[RFC PATCH 00/20] Introduce the famfs shared-memory file system

[RFC PATCH 00/20] Introduce the famfs shared-memory file system

[John Groves]

This patch set introduces famfs[1] - a special-purpose fs-dax file system
for sharable disaggregated or fabric-attached memory (FAM). Famfs is not
CXL-specific in anyway way.

* Famfs creates a simple access method for storing and sharing data in
  sharable memory. The memory is exposed and accessed as memory-mappable
  dax files.
* Famfs supports multiple hosts mounting the same file system from the
  same memory (something existing fs-dax file systems don't do).
* A famfs file system can be created on either a /dev/pmem device in fs-dax
  mode, or a /dev/dax device in devdax mode (the latter depending on
  patches 2-6 of this series).

The famfs kernel file system is part the famfs framework; additional
components in user space[2] handle metadata and direct the famfs kernel
module to instantiate files that map to specific memory. The famfs user
space has documentation and a reasonably thorough test suite.

The famfs kernel module never accesses the shared memory directly (either
data or metadata). Because of this, shared memory managed by the famfs
framework does not create a RAS "blast radius" problem that should be able
to crash or de-stabilize the kernel. Poison or timeouts in famfs memory
can be expected to kill apps via SIGBUS and cause mounts to be disabled
due to memory failure notifications.

Famfs does not attempt to solve concurrency or coherency problems for apps,
although it does solve these problems in regard to its own data structures.
Apps may encounter hard concurrency problems, but there are use cases that
are imminently useful and uncomplicated from a concurrency perspective:
serial sharing is one (only one host at a time has access), and read-only
concurrent sharing is another (all hosts can read-cache without worry).

Contents:

* famfs kernel documentation [patch 1]. Note that evolving famfs user
  documentation is at [2]
* dev_dax_iomap patchset [patches 2-6] - This enables fs-dax to use the
  iomap interface via a character /dev/dax device (e.g. /dev/dax0.0). For
  historical reasons the iomap infrastructure was enabled only for
  /dev/pmem devices (which are dax block devices). As famfs is the first
  fs-dax file system that works on /dev/dax, this patch series fills in
  the bare minimum infrastructure to enable iomap api usage with /dev/dax.
* famfs patchset [patches 7-20] - this introduces the kernel component of
  famfs.

IMPORTANT NOTE: There is a developing consensus that /dev/dax requires
some fundamental re-factoring (e.g. [3]) that is related but outside the
scope of this series.

Some observations about using sharable memory

* It does not make sense to online sharable memory as system-ram.
  System-ram gets zeroed when it is onlined, so sharing is basically
  nonsense.
* It does not make sense to put struct page's in sharable memory, because
  those can't be shared. However, separately providing non-sharable
  capacity to be used for struct page's might be a sensible approach if the
  size of struct page array for sharable memory is too large to put in
  conventional system-ram (albeit with possible RAS implications).
* Sharable memory is pmem-like, in that a host is likely to connect in
  order to gain access to data that is already in the memory. Moreover
  the power domain for shared memory is separate for that of the server.
  Having observed that, famfs is not intended for persistent storage. It is
  intended for sharing data sets in memory during a time frame where the
  memory and the compute nodes are expected to remain operational - such
  as during a clustered data analytics job.

Could we do this with FUSE?

The key performance requirement for famfs is efficient handling of VMA
faults. This requires caching the complete dax extent lists for all active
files so faults can be handled without upcalls, which FUSE does not do.
It would probably be possible to put this capability FUSE, but we think
that keeping famfs separate from FUSE is the simpler approach.

This patch set is available as a branch at [5]

References

[1] https://lpc.events/event/17/contributions/1455/
[2] https://github.com/cxl-micron-reskit/famfs
[3] https://lore.kernel.org/all/166630293549.1017198.3833687373550679565.stgit@dwillia2-xfh.jf.intel.com/
[4] https://www.computeexpresslink.org/download-the-specification
[5] https://github.com/cxl-micron-reskit/famfs-linux

John Groves (20):
  famfs: Documentation
  dev_dax_iomap: Add fs_dax_get() func to prepare dax for fs-dax usage
  dev_dax_iomap: Move dax_pgoff_to_phys from device.c to bus.c since
    both need it now
  dev_dax_iomap: Save the kva from memremap
  dev_dax_iomap: Add dax_operations for use by fs-dax on devdax
  dev_dax_iomap: Add CONFIG_DEV_DAX_IOMAP kernel build parameter
  famfs: Add include/linux/famfs_ioctl.h
  famfs: Add famfs_internal.h
  famfs: Add super_operations
  famfs: famfs_open_device() & dax_holder_operations
  famfs: Add fs_context_operations
  famfs: Add inode_operations and file_system_type
  famfs: Add iomap_ops
  famfs: Add struct file_operations
  famfs: Add ioctl to file_operations
  famfs: Add fault counters
  famfs: Add module stuff
  famfs: Support character dax via the dev_dax_iomap patch
  famfs: Update MAINTAINERS file
  famfs: Add Kconfig and Makefile plumbing

 Documentation/filesystems/famfs.rst | 124 +++++
 MAINTAINERS                         |  11 +
 drivers/dax/Kconfig                 |   6 +
 drivers/dax/bus.c                   | 131 ++++++
 drivers/dax/dax-private.h           |   1 +
 drivers/dax/device.c                |  38 +-
 drivers/dax/super.c                 |  38 ++
 fs/Kconfig                          |   2 +
 fs/Makefile                         |   1 +
 fs/famfs/Kconfig                    |  10 +
 fs/famfs/Makefile                   |   5 +
 fs/famfs/famfs_file.c               | 704 ++++++++++++++++++++++++++++
 fs/famfs/famfs_inode.c              | 586 +++++++++++++++++++++++
 fs/famfs/famfs_internal.h           | 126 +++++
 include/linux/dax.h                 |   5 +
 include/uapi/linux/famfs_ioctl.h    |  56 +++
 16 files changed, 1821 insertions(+), 23 deletions(-)
 create mode 100644 Documentation/filesystems/famfs.rst
 create mode 100644 fs/famfs/Kconfig
 create mode 100644 fs/famfs/Makefile
 create mode 100644 fs/famfs/famfs_file.c
 create mode 100644 fs/famfs/famfs_inode.c
 create mode 100644 fs/famfs/famfs_internal.h
 create mode 100644 include/uapi/linux/famfs_ioctl.h


base-commit: 841c35169323cd833294798e58b9bf63fa4fa1de
-- 
2.43.0

[RFC PATCH 01/20] famfs: Documentation

[John Groves]

Introduce Documentation/filesystems/famfs.rst into the Documentation
tree

Signed-off-by: John Groves <john@groves.net>
---
 Documentation/filesystems/famfs.rst | 124 ++++++++++++++++++++++++++++
 1 file changed, 124 insertions(+)
 create mode 100644 Documentation/filesystems/famfs.rst

diff --git a/Documentation/filesystems/famfs.rst b/Documentation/filesystems/famfs.rst
new file mode 100644
index 000000000000..c2cc50c10d03
--- /dev/null
+++ b/Documentation/filesystems/famfs.rst
@@ -0,0 +1,124 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. _famfs_index:
+
+==================================================================
+famfs: The kernel component of the famfs shared memory file system
+==================================================================
+
+- Copyright (C) 2024 Micron Technology, Inc.
+
+Introduction
+============
+Compute Express Link (CXL) provides a mechanism for disaggregated or
+fabric-attached memory (FAM). This creates opportunities for data sharing;
+clustered apps that would otherwise have to shard or replicate data can
+share one copy in disaggregated memory.
+
+Famfs, which is not CXL-specific in any way, provides a mechanism for
+multiple hosts to use data in shared memory, by giving it a file system
+interface. With famfs, any app that understands files (which is all of
+them, right?) can access data sets in shared memory. Although famfs
+supports read and write calls, the real point is to support mmap, which
+provides direct (dax) access to the memory - either writable or read-only.
+
+Shared memory can pose complex coherency and synchronization issues, but
+there are also simple cases. Two simple and eminently useful patterns that
+occur frequently in data analytics and AI are:
+
+* Serial Sharing - Only one host or process at a time has access to a file
+* Read-only Sharing - Multiple hosts or processes share read-only access
+  to a file
+
+The famfs kernel file system is part of the famfs framework; User space
+components [1] handle metadata allocation and distribution, and direct the
+famfs kernel module to instantiate files that map to specific memory.
+
+The famfs framework manages coherency of its own metadata and structures,
+but does not attempt to manage coherency for applications.
+
+Famfs also provides data isolation between files. That is, even though
+the host has access to an entire memory "device" (as a dax device), apps
+cannot write to memory for which the file is read-only, and mapping one
+file provides isolation from the memory of all other files. This is pretty
+basic, but some experimental shared memory usage patterns provide no such
+isolation.
+
+Principles of Operation
+=======================
+
+Without its user space components, the famfs kernel module is just a
+semi-functional clone of ramfs with latent fs-dax support. The user space
+components maintain superblocks and metadata logs, and use the famfs kernel
+component to provide a file system view of shared memory across multiple
+hosts.
+
+Each host has an independent instance of the famfs kernel module. After
+mount, files are not visible until the user space component instantiates
+them (normally by playing the famfs metadata log).
+
+Once instantiated, files on each host can point to the same shared memory,
+but in-memory metadata (inodes, etc.) is ephemeral on each host that has a
+famfs instance mounted. Like ramfs, the famfs in-kernel file system has no
+backing store for metadata modifications. If metadata is ever persisted,
+that must be done by the user space components. However, mutations to file
+data are saved to the shared memory - subject to write permission and
+processor cache behavior.
+
+
+Famfs is Not a Conventional File System
+---------------------------------------
+
+Famfs files can be accessed by conventional means, but there are
+limitations. The kernel component of famfs is not involved in the
+allocation of backing memory for files at all; the famfs user space
+creates files and passes the allocation extent lists into the kernel via
+the per-file FAMFSIOC_MAP_CREATE ioctl. A file that lacks this metadata is
+treated as invalid by the famfs kernel module. As a practical matter files
+must be created via the famfs library or cli, but they can be consumed as
+if they were conventional files.
+
+Famfs differs in some important ways from conventional file systems:
+
+* Files must be pre-allocated by the famfs framework; Allocation is never
+  performed on write.
+* Any operation that changes a file's size is considered to put the file
+  in an invalid state, disabling access to the data. It may be possible to
+  revisit this in the future.
+* (Typically the famfs user space can restore files to a valid state by
+  replaying the famfs metadata log.)
+
+Famfs exists to apply the existing file system abstractions on top of
+shared memory so applications and workflows can more easily consume it.
+
+Key Requirements
+================
+
+The primary requirements for famfs are:
+
+1. Must support a file system abstraction backed by sharable dax memory
+2. Files must efficiently handle VMA faults
+3. Must support metadata distribution in a sharable way
+4. Must handle clients with a stale copy of metadata
+
+The famfs kernel component takes care of 1-2 above.
+
+Requirements 3 and 4 are handled by the user space components, and are
+largely orthogonal to the functionality of the famfs kernel module.
+
+Requirements 3 and 4 cannot be met by conventional fs-dax file systems
+(e.g. xfs and ext4) because they use write-back metadata; it is not valid
+to mount such a file system on two hosts from the same in-memory image.
+
+
+Famfs Usage
+===========
+
+Famfs usage is documented at [1].
+
+
+References
+==========
+
+- [1] Famfs user space repository and documentation
+      https://github.com/cxl-micron-reskit/famfs
-- 
2.43.0

[RFC PATCH 02/20] dev_dax_iomap: Add fs_dax_get() func to prepare dax for fs-dax usage

[John Groves]

This function should be called by fs-dax file systems after opening the
devdax device. This adds holder_operations.

This function serves the same role as fs_dax_get_by_bdev(), which dax
file systems call after opening the pmem block device.

Signed-off-by: John Groves <john@groves.net>
---
 drivers/dax/super.c | 38 ++++++++++++++++++++++++++++++++++++++
 include/linux/dax.h |  5 +++++
 2 files changed, 43 insertions(+)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index f4b635526345..fc96362de237 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -121,6 +121,44 @@ void fs_put_dax(struct dax_device *dax_dev, void *holder)
 EXPORT_SYMBOL_GPL(fs_put_dax);
 #endif /* CONFIG_BLOCK && CONFIG_FS_DAX */
 
+#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
+
+/**
+ * fs_dax_get()
+ *
+ * fs-dax file systems call this function to prepare to use a devdax device for fsdax.
+ * This is like fs_dax_get_by_bdev(), but the caller already has struct dev_dax (and there
+ * is no bdev). The holder makes this exclusive.
+ *
+ * @dax_dev: dev to be prepared for fs-dax usage
+ * @holder: filesystem or mapped device inside the dax_device
+ * @hops: operations for the inner holder
+ *
+ * Returns: 0 on success, -1 on failure
+ */
+int fs_dax_get(
+	struct dax_device *dax_dev,
+	void *holder,
+	const struct dax_holder_operations *hops)
+{
+	/* dax_dev->ops should have been populated by devm_create_dev_dax() */
+	if (WARN_ON(!dax_dev->ops))
+		return -1;
+
+	if (!dax_dev || !dax_alive(dax_dev) || !igrab(&dax_dev->inode))
+		return -1;
+
+	if (cmpxchg(&dax_dev->holder_data, NULL, holder)) {
+		pr_warn("%s: holder_data already set\n", __func__);
+		return -1;
+	}
+	dax_dev->holder_ops = hops;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(fs_dax_get);
+#endif /* DEV_DAX_IOMAP */
+
 enum dax_device_flags {
 	/* !alive + rcu grace period == no new operations / mappings */
 	DAXDEV_ALIVE,
diff --git a/include/linux/dax.h b/include/linux/dax.h
index b463502b16e1..e973289bfde3 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -57,7 +57,12 @@ struct dax_holder_operations {
 
 #if IS_ENABLED(CONFIG_DAX)
 struct dax_device *alloc_dax(void *private, const struct dax_operations *ops);
+
+#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
+int fs_dax_get(struct dax_device *dax_dev, void *holder, const struct dax_holder_operations *hops);
+#endif
 void *dax_holder(struct dax_device *dax_dev);
+struct dax_device *inode_dax(struct inode *inode);
 void put_dax(struct dax_device *dax_dev);
 void kill_dax(struct dax_device *dax_dev);
 void dax_write_cache(struct dax_device *dax_dev, bool wc);
-- 
2.43.0

[RFC PATCH 03/20] dev_dax_iomap: Move dax_pgoff_to_phys from device.c to bus.c since both need it now

[John Groves]

bus.c can't call functions in device.c - that creates a circular linkage
dependency.

Signed-off-by: John Groves <john@groves.net>
---
 drivers/dax/bus.c    | 24 ++++++++++++++++++++++++
 drivers/dax/device.c | 23 -----------------------
 2 files changed, 24 insertions(+), 23 deletions(-)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 1ff1ab5fa105..664e8c1b9930 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -1325,6 +1325,30 @@ static const struct device_type dev_dax_type = {
 	.groups = dax_attribute_groups,
 };
 
+/* see "strong" declaration in tools/testing/nvdimm/dax-dev.c  */
+__weak phys_addr_t dax_pgoff_to_phys(struct dev_dax *dev_dax, pgoff_t pgoff,
+			      unsigned long size)
+{
+	int i;
+
+	for (i = 0; i < dev_dax->nr_range; i++) {
+		struct dev_dax_range *dax_range = &dev_dax->ranges[i];
+		struct range *range = &dax_range->range;
+		unsigned long long pgoff_end;
+		phys_addr_t phys;
+
+		pgoff_end = dax_range->pgoff + PHYS_PFN(range_len(range)) - 1;
+		if (pgoff < dax_range->pgoff || pgoff > pgoff_end)
+			continue;
+		phys = PFN_PHYS(pgoff - dax_range->pgoff) + range->start;
+		if (phys + size - 1 <= range->end)
+			return phys;
+		break;
+	}
+	return -1;
+}
+EXPORT_SYMBOL_GPL(dax_pgoff_to_phys);
+
 struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
 {
 	struct dax_region *dax_region = data->dax_region;
diff --git a/drivers/dax/device.c b/drivers/dax/device.c
index 93ebedc5ec8c..40ba660013cf 100644
--- a/drivers/dax/device.c
+++ b/drivers/dax/device.c
@@ -50,29 +50,6 @@ static int check_vma(struct dev_dax *dev_dax, struct vm_area_struct *vma,
 	return 0;
 }
 
-/* see "strong" declaration in tools/testing/nvdimm/dax-dev.c */
-__weak phys_addr_t dax_pgoff_to_phys(struct dev_dax *dev_dax, pgoff_t pgoff,
-		unsigned long size)
-{
-	int i;
-
-	for (i = 0; i < dev_dax->nr_range; i++) {
-		struct dev_dax_range *dax_range = &dev_dax->ranges[i];
-		struct range *range = &dax_range->range;
-		unsigned long long pgoff_end;
-		phys_addr_t phys;
-
-		pgoff_end = dax_range->pgoff + PHYS_PFN(range_len(range)) - 1;
-		if (pgoff < dax_range->pgoff || pgoff > pgoff_end)
-			continue;
-		phys = PFN_PHYS(pgoff - dax_range->pgoff) + range->start;
-		if (phys + size - 1 <= range->end)
-			return phys;
-		break;
-	}
-	return -1;
-}
-
 static void dax_set_mapping(struct vm_fault *vmf, pfn_t pfn,
 			      unsigned long fault_size)
 {
-- 
2.43.0

[RFC PATCH 04/20] dev_dax_iomap: Save the kva from memremap

[John Groves]

Save the kva from memremap because we need it for iomap rw support

Prior to famfs, there were no iomap users of /dev/dax - so the virtual
address from memremap was not needed.

Also: in some cases dev_dax_probe() is called with the first
dev_dax->range offset past pgmap[0].range. In those cases we need to
add the difference to virt_addr in order to have the physaddr's in
dev_dax->ranges match dev_dax->virt_addr.

Dragons...

Signed-off-by: John Groves <john@groves.net>
---
 drivers/dax/dax-private.h |  1 +
 drivers/dax/device.c      | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
index 446617b73aea..894eb1c66b4a 100644
--- a/drivers/dax/dax-private.h
+++ b/drivers/dax/dax-private.h
@@ -63,6 +63,7 @@ struct dax_mapping {
 struct dev_dax {
 	struct dax_region *region;
 	struct dax_device *dax_dev;
+	u64 virt_addr;
 	unsigned int align;
 	int target_node;
 	bool dyn_id;
diff --git a/drivers/dax/device.c b/drivers/dax/device.c
index 40ba660013cf..6cd79d00fe1b 100644
--- a/drivers/dax/device.c
+++ b/drivers/dax/device.c
@@ -372,6 +372,7 @@ static int dev_dax_probe(struct dev_dax *dev_dax)
 	struct dax_device *dax_dev = dev_dax->dax_dev;
 	struct device *dev = &dev_dax->dev;
 	struct dev_pagemap *pgmap;
+	u64 data_offset = 0;
 	struct inode *inode;
 	struct cdev *cdev;
 	void *addr;
@@ -426,6 +427,20 @@ static int dev_dax_probe(struct dev_dax *dev_dax)
 	if (IS_ERR(addr))
 		return PTR_ERR(addr);
 
+	/* Detect whether the data is at a non-zero offset into the memory */
+	if (pgmap->range.start != dev_dax->ranges[0].range.start) {
+		u64 phys = (u64)dev_dax->ranges[0].range.start;
+		u64 pgmap_phys = (u64)dev_dax->pgmap[0].range.start;
+		u64 vmemmap_shift = (u64)dev_dax->pgmap[0].vmemmap_shift;
+
+		if (!WARN_ON(pgmap_phys > phys))
+			data_offset = phys - pgmap_phys;
+
+		pr_notice("%s: offset detected phys=%llx pgmap_phys=%llx offset=%llx shift=%llx\n",
+		       __func__, phys, pgmap_phys, data_offset, vmemmap_shift);
+	}
+	dev_dax->virt_addr = (u64)addr + data_offset;
+
 	inode = dax_inode(dax_dev);
 	cdev = inode->i_cdev;
 	cdev_init(cdev, &dax_fops);
-- 
2.43.0

[RFC PATCH 05/20] dev_dax_iomap: Add dax_operations for use by fs-dax on devdax

[John Groves]

Notes about this commit:

* These methods are based somewhat loosely on pmem_dax_ops from
  drivers/nvdimm/pmem.c

* dev_dax_direct_access() is returns the hpa, pfn and kva. The kva was
  newly stored as dev_dax->virt_addr by dev_dax_probe().

* The hpa/pfn are used for mmap (dax_iomap_fault()), and the kva is used
  for read/write (dax_iomap_rw())

* dev_dax_recovery_write() and dev_dax_zero_page_range() have not been
  tested yet. I'm looking for suggestions as to how to test those.

Signed-off-by: John Groves <john@groves.net>
---
 drivers/dax/bus.c | 107 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 664e8c1b9930..06fcda810674 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -10,6 +10,12 @@
 #include "dax-private.h"
 #include "bus.h"
 
+#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
+#include <linux/backing-dev.h>
+#include <linux/pfn_t.h>
+#include <linux/range.h>
+#endif
+
 static DEFINE_MUTEX(dax_bus_lock);
 
 #define DAX_NAME_LEN 30
@@ -1349,6 +1355,101 @@ __weak phys_addr_t dax_pgoff_to_phys(struct dev_dax *dev_dax, pgoff_t pgoff,
 }
 EXPORT_SYMBOL_GPL(dax_pgoff_to_phys);
 
+#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
+
+static void write_dax(void *pmem_addr, struct page *page,
+		unsigned int off, unsigned int len)
+{
+	unsigned int chunk;
+	void *mem;
+
+	while (len) {
+		mem = kmap_local_page(page);
+		chunk = min_t(unsigned int, len, PAGE_SIZE - off);
+		memcpy_flushcache(pmem_addr, mem + off, chunk);
+		kunmap_local(mem);
+		len -= chunk;
+		off = 0;
+		page++;
+		pmem_addr += chunk;
+	}
+}
+
+static long __dev_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff,
+			     long nr_pages, enum dax_access_mode mode, void **kaddr,
+			     pfn_t *pfn)
+{
+	struct dev_dax *dev_dax = dax_get_private(dax_dev);
+	size_t dax_size = dev_dax_size(dev_dax);
+	size_t size = nr_pages << PAGE_SHIFT;
+	size_t offset = pgoff << PAGE_SHIFT;
+	phys_addr_t phys;
+	u64 virt_addr = dev_dax->virt_addr + offset;
+	pfn_t local_pfn;
+	u64 flags = PFN_DEV|PFN_MAP;
+
+	WARN_ON(!dev_dax->virt_addr); /* virt_addr must be saved for direct_access */
+
+	phys = dax_pgoff_to_phys(dev_dax, pgoff, nr_pages << PAGE_SHIFT);
+
+	if (kaddr)
+		*kaddr = (void *)virt_addr;
+
+	local_pfn = phys_to_pfn_t(phys, flags); /* are flags correct? */
+	if (pfn)
+		*pfn = local_pfn;
+
+	/* This the valid size at the specified address */
+	return PHYS_PFN(min_t(size_t, size, dax_size - offset));
+}
+
+static int dev_dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff,
+				    size_t nr_pages)
+{
+	long resid = nr_pages << PAGE_SHIFT;
+	long offset = pgoff << PAGE_SHIFT;
+
+	/* Break into one write per dax region */
+	while (resid > 0) {
+		void *kaddr;
+		pgoff_t poff = offset >> PAGE_SHIFT;
+		long len = __dev_dax_direct_access(dax_dev, poff,
+						   nr_pages, DAX_ACCESS, &kaddr, NULL);
+		len = min_t(long, len, PAGE_SIZE);
+		write_dax(kaddr, ZERO_PAGE(0), offset, len);
+
+		offset += len;
+		resid  -= len;
+	}
+	return 0;
+}
+
+static long dev_dax_direct_access(struct dax_device *dax_dev,
+		pgoff_t pgoff, long nr_pages, enum dax_access_mode mode,
+		void **kaddr, pfn_t *pfn)
+{
+	return __dev_dax_direct_access(dax_dev, pgoff, nr_pages, mode, kaddr, pfn);
+}
+
+static size_t dev_dax_recovery_write(struct dax_device *dax_dev, pgoff_t pgoff,
+		void *addr, size_t bytes, struct iov_iter *i)
+{
+	size_t len, off;
+
+	off = offset_in_page(addr);
+	len = PFN_PHYS(PFN_UP(off + bytes));
+
+	return _copy_from_iter_flushcache(addr, bytes, i);
+}
+
+static const struct dax_operations dev_dax_ops = {
+	.direct_access = dev_dax_direct_access,
+	.zero_page_range = dev_dax_zero_page_range,
+	.recovery_write = dev_dax_recovery_write,
+};
+
+#endif /* IS_ENABLED(CONFIG_DEV_DAX_IOMAP) */
+
 struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
 {
 	struct dax_region *dax_region = data->dax_region;
@@ -1404,11 +1505,17 @@ struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
 		}
 	}
 
+#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
+	/* holder_ops currently populated separately in a slightly hacky way */
+	dax_dev = alloc_dax(dev_dax, &dev_dax_ops);
+#else
 	/*
 	 * No dax_operations since there is no access to this device outside of
 	 * mmap of the resulting character device.
 	 */
 	dax_dev = alloc_dax(dev_dax, NULL);
+#endif
+
 	if (IS_ERR(dax_dev)) {
 		rc = PTR_ERR(dax_dev);
 		goto err_alloc_dax;
-- 
2.43.0

[RFC PATCH 06/20] dev_dax_iomap: Add CONFIG_DEV_DAX_IOMAP kernel build parameter

[John Groves]

Add the CONFIG_DEV_DAX_IOMAP kernel config parameter to control building
of the iomap functionality to support fsdax on devdax.

Signed-off-by: John Groves <john@groves.net>
---
 drivers/dax/Kconfig | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
index a88744244149..b1ebcc77120b 100644
--- a/drivers/dax/Kconfig
+++ b/drivers/dax/Kconfig
@@ -78,4 +78,10 @@ config DEV_DAX_KMEM
 
 	  Say N if unsure.
 
+config DEV_DAX_IOMAP
+       depends on DEV_DAX && DAX
+       def_bool y
+       help
+         Support iomap mapping of devdax devices (for FS-DAX file
+         systems that reside on character /dev/dax devices)
 endif
-- 
2.43.0

[RFC PATCH 07/20] famfs: Add include/linux/famfs_ioctl.h

[John Groves]

Add uapi include file for famfs. The famfs user space uses ioctl on
individual files to pass in mapping information and file size. This
would be hard to do via sysfs or other means, since it's
file-specific.

Signed-off-by: John Groves <john@groves.net>
---
 include/uapi/linux/famfs_ioctl.h | 56 ++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 include/uapi/linux/famfs_ioctl.h

diff --git a/include/uapi/linux/famfs_ioctl.h b/include/uapi/linux/famfs_ioctl.h
new file mode 100644
index 000000000000..6b3e6452d02f
--- /dev/null
+++ b/include/uapi/linux/famfs_ioctl.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * famfs - dax file system for shared fabric-attached memory
+ *
+ * Copyright 2023-2024 Micron Technology, Inc.
+ *
+ * This file system, originally based on ramfs the dax support from xfs,
+ * is intended to allow multiple host systems to mount a common file system
+ * view of dax files that map to shared memory.
+ */
+#ifndef FAMFS_IOCTL_H
+#define FAMFS_IOCTL_H
+
+#include <linux/ioctl.h>
+#include <linux/uuid.h>
+
+#define FAMFS_MAX_EXTENTS 2
+
+enum extent_type {
+	SIMPLE_DAX_EXTENT = 13,
+	INVALID_EXTENT_TYPE,
+};
+
+struct famfs_extent {
+	__u64              offset;
+	__u64              len;
+};
+
+enum famfs_file_type {
+	FAMFS_REG,
+	FAMFS_SUPERBLOCK,
+	FAMFS_LOG,
+};
+
+/**
+ * struct famfs_ioc_map
+ *
+ * This is the metadata that indicates where the memory is for a famfs file
+ */
+struct famfs_ioc_map {
+	enum extent_type          extent_type;
+	enum famfs_file_type      file_type;
+	__u64                     file_size;
+	__u64                     ext_list_count;
+	struct famfs_extent       ext_list[FAMFS_MAX_EXTENTS];
+};
+
+#define FAMFSIOC_MAGIC 'u'
+
+/* famfs file ioctl opcodes */
+#define FAMFSIOC_MAP_CREATE    _IOW(FAMFSIOC_MAGIC, 1, struct famfs_ioc_map)
+#define FAMFSIOC_MAP_GET       _IOR(FAMFSIOC_MAGIC, 2, struct famfs_ioc_map)
+#define FAMFSIOC_MAP_GETEXT    _IOR(FAMFSIOC_MAGIC, 3, struct famfs_extent)
+#define FAMFSIOC_NOP           _IO(FAMFSIOC_MAGIC,  4)
+
+#endif /* FAMFS_IOCTL_H */
-- 
2.43.0

[RFC PATCH 08/20] famfs: Add famfs_internal.h

[John Groves]

Add the famfs_internal.h include file. This contains internal data
structures such as the per-file metadata structure (famfs_file_meta)
and extent formats.

Signed-off-by: John Groves <john@groves.net>
---
 fs/famfs/famfs_internal.h | 53 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 fs/famfs/famfs_internal.h

diff --git a/fs/famfs/famfs_internal.h b/fs/famfs/famfs_internal.h
new file mode 100644
index 000000000000..af3990d43305
--- /dev/null
+++ b/fs/famfs/famfs_internal.h
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * famfs - dax file system for shared fabric-attached memory
+ *
+ * Copyright 2023-2024 Micron Technology, Inc.
+ *
+ * This file system, originally based on ramfs the dax support from xfs,
+ * is intended to allow multiple host systems to mount a common file system
+ * view of dax files that map to shared memory.
+ */
+#ifndef FAMFS_INTERNAL_H
+#define FAMFS_INTERNAL_H
+
+#include <linux/atomic.h>
+#include <linux/famfs_ioctl.h>
+
+#define FAMFS_MAGIC 0x87b282ff
+
+#define FAMFS_BLKDEV_MODE (FMODE_READ|FMODE_WRITE)
+
+extern const struct file_operations      famfs_file_operations;
+
+/*
+ * Each famfs dax file has this hanging from its inode->i_private.
+ */
+struct famfs_file_meta {
+	int                   error;
+	enum famfs_file_type  file_type;
+	size_t                file_size;
+	enum extent_type      tfs_extent_type;
+	size_t                tfs_extent_ct;
+	struct famfs_extent   tfs_extents[];  /* flexible array */
+};
+
+struct famfs_mount_opts {
+	umode_t mode;
+};
+
+extern const struct iomap_ops             famfs_iomap_ops;
+extern const struct vm_operations_struct  famfs_file_vm_ops;
+
+#define ROOTDEV_STRLEN 80
+
+struct famfs_fs_info {
+	struct famfs_mount_opts  mount_opts;
+	struct file             *dax_filp;
+	struct dax_device       *dax_devp;
+	struct bdev_handle      *bdev_handle;
+	struct list_head         fsi_list;
+	char                    *rootdev;
+};
+
+#endif /* FAMFS_INTERNAL_H */
-- 
2.43.0

[RFC PATCH 09/20] famfs: Add super_operations

[John Groves]

Introduce the famfs superblock operations

Signed-off-by: John Groves <john@groves.net>
---
 fs/famfs/famfs_inode.c | 72 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 fs/famfs/famfs_inode.c

diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
new file mode 100644
index 000000000000..3329aff000d1
--- /dev/null
+++ b/fs/famfs/famfs_inode.c
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * famfs - dax file system for shared fabric-attached memory
+ *
+ * Copyright 2023-2024 Micron Technology, inc
+ *
+ * This file system, originally based on ramfs the dax support from xfs,
+ * is intended to allow multiple host systems to mount a common file system
+ * view of dax files that map to shared memory.
+ */
+
+#include <linux/fs.h>
+#include <linux/pagemap.h>
+#include <linux/highmem.h>
+#include <linux/time.h>
+#include <linux/init.h>
+#include <linux/string.h>
+#include <linux/backing-dev.h>
+#include <linux/sched.h>
+#include <linux/parser.h>
+#include <linux/magic.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/fs_context.h>
+#include <linux/fs_parser.h>
+#include <linux/seq_file.h>
+#include <linux/dax.h>
+#include <linux/hugetlb.h>
+#include <linux/uio.h>
+#include <linux/iomap.h>
+#include <linux/path.h>
+#include <linux/namei.h>
+#include <linux/pfn_t.h>
+#include <linux/blkdev.h>
+
+#include "famfs_internal.h"
+
+#define FAMFS_DEFAULT_MODE	0755
+
+static const struct super_operations famfs_ops;
+static const struct inode_operations famfs_file_inode_operations;
+static const struct inode_operations famfs_dir_inode_operations;
+
+/**********************************************************************************
+ * famfs super_operations
+ *
+ * TODO: implement a famfs_statfs() that shows size, free and available space, etc.
+ */
+
+/**
+ * famfs_show_options() - Display the mount options in /proc/mounts.
+ */
+static int famfs_show_options(
+	struct seq_file *m,
+	struct dentry   *root)
+{
+	struct famfs_fs_info *fsi = root->d_sb->s_fs_info;
+
+	if (fsi->mount_opts.mode != FAMFS_DEFAULT_MODE)
+		seq_printf(m, ",mode=%o", fsi->mount_opts.mode);
+
+	return 0;
+}
+
+static const struct super_operations famfs_ops = {
+	.statfs		= simple_statfs,
+	.drop_inode	= generic_delete_inode,
+	.show_options	= famfs_show_options,
+};
+
+
+MODULE_LICENSE("GPL");
-- 
2.43.0

[RFC PATCH 10/20] famfs: famfs_open_device() & dax_holder_operations

[John Groves]

Famfs works on both /dev/pmem and /dev/dax devices. This commit introduces
the function that opens a block (pmem) device and the struct
dax_holder_operations that are needed for that ABI.

In this commit, support for opening character /dev/dax is stubbed. A
later commit introduces this capability.

Signed-off-by: John Groves <john@groves.net>
---
 fs/famfs/famfs_inode.c | 83 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)

diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
index 3329aff000d1..82c861998093 100644
--- a/fs/famfs/famfs_inode.c
+++ b/fs/famfs/famfs_inode.c
@@ -68,5 +68,88 @@ static const struct super_operations famfs_ops = {
 	.show_options	= famfs_show_options,
 };
 
+/***************************************************************************************
+ * dax_holder_operations for block dax
+ */
+
+static int
+famfs_blk_dax_notify_failure(
+	struct dax_device	*dax_devp,
+	u64			offset,
+	u64			len,
+	int			mf_flags)
+{
+
+	pr_err("%s: dax_devp %llx offset %llx len %lld mf_flags %x\n",
+	       __func__, (u64)dax_devp, (u64)offset, (u64)len, mf_flags);
+	return -EOPNOTSUPP;
+}
+
+const struct dax_holder_operations famfs_blk_dax_holder_ops = {
+	.notify_failure		= famfs_blk_dax_notify_failure,
+};
+
+static int
+famfs_open_char_device(
+	struct super_block *sb,
+	struct fs_context  *fc)
+{
+	pr_err("%s: Root device is %s, but your kernel does not support famfs on /dev/dax\n",
+	       __func__, fc->source);
+	return -ENODEV;
+}
+
+/**
+ * famfs_open_device()
+ *
+ * Open the memory device. If it looks like /dev/dax, call famfs_open_char_device().
+ * Otherwise try to open it as a block/pmem device.
+ */
+static int
+famfs_open_device(
+	struct super_block *sb,
+	struct fs_context  *fc)
+{
+	struct famfs_fs_info *fsi = sb->s_fs_info;
+	struct dax_device    *dax_devp;
+	u64 start_off = 0;
+	struct bdev_handle   *handlep;
+
+	if (fsi->dax_devp) {
+		pr_err("%s: already mounted\n", __func__);
+		return -EALREADY;
+	}
+
+	if (strstr(fc->source, "/dev/dax")) /* There is probably a better way to check this */
+		return famfs_open_char_device(sb, fc);
+
+	if (!strstr(fc->source, "/dev/pmem")) { /* There is probably a better way to check this */
+		pr_err("%s: primary backing dev (%s) is not pmem\n",
+		       __func__, fc->source);
+		return -EINVAL;
+	}
+
+	handlep = bdev_open_by_path(fc->source, FAMFS_BLKDEV_MODE, fsi, &fs_holder_ops);
+	if (IS_ERR(handlep->bdev)) {
+		pr_err("%s: failed blkdev_get_by_path(%s)\n", __func__, fc->source);
+		return PTR_ERR(handlep->bdev);
+	}
+
+	dax_devp = fs_dax_get_by_bdev(handlep->bdev, &start_off,
+				      fsi  /* holder */,
+				      &famfs_blk_dax_holder_ops);
+	if (IS_ERR(dax_devp)) {
+		pr_err("%s: unable to get daxdev from handlep->bdev\n", __func__);
+		bdev_release(handlep);
+		return -ENODEV;
+	}
+	fsi->bdev_handle = handlep;
+	fsi->dax_devp    = dax_devp;
+
+	pr_notice("%s: root device is block dax (%s)\n", __func__, fc->source);
+	return 0;
+}
+
+
 
 MODULE_LICENSE("GPL");
-- 
2.43.0

[RFC PATCH 11/20] famfs: Add fs_context_operations

[John Groves]

This commit introduces the famfs fs_context_operations and
famfs_get_inode() which is used by the context operations.

Signed-off-by: John Groves <john@groves.net>
---
 fs/famfs/famfs_inode.c | 178 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 178 insertions(+)

diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
index 82c861998093..f98f82962d7b 100644
--- a/fs/famfs/famfs_inode.c
+++ b/fs/famfs/famfs_inode.c
@@ -41,6 +41,50 @@ static const struct super_operations famfs_ops;
 static const struct inode_operations famfs_file_inode_operations;
 static const struct inode_operations famfs_dir_inode_operations;
 
+static struct inode *famfs_get_inode(
+	struct super_block *sb,
+	const struct inode *dir,
+	umode_t             mode,
+	dev_t               dev)
+{
+	struct inode *inode = new_inode(sb);
+
+	if (inode) {
+		struct timespec64       tv;
+
+		inode->i_ino = get_next_ino();
+		inode_init_owner(&nop_mnt_idmap, inode, dir, mode);
+		inode->i_mapping->a_ops = &ram_aops;
+		mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
+		mapping_set_unevictable(inode->i_mapping);
+		tv = inode_set_ctime_current(inode);
+		inode_set_mtime_to_ts(inode, tv);
+		inode_set_atime_to_ts(inode, tv);
+
+		switch (mode & S_IFMT) {
+		default:
+			init_special_inode(inode, mode, dev);
+			break;
+		case S_IFREG:
+			inode->i_op = &famfs_file_inode_operations;
+			inode->i_fop = &famfs_file_operations;
+			break;
+		case S_IFDIR:
+			inode->i_op = &famfs_dir_inode_operations;
+			inode->i_fop = &simple_dir_operations;
+
+			/* Directory inodes start off with i_nlink == 2 (for "." entry) */
+			inc_nlink(inode);
+			break;
+		case S_IFLNK:
+			inode->i_op = &page_symlink_inode_operations;
+			inode_nohighmem(inode);
+			break;
+		}
+	}
+	return inode;
+}
+
 /**********************************************************************************
  * famfs super_operations
  *
@@ -150,6 +194,140 @@ famfs_open_device(
 	return 0;
 }
 
+/*****************************************************************************************
+ * fs_context_operations
+ */
+static int
+famfs_fill_super(
+	struct super_block *sb,
+	struct fs_context  *fc)
+{
+	struct famfs_fs_info *fsi = sb->s_fs_info;
+	struct inode *inode;
+	int rc = 0;
+
+	sb->s_maxbytes		= MAX_LFS_FILESIZE;
+	sb->s_blocksize		= PAGE_SIZE;
+	sb->s_blocksize_bits	= PAGE_SHIFT;
+	sb->s_magic		= FAMFS_MAGIC;
+	sb->s_op		= &famfs_ops;
+	sb->s_time_gran		= 1;
+
+	rc = famfs_open_device(sb, fc);
+	if (rc)
+		goto out;
+
+	inode = famfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0);
+	sb->s_root = d_make_root(inode);
+	if (!sb->s_root)
+		rc = -ENOMEM;
+
+out:
+	return rc;
+}
+
+enum famfs_param {
+	Opt_mode,
+	Opt_dax,
+};
+
+const struct fs_parameter_spec famfs_fs_parameters[] = {
+	fsparam_u32oct("mode",	  Opt_mode),
+	fsparam_string("dax",     Opt_dax),
+	{}
+};
+
+static int famfs_parse_param(
+	struct fs_context   *fc,
+	struct fs_parameter *param)
+{
+	struct famfs_fs_info *fsi = fc->s_fs_info;
+	struct fs_parse_result result;
+	int opt;
+
+	opt = fs_parse(fc, famfs_fs_parameters, param, &result);
+	if (opt == -ENOPARAM) {
+		opt = vfs_parse_fs_param_source(fc, param);
+		if (opt != -ENOPARAM)
+			return opt;
+
+		return 0;
+	}
+	if (opt < 0)
+		return opt;
+
+	switch (opt) {
+	case Opt_mode:
+		fsi->mount_opts.mode = result.uint_32 & S_IALLUGO;
+		break;
+	case Opt_dax:
+		if (strcmp(param->string, "always"))
+			pr_notice("%s: invalid dax mode %s\n",
+				  __func__, param->string);
+		break;
+	}
+
+	return 0;
+}
+
+static DEFINE_MUTEX(famfs_context_mutex);
+static LIST_HEAD(famfs_context_list);
+
+static int famfs_get_tree(struct fs_context *fc)
+{
+	struct famfs_fs_info *fsi_entry;
+	struct famfs_fs_info *fsi = fc->s_fs_info;
+
+	fsi->rootdev = kstrdup(fc->source, GFP_KERNEL);
+	if (!fsi->rootdev)
+		return -ENOMEM;
+
+	/* Fail if famfs is already mounted from the same device */
+	mutex_lock(&famfs_context_mutex);
+	list_for_each_entry(fsi_entry, &famfs_context_list, fsi_list) {
+		if (strcmp(fsi_entry->rootdev, fc->source) == 0) {
+			mutex_unlock(&famfs_context_mutex);
+			pr_err("%s: already mounted from rootdev %s\n", __func__, fc->source);
+			return -EALREADY;
+		}
+	}
+
+	list_add(&fsi->fsi_list, &famfs_context_list);
+	mutex_unlock(&famfs_context_mutex);
+
+	return get_tree_nodev(fc, famfs_fill_super);
+
+}
+
+static void famfs_free_fc(struct fs_context *fc)
+{
+	struct famfs_fs_info *fsi = fc->s_fs_info;
+
+	if (fsi && fsi->rootdev)
+		kfree(fsi->rootdev);
+
+	kfree(fsi);
+}
+
+static const struct fs_context_operations famfs_context_ops = {
+	.free		= famfs_free_fc,
+	.parse_param	= famfs_parse_param,
+	.get_tree	= famfs_get_tree,
+};
+
+static int famfs_init_fs_context(struct fs_context *fc)
+{
+	struct famfs_fs_info *fsi;
+
+	fsi = kzalloc(sizeof(*fsi), GFP_KERNEL);
+	if (!fsi)
+		return -ENOMEM;
+
+	fsi->mount_opts.mode = FAMFS_DEFAULT_MODE;
+	fc->s_fs_info        = fsi;
+	fc->ops              = &famfs_context_ops;
+	return 0;
+}
 
 
 MODULE_LICENSE("GPL");
-- 
2.43.0

[RFC PATCH 12/20] famfs: Add inode_operations and file_system_type

[John Groves]

This commit introduces the famfs inode_operations. There is nothing really
unique to famfs here in the inode_operations..

This commit also introduces the famfs_file_system_type struct and the
famfs_kill_sb() function.

