// SPDX-License-Identifier: GPL-2.0+
/*
 * NILFS B-tree.
 *
 * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
 *
 * Written by Koji Sato.
 */

#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"
#include "dat.h"

static void __nilfs_btree_init(struct nilfs_bmap *bmap);

static struct nilfs_btree_path *nilfs_btree_alloc_path(void)
{
        struct nilfs_btree_path *path;
        int level = NILFS_BTREE_LEVEL_DATA;

        path = kmem_cache_alloc(nilfs_btree_path_cache, GFP_NOFS);
        if (path == NULL)
                goto out;

        for (; 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;
        }

out:
        return path;
}

static void nilfs_btree_free_path(struct nilfs_btree_path *path)
{
        int level = NILFS_BTREE_LEVEL_DATA;

        for (; level < NILFS_BTREE_LEVEL_MAX; level++)
                brelse(path[level].bp_bh);

        kmem_cache_free(nilfs_btree_path_cache, path);
}

/*
 * B-tree node operations
 */
static int nilfs_btree_get_new_block(const struct nilfs_bmap *btree,
                                     __u64 ptr, struct buffer_head **bhp)
{
        struct inode *btnc_inode = NILFS_BMAP_I(btree)->i_assoc_inode;
        struct address_space *btnc = btnc_inode->i_mapping;
        struct buffer_head *bh;

        bh = nilfs_btnode_create_block(btnc, ptr);
        if (IS_ERR(bh))
                return PTR_ERR(bh);

        set_buffer_nilfs_volatile(bh);
        *bhp = bh;
        return 0;
}

static int nilfs_btree_node_get_flags(const struct nilfs_btree_node *node)
{
        return node->bn_flags;
}

static void
nilfs_btree_node_set_flags(struct nilfs_btree_node *node, int flags)
{
        node->bn_flags = flags;
}

static int nilfs_btree_node_root(const struct nilfs_btree_node *node)
{
        return nilfs_btree_node_get_flags(node) & NILFS_BTREE_NODE_ROOT;
}

static int nilfs_btree_node_get_level(const struct nilfs_btree_node *node)
{
        return node->bn_level;
}

static void
nilfs_btree_node_set_level(struct nilfs_btree_node *node, int level)
{
        node->bn_level = level;
}

static int nilfs_btree_node_get_nchildren(const struct nilfs_btree_node *node)
{
        return le16_to_cpu(node->bn_nchildren);
}

static void
nilfs_btree_node_set_nchildren(struct nilfs_btree_node *node, int nchildren)
{
        node->bn_nchildren = cpu_to_le16(nchildren);
}

static int nilfs_btree_node_size(const struct nilfs_bmap *btree)
{
        return i_blocksize(btree->b_inode);
}

static int nilfs_btree_nchildren_per_block(const struct nilfs_bmap *btree)
{
        return btree->b_nchildren_per_block;
}

static __le64 *
nilfs_btree_node_dkeys(const struct nilfs_btree_node *node)
{
        return (__le64 *)((char *)(node + 1) +
                          (nilfs_btree_node_root(node) ?
                           0 : NILFS_BTREE_NODE_EXTRA_PAD_SIZE));
}

static __le64 *
nilfs_btree_node_dptrs(const struct nilfs_btree_node *node, int ncmax)
{
        return (__le64 *)(nilfs_btree_node_dkeys(node) + ncmax);
}

static __u64
nilfs_btree_node_get_key(const struct nilfs_btree_node *node, int index)
{
        return le64_to_cpu(*(nilfs_btree_node_dkeys(node) + index));
}

static void
nilfs_btree_node_set_key(struct nilfs_btree_node *node, int index, __u64 key)
{
        *(nilfs_btree_node_dkeys(node) + index) = cpu_to_le64(key);
}

static __u64
nilfs_btree_node_get_ptr(const struct nilfs_btree_node *node, int index,
                         int ncmax)
{
        return le64_to_cpu(*(nilfs_btree_node_dptrs(node, ncmax) + index));
}

static void
nilfs_btree_node_set_ptr(struct nilfs_btree_node *node, int index, __u64 ptr,
                         int ncmax)
{
        *(nilfs_btree_node_dptrs(node, ncmax) + index) = cpu_to_le64(ptr);
}

static void nilfs_btree_node_init(struct nilfs_btree_node *node, int flags,
                                  int level, int nchildren, int ncmax,
                                  const __u64 *keys, const __u64 *ptrs)
{
        __le64 *dkeys;
        __le64 *dptrs;
        int i;

        nilfs_btree_node_set_flags(node, flags);
        nilfs_btree_node_set_level(node, level);
        nilfs_btree_node_set_nchildren(node, nchildren);

        dkeys = nilfs_btree_node_dkeys(node);
        dptrs = nilfs_btree_node_dptrs(node, ncmax);
        for (i = 0; i < nchildren; i++) {
                dkeys[i] = cpu_to_le64(keys[i]);
                dptrs[i] = cpu_to_le64(ptrs[i]);
        }
}

/* Assume the buffer heads corresponding to left and right are locked. */
static void nilfs_btree_node_move_left(struct nilfs_btree_node *left,
                                       struct nilfs_btree_node *right,
                                       int n, int lncmax, int rncmax)
{
        __le64 *ldkeys, *rdkeys;
        __le64 *ldptrs, *rdptrs;
        int lnchildren, rnchildren;

        ldkeys = nilfs_btree_node_dkeys(left);
        ldptrs = nilfs_btree_node_dptrs(left, lncmax);
        lnchildren = nilfs_btree_node_get_nchildren(left);

        rdkeys = nilfs_btree_node_dkeys(right);
        rdptrs = nilfs_btree_node_dptrs(right, rncmax);
        rnchildren = nilfs_btree_node_get_nchildren(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(left, lnchildren);
        nilfs_btree_node_set_nchildren(right, rnchildren);
}

/* Assume that the buffer heads corresponding to left and right are locked. */
static void nilfs_btree_node_move_right(struct nilfs_btree_node *left,
                                        struct nilfs_btree_node *right,
                                        int n, int lncmax, int rncmax)
{
        __le64 *ldkeys, *rdkeys;
        __le64 *ldptrs, *rdptrs;
        int lnchildren, rnchildren;

        ldkeys = nilfs_btree_node_dkeys(left);
        ldptrs = nilfs_btree_node_dptrs(left, lncmax);
        lnchildren = nilfs_btree_node_get_nchildren(left);

        rdkeys = nilfs_btree_node_dkeys(right);
        rdptrs = nilfs_btree_node_dptrs(right, rncmax);
        rnchildren = nilfs_btree_node_get_nchildren(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(left, lnchildren);
        nilfs_btree_node_set_nchildren(right, rnchildren);
}

/* Assume that the buffer head corresponding to node is locked. */
static void nilfs_btree_node_insert(struct nilfs_btree_node *node, int index,
                                    __u64 key, __u64 ptr, int ncmax)
{
        __le64 *dkeys;
        __le64 *dptrs;
        int nchildren;

        dkeys = nilfs_btree_node_dkeys(node);
        dptrs = nilfs_btree_node_dptrs(node, ncmax);
        nchildren = nilfs_btree_node_get_nchildren(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] = cpu_to_le64(key);
        dptrs[index] = cpu_to_le64(ptr);
        nchildren++;
        nilfs_btree_node_set_nchildren(node, nchildren);
}

/* Assume that the buffer head corresponding to node is locked. */
static void nilfs_btree_node_delete(struct nilfs_btree_node *node, int index,
                                    __u64 *keyp, __u64 *ptrp, int ncmax)
{
        __u64 key;
        __u64 ptr;
        __le64 *dkeys;
        __le64 *dptrs;
        int nchildren;

        dkeys = nilfs_btree_node_dkeys(node);
        dptrs = nilfs_btree_node_dptrs(node, ncmax);
        key = le64_to_cpu(dkeys[index]);
        ptr = le64_to_cpu(dptrs[index]);
        nchildren = nilfs_btree_node_get_nchildren(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(node, nchildren);
}

static int nilfs_btree_node_lookup(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(node) - 1;
        index = 0;
        s = 0;
        while (low <= high) {
                index = (low + high) / 2;
                nkey = nilfs_btree_node_get_key(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(node) > NILFS_BTREE_LEVEL_NODE_MIN) {
                if (s > 0 && index > 0)
                        index--;
        } else if (s < 0)
                index++;

 out:
        *indexp = index;

        return s == 0;
}

/**
 * nilfs_btree_node_broken - verify consistency of btree node
 * @node: btree node block to be examined
 * @size: node size (in bytes)
 * @inode: host inode of btree
 * @blocknr: block number
 *
 * Return: 0 if normal, 1 if the node is broken.
 */
static int nilfs_btree_node_broken(const struct nilfs_btree_node *node,
                                   size_t size, struct inode *inode,
                                   sector_t blocknr)
{
        int level, flags, nchildren;
        int ret = 0;

        level = nilfs_btree_node_get_level(node);
        flags = nilfs_btree_node_get_flags(node);
        nchildren = nilfs_btree_node_get_nchildren(node);

        if (unlikely(level < NILFS_BTREE_LEVEL_NODE_MIN ||
                     level >= NILFS_BTREE_LEVEL_MAX ||
                     (flags & NILFS_BTREE_NODE_ROOT) ||
                     nchildren <= 0 ||
                     nchildren > NILFS_BTREE_NODE_NCHILDREN_MAX(size))) {
                nilfs_crit(inode->i_sb,
                           "bad btree node (ino=%lu, blocknr=%llu): level = %d, flags = 0x%x, nchildren = %d",
                           inode->i_ino, (unsigned long long)blocknr, level,
                           flags, nchildren);
                ret = 1;
        }
        return ret;
}

