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

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Message-Id: <b15e98a7c6129f8b5f0a7748061e93865bb944e1.1599750901.git.anand.jain@oracle.com>
Date:   Thu,  8 Oct 2020 18:59:51 +0800
From:   Anand Jain <anand.jain@...cle.com>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     wqu@...e.com, fdmanana@...e.com, dsterba@...e.com,
        linux-btrfs@...r.kernel.org
Subject: [PATCH stable-5.4 3/6] btrfs: volumes: Use more straightforward way to calculate map length

From: Qu Wenruo <wqu@...e.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 <jthumshirn@...e.de>
Reviewed-by: Josef Bacik <josef@...icpanda.com>
Signed-off-by: Qu Wenruo <wqu@...e.com>
Reviewed-by: David Sterba <dsterba@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Anand Jain <anand.jain@...cle.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