Signed-off-by: John Groves <john@groves.net>
---
 fs/famfs/famfs_inode.c | 132 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 132 insertions(+)

diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
index f98f82962d7b..ab46ec50b70d 100644
--- a/fs/famfs/famfs_inode.c
+++ b/fs/famfs/famfs_inode.c
@@ -85,6 +85,109 @@ static struct inode *famfs_get_inode(
 	return inode;
 }
 
+/***************************************************************************
+ * famfs inode_operations: these are currently pretty much boilerplate
+ */
+
+static const struct inode_operations famfs_file_inode_operations = {
+	/* All generic */
+	.setattr	   = simple_setattr,
+	.getattr	   = simple_getattr,
+};
+
+
+/*
+ * File creation. Allocate an inode, and we're done..
+ */
+/* SMP-safe */
+static int
+famfs_mknod(
+	struct mnt_idmap *idmap,
+	struct inode     *dir,
+	struct dentry    *dentry,
+	umode_t           mode,
+	dev_t             dev)
+{
+	struct inode *inode = famfs_get_inode(dir->i_sb, dir, mode, dev);
+	int error           = -ENOSPC;
+
+	if (inode) {
+		struct timespec64       tv;
+
+		d_instantiate(dentry, inode);
+		dget(dentry);	/* Extra count - pin the dentry in core */
+		error = 0;
+		tv = inode_set_ctime_current(inode);
+		inode_set_mtime_to_ts(inode, tv);
+		inode_set_atime_to_ts(inode, tv);
+	}
+	return error;
+}
+
+static int famfs_mkdir(
+	struct mnt_idmap *idmap,
+	struct inode     *dir,
+	struct dentry    *dentry,
+	umode_t           mode)
+{
+	int retval = famfs_mknod(&nop_mnt_idmap, dir, dentry, mode | S_IFDIR, 0);
+
+	if (!retval)
+		inc_nlink(dir);
+
+	return retval;
+}
+
+static int famfs_create(
+	struct mnt_idmap *idmap,
+	struct inode     *dir,
+	struct dentry    *dentry,
+	umode_t           mode,
+	bool              excl)
+{
+	return famfs_mknod(&nop_mnt_idmap, dir, dentry, mode | S_IFREG, 0);
+}
+
+static int famfs_symlink(
+	struct mnt_idmap *idmap,
+	struct inode     *dir,
+	struct dentry    *dentry,
+	const char       *symname)
+{
+	struct inode *inode;
+	int error = -ENOSPC;
+
+	inode = famfs_get_inode(dir->i_sb, dir, S_IFLNK | 0777, 0);
+	if (inode) {
+		int l = strlen(symname)+1;
+
+		error = page_symlink(inode, symname, l);
+		if (!error) {
+			struct timespec64       tv;
+
+			d_instantiate(dentry, inode);
+			dget(dentry);
+			tv = inode_set_ctime_current(inode);
+			inode_set_mtime_to_ts(inode, tv);
+			inode_set_atime_to_ts(inode, tv);
+		} else
+			iput(inode);
+	}
+	return error;
+}
+
+static const struct inode_operations famfs_dir_inode_operations = {
+	.create		= famfs_create,
+	.lookup		= simple_lookup,
+	.link		= simple_link,
+	.unlink		= simple_unlink,
+	.symlink	= famfs_symlink,
+	.mkdir		= famfs_mkdir,
+	.rmdir		= simple_rmdir,
+	.mknod		= famfs_mknod,
+	.rename		= simple_rename,
+};
+
 /**********************************************************************************
  * famfs super_operations
  *
@@ -329,5 +432,34 @@ static int famfs_init_fs_context(struct fs_context *fc)
 	return 0;
 }
 
+static void famfs_kill_sb(struct super_block *sb)
+{
+	struct famfs_fs_info *fsi = sb->s_fs_info;
+
+	mutex_lock(&famfs_context_mutex);
+	list_del(&fsi->fsi_list);
+	mutex_unlock(&famfs_context_mutex);
+
+	if (fsi->bdev_handle)
+		bdev_release(fsi->bdev_handle);
+	if (fsi->dax_devp)
+		fs_put_dax(fsi->dax_devp, fsi);
+	if (fsi->dax_filp) /* This only happens if it's char dax */
+		filp_close(fsi->dax_filp, NULL);
+
+	if (fsi && fsi->rootdev)
+		kfree(fsi->rootdev);
+	kfree(fsi);
+	kill_litter_super(sb);
+}
+
+#define MODULE_NAME "famfs"
+static struct file_system_type famfs_fs_type = {
+	.name		  = MODULE_NAME,
+	.init_fs_context  = famfs_init_fs_context,
+	.parameters	  = famfs_fs_parameters,
+	.kill_sb	  = famfs_kill_sb,
+	.fs_flags	  = FS_USERNS_MOUNT,
+};
 
 MODULE_LICENSE("GPL");
-- 
2.43.0

[RFC PATCH 13/20] famfs: Add iomap_ops

[John Groves]

This commit introduces the famfs iomap_ops. When either
dax_iomap_fault() or dax_iomap_rw() is called, we get a callback
via our iomap_begin() handler. The question being asked is
"please resolve (file, offset) to (daxdev, offset)". The function
famfs_meta_to_dax_offset() does this.

The per-file metadata is just an extent list to the
backing dax dev.  The order of this resolution is O(N) for N
extents. Note with the current user space, files usually have
only one extent.

Signed-off-by: John Groves <john@groves.net>
---
 fs/famfs/famfs_file.c | 245 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 245 insertions(+)
 create mode 100644 fs/famfs/famfs_file.c

diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c
new file mode 100644
index 000000000000..fc667d5f7be8
--- /dev/null
+++ b/fs/famfs/famfs_file.c
@@ -0,0 +1,245 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * famfs - dax file system for shared fabric-attached memory
+ *
+ * Copyright 2023-2024 Micron Technology, Inc.
+ *
+ * This file system, originally based on ramfs the dax support from xfs,
+ * is intended to allow multiple host systems to mount a common file system
+ * view of dax files that map to shared memory.
+ */
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/dax.h>
+#include <linux/uio.h>
+#include <linux/iomap.h>
+#include <uapi/linux/famfs_ioctl.h>
+#include "famfs_internal.h"
+
+/*********************************************************************
+ * iomap_operations
+ *
+ * This stuff uses the iomap (dax-related) helpers to resolve file offsets to
+ * offsets within a dax device.
+ */
+
+/**
+ * famfs_meta_to_dax_offset()
+ *
+ * This function is called by famfs_iomap_begin() to resolve an offset in a file to
+ * an offset in a dax device. This is upcalled from dax from calls to both
+ * dax_iomap_fault() and dax_iomap_rw(). Dax finishes the job resolving a fault to
+ * a specific physical page (the fault case) or doing a memcpy variant (the rw case)
+ *
+ * Pages can be PTE (4k), PMD (2MiB) or (theoretically) PuD (1GiB)
+ * (these sizes are for X86; may vary on other cpu architectures
+ *
+ * @inode  - the file where the fault occurred
+ * @iomap  - struct iomap to be filled in to indicate where to find the right memory, relative
+ *           to a dax device.
+ * @offset - the offset within the file where the fault occurred (will be page boundary)
+ * @len    - the length of the faulted mapping (will be a page multiple)
+ *           (will be trimmed in *iomap if it's disjoint in the extent list)
+ * @flags
+ */
+static int
+famfs_meta_to_dax_offset(
+	struct inode *inode,
+	struct iomap *iomap,
+	loff_t        offset,
+	loff_t        len,
+	unsigned int  flags)
+{
+	struct famfs_file_meta *meta = (struct famfs_file_meta *)inode->i_private;
+	int i;
+	loff_t local_offset = offset;
+	struct famfs_fs_info  *fsi = inode->i_sb->s_fs_info;
+
+	iomap->offset = offset; /* file offset */
+
+	for (i = 0; i < meta->tfs_extent_ct; i++) {
+		loff_t dax_ext_offset = meta->tfs_extents[i].offset;
+		loff_t dax_ext_len    = meta->tfs_extents[i].len;
+
+		if ((dax_ext_offset == 0) && (meta->file_type != FAMFS_SUPERBLOCK))
+			pr_err("%s: zero offset on non-superblock file!!\n", __func__);
+
+		/* local_offset is the offset minus the size of extents skipped so far;
+		 * If local_offset < dax_ext_len, the data of interest starts in this extent
+		 */
+		if (local_offset < dax_ext_len) {
+			loff_t ext_len_remainder = dax_ext_len - local_offset;
+
+			/*+
+			 * OK, we found the file metadata extent where this data begins
+			 * @local_offset      - The offset within the current extent
+			 * @ext_len_remainder - Remaining length of ext after skipping local_offset
+			 *
+			 * iomap->addr is the offset within the dax device where that data
+			 * starts
+			 */
+			iomap->addr    = dax_ext_offset + local_offset; /* dax dev offset */
+			iomap->offset  = offset; /* file offset */
+			iomap->length  = min_t(loff_t, len, ext_len_remainder);
+			iomap->dax_dev = fsi->dax_devp;
+			iomap->type    = IOMAP_MAPPED;
+			iomap->flags   = flags;
+
+			return 0;
+		}
+		local_offset -= dax_ext_len; /* Get ready for the next extent */
+	}
+
+	/* Set iomap to zero length in this case, and return 0
+	 * This just means that the r/w is past EOF
+	 */
+	iomap->addr    = offset;
+	iomap->offset  = offset; /* file offset */
+	iomap->length  = 0; /* this had better result in no access to dax mem */
+	iomap->dax_dev = fsi->dax_devp;
+	iomap->type    = IOMAP_MAPPED;
+	iomap->flags   = flags;
+
+	return 0;
+}
+
+/**
+ * famfs_iomap_begin()
+ *
+ * This function is pretty simple because files are
+ * * never partially allocated
+ * * never have holes (never sparse)
+ * * never "allocate on write"
+ */
+static int
+famfs_iomap_begin(
+	struct inode	       *inode,
+	loff_t			offset,
+	loff_t			length,
+	unsigned int		flags,
+	struct iomap	       *iomap,
+	struct iomap	       *srcmap)
+{
+	struct famfs_file_meta *meta = inode->i_private;
+	size_t size;
+	int rc;
+
+	size = i_size_read(inode);
+
+	WARN_ON(size != meta->file_size);
+
+	rc = famfs_meta_to_dax_offset(inode, iomap, offset, length, flags);
+
+	return rc;
+}
+
+/* Note: We never need a special set of write_iomap_ops because famfs never
+ * performs allocation on write.
+ */
+const struct iomap_ops famfs_iomap_ops = {
+	.iomap_begin		= famfs_iomap_begin,
+};
+
+/*********************************************************************
+ * vm_operations
+ */
+static vm_fault_t
+__famfs_filemap_fault(
+	struct vm_fault		*vmf,
+	unsigned int		pe_size,
+	bool			write_fault)
+{
+	struct inode		*inode = file_inode(vmf->vma->vm_file);
+	vm_fault_t		ret;
+
+	if (write_fault) {
+		sb_start_pagefault(inode->i_sb);
+		file_update_time(vmf->vma->vm_file);
+	}
+
+	if (IS_DAX(inode)) {
+		pfn_t pfn;
+
+		ret = dax_iomap_fault(vmf, pe_size, &pfn, NULL, &famfs_iomap_ops);
+		if (ret & VM_FAULT_NEEDDSYNC)
+			ret = dax_finish_sync_fault(vmf, pe_size, pfn);
+	} else {
+		/* All famfs faults will be dax... */
+		pr_err("%s: oops, non-dax fault\n", __func__);
+		ret = VM_FAULT_SIGBUS;
+	}
+
+	if (write_fault)
+		sb_end_pagefault(inode->i_sb);
+
+	return ret;
+}
+
+static inline bool
+famfs_is_write_fault(
+	struct vm_fault		*vmf)
+{
+	return (vmf->flags & FAULT_FLAG_WRITE) &&
+	       (vmf->vma->vm_flags & VM_SHARED);
+}
+
+static vm_fault_t
+famfs_filemap_fault(
+	struct vm_fault		*vmf)
+{
+	/* DAX can shortcut the normal fault path on write faults! */
+	return __famfs_filemap_fault(vmf, 0,
+			IS_DAX(file_inode(vmf->vma->vm_file)) && famfs_is_write_fault(vmf));
+}
+
+static vm_fault_t
+famfs_filemap_huge_fault(
+	struct vm_fault	*vmf,
+	unsigned int	 pe_size)
+{
+	if (!IS_DAX(file_inode(vmf->vma->vm_file))) {
+		pr_err("%s: file not marked IS_DAX!!\n", __func__);
+		return VM_FAULT_SIGBUS;
+	}
+
+	/* DAX can shortcut the normal fault path on write faults! */
+	return __famfs_filemap_fault(vmf, pe_size, famfs_is_write_fault(vmf));
+}
+
+static vm_fault_t
+famfs_filemap_page_mkwrite(
+	struct vm_fault		*vmf)
+{
+	return __famfs_filemap_fault(vmf, 0, true);
+}
+
+static vm_fault_t
+famfs_filemap_pfn_mkwrite(
+	struct vm_fault		*vmf)
+{
+	return __famfs_filemap_fault(vmf, 0, true);
+}
+
+static vm_fault_t
+famfs_filemap_map_pages(
+	struct vm_fault	       *vmf,
+	pgoff_t			start_pgoff,
+	pgoff_t			end_pgoff)
+{
+	vm_fault_t ret;
+
+	ret = filemap_map_pages(vmf, start_pgoff, end_pgoff);
+	return ret;
+}
+
+const struct vm_operations_struct famfs_file_vm_ops = {
+	.fault		= famfs_filemap_fault,
+	.huge_fault	= famfs_filemap_huge_fault,
+	.map_pages	= famfs_filemap_map_pages,
+	.page_mkwrite	= famfs_filemap_page_mkwrite,
+	.pfn_mkwrite	= famfs_filemap_pfn_mkwrite,
+};
+
-- 
2.43.0

[RFC PATCH 14/20] famfs: Add struct file_operations

[John Groves]

This commit introduces the famfs file_operations. We call
thp_get_unmapped_area() to force PMD page alignment. Our read and
write handlers (famfs_dax_read_iter() and famfs_dax_write_iter())
call dax_iomap_rw() to do the work.

famfs_file_invalid() checks for various ways a famfs file can be
in an invalid state so we can fail I/O or fault resolution in those
cases. Those cases include the following:

* No famfs metadata
* file i_size does not match the originally allocated size
* file is not flagged as DAX
* errors were detected previously on the file

An invalid file can often be fixed by replaying the log, or by
umount/mount/log replay - all of which are user space operations.

Signed-off-by: John Groves <john@groves.net>
---
 fs/famfs/famfs_file.c | 136 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 136 insertions(+)

diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c
index fc667d5f7be8..5228e9de1e3b 100644
--- a/fs/famfs/famfs_file.c
+++ b/fs/famfs/famfs_file.c
@@ -19,6 +19,142 @@
 #include <uapi/linux/famfs_ioctl.h>
 #include "famfs_internal.h"
 
+/*********************************************************************
+ * file_operations
+ */
+
+/* Reject I/O to files that aren't in a valid state */
+static ssize_t
+famfs_file_invalid(struct inode *inode)
+{
+	size_t i_size       = i_size_read(inode);
+	struct famfs_file_meta *meta = inode->i_private;
+
+	if (!meta) {
+		pr_err("%s: un-initialized famfs file\n", __func__);
+		return -EIO;
+	}
+	if (i_size != meta->file_size) {
+		pr_err("%s: something changed the size from  %ld to %ld\n",
+		       __func__, meta->file_size, i_size);
+		meta->error = 1;
+		return -ENXIO;
+	}
+	if (!IS_DAX(inode)) {
+		pr_err("%s: inode %llx IS_DAX is false\n", __func__, (u64)inode);
+		meta->error = 1;
+		return -ENXIO;
+	}
+	if (meta->error) {
+		pr_err("%s: previously detected metadata errors\n", __func__);
+		meta->error = 1;
+		return -EIO;
+	}
+	return 0;
+}
+
+static ssize_t
+famfs_dax_read_iter(
+	struct kiocb		*iocb,
+	struct iov_iter		*to)
+{
+	struct inode *inode = iocb->ki_filp->f_mapping->host;
+	size_t i_size       = i_size_read(inode);
+	size_t count        = iov_iter_count(to);
+	size_t max_count;
+	ssize_t rc;
+
+	rc = famfs_file_invalid(inode);
+	if (rc)
+		return rc;
+
+	max_count = max_t(size_t, 0, i_size - iocb->ki_pos);
+
+	if (count > max_count)
+		iov_iter_truncate(to, max_count);
+
+	if (!iov_iter_count(to))
+		return 0;
+
+	rc = dax_iomap_rw(iocb, to, &famfs_iomap_ops);
+
+	file_accessed(iocb->ki_filp);
+	return rc;
+}
+
+/**
+ * famfs_write_iter()
+ *
+ * We need our own write-iter in order to prevent append
+ */
+static ssize_t
+famfs_dax_write_iter(
+	struct kiocb    *iocb,
+	struct iov_iter *from)
+{
+	struct inode *inode = iocb->ki_filp->f_mapping->host;
+	size_t i_size       = i_size_read(inode);
+	size_t count        = iov_iter_count(from);
+	size_t max_count;
+	ssize_t rc;
+
+	rc = famfs_file_invalid(inode);
+	if (rc)
+		return rc;
+
+	/* Starting offset of write is: iocb->ki_pos
+	 * length is iov_iter_count(from)
+	 */
+	max_count = max_t(size_t, 0, i_size - iocb->ki_pos);
+
+	/* If write would go past EOF, truncate it to end at EOF since famfs does not
+	 * alloc-on-write
+	 */
+	if (count > max_count)
+		iov_iter_truncate(from, max_count);
+
+	if (!iov_iter_count(from))
+		return 0;
+
+	return dax_iomap_rw(iocb, from, &famfs_iomap_ops);
+}
+
+static int
+famfs_file_mmap(
+	struct file		*file,
+	struct vm_area_struct	*vma)
+{
+	struct inode		*inode = file_inode(file);
+	ssize_t rc;
+
+	rc = famfs_file_invalid(inode);
+	if (rc)
+		return (int)rc;
+
+	file_accessed(file);
+	vma->vm_ops = &famfs_file_vm_ops;
+	vm_flags_set(vma, VM_HUGEPAGE);
+	return 0;
+}
+
+const struct file_operations famfs_file_operations = {
+	.owner             = THIS_MODULE,
+
+	/* Custom famfs operations */
+	.write_iter	   = famfs_dax_write_iter,
+	.read_iter	   = famfs_dax_read_iter,
+	.mmap		   = famfs_file_mmap,
+
+	/* Force PMD alignment for mmap */
+	.get_unmapped_area = thp_get_unmapped_area,
+
+	/* Generic Operations */
+	.fsync		   = noop_fsync,
+	.splice_read	   = filemap_splice_read,
+	.splice_write	   = iter_file_splice_write,
+	.llseek		   = generic_file_llseek,
+};
+
 /*********************************************************************
  * iomap_operations
  *
-- 
2.43.0

[RFC PATCH 15/20] famfs: Add ioctl to file_operations

[John Groves]

This commit introduces the per-file ioctl function famfs_file_ioctl()
into struct file_operations, and introduces the famfs_file_init_dax()
function (which is called by famfs_file_ioct())

famfs_file_init_dax() associates a dax extent list with a file, making
it into a proper famfs file. It is called from the FAMFSIOC_MAP_CREATE
ioctl. Starting with an empty file (which is basically a ramfs file),
this turns the file into a DAX file backed by the specified extent list.

The other ioctls are:

FAMFSIOC_NOP - A convenient way for user space to verify it's a famfs file
FAMFSIOC_MAP_GET - Get the header of the metadata for a file
FAMFSIOC_MAP_GETEXT - Get the extents for a file

The latter two, together, are comparable to xfs_bmap. Our user space tools
use them primarly in testing.

Signed-off-by: John Groves <john@groves.net>
---
 fs/famfs/famfs_file.c | 226 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 226 insertions(+)

diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c
index 5228e9de1e3b..fd42d5966982 100644
--- a/fs/famfs/famfs_file.c
+++ b/fs/famfs/famfs_file.c
@@ -19,6 +19,231 @@
 #include <uapi/linux/famfs_ioctl.h>
 #include "famfs_internal.h"
 
+/**
+ * famfs_map_meta_alloc() - Allocate famfs file metadata
+ * @mapp:       Pointer to an mcache_map_meta pointer
+ * @ext_count:  The number of extents needed
+ */
+static int
+famfs_meta_alloc(
+	struct famfs_file_meta  **metap,
+	size_t                    ext_count)
+{
+	struct famfs_file_meta *meta;
+	size_t                  metasz;
+
+	*metap = NULL;
+
+	metasz = sizeof(*meta) + sizeof(*(meta->tfs_extents)) * ext_count;
+
+	meta = kzalloc(metasz, GFP_KERNEL);
+	if (!meta)
+		return -ENOMEM;
+
+	meta->tfs_extent_ct = ext_count;
+	*metap = meta;
+
+	return 0;
+}
+
+static void
+famfs_meta_free(
+	struct famfs_file_meta *map)
+{
+	kfree(map);
+}
+
+/**
+ * famfs_file_init_dax() - FAMFSIOC_MAP_CREATE ioctl handler
+ * @file:
+ * @arg:        ptr to struct mcioc_map in user space
+ *
+ * Setup the dax mapping for a file. Files are created empty, and then function is called
+ * (by famfs_file_ioctl()) to setup the mapping and set the file size.
+ */
+static int
+famfs_file_init_dax(
+	struct file    *file,
+	void __user    *arg)
+{
+	struct famfs_extent    *tfs_extents = NULL;
+	struct famfs_file_meta *meta = NULL;
+	struct inode           *inode;
+	struct famfs_ioc_map    imap;
+	struct famfs_fs_info   *fsi;
+	struct super_block     *sb;
+	int    alignment_errs = 0;
+	size_t extent_total = 0;
+	size_t ext_count;
+	int    rc = 0;
+	int    i;
+
+	rc = copy_from_user(&imap, arg, sizeof(imap));
+	if (rc)
+		return -EFAULT;
+
+	ext_count = imap.ext_list_count;
+	if (ext_count < 1) {
+		rc = -ENOSPC;
+		goto errout;
+	}
+
+	if (ext_count > FAMFS_MAX_EXTENTS) {
+		rc = -E2BIG;
+		goto errout;
+	}
+
+	inode = file_inode(file);
+	if (!inode) {
+		rc = -EBADF;
+		goto errout;
+	}
+	sb  = inode->i_sb;
+	fsi = inode->i_sb->s_fs_info;
+
+	tfs_extents = &imap.ext_list[0];
+
+	rc = famfs_meta_alloc(&meta, ext_count);
+	if (rc)
+		goto errout;
+
+	meta->file_type = imap.file_type;
+	meta->file_size = imap.file_size;
+
+	/* Fill in the internal file metadata structure */
+	for (i = 0; i < imap.ext_list_count; i++) {
+		size_t len;
+		off_t  offset;
+
+		offset = imap.ext_list[i].offset;
+		len    = imap.ext_list[i].len;
+
+		extent_total += len;
+
+		if (WARN_ON(offset == 0 && meta->file_type != FAMFS_SUPERBLOCK)) {
+			rc = -EINVAL;
+			goto errout;
+		}
+
+		meta->tfs_extents[i].offset = offset;
+		meta->tfs_extents[i].len    = len;
+
+		/* All extent addresses/offsets must be 2MiB aligned,
+		 * and all but the last length must be a 2MiB multiple.
+		 */
+		if (!IS_ALIGNED(offset, PMD_SIZE)) {
+			pr_err("%s: error ext %d hpa %lx not aligned\n",
+			       __func__, i, offset);
+			alignment_errs++;
+		}
+		if (i < (imap.ext_list_count - 1) && !IS_ALIGNED(len, PMD_SIZE)) {
+			pr_err("%s: error ext %d length %ld not aligned\n",
+			       __func__, i, len);
+			alignment_errs++;
+		}
+	}
+
+	/*
+	 * File size can be <= ext list size, since extent sizes are constrained
+	 * to PMD multiples
+	 */
+	if (imap.file_size > extent_total) {
+		pr_err("%s: file size %lld larger than ext list size %lld\n",
+		       __func__, (u64)imap.file_size, (u64)extent_total);
+		rc = -EINVAL;
+		goto errout;
+	}
+
+	if (alignment_errs > 0) {
+		pr_err("%s: there were %d alignment errors in the extent list\n",
+		       __func__, alignment_errs);
+		rc = -EINVAL;
+		goto errout;
+	}
+
+	/* Publish the famfs metadata on inode->i_private */
+	inode_lock(inode);
+	if (inode->i_private) {
+		rc = -EEXIST; /* file already has famfs metadata */
+	} else {
+		inode->i_private = meta;
+		i_size_write(inode, imap.file_size);
+		inode->i_flags |= S_DAX;
+	}
+	inode_unlock(inode);
+
+ errout:
+	if (rc)
+		famfs_meta_free(meta);
+
+	return rc;
+}
+
+/**
+ * famfs_file_ioctl() -  top-level famfs file ioctl handler
+ * @file:
+ * @cmd:
+ * @arg:
+ */
+static
+long
+famfs_file_ioctl(
+	struct file    *file,
+	unsigned int    cmd,
+	unsigned long   arg)
+{
+	long rc;
+
+	switch (cmd) {
+	case FAMFSIOC_NOP:
+		rc = 0;
+		break;
+
+	case FAMFSIOC_MAP_CREATE:
+		rc = famfs_file_init_dax(file, (void *)arg);
+		break;
+
+	case FAMFSIOC_MAP_GET: {
+		struct inode *inode = file_inode(file);
+		struct famfs_file_meta *meta = inode->i_private;
+		struct famfs_ioc_map umeta;
+
+		memset(&umeta, 0, sizeof(umeta));
+
+		if (meta) {
+			/* TODO: do more to harmonize these structures */
+			umeta.extent_type    = meta->tfs_extent_type;
+			umeta.file_size      = i_size_read(inode);
+			umeta.ext_list_count = meta->tfs_extent_ct;
+
+			rc = copy_to_user((void __user *)arg, &umeta, sizeof(umeta));
+			if (rc)
+				pr_err("%s: copy_to_user returned %ld\n", __func__, rc);
+
+		} else {
+			rc = -EINVAL;
+		}
+	}
+		break;
+	case FAMFSIOC_MAP_GETEXT: {
+		struct inode *inode = file_inode(file);
+		struct famfs_file_meta *meta = inode->i_private;
+
+		if (meta)
+			rc = copy_to_user((void __user *)arg, meta->tfs_extents,
+					  meta->tfs_extent_ct * sizeof(struct famfs_extent));
+		else
+			rc = -EINVAL;
+	}
+		break;
+	default:
+		rc = -ENOTTY;
+		break;
+	}
+
+	return rc;
+}
+
 /*********************************************************************
  * file_operations
  */
@@ -143,6 +368,7 @@ const struct file_operations famfs_file_operations = {
 	/* Custom famfs operations */
 	.write_iter	   = famfs_dax_write_iter,
 	.read_iter	   = famfs_dax_read_iter,
+	.unlocked_ioctl    = famfs_file_ioctl,
 	.mmap		   = famfs_file_mmap,
 
 	/* Force PMD alignment for mmap */
-- 
2.43.0

[RFC PATCH 16/20] famfs: Add fault counters

[John Groves]

One of the key requirements for famfs is that it service vma faults
efficiently. Our metadata helps - the search order is n for n extents,
and n is usually 1. But we can still observe gnarly lock contention
in mm if PTE faults are happening. This commit introduces fault counters
that can be enabled and read via /sys/fs/famfs/...

These counters have proved useful in troubleshooting situations where
PTE faults were happening instead of PMD. No performance impact when
disabled.

Signed-off-by: John Groves <john@groves.net>
---
 fs/famfs/famfs_file.c     | 97 +++++++++++++++++++++++++++++++++++++++
 fs/famfs/famfs_internal.h | 73 +++++++++++++++++++++++++++++
 2 files changed, 170 insertions(+)

diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c
index fd42d5966982..a626f8a89790 100644
--- a/fs/famfs/famfs_file.c
+++ b/fs/famfs/famfs_file.c
@@ -19,6 +19,100 @@
 #include <uapi/linux/famfs_ioctl.h>
 #include "famfs_internal.h"
 
+/***************************************************************************************
+ * filemap_fault counters
+ *
+ * The counters and the fault_count_enable file live at
+ * /sys/fs/famfs/
+ */
+struct famfs_fault_counters ffc;
+static int fault_count_enable;
+
+static ssize_t
+fault_count_enable_show(struct kobject *kobj,
+			struct kobj_attribute *attr,
+			char *buf)
+{
+	return sprintf(buf, "%d\n", fault_count_enable);
+}
+
+static ssize_t
+fault_count_enable_store(struct kobject        *kobj,
+			 struct kobj_attribute *attr,
+			 const char            *buf,
+			 size_t                 count)
+{
+	int value;
+	int rc;
+
+	rc = sscanf(buf, "%d", &value);
+	if (rc != 1)
+		return 0;
+
+	if (value > 0) /* clear fault counters when enabling, but not when disabling */
+		famfs_clear_fault_counters(&ffc);
+
+	fault_count_enable = value;
+	return count;
+}
+
+/* Individual fault counters are read-only */
+static ssize_t
+fault_count_pte_show(struct kobject *kobj,
+		     struct kobj_attribute *attr,
+		     char *buf)
+{
+	return sprintf(buf, "%llu", famfs_pte_fault_ct(&ffc));
+}
+
+static ssize_t
+fault_count_pmd_show(struct kobject *kobj,
+		     struct kobj_attribute *attr,
+		     char *buf)
+{
+	return sprintf(buf, "%llu", famfs_pmd_fault_ct(&ffc));
+}
+
+static ssize_t
+fault_count_pud_show(struct kobject *kobj,
+		     struct kobj_attribute *attr,
+		     char *buf)
+{
+	return sprintf(buf, "%llu", famfs_pud_fault_ct(&ffc));
+}
+
+static struct kobj_attribute fault_count_enable_attribute = __ATTR(fault_count_enable,
+								   0660,
+								   fault_count_enable_show,
+								   fault_count_enable_store);
+static struct kobj_attribute fault_count_pte_attribute = __ATTR(pte_fault_ct,
+								0440,
+								fault_count_pte_show,
+								NULL);
+static struct kobj_attribute fault_count_pmd_attribute = __ATTR(pmd_fault_ct,
+								0440,
+								fault_count_pmd_show,
+								NULL);
+static struct kobj_attribute fault_count_pud_attribute = __ATTR(pud_fault_ct,
+								0440,
+								fault_count_pud_show,
+								NULL);
+
+
+static struct attribute *attrs[] = {
+	&fault_count_enable_attribute.attr,
+	&fault_count_pte_attribute.attr,
+	&fault_count_pmd_attribute.attr,
+	&fault_count_pud_attribute.attr,
+	NULL,
+};
+
+struct attribute_group famfs_attr_group = {
+	.attrs = attrs,
+};
+
+/* End fault counters */
+
 /**
  * famfs_map_meta_alloc() - Allocate famfs file metadata
  * @mapp:       Pointer to an mcache_map_meta pointer
@@ -525,6 +619,9 @@ __famfs_filemap_fault(
 	if (IS_DAX(inode)) {
 		pfn_t pfn;
 
+		if (fault_count_enable)
+			famfs_inc_fault_counter_by_order(&ffc, pe_size);
+
 		ret = dax_iomap_fault(vmf, pe_size, &pfn, NULL, &famfs_iomap_ops);
 		if (ret & VM_FAULT_NEEDDSYNC)
 			ret = dax_finish_sync_fault(vmf, pe_size, pfn);
diff --git a/fs/famfs/famfs_internal.h b/fs/famfs/famfs_internal.h
index af3990d43305..987cb172a149 100644
--- a/fs/famfs/famfs_internal.h
+++ b/fs/famfs/famfs_internal.h
@@ -50,4 +50,77 @@ struct famfs_fs_info {
 	char                    *rootdev;
 };
 
+/*
+ * filemap_fault counters
+ */
+extern struct attribute_group famfs_attr_group;
+
+enum famfs_fault {
+	FAMFS_PTE = 0,
+	FAMFS_PMD,
+	FAMFS_PUD,
+	FAMFS_NUM_FAULT_TYPES,
+};
+
+static inline int valid_fault_type(int type)
+{
+	if (unlikely(type < 0 || type > FAMFS_PUD))
+		return 0;
+	return 1;
+}
+
+struct famfs_fault_counters {
+	atomic64_t fault_ct[FAMFS_NUM_FAULT_TYPES];
+};
+
+extern struct famfs_fault_counters ffc;
+
+static inline void famfs_clear_fault_counters(struct famfs_fault_counters *fc)
+{
+	int i;
+
+	for (i = 0; i < FAMFS_NUM_FAULT_TYPES; i++)
+		atomic64_set(&fc->fault_ct[i], 0);
+}
+
+static inline void famfs_inc_fault_counter(struct famfs_fault_counters *fc,
+					   enum famfs_fault type)
+{
+	if (valid_fault_type(type))
+		atomic64_inc(&fc->fault_ct[type]);
+}
+
+static inline void famfs_inc_fault_counter_by_order(struct famfs_fault_counters *fc, int order)
+{
+	int pgf = -1;
+
+	switch (order) {
+	case 0:
+		pgf = FAMFS_PTE;
+		break;
+	case PMD_ORDER:
+		pgf = FAMFS_PMD;
+		break;
+	case PUD_ORDER:
+		pgf = FAMFS_PUD;
+		break;
+	}
+	famfs_inc_fault_counter(fc, pgf);
+}
+
+static inline u64 famfs_pte_fault_ct(struct famfs_fault_counters *fc)
+{
+	return atomic64_read(&fc->fault_ct[FAMFS_PTE]);
+}
+
+static inline u64 famfs_pmd_fault_ct(struct famfs_fault_counters *fc)
+{
+	return atomic64_read(&fc->fault_ct[FAMFS_PMD]);
+}
+
+static inline u64 famfs_pud_fault_ct(struct famfs_fault_counters *fc)
+{
+	return atomic64_read(&fc->fault_ct[FAMFS_PUD]);
+}
+
 #endif /* FAMFS_INTERNAL_H */
-- 
2.43.0

[RFC PATCH 17/20] famfs: Add module stuff

[John Groves]

This commit introduces the module init and exit machinery for famfs.

Signed-off-by: John Groves <john@groves.net>
---
 fs/famfs/famfs_inode.c | 44 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
index ab46ec50b70d..0d659820e8ff 100644
--- a/fs/famfs/famfs_inode.c
+++ b/fs/famfs/famfs_inode.c
@@ -462,4 +462,48 @@ static struct file_system_type famfs_fs_type = {
 	.fs_flags	  = FS_USERNS_MOUNT,
 };
 
+/*****************************************************************************************
+ * Module stuff
+ */
+static struct kobject *famfs_kobj;
+
+static int __init init_famfs_fs(void)
+{
+	int rc;
+
+#if defined(CONFIG_DEV_DAX_IOMAP)
+	pr_notice("%s: Your kernel supports famfs on /dev/dax\n", __func__);
+#else
+	pr_notice("%s: Your kernel does not support famfs on /dev/dax\n", __func__);
+#endif
+	famfs_kobj = kobject_create_and_add(MODULE_NAME, fs_kobj);
+	if (!famfs_kobj) {
+		pr_warn("Failed to create kobject\n");
+		return -ENOMEM;
+	}
+
+	rc = sysfs_create_group(famfs_kobj, &famfs_attr_group);
+	if (rc) {
+		kobject_put(famfs_kobj);
+		pr_warn("%s: Failed to create sysfs group\n", __func__);
+		return rc;
+	}
+
+	return register_filesystem(&famfs_fs_type);
+}
+
+static void
+__exit famfs_exit(void)
+{
+	sysfs_remove_group(famfs_kobj,  &famfs_attr_group);
+	kobject_put(famfs_kobj);
+	unregister_filesystem(&famfs_fs_type);
+	pr_info("%s: unregistered\n", __func__);
+}
+
+
+fs_initcall(init_famfs_fs);
+module_exit(famfs_exit);
+
+MODULE_AUTHOR("John Groves, Micron Technology");
 MODULE_LICENSE("GPL");
-- 
2.43.0

[RFC PATCH 18/20] famfs: Support character dax via the dev_dax_iomap patch

[John Groves]

This commit introduces the ability to open a character /dev/dax device
instead of a block /dev/pmem device. This rests on the dev_dax_iomap
patches earlier in this series.

Signed-off-by: John Groves <john@groves.net>
---
 fs/famfs/famfs_inode.c | 97 +++++++++++++++++++++++++++++++++++++-----
 1 file changed, 87 insertions(+), 10 deletions(-)

diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
index 0d659820e8ff..7d65ac497147 100644
--- a/fs/famfs/famfs_inode.c
+++ b/fs/famfs/famfs_inode.c
@@ -215,6 +215,93 @@ static const struct super_operations famfs_ops = {
 	.show_options	= famfs_show_options,
 };
 
+/*****************************************************************************/
+
+#if defined(CONFIG_DEV_DAX_IOMAP)
+
+/*
+ * famfs dax_operations  (for char dax)
+ */
+static int
+famfs_dax_notify_failure(struct dax_device *dax_dev, u64 offset,
+			u64 len, int mf_flags)
+{
+	pr_err("%s: offset %lld len %llu flags %x\n", __func__,
+	       offset, len, mf_flags);
+	return -EOPNOTSUPP;
+}
+
+static const struct dax_holder_operations famfs_dax_holder_ops = {
+	.notify_failure		= famfs_dax_notify_failure,
+};
+
+/*****************************************************************************/
+
+/**
+ * famfs_open_char_device()
+ *
+ * Open a /dev/dax device. This only works in kernels with the dev_dax_iomap patch
+ */
+static int
+famfs_open_char_device(
+	struct super_block *sb,
+	struct fs_context  *fc)
+{
+	struct famfs_fs_info *fsi = sb->s_fs_info;
+	struct dax_device    *dax_devp;
+	struct inode         *daxdev_inode;
+
+	int rc = 0;
+
+	pr_notice("%s: Opening character dax device %s\n", __func__, fc->source);
+
+	fsi->dax_filp = filp_open(fc->source, O_RDWR, 0);
+	if (IS_ERR(fsi->dax_filp)) {
+		pr_err("%s: failed to open dax device %s\n",
+		       __func__, fc->source);
+		fsi->dax_filp = NULL;
+		return PTR_ERR(fsi->dax_filp);
+	}
+
+	daxdev_inode = file_inode(fsi->dax_filp);
+	dax_devp     = inode_dax(daxdev_inode);
+	if (IS_ERR(dax_devp)) {
+		pr_err("%s: unable to get daxdev from inode for %s\n",
+		       __func__, fc->source);
+		rc = -ENODEV;
+		goto char_err;
+	}
+
+	rc = fs_dax_get(dax_devp, fsi, &famfs_dax_holder_ops);
+	if (rc) {
+		pr_info("%s: err attaching famfs_dax_holder_ops\n", __func__);
+		goto char_err;
+	}
+
+	fsi->bdev_handle = NULL;
+	fsi->dax_devp = dax_devp;
+
+	return 0;
+
+char_err:
+	filp_close(fsi->dax_filp, NULL);
+	return rc;
+}
+
+#else /* CONFIG_DEV_DAX_IOMAP */
+static int
+famfs_open_char_device(
+	struct super_block *sb,
+	struct fs_context  *fc)
+{
+	pr_err("%s: Root device is %s, but your kernel does not support famfs on /dev/dax\n",
+	       __func__, fc->source);
+	return -ENODEV;
+}
+
+
+#endif /* CONFIG_DEV_DAX_IOMAP */
+
 /***************************************************************************************
  * dax_holder_operations for block dax
  */
@@ -236,16 +323,6 @@ const struct dax_holder_operations famfs_blk_dax_holder_ops = {
 	.notify_failure		= famfs_blk_dax_notify_failure,
 };
 
-static int
-famfs_open_char_device(
-	struct super_block *sb,
-	struct fs_context  *fc)
-{
-	pr_err("%s: Root device is %s, but your kernel does not support famfs on /dev/dax\n",
-	       __func__, fc->source);
-	return -ENODEV;
-}
-
 /**
  * famfs_open_device()
  *
-- 
2.43.0

[RFC PATCH 19/20] famfs: Update MAINTAINERS file

[John Groves]

This patch introduces famfs into the MAINTAINERS file

Signed-off-by: John Groves <john@groves.net>
---
 MAINTAINERS | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 73d898383e51..e4e8bf3602bb 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8097,6 +8097,17 @@ F:	Documentation/networking/failover.rst
 F:	include/net/failover.h
 F:	net/core/failover.c
 
+FAMFS
+M:	John Groves <jgroves@micron.com>
+M:	John Groves <John@Groves.net>
+M:	John Groves <john@jagalactic.com>
+L:	linux-cxl@vger.kernel.org
+L:	linux-fsdevel@vger.kernel.org
+S:	Supported
+F:	Documentation/filesystems/famfs.rst
+F:	fs/famfs
+F:	include/uapi/linux/famfs_ioctl.h
+
 FANOTIFY
 M:	Jan Kara <jack@suse.cz>
 R:	Amir Goldstein <amir73il@gmail.com>
-- 
2.43.0

[RFC PATCH 20/20] famfs: Add Kconfig and Makefile plumbing

[John Groves]

Add famfs Kconfig and Makefile, and hook into fs/Kconfig and fs/Makefile

Signed-off-by: John Groves <john@groves.net>
---
 fs/Kconfig        |  2 ++
 fs/Makefile       |  1 +
 fs/famfs/Kconfig  | 10 ++++++++++
 fs/famfs/Makefile |  5 +++++
 4 files changed, 18 insertions(+)
 create mode 100644 fs/famfs/Kconfig
 create mode 100644 fs/famfs/Makefile

diff --git a/fs/Kconfig b/fs/Kconfig
index 89fdbefd1075..8a11625a54a2 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -141,6 +141,8 @@ source "fs/autofs/Kconfig"
 source "fs/fuse/Kconfig"
 source "fs/overlayfs/Kconfig"
 
+source "fs/famfs/Kconfig"
+
 menu "Caches"
 
 source "fs/netfs/Kconfig"
diff --git a/fs/Makefile b/fs/Makefile
index c09016257f05..382c1ea4f4c3 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -130,3 +130,4 @@ obj-$(CONFIG_EFIVAR_FS)		+= efivarfs/
 obj-$(CONFIG_EROFS_FS)		+= erofs/
 obj-$(CONFIG_VBOXSF_FS)		+= vboxsf/
 obj-$(CONFIG_ZONEFS_FS)		+= zonefs/
+obj-$(CONFIG_FAMFS)             += famfs/
diff --git a/fs/famfs/Kconfig b/fs/famfs/Kconfig
new file mode 100644
index 000000000000..e450928d8912
--- /dev/null
+++ b/fs/famfs/Kconfig
@@ -0,0 +1,10 @@
+
+
+config FAMFS
+       tristate "famfs: shared memory file system"
+       depends on DEV_DAX && FS_DAX
+       help
+         Support for the famfs file system. Famfs is a dax file system that
+	 can support scale-out shared access to fabric-attached memory
+	 (e.g. CXL shared memory). Famfs is not a general purpose file system;
+	 it is an enabler for data sets in shared memory.
diff --git a/fs/famfs/Makefile b/fs/famfs/Makefile
new file mode 100644
index 000000000000..8cac90c090a4
--- /dev/null
+++ b/fs/famfs/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_FAMFS) += famfs.o
+
+famfs-y := famfs_inode.o famfs_file.o
-- 
2.43.0

Re: [RFC PATCH 16/20] famfs: Add fault counters

[Dave Hansen]

On 2/23/24 09:42, John Groves wrote:
> One of the key requirements for famfs is that it service vma faults
> efficiently. Our metadata helps - the search order is n for n extents,
> and n is usually 1. But we can still observe gnarly lock contention
> in mm if PTE faults are happening. This commit introduces fault counters
> that can be enabled and read via /sys/fs/famfs/...
> 
> These counters have proved useful in troubleshooting situations where
> PTE faults were happening instead of PMD. No performance impact when
> disabled.

This seems kinda wonky.  Why does _this_ specific filesystem need its
own fault counters.  Seems like something we'd want to do much more
generically, if it is needed at all.

Was the issue here just that vm_ops->fault() was getting called instead
of ->huge_fault()?  Or something more subtle?

Re: [RFC PATCH 16/20] famfs: Add fault counters

[John Groves]

On 24/02/23 10:23AM, Dave Hansen wrote:
> On 2/23/24 09:42, John Groves wrote:
> > One of the key requirements for famfs is that it service vma faults
> > efficiently. Our metadata helps - the search order is n for n extents,
> > and n is usually 1. But we can still observe gnarly lock contention
> > in mm if PTE faults are happening. This commit introduces fault counters
> > that can be enabled and read via /sys/fs/famfs/...
> > 
> > These counters have proved useful in troubleshooting situations where
> > PTE faults were happening instead of PMD. No performance impact when
> > disabled.
> 
> This seems kinda wonky.  Why does _this_ specific filesystem need its
> own fault counters.  Seems like something we'd want to do much more
> generically, if it is needed at all.
> 
> Was the issue here just that vm_ops->fault() was getting called instead
> of ->huge_fault()?  Or something more subtle?

