Btrfs: Do more extensive readahead during tree searches

[deliverable/linux.git] / fs / btrfs / ctree.c

/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * 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., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"

static int split_node(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root, struct btrfs_path *path, int level);
static int split_leaf(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root, struct btrfs_key *ins_key,
                      struct btrfs_path *path, int data_size);
static int push_node_left(struct btrfs_trans_handle *trans, struct btrfs_root
                          *root, struct buffer_head *dst, struct buffer_head
                          *src);
static int balance_node_right(struct btrfs_trans_handle *trans, struct
                              btrfs_root *root, struct buffer_head *dst_buf,
                              struct buffer_head *src_buf);
static int del_ptr(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                   struct btrfs_path *path, int level, int slot);

inline void btrfs_init_path(struct btrfs_path *p)
{
        memset(p, 0, sizeof(*p));
}

struct btrfs_path *btrfs_alloc_path(void)
{
        struct btrfs_path *path;
        path = kmem_cache_alloc(btrfs_path_cachep, GFP_NOFS);
        if (path) {
                btrfs_init_path(path);
                path->reada = 1;
        }
        return path;
}

void btrfs_free_path(struct btrfs_path *p)
{
        btrfs_release_path(NULL, p);
        kmem_cache_free(btrfs_path_cachep, p);
}

void btrfs_release_path(struct btrfs_root *root, struct btrfs_path *p)
{
        int i;
        for (i = 0; i < BTRFS_MAX_LEVEL; i++) {
                if (!p->nodes[i])
                        break;
                btrfs_block_release(root, p->nodes[i]);
        }
        memset(p, 0, sizeof(*p));
}

static int __btrfs_cow_block(struct btrfs_trans_handle *trans, struct btrfs_root
                           *root, struct buffer_head *buf, struct buffer_head
                           *parent, int parent_slot, struct buffer_head
                           **cow_ret, u64 search_start, u64 empty_size)
{
        struct buffer_head *cow;
        struct btrfs_node *cow_node;
        int ret = 0;
        int different_trans = 0;

        WARN_ON(root->ref_cows && trans->transid != root->last_trans);
        WARN_ON(!buffer_uptodate(buf));
        cow = btrfs_alloc_free_block(trans, root, search_start, empty_size);
        if (IS_ERR(cow))
                return PTR_ERR(cow);

        cow_node = btrfs_buffer_node(cow);
        if (buf->b_size != root->blocksize || cow->b_size != root->blocksize)
                WARN_ON(1);

        memcpy(cow_node, btrfs_buffer_node(buf), root->blocksize);
        btrfs_set_header_blocknr(&cow_node->header, bh_blocknr(cow));
        btrfs_set_header_generation(&cow_node->header, trans->transid);
        btrfs_set_header_owner(&cow_node->header, root->root_key.objectid);

        WARN_ON(btrfs_header_generation(btrfs_buffer_header(buf)) >
                trans->transid);
        if (btrfs_header_generation(btrfs_buffer_header(buf)) !=
                                    trans->transid) {
                different_trans = 1;
                ret = btrfs_inc_ref(trans, root, buf);
                if (ret)
                        return ret;
        } else {
                clean_tree_block(trans, root, buf);
        }

        if (buf == root->node) {
                root->node = cow;
                get_bh(cow);
                if (buf != root->commit_root) {
                        btrfs_free_extent(trans, root, bh_blocknr(buf), 1, 1);
                }
                btrfs_block_release(root, buf);
        } else {
                btrfs_set_node_blockptr(btrfs_buffer_node(parent), parent_slot,
                                        bh_blocknr(cow));
                btrfs_mark_buffer_dirty(parent);
                WARN_ON(btrfs_header_generation(btrfs_buffer_header(parent)) !=
                                    trans->transid);
                btrfs_free_extent(trans, root, bh_blocknr(buf), 1, 1);
        }
        btrfs_block_release(root, buf);
        btrfs_mark_buffer_dirty(cow);
        *cow_ret = cow;
        return 0;
}

int btrfs_cow_block(struct btrfs_trans_handle *trans, struct btrfs_root
                           *root, struct buffer_head *buf, struct buffer_head
                           *parent, int parent_slot, struct buffer_head
                           **cow_ret)
{
        u64 search_start;
        if (trans->transaction != root->fs_info->running_transaction) {
                printk(KERN_CRIT "trans %Lu running %Lu\n", trans->transid,
                       root->fs_info->running_transaction->transid);
                WARN_ON(1);
        }
        if (trans->transid != root->fs_info->generation) {
                printk(KERN_CRIT "trans %Lu running %Lu\n", trans->transid,
                       root->fs_info->generation);
                WARN_ON(1);
        }
        if (btrfs_header_generation(btrfs_buffer_header(buf)) ==
                                    trans->transid) {
                *cow_ret = buf;
                return 0;
        }

        search_start = bh_blocknr(buf) & ~((u64)65535);
        return __btrfs_cow_block(trans, root, buf, parent,
                                 parent_slot, cow_ret, search_start, 0);
}

static int close_blocks(u64 blocknr, u64 other)
{
        if (blocknr < other && other - blocknr < 8)
                return 1;
        if (blocknr > other && blocknr - other < 8)
                return 1;
        return 0;
}

static int should_defrag_leaf(struct buffer_head *bh)
{
        struct btrfs_leaf *leaf = btrfs_buffer_leaf(bh);
        struct btrfs_disk_key *key;
        u32 nritems;

        if (buffer_defrag(bh))
                return 1;

        nritems = btrfs_header_nritems(&leaf->header);
        if (nritems == 0)
                return 0;

        key = &leaf->items[0].key;
        if (btrfs_disk_key_type(key) == BTRFS_DIR_ITEM_KEY)
                return 1;

        key = &leaf->items[nritems-1].key;
        if (btrfs_disk_key_type(key) == BTRFS_DIR_ITEM_KEY)
                return 1;
        if (nritems > 4) {
                key = &leaf->items[nritems/2].key;
                if (btrfs_disk_key_type(key) == BTRFS_DIR_ITEM_KEY)
                        return 1;
        }
        return 0;
}

int btrfs_realloc_node(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root, struct buffer_head *parent,
                       int cache_only, u64 *last_ret)
{
        struct btrfs_node *parent_node;
        struct buffer_head *cur_bh;
        struct buffer_head *tmp_bh;
        u64 blocknr;
        u64 search_start = *last_ret;
        u64 last_block = 0;
        u64 other;
        u32 parent_nritems;
        int start_slot;
        int end_slot;
        int i;
        int err = 0;
        int parent_level;

        if (trans->transaction != root->fs_info->running_transaction) {
                printk(KERN_CRIT "trans %Lu running %Lu\n", trans->transid,
                       root->fs_info->running_transaction->transid);
                WARN_ON(1);
        }
        if (trans->transid != root->fs_info->generation) {
                printk(KERN_CRIT "trans %Lu running %Lu\n", trans->transid,
                       root->fs_info->generation);
                WARN_ON(1);
        }
        parent_node = btrfs_buffer_node(parent);
        parent_nritems = btrfs_header_nritems(&parent_node->header);
        parent_level = btrfs_header_level(&parent_node->header);

        start_slot = 0;
        end_slot = parent_nritems;

        if (parent_nritems == 1)
                return 0;

        for (i = start_slot; i < end_slot; i++) {
                int close = 1;
                blocknr = btrfs_node_blockptr(parent_node, i);
                if (last_block == 0)
                        last_block = blocknr;
                if (i > 0) {
                        other = btrfs_node_blockptr(parent_node, i - 1);
                        close = close_blocks(blocknr, other);
                }
                if (close && i < end_slot - 1) {
                        other = btrfs_node_blockptr(parent_node, i + 1);
                        close = close_blocks(blocknr, other);
                }
                if (close) {
                        last_block = blocknr;
                        continue;
                }

                cur_bh = btrfs_find_tree_block(root, blocknr);
                if (!cur_bh || !buffer_uptodate(cur_bh) ||
                    buffer_locked(cur_bh) ||
                    (parent_level != 1 && !buffer_defrag(cur_bh)) ||
                    (parent_level == 1 && !should_defrag_leaf(cur_bh))) {
                        if (cache_only) {
                                brelse(cur_bh);
                                continue;
                        }
                        if (!cur_bh || !buffer_uptodate(cur_bh) ||
                            buffer_locked(cur_bh)) {
                                brelse(cur_bh);
                                cur_bh = read_tree_block(root, blocknr);
                        }
                }
                if (search_start == 0)
                        search_start = last_block & ~((u64)65535);

                err = __btrfs_cow_block(trans, root, cur_bh, parent, i,
                                        &tmp_bh, search_start,
                                        min(8, end_slot - i));
                if (err)
                        break;
                search_start = bh_blocknr(tmp_bh);
                *last_ret = search_start;
                if (parent_level == 1)
                        clear_buffer_defrag(tmp_bh);
                brelse(tmp_bh);
        }
        return err;
}

/*
 * The leaf data grows from end-to-front in the node.
 * this returns the address of the start of the last item,
 * which is the stop of the leaf data stack
 */
static inline unsigned int leaf_data_end(struct btrfs_root *root,
                                         struct btrfs_leaf *leaf)
{
        u32 nr = btrfs_header_nritems(&leaf->header);
        if (nr == 0)
                return BTRFS_LEAF_DATA_SIZE(root);
        return btrfs_item_offset(leaf->items + nr - 1);
}

