[PATCH 1/1] virtio: disable partitions scanning for no partitions block

[Yury Kamenev <damtev@yandex-team.ru>]

Signed-off-by: Yury Kamenev <damtev@yandex-team.ru>
---
 .../admin-guide/kernel-parameters.txt         |  3 +++
 drivers/block/Kconfig                         |  7 +++++
 drivers/block/virtio_blk.c                    | 26 +++++++++++++++++++
 include/uapi/linux/virtio_blk.h               |  2 ++
 4 files changed, 38 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index bdb22006f713..941bdaf5c167 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6076,6 +6076,9 @@
 			brightness level.
 			default: 1

+	virtiopartscan
+		Enable virtio block device partition scanning omission based on VIRTIO_BLK_F_NO_PART_SCAN feature flag.
+
 	virtio_mmio.device=
 			[VMMIO] Memory mapped virtio (platform) device.

diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index 63056cfd4b62..69ecd3fd7037 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -399,6 +399,13 @@ config VIRTIO_BLK
 	  This is the virtual block driver for virtio.  It can be used with
           QEMU based VMMs (like KVM or Xen).  Say Y or M.

+config VIRTIO_BLK_NO_PART_SCAN
+	bool "Disable partition scanning for devices with no partitions"
+	depends on VIRTIO_BLK
+	help
+	  Disable partition scanning for devices with no partitions.
+	  Can reduce the kernel start time for tiny systems like squashfs images.
+
 config BLK_DEV_RBD
 	tristate "Rados block device (RBD)"
 	depends on INET && BLOCK
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 4b49df2dfd23..479711d3791c 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -692,6 +692,19 @@ static const struct blk_mq_ops virtio_mq_ops = {
 static unsigned int virtblk_queue_depth;
 module_param_named(queue_depth, virtblk_queue_depth, uint, 0444);

+#ifndef MODULE
+#ifdef CONFIG_VIRTIO_BLK_NO_PART_SCAN
+static int partitions_scanning_disable __read_mostly;
+
+static int __init partitions_scanning_setup(char *__unused)
+{
+	partitions_scanning_disable = 1;
+	return 1;
+}
+__setup("nopartscan", partitions_scanning_setup);
+#endif
+#endif
+
 static int virtblk_probe(struct virtio_device *vdev)
 {
 	struct virtio_blk *vblk;
@@ -790,6 +803,13 @@ static int virtblk_probe(struct virtio_device *vdev)
 	vblk->disk->flags |= GENHD_FL_EXT_DEVT;
 	vblk->index = index;

+#ifdef CONFIG_VIRTIO_BLK_NO_PART_SCAN
+	if (unlikely(partitions_scanning_disable))
+		/* disable partitions scanning if it was stated in virtio features*/
+		if (virtio_has_feature(vdev, VIRTIO_BLK_F_NO_PART_SCAN))
+			vblk->disk->flags |= GENHD_FL_NO_PART_SCAN;
+#endif
+
 	/* configure queue flush support */
 	virtblk_update_cache_mode(vdev);

@@ -966,6 +986,9 @@ static unsigned int features_legacy[] = {
 	VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
 	VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
 	VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD, VIRTIO_BLK_F_WRITE_ZEROES,
+#ifdef CONFIG_VIRTIO_BLK_NO_PART_SCAN
+	VIRTIO_BLK_F_NO_PART_SCAN,
+#endif
 }
 ;
 static unsigned int features[] = {
@@ -973,6 +996,9 @@ static unsigned int features[] = {
 	VIRTIO_BLK_F_RO, VIRTIO_BLK_F_BLK_SIZE,
 	VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_TOPOLOGY, VIRTIO_BLK_F_CONFIG_WCE,
 	VIRTIO_BLK_F_MQ, VIRTIO_BLK_F_DISCARD, VIRTIO_BLK_F_WRITE_ZEROES,
+#ifdef CONFIG_VIRTIO_BLK_NO_PART_SCAN
+	VIRTIO_BLK_F_NO_PART_SCAN,
+#endif
 };

 static struct virtio_driver virtio_blk = {
diff --git a/include/uapi/linux/virtio_blk.h b/include/uapi/linux/virtio_blk.h
index d888f013d9ff..9b381675342a 100644
--- a/include/uapi/linux/virtio_blk.h
+++ b/include/uapi/linux/virtio_blk.h
@@ -40,6 +40,7 @@
 #define VIRTIO_BLK_F_MQ		12	/* support more than one vq */
 #define VIRTIO_BLK_F_DISCARD	13	/* DISCARD is supported */
 #define VIRTIO_BLK_F_WRITE_ZEROES	14	/* WRITE ZEROES is supported */
+#define VIRTIO_BLK_F_NO_PART_SCAN	16	/* Disable partition scanning */

 /* Legacy feature bits */
 #ifndef VIRTIO_BLK_NO_LEGACY
--
2.24.3 (Apple Git-128)