivers/block/blk-snap/ctrl_sysfs.c b/drivers/block/blk-snap/ctrl_sysfs.c
new file mode 100644
index 000000000000..4ec78e85b510
--- /dev/null
+++ b/drivers/block/blk-snap/ctrl_sysfs.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-ctrl"
+#include "common.h"
+#include "ctrl_sysfs.h"
+#include "ctrl_fops.h"
+#include "blk-snap-ctl.h"
+
+#include <linux/blkdev.h>
+#include <linux/sysfs.h>
+
+static ssize_t major_show(struct class *class, struct class_attribute *attr, char *buf)
+{
+	sprintf(buf, "%d", get_blk_snap_major());
+	return strlen(buf);
+}
+
+CLASS_ATTR_RO(major); // declare class_attr_major
+static struct class *blk_snap_class;
+
+static struct device *blk_snap_device;
+
+int ctrl_sysfs_init(void)
+{
+	struct device *dev;
+	int res;
+
+	blk_snap_class = class_create(THIS_MODULE, MODULE_NAME);
+	if (IS_ERR(blk_snap_class)) {
+		res = PTR_ERR(blk_snap_class);
+
+		pr_err("Bad class create. errno=%d\n", 0 - res);
+		return res;
+	}
+
+	pr_info("Create 'major' sysfs attribute\n");
+	res = class_create_file(blk_snap_class, &class_attr_major);
+	if (res != SUCCESS) {
+		pr_err("Failed to create 'major' sysfs file\n");
+
+		class_destroy(blk_snap_class);
+		blk_snap_class = NULL;
+		return res;
+	}
+
+	dev = device_create(blk_snap_class, NULL, MKDEV(get_blk_snap_major(), 0), NULL,
+			    MODULE_NAME);
+	if (IS_ERR(dev)) {
+		res = PTR_ERR(dev);
+		pr_err("Failed to create device, errno=%d\n", res);
+
+		class_remove_file(blk_snap_class, &class_attr_major);
+		class_destroy(blk_snap_class);
+		blk_snap_class = NULL;
+		return res;
+	}
+
+	blk_snap_device = dev;
+	return res;
+}
+
+void ctrl_sysfs_done(void)
+{
+	if (blk_snap_device) {
+		device_unregister(blk_snap_device);
+		blk_snap_device = NULL;
+	}
+
+	if (blk_snap_class != NULL) {
+		class_remove_file(blk_snap_class, &class_attr_major);
+		class_destroy(blk_snap_class);
+		blk_snap_class = NULL;
+	}
+}
diff --git a/drivers/block/blk-snap/ctrl_sysfs.h b/drivers/block/blk-snap/ctrl_sysfs.h
new file mode 100644
index 000000000000..27a2a4d3da4c
--- /dev/null
+++ b/drivers/block/blk-snap/ctrl_sysfs.h
@@ -0,0 +1,5 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+int ctrl_sysfs_init(void);
+void ctrl_sysfs_done(void);
diff --git a/drivers/block/blk-snap/defer_io.c b/drivers/block/blk-snap/defer_io.c
new file mode 100644
index 000000000000..309216fe7319
--- /dev/null
+++ b/drivers/block/blk-snap/defer_io.c
@@ -0,0 +1,397 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-defer_io"
+#include "common.h"
+#include "defer_io.h"
+#include "blk_deferred.h"
+#include "tracker.h"
+#include "blk_util.h"
+
+#include <linux/kthread.h>
+
+#define BLK_IMAGE_THROTTLE_TIMEOUT (1 * HZ) //delay 1 sec
+//#define BLK_IMAGE_THROTTLE_TIMEOUT ( HZ/1000 * 10 )	//delay 10 ms
+
+
+
+struct defer_io_orig_rq {
+	struct list_head link;
+	struct defer_io_queue *queue;
+
+	struct bio *bio;
+	struct tracker *tracker;
+};
+
+static inline void defer_io_queue_init(struct defer_io_queue *queue)
+{
+	INIT_LIST_HEAD(&queue->list);
+
+	spin_lock_init(&queue->lock);
+
+	atomic_set(&queue->in_queue_cnt, 0);
+	atomic_set(&queue->active_state, true);
+}
+
+static inline struct defer_io_orig_rq *defer_io_queue_new(struct defer_io_queue *queue, struct bio *bio)
+{
+	struct defer_io_orig_rq *dio_rq;
+
+	dio_rq = kzalloc(sizeof(struct defer_io_orig_rq), GFP_NOIO);
+	if (dio_rq == NULL)
+		return NULL;
+
+	dio_rq->bio = bio;
+	bio_get(dio_rq->bio);
+
+	INIT_LIST_HEAD(&dio_rq->link);
+	dio_rq->queue = queue;
+
+	return dio_rq;
+}
+
+static inline void defer_io_queue_free(struct defer_io_orig_rq *dio_rq)
+{
+	if (likely(dio_rq)) {
+		if (likely(dio_rq->bio)) {
+			bio_put(dio_rq->bio);
+			dio_rq->bio = NULL;
+		}
+		kfree(dio_rq);
+	}
+}
+
+static int defer_io_queue_push_back(struct defer_io_queue *queue, struct defer_io_orig_rq *dio_rq)
+{
+	int res = SUCCESS;
+
+	spin_lock(&queue->lock);
+
+	if (atomic_read(&queue->active_state)) {
+		list_add_tail(&dio_rq->link, &queue->list);
+		atomic_inc(&queue->in_queue_cnt);
+	} else
+		res = -EACCES;
+
+	spin_unlock(&queue->lock);
+	return res;
+}
+
+static struct defer_io_orig_rq *defer_io_queue_get_first(struct defer_io_queue *queue)
+{
+	struct defer_io_orig_rq *dio_rq = NULL;
+
+	spin_lock(&queue->lock);
+
+	if (!list_empty(&queue->list)) {
+		dio_rq = list_entry(queue->list.next, struct defer_io_orig_rq, link);
+		list_del(&dio_rq->link);
+		atomic_dec(&queue->in_queue_cnt);
+	}
+
+	spin_unlock(&queue->lock);
+
+	return dio_rq;
+}
+
+static bool defer_io_queue_active(struct defer_io_queue *queue, bool state)
+{
+	bool prev_state;
+
+	spin_lock(&queue->lock);
+
+	prev_state = atomic_read(&queue->active_state);
+	atomic_set(&queue->active_state, state);
+
+	spin_unlock(&queue->lock);
+
+	return prev_state;
+}
+
+#define defer_io_queue_empty(queue) (atomic_read(&(queue).in_queue_cnt) == 0)
+
+static void _defer_io_finish(struct defer_io *defer_io, struct defer_io_queue *queue_in_progress)
+{
+	while (!defer_io_queue_empty(*queue_in_progress)) {
+		struct tracker *tracker = NULL;
+		bool cbt_locked = false;
+		bool is_write_bio;
+		sector_t sectCount = 0;
+
+		struct defer_io_orig_rq *orig_req = defer_io_queue_get_first(queue_in_progress);
+
+		is_write_bio = bio_data_dir(orig_req->bio) && bio_has_data(orig_req->bio);
+
+		if (orig_req->tracker && is_write_bio) {
+			tracker = orig_req->tracker;
+			cbt_locked = tracker_cbt_bitmap_lock(tracker);
+			if (cbt_locked) {
+				sectCount = bio_sectors(orig_req->bio);
+				tracker_cbt_bitmap_set(tracker, orig_req->bio->bi_iter.bi_sector,
+						       sectCount);
+			}
+		}
+
+		submit_bio_direct(orig_req->bio);
+
+		if (cbt_locked)
+			tracker_cbt_bitmap_unlock(tracker);
+
+		defer_io_queue_free(orig_req);
+	}
+}
+
+static int _defer_io_copy_prepare(struct defer_io *defer_io,
+				  struct defer_io_queue *queue_in_process,
+				  struct blk_deferred_request **dio_copy_req)
+{
+	int res = SUCCESS;
+	int dios_count = 0;
+	sector_t dios_sectors_count = 0;
+
+	//fill copy_request set
+	while (!defer_io_queue_empty(defer_io->dio_queue) &&
+	       (dios_count < DEFER_IO_DIO_REQUEST_LENGTH) &&
+	       (dios_sectors_count < DEFER_IO_DIO_REQUEST_SECTORS_COUNT)) {
+		struct defer_io_orig_rq *dio_orig_req =
+			(struct defer_io_orig_rq *)defer_io_queue_get_first(&defer_io->dio_queue);
+		atomic_dec(&defer_io->queue_filling_count);
+
+		defer_io_queue_push_back(queue_in_process, dio_orig_req);
+
+		if (!kthread_should_stop() &&
+		    !snapstore_device_is_corrupted(defer_io->snapstore_device)) {
+			if (bio_data_dir(dio_orig_req->bio) && bio_has_data(dio_orig_req->bio)) {
+				struct blk_range copy_range;
+
+				copy_range.ofs = dio_orig_req->bio->bi_iter.bi_sector;
+				copy_range.cnt = bio_sectors(dio_orig_req->bio);
+				res = snapstore_device_prepare_requests(defer_io->snapstore_device,
+									&copy_range, dio_copy_req);
+				if (res != SUCCESS) {
+					pr_err("Unable to execute Copy On Write algorithm: failed to add ranges to copy to snapstore request. errno=%d\n",
+					       res);
+					break;
+				}
+
+				dios_sectors_count += copy_range.cnt;
+			}
+		}
+		++dios_count;
+	}
+	return res;
+}
+
+static int defer_io_work_thread(void *p)
+{
+	struct defer_io_queue queue_in_process = { 0 };
+	struct defer_io *defer_io = NULL;
+
+	//set_user_nice( current, -20 ); //MIN_NICE
+	defer_io_queue_init(&queue_in_process);
+
+	defer_io = defer_io_get_resource((struct defer_io *)p);
+	pr_info("Defer IO thread for original device [%d:%d] started\n",
+		MAJOR(defer_io->original_dev_id), MINOR(defer_io->original_dev_id));
+
+	while (!kthread_should_stop() || !defer_io_queue_empty(defer_io->dio_queue)) {
+		if (defer_io_queue_empty(defer_io->dio_queue)) {
+			int res = wait_event_interruptible_timeout(
+				defer_io->queue_add_event,
+				(!defer_io_queue_empty(defer_io->dio_queue)),
+				BLK_IMAGE_THROTTLE_TIMEOUT);
+			if (-ERESTARTSYS == res)
+				pr_err("Signal received in defer IO thread. Waiting for completion with code ERESTARTSYS\n");
+		}
+
+		if (!defer_io_queue_empty(defer_io->dio_queue)) {
+			int dio_copy_result = SUCCESS;
+			struct blk_deferred_request *dio_copy_req = NULL;
+
+			mutex_lock(&defer_io->snapstore_device->store_block_map_locker);
+			do {
+				dio_copy_result = _defer_io_copy_prepare(
+					defer_io, &queue_in_process, &dio_copy_req);
+				if (dio_copy_result != SUCCESS) {
+					pr_err("Unable to process defer IO request: failed to prepare copy request. erro=%d\n",
+					       dio_copy_result);
+					break;
+				}
+				if (dio_copy_req == NULL)
+					break; //nothing to copy
+
+				dio_copy_result = blk_deferred_request_read_original(
+					defer_io->original_blk_dev, dio_copy_req);
+				if (dio_copy_result != SUCCESS) {
+					pr_err("Unable to process defer IO request: failed to read data to copy request. errno=%d\n",
+					       dio_copy_result);
+					break;
+				}
+				dio_copy_result = snapstore_device_store(defer_io->snapstore_device,
+									 dio_copy_req);
+				if (dio_copy_result != SUCCESS) {
+					pr_err("Unable to process defer IO request: failed to write data from copy request. errno=%d\n",
+					       dio_copy_result);
+					break;
+				}
+
+			} while (false);
+			_defer_io_finish(defer_io, &queue_in_process);
+			mutex_unlock(&defer_io->snapstore_device->store_block_map_locker);
+
+			if (dio_copy_req) {
+				if (dio_copy_result == -EDEADLK)
+					blk_deferred_request_deadlocked(dio_copy_req);
+				else
+					blk_deferred_request_free(dio_copy_req);
+			}
+		}
+
+		//wake up snapimage if defer io queue empty
+		if (defer_io_queue_empty(defer_io->dio_queue))
+			wake_up_interruptible(&defer_io->queue_throttle_waiter);
+	}
+	defer_io_queue_active(&defer_io->dio_queue, false);
+
+	//waiting for all sent request complete
+	_defer_io_finish(defer_io, &defer_io->dio_queue);
+
+	pr_info("Defer IO thread for original device [%d:%d] completed\n",
+		MAJOR(defer_io->original_dev_id), MINOR(defer_io->original_dev_id));
+	defer_io_put_resource(defer_io);
+	return SUCCESS;
+}
+
+static void _defer_io_destroy(struct defer_io *defer_io)
+{
+	if (defer_io == NULL)
+		return;
+
+	if (defer_io->dio_thread)
+		defer_io_stop(defer_io);
+
+	if (defer_io->snapstore_device)
+		snapstore_device_put_resource(defer_io->snapstore_device);
+
+	kfree(defer_io);
+	pr_info("Defer IO processor was destroyed\n");
+}
+
+static void defer_io_destroy_cb(struct kref *kref)
+{
+	_defer_io_destroy(container_of(kref, struct defer_io, refcount));
+}
+
+struct defer_io *defer_io_get_resource(struct defer_io *defer_io)
+{
+	if (defer_io)
+		kref_get(&defer_io->refcount);
+
+	return defer_io;
+}
+
+void defer_io_put_resource(struct defer_io *defer_io)
+{
+	if (defer_io)
+		kref_put(&defer_io->refcount, defer_io_destroy_cb);
+}
+
+int defer_io_create(dev_t dev_id, struct block_device *blk_dev, struct defer_io **pp_defer_io)
+{
+	int res = SUCCESS;
+	struct defer_io *defer_io = NULL;
+	struct snapstore_device *snapstore_device;
+
+	pr_info("Defer IO processor was created for device [%d:%d]\n", MAJOR(dev_id),
+		MINOR(dev_id));
+
+	defer_io = kzalloc(sizeof(struct defer_io), GFP_KERNEL);
+	if (defer_io == NULL)
+		return -ENOMEM;
+
+	snapstore_device = snapstore_device_find_by_dev_id(dev_id);
+	if (snapstore_device == NULL) {
+		pr_err("Unable to create defer IO processor: failed to initialize snapshot data for device [%d:%d]\n",
+		       MAJOR(dev_id), MINOR(dev_id));
+
+		kfree(defer_io);
+		return -ENODATA;
+	}
+
+	defer_io->snapstore_device = snapstore_device_get_resource(snapstore_device);
+	defer_io->original_dev_id = dev_id;
+	defer_io->original_blk_dev = blk_dev;
+
+	kref_init(&defer_io->refcount);
+
+	defer_io_queue_init(&defer_io->dio_queue);
+
+	init_waitqueue_head(&defer_io->queue_add_event);
+
+	atomic_set(&defer_io->queue_filling_count, 0);
+
+	init_waitqueue_head(&defer_io->queue_throttle_waiter);
+
+	defer_io->dio_thread = kthread_create(defer_io_work_thread, (void *)defer_io,
+					      "blksnapdeferio%d:%d", MAJOR(dev_id), MINOR(dev_id));
+	if (IS_ERR(defer_io->dio_thread)) {
+		res = PTR_ERR(defer_io->dio_thread);
+		pr_err("Unable to create defer IO processor: failed to create thread. errno=%d\n",
+		       res);
+
+		_defer_io_destroy(defer_io);
+		defer_io = NULL;
+		*pp_defer_io = NULL;
+
+		return res;
+	}
+
+	wake_up_process(defer_io->dio_thread);
+
+	*pp_defer_io = defer_io;
+	pr_info("Defer IO processor was created\n");
+
+	return SUCCESS;
+}
+
+int defer_io_stop(struct defer_io *defer_io)
+{
+	int res = SUCCESS;
+
+	pr_info("Defer IO thread for the device stopped [%d:%d]\n",
+		MAJOR(defer_io->original_dev_id), MINOR(defer_io->original_dev_id));
+
+	if (defer_io->dio_thread != NULL) {
+		struct task_struct *dio_thread = defer_io->dio_thread;
+
+		defer_io->dio_thread = NULL;
+		res = kthread_stop(dio_thread); //stopping and waiting.
+		if (res != SUCCESS)
+			pr_err("Failed to stop defer IO thread. errno=%d\n", res);
+	}
+
+	return res;
+}
+
+int defer_io_redirect_bio(struct defer_io *defer_io, struct bio *bio, void *tracker)
+{
+	struct defer_io_orig_rq *dio_orig_req;
+
+	if (snapstore_device_is_corrupted(defer_io->snapstore_device))
+		return -ENODATA;
+
+	dio_orig_req = defer_io_queue_new(&defer_io->dio_queue, bio);
+	if (dio_orig_req == NULL)
+		return -ENOMEM;
+
+	dio_orig_req->tracker = (struct tracker *)tracker;
+
+	if (defer_io_queue_push_back(&defer_io->dio_queue, dio_orig_req) != SUCCESS) {
+		defer_io_queue_free(dio_orig_req);
+		return -EFAULT;
+	}
+
+	atomic_inc(&defer_io->queue_filling_count);
+
+	wake_up_interruptible(&defer_io->queue_add_event);
+
+	return SUCCESS;
+}
diff --git a/drivers/block/blk-snap/defer_io.h b/drivers/block/blk-snap/defer_io.h
new file mode 100644
index 000000000000..27c3bb03241f
--- /dev/null
+++ b/drivers/block/blk-snap/defer_io.h
@@ -0,0 +1,39 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+#include <linux/kref.h>
+#include "snapstore_device.h"
+
+struct defer_io_queue {
+	struct list_head list;
+	spinlock_t lock;
+
+	atomic_t active_state;
+	atomic_t in_queue_cnt;
+};
+
+struct defer_io {
+	struct kref refcount;
+
+	wait_queue_head_t queue_add_event;
+
+	atomic_t queue_filling_count;
+	wait_queue_head_t queue_throttle_waiter;
+
+	dev_t original_dev_id;
+	struct block_device *original_blk_dev;
+
+	struct snapstore_device *snapstore_device;
+
+	struct task_struct *dio_thread;
+
+	struct defer_io_queue dio_queue;
+};
+
+int defer_io_create(dev_t dev_id, struct block_device *blk_dev, struct defer_io **pp_defer_io);
+int defer_io_stop(struct defer_io *defer_io);
+
+struct defer_io *defer_io_get_resource(struct defer_io *defer_io);
+void defer_io_put_resource(struct defer_io *defer_io);
+
+int defer_io_redirect_bio(struct defer_io *defer_io, struct bio *bio, void *tracker);
diff --git a/drivers/block/blk-snap/main.c b/drivers/block/blk-snap/main.c
new file mode 100644
index 000000000000..d1d4e08a4890
--- /dev/null
+++ b/drivers/block/blk-snap/main.c
@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "common.h"
+#include "version.h"
+#include "blk-snap-ctl.h"
+#include "params.h"
+#include "ctrl_fops.h"
+#include "ctrl_pipe.h"
+#include "ctrl_sysfs.h"
+#include "snapimage.h"
+#include "snapstore.h"
+#include "snapstore_device.h"
+#include "snapshot.h"
+#include "tracker.h"
+#include "tracking.h"
+#include <linux/module.h>
+
+int __init blk_snap_init(void)
+{
+	int result = SUCCESS;
+
+	pr_info("Loading\n");
+
+	params_check();
+
+	result = ctrl_init();
+	if (result != SUCCESS)
+		return result;
+
+	result = blk_redirect_bioset_create();
+	if (result != SUCCESS)
+		return result;
+
+	result = blk_deferred_bioset_create();
+	if (result != SUCCESS)
+		return result;
+
+	result = snapimage_init();
+	if (result != SUCCESS)
+		return result;
+
+	result = ctrl_sysfs_init();
+	if (result != SUCCESS)
+		return result;
+
+	result = tracking_init();
+	if (result != SUCCESS)
+		return result;
+
+	return result;
+}
+
+void __exit blk_snap_exit(void)
+{
+	pr_info("Unloading module\n");
+
+	ctrl_sysfs_done();
+
+	snapshot_done();
+
+	snapstore_device_done();
+	snapstore_done();
+
+	tracker_done();
+	tracking_done();
+
+	snapimage_done();
+
+	blk_deferred_bioset_free();
+	blk_deferred_done();
+
+	blk_redirect_bioset_free();
+
+	ctrl_done();
+}
+
+module_init(blk_snap_init);
+module_exit(blk_snap_exit);
+
+MODULE_DESCRIPTION("Block Layer Snapshot Kernel Module");
+MODULE_VERSION(FILEVER_STR);
+MODULE_AUTHOR("Veeam Software Group GmbH");
+MODULE_LICENSE("GPL");
diff --git a/drivers/block/blk-snap/params.c b/drivers/block/blk-snap/params.c
new file mode 100644
index 000000000000..7eba3c8bf395
--- /dev/null
+++ b/drivers/block/blk-snap/params.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "common.h"
+#include "params.h"
+#include <linux/module.h>
+
+int snapstore_block_size_pow = 14;
+int change_tracking_block_size_pow = 18;
+
+int get_snapstore_block_size_pow(void)
+{
+	return snapstore_block_size_pow;
+}
+
+int inc_snapstore_block_size_pow(void)
+{
+	if (snapstore_block_size_pow > 30)
+		return -EFAULT;
+
+	++snapstore_block_size_pow;
+	return SUCCESS;
+}
+
+int get_change_tracking_block_size_pow(void)
+{
+	return change_tracking_block_size_pow;
+}
+
+void params_check(void)
+{
+	pr_info("snapstore_block_size_pow: %d\n", snapstore_block_size_pow);
+	pr_info("change_tracking_block_size_pow: %d\n", change_tracking_block_size_pow);
+
+	if (snapstore_block_size_pow > 23) {
+		snapstore_block_size_pow = 23;
+		pr_info("Limited snapstore_block_size_pow: %d\n", snapstore_block_size_pow);
+	} else if (snapstore_block_size_pow < 12) {
+		snapstore_block_size_pow = 12;
+		pr_info("Limited snapstore_block_size_pow: %d\n", snapstore_block_size_pow);
+	}
+
+	if (change_tracking_block_size_pow > 23) {
+		change_tracking_block_size_pow = 23;
+		pr_info("Limited change_tracking_block_size_pow: %d\n",
+			change_tracking_block_size_pow);
+	} else if (change_tracking_block_size_pow < 12) {
+		change_tracking_block_size_pow = 12;
+		pr_info("Limited change_tracking_block_size_pow: %d\n",
+			change_tracking_block_size_pow);
+	}
+}
+
+module_param_named(snapstore_block_size_pow, snapstore_block_size_pow, int, 0644);
+MODULE_PARM_DESC(snapstore_block_size_pow,
+		 "Snapstore block size binary pow. 20 for 1MiB block size");
+
+module_param_named(change_tracking_block_size_pow, change_tracking_block_size_pow, int, 0644);
+MODULE_PARM_DESC(change_tracking_block_size_pow,
+		 "Change-tracking block size binary pow. 18 for 256 KiB block size");
diff --git a/drivers/block/blk-snap/params.h b/drivers/block/blk-snap/params.h
new file mode 100644
index 000000000000..c1b853a1363b
--- /dev/null
+++ b/drivers/block/blk-snap/params.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#pragma once
+
+int get_snapstore_block_size_pow(void);
+int inc_snapstore_block_size_pow(void);
+
+static inline sector_t snapstore_block_shift(void)
+{
+	return get_snapstore_block_size_pow() - SECTOR_SHIFT;
+};
+
+static inline sector_t snapstore_block_size(void)
+{
+	return 1ull << snapstore_block_shift();
+};
+
+static inline sector_t snapstore_block_mask(void)
+{
+	return snapstore_block_size() - 1ull;
+};
+
+int get_change_tracking_block_size_pow(void);
+
+static inline unsigned int change_tracking_block_size(void)
+{
+	return 1 << get_change_tracking_block_size_pow();
+};
+
+void params_check(void);
diff --git a/drivers/block/blk-snap/rangevector.c b/drivers/block/blk-snap/rangevector.c
new file mode 100644
index 000000000000..49fe4589b6f7
--- /dev/null
+++ b/drivers/block/blk-snap/rangevector.c
@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "common.h"
+#include "rangevector.h"
+
+#define SECTION "ranges	"
+
+static inline sector_t range_node_start(struct blk_range_tree_node *range_node)
+{
+	return range_node->range.ofs;
+}
+
+static inline sector_t range_node_last(struct blk_range_tree_node *range_node)
+{
+	return range_node->range.ofs + range_node->range.cnt - 1;
+}
+
+#ifndef INTERVAL_TREE_DEFINE
+#pragma message("INTERVAL_TREE_DEFINE is undefined")
+#endif
+INTERVAL_TREE_DEFINE(struct blk_range_tree_node, _node, sector_t, _subtree_last,
+		     range_node_start, range_node_last, static inline, _blk_range_rb)
+
+void blk_range_rb_insert(struct blk_range_tree_node *node, struct rb_root_cached *root)
+{
+	_blk_range_rb_insert(node, root);
+}
+
+void blk_range_rb_remove(struct blk_range_tree_node *node, struct rb_root_cached *root)
+{
+	_blk_range_rb_remove(node, root);
+}
+
+struct blk_range_tree_node *blk_range_rb_iter_first(struct rb_root_cached *root, sector_t start,
+						    sector_t last)
+{
+	return _blk_range_rb_iter_first(root, start, last);
+}
+
+struct blk_range_tree_node *blk_range_rb_iter_next(struct blk_range_tree_node *node, sector_t start,
+						   sector_t last)
+{
+	return _blk_range_rb_iter_next(node, start, last);
+}
+
+void rangevector_init(struct rangevector *rangevector)
+{
+	init_rwsem(&rangevector->lock);
+
+	rangevector->root = RB_ROOT_CACHED;
+}
+
+void rangevector_done(struct rangevector *rangevector)
+{
+	struct rb_node *rb_node = NULL;
+
+	down_write(&rangevector->lock);
+	rb_node = rb_first_cached(&rangevector->root);
+	while (rb_node) {
+		struct blk_range_tree_node *range_node = (struct blk_range_tree_node *)
+			rb_node; //container_of(rb_node, struct blk_range_tree_node, node);
+
+		blk_range_rb_remove(range_node, &rangevector->root);
+		kfree(range_node);
+
+		rb_node = rb_first_cached(&rangevector->root);
+	}
+	up_write(&rangevector->lock);
+}
+
+int rangevector_add(struct rangevector *rangevector, struct blk_range *rg)
+{
+	struct blk_range_tree_node *range_node;
+
+	range_node = kzalloc(sizeof(struct blk_range_tree_node), GFP_KERNEL);
+	if (range_node)
+		return -ENOMEM;
+
+	range_node->range = *rg;
+
+	down_write(&rangevector->lock);
+	blk_range_rb_insert(range_node, &rangevector->root);
+	up_write(&rangevector->lock);
+
+	return SUCCESS;
+}
diff --git a/drivers/block/blk-snap/rangevector.h b/drivers/block/blk-snap/rangevector.h
new file mode 100644
index 000000000000..5ff439423178
--- /dev/null
+++ b/drivers/block/blk-snap/rangevector.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#pragma once
+
+#include <linux/interval_tree_generic.h>
+
+struct blk_range_tree_node {
+	struct rb_node _node;
+	struct blk_range range;
+	sector_t _subtree_last;
+};
+
+void blk_range_rb_insert(struct blk_range_tree_node *node, struct rb_root_cached *root);
+
+void blk_range_rb_remove(struct blk_range_tree_node *node, struct rb_root_cached *root);
+
+struct blk_range_tree_node *blk_range_rb_iter_first(struct rb_root_cached *root, sector_t start,
+						    sector_t last);
+
+struct blk_range_tree_node *blk_range_rb_iter_next(struct blk_range_tree_node *node, sector_t start,
+						   sector_t last);
+
+struct rangevector {
+	struct rb_root_cached root;
+	struct rw_semaphore lock;
+};
+
+void rangevector_init(struct rangevector *rangevector);
+
+void rangevector_done(struct rangevector *rangevector);
+
+int rangevector_add(struct rangevector *rangevector, struct blk_range *rg);
diff --git a/drivers/block/blk-snap/snapimage.c b/drivers/block/blk-snap/snapimage.c
new file mode 100644
index 000000000000..da971486cbef
--- /dev/null
+++ b/drivers/block/blk-snap/snapimage.c
@@ -0,0 +1,982 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-snapimage"
+#include "common.h"
+#include "snapimage.h"
+#include "blk_util.h"
+#include "defer_io.h"
+#include "cbt_map.h"
+#include "tracker.h"
+
+#include <asm/div64.h>
+#include <linux/cdrom.h>
+#include <linux/blk-mq.h>
+#include <linux/hdreg.h>
+#include <linux/kthread.h>
+
+#define SNAPIMAGE_MAX_DEVICES 2048
+
+int snapimage_major;
+unsigned long *snapimage_minors;
+DEFINE_SPINLOCK(snapimage_minors_lock);
+
+LIST_HEAD(snap_images);
+DECLARE_RWSEM(snap_images_lock);
+
+DECLARE_RWSEM(snap_image_destroy_lock);
+
+struct snapimage {
+	struct list_head link;
+
+	sector_t capacity;
+	dev_t original_dev;
+
+	struct defer_io *defer_io;
+	struct cbt_map *cbt_map;
+
+	dev_t image_dev;
+
+	struct request_queue *queue;
+	struct gendisk *disk;
+
+	atomic_t own_cnt;
+
+	struct redirect_bio_queue image_queue;
+
+	struct task_struct *rq_processor;
+
+	wait_queue_head_t rq_proc_event;
+	wait_queue_head_t rq_complete_event;
+
+	struct mutex open_locker;
+	struct block_device *open_bdev;
+
+	size_t open_cnt;
+};
+
+int _snapimage_open(struct block_device *bdev, fmode_t mode)
+{
+	int res = SUCCESS;
+
+	if (bdev->bd_disk == NULL) {
+		pr_err("Unable to open snapshot image: bd_disk is NULL. Device [%d:%d]\n",
+		       MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
+		pr_err("Block device object %p\n", bdev);
+		return -ENODEV;
+	}
+
+	down_read(&snap_image_destroy_lock);
+	do {
+		struct snapimage *image = bdev->bd_disk->private_data;
+
+		if (image == NULL) {
+			pr_err("Unable to open snapshot image: private data is not initialized. Block device object %p\n",
+			       bdev);
+			res = -ENODEV;
+			break;
+		}
+
+		mutex_lock(&image->open_locker);
+		{
+			if (image->open_cnt == 0)
+				image->open_bdev = bdev;
+
+			image->open_cnt++;
+		}
+		mutex_unlock(&image->open_locker);
+	} while (false);
+	up_read(&snap_image_destroy_lock);
+	return res;
+}
+
+static inline uint64_t do_div_inline(uint64_t division, uint32_t divisor)
+{
+	do_div(division, divisor);
+	return division;
+}
+
+int _snapimage_getgeo(struct block_device *bdev, struct hd_geometry *geo)
+{
+	int res = SUCCESS;
+	sector_t quotient;
+
+	down_read(&snap_image_destroy_lock);
+	do {
+		struct snapimage *image = bdev->bd_disk->private_data;
+
+		if (image == NULL) {
+			pr_err("Unable to open snapshot image: private data is not initialized. Block device object %p\n",
+			       bdev);
+			res = -ENODEV;
+			break;
+		}
+
+		pr_info("Getting geo for snapshot image device [%d:%d]\n", MAJOR(image->image_dev),
+			MINOR(image->image_dev));
+
+		geo->start = 0;
+		if (image->capacity > 63) {
+			geo->sectors = 63;
+			quotient = do_div_inline(image->capacity + (63 - 1), 63);
+
+			if (quotient > 255ULL) {
+				geo->heads = 255;
+				geo->cylinders =
+					(unsigned short)do_div_inline(quotient + (255 - 1), 255);
+			} else {
+				geo->heads = (unsigned char)quotient;
+				geo->cylinders = 1;
+			}
+		} else {
+			geo->sectors = (unsigned char)image->capacity;
+			geo->cylinders = 1;
+			geo->heads = 1;
+		}
+
+		pr_info("Image device geo: capacity=%lld, heads=%d, cylinders=%d, sectors=%d\n",
+			image->capacity, geo->heads, geo->cylinders, geo->sectors);
+	} while (false);
+	up_read(&snap_image_destroy_lock);
+
+	return res;
+}
+
+void _snapimage_close(struct gendisk *disk, fmode_t mode)
+{
+	if (disk->private_data != NULL) {
+		down_read(&snap_image_destroy_lock);
+		do {
+			struct snapimage *image = disk->private_data;
+
+			mutex_lock(&image->open_locker);
+			{
+				if (image->open_cnt > 0)
+					image->open_cnt--;
+
+				if (image->open_cnt == 0)
+					image->open_bdev = NULL;
+			}
+			mutex_unlock(&image->open_locker);
+		} while (false);
+		up_read(&snap_image_destroy_lock);
+	} else
+		pr_err("Unable to close snapshot image: private data is not initialized\n");
+}
+
+int _snapimage_ioctl(struct block_device *bdev, fmode_t mode, unsigned int cmd, unsigned long arg)
+{
+	int res = -ENOTTY;
+
+	down_read(&snap_image_destroy_lock);
+	{
+		struct snapimage *image = bdev->bd_disk->private_data;
+
+		switch (cmd) {
+			/*
+			 * The only command we need to interpret is HDIO_GETGEO, since
+			 * we can't partition the drive otherwise.  We have no real
+			 * geometry, of course, so make something up.
+			 */
+		case HDIO_GETGEO: {
+			unsigned long len;
+			struct hd_geometry geo;
+
+			res = _snapimage_getgeo(bdev, &geo);
+
+			len = copy_to_user((void *)arg, &geo, sizeof(geo));
+			if (len != 0)
+				res = -EFAULT;
+			else
+				res = SUCCESS;
+		} break;
+		case CDROM_GET_CAPABILITY: //0x5331  / * get capabilities * /
+		{
+			struct gendisk *disk = bdev->bd_disk;
+
+			if (bdev->bd_disk && (disk->flags & GENHD_FL_CD))
+				res = SUCCESS;
+			else
+				res = -EINVAL;
+		} break;
+
+		default:
+			pr_info("Snapshot image ioctl receive unsupported command\n");
+			pr_info("Device [%d:%d], command 0x%x, arg 0x%lx\n",
+				MAJOR(image->image_dev), MINOR(image->image_dev), cmd, arg);
+
+			res = -ENOTTY; /* unknown command */
+		}
+	}
+	up_read(&snap_image_destroy_lock);
+	return res;
+}
+
+blk_qc_t _snapimage_submit_bio(struct bio *bio);
+
+const struct block_device_operations snapimage_ops = {
+	.owner = THIS_MODULE,
+	.submit_bio = _snapimage_submit_bio,
+	.open = _snapimage_open,
+	.ioctl = _snapimage_ioctl,
+	.release = _snapimage_close,
+};
+
+static inline int _snapimage_request_read(struct snapimage *image,
+					  struct blk_redirect_bio *rq_redir)
+{
+	struct snapstore_device *snapstore_device = image->defer_io->snapstore_device;
+
+	return snapstore_device_read(snapstore_device, rq_redir);
+}
+
+int _snapimage_request_write(struct snapimage *image, struct blk_redirect_bio *rq_redir)
+{
+	struct snapstore_device *snapstore_device;
+	struct cbt_map *cbt_map;
+	int res = SUCCESS;
+
+	if (unlikely((image->defer_io == NULL) || (image->cbt_map == NULL))) {
+		pr_err("Invalid snapshot image structure");
+		return -EINVAL;
+	}
+
+
+	snapstore_device = image->defer_io->snapstore_device;
+	cbt_map = image->cbt_map;
+
+	if (snapstore_device_is_corrupted(snapstore_device))
+		return -ENODATA;
+
+	if (!bio_has_data(rq_redir->bio)) {
+		pr_warn("Snapshot image receive empty block IO. flags=%u\n",
+			rq_redir->bio->bi_flags);
+
+		blk_redirect_complete(rq_redir, SUCCESS);
+		return SUCCESS;
+	}
+
+	if (cbt_map != NULL) {
+		sector_t ofs = rq_redir->bio->bi_iter.bi_sector;
+		sector_t cnt = bio_sectors(rq_redir->bio);
+
+		res = cbt_map_set_both(cbt_map, ofs, cnt);
+		if (res != SUCCESS)
+			pr_err("Unable to write data to snapshot image: failed to set CBT map. errno=%d\n",
+			       res);
+	}
+
+	res = snapstore_device_write(snapstore_device, rq_redir);
+
+	if (res != SUCCESS) {
+		pr_err("Failed to write data to snapshot image\n");
+		return res;
+	}
+
+	return res;
+}
+
+void _snapimage_processing(struct snapimage *image)
+{
+	int res = SUCCESS;
+	struct blk_redirect_bio *rq_redir;
+
+	rq_redir = redirect_bio_queue_get_first(&image->image_queue);
+
+	if (bio_data_dir(rq_redir->bio) == READ) {
+		res = _snapimage_request_read(image, rq_redir);
+		if (res != SUCCESS)
+			pr_err("Failed to read data from snapshot image. errno=%d\n", res);
+
+	} else {
+		res = _snapimage_request_write(image, rq_redir);
+		if (res != SUCCESS)
+			pr_err("Failed to write data to snapshot image. errno=%d\n", res);
+	}
+
+	if (res != SUCCESS)
+		blk_redirect_complete(rq_redir, res);
+}
+
+int snapimage_processor_waiting(struct snapimage *image)
+{
+	int res = SUCCESS;
+
+	if (redirect_bio_queue_empty(image->image_queue)) {
+		res = wait_event_interruptible_timeout(
+			image->rq_proc_event,
+			(!redirect_bio_queue_empty(image->image_queue) || kthread_should_stop()),
+			5 * HZ);
+		if (res > 0)
+			res = SUCCESS;
+		else if (res == 0)
+			res = -ETIME;
+	}
+	return res;
+}
+
+int snapimage_processor_thread(void *data)
+{
+	struct snapimage *image = data;
+
+	pr_info("Snapshot image thread for device [%d:%d] start\n", MAJOR(image->image_dev),
+		MINOR(image->image_dev));
+
+	add_disk(image->disk);
+
+	//priority
+	set_user_nice(current, -20); //MIN_NICE
+
+	while (!kthread_should_stop()) {
+		int res = snapimage_processor_waiting(image);
+
+		if (res == SUCCESS) {
+			if (!redirect_bio_queue_empty(image->image_queue))
+				_snapimage_processing(image);
+		} else if (res != -ETIME) {
+			pr_err("Failed to wait snapshot image thread queue. errno=%d\n", res);
+			return res;
+		}
+		schedule();
+	}
+	pr_info("Snapshot image disk delete\n");
+	del_gendisk(image->disk);
+
+	while (!redirect_bio_queue_empty(image->image_queue))
+		_snapimage_processing(image);
+
+	pr_info("Snapshot image thread for device [%d:%d] complete", MAJOR(image->image_dev),
+		MINOR(image->image_dev));
+	return 0;
+}
+
+static inline void _snapimage_bio_complete(struct bio *bio, int err)
+{
+	if (err == SUCCESS)
+		bio->bi_status = BLK_STS_OK;
+	else
+		bio->bi_status = BLK_STS_IOERR;
+
+	bio_endio(bio);
+}
+
+void _snapimage_bio_complete_cb(void *complete_param, struct bio *bio, int err)
+{
+	struct snapimage *image = (struct snapimage *)complete_param;
+
+	_snapimage_bio_complete(bio, err);
+
+	if (redirect_bio_queue_unactive(image->image_queue))
+		wake_up_interruptible(&image->rq_complete_event);
+
+	atomic_dec(&image->own_cnt);
+}
+
+int _snapimage_throttling(struct defer_io *defer_io)
+{
+	return wait_event_interruptible(defer_io->queue_throttle_waiter,
+					redirect_bio_queue_empty(defer_io->dio_queue));
+}
+
+blk_qc_t _snapimage_submit_bio(struct bio *bio)
+{
+	blk_qc_t result = SUCCESS;
+	struct request_queue *q = bio->bi_disk->queue;
+	struct snapimage *image = q->queuedata;
+
+	if (unlikely(blk_mq_queue_stopped(q))) {
+		pr_info("Failed to make snapshot image request. Queue already is not active.");
+		pr_info("Queue flags=%lx\n", q->queue_flags);
+
+		_snapimage_bio_complete(bio, -ENODEV);
+
+		return result;
+	}
+
+	atomic_inc(&image->own_cnt);
+	do {
+		int res;
+		struct blk_redirect_bio *rq_redir;
+
+		if (false == atomic_read(&(image->image_queue.active_state))) {
+			_snapimage_bio_complete(bio, -ENODEV);
+			break;
+		}
+
+		if (snapstore_device_is_corrupted(image->defer_io->snapstore_device)) {
+			_snapimage_bio_complete(bio, -ENODATA);
+			break;
+		}
+
+		res = _snapimage_throttling(image->defer_io);
+		if (res != SUCCESS) {
+			pr_err("Failed to throttle snapshot image device. errno=%d\n", res);
+			_snapimage_bio_complete(bio, res);
+			break;
+		}
+
+		rq_redir = redirect_bio_queue_new(&image->image_queue);
+		if (rq_redir == NULL) {
+			pr_err("Unable to make snapshot image request: failed to allocate redirect bio structure\n");
+			_snapimage_bio_complete(bio, -ENOMEM);
+			break;
+		}
+		rq_redir->bio = bio;
+		rq_redir->complete_cb = _snapimage_bio_complete_cb;
+		rq_redir->complete_param = (void *)image;
+		atomic_inc(&image->own_cnt);
+
+		res = redirect_bio_queue_push_back(&image->image_queue, rq_redir);
+		if (res == SUCCESS)
+			wake_up(&image->rq_proc_event);
+		else {
+			redirect_bio_queue_free(rq_redir);
+			_snapimage_bio_complete(bio, -EIO);
+
+			if (redirect_bio_queue_unactive(image->image_queue))
+				wake_up_interruptible(&image->rq_complete_event);
+		}
+
+	} while (false);
+	atomic_dec(&image->own_cnt);
+
+	return result;
+}
+
+struct blk_dev_info {
+	size_t blk_size;
+	sector_t start_sect;
+	sector_t count_sect;
+
+	unsigned int io_min;
+	unsigned int physical_block_size;
+	unsigned short logical_block_size;
+};
+
+static int _blk_dev_get_info(struct block_device *blk_dev, struct blk_dev_info *pdev_info)
+{
+	sector_t SectorStart;
+	sector_t SectorsCapacity;
+
+	if (blk_dev->bd_part)
+		SectorsCapacity = blk_dev->bd_part->nr_sects;
+	else if (blk_dev->bd_disk)
+		SectorsCapacity = get_capacity(blk_dev->bd_disk);
+	else
+		return -EINVAL;
+
+	SectorStart = get_start_sect(blk_dev);
+
+	pdev_info->physical_block_size = blk_dev->bd_disk->queue->limits.physical_block_size;
+	pdev_info->logical_block_size = blk_dev->bd_disk->queue->limits.logical_block_size;
+	pdev_info->io_min = blk_dev->bd_disk->queue->limits.io_min;
+
+	pdev_info->blk_size = block_size(blk_dev);
+	pdev_info->start_sect = SectorStart;
+	pdev_info->count_sect = SectorsCapacity;
+	return SUCCESS;
+}
+
+static int blk_dev_get_info(dev_t dev_id, struct blk_dev_info *pdev_info)
+{
+	int result = SUCCESS;
+	struct block_device *blk_dev;
+
+	result = blk_dev_open(dev_id, &blk_dev);
+	if (result != SUCCESS) {
+		pr_err("Failed to open device [%d:%d]\n", MAJOR(dev_id), MINOR(dev_id));
+		return result;
+	}
+
+	result = _blk_dev_get_info(blk_dev, pdev_info);
+	if (result != SUCCESS)
+		pr_err("Failed to identify block device [%d:%d]\n", MAJOR(dev_id), MINOR(dev_id));
+
+	blk_dev_close(blk_dev);
+
+	return result;
+}
+
+static inline void _snapimage_free(struct snapimage *image)
+{
+	defer_io_put_resource(image->defer_io);
+	cbt_map_put_resource(image->cbt_map);
+	image->defer_io = NULL;
+}
+
+static void _snapimage_stop(struct snapimage *image)
+{
+	if (image->rq_processor != NULL) {
+		if (redirect_bio_queue_active(&image->image_queue, false)) {
+			struct request_queue *q = image->queue;
+
+			pr_info("Snapshot image request processing stop\n");
+
+			if (!blk_queue_stopped(q)) {
+				blk_sync_queue(q);
+				blk_mq_stop_hw_queues(q);
+			}
+		}
+
+		pr_info("Snapshot image thread stop\n");
+		kthread_stop(image->rq_processor);
+		image->rq_processor = NULL;
+
+		while (!redirect_bio_queue_unactive(image->image_queue))
+			wait_event_interruptible(image->rq_complete_event,
+						 redirect_bio_queue_unactive(image->image_queue));
+	}
+}
+
+static void _snapimage_destroy(struct snapimage *image)
+{
+	if (image->rq_processor != NULL)
+		_snapimage_stop(image);
+
+	if (image->queue) {
+		pr_info("Snapshot image queue cleanup\n");
+		blk_cleanup_queue(image->queue);
+		image->queue = NULL;
+	}
+
+	if (image->disk != NULL) {
+		struct gendisk *disk;
+
+		disk = image->disk;
+		image->disk = NULL;
+
+		pr_info("Snapshot image disk structure release\n");
+
+		disk->private_data = NULL;
+		put_disk(disk);
+	}
+
+	spin_lock(&snapimage_minors_lock);
+	bitmap_clear(snapimage_minors, MINOR(image->image_dev), 1u);
+	spin_unlock(&snapimage_minors_lock);
+}
+
+int snapimage_create(dev_t original_dev)
+{
+	int res = SUCCESS;
+	struct tracker *tracker = NULL;
+	struct snapimage *image = NULL;
+	struct gendisk *disk = NULL;
+	int minor;
+	struct blk_dev_info original_dev_info;
+
+	pr_info("Create snapshot image for device [%d:%d]\n", MAJOR(original_dev),
+		MINOR(original_dev));
+
+	res = blk_dev_get_info(original_dev, &original_dev_info);
+	if (res != SUCCESS) {
+		pr_err("Failed to obtain original device info\n");
+		return res;
+	}
+
+	res = tracker_find_by_dev_id(original_dev, &tracker);
+	if (res != SUCCESS) {
+		pr_err("Unable to create snapshot image: cannot find tracker for device [%d:%d]\n",
+		       MAJOR(original_dev), MINOR(original_dev));
+		return res;
+	}
+
+	image = kzalloc(sizeof(struct snapimage), GFP_KERNEL);
+	if (image == NULL)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&image->link);
+
+	do {
+		spin_lock(&snapimage_minors_lock);
+		minor = bitmap_find_free_region(snapimage_minors, SNAPIMAGE_MAX_DEVICES, 0);
+		spin_unlock(&snapimage_minors_lock);
+
+		if (minor < SUCCESS) {
+			pr_err("Failed to allocate minor for snapshot image device. errno=%d\n",
+			       0 - minor);
+			break;
+		}
+
+		image->rq_processor = NULL;
+
+		image->capacity = original_dev_info.count_sect;
+
+		image->defer_io = defer_io_get_resource(tracker->defer_io);
+		image->cbt_map = cbt_map_get_resource(tracker->cbt_map);
+		image->original_dev = original_dev;
+
+		image->image_dev = MKDEV(snapimage_major, minor);
+		pr_info("Snapshot image device id [%d:%d]\n", MAJOR(image->image_dev),
+			MINOR(image->image_dev));
+
+		atomic_set(&image->own_cnt, 0);
+
+		mutex_init(&image->open_locker);
+		image->open_bdev = NULL;
+		image->open_cnt = 0;
+
+		image->queue = blk_alloc_queue(NUMA_NO_NODE);
+		if (image->queue == NULL) {
+			res = -ENOMEM;
+			break;
+		}
+		image->queue->queuedata = image;
+
+		blk_queue_max_segment_size(image->queue, 1024 * PAGE_SIZE);
+
+		{
+			unsigned int physical_block_size = original_dev_info.physical_block_size;
+			unsigned short logical_block_size = original_dev_info.logical_block_size;
+
+			pr_info("Snapshot image physical block size %d\n", physical_block_size);
+			pr_info("Snapshot image logical block size %d\n", logical_block_size);
+
+			blk_queue_physical_block_size(image->queue, physical_block_size);
+			blk_queue_logical_block_size(image->queue, logical_block_size);
+		}
+		disk = alloc_disk(1); //only one partition on disk
+		if (disk == NULL) {
+			pr_err("Failed to allocate disk for snapshot image device\n");
+			res = -ENOMEM;
+			break;
+		}
+		image->disk = disk;
+
+		if (snprintf(disk->disk_name, DISK_NAME_LEN, "%s%d", SNAP_IMAGE_NAME, minor) < 0) {
+			pr_err("Unable to set disk name for snapshot image device: invalid minor %d\n",
+			       minor);
+			res = -EINVAL;
+			break;
+		}
+
+		pr_info("Snapshot image disk name [%s]", disk->disk_name);
+
+		disk->flags |= GENHD_FL_NO_PART_SCAN;
+		disk->flags |= GENHD_FL_REMOVABLE;
+
+		disk->major = snapimage_major;
+		disk->minors = 1; // one disk have only one partition.
+		disk->first_minor = minor;
+
+		disk->private_data = image;
+
+		disk->fops = &snapimage_ops;
+		disk->queue = image->queue;
+
+		set_capacity(disk, image->capacity);
+		pr_info("Snapshot image device capacity %lld bytes",
+			(u64)from_sectors(image->capacity));
+
+		//res = -ENOMEM;
+		redirect_bio_queue_init(&image->image_queue);
+
+		{
+			struct task_struct *task =
+				kthread_create(snapimage_processor_thread, image, disk->disk_name);
+			if (IS_ERR(task)) {
+				res = PTR_ERR(task);
+				pr_err("Failed to create request processing thread for snapshot image device. errno=%d\n",
+				       res);
+				break;
+			}
+			image->rq_processor = task;
+		}
+		init_waitqueue_head(&image->rq_complete_event);
+
+		init_waitqueue_head(&image->rq_proc_event);
+		wake_up_process(image->rq_processor);
+	} while (false);
+
+	if (res == SUCCESS) {
+		down_write(&snap_images_lock);
+		list_add_tail(&image->link, &snap_images);
+		up_write(&snap_images_lock);
+	} else {
+		_snapimage_destroy(image);
+		_snapimage_free(image);
+
+		kfree(image);
+		image = NULL;
+	}
+	return res;
+}
+
+static struct snapimage *snapimage_find(dev_t original_dev)
+{
+	struct snapimage *image = NULL;
+
+	down_read(&snap_images_lock);
+	if (!list_empty(&snap_images)) {
+		struct list_head *_list_head;
+
+		list_for_each(_list_head, &snap_images) {
+			struct snapimage *_image = list_entry(_list_head, struct snapimage, link);
+
+			if (_image->original_dev == original_dev) {
+				image = _image;
+				break;
+			}
+		}
+	}
+	up_read(&snap_images_lock);
+
+	return image;
+}
+
+void snapimage_stop(dev_t original_dev)
+{
+	struct snapimage *image;
+
+	pr_info("Snapshot image processing stop for original device [%d:%d]\n", MAJOR(original_dev),
+		MINOR(original_dev));
+
+	down_read(&snap_image_destroy_lock);
+
+	image = snapimage_find(original_dev);
+	if (image != NULL)
+		_snapimage_stop(image);
+	else
+		pr_err("Snapshot image [%d:%d] not found\n", MAJOR(original_dev),
+		       MINOR(original_dev));
+
+	up_read(&snap_image_destroy_lock);
+}
+
+void snapimage_destroy(dev_t original_dev)
+{
+	struct snapimage *image = NULL;
+
+	pr_info("Destroy snapshot image for device [%d:%d]\n", MAJOR(original_dev),
+		MINOR(original_dev));
+
+	down_write(&snap_images_lock);
+	if (!list_empty(&snap_images)) {
+		struct list_head *_list_head;
+
+		list_for_each(_list_head, &snap_images) {
+			struct snapimage *_image = list_entry(_list_head, struct snapimage, link);
+
+			if (_image->original_dev == original_dev) {
+				image = _image;
+				list_del(&image->link);
+				break;
+			}
+		}
+	}
+	up_write(&snap_images_lock);
+
+	if (image != NULL) {
+		down_write(&snap_image_destroy_lock);
+
+		_snapimage_destroy(image);
+		_snapimage_free(image);
+
+		kfree(image);
+		image = NULL;
+
+		up_write(&snap_image_destroy_lock);
+	} else
+		pr_err("Snapshot image [%d:%d] not found\n", MAJOR(original_dev),
+		       MINOR(original_dev));
+}
+
+void snapimage_destroy_for(dev_t *p_dev, int count)
+{
+	int inx = 0;
+
+	for (; inx < count; ++inx)
+		snapimage_destroy(p_dev[inx]);
+}
+
+int snapimage_create_for(dev_t *p_dev, int count)
+{
+	int res = SUCCESS;
+	int inx = 0;
+
+	for (; inx < count; ++inx) {
+		res = snapimage_create(p_dev[inx]);
+		if (res != SUCCESS) {
+			pr_err("Failed to create snapshot image for original device [%d:%d]\n",
+			       MAJOR(p_dev[inx]), MINOR(p_dev[inx]));
+			break;
+		}
+	}
+	if (res != SUCCESS)
+		if (inx > 0)
+			snapimage_destroy_for(p_dev, inx - 1);
+	return res;
+}
+
+int snapimage_init(void)
+{
+	int res = SUCCESS;
+
+	res = register_blkdev(snapimage_major, SNAP_IMAGE_NAME);
+	if (res >= SUCCESS) {
+		snapimage_major = res;
+		pr_info("Snapshot image block device major %d was registered\n", snapimage_major);
+		res = SUCCESS;
+
+		spin_lock(&snapimage_minors_lock);
+		snapimage_minors = bitmap_zalloc(SNAPIMAGE_MAX_DEVICES, GFP_KERNEL);
+		spin_unlock(&snapimage_minors_lock);
+
+		if (snapimage_minors == NULL)
+			pr_err("Failed to initialize bitmap of minors\n");
+	} else
+		pr_err("Failed to register snapshot image block device. errno=%d\n", res);
+
+	return res;
+}
+
+void snapimage_done(void)
+{
+	down_write(&snap_image_destroy_lock);
+	while (true) {
+		struct snapimage *image = NULL;
+
+		down_write(&snap_images_lock);
+		if (!list_empty(&snap_images)) {
+			image = list_entry(snap_images.next, struct snapimage, link);
+
+			list_del(&image->link);
+		}
+		up_write(&snap_images_lock);
+
+		if (image == NULL)
+			break;
+
+		pr_err("Snapshot image for device was unexpectedly removed [%d:%d]\n",
+		       MAJOR(image->original_dev), MINOR(image->original_dev));
+
+		_snapimage_destroy(image);
+		_snapimage_free(image);
+
+		kfree(image);
+		image = NULL;
+	}
+
+	spin_lock(&snapimage_minors_lock);
+	bitmap_free(snapimage_minors);
+	snapimage_minors = NULL;
+	spin_unlock(&snapimage_minors_lock);
+
+	if (!list_empty(&snap_images))
+		pr_err("Failed to release snapshot images container\n");
+
+	unregister_blkdev(snapimage_major, SNAP_IMAGE_NAME);
+	pr_info("Snapshot image block device [%d] was unregistered\n", snapimage_major);
+
+	up_write(&snap_image_destroy_lock);
+}
+
+int snapimage_collect_images(int count, struct image_info_s *p_user_image_info, int *p_real_count)
+{
+	int res = SUCCESS;
+	int real_count = 0;
+
+	down_read(&snap_images_lock);
+	if (!list_empty(&snap_images)) {
+		struct list_head *_list_head;
+
+		list_for_each(_list_head, &snap_images)
+			real_count++;
+	}
+	up_read(&snap_images_lock);
+	*p_real_count = real_count;
+
+	if (count < real_count)
+		res = -ENODATA;
+
+	real_count = min(count, real_count);
+	if (real_count > 0) {
+		unsigned long len;
+		struct image_info_s *p_kernel_image_info = NULL;
+		size_t buff_size;
+
+		buff_size = sizeof(struct image_info_s) * real_count;
+		p_kernel_image_info = kzalloc(buff_size, GFP_KERNEL);
+		if (p_kernel_image_info == NULL) {
+			pr_err("Unable to collect snapshot images: not enough memory. size=%zu\n",
+			       buff_size);
+			return res = -ENOMEM;
+		}
+
+		down_read(&snap_image_destroy_lock);
+		down_read(&snap_images_lock);
+
+		if (!list_empty(&snap_images)) {
+			size_t inx = 0;
+			struct list_head *_list_head;
+
+			list_for_each(_list_head, &snap_images) {
+				struct snapimage *img =
+					list_entry(_list_head, struct snapimage, link);
+
+				real_count++;
+
+				p_kernel_image_info[inx].original_dev_id.major =
+					MAJOR(img->original_dev);
+				p_kernel_image_info[inx].original_dev_id.minor =
+					MINOR(img->original_dev);
+
+				p_kernel_image_info[inx].snapshot_dev_id.major =
+					MAJOR(img->image_dev);
+				p_kernel_image_info[inx].snapshot_dev_id.minor =
+					MINOR(img->image_dev);
+
+				++inx;
+				if (inx > real_count)
+					break;
+			}
+		}
+
+		up_read(&snap_images_lock);
+		up_read(&snap_image_destroy_lock);
+
+		len = copy_to_user(p_user_image_info, p_kernel_image_info, buff_size);
+		if (len != 0) {
+			pr_err("Unable to collect snapshot images: failed to copy data to user buffer\n");
+			res = -ENODATA;
+		}
+
+		kfree(p_kernel_image_info);
+	}
+
+	return res;
+}
+
+int snapimage_mark_dirty_blocks(dev_t image_dev_id, struct block_range_s *block_ranges,
+				unsigned int count)
+{
+	size_t inx = 0;
+	int res = SUCCESS;
+
+	pr_info("Marking [%d] dirty blocks for image device [%d:%d]\n", count, MAJOR(image_dev_id),
+		MINOR(image_dev_id));
+
+	down_read(&snap_image_destroy_lock);
+	do {
+		struct snapimage *image = snapimage_find(image_dev_id);
+
+		if (image == NULL) {
+			pr_err("Cannot find device [%d:%d]\n", MAJOR(image_dev_id),
+			       MINOR(image_dev_id));
+			res = -ENODEV;
+			break;
+		}
+
+		for (inx = 0; inx < count; ++inx) {
+			sector_t ofs = (sector_t)block_ranges[inx].ofs;
+			sector_t cnt = (sector_t)block_ranges[inx].cnt;
+
+			res = cbt_map_set_both(image->cbt_map, ofs, cnt);
+			if (res != SUCCESS) {
+				pr_err("Failed to set CBT table. errno=%d\n", res);
+				break;
+			}
+		}
+	} while (false);
+	up_read(&snap_image_destroy_lock);
+
+	return res;
+}
diff --git a/drivers/block/blk-snap/snapimage.h b/drivers/block/blk-snap/snapimage.h
new file mode 100644
index 000000000000..67995c321496
--- /dev/null
+++ b/drivers/block/blk-snap/snapimage.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#pragma once
+
+#include "blk-snap-ctl.h"
+
+int snapimage_init(void);
+void snapimage_done(void);
+int snapimage_create_for(dev_t *p_dev, int count);
+
+void snapimage_stop(dev_t original_dev);
+void snapimage_destroy(dev_t original_dev);
+
+int snapimage_collect_images(int count, struct image_info_s *p_user_image_info, int *p_real_count);
+
+int snapimage_mark_dirty_blocks(dev_t image_dev_id, struct block_range_s *block_ranges,
+				unsigned int count);
diff --git a/drivers/block/blk-snap/snapshot.c b/drivers/block/blk-snap/snapshot.c
new file mode 100644
index 000000000000..fdef713103d2
--- /dev/null
+++ b/drivers/block/blk-snap/snapshot.c
@@ -0,0 +1,225 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-snapshot"
+#include "common.h"
+#include "snapshot.h"
+#include "tracker.h"
+#include "snapimage.h"
+#include "tracking.h"
+
+LIST_HEAD(snapshots);
+DECLARE_RWSEM(snapshots_lock);
+
+
+static int _snapshot_remove_device(dev_t dev_id)
+{
+	int result;
+	struct tracker *tracker = NULL;
+
+	result = tracker_find_by_dev_id(dev_id, &tracker);
+	if (result != SUCCESS) {
+		if (result == -ENODEV)
+			pr_err("Cannot find device by device id=[%d:%d]\n", MAJOR(dev_id),
+			       MINOR(dev_id));
+		else
+			pr_err("Failed to find device by device id=[%d:%d]\n", MAJOR(dev_id),
+			       MINOR(dev_id));
+		return SUCCESS;
+	}
+
+	if (result != SUCCESS)
+		return result;
+
+	tracker->snapshot_id = 0ull;
+
+	pr_info("Device [%d:%d] successfully removed from snapshot\n", MAJOR(dev_id),
+		MINOR(dev_id));
+	return SUCCESS;
+}
+
+static void _snapshot_cleanup(struct snapshot *snapshot)
+{
+	int inx;
+
+	for (inx = 0; inx < snapshot->dev_id_set_size; ++inx) {
+
+		if (_snapshot_remove_device(snapshot->dev_id_set[inx]) != SUCCESS)
+			pr_err("Failed to remove device [%d:%d] from snapshot\n",
+			       MAJOR(snapshot->dev_id_set[inx]), MINOR(snapshot->dev_id_set[inx]));
+	}
+
+	if (snapshot->dev_id_set != NULL)
+		kfree(snapshot->dev_id_set);
+	kfree(snapshot);
+}
+
+static void _snapshot_destroy(struct snapshot *snapshot)
+{
+	size_t inx;
+
+	for (inx = 0; inx < snapshot->dev_id_set_size; ++inx)
+		snapimage_stop(snapshot->dev_id_set[inx]);
+
+	pr_info("Release snapshot [0x%llx]\n", snapshot->id);
+
+	tracker_release_snapshot(snapshot->dev_id_set, snapshot->dev_id_set_size);
+
+	for (inx = 0; inx < snapshot->dev_id_set_size; ++inx)
+		snapimage_destroy(snapshot->dev_id_set[inx]);
+
+	_snapshot_cleanup(snapshot);
+}
+
+
+static int _snapshot_new(dev_t *p_dev, int count, struct snapshot **pp_snapshot)
+{
+	struct snapshot *p_snapshot = NULL;
+	dev_t *snap_set = NULL;
+
+	p_snapshot = kzalloc(sizeof(struct snapshot), GFP_KERNEL);
+	if (p_snapshot == NULL)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&p_snapshot->link);
+
+	p_snapshot->id = (unsigned long)(p_snapshot);
+
+	snap_set = kcalloc(count, sizeof(dev_t), GFP_KERNEL);
+	if (snap_set == NULL) {
+		kfree(p_snapshot);
+
+		pr_err("Unable to create snapshot: faile to allocate memory for snapshot map\n");
+		return -ENOMEM;
+	}
+	memcpy(snap_set, p_dev, sizeof(dev_t) * count);
+
+	p_snapshot->dev_id_set_size = count;
+	p_snapshot->dev_id_set = snap_set;
+
+	down_write(&snapshots_lock);
+	list_add_tail(&snapshots, &p_snapshot->link);
+	up_write(&snapshots_lock);
+
+	*pp_snapshot = p_snapshot;
+
+	return SUCCESS;
+}
+
+void snapshot_done(void)
+{
+	struct snapshot *snap;
+
+	pr_info("Removing all snapshots\n");
+	do {
+		snap = NULL;
+		down_write(&snapshots_lock);
+		if (!list_empty(&snapshots)) {
+			struct snapshot *snap = list_entry(snapshots.next, struct snapshot, link);
+
+			list_del(&snap->link);
+		}
+		up_write(&snapshots_lock);
+
+		if (snap)
+			_snapshot_destroy(snap);
+
+	} while (snap);
+}
+
+int snapshot_create(dev_t *dev_id_set, unsigned int dev_id_set_size,
+		    unsigned long long *p_snapshot_id)
+{
+	struct snapshot *snapshot = NULL;
+	int result = SUCCESS;
+	unsigned int inx;
+
+	pr_info("Create snapshot for devices:\n");
+	for (inx = 0; inx < dev_id_set_size; ++inx)
+		pr_info("\t%d:%d\n", MAJOR(dev_id_set[inx]), MINOR(dev_id_set[inx]));
+
+	result = _snapshot_new(dev_id_set, dev_id_set_size, &snapshot);
+	if (result != SUCCESS) {
+		pr_err("Unable to create snapshot: failed to allocate snapshot structure\n");
+		return result;
+	}
+
+	do {
+		result = -ENODEV;
+		for (inx = 0; inx < snapshot->dev_id_set_size; ++inx) {
+			dev_t dev_id = snapshot->dev_id_set[inx];
+
+			result = tracking_add(dev_id, snapshot->id);
+			if (result == -EALREADY)
+				result = SUCCESS;
+			else if (result != SUCCESS) {
+				pr_err("Unable to create snapshot\n");
+				pr_err("Failed to add device [%d:%d] to snapshot tracking\n",
+				       MAJOR(dev_id), MINOR(dev_id));
+				break;
+			}
+		}
+		if (result != SUCCESS)
+			break;
+
+		result = tracker_capture_snapshot(snapshot->dev_id_set, snapshot->dev_id_set_size);
+		if (result != SUCCESS) {
+			pr_err("Unable to create snapshot: failed to capture snapshot [0x%llx]\n",
+			       snapshot->id);
+			break;
+		}
+
+		result = snapimage_create_for(snapshot->dev_id_set, snapshot->dev_id_set_size);
+		if (result != SUCCESS) {
+			pr_err("Unable to create snapshot\n");
+			pr_err("Failed to create snapshot image devices\n");
+
+			tracker_release_snapshot(snapshot->dev_id_set, snapshot->dev_id_set_size);
+			break;
+		}
+
+		*p_snapshot_id = snapshot->id;
+		pr_info("Snapshot [0x%llx] was created\n", snapshot->id);
+	} while (false);
+
+	if (result != SUCCESS) {
+		pr_info("Snapshot [0x%llx] cleanup\n", snapshot->id);
+
+		down_write(&snapshots_lock);
+		list_del(&snapshot->link);
+		up_write(&snapshots_lock);
+
+		_snapshot_cleanup(snapshot);
+	}
+	return result;
+}
+
+int snapshot_destroy(unsigned long long snapshot_id)
+{
+	struct snapshot *snapshot = NULL;
+
+	pr_info("Destroy snapshot [0x%llx]\n", snapshot_id);
+
+	down_read(&snapshots_lock);
+	if (!list_empty(&snapshots)) {
+		struct list_head *_head;
+
+		list_for_each(_head, &snapshots) {
+			struct snapshot *_snap = list_entry(_head, struct snapshot, link);
+
+			if (_snap->id == snapshot_id) {
+				snapshot = _snap;
+				list_del(&snapshot->link);
+				break;
+			}
+		}
+	}
+	up_read(&snapshots_lock);
+
+	if (snapshot == NULL) {
+		pr_err("Unable to destroy snapshot [0x%llx]: cannot find snapshot by id\n",
+		       snapshot_id);
+		return -ENODEV;
+	}
+
+	_snapshot_destroy(snapshot);
+	return SUCCESS;
+}
diff --git a/drivers/block/blk-snap/snapshot.h b/drivers/block/blk-snap/snapshot.h
new file mode 100644
index 000000000000..59fb4dba0241
--- /dev/null
+++ b/drivers/block/blk-snap/snapshot.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#pragma once
+
+struct snapshot {
+	struct list_head link;
+	unsigned long long id;
+
+	dev_t *dev_id_set; //array of assigned devices
+	int dev_id_set_size;
+};
+
+void snapshot_done(void);
+
+int snapshot_create(dev_t *dev_id_set, unsigned int dev_id_set_size,
+		    unsigned long long *p_snapshot_id);
+
+int snapshot_destroy(unsigned long long snapshot_id);
diff --git a/drivers/block/blk-snap/snapstore.c b/drivers/block/blk-snap/snapstore.c
new file mode 100644
index 000000000000..0bedeaeec021
--- /dev/null
+++ b/drivers/block/blk-snap/snapstore.c
@@ -0,0 +1,929 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-snapstore"
+#include "common.h"
+#include "snapstore.h"
+#include "snapstore_device.h"
+#include "big_buffer.h"
+#include "params.h"
+
+LIST_HEAD(snapstores);
+DECLARE_RWSEM(snapstores_lock);
+
+bool _snapstore_check_halffill(struct snapstore *snapstore, sector_t *fill_status)
+{
+	struct blk_descr_pool *pool = NULL;
+
+	if (snapstore->file)
+		pool = &snapstore->file->pool;
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+	else if (snapstore->multidev)
+		pool = &snapstore->multidev->pool;
+#endif
+	else if (snapstore->mem)
+		pool = &snapstore->mem->pool;
+
+	if (pool)
+		return blk_descr_pool_check_halffill(pool, snapstore->empty_limit, fill_status);
+
+	return false;
+}
+
+void _snapstore_destroy(struct snapstore *snapstore)
+{
+	sector_t fill_status;
+
+	pr_info("Destroy snapstore with id %pUB\n", &snapstore->id);
+
+	_snapstore_check_halffill(snapstore, &fill_status);
+
+	down_write(&snapstores_lock);
+	list_del(&snapstore->link);
+	up_write(&snapstores_lock);
+
+	if (snapstore->mem != NULL)
+		snapstore_mem_destroy(snapstore->mem);
+	if (snapstore->multidev != NULL)
+		snapstore_multidev_destroy(snapstore->multidev);
+	if (snapstore->file != NULL)
+		snapstore_file_destroy(snapstore->file);
+
+	if (snapstore->ctrl_pipe) {
+		struct ctrl_pipe *pipe;
+
+		pipe = snapstore->ctrl_pipe;
+		snapstore->ctrl_pipe = NULL;
+
+		ctrl_pipe_request_terminate(pipe, fill_status);
+
+		ctrl_pipe_put_resource(pipe);
+	}
+
+	kfree(snapstore);
+}
+
+static void _snapstore_destroy_cb(struct kref *kref)
+{
+	struct snapstore *snapstore = container_of(kref, struct snapstore, refcount);
+
+	_snapstore_destroy(snapstore);
+}
+
+struct snapstore *snapstore_get(struct snapstore *snapstore)
+{
+	if (snapstore)
+		kref_get(&snapstore->refcount);
+
+	return snapstore;
+}
+
+void snapstore_put(struct snapstore *snapstore)
+{
+	if (snapstore)
+		kref_put(&snapstore->refcount, _snapstore_destroy_cb);
+}
+
+void snapstore_done(void)
+{
+	bool is_empty;
+
+	down_read(&snapstores_lock);
+	is_empty = list_empty(&snapstores);
+	up_read(&snapstores_lock);
+
+	if (!is_empty)
+		pr_err("Unable to perform snapstore cleanup: container is not empty\n");
+}
+
+int snapstore_create(uuid_t *id, dev_t snapstore_dev_id, dev_t *dev_id_set,
+		     size_t dev_id_set_length)
+{
+	int res = SUCCESS;
+	size_t dev_id_inx;
+	struct snapstore *snapstore = NULL;
+
+	if (dev_id_set_length == 0)
+		return -EINVAL;
+
+	snapstore = kzalloc(sizeof(struct snapstore), GFP_KERNEL);
+	if (snapstore == NULL)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&snapstore->link);
+	uuid_copy(&snapstore->id, id);
+
+	pr_info("Create snapstore with id %pUB\n", &snapstore->id);
+
+	snapstore->mem = NULL;
+	snapstore->multidev = NULL;
+	snapstore->file = NULL;
+
+	snapstore->ctrl_pipe = NULL;
+	snapstore->empty_limit = (sector_t)(64 * (1024 * 1024 / SECTOR_SIZE)); //by default value
+	snapstore->halffilled = false;
+	snapstore->overflowed = false;
+
+	if (snapstore_dev_id == 0)
+		pr_info("Memory snapstore create\n");
+
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+	else if (snapstore_dev_id == 0xFFFFffff) {
+		struct snapstore_multidev *multidev = NULL;
+
+		res = snapstore_multidev_create(&multidev);
+		if (res != SUCCESS) {
+			kfree(snapstore);
+
+			pr_err("Failed to create multidevice snapstore %pUB\n", id);
+			return res;
+		}
+		snapstore->multidev = multidev;
+	}
+#endif
+	else {
+		struct snapstore_file *file = NULL;
+
+		res = snapstore_file_create(snapstore_dev_id, &file);
+		if (res != SUCCESS) {
+			kfree(snapstore);
+
+			pr_err("Failed to create snapstore file for snapstore %pUB\n", id);
+			return res;
+		}
+		snapstore->file = file;
+	}
+
+	down_write(&snapstores_lock);
+	list_add_tail(&snapstores, &snapstore->link);
+	up_write(&snapstores_lock);
+
+	kref_init(&snapstore->refcount);
+
+	for (dev_id_inx = 0; dev_id_inx < dev_id_set_length; ++dev_id_inx) {
+		res = snapstore_device_create(dev_id_set[dev_id_inx], snapstore);
+		if (res != SUCCESS)
+			break;
+	}
+
+	if (res != SUCCESS)
+		snapstore_device_cleanup(id);
+
+	snapstore_put(snapstore);
+	return res;
+}
+
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+int snapstore_create_multidev(uuid_t *id, dev_t *dev_id_set, size_t dev_id_set_length)
+{
+	int res = SUCCESS;
+	size_t dev_id_inx;
+	struct snapstore *snapstore = NULL;
+	struct snapstore_multidev *multidev = NULL;
+
+	if (dev_id_set_length == 0)
+		return -EINVAL;
+
+	snapstore = kzalloc(sizeof(struct snapstore), GFP_KERNEL);
+	if (snapstore == NULL)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&snapstore->link);
+
+	uuid_copy(&snapstore->id, id);
+
+	pr_info("Create snapstore with id %pUB\n", &snapstore->id);
+
+	snapstore->mem = NULL;
+	snapstore->file = NULL;
+	snapstore->multidev = NULL;
+
+	snapstore->ctrl_pipe = NULL;
+	snapstore->empty_limit = (sector_t)(64 * (1024 * 1024 / SECTOR_SIZE)); //by default value
+	snapstore->halffilled = false;
+	snapstore->overflowed = false;
+
+	res = snapstore_multidev_create(&multidev);
+	if (res != SUCCESS) {
+		kfree(snapstore);
+
+		pr_err("Failed to create snapstore file for snapstore %pUB\n", id);
+		return res;
+	}
+	snapstore->multidev = multidev;
+
+	down_write(&snapstores_lock);
+	list_add_tail(&snapstore->link, &snapstores);
+	up_write(&snapstores_lock);
+
+	kref_init(&snapstore->refcount);
+
+	for (dev_id_inx = 0; dev_id_inx < dev_id_set_length; ++dev_id_inx) {
+		res = snapstore_device_create(dev_id_set[dev_id_inx], snapstore);
+		if (res != SUCCESS)
+			break;
+	}
+
+	if (res != SUCCESS)
+		snapstore_device_cleanup(id);
+
+	snapstore_put(snapstore);
+	return res;
+}
+#endif
+
+int snapstore_cleanup(uuid_t *id, u64 *filled_bytes)
+{
+	int res;
+	sector_t filled;
+
+	res = snapstore_check_halffill(id, &filled);
+	if (res == SUCCESS) {
+		*filled_bytes = (u64)from_sectors(filled);
+
+		pr_info("Snapstore fill size: %lld MiB\n", (*filled_bytes >> 20));
+	} else {
+		*filled_bytes = -1;
+		pr_err("Failed to obtain snapstore data filled size\n");
+	}
+
+	return snapstore_device_cleanup(id);
+}
+
+struct snapstore *_snapstore_find(uuid_t *id)
+{
+	struct snapstore *result = NULL;
+
+	down_read(&snapstores_lock);
+	if (!list_empty(&snapstores)) {
+		struct list_head *_head;
+
+		list_for_each(_head, &snapstores) {
+			struct snapstore *snapstore = list_entry(_head, struct snapstore, link);
+
+			if (uuid_equal(&snapstore->id, id)) {
+				result = snapstore;
+				break;
+			}
+		}
+	}
+	up_read(&snapstores_lock);
+
+	return result;
+}
+
+int snapstore_stretch_initiate(uuid_t *unique_id, struct ctrl_pipe *ctrl_pipe, sector_t empty_limit)
+{
+	struct snapstore *snapstore;
+
+	snapstore = _snapstore_find(unique_id);
+	if (snapstore == NULL) {
+		pr_err("Unable to initiate stretch snapstore: ");
+		pr_err("cannot find snapstore by uuid %pUB\n", unique_id);
+		return -ENODATA;
+	}
+
+	snapstore->ctrl_pipe = ctrl_pipe_get_resource(ctrl_pipe);
+	snapstore->empty_limit = empty_limit;
+
+	return SUCCESS;
+}
+
+int snapstore_add_memory(uuid_t *id, unsigned long long sz)
+{
+	int res = SUCCESS;
+	struct snapstore *snapstore = NULL;
+	size_t available_blocks = (size_t)(sz >> (snapstore_block_shift() + SECTOR_SHIFT));
+	size_t current_block = 0;
+
+	pr_info("Adding %lld bytes to the snapstore\n", sz);
+
+	snapstore = _snapstore_find(id);
+	if (snapstore == NULL) {
+		pr_err("Unable to add memory block to the snapstore: ");
+		pr_err("cannot found snapstore by id %pUB\n", id);
+		return -ENODATA;
+	}
+
+	if (snapstore->file != NULL) {
+		pr_err("Unable to add memory block to the snapstore: ");
+		pr_err("snapstore file is already created\n");
+		return -EINVAL;
+	}
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+	if (snapstore->multidev != NULL) {
+		pr_err("Unable to add memory block to the snapstore: ");
+		pr_err("snapstore multidevice is already created\n");
+		return -EINVAL;
+	}
+#endif
+	if (snapstore->mem != NULL) {
+		pr_err("Unable to add memory block to the snapstore: ");
+		pr_err("snapstore memory buffer is already created\n");
+		return -EINVAL;
+	}
+
+	snapstore->mem = snapstore_mem_create(available_blocks);
+	for (current_block = 0; current_block < available_blocks; ++current_block) {
+		void *buffer = snapstore_mem_get_block(snapstore->mem);
+
+		if (buffer == NULL) {
+			pr_err("Unable to add memory block to the snapstore: ");
+			pr_err("not enough memory\n");
+			res = -ENOMEM;
+			break;
+		}
+
+		res = blk_descr_mem_pool_add(&snapstore->mem->pool, buffer);
+		if (res != SUCCESS) {
+			pr_err("Unable to add memory block to the snapstore: ");
+			pr_err("failed to initialize new block\n");
+			break;
+		}
+	}
+	if (res != SUCCESS) {
+		snapstore_mem_destroy(snapstore->mem);
+		snapstore->mem = NULL;
+	}
+
+	return res;
+}
+
+int rangelist_add(struct list_head *rglist, struct blk_range *rg)
+{
+	struct blk_range_link *range_link;
+
+	range_link = kzalloc(sizeof(struct blk_range_link), GFP_KERNEL);
+	if (range_link == NULL)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&range_link->link);
+
+	range_link->rg.ofs = rg->ofs;
+	range_link->rg.cnt = rg->cnt;
+
+	list_add_tail(&range_link->link, rglist);
+
+	return SUCCESS;
+}
+
+int snapstore_add_file(uuid_t *id, struct big_buffer *ranges, size_t ranges_cnt)
+{
+	int res = SUCCESS;
+	struct snapstore *snapstore = NULL;
+	struct snapstore_device *snapstore_device = NULL;
+	sector_t current_blk_size = 0;
+	LIST_HEAD(blk_rangelist);
+	size_t inx;
+
+	pr_info("Snapstore add %zu ranges\n", ranges_cnt);
+
+	if ((ranges_cnt == 0) || (ranges == NULL))
+		return -EINVAL;
+
+	snapstore = _snapstore_find(id);
+	if (snapstore == NULL) {
+		pr_err("Unable to add file to snapstore: ");
+		pr_err("cannot find snapstore by id %pUB\n", id);
+		return -ENODATA;
+	}
+
+	if (snapstore->file == NULL) {
+		pr_err("Unable to add file to snapstore: ");
+		pr_err("snapstore file was not initialized\n");
+		return -EFAULT;
+	}
+
+	snapstore_device =
+		snapstore_device_find_by_dev_id(snapstore->file->blk_dev_id); //for zeroed
+
+	for (inx = 0; inx < ranges_cnt; ++inx) {
+		size_t blocks_count = 0;
+		sector_t range_offset = 0;
+
+		struct blk_range range;