/*
 * compare two keys in a memcmp fashion
 */
static int comp_keys(struct btrfs_disk_key *disk, struct btrfs_key *k2)
{
        struct btrfs_key k1;

        btrfs_disk_key_to_cpu(&k1, disk);

        if (k1.objectid > k2->objectid)
                return 1;
        if (k1.objectid < k2->objectid)
                return -1;
        if (k1.flags > k2->flags)
                return 1;
        if (k1.flags < k2->flags)
                return -1;
        if (k1.offset > k2->offset)
                return 1;
        if (k1.offset < k2->offset)
                return -1;
        return 0;
}

static int check_node(struct btrfs_root *root, struct btrfs_path *path,
                      int level)
{
        struct btrfs_node *parent = NULL;
        struct btrfs_node *node = btrfs_buffer_node(path->nodes[level]);
        int parent_slot;
        int slot;
        struct btrfs_key cpukey;
        u32 nritems = btrfs_header_nritems(&node->header);

        if (path->nodes[level + 1])
                parent = btrfs_buffer_node(path->nodes[level + 1]);

        slot = path->slots[level];
        BUG_ON(!buffer_uptodate(path->nodes[level]));
        BUG_ON(nritems == 0);
        if (parent) {
                struct btrfs_disk_key *parent_key;

                parent_slot = path->slots[level + 1];
                parent_key = &parent->ptrs[parent_slot].key;
                BUG_ON(memcmp(parent_key, &node->ptrs[0].key,
                              sizeof(struct btrfs_disk_key)));
                BUG_ON(btrfs_node_blockptr(parent, parent_slot) !=
                       btrfs_header_blocknr(&node->header));
        }
        BUG_ON(nritems > BTRFS_NODEPTRS_PER_BLOCK(root));
        if (slot != 0) {
                btrfs_disk_key_to_cpu(&cpukey, &node->ptrs[slot - 1].key);
                BUG_ON(comp_keys(&node->ptrs[slot].key, &cpukey) <= 0);
        }
        if (slot < nritems - 1) {
                btrfs_disk_key_to_cpu(&cpukey, &node->ptrs[slot + 1].key);
                BUG_ON(comp_keys(&node->ptrs[slot].key, &cpukey) >= 0);
        }
        return 0;
}

static int check_leaf(struct btrfs_root *root, struct btrfs_path *path,
                      int level)
{
        struct btrfs_leaf *leaf = btrfs_buffer_leaf(path->nodes[level]);
        struct btrfs_node *parent = NULL;
        int parent_slot;
        int slot = path->slots[0];
        struct btrfs_key cpukey;

        u32 nritems = btrfs_header_nritems(&leaf->header);

        if (path->nodes[level + 1])
                parent = btrfs_buffer_node(path->nodes[level + 1]);

        BUG_ON(btrfs_leaf_free_space(root, leaf) < 0);

        if (nritems == 0)
                return 0;

        if (parent) {
                struct btrfs_disk_key *parent_key;

                parent_slot = path->slots[level + 1];
                parent_key = &parent->ptrs[parent_slot].key;

                BUG_ON(memcmp(parent_key, &leaf->items[0].key,
                       sizeof(struct btrfs_disk_key)));
                BUG_ON(btrfs_node_blockptr(parent, parent_slot) !=
                       btrfs_header_blocknr(&leaf->header));
        }
        if (slot != 0) {
                btrfs_disk_key_to_cpu(&cpukey, &leaf->items[slot - 1].key);
                BUG_ON(comp_keys(&leaf->items[slot].key, &cpukey) <= 0);
                BUG_ON(btrfs_item_offset(leaf->items + slot - 1) !=
                        btrfs_item_end(leaf->items + slot));
        }
        if (slot < nritems - 1) {
                btrfs_disk_key_to_cpu(&cpukey, &leaf->items[slot + 1].key);
                BUG_ON(comp_keys(&leaf->items[slot].key, &cpukey) >= 0);
                BUG_ON(btrfs_item_offset(leaf->items + slot) !=
                        btrfs_item_end(leaf->items + slot + 1));
        }
        BUG_ON(btrfs_item_offset(leaf->items) +
               btrfs_item_size(leaf->items) != BTRFS_LEAF_DATA_SIZE(root));
        return 0;
}

static int check_block(struct btrfs_root *root, struct btrfs_path *path,
                        int level)
{
        struct btrfs_node *node = btrfs_buffer_node(path->nodes[level]);
        if (memcmp(node->header.fsid, root->fs_info->disk_super->fsid,
                   sizeof(node->header.fsid)))
                BUG();
        if (level == 0)
                return check_leaf(root, path, level);
        return check_node(root, path, level);
}

/*
 * search for key in the array p.  items p are item_size apart
 * and there are 'max' items in p
 * the slot in the array is returned via slot, and it points to
 * the place where you would insert key if it is not found in
 * the array.
 *
 * slot may point to max if the key is bigger than all of the keys
 */
static int generic_bin_search(char *p, int item_size, struct btrfs_key *key,
                       int max, int *slot)
{
        int low = 0;
        int high = max;
        int mid;
        int ret;
        struct btrfs_disk_key *tmp;

        while(low < high) {
                mid = (low + high) / 2;
                tmp = (struct btrfs_disk_key *)(p + mid * item_size);
                ret = comp_keys(tmp, key);

                if (ret < 0)
                        low = mid + 1;
                else if (ret > 0)
                        high = mid;
                else {
                        *slot = mid;
                        return 0;
                }
        }
        *slot = low;
        return 1;
}

/*
 * simple bin_search frontend that does the right thing for
 * leaves vs nodes
 */
static int bin_search(struct btrfs_node *c, struct btrfs_key *key, int *slot)
{
        if (btrfs_is_leaf(c)) {
                struct btrfs_leaf *l = (struct btrfs_leaf *)c;
                return generic_bin_search((void *)l->items,
                                          sizeof(struct btrfs_item),
                                          key, btrfs_header_nritems(&c->header),
                                          slot);
        } else {
                return generic_bin_search((void *)c->ptrs,
                                          sizeof(struct btrfs_key_ptr),
                                          key, btrfs_header_nritems(&c->header),
                                          slot);
        }
        return -1;
}

static struct buffer_head *read_node_slot(struct btrfs_root *root,
                                   struct buffer_head *parent_buf,
                                   int slot)
{
        struct btrfs_node *node = btrfs_buffer_node(parent_buf);
        if (slot < 0)
                return NULL;
        if (slot >= btrfs_header_nritems(&node->header))
                return NULL;
        return read_tree_block(root, btrfs_node_blockptr(node, slot));
}

static int balance_level(struct btrfs_trans_handle *trans, struct btrfs_root
                         *root, struct btrfs_path *path, int level)
{
        struct buffer_head *right_buf;
        struct buffer_head *mid_buf;
        struct buffer_head *left_buf;
        struct buffer_head *parent_buf = NULL;
        struct btrfs_node *right = NULL;
        struct btrfs_node *mid;
        struct btrfs_node *left = NULL;
        struct btrfs_node *parent = NULL;
        int ret = 0;
        int wret;
        int pslot;
        int orig_slot = path->slots[level];
        int err_on_enospc = 0;
        u64 orig_ptr;

        if (level == 0)
                return 0;

        mid_buf = path->nodes[level];
        mid = btrfs_buffer_node(mid_buf);
        orig_ptr = btrfs_node_blockptr(mid, orig_slot);

        if (level < BTRFS_MAX_LEVEL - 1)
                parent_buf = path->nodes[level + 1];
        pslot = path->slots[level + 1];

        /*
         * deal with the case where there is only one pointer in the root
         * by promoting the node below to a root
         */
        if (!parent_buf) {
                struct buffer_head *child;
                u64 blocknr = bh_blocknr(mid_buf);

                if (btrfs_header_nritems(&mid->header) != 1)
                        return 0;

                /* promote the child to a root */
                child = read_node_slot(root, mid_buf, 0);
                BUG_ON(!child);
                root->node = child;
                path->nodes[level] = NULL;
                clean_tree_block(trans, root, mid_buf);
                wait_on_buffer(mid_buf);
                /* once for the path */
                btrfs_block_release(root, mid_buf);
                /* once for the root ptr */
                btrfs_block_release(root, mid_buf);
                return btrfs_free_extent(trans, root, blocknr, 1, 1);
        }
        parent = btrfs_buffer_node(parent_buf);

        if (btrfs_header_nritems(&mid->header) >
            BTRFS_NODEPTRS_PER_BLOCK(root) / 4)
                return 0;

        if (btrfs_header_nritems(&mid->header) < 2)
                err_on_enospc = 1;

        left_buf = read_node_slot(root, parent_buf, pslot - 1);
        if (left_buf) {
                wret = btrfs_cow_block(trans, root, left_buf,
                                       parent_buf, pslot - 1, &left_buf);
                if (wret) {
                        ret = wret;
                        goto enospc;
                }
        }
        right_buf = read_node_slot(root, parent_buf, pslot + 1);
        if (right_buf) {
                wret = btrfs_cow_block(trans, root, right_buf,
                                       parent_buf, pslot + 1, &right_buf);
                if (wret) {
                        ret = wret;
                        goto enospc;
                }
        }

