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

/*
 * Copyright (C) 2007,2008 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 <linux/sched.h>
#include <linux/slab.h>
#include <linux/rbtree.h>
#include <linux/vmalloc.h>
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "print-tree.h"
#include "locking.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, int extend);
static int push_node_left(struct btrfs_trans_handle *trans,
                          struct btrfs_root *root, struct extent_buffer *dst,
                          struct extent_buffer *src, int empty);
static int balance_node_right(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root,
                              struct extent_buffer *dst_buf,
                              struct extent_buffer *src_buf);
static void del_ptr(struct btrfs_root *root, struct btrfs_path *path,
                    int level, int slot);
static int tree_mod_log_free_eb(struct btrfs_fs_info *fs_info,
                                 struct extent_buffer *eb);

struct btrfs_path *btrfs_alloc_path(void)
{
        struct btrfs_path *path;
        path = kmem_cache_zalloc(btrfs_path_cachep, GFP_NOFS);
        return path;
}

/*
 * set all locked nodes in the path to blocking locks.  This should
 * be done before scheduling
 */
noinline void btrfs_set_path_blocking(struct btrfs_path *p)
{
        int i;
        for (i = 0; i < BTRFS_MAX_LEVEL; i++) {
                if (!p->nodes[i] || !p->locks[i])
                        continue;
                btrfs_set_lock_blocking_rw(p->nodes[i], p->locks[i]);
                if (p->locks[i] == BTRFS_READ_LOCK)
                        p->locks[i] = BTRFS_READ_LOCK_BLOCKING;
                else if (p->locks[i] == BTRFS_WRITE_LOCK)
                        p->locks[i] = BTRFS_WRITE_LOCK_BLOCKING;
        }
}

/*
 * reset all the locked nodes in the patch to spinning locks.
 *
 * held is used to keep lockdep happy, when lockdep is enabled
 * we set held to a blocking lock before we go around and
 * retake all the spinlocks in the path.  You can safely use NULL
 * for held
 */
noinline void btrfs_clear_path_blocking(struct btrfs_path *p,
                                        struct extent_buffer *held, int held_rw)
{
        int i;

        if (held) {
                btrfs_set_lock_blocking_rw(held, held_rw);
                if (held_rw == BTRFS_WRITE_LOCK)
                        held_rw = BTRFS_WRITE_LOCK_BLOCKING;
                else if (held_rw == BTRFS_READ_LOCK)
                        held_rw = BTRFS_READ_LOCK_BLOCKING;
        }
        btrfs_set_path_blocking(p);

        for (i = BTRFS_MAX_LEVEL - 1; i >= 0; i--) {
                if (p->nodes[i] && p->locks[i]) {
                        btrfs_clear_lock_blocking_rw(p->nodes[i], p->locks[i]);
                        if (p->locks[i] == BTRFS_WRITE_LOCK_BLOCKING)
                                p->locks[i] = BTRFS_WRITE_LOCK;
                        else if (p->locks[i] == BTRFS_READ_LOCK_BLOCKING)
                                p->locks[i] = BTRFS_READ_LOCK;
                }
        }

        if (held)
                btrfs_clear_lock_blocking_rw(held, held_rw);
}

/* this also releases the path */
void btrfs_free_path(struct btrfs_path *p)
{
        if (!p)
                return;
        btrfs_release_path(p);
        kmem_cache_free(btrfs_path_cachep, p);
}

/*
 * path release drops references on the extent buffers in the path
 * and it drops any locks held by this path
 *
 * It is safe to call this on paths that no locks or extent buffers held.
 */
noinline void btrfs_release_path(struct btrfs_path *p)
{
        int i;

        for (i = 0; i < BTRFS_MAX_LEVEL; i++) {
                p->slots[i] = 0;
                if (!p->nodes[i])
                        continue;
                if (p->locks[i]) {
                        btrfs_tree_unlock_rw(p->nodes[i], p->locks[i]);
                        p->locks[i] = 0;
                }
                free_extent_buffer(p->nodes[i]);
                p->nodes[i] = NULL;
        }
}

/*
 * safely gets a reference on the root node of a tree.  A lock
 * is not taken, so a concurrent writer may put a different node
 * at the root of the tree.  See btrfs_lock_root_node for the
 * looping required.
 *
 * The extent buffer returned by this has a reference taken, so
 * it won't disappear.  It may stop being the root of the tree
 * at any time because there are no locks held.
 */
struct extent_buffer *btrfs_root_node(struct btrfs_root *root)
{
        struct extent_buffer *eb;

        while (1) {
                rcu_read_lock();
                eb = rcu_dereference(root->node);

                /*
                 * RCU really hurts here, we could free up the root node because
                 * it was COWed but we may not get the new root node yet so do
                 * the inc_not_zero dance and if it doesn't work then
                 * synchronize_rcu and try again.
                 */
                if (atomic_inc_not_zero(&eb->refs)) {
                        rcu_read_unlock();
                        break;
                }
                rcu_read_unlock();
                synchronize_rcu();
        }
        return eb;
}

/* loop around taking references on and locking the root node of the
 * tree until you end up with a lock on the root.  A locked buffer
 * is returned, with a reference held.
 */
struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root)
{
        struct extent_buffer *eb;

        while (1) {
                eb = btrfs_root_node(root);
                btrfs_tree_lock(eb);
                if (eb == root->node)
                        break;
                btrfs_tree_unlock(eb);
                free_extent_buffer(eb);
        }
        return eb;
}

/* loop around taking references on and locking the root node of the
 * tree until you end up with a lock on the root.  A locked buffer
 * is returned, with a reference held.
 */
static struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root)
{
        struct extent_buffer *eb;

        while (1) {
                eb = btrfs_root_node(root);
                btrfs_tree_read_lock(eb);
                if (eb == root->node)
                        break;
                btrfs_tree_read_unlock(eb);
                free_extent_buffer(eb);
        }
        return eb;
}

/* cowonly root (everything not a reference counted cow subvolume), just get
 * put onto a simple dirty list.  transaction.c walks this to make sure they
 * get properly updated on disk.
 */
static void add_root_to_dirty_list(struct btrfs_root *root)
{
        if (test_bit(BTRFS_ROOT_DIRTY, &root->state) ||
            !test_bit(BTRFS_ROOT_TRACK_DIRTY, &root->state))
                return;

        spin_lock(&root->fs_info->trans_lock);
        if (!test_and_set_bit(BTRFS_ROOT_DIRTY, &root->state)) {
                /* Want the extent tree to be the last on the list */
                if (root->objectid == BTRFS_EXTENT_TREE_OBJECTID)
                        list_move_tail(&root->dirty_list,
                                       &root->fs_info->dirty_cowonly_roots);
                else
                        list_move(&root->dirty_list,
                                  &root->fs_info->dirty_cowonly_roots);
        }
        spin_unlock(&root->fs_info->trans_lock);
}

/*
 * used by snapshot creation to make a copy of a root for a tree with
 * a given objectid.  The buffer with the new root node is returned in
 * cow_ret, and this func returns zero on success or a negative error code.
 */
int btrfs_copy_root(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root,
                      struct extent_buffer *buf,
                      struct extent_buffer **cow_ret, u64 new_root_objectid)
{
        struct extent_buffer *cow;
        int ret = 0;
        int level;
        struct btrfs_disk_key disk_key;

        WARN_ON(test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
                trans->transid != root->fs_info->running_transaction->transid);
        WARN_ON(test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
                trans->transid != root->last_trans);

        level = btrfs_header_level(buf);
        if (level == 0)
                btrfs_item_key(buf, &disk_key, 0);
        else
                btrfs_node_key(buf, &disk_key, 0);

        cow = btrfs_alloc_tree_block(trans, root, 0, new_root_objectid,
                        &disk_key, level, buf->start, 0);
        if (IS_ERR(cow))
                return PTR_ERR(cow);

        copy_extent_buffer(cow, buf, 0, 0, cow->len);
        btrfs_set_header_bytenr(cow, cow->start);
        btrfs_set_header_generation(cow, trans->transid);
        btrfs_set_header_backref_rev(cow, BTRFS_MIXED_BACKREF_REV);
        btrfs_clear_header_flag(cow, BTRFS_HEADER_FLAG_WRITTEN |
                                     BTRFS_HEADER_FLAG_RELOC);
        if (new_root_objectid == BTRFS_TREE_RELOC_OBJECTID)
                btrfs_set_header_flag(cow, BTRFS_HEADER_FLAG_RELOC);
        else
                btrfs_set_header_owner(cow, new_root_objectid);

        write_extent_buffer(cow, root->fs_info->fsid, btrfs_header_fsid(),
                            BTRFS_FSID_SIZE);