+		struct ioctl_range_s *ioctl_range;
+
+		ioctl_range = big_buffer_get_element(ranges, inx, sizeof(struct ioctl_range_s));
+		if (ioctl_range == NULL) {
+			pr_err("Invalid count of ranges\n");
+			res = -ENODATA;
+			break;
+		}
+
+		range.ofs = (sector_t)to_sectors(ioctl_range->left);
+		range.cnt = (blkcnt_t)to_sectors(ioctl_range->right) - range.ofs;
+
+		while (range_offset < range.cnt) {
+			struct blk_range rg;
+
+			rg.ofs = range.ofs + range_offset;
+			rg.cnt = min_t(sector_t, (range.cnt - range_offset),
+				       (snapstore_block_size() - current_blk_size));
+
+			range_offset += rg.cnt;
+
+			res = rangelist_add(&blk_rangelist, &rg);
+			if (res != SUCCESS) {
+				pr_err("Unable to add file to snapstore: ");
+				pr_err("cannot add range to rangelist\n");
+				break;
+			}
+
+			//zero sectors logic
+			if (snapstore_device != NULL) {
+				res = rangevector_add(&snapstore_device->zero_sectors, &rg);
+				if (res != SUCCESS) {
+					pr_err("Unable to add file to snapstore: ");
+					pr_err("cannot add range to zero_sectors tree\n");
+					break;
+				}
+			}
+
+			current_blk_size += rg.cnt;
+
+			if (current_blk_size == snapstore_block_size()) { //allocate  block
+				res = blk_descr_file_pool_add(&snapstore->file->pool,
+							      &blk_rangelist);
+				if (res != SUCCESS) {
+					pr_err("Unable to add file to snapstore: ");
+					pr_err("cannot initialize new block\n");
+					break;
+				}
+
+				snapstore->halffilled = false;
+
+				current_blk_size = 0;
+				INIT_LIST_HEAD(&blk_rangelist); //renew list
+				++blocks_count;
+			}
+		}
+		if (res != SUCCESS)
+			break;
+	}
+
+	if ((res == SUCCESS) && (current_blk_size != 0))
+		pr_warn("Snapstore portion was not ordered by Copy-on-Write block size\n");
+
+	return res;
+}
+
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+static int rangelist_ex_add(struct list_head *list, struct blk_range *rg,
+			    struct block_device *blk_dev)
+{
+	struct blk_range_link_ex *range_link =
+		kzalloc(sizeof(struct blk_range_link_ex), GFP_KERNEL);
+	if (range_link == NULL)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&range_link->link);
+
+	range_link->rg.ofs = rg->ofs;
+	range_link->rg.cnt = rg->cnt;
+	range_link->blk_dev = blk_dev;
+
+	list_add_tail(&range_link->link, list);
+
+	return SUCCESS;
+}
+
+int snapstore_add_multidev(uuid_t *id, dev_t dev_id, struct big_buffer *ranges, size_t ranges_cnt)
+{
+	int res = SUCCESS;
+	struct snapstore *snapstore = NULL;
+	sector_t current_blk_size = 0;
+	size_t inx;
+	LIST_HEAD(blk_rangelist);
+
+	pr_info("Snapstore add %zu ranges for device [%d:%d]\n", ranges_cnt, MAJOR(dev_id),
+		MINOR(dev_id));
+
+	if ((ranges_cnt == 0) || (ranges == NULL))
+		return -EINVAL;
+
+	snapstore = _snapstore_find(id);
+	if (snapstore == NULL) {
+		pr_err("Unable to add file to multidevice snapstore: ");
+		pr_err("cannot find snapstore by id %pUB\n", id);
+		return -ENODATA;
+	}
+
+	if (snapstore->multidev == NULL) {
+		pr_err("Unable to add file to multidevice snapstore: ");
+		pr_err("it was not initialized\n");
+		return -EFAULT;
+	}
+
+	for (inx = 0; inx < ranges_cnt; ++inx) {
+		size_t blocks_count = 0;
+		sector_t range_offset = 0;
+		struct blk_range range;
+		struct ioctl_range_s *data;
+
+		data = big_buffer_get_element(ranges, inx, sizeof(struct ioctl_range_s));
+		if (data == NULL) {
+			pr_err("Invalid count of ranges\n");
+			res = -ENODATA;
+			break;
+		}
+
+		range.ofs = (sector_t)to_sectors(data->left);
+		range.cnt = (blkcnt_t)to_sectors(data->right) - range.ofs;
+
+		while (range_offset < range.cnt) {
+			struct blk_range rg;
+			struct block_device *blk_dev = NULL;
+
+			rg.ofs = range.ofs + range_offset;
+			rg.cnt = min_t(sector_t,
+				       range.cnt - range_offset,
+				       snapstore_block_size() - current_blk_size);
+
+			range_offset += rg.cnt;
+
+			blk_dev = snapstore_multidev_get_device(snapstore->multidev, dev_id);
+			if (blk_dev == NULL) {
+				pr_err("Cannot find or open device [%d:%d] for multidevice snapstore\n",
+				       MAJOR(dev_id), MINOR(dev_id));
+				res = -ENODEV;
+				break;
+			}
+
+			res = rangelist_ex_add(&blk_rangelist, &rg, blk_dev);
+			if (res != SUCCESS) {
+				pr_err("Unable to add file to multidevice snapstore: ");
+				pr_err("failed to add range to rangelist\n");
+				break;
+			}
+
+			/*
+			 * zero sectors logic is not implemented for multidevice snapstore
+			 */
+
+			current_blk_size += rg.cnt;
+
+			if (current_blk_size == snapstore_block_size()) { //allocate  block
+				res = blk_descr_multidev_pool_add(&snapstore->multidev->pool,
+								  &blk_rangelist);
+				if (res != SUCCESS) {
+					pr_err("Unable to add file to multidevice snapstore: ");
+					pr_err("failed to initialize new block\n");
+					break;
+				}
+
+				snapstore->halffilled = false;
+
+				current_blk_size = 0;
+				INIT_LIST_HEAD(&blk_rangelist);
+				++blocks_count;
+			}
+		}
+		if (res != SUCCESS)
+			break;
+	}
+
+	if ((res == SUCCESS) && (current_blk_size != 0))
+		pr_warn("Snapstore portion was not ordered by Copy-on-Write block size\n");
+
+	return res;
+}
+#endif
+
+void snapstore_order_border(struct blk_range *in, struct blk_range *out)
+{
+	struct blk_range unorder;
+
+	unorder.ofs = in->ofs & snapstore_block_mask();
+	out->ofs = in->ofs & ~snapstore_block_mask();
+	out->cnt = in->cnt + unorder.ofs;
+
+	unorder.cnt = out->cnt & snapstore_block_mask();
+	if (unorder.cnt != 0)
+		out->cnt += (snapstore_block_size() - unorder.cnt);
+}
+
+union blk_descr_unify snapstore_get_empty_block(struct snapstore *snapstore)
+{
+	union blk_descr_unify result = { NULL };
+
+	if (snapstore->overflowed)
+		return result;
+
+	if (snapstore->file != NULL)
+		result = blk_descr_file_pool_take(&snapstore->file->pool);
+	else if (snapstore->multidev != NULL)
+		result = blk_descr_multidev_pool_take(&snapstore->multidev->pool);
+	else if (snapstore->mem != NULL)
+		result = blk_descr_mem_pool_take(&snapstore->mem->pool);
+
+	if (result.ptr == NULL) {
+		if (snapstore->ctrl_pipe) {
+			sector_t fill_status;
+
+			_snapstore_check_halffill(snapstore, &fill_status);
+			ctrl_pipe_request_overflow(snapstore->ctrl_pipe, -EINVAL,
+						   (u64)from_sectors(fill_status));
+		}
+		snapstore->overflowed = true;
+	}
+
+	return result;
+}
+
+int snapstore_check_halffill(uuid_t *unique_id, sector_t *fill_status)
+{
+	struct snapstore *snapstore;
+
+	snapstore = _snapstore_find(unique_id);
+	if (snapstore == NULL) {
+		pr_err("Cannot find snapstore by uuid %pUB\n", unique_id);
+		return -ENODATA;
+	}
+
+	_snapstore_check_halffill(snapstore, fill_status);
+
+	return SUCCESS;
+}
+
+int snapstore_request_store(struct snapstore *snapstore, struct blk_deferred_request *dio_copy_req)
+{
+	int res = SUCCESS;
+
+	if (snapstore->ctrl_pipe) {
+		if (!snapstore->halffilled) {
+			sector_t fill_status = 0;
+
+			if (_snapstore_check_halffill(snapstore, &fill_status)) {
+				snapstore->halffilled = true;
+				ctrl_pipe_request_halffill(snapstore->ctrl_pipe,
+							   (u64)from_sectors(fill_status));
+			}
+		}
+	}
+
+	if (snapstore->file)
+		res = blk_deferred_request_store_file(snapstore->file->blk_dev, dio_copy_req);
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+	else if (snapstore->multidev)
+		res = blk_deferred_request_store_multidev(dio_copy_req);
+#endif
+	else if (snapstore->mem)
+		res = blk_deferred_request_store_mem(dio_copy_req);
+	else
+		res = -EINVAL;
+
+	return res;
+}
+
+static int _snapstore_redirect_read_file(struct blk_redirect_bio *rq_redir,
+					 struct block_device *snapstore_blk_dev,
+					 struct blk_descr_file *file,
+					 sector_t block_ofs,
+					 sector_t rq_ofs, sector_t rq_count)
+{
+	int res = SUCCESS;
+	sector_t current_ofs = 0;
+	struct list_head *_list_head;
+
+	if (unlikely(list_empty(&file->rangelist))) {
+		pr_err("Invalid file block descriptor");
+		return -EINVAL;
+	}
+
+	list_for_each(_list_head, &file->rangelist) {
+		struct blk_range_link *range_link;
+
+		range_link = list_entry(_list_head, struct blk_range_link, link);
+		if (current_ofs >= rq_count)
+			break;
+
+		if (range_link->rg.cnt > block_ofs) {
+			sector_t pos = range_link->rg.ofs + block_ofs;
+			sector_t len = min_t(sector_t,
+					     range_link->rg.cnt - block_ofs,
+					     rq_count - current_ofs);
+
+			res = blk_dev_redirect_part(rq_redir, READ, snapstore_blk_dev, pos,
+						    rq_ofs + current_ofs, len);
+			if (res != SUCCESS) {
+				pr_err("Failed to read from snapstore file. Sector #%lld\n",
+				       pos);
+				break;
+			}
+
+			current_ofs += len;
+			block_ofs = 0;
+		} else
+			block_ofs -= range_link->rg.cnt;
+	}
+
+	if (res != SUCCESS)
+		pr_err("Failed to read from file snapstore\n");
+	return res;
+}
+
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+static int _snapstore_redirect_read_multidev(struct blk_redirect_bio *rq_redir,
+					      struct blk_descr_multidev *multidev,
+					      sector_t block_ofs,
+					      sector_t rq_ofs, sector_t rq_count)
+{
+	int res = SUCCESS;
+	sector_t current_ofs = 0;
+	struct list_head *_list_head;
+
+	if (unlikely(list_empty(&multidev->rangelist))) {
+		pr_err("Invalid multidev block descriptor");
+		return -EINVAL;
+	}
+
+	list_for_each(_list_head, &multidev->rangelist) {
+		struct blk_range_link_ex *range_link =
+			list_entry(_list_head, struct blk_range_link_ex, link);
+
+		if (current_ofs >= rq_count)
+			break;
+
+		if (range_link->rg.cnt > block_ofs) {
+			sector_t pos = range_link->rg.ofs + block_ofs;
+			sector_t len = min_t(sector_t,
+					     range_link->rg.cnt - block_ofs,
+					     rq_count - current_ofs);
+
+			res = blk_dev_redirect_part(rq_redir, READ, range_link->blk_dev, pos,
+						    rq_ofs + current_ofs, len);
+
+			if (res != SUCCESS) {
+				pr_err("Failed to read from snapstore file. Sector #%lld\n", pos);
+				break;
+			}
+
+			current_ofs += len;
+			block_ofs = 0;
+		} else
+			block_ofs -= range_link->rg.cnt;
+	}
+
+	if (res != SUCCESS)
+		pr_err("Failed to read from multidev snapstore\n");
+	return res;
+}
+#endif
+
+int snapstore_redirect_read(struct blk_redirect_bio *rq_redir, struct snapstore *snapstore,
+			    union blk_descr_unify blk_descr, sector_t target_pos, sector_t rq_ofs,
+			    sector_t rq_count)
+{
+	int res = SUCCESS;
+	sector_t block_ofs = target_pos & snapstore_block_mask();
+
+	if (snapstore->file)
+		res = _snapstore_redirect_read_file(rq_redir, snapstore->file->blk_dev,
+						    blk_descr.file, block_ofs, rq_ofs, rq_count);
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+	else if (snapstore->multidev)
+		res = _snapstore_redirect_read_multidev(rq_redir, blk_descr.multidev, block_ofs,
+							rq_ofs, rq_count);
+#endif
+	else if (snapstore->mem) {
+		res = blk_dev_redirect_memcpy_part(
+			rq_redir, READ, blk_descr.mem->buff + (size_t)from_sectors(block_ofs),
+			rq_ofs, rq_count);
+
+		if (res != SUCCESS)
+			pr_err("Failed to read from snapstore memory\n");
+	} else
+		res = -EINVAL;
+
+	if (res != SUCCESS)
+		pr_err("Failed to read from snapstore. Offset %lld sector\n", target_pos);
+	return res;
+}
+
+static int _snapstore_redirect_write_file(struct blk_redirect_bio *rq_redir,
+					  struct block_device *snapstore_blk_dev,
+					  struct blk_descr_file *file,
+					  sector_t block_ofs,
+					  sector_t rq_ofs, sector_t rq_count)
+{
+	int res = SUCCESS;
+	sector_t current_ofs = 0;
+	struct list_head *_list_head;
+
+	if (unlikely(list_empty(&file->rangelist))) {
+		pr_err("Invalid file block descriptor");
+		return -EINVAL;
+	}
+
+	list_for_each(_list_head, &file->rangelist) {
+		struct blk_range_link *range_link;
+
+		range_link = list_entry(_list_head, struct blk_range_link, link);
+		if (current_ofs >= rq_count)
+			break;
+
+		if (range_link->rg.cnt > block_ofs) {
+			sector_t pos = range_link->rg.ofs + block_ofs;
+			sector_t len = min_t(sector_t,
+					     range_link->rg.cnt - block_ofs,
+					     rq_count - current_ofs);
+
+			res = blk_dev_redirect_part(rq_redir, WRITE, snapstore_blk_dev, pos,
+						    rq_ofs + current_ofs, len);
+
+			if (res != SUCCESS) {
+				pr_err("Failed to write to snapstore file. Sector #%lld\n",
+				       pos);
+				break;
+			}
+
+			current_ofs += len;
+			block_ofs = 0;
+		} else
+			block_ofs -= range_link->rg.cnt;
+	}
+	if (res != SUCCESS)
+		pr_err("Failed to write to file snapstore\n");
+	return res;
+}
+
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+static int _snapstore_redirect_write_multidev(struct blk_redirect_bio *rq_redir,
+					      struct blk_descr_multidev *multidev,
+					      sector_t block_ofs,
+					      sector_t rq_ofs, sector_t rq_count)
+{
+	int res = SUCCESS;
+	sector_t current_ofs = 0;
+	struct list_head *_list_head;
+
+	if (unlikely(list_empty(&multidev->rangelist))) {
+		pr_err("Invalid multidev block descriptor");
+		return -EINVAL;
+	}
+
+	list_for_each(_list_head, &multidev->rangelist) {
+		struct blk_range_link_ex *range_link;
+
+		range_link = list_entry(_list_head, struct blk_range_link_ex, link);
+		if (current_ofs >= rq_count)
+			break;
+
+		if (range_link->rg.cnt > block_ofs) {
+			sector_t pos = range_link->rg.ofs + block_ofs;
+			sector_t len = min_t(sector_t,
+					     range_link->rg.cnt - block_ofs,
+					     rq_count - current_ofs);
+
+			res = blk_dev_redirect_part(rq_redir, WRITE, range_link->blk_dev, pos,
+						    rq_ofs + current_ofs, len);
+
+			if (res != SUCCESS) {
+				pr_err("Failed to write to snapstore file. Sector #%lld\n",
+				       pos);
+				break;
+			}
+
+			current_ofs += len;
+			block_ofs = 0;
+		} else
+			block_ofs -= range_link->rg.cnt;
+	}
+
+	if (res != SUCCESS)
+		pr_err("Failed to write to multidevice snapstore\n");
+	return res;
+}
+#endif
+
+int snapstore_redirect_write(struct blk_redirect_bio *rq_redir, struct snapstore *snapstore,
+			     union blk_descr_unify blk_descr, sector_t target_pos, sector_t rq_ofs,
+			     sector_t rq_count)
+{
+	int res = SUCCESS;
+	sector_t block_ofs = target_pos & snapstore_block_mask();
+
+	if (snapstore->file)
+		res = _snapstore_redirect_write_file(rq_redir, snapstore->file->blk_dev,
+						     blk_descr.file, block_ofs, rq_ofs, rq_count);
+
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+	else if (snapstore->multidev)
+		res = _snapstore_redirect_write_multidev(rq_redir, blk_descr.multidev,
+							 block_ofs, rq_ofs, rq_count);
+#endif
+	else if (snapstore->mem) {
+		res = blk_dev_redirect_memcpy_part(
+			rq_redir, WRITE, blk_descr.mem->buff + (size_t)from_sectors(block_ofs),
+			rq_ofs, rq_count);
+
+		if (res != SUCCESS)
+			pr_err("Failed to write to memory snapstore\n");
+	} else {
+		pr_err("Unable to write to snapstore: invalid type of snapstore device\n");
+		res = -EINVAL;
+	}
+
+	if (res != SUCCESS)
+		pr_err("Failed to write to snapstore. Offset %lld sector\n", target_pos);
+	return res;
+}
diff --git a/drivers/block/blk-snap/snapstore.h b/drivers/block/blk-snap/snapstore.h
new file mode 100644
index 000000000000..db34ad2e2c58
--- /dev/null
+++ b/drivers/block/blk-snap/snapstore.h
@@ -0,0 +1,68 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#pragma once
+
+#include <linux/uuid.h>
+#include <linux/kref.h>
+#include "blk-snap-ctl.h"
+#include "rangevector.h"
+#include "snapstore_mem.h"
+#include "snapstore_file.h"
+#include "snapstore_multidev.h"
+#include "blk_redirect.h"
+#include "ctrl_pipe.h"
+#include "big_buffer.h"
+
+struct snapstore {
+	struct list_head link;
+	struct kref refcount;
+
+	uuid_t id;
+
+	struct snapstore_mem *mem;
+	struct snapstore_file *file;
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+	struct snapstore_multidev *multidev;
+#endif
+
+	struct ctrl_pipe *ctrl_pipe;
+	sector_t empty_limit;
+
+	bool halffilled;
+	bool overflowed;
+};
+
+void snapstore_done(void);
+
+int snapstore_create(uuid_t *id, dev_t snapstore_dev_id, dev_t *dev_id_set,
+		     size_t dev_id_set_length);
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+int snapstore_create_multidev(uuid_t *id, dev_t *dev_id_set, size_t dev_id_set_length);
+#endif
+int snapstore_cleanup(uuid_t *id, u64 *filled_bytes);
+
+struct snapstore *snapstore_get(struct snapstore *snapstore);
+void snapstore_put(struct snapstore *snapstore);
+
+int snapstore_stretch_initiate(uuid_t *unique_id, struct ctrl_pipe *ctrl_pipe,
+			       sector_t empty_limit);
+
+int snapstore_add_memory(uuid_t *id, unsigned long long sz);
+int snapstore_add_file(uuid_t *id, struct big_buffer *ranges, size_t ranges_cnt);
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+int snapstore_add_multidev(uuid_t *id, dev_t dev_id, struct big_buffer *ranges, size_t ranges_cnt);
+#endif
+
+void snapstore_order_border(struct blk_range *in, struct blk_range *out);
+
+union blk_descr_unify snapstore_get_empty_block(struct snapstore *snapstore);
+
+int snapstore_request_store(struct snapstore *snapstore, struct blk_deferred_request *dio_copy_req);
+
+int snapstore_redirect_read(struct blk_redirect_bio *rq_redir, struct snapstore *snapstore,
+			    union blk_descr_unify blk_descr, sector_t target_pos, sector_t rq_ofs,
+			    sector_t rq_count);
+int snapstore_redirect_write(struct blk_redirect_bio *rq_redir, struct snapstore *snapstore,
+			     union blk_descr_unify blk_descr, sector_t target_pos, sector_t rq_ofs,
+			     sector_t rq_count);
+
+int snapstore_check_halffill(uuid_t *unique_id, sector_t *fill_status);
diff --git a/drivers/block/blk-snap/snapstore_device.c b/drivers/block/blk-snap/snapstore_device.c
new file mode 100644
index 000000000000..6fdeebacce22
--- /dev/null
+++ b/drivers/block/blk-snap/snapstore_device.c
@@ -0,0 +1,532 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-snapstore"
+#include "common.h"
+#include "snapstore_device.h"
+#include "snapstore.h"
+#include "params.h"
+#include "blk_util.h"
+
+LIST_HEAD(snapstore_devices);
+DECLARE_RWSEM(snapstore_devices_lock);
+
+static inline void _snapstore_device_descr_write_lock(struct snapstore_device *snapstore_device)
+{
+	mutex_lock(&snapstore_device->store_block_map_locker);
+}
+static inline void _snapstore_device_descr_write_unlock(struct snapstore_device *snapstore_device)
+{
+	mutex_unlock(&snapstore_device->store_block_map_locker);
+}
+
+void snapstore_device_done(void)
+{
+	struct snapstore_device *snapstore_device = NULL;
+
+	do {
+		down_write(&snapstore_devices_lock);
+		if (!list_empty(&snapstore_devices)) {
+			snapstore_device =
+				list_entry(snapstore_devices.next, struct snapstore_device, link);
+			list_del(&snapstore_device->link);
+		}
+		up_write(&snapstore_devices_lock);
+
+		if (snapstore_device)
+			snapstore_device_put_resource(snapstore_device);
+	} while (snapstore_device);
+}
+
+struct snapstore_device *snapstore_device_find_by_dev_id(dev_t dev_id)
+{
+	struct snapstore_device *result = NULL;
+
+	down_read(&snapstore_devices_lock);
+	if (!list_empty(&snapstore_devices)) {
+		struct list_head *_head;
+
+		list_for_each(_head, &snapstore_devices) {
+			struct snapstore_device *snapstore_device =
+				list_entry(_head, struct snapstore_device, link);
+
+			if (dev_id == snapstore_device->dev_id) {
+				result = snapstore_device;
+				break;
+			}
+		}
+	}
+	up_read(&snapstore_devices_lock);
+
+	return result;
+}
+
+struct snapstore_device *_snapstore_device_get_by_snapstore_id(uuid_t *id)
+{
+	struct snapstore_device *result = NULL;
+
+	down_write(&snapstore_devices_lock);
+	if (!list_empty(&snapstore_devices)) {
+		struct list_head *_head;
+
+		list_for_each(_head, &snapstore_devices) {
+			struct snapstore_device *snapstore_device =
+				list_entry(_head, struct snapstore_device, link);
+
+			if (uuid_equal(id, &snapstore_device->snapstore->id)) {
+				result = snapstore_device;
+				list_del(&snapstore_device->link);
+				break;
+			}
+		}
+	}
+	up_write(&snapstore_devices_lock);
+
+	return result;
+}
+
+static void _snapstore_device_destroy(struct snapstore_device *snapstore_device)
+{
+	pr_info("Destroy snapstore device\n");
+
+	xa_destroy(&snapstore_device->store_block_map);
+
+	if (snapstore_device->orig_blk_dev != NULL)
+		blk_dev_close(snapstore_device->orig_blk_dev);
+
+	rangevector_done(&snapstore_device->zero_sectors);
+
+	if (snapstore_device->snapstore) {
+		pr_info("Snapstore uuid %pUB\n", &snapstore_device->snapstore->id);
+
+		snapstore_put(snapstore_device->snapstore);
+		snapstore_device->snapstore = NULL;
+	}
+
+	kfree(snapstore_device);
+}
+
+static void snapstore_device_free_cb(struct kref *kref)
+{
+	struct snapstore_device *snapstore_device =
+		container_of(kref, struct snapstore_device, refcount);
+
+	_snapstore_device_destroy(snapstore_device);
+}
+
+struct snapstore_device *snapstore_device_get_resource(struct snapstore_device *snapstore_device)
+{
+	if (snapstore_device)
+		kref_get(&snapstore_device->refcount);
+
+	return snapstore_device;
+};
+
+void snapstore_device_put_resource(struct snapstore_device *snapstore_device)
+{
+	if (snapstore_device)
+		kref_put(&snapstore_device->refcount, snapstore_device_free_cb);
+};
+
+int snapstore_device_cleanup(uuid_t *id)
+{
+	int result = SUCCESS;
+	struct snapstore_device *snapstore_device = NULL;
+
+	while (NULL != (snapstore_device = _snapstore_device_get_by_snapstore_id(id))) {
+		pr_info("Cleanup snapstore device for device [%d:%d]\n",
+			MAJOR(snapstore_device->dev_id), MINOR(snapstore_device->dev_id));
+
+		snapstore_device_put_resource(snapstore_device);
+	}
+	return result;
+}
+
+int snapstore_device_create(dev_t dev_id, struct snapstore *snapstore)
+{
+	int res = SUCCESS;
+	struct snapstore_device *snapstore_device =
+		kzalloc(sizeof(struct snapstore_device), GFP_KERNEL);
+
+	if (snapstore_device == NULL)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&snapstore_device->link);
+	snapstore_device->dev_id = dev_id;
+
+	res = blk_dev_open(dev_id, &snapstore_device->orig_blk_dev);
+	if (res != SUCCESS) {
+		kfree(snapstore_device);
+
+		pr_err("Unable to create snapstore device: failed to open original device [%d:%d]\n",
+		       MAJOR(dev_id), MINOR(dev_id));
+		return res;
+	}
+
+	kref_init(&snapstore_device->refcount);
+
+	snapstore_device->snapstore = NULL;
+	snapstore_device->err_code = SUCCESS;
+	snapstore_device->corrupted = false;
+	atomic_set(&snapstore_device->req_failed_cnt, 0);
+
+	mutex_init(&snapstore_device->store_block_map_locker);
+
+	rangevector_init(&snapstore_device->zero_sectors);
+
+	xa_init(&snapstore_device->store_block_map);
+
+	snapstore_device->snapstore = snapstore_get(snapstore);
+
+	down_write(&snapstore_devices_lock);
+	list_add_tail(&snapstore_device->link, &snapstore_devices);
+	up_write(&snapstore_devices_lock);
+
+	return SUCCESS;
+}
+
+int snapstore_device_add_request(struct snapstore_device *snapstore_device,
+				 unsigned long block_index,
+				 struct blk_deferred_request **dio_copy_req)
+{
+	int res = SUCCESS;
+	union blk_descr_unify blk_descr = { NULL };
+	struct blk_deferred_io *dio = NULL;
+	bool req_new = false;
+
+	blk_descr = snapstore_get_empty_block(snapstore_device->snapstore);
+	if (blk_descr.ptr == NULL) {
+		pr_err("Unable to add block to defer IO request: failed to allocate next block\n");
+		return -ENODATA;
+	}
+
+	res = xa_err(
+		xa_store(&snapstore_device->store_block_map, block_index, blk_descr.ptr, GFP_NOIO));
+	if (res != SUCCESS) {
+		pr_err("Unable to add block to defer IO request: failed to set block descriptor to descriptors array. errno=%d\n",
+		       res);
+		return res;
+	}
+
+	if (*dio_copy_req == NULL) {
+		*dio_copy_req = blk_deferred_request_new();
+		if (*dio_copy_req == NULL) {
+			pr_err("Unable to add block to defer IO request: failed to allocate defer IO request\n");
+			return -ENOMEM;
+		}
+		req_new = true;
+	}
+
+	do {
+		dio = blk_deferred_alloc(block_index, blk_descr);
+		if (dio == NULL) {
+			pr_err("Unabled to add block to defer IO request: failed to allocate defer IO\n");
+			res = -ENOMEM;
+			break;
+		}
+
+		res = blk_deferred_request_add(*dio_copy_req, dio);
+		if (res != SUCCESS)
+			pr_err("Unable to add block to defer IO request: failed to add defer IO to request\n");
+	} while (false);
+
+	if (res != SUCCESS) {
+		if (dio != NULL) {
+			blk_deferred_free(dio);
+			dio = NULL;
+		}
+		if (req_new) {
+			blk_deferred_request_free(*dio_copy_req);
+			*dio_copy_req = NULL;
+		}
+	}
+
+	return res;
+}
+
+int snapstore_device_prepare_requests(struct snapstore_device *snapstore_device,
+				      struct blk_range *copy_range,
+				      struct blk_deferred_request **dio_copy_req)
+{
+	int res = SUCCESS;
+	unsigned long inx = 0;
+	unsigned long first = (unsigned long)(copy_range->ofs >> snapstore_block_shift());
+	unsigned long last =
+		(unsigned long)((copy_range->ofs + copy_range->cnt - 1) >> snapstore_block_shift());
+
+	for (inx = first; inx <= last; inx++) {
+		if (xa_load(&snapstore_device->store_block_map, inx) == NULL) {
+			res = snapstore_device_add_request(snapstore_device, inx, dio_copy_req);
+			if (res != SUCCESS) {
+				pr_err("Failed to create copy defer IO request. errno=%d\n", res);
+				break;
+			}
+		}
+		/*
+		 * If xa_load() return not NULL, then block already stored.
+		 */
+	}
+	if (res != SUCCESS)
+		snapstore_device_set_corrupted(snapstore_device, res);
+
+	return res;
+}
+
+int snapstore_device_store(struct snapstore_device *snapstore_device,
+			   struct blk_deferred_request *dio_copy_req)
+{
+	int res;
+
+	res = snapstore_request_store(snapstore_device->snapstore, dio_copy_req);
+	if (res != SUCCESS)
+		snapstore_device_set_corrupted(snapstore_device, res);
+
+	return res;
+}
+
+int snapstore_device_read(struct snapstore_device *snapstore_device,
+			  struct blk_redirect_bio *rq_redir)
+{
+	int res = SUCCESS;
+
+	unsigned long block_index;
+	unsigned long block_index_last;
+	unsigned long block_index_first;
+
+	sector_t blk_ofs_start = 0; //device range start
+	sector_t blk_ofs_count = 0; //device range length
+
+	struct blk_range rq_range;
+	struct rangevector *zero_sectors = &snapstore_device->zero_sectors;
+
+	if (snapstore_device_is_corrupted(snapstore_device))
+		return -ENODATA;
+
+	rq_range.cnt = bio_sectors(rq_redir->bio);
+	rq_range.ofs = rq_redir->bio->bi_iter.bi_sector;
+
+	if (!bio_has_data(rq_redir->bio)) {
+		pr_warn("Empty bio was found during reading from snapstore device. flags=%u\n",
+			rq_redir->bio->bi_flags);
+
+		blk_redirect_complete(rq_redir, SUCCESS);
+		return SUCCESS;
+	}
+
+	block_index_first = (unsigned long)(rq_range.ofs >> snapstore_block_shift());
+	block_index_last =
+		(unsigned long)((rq_range.ofs + rq_range.cnt - 1) >> snapstore_block_shift());
+
+	_snapstore_device_descr_write_lock(snapstore_device);
+	for (block_index = block_index_first; block_index <= block_index_last; ++block_index) {
+		union blk_descr_unify blk_descr;
+
+		blk_ofs_count = min_t(sector_t,
+				      (((sector_t)(block_index + 1)) << snapstore_block_shift()) -
+					      (rq_range.ofs + blk_ofs_start),
+				      rq_range.cnt - blk_ofs_start);
+
+		blk_descr = (union blk_descr_unify)xa_load(&snapstore_device->store_block_map,
+							   block_index);
+		if (blk_descr.ptr) {
+			//push snapstore read
+			res = snapstore_redirect_read(rq_redir, snapstore_device->snapstore,
+						      blk_descr, rq_range.ofs + blk_ofs_start,
+						      blk_ofs_start, blk_ofs_count);
+			if (res != SUCCESS) {
+				pr_err("Failed to read from snapstore device\n");
+				break;
+			}
+		} else {
+			//device read with zeroing
+			if (zero_sectors)
+				res = blk_dev_redirect_read_zeroed(rq_redir,
+								   snapstore_device->orig_blk_dev,
+								   rq_range.ofs, blk_ofs_start,
+								   blk_ofs_count, zero_sectors);
+			else
+				res = blk_dev_redirect_part(rq_redir, READ,
+							    snapstore_device->orig_blk_dev,
+							    rq_range.ofs + blk_ofs_start,
+							    blk_ofs_start, blk_ofs_count);
+
+			if (res != SUCCESS) {
+				pr_err("Failed to redirect read request to the original device [%d:%d]\n",
+				       MAJOR(snapstore_device->dev_id),
+				       MINOR(snapstore_device->dev_id));
+				break;
+			}
+		}
+
+		blk_ofs_start += blk_ofs_count;
+	}
+
+	if (res == SUCCESS) {
+		if (atomic64_read(&rq_redir->bio_count) > 0ll) //async direct access needed
+			blk_dev_redirect_submit(rq_redir);
+		else
+			blk_redirect_complete(rq_redir, res);
+	} else {
+		pr_err("Failed to read from snapstore device. errno=%d\n", res);
+		pr_err("Position %lld sector, length %lld sectors\n", rq_range.ofs, rq_range.cnt);
+	}
+	_snapstore_device_descr_write_unlock(snapstore_device);
+
+	return res;
+}
+
+int _snapstore_device_copy_on_write(struct snapstore_device *snapstore_device,
+				    struct blk_range *rq_range)
+{
+	int res = SUCCESS;
+	struct blk_deferred_request *dio_copy_req = NULL;
+
+	mutex_lock(&snapstore_device->store_block_map_locker);
+	do {
+		res = snapstore_device_prepare_requests(snapstore_device, rq_range, &dio_copy_req);
+		if (res != SUCCESS) {
+			pr_err("Failed to create defer IO request for range. errno=%d\n", res);
+			break;
+		}
+
+		if (dio_copy_req == NULL)
+			break; //nothing to copy
+
+		res = blk_deferred_request_read_original(snapstore_device->orig_blk_dev,
+							 dio_copy_req);
+		if (res != SUCCESS) {
+			pr_err("Failed to read data from the original device. errno=%d\n", res);
+			break;
+		}
+
+		res = snapstore_device_store(snapstore_device, dio_copy_req);
+		if (res != SUCCESS) {
+			pr_err("Failed to write data to snapstore. errno=%d\n", res);
+			break;
+		}
+	} while (false);
+	mutex_unlock(&snapstore_device->store_block_map_locker);
+
+	if (dio_copy_req) {
+		if (res == -EDEADLK)
+			blk_deferred_request_deadlocked(dio_copy_req);
+		else
+			blk_deferred_request_free(dio_copy_req);
+	}
+
+	return res;
+}
+
+int snapstore_device_write(struct snapstore_device *snapstore_device,
+			   struct blk_redirect_bio *rq_redir)
+{
+	int res = SUCCESS;
+	unsigned long block_index;
+	unsigned long block_index_last;
+	unsigned long block_index_first;
+	sector_t blk_ofs_start = 0; //device range start
+	sector_t blk_ofs_count = 0; //device range length
+	struct blk_range rq_range;
+
+	if (snapstore_device_is_corrupted(snapstore_device))
+		return -ENODATA;
+
+	rq_range.cnt = bio_sectors(rq_redir->bio);
+	rq_range.ofs = rq_redir->bio->bi_iter.bi_sector;
+
+	if (!bio_has_data(rq_redir->bio)) {
+		pr_warn("Empty bio was found during reading from snapstore device. flags=%u\n",
+			rq_redir->bio->bi_flags);
+
+		blk_redirect_complete(rq_redir, SUCCESS);
+		return SUCCESS;
+	}
+
+	// do copy to snapstore previously
+	res = _snapstore_device_copy_on_write(snapstore_device, &rq_range);
+
+	block_index_first = (unsigned long)(rq_range.ofs >> snapstore_block_shift());
+	block_index_last =
+		(unsigned long)((rq_range.ofs + rq_range.cnt - 1) >> snapstore_block_shift());
+
+	_snapstore_device_descr_write_lock(snapstore_device);
+	for (block_index = block_index_first; block_index <= block_index_last; ++block_index) {
+		union blk_descr_unify blk_descr;
+
+		blk_ofs_count = min_t(sector_t,
+				      (((sector_t)(block_index + 1)) << snapstore_block_shift()) -
+					      (rq_range.ofs + blk_ofs_start),
+				      rq_range.cnt - blk_ofs_start);
+
+		blk_descr = (union blk_descr_unify)xa_load(&snapstore_device->store_block_map,
+							   block_index);
+		if (blk_descr.ptr == NULL) {
+			pr_err("Unable to write from snapstore device: invalid snapstore block descriptor\n");
+			res = -EIO;
+			break;
+		}
+
+		res = snapstore_redirect_write(rq_redir, snapstore_device->snapstore, blk_descr,
+					       rq_range.ofs + blk_ofs_start, blk_ofs_start,
+					       blk_ofs_count);
+		if (res != SUCCESS) {
+			pr_err("Unable to write from snapstore device: failed to redirect write request to snapstore\n");
+			break;
+		}
+
+		blk_ofs_start += blk_ofs_count;
+	}
+	if (res == SUCCESS) {
+		if (atomic64_read(&rq_redir->bio_count) > 0) { //async direct access needed
+			blk_dev_redirect_submit(rq_redir);
+		} else {
+			blk_redirect_complete(rq_redir, res);
+		}
+	} else {
+		pr_err("Failed to write from snapstore device. errno=%d\n", res);
+		pr_err("Position %lld sector, length %lld sectors\n", rq_range.ofs, rq_range.cnt);
+
+		snapstore_device_set_corrupted(snapstore_device, res);
+	}
+	_snapstore_device_descr_write_unlock(snapstore_device);
+	return res;
+}
+
+bool snapstore_device_is_corrupted(struct snapstore_device *snapstore_device)
+{
+	if (snapstore_device == NULL)
+		return true;
+
+	if (snapstore_device->corrupted) {
+		if (atomic_read(&snapstore_device->req_failed_cnt) == 0)
+			pr_err("Snapshot device is corrupted for [%d:%d]\n",
+			       MAJOR(snapstore_device->dev_id), MINOR(snapstore_device->dev_id));
+
+		atomic_inc(&snapstore_device->req_failed_cnt);
+		return true;
+	}
+
+	return false;
+}
+
+void snapstore_device_set_corrupted(struct snapstore_device *snapstore_device, int err_code)
+{
+	if (!snapstore_device->corrupted) {
+		atomic_set(&snapstore_device->req_failed_cnt, 0);
+		snapstore_device->corrupted = true;
+		snapstore_device->err_code = abs(err_code);
+
+		pr_err("Set snapshot device is corrupted for [%d:%d]\n",
+		       MAJOR(snapstore_device->dev_id), MINOR(snapstore_device->dev_id));
+	}
+}
+
+int snapstore_device_errno(dev_t dev_id, int *p_err_code)
+{
+	struct snapstore_device *snapstore_device;
+
+	snapstore_device = snapstore_device_find_by_dev_id(dev_id);
+	if (snapstore_device == NULL)
+		return -ENODATA;
+
+	*p_err_code = snapstore_device->err_code;
+	return SUCCESS;
+}
diff --git a/drivers/block/blk-snap/snapstore_device.h b/drivers/block/blk-snap/snapstore_device.h
new file mode 100644
index 000000000000..729b3c05ef70
--- /dev/null
+++ b/drivers/block/blk-snap/snapstore_device.h
@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#pragma once
+
+#include "rangevector.h"
+#include "blk_deferred.h"
+#include "blk_redirect.h"
+#include "snapstore.h"
+#include <linux/xarray.h>
+#include <linux/kref.h>
+
+struct snapstore_device {
+	struct list_head link;
+	struct kref refcount;
+
+	dev_t dev_id;
+	struct snapstore *snapstore;
+
+	struct block_device *orig_blk_dev;
+
+	struct xarray store_block_map; // map block index to read block offset
+	struct mutex store_block_map_locker;
+
+	struct rangevector zero_sectors;
+
+	atomic_t req_failed_cnt;
+	int err_code;
+	bool corrupted;
+};
+
+void snapstore_device_done(void);
+
+struct snapstore_device *snapstore_device_get_resource(struct snapstore_device *snapstore_device);
+void snapstore_device_put_resource(struct snapstore_device *snapstore_device);
+
+struct snapstore_device *snapstore_device_find_by_dev_id(dev_t dev_id);
+
+int snapstore_device_create(dev_t dev_id, struct snapstore *snapstore);
+
+int snapstore_device_cleanup(uuid_t *id);
+
+int snapstore_device_prepare_requests(struct snapstore_device *snapstore_device,
+				      struct blk_range *copy_range,
+				      struct blk_deferred_request **dio_copy_req);
+int snapstore_device_store(struct snapstore_device *snapstore_device,
+			   struct blk_deferred_request *dio_copy_req);
+
+int snapstore_device_read(struct snapstore_device *snapstore_device,
+			  struct blk_redirect_bio *rq_redir); //request from image
+int snapstore_device_write(struct snapstore_device *snapstore_device,
+			   struct blk_redirect_bio *rq_redir); //request from image
+
+bool snapstore_device_is_corrupted(struct snapstore_device *snapstore_device);
+void snapstore_device_set_corrupted(struct snapstore_device *snapstore_device, int err_code);
+int snapstore_device_errno(dev_t dev_id, int *p_err_code);
+
+static inline void _snapstore_device_descr_read_lock(struct snapstore_device *snapstore_device)
+{
+	mutex_lock(&snapstore_device->store_block_map_locker);
+}
+static inline void _snapstore_device_descr_read_unlock(struct snapstore_device *snapstore_device)
+{
+	mutex_unlock(&snapstore_device->store_block_map_locker);
+}
diff --git a/drivers/block/blk-snap/snapstore_file.c b/drivers/block/blk-snap/snapstore_file.c
new file mode 100644
index 000000000000..a5c959a8070c
--- /dev/null
+++ b/drivers/block/blk-snap/snapstore_file.c
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-snapstore"
+#include "common.h"
+#include "snapstore_file.h"
+#include "blk_util.h"
+
+int snapstore_file_create(dev_t dev_id, struct snapstore_file **pfile)
+{
+	int res = SUCCESS;
+	struct snapstore_file *file;
+
+	pr_info("Single device file snapstore was created on device [%d:%d]\n", MAJOR(dev_id),
+	       MINOR(dev_id));
+
+	file = kzalloc(sizeof(struct snapstore_file), GFP_KERNEL);
+	if (file == NULL)
+		return -ENOMEM;
+
+	res = blk_dev_open(dev_id, &file->blk_dev);
+	if (res != SUCCESS) {
+		kfree(file);
+		pr_err("Unable to create snapstore file: failed to open device [%d:%d]. errno=%d",
+		       MAJOR(dev_id), MINOR(dev_id), res);
+		return res;
+	}
+	{
+		struct request_queue *q = bdev_get_queue(file->blk_dev);
+
+		pr_info("snapstore device logical block size %d\n", q->limits.logical_block_size);
+		pr_info("snapstore device physical block size %d\n", q->limits.physical_block_size);
+	}
+
+	file->blk_dev_id = dev_id;
+	blk_descr_file_pool_init(&file->pool);
+
+	*pfile = file;
+	return res;
+}
+
+void snapstore_file_destroy(struct snapstore_file *file)
+{
+	if (file) {
+		blk_descr_file_pool_done(&file->pool);
+
+		if (file->blk_dev != NULL) {
+			blk_dev_close(file->blk_dev);
+			file->blk_dev = NULL;
+		}
+
+		kfree(file);
+	}
+}
diff --git a/drivers/block/blk-snap/snapstore_file.h b/drivers/block/blk-snap/snapstore_file.h
new file mode 100644
index 000000000000..effd9d888781
--- /dev/null
+++ b/drivers/block/blk-snap/snapstore_file.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#pragma once
+
+#include "blk_deferred.h"
+
+struct snapstore_file {
+	dev_t blk_dev_id;
+	struct block_device *blk_dev;
+
+	struct blk_descr_pool pool;
+};
+
+int snapstore_file_create(dev_t dev_id, struct snapstore_file **pfile);
+
+void snapstore_file_destroy(struct snapstore_file *file);
diff --git a/drivers/block/blk-snap/snapstore_mem.c b/drivers/block/blk-snap/snapstore_mem.c
new file mode 100644
index 000000000000..29a607617d99
--- /dev/null
+++ b/drivers/block/blk-snap/snapstore_mem.c
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-snapstore"
+#include "common.h"
+#include "snapstore_mem.h"
+#include "params.h"
+
+#include <linux/vmalloc.h>
+
+struct buffer_el {
+	struct list_head link;
+	void *buff;
+};
+
+struct snapstore_mem *snapstore_mem_create(size_t available_blocks)
+{
+	struct snapstore_mem *mem = kzalloc(sizeof(struct snapstore_mem), GFP_KERNEL);
+
+	if (mem == NULL)
+		return NULL;
+
+	blk_descr_mem_pool_init(&mem->pool, available_blocks);
+
+	mem->blocks_limit = available_blocks;
+
+	INIT_LIST_HEAD(&mem->blocks);
+	mutex_init(&mem->blocks_lock);
+
+	return mem;
+}
+
+void snapstore_mem_destroy(struct snapstore_mem *mem)
+{
+	struct buffer_el *buffer_el;
+
+	if (mem == NULL)
+		return;
+
+	do {
+		buffer_el = NULL;
+
+		mutex_lock(&mem->blocks_lock);
+		if (!list_empty(&mem->blocks)) {
+			buffer_el = list_entry(mem->blocks.next, struct buffer_el, link);
+
+			list_del(&buffer_el->link);
+		}
+		mutex_unlock(&mem->blocks_lock);
+
+		if (buffer_el) {
+			vfree(buffer_el->buff);
+			kfree(buffer_el);
+		}
+	} while (buffer_el);
+
+	blk_descr_mem_pool_done(&mem->pool);
+
+	kfree(mem);
+}
+
+void *snapstore_mem_get_block(struct snapstore_mem *mem)
+{
+	struct buffer_el *buffer_el;
+
+	if (mem->blocks_allocated >= mem->blocks_limit) {
+		pr_err("Unable to get block from snapstore in memory\n");
+		pr_err("Block limit is reached, allocated %zu, limit %zu\n", mem->blocks_allocated,
+		       mem->blocks_limit);
+		return NULL;
+	}
+
+	buffer_el = kzalloc(sizeof(struct buffer_el), GFP_KERNEL);
+	if (buffer_el == NULL)
+		return NULL;
+	INIT_LIST_HEAD(&buffer_el->link);
+
+	buffer_el->buff = vmalloc(snapstore_block_size() * SECTOR_SIZE);
+	if (buffer_el->buff == NULL) {
+		kfree(buffer_el);
+		return NULL;
+	}
+
+	++mem->blocks_allocated;
+	if (0 == (mem->blocks_allocated & 0x7F))
+		pr_info("%zu MiB was allocated\n", mem->blocks_allocated);
+
+	mutex_lock(&mem->blocks_lock);
+	list_add_tail(&buffer_el->link, &mem->blocks);
+	mutex_unlock(&mem->blocks_lock);
+
+	return buffer_el->buff;
+}
diff --git a/drivers/block/blk-snap/snapstore_mem.h b/drivers/block/blk-snap/snapstore_mem.h
new file mode 100644
index 000000000000..9044a6525966
--- /dev/null
+++ b/drivers/block/blk-snap/snapstore_mem.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#pragma once
+
+#include "blk_descr_mem.h"
+
+struct snapstore_mem {
+	struct list_head blocks;
+	struct mutex blocks_lock;
+
+	size_t blocks_limit;
+	size_t blocks_allocated;
+
+	struct blk_descr_pool pool;
+};
+
+struct snapstore_mem *snapstore_mem_create(size_t available_blocks);
+
+void snapstore_mem_destroy(struct snapstore_mem *mem);
+
+void *snapstore_mem_get_block(struct snapstore_mem *mem);
diff --git a/drivers/block/blk-snap/snapstore_multidev.c b/drivers/block/blk-snap/snapstore_multidev.c
new file mode 100644
index 000000000000..bb6bfefa68d7
--- /dev/null
+++ b/drivers/block/blk-snap/snapstore_multidev.c
@@ -0,0 +1,118 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-snapstore"
+#include "common.h"
+
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+
+#include "snapstore_multidev.h"
+#include "blk_util.h"
+
+struct multidev_el {
+	struct list_head link;
+
+	dev_t dev_id;
+	struct block_device *blk_dev;
+};
+
+int snapstore_multidev_create(struct snapstore_multidev **p_multidev)
+{
+	int res = SUCCESS;
+	struct snapstore_multidev *multidev;
+
+	pr_info("Multidevice file snapstore create\n");
+
+	multidev = kzalloc(sizeof(struct snapstore_multidev), GFP_KERNEL);
+	if (multidev == NULL)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&multidev->devicelist);
+	spin_lock_init(&multidev->devicelist_lock);
+
+	blk_descr_multidev_pool_init(&multidev->pool);
+
+	*p_multidev = multidev;
+	return res;
+}
+
+void snapstore_multidev_destroy(struct snapstore_multidev *multidev)
+{
+	struct multidev_el *el;
+
+	blk_descr_multidev_pool_done(&multidev->pool);
+
+	do {
+		el = NULL;
+		spin_lock(&multidev->devicelist_lock);
+		if (!list_empty(&multidev->devicelist)) {
+			el = list_entry(multidev->devicelist.next, struct multidev_el, link);
+
+			list_del(&el->link);
+		}
+		spin_unlock(&multidev->devicelist_lock);
+
+		if (el) {
+			blk_dev_close(el->blk_dev);
+
+			pr_info("Close device for multidevice snapstore [%d:%d]\n",
+				MAJOR(el->dev_id), MINOR(el->dev_id));
+
+			kfree(el);
+		}
+	} while (el);
+
+	kfree(multidev);
+}
+
+struct multidev_el *snapstore_multidev_find(struct snapstore_multidev *multidev, dev_t dev_id)
+{
+	struct multidev_el *el = NULL;
+
+	spin_lock(&multidev->devicelist_lock);
+	if (!list_empty(&multidev->devicelist)) {
+		struct list_head *_head;
+
+		list_for_each(_head, &multidev->devicelist) {
+			struct multidev_el *_el = list_entry(_head, struct multidev_el, link);
+
+			if (_el->dev_id == dev_id) {
+				el = _el;
+				break;
+			}
+		}
+	}
+	spin_unlock(&multidev->devicelist_lock);
+
+	return el;
+}
+
+struct block_device *snapstore_multidev_get_device(struct snapstore_multidev *multidev,
+						   dev_t dev_id)
+{
+	int res;
+	struct block_device *blk_dev = NULL;
+	struct multidev_el *el = snapstore_multidev_find(multidev, dev_id);
+
+	if (el)
+		return el->blk_dev;
+
+	res = blk_dev_open(dev_id, &blk_dev);
+	if (res != SUCCESS) {
+		pr_err("Unable to add device to snapstore multidevice file\n");
+		pr_err("Failed to open [%d:%d]. errno=%d", MAJOR(dev_id), MINOR(dev_id), res);
+		return NULL;
+	}
+
+	el = kzalloc(sizeof(struct multidev_el), GFP_KERNEL);
+	INIT_LIST_HEAD(&el->link);
+
+	el->blk_dev = blk_dev;
+	el->dev_id = dev_id;
+
+	spin_lock(&multidev->devicelist_lock);
+	list_add_tail(&el->link, &multidev->devicelist);
+	spin_unlock(&multidev->devicelist_lock);
+
+	return el->blk_dev;
+}
+
+#endif
diff --git a/drivers/block/blk-snap/snapstore_multidev.h b/drivers/block/blk-snap/snapstore_multidev.h
new file mode 100644
index 000000000000..40c1c3a41b08
--- /dev/null
+++ b/drivers/block/blk-snap/snapstore_multidev.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#pragma once
+
+#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
+
+#include "blk_deferred.h"
+#include "blk_descr_multidev.h"
+
+struct snapstore_multidev {
+	struct list_head devicelist; //for mapping device id to opened device struct pointer
+	spinlock_t devicelist_lock;
+
+	struct blk_descr_pool pool;
+};
+
+int snapstore_multidev_create(struct snapstore_multidev **p_file);
+
+void snapstore_multidev_destroy(struct snapstore_multidev *file);
+
+struct block_device *snapstore_multidev_get_device(struct snapstore_multidev *multidev,
+						   dev_t dev_id);
+#endif
diff --git a/drivers/block/blk-snap/tracker.c b/drivers/block/blk-snap/tracker.c
new file mode 100644
index 000000000000..3cda996d3f0a
--- /dev/null
+++ b/drivers/block/blk-snap/tracker.c
@@ -0,0 +1,449 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-tracker"
+#include "common.h"
+#include "tracker.h"
+#include "blk_util.h"
+#include "params.h"
+
+LIST_HEAD(trackers);
+DEFINE_RWLOCK(trackers_lock);
+
+void tracker_done(void)
+{
+	tracker_remove_all();
+}
+
+int tracker_find_by_bio(struct bio *bio, struct tracker **ptracker)
+{
+	int result = -ENODATA;
+
+	read_lock(&trackers_lock);
+	if (!list_empty(&trackers)) {
+		struct list_head *_head;
+
+		list_for_each(_head, &trackers) {
+			struct tracker *_tracker = list_entry(_head, struct tracker, link);
+
+			if ((bio->bi_disk == _tracker->target_dev->bd_disk) &&
+			    (bio->bi_partno == _tracker->target_dev->bd_partno)) {
+				if (ptracker != NULL)
+					*ptracker = _tracker;
+
+				result = SUCCESS;
+				break;
+			}
+		}
+	}
+	read_unlock(&trackers_lock);
+
+	return result;
+}
+
+int tracker_find_by_dev_id(dev_t dev_id, struct tracker **ptracker)
+{
+	int result = -ENODATA;
+
+	read_lock(&trackers_lock);
+	if (!list_empty(&trackers)) {
+		struct list_head *_head;
+
+		list_for_each(_head, &trackers) {
+			struct tracker *_tracker = list_entry(_head, struct tracker, link);
+
+			if (_tracker->original_dev_id == dev_id) {
+				if (ptracker != NULL)
+					*ptracker = _tracker;
+
+				result = SUCCESS;
+				break;
+			}
+		}
+	}
+	read_unlock(&trackers_lock);
+
+	return result;
+}
+
+int tracker_enum_cbt_info(int max_count, struct cbt_info_s *p_cbt_info, int *p_count)
+{
+	int result = SUCCESS;
+	int count = 0;
+
+	read_lock(&trackers_lock);
+	if (!list_empty(&trackers)) {
+		struct list_head *_head;
+
+		list_for_each(_head, &trackers) {
+			struct tracker *tracker = list_entry(_head, struct tracker, link);
+
+			if (count >= max_count) {
+				result = -ENOBUFS;
+				break; //don`t continue
+			}
+
+			if (p_cbt_info != NULL) {
+				p_cbt_info[count].dev_id.major = MAJOR(tracker->original_dev_id);
+				p_cbt_info[count].dev_id.minor = MINOR(tracker->original_dev_id);
+
+				if (tracker->cbt_map) {
+					p_cbt_info[count].cbt_map_size = tracker->cbt_map->map_size;
+					p_cbt_info[count].snap_number =
+						(unsigned char)
+							tracker->cbt_map->snap_number_previous;
+					uuid_copy((uuid_t *)(p_cbt_info[count].generationId),
+						  &tracker->cbt_map->generationId);
+				} else {
+					p_cbt_info[count].cbt_map_size = 0;
+					p_cbt_info[count].snap_number = 0;
+				}
+
+				p_cbt_info[count].dev_capacity = (u64)from_sectors(
+					part_nr_sects_read(tracker->target_dev->bd_part));
+			}
+
+			++count;
+		}
+	}
+	read_unlock(&trackers_lock);
+
+	if (result == SUCCESS)
+		if (count == 0)
+			result = -ENODATA;
+
+	*p_count = count;
+	return result;
+}
+
+static void blk_thaw_bdev(dev_t dev_id, struct block_device *device,
+					 struct super_block *superblock)
+{
+	if (superblock == NULL)
+		return;
+
+	if (thaw_bdev(device, superblock) == SUCCESS)
+		pr_info("Device [%d:%d] was unfrozen\n", MAJOR(dev_id), MINOR(dev_id));
+	else
+		pr_err("Failed to unfreeze device [%d:%d]\n", MAJOR(dev_id), MINOR(dev_id));
+}
+
+static int blk_freeze_bdev(dev_t dev_id, struct block_device *device,
+			   struct super_block **psuperblock)
+{
+	struct super_block *superblock;
+
+	if (device->bd_super == NULL) {
+		pr_warn("Unable to freeze device [%d:%d]: no superblock was found\n",
+			MAJOR(dev_id), MINOR(dev_id));
+		return SUCCESS;
+	}
+
+	superblock = freeze_bdev(device);
+	if (IS_ERR_OR_NULL(superblock)) {
+		int result;
+
+		pr_err("Failed to freeze device [%d:%d]\n", MAJOR(dev_id), MINOR(dev_id));
+
+		if (superblock == NULL)
+			result = -ENODEV;
+		else {
+			result = PTR_ERR(superblock);
+			pr_err("Error code: %d\n", result);
+		}
+		return result;
+	}
+
+	pr_info("Device [%d:%d] was frozen\n", MAJOR(dev_id), MINOR(dev_id));
+	*psuperblock = superblock;
+
+	return SUCCESS;
+}
+
+int _tracker_create(struct tracker *tracker, void *filter, bool attach_filter)
+{
+	int result = SUCCESS;
+	unsigned int sect_in_block_degree;
+	sector_t capacity;
+	struct super_block *superblock = NULL;
+
+	result = blk_dev_open(tracker->original_dev_id, &tracker->target_dev);
+	if (result != SUCCESS)
+		return ENODEV;
+
+	pr_info("Create tracker for device [%d:%d]. Capacity 0x%llx sectors\n",
+		MAJOR(tracker->original_dev_id), MINOR(tracker->original_dev_id),
+		(unsigned long long)part_nr_sects_read(tracker->target_dev->bd_part));
+
+	sect_in_block_degree = get_change_tracking_block_size_pow() - SECTOR_SHIFT;
+	capacity = part_nr_sects_read(tracker->target_dev->bd_part);
+
+	tracker->cbt_map = cbt_map_create(sect_in_block_degree, capacity);
+	if (tracker->cbt_map == NULL) {
+		pr_err("Failed to create tracker for device [%d:%d]\n",
+		       MAJOR(tracker->original_dev_id), MINOR(tracker->original_dev_id));
+		tracker_remove(tracker);
+		return -ENOMEM;
+	}
+
+	tracker->snapshot_id = 0ull;
+
+	if (attach_filter) {
+		blk_freeze_bdev(tracker->original_dev_id, tracker->target_dev, &superblock);
+
+		blk_filter_attach(tracker->original_dev_id, filter, tracker);
+
+		blk_thaw_bdev(tracker->original_dev_id, tracker->target_dev, superblock);
+	}
+
+	return SUCCESS;
+}
+
+int tracker_create(dev_t dev_id, void *filter, struct tracker **ptracker)
+{
+	int ret;
+	struct tracker *tracker = NULL;
+
+	*ptracker = NULL;
+
+	tracker = kzalloc(sizeof(struct tracker), GFP_KERNEL);
+	if (tracker == NULL)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&tracker->link);
+	atomic_set(&tracker->is_captured, false);
+	tracker->original_dev_id = dev_id;
+
+	write_lock(&trackers_lock);
+	list_add_tail(&tracker->link, &trackers);
+	write_unlock(&trackers_lock);
+
+	ret = _tracker_create(tracker, filter, true);
+	if (ret < 0) {
+		tracker_remove(tracker);
+		return ret;
+	}
+
+	*ptracker = tracker;
+	if (ret == ENODEV)
+		pr_info("Cannot attach to unknown device [%d:%d]",
+		       MAJOR(tracker->original_dev_id), MINOR(tracker->original_dev_id));
+
+	return ret;
+}
+
+void _tracker_remove(struct tracker *tracker, bool detach_filter)
+{
+	struct super_block *superblock = NULL;
+
+	if (tracker->target_dev != NULL) {
+		if (detach_filter) {
+			blk_freeze_bdev(tracker->original_dev_id, tracker->target_dev, &superblock);
+
+			blk_filter_detach(tracker->original_dev_id);
+
+			blk_thaw_bdev(tracker->original_dev_id, tracker->target_dev, superblock);
+		}
+
+		blk_dev_close(tracker->target_dev);
+		tracker->target_dev = NULL;
+	}
+
+	if (tracker->cbt_map != NULL) {
+		cbt_map_put_resource(tracker->cbt_map);
+		tracker->cbt_map = NULL;
+	}
+}
+
+void tracker_remove(struct tracker *tracker)
+{
+	_tracker_remove(tracker, true);
+
+	write_lock(&trackers_lock);
+	list_del(&tracker->link);
+	write_unlock(&trackers_lock);
+
+	kfree(tracker);
+}
+
+void tracker_remove_all(void)
+{
+	struct tracker *tracker;
+
+	pr_info("Removing all devices from tracking\n");
+
+	do {
+		tracker = NULL;
+
+		write_lock(&trackers_lock);
+		if (!list_empty(&trackers)) {
+			tracker = list_entry(trackers.next, struct tracker, link);
+
+			list_del(&tracker->link);
+		}
+		write_unlock(&trackers_lock);
+
+		if (tracker) {
+			_tracker_remove(tracker, true);
+			kfree(tracker);
+		}
+	} while (tracker);
+}
+
+void tracker_cbt_bitmap_set(struct tracker *tracker, sector_t sector, sector_t sector_cnt)
+{
+	if (tracker->cbt_map == NULL)
+		return;
+
+	if (tracker->cbt_map->device_capacity != part_nr_sects_read(tracker->target_dev->bd_part)) {
+		pr_warn("Device resize detected\n");
+		tracker->cbt_map->active = false;
+		return;
+	}
+
+	if (cbt_map_set(tracker->cbt_map, sector, sector_cnt) != SUCCESS) { //cbt corrupt
+		pr_warn("CBT fault detected\n");
+		tracker->cbt_map->active = false;
+		return;
+	}
+}
+
+bool tracker_cbt_bitmap_lock(struct tracker *tracker)
+{
+	if (tracker->cbt_map == NULL)
+		return false;
+
+	cbt_map_read_lock(tracker->cbt_map);
+	if (!tracker->cbt_map->active) {
+		cbt_map_read_unlock(tracker->cbt_map);
+		return false;
+	}
+
+	return true;
+}
+
+void tracker_cbt_bitmap_unlock(struct tracker *tracker)
+{
+	if (tracker->cbt_map)
+		cbt_map_read_unlock(tracker->cbt_map);
+}
+
+int _tracker_capture_snapshot(struct tracker *tracker)
+{
+	int result = SUCCESS;
+
+	result = defer_io_create(tracker->original_dev_id, tracker->target_dev, &tracker->defer_io);
+	if (result != SUCCESS) {
+		pr_err("Failed to create defer IO processor\n");
+		return result;
+	}
+
+	atomic_set(&tracker->is_captured, true);
+
+	if (tracker->cbt_map != NULL) {
+		cbt_map_write_lock(tracker->cbt_map);
+		cbt_map_switch(tracker->cbt_map);
+		cbt_map_write_unlock(tracker->cbt_map);
+
+		pr_info("Snapshot captured for device [%d:%d]. New snap number %ld\n",
+			MAJOR(tracker->original_dev_id), MINOR(tracker->original_dev_id),
+			tracker->cbt_map->snap_number_active);
+	}
+
+	return result;
+}
+
+int tracker_capture_snapshot(dev_t *dev_id_set, int dev_id_set_size)
+{
+	int result = SUCCESS;
+	int inx = 0;
+
+	for (inx = 0; inx < dev_id_set_size; ++inx) {
+		struct super_block *superblock = NULL;
+		struct tracker *tracker = NULL;
+		dev_t dev_id = dev_id_set[inx];
+
+		result = tracker_find_by_dev_id(dev_id, &tracker);
+		if (result != SUCCESS) {
+			pr_err("Unable to capture snapshot: cannot find device [%d:%d]\n",
+			       MAJOR(dev_id), MINOR(dev_id));
+			break;
+		}
+
+
+		blk_freeze_bdev(tracker->original_dev_id, tracker->target_dev, &superblock);
+		blk_filter_freeze(tracker->target_dev);
+
+		result = _tracker_capture_snapshot(tracker);
+		if (result != SUCCESS)
+			pr_err("Failed to capture snapshot for device [%d:%d]\n",
+			       MAJOR(dev_id), MINOR(dev_id));
+
+		blk_filter_thaw(tracker->target_dev);
+		blk_thaw_bdev(tracker->original_dev_id, tracker->target_dev, superblock);
+	}
+	if (result != SUCCESS)
+		return result;
+
+	for (inx = 0; inx < dev_id_set_size; ++inx) {
+		struct tracker *tracker = NULL;
+		dev_t dev_id = dev_id_set[inx];
+
+		result = tracker_find_by_dev_id(dev_id, &tracker);
+		if (result != SUCCESS) {
+			pr_err("Unable to capture snapshot: cannot find device [%d:%d]\n",
+			       MAJOR(dev_id), MINOR(dev_id));
+			continue;
+		}
+
+		if (snapstore_device_is_corrupted(tracker->defer_io->snapstore_device)) {
+			pr_err("Unable to freeze devices [%d:%d]: snapshot data is corrupted\n",
+			       MAJOR(dev_id), MINOR(dev_id));
+			result = -EDEADLK;
+			break;
+		}
+	}
+
+	if (result != SUCCESS) {
+		pr_err("Failed to capture snapshot. errno=%d\n", result);
+
+		tracker_release_snapshot(dev_id_set, dev_id_set_size);
+	}
+	return result;
+}
+
+void _tracker_release_snapshot(struct tracker *tracker)
+{
+	struct super_block *superblock = NULL;
+	struct defer_io *defer_io = tracker->defer_io;
+
+	blk_freeze_bdev(tracker->original_dev_id, tracker->target_dev, &superblock);
+	blk_filter_freeze(tracker->target_dev);
+	{ //locked region
+		atomic_set(&tracker->is_captured, false); //clear freeze flag
+
+		tracker->defer_io = NULL;
+	}
+	blk_filter_thaw(tracker->target_dev);
+
+	blk_thaw_bdev(tracker->original_dev_id, tracker->target_dev, superblock);
+
+	defer_io_stop(defer_io);
+	defer_io_put_resource(defer_io);
+}
+
+void tracker_release_snapshot(dev_t *dev_id_set, int dev_id_set_size)
+{
+	int inx = 0;
+
+	for (; inx < dev_id_set_size; ++inx) {
+		int status;
+		struct tracker *p_tracker = NULL;
+		dev_t dev = dev_id_set[inx];
+
+		status = tracker_find_by_dev_id(dev, &p_tracker);
+		if (status == SUCCESS)
+			_tracker_release_snapshot(p_tracker);
+		else
+			pr_err("Unable to release snapshot: cannot find tracker for device [%d:%d]\n",
+			       MAJOR(dev), MINOR(dev));
+	}
+}
diff --git a/drivers/block/blk-snap/tracker.h b/drivers/block/blk-snap/tracker.h
new file mode 100644
index 000000000000..9fff7c0942c3
--- /dev/null
+++ b/drivers/block/blk-snap/tracker.h
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#pragma once
+#include "cbt_map.h"
+#include "defer_io.h"
+#include "blk-snap-ctl.h"
+#include "snapshot.h"
+
+struct tracker {
+	struct list_head link;
+	dev_t original_dev_id;
+	struct block_device *target_dev;
+	struct cbt_map *cbt_map;
+	atomic_t is_captured;
+	struct defer_io *defer_io;
+	unsigned long long snapshot_id; // current snapshot for this device
+};
+
+void tracker_done(void);
+
+int tracker_find_by_bio(struct bio *bio, struct tracker **ptracker);
+int tracker_find_by_dev_id(dev_t dev_id, struct tracker **ptracker);
+
+int tracker_enum_cbt_info(int max_count, struct cbt_info_s *p_cbt_info, int *p_count);
+
+int tracker_capture_snapshot(dev_t *dev_id_set, int dev_id_set_size);
+void tracker_release_snapshot(dev_t *dev_id_set, int dev_id_set_size);
+
+int _tracker_create(struct tracker *tracker, void *filter, bool attach_filter);
+int tracker_create(dev_t dev_id, void *filter, struct tracker **ptracker);
+
+void _tracker_remove(struct tracker *tracker, bool detach_filter);
+void tracker_remove(struct tracker *tracker);
+void tracker_remove_all(void);
+
+void tracker_cbt_bitmap_set(struct tracker *tracker, sector_t sector, sector_t sector_cnt);
+
+bool tracker_cbt_bitmap_lock(struct tracker *tracker);
+void tracker_cbt_bitmap_unlock(struct tracker *tracker);
diff --git a/drivers/block/blk-snap/tracking.c b/drivers/block/blk-snap/tracking.c
new file mode 100644
index 000000000000..55e18891bb96
--- /dev/null
+++ b/drivers/block/blk-snap/tracking.c
@@ -0,0 +1,270 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BLK_SNAP_SECTION "-tracking"
+#include "common.h"
+#include "tracking.h"
+#include "tracker.h"
+#include "blk_util.h"
+#include "defer_io.h"
+#include "params.h"
+
+#include <linux/blk-filter.h>
+
+/* pointer to block layer filter */
+void *filter;
+
+/*
+ * _tracking_submit_bio() - Intercept bio by block io layer filter
+ */
+static bool _tracking_submit_bio(struct bio *bio, void *filter_data)
+{
+	int res;
+	bool cbt_locked = false;
+	struct tracker *tracker = filter_data;
+
+	if (!tracker)
+		return false;
+
+	//intercepting
+	if (atomic_read(&tracker->is_captured)) {
+		//snapshot is captured, call bio redirect algorithm
+
+		res = defer_io_redirect_bio(tracker->defer_io, bio, tracker);
+		if (res == SUCCESS)
+			return true;
+	}
+
+	cbt_locked = false;
+	if (tracker && bio_data_dir(bio) && bio_has_data(bio)) {
+		//call CBT algorithm
+		cbt_locked = tracker_cbt_bitmap_lock(tracker);
+		if (cbt_locked) {
+			sector_t sectStart = bio->bi_iter.bi_sector;
+			sector_t sectCount = bio_sectors(bio);
+
+			tracker_cbt_bitmap_set(tracker, sectStart, sectCount);
+		}
+	}
+	if (cbt_locked)
+		tracker_cbt_bitmap_unlock(tracker);
+
+	return false;
+}
+
+static bool _tracking_part_add(dev_t devt, void **p_filter_data)
+{
+	int result;
+	struct tracker *tracker = NULL;
+
+	pr_info("new block device [%d:%d] in system\n", MAJOR(devt), MINOR(devt));
+
+	result = tracker_find_by_dev_id(devt, &tracker);
+	if (result != SUCCESS)
+		return false; /*do not track this device*/
+
+	if (_tracker_create(tracker, filter, false)) {
+		pr_err("Failed to attach new device to tracker. errno=%d\n", result);
+		return false; /*failed to attach new device to tracker*/
+	}
+
+	*p_filter_data = tracker;
+	return true;
+}
+
+static void _tracking_part_del(void *private_data)
+{
+	struct tracker *tracker = private_data;
+
+	if (!tracker)
+		return;
+
+	pr_info("delete block device [%d:%d] from system\n",
+		MAJOR(tracker->original_dev_id), MINOR(tracker->original_dev_id));
+
+	_tracker_remove(tracker, false);
+}
+
+struct blk_filter_ops filter_ops = {
+	.filter_bio = _tracking_submit_bio,
+	.part_add = _tracking_part_add,
+	.part_del = _tracking_part_del };
+
+
+
+int tracking_init(void)
+{
+	filter = blk_filter_register(&filter_ops);
+	if (!filter)
+		return -ENOMEM;
+	return SUCCESS;
+}
+
+void tracking_done(void)
+{
+	if (filter) {
+		blk_filter_unregister(filter);
+		filter = NULL;
+	}
+}
+
+static int _add_already_tracked(dev_t dev_id, unsigned long long snapshot_id,
+				struct tracker *tracker)
+{
+	int result = SUCCESS;
+	bool cbt_reset_needed = false;
+
+	if ((snapshot_id != 0ull) && (tracker->snapshot_id == 0ull))
+		tracker->snapshot_id = snapshot_id; // set new snapshot id
+
+	if (tracker->cbt_map == NULL) {
+		unsigned int sect_in_block_degree =
+			get_change_tracking_block_size_pow() - SECTOR_SHIFT;
+		tracker->cbt_map = cbt_map_create(sect_in_block_degree - SECTOR_SHIFT,
+						  part_nr_sects_read(tracker->target_dev->bd_part));
+		if (tracker->cbt_map == NULL)
+			return -ENOMEM;
+
+		// skip snapshot id
+		tracker->snapshot_id = snapshot_id;
+		return SUCCESS;
+	}
+
+	if (!tracker->cbt_map->active) {
+		cbt_reset_needed = true;
+		pr_warn("Nonactive CBT table detected. CBT fault\n");
+	}
+
+	if (tracker->cbt_map->device_capacity != part_nr_sects_read(tracker->target_dev->bd_part)) {
+		cbt_reset_needed = true;
+		pr_warn("Device resize detected. CBT fault\n");
+	}
+
+	if (!cbt_reset_needed)
+		return SUCCESS;
+
+	_tracker_remove(tracker, true);
+
+	result = _tracker_create(tracker, filter, true);
+	if (result != SUCCESS) {
+		pr_err("Failed to create tracker. errno=%d\n", result);
+		return result;
+	}
+
+	tracker->snapshot_id = snapshot_id;
+
+	return SUCCESS;
+}
+
+static int _create_new_tracker(dev_t dev_id, unsigned long long snapshot_id)
+{
+	int result;
+	struct tracker *tracker = NULL;
+
+	result = tracker_create(dev_id, filter, &tracker);
+	if (result != SUCCESS) {
+		pr_err("Failed to create tracker. errno=%d\n", result);
+		return result;
+	}
+
+	tracker->snapshot_id = snapshot_id;
+
+	return SUCCESS;
+}
+
+
+int tracking_add(dev_t dev_id, unsigned long long snapshot_id)
+{
+	int result;
+	struct tracker *tracker = NULL;
+
+	pr_info("Adding device [%d:%d] under tracking\n", MAJOR(dev_id), MINOR(dev_id));
+
+	result = tracker_find_by_dev_id(dev_id, &tracker);
+	if (result == SUCCESS) {
+		//pr_info("Device [%d:%d] is already tracked\n", MAJOR(dev_id), MINOR(dev_id));
+		result = _add_already_tracked(dev_id, snapshot_id, tracker);
+		if (result == SUCCESS)
+			result = -EALREADY;
+	} else if (-ENODATA == result)
+		result = _create_new_tracker(dev_id, snapshot_id);
+	else {
+		pr_err("Unable to add device [%d:%d] under tracking\n", MAJOR(dev_id),
+			MINOR(dev_id));
+		pr_err("Invalid trackers container. errno=%d\n", result);
+	}
+
+	return result;
+}
+
+int tracking_remove(dev_t dev_id)
+{
+	int result;
+	struct tracker *tracker = NULL;
+
+	pr_info("Removing device [%d:%d] from tracking\n", MAJOR(dev_id), MINOR(dev_id));
+
+	result = tracker_find_by_dev_id(dev_id, &tracker);
+	if (result != SUCCESS) {
+		pr_err("Unable to remove device [%d:%d] from tracking: ",
+		       MAJOR(dev_id), MINOR(dev_id));
+
+		if (-ENODATA == result)
+			pr_err("tracker not found\n");
+		else
+			pr_err("tracker container failed. errno=%d\n", result);
+
+		return result;
+	}
+
+	if (tracker->snapshot_id != 0ull) {
+		pr_err("Unable to remove device [%d:%d] from tracking: ",
+		       MAJOR(dev_id), MINOR(dev_id));
+		pr_err("snapshot [0x%llx] already exist\n", tracker->snapshot_id);
+		return -EBUSY;
+	}
+
+	tracker_remove(tracker);
+
+	return SUCCESS;
+}
+
+int tracking_collect(int max_count, struct cbt_info_s *p_cbt_info, int *p_count)
+{
+	int res = tracker_enum_cbt_info(max_count, p_cbt_info, p_count);
+
+	if (res == SUCCESS)
+		pr_info("%d devices found under tracking\n", *p_count);
+	else if (res == -ENODATA) {
+		pr_info("There are no devices under tracking\n");
+		*p_count = 0;
+		res = SUCCESS;
+	} else
+		pr_err("Failed to collect devices under tracking. errno=%d", res);
+
+	return res;
+}
+
+int tracking_read_cbt_bitmap(dev_t dev_id, unsigned int offset, size_t length,
+			     void __user *user_buff)
+{
+	int result = SUCCESS;
+	struct tracker *tracker = NULL;
+
+	result = tracker_find_by_dev_id(dev_id, &tracker);
+	if (result == SUCCESS) {
+		if (atomic_read(&tracker->is_captured))
+			result = cbt_map_read_to_user(tracker->cbt_map, user_buff, offset, length);
+		else {
+			pr_err("Unable to read CBT bitmap for device [%d:%d]: ", MAJOR(dev_id),
+			       MINOR(dev_id));
+			pr_err("device is not captured by snapshot\n");
+			result = -EPERM;
+		}
+	} else if (-ENODATA == result) {
+		pr_err("Unable to read CBT bitmap for device [%d:%d]: ", MAJOR(dev_id),
+		       MINOR(dev_id));
+		pr_err("device not found\n");
+	} else
+		pr_err("Failed to find devices under tracking. errno=%d", result);
+
+	return result;
+}
diff --git a/drivers/block/blk-snap/tracking.h b/drivers/block/blk-snap/tracking.h
new file mode 100644
index 000000000000..22bd5ba54963
--- /dev/null
+++ b/drivers/block/blk-snap/tracking.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#pragma once
+#include "blk-snap-ctl.h"
+#include <linux/bio.h>
+
+int  tracking_init(void);
+void tracking_done(void);
+
+int tracking_add(dev_t dev_id, unsigned long long snapshot_id);
+int tracking_remove(dev_t dev_id);
+int tracking_collect(int max_count, struct cbt_info_s *p_cbt_info, int *p_count);
+int tracking_read_cbt_bitmap(dev_t dev_id, unsigned int offset, size_t length,
+			     void __user *user_buff);
diff --git a/drivers/block/blk-snap/version.h b/drivers/block/blk-snap/version.h
new file mode 100644
index 000000000000..a4431da73611
--- /dev/null
+++ b/drivers/block/blk-snap/version.h
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#pragma once
+
+#define FILEVER_MAJOR 5
+#define FILEVER_MINOR 0
+#define FILEVER_REVISION 0
+#define FILEVER_STR "5.0.0"
-- 
2.20.1