        /* first, try to make some room in the middle buffer */
        if (left_buf) {
                left = btrfs_buffer_node(left_buf);
                orig_slot += btrfs_header_nritems(&left->header);
                wret = push_node_left(trans, root, left_buf, mid_buf);
                if (wret < 0)
                        ret = wret;
                if (btrfs_header_nritems(&mid->header) < 2)
                        err_on_enospc = 1;
        }

        /*
         * then try to empty the right most buffer into the middle
         */
        if (right_buf) {
                right = btrfs_buffer_node(right_buf);
                wret = push_node_left(trans, root, mid_buf, right_buf);
                if (wret < 0 && wret != -ENOSPC)
                        ret = wret;
                if (btrfs_header_nritems(&right->header) == 0) {
                        u64 blocknr = bh_blocknr(right_buf);
                        clean_tree_block(trans, root, right_buf);
                        wait_on_buffer(right_buf);
                        btrfs_block_release(root, right_buf);
                        right_buf = NULL;
                        right = NULL;
                        wret = del_ptr(trans, root, path, level + 1, pslot +
                                       1);
                        if (wret)
                                ret = wret;
                        wret = btrfs_free_extent(trans, root, blocknr, 1, 1);
                        if (wret)
                                ret = wret;
                } else {
                        btrfs_memcpy(root, parent,
                                     &parent->ptrs[pslot + 1].key,
                                     &right->ptrs[0].key,
                                     sizeof(struct btrfs_disk_key));
                        btrfs_mark_buffer_dirty(parent_buf);
                }
        }
        if (btrfs_header_nritems(&mid->header) == 1) {
                /*
                 * we're not allowed to leave a node with one item in the
                 * tree during a delete.  A deletion from lower in the tree
                 * could try to delete the only pointer in this node.
                 * So, pull some keys from the left.
                 * There has to be a left pointer at this point because
                 * otherwise we would have pulled some pointers from the
                 * right
                 */
                BUG_ON(!left_buf);
                wret = balance_node_right(trans, root, mid_buf, left_buf);
                if (wret < 0) {
                        ret = wret;
                        goto enospc;
                }
                BUG_ON(wret == 1);
        }
        if (btrfs_header_nritems(&mid->header) == 0) {
                /* we've managed to empty the middle node, drop it */
                u64 blocknr = bh_blocknr(mid_buf);
                clean_tree_block(trans, root, mid_buf);
                wait_on_buffer(mid_buf);
                btrfs_block_release(root, mid_buf);
                mid_buf = NULL;
                mid = NULL;
                wret = del_ptr(trans, root, path, level + 1, pslot);
                if (wret)
                        ret = wret;
                wret = btrfs_free_extent(trans, root, blocknr, 1, 1);
                if (wret)
                        ret = wret;
        } else {
                /* update the parent key to reflect our changes */
                btrfs_memcpy(root, parent,
                             &parent->ptrs[pslot].key, &mid->ptrs[0].key,
                             sizeof(struct btrfs_disk_key));
                btrfs_mark_buffer_dirty(parent_buf);
        }

        /* update the path */
        if (left_buf) {
                if (btrfs_header_nritems(&left->header) > orig_slot) {
                        get_bh(left_buf);
                        path->nodes[level] = left_buf;
                        path->slots[level + 1] -= 1;
                        path->slots[level] = orig_slot;
                        if (mid_buf)
                                btrfs_block_release(root, mid_buf);
                } else {
                        orig_slot -= btrfs_header_nritems(&left->header);
                        path->slots[level] = orig_slot;
                }
        }
        /* double check we haven't messed things up */
        check_block(root, path, level);
        if (orig_ptr !=
            btrfs_node_blockptr(btrfs_buffer_node(path->nodes[level]),
                                path->slots[level]))
                BUG();
enospc:
        if (right_buf)
                btrfs_block_release(root, right_buf);
        if (left_buf)
                btrfs_block_release(root, left_buf);
        return ret;
}

/* returns zero if the push worked, non-zero otherwise */
static int push_nodes_for_insert(struct btrfs_trans_handle *trans,
                                struct btrfs_root *root,
                                struct btrfs_path *path, int level)
{
        struct buffer_head *right_buf;
        struct buffer_head *mid_buf;
        struct buffer_head *left_buf;
        struct buffer_head *parent_buf = NULL;
        struct btrfs_node *right = NULL;
        struct btrfs_node *mid;
        struct btrfs_node *left = NULL;
        struct btrfs_node *parent = NULL;
        int ret = 0;
        int wret;
        int pslot;
        int orig_slot = path->slots[level];
        u64 orig_ptr;

        if (level == 0)
                return 1;

        mid_buf = path->nodes[level];
        mid = btrfs_buffer_node(mid_buf);
        orig_ptr = btrfs_node_blockptr(mid, orig_slot);

        if (level < BTRFS_MAX_LEVEL - 1)
                parent_buf = path->nodes[level + 1];
        pslot = path->slots[level + 1];

        if (!parent_buf)
                return 1;
        parent = btrfs_buffer_node(parent_buf);

        left_buf = read_node_slot(root, parent_buf, pslot - 1);

        /* first, try to make some room in the middle buffer */
        if (left_buf) {
                u32 left_nr;
                left = btrfs_buffer_node(left_buf);
                left_nr = btrfs_header_nritems(&left->header);
                if (left_nr >= BTRFS_NODEPTRS_PER_BLOCK(root) - 1) {
                        wret = 1;
                } else {
                        ret = btrfs_cow_block(trans, root, left_buf, parent_buf,
                                              pslot - 1, &left_buf);
                        if (ret)
                                wret = 1;
                        else {
                                left = btrfs_buffer_node(left_buf);
                                wret = push_node_left(trans, root,
                                                      left_buf, mid_buf);
                        }
                }
                if (wret < 0)
                        ret = wret;
                if (wret == 0) {
                        orig_slot += left_nr;
                        btrfs_memcpy(root, parent,
                                     &parent->ptrs[pslot].key,
                                     &mid->ptrs[0].key,
                                     sizeof(struct btrfs_disk_key));
                        btrfs_mark_buffer_dirty(parent_buf);
                        if (btrfs_header_nritems(&left->header) > orig_slot) {
                                path->nodes[level] = left_buf;
                                path->slots[level + 1] -= 1;
                                path->slots[level] = orig_slot;
                                btrfs_block_release(root, mid_buf);
                        } else {
                                orig_slot -=
                                        btrfs_header_nritems(&left->header);
                                path->slots[level] = orig_slot;
                                btrfs_block_release(root, left_buf);
                        }
                        check_node(root, path, level);
                        return 0;
                }
                btrfs_block_release(root, left_buf);
        }
        right_buf = read_node_slot(root, parent_buf, pslot + 1);

        /*
         * then try to empty the right most buffer into the middle
         */
        if (right_buf) {
                u32 right_nr;
                right = btrfs_buffer_node(right_buf);
                right_nr = btrfs_header_nritems(&right->header);
                if (right_nr >= BTRFS_NODEPTRS_PER_BLOCK(root) - 1) {
                        wret = 1;
                } else {
                        ret = btrfs_cow_block(trans, root, right_buf,
                                              parent_buf, pslot + 1,
                                              &right_buf);
                        if (ret)
                                wret = 1;
                        else {
                                right = btrfs_buffer_node(right_buf);
                                wret = balance_node_right(trans, root,
                                                          right_buf, mid_buf);
                        }
                }
                if (wret < 0)
                        ret = wret;
                if (wret == 0) {
                        btrfs_memcpy(root, parent,
                                     &parent->ptrs[pslot + 1].key,
                                     &right->ptrs[0].key,
                                     sizeof(struct btrfs_disk_key));
                        btrfs_mark_buffer_dirty(parent_buf);
                        if (btrfs_header_nritems(&mid->header) <= orig_slot) {
                                path->nodes[level] = right_buf;
                                path->slots[level + 1] += 1;
                                path->slots[level] = orig_slot -
                                        btrfs_header_nritems(&mid->header);
                                btrfs_block_release(root, mid_buf);
                        } else {
                                btrfs_block_release(root, right_buf);
                        }
                        check_node(root, path, level);
                        return 0;
                }
                btrfs_block_release(root, right_buf);
        }
        check_node(root, path, level);
        return 1;
}

