[XFS] Ondisk format extension for extended attributes (attr2). Basica…

…lly,

the data/attr forks now grow up/down from either end of the literal area,
rather than dividing the literal area into two chunks and growing both
upward.  Means we can now make much more efficient use of the attribute
space, incl. fitting DMF attributes inline in 256 byte inodes, and large
jumps in dbench3 performance numbers.  It is self enabling, but can be
forced on/off via the attr2/noattr2 mount options.

SGI-PV: 941645
SGI-Modid: xfs-linux:xfs-kern:23836a

Signed-off-by: Nathan Scott <nathans@sgi.com>

fs/xfs/xfs_clnt.h

@@ -70,7 +70,7 @@ struct xfs_mount_args {
 /*
  * XFS mount option flags
  */
-#define	XFSMNT_CHKLOG		0x00000001	/* check log */
+#define	XFSMNT_COMPAT_ATTR	0x00000001	/* do not use ATTR2 format */
 #define	XFSMNT_WSYNC		0x00000002	/* safe mode nfs mount
 						 * compatible */
 #define	XFSMNT_INO64		0x00000004	/* move inode numbers up