/**
 * nilfs_btree_root_broken - verify consistency of btree root node
 * @node: btree root node to be examined
 * @inode: host inode of btree
 *
 * Return: 0 if normal, 1 if the root node is broken.
 */
static int nilfs_btree_root_broken(const struct nilfs_btree_node *node,
                                   struct inode *inode)
{
        int level, flags, nchildren;
        int ret = 0;

        level = nilfs_btree_node_get_level(node);
        flags = nilfs_btree_node_get_flags(node);
        nchildren = nilfs_btree_node_get_nchildren(node);

        if (unlikely(level < NILFS_BTREE_LEVEL_NODE_MIN ||
                     level >= NILFS_BTREE_LEVEL_MAX ||
                     nchildren < 0 ||
                     nchildren > NILFS_BTREE_ROOT_NCHILDREN_MAX ||
                     (nchildren == 0 && level > NILFS_BTREE_LEVEL_NODE_MIN))) {
                nilfs_crit(inode->i_sb,
                           "bad btree root (ino=%lu): level = %d, flags = 0x%x, nchildren = %d",
                           inode->i_ino, level, flags, nchildren);
                ret = 1;
        }
        return ret;
}

int nilfs_btree_broken_node_block(struct buffer_head *bh)
{
        struct inode *inode;
        int ret;

        if (buffer_nilfs_checked(bh))
                return 0;

        inode = bh->b_folio->mapping->host;
        ret = nilfs_btree_node_broken((struct nilfs_btree_node *)bh->b_data,
                                      bh->b_size, inode, bh->b_blocknr);
        if (likely(!ret))
                set_buffer_nilfs_checked(bh);
        return ret;
}

static struct nilfs_btree_node *
nilfs_btree_get_root(const struct nilfs_bmap *btree)
{
        return (struct nilfs_btree_node *)btree->b_u.u_data;
}

static struct nilfs_btree_node *
nilfs_btree_get_nonroot_node(const struct nilfs_btree_path *path, int level)
{
        return (struct nilfs_btree_node *)path[level].bp_bh->b_data;
}

static struct nilfs_btree_node *
nilfs_btree_get_sib_node(const struct nilfs_btree_path *path, int level)
{
        return (struct nilfs_btree_node *)path[level].bp_sib_bh->b_data;
}

static int nilfs_btree_height(const struct nilfs_bmap *btree)
{
        return nilfs_btree_node_get_level(nilfs_btree_get_root(btree)) + 1;
}

static struct nilfs_btree_node *
nilfs_btree_get_node(const struct nilfs_bmap *btree,
                     const struct nilfs_btree_path *path,
                     int level, int *ncmaxp)
{
        struct nilfs_btree_node *node;

        if (level == nilfs_btree_height(btree) - 1) {
                node = nilfs_btree_get_root(btree);
                *ncmaxp = NILFS_BTREE_ROOT_NCHILDREN_MAX;
        } else {
                node = nilfs_btree_get_nonroot_node(path, level);
                *ncmaxp = nilfs_btree_nchildren_per_block(btree);
        }
        return node;
}

static int nilfs_btree_bad_node(const struct nilfs_bmap *btree,
                                struct nilfs_btree_node *node, int level)
{
        if (unlikely(nilfs_btree_node_get_level(node) != level)) {
                dump_stack();
                nilfs_crit(btree->b_inode->i_sb,
                           "btree level mismatch (ino=%lu): %d != %d",
                           btree->b_inode->i_ino,
                           nilfs_btree_node_get_level(node), level);
                return 1;
        }
        return 0;
}

struct nilfs_btree_readahead_info {
        struct nilfs_btree_node *node;  /* parent node */
        int max_ra_blocks;              /* max nof blocks to read ahead */
        int index;                      /* current index on the parent node */
        int ncmax;                      /* nof children in the parent node */
};

static int __nilfs_btree_get_block(const struct nilfs_bmap *btree, __u64 ptr,
                                   struct buffer_head **bhp,
                                   const struct nilfs_btree_readahead_info *ra)
{
        struct inode *btnc_inode = NILFS_BMAP_I(btree)->i_assoc_inode;
        struct address_space *btnc = btnc_inode->i_mapping;
        struct buffer_head *bh, *ra_bh;
        sector_t submit_ptr = 0;
        int ret;

        ret = nilfs_btnode_submit_block(btnc, ptr, 0, REQ_OP_READ, &bh,
                                        &submit_ptr);
        if (ret) {
                if (likely(ret == -EEXIST))
                        goto out_check;
                if (ret == -ENOENT) {
                        /*
                         * Block address translation failed due to invalid
                         * value of 'ptr'.  In this case, return internal code
                         * -EINVAL (broken bmap) to notify bmap layer of fatal
                         * metadata corruption.
                         */
                        ret = -EINVAL;
                }
                return ret;
        }

        if (ra) {
                int i, n;
                __u64 ptr2;

                /* read ahead sibling nodes */
                for (n = ra->max_ra_blocks, i = ra->index + 1;
                     n > 0 && i < ra->ncmax; n--, i++) {
                        ptr2 = nilfs_btree_node_get_ptr(ra->node, i, ra->ncmax);

                        ret = nilfs_btnode_submit_block(btnc, ptr2, 0,
                                                REQ_OP_READ | REQ_RAHEAD,
                                                &ra_bh, &submit_ptr);
                        if (likely(!ret || ret == -EEXIST))
                                brelse(ra_bh);
                        else if (ret != -EBUSY)
                                break;
                        if (!buffer_locked(bh))
                                goto out_no_wait;
                }
        }

        wait_on_buffer(bh);

 out_no_wait:
        if (!buffer_uptodate(bh)) {
                nilfs_err(btree->b_inode->i_sb,
                          "I/O error reading b-tree node block (ino=%lu, blocknr=%llu)",
                          btree->b_inode->i_ino, (unsigned long long)ptr);
                brelse(bh);
                return -EIO;
        }

 out_check:
        if (nilfs_btree_broken_node_block(bh)) {
                clear_buffer_uptodate(bh);
                brelse(bh);
                return -EINVAL;
        }

        *bhp = bh;
        return 0;
}

static int nilfs_btree_get_block(const struct nilfs_bmap *btree, __u64 ptr,
                                   struct buffer_head **bhp)
{
        return __nilfs_btree_get_block(btree, ptr, bhp, NULL);
}

static int nilfs_btree_do_lookup(const struct nilfs_bmap *btree,
                                 struct nilfs_btree_path *path,
                                 __u64 key, __u64 *ptrp, int minlevel,
                                 int readahead)
{
        struct nilfs_btree_node *node;
        struct nilfs_btree_readahead_info p, *ra;
        __u64 ptr;
        int level, index, found, ncmax, ret;

        node = nilfs_btree_get_root(btree);
        level = nilfs_btree_node_get_level(node);
        if (level < minlevel || nilfs_btree_node_get_nchildren(node) <= 0)
                return -ENOENT;

        found = nilfs_btree_node_lookup(node, key, &index);
        ptr = nilfs_btree_node_get_ptr(node, index,
                                       NILFS_BTREE_ROOT_NCHILDREN_MAX);
        path[level].bp_bh = NULL;
        path[level].bp_index = index;

        ncmax = nilfs_btree_nchildren_per_block(btree);

        while (--level >= minlevel) {
                ra = NULL;
                if (level == NILFS_BTREE_LEVEL_NODE_MIN && readahead) {
                        p.node = nilfs_btree_get_node(btree, path, level + 1,
                                                      &p.ncmax);
                        p.index = index;
                        p.max_ra_blocks = 7;
                        ra = &p;
                }
                ret = __nilfs_btree_get_block(btree, ptr, &path[level].bp_bh,
                                              ra);
                if (ret < 0)
                        return ret;

                node = nilfs_btree_get_nonroot_node(path, level);
                if (nilfs_btree_bad_node(btree, node, level))
                        return -EINVAL;
                if (!found)
                        found = nilfs_btree_node_lookup(node, key, &index);
                else
                        index = 0;
                if (index < ncmax) {
                        ptr = nilfs_btree_node_get_ptr(node, index, ncmax);
                } else {
                        WARN_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_bmap *btree,
                                      struct nilfs_btree_path *path,
                                      __u64 *keyp, __u64 *ptrp)
{
        struct nilfs_btree_node *node;
        __u64 ptr;
        int index, level, ncmax, ret;

        node = nilfs_btree_get_root(btree);
        index = nilfs_btree_node_get_nchildren(node) - 1;
        if (index < 0)
                return -ENOENT;
        level = nilfs_btree_node_get_level(node);
        ptr = nilfs_btree_node_get_ptr(node, index,
                                       NILFS_BTREE_ROOT_NCHILDREN_MAX);
        path[level].bp_bh = NULL;
        path[level].bp_index = index;
        ncmax = nilfs_btree_nchildren_per_block(btree);

        for (level--; level > 0; level--) {
                ret = nilfs_btree_get_block(btree, ptr, &path[level].bp_bh);
                if (ret < 0)
                        return ret;
                node = nilfs_btree_get_nonroot_node(path, level);
                if (nilfs_btree_bad_node(btree, node, level))
                        return -EINVAL;
                index = nilfs_btree_node_get_nchildren(node) - 1;
                ptr = nilfs_btree_node_get_ptr(node, index, ncmax);
                path[level].bp_index = index;
        }

        if (keyp != NULL)
                *keyp = nilfs_btree_node_get_key(node, index);
        if (ptrp != NULL)
                *ptrp = ptr;

        return 0;
}

/**
 * nilfs_btree_get_next_key - get next valid key from btree path array
 * @btree: bmap struct of btree
 * @path: array of nilfs_btree_path struct
 * @minlevel: start level
 * @nextkey: place to store the next valid key
 *
 * Return: 0 if the next key was found, %-ENOENT if not found.
 */
static int nilfs_btree_get_next_key(const struct nilfs_bmap *btree,
                                    const struct nilfs_btree_path *path,
                                    int minlevel, __u64 *nextkey)
{
        struct nilfs_btree_node *node;
        int maxlevel = nilfs_btree_height(btree) - 1;
        int index, next_adj, level;