/*
 * readahead one full node of leaves
 */
static void reada_for_search(struct btrfs_root *root, struct btrfs_path *path,
                             int level, int slot)
{
        struct btrfs_node *node;
        int i;
        u32 nritems;
        u64 item_objectid;
        u64 blocknr;
        u64 search;
        u64 cluster_start;
        int ret;
        int nread = 0;
        int direction = path->reada;
        struct radix_tree_root found;
        unsigned long gang[8];
        struct buffer_head *bh;

        if (level == 0)
                return;

        if (!path->nodes[level])
                return;

        node = btrfs_buffer_node(path->nodes[level]);
        search = btrfs_node_blockptr(node, slot);
        bh = btrfs_find_tree_block(root, search);
        if (bh) {
                brelse(bh);
                return;
        }

        init_bit_radix(&found);
        nritems = btrfs_header_nritems(&node->header);
        for (i = slot; i < nritems; i++) {
                item_objectid = btrfs_disk_key_objectid(&node->ptrs[i].key);
                blocknr = btrfs_node_blockptr(node, i);
                set_radix_bit(&found, blocknr);
        }
        if (direction > 0) {
                cluster_start = search - 4;
                if (cluster_start > search)
                        cluster_start = 0;
        } else
                cluster_start = search + 4;
        while(1) {
                ret = find_first_radix_bit(&found, gang, 0, ARRAY_SIZE(gang));
                if (!ret)
                        break;
                for (i = 0; i < ret; i++) {
                        blocknr = gang[i];
                        clear_radix_bit(&found, blocknr);
                        if (path->reada == 1 && nread > 16)
                                continue;
                        if (close_blocks(cluster_start, blocknr)) {
                                readahead_tree_block(root, blocknr);
                                nread++;
                                cluster_start = blocknr;
                        }
                }
        }
}
/*
 * look for key in the tree.  path is filled in with nodes along the way
 * if key is found, we return zero and you can find the item in the leaf
 * level of the path (level 0)
 *
 * If the key isn't found, the path points to the slot where it should
 * be inserted, and 1 is returned.  If there are other errors during the
 * search a negative error number is returned.
 *
 * if ins_len > 0, nodes and leaves will be split as we walk down the
 * tree.  if ins_len < 0, nodes will be merged as we walk down the tree (if
 * possible)
 */
int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root, struct btrfs_key *key, struct btrfs_path *p, int
                      ins_len, int cow)
{
        struct buffer_head *b;
        struct buffer_head *cow_buf;
        struct btrfs_node *c;
        u64 blocknr;
        int slot;
        int ret;
        int level;
        int should_reada = p->reada;
        u8 lowest_level = 0;

        lowest_level = p->lowest_level;
        WARN_ON(lowest_level && ins_len);
        WARN_ON(p->nodes[0] != NULL);
        WARN_ON(!mutex_is_locked(&root->fs_info->fs_mutex));
again:
        b = root->node;
        get_bh(b);
        while (b) {
                c = btrfs_buffer_node(b);
                level = btrfs_header_level(&c->header);
                if (cow) {
                        int wret;
                        wret = btrfs_cow_block(trans, root, b,
                                               p->nodes[level + 1],
                                               p->slots[level + 1],
                                               &cow_buf);
                        if (wret) {
                                btrfs_block_release(root, cow_buf);
                                return wret;
                        }
                        b = cow_buf;
                        c = btrfs_buffer_node(b);
                }
                BUG_ON(!cow && ins_len);
                if (level != btrfs_header_level(&c->header))
                        WARN_ON(1);
                level = btrfs_header_level(&c->header);
                p->nodes[level] = b;
                ret = check_block(root, p, level);
                if (ret)
                        return -1;
                ret = bin_search(c, key, &slot);
                if (!btrfs_is_leaf(c)) {
                        if (ret && slot > 0)
                                slot -= 1;
                        p->slots[level] = slot;
                        if (ins_len > 0 && btrfs_header_nritems(&c->header) >=
                            BTRFS_NODEPTRS_PER_BLOCK(root) - 1) {
                                int sret = split_node(trans, root, p, level);
                                BUG_ON(sret > 0);
                                if (sret)
                                        return sret;
                                b = p->nodes[level];
                                c = btrfs_buffer_node(b);
                                slot = p->slots[level];
                        } else if (ins_len < 0) {
                                int sret = balance_level(trans, root, p,
                                                         level);
                                if (sret)
                                        return sret;
                                b = p->nodes[level];
                                if (!b)
                                        goto again;
                                c = btrfs_buffer_node(b);
                                slot = p->slots[level];
                                BUG_ON(btrfs_header_nritems(&c->header) == 1);
                        }
                        /* this is only true while dropping a snapshot */
                        if (level == lowest_level)
                                break;
                        blocknr = btrfs_node_blockptr(c, slot);
                        if (should_reada)
                                reada_for_search(root, p, level, slot);
                        b = read_tree_block(root, btrfs_node_blockptr(c, slot));

                } else {
                        struct btrfs_leaf *l = (struct btrfs_leaf *)c;
                        p->slots[level] = slot;
                        if (ins_len > 0 && btrfs_leaf_free_space(root, l) <
                            sizeof(struct btrfs_item) + ins_len) {
                                int sret = split_leaf(trans, root, key,
                                                      p, ins_len);
                                BUG_ON(sret > 0);
                                if (sret)
                                        return sret;
                        }
                        return ret;
                }
        }
        return 1;
}

/*
 * adjust the pointers going up the tree, starting at level
 * making sure the right key of each node is points to 'key'.
 * This is used after shifting pointers to the left, so it stops
 * fixing up pointers when a given leaf/node is not in slot 0 of the
 * higher levels
 *
 * If this fails to write a tree block, it returns -1, but continues
 * fixing up the blocks in ram so the tree is consistent.
 */
static int fixup_low_keys(struct btrfs_trans_handle *trans, struct btrfs_root
                          *root, struct btrfs_path *path, struct btrfs_disk_key
                          *key, int level)
{
        int i;
        int ret = 0;
        for (i = level; i < BTRFS_MAX_LEVEL; i++) {
                struct btrfs_node *t;
                int tslot = path->slots[i];
                if (!path->nodes[i])
                        break;
                t = btrfs_buffer_node(path->nodes[i]);
                btrfs_memcpy(root, t, &t->ptrs[tslot].key, key, sizeof(*key));
                btrfs_mark_buffer_dirty(path->nodes[i]);
                if (tslot != 0)
                        break;
        }
        return ret;
}

/*
 * try to push data from one node into the next node left in the
 * tree.
 *
 * returns 0 if some ptrs were pushed left, < 0 if there was some horrible
 * error, and > 0 if there was no room in the left hand block.
 */
static int push_node_left(struct btrfs_trans_handle *trans, struct btrfs_root
                          *root, struct buffer_head *dst_buf, struct
                          buffer_head *src_buf)
{
        struct btrfs_node *src = btrfs_buffer_node(src_buf);
        struct btrfs_node *dst = btrfs_buffer_node(dst_buf);
        int push_items = 0;
        int src_nritems;
        int dst_nritems;
        int ret = 0;

        src_nritems = btrfs_header_nritems(&src->header);
        dst_nritems = btrfs_header_nritems(&dst->header);
        push_items = BTRFS_NODEPTRS_PER_BLOCK(root) - dst_nritems;

        if (push_items <= 0) {
                return 1;
        }

        if (src_nritems < push_items)
                push_items = src_nritems;

        btrfs_memcpy(root, dst, dst->ptrs + dst_nritems, src->ptrs,
                     push_items * sizeof(struct btrfs_key_ptr));
        if (push_items < src_nritems) {
                btrfs_memmove(root, src, src->ptrs, src->ptrs + push_items,
                        (src_nritems - push_items) *
                        sizeof(struct btrfs_key_ptr));
        }
        btrfs_set_header_nritems(&src->header, src_nritems - push_items);
        btrfs_set_header_nritems(&dst->header, dst_nritems + push_items);
        btrfs_mark_buffer_dirty(src_buf);
        btrfs_mark_buffer_dirty(dst_buf);
        return ret;
}

/*
 * try to push data from one node into the next node right in the
 * tree.
 *
 * returns 0 if some ptrs were pushed, < 0 if there was some horrible
 * error, and > 0 if there was no room in the right hand block.
 *
 * this will  only push up to 1/2 the contents of the left node over
 */
static int balance_node_right(struct btrfs_trans_handle *trans, struct
                              btrfs_root *root, struct buffer_head *dst_buf,
                              struct buffer_head *src_buf)
{
        struct btrfs_node *src = btrfs_buffer_node(src_buf);
        struct btrfs_node *dst = btrfs_buffer_node(dst_buf);
        int push_items = 0;
        int max_push;
        int src_nritems;
        int dst_nritems;
        int ret = 0;

        src_nritems = btrfs_header_nritems(&src->header);
        dst_nritems = btrfs_header_nritems(&dst->header);
        push_items = BTRFS_NODEPTRS_PER_BLOCK(root) - dst_nritems;
        if (push_items <= 0) {
                return 1;
        }

        max_push = src_nritems / 2 + 1;
        /* don't try to empty the node */
        if (max_push > src_nritems)
                return 1;
        if (max_push < push_items)
                push_items = max_push;

        btrfs_memmove(root, dst, dst->ptrs + push_items, dst->ptrs,
                      dst_nritems * sizeof(struct btrfs_key_ptr));

        btrfs_memcpy(root, dst, dst->ptrs,
                     src->ptrs + src_nritems - push_items,
                     push_items * sizeof(struct btrfs_key_ptr));

        btrfs_set_header_nritems(&src->header, src_nritems - push_items);
        btrfs_set_header_nritems(&dst->header, dst_nritems + push_items);

        btrfs_mark_buffer_dirty(src_buf);
        btrfs_mark_buffer_dirty(dst_buf);
        return ret;
}

/*
 * helper function to insert a new root level in the tree.
 * A new node is allocated, and a single item is inserted to
 * point to the existing root
 *
 * returns zero on success or < 0 on failure.
 */
static int insert_new_root(struct btrfs_trans_handle *trans, struct btrfs_root
                           *root, struct btrfs_path *path, int level)
{
        struct buffer_head *t;
        struct btrfs_node *lower;
        struct btrfs_node *c;
        struct btrfs_disk_key *lower_key;

