xfs: remove the magic numbers in xfs_btree_block-related len macros

replace the magic numbers by offsetof(...) and sizeof(...), and add two
extra checks on xfs_check_ondisk_structs()

[dchinner: renamed header structures to be more descriptive]

Signed-off-by: Hou Tao <houtao1@huawei.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

2 files changed, 43 insertions, 25 deletions

diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
index dc97eb21af07..adb204d40f22 100644
--- a/fs/xfs/libxfs/xfs_format.h
+++ b/fs/xfs/libxfs/xfs_format.h
@@ -1435,41 +1435,57 @@ typedef __be64 xfs_bmbt_ptr_t, xfs_bmdr_ptr_t;
  * with the crc feature bit, and all accesses to them must be conditional on
  * that flag.
  */
+/* short form block header */
+struct xfs_btree_block_shdr {
+        __be32          bb_leftsib;
+        __be32          bb_rightsib;
+
+        __be64          bb_blkno;
+        __be64          bb_lsn;
+        uuid_t          bb_uuid;
+        __be32          bb_owner;
+        __le32          bb_crc;
+};
+
+/* long form block header */
+struct xfs_btree_block_lhdr {
+        __be64          bb_leftsib;
+        __be64          bb_rightsib;
+
+        __be64          bb_blkno;
+        __be64          bb_lsn;
+        uuid_t          bb_uuid;
+        __be64          bb_owner;
+        __le32          bb_crc;
+        __be32          bb_pad; /* padding for alignment */
+};
+
 struct xfs_btree_block {
         __be32          bb_magic;       /* magic number for block type */
         __be16          bb_level;       /* 0 is a leaf */
         __be16          bb_numrecs;     /* current # of data records */
         union {
-                struct {
-                        __be32          bb_leftsib;
-                        __be32          bb_rightsib;
-
-                        __be64          bb_blkno;
-                        __be64          bb_lsn;
-                        uuid_t          bb_uuid;
-                        __be32          bb_owner;
-                        __le32          bb_crc;
-                } s;                    /* short form pointers */
-                struct  {
-                        __be64          bb_leftsib;
-                        __be64          bb_rightsib;
-
-                        __be64          bb_blkno;
-                        __be64          bb_lsn;
-                        uuid_t          bb_uuid;
-                        __be64          bb_owner;
-                        __le32          bb_crc;
-                        __be32          bb_pad; /* padding for alignment */
-                } l;                    /* long form pointers */
+                struct xfs_btree_block_shdr s;
+                struct xfs_btree_block_lhdr l;
         } bb_u;                         /* rest */
 };
 
-#define XFS_BTREE_SBLOCK_LEN    16      /* size of a short form block */
-#define XFS_BTREE_LBLOCK_LEN    24      /* size of a long form block */
+/* size of a short form block */
+#define XFS_BTREE_SBLOCK_LEN \
+        (offsetof(struct xfs_btree_block, bb_u) + \
+         offsetof(struct xfs_btree_block_shdr, bb_blkno))
+/* size of a long form block */
+#define XFS_BTREE_LBLOCK_LEN \
+        (offsetof(struct xfs_btree_block, bb_u) + \
+         offsetof(struct xfs_btree_block_lhdr, bb_blkno))
 
 /* sizes of CRC enabled btree blocks */
-#define XFS_BTREE_SBLOCK_CRC_LEN        (XFS_BTREE_SBLOCK_LEN + 40)
-#define XFS_BTREE_LBLOCK_CRC_LEN        (XFS_BTREE_LBLOCK_LEN + 48)
+#define XFS_BTREE_SBLOCK_CRC_LEN \
+        (offsetof(struct xfs_btree_block, bb_u) + \
+         sizeof(struct xfs_btree_block_shdr))
+#define XFS_BTREE_LBLOCK_CRC_LEN \
+        (offsetof(struct xfs_btree_block, bb_u) + \
+         sizeof(struct xfs_btree_block_lhdr))
 
 #define XFS_BTREE_SBLOCK_CRC_OFF \
         offsetof(struct xfs_btree_block, bb_u.s.bb_crc)
diff --git a/fs/xfs/xfs_ondisk.h b/fs/xfs/xfs_ondisk.h
index 184c44effdd5..20a0d266964b 100644
--- a/fs/xfs/xfs_ondisk.h
+++ b/fs/xfs/xfs_ondisk.h
@@ -34,6 +34,8 @@ xfs_check_ondisk_structs(void)
         XFS_CHECK_STRUCT_SIZE(struct xfs_bmbt_key,              8);
         XFS_CHECK_STRUCT_SIZE(struct xfs_bmbt_rec,              16);
         XFS_CHECK_STRUCT_SIZE(struct xfs_bmdr_block,            4);
+        XFS_CHECK_STRUCT_SIZE(struct xfs_btree_block_shdr,      48);
+        XFS_CHECK_STRUCT_SIZE(struct xfs_btree_block_lhdr,      64);
         XFS_CHECK_STRUCT_SIZE(struct xfs_btree_block,           72);
         XFS_CHECK_STRUCT_SIZE(struct xfs_dinode,                176);
         XFS_CHECK_STRUCT_SIZE(struct xfs_disk_dquot,            104);