        /* Next index is already set to bp_index for leaf nodes. */
        next_adj = 0;
        for (level = minlevel; level <= maxlevel; level++) {
                if (level == maxlevel)
                        node = nilfs_btree_get_root(btree);
                else
                        node = nilfs_btree_get_nonroot_node(path, level);

                index = path[level].bp_index + next_adj;
                if (index < nilfs_btree_node_get_nchildren(node)) {
                        /* Next key is in this node */
                        *nextkey = nilfs_btree_node_get_key(node, index);
                        return 0;
                }
                /* For non-leaf nodes, next index is stored at bp_index + 1. */
                next_adj = 1;
        }
        return -ENOENT;
}

static int nilfs_btree_lookup(const struct nilfs_bmap *btree,
                              __u64 key, int level, __u64 *ptrp)
{
        struct nilfs_btree_path *path;
        int ret;

        path = nilfs_btree_alloc_path();
        if (path == NULL)
                return -ENOMEM;

        ret = nilfs_btree_do_lookup(btree, path, key, ptrp, level, 0);

        nilfs_btree_free_path(path);

        return ret;
}

static int nilfs_btree_lookup_contig(const struct nilfs_bmap *btree,
                                     __u64 key, __u64 *ptrp,
                                     unsigned int maxblocks)
{
        struct nilfs_btree_path *path;
        struct nilfs_btree_node *node;
        struct inode *dat = NULL;
        __u64 ptr, ptr2;
        sector_t blocknr;
        int level = NILFS_BTREE_LEVEL_NODE_MIN;
        int ret, cnt, index, maxlevel, ncmax;
        struct nilfs_btree_readahead_info p;

        path = nilfs_btree_alloc_path();
        if (path == NULL)
                return -ENOMEM;

        ret = nilfs_btree_do_lookup(btree, path, key, &ptr, level, 1);
        if (ret < 0)
                goto out;

        if (NILFS_BMAP_USE_VBN(btree)) {
                dat = nilfs_bmap_get_dat(btree);
                ret = nilfs_dat_translate(dat, ptr, &blocknr);
                if (ret < 0)
                        goto dat_error;
                ptr = blocknr;
        }
        cnt = 1;
        if (cnt == maxblocks)
                goto end;

        maxlevel = nilfs_btree_height(btree) - 1;
        node = nilfs_btree_get_node(btree, path, level, &ncmax);
        index = path[level].bp_index + 1;
        for (;;) {
                while (index < nilfs_btree_node_get_nchildren(node)) {
                        if (nilfs_btree_node_get_key(node, index) !=
                            key + cnt)
                                goto end;
                        ptr2 = nilfs_btree_node_get_ptr(node, index, ncmax);
                        if (dat) {
                                ret = nilfs_dat_translate(dat, ptr2, &blocknr);
                                if (ret < 0)
                                        goto dat_error;
                                ptr2 = blocknr;
                        }
                        if (ptr2 != ptr + cnt || ++cnt == maxblocks)
                                goto end;
                        index++;
                }
                if (level == maxlevel)
                        break;

                /* look-up right sibling node */
                p.node = nilfs_btree_get_node(btree, path, level + 1, &p.ncmax);
                p.index = path[level + 1].bp_index + 1;
                p.max_ra_blocks = 7;
                if (p.index >= nilfs_btree_node_get_nchildren(p.node) ||
                    nilfs_btree_node_get_key(p.node, p.index) != key + cnt)
                        break;
                ptr2 = nilfs_btree_node_get_ptr(p.node, p.index, p.ncmax);
                path[level + 1].bp_index = p.index;

                brelse(path[level].bp_bh);
                path[level].bp_bh = NULL;

                ret = __nilfs_btree_get_block(btree, ptr2, &path[level].bp_bh,
                                              &p);
                if (ret < 0)
                        goto out;
                node = nilfs_btree_get_nonroot_node(path, level);
                ncmax = nilfs_btree_nchildren_per_block(btree);
                index = 0;
                path[level].bp_index = index;
        }
 end:
        *ptrp = ptr;
        ret = cnt;
 out:
        nilfs_btree_free_path(path);
        return ret;

 dat_error:
        if (ret == -ENOENT)
                ret = -EINVAL;  /* Notify bmap layer of metadata corruption */
        goto out;
}

static void nilfs_btree_promote_key(struct nilfs_bmap *btree,
                                    struct nilfs_btree_path *path,
                                    int level, __u64 key)
{
        if (level < nilfs_btree_height(btree) - 1) {
                do {
                        nilfs_btree_node_set_key(
                                nilfs_btree_get_nonroot_node(path, level),
                                path[level].bp_index, key);
                        if (!buffer_dirty(path[level].bp_bh))
                                mark_buffer_dirty(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(nilfs_btree_get_root(btree),
                                         path[level].bp_index, key);
        }
}

static void nilfs_btree_do_insert(struct nilfs_bmap *btree,
                                  struct nilfs_btree_path *path,
                                  int level, __u64 *keyp, __u64 *ptrp)
{
        struct nilfs_btree_node *node;
        int ncblk;

        if (level < nilfs_btree_height(btree) - 1) {
                node = nilfs_btree_get_nonroot_node(path, level);
                ncblk = nilfs_btree_nchildren_per_block(btree);
                nilfs_btree_node_insert(node, path[level].bp_index,
                                        *keyp, *ptrp, ncblk);
                if (!buffer_dirty(path[level].bp_bh))
                        mark_buffer_dirty(path[level].bp_bh);

                if (path[level].bp_index == 0)
                        nilfs_btree_promote_key(btree, path, level + 1,
                                                nilfs_btree_node_get_key(node,
                                                                         0));
        } else {
                node = nilfs_btree_get_root(btree);
                nilfs_btree_node_insert(node, path[level].bp_index,
                                        *keyp, *ptrp,
                                        NILFS_BTREE_ROOT_NCHILDREN_MAX);
        }
}

static void nilfs_btree_carry_left(struct nilfs_bmap *btree,
                                   struct nilfs_btree_path *path,
                                   int level, __u64 *keyp, __u64 *ptrp)
{
        struct nilfs_btree_node *node, *left;
        int nchildren, lnchildren, n, move, ncblk;

        node = nilfs_btree_get_nonroot_node(path, level);
        left = nilfs_btree_get_sib_node(path, level);
        nchildren = nilfs_btree_node_get_nchildren(node);
        lnchildren = nilfs_btree_node_get_nchildren(left);
        ncblk = nilfs_btree_nchildren_per_block(btree);
        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(left, node, n, ncblk, ncblk);

        if (!buffer_dirty(path[level].bp_bh))
                mark_buffer_dirty(path[level].bp_bh);
        if (!buffer_dirty(path[level].bp_sib_bh))
                mark_buffer_dirty(path[level].bp_sib_bh);

        nilfs_btree_promote_key(btree, path, level + 1,
                                nilfs_btree_node_get_key(node, 0));

        if (move) {
                brelse(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 {
                brelse(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_bmap *btree,
                                    struct nilfs_btree_path *path,
                                    int level, __u64 *keyp, __u64 *ptrp)
{
        struct nilfs_btree_node *node, *right;
        int nchildren, rnchildren, n, move, ncblk;

        node = nilfs_btree_get_nonroot_node(path, level);
        right = nilfs_btree_get_sib_node(path, level);
        nchildren = nilfs_btree_node_get_nchildren(node);
        rnchildren = nilfs_btree_node_get_nchildren(right);
        ncblk = nilfs_btree_nchildren_per_block(btree);
        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(node, right, n, ncblk, ncblk);

        if (!buffer_dirty(path[level].bp_bh))
                mark_buffer_dirty(path[level].bp_bh);
        if (!buffer_dirty(path[level].bp_sib_bh))
                mark_buffer_dirty(path[level].bp_sib_bh);

        path[level + 1].bp_index++;
        nilfs_btree_promote_key(btree, path, level + 1,
                                nilfs_btree_node_get_key(right, 0));
        path[level + 1].bp_index--;

        if (move) {
                brelse(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(node);
                path[level + 1].bp_index++;
        } else {
                brelse(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_bmap *btree,
                              struct nilfs_btree_path *path,
                              int level, __u64 *keyp, __u64 *ptrp)
{
        struct nilfs_btree_node *node, *right;
        int nchildren, n, move, ncblk;

        node = nilfs_btree_get_nonroot_node(path, level);
        right = nilfs_btree_get_sib_node(path, level);
        nchildren = nilfs_btree_node_get_nchildren(node);
        ncblk = nilfs_btree_nchildren_per_block(btree);
        move = 0;

        n = (nchildren + 1) / 2;
        if (n > nchildren - path[level].bp_index) {
                n--;
                move = 1;
        }

        nilfs_btree_node_move_right(node, right, n, ncblk, ncblk);

        if (!buffer_dirty(path[level].bp_bh))
                mark_buffer_dirty(path[level].bp_bh);
        if (!buffer_dirty(path[level].bp_sib_bh))
                mark_buffer_dirty(path[level].bp_sib_bh);

        if (move) {
                path[level].bp_index -= nilfs_btree_node_get_nchildren(node);
                nilfs_btree_node_insert(right, path[level].bp_index,
                                        *keyp, *ptrp, ncblk);