Thanks for your reply Dave!

First, I'm willing to pull the fault counters out if the brain trust doesn't
like them.

I put them in because we were running benchmarks of computational data
analytics and and noted that jobs took 3x as long on famfs as raw dax -
which indicated I was doing something wrong, because it should be equivalent
or very close.

The the solution was to call thp_get_unmapped_area() in
famfs_file_operations, and performance doesn't vary significantly from raw
dax now. Prior to that I wasn't making sure the mmap address was PMD aligned.

After that I wanted a way to be double-secret-certain that it was servicing
PMD faults as intended. Which it basically always is, so far. (The smoke
tests in user space check this.)

John

Re: [RFC PATCH 16/20] famfs: Add fault counters

[Dan Williams]

John Groves wrote:
> On 24/02/23 10:23AM, Dave Hansen wrote:
> > On 2/23/24 09:42, John Groves wrote:
> > > One of the key requirements for famfs is that it service vma faults
> > > efficiently. Our metadata helps - the search order is n for n extents,
> > > and n is usually 1. But we can still observe gnarly lock contention
> > > in mm if PTE faults are happening. This commit introduces fault counters
> > > that can be enabled and read via /sys/fs/famfs/...
> > > 
> > > These counters have proved useful in troubleshooting situations where
> > > PTE faults were happening instead of PMD. No performance impact when
> > > disabled.
> > 
> > This seems kinda wonky.  Why does _this_ specific filesystem need its
> > own fault counters.  Seems like something we'd want to do much more
> > generically, if it is needed at all.
> > 
> > Was the issue here just that vm_ops->fault() was getting called instead
> > of ->huge_fault()?  Or something more subtle?
> 
> Thanks for your reply Dave!
> 
> First, I'm willing to pull the fault counters out if the brain trust doesn't
> like them.
> 
> I put them in because we were running benchmarks of computational data
> analytics and and noted that jobs took 3x as long on famfs as raw dax -
> which indicated I was doing something wrong, because it should be equivalent
> or very close.
> 
> The the solution was to call thp_get_unmapped_area() in
> famfs_file_operations, and performance doesn't vary significantly from raw
> dax now. Prior to that I wasn't making sure the mmap address was PMD aligned.
> 
> After that I wanted a way to be double-secret-certain that it was servicing
> PMD faults as intended. Which it basically always is, so far. (The smoke
> tests in user space check this.)

We had similar unit test regression concerns with fsdax where some
upstream change silently broke PMD faults. The solution there was trace
points in the fault handlers and a basic test that knows apriori that it
*should* be triggering a certain number of huge faults:

https://github.com/pmem/ndctl/blob/main/test/dax.sh#L31

Re: [RFC PATCH 16/20] famfs: Add fault counters

[John Groves]

On 24/02/23 12:04PM, Dan Williams wrote:
> John Groves wrote:
> > On 24/02/23 10:23AM, Dave Hansen wrote:
> > > On 2/23/24 09:42, John Groves wrote:
> > > > One of the key requirements for famfs is that it service vma faults
> > > > efficiently. Our metadata helps - the search order is n for n extents,
> > > > and n is usually 1. But we can still observe gnarly lock contention
> > > > in mm if PTE faults are happening. This commit introduces fault counters
> > > > that can be enabled and read via /sys/fs/famfs/...
> > > > 
> > > > These counters have proved useful in troubleshooting situations where
> > > > PTE faults were happening instead of PMD. No performance impact when
> > > > disabled.
> > > 
> > > This seems kinda wonky.  Why does _this_ specific filesystem need its
> > > own fault counters.  Seems like something we'd want to do much more
> > > generically, if it is needed at all.
> > > 
> > > Was the issue here just that vm_ops->fault() was getting called instead
> > > of ->huge_fault()?  Or something more subtle?
> > 
> > Thanks for your reply Dave!
> > 
> > First, I'm willing to pull the fault counters out if the brain trust doesn't
> > like them.
> > 
> > I put them in because we were running benchmarks of computational data
> > analytics and and noted that jobs took 3x as long on famfs as raw dax -
> > which indicated I was doing something wrong, because it should be equivalent
> > or very close.
> > 
> > The the solution was to call thp_get_unmapped_area() in
> > famfs_file_operations, and performance doesn't vary significantly from raw
> > dax now. Prior to that I wasn't making sure the mmap address was PMD aligned.
> > 
> > After that I wanted a way to be double-secret-certain that it was servicing
> > PMD faults as intended. Which it basically always is, so far. (The smoke
> > tests in user space check this.)
> 
> We had similar unit test regression concerns with fsdax where some
> upstream change silently broke PMD faults. The solution there was trace
> points in the fault handlers and a basic test that knows apriori that it
> *should* be triggering a certain number of huge faults:
> 
> https://github.com/pmem/ndctl/blob/main/test/dax.sh#L31

Good approach, thanks Dan! My working assumption is that we'll be able to make
that approach work in the famfs tests. So the fault counters should go away
in the next version.

John

Re: [RFC PATCH 16/20] famfs: Add fault counters

[Dave Hansen]

On 2/23/24 12:39, John Groves wrote:
>> We had similar unit test regression concerns with fsdax where some
>> upstream change silently broke PMD faults. The solution there was trace
>> points in the fault handlers and a basic test that knows apriori that it
>> *should* be triggering a certain number of huge faults:
>>
>> https://github.com/pmem/ndctl/blob/main/test/dax.sh#L31
> Good approach, thanks Dan! My working assumption is that we'll be able to make
> that approach work in the famfs tests. So the fault counters should go away
> in the next version.

I do really suspect there's something more generic that should be done
here.  Maybe we need a generic 'huge_faults' perf event to pair up with
the good ol' faults that we already have:

# perf stat -e faults /bin/ls

 Performance counter stats for '/bin/ls':

               104      faults


       0.001499862 seconds time elapsed

       0.001490000 seconds user
       0.000000000 seconds sys

Re: [RFC PATCH 16/20] famfs: Add fault counters

[Dan Williams]

Dave Hansen wrote:
> On 2/23/24 12:39, John Groves wrote:
> >> We had similar unit test regression concerns with fsdax where some
> >> upstream change silently broke PMD faults. The solution there was trace
> >> points in the fault handlers and a basic test that knows apriori that it
> >> *should* be triggering a certain number of huge faults:
> >>
> >> https://github.com/pmem/ndctl/blob/main/test/dax.sh#L31
> > Good approach, thanks Dan! My working assumption is that we'll be able to make
> > that approach work in the famfs tests. So the fault counters should go away
> > in the next version.
> 
> I do really suspect there's something more generic that should be done
> here.  Maybe we need a generic 'huge_faults' perf event to pair up with
> the good ol' faults that we already have:
> 
> # perf stat -e faults /bin/ls
> 
>  Performance counter stats for '/bin/ls':
> 
>                104      faults
> 
> 
>        0.001499862 seconds time elapsed
> 
>        0.001490000 seconds user
>        0.000000000 seconds sys

Certainly something like that would have satisified this sanity test use
case. I will note that mm_account_fault() would need some help to figure
out the size of the page table entry that got installed. Maybe
extensions to vm_fault_reason to add VM_FAULT_P*D? That compliments
VM_FAULT_FALLBACK to indicate whether, for example, the fallback went
from PUD to PMD, or all the way back to PTE.

Then use cases like this could just add a dynamic probe in
mm_account_fault(). No real need for a new tracepoint unless there was a
use case for this outside of regression testing fault handlers, right?

Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

[Luis Chamberlain]

On Fri, Feb 23, 2024 at 11:41:44AM -0600, John Groves wrote:
> This patch set introduces famfs[1] - a special-purpose fs-dax file system
> for sharable disaggregated or fabric-attached memory (FAM). Famfs is not
> CXL-specific in anyway way.
> 
> * Famfs creates a simple access method for storing and sharing data in
>   sharable memory. The memory is exposed and accessed as memory-mappable
>   dax files.
> * Famfs supports multiple hosts mounting the same file system from the
>   same memory (something existing fs-dax file systems don't do).
> * A famfs file system can be created on either a /dev/pmem device in fs-dax
>   mode, or a /dev/dax device in devdax mode (the latter depending on
>   patches 2-6 of this series).
> 
> The famfs kernel file system is part the famfs framework; additional
> components in user space[2] handle metadata and direct the famfs kernel
> module to instantiate files that map to specific memory. The famfs user
> space has documentation and a reasonably thorough test suite.
> 
> The famfs kernel module never accesses the shared memory directly (either
> data or metadata). Because of this, shared memory managed by the famfs
> framework does not create a RAS "blast radius" problem that should be able
> to crash or de-stabilize the kernel. Poison or timeouts in famfs memory
> can be expected to kill apps via SIGBUS and cause mounts to be disabled
> due to memory failure notifications.
> 
> Famfs does not attempt to solve concurrency or coherency problems for apps,
> although it does solve these problems in regard to its own data structures.
> Apps may encounter hard concurrency problems, but there are use cases that
> are imminently useful and uncomplicated from a concurrency perspective:
> serial sharing is one (only one host at a time has access), and read-only
> concurrent sharing is another (all hosts can read-cache without worry).

Can you do me a favor, curious if you can run a test like this:

fio -name=ten-1g-per-thread --nrfiles=10 -bs=2M -ioengine=io_uring                                                                                                                            
-direct=1                                                                                                                                                                                    
--group_reporting=1 --alloc-size=1048576 --filesize=1GiB                                                                                                                                      
--readwrite=write --fallocate=none --numjobs=$(nproc) --create_on_open=1                                                                                                                      
--directory=/mnt 

What do you get for throughput?

The absolute large the system an capacity the better.

  Luis

Re: [RFC PATCH 07/20] famfs: Add include/linux/famfs_ioctl.h

[Randy Dunlap]

Hi--

On 2/23/24 09:41, John Groves wrote:
> Add uapi include file for famfs. The famfs user space uses ioctl on
> individual files to pass in mapping information and file size. This
> would be hard to do via sysfs or other means, since it's
> file-specific.
> 
> Signed-off-by: John Groves <john@groves.net>
> ---
>  include/uapi/linux/famfs_ioctl.h | 56 ++++++++++++++++++++++++++++++++
>  1 file changed, 56 insertions(+)
>  create mode 100644 include/uapi/linux/famfs_ioctl.h
> 
> diff --git a/include/uapi/linux/famfs_ioctl.h b/include/uapi/linux/famfs_ioctl.h
> new file mode 100644
> index 000000000000..6b3e6452d02f
> --- /dev/null
> +++ b/include/uapi/linux/famfs_ioctl.h
> @@ -0,0 +1,56 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/*
> + * famfs - dax file system for shared fabric-attached memory
> + *
> + * Copyright 2023-2024 Micron Technology, Inc.
> + *
> + * This file system, originally based on ramfs the dax support from xfs,

      This is confusing to me. Is it just me? ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

> + * is intended to allow multiple host systems to mount a common file system
> + * view of dax files that map to shared memory.
> + */
> +#ifndef FAMFS_IOCTL_H
> +#define FAMFS_IOCTL_H
> +
> +#include <linux/ioctl.h>
> +#include <linux/uuid.h>
> +
> +#define FAMFS_MAX_EXTENTS 2
> +
> +enum extent_type {
> +	SIMPLE_DAX_EXTENT = 13,
> +	INVALID_EXTENT_TYPE,
> +};
> +
> +struct famfs_extent {
> +	__u64              offset;
> +	__u64              len;
> +};
> +
> +enum famfs_file_type {
> +	FAMFS_REG,
> +	FAMFS_SUPERBLOCK,
> +	FAMFS_LOG,
> +};
> +
> +/**

"/**" is used to begin kernel-doc comments, but this comment block is missing
a few entries to make it be kernel-doc compatible. Please either add them
or just use "/*" to begin the comment.

> + * struct famfs_ioc_map
> + *
> + * This is the metadata that indicates where the memory is for a famfs file
> + */
> +struct famfs_ioc_map {
> +	enum extent_type          extent_type;
> +	enum famfs_file_type      file_type;
> +	__u64                     file_size;
> +	__u64                     ext_list_count;
> +	struct famfs_extent       ext_list[FAMFS_MAX_EXTENTS];
> +};
> +
> +#define FAMFSIOC_MAGIC 'u'

This 'u' value should be documented in
Documentation/userspace-api/ioctl/ioctl-number.rst.

and if possible, you might want to use values like 0x5x or 0x8x
that don't conflict with the ioctl numbers that are already used
in the 'u' space.

> +
> +/* famfs file ioctl opcodes */
> +#define FAMFSIOC_MAP_CREATE    _IOW(FAMFSIOC_MAGIC, 1, struct famfs_ioc_map)
> +#define FAMFSIOC_MAP_GET       _IOR(FAMFSIOC_MAGIC, 2, struct famfs_ioc_map)
> +#define FAMFSIOC_MAP_GETEXT    _IOR(FAMFSIOC_MAGIC, 3, struct famfs_extent)
> +#define FAMFSIOC_NOP           _IO(FAMFSIOC_MAGIC,  4)
> +
> +#endif /* FAMFS_IOCTL_H */

-- 
#Randy

Re: [RFC PATCH 20/20] famfs: Add Kconfig and Makefile plumbing

[Randy Dunlap]

Hi,

On 2/23/24 09:42, John Groves wrote:
> Add famfs Kconfig and Makefile, and hook into fs/Kconfig and fs/Makefile
> 
> Signed-off-by: John Groves <john@groves.net>
> ---
>  fs/Kconfig        |  2 ++
>  fs/Makefile       |  1 +
>  fs/famfs/Kconfig  | 10 ++++++++++
>  fs/famfs/Makefile |  5 +++++
>  4 files changed, 18 insertions(+)
>  create mode 100644 fs/famfs/Kconfig
>  create mode 100644 fs/famfs/Makefile
> 
> diff --git a/fs/Kconfig b/fs/Kconfig
> index 89fdbefd1075..8a11625a54a2 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -141,6 +141,8 @@ source "fs/autofs/Kconfig"
>  source "fs/fuse/Kconfig"
>  source "fs/overlayfs/Kconfig"
>  
> +source "fs/famfs/Kconfig"
> +
>  menu "Caches"
>  
>  source "fs/netfs/Kconfig"
> diff --git a/fs/Makefile b/fs/Makefile
> index c09016257f05..382c1ea4f4c3 100644
> --- a/fs/Makefile
> +++ b/fs/Makefile
> @@ -130,3 +130,4 @@ obj-$(CONFIG_EFIVAR_FS)		+= efivarfs/
>  obj-$(CONFIG_EROFS_FS)		+= erofs/
>  obj-$(CONFIG_VBOXSF_FS)		+= vboxsf/
>  obj-$(CONFIG_ZONEFS_FS)		+= zonefs/
> +obj-$(CONFIG_FAMFS)             += famfs/
> diff --git a/fs/famfs/Kconfig b/fs/famfs/Kconfig
> new file mode 100644
> index 000000000000..e450928d8912
> --- /dev/null
> +++ b/fs/famfs/Kconfig
> @@ -0,0 +1,10 @@
> +
> +
> +config FAMFS
> +       tristate "famfs: shared memory file system"
> +       depends on DEV_DAX && FS_DAX
> +       help
> +         Support for the famfs file system. Famfs is a dax file system that
> +	 can support scale-out shared access to fabric-attached memory
> +	 (e.g. CXL shared memory). Famfs is not a general purpose file system;
> +	 it is an enabler for data sets in shared memory.

Please use one tab + 2 spaces to indent help text (below the "help" keyword)
as documented in Documentation/process/coding-style.rst.

> diff --git a/fs/famfs/Makefile b/fs/famfs/Makefile
> new file mode 100644
> index 000000000000..8cac90c090a4
> --- /dev/null
> +++ b/fs/famfs/Makefile
> @@ -0,0 +1,5 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +obj-$(CONFIG_FAMFS) += famfs.o
> +
> +famfs-y := famfs_inode.o famfs_file.o

-- 
#Randy

Re: [RFC PATCH 07/20] famfs: Add include/linux/famfs_ioctl.h

[John Groves]

On 24/02/23 05:39PM, Randy Dunlap wrote:
> Hi--
> 
> On 2/23/24 09:41, John Groves wrote:
> > Add uapi include file for famfs. The famfs user space uses ioctl on
> > individual files to pass in mapping information and file size. This
> > would be hard to do via sysfs or other means, since it's
> > file-specific.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> > ---
> >  include/uapi/linux/famfs_ioctl.h | 56 ++++++++++++++++++++++++++++++++
> >  1 file changed, 56 insertions(+)
> >  create mode 100644 include/uapi/linux/famfs_ioctl.h
> > 
> > diff --git a/include/uapi/linux/famfs_ioctl.h b/include/uapi/linux/famfs_ioctl.h
> > new file mode 100644
> > index 000000000000..6b3e6452d02f
> > --- /dev/null
> > +++ b/include/uapi/linux/famfs_ioctl.h
> > @@ -0,0 +1,56 @@
> > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > +/*
> > + * famfs - dax file system for shared fabric-attached memory
> > + *
> > + * Copyright 2023-2024 Micron Technology, Inc.
> > + *
> > + * This file system, originally based on ramfs the dax support from xfs,
> 
>       This is confusing to me. Is it just me? ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Thanks Randy. I think I was trying to say "based on ramfs *plus* the dax
support from xfs. But I'll try to come up with something more clear than
that...

> 
> > + * is intended to allow multiple host systems to mount a common file system
> > + * view of dax files that map to shared memory.
> > + */
> > +#ifndef FAMFS_IOCTL_H
> > +#define FAMFS_IOCTL_H
> > +
> > +#include <linux/ioctl.h>
> > +#include <linux/uuid.h>
> > +
> > +#define FAMFS_MAX_EXTENTS 2
> > +
> > +enum extent_type {
> > +	SIMPLE_DAX_EXTENT = 13,
> > +	INVALID_EXTENT_TYPE,
> > +};
> > +
> > +struct famfs_extent {
> > +	__u64              offset;
> > +	__u64              len;
> > +};
> > +
> > +enum famfs_file_type {
> > +	FAMFS_REG,
> > +	FAMFS_SUPERBLOCK,
> > +	FAMFS_LOG,
> > +};
> > +
> > +/**
> 
> "/**" is used to begin kernel-doc comments, but this comment block is missing
> a few entries to make it be kernel-doc compatible. Please either add them
> or just use "/*" to begin the comment.

Will do, thanks. And I'll check the whole code base for other instances;
I won't be surprise if I was sloop about that in more than one place.

> 
> > + * struct famfs_ioc_map
> > + *
> > + * This is the metadata that indicates where the memory is for a famfs file
> > + */
> > +struct famfs_ioc_map {
> > +	enum extent_type          extent_type;
> > +	enum famfs_file_type      file_type;
> > +	__u64                     file_size;
> > +	__u64                     ext_list_count;
> > +	struct famfs_extent       ext_list[FAMFS_MAX_EXTENTS];
> > +};
> > +
> > +#define FAMFSIOC_MAGIC 'u'
> 
> This 'u' value should be documented in
> Documentation/userspace-api/ioctl/ioctl-number.rst.
> 
> and if possible, you might want to use values like 0x5x or 0x8x
> that don't conflict with the ioctl numbers that are already used
> in the 'u' space.

Will do. I was trying to be too clever there, invoking "mu" for
micron. 

> 
> > +
> > +/* famfs file ioctl opcodes */
> > +#define FAMFSIOC_MAP_CREATE    _IOW(FAMFSIOC_MAGIC, 1, struct famfs_ioc_map)
> > +#define FAMFSIOC_MAP_GET       _IOR(FAMFSIOC_MAGIC, 2, struct famfs_ioc_map)
> > +#define FAMFSIOC_MAP_GETEXT    _IOR(FAMFSIOC_MAGIC, 3, struct famfs_extent)
> > +#define FAMFSIOC_NOP           _IO(FAMFSIOC_MAGIC,  4)
> > +
> > +#endif /* FAMFS_IOCTL_H */
> 
> -- 
> #Randy

Thank you for taking the time to look it over, Randy.

John

Re: [RFC PATCH 20/20] famfs: Add Kconfig and Makefile plumbing

[John Groves]

On 24/02/23 05:50PM, Randy Dunlap wrote:
> Hi,
> 
> On 2/23/24 09:42, John Groves wrote:
> > Add famfs Kconfig and Makefile, and hook into fs/Kconfig and fs/Makefile
> > 
> > Signed-off-by: John Groves <john@groves.net>
> > ---
> >  fs/Kconfig        |  2 ++
> >  fs/Makefile       |  1 +
> >  fs/famfs/Kconfig  | 10 ++++++++++
> >  fs/famfs/Makefile |  5 +++++
> >  4 files changed, 18 insertions(+)
> >  create mode 100644 fs/famfs/Kconfig
> >  create mode 100644 fs/famfs/Makefile
> > 
> > diff --git a/fs/Kconfig b/fs/Kconfig
> > index 89fdbefd1075..8a11625a54a2 100644
> > --- a/fs/Kconfig
> > +++ b/fs/Kconfig
> > @@ -141,6 +141,8 @@ source "fs/autofs/Kconfig"
> >  source "fs/fuse/Kconfig"
> >  source "fs/overlayfs/Kconfig"
> >  
> > +source "fs/famfs/Kconfig"
> > +
> >  menu "Caches"
> >  
> >  source "fs/netfs/Kconfig"
> > diff --git a/fs/Makefile b/fs/Makefile
> > index c09016257f05..382c1ea4f4c3 100644
> > --- a/fs/Makefile
> > +++ b/fs/Makefile
> > @@ -130,3 +130,4 @@ obj-$(CONFIG_EFIVAR_FS)		+= efivarfs/
> >  obj-$(CONFIG_EROFS_FS)		+= erofs/
> >  obj-$(CONFIG_VBOXSF_FS)		+= vboxsf/
> >  obj-$(CONFIG_ZONEFS_FS)		+= zonefs/
> > +obj-$(CONFIG_FAMFS)             += famfs/
> > diff --git a/fs/famfs/Kconfig b/fs/famfs/Kconfig
> > new file mode 100644
> > index 000000000000..e450928d8912
> > --- /dev/null
> > +++ b/fs/famfs/Kconfig
> > @@ -0,0 +1,10 @@
> > +
> > +
> > +config FAMFS
> > +       tristate "famfs: shared memory file system"
> > +       depends on DEV_DAX && FS_DAX
> > +       help
> > +         Support for the famfs file system. Famfs is a dax file system that
> > +	 can support scale-out shared access to fabric-attached memory
> > +	 (e.g. CXL shared memory). Famfs is not a general purpose file system;
> > +	 it is an enabler for data sets in shared memory.
> 
> Please use one tab + 2 spaces to indent help text (below the "help" keyword)
> as documented in Documentation/process/coding-style.rst.

Will do, thank you!

John

Re: [RFC PATCH 07/20] famfs: Add include/linux/famfs_ioctl.h

[Randy Dunlap]

Hi John,

On 2/23/24 18:23, John Groves wrote:
>>> +
>>> +#define FAMFSIOC_MAGIC 'u'
>> This 'u' value should be documented in
>> Documentation/userspace-api/ioctl/ioctl-number.rst.
>>
>> and if possible, you might want to use values like 0x5x or 0x8x
>> that don't conflict with the ioctl numbers that are already used
>> in the 'u' space.
> Will do. I was trying to be too clever there, invoking "mu" for
> micron. 

I might have been unclear about this one.
It's OK to use 'u' but the values 1-4 below conflict in the 'u' space:

'u'   00-1F  linux/smb_fs.h                                          gone
'u'   20-3F  linux/uvcvideo.h                                        USB video class host driver
'u'   40-4f  linux/udmabuf.h

so if you could use
'u'   50-5f
or
'u'   80-8f

then those conflicts wouldn't be there.
HTH.

>>> +
>>> +/* famfs file ioctl opcodes */
>>> +#define FAMFSIOC_MAP_CREATE    _IOW(FAMFSIOC_MAGIC, 1, struct famfs_ioc_map)
>>> +#define FAMFSIOC_MAP_GET       _IOR(FAMFSIOC_MAGIC, 2, struct famfs_ioc_map)
>>> +#define FAMFSIOC_MAP_GETEXT    _IOR(FAMFSIOC_MAGIC, 3, struct famfs_extent)
>>> +#define FAMFSIOC_NOP           _IO(FAMFSIOC_MAGIC,  4)

-- 
#Randy

Re: [RFC PATCH 16/20] famfs: Add fault counters

[Matthew Wilcox]

On Fri, Feb 23, 2024 at 03:50:33PM -0800, Dan Williams wrote:
> Certainly something like that would have satisified this sanity test use
> case. I will note that mm_account_fault() would need some help to figure
> out the size of the page table entry that got installed. Maybe
> extensions to vm_fault_reason to add VM_FAULT_P*D? That compliments
> VM_FAULT_FALLBACK to indicate whether, for example, the fallback went
> from PUD to PMD, or all the way back to PTE.

ugh, no, it's more complicated than that.  look at the recent changes to
set_ptes().  we can now install PTEs of many different sizes, depending
on the architecture.  someday i look forward to supporting all the page
sizes on parisc (4k, 16k, 64k, 256k, ... 4G)

Re: [RFC PATCH 16/20] famfs: Add fault counters

[Dan Williams]

Matthew Wilcox wrote:
> On Fri, Feb 23, 2024 at 03:50:33PM -0800, Dan Williams wrote:
> > Certainly something like that would have satisified this sanity test use
> > case. I will note that mm_account_fault() would need some help to figure
> > out the size of the page table entry that got installed. Maybe
> > extensions to vm_fault_reason to add VM_FAULT_P*D? That compliments
> > VM_FAULT_FALLBACK to indicate whether, for example, the fallback went
> > from PUD to PMD, or all the way back to PTE.
> 
> ugh, no, it's more complicated than that.  look at the recent changes to
> set_ptes().  we can now install PTEs of many different sizes, depending
> on the architecture.  someday i look forward to supporting all the page
> sizes on parisc (4k, 16k, 64k, 256k, ... 4G)

Nice!

There are enough bits in vm_fault_t to represent many page sizes instead
of the entry type as I suggested, but I would defer to you or Dave on
how to make "installed pte size" generically traceable per Dave's
suggestion.

Re: [RFC PATCH 07/20] famfs: Add include/linux/famfs_ioctl.h

[John Groves]

On 24/02/23 07:27PM, Randy Dunlap wrote:
> Hi John,
> 
> On 2/23/24 18:23, John Groves wrote:
> >>> +
> >>> +#define FAMFSIOC_MAGIC 'u'
> >> This 'u' value should be documented in
> >> Documentation/userspace-api/ioctl/ioctl-number.rst.
> >>
> >> and if possible, you might want to use values like 0x5x or 0x8x
> >> that don't conflict with the ioctl numbers that are already used
> >> in the 'u' space.
> > Will do. I was trying to be too clever there, invoking "mu" for
> > micron. 
> 
> I might have been unclear about this one.
> It's OK to use 'u' but the values 1-4 below conflict in the 'u' space:
> 
> 'u'   00-1F  linux/smb_fs.h                                          gone
> 'u'   20-3F  linux/uvcvideo.h                                        USB video class host driver
> 'u'   40-4f  linux/udmabuf.h
> 
> so if you could use
> 'u'   50-5f
> or
> 'u'   80-8f
> 
> then those conflicts wouldn't be there.
> HTH.
> 
> >>> +
> >>> +/* famfs file ioctl opcodes */
> >>> +#define FAMFSIOC_MAP_CREATE    _IOW(FAMFSIOC_MAGIC, 1, struct famfs_ioc_map)
> >>> +#define FAMFSIOC_MAP_GET       _IOR(FAMFSIOC_MAGIC, 2, struct famfs_ioc_map)
> >>> +#define FAMFSIOC_MAP_GETEXT    _IOR(FAMFSIOC_MAGIC, 3, struct famfs_extent)
> >>> +#define FAMFSIOC_NOP           _IO(FAMFSIOC_MAGIC,  4)
> 
> -- 
> #Randy

Thanks Randy; I think I'm the one that didn't read carefully enough.

Does this look right?

diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst
index 457e16f06e04..44a44809657b 100644
--- a/Documentation/userspace-api/ioctl/ioctl-number.rst
+++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
@@ -288,6 +288,7 @@ Code  Seq#    Include File                                           Comments
 'u'   00-1F  linux/smb_fs.h                                          gone
 'u'   20-3F  linux/uvcvideo.h                                        USB video class host driver
 'u'   40-4f  linux/udmabuf.h                                         userspace dma-buf misc device
+'u'   50-5F  linux/famfs_ioctl.h                                     famfs shared memory file system
 'v'   00-1F  linux/ext2_fs.h                                         conflict!
 'v'   00-1F  linux/fs.h                                              conflict!
 'v'   00-0F  linux/sonypi.h                                          conflict!
diff --git a/include/uapi/linux/famfs_ioctl.h b/include/uapi/linux/famfs_ioctl.h
index 6b3e6452d02f..57521898ed57 100644
--- a/include/uapi/linux/famfs_ioctl.h
+++ b/include/uapi/linux/famfs_ioctl.h
@@ -48,9 +48,9 @@ struct famfs_ioc_map {
 #define FAMFSIOC_MAGIC 'u'

 /* famfs file ioctl opcodes */
-#define FAMFSIOC_MAP_CREATE    _IOW(FAMFSIOC_MAGIC, 1, struct famfs_ioc_map)
-#define FAMFSIOC_MAP_GET       _IOR(FAMFSIOC_MAGIC, 2, struct famfs_ioc_map)
-#define FAMFSIOC_MAP_GETEXT    _IOR(FAMFSIOC_MAGIC, 3, struct famfs_extent)
-#define FAMFSIOC_NOP           _IO(FAMFSIOC_MAGIC,  4)
+#define FAMFSIOC_MAP_CREATE    _IOW(FAMFSIOC_MAGIC, 0x50, struct famfs_ioc_map)
+#define FAMFSIOC_MAP_GET       _IOR(FAMFSIOC_MAGIC, 0x51, struct famfs_ioc_map)
+#define FAMFSIOC_MAP_GETEXT    _IOR(FAMFSIOC_MAGIC, 0x52, struct famfs_extent)
+#define FAMFSIOC_NOP           _IO(FAMFSIOC_MAGIC,  0x53)

Thank you!
John

Re: [RFC PATCH 07/20] famfs: Add include/linux/famfs_ioctl.h

[Randy Dunlap]

On 2/24/24 15:32, John Groves wrote:
> On 24/02/23 07:27PM, Randy Dunlap wrote:
>> Hi John,
>>
>> On 2/23/24 18:23, John Groves wrote:
>>>>> +
>>>>> +#define FAMFSIOC_MAGIC 'u'
>>>> This 'u' value should be documented in
>>>> Documentation/userspace-api/ioctl/ioctl-number.rst.
>>>>
>>>> and if possible, you might want to use values like 0x5x or 0x8x
>>>> that don't conflict with the ioctl numbers that are already used
>>>> in the 'u' space.
>>> Will do. I was trying to be too clever there, invoking "mu" for
>>> micron. 
>>
>> I might have been unclear about this one.
>> It's OK to use 'u' but the values 1-4 below conflict in the 'u' space:
>>
>> 'u'   00-1F  linux/smb_fs.h                                          gone
>> 'u'   20-3F  linux/uvcvideo.h                                        USB video class host driver
>> 'u'   40-4f  linux/udmabuf.h
>>
>> so if you could use
>> 'u'   50-5f
>> or
>> 'u'   80-8f
>>
>> then those conflicts wouldn't be there.
>> HTH.
>>
>>>>> +
>>>>> +/* famfs file ioctl opcodes */
>>>>> +#define FAMFSIOC_MAP_CREATE    _IOW(FAMFSIOC_MAGIC, 1, struct famfs_ioc_map)
>>>>> +#define FAMFSIOC_MAP_GET       _IOR(FAMFSIOC_MAGIC, 2, struct famfs_ioc_map)
>>>>> +#define FAMFSIOC_MAP_GETEXT    _IOR(FAMFSIOC_MAGIC, 3, struct famfs_extent)
>>>>> +#define FAMFSIOC_NOP           _IO(FAMFSIOC_MAGIC,  4)
>>
>> -- 
>> #Randy
> 
> Thanks Randy; I think I'm the one that didn't read carefully enough.
> 
> Does this look right?
> 
> diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst
> index 457e16f06e04..44a44809657b 100644
> --- a/Documentation/userspace-api/ioctl/ioctl-number.rst
> +++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
> @@ -288,6 +288,7 @@ Code  Seq#    Include File                                           Comments
>  'u'   00-1F  linux/smb_fs.h                                          gone
>  'u'   20-3F  linux/uvcvideo.h                                        USB video class host driver
>  'u'   40-4f  linux/udmabuf.h                                         userspace dma-buf misc device
> +'u'   50-5F  linux/famfs_ioctl.h                                     famfs shared memory file system
>  'v'   00-1F  linux/ext2_fs.h                                         conflict!
>  'v'   00-1F  linux/fs.h                                              conflict!
>  'v'   00-0F  linux/sonypi.h                                          conflict!
> diff --git a/include/uapi/linux/famfs_ioctl.h b/include/uapi/linux/famfs_ioctl.h
> index 6b3e6452d02f..57521898ed57 100644
> --- a/include/uapi/linux/famfs_ioctl.h
> +++ b/include/uapi/linux/famfs_ioctl.h
> @@ -48,9 +48,9 @@ struct famfs_ioc_map {
>  #define FAMFSIOC_MAGIC 'u'
> 
>  /* famfs file ioctl opcodes */
> -#define FAMFSIOC_MAP_CREATE    _IOW(FAMFSIOC_MAGIC, 1, struct famfs_ioc_map)
> -#define FAMFSIOC_MAP_GET       _IOR(FAMFSIOC_MAGIC, 2, struct famfs_ioc_map)
> -#define FAMFSIOC_MAP_GETEXT    _IOR(FAMFSIOC_MAGIC, 3, struct famfs_extent)
> -#define FAMFSIOC_NOP           _IO(FAMFSIOC_MAGIC,  4)
> +#define FAMFSIOC_MAP_CREATE    _IOW(FAMFSIOC_MAGIC, 0x50, struct famfs_ioc_map)
> +#define FAMFSIOC_MAP_GET       _IOR(FAMFSIOC_MAGIC, 0x51, struct famfs_ioc_map)
> +#define FAMFSIOC_MAP_GETEXT    _IOR(FAMFSIOC_MAGIC, 0x52, struct famfs_extent)
> +#define FAMFSIOC_NOP           _IO(FAMFSIOC_MAGIC,  0x53)
> 
> Thank you!
> John
> 

Yes, that looks good.
Thanks.

-- 
#Randy

Re: [RFC PATCH 02/20] dev_dax_iomap: Add fs_dax_get() func to prepare dax for fs-dax usage

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:41:46 -0600
John Groves <John@Groves.net> wrote:

> This function should be called by fs-dax file systems after opening the
> devdax device. This adds holder_operations.
> 
> This function serves the same role as fs_dax_get_by_bdev(), which dax
> file systems call after opening the pmem block device.
> 
> Signed-off-by: John Groves <john@groves.net>

A few trivial comments form a first read to get my head around this.

Yeah, it is only an RFC, but who doesn't like tidy code? :)


> ---
>  drivers/dax/super.c | 38 ++++++++++++++++++++++++++++++++++++++
>  include/linux/dax.h |  5 +++++
>  2 files changed, 43 insertions(+)
> 
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index f4b635526345..fc96362de237 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -121,6 +121,44 @@ void fs_put_dax(struct dax_device *dax_dev, void *holder)
>  EXPORT_SYMBOL_GPL(fs_put_dax);
>  #endif /* CONFIG_BLOCK && CONFIG_FS_DAX */
>  
> +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
> +
> +/**
> + * fs_dax_get()

Smells like kernel doc but fairly sure it needs a short description.
Have you sanity checked for warnings when running scripts/kerneldoc on it?

> + *
> + * fs-dax file systems call this function to prepare to use a devdax device for fsdax.
Trivial but lines too long. Keep under 80 chars unless there is a strong
readability arguement for not doing so.


> + * This is like fs_dax_get_by_bdev(), but the caller already has struct dev_dax (and there
> + * is no bdev). The holder makes this exclusive.

Not familiar with this area: what does exclusive mean here?

> + *
> + * @dax_dev: dev to be prepared for fs-dax usage
> + * @holder: filesystem or mapped device inside the dax_device
> + * @hops: operations for the inner holder
> + *
> + * Returns: 0 on success, -1 on failure

Why not return < 0 and use somewhat useful return values?

> + */
> +int fs_dax_get(
> +	struct dax_device *dax_dev,
> +	void *holder,
> +	const struct dax_holder_operations *hops)

Match local style for indents - it's a bit inconsistent but probably...

int fs_dax_get(struct dad_device *dev_dax, void *holder,
	       const struct dax_holder_operations *hops)

> +{
> +	/* dax_dev->ops should have been populated by devm_create_dev_dax() */
> +	if (WARN_ON(!dax_dev->ops))
> +		return -1;
> +
> +	if (!dax_dev || !dax_alive(dax_dev) || !igrab(&dax_dev->inode))

You dereferenced dax_dev on the line above so check is too late or
unnecessary

> +		return -1;
> +
> +	if (cmpxchg(&dax_dev->holder_data, NULL, holder)) {
> +		pr_warn("%s: holder_data already set\n", __func__);

Perhaps nicer to use a pr_fmt() deal with the func name if you need it.
or make it pr_debug and let dynamic debug control formatting if anyone
wants the function name.

> +		return -1;
> +	}
> +	dax_dev->holder_ops = hops;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(fs_dax_get);
> +#endif /* DEV_DAX_IOMAP */
> +
>  enum dax_device_flags {
>  	/* !alive + rcu grace period == no new operations / mappings */
>  	DAXDEV_ALIVE,
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index b463502b16e1..e973289bfde3 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -57,7 +57,12 @@ struct dax_holder_operations {
>  
>  #if IS_ENABLED(CONFIG_DAX)
>  struct dax_device *alloc_dax(void *private, const struct dax_operations *ops);
> +
> +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
> +int fs_dax_get(struct dax_device *dax_dev, void *holder, const struct dax_holder_operations *hops);
line wrap < 80 chars

> +#endif
>  void *dax_holder(struct dax_device *dax_dev);
> +struct dax_device *inode_dax(struct inode *inode);

Unrelated change?

>  void put_dax(struct dax_device *dax_dev);
>  void kill_dax(struct dax_device *dax_dev);
>  void dax_write_cache(struct dax_device *dax_dev, bool wc);

Re: [RFC PATCH 03/20] dev_dax_iomap: Move dax_pgoff_to_phys from device.c to bus.c since both need it now

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:41:47 -0600
John Groves <John@Groves.net> wrote:

> bus.c can't call functions in device.c - that creates a circular linkage
> dependency.
> 
> Signed-off-by: John Groves <john@groves.net>

This also adds the export which you should mention!

Do they need it already? Seems like tense of patch title
may be wrong.

> ---
>  drivers/dax/bus.c    | 24 ++++++++++++++++++++++++
>  drivers/dax/device.c | 23 -----------------------
>  2 files changed, 24 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 1ff1ab5fa105..664e8c1b9930 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -1325,6 +1325,30 @@ static const struct device_type dev_dax_type = {
>  	.groups = dax_attribute_groups,
>  };
>  
> +/* see "strong" declaration in tools/testing/nvdimm/dax-dev.c  */
> +__weak phys_addr_t dax_pgoff_to_phys(struct dev_dax *dev_dax, pgoff_t pgoff,
> +			      unsigned long size)
> +{
> +	int i;
> +
> +	for (i = 0; i < dev_dax->nr_range; i++) {
> +		struct dev_dax_range *dax_range = &dev_dax->ranges[i];
> +		struct range *range = &dax_range->range;
> +		unsigned long long pgoff_end;
> +		phys_addr_t phys;
> +
> +		pgoff_end = dax_range->pgoff + PHYS_PFN(range_len(range)) - 1;
> +		if (pgoff < dax_range->pgoff || pgoff > pgoff_end)
> +			continue;
> +		phys = PFN_PHYS(pgoff - dax_range->pgoff) + range->start;
> +		if (phys + size - 1 <= range->end)
> +			return phys;
> +		break;
> +	}
> +	return -1;

Not related to your patch but returning -1 in a phys_addr_t isn't ideal.
I assume aim is all bits set as a marker, in which case
PHYS_ADDR_MAX from limits.h would make things clearer.

> +}
> +EXPORT_SYMBOL_GPL(dax_pgoff_to_phys);
> +
>  struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
>  {
>  	struct dax_region *dax_region = data->dax_region;
> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> index 93ebedc5ec8c..40ba660013cf 100644
> --- a/drivers/dax/device.c
> +++ b/drivers/dax/device.c
> @@ -50,29 +50,6 @@ static int check_vma(struct dev_dax *dev_dax, struct vm_area_struct *vma,
>  	return 0;
>  }
>  
> -/* see "strong" declaration in tools/testing/nvdimm/dax-dev.c */
> -__weak phys_addr_t dax_pgoff_to_phys(struct dev_dax *dev_dax, pgoff_t pgoff,
> -		unsigned long size)
> -{
> -	int i;
> -
> -	for (i = 0; i < dev_dax->nr_range; i++) {
> -		struct dev_dax_range *dax_range = &dev_dax->ranges[i];
> -		struct range *range = &dax_range->range;
> -		unsigned long long pgoff_end;
> -		phys_addr_t phys;
> -
> -		pgoff_end = dax_range->pgoff + PHYS_PFN(range_len(range)) - 1;
> -		if (pgoff < dax_range->pgoff || pgoff > pgoff_end)
> -			continue;
> -		phys = PFN_PHYS(pgoff - dax_range->pgoff) + range->start;
> -		if (phys + size - 1 <= range->end)
> -			return phys;
> -		break;
> -	}
> -	return -1;
> -}
> -
>  static void dax_set_mapping(struct vm_fault *vmf, pfn_t pfn,
>  			      unsigned long fault_size)
>  {

Re: [RFC PATCH 04/20] dev_dax_iomap: Save the kva from memremap

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:41:48 -0600
John Groves <John@Groves.net> wrote:

> Save the kva from memremap because we need it for iomap rw support
> 
> Prior to famfs, there were no iomap users of /dev/dax - so the virtual
> address from memremap was not needed.
> 
> Also: in some cases dev_dax_probe() is called with the first
> dev_dax->range offset past pgmap[0].range. In those cases we need to
> add the difference to virt_addr in order to have the physaddr's in
> dev_dax->ranges match dev_dax->virt_addr.

Probably good to have info on when this happens and preferably why
this dragon is there.

> 
> Dragons...
> 
> Signed-off-by: John Groves <john@groves.net>
> ---
>  drivers/dax/dax-private.h |  1 +
>  drivers/dax/device.c      | 15 +++++++++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
> index 446617b73aea..894eb1c66b4a 100644
> --- a/drivers/dax/dax-private.h
> +++ b/drivers/dax/dax-private.h
> @@ -63,6 +63,7 @@ struct dax_mapping {
>  struct dev_dax {
>  	struct dax_region *region;
>  	struct dax_device *dax_dev;
> +	u64 virt_addr;

Why as a u64? If it's a virt address why not just void *?

>  	unsigned int align;
>  	int target_node;
>  	bool dyn_id;
> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> index 40ba660013cf..6cd79d00fe1b 100644
> --- a/drivers/dax/device.c
> +++ b/drivers/dax/device.c
> @@ -372,6 +372,7 @@ static int dev_dax_probe(struct dev_dax *dev_dax)
>  	struct dax_device *dax_dev = dev_dax->dax_dev;
>  	struct device *dev = &dev_dax->dev;
>  	struct dev_pagemap *pgmap;
> +	u64 data_offset = 0;
>  	struct inode *inode;
>  	struct cdev *cdev;
>  	void *addr;
> @@ -426,6 +427,20 @@ static int dev_dax_probe(struct dev_dax *dev_dax)
>  	if (IS_ERR(addr))
>  		return PTR_ERR(addr);
>  
> +	/* Detect whether the data is at a non-zero offset into the memory */
> +	if (pgmap->range.start != dev_dax->ranges[0].range.start) {
> +		u64 phys = (u64)dev_dax->ranges[0].range.start;

Why the cast? Ranges use u64s internally.

> +		u64 pgmap_phys = (u64)dev_dax->pgmap[0].range.start;
> +		u64 vmemmap_shift = (u64)dev_dax->pgmap[0].vmemmap_shift;
> +
> +		if (!WARN_ON(pgmap_phys > phys))
> +			data_offset = phys - pgmap_phys;
> +
> +		pr_notice("%s: offset detected phys=%llx pgmap_phys=%llx offset=%llx shift=%llx\n",
> +		       __func__, phys, pgmap_phys, data_offset, vmemmap_shift);

pr_debug() + dynamic debug will then deal with __func__ for you.

