diff --git a/fs/nilfs2/btree.c b/fs/nilfs2/btree.c
new file mode 100644
index 000000000000..893f0190a61f
--- /dev/null
+++ b/fs/nilfs2/btree.c
@@ -0,0 +1,2276 @@
+/*
+ * btree.c - NILFS B-tree.
+ *
+ * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Written by Koji Sato <koji@osrg.net>.
+ */
+
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/errno.h>
+#include <linux/pagevec.h>
+#include "nilfs.h"
+#include "page.h"
+#include "btnode.h"
+#include "btree.h"
+#include "alloc.h"
+
+/**
+ * struct nilfs_btree_path - A path on which B-tree operations are executed
+ * @bp_bh: buffer head of node block
+ * @bp_sib_bh: buffer head of sibling node block
+ * @bp_index: index of child node
+ * @bp_oldreq: ptr end request for old ptr
+ * @bp_newreq: ptr alloc request for new ptr
+ * @bp_op: rebalance operation
+ */
+struct nilfs_btree_path {
+	struct buffer_head *bp_bh;
+	struct buffer_head *bp_sib_bh;
+	int bp_index;
+	union nilfs_bmap_ptr_req bp_oldreq;
+	union nilfs_bmap_ptr_req bp_newreq;
+	struct nilfs_btnode_chkey_ctxt bp_ctxt;
+	void (*bp_op)(struct nilfs_btree *, struct nilfs_btree_path *,
+		      int, __u64 *, __u64 *);
+};
+
+/*
+ * B-tree path operations
+ */
+
+static struct kmem_cache *nilfs_btree_path_cache;
+
+int __init nilfs_btree_path_cache_init(void)
+{
+	nilfs_btree_path_cache =
+		kmem_cache_create("nilfs2_btree_path_cache",
+				  sizeof(struct nilfs_btree_path) *
+				  NILFS_BTREE_LEVEL_MAX, 0, 0, NULL);
+	return (nilfs_btree_path_cache != NULL) ? 0 : -ENOMEM;
+}
+
+void nilfs_btree_path_cache_destroy(void)
+{
+	kmem_cache_destroy(nilfs_btree_path_cache);
+}
+
+static inline struct nilfs_btree_path *
+nilfs_btree_alloc_path(const struct nilfs_btree *btree)
+{
+	return (struct nilfs_btree_path *)
+		kmem_cache_alloc(nilfs_btree_path_cache, GFP_NOFS);
+}
+
+static inline void nilfs_btree_free_path(const struct nilfs_btree *btree,
+					 struct nilfs_btree_path *path)
+{
+	kmem_cache_free(nilfs_btree_path_cache, path);
+}
+
+static void nilfs_btree_init_path(const struct nilfs_btree *btree,
+				  struct nilfs_btree_path *path)
+{
+	int level;
+
+	for (level = NILFS_BTREE_LEVEL_DATA;
+	     level < NILFS_BTREE_LEVEL_MAX;
+	     level++) {
+		path[level].bp_bh = NULL;
+		path[level].bp_sib_bh = NULL;
+		path[level].bp_index = 0;
+		path[level].bp_oldreq.bpr_ptr = NILFS_BMAP_INVALID_PTR;
+		path[level].bp_newreq.bpr_ptr = NILFS_BMAP_INVALID_PTR;
+		path[level].bp_op = NULL;
+	}
+}
+
+static void nilfs_btree_clear_path(const struct nilfs_btree *btree,
+				   struct nilfs_btree_path *path)
+{
+	int level;
+
+	for (level = NILFS_BTREE_LEVEL_DATA;
+	     level < NILFS_BTREE_LEVEL_MAX;
+	     level++) {
+		if (path[level].bp_bh != NULL) {
+			nilfs_bmap_put_block(&btree->bt_bmap,
+					     path[level].bp_bh);
+			path[level].bp_bh = NULL;
+		}
+		/* sib_bh is released or deleted by prepare or commit
+		 * operations. */
+		path[level].bp_sib_bh = NULL;
+		path[level].bp_index = 0;
+		path[level].bp_oldreq.bpr_ptr = NILFS_BMAP_INVALID_PTR;
+		path[level].bp_newreq.bpr_ptr = NILFS_BMAP_INVALID_PTR;
+		path[level].bp_op = NULL;
+	}
+}
+
+
+/*
+ * B-tree node operations
+ */
+
+static inline int
+nilfs_btree_node_get_flags(const struct nilfs_btree *btree,
+			   const struct nilfs_btree_node *node)
+{
+	return node->bn_flags;
+}
+
+static inline void
+nilfs_btree_node_set_flags(struct nilfs_btree *btree,
+			   struct nilfs_btree_node *node,
+			   int flags)
+{
+	node->bn_flags = flags;
+}
+
+static inline int nilfs_btree_node_root(const struct nilfs_btree *btree,
+					const struct nilfs_btree_node *node)
+{
+	return nilfs_btree_node_get_flags(btree, node) & NILFS_BTREE_NODE_ROOT;
+}
+
+static inline int
+nilfs_btree_node_get_level(const struct nilfs_btree *btree,
+			   const struct nilfs_btree_node *node)
+{
+	return node->bn_level;
+}
+
+static inline void
+nilfs_btree_node_set_level(struct nilfs_btree *btree,
+			   struct nilfs_btree_node *node,
+			   int level)
+{
+	node->bn_level = level;
+}
+
+static inline int
+nilfs_btree_node_get_nchildren(const struct nilfs_btree *btree,
+			       const struct nilfs_btree_node *node)
+{
+	return le16_to_cpu(node->bn_nchildren);
+}
+
+static inline void
+nilfs_btree_node_set_nchildren(struct nilfs_btree *btree,
+			       struct nilfs_btree_node *node,
+			       int nchildren)
+{
+	node->bn_nchildren = cpu_to_le16(nchildren);
+}
+
+static inline int
+nilfs_btree_node_size(const struct nilfs_btree *btree)
+{
+	return 1 << btree->bt_bmap.b_inode->i_blkbits;
+}
+
+static inline int
+nilfs_btree_node_nchildren_min(const struct nilfs_btree *btree,
+			       const struct nilfs_btree_node *node)
+{
+	return nilfs_btree_node_root(btree, node) ?
+		NILFS_BTREE_ROOT_NCHILDREN_MIN :
+		NILFS_BTREE_NODE_NCHILDREN_MIN(nilfs_btree_node_size(btree));
+}
+
+static inline int
+nilfs_btree_node_nchildren_max(const struct nilfs_btree *btree,
+			       const struct nilfs_btree_node *node)
+{
+	return nilfs_btree_node_root(btree, node) ?
+		NILFS_BTREE_ROOT_NCHILDREN_MAX :
+		NILFS_BTREE_NODE_NCHILDREN_MAX(nilfs_btree_node_size(btree));
+}
+
+static inline __le64 *
+nilfs_btree_node_dkeys(const struct nilfs_btree *btree,
+		       const struct nilfs_btree_node *node)
+{
+	return (__le64 *)((char *)(node + 1) +
+			  (nilfs_btree_node_root(btree, node) ?
+			   0 : NILFS_BTREE_NODE_EXTRA_PAD_SIZE));
+}
+
+static inline __le64 *
+nilfs_btree_node_dptrs(const struct nilfs_btree *btree,
+		       const struct nilfs_btree_node *node)
+{
+	return (__le64 *)(nilfs_btree_node_dkeys(btree, node) +
+			  nilfs_btree_node_nchildren_max(btree, node));
+}
+
+static inline __u64
+nilfs_btree_node_get_key(const struct nilfs_btree *btree,
+			 const struct nilfs_btree_node *node, int index)
+{
+	return nilfs_bmap_dkey_to_key(*(nilfs_btree_node_dkeys(btree, node) +
+					index));
+}
+
+static inline void
+nilfs_btree_node_set_key(struct nilfs_btree *btree,
+			 struct nilfs_btree_node *node, int index, __u64 key)
+{
+	*(nilfs_btree_node_dkeys(btree, node) + index) =
+		nilfs_bmap_key_to_dkey(key);
+}
+
+static inline __u64
+nilfs_btree_node_get_ptr(const struct nilfs_btree *btree,
+			 const struct nilfs_btree_node *node,
+			 int index)
+{
+	return nilfs_bmap_dptr_to_ptr(*(nilfs_btree_node_dptrs(btree, node) +
+					index));
+}
+
+static inline void
+nilfs_btree_node_set_ptr(struct nilfs_btree *btree,
+			 struct nilfs_btree_node *node,
+			 int index,
+			 __u64 ptr)
+{
+	*(nilfs_btree_node_dptrs(btree, node) + index) =
+		nilfs_bmap_ptr_to_dptr(ptr);
+}
+
+static void nilfs_btree_node_init(struct nilfs_btree *btree,
+				  struct nilfs_btree_node *node,
+				  int flags, int level, int nchildren,
+				  const __u64 *keys, const __u64 *ptrs)
+{
+	__le64 *dkeys;
+	__le64 *dptrs;
+	int i;
+
+	nilfs_btree_node_set_flags(btree, node, flags);
+	nilfs_btree_node_set_level(btree, node, level);
+	nilfs_btree_node_set_nchildren(btree, node, nchildren);
+
+	dkeys = nilfs_btree_node_dkeys(btree, node);
+	dptrs = nilfs_btree_node_dptrs(btree, node);
+	for (i = 0; i < nchildren; i++) {
+		dkeys[i] = nilfs_bmap_key_to_dkey(keys[i]);
+		dptrs[i] = nilfs_bmap_ptr_to_dptr(ptrs[i]);
+	}
+}
+
+/* Assume the buffer heads corresponding to left and right are locked. */
+static void nilfs_btree_node_move_left(struct nilfs_btree *btree,
+				       struct nilfs_btree_node *left,
+				       struct nilfs_btree_node *right,
+				       int n)
+{
+	__le64 *ldkeys, *rdkeys;
+	__le64 *ldptrs, *rdptrs;
+	int lnchildren, rnchildren;
+
+	ldkeys = nilfs_btree_node_dkeys(btree, left);
+	ldptrs = nilfs_btree_node_dptrs(btree, left);
+	lnchildren = nilfs_btree_node_get_nchildren(btree, left);
+
+	rdkeys = nilfs_btree_node_dkeys(btree, right);
+	rdptrs = nilfs_btree_node_dptrs(btree, right);
+	rnchildren = nilfs_btree_node_get_nchildren(btree, right);
+
+	memcpy(ldkeys + lnchildren, rdkeys, n * sizeof(*rdkeys));
+	memcpy(ldptrs + lnchildren, rdptrs, n * sizeof(*rdptrs));
+	memmove(rdkeys, rdkeys + n, (rnchildren - n) * sizeof(*rdkeys));
+	memmove(rdptrs, rdptrs + n, (rnchildren - n) * sizeof(*rdptrs));
+
+	lnchildren += n;
+	rnchildren -= n;
+	nilfs_btree_node_set_nchildren(btree, left, lnchildren);
+	nilfs_btree_node_set_nchildren(btree, right, rnchildren);
+}
+
+/* Assume that the buffer heads corresponding to left and right are locked. */
+static void nilfs_btree_node_move_right(struct nilfs_btree *btree,
+					struct nilfs_btree_node *left,
+					struct nilfs_btree_node *right,
+					int n)
+{
+	__le64 *ldkeys, *rdkeys;
+	__le64 *ldptrs, *rdptrs;
+	int lnchildren, rnchildren;
+
+	ldkeys = nilfs_btree_node_dkeys(btree, left);
+	ldptrs = nilfs_btree_node_dptrs(btree, left);
+	lnchildren = nilfs_btree_node_get_nchildren(btree, left);
+
+	rdkeys = nilfs_btree_node_dkeys(btree, right);
