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rbd: set discard_alignment to zero

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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>
This commit is contained in:
David Disseldorp 2017-11-02 01:05:11 +01:00 committed by Ilya Dryomov
parent ec1dff25b0
commit 7c08428979
1 changed files with 0 additions and 1 deletions
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drivers/block/rbd.c
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@ -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);