libxfs: pack the agfl header structure so XFS_AGFL_SIZE is correct

commit 96f859d52bcb1c6ea6f3388d39862bf7143e2f30 upstream.

Because struct xfs_agfl is 36 bytes long and has a 64-bit integer
inside it, gcc will quietly round the structure size up to the nearest
64 bits -- in this case, 40 bytes.  This results in the XFS_AGFL_SIZE
macro returning incorrect results for v5 filesystems on 64-bit
machines (118 items instead of 119).  As a result, a 32-bit xfs_repair
will see garbage in AGFL item 119 and complain.

Therefore, tell gcc not to pad the structure so that the AGFL size
calculation is correct.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

diff --git a/fs/xfs/xfs_ag.h b/fs/xfs/xfs_ag.h
index 1cb740afd674e8fd3f5ce0a3f47bfc00f8b36471..78ec58fc282e92fab848dd6fc2cf90f09306405c 100644 (file)
--- a/fs/xfs/xfs_ag.h
+++ b/fs/xfs/xfs_ag.h
@@ -224,7 +224,7 @@ typedef struct xfs_agfl {
        __be64          agfl_lsn;
        __be32          agfl_crc;
        __be32          agfl_bno[];     /* actually XFS_AGFL_SIZE(mp) */
-} xfs_agfl_t;
+} __attribute__((packed)) xfs_agfl_t;
 
 /*
  * tags for inode radix tree