+	rdptrs = nilfs_btree_node_dptrs(btree, right);
+	rnchildren = nilfs_btree_node_get_nchildren(btree, right);
+
+	memmove(rdkeys + n, rdkeys, rnchildren * sizeof(*rdkeys));
+	memmove(rdptrs + n, rdptrs, rnchildren * sizeof(*rdptrs));
+	memcpy(rdkeys, ldkeys + lnchildren - n, n * sizeof(*rdkeys));
+	memcpy(rdptrs, ldptrs + lnchildren - n, n * sizeof(*rdptrs));
+
+	lnchildren -= n;
+	rnchildren += n;
+	nilfs_btree_node_set_nchildren(btree, left, lnchildren);
+	nilfs_btree_node_set_nchildren(btree, right, rnchildren);
+}
+
+/* Assume that the buffer head corresponding to node is locked. */
+static void nilfs_btree_node_insert(struct nilfs_btree *btree,
+				    struct nilfs_btree_node *node,
+				    __u64 key, __u64 ptr, int index)
+{
+	__le64 *dkeys;
+	__le64 *dptrs;
+	int nchildren;
+
+	dkeys = nilfs_btree_node_dkeys(btree, node);
+	dptrs = nilfs_btree_node_dptrs(btree, node);
+	nchildren = nilfs_btree_node_get_nchildren(btree, node);
+	if (index < nchildren) {
+		memmove(dkeys + index + 1, dkeys + index,
+			(nchildren - index) * sizeof(*dkeys));
+		memmove(dptrs + index + 1, dptrs + index,
+			(nchildren - index) * sizeof(*dptrs));
+	}
+	dkeys[index] = nilfs_bmap_key_to_dkey(key);
+	dptrs[index] = nilfs_bmap_ptr_to_dptr(ptr);
+	nchildren++;
+	nilfs_btree_node_set_nchildren(btree, node, nchildren);
+}
+
+/* Assume that the buffer head corresponding to node is locked. */
+static void nilfs_btree_node_delete(struct nilfs_btree *btree,
+				    struct nilfs_btree_node *node,
+				    __u64 *keyp, __u64 *ptrp, int index)
+{
+	__u64 key;
+	__u64 ptr;
+	__le64 *dkeys;
+	__le64 *dptrs;
+	int nchildren;
+
+	dkeys = nilfs_btree_node_dkeys(btree, node);
+	dptrs = nilfs_btree_node_dptrs(btree, node);
+	key = nilfs_bmap_dkey_to_key(dkeys[index]);
+	ptr = nilfs_bmap_dptr_to_ptr(dptrs[index]);
+	nchildren = nilfs_btree_node_get_nchildren(btree, node);
+	if (keyp != NULL)
+		*keyp = key;
+	if (ptrp != NULL)
+		*ptrp = ptr;
+
+	if (index < nchildren - 1) {
+		memmove(dkeys + index, dkeys + index + 1,
+			(nchildren - index - 1) * sizeof(*dkeys));
+		memmove(dptrs + index, dptrs + index + 1,
+			(nchildren - index - 1) * sizeof(*dptrs));
+	}
+	nchildren--;
+	nilfs_btree_node_set_nchildren(btree, node, nchildren);
+}
+
+static int nilfs_btree_node_lookup(const struct nilfs_btree *btree,
+				   const struct nilfs_btree_node *node,
+				   __u64 key, int *indexp)
+{
+	__u64 nkey;
+	int index, low, high, s;
+
+	/* binary search */
+	low = 0;
+	high = nilfs_btree_node_get_nchildren(btree, node) - 1;
+	index = 0;
+	s = 0;
+	while (low <= high) {
+		index = (low + high) / 2;
+		nkey = nilfs_btree_node_get_key(btree, node, index);
+		if (nkey == key) {
+			s = 0;
+			goto out;
+		} else if (nkey < key) {
+			low = index + 1;
+			s = -1;
+		} else {
+			high = index - 1;
+			s = 1;
+		}
+	}
+
+	/* adjust index */
+	if (nilfs_btree_node_get_level(btree, node) >
+	    NILFS_BTREE_LEVEL_NODE_MIN) {
+		if ((s > 0) && (index > 0))
+			index--;
+	} else if (s < 0)
+		index++;
+
+ out:
+	BUG_ON(indexp == NULL);
+	*indexp = index;
+
+	return s == 0;
+}
+
+static inline struct nilfs_btree_node *
+nilfs_btree_get_root(const struct nilfs_btree *btree)
+{
+	return (struct nilfs_btree_node *)btree->bt_bmap.b_u.u_data;
+}
+
+static inline struct nilfs_btree_node *
+nilfs_btree_get_nonroot_node(const struct nilfs_btree *btree,
+			     const struct nilfs_btree_path *path,
+			     int level)
+{
+	return (struct nilfs_btree_node *)path[level].bp_bh->b_data;
+}
+
+static inline struct nilfs_btree_node *
+nilfs_btree_get_sib_node(const struct nilfs_btree *btree,
+			 const struct nilfs_btree_path *path,
+			 int level)
+{
+	return (struct nilfs_btree_node *)path[level].bp_sib_bh->b_data;
+}
+
+static inline int nilfs_btree_height(const struct nilfs_btree *btree)
+{
+	return nilfs_btree_node_get_level(btree, nilfs_btree_get_root(btree))
+		+ 1;
+}
+
+static inline struct nilfs_btree_node *
+nilfs_btree_get_node(const struct nilfs_btree *btree,
+		     const struct nilfs_btree_path *path,
+		     int level)
+{
+	return (level == nilfs_btree_height(btree) - 1) ?
+		nilfs_btree_get_root(btree) :
+		nilfs_btree_get_nonroot_node(btree, path, level);
+}
+
+static int nilfs_btree_do_lookup(const struct nilfs_btree *btree,
+				 struct nilfs_btree_path *path,
+				 __u64 key, __u64 *ptrp, int minlevel)
+{
+	struct nilfs_btree_node *node;
+	__u64 ptr;
+	int level, index, found, ret;
+
+	BUG_ON(minlevel <= NILFS_BTREE_LEVEL_DATA);
+
+	node = nilfs_btree_get_root(btree);
+	level = nilfs_btree_node_get_level(btree, node);
+	if ((level < minlevel) ||
+	    (nilfs_btree_node_get_nchildren(btree, node) <= 0))
+		return -ENOENT;
+
+	found = nilfs_btree_node_lookup(btree, node, key, &index);
+	ptr = nilfs_btree_node_get_ptr(btree, node, index);
+	path[level].bp_bh = NULL;
+	path[level].bp_index = index;
+
+	for (level--; level >= minlevel; level--) {
+		ret = nilfs_bmap_get_block(&btree->bt_bmap, ptr,
+					   &path[level].bp_bh);
+		if (ret < 0)
+			return ret;
+		node = nilfs_btree_get_nonroot_node(btree, path, level);
+		BUG_ON(level != nilfs_btree_node_get_level(btree, node));
+		if (!found)
+			found = nilfs_btree_node_lookup(btree, node, key,
+							&index);
+		else
+			index = 0;
+		if (index < nilfs_btree_node_nchildren_max(btree, node))
+			ptr = nilfs_btree_node_get_ptr(btree, node, index);
+		else {
+			BUG_ON(found || level != NILFS_BTREE_LEVEL_NODE_MIN);
+			/* insert */
+			ptr = NILFS_BMAP_INVALID_PTR;
+		}
+		path[level].bp_index = index;
+	}
+	if (!found)
+		return -ENOENT;
+
+	if (ptrp != NULL)
+		*ptrp = ptr;
+
+	return 0;
+}
+
+static int nilfs_btree_do_lookup_last(const struct nilfs_btree *btree,
+				      struct nilfs_btree_path *path,
+				      __u64 *keyp, __u64 *ptrp)
+{
+	struct nilfs_btree_node *node;
+	__u64 ptr;
+	int index, level, ret;
+
+	node = nilfs_btree_get_root(btree);
+	index = nilfs_btree_node_get_nchildren(btree, node) - 1;
+	if (index < 0)
+		return -ENOENT;
+	level = nilfs_btree_node_get_level(btree, node);
+	ptr = nilfs_btree_node_get_ptr(btree, node, index);
+	path[level].bp_bh = NULL;
+	path[level].bp_index = index;
+
+	for (level--; level > 0; level--) {
+		ret = nilfs_bmap_get_block(&btree->bt_bmap, ptr,
+					   &path[level].bp_bh);
+		if (ret < 0)
+			return ret;
+		node = nilfs_btree_get_nonroot_node(btree, path, level);
+		BUG_ON(level != nilfs_btree_node_get_level(btree, node));
+		index = nilfs_btree_node_get_nchildren(btree, node) - 1;
+		ptr = nilfs_btree_node_get_ptr(btree, node, index);
+		path[level].bp_index = index;
+	}
+
+	if (keyp != NULL)
+		*keyp = nilfs_btree_node_get_key(btree, node, index);
+	if (ptrp != NULL)
+		*ptrp = ptr;
+
+	return 0;
+}
+
+static int nilfs_btree_lookup(const struct nilfs_bmap *bmap,
+			      __u64 key, int level, __u64 *ptrp)
+{
+	struct nilfs_btree *btree;
+	struct nilfs_btree_path *path;
+	__u64 ptr;
+	int ret;
+
+	btree = (struct nilfs_btree *)bmap;
+	path = nilfs_btree_alloc_path(btree);
+	if (path == NULL)
+		return -ENOMEM;
+	nilfs_btree_init_path(btree, path);
+
+	ret = nilfs_btree_do_lookup(btree, path, key, &ptr, level);
+
+	if (ptrp != NULL)
+		*ptrp = ptr;
+
+	nilfs_btree_clear_path(btree, path);
+	nilfs_btree_free_path(btree, path);
+
+	return ret;
+}
+
+static void nilfs_btree_promote_key(struct nilfs_btree *btree,
+				    struct nilfs_btree_path *path,
+				    int level, __u64 key)
+{
+	if (level < nilfs_btree_height(btree) - 1) {
+		do {
+			lock_buffer(path[level].bp_bh);
+			nilfs_btree_node_set_key(
+				btree,
+				nilfs_btree_get_nonroot_node(
+					btree, path, level),
+				path[level].bp_index, key);
+			if (!buffer_dirty(path[level].bp_bh))
+				nilfs_btnode_mark_dirty(path[level].bp_bh);
+			unlock_buffer(path[level].bp_bh);
+		} while ((path[level].bp_index == 0) &&
+			 (++level < nilfs_btree_height(btree) - 1));
+	}
+
+	/* root */
+	if (level == nilfs_btree_height(btree) - 1) {
+		nilfs_btree_node_set_key(btree,
+					 nilfs_btree_get_root(btree),
+					 path[level].bp_index, key);
+	}
+}
+
+static void nilfs_btree_do_insert(struct nilfs_btree *btree,
+				  struct nilfs_btree_path *path,
+				  int level, __u64 *keyp, __u64 *ptrp)
+{
+	struct nilfs_btree_node *node;
+
+	if (level < nilfs_btree_height(btree) - 1) {
+		lock_buffer(path[level].bp_bh);
+		node = nilfs_btree_get_nonroot_node(btree, path, level);
+		nilfs_btree_node_insert(btree, node, *keyp, *ptrp,
+					path[level].bp_index);
+		if (!buffer_dirty(path[level].bp_bh))
+			nilfs_btnode_mark_dirty(path[level].bp_bh);
+		unlock_buffer(path[level].bp_bh);
+
+		if (path[level].bp_index == 0)
+			nilfs_btree_promote_key(btree, path, level + 1,
+						nilfs_btree_node_get_key(
+							btree, node, 0));
+	} else {
