rbd: set discard_alignment to zero

RBD devices are currently incorrectly initialised with the block queue
discard_alignment set to the underlying RADOS object size.

As per Documentation/ABI/testing/sysfs-block:
  The discard_alignment parameter indicates how many bytes the beginning
  of the device is offset from the internal allocation unit's natural
  alignment.

Correcting the discard_alignment parameter from the RADOS object size to
zero (the blk_set_default_limits() default) has no effect on how discard
requests are propagated through the block layer - @alignment in
__blkdev_issue_discard() remains zero. However, it does fix the UNMAP
granularity alignment value advertised to SCSI initiators via the Block
Limits VPD.

Signed-off-by: David Disseldorp <ddiss@suse.de>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 53b1ced21a139ac47f13e096e32299c23b0f0794..8c132a7fbd2c46f9785f7b8ce16a74ee9a2fb60b 100644 (file)
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -4390,7 +4390,6 @@ static int rbd_init_disk(struct rbd_device *rbd_dev)
        /* enable the discard support */
        queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
        q->limits.discard_granularity = segment_size;
-       q->limits.discard_alignment = segment_size;
        blk_queue_max_discard_sectors(q, segment_size / SECTOR_SIZE);
        blk_queue_max_write_zeroes_sectors(q, segment_size / SECTOR_SIZE);