> +	}
> +	dev_dax->virt_addr = (u64)addr + data_offset;
> +
>  	inode = dax_inode(dax_dev);
>  	cdev = inode->i_cdev;
>  	cdev_init(cdev, &dax_fops);

Re: [RFC PATCH 05/20] dev_dax_iomap: Add dax_operations for use by fs-dax on devdax

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:41:49 -0600
John Groves <John@Groves.net> wrote:

> Notes about this commit:
> 
> * These methods are based somewhat loosely on pmem_dax_ops from
>   drivers/nvdimm/pmem.c
> 
> * dev_dax_direct_access() is returns the hpa, pfn and kva. The kva was
>   newly stored as dev_dax->virt_addr by dev_dax_probe().
> 
> * The hpa/pfn are used for mmap (dax_iomap_fault()), and the kva is used
>   for read/write (dax_iomap_rw())
> 
> * dev_dax_recovery_write() and dev_dax_zero_page_range() have not been
>   tested yet. I'm looking for suggestions as to how to test those.
> 
> Signed-off-by: John Groves <john@groves.net>
> ---
>  drivers/dax/bus.c | 107 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 107 insertions(+)
> 
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 664e8c1b9930..06fcda810674 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -10,6 +10,12 @@
>  #include "dax-private.h"
>  #include "bus.h"
>  
> +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
> +#include <linux/backing-dev.h>
> +#include <linux/pfn_t.h>
> +#include <linux/range.h>
> +#endif
> +

Is it worth avoiding includes based on config? Probably not.

>  static DEFINE_MUTEX(dax_bus_lock);
>  
>  #define DAX_NAME_LEN 30
> @@ -1349,6 +1355,101 @@ __weak phys_addr_t dax_pgoff_to_phys(struct dev_dax *dev_dax, pgoff_t pgoff,
>  }
>  EXPORT_SYMBOL_GPL(dax_pgoff_to_phys);
>  
> +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
> +

> +
> +static long __dev_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff,
> +			     long nr_pages, enum dax_access_mode mode, void **kaddr,
> +			     pfn_t *pfn)
> +{
> +	struct dev_dax *dev_dax = dax_get_private(dax_dev);
> +	size_t dax_size = dev_dax_size(dev_dax);
> +	size_t size = nr_pages << PAGE_SHIFT;
> +	size_t offset = pgoff << PAGE_SHIFT;
> +	phys_addr_t phys;
> +	u64 virt_addr = dev_dax->virt_addr + offset;
> +	pfn_t local_pfn;
> +	u64 flags = PFN_DEV|PFN_MAP;
> +
> +	WARN_ON(!dev_dax->virt_addr); /* virt_addr must be saved for direct_access */
Fair enough, but from local code point of view, does it make sense to check this
if !kaddr as we won't use this.
> +
> +	phys = dax_pgoff_to_phys(dev_dax, pgoff, nr_pages << PAGE_SHIFT);
> +
> +	if (kaddr)
> +		*kaddr = (void *)virt_addr;

Back to earlier comment on virt_addr as a void *. Definitely looking like
that would be more accurate and simpler!  Also not much point in computing
virt_addr unless kaddr is good.

> +
> +	local_pfn = phys_to_pfn_t(phys, flags); /* are flags correct? */
If you aren't going to do anything with it for !pfn, move it under the if (pfn).

> +	if (pfn)
> +		*pfn = local_pfn;
> +
> +	/* This the valid size at the specified address */
> +	return PHYS_PFN(min_t(size_t, size, dax_size - offset));
> +}
> +

> +
> +static const struct dax_operations dev_dax_ops = {
> +	.direct_access = dev_dax_direct_access,
> +	.zero_page_range = dev_dax_zero_page_range,
> +	.recovery_write = dev_dax_recovery_write,
> +};
> +
> +#endif /* IS_ENABLED(CONFIG_DEV_DAX_IOMAP) */
> +
>  struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
>  {
>  	struct dax_region *dax_region = data->dax_region;
> @@ -1404,11 +1505,17 @@ struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
>  		}
>  	}
>  

If we were to make this 

	if (IS_ENABLED(CONFIG_DEV_DAX_IOMAP))

etc can we avoid the ifdef stuff above and let dead code removal deal with it?
Might need a few stubs - I haven't tried.

> +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
> +	/* holder_ops currently populated separately in a slightly hacky way */
> +	dax_dev = alloc_dax(dev_dax, &dev_dax_ops);
> +#else
>  	/*
>  	 * No dax_operations since there is no access to this device outside of
>  	 * mmap of the resulting character device.
>  	 */
>  	dax_dev = alloc_dax(dev_dax, NULL);
> +#endif
> +
>  	if (IS_ERR(dax_dev)) {
>  		rc = PTR_ERR(dax_dev);
>  		goto err_alloc_dax;

Re: [RFC PATCH 06/20] dev_dax_iomap: Add CONFIG_DEV_DAX_IOMAP kernel build parameter

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:41:50 -0600
John Groves <John@Groves.net> wrote:

> Add the CONFIG_DEV_DAX_IOMAP kernel config parameter to control building
> of the iomap functionality to support fsdax on devdax.

I would squash with previous patch.

Only reason I ever see for separate Kconfig patches is when there is something
complex in the dependencies and you want to talk about it in depth in the
patch description. That's not true here so no need for separate patch.

> 
> Signed-off-by: John Groves <john@groves.net>
> ---
>  drivers/dax/Kconfig | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
> index a88744244149..b1ebcc77120b 100644
> --- a/drivers/dax/Kconfig
> +++ b/drivers/dax/Kconfig
> @@ -78,4 +78,10 @@ config DEV_DAX_KMEM
>  
>  	  Say N if unsure.
>  
> +config DEV_DAX_IOMAP
> +       depends on DEV_DAX && DAX
> +       def_bool y
> +       help
> +         Support iomap mapping of devdax devices (for FS-DAX file
> +         systems that reside on character /dev/dax devices)
>  endif

Re: [RFC PATCH 07/20] famfs: Add include/linux/famfs_ioctl.h

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:41:51 -0600
John Groves <John@Groves.net> wrote:

> Add uapi include file for famfs. The famfs user space uses ioctl on
> individual files to pass in mapping information and file size. This
> would be hard to do via sysfs or other means, since it's
> file-specific.
> 
> Signed-off-by: John Groves <john@groves.net>
> ---
>  include/uapi/linux/famfs_ioctl.h | 56 ++++++++++++++++++++++++++++++++
>  1 file changed, 56 insertions(+)
>  create mode 100644 include/uapi/linux/famfs_ioctl.h
> 
> diff --git a/include/uapi/linux/famfs_ioctl.h b/include/uapi/linux/famfs_ioctl.h
> new file mode 100644
> index 000000000000..6b3e6452d02f
> --- /dev/null
> +++ b/include/uapi/linux/famfs_ioctl.h
> @@ -0,0 +1,56 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/*
> + * famfs - dax file system for shared fabric-attached memory
> + *
> + * Copyright 2023-2024 Micron Technology, Inc.
> + *
> + * This file system, originally based on ramfs the dax support from xfs,
> + * is intended to allow multiple host systems to mount a common file system
> + * view of dax files that map to shared memory.
> + */
> +#ifndef FAMFS_IOCTL_H
> +#define FAMFS_IOCTL_H
> +
> +#include <linux/ioctl.h>
> +#include <linux/uuid.h>
> +
> +#define FAMFS_MAX_EXTENTS 2
Why 2?
> +
> +enum extent_type {
> +	SIMPLE_DAX_EXTENT = 13,

Comment on this would be good to have

> +	INVALID_EXTENT_TYPE,
> +};
> +
> +struct famfs_extent {
> +	__u64              offset;
> +	__u64              len;
> +};
> +
> +enum famfs_file_type {
> +	FAMFS_REG,
> +	FAMFS_SUPERBLOCK,
> +	FAMFS_LOG,
> +};
> +
> +/**
> + * struct famfs_ioc_map
> + *
> + * This is the metadata that indicates where the memory is for a famfs file
> + */
> +struct famfs_ioc_map {
> +	enum extent_type          extent_type;
> +	enum famfs_file_type      file_type;

These are going to be potentially varying in size depending on arch, compiler
settings etc.  Been a while, but I though best practice for uapi was always
fixed size elements even though we lose the typing.


> +	__u64                     file_size;
> +	__u64                     ext_list_count;
> +	struct famfs_extent       ext_list[FAMFS_MAX_EXTENTS];
> +};
> +
> +#define FAMFSIOC_MAGIC 'u'
> +
> +/* famfs file ioctl opcodes */
> +#define FAMFSIOC_MAP_CREATE    _IOW(FAMFSIOC_MAGIC, 1, struct famfs_ioc_map)
> +#define FAMFSIOC_MAP_GET       _IOR(FAMFSIOC_MAGIC, 2, struct famfs_ioc_map)
> +#define FAMFSIOC_MAP_GETEXT    _IOR(FAMFSIOC_MAGIC, 3, struct famfs_extent)
> +#define FAMFSIOC_NOP           _IO(FAMFSIOC_MAGIC,  4)
> +
> +#endif /* FAMFS_IOCTL_H */

Re: [RFC PATCH 08/20] famfs: Add famfs_internal.h

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:41:52 -0600
John Groves <John@Groves.net> wrote:

> Add the famfs_internal.h include file. This contains internal data
> structures such as the per-file metadata structure (famfs_file_meta)
> and extent formats.
> 
> Signed-off-by: John Groves <john@groves.net>
Hi John,

Build this up as you add the definitions in later patches.

Separate header patches just make people jump back and forth when trying
to review.  Obviously more work to build this stuff up cleanly but
it's worth doing to save review time.

Generally I'd plumb up Kconfig and Makefile a the beginning as it means
that the set is bisectable and we can check the logic of building each stage.
That is harder to do but tends to bring benefits in forcing clear step
wise approach on a patch set. Feel free to ignore this one though as it
can slow things down.

A few trivial comments inline.

> ---
>  fs/famfs/famfs_internal.h | 53 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 53 insertions(+)
>  create mode 100644 fs/famfs/famfs_internal.h
> 
> diff --git a/fs/famfs/famfs_internal.h b/fs/famfs/famfs_internal.h
> new file mode 100644
> index 000000000000..af3990d43305
> --- /dev/null
> +++ b/fs/famfs/famfs_internal.h
> @@ -0,0 +1,53 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * famfs - dax file system for shared fabric-attached memory
> + *
> + * Copyright 2023-2024 Micron Technology, Inc.
> + *
> + * This file system, originally based on ramfs the dax support from xfs,
> + * is intended to allow multiple host systems to mount a common file system
> + * view of dax files that map to shared memory.
> + */
> +#ifndef FAMFS_INTERNAL_H
> +#define FAMFS_INTERNAL_H
> +
> +#include <linux/atomic.h>

Why?

> +#include <linux/famfs_ioctl.h>
> +
> +#define FAMFS_MAGIC 0x87b282ff
> +
> +#define FAMFS_BLKDEV_MODE (FMODE_READ|FMODE_WRITE)

Spaces around | 

> +
> +extern const struct file_operations      famfs_file_operations;

I wouldn't force alignment. It rots too often as new stuff gets added
and doesn't really help readability much.

> +
> +/*
> + * Each famfs dax file has this hanging from its inode->i_private.
> + */
> +struct famfs_file_meta {
> +	int                   error;
> +	enum famfs_file_type  file_type;
> +	size_t                file_size;
> +	enum extent_type      tfs_extent_type;
> +	size_t                tfs_extent_ct;
> +	struct famfs_extent   tfs_extents[];  /* flexible array */

Comment kind of obvious ;) I'd drop it.  Though we have
magic markings for __counted_by which would be good to use from the start.



> +};
> +
> +struct famfs_mount_opts {
> +	umode_t mode;
> +};
> +
> +extern const struct iomap_ops             famfs_iomap_ops;
> +extern const struct vm_operations_struct  famfs_file_vm_ops;
> +
> +#define ROOTDEV_STRLEN 80

Why?  You aren't creating an array of this size here so I can't
immediately see what the define is for.

> +
> +struct famfs_fs_info {
> +	struct famfs_mount_opts  mount_opts;
> +	struct file             *dax_filp;
> +	struct dax_device       *dax_devp;
> +	struct bdev_handle      *bdev_handle;
> +	struct list_head         fsi_list;
> +	char                    *rootdev;
> +};
> +
> +#endif /* FAMFS_INTERNAL_H */

Re: [RFC PATCH 09/20] famfs: Add super_operations

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:41:53 -0600
John Groves <John@Groves.net> wrote:

> Introduce the famfs superblock operations
> 
> Signed-off-by: John Groves <john@groves.net>
> ---
>  fs/famfs/famfs_inode.c | 72 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 72 insertions(+)
>  create mode 100644 fs/famfs/famfs_inode.c
> 
> diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> new file mode 100644
> index 000000000000..3329aff000d1
> --- /dev/null
> +++ b/fs/famfs/famfs_inode.c
> @@ -0,0 +1,72 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * famfs - dax file system for shared fabric-attached memory
> + *
> + * Copyright 2023-2024 Micron Technology, inc
> + *
> + * This file system, originally based on ramfs the dax support from xfs,
> + * is intended to allow multiple host systems to mount a common file system
> + * view of dax files that map to shared memory.
> + */
> +
> +#include <linux/fs.h>
> +#include <linux/pagemap.h>
> +#include <linux/highmem.h>
> +#include <linux/time.h>
> +#include <linux/init.h>
> +#include <linux/string.h>
> +#include <linux/backing-dev.h>
> +#include <linux/sched.h>
> +#include <linux/parser.h>
> +#include <linux/magic.h>
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +#include <linux/fs_context.h>
> +#include <linux/fs_parser.h>
> +#include <linux/seq_file.h>
> +#include <linux/dax.h>
> +#include <linux/hugetlb.h>
> +#include <linux/uio.h>
> +#include <linux/iomap.h>
> +#include <linux/path.h>
> +#include <linux/namei.h>
> +#include <linux/pfn_t.h>
> +#include <linux/blkdev.h>

That's a lot of header for such a small patch.. I'm going to guess
they aren't all used - bring them in as you need them - I hope
you never need some of these!


> +
> +#include "famfs_internal.h"
> +
> +#define FAMFS_DEFAULT_MODE	0755
> +
> +static const struct super_operations famfs_ops;
> +static const struct inode_operations famfs_file_inode_operations;
> +static const struct inode_operations famfs_dir_inode_operations;

Why are these all up here?

> +
> +/**********************************************************************************
> + * famfs super_operations
> + *
> + * TODO: implement a famfs_statfs() that shows size, free and available space, etc.
> + */
> +
> +/**
> + * famfs_show_options() - Display the mount options in /proc/mounts.
Run kernel doc script + fix all warnings.

> + */
> +static int famfs_show_options(
> +	struct seq_file *m,
> +	struct dentry   *root)
Not that familiar with fs code, but this unusual kernel style. I'd go with 
something more common

static int famfs_show_options(struct seq_file *m, struct dentry *root)

> +{
> +	struct famfs_fs_info *fsi = root->d_sb->s_fs_info;
> +
> +	if (fsi->mount_opts.mode != FAMFS_DEFAULT_MODE)
> +		seq_printf(m, ",mode=%o", fsi->mount_opts.mode);
> +
> +	return 0;
> +}
> +
> +static const struct super_operations famfs_ops = {
> +	.statfs		= simple_statfs,
> +	.drop_inode	= generic_delete_inode,
> +	.show_options	= famfs_show_options,
> +};
> +
> +
One blank line probably fine.


Add the rest of the stuff a module normally has, author etc in this
patch.

> +MODULE_LICENSE("GPL");

Re: [RFC PATCH 10/20] famfs: famfs_open_device() & dax_holder_operations

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:41:54 -0600
John Groves <John@Groves.net> wrote:

> Famfs works on both /dev/pmem and /dev/dax devices. This commit introduces
> the function that opens a block (pmem) device and the struct
> dax_holder_operations that are needed for that ABI.
> 
> In this commit, support for opening character /dev/dax is stubbed. A
> later commit introduces this capability.
> 
> Signed-off-by: John Groves <john@groves.net>

Formatting comments mostly same as previous patches, so I'll stop repeating them.

> ---
>  fs/famfs/famfs_inode.c | 83 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 83 insertions(+)
> 
> diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> index 3329aff000d1..82c861998093 100644
> --- a/fs/famfs/famfs_inode.c
> +++ b/fs/famfs/famfs_inode.c
> @@ -68,5 +68,88 @@ static const struct super_operations famfs_ops = {
>  	.show_options	= famfs_show_options,
>  };
>  
> +/***************************************************************************************
> + * dax_holder_operations for block dax
> + */
> +
> +static int
> +famfs_blk_dax_notify_failure(
> +	struct dax_device	*dax_devp,
> +	u64			offset,
> +	u64			len,
> +	int			mf_flags)
> +{
> +
> +	pr_err("%s: dax_devp %llx offset %llx len %lld mf_flags %x\n",
> +	       __func__, (u64)dax_devp, (u64)offset, (u64)len, mf_flags);
> +	return -EOPNOTSUPP;
> +}
> +
> +const struct dax_holder_operations famfs_blk_dax_holder_ops = {
> +	.notify_failure		= famfs_blk_dax_notify_failure,
> +};
> +
> +static int
> +famfs_open_char_device(
> +	struct super_block *sb,
> +	struct fs_context  *fc)
> +{
> +	pr_err("%s: Root device is %s, but your kernel does not support famfs on /dev/dax\n",
> +	       __func__, fc->source);
> +	return -ENODEV;
> +}
> +
> +/**
> + * famfs_open_device()
> + *
> + * Open the memory device. If it looks like /dev/dax, call famfs_open_char_device().
> + * Otherwise try to open it as a block/pmem device.
> + */
> +static int
> +famfs_open_device(
> +	struct super_block *sb,
> +	struct fs_context  *fc)
> +{
> +	struct famfs_fs_info *fsi = sb->s_fs_info;
> +	struct dax_device    *dax_devp;
> +	u64 start_off = 0;
> +	struct bdev_handle   *handlep;
Definitely don't force alignment in local parameter definitions.
Always goes wrong and makes for unreadable mess in patches!

> +
> +	if (fsi->dax_devp) {
> +		pr_err("%s: already mounted\n", __func__);
Fine to fail but worth a error message? Not sure on convention on this but seems noisy
and maybe in userspace control which isn't good.
> +		return -EALREADY;
> +	}
> +
> +	if (strstr(fc->source, "/dev/dax")) /* There is probably a better way to check this */
> +		return famfs_open_char_device(sb, fc);
> +
> +	if (!strstr(fc->source, "/dev/pmem")) { /* There is probably a better way to check this */
> +		pr_err("%s: primary backing dev (%s) is not pmem\n",
> +		       __func__, fc->source);
> +		return -EINVAL;
> +	}
> +
> +	handlep = bdev_open_by_path(fc->source, FAMFS_BLKDEV_MODE, fsi, &fs_holder_ops);
> +	if (IS_ERR(handlep->bdev)) {
> +		pr_err("%s: failed blkdev_get_by_path(%s)\n", __func__, fc->source);
> +		return PTR_ERR(handlep->bdev);
> +	}
> +
> +	dax_devp = fs_dax_get_by_bdev(handlep->bdev, &start_off,
> +				      fsi  /* holder */,
> +				      &famfs_blk_dax_holder_ops);
> +	if (IS_ERR(dax_devp)) {
> +		pr_err("%s: unable to get daxdev from handlep->bdev\n", __func__);
> +		bdev_release(handlep);
> +		return -ENODEV;
> +	}
> +	fsi->bdev_handle = handlep;
> +	fsi->dax_devp    = dax_devp;
> +
> +	pr_notice("%s: root device is block dax (%s)\n", __func__, fc->source);

pr_debug()  Kernel log is too noisy anyway! + I'd assume we can tell this succeeded
in lots of other ways.


> +	return 0;
> +}
> +
> +
>  
>  MODULE_LICENSE("GPL");

Re: [RFC PATCH 11/20] famfs: Add fs_context_operations

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:41:55 -0600
John Groves <John@Groves.net> wrote:

> This commit introduces the famfs fs_context_operations and
> famfs_get_inode() which is used by the context operations.
> 
> Signed-off-by: John Groves <john@groves.net>
Trivial comments inline.

> ---
>  fs/famfs/famfs_inode.c | 178 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 178 insertions(+)
> 
> diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> index 82c861998093..f98f82962d7b 100644
> --- a/fs/famfs/famfs_inode.c
> +++ b/fs/famfs/famfs_inode.c
> @@ -41,6 +41,50 @@ static const struct super_operations famfs_ops;
>  static const struct inode_operations famfs_file_inode_operations;
>  static const struct inode_operations famfs_dir_inode_operations;
>  
> +static struct inode *famfs_get_inode(
> +	struct super_block *sb,
> +	const struct inode *dir,
> +	umode_t             mode,
> +	dev_t               dev)
> +{
> +	struct inode *inode = new_inode(sb);
> +
> +	if (inode) {
reverse logic would be simpler and reduce indent.

	if (!inode)
		return NULL;


> +		struct timespec64       tv;
> +
> +		inode->i_ino = get_next_ino();
> +		inode_init_owner(&nop_mnt_idmap, inode, dir, mode);
> +		inode->i_mapping->a_ops = &ram_aops;
> +		mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
> +		mapping_set_unevictable(inode->i_mapping);
> +		tv = inode_set_ctime_current(inode);
> +		inode_set_mtime_to_ts(inode, tv);
> +		inode_set_atime_to_ts(inode, tv);
> +
> +		switch (mode & S_IFMT) {
> +		default:
> +			init_special_inode(inode, mode, dev);
> +			break;
> +		case S_IFREG:
> +			inode->i_op = &famfs_file_inode_operations;
> +			inode->i_fop = &famfs_file_operations;
> +			break;
> +		case S_IFDIR:
> +			inode->i_op = &famfs_dir_inode_operations;
> +			inode->i_fop = &simple_dir_operations;
> +
> +			/* Directory inodes start off with i_nlink == 2 (for "." entry) */
> +			inc_nlink(inode);
> +			break;
> +		case S_IFLNK:
> +			inode->i_op = &page_symlink_inode_operations;
> +			inode_nohighmem(inode);
> +			break;
> +		}
> +	}
> +	return inode;
> +}
> +
>  /**********************************************************************************
>   * famfs super_operations
>   *
> @@ -150,6 +194,140 @@ famfs_open_device(
>  	return 0;
>  }
>  
> +/*****************************************************************************************
> + * fs_context_operations
> + */
> +static int
> +famfs_fill_super(
> +	struct super_block *sb,
> +	struct fs_context  *fc)
> +{
> +	struct famfs_fs_info *fsi = sb->s_fs_info;
> +	struct inode *inode;
> +	int rc = 0;
Always initialized so no need to do it here.

> +
> +	sb->s_maxbytes		= MAX_LFS_FILESIZE;
> +	sb->s_blocksize		= PAGE_SIZE;
> +	sb->s_blocksize_bits	= PAGE_SHIFT;
> +	sb->s_magic		= FAMFS_MAGIC;
> +	sb->s_op		= &famfs_ops;
> +	sb->s_time_gran		= 1;
> +
> +	rc = famfs_open_device(sb, fc);
> +	if (rc)
> +		goto out;
		return rc; //unless you need to do more in out in later patch..

> +
> +	inode = famfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0);
> +	sb->s_root = d_make_root(inode);
> +	if (!sb->s_root)
> +		rc = -ENOMEM;
		return -ENOMEM;

	return 0;

> +
> +out:
> +	return rc;
> +}
> +
> +enum famfs_param {
> +	Opt_mode,
> +	Opt_dax,
Why capital O?

> +};
> +

...

> +
> +static DEFINE_MUTEX(famfs_context_mutex);
> +static LIST_HEAD(famfs_context_list);
> +
> +static int famfs_get_tree(struct fs_context *fc)
> +{
> +	struct famfs_fs_info *fsi_entry;
> +	struct famfs_fs_info *fsi = fc->s_fs_info;
> +
> +	fsi->rootdev = kstrdup(fc->source, GFP_KERNEL);
> +	if (!fsi->rootdev)
> +		return -ENOMEM;
> +
> +	/* Fail if famfs is already mounted from the same device */
> +	mutex_lock(&famfs_context_mutex);

New toys might be good to use from start to avoid need for explicit
unlocks in error paths.

	scoped_guard(mutex, &famfs_context_mutex) {
		list_for_each_entry(fsi_entry, &famfs_context_list, fsi_list) {
			if (strcmp(fsi_entry->rootdev, cs_source) == 0) {
			//could invert with a continue to reduce indent
			// or factor this out as a little helper.
			// famfs_check_not_mounted()
				pr_err();
				return -EALREADY;
			}
		}	
		list_add(&fsi->fs_list, &famfs_context_list);
	}

	return get_tree_nodev(...

> +	list_for_each_entry(fsi_entry, &famfs_context_list, fsi_list) {
> +		if (strcmp(fsi_entry->rootdev, fc->source) == 0) {
> +			mutex_unlock(&famfs_context_mutex);
> +			pr_err("%s: already mounted from rootdev %s\n", __func__, fc->source);
> +			return -EALREADY;
> +		}
> +	}
> +
> +	list_add(&fsi->fsi_list, &famfs_context_list);
> +	mutex_unlock(&famfs_context_mutex);
> +
> +	return get_tree_nodev(fc, famfs_fill_super);
> +
> +}

>  
>  MODULE_LICENSE("GPL");

Re: [RFC PATCH 12/20] famfs: Add inode_operations and file_system_type

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:41:56 -0600
John Groves <John@Groves.net> wrote:

> This commit introduces the famfs inode_operations. There is nothing really
> unique to famfs here in the inode_operations..
> 
> This commit also introduces the famfs_file_system_type struct and the
> famfs_kill_sb() function.
> 
> Signed-off-by: John Groves <john@groves.net>

Trivial comments only.

> +
> +/*
> + * File creation. Allocate an inode, and we're done..
> + */
> +/* SMP-safe */
> +static int
> +famfs_mknod(
> +	struct mnt_idmap *idmap,
> +	struct inode     *dir,
> +	struct dentry    *dentry,
> +	umode_t           mode,
> +	dev_t             dev)
> +{
> +	struct inode *inode = famfs_get_inode(dir->i_sb, dir, mode, dev);
> +	int error           = -ENOSPC;
> +
> +	if (inode) {

As below. I would flip it for cleaner code/ shorter indent etc.

> +		struct timespec64       tv;
> +
> +		d_instantiate(dentry, inode);
> +		dget(dentry);	/* Extra count - pin the dentry in core */
> +		error = 0;
> +		tv = inode_set_ctime_current(inode);
> +		inode_set_mtime_to_ts(inode, tv);
> +		inode_set_atime_to_ts(inode, tv);
> +	}
> +	return error;
> +}
> +
> +static int famfs_mkdir(
> +	struct mnt_idmap *idmap,
> +	struct inode     *dir,
> +	struct dentry    *dentry,
> +	umode_t           mode)
> +{
> +	int retval = famfs_mknod(&nop_mnt_idmap, dir, dentry, mode | S_IFDIR, 0);
> +
> +	if (!retval)
> +		inc_nlink(dir);

Copy local style, so fine if this is common pattern, otherwise I'd go for
consistent error cases out of line as easier for us sleepy caffeine 
deprived reviewers.


	if (retval)
		return retval;

	inc_nlink(dir);

	return 0;
> +
> +	return retval;
> +}
> +
> +static int famfs_create(
> +	struct mnt_idmap *idmap,
> +	struct inode     *dir,
> +	struct dentry    *dentry,
> +	umode_t           mode,
> +	bool              excl)
> +{
> +	return famfs_mknod(&nop_mnt_idmap, dir, dentry, mode | S_IFREG, 0);
> +}
> +
> +static int famfs_symlink(
> +	struct mnt_idmap *idmap,
> +	struct inode     *dir,
> +	struct dentry    *dentry,
> +	const char       *symname)
> +{
> +	struct inode *inode;
> +	int error = -ENOSPC;
> +
> +	inode = famfs_get_inode(dir->i_sb, dir, S_IFLNK | 0777, 0);
	if (!inode)
		return -ENOSPC;

> +	if (inode) {
> +		int l = strlen(symname)+1;
> +
> +		error = page_symlink(inode, symname, l);
	if (error) {
		iput(inode);
		return error;
	}
	
	...

> +		if (!error) {
> +			struct timespec64       tv;
> +
> +			d_instantiate(dentry, inode);
> +			dget(dentry);
> +			tv = inode_set_ctime_current(inode);
> +			inode_set_mtime_to_ts(inode, tv);
> +			inode_set_atime_to_ts(inode, tv);
> +		} else
> +			iput(inode);
> +	}
> +	return error;
> +}

Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

[John Groves]

On 24/02/23 04:07PM, Luis Chamberlain wrote:
> On Fri, Feb 23, 2024 at 11:41:44AM -0600, John Groves wrote:
> > This patch set introduces famfs[1] - a special-purpose fs-dax file system
> > for sharable disaggregated or fabric-attached memory (FAM). Famfs is not
> > CXL-specific in anyway way.
> > 
> > * Famfs creates a simple access method for storing and sharing data in
> >   sharable memory. The memory is exposed and accessed as memory-mappable
> >   dax files.
> > * Famfs supports multiple hosts mounting the same file system from the
> >   same memory (something existing fs-dax file systems don't do).
> > * A famfs file system can be created on either a /dev/pmem device in fs-dax
> >   mode, or a /dev/dax device in devdax mode (the latter depending on
> >   patches 2-6 of this series).
> > 
> > The famfs kernel file system is part the famfs framework; additional
> > components in user space[2] handle metadata and direct the famfs kernel
> > module to instantiate files that map to specific memory. The famfs user
> > space has documentation and a reasonably thorough test suite.
> > 
> > The famfs kernel module never accesses the shared memory directly (either
> > data or metadata). Because of this, shared memory managed by the famfs
> > framework does not create a RAS "blast radius" problem that should be able
> > to crash or de-stabilize the kernel. Poison or timeouts in famfs memory
> > can be expected to kill apps via SIGBUS and cause mounts to be disabled
> > due to memory failure notifications.
> > 
> > Famfs does not attempt to solve concurrency or coherency problems for apps,
> > although it does solve these problems in regard to its own data structures.
> > Apps may encounter hard concurrency problems, but there are use cases that
> > are imminently useful and uncomplicated from a concurrency perspective:
> > serial sharing is one (only one host at a time has access), and read-only
> > concurrent sharing is another (all hosts can read-cache without worry).
> 
> Can you do me a favor, curious if you can run a test like this:
> 
> fio -name=ten-1g-per-thread --nrfiles=10 -bs=2M -ioengine=io_uring                                                                                                                            
> -direct=1                                                                                                                                                                                    
> --group_reporting=1 --alloc-size=1048576 --filesize=1GiB                                                                                                                                      
> --readwrite=write --fallocate=none --numjobs=$(nproc) --create_on_open=1                                                                                                                      
> --directory=/mnt 
> 
> What do you get for throughput?
> 
> The absolute large the system an capacity the better.
> 
>   Luis

Luis,

First, thanks for paying attention. I think I need to clarify a few things
about famfs and then check how that modifies your ask; apologies if some
are obvious. You should tell me whether this is still interesting given
these clarifications and limitations, or if there is something else you'd
like to see tested instead. But read on, I have run the closest tests I
can.

Famfs files just map to dax memory; they don't have a backing store. So the
io_uring and direct=1 options don't work. The coolness is that the files &
memory can be shared, and that apps can deal with files rather than having
to learn new abstractions.

Famfs files are never allocate-on-write, so (--fallocate=none is ok, but
"actual" fallocate doesn't work - and --create_on_open desn't work). But it
seems to be happy if I preallocate the files for the test.

I don't currently have custody of a really beefy system (can get one, just
need to plan ahead). My primary dev system is a 48 HT core E5-2690 v3 @
2.60G (around 10 years old).

I have a 128GB dax device that is backed by ddr4 via efi_fake_mem. So I
can't do 48 x 10 x 1G, but I can do 48 x 10 x 256M. I ran this on
ddr4-backed famfs, and xfs backed by a sata ssd. Probably not fair, but
it's what I have on a Sunday evening.

I can get access to a beefy system with real cxl memory, though don't
assume 100% I can report performance on that - will check into that. But
think about what you're looking for in light of the fact that famfs is just
a shared-memory file system, so no O_DIRECT or io_uring. Basically just
(hopefully efficient) vma fault handling and metadata distribution.

###

Here is famfs. I had to drop the io_uring and script up alloc/creation
of the files (sudo famfs creat -s 256M /mnt/famfs/foo)

$ fio -name=ten-256m-per-thread --nrfiles=10 -bs=2M --group_reporting=1 --alloc-size=1048576 --filesize=100MiB --readwrite=write --fallocate=none --numjobs=48 --create_on_open=0 --directory=/mnt/famfs
ten-256m-per-thread: (g=0): rw=write, bs=(R) 2048KiB-2048KiB, (W) 2048KiB-2048KiB, (T) 2048KiB-2048KiB, ioengine=psync, iodepth=1
...
fio-3.33
Starting 48 processes
Jobs: 40 (f=400)
ten-256m-per-thread: (groupid=0, jobs=48): err= 0: pid=201738: Mon Feb 26 06:48:21 2024
  write: IOPS=15.2k, BW=29.6GiB/s (31.8GB/s)(44.7GiB/1511msec); 0 zone resets
    clat (usec): min=156, max=54645, avg=2077.40, stdev=1730.77
     lat (usec): min=171, max=54686, avg=2404.87, stdev=2056.50
    clat percentiles (usec):
     |  1.00th=[  196],  5.00th=[  243], 10.00th=[  367], 20.00th=[  644],
     | 30.00th=[  857], 40.00th=[ 1352], 50.00th=[ 1876], 60.00th=[ 2442],
     | 70.00th=[ 2868], 80.00th=[ 3228], 90.00th=[ 3884], 95.00th=[ 4555],
     | 99.00th=[ 6390], 99.50th=[ 7439], 99.90th=[16450], 99.95th=[23987],
     | 99.99th=[46924]
   bw (  MiB/s): min=21544, max=28034, per=81.80%, avg=24789.35, stdev=130.16, samples=81
   iops        : min=10756, max=14000, avg=12378.00, stdev=65.06, samples=81
  lat (usec)   : 250=5.42%, 500=9.67%, 750=8.07%, 1000=11.77%
  lat (msec)   : 2=16.87%, 4=39.59%, 10=8.37%, 20=0.17%, 50=0.07%
  lat (msec)   : 100=0.01%
  cpu          : usr=13.26%, sys=81.62%, ctx=2075, majf=0, minf=18159
  IO depths    : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     issued rwts: total=0,22896,0,0 short=0,0,0,0 dropped=0,0,0,0
     latency   : target=0, window=0, percentile=100.00%, depth=1

Run status group 0 (all jobs):
  WRITE: bw=29.6GiB/s (31.8GB/s), 29.6GiB/s-29.6GiB/s (31.8GB/s-31.8GB/s), io=44.7GiB (48.0GB), run=1511-1511msec

$ sudo famfs fsck -h /mnt/famfs
Famfs Superblock:
  Filesystem UUID: 591f3f62-0a79-4543-9ab5-e02dc807c76c
  System UUID:     00000000-0000-0000-0000-0cc47aaaa734
  sizeof superblock: 168
  num_daxdevs:              1
  primary: /dev/dax1.0   137438953472

Log stats:
  # of log entriesi in use: 480 of 25575
  Log size in use:          157488
  No allocation errors found

Capacity:
  Device capacity:        128.00G
  Bitmap capacity:        127.99G
  Sum of file sizes:      120.00G
  Allocated space:        120.00G
  Free space:             7.99G
  Space amplification:     1.00
  Percent used:            93.8%

Famfs log:
  480 of 25575 entries used
  480 files
  0 directories

###

Here is the same fio command, plus --ioengine=io_uring and --direct=1. It's
apples and oranges, since famfs is a memory interface and not a storage
interface. This is run on an xfs file system on a SATA ssd.

Note units are msec here, usec above.

fio -name=ten-256m-per-thread --nrfiles=10 -bs=2M --group_reporting=1 --alloc-size=1048576 --filesize=256MiB --readwrite=write --fallocate=none --numjobs=48 --create_on_open=0 --ioengine=io_uring --direct=1 --directory=/home/jmg/t1
ten-256m-per-thread: (g=0): rw=write, bs=(R) 2048KiB-2048KiB, (W) 2048KiB-2048KiB, (T) 2048KiB-2048KiB, ioengine=io_uring, iodepth=1
...
fio-3.33
Starting 48 processes
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
Jobs: 37 (f=370): [W(1),_(2),W(2),_(1),W(1),_(1),W(6),_(1),W(1),_(1),W(1),_(1),W(1),_(1),W(1),_(1),W(13),_(1),W(5),_(1),W(5)][72.1%][w=454MiB/s][w=227 IOPS][eta 01m:32sJobs: 37 (f=370): [W(1),_(2),W(2),_(1),W(1),_(1),W(6),_(1),W(1),_(1),W(1),_(1),W(1),_(1),W(1),_(1),W(13),_(1),W(5),_(1),W(5)][72.4%][w=456MiB/s][w=228 IOPS][eta 01m:31sJobs: 36 (f=360): [W(1),_(2),W(2),_(1),W(1),_(1),W(6),_(1),W(1),_(1),W(1),_(1),W(1),_(3),W(13),_(1),W(5),_(1),W(5)][72.9%][w=454MiB/s][w=227 IOPS][eta 01m:29s]         Jobs: 33 (f=330): [_(3),W(2),_(1),W(1),_(1),W(1),_(1),W(4),_(1),W(1),_(1),W(1),_(1),W(1),_(3),W(13),_(1),W(5),_(1),W(2),_(1),W(2)][73.0%][w=458MiB/s][w=229 IOPS][eta 01Jobs: 30 (f=300): [_(3),W(2),_(1),W(1),_(1),W(1),_(2),W(3),_(1),W(1),_(3),W(1),_(3),W(7),_(1),W(5),_(1),W(5),_(1),W(2),_(1),W(2)][73.6%][w=462MiB/s][w=231 IOPS][eta 01mJobs: 28 (f=280): [_(3),W(2),_(1),W(1),_(1),W(1),_(2),W(3),_(5),W(1),_(3),W(7),_(1),W(5),_(1),W(5),_(1),W(2),_(2),W(1)][74.1%][w=456MiB/s][w=228 IOPS][eta 01m:25s]     Jobs: 25 (f=250): [_(3),W(2),_(1),W(1),_(1),W(1),_(2),W(1),_(1),W(1),_(5),W(1),_(3),W(2),_(1),W(4),_(1),W(5),_(1),W(5),_(2),W(1),_(2),W(1)][75.1%][w=458MiB/s][w=229 IOPJobs: 24 (f=240): [_(3),W(2),_(1),W(1),_(1),W(1),_(2),W(1),_(1),W(1),_(5),W(1),_(3),W(2),_(1),W(3),_(2),W(5),_(1),W(5),_(2),W(1),_(2),W(1)][75.6%][w=456MiB/s][w=228 IOPJobs: 23 (f=230): [_(3),W(2),_(1),W(1),_(1),W(1),_(2),W(1),_(1),W(1),_(5),E(1),_(3),W(2),_(1),W(3),_(2),W(5),_(1),W(5),_(2),W(1),_(2),W(1)][76.2%][w=452MiB/s][w=226 IOPJobs: 20 (f=200): [_(3),W(2),_(1),W(1),_(1),W(1),_(2),W(1),_(11),W(2),_(1),W(3),_(2),W(5),_(1),W(3),_(1),W(1),_(2),W(1),_(3)][76.7%][w=448MiB/s][w=224 IOPS][eta 01m:15sJobs: 19 (f=190): [_(3),W(2),_(1),W(1),_(1),W(1),_(2),W(1),_(11),W(2),_(1),W(3),_(2),W(5),_(2),W(2),_(1),W(1),_(2),W(1),_(3)][77.5%][w=464MiB/s][w=232 IOPS][eta 01m:12sJobs: 18 (f=180): [_(3),W(2),_(3),W(1),_(2),W(1),_(11),W(2),_(1),W(3),_(2),W(5),_(2),W(2),_(1),W(1),_(2),W(1),_(3)][78.8%][w=478MiB/s][w=239 IOPS][eta 01m:07s]         Jobs: 4 (f=40): [_(3),W(1),_(22),W(1),_(12),W(1),_(4),W(1),_(3)][92.4%][w=462MiB/s][w=231 IOPS][eta 00m:21s]                                                   
ten-256m-per-thread: (groupid=0, jobs=48): err= 0: pid=210709: Mon Feb 26 07:20:51 2024
  write: IOPS=228, BW=458MiB/s (480MB/s)(114GiB/255942msec); 0 zone resets
    slat (usec): min=39, max=776, avg=186.65, stdev=49.13
    clat (msec): min=4, max=6718, avg=199.27, stdev=324.82
     lat (msec): min=4, max=6718, avg=199.45, stdev=324.82
    clat percentiles (msec):
     |  1.00th=[   30],  5.00th=[   47], 10.00th=[   60], 20.00th=[   69],
     | 30.00th=[   78], 40.00th=[   85], 50.00th=[   95], 60.00th=[  114],
     | 70.00th=[  142], 80.00th=[  194], 90.00th=[  409], 95.00th=[  810],
     | 99.00th=[ 1703], 99.50th=[ 2140], 99.90th=[ 3037], 99.95th=[ 3440],
     | 99.99th=[ 4665]
   bw (  KiB/s): min=195570, max=2422953, per=100.00%, avg=653513.53, stdev=8137.30, samples=17556
   iops        : min=   60, max= 1180, avg=314.22, stdev= 3.98, samples=17556
  lat (msec)   : 10=0.11%, 20=0.37%, 50=5.35%, 100=47.30%, 250=32.22%
  lat (msec)   : 500=6.11%, 750=2.98%, 1000=1.98%, 2000=2.97%, >=2000=0.60%
  cpu          : usr=0.10%, sys=0.01%, ctx=58709, majf=0, minf=669
  IO depths    : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     issued rwts: total=0,58560,0,0 short=0,0,0,0 dropped=0,0,0,0
     latency   : target=0, window=0, percentile=100.00%, depth=1

Run status group 0 (all jobs):
  WRITE: bw=458MiB/s (480MB/s), 458MiB/s-458MiB/s (480MB/s-480MB/s), io=114GiB (123GB), run=255942-255942msec

Disk stats (read/write):
    dm-2: ios=11/82263, merge=0/0, ticks=270/13403617, in_queue=13403887, util=97.10%, aggrios=11/152359, aggrmerge=0/5087, aggrticks=271/11493029, aggrin_queue=11494994, aggrutil=100.00%
  sdb: ios=11/152359, merge=0/5087, ticks=271/11493029, in_queue=11494994, util=100.00%

###

Let me know what else you'd like to see tried.

Regards,
John

Re: [RFC PATCH 13/20] famfs: Add iomap_ops

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:41:57 -0600
John Groves <John@Groves.net> wrote:

> This commit introduces the famfs iomap_ops. When either
> dax_iomap_fault() or dax_iomap_rw() is called, we get a callback
> via our iomap_begin() handler. The question being asked is
> "please resolve (file, offset) to (daxdev, offset)". The function
> famfs_meta_to_dax_offset() does this.
> 
> The per-file metadata is just an extent list to the
> backing dax dev.  The order of this resolution is O(N) for N
> extents. Note with the current user space, files usually have
> only one extent.
> 
> Signed-off-by: John Groves <john@groves.net>

> ---
>  fs/famfs/famfs_file.c | 245 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 245 insertions(+)
>  create mode 100644 fs/famfs/famfs_file.c
> 
> diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c
> new file mode 100644
> index 000000000000..fc667d5f7be8
> --- /dev/null
> +++ b/fs/famfs/famfs_file.c
> @@ -0,0 +1,245 @@

> +static int
> +famfs_meta_to_dax_offset(
> +	struct inode *inode,
> +	struct iomap *iomap,
> +	loff_t        offset,
> +	loff_t        len,
> +	unsigned int  flags)
> +{
> +	struct famfs_file_meta *meta = (struct famfs_file_meta *)inode->i_private;

i_private is void * so no need for explicit cast (C spec says this is always fine without)


> +
> +/**
> + * famfs_iomap_begin()
> + *
> + * This function is pretty simple because files are
> + * * never partially allocated
> + * * never have holes (never sparse)
> + * * never "allocate on write"
> + */
> +static int
> +famfs_iomap_begin(
> +	struct inode	       *inode,
> +	loff_t			offset,
> +	loff_t			length,
> +	unsigned int		flags,
> +	struct iomap	       *iomap,
> +	struct iomap	       *srcmap)
> +{
> +	struct famfs_file_meta *meta = inode->i_private;
> +	size_t size;
> +	int rc;
> +
> +	size = i_size_read(inode);
> +
> +	WARN_ON(size != meta->file_size);
> +
> +	rc = famfs_meta_to_dax_offset(inode, iomap, offset, length, flags);
> +
> +	return rc;
	return famfs_meta_...