+		node = nilfs_btree_get_root(btree);
+		nilfs_btree_node_insert(btree, node, *keyp, *ptrp,
+					path[level].bp_index);
+	}
+}
+
+static void nilfs_btree_carry_left(struct nilfs_btree *btree,
+				   struct nilfs_btree_path *path,
+				   int level, __u64 *keyp, __u64 *ptrp)
+{
+	struct nilfs_btree_node *node, *left;
+	int nchildren, lnchildren, n, move;
+
+	lock_buffer(path[level].bp_bh);
+	lock_buffer(path[level].bp_sib_bh);
+
+	node = nilfs_btree_get_nonroot_node(btree, path, level);
+	left = nilfs_btree_get_sib_node(btree, path, level);
+	nchildren = nilfs_btree_node_get_nchildren(btree, node);
+	lnchildren = nilfs_btree_node_get_nchildren(btree, left);
+	move = 0;
+
+	n = (nchildren + lnchildren + 1) / 2 - lnchildren;
+	if (n > path[level].bp_index) {
+		/* move insert point */
+		n--;
+		move = 1;
+	}
+
+	nilfs_btree_node_move_left(btree, left, node, n);
+
+	if (!buffer_dirty(path[level].bp_bh))
+		nilfs_btnode_mark_dirty(path[level].bp_bh);
+	if (!buffer_dirty(path[level].bp_sib_bh))
+		nilfs_btnode_mark_dirty(path[level].bp_sib_bh);
+
+	unlock_buffer(path[level].bp_bh);
+	unlock_buffer(path[level].bp_sib_bh);
+
+	nilfs_btree_promote_key(btree, path, level + 1,
+				nilfs_btree_node_get_key(btree, node, 0));
+
+	if (move) {
+		nilfs_bmap_put_block(&btree->bt_bmap, path[level].bp_bh);
+		path[level].bp_bh = path[level].bp_sib_bh;
+		path[level].bp_sib_bh = NULL;
+		path[level].bp_index += lnchildren;
+		path[level + 1].bp_index--;
+	} else {
+		nilfs_bmap_put_block(&btree->bt_bmap, path[level].bp_sib_bh);
+		path[level].bp_sib_bh = NULL;
+		path[level].bp_index -= n;
+	}
+
+	nilfs_btree_do_insert(btree, path, level, keyp, ptrp);
+}
+
+static void nilfs_btree_carry_right(struct nilfs_btree *btree,
+				    struct nilfs_btree_path *path,
+				    int level, __u64 *keyp, __u64 *ptrp)
+{
+	struct nilfs_btree_node *node, *right;
+	int nchildren, rnchildren, n, move;
+
+	lock_buffer(path[level].bp_bh);
+	lock_buffer(path[level].bp_sib_bh);
+
+	node = nilfs_btree_get_nonroot_node(btree, path, level);
+	right = nilfs_btree_get_sib_node(btree, path, level);
+	nchildren = nilfs_btree_node_get_nchildren(btree, node);
+	rnchildren = nilfs_btree_node_get_nchildren(btree, right);
+	move = 0;
+
+	n = (nchildren + rnchildren + 1) / 2 - rnchildren;
+	if (n > nchildren - path[level].bp_index) {
+		/* move insert point */
+		n--;
+		move = 1;
+	}
+
+	nilfs_btree_node_move_right(btree, node, right, n);
+
+	if (!buffer_dirty(path[level].bp_bh))
+		nilfs_btnode_mark_dirty(path[level].bp_bh);
+	if (!buffer_dirty(path[level].bp_sib_bh))
+		nilfs_btnode_mark_dirty(path[level].bp_sib_bh);
+
+	unlock_buffer(path[level].bp_bh);
+	unlock_buffer(path[level].bp_sib_bh);
+
+	path[level + 1].bp_index++;
+	nilfs_btree_promote_key(btree, path, level + 1,
+				nilfs_btree_node_get_key(btree, right, 0));
+	path[level + 1].bp_index--;
+
+	if (move) {
+		nilfs_bmap_put_block(&btree->bt_bmap, path[level].bp_bh);
+		path[level].bp_bh = path[level].bp_sib_bh;
+		path[level].bp_sib_bh = NULL;
+		path[level].bp_index -=
+			nilfs_btree_node_get_nchildren(btree, node);
+		path[level + 1].bp_index++;
+	} else {
+		nilfs_bmap_put_block(&btree->bt_bmap, path[level].bp_sib_bh);
+		path[level].bp_sib_bh = NULL;
+	}
+
+	nilfs_btree_do_insert(btree, path, level, keyp, ptrp);
+}
+
+static void nilfs_btree_split(struct nilfs_btree *btree,
+			      struct nilfs_btree_path *path,
+			      int level, __u64 *keyp, __u64 *ptrp)
+{
+	struct nilfs_btree_node *node, *right;
+	__u64 newkey;
+	__u64 newptr;
+	int nchildren, n, move;
+
+	lock_buffer(path[level].bp_bh);
+	lock_buffer(path[level].bp_sib_bh);
+
+	node = nilfs_btree_get_nonroot_node(btree, path, level);
+	right = nilfs_btree_get_sib_node(btree, path, level);
+	nchildren = nilfs_btree_node_get_nchildren(btree, node);
+	move = 0;
+
+	n = (nchildren + 1) / 2;
+	if (n > nchildren - path[level].bp_index) {
+		n--;
+		move = 1;
+	}
+
+	nilfs_btree_node_move_right(btree, node, right, n);
+
+	if (!buffer_dirty(path[level].bp_bh))
+		nilfs_btnode_mark_dirty(path[level].bp_bh);
+	if (!buffer_dirty(path[level].bp_sib_bh))
+		nilfs_btnode_mark_dirty(path[level].bp_sib_bh);
+
+	unlock_buffer(path[level].bp_bh);
+	unlock_buffer(path[level].bp_sib_bh);
+
+	newkey = nilfs_btree_node_get_key(btree, right, 0);
+	newptr = path[level].bp_newreq.bpr_ptr;
+
+	if (move) {
+		path[level].bp_index -=
+			nilfs_btree_node_get_nchildren(btree, node);
+		nilfs_btree_node_insert(btree, right, *keyp, *ptrp,
+					path[level].bp_index);
+
+		*keyp = nilfs_btree_node_get_key(btree, right, 0);
+		*ptrp = path[level].bp_newreq.bpr_ptr;
+
+		nilfs_bmap_put_block(&btree->bt_bmap, path[level].bp_bh);
+		path[level].bp_bh = path[level].bp_sib_bh;
+		path[level].bp_sib_bh = NULL;
+	} else {
+		nilfs_btree_do_insert(btree, path, level, keyp, ptrp);
+
+		*keyp = nilfs_btree_node_get_key(btree, right, 0);
+		*ptrp = path[level].bp_newreq.bpr_ptr;
+
+		nilfs_bmap_put_block(&btree->bt_bmap, path[level].bp_sib_bh);
+		path[level].bp_sib_bh = NULL;
+	}
+
+	path[level + 1].bp_index++;
+}
+
+static void nilfs_btree_grow(struct nilfs_btree *btree,
+			     struct nilfs_btree_path *path,
+			     int level, __u64 *keyp, __u64 *ptrp)
+{
+	struct nilfs_btree_node *root, *child;
+	int n;
+
+	lock_buffer(path[level].bp_sib_bh);
+
+	root = nilfs_btree_get_root(btree);
+	child = nilfs_btree_get_sib_node(btree, path, level);
+
+	n = nilfs_btree_node_get_nchildren(btree, root);
+
+	nilfs_btree_node_move_right(btree, root, child, n);
+	nilfs_btree_node_set_level(btree, root, level + 1);
+
+	if (!buffer_dirty(path[level].bp_sib_bh))
+		nilfs_btnode_mark_dirty(path[level].bp_sib_bh);
+
+	unlock_buffer(path[level].bp_sib_bh);
+
+	path[level].bp_bh = path[level].bp_sib_bh;
+	path[level].bp_sib_bh = NULL;
+
+	nilfs_btree_do_insert(btree, path, level, keyp, ptrp);
+
+	*keyp = nilfs_btree_node_get_key(btree, child, 0);
+	*ptrp = path[level].bp_newreq.bpr_ptr;
+}
+
+static __u64 nilfs_btree_find_near(const struct nilfs_btree *btree,
+				   const struct nilfs_btree_path *path)
+{
+	struct nilfs_btree_node *node;
+	int level;
+
+	if (path == NULL)
+		return NILFS_BMAP_INVALID_PTR;
+
+	/* left sibling */
+	level = NILFS_BTREE_LEVEL_NODE_MIN;
+	if (path[level].bp_index > 0) {
+		node = nilfs_btree_get_node(btree, path, level);
+		return nilfs_btree_node_get_ptr(btree, node,
+						path[level].bp_index - 1);
+	}
+
+	/* parent */
+	level = NILFS_BTREE_LEVEL_NODE_MIN + 1;
+	if (level <= nilfs_btree_height(btree) - 1) {
+		node = nilfs_btree_get_node(btree, path, level);
+		return nilfs_btree_node_get_ptr(btree, node,
+						path[level].bp_index);
+	}
+
+	return NILFS_BMAP_INVALID_PTR;
+}
+
+static __u64 nilfs_btree_find_target_v(const struct nilfs_btree *btree,
+				       const struct nilfs_btree_path *path,
+				       __u64 key)
+{
+	__u64 ptr;
+
+	ptr = nilfs_bmap_find_target_seq(&btree->bt_bmap, key);
+	if (ptr != NILFS_BMAP_INVALID_PTR)
+		/* sequential access */
+		return ptr;
+	else {
+		ptr = nilfs_btree_find_near(btree, path);
+		if (ptr != NILFS_BMAP_INVALID_PTR)
+			/* near */
+			return ptr;
+	}
+	/* block group */
+	return nilfs_bmap_find_target_in_group(&btree->bt_bmap);
+}
+
+static void nilfs_btree_set_target_v(struct nilfs_btree *btree, __u64 key,
+				     __u64 ptr)
+{
+	btree->bt_bmap.b_last_allocated_key = key;
+	btree->bt_bmap.b_last_allocated_ptr = ptr;
+}
+
+static int nilfs_btree_prepare_insert(struct nilfs_btree *btree,
+				      struct nilfs_btree_path *path,
+				      int *levelp, __u64 key, __u64 ptr,
+				      struct nilfs_bmap_stats *stats)
+{
+	struct buffer_head *bh;
+	struct nilfs_btree_node *node, *parent, *sib;
+	__u64 sibptr;
+	int pindex, level, ret;
+
+	stats->bs_nblocks = 0;
+	level = NILFS_BTREE_LEVEL_DATA;
+
+	/* allocate a new ptr for data block */
+	if (btree->bt_ops->btop_find_target != NULL)
+		path[level].bp_newreq.bpr_ptr =
+			(*btree->bt_ops->btop_find_target)(btree, path, key);
+
+	ret = (*btree->bt_bmap.b_pops->bpop_prepare_alloc_ptr)(
+		&btree->bt_bmap, &path[level].bp_newreq);
+	if (ret < 0)
+		goto err_out_data;
+
+	for (level = NILFS_BTREE_LEVEL_NODE_MIN;
+	     level < nilfs_btree_height(btree) - 1;
+	     level++) {
+		node = nilfs_btree_get_nonroot_node(btree, path, level);
+		if (nilfs_btree_node_get_nchildren(btree, node) <
+		    nilfs_btree_node_nchildren_max(btree, node)) {
+			path[level].bp_op = nilfs_btree_do_insert;
+			stats->bs_nblocks++;
+			goto out;
+		}
+
+		parent = nilfs_btree_get_node(btree, path, level + 1);
+		pindex = path[level + 1].bp_index;
+
+		/* left sibling */
+		if (pindex > 0) {
+			sibptr = nilfs_btree_node_get_ptr(btree, parent,
+							  pindex - 1);
+			ret = nilfs_bmap_get_block(&btree->bt_bmap, sibptr,
+						   &bh);