        WARN_ON(btrfs_header_generation(buf) > trans->transid);
        if (new_root_objectid == BTRFS_TREE_RELOC_OBJECTID)
                ret = btrfs_inc_ref(trans, root, cow, 1);
        else
                ret = btrfs_inc_ref(trans, root, cow, 0);

        if (ret)
                return ret;

        btrfs_mark_buffer_dirty(cow);
        *cow_ret = cow;
        return 0;
}

enum mod_log_op {
        MOD_LOG_KEY_REPLACE,
        MOD_LOG_KEY_ADD,
        MOD_LOG_KEY_REMOVE,
        MOD_LOG_KEY_REMOVE_WHILE_FREEING,
        MOD_LOG_KEY_REMOVE_WHILE_MOVING,
        MOD_LOG_MOVE_KEYS,
        MOD_LOG_ROOT_REPLACE,
};

struct tree_mod_move {
        int dst_slot;
        int nr_items;
};

struct tree_mod_root {
        u64 logical;
        u8 level;
};

struct tree_mod_elem {
        struct rb_node node;
        u64 logical;
        u64 seq;
        enum mod_log_op op;

        /* this is used for MOD_LOG_KEY_* and MOD_LOG_MOVE_KEYS operations */
        int slot;

        /* this is used for MOD_LOG_KEY* and MOD_LOG_ROOT_REPLACE */
        u64 generation;

        /* those are used for op == MOD_LOG_KEY_{REPLACE,REMOVE} */
        struct btrfs_disk_key key;
        u64 blockptr;

        /* this is used for op == MOD_LOG_MOVE_KEYS */
        struct tree_mod_move move;

        /* this is used for op == MOD_LOG_ROOT_REPLACE */
        struct tree_mod_root old_root;
};

static inline void tree_mod_log_read_lock(struct btrfs_fs_info *fs_info)
{
        read_lock(&fs_info->tree_mod_log_lock);
}

static inline void tree_mod_log_read_unlock(struct btrfs_fs_info *fs_info)
{
        read_unlock(&fs_info->tree_mod_log_lock);
}

static inline void tree_mod_log_write_lock(struct btrfs_fs_info *fs_info)
{
        write_lock(&fs_info->tree_mod_log_lock);
}

static inline void tree_mod_log_write_unlock(struct btrfs_fs_info *fs_info)
{
        write_unlock(&fs_info->tree_mod_log_lock);
}

/*
 * Pull a new tree mod seq number for our operation.
 */
static inline u64 btrfs_inc_tree_mod_seq(struct btrfs_fs_info *fs_info)
{
        return atomic64_inc_return(&fs_info->tree_mod_seq);
}

/*
 * This adds a new blocker to the tree mod log's blocker list if the @elem
 * passed does not already have a sequence number set. So when a caller expects
 * to record tree modifications, it should ensure to set elem->seq to zero
 * before calling btrfs_get_tree_mod_seq.
 * Returns a fresh, unused tree log modification sequence number, even if no new
 * blocker was added.
 */
u64 btrfs_get_tree_mod_seq(struct btrfs_fs_info *fs_info,
                           struct seq_list *elem)
{
        tree_mod_log_write_lock(fs_info);
        spin_lock(&fs_info->tree_mod_seq_lock);
        if (!elem->seq) {
                elem->seq = btrfs_inc_tree_mod_seq(fs_info);
                list_add_tail(&elem->list, &fs_info->tree_mod_seq_list);
        }
        spin_unlock(&fs_info->tree_mod_seq_lock);
        tree_mod_log_write_unlock(fs_info);

        return elem->seq;
}

void btrfs_put_tree_mod_seq(struct btrfs_fs_info *fs_info,
                            struct seq_list *elem)
{
        struct rb_root *tm_root;
        struct rb_node *node;
        struct rb_node *next;
        struct seq_list *cur_elem;
        struct tree_mod_elem *tm;
        u64 min_seq = (u64)-1;
        u64 seq_putting = elem->seq;

        if (!seq_putting)
                return;

        spin_lock(&fs_info->tree_mod_seq_lock);
        list_del(&elem->list);
        elem->seq = 0;

        list_for_each_entry(cur_elem, &fs_info->tree_mod_seq_list, list) {
                if (cur_elem->seq < min_seq) {
                        if (seq_putting > cur_elem->seq) {
                                /*
                                 * blocker with lower sequence number exists, we
                                 * cannot remove anything from the log
                                 */
                                spin_unlock(&fs_info->tree_mod_seq_lock);
                                return;
                        }
                        min_seq = cur_elem->seq;
                }
        }
        spin_unlock(&fs_info->tree_mod_seq_lock);

        /*
         * anything that's lower than the lowest existing (read: blocked)
         * sequence number can be removed from the tree.
         */
        tree_mod_log_write_lock(fs_info);
        tm_root = &fs_info->tree_mod_log;
        for (node = rb_first(tm_root); node; node = next) {
                next = rb_next(node);
                tm = container_of(node, struct tree_mod_elem, node);
                if (tm->seq > min_seq)
                        continue;
                rb_erase(node, tm_root);
                kfree(tm);
        }
        tree_mod_log_write_unlock(fs_info);
}

/*
 * key order of the log:
 *       node/leaf start address -> sequence
 *
 * The 'start address' is the logical address of the *new* root node
 * for root replace operations, or the logical address of the affected
 * block for all other operations.
 *
 * Note: must be called with write lock (tree_mod_log_write_lock).
 */
static noinline int
__tree_mod_log_insert(struct btrfs_fs_info *fs_info, struct tree_mod_elem *tm)
{
        struct rb_root *tm_root;
        struct rb_node **new;
        struct rb_node *parent = NULL;
        struct tree_mod_elem *cur;

        BUG_ON(!tm);

        tm->seq = btrfs_inc_tree_mod_seq(fs_info);

        tm_root = &fs_info->tree_mod_log;
        new = &tm_root->rb_node;
        while (*new) {
                cur = container_of(*new, struct tree_mod_elem, node);
                parent = *new;
                if (cur->logical < tm->logical)
                        new = &((*new)->rb_left);
                else if (cur->logical > tm->logical)
                        new = &((*new)->rb_right);
                else if (cur->seq < tm->seq)
                        new = &((*new)->rb_left);
                else if (cur->seq > tm->seq)
                        new = &((*new)->rb_right);
                else
                        return -EEXIST;
        }

        rb_link_node(&tm->node, parent, new);
        rb_insert_color(&tm->node, tm_root);
        return 0;
}