                *keyp = nilfs_btree_node_get_key(right, 0);
                *ptrp = path[level].bp_newreq.bpr_ptr;

                brelse(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(right, 0);
                *ptrp = path[level].bp_newreq.bpr_ptr;

                brelse(path[level].bp_sib_bh);
                path[level].bp_sib_bh = NULL;
        }

        path[level + 1].bp_index++;
}

static void nilfs_btree_grow(struct nilfs_bmap *btree,
                             struct nilfs_btree_path *path,
                             int level, __u64 *keyp, __u64 *ptrp)
{
        struct nilfs_btree_node *root, *child;
        int n, ncblk;

        root = nilfs_btree_get_root(btree);
        child = nilfs_btree_get_sib_node(path, level);
        ncblk = nilfs_btree_nchildren_per_block(btree);

        n = nilfs_btree_node_get_nchildren(root);

        nilfs_btree_node_move_right(root, child, n,
                                    NILFS_BTREE_ROOT_NCHILDREN_MAX, ncblk);
        nilfs_btree_node_set_level(root, level + 1);

        if (!buffer_dirty(path[level].bp_sib_bh))
                mark_buffer_dirty(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(child, 0);
        *ptrp = path[level].bp_newreq.bpr_ptr;
}

static __u64 nilfs_btree_find_near(const struct nilfs_bmap *btree,
                                   const struct nilfs_btree_path *path)
{
        struct nilfs_btree_node *node;
        int level, ncmax;

        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, &ncmax);
                return nilfs_btree_node_get_ptr(node,
                                                path[level].bp_index - 1,
                                                ncmax);
        }

        /* parent */
        level = NILFS_BTREE_LEVEL_NODE_MIN + 1;
        if (level <= nilfs_btree_height(btree) - 1) {
                node = nilfs_btree_get_node(btree, path, level, &ncmax);
                return nilfs_btree_node_get_ptr(node, path[level].bp_index,
                                                ncmax);
        }

        return NILFS_BMAP_INVALID_PTR;
}

static __u64 nilfs_btree_find_target_v(const struct nilfs_bmap *btree,
                                       const struct nilfs_btree_path *path,
                                       __u64 key)
{
        __u64 ptr;

        ptr = nilfs_bmap_find_target_seq(btree, key);
        if (ptr != NILFS_BMAP_INVALID_PTR)
                /* sequential access */
                return ptr;

        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);
}

static int nilfs_btree_prepare_insert(struct nilfs_bmap *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, ncmax, ncblk, ret;
        struct inode *dat = NULL;

        stats->bs_nblocks = 0;
        level = NILFS_BTREE_LEVEL_DATA;

        /* allocate a new ptr for data block */
        if (NILFS_BMAP_USE_VBN(btree)) {
                path[level].bp_newreq.bpr_ptr =
                        nilfs_btree_find_target_v(btree, path, key);
                dat = nilfs_bmap_get_dat(btree);
        }

        ret = nilfs_bmap_prepare_alloc_ptr(btree, &path[level].bp_newreq, dat);
        if (ret < 0)
                goto err_out_data;

        ncblk = nilfs_btree_nchildren_per_block(btree);

        for (level = NILFS_BTREE_LEVEL_NODE_MIN;
             level < nilfs_btree_height(btree) - 1;
             level++) {
                node = nilfs_btree_get_nonroot_node(path, level);
                if (nilfs_btree_node_get_nchildren(node) < ncblk) {
                        path[level].bp_op = nilfs_btree_do_insert;
                        stats->bs_nblocks++;
                        goto out;
                }

                parent = nilfs_btree_get_node(btree, path, level + 1, &ncmax);
                pindex = path[level + 1].bp_index;

                /* left sibling */
                if (pindex > 0) {
                        sibptr = nilfs_btree_node_get_ptr(parent, pindex - 1,
                                                          ncmax);
                        ret = nilfs_btree_get_block(btree, sibptr, &bh);
                        if (ret < 0)
                                goto err_out_child_node;
                        sib = (struct nilfs_btree_node *)bh->b_data;
                        if (nilfs_btree_node_get_nchildren(sib) < ncblk) {
                                path[level].bp_sib_bh = bh;
                                path[level].bp_op = nilfs_btree_carry_left;
                                stats->bs_nblocks++;
                                goto out;
                        } else {
                                brelse(bh);
                        }
                }

                /* right sibling */
                if (pindex < nilfs_btree_node_get_nchildren(parent) - 1) {
                        sibptr = nilfs_btree_node_get_ptr(parent, pindex + 1,
                                                          ncmax);
                        ret = nilfs_btree_get_block(btree, sibptr, &bh);
                        if (ret < 0)
                                goto err_out_child_node;
                        sib = (struct nilfs_btree_node *)bh->b_data;
                        if (nilfs_btree_node_get_nchildren(sib) < ncblk) {
                                path[level].bp_sib_bh = bh;
                                path[level].bp_op = nilfs_btree_carry_right;
                                stats->bs_nblocks++;
                                goto out;
                        } else {
                                brelse(bh);
                        }
                }

                /* split */
                path[level].bp_newreq.bpr_ptr =
                        path[level - 1].bp_newreq.bpr_ptr + 1;
                ret = nilfs_bmap_prepare_alloc_ptr(btree,
                                                   &path[level].bp_newreq, dat);
                if (ret < 0)
                        goto err_out_child_node;
                ret = nilfs_btree_get_new_block(btree,
                                                path[level].bp_newreq.bpr_ptr,
                                                &bh);
                if (ret < 0)
                        goto err_out_curr_node;

                stats->bs_nblocks++;

                sib = (struct nilfs_btree_node *)bh->b_data;
                nilfs_btree_node_init(sib, 0, level, 0, ncblk, NULL, NULL);
                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(node) <
            NILFS_BTREE_ROOT_NCHILDREN_MAX) {
                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 = nilfs_bmap_prepare_alloc_ptr(btree, &path[level].bp_newreq, dat);
        if (ret < 0)
                goto err_out_child_node;
        ret = nilfs_btree_get_new_block(btree, path[level].bp_newreq.bpr_ptr,
                                        &bh);
        if (ret < 0)
                goto err_out_curr_node;

        nilfs_btree_node_init((struct nilfs_btree_node *)bh->b_data,
                              0, level, 0, ncblk, NULL, NULL);
        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:
        nilfs_bmap_abort_alloc_ptr(btree, &path[level].bp_newreq, dat);
 err_out_child_node:
        for (level--; level > NILFS_BTREE_LEVEL_DATA; level--) {
                nilfs_btnode_delete(path[level].bp_sib_bh);
                nilfs_bmap_abort_alloc_ptr(btree, &path[level].bp_newreq, dat);

        }

        nilfs_bmap_abort_alloc_ptr(btree, &path[level].bp_newreq, dat);
 err_out_data:
        *levelp = level;
        stats->bs_nblocks = 0;
        return ret;
}

static void nilfs_btree_commit_insert(struct nilfs_bmap *btree,
                                      struct nilfs_btree_path *path,
                                      int maxlevel, __u64 key, __u64 ptr)
{
        struct inode *dat = NULL;
        int level;

        set_buffer_nilfs_volatile((struct buffer_head *)((unsigned long)ptr));
        ptr = path[NILFS_BTREE_LEVEL_DATA].bp_newreq.bpr_ptr;
        if (NILFS_BMAP_USE_VBN(btree)) {
                nilfs_bmap_set_target_v(btree, key, ptr);
                dat = nilfs_bmap_get_dat(btree);
        }

        for (level = NILFS_BTREE_LEVEL_NODE_MIN; level <= maxlevel; level++) {
                nilfs_bmap_commit_alloc_ptr(btree,
                                            &path[level - 1].bp_newreq, dat);
                path[level].bp_op(btree, path, level, &key, &ptr);
        }

        if (!nilfs_bmap_dirty(btree))
                nilfs_bmap_set_dirty(btree);
}

static int nilfs_btree_insert(struct nilfs_bmap *btree, __u64 key, __u64 ptr)
{
        struct nilfs_btree_path *path;
        struct nilfs_bmap_stats stats;
        int level, ret;

        path = nilfs_btree_alloc_path();
        if (path == NULL)
                return -ENOMEM;

        ret = nilfs_btree_do_lookup(btree, path, key, NULL,
                                    NILFS_BTREE_LEVEL_NODE_MIN, 0);
        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_inode_add_blocks(btree->b_inode, stats.bs_nblocks);

 out:
        nilfs_btree_free_path(path);
        return ret;
}

static void nilfs_btree_do_delete(struct nilfs_bmap *btree,
                                  struct nilfs_btree_path *path,
                                  int level, __u64 *keyp, __u64 *ptrp)
{
        struct nilfs_btree_node *node;
        int ncblk;