Re: [PATCH 2/2] blk-snap - snapshots and change-tracking for block devices

[Pavel Machek]

[-- Attachment #1: Type: text/plain, Size: 948 bytes --]


We'll need some changelog here.

> Signed-off-by: Sergei Shtepa <sergei.shtepa@veeam.com>


> --- /dev/null
> +++ b/drivers/block/blk-snap/blk-snap-ctl.h
> @@ -0,0 +1,190 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once

once?

> +#define MODULE_NAME "blk-snap"
> +#define SNAP_IMAGE_NAME "blk-snap-image"
> +
> +#define SUCCESS 0
> +
> +#define MAX_TRACKING_DEVICE_COUNT 256
> +
> +#define BLK_SNAP 'V'
> +
> +#pragma pack(push, 1)
> +//////////////////////////////////////////////////////////////////////////
> +// version

This is not normal comment style.

> +#define BLK_SNAP_COMPATIBILITY_SNAPSTORE 0x0000000000000001ull /* rudiment */
> +//#define BLK_SNAP_COMPATIBILITY_BTRFS	 0x0000000000000002ull /* rudiment */
> +#define BLK_SNAP_COMPATIBILITY_MULTIDEV 0x0000000000000004ull

Don't comment out code.

Best regards,
								Pavel

-- 
http://www.livejournal.com/~pavelmachek

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 195 bytes --]

Re: [PATCH 2/2] blk-snap - snapshots and change-tracking for block devices

[Sergei Shtepa]

#pragma once still banned? I think need to add a check for this ./scripts/checkpatch.pl.
Comment code style - ok, thank you.
-- 
Sergei Shtepa
Veeam Software developer.

Re: [PATCH 2/2] blk-snap - snapshots and change-tracking for block devices

[Damien Le Moal]

No commit message...

And this is a 8600+ lines patch.
Can you split this into manageable pieces ?

I do not think anybody will review such a huge patch.