+			if (ret < 0)
+				goto err_out_child_node;
+			sib = (struct nilfs_btree_node *)bh->b_data;
+			if (nilfs_btree_node_get_nchildren(btree, sib) <
+			    nilfs_btree_node_nchildren_max(btree, sib)) {
+				path[level].bp_sib_bh = bh;
+				path[level].bp_op = nilfs_btree_carry_left;
+				stats->bs_nblocks++;
+				goto out;
+			} else
+				nilfs_bmap_put_block(&btree->bt_bmap, bh);
+		}
+
+		/* right sibling */
+		if (pindex <
+		    nilfs_btree_node_get_nchildren(btree, parent) - 1) {
+			sibptr = nilfs_btree_node_get_ptr(btree, parent,
+							  pindex + 1);
+			ret = nilfs_bmap_get_block(&btree->bt_bmap, sibptr,
+						   &bh);
+			if (ret < 0)
+				goto err_out_child_node;
+			sib = (struct nilfs_btree_node *)bh->b_data;
+			if (nilfs_btree_node_get_nchildren(btree, sib) <
+			    nilfs_btree_node_nchildren_max(btree, sib)) {
+				path[level].bp_sib_bh = bh;
+				path[level].bp_op = nilfs_btree_carry_right;
+				stats->bs_nblocks++;
+				goto out;
+			} else
+				nilfs_bmap_put_block(&btree->bt_bmap, bh);
+		}
+
+		/* split */
+		path[level].bp_newreq.bpr_ptr =
+			path[level - 1].bp_newreq.bpr_ptr + 1;
+		ret = (*btree->bt_bmap.b_pops->bpop_prepare_alloc_ptr)(
+			&btree->bt_bmap, &path[level].bp_newreq);
+		if (ret < 0)
+			goto err_out_child_node;
+		ret = nilfs_bmap_get_new_block(&btree->bt_bmap,
+					       path[level].bp_newreq.bpr_ptr,
+					       &bh);
+		if (ret < 0)
+			goto err_out_curr_node;
+
+		stats->bs_nblocks++;
+
+		lock_buffer(bh);
+		nilfs_btree_node_init(btree,
+				      (struct nilfs_btree_node *)bh->b_data,
+				      0, level, 0, NULL, NULL);
+		unlock_buffer(bh);
+		path[level].bp_sib_bh = bh;
+		path[level].bp_op = nilfs_btree_split;
+	}
+
+	/* root */
+	node = nilfs_btree_get_root(btree);
+	if (nilfs_btree_node_get_nchildren(btree, node) <
+	    nilfs_btree_node_nchildren_max(btree, node)) {
+		path[level].bp_op = nilfs_btree_do_insert;
+		stats->bs_nblocks++;
+		goto out;
+	}
+
+	/* grow */
+	path[level].bp_newreq.bpr_ptr = path[level - 1].bp_newreq.bpr_ptr + 1;
+	ret = (*btree->bt_bmap.b_pops->bpop_prepare_alloc_ptr)(
+		&btree->bt_bmap, &path[level].bp_newreq);
+	if (ret < 0)
+		goto err_out_child_node;
+	ret = nilfs_bmap_get_new_block(&btree->bt_bmap,
+				       path[level].bp_newreq.bpr_ptr, &bh);
+	if (ret < 0)
+		goto err_out_curr_node;
+
+	lock_buffer(bh);
+	nilfs_btree_node_init(btree, (struct nilfs_btree_node *)bh->b_data,
+			      0, level, 0, NULL, NULL);
+	unlock_buffer(bh);
+	path[level].bp_sib_bh = bh;
+	path[level].bp_op = nilfs_btree_grow;
+
+	level++;
+	path[level].bp_op = nilfs_btree_do_insert;
+
+	/* a newly-created node block and a data block are added */
+	stats->bs_nblocks += 2;
+
+	/* success */
+ out:
+	*levelp = level;
+	return ret;
+
+	/* error */
+ err_out_curr_node:
+	(*btree->bt_bmap.b_pops->bpop_abort_alloc_ptr)(&btree->bt_bmap,
+						       &path[level].bp_newreq);
+ err_out_child_node:
+	for (level--; level > NILFS_BTREE_LEVEL_DATA; level--) {
+		nilfs_bmap_delete_block(&btree->bt_bmap, path[level].bp_sib_bh);
+		(*btree->bt_bmap.b_pops->bpop_abort_alloc_ptr)(
+			&btree->bt_bmap, &path[level].bp_newreq);
+
+	}
+
+	(*btree->bt_bmap.b_pops->bpop_abort_alloc_ptr)(&btree->bt_bmap,
+						       &path[level].bp_newreq);
+ err_out_data:
+	*levelp = level;
+	stats->bs_nblocks = 0;
+	return ret;
+}
+
+static void nilfs_btree_commit_insert(struct nilfs_btree *btree,
+				      struct nilfs_btree_path *path,
+				      int maxlevel, __u64 key, __u64 ptr)
+{
+	int level;
+
+	set_buffer_nilfs_volatile((struct buffer_head *)((unsigned long)ptr));
+	ptr = path[NILFS_BTREE_LEVEL_DATA].bp_newreq.bpr_ptr;
+	if (btree->bt_ops->btop_set_target != NULL)
+		(*btree->bt_ops->btop_set_target)(btree, key, ptr);
+
+	for (level = NILFS_BTREE_LEVEL_NODE_MIN; level <= maxlevel; level++) {
+		if (btree->bt_bmap.b_pops->bpop_commit_alloc_ptr != NULL) {
+			(*btree->bt_bmap.b_pops->bpop_commit_alloc_ptr)(
+				&btree->bt_bmap, &path[level - 1].bp_newreq);
+		}
+		(*path[level].bp_op)(btree, path, level, &key, &ptr);
+	}
+
+	if (!nilfs_bmap_dirty(&btree->bt_bmap))
+		nilfs_bmap_set_dirty(&btree->bt_bmap);
+}
+
+static int nilfs_btree_insert(struct nilfs_bmap *bmap, __u64 key, __u64 ptr)
+{
+	struct nilfs_btree *btree;
+	struct nilfs_btree_path *path;
+	struct nilfs_bmap_stats stats;
+	int level, ret;
+
+	btree = (struct nilfs_btree *)bmap;
+	path = nilfs_btree_alloc_path(btree);
+	if (path == NULL)
+		return -ENOMEM;
+	nilfs_btree_init_path(btree, path);
+
+	ret = nilfs_btree_do_lookup(btree, path, key, NULL,
+				    NILFS_BTREE_LEVEL_NODE_MIN);
+	if (ret != -ENOENT) {
+		if (ret == 0)
+			ret = -EEXIST;
+		goto out;
+	}
+
+	ret = nilfs_btree_prepare_insert(btree, path, &level, key, ptr, &stats);
+	if (ret < 0)
+		goto out;
+	nilfs_btree_commit_insert(btree, path, level, key, ptr);
+	nilfs_bmap_add_blocks(bmap, stats.bs_nblocks);
+
+ out:
+	nilfs_btree_clear_path(btree, path);
+	nilfs_btree_free_path(btree, path);
+	return ret;
+}
+
+static void nilfs_btree_do_delete(struct nilfs_btree *btree,
+				  struct nilfs_btree_path *path,
+				  int level, __u64 *keyp, __u64 *ptrp)
+{
+	struct nilfs_btree_node *node;
+
+	if (level < nilfs_btree_height(btree) - 1) {
+		lock_buffer(path[level].bp_bh);
+		node = nilfs_btree_get_nonroot_node(btree, path, level);
+		nilfs_btree_node_delete(btree, node, keyp, ptrp,
+					path[level].bp_index);
+		if (!buffer_dirty(path[level].bp_bh))
+			nilfs_btnode_mark_dirty(path[level].bp_bh);
+		unlock_buffer(path[level].bp_bh);
+		if (path[level].bp_index == 0)
+			nilfs_btree_promote_key(btree, path, level + 1,
+				nilfs_btree_node_get_key(btree, node, 0));
+	} else {
+		node = nilfs_btree_get_root(btree);
+		nilfs_btree_node_delete(btree, node, keyp, ptrp,
+					path[level].bp_index);
+	}
+}
+
+static void nilfs_btree_borrow_left(struct nilfs_btree *btree,
+				    struct nilfs_btree_path *path,
+				    int level, __u64 *keyp, __u64 *ptrp)
+{
+	struct nilfs_btree_node *node, *left;
+	int nchildren, lnchildren, n;
+
+	nilfs_btree_do_delete(btree, path, level, keyp, ptrp);
+
+	lock_buffer(path[level].bp_bh);
+	lock_buffer(path[level].bp_sib_bh);
+
+	node = nilfs_btree_get_nonroot_node(btree, path, level);
+	left = nilfs_btree_get_sib_node(btree, path, level);
+	nchildren = nilfs_btree_node_get_nchildren(btree, node);
+	lnchildren = nilfs_btree_node_get_nchildren(btree, left);
+
+	n = (nchildren + lnchildren) / 2 - nchildren;
+
+	nilfs_btree_node_move_right(btree, left, node, n);
+
+	if (!buffer_dirty(path[level].bp_bh))
+		nilfs_btnode_mark_dirty(path[level].bp_bh);
+	if (!buffer_dirty(path[level].bp_sib_bh))
+		nilfs_btnode_mark_dirty(path[level].bp_sib_bh);
+
+	unlock_buffer(path[level].bp_bh);
+	unlock_buffer(path[level].bp_sib_bh);
+
+	nilfs_btree_promote_key(btree, path, level + 1,
+				nilfs_btree_node_get_key(btree, node, 0));
+
+	nilfs_bmap_put_block(&btree->bt_bmap, path[level].bp_sib_bh);
+	path[level].bp_sib_bh = NULL;
+	path[level].bp_index += n;
+}
+
+static void nilfs_btree_borrow_right(struct nilfs_btree *btree,
+				     struct nilfs_btree_path *path,
+				     int level, __u64 *keyp, __u64 *ptrp)
+{
+	struct nilfs_btree_node *node, *right;
+	int nchildren, rnchildren, n;
+
+	nilfs_btree_do_delete(btree, path, level, keyp, ptrp);
+
+	lock_buffer(path[level].bp_bh);
+	lock_buffer(path[level].bp_sib_bh);
+
+	node = nilfs_btree_get_nonroot_node(btree, path, level);
+	right = nilfs_btree_get_sib_node(btree, path, level);
+	nchildren = nilfs_btree_node_get_nchildren(btree, node);
+	rnchildren = nilfs_btree_node_get_nchildren(btree, right);
+
+	n = (nchildren + rnchildren) / 2 - nchildren;
+
+	nilfs_btree_node_move_left(btree, node, right, n);
+
+	if (!buffer_dirty(path[level].bp_bh))
+		nilfs_btnode_mark_dirty(path[level].bp_bh);
+	if (!buffer_dirty(path[level].bp_sib_bh))
+		nilfs_btnode_mark_dirty(path[level].bp_sib_bh);
+
+	unlock_buffer(path[level].bp_bh);
+	unlock_buffer(path[level].bp_sib_bh);
+
+	path[level + 1].bp_index++;
+	nilfs_btree_promote_key(btree, path, level + 1,
+				nilfs_btree_node_get_key(btree, right, 0));
+	path[level + 1].bp_index--;
+
+	nilfs_bmap_put_block(&btree->bt_bmap, path[level].bp_sib_bh);
+	path[level].bp_sib_bh = NULL;
+}
+
+static void nilfs_btree_concat_left(struct nilfs_btree *btree,
+				    struct nilfs_btree_path *path,
+				    int level, __u64 *keyp, __u64 *ptrp)
+{
+	struct nilfs_btree_node *node, *left;
+	int n;
+
+	nilfs_btree_do_delete(btree, path, level, keyp, ptrp);
+
+	lock_buffer(path[level].bp_bh);
+	lock_buffer(path[level].bp_sib_bh);
+
+	node = nilfs_btree_get_nonroot_node(btree, path, level);
+	left = nilfs_btree_get_sib_node(btree, path, level);
+
+	n = nilfs_btree_node_get_nchildren(btree, node);
+
