ocfs2: Add directory block trailers.

Future ocfs2 features metaecc and indexed directories need to store a
little bit of data in each dirblock.  For compatibility, we place this
in a trailer at the end of the dirblock.  The trailer plays itself as an
empty dirent, so that if the features are turned off, it can be reused
without requiring a tunefs scan.

This code adds the trailer and validates it when the block is read in.

[ Mark is the original author, but I reinserted this code before his
  dir index work.  -- Joel ]

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/fs/ocfs2/ocfs2_fs.h b/fs/ocfs2/ocfs2_fs.h
index 290fa26fba6e..af0013b9c17f 100644
--- a/fs/ocfs2/ocfs2_fs.h
+++ b/fs/ocfs2/ocfs2_fs.h
@@ -65,6 +65,7 @@
 #define OCFS2_EXTENT_BLOCK_SIGNATURE    "EXBLK01"
 #define OCFS2_GROUP_DESC_SIGNATURE      "GROUP01"
 #define OCFS2_XATTR_BLOCK_SIGNATURE     "XATTR01"
+#define OCFS2_DIR_TRAILER_SIGNATURE     "DIRTRL1"
 
 /* Compatibility flags */
 #define OCFS2_HAS_COMPAT_FEATURE(sb,mask)                       \
@@ -752,6 +753,34 @@ struct ocfs2_dir_entry {
 } __attribute__ ((packed));
 
 /*
+ * Per-block record for the unindexed directory btree. This is carefully
+ * crafted so that the rec_len and name_len records of an ocfs2_dir_entry are
+ * mirrored. That way, the directory manipulation code needs a minimal amount
+ * of update.
+ *
+ * NOTE: Keep this structure aligned to a multiple of 4 bytes.
+ */
+struct ocfs2_dir_block_trailer {
+/*00*/  __le64          db_compat_inode;        /* Always zero. Was inode */
+
+        __le16          db_compat_rec_len;      /* Backwards compatible with
+                                                 * ocfs2_dir_entry. */
+        __u8            db_compat_name_len;     /* Always zero. Was name_len */
+        __u8            db_reserved0;
+        __le16          db_reserved1;
+        __le16          db_free_rec_len;        /* Size of largest empty hole
+                                                 * in this block. (unused) */
+/*10*/  __u8            db_signature[8];        /* Signature for verification */
+        __le64          db_reserved2;
+        __le64          db_free_next;           /* Next block in list (unused) */
+/*20*/  __le64          db_blkno;               /* Offset on disk, in blocks */
+        __le64          db_parent_dinode;       /* dinode which owns me, in
+                                                   blocks */
+/*30*/  __le64          db_check;               /* Error checking */
+/*40*/
+};
+
+/*
  * On disk allocator group structure for OCFS2
  */
 struct ocfs2_group_desc