[PATCH 3.13 179/212] dm cache: always split discards on cache block boundaries

[Kamal Mostafa]

3.13.11.4 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Heinz Mauelshagen <heinzm at redhat.com>

commit f1daa838e861ae1a0fb7cd9721a21258430fcc8c upstream.

The DM cache target cannot cope with discards that span multiple cache
blocks, so each discard bio that spans more than one cache block must
get split by the DM core.

Signed-off-by: Heinz Mauelshagen <heinzm at redhat.com>
Acked-by: Joe Thornber <ejt at redhat.com>
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/md/dm-cache-target.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 1d30f65..fd92101 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -2184,6 +2184,8 @@ static int cache_create(struct cache_args *ca, struct cache **result)
 	ti->num_discard_bios = 1;
 	ti->discards_supported = true;
 	ti->discard_zeroes_data_unsupported = true;
+	/* Discard bios must be split on a block boundary */
+	ti->split_discard_bios = true;
 
 	cache->features = ca->features;
 	ti->per_bio_data_size = get_per_bio_data_size(cache);
-- 
1.9.1