+	nilfs_btree_node_move_left(btree, left, node, n);
+
+	if (!buffer_dirty(path[level].bp_sib_bh))
+		nilfs_btnode_mark_dirty(path[level].bp_sib_bh);
+
+	unlock_buffer(path[level].bp_bh);
+	unlock_buffer(path[level].bp_sib_bh);
+
+	nilfs_bmap_delete_block(&btree->bt_bmap, path[level].bp_bh);
+	path[level].bp_bh = path[level].bp_sib_bh;
+	path[level].bp_sib_bh = NULL;
+	path[level].bp_index += nilfs_btree_node_get_nchildren(btree, left);
+}
+
+static void nilfs_btree_concat_right(struct nilfs_btree *btree,
+				     struct nilfs_btree_path *path,
+				     int level, __u64 *keyp, __u64 *ptrp)
+{
+	struct nilfs_btree_node *node, *right;
+	int n;
+
+	nilfs_btree_do_delete(btree, path, level, keyp, ptrp);
+
+	lock_buffer(path[level].bp_bh);
+	lock_buffer(path[level].bp_sib_bh);
+
+	node = nilfs_btree_get_nonroot_node(btree, path, level);
+	right = nilfs_btree_get_sib_node(btree, path, level);
+
+	n = nilfs_btree_node_get_nchildren(btree, right);
+
+	nilfs_btree_node_move_left(btree, node, right, n);
+
+	if (!buffer_dirty(path[level].bp_bh))
+		nilfs_btnode_mark_dirty(path[level].bp_bh);
+
+	unlock_buffer(path[level].bp_bh);
+	unlock_buffer(path[level].bp_sib_bh);
+
+	nilfs_bmap_delete_block(&btree->bt_bmap, path[level].bp_sib_bh);
+	path[level].bp_sib_bh = NULL;
+	path[level + 1].bp_index++;
+}
+
+static void nilfs_btree_shrink(struct nilfs_btree *btree,
+			       struct nilfs_btree_path *path,
+			       int level, __u64 *keyp, __u64 *ptrp)
+{
+	struct nilfs_btree_node *root, *child;
+	int n;
+
+	nilfs_btree_do_delete(btree, path, level, keyp, ptrp);
+
+	lock_buffer(path[level].bp_bh);
+	root = nilfs_btree_get_root(btree);
+	child = nilfs_btree_get_nonroot_node(btree, path, level);
+
+	nilfs_btree_node_delete(btree, root, NULL, NULL, 0);
+	nilfs_btree_node_set_level(btree, root, level);
+	n = nilfs_btree_node_get_nchildren(btree, child);
+	nilfs_btree_node_move_left(btree, root, child, n);
+	unlock_buffer(path[level].bp_bh);
+
+	nilfs_bmap_delete_block(&btree->bt_bmap, path[level].bp_bh);
+	path[level].bp_bh = NULL;
+}
+
+
+static int nilfs_btree_prepare_delete(struct nilfs_btree *btree,
+				      struct nilfs_btree_path *path,
+				      int *levelp,
+				      struct nilfs_bmap_stats *stats)
+{
+	struct buffer_head *bh;
+	struct nilfs_btree_node *node, *parent, *sib;
+	__u64 sibptr;
+	int pindex, level, ret;
+
+	ret = 0;
+	stats->bs_nblocks = 0;
+	for (level = NILFS_BTREE_LEVEL_NODE_MIN;
+	     level < nilfs_btree_height(btree) - 1;
+	     level++) {
+		node = nilfs_btree_get_nonroot_node(btree, path, level);
+		path[level].bp_oldreq.bpr_ptr =
+			nilfs_btree_node_get_ptr(btree, node,
+						 path[level].bp_index);
+		if (btree->bt_bmap.b_pops->bpop_prepare_end_ptr != NULL) {
+			ret = (*btree->bt_bmap.b_pops->bpop_prepare_end_ptr)(
+				&btree->bt_bmap, &path[level].bp_oldreq);
+			if (ret < 0)
+				goto err_out_child_node;
+		}
+
+		if (nilfs_btree_node_get_nchildren(btree, node) >
+		    nilfs_btree_node_nchildren_min(btree, node)) {
+			path[level].bp_op = nilfs_btree_do_delete;
+			stats->bs_nblocks++;
+			goto out;
+		}
+
+		parent = nilfs_btree_get_node(btree, path, level + 1);
+		pindex = path[level + 1].bp_index;
+
+		if (pindex > 0) {
+			/* left sibling */
+			sibptr = nilfs_btree_node_get_ptr(btree, parent,
+							  pindex - 1);
+			ret = nilfs_bmap_get_block(&btree->bt_bmap, sibptr,
+						   &bh);
+			if (ret < 0)
+				goto err_out_curr_node;
+			sib = (struct nilfs_btree_node *)bh->b_data;
+			if (nilfs_btree_node_get_nchildren(btree, sib) >
+			    nilfs_btree_node_nchildren_min(btree, sib)) {
+				path[level].bp_sib_bh = bh;
+				path[level].bp_op = nilfs_btree_borrow_left;
+				stats->bs_nblocks++;
+				goto out;
+			} else {
+				path[level].bp_sib_bh = bh;
+				path[level].bp_op = nilfs_btree_concat_left;
+				stats->bs_nblocks++;
+				/* continue; */
+			}
+		} else if (pindex <
+			   nilfs_btree_node_get_nchildren(btree, parent) - 1) {
+			/* right sibling */
+			sibptr = nilfs_btree_node_get_ptr(btree, parent,
+							  pindex + 1);
+			ret = nilfs_bmap_get_block(&btree->bt_bmap, sibptr,
+						   &bh);
+			if (ret < 0)
+				goto err_out_curr_node;
+			sib = (struct nilfs_btree_node *)bh->b_data;
+			if (nilfs_btree_node_get_nchildren(btree, sib) >
+			    nilfs_btree_node_nchildren_min(btree, sib)) {
+				path[level].bp_sib_bh = bh;
+				path[level].bp_op = nilfs_btree_borrow_right;
+				stats->bs_nblocks++;
+				goto out;
+			} else {
+				path[level].bp_sib_bh = bh;
+				path[level].bp_op = nilfs_btree_concat_right;
+				stats->bs_nblocks++;
+				/* continue; */
+			}
+		} else {
+			/* no siblings */
+			/* the only child of the root node */
+			BUG_ON(level != nilfs_btree_height(btree) - 2);
+			if (nilfs_btree_node_get_nchildren(btree, node) - 1 <=
+			    NILFS_BTREE_ROOT_NCHILDREN_MAX) {
+				path[level].bp_op = nilfs_btree_shrink;
+				stats->bs_nblocks += 2;
+			} else {
+				path[level].bp_op = nilfs_btree_do_delete;
+				stats->bs_nblocks++;
+			}
+
+			goto out;
+
+		}
+	}
+
+	node = nilfs_btree_get_root(btree);
+	path[level].bp_oldreq.bpr_ptr =
+		nilfs_btree_node_get_ptr(btree, node, path[level].bp_index);
+	if (btree->bt_bmap.b_pops->bpop_prepare_end_ptr != NULL) {
+		ret = (*btree->bt_bmap.b_pops->bpop_prepare_end_ptr)(
+			&btree->bt_bmap, &path[level].bp_oldreq);
+		if (ret < 0)
+			goto err_out_child_node;
+	}
+	/* child of the root node is deleted */
+	path[level].bp_op = nilfs_btree_do_delete;
+	stats->bs_nblocks++;
+
+	/* success */
+ out:
+	*levelp = level;
+	return ret;
+
+	/* error */
+ err_out_curr_node:
+	if (btree->bt_bmap.b_pops->bpop_abort_end_ptr != NULL)
+		(*btree->bt_bmap.b_pops->bpop_abort_end_ptr)(
+			&btree->bt_bmap, &path[level].bp_oldreq);
+ err_out_child_node:
+	for (level--; level >= NILFS_BTREE_LEVEL_NODE_MIN; level--) {
+		nilfs_bmap_put_block(&btree->bt_bmap, path[level].bp_sib_bh);
+		if (btree->bt_bmap.b_pops->bpop_abort_end_ptr != NULL)
+			(*btree->bt_bmap.b_pops->bpop_abort_end_ptr)(
+				&btree->bt_bmap, &path[level].bp_oldreq);
+	}
+	*levelp = level;
+	stats->bs_nblocks = 0;
+	return ret;
+}
+
+static void nilfs_btree_commit_delete(struct nilfs_btree *btree,
+				      struct nilfs_btree_path *path,
+				      int maxlevel)
+{
+	int level;
+
+	for (level = NILFS_BTREE_LEVEL_NODE_MIN; level <= maxlevel; level++) {
+		if (btree->bt_bmap.b_pops->bpop_commit_end_ptr != NULL)
+			(*btree->bt_bmap.b_pops->bpop_commit_end_ptr)(
+				&btree->bt_bmap, &path[level].bp_oldreq);
+		(*path[level].bp_op)(btree, path, level, NULL, NULL);
+	}
+
+	if (!nilfs_bmap_dirty(&btree->bt_bmap))
+		nilfs_bmap_set_dirty(&btree->bt_bmap);
+}
+
+static int nilfs_btree_delete(struct nilfs_bmap *bmap, __u64 key)
+
+{
+	struct nilfs_btree *btree;
+	struct nilfs_btree_path *path;
+	struct nilfs_bmap_stats stats;
+	int level, ret;
+
+	btree = (struct nilfs_btree *)bmap;
+	path = nilfs_btree_alloc_path(btree);
+	if (path == NULL)
+		return -ENOMEM;
+	nilfs_btree_init_path(btree, path);
+	ret = nilfs_btree_do_lookup(btree, path, key, NULL,
+				    NILFS_BTREE_LEVEL_NODE_MIN);
+	if (ret < 0)
+		goto out;
+
+	ret = nilfs_btree_prepare_delete(btree, path, &level, &stats);
+	if (ret < 0)
+		goto out;
+	nilfs_btree_commit_delete(btree, path, level);
+	nilfs_bmap_sub_blocks(bmap, stats.bs_nblocks);
+
+out:
+	nilfs_btree_clear_path(btree, path);
+	nilfs_btree_free_path(btree, path);
+	return ret;
+}
+
+static int nilfs_btree_last_key(const struct nilfs_bmap *bmap, __u64 *keyp)
+{
+	struct nilfs_btree *btree;
+	struct nilfs_btree_path *path;
+	int ret;
+
+	btree = (struct nilfs_btree *)bmap;
+	path = nilfs_btree_alloc_path(btree);
+	if (path == NULL)
+		return -ENOMEM;
+	nilfs_btree_init_path(btree, path);
+
+	ret = nilfs_btree_do_lookup_last(btree, path, keyp, NULL);
+
+	nilfs_btree_clear_path(btree, path);
+	nilfs_btree_free_path(btree, path);
+
+	return ret;
+}
+
+static int nilfs_btree_check_delete(struct nilfs_bmap *bmap, __u64 key)
+{
+	struct buffer_head *bh;
+	struct nilfs_btree *btree;
+	struct nilfs_btree_node *root, *node;
+	__u64 maxkey, nextmaxkey;
+	__u64 ptr;
+	int nchildren, ret;
+
+	btree = (struct nilfs_btree *)bmap;
+	root = nilfs_btree_get_root(btree);
+	switch (nilfs_btree_height(btree)) {
+	case 2:
+		bh = NULL;
+		node = root;
+		break;
+	case 3:
+		nchildren = nilfs_btree_node_get_nchildren(btree, root);
+		if (nchildren > 1)
+			return 0;
+		ptr = nilfs_btree_node_get_ptr(btree, root, nchildren - 1);
+		ret = nilfs_bmap_get_block(bmap, ptr, &bh);
+		if (ret < 0)
+			return ret;
+		node = (struct nilfs_btree_node *)bh->b_data;
+		break;
+	default:
+		return 0;
+	}
+
+	nchildren = nilfs_btree_node_get_nchildren(btree, node);
+	maxkey = nilfs_btree_node_get_key(btree, node, nchildren - 1);
+	nextmaxkey = (nchildren > 1) ?
