btrfs: define BTRFS_MAGIC as a u64 value

super.magic is an le64 but it's treated as an unterminated string when
compared against BTRFS_MAGIC which is defined as a string.  Instead
define BTRFS_MAGIC as a normal hex value and use endian helpers to
compare it to the super's magic.

I tested this by mounting an fs made before the change and made sure
that it didn't introduce sparse errors.  This matches a similar cleanup
that is pending in btrfs-progs.  David Sterba pointed out that we should
fix the kernel side as well :).

Signed-off-by: Zach Brown <zab@redhat.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 1 insertions, 2 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 567076542d1d..72b1cf1b2b5e 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -855,8 +855,7 @@ int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder,
         disk_super = p + (bytenr & ~PAGE_CACHE_MASK);
 
         if (btrfs_super_bytenr(disk_super) != bytenr ||
-            strncmp((char *)(&disk_super->magic), BTRFS_MAGIC,
-                    sizeof(disk_super->magic)))
+            disk_super->magic != cpu_to_le64(BTRFS_MAGIC))
                 goto error_unmap;
 
         devid = btrfs_stack_device_id(&disk_super->dev_item);