        if (level < nilfs_btree_height(btree) - 1) {
                node = nilfs_btree_get_nonroot_node(path, level);
                ncblk = nilfs_btree_nchildren_per_block(btree);
                nilfs_btree_node_delete(node, path[level].bp_index,
                                        keyp, ptrp, ncblk);
                if (!buffer_dirty(path[level].bp_bh))
                        mark_buffer_dirty(path[level].bp_bh);
                if (path[level].bp_index == 0)
                        nilfs_btree_promote_key(btree, path, level + 1,
                                nilfs_btree_node_get_key(node, 0));
        } else {
                node = nilfs_btree_get_root(btree);
                nilfs_btree_node_delete(node, path[level].bp_index,
                                        keyp, ptrp,
                                        NILFS_BTREE_ROOT_NCHILDREN_MAX);
        }
}

static void nilfs_btree_borrow_left(struct nilfs_bmap *btree,
                                    struct nilfs_btree_path *path,
                                    int level, __u64 *keyp, __u64 *ptrp)
{
        struct nilfs_btree_node *node, *left;
        int nchildren, lnchildren, n, ncblk;

        nilfs_btree_do_delete(btree, path, level, keyp, ptrp);

        node = nilfs_btree_get_nonroot_node(path, level);
        left = nilfs_btree_get_sib_node(path, level);
        nchildren = nilfs_btree_node_get_nchildren(node);
        lnchildren = nilfs_btree_node_get_nchildren(left);
        ncblk = nilfs_btree_nchildren_per_block(btree);

        n = (nchildren + lnchildren) / 2 - nchildren;

        nilfs_btree_node_move_right(left, node, n, ncblk, ncblk);

        if (!buffer_dirty(path[level].bp_bh))
                mark_buffer_dirty(path[level].bp_bh);
        if (!buffer_dirty(path[level].bp_sib_bh))
                mark_buffer_dirty(path[level].bp_sib_bh);

        nilfs_btree_promote_key(btree, path, level + 1,
                                nilfs_btree_node_get_key(node, 0));

        brelse(path[level].bp_sib_bh);
        path[level].bp_sib_bh = NULL;
        path[level].bp_index += n;
}

static void nilfs_btree_borrow_right(struct nilfs_bmap *btree,
                                     struct nilfs_btree_path *path,
                                     int level, __u64 *keyp, __u64 *ptrp)
{
        struct nilfs_btree_node *node, *right;
        int nchildren, rnchildren, n, ncblk;

        nilfs_btree_do_delete(btree, path, level, keyp, ptrp);

        node = nilfs_btree_get_nonroot_node(path, level);
        right = nilfs_btree_get_sib_node(path, level);
        nchildren = nilfs_btree_node_get_nchildren(node);
        rnchildren = nilfs_btree_node_get_nchildren(right);
        ncblk = nilfs_btree_nchildren_per_block(btree);

        n = (nchildren + rnchildren) / 2 - nchildren;

        nilfs_btree_node_move_left(node, right, n, ncblk, ncblk);

        if (!buffer_dirty(path[level].bp_bh))
                mark_buffer_dirty(path[level].bp_bh);
        if (!buffer_dirty(path[level].bp_sib_bh))
                mark_buffer_dirty(path[level].bp_sib_bh);

        path[level + 1].bp_index++;
        nilfs_btree_promote_key(btree, path, level + 1,
                                nilfs_btree_node_get_key(right, 0));
        path[level + 1].bp_index--;

        brelse(path[level].bp_sib_bh);
        path[level].bp_sib_bh = NULL;
}

static void nilfs_btree_concat_left(struct nilfs_bmap *btree,
                                    struct nilfs_btree_path *path,
                                    int level, __u64 *keyp, __u64 *ptrp)
{
        struct nilfs_btree_node *node, *left;
        int n, ncblk;

        nilfs_btree_do_delete(btree, path, level, keyp, ptrp);

        node = nilfs_btree_get_nonroot_node(path, level);
        left = nilfs_btree_get_sib_node(path, level);
        ncblk = nilfs_btree_nchildren_per_block(btree);

        n = nilfs_btree_node_get_nchildren(node);

        nilfs_btree_node_move_left(left, node, n, ncblk, ncblk);

        if (!buffer_dirty(path[level].bp_sib_bh))
                mark_buffer_dirty(path[level].bp_sib_bh);

        nilfs_btnode_delete(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(left);
}

static void nilfs_btree_concat_right(struct nilfs_bmap *btree,
                                     struct nilfs_btree_path *path,
                                     int level, __u64 *keyp, __u64 *ptrp)
{
        struct nilfs_btree_node *node, *right;
        int n, ncblk;

        nilfs_btree_do_delete(btree, path, level, keyp, ptrp);

        node = nilfs_btree_get_nonroot_node(path, level);
        right = nilfs_btree_get_sib_node(path, level);
        ncblk = nilfs_btree_nchildren_per_block(btree);

        n = nilfs_btree_node_get_nchildren(right);

        nilfs_btree_node_move_left(node, right, n, ncblk, ncblk);

        if (!buffer_dirty(path[level].bp_bh))
                mark_buffer_dirty(path[level].bp_bh);

        nilfs_btnode_delete(path[level].bp_sib_bh);
        path[level].bp_sib_bh = NULL;
        path[level + 1].bp_index++;
}

static void nilfs_btree_shrink(struct nilfs_bmap *btree,
                               struct nilfs_btree_path *path,
                               int level, __u64 *keyp, __u64 *ptrp)
{
        struct nilfs_btree_node *root, *child;
        int n, ncblk;

        nilfs_btree_do_delete(btree, path, level, keyp, ptrp);

        root = nilfs_btree_get_root(btree);
        child = nilfs_btree_get_nonroot_node(path, level);
        ncblk = nilfs_btree_nchildren_per_block(btree);

        nilfs_btree_node_delete(root, 0, NULL, NULL,
                                NILFS_BTREE_ROOT_NCHILDREN_MAX);
        nilfs_btree_node_set_level(root, level);
        n = nilfs_btree_node_get_nchildren(child);
        nilfs_btree_node_move_left(root, child, n,
                                   NILFS_BTREE_ROOT_NCHILDREN_MAX, ncblk);

        nilfs_btnode_delete(path[level].bp_bh);
        path[level].bp_bh = NULL;
}

static void nilfs_btree_nop(struct nilfs_bmap *btree,
                            struct nilfs_btree_path *path,
                            int level, __u64 *keyp, __u64 *ptrp)
{
}

static int nilfs_btree_prepare_delete(struct nilfs_bmap *btree,
                                      struct nilfs_btree_path *path,
                                      int *levelp,
                                      struct nilfs_bmap_stats *stats,
                                      struct inode *dat)
{
        struct buffer_head *bh;
        struct nilfs_btree_node *node, *parent, *sib;
        __u64 sibptr;
        int pindex, dindex, level, ncmin, ncmax, ncblk, ret;

        ret = 0;
        stats->bs_nblocks = 0;
        ncmin = NILFS_BTREE_NODE_NCHILDREN_MIN(nilfs_btree_node_size(btree));
        ncblk = nilfs_btree_nchildren_per_block(btree);

        for (level = NILFS_BTREE_LEVEL_NODE_MIN, dindex = path[level].bp_index;
             level < nilfs_btree_height(btree) - 1;
             level++) {
                node = nilfs_btree_get_nonroot_node(path, level);
                path[level].bp_oldreq.bpr_ptr =
                        nilfs_btree_node_get_ptr(node, dindex, ncblk);
                ret = nilfs_bmap_prepare_end_ptr(btree,
                                                 &path[level].bp_oldreq, dat);
                if (ret < 0)
                        goto err_out_child_node;

                if (nilfs_btree_node_get_nchildren(node) > ncmin) {
                        path[level].bp_op = nilfs_btree_do_delete;
                        stats->bs_nblocks++;
                        goto out;
                }

                parent = nilfs_btree_get_node(btree, path, level + 1, &ncmax);
                pindex = path[level + 1].bp_index;
                dindex = pindex;

                if (pindex > 0) {
                        /* left sibling */
                        sibptr = nilfs_btree_node_get_ptr(parent, pindex - 1,
                                                          ncmax);
                        ret = nilfs_btree_get_block(btree, sibptr, &bh);
                        if (ret < 0)
                                goto err_out_curr_node;
                        sib = (struct nilfs_btree_node *)bh->b_data;
                        if (nilfs_btree_node_get_nchildren(sib) > ncmin) {
                                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(parent) - 1) {
                        /* right sibling */
                        sibptr = nilfs_btree_node_get_ptr(parent, pindex + 1,
                                                          ncmax);
                        ret = nilfs_btree_get_block(btree, sibptr, &bh);
                        if (ret < 0)
                                goto err_out_curr_node;
                        sib = (struct nilfs_btree_node *)bh->b_data;
                        if (nilfs_btree_node_get_nchildren(sib) > ncmin) {
                                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++;
                                /*
                                 * When merging right sibling node
                                 * into the current node, pointer to
                                 * the right sibling node must be
                                 * terminated instead.  The adjustment
                                 * below is required for that.
                                 */
                                dindex = pindex + 1;
                                /* continue; */
                        }
                } else {
                        /* no siblings */
                        /* the only child of the root node */
                        WARN_ON(level != nilfs_btree_height(btree) - 2);
                        if (nilfs_btree_node_get_nchildren(node) - 1 <=
                            NILFS_BTREE_ROOT_NCHILDREN_MAX) {
                                path[level].bp_op = nilfs_btree_shrink;
                                stats->bs_nblocks += 2;
                                level++;
                                path[level].bp_op = nilfs_btree_nop;
                                goto shrink_root_child;
                        } else {
                                path[level].bp_op = nilfs_btree_do_delete;
                                stats->bs_nblocks++;
                                goto out;
                        }
                }
        }