        BUG_ON(path->nodes[level]);
        BUG_ON(path->nodes[level-1] != root->node);

        t = btrfs_alloc_free_block(trans, root, root->node->b_blocknr, 0);
        if (IS_ERR(t))
                return PTR_ERR(t);
        c = btrfs_buffer_node(t);
        memset(c, 0, root->blocksize);
        btrfs_set_header_nritems(&c->header, 1);
        btrfs_set_header_level(&c->header, level);
        btrfs_set_header_blocknr(&c->header, bh_blocknr(t));
        btrfs_set_header_generation(&c->header, trans->transid);
        btrfs_set_header_owner(&c->header, root->root_key.objectid);
        lower = btrfs_buffer_node(path->nodes[level-1]);
        memcpy(c->header.fsid, root->fs_info->disk_super->fsid,
               sizeof(c->header.fsid));
        if (btrfs_is_leaf(lower))
                lower_key = &((struct btrfs_leaf *)lower)->items[0].key;
        else
                lower_key = &lower->ptrs[0].key;
        btrfs_memcpy(root, c, &c->ptrs[0].key, lower_key,
                     sizeof(struct btrfs_disk_key));
        btrfs_set_node_blockptr(c, 0, bh_blocknr(path->nodes[level - 1]));

        btrfs_mark_buffer_dirty(t);

        /* the super has an extra ref to root->node */
        btrfs_block_release(root, root->node);
        root->node = t;
        get_bh(t);
        path->nodes[level] = t;
        path->slots[level] = 0;
        return 0;
}

/*
 * worker function to insert a single pointer in a node.
 * the node should have enough room for the pointer already
 *
 * slot and level indicate where you want the key to go, and
 * blocknr is the block the key points to.
 *
 * returns zero on success and < 0 on any error
 */
static int insert_ptr(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root, struct btrfs_path *path, struct btrfs_disk_key
                      *key, u64 blocknr, int slot, int level)
{
        struct btrfs_node *lower;
        int nritems;

        BUG_ON(!path->nodes[level]);
        lower = btrfs_buffer_node(path->nodes[level]);
        nritems = btrfs_header_nritems(&lower->header);
        if (slot > nritems)
                BUG();
        if (nritems == BTRFS_NODEPTRS_PER_BLOCK(root))
                BUG();
        if (slot != nritems) {
                btrfs_memmove(root, lower, lower->ptrs + slot + 1,
                              lower->ptrs + slot,
                              (nritems - slot) * sizeof(struct btrfs_key_ptr));
        }
        btrfs_memcpy(root, lower, &lower->ptrs[slot].key,
                     key, sizeof(struct btrfs_disk_key));
        btrfs_set_node_blockptr(lower, slot, blocknr);
        btrfs_set_header_nritems(&lower->header, nritems + 1);
        btrfs_mark_buffer_dirty(path->nodes[level]);
        check_node(root, path, level);
        return 0;
}

/*
 * split the node at the specified level in path in two.
 * The path is corrected to point to the appropriate node after the split
 *
 * Before splitting this tries to make some room in the node by pushing
 * left and right, if either one works, it returns right away.
 *
 * returns 0 on success and < 0 on failure
 */
static int split_node(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root, struct btrfs_path *path, int level)
{
        struct buffer_head *t;
        struct btrfs_node *c;
        struct buffer_head *split_buffer;
        struct btrfs_node *split;
        int mid;
        int ret;
        int wret;
        u32 c_nritems;

        t = path->nodes[level];
        c = btrfs_buffer_node(t);
        if (t == root->node) {
                /* trying to split the root, lets make a new one */
                ret = insert_new_root(trans, root, path, level + 1);
                if (ret)
                        return ret;
        } else {
                ret = push_nodes_for_insert(trans, root, path, level);
                t = path->nodes[level];
                c = btrfs_buffer_node(t);
                if (!ret &&
                    btrfs_header_nritems(&c->header) <
                    BTRFS_NODEPTRS_PER_BLOCK(root) - 1)
                        return 0;
                if (ret < 0)
                        return ret;
        }

        c_nritems = btrfs_header_nritems(&c->header);
        split_buffer = btrfs_alloc_free_block(trans, root, t->b_blocknr, 0);
        if (IS_ERR(split_buffer))
                return PTR_ERR(split_buffer);

        split = btrfs_buffer_node(split_buffer);
        btrfs_set_header_flags(&split->header, btrfs_header_flags(&c->header));
        btrfs_set_header_level(&split->header, btrfs_header_level(&c->header));
        btrfs_set_header_blocknr(&split->header, bh_blocknr(split_buffer));
        btrfs_set_header_generation(&split->header, trans->transid);
        btrfs_set_header_owner(&split->header, root->root_key.objectid);
        memcpy(split->header.fsid, root->fs_info->disk_super->fsid,
               sizeof(split->header.fsid));
        mid = (c_nritems + 1) / 2;
        btrfs_memcpy(root, split, split->ptrs, c->ptrs + mid,
                     (c_nritems - mid) * sizeof(struct btrfs_key_ptr));
        btrfs_set_header_nritems(&split->header, c_nritems - mid);
        btrfs_set_header_nritems(&c->header, mid);
        ret = 0;

        btrfs_mark_buffer_dirty(t);
        btrfs_mark_buffer_dirty(split_buffer);
        wret = insert_ptr(trans, root, path, &split->ptrs[0].key,
                          bh_blocknr(split_buffer), path->slots[level + 1] + 1,
                          level + 1);
        if (wret)
                ret = wret;

        if (path->slots[level] >= mid) {
                path->slots[level] -= mid;
                btrfs_block_release(root, t);
                path->nodes[level] = split_buffer;
                path->slots[level + 1] += 1;
        } else {
                btrfs_block_release(root, split_buffer);
        }
        return ret;
}

/*
 * how many bytes are required to store the items in a leaf.  start
 * and nr indicate which items in the leaf to check.  This totals up the
 * space used both by the item structs and the item data
 */
static int leaf_space_used(struct btrfs_leaf *l, int start, int nr)
{
        int data_len;
        int nritems = btrfs_header_nritems(&l->header);
        int end = min(nritems, start + nr) - 1;

        if (!nr)
                return 0;
        data_len = btrfs_item_end(l->items + start);
        data_len = data_len - btrfs_item_offset(l->items + end);
        data_len += sizeof(struct btrfs_item) * nr;
        WARN_ON(data_len < 0);
        return data_len;
}

/*
 * The space between the end of the leaf items and
 * the start of the leaf data.  IOW, how much room
 * the leaf has left for both items and data
 */
int btrfs_leaf_free_space(struct btrfs_root *root, struct btrfs_leaf *leaf)
{
        int nritems = btrfs_header_nritems(&leaf->header);
        return BTRFS_LEAF_DATA_SIZE(root) - leaf_space_used(leaf, 0, nritems);
}

/*
 * push some data in the path leaf to the right, trying to free up at
 * least data_size bytes.  returns zero if the push worked, nonzero otherwise
 *
 * returns 1 if the push failed because the other node didn't have enough
 * room, 0 if everything worked out and < 0 if there were major errors.
 */
static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
                           *root, struct btrfs_path *path, int data_size)
{
        struct buffer_head *left_buf = path->nodes[0];
        struct btrfs_leaf *left = btrfs_buffer_leaf(left_buf);
        struct btrfs_leaf *right;
        struct buffer_head *right_buf;
        struct buffer_head *upper;
        struct btrfs_node *upper_node;
        int slot;
        int i;
        int free_space;
        int push_space = 0;
        int push_items = 0;
        struct btrfs_item *item;
        u32 left_nritems;
        u32 right_nritems;
        int ret;

        slot = path->slots[1];
        if (!path->nodes[1]) {
                return 1;
        }
        upper = path->nodes[1];
        upper_node = btrfs_buffer_node(upper);
        if (slot >= btrfs_header_nritems(&upper_node->header) - 1) {
                return 1;
        }
        right_buf = read_tree_block(root,
                    btrfs_node_blockptr(btrfs_buffer_node(upper), slot + 1));
        right = btrfs_buffer_leaf(right_buf);
        free_space = btrfs_leaf_free_space(root, right);
        if (free_space < data_size + sizeof(struct btrfs_item)) {
                btrfs_block_release(root, right_buf);
                return 1;
        }
        /* cow and double check */
        ret = btrfs_cow_block(trans, root, right_buf, upper,
                              slot + 1, &right_buf);
        if (ret) {
                btrfs_block_release(root, right_buf);
                return 1;
        }
        right = btrfs_buffer_leaf(right_buf);
        free_space = btrfs_leaf_free_space(root, right);
        if (free_space < data_size + sizeof(struct btrfs_item)) {
                btrfs_block_release(root, right_buf);
                return 1;
        }

        left_nritems = btrfs_header_nritems(&left->header);
        if (left_nritems == 0) {
                btrfs_block_release(root, right_buf);
                return 1;
        }
        for (i = left_nritems - 1; i >= 1; i--) {
                item = left->items + i;
                if (path->slots[0] == i)
                        push_space += data_size + sizeof(*item);
                if (btrfs_item_size(item) + sizeof(*item) + push_space >
                    free_space)
                        break;
                push_items++;
                push_space += btrfs_item_size(item) + sizeof(*item);
        }
        if (push_items == 0) {
                btrfs_block_release(root, right_buf);
                return 1;
        }
        if (push_items == left_nritems)
                WARN_ON(1);
        right_nritems = btrfs_header_nritems(&right->header);
        /* push left to right */
        push_space = btrfs_item_end(left->items + left_nritems - push_items);
        push_space -= leaf_data_end(root, left);
        /* make room in the right data area */
        btrfs_memmove(root, right, btrfs_leaf_data(right) +
                      leaf_data_end(root, right) - push_space,
                      btrfs_leaf_data(right) +
                      leaf_data_end(root, right), BTRFS_LEAF_DATA_SIZE(root) -
                      leaf_data_end(root, right));
        /* copy from the left data area */
        btrfs_memcpy(root, right, btrfs_leaf_data(right) +
                     BTRFS_LEAF_DATA_SIZE(root) - push_space,
                     btrfs_leaf_data(left) + leaf_data_end(root, left),
                     push_space);
        btrfs_memmove(root, right, right->items + push_items, right->items,
                right_nritems * sizeof(struct btrfs_item));
        /* copy the items from left to right */
        btrfs_memcpy(root, right, right->items, left->items +
                     left_nritems - push_items,
                     push_items * sizeof(struct btrfs_item));

