xfs: introduce the CoW fork

Introduce a new in-core fork for storing copy-on-write delalloc
reservations and allocated extents that are in the process of being
written out.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/xfs_inode.h

@@ -47,6 +47,7 @@ typedef struct xfs_inode {
 
 	/* Extent information. */
 	xfs_ifork_t		*i_afp;		/* attribute fork pointer */
+	xfs_ifork_t		*i_cowfp;	/* copy on write extents */
 	xfs_ifork_t		i_df;		/* data fork */
 
 	/* operations vectors */
@@ -65,6 +66,9 @@ typedef struct xfs_inode {
 
 	struct xfs_icdinode	i_d;		/* most of ondisk inode */
 
+	xfs_extnum_t		i_cnextents;	/* # of extents in cow fork */
+	unsigned int		i_cformat;	/* format of cow fork */
+
 	/* VFS inode */
 	struct inode		i_vnode;	/* embedded VFS inode */
 } xfs_inode_t;