        /* child of the root node is deleted */
        path[level].bp_op = nilfs_btree_do_delete;
        stats->bs_nblocks++;

shrink_root_child:
        node = nilfs_btree_get_root(btree);
        path[level].bp_oldreq.bpr_ptr =
                nilfs_btree_node_get_ptr(node, dindex,
                                         NILFS_BTREE_ROOT_NCHILDREN_MAX);

        ret = nilfs_bmap_prepare_end_ptr(btree, &path[level].bp_oldreq, dat);
        if (ret < 0)
                goto err_out_child_node;

        /* success */
 out:
        *levelp = level;
        return ret;

        /* error */
 err_out_curr_node:
        nilfs_bmap_abort_end_ptr(btree, &path[level].bp_oldreq, dat);
 err_out_child_node:
        for (level--; level >= NILFS_BTREE_LEVEL_NODE_MIN; level--) {
                brelse(path[level].bp_sib_bh);
                nilfs_bmap_abort_end_ptr(btree, &path[level].bp_oldreq, dat);
        }
        *levelp = level;
        stats->bs_nblocks = 0;
        return ret;
}

static void nilfs_btree_commit_delete(struct nilfs_bmap *btree,
                                      struct nilfs_btree_path *path,
                                      int maxlevel, struct inode *dat)
{
        int level;

        for (level = NILFS_BTREE_LEVEL_NODE_MIN; level <= maxlevel; level++) {
                nilfs_bmap_commit_end_ptr(btree, &path[level].bp_oldreq, dat);
                path[level].bp_op(btree, path, level, NULL, NULL);
        }

        if (!nilfs_bmap_dirty(btree))
                nilfs_bmap_set_dirty(btree);
}

static int nilfs_btree_delete(struct nilfs_bmap *btree, __u64 key)

{
        struct nilfs_btree_path *path;
        struct nilfs_bmap_stats stats;
        struct inode *dat;
        int level, ret;

        path = nilfs_btree_alloc_path();
        if (path == NULL)
                return -ENOMEM;

        ret = nilfs_btree_do_lookup(btree, path, key, NULL,
                                    NILFS_BTREE_LEVEL_NODE_MIN, 0);
        if (ret < 0)
                goto out;


        dat = NILFS_BMAP_USE_VBN(btree) ? nilfs_bmap_get_dat(btree) : NULL;

        ret = nilfs_btree_prepare_delete(btree, path, &level, &stats, dat);
        if (ret < 0)
                goto out;
        nilfs_btree_commit_delete(btree, path, level, dat);
        nilfs_inode_sub_blocks(btree->b_inode, stats.bs_nblocks);

out:
        nilfs_btree_free_path(path);
        return ret;
}

static int nilfs_btree_seek_key(const struct nilfs_bmap *btree, __u64 start,
                                __u64 *keyp)
{
        struct nilfs_btree_path *path;
        const int minlevel = NILFS_BTREE_LEVEL_NODE_MIN;
        int ret;

        path = nilfs_btree_alloc_path();
        if (!path)
                return -ENOMEM;

        ret = nilfs_btree_do_lookup(btree, path, start, NULL, minlevel, 0);
        if (!ret)
                *keyp = start;
        else if (ret == -ENOENT)
                ret = nilfs_btree_get_next_key(btree, path, minlevel, keyp);

        nilfs_btree_free_path(path);
        return ret;
}

static int nilfs_btree_last_key(const struct nilfs_bmap *btree, __u64 *keyp)
{
        struct nilfs_btree_path *path;
        int ret;

        path = nilfs_btree_alloc_path();
        if (path == NULL)
                return -ENOMEM;

        ret = nilfs_btree_do_lookup_last(btree, path, keyp, NULL);

        nilfs_btree_free_path(path);

        return ret;
}

static int nilfs_btree_check_delete(struct nilfs_bmap *btree, __u64 key)
{
        struct buffer_head *bh;
        struct nilfs_btree_node *root, *node;
        __u64 maxkey, nextmaxkey;
        __u64 ptr;
        int nchildren, ret;

        root = nilfs_btree_get_root(btree);
        nchildren = nilfs_btree_node_get_nchildren(root);
        if (unlikely(nchildren == 0))
                return 0;

        switch (nilfs_btree_height(btree)) {
        case 2:
                bh = NULL;
                node = root;
                break;
        case 3:
                if (nchildren > 1)
                        return 0;
                ptr = nilfs_btree_node_get_ptr(root, nchildren - 1,
                                               NILFS_BTREE_ROOT_NCHILDREN_MAX);
                ret = nilfs_btree_get_block(btree, ptr, &bh);
                if (ret < 0)
                        return ret;
                node = (struct nilfs_btree_node *)bh->b_data;
                nchildren = nilfs_btree_node_get_nchildren(node);
                break;
        default:
                return 0;
        }

        maxkey = nilfs_btree_node_get_key(node, nchildren - 1);
        nextmaxkey = (nchildren > 1) ?
                nilfs_btree_node_get_key(node, nchildren - 2) : 0;
        brelse(bh);

        return (maxkey == key) && (nextmaxkey < NILFS_BMAP_LARGE_LOW);
}

static int nilfs_btree_gather_data(struct nilfs_bmap *btree,
                                   __u64 *keys, __u64 *ptrs, int nitems)
{
        struct buffer_head *bh;
        struct nilfs_btree_node *node, *root;
        __le64 *dkeys;
        __le64 *dptrs;
        __u64 ptr;
        int nchildren, ncmax, i, ret;

        root = nilfs_btree_get_root(btree);
        switch (nilfs_btree_height(btree)) {
        case 2:
                bh = NULL;
                node = root;
                ncmax = NILFS_BTREE_ROOT_NCHILDREN_MAX;
                break;
        case 3:
                nchildren = nilfs_btree_node_get_nchildren(root);
                WARN_ON(nchildren > 1);
                ptr = nilfs_btree_node_get_ptr(root, nchildren - 1,
                                               NILFS_BTREE_ROOT_NCHILDREN_MAX);
                ret = nilfs_btree_get_block(btree, ptr, &bh);
                if (ret < 0)
                        return ret;
                node = (struct nilfs_btree_node *)bh->b_data;
                ncmax = nilfs_btree_nchildren_per_block(btree);
                break;
        default:
                node = NULL;
                return -EINVAL;
        }

        nchildren = nilfs_btree_node_get_nchildren(node);
        if (nchildren < nitems)
                nitems = nchildren;
        dkeys = nilfs_btree_node_dkeys(node);
        dptrs = nilfs_btree_node_dptrs(node, ncmax);
        for (i = 0; i < nitems; i++) {
                keys[i] = le64_to_cpu(dkeys[i]);
                ptrs[i] = le64_to_cpu(dptrs[i]);
        }

        brelse(bh);

        return nitems;
}

static int
nilfs_btree_prepare_convert_and_insert(struct nilfs_bmap *btree, __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 inode *dat = NULL;
        int ret;

        stats->bs_nblocks = 0;

        /* for data */
        /* cannot find near ptr */
        if (NILFS_BMAP_USE_VBN(btree)) {
                dreq->bpr_ptr = nilfs_btree_find_target_v(btree, NULL, key);
                dat = nilfs_bmap_get_dat(btree);
        }

        ret = nilfs_attach_btree_node_cache(&NILFS_BMAP_I(btree)->vfs_inode);
        if (ret < 0)
                return ret;

        ret = nilfs_bmap_prepare_alloc_ptr(btree, dreq, dat);
        if (ret < 0)
                return ret;

        *bhp = NULL;
        stats->bs_nblocks++;
        if (nreq != NULL) {
                nreq->bpr_ptr = dreq->bpr_ptr + 1;
                ret = nilfs_bmap_prepare_alloc_ptr(btree, nreq, dat);
                if (ret < 0)
                        goto err_out_dreq;

                ret = nilfs_btree_get_new_block(btree, nreq->bpr_ptr, &bh);
                if (ret < 0)
                        goto err_out_nreq;

                *bhp = bh;
                stats->bs_nblocks++;
        }

        /* success */
        return 0;

        /* error */
 err_out_nreq:
        nilfs_bmap_abort_alloc_ptr(btree, nreq, dat);
 err_out_dreq:
        nilfs_bmap_abort_alloc_ptr(btree, dreq, dat);
        stats->bs_nblocks = 0;
        return ret;

}

static void
nilfs_btree_commit_convert_and_insert(struct nilfs_bmap *btree,
                                      __u64 key, __u64 ptr,
                                      const __u64 *keys, const __u64 *ptrs,
                                      int n,
                                      union nilfs_bmap_ptr_req *dreq,
                                      union nilfs_bmap_ptr_req *nreq,
                                      struct buffer_head *bh)
{
        struct nilfs_btree_node *node;
        struct inode *dat;
        __u64 tmpptr;
        int ncblk;

        /* free resources */
        if (btree->b_ops->bop_clear != NULL)
                btree->b_ops->bop_clear(btree);

        /* ptr must be a pointer to a buffer head. */
        set_buffer_nilfs_volatile((struct buffer_head *)((unsigned long)ptr));

        /* convert and insert */
        dat = NILFS_BMAP_USE_VBN(btree) ? nilfs_bmap_get_dat(btree) : NULL;
        __nilfs_btree_init(btree);
        if (nreq != NULL) {
                nilfs_bmap_commit_alloc_ptr(btree, dreq, dat);
                nilfs_bmap_commit_alloc_ptr(btree, nreq, dat);