> +}


> +static vm_fault_t
> +famfs_filemap_map_pages(
> +	struct vm_fault	       *vmf,
> +	pgoff_t			start_pgoff,
> +	pgoff_t			end_pgoff)
> +{
> +	vm_fault_t ret;
> +
> +	ret = filemap_map_pages(vmf, start_pgoff, end_pgoff);
> +	return ret;
	return filename_map_pages()....

> +}
> +
>

Re: [RFC PATCH 14/20] famfs: Add struct file_operations

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:41:58 -0600
John Groves <John@Groves.net> wrote:

> This commit introduces the famfs file_operations. We call
> thp_get_unmapped_area() to force PMD page alignment. Our read and
> write handlers (famfs_dax_read_iter() and famfs_dax_write_iter())
> call dax_iomap_rw() to do the work.
> 
> famfs_file_invalid() checks for various ways a famfs file can be
> in an invalid state so we can fail I/O or fault resolution in those
> cases. Those cases include the following:
> 
> * No famfs metadata
> * file i_size does not match the originally allocated size
> * file is not flagged as DAX
> * errors were detected previously on the file
> 
> An invalid file can often be fixed by replaying the log, or by
> umount/mount/log replay - all of which are user space operations.
> 
> Signed-off-by: John Groves <john@groves.net>
> ---
>  fs/famfs/famfs_file.c | 136 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 136 insertions(+)
> 
> diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c
> index fc667d5f7be8..5228e9de1e3b 100644
> --- a/fs/famfs/famfs_file.c
> +++ b/fs/famfs/famfs_file.c
> @@ -19,6 +19,142 @@
>  #include <uapi/linux/famfs_ioctl.h>
>  #include "famfs_internal.h"
>  
> +/*********************************************************************
> + * file_operations
> + */
> +
> +/* Reject I/O to files that aren't in a valid state */
> +static ssize_t
> +famfs_file_invalid(struct inode *inode)
> +{
> +	size_t i_size       = i_size_read(inode);
> +	struct famfs_file_meta *meta = inode->i_private;
> +
> +	if (!meta) {
> +		pr_err("%s: un-initialized famfs file\n", __func__);
> +		return -EIO;
> +	}
> +	if (i_size != meta->file_size) {
> +		pr_err("%s: something changed the size from  %ld to %ld\n",
> +		       __func__, meta->file_size, i_size);
> +		meta->error = 1;
> +		return -ENXIO;
> +	}
> +	if (!IS_DAX(inode)) {
> +		pr_err("%s: inode %llx IS_DAX is false\n", __func__, (u64)inode);
> +		meta->error = 1;
> +		return -ENXIO;
> +	}
> +	if (meta->error) {
> +		pr_err("%s: previously detected metadata errors\n", __func__);
> +		meta->error = 1;

Already set?  If treating it as only a boolean, maybe make it one?

> +		return -EIO;
> +	}
> +	return 0;
> +}

Re: [RFC PATCH 15/20] famfs: Add ioctl to file_operations

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:41:59 -0600
John Groves <John@Groves.net> wrote:

> This commit introduces the per-file ioctl function famfs_file_ioctl()
> into struct file_operations, and introduces the famfs_file_init_dax()
> function (which is called by famfs_file_ioct())
> 
> famfs_file_init_dax() associates a dax extent list with a file, making
> it into a proper famfs file. It is called from the FAMFSIOC_MAP_CREATE
> ioctl. Starting with an empty file (which is basically a ramfs file),
> this turns the file into a DAX file backed by the specified extent list.
> 
> The other ioctls are:
> 
> FAMFSIOC_NOP - A convenient way for user space to verify it's a famfs file
> FAMFSIOC_MAP_GET - Get the header of the metadata for a file
> FAMFSIOC_MAP_GETEXT - Get the extents for a file
> 
> The latter two, together, are comparable to xfs_bmap. Our user space tools
> use them primarly in testing.
> 
> Signed-off-by: John Groves <john@groves.net>
A few more comments inline. Nothing fundamental just nice to have
simplifications of the code.

> ---
>  fs/famfs/famfs_file.c | 226 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 226 insertions(+)
> 
> diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c
> index 5228e9de1e3b..fd42d5966982 100644
> --- a/fs/famfs/famfs_file.c
> +++ b/fs/famfs/famfs_file.c
> @@ -19,6 +19,231 @@
>  #include <uapi/linux/famfs_ioctl.h>
>  #include "famfs_internal.h"
>  
> +/**
> + * famfs_map_meta_alloc() - Allocate famfs file metadata
> + * @mapp:       Pointer to an mcache_map_meta pointer
> + * @ext_count:  The number of extents needed
> + */
> +static int
> +famfs_meta_alloc(
> +	struct famfs_file_meta  **metap,
> +	size_t                    ext_count)
> +{
> +	struct famfs_file_meta *meta;
> +	size_t                  metasz;
> +
> +	*metap = NULL;

Not responsibility of caller?

> +
> +	metasz = sizeof(*meta) + sizeof(*(meta->tfs_extents)) * ext_count;

Looks like struct_size() would be appropriate.


> +
> +	meta = kzalloc(metasz, GFP_KERNEL);
> +	if (!meta)
> +		return -ENOMEM;
> +
> +	meta->tfs_extent_ct = ext_count;
> +	*metap = meta;
> +
> +	return 0;
> +}
> +
> +static void
> +famfs_meta_free(
> +	struct famfs_file_meta *map)
> +{
> +	kfree(map);
Given this is just kfree you can use __free magic to simplify things below.

> +}
> +
> +/**
> + * famfs_file_init_dax() - FAMFSIOC_MAP_CREATE ioctl handler
> + * @file:
> + * @arg:        ptr to struct mcioc_map in user space
> + *
> + * Setup the dax mapping for a file. Files are created empty, and then function is called
> + * (by famfs_file_ioctl()) to setup the mapping and set the file size.
> + */
> +static int
> +famfs_file_init_dax(
> +	struct file    *file,
> +	void __user    *arg)
> +{
> +	struct famfs_extent    *tfs_extents = NULL;
> +	struct famfs_file_meta *meta = NULL;
> +	struct inode           *inode;
> +	struct famfs_ioc_map    imap;
> +	struct famfs_fs_info   *fsi;
> +	struct super_block     *sb;
> +	int    alignment_errs = 0;
> +	size_t extent_total = 0;
> +	size_t ext_count;
> +	int    rc = 0;
> +	int    i;
> +
> +	rc = copy_from_user(&imap, arg, sizeof(imap));
> +	if (rc)
> +		return -EFAULT;
> +
> +	ext_count = imap.ext_list_count;
> +	if (ext_count < 1) {
> +		rc = -ENOSPC;
> +		goto errout;
		meta data not yet allocated.
		return -ENOSPC;

> +	}
> +
> +	if (ext_count > FAMFS_MAX_EXTENTS) {
> +		rc = -E2BIG;
> +		goto errout;	
		return 

> +	}
> +
> +	inode = file_inode(file);
> +	if (!inode) {
> +		rc = -EBADF;
> +		goto errout;
		return;

> +	}
> +	sb  = inode->i_sb;
> +	fsi = inode->i_sb->s_fs_info;
> +
> +	tfs_extents = &imap.ext_list[0];
> +
> +	rc = famfs_meta_alloc(&meta, ext_count);
> +	if (rc)
> +		goto errout;
	return ...

	only after this point should there be any
	meta data to free on exit?

> +
> +	meta->file_type = imap.file_type;
> +	meta->file_size = imap.file_size;
> +
> +	/* Fill in the internal file metadata structure */
> +	for (i = 0; i < imap.ext_list_count; i++) {
> +		size_t len;
> +		off_t  offset;
> +
> +		offset = imap.ext_list[i].offset;
> +		len    = imap.ext_list[i].len;
> +
> +		extent_total += len;
> +
> +		if (WARN_ON(offset == 0 && meta->file_type != FAMFS_SUPERBLOCK)) {
> +			rc = -EINVAL;
> +			goto errout;
> +		}
> +
> +		meta->tfs_extents[i].offset = offset;
> +		meta->tfs_extents[i].len    = len;
> +
> +		/* All extent addresses/offsets must be 2MiB aligned,
> +		 * and all but the last length must be a 2MiB multiple.
> +		 */
> +		if (!IS_ALIGNED(offset, PMD_SIZE)) {
> +			pr_err("%s: error ext %d hpa %lx not aligned\n",
> +			       __func__, i, offset);
> +			alignment_errs++;
> +		}
> +		if (i < (imap.ext_list_count - 1) && !IS_ALIGNED(len, PMD_SIZE)) {
> +			pr_err("%s: error ext %d length %ld not aligned\n",
> +			       __func__, i, len);
> +			alignment_errs++;
> +		}
> +	}
> +
> +	/*
> +	 * File size can be <= ext list size, since extent sizes are constrained
> +	 * to PMD multiples
> +	 */
> +	if (imap.file_size > extent_total) {
> +		pr_err("%s: file size %lld larger than ext list size %lld\n",
> +		       __func__, (u64)imap.file_size, (u64)extent_total);
> +		rc = -EINVAL;
> +		goto errout;
> +	}
> +
> +	if (alignment_errs > 0) {
> +		pr_err("%s: there were %d alignment errors in the extent list\n",
> +		       __func__, alignment_errs);
> +		rc = -EINVAL;
> +		goto errout;
> +	}
> +
> +	/* Publish the famfs metadata on inode->i_private */
> +	inode_lock(inode);

Easy to add a guard definition - maybe useful enough to bother as can then do
this which makes the error handling align with other cases.

	scoped_guard(inode_sem, inode) {
		if (inode->i_private) {
			rc = -EEXIST;
			goto errout;
		}
		inode->...

	}
> +	if (inode->i_private) {
> +		rc = -EEXIST; /* file already has famfs metadata */
> +	} else {
> +		inode->i_private = meta;

You could use __free on the meta data and 
		inode->i_private = no_ptr_free(meta);
here. Then all your earlier error paths become direct returns.

> +		i_size_write(inode, imap.file_size);
> +		inode->i_flags |= S_DAX;
> +	}
> +	inode_unlock(inode);
> +
> + errout:
> +	if (rc)
> +		famfs_meta_free(meta);
A separate error path is going to be easier to follow as no if (rc)

> +
> +	return rc;
> +}
> +
> +/**
> + * famfs_file_ioctl() -  top-level famfs file ioctl handler
> + * @file:
> + * @cmd:
> + * @arg:
> + */
> +static
> +long
> +famfs_file_ioctl(
> +	struct file    *file,
> +	unsigned int    cmd,
> +	unsigned long   arg)
> +{
> +	long rc;
> +
> +	switch (cmd) {
> +	case FAMFSIOC_NOP:
> +		rc = 0;
		return 0;
> +		break;
> +
> +	case FAMFSIOC_MAP_CREATE:
> +		rc = famfs_file_init_dax(file, (void *)arg);
		return famfs_file_init_dax()

> +		break;
> +
> +	case FAMFSIOC_MAP_GET: {
> +		struct inode *inode = file_inode(file);
> +		struct famfs_file_meta *meta = inode->i_private;
> +		struct famfs_ioc_map umeta;
> +
> +		memset(&umeta, 0, sizeof(umeta));
> +
> +		if (meta) {
> +			/* TODO: do more to harmonize these structures */
> +			umeta.extent_type    = meta->tfs_extent_type;
> +			umeta.file_size      = i_size_read(inode);
> +			umeta.ext_list_count = meta->tfs_extent_ct;
> +
> +			rc = copy_to_user((void __user *)arg, &umeta, sizeof(umeta));
> +			if (rc)
> +				pr_err("%s: copy_to_user returned %ld\n", __func__, rc);
> +
> +		} else {
> +			rc = -EINVAL;
> +		}
Flip logic.

		if (!meta)
			return -EINVAL;

		umeta ...
		return 0;

> +	}
> +		break;
> +	case FAMFSIOC_MAP_GETEXT: {
> +		struct inode *inode = file_inode(file);
> +		struct famfs_file_meta *meta = inode->i_private;
> +
> +		if (meta)
> +			rc = copy_to_user((void __user *)arg, meta->tfs_extents,
> +					  meta->tfs_extent_ct * sizeof(struct famfs_extent));
> +		else
> +			rc = -EINVAL;
		if (!meta)
			return -EINVAL;

		return copy_to_user

> +	}
> +		break;
> +	default:
> +		rc = -ENOTTY;
return -ENOTTY;

> +		break;
> +	}
> +
> +	return rc;
Early returns will simplify the flow for anyone reading this.

> +}

Re: [RFC PATCH 17/20] famfs: Add module stuff

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:42:01 -0600
John Groves <John@Groves.net> wrote:

> This commit introduces the module init and exit machinery for famfs.
> 
> Signed-off-by: John Groves <john@groves.net>
I'd prefer to see this from the start with the functionality of the module
built up as you go + build logic in place.  Makes it easy to spot places
where the patches aren't appropriately self constrained. 
> ---
>  fs/famfs/famfs_inode.c | 44 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
> 
> diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> index ab46ec50b70d..0d659820e8ff 100644
> --- a/fs/famfs/famfs_inode.c
> +++ b/fs/famfs/famfs_inode.c
> @@ -462,4 +462,48 @@ static struct file_system_type famfs_fs_type = {
>  	.fs_flags	  = FS_USERNS_MOUNT,
>  };
>  
> +/*****************************************************************************************
> + * Module stuff

I'd drop these drivers structure comments. They add little beyond
a high possibility of being wrong after the code has evolved a bit.

> + */
> +static struct kobject *famfs_kobj;
> +
> +static int __init init_famfs_fs(void)
> +{
> +	int rc;
> +
> +#if defined(CONFIG_DEV_DAX_IOMAP)
> +	pr_notice("%s: Your kernel supports famfs on /dev/dax\n", __func__);
> +#else
> +	pr_notice("%s: Your kernel does not support famfs on /dev/dax\n", __func__);
> +#endif
> +	famfs_kobj = kobject_create_and_add(MODULE_NAME, fs_kobj);
> +	if (!famfs_kobj) {
> +		pr_warn("Failed to create kobject\n");
> +		return -ENOMEM;
> +	}
> +
> +	rc = sysfs_create_group(famfs_kobj, &famfs_attr_group);
> +	if (rc) {
> +		kobject_put(famfs_kobj);
> +		pr_warn("%s: Failed to create sysfs group\n", __func__);
> +		return rc;
> +	}
> +
> +	return register_filesystem(&famfs_fs_type);

If this fails, do we not leak the kobj and sysfs groups?

> +}
> +
> +static void
> +__exit famfs_exit(void)
> +{
> +	sysfs_remove_group(famfs_kobj,  &famfs_attr_group);
> +	kobject_put(famfs_kobj);
> +	unregister_filesystem(&famfs_fs_type);
> +	pr_info("%s: unregistered\n", __func__);
> +}
> +
> +
> +fs_initcall(init_famfs_fs);
> +module_exit(famfs_exit);
> +
> +MODULE_AUTHOR("John Groves, Micron Technology");
>  MODULE_LICENSE("GPL");

Re: [RFC PATCH 18/20] famfs: Support character dax via the dev_dax_iomap patch

[Jonathan Cameron]

On Fri, 23 Feb 2024 11:42:02 -0600
John Groves <John@Groves.net> wrote:

> This commit introduces the ability to open a character /dev/dax device
> instead of a block /dev/pmem device. This rests on the dev_dax_iomap
> patches earlier in this series.

Not sure the back reference is needed given it's in the series.

> 
> Signed-off-by: John Groves <john@groves.net>
> ---
>  fs/famfs/famfs_inode.c | 97 +++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 87 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> index 0d659820e8ff..7d65ac497147 100644
> --- a/fs/famfs/famfs_inode.c
> +++ b/fs/famfs/famfs_inode.c
> @@ -215,6 +215,93 @@ static const struct super_operations famfs_ops = {
>  	.show_options	= famfs_show_options,
>  };
>  
> +/*****************************************************************************/
> +
> +#if defined(CONFIG_DEV_DAX_IOMAP)
> +
> +/*
> + * famfs dax_operations  (for char dax)
> + */
> +static int
> +famfs_dax_notify_failure(struct dax_device *dax_dev, u64 offset,
> +			u64 len, int mf_flags)
> +{
> +	pr_err("%s: offset %lld len %llu flags %x\n", __func__,
> +	       offset, len, mf_flags);
> +	return -EOPNOTSUPP;
> +}
> +
> +static const struct dax_holder_operations famfs_dax_holder_ops = {
> +	.notify_failure		= famfs_dax_notify_failure,
> +};
> +
> +/*****************************************************************************/
> +
> +/**
> + * famfs_open_char_device()
> + *
> + * Open a /dev/dax device. This only works in kernels with the dev_dax_iomap patch

That comment you definitely don't need as this won't get merged without
that patch being in place.


> + */
> +static int
> +famfs_open_char_device(
> +	struct super_block *sb,
> +	struct fs_context  *fc)
> +{
> +	struct famfs_fs_info *fsi = sb->s_fs_info;
> +	struct dax_device    *dax_devp;
> +	struct inode         *daxdev_inode;
> +
> +	int rc = 0;
set in all paths where it's used.

> +
> +	pr_notice("%s: Opening character dax device %s\n", __func__, fc->source);

pr_debug

> +
> +	fsi->dax_filp = filp_open(fc->source, O_RDWR, 0);
> +	if (IS_ERR(fsi->dax_filp)) {
> +		pr_err("%s: failed to open dax device %s\n",
> +		       __func__, fc->source);
> +		fsi->dax_filp = NULL;
Better to use a local variable

	fp = filp_open(fc->source, O_RDWR, 0);
	if (IS_ERR(fp)) {
		pr_err.
		return;
	}
	fsi->dax_filp = fp;
or similar.

> +		return PTR_ERR(fsi->dax_filp);
> +	}
> +
> +	daxdev_inode = file_inode(fsi->dax_filp);
> +	dax_devp     = inode_dax(daxdev_inode);
> +	if (IS_ERR(dax_devp)) {
> +		pr_err("%s: unable to get daxdev from inode for %s\n",
> +		       __func__, fc->source);
> +		rc = -ENODEV;
> +		goto char_err;
> +	}
> +
> +	rc = fs_dax_get(dax_devp, fsi, &famfs_dax_holder_ops);
> +	if (rc) {
> +		pr_info("%s: err attaching famfs_dax_holder_ops\n", __func__);
> +		goto char_err;
> +	}
> +
> +	fsi->bdev_handle = NULL;
> +	fsi->dax_devp = dax_devp;
> +
> +	return 0;
> +
> +char_err:
> +	filp_close(fsi->dax_filp, NULL);

You carefully set fsi->dax_filp to null in other other error paths.
Why there and not here?

> +	return rc;
> +}
> +
> +#else /* CONFIG_DEV_DAX_IOMAP */
> +static int
> +famfs_open_char_device(
> +	struct super_block *sb,
> +	struct fs_context  *fc)
> +{
> +	pr_err("%s: Root device is %s, but your kernel does not support famfs on /dev/dax\n",
> +	       __func__, fc->source);
> +	return -ENODEV;
> +}
> +
> +
> +#endif /* CONFIG_DEV_DAX_IOMAP */
> +
>  /***************************************************************************************
>   * dax_holder_operations for block dax
>   */
> @@ -236,16 +323,6 @@ const struct dax_holder_operations famfs_blk_dax_holder_ops = {
>  	.notify_failure		= famfs_blk_dax_notify_failure,
>  };
>  

Put it in right place earlier! Makes this less noisy.

> -static int
> -famfs_open_char_device(
> -	struct super_block *sb,
> -	struct fs_context  *fc)
> -{
> -	pr_err("%s: Root device is %s, but your kernel does not support famfs on /dev/dax\n",
> -	       __func__, fc->source);
> -	return -ENODEV;
> -}
> -
>  /**
>   * famfs_open_device()
>   *

Re: [RFC PATCH 02/20] dev_dax_iomap: Add fs_dax_get() func to prepare dax for fs-dax usage

[John Groves]

On 24/02/26 12:05PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:46 -0600
> John Groves <John@Groves.net> wrote:
> 
> > This function should be called by fs-dax file systems after opening the
> > devdax device. This adds holder_operations.
> > 
> > This function serves the same role as fs_dax_get_by_bdev(), which dax
> > file systems call after opening the pmem block device.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> 
> A few trivial comments form a first read to get my head around this.
> 
> Yeah, it is only an RFC, but who doesn't like tidy code? :)

Hope your eyes don't burn too much ;)
> 
> 
> > ---
> >  drivers/dax/super.c | 38 ++++++++++++++++++++++++++++++++++++++
> >  include/linux/dax.h |  5 +++++
> >  2 files changed, 43 insertions(+)
> > 
> > diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> > index f4b635526345..fc96362de237 100644
> > --- a/drivers/dax/super.c
> > +++ b/drivers/dax/super.c
> > @@ -121,6 +121,44 @@ void fs_put_dax(struct dax_device *dax_dev, void *holder)
> >  EXPORT_SYMBOL_GPL(fs_put_dax);
> >  #endif /* CONFIG_BLOCK && CONFIG_FS_DAX */
> >  
> > +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
> > +
> > +/**
> > + * fs_dax_get()
> 
> Smells like kernel doc but fairly sure it needs a short description.
> Have you sanity checked for warnings when running scripts/kerneldoc on it?

Right, and there were other cases. Randy pointed one out, and I've already
gone through and "fixed" them.

> 
> > + *
> > + * fs-dax file systems call this function to prepare to use a devdax device for fsdax.
> Trivial but lines too long. Keep under 80 chars unless there is a strong
> readability arguement for not doing so.

I was under the impression the "kids these days" have a 100 column standard.
But I will go through and limit line to 80 except where it gets too awkward.

> 
> 
> > + * This is like fs_dax_get_by_bdev(), but the caller already has struct dev_dax (and there
> > + * is no bdev). The holder makes this exclusive.
> 
> Not familiar with this area: what does exclusive mean here?

The holder_ops are set via cmpxchg, in such a way that if there are already
holder_ops, the call to fs_dax_get() will fail. (as it should)

> 
> > + *
> > + * @dax_dev: dev to be prepared for fs-dax usage
> > + * @holder: filesystem or mapped device inside the dax_device
> > + * @hops: operations for the inner holder
> > + *
> > + * Returns: 0 on success, -1 on failure
> 
> Why not return < 0 and use somewhat useful return values?

Good idea, will do.

> 
> > + */
> > +int fs_dax_get(
> > +	struct dax_device *dax_dev,
> > +	void *holder,
> > +	const struct dax_holder_operations *hops)
> 
> Match local style for indents - it's a bit inconsistent but probably...
> 
> int fs_dax_get(struct dad_device *dev_dax, void *holder,
> 	       const struct dax_holder_operations *hops)

Done

> 
> > +{
> > +	/* dax_dev->ops should have been populated by devm_create_dev_dax() */
> > +	if (WARN_ON(!dax_dev->ops))
> > +		return -1;
> > +
> > +	if (!dax_dev || !dax_alive(dax_dev) || !igrab(&dax_dev->inode))
> 
> You dereferenced dax_dev on the line above so check is too late or
> unnecessary

Good catch, thank you!

> 
> > +		return -1;
> > +
> > +	if (cmpxchg(&dax_dev->holder_data, NULL, holder)) {
> > +		pr_warn("%s: holder_data already set\n", __func__);
> 
> Perhaps nicer to use a pr_fmt() deal with the func name if you need it.
> or make it pr_debug and let dynamic debug control formatting if anyone
> wants the function name.

Sounds good.

> 
> > +		return -1;
> > +	}
> > +	dax_dev->holder_ops = hops;
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(fs_dax_get);
> > +#endif /* DEV_DAX_IOMAP */
> > +
> >  enum dax_device_flags {
> >  	/* !alive + rcu grace period == no new operations / mappings */
> >  	DAXDEV_ALIVE,
> > diff --git a/include/linux/dax.h b/include/linux/dax.h
> > index b463502b16e1..e973289bfde3 100644
> > --- a/include/linux/dax.h
> > +++ b/include/linux/dax.h
> > @@ -57,7 +57,12 @@ struct dax_holder_operations {
> >  
> >  #if IS_ENABLED(CONFIG_DAX)
> >  struct dax_device *alloc_dax(void *private, const struct dax_operations *ops);
> > +
> > +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
> > +int fs_dax_get(struct dax_device *dax_dev, void *holder, const struct dax_holder_operations *hops);
> line wrap < 80 chars

Roger that

> 
> > +#endif
> >  void *dax_holder(struct dax_device *dax_dev);
> > +struct dax_device *inode_dax(struct inode *inode);
> 
> Unrelated change?

Kinda, but I'm not sure there is a better home for this one. Patch 18,
which is a famfs patch, calls inode_dax(). It was already exported but not
prototyped in dax.h.

Mixing it in with other dev_dax_iomap content seems better than mixing it
with famfs content. Could make it a separate patch, but I was trying to
some old docs that said keep patch sets <=15 - which I deemed impossible here.

What say others?

> 
> >  void put_dax(struct dax_device *dax_dev);
> >  void kill_dax(struct dax_device *dax_dev);
> >  void dax_write_cache(struct dax_device *dax_dev, bool wc);
> 

Thanks Jonathan!

Re: [RFC PATCH 03/20] dev_dax_iomap: Move dax_pgoff_to_phys from device.c to bus.c since both need it now

[John Groves]

On 24/02/26 12:10PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:47 -0600
> John Groves <John@Groves.net> wrote:
> 
> > bus.c can't call functions in device.c - that creates a circular linkage
> > dependency.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> 
> This also adds the export which you should mention!
> 
> Do they need it already? Seems like tense of patch title
> may be wrong.

I added "Also exports dax_pgoff_to_phys() since both bus.c and
device.c now call it."

The export is necessary because bus.c and device.c are not in the same .ko

Let me know if it seems like I'm misunderstanding...

> 
> > ---
> >  drivers/dax/bus.c    | 24 ++++++++++++++++++++++++
> >  drivers/dax/device.c | 23 -----------------------
> >  2 files changed, 24 insertions(+), 23 deletions(-)
> > 
> > diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> > index 1ff1ab5fa105..664e8c1b9930 100644
> > --- a/drivers/dax/bus.c
> > +++ b/drivers/dax/bus.c
> > @@ -1325,6 +1325,30 @@ static const struct device_type dev_dax_type = {
> >  	.groups = dax_attribute_groups,
> >  };
> >  
> > +/* see "strong" declaration in tools/testing/nvdimm/dax-dev.c  */
> > +__weak phys_addr_t dax_pgoff_to_phys(struct dev_dax *dev_dax, pgoff_t pgoff,
> > +			      unsigned long size)
> > +{
> > +	int i;
> > +
> > +	for (i = 0; i < dev_dax->nr_range; i++) {
> > +		struct dev_dax_range *dax_range = &dev_dax->ranges[i];
> > +		struct range *range = &dax_range->range;
> > +		unsigned long long pgoff_end;
> > +		phys_addr_t phys;
> > +
> > +		pgoff_end = dax_range->pgoff + PHYS_PFN(range_len(range)) - 1;
> > +		if (pgoff < dax_range->pgoff || pgoff > pgoff_end)
> > +			continue;
> > +		phys = PFN_PHYS(pgoff - dax_range->pgoff) + range->start;
> > +		if (phys + size - 1 <= range->end)
> > +			return phys;
> > +		break;
> > +	}
> > +	return -1;
> 
> Not related to your patch but returning -1 in a phys_addr_t isn't ideal.
> I assume aim is all bits set as a marker, in which case
> PHYS_ADDR_MAX from limits.h would make things clearer.

Perhaps Dan or the other dax people can comment on this? I just moved the
function verbatim, but Jonathan makes a good point!

Thanks,
John

Re: [RFC PATCH 04/20] dev_dax_iomap: Save the kva from memremap

[John Groves]

On 24/02/26 12:21PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:48 -0600
> John Groves <John@Groves.net> wrote:
> 
> > Save the kva from memremap because we need it for iomap rw support
> > 
> > Prior to famfs, there were no iomap users of /dev/dax - so the virtual
> > address from memremap was not needed.
> > 
> > Also: in some cases dev_dax_probe() is called with the first
> > dev_dax->range offset past pgmap[0].range. In those cases we need to
> > add the difference to virt_addr in order to have the physaddr's in
> > dev_dax->ranges match dev_dax->virt_addr.
> 
> Probably good to have info on when this happens and preferably why
> this dragon is there.

I added this paragraph:

  This happens with devdax devices that started as pmem and got converted
  to devdax. I'm not sure whether the offset is due to label storage, or
  page tables. Dan?

...which is also insufficient, but perhaps Dan or somebody else from the
dax side can correct this.

> 
> > 
> > Dragons...
> > 
> > Signed-off-by: John Groves <john@groves.net>
> > ---
> >  drivers/dax/dax-private.h |  1 +
> >  drivers/dax/device.c      | 15 +++++++++++++++
> >  2 files changed, 16 insertions(+)
> > 
> > diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
> > index 446617b73aea..894eb1c66b4a 100644
> > --- a/drivers/dax/dax-private.h
> > +++ b/drivers/dax/dax-private.h
> > @@ -63,6 +63,7 @@ struct dax_mapping {
> >  struct dev_dax {
> >  	struct dax_region *region;
> >  	struct dax_device *dax_dev;
> > +	u64 virt_addr;
> 
> Why as a u64? If it's a virt address why not just void *?

Changed to void * - thanks

> 
> >  	unsigned int align;
> >  	int target_node;
> >  	bool dyn_id;
> > diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> > index 40ba660013cf..6cd79d00fe1b 100644
> > --- a/drivers/dax/device.c
> > +++ b/drivers/dax/device.c
> > @@ -372,6 +372,7 @@ static int dev_dax_probe(struct dev_dax *dev_dax)
> >  	struct dax_device *dax_dev = dev_dax->dax_dev;
> >  	struct device *dev = &dev_dax->dev;
> >  	struct dev_pagemap *pgmap;
> > +	u64 data_offset = 0;
> >  	struct inode *inode;
> >  	struct cdev *cdev;
> >  	void *addr;
> > @@ -426,6 +427,20 @@ static int dev_dax_probe(struct dev_dax *dev_dax)
> >  	if (IS_ERR(addr))
> >  		return PTR_ERR(addr);
> >  
> > +	/* Detect whether the data is at a non-zero offset into the memory */
> > +	if (pgmap->range.start != dev_dax->ranges[0].range.start) {
> > +		u64 phys = (u64)dev_dax->ranges[0].range.start;
> 
> Why the cast? Ranges use u64s internally.

I've removed all the unnecessary casts in this function - thanks
for the catch

> 
> > +		u64 pgmap_phys = (u64)dev_dax->pgmap[0].range.start;
> > +		u64 vmemmap_shift = (u64)dev_dax->pgmap[0].vmemmap_shift;
> > +
> > +		if (!WARN_ON(pgmap_phys > phys))
> > +			data_offset = phys - pgmap_phys;
> > +
> > +		pr_notice("%s: offset detected phys=%llx pgmap_phys=%llx offset=%llx shift=%llx\n",
> > +		       __func__, phys, pgmap_phys, data_offset, vmemmap_shift);
> 
> pr_debug() + dynamic debug will then deal with __func__ for you.

Thanks - yeah that would be better than just taking it out...

> 
> > +	}
> > +	dev_dax->virt_addr = (u64)addr + data_offset;
> > +
> >  	inode = dax_inode(dax_dev);
> >  	cdev = inode->i_cdev;
> >  	cdev_init(cdev, &dax_fops);
> 

Thanks,
John

Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

[Luis Chamberlain]

On Mon, Feb 26, 2024 at 07:27:18AM -0600, John Groves wrote:
> Run status group 0 (all jobs):
>   WRITE: bw=29.6GiB/s (31.8GB/s), 29.6GiB/s-29.6GiB/s (31.8GB/s-31.8GB/s), io=44.7GiB (48.0GB), run=1511-1511msec

> This is run on an xfs file system on a SATA ssd.

To compare more closer apples to apples, wouldn't it make more sense
to try this with XFS on pmem (with fio -direct=1)?

  Luis

Re: [RFC PATCH 05/20] dev_dax_iomap: Add dax_operations for use by fs-dax on devdax

[John Groves]

On 24/02/26 12:32PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:49 -0600
> John Groves <John@Groves.net> wrote:
> 
> > Notes about this commit:
> > 
> > * These methods are based somewhat loosely on pmem_dax_ops from
> >   drivers/nvdimm/pmem.c
> > 
> > * dev_dax_direct_access() is returns the hpa, pfn and kva. The kva was
> >   newly stored as dev_dax->virt_addr by dev_dax_probe().
> > 
> > * The hpa/pfn are used for mmap (dax_iomap_fault()), and the kva is used
> >   for read/write (dax_iomap_rw())
> > 
> > * dev_dax_recovery_write() and dev_dax_zero_page_range() have not been
> >   tested yet. I'm looking for suggestions as to how to test those.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> > ---
> >  drivers/dax/bus.c | 107 ++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 107 insertions(+)
> > 
> > diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> > index 664e8c1b9930..06fcda810674 100644
> > --- a/drivers/dax/bus.c
> > +++ b/drivers/dax/bus.c
> > @@ -10,6 +10,12 @@
> >  #include "dax-private.h"
> >  #include "bus.h"
> >  
> > +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
> > +#include <linux/backing-dev.h>
> > +#include <linux/pfn_t.h>
> > +#include <linux/range.h>
> > +#endif
> > +
> 
> Is it worth avoiding includes based on config? Probably not.

Just trying to demonstrate that I can be tedious :D
I'll drop the #if unless somebody disagrees.

> 
> >  static DEFINE_MUTEX(dax_bus_lock);
> >  
> >  #define DAX_NAME_LEN 30
> > @@ -1349,6 +1355,101 @@ __weak phys_addr_t dax_pgoff_to_phys(struct dev_dax *dev_dax, pgoff_t pgoff,
> >  }
> >  EXPORT_SYMBOL_GPL(dax_pgoff_to_phys);
> >  
> > +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
> > +
> 
> > +
> > +static long __dev_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff,
> > +			     long nr_pages, enum dax_access_mode mode, void **kaddr,
> > +			     pfn_t *pfn)
> > +{
> > +	struct dev_dax *dev_dax = dax_get_private(dax_dev);
> > +	size_t dax_size = dev_dax_size(dev_dax);
> > +	size_t size = nr_pages << PAGE_SHIFT;
> > +	size_t offset = pgoff << PAGE_SHIFT;
> > +	phys_addr_t phys;
> > +	u64 virt_addr = dev_dax->virt_addr + offset;
> > +	pfn_t local_pfn;
> > +	u64 flags = PFN_DEV|PFN_MAP;
> > +
> > +	WARN_ON(!dev_dax->virt_addr); /* virt_addr must be saved for direct_access */
> Fair enough, but from local code point of view, does it make sense to check this
> if !kaddr as we won't use this.

Hmm. This gets called with kaddr=NULL for mmap faults, and with non-NULL
kaddr for read/write (which need the virt_addr to do a memcpy variant).
If dev_dax->virt-addr is NULL, mmap will work but read/write will hork.

I lean toward keeping the warning. With these updates, it's broken if
read/write are broken.

> > +
> > +	phys = dax_pgoff_to_phys(dev_dax, pgoff, nr_pages << PAGE_SHIFT);
> > +
> > +	if (kaddr)
> > +		*kaddr = (void *)virt_addr;
> 
> Back to earlier comment on virt_addr as a void *. Definitely looking like
> that would be more accurate and simpler!  Also not much point in computing
> virt_addr unless kaddr is good.

Yes, done (the void *).

the computation is copied directly from drivers/nvdimm/__pmem_direct_access() -
which does not warn if virt_addr is null. Actually I suppose this code should
just trust that dev_dax_probe sets virt_addr, and not warn?

So I'm now contradicting myself above...

> 
> > +
> > +	local_pfn = phys_to_pfn_t(phys, flags); /* are flags correct? */
> If you aren't going to do anything with it for !pfn, move it under the if (pfn).
> 
> > +	if (pfn)
> > +		*pfn = local_pfn;
> > +
> > +	/* This the valid size at the specified address */
> > +	return PHYS_PFN(min_t(size_t, size, dax_size - offset));
> > +}
> > +
> 
> > +
> > +static const struct dax_operations dev_dax_ops = {
> > +	.direct_access = dev_dax_direct_access,
> > +	.zero_page_range = dev_dax_zero_page_range,
> > +	.recovery_write = dev_dax_recovery_write,
> > +};
> > +
> > +#endif /* IS_ENABLED(CONFIG_DEV_DAX_IOMAP) */
> > +
> >  struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
> >  {
> >  	struct dax_region *dax_region = data->dax_region;
> > @@ -1404,11 +1505,17 @@ struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
> >  		}
> >  	}
> >  
> 
> If we were to make this 
> 
> 	if (IS_ENABLED(CONFIG_DEV_DAX_IOMAP))
> 
> etc can we avoid the ifdef stuff above and let dead code removal deal with it?
> Might need a few stubs - I haven't tried.

Better, thanks. No stubs needed.

> 
> > +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
> > +	/* holder_ops currently populated separately in a slightly hacky way */
> > +	dax_dev = alloc_dax(dev_dax, &dev_dax_ops);
> > +#else
> >  	/*
> >  	 * No dax_operations since there is no access to this device outside of
> >  	 * mmap of the resulting character device.
> >  	 */
> >  	dax_dev = alloc_dax(dev_dax, NULL);
> > +#endif

Thanks!
John

Re: [RFC PATCH 06/20] dev_dax_iomap: Add CONFIG_DEV_DAX_IOMAP kernel build parameter

[John Groves]

On 24/02/26 12:34PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:50 -0600
> John Groves <John@Groves.net> wrote:
> 
> > Add the CONFIG_DEV_DAX_IOMAP kernel config parameter to control building
> > of the iomap functionality to support fsdax on devdax.
> 
> I would squash with previous patch.
> 
> Only reason I ever see for separate Kconfig patches is when there is something
> complex in the dependencies and you want to talk about it in depth in the
> patch description. That's not true here so no need for separate patch.

Done

Thanks,
John

Re: [RFC PATCH 07/20] famfs: Add include/linux/famfs_ioctl.h

[John Groves]

On 24/02/26 12:39PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:51 -0600
> John Groves <John@Groves.net> wrote:
> 
> > Add uapi include file for famfs. The famfs user space uses ioctl on
> > individual files to pass in mapping information and file size. This
> > would be hard to do via sysfs or other means, since it's
> > file-specific.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> > ---
> >  include/uapi/linux/famfs_ioctl.h | 56 ++++++++++++++++++++++++++++++++
> >  1 file changed, 56 insertions(+)
> >  create mode 100644 include/uapi/linux/famfs_ioctl.h
> > 
> > diff --git a/include/uapi/linux/famfs_ioctl.h b/include/uapi/linux/famfs_ioctl.h
> > new file mode 100644
> > index 000000000000..6b3e6452d02f
> > --- /dev/null
> > +++ b/include/uapi/linux/famfs_ioctl.h
> > @@ -0,0 +1,56 @@
> > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > +/*
> > + * famfs - dax file system for shared fabric-attached memory
> > + *
> > + * Copyright 2023-2024 Micron Technology, Inc.
> > + *
> > + * This file system, originally based on ramfs the dax support from xfs,
> > + * is intended to allow multiple host systems to mount a common file system
> > + * view of dax files that map to shared memory.
> > + */
> > +#ifndef FAMFS_IOCTL_H
> > +#define FAMFS_IOCTL_H
> > +
> > +#include <linux/ioctl.h>
> > +#include <linux/uuid.h>
> > +
> > +#define FAMFS_MAX_EXTENTS 2
> Why 2?

You catch everything! 

This limit is in place to avoid supporting somethign we're not testing. It
will probably be raised later.

Currently user space doesn't support deleting files, which makes it easy
to ignore whether any clients have a stale view of metadata. If there is
no delete, there's actually no reason to have more than 1 extent.

> > +
> > +enum extent_type {
> > +	SIMPLE_DAX_EXTENT = 13,
> 
> Comment on this would be good to have

Done. Basically we anticipate there being other types of extents in the
future.

> 
> > +	INVALID_EXTENT_TYPE,
> > +};
> > +
> > +struct famfs_extent {
> > +	__u64              offset;
> > +	__u64              len;
> > +};
> > +
> > +enum famfs_file_type {
> > +	FAMFS_REG,
> > +	FAMFS_SUPERBLOCK,
> > +	FAMFS_LOG,
> > +};
> > +
> > +/**
> > + * struct famfs_ioc_map
> > + *
> > + * This is the metadata that indicates where the memory is for a famfs file
> > + */
> > +struct famfs_ioc_map {
> > +	enum extent_type          extent_type;
> > +	enum famfs_file_type      file_type;
> 
> These are going to be potentially varying in size depending on arch, compiler
> settings etc.  Been a while, but I though best practice for uapi was always
> fixed size elements even though we lose the typing.

I might not be following you fully here. User space is running the same
arch as kernel, so an enum can't be a different size, right? It could be
a different size on different arches, but this is just between user/kernel.

I initially thought of XDR for on-media-format, which file systems need
to do with on-media structs (superblocks, logs, inodes, etc. etc.). But
this struct is not used in that way.

In fact, famfs' on-media/in-memory metadata (superblock, log, log entries)
is only ever read read and written by user space - so it's the user space
code that needs XDR on-media-format handling.

So to clarify - do you think those enums should be u32 or the like?

Thanks!
John

Re: [RFC PATCH 07/20] famfs: Add include/linux/famfs_ioctl.h

[Jonathan Cameron]

On Mon, 26 Feb 2024 10:44:43 -0600
John Groves <John@groves.net> wrote:

> On 24/02/26 12:39PM, Jonathan Cameron wrote:
> > On Fri, 23 Feb 2024 11:41:51 -0600
> > John Groves <John@Groves.net> wrote:
> >   
> > > Add uapi include file for famfs. The famfs user space uses ioctl on
> > > individual files to pass in mapping information and file size. This
> > > would be hard to do via sysfs or other means, since it's
> > > file-specific.
> > > 
> > > Signed-off-by: John Groves <john@groves.net>
> > > ---
> > >  include/uapi/linux/famfs_ioctl.h | 56 ++++++++++++++++++++++++++++++++
> > >  1 file changed, 56 insertions(+)
> > >  create mode 100644 include/uapi/linux/famfs_ioctl.h
> > > 
> > > diff --git a/include/uapi/linux/famfs_ioctl.h b/include/uapi/linux/famfs_ioctl.h
> > > new file mode 100644
> > > index 000000000000..6b3e6452d02f
> > > --- /dev/null
> > > +++ b/include/uapi/linux/famfs_ioctl.h
> > > @@ -0,0 +1,56 @@
> > > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > > +/*
> > > + * famfs - dax file system for shared fabric-attached memory
> > > + *
> > > + * Copyright 2023-2024 Micron Technology, Inc.
> > > + *
> > > + * This file system, originally based on ramfs the dax support from xfs,
> > > + * is intended to allow multiple host systems to mount a common file system
> > > + * view of dax files that map to shared memory.
> > > + */
> > > +#ifndef FAMFS_IOCTL_H
> > > +#define FAMFS_IOCTL_H
> > > +
> > > +#include <linux/ioctl.h>
> > > +#include <linux/uuid.h>
> > > +
> > > +#define FAMFS_MAX_EXTENTS 2  
> > Why 2?  
> 
> You catch everything! 
> 
> This limit is in place to avoid supporting somethign we're not testing. It
> will probably be raised later.
> 
> Currently user space doesn't support deleting files, which makes it easy
> to ignore whether any clients have a stale view of metadata. If there is
> no delete, there's actually no reason to have more than 1 extent.
Then have 1. + a Comment on why it is 1.
> 
> > > +
> > > +enum extent_type {
> > > +	SIMPLE_DAX_EXTENT = 13,  
> > 
> > Comment on this would be good to have  
> 
> Done. Basically we anticipate there being other types of extents in the
> future.

I was more curious about the 13!

