From: Mikulas Patocka <[email-masked]>

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 <[email-masked]>
Signed-off-by: Alasdair G Kergon <[email-masked]>

---
 drivers/md/dm.c               |    5 ++++-
 include/linux/device-mapper.h |    6 ++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

Index: linux/drivers/md/dm.c
===================================================================
--- linux.orig/drivers/md/dm.c
+++ linux/drivers/md/dm.c
@@ -1215,7 +1215,10 @@ static int __clone_and_map_discard(struc
 		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);
 
Index: linux/include/linux/device-mapper.h
===================================================================
--- linux.orig/include/linux/device-mapper.h
+++ linux/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;