[PATCH 2/4 RESEND] btrfs: fix vanished compression property after failed set

[Anand Jain <anand.jain@oracle.com>]

The compression property resets to NULL, instead of the old value if we
fail to set the new compression parameter.

btrfs prop get /btrfs compression
  compression=lzo
btrfs prop set /btrfs compression zli
  ERROR: failed to set compression for /btrfs: Invalid argument
btrfs prop get /btrfs compression

This is because the compression property ->validate() is successful for
'zli' as the strncmp() used the len passed from the userland.

Fix it by using the expected string length in strncmp().

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 fs/btrfs/props.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
index 3cc007e3c7f8..72a06c4d3c70 100644
--- a/fs/btrfs/props.c
+++ b/fs/btrfs/props.c
@@ -275,11 +275,11 @@ static int prop_compression_validate(const char *value, size_t len)
 	if (!value)
 		return 0;
 
-	if (!strncmp("lzo", value, len))
+	if (!strncmp("lzo", value, 3))
 		return 0;
-	else if (!strncmp("zlib", value, len))
+	else if (!strncmp("zlib", value, 4))
 		return 0;
-	else if (!strncmp("zstd", value, len))
+	else if (!strncmp("zstd", value, 4))
 		return 0;
 
 	return -EINVAL;
-- 
1.8.3.1