/*
 * Determines if logging can be omitted. Returns 1 if it can. Otherwise, it
 * returns zero with the tree_mod_log_lock acquired. The caller must hold
 * this until all tree mod log insertions are recorded in the rb tree and then
 * call tree_mod_log_write_unlock() to release.
 */
static inline int tree_mod_dont_log(struct btrfs_fs_info *fs_info,
                                    struct extent_buffer *eb) {
        smp_mb();
        if (list_empty(&(fs_info)->tree_mod_seq_list))
                return 1;
        if (eb && btrfs_header_level(eb) == 0)
                return 1;

        tree_mod_log_write_lock(fs_info);
        if (list_empty(&(fs_info)->tree_mod_seq_list)) {
                tree_mod_log_write_unlock(fs_info);
                return 1;
        }

        return 0;
}

/* Similar to tree_mod_dont_log, but doesn't acquire any locks. */
static inline int tree_mod_need_log(const struct btrfs_fs_info *fs_info,
                                    struct extent_buffer *eb)
{
        smp_mb();
        if (list_empty(&(fs_info)->tree_mod_seq_list))
                return 0;
        if (eb && btrfs_header_level(eb) == 0)
                return 0;

        return 1;
}

static struct tree_mod_elem *
alloc_tree_mod_elem(struct extent_buffer *eb, int slot,
                    enum mod_log_op op, gfp_t flags)
{
        struct tree_mod_elem *tm;

        tm = kzalloc(sizeof(*tm), flags);
        if (!tm)
                return NULL;

        tm->logical = eb->start;
        if (op != MOD_LOG_KEY_ADD) {
                btrfs_node_key(eb, &tm->key, slot);
                tm->blockptr = btrfs_node_blockptr(eb, slot);
        }
        tm->op = op;
        tm->slot = slot;
        tm->generation = btrfs_node_ptr_generation(eb, slot);
        RB_CLEAR_NODE(&tm->node);

        return tm;
}

static noinline int
tree_mod_log_insert_key(struct btrfs_fs_info *fs_info,
                        struct extent_buffer *eb, int slot,
                        enum mod_log_op op, gfp_t flags)
{
        struct tree_mod_elem *tm;
        int ret;

        if (!tree_mod_need_log(fs_info, eb))
                return 0;

        tm = alloc_tree_mod_elem(eb, slot, op, flags);
        if (!tm)
                return -ENOMEM;

        if (tree_mod_dont_log(fs_info, eb)) {
                kfree(tm);
                return 0;
        }

        ret = __tree_mod_log_insert(fs_info, tm);
        tree_mod_log_write_unlock(fs_info);
        if (ret)
                kfree(tm);

        return ret;
}

static noinline int
tree_mod_log_insert_move(struct btrfs_fs_info *fs_info,
                         struct extent_buffer *eb, int dst_slot, int src_slot,
                         int nr_items, gfp_t flags)
{
        struct tree_mod_elem *tm = NULL;
        struct tree_mod_elem **tm_list = NULL;
        int ret = 0;
        int i;
        int locked = 0;

        if (!tree_mod_need_log(fs_info, eb))
                return 0;

        tm_list = kcalloc(nr_items, sizeof(struct tree_mod_elem *), flags);
        if (!tm_list)
                return -ENOMEM;

        tm = kzalloc(sizeof(*tm), flags);
        if (!tm) {
                ret = -ENOMEM;
                goto free_tms;
        }

        tm->logical = eb->start;
        tm->slot = src_slot;
        tm->move.dst_slot = dst_slot;
        tm->move.nr_items = nr_items;
        tm->op = MOD_LOG_MOVE_KEYS;

        for (i = 0; i + dst_slot < src_slot && i < nr_items; i++) {
                tm_list[i] = alloc_tree_mod_elem(eb, i + dst_slot,
                    MOD_LOG_KEY_REMOVE_WHILE_MOVING, flags);
                if (!tm_list[i]) {
                        ret = -ENOMEM;
                        goto free_tms;
                }
        }

        if (tree_mod_dont_log(fs_info, eb))
                goto free_tms;
        locked = 1;

        /*
         * When we override something during the move, we log these removals.
         * This can only happen when we move towards the beginning of the
         * buffer, i.e. dst_slot < src_slot.
         */
        for (i = 0; i + dst_slot < src_slot && i < nr_items; i++) {
                ret = __tree_mod_log_insert(fs_info, tm_list[i]);
                if (ret)
                        goto free_tms;
        }

        ret = __tree_mod_log_insert(fs_info, tm);
        if (ret)
                goto free_tms;
        tree_mod_log_write_unlock(fs_info);
        kfree(tm_list);

        return 0;
free_tms:
        for (i = 0; i < nr_items; i++) {
                if (tm_list[i] && !RB_EMPTY_NODE(&tm_list[i]->node))
                        rb_erase(&tm_list[i]->node, &fs_info->tree_mod_log);
                kfree(tm_list[i]);
        }
        if (locked)
                tree_mod_log_write_unlock(fs_info);
        kfree(tm_list);
        kfree(tm);

        return ret;
}

static inline int
__tree_mod_log_free_eb(struct btrfs_fs_info *fs_info,
                       struct tree_mod_elem **tm_list,
                       int nritems)
{
        int i, j;
        int ret;

        for (i = nritems - 1; i >= 0; i--) {
                ret = __tree_mod_log_insert(fs_info, tm_list[i]);
                if (ret) {
                        for (j = nritems - 1; j > i; j--)
                                rb_erase(&tm_list[j]->node,
                                         &fs_info->tree_mod_log);
                        return ret;
                }
        }

        return 0;
}

static noinline int
tree_mod_log_insert_root(struct btrfs_fs_info *fs_info,
                         struct extent_buffer *old_root,
                         struct extent_buffer *new_root, gfp_t flags,
                         int log_removal)
{
        struct tree_mod_elem *tm = NULL;
        struct tree_mod_elem **tm_list = NULL;
        int nritems = 0;
        int ret = 0;
        int i;

        if (!tree_mod_need_log(fs_info, NULL))
                return 0;

        if (log_removal && btrfs_header_level(old_root) > 0) {
                nritems = btrfs_header_nritems(old_root);
                tm_list = kcalloc(nritems, sizeof(struct tree_mod_elem *),
                                  flags);
                if (!tm_list) {
                        ret = -ENOMEM;
                        goto free_tms;
                }
                for (i = 0; i < nritems; i++) {
                        tm_list[i] = alloc_tree_mod_elem(old_root, i,
                            MOD_LOG_KEY_REMOVE_WHILE_FREEING, flags);
                        if (!tm_list[i]) {
                                ret = -ENOMEM;
                                goto free_tms;
                        }
                }
        }

        tm = kzalloc(sizeof(*tm), flags);
        if (!tm) {
                ret = -ENOMEM;
                goto free_tms;
        }

        tm->logical = new_root->start;
        tm->old_root.logical = old_root->start;
        tm->old_root.level = btrfs_header_level(old_root);
        tm->generation = btrfs_header_generation(old_root);
        tm->op = MOD_LOG_ROOT_REPLACE;

        if (tree_mod_dont_log(fs_info, NULL))
                goto free_tms;

        if (tm_list)
                ret = __tree_mod_log_free_eb(fs_info, tm_list, nritems);
        if (!ret)
                ret = __tree_mod_log_insert(fs_info, tm);

        tree_mod_log_write_unlock(fs_info);
        if (ret)
                goto free_tms;
        kfree(tm_list);

        return ret;

free_tms:
        if (tm_list) {
                for (i = 0; i < nritems; i++)
                        kfree(tm_list[i]);
                kfree(tm_list);
        }
        kfree(tm);

        return ret;
}

static struct tree_mod_elem *
__tree_mod_log_search(struct btrfs_fs_info *fs_info, u64 start, u64 min_seq,
                      int smallest)
{
        struct rb_root *tm_root;
        struct rb_node *node;
        struct tree_mod_elem *cur = NULL;
        struct tree_mod_elem *found = NULL;

        tree_mod_log_read_lock(fs_info);
        tm_root = &fs_info->tree_mod_log;
        node = tm_root->rb_node;
        while (node) {
                cur = container_of(node, struct tree_mod_elem, node);
                if (cur->logical < start) {
                        node = node->rb_left;
                } else if (cur->logical > start) {
                        node = node->rb_right;
                } else if (cur->seq < min_seq) {
                        node = node->rb_left;
                } else if (!smallest) {
                        /* we want the node with the highest seq */
                        if (found)
                                BUG_ON(found->seq > cur->seq);
                        found = cur;
                        node = node->rb_left;
                } else if (cur->seq > min_seq) {
                        /* we want the node with the smallest seq */
                        if (found)
                                BUG_ON(found->seq < cur->seq);
                        found = cur;
                        node = node->rb_right;
                } else {
                        found = cur;
                        break;
                }
        }
        tree_mod_log_read_unlock(fs_info);

        return found;
}

/*
 * this returns the element from the log with the smallest time sequence
 * value that's in the log (the oldest log item). any element with a time
 * sequence lower than min_seq will be ignored.
 */
static struct tree_mod_elem *
tree_mod_log_search_oldest(struct btrfs_fs_info *fs_info, u64 start,
                           u64 min_seq)
{
        return __tree_mod_log_search(fs_info, start, min_seq, 1);
}

