block: loop: set discard granularity and alignment for block device backed loop

In case of block device backend, if the backend supports write zeros, the
loop device will set queue flag of QUEUE_FLAG_DISCARD. However,
limits.discard_granularity isn't setup, and this way is wrong,
see the following description in Documentation/ABI/testing/sysfs-block:

	A discard_granularity of 0 means that the device does not support
	discard functionality.

Especially 9b15d109a6b2 ("block: improve discard bio alignment in
__blkdev_issue_discard()") starts to take q->limits.discard_granularity
for computing max discard sectors. And zero discard granularity may cause
kernel oops, or fail discard request even though the loop queue claims
discard support via QUEUE_FLAG_DISCARD.

Fix the issue by setup discard granularity and alignment.

Fixes: c52abf563049 ("loop: Better discard support for block devices")
Signed-off-by: Ming Lei <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Acked-by: Coly Li <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Cc: Xiao Ni <[email protected]>
Cc: Martin K. Petersen <[email protected]>
Cc: Evan Green <[email protected]>
Cc: Gwendal Grignou <[email protected]>
Cc: Chaitanya Kulkarni <[email protected]>
Cc: Andrzej Pietrasiewicz <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

0 files changed, 0 insertions, 0 deletions