[PATCH stable-5.4 3/6] btrfs: volumes: Use more straightforward way to calculate map length

[Anand Jain]

From: Qu Wenruo <w...@suse.com>

commit 2d974619a77f106f3d1341686dea95c0eaad601f upstream.

The old code goes:

        offset = logical - em->start;
        length = min_t(u64, em->len - offset, length);

Where @length calculation is dependent on offset, it can take reader
several more seconds to find it's just the same code as:

        offset = logical - em->start;
        length = min_t(u64, em->start + em->len - logical, length);

Use above code to make the length calculate independent from other
variable, thus slightly increase the readability.

Reviewed-by: Johannes Thumshirn <jthumsh...@suse.de>
Reviewed-by: Josef Bacik <jo...@toxicpanda.com>
Signed-off-by: Qu Wenruo <w...@suse.com>
Reviewed-by: David Sterba <dste...@suse.com>
Signed-off-by: David Sterba <dste...@suse.com>
Signed-off-by: Anand Jain <anand.j...@oracle.com>
---
 fs/btrfs/volumes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 196ddbcd2936..1dba45d43485 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5712,7 +5712,7 @@ static int __btrfs_map_block_for_discard(struct 
btrfs_fs_info *fs_info,
        }
 
        offset = logical - em->start;
-       length = min_t(u64, em->len - offset, length);
+       length = min_t(u64, em->start + em->len - logical, length);
 
        stripe_len = map->stripe_len;
        /*
-- 
2.25.1