> 
> >   
> > > +	INVALID_EXTENT_TYPE,
> > > +};
> > > +
> > > +struct famfs_extent {
> > > +	__u64              offset;
> > > +	__u64              len;
> > > +};
> > > +
> > > +enum famfs_file_type {
> > > +	FAMFS_REG,
> > > +	FAMFS_SUPERBLOCK,
> > > +	FAMFS_LOG,
> > > +};
> > > +
> > > +/**
> > > + * struct famfs_ioc_map
> > > + *
> > > + * This is the metadata that indicates where the memory is for a famfs file
> > > + */
> > > +struct famfs_ioc_map {
> > > +	enum extent_type          extent_type;
> > > +	enum famfs_file_type      file_type;  
> > 
> > These are going to be potentially varying in size depending on arch, compiler
> > settings etc.  Been a while, but I though best practice for uapi was always
> > fixed size elements even though we lose the typing.  
> 
> I might not be following you fully here. User space is running the same
> arch as kernel, so an enum can't be a different size, right? It could be
> a different size on different arches, but this is just between user/kernel.

I can't remember why, but this has bitten me in the past.
Ah, should have known Daniel would have written something on it ;)
https://www.kernel.org/doc/html/next/process/botching-up-ioctls.html

It's the fun of need for compat ioctls with 32bit userspace on 64bit kernels.

The alignment one is key as well. That bit me more than once due to
32bit x86 aligning 64 bit integers at 32 bits.

We could just not support these cases but it's easy to get right so why
bother with complexity of ruling them out.

> 
> I initially thought of XDR for on-media-format, which file systems need
> to do with on-media structs (superblocks, logs, inodes, etc. etc.). But
> this struct is not used in that way.
> 
> In fact, famfs' on-media/in-memory metadata (superblock, log, log entries)
> is only ever read read and written by user space - so it's the user space
> code that needs XDR on-media-format handling.
> 
> So to clarify - do you think those enums should be u32 or the like?

Yes. As it's userspace, uint32_t maybe or __u32. I 'think'
both are acceptable in uapi headers these days.

> 
> Thanks!
> John
> 

Re: [RFC PATCH 08/20] famfs: Add famfs_internal.h

[John Groves]

On 24/02/26 12:48PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:52 -0600
> John Groves <John@Groves.net> wrote:
> 
> > Add the famfs_internal.h include file. This contains internal data
> > structures such as the per-file metadata structure (famfs_file_meta)
> > and extent formats.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> Hi John,
> 
> Build this up as you add the definitions in later patches.
> 
> Separate header patches just make people jump back and forth when trying
> to review.  Obviously more work to build this stuff up cleanly but
> it's worth doing to save review time.
> 

Ohhhhkaaaaay. I think you're right, just not looking forward to
all that rebasing.

> Generally I'd plumb up Kconfig and Makefile a the beginning as it means
> that the set is bisectable and we can check the logic of building each stage.
> That is harder to do but tends to bring benefits in forcing clear step
> wise approach on a patch set. Feel free to ignore this one though as it
> can slow things down.

I'm not sure that's practical. A file system needs a bunch of different
kinds of operations
- super_operations
- fs_context_operations
- inode_operations
- file_operations
- dax holder_operations, iomap_ops
- etc.

Will think about the dependency graph of these entities, but I'm not sure
it's tractable...

> 
> A few trivial comments inline.
> 
> > ---
> >  fs/famfs/famfs_internal.h | 53 +++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 53 insertions(+)
> >  create mode 100644 fs/famfs/famfs_internal.h
> > 
> > diff --git a/fs/famfs/famfs_internal.h b/fs/famfs/famfs_internal.h
> > new file mode 100644
> > index 000000000000..af3990d43305
> > --- /dev/null
> > +++ b/fs/famfs/famfs_internal.h
> > @@ -0,0 +1,53 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * famfs - dax file system for shared fabric-attached memory
> > + *
> > + * Copyright 2023-2024 Micron Technology, Inc.
> > + *
> > + * This file system, originally based on ramfs the dax support from xfs,
> > + * is intended to allow multiple host systems to mount a common file system
> > + * view of dax files that map to shared memory.
> > + */
> > +#ifndef FAMFS_INTERNAL_H
> > +#define FAMFS_INTERNAL_H
> > +
> > +#include <linux/atomic.h>
> 
> Why?

Because fault counters are the one phased change to this file, and this
should have been with that. That may go away, but either way I'll do the
phased thing with this file.

> 
> > +#include <linux/famfs_ioctl.h>
> > +
> > +#define FAMFS_MAGIC 0x87b282ff
> > +
> > +#define FAMFS_BLKDEV_MODE (FMODE_READ|FMODE_WRITE)
> 
> Spaces around | 

Done

> 
> > +
> > +extern const struct file_operations      famfs_file_operations;
> 
> I wouldn't force alignment. It rots too often as new stuff gets added
> and doesn't really help readability much.

OK

> 
> > +
> > +/*
> > + * Each famfs dax file has this hanging from its inode->i_private.
> > + */
> > +struct famfs_file_meta {
> > +	int                   error;
> > +	enum famfs_file_type  file_type;
> > +	size_t                file_size;
> > +	enum extent_type      tfs_extent_type;
> > +	size_t                tfs_extent_ct;
> > +	struct famfs_extent   tfs_extents[];  /* flexible array */
> 
> Comment kind of obvious ;) I'd drop it.  Though we have
> magic markings for __counted_by which would be good to use from the start.

Done

> 
> 
> 
> > +};
> > +
> > +struct famfs_mount_opts {
> > +	umode_t mode;
> > +};
> > +
> > +extern const struct iomap_ops             famfs_iomap_ops;
> > +extern const struct vm_operations_struct  famfs_file_vm_ops;
> > +
> > +#define ROOTDEV_STRLEN 80
> 
> Why?  You aren't creating an array of this size here so I can't
> immediately see what the define is for.

Oversight. It was a char array but I switched to strdup() and 
failed to delete this. Gone now, thanks.

Thanks,
John

Re: [RFC PATCH 07/20] famfs: Add include/linux/famfs_ioctl.h

[John Groves]

On 24/02/26 04:56PM, Jonathan Cameron wrote:
> On Mon, 26 Feb 2024 10:44:43 -0600
> John Groves <John@groves.net> wrote:
> 
> > On 24/02/26 12:39PM, Jonathan Cameron wrote:
> > > On Fri, 23 Feb 2024 11:41:51 -0600
> > > John Groves <John@Groves.net> wrote:
> > >   
> > > > Add uapi include file for famfs. The famfs user space uses ioctl on
> > > > individual files to pass in mapping information and file size. This
> > > > would be hard to do via sysfs or other means, since it's
> > > > file-specific.
> > > > 
> > > > Signed-off-by: John Groves <john@groves.net>
> > > > ---
> > > >  include/uapi/linux/famfs_ioctl.h | 56 ++++++++++++++++++++++++++++++++
> > > >  1 file changed, 56 insertions(+)
> > > >  create mode 100644 include/uapi/linux/famfs_ioctl.h
> > > > 
> > > > diff --git a/include/uapi/linux/famfs_ioctl.h b/include/uapi/linux/famfs_ioctl.h
> > > > new file mode 100644
> > > > index 000000000000..6b3e6452d02f
> > > > --- /dev/null
> > > > +++ b/include/uapi/linux/famfs_ioctl.h
> > > > @@ -0,0 +1,56 @@
> > > > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > > > +/*
> > > > + * famfs - dax file system for shared fabric-attached memory
> > > > + *
> > > > + * Copyright 2023-2024 Micron Technology, Inc.
> > > > + *
> > > > + * This file system, originally based on ramfs the dax support from xfs,
> > > > + * is intended to allow multiple host systems to mount a common file system
> > > > + * view of dax files that map to shared memory.
> > > > + */
> > > > +#ifndef FAMFS_IOCTL_H
> > > > +#define FAMFS_IOCTL_H
> > > > +
> > > > +#include <linux/ioctl.h>
> > > > +#include <linux/uuid.h>
> > > > +
> > > > +#define FAMFS_MAX_EXTENTS 2  
> > > Why 2?  
> > 
> > You catch everything! 
> > 
> > This limit is in place to avoid supporting somethign we're not testing. It
> > will probably be raised later.
> > 
> > Currently user space doesn't support deleting files, which makes it easy
> > to ignore whether any clients have a stale view of metadata. If there is
> > no delete, there's actually no reason to have more than 1 extent.
> Then have 1. + a Comment on why it is 1.

Actually we test the 2 case. That seemed important to testing ioctl and
famfs_meta_to_dax_offset(). It just doesn't yet happen in the wild. Will
clarify with a comment.

> > 
> > > > +
> > > > +enum extent_type {
> > > > +	SIMPLE_DAX_EXTENT = 13,  
> > > 
> > > Comment on this would be good to have  
> > 
> > Done. Basically we anticipate there being other types of extents in the
> > future.
> 
> I was more curious about the 13!

I think I was just being feisty that day. Will drop that...

> 
> > 
> > >   
> > > > +	INVALID_EXTENT_TYPE,
> > > > +};
> > > > +
> > > > +struct famfs_extent {
> > > > +	__u64              offset;
> > > > +	__u64              len;
> > > > +};
> > > > +
> > > > +enum famfs_file_type {
> > > > +	FAMFS_REG,
> > > > +	FAMFS_SUPERBLOCK,
> > > > +	FAMFS_LOG,
> > > > +};
> > > > +
> > > > +/**
> > > > + * struct famfs_ioc_map
> > > > + *
> > > > + * This is the metadata that indicates where the memory is for a famfs file
> > > > + */
> > > > +struct famfs_ioc_map {
> > > > +	enum extent_type          extent_type;
> > > > +	enum famfs_file_type      file_type;  
> > > 
> > > These are going to be potentially varying in size depending on arch, compiler
> > > settings etc.  Been a while, but I though best practice for uapi was always
> > > fixed size elements even though we lose the typing.  
> > 
> > I might not be following you fully here. User space is running the same
> > arch as kernel, so an enum can't be a different size, right? It could be
> > a different size on different arches, but this is just between user/kernel.
> 
> I can't remember why, but this has bitten me in the past.
> Ah, should have known Daniel would have written something on it ;)
> https://www.kernel.org/doc/html/next/process/botching-up-ioctls.html
> 
> It's the fun of need for compat ioctls with 32bit userspace on 64bit kernels.
> 
> The alignment one is key as well. That bit me more than once due to
> 32bit x86 aligning 64 bit integers at 32 bits.
> 
> We could just not support these cases but it's easy to get right so why
> bother with complexity of ruling them out.

Makes sense. Will do.

> 
> > 
> > I initially thought of XDR for on-media-format, which file systems need
> > to do with on-media structs (superblocks, logs, inodes, etc. etc.). But
> > this struct is not used in that way.
> > 
> > In fact, famfs' on-media/in-memory metadata (superblock, log, log entries)
> > is only ever read read and written by user space - so it's the user space
> > code that needs XDR on-media-format handling.
> > 
> > So to clarify - do you think those enums should be u32 or the like?
> 
> Yes. As it's userspace, uint32_t maybe or __u32. I 'think'
> both are acceptable in uapi headers these days.

Roger that.

Thanks,
John

Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

[John Groves]

On 24/02/26 07:53AM, Luis Chamberlain wrote:
> On Mon, Feb 26, 2024 at 07:27:18AM -0600, John Groves wrote:
> > Run status group 0 (all jobs):
> >   WRITE: bw=29.6GiB/s (31.8GB/s), 29.6GiB/s-29.6GiB/s (31.8GB/s-31.8GB/s), io=44.7GiB (48.0GB), run=1511-1511msec
> 
> > This is run on an xfs file system on a SATA ssd.
> 
> To compare more closer apples to apples, wouldn't it make more sense
> to try this with XFS on pmem (with fio -direct=1)?
> 
>   Luis

Makes sense. Here is the same command line I used with xfs before, but 
now it's on /dev/pmem0 (the same 128G, but converted from devdax to pmem
because xfs requires that.

fio -name=ten-256m-per-thread --nrfiles=10 -bs=2M --group_reporting=1 --alloc-size=1048576 --filesize=256MiB --readwrite=write --fallocate=none --numjobs=48 --create_on_open=0 --ioengine=io_uring --direct=1 --directory=/mnt/xfs
ten-256m-per-thread: (g=0): rw=write, bs=(R) 2048KiB-2048KiB, (W) 2048KiB-2048KiB, (T) 2048KiB-2048KiB, ioengine=io_uring, iodepth=1
...
fio-3.33
Starting 48 processes
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
Jobs: 36 (f=360): [W(3),_(1),W(3),_(1),W(1),_(1),W(6),_(1),W(1),_(1),W(1),_(1),W(7),_(1),W(3),_(1),W(2),_(2),W(4),_(1),W(5),_(1)][77.8%][w=15.1GiB/s][w=7750 IOPS][eta 00m:02s]
ten-256m-per-thread: (groupid=0, jobs=48): err= 0: pid=8798: Mon Feb 26 15:10:30 2024
  write: IOPS=7582, BW=14.8GiB/s (15.9GB/s)(114GiB/7723msec); 0 zone resets
    slat (usec): min=23, max=7352, avg=131.80, stdev=151.63
    clat (usec): min=385, max=22638, avg=5789.74, stdev=3124.93
     lat (usec): min=432, max=22724, avg=5921.54, stdev=3133.18
    clat percentiles (usec):
     |  1.00th=[  799],  5.00th=[ 1467], 10.00th=[ 2073], 20.00th=[ 3097],
     | 30.00th=[ 3949], 40.00th=[ 4752], 50.00th=[ 5473], 60.00th=[ 6194],
     | 70.00th=[ 7046], 80.00th=[ 8029], 90.00th=[ 9634], 95.00th=[11338],
     | 99.00th=[16319], 99.50th=[17957], 99.90th=[20055], 99.95th=[20579],
     | 99.99th=[21365]
   bw (  MiB/s): min=10852, max=26980, per=100.00%, avg=15940.43, stdev=88.61, samples=665
   iops        : min= 5419, max=13477, avg=7963.08, stdev=44.28, samples=665
  lat (usec)   : 500=0.15%, 750=0.47%, 1000=1.34%
  lat (msec)   : 2=7.40%, 4=21.46%, 10=60.57%, 20=8.50%, 50=0.11%
  cpu          : usr=2.33%, sys=0.32%, ctx=58806, majf=0, minf=36301
  IO depths    : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     issued rwts: total=0,58560,0,0 short=0,0,0,0 dropped=0,0,0,0
     latency   : target=0, window=0, percentile=100.00%, depth=1

Run status group 0 (all jobs):
  WRITE: bw=14.8GiB/s (15.9GB/s), 14.8GiB/s-14.8GiB/s (15.9GB/s-15.9GB/s), io=114GiB (123GB), run=7723-7723msec

Disk stats (read/write):
  pmem0: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%


I only have some educated guesses as to why famfs is faster. Since files 
are preallocated, they're always contiguous. And famfs is vastly simpler
because it isn't aimed at general purpose uses cases (and indeed can't
handle them).

Regards,
John

Re: [RFC PATCH 09/20] famfs: Add super_operations

[John Groves]

On 24/02/26 12:51PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:53 -0600
> John Groves <John@Groves.net> wrote:
> 
> > Introduce the famfs superblock operations
> > 
> > Signed-off-by: John Groves <john@groves.net>
> > ---
> >  fs/famfs/famfs_inode.c | 72 ++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 72 insertions(+)
> >  create mode 100644 fs/famfs/famfs_inode.c
> > 
> > diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> > new file mode 100644
> > index 000000000000..3329aff000d1
> > --- /dev/null
> > +++ b/fs/famfs/famfs_inode.c
> > @@ -0,0 +1,72 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * famfs - dax file system for shared fabric-attached memory
> > + *
> > + * Copyright 2023-2024 Micron Technology, inc
> > + *
> > + * This file system, originally based on ramfs the dax support from xfs,
> > + * is intended to allow multiple host systems to mount a common file system
> > + * view of dax files that map to shared memory.
> > + */
> > +
> > +#include <linux/fs.h>
> > +#include <linux/pagemap.h>
> > +#include <linux/highmem.h>
> > +#include <linux/time.h>
> > +#include <linux/init.h>
> > +#include <linux/string.h>
> > +#include <linux/backing-dev.h>
> > +#include <linux/sched.h>
> > +#include <linux/parser.h>
> > +#include <linux/magic.h>
> > +#include <linux/slab.h>
> > +#include <linux/uaccess.h>
> > +#include <linux/fs_context.h>
> > +#include <linux/fs_parser.h>
> > +#include <linux/seq_file.h>
> > +#include <linux/dax.h>
> > +#include <linux/hugetlb.h>
> > +#include <linux/uio.h>
> > +#include <linux/iomap.h>
> > +#include <linux/path.h>
> > +#include <linux/namei.h>
> > +#include <linux/pfn_t.h>
> > +#include <linux/blkdev.h>
> 
> That's a lot of header for such a small patch.. I'm going to guess
> they aren't all used - bring them in as you need them - I hope
> you never need some of these!

I didn't phase in headers in this series. Based on these recommendations,
the next version of this series is gonna have to be 100% constructed from
scratch, but okay. My head hurts just thinking about it. I need a nap...

I've been rebasing for 3 weeks to get this series out, and it occurs to
me that maybe there are tools I'm not aware of that make it eaiser? I'm
just typing "rebase -i..." 200 times a day. Is there a less soul-crushing way?

> 
> 
> > +
> > +#include "famfs_internal.h"
> > +
> > +#define FAMFS_DEFAULT_MODE	0755
> > +
> > +static const struct super_operations famfs_ops;
> > +static const struct inode_operations famfs_file_inode_operations;
> > +static const struct inode_operations famfs_dir_inode_operations;
> 
> Why are these all up here?

These forward declarations are needed by a later patch in the series.
They were in famfs_internal.h, but they are only used in this file, so
I moved them here.

For all answers such as this, I will hereafter reply "rebase fu", with
further clarification only if necessary.

> 
> > +
> > +/**********************************************************************************
> > + * famfs super_operations
> > + *
> > + * TODO: implement a famfs_statfs() that shows size, free and available space, etc.
> > + */
> > +
> > +/**
> > + * famfs_show_options() - Display the mount options in /proc/mounts.
> Run kernel doc script + fix all warnings.

Will do; I actually think I have already fixed those...

> 
> > + */
> > +static int famfs_show_options(
> > +	struct seq_file *m,
> > +	struct dentry   *root)
> Not that familiar with fs code, but this unusual kernel style. I'd go with 
> something more common
> 
> static int famfs_show_options(struct seq_file *m, struct dentry *root)

Done. To all functions...

> 
> > +{
> > +	struct famfs_fs_info *fsi = root->d_sb->s_fs_info;
> > +
> > +	if (fsi->mount_opts.mode != FAMFS_DEFAULT_MODE)
> > +		seq_printf(m, ",mode=%o", fsi->mount_opts.mode);
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct super_operations famfs_ops = {
> > +	.statfs		= simple_statfs,
> > +	.drop_inode	= generic_delete_inode,
> > +	.show_options	= famfs_show_options,
> > +};
> > +
> > +
> One blank line probably fine.

Done

> 
> 
> Add the rest of the stuff a module normally has, author etc in this
> patch.

Because "rebase fu" I'm not sure the order will remain the same. Will
try not to make anybody tell me this again though...

John

Re: [RFC PATCH 10/20] famfs: famfs_open_device() & dax_holder_operations

[John Groves]

On 24/02/26 12:56PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:54 -0600
> John Groves <John@Groves.net> wrote:
> 
> > Famfs works on both /dev/pmem and /dev/dax devices. This commit introduces
> > the function that opens a block (pmem) device and the struct
> > dax_holder_operations that are needed for that ABI.
> > 
> > In this commit, support for opening character /dev/dax is stubbed. A
> > later commit introduces this capability.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> 
> Formatting comments mostly same as previous patches, so I'll stop repeating them.

I tried to bulk apply those recommendations.

> 
> > ---
> >  fs/famfs/famfs_inode.c | 83 ++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 83 insertions(+)
> > 
> > diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> > index 3329aff000d1..82c861998093 100644
> > --- a/fs/famfs/famfs_inode.c
> > +++ b/fs/famfs/famfs_inode.c
> > @@ -68,5 +68,88 @@ static const struct super_operations famfs_ops = {
> >  	.show_options	= famfs_show_options,
> >  };
> >  
> > +/***************************************************************************************
> > + * dax_holder_operations for block dax
> > + */
> > +
> > +static int
> > +famfs_blk_dax_notify_failure(
> > +	struct dax_device	*dax_devp,
> > +	u64			offset,
> > +	u64			len,
> > +	int			mf_flags)
> > +{
> > +
> > +	pr_err("%s: dax_devp %llx offset %llx len %lld mf_flags %x\n",
> > +	       __func__, (u64)dax_devp, (u64)offset, (u64)len, mf_flags);
> > +	return -EOPNOTSUPP;
> > +}
> > +
> > +const struct dax_holder_operations famfs_blk_dax_holder_ops = {
> > +	.notify_failure		= famfs_blk_dax_notify_failure,
> > +};
> > +
> > +static int
> > +famfs_open_char_device(
> > +	struct super_block *sb,
> > +	struct fs_context  *fc)
> > +{
> > +	pr_err("%s: Root device is %s, but your kernel does not support famfs on /dev/dax\n",
> > +	       __func__, fc->source);
> > +	return -ENODEV;
> > +}
> > +
> > +/**
> > + * famfs_open_device()
> > + *
> > + * Open the memory device. If it looks like /dev/dax, call famfs_open_char_device().
> > + * Otherwise try to open it as a block/pmem device.
> > + */
> > +static int
> > +famfs_open_device(
> > +	struct super_block *sb,
> > +	struct fs_context  *fc)
> > +{
> > +	struct famfs_fs_info *fsi = sb->s_fs_info;
> > +	struct dax_device    *dax_devp;
> > +	u64 start_off = 0;
> > +	struct bdev_handle   *handlep;
> Definitely don't force alignment in local parameter definitions.
> Always goes wrong and makes for unreadable mess in patches!

Okay, undone. Everywhere.

> 
> > +
> > +	if (fsi->dax_devp) {
> > +		pr_err("%s: already mounted\n", __func__);
> Fine to fail but worth a error message? Not sure on convention on this but seems noisy
> and maybe in userspace control which isn't good.

Changing to pr_debug. Would be good to have access to it in that way

> > +		return -EALREADY;
> > +	}
> > +
> > +	if (strstr(fc->source, "/dev/dax")) /* There is probably a better way to check this */
> > +		return famfs_open_char_device(sb, fc);
> > +
> > +	if (!strstr(fc->source, "/dev/pmem")) { /* There is probably a better way to check this */
> > +		pr_err("%s: primary backing dev (%s) is not pmem\n",
> > +		       __func__, fc->source);
> > +		return -EINVAL;
> > +	}
> > +
> > +	handlep = bdev_open_by_path(fc->source, FAMFS_BLKDEV_MODE, fsi, &fs_holder_ops);
> > +	if (IS_ERR(handlep->bdev)) {
> > +		pr_err("%s: failed blkdev_get_by_path(%s)\n", __func__, fc->source);
> > +		return PTR_ERR(handlep->bdev);
> > +	}
> > +
> > +	dax_devp = fs_dax_get_by_bdev(handlep->bdev, &start_off,
> > +				      fsi  /* holder */,
> > +				      &famfs_blk_dax_holder_ops);
> > +	if (IS_ERR(dax_devp)) {
> > +		pr_err("%s: unable to get daxdev from handlep->bdev\n", __func__);
> > +		bdev_release(handlep);
> > +		return -ENODEV;
> > +	}
> > +	fsi->bdev_handle = handlep;
> > +	fsi->dax_devp    = dax_devp;
> > +
> > +	pr_notice("%s: root device is block dax (%s)\n", __func__, fc->source);
> 
> pr_debug()  Kernel log is too noisy anyway! + I'd assume we can tell this succeeded
> in lots of other ways.

Done

> 
> 
> > +	return 0;
> > +}
> > +
> > +
> >  
> >  MODULE_LICENSE("GPL");

Thanks,
John
> 

Re: [RFC PATCH 11/20] famfs: Add fs_context_operations

[John Groves]

On 24/02/26 01:20PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:55 -0600
> John Groves <John@Groves.net> wrote:
> 
> > This commit introduces the famfs fs_context_operations and
> > famfs_get_inode() which is used by the context operations.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> Trivial comments inline.
> 
> > ---
> >  fs/famfs/famfs_inode.c | 178 +++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 178 insertions(+)
> > 
> > diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> > index 82c861998093..f98f82962d7b 100644
> > --- a/fs/famfs/famfs_inode.c
> > +++ b/fs/famfs/famfs_inode.c
> > @@ -41,6 +41,50 @@ static const struct super_operations famfs_ops;
> >  static const struct inode_operations famfs_file_inode_operations;
> >  static const struct inode_operations famfs_dir_inode_operations;
> >  
> > +static struct inode *famfs_get_inode(
> > +	struct super_block *sb,
> > +	const struct inode *dir,
> > +	umode_t             mode,
> > +	dev_t               dev)
> > +{
> > +	struct inode *inode = new_inode(sb);
> > +
> > +	if (inode) {
> reverse logic would be simpler and reduce indent.
> 
> 	if (!inode)
> 		return NULL;
> 

Good one - I can be derpy this way. Although I'd bet I just copied that
from ramfs...

> 
> > +		struct timespec64       tv;
> > +
> > +		inode->i_ino = get_next_ino();
> > +		inode_init_owner(&nop_mnt_idmap, inode, dir, mode);
> > +		inode->i_mapping->a_ops = &ram_aops;
> > +		mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
> > +		mapping_set_unevictable(inode->i_mapping);
> > +		tv = inode_set_ctime_current(inode);
> > +		inode_set_mtime_to_ts(inode, tv);
> > +		inode_set_atime_to_ts(inode, tv);
> > +
> > +		switch (mode & S_IFMT) {
> > +		default:
> > +			init_special_inode(inode, mode, dev);
> > +			break;
> > +		case S_IFREG:
> > +			inode->i_op = &famfs_file_inode_operations;
> > +			inode->i_fop = &famfs_file_operations;
> > +			break;
> > +		case S_IFDIR:
> > +			inode->i_op = &famfs_dir_inode_operations;
> > +			inode->i_fop = &simple_dir_operations;
> > +
> > +			/* Directory inodes start off with i_nlink == 2 (for "." entry) */
> > +			inc_nlink(inode);
> > +			break;
> > +		case S_IFLNK:
> > +			inode->i_op = &page_symlink_inode_operations;
> > +			inode_nohighmem(inode);
> > +			break;
> > +		}
> > +	}
> > +	return inode;
> > +}
> > +
> >  /**********************************************************************************
> >   * famfs super_operations
> >   *
> > @@ -150,6 +194,140 @@ famfs_open_device(
> >  	return 0;
> >  }
> >  
> > +/*****************************************************************************************
> > + * fs_context_operations
> > + */
> > +static int
> > +famfs_fill_super(
> > +	struct super_block *sb,
> > +	struct fs_context  *fc)
> > +{
> > +	struct famfs_fs_info *fsi = sb->s_fs_info;
> > +	struct inode *inode;
> > +	int rc = 0;
> Always initialized so no need to do it here.

Fixed in more than one place.

> 
> > +
> > +	sb->s_maxbytes		= MAX_LFS_FILESIZE;
> > +	sb->s_blocksize		= PAGE_SIZE;
> > +	sb->s_blocksize_bits	= PAGE_SHIFT;
> > +	sb->s_magic		= FAMFS_MAGIC;
> > +	sb->s_op		= &famfs_ops;
> > +	sb->s_time_gran		= 1;
> > +
> > +	rc = famfs_open_device(sb, fc);
> > +	if (rc)
> > +		goto out;
> 		return rc; //unless you need to do more in out in later patch..

Done

> 
> > +
> > +	inode = famfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0);
> > +	sb->s_root = d_make_root(inode);
> > +	if (!sb->s_root)
> > +		rc = -ENOMEM;
> 		return -ENOMEM;

Done

> 
> 	return 0;

Done

> 
> > +
> > +out:
> > +	return rc;
> > +}
> > +
> > +enum famfs_param {
> > +	Opt_mode,
> > +	Opt_dax,
> Why capital O?

Direct copy from ramfs

> 
> > +};
> > +
> 
> ...
> 
> > +
> > +static DEFINE_MUTEX(famfs_context_mutex);
> > +static LIST_HEAD(famfs_context_list);
> > +
> > +static int famfs_get_tree(struct fs_context *fc)
> > +{
> > +	struct famfs_fs_info *fsi_entry;
> > +	struct famfs_fs_info *fsi = fc->s_fs_info;
> > +
> > +	fsi->rootdev = kstrdup(fc->source, GFP_KERNEL);
> > +	if (!fsi->rootdev)
> > +		return -ENOMEM;
> > +
> > +	/* Fail if famfs is already mounted from the same device */
> > +	mutex_lock(&famfs_context_mutex);
> 
> New toys might be good to use from start to avoid need for explicit
> unlocks in error paths.
> 
> 	scoped_guard(mutex, &famfs_context_mutex) {
> 		list_for_each_entry(fsi_entry, &famfs_context_list, fsi_list) {
> 			if (strcmp(fsi_entry->rootdev, cs_source) == 0) {
> 			//could invert with a continue to reduce indent
> 			// or factor this out as a little helper.
> 			// famfs_check_not_mounted()
> 				pr_err();
> 				return -EALREADY;
> 			}
> 		}	
> 		list_add(&fsi->fs_list, &famfs_context_list);
> 	}
> 
> 	return get_tree_nodev(...

Hey, I like this one. Thanks!

John

Re: [RFC PATCH 12/20] famfs: Add inode_operations and file_system_type

[John Groves]

On 24/02/26 01:25PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:56 -0600
> John Groves <John@Groves.net> wrote:
> 
> > This commit introduces the famfs inode_operations. There is nothing really
> > unique to famfs here in the inode_operations..
> > 
> > This commit also introduces the famfs_file_system_type struct and the
> > famfs_kill_sb() function.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> 
> Trivial comments only.
> 
> > +
> > +/*
> > + * File creation. Allocate an inode, and we're done..
> > + */
> > +/* SMP-safe */
> > +static int
> > +famfs_mknod(
> > +	struct mnt_idmap *idmap,
> > +	struct inode     *dir,
> > +	struct dentry    *dentry,
> > +	umode_t           mode,
> > +	dev_t             dev)
> > +{
> > +	struct inode *inode = famfs_get_inode(dir->i_sb, dir, mode, dev);
> > +	int error           = -ENOSPC;
> > +
> > +	if (inode) {
> 
> As below. I would flip it for cleaner code/ shorter indent etc.

Nice - done.

> 
> > +		struct timespec64       tv;
> > +
> > +		d_instantiate(dentry, inode);
> > +		dget(dentry);	/* Extra count - pin the dentry in core */
> > +		error = 0;
> > +		tv = inode_set_ctime_current(inode);
> > +		inode_set_mtime_to_ts(inode, tv);
> > +		inode_set_atime_to_ts(inode, tv);
> > +	}
> > +	return error;
> > +}
> > +
> > +static int famfs_mkdir(
> > +	struct mnt_idmap *idmap,
> > +	struct inode     *dir,
> > +	struct dentry    *dentry,
> > +	umode_t           mode)
> > +{
> > +	int retval = famfs_mknod(&nop_mnt_idmap, dir, dentry, mode | S_IFDIR, 0);
> > +
> > +	if (!retval)
> > +		inc_nlink(dir);
> 
> Copy local style, so fine if this is common pattern, otherwise I'd go for
> consistent error cases out of line as easier for us sleepy caffeine 
> deprived reviewers.
> 
> 
> 	if (retval)
> 		return retval;
> 
> 	inc_nlink(dir);
> 
> 	return 0;

Agree, done.

> > +
> > +	return retval;
> > +}
> > +
> > +static int famfs_create(
> > +	struct mnt_idmap *idmap,
> > +	struct inode     *dir,
> > +	struct dentry    *dentry,
> > +	umode_t           mode,
> > +	bool              excl)
> > +{
> > +	return famfs_mknod(&nop_mnt_idmap, dir, dentry, mode | S_IFREG, 0);
> > +}
> > +
> > +static int famfs_symlink(
> > +	struct mnt_idmap *idmap,
> > +	struct inode     *dir,
> > +	struct dentry    *dentry,
> > +	const char       *symname)
> > +{
> > +	struct inode *inode;
> > +	int error = -ENOSPC;
> > +
> > +	inode = famfs_get_inode(dir->i_sb, dir, S_IFLNK | 0777, 0);
> 	if (!inode)
> 		return -ENOSPC;
> 
> > +	if (inode) {
> > +		int l = strlen(symname)+1;
> > +
> > +		error = page_symlink(inode, symname, l);
> 	if (error) {
> 		iput(inode);
> 		return error;
> 	}
> 	
> 	...
> 

Right, I like it. This was some tortured conditioning, which came from
somewhere. I deny responsibility :D

Thanks,
John

Re: [RFC PATCH 13/20] famfs: Add iomap_ops

[John Groves]

On 24/02/26 01:30PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:57 -0600
> John Groves <John@Groves.net> wrote:
> 
> > This commit introduces the famfs iomap_ops. When either
> > dax_iomap_fault() or dax_iomap_rw() is called, we get a callback
> > via our iomap_begin() handler. The question being asked is
> > "please resolve (file, offset) to (daxdev, offset)". The function
> > famfs_meta_to_dax_offset() does this.
> > 
> > The per-file metadata is just an extent list to the
> > backing dax dev.  The order of this resolution is O(N) for N
> > extents. Note with the current user space, files usually have
> > only one extent.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> 
> > ---
> >  fs/famfs/famfs_file.c | 245 ++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 245 insertions(+)
> >  create mode 100644 fs/famfs/famfs_file.c
> > 
> > diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c
> > new file mode 100644
> > index 000000000000..fc667d5f7be8
> > --- /dev/null
> > +++ b/fs/famfs/famfs_file.c
> > @@ -0,0 +1,245 @@
> 
> > +static int
> > +famfs_meta_to_dax_offset(
> > +	struct inode *inode,
> > +	struct iomap *iomap,
> > +	loff_t        offset,
> > +	loff_t        len,
> > +	unsigned int  flags)
> > +{
> > +	struct famfs_file_meta *meta = (struct famfs_file_meta *)inode->i_private;
> 
> i_private is void * so no need for explicit cast (C spec says this is always fine without)

Yessir.

> 
> 
> > +
> > +/**
> > + * famfs_iomap_begin()
> > + *
> > + * This function is pretty simple because files are
> > + * * never partially allocated
> > + * * never have holes (never sparse)
> > + * * never "allocate on write"
> > + */
> > +static int
> > +famfs_iomap_begin(
> > +	struct inode	       *inode,
> > +	loff_t			offset,
> > +	loff_t			length,
> > +	unsigned int		flags,
> > +	struct iomap	       *iomap,
> > +	struct iomap	       *srcmap)
> > +{
> > +	struct famfs_file_meta *meta = inode->i_private;
> > +	size_t size;
> > +	int rc;
> > +
> > +	size = i_size_read(inode);
> > +
> > +	WARN_ON(size != meta->file_size);
> > +
> > +	rc = famfs_meta_to_dax_offset(inode, iomap, offset, length, flags);
> > +
> > +	return rc;
> 	return famfs_meta_...

Done

> 
> > +}
> 
> 
> > +static vm_fault_t
> > +famfs_filemap_map_pages(
> > +	struct vm_fault	       *vmf,
> > +	pgoff_t			start_pgoff,
> > +	pgoff_t			end_pgoff)
> > +{
> > +	vm_fault_t ret;
> > +
> > +	ret = filemap_map_pages(vmf, start_pgoff, end_pgoff);
> > +	return ret;
> 	return filename_map_pages()....

Done, thanks

John

Re: [RFC PATCH 14/20] famfs: Add struct file_operations

[John Groves]

On 24/02/26 01:32PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:58 -0600
> John Groves <John@Groves.net> wrote:
> 
> > This commit introduces the famfs file_operations. We call
> > thp_get_unmapped_area() to force PMD page alignment. Our read and
> > write handlers (famfs_dax_read_iter() and famfs_dax_write_iter())
> > call dax_iomap_rw() to do the work.
> > 
> > famfs_file_invalid() checks for various ways a famfs file can be
> > in an invalid state so we can fail I/O or fault resolution in those
> > cases. Those cases include the following:
> > 
> > * No famfs metadata
> > * file i_size does not match the originally allocated size
> > * file is not flagged as DAX
> > * errors were detected previously on the file
> > 
> > An invalid file can often be fixed by replaying the log, or by
> > umount/mount/log replay - all of which are user space operations.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> > ---
> >  fs/famfs/famfs_file.c | 136 ++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 136 insertions(+)
> > 
> > diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c
> > index fc667d5f7be8..5228e9de1e3b 100644
> > --- a/fs/famfs/famfs_file.c
> > +++ b/fs/famfs/famfs_file.c
> > @@ -19,6 +19,142 @@
> >  #include <uapi/linux/famfs_ioctl.h>
> >  #include "famfs_internal.h"
> >  
> > +/*********************************************************************
> > + * file_operations
> > + */
> > +
> > +/* Reject I/O to files that aren't in a valid state */
> > +static ssize_t
> > +famfs_file_invalid(struct inode *inode)
> > +{
> > +	size_t i_size       = i_size_read(inode);
> > +	struct famfs_file_meta *meta = inode->i_private;
> > +
> > +	if (!meta) {
> > +		pr_err("%s: un-initialized famfs file\n", __func__);
> > +		return -EIO;
> > +	}
> > +	if (i_size != meta->file_size) {
> > +		pr_err("%s: something changed the size from  %ld to %ld\n",
> > +		       __func__, meta->file_size, i_size);
> > +		meta->error = 1;
> > +		return -ENXIO;
> > +	}
> > +	if (!IS_DAX(inode)) {
> > +		pr_err("%s: inode %llx IS_DAX is false\n", __func__, (u64)inode);
> > +		meta->error = 1;
> > +		return -ENXIO;
> > +	}
> > +	if (meta->error) {
> > +		pr_err("%s: previously detected metadata errors\n", __func__);
> > +		meta->error = 1;
> 
> Already set?  If treating it as only a boolean, maybe make it one?

Done, thanks

John

Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

[Luis Chamberlain]

On Mon, Feb 26, 2024 at 1:16 PM John Groves <John@groves.net> wrote:
>
> On 24/02/26 07:53AM, Luis Chamberlain wrote:
> > On Mon, Feb 26, 2024 at 07:27:18AM -0600, John Groves wrote:
> > > Run status group 0 (all jobs):
> > >   WRITE: bw=29.6GiB/s (31.8GB/s), 29.6GiB/s-29.6GiB/s (31.8GB/s-31.8GB/s), io=44.7GiB (48.0GB), run=1511-1511msec
> >
> > > This is run on an xfs file system on a SATA ssd.
> >
> > To compare more closer apples to apples, wouldn't it make more sense
> > to try this with XFS on pmem (with fio -direct=1)?
> >
> >   Luis
>
> Makes sense. Here is the same command line I used with xfs before, but
> now it's on /dev/pmem0 (the same 128G, but converted from devdax to pmem
> because xfs requires that.
>
> fio -name=ten-256m-per-thread --nrfiles=10 -bs=2M --group_reporting=1 --alloc-size=1048576 --filesize=256MiB --readwrite=write --fallocate=none --numjobs=48 --create_on_open=0 --ioengine=io_uring --direct=1 --directory=/mnt/xfs

Could you try with mkfs.xfs -d agcount=1024

 Luis

Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

[John Groves]

On 24/02/26 04:58PM, Luis Chamberlain wrote:
> On Mon, Feb 26, 2024 at 1:16 PM John Groves <John@groves.net> wrote:
> >
> > On 24/02/26 07:53AM, Luis Chamberlain wrote:
> > > On Mon, Feb 26, 2024 at 07:27:18AM -0600, John Groves wrote:
> > > > Run status group 0 (all jobs):
> > > >   WRITE: bw=29.6GiB/s (31.8GB/s), 29.6GiB/s-29.6GiB/s (31.8GB/s-31.8GB/s), io=44.7GiB (48.0GB), run=1511-1511msec
> > >
> > > > This is run on an xfs file system on a SATA ssd.
> > >
> > > To compare more closer apples to apples, wouldn't it make more sense
> > > to try this with XFS on pmem (with fio -direct=1)?
> > >
> > >   Luis
> >
> > Makes sense. Here is the same command line I used with xfs before, but
> > now it's on /dev/pmem0 (the same 128G, but converted from devdax to pmem
> > because xfs requires that.
> >
> > fio -name=ten-256m-per-thread --nrfiles=10 -bs=2M --group_reporting=1 --alloc-size=1048576 --filesize=256MiB --readwrite=write --fallocate=none --numjobs=48 --create_on_open=0 --ioengine=io_uring --direct=1 --directory=/mnt/xfs
> 
> Could you try with mkfs.xfs -d agcount=1024
> 
>  Luis

$ luis/fio-xfsdax.sh 
+ sudo mkfs.xfs -d agcount=1024 -m reflink=0 -f /dev/pmem0
meta-data=/dev/pmem0             isize=512    agcount=1024, agsize=32768 blks
         =                       sectsz=4096  attr=2, projid32bit=1
         =                       crc=1        finobt=1, sparse=1, rmapbt=0
         =                       reflink=0    bigtime=1 inobtcount=1 nrext64=0
data     =                       bsize=4096   blocks=33554432, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0, ftype=1
log      =internal log           bsize=4096   blocks=16384, version=2
         =                       sectsz=4096  sunit=1 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
+ sudo mount -o dax /dev/pmem0 /mnt/xfs
+ sudo chown jmg:jmg /mnt/xfs
+ ls -al /mnt/xfs
total 0
drwxr-xr-x  2 jmg  jmg   6 Feb 26 19:56 .
drwxr-xr-x. 4 root root 30 Feb 26 14:58 ..
++ nproc
+ fio -name=ten-256m-per-thread --nrfiles=10 -bs=2M --group_reporting=1 --alloc-size=1048576 --filesize=256MiB --readwrite=write --fallocate=none --numjobs=48 --create_on_open=0 --ioengine=io_uring --direct=1 --directory=/mnt/xfs
ten-256m-per-thread: (g=0): rw=write, bs=(R) 2048KiB-2048KiB, (W) 2048KiB-2048KiB, (T) 2048KiB-2048KiB, ioengine=io_uring, iodepth=1
...
fio-3.33
Starting 48 processes
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
ten-256m-per-thread: Laying out IO files (10 files / total 2441MiB)
Jobs: 17 (f=170): [_(2),W(1),_(8),W(2),_(7),W(3),_(2),W(2),_(3),W(2),_(2),W(1),_(2),W(1),_(1),W(3),_(4),W(2)][Jobs: 1 (f=10): [_(47),W(1)][100.0%][w=8022MiB/s][w=4011 IOPS][eta 00m:00s]                                                                                
ten-256m-per-thread: (groupid=0, jobs=48): err= 0: pid=141563: Mon Feb 26 19:56:28 2024
  write: IOPS=6578, BW=12.8GiB/s (13.8GB/s)(114GiB/8902msec); 0 zone resets
    slat (usec): min=18, max=60593, avg=1230.85, stdev=1799.97
    clat (usec): min=2, max=98969, avg=5133.25, stdev=5141.07
     lat (usec): min=294, max=99725, avg=6364.09, stdev=5440.30
    clat percentiles (usec):
     |  1.00th=[   11],  5.00th=[   46], 10.00th=[  217], 20.00th=[ 2376],
     | 30.00th=[ 2999], 40.00th=[ 3556], 50.00th=[ 3785], 60.00th=[ 3982],
     | 70.00th=[ 4228], 80.00th=[ 7504], 90.00th=[13173], 95.00th=[14091],
     | 99.00th=[21890], 99.50th=[27919], 99.90th=[45351], 99.95th=[57934],
     | 99.99th=[82314]
   bw (  MiB/s): min= 5085, max=27367, per=100.00%, avg=14361.95, stdev=165.61, samples=719
   iops        : min= 2516, max=13670, avg=7160.17, stdev=82.88, samples=719
  lat (usec)   : 4=0.05%, 10=0.72%, 20=2.23%, 50=2.48%, 100=3.02%
  lat (usec)   : 250=1.54%, 500=2.37%, 750=1.34%, 1000=0.75%
  lat (msec)   : 2=3.20%, 4=43.10%, 10=23.05%, 20=14.81%, 50=1.25%
  lat (msec)   : 100=0.08%
  cpu          : usr=10.18%, sys=0.79%, ctx=67227, majf=0, minf=38511
  IO depths    : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     issued rwts: total=0,58560,0,0 short=0,0,0,0 dropped=0,0,0,0
     latency   : target=0, window=0, percentile=100.00%, depth=1

Run status group 0 (all jobs):
  WRITE: bw=12.8GiB/s (13.8GB/s), 12.8GiB/s-12.8GiB/s (13.8GB/s-13.8GB/s), io=114GiB (123GB), run=8902-8902msec

Disk stats (read/write):
  pmem0: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%


I ran it several times with similar results.

