[PATCH 1/4] block: don't unconditionally set max_discard_sectors in blk_queue_max_discard_sectors

[Christoph Hellwig]

max_discard_sectors is split into a hardware and a tunable value, but
blk_queue_max_discard_sectors sets both unconditionally, thus dropping
any user stored value on a rescan.  Fix blk_queue_max_discard_sectors to
only set max_discard_sectors if it either wasn't set, or the new hardware
limit is smaller than the previous user limit.

Fixes: 0034af036554 ("block: make /sys/block/<dev>/queue/discard_max_bytes writeable")
Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 block/blk-settings.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 0046b447268f91..978d2e1fd67a51 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -179,7 +179,9 @@ void blk_queue_max_discard_sectors(struct request_queue *q,
 		unsigned int max_discard_sectors)
 {
 	q->limits.max_hw_discard_sectors = max_discard_sectors;
-	q->limits.max_discard_sectors = max_discard_sectors;
+	if (!q->limits.max_discard_sectors ||
+	     q->limits.max_discard_sectors > max_discard_sectors)
+		q->limits.max_discard_sectors = max_discard_sectors;
 }
 EXPORT_SYMBOL(blk_queue_max_discard_sectors);
 
-- 
2.39.2