block: reorganize rounding of max_discard_sectors

Mostly a preparation for the next patch.

In principle this fixes an infinite loop if max_discard_sectors < granularity,
but that really shouldn't happen.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Tested-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 5 insertions, 4 deletions

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 2b461b496a78..16b06f62e68c 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -44,6 +44,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
         struct request_queue *q = bdev_get_queue(bdev);
         int type = REQ_WRITE | REQ_DISCARD;
         unsigned int max_discard_sectors;
+        unsigned int granularity;
         struct bio_batch bb;
         struct bio *bio;
         int ret = 0;
@@ -54,18 +55,18 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
         if (!blk_queue_discard(q))
                 return -EOPNOTSUPP;
 
+        /* Zero-sector (unknown) and one-sector granularities are the same.  */
+        granularity = max(q->limits.discard_granularity >> 9, 1U);
+
         /*
          * Ensure that max_discard_sectors is of the proper
          * granularity
          */
         max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
+        max_discard_sectors = round_down(max_discard_sectors, granularity);
         if (unlikely(!max_discard_sectors)) {
                 /* Avoid infinite loop below. Being cautious never hurts. */
                 return -EOPNOTSUPP;
-        } else if (q->limits.discard_granularity) {
-                unsigned int disc_sects = q->limits.discard_granularity >> 9;
-
-                max_discard_sectors &= ~(disc_sects - 1);
         }
 
         if (flags & BLKDEV_DISCARD_SECURE) {