        /* update the item pointers */
        right_nritems += push_items;
        btrfs_set_header_nritems(&right->header, right_nritems);
        push_space = BTRFS_LEAF_DATA_SIZE(root);
        for (i = 0; i < right_nritems; i++) {
                btrfs_set_item_offset(right->items + i, push_space -
                                      btrfs_item_size(right->items + i));
                push_space = btrfs_item_offset(right->items + i);
        }
        left_nritems -= push_items;
        btrfs_set_header_nritems(&left->header, left_nritems);

        btrfs_mark_buffer_dirty(left_buf);
        btrfs_mark_buffer_dirty(right_buf);

        btrfs_memcpy(root, upper_node, &upper_node->ptrs[slot + 1].key,
                &right->items[0].key, sizeof(struct btrfs_disk_key));
        btrfs_mark_buffer_dirty(upper);

        /* then fixup the leaf pointer in the path */
        if (path->slots[0] >= left_nritems) {
                path->slots[0] -= left_nritems;
                btrfs_block_release(root, path->nodes[0]);
                path->nodes[0] = right_buf;
                path->slots[1] += 1;
        } else {
                btrfs_block_release(root, right_buf);
        }
        if (path->nodes[1])
                check_node(root, path, 1);
        return 0;
}
/*
 * push some data in the path leaf to the left, trying to free up at
 * least data_size bytes.  returns zero if the push worked, nonzero otherwise
 */
static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
                          *root, struct btrfs_path *path, int data_size)
{
        struct buffer_head *right_buf = path->nodes[0];
        struct btrfs_leaf *right = btrfs_buffer_leaf(right_buf);
        struct buffer_head *t;
        struct btrfs_leaf *left;
        int slot;
        int i;
        int free_space;
        int push_space = 0;
        int push_items = 0;
        struct btrfs_item *item;
        u32 old_left_nritems;
        int ret = 0;
        int wret;

        slot = path->slots[1];
        if (slot == 0) {
                return 1;
        }
        if (!path->nodes[1]) {
                return 1;
        }
        t = read_tree_block(root,
            btrfs_node_blockptr(btrfs_buffer_node(path->nodes[1]), slot - 1));
        left = btrfs_buffer_leaf(t);
        free_space = btrfs_leaf_free_space(root, left);
        if (free_space < data_size + sizeof(struct btrfs_item)) {
                btrfs_block_release(root, t);
                return 1;
        }

        /* cow and double check */
        ret = btrfs_cow_block(trans, root, t, path->nodes[1], slot - 1, &t);
        if (ret) {
                /* we hit -ENOSPC, but it isn't fatal here */
                return 1;
        }
        left = btrfs_buffer_leaf(t);
        free_space = btrfs_leaf_free_space(root, left);
        if (free_space < data_size + sizeof(struct btrfs_item)) {
                btrfs_block_release(root, t);
                return 1;
        }

        if (btrfs_header_nritems(&right->header) == 0) {
                btrfs_block_release(root, t);
                return 1;
        }

        for (i = 0; i < btrfs_header_nritems(&right->header) - 1; i++) {
                item = right->items + i;
                if (path->slots[0] == i)
                        push_space += data_size + sizeof(*item);
                if (btrfs_item_size(item) + sizeof(*item) + push_space >
                    free_space)
                        break;
                push_items++;
                push_space += btrfs_item_size(item) + sizeof(*item);
        }
        if (push_items == 0) {
                btrfs_block_release(root, t);
                return 1;
        }
        if (push_items == btrfs_header_nritems(&right->header))
                WARN_ON(1);
        /* push data from right to left */
        btrfs_memcpy(root, left, left->items +
                     btrfs_header_nritems(&left->header),
                     right->items, push_items * sizeof(struct btrfs_item));
        push_space = BTRFS_LEAF_DATA_SIZE(root) -
                     btrfs_item_offset(right->items + push_items -1);
        btrfs_memcpy(root, left, btrfs_leaf_data(left) +
                     leaf_data_end(root, left) - push_space,
                     btrfs_leaf_data(right) +
                     btrfs_item_offset(right->items + push_items - 1),
                     push_space);
        old_left_nritems = btrfs_header_nritems(&left->header);
        BUG_ON(old_left_nritems < 0);

        for (i = old_left_nritems; i < old_left_nritems + push_items; i++) {
                u32 ioff = btrfs_item_offset(left->items + i);
                btrfs_set_item_offset(left->items + i, ioff -
                                     (BTRFS_LEAF_DATA_SIZE(root) -
                                      btrfs_item_offset(left->items +
                                                        old_left_nritems - 1)));
        }
        btrfs_set_header_nritems(&left->header, old_left_nritems + push_items);

        /* fixup right node */
        push_space = btrfs_item_offset(right->items + push_items - 1) -
                     leaf_data_end(root, right);
        btrfs_memmove(root, right, btrfs_leaf_data(right) +
                      BTRFS_LEAF_DATA_SIZE(root) - push_space,
                      btrfs_leaf_data(right) +
                      leaf_data_end(root, right), push_space);
        btrfs_memmove(root, right, right->items, right->items + push_items,
                (btrfs_header_nritems(&right->header) - push_items) *
                sizeof(struct btrfs_item));
        btrfs_set_header_nritems(&right->header,
                                 btrfs_header_nritems(&right->header) -
                                 push_items);
        push_space = BTRFS_LEAF_DATA_SIZE(root);

        for (i = 0; i < btrfs_header_nritems(&right->header); i++) {
                btrfs_set_item_offset(right->items + i, push_space -
                                      btrfs_item_size(right->items + i));
                push_space = btrfs_item_offset(right->items + i);
        }

        btrfs_mark_buffer_dirty(t);
        btrfs_mark_buffer_dirty(right_buf);

        wret = fixup_low_keys(trans, root, path, &right->items[0].key, 1);
        if (wret)
                ret = wret;

        /* then fixup the leaf pointer in the path */
        if (path->slots[0] < push_items) {
                path->slots[0] += old_left_nritems;
                btrfs_block_release(root, path->nodes[0]);
                path->nodes[0] = t;
                path->slots[1] -= 1;
        } else {
                btrfs_block_release(root, t);
                path->slots[0] -= push_items;
        }
        BUG_ON(path->slots[0] < 0);
        if (path->nodes[1])
                check_node(root, path, 1);
        return ret;
}

/*
 * split the path's leaf in two, making sure there is at least data_size
 * available for the resulting leaf level of the path.
 *
 * returns 0 if all went well and < 0 on failure.
 */
static int split_leaf(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root, struct btrfs_key *ins_key,
                      struct btrfs_path *path, int data_size)
{
        struct buffer_head *l_buf;
        struct btrfs_leaf *l;
        u32 nritems;
        int mid;
        int slot;
        struct btrfs_leaf *right;
        struct buffer_head *right_buffer;
        int space_needed = data_size + sizeof(struct btrfs_item);
        int data_copy_size;
        int rt_data_off;
        int i;
        int ret = 0;
        int wret;
        int double_split = 0;
        struct btrfs_disk_key disk_key;

        /* first try to make some room by pushing left and right */
        wret = push_leaf_left(trans, root, path, data_size);
        if (wret < 0)
                return wret;
        if (wret) {
                wret = push_leaf_right(trans, root, path, data_size);
                if (wret < 0)
                        return wret;
        }
        l_buf = path->nodes[0];
        l = btrfs_buffer_leaf(l_buf);