On 2020/10/21 18:05, Sergei Shtepa wrote:
> Signed-off-by: Sergei Shtepa <sergei.shtepa@veeam.com>
> ---
>  drivers/block/Kconfig                       |   2 +
>  drivers/block/Makefile                      |   1 +
>  drivers/block/blk-snap/Kconfig              |  24 +
>  drivers/block/blk-snap/Makefile             |  28 +
>  drivers/block/blk-snap/big_buffer.c         | 193 ++++
>  drivers/block/blk-snap/big_buffer.h         |  24 +
>  drivers/block/blk-snap/blk-snap-ctl.h       | 190 ++++
>  drivers/block/blk-snap/blk_deferred.c       | 566 +++++++++++
>  drivers/block/blk-snap/blk_deferred.h       |  67 ++
>  drivers/block/blk-snap/blk_descr_file.c     |  82 ++
>  drivers/block/blk-snap/blk_descr_file.h     |  26 +
>  drivers/block/blk-snap/blk_descr_mem.c      |  66 ++
>  drivers/block/blk-snap/blk_descr_mem.h      |  14 +
>  drivers/block/blk-snap/blk_descr_multidev.c |  86 ++
>  drivers/block/blk-snap/blk_descr_multidev.h |  25 +
>  drivers/block/blk-snap/blk_descr_pool.c     | 190 ++++
>  drivers/block/blk-snap/blk_descr_pool.h     |  38 +
>  drivers/block/blk-snap/blk_redirect.c       | 507 ++++++++++
>  drivers/block/blk-snap/blk_redirect.h       |  73 ++
>  drivers/block/blk-snap/blk_util.c           |  33 +
>  drivers/block/blk-snap/blk_util.h           |  33 +
>  drivers/block/blk-snap/cbt_map.c            | 210 +++++
>  drivers/block/blk-snap/cbt_map.h            |  62 ++
>  drivers/block/blk-snap/common.h             |  31 +
>  drivers/block/blk-snap/ctrl_fops.c          | 691 ++++++++++++++
>  drivers/block/blk-snap/ctrl_fops.h          |  19 +
>  drivers/block/blk-snap/ctrl_pipe.c          | 562 +++++++++++
>  drivers/block/blk-snap/ctrl_pipe.h          |  34 +
>  drivers/block/blk-snap/ctrl_sysfs.c         |  73 ++
>  drivers/block/blk-snap/ctrl_sysfs.h         |   5 +
>  drivers/block/blk-snap/defer_io.c           | 397 ++++++++
>  drivers/block/blk-snap/defer_io.h           |  39 +
>  drivers/block/blk-snap/main.c               |  82 ++
>  drivers/block/blk-snap/params.c             |  58 ++
>  drivers/block/blk-snap/params.h             |  29 +
>  drivers/block/blk-snap/rangevector.c        |  85 ++
>  drivers/block/blk-snap/rangevector.h        |  31 +
>  drivers/block/blk-snap/snapimage.c          | 982 ++++++++++++++++++++
>  drivers/block/blk-snap/snapimage.h          |  16 +
>  drivers/block/blk-snap/snapshot.c           | 225 +++++
>  drivers/block/blk-snap/snapshot.h           |  17 +
>  drivers/block/blk-snap/snapstore.c          | 929 ++++++++++++++++++
>  drivers/block/blk-snap/snapstore.h          |  68 ++
>  drivers/block/blk-snap/snapstore_device.c   | 532 +++++++++++
>  drivers/block/blk-snap/snapstore_device.h   |  63 ++
>  drivers/block/blk-snap/snapstore_file.c     |  52 ++
>  drivers/block/blk-snap/snapstore_file.h     |  15 +
>  drivers/block/blk-snap/snapstore_mem.c      |  91 ++
>  drivers/block/blk-snap/snapstore_mem.h      |  20 +
>  drivers/block/blk-snap/snapstore_multidev.c | 118 +++
>  drivers/block/blk-snap/snapstore_multidev.h |  22 +
>  drivers/block/blk-snap/tracker.c            | 449 +++++++++
>  drivers/block/blk-snap/tracker.h            |  38 +
>  drivers/block/blk-snap/tracking.c           | 270 ++++++
>  drivers/block/blk-snap/tracking.h           |  13 +
>  drivers/block/blk-snap/version.h            |   7 +
>  56 files changed, 8603 insertions(+)
>  create mode 100644 drivers/block/blk-snap/Kconfig
>  create mode 100644 drivers/block/blk-snap/Makefile
>  create mode 100644 drivers/block/blk-snap/big_buffer.c
>  create mode 100644 drivers/block/blk-snap/big_buffer.h
>  create mode 100644 drivers/block/blk-snap/blk-snap-ctl.h
>  create mode 100644 drivers/block/blk-snap/blk_deferred.c
>  create mode 100644 drivers/block/blk-snap/blk_deferred.h
>  create mode 100644 drivers/block/blk-snap/blk_descr_file.c
>  create mode 100644 drivers/block/blk-snap/blk_descr_file.h
>  create mode 100644 drivers/block/blk-snap/blk_descr_mem.c
>  create mode 100644 drivers/block/blk-snap/blk_descr_mem.h
>  create mode 100644 drivers/block/blk-snap/blk_descr_multidev.c
>  create mode 100644 drivers/block/blk-snap/blk_descr_multidev.h
>  create mode 100644 drivers/block/blk-snap/blk_descr_pool.c
>  create mode 100644 drivers/block/blk-snap/blk_descr_pool.h
>  create mode 100644 drivers/block/blk-snap/blk_redirect.c
>  create mode 100644 drivers/block/blk-snap/blk_redirect.h
>  create mode 100644 drivers/block/blk-snap/blk_util.c
>  create mode 100644 drivers/block/blk-snap/blk_util.h
>  create mode 100644 drivers/block/blk-snap/cbt_map.c
>  create mode 100644 drivers/block/blk-snap/cbt_map.h
>  create mode 100644 drivers/block/blk-snap/common.h
>  create mode 100644 drivers/block/blk-snap/ctrl_fops.c
>  create mode 100644 drivers/block/blk-snap/ctrl_fops.h
>  create mode 100644 drivers/block/blk-snap/ctrl_pipe.c
>  create mode 100644 drivers/block/blk-snap/ctrl_pipe.h
>  create mode 100644 drivers/block/blk-snap/ctrl_sysfs.c
>  create mode 100644 drivers/block/blk-snap/ctrl_sysfs.h
>  create mode 100644 drivers/block/blk-snap/defer_io.c
>  create mode 100644 drivers/block/blk-snap/defer_io.h
>  create mode 100644 drivers/block/blk-snap/main.c
>  create mode 100644 drivers/block/blk-snap/params.c
>  create mode 100644 drivers/block/blk-snap/params.h
>  create mode 100644 drivers/block/blk-snap/rangevector.c
>  create mode 100644 drivers/block/blk-snap/rangevector.h
>  create mode 100644 drivers/block/blk-snap/snapimage.c
>  create mode 100644 drivers/block/blk-snap/snapimage.h
>  create mode 100644 drivers/block/blk-snap/snapshot.c
>  create mode 100644 drivers/block/blk-snap/snapshot.h
>  create mode 100644 drivers/block/blk-snap/snapstore.c
>  create mode 100644 drivers/block/blk-snap/snapstore.h
>  create mode 100644 drivers/block/blk-snap/snapstore_device.c
>  create mode 100644 drivers/block/blk-snap/snapstore_device.h
>  create mode 100644 drivers/block/blk-snap/snapstore_file.c
>  create mode 100644 drivers/block/blk-snap/snapstore_file.h
>  create mode 100644 drivers/block/blk-snap/snapstore_mem.c
>  create mode 100644 drivers/block/blk-snap/snapstore_mem.h
>  create mode 100644 drivers/block/blk-snap/snapstore_multidev.c
>  create mode 100644 drivers/block/blk-snap/snapstore_multidev.h
>  create mode 100644 drivers/block/blk-snap/tracker.c
>  create mode 100644 drivers/block/blk-snap/tracker.h
>  create mode 100644 drivers/block/blk-snap/tracking.c
>  create mode 100644 drivers/block/blk-snap/tracking.h
>  create mode 100644 drivers/block/blk-snap/version.h
> 
> diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
> index ecceaaa1a66f..c53ef661110f 100644
> --- a/drivers/block/Kconfig
> +++ b/drivers/block/Kconfig
> @@ -460,4 +460,6 @@ config BLK_DEV_RSXX
>  
>  source "drivers/block/rnbd/Kconfig"
>  
> +source "drivers/block/blk-snap/Kconfig"
> +
>  endif # BLK_DEV
> diff --git a/drivers/block/Makefile b/drivers/block/Makefile
> index e1f63117ee94..312000598944 100644
> --- a/drivers/block/Makefile
> +++ b/drivers/block/Makefile
> @@ -40,6 +40,7 @@ obj-$(CONFIG_BLK_DEV_PCIESSD_MTIP32XX)	+= mtip32xx/
>  obj-$(CONFIG_BLK_DEV_RSXX) += rsxx/
>  obj-$(CONFIG_ZRAM) += zram/
>  obj-$(CONFIG_BLK_DEV_RNBD)	+= rnbd/
> +obj-$(CONFIG_BLK_SNAP)	+= blk-snap/
>  
>  obj-$(CONFIG_BLK_DEV_NULL_BLK)	+= null_blk.o
>  null_blk-objs	:= null_blk_main.o
> diff --git a/drivers/block/blk-snap/Kconfig b/drivers/block/blk-snap/Kconfig
> new file mode 100644
> index 000000000000..7a2db99a80dd
> --- /dev/null
> +++ b/drivers/block/blk-snap/Kconfig
> @@ -0,0 +1,24 @@
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# blk-snap block io layer filter module configuration
> +#
> +#
> +#select BLK_FILTER
> +
> +config BLK_SNAP
> +	tristate "Block device snapshot filter"
> +	depends on BLK_FILTER
> +	help
> +
> +	  Allow to create snapshots and track block changes for a block
> +	  devices. Designed for creating backups for any block devices
> +	  (without device mapper). Snapshots are temporary and are released
> +	  then backup is completed. Change block tracking allows you to
> +	  create incremental or differential backups.
> +
> +config BLK_SNAP_SNAPSTORE_MULTIDEV
> +	bool "Multi device snapstore configuration support"
> +	depends on BLK_SNAP
> +	help
> +
> +	  Allow to create snapstore on multiple block devices.
> diff --git a/drivers/block/blk-snap/Makefile b/drivers/block/blk-snap/Makefile
> new file mode 100644
> index 000000000000..1d628e8e1862
> --- /dev/null
> +++ b/drivers/block/blk-snap/Makefile
> @@ -0,0 +1,28 @@
> +# SPDX-License-Identifier: GPL-2.0
> +blk-snap-y += blk_deferred.o
> +blk-snap-y += blk_descr_file.o
> +blk-snap-y += blk_descr_mem.o
> +blk-snap-y += blk_descr_multidev.o
> +blk-snap-y += blk_descr_pool.o
> +blk-snap-y += blk_redirect.o
> +blk-snap-y += blk_util.o
> +blk-snap-y += cbt_map.o
> +blk-snap-y += ctrl_fops.o
> +blk-snap-y += ctrl_pipe.o
> +blk-snap-y += ctrl_sysfs.o
> +blk-snap-y += defer_io.o
> +blk-snap-y += main.o
> +blk-snap-y += params.o
> +blk-snap-y += big_buffer.o
> +blk-snap-y += rangevector.o
> +blk-snap-y += snapimage.o
> +blk-snap-y += snapshot.o
> +blk-snap-y += snapstore.o
> +blk-snap-y += snapstore_device.o
> +blk-snap-y += snapstore_file.o
> +blk-snap-y += snapstore_mem.o
> +blk-snap-y += snapstore_multidev.o
> +blk-snap-y += tracker.o
> +blk-snap-y += tracking.o
> +
> +obj-$(CONFIG_BLK_SNAP)	 += blk-snap.o
> diff --git a/drivers/block/blk-snap/big_buffer.c b/drivers/block/blk-snap/big_buffer.c
> new file mode 100644
> index 000000000000..c0a75255a807
> --- /dev/null
> +++ b/drivers/block/blk-snap/big_buffer.c
> @@ -0,0 +1,193 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "common.h"
> +#include <linux/mm.h>
> +#include "big_buffer.h"
> +
> +static inline size_t page_count_calc(size_t buffer_size)
> +{
> +	size_t page_count = buffer_size / PAGE_SIZE;
> +
> +	if (buffer_size & (PAGE_SIZE - 1))
> +		page_count += 1;
> +	return page_count;
> +}
> +
> +struct big_buffer *big_buffer_alloc(size_t buffer_size, int gfp_opt)
> +{
> +	int res = SUCCESS;
> +	struct big_buffer *bbuff;
> +	size_t count;
> +	size_t inx;
> +
> +	count = page_count_calc(buffer_size);
> +
> +	bbuff = kzalloc(sizeof(struct big_buffer) + count * sizeof(void *), gfp_opt);
> +	if (bbuff == NULL)
> +		return NULL;
> +
> +	bbuff->pg_cnt = count;
> +	for (inx = 0; inx < bbuff->pg_cnt; ++inx) {
> +		struct page *pg = alloc_page(gfp_opt);
> +
> +		if (!pg) {
> +			res = -ENOMEM;
> +			break;
> +		}
> +		bbuff->pg[inx] = page_address(pg);
> +	}
> +
> +	if (res != SUCCESS) {
> +		big_buffer_free(bbuff);
> +		return NULL;
> +	}
> +
> +	return bbuff;
> +}
> +
> +void big_buffer_free(struct big_buffer *bbuff)
> +{
> +	size_t inx;
> +	size_t count = bbuff->pg_cnt;
> +
> +	if (bbuff == NULL)
> +		return;
> +
> +	for (inx = 0; inx < count; ++inx)
> +		if (bbuff->pg[inx] != NULL)
> +			free_page((unsigned long)bbuff->pg[inx]);
> +
> +	kfree(bbuff);
> +}
> +
> +size_t big_buffer_copy_to_user(char __user *dst_user, size_t offset, struct big_buffer *bbuff,
> +			       size_t length)
> +{
> +	size_t left_data_length;
> +	int page_inx = offset / PAGE_SIZE;
> +	size_t processed_len = 0;
> +	size_t unordered = offset & (PAGE_SIZE - 1);
> +
> +	if (unordered != 0) { //first
> +		size_t page_len = min_t(size_t, (PAGE_SIZE - unordered), length);
> +
> +		left_data_length = copy_to_user(dst_user + processed_len,
> +						bbuff->pg[page_inx] + unordered, page_len);
> +		if (left_data_length != 0) {
> +			pr_err("Failed to copy data from big_buffer to user buffer\n");
> +			return processed_len;
> +		}
> +
> +		++page_inx;
> +		processed_len += page_len;
> +	}
> +
> +	while ((processed_len < length) && (page_inx < bbuff->pg_cnt)) {
> +		size_t page_len = min_t(size_t, PAGE_SIZE, (length - processed_len));
> +
> +		left_data_length =
> +			copy_to_user(dst_user + processed_len, bbuff->pg[page_inx], page_len);
> +		if (left_data_length != 0) {
> +			pr_err("Failed to copy data from big_buffer to user buffer\n");
> +			break;
> +		}
> +
> +		++page_inx;
> +		processed_len += page_len;
> +	}
> +
> +	return processed_len;
> +}
> +
> +size_t big_buffer_copy_from_user(const char __user *src_user, size_t offset,
> +				 struct big_buffer *bbuff, size_t length)
> +{
> +	size_t left_data_length;
> +	int page_inx = offset / PAGE_SIZE;
> +	size_t processed_len = 0;
> +	size_t unordered = offset & (PAGE_SIZE - 1);
> +
> +	if (unordered != 0) { //first
> +		size_t page_len = min_t(size_t, (PAGE_SIZE - unordered), length);
> +
> +		left_data_length = copy_from_user(bbuff->pg[page_inx] + unordered,
> +						  src_user + processed_len, page_len);
> +		if (left_data_length != 0) {
> +			pr_err("Failed to copy data from user buffer to big_buffer\n");
> +			return processed_len;
> +		}
> +
> +		++page_inx;
> +		processed_len += page_len;
> +	}
> +
> +	while ((processed_len < length) && (page_inx < bbuff->pg_cnt)) {
> +		size_t page_len = min_t(size_t, PAGE_SIZE, (length - processed_len));
> +
> +		left_data_length =
> +			copy_from_user(bbuff->pg[page_inx], src_user + processed_len, page_len);
> +		if (left_data_length != 0) {
> +			pr_err("Failed to copy data from user buffer to big_buffer\n");
> +			break;
> +		}
> +
> +		++page_inx;
> +		processed_len += page_len;
> +	}
> +
> +	return processed_len;
> +}
> +
> +void *big_buffer_get_element(struct big_buffer *bbuff, size_t index, size_t sizeof_element)
> +{
> +	size_t elements_in_page = PAGE_SIZE / sizeof_element;
> +	size_t pg_inx = index / elements_in_page;
> +	size_t pg_ofs = (index - (pg_inx * elements_in_page)) * sizeof_element;
> +
> +	if (pg_inx >= bbuff->pg_cnt)
> +		return NULL;
> +
> +	return bbuff->pg[pg_inx] + pg_ofs;
> +}
> +
> +void big_buffer_memset(struct big_buffer *bbuff, int value)
> +{
> +	size_t inx;
> +
> +	for (inx = 0; inx < bbuff->pg_cnt; ++inx)
> +		memset(bbuff->pg[inx], value, PAGE_SIZE);
> +}
> +
> +void big_buffer_memcpy(struct big_buffer *dst, struct big_buffer *src)
> +{
> +	size_t inx;
> +	size_t count = min_t(size_t, dst->pg_cnt, src->pg_cnt);
> +
> +	for (inx = 0; inx < count; ++inx)
> +		memcpy(dst->pg[inx], src->pg[inx], PAGE_SIZE);
> +}
> +
> +int big_buffer_byte_get(struct big_buffer *bbuff, size_t inx, u8 *value)
> +{
> +	size_t page_inx = inx >> PAGE_SHIFT;
> +	size_t byte_pos = inx & (PAGE_SIZE - 1);
> +
> +	if (page_inx >= bbuff->pg_cnt)
> +		return -ENODATA;
> +
> +	*value = bbuff->pg[page_inx][byte_pos];
> +
> +	return SUCCESS;
> +}
> +
> +int big_buffer_byte_set(struct big_buffer *bbuff, size_t inx, u8 value)
> +{
> +	size_t page_inx = inx >> PAGE_SHIFT;
> +	size_t byte_pos = inx & (PAGE_SIZE - 1);
> +
> +	if (page_inx >= bbuff->pg_cnt)
> +		return -ENODATA;
> +
> +	bbuff->pg[page_inx][byte_pos] = value;
> +
> +	return SUCCESS;
> +}
> diff --git a/drivers/block/blk-snap/big_buffer.h b/drivers/block/blk-snap/big_buffer.h
> new file mode 100644
> index 000000000000..f38ab5288b05
> --- /dev/null
> +++ b/drivers/block/blk-snap/big_buffer.h
> @@ -0,0 +1,24 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +struct big_buffer {
> +	size_t pg_cnt;
> +	u8 *pg[0];
> +};
> +
> +struct big_buffer *big_buffer_alloc(size_t count, int gfp_opt);
> +void big_buffer_free(struct big_buffer *bbuff);
> +
> +size_t big_buffer_copy_to_user(char __user *dst_user_buffer, size_t offset,
> +			       struct big_buffer *bbuff, size_t length);
> +size_t big_buffer_copy_from_user(const char __user *src_user_buffer, size_t offset,
> +				 struct big_buffer *bbuff, size_t length);
> +
> +void *big_buffer_get_element(struct big_buffer *bbuff, size_t index, size_t sizeof_element);
> +
> +void big_buffer_memset(struct big_buffer *bbuff, int value);
> +void big_buffer_memcpy(struct big_buffer *dst, struct big_buffer *src);
> +
> +//byte access
> +int big_buffer_byte_get(struct big_buffer *bbuff, size_t inx, u8 *value);
> +int big_buffer_byte_set(struct big_buffer *bbuff, size_t inx, u8 value);
> diff --git a/drivers/block/blk-snap/blk-snap-ctl.h b/drivers/block/blk-snap/blk-snap-ctl.h
> new file mode 100644
> index 000000000000..4ffd836836b1
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk-snap-ctl.h
> @@ -0,0 +1,190 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +#define MODULE_NAME "blk-snap"
> +#define SNAP_IMAGE_NAME "blk-snap-image"
> +
> +#define SUCCESS 0
> +
> +#define MAX_TRACKING_DEVICE_COUNT 256
> +
> +#define BLK_SNAP 'V'
> +
> +#pragma pack(push, 1)
> +//////////////////////////////////////////////////////////////////////////
> +// version
> +
> +#define BLK_SNAP_COMPATIBILITY_SNAPSTORE 0x0000000000000001ull /* rudiment */
> +//#define BLK_SNAP_COMPATIBILITY_BTRFS	 0x0000000000000002ull /* rudiment */
> +#define BLK_SNAP_COMPATIBILITY_MULTIDEV 0x0000000000000004ull
> +
> +struct ioctl_compatibility_flags_s {
> +	unsigned long long flags;
> +};
> +#define IOCTL_COMPATIBILITY_FLAGS _IOW(BLK_SNAP, 0, struct ioctl_compatibility_flags_s)
> +
> +struct ioctl_getversion_s {
> +	unsigned short major;
> +	unsigned short minor;
> +	unsigned short revision;
> +	unsigned short build;
> +};
> +#define IOCTL_GETVERSION _IOW(BLK_SNAP, 1, struct ioctl_getversion_s)
> +
> +//////////////////////////////////////////////////////////////////////////
> +// tracking
> +struct ioctl_dev_id_s {
> +	int major;
> +	int minor;
> +};
> +#define IOCTL_TRACKING_ADD _IOW(BLK_SNAP, 2, struct ioctl_dev_id_s)
> +
> +#define IOCTL_TRACKING_REMOVE _IOW(BLK_SNAP, 3, struct ioctl_dev_id_s)
> +
> +struct cbt_info_s {
> +	struct ioctl_dev_id_s dev_id;
> +	unsigned long long dev_capacity;
> +	unsigned int cbt_map_size;
> +	unsigned char snap_number;
> +	unsigned char generationId[16];
> +};
> +struct ioctl_tracking_collect_s {
> +	unsigned int count;
> +	union {
> +		struct cbt_info_s *p_cbt_info;
> +		unsigned long long ull_cbt_info;
> +	};
> +};
> +#define IOCTL_TRACKING_COLLECT _IOW(BLK_SNAP, 4, struct ioctl_tracking_collect_s)
> +
> +#define IOCTL_TRACKING_BLOCK_SIZE _IOW(BLK_SNAP, 5, unsigned int)
> +
> +struct ioctl_tracking_read_cbt_bitmap_s {
> +	struct ioctl_dev_id_s dev_id;
> +	unsigned int offset;
> +	unsigned int length;
> +	union {
> +		unsigned char *buff;
> +		unsigned long long ull_buff;
> +	};
> +};
> +#define IOCTL_TRACKING_READ_CBT_BITMAP _IOR(BLK_SNAP, 6, struct ioctl_tracking_read_cbt_bitmap_s)
> +
> +struct block_range_s {
> +	unsigned long long ofs; //sectors
> +	unsigned long long cnt; //sectors
> +};
> +
> +struct ioctl_tracking_mark_dirty_blocks_s {
> +	struct ioctl_dev_id_s image_dev_id;
> +	unsigned int count;
> +	union {
> +		struct block_range_s *p_dirty_blocks;
> +		unsigned long long ull_dirty_blocks;
> +	};
> +};
> +#define IOCTL_TRACKING_MARK_DIRTY_BLOCKS                                                           \
> +	_IOR(BLK_SNAP, 7, struct ioctl_tracking_mark_dirty_blocks_s)
> +//////////////////////////////////////////////////////////////////////////
> +// snapshot
> +
> +struct ioctl_snapshot_create_s {
> +	unsigned long long snapshot_id;
> +	unsigned int count;
> +	union {
> +		struct ioctl_dev_id_s *p_dev_id;
> +		unsigned long long ull_dev_id;
> +	};
> +};
> +#define IOCTL_SNAPSHOT_CREATE _IOW(BLK_SNAP, 0x10, struct ioctl_snapshot_create_s)
> +
> +#define IOCTL_SNAPSHOT_DESTROY _IOR(BLK_SNAP, 0x11, unsigned long long)
> +
> +struct ioctl_snapshot_errno_s {
> +	struct ioctl_dev_id_s dev_id;
> +	int err_code;
> +};
> +#define IOCTL_SNAPSHOT_ERRNO _IOW(BLK_SNAP, 0x12, struct ioctl_snapshot_errno_s)
> +
> +struct ioctl_range_s {
> +	unsigned long long left;
> +	unsigned long long right;
> +};
> +
> +//////////////////////////////////////////////////////////////////////////
> +// snapstore
> +struct ioctl_snapstore_create_s {
> +	unsigned char id[16];
> +	struct ioctl_dev_id_s snapstore_dev_id;
> +	unsigned int count;
> +	union {
> +		struct ioctl_dev_id_s *p_dev_id;
> +		unsigned long long ull_dev_id;
> +	};
> +};
> +#define IOCTL_SNAPSTORE_CREATE _IOR(BLK_SNAP, 0x28, struct ioctl_snapstore_create_s)
> +
> +struct ioctl_snapstore_file_add_s {
> +	unsigned char id[16];
> +	unsigned int range_count;
> +	union {
> +		struct ioctl_range_s *ranges;
> +		unsigned long long ull_ranges;
> +	};
> +};
> +#define IOCTL_SNAPSTORE_FILE _IOR(BLK_SNAP, 0x29, struct ioctl_snapstore_file_add_s)
> +
> +struct ioctl_snapstore_memory_limit_s {
> +	unsigned char id[16];
> +	unsigned long long size;
> +};
> +#define IOCTL_SNAPSTORE_MEMORY _IOR(BLK_SNAP, 0x2A, struct ioctl_snapstore_memory_limit_s)
> +
> +struct ioctl_snapstore_cleanup_s {
> +	unsigned char id[16];
> +	unsigned long long filled_bytes;
> +};
> +#define IOCTL_SNAPSTORE_CLEANUP _IOW(BLK_SNAP, 0x2B, struct ioctl_snapstore_cleanup_s)
> +
> +struct ioctl_snapstore_file_add_multidev_s {
> +	unsigned char id[16];
> +	struct ioctl_dev_id_s dev_id;
> +	unsigned int range_count;
> +	union {
> +		struct ioctl_range_s *ranges;
> +		unsigned long long ull_ranges;
> +	};
> +};
> +#define IOCTL_SNAPSTORE_FILE_MULTIDEV                                                              \
> +	_IOR(BLK_SNAP, 0x2C, struct ioctl_snapstore_file_add_multidev_s)
> +//////////////////////////////////////////////////////////////////////////
> +// collect snapshot images
> +
> +struct image_info_s {
> +	struct ioctl_dev_id_s original_dev_id;
> +	struct ioctl_dev_id_s snapshot_dev_id;
> +};
> +
> +struct ioctl_collect_snapshot_images_s {
> +	int count; //
> +	union {
> +		struct image_info_s *p_image_info;
> +		unsigned long long ull_image_info;
> +	};
> +};
> +#define IOCTL_COLLECT_SNAPSHOT_IMAGES _IOW(BLK_SNAP, 0x30, struct ioctl_collect_snapshot_images_s)
> +
> +#pragma pack(pop)
> +
> +// commands for character device interface
> +#define BLK_SNAP_CHARCMD_UNDEFINED 0x00
> +#define BLK_SNAP_CHARCMD_ACKNOWLEDGE 0x01
> +#define BLK_SNAP_CHARCMD_INVALID 0xFF
> +// to module commands
> +#define BLK_SNAP_CHARCMD_INITIATE 0x21
> +#define BLK_SNAP_CHARCMD_NEXT_PORTION 0x22
> +#define BLK_SNAP_CHARCMD_NEXT_PORTION_MULTIDEV 0x23
> +// from module commands
> +#define BLK_SNAP_CHARCMD_HALFFILL 0x41
> +#define BLK_SNAP_CHARCMD_OVERFLOW 0x42
> +#define BLK_SNAP_CHARCMD_TERMINATE 0x43
> diff --git a/drivers/block/blk-snap/blk_deferred.c b/drivers/block/blk-snap/blk_deferred.c
> new file mode 100644
> index 000000000000..1d0b7d2c4d71
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk_deferred.c
> @@ -0,0 +1,566 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-deferred"
> +#include "common.h"
> +
> +#include "blk_deferred.h"
> +#include "blk_util.h"
> +#include "snapstore.h"
> +#include "params.h"
> +
> +struct bio_set blk_deferred_bioset = { 0 };
> +
> +struct dio_bio_complete {
> +	struct blk_deferred_request *dio_req;
> +	sector_t bio_sect_len;
> +};
> +
> +struct dio_deadlocked_list {
> +	struct list_head link;
> +
> +	struct blk_deferred_request *dio_req;
> +};
> +
> +LIST_HEAD(dio_deadlocked_list);
> +DEFINE_RWLOCK(dio_deadlocked_list_lock);
> +
> +atomic64_t dio_alloc_count = ATOMIC64_INIT(0);
> +atomic64_t dio_free_count = ATOMIC64_INIT(0);
> +
> +void blk_deferred_done(void)
> +{
> +	struct dio_deadlocked_list *dio_locked;
> +
> +	do {
> +		dio_locked = NULL;
> +
> +		write_lock(&dio_deadlocked_list_lock);
> +		if (!list_empty(&dio_deadlocked_list)) {
> +			dio_locked = list_entry(dio_deadlocked_list.next,
> +						struct dio_deadlocked_list, link);
> +
> +			list_del(&dio_locked->link);
> +		}
> +		write_unlock(&dio_deadlocked_list_lock);
> +
> +		if (dio_locked) {
> +			if (dio_locked->dio_req->sect_len ==
> +			    atomic64_read(&dio_locked->dio_req->sect_processed))
> +				blk_deferred_request_free(dio_locked->dio_req);
> +			else
> +				pr_err("Locked defer IO is still in memory\n");
> +
> +			kfree(dio_locked);
> +		}
> +	} while (dio_locked);
> +}
> +
> +void blk_deferred_request_deadlocked(struct blk_deferred_request *dio_req)
> +{
> +	struct dio_deadlocked_list *dio_locked =
> +		kzalloc(sizeof(struct dio_deadlocked_list), GFP_KERNEL);
> +
> +	dio_locked->dio_req = dio_req;
> +
> +	write_lock(&dio_deadlocked_list_lock);
> +	list_add_tail(&dio_locked->link, &dio_deadlocked_list);
> +	write_unlock(&dio_deadlocked_list_lock);
> +
> +	pr_warn("Deadlock with defer IO\n");
> +}
> +
> +void blk_deferred_free(struct blk_deferred_io *dio)
> +{
> +	size_t inx = 0;
> +
> +	if (dio->page_array != NULL) {
> +		while (dio->page_array[inx] != NULL) {
> +			__free_page(dio->page_array[inx]);
> +			dio->page_array[inx] = NULL;
> +
> +			++inx;
> +		}
> +
> +		kfree(dio->page_array);
> +		dio->page_array = NULL;
> +	}
> +	kfree(dio);
> +}
> +
> +struct blk_deferred_io *blk_deferred_alloc(unsigned long block_index,
> +					   union blk_descr_unify blk_descr)
> +{
> +	size_t inx;
> +	size_t page_count;
> +	struct blk_deferred_io *dio = kmalloc(sizeof(struct blk_deferred_io), GFP_NOIO);
> +
> +	if (dio == NULL)
> +		return NULL;
> +
> +	INIT_LIST_HEAD(&dio->link);
> +
> +	dio->blk_descr = blk_descr;
> +	dio->blk_index = block_index;
> +
> +	dio->sect.ofs = block_index << snapstore_block_shift();
> +	dio->sect.cnt = snapstore_block_size();
> +
> +	page_count = snapstore_block_size() / (PAGE_SIZE / SECTOR_SIZE);
> +	/*
> +	 * empty pointer on the end
> +	 */
> +	dio->page_array = kzalloc((page_count + 1) * sizeof(struct page *), GFP_NOIO);
> +	if (dio->page_array == NULL) {
> +		blk_deferred_free(dio);
> +		return NULL;
> +	}
> +
> +	for (inx = 0; inx < page_count; inx++) {
> +		dio->page_array[inx] = alloc_page(GFP_NOIO);
> +		if (dio->page_array[inx] == NULL) {
> +			pr_err("Failed to allocate page\n");
> +			blk_deferred_free(dio);
> +			return NULL;
> +		}
> +	}
> +
> +	return dio;
> +}
> +
> +int blk_deferred_bioset_create(void)
> +{
> +	return bioset_init(&blk_deferred_bioset, 64, sizeof(struct dio_bio_complete),
> +			   BIOSET_NEED_BVECS | BIOSET_NEED_RESCUER);
> +}
> +
> +void blk_deferred_bioset_free(void)
> +{
> +	bioset_exit(&blk_deferred_bioset);
> +}
> +
> +struct bio *_blk_deferred_bio_alloc(int nr_iovecs)
> +{
> +	struct bio *new_bio = bio_alloc_bioset(GFP_NOIO, nr_iovecs, &blk_deferred_bioset);
> +
> +	if (new_bio == NULL)
> +		return NULL;
> +
> +	new_bio->bi_end_io = blk_deferred_bio_endio;
> +	new_bio->bi_private = ((void *)new_bio) - sizeof(struct dio_bio_complete);
> +
> +	return new_bio;
> +}
> +
> +static void blk_deferred_complete(struct blk_deferred_request *dio_req, sector_t portion_sect_cnt,
> +				  int result)
> +{
> +	atomic64_add(portion_sect_cnt, &dio_req->sect_processed);
> +
> +	if (dio_req->sect_len == atomic64_read(&dio_req->sect_processed))
> +		complete(&dio_req->complete);
> +
> +	if (result != SUCCESS) {
> +		dio_req->result = result;
> +		pr_err("Failed to process defer IO request. errno=%d\n", result);
> +	}
> +}
> +
> +void blk_deferred_bio_endio(struct bio *bio)
> +{
> +	int local_err;
> +	struct dio_bio_complete *complete_param = (struct dio_bio_complete *)bio->bi_private;
> +
> +	if (complete_param == NULL) {
> +		//bio already complete
> +	} else {
> +		if (bio->bi_status != BLK_STS_OK)
> +			local_err = -EIO;
> +		else
> +			local_err = SUCCESS;
> +
> +		blk_deferred_complete(complete_param->dio_req, complete_param->bio_sect_len,
> +				      local_err);
> +		bio->bi_private = NULL;
> +	}
> +
> +	bio_put(bio);
> +}
> +
> +static inline size_t _page_count_calculate(sector_t size_sector)
> +{
> +	size_t page_count = size_sector / (PAGE_SIZE / SECTOR_SIZE);
> +
> +	if (unlikely(size_sector & ((PAGE_SIZE / SECTOR_SIZE) - 1)))
> +		page_count += 1;
> +
> +	return page_count;
> +}
> +
> +sector_t _blk_deferred_submit_pages(struct block_device *blk_dev,
> +				    struct blk_deferred_request *dio_req, int direction,
> +				    sector_t arr_ofs, struct page **page_array, sector_t ofs_sector,
> +				    sector_t size_sector)
> +{
> +	struct bio *bio = NULL;
> +	int nr_iovecs;
> +	int page_inx = arr_ofs >> (PAGE_SHIFT - SECTOR_SHIFT);
> +	sector_t process_sect = 0;
> +
> +	nr_iovecs = _page_count_calculate(size_sector);
> +
> +	while (NULL == (bio = _blk_deferred_bio_alloc(nr_iovecs))) {
> +		size_sector = (size_sector >> 1) & ~((PAGE_SIZE / SECTOR_SIZE) - 1);
> +		if (size_sector == 0)
> +			return 0;
> +
> +		nr_iovecs = _page_count_calculate(size_sector);
> +	}
> +
> +	bio_set_dev(bio, blk_dev);
> +
> +	if (direction == READ)
> +		bio_set_op_attrs(bio, REQ_OP_READ, 0);
> +	else
> +		bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
> +
> +	bio->bi_iter.bi_sector = ofs_sector;
> +
> +	{ //add first
> +		sector_t unordered = arr_ofs & ((PAGE_SIZE / SECTOR_SIZE) - 1);
> +		sector_t bvec_len_sect =
> +			min_t(sector_t, ((PAGE_SIZE / SECTOR_SIZE) - unordered), size_sector);
> +		struct page *page = page_array[page_inx];
> +		unsigned int len = (unsigned int)from_sectors(bvec_len_sect);
> +		unsigned int offset = (unsigned int)from_sectors(unordered);
> +
> +		if (unlikely(page == NULL)) {
> +			pr_err("NULL found in page array");
> +			bio_put(bio);
> +			return 0;
> +		}
> +		if (unlikely(bio_add_page(bio, page, len, offset) != len)) {
> +			bio_put(bio);
> +			return 0;
> +		}
> +		++page_inx;
> +		process_sect += bvec_len_sect;
> +	}
> +
> +	while (process_sect < size_sector) {
> +		sector_t bvec_len_sect =
> +			min_t(sector_t, (PAGE_SIZE / SECTOR_SIZE), (size_sector - process_sect));
> +		struct page *page = page_array[page_inx];
> +		unsigned int len = (unsigned int)from_sectors(bvec_len_sect);
> +
> +
> +		if (unlikely(page == NULL)) {
> +			pr_err("NULL found in page array");
> +			break;
> +		}
> +		if (unlikely(bio_add_page(bio, page, len, 0) != len))
> +			break;
> +
> +		++page_inx;
> +		process_sect += bvec_len_sect;
> +	}
> +
> +	((struct dio_bio_complete *)bio->bi_private)->dio_req = dio_req;
> +	((struct dio_bio_complete *)bio->bi_private)->bio_sect_len = process_sect;
> +
> +	submit_bio_direct(bio);
> +
> +	return process_sect;
> +}
> +
> +sector_t blk_deferred_submit_pages(struct block_device *blk_dev,
> +				   struct blk_deferred_request *dio_req, int direction,
> +				   sector_t arr_ofs, struct page **page_array, sector_t ofs_sector,
> +				   sector_t size_sector)
> +{
> +	sector_t process_sect = 0;
> +
> +	do {
> +		sector_t portion_sect = _blk_deferred_submit_pages(
> +			blk_dev, dio_req, direction, arr_ofs + process_sect, page_array,
> +			ofs_sector + process_sect, size_sector - process_sect);
> +		if (portion_sect == 0) {
> +			pr_err("Failed to submit defer IO pages. Only [%lld] sectors processed\n",
> +			       process_sect);
> +			break;
> +		}
> +		process_sect += portion_sect;
> +	} while (process_sect < size_sector);
> +
> +	return process_sect;
> +}
> +
> +struct blk_deferred_request *blk_deferred_request_new(void)
> +{
> +	struct blk_deferred_request *dio_req = NULL;
> +
> +	dio_req = kzalloc(sizeof(struct blk_deferred_request), GFP_NOIO);
> +	if (dio_req == NULL)
> +		return NULL;
> +
> +	INIT_LIST_HEAD(&dio_req->dios);
> +
> +	dio_req->result = SUCCESS;
> +	atomic64_set(&dio_req->sect_processed, 0);
> +	dio_req->sect_len = 0;
> +	init_completion(&dio_req->complete);
> +
> +	return dio_req;
> +}
> +
> +bool blk_deferred_request_already_added(struct blk_deferred_request *dio_req,
> +					unsigned long block_index)
> +{
> +	bool result = false;
> +	struct list_head *_list_head;
> +
> +	if (list_empty(&dio_req->dios))
> +		return result;
> +
> +	list_for_each(_list_head, &dio_req->dios) {
> +		struct blk_deferred_io *dio = list_entry(_list_head, struct blk_deferred_io, link);
> +
> +		if (dio->blk_index == block_index) {
> +			result = true;
> +			break;
> +		}
> +	}
> +
> +	return result;
> +}
> +
> +int blk_deferred_request_add(struct blk_deferred_request *dio_req, struct blk_deferred_io *dio)
> +{
> +	list_add_tail(&dio->link, &dio_req->dios);
> +	dio_req->sect_len += dio->sect.cnt;
> +
> +	return SUCCESS;
> +}
> +
> +void blk_deferred_request_free(struct blk_deferred_request *dio_req)
> +{
> +	if (dio_req != NULL) {
> +		while (!list_empty(&dio_req->dios)) {
> +			struct blk_deferred_io *dio =
> +				list_entry(dio_req->dios.next, struct blk_deferred_io, link);
> +
> +			list_del(&dio->link);
> +
> +			blk_deferred_free(dio);
> +		}
> +		kfree(dio_req);
> +	}
> +}
> +
> +void blk_deferred_request_waiting_skip(struct blk_deferred_request *dio_req)
> +{
> +	init_completion(&dio_req->complete);
> +	atomic64_set(&dio_req->sect_processed, 0);
> +}
> +
> +int blk_deferred_request_wait(struct blk_deferred_request *dio_req)
> +{
> +	u64 start_jiffies = get_jiffies_64();
> +	u64 current_jiffies;
> +
> +	while (wait_for_completion_timeout(&dio_req->complete, (HZ * 1)) == 0) {
> +		current_jiffies = get_jiffies_64();
> +		if (jiffies_to_msecs(current_jiffies - start_jiffies) > 60 * 1000) {
> +			pr_warn("Defer IO request timeout\n");
> +			return -EDEADLK;
> +		}
> +	}
> +
> +	return dio_req->result;
> +}
> +
> +int blk_deferred_request_read_original(struct block_device *original_blk_dev,
> +				       struct blk_deferred_request *dio_copy_req)
> +{
> +	int res = -ENODATA;
> +	struct list_head *_list_head;
> +
> +	blk_deferred_request_waiting_skip(dio_copy_req);
> +
> +	if (list_empty(&dio_copy_req->dios))
> +		return res;
> +
> +	list_for_each(_list_head, &dio_copy_req->dios) {
> +		struct blk_deferred_io *dio = list_entry(_list_head, struct blk_deferred_io, link);
> +
> +		sector_t ofs = dio->sect.ofs;
> +		sector_t cnt = dio->sect.cnt;
> +
> +		if (cnt != blk_deferred_submit_pages(original_blk_dev, dio_copy_req, READ, 0,
> +						     dio->page_array, ofs, cnt)) {
> +			pr_err("Failed to submit reading defer IO request. offset=%lld\n",
> +			       dio->sect.ofs);
> +			res = -EIO;
> +			break;
> +		}
> +		res = SUCCESS;
> +	}
> +
> +	if (res == SUCCESS)
> +		res = blk_deferred_request_wait(dio_copy_req);
> +
> +	return res;
> +}
> +
> +
> +static int _store_file(struct block_device *blk_dev, struct blk_deferred_request *dio_copy_req,
> +		       struct blk_descr_file *blk_descr, struct page **page_array)
> +{
> +	struct list_head *_rangelist_head;
> +	sector_t page_array_ofs = 0;
> +
> +	if (unlikely(list_empty(&blk_descr->rangelist))) {
> +		pr_err("Invalid block descriptor");
> +		return -EINVAL;
> +	}
> +	list_for_each(_rangelist_head, &blk_descr->rangelist) {
> +		struct blk_range_link *range_link;
> +		sector_t process_sect;
> +
> +		range_link = list_entry(_rangelist_head, struct blk_range_link, link);
> +		process_sect = blk_deferred_submit_pages(blk_dev, dio_copy_req, WRITE,
> +							 page_array_ofs, page_array,
> +							 range_link->rg.ofs, range_link->rg.cnt);
> +		if (range_link->rg.cnt != process_sect) {
> +			pr_err("Failed to submit defer IO request for storing\n");
> +			return -EIO;
> +		}
> +		page_array_ofs += range_link->rg.cnt;
> +	}
> +	return SUCCESS;
> +}
> +
> +int blk_deferred_request_store_file(struct block_device *blk_dev,
> +				    struct blk_deferred_request *dio_copy_req)
> +{
> +	struct list_head *_dio_list_head;
> +
> +	blk_deferred_request_waiting_skip(dio_copy_req);
> +
> +	if (unlikely(list_empty(&dio_copy_req->dios))) {
> +		pr_err("Invalid deferred io request");
> +		return -EINVAL;
> +	}
> +	list_for_each(_dio_list_head, &dio_copy_req->dios) {
> +		int res;
> +		struct blk_deferred_io *dio;
> +
> +		dio = list_entry(_dio_list_head, struct blk_deferred_io, link);
> +		res = _store_file(blk_dev, dio_copy_req, dio->blk_descr.file, dio->page_array);
> +		if (res != SUCCESS)
> +			return res;
> +	}
> +
> +	return blk_deferred_request_wait(dio_copy_req);
> +}
> +
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +
> +static int _store_multidev(struct blk_deferred_request *dio_copy_req,
> +			   struct blk_descr_multidev *blk_descr, struct page **page_array)
> +{
> +	struct list_head *_ranges_list_head;
> +	sector_t page_array_ofs = 0;
> +
> +	if (unlikely(list_empty(&blk_descr->rangelist))) {
> +		pr_err("Invalid block descriptor");
> +		return -EINVAL;
> +	}
> +	list_for_each(_ranges_list_head, &blk_descr->rangelist) {
> +		sector_t process_sect;
> +		struct blk_range_link_ex *range_link;
> +
> +		range_link = list_entry(_ranges_list_head, struct blk_range_link_ex, link);
> +		process_sect = blk_deferred_submit_pages(range_link->blk_dev, dio_copy_req, WRITE,
> +							 page_array_ofs, page_array,
> +							 range_link->rg.ofs, range_link->rg.cnt);
> +		if (range_link->rg.cnt != process_sect) {
> +			pr_err("Failed to submit defer IO request for storing\n");
> +			return -EIO;
> +		}
> +
> +		page_array_ofs += range_link->rg.cnt;
> +	}
> +
> +	return SUCCESS;
> +}
> +
> +int blk_deferred_request_store_multidev(struct blk_deferred_request *dio_copy_req)
> +{
> +	struct list_head *_dio_list_head;
> +
> +	blk_deferred_request_waiting_skip(dio_copy_req);
> +
> +	if (unlikely(list_empty(&dio_copy_req->dios))) {
> +		pr_err("Invalid deferred io request");
> +		return -EINVAL;
> +	}
> +	list_for_each(_dio_list_head, &dio_copy_req->dios) {
> +		int res;
> +		struct blk_deferred_io *dio;
> +
> +		dio = list_entry(_dio_list_head, struct blk_deferred_io, link);
> +		res = _store_multidev(dio_copy_req, dio->blk_descr.multidev, dio->page_array);
> +		if (res != SUCCESS)
> +			return res;
> +	}
> +
> +	return blk_deferred_request_wait(dio_copy_req);
> +}
> +#endif
> +
> +static size_t _store_pages(void *dst, struct page **page_array, size_t length)
> +{
> +	size_t page_inx = 0;
> +	size_t processed_len = 0;
> +
> +	while ((processed_len < length) && (page_array[page_inx] != NULL)) {
> +		void *src;
> +		size_t page_len = min_t(size_t, PAGE_SIZE, (length - processed_len));
> +
> +		src = page_address(page_array[page_inx]);
> +		memcpy(dst + processed_len, src, page_len);
> +
> +		++page_inx;
> +		processed_len += page_len;
> +	}
> +
> +	return processed_len;
> +}
> +
> +int blk_deferred_request_store_mem(struct blk_deferred_request *dio_copy_req)
> +{
> +	int res = SUCCESS;
> +	sector_t processed = 0;
> +
> +	if (!list_empty(&dio_copy_req->dios)) {
> +		struct list_head *_list_head;
> +
> +		list_for_each(_list_head, &dio_copy_req->dios) {
> +			size_t length;
> +			size_t portion;
> +			struct blk_deferred_io *dio;
> +
> +			dio = list_entry(_list_head, struct blk_deferred_io, link);
> +			length = snapstore_block_size() * SECTOR_SIZE;
> +
> +			portion = _store_pages(dio->blk_descr.mem->buff, dio->page_array, length);
> +			if (unlikely(portion != length)) {
> +				res = -EIO;
> +				break;
> +			}
> +			processed += (sector_t)to_sectors(portion);
> +		}
> +	}
> +
> +	blk_deferred_complete(dio_copy_req, processed, res);
> +	return res;
> +}
> diff --git a/drivers/block/blk-snap/blk_deferred.h b/drivers/block/blk-snap/blk_deferred.h
> new file mode 100644
> index 000000000000..3c516a835c25
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk_deferred.h
> @@ -0,0 +1,67 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +#include "blk_descr_file.h"
> +#include "blk_descr_mem.h"
> +#include "blk_descr_multidev.h"
> +
> +#define DEFER_IO_DIO_REQUEST_LENGTH 250
> +#define DEFER_IO_DIO_REQUEST_SECTORS_COUNT (10 * 1024 * 1024 / SECTOR_SIZE)
> +
> +struct blk_deferred_io {
> +	struct list_head link;
> +
> +	unsigned long blk_index;
> +	union blk_descr_unify blk_descr;
> +
> +	struct blk_range sect;
> +
> +	struct page **page_array; //null pointer on tail
> +};
> +
> +struct blk_deferred_request {
> +	struct completion complete;
> +	sector_t sect_len;
> +	atomic64_t sect_processed;
> +	int result;
> +
> +	struct list_head dios;
> +};
> +
> +void blk_deferred_done(void);
> +
> +struct blk_deferred_io *blk_deferred_alloc(unsigned long block_index,
> +					   union blk_descr_unify blk_descr);
> +void blk_deferred_free(struct blk_deferred_io *dio);
> +
> +void blk_deferred_bio_endio(struct bio *bio);
> +
> +sector_t blk_deferred_submit_pages(struct block_device *blk_dev,
> +				   struct blk_deferred_request *dio_req, int direction,
> +				   sector_t arr_ofs, struct page **page_array, sector_t ofs_sector,
> +				   sector_t size_sector);
> +
> +struct blk_deferred_request *blk_deferred_request_new(void);
> +
> +bool blk_deferred_request_already_added(struct blk_deferred_request *dio_req,
> +					unsigned long block_index);
> +
> +int blk_deferred_request_add(struct blk_deferred_request *dio_req, struct blk_deferred_io *dio);
> +void blk_deferred_request_free(struct blk_deferred_request *dio_req);
> +void blk_deferred_request_deadlocked(struct blk_deferred_request *dio_req);
> +
> +void blk_deferred_request_waiting_skip(struct blk_deferred_request *dio_req);
> +int blk_deferred_request_wait(struct blk_deferred_request *dio_req);
> +
> +int blk_deferred_bioset_create(void);
> +void blk_deferred_bioset_free(void);
> +
> +int blk_deferred_request_read_original(struct block_device *original_blk_dev,
> +				       struct blk_deferred_request *dio_copy_req);
> +
> +int blk_deferred_request_store_file(struct block_device *blk_dev,
> +				    struct blk_deferred_request *dio_copy_req);
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +int blk_deferred_request_store_multidev(struct blk_deferred_request *dio_copy_req);
> +#endif
> +int blk_deferred_request_store_mem(struct blk_deferred_request *dio_copy_req);
> diff --git a/drivers/block/blk-snap/blk_descr_file.c b/drivers/block/blk-snap/blk_descr_file.c
> new file mode 100644
> index 000000000000..fca298d35744
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk_descr_file.c
> @@ -0,0 +1,82 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-blk_descr"
> +#include "common.h"
> +
> +#include "blk_descr_file.h"
> +
> +static inline void list_assign(struct list_head *dst, struct list_head *src)
> +{
> +	dst->next = src->next;
> +	dst->prev = src->prev;
> +
> +	src->next->prev = dst;
> +	src->prev->next = dst;
> +}
> +
> +static inline void blk_descr_file_init(struct blk_descr_file *blk_descr,
> +				       struct list_head *rangelist)
> +{
> +	list_assign(&blk_descr->rangelist, rangelist);
> +}
> +
> +static inline void blk_descr_file_done(struct blk_descr_file *blk_descr)
> +{
> +	struct blk_range_link *range_link;
> +
> +	while (!list_empty(&blk_descr->rangelist)) {
> +		range_link = list_entry(blk_descr->rangelist.next, struct blk_range_link, link);
> +
> +		list_del(&range_link->link);
> +		kfree(range_link);
> +	}
> +}
> +
> +void blk_descr_file_pool_init(struct blk_descr_pool *pool)
> +{
> +	blk_descr_pool_init(pool, 0);
> +}
> +
> +void _blk_descr_file_cleanup(void *descr_array, size_t count)
> +{
> +	size_t inx;
> +	struct blk_descr_file *file_blocks = descr_array;
> +
> +	for (inx = 0; inx < count; ++inx)
> +		blk_descr_file_done(file_blocks + inx);
> +}
> +
> +void blk_descr_file_pool_done(struct blk_descr_pool *pool)
> +{
> +	blk_descr_pool_done(pool, _blk_descr_file_cleanup);
> +}
> +
> +static union blk_descr_unify _blk_descr_file_allocate(void *descr_array, size_t index, void *arg)
> +{
> +	union blk_descr_unify blk_descr;
> +	struct blk_descr_file *file_blocks = descr_array;
> +
> +	blk_descr.file = &file_blocks[index];
> +
> +	blk_descr_file_init(blk_descr.file, (struct list_head *)arg);
> +
> +	return blk_descr;
> +}
> +
> +int blk_descr_file_pool_add(struct blk_descr_pool *pool, struct list_head *rangelist)
> +{
> +	union blk_descr_unify blk_descr;
> +
> +	blk_descr = blk_descr_pool_alloc(pool, sizeof(struct blk_descr_file),
> +					 _blk_descr_file_allocate, (void *)rangelist);
> +	if (blk_descr.ptr == NULL) {
> +		pr_err("Failed to allocate block descriptor\n");
> +		return -ENOMEM;
> +	}
> +
> +	return SUCCESS;
> +}
> +
> +union blk_descr_unify blk_descr_file_pool_take(struct blk_descr_pool *pool)
> +{
> +	return blk_descr_pool_take(pool, sizeof(struct blk_descr_file));
> +}
> diff --git a/drivers/block/blk-snap/blk_descr_file.h b/drivers/block/blk-snap/blk_descr_file.h
> new file mode 100644
> index 000000000000..0e9a5e3efdea
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk_descr_file.h
> @@ -0,0 +1,26 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +#include "blk_descr_pool.h"
> +
> +struct blk_descr_file {
> +	struct list_head rangelist;
> +};
> +
> +struct blk_range_link {
> +	struct list_head link;
> +	struct blk_range rg;
> +};
> +
> +void blk_descr_file_pool_init(struct blk_descr_pool *pool);
> +void blk_descr_file_pool_done(struct blk_descr_pool *pool);
> +
> +/*
> + * allocate new empty block in pool
> + */
> +int blk_descr_file_pool_add(struct blk_descr_pool *pool, struct list_head *rangelist);
> +
> +/*
> + * take empty block from pool
> + */
> +union blk_descr_unify blk_descr_file_pool_take(struct blk_descr_pool *pool);
> diff --git a/drivers/block/blk-snap/blk_descr_mem.c b/drivers/block/blk-snap/blk_descr_mem.c
> new file mode 100644
> index 000000000000..cd326ac150b6
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk_descr_mem.c
> @@ -0,0 +1,66 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-blk_descr"
> +#include "common.h"
> +#include "blk_descr_mem.h"
> +
> +#define SECTION "blk_descr "
> +
> +static inline void blk_descr_mem_init(struct blk_descr_mem *blk_descr, void *ptr)
> +{
> +	blk_descr->buff = ptr;
> +}
> +
> +static inline void blk_descr_mem_done(struct blk_descr_mem *blk_descr)
> +{
> +	blk_descr->buff = NULL;
> +}
> +
> +void blk_descr_mem_pool_init(struct blk_descr_pool *pool, size_t available_blocks)
> +{
> +	blk_descr_pool_init(pool, available_blocks);
> +}
> +
> +void blk_descr_mem_cleanup(void *descr_array, size_t count)
> +{
> +	size_t inx;
> +	struct blk_descr_mem *mem_blocks = descr_array;
> +
> +	for (inx = 0; inx < count; ++inx)
> +		blk_descr_mem_done(mem_blocks + inx);
> +}
> +
> +void blk_descr_mem_pool_done(struct blk_descr_pool *pool)
> +{
> +	blk_descr_pool_done(pool, blk_descr_mem_cleanup);
> +}
> +
> +static union blk_descr_unify blk_descr_mem_alloc(void *descr_array, size_t index, void *arg)
> +{
> +	union blk_descr_unify blk_descr;
> +	struct blk_descr_mem *mem_blocks = descr_array;
> +
> +	blk_descr.mem = &mem_blocks[index];
> +
> +	blk_descr_mem_init(blk_descr.mem, (void *)arg);
> +
> +	return blk_descr;
> +}
> +
> +int blk_descr_mem_pool_add(struct blk_descr_pool *pool, void *buffer)
> +{
> +	union blk_descr_unify blk_descr;
> +
> +	blk_descr = blk_descr_pool_alloc(pool, sizeof(struct blk_descr_mem),
> +					 blk_descr_mem_alloc, buffer);
> +	if (blk_descr.ptr == NULL) {
> +		pr_err("Failed to allocate block descriptor\n");
> +		return -ENOMEM;
> +	}
> +
> +	return SUCCESS;
> +}
> +
> +union blk_descr_unify blk_descr_mem_pool_take(struct blk_descr_pool *pool)
> +{
> +	return blk_descr_pool_take(pool, sizeof(struct blk_descr_mem));
> +}
> diff --git a/drivers/block/blk-snap/blk_descr_mem.h b/drivers/block/blk-snap/blk_descr_mem.h
> new file mode 100644
> index 000000000000..43e8de76c07c
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk_descr_mem.h
> @@ -0,0 +1,14 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +#include "blk_descr_pool.h"
> +
> +struct blk_descr_mem {
> +	void *buff; //pointer to snapstore block in memory
> +};
> +
> +void blk_descr_mem_pool_init(struct blk_descr_pool *pool, size_t available_blocks);
> +void blk_descr_mem_pool_done(struct blk_descr_pool *pool);
> +
> +int blk_descr_mem_pool_add(struct blk_descr_pool *pool, void *buffer);
> +union blk_descr_unify blk_descr_mem_pool_take(struct blk_descr_pool *pool);
> diff --git a/drivers/block/blk-snap/blk_descr_multidev.c b/drivers/block/blk-snap/blk_descr_multidev.c
> new file mode 100644
> index 000000000000..cf5e0ed6f781
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk_descr_multidev.c
> @@ -0,0 +1,86 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-blk_descr"
> +#include "common.h"
> +
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +#include "blk_descr_multidev.h"
> +
> +static inline void list_assign(struct list_head *dst, struct list_head *src)
> +{
> +	dst->next = src->next;
> +	dst->prev = src->prev;
> +
> +	src->next->prev = dst;
> +	src->prev->next = dst;
> +}
> +
> +static inline void blk_descr_multidev_init(struct blk_descr_multidev *blk_descr,
> +					   struct list_head *rangelist)
> +{
> +	list_assign(&blk_descr->rangelist, rangelist);
> +}
> +
> +static inline void blk_descr_multidev_done(struct blk_descr_multidev *blk_descr)
> +{
> +	struct blk_range_link_ex *rangelist;
> +
> +	while (!list_empty(&blk_descr->rangelist)) {
> +		rangelist = list_entry(blk_descr->rangelist.next,
> +				       struct blk_range_link_ex, link);
> +
> +		list_del(&rangelist->link);
> +		kfree(rangelist);
> +	}
> +}
> +
> +void blk_descr_multidev_pool_init(struct blk_descr_pool *pool)
> +{
> +	blk_descr_pool_init(pool, 0);
> +}
> +
> +static void blk_descr_multidev_cleanup(void *descr_array, size_t count)
> +{
> +	size_t inx;
> +	struct blk_descr_multidev *descr_multidev = descr_array;
> +
> +	for (inx = 0; inx < count; ++inx)
> +		blk_descr_multidev_done(descr_multidev + inx);
> +}
> +
> +void blk_descr_multidev_pool_done(struct blk_descr_pool *pool)
> +{
> +	blk_descr_pool_done(pool, blk_descr_multidev_cleanup);
> +}
> +
> +static union blk_descr_unify blk_descr_multidev_allocate(void *descr_array, size_t index, void *arg)
> +{
> +	union blk_descr_unify blk_descr;
> +	struct blk_descr_multidev *multidev_blocks = descr_array;
> +
> +	blk_descr.multidev = &multidev_blocks[index];
> +
> +	blk_descr_multidev_init(blk_descr.multidev, (struct list_head *)arg);
> +
> +	return blk_descr;
> +}
> +
> +int blk_descr_multidev_pool_add(struct blk_descr_pool *pool, struct list_head *rangelist)
> +{
> +	union blk_descr_unify blk_descr;
> +
> +	blk_descr = blk_descr_pool_alloc(pool, sizeof(struct blk_descr_multidev),
> +					 blk_descr_multidev_allocate, (void *)rangelist);
> +	if (blk_descr.ptr == NULL) {
> +		pr_err("Failed to allocate block descriptor\n");
> +		return -ENOMEM;
> +	}
> +
> +	return SUCCESS;
> +}
> +
> +union blk_descr_unify blk_descr_multidev_pool_take(struct blk_descr_pool *pool)
> +{
> +	return blk_descr_pool_take(pool, sizeof(struct blk_descr_multidev));
> +}
> +
> +#endif //CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> diff --git a/drivers/block/blk-snap/blk_descr_multidev.h b/drivers/block/blk-snap/blk_descr_multidev.h
> new file mode 100644
> index 000000000000..0145b0d78b10
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk_descr_multidev.h
> @@ -0,0 +1,25 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +
> +#include "blk_descr_pool.h"
> +
> +struct blk_descr_multidev {
> +	struct list_head rangelist;
> +};
> +
> +struct blk_range_link_ex {
> +	struct list_head link;
> +	struct blk_range rg;
> +	struct block_device *blk_dev;
> +};
> +
> +void blk_descr_multidev_pool_init(struct blk_descr_pool *pool);
> +void blk_descr_multidev_pool_done(struct blk_descr_pool *pool);
> +
> +int blk_descr_multidev_pool_add(struct blk_descr_pool *pool,
> +				struct list_head *rangelist); //allocate new empty block
> +union blk_descr_unify blk_descr_multidev_pool_take(struct blk_descr_pool *pool); //take empty
> +
> +#endif //CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> diff --git a/drivers/block/blk-snap/blk_descr_pool.c b/drivers/block/blk-snap/blk_descr_pool.c
> new file mode 100644
> index 000000000000..b1fe2ba9c2d0
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk_descr_pool.c
> @@ -0,0 +1,190 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-blk_descr"
> +#include "common.h"
> +#include "blk_descr_pool.h"
> +#include "params.h"
> +
> +struct pool_el {
> +	struct list_head link;
> +
> +	size_t used_cnt; // used blocks
> +	size_t capacity; // blocks array capacity
> +
> +	u8 descr_array[0];
> +};
> +
> +static void *kmalloc_huge(size_t max_size, size_t min_size, gfp_t flags, size_t *p_allocated_size)
> +{
> +	void *ptr = NULL;
> +
> +	do {
> +		ptr = kmalloc(max_size, flags | __GFP_NOWARN | __GFP_RETRY_MAYFAIL);
> +
> +		if (ptr != NULL) {
> +			*p_allocated_size = max_size;
> +			return ptr;
> +		}
> +		pr_err("Failed to allocate buffer size=%zu\n", max_size);
> +		max_size = max_size >> 1;
> +	} while (max_size >= min_size);
> +
> +	pr_err("Failed to allocate buffer.");
> +	return NULL;
> +}
> +
> +static struct pool_el *pool_el_alloc(size_t blk_descr_size)
> +{
> +	size_t el_size;
> +	struct pool_el *el;
> +
> +	el = kmalloc_huge(8 * PAGE_SIZE, PAGE_SIZE, GFP_NOIO, &el_size);
> +	if (el == NULL)
> +		return NULL;
> +
> +	el->capacity = (el_size - sizeof(struct pool_el)) / blk_descr_size;
> +	el->used_cnt = 0;
> +
> +	INIT_LIST_HEAD(&el->link);
> +
> +	return el;
> +}
> +
> +static void _pool_el_free(struct pool_el *el)
> +{
> +	if (el != NULL)
> +		kfree(el);
> +}
> +
> +void blk_descr_pool_init(struct blk_descr_pool *pool, size_t available_blocks)
> +{
> +	mutex_init(&pool->lock);
> +
> +	INIT_LIST_HEAD(&pool->head);
> +
> +	pool->blocks_cnt = 0;
> +
> +	pool->total_cnt = available_blocks;
> +	pool->take_cnt = 0;
> +}
> +
> +void blk_descr_pool_done(struct blk_descr_pool *pool,
> +			 void (*blocks_cleanup_cb)(void *descr_array, size_t count))
> +{
> +	mutex_lock(&pool->lock);
> +	while (!list_empty(&pool->head)) {
> +		struct pool_el *el;
> +
> +		el = list_entry(pool->head.next, struct pool_el, link);
> +		if (el == NULL)
> +			break;
> +
> +		list_del(&el->link);
> +		--pool->blocks_cnt;
> +
> +		pool->total_cnt -= el->used_cnt;
> +
> +		blocks_cleanup_cb(el->descr_array, el->used_cnt);
> +
> +		_pool_el_free(el);
> +	}
> +	mutex_unlock(&pool->lock);
> +}
> +
> +union blk_descr_unify blk_descr_pool_alloc(
> +	struct blk_descr_pool *pool, size_t blk_descr_size,
> +	union blk_descr_unify (*block_alloc_cb)(void *descr_array, size_t index, void *arg),
> +	void *arg)
> +{
> +	union blk_descr_unify blk_descr = { NULL };
> +
> +	mutex_lock(&pool->lock);
> +	do {
> +		struct pool_el *el = NULL;
> +
> +		if (!list_empty(&pool->head)) {
> +			el = list_entry(pool->head.prev, struct pool_el, link);
> +			if (el->used_cnt == el->capacity)
> +				el = NULL;
> +		}
> +
> +		if (el == NULL) {
> +			el = pool_el_alloc(blk_descr_size);
> +			if (el == NULL)
> +				break;
> +
> +			list_add_tail(&el->link, &pool->head);
> +
> +			++pool->blocks_cnt;
> +		}
> +
> +		blk_descr = block_alloc_cb(el->descr_array, el->used_cnt, arg);
> +
> +		++el->used_cnt;
> +		++pool->total_cnt;
> +
> +	} while (false);
> +	mutex_unlock(&pool->lock);
> +
> +	return blk_descr;
> +}
> +
> +static union blk_descr_unify __blk_descr_pool_at(struct blk_descr_pool *pool, size_t blk_descr_size,
> +						 size_t index)
> +{
> +	union blk_descr_unify bkl_descr = { NULL };
> +	size_t curr_inx = 0;
> +	struct pool_el *el;
> +	struct list_head *_list_head;
> +
> +	if (list_empty(&(pool)->head))
> +		return bkl_descr;
> +
> +	list_for_each(_list_head, &(pool)->head) {
> +		el = list_entry(_list_head, struct pool_el, link);
> +
> +		if ((index >= curr_inx) && (index < (curr_inx + el->used_cnt))) {
> +			bkl_descr.ptr = el->descr_array + (index - curr_inx) * blk_descr_size;
> +			break;
> +		}
> +		curr_inx += el->used_cnt;
> +	}
> +
> +	return bkl_descr;
> +}
> +
> +union blk_descr_unify blk_descr_pool_take(struct blk_descr_pool *pool, size_t blk_descr_size)
> +{
> +	union blk_descr_unify result = { NULL };
> +
> +	mutex_lock(&pool->lock);
> +	do {
> +		if (pool->take_cnt >= pool->total_cnt) {
> +			pr_err("Unable to get block descriptor: ");
> +			pr_err("not enough descriptors, already took %zu, total %zu\n",
> +			       pool->take_cnt, pool->total_cnt);
> +			break;
> +		}
> +
> +		result = __blk_descr_pool_at(pool, blk_descr_size, pool->take_cnt);
> +		if (result.ptr == NULL) {
> +			pr_err("Unable to get block descriptor: ");
> +			pr_err("not enough descriptors, already took %zu, total %zu\n",
> +			       pool->take_cnt, pool->total_cnt);
> +			break;
> +		}
> +
> +		++pool->take_cnt;
> +	} while (false);
> +	mutex_unlock(&pool->lock);
> +	return result;
> +}
> +
> +bool blk_descr_pool_check_halffill(struct blk_descr_pool *pool, sector_t empty_limit,
> +				   sector_t *fill_status)
> +{
> +	size_t empty_blocks = (pool->total_cnt - pool->take_cnt);
> +
> +	*fill_status = (sector_t)(pool->take_cnt) << snapstore_block_shift();
> +
> +	return (empty_blocks < (size_t)(empty_limit >> snapstore_block_shift()));
> +}
> diff --git a/drivers/block/blk-snap/blk_descr_pool.h b/drivers/block/blk-snap/blk_descr_pool.h
> new file mode 100644
> index 000000000000..32f8b8c4103e
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk_descr_pool.h
> @@ -0,0 +1,38 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +struct blk_descr_mem;
> +struct blk_descr_file;
> +struct blk_descr_multidev;
> +
> +union blk_descr_unify {
> +	void *ptr;
> +	struct blk_descr_mem *mem;
> +	struct blk_descr_file *file;
> +	struct blk_descr_multidev *multidev;
> +};
> +
> +struct blk_descr_pool {
> +	struct list_head head;
> +	struct mutex lock;
> +
> +	size_t blocks_cnt; // count of struct pool_el
> +
> +	size_t total_cnt;  // total count of block descriptors
> +	size_t take_cnt;   // take count of block descriptors
> +};
> +
> +void blk_descr_pool_init(struct blk_descr_pool *pool, size_t available_blocks);
> +
> +void blk_descr_pool_done(struct blk_descr_pool *pool,
> +			 void (*blocks_cleanup_cb)(void *descr_array, size_t count));
> +
> +union blk_descr_unify blk_descr_pool_alloc(
> +	struct blk_descr_pool *pool, size_t blk_descr_size,
> +	union blk_descr_unify (*block_alloc_cb)(void *descr_array, size_t index, void *arg),
> +	void *arg);
> +
> +union blk_descr_unify blk_descr_pool_take(struct blk_descr_pool *pool, size_t blk_descr_size);
> +
> +bool blk_descr_pool_check_halffill(struct blk_descr_pool *pool, sector_t empty_limit,
> +				   sector_t *fill_status);
> diff --git a/drivers/block/blk-snap/blk_redirect.c b/drivers/block/blk-snap/blk_redirect.c
> new file mode 100644
> index 000000000000..4c28a8cb4275
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk_redirect.c
> @@ -0,0 +1,507 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-redirect"
> +#include "common.h"
> +#include "blk_util.h"
> +#include "blk_redirect.h"
> +
> +#define bio_vec_sectors(bv) (bv.bv_len >> SECTOR_SHIFT)
> +
> +struct bio_set blk_redirect_bioset = { 0 };
> +
> +int blk_redirect_bioset_create(void)
> +{
> +	return bioset_init(&blk_redirect_bioset, 64, 0, BIOSET_NEED_BVECS | BIOSET_NEED_RESCUER);
> +}
> +
> +void blk_redirect_bioset_free(void)
> +{
> +	bioset_exit(&blk_redirect_bioset);
> +}
> +
> +void blk_redirect_bio_endio(struct bio *bb)
> +{
> +	struct blk_redirect_bio *rq_redir = (struct blk_redirect_bio *)bb->bi_private;
> +
> +	if (rq_redir != NULL) {
> +		int err = SUCCESS;
> +
> +		if (bb->bi_status != BLK_STS_OK)
> +			err = -EIO;
> +
> +		if (err != SUCCESS) {
> +			pr_err("Failed to process redirect IO request. errno=%d\n", 0 - err);
> +
> +			if (rq_redir->err == SUCCESS)
> +				rq_redir->err = err;
> +		}
> +
> +		if (atomic64_dec_and_test(&rq_redir->bio_count))
> +			blk_redirect_complete(rq_redir, rq_redir->err);
> +	}
> +	bio_put(bb);
> +}
> +
> +struct bio *_blk_dev_redirect_bio_alloc(int nr_iovecs, void *bi_private)
> +{
> +	struct bio *new_bio;
> +
> +	new_bio = bio_alloc_bioset(GFP_NOIO, nr_iovecs, &blk_redirect_bioset);
> +	if (new_bio == NULL)
> +		return NULL;
> +
> +	new_bio->bi_end_io = blk_redirect_bio_endio;
> +	new_bio->bi_private = bi_private;
> +
> +	return new_bio;
> +}
> +
> +struct blk_redirect_bio_list *_redirect_bio_allocate_list(struct bio *new_bio)
> +{
> +	struct blk_redirect_bio_list *next;
> +
> +	next = kzalloc(sizeof(struct blk_redirect_bio_list), GFP_NOIO);
> +	if (next == NULL)
> +		return NULL;
> +
> +	next->next = NULL;
> +	next->this = new_bio;
> +
> +	return next;
> +}
> +
> +int bio_endio_list_push(struct blk_redirect_bio *rq_redir, struct bio *new_bio)
> +{
> +	struct blk_redirect_bio_list *head;
> +
> +	if (rq_redir->bio_list_head == NULL) {
> +		//list is empty, add first bio
> +		rq_redir->bio_list_head = _redirect_bio_allocate_list(new_bio);
> +		if (rq_redir->bio_list_head == NULL)
> +			return -ENOMEM;
> +		return SUCCESS;
> +	}
> +
> +	// seek end of list
> +	head = rq_redir->bio_list_head;
> +	while (head->next != NULL)
> +		head = head->next;
> +
> +	//append new bio to the end of list
> +	head->next = _redirect_bio_allocate_list(new_bio);
> +	if (head->next == NULL)
> +		return -ENOMEM;
> +
> +	return SUCCESS;
> +}
> +
> +void bio_endio_list_cleanup(struct blk_redirect_bio_list *curr)
> +{
> +	while (curr != NULL) {
> +		struct blk_redirect_bio_list *next;
> +
> +		next = curr->next;
> +		kfree(curr);
> +		curr = next;
> +	}
> +}
> +
> +static unsigned int get_max_sect(struct block_device *blk_dev)
> +{
> +	struct request_queue *q = bdev_get_queue(blk_dev);
> +
> +	return min((unsigned int)(BIO_MAX_PAGES << (PAGE_SHIFT - SECTOR_SHIFT)),
> +		   q->limits.max_sectors);
> +}
> +
> +static int _blk_dev_redirect_part_fast(struct blk_redirect_bio *rq_redir, int direction,
> +				       struct block_device *blk_dev, sector_t target_pos,
> +				       sector_t rq_ofs, sector_t rq_count)
> +{
> +	__label__ _fail_out;
> +	__label__ _reprocess_bv;
> +
> +	int res = SUCCESS;
> +
> +	struct bio_vec bvec;
> +	struct bvec_iter iter;
> +
> +	struct bio *new_bio = NULL;
> +
> +	sector_t sect_ofs = 0;
> +	sector_t processed_sectors = 0;
> +	int nr_iovecs;
> +	struct blk_redirect_bio_list *bio_endio_rec;
> +
> +	nr_iovecs = get_max_sect(blk_dev) >> (PAGE_SHIFT - SECTOR_SHIFT);
> +
> +	bio_for_each_segment(bvec, rq_redir->bio, iter) {
> +		sector_t bvec_ofs;
> +		sector_t bvec_sectors;
> +
> +		unsigned int len;
> +		unsigned int offset;
> +
> +		if ((sect_ofs + bio_vec_sectors(bvec)) <= rq_ofs) {
> +			sect_ofs += bio_vec_sectors(bvec);
> +			continue;
> +		}
> +		if (sect_ofs >= (rq_ofs + rq_count))
> +			break;
> +
> +		bvec_ofs = 0;
> +		if (sect_ofs < rq_ofs)
> +			bvec_ofs = rq_ofs - sect_ofs;
> +
> +		bvec_sectors = bio_vec_sectors(bvec) - bvec_ofs;
> +		if (bvec_sectors > (rq_count - processed_sectors))
> +			bvec_sectors = rq_count - processed_sectors;
> +
> +		if (bvec_sectors == 0) {
> +			res = -EIO;
> +			goto _fail_out;
> +		}
> +
> +_reprocess_bv:
> +		if (new_bio == NULL) {
> +			new_bio = _blk_dev_redirect_bio_alloc(nr_iovecs, rq_redir);
> +			while (new_bio == NULL) {
> +				pr_err("Unable to allocate new bio for redirect IO.\n");
> +				res = -ENOMEM;
> +				goto _fail_out;
> +			}
> +
> +			bio_set_dev(new_bio, blk_dev);
> +
> +			if (direction == READ)
> +				bio_set_op_attrs(new_bio, REQ_OP_READ, 0);
> +
> +			if (direction == WRITE)
> +				bio_set_op_attrs(new_bio, REQ_OP_WRITE, 0);
> +
> +			new_bio->bi_iter.bi_sector = target_pos + processed_sectors;
> +		}
> +
> +		len = (unsigned int)from_sectors(bvec_sectors);
> +		offset = bvec.bv_offset + (unsigned int)from_sectors(bvec_ofs);
> +		if (unlikely(bio_add_page(new_bio, bvec.bv_page, len, offset) != len)) {
> +			if (bio_sectors(new_bio) == 0) {
> +				res = -EIO;
> +				goto _fail_out;
> +			}
> +
> +			res = bio_endio_list_push(rq_redir, new_bio);
> +			if (res != SUCCESS) {
> +				pr_err("Failed to add bio into bio_endio_list\n");
> +				goto _fail_out;
> +			}
> +
> +			atomic64_inc(&rq_redir->bio_count);
> +			new_bio = NULL;
> +
> +			goto _reprocess_bv;
> +		}
> +		processed_sectors += bvec_sectors;
> +
> +		sect_ofs += bio_vec_sectors(bvec);
> +	}
> +
> +	if (new_bio != NULL) {
> +		res = bio_endio_list_push(rq_redir, new_bio);
> +		if (res != SUCCESS) {
> +			pr_err("Failed to add bio into bio_endio_list\n");
> +			goto _fail_out;
> +		}
> +
> +		atomic64_inc(&rq_redir->bio_count);
> +		new_bio = NULL;
> +	}
> +
> +	return SUCCESS;
> +
> +_fail_out:
> +	bio_endio_rec = rq_redir->bio_list_head;
> +	while (bio_endio_rec != NULL) {
> +		if (bio_endio_rec->this != NULL)
> +			bio_put(bio_endio_rec->this);
> +
> +		bio_endio_rec = bio_endio_rec->next;
> +	}
> +
> +	bio_endio_list_cleanup(bio_endio_rec);
> +
> +	pr_err("Failed to process part of redirect IO request. rq_ofs=%lld, rq_count=%lld\n",
> +	       rq_ofs, rq_count);
> +	return res;
> +}
> +
> +int blk_dev_redirect_part(struct blk_redirect_bio *rq_redir, int direction,
> +			  struct block_device *blk_dev, sector_t target_pos, sector_t rq_ofs,
> +			  sector_t rq_count)
> +{
> +	struct request_queue *q = bdev_get_queue(blk_dev);
> +	sector_t logical_block_size_mask =
> +		(sector_t)((q->limits.logical_block_size >> SECTOR_SHIFT) - 1);
> +
> +	if (likely(logical_block_size_mask == 0))
> +		return _blk_dev_redirect_part_fast(rq_redir, direction, blk_dev, target_pos, rq_ofs,
> +						   rq_count);
> +
> +	if (likely((0 == (target_pos & logical_block_size_mask)) &&
> +		   (0 == (rq_count & logical_block_size_mask))))
> +		return _blk_dev_redirect_part_fast(rq_redir, direction, blk_dev, target_pos, rq_ofs,
> +						   rq_count);
> +
> +	return -EFAULT;
> +}
> +
> +void blk_dev_redirect_submit(struct blk_redirect_bio *rq_redir)
> +{
> +	struct blk_redirect_bio_list *head;
> +	struct blk_redirect_bio_list *curr;
> +
> +	head = curr = rq_redir->bio_list_head;
> +	rq_redir->bio_list_head = NULL;
> +
> +	while (curr != NULL) {
> +		submit_bio_direct(curr->this);
> +
> +		curr = curr->next;
> +	}
> +
> +	bio_endio_list_cleanup(head);
> +}
> +
> +int blk_dev_redirect_memcpy_part(struct blk_redirect_bio *rq_redir, int direction, void *buff,
> +				 sector_t rq_ofs, sector_t rq_count)
> +{
> +	struct bio_vec bvec;
> +	struct bvec_iter iter;
> +
> +	sector_t sect_ofs = 0;
> +	sector_t processed_sectors = 0;
> +
> +	bio_for_each_segment(bvec, rq_redir->bio, iter) {
> +		void *mem;
> +		sector_t bvec_ofs;
> +		sector_t bvec_sectors;
> +
> +		if ((sect_ofs + bio_vec_sectors(bvec)) <= rq_ofs) {
> +			sect_ofs += bio_vec_sectors(bvec);
> +			continue;
> +		}
> +
> +		if (sect_ofs >= (rq_ofs + rq_count))
> +			break;
> +
> +		bvec_ofs = 0;
> +		if (sect_ofs < rq_ofs)
> +			bvec_ofs = rq_ofs - sect_ofs;
> +
> +		bvec_sectors = bio_vec_sectors(bvec) - bvec_ofs;
> +		if (bvec_sectors > (rq_count - processed_sectors))
> +			bvec_sectors = rq_count - processed_sectors;
> +
> +		mem = kmap_atomic(bvec.bv_page);
> +		if (direction == READ) {
> +			memcpy(mem + bvec.bv_offset + (unsigned int)from_sectors(bvec_ofs),
> +			       buff + (unsigned int)from_sectors(processed_sectors),
> +			       (unsigned int)from_sectors(bvec_sectors));
> +		} else {
> +			memcpy(buff + (unsigned int)from_sectors(processed_sectors),
> +			       mem + bvec.bv_offset + (unsigned int)from_sectors(bvec_ofs),
> +			       (unsigned int)from_sectors(bvec_sectors));
> +		}
> +		kunmap_atomic(mem);
> +
> +		processed_sectors += bvec_sectors;
> +
> +		sect_ofs += bio_vec_sectors(bvec);
> +	}
> +
> +	return SUCCESS;
> +}
> +
> +int blk_dev_redirect_zeroed_part(struct blk_redirect_bio *rq_redir, sector_t rq_ofs,
> +				 sector_t rq_count)
> +{
> +	struct bio_vec bvec;
> +	struct bvec_iter iter;
> +
> +	sector_t sect_ofs = 0;
> +	sector_t processed_sectors = 0;
> +
> +	bio_for_each_segment(bvec, rq_redir->bio, iter) {