                /* create child node at level 1 */
                node = (struct nilfs_btree_node *)bh->b_data;
                ncblk = nilfs_btree_nchildren_per_block(btree);
                nilfs_btree_node_init(node, 0, 1, n, ncblk, keys, ptrs);
                nilfs_btree_node_insert(node, n, key, dreq->bpr_ptr, ncblk);
                if (!buffer_dirty(bh))
                        mark_buffer_dirty(bh);
                if (!nilfs_bmap_dirty(btree))
                        nilfs_bmap_set_dirty(btree);

                brelse(bh);

                /* create root node at level 2 */
                node = nilfs_btree_get_root(btree);
                tmpptr = nreq->bpr_ptr;
                nilfs_btree_node_init(node, NILFS_BTREE_NODE_ROOT, 2, 1,
                                      NILFS_BTREE_ROOT_NCHILDREN_MAX,
                                      &keys[0], &tmpptr);
        } else {
                nilfs_bmap_commit_alloc_ptr(btree, dreq, dat);

                /* create root node at level 1 */
                node = nilfs_btree_get_root(btree);
                nilfs_btree_node_init(node, NILFS_BTREE_NODE_ROOT, 1, n,
                                      NILFS_BTREE_ROOT_NCHILDREN_MAX,
                                      keys, ptrs);
                nilfs_btree_node_insert(node, n, key, dreq->bpr_ptr,
                                        NILFS_BTREE_ROOT_NCHILDREN_MAX);
                if (!nilfs_bmap_dirty(btree))
                        nilfs_bmap_set_dirty(btree);
        }

        if (NILFS_BMAP_USE_VBN(btree))
                nilfs_bmap_set_target_v(btree, key, dreq->bpr_ptr);
}

/**
 * nilfs_btree_convert_and_insert - Convert and insert entries into a B-tree
 * @btree: NILFS B-tree structure
 * @key: Key of the new entry to be inserted
 * @ptr: Pointer (block number) associated with the key to be inserted
 * @keys: Array of keys to be inserted in addition to @key
 * @ptrs: Array of pointers associated with @keys
 * @n: Number of keys and pointers in @keys and @ptrs
 *
 * This function is used to insert a new entry specified by @key and @ptr,
 * along with additional entries specified by @keys and @ptrs arrays, into a
 * NILFS B-tree.
 * It prepares the necessary changes by allocating the required blocks and any
 * necessary intermediate nodes. It converts configurations from other forms of
 * block mapping (the one that currently exists is direct mapping) to a B-tree.
 *
 * Return: 0 on success or a negative error code on failure.
 */
int nilfs_btree_convert_and_insert(struct nilfs_bmap *btree,
                                   __u64 key, __u64 ptr,
                                   const __u64 *keys, const __u64 *ptrs, int n)
{
        struct buffer_head *bh = NULL;
        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(
                           nilfs_btree_node_size(btree))) {
                di = &dreq;
                ni = &nreq;
        } else {
                di = NULL;
                ni = NULL;
                BUG();
        }

        ret = nilfs_btree_prepare_convert_and_insert(btree, key, di, ni, &bh,
                                                     &stats);
        if (ret < 0)
                return ret;
        nilfs_btree_commit_convert_and_insert(btree, key, ptr, keys, ptrs, n,
                                              di, ni, bh);
        nilfs_inode_add_blocks(btree->b_inode, stats.bs_nblocks);
        return 0;
}

static int nilfs_btree_propagate_p(struct nilfs_bmap *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))
                mark_buffer_dirty(path[level].bp_bh);

        return 0;
}

static int nilfs_btree_prepare_update_v(struct nilfs_bmap *btree,
                                        struct nilfs_btree_path *path,
                                        int level, struct inode *dat)
{
        struct nilfs_btree_node *parent;
        int ncmax, ret;

        parent = nilfs_btree_get_node(btree, path, level + 1, &ncmax);
        path[level].bp_oldreq.bpr_ptr =
                nilfs_btree_node_get_ptr(parent, path[level + 1].bp_index,
                                         ncmax);
        path[level].bp_newreq.bpr_ptr = path[level].bp_oldreq.bpr_ptr + 1;
        ret = nilfs_dat_prepare_update(dat, &path[level].bp_oldreq.bpr_req,
                                       &path[level].bp_newreq.bpr_req);
        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)->i_assoc_inode->i_mapping,
                        &path[level].bp_ctxt);
                if (ret < 0) {
                        nilfs_dat_abort_update(dat,
                                               &path[level].bp_oldreq.bpr_req,
                                               &path[level].bp_newreq.bpr_req);
                        return ret;
                }
        }

        return 0;
}

static void nilfs_btree_commit_update_v(struct nilfs_bmap *btree,
                                        struct nilfs_btree_path *path,
                                        int level, struct inode *dat)
{
        struct nilfs_btree_node *parent;
        int ncmax;

        nilfs_dat_commit_update(dat, &path[level].bp_oldreq.bpr_req,
                                &path[level].bp_newreq.bpr_req,
                                btree->b_ptr_type == NILFS_BMAP_PTR_VS);

        if (buffer_nilfs_node(path[level].bp_bh)) {
                nilfs_btnode_commit_change_key(
                        NILFS_BMAP_I(btree)->i_assoc_inode->i_mapping,
                        &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, &ncmax);
        nilfs_btree_node_set_ptr(parent, path[level + 1].bp_index,
                                 path[level].bp_newreq.bpr_ptr, ncmax);
}

static void nilfs_btree_abort_update_v(struct nilfs_bmap *btree,
                                       struct nilfs_btree_path *path,
                                       int level, struct inode *dat)
{
        nilfs_dat_abort_update(dat, &path[level].bp_oldreq.bpr_req,
                               &path[level].bp_newreq.bpr_req);
        if (buffer_nilfs_node(path[level].bp_bh))
                nilfs_btnode_abort_change_key(
                        NILFS_BMAP_I(btree)->i_assoc_inode->i_mapping,
                        &path[level].bp_ctxt);
}

static int nilfs_btree_prepare_propagate_v(struct nilfs_bmap *btree,
                                           struct nilfs_btree_path *path,
                                           int minlevel, int *maxlevelp,
                                           struct inode *dat)
{
        int level, ret;

        level = minlevel;
        if (!buffer_nilfs_volatile(path[level].bp_bh)) {
                ret = nilfs_btree_prepare_update_v(btree, path, level, dat);
                if (ret < 0)
                        return ret;
        }
        while ((++level < nilfs_btree_height(btree) - 1) &&
               !buffer_dirty(path[level].bp_bh)) {

                WARN_ON(buffer_nilfs_volatile(path[level].bp_bh));
                ret = nilfs_btree_prepare_update_v(btree, path, level, dat);
                if (ret < 0)
                        goto out;
        }

        /* success */
        *maxlevelp = level - 1;
        return 0;

        /* error */
 out:
        while (--level > minlevel)
                nilfs_btree_abort_update_v(btree, path, level, dat);
        if (!buffer_nilfs_volatile(path[level].bp_bh))
                nilfs_btree_abort_update_v(btree, path, level, dat);
        return ret;
}

static void nilfs_btree_commit_propagate_v(struct nilfs_bmap *btree,
                                           struct nilfs_btree_path *path,
                                           int minlevel, int maxlevel,
                                           struct buffer_head *bh,
                                           struct inode *dat)
{
        int level;

        if (!buffer_nilfs_volatile(path[minlevel].bp_bh))
                nilfs_btree_commit_update_v(btree, path, minlevel, dat);

        for (level = minlevel + 1; level <= maxlevel; level++)
                nilfs_btree_commit_update_v(btree, path, level, dat);
}

static int nilfs_btree_propagate_v(struct nilfs_bmap *btree,
                                   struct nilfs_btree_path *path,
                                   int level, struct buffer_head *bh)
{
        int maxlevel = 0, ret;
        struct nilfs_btree_node *parent;
        struct inode *dat = nilfs_bmap_get_dat(btree);
        __u64 ptr;
        int ncmax;

        get_bh(bh);
        path[level].bp_bh = bh;
        ret = nilfs_btree_prepare_propagate_v(btree, path, level, &maxlevel,
                                              dat);
        if (ret < 0)
                goto out;

        if (buffer_nilfs_volatile(path[level].bp_bh)) {
                parent = nilfs_btree_get_node(btree, path, level + 1, &ncmax);
                ptr = nilfs_btree_node_get_ptr(parent,
                                               path[level + 1].bp_index,
                                               ncmax);
                ret = nilfs_dat_mark_dirty(dat, ptr);
                if (ret < 0)
                        goto out;
        }

        nilfs_btree_commit_propagate_v(btree, path, level, maxlevel, bh, dat);

 out:
        brelse(path[level].bp_bh);
        path[level].bp_bh = NULL;
        return ret;
}

static int nilfs_btree_propagate(struct nilfs_bmap *btree,
                                 struct buffer_head *bh)
{
        struct nilfs_btree_path *path;
        struct nilfs_btree_node *node;
        __u64 key;
        int level, ret;

