xfs: fold xfs_bmbt_init_common into xfs_bmbt_init_cursor

Make the levels initialization in xfs_bmbt_init_cursor conditional
and merge the two helpers.

This requires the fakeroot case to now pass a -1 whichfork directly
into xfs_bmbt_init_cursor, and some special casing for that, but
at least this scheme to deal with the fake btree root is handled and
documented in once place now.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
[djwong: tidy up a multline ternary]
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/libxfs/xfs_bmap_btree.c

@@ -544,44 +544,46 @@ const struct xfs_btree_ops xfs_bmbt_ops = {
 	.keys_contiguous	= xfs_bmbt_keys_contiguous,
 };
 
-static struct xfs_btree_cur *
-xfs_bmbt_init_common(
+/*
+ * Create a new bmap btree cursor.
+ *
+ * For staging cursors -1 in passed in whichfork.
+ */
+struct xfs_btree_cur *
+xfs_bmbt_init_cursor(
 	struct xfs_mount	*mp,
 	struct xfs_trans	*tp,
 	struct xfs_inode	*ip,
 	int			whichfork)
 {
 	struct xfs_btree_cur	*cur;
+	unsigned int		maxlevels;
 
 	ASSERT(whichfork != XFS_COW_FORK);
 
+	/*
+	 * The Data fork always has larger maxlevel, so use that for staging
+	 * cursors.
+	 */
+	switch (whichfork) {
+	case XFS_STAGING_FORK:
+		maxlevels = mp->m_bm_maxlevels[XFS_DATA_FORK];
+		break;
+	default:
+		maxlevels = mp->m_bm_maxlevels[whichfork];
+		break;
+	}
 	cur = xfs_btree_alloc_cursor(mp, tp, XFS_BTNUM_BMAP, &xfs_bmbt_ops,
-			mp->m_bm_maxlevels[whichfork], xfs_bmbt_cur_cache);
-
+			maxlevels, xfs_bmbt_cur_cache);
 	cur->bc_ino.ip = ip;
+	cur->bc_ino.whichfork = whichfork;
 	cur->bc_bmap.allocated = 0;
-	return cur;
-}
-
-/*
- * Allocate a new bmap btree cursor.
- */
-struct xfs_btree_cur *
-xfs_bmbt_init_cursor(
-	struct xfs_mount	*mp,
-	struct xfs_trans	*tp,
-	struct xfs_inode	*ip,
-	int			whichfork)
-{
+	if (whichfork != XFS_STAGING_FORK) {
 		struct xfs_ifork	*ifp = xfs_ifork_ptr(ip, whichfork);
-	struct xfs_btree_cur	*cur;
-
-	cur = xfs_bmbt_init_common(mp, tp, ip, whichfork);
 
 		cur->bc_nlevels = be16_to_cpu(ifp->if_broot->bb_level) + 1;
 		cur->bc_ino.forksize = xfs_inode_fork_size(ip, whichfork);
-	cur->bc_ino.whichfork = whichfork;
-
+	}
 	return cur;
 }
 
@@ -610,11 +612,7 @@ xfs_bmbt_stage_cursor(
 {
 	struct xfs_btree_cur	*cur;
 
-	/* data fork always has larger maxheight */
-	cur = xfs_bmbt_init_common(mp, NULL, ip, XFS_DATA_FORK);
-
-	/* Don't let anyone think we're attached to the real fork yet. */
-	cur->bc_ino.whichfork = XFS_STAGING_FORK;
+	cur = xfs_bmbt_init_cursor(mp, NULL, ip, XFS_STAGING_FORK);
 	xfs_btree_stage_ifakeroot(cur, ifake);
 	return cur;
 }