[dm-devel] [PATCH] block: properly stack underlying max_segment_size to DM device

[Mike Snitzer]

Without this patch all DM devices will default to BLK_MAX_SEGMENT_SIZE
(65536) even if the underlying device(s) have a larger value -- this is
due to blk_stack_limits() using min_not_zero() when stacking the
max_segment_size limit.

# cat /sys/block/sda/queue/max_segment_size
1073741824

# cat /sys/block/dm-0/queue/max_segment_size
before patch:
65536

after patch:
1073741824

Reported-by: Lukasz Flis <l.flis at cyfronet.pl>
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
Cc: stable at vger.kernel.org # v3.3+
---
 block/blk-settings.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index c50ecf0..29f28bb 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -143,6 +143,7 @@ void blk_set_stacking_limits(struct queue_limits *lim)
 	/* Inherit limits from component devices */
 	lim->discard_zeroes_data = 1;
 	lim->max_segments = USHRT_MAX;
+	lim->max_segment_size = UINT_MAX;
 	lim->max_hw_sectors = UINT_MAX;
 	lim->max_sectors = UINT_MAX;
 	lim->max_write_same_sectors = UINT_MAX;
-- 
1.7.4.4