> +		void *mem;
> +		sector_t bvec_ofs;
> +		sector_t bvec_sectors;
> +
> +		if ((sect_ofs + bio_vec_sectors(bvec)) <= rq_ofs) {
> +			sect_ofs += bio_vec_sectors(bvec);
> +			continue;
> +		}
> +
> +		if (sect_ofs >= (rq_ofs + rq_count))
> +			break;
> +
> +		bvec_ofs = 0;
> +		if (sect_ofs < rq_ofs)
> +			bvec_ofs = rq_ofs - sect_ofs;
> +
> +		bvec_sectors = bio_vec_sectors(bvec) - bvec_ofs;
> +		if (bvec_sectors > (rq_count - processed_sectors))
> +			bvec_sectors = rq_count - processed_sectors;
> +
> +		mem = kmap_atomic(bvec.bv_page);
> +		memset(mem + bvec.bv_offset + (unsigned int)from_sectors(bvec_ofs), 0,
> +		       (unsigned int)from_sectors(bvec_sectors));
> +		kunmap_atomic(mem);
> +
> +		processed_sectors += bvec_sectors;
> +
> +		sect_ofs += bio_vec_sectors(bvec);
> +	}
> +
> +	return SUCCESS;
> +}
> +
> +int blk_dev_redirect_read_zeroed(struct blk_redirect_bio *rq_redir, struct block_device *blk_dev,
> +				 sector_t rq_pos, sector_t blk_ofs_start, sector_t blk_ofs_count,
> +				 struct rangevector *zero_sectors)
> +{
> +	int res = SUCCESS;
> +	struct blk_range_tree_node *range_node;
> +
> +	sector_t ofs = 0;
> +
> +	sector_t from = rq_pos + blk_ofs_start;
> +	sector_t to = rq_pos + blk_ofs_start + blk_ofs_count - 1;
> +
> +	down_read(&zero_sectors->lock);
> +	range_node = blk_range_rb_iter_first(&zero_sectors->root, from, to);
> +	while (range_node) {
> +		struct blk_range *zero_range = &range_node->range;
> +		sector_t current_portion;
> +
> +		if (zero_range->ofs > rq_pos + blk_ofs_start + ofs) {
> +			sector_t pre_zero_cnt = zero_range->ofs - (rq_pos + blk_ofs_start + ofs);
> +
> +			res = blk_dev_redirect_part(rq_redir, READ, blk_dev,
> +						    rq_pos + blk_ofs_start + ofs,
> +						    blk_ofs_start + ofs, pre_zero_cnt);
> +			if (res != SUCCESS)
> +				break;
> +
> +			ofs += pre_zero_cnt;
> +		}
> +
> +		current_portion = min_t(sector_t, zero_range->cnt, blk_ofs_count - ofs);
> +
> +		res = blk_dev_redirect_zeroed_part(rq_redir, blk_ofs_start + ofs, current_portion);
> +		if (res != SUCCESS)
> +			break;
> +
> +		ofs += current_portion;
> +
> +		range_node = blk_range_rb_iter_next(range_node, from, to);
> +	}
> +	up_read(&zero_sectors->lock);
> +
> +	if (res == SUCCESS)
> +		if ((blk_ofs_count - ofs) > 0)
> +			res = blk_dev_redirect_part(rq_redir, READ, blk_dev,
> +						    rq_pos + blk_ofs_start + ofs,
> +						    blk_ofs_start + ofs, blk_ofs_count - ofs);
> +
> +	return res;
> +}
> +void blk_redirect_complete(struct blk_redirect_bio *rq_redir, int res)
> +{
> +	rq_redir->complete_cb(rq_redir->complete_param, rq_redir->bio, res);
> +	redirect_bio_queue_free(rq_redir);
> +}
> +
> +void redirect_bio_queue_init(struct redirect_bio_queue *queue)
> +{
> +	INIT_LIST_HEAD(&queue->list);
> +
> +	spin_lock_init(&queue->lock);
> +
> +	atomic_set(&queue->in_queue_cnt, 0);
> +	atomic_set(&queue->alloc_cnt, 0);
> +
> +	atomic_set(&queue->active_state, true);
> +}
> +
> +struct blk_redirect_bio *redirect_bio_queue_new(struct redirect_bio_queue *queue)
> +{
> +	struct blk_redirect_bio *rq_redir = kzalloc(sizeof(struct blk_redirect_bio), GFP_NOIO);
> +
> +	if (rq_redir == NULL)
> +		return NULL;
> +
> +	atomic_inc(&queue->alloc_cnt);
> +
> +	INIT_LIST_HEAD(&rq_redir->link);
> +	rq_redir->queue = queue;
> +
> +	return rq_redir;
> +}
> +
> +void redirect_bio_queue_free(struct blk_redirect_bio *rq_redir)
> +{
> +	if (rq_redir) {
> +		if (rq_redir->queue)
> +			atomic_dec(&rq_redir->queue->alloc_cnt);
> +
> +		kfree(rq_redir);
> +	}
> +}
> +
> +int redirect_bio_queue_push_back(struct redirect_bio_queue *queue,
> +				 struct blk_redirect_bio *rq_redir)
> +{
> +	int res = SUCCESS;
> +
> +	spin_lock(&queue->lock);
> +
> +	if (atomic_read(&queue->active_state)) {
> +		INIT_LIST_HEAD(&rq_redir->link);
> +		list_add_tail(&rq_redir->link, &queue->list);
> +		atomic_inc(&queue->in_queue_cnt);
> +	} else
> +		res = -EACCES;
> +
> +	spin_unlock(&queue->lock);
> +	return res;
> +}
> +
> +struct blk_redirect_bio *redirect_bio_queue_get_first(struct redirect_bio_queue *queue)
> +{
> +	struct blk_redirect_bio *rq_redir = NULL;
> +
> +	spin_lock(&queue->lock);
> +
> +	if (!list_empty(&queue->list)) {
> +		rq_redir = list_entry(queue->list.next, struct blk_redirect_bio, link);
> +		list_del(&rq_redir->link);
> +		atomic_dec(&queue->in_queue_cnt);
> +	}
> +
> +	spin_unlock(&queue->lock);
> +
> +	return rq_redir;
> +}
> +
> +bool redirect_bio_queue_active(struct redirect_bio_queue *queue, bool state)
> +{
> +	bool prev_state;
> +
> +	spin_lock(&queue->lock);
> +
> +	prev_state = atomic_read(&queue->active_state);
> +	atomic_set(&queue->active_state, state);
> +
> +	spin_unlock(&queue->lock);
> +
> +	return prev_state;
> +}
> diff --git a/drivers/block/blk-snap/blk_redirect.h b/drivers/block/blk-snap/blk_redirect.h
> new file mode 100644
> index 000000000000..aae23e78ebe2
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk_redirect.h
> @@ -0,0 +1,73 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +#include "rangevector.h"
> +
> +int blk_redirect_bioset_create(void);
> +void blk_redirect_bioset_free(void);
> +
> +void blk_redirect_bio_endio(struct bio *bb);
> +
> +struct blk_redirect_bio_list {
> +	struct blk_redirect_bio_list *next;
> +	struct bio *this;
> +};
> +
> +struct redirect_bio_queue {
> +	struct list_head list;
> +	spinlock_t lock;
> +
> +	atomic_t active_state;
> +	atomic_t in_queue_cnt;
> +	atomic_t alloc_cnt;
> +};
> +
> +struct blk_redirect_bio {
> +	struct list_head link;
> +	struct redirect_bio_queue *queue;
> +
> +	struct bio *bio;
> +	int err;
> +	struct blk_redirect_bio_list *bio_list_head; //list of created bios
> +	atomic64_t bio_count;
> +
> +	void *complete_param;
> +	void (*complete_cb)(void *complete_param, struct bio *rq, int err);
> +};
> +
> +int blk_dev_redirect_part(struct blk_redirect_bio *rq_redir, int direction,
> +			  struct block_device *blk_dev, sector_t target_pos, sector_t rq_ofs,
> +			  sector_t rq_count);
> +
> +void blk_dev_redirect_submit(struct blk_redirect_bio *rq_redir);
> +
> +int blk_dev_redirect_memcpy_part(struct blk_redirect_bio *rq_redir, int direction, void *src_buff,
> +				 sector_t rq_ofs, sector_t rq_count);
> +
> +int blk_dev_redirect_zeroed_part(struct blk_redirect_bio *rq_redir, sector_t rq_ofs,
> +				 sector_t rq_count);
> +
> +int blk_dev_redirect_read_zeroed(struct blk_redirect_bio *rq_redir, struct block_device *blk_dev,
> +				 sector_t rq_pos, sector_t blk_ofs_start, sector_t blk_ofs_count,
> +				 struct rangevector *zero_sectors);
> +
> +void blk_redirect_complete(struct blk_redirect_bio *rq_redir, int res);
> +
> +void redirect_bio_queue_init(struct redirect_bio_queue *queue);
> +
> +struct blk_redirect_bio *redirect_bio_queue_new(struct redirect_bio_queue *queue);
> +
> +void redirect_bio_queue_free(struct blk_redirect_bio *rq_redir);
> +
> +int redirect_bio_queue_push_back(struct redirect_bio_queue *queue,
> +				 struct blk_redirect_bio *rq_redir);
> +
> +struct blk_redirect_bio *redirect_bio_queue_get_first(struct redirect_bio_queue *queue);
> +
> +bool redirect_bio_queue_active(struct redirect_bio_queue *queue, bool state);
> +
> +#define redirect_bio_queue_empty(queue) (atomic_read(&(queue).in_queue_cnt) == 0)
> +
> +#define redirect_bio_queue_unactive(queue)                                                         \
> +	((atomic_read(&((queue).active_state)) == false) &&                                        \
> +	 (atomic_read(&((queue).alloc_cnt)) == 0))
> diff --git a/drivers/block/blk-snap/blk_util.c b/drivers/block/blk-snap/blk_util.c
> new file mode 100644
> index 000000000000..57db70b86516
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk_util.c
> @@ -0,0 +1,33 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "common.h"
> +#include "blk_util.h"
> +
> +int blk_dev_open(dev_t dev_id, struct block_device **p_blk_dev)
> +{
> +	int result = SUCCESS;
> +	struct block_device *blk_dev;
> +	int refCount;
> +
> +	blk_dev = bdget(dev_id);
> +	if (blk_dev == NULL) {
> +		pr_err("Unable to open device [%d:%d]: bdget return NULL\n", MAJOR(dev_id),
> +		       MINOR(dev_id));
> +		return -ENODEV;
> +	}
> +
> +	refCount = blkdev_get(blk_dev, FMODE_READ | FMODE_WRITE, NULL);
> +	if (refCount < 0) {
> +		pr_err("Unable to open device [%d:%d]: blkdev_get return error code %d\n",
> +		       MAJOR(dev_id), MINOR(dev_id), 0 - refCount);
> +		result = refCount;
> +	}
> +
> +	if (result == SUCCESS)
> +		*p_blk_dev = blk_dev;
> +	return result;
> +}
> +
> +void blk_dev_close(struct block_device *blk_dev)
> +{
> +	blkdev_put(blk_dev, FMODE_READ);
> +}
> diff --git a/drivers/block/blk-snap/blk_util.h b/drivers/block/blk-snap/blk_util.h
> new file mode 100644
> index 000000000000..0776f2faa668
> --- /dev/null
> +++ b/drivers/block/blk-snap/blk_util.h
> @@ -0,0 +1,33 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +int blk_dev_open(dev_t dev_id, struct block_device **p_blk_dev);
> +void blk_dev_close(struct block_device *blk_dev);
> +
> +/*
> + * this function was copied from block/blk.h
> + */
> +static inline sector_t part_nr_sects_read(struct hd_struct *part)
> +{
> +#if (BITS_PER_LONG == 32) && defined(CONFIG_SMP)
> +	sector_t nr_sects;
> +	unsigned int seq;
> +
> +	do {
> +		seq = read_seqcount_begin(&part->nr_sects_seq);
> +		nr_sects = part->nr_sects;
> +	} while (read_seqcount_retry(&part->nr_sects_seq, seq));
> +
> +	return nr_sects;
> +#elif (BITS_PER_LONG == 32) && defined(CONFIG_PREEMPTION)
> +	sector_t nr_sects;
> +
> +	preempt_disable();
> +	nr_sects = part->nr_sects;
> +	preempt_enable();
> +
> +	return nr_sects;
> +#else
> +	return part->nr_sects;
> +#endif
> +}
> diff --git a/drivers/block/blk-snap/cbt_map.c b/drivers/block/blk-snap/cbt_map.c
> new file mode 100644
> index 000000000000..e913069d1a57
> --- /dev/null
> +++ b/drivers/block/blk-snap/cbt_map.c
> @@ -0,0 +1,210 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-cbt_map"
> +#include "common.h"
> +#include "cbt_map.h"
> +
> +int cbt_map_allocate(struct cbt_map *cbt_map, unsigned int cbt_sect_in_block_degree,
> +		     sector_t device_capacity)
> +{
> +	sector_t size_mod;
> +
> +	cbt_map->sect_in_block_degree = cbt_sect_in_block_degree;
> +	cbt_map->device_capacity = device_capacity;
> +	cbt_map->map_size = (device_capacity >> (sector_t)cbt_sect_in_block_degree);
> +
> +	pr_info("Allocate CBT map of %zu\n", cbt_map->map_size);
> +
> +	size_mod = (device_capacity & ((sector_t)(1 << cbt_sect_in_block_degree) - 1));
> +	if (size_mod)
> +		cbt_map->map_size++;
> +
> +	cbt_map->read_map = big_buffer_alloc(cbt_map->map_size, GFP_KERNEL);
> +	if (cbt_map->read_map != NULL)
> +		big_buffer_memset(cbt_map->read_map, 0);
> +
> +	cbt_map->write_map = big_buffer_alloc(cbt_map->map_size, GFP_KERNEL);
> +	if (cbt_map->write_map != NULL)
> +		big_buffer_memset(cbt_map->write_map, 0);
> +
> +	if ((cbt_map->read_map == NULL) || (cbt_map->write_map == NULL)) {
> +		pr_err("Cannot allocate CBT map. map_size=%zu\n", cbt_map->map_size);
> +		return -ENOMEM;
> +	}
> +
> +	cbt_map->snap_number_previous = 0;
> +	cbt_map->snap_number_active = 1;
> +	generate_random_uuid(cbt_map->generationId.b);
> +	cbt_map->active = true;
> +
> +	cbt_map->state_changed_sectors = 0;
> +	cbt_map->state_dirty_sectors = 0;
> +
> +	return SUCCESS;
> +}
> +
> +void cbt_map_deallocate(struct cbt_map *cbt_map)
> +{
> +	if (cbt_map->read_map != NULL) {
> +		big_buffer_free(cbt_map->read_map);
> +		cbt_map->read_map = NULL;
> +	}
> +
> +	if (cbt_map->write_map != NULL) {
> +		big_buffer_free(cbt_map->write_map);
> +		cbt_map->write_map = NULL;
> +	}
> +
> +	cbt_map->active = false;
> +}
> +
> +static void cbt_map_destroy(struct cbt_map *cbt_map)
> +{
> +	pr_info("CBT map destroy\n");
> +	if (cbt_map != NULL) {
> +		cbt_map_deallocate(cbt_map);
> +
> +		kfree(cbt_map);
> +	}
> +}
> +
> +struct cbt_map *cbt_map_create(unsigned int cbt_sect_in_block_degree, sector_t device_capacity)
> +{
> +	struct cbt_map *cbt_map = NULL;
> +
> +	pr_info("CBT map create\n");
> +
> +	cbt_map = kzalloc(sizeof(struct cbt_map), GFP_KERNEL);
> +	if (cbt_map == NULL)
> +		return NULL;
> +
> +	if (cbt_map_allocate(cbt_map, cbt_sect_in_block_degree, device_capacity) != SUCCESS) {
> +		cbt_map_destroy(cbt_map);
> +		return NULL;
> +	}
> +
> +	spin_lock_init(&cbt_map->locker);
> +	init_rwsem(&cbt_map->rw_lock);
> +	kref_init(&cbt_map->refcount);
> +
> +	return cbt_map;
> +}
> +
> +void cbt_map_destroy_cb(struct kref *kref)
> +{
> +	cbt_map_destroy(container_of(kref, struct cbt_map, refcount));
> +}
> +
> +struct cbt_map *cbt_map_get_resource(struct cbt_map *cbt_map)
> +{
> +	if (cbt_map)
> +		kref_get(&cbt_map->refcount);
> +
> +	return cbt_map;
> +}
> +
> +void cbt_map_put_resource(struct cbt_map *cbt_map)
> +{
> +	if (cbt_map)
> +		kref_put(&cbt_map->refcount, cbt_map_destroy_cb);
> +}
> +
> +void cbt_map_switch(struct cbt_map *cbt_map)
> +{
> +	pr_info("CBT map switch\n");
> +	spin_lock(&cbt_map->locker);
> +
> +	big_buffer_memcpy(cbt_map->read_map, cbt_map->write_map);
> +
> +	cbt_map->snap_number_previous = cbt_map->snap_number_active;
> +	++cbt_map->snap_number_active;
> +	if (cbt_map->snap_number_active == 256) {
> +		cbt_map->snap_number_active = 1;
> +
> +		big_buffer_memset(cbt_map->write_map, 0);
> +
> +		generate_random_uuid(cbt_map->generationId.b);
> +
> +		pr_info("CBT reset\n");
> +	}
> +	spin_unlock(&cbt_map->locker);
> +}
> +
> +int _cbt_map_set(struct cbt_map *cbt_map, sector_t sector_start, sector_t sector_cnt,
> +		 u8 snap_number, struct big_buffer *map)
> +{
> +	int res = SUCCESS;
> +	size_t cbt_block;
> +	size_t cbt_block_first = (size_t)(sector_start >> cbt_map->sect_in_block_degree);
> +	size_t cbt_block_last = (size_t)((sector_start + sector_cnt - 1) >>
> +					 cbt_map->sect_in_block_degree); //inclusive
> +
> +	for (cbt_block = cbt_block_first; cbt_block <= cbt_block_last; ++cbt_block) {
> +		if (cbt_block < cbt_map->map_size) {
> +			u8 num;
> +
> +			res = big_buffer_byte_get(map, cbt_block, &num);
> +			if (res == SUCCESS)
> +				if (num < snap_number)
> +					res = big_buffer_byte_set(map, cbt_block, snap_number);
> +		} else
> +			res = -EINVAL;
> +
> +		if (res != SUCCESS) {
> +			pr_err("Block index is too large. #%zu was demanded, map size %zu\n",
> +			       cbt_block, cbt_map->map_size);
> +			break;
> +		}
> +	}
> +	return res;
> +}
> +
> +int cbt_map_set(struct cbt_map *cbt_map, sector_t sector_start, sector_t sector_cnt)
> +{
> +	int res = SUCCESS;
> +
> +	spin_lock(&cbt_map->locker);
> +
> +	res = _cbt_map_set(cbt_map, sector_start, sector_cnt, (u8)cbt_map->snap_number_active,
> +			   cbt_map->write_map);
> +	cbt_map->state_changed_sectors += sector_cnt;
> +
> +	spin_unlock(&cbt_map->locker);
> +	return res;
> +}
> +
> +int cbt_map_set_both(struct cbt_map *cbt_map, sector_t sector_start, sector_t sector_cnt)
> +{
> +	int res = SUCCESS;
> +
> +	spin_lock(&cbt_map->locker);
> +
> +	res = _cbt_map_set(cbt_map, sector_start, sector_cnt,
> +			   (u8)cbt_map->snap_number_active, cbt_map->write_map);
> +	if (res == SUCCESS)
> +		res = _cbt_map_set(cbt_map, sector_start, sector_cnt,
> +				   (u8)cbt_map->snap_number_previous, cbt_map->read_map);
> +	cbt_map->state_dirty_sectors += sector_cnt;
> +
> +	spin_unlock(&cbt_map->locker);
> +	return res;
> +}
> +
> +size_t cbt_map_read_to_user(struct cbt_map *cbt_map, void __user *user_buff, size_t offset,
> +			    size_t size)
> +{
> +	size_t readed = 0;
> +	size_t left_size;
> +	size_t real_size = min((cbt_map->map_size - offset), size);
> +
> +	left_size = real_size -
> +		    big_buffer_copy_to_user(user_buff, offset, cbt_map->read_map, real_size);
> +
> +	if (left_size == 0)
> +		readed = real_size;
> +	else {
> +		pr_err("Not all CBT data was read. Left [%zu] bytes\n", left_size);
> +		readed = real_size - left_size;
> +	}
> +
> +	return readed;
> +}
> diff --git a/drivers/block/blk-snap/cbt_map.h b/drivers/block/blk-snap/cbt_map.h
> new file mode 100644
> index 000000000000..cb52b09531fe
> --- /dev/null
> +++ b/drivers/block/blk-snap/cbt_map.h
> @@ -0,0 +1,62 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +#include "big_buffer.h"
> +#include <linux/kref.h>
> +#include <linux/uuid.h>
> +
> +struct cbt_map {
> +	struct kref refcount;
> +
> +	spinlock_t locker;
> +
> +	size_t sect_in_block_degree;
> +	sector_t device_capacity;
> +	size_t map_size;
> +
> +	struct big_buffer *read_map;
> +	struct big_buffer *write_map;
> +
> +	unsigned long snap_number_active;
> +	unsigned long snap_number_previous;
> +	uuid_t generationId;
> +
> +	bool active;
> +
> +	struct rw_semaphore rw_lock;
> +
> +	sector_t state_changed_sectors;
> +	sector_t state_dirty_sectors;
> +};
> +
> +struct cbt_map *cbt_map_create(unsigned int cbt_sect_in_block_degree, sector_t device_capacity);
> +
> +struct cbt_map *cbt_map_get_resource(struct cbt_map *cbt_map);
> +void cbt_map_put_resource(struct cbt_map *cbt_map);
> +
> +void cbt_map_switch(struct cbt_map *cbt_map);
> +int cbt_map_set(struct cbt_map *cbt_map, sector_t sector_start, sector_t sector_cnt);
> +int cbt_map_set_both(struct cbt_map *cbt_map, sector_t sector_start, sector_t sector_cnt);
> +
> +size_t cbt_map_read_to_user(struct cbt_map *cbt_map, void __user *user_buffer, size_t offset,
> +			    size_t size);
> +
> +static inline void cbt_map_read_lock(struct cbt_map *cbt_map)
> +{
> +	down_read(&cbt_map->rw_lock);
> +};
> +
> +static inline void cbt_map_read_unlock(struct cbt_map *cbt_map)
> +{
> +	up_read(&cbt_map->rw_lock);
> +};
> +
> +static inline void cbt_map_write_lock(struct cbt_map *cbt_map)
> +{
> +	down_write(&cbt_map->rw_lock);
> +};
> +
> +static inline void cbt_map_write_unlock(struct cbt_map *cbt_map)
> +{
> +	up_write(&cbt_map->rw_lock);
> +};
> diff --git a/drivers/block/blk-snap/common.h b/drivers/block/blk-snap/common.h
> new file mode 100644
> index 000000000000..bbd5e98ab2a6
> --- /dev/null
> +++ b/drivers/block/blk-snap/common.h
> @@ -0,0 +1,31 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +#ifndef BLK_SNAP_SECTION
> +#define BLK_SNAP_SECTION ""
> +#endif
> +#define pr_fmt(fmt) KBUILD_MODNAME BLK_SNAP_SECTION ": " fmt
> +
> +#include <linux/version.h> /*rudiment - needed for using KERNEL_VERSION */
> +
> +#include <linux/types.h>
> +#include <linux/errno.h>
> +#include <linux/mutex.h>
> +#include <linux/rwsem.h>
> +#include <linux/spinlock.h>
> +#include <linux/slab.h>
> +#include <linux/list.h>
> +#include <linux/atomic.h>
> +#include <linux/blkdev.h>
> +
> +#define from_sectors(_sectors) (_sectors << SECTOR_SHIFT)
> +#define to_sectors(_byte_size) (_byte_size >> SECTOR_SHIFT)
> +
> +struct blk_range {
> +	sector_t ofs;
> +	blkcnt_t cnt;
> +};
> +
> +#ifndef SUCCESS
> +#define SUCCESS 0
> +#endif
> diff --git a/drivers/block/blk-snap/ctrl_fops.c b/drivers/block/blk-snap/ctrl_fops.c
> new file mode 100644
> index 000000000000..b7b18539ee96
> --- /dev/null
> +++ b/drivers/block/blk-snap/ctrl_fops.c
> @@ -0,0 +1,691 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-ctrl"
> +#include "common.h"
> +#include "blk-snap-ctl.h"
> +#include "ctrl_fops.h"
> +#include "version.h"
> +#include "tracking.h"
> +#include "snapshot.h"
> +#include "snapstore.h"
> +#include "snapimage.h"
> +#include "tracker.h"
> +#include "blk_deferred.h"
> +#include "big_buffer.h"
> +#include "params.h"
> +
> +#include <linux/module.h>
> +#include <linux/poll.h>
> +#include <linux/uaccess.h>
> +
> +int blk_snap_major; //zero by default
> +
> +const struct file_operations ctrl_fops = { .owner = THIS_MODULE,
> +					   .read = ctrl_read,
> +					   .write = ctrl_write,
> +					   .open = ctrl_open,
> +					   .release = ctrl_release,
> +					   .poll = ctrl_poll,
> +					   .unlocked_ioctl = ctrl_unlocked_ioctl };
> +
> +atomic_t dev_open_cnt = ATOMIC_INIT(0);
> +
> +const struct ioctl_getversion_s version = { .major = FILEVER_MAJOR,
> +					    .minor = FILEVER_MINOR,
> +					    .revision = FILEVER_REVISION,
> +					    .build = 0 };
> +
> +int get_blk_snap_major(void)
> +{
> +	return blk_snap_major;
> +}
> +
> +int ctrl_init(void)
> +{
> +	int ret;
> +
> +	ret = register_chrdev(0, MODULE_NAME, &ctrl_fops);
> +	if (ret < 0) {
> +		pr_err("Failed to register a character device. errno=%d\n", blk_snap_major);
> +		return ret;
> +	}
> +
> +	blk_snap_major = ret;
> +	pr_info("Module major [%d]\n", blk_snap_major);
> +	return SUCCESS;
> +}
> +
> +void ctrl_done(void)
> +{
> +	unregister_chrdev(blk_snap_major, MODULE_NAME);
> +	ctrl_pipe_done();
> +}
> +
> +ssize_t ctrl_read(struct file *fl, char __user *buffer, size_t length, loff_t *offset)
> +{
> +	ssize_t bytes_read = 0;
> +	struct ctrl_pipe *pipe = (struct ctrl_pipe *)fl->private_data;
> +
> +	if (pipe == NULL) {
> +		pr_err("Unable to read from pipe: invalid pipe pointer\n");
> +		return -EINVAL;
> +	}
> +
> +	bytes_read = ctrl_pipe_read(pipe, buffer, length);
> +	if (bytes_read == 0)
> +		if (fl->f_flags & O_NONBLOCK)
> +			bytes_read = -EAGAIN;
> +
> +	return bytes_read;
> +}
> +
> +ssize_t ctrl_write(struct file *fl, const char __user *buffer, size_t length, loff_t *offset)
> +{
> +	struct ctrl_pipe *pipe = (struct ctrl_pipe *)fl->private_data;
> +
> +	if (pipe == NULL) {
> +		pr_err("Unable to write into pipe: invalid pipe pointer\n");
> +		return -EINVAL;
> +	}
> +
> +	return ctrl_pipe_write(pipe, buffer, length);
> +}
> +
> +unsigned int ctrl_poll(struct file *fl, struct poll_table_struct *wait)
> +{
> +	struct ctrl_pipe *pipe = (struct ctrl_pipe *)fl->private_data;
> +
> +	if (pipe == NULL) {
> +		pr_err("Unable to poll pipe: invalid pipe pointer\n");
> +		return -EINVAL;
> +	}
> +
> +	return ctrl_pipe_poll(pipe);
> +}
> +
> +int ctrl_open(struct inode *inode, struct file *fl)
> +{
> +	fl->f_pos = 0;
> +
> +	if (false == try_module_get(THIS_MODULE))
> +		return -EINVAL;
> +
> +	fl->private_data = (void *)ctrl_pipe_new();
> +	if (fl->private_data == NULL) {
> +		pr_err("Failed to open ctrl file\n");
> +		return -ENOMEM;
> +	}
> +
> +	atomic_inc(&dev_open_cnt);
> +
> +	return SUCCESS;
> +}
> +
> +int ctrl_release(struct inode *inode, struct file *fl)
> +{
> +	int result = SUCCESS;
> +
> +	if (atomic_read(&dev_open_cnt) > 0) {
> +		module_put(THIS_MODULE);
> +		ctrl_pipe_put_resource((struct ctrl_pipe *)fl->private_data);
> +
> +		atomic_dec(&dev_open_cnt);
> +	} else {
> +		pr_err("Unable to close ctrl file: the file is already closed\n");
> +		result = -EALREADY;
> +	}
> +
> +	return result;
> +}
> +
> +int ioctl_compatibility_flags(unsigned long arg)
> +{
> +	unsigned long len;
> +	struct ioctl_compatibility_flags_s param;
> +
> +	param.flags = 0;
> +	param.flags |= BLK_SNAP_COMPATIBILITY_SNAPSTORE;
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +	param.flags |= BLK_SNAP_COMPATIBILITY_MULTIDEV;
> +#endif
> +	len = copy_to_user((void *)arg, &param, sizeof(struct ioctl_compatibility_flags_s));
> +	if (len != 0) {
> +		pr_err("Unable to get compatibility flags: invalid user buffer\n");
> +		return -EINVAL;
> +	}
> +
> +	return SUCCESS;
> +}
> +
> +int ioctl_get_version(unsigned long arg)
> +{
> +	unsigned long len;
> +
> +	pr_info("Get version\n");
> +
> +	len = copy_to_user((void *)arg, &version, sizeof(struct ioctl_getversion_s));
> +	if (len != 0) {
> +		pr_err("Unable to get version: invalid user buffer\n");
> +		return -ENODATA;
> +	}
> +
> +	return SUCCESS;
> +}
> +
> +int ioctl_tracking_add(unsigned long arg)
> +{
> +	unsigned long len;
> +	struct ioctl_dev_id_s dev;
> +
> +	len = copy_from_user(&dev, (void *)arg, sizeof(struct ioctl_dev_id_s));
> +	if (len != 0) {
> +		pr_err("Unable to add device under tracking: invalid user buffer\n");
> +		return -ENODATA;
> +	}
> +
> +	return tracking_add(MKDEV(dev.major, dev.minor), 0ull);
> +}
> +
> +int ioctl_tracking_remove(unsigned long arg)
> +{
> +	struct ioctl_dev_id_s dev;
> +
> +	if (copy_from_user(&dev, (void *)arg, sizeof(struct ioctl_dev_id_s)) != 0) {
> +		pr_err("Unable to remove device from tracking: invalid user buffer\n");
> +		return -ENODATA;
> +	}
> +	return tracking_remove(MKDEV(dev.major, dev.minor));
> +	;
> +}
> +
> +int ioctl_tracking_collect(unsigned long arg)
> +{
> +	unsigned long len;
> +	int res;
> +	struct ioctl_tracking_collect_s get;
> +
> +	pr_info("Collecting tracking devices:\n");
> +
> +	len = copy_from_user(&get, (void *)arg, sizeof(struct ioctl_tracking_collect_s));
> +	if (len  != 0) {
> +		pr_err("Unable to collect tracking devices: invalid user buffer\n");
> +		return -ENODATA;
> +	}
> +
> +	if (get.p_cbt_info == NULL) {
> +		res = tracking_collect(0x7FFFffff, NULL, &get.count);
> +		if (res == SUCCESS) {
> +			len = copy_to_user((void *)arg, (void *)&get,
> +					   sizeof(struct ioctl_tracking_collect_s));
> +			if (len != 0) {
> +				pr_err("Unable to collect tracking devices: invalid user buffer for arguments\n");
> +				res = -ENODATA;
> +			}
> +		} else {
> +			pr_err("Failed to execute tracking_collect. errno=%d\n", res);
> +		}
> +	} else {
> +		struct cbt_info_s *p_cbt_info = NULL;
> +
> +		p_cbt_info = kcalloc(get.count, sizeof(struct cbt_info_s), GFP_KERNEL);
> +		if (p_cbt_info == NULL)
> +			return -ENOMEM;
> +
> +		do {
> +			res = tracking_collect(get.count, p_cbt_info, &get.count);
> +			if (res != SUCCESS) {
> +				pr_err("Failed to execute tracking_collect. errno=%d\n", res);
> +				break;
> +			}
> +			len = copy_to_user(get.p_cbt_info, p_cbt_info,
> +					      get.count * sizeof(struct cbt_info_s));
> +			if (len != 0) {
> +				pr_err("Unable to collect tracking devices: invalid user buffer for CBT info\n");
> +				res = -ENODATA;
> +				break;
> +			}
> +
> +			len = copy_to_user((void *)arg, (void *)&get,
> +					   sizeof(struct ioctl_tracking_collect_s));
> +			if (len != 0) {
> +				pr_err("Unable to collect tracking devices: invalid user buffer for arguments\n");
> +				res = -ENODATA;
> +				break;
> +			}
> +
> +		} while (false);
> +
> +		kfree(p_cbt_info);
> +		p_cbt_info = NULL;
> +	}
> +	return res;
> +}
> +
> +int ioctl_tracking_block_size(unsigned long arg)
> +{
> +	unsigned long len;
> +	unsigned int blk_sz = change_tracking_block_size();
> +
> +	len = copy_to_user((void *)arg, &blk_sz, sizeof(unsigned int));
> +	if (len != 0) {
> +		pr_err("Unable to get tracking block size: invalid user buffer for arguments\n");
> +		return -ENODATA;
> +	}
> +	return SUCCESS;
> +}
> +
> +int ioctl_tracking_read_cbt_map(unsigned long arg)
> +{
> +	dev_t dev_id;
> +	unsigned long len;
> +	struct ioctl_tracking_read_cbt_bitmap_s readbitmap;
> +
> +	len = copy_from_user(&readbitmap, (void *)arg,
> +				sizeof(struct ioctl_tracking_read_cbt_bitmap_s));
> +	if (len != 0) {
> +		pr_err("Unable to read CBT map: invalid user buffer\n");
> +		return -ENODATA;
> +	}
> +
> +	dev_id = MKDEV(readbitmap.dev_id.major, readbitmap.dev_id.minor);
> +	return tracking_read_cbt_bitmap(dev_id, readbitmap.offset, readbitmap.length,
> +					(void *)readbitmap.buff);
> +}
> +
> +int ioctl_tracking_mark_dirty_blocks(unsigned long arg)
> +{
> +	unsigned long len;
> +	struct ioctl_tracking_mark_dirty_blocks_s param;
> +	struct block_range_s *p_dirty_blocks;
> +	size_t buffer_size;
> +	int result = SUCCESS;
> +
> +	len = copy_from_user(&param, (void *)arg,
> +			     sizeof(struct ioctl_tracking_mark_dirty_blocks_s));
> +	if (len != 0) {
> +		pr_err("Unable to mark dirty blocks: invalid user buffer\n");
> +		return -ENODATA;
> +	}
> +
> +	buffer_size = param.count * sizeof(struct block_range_s);
> +	p_dirty_blocks = kzalloc(buffer_size, GFP_KERNEL);
> +	if (p_dirty_blocks == NULL) {
> +		pr_err("Unable to mark dirty blocks: cannot allocate [%zu] bytes\n", buffer_size);
> +		return -ENOMEM;
> +	}
> +
> +	do {
> +		dev_t image_dev_id;
> +
> +		len = copy_from_user(p_dirty_blocks, (void *)param.p_dirty_blocks, buffer_size);
> +		if (len != 0) {
> +			pr_err("Unable to mark dirty blocks: invalid user buffer\n");
> +			result = -ENODATA;
> +			break;
> +		}
> +
> +		image_dev_id = MKDEV(param.image_dev_id.major, param.image_dev_id.minor);
> +		result = snapimage_mark_dirty_blocks(image_dev_id, p_dirty_blocks, param.count);
> +	} while (false);
> +	kfree(p_dirty_blocks);
> +
> +	return result;
> +}
> +
> +int ioctl_snapshot_create(unsigned long arg)
> +{
> +	unsigned long len;
> +	size_t dev_id_buffer_size;
> +	int status;
> +	struct ioctl_snapshot_create_s param;
> +	struct ioctl_dev_id_s *pk_dev_id = NULL;
> +
> +	len = copy_from_user(&param, (void *)arg, sizeof(struct ioctl_snapshot_create_s));
> +	if (len != 0) {
> +		pr_err("Unable to create snapshot: invalid user buffer\n");
> +		return -ENODATA;
> +	}
> +
> +	dev_id_buffer_size = sizeof(struct ioctl_dev_id_s) * param.count;
> +	pk_dev_id = kzalloc(dev_id_buffer_size, GFP_KERNEL);
> +	if (pk_dev_id == NULL) {
> +		pr_err("Unable to create snapshot: cannot allocate [%zu] bytes\n",
> +		       dev_id_buffer_size);
> +		return -ENOMEM;
> +	}
> +
> +	do {
> +		size_t dev_buffer_size;
> +		dev_t *p_dev = NULL;
> +		int inx = 0;
> +
> +		len = copy_from_user(pk_dev_id, (void *)param.p_dev_id,
> +				     param.count * sizeof(struct ioctl_dev_id_s));
> +		if (len != 0) {
> +			pr_err("Unable to create snapshot: invalid user buffer for parameters\n");
> +			status = -ENODATA;
> +			break;
> +		}
> +
> +		dev_buffer_size = sizeof(dev_t) * param.count;
> +		p_dev = kzalloc(dev_buffer_size, GFP_KERNEL);
> +		if (p_dev == NULL) {
> +			pr_err("Unable to create snapshot: cannot allocate [%zu] bytes\n",
> +			       dev_buffer_size);
> +			status = -ENOMEM;
> +			break;
> +		}
> +
> +		for (inx = 0; inx < param.count; ++inx)
> +			p_dev[inx] = MKDEV(pk_dev_id[inx].major, pk_dev_id[inx].minor);
> +
> +		status = snapshot_create(p_dev, param.count, &param.snapshot_id);
> +
> +		kfree(p_dev);
> +		p_dev = NULL;
> +
> +	} while (false);
> +	kfree(pk_dev_id);
> +	pk_dev_id = NULL;
> +
> +	if (status == SUCCESS) {
> +		len = copy_to_user((void *)arg, &param, sizeof(struct ioctl_snapshot_create_s));
> +		if (len != 0) {
> +			pr_err("Unable to create snapshot: invalid user buffer\n");
> +			status = -ENODATA;
> +		}
> +	}
> +
> +	return status;
> +}
> +
> +int ioctl_snapshot_destroy(unsigned long arg)
> +{
> +	unsigned long len;
> +	unsigned long long param;
> +
> +	len = copy_from_user(&param, (void *)arg, sizeof(unsigned long long));
> +	if (len != 0) {
> +		pr_err("Unable to destroy snapshot: invalid user buffer\n");
> +		return -ENODATA;
> +	}
> +
> +	return snapshot_destroy(param);
> +}
> +
> +static inline dev_t _snapstore_dev(struct ioctl_dev_id_s *dev_id)
> +{
> +	if ((dev_id->major == 0) && (dev_id->minor == 0))
> +		return 0; //memory snapstore
> +
> +	if ((dev_id->major == -1) && (dev_id->minor == -1))
> +		return 0xFFFFffff; //multidevice snapstore
> +
> +	return MKDEV(dev_id->major, dev_id->minor);
> +}
> +
> +int ioctl_snapstore_create(unsigned long arg)
> +{
> +	unsigned long len;
> +	int res = SUCCESS;
> +	struct ioctl_snapstore_create_s param;
> +	size_t inx = 0;
> +	dev_t *dev_id_set = NULL;
> +
> +	len = copy_from_user(&param, (void *)arg, sizeof(struct ioctl_snapstore_create_s));
> +	if (len != 0) {
> +		pr_err("Unable to create snapstore: invalid user buffer\n");
> +		return -EINVAL;
> +	}
> +
> +	dev_id_set = kcalloc(param.count, sizeof(dev_t), GFP_KERNEL);
> +	if (dev_id_set == NULL)
> +		return -ENOMEM;
> +
> +	for (inx = 0; inx < param.count; ++inx) {
> +		struct ioctl_dev_id_s dev_id;
> +
> +		len = copy_from_user(&dev_id, param.p_dev_id + inx, sizeof(struct ioctl_dev_id_s));
> +		if (len != 0) {
> +			pr_err("Unable to create snapstore: ");
> +			pr_err("invalid user buffer for parameters\n");
> +
> +			res = -ENODATA;
> +			break;
> +		}
> +
> +		dev_id_set[inx] = MKDEV(dev_id.major, dev_id.minor);
> +	}
> +
> +	if (res == SUCCESS)
> +		res = snapstore_create((uuid_t *)param.id, _snapstore_dev(&param.snapstore_dev_id),
> +				       dev_id_set, (size_t)param.count);
> +
> +	kfree(dev_id_set);
> +
> +	return res;
> +}
> +
> +int ioctl_snapstore_file(unsigned long arg)
> +{
> +	unsigned long len;
> +	int res = SUCCESS;
> +	struct ioctl_snapstore_file_add_s param;
> +	struct big_buffer *ranges = NULL;
> +	size_t ranges_buffer_size;
> +
> +	len = copy_from_user(&param, (void *)arg, sizeof(struct ioctl_snapstore_file_add_s));
> +	if (len != 0) {
> +		pr_err("Unable to add file to snapstore: invalid user buffer\n");
> +		return -EINVAL;
> +	}
> +
> +	ranges_buffer_size = sizeof(struct ioctl_range_s) * param.range_count;
> +
> +	ranges = big_buffer_alloc(ranges_buffer_size, GFP_KERNEL);
> +	if (ranges == NULL) {
> +		pr_err("Unable to add file to snapstore: cannot allocate [%zu] bytes\n",
> +		       ranges_buffer_size);
> +		return -ENOMEM;
> +	}
> +
> +	if (big_buffer_copy_from_user((void *)param.ranges, 0, ranges, ranges_buffer_size)
> +		!= ranges_buffer_size) {
> +
> +		pr_err("Unable to add file to snapstore: invalid user buffer for parameters\n");
> +		res = -ENODATA;
> +	} else
> +		res = snapstore_add_file((uuid_t *)(param.id), ranges, (size_t)param.range_count);
> +
> +	big_buffer_free(ranges);
> +
> +	return res;
> +}
> +
> +int ioctl_snapstore_memory(unsigned long arg)
> +{
> +	unsigned long len;
> +	int res = SUCCESS;
> +	struct ioctl_snapstore_memory_limit_s param;
> +
> +	len = copy_from_user(&param, (void *)arg, sizeof(struct ioctl_snapstore_memory_limit_s));
> +	if (len != 0) {
> +		pr_err("Unable to add memory block to snapstore: invalid user buffer\n");
> +		return -EINVAL;
> +	}
> +
> +	res = snapstore_add_memory((uuid_t *)param.id, param.size);
> +
> +	return res;
> +}
> +int ioctl_snapstore_cleanup(unsigned long arg)
> +{
> +	unsigned long len;
> +	int res = SUCCESS;
> +	struct ioctl_snapstore_cleanup_s param;
> +
> +	len = copy_from_user(&param, (void *)arg, sizeof(struct ioctl_snapstore_cleanup_s));
> +	if (len != 0) {
> +		pr_err("Unable to perform snapstore cleanup: invalid user buffer\n");
> +		return -EINVAL;
> +	}
> +
> +	pr_info("Cleanup snapstore %pUB\n", (uuid_t *)param.id);
> +	res = snapstore_cleanup((uuid_t *)param.id, &param.filled_bytes);
> +
> +	if (res == SUCCESS) {
> +		if (0 !=
> +		    copy_to_user((void *)arg, &param, sizeof(struct ioctl_snapstore_cleanup_s))) {
> +			pr_err("Unable to perform snapstore cleanup: invalid user buffer\n");
> +			res = -ENODATA;
> +		}
> +	}
> +
> +	return res;
> +}
> +
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +int ioctl_snapstore_file_multidev(unsigned long arg)
> +{
> +	unsigned long len;
> +	int res = SUCCESS;
> +	struct ioctl_snapstore_file_add_multidev_s param;
> +	struct big_buffer *ranges = NULL; //struct ioctl_range_s* ranges = NULL;
> +	size_t ranges_buffer_size;
> +
> +	len = copy_from_user(&param, (void *)arg,
> +				sizeof(struct ioctl_snapstore_file_add_multidev_s));
> +	if (len != 0) {
> +		pr_err("Unable to add file to multidev snapstore: invalid user buffer\n");
> +		return -EINVAL;
> +	}
> +
> +	ranges_buffer_size = sizeof(struct ioctl_range_s) * param.range_count;
> +
> +	ranges = big_buffer_alloc(ranges_buffer_size, GFP_KERNEL);
> +	if (ranges == NULL) {
> +		pr_err("Unable to add file to multidev snapstore: cannot allocate [%zu] bytes\n",
> +		       ranges_buffer_size);
> +		return -ENOMEM;
> +	}
> +
> +	do {
> +		uuid_t *id = (uuid_t *)(param.id);
> +		dev_t snapstore_device = MKDEV(param.dev_id.major, param.dev_id.minor);
> +		size_t ranges_cnt = (size_t)param.range_count;
> +
> +		if (ranges_buffer_size != big_buffer_copy_from_user((void *)param.ranges, 0, ranges,
> +								    ranges_buffer_size)) {
> +			pr_err("Unable to add file to snapstore: invalid user buffer for parameters\n");
> +			res = -ENODATA;
> +			break;
> +		}
> +
> +		res = snapstore_add_multidev(id, snapstore_device, ranges, ranges_cnt);
> +	} while (false);
> +	big_buffer_free(ranges);
> +
> +	return res;
> +}
> +
> +#endif
> +//////////////////////////////////////////////////////////////////////////
> +
> +/*
> + * Snapshot get errno for device
> + */
> +int ioctl_snapshot_errno(unsigned long arg)
> +{
> +	unsigned long len;
> +	int res;
> +	struct ioctl_snapshot_errno_s param;
> +
> +	len = copy_from_user(&param, (void *)arg, sizeof(struct ioctl_dev_id_s));
> +	if (len != 0) {
> +		pr_err("Unable failed to get snapstore error code: invalid user buffer\n");
> +		return -EINVAL;
> +	}
> +
> +	res = snapstore_device_errno(MKDEV(param.dev_id.major, param.dev_id.minor),
> +				     &param.err_code);
> +
> +	if (res != SUCCESS)
> +		return res;
> +
> +	len = copy_to_user((void *)arg, &param, sizeof(struct ioctl_snapshot_errno_s));
> +	if (len != 0) {
> +		pr_err("Unable to get snapstore error code: invalid user buffer\n");
> +		return -EINVAL;
> +	}
> +
> +	return SUCCESS;
> +}
> +
> +int ioctl_collect_snapimages(unsigned long arg)
> +{
> +	unsigned long len;
> +	int status = SUCCESS;
> +	struct ioctl_collect_snapshot_images_s param;
> +
> +	len = copy_from_user(&param, (void *)arg, sizeof(struct ioctl_collect_snapshot_images_s));
> +	if (len != 0) {
> +		pr_err("Unable to collect snapshot images: invalid user buffer\n");
> +		return -ENODATA;
> +	}
> +
> +	status = snapimage_collect_images(param.count, param.p_image_info, &param.count);
> +
> +	len = copy_to_user((void *)arg, &param, sizeof(struct ioctl_collect_snapshot_images_s));
> +	if (len != 0) {
> +		pr_err("Unable to collect snapshot images: invalid user buffer\n");
> +		return -ENODATA;
> +	}
> +
> +	return status;
> +}
> +
> +struct blk_snap_ioctl_table {
> +	unsigned int cmd;
> +	int (*fn)(unsigned long arg);
> +};
> +
> +static struct blk_snap_ioctl_table blk_snap_ioctl_table[] = {
> +	{ (IOCTL_COMPATIBILITY_FLAGS), ioctl_compatibility_flags },
> +	{ (IOCTL_GETVERSION), ioctl_get_version },
> +
> +	{ (IOCTL_TRACKING_ADD), ioctl_tracking_add },
> +	{ (IOCTL_TRACKING_REMOVE), ioctl_tracking_remove },
> +	{ (IOCTL_TRACKING_COLLECT), ioctl_tracking_collect },
> +	{ (IOCTL_TRACKING_BLOCK_SIZE), ioctl_tracking_block_size },
> +	{ (IOCTL_TRACKING_READ_CBT_BITMAP), ioctl_tracking_read_cbt_map },
> +	{ (IOCTL_TRACKING_MARK_DIRTY_BLOCKS), ioctl_tracking_mark_dirty_blocks },
> +
> +	{ (IOCTL_SNAPSHOT_CREATE), ioctl_snapshot_create },
> +	{ (IOCTL_SNAPSHOT_DESTROY), ioctl_snapshot_destroy },
> +	{ (IOCTL_SNAPSHOT_ERRNO), ioctl_snapshot_errno },
> +
> +	{ (IOCTL_SNAPSTORE_CREATE), ioctl_snapstore_create },
> +	{ (IOCTL_SNAPSTORE_FILE), ioctl_snapstore_file },
> +	{ (IOCTL_SNAPSTORE_MEMORY), ioctl_snapstore_memory },
> +	{ (IOCTL_SNAPSTORE_CLEANUP), ioctl_snapstore_cleanup },
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +	{ (IOCTL_SNAPSTORE_FILE_MULTIDEV), ioctl_snapstore_file_multidev },
> +#endif
> +	{ (IOCTL_COLLECT_SNAPSHOT_IMAGES), ioctl_collect_snapimages },
> +	{ 0, NULL }
> +};
> +
> +long ctrl_unlocked_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> +{
> +	long status = -ENOTTY;
> +	size_t inx = 0;
> +
> +	while (blk_snap_ioctl_table[inx].cmd != 0) {
> +		if (blk_snap_ioctl_table[inx].cmd == cmd) {
> +			status = blk_snap_ioctl_table[inx].fn(arg);
> +			break;
> +		}
> +		++inx;
> +	}
> +
> +	return status;
> +}
> diff --git a/drivers/block/blk-snap/ctrl_fops.h b/drivers/block/blk-snap/ctrl_fops.h
> new file mode 100644
> index 000000000000..98072b61aa96
> --- /dev/null
> +++ b/drivers/block/blk-snap/ctrl_fops.h
> @@ -0,0 +1,19 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +#include <linux/fs.h>
> +
> +int get_blk_snap_major(void);
> +
> +int ctrl_init(void);
> +void ctrl_done(void);
> +
> +int ctrl_open(struct inode *inode, struct file *file);
> +int ctrl_release(struct inode *inode, struct file *file);
> +
> +ssize_t ctrl_read(struct file *filp, char __user *buffer, size_t length, loff_t *offset);
> +ssize_t ctrl_write(struct file *filp, const char __user *buffer, size_t length, loff_t *offset);
> +
> +unsigned int ctrl_poll(struct file *filp, struct poll_table_struct *wait);
> +
> +long ctrl_unlocked_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
> diff --git a/drivers/block/blk-snap/ctrl_pipe.c b/drivers/block/blk-snap/ctrl_pipe.c
> new file mode 100644
> index 000000000000..73cfbca93487
> --- /dev/null
> +++ b/drivers/block/blk-snap/ctrl_pipe.c
> @@ -0,0 +1,562 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-ctrl"
> +#include "common.h"
> +#include "ctrl_pipe.h"
> +#include "version.h"
> +#include "blk-snap-ctl.h"
> +#include "snapstore.h"
> +#include "big_buffer.h"
> +
> +#include <linux/poll.h>
> +#include <linux/uuid.h>
> +
> +#define CMD_TO_USER_FIFO_SIZE 1024
> +
> +LIST_HEAD(ctl_pipes);
> +DECLARE_RWSEM(ctl_pipes_lock);
> +
> +
> +static void ctrl_pipe_push_request(struct ctrl_pipe *pipe, unsigned int *cmd, size_t cmd_len)
> +{
> +	kfifo_in_spinlocked(&pipe->cmd_to_user, cmd, (cmd_len * sizeof(unsigned int)),
> +			    &pipe->cmd_to_user_lock);
> +
> +	wake_up(&pipe->readq);
> +}
> +
> +static void ctrl_pipe_request_acknowledge(struct ctrl_pipe *pipe, unsigned int result)
> +{
> +	unsigned int cmd[2];
> +
> +	cmd[0] = BLK_SNAP_CHARCMD_ACKNOWLEDGE;
> +	cmd[1] = result;
> +
> +	ctrl_pipe_push_request(pipe, cmd, 2);
> +}
> +
> +static inline dev_t _snapstore_dev(struct ioctl_dev_id_s *dev_id)
> +{
> +	if ((dev_id->major == 0) && (dev_id->minor == 0))
> +		return 0; //memory snapstore
> +
> +	if ((dev_id->major == -1) && (dev_id->minor == -1))
> +		return 0xFFFFffff; //multidevice snapstore
> +
> +	return MKDEV(dev_id->major, dev_id->minor);
> +}
> +
> +static ssize_t ctrl_pipe_command_initiate(struct ctrl_pipe *pipe, const char __user *buffer,
> +					  size_t length)
> +{
> +	unsigned long len;
> +	int result = SUCCESS;
> +	ssize_t processed = 0;
> +	char *kernel_buffer;
> +
> +	kernel_buffer = kmalloc(length, GFP_KERNEL);
> +	if (kernel_buffer == NULL)
> +		return -ENOMEM;
> +
> +	len = copy_from_user(kernel_buffer, buffer, length);
> +	if (len != 0) {
> +		kfree(kernel_buffer);
> +		pr_err("Unable to write to pipe: invalid user buffer\n");
> +		return -EINVAL;
> +	}
> +
> +	do {
> +		u64 stretch_empty_limit;
> +		unsigned int dev_id_list_length;
> +		uuid_t *unique_id;
> +		struct ioctl_dev_id_s *snapstore_dev_id;
> +		struct ioctl_dev_id_s *dev_id_list;
> +
> +		//get snapstore uuid
> +		if ((length - processed) < 16) {
> +			pr_err("Unable to get snapstore uuid: invalid ctrl pipe initiate command. length=%zu\n",
> +			       length);
> +			break;
> +		}
> +		unique_id = (uuid_t *)(kernel_buffer + processed);
> +		processed += 16;
> +
> +		//get snapstore empty limit
> +		if ((length - processed) < sizeof(u64)) {
> +			pr_err("Unable to get stretch snapstore limit: invalid ctrl pipe initiate command. length=%zu\n",
> +			       length);
> +			break;
> +		}
> +		stretch_empty_limit = *(u64 *)(kernel_buffer + processed);
> +		processed += sizeof(u64);
> +
> +		//get snapstore device id
> +		if ((length - processed) < sizeof(struct ioctl_dev_id_s)) {
> +			pr_err("Unable to get snapstore device id: invalid ctrl pipe initiate command. length=%zu\n",
> +			       length);
> +			break;
> +		}
> +		snapstore_dev_id = (struct ioctl_dev_id_s *)(kernel_buffer + processed);
> +		processed += sizeof(struct ioctl_dev_id_s);
> +
> +		//get device id list length
> +		if ((length - processed) < 4) {
> +			pr_err("Unable to get device id list length: ivalid ctrl pipe initiate command. length=%zu\n",
> +			       length);
> +			break;
> +		}
> +		dev_id_list_length = *(unsigned int *)(kernel_buffer + processed);
> +		processed += sizeof(unsigned int);
> +
> +		//get devices id list
> +		if ((length - processed) < (dev_id_list_length * sizeof(struct ioctl_dev_id_s))) {
> +			pr_err("Unable to get all devices from device id list: invalid ctrl pipe initiate command. length=%zu\n",
> +			       length);
> +			break;
> +		}
> +		dev_id_list = (struct ioctl_dev_id_s *)(kernel_buffer + processed);
> +		processed += (dev_id_list_length * sizeof(struct ioctl_dev_id_s));
> +
> +		{
> +			size_t inx;
> +			dev_t *dev_set;
> +			size_t dev_id_set_length = (size_t)dev_id_list_length;
> +
> +			dev_set = kcalloc(dev_id_set_length, sizeof(dev_t), GFP_KERNEL);
> +			if (dev_set == NULL) {
> +				result = -ENOMEM;
> +				break;
> +			}
> +
> +			for (inx = 0; inx < dev_id_set_length; ++inx)
> +				dev_set[inx] =
> +					MKDEV(dev_id_list[inx].major, dev_id_list[inx].minor);
> +
> +			result = snapstore_create(unique_id, _snapstore_dev(snapstore_dev_id),
> +						  dev_set, dev_id_set_length);
> +			kfree(dev_set);
> +			if (result != SUCCESS) {
> +				pr_err("Failed to create snapstore\n");
> +				break;
> +			}
> +
> +			result = snapstore_stretch_initiate(
> +				unique_id, pipe, (sector_t)to_sectors(stretch_empty_limit));
> +			if (result != SUCCESS) {
> +				pr_err("Failed to initiate stretch snapstore %pUB\n", unique_id);
> +				break;
> +			}
> +		}
> +	} while (false);
> +	kfree(kernel_buffer);
> +	ctrl_pipe_request_acknowledge(pipe, result);
> +
> +	if (result == SUCCESS)
> +		return processed;
> +	return result;
> +}
> +
> +static ssize_t ctrl_pipe_command_next_portion(struct ctrl_pipe *pipe, const char __user *buffer,
> +					      size_t length)
> +{
> +	unsigned long len;
> +	int result = SUCCESS;
> +	ssize_t processed = 0;
> +	struct big_buffer *ranges = NULL;
> +
> +	do {
> +		uuid_t unique_id;
> +		unsigned int ranges_length;
> +		size_t ranges_buffer_size;
> +
> +		//get snapstore id
> +		if ((length - processed) < 16) {
> +			pr_err("Unable to get snapstore id: ");
> +			pr_err("invalid ctrl pipe next portion command. length=%zu\n",
> +			       length);
> +			break;
> +		}
> +		len = copy_from_user(&unique_id, buffer + processed, sizeof(uuid_t));
> +		if (len != 0) {
> +			pr_err("Unable to write to pipe: invalid user buffer\n");
> +			processed = -EINVAL;
> +			break;
> +		}
> +		processed += 16;
> +
> +		//get ranges length
> +		if ((length - processed) < 4) {
> +			pr_err("Unable to get device id list length: ");
> +			pr_err("invalid ctrl pipe next portion command. length=%zu\n",
> +			       length);
> +			break;
> +		}
> +		len = copy_from_user(&ranges_length, buffer + processed, sizeof(unsigned int));
> +		if (len != 0) {
> +			pr_err("Unable to write to pipe: invalid user buffer\n");
> +			processed = -EINVAL;
> +			break;
> +		}
> +		processed += sizeof(unsigned int);
> +
> +		ranges_buffer_size = ranges_length * sizeof(struct ioctl_range_s);
> +
> +		// ranges
> +		if ((length - processed) < (ranges_buffer_size)) {
> +			pr_err("Unable to get all ranges: ");
> +			pr_err("invalid ctrl pipe next portion command. length=%zu\n",
> +			       length);
> +			break;
> +		}
> +		ranges = big_buffer_alloc(ranges_buffer_size, GFP_KERNEL);
> +		if (ranges == NULL) {
> +			pr_err("Unable to allocate page array buffer: ");
> +			pr_err("failed to process next portion command\n");
> +			processed = -ENOMEM;
> +			break;
> +		}
> +		if (ranges_buffer_size !=
> +		    big_buffer_copy_from_user(buffer + processed, 0, ranges, ranges_buffer_size)) {
> +			pr_err("Unable to process next portion command: ");
> +			pr_err("invalid user buffer for parameters\n");
> +			processed = -EINVAL;
> +			break;
> +		}
> +		processed += ranges_buffer_size;
> +
> +		{
> +			result = snapstore_add_file(&unique_id, ranges, ranges_length);
> +
> +			if (result != SUCCESS) {
> +				pr_err("Failed to add file to snapstore\n");
> +				result = -ENODEV;
> +				break;
> +			}
> +		}
> +	} while (false);
> +	if (ranges)
> +		big_buffer_free(ranges);
> +
> +	if (result == SUCCESS)
> +		return processed;
> +	return result;
> +}
> +
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +static ssize_t ctrl_pipe_command_next_portion_multidev(struct ctrl_pipe *pipe,
> +						       const char __user *buffer, size_t length)
> +{
> +	unsigned long len;
> +	int result = SUCCESS;
> +	ssize_t processed = 0;
> +	struct big_buffer *ranges = NULL;
> +
> +	do {
> +		uuid_t unique_id;
> +		int snapstore_major;
> +		int snapstore_minor;
> +		unsigned int ranges_length;
> +		size_t ranges_buffer_size;
> +
> +		//get snapstore id
> +		if ((length - processed) < 16) {
> +			pr_err("Unable to get snapstore id: ");
> +			pr_err("invalid ctrl pipe next portion command. length=%zu\n",
> +			       length);
> +			break;
> +		}
> +		len = copy_from_user(&unique_id, buffer + processed, sizeof(uuid_t));
> +		if (len != 0) {
> +			pr_err("Unable to write to pipe: invalid user buffer\n");
> +			processed = -EINVAL;
> +			break;
> +		}
> +		processed += 16;
> +
> +		//get device id
> +		if ((length - processed) < 8) {
> +			pr_err("Unable to get device id list length: ");
> +			pr_err("invalid ctrl pipe next portion command. length=%zu\n", length);
> +			break;
> +		}
> +		len = copy_from_user(&snapstore_major, buffer + processed, sizeof(unsigned int));
> +		if (len != 0) {
> +			pr_err("Unable to write to pipe: invalid user buffer\n");
> +			processed = -EINVAL;
> +			break;
> +		}
> +		processed += sizeof(unsigned int);
> +
> +		len = copy_from_user(&snapstore_minor, buffer + processed, sizeof(unsigned int));
> +		if (len != 0) {
> +			pr_err("Unable to write to pipe: invalid user buffer\n");
> +			processed = -EINVAL;
> +			break;
> +		}
> +		processed += sizeof(unsigned int);
> +
> +		//get ranges length
> +		if ((length - processed) < 4) {
> +			pr_err("Unable to get device id list length: ");
> +			pr_err("invalid ctrl pipe next portion command. length=%zu\n",
> +			       length);
> +			break;
> +		}
> +		len = copy_from_user(&ranges_length, buffer + processed, sizeof(unsigned int));
> +		if (len != 0) {
> +			pr_err("Unable to write to pipe: invalid user buffer\n");
> +			processed = -EINVAL;
> +			break;
> +		}
> +		processed += sizeof(unsigned int);
> +
> +		ranges_buffer_size = ranges_length * sizeof(struct ioctl_range_s);
> +
> +		// ranges
> +		if ((length - processed) < (ranges_buffer_size)) {
> +			pr_err("Unable to get all ranges: ");
> +			pr_err("invalid ctrl pipe next portion command.  length=%zu\n",
> +			       length);
> +			break;
> +		}
> +		ranges = big_buffer_alloc(ranges_buffer_size, GFP_KERNEL);
> +		if (ranges == NULL) {
> +			pr_err("Unable to process next portion command: ");
> +			pr_err("failed to allocate page array buffer\n");
> +			processed = -ENOMEM;
> +			break;
> +		}
> +		if (ranges_buffer_size !=
> +		    big_buffer_copy_from_user(buffer + processed, 0, ranges, ranges_buffer_size)) {
> +			pr_err("Unable to process next portion command: ");
> +			pr_err("invalid user buffer from parameters\n");
> +			processed = -EINVAL;
> +			break;
> +		}
> +		processed += ranges_buffer_size;
> +
> +		{
> +			result = snapstore_add_multidev(&unique_id,
> +							MKDEV(snapstore_major, snapstore_minor),
> +							ranges, ranges_length);
> +
> +			if (result != SUCCESS) {
> +				pr_err("Failed to add file to snapstore\n");
> +				result = -ENODEV;
> +				break;
> +			}
> +		}
> +	} while (false);
> +	if (ranges)
> +		big_buffer_free(ranges);
> +
> +	if (result == SUCCESS)
> +		return processed;
> +
> +	return result;
> +}
> +#endif
> +
> +static void ctrl_pipe_release_cb(struct kref *kref)
> +{
> +	struct ctrl_pipe *pipe = container_of(kref, struct ctrl_pipe, refcount);
> +
> +	down_write(&ctl_pipes_lock);
> +	list_del(&pipe->link);
> +	up_write(&ctl_pipes_lock);
> +
> +	kfifo_free(&pipe->cmd_to_user);
> +
> +	kfree(pipe);
> +}
> +
> +struct ctrl_pipe *ctrl_pipe_get_resource(struct ctrl_pipe *pipe)
> +{
> +	if (pipe)
> +		kref_get(&pipe->refcount);
> +
> +	return pipe;
> +}
> +
> +void ctrl_pipe_put_resource(struct ctrl_pipe *pipe)
> +{
> +	if (pipe)
> +		kref_put(&pipe->refcount, ctrl_pipe_release_cb);
> +}
> +
> +void ctrl_pipe_done(void)
> +{
> +	bool is_empty;
> +
> +	pr_info("Ctrl pipes - done\n");
> +
> +	down_write(&ctl_pipes_lock);
> +	is_empty = list_empty(&ctl_pipes);
> +	up_write(&ctl_pipes_lock);
> +
> +	if (!is_empty)
> +		pr_err("Unable to perform ctrl pipes cleanup: container is not empty\n");
> +}
> +
> +struct ctrl_pipe *ctrl_pipe_new(void)
> +{
> +	int ret;
> +	struct ctrl_pipe *pipe;
> +
> +	pipe = kzalloc(sizeof(struct ctrl_pipe), GFP_KERNEL);
> +	if (pipe == NULL)
> +		return NULL;
> +
> +	INIT_LIST_HEAD(&pipe->link);
> +
> +	ret = kfifo_alloc(&pipe->cmd_to_user, CMD_TO_USER_FIFO_SIZE, GFP_KERNEL);
> +	if (ret) {
> +		pr_err("Failed to allocate fifo. errno=%d.\n", ret);
> +		kfree(pipe);
> +		return NULL;
> +	}
> +	spin_lock_init(&pipe->cmd_to_user_lock);
> +
> +	kref_init(&pipe->refcount);
> +
> +	init_waitqueue_head(&pipe->readq);
> +
> +	down_write(&ctl_pipes_lock);
> +	list_add_tail(&pipe->link, &ctl_pipes);
> +	up_write(&ctl_pipes_lock);
> +
> +	return pipe;
> +}
> +
> +ssize_t ctrl_pipe_read(struct ctrl_pipe *pipe, char __user *buffer, size_t length)
> +{
> +	int ret;
> +	unsigned int processed = 0;
> +
> +	if (kfifo_is_empty_spinlocked(&pipe->cmd_to_user, &pipe->cmd_to_user_lock)) {
> +		//nothing to read
> +		ret = wait_event_interruptible(pipe->readq,
> +					       !kfifo_is_empty_spinlocked(&pipe->cmd_to_user,
> +									&pipe->cmd_to_user_lock));
> +		if (ret) {
> +			pr_err("Unable to wait for pipe read queue: interrupt signal was received\n");
> +			return -ERESTARTSYS;
> +		}
> +	}
> +
> +	ret = kfifo_to_user(&pipe->cmd_to_user, buffer, length, &processed);
> +	if (ret) {
> +		pr_err("Failed to read command from ctrl pipe\n");
> +		return ret;
> +	}
> +
> +	return (ssize_t)processed;
> +}
> +
> +ssize_t ctrl_pipe_write(struct ctrl_pipe *pipe, const char __user *buffer, size_t length)
> +{
> +	ssize_t processed = 0;
> +
> +	do {
> +		unsigned long len;
> +		unsigned int command;
> +
> +		if ((length - processed) < 4) {
> +			pr_err("Unable to write command to ctrl pipe: invalid command length=%zu\n",
> +			       length);
> +			break;
> +		}
> +		len = copy_from_user(&command, buffer + processed, sizeof(unsigned int));
> +		if (len != 0) {
> +			pr_err("Unable to write to pipe: invalid user buffer\n");
> +			processed = -EINVAL;
> +			break;
> +		}
> +		processed += sizeof(unsigned int);
> +		//+4
> +		switch (command) {
> +		case BLK_SNAP_CHARCMD_INITIATE: {
> +			ssize_t res = ctrl_pipe_command_initiate(pipe, buffer + processed,
> +								 length - processed);
> +			if (res >= 0)
> +				processed += res;
> +			else
> +				processed = res;
> +		} break;
> +		case BLK_SNAP_CHARCMD_NEXT_PORTION: {
> +			ssize_t res = ctrl_pipe_command_next_portion(pipe, buffer + processed,
> +								     length - processed);
> +			if (res >= 0)
> +				processed += res;
> +			else
> +				processed = res;
> +		} break;
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +		case BLK_SNAP_CHARCMD_NEXT_PORTION_MULTIDEV: {
> +			ssize_t res = ctrl_pipe_command_next_portion_multidev(
> +				pipe, buffer + processed, length - processed);
> +			if (res >= 0)
> +				processed += res;
> +			else
> +				processed = res;
> +		} break;
> +#endif
> +		default:
> +			pr_err("Ctrl pipe write error: invalid command [0x%x] received\n", command);
> +			break;
> +		}
> +	} while (false);
> +	return processed;
> +}
> +
> +unsigned int ctrl_pipe_poll(struct ctrl_pipe *pipe)
> +{
> +	unsigned int mask = 0;
> +
> +	if (!kfifo_is_empty_spinlocked(&pipe->cmd_to_user, &pipe->cmd_to_user_lock))
> +		mask |= (POLLIN | POLLRDNORM); /* readable */
> +
> +	mask |= (POLLOUT | POLLWRNORM); /* writable */
> +
> +	return mask;
> +}
> +
> +void ctrl_pipe_request_halffill(struct ctrl_pipe *pipe, unsigned long long filled_status)
> +{
> +	unsigned int cmd[3];
> +
> +	pr_info("Snapstore is half-full\n");
> +
> +	cmd[0] = (unsigned int)BLK_SNAP_CHARCMD_HALFFILL;
> +	cmd[1] = (unsigned int)(filled_status & 0xFFFFffff); //lo
> +	cmd[2] = (unsigned int)(filled_status >> 32);
> +
> +	ctrl_pipe_push_request(pipe, cmd, 3);
> +}
> +
> +void ctrl_pipe_request_overflow(struct ctrl_pipe *pipe, unsigned int error_code,
> +				unsigned long long filled_status)
> +{
> +	unsigned int cmd[4];
> +
> +	pr_info("Snapstore overflow\n");
> +
> +	cmd[0] = (unsigned int)BLK_SNAP_CHARCMD_OVERFLOW;
> +	cmd[1] = error_code;
> +	cmd[2] = (unsigned int)(filled_status & 0xFFFFffff); //lo
> +	cmd[3] = (unsigned int)(filled_status >> 32);
> +
> +	ctrl_pipe_push_request(pipe, cmd, 4);
> +}
> +
> +void ctrl_pipe_request_terminate(struct ctrl_pipe *pipe, unsigned long long filled_status)
> +{
> +	unsigned int cmd[3];
> +
> +	pr_info("Snapstore termination\n");
> +
> +	cmd[0] = (unsigned int)BLK_SNAP_CHARCMD_TERMINATE;
> +	cmd[1] = (unsigned int)(filled_status & 0xFFFFffff); //lo
> +	cmd[2] = (unsigned int)(filled_status >> 32);
> +
> +	ctrl_pipe_push_request(pipe, cmd, 3);
> +}
> diff --git a/drivers/block/blk-snap/ctrl_pipe.h b/drivers/block/blk-snap/ctrl_pipe.h
> new file mode 100644
> index 000000000000..1aa1099eec25
> --- /dev/null
> +++ b/drivers/block/blk-snap/ctrl_pipe.h
> @@ -0,0 +1,34 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +#include <linux/kref.h>
> +#include <linux/wait.h>
> +#include <linux/kfifo.h>
> +
> +struct ctrl_pipe {
> +	struct list_head link;
> +
> +	struct kref refcount;
> +
> +	wait_queue_head_t readq;
> +
> +	struct kfifo cmd_to_user;
> +	spinlock_t cmd_to_user_lock;
> +};
> +
> +struct ctrl_pipe *ctrl_pipe_get_resource(struct ctrl_pipe *pipe);
> +void ctrl_pipe_put_resource(struct ctrl_pipe *pipe);
> +
> +void ctrl_pipe_done(void);
> +
> +struct ctrl_pipe *ctrl_pipe_new(void);
> +
> +ssize_t ctrl_pipe_read(struct ctrl_pipe *pipe, char __user *buffer, size_t length);
> +ssize_t ctrl_pipe_write(struct ctrl_pipe *pipe, const char __user *buffer, size_t length);
> +
> +unsigned int ctrl_pipe_poll(struct ctrl_pipe *pipe);
> +
> +void ctrl_pipe_request_halffill(struct ctrl_pipe *pipe, unsigned long long filled_status);
> +void ctrl_pipe_request_overflow(struct ctrl_pipe *pipe, unsigned int error_code,
> +				unsigned long long filled_status);
> +void ctrl_pipe_request_terminate(struct ctrl_pipe *pipe, unsigned long long filled_status);
> diff --git a/drivers/block/blk-snap/ctrl_sysfs.c b/drivers/block/blk-snap/ctrl_sysfs.c
> new file mode 100644
> index 000000000000..4ec78e85b510
> --- /dev/null
> +++ b/drivers/block/blk-snap/ctrl_sysfs.c
> @@ -0,0 +1,73 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-ctrl"
> +#include "common.h"
> +#include "ctrl_sysfs.h"
> +#include "ctrl_fops.h"
> +#include "blk-snap-ctl.h"
> +
> +#include <linux/blkdev.h>
> +#include <linux/sysfs.h>
> +
> +static ssize_t major_show(struct class *class, struct class_attribute *attr, char *buf)
> +{
> +	sprintf(buf, "%d", get_blk_snap_major());
> +	return strlen(buf);
> +}
> +
> +CLASS_ATTR_RO(major); // declare class_attr_major
> +static struct class *blk_snap_class;
> +
> +static struct device *blk_snap_device;
> +
> +int ctrl_sysfs_init(void)
> +{
> +	struct device *dev;
> +	int res;
> +
> +	blk_snap_class = class_create(THIS_MODULE, MODULE_NAME);
> +	if (IS_ERR(blk_snap_class)) {
> +		res = PTR_ERR(blk_snap_class);
> +
> +		pr_err("Bad class create. errno=%d\n", 0 - res);
> +		return res;
> +	}
> +
> +	pr_info("Create 'major' sysfs attribute\n");
> +	res = class_create_file(blk_snap_class, &class_attr_major);
> +	if (res != SUCCESS) {
> +		pr_err("Failed to create 'major' sysfs file\n");
> +
> +		class_destroy(blk_snap_class);
> +		blk_snap_class = NULL;
> +		return res;
> +	}
> +
> +	dev = device_create(blk_snap_class, NULL, MKDEV(get_blk_snap_major(), 0), NULL,
> +			    MODULE_NAME);
> +	if (IS_ERR(dev)) {
> +		res = PTR_ERR(dev);
> +		pr_err("Failed to create device, errno=%d\n", res);
> +
> +		class_remove_file(blk_snap_class, &class_attr_major);
> +		class_destroy(blk_snap_class);
> +		blk_snap_class = NULL;
> +		return res;
> +	}
> +
> +	blk_snap_device = dev;
> +	return res;
> +}
> +
> +void ctrl_sysfs_done(void)
> +{
> +	if (blk_snap_device) {
> +		device_unregister(blk_snap_device);
> +		blk_snap_device = NULL;
> +	}
> +
> +	if (blk_snap_class != NULL) {
> +		class_remove_file(blk_snap_class, &class_attr_major);
> +		class_destroy(blk_snap_class);
> +		blk_snap_class = NULL;
> +	}
> +}
> diff --git a/drivers/block/blk-snap/ctrl_sysfs.h b/drivers/block/blk-snap/ctrl_sysfs.h
> new file mode 100644
> index 000000000000..27a2a4d3da4c
> --- /dev/null
> +++ b/drivers/block/blk-snap/ctrl_sysfs.h
> @@ -0,0 +1,5 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +int ctrl_sysfs_init(void);
> +void ctrl_sysfs_done(void);
> diff --git a/drivers/block/blk-snap/defer_io.c b/drivers/block/blk-snap/defer_io.c
> new file mode 100644
> index 000000000000..309216fe7319
> --- /dev/null
> +++ b/drivers/block/blk-snap/defer_io.c
> @@ -0,0 +1,397 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-defer_io"
> +#include "common.h"
> +#include "defer_io.h"
> +#include "blk_deferred.h"
> +#include "tracker.h"
> +#include "blk_util.h"
> +
> +#include <linux/kthread.h>
> +
> +#define BLK_IMAGE_THROTTLE_TIMEOUT (1 * HZ) //delay 1 sec
> +//#define BLK_IMAGE_THROTTLE_TIMEOUT ( HZ/1000 * 10 )	//delay 10 ms
> +
> +
> +
> +struct defer_io_orig_rq {
> +	struct list_head link;
> +	struct defer_io_queue *queue;
> +
> +	struct bio *bio;
> +	struct tracker *tracker;
> +};
> +
> +static inline void defer_io_queue_init(struct defer_io_queue *queue)
> +{
> +	INIT_LIST_HEAD(&queue->list);
> +
> +	spin_lock_init(&queue->lock);
> +
> +	atomic_set(&queue->in_queue_cnt, 0);
> +	atomic_set(&queue->active_state, true);
> +}
> +
> +static inline struct defer_io_orig_rq *defer_io_queue_new(struct defer_io_queue *queue, struct bio *bio)
> +{
> +	struct defer_io_orig_rq *dio_rq;
> +
> +	dio_rq = kzalloc(sizeof(struct defer_io_orig_rq), GFP_NOIO);
> +	if (dio_rq == NULL)
> +		return NULL;
> +
> +	dio_rq->bio = bio;
> +	bio_get(dio_rq->bio);
> +
> +	INIT_LIST_HEAD(&dio_rq->link);
> +	dio_rq->queue = queue;
> +
> +	return dio_rq;
> +}
> +
> +static inline void defer_io_queue_free(struct defer_io_orig_rq *dio_rq)
> +{
> +	if (likely(dio_rq)) {
> +		if (likely(dio_rq->bio)) {
> +			bio_put(dio_rq->bio);
> +			dio_rq->bio = NULL;
> +		}
> +		kfree(dio_rq);
> +	}
> +}
> +
> +static int defer_io_queue_push_back(struct defer_io_queue *queue, struct defer_io_orig_rq *dio_rq)
> +{
> +	int res = SUCCESS;
> +
> +	spin_lock(&queue->lock);
> +
> +	if (atomic_read(&queue->active_state)) {
> +		list_add_tail(&dio_rq->link, &queue->list);
> +		atomic_inc(&queue->in_queue_cnt);
> +	} else
> +		res = -EACCES;
> +
> +	spin_unlock(&queue->lock);
> +	return res;
> +}
> +
> +static struct defer_io_orig_rq *defer_io_queue_get_first(struct defer_io_queue *queue)
> +{
> +	struct defer_io_orig_rq *dio_rq = NULL;
> +
> +	spin_lock(&queue->lock);
> +
> +	if (!list_empty(&queue->list)) {
> +		dio_rq = list_entry(queue->list.next, struct defer_io_orig_rq, link);
> +		list_del(&dio_rq->link);
> +		atomic_dec(&queue->in_queue_cnt);
> +	}
> +
> +	spin_unlock(&queue->lock);
> +
> +	return dio_rq;
> +}
> +
> +static bool defer_io_queue_active(struct defer_io_queue *queue, bool state)
> +{
> +	bool prev_state;
> +
> +	spin_lock(&queue->lock);
> +
> +	prev_state = atomic_read(&queue->active_state);
> +	atomic_set(&queue->active_state, state);
> +
> +	spin_unlock(&queue->lock);
> +
> +	return prev_state;
> +}
> +
> +#define defer_io_queue_empty(queue) (atomic_read(&(queue).in_queue_cnt) == 0)
> +
> +static void _defer_io_finish(struct defer_io *defer_io, struct defer_io_queue *queue_in_progress)
> +{
> +	while (!defer_io_queue_empty(*queue_in_progress)) {
> +		struct tracker *tracker = NULL;
> +		bool cbt_locked = false;
> +		bool is_write_bio;
> +		sector_t sectCount = 0;
> +
> +		struct defer_io_orig_rq *orig_req = defer_io_queue_get_first(queue_in_progress);
> +
> +		is_write_bio = bio_data_dir(orig_req->bio) && bio_has_data(orig_req->bio);
> +
> +		if (orig_req->tracker && is_write_bio) {
> +			tracker = orig_req->tracker;
> +			cbt_locked = tracker_cbt_bitmap_lock(tracker);
> +			if (cbt_locked) {
> +				sectCount = bio_sectors(orig_req->bio);
> +				tracker_cbt_bitmap_set(tracker, orig_req->bio->bi_iter.bi_sector,
> +						       sectCount);
> +			}
> +		}
> +
> +		submit_bio_direct(orig_req->bio);
> +
> +		if (cbt_locked)
> +			tracker_cbt_bitmap_unlock(tracker);
> +
> +		defer_io_queue_free(orig_req);
> +	}
> +}
> +
> +static int _defer_io_copy_prepare(struct defer_io *defer_io,
> +				  struct defer_io_queue *queue_in_process,
> +				  struct blk_deferred_request **dio_copy_req)
> +{
> +	int res = SUCCESS;
> +	int dios_count = 0;
> +	sector_t dios_sectors_count = 0;
> +
> +	//fill copy_request set
> +	while (!defer_io_queue_empty(defer_io->dio_queue) &&
> +	       (dios_count < DEFER_IO_DIO_REQUEST_LENGTH) &&
> +	       (dios_sectors_count < DEFER_IO_DIO_REQUEST_SECTORS_COUNT)) {
> +		struct defer_io_orig_rq *dio_orig_req =
> +			(struct defer_io_orig_rq *)defer_io_queue_get_first(&defer_io->dio_queue);
> +		atomic_dec(&defer_io->queue_filling_count);
> +
> +		defer_io_queue_push_back(queue_in_process, dio_orig_req);
> +
> +		if (!kthread_should_stop() &&
> +		    !snapstore_device_is_corrupted(defer_io->snapstore_device)) {
> +			if (bio_data_dir(dio_orig_req->bio) && bio_has_data(dio_orig_req->bio)) {
> +				struct blk_range copy_range;
> +
> +				copy_range.ofs = dio_orig_req->bio->bi_iter.bi_sector;
> +				copy_range.cnt = bio_sectors(dio_orig_req->bio);
> +				res = snapstore_device_prepare_requests(defer_io->snapstore_device,
> +									&copy_range, dio_copy_req);
> +				if (res != SUCCESS) {
> +					pr_err("Unable to execute Copy On Write algorithm: failed to add ranges to copy to snapstore request. errno=%d\n",
> +					       res);
> +					break;
> +				}
> +
> +				dios_sectors_count += copy_range.cnt;
> +			}
> +		}
> +		++dios_count;
> +	}
> +	return res;
> +}
> +
> +static int defer_io_work_thread(void *p)
> +{
> +	struct defer_io_queue queue_in_process = { 0 };
> +	struct defer_io *defer_io = NULL;
> +
> +	//set_user_nice( current, -20 ); //MIN_NICE
> +	defer_io_queue_init(&queue_in_process);
> +
> +	defer_io = defer_io_get_resource((struct defer_io *)p);
> +	pr_info("Defer IO thread for original device [%d:%d] started\n",
> +		MAJOR(defer_io->original_dev_id), MINOR(defer_io->original_dev_id));
> +
> +	while (!kthread_should_stop() || !defer_io_queue_empty(defer_io->dio_queue)) {
> +		if (defer_io_queue_empty(defer_io->dio_queue)) {
> +			int res = wait_event_interruptible_timeout(
> +				defer_io->queue_add_event,
> +				(!defer_io_queue_empty(defer_io->dio_queue)),
> +				BLK_IMAGE_THROTTLE_TIMEOUT);
> +			if (-ERESTARTSYS == res)
> +				pr_err("Signal received in defer IO thread. Waiting for completion with code ERESTARTSYS\n");
> +		}
> +
> +		if (!defer_io_queue_empty(defer_io->dio_queue)) {
> +			int dio_copy_result = SUCCESS;
> +			struct blk_deferred_request *dio_copy_req = NULL;
> +
> +			mutex_lock(&defer_io->snapstore_device->store_block_map_locker);
> +			do {
> +				dio_copy_result = _defer_io_copy_prepare(