/*
 * this returns the element from the log with the largest time sequence
 * value that's in the log (the most recent log item). any element with
 * a time sequence lower than min_seq will be ignored.
 */
static struct tree_mod_elem *
tree_mod_log_search(struct btrfs_fs_info *fs_info, u64 start, u64 min_seq)
{
        return __tree_mod_log_search(fs_info, start, min_seq, 0);
}

static noinline int
tree_mod_log_eb_copy(struct btrfs_fs_info *fs_info, struct extent_buffer *dst,
                     struct extent_buffer *src, unsigned long dst_offset,
                     unsigned long src_offset, int nr_items)
{
        int ret = 0;
        struct tree_mod_elem **tm_list = NULL;
        struct tree_mod_elem **tm_list_add, **tm_list_rem;
        int i;
        int locked = 0;

        if (!tree_mod_need_log(fs_info, NULL))
                return 0;

        if (btrfs_header_level(dst) == 0 && btrfs_header_level(src) == 0)
                return 0;

        tm_list = kcalloc(nr_items * 2, sizeof(struct tree_mod_elem *),
                          GFP_NOFS);
        if (!tm_list)
                return -ENOMEM;

        tm_list_add = tm_list;
        tm_list_rem = tm_list + nr_items;
        for (i = 0; i < nr_items; i++) {
                tm_list_rem[i] = alloc_tree_mod_elem(src, i + src_offset,
                    MOD_LOG_KEY_REMOVE, GFP_NOFS);
                if (!tm_list_rem[i]) {
                        ret = -ENOMEM;
                        goto free_tms;
                }

                tm_list_add[i] = alloc_tree_mod_elem(dst, i + dst_offset,
                    MOD_LOG_KEY_ADD, GFP_NOFS);
                if (!tm_list_add[i]) {
                        ret = -ENOMEM;
                        goto free_tms;
                }
        }

        if (tree_mod_dont_log(fs_info, NULL))
                goto free_tms;
        locked = 1;

        for (i = 0; i < nr_items; i++) {
                ret = __tree_mod_log_insert(fs_info, tm_list_rem[i]);
                if (ret)
                        goto free_tms;
                ret = __tree_mod_log_insert(fs_info, tm_list_add[i]);
                if (ret)
                        goto free_tms;
        }

        tree_mod_log_write_unlock(fs_info);
        kfree(tm_list);

        return 0;

free_tms:
        for (i = 0; i < nr_items * 2; i++) {
                if (tm_list[i] && !RB_EMPTY_NODE(&tm_list[i]->node))
                        rb_erase(&tm_list[i]->node, &fs_info->tree_mod_log);
                kfree(tm_list[i]);
        }
        if (locked)
                tree_mod_log_write_unlock(fs_info);
        kfree(tm_list);

        return ret;
}

static inline void
tree_mod_log_eb_move(struct btrfs_fs_info *fs_info, struct extent_buffer *dst,
                     int dst_offset, int src_offset, int nr_items)
{
        int ret;
        ret = tree_mod_log_insert_move(fs_info, dst, dst_offset, src_offset,
                                       nr_items, GFP_NOFS);
        BUG_ON(ret < 0);
}

static noinline void
tree_mod_log_set_node_key(struct btrfs_fs_info *fs_info,
                          struct extent_buffer *eb, int slot, int atomic)
{
        int ret;

        ret = tree_mod_log_insert_key(fs_info, eb, slot,
                                        MOD_LOG_KEY_REPLACE,
                                        atomic ? GFP_ATOMIC : GFP_NOFS);
        BUG_ON(ret < 0);
}

static noinline int
tree_mod_log_free_eb(struct btrfs_fs_info *fs_info, struct extent_buffer *eb)
{
        struct tree_mod_elem **tm_list = NULL;
        int nritems = 0;
        int i;
        int ret = 0;

        if (btrfs_header_level(eb) == 0)
                return 0;

        if (!tree_mod_need_log(fs_info, NULL))
                return 0;

        nritems = btrfs_header_nritems(eb);
        tm_list = kcalloc(nritems, sizeof(struct tree_mod_elem *), GFP_NOFS);
        if (!tm_list)
                return -ENOMEM;

        for (i = 0; i < nritems; i++) {
                tm_list[i] = alloc_tree_mod_elem(eb, i,
                    MOD_LOG_KEY_REMOVE_WHILE_FREEING, GFP_NOFS);
                if (!tm_list[i]) {
                        ret = -ENOMEM;
                        goto free_tms;
                }
        }

        if (tree_mod_dont_log(fs_info, eb))
                goto free_tms;

        ret = __tree_mod_log_free_eb(fs_info, tm_list, nritems);
        tree_mod_log_write_unlock(fs_info);
        if (ret)
                goto free_tms;
        kfree(tm_list);

        return 0;

free_tms:
        for (i = 0; i < nritems; i++)
                kfree(tm_list[i]);
        kfree(tm_list);

        return ret;
}

static noinline void
tree_mod_log_set_root_pointer(struct btrfs_root *root,
                              struct extent_buffer *new_root_node,
                              int log_removal)
{
        int ret;
        ret = tree_mod_log_insert_root(root->fs_info, root->node,
                                       new_root_node, GFP_NOFS, log_removal);
        BUG_ON(ret < 0);
}

/*
 * check if the tree block can be shared by multiple trees
 */
int btrfs_block_can_be_shared(struct btrfs_root *root,
                              struct extent_buffer *buf)
{
        /*
         * Tree blocks not in reference counted trees and tree roots
         * are never shared. If a block was allocated after the last
         * snapshot and the block was not allocated by tree relocation,
         * we know the block is not shared.
         */
        if (test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
            buf != root->node && buf != root->commit_root &&
            (btrfs_header_generation(buf) <=
             btrfs_root_last_snapshot(&root->root_item) ||
             btrfs_header_flag(buf, BTRFS_HEADER_FLAG_RELOC)))
                return 1;
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
        if (test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
            btrfs_header_backref_rev(buf) < BTRFS_MIXED_BACKREF_REV)
                return 1;
#endif
        return 0;
}

static noinline int update_ref_for_cow(struct btrfs_trans_handle *trans,
                                       struct btrfs_root *root,
                                       struct extent_buffer *buf,
                                       struct extent_buffer *cow,
                                       int *last_ref)
{
        u64 refs;
        u64 owner;
        u64 flags;
        u64 new_flags = 0;
        int ret;

        /*
         * Backrefs update rules:
         *
         * Always use full backrefs for extent pointers in tree block
         * allocated by tree relocation.
         *
         * If a shared tree block is no longer referenced by its owner
         * tree (btrfs_header_owner(buf) == root->root_key.objectid),
         * use full backrefs for extent pointers in tree block.
         *
         * If a tree block is been relocating
         * (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID),
         * use full backrefs for extent pointers in tree block.
         * The reason for this is some operations (such as drop tree)
         * are only allowed for blocks use full backrefs.
         */

        if (btrfs_block_can_be_shared(root, buf)) {
                ret = btrfs_lookup_extent_info(trans, root, buf->start,
                                               btrfs_header_level(buf), 1,
                                               &refs, &flags);
                if (ret)
                        return ret;
                if (refs == 0) {
                        ret = -EROFS;
                        btrfs_handle_fs_error(root->fs_info, ret, NULL);
                        return ret;
                }
        } else {
                refs = 1;
                if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID ||
                    btrfs_header_backref_rev(buf) < BTRFS_MIXED_BACKREF_REV)
                        flags = BTRFS_BLOCK_FLAG_FULL_BACKREF;
                else
                        flags = 0;
        }

        owner = btrfs_header_owner(buf);
        BUG_ON(owner == BTRFS_TREE_RELOC_OBJECTID &&
               !(flags & BTRFS_BLOCK_FLAG_FULL_BACKREF));

        if (refs > 1) {
                if ((owner == root->root_key.objectid ||
                     root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID) &&
                    !(flags & BTRFS_BLOCK_FLAG_FULL_BACKREF)) {
                        ret = btrfs_inc_ref(trans, root, buf, 1);
                        BUG_ON(ret); /* -ENOMEM */

