dm: introduce split_discard_requests

This patch introduces a new variable split_discard_requests. It can be
set by targets so that discard requests are split on max_io_len
boundaries.

When split_discard_requests is not set, discard requests are only split on
boundaries between targets, as was the case before this patch.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

2 files changed, 10 insertions, 1 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 415c2803c0c9..4e09b6ff5b49 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1215,7 +1215,10 @@ static int __clone_and_map_discard(struct clone_info *ci)
                 if (!ti->num_discard_requests)
                         return -EOPNOTSUPP;
 
-                len = min(ci->sector_count, max_io_len_target_boundary(ci->sector, ti));
+                if (!ti->split_discard_requests)
+                        len = min(ci->sector_count, max_io_len_target_boundary(ci->sector, ti));
+                else
+                        len = min(ci->sector_count, max_io_len(ci->sector, ti));
 
                 __issue_target_requests(ci, ti, ti->num_discard_requests, len);
 
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index b19c1e189a68..8bdbbfce759a 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -218,6 +218,12 @@ struct dm_target {
         unsigned discards_supported:1;
 
         /*
+         * Set if the target required discard request to be split
+         * on max_io_len boundary.
+         */
+        unsigned split_discard_requests:1;
+
+        /*
          * Set if this target does not return zeroes on discarded blocks.
          */
         unsigned discard_zeroes_data_unsupported:1;