[PATCH 5.17-stable] block, loop: support partitions without scanning

[PATCH 5.17-stable] block, loop: support partitions without scanning

[Christoph Hellwig]

Historically we did distinguish between a flag that surpressed partition
scanning, and a combinations of the minors variable and another flag if
any partitions were supported.  This was generally confusing and doesn't
make much sense, but some corner case uses of the loop driver actually
do want to support manually added partitions on a device that does not
actively scan for partitions.  To make things worsee the loop driver
also wants to dynamically toggle the scanning for partitions on a live
gendisk, which makes the disk->flags updates non-atomic.

Introduce a new GD_SUPPRESS_PART_SCAN bit in disk->state that disables
just scanning for partitions, and toggle that instead of GENHD_FL_NO_PART
in the loop driver.

Fixes: 1ebe2e5f9d68 ("block: remove GENHD_FL_EXT_DEVT")
Reported-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20220527055806.1972352-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
(cherry picked from commit b9684a71fca793213378dd410cd11675d973eaa1)
---
 block/genhd.c         | 2 ++
 drivers/block/loop.c  | 8 ++++----
 include/linux/genhd.h | 1 +
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 9d9d702d077873..c284c1cf339672 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -380,6 +380,8 @@ int disk_scan_partitions(struct gendisk *disk, fmode_t mode)
 
 	if (disk->flags & (GENHD_FL_NO_PART | GENHD_FL_HIDDEN))
 		return -EINVAL;
+	if (test_bit(GD_SUPPRESS_PART_SCAN, &disk->state))
+		return -EINVAL;
 	if (disk->open_partitions)
 		return -EBUSY;
 
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index d46a3d5d0c2ec9..3411d3c0a5b0fc 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1067,7 +1067,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
 		lo->lo_flags |= LO_FLAGS_PARTSCAN;
 	partscan = lo->lo_flags & LO_FLAGS_PARTSCAN;
 	if (partscan)
-		lo->lo_disk->flags &= ~GENHD_FL_NO_PART;
+		clear_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state);
 
 	loop_global_unlock(lo, is_loop);
 	if (partscan)
@@ -1186,7 +1186,7 @@ static void __loop_clr_fd(struct loop_device *lo, bool release)
 	 */
 	lo->lo_flags = 0;
 	if (!part_shift)
-		lo->lo_disk->flags |= GENHD_FL_NO_PART;
+		set_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state);
 	mutex_lock(&lo->lo_mutex);
 	lo->lo_state = Lo_unbound;
 	mutex_unlock(&lo->lo_mutex);
@@ -1296,7 +1296,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
 
 	if (!err && (lo->lo_flags & LO_FLAGS_PARTSCAN) &&
 	     !(prev_lo_flags & LO_FLAGS_PARTSCAN)) {
-		lo->lo_disk->flags &= ~GENHD_FL_NO_PART;
+		clear_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state);
 		partscan = true;
 	}
 out_unlock:
@@ -2028,7 +2028,7 @@ static int loop_add(int i)
 	 * userspace tools. Parameters like this in general should be avoided.
 	 */
 	if (!part_shift)
-		disk->flags |= GENHD_FL_NO_PART;
+		set_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
 	atomic_set(&lo->lo_refcnt, 0);
 	mutex_init(&lo->lo_mutex);
 	lo->lo_number		= i;
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 6906a45bc761a4..2cb105f120282e 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -110,6 +110,7 @@ struct gendisk {
 #define GD_READ_ONLY			1
 #define GD_DEAD				2
 #define GD_NATIVE_CAPACITY		3
+#define GD_SUPPRESS_PART_SCAN		5
 
 	struct mutex open_mutex;	/* open/close mutex */
 	unsigned open_partitions;	/* number of open partitions */
-- 
2.30.2

Re: [PATCH 5.17-stable] block, loop: support partitions without scanning

[Greg KH]

On Thu, Jun 09, 2022 at 06:24:32AM +0200, Christoph Hellwig wrote:
> Historically we did distinguish between a flag that surpressed partition
> scanning, and a combinations of the minors variable and another flag if
> any partitions were supported.  This was generally confusing and doesn't
> make much sense, but some corner case uses of the loop driver actually
> do want to support manually added partitions on a device that does not
> actively scan for partitions.  To make things worsee the loop driver
> also wants to dynamically toggle the scanning for partitions on a live
> gendisk, which makes the disk->flags updates non-atomic.
> 
> Introduce a new GD_SUPPRESS_PART_SCAN bit in disk->state that disables
> just scanning for partitions, and toggle that instead of GENHD_FL_NO_PART
> in the loop driver.
> 
> Fixes: 1ebe2e5f9d68 ("block: remove GENHD_FL_EXT_DEVT")
> Reported-by: Ming Lei <ming.lei@redhat.com>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Ming Lei <ming.lei@redhat.com>
> Link: https://lore.kernel.org/r/20220527055806.1972352-1-hch@lst.de
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> (cherry picked from commit b9684a71fca793213378dd410cd11675d973eaa1)

Both queued up, thanks.

greg k-h