In btrfs_get_acl() the first call of btr_getxattr() is for getting the
length of attribute, the value buffer is never used in this case. So
it's better to replace empty string with NULL.
Signed-off-by: NChengguang Xu <cgxu519@gmx.com>
Reviewed-by: NNikolay Borisov <nborisov@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>