Avoid a VLA[1] by using a real constant expression instead of a variable.
The compiler should be able to optimize the original code and avoid using
an actual VLA. Anyway this change is useful because it will avoid a false
positive with -Wvla, it might also help the compiler generating better
code.

[1] https://lkml.org/lkml/2018/3/7/621

Signed-off-by: Salvatore Mesoraca <s.mesorac...@gmail.com>
---
 fs/btrfs/disk-io.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 21f34ad..88cef92 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -403,8 +403,7 @@ static int btrfs_check_super_csum(struct btrfs_fs_info 
*fs_info,
 
        if (csum_type == BTRFS_CSUM_TYPE_CRC32) {
                u32 crc = ~(u32)0;
-               const int csum_size = sizeof(crc);
-               char result[csum_size];
+               char result[sizeof(crc)];
 
                /*
                 * The super_block structure does not span the whole
@@ -415,7 +414,7 @@ static int btrfs_check_super_csum(struct btrfs_fs_info 
*fs_info,
                                crc, BTRFS_SUPER_INFO_SIZE - BTRFS_CSUM_SIZE);
                btrfs_csum_final(crc, result);
 
-               if (memcmp(raw_disk_sb, result, csum_size))
+               if (memcmp(raw_disk_sb, result, sizeof(result)))
                        ret = 1;
        }
 
-- 
1.9.1

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