From: Mikulas Patocka 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 Signed-off-by: Alasdair G Kergon --- 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;