xfs: remove if_lastex

The if_lastex field in struct xfs_ifork is only used as a temporary
index during xfs_bmapi and xfs_bunmapi.  Instead of using the inode
fork to store it keep it local in the callchain.  Fortunately this
is very easy as we already pass a stack copy of it down the whole
chain which can simplify be changed to be passed by reference.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>

fs/xfs/xfs_inode.c

@@ -920,7 +920,6 @@ xfs_iread_extents(
 	/*
 	 * We know that the size is valid (it's checked in iformat_btree)
 	 */
-	ifp->if_lastex = NULLEXTNUM;
 	ifp->if_bytes = ifp->if_real_bytes = 0;
 	ifp->if_flags |= XFS_IFEXTENTS;
 	xfs_iext_add(ifp, 0, nextents);
@@ -3191,7 +3190,6 @@ xfs_iext_add(
 		}
 		ifp->if_u1.if_extents = ifp->if_u2.if_inline_ext;
 		ifp->if_real_bytes = 0;
-		ifp->if_lastex = nextents + ext_diff;
 	}
 	/*
 	 * Otherwise use a linear (direct) extent list.

fs/xfs/xfs_inode.h

@@ -67,7 +67,6 @@ typedef struct xfs_ifork {
 	short			if_broot_bytes;	/* bytes allocated for root */
 	unsigned char		if_flags;	/* per-fork flags */
 	unsigned char		if_ext_max;	/* max # of extent records */
-	xfs_extnum_t		if_lastex;	/* last if_extents used */
 	union {
 		xfs_bmbt_rec_host_t *if_extents;/* linear map file exts */
 		xfs_ext_irec_t	*if_ext_irec;	/* irec map file exts */