linux-kernel - [PATCH 5.4 28/85] btrfs: volumes: Use more straightforward way to calculate map length

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Date:   Mon, 12 Oct 2020 15:26:51 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Johannes Thumshirn <jthumshirn@...e.de>,
        Josef Bacik <josef@...icpanda.com>, Qu Wenruo <wqu@...e.com>,
        David Sterba <dsterba@...e.com>,
        Anand Jain <anand.jain@...cle.com>
Subject: [PATCH 5.4 28/85] 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/btrfs/volumes.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5714,7 +5714,7 @@ static int __btrfs_map_block_for_discard
 	}
 
 	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;
 	/*