        /* did the pushes work? */
        if (btrfs_leaf_free_space(root, l) >=
            sizeof(struct btrfs_item) + data_size)
                return 0;

        if (!path->nodes[1]) {
                ret = insert_new_root(trans, root, path, 1);
                if (ret)
                        return ret;
        }
        slot = path->slots[0];
        nritems = btrfs_header_nritems(&l->header);
        mid = (nritems + 1)/ 2;

        right_buffer = btrfs_alloc_free_block(trans, root, l_buf->b_blocknr, 0);
        if (IS_ERR(right_buffer))
                return PTR_ERR(right_buffer);

        right = btrfs_buffer_leaf(right_buffer);
        memset(&right->header, 0, sizeof(right->header));
        btrfs_set_header_blocknr(&right->header, bh_blocknr(right_buffer));
        btrfs_set_header_generation(&right->header, trans->transid);
        btrfs_set_header_owner(&right->header, root->root_key.objectid);
        btrfs_set_header_level(&right->header, 0);
        memcpy(right->header.fsid, root->fs_info->disk_super->fsid,
               sizeof(right->header.fsid));
        if (mid <= slot) {
                if (nritems == 1 ||
                    leaf_space_used(l, mid, nritems - mid) + space_needed >
                        BTRFS_LEAF_DATA_SIZE(root)) {
                        if (slot >= nritems) {
                                btrfs_cpu_key_to_disk(&disk_key, ins_key);
                                btrfs_set_header_nritems(&right->header, 0);
                                wret = insert_ptr(trans, root, path,
                                                  &disk_key,
                                                  bh_blocknr(right_buffer),
                                                  path->slots[1] + 1, 1);
                                if (wret)
                                        ret = wret;
                                btrfs_block_release(root, path->nodes[0]);
                                path->nodes[0] = right_buffer;
                                path->slots[0] = 0;
                                path->slots[1] += 1;
                                return ret;
                        }
                        mid = slot;
                        double_split = 1;
                }
        } else {
                if (leaf_space_used(l, 0, mid + 1) + space_needed >
                        BTRFS_LEAF_DATA_SIZE(root)) {
                        if (slot == 0) {
                                btrfs_cpu_key_to_disk(&disk_key, ins_key);
                                btrfs_set_header_nritems(&right->header, 0);
                                wret = insert_ptr(trans, root, path,
                                                  &disk_key,
                                                  bh_blocknr(right_buffer),
                                                  path->slots[1], 1);
                                if (wret)
                                        ret = wret;
                                btrfs_block_release(root, path->nodes[0]);
                                path->nodes[0] = right_buffer;
                                path->slots[0] = 0;
                                if (path->slots[1] == 0) {
                                        wret = fixup_low_keys(trans, root,
                                                   path, &disk_key, 1);
                                        if (wret)
                                                ret = wret;
                                }
                                return ret;
                        }
                        mid = slot;
                        double_split = 1;
                }
        }
        btrfs_set_header_nritems(&right->header, nritems - mid);
        data_copy_size = btrfs_item_end(l->items + mid) -
                         leaf_data_end(root, l);
        btrfs_memcpy(root, right, right->items, l->items + mid,
                     (nritems - mid) * sizeof(struct btrfs_item));
        btrfs_memcpy(root, right,
                     btrfs_leaf_data(right) + BTRFS_LEAF_DATA_SIZE(root) -
                     data_copy_size, btrfs_leaf_data(l) +
                     leaf_data_end(root, l), data_copy_size);
        rt_data_off = BTRFS_LEAF_DATA_SIZE(root) -
                      btrfs_item_end(l->items + mid);

        for (i = 0; i < btrfs_header_nritems(&right->header); i++) {
                u32 ioff = btrfs_item_offset(right->items + i);
                btrfs_set_item_offset(right->items + i, ioff + rt_data_off);
        }

        btrfs_set_header_nritems(&l->header, mid);
        ret = 0;
        wret = insert_ptr(trans, root, path, &right->items[0].key,
                          bh_blocknr(right_buffer), path->slots[1] + 1, 1);
        if (wret)
                ret = wret;
        btrfs_mark_buffer_dirty(right_buffer);
        btrfs_mark_buffer_dirty(l_buf);
        BUG_ON(path->slots[0] != slot);
        if (mid <= slot) {
                btrfs_block_release(root, path->nodes[0]);
                path->nodes[0] = right_buffer;
                path->slots[0] -= mid;
                path->slots[1] += 1;
        } else
                btrfs_block_release(root, right_buffer);
        BUG_ON(path->slots[0] < 0);
        check_node(root, path, 1);

        if (!double_split)
                return ret;
        right_buffer = btrfs_alloc_free_block(trans, root, l_buf->b_blocknr, 0);
        if (IS_ERR(right_buffer))
                return PTR_ERR(right_buffer);

        right = btrfs_buffer_leaf(right_buffer);
        memset(&right->header, 0, sizeof(right->header));
        btrfs_set_header_blocknr(&right->header, bh_blocknr(right_buffer));
        btrfs_set_header_generation(&right->header, trans->transid);
        btrfs_set_header_owner(&right->header, root->root_key.objectid);
        btrfs_set_header_level(&right->header, 0);
        memcpy(right->header.fsid, root->fs_info->disk_super->fsid,
               sizeof(right->header.fsid));
        btrfs_cpu_key_to_disk(&disk_key, ins_key);
        btrfs_set_header_nritems(&right->header, 0);
        wret = insert_ptr(trans, root, path,
                          &disk_key,
                          bh_blocknr(right_buffer),
                          path->slots[1], 1);
        if (wret)
                ret = wret;
        if (path->slots[1] == 0) {
                wret = fixup_low_keys(trans, root, path, &disk_key, 1);
                if (wret)
                        ret = wret;
        }
        btrfs_block_release(root, path->nodes[0]);
        path->nodes[0] = right_buffer;
        path->slots[0] = 0;
        check_node(root, path, 1);
        check_leaf(root, path, 0);
        return ret;
}

int btrfs_truncate_item(struct btrfs_trans_handle *trans,
                        struct btrfs_root *root,
                        struct btrfs_path *path,
                        u32 new_size)
{
        int ret = 0;
        int slot;
        int slot_orig;
        struct btrfs_leaf *leaf;
        struct buffer_head *leaf_buf;
        u32 nritems;
        unsigned int data_end;
        unsigned int old_data_start;
        unsigned int old_size;
        unsigned int size_diff;
        int i;

        slot_orig = path->slots[0];
        leaf_buf = path->nodes[0];
        leaf = btrfs_buffer_leaf(leaf_buf);

        nritems = btrfs_header_nritems(&leaf->header);
        data_end = leaf_data_end(root, leaf);

        slot = path->slots[0];
        old_data_start = btrfs_item_offset(leaf->items + slot);
        old_size = btrfs_item_size(leaf->items + slot);
        BUG_ON(old_size <= new_size);
        size_diff = old_size - new_size;

        BUG_ON(slot < 0);
        BUG_ON(slot >= nritems);

        /*
         * item0..itemN ... dataN.offset..dataN.size .. data0.size
         */
        /* first correct the data pointers */
        for (i = slot; i < nritems; i++) {
                u32 ioff = btrfs_item_offset(leaf->items + i);
                btrfs_set_item_offset(leaf->items + i,
                                      ioff + size_diff);
        }
        /* shift the data */
        btrfs_memmove(root, leaf, btrfs_leaf_data(leaf) +
                      data_end + size_diff, btrfs_leaf_data(leaf) +
                      data_end, old_data_start + new_size - data_end);
        btrfs_set_item_size(leaf->items + slot, new_size);
        btrfs_mark_buffer_dirty(leaf_buf);

        ret = 0;
        if (btrfs_leaf_free_space(root, leaf) < 0)
                BUG();
        check_leaf(root, path, 0);
        return ret;
}

int btrfs_extend_item(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root, struct btrfs_path *path, u32 data_size)
{
        int ret = 0;
        int slot;
        int slot_orig;
        struct btrfs_leaf *leaf;
        struct buffer_head *leaf_buf;
        u32 nritems;
        unsigned int data_end;
        unsigned int old_data;
        unsigned int old_size;
        int i;

        slot_orig = path->slots[0];
        leaf_buf = path->nodes[0];
        leaf = btrfs_buffer_leaf(leaf_buf);

        nritems = btrfs_header_nritems(&leaf->header);
        data_end = leaf_data_end(root, leaf);

        if (btrfs_leaf_free_space(root, leaf) < data_size)
                BUG();
        slot = path->slots[0];
        old_data = btrfs_item_end(leaf->items + slot);

        BUG_ON(slot < 0);
        BUG_ON(slot >= nritems);

        /*
         * item0..itemN ... dataN.offset..dataN.size .. data0.size
         */
        /* first correct the data pointers */
        for (i = slot; i < nritems; i++) {
                u32 ioff = btrfs_item_offset(leaf->items + i);
                btrfs_set_item_offset(leaf->items + i,
                                      ioff - data_size);
        }
        /* shift the data */
        btrfs_memmove(root, leaf, btrfs_leaf_data(leaf) +
                      data_end - data_size, btrfs_leaf_data(leaf) +
                      data_end, old_data - data_end);
        data_end = old_data;
        old_size = btrfs_item_size(leaf->items + slot);
        btrfs_set_item_size(leaf->items + slot, old_size + data_size);
        btrfs_mark_buffer_dirty(leaf_buf);

        ret = 0;
        if (btrfs_leaf_free_space(root, leaf) < 0)
                BUG();
        check_leaf(root, path, 0);
        return ret;
}

/*
 * Given a key and some data, insert an item into the tree.
 * This does all the path init required, making room in the tree if needed.
 */
int btrfs_insert_empty_item(struct btrfs_trans_handle *trans, struct btrfs_root
                            *root, struct btrfs_path *path, struct btrfs_key
                            *cpu_key, u32 data_size)
{
        int ret = 0;
        int slot;
        int slot_orig;
        struct btrfs_leaf *leaf;
        struct buffer_head *leaf_buf;
        u32 nritems;
        unsigned int data_end;
        struct btrfs_disk_key disk_key;

        btrfs_cpu_key_to_disk(&disk_key, cpu_key);