                        if (root->root_key.objectid ==
                            BTRFS_TREE_RELOC_OBJECTID) {
                                ret = btrfs_dec_ref(trans, root, buf, 0);
                                BUG_ON(ret); /* -ENOMEM */
                                ret = btrfs_inc_ref(trans, root, cow, 1);
                                BUG_ON(ret); /* -ENOMEM */
                        }
                        new_flags |= BTRFS_BLOCK_FLAG_FULL_BACKREF;
                } else {

                        if (root->root_key.objectid ==
                            BTRFS_TREE_RELOC_OBJECTID)
                                ret = btrfs_inc_ref(trans, root, cow, 1);
                        else
                                ret = btrfs_inc_ref(trans, root, cow, 0);
                        BUG_ON(ret); /* -ENOMEM */
                }
                if (new_flags != 0) {
                        int level = btrfs_header_level(buf);

                        ret = btrfs_set_disk_extent_flags(trans, root,
                                                          buf->start,
                                                          buf->len,
                                                          new_flags, level, 0);
                        if (ret)
                                return ret;
                }
        } else {
                if (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF) {
                        if (root->root_key.objectid ==
                            BTRFS_TREE_RELOC_OBJECTID)
                                ret = btrfs_inc_ref(trans, root, cow, 1);
                        else
                                ret = btrfs_inc_ref(trans, root, cow, 0);
                        BUG_ON(ret); /* -ENOMEM */
                        ret = btrfs_dec_ref(trans, root, buf, 1);
                        BUG_ON(ret); /* -ENOMEM */
                }
                clean_tree_block(trans, root->fs_info, buf);
                *last_ref = 1;
        }
        return 0;
}

/*
 * does the dirty work in cow of a single block.  The parent block (if
 * supplied) is updated to point to the new cow copy.  The new buffer is marked
 * dirty and returned locked.  If you modify the block it needs to be marked
 * dirty again.
 *
 * search_start -- an allocation hint for the new block
 *
 * empty_size -- a hint that you plan on doing more cow.  This is the size in
 * bytes the allocator should try to find free next to the block it returns.
 * This is just a hint and may be ignored by the allocator.
 */
static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
                             struct btrfs_root *root,
                             struct extent_buffer *buf,
                             struct extent_buffer *parent, int parent_slot,
                             struct extent_buffer **cow_ret,
                             u64 search_start, u64 empty_size)
{
        struct btrfs_disk_key disk_key;
        struct extent_buffer *cow;
        int level, ret;
        int last_ref = 0;
        int unlock_orig = 0;
        u64 parent_start;

        if (*cow_ret == buf)
                unlock_orig = 1;

        btrfs_assert_tree_locked(buf);

        WARN_ON(test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
                trans->transid != root->fs_info->running_transaction->transid);
        WARN_ON(test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
                trans->transid != root->last_trans);

        level = btrfs_header_level(buf);

        if (level == 0)
                btrfs_item_key(buf, &disk_key, 0);
        else
                btrfs_node_key(buf, &disk_key, 0);

        if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID) {
                if (parent)
                        parent_start = parent->start;
                else
                        parent_start = 0;
        } else
                parent_start = 0;

        cow = btrfs_alloc_tree_block(trans, root, parent_start,
                        root->root_key.objectid, &disk_key, level,
                        search_start, empty_size);
        if (IS_ERR(cow))
                return PTR_ERR(cow);

        /* cow is set to blocking by btrfs_init_new_buffer */

        copy_extent_buffer(cow, buf, 0, 0, cow->len);
        btrfs_set_header_bytenr(cow, cow->start);
        btrfs_set_header_generation(cow, trans->transid);
        btrfs_set_header_backref_rev(cow, BTRFS_MIXED_BACKREF_REV);
        btrfs_clear_header_flag(cow, BTRFS_HEADER_FLAG_WRITTEN |
                                     BTRFS_HEADER_FLAG_RELOC);
        if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
                btrfs_set_header_flag(cow, BTRFS_HEADER_FLAG_RELOC);
        else
                btrfs_set_header_owner(cow, root->root_key.objectid);

        write_extent_buffer(cow, root->fs_info->fsid, btrfs_header_fsid(),
                            BTRFS_FSID_SIZE);

        ret = update_ref_for_cow(trans, root, buf, cow, &last_ref);
        if (ret) {
                btrfs_abort_transaction(trans, ret);
                return ret;
        }

        if (test_bit(BTRFS_ROOT_REF_COWS, &root->state)) {
                ret = btrfs_reloc_cow_block(trans, root, buf, cow);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        return ret;
                }
        }

        if (buf == root->node) {
                WARN_ON(parent && parent != buf);
                if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID ||
                    btrfs_header_backref_rev(buf) < BTRFS_MIXED_BACKREF_REV)
                        parent_start = buf->start;
                else
                        parent_start = 0;

                extent_buffer_get(cow);
                tree_mod_log_set_root_pointer(root, cow, 1);
                rcu_assign_pointer(root->node, cow);

                btrfs_free_tree_block(trans, root, buf, parent_start,
                                      last_ref);
                free_extent_buffer(buf);
                add_root_to_dirty_list(root);
        } else {
                if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
                        parent_start = parent->start;
                else
                        parent_start = 0;

                WARN_ON(trans->transid != btrfs_header_generation(parent));
                tree_mod_log_insert_key(root->fs_info, parent, parent_slot,
                                        MOD_LOG_KEY_REPLACE, GFP_NOFS);
                btrfs_set_node_blockptr(parent, parent_slot,
                                        cow->start);
                btrfs_set_node_ptr_generation(parent, parent_slot,
                                              trans->transid);
                btrfs_mark_buffer_dirty(parent);
                if (last_ref) {
                        ret = tree_mod_log_free_eb(root->fs_info, buf);
                        if (ret) {
                                btrfs_abort_transaction(trans, ret);
                                return ret;
                        }
                }
                btrfs_free_tree_block(trans, root, buf, parent_start,
                                      last_ref);
        }
        if (unlock_orig)
                btrfs_tree_unlock(buf);
        free_extent_buffer_stale(buf);
        btrfs_mark_buffer_dirty(cow);
        *cow_ret = cow;
        return 0;
}

/*
 * returns the logical address of the oldest predecessor of the given root.
 * entries older than time_seq are ignored.
 */
static struct tree_mod_elem *
__tree_mod_log_oldest_root(struct btrfs_fs_info *fs_info,
                           struct extent_buffer *eb_root, u64 time_seq)
{
        struct tree_mod_elem *tm;
        struct tree_mod_elem *found = NULL;
        u64 root_logical = eb_root->start;
        int looped = 0;

        if (!time_seq)
                return NULL;

        /*
         * the very last operation that's logged for a root is the
         * replacement operation (if it is replaced at all). this has
         * the logical address of the *new* root, making it the very
         * first operation that's logged for this root.
         */
        while (1) {
                tm = tree_mod_log_search_oldest(fs_info, root_logical,
                                                time_seq);
                if (!looped && !tm)
                        return NULL;
                /*
                 * if there are no tree operation for the oldest root, we simply
                 * return it. this should only happen if that (old) root is at
                 * level 0.
                 */
                if (!tm)
                        break;

                /*
                 * if there's an operation that's not a root replacement, we
                 * found the oldest version of our root. normally, we'll find a
                 * MOD_LOG_KEY_REMOVE_WHILE_FREEING operation here.
                 */
                if (tm->op != MOD_LOG_ROOT_REPLACE)
                        break;

                found = tm;
                root_logical = tm->old_root.logical;
                looped = 1;
        }

