xfs: cleanup xfs_bmap_last_before

Rewrite the function using xfs_iext_lookup_extent and xfs_iext_get_extent,
and massage the flow into something easily understandable.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/libxfs/xfs_bmap.c

@@ -1523,44 +1523,44 @@ xfs_bmap_first_unused(
  */
 int						/* error */
 xfs_bmap_last_before(
-	xfs_trans_t	*tp,			/* transaction pointer */
-	xfs_inode_t	*ip,			/* incore inode */
-	xfs_fileoff_t	*last_block,		/* last block */
-	int		whichfork)		/* data or attr fork */
+	struct xfs_trans	*tp,		/* transaction pointer */
+	struct xfs_inode	*ip,		/* incore inode */
+	xfs_fileoff_t		*last_block,	/* last block */
+	int			whichfork)	/* data or attr fork */
 {
-	xfs_fileoff_t	bno;			/* input file offset */
-	int		eof;			/* hit end of file */
-	xfs_bmbt_rec_host_t *ep;		/* pointer to last extent */
-	int		error;			/* error return value */
-	xfs_bmbt_irec_t	got;			/* current extent value */
-	xfs_ifork_t	*ifp;			/* inode fork pointer */
-	xfs_extnum_t	lastx;			/* last extent used */
-	xfs_bmbt_irec_t	prev;			/* previous extent value */
+	struct xfs_ifork	*ifp = XFS_IFORK_PTR(ip, whichfork);
+	struct xfs_bmbt_irec	got;
+	xfs_extnum_t		idx;
+	int			error;
 
-	if (XFS_IFORK_FORMAT(ip, whichfork) != XFS_DINODE_FMT_BTREE &&
-	    XFS_IFORK_FORMAT(ip, whichfork) != XFS_DINODE_FMT_EXTENTS &&
-	    XFS_IFORK_FORMAT(ip, whichfork) != XFS_DINODE_FMT_LOCAL)
-	       return -EIO;
-	if (XFS_IFORK_FORMAT(ip, whichfork) == XFS_DINODE_FMT_LOCAL) {
+	switch (XFS_IFORK_FORMAT(ip, whichfork)) {
+	case XFS_DINODE_FMT_LOCAL:
 		*last_block = 0;
 		return 0;
+	case XFS_DINODE_FMT_BTREE:
+	case XFS_DINODE_FMT_EXTENTS:
+		break;
+	default:
+		return -EIO;
 	}
-	ifp = XFS_IFORK_PTR(ip, whichfork);
-	if (!(ifp->if_flags & XFS_IFEXTENTS) &&
-	    (error = xfs_iread_extents(tp, ip, whichfork)))
-		return error;
-	bno = *last_block - 1;
-	ep = xfs_bmap_search_extents(ip, bno, whichfork, &eof, &lastx, &got,
-		&prev);
-	if (eof || xfs_bmbt_get_startoff(ep) > bno) {
-		if (prev.br_startoff == NULLFILEOFF)
-			*last_block = 0;
-		else
-			*last_block = prev.br_startoff + prev.br_blockcount;
+
+	if (!(ifp->if_flags & XFS_IFEXTENTS)) {
+		error = xfs_iread_extents(tp, ip, whichfork);
+		if (error)
+			return error;
 	}
-	/*
-	 * Otherwise *last_block is already the right answer.
-	 */
+
+	if (xfs_iext_lookup_extent(ip, ifp, *last_block - 1, &idx, &got)) {
+		if (got.br_startoff <= *last_block - 1)
+			return 0;
+	}
+
+	if (xfs_iext_get_extent(ifp, idx - 1, &got)) {
+		*last_block = got.br_startoff + got.br_blockcount;
+		return 0;
+	}
+
+	*last_block = 0;
 	return 0;
 }