        /* create a root if there isn't one */
        if (!root->node)
                BUG();
        ret = btrfs_search_slot(trans, root, cpu_key, path, data_size, 1);
        if (ret == 0) {
                return -EEXIST;
        }
        if (ret < 0)
                goto out;

        slot_orig = path->slots[0];
        leaf_buf = path->nodes[0];
        leaf = btrfs_buffer_leaf(leaf_buf);

        nritems = btrfs_header_nritems(&leaf->header);
        data_end = leaf_data_end(root, leaf);

        if (btrfs_leaf_free_space(root, leaf) <
            sizeof(struct btrfs_item) + data_size) {
                BUG();
        }
        slot = path->slots[0];
        BUG_ON(slot < 0);
        if (slot != nritems) {
                int i;
                unsigned int old_data = btrfs_item_end(leaf->items + slot);

                /*
                 * item0..itemN ... dataN.offset..dataN.size .. data0.size
                 */
                /* first correct the data pointers */
                for (i = slot; i < nritems; i++) {
                        u32 ioff = btrfs_item_offset(leaf->items + i);
                        btrfs_set_item_offset(leaf->items + i,
                                              ioff - data_size);
                }

                /* shift the items */
                btrfs_memmove(root, leaf, leaf->items + slot + 1,
                              leaf->items + slot,
                              (nritems - slot) * sizeof(struct btrfs_item));

                /* shift the data */
                btrfs_memmove(root, leaf, btrfs_leaf_data(leaf) +
                              data_end - data_size, btrfs_leaf_data(leaf) +
                              data_end, old_data - data_end);
                data_end = old_data;
        }
        /* setup the item for the new data */
        btrfs_memcpy(root, leaf, &leaf->items[slot].key, &disk_key,
                     sizeof(struct btrfs_disk_key));
        btrfs_set_item_offset(leaf->items + slot, data_end - data_size);
        btrfs_set_item_size(leaf->items + slot, data_size);
        btrfs_set_header_nritems(&leaf->header, nritems + 1);
        btrfs_mark_buffer_dirty(leaf_buf);

        ret = 0;
        if (slot == 0)
                ret = fixup_low_keys(trans, root, path, &disk_key, 1);

        if (btrfs_leaf_free_space(root, leaf) < 0)
                BUG();
        check_leaf(root, path, 0);
out:
        return ret;
}

/*
 * Given a key and some data, insert an item into the tree.
 * This does all the path init required, making room in the tree if needed.
 */
int btrfs_insert_item(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root, struct btrfs_key *cpu_key, void *data, u32
                      data_size)
{
        int ret = 0;
        struct btrfs_path *path;
        u8 *ptr;

        path = btrfs_alloc_path();
        BUG_ON(!path);
        ret = btrfs_insert_empty_item(trans, root, path, cpu_key, data_size);
        if (!ret) {
                ptr = btrfs_item_ptr(btrfs_buffer_leaf(path->nodes[0]),
                                     path->slots[0], u8);
                btrfs_memcpy(root, path->nodes[0]->b_data,
                             ptr, data, data_size);
                btrfs_mark_buffer_dirty(path->nodes[0]);
        }
        btrfs_free_path(path);
        return ret;
}

/*
 * delete the pointer from a given node.
 *
 * If the delete empties a node, the node is removed from the tree,
 * continuing all the way the root if required.  The root is converted into
 * a leaf if all the nodes are emptied.
 */
static int del_ptr(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                   struct btrfs_path *path, int level, int slot)
{
        struct btrfs_node *node;
        struct buffer_head *parent = path->nodes[level];
        u32 nritems;
        int ret = 0;
        int wret;

        node = btrfs_buffer_node(parent);
        nritems = btrfs_header_nritems(&node->header);
        if (slot != nritems -1) {
                btrfs_memmove(root, node, node->ptrs + slot,
                              node->ptrs + slot + 1,
                              sizeof(struct btrfs_key_ptr) *
                              (nritems - slot - 1));
        }
        nritems--;
        btrfs_set_header_nritems(&node->header, nritems);
        if (nritems == 0 && parent == root->node) {
                struct btrfs_header *header = btrfs_buffer_header(root->node);
                BUG_ON(btrfs_header_level(header) != 1);
                /* just turn the root into a leaf and break */
                btrfs_set_header_level(header, 0);
        } else if (slot == 0) {
                wret = fixup_low_keys(trans, root, path, &node->ptrs[0].key,
                                      level + 1);
                if (wret)
                        ret = wret;
        }
        btrfs_mark_buffer_dirty(parent);
        return ret;
}

/*
 * delete the item at the leaf level in path.  If that empties
 * the leaf, remove it from the tree
 */
int btrfs_del_item(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                   struct btrfs_path *path)
{
        int slot;
        struct btrfs_leaf *leaf;
        struct buffer_head *leaf_buf;
        int doff;
        int dsize;
        int ret = 0;
        int wret;
        u32 nritems;

        leaf_buf = path->nodes[0];
        leaf = btrfs_buffer_leaf(leaf_buf);
        slot = path->slots[0];
        doff = btrfs_item_offset(leaf->items + slot);
        dsize = btrfs_item_size(leaf->items + slot);
        nritems = btrfs_header_nritems(&leaf->header);

        if (slot != nritems - 1) {
                int i;
                int data_end = leaf_data_end(root, leaf);
                btrfs_memmove(root, leaf, btrfs_leaf_data(leaf) +
                              data_end + dsize,
                              btrfs_leaf_data(leaf) + data_end,
                              doff - data_end);
                for (i = slot + 1; i < nritems; i++) {
                        u32 ioff = btrfs_item_offset(leaf->items + i);
                        btrfs_set_item_offset(leaf->items + i, ioff + dsize);
                }
                btrfs_memmove(root, leaf, leaf->items + slot,
                              leaf->items + slot + 1,
                              sizeof(struct btrfs_item) *
                              (nritems - slot - 1));
        }
        btrfs_set_header_nritems(&leaf->header, nritems - 1);
        nritems--;
        /* delete the leaf if we've emptied it */
        if (nritems == 0) {
                if (leaf_buf == root->node) {
                        btrfs_set_header_level(&leaf->header, 0);
                } else {
                        clean_tree_block(trans, root, leaf_buf);
                        wait_on_buffer(leaf_buf);
                        wret = del_ptr(trans, root, path, 1, path->slots[1]);
                        if (wret)
                                ret = wret;
                        wret = btrfs_free_extent(trans, root,
                                                 bh_blocknr(leaf_buf), 1, 1);
                        if (wret)
                                ret = wret;
                }
        } else {
                int used = leaf_space_used(leaf, 0, nritems);
                if (slot == 0) {
                        wret = fixup_low_keys(trans, root, path,
                                              &leaf->items[0].key, 1);
                        if (wret)
                                ret = wret;
                }

                /* delete the leaf if it is mostly empty */
                if (used < BTRFS_LEAF_DATA_SIZE(root) / 3) {
                        /* push_leaf_left fixes the path.
                         * make sure the path still points to our leaf
                         * for possible call to del_ptr below
                         */
                        slot = path->slots[1];
                        get_bh(leaf_buf);
                        wret = push_leaf_left(trans, root, path, 1);
                        if (wret < 0 && wret != -ENOSPC)
                                ret = wret;
                        if (path->nodes[0] == leaf_buf &&
                            btrfs_header_nritems(&leaf->header)) {
                                wret = push_leaf_right(trans, root, path, 1);
                                if (wret < 0 && wret != -ENOSPC)
                                        ret = wret;
                        }
                        if (btrfs_header_nritems(&leaf->header) == 0) {
                                u64 blocknr = bh_blocknr(leaf_buf);
                                clean_tree_block(trans, root, leaf_buf);
                                wait_on_buffer(leaf_buf);
                                wret = del_ptr(trans, root, path, 1, slot);
                                if (wret)
                                        ret = wret;
                                btrfs_block_release(root, leaf_buf);
                                wret = btrfs_free_extent(trans, root, blocknr,
                                                         1, 1);
                                if (wret)
                                        ret = wret;
                        } else {
                                btrfs_mark_buffer_dirty(leaf_buf);
                                btrfs_block_release(root, leaf_buf);
                        }
                } else {
                        btrfs_mark_buffer_dirty(leaf_buf);
                }
        }
        return ret;
}

/*
 * walk up the tree as far as required to find the next leaf.
 * returns 0 if it found something or 1 if there are no greater leaves.
 * returns < 0 on io errors.
 */
int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
{
        int slot;
        int level = 1;
        u64 blocknr;
        struct buffer_head *c;
        struct btrfs_node *c_node;
        struct buffer_head *next = NULL;

        while(level < BTRFS_MAX_LEVEL) {
                if (!path->nodes[level])
                        return 1;
                slot = path->slots[level] + 1;
                c = path->nodes[level];
                c_node = btrfs_buffer_node(c);
                if (slot >= btrfs_header_nritems(&c_node->header)) {
                        level++;
                        continue;
                }
                blocknr = btrfs_node_blockptr(c_node, slot);
                if (next)
                        btrfs_block_release(root, next);
                if (path->reada)
                        reada_for_search(root, path, level, slot);
                next = read_tree_block(root, blocknr);
                break;
        }
        path->slots[level] = slot;
        while(1) {
                level--;
                c = path->nodes[level];
                btrfs_block_release(root, c);
                path->nodes[level] = next;
                path->slots[level] = 0;
                if (!level)
                        break;
                if (path->reada)
                        reada_for_search(root, path, level, 0);
                next = read_tree_block(root,
                       btrfs_node_blockptr(btrfs_buffer_node(next), 0));
        }
        return 0;
}