+		nilfs_btree_node_get_key(btree, node, nchildren - 2) : 0;
+	if (bh != NULL)
+		nilfs_bmap_put_block(bmap, bh);
+
+	return (maxkey == key) && (nextmaxkey < bmap->b_low);
+}
+
+static int nilfs_btree_gather_data(struct nilfs_bmap *bmap,
+				   __u64 *keys, __u64 *ptrs, int nitems)
+{
+	struct buffer_head *bh;
+	struct nilfs_btree *btree;
+	struct nilfs_btree_node *node, *root;
+	__le64 *dkeys;
+	__le64 *dptrs;
+	__u64 ptr;
+	int nchildren, i, ret;
+
+	btree = (struct nilfs_btree *)bmap;
+	root = nilfs_btree_get_root(btree);
+	switch (nilfs_btree_height(btree)) {
+	case 2:
+		bh = NULL;
+		node = root;
+		break;
+	case 3:
+		nchildren = nilfs_btree_node_get_nchildren(btree, root);
+		BUG_ON(nchildren > 1);
+		ptr = nilfs_btree_node_get_ptr(btree, root, nchildren - 1);
+		ret = nilfs_bmap_get_block(bmap, ptr, &bh);
+		if (ret < 0)
+			return ret;
+		node = (struct nilfs_btree_node *)bh->b_data;
+		break;
+	default:
+		node = NULL;
+		BUG();
+	}
+
+	nchildren = nilfs_btree_node_get_nchildren(btree, node);
+	if (nchildren < nitems)
+		nitems = nchildren;
+	dkeys = nilfs_btree_node_dkeys(btree, node);
+	dptrs = nilfs_btree_node_dptrs(btree, node);
+	for (i = 0; i < nitems; i++) {
+		keys[i] = nilfs_bmap_dkey_to_key(dkeys[i]);
+		ptrs[i] = nilfs_bmap_dptr_to_ptr(dptrs[i]);
+	}
+
+	if (bh != NULL)
+		nilfs_bmap_put_block(bmap, bh);
+
+	return nitems;
+}
+
+static int
+nilfs_btree_prepare_convert_and_insert(struct nilfs_bmap *bmap, __u64 key,
+				       union nilfs_bmap_ptr_req *dreq,
+				       union nilfs_bmap_ptr_req *nreq,
+				       struct buffer_head **bhp,
+				       struct nilfs_bmap_stats *stats)
+{
+	struct buffer_head *bh;
+	struct nilfs_btree *btree;
+	int ret;
+
+	btree = (struct nilfs_btree *)bmap;
+	stats->bs_nblocks = 0;
+
+	/* for data */
+	/* cannot find near ptr */
+	if (btree->bt_ops->btop_find_target != NULL)
+		dreq->bpr_ptr
+			= (*btree->bt_ops->btop_find_target)(btree, NULL, key);
+	ret = (*bmap->b_pops->bpop_prepare_alloc_ptr)(bmap, dreq);
+	if (ret < 0)
+		return ret;
+
+	*bhp = NULL;
+	stats->bs_nblocks++;
+	if (nreq != NULL) {
+		nreq->bpr_ptr = dreq->bpr_ptr + 1;
+		ret = (*bmap->b_pops->bpop_prepare_alloc_ptr)(bmap, nreq);
+		if (ret < 0)
+			goto err_out_dreq;
+
+		ret = nilfs_bmap_get_new_block(bmap, nreq->bpr_ptr, &bh);
+		if (ret < 0)
+			goto err_out_nreq;
+
+		*bhp = bh;
+		stats->bs_nblocks++;
+	}
+
+	/* success */
+	return 0;
+
+	/* error */
+ err_out_nreq:
+	(*bmap->b_pops->bpop_abort_alloc_ptr)(bmap, nreq);
+ err_out_dreq:
+	(*bmap->b_pops->bpop_abort_alloc_ptr)(bmap, dreq);
+	stats->bs_nblocks = 0;
+	return ret;
+
+}
+
+static void
+nilfs_btree_commit_convert_and_insert(struct nilfs_bmap *bmap,
+				      __u64 key, __u64 ptr,
+				      const __u64 *keys, const __u64 *ptrs,
+				      int n, __u64 low, __u64 high,
+				      union nilfs_bmap_ptr_req *dreq,
+				      union nilfs_bmap_ptr_req *nreq,
+				      struct buffer_head *bh)
+{
+	struct nilfs_btree *btree;
+	struct nilfs_btree_node *node;
+	__u64 tmpptr;
+
+	/* free resources */
+	if (bmap->b_ops->bop_clear != NULL)
+		(*bmap->b_ops->bop_clear)(bmap);
+
+	/* ptr must be a pointer to a buffer head. */
+	set_buffer_nilfs_volatile((struct buffer_head *)((unsigned long)ptr));
+
+	/* convert and insert */
+	btree = (struct nilfs_btree *)bmap;
+	nilfs_btree_init(bmap, low, high);
+	if (nreq != NULL) {
+		if (bmap->b_pops->bpop_commit_alloc_ptr != NULL) {
+			(*bmap->b_pops->bpop_commit_alloc_ptr)(bmap, dreq);
+			(*bmap->b_pops->bpop_commit_alloc_ptr)(bmap, nreq);
+		}
+
+		/* create child node at level 1 */
+		lock_buffer(bh);
+		node = (struct nilfs_btree_node *)bh->b_data;
+		nilfs_btree_node_init(btree, node, 0, 1, n, keys, ptrs);
+		nilfs_btree_node_insert(btree, node,
+					key, dreq->bpr_ptr, n);
+		if (!buffer_dirty(bh))
+			nilfs_btnode_mark_dirty(bh);
+		if (!nilfs_bmap_dirty(bmap))
+			nilfs_bmap_set_dirty(bmap);
+
+		unlock_buffer(bh);
+		nilfs_bmap_put_block(bmap, bh);
+
+		/* create root node at level 2 */
+		node = nilfs_btree_get_root(btree);
+		tmpptr = nreq->bpr_ptr;
+		nilfs_btree_node_init(btree, node, NILFS_BTREE_NODE_ROOT,
+				      2, 1, &keys[0], &tmpptr);
+	} else {
+		if (bmap->b_pops->bpop_commit_alloc_ptr != NULL)
+			(*bmap->b_pops->bpop_commit_alloc_ptr)(bmap, dreq);
+
+		/* create root node at level 1 */
+		node = nilfs_btree_get_root(btree);
+		nilfs_btree_node_init(btree, node, NILFS_BTREE_NODE_ROOT,
+				      1, n, keys, ptrs);
+		nilfs_btree_node_insert(btree, node,
+					key, dreq->bpr_ptr, n);
+		if (!nilfs_bmap_dirty(bmap))
+			nilfs_bmap_set_dirty(bmap);
+	}
+
+	if (btree->bt_ops->btop_set_target != NULL)
+		(*btree->bt_ops->btop_set_target)(btree, key, dreq->bpr_ptr);
+}
+
+/**
+ * nilfs_btree_convert_and_insert -
+ * @bmap:
+ * @key:
+ * @ptr:
+ * @keys:
+ * @ptrs:
+ * @n:
+ * @low:
+ * @high:
+ */
+int nilfs_btree_convert_and_insert(struct nilfs_bmap *bmap,
+				   __u64 key, __u64 ptr,
+				   const __u64 *keys, const __u64 *ptrs,
+				   int n, __u64 low, __u64 high)
+{
+	struct buffer_head *bh;
+	union nilfs_bmap_ptr_req dreq, nreq, *di, *ni;
+	struct nilfs_bmap_stats stats;
+	int ret;
+
+	if (n + 1 <= NILFS_BTREE_ROOT_NCHILDREN_MAX) {
+		di = &dreq;
+		ni = NULL;
+	} else if ((n + 1) <= NILFS_BTREE_NODE_NCHILDREN_MAX(
+			   1 << bmap->b_inode->i_blkbits)) {
+		di = &dreq;
+		ni = &nreq;
+	} else {
+		di = NULL;
+		ni = NULL;
+		BUG();
+	}
+
+	ret = nilfs_btree_prepare_convert_and_insert(bmap, key, di, ni, &bh,
+						     &stats);
+	if (ret < 0)
+		return ret;
+	nilfs_btree_commit_convert_and_insert(bmap, key, ptr, keys, ptrs, n,
+					      low, high, di, ni, bh);
+	nilfs_bmap_add_blocks(bmap, stats.bs_nblocks);
+	return 0;
+}
+
+static int nilfs_btree_propagate_p(struct nilfs_btree *btree,
+				   struct nilfs_btree_path *path,
+				   int level,
+				   struct buffer_head *bh)
+{
+	while ((++level < nilfs_btree_height(btree) - 1) &&
+	       !buffer_dirty(path[level].bp_bh))
+		nilfs_btnode_mark_dirty(path[level].bp_bh);
+
+	return 0;
+}
+
+static int nilfs_btree_prepare_update_v(struct nilfs_btree *btree,
+					struct nilfs_btree_path *path,
+					int level)
+{
+	struct nilfs_btree_node *parent;
+	int ret;
+
+	parent = nilfs_btree_get_node(btree, path, level + 1);
+	path[level].bp_oldreq.bpr_ptr =
+		nilfs_btree_node_get_ptr(btree, parent,
+					 path[level + 1].bp_index);
+	path[level].bp_newreq.bpr_ptr = path[level].bp_oldreq.bpr_ptr + 1;
+	ret = nilfs_bmap_prepare_update(&btree->bt_bmap,
+					&path[level].bp_oldreq,
+					&path[level].bp_newreq);
+	if (ret < 0)
+		return ret;
+
+	if (buffer_nilfs_node(path[level].bp_bh)) {
+		path[level].bp_ctxt.oldkey = path[level].bp_oldreq.bpr_ptr;
+		path[level].bp_ctxt.newkey = path[level].bp_newreq.bpr_ptr;
+		path[level].bp_ctxt.bh = path[level].bp_bh;
+		ret = nilfs_btnode_prepare_change_key(
+			&NILFS_BMAP_I(&btree->bt_bmap)->i_btnode_cache,
+			&path[level].bp_ctxt);
+		if (ret < 0) {
+			nilfs_bmap_abort_update(&btree->bt_bmap,
+						&path[level].bp_oldreq,
+						&path[level].bp_newreq);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+static void nilfs_btree_commit_update_v(struct nilfs_btree *btree,
+					struct nilfs_btree_path *path,
+					int level)
+{
+	struct nilfs_btree_node *parent;
+
+	nilfs_bmap_commit_update(&btree->bt_bmap,
+				 &path[level].bp_oldreq,
+				 &path[level].bp_newreq);
+
+	if (buffer_nilfs_node(path[level].bp_bh)) {
+		nilfs_btnode_commit_change_key(
+			&NILFS_BMAP_I(&btree->bt_bmap)->i_btnode_cache,
+			&path[level].bp_ctxt);
+		path[level].bp_bh = path[level].bp_ctxt.bh;
+	}
+	set_buffer_nilfs_volatile(path[level].bp_bh);
+
+	parent = nilfs_btree_get_node(btree, path, level + 1);
+	nilfs_btree_node_set_ptr(btree, parent, path[level + 1].bp_index,