> +					defer_io, &queue_in_process, &dio_copy_req);
> +				if (dio_copy_result != SUCCESS) {
> +					pr_err("Unable to process defer IO request: failed to prepare copy request. erro=%d\n",
> +					       dio_copy_result);
> +					break;
> +				}
> +				if (dio_copy_req == NULL)
> +					break; //nothing to copy
> +
> +				dio_copy_result = blk_deferred_request_read_original(
> +					defer_io->original_blk_dev, dio_copy_req);
> +				if (dio_copy_result != SUCCESS) {
> +					pr_err("Unable to process defer IO request: failed to read data to copy request. errno=%d\n",
> +					       dio_copy_result);
> +					break;
> +				}
> +				dio_copy_result = snapstore_device_store(defer_io->snapstore_device,
> +									 dio_copy_req);
> +				if (dio_copy_result != SUCCESS) {
> +					pr_err("Unable to process defer IO request: failed to write data from copy request. errno=%d\n",
> +					       dio_copy_result);
> +					break;
> +				}
> +
> +			} while (false);
> +			_defer_io_finish(defer_io, &queue_in_process);
> +			mutex_unlock(&defer_io->snapstore_device->store_block_map_locker);
> +
> +			if (dio_copy_req) {
> +				if (dio_copy_result == -EDEADLK)
> +					blk_deferred_request_deadlocked(dio_copy_req);
> +				else
> +					blk_deferred_request_free(dio_copy_req);
> +			}
> +		}
> +
> +		//wake up snapimage if defer io queue empty
> +		if (defer_io_queue_empty(defer_io->dio_queue))
> +			wake_up_interruptible(&defer_io->queue_throttle_waiter);
> +	}
> +	defer_io_queue_active(&defer_io->dio_queue, false);
> +
> +	//waiting for all sent request complete
> +	_defer_io_finish(defer_io, &defer_io->dio_queue);
> +
> +	pr_info("Defer IO thread for original device [%d:%d] completed\n",
> +		MAJOR(defer_io->original_dev_id), MINOR(defer_io->original_dev_id));
> +	defer_io_put_resource(defer_io);
> +	return SUCCESS;
> +}
> +
> +static void _defer_io_destroy(struct defer_io *defer_io)
> +{
> +	if (defer_io == NULL)
> +		return;
> +
> +	if (defer_io->dio_thread)
> +		defer_io_stop(defer_io);
> +
> +	if (defer_io->snapstore_device)
> +		snapstore_device_put_resource(defer_io->snapstore_device);
> +
> +	kfree(defer_io);
> +	pr_info("Defer IO processor was destroyed\n");
> +}
> +
> +static void defer_io_destroy_cb(struct kref *kref)
> +{
> +	_defer_io_destroy(container_of(kref, struct defer_io, refcount));
> +}
> +
> +struct defer_io *defer_io_get_resource(struct defer_io *defer_io)
> +{
> +	if (defer_io)
> +		kref_get(&defer_io->refcount);
> +
> +	return defer_io;
> +}
> +
> +void defer_io_put_resource(struct defer_io *defer_io)
> +{
> +	if (defer_io)
> +		kref_put(&defer_io->refcount, defer_io_destroy_cb);
> +}
> +
> +int defer_io_create(dev_t dev_id, struct block_device *blk_dev, struct defer_io **pp_defer_io)
> +{
> +	int res = SUCCESS;
> +	struct defer_io *defer_io = NULL;
> +	struct snapstore_device *snapstore_device;
> +
> +	pr_info("Defer IO processor was created for device [%d:%d]\n", MAJOR(dev_id),
> +		MINOR(dev_id));
> +
> +	defer_io = kzalloc(sizeof(struct defer_io), GFP_KERNEL);
> +	if (defer_io == NULL)
> +		return -ENOMEM;
> +
> +	snapstore_device = snapstore_device_find_by_dev_id(dev_id);
> +	if (snapstore_device == NULL) {
> +		pr_err("Unable to create defer IO processor: failed to initialize snapshot data for device [%d:%d]\n",
> +		       MAJOR(dev_id), MINOR(dev_id));
> +
> +		kfree(defer_io);
> +		return -ENODATA;
> +	}
> +
> +	defer_io->snapstore_device = snapstore_device_get_resource(snapstore_device);
> +	defer_io->original_dev_id = dev_id;
> +	defer_io->original_blk_dev = blk_dev;
> +
> +	kref_init(&defer_io->refcount);
> +
> +	defer_io_queue_init(&defer_io->dio_queue);
> +
> +	init_waitqueue_head(&defer_io->queue_add_event);
> +
> +	atomic_set(&defer_io->queue_filling_count, 0);
> +
> +	init_waitqueue_head(&defer_io->queue_throttle_waiter);
> +
> +	defer_io->dio_thread = kthread_create(defer_io_work_thread, (void *)defer_io,
> +					      "blksnapdeferio%d:%d", MAJOR(dev_id), MINOR(dev_id));
> +	if (IS_ERR(defer_io->dio_thread)) {
> +		res = PTR_ERR(defer_io->dio_thread);
> +		pr_err("Unable to create defer IO processor: failed to create thread. errno=%d\n",
> +		       res);
> +
> +		_defer_io_destroy(defer_io);
> +		defer_io = NULL;
> +		*pp_defer_io = NULL;
> +
> +		return res;
> +	}
> +
> +	wake_up_process(defer_io->dio_thread);
> +
> +	*pp_defer_io = defer_io;
> +	pr_info("Defer IO processor was created\n");
> +
> +	return SUCCESS;
> +}
> +
> +int defer_io_stop(struct defer_io *defer_io)
> +{
> +	int res = SUCCESS;
> +
> +	pr_info("Defer IO thread for the device stopped [%d:%d]\n",
> +		MAJOR(defer_io->original_dev_id), MINOR(defer_io->original_dev_id));
> +
> +	if (defer_io->dio_thread != NULL) {
> +		struct task_struct *dio_thread = defer_io->dio_thread;
> +
> +		defer_io->dio_thread = NULL;
> +		res = kthread_stop(dio_thread); //stopping and waiting.
> +		if (res != SUCCESS)
> +			pr_err("Failed to stop defer IO thread. errno=%d\n", res);
> +	}
> +
> +	return res;
> +}
> +
> +int defer_io_redirect_bio(struct defer_io *defer_io, struct bio *bio, void *tracker)
> +{
> +	struct defer_io_orig_rq *dio_orig_req;
> +
> +	if (snapstore_device_is_corrupted(defer_io->snapstore_device))
> +		return -ENODATA;
> +
> +	dio_orig_req = defer_io_queue_new(&defer_io->dio_queue, bio);
> +	if (dio_orig_req == NULL)
> +		return -ENOMEM;
> +
> +	dio_orig_req->tracker = (struct tracker *)tracker;
> +
> +	if (defer_io_queue_push_back(&defer_io->dio_queue, dio_orig_req) != SUCCESS) {
> +		defer_io_queue_free(dio_orig_req);
> +		return -EFAULT;
> +	}
> +
> +	atomic_inc(&defer_io->queue_filling_count);
> +
> +	wake_up_interruptible(&defer_io->queue_add_event);
> +
> +	return SUCCESS;
> +}
> diff --git a/drivers/block/blk-snap/defer_io.h b/drivers/block/blk-snap/defer_io.h
> new file mode 100644
> index 000000000000..27c3bb03241f
> --- /dev/null
> +++ b/drivers/block/blk-snap/defer_io.h
> @@ -0,0 +1,39 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +#include <linux/kref.h>
> +#include "snapstore_device.h"
> +
> +struct defer_io_queue {
> +	struct list_head list;
> +	spinlock_t lock;
> +
> +	atomic_t active_state;
> +	atomic_t in_queue_cnt;
> +};
> +
> +struct defer_io {
> +	struct kref refcount;
> +
> +	wait_queue_head_t queue_add_event;
> +
> +	atomic_t queue_filling_count;
> +	wait_queue_head_t queue_throttle_waiter;
> +
> +	dev_t original_dev_id;
> +	struct block_device *original_blk_dev;
> +
> +	struct snapstore_device *snapstore_device;
> +
> +	struct task_struct *dio_thread;
> +
> +	struct defer_io_queue dio_queue;
> +};
> +
> +int defer_io_create(dev_t dev_id, struct block_device *blk_dev, struct defer_io **pp_defer_io);
> +int defer_io_stop(struct defer_io *defer_io);
> +
> +struct defer_io *defer_io_get_resource(struct defer_io *defer_io);
> +void defer_io_put_resource(struct defer_io *defer_io);
> +
> +int defer_io_redirect_bio(struct defer_io *defer_io, struct bio *bio, void *tracker);
> diff --git a/drivers/block/blk-snap/main.c b/drivers/block/blk-snap/main.c
> new file mode 100644
> index 000000000000..d1d4e08a4890
> --- /dev/null
> +++ b/drivers/block/blk-snap/main.c
> @@ -0,0 +1,82 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "common.h"
> +#include "version.h"
> +#include "blk-snap-ctl.h"
> +#include "params.h"
> +#include "ctrl_fops.h"
> +#include "ctrl_pipe.h"
> +#include "ctrl_sysfs.h"
> +#include "snapimage.h"
> +#include "snapstore.h"
> +#include "snapstore_device.h"
> +#include "snapshot.h"
> +#include "tracker.h"
> +#include "tracking.h"
> +#include <linux/module.h>
> +
> +int __init blk_snap_init(void)
> +{
> +	int result = SUCCESS;
> +
> +	pr_info("Loading\n");
> +
> +	params_check();
> +
> +	result = ctrl_init();
> +	if (result != SUCCESS)
> +		return result;
> +
> +	result = blk_redirect_bioset_create();
> +	if (result != SUCCESS)
> +		return result;
> +
> +	result = blk_deferred_bioset_create();
> +	if (result != SUCCESS)
> +		return result;
> +
> +	result = snapimage_init();
> +	if (result != SUCCESS)
> +		return result;
> +
> +	result = ctrl_sysfs_init();
> +	if (result != SUCCESS)
> +		return result;
> +
> +	result = tracking_init();
> +	if (result != SUCCESS)
> +		return result;
> +
> +	return result;
> +}
> +
> +void __exit blk_snap_exit(void)
> +{
> +	pr_info("Unloading module\n");
> +
> +	ctrl_sysfs_done();
> +
> +	snapshot_done();
> +
> +	snapstore_device_done();
> +	snapstore_done();
> +
> +	tracker_done();
> +	tracking_done();
> +
> +	snapimage_done();
> +
> +	blk_deferred_bioset_free();
> +	blk_deferred_done();
> +
> +	blk_redirect_bioset_free();
> +
> +	ctrl_done();
> +}
> +
> +module_init(blk_snap_init);
> +module_exit(blk_snap_exit);
> +
> +MODULE_DESCRIPTION("Block Layer Snapshot Kernel Module");
> +MODULE_VERSION(FILEVER_STR);
> +MODULE_AUTHOR("Veeam Software Group GmbH");
> +MODULE_LICENSE("GPL");
> diff --git a/drivers/block/blk-snap/params.c b/drivers/block/blk-snap/params.c
> new file mode 100644
> index 000000000000..7eba3c8bf395
> --- /dev/null
> +++ b/drivers/block/blk-snap/params.c
> @@ -0,0 +1,58 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "common.h"
> +#include "params.h"
> +#include <linux/module.h>
> +
> +int snapstore_block_size_pow = 14;
> +int change_tracking_block_size_pow = 18;
> +
> +int get_snapstore_block_size_pow(void)
> +{
> +	return snapstore_block_size_pow;
> +}
> +
> +int inc_snapstore_block_size_pow(void)
> +{
> +	if (snapstore_block_size_pow > 30)
> +		return -EFAULT;
> +
> +	++snapstore_block_size_pow;
> +	return SUCCESS;
> +}
> +
> +int get_change_tracking_block_size_pow(void)
> +{
> +	return change_tracking_block_size_pow;
> +}
> +
> +void params_check(void)
> +{
> +	pr_info("snapstore_block_size_pow: %d\n", snapstore_block_size_pow);
> +	pr_info("change_tracking_block_size_pow: %d\n", change_tracking_block_size_pow);
> +
> +	if (snapstore_block_size_pow > 23) {
> +		snapstore_block_size_pow = 23;
> +		pr_info("Limited snapstore_block_size_pow: %d\n", snapstore_block_size_pow);
> +	} else if (snapstore_block_size_pow < 12) {
> +		snapstore_block_size_pow = 12;
> +		pr_info("Limited snapstore_block_size_pow: %d\n", snapstore_block_size_pow);
> +	}
> +
> +	if (change_tracking_block_size_pow > 23) {
> +		change_tracking_block_size_pow = 23;
> +		pr_info("Limited change_tracking_block_size_pow: %d\n",
> +			change_tracking_block_size_pow);
> +	} else if (change_tracking_block_size_pow < 12) {
> +		change_tracking_block_size_pow = 12;
> +		pr_info("Limited change_tracking_block_size_pow: %d\n",
> +			change_tracking_block_size_pow);
> +	}
> +}
> +
> +module_param_named(snapstore_block_size_pow, snapstore_block_size_pow, int, 0644);
> +MODULE_PARM_DESC(snapstore_block_size_pow,
> +		 "Snapstore block size binary pow. 20 for 1MiB block size");
> +
> +module_param_named(change_tracking_block_size_pow, change_tracking_block_size_pow, int, 0644);
> +MODULE_PARM_DESC(change_tracking_block_size_pow,
> +		 "Change-tracking block size binary pow. 18 for 256 KiB block size");
> diff --git a/drivers/block/blk-snap/params.h b/drivers/block/blk-snap/params.h
> new file mode 100644
> index 000000000000..c1b853a1363b
> --- /dev/null
> +++ b/drivers/block/blk-snap/params.h
> @@ -0,0 +1,29 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +#pragma once
> +
> +int get_snapstore_block_size_pow(void);
> +int inc_snapstore_block_size_pow(void);
> +
> +static inline sector_t snapstore_block_shift(void)
> +{
> +	return get_snapstore_block_size_pow() - SECTOR_SHIFT;
> +};
> +
> +static inline sector_t snapstore_block_size(void)
> +{
> +	return 1ull << snapstore_block_shift();
> +};
> +
> +static inline sector_t snapstore_block_mask(void)
> +{
> +	return snapstore_block_size() - 1ull;
> +};
> +
> +int get_change_tracking_block_size_pow(void);
> +
> +static inline unsigned int change_tracking_block_size(void)
> +{
> +	return 1 << get_change_tracking_block_size_pow();
> +};
> +
> +void params_check(void);
> diff --git a/drivers/block/blk-snap/rangevector.c b/drivers/block/blk-snap/rangevector.c
> new file mode 100644
> index 000000000000..49fe4589b6f7
> --- /dev/null
> +++ b/drivers/block/blk-snap/rangevector.c
> @@ -0,0 +1,85 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "common.h"
> +#include "rangevector.h"
> +
> +#define SECTION "ranges	"
> +
> +static inline sector_t range_node_start(struct blk_range_tree_node *range_node)
> +{
> +	return range_node->range.ofs;
> +}
> +
> +static inline sector_t range_node_last(struct blk_range_tree_node *range_node)
> +{
> +	return range_node->range.ofs + range_node->range.cnt - 1;
> +}
> +
> +#ifndef INTERVAL_TREE_DEFINE
> +#pragma message("INTERVAL_TREE_DEFINE is undefined")
> +#endif
> +INTERVAL_TREE_DEFINE(struct blk_range_tree_node, _node, sector_t, _subtree_last,
> +		     range_node_start, range_node_last, static inline, _blk_range_rb)
> +
> +void blk_range_rb_insert(struct blk_range_tree_node *node, struct rb_root_cached *root)
> +{
> +	_blk_range_rb_insert(node, root);
> +}
> +
> +void blk_range_rb_remove(struct blk_range_tree_node *node, struct rb_root_cached *root)
> +{
> +	_blk_range_rb_remove(node, root);
> +}
> +
> +struct blk_range_tree_node *blk_range_rb_iter_first(struct rb_root_cached *root, sector_t start,
> +						    sector_t last)
> +{
> +	return _blk_range_rb_iter_first(root, start, last);
> +}
> +
> +struct blk_range_tree_node *blk_range_rb_iter_next(struct blk_range_tree_node *node, sector_t start,
> +						   sector_t last)
> +{
> +	return _blk_range_rb_iter_next(node, start, last);
> +}
> +
> +void rangevector_init(struct rangevector *rangevector)
> +{
> +	init_rwsem(&rangevector->lock);
> +
> +	rangevector->root = RB_ROOT_CACHED;
> +}
> +
> +void rangevector_done(struct rangevector *rangevector)
> +{
> +	struct rb_node *rb_node = NULL;
> +
> +	down_write(&rangevector->lock);
> +	rb_node = rb_first_cached(&rangevector->root);
> +	while (rb_node) {
> +		struct blk_range_tree_node *range_node = (struct blk_range_tree_node *)
> +			rb_node; //container_of(rb_node, struct blk_range_tree_node, node);
> +
> +		blk_range_rb_remove(range_node, &rangevector->root);
> +		kfree(range_node);
> +
> +		rb_node = rb_first_cached(&rangevector->root);
> +	}
> +	up_write(&rangevector->lock);
> +}
> +
> +int rangevector_add(struct rangevector *rangevector, struct blk_range *rg)
> +{
> +	struct blk_range_tree_node *range_node;
> +
> +	range_node = kzalloc(sizeof(struct blk_range_tree_node), GFP_KERNEL);
> +	if (range_node)
> +		return -ENOMEM;
> +
> +	range_node->range = *rg;
> +
> +	down_write(&rangevector->lock);
> +	blk_range_rb_insert(range_node, &rangevector->root);
> +	up_write(&rangevector->lock);
> +
> +	return SUCCESS;
> +}
> diff --git a/drivers/block/blk-snap/rangevector.h b/drivers/block/blk-snap/rangevector.h
> new file mode 100644
> index 000000000000..5ff439423178
> --- /dev/null
> +++ b/drivers/block/blk-snap/rangevector.h
> @@ -0,0 +1,31 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#pragma once
> +
> +#include <linux/interval_tree_generic.h>
> +
> +struct blk_range_tree_node {
> +	struct rb_node _node;
> +	struct blk_range range;
> +	sector_t _subtree_last;
> +};
> +
> +void blk_range_rb_insert(struct blk_range_tree_node *node, struct rb_root_cached *root);
> +
> +void blk_range_rb_remove(struct blk_range_tree_node *node, struct rb_root_cached *root);
> +
> +struct blk_range_tree_node *blk_range_rb_iter_first(struct rb_root_cached *root, sector_t start,
> +						    sector_t last);
> +
> +struct blk_range_tree_node *blk_range_rb_iter_next(struct blk_range_tree_node *node, sector_t start,
> +						   sector_t last);
> +
> +struct rangevector {
> +	struct rb_root_cached root;
> +	struct rw_semaphore lock;
> +};
> +
> +void rangevector_init(struct rangevector *rangevector);
> +
> +void rangevector_done(struct rangevector *rangevector);
> +
> +int rangevector_add(struct rangevector *rangevector, struct blk_range *rg);
> diff --git a/drivers/block/blk-snap/snapimage.c b/drivers/block/blk-snap/snapimage.c
> new file mode 100644
> index 000000000000..da971486cbef
> --- /dev/null
> +++ b/drivers/block/blk-snap/snapimage.c
> @@ -0,0 +1,982 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-snapimage"
> +#include "common.h"
> +#include "snapimage.h"
> +#include "blk_util.h"
> +#include "defer_io.h"
> +#include "cbt_map.h"
> +#include "tracker.h"
> +
> +#include <asm/div64.h>
> +#include <linux/cdrom.h>
> +#include <linux/blk-mq.h>
> +#include <linux/hdreg.h>
> +#include <linux/kthread.h>
> +
> +#define SNAPIMAGE_MAX_DEVICES 2048
> +
> +int snapimage_major;
> +unsigned long *snapimage_minors;
> +DEFINE_SPINLOCK(snapimage_minors_lock);
> +
> +LIST_HEAD(snap_images);
> +DECLARE_RWSEM(snap_images_lock);
> +
> +DECLARE_RWSEM(snap_image_destroy_lock);
> +
> +struct snapimage {
> +	struct list_head link;
> +
> +	sector_t capacity;
> +	dev_t original_dev;
> +
> +	struct defer_io *defer_io;
> +	struct cbt_map *cbt_map;
> +
> +	dev_t image_dev;
> +
> +	struct request_queue *queue;
> +	struct gendisk *disk;
> +
> +	atomic_t own_cnt;
> +
> +	struct redirect_bio_queue image_queue;
> +
> +	struct task_struct *rq_processor;
> +
> +	wait_queue_head_t rq_proc_event;
> +	wait_queue_head_t rq_complete_event;
> +
> +	struct mutex open_locker;
> +	struct block_device *open_bdev;
> +
> +	size_t open_cnt;
> +};
> +
> +int _snapimage_open(struct block_device *bdev, fmode_t mode)
> +{
> +	int res = SUCCESS;
> +
> +	if (bdev->bd_disk == NULL) {
> +		pr_err("Unable to open snapshot image: bd_disk is NULL. Device [%d:%d]\n",
> +		       MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
> +		pr_err("Block device object %p\n", bdev);
> +		return -ENODEV;
> +	}
> +
> +	down_read(&snap_image_destroy_lock);
> +	do {
> +		struct snapimage *image = bdev->bd_disk->private_data;
> +
> +		if (image == NULL) {
> +			pr_err("Unable to open snapshot image: private data is not initialized. Block device object %p\n",
> +			       bdev);
> +			res = -ENODEV;
> +			break;
> +		}
> +
> +		mutex_lock(&image->open_locker);
> +		{
> +			if (image->open_cnt == 0)
> +				image->open_bdev = bdev;
> +
> +			image->open_cnt++;
> +		}
> +		mutex_unlock(&image->open_locker);
> +	} while (false);
> +	up_read(&snap_image_destroy_lock);
> +	return res;
> +}
> +
> +static inline uint64_t do_div_inline(uint64_t division, uint32_t divisor)
> +{
> +	do_div(division, divisor);
> +	return division;
> +}
> +
> +int _snapimage_getgeo(struct block_device *bdev, struct hd_geometry *geo)
> +{
> +	int res = SUCCESS;
> +	sector_t quotient;
> +
> +	down_read(&snap_image_destroy_lock);
> +	do {
> +		struct snapimage *image = bdev->bd_disk->private_data;
> +
> +		if (image == NULL) {
> +			pr_err("Unable to open snapshot image: private data is not initialized. Block device object %p\n",
> +			       bdev);
> +			res = -ENODEV;
> +			break;
> +		}
> +
> +		pr_info("Getting geo for snapshot image device [%d:%d]\n", MAJOR(image->image_dev),
> +			MINOR(image->image_dev));
> +
> +		geo->start = 0;
> +		if (image->capacity > 63) {
> +			geo->sectors = 63;
> +			quotient = do_div_inline(image->capacity + (63 - 1), 63);
> +
> +			if (quotient > 255ULL) {
> +				geo->heads = 255;
> +				geo->cylinders =
> +					(unsigned short)do_div_inline(quotient + (255 - 1), 255);
> +			} else {
> +				geo->heads = (unsigned char)quotient;
> +				geo->cylinders = 1;
> +			}
> +		} else {
> +			geo->sectors = (unsigned char)image->capacity;
> +			geo->cylinders = 1;
> +			geo->heads = 1;
> +		}
> +
> +		pr_info("Image device geo: capacity=%lld, heads=%d, cylinders=%d, sectors=%d\n",
> +			image->capacity, geo->heads, geo->cylinders, geo->sectors);
> +	} while (false);
> +	up_read(&snap_image_destroy_lock);
> +
> +	return res;
> +}
> +
> +void _snapimage_close(struct gendisk *disk, fmode_t mode)
> +{
> +	if (disk->private_data != NULL) {
> +		down_read(&snap_image_destroy_lock);
> +		do {
> +			struct snapimage *image = disk->private_data;
> +
> +			mutex_lock(&image->open_locker);
> +			{
> +				if (image->open_cnt > 0)
> +					image->open_cnt--;
> +
> +				if (image->open_cnt == 0)
> +					image->open_bdev = NULL;
> +			}
> +			mutex_unlock(&image->open_locker);
> +		} while (false);
> +		up_read(&snap_image_destroy_lock);
> +	} else
> +		pr_err("Unable to close snapshot image: private data is not initialized\n");
> +}
> +
> +int _snapimage_ioctl(struct block_device *bdev, fmode_t mode, unsigned int cmd, unsigned long arg)
> +{
> +	int res = -ENOTTY;
> +
> +	down_read(&snap_image_destroy_lock);
> +	{
> +		struct snapimage *image = bdev->bd_disk->private_data;
> +
> +		switch (cmd) {
> +			/*
> +			 * The only command we need to interpret is HDIO_GETGEO, since
> +			 * we can't partition the drive otherwise.  We have no real
> +			 * geometry, of course, so make something up.
> +			 */
> +		case HDIO_GETGEO: {
> +			unsigned long len;
> +			struct hd_geometry geo;
> +
> +			res = _snapimage_getgeo(bdev, &geo);
> +
> +			len = copy_to_user((void *)arg, &geo, sizeof(geo));
> +			if (len != 0)
> +				res = -EFAULT;
> +			else
> +				res = SUCCESS;
> +		} break;
> +		case CDROM_GET_CAPABILITY: //0x5331  / * get capabilities * /
> +		{
> +			struct gendisk *disk = bdev->bd_disk;
> +
> +			if (bdev->bd_disk && (disk->flags & GENHD_FL_CD))
> +				res = SUCCESS;
> +			else
> +				res = -EINVAL;
> +		} break;
> +
> +		default:
> +			pr_info("Snapshot image ioctl receive unsupported command\n");
> +			pr_info("Device [%d:%d], command 0x%x, arg 0x%lx\n",
> +				MAJOR(image->image_dev), MINOR(image->image_dev), cmd, arg);
> +
> +			res = -ENOTTY; /* unknown command */
> +		}
> +	}
> +	up_read(&snap_image_destroy_lock);
> +	return res;
> +}
> +
> +blk_qc_t _snapimage_submit_bio(struct bio *bio);
> +
> +const struct block_device_operations snapimage_ops = {
> +	.owner = THIS_MODULE,
> +	.submit_bio = _snapimage_submit_bio,
> +	.open = _snapimage_open,
> +	.ioctl = _snapimage_ioctl,
> +	.release = _snapimage_close,
> +};
> +
> +static inline int _snapimage_request_read(struct snapimage *image,
> +					  struct blk_redirect_bio *rq_redir)
> +{
> +	struct snapstore_device *snapstore_device = image->defer_io->snapstore_device;
> +
> +	return snapstore_device_read(snapstore_device, rq_redir);
> +}
> +
> +int _snapimage_request_write(struct snapimage *image, struct blk_redirect_bio *rq_redir)
> +{
> +	struct snapstore_device *snapstore_device;
> +	struct cbt_map *cbt_map;
> +	int res = SUCCESS;
> +
> +	if (unlikely((image->defer_io == NULL) || (image->cbt_map == NULL))) {
> +		pr_err("Invalid snapshot image structure");
> +		return -EINVAL;
> +	}
> +
> +
> +	snapstore_device = image->defer_io->snapstore_device;
> +	cbt_map = image->cbt_map;
> +
> +	if (snapstore_device_is_corrupted(snapstore_device))
> +		return -ENODATA;
> +
> +	if (!bio_has_data(rq_redir->bio)) {
> +		pr_warn("Snapshot image receive empty block IO. flags=%u\n",
> +			rq_redir->bio->bi_flags);
> +
> +		blk_redirect_complete(rq_redir, SUCCESS);
> +		return SUCCESS;
> +	}
> +
> +	if (cbt_map != NULL) {
> +		sector_t ofs = rq_redir->bio->bi_iter.bi_sector;
> +		sector_t cnt = bio_sectors(rq_redir->bio);
> +
> +		res = cbt_map_set_both(cbt_map, ofs, cnt);
> +		if (res != SUCCESS)
> +			pr_err("Unable to write data to snapshot image: failed to set CBT map. errno=%d\n",
> +			       res);
> +	}
> +
> +	res = snapstore_device_write(snapstore_device, rq_redir);
> +
> +	if (res != SUCCESS) {
> +		pr_err("Failed to write data to snapshot image\n");
> +		return res;
> +	}
> +
> +	return res;
> +}
> +
> +void _snapimage_processing(struct snapimage *image)
> +{
> +	int res = SUCCESS;
> +	struct blk_redirect_bio *rq_redir;
> +
> +	rq_redir = redirect_bio_queue_get_first(&image->image_queue);
> +
> +	if (bio_data_dir(rq_redir->bio) == READ) {
> +		res = _snapimage_request_read(image, rq_redir);
> +		if (res != SUCCESS)
> +			pr_err("Failed to read data from snapshot image. errno=%d\n", res);
> +
> +	} else {
> +		res = _snapimage_request_write(image, rq_redir);
> +		if (res != SUCCESS)
> +			pr_err("Failed to write data to snapshot image. errno=%d\n", res);
> +	}
> +
> +	if (res != SUCCESS)
> +		blk_redirect_complete(rq_redir, res);
> +}
> +
> +int snapimage_processor_waiting(struct snapimage *image)
> +{
> +	int res = SUCCESS;
> +
> +	if (redirect_bio_queue_empty(image->image_queue)) {
> +		res = wait_event_interruptible_timeout(
> +			image->rq_proc_event,
> +			(!redirect_bio_queue_empty(image->image_queue) || kthread_should_stop()),
> +			5 * HZ);
> +		if (res > 0)
> +			res = SUCCESS;
> +		else if (res == 0)
> +			res = -ETIME;
> +	}
> +	return res;
> +}
> +
> +int snapimage_processor_thread(void *data)
> +{
> +	struct snapimage *image = data;
> +
> +	pr_info("Snapshot image thread for device [%d:%d] start\n", MAJOR(image->image_dev),
> +		MINOR(image->image_dev));
> +
> +	add_disk(image->disk);
> +
> +	//priority
> +	set_user_nice(current, -20); //MIN_NICE
> +
> +	while (!kthread_should_stop()) {
> +		int res = snapimage_processor_waiting(image);
> +
> +		if (res == SUCCESS) {
> +			if (!redirect_bio_queue_empty(image->image_queue))
> +				_snapimage_processing(image);
> +		} else if (res != -ETIME) {
> +			pr_err("Failed to wait snapshot image thread queue. errno=%d\n", res);
> +			return res;
> +		}
> +		schedule();
> +	}
> +	pr_info("Snapshot image disk delete\n");
> +	del_gendisk(image->disk);
> +
> +	while (!redirect_bio_queue_empty(image->image_queue))
> +		_snapimage_processing(image);
> +
> +	pr_info("Snapshot image thread for device [%d:%d] complete", MAJOR(image->image_dev),
> +		MINOR(image->image_dev));
> +	return 0;
> +}
> +
> +static inline void _snapimage_bio_complete(struct bio *bio, int err)
> +{
> +	if (err == SUCCESS)
> +		bio->bi_status = BLK_STS_OK;
> +	else
> +		bio->bi_status = BLK_STS_IOERR;
> +
> +	bio_endio(bio);
> +}
> +
> +void _snapimage_bio_complete_cb(void *complete_param, struct bio *bio, int err)
> +{
> +	struct snapimage *image = (struct snapimage *)complete_param;
> +
> +	_snapimage_bio_complete(bio, err);
> +
> +	if (redirect_bio_queue_unactive(image->image_queue))
> +		wake_up_interruptible(&image->rq_complete_event);
> +
> +	atomic_dec(&image->own_cnt);
> +}
> +
> +int _snapimage_throttling(struct defer_io *defer_io)
> +{
> +	return wait_event_interruptible(defer_io->queue_throttle_waiter,
> +					redirect_bio_queue_empty(defer_io->dio_queue));
> +}
> +
> +blk_qc_t _snapimage_submit_bio(struct bio *bio)
> +{
> +	blk_qc_t result = SUCCESS;
> +	struct request_queue *q = bio->bi_disk->queue;
> +	struct snapimage *image = q->queuedata;
> +
> +	if (unlikely(blk_mq_queue_stopped(q))) {
> +		pr_info("Failed to make snapshot image request. Queue already is not active.");
> +		pr_info("Queue flags=%lx\n", q->queue_flags);
> +
> +		_snapimage_bio_complete(bio, -ENODEV);
> +
> +		return result;
> +	}
> +
> +	atomic_inc(&image->own_cnt);
> +	do {
> +		int res;
> +		struct blk_redirect_bio *rq_redir;
> +
> +		if (false == atomic_read(&(image->image_queue.active_state))) {
> +			_snapimage_bio_complete(bio, -ENODEV);
> +			break;
> +		}
> +
> +		if (snapstore_device_is_corrupted(image->defer_io->snapstore_device)) {
> +			_snapimage_bio_complete(bio, -ENODATA);
> +			break;
> +		}
> +
> +		res = _snapimage_throttling(image->defer_io);
> +		if (res != SUCCESS) {
> +			pr_err("Failed to throttle snapshot image device. errno=%d\n", res);
> +			_snapimage_bio_complete(bio, res);
> +			break;
> +		}
> +
> +		rq_redir = redirect_bio_queue_new(&image->image_queue);
> +		if (rq_redir == NULL) {
> +			pr_err("Unable to make snapshot image request: failed to allocate redirect bio structure\n");
> +			_snapimage_bio_complete(bio, -ENOMEM);
> +			break;
> +		}
> +		rq_redir->bio = bio;
> +		rq_redir->complete_cb = _snapimage_bio_complete_cb;
> +		rq_redir->complete_param = (void *)image;
> +		atomic_inc(&image->own_cnt);
> +
> +		res = redirect_bio_queue_push_back(&image->image_queue, rq_redir);
> +		if (res == SUCCESS)
> +			wake_up(&image->rq_proc_event);
> +		else {
> +			redirect_bio_queue_free(rq_redir);
> +			_snapimage_bio_complete(bio, -EIO);
> +
> +			if (redirect_bio_queue_unactive(image->image_queue))
> +				wake_up_interruptible(&image->rq_complete_event);
> +		}
> +
> +	} while (false);
> +	atomic_dec(&image->own_cnt);
> +
> +	return result;
> +}
> +
> +struct blk_dev_info {
> +	size_t blk_size;
> +	sector_t start_sect;
> +	sector_t count_sect;
> +
> +	unsigned int io_min;
> +	unsigned int physical_block_size;
> +	unsigned short logical_block_size;
> +};
> +
> +static int _blk_dev_get_info(struct block_device *blk_dev, struct blk_dev_info *pdev_info)
> +{
> +	sector_t SectorStart;
> +	sector_t SectorsCapacity;
> +
> +	if (blk_dev->bd_part)
> +		SectorsCapacity = blk_dev->bd_part->nr_sects;
> +	else if (blk_dev->bd_disk)
> +		SectorsCapacity = get_capacity(blk_dev->bd_disk);
> +	else
> +		return -EINVAL;
> +
> +	SectorStart = get_start_sect(blk_dev);
> +
> +	pdev_info->physical_block_size = blk_dev->bd_disk->queue->limits.physical_block_size;
> +	pdev_info->logical_block_size = blk_dev->bd_disk->queue->limits.logical_block_size;
> +	pdev_info->io_min = blk_dev->bd_disk->queue->limits.io_min;
> +
> +	pdev_info->blk_size = block_size(blk_dev);
> +	pdev_info->start_sect = SectorStart;
> +	pdev_info->count_sect = SectorsCapacity;
> +	return SUCCESS;
> +}
> +
> +static int blk_dev_get_info(dev_t dev_id, struct blk_dev_info *pdev_info)
> +{
> +	int result = SUCCESS;
> +	struct block_device *blk_dev;
> +
> +	result = blk_dev_open(dev_id, &blk_dev);
> +	if (result != SUCCESS) {
> +		pr_err("Failed to open device [%d:%d]\n", MAJOR(dev_id), MINOR(dev_id));
> +		return result;
> +	}
> +
> +	result = _blk_dev_get_info(blk_dev, pdev_info);
> +	if (result != SUCCESS)
> +		pr_err("Failed to identify block device [%d:%d]\n", MAJOR(dev_id), MINOR(dev_id));
> +
> +	blk_dev_close(blk_dev);
> +
> +	return result;
> +}
> +
> +static inline void _snapimage_free(struct snapimage *image)
> +{
> +	defer_io_put_resource(image->defer_io);
> +	cbt_map_put_resource(image->cbt_map);
> +	image->defer_io = NULL;
> +}
> +
> +static void _snapimage_stop(struct snapimage *image)
> +{
> +	if (image->rq_processor != NULL) {
> +		if (redirect_bio_queue_active(&image->image_queue, false)) {
> +			struct request_queue *q = image->queue;
> +
> +			pr_info("Snapshot image request processing stop\n");
> +
> +			if (!blk_queue_stopped(q)) {
> +				blk_sync_queue(q);
> +				blk_mq_stop_hw_queues(q);
> +			}
> +		}
> +
> +		pr_info("Snapshot image thread stop\n");
> +		kthread_stop(image->rq_processor);
> +		image->rq_processor = NULL;
> +
> +		while (!redirect_bio_queue_unactive(image->image_queue))
> +			wait_event_interruptible(image->rq_complete_event,
> +						 redirect_bio_queue_unactive(image->image_queue));
> +	}
> +}
> +
> +static void _snapimage_destroy(struct snapimage *image)
> +{
> +	if (image->rq_processor != NULL)
> +		_snapimage_stop(image);
> +
> +	if (image->queue) {
> +		pr_info("Snapshot image queue cleanup\n");
> +		blk_cleanup_queue(image->queue);
> +		image->queue = NULL;
> +	}
> +
> +	if (image->disk != NULL) {
> +		struct gendisk *disk;
> +
> +		disk = image->disk;
> +		image->disk = NULL;
> +
> +		pr_info("Snapshot image disk structure release\n");
> +
> +		disk->private_data = NULL;
> +		put_disk(disk);
> +	}
> +
> +	spin_lock(&snapimage_minors_lock);
> +	bitmap_clear(snapimage_minors, MINOR(image->image_dev), 1u);
> +	spin_unlock(&snapimage_minors_lock);
> +}
> +
> +int snapimage_create(dev_t original_dev)
> +{
> +	int res = SUCCESS;
> +	struct tracker *tracker = NULL;
> +	struct snapimage *image = NULL;
> +	struct gendisk *disk = NULL;
> +	int minor;
> +	struct blk_dev_info original_dev_info;
> +
> +	pr_info("Create snapshot image for device [%d:%d]\n", MAJOR(original_dev),
> +		MINOR(original_dev));
> +
> +	res = blk_dev_get_info(original_dev, &original_dev_info);
> +	if (res != SUCCESS) {
> +		pr_err("Failed to obtain original device info\n");
> +		return res;
> +	}
> +
> +	res = tracker_find_by_dev_id(original_dev, &tracker);
> +	if (res != SUCCESS) {
> +		pr_err("Unable to create snapshot image: cannot find tracker for device [%d:%d]\n",
> +		       MAJOR(original_dev), MINOR(original_dev));
> +		return res;
> +	}
> +
> +	image = kzalloc(sizeof(struct snapimage), GFP_KERNEL);
> +	if (image == NULL)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&image->link);
> +
> +	do {
> +		spin_lock(&snapimage_minors_lock);
> +		minor = bitmap_find_free_region(snapimage_minors, SNAPIMAGE_MAX_DEVICES, 0);
> +		spin_unlock(&snapimage_minors_lock);
> +
> +		if (minor < SUCCESS) {
> +			pr_err("Failed to allocate minor for snapshot image device. errno=%d\n",
> +			       0 - minor);
> +			break;
> +		}
> +
> +		image->rq_processor = NULL;
> +
> +		image->capacity = original_dev_info.count_sect;
> +
> +		image->defer_io = defer_io_get_resource(tracker->defer_io);
> +		image->cbt_map = cbt_map_get_resource(tracker->cbt_map);
> +		image->original_dev = original_dev;
> +
> +		image->image_dev = MKDEV(snapimage_major, minor);
> +		pr_info("Snapshot image device id [%d:%d]\n", MAJOR(image->image_dev),
> +			MINOR(image->image_dev));
> +
> +		atomic_set(&image->own_cnt, 0);
> +
> +		mutex_init(&image->open_locker);
> +		image->open_bdev = NULL;
> +		image->open_cnt = 0;
> +
> +		image->queue = blk_alloc_queue(NUMA_NO_NODE);
> +		if (image->queue == NULL) {
> +			res = -ENOMEM;
> +			break;
> +		}
> +		image->queue->queuedata = image;
> +
> +		blk_queue_max_segment_size(image->queue, 1024 * PAGE_SIZE);
> +
> +		{
> +			unsigned int physical_block_size = original_dev_info.physical_block_size;
> +			unsigned short logical_block_size = original_dev_info.logical_block_size;
> +
> +			pr_info("Snapshot image physical block size %d\n", physical_block_size);
> +			pr_info("Snapshot image logical block size %d\n", logical_block_size);
> +
> +			blk_queue_physical_block_size(image->queue, physical_block_size);
> +			blk_queue_logical_block_size(image->queue, logical_block_size);
> +		}
> +		disk = alloc_disk(1); //only one partition on disk
> +		if (disk == NULL) {
> +			pr_err("Failed to allocate disk for snapshot image device\n");
> +			res = -ENOMEM;
> +			break;
> +		}
> +		image->disk = disk;
> +
> +		if (snprintf(disk->disk_name, DISK_NAME_LEN, "%s%d", SNAP_IMAGE_NAME, minor) < 0) {
> +			pr_err("Unable to set disk name for snapshot image device: invalid minor %d\n",
> +			       minor);
> +			res = -EINVAL;
> +			break;
> +		}
> +
> +		pr_info("Snapshot image disk name [%s]", disk->disk_name);
> +
> +		disk->flags |= GENHD_FL_NO_PART_SCAN;
> +		disk->flags |= GENHD_FL_REMOVABLE;
> +
> +		disk->major = snapimage_major;
> +		disk->minors = 1; // one disk have only one partition.
> +		disk->first_minor = minor;
> +
> +		disk->private_data = image;
> +
> +		disk->fops = &snapimage_ops;
> +		disk->queue = image->queue;
> +
> +		set_capacity(disk, image->capacity);
> +		pr_info("Snapshot image device capacity %lld bytes",
> +			(u64)from_sectors(image->capacity));
> +
> +		//res = -ENOMEM;
> +		redirect_bio_queue_init(&image->image_queue);
> +
> +		{
> +			struct task_struct *task =
> +				kthread_create(snapimage_processor_thread, image, disk->disk_name);
> +			if (IS_ERR(task)) {
> +				res = PTR_ERR(task);
> +				pr_err("Failed to create request processing thread for snapshot image device. errno=%d\n",
> +				       res);
> +				break;
> +			}
> +			image->rq_processor = task;
> +		}
> +		init_waitqueue_head(&image->rq_complete_event);
> +
> +		init_waitqueue_head(&image->rq_proc_event);
> +		wake_up_process(image->rq_processor);
> +	} while (false);
> +
> +	if (res == SUCCESS) {
> +		down_write(&snap_images_lock);
> +		list_add_tail(&image->link, &snap_images);
> +		up_write(&snap_images_lock);
> +	} else {
> +		_snapimage_destroy(image);
> +		_snapimage_free(image);
> +
> +		kfree(image);
> +		image = NULL;
> +	}
> +	return res;
> +}
> +
> +static struct snapimage *snapimage_find(dev_t original_dev)
> +{
> +	struct snapimage *image = NULL;
> +
> +	down_read(&snap_images_lock);
> +	if (!list_empty(&snap_images)) {
> +		struct list_head *_list_head;
> +
> +		list_for_each(_list_head, &snap_images) {
> +			struct snapimage *_image = list_entry(_list_head, struct snapimage, link);
> +
> +			if (_image->original_dev == original_dev) {
> +				image = _image;
> +				break;
> +			}
> +		}
> +	}
> +	up_read(&snap_images_lock);
> +
> +	return image;
> +}
> +
> +void snapimage_stop(dev_t original_dev)
> +{
> +	struct snapimage *image;
> +
> +	pr_info("Snapshot image processing stop for original device [%d:%d]\n", MAJOR(original_dev),
> +		MINOR(original_dev));
> +
> +	down_read(&snap_image_destroy_lock);
> +
> +	image = snapimage_find(original_dev);
> +	if (image != NULL)
> +		_snapimage_stop(image);
> +	else
> +		pr_err("Snapshot image [%d:%d] not found\n", MAJOR(original_dev),
> +		       MINOR(original_dev));
> +
> +	up_read(&snap_image_destroy_lock);
> +}
> +
> +void snapimage_destroy(dev_t original_dev)
> +{
> +	struct snapimage *image = NULL;
> +
> +	pr_info("Destroy snapshot image for device [%d:%d]\n", MAJOR(original_dev),
> +		MINOR(original_dev));
> +
> +	down_write(&snap_images_lock);
> +	if (!list_empty(&snap_images)) {
> +		struct list_head *_list_head;
> +
> +		list_for_each(_list_head, &snap_images) {
> +			struct snapimage *_image = list_entry(_list_head, struct snapimage, link);
> +
> +			if (_image->original_dev == original_dev) {
> +				image = _image;
> +				list_del(&image->link);
> +				break;
> +			}
> +		}
> +	}
> +	up_write(&snap_images_lock);
> +
> +	if (image != NULL) {
> +		down_write(&snap_image_destroy_lock);
> +
> +		_snapimage_destroy(image);
> +		_snapimage_free(image);
> +
> +		kfree(image);
> +		image = NULL;
> +
> +		up_write(&snap_image_destroy_lock);
> +	} else
> +		pr_err("Snapshot image [%d:%d] not found\n", MAJOR(original_dev),
> +		       MINOR(original_dev));
> +}
> +
> +void snapimage_destroy_for(dev_t *p_dev, int count)
> +{
> +	int inx = 0;
> +
> +	for (; inx < count; ++inx)
> +		snapimage_destroy(p_dev[inx]);
> +}
> +
> +int snapimage_create_for(dev_t *p_dev, int count)
> +{
> +	int res = SUCCESS;
> +	int inx = 0;
> +
> +	for (; inx < count; ++inx) {
> +		res = snapimage_create(p_dev[inx]);
> +		if (res != SUCCESS) {
> +			pr_err("Failed to create snapshot image for original device [%d:%d]\n",
> +			       MAJOR(p_dev[inx]), MINOR(p_dev[inx]));
> +			break;
> +		}
> +	}
> +	if (res != SUCCESS)
> +		if (inx > 0)
> +			snapimage_destroy_for(p_dev, inx - 1);
> +	return res;
> +}
> +
> +int snapimage_init(void)
> +{
> +	int res = SUCCESS;
> +
> +	res = register_blkdev(snapimage_major, SNAP_IMAGE_NAME);
> +	if (res >= SUCCESS) {
> +		snapimage_major = res;
> +		pr_info("Snapshot image block device major %d was registered\n", snapimage_major);
> +		res = SUCCESS;
> +
> +		spin_lock(&snapimage_minors_lock);
> +		snapimage_minors = bitmap_zalloc(SNAPIMAGE_MAX_DEVICES, GFP_KERNEL);
> +		spin_unlock(&snapimage_minors_lock);
> +
> +		if (snapimage_minors == NULL)
> +			pr_err("Failed to initialize bitmap of minors\n");
> +	} else
> +		pr_err("Failed to register snapshot image block device. errno=%d\n", res);
> +
> +	return res;
> +}
> +
> +void snapimage_done(void)
> +{
> +	down_write(&snap_image_destroy_lock);
> +	while (true) {
> +		struct snapimage *image = NULL;
> +
> +		down_write(&snap_images_lock);
> +		if (!list_empty(&snap_images)) {
> +			image = list_entry(snap_images.next, struct snapimage, link);
> +
> +			list_del(&image->link);
> +		}
> +		up_write(&snap_images_lock);
> +
> +		if (image == NULL)
> +			break;
> +
> +		pr_err("Snapshot image for device was unexpectedly removed [%d:%d]\n",
> +		       MAJOR(image->original_dev), MINOR(image->original_dev));
> +
> +		_snapimage_destroy(image);
> +		_snapimage_free(image);
> +
> +		kfree(image);
> +		image = NULL;
> +	}
> +
> +	spin_lock(&snapimage_minors_lock);
> +	bitmap_free(snapimage_minors);
> +	snapimage_minors = NULL;
> +	spin_unlock(&snapimage_minors_lock);
> +
> +	if (!list_empty(&snap_images))
> +		pr_err("Failed to release snapshot images container\n");
> +
> +	unregister_blkdev(snapimage_major, SNAP_IMAGE_NAME);
> +	pr_info("Snapshot image block device [%d] was unregistered\n", snapimage_major);
> +
> +	up_write(&snap_image_destroy_lock);
> +}
> +
> +int snapimage_collect_images(int count, struct image_info_s *p_user_image_info, int *p_real_count)
> +{
> +	int res = SUCCESS;
> +	int real_count = 0;
> +
> +	down_read(&snap_images_lock);
> +	if (!list_empty(&snap_images)) {
> +		struct list_head *_list_head;
> +
> +		list_for_each(_list_head, &snap_images)
> +			real_count++;
> +	}
> +	up_read(&snap_images_lock);
> +	*p_real_count = real_count;
> +
> +	if (count < real_count)
> +		res = -ENODATA;
> +
> +	real_count = min(count, real_count);
> +	if (real_count > 0) {
> +		unsigned long len;
> +		struct image_info_s *p_kernel_image_info = NULL;
> +		size_t buff_size;
> +
> +		buff_size = sizeof(struct image_info_s) * real_count;
> +		p_kernel_image_info = kzalloc(buff_size, GFP_KERNEL);
> +		if (p_kernel_image_info == NULL) {
> +			pr_err("Unable to collect snapshot images: not enough memory. size=%zu\n",
> +			       buff_size);
> +			return res = -ENOMEM;
> +		}
> +
> +		down_read(&snap_image_destroy_lock);
> +		down_read(&snap_images_lock);
> +
> +		if (!list_empty(&snap_images)) {
> +			size_t inx = 0;
> +			struct list_head *_list_head;
> +
> +			list_for_each(_list_head, &snap_images) {
> +				struct snapimage *img =
> +					list_entry(_list_head, struct snapimage, link);
> +
> +				real_count++;
> +
> +				p_kernel_image_info[inx].original_dev_id.major =
> +					MAJOR(img->original_dev);
> +				p_kernel_image_info[inx].original_dev_id.minor =
> +					MINOR(img->original_dev);
> +
> +				p_kernel_image_info[inx].snapshot_dev_id.major =
> +					MAJOR(img->image_dev);
> +				p_kernel_image_info[inx].snapshot_dev_id.minor =
> +					MINOR(img->image_dev);
> +
> +				++inx;
> +				if (inx > real_count)
> +					break;
> +			}
> +		}
> +
> +		up_read(&snap_images_lock);
> +		up_read(&snap_image_destroy_lock);
> +
> +		len = copy_to_user(p_user_image_info, p_kernel_image_info, buff_size);
> +		if (len != 0) {
> +			pr_err("Unable to collect snapshot images: failed to copy data to user buffer\n");
> +			res = -ENODATA;
> +		}
> +
> +		kfree(p_kernel_image_info);
> +	}
> +
> +	return res;
> +}
> +
> +int snapimage_mark_dirty_blocks(dev_t image_dev_id, struct block_range_s *block_ranges,
> +				unsigned int count)
> +{
> +	size_t inx = 0;
> +	int res = SUCCESS;
> +
> +	pr_info("Marking [%d] dirty blocks for image device [%d:%d]\n", count, MAJOR(image_dev_id),
> +		MINOR(image_dev_id));
> +
> +	down_read(&snap_image_destroy_lock);
> +	do {
> +		struct snapimage *image = snapimage_find(image_dev_id);
> +
> +		if (image == NULL) {
> +			pr_err("Cannot find device [%d:%d]\n", MAJOR(image_dev_id),
> +			       MINOR(image_dev_id));
> +			res = -ENODEV;
> +			break;
> +		}
> +
> +		for (inx = 0; inx < count; ++inx) {
> +			sector_t ofs = (sector_t)block_ranges[inx].ofs;
> +			sector_t cnt = (sector_t)block_ranges[inx].cnt;
> +
> +			res = cbt_map_set_both(image->cbt_map, ofs, cnt);
> +			if (res != SUCCESS) {
> +				pr_err("Failed to set CBT table. errno=%d\n", res);
> +				break;
> +			}
> +		}
> +	} while (false);
> +	up_read(&snap_image_destroy_lock);
> +
> +	return res;
> +}
> diff --git a/drivers/block/blk-snap/snapimage.h b/drivers/block/blk-snap/snapimage.h
> new file mode 100644
> index 000000000000..67995c321496
> --- /dev/null
> +++ b/drivers/block/blk-snap/snapimage.h
> @@ -0,0 +1,16 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#pragma once
> +
> +#include "blk-snap-ctl.h"
> +
> +int snapimage_init(void);
> +void snapimage_done(void);
> +int snapimage_create_for(dev_t *p_dev, int count);
> +
> +void snapimage_stop(dev_t original_dev);
> +void snapimage_destroy(dev_t original_dev);
> +
> +int snapimage_collect_images(int count, struct image_info_s *p_user_image_info, int *p_real_count);
> +
> +int snapimage_mark_dirty_blocks(dev_t image_dev_id, struct block_range_s *block_ranges,
> +				unsigned int count);
> diff --git a/drivers/block/blk-snap/snapshot.c b/drivers/block/blk-snap/snapshot.c
> new file mode 100644
> index 000000000000..fdef713103d2
> --- /dev/null
> +++ b/drivers/block/blk-snap/snapshot.c
> @@ -0,0 +1,225 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-snapshot"
> +#include "common.h"
> +#include "snapshot.h"
> +#include "tracker.h"
> +#include "snapimage.h"
> +#include "tracking.h"
> +
> +LIST_HEAD(snapshots);
> +DECLARE_RWSEM(snapshots_lock);
> +
> +
> +static int _snapshot_remove_device(dev_t dev_id)
> +{
> +	int result;
> +	struct tracker *tracker = NULL;
> +
> +	result = tracker_find_by_dev_id(dev_id, &tracker);
> +	if (result != SUCCESS) {
> +		if (result == -ENODEV)
> +			pr_err("Cannot find device by device id=[%d:%d]\n", MAJOR(dev_id),
> +			       MINOR(dev_id));
> +		else
> +			pr_err("Failed to find device by device id=[%d:%d]\n", MAJOR(dev_id),
> +			       MINOR(dev_id));
> +		return SUCCESS;
> +	}
> +
> +	if (result != SUCCESS)
> +		return result;
> +
> +	tracker->snapshot_id = 0ull;
> +
> +	pr_info("Device [%d:%d] successfully removed from snapshot\n", MAJOR(dev_id),
> +		MINOR(dev_id));
> +	return SUCCESS;
> +}
> +
> +static void _snapshot_cleanup(struct snapshot *snapshot)
> +{
> +	int inx;
> +
> +	for (inx = 0; inx < snapshot->dev_id_set_size; ++inx) {
> +
> +		if (_snapshot_remove_device(snapshot->dev_id_set[inx]) != SUCCESS)
> +			pr_err("Failed to remove device [%d:%d] from snapshot\n",
> +			       MAJOR(snapshot->dev_id_set[inx]), MINOR(snapshot->dev_id_set[inx]));
> +	}
> +
> +	if (snapshot->dev_id_set != NULL)
> +		kfree(snapshot->dev_id_set);
> +	kfree(snapshot);
> +}
> +
> +static void _snapshot_destroy(struct snapshot *snapshot)
> +{
> +	size_t inx;
> +
> +	for (inx = 0; inx < snapshot->dev_id_set_size; ++inx)
> +		snapimage_stop(snapshot->dev_id_set[inx]);
> +
> +	pr_info("Release snapshot [0x%llx]\n", snapshot->id);
> +
> +	tracker_release_snapshot(snapshot->dev_id_set, snapshot->dev_id_set_size);
> +
> +	for (inx = 0; inx < snapshot->dev_id_set_size; ++inx)
> +		snapimage_destroy(snapshot->dev_id_set[inx]);
> +
> +	_snapshot_cleanup(snapshot);
> +}
> +
> +
> +static int _snapshot_new(dev_t *p_dev, int count, struct snapshot **pp_snapshot)
> +{
> +	struct snapshot *p_snapshot = NULL;
> +	dev_t *snap_set = NULL;
> +
> +	p_snapshot = kzalloc(sizeof(struct snapshot), GFP_KERNEL);
> +	if (p_snapshot == NULL)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&p_snapshot->link);
> +
> +	p_snapshot->id = (unsigned long)(p_snapshot);
> +
> +	snap_set = kcalloc(count, sizeof(dev_t), GFP_KERNEL);
> +	if (snap_set == NULL) {
> +		kfree(p_snapshot);
> +
> +		pr_err("Unable to create snapshot: faile to allocate memory for snapshot map\n");
> +		return -ENOMEM;
> +	}
> +	memcpy(snap_set, p_dev, sizeof(dev_t) * count);
> +
> +	p_snapshot->dev_id_set_size = count;
> +	p_snapshot->dev_id_set = snap_set;
> +
> +	down_write(&snapshots_lock);
> +	list_add_tail(&snapshots, &p_snapshot->link);
> +	up_write(&snapshots_lock);
> +
> +	*pp_snapshot = p_snapshot;
> +
> +	return SUCCESS;
> +}
> +
> +void snapshot_done(void)
> +{
> +	struct snapshot *snap;
> +
> +	pr_info("Removing all snapshots\n");
> +	do {
> +		snap = NULL;
> +		down_write(&snapshots_lock);
> +		if (!list_empty(&snapshots)) {
> +			struct snapshot *snap = list_entry(snapshots.next, struct snapshot, link);
> +
> +			list_del(&snap->link);
> +		}
> +		up_write(&snapshots_lock);
> +
> +		if (snap)
> +			_snapshot_destroy(snap);
> +
> +	} while (snap);
> +}
> +
> +int snapshot_create(dev_t *dev_id_set, unsigned int dev_id_set_size,
> +		    unsigned long long *p_snapshot_id)
> +{
> +	struct snapshot *snapshot = NULL;
> +	int result = SUCCESS;
> +	unsigned int inx;
> +
> +	pr_info("Create snapshot for devices:\n");
> +	for (inx = 0; inx < dev_id_set_size; ++inx)
> +		pr_info("\t%d:%d\n", MAJOR(dev_id_set[inx]), MINOR(dev_id_set[inx]));
> +
> +	result = _snapshot_new(dev_id_set, dev_id_set_size, &snapshot);
> +	if (result != SUCCESS) {
> +		pr_err("Unable to create snapshot: failed to allocate snapshot structure\n");
> +		return result;
> +	}
> +
> +	do {
> +		result = -ENODEV;
> +		for (inx = 0; inx < snapshot->dev_id_set_size; ++inx) {
> +			dev_t dev_id = snapshot->dev_id_set[inx];
> +
> +			result = tracking_add(dev_id, snapshot->id);
> +			if (result == -EALREADY)
> +				result = SUCCESS;
> +			else if (result != SUCCESS) {
> +				pr_err("Unable to create snapshot\n");
> +				pr_err("Failed to add device [%d:%d] to snapshot tracking\n",
> +				       MAJOR(dev_id), MINOR(dev_id));
> +				break;
> +			}
> +		}
> +		if (result != SUCCESS)
> +			break;
> +
> +		result = tracker_capture_snapshot(snapshot->dev_id_set, snapshot->dev_id_set_size);
> +		if (result != SUCCESS) {
> +			pr_err("Unable to create snapshot: failed to capture snapshot [0x%llx]\n",
> +			       snapshot->id);
> +			break;
> +		}
> +
> +		result = snapimage_create_for(snapshot->dev_id_set, snapshot->dev_id_set_size);
> +		if (result != SUCCESS) {
> +			pr_err("Unable to create snapshot\n");
> +			pr_err("Failed to create snapshot image devices\n");
> +
> +			tracker_release_snapshot(snapshot->dev_id_set, snapshot->dev_id_set_size);
> +			break;
> +		}
> +
> +		*p_snapshot_id = snapshot->id;
> +		pr_info("Snapshot [0x%llx] was created\n", snapshot->id);
> +	} while (false);
> +
> +	if (result != SUCCESS) {
> +		pr_info("Snapshot [0x%llx] cleanup\n", snapshot->id);
> +
> +		down_write(&snapshots_lock);
> +		list_del(&snapshot->link);
> +		up_write(&snapshots_lock);
> +
> +		_snapshot_cleanup(snapshot);
> +	}
> +	return result;
> +}
> +
> +int snapshot_destroy(unsigned long long snapshot_id)
> +{
> +	struct snapshot *snapshot = NULL;
> +
> +	pr_info("Destroy snapshot [0x%llx]\n", snapshot_id);
> +
> +	down_read(&snapshots_lock);
> +	if (!list_empty(&snapshots)) {
> +		struct list_head *_head;
> +
> +		list_for_each(_head, &snapshots) {
> +			struct snapshot *_snap = list_entry(_head, struct snapshot, link);
> +
> +			if (_snap->id == snapshot_id) {
> +				snapshot = _snap;
> +				list_del(&snapshot->link);
> +				break;
> +			}
> +		}
> +	}
> +	up_read(&snapshots_lock);
> +
> +	if (snapshot == NULL) {
> +		pr_err("Unable to destroy snapshot [0x%llx]: cannot find snapshot by id\n",
> +		       snapshot_id);
> +		return -ENODEV;
> +	}
> +
> +	_snapshot_destroy(snapshot);
> +	return SUCCESS;
> +}
> diff --git a/drivers/block/blk-snap/snapshot.h b/drivers/block/blk-snap/snapshot.h
> new file mode 100644
> index 000000000000..59fb4dba0241
> --- /dev/null
> +++ b/drivers/block/blk-snap/snapshot.h
> @@ -0,0 +1,17 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#pragma once
> +
> +struct snapshot {
> +	struct list_head link;
> +	unsigned long long id;
> +
> +	dev_t *dev_id_set; //array of assigned devices
> +	int dev_id_set_size;
> +};
> +
> +void snapshot_done(void);
> +
> +int snapshot_create(dev_t *dev_id_set, unsigned int dev_id_set_size,
> +		    unsigned long long *p_snapshot_id);
> +
> +int snapshot_destroy(unsigned long long snapshot_id);
> diff --git a/drivers/block/blk-snap/snapstore.c b/drivers/block/blk-snap/snapstore.c
> new file mode 100644
> index 000000000000..0bedeaeec021
> --- /dev/null
> +++ b/drivers/block/blk-snap/snapstore.c
> @@ -0,0 +1,929 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-snapstore"
> +#include "common.h"
> +#include "snapstore.h"
> +#include "snapstore_device.h"
> +#include "big_buffer.h"
> +#include "params.h"
> +
> +LIST_HEAD(snapstores);
> +DECLARE_RWSEM(snapstores_lock);
> +
> +bool _snapstore_check_halffill(struct snapstore *snapstore, sector_t *fill_status)
> +{
> +	struct blk_descr_pool *pool = NULL;
> +
> +	if (snapstore->file)
> +		pool = &snapstore->file->pool;
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +	else if (snapstore->multidev)
> +		pool = &snapstore->multidev->pool;
> +#endif
> +	else if (snapstore->mem)
> +		pool = &snapstore->mem->pool;
> +
> +	if (pool)
> +		return blk_descr_pool_check_halffill(pool, snapstore->empty_limit, fill_status);
> +
> +	return false;
> +}
> +
> +void _snapstore_destroy(struct snapstore *snapstore)
> +{
> +	sector_t fill_status;
> +
> +	pr_info("Destroy snapstore with id %pUB\n", &snapstore->id);
> +
> +	_snapstore_check_halffill(snapstore, &fill_status);
> +
> +	down_write(&snapstores_lock);
> +	list_del(&snapstore->link);
> +	up_write(&snapstores_lock);
> +
> +	if (snapstore->mem != NULL)
> +		snapstore_mem_destroy(snapstore->mem);
> +	if (snapstore->multidev != NULL)
> +		snapstore_multidev_destroy(snapstore->multidev);
> +	if (snapstore->file != NULL)
> +		snapstore_file_destroy(snapstore->file);
> +
> +	if (snapstore->ctrl_pipe) {
> +		struct ctrl_pipe *pipe;
> +
> +		pipe = snapstore->ctrl_pipe;
> +		snapstore->ctrl_pipe = NULL;
> +
> +		ctrl_pipe_request_terminate(pipe, fill_status);
> +
> +		ctrl_pipe_put_resource(pipe);
> +	}
> +
> +	kfree(snapstore);
> +}
> +
> +static void _snapstore_destroy_cb(struct kref *kref)
> +{
> +	struct snapstore *snapstore = container_of(kref, struct snapstore, refcount);
> +
> +	_snapstore_destroy(snapstore);
> +}
> +
> +struct snapstore *snapstore_get(struct snapstore *snapstore)
> +{
> +	if (snapstore)
> +		kref_get(&snapstore->refcount);
> +
> +	return snapstore;
> +}
> +
> +void snapstore_put(struct snapstore *snapstore)
> +{
> +	if (snapstore)
> +		kref_put(&snapstore->refcount, _snapstore_destroy_cb);
> +}
> +
> +void snapstore_done(void)
> +{
> +	bool is_empty;
> +
> +	down_read(&snapstores_lock);
> +	is_empty = list_empty(&snapstores);
> +	up_read(&snapstores_lock);
> +
> +	if (!is_empty)
> +		pr_err("Unable to perform snapstore cleanup: container is not empty\n");
> +}
> +
> +int snapstore_create(uuid_t *id, dev_t snapstore_dev_id, dev_t *dev_id_set,
> +		     size_t dev_id_set_length)
> +{
> +	int res = SUCCESS;
> +	size_t dev_id_inx;
> +	struct snapstore *snapstore = NULL;
> +
> +	if (dev_id_set_length == 0)
> +		return -EINVAL;
> +
> +	snapstore = kzalloc(sizeof(struct snapstore), GFP_KERNEL);
> +	if (snapstore == NULL)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&snapstore->link);
> +	uuid_copy(&snapstore->id, id);
> +
> +	pr_info("Create snapstore with id %pUB\n", &snapstore->id);
> +
> +	snapstore->mem = NULL;
> +	snapstore->multidev = NULL;
> +	snapstore->file = NULL;
> +
> +	snapstore->ctrl_pipe = NULL;
> +	snapstore->empty_limit = (sector_t)(64 * (1024 * 1024 / SECTOR_SIZE)); //by default value
> +	snapstore->halffilled = false;
> +	snapstore->overflowed = false;
> +
> +	if (snapstore_dev_id == 0)
> +		pr_info("Memory snapstore create\n");
> +
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +	else if (snapstore_dev_id == 0xFFFFffff) {
> +		struct snapstore_multidev *multidev = NULL;
> +
> +		res = snapstore_multidev_create(&multidev);
> +		if (res != SUCCESS) {
> +			kfree(snapstore);
> +
> +			pr_err("Failed to create multidevice snapstore %pUB\n", id);
> +			return res;
> +		}
> +		snapstore->multidev = multidev;
> +	}
> +#endif
> +	else {
> +		struct snapstore_file *file = NULL;
> +
> +		res = snapstore_file_create(snapstore_dev_id, &file);
> +		if (res != SUCCESS) {
> +			kfree(snapstore);
> +
> +			pr_err("Failed to create snapstore file for snapstore %pUB\n", id);
> +			return res;
> +		}
> +		snapstore->file = file;
> +	}
> +
> +	down_write(&snapstores_lock);
> +	list_add_tail(&snapstores, &snapstore->link);
> +	up_write(&snapstores_lock);
> +
> +	kref_init(&snapstore->refcount);
> +
> +	for (dev_id_inx = 0; dev_id_inx < dev_id_set_length; ++dev_id_inx) {
> +		res = snapstore_device_create(dev_id_set[dev_id_inx], snapstore);
> +		if (res != SUCCESS)
> +			break;
> +	}
> +
> +	if (res != SUCCESS)
> +		snapstore_device_cleanup(id);
> +
> +	snapstore_put(snapstore);
> +	return res;
> +}
> +
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +int snapstore_create_multidev(uuid_t *id, dev_t *dev_id_set, size_t dev_id_set_length)
> +{
> +	int res = SUCCESS;
> +	size_t dev_id_inx;
> +	struct snapstore *snapstore = NULL;
> +	struct snapstore_multidev *multidev = NULL;
> +
> +	if (dev_id_set_length == 0)
> +		return -EINVAL;
> +
> +	snapstore = kzalloc(sizeof(struct snapstore), GFP_KERNEL);
> +	if (snapstore == NULL)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&snapstore->link);
> +
> +	uuid_copy(&snapstore->id, id);
> +
> +	pr_info("Create snapstore with id %pUB\n", &snapstore->id);
> +
> +	snapstore->mem = NULL;
> +	snapstore->file = NULL;
> +	snapstore->multidev = NULL;
> +
> +	snapstore->ctrl_pipe = NULL;
> +	snapstore->empty_limit = (sector_t)(64 * (1024 * 1024 / SECTOR_SIZE)); //by default value
> +	snapstore->halffilled = false;
> +	snapstore->overflowed = false;
> +
> +	res = snapstore_multidev_create(&multidev);
> +	if (res != SUCCESS) {
> +		kfree(snapstore);
> +
> +		pr_err("Failed to create snapstore file for snapstore %pUB\n", id);
> +		return res;
> +	}
> +	snapstore->multidev = multidev;
> +
> +	down_write(&snapstores_lock);
> +	list_add_tail(&snapstore->link, &snapstores);
> +	up_write(&snapstores_lock);
> +
> +	kref_init(&snapstore->refcount);
> +
> +	for (dev_id_inx = 0; dev_id_inx < dev_id_set_length; ++dev_id_inx) {
> +		res = snapstore_device_create(dev_id_set[dev_id_inx], snapstore);
> +		if (res != SUCCESS)
> +			break;
> +	}
> +
> +	if (res != SUCCESS)
> +		snapstore_device_cleanup(id);
> +
> +	snapstore_put(snapstore);
> +	return res;
> +}
> +#endif
> +
> +int snapstore_cleanup(uuid_t *id, u64 *filled_bytes)
> +{
> +	int res;
> +	sector_t filled;
> +
> +	res = snapstore_check_halffill(id, &filled);
> +	if (res == SUCCESS) {
> +		*filled_bytes = (u64)from_sectors(filled);
> +
> +		pr_info("Snapstore fill size: %lld MiB\n", (*filled_bytes >> 20));
> +	} else {
> +		*filled_bytes = -1;
> +		pr_err("Failed to obtain snapstore data filled size\n");
> +	}
> +
> +	return snapstore_device_cleanup(id);
> +}
> +
> +struct snapstore *_snapstore_find(uuid_t *id)
> +{
> +	struct snapstore *result = NULL;
> +
> +	down_read(&snapstores_lock);
> +	if (!list_empty(&snapstores)) {
> +		struct list_head *_head;
> +
> +		list_for_each(_head, &snapstores) {
> +			struct snapstore *snapstore = list_entry(_head, struct snapstore, link);
> +
> +			if (uuid_equal(&snapstore->id, id)) {
> +				result = snapstore;
> +				break;
> +			}
> +		}
> +	}
> +	up_read(&snapstores_lock);
> +
> +	return result;
> +}
> +
> +int snapstore_stretch_initiate(uuid_t *unique_id, struct ctrl_pipe *ctrl_pipe, sector_t empty_limit)
> +{
> +	struct snapstore *snapstore;
> +
> +	snapstore = _snapstore_find(unique_id);
> +	if (snapstore == NULL) {
> +		pr_err("Unable to initiate stretch snapstore: ");
> +		pr_err("cannot find snapstore by uuid %pUB\n", unique_id);
> +		return -ENODATA;
> +	}
> +
> +	snapstore->ctrl_pipe = ctrl_pipe_get_resource(ctrl_pipe);
> +	snapstore->empty_limit = empty_limit;
> +
> +	return SUCCESS;
> +}
> +
> +int snapstore_add_memory(uuid_t *id, unsigned long long sz)
> +{
> +	int res = SUCCESS;
> +	struct snapstore *snapstore = NULL;
> +	size_t available_blocks = (size_t)(sz >> (snapstore_block_shift() + SECTOR_SHIFT));
> +	size_t current_block = 0;
> +
> +	pr_info("Adding %lld bytes to the snapstore\n", sz);
> +
> +	snapstore = _snapstore_find(id);
> +	if (snapstore == NULL) {
> +		pr_err("Unable to add memory block to the snapstore: ");
> +		pr_err("cannot found snapstore by id %pUB\n", id);
> +		return -ENODATA;
> +	}
> +
> +	if (snapstore->file != NULL) {
> +		pr_err("Unable to add memory block to the snapstore: ");
> +		pr_err("snapstore file is already created\n");
> +		return -EINVAL;
> +	}
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +	if (snapstore->multidev != NULL) {
> +		pr_err("Unable to add memory block to the snapstore: ");
> +		pr_err("snapstore multidevice is already created\n");
> +		return -EINVAL;
> +	}
> +#endif
> +	if (snapstore->mem != NULL) {
> +		pr_err("Unable to add memory block to the snapstore: ");
> +		pr_err("snapstore memory buffer is already created\n");
> +		return -EINVAL;
> +	}
> +
> +	snapstore->mem = snapstore_mem_create(available_blocks);
> +	for (current_block = 0; current_block < available_blocks; ++current_block) {
> +		void *buffer = snapstore_mem_get_block(snapstore->mem);
> +
> +		if (buffer == NULL) {
> +			pr_err("Unable to add memory block to the snapstore: ");
> +			pr_err("not enough memory\n");
> +			res = -ENOMEM;
> +			break;
> +		}
> +
> +		res = blk_descr_mem_pool_add(&snapstore->mem->pool, buffer);
> +		if (res != SUCCESS) {
> +			pr_err("Unable to add memory block to the snapstore: ");
> +			pr_err("failed to initialize new block\n");
> +			break;
> +		}
> +	}
> +	if (res != SUCCESS) {
> +		snapstore_mem_destroy(snapstore->mem);
> +		snapstore->mem = NULL;
> +	}
> +
> +	return res;
> +}
> +
> +int rangelist_add(struct list_head *rglist, struct blk_range *rg)
> +{
> +	struct blk_range_link *range_link;
> +
> +	range_link = kzalloc(sizeof(struct blk_range_link), GFP_KERNEL);
> +	if (range_link == NULL)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&range_link->link);
> +
> +	range_link->rg.ofs = rg->ofs;
> +	range_link->rg.cnt = rg->cnt;
> +
> +	list_add_tail(&range_link->link, rglist);
> +
> +	return SUCCESS;
> +}
> +
> +int snapstore_add_file(uuid_t *id, struct big_buffer *ranges, size_t ranges_cnt)
> +{
> +	int res = SUCCESS;
> +	struct snapstore *snapstore = NULL;
> +	struct snapstore_device *snapstore_device = NULL;
> +	sector_t current_blk_size = 0;
> +	LIST_HEAD(blk_rangelist);
> +	size_t inx;
> +
> +	pr_info("Snapstore add %zu ranges\n", ranges_cnt);
> +
> +	if ((ranges_cnt == 0) || (ranges == NULL))
> +		return -EINVAL;
> +
> +	snapstore = _snapstore_find(id);
> +	if (snapstore == NULL) {
> +		pr_err("Unable to add file to snapstore: ");
> +		pr_err("cannot find snapstore by id %pUB\n", id);
> +		return -ENODATA;
> +	}
> +
> +	if (snapstore->file == NULL) {
> +		pr_err("Unable to add file to snapstore: ");
> +		pr_err("snapstore file was not initialized\n");
> +		return -EFAULT;
> +	}
> +
> +	snapstore_device =
> +		snapstore_device_find_by_dev_id(snapstore->file->blk_dev_id); //for zeroed
> +
> +	for (inx = 0; inx < ranges_cnt; ++inx) {
> +		size_t blocks_count = 0;
> +		sector_t range_offset = 0;
> +
> +		struct blk_range range;
> +		struct ioctl_range_s *ioctl_range;
> +
> +		ioctl_range = big_buffer_get_element(ranges, inx, sizeof(struct ioctl_range_s));
> +		if (ioctl_range == NULL) {
> +			pr_err("Invalid count of ranges\n");
> +			res = -ENODATA;
> +			break;
> +		}
> +
> +		range.ofs = (sector_t)to_sectors(ioctl_range->left);
> +		range.cnt = (blkcnt_t)to_sectors(ioctl_range->right) - range.ofs;
> +
> +		while (range_offset < range.cnt) {
> +			struct blk_range rg;
> +
> +			rg.ofs = range.ofs + range_offset;
> +			rg.cnt = min_t(sector_t, (range.cnt - range_offset),
> +				       (snapstore_block_size() - current_blk_size));
> +
> +			range_offset += rg.cnt;
> +
> +			res = rangelist_add(&blk_rangelist, &rg);
> +			if (res != SUCCESS) {
> +				pr_err("Unable to add file to snapstore: ");
> +				pr_err("cannot add range to rangelist\n");
> +				break;
> +			}
> +
> +			//zero sectors logic
> +			if (snapstore_device != NULL) {
> +				res = rangevector_add(&snapstore_device->zero_sectors, &rg);
> +				if (res != SUCCESS) {
> +					pr_err("Unable to add file to snapstore: ");
> +					pr_err("cannot add range to zero_sectors tree\n");
> +					break;
> +				}
> +			}
> +
> +			current_blk_size += rg.cnt;
> +
> +			if (current_blk_size == snapstore_block_size()) { //allocate  block
> +				res = blk_descr_file_pool_add(&snapstore->file->pool,
> +							      &blk_rangelist);
> +				if (res != SUCCESS) {
> +					pr_err("Unable to add file to snapstore: ");
> +					pr_err("cannot initialize new block\n");
> +					break;
> +				}
> +
> +				snapstore->halffilled = false;
> +
> +				current_blk_size = 0;
> +				INIT_LIST_HEAD(&blk_rangelist); //renew list
> +				++blocks_count;
> +			}
> +		}
> +		if (res != SUCCESS)
> +			break;
> +	}
> +
> +	if ((res == SUCCESS) && (current_blk_size != 0))
> +		pr_warn("Snapstore portion was not ordered by Copy-on-Write block size\n");
> +
> +	return res;
> +}
> +
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +static int rangelist_ex_add(struct list_head *list, struct blk_range *rg,
> +			    struct block_device *blk_dev)
> +{
> +	struct blk_range_link_ex *range_link =
> +		kzalloc(sizeof(struct blk_range_link_ex), GFP_KERNEL);
> +	if (range_link == NULL)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&range_link->link);
> +
> +	range_link->rg.ofs = rg->ofs;
> +	range_link->rg.cnt = rg->cnt;
> +	range_link->blk_dev = blk_dev;
> +
> +	list_add_tail(&range_link->link, list);
> +
> +	return SUCCESS;
> +}
> +
> +int snapstore_add_multidev(uuid_t *id, dev_t dev_id, struct big_buffer *ranges, size_t ranges_cnt)
> +{
> +	int res = SUCCESS;
> +	struct snapstore *snapstore = NULL;
> +	sector_t current_blk_size = 0;
> +	size_t inx;
> +	LIST_HEAD(blk_rangelist);
> +
> +	pr_info("Snapstore add %zu ranges for device [%d:%d]\n", ranges_cnt, MAJOR(dev_id),
> +		MINOR(dev_id));
> +
> +	if ((ranges_cnt == 0) || (ranges == NULL))
> +		return -EINVAL;
> +
> +	snapstore = _snapstore_find(id);
> +	if (snapstore == NULL) {
> +		pr_err("Unable to add file to multidevice snapstore: ");
> +		pr_err("cannot find snapstore by id %pUB\n", id);
> +		return -ENODATA;
> +	}
> +
> +	if (snapstore->multidev == NULL) {
> +		pr_err("Unable to add file to multidevice snapstore: ");
> +		pr_err("it was not initialized\n");
> +		return -EFAULT;
> +	}
> +
> +	for (inx = 0; inx < ranges_cnt; ++inx) {
> +		size_t blocks_count = 0;
> +		sector_t range_offset = 0;
> +		struct blk_range range;
> +		struct ioctl_range_s *data;
> +
> +		data = big_buffer_get_element(ranges, inx, sizeof(struct ioctl_range_s));
> +		if (data == NULL) {
> +			pr_err("Invalid count of ranges\n");
> +			res = -ENODATA;
> +			break;
> +		}
> +
> +		range.ofs = (sector_t)to_sectors(data->left);
> +		range.cnt = (blkcnt_t)to_sectors(data->right) - range.ofs;
> +
> +		while (range_offset < range.cnt) {
> +			struct blk_range rg;
> +			struct block_device *blk_dev = NULL;
> +
> +			rg.ofs = range.ofs + range_offset;
> +			rg.cnt = min_t(sector_t,
> +				       range.cnt - range_offset,
> +				       snapstore_block_size() - current_blk_size);
> +
> +			range_offset += rg.cnt;
> +
> +			blk_dev = snapstore_multidev_get_device(snapstore->multidev, dev_id);
> +			if (blk_dev == NULL) {
> +				pr_err("Cannot find or open device [%d:%d] for multidevice snapstore\n",