Regards,
John

Re: [RFC PATCH 08/20] famfs: Add famfs_internal.h

[Jonathan Cameron]

On Mon, 26 Feb 2024 11:35:17 -0600
John Groves <John@groves.net> wrote:

> On 24/02/26 12:48PM, Jonathan Cameron wrote:
> > On Fri, 23 Feb 2024 11:41:52 -0600
> > John Groves <John@Groves.net> wrote:
> >   
> > > Add the famfs_internal.h include file. This contains internal data
> > > structures such as the per-file metadata structure (famfs_file_meta)
> > > and extent formats.
> > > 
> > > Signed-off-by: John Groves <john@groves.net>  
> > Hi John,
> > 
> > Build this up as you add the definitions in later patches.
> > 
> > Separate header patches just make people jump back and forth when trying
> > to review.  Obviously more work to build this stuff up cleanly but
> > it's worth doing to save review time.
> >   
> 
> Ohhhhkaaaaay. I think you're right, just not looking forward to
> all that rebasing.

:)  Patch mangling is half the fun of upstream development :)

> 
> > Generally I'd plumb up Kconfig and Makefile a the beginning as it means
> > that the set is bisectable and we can check the logic of building each stage.
> > That is harder to do but tends to bring benefits in forcing clear step
> > wise approach on a patch set. Feel free to ignore this one though as it
> > can slow things down.  
> 
> I'm not sure that's practical. A file system needs a bunch of different
> kinds of operations
> - super_operations
> - fs_context_operations
> - inode_operations
> - file_operations
> - dax holder_operations, iomap_ops
> - etc.
> 
> Will think about the dependency graph of these entities, but I'm not sure
> it's tractable...

Sure.  There's a difference though between doing something useful (or
even successfully loading) and being able to build it at intermediate steps.
I'm only looking for buildability.

If not possible, even with a few stubs, empty ops structures etc
then fair enough.

Jonathan

Re: [RFC PATCH 09/20] famfs: Add super_operations

[Jonathan Cameron]

On Mon, 26 Feb 2024 15:47:53 -0600
John Groves <John@groves.net> wrote:

> On 24/02/26 12:51PM, Jonathan Cameron wrote:
> > On Fri, 23 Feb 2024 11:41:53 -0600
> > John Groves <John@Groves.net> wrote:
> >   
> > > Introduce the famfs superblock operations
> > > 
> > > Signed-off-by: John Groves <john@groves.net>
> > > ---
> > >  fs/famfs/famfs_inode.c | 72 ++++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 72 insertions(+)
> > >  create mode 100644 fs/famfs/famfs_inode.c
> > > 
> > > diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> > > new file mode 100644
> > > index 000000000000..3329aff000d1
> > > --- /dev/null
> > > +++ b/fs/famfs/famfs_inode.c
> > > @@ -0,0 +1,72 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/*
> > > + * famfs - dax file system for shared fabric-attached memory
> > > + *
> > > + * Copyright 2023-2024 Micron Technology, inc
> > > + *
> > > + * This file system, originally based on ramfs the dax support from xfs,
> > > + * is intended to allow multiple host systems to mount a common file system
> > > + * view of dax files that map to shared memory.
> > > + */
> > > +
> > > +#include <linux/fs.h>
> > > +#include <linux/pagemap.h>
> > > +#include <linux/highmem.h>
> > > +#include <linux/time.h>
> > > +#include <linux/init.h>
> > > +#include <linux/string.h>
> > > +#include <linux/backing-dev.h>
> > > +#include <linux/sched.h>
> > > +#include <linux/parser.h>
> > > +#include <linux/magic.h>
> > > +#include <linux/slab.h>
> > > +#include <linux/uaccess.h>
> > > +#include <linux/fs_context.h>
> > > +#include <linux/fs_parser.h>
> > > +#include <linux/seq_file.h>
> > > +#include <linux/dax.h>
> > > +#include <linux/hugetlb.h>
> > > +#include <linux/uio.h>
> > > +#include <linux/iomap.h>
> > > +#include <linux/path.h>
> > > +#include <linux/namei.h>
> > > +#include <linux/pfn_t.h>
> > > +#include <linux/blkdev.h>  
> > 
> > That's a lot of header for such a small patch.. I'm going to guess
> > they aren't all used - bring them in as you need them - I hope
> > you never need some of these!  
> 
> I didn't phase in headers in this series. Based on these recommendations,
> the next version of this series is gonna have to be 100% constructed from
> scratch, but okay. My head hurts just thinking about it. I need a nap...
> 
> I've been rebasing for 3 weeks to get this series out, and it occurs to
> me that maybe there are tools I'm not aware of that make it eaiser? I'm
> just typing "rebase -i..." 200 times a day. Is there a less soul-crushing way?

Hmm. There are things that make it easier to pick and chose parts of a
big diff for different patches.  Some combination of 
git reset HEAD~1
and one of the 'graphical' tools like tig that let you pick lines.

That lets you quickly break up a patch where you want to move things, then
you can reorder the patches to put them next to where you want to move
changes to and rely on git rebase -i with f or s to squash them.

Figuring out optimum path to the eventual break up you want is
a skill though.  When doing this sort of mangling I tend to get it wrong
and shout at my computer a few times a day ;)
Then git rebase --abort and try again.

End result is that you end up with coherent series and it looks like
you wrote perfect code in nice steps from the start!

Jonathan

Re: [RFC PATCH 08/20] famfs: Add famfs_internal.h

[Christian Brauner]

On Fri, Feb 23, 2024 at 11:41:52AM -0600, John Groves wrote:
> Add the famfs_internal.h include file. This contains internal data
> structures such as the per-file metadata structure (famfs_file_meta)
> and extent formats.
> 
> Signed-off-by: John Groves <john@groves.net>
> ---
>  fs/famfs/famfs_internal.h | 53 +++++++++++++++++++++++++++++++++++++++

Already mentioned in another reply here but adding a bunch of types such
as famfs_file_operations that aren't even defines is pretty odd. So you
should reorder this.

>  1 file changed, 53 insertions(+)
>  create mode 100644 fs/famfs/famfs_internal.h
> 
> diff --git a/fs/famfs/famfs_internal.h b/fs/famfs/famfs_internal.h
> new file mode 100644
> index 000000000000..af3990d43305
> --- /dev/null
> +++ b/fs/famfs/famfs_internal.h
> @@ -0,0 +1,53 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * famfs - dax file system for shared fabric-attached memory
> + *
> + * Copyright 2023-2024 Micron Technology, Inc.
> + *
> + * This file system, originally based on ramfs the dax support from xfs,
> + * is intended to allow multiple host systems to mount a common file system
> + * view of dax files that map to shared memory.
> + */
> +#ifndef FAMFS_INTERNAL_H
> +#define FAMFS_INTERNAL_H
> +
> +#include <linux/atomic.h>
> +#include <linux/famfs_ioctl.h>
> +
> +#define FAMFS_MAGIC 0x87b282ff

That needs to go into include/uapi/linux/magic.h.

> +
> +#define FAMFS_BLKDEV_MODE (FMODE_READ|FMODE_WRITE)
> +
> +extern const struct file_operations      famfs_file_operations;
> +
> +/*
> + * Each famfs dax file has this hanging from its inode->i_private.
> + */
> +struct famfs_file_meta {
> +	int                   error;
> +	enum famfs_file_type  file_type;
> +	size_t                file_size;
> +	enum extent_type      tfs_extent_type;
> +	size_t                tfs_extent_ct;
> +	struct famfs_extent   tfs_extents[];  /* flexible array */
> +};
> +
> +struct famfs_mount_opts {
> +	umode_t mode;
> +};
> +
> +extern const struct iomap_ops             famfs_iomap_ops;
> +extern const struct vm_operations_struct  famfs_file_vm_ops;
> +
> +#define ROOTDEV_STRLEN 80
> +
> +struct famfs_fs_info {
> +	struct famfs_mount_opts  mount_opts;
> +	struct file             *dax_filp;
> +	struct dax_device       *dax_devp;
> +	struct bdev_handle      *bdev_handle;
> +	struct list_head         fsi_list;
> +	char                    *rootdev;
> +};
> +
> +#endif /* FAMFS_INTERNAL_H */
> -- 
> 2.43.0
> 

Re: [RFC PATCH 10/20] famfs: famfs_open_device() & dax_holder_operations

[Christian Brauner]

On Fri, Feb 23, 2024 at 11:41:54AM -0600, John Groves wrote:
> Famfs works on both /dev/pmem and /dev/dax devices. This commit introduces
> the function that opens a block (pmem) device and the struct
> dax_holder_operations that are needed for that ABI.
> 
> In this commit, support for opening character /dev/dax is stubbed. A
> later commit introduces this capability.
> 
> Signed-off-by: John Groves <john@groves.net>
> ---
>  fs/famfs/famfs_inode.c | 83 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 83 insertions(+)
> 
> diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> index 3329aff000d1..82c861998093 100644
> --- a/fs/famfs/famfs_inode.c
> +++ b/fs/famfs/famfs_inode.c
> @@ -68,5 +68,88 @@ static const struct super_operations famfs_ops = {
>  	.show_options	= famfs_show_options,
>  };
>  
> +/***************************************************************************************
> + * dax_holder_operations for block dax
> + */
> +
> +static int
> +famfs_blk_dax_notify_failure(
> +	struct dax_device	*dax_devp,
> +	u64			offset,
> +	u64			len,
> +	int			mf_flags)
> +{
> +
> +	pr_err("%s: dax_devp %llx offset %llx len %lld mf_flags %x\n",
> +	       __func__, (u64)dax_devp, (u64)offset, (u64)len, mf_flags);
> +	return -EOPNOTSUPP;
> +}
> +
> +const struct dax_holder_operations famfs_blk_dax_holder_ops = {
> +	.notify_failure		= famfs_blk_dax_notify_failure,
> +};
> +
> +static int
> +famfs_open_char_device(
> +	struct super_block *sb,
> +	struct fs_context  *fc)
> +{
> +	pr_err("%s: Root device is %s, but your kernel does not support famfs on /dev/dax\n",
> +	       __func__, fc->source);
> +	return -ENODEV;
> +}
> +
> +/**
> + * famfs_open_device()
> + *
> + * Open the memory device. If it looks like /dev/dax, call famfs_open_char_device().
> + * Otherwise try to open it as a block/pmem device.
> + */
> +static int
> +famfs_open_device(

I'm confused why that function is added here but it's completely unclear
in what wider context it's called. This is really hard to follow.

> +	struct super_block *sb,
> +	struct fs_context  *fc)
> +{
> +	struct famfs_fs_info *fsi = sb->s_fs_info;
> +	struct dax_device    *dax_devp;
> +	u64 start_off = 0;
> +	struct bdev_handle   *handlep;
> +
> +	if (fsi->dax_devp) {
> +		pr_err("%s: already mounted\n", __func__);
> +		return -EALREADY;
> +	}
> +
> +	if (strstr(fc->source, "/dev/dax")) /* There is probably a better way to check this */
> +		return famfs_open_char_device(sb, fc);
> +
> +	if (!strstr(fc->source, "/dev/pmem")) { /* There is probably a better way to check this */

Yeah, this is not just a bit ugly but also likely wrong because:

sudo mount --bind /dev/pmem /opt/muhaha

fsconfig(fd_fs, FSCONFIG_SET_STRING, "source", "/opt/muhaha", [...])

or a simple mknod to create that device somewhere else. You likely want:

lookup_bdev(fc->source, &dev);

if (!DEVICE_NUMBER_SOMETHING_SOMETHING_SANE(dev))
	return invalfc(fc, "SOMETHING SOMETHING...

bdev_open_by_dev(dev, ....)

(This reminds me that I should get back to making it possible to specify
"source" as a file descriptor instead of a mere string with the new
mount api...)

> +		pr_err("%s: primary backing dev (%s) is not pmem\n",
> +		       __func__, fc->source);
> +		return -EINVAL;
> +	}
> +
> +	handlep = bdev_open_by_path(fc->source, FAMFS_BLKDEV_MODE, fsi, &fs_holder_ops);

Hm, I suspected that FAMFS_BLKDEV_MODE would be wrong based on:
https://lore.kernel.org/r/13556dbbd8d0f51bc31e3bdec796283fe85c6baf.1708709155.git.john@groves.net

It's defined as FMODE_READ | FMODE_WRITE which is wrong. But these
helpers want BLOCK_OPEN_READ | BLOCK_OPEN_WRITE.

> +	if (IS_ERR(handlep->bdev)) {

@bdev_handle will be gone as of v6.9 so you might want to wait until
then to resend.

> +		pr_err("%s: failed blkdev_get_by_path(%s)\n", __func__, fc->source);
> +		return PTR_ERR(handlep->bdev);
> +	}
> +
> +	dax_devp = fs_dax_get_by_bdev(handlep->bdev, &start_off,
> +				      fsi  /* holder */,
> +				      &famfs_blk_dax_holder_ops);
> +	if (IS_ERR(dax_devp)) {
> +		pr_err("%s: unable to get daxdev from handlep->bdev\n", __func__);
> +		bdev_release(handlep);
> +		return -ENODEV;
> +	}
> +	fsi->bdev_handle = handlep;
> +	fsi->dax_devp    = dax_devp;
> +
> +	pr_notice("%s: root device is block dax (%s)\n", __func__, fc->source);
> +	return 0;
> +}
> +
> +
>  
>  MODULE_LICENSE("GPL");
> -- 
> 2.43.0
> 

Re: [RFC PATCH 11/20] famfs: Add fs_context_operations

[Christian Brauner]

On Fri, Feb 23, 2024 at 11:41:55AM -0600, John Groves wrote:
> This commit introduces the famfs fs_context_operations and
> famfs_get_inode() which is used by the context operations.
> 
> Signed-off-by: John Groves <john@groves.net>
> ---
>  fs/famfs/famfs_inode.c | 178 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 178 insertions(+)
> 
> diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> index 82c861998093..f98f82962d7b 100644
> --- a/fs/famfs/famfs_inode.c
> +++ b/fs/famfs/famfs_inode.c
> @@ -41,6 +41,50 @@ static const struct super_operations famfs_ops;
>  static const struct inode_operations famfs_file_inode_operations;
>  static const struct inode_operations famfs_dir_inode_operations;
>  
> +static struct inode *famfs_get_inode(
> +	struct super_block *sb,
> +	const struct inode *dir,
> +	umode_t             mode,
> +	dev_t               dev)
> +{
> +	struct inode *inode = new_inode(sb);
> +
> +	if (inode) {
> +		struct timespec64       tv;
> +
> +		inode->i_ino = get_next_ino();
> +		inode_init_owner(&nop_mnt_idmap, inode, dir, mode);
> +		inode->i_mapping->a_ops = &ram_aops;
> +		mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
> +		mapping_set_unevictable(inode->i_mapping);
> +		tv = inode_set_ctime_current(inode);
> +		inode_set_mtime_to_ts(inode, tv);
> +		inode_set_atime_to_ts(inode, tv);
> +
> +		switch (mode & S_IFMT) {
> +		default:
> +			init_special_inode(inode, mode, dev);
> +			break;
> +		case S_IFREG:
> +			inode->i_op = &famfs_file_inode_operations;
> +			inode->i_fop = &famfs_file_operations;
> +			break;
> +		case S_IFDIR:
> +			inode->i_op = &famfs_dir_inode_operations;
> +			inode->i_fop = &simple_dir_operations;
> +
> +			/* Directory inodes start off with i_nlink == 2 (for "." entry) */
> +			inc_nlink(inode);
> +			break;
> +		case S_IFLNK:
> +			inode->i_op = &page_symlink_inode_operations;
> +			inode_nohighmem(inode);
> +			break;
> +		}
> +	}
> +	return inode;
> +}
> +
>  /**********************************************************************************
>   * famfs super_operations
>   *
> @@ -150,6 +194,140 @@ famfs_open_device(
>  	return 0;
>  }
>  
> +/*****************************************************************************************
> + * fs_context_operations
> + */
> +static int
> +famfs_fill_super(
> +	struct super_block *sb,
> +	struct fs_context  *fc)
> +{
> +	struct famfs_fs_info *fsi = sb->s_fs_info;
> +	struct inode *inode;
> +	int rc = 0;
> +
> +	sb->s_maxbytes		= MAX_LFS_FILESIZE;
> +	sb->s_blocksize		= PAGE_SIZE;
> +	sb->s_blocksize_bits	= PAGE_SHIFT;
> +	sb->s_magic		= FAMFS_MAGIC;
> +	sb->s_op		= &famfs_ops;
> +	sb->s_time_gran		= 1;
> +
> +	rc = famfs_open_device(sb, fc);
> +	if (rc)
> +		goto out;
> +
> +	inode = famfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0);
> +	sb->s_root = d_make_root(inode);
> +	if (!sb->s_root)
> +		rc = -ENOMEM;
> +
> +out:
> +	return rc;
> +}
> +
> +enum famfs_param {
> +	Opt_mode,
> +	Opt_dax,
> +};
> +
> +const struct fs_parameter_spec famfs_fs_parameters[] = {
> +	fsparam_u32oct("mode",	  Opt_mode),
> +	fsparam_string("dax",     Opt_dax),
> +	{}
> +};
> +
> +static int famfs_parse_param(
> +	struct fs_context   *fc,
> +	struct fs_parameter *param)
> +{
> +	struct famfs_fs_info *fsi = fc->s_fs_info;
> +	struct fs_parse_result result;
> +	int opt;
> +
> +	opt = fs_parse(fc, famfs_fs_parameters, param, &result);
> +	if (opt == -ENOPARAM) {
> +		opt = vfs_parse_fs_param_source(fc, param);
> +		if (opt != -ENOPARAM)
> +			return opt;

I'm not sure I understand this. But in any case add, you should add
Opt_source to enum famfs_param and then add

        fsparam_string("source",        Opt_source),

to famfs_fs_parameters. Then you can add:

famfs_parse_source(fc, param);

You might want to consider validating your devices right away. So think
about:

fd_fs = fsopen("famfs", ...);
ret = fsconfig(fd_fs, FSCONFIG_SET_STRING, "source", "/definitely/not/valid/device", ...) // succeeds
ret = fsconfig(fd_fs, FSCONFIG_SET_FLAG, "OPTION_1", ...) // succeeds
ret = fsconfig(fd_fs, FSCONFIG_SET_FLAG, "OPTION_2", ...) // succeeds 
ret = fsconfig(fd_fs, FSCONFIG_SET_FLAG, "OPTION_3", ...) // succeeds 
ret = fsconfig(fd_fs, FSCONFIG_SET_FLAG, "OPTION_N", ...) // succeeds 
ret = fsconfig(fd_fs, FSCONFIG_CMD_CREATE, ...) // superblock creation failed

So what failed exactly? Yes, you can log into the fscontext and dmesg
that it's @source that's the issue but it's annoying for userspace to
setup a whole mount context only to figure out that some option was
wrong at the end of it.

So validating

famfs_parse_source(...)
{
	if (fc->source)
		return invalfc(fc, "Uhm, we already have a source....
	
       lookup_bdev(fc->source, &dev)
       // validate it's a device you're actually happy to use

       fc->source = param->string;
       param->string = NULL;
}

Your ->get_tree implementation that actually creates/finds the
superblock will validate fc->source again and yes, there's a race here
in so far as the path that fc->source points to could change in between
validating this in famfs_parse_source() and ->get_tree() superblock
creation. This is fixable even right now but then you couldn't reuse
common infrastrucute so I would just accept that race for now and we
should provide a nicer mechanism on the vfs layer.

> +
> +		return 0;
> +	}
> +	if (opt < 0)
> +		return opt;
> +
> +	switch (opt) {
> +	case Opt_mode:
> +		fsi->mount_opts.mode = result.uint_32 & S_IALLUGO;
> +		break;
> +	case Opt_dax:
> +		if (strcmp(param->string, "always"))
> +			pr_notice("%s: invalid dax mode %s\n",
> +				  __func__, param->string);
> +		break;
> +	}
> +
> +	return 0;
> +}
> +
> +static DEFINE_MUTEX(famfs_context_mutex);
> +static LIST_HEAD(famfs_context_list);
> +
> +static int famfs_get_tree(struct fs_context *fc)
> +{
> +	struct famfs_fs_info *fsi_entry;
> +	struct famfs_fs_info *fsi = fc->s_fs_info;
> +
> +	fsi->rootdev = kstrdup(fc->source, GFP_KERNEL);
> +	if (!fsi->rootdev)
> +		return -ENOMEM;
> +
> +	/* Fail if famfs is already mounted from the same device */
> +	mutex_lock(&famfs_context_mutex);
> +	list_for_each_entry(fsi_entry, &famfs_context_list, fsi_list) {
> +		if (strcmp(fsi_entry->rootdev, fc->source) == 0) {
> +			mutex_unlock(&famfs_context_mutex);
> +			pr_err("%s: already mounted from rootdev %s\n", __func__, fc->source);
> +			return -EALREADY;

What errno is EALREADY? Isn't that socket stuff. In any case, it seems
you want EBUSY?

But bigger picture I'm lost. And why do you keep that list based on
strings? What if I do:

mount -t famfs /dev/pmem1234 /mnt # succeeds

mount -t famfs /dev/pmem1234 /opt # ah, fsck me, this fails.. But wait a minute....

mount --bind /dev/pmem1234 /evil-masterplan

mount -t famfs /evil-masterplan /opt # succeeds. YAY

I believe that would trivially defeat your check.

> +		}
> +	}
> +
> +	list_add(&fsi->fsi_list, &famfs_context_list);
> +	mutex_unlock(&famfs_context_mutex);
> +
> +	return get_tree_nodev(fc, famfs_fill_super);

So why isn't this using get_tree_bdev()? Note that a while ago I
added FSCONFIG_CMD_CREAT_EXCL which prevents silent superblock reuse. To
implement that I added fs_context->exclusive. If you unconditionally set
fc->exclusive = 1 in your famfs_init_fs_context() and use
get_tree_bdev() it will give you EBUSY if fc->source is already in use -
including other famfs instances.

I also fail to yet understand how that function which actually opens the block
device and gets the dax device figures into this. It's a bit hard to follow
what's going on since you add all those unused functions and types so there's
never a wider context to see that stuff in.

> +
> +}
> +
> +static void famfs_free_fc(struct fs_context *fc)
> +{
> +	struct famfs_fs_info *fsi = fc->s_fs_info;
> +
> +	if (fsi && fsi->rootdev)
> +		kfree(fsi->rootdev);
> +
> +	kfree(fsi);
> +}
> +
> +static const struct fs_context_operations famfs_context_ops = {
> +	.free		= famfs_free_fc,
> +	.parse_param	= famfs_parse_param,
> +	.get_tree	= famfs_get_tree,
> +};
> +
> +static int famfs_init_fs_context(struct fs_context *fc)
> +{
> +	struct famfs_fs_info *fsi;
> +
> +	fsi = kzalloc(sizeof(*fsi), GFP_KERNEL);
> +	if (!fsi)
> +		return -ENOMEM;
> +
> +	fsi->mount_opts.mode = FAMFS_DEFAULT_MODE;
> +	fc->s_fs_info        = fsi;
> +	fc->ops              = &famfs_context_ops;
> +	return 0;
> +}
>  
>  
>  MODULE_LICENSE("GPL");
> -- 
> 2.43.0
> 

Re: [RFC PATCH 08/20] famfs: Add famfs_internal.h

[John Groves]

On 24/02/27 02:38PM, Christian Brauner wrote:
> On Fri, Feb 23, 2024 at 11:41:52AM -0600, John Groves wrote:
> > Add the famfs_internal.h include file. This contains internal data
> > structures such as the per-file metadata structure (famfs_file_meta)
> > and extent formats.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> > ---
> >  fs/famfs/famfs_internal.h | 53 +++++++++++++++++++++++++++++++++++++++
> 
> Already mentioned in another reply here but adding a bunch of types such
> as famfs_file_operations that aren't even defines is pretty odd. So you
> should reorder this.

Acknowledged, thanks. V2 will phase in only what is needed by the
code in each patch.

> 
> >  1 file changed, 53 insertions(+)
> >  create mode 100644 fs/famfs/famfs_internal.h
> > 
> > diff --git a/fs/famfs/famfs_internal.h b/fs/famfs/famfs_internal.h
> > new file mode 100644
> > index 000000000000..af3990d43305
> > --- /dev/null
> > +++ b/fs/famfs/famfs_internal.h
> > @@ -0,0 +1,53 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * famfs - dax file system for shared fabric-attached memory
> > + *
> > + * Copyright 2023-2024 Micron Technology, Inc.
> > + *
> > + * This file system, originally based on ramfs the dax support from xfs,
> > + * is intended to allow multiple host systems to mount a common file system
> > + * view of dax files that map to shared memory.
> > + */
> > +#ifndef FAMFS_INTERNAL_H
> > +#define FAMFS_INTERNAL_H
> > +
> > +#include <linux/atomic.h>
> > +#include <linux/famfs_ioctl.h>
> > +
> > +#define FAMFS_MAGIC 0x87b282ff
> 
> That needs to go into include/uapi/linux/magic.h.

Done for v2.

Thank you,
John

Re: [RFC PATCH 09/20] famfs: Add super_operations

[John Groves]

On 24/02/26 12:51PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:53 -0600
> John Groves <John@Groves.net> wrote:
> > + */
> > +static int famfs_show_options(
> > +	struct seq_file *m,
> > +	struct dentry   *root)
> Not that familiar with fs code, but this unusual kernel style. I'd go with 
> something more common
> 
> static int famfs_show_options(struct seq_file *m, struct dentry *root)

Actually, xfs does function declarations and prototypes this way, not sure if
it's everywhere. But I like this format because changing one argument usually
doesn't put un-changed args into the diff.

So I may keep this style after all.

John

Re: [RFC PATCH 10/20] famfs: famfs_open_device() & dax_holder_operations

[John Groves]

On 24/02/27 02:39PM, Christian Brauner wrote:
> On Fri, Feb 23, 2024 at 11:41:54AM -0600, John Groves wrote:
> > Famfs works on both /dev/pmem and /dev/dax devices. This commit introduces
> > the function that opens a block (pmem) device and the struct
> > dax_holder_operations that are needed for that ABI.
> > 
> > In this commit, support for opening character /dev/dax is stubbed. A
> > later commit introduces this capability.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> > ---
> >  fs/famfs/famfs_inode.c | 83 ++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 83 insertions(+)
> > 
> > diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> > index 3329aff000d1..82c861998093 100644
> > --- a/fs/famfs/famfs_inode.c
> > +++ b/fs/famfs/famfs_inode.c
> > @@ -68,5 +68,88 @@ static const struct super_operations famfs_ops = {
> >  	.show_options	= famfs_show_options,
> >  };
> >  
> > +/***************************************************************************************
> > + * dax_holder_operations for block dax
> > + */
> > +
> > +static int
> > +famfs_blk_dax_notify_failure(
> > +	struct dax_device	*dax_devp,
> > +	u64			offset,
> > +	u64			len,
> > +	int			mf_flags)
> > +{
> > +
> > +	pr_err("%s: dax_devp %llx offset %llx len %lld mf_flags %x\n",
> > +	       __func__, (u64)dax_devp, (u64)offset, (u64)len, mf_flags);
> > +	return -EOPNOTSUPP;
> > +}
> > +
> > +const struct dax_holder_operations famfs_blk_dax_holder_ops = {
> > +	.notify_failure		= famfs_blk_dax_notify_failure,
> > +};
> > +
> > +static int
> > +famfs_open_char_device(
> > +	struct super_block *sb,
> > +	struct fs_context  *fc)
> > +{
> > +	pr_err("%s: Root device is %s, but your kernel does not support famfs on /dev/dax\n",
> > +	       __func__, fc->source);
> > +	return -ENODEV;
> > +}
> > +
> > +/**
> > + * famfs_open_device()
> > + *
> > + * Open the memory device. If it looks like /dev/dax, call famfs_open_char_device().
> > + * Otherwise try to open it as a block/pmem device.
> > + */
> > +static int
> > +famfs_open_device(
> 
> I'm confused why that function is added here but it's completely unclear
> in what wider context it's called. This is really hard to follow.

First, thank you for taking the time to do a thoughtful review.

I didn't factor this series correctly. The next one will be
"module-operations-up" unless you or somebody suggests a more sensible
approach.

Some background that might be useful: this work is really targeted for 
/dev/dax, but it started on /dev/pmem because the iomap interface wasn't 
working on /dev/dax. This patch addresses that (the dev_dax_iomap commits), 
although it's likely that code will evolve.

The current famfs code base tries to support both pmem (block) and /dev/dax 
(char), but I'm now thinking it should move to /dev/dax-only (no block 
support).

/dev/pmem devices can converted to /dev/dax mode anyway, so I'm not sure 
there is a reason to support both interfaces. (Need to think a bit more on 
that...).

> 
> > +	struct super_block *sb,
> > +	struct fs_context  *fc)
> > +{
> > +	struct famfs_fs_info *fsi = sb->s_fs_info;
> > +	struct dax_device    *dax_devp;
> > +	u64 start_off = 0;
> > +	struct bdev_handle   *handlep;
> > +
> > +	if (fsi->dax_devp) {
> > +		pr_err("%s: already mounted\n", __func__);
> > +		return -EALREADY;
> > +	}
> > +
> > +	if (strstr(fc->source, "/dev/dax")) /* There is probably a better way to check this */
> > +		return famfs_open_char_device(sb, fc);
> > +
> > +	if (!strstr(fc->source, "/dev/pmem")) { /* There is probably a better way to check this */
> 
> Yeah, this is not just a bit ugly but also likely wrong because:
> 
> sudo mount --bind /dev/pmem /opt/muhaha
> 
> fsconfig(fd_fs, FSCONFIG_SET_STRING, "source", "/opt/muhaha", [...])
> 
> or a simple mknod to create that device somewhere else. You likely want:
> 
> lookup_bdev(fc->source, &dev);
> 
> if (!DEVICE_NUMBER_SOMETHING_SOMETHING_SANE(dev))
> 	return invalfc(fc, "SOMETHING SOMETHING...
> 
> bdev_open_by_dev(dev, ....)
> 
> (This reminds me that I should get back to making it possible to specify
> "source" as a file descriptor instead of a mere string with the new
> mount api...)

All good points - sorry for the flakyness here.

I think the solution is to stop trying to support both pmem and dax. Then 
I don't need to distinguish between different device types.

> 
> > +		pr_err("%s: primary backing dev (%s) is not pmem\n",
> > +		       __func__, fc->source);
> > +		return -EINVAL;
> > +	}
> > +
> > +	handlep = bdev_open_by_path(fc->source, FAMFS_BLKDEV_MODE, fsi, &fs_holder_ops);
> 
> Hm, I suspected that FAMFS_BLKDEV_MODE would be wrong based on:
> https://lore.kernel.org/r/13556dbbd8d0f51bc31e3bdec796283fe85c6baf.1708709155.git.john@groves.net
> 
> It's defined as FMODE_READ | FMODE_WRITE which is wrong. But these
> helpers want BLOCK_OPEN_READ | BLOCK_OPEN_WRITE.

Dropping pmem/block support will also make this go away

> 
> > +	if (IS_ERR(handlep->bdev)) {
> 
> @bdev_handle will be gone as of v6.9 so you might want to wait until
> then to resend.

And this dependency will also disappear...

Thank you!!
John

Re: [RFC PATCH 17/20] famfs: Add module stuff

[John Groves]

On 24/02/26 01:47PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:42:01 -0600
> John Groves <John@Groves.net> wrote:
> 
> > This commit introduces the module init and exit machinery for famfs.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> I'd prefer to see this from the start with the functionality of the module
> built up as you go + build logic in place.  Makes it easy to spot places
> where the patches aren't appropriately self constrained. 
> > ---
> >  fs/famfs/famfs_inode.c | 44 ++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 44 insertions(+)
> > 
> > diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> > index ab46ec50b70d..0d659820e8ff 100644
> > --- a/fs/famfs/famfs_inode.c
> > +++ b/fs/famfs/famfs_inode.c
> > @@ -462,4 +462,48 @@ static struct file_system_type famfs_fs_type = {
> >  	.fs_flags	  = FS_USERNS_MOUNT,
> >  };
> >  
> > +/*****************************************************************************************
> > + * Module stuff
> 
> I'd drop these drivers structure comments. They add little beyond
> a high possibility of being wrong after the code has evolved a bit.

Probably will do with the module-ops-up refactor for v2

> 
> > + */
> > +static struct kobject *famfs_kobj;
> > +
> > +static int __init init_famfs_fs(void)
> > +{
> > +	int rc;
> > +
> > +#if defined(CONFIG_DEV_DAX_IOMAP)
> > +	pr_notice("%s: Your kernel supports famfs on /dev/dax\n", __func__);
> > +#else
> > +	pr_notice("%s: Your kernel does not support famfs on /dev/dax\n", __func__);
> > +#endif
> > +	famfs_kobj = kobject_create_and_add(MODULE_NAME, fs_kobj);
> > +	if (!famfs_kobj) {
> > +		pr_warn("Failed to create kobject\n");
> > +		return -ENOMEM;
> > +	}
> > +
> > +	rc = sysfs_create_group(famfs_kobj, &famfs_attr_group);
> > +	if (rc) {
> > +		kobject_put(famfs_kobj);
> > +		pr_warn("%s: Failed to create sysfs group\n", __func__);
> > +		return rc;
> > +	}
> > +
> > +	return register_filesystem(&famfs_fs_type);
> 
> If this fails, do we not leak the kobj and sysfs groups?

Good catch, thanks! Fixed for now- but the kobj is also likely to go away. Will
endeavor to get it right...

Thanks,
John

Re: [RFC PATCH 18/20] famfs: Support character dax via the dev_dax_iomap patch

[John Groves]

On 24/02/26 01:52PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:42:02 -0600
> John Groves <John@Groves.net> wrote:
> 
> > This commit introduces the ability to open a character /dev/dax device
> > instead of a block /dev/pmem device. This rests on the dev_dax_iomap
> > patches earlier in this series.
> 
> Not sure the back reference is needed given it's in the series.

Roger that

> 
> > 
> > Signed-off-by: John Groves <john@groves.net>
> > ---
> >  fs/famfs/famfs_inode.c | 97 +++++++++++++++++++++++++++++++++++++-----
> >  1 file changed, 87 insertions(+), 10 deletions(-)
> > 
> > diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> > index 0d659820e8ff..7d65ac497147 100644
> > --- a/fs/famfs/famfs_inode.c
> > +++ b/fs/famfs/famfs_inode.c
> > @@ -215,6 +215,93 @@ static const struct super_operations famfs_ops = {
> >  	.show_options	= famfs_show_options,
> >  };
> >  
> > +/*****************************************************************************/
> > +
> > +#if defined(CONFIG_DEV_DAX_IOMAP)
> > +
> > +/*
> > + * famfs dax_operations  (for char dax)
> > + */
> > +static int
> > +famfs_dax_notify_failure(struct dax_device *dax_dev, u64 offset,
> > +			u64 len, int mf_flags)
> > +{
> > +	pr_err("%s: offset %lld len %llu flags %x\n", __func__,
> > +	       offset, len, mf_flags);
> > +	return -EOPNOTSUPP;
> > +}
> > +
> > +static const struct dax_holder_operations famfs_dax_holder_ops = {
> > +	.notify_failure		= famfs_dax_notify_failure,
> > +};
> > +
> > +/*****************************************************************************/
> > +
> > +/**
> > + * famfs_open_char_device()
> > + *
> > + * Open a /dev/dax device. This only works in kernels with the dev_dax_iomap patch
> 
> That comment you definitely don't need as this won't get merged without
> that patch being in place.

This will be gone from v2. I'm 90% sure there is no reason to keep the block
device backing support (pmem), since devdax is the point AND pmem can be
converted to devdax mode. So famfs will become devdax only...etc.

This was under development for quite a few months, and actually working,
I got the dev_dax_iomap right (er, "right enough" for it to work :D). But now
that dev_dax_iomap looks basically stable, pmem/block support can come out.

> 
> 
> > + */
> > +static int
> > +famfs_open_char_device(
> > +	struct super_block *sb,
> > +	struct fs_context  *fc)
> > +{
> > +	struct famfs_fs_info *fsi = sb->s_fs_info;
> > +	struct dax_device    *dax_devp;
> > +	struct inode         *daxdev_inode;
> > +
> > +	int rc = 0;
> set in all paths where it's used.
> 
> > +
> > +	pr_notice("%s: Opening character dax device %s\n", __func__, fc->source);
> 
> pr_debug

Done

> 
> > +
> > +	fsi->dax_filp = filp_open(fc->source, O_RDWR, 0);
> > +	if (IS_ERR(fsi->dax_filp)) {
> > +		pr_err("%s: failed to open dax device %s\n",
> > +		       __func__, fc->source);
> > +		fsi->dax_filp = NULL;
> Better to use a local variable
> 
> 	fp = filp_open(fc->source, O_RDWR, 0);
> 	if (IS_ERR(fp)) {
> 		pr_err.
> 		return;
> 	}
> 	fsi->dax_filp = fp;
> or similar.

Done, thanks.

> 
> > +		return PTR_ERR(fsi->dax_filp);
> > +	}
> > +
> > +	daxdev_inode = file_inode(fsi->dax_filp);
> > +	dax_devp     = inode_dax(daxdev_inode);
> > +	if (IS_ERR(dax_devp)) {
> > +		pr_err("%s: unable to get daxdev from inode for %s\n",
> > +		       __func__, fc->source);
> > +		rc = -ENODEV;
> > +		goto char_err;
> > +	}
> > +
> > +	rc = fs_dax_get(dax_devp, fsi, &famfs_dax_holder_ops);
> > +	if (rc) {
> > +		pr_info("%s: err attaching famfs_dax_holder_ops\n", __func__);
> > +		goto char_err;
> > +	}
> > +
> > +	fsi->bdev_handle = NULL;
> > +	fsi->dax_devp = dax_devp;
> > +
> > +	return 0;
> > +
> > +char_err:
> > +	filp_close(fsi->dax_filp, NULL);
> 
> You carefully set fsi->dax_filp to null in other other error paths.
> Why there and not here?

Why indeed - done now.

> 
> > +	return rc;
> > +}
> > +
> > +#else /* CONFIG_DEV_DAX_IOMAP */
> > +static int
> > +famfs_open_char_device(
> > +	struct super_block *sb,
> > +	struct fs_context  *fc)
> > +{
> > +	pr_err("%s: Root device is %s, but your kernel does not support famfs on /dev/dax\n",
> > +	       __func__, fc->source);
> > +	return -ENODEV;
> > +}
> > +
> > +
> > +#endif /* CONFIG_DEV_DAX_IOMAP */
> > +
> >  /***************************************************************************************
> >   * dax_holder_operations for block dax
> >   */
> > @@ -236,16 +323,6 @@ const struct dax_holder_operations famfs_blk_dax_holder_ops = {
> >  	.notify_failure		= famfs_blk_dax_notify_failure,
> >  };
> >  
> 
> Put it in right place earlier! Makes this less noisy.

This will be eliminated by the move to /dev/dax-only

Thanks,
John

Re: [RFC PATCH 11/20] famfs: Add fs_context_operations

[John Groves]

On 24/02/27 02:41PM, Christian Brauner wrote:
> On Fri, Feb 23, 2024 at 11:41:55AM -0600, John Groves wrote:
> > This commit introduces the famfs fs_context_operations and
> > famfs_get_inode() which is used by the context operations.
> > 
> > Signed-off-by: John Groves <john@groves.net>
> > ---
> >  fs/famfs/famfs_inode.c | 178 +++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 178 insertions(+)
> > 
> > diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> > index 82c861998093..f98f82962d7b 100644
> > --- a/fs/famfs/famfs_inode.c
> > +++ b/fs/famfs/famfs_inode.c

<snip>

> > +enum famfs_param {
> > +	Opt_mode,
> > +	Opt_dax,
> > +};
> > +
> > +const struct fs_parameter_spec famfs_fs_parameters[] = {
> > +	fsparam_u32oct("mode",	  Opt_mode),
> > +	fsparam_string("dax",     Opt_dax),
> > +	{}
> > +};
> > +
> > +static int famfs_parse_param(
> > +	struct fs_context   *fc,
> > +	struct fs_parameter *param)
> > +{
> > +	struct famfs_fs_info *fsi = fc->s_fs_info;
> > +	struct fs_parse_result result;
> > +	int opt;
> > +
> > +	opt = fs_parse(fc, famfs_fs_parameters, param, &result);
> > +	if (opt == -ENOPARAM) {
> > +		opt = vfs_parse_fs_param_source(fc, param);
> > +		if (opt != -ENOPARAM)
> > +			return opt;
> 
> I'm not sure I understand this. But in any case add, you should add
> Opt_source to enum famfs_param and then add
> 
>         fsparam_string("source",        Opt_source),
> 
> to famfs_fs_parameters. Then you can add:
> 
> famfs_parse_source(fc, param);
> 
> You might want to consider validating your devices right away. So think
> about:
> 
> fd_fs = fsopen("famfs", ...);
> ret = fsconfig(fd_fs, FSCONFIG_SET_STRING, "source", "/definitely/not/valid/device", ...) // succeeds
> ret = fsconfig(fd_fs, FSCONFIG_SET_FLAG, "OPTION_1", ...) // succeeds
> ret = fsconfig(fd_fs, FSCONFIG_SET_FLAG, "OPTION_2", ...) // succeeds 
> ret = fsconfig(fd_fs, FSCONFIG_SET_FLAG, "OPTION_3", ...) // succeeds 
> ret = fsconfig(fd_fs, FSCONFIG_SET_FLAG, "OPTION_N", ...) // succeeds 
> ret = fsconfig(fd_fs, FSCONFIG_CMD_CREATE, ...) // superblock creation failed
> 
> So what failed exactly? Yes, you can log into the fscontext and dmesg
> that it's @source that's the issue but it's annoying for userspace to
> setup a whole mount context only to figure out that some option was
> wrong at the end of it.
> 
> So validating
> 
> famfs_parse_source(...)
> {
> 	if (fc->source)
> 		return invalfc(fc, "Uhm, we already have a source....
> 	
>        lookup_bdev(fc->source, &dev)
>        // validate it's a device you're actually happy to use
> 
>        fc->source = param->string;
>        param->string = NULL;
> }
> 
> Your ->get_tree implementation that actually creates/finds the
> superblock will validate fc->source again and yes, there's a race here
> in so far as the path that fc->source points to could change in between
> validating this in famfs_parse_source() and ->get_tree() superblock
> creation. This is fixable even right now but then you couldn't reuse
> common infrastrucute so I would just accept that race for now and we
> should provide a nicer mechanism on the vfs layer.

I wasn't aware of the new fsconfig interface. Is there documentation or a
file sytsem that already uses it that I should refer to? I didn't find an
obvious candidate, but it might be me. If it should be obvious from the
example above, tell me and I'll try harder.

My famfs code above was copied from ramfs. If you point me to 
documentation I might send you a ramfs fsconfig patch too :D.

> 
> > +
> > +		return 0;
> > +	}
> > +	if (opt < 0)
> > +		return opt;
> > +
> > +	switch (opt) {
> > +	case Opt_mode:
> > +		fsi->mount_opts.mode = result.uint_32 & S_IALLUGO;
> > +		break;
> > +	case Opt_dax:
> > +		if (strcmp(param->string, "always"))
> > +			pr_notice("%s: invalid dax mode %s\n",
> > +				  __func__, param->string);
> > +		break;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static DEFINE_MUTEX(famfs_context_mutex);
> > +static LIST_HEAD(famfs_context_list);
> > +
> > +static int famfs_get_tree(struct fs_context *fc)
> > +{
> > +	struct famfs_fs_info *fsi_entry;
> > +	struct famfs_fs_info *fsi = fc->s_fs_info;
> > +
> > +	fsi->rootdev = kstrdup(fc->source, GFP_KERNEL);
> > +	if (!fsi->rootdev)
> > +		return -ENOMEM;
> > +
> > +	/* Fail if famfs is already mounted from the same device */
> > +	mutex_lock(&famfs_context_mutex);
> > +	list_for_each_entry(fsi_entry, &famfs_context_list, fsi_list) {
> > +		if (strcmp(fsi_entry->rootdev, fc->source) == 0) {
> > +			mutex_unlock(&famfs_context_mutex);
> > +			pr_err("%s: already mounted from rootdev %s\n", __func__, fc->source);
> > +			return -EALREADY;
> 
> What errno is EALREADY? Isn't that socket stuff. In any case, it seems
> you want EBUSY?

Thanks... That should probaby be EBUSY. But the whole famfs_context_list
should probably also be removed. More below...