        WARN_ON(!buffer_dirty(bh));

        path = nilfs_btree_alloc_path();
        if (path == NULL)
                return -ENOMEM;

        if (buffer_nilfs_node(bh)) {
                node = (struct nilfs_btree_node *)bh->b_data;
                key = nilfs_btree_node_get_key(node, 0);
                level = nilfs_btree_node_get_level(node);
        } else {
                key = nilfs_bmap_data_get_key(btree, bh);
                level = NILFS_BTREE_LEVEL_DATA;
        }

        ret = nilfs_btree_do_lookup(btree, path, key, NULL, level + 1, 0);
        if (ret < 0) {
                if (unlikely(ret == -ENOENT)) {
                        nilfs_crit(btree->b_inode->i_sb,
                                   "writing node/leaf block does not appear in b-tree (ino=%lu) at key=%llu, level=%d",
                                   btree->b_inode->i_ino,
                                   (unsigned long long)key, level);
                        ret = -EINVAL;
                }
                goto out;
        }

        ret = NILFS_BMAP_USE_VBN(btree) ?
                nilfs_btree_propagate_v(btree, path, level, bh) :
                nilfs_btree_propagate_p(btree, path, level, bh);

 out:
        nilfs_btree_free_path(path);

        return ret;
}

static int nilfs_btree_propagate_gc(struct nilfs_bmap *btree,
                                    struct buffer_head *bh)
{
        return nilfs_dat_mark_dirty(nilfs_bmap_get_dat(btree), bh->b_blocknr);
}

static void nilfs_btree_add_dirty_buffer(struct nilfs_bmap *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(node, 0);
        level = nilfs_btree_node_get_level(node);
        if (level < NILFS_BTREE_LEVEL_NODE_MIN ||
            level >= NILFS_BTREE_LEVEL_MAX) {
                dump_stack();
                nilfs_warn(btree->b_inode->i_sb,
                           "invalid btree level: %d (key=%llu, ino=%lu, blocknr=%llu)",
                           level, (unsigned long long)key,
                           btree->b_inode->i_ino,
                           (unsigned long long)bh->b_blocknr);
                return;
        }

        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(cnode, 0);
                if (key < ckey)
                        break;
        }
        list_add_tail(&bh->b_assoc_buffers, head);
}

static void nilfs_btree_lookup_dirty_buffers(struct nilfs_bmap *btree,
                                             struct list_head *listp)
{
        struct inode *btnc_inode = NILFS_BMAP_I(btree)->i_assoc_inode;
        struct address_space *btcache = btnc_inode->i_mapping;
        struct list_head lists[NILFS_BTREE_LEVEL_MAX];
        struct folio_batch fbatch;
        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]);

        folio_batch_init(&fbatch);

        while (filemap_get_folios_tag(btcache, &index, (pgoff_t)-1,
                                PAGECACHE_TAG_DIRTY, &fbatch)) {
                for (i = 0; i < folio_batch_count(&fbatch); i++) {
                        bh = head = folio_buffers(fbatch.folios[i]);
                        do {
                                if (buffer_dirty(bh))
                                        nilfs_btree_add_dirty_buffer(btree,
                                                                     lists, bh);
                        } while ((bh = bh->b_this_page) != head);
                }
                folio_batch_release(&fbatch);
                cond_resched();
        }

        for (level = NILFS_BTREE_LEVEL_NODE_MIN;
             level < NILFS_BTREE_LEVEL_MAX;
             level++)
                list_splice_tail(&lists[level], listp);
}

static int nilfs_btree_assign_p(struct nilfs_bmap *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 ncmax, ret;

        parent = nilfs_btree_get_node(btree, path, level + 1, &ncmax);
        ptr = nilfs_btree_node_get_ptr(parent, path[level + 1].bp_index,
                                       ncmax);
        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)->i_assoc_inode->i_mapping,
                        &path[level].bp_ctxt);
                if (ret < 0)
                        return ret;
                nilfs_btnode_commit_change_key(
                        NILFS_BMAP_I(btree)->i_assoc_inode->i_mapping,
                        &path[level].bp_ctxt);
                *bh = path[level].bp_ctxt.bh;
        }

        nilfs_btree_node_set_ptr(parent, path[level + 1].bp_index, blocknr,
                                 ncmax);

        key = nilfs_btree_node_get_key(parent, path[level + 1].bp_index);
        /* on-disk format */
        binfo->bi_dat.bi_blkoff = cpu_to_le64(key);
        binfo->bi_dat.bi_level = level;
        memset(binfo->bi_dat.bi_pad, 0, sizeof(binfo->bi_dat.bi_pad));

        return 0;
}

static int nilfs_btree_assign_v(struct nilfs_bmap *btree,
                                struct nilfs_btree_path *path,
                                int level,
                                struct buffer_head **bh,
                                sector_t blocknr,
                                union nilfs_binfo *binfo)
{
        struct nilfs_btree_node *parent;
        struct inode *dat = nilfs_bmap_get_dat(btree);
        __u64 key;
        __u64 ptr;
        union nilfs_bmap_ptr_req req;
        int ncmax, ret;

        parent = nilfs_btree_get_node(btree, path, level + 1, &ncmax);
        ptr = nilfs_btree_node_get_ptr(parent, path[level + 1].bp_index,
                                       ncmax);
        req.bpr_ptr = ptr;
        ret = nilfs_dat_prepare_start(dat, &req.bpr_req);
        if (ret < 0)
                return ret;
        nilfs_dat_commit_start(dat, &req.bpr_req, blocknr);

        key = nilfs_btree_node_get_key(parent, path[level + 1].bp_index);
        /* on-disk format */
        binfo->bi_v.bi_vblocknr = cpu_to_le64(ptr);
        binfo->bi_v.bi_blkoff = cpu_to_le64(key);

        return 0;
}

static int nilfs_btree_assign(struct nilfs_bmap *btree,
                              struct buffer_head **bh,
                              sector_t blocknr,
                              union nilfs_binfo *binfo)
{
        struct nilfs_btree_path *path;
        struct nilfs_btree_node *node;
        __u64 key;
        int level, ret;

        path = nilfs_btree_alloc_path();
        if (path == NULL)
                return -ENOMEM;

        if (buffer_nilfs_node(*bh)) {
                node = (struct nilfs_btree_node *)(*bh)->b_data;
                key = nilfs_btree_node_get_key(node, 0);
                level = nilfs_btree_node_get_level(node);
        } else {
                key = nilfs_bmap_data_get_key(btree, *bh);
                level = NILFS_BTREE_LEVEL_DATA;
        }

        ret = nilfs_btree_do_lookup(btree, path, key, NULL, level + 1, 0);
        if (ret < 0) {
                WARN_ON(ret == -ENOENT);
                goto out;
        }

        ret = NILFS_BMAP_USE_VBN(btree) ?
                nilfs_btree_assign_v(btree, path, level, bh, blocknr, binfo) :
                nilfs_btree_assign_p(btree, path, level, bh, blocknr, binfo);

 out:
        nilfs_btree_free_path(path);

        return ret;
}

static int nilfs_btree_assign_gc(struct nilfs_bmap *btree,
                                 struct buffer_head **bh,
                                 sector_t blocknr,
                                 union nilfs_binfo *binfo)
{
        struct nilfs_btree_node *node;
        __u64 key;
        int ret;

        ret = nilfs_dat_move(nilfs_bmap_get_dat(btree), (*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(node, 0);
        } else
                key = nilfs_bmap_data_get_key(btree, *bh);

        /* on-disk format */
        binfo->bi_v.bi_vblocknr = cpu_to_le64((*bh)->b_blocknr);
        binfo->bi_v.bi_blkoff = cpu_to_le64(key);

        return 0;
}

static int nilfs_btree_mark(struct nilfs_bmap *btree, __u64 key, int level)
{
        struct buffer_head *bh;
        struct nilfs_btree_path *path;
        __u64 ptr;
        int ret;

        path = nilfs_btree_alloc_path();
        if (path == NULL)
                return -ENOMEM;

        ret = nilfs_btree_do_lookup(btree, path, key, &ptr, level + 1, 0);
        if (ret < 0) {
                WARN_ON(ret == -ENOENT);
                goto out;
        }
        ret = nilfs_btree_get_block(btree, ptr, &bh);
        if (ret < 0) {
                WARN_ON(ret == -ENOENT);
                goto out;
        }

        if (!buffer_dirty(bh))
                mark_buffer_dirty(bh);
        brelse(bh);
        if (!nilfs_bmap_dirty(btree))
                nilfs_bmap_set_dirty(btree);

 out:
        nilfs_btree_free_path(path);
        return ret;
}

static const struct nilfs_bmap_operations nilfs_btree_ops = {
        .bop_lookup             =       nilfs_btree_lookup,
        .bop_lookup_contig      =       nilfs_btree_lookup_contig,
        .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_seek_key           =       nilfs_btree_seek_key,
        .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_lookup_contig      =       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_seek_key           =       NULL,
        .bop_last_key           =       NULL,

        .bop_check_insert       =       NULL,
        .bop_check_delete       =       NULL,
        .bop_gather_data        =       NULL,
};

static void __nilfs_btree_init(struct nilfs_bmap *bmap)
{
        bmap->b_ops = &nilfs_btree_ops;
        bmap->b_nchildren_per_block =
                NILFS_BTREE_NODE_NCHILDREN_MAX(nilfs_btree_node_size(bmap));
}

int nilfs_btree_init(struct nilfs_bmap *bmap)
{
        int ret = 0;

        __nilfs_btree_init(bmap);

        if (nilfs_btree_root_broken(nilfs_btree_get_root(bmap), bmap->b_inode))
                ret = -EIO;
        else
                ret = nilfs_attach_btree_node_cache(
                        &NILFS_BMAP_I(bmap)->vfs_inode);

        return ret;
}

void nilfs_btree_init_gc(struct nilfs_bmap *bmap)
{
        bmap->b_ops = &nilfs_btree_ops_gc;
        bmap->b_nchildren_per_block =
                NILFS_BTREE_NODE_NCHILDREN_MAX(nilfs_btree_node_size(bmap));
}