> +				       MAJOR(dev_id), MINOR(dev_id));
> +				res = -ENODEV;
> +				break;
> +			}
> +
> +			res = rangelist_ex_add(&blk_rangelist, &rg, blk_dev);
> +			if (res != SUCCESS) {
> +				pr_err("Unable to add file to multidevice snapstore: ");
> +				pr_err("failed to add range to rangelist\n");
> +				break;
> +			}
> +
> +			/*
> +			 * zero sectors logic is not implemented for multidevice snapstore
> +			 */
> +
> +			current_blk_size += rg.cnt;
> +
> +			if (current_blk_size == snapstore_block_size()) { //allocate  block
> +				res = blk_descr_multidev_pool_add(&snapstore->multidev->pool,
> +								  &blk_rangelist);
> +				if (res != SUCCESS) {
> +					pr_err("Unable to add file to multidevice snapstore: ");
> +					pr_err("failed to initialize new block\n");
> +					break;
> +				}
> +
> +				snapstore->halffilled = false;
> +
> +				current_blk_size = 0;
> +				INIT_LIST_HEAD(&blk_rangelist);
> +				++blocks_count;
> +			}
> +		}
> +		if (res != SUCCESS)
> +			break;
> +	}
> +
> +	if ((res == SUCCESS) && (current_blk_size != 0))
> +		pr_warn("Snapstore portion was not ordered by Copy-on-Write block size\n");
> +
> +	return res;
> +}
> +#endif
> +
> +void snapstore_order_border(struct blk_range *in, struct blk_range *out)
> +{
> +	struct blk_range unorder;
> +
> +	unorder.ofs = in->ofs & snapstore_block_mask();
> +	out->ofs = in->ofs & ~snapstore_block_mask();
> +	out->cnt = in->cnt + unorder.ofs;
> +
> +	unorder.cnt = out->cnt & snapstore_block_mask();
> +	if (unorder.cnt != 0)
> +		out->cnt += (snapstore_block_size() - unorder.cnt);
> +}
> +
> +union blk_descr_unify snapstore_get_empty_block(struct snapstore *snapstore)
> +{
> +	union blk_descr_unify result = { NULL };
> +
> +	if (snapstore->overflowed)
> +		return result;
> +
> +	if (snapstore->file != NULL)
> +		result = blk_descr_file_pool_take(&snapstore->file->pool);
> +	else if (snapstore->multidev != NULL)
> +		result = blk_descr_multidev_pool_take(&snapstore->multidev->pool);
> +	else if (snapstore->mem != NULL)
> +		result = blk_descr_mem_pool_take(&snapstore->mem->pool);
> +
> +	if (result.ptr == NULL) {
> +		if (snapstore->ctrl_pipe) {
> +			sector_t fill_status;
> +
> +			_snapstore_check_halffill(snapstore, &fill_status);
> +			ctrl_pipe_request_overflow(snapstore->ctrl_pipe, -EINVAL,
> +						   (u64)from_sectors(fill_status));
> +		}
> +		snapstore->overflowed = true;
> +	}
> +
> +	return result;
> +}
> +
> +int snapstore_check_halffill(uuid_t *unique_id, sector_t *fill_status)
> +{
> +	struct snapstore *snapstore;
> +
> +	snapstore = _snapstore_find(unique_id);
> +	if (snapstore == NULL) {
> +		pr_err("Cannot find snapstore by uuid %pUB\n", unique_id);
> +		return -ENODATA;
> +	}
> +
> +	_snapstore_check_halffill(snapstore, fill_status);
> +
> +	return SUCCESS;
> +}
> +
> +int snapstore_request_store(struct snapstore *snapstore, struct blk_deferred_request *dio_copy_req)
> +{
> +	int res = SUCCESS;
> +
> +	if (snapstore->ctrl_pipe) {
> +		if (!snapstore->halffilled) {
> +			sector_t fill_status = 0;
> +
> +			if (_snapstore_check_halffill(snapstore, &fill_status)) {
> +				snapstore->halffilled = true;
> +				ctrl_pipe_request_halffill(snapstore->ctrl_pipe,
> +							   (u64)from_sectors(fill_status));
> +			}
> +		}
> +	}
> +
> +	if (snapstore->file)
> +		res = blk_deferred_request_store_file(snapstore->file->blk_dev, dio_copy_req);
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +	else if (snapstore->multidev)
> +		res = blk_deferred_request_store_multidev(dio_copy_req);
> +#endif
> +	else if (snapstore->mem)
> +		res = blk_deferred_request_store_mem(dio_copy_req);
> +	else
> +		res = -EINVAL;
> +
> +	return res;
> +}
> +
> +static int _snapstore_redirect_read_file(struct blk_redirect_bio *rq_redir,
> +					 struct block_device *snapstore_blk_dev,
> +					 struct blk_descr_file *file,
> +					 sector_t block_ofs,
> +					 sector_t rq_ofs, sector_t rq_count)
> +{
> +	int res = SUCCESS;
> +	sector_t current_ofs = 0;
> +	struct list_head *_list_head;
> +
> +	if (unlikely(list_empty(&file->rangelist))) {
> +		pr_err("Invalid file block descriptor");
> +		return -EINVAL;
> +	}
> +
> +	list_for_each(_list_head, &file->rangelist) {
> +		struct blk_range_link *range_link;
> +
> +		range_link = list_entry(_list_head, struct blk_range_link, link);
> +		if (current_ofs >= rq_count)
> +			break;
> +
> +		if (range_link->rg.cnt > block_ofs) {
> +			sector_t pos = range_link->rg.ofs + block_ofs;
> +			sector_t len = min_t(sector_t,
> +					     range_link->rg.cnt - block_ofs,
> +					     rq_count - current_ofs);
> +
> +			res = blk_dev_redirect_part(rq_redir, READ, snapstore_blk_dev, pos,
> +						    rq_ofs + current_ofs, len);
> +			if (res != SUCCESS) {
> +				pr_err("Failed to read from snapstore file. Sector #%lld\n",
> +				       pos);
> +				break;
> +			}
> +
> +			current_ofs += len;
> +			block_ofs = 0;
> +		} else
> +			block_ofs -= range_link->rg.cnt;
> +	}
> +
> +	if (res != SUCCESS)
> +		pr_err("Failed to read from file snapstore\n");
> +	return res;
> +}
> +
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +static int _snapstore_redirect_read_multidev(struct blk_redirect_bio *rq_redir,
> +					      struct blk_descr_multidev *multidev,
> +					      sector_t block_ofs,
> +					      sector_t rq_ofs, sector_t rq_count)
> +{
> +	int res = SUCCESS;
> +	sector_t current_ofs = 0;
> +	struct list_head *_list_head;
> +
> +	if (unlikely(list_empty(&multidev->rangelist))) {
> +		pr_err("Invalid multidev block descriptor");
> +		return -EINVAL;
> +	}
> +
> +	list_for_each(_list_head, &multidev->rangelist) {
> +		struct blk_range_link_ex *range_link =
> +			list_entry(_list_head, struct blk_range_link_ex, link);
> +
> +		if (current_ofs >= rq_count)
> +			break;
> +
> +		if (range_link->rg.cnt > block_ofs) {
> +			sector_t pos = range_link->rg.ofs + block_ofs;
> +			sector_t len = min_t(sector_t,
> +					     range_link->rg.cnt - block_ofs,
> +					     rq_count - current_ofs);
> +
> +			res = blk_dev_redirect_part(rq_redir, READ, range_link->blk_dev, pos,
> +						    rq_ofs + current_ofs, len);
> +
> +			if (res != SUCCESS) {
> +				pr_err("Failed to read from snapstore file. Sector #%lld\n", pos);
> +				break;
> +			}
> +
> +			current_ofs += len;
> +			block_ofs = 0;
> +		} else
> +			block_ofs -= range_link->rg.cnt;
> +	}
> +
> +	if (res != SUCCESS)
> +		pr_err("Failed to read from multidev snapstore\n");
> +	return res;
> +}
> +#endif
> +
> +int snapstore_redirect_read(struct blk_redirect_bio *rq_redir, struct snapstore *snapstore,
> +			    union blk_descr_unify blk_descr, sector_t target_pos, sector_t rq_ofs,
> +			    sector_t rq_count)
> +{
> +	int res = SUCCESS;
> +	sector_t block_ofs = target_pos & snapstore_block_mask();
> +
> +	if (snapstore->file)
> +		res = _snapstore_redirect_read_file(rq_redir, snapstore->file->blk_dev,
> +						    blk_descr.file, block_ofs, rq_ofs, rq_count);
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +	else if (snapstore->multidev)
> +		res = _snapstore_redirect_read_multidev(rq_redir, blk_descr.multidev, block_ofs,
> +							rq_ofs, rq_count);
> +#endif
> +	else if (snapstore->mem) {
> +		res = blk_dev_redirect_memcpy_part(
> +			rq_redir, READ, blk_descr.mem->buff + (size_t)from_sectors(block_ofs),
> +			rq_ofs, rq_count);
> +
> +		if (res != SUCCESS)
> +			pr_err("Failed to read from snapstore memory\n");
> +	} else
> +		res = -EINVAL;
> +
> +	if (res != SUCCESS)
> +		pr_err("Failed to read from snapstore. Offset %lld sector\n", target_pos);
> +	return res;
> +}
> +
> +static int _snapstore_redirect_write_file(struct blk_redirect_bio *rq_redir,
> +					  struct block_device *snapstore_blk_dev,
> +					  struct blk_descr_file *file,
> +					  sector_t block_ofs,
> +					  sector_t rq_ofs, sector_t rq_count)
> +{
> +	int res = SUCCESS;
> +	sector_t current_ofs = 0;
> +	struct list_head *_list_head;
> +
> +	if (unlikely(list_empty(&file->rangelist))) {
> +		pr_err("Invalid file block descriptor");
> +		return -EINVAL;
> +	}
> +
> +	list_for_each(_list_head, &file->rangelist) {
> +		struct blk_range_link *range_link;
> +
> +		range_link = list_entry(_list_head, struct blk_range_link, link);
> +		if (current_ofs >= rq_count)
> +			break;
> +
> +		if (range_link->rg.cnt > block_ofs) {
> +			sector_t pos = range_link->rg.ofs + block_ofs;
> +			sector_t len = min_t(sector_t,
> +					     range_link->rg.cnt - block_ofs,
> +					     rq_count - current_ofs);
> +
> +			res = blk_dev_redirect_part(rq_redir, WRITE, snapstore_blk_dev, pos,
> +						    rq_ofs + current_ofs, len);
> +
> +			if (res != SUCCESS) {
> +				pr_err("Failed to write to snapstore file. Sector #%lld\n",
> +				       pos);
> +				break;
> +			}
> +
> +			current_ofs += len;
> +			block_ofs = 0;
> +		} else
> +			block_ofs -= range_link->rg.cnt;
> +	}
> +	if (res != SUCCESS)
> +		pr_err("Failed to write to file snapstore\n");
> +	return res;
> +}
> +
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +static int _snapstore_redirect_write_multidev(struct blk_redirect_bio *rq_redir,
> +					      struct blk_descr_multidev *multidev,
> +					      sector_t block_ofs,
> +					      sector_t rq_ofs, sector_t rq_count)
> +{
> +	int res = SUCCESS;
> +	sector_t current_ofs = 0;
> +	struct list_head *_list_head;
> +
> +	if (unlikely(list_empty(&multidev->rangelist))) {
> +		pr_err("Invalid multidev block descriptor");
> +		return -EINVAL;
> +	}
> +
> +	list_for_each(_list_head, &multidev->rangelist) {
> +		struct blk_range_link_ex *range_link;
> +
> +		range_link = list_entry(_list_head, struct blk_range_link_ex, link);
> +		if (current_ofs >= rq_count)
> +			break;
> +
> +		if (range_link->rg.cnt > block_ofs) {
> +			sector_t pos = range_link->rg.ofs + block_ofs;
> +			sector_t len = min_t(sector_t,
> +					     range_link->rg.cnt - block_ofs,
> +					     rq_count - current_ofs);
> +
> +			res = blk_dev_redirect_part(rq_redir, WRITE, range_link->blk_dev, pos,
> +						    rq_ofs + current_ofs, len);
> +
> +			if (res != SUCCESS) {
> +				pr_err("Failed to write to snapstore file. Sector #%lld\n",
> +				       pos);
> +				break;
> +			}
> +
> +			current_ofs += len;
> +			block_ofs = 0;
> +		} else
> +			block_ofs -= range_link->rg.cnt;
> +	}
> +
> +	if (res != SUCCESS)
> +		pr_err("Failed to write to multidevice snapstore\n");
> +	return res;
> +}
> +#endif
> +
> +int snapstore_redirect_write(struct blk_redirect_bio *rq_redir, struct snapstore *snapstore,
> +			     union blk_descr_unify blk_descr, sector_t target_pos, sector_t rq_ofs,
> +			     sector_t rq_count)
> +{
> +	int res = SUCCESS;
> +	sector_t block_ofs = target_pos & snapstore_block_mask();
> +
> +	if (snapstore->file)
> +		res = _snapstore_redirect_write_file(rq_redir, snapstore->file->blk_dev,
> +						     blk_descr.file, block_ofs, rq_ofs, rq_count);
> +
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +	else if (snapstore->multidev)
> +		res = _snapstore_redirect_write_multidev(rq_redir, blk_descr.multidev,
> +							 block_ofs, rq_ofs, rq_count);
> +#endif
> +	else if (snapstore->mem) {
> +		res = blk_dev_redirect_memcpy_part(
> +			rq_redir, WRITE, blk_descr.mem->buff + (size_t)from_sectors(block_ofs),
> +			rq_ofs, rq_count);
> +
> +		if (res != SUCCESS)
> +			pr_err("Failed to write to memory snapstore\n");
> +	} else {
> +		pr_err("Unable to write to snapstore: invalid type of snapstore device\n");
> +		res = -EINVAL;
> +	}
> +
> +	if (res != SUCCESS)
> +		pr_err("Failed to write to snapstore. Offset %lld sector\n", target_pos);
> +	return res;
> +}
> diff --git a/drivers/block/blk-snap/snapstore.h b/drivers/block/blk-snap/snapstore.h
> new file mode 100644
> index 000000000000..db34ad2e2c58
> --- /dev/null
> +++ b/drivers/block/blk-snap/snapstore.h
> @@ -0,0 +1,68 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#pragma once
> +
> +#include <linux/uuid.h>
> +#include <linux/kref.h>
> +#include "blk-snap-ctl.h"
> +#include "rangevector.h"
> +#include "snapstore_mem.h"
> +#include "snapstore_file.h"
> +#include "snapstore_multidev.h"
> +#include "blk_redirect.h"
> +#include "ctrl_pipe.h"
> +#include "big_buffer.h"
> +
> +struct snapstore {
> +	struct list_head link;
> +	struct kref refcount;
> +
> +	uuid_t id;
> +
> +	struct snapstore_mem *mem;
> +	struct snapstore_file *file;
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +	struct snapstore_multidev *multidev;
> +#endif
> +
> +	struct ctrl_pipe *ctrl_pipe;
> +	sector_t empty_limit;
> +
> +	bool halffilled;
> +	bool overflowed;
> +};
> +
> +void snapstore_done(void);
> +
> +int snapstore_create(uuid_t *id, dev_t snapstore_dev_id, dev_t *dev_id_set,
> +		     size_t dev_id_set_length);
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +int snapstore_create_multidev(uuid_t *id, dev_t *dev_id_set, size_t dev_id_set_length);
> +#endif
> +int snapstore_cleanup(uuid_t *id, u64 *filled_bytes);
> +
> +struct snapstore *snapstore_get(struct snapstore *snapstore);
> +void snapstore_put(struct snapstore *snapstore);
> +
> +int snapstore_stretch_initiate(uuid_t *unique_id, struct ctrl_pipe *ctrl_pipe,
> +			       sector_t empty_limit);
> +
> +int snapstore_add_memory(uuid_t *id, unsigned long long sz);
> +int snapstore_add_file(uuid_t *id, struct big_buffer *ranges, size_t ranges_cnt);
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +int snapstore_add_multidev(uuid_t *id, dev_t dev_id, struct big_buffer *ranges, size_t ranges_cnt);
> +#endif
> +
> +void snapstore_order_border(struct blk_range *in, struct blk_range *out);
> +
> +union blk_descr_unify snapstore_get_empty_block(struct snapstore *snapstore);
> +
> +int snapstore_request_store(struct snapstore *snapstore, struct blk_deferred_request *dio_copy_req);
> +
> +int snapstore_redirect_read(struct blk_redirect_bio *rq_redir, struct snapstore *snapstore,
> +			    union blk_descr_unify blk_descr, sector_t target_pos, sector_t rq_ofs,
> +			    sector_t rq_count);
> +int snapstore_redirect_write(struct blk_redirect_bio *rq_redir, struct snapstore *snapstore,
> +			     union blk_descr_unify blk_descr, sector_t target_pos, sector_t rq_ofs,
> +			     sector_t rq_count);
> +
> +int snapstore_check_halffill(uuid_t *unique_id, sector_t *fill_status);
> diff --git a/drivers/block/blk-snap/snapstore_device.c b/drivers/block/blk-snap/snapstore_device.c
> new file mode 100644
> index 000000000000..6fdeebacce22
> --- /dev/null
> +++ b/drivers/block/blk-snap/snapstore_device.c
> @@ -0,0 +1,532 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-snapstore"
> +#include "common.h"
> +#include "snapstore_device.h"
> +#include "snapstore.h"
> +#include "params.h"
> +#include "blk_util.h"
> +
> +LIST_HEAD(snapstore_devices);
> +DECLARE_RWSEM(snapstore_devices_lock);
> +
> +static inline void _snapstore_device_descr_write_lock(struct snapstore_device *snapstore_device)
> +{
> +	mutex_lock(&snapstore_device->store_block_map_locker);
> +}
> +static inline void _snapstore_device_descr_write_unlock(struct snapstore_device *snapstore_device)
> +{
> +	mutex_unlock(&snapstore_device->store_block_map_locker);
> +}
> +
> +void snapstore_device_done(void)
> +{
> +	struct snapstore_device *snapstore_device = NULL;
> +
> +	do {
> +		down_write(&snapstore_devices_lock);
> +		if (!list_empty(&snapstore_devices)) {
> +			snapstore_device =
> +				list_entry(snapstore_devices.next, struct snapstore_device, link);
> +			list_del(&snapstore_device->link);
> +		}
> +		up_write(&snapstore_devices_lock);
> +
> +		if (snapstore_device)
> +			snapstore_device_put_resource(snapstore_device);
> +	} while (snapstore_device);
> +}
> +
> +struct snapstore_device *snapstore_device_find_by_dev_id(dev_t dev_id)
> +{
> +	struct snapstore_device *result = NULL;
> +
> +	down_read(&snapstore_devices_lock);
> +	if (!list_empty(&snapstore_devices)) {
> +		struct list_head *_head;
> +
> +		list_for_each(_head, &snapstore_devices) {
> +			struct snapstore_device *snapstore_device =
> +				list_entry(_head, struct snapstore_device, link);
> +
> +			if (dev_id == snapstore_device->dev_id) {
> +				result = snapstore_device;
> +				break;
> +			}
> +		}
> +	}
> +	up_read(&snapstore_devices_lock);
> +
> +	return result;
> +}
> +
> +struct snapstore_device *_snapstore_device_get_by_snapstore_id(uuid_t *id)
> +{
> +	struct snapstore_device *result = NULL;
> +
> +	down_write(&snapstore_devices_lock);
> +	if (!list_empty(&snapstore_devices)) {
> +		struct list_head *_head;
> +
> +		list_for_each(_head, &snapstore_devices) {
> +			struct snapstore_device *snapstore_device =
> +				list_entry(_head, struct snapstore_device, link);
> +
> +			if (uuid_equal(id, &snapstore_device->snapstore->id)) {
> +				result = snapstore_device;
> +				list_del(&snapstore_device->link);
> +				break;
> +			}
> +		}
> +	}
> +	up_write(&snapstore_devices_lock);
> +
> +	return result;
> +}
> +
> +static void _snapstore_device_destroy(struct snapstore_device *snapstore_device)
> +{
> +	pr_info("Destroy snapstore device\n");
> +
> +	xa_destroy(&snapstore_device->store_block_map);
> +
> +	if (snapstore_device->orig_blk_dev != NULL)
> +		blk_dev_close(snapstore_device->orig_blk_dev);
> +
> +	rangevector_done(&snapstore_device->zero_sectors);
> +
> +	if (snapstore_device->snapstore) {
> +		pr_info("Snapstore uuid %pUB\n", &snapstore_device->snapstore->id);
> +
> +		snapstore_put(snapstore_device->snapstore);
> +		snapstore_device->snapstore = NULL;
> +	}
> +
> +	kfree(snapstore_device);
> +}
> +
> +static void snapstore_device_free_cb(struct kref *kref)
> +{
> +	struct snapstore_device *snapstore_device =
> +		container_of(kref, struct snapstore_device, refcount);
> +
> +	_snapstore_device_destroy(snapstore_device);
> +}
> +
> +struct snapstore_device *snapstore_device_get_resource(struct snapstore_device *snapstore_device)
> +{
> +	if (snapstore_device)
> +		kref_get(&snapstore_device->refcount);
> +
> +	return snapstore_device;
> +};
> +
> +void snapstore_device_put_resource(struct snapstore_device *snapstore_device)
> +{
> +	if (snapstore_device)
> +		kref_put(&snapstore_device->refcount, snapstore_device_free_cb);
> +};
> +
> +int snapstore_device_cleanup(uuid_t *id)
> +{
> +	int result = SUCCESS;
> +	struct snapstore_device *snapstore_device = NULL;
> +
> +	while (NULL != (snapstore_device = _snapstore_device_get_by_snapstore_id(id))) {
> +		pr_info("Cleanup snapstore device for device [%d:%d]\n",
> +			MAJOR(snapstore_device->dev_id), MINOR(snapstore_device->dev_id));
> +
> +		snapstore_device_put_resource(snapstore_device);
> +	}
> +	return result;
> +}
> +
> +int snapstore_device_create(dev_t dev_id, struct snapstore *snapstore)
> +{
> +	int res = SUCCESS;
> +	struct snapstore_device *snapstore_device =
> +		kzalloc(sizeof(struct snapstore_device), GFP_KERNEL);
> +
> +	if (snapstore_device == NULL)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&snapstore_device->link);
> +	snapstore_device->dev_id = dev_id;
> +
> +	res = blk_dev_open(dev_id, &snapstore_device->orig_blk_dev);
> +	if (res != SUCCESS) {
> +		kfree(snapstore_device);
> +
> +		pr_err("Unable to create snapstore device: failed to open original device [%d:%d]\n",
> +		       MAJOR(dev_id), MINOR(dev_id));
> +		return res;
> +	}
> +
> +	kref_init(&snapstore_device->refcount);
> +
> +	snapstore_device->snapstore = NULL;
> +	snapstore_device->err_code = SUCCESS;
> +	snapstore_device->corrupted = false;
> +	atomic_set(&snapstore_device->req_failed_cnt, 0);
> +
> +	mutex_init(&snapstore_device->store_block_map_locker);
> +
> +	rangevector_init(&snapstore_device->zero_sectors);
> +
> +	xa_init(&snapstore_device->store_block_map);
> +
> +	snapstore_device->snapstore = snapstore_get(snapstore);
> +
> +	down_write(&snapstore_devices_lock);
> +	list_add_tail(&snapstore_device->link, &snapstore_devices);
> +	up_write(&snapstore_devices_lock);
> +
> +	return SUCCESS;
> +}
> +
> +int snapstore_device_add_request(struct snapstore_device *snapstore_device,
> +				 unsigned long block_index,
> +				 struct blk_deferred_request **dio_copy_req)
> +{
> +	int res = SUCCESS;
> +	union blk_descr_unify blk_descr = { NULL };
> +	struct blk_deferred_io *dio = NULL;
> +	bool req_new = false;
> +
> +	blk_descr = snapstore_get_empty_block(snapstore_device->snapstore);
> +	if (blk_descr.ptr == NULL) {
> +		pr_err("Unable to add block to defer IO request: failed to allocate next block\n");
> +		return -ENODATA;
> +	}
> +
> +	res = xa_err(
> +		xa_store(&snapstore_device->store_block_map, block_index, blk_descr.ptr, GFP_NOIO));
> +	if (res != SUCCESS) {
> +		pr_err("Unable to add block to defer IO request: failed to set block descriptor to descriptors array. errno=%d\n",
> +		       res);
> +		return res;
> +	}
> +
> +	if (*dio_copy_req == NULL) {
> +		*dio_copy_req = blk_deferred_request_new();
> +		if (*dio_copy_req == NULL) {
> +			pr_err("Unable to add block to defer IO request: failed to allocate defer IO request\n");
> +			return -ENOMEM;
> +		}
> +		req_new = true;
> +	}
> +
> +	do {
> +		dio = blk_deferred_alloc(block_index, blk_descr);
> +		if (dio == NULL) {
> +			pr_err("Unabled to add block to defer IO request: failed to allocate defer IO\n");
> +			res = -ENOMEM;
> +			break;
> +		}
> +
> +		res = blk_deferred_request_add(*dio_copy_req, dio);
> +		if (res != SUCCESS)
> +			pr_err("Unable to add block to defer IO request: failed to add defer IO to request\n");
> +	} while (false);
> +
> +	if (res != SUCCESS) {
> +		if (dio != NULL) {
> +			blk_deferred_free(dio);
> +			dio = NULL;
> +		}
> +		if (req_new) {
> +			blk_deferred_request_free(*dio_copy_req);
> +			*dio_copy_req = NULL;
> +		}
> +	}
> +
> +	return res;
> +}
> +
> +int snapstore_device_prepare_requests(struct snapstore_device *snapstore_device,
> +				      struct blk_range *copy_range,
> +				      struct blk_deferred_request **dio_copy_req)
> +{
> +	int res = SUCCESS;
> +	unsigned long inx = 0;
> +	unsigned long first = (unsigned long)(copy_range->ofs >> snapstore_block_shift());
> +	unsigned long last =
> +		(unsigned long)((copy_range->ofs + copy_range->cnt - 1) >> snapstore_block_shift());
> +
> +	for (inx = first; inx <= last; inx++) {
> +		if (xa_load(&snapstore_device->store_block_map, inx) == NULL) {
> +			res = snapstore_device_add_request(snapstore_device, inx, dio_copy_req);
> +			if (res != SUCCESS) {
> +				pr_err("Failed to create copy defer IO request. errno=%d\n", res);
> +				break;
> +			}
> +		}
> +		/*
> +		 * If xa_load() return not NULL, then block already stored.
> +		 */
> +	}
> +	if (res != SUCCESS)
> +		snapstore_device_set_corrupted(snapstore_device, res);
> +
> +	return res;
> +}
> +
> +int snapstore_device_store(struct snapstore_device *snapstore_device,
> +			   struct blk_deferred_request *dio_copy_req)
> +{
> +	int res;
> +
> +	res = snapstore_request_store(snapstore_device->snapstore, dio_copy_req);
> +	if (res != SUCCESS)
> +		snapstore_device_set_corrupted(snapstore_device, res);
> +
> +	return res;
> +}
> +
> +int snapstore_device_read(struct snapstore_device *snapstore_device,
> +			  struct blk_redirect_bio *rq_redir)
> +{
> +	int res = SUCCESS;
> +
> +	unsigned long block_index;
> +	unsigned long block_index_last;
> +	unsigned long block_index_first;
> +
> +	sector_t blk_ofs_start = 0; //device range start
> +	sector_t blk_ofs_count = 0; //device range length
> +
> +	struct blk_range rq_range;
> +	struct rangevector *zero_sectors = &snapstore_device->zero_sectors;
> +
> +	if (snapstore_device_is_corrupted(snapstore_device))
> +		return -ENODATA;
> +
> +	rq_range.cnt = bio_sectors(rq_redir->bio);
> +	rq_range.ofs = rq_redir->bio->bi_iter.bi_sector;
> +
> +	if (!bio_has_data(rq_redir->bio)) {
> +		pr_warn("Empty bio was found during reading from snapstore device. flags=%u\n",
> +			rq_redir->bio->bi_flags);
> +
> +		blk_redirect_complete(rq_redir, SUCCESS);
> +		return SUCCESS;
> +	}
> +
> +	block_index_first = (unsigned long)(rq_range.ofs >> snapstore_block_shift());
> +	block_index_last =
> +		(unsigned long)((rq_range.ofs + rq_range.cnt - 1) >> snapstore_block_shift());
> +
> +	_snapstore_device_descr_write_lock(snapstore_device);
> +	for (block_index = block_index_first; block_index <= block_index_last; ++block_index) {
> +		union blk_descr_unify blk_descr;
> +
> +		blk_ofs_count = min_t(sector_t,
> +				      (((sector_t)(block_index + 1)) << snapstore_block_shift()) -
> +					      (rq_range.ofs + blk_ofs_start),
> +				      rq_range.cnt - blk_ofs_start);
> +
> +		blk_descr = (union blk_descr_unify)xa_load(&snapstore_device->store_block_map,
> +							   block_index);
> +		if (blk_descr.ptr) {
> +			//push snapstore read
> +			res = snapstore_redirect_read(rq_redir, snapstore_device->snapstore,
> +						      blk_descr, rq_range.ofs + blk_ofs_start,
> +						      blk_ofs_start, blk_ofs_count);
> +			if (res != SUCCESS) {
> +				pr_err("Failed to read from snapstore device\n");
> +				break;
> +			}
> +		} else {
> +			//device read with zeroing
> +			if (zero_sectors)
> +				res = blk_dev_redirect_read_zeroed(rq_redir,
> +								   snapstore_device->orig_blk_dev,
> +								   rq_range.ofs, blk_ofs_start,
> +								   blk_ofs_count, zero_sectors);
> +			else
> +				res = blk_dev_redirect_part(rq_redir, READ,
> +							    snapstore_device->orig_blk_dev,
> +							    rq_range.ofs + blk_ofs_start,
> +							    blk_ofs_start, blk_ofs_count);
> +
> +			if (res != SUCCESS) {
> +				pr_err("Failed to redirect read request to the original device [%d:%d]\n",
> +				       MAJOR(snapstore_device->dev_id),
> +				       MINOR(snapstore_device->dev_id));
> +				break;
> +			}
> +		}
> +
> +		blk_ofs_start += blk_ofs_count;
> +	}
> +
> +	if (res == SUCCESS) {
> +		if (atomic64_read(&rq_redir->bio_count) > 0ll) //async direct access needed
> +			blk_dev_redirect_submit(rq_redir);
> +		else
> +			blk_redirect_complete(rq_redir, res);
> +	} else {
> +		pr_err("Failed to read from snapstore device. errno=%d\n", res);
> +		pr_err("Position %lld sector, length %lld sectors\n", rq_range.ofs, rq_range.cnt);
> +	}
> +	_snapstore_device_descr_write_unlock(snapstore_device);
> +
> +	return res;
> +}
> +
> +int _snapstore_device_copy_on_write(struct snapstore_device *snapstore_device,
> +				    struct blk_range *rq_range)
> +{
> +	int res = SUCCESS;
> +	struct blk_deferred_request *dio_copy_req = NULL;
> +
> +	mutex_lock(&snapstore_device->store_block_map_locker);
> +	do {
> +		res = snapstore_device_prepare_requests(snapstore_device, rq_range, &dio_copy_req);
> +		if (res != SUCCESS) {
> +			pr_err("Failed to create defer IO request for range. errno=%d\n", res);
> +			break;
> +		}
> +
> +		if (dio_copy_req == NULL)
> +			break; //nothing to copy
> +
> +		res = blk_deferred_request_read_original(snapstore_device->orig_blk_dev,
> +							 dio_copy_req);
> +		if (res != SUCCESS) {
> +			pr_err("Failed to read data from the original device. errno=%d\n", res);
> +			break;
> +		}
> +
> +		res = snapstore_device_store(snapstore_device, dio_copy_req);
> +		if (res != SUCCESS) {
> +			pr_err("Failed to write data to snapstore. errno=%d\n", res);
> +			break;
> +		}
> +	} while (false);
> +	mutex_unlock(&snapstore_device->store_block_map_locker);
> +
> +	if (dio_copy_req) {
> +		if (res == -EDEADLK)
> +			blk_deferred_request_deadlocked(dio_copy_req);
> +		else
> +			blk_deferred_request_free(dio_copy_req);
> +	}
> +
> +	return res;
> +}
> +
> +int snapstore_device_write(struct snapstore_device *snapstore_device,
> +			   struct blk_redirect_bio *rq_redir)
> +{
> +	int res = SUCCESS;
> +	unsigned long block_index;
> +	unsigned long block_index_last;
> +	unsigned long block_index_first;
> +	sector_t blk_ofs_start = 0; //device range start
> +	sector_t blk_ofs_count = 0; //device range length
> +	struct blk_range rq_range;
> +
> +	if (snapstore_device_is_corrupted(snapstore_device))
> +		return -ENODATA;
> +
> +	rq_range.cnt = bio_sectors(rq_redir->bio);
> +	rq_range.ofs = rq_redir->bio->bi_iter.bi_sector;
> +
> +	if (!bio_has_data(rq_redir->bio)) {
> +		pr_warn("Empty bio was found during reading from snapstore device. flags=%u\n",
> +			rq_redir->bio->bi_flags);
> +
> +		blk_redirect_complete(rq_redir, SUCCESS);
> +		return SUCCESS;
> +	}
> +
> +	// do copy to snapstore previously
> +	res = _snapstore_device_copy_on_write(snapstore_device, &rq_range);
> +
> +	block_index_first = (unsigned long)(rq_range.ofs >> snapstore_block_shift());
> +	block_index_last =
> +		(unsigned long)((rq_range.ofs + rq_range.cnt - 1) >> snapstore_block_shift());
> +
> +	_snapstore_device_descr_write_lock(snapstore_device);
> +	for (block_index = block_index_first; block_index <= block_index_last; ++block_index) {
> +		union blk_descr_unify blk_descr;
> +
> +		blk_ofs_count = min_t(sector_t,
> +				      (((sector_t)(block_index + 1)) << snapstore_block_shift()) -
> +					      (rq_range.ofs + blk_ofs_start),
> +				      rq_range.cnt - blk_ofs_start);
> +
> +		blk_descr = (union blk_descr_unify)xa_load(&snapstore_device->store_block_map,
> +							   block_index);
> +		if (blk_descr.ptr == NULL) {
> +			pr_err("Unable to write from snapstore device: invalid snapstore block descriptor\n");
> +			res = -EIO;
> +			break;
> +		}
> +
> +		res = snapstore_redirect_write(rq_redir, snapstore_device->snapstore, blk_descr,
> +					       rq_range.ofs + blk_ofs_start, blk_ofs_start,
> +					       blk_ofs_count);
> +		if (res != SUCCESS) {
> +			pr_err("Unable to write from snapstore device: failed to redirect write request to snapstore\n");
> +			break;
> +		}
> +
> +		blk_ofs_start += blk_ofs_count;
> +	}
> +	if (res == SUCCESS) {
> +		if (atomic64_read(&rq_redir->bio_count) > 0) { //async direct access needed
> +			blk_dev_redirect_submit(rq_redir);
> +		} else {
> +			blk_redirect_complete(rq_redir, res);
> +		}
> +	} else {
> +		pr_err("Failed to write from snapstore device. errno=%d\n", res);
> +		pr_err("Position %lld sector, length %lld sectors\n", rq_range.ofs, rq_range.cnt);
> +
> +		snapstore_device_set_corrupted(snapstore_device, res);
> +	}
> +	_snapstore_device_descr_write_unlock(snapstore_device);
> +	return res;
> +}
> +
> +bool snapstore_device_is_corrupted(struct snapstore_device *snapstore_device)
> +{
> +	if (snapstore_device == NULL)
> +		return true;
> +
> +	if (snapstore_device->corrupted) {
> +		if (atomic_read(&snapstore_device->req_failed_cnt) == 0)
> +			pr_err("Snapshot device is corrupted for [%d:%d]\n",
> +			       MAJOR(snapstore_device->dev_id), MINOR(snapstore_device->dev_id));
> +
> +		atomic_inc(&snapstore_device->req_failed_cnt);
> +		return true;
> +	}
> +
> +	return false;
> +}
> +
> +void snapstore_device_set_corrupted(struct snapstore_device *snapstore_device, int err_code)
> +{
> +	if (!snapstore_device->corrupted) {
> +		atomic_set(&snapstore_device->req_failed_cnt, 0);
> +		snapstore_device->corrupted = true;
> +		snapstore_device->err_code = abs(err_code);
> +
> +		pr_err("Set snapshot device is corrupted for [%d:%d]\n",
> +		       MAJOR(snapstore_device->dev_id), MINOR(snapstore_device->dev_id));
> +	}
> +}
> +
> +int snapstore_device_errno(dev_t dev_id, int *p_err_code)
> +{
> +	struct snapstore_device *snapstore_device;
> +
> +	snapstore_device = snapstore_device_find_by_dev_id(dev_id);
> +	if (snapstore_device == NULL)
> +		return -ENODATA;
> +
> +	*p_err_code = snapstore_device->err_code;
> +	return SUCCESS;
> +}
> diff --git a/drivers/block/blk-snap/snapstore_device.h b/drivers/block/blk-snap/snapstore_device.h
> new file mode 100644
> index 000000000000..729b3c05ef70
> --- /dev/null
> +++ b/drivers/block/blk-snap/snapstore_device.h
> @@ -0,0 +1,63 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#pragma once
> +
> +#include "rangevector.h"
> +#include "blk_deferred.h"
> +#include "blk_redirect.h"
> +#include "snapstore.h"
> +#include <linux/xarray.h>
> +#include <linux/kref.h>
> +
> +struct snapstore_device {
> +	struct list_head link;
> +	struct kref refcount;
> +
> +	dev_t dev_id;
> +	struct snapstore *snapstore;
> +
> +	struct block_device *orig_blk_dev;
> +
> +	struct xarray store_block_map; // map block index to read block offset
> +	struct mutex store_block_map_locker;
> +
> +	struct rangevector zero_sectors;
> +
> +	atomic_t req_failed_cnt;
> +	int err_code;
> +	bool corrupted;
> +};
> +
> +void snapstore_device_done(void);
> +
> +struct snapstore_device *snapstore_device_get_resource(struct snapstore_device *snapstore_device);
> +void snapstore_device_put_resource(struct snapstore_device *snapstore_device);
> +
> +struct snapstore_device *snapstore_device_find_by_dev_id(dev_t dev_id);
> +
> +int snapstore_device_create(dev_t dev_id, struct snapstore *snapstore);
> +
> +int snapstore_device_cleanup(uuid_t *id);
> +
> +int snapstore_device_prepare_requests(struct snapstore_device *snapstore_device,
> +				      struct blk_range *copy_range,
> +				      struct blk_deferred_request **dio_copy_req);
> +int snapstore_device_store(struct snapstore_device *snapstore_device,
> +			   struct blk_deferred_request *dio_copy_req);
> +
> +int snapstore_device_read(struct snapstore_device *snapstore_device,
> +			  struct blk_redirect_bio *rq_redir); //request from image
> +int snapstore_device_write(struct snapstore_device *snapstore_device,
> +			   struct blk_redirect_bio *rq_redir); //request from image
> +
> +bool snapstore_device_is_corrupted(struct snapstore_device *snapstore_device);
> +void snapstore_device_set_corrupted(struct snapstore_device *snapstore_device, int err_code);
> +int snapstore_device_errno(dev_t dev_id, int *p_err_code);
> +
> +static inline void _snapstore_device_descr_read_lock(struct snapstore_device *snapstore_device)
> +{
> +	mutex_lock(&snapstore_device->store_block_map_locker);
> +}
> +static inline void _snapstore_device_descr_read_unlock(struct snapstore_device *snapstore_device)
> +{
> +	mutex_unlock(&snapstore_device->store_block_map_locker);
> +}
> diff --git a/drivers/block/blk-snap/snapstore_file.c b/drivers/block/blk-snap/snapstore_file.c
> new file mode 100644
> index 000000000000..a5c959a8070c
> --- /dev/null
> +++ b/drivers/block/blk-snap/snapstore_file.c
> @@ -0,0 +1,52 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-snapstore"
> +#include "common.h"
> +#include "snapstore_file.h"
> +#include "blk_util.h"
> +
> +int snapstore_file_create(dev_t dev_id, struct snapstore_file **pfile)
> +{
> +	int res = SUCCESS;
> +	struct snapstore_file *file;
> +
> +	pr_info("Single device file snapstore was created on device [%d:%d]\n", MAJOR(dev_id),
> +	       MINOR(dev_id));
> +
> +	file = kzalloc(sizeof(struct snapstore_file), GFP_KERNEL);
> +	if (file == NULL)
> +		return -ENOMEM;
> +
> +	res = blk_dev_open(dev_id, &file->blk_dev);
> +	if (res != SUCCESS) {
> +		kfree(file);
> +		pr_err("Unable to create snapstore file: failed to open device [%d:%d]. errno=%d",
> +		       MAJOR(dev_id), MINOR(dev_id), res);
> +		return res;
> +	}
> +	{
> +		struct request_queue *q = bdev_get_queue(file->blk_dev);
> +
> +		pr_info("snapstore device logical block size %d\n", q->limits.logical_block_size);
> +		pr_info("snapstore device physical block size %d\n", q->limits.physical_block_size);
> +	}
> +
> +	file->blk_dev_id = dev_id;
> +	blk_descr_file_pool_init(&file->pool);
> +
> +	*pfile = file;
> +	return res;
> +}
> +
> +void snapstore_file_destroy(struct snapstore_file *file)
> +{
> +	if (file) {
> +		blk_descr_file_pool_done(&file->pool);
> +
> +		if (file->blk_dev != NULL) {
> +			blk_dev_close(file->blk_dev);
> +			file->blk_dev = NULL;
> +		}
> +
> +		kfree(file);
> +	}
> +}
> diff --git a/drivers/block/blk-snap/snapstore_file.h b/drivers/block/blk-snap/snapstore_file.h
> new file mode 100644
> index 000000000000..effd9d888781
> --- /dev/null
> +++ b/drivers/block/blk-snap/snapstore_file.h
> @@ -0,0 +1,15 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#pragma once
> +
> +#include "blk_deferred.h"
> +
> +struct snapstore_file {
> +	dev_t blk_dev_id;
> +	struct block_device *blk_dev;
> +
> +	struct blk_descr_pool pool;
> +};
> +
> +int snapstore_file_create(dev_t dev_id, struct snapstore_file **pfile);
> +
> +void snapstore_file_destroy(struct snapstore_file *file);
> diff --git a/drivers/block/blk-snap/snapstore_mem.c b/drivers/block/blk-snap/snapstore_mem.c
> new file mode 100644
> index 000000000000..29a607617d99
> --- /dev/null
> +++ b/drivers/block/blk-snap/snapstore_mem.c
> @@ -0,0 +1,91 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-snapstore"
> +#include "common.h"
> +#include "snapstore_mem.h"
> +#include "params.h"
> +
> +#include <linux/vmalloc.h>
> +
> +struct buffer_el {
> +	struct list_head link;
> +	void *buff;
> +};
> +
> +struct snapstore_mem *snapstore_mem_create(size_t available_blocks)
> +{
> +	struct snapstore_mem *mem = kzalloc(sizeof(struct snapstore_mem), GFP_KERNEL);
> +
> +	if (mem == NULL)
> +		return NULL;
> +
> +	blk_descr_mem_pool_init(&mem->pool, available_blocks);
> +
> +	mem->blocks_limit = available_blocks;
> +
> +	INIT_LIST_HEAD(&mem->blocks);
> +	mutex_init(&mem->blocks_lock);
> +
> +	return mem;
> +}
> +
> +void snapstore_mem_destroy(struct snapstore_mem *mem)
> +{
> +	struct buffer_el *buffer_el;
> +
> +	if (mem == NULL)
> +		return;
> +
> +	do {
> +		buffer_el = NULL;
> +
> +		mutex_lock(&mem->blocks_lock);
> +		if (!list_empty(&mem->blocks)) {
> +			buffer_el = list_entry(mem->blocks.next, struct buffer_el, link);
> +
> +			list_del(&buffer_el->link);
> +		}
> +		mutex_unlock(&mem->blocks_lock);
> +
> +		if (buffer_el) {
> +			vfree(buffer_el->buff);
> +			kfree(buffer_el);
> +		}
> +	} while (buffer_el);
> +
> +	blk_descr_mem_pool_done(&mem->pool);
> +
> +	kfree(mem);
> +}
> +
> +void *snapstore_mem_get_block(struct snapstore_mem *mem)
> +{
> +	struct buffer_el *buffer_el;
> +
> +	if (mem->blocks_allocated >= mem->blocks_limit) {
> +		pr_err("Unable to get block from snapstore in memory\n");
> +		pr_err("Block limit is reached, allocated %zu, limit %zu\n", mem->blocks_allocated,
> +		       mem->blocks_limit);
> +		return NULL;
> +	}
> +
> +	buffer_el = kzalloc(sizeof(struct buffer_el), GFP_KERNEL);
> +	if (buffer_el == NULL)
> +		return NULL;
> +	INIT_LIST_HEAD(&buffer_el->link);
> +
> +	buffer_el->buff = vmalloc(snapstore_block_size() * SECTOR_SIZE);
> +	if (buffer_el->buff == NULL) {
> +		kfree(buffer_el);
> +		return NULL;
> +	}
> +
> +	++mem->blocks_allocated;
> +	if (0 == (mem->blocks_allocated & 0x7F))
> +		pr_info("%zu MiB was allocated\n", mem->blocks_allocated);
> +
> +	mutex_lock(&mem->blocks_lock);
> +	list_add_tail(&buffer_el->link, &mem->blocks);
> +	mutex_unlock(&mem->blocks_lock);
> +
> +	return buffer_el->buff;
> +}
> diff --git a/drivers/block/blk-snap/snapstore_mem.h b/drivers/block/blk-snap/snapstore_mem.h
> new file mode 100644
> index 000000000000..9044a6525966
> --- /dev/null
> +++ b/drivers/block/blk-snap/snapstore_mem.h
> @@ -0,0 +1,20 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#pragma once
> +
> +#include "blk_descr_mem.h"
> +
> +struct snapstore_mem {
> +	struct list_head blocks;
> +	struct mutex blocks_lock;
> +
> +	size_t blocks_limit;
> +	size_t blocks_allocated;
> +
> +	struct blk_descr_pool pool;
> +};
> +
> +struct snapstore_mem *snapstore_mem_create(size_t available_blocks);
> +
> +void snapstore_mem_destroy(struct snapstore_mem *mem);
> +
> +void *snapstore_mem_get_block(struct snapstore_mem *mem);
> diff --git a/drivers/block/blk-snap/snapstore_multidev.c b/drivers/block/blk-snap/snapstore_multidev.c
> new file mode 100644
> index 000000000000..bb6bfefa68d7
> --- /dev/null
> +++ b/drivers/block/blk-snap/snapstore_multidev.c
> @@ -0,0 +1,118 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-snapstore"
> +#include "common.h"
> +
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +
> +#include "snapstore_multidev.h"
> +#include "blk_util.h"
> +
> +struct multidev_el {
> +	struct list_head link;
> +
> +	dev_t dev_id;
> +	struct block_device *blk_dev;
> +};
> +
> +int snapstore_multidev_create(struct snapstore_multidev **p_multidev)
> +{
> +	int res = SUCCESS;
> +	struct snapstore_multidev *multidev;
> +
> +	pr_info("Multidevice file snapstore create\n");
> +
> +	multidev = kzalloc(sizeof(struct snapstore_multidev), GFP_KERNEL);
> +	if (multidev == NULL)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&multidev->devicelist);
> +	spin_lock_init(&multidev->devicelist_lock);
> +
> +	blk_descr_multidev_pool_init(&multidev->pool);
> +
> +	*p_multidev = multidev;
> +	return res;
> +}
> +
> +void snapstore_multidev_destroy(struct snapstore_multidev *multidev)
> +{
> +	struct multidev_el *el;
> +
> +	blk_descr_multidev_pool_done(&multidev->pool);
> +
> +	do {
> +		el = NULL;
> +		spin_lock(&multidev->devicelist_lock);
> +		if (!list_empty(&multidev->devicelist)) {
> +			el = list_entry(multidev->devicelist.next, struct multidev_el, link);
> +
> +			list_del(&el->link);
> +		}
> +		spin_unlock(&multidev->devicelist_lock);
> +
> +		if (el) {
> +			blk_dev_close(el->blk_dev);
> +
> +			pr_info("Close device for multidevice snapstore [%d:%d]\n",
> +				MAJOR(el->dev_id), MINOR(el->dev_id));
> +
> +			kfree(el);
> +		}
> +	} while (el);
> +
> +	kfree(multidev);
> +}
> +
> +struct multidev_el *snapstore_multidev_find(struct snapstore_multidev *multidev, dev_t dev_id)
> +{
> +	struct multidev_el *el = NULL;
> +
> +	spin_lock(&multidev->devicelist_lock);
> +	if (!list_empty(&multidev->devicelist)) {
> +		struct list_head *_head;
> +
> +		list_for_each(_head, &multidev->devicelist) {
> +			struct multidev_el *_el = list_entry(_head, struct multidev_el, link);
> +
> +			if (_el->dev_id == dev_id) {
> +				el = _el;
> +				break;
> +			}
> +		}
> +	}
> +	spin_unlock(&multidev->devicelist_lock);
> +
> +	return el;
> +}
> +
> +struct block_device *snapstore_multidev_get_device(struct snapstore_multidev *multidev,
> +						   dev_t dev_id)
> +{
> +	int res;
> +	struct block_device *blk_dev = NULL;
> +	struct multidev_el *el = snapstore_multidev_find(multidev, dev_id);
> +
> +	if (el)
> +		return el->blk_dev;
> +
> +	res = blk_dev_open(dev_id, &blk_dev);
> +	if (res != SUCCESS) {
> +		pr_err("Unable to add device to snapstore multidevice file\n");
> +		pr_err("Failed to open [%d:%d]. errno=%d", MAJOR(dev_id), MINOR(dev_id), res);
> +		return NULL;
> +	}
> +
> +	el = kzalloc(sizeof(struct multidev_el), GFP_KERNEL);
> +	INIT_LIST_HEAD(&el->link);
> +
> +	el->blk_dev = blk_dev;
> +	el->dev_id = dev_id;
> +
> +	spin_lock(&multidev->devicelist_lock);
> +	list_add_tail(&el->link, &multidev->devicelist);
> +	spin_unlock(&multidev->devicelist_lock);
> +
> +	return el->blk_dev;
> +}
> +
> +#endif
> diff --git a/drivers/block/blk-snap/snapstore_multidev.h b/drivers/block/blk-snap/snapstore_multidev.h
> new file mode 100644
> index 000000000000..40c1c3a41b08
> --- /dev/null
> +++ b/drivers/block/blk-snap/snapstore_multidev.h
> @@ -0,0 +1,22 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#pragma once
> +
> +#ifdef CONFIG_BLK_SNAP_SNAPSTORE_MULTIDEV
> +
> +#include "blk_deferred.h"
> +#include "blk_descr_multidev.h"
> +
> +struct snapstore_multidev {
> +	struct list_head devicelist; //for mapping device id to opened device struct pointer
> +	spinlock_t devicelist_lock;
> +
> +	struct blk_descr_pool pool;
> +};
> +
> +int snapstore_multidev_create(struct snapstore_multidev **p_file);
> +
> +void snapstore_multidev_destroy(struct snapstore_multidev *file);
> +
> +struct block_device *snapstore_multidev_get_device(struct snapstore_multidev *multidev,
> +						   dev_t dev_id);
> +#endif
> diff --git a/drivers/block/blk-snap/tracker.c b/drivers/block/blk-snap/tracker.c
> new file mode 100644
> index 000000000000..3cda996d3f0a
> --- /dev/null
> +++ b/drivers/block/blk-snap/tracker.c
> @@ -0,0 +1,449 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-tracker"
> +#include "common.h"
> +#include "tracker.h"
> +#include "blk_util.h"
> +#include "params.h"
> +
> +LIST_HEAD(trackers);
> +DEFINE_RWLOCK(trackers_lock);
> +
> +void tracker_done(void)
> +{
> +	tracker_remove_all();
> +}
> +
> +int tracker_find_by_bio(struct bio *bio, struct tracker **ptracker)
> +{
> +	int result = -ENODATA;
> +
> +	read_lock(&trackers_lock);
> +	if (!list_empty(&trackers)) {
> +		struct list_head *_head;
> +
> +		list_for_each(_head, &trackers) {
> +			struct tracker *_tracker = list_entry(_head, struct tracker, link);
> +
> +			if ((bio->bi_disk == _tracker->target_dev->bd_disk) &&
> +			    (bio->bi_partno == _tracker->target_dev->bd_partno)) {
> +				if (ptracker != NULL)
> +					*ptracker = _tracker;
> +
> +				result = SUCCESS;
> +				break;
> +			}
> +		}
> +	}
> +	read_unlock(&trackers_lock);
> +
> +	return result;
> +}
> +
> +int tracker_find_by_dev_id(dev_t dev_id, struct tracker **ptracker)
> +{
> +	int result = -ENODATA;
> +
> +	read_lock(&trackers_lock);
> +	if (!list_empty(&trackers)) {
> +		struct list_head *_head;
> +
> +		list_for_each(_head, &trackers) {
> +			struct tracker *_tracker = list_entry(_head, struct tracker, link);
> +
> +			if (_tracker->original_dev_id == dev_id) {
> +				if (ptracker != NULL)
> +					*ptracker = _tracker;
> +
> +				result = SUCCESS;
> +				break;
> +			}
> +		}
> +	}
> +	read_unlock(&trackers_lock);
> +
> +	return result;
> +}
> +
> +int tracker_enum_cbt_info(int max_count, struct cbt_info_s *p_cbt_info, int *p_count)
> +{
> +	int result = SUCCESS;
> +	int count = 0;
> +
> +	read_lock(&trackers_lock);
> +	if (!list_empty(&trackers)) {
> +		struct list_head *_head;
> +
> +		list_for_each(_head, &trackers) {
> +			struct tracker *tracker = list_entry(_head, struct tracker, link);
> +
> +			if (count >= max_count) {
> +				result = -ENOBUFS;
> +				break; //don`t continue
> +			}
> +
> +			if (p_cbt_info != NULL) {
> +				p_cbt_info[count].dev_id.major = MAJOR(tracker->original_dev_id);
> +				p_cbt_info[count].dev_id.minor = MINOR(tracker->original_dev_id);
> +
> +				if (tracker->cbt_map) {
> +					p_cbt_info[count].cbt_map_size = tracker->cbt_map->map_size;
> +					p_cbt_info[count].snap_number =
> +						(unsigned char)
> +							tracker->cbt_map->snap_number_previous;
> +					uuid_copy((uuid_t *)(p_cbt_info[count].generationId),
> +						  &tracker->cbt_map->generationId);
> +				} else {
> +					p_cbt_info[count].cbt_map_size = 0;
> +					p_cbt_info[count].snap_number = 0;
> +				}
> +
> +				p_cbt_info[count].dev_capacity = (u64)from_sectors(
> +					part_nr_sects_read(tracker->target_dev->bd_part));
> +			}
> +
> +			++count;
> +		}
> +	}
> +	read_unlock(&trackers_lock);
> +
> +	if (result == SUCCESS)
> +		if (count == 0)
> +			result = -ENODATA;
> +
> +	*p_count = count;
> +	return result;
> +}
> +
> +static void blk_thaw_bdev(dev_t dev_id, struct block_device *device,
> +					 struct super_block *superblock)
> +{
> +	if (superblock == NULL)
> +		return;
> +
> +	if (thaw_bdev(device, superblock) == SUCCESS)
> +		pr_info("Device [%d:%d] was unfrozen\n", MAJOR(dev_id), MINOR(dev_id));
> +	else
> +		pr_err("Failed to unfreeze device [%d:%d]\n", MAJOR(dev_id), MINOR(dev_id));
> +}
> +
> +static int blk_freeze_bdev(dev_t dev_id, struct block_device *device,
> +			   struct super_block **psuperblock)
> +{
> +	struct super_block *superblock;
> +
> +	if (device->bd_super == NULL) {
> +		pr_warn("Unable to freeze device [%d:%d]: no superblock was found\n",
> +			MAJOR(dev_id), MINOR(dev_id));
> +		return SUCCESS;
> +	}
> +
> +	superblock = freeze_bdev(device);
> +	if (IS_ERR_OR_NULL(superblock)) {
> +		int result;
> +
> +		pr_err("Failed to freeze device [%d:%d]\n", MAJOR(dev_id), MINOR(dev_id));
> +
> +		if (superblock == NULL)
> +			result = -ENODEV;
> +		else {
> +			result = PTR_ERR(superblock);
> +			pr_err("Error code: %d\n", result);
> +		}
> +		return result;
> +	}
> +
> +	pr_info("Device [%d:%d] was frozen\n", MAJOR(dev_id), MINOR(dev_id));
> +	*psuperblock = superblock;
> +
> +	return SUCCESS;
> +}
> +
> +int _tracker_create(struct tracker *tracker, void *filter, bool attach_filter)
> +{
> +	int result = SUCCESS;
> +	unsigned int sect_in_block_degree;
> +	sector_t capacity;
> +	struct super_block *superblock = NULL;
> +
> +	result = blk_dev_open(tracker->original_dev_id, &tracker->target_dev);
> +	if (result != SUCCESS)
> +		return ENODEV;
> +
> +	pr_info("Create tracker for device [%d:%d]. Capacity 0x%llx sectors\n",
> +		MAJOR(tracker->original_dev_id), MINOR(tracker->original_dev_id),
> +		(unsigned long long)part_nr_sects_read(tracker->target_dev->bd_part));
> +
> +	sect_in_block_degree = get_change_tracking_block_size_pow() - SECTOR_SHIFT;
> +	capacity = part_nr_sects_read(tracker->target_dev->bd_part);
> +
> +	tracker->cbt_map = cbt_map_create(sect_in_block_degree, capacity);
> +	if (tracker->cbt_map == NULL) {
> +		pr_err("Failed to create tracker for device [%d:%d]\n",
> +		       MAJOR(tracker->original_dev_id), MINOR(tracker->original_dev_id));
> +		tracker_remove(tracker);
> +		return -ENOMEM;
> +	}
> +
> +	tracker->snapshot_id = 0ull;
> +
> +	if (attach_filter) {
> +		blk_freeze_bdev(tracker->original_dev_id, tracker->target_dev, &superblock);
> +
> +		blk_filter_attach(tracker->original_dev_id, filter, tracker);
> +
> +		blk_thaw_bdev(tracker->original_dev_id, tracker->target_dev, superblock);
> +	}
> +
> +	return SUCCESS;
> +}
> +
> +int tracker_create(dev_t dev_id, void *filter, struct tracker **ptracker)
> +{
> +	int ret;
> +	struct tracker *tracker = NULL;
> +
> +	*ptracker = NULL;
> +
> +	tracker = kzalloc(sizeof(struct tracker), GFP_KERNEL);
> +	if (tracker == NULL)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&tracker->link);
> +	atomic_set(&tracker->is_captured, false);
> +	tracker->original_dev_id = dev_id;
> +
> +	write_lock(&trackers_lock);
> +	list_add_tail(&tracker->link, &trackers);
> +	write_unlock(&trackers_lock);
> +
> +	ret = _tracker_create(tracker, filter, true);
> +	if (ret < 0) {
> +		tracker_remove(tracker);
> +		return ret;
> +	}
> +
> +	*ptracker = tracker;
> +	if (ret == ENODEV)
> +		pr_info("Cannot attach to unknown device [%d:%d]",
> +		       MAJOR(tracker->original_dev_id), MINOR(tracker->original_dev_id));
> +
> +	return ret;
> +}
> +
> +void _tracker_remove(struct tracker *tracker, bool detach_filter)
> +{
> +	struct super_block *superblock = NULL;
> +
> +	if (tracker->target_dev != NULL) {
> +		if (detach_filter) {
> +			blk_freeze_bdev(tracker->original_dev_id, tracker->target_dev, &superblock);
> +
> +			blk_filter_detach(tracker->original_dev_id);
> +
> +			blk_thaw_bdev(tracker->original_dev_id, tracker->target_dev, superblock);
> +		}
> +
> +		blk_dev_close(tracker->target_dev);
> +		tracker->target_dev = NULL;
> +	}
> +
> +	if (tracker->cbt_map != NULL) {
> +		cbt_map_put_resource(tracker->cbt_map);
> +		tracker->cbt_map = NULL;
> +	}
> +}
> +
> +void tracker_remove(struct tracker *tracker)
> +{
> +	_tracker_remove(tracker, true);
> +
> +	write_lock(&trackers_lock);
> +	list_del(&tracker->link);
> +	write_unlock(&trackers_lock);
> +
> +	kfree(tracker);
> +}
> +
> +void tracker_remove_all(void)
> +{
> +	struct tracker *tracker;
> +
> +	pr_info("Removing all devices from tracking\n");
> +
> +	do {
> +		tracker = NULL;
> +
> +		write_lock(&trackers_lock);
> +		if (!list_empty(&trackers)) {
> +			tracker = list_entry(trackers.next, struct tracker, link);
> +
> +			list_del(&tracker->link);
> +		}
> +		write_unlock(&trackers_lock);
> +
> +		if (tracker) {
> +			_tracker_remove(tracker, true);
> +			kfree(tracker);
> +		}
> +	} while (tracker);
> +}
> +
> +void tracker_cbt_bitmap_set(struct tracker *tracker, sector_t sector, sector_t sector_cnt)
> +{
> +	if (tracker->cbt_map == NULL)
> +		return;
> +
> +	if (tracker->cbt_map->device_capacity != part_nr_sects_read(tracker->target_dev->bd_part)) {
> +		pr_warn("Device resize detected\n");
> +		tracker->cbt_map->active = false;
> +		return;
> +	}
> +
> +	if (cbt_map_set(tracker->cbt_map, sector, sector_cnt) != SUCCESS) { //cbt corrupt
> +		pr_warn("CBT fault detected\n");
> +		tracker->cbt_map->active = false;
> +		return;
> +	}
> +}
> +
> +bool tracker_cbt_bitmap_lock(struct tracker *tracker)
> +{
> +	if (tracker->cbt_map == NULL)
> +		return false;
> +
> +	cbt_map_read_lock(tracker->cbt_map);
> +	if (!tracker->cbt_map->active) {
> +		cbt_map_read_unlock(tracker->cbt_map);
> +		return false;
> +	}
> +
> +	return true;
> +}
> +
> +void tracker_cbt_bitmap_unlock(struct tracker *tracker)
> +{
> +	if (tracker->cbt_map)
> +		cbt_map_read_unlock(tracker->cbt_map);
> +}
> +
> +int _tracker_capture_snapshot(struct tracker *tracker)
> +{
> +	int result = SUCCESS;
> +
> +	result = defer_io_create(tracker->original_dev_id, tracker->target_dev, &tracker->defer_io);
> +	if (result != SUCCESS) {
> +		pr_err("Failed to create defer IO processor\n");
> +		return result;
> +	}
> +
> +	atomic_set(&tracker->is_captured, true);
> +
> +	if (tracker->cbt_map != NULL) {
> +		cbt_map_write_lock(tracker->cbt_map);
> +		cbt_map_switch(tracker->cbt_map);
> +		cbt_map_write_unlock(tracker->cbt_map);
> +
> +		pr_info("Snapshot captured for device [%d:%d]. New snap number %ld\n",
> +			MAJOR(tracker->original_dev_id), MINOR(tracker->original_dev_id),
> +			tracker->cbt_map->snap_number_active);
> +	}
> +
> +	return result;
> +}
> +
> +int tracker_capture_snapshot(dev_t *dev_id_set, int dev_id_set_size)
> +{
> +	int result = SUCCESS;
> +	int inx = 0;
> +
> +	for (inx = 0; inx < dev_id_set_size; ++inx) {
> +		struct super_block *superblock = NULL;
> +		struct tracker *tracker = NULL;
> +		dev_t dev_id = dev_id_set[inx];
> +
> +		result = tracker_find_by_dev_id(dev_id, &tracker);
> +		if (result != SUCCESS) {
> +			pr_err("Unable to capture snapshot: cannot find device [%d:%d]\n",
> +			       MAJOR(dev_id), MINOR(dev_id));
> +			break;
> +		}
> +
> +
> +		blk_freeze_bdev(tracker->original_dev_id, tracker->target_dev, &superblock);
> +		blk_filter_freeze(tracker->target_dev);
> +
> +		result = _tracker_capture_snapshot(tracker);
> +		if (result != SUCCESS)
> +			pr_err("Failed to capture snapshot for device [%d:%d]\n",
> +			       MAJOR(dev_id), MINOR(dev_id));
> +
> +		blk_filter_thaw(tracker->target_dev);
> +		blk_thaw_bdev(tracker->original_dev_id, tracker->target_dev, superblock);
> +	}
> +	if (result != SUCCESS)
> +		return result;
> +
> +	for (inx = 0; inx < dev_id_set_size; ++inx) {
> +		struct tracker *tracker = NULL;
> +		dev_t dev_id = dev_id_set[inx];
> +
> +		result = tracker_find_by_dev_id(dev_id, &tracker);
> +		if (result != SUCCESS) {
> +			pr_err("Unable to capture snapshot: cannot find device [%d:%d]\n",
> +			       MAJOR(dev_id), MINOR(dev_id));
> +			continue;
> +		}
> +
> +		if (snapstore_device_is_corrupted(tracker->defer_io->snapstore_device)) {
> +			pr_err("Unable to freeze devices [%d:%d]: snapshot data is corrupted\n",
> +			       MAJOR(dev_id), MINOR(dev_id));
> +			result = -EDEADLK;
> +			break;
> +		}
> +	}
> +
> +	if (result != SUCCESS) {
> +		pr_err("Failed to capture snapshot. errno=%d\n", result);
> +
> +		tracker_release_snapshot(dev_id_set, dev_id_set_size);
> +	}
> +	return result;
> +}
> +
> +void _tracker_release_snapshot(struct tracker *tracker)
> +{
> +	struct super_block *superblock = NULL;
> +	struct defer_io *defer_io = tracker->defer_io;
> +
> +	blk_freeze_bdev(tracker->original_dev_id, tracker->target_dev, &superblock);
> +	blk_filter_freeze(tracker->target_dev);
> +	{ //locked region
> +		atomic_set(&tracker->is_captured, false); //clear freeze flag
> +
> +		tracker->defer_io = NULL;
> +	}
> +	blk_filter_thaw(tracker->target_dev);
> +
> +	blk_thaw_bdev(tracker->original_dev_id, tracker->target_dev, superblock);
> +
> +	defer_io_stop(defer_io);
> +	defer_io_put_resource(defer_io);
> +}
> +
> +void tracker_release_snapshot(dev_t *dev_id_set, int dev_id_set_size)
> +{
> +	int inx = 0;
> +
> +	for (; inx < dev_id_set_size; ++inx) {
> +		int status;
> +		struct tracker *p_tracker = NULL;
> +		dev_t dev = dev_id_set[inx];
> +
> +		status = tracker_find_by_dev_id(dev, &p_tracker);
> +		if (status == SUCCESS)
> +			_tracker_release_snapshot(p_tracker);
> +		else
> +			pr_err("Unable to release snapshot: cannot find tracker for device [%d:%d]\n",
> +			       MAJOR(dev), MINOR(dev));
> +	}
> +}
> diff --git a/drivers/block/blk-snap/tracker.h b/drivers/block/blk-snap/tracker.h
> new file mode 100644
> index 000000000000..9fff7c0942c3
> --- /dev/null
> +++ b/drivers/block/blk-snap/tracker.h
> @@ -0,0 +1,38 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#pragma once
> +#include "cbt_map.h"
> +#include "defer_io.h"
> +#include "blk-snap-ctl.h"
> +#include "snapshot.h"
> +
> +struct tracker {
> +	struct list_head link;
> +	dev_t original_dev_id;
> +	struct block_device *target_dev;
> +	struct cbt_map *cbt_map;
> +	atomic_t is_captured;
> +	struct defer_io *defer_io;
> +	unsigned long long snapshot_id; // current snapshot for this device
> +};
> +
> +void tracker_done(void);
> +
> +int tracker_find_by_bio(struct bio *bio, struct tracker **ptracker);
> +int tracker_find_by_dev_id(dev_t dev_id, struct tracker **ptracker);
> +
> +int tracker_enum_cbt_info(int max_count, struct cbt_info_s *p_cbt_info, int *p_count);
> +
> +int tracker_capture_snapshot(dev_t *dev_id_set, int dev_id_set_size);
> +void tracker_release_snapshot(dev_t *dev_id_set, int dev_id_set_size);
> +
> +int _tracker_create(struct tracker *tracker, void *filter, bool attach_filter);
> +int tracker_create(dev_t dev_id, void *filter, struct tracker **ptracker);
> +
> +void _tracker_remove(struct tracker *tracker, bool detach_filter);
> +void tracker_remove(struct tracker *tracker);
> +void tracker_remove_all(void);
> +
> +void tracker_cbt_bitmap_set(struct tracker *tracker, sector_t sector, sector_t sector_cnt);
> +
> +bool tracker_cbt_bitmap_lock(struct tracker *tracker);
> +void tracker_cbt_bitmap_unlock(struct tracker *tracker);
> diff --git a/drivers/block/blk-snap/tracking.c b/drivers/block/blk-snap/tracking.c
> new file mode 100644
> index 000000000000..55e18891bb96
> --- /dev/null
> +++ b/drivers/block/blk-snap/tracking.c
> @@ -0,0 +1,270 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define BLK_SNAP_SECTION "-tracking"
> +#include "common.h"
> +#include "tracking.h"
> +#include "tracker.h"
> +#include "blk_util.h"
> +#include "defer_io.h"
> +#include "params.h"
> +
> +#include <linux/blk-filter.h>
> +
> +/* pointer to block layer filter */
> +void *filter;
> +
> +/*
> + * _tracking_submit_bio() - Intercept bio by block io layer filter
> + */
> +static bool _tracking_submit_bio(struct bio *bio, void *filter_data)
> +{
> +	int res;
> +	bool cbt_locked = false;
> +	struct tracker *tracker = filter_data;
> +
> +	if (!tracker)
> +		return false;
> +
> +	//intercepting
> +	if (atomic_read(&tracker->is_captured)) {
> +		//snapshot is captured, call bio redirect algorithm
> +
> +		res = defer_io_redirect_bio(tracker->defer_io, bio, tracker);
> +		if (res == SUCCESS)
> +			return true;
> +	}
> +
> +	cbt_locked = false;
> +	if (tracker && bio_data_dir(bio) && bio_has_data(bio)) {
> +		//call CBT algorithm
> +		cbt_locked = tracker_cbt_bitmap_lock(tracker);
> +		if (cbt_locked) {
> +			sector_t sectStart = bio->bi_iter.bi_sector;
> +			sector_t sectCount = bio_sectors(bio);
> +
> +			tracker_cbt_bitmap_set(tracker, sectStart, sectCount);
> +		}
> +	}
> +	if (cbt_locked)
> +		tracker_cbt_bitmap_unlock(tracker);
> +
> +	return false;
> +}
> +
> +static bool _tracking_part_add(dev_t devt, void **p_filter_data)
> +{
> +	int result;
> +	struct tracker *tracker = NULL;
> +
> +	pr_info("new block device [%d:%d] in system\n", MAJOR(devt), MINOR(devt));
> +
> +	result = tracker_find_by_dev_id(devt, &tracker);
> +	if (result != SUCCESS)
> +		return false; /*do not track this device*/
> +
> +	if (_tracker_create(tracker, filter, false)) {
> +		pr_err("Failed to attach new device to tracker. errno=%d\n", result);
> +		return false; /*failed to attach new device to tracker*/
> +	}
> +
> +	*p_filter_data = tracker;
> +	return true;
> +}
> +
> +static void _tracking_part_del(void *private_data)
> +{
> +	struct tracker *tracker = private_data;
> +
> +	if (!tracker)
> +		return;
> +
> +	pr_info("delete block device [%d:%d] from system\n",
> +		MAJOR(tracker->original_dev_id), MINOR(tracker->original_dev_id));
> +
> +	_tracker_remove(tracker, false);
> +}
> +
> +struct blk_filter_ops filter_ops = {
> +	.filter_bio = _tracking_submit_bio,
> +	.part_add = _tracking_part_add,
> +	.part_del = _tracking_part_del };
> +
> +
> +
> +int tracking_init(void)
> +{
> +	filter = blk_filter_register(&filter_ops);
> +	if (!filter)
> +		return -ENOMEM;
> +	return SUCCESS;
> +}
> +
> +void tracking_done(void)
> +{
> +	if (filter) {
> +		blk_filter_unregister(filter);
> +		filter = NULL;
> +	}
> +}
> +
> +static int _add_already_tracked(dev_t dev_id, unsigned long long snapshot_id,
> +				struct tracker *tracker)
> +{
> +	int result = SUCCESS;
> +	bool cbt_reset_needed = false;
> +
> +	if ((snapshot_id != 0ull) && (tracker->snapshot_id == 0ull))
> +		tracker->snapshot_id = snapshot_id; // set new snapshot id
> +
> +	if (tracker->cbt_map == NULL) {
> +		unsigned int sect_in_block_degree =
> +			get_change_tracking_block_size_pow() - SECTOR_SHIFT;
> +		tracker->cbt_map = cbt_map_create(sect_in_block_degree - SECTOR_SHIFT,
> +						  part_nr_sects_read(tracker->target_dev->bd_part));
> +		if (tracker->cbt_map == NULL)
> +			return -ENOMEM;
> +
> +		// skip snapshot id
> +		tracker->snapshot_id = snapshot_id;
> +		return SUCCESS;
> +	}
> +
> +	if (!tracker->cbt_map->active) {
> +		cbt_reset_needed = true;
> +		pr_warn("Nonactive CBT table detected. CBT fault\n");
> +	}
> +
> +	if (tracker->cbt_map->device_capacity != part_nr_sects_read(tracker->target_dev->bd_part)) {
> +		cbt_reset_needed = true;
> +		pr_warn("Device resize detected. CBT fault\n");
> +	}
> +
> +	if (!cbt_reset_needed)
> +		return SUCCESS;
> +
> +	_tracker_remove(tracker, true);
> +
> +	result = _tracker_create(tracker, filter, true);
> +	if (result != SUCCESS) {
> +		pr_err("Failed to create tracker. errno=%d\n", result);
> +		return result;
> +	}
> +
> +	tracker->snapshot_id = snapshot_id;
> +
> +	return SUCCESS;
> +}
> +
> +static int _create_new_tracker(dev_t dev_id, unsigned long long snapshot_id)
> +{
> +	int result;
> +	struct tracker *tracker = NULL;
> +
> +	result = tracker_create(dev_id, filter, &tracker);
> +	if (result != SUCCESS) {
> +		pr_err("Failed to create tracker. errno=%d\n", result);
> +		return result;
> +	}
> +
> +	tracker->snapshot_id = snapshot_id;
> +
> +	return SUCCESS;
> +}
> +
> +
> +int tracking_add(dev_t dev_id, unsigned long long snapshot_id)
> +{
> +	int result;
> +	struct tracker *tracker = NULL;
> +
> +	pr_info("Adding device [%d:%d] under tracking\n", MAJOR(dev_id), MINOR(dev_id));
> +
> +	result = tracker_find_by_dev_id(dev_id, &tracker);
> +	if (result == SUCCESS) {
> +		//pr_info("Device [%d:%d] is already tracked\n", MAJOR(dev_id), MINOR(dev_id));
> +		result = _add_already_tracked(dev_id, snapshot_id, tracker);
> +		if (result == SUCCESS)
> +			result = -EALREADY;
> +	} else if (-ENODATA == result)
> +		result = _create_new_tracker(dev_id, snapshot_id);
> +	else {
> +		pr_err("Unable to add device [%d:%d] under tracking\n", MAJOR(dev_id),
> +			MINOR(dev_id));
> +		pr_err("Invalid trackers container. errno=%d\n", result);
> +	}
> +
> +	return result;
> +}
> +
> +int tracking_remove(dev_t dev_id)
> +{
> +	int result;
> +	struct tracker *tracker = NULL;
> +
> +	pr_info("Removing device [%d:%d] from tracking\n", MAJOR(dev_id), MINOR(dev_id));
> +
> +	result = tracker_find_by_dev_id(dev_id, &tracker);
> +	if (result != SUCCESS) {
> +		pr_err("Unable to remove device [%d:%d] from tracking: ",
> +		       MAJOR(dev_id), MINOR(dev_id));
> +
> +		if (-ENODATA == result)
> +			pr_err("tracker not found\n");
> +		else
> +			pr_err("tracker container failed. errno=%d\n", result);
> +
> +		return result;
> +	}
> +
> +	if (tracker->snapshot_id != 0ull) {
> +		pr_err("Unable to remove device [%d:%d] from tracking: ",
> +		       MAJOR(dev_id), MINOR(dev_id));
> +		pr_err("snapshot [0x%llx] already exist\n", tracker->snapshot_id);
> +		return -EBUSY;
> +	}
> +
> +	tracker_remove(tracker);
> +
> +	return SUCCESS;
> +}
> +
> +int tracking_collect(int max_count, struct cbt_info_s *p_cbt_info, int *p_count)
> +{
> +	int res = tracker_enum_cbt_info(max_count, p_cbt_info, p_count);
> +
> +	if (res == SUCCESS)
> +		pr_info("%d devices found under tracking\n", *p_count);
> +	else if (res == -ENODATA) {
> +		pr_info("There are no devices under tracking\n");
> +		*p_count = 0;
> +		res = SUCCESS;
> +	} else
> +		pr_err("Failed to collect devices under tracking. errno=%d", res);
> +
> +	return res;
> +}
> +
> +int tracking_read_cbt_bitmap(dev_t dev_id, unsigned int offset, size_t length,
> +			     void __user *user_buff)
> +{
> +	int result = SUCCESS;
> +	struct tracker *tracker = NULL;
> +
> +	result = tracker_find_by_dev_id(dev_id, &tracker);
> +	if (result == SUCCESS) {
> +		if (atomic_read(&tracker->is_captured))
> +			result = cbt_map_read_to_user(tracker->cbt_map, user_buff, offset, length);
> +		else {
> +			pr_err("Unable to read CBT bitmap for device [%d:%d]: ", MAJOR(dev_id),
> +			       MINOR(dev_id));
> +			pr_err("device is not captured by snapshot\n");
> +			result = -EPERM;
> +		}
> +	} else if (-ENODATA == result) {
> +		pr_err("Unable to read CBT bitmap for device [%d:%d]: ", MAJOR(dev_id),
> +		       MINOR(dev_id));
> +		pr_err("device not found\n");
> +	} else
> +		pr_err("Failed to find devices under tracking. errno=%d", result);
> +
> +	return result;
> +}
> diff --git a/drivers/block/blk-snap/tracking.h b/drivers/block/blk-snap/tracking.h
> new file mode 100644
> index 000000000000..22bd5ba54963
> --- /dev/null
> +++ b/drivers/block/blk-snap/tracking.h
> @@ -0,0 +1,13 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#pragma once
> +#include "blk-snap-ctl.h"
> +#include <linux/bio.h>
> +
> +int  tracking_init(void);
> +void tracking_done(void);
> +
> +int tracking_add(dev_t dev_id, unsigned long long snapshot_id);
> +int tracking_remove(dev_t dev_id);
> +int tracking_collect(int max_count, struct cbt_info_s *p_cbt_info, int *p_count);
> +int tracking_read_cbt_bitmap(dev_t dev_id, unsigned int offset, size_t length,
> +			     void __user *user_buff);
> diff --git a/drivers/block/blk-snap/version.h b/drivers/block/blk-snap/version.h
> new file mode 100644
> index 000000000000..a4431da73611
> --- /dev/null
> +++ b/drivers/block/blk-snap/version.h
> @@ -0,0 +1,7 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#pragma once
> +
> +#define FILEVER_MAJOR 5
> +#define FILEVER_MINOR 0
> +#define FILEVER_REVISION 0
> +#define FILEVER_STR "5.0.0"
> 