> 
> But bigger picture I'm lost. And why do you keep that list based on
> strings? What if I do:
> 
> mount -t famfs /dev/pmem1234 /mnt # succeeds
> 
> mount -t famfs /dev/pmem1234 /opt # ah, fsck me, this fails.. But wait a minute....
> 
> mount --bind /dev/pmem1234 /evil-masterplan
> 
> mount -t famfs /evil-masterplan /opt # succeeds. YAY
> 
> I believe that would trivially defeat your check.
> 

And I suspect this is related to the get_tree issue you noticed below.

This famfs code was working in 6.5 without keeping the linked list of devices,
but in 6.6/6.7/6.8 it works provided you don't try to repeat a mount command
that has already succeeded. I'm not sure why 6.5 protected me from that,
but the later versions don't. In 6.6+ That hits a BUG_ON (have specifics on 
that but not handy right now).

So for a while we just removed repeated mount requests from the famfs smoke
tests, but eventually I implemented the list above, which - though you're right
it would be easy to circumvent and therefore is not right - it did solve the
problem that we were testing for.

I suspect that correctly handling get_tree might solve this problem.

Please assume that linked list will be removed - it was not the right solution.

More below...

> > +		}
> > +	}
> > +
> > +	list_add(&fsi->fsi_list, &famfs_context_list);
> > +	mutex_unlock(&famfs_context_mutex);
> > +
> > +	return get_tree_nodev(fc, famfs_fill_super);
> 
> So why isn't this using get_tree_bdev()? Note that a while ago I
> added FSCONFIG_CMD_CREAT_EXCL which prevents silent superblock reuse. To
> implement that I added fs_context->exclusive. If you unconditionally set
> fc->exclusive = 1 in your famfs_init_fs_context() and use
> get_tree_bdev() it will give you EBUSY if fc->source is already in use -
> including other famfs instances.
> 
> I also fail to yet understand how that function which actually opens the block
> device and gets the dax device figures into this. It's a bit hard to follow
> what's going on since you add all those unused functions and types so there's
> never a wider context to see that stuff in.

Clearly that's a bug in my code. That get_tree_nodev() is from ramfs, which
was the starting point for famfs.

I'm wondering if doing this correctly (get_tree_bdev() when it's pmem) would
have solved my double mount problem on 6.6 onward.

However, there's another wrinkle: I'm concluding
(see https://lore.kernel.org/linux-fsdevel/ups6cvjw6bx5m3hotn452brbbcgemnarsasre6ep2lbe4tpjsy@ezp6oh5c72ur/)
that famfs should drop block support and just work with /dev/dax. So famfs 
may be the first file system to be hosted on a character device? Certainly 
first on character dax. 

Given that, what variant of get_tree() should it call? Should it add 
get_tree_dax()? I'm not yet familiar enough with that code to have a worthy 
opinion on this.

Please let me know what you think.

Thank you for the serious review!
John

Re: [RFC PATCH 08/20] famfs: Add famfs_internal.h

[John Groves]

On 24/02/27 10:28AM, Jonathan Cameron wrote:
> On Mon, 26 Feb 2024 11:35:17 -0600
> John Groves <John@groves.net> wrote:
> 
> > On 24/02/26 12:48PM, Jonathan Cameron wrote:
> > > On Fri, 23 Feb 2024 11:41:52 -0600
> > > John Groves <John@Groves.net> wrote:
> > >   
> > > > Add the famfs_internal.h include file. This contains internal data
> > > > structures such as the per-file metadata structure (famfs_file_meta)
> > > > and extent formats.
> > > > 
> > > > Signed-off-by: John Groves <john@groves.net>  
> > > Hi John,
> > > 
> > > Build this up as you add the definitions in later patches.
> > > 
> > > Separate header patches just make people jump back and forth when trying
> > > to review.  Obviously more work to build this stuff up cleanly but
> > > it's worth doing to save review time.
> > >   
> > 
> > Ohhhhkaaaaay. I think you're right, just not looking forward to
> > all that rebasing.
> 
> :)  Patch mangling is half the fun of upstream development :)
> 
> > 
> > > Generally I'd plumb up Kconfig and Makefile a the beginning as it means
> > > that the set is bisectable and we can check the logic of building each stage.
> > > That is harder to do but tends to bring benefits in forcing clear step
> > > wise approach on a patch set. Feel free to ignore this one though as it
> > > can slow things down.  
> > 
> > I'm not sure that's practical. A file system needs a bunch of different
> > kinds of operations
> > - super_operations
> > - fs_context_operations
> > - inode_operations
> > - file_operations
> > - dax holder_operations, iomap_ops
> > - etc.
> > 
> > Will think about the dependency graph of these entities, but I'm not sure
> > it's tractable...
> 
> Sure.  There's a difference though between doing something useful (or
> even successfully loading) and being able to build it at intermediate steps.
> I'm only looking for buildability.
> 
> If not possible, even with a few stubs, empty ops structures etc
> then fair enough.
> 
> Jonathan

I'm through at least the first stage of grief on this. By the time we're
through this I'll be able to reconstitute the whole bloody thing from memory,
backwards :D

John

Re: [RFC PATCH 11/20] famfs: Add fs_context_operations

[Randy Dunlap]

On 2/27/24 16:59, John Groves wrote:
> On 24/02/27 02:41PM, Christian Brauner wrote:
>> On Fri, Feb 23, 2024 at 11:41:55AM -0600, John Groves wrote:
>>> This commit introduces the famfs fs_context_operations and
>>> famfs_get_inode() which is used by the context operations.
>>>
>>> Signed-off-by: John Groves <john@groves.net>
>>> ---
>>>  fs/famfs/famfs_inode.c | 178 +++++++++++++++++++++++++++++++++++++++++
>>>  1 file changed, 178 insertions(+)
>>>
>>> diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
>>> index 82c861998093..f98f82962d7b 100644
>>> --- a/fs/famfs/famfs_inode.c
>>> +++ b/fs/famfs/famfs_inode.c
> 
> <snip>
> 

> 
> I wasn't aware of the new fsconfig interface. Is there documentation or a
> file sytsem that already uses it that I should refer to? I didn't find an
> obvious candidate, but it might be me. If it should be obvious from the
> example above, tell me and I'll try harder.

> My famfs code above was copied from ramfs. If you point me to 
> documentation I might send you a ramfs fsconfig patch too :D.

All that I found was the commit to add fsconfig to the kernel tree:

commit ecdab150fddb
Author: David Howells <dhowells@redhat.com>
Date:   Thu Nov 1 23:36:09 2018 +0000

    vfs: syscall: Add fsconfig() for configuring and managing a context

and the lore archive for its discussion:
https://lore.kernel.org/all/153313723557.13253.9055982745313603422.stgit@warthog.procyon.org.uk/


plus David's userspace man page addition for it:
https://lore.kernel.org/linux-fsdevel/159680897140.29015.15318866561972877762.stgit@warthog.procyon.org.uk/


-- 
#Randy

Re: [RFC PATCH 11/20] famfs: Add fs_context_operations

[Christian Brauner]

> plus David's userspace man page addition for it:
> https://lore.kernel.org/linux-fsdevel/159680897140.29015.15318866561972877762.stgit@warthog.procyon.org.uk/

Up to date manpages are
https://github.com/brauner/man-pages-md

Re: [RFC PATCH 11/20] famfs: Add fs_context_operations

[Christian Brauner]

> I wasn't aware of the new fsconfig interface. Is there documentation or a
> file sytsem that already uses it that I should refer to? I didn't find an
> obvious candidate, but it might be me. If it should be obvious from the
> example above, tell me and I'll try harder.
> 
> My famfs code above was copied from ramfs. If you point me to 

Ok, but that's the wrong filesystem to use as a model imho. Because it
really doesn't deal with devices at all. That's why it uses
get_tree_nodev() with "nodev" as in "no device" kinda. So ramfs doesn't
have any of these issues. Whereas your filesystems is dealing with
devices dax (or pmem).

> documentation I might send you a ramfs fsconfig patch too :D.

So the manpages are at:

https://github.com/brauner/man-pages-md

But really, there shouldn't be anything that needs to change for ramfs.

> > What errno is EALREADY? Isn't that socket stuff. In any case, it seems
> > you want EBUSY?
> 
> Thanks... That should probaby be EBUSY. But the whole famfs_context_list
> should probably also be removed. More below...
> 
> > 
> > But bigger picture I'm lost. And why do you keep that list based on
> > strings? What if I do:
> > 
> > mount -t famfs /dev/pmem1234 /mnt # succeeds
> > 
> > mount -t famfs /dev/pmem1234 /opt # ah, fsck me, this fails.. But wait a minute....
> > 
> > mount --bind /dev/pmem1234 /evil-masterplan
> > 
> > mount -t famfs /evil-masterplan /opt # succeeds. YAY
> > 
> > I believe that would trivially defeat your check.
> > 
> 
> And I suspect this is related to the get_tree issue you noticed below.
> 
> This famfs code was working in 6.5 without keeping the linked list of devices,
> but in 6.6/6.7/6.8 it works provided you don't try to repeat a mount command
> that has already succeeded. I'm not sure why 6.5 protected me from that,
> but the later versions don't. In 6.6+ That hits a BUG_ON (have specifics on 
> that but not handy right now).

get_tree_nodev() by default will always allocate a new superblock. This
is how tmpfs and ramfs work. If you do:

mount -t tmpfs tmpfs /mnt
mount -t tmpfs tmpfs /opt

You get two new, independent superblocks. This is what you want for
these multi-instance filesystems: each new mount creates a new instance.

If famfs doesn't want to allow reusing devices - which I very much think
it wants to prevent - then it cannot use get_tree_nodev() directly
without having a hack like you did. Because you'll get a new superblock
no problem. So the fact that it did work somehow likely was a bug in
your code.

The reason your code causes crashes is very likely this:

struct famfs_fs_info *fsi = sb->s_fs_info;
handlep = bdev_open_by_path(fc->source, FAMFS_BLKDEV_MODE, fsi, &fs_holder_ops);

If you look at Documentation/filesystems/porting.rst you should see that
if you use @fs_holder_ops then your holder should be the struct
super_block, not your personal fsinfo.

> So for a while we just removed repeated mount requests from the famfs smoke
> tests, but eventually I implemented the list above, which - though you're right
> it would be easy to circumvent and therefore is not right - it did solve the
> problem that we were testing for.
> 
> I suspect that correctly handling get_tree might solve this problem.
> 
> Please assume that linked list will be removed - it was not the right solution.
> 
> More below...
> 
> > > +		}
> > > +	}
> > > +
> > > +	list_add(&fsi->fsi_list, &famfs_context_list);
> > > +	mutex_unlock(&famfs_context_mutex);
> > > +
> > > +	return get_tree_nodev(fc, famfs_fill_super);
> > 
> > So why isn't this using get_tree_bdev()? Note that a while ago I
> > added FSCONFIG_CMD_CREAT_EXCL which prevents silent superblock reuse. To
> > implement that I added fs_context->exclusive. If you unconditionally set
> > fc->exclusive = 1 in your famfs_init_fs_context() and use
> > get_tree_bdev() it will give you EBUSY if fc->source is already in use -
> > including other famfs instances.
> > 
> > I also fail to yet understand how that function which actually opens the block
> > device and gets the dax device figures into this. It's a bit hard to follow
> > what's going on since you add all those unused functions and types so there's
> > never a wider context to see that stuff in.
> 
> Clearly that's a bug in my code. That get_tree_nodev() is from ramfs, which
> was the starting point for famfs.
> 
> I'm wondering if doing this correctly (get_tree_bdev() when it's pmem) would
> have solved my double mount problem on 6.6 onward.
> 
> However, there's another wrinkle: I'm concluding
> (see https://lore.kernel.org/linux-fsdevel/ups6cvjw6bx5m3hotn452brbbcgemnarsasre6ep2lbe4tpjsy@ezp6oh5c72ur/)
> that famfs should drop block support and just work with /dev/dax. So famfs 
> may be the first file system to be hosted on a character device? Certainly 
> first on character dax. 

Ugh, ok. I defer to others whether that makes sense or not. It would be
a lot easier for you if you used pmem block devices, I guess because it
would be easy to detect reuse in common infrastructure.

But also, I'm looking at your code a bit closer. There's a bit of a
wrinkle the way it's currently written...

Say someone went a bit weird and did:

mount -t xfs xfs /dev/sda /my/xfs-filesystem
mknod DAX_DEVICE /my/xfs-filesystem/dax1234

and then did:

mount -t famfs famfs /my/xfs-filesystem/dax1234 /mnt

Internally in famfs you do:

fsi->dax_filp = filp_open(fc->source, O_RDWR, 0);

and you stash that file... Which means that you are pinning that xfs
filesystems implicitly. IOW, if someone does:

umount /my/xfs-filesystem

they get EBUSY for completely opaque reasons. And if they did:

umount -l /my/xfs-filesystem

followed by mounting that xfs filesystem again they'd get the same
superblock for that xfs filesystem.

What I'm trying to say is that I think you cannot pin another filesystem
like this when you open that device.

IOW, you either need to stash the plain dax device or dax needs to
become it's own tiny internal pseudo fs such that we can open dax
devices internally just like files. Which might actually also be worth
doing. But I'm not the maintainer of that.

> 
> Given that, what variant of get_tree() should it call? Should it add 
> get_tree_dax()? I'm not yet familiar enough with that code to have a worthy 
> opinion on this.

I don't think we need a common helper if famfs would be the only user of this.
But maybe I'm wrong. But roughly you'd need something similar to what we
do for block devices, I'd reckon. So lookup_daxdev() which is similar to
lookup_bdev() and allows you to translate from path to dax device
number maybe.

lookup_daxdev(const char *name, struct dax_dev? *daxdev)
{
	/* Don't actually open the dax device pointlessly */
	kern_path(fc->source, LOOKUP_FOLLOW, path);
	if (!S_ISCHR(inode->i_mode))
		// fail
	if (!may_open_dev(&path))
		// fail

	// check dax device and pin

	// get rid of path references
	path_put(&path);
}

famfs_get_tree(/* broken broken broken */)
{

	lookup_daxdev(fc->source, &ddev);

	sb = sget_fc(fc, famfs_test_super, set_anon_super_fc)
	if (IS_ERR(sb))
		// Error here may mean (aside from memory):
		// * superblock incompatible bc of read-write vs read-only
		// * non-matching user namespace
		// * FSCONFIG_CMD_CREATE_EXCL requested by mounter

	if (!sb->s_root) {
		// fill_super; new sb; dax device currently not used.
	} else {
		// A superblock for that dax device already exists and
		// may be reused. Any additional rejection reasons for
		// such an sb are up to the filesystem.
	}

	// Now really open or claim the dax device.
	// If you fail get rid of the superblock
	// (deactivate_locked_super()).

All handwavy, I know and probably I forgot details. But for you to fill
that in. ;)

Re: [RFC PATCH 11/20] famfs: Add fs_context_operations

[Christian Brauner]

On Wed, Feb 28, 2024 at 11:07:20AM +0100, Christian Brauner wrote:
> > I wasn't aware of the new fsconfig interface. Is there documentation or a
> > file sytsem that already uses it that I should refer to? I didn't find an
> > obvious candidate, but it might be me. If it should be obvious from the
> > example above, tell me and I'll try harder.
> > 
> > My famfs code above was copied from ramfs. If you point me to 
> 
> Ok, but that's the wrong filesystem to use as a model imho. Because it
> really doesn't deal with devices at all. That's why it uses
> get_tree_nodev() with "nodev" as in "no device" kinda. So ramfs doesn't
> have any of these issues. Whereas your filesystems is dealing with
> devices dax (or pmem).
> 
> > documentation I might send you a ramfs fsconfig patch too :D.
> 
> So the manpages are at:
> 
> https://github.com/brauner/man-pages-md
> 
> But really, there shouldn't be anything that needs to change for ramfs.
> 
> > > What errno is EALREADY? Isn't that socket stuff. In any case, it seems
> > > you want EBUSY?
> > 
> > Thanks... That should probaby be EBUSY. But the whole famfs_context_list
> > should probably also be removed. More below...
> > 
> > > 
> > > But bigger picture I'm lost. And why do you keep that list based on
> > > strings? What if I do:
> > > 
> > > mount -t famfs /dev/pmem1234 /mnt # succeeds
> > > 
> > > mount -t famfs /dev/pmem1234 /opt # ah, fsck me, this fails.. But wait a minute....
> > > 
> > > mount --bind /dev/pmem1234 /evil-masterplan
> > > 
> > > mount -t famfs /evil-masterplan /opt # succeeds. YAY
> > > 
> > > I believe that would trivially defeat your check.
> > > 
> > 
> > And I suspect this is related to the get_tree issue you noticed below.
> > 
> > This famfs code was working in 6.5 without keeping the linked list of devices,
> > but in 6.6/6.7/6.8 it works provided you don't try to repeat a mount command
> > that has already succeeded. I'm not sure why 6.5 protected me from that,
> > but the later versions don't. In 6.6+ That hits a BUG_ON (have specifics on 
> > that but not handy right now).
> 
> get_tree_nodev() by default will always allocate a new superblock. This
> is how tmpfs and ramfs work. If you do:
> 
> mount -t tmpfs tmpfs /mnt
> mount -t tmpfs tmpfs /opt
> 
> You get two new, independent superblocks. This is what you want for
> these multi-instance filesystems: each new mount creates a new instance.
> 
> If famfs doesn't want to allow reusing devices - which I very much think
> it wants to prevent - then it cannot use get_tree_nodev() directly
> without having a hack like you did. Because you'll get a new superblock
> no problem. So the fact that it did work somehow likely was a bug in
> your code.
> 
> The reason your code causes crashes is very likely this:
> 
> struct famfs_fs_info *fsi = sb->s_fs_info;
> handlep = bdev_open_by_path(fc->source, FAMFS_BLKDEV_MODE, fsi, &fs_holder_ops);
> 
> If you look at Documentation/filesystems/porting.rst you should see that
> if you use @fs_holder_ops then your holder should be the struct
> super_block, not your personal fsinfo.
> 
> > So for a while we just removed repeated mount requests from the famfs smoke
> > tests, but eventually I implemented the list above, which - though you're right
> > it would be easy to circumvent and therefore is not right - it did solve the
> > problem that we were testing for.
> > 
> > I suspect that correctly handling get_tree might solve this problem.
> > 
> > Please assume that linked list will be removed - it was not the right solution.
> > 
> > More below...
> > 
> > > > +		}
> > > > +	}
> > > > +
> > > > +	list_add(&fsi->fsi_list, &famfs_context_list);
> > > > +	mutex_unlock(&famfs_context_mutex);
> > > > +
> > > > +	return get_tree_nodev(fc, famfs_fill_super);
> > > 
> > > So why isn't this using get_tree_bdev()? Note that a while ago I
> > > added FSCONFIG_CMD_CREAT_EXCL which prevents silent superblock reuse. To
> > > implement that I added fs_context->exclusive. If you unconditionally set
> > > fc->exclusive = 1 in your famfs_init_fs_context() and use
> > > get_tree_bdev() it will give you EBUSY if fc->source is already in use -
> > > including other famfs instances.
> > > 
> > > I also fail to yet understand how that function which actually opens the block
> > > device and gets the dax device figures into this. It's a bit hard to follow
> > > what's going on since you add all those unused functions and types so there's
> > > never a wider context to see that stuff in.
> > 
> > Clearly that's a bug in my code. That get_tree_nodev() is from ramfs, which
> > was the starting point for famfs.
> > 
> > I'm wondering if doing this correctly (get_tree_bdev() when it's pmem) would
> > have solved my double mount problem on 6.6 onward.
> > 
> > However, there's another wrinkle: I'm concluding
> > (see https://lore.kernel.org/linux-fsdevel/ups6cvjw6bx5m3hotn452brbbcgemnarsasre6ep2lbe4tpjsy@ezp6oh5c72ur/)
> > that famfs should drop block support and just work with /dev/dax. So famfs 
> > may be the first file system to be hosted on a character device? Certainly 
> > first on character dax. 
> 
> Ugh, ok. I defer to others whether that makes sense or not. It would be
> a lot easier for you if you used pmem block devices, I guess because it
> would be easy to detect reuse in common infrastructure.
> 
> But also, I'm looking at your code a bit closer. There's a bit of a
> wrinkle the way it's currently written...
> 
> Say someone went a bit weird and did:
> 
> mount -t xfs xfs /dev/sda /my/xfs-filesystem
> mknod DAX_DEVICE /my/xfs-filesystem/dax1234
> 
> and then did:
> 
> mount -t famfs famfs /my/xfs-filesystem/dax1234 /mnt
> 
> Internally in famfs you do:
> 
> fsi->dax_filp = filp_open(fc->source, O_RDWR, 0);
> 
> and you stash that file... Which means that you are pinning that xfs
> filesystems implicitly. IOW, if someone does:
> 
> umount /my/xfs-filesystem
> 
> they get EBUSY for completely opaque reasons. And if they did:
> 
> umount -l /my/xfs-filesystem
> 
> followed by mounting that xfs filesystem again they'd get the same
> superblock for that xfs filesystem.
> 
> What I'm trying to say is that I think you cannot pin another filesystem
> like this when you open that device.
> 
> IOW, you either need to stash the plain dax device or dax needs to
> become it's own tiny internal pseudo fs such that we can open dax
> devices internally just like files. Which might actually also be worth
> doing. But I'm not the maintainer of that.

Ah, I see it's already like that and I was looking at the wrong file.
Great! So in that case you could add helper to open dax devices as
files:

struct file *dax_file_open(struct dax_device *dev, int flags, /* other stuff */)
{
	/* open that thing */
        dax_file = alloc_file_pseudo(dax_inode, dax_vfsmnt, "", flags | O_LARGEFILE, &something_fops);
}

and then you can treat them as regular files without running into the
issues I pointed out.

Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

[Dave Chinner]

On Mon, Feb 26, 2024 at 08:05:58PM -0600, John Groves wrote:
> On 24/02/26 04:58PM, Luis Chamberlain wrote:
> > On Mon, Feb 26, 2024 at 1:16 PM John Groves <John@groves.net> wrote:
> > >
> > > On 24/02/26 07:53AM, Luis Chamberlain wrote:
> > > > On Mon, Feb 26, 2024 at 07:27:18AM -0600, John Groves wrote:
> > > > > Run status group 0 (all jobs):
> > > > >   WRITE: bw=29.6GiB/s (31.8GB/s), 29.6GiB/s-29.6GiB/s (31.8GB/s-31.8GB/s), io=44.7GiB (48.0GB), run=1511-1511msec
> > > >
> > > > > This is run on an xfs file system on a SATA ssd.
> > > >
> > > > To compare more closer apples to apples, wouldn't it make more sense
> > > > to try this with XFS on pmem (with fio -direct=1)?
> > > >
> > > >   Luis
> > >
> > > Makes sense. Here is the same command line I used with xfs before, but
> > > now it's on /dev/pmem0 (the same 128G, but converted from devdax to pmem
> > > because xfs requires that.
> > >
> > > fio -name=ten-256m-per-thread --nrfiles=10 -bs=2M --group_reporting=1 --alloc-size=1048576 --filesize=256MiB --readwrite=write --fallocate=none --numjobs=48 --create_on_open=0 --ioengine=io_uring --direct=1 --directory=/mnt/xfs
> > 
> > Could you try with mkfs.xfs -d agcount=1024

Won't change anything for the better, may make things worse.

>    bw (  MiB/s): min= 5085, max=27367, per=100.00%, avg=14361.95, stdev=165.61, samples=719
>    iops        : min= 2516, max=13670, avg=7160.17, stdev=82.88, samples=719
>   lat (usec)   : 4=0.05%, 10=0.72%, 20=2.23%, 50=2.48%, 100=3.02%
>   lat (usec)   : 250=1.54%, 500=2.37%, 750=1.34%, 1000=0.75%
>   lat (msec)   : 2=3.20%, 4=43.10%, 10=23.05%, 20=14.81%, 50=1.25%

Most of the IO latencies are up round the 4-20ms marks. That seems
kinda high for a 2MB IO. With a memcpy speed of 10GB/s, the 2MB
should only take a couple of hundred microseconds. For Famfs, the
latencies appear to be around 1-4ms.

So where's all that extra time coming from?


>   lat (msec)   : 100=0.08%
>   cpu          : usr=10.18%, sys=0.79%, ctx=67227, majf=0, minf=38511

And why is system time reporting at almost zero instead of almost
all the remaining cpu time (i.e. up at 80-90%)?

Can you run call-graph kernel profiles for XFS and famfs whilst
running this workload so we have some insight into what is behaving
differently here?

-Dave.
-- 
Dave Chinner
david@fromorbit.com

Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

[Amir Goldstein]

On Fri, Feb 23, 2024 at 7:42 PM John Groves <John@groves.net> wrote:
>
> This patch set introduces famfs[1] - a special-purpose fs-dax file system
> for sharable disaggregated or fabric-attached memory (FAM). Famfs is not
> CXL-specific in anyway way.
>
> * Famfs creates a simple access method for storing and sharing data in
>   sharable memory. The memory is exposed and accessed as memory-mappable
>   dax files.
> * Famfs supports multiple hosts mounting the same file system from the
>   same memory (something existing fs-dax file systems don't do).
> * A famfs file system can be created on either a /dev/pmem device in fs-dax
>   mode, or a /dev/dax device in devdax mode (the latter depending on
>   patches 2-6 of this series).
>
> The famfs kernel file system is part the famfs framework; additional
> components in user space[2] handle metadata and direct the famfs kernel
> module to instantiate files that map to specific memory. The famfs user
> space has documentation and a reasonably thorough test suite.
>

So can we say that Famfs is Fuse specialized for DAX?

I am asking because you seem to have asked it first:
https://lore.kernel.org/linux-fsdevel/0100018b2439ebf3-a442db6f-f685-4bc4-b4b0-28dc333f6712-000000@email.amazonses.com/
I guess that you did not get your answers to your questions before or at LPC?

I did not see your question back in October.
Let me try to answer your questions and we can discuss later if a new dedicated
kernel driver + userspace API is really needed, or if FUSE could be used as is
extended for your needs.

You wrote:
"...My naive reading of the existence of some sort of fuse/dax support
for virtiofs
suggested that there might be a way of doing this - but I may be wrong
about that."

I'm not virtiofs expert, but I don't think that you are wrong about this.
IIUC, virtiofsd could map arbitrary memory region to any fuse file mmaped
by virtiofs client.

So what are the gaps between virtiofs and famfs that justify a new filesystem
driver and new userspace API?

Thanks,
Amir.

Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

[John Groves]

Hi Dave!

On 24/02/29 01:15PM, Dave Chinner wrote:
> On Mon, Feb 26, 2024 at 08:05:58PM -0600, John Groves wrote:
> > On 24/02/26 04:58PM, Luis Chamberlain wrote:
> > > On Mon, Feb 26, 2024 at 1:16 PM John Groves <John@groves.net> wrote:
> > > >
> > > > On 24/02/26 07:53AM, Luis Chamberlain wrote:
> > > > > On Mon, Feb 26, 2024 at 07:27:18AM -0600, John Groves wrote:
> > > > > > Run status group 0 (all jobs):
> > > > > >   WRITE: bw=29.6GiB/s (31.8GB/s), 29.6GiB/s-29.6GiB/s (31.8GB/s-31.8GB/s), io=44.7GiB (48.0GB), run=1511-1511msec
> > > > >
> > > > > > This is run on an xfs file system on a SATA ssd.
> > > > >
> > > > > To compare more closer apples to apples, wouldn't it make more sense
> > > > > to try this with XFS on pmem (with fio -direct=1)?
> > > > >
> > > > >   Luis
> > > >
> > > > Makes sense. Here is the same command line I used with xfs before, but
> > > > now it's on /dev/pmem0 (the same 128G, but converted from devdax to pmem
> > > > because xfs requires that.
> > > >
> > > > fio -name=ten-256m-per-thread --nrfiles=10 -bs=2M --group_reporting=1 --alloc-size=1048576 --filesize=256MiB --readwrite=write --fallocate=none --numjobs=48 --create_on_open=0 --ioengine=io_uring --direct=1 --directory=/mnt/xfs
> > > 
> > > Could you try with mkfs.xfs -d agcount=1024
> 
> Won't change anything for the better, may make things worse.

I dropped that arg, though performance looked about the same either way.

> 
> >    bw (  MiB/s): min= 5085, max=27367, per=100.00%, avg=14361.95, stdev=165.61, samples=719
> >    iops        : min= 2516, max=13670, avg=7160.17, stdev=82.88, samples=719
> >   lat (usec)   : 4=0.05%, 10=0.72%, 20=2.23%, 50=2.48%, 100=3.02%
> >   lat (usec)   : 250=1.54%, 500=2.37%, 750=1.34%, 1000=0.75%
> >   lat (msec)   : 2=3.20%, 4=43.10%, 10=23.05%, 20=14.81%, 50=1.25%
> 
> Most of the IO latencies are up round the 4-20ms marks. That seems
> kinda high for a 2MB IO. With a memcpy speed of 10GB/s, the 2MB
> should only take a couple of hundred microseconds. For Famfs, the
> latencies appear to be around 1-4ms.
> 
> So where's all that extra time coming from?

Below, you will see two runs with performance and latency distribution
about the same as famfs (the answer for that was --fallocate=native).

> 
> 
> >   lat (msec)   : 100=0.08%
> >   cpu          : usr=10.18%, sys=0.79%, ctx=67227, majf=0, minf=38511
> 
> And why is system time reporting at almost zero instead of almost
> all the remaining cpu time (i.e. up at 80-90%)?

Something weird is going on with the cpu reporting. Sometimes sys=~0, but other times
it's about what you would expect. I suspect some sort of measurement error,
like maybe the method doesn't work with my cpu model? (I'm grasping, but with
a somewhat rational basis...)

I pasted two xfs runs below. The first has the wonky cpu sys value, and
the second looks about like what one would expect.

> 
> Can you run call-graph kernel profiles for XFS and famfs whilst
> running this workload so we have some insight into what is behaving
> differently here?

Can you point me to an example of how to do that?

> 
> -Dave.
> -- 
> Dave Chinner
> david@fromorbit.com


I'd been thinking about the ~2x gap for a few days, and the most obvious
difference is famfs files must be preallocated (like fallocate, but works
a bit differently since allocation happens in user space). I just checked 
one of the xfs files, and it had maybe 80 extents (whereas the famfs 
files always have 1 extent here).

FWIW I ran xfs with and without io_uring, and there was no apparent
difference (which makes sense to me because it's not block I/O).

The prior ~2x gap still seems like a lot of overhead for extent list 
mapping to memory, but adding --fallocate=native to the xfs test brought 
it into line with famfs:


+ fio -name=ten-256m-per-thread --nrfiles=10 -bs=2M --group_reporting=1 --alloc-size=1048576 --filesize=256MiB --readwrite=write --fallocate=native --numjobs=48 --create_on_open=0 --ioengine=io_uring --direct=1 --directory=/mnt/xfs
ten-256m-per-thread: (g=0): rw=write, bs=(R) 2048KiB-2048KiB, (W) 2048KiB-2048KiB, (T) 2048KiB-2048KiB, ioengine=io_uring, iodepth=1
...
fio-3.33
Starting 48 processes
Jobs: 38 (f=380): [W(5),_(1),W(12),_(1),W(3),_(1),W(2),_(1),W(2),_(1),W(1),_(1),W(1),_(1),W(6),_(1),W(6),_(2)][57.1%][w=28.0GiB/s][w=14.3k IOPS][eta 00m:03s]
ten-256m-per-thread: (groupid=0, jobs=48): err= 0: pid=1452590: Thu Feb 29 07:46:06 2024
  write: IOPS=15.3k, BW=29.8GiB/s (32.0GB/s)(114GiB/3838msec); 0 zone resets
    slat (usec): min=17, max=55364, avg=668.20, stdev=1120.41
    clat (nsec): min=1368, max=99619k, avg=1982477.32, stdev=2198309.32
     lat (usec): min=179, max=99813, avg=2650.68, stdev=2485.15
    clat percentiles (usec):
     |  1.00th=[    4],  5.00th=[   14], 10.00th=[  172], 20.00th=[  420],
     | 30.00th=[  644], 40.00th=[ 1057], 50.00th=[ 1582], 60.00th=[ 2008],
     | 70.00th=[ 2343], 80.00th=[ 3097], 90.00th=[ 4555], 95.00th=[ 5473],
     | 99.00th=[ 8717], 99.50th=[11863], 99.90th=[20055], 99.95th=[27657],
     | 99.99th=[49546]
   bw (  MiB/s): min=20095, max=59216, per=100.00%, avg=35985.47, stdev=318.61, samples=280
   iops        : min=10031, max=29587, avg=17970.76, stdev=159.29, samples=280
  lat (usec)   : 2=0.06%, 4=1.02%, 10=2.33%, 20=4.29%, 50=1.85%
  lat (usec)   : 100=0.20%, 250=3.26%, 500=11.23%, 750=8.87%, 1000=5.82%
  lat (msec)   : 2=20.95%, 4=26.74%, 10=12.60%, 20=0.66%, 50=0.09%
  lat (msec)   : 100=0.01%
  cpu          : usr=15.48%, sys=1.17%, ctx=62654, majf=0, minf=22801
  IO depths    : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     issued rwts: total=0,58560,0,0 short=0,0,0,0 dropped=0,0,0,0
     latency   : target=0, window=0, percentile=100.00%, depth=1

Run status group 0 (all jobs):
  WRITE: bw=29.8GiB/s (32.0GB/s), 29.8GiB/s-29.8GiB/s (32.0GB/s-32.0GB/s), io=114GiB (123GB), run=3838-3838msec

Disk stats (read/write):
  pmem0: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%


## Here is a run where the cpu looks "normal"

+ fio -name=ten-256m-per-thread --nrfiles=10 -bs=2M --group_reporting=1 --alloc-size=1048576 --filesize=256MiB --readwrite=write --fallocate=native --numjobs=48 --create_on_open=0 --direct=1 --directory=/mnt/xfs
ten-256m-per-thread: (g=0): rw=write, bs=(R) 2048KiB-2048KiB, (W) 2048KiB-2048KiB, (T) 2048KiB-2048KiB, ioengine=psync, iodepth=1
...
fio-3.33
Starting 48 processes
Jobs: 19 (f=190): [W(2),_(1),W(2),_(8),W(1),_(3),W(1),_(1),W(2),_(2),W(1),_(1),W(3),_(2),W(1),_(1),W(1),_(2),W(2),_(7),W(3),_(1)][55.6%][w=26.7GiB/s][w=13.6k IOPS][eta 00m:04s]
ten-256m-per-thread: (groupid=0, jobs=48): err= 0: pid=1463615: Thu Feb 29 08:19:53 2024
  write: IOPS=12.4k, BW=24.1GiB/s (25.9GB/s)(114GiB/4736msec); 0 zone resets
    clat (usec): min=138, max=117903, avg=2581.99, stdev=2704.61
     lat (usec): min=152, max=120405, avg=3019.04, stdev=2964.47
    clat percentiles (usec):
     |  1.00th=[  161],  5.00th=[  249], 10.00th=[  627], 20.00th=[ 1270],
     | 30.00th=[ 1631], 40.00th=[ 1942], 50.00th=[ 2089], 60.00th=[ 2212],
     | 70.00th=[ 2343], 80.00th=[ 2704], 90.00th=[ 5866], 95.00th=[ 6849],
     | 99.00th=[12387], 99.50th=[14353], 99.90th=[26084], 99.95th=[38536],
     | 99.99th=[78119]
   bw (  MiB/s): min=21204, max=47040, per=100.00%, avg=29005.40, stdev=237.31, samples=329
   iops        : min=10577, max=23497, avg=14479.74, stdev=118.65, samples=329
  lat (usec)   : 250=5.04%, 500=4.03%, 750=2.37%, 1000=3.13%
  lat (msec)   : 2=29.39%, 4=41.05%, 10=13.37%, 20=1.45%, 50=0.15%
  lat (msec)   : 100=0.03%, 250=0.01%
  cpu          : usr=14.43%, sys=78.18%, ctx=5272, majf=0, minf=15708
  IO depths    : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     issued rwts: total=0,58560,0,0 short=0,0,0,0 dropped=0,0,0,0
     latency   : target=0, window=0, percentile=100.00%, depth=1

Run status group 0 (all jobs):
  WRITE: bw=24.1GiB/s (25.9GB/s), 24.1GiB/s-24.1GiB/s (25.9GB/s-25.9GB/s), io=114GiB (123GB), run=4736-4736msec

Disk stats (read/write):
  pmem0: ios=0/0, merge=0/0, ticks=0/0, in_queue=0, util=0.00%


Cheers,
John

Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

[John Groves]

On 24/02/29 08:52AM, Amir Goldstein wrote:
> On Fri, Feb 23, 2024 at 7:42 PM John Groves <John@groves.net> wrote:
> >
> > This patch set introduces famfs[1] - a special-purpose fs-dax file system
> > for sharable disaggregated or fabric-attached memory (FAM). Famfs is not
> > CXL-specific in anyway way.
> >
> > * Famfs creates a simple access method for storing and sharing data in
> >   sharable memory. The memory is exposed and accessed as memory-mappable
> >   dax files.
> > * Famfs supports multiple hosts mounting the same file system from the
> >   same memory (something existing fs-dax file systems don't do).
> > * A famfs file system can be created on either a /dev/pmem device in fs-dax
> >   mode, or a /dev/dax device in devdax mode (the latter depending on
> >   patches 2-6 of this series).
> >
> > The famfs kernel file system is part the famfs framework; additional
> > components in user space[2] handle metadata and direct the famfs kernel
> > module to instantiate files that map to specific memory. The famfs user
> > space has documentation and a reasonably thorough test suite.
> >
> 
> So can we say that Famfs is Fuse specialized for DAX?
> 
> I am asking because you seem to have asked it first:
> https://lore.kernel.org/linux-fsdevel/0100018b2439ebf3-a442db6f-f685-4bc4-b4b0-28dc333f6712-000000@email.amazonses.com/
> I guess that you did not get your answers to your questions before or at LPC?

Thanks for paying attention Amir. I think there is some validity to thinking
of famfs as Fuse for DAX. Administration / metadata originating in user space
is similar (but doing it this way also helps reduce RAS exposure to memory 
that might have a more complex connection path).

One way it differs from fuse is that famfs is very much aimed at use
cases that require performance. *Accessing* files must run at full
memory speeds.

> 
> I did not see your question back in October.
> Let me try to answer your questions and we can discuss later if a new dedicated
> kernel driver + userspace API is really needed, or if FUSE could be used as is
> extended for your needs.
> 
> You wrote:
> "...My naive reading of the existence of some sort of fuse/dax support
> for virtiofs
> suggested that there might be a way of doing this - but I may be wrong
> about that."
> 
> I'm not virtiofs expert, but I don't think that you are wrong about this.
> IIUC, virtiofsd could map arbitrary memory region to any fuse file mmaped
> by virtiofs client.
> 
> So what are the gaps between virtiofs and famfs that justify a new filesystem
> driver and new userspace API?

I have a lot of thoughts here, and an actual conversation might be good
sooner rather than later. I hope to be at LSFMM to discuss this - if you agree,
put in a vote for my topic ;). But if you want to talk sooner than that, I'm
interested.

I think one piece of evidence that this isn't possible with Fuse today is that
I had to plumb the iomap interface for /dev/dax in this patch set. That is the
way that fs-dax file systems communicate with the dax layer for fault 
resolution. If fuse/virtiofs handles dax somehow without the iomap interface,
I suspect it's doing something somehow simpler, /and/ that might need to get 
reconciled with the fs-dax methodology. Or maybe I don't know what I'm talking
about (in which case, please help :D).

I think one thing that might make sense would be to bring up this functionality
as a standalone file system, and then consider merging it into fuse when &
if the time seems right. 

Famfs doesn't currently have any up-calls. User space plays the log and tells
the kmod to instantiate files with extent lists to dax. Access happens with
zero user space involvement.

The important thing, the thing I'm currently paid for, is making it
practical to use disaggregated shared memory - it's ultimately not important 
which mechanism is used to enable a filesystem access method for memory.

But caching metadata in the kernel for efficient fault handling is the
only way to get it to perform at "memory speeds" so that appears critical.

One final observation: famfs has significantly more code in user space than
in kernel space, and it's the user side that is likely to grow over time.
That logic is at least theoretically independent of the kernel ABI.

> 
> Thanks,
> Amir.

Thanks!
John

Re: [RFC PATCH 00/20] Introduce the famfs shared-memory file system

[Dave Chinner]

On Thu, Feb 29, 2024 at 08:52:48AM -0600, John Groves wrote:
> On 24/02/29 01:15PM, Dave Chinner wrote:
> > On Mon, Feb 26, 2024 at 08:05:58PM -0600, John Groves wrote:
> > >    bw (  MiB/s): min= 5085, max=27367, per=100.00%, avg=14361.95, stdev=165.61, samples=719
> > >    iops        : min= 2516, max=13670, avg=7160.17, stdev=82.88, samples=719
> > >   lat (usec)   : 4=0.05%, 10=0.72%, 20=2.23%, 50=2.48%, 100=3.02%
> > >   lat (usec)   : 250=1.54%, 500=2.37%, 750=1.34%, 1000=0.75%
> > >   lat (msec)   : 2=3.20%, 4=43.10%, 10=23.05%, 20=14.81%, 50=1.25%
> > 
> > Most of the IO latencies are up round the 4-20ms marks. That seems
> > kinda high for a 2MB IO. With a memcpy speed of 10GB/s, the 2MB
> > should only take a couple of hundred microseconds. For Famfs, the
> > latencies appear to be around 1-4ms.
> > 
> > So where's all that extra time coming from?
> 
> Below, you will see two runs with performance and latency distribution
> about the same as famfs (the answer for that was --fallocate=native).

Ah, that is exactly what I suspected, and was wanting profiles
because that will show up in them clearly.

> > >   lat (msec)   : 100=0.08%
> > >   cpu          : usr=10.18%, sys=0.79%, ctx=67227, majf=0, minf=38511
> > 
> > And why is system time reporting at almost zero instead of almost
> > all the remaining cpu time (i.e. up at 80-90%)?
> 
> Something weird is going on with the cpu reporting. Sometimes sys=~0, but other times
> it's about what you would expect. I suspect some sort of measurement error,
> like maybe the method doesn't work with my cpu model? (I'm grasping, but with
> a somewhat rational basis...)
> 
> I pasted two xfs runs below. The first has the wonky cpu sys value, and
> the second looks about like what one would expect.
> 
> > 
> > Can you run call-graph kernel profiles for XFS and famfs whilst
> > running this workload so we have some insight into what is behaving
> > differently here?
> 
> Can you point me to an example of how to do that?

perf record --call-graph ...
pref report --call-graph ...


> I'd been thinking about the ~2x gap for a few days, and the most obvious
> difference is famfs files must be preallocated (like fallocate, but works
> a bit differently since allocation happens in user space). I just checked 
> one of the xfs files, and it had maybe 80 extents (whereas the famfs 
> files always have 1 extent here).

Which is about 4MB per extent. Extent size is not the problem for
zero-seek-latency storage hardware, though.

Essentially what you are seeing is interleaving extent allocation
between all the files because they are located in the same
directory. The locality algorithm is trying to place the data
extents close to the owner inode, but the indoes are also all close
together because they are located in the same AG as the parent
directory inode. Allocation concurrency is created by placing new
directories in different allocation groups, so we end up with
workloads in different directories being largely isolated from each
other.

However, that means when you are trying to write to many files in
the same directory at the same time, they are largely all competing
for the same AG lock to do block allocation during IO submission.
That creates interleaving of write() sized extents between different
files. We use speculative preallocation for buffered IO to avoid
this, and for direct IO the application needs to use extent size hints
or preallocation to avoid this contention based interleaving.

IOWs, by using fallocate() to preallocate all the space there will
be no allocation during IO submission and so the serialisation that
occurs due to competing allocations just goes away...

> FWIW I ran xfs with and without io_uring, and there was no apparent
> difference (which makes sense to me because it's not block I/O).
> 
> The prior ~2x gap still seems like a lot of overhead for extent list 
> mapping to memory, but adding --fallocate=native to the xfs test brought 
> it into line with famfs:

As I suspected. :)

As for CPU usage accounting, the number of context switches says it
all.

"Bad":

>   cpu          : usr=15.48%, sys=1.17%, ctx=62654, majf=0, minf=22801

"good":

>   cpu          : usr=14.43%, sys=78.18%, ctx=5272, majf=0, minf=15708

I'd say that in the "bad" case most of the kernel work is being
shuffled off to kernel threads to do the work and so it doesn't get
accounted to the submission task.  In comparison, in the "good" case
the work is being done in the submission thread and hence there's a
lot fewer context switches and the system time is correctly
accounted to the submission task.

Perhaps an io_uring task accounting problem?

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com