xfs: handle cow fork in xfs_bmap_trace_exlist

By inspection, xfs_bmap_trace_exlist isn't handling cow forks,
and will trace the data fork instead.

Fix this by setting state appropriately if whichfork
== XFS_COW_FORK.

()___()
< @ @ >
 |   |
 {o_o}
  (|)
Signed-off-by: NEric Sandeen <sandeen@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDave Chinner <david@fromorbit.com>

fs/xfs/libxfs/xfs_bmap.c

@@ -518,7 +518,7 @@ void
 xfs_bmap_trace_exlist(
 	xfs_inode_t	*ip,		/* incore inode pointer */
 	xfs_extnum_t	cnt,		/* count of entries in the list */
-	int		whichfork,	/* data or attr fork */
+	int		whichfork,	/* data or attr or cow fork */
 	unsigned long	caller_ip)
 {
 	xfs_extnum_t	idx;		/* extent record index */
@@ -527,6 +527,8 @@ xfs_bmap_trace_exlist(
 
 	if (whichfork == XFS_ATTR_FORK)
 		state |= BMAP_ATTRFORK;
+	else if (whichfork == XFS_COW_FORK)
+		state |= BMAP_COWFORK;
 
 	ifp = XFS_IFORK_PTR(ip, whichfork);
 	ASSERT(cnt == xfs_iext_count(ifp));