        /* if there's no old root to return, return what we found instead */
        if (!found)
                found = tm;

        return found;
}

/*
 * tm is a pointer to the first operation to rewind within eb. then, all
 * previous operations will be rewound (until we reach something older than
 * time_seq).
 */
static void
__tree_mod_log_rewind(struct btrfs_fs_info *fs_info, struct extent_buffer *eb,
                      u64 time_seq, struct tree_mod_elem *first_tm)
{
        u32 n;
        struct rb_node *next;
        struct tree_mod_elem *tm = first_tm;
        unsigned long o_dst;
        unsigned long o_src;
        unsigned long p_size = sizeof(struct btrfs_key_ptr);

        n = btrfs_header_nritems(eb);
        tree_mod_log_read_lock(fs_info);
        while (tm && tm->seq >= time_seq) {
                /*
                 * all the operations are recorded with the operator used for
                 * the modification. as we're going backwards, we do the
                 * opposite of each operation here.
                 */
                switch (tm->op) {
                case MOD_LOG_KEY_REMOVE_WHILE_FREEING:
                        BUG_ON(tm->slot < n);
                        /* Fallthrough */
                case MOD_LOG_KEY_REMOVE_WHILE_MOVING:
                case MOD_LOG_KEY_REMOVE:
                        btrfs_set_node_key(eb, &tm->key, tm->slot);
                        btrfs_set_node_blockptr(eb, tm->slot, tm->blockptr);
                        btrfs_set_node_ptr_generation(eb, tm->slot,
                                                      tm->generation);
                        n++;
                        break;
                case MOD_LOG_KEY_REPLACE:
                        BUG_ON(tm->slot >= n);
                        btrfs_set_node_key(eb, &tm->key, tm->slot);
                        btrfs_set_node_blockptr(eb, tm->slot, tm->blockptr);
                        btrfs_set_node_ptr_generation(eb, tm->slot,
                                                      tm->generation);
                        break;
                case MOD_LOG_KEY_ADD:
                        /* if a move operation is needed it's in the log */
                        n--;
                        break;
                case MOD_LOG_MOVE_KEYS:
                        o_dst = btrfs_node_key_ptr_offset(tm->slot);
                        o_src = btrfs_node_key_ptr_offset(tm->move.dst_slot);
                        memmove_extent_buffer(eb, o_dst, o_src,
                                              tm->move.nr_items * p_size);
                        break;
                case MOD_LOG_ROOT_REPLACE:
                        /*
                         * this operation is special. for roots, this must be
                         * handled explicitly before rewinding.
                         * for non-roots, this operation may exist if the node
                         * was a root: root A -> child B; then A gets empty and
                         * B is promoted to the new root. in the mod log, we'll
                         * have a root-replace operation for B, a tree block
                         * that is no root. we simply ignore that operation.
                         */
                        break;
                }
                next = rb_next(&tm->node);
                if (!next)
                        break;
                tm = container_of(next, struct tree_mod_elem, node);
                if (tm->logical != first_tm->logical)
                        break;
        }
        tree_mod_log_read_unlock(fs_info);
        btrfs_set_header_nritems(eb, n);
}

/*
 * Called with eb read locked. If the buffer cannot be rewound, the same buffer
 * is returned. If rewind operations happen, a fresh buffer is returned. The
 * returned buffer is always read-locked. If the returned buffer is not the
 * input buffer, the lock on the input buffer is released and the input buffer
 * is freed (its refcount is decremented).
 */
static struct extent_buffer *
tree_mod_log_rewind(struct btrfs_fs_info *fs_info, struct btrfs_path *path,
                    struct extent_buffer *eb, u64 time_seq)
{
        struct extent_buffer *eb_rewin;
        struct tree_mod_elem *tm;

        if (!time_seq)
                return eb;

        if (btrfs_header_level(eb) == 0)
                return eb;

        tm = tree_mod_log_search(fs_info, eb->start, time_seq);
        if (!tm)
                return eb;

        btrfs_set_path_blocking(path);
        btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);

        if (tm->op == MOD_LOG_KEY_REMOVE_WHILE_FREEING) {
                BUG_ON(tm->slot != 0);
                eb_rewin = alloc_dummy_extent_buffer(fs_info, eb->start,
                                                eb->len);
                if (!eb_rewin) {
                        btrfs_tree_read_unlock_blocking(eb);
                        free_extent_buffer(eb);
                        return NULL;
                }
                btrfs_set_header_bytenr(eb_rewin, eb->start);
                btrfs_set_header_backref_rev(eb_rewin,
                                             btrfs_header_backref_rev(eb));
                btrfs_set_header_owner(eb_rewin, btrfs_header_owner(eb));
                btrfs_set_header_level(eb_rewin, btrfs_header_level(eb));
        } else {
                eb_rewin = btrfs_clone_extent_buffer(eb);
                if (!eb_rewin) {
                        btrfs_tree_read_unlock_blocking(eb);
                        free_extent_buffer(eb);
                        return NULL;
                }
        }

        btrfs_clear_path_blocking(path, NULL, BTRFS_READ_LOCK);
        btrfs_tree_read_unlock_blocking(eb);
        free_extent_buffer(eb);

        extent_buffer_get(eb_rewin);
        btrfs_tree_read_lock(eb_rewin);
        __tree_mod_log_rewind(fs_info, eb_rewin, time_seq, tm);
        WARN_ON(btrfs_header_nritems(eb_rewin) >
                BTRFS_NODEPTRS_PER_BLOCK(fs_info->tree_root));

        return eb_rewin;
}

/*
 * get_old_root() rewinds the state of @root's root node to the given @time_seq
 * value. If there are no changes, the current root->root_node is returned. If
 * anything changed in between, there's a fresh buffer allocated on which the
 * rewind operations are done. In any case, the returned buffer is read locked.
 * Returns NULL on error (with no locks held).
 */
static inline struct extent_buffer *
get_old_root(struct btrfs_root *root, u64 time_seq)
{
        struct tree_mod_elem *tm;
        struct extent_buffer *eb = NULL;
        struct extent_buffer *eb_root;
        struct extent_buffer *old;
        struct tree_mod_root *old_root = NULL;
        u64 old_generation = 0;
        u64 logical;

        eb_root = btrfs_read_lock_root_node(root);
        tm = __tree_mod_log_oldest_root(root->fs_info, eb_root, time_seq);
        if (!tm)
                return eb_root;

        if (tm->op == MOD_LOG_ROOT_REPLACE) {
                old_root = &tm->old_root;
                old_generation = tm->generation;
                logical = old_root->logical;
        } else {
                logical = eb_root->start;
        }

        tm = tree_mod_log_search(root->fs_info, logical, time_seq);
        if (old_root && tm && tm->op != MOD_LOG_KEY_REMOVE_WHILE_FREEING) {
                btrfs_tree_read_unlock(eb_root);
                free_extent_buffer(eb_root);
                old = read_tree_block(root, logical, 0);
                if (WARN_ON(IS_ERR(old) || !extent_buffer_uptodate(old))) {
                        if (!IS_ERR(old))
                                free_extent_buffer(old);
                        btrfs_warn(root->fs_info,
                                "failed to read tree block %llu from get_old_root", logical);
                } else {
                        eb = btrfs_clone_extent_buffer(old);
                        free_extent_buffer(old);
                }
        } else if (old_root) {
                btrfs_tree_read_unlock(eb_root);
                free_extent_buffer(eb_root);
                eb = alloc_dummy_extent_buffer(root->fs_info, logical,
                                        root->nodesize);
        } else {
                btrfs_set_lock_blocking_rw(eb_root, BTRFS_READ_LOCK);
                eb = btrfs_clone_extent_buffer(eb_root);
                btrfs_tree_read_unlock_blocking(eb_root);
                free_extent_buffer(eb_root);
        }

        if (!eb)
                return NULL;
        extent_buffer_get(eb);
        btrfs_tree_read_lock(eb);
        if (old_root) {
                btrfs_set_header_bytenr(eb, eb->start);
                btrfs_set_header_backref_rev(eb, BTRFS_MIXED_BACKREF_REV);
                btrfs_set_header_owner(eb, btrfs_header_owner(eb_root));
                btrfs_set_header_level(eb, old_root->level);
                btrfs_set_header_generation(eb, old_generation);
        }
        if (tm)
                __tree_mod_log_rewind(root->fs_info, eb, time_seq, tm);
        else
                WARN_ON(btrfs_header_level(eb) != 0);
        WARN_ON(btrfs_header_nritems(eb) > BTRFS_NODEPTRS_PER_BLOCK(root));

        return eb;
}

int btrfs_old_root_level(struct btrfs_root *root, u64 time_seq)
{
        struct tree_mod_elem *tm;
        int level;
        struct extent_buffer *eb_root = btrfs_root_node(root);

        tm = __tree_mod_log_oldest_root(root->fs_info, eb_root, time_seq);
        if (tm && tm->op == MOD_LOG_ROOT_REPLACE) {
                level = tm->old_root.level;
        } else {
                level = btrfs_header_level(eb_root);
        }
        free_extent_buffer(eb_root);

        return level;
}

static inline int should_cow_block(struct btrfs_trans_handle *trans,
                                   struct btrfs_root *root,
                                   struct extent_buffer *buf)
{
        if (btrfs_is_testing(root->fs_info))
                return 0;

