xfs: add CRC infrastructure

- add a mount feature bit for CRC enabled filesystems
 - add some helpers for generating and verifying the CRCs
 - add a copy_uuid helper

The checksumming helpers are loosely based on similar ones in sctp,
all other bits come from Dave Chinner.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

fs/xfs/xfs_sb.h

@@ -81,6 +81,7 @@ struct xfs_mount;
 #define XFS_SB_VERSION2_ATTR2BIT	0x00000008	/* Inline attr rework */
 #define XFS_SB_VERSION2_PARENTBIT	0x00000010	/* parent pointers */
 #define XFS_SB_VERSION2_PROJID32BIT	0x00000080	/* 32 bit project id */
+#define XFS_SB_VERSION2_CRCBIT		0x00000100	/* metadata CRCs */
 
 #define	XFS_SB_VERSION2_OKREALFBITS	\
 	(XFS_SB_VERSION2_LAZYSBCOUNTBIT	| \
@@ -503,6 +504,12 @@ static inline int xfs_sb_version_hasprojid32bit(xfs_sb_t *sbp)
 		(sbp->sb_features2 & XFS_SB_VERSION2_PROJID32BIT);
 }
 
+static inline int xfs_sb_version_hascrc(xfs_sb_t *sbp)
+{
+	return (xfs_sb_version_hasmorebits(sbp) &&
+		(sbp->sb_features2 & XFS_SB_VERSION2_CRCBIT));
+}
+
 /*
  * end of superblock version macros
  */