-- 
Damien Le Moal
Western Digital Research

Re: [PATCH 2/2] blk-snap - snapshots and change-tracking for block devices

[Sergei Shtepa]

> And this is a 8600+ lines patch.
> Can you split this into manageable pieces ?

Yes, the module was quite large. But I think it's not good to show
the elephant in parts. 
https://en.wikipedia.org/wiki/Blind_men_and_an_elephant

> I do not think anybody will review such a huge patch.

Yes, it will be a lot of work. But I hope that the code architecture
and splitting entities into separate files will help.

If someone can advise how to divide a module into a chain of patches,
I will be happy. I do not dare to divide it without losing meaning.

-- 
Sergei Shtepa
Veeam Software developer.

Re: [PATCH 2/2] blk-snap - snapshots and change-tracking for block devices

[kernel test robot]

[-- Attachment #1: Type: text/plain, Size: 27626 bytes --]

Hi Sergei,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on xfs-linux/for-next]
[also build test WARNING on hnaz-linux-mm/master v5.9]
[cannot apply to block/for-next linus/master next-20201021]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Sergei-Shtepa/block-layer-filter-and-block-device-snapshot-module/20201021-170553
base:   https://git.kernel.org/pub/scm/fs/xfs/xfs-linux.git for-next
config: m68k-allmodconfig (attached as .config)
compiler: m68k-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/dbf569c929b7f5795312a2a87bb61f2cb91a9b44
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Sergei-Shtepa/block-layer-filter-and-block-device-snapshot-module/20201021-170553
        git checkout dbf569c929b7f5795312a2a87bb61f2cb91a9b44
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=m68k 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   In file included from include/linux/kernel.h:11,
                    from include/linux/list.h:9,
                    from include/linux/mutex.h:15,
                    from drivers/block/blk-snap/common.h:13,
                    from drivers/block/blk-snap/blk_deferred.c:3:
   include/linux/scatterlist.h: In function 'sg_set_buf':
   arch/m68k/include/asm/page_mm.h:169:49: warning: ordered comparison of pointer with null pointer [-Wextra]
     169 | #define virt_addr_valid(kaddr) ((void *)(kaddr) >= (void *)PAGE_OFFSET && (void *)(kaddr) < high_memory)
         |                                                 ^~
   include/linux/compiler.h:78:42: note: in definition of macro 'unlikely'
      78 | # define unlikely(x) __builtin_expect(!!(x), 0)
         |                                          ^
   include/linux/scatterlist.h:143:2: note: in expansion of macro 'BUG_ON'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |  ^~~~~~
   include/linux/scatterlist.h:143:10: note: in expansion of macro 'virt_addr_valid'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |          ^~~~~~~~~~~~~~~
   drivers/block/blk-snap/blk_deferred.c: At top level:
>> drivers/block/blk-snap/blk_deferred.c:140:13: warning: no previous prototype for '_blk_deferred_bio_alloc' [-Wmissing-prototypes]
     140 | struct bio *_blk_deferred_bio_alloc(int nr_iovecs)
         |             ^~~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/blk_deferred.c:198:10: warning: no previous prototype for '_blk_deferred_submit_pages' [-Wmissing-prototypes]
     198 | sector_t _blk_deferred_submit_pages(struct block_device *blk_dev,
         |          ^~~~~~~~~~~~~~~~~~~~~~~~~~
--
   In file included from include/linux/kernel.h:11,
                    from include/linux/list.h:9,
                    from include/linux/mutex.h:15,
                    from drivers/block/blk-snap/common.h:13,
                    from drivers/block/blk-snap/blk_descr_file.c:3:
   include/linux/scatterlist.h: In function 'sg_set_buf':
   arch/m68k/include/asm/page_mm.h:169:49: warning: ordered comparison of pointer with null pointer [-Wextra]
     169 | #define virt_addr_valid(kaddr) ((void *)(kaddr) >= (void *)PAGE_OFFSET && (void *)(kaddr) < high_memory)
         |                                                 ^~
   include/linux/compiler.h:78:42: note: in definition of macro 'unlikely'
      78 | # define unlikely(x) __builtin_expect(!!(x), 0)
         |                                          ^
   include/linux/scatterlist.h:143:2: note: in expansion of macro 'BUG_ON'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |  ^~~~~~
   include/linux/scatterlist.h:143:10: note: in expansion of macro 'virt_addr_valid'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |          ^~~~~~~~~~~~~~~
   drivers/block/blk-snap/blk_descr_file.c: At top level:
>> drivers/block/blk-snap/blk_descr_file.c:39:6: warning: no previous prototype for '_blk_descr_file_cleanup' [-Wmissing-prototypes]
      39 | void _blk_descr_file_cleanup(void *descr_array, size_t count)
         |      ^~~~~~~~~~~~~~~~~~~~~~~
--
   In file included from include/linux/kernel.h:11,
                    from include/linux/list.h:9,
                    from include/linux/mutex.h:15,
                    from drivers/block/blk-snap/common.h:13,
                    from drivers/block/blk-snap/blk_descr_mem.c:3:
   include/linux/scatterlist.h: In function 'sg_set_buf':
   arch/m68k/include/asm/page_mm.h:169:49: warning: ordered comparison of pointer with null pointer [-Wextra]
     169 | #define virt_addr_valid(kaddr) ((void *)(kaddr) >= (void *)PAGE_OFFSET && (void *)(kaddr) < high_memory)
         |                                                 ^~
   include/linux/compiler.h:78:42: note: in definition of macro 'unlikely'
      78 | # define unlikely(x) __builtin_expect(!!(x), 0)
         |                                          ^
   include/linux/scatterlist.h:143:2: note: in expansion of macro 'BUG_ON'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |  ^~~~~~
   include/linux/scatterlist.h:143:10: note: in expansion of macro 'virt_addr_valid'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |          ^~~~~~~~~~~~~~~
   drivers/block/blk-snap/blk_descr_mem.c: At top level:
>> drivers/block/blk-snap/blk_descr_mem.c:23:6: warning: no previous prototype for 'blk_descr_mem_cleanup' [-Wmissing-prototypes]
      23 | void blk_descr_mem_cleanup(void *descr_array, size_t count)
         |      ^~~~~~~~~~~~~~~~~~~~~
--
   In file included from include/linux/kernel.h:11,
                    from include/linux/list.h:9,
                    from include/linux/mutex.h:15,
                    from drivers/block/blk-snap/common.h:13,
                    from drivers/block/blk-snap/blk_redirect.c:3:
   include/linux/scatterlist.h: In function 'sg_set_buf':
   arch/m68k/include/asm/page_mm.h:169:49: warning: ordered comparison of pointer with null pointer [-Wextra]
     169 | #define virt_addr_valid(kaddr) ((void *)(kaddr) >= (void *)PAGE_OFFSET && (void *)(kaddr) < high_memory)
         |                                                 ^~
   include/linux/compiler.h:78:42: note: in definition of macro 'unlikely'
      78 | # define unlikely(x) __builtin_expect(!!(x), 0)
         |                                          ^
   include/linux/scatterlist.h:143:2: note: in expansion of macro 'BUG_ON'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |  ^~~~~~
   include/linux/scatterlist.h:143:10: note: in expansion of macro 'virt_addr_valid'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |          ^~~~~~~~~~~~~~~
   drivers/block/blk-snap/blk_redirect.c: At top level:
>> drivers/block/blk-snap/blk_redirect.c:44:13: warning: no previous prototype for '_blk_dev_redirect_bio_alloc' [-Wmissing-prototypes]
      44 | struct bio *_blk_dev_redirect_bio_alloc(int nr_iovecs, void *bi_private)
         |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/blk_redirect.c:58:31: warning: no previous prototype for '_redirect_bio_allocate_list' [-Wmissing-prototypes]
      58 | struct blk_redirect_bio_list *_redirect_bio_allocate_list(struct bio *new_bio)
         |                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/blk_redirect.c:72:5: warning: no previous prototype for 'bio_endio_list_push' [-Wmissing-prototypes]
      72 | int bio_endio_list_push(struct blk_redirect_bio *rq_redir, struct bio *new_bio)
         |     ^~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/blk_redirect.c:97:6: warning: no previous prototype for 'bio_endio_list_cleanup' [-Wmissing-prototypes]
      97 | void bio_endio_list_cleanup(struct blk_redirect_bio_list *curr)
         |      ^~~~~~~~~~~~~~~~~~~~~~
--
   In file included from include/linux/kernel.h:11,
                    from include/linux/list.h:9,
                    from include/linux/mutex.h:15,
                    from drivers/block/blk-snap/common.h:13,
                    from drivers/block/blk-snap/cbt_map.c:3:
   include/linux/scatterlist.h: In function 'sg_set_buf':
   arch/m68k/include/asm/page_mm.h:169:49: warning: ordered comparison of pointer with null pointer [-Wextra]
     169 | #define virt_addr_valid(kaddr) ((void *)(kaddr) >= (void *)PAGE_OFFSET && (void *)(kaddr) < high_memory)
         |                                                 ^~
   include/linux/compiler.h:78:42: note: in definition of macro 'unlikely'
      78 | # define unlikely(x) __builtin_expect(!!(x), 0)
         |                                          ^
   include/linux/scatterlist.h:143:2: note: in expansion of macro 'BUG_ON'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |  ^~~~~~
   include/linux/scatterlist.h:143:10: note: in expansion of macro 'virt_addr_valid'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |          ^~~~~~~~~~~~~~~
   drivers/block/blk-snap/cbt_map.c: At top level:
>> drivers/block/blk-snap/cbt_map.c:6:5: warning: no previous prototype for 'cbt_map_allocate' [-Wmissing-prototypes]
       6 | int cbt_map_allocate(struct cbt_map *cbt_map, unsigned int cbt_sect_in_block_degree,
         |     ^~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/cbt_map.c:45:6: warning: no previous prototype for 'cbt_map_deallocate' [-Wmissing-prototypes]
      45 | void cbt_map_deallocate(struct cbt_map *cbt_map)
         |      ^~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/cbt_map.c:92:6: warning: no previous prototype for 'cbt_map_destroy_cb' [-Wmissing-prototypes]
      92 | void cbt_map_destroy_cb(struct kref *kref)
         |      ^~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/cbt_map.c:132:5: warning: no previous prototype for '_cbt_map_set' [-Wmissing-prototypes]
     132 | int _cbt_map_set(struct cbt_map *cbt_map, sector_t sector_start, sector_t sector_cnt,
         |     ^~~~~~~~~~~~
--
   In file included from include/linux/kernel.h:11,
                    from include/linux/list.h:9,
                    from include/linux/mutex.h:15,
                    from drivers/block/blk-snap/common.h:13,
                    from drivers/block/blk-snap/ctrl_fops.c:3:
   include/linux/scatterlist.h: In function 'sg_set_buf':
   arch/m68k/include/asm/page_mm.h:169:49: warning: ordered comparison of pointer with null pointer [-Wextra]
     169 | #define virt_addr_valid(kaddr) ((void *)(kaddr) >= (void *)PAGE_OFFSET && (void *)(kaddr) < high_memory)
         |                                                 ^~
   include/linux/compiler.h:78:42: note: in definition of macro 'unlikely'
      78 | # define unlikely(x) __builtin_expect(!!(x), 0)
         |                                          ^
   include/linux/scatterlist.h:143:2: note: in expansion of macro 'BUG_ON'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |  ^~~~~~
   include/linux/scatterlist.h:143:10: note: in expansion of macro 'virt_addr_valid'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |          ^~~~~~~~~~~~~~~
   drivers/block/blk-snap/ctrl_fops.c: At top level:
>> drivers/block/blk-snap/ctrl_fops.c:140:5: warning: no previous prototype for 'ioctl_compatibility_flags' [-Wmissing-prototypes]
     140 | int ioctl_compatibility_flags(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:159:5: warning: no previous prototype for 'ioctl_get_version' [-Wmissing-prototypes]
     159 | int ioctl_get_version(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:174:5: warning: no previous prototype for 'ioctl_tracking_add' [-Wmissing-prototypes]
     174 | int ioctl_tracking_add(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:188:5: warning: no previous prototype for 'ioctl_tracking_remove' [-Wmissing-prototypes]
     188 | int ioctl_tracking_remove(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:200:5: warning: no previous prototype for 'ioctl_tracking_collect' [-Wmissing-prototypes]
     200 | int ioctl_tracking_collect(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:263:5: warning: no previous prototype for 'ioctl_tracking_block_size' [-Wmissing-prototypes]
     263 | int ioctl_tracking_block_size(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:276:5: warning: no previous prototype for 'ioctl_tracking_read_cbt_map' [-Wmissing-prototypes]
     276 | int ioctl_tracking_read_cbt_map(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:294:5: warning: no previous prototype for 'ioctl_tracking_mark_dirty_blocks' [-Wmissing-prototypes]
     294 | int ioctl_tracking_mark_dirty_blocks(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:334:5: warning: no previous prototype for 'ioctl_snapshot_create' [-Wmissing-prototypes]
     334 | int ioctl_snapshot_create(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:401:5: warning: no previous prototype for 'ioctl_snapshot_destroy' [-Wmissing-prototypes]
     401 | int ioctl_snapshot_destroy(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:426:5: warning: no previous prototype for 'ioctl_snapstore_create' [-Wmissing-prototypes]
     426 | int ioctl_snapstore_create(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:468:5: warning: no previous prototype for 'ioctl_snapstore_file' [-Wmissing-prototypes]
     468 | int ioctl_snapstore_file(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:504:5: warning: no previous prototype for 'ioctl_snapstore_memory' [-Wmissing-prototypes]
     504 | int ioctl_snapstore_memory(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:520:5: warning: no previous prototype for 'ioctl_snapstore_cleanup' [-Wmissing-prototypes]
     520 | int ioctl_snapstore_cleanup(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:547:5: warning: no previous prototype for 'ioctl_snapstore_file_multidev' [-Wmissing-prototypes]
     547 | int ioctl_snapstore_file_multidev(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:596:5: warning: no previous prototype for 'ioctl_snapshot_errno' [-Wmissing-prototypes]
     596 | int ioctl_snapshot_errno(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/ctrl_fops.c:623:5: warning: no previous prototype for 'ioctl_collect_snapimages' [-Wmissing-prototypes]
     623 | int ioctl_collect_snapimages(unsigned long arg)
         |     ^~~~~~~~~~~~~~~~~~~~~~~~
--
   In file included from include/linux/kernel.h:11,
                    from include/linux/list.h:9,
                    from include/linux/mutex.h:15,
                    from drivers/block/blk-snap/common.h:13,
                    from drivers/block/blk-snap/main.c:2:
   include/linux/scatterlist.h: In function 'sg_set_buf':
   arch/m68k/include/asm/page_mm.h:169:49: warning: ordered comparison of pointer with null pointer [-Wextra]
     169 | #define virt_addr_valid(kaddr) ((void *)(kaddr) >= (void *)PAGE_OFFSET && (void *)(kaddr) < high_memory)
         |                                                 ^~
   include/linux/compiler.h:78:42: note: in definition of macro 'unlikely'
      78 | # define unlikely(x) __builtin_expect(!!(x), 0)
         |                                          ^
   include/linux/scatterlist.h:143:2: note: in expansion of macro 'BUG_ON'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |  ^~~~~~
   include/linux/scatterlist.h:143:10: note: in expansion of macro 'virt_addr_valid'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |          ^~~~~~~~~~~~~~~
   drivers/block/blk-snap/main.c: At top level:
>> drivers/block/blk-snap/main.c:17:12: warning: no previous prototype for 'blk_snap_init' [-Wmissing-prototypes]
      17 | int __init blk_snap_init(void)
         |            ^~~~~~~~~~~~~
>> drivers/block/blk-snap/main.c:52:13: warning: no previous prototype for 'blk_snap_exit' [-Wmissing-prototypes]
      52 | void __exit blk_snap_exit(void)
         |             ^~~~~~~~~~~~~
--
   In file included from include/linux/kernel.h:11,
                    from include/linux/list.h:9,
                    from include/linux/mutex.h:15,
                    from drivers/block/blk-snap/common.h:13,
                    from drivers/block/blk-snap/snapimage.c:3:
   include/linux/scatterlist.h: In function 'sg_set_buf':
   arch/m68k/include/asm/page_mm.h:169:49: warning: ordered comparison of pointer with null pointer [-Wextra]
     169 | #define virt_addr_valid(kaddr) ((void *)(kaddr) >= (void *)PAGE_OFFSET && (void *)(kaddr) < high_memory)
         |                                                 ^~
   include/linux/compiler.h:78:42: note: in definition of macro 'unlikely'
      78 | # define unlikely(x) __builtin_expect(!!(x), 0)
         |                                          ^
   include/linux/scatterlist.h:143:2: note: in expansion of macro 'BUG_ON'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |  ^~~~~~
   include/linux/scatterlist.h:143:10: note: in expansion of macro 'virt_addr_valid'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |          ^~~~~~~~~~~~~~~
   drivers/block/blk-snap/snapimage.c: At top level:
>> drivers/block/blk-snap/snapimage.c:56:5: warning: no previous prototype for '_snapimage_open' [-Wmissing-prototypes]
      56 | int _snapimage_open(struct block_device *bdev, fmode_t mode)
         |     ^~~~~~~~~~~~~~~
>> drivers/block/blk-snap/snapimage.c:97:5: warning: no previous prototype for '_snapimage_getgeo' [-Wmissing-prototypes]
      97 | int _snapimage_getgeo(struct block_device *bdev, struct hd_geometry *geo)
         |     ^~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/snapimage.c:143:6: warning: no previous prototype for '_snapimage_close' [-Wmissing-prototypes]
     143 | void _snapimage_close(struct gendisk *disk, fmode_t mode)
         |      ^~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/snapimage.c:165:5: warning: no previous prototype for '_snapimage_ioctl' [-Wmissing-prototypes]
     165 | int _snapimage_ioctl(struct block_device *bdev, fmode_t mode, unsigned int cmd, unsigned long arg)
         |     ^~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/snapimage.c:231:5: warning: no previous prototype for '_snapimage_request_write' [-Wmissing-prototypes]
     231 | int _snapimage_request_write(struct snapimage *image, struct blk_redirect_bio *rq_redir)
         |     ^~~~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/snapimage.c:277:6: warning: no previous prototype for '_snapimage_processing' [-Wmissing-prototypes]
     277 | void _snapimage_processing(struct snapimage *image)
         |      ^~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/snapimage.c:299:5: warning: no previous prototype for 'snapimage_processor_waiting' [-Wmissing-prototypes]
     299 | int snapimage_processor_waiting(struct snapimage *image)
         |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/snapimage.c:316:5: warning: no previous prototype for 'snapimage_processor_thread' [-Wmissing-prototypes]
     316 | int snapimage_processor_thread(void *data)
         |     ^~~~~~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/snapimage.c:361:6: warning: no previous prototype for '_snapimage_bio_complete_cb' [-Wmissing-prototypes]
     361 | void _snapimage_bio_complete_cb(void *complete_param, struct bio *bio, int err)
         |      ^~~~~~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/snapimage.c:373:5: warning: no previous prototype for '_snapimage_throttling' [-Wmissing-prototypes]
     373 | int _snapimage_throttling(struct defer_io *defer_io)
         |     ^~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/snapimage.c:557:5: warning: no previous prototype for 'snapimage_create' [-Wmissing-prototypes]
     557 | int snapimage_create(dev_t original_dev)
         |     ^~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/snapimage.c:782:6: warning: no previous prototype for 'snapimage_destroy_for' [-Wmissing-prototypes]
     782 | void snapimage_destroy_for(dev_t *p_dev, int count)
         |      ^~~~~~~~~~~~~~~~~~~~~
--
   In file included from include/linux/kernel.h:11,
                    from include/linux/list.h:9,
                    from include/linux/mutex.h:15,
                    from drivers/block/blk-snap/common.h:13,
                    from drivers/block/blk-snap/snapstore.c:3:
   include/linux/scatterlist.h: In function 'sg_set_buf':
   arch/m68k/include/asm/page_mm.h:169:49: warning: ordered comparison of pointer with null pointer [-Wextra]
     169 | #define virt_addr_valid(kaddr) ((void *)(kaddr) >= (void *)PAGE_OFFSET && (void *)(kaddr) < high_memory)
         |                                                 ^~
   include/linux/compiler.h:78:42: note: in definition of macro 'unlikely'
      78 | # define unlikely(x) __builtin_expect(!!(x), 0)
         |                                          ^
   include/linux/scatterlist.h:143:2: note: in expansion of macro 'BUG_ON'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |  ^~~~~~
   include/linux/scatterlist.h:143:10: note: in expansion of macro 'virt_addr_valid'
     143 |  BUG_ON(!virt_addr_valid(buf));
         |          ^~~~~~~~~~~~~~~
   drivers/block/blk-snap/snapstore.c: At top level:
>> drivers/block/blk-snap/snapstore.c:12:6: warning: no previous prototype for '_snapstore_check_halffill' [-Wmissing-prototypes]
      12 | bool _snapstore_check_halffill(struct snapstore *snapstore, sector_t *fill_status)
         |      ^~~~~~~~~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/snapstore.c:31:6: warning: no previous prototype for '_snapstore_destroy' [-Wmissing-prototypes]
      31 | void _snapstore_destroy(struct snapstore *snapstore)
         |      ^~~~~~~~~~~~~~~~~~
>> drivers/block/blk-snap/snapstore.c:251:19: warning: no previous prototype for '_snapstore_find' [-Wmissing-prototypes]
     251 | struct snapstore *_snapstore_find(uuid_t *id)
         |                   ^~~~~~~~~~~~~~~
>> drivers/block/blk-snap/snapstore.c:350:5: warning: no previous prototype for 'rangelist_add' [-Wmissing-prototypes]
     350 | int rangelist_add(struct list_head *rglist, struct blk_range *rg)
         |     ^~~~~~~~~~~~~
..

vim +/_blk_deferred_bio_alloc +140 drivers/block/blk-snap/blk_deferred.c

   139	
 > 140	struct bio *_blk_deferred_bio_alloc(int nr_iovecs)
   141	{
   142		struct bio *new_bio = bio_alloc_bioset(GFP_NOIO, nr_iovecs, &blk_deferred_bioset);
   143	
   144		if (new_bio == NULL)
   145			return NULL;
   146	
   147		new_bio->bi_end_io = blk_deferred_bio_endio;
   148		new_bio->bi_private = ((void *)new_bio) - sizeof(struct dio_bio_complete);
   149	
   150		return new_bio;
   151	}
   152	
   153	static void blk_deferred_complete(struct blk_deferred_request *dio_req, sector_t portion_sect_cnt,
   154					  int result)
   155	{
   156		atomic64_add(portion_sect_cnt, &dio_req->sect_processed);
   157	
   158		if (dio_req->sect_len == atomic64_read(&dio_req->sect_processed))
   159			complete(&dio_req->complete);
   160	
   161		if (result != SUCCESS) {
   162			dio_req->result = result;
   163			pr_err("Failed to process defer IO request. errno=%d\n", result);
   164		}
   165	}
   166	
   167	void blk_deferred_bio_endio(struct bio *bio)
   168	{
   169		int local_err;
   170		struct dio_bio_complete *complete_param = (struct dio_bio_complete *)bio->bi_private;
   171	
   172		if (complete_param == NULL) {
   173			//bio already complete
   174		} else {
   175			if (bio->bi_status != BLK_STS_OK)
   176				local_err = -EIO;
   177			else
   178				local_err = SUCCESS;
   179	
   180			blk_deferred_complete(complete_param->dio_req, complete_param->bio_sect_len,
   181					      local_err);
   182			bio->bi_private = NULL;
   183		}
   184	
   185		bio_put(bio);
   186	}
   187	
   188	static inline size_t _page_count_calculate(sector_t size_sector)
   189	{
   190		size_t page_count = size_sector / (PAGE_SIZE / SECTOR_SIZE);
   191	
   192		if (unlikely(size_sector & ((PAGE_SIZE / SECTOR_SIZE) - 1)))
   193			page_count += 1;
   194	
   195		return page_count;
   196	}
   197	
 > 198	sector_t _blk_deferred_submit_pages(struct block_device *blk_dev,
   199					    struct blk_deferred_request *dio_req, int direction,
   200					    sector_t arr_ofs, struct page **page_array, sector_t ofs_sector,
   201					    sector_t size_sector)
   202	{
   203		struct bio *bio = NULL;
   204		int nr_iovecs;
   205		int page_inx = arr_ofs >> (PAGE_SHIFT - SECTOR_SHIFT);
   206		sector_t process_sect = 0;
   207	
   208		nr_iovecs = _page_count_calculate(size_sector);
   209	
   210		while (NULL == (bio = _blk_deferred_bio_alloc(nr_iovecs))) {
   211			size_sector = (size_sector >> 1) & ~((PAGE_SIZE / SECTOR_SIZE) - 1);
   212			if (size_sector == 0)
   213				return 0;
   214	
   215			nr_iovecs = _page_count_calculate(size_sector);
   216		}
   217	
   218		bio_set_dev(bio, blk_dev);
   219	
   220		if (direction == READ)
   221			bio_set_op_attrs(bio, REQ_OP_READ, 0);
   222		else
   223			bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
   224	
   225		bio->bi_iter.bi_sector = ofs_sector;
   226	
   227		{ //add first
   228			sector_t unordered = arr_ofs & ((PAGE_SIZE / SECTOR_SIZE) - 1);
   229			sector_t bvec_len_sect =
   230				min_t(sector_t, ((PAGE_SIZE / SECTOR_SIZE) - unordered), size_sector);
   231			struct page *page = page_array[page_inx];
   232			unsigned int len = (unsigned int)from_sectors(bvec_len_sect);
   233			unsigned int offset = (unsigned int)from_sectors(unordered);
   234	
   235			if (unlikely(page == NULL)) {
   236				pr_err("NULL found in page array");
   237				bio_put(bio);
   238				return 0;
   239			}
   240			if (unlikely(bio_add_page(bio, page, len, offset) != len)) {
   241				bio_put(bio);
   242				return 0;
   243			}
   244			++page_inx;
   245			process_sect += bvec_len_sect;
   246		}
   247	
   248		while (process_sect < size_sector) {
   249			sector_t bvec_len_sect =
   250				min_t(sector_t, (PAGE_SIZE / SECTOR_SIZE), (size_sector - process_sect));
   251			struct page *page = page_array[page_inx];
   252			unsigned int len = (unsigned int)from_sectors(bvec_len_sect);
   253	
   254	
   255			if (unlikely(page == NULL)) {
   256				pr_err("NULL found in page array");
   257				break;
   258			}
   259			if (unlikely(bio_add_page(bio, page, len, 0) != len))
   260				break;
   261	
   262			++page_inx;
   263			process_sect += bvec_len_sect;
   264		}
   265	
   266		((struct dio_bio_complete *)bio->bi_private)->dio_req = dio_req;
   267		((struct dio_bio_complete *)bio->bi_private)->bio_sect_len = process_sect;
   268	
   269		submit_bio_direct(bio);
   270	
   271		return process_sect;
   272	}
   273	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 57841 bytes --]

Re: [PATCH 2/2] blk-snap - snapshots and change-tracking for block devices

[Randy Dunlap]

On 10/21/20 2:04 AM, Sergei Shtepa wrote:
> diff --git a/drivers/block/blk-snap/Kconfig b/drivers/block/blk-snap/Kconfig
> new file mode 100644
> index 000000000000..7a2db99a80dd
> --- /dev/null
> +++ b/drivers/block/blk-snap/Kconfig
> @@ -0,0 +1,24 @@
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# blk-snap block io layer filter module configuration
> +#
> +#
> +#select BLK_FILTER
> +
> +config BLK_SNAP
> +	tristate "Block device snapshot filter"
> +	depends on BLK_FILTER
> +	help
> +

No blank line here.

> +	  Allow to create snapshots and track block changes for a block

	                                                    for block

> +	  devices. Designed for creating backups for any block devices
> +	  (without device mapper). Snapshots are temporary and are released
> +	  then backup is completed. Change block tracking allows you to

	  when

> +	  create incremental or differential backups.
> +
> +config BLK_SNAP_SNAPSTORE_MULTIDEV
> +	bool "Multi device snapstore configuration support"
> +	depends on BLK_SNAP
> +	help
> +
No blank line here.

> +	  Allow to create snapstore on multiple block devices.


thanks.
-- 
~Randy

Re: [PATCH 0/2] block layer filter and block device snapshot module

[Hannes Reinecke]

On 10/21/20 11:04 AM, Sergei Shtepa wrote:
> Hello everyone! Requesting for your comments and suggestions.
> 
> # blk-filter
> 
> Block layer filter allows to intercept BIO requests to a block device.
> 
> Interception is performed at the very beginning of the BIO request
> processing, and therefore does not affect the operation of the request
> processing queue. This also makes it possible to intercept requests from
> a specific block device, rather than from the entire disk.
> 
> The logic of the submit_bio function has been changed - since the
> function execution results are not processed anywhere (except for swap
> and direct-io) the function won't return a value anymore.
> 
> Now the submit_bio_direct() function is called whenever the result of
> the blk_qc_t function is required. submit_bio_direct() is not
> intercepted by the block layer filter. This is logical for swap and
> direct-io.
> 
> Block layer filter allows you to enable and disable the filter driver on
> the fly. When a new block device is added, the filter driver can start
> filtering this device. When you delete a device, the filter can remove
> its own filter.
> 
> The idea of multiple altitudes had to be abandoned in order to simplify
> implementation and make it more reliable. Different filter drivers can
> work simultaneously, but each on its own block device.
> 
> # blk-snap
> 
> We propose a new kernel module - blk-snap. This module implements
> snapshot and changed block tracking functionality. It is intended to
> create backup copies of any block devices without usage of device mapper.
> Snapshots are temporary and are destroyed after the backup process has
> finished. Changed block tracking allows for incremental and differential
> backup copies.
> 
> blk-snap uses block layer filter. Block layer filter provides a callback
> to intercept bio-requests. If a block device disappears for whatever
> reason, send a synchronous request to remove the device from filtering.
> 
> blk-snap kernel module is a product of a deep refactoring of the
> out-of-tree kernel veeamsnap kernel module
> (https://github.com/veeam/veeamsnap/):
> * all conditional compilation branches that served for the purpose of
>    compatibility with older kernels have been removed;
> * linux kernel code style has been applied;
> * blk-snap mostly takes advantage of the existing kernel code instead of
>    reinventing the wheel;
> * all redundant code (such as persistent cbt and snapstore collector)
>    has been removed.
> 
> Several important things are still have to be done:
> * refactor the module interface for interaction with a user-space code -
>    it is already clear that the implementation of some calls can be
>    improved.
> 
> Your feedback would be greatly appreciated!
> 
> Sergei Shtepa (2):
>    Block layer filter - second version
>    blk-snap - snapshots and change-tracking for block devices
> 
>   block/Kconfig                               |  11 +
>   block/Makefile                              |   1 +
>   block/blk-core.c                            |  52 +-
>   block/blk-filter-internal.h                 |  29 +
>   block/blk-filter.c                          | 286 ++++++
>   block/partitions/core.c                     |  14 +-
>   drivers/block/Kconfig                       |   2 +
>   drivers/block/Makefile                      |   1 +
>   drivers/block/blk-snap/Kconfig              |  24 +
>   drivers/block/blk-snap/Makefile             |  28 +
>   drivers/block/blk-snap/big_buffer.c         | 193 ++++
>   drivers/block/blk-snap/big_buffer.h         |  24 +
>   drivers/block/blk-snap/blk-snap-ctl.h       | 190 ++++
>   drivers/block/blk-snap/blk_deferred.c       | 566 +++++++++++
>   drivers/block/blk-snap/blk_deferred.h       |  67 ++
>   drivers/block/blk-snap/blk_descr_file.c     |  82 ++
>   drivers/block/blk-snap/blk_descr_file.h     |  26 +
>   drivers/block/blk-snap/blk_descr_mem.c      |  66 ++
>   drivers/block/blk-snap/blk_descr_mem.h      |  14 +
>   drivers/block/blk-snap/blk_descr_multidev.c |  86 ++
>   drivers/block/blk-snap/blk_descr_multidev.h |  25 +
>   drivers/block/blk-snap/blk_descr_pool.c     | 190 ++++
>   drivers/block/blk-snap/blk_descr_pool.h     |  38 +
>   drivers/block/blk-snap/blk_redirect.c       | 507 ++++++++++
>   drivers/block/blk-snap/blk_redirect.h       |  73 ++
>   drivers/block/blk-snap/blk_util.c           |  33 +
>   drivers/block/blk-snap/blk_util.h           |  33 +
>   drivers/block/blk-snap/cbt_map.c            | 210 +++++
>   drivers/block/blk-snap/cbt_map.h            |  62 ++
>   drivers/block/blk-snap/common.h             |  31 +
>   drivers/block/blk-snap/ctrl_fops.c          | 691 ++++++++++++++
>   drivers/block/blk-snap/ctrl_fops.h          |  19 +
>   drivers/block/blk-snap/ctrl_pipe.c          | 562 +++++++++++
>   drivers/block/blk-snap/ctrl_pipe.h          |  34 +
>   drivers/block/blk-snap/ctrl_sysfs.c         |  73 ++
>   drivers/block/blk-snap/ctrl_sysfs.h         |   5 +
>   drivers/block/blk-snap/defer_io.c           | 397 ++++++++
>   drivers/block/blk-snap/defer_io.h           |  39 +
>   drivers/block/blk-snap/main.c               |  82 ++
>   drivers/block/blk-snap/params.c             |  58 ++
>   drivers/block/blk-snap/params.h             |  29 +
>   drivers/block/blk-snap/rangevector.c        |  85 ++
>   drivers/block/blk-snap/rangevector.h        |  31 +
>   drivers/block/blk-snap/snapimage.c          | 982 ++++++++++++++++++++
>   drivers/block/blk-snap/snapimage.h          |  16 +
>   drivers/block/blk-snap/snapshot.c           | 225 +++++
>   drivers/block/blk-snap/snapshot.h           |  17 +
>   drivers/block/blk-snap/snapstore.c          | 929 ++++++++++++++++++
>   drivers/block/blk-snap/snapstore.h          |  68 ++
>   drivers/block/blk-snap/snapstore_device.c   | 532 +++++++++++
>   drivers/block/blk-snap/snapstore_device.h   |  63 ++
>   drivers/block/blk-snap/snapstore_file.c     |  52 ++
>   drivers/block/blk-snap/snapstore_file.h     |  15 +
>   drivers/block/blk-snap/snapstore_mem.c      |  91 ++
>   drivers/block/blk-snap/snapstore_mem.h      |  20 +
>   drivers/block/blk-snap/snapstore_multidev.c | 118 +++
>   drivers/block/blk-snap/snapstore_multidev.h |  22 +
>   drivers/block/blk-snap/tracker.c            | 449 +++++++++
>   drivers/block/blk-snap/tracker.h            |  38 +
>   drivers/block/blk-snap/tracking.c           | 270 ++++++
>   drivers/block/blk-snap/tracking.h           |  13 +
>   drivers/block/blk-snap/version.h            |   7 +
>   fs/block_dev.c                              |   6 +-
>   fs/direct-io.c                              |   2 +-
>   fs/iomap/direct-io.c                        |   2 +-
>   include/linux/bio.h                         |   4 +-
>   include/linux/blk-filter.h                  |  76 ++
>   include/linux/genhd.h                       |   8 +-
>   kernel/power/swap.c                         |   2 +-
>   mm/page_io.c                                |   4 +-
>   70 files changed, 9074 insertions(+), 26 deletions(-)
>   create mode 100644 block/blk-filter-internal.h
>   create mode 100644 block/blk-filter.c
>   create mode 100644 drivers/block/blk-snap/Kconfig
>   create mode 100644 drivers/block/blk-snap/Makefile
>   create mode 100644 drivers/block/blk-snap/big_buffer.c
>   create mode 100644 drivers/block/blk-snap/big_buffer.h
>   create mode 100644 drivers/block/blk-snap/blk-snap-ctl.h
>   create mode 100644 drivers/block/blk-snap/blk_deferred.c
>   create mode 100644 drivers/block/blk-snap/blk_deferred.h
>   create mode 100644 drivers/block/blk-snap/blk_descr_file.c
>   create mode 100644 drivers/block/blk-snap/blk_descr_file.h
>   create mode 100644 drivers/block/blk-snap/blk_descr_mem.c
>   create mode 100644 drivers/block/blk-snap/blk_descr_mem.h
>   create mode 100644 drivers/block/blk-snap/blk_descr_multidev.c
>   create mode 100644 drivers/block/blk-snap/blk_descr_multidev.h
>   create mode 100644 drivers/block/blk-snap/blk_descr_pool.c
>   create mode 100644 drivers/block/blk-snap/blk_descr_pool.h
>   create mode 100644 drivers/block/blk-snap/blk_redirect.c
>   create mode 100644 drivers/block/blk-snap/blk_redirect.h
>   create mode 100644 drivers/block/blk-snap/blk_util.c
>   create mode 100644 drivers/block/blk-snap/blk_util.h
>   create mode 100644 drivers/block/blk-snap/cbt_map.c
>   create mode 100644 drivers/block/blk-snap/cbt_map.h
>   create mode 100644 drivers/block/blk-snap/common.h
>   create mode 100644 drivers/block/blk-snap/ctrl_fops.c
>   create mode 100644 drivers/block/blk-snap/ctrl_fops.h
>   create mode 100644 drivers/block/blk-snap/ctrl_pipe.c
>   create mode 100644 drivers/block/blk-snap/ctrl_pipe.h
>   create mode 100644 drivers/block/blk-snap/ctrl_sysfs.c
>   create mode 100644 drivers/block/blk-snap/ctrl_sysfs.h
>   create mode 100644 drivers/block/blk-snap/defer_io.c
>   create mode 100644 drivers/block/blk-snap/defer_io.h
>   create mode 100644 drivers/block/blk-snap/main.c
>   create mode 100644 drivers/block/blk-snap/params.c
>   create mode 100644 drivers/block/blk-snap/params.h
>   create mode 100644 drivers/block/blk-snap/rangevector.c
>   create mode 100644 drivers/block/blk-snap/rangevector.h
>   create mode 100644 drivers/block/blk-snap/snapimage.c
>   create mode 100644 drivers/block/blk-snap/snapimage.h
>   create mode 100644 drivers/block/blk-snap/snapshot.c
>   create mode 100644 drivers/block/blk-snap/snapshot.h
>   create mode 100644 drivers/block/blk-snap/snapstore.c
>   create mode 100644 drivers/block/blk-snap/snapstore.h
>   create mode 100644 drivers/block/blk-snap/snapstore_device.c
>   create mode 100644 drivers/block/blk-snap/snapstore_device.h
>   create mode 100644 drivers/block/blk-snap/snapstore_file.c
>   create mode 100644 drivers/block/blk-snap/snapstore_file.h
>   create mode 100644 drivers/block/blk-snap/snapstore_mem.c
>   create mode 100644 drivers/block/blk-snap/snapstore_mem.h
>   create mode 100644 drivers/block/blk-snap/snapstore_multidev.c
>   create mode 100644 drivers/block/blk-snap/snapstore_multidev.h
>   create mode 100644 drivers/block/blk-snap/tracker.c
>   create mode 100644 drivers/block/blk-snap/tracker.h
>   create mode 100644 drivers/block/blk-snap/tracking.c
>   create mode 100644 drivers/block/blk-snap/tracking.h
>   create mode 100644 drivers/block/blk-snap/version.h
>   create mode 100644 include/linux/blk-filter.h
> 
> --
> 2.20.1
> 
I do understand where you are coming from, but then we already have a 
dm-snap which does exactly what you want to achieve.
Of course, that would require a reconfiguration of the storage stack on 
the machine, which is not always possible (or desired).

What I _could_ imagine would be a 'dm-intercept' thingie, which 
redirects the current submit_bio() function for any block device, and 
re-routes that to a linear device-mapper device pointing back to the 
original block device.

That way you could attach it to basically any block device, _and_ can 
use the existing device-mapper functionality to do fancy stuff once the 
submit_io() callback has been re-routed.

And it also would help in other scenarios, too; with such a 
functionality we could seamlessly clone devices without having to move 
the whole setup to device-mapper first.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@suse.de			                  +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Felix Imendörffer

Re: [PATCH 0/2] block layer filter and block device snapshot module

[Sergei Shtepa]

The 10/21/2020 16:31, Hannes Reinecke wrote:
> I do understand where you are coming from, but then we already have a 
> dm-snap which does exactly what you want to achieve.
> Of course, that would require a reconfiguration of the storage stack on 
> the machine, which is not always possible (or desired).

Yes, reconfiguring the storage stack on a machine is almost impossible.

> 
> What I _could_ imagine would be a 'dm-intercept' thingie, which 
> redirects the current submit_bio() function for any block device, and 
> re-routes that to a linear device-mapper device pointing back to the 
> original block device.
> 
> That way you could attach it to basically any block device, _and_ can 
> use the existing device-mapper functionality to do fancy stuff once the 
> submit_io() callback has been re-routed.
> 
> And it also would help in other scenarios, too; with such a 
> functionality we could seamlessly clone devices without having to move 
> the whole setup to device-mapper first.

Hm... 
Did I understand correctly that the filter itself can be left approximately
as it is, but the blk-snap module can be replaced with 'dm-intercept',
which would use the re-route mechanism from the dm?
I think I may be able to implement it, if you describe your idea in more
detail.


-- 
Sergei Shtepa
Veeam Software developer.

Re: [PATCH 0/2] block layer filter and block device snapshot module

[Hannes Reinecke]

On 10/21/20 4:10 PM, Sergei Shtepa wrote:
> The 10/21/2020 16:31, Hannes Reinecke wrote:
>> I do understand where you are coming from, but then we already have a
>> dm-snap which does exactly what you want to achieve.
>> Of course, that would require a reconfiguration of the storage stack on
>> the machine, which is not always possible (or desired).
> 
> Yes, reconfiguring the storage stack on a machine is almost impossible.
> 
>>
>> What I _could_ imagine would be a 'dm-intercept' thingie, which
>> redirects the current submit_bio() function for any block device, and
>> re-routes that to a linear device-mapper device pointing back to the
>> original block device.
>>
>> That way you could attach it to basically any block device, _and_ can
>> use the existing device-mapper functionality to do fancy stuff once the
>> submit_io() callback has been re-routed.
>>
>> And it also would help in other scenarios, too; with such a
>> functionality we could seamlessly clone devices without having to move
>> the whole setup to device-mapper first.
> 
> Hm...
> Did I understand correctly that the filter itself can be left approximately
> as it is, but the blk-snap module can be replaced with 'dm-intercept',
> which would use the re-route mechanism from the dm?
> I think I may be able to implement it, if you describe your idea in more
> detail.
> 
> 
Actually, once we have an dm-intercept, why do you need the block-layer 
filter at all?
 From you initial description the block-layer filter was implemented 
such that blk-snap could work; but if we have dm-intercept (and with it 
the ability to use device-mapper functionality even for normal block 
devices) there wouldn't be any need for the block-layer filter, no?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

Re: [PATCH 0/2] block layer filter and block device snapshot module

[Sergei Shtepa]

The 10/22/2020 08:58, Hannes Reinecke wrote:
> On 10/21/20 4:10 PM, Sergei Shtepa wrote:
> > The 10/21/2020 16:31, Hannes Reinecke wrote:
> >> I do understand where you are coming from, but then we already have a
> >> dm-snap which does exactly what you want to achieve.
> >> Of course, that would require a reconfiguration of the storage stack on
> >> the machine, which is not always possible (or desired).
> > 
> > Yes, reconfiguring the storage stack on a machine is almost impossible.
> > 
> >>
> >> What I _could_ imagine would be a 'dm-intercept' thingie, which
> >> redirects the current submit_bio() function for any block device, and
> >> re-routes that to a linear device-mapper device pointing back to the
> >> original block device.
> >>
> >> That way you could attach it to basically any block device, _and_ can
> >> use the existing device-mapper functionality to do fancy stuff once the
> >> submit_io() callback has been re-routed.
> >>
> >> And it also would help in other scenarios, too; with such a
> >> functionality we could seamlessly clone devices without having to move
> >> the whole setup to device-mapper first.
> > 
> > Hm...
> > Did I understand correctly that the filter itself can be left approximately
> > as it is, but the blk-snap module can be replaced with 'dm-intercept',
> > which would use the re-route mechanism from the dm?
> > I think I may be able to implement it, if you describe your idea in more
> > detail.
> > 
> > 
> Actually, once we have an dm-intercept, why do you need the block-layer 
> filter at all?
>  From you initial description the block-layer filter was implemented 
> such that blk-snap could work; but if we have dm-intercept (and with it 
> the ability to use device-mapper functionality even for normal block 
> devices) there wouldn't be any need for the block-layer filter, no?

Maybe, but the problem is that I can't imagine how to implement
dm-intercept yet. 
How to use dm to implement interception without changing the stack
of block devices. We'll have to make a hook somewhere, isn`t it?

> 
> Cheers,
> 
> Hannes
> -- 
> Dr. Hannes Reinecke                Kernel Storage Architect
> hare@suse.de                              +49 911 74053 688
> SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
> HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

-- 
Sergei Shtepa
Veeam Software developer.

Re: [PATCH 0/2] block layer filter and block device snapshot module

[Damien Le Moal]

On 2020/10/22 18:43, Sergei Shtepa wrote:
> The 10/22/2020 08:58, Hannes Reinecke wrote:
>> On 10/21/20 4:10 PM, Sergei Shtepa wrote:
>>> The 10/21/2020 16:31, Hannes Reinecke wrote:
>>>> I do understand where you are coming from, but then we already have a
>>>> dm-snap which does exactly what you want to achieve.
>>>> Of course, that would require a reconfiguration of the storage stack on
>>>> the machine, which is not always possible (or desired).
>>>
>>> Yes, reconfiguring the storage stack on a machine is almost impossible.
>>>
>>>>
>>>> What I _could_ imagine would be a 'dm-intercept' thingie, which
>>>> redirects the current submit_bio() function for any block device, and
>>>> re-routes that to a linear device-mapper device pointing back to the
>>>> original block device.
>>>>
>>>> That way you could attach it to basically any block device, _and_ can
>>>> use the existing device-mapper functionality to do fancy stuff once the
>>>> submit_io() callback has been re-routed.
>>>>
>>>> And it also would help in other scenarios, too; with such a
>>>> functionality we could seamlessly clone devices without having to move
>>>> the whole setup to device-mapper first.
>>>
>>> Hm...
>>> Did I understand correctly that the filter itself can be left approximately
>>> as it is, but the blk-snap module can be replaced with 'dm-intercept',
>>> which would use the re-route mechanism from the dm?
>>> I think I may be able to implement it, if you describe your idea in more
>>> detail.
>>>
>>>
>> Actually, once we have an dm-intercept, why do you need the block-layer 
>> filter at all?
>>  From you initial description the block-layer filter was implemented 
>> such that blk-snap could work; but if we have dm-intercept (and with it 
>> the ability to use device-mapper functionality even for normal block 
>> devices) there wouldn't be any need for the block-layer filter, no?
> 
> Maybe, but the problem is that I can't imagine how to implement
> dm-intercept yet. 
> How to use dm to implement interception without changing the stack
> of block devices. We'll have to make a hook somewhere, isn`t it?

Once your dm-intercept target driver is inserted with "dmsetup" or any user land
tool you implement using libdevicemapper, the "hooks" will naturally be in place
since the dm infrastructure already does that: all submitted BIOs will be passed
to dm-intercept through the "map" operation defined in the target_type
descriptor. It is then that driver job to execute the BIOs as it sees fit.

Look at simple device mappers like dm-linear or dm-flakey for hints of how
things work (driver/md/dm-linear.c). More complex dm drivers like dm-crypt,
dm-writecache or dm-thin can give you hints about more features of device mapper.
Functions such as __map_bio() in drivers/md/dm.c are the core of DM and show
what happens to BIOs depending on the the return value of the map operation.
dm_submit_bio() and __split_and_process_bio() is the entry points for BIO
processing in DM.

> 
>>
>> Cheers,
>>
>> Hannes
>> -- 
>> Dr. Hannes Reinecke                Kernel Storage Architect
>> hare@suse.de                              +49 911 74053 688
>> SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
>> HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer
> 


-- 
Damien Le Moal
Western Digital Research

Re: [PATCH 0/2] block layer filter and block device snapshot module

[Sergei Shtepa]

The 10/22/2020 13:28, Damien Le Moal wrote:
> On 2020/10/22 18:43, Sergei Shtepa wrote:
> > 
> > Maybe, but the problem is that I can't imagine how to implement
> > dm-intercept yet. 
> > How to use dm to implement interception without changing the stack
> > of block devices. We'll have to make a hook somewhere, isn`t it?
> 
> Once your dm-intercept target driver is inserted with "dmsetup" or any user land
> tool you implement using libdevicemapper, the "hooks" will naturally be in place
> since the dm infrastructure already does that: all submitted BIOs will be passed
> to dm-intercept through the "map" operation defined in the target_type
> descriptor. It is then that driver job to execute the BIOs as it sees fit.
> 
> Look at simple device mappers like dm-linear or dm-flakey for hints of how
> things work (driver/md/dm-linear.c). More complex dm drivers like dm-crypt,
> dm-writecache or dm-thin can give you hints about more features of device mapper.
> Functions such as __map_bio() in drivers/md/dm.c are the core of DM and show
> what happens to BIOs depending on the the return value of the map operation.
> dm_submit_bio() and __split_and_process_bio() is the entry points for BIO
> processing in DM.
> 

Is there something I don't understand? Please correct me.

Let me remind that by the condition of the problem, we can't change
the configuration of the block device stack.

Let's imagine this configuration: /root mount point on ext filesystem
on /dev/sda1.
+---------------+
|               |
|  /root        |
|               |
+---------------+
|               |
| EXT FS        |
|               |
+---------------+
|               |
| block layer   |
|               |
| sda queue     |
|               |
+---------------+
|               |
| scsi driver   |
|               |
+---------------+

We need to add change block tracking (CBT) and snapshot functionality for
incremental backup.

With the DM we need to change the block device stack. Add device /dev/sda1
to LVM Volume group, create logical volume, change /etc/fstab and reboot.

The new scheme will look like this:
+---------------+
|               |
|  /root        |
|               |
+---------------+
|               |
| EXT FS        |
|               |
+---------------+
|               |
| LV-root       |
|               |
+------------------+
|                  |
| dm-cbt & dm-snap |
|                  |
+------------------+
|               |
| sda queue     |
|               |
+---------------+
|               |
| scsi driver   |
|               |
+---------------+

But I cannot change block device stack. And so I propose a scheme with
interception.
+---------------+
|               |
|  /root        |
|               |
+---------------+
|               |
| EXT FS        |
|               |
+---------------+   +-----------------+
|  |            |   |                 |
|  | blk-filter |-> | cbt & snapshot  |
|  |            |<- |                 |
|  +------------+   +-----------------+
|               |
| sda blk queue |
|               |
+---------------+
|               |
| scsi driver   |
|               |
+---------------+

Perhaps I can make "cbt & snapshot" inside the DM, but without interception
in any case, it will not work. Isn't that right?

-- 
Sergei Shtepa
Veeam Software developer.

Re: [PATCH 0/2] block layer filter and block device snapshot module

[Darrick J. Wong]

On Thu, Oct 22, 2020 at 04:52:13PM +0300, Sergei Shtepa wrote:
> The 10/22/2020 13:28, Damien Le Moal wrote:
> > On 2020/10/22 18:43, Sergei Shtepa wrote:
> > > 
> > > Maybe, but the problem is that I can't imagine how to implement
> > > dm-intercept yet. 
> > > How to use dm to implement interception without changing the stack
> > > of block devices. We'll have to make a hook somewhere, isn`t it?
> > 
> > Once your dm-intercept target driver is inserted with "dmsetup" or any user land
> > tool you implement using libdevicemapper, the "hooks" will naturally be in place
> > since the dm infrastructure already does that: all submitted BIOs will be passed
> > to dm-intercept through the "map" operation defined in the target_type
> > descriptor. It is then that driver job to execute the BIOs as it sees fit.
> > 
> > Look at simple device mappers like dm-linear or dm-flakey for hints of how
> > things work (driver/md/dm-linear.c). More complex dm drivers like dm-crypt,
> > dm-writecache or dm-thin can give you hints about more features of device mapper.
> > Functions such as __map_bio() in drivers/md/dm.c are the core of DM and show
> > what happens to BIOs depending on the the return value of the map operation.
> > dm_submit_bio() and __split_and_process_bio() is the entry points for BIO
> > processing in DM.
> > 
> 
> Is there something I don't understand? Please correct me.
> 
> Let me remind that by the condition of the problem, we can't change
> the configuration of the block device stack.
> 
> Let's imagine this configuration: /root mount point on ext filesystem
> on /dev/sda1.
> +---------------+
> |               |
> |  /root        |
> |               |
> +---------------+
> |               |
> | EXT FS        |
> |               |
> +---------------+
> |               |
> | block layer   |
> |               |
> | sda queue     |
> |               |
> +---------------+
> |               |
> | scsi driver   |
> |               |
> +---------------+
> 
> We need to add change block tracking (CBT) and snapshot functionality for
> incremental backup.
> 
> With the DM we need to change the block device stack. Add device /dev/sda1
> to LVM Volume group, create logical volume, change /etc/fstab and reboot.
> 
> The new scheme will look like this:
> +---------------+
> |               |
> |  /root        |
> |               |
> +---------------+
> |               |
> | EXT FS        |
> |               |
> +---------------+
> |               |
> | LV-root       |
> |               |
> +------------------+
> |                  |
> | dm-cbt & dm-snap |
> |                  |
> +------------------+
> |               |
> | sda queue     |
> |               |
> +---------------+
> |               |
> | scsi driver   |
> |               |
> +---------------+
> 
> But I cannot change block device stack. And so I propose a scheme with
> interception.
> +---------------+
> |               |
> |  /root        |
> |               |
> +---------------+
> |               |
> | EXT FS        |
> |               |
> +---------------+   +-----------------+
> |  |            |   |                 |
> |  | blk-filter |-> | cbt & snapshot  |
> |  |            |<- |                 |
> |  +------------+   +-----------------+
> |               |
> | sda blk queue |
> |               |
> +---------------+
> |               |
> | scsi driver   |
> |               |
> +---------------+
> 
> Perhaps I can make "cbt & snapshot" inside the DM, but without interception
> in any case, it will not work. Isn't that right?

Stupid question: Why don't you change the block layer to make it
possible to insert device mapper devices after the blockdev has been set
up?

--D

> 
> -- 
> Sergei Shtepa
> Veeam Software developer.

Re: [PATCH 0/2] block layer filter and block device snapshot module

[Mike Snitzer]

On Thu, Oct 22, 2020 at 11:14 AM Darrick J. Wong
<darrick.wong@oracle.com> wrote:
>
> On Thu, Oct 22, 2020 at 04:52:13PM +0300, Sergei Shtepa wrote:
> > The 10/22/2020 13:28, Damien Le Moal wrote:
> > > On 2020/10/22 18:43, Sergei Shtepa wrote:
> > > >
> > > > Maybe, but the problem is that I can't imagine how to implement
> > > > dm-intercept yet.
> > > > How to use dm to implement interception without changing the stack
> > > > of block devices. We'll have to make a hook somewhere, isn`t it?
> > >
> > > Once your dm-intercept target driver is inserted with "dmsetup" or any user land
> > > tool you implement using libdevicemapper, the "hooks" will naturally be in place
> > > since the dm infrastructure already does that: all submitted BIOs will be passed
> > > to dm-intercept through the "map" operation defined in the target_type
> > > descriptor. It is then that driver job to execute the BIOs as it sees fit.
> > >
> > > Look at simple device mappers like dm-linear or dm-flakey for hints of how
> > > things work (driver/md/dm-linear.c). More complex dm drivers like dm-crypt,
> > > dm-writecache or dm-thin can give you hints about more features of device mapper.
> > > Functions such as __map_bio() in drivers/md/dm.c are the core of DM and show
> > > what happens to BIOs depending on the the return value of the map operation.
> > > dm_submit_bio() and __split_and_process_bio() is the entry points for BIO
> > > processing in DM.
> > >
> >
> > Is there something I don't understand? Please correct me.
> >
> > Let me remind that by the condition of the problem, we can't change
> > the configuration of the block device stack.
> >
> > Let's imagine this configuration: /root mount point on ext filesystem
> > on /dev/sda1.
> > +---------------+
> > |               |
> > |  /root        |
> > |               |
> > +---------------+
> > |               |
> > | EXT FS        |
> > |               |
> > +---------------+
> > |               |
> > | block layer   |
> > |               |
> > | sda queue     |
> > |               |
> > +---------------+
> > |               |
> > | scsi driver   |
> > |               |
> > +---------------+
> >
> > We need to add change block tracking (CBT) and snapshot functionality for
> > incremental backup.
> >
> > With the DM we need to change the block device stack. Add device /dev/sda1
> > to LVM Volume group, create logical volume, change /etc/fstab and reboot.
> >
> > The new scheme will look like this:
> > +---------------+
> > |               |
> > |  /root        |
> > |               |
> > +---------------+
> > |               |
> > | EXT FS        |
> > |               |
> > +---------------+
> > |               |
> > | LV-root       |
> > |               |
> > +------------------+
> > |                  |
> > | dm-cbt & dm-snap |
> > |                  |
> > +------------------+
> > |               |
> > | sda queue     |
> > |               |
> > +---------------+
> > |               |
> > | scsi driver   |
> > |               |
> > +---------------+
> >
> > But I cannot change block device stack. And so I propose a scheme with
> > interception.
> > +---------------+
> > |               |
> > |  /root        |
> > |               |
> > +---------------+
> > |               |
> > | EXT FS        |
> > |               |
> > +---------------+   +-----------------+
> > |  |            |   |                 |
> > |  | blk-filter |-> | cbt & snapshot  |
> > |  |            |<- |                 |
> > |  +------------+   +-----------------+
> > |               |
> > | sda blk queue |
> > |               |
> > +---------------+
> > |               |
> > | scsi driver   |
> > |               |
> > +---------------+
> >
> > Perhaps I can make "cbt & snapshot" inside the DM, but without interception
> > in any case, it will not work. Isn't that right?
>
> Stupid question: Why don't you change the block layer to make it
> possible to insert device mapper devices after the blockdev has been set
> up?

Not a stupid question.  Definitely something that us DM developers
have wanted to do for a while.  Devil is in the details but it is the
right way forward.

Otherwise, this intercept is really just a DM-lite remapping layer
without any of DM's well established capabilities.  Encouragingly, all
of the replies have effectively echoed this point.  (amusingly, seems
every mailing list under the sun is on the cc except dm-devel... now
rectified)

Alasdair has some concrete ideas on this line of work; I'm trying to
encourage him to reply ;)

Mike

Re: [PATCH 0/2] block layer filter and block device snapshot module

[hch]

On Thu, Oct 22, 2020 at 01:54:16PM -0400, Mike Snitzer wrote:
> On Thu, Oct 22, 2020 at 11:14 AM Darrick J. Wong
> > Stupid question: Why don't you change the block layer to make it
> > possible to insert device mapper devices after the blockdev has been set
> > up?
> 
> Not a stupid question.  Definitely something that us DM developers
> have wanted to do for a while.  Devil is in the details but it is the
> right way forward.
> 

Yes, I think that is the right thing to do.  And I don't think it should
be all that hard.  All we'd need in the I/O path is something like the
pseudo-patch below, which will allow the interposer driver to resubmit
bios using submit_bio_noacct as long as the driver sets BIO_INTERPOSED.

diff --git a/block/blk-core.c b/block/blk-core.c
index ac00d2fa4eb48d..3f6f1eb565e0a8 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1051,6 +1051,9 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
 		return BLK_QC_T_NONE;
 	}
 
+	if (blk_has_interposer(bio->bi_disk) &&
+	    !(bio->bi_flags & BIO_INTERPOSED))
+		return __submit_bio_interposed(bio);
 	if (!bio->bi_disk->fops->submit_bio)
 		return __submit_bio_noacct_mq(bio);
 	return __submit_bio_noacct(bio);

Re: [PATCH 0/2] block layer filter and block device snapshot module

[Hannes Reinecke]

On 10/23/20 11:13 AM, hch@infradead.org wrote:
> On Thu, Oct 22, 2020 at 01:54:16PM -0400, Mike Snitzer wrote:
>> On Thu, Oct 22, 2020 at 11:14 AM Darrick J. Wong
>>> Stupid question: Why don't you change the block layer to make it
>>> possible to insert device mapper devices after the blockdev has been set
>>> up?
>>
>> Not a stupid question.  Definitely something that us DM developers
>> have wanted to do for a while.  Devil is in the details but it is the
>> right way forward.
>>
> 
> Yes, I think that is the right thing to do.  And I don't think it should
> be all that hard.  All we'd need in the I/O path is something like the
> pseudo-patch below, which will allow the interposer driver to resubmit
> bios using submit_bio_noacct as long as the driver sets BIO_INTERPOSED.
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index ac00d2fa4eb48d..3f6f1eb565e0a8 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1051,6 +1051,9 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
>   		return BLK_QC_T_NONE;
>   	}
>   
> +	if (blk_has_interposer(bio->bi_disk) &&
> +	    !(bio->bi_flags & BIO_INTERPOSED))
> +		return __submit_bio_interposed(bio);
>   	if (!bio->bi_disk->fops->submit_bio)
>   		return __submit_bio_noacct_mq(bio);
>   	return __submit_bio_noacct(bio);
> 
My thoughts went more into the direction of hooking into ->submit_bio, 
seeing that it's a NULL pointer for most (all?) block drivers.

But sure, I'll check how the interposer approach would turn out.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

Re: [PATCH 0/2] block layer filter and block device snapshot module

[Sergei Shtepa]

The 10/23/2020 13:31, Hannes Reinecke wrote:
> On 10/23/20 11:13 AM, hch@infradead.org wrote:
> > On Thu, Oct 22, 2020 at 01:54:16PM -0400, Mike Snitzer wrote:
> >> On Thu, Oct 22, 2020 at 11:14 AM Darrick J. Wong
> >>> Stupid question: Why don't you change the block layer to make it
> >>> possible to insert device mapper devices after the blockdev has been set
> >>> up?
> >>
> >> Not a stupid question.  Definitely something that us DM developers
> >> have wanted to do for a while.  Devil is in the details but it is the
> >> right way forward.
> >>
> > 
> > Yes, I think that is the right thing to do.  And I don't think it should
> > be all that hard.  All we'd need in the I/O path is something like the
> > pseudo-patch below, which will allow the interposer driver to resubmit
> > bios using submit_bio_noacct as long as the driver sets BIO_INTERPOSED.
> > 
> > diff --git a/block/blk-core.c b/block/blk-core.c
> > index ac00d2fa4eb48d..3f6f1eb565e0a8 100644
> > --- a/block/blk-core.c
> > +++ b/block/blk-core.c
> > @@ -1051,6 +1051,9 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
> >   		return BLK_QC_T_NONE;
> >   	}
> >   
> > +	if (blk_has_interposer(bio->bi_disk) &&
> > +	    !(bio->bi_flags & BIO_INTERPOSED))
> > +		return __submit_bio_interposed(bio);
> >   	if (!bio->bi_disk->fops->submit_bio)
> >   		return __submit_bio_noacct_mq(bio);
> >   	return __submit_bio_noacct(bio);
> > 

It`s will be great! Approximately this interception capability is not
enough now.

> My thoughts went more into the direction of hooking into ->submit_bio, 
> seeing that it's a NULL pointer for most (all?) block drivers.
> 
> But sure, I'll check how the interposer approach would turn out.

If anyone will do the patch blk-interposer, please add me to CC.
I will try to offer my module that will use blk-interposer.

-- 
Sergei Shtepa
Veeam Software developer.

Re: [dm-devel] [PATCH 0/2] block layer filter and block device snapshot module

[hch]

On Fri, Oct 23, 2020 at 12:31:05PM +0200, Hannes Reinecke wrote:
> My thoughts went more into the direction of hooking into ->submit_bio,
> seeing that it's a NULL pointer for most (all?) block drivers.
> 
> But sure, I'll check how the interposer approach would turn out.

submit_bio is owned by the underlying device, and for a good reason
stored in a const struct..

Re: [PATCH 0/2] block layer filter and block device snapshot module

[Mike Snitzer]

On Wed, Oct 21, 2020 at 5:04 AM Sergei Shtepa <sergei.shtepa@veeam.com> wrote:
>
> Hello everyone! Requesting for your comments and suggestions.
>
> # blk-filter
>
> Block layer filter allows to intercept BIO requests to a block device.
>
> Interception is performed at the very beginning of the BIO request
> processing, and therefore does not affect the operation of the request
> processing queue. This also makes it possible to intercept requests from
> a specific block device, rather than from the entire disk.
>
> The logic of the submit_bio function has been changed - since the
> function execution results are not processed anywhere (except for swap
> and direct-io) the function won't return a value anymore.

Your desire to switch to a void return comes exactly when I've noticed
we need it.

->submit_bio's blk_qc_t return is the cookie assigned by blk-mq.  Up
to this point we haven't actually used it for bio-based devices but it
seems clear we'll soon need for bio-based IO polling support.

Just today, I've been auditing drivers/md/dm.c with an eye toward
properly handling the blk_qc_t return (or lack thereof) from various
DM methods.

It could easily be that __submit_bio_noacct and __submit_bio_noacct_mq
will be updated to do something meaningful with the returned cookie
(or that DM will) to facilitate proper IO polling.

Mike