        /* ensure we can see the force_cow */
        smp_rmb();

        /*
         * We do not need to cow a block if
         * 1) this block is not created or changed in this transaction;
         * 2) this block does not belong to TREE_RELOC tree;
         * 3) the root is not forced COW.
         *
         * What is forced COW:
         *    when we create snapshot during committing the transaction,
         *    after we've finished coping src root, we must COW the shared
         *    block to ensure the metadata consistency.
         */
        if (btrfs_header_generation(buf) == trans->transid &&
            !btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN) &&
            !(root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID &&
              btrfs_header_flag(buf, BTRFS_HEADER_FLAG_RELOC)) &&
            !test_bit(BTRFS_ROOT_FORCE_COW, &root->state))
                return 0;
        return 1;
}

/*
 * cows a single block, see __btrfs_cow_block for the real work.
 * This version of it has extra checks so that a block isn't COWed more than
 * once per transaction, as long as it hasn't been written yet
 */
noinline int btrfs_cow_block(struct btrfs_trans_handle *trans,
                    struct btrfs_root *root, struct extent_buffer *buf,
                    struct extent_buffer *parent, int parent_slot,
                    struct extent_buffer **cow_ret)
{
        u64 search_start;
        int ret;

        if (trans->transaction != root->fs_info->running_transaction)
                WARN(1, KERN_CRIT "trans %llu running %llu\n",
                       trans->transid,
                       root->fs_info->running_transaction->transid);

        if (trans->transid != root->fs_info->generation)
                WARN(1, KERN_CRIT "trans %llu running %llu\n",
                       trans->transid, root->fs_info->generation);

        if (!should_cow_block(trans, root, buf)) {
                trans->dirty = true;
                *cow_ret = buf;
                return 0;
        }

        search_start = buf->start & ~((u64)SZ_1G - 1);

        if (parent)
                btrfs_set_lock_blocking(parent);
        btrfs_set_lock_blocking(buf);

        ret = __btrfs_cow_block(trans, root, buf, parent,
                                 parent_slot, cow_ret, search_start, 0);

        trace_btrfs_cow_block(root, buf, *cow_ret);

        return ret;
}

/*
 * helper function for defrag to decide if two blocks pointed to by a
 * node are actually close by
 */
static int close_blocks(u64 blocknr, u64 other, u32 blocksize)
{
        if (blocknr < other && other - (blocknr + blocksize) < 32768)
                return 1;
        if (blocknr > other && blocknr - (other + blocksize) < 32768)
                return 1;
        return 0;
}

/*
 * 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);

        return btrfs_comp_cpu_keys(&k1, k2);
}

/*
 * same as comp_keys only with two btrfs_key's
 */
int btrfs_comp_cpu_keys(struct btrfs_key *k1, struct btrfs_key *k2)
{
        if (k1->objectid > k2->objectid)
                return 1;
        if (k1->objectid < k2->objectid)
                return -1;
        if (k1->type > k2->type)
                return 1;
        if (k1->type < k2->type)
                return -1;
        if (k1->offset > k2->offset)
                return 1;
        if (k1->offset < k2->offset)
                return -1;
        return 0;
}

/*
 * this is used by the defrag code to go through all the
 * leaves pointed to by a node and reallocate them so that
 * disk order is close to key order
 */
int btrfs_realloc_node(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root, struct extent_buffer *parent,
                       int start_slot, u64 *last_ret,
                       struct btrfs_key *progress)
{
        struct extent_buffer *cur;
        u64 blocknr;
        u64 gen;
        u64 search_start = *last_ret;
        u64 last_block = 0;
        u64 other;
        u32 parent_nritems;
        int end_slot;
        int i;
        int err = 0;
        int parent_level;
        int uptodate;
        u32 blocksize;
        int progress_passed = 0;
        struct btrfs_disk_key disk_key;

        parent_level = btrfs_header_level(parent);

        WARN_ON(trans->transaction != root->fs_info->running_transaction);
        WARN_ON(trans->transid != root->fs_info->generation);

        parent_nritems = btrfs_header_nritems(parent);
        blocksize = root->nodesize;
        end_slot = parent_nritems - 1;

        if (parent_nritems <= 1)
                return 0;

        btrfs_set_lock_blocking(parent);

        for (i = start_slot; i <= end_slot; i++) {
                int close = 1;

                btrfs_node_key(parent, &disk_key, i);
                if (!progress_passed && comp_keys(&disk_key, progress) < 0)
                        continue;

                progress_passed = 1;
                blocknr = btrfs_node_blockptr(parent, i);
                gen = btrfs_node_ptr_generation(parent, i);
                if (last_block == 0)
                        last_block = blocknr;

                if (i > 0) {
                        other = btrfs_node_blockptr(parent, i - 1);
                        close = close_blocks(blocknr, other, blocksize);
                }
                if (!close && i < end_slot) {
                        other = btrfs_node_blockptr(parent, i + 1);
                        close = close_blocks(blocknr, other, blocksize);
                }
                if (close) {
                        last_block = blocknr;
                        continue;
                }

                cur = btrfs_find_tree_block(root->fs_info, blocknr);
                if (cur)
                        uptodate = btrfs_buffer_uptodate(cur, gen, 0);
                else
                        uptodate = 0;
                if (!cur || !uptodate) {
                        if (!cur) {
                                cur = read_tree_block(root, blocknr, gen);
                                if (IS_ERR(cur)) {
                                        return PTR_ERR(cur);
                                } else if (!extent_buffer_uptodate(cur)) {
                                        free_extent_buffer(cur);
                                        return -EIO;
                                }
                        } else if (!uptodate) {
                                err = btrfs_read_buffer(cur, gen);
                                if (err) {
                                        free_extent_buffer(cur);
                                        return err;
                                }
                        }
                }
                if (search_start == 0)
                        search_start = last_block;

                btrfs_tree_lock(cur);
                btrfs_set_lock_blocking(cur);
                err = __btrfs_cow_block(trans, root, cur, parent, i,
                                        &cur, search_start,
                                        min(16 * blocksize,
                                            (end_slot - i) * blocksize));
                if (err) {
                        btrfs_tree_unlock(cur);
                        free_extent_buffer(cur);
                        break;
                }
                search_start = cur->start;
                last_block = cur->start;
                *last_ret = search_start;
                btrfs_tree_unlock(cur);
                free_extent_buffer(cur);
        }
        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 extent_buffer *leaf)
{
        u32 nr = btrfs_header_nritems(leaf);
        if (nr == 0)
                return BTRFS_LEAF_DATA_SIZE(root);
        return btrfs_item_offset_nr(leaf, nr - 1);
}


/*
 * search for key in the extent_buffer.  The items start at offset p,
 * and they are item_size apart.  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 noinline int generic_bin_search(struct extent_buffer *eb,
                                       unsigned long 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 = NULL;
        struct btrfs_disk_key unaligned;
        unsigned long offset;
        char *kaddr = NULL;
        unsigned long map_start = 0;
        unsigned long map_len = 0;
        int err;

        if (low > high) {
                btrfs_err(eb->fs_info,
                 "%s: low (%d) > high (%d) eb %llu owner %llu level %d",
                          __func__, low, high, eb->start,
                          btrfs_header_owner(eb), btrfs_header_level(eb));
                return -EINVAL;
        }

        while (low < high) {
                mid = (low + high) / 2;
                offset = p + mid * item_size;

                if (!kaddr || offset < map_start ||
                    (offset + sizeof(struct btrfs_disk_key)) >
                    map_start + map_len) {

                        err = map_private_extent_buffer(eb, offset,
                                                sizeof(struct btrfs_disk_key),
                                                &kaddr, &map_start, &map_len);