+				 path[level].bp_newreq.bpr_ptr);
+}
+
+static void nilfs_btree_abort_update_v(struct nilfs_btree *btree,
+				       struct nilfs_btree_path *path,
+				       int level)
+{
+	nilfs_bmap_abort_update(&btree->bt_bmap,
+				&path[level].bp_oldreq,
+				&path[level].bp_newreq);
+	if (buffer_nilfs_node(path[level].bp_bh))
+		nilfs_btnode_abort_change_key(
+			&NILFS_BMAP_I(&btree->bt_bmap)->i_btnode_cache,
+			&path[level].bp_ctxt);
+}
+
+static int nilfs_btree_prepare_propagate_v(struct nilfs_btree *btree,
+					   struct nilfs_btree_path *path,
+					   int minlevel,
+					   int *maxlevelp)
+{
+	int level, ret;
+
+	level = minlevel;
+	if (!buffer_nilfs_volatile(path[level].bp_bh)) {
+		ret = nilfs_btree_prepare_update_v(btree, path, level);
+		if (ret < 0)
+			return ret;
+	}
+	while ((++level < nilfs_btree_height(btree) - 1) &&
+	       !buffer_dirty(path[level].bp_bh)) {
+
+		BUG_ON(buffer_nilfs_volatile(path[level].bp_bh));
+		ret = nilfs_btree_prepare_update_v(btree, path, level);
+		if (ret < 0)
+			goto out;
+	}
+
+	/* success */
+	BUG_ON(maxlevelp == NULL);
+	*maxlevelp = level - 1;
+	return 0;
+
+	/* error */
+ out:
+	while (--level > minlevel)
+		nilfs_btree_abort_update_v(btree, path, level);
+	if (!buffer_nilfs_volatile(path[level].bp_bh))
+		nilfs_btree_abort_update_v(btree, path, level);
+	return ret;
+}
+
+static void nilfs_btree_commit_propagate_v(struct nilfs_btree *btree,
+					   struct nilfs_btree_path *path,
+					   int minlevel,
+					   int maxlevel,
+					   struct buffer_head *bh)
+{
+	int level;
+
+	if (!buffer_nilfs_volatile(path[minlevel].bp_bh))
+		nilfs_btree_commit_update_v(btree, path, minlevel);
+
+	for (level = minlevel + 1; level <= maxlevel; level++)
+		nilfs_btree_commit_update_v(btree, path, level);
+}
+
+static int nilfs_btree_propagate_v(struct nilfs_btree *btree,
+				   struct nilfs_btree_path *path,
+				   int level,
+				   struct buffer_head *bh)
+{
+	int maxlevel, ret;
+	struct nilfs_btree_node *parent;
+	__u64 ptr;
+
+	get_bh(bh);
+	path[level].bp_bh = bh;
+	ret = nilfs_btree_prepare_propagate_v(btree, path, level, &maxlevel);
+	if (ret < 0)
+		goto out;
+
+	if (buffer_nilfs_volatile(path[level].bp_bh)) {
+		parent = nilfs_btree_get_node(btree, path, level + 1);
+		ptr = nilfs_btree_node_get_ptr(btree, parent,
+					       path[level + 1].bp_index);
+		ret = nilfs_bmap_mark_dirty(&btree->bt_bmap, ptr);
+		if (ret < 0)
+			goto out;
+	}
+
+	nilfs_btree_commit_propagate_v(btree, path, level, maxlevel, bh);
+
+ out:
+	brelse(path[level].bp_bh);
+	path[level].bp_bh = NULL;
+	return ret;
+}
+
+static int nilfs_btree_propagate(const struct nilfs_bmap *bmap,
+				 struct buffer_head *bh)
+{
+	struct nilfs_btree *btree;
+	struct nilfs_btree_path *path;
+	struct nilfs_btree_node *node;
+	__u64 key;
+	int level, ret;
+
+	BUG_ON(!buffer_dirty(bh));
+
+	btree = (struct nilfs_btree *)bmap;
+	path = nilfs_btree_alloc_path(btree);
+	if (path == NULL)
+		return -ENOMEM;
+	nilfs_btree_init_path(btree, path);
+
+	if (buffer_nilfs_node(bh)) {
+		node = (struct nilfs_btree_node *)bh->b_data;
+		key = nilfs_btree_node_get_key(btree, node, 0);
+		level = nilfs_btree_node_get_level(btree, node);
+	} else {
+		key = nilfs_bmap_data_get_key(bmap, bh);
+		level = NILFS_BTREE_LEVEL_DATA;
+	}
+
+	ret = nilfs_btree_do_lookup(btree, path, key, NULL, level + 1);
+	if (ret < 0) {
+		/* BUG_ON(ret == -ENOENT); */
+		if (ret == -ENOENT) {
+			printk(KERN_CRIT "%s: key = %llu, level == %d\n",
+			       __func__, (unsigned long long)key, level);
+			BUG();
+		}
+		goto out;
+	}
+
+	ret = (*btree->bt_ops->btop_propagate)(btree, path, level, bh);
+
+ out:
+	nilfs_btree_clear_path(btree, path);
+	nilfs_btree_free_path(btree, path);
+
+	return ret;
+}
+
+static int nilfs_btree_propagate_gc(const struct nilfs_bmap *bmap,
+				    struct buffer_head *bh)
+{
+	return nilfs_bmap_mark_dirty(bmap, bh->b_blocknr);
+}
+
+static void nilfs_btree_add_dirty_buffer(struct nilfs_btree *btree,
+					 struct list_head *lists,
+					 struct buffer_head *bh)
+{
+	struct list_head *head;
+	struct buffer_head *cbh;
+	struct nilfs_btree_node *node, *cnode;
+	__u64 key, ckey;
+	int level;
+
+	get_bh(bh);
+	node = (struct nilfs_btree_node *)bh->b_data;
+	key = nilfs_btree_node_get_key(btree, node, 0);
+	level = nilfs_btree_node_get_level(btree, node);
+	list_for_each(head, &lists[level]) {
+		cbh = list_entry(head, struct buffer_head, b_assoc_buffers);
+		cnode = (struct nilfs_btree_node *)cbh->b_data;
+		ckey = nilfs_btree_node_get_key(btree, cnode, 0);
+		if (key < ckey)
+			break;
+	}
+	list_add_tail(&bh->b_assoc_buffers, head);
+}
+
+static void nilfs_btree_lookup_dirty_buffers(struct nilfs_bmap *bmap,
+					     struct list_head *listp)
+{
+	struct nilfs_btree *btree = (struct nilfs_btree *)bmap;
+	struct address_space *btcache = &NILFS_BMAP_I(bmap)->i_btnode_cache;
+	struct list_head lists[NILFS_BTREE_LEVEL_MAX];
+	struct pagevec pvec;
+	struct buffer_head *bh, *head;
+	pgoff_t index = 0;
+	int level, i;
+
+	for (level = NILFS_BTREE_LEVEL_NODE_MIN;
+	     level < NILFS_BTREE_LEVEL_MAX;
+	     level++)
+		INIT_LIST_HEAD(&lists[level]);
+
+	pagevec_init(&pvec, 0);
+
+	while (pagevec_lookup_tag(&pvec, btcache, &index, PAGECACHE_TAG_DIRTY,
+				  PAGEVEC_SIZE)) {
+		for (i = 0; i < pagevec_count(&pvec); i++) {
+			bh = head = page_buffers(pvec.pages[i]);
+			do {
+				if (buffer_dirty(bh))
+					nilfs_btree_add_dirty_buffer(btree,
+								     lists, bh);
+			} while ((bh = bh->b_this_page) != head);
+		}
+		pagevec_release(&pvec);
+		cond_resched();
+	}
+
+	for (level = NILFS_BTREE_LEVEL_NODE_MIN;
+	     level < NILFS_BTREE_LEVEL_MAX;
+	     level++)
+		list_splice(&lists[level], listp->prev);
+}
+
+static int nilfs_btree_assign_p(struct nilfs_btree *btree,
+				struct nilfs_btree_path *path,
+				int level,
+				struct buffer_head **bh,
+				sector_t blocknr,
+				union nilfs_binfo *binfo)
+{
+	struct nilfs_btree_node *parent;
+	__u64 key;
+	__u64 ptr;
+	int ret;
+
+	parent = nilfs_btree_get_node(btree, path, level + 1);
+	ptr = nilfs_btree_node_get_ptr(btree, parent,
+				       path[level + 1].bp_index);
+	if (buffer_nilfs_node(*bh)) {
+		path[level].bp_ctxt.oldkey = ptr;
+		path[level].bp_ctxt.newkey = blocknr;
+		path[level].bp_ctxt.bh = *bh;
+		ret = nilfs_btnode_prepare_change_key(
+			&NILFS_BMAP_I(&btree->bt_bmap)->i_btnode_cache,
+			&path[level].bp_ctxt);
+		if (ret < 0)
+			return ret;
+		nilfs_btnode_commit_change_key(
+			&NILFS_BMAP_I(&btree->bt_bmap)->i_btnode_cache,
+			&path[level].bp_ctxt);
+		*bh = path[level].bp_ctxt.bh;
+	}
+
+	nilfs_btree_node_set_ptr(btree, parent,
+				 path[level + 1].bp_index, blocknr);
+
+	key = nilfs_btree_node_get_key(btree, parent,
+				       path[level + 1].bp_index);
+	/* on-disk format */
+	binfo->bi_dat.bi_blkoff = nilfs_bmap_key_to_dkey(key);
+	binfo->bi_dat.bi_level = level;
+
+	return 0;
+}
+
+static int nilfs_btree_assign_v(struct nilfs_btree *btree,
+				struct nilfs_btree_path *path,
+				int level,
+				struct buffer_head **bh,
+				sector_t blocknr,
+				union nilfs_binfo *binfo)
+{
+	struct nilfs_btree_node *parent;
+	__u64 key;
+	__u64 ptr;
+	union nilfs_bmap_ptr_req req;
+	int ret;
+
+	parent = nilfs_btree_get_node(btree, path, level + 1);
+	ptr = nilfs_btree_node_get_ptr(btree, parent,
+				       path[level + 1].bp_index);
+	req.bpr_ptr = ptr;
+	ret = (*btree->bt_bmap.b_pops->bpop_prepare_start_ptr)(&btree->bt_bmap,
+							       &req);
+	if (ret < 0)
+		return ret;
+	(*btree->bt_bmap.b_pops->bpop_commit_start_ptr)(&btree->bt_bmap,
+							&req, blocknr);
+
+	key = nilfs_btree_node_get_key(btree, parent,
+				       path[level + 1].bp_index);
+	/* on-disk format */
+	binfo->bi_v.bi_vblocknr = nilfs_bmap_ptr_to_dptr(ptr);
+	binfo->bi_v.bi_blkoff = nilfs_bmap_key_to_dkey(key);
