block: Expose discard granularity

While SSDs track block usage on a per-sector basis, RAID arrays often
have allocation blocks that are bigger.  Allow the discard granularity
and alignment to be set and teach the topology stacking logic how to
handle them.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 297df45ffd0..c6c0c41af35 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -91,6 +91,7 @@ struct hd_struct {
 	sector_t start_sect;
 	sector_t nr_sects;
 	sector_t alignment_offset;
+	unsigned int discard_alignment;
 	struct device __dev;
 	struct kobject *holder_dir;
 	int policy, partno;