commit 42c9cdfe1e11e083dceb0f0c4977b758cf7403b9
author Mike Snitzer <snitzer@redhat.com> Fri Jul 20 14:57:38 2018 -0400
committer Jens Axboe <axboe@kernel.dk> Tue Jul 24 14:46:39 2018 -0600
tree c5f0822ca961b526f1a36d376bb469718f2c3fa9
parent c55183c9aaa00d2bbb578169a480e31aff3d397c

block: allow max_discard_segments to be stacked

Set max_discard_segments to USHRT_MAX in blk_set_stacking_limits() so
that blk_stack_limits() can stack up this limit for stacked devices.

before:

$ cat /sys/block/nvme0n1/queue/max_discard_segments
256
$ cat /sys/block/dm-0/queue/max_discard_segments
1

after:

$ cat /sys/block/nvme0n1/queue/max_discard_segments
256
$ cat /sys/block/dm-0/queue/max_discard_segments
256

Fixes: 1e739730c5b9e ("block: optionally merge discontiguous discard bios into a single request")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-settings.c

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 053de87..ffd4599 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -128,7 +128,7 @@ void blk_set_stacking_limits(struct queue_limits *lim)
 
 	/* Inherit limits from component devices */
 	lim->max_segments = USHRT_MAX;
-	lim->max_discard_segments = 1;
+	lim->max_discard_segments = USHRT_MAX;
 	lim->max_hw_sectors = UINT_MAX;
 	lim->max_segment_size = UINT_MAX;
 	lim->max_sectors = UINT_MAX;