+
+	return 0;
+}
+
+static int nilfs_btree_assign(struct nilfs_bmap *bmap,
+			      struct buffer_head **bh,
+			      sector_t blocknr,
+			      union nilfs_binfo *binfo)
+{
+	struct nilfs_btree *btree;
+	struct nilfs_btree_path *path;
+	struct nilfs_btree_node *node;
+	__u64 key;
+	int level, ret;
+
+	btree = (struct nilfs_btree *)bmap;
+	path = nilfs_btree_alloc_path(btree);
+	if (path == NULL)
+		return -ENOMEM;
+	nilfs_btree_init_path(btree, path);
+
+	if (buffer_nilfs_node(*bh)) {
+		node = (struct nilfs_btree_node *)(*bh)->b_data;
+		key = nilfs_btree_node_get_key(btree, node, 0);
+		level = nilfs_btree_node_get_level(btree, node);
+	} else {
+		key = nilfs_bmap_data_get_key(bmap, *bh);
+		level = NILFS_BTREE_LEVEL_DATA;
+	}
+
+	ret = nilfs_btree_do_lookup(btree, path, key, NULL, level + 1);
+	if (ret < 0) {
+		BUG_ON(ret == -ENOENT);
+		goto out;
+	}
+
+	ret = (*btree->bt_ops->btop_assign)(btree, path, level, bh,
+					    blocknr, binfo);
+
+ out:
+	nilfs_btree_clear_path(btree, path);
+	nilfs_btree_free_path(btree, path);
+
+	return ret;
+}
+
+static int nilfs_btree_assign_gc(struct nilfs_bmap *bmap,
+				 struct buffer_head **bh,
+				 sector_t blocknr,
+				 union nilfs_binfo *binfo)
+{
+	struct nilfs_btree *btree;
+	struct nilfs_btree_node *node;
+	__u64 key;
+	int ret;
+
+	btree = (struct nilfs_btree *)bmap;
+	ret = nilfs_bmap_move_v(bmap, (*bh)->b_blocknr, blocknr);
+	if (ret < 0)
+		return ret;
+
+	if (buffer_nilfs_node(*bh)) {
+		node = (struct nilfs_btree_node *)(*bh)->b_data;
+		key = nilfs_btree_node_get_key(btree, node, 0);
+	} else
+		key = nilfs_bmap_data_get_key(bmap, *bh);
+
+	/* on-disk format */
+	binfo->bi_v.bi_vblocknr = cpu_to_le64((*bh)->b_blocknr);
+	binfo->bi_v.bi_blkoff = nilfs_bmap_key_to_dkey(key);
+
+	return 0;
+}
+
+static int nilfs_btree_mark(struct nilfs_bmap *bmap, __u64 key, int level)
+{
+	struct buffer_head *bh;
+	struct nilfs_btree *btree;
+	struct nilfs_btree_path *path;
+	__u64 ptr;
+	int ret;
+
+	btree = (struct nilfs_btree *)bmap;
+	path = nilfs_btree_alloc_path(btree);
+	if (path == NULL)
+		return -ENOMEM;
+	nilfs_btree_init_path(btree, path);
+
+	ret = nilfs_btree_do_lookup(btree, path, key, &ptr, level + 1);
+	if (ret < 0) {
+		BUG_ON(ret == -ENOENT);
+		goto out;
+	}
+	ret = nilfs_bmap_get_block(&btree->bt_bmap, ptr, &bh);
+	if (ret < 0) {
+		BUG_ON(ret == -ENOENT);
+		goto out;
+	}
+
+	if (!buffer_dirty(bh))
+		nilfs_btnode_mark_dirty(bh);
+	nilfs_bmap_put_block(&btree->bt_bmap, bh);
+	if (!nilfs_bmap_dirty(&btree->bt_bmap))
+		nilfs_bmap_set_dirty(&btree->bt_bmap);
+
+ out:
+	nilfs_btree_clear_path(btree, path);
+	nilfs_btree_free_path(btree, path);
+	return ret;
+}
+
+static const struct nilfs_bmap_operations nilfs_btree_ops = {
+	.bop_lookup		=	nilfs_btree_lookup,
+	.bop_insert		=	nilfs_btree_insert,
+	.bop_delete		=	nilfs_btree_delete,
+	.bop_clear		=	NULL,
+
+	.bop_propagate		=	nilfs_btree_propagate,
+
+	.bop_lookup_dirty_buffers =	nilfs_btree_lookup_dirty_buffers,
+
+	.bop_assign		=	nilfs_btree_assign,
+	.bop_mark		=	nilfs_btree_mark,
+
+	.bop_last_key		=	nilfs_btree_last_key,
+	.bop_check_insert	=	NULL,
+	.bop_check_delete	=	nilfs_btree_check_delete,
+	.bop_gather_data	=	nilfs_btree_gather_data,
+};
+
+static const struct nilfs_bmap_operations nilfs_btree_ops_gc = {
+	.bop_lookup		=	NULL,
+	.bop_insert		=	NULL,
+	.bop_delete		=	NULL,
+	.bop_clear		=	NULL,
+
+	.bop_propagate		=	nilfs_btree_propagate_gc,
+
+	.bop_lookup_dirty_buffers =	nilfs_btree_lookup_dirty_buffers,
+
+	.bop_assign		=	nilfs_btree_assign_gc,
+	.bop_mark		=	NULL,
+
+	.bop_last_key		=	NULL,
+	.bop_check_insert	=	NULL,
+	.bop_check_delete	=	NULL,
+	.bop_gather_data	=	NULL,
+};
+
+static const struct nilfs_btree_operations nilfs_btree_ops_v = {
+	.btop_find_target	=	nilfs_btree_find_target_v,
+	.btop_set_target	=	nilfs_btree_set_target_v,
+	.btop_propagate		=	nilfs_btree_propagate_v,
+	.btop_assign		=	nilfs_btree_assign_v,
+};
+
+static const struct nilfs_btree_operations nilfs_btree_ops_p = {
+	.btop_find_target	=	NULL,
+	.btop_set_target	=	NULL,
+	.btop_propagate		=	nilfs_btree_propagate_p,
+	.btop_assign		=	nilfs_btree_assign_p,
+};
+
+int nilfs_btree_init(struct nilfs_bmap *bmap, __u64 low, __u64 high)
+{
+	struct nilfs_btree *btree;
+
+	btree = (struct nilfs_btree *)bmap;
+	bmap->b_ops = &nilfs_btree_ops;
+	bmap->b_low = low;
+	bmap->b_high = high;
+	switch (bmap->b_inode->i_ino) {
+	case NILFS_DAT_INO:
+		btree->bt_ops = &nilfs_btree_ops_p;
+		break;
+	default:
+		btree->bt_ops = &nilfs_btree_ops_v;
+		break;
+	}
+
+	return 0;
+}
+
+void nilfs_btree_init_gc(struct nilfs_bmap *bmap)
+{
+	bmap->b_low = NILFS_BMAP_LARGE_LOW;
+	bmap->b_high = NILFS_BMAP_LARGE_HIGH;
+	bmap->b_ops = &nilfs_btree_ops_gc;
+}
diff --git a/fs/nilfs2/btree.h b/fs/nilfs2/btree.h
new file mode 100644
index 000000000000..4766deb52fb1
--- /dev/null
+++ b/fs/nilfs2/btree.h
@@ -0,0 +1,117 @@
+/*
+ * btree.h - NILFS B-tree.
+ *
+ * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Written by Koji Sato <koji@osrg.net>.
+ */
+
+#ifndef _NILFS_BTREE_H
+#define _NILFS_BTREE_H
+
+#include <linux/types.h>
+#include <linux/buffer_head.h>
+#include <linux/list.h>
+#include <linux/nilfs2_fs.h>
+#include "btnode.h"
+#include "bmap.h"
+
+struct nilfs_btree;
+struct nilfs_btree_path;
+
+/**
+ * struct nilfs_btree_operations - B-tree operation table
+ */
+struct nilfs_btree_operations {
+	__u64 (*btop_find_target)(const struct nilfs_btree *,
+				  const struct nilfs_btree_path *, __u64);
+	void (*btop_set_target)(struct nilfs_btree *, __u64, __u64);
+
+	struct the_nilfs *(*btop_get_nilfs)(struct nilfs_btree *);
+
+	int (*btop_propagate)(struct nilfs_btree *,
+			      struct nilfs_btree_path *,
+			      int,
+			      struct buffer_head *);
+	int (*btop_assign)(struct nilfs_btree *,
+			   struct nilfs_btree_path *,
+			   int,
+			   struct buffer_head **,
+			   sector_t,
+			   union nilfs_binfo *);
+};
+
+/**
+ * struct nilfs_btree_node - B-tree node
+ * @bn_flags: flags
+ * @bn_level: level
+ * @bn_nchildren: number of children
+ * @bn_pad: padding
+ */
+struct nilfs_btree_node {
+	__u8 bn_flags;
+	__u8 bn_level;
+	__le16 bn_nchildren;
+	__le32 bn_pad;
+};
+
+/* flags */
+#define NILFS_BTREE_NODE_ROOT	0x01
+
+/* level */
+#define NILFS_BTREE_LEVEL_DATA		0
+#define NILFS_BTREE_LEVEL_NODE_MIN	(NILFS_BTREE_LEVEL_DATA + 1)
+#define NILFS_BTREE_LEVEL_MAX		14
+
+/**
+ * struct nilfs_btree - B-tree structure
+ * @bt_bmap: bmap base structure
+ * @bt_ops: B-tree operation table
+ */
+struct nilfs_btree {
+	struct nilfs_bmap bt_bmap;
+
+	/* B-tree-specific members */
+	const struct nilfs_btree_operations *bt_ops;
+};
+
+
+#define NILFS_BTREE_ROOT_SIZE		NILFS_BMAP_SIZE
+#define NILFS_BTREE_ROOT_NCHILDREN_MAX					\
+	((NILFS_BTREE_ROOT_SIZE - sizeof(struct nilfs_btree_node)) /	\
+	 (sizeof(__le64 /* dkey */) + sizeof(__le64 /* dptr */)))
+#define NILFS_BTREE_ROOT_NCHILDREN_MIN	0
+#define NILFS_BTREE_NODE_EXTRA_PAD_SIZE	(sizeof(__le64))
+#define NILFS_BTREE_NODE_NCHILDREN_MAX(nodesize)			\
+	(((nodesize) - sizeof(struct nilfs_btree_node) -		\
+		NILFS_BTREE_NODE_EXTRA_PAD_SIZE) /			\
+	 (sizeof(__le64 /* dkey */) + sizeof(__le64 /* dptr */)))
+#define NILFS_BTREE_NODE_NCHILDREN_MIN(nodesize)			\
+	((NILFS_BTREE_NODE_NCHILDREN_MAX(nodesize) - 1) / 2 + 1)
+#define NILFS_BTREE_KEY_MIN	((__u64)0)
+#define NILFS_BTREE_KEY_MAX	(~(__u64)0)
+
+
+int nilfs_btree_path_cache_init(void);
+void nilfs_btree_path_cache_destroy(void);
+int nilfs_btree_init(struct nilfs_bmap *, __u64, __u64);
+int nilfs_btree_convert_and_insert(struct nilfs_bmap *, __u64, __u64,
+				   const __u64 *, const __u64 *,
+				   int, __u64, __u64);
+void nilfs_btree_init_gc(struct nilfs_bmap *);
+
+#endif	/* _NILFS_BTREE_H */