                        if (!err) {
                                tmp = (struct btrfs_disk_key *)(kaddr + offset -
                                                        map_start);
                        } else if (err == 1) {
                                read_extent_buffer(eb, &unaligned,
                                                   offset, sizeof(unaligned));
                                tmp = &unaligned;
                        } else {
                                return err;
                        }

                } else {
                        tmp = (struct btrfs_disk_key *)(kaddr + offset -
                                                        map_start);
                }
                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 extent_buffer *eb, struct btrfs_key *key,
                      int level, int *slot)
{
        if (level == 0)
                return generic_bin_search(eb,
                                          offsetof(struct btrfs_leaf, items),
                                          sizeof(struct btrfs_item),
                                          key, btrfs_header_nritems(eb),
                                          slot);
        else
                return generic_bin_search(eb,
                                          offsetof(struct btrfs_node, ptrs),
                                          sizeof(struct btrfs_key_ptr),
                                          key, btrfs_header_nritems(eb),
                                          slot);
}

int btrfs_bin_search(struct extent_buffer *eb, struct btrfs_key *key,
                     int level, int *slot)
{
        return bin_search(eb, key, level, slot);
}

static void root_add_used(struct btrfs_root *root, u32 size)
{
        spin_lock(&root->accounting_lock);
        btrfs_set_root_used(&root->root_item,
                            btrfs_root_used(&root->root_item) + size);
        spin_unlock(&root->accounting_lock);
}

static void root_sub_used(struct btrfs_root *root, u32 size)
{
        spin_lock(&root->accounting_lock);
        btrfs_set_root_used(&root->root_item,
                            btrfs_root_used(&root->root_item) - size);
        spin_unlock(&root->accounting_lock);
}

/* given a node and slot number, this reads the blocks it points to.  The
 * extent buffer is returned with a reference taken (but unlocked).
 */
static noinline struct extent_buffer *read_node_slot(struct btrfs_root *root,
                                   struct extent_buffer *parent, int slot)
{
        int level = btrfs_header_level(parent);
        struct extent_buffer *eb;

        if (slot < 0 || slot >= btrfs_header_nritems(parent))
                return ERR_PTR(-ENOENT);

        BUG_ON(level == 0);

        eb = read_tree_block(root, btrfs_node_blockptr(parent, slot),
                             btrfs_node_ptr_generation(parent, slot));
        if (!IS_ERR(eb) && !extent_buffer_uptodate(eb)) {
                free_extent_buffer(eb);
                eb = ERR_PTR(-EIO);
        }

        return eb;
}

/*
 * node level balancing, used to make sure nodes are in proper order for
 * item deletion.  We balance from the top down, so we have to make sure
 * that a deletion won't leave an node completely empty later on.
 */
static noinline int balance_level(struct btrfs_trans_handle *trans,
                         struct btrfs_root *root,
                         struct btrfs_path *path, int level)
{
        struct extent_buffer *right = NULL;
        struct extent_buffer *mid;
        struct extent_buffer *left = NULL;
        struct extent_buffer *parent = NULL;
        int ret = 0;
        int wret;
        int pslot;
        int orig_slot = path->slots[level];
        u64 orig_ptr;

        if (level == 0)
                return 0;

        mid = path->nodes[level];

        WARN_ON(path->locks[level] != BTRFS_WRITE_LOCK &&
                path->locks[level] != BTRFS_WRITE_LOCK_BLOCKING);
        WARN_ON(btrfs_header_generation(mid) != trans->transid);

        orig_ptr = btrfs_node_blockptr(mid, orig_slot);

        if (level < BTRFS_MAX_LEVEL - 1) {
                parent = 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) {
                struct extent_buffer *child;

                if (btrfs_header_nritems(mid) != 1)
                        return 0;

                /* promote the child to a root */
                child = read_node_slot(root, mid, 0);
                if (IS_ERR(child)) {
                        ret = PTR_ERR(child);
                        btrfs_handle_fs_error(root->fs_info, ret, NULL);
                        goto enospc;
                }

                btrfs_tree_lock(child);
                btrfs_set_lock_blocking(child);
                ret = btrfs_cow_block(trans, root, child, mid, 0, &child);
                if (ret) {
                        btrfs_tree_unlock(child);
                        free_extent_buffer(child);
                        goto enospc;
                }

                tree_mod_log_set_root_pointer(root, child, 1);
                rcu_assign_pointer(root->node, child);

                add_root_to_dirty_list(root);
                btrfs_tree_unlock(child);

                path->locks[level] = 0;
                path->nodes[level] = NULL;
                clean_tree_block(trans, root->fs_info, mid);
                btrfs_tree_unlock(mid);
                /* once for the path */
                free_extent_buffer(mid);

                root_sub_used(root, mid->len);
                btrfs_free_tree_block(trans, root, mid, 0, 1);
                /* once for the root ptr */
                free_extent_buffer_stale(mid);
                return 0;
        }
        if (btrfs_header_nritems(mid) >
            BTRFS_NODEPTRS_PER_BLOCK(root) / 4)
                return 0;

        left = read_node_slot(root, parent, pslot - 1);
        if (IS_ERR(left))
                left = NULL;

        if (left) {
                btrfs_tree_lock(left);
                btrfs_set_lock_blocking(left);
                wret = btrfs_cow_block(trans, root, left,
                                       parent, pslot - 1, &left);
                if (wret) {
                        ret = wret;
                        goto enospc;
                }
        }

        right = read_node_slot(root, parent, pslot + 1);
        if (IS_ERR(right))
                right = NULL;

        if (right) {
                btrfs_tree_lock(right);
                btrfs_set_lock_blocking(right);
                wret = btrfs_cow_block(trans, root, right,
                                       parent, pslot + 1, &right);
                if (wret) {
                        ret = wret;
                        goto enospc;
                }
        }

        /* first, try to make some room in the middle buffer */
        if (left) {
                orig_slot += btrfs_header_nritems(left);
                wret = push_node_left(trans, root, left, mid, 1);
                if (wret < 0)
                        ret = wret;
        }

        /*
         * then try to empty the right most buffer into the middle
         */
        if (right) {
                wret = push_node_left(trans, root, mid, right, 1);
                if (wret < 0 && wret != -ENOSPC)
                        ret = wret;
                if (btrfs_header_nritems(right) == 0) {
                        clean_tree_block(trans, root->fs_info, right);
                        btrfs_tree_unlock(right);
                        del_ptr(root, path, level + 1, pslot + 1);
                        root_sub_used(root, right->len);
                        btrfs_free_tree_block(trans, root, right, 0, 1);
                        free_extent_buffer_stale(right);
                        right = NULL;
                } else {
                        struct btrfs_disk_key right_key;
                        btrfs_node_key(right, &right_key, 0);
                        tree_mod_log_set_node_key(root->fs_info, parent,
                                                  pslot + 1, 0);
                        btrfs_set_node_key(parent, &right_key, pslot + 1);
                        btrfs_mark_buffer_dirty(parent);
                }
        }
        if (btrfs_header_nritems(mid) == 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
                 */
                if (!left) {
                        ret = -EROFS;
                        btrfs_handle_fs_error(root->fs_info, ret, NULL);
                        goto enospc;
                }
                wret = balance_node_right(trans, root, mid, left);
                if (wret < 0) {
                        ret = wret;
                        goto enospc;
                }
                if (wret == 1) {
                        wret = push_node_left(trans, root, left, mid, 1);
                        if (wret < 0)
                                ret = wret;
                }
                BUG_ON(wret == 1);
        }
        if (btrfs_header_nritems(mid) == 0) {
                clean_tree_block(trans, root->fs_info, mid);
                btrfs_tree_unlock(mid);
                del_ptr(root, path, level + 1, pslot);
                root_sub_used(root, mid->len);
                btrfs_free_tree_block(trans, root, mid, 0, 1);
                free_extent_buffer_stale(mid);
                mid = NULL;
        } else {
                /* update the parent key to reflect our changes */
                struct btrfs_disk_key mid_key;
                btrfs_node_key(mid, &mid_key, 0);
                tree_mod_log_set_node_key(root->fs_info, parent,
                                          pslot, 0);
                btrfs_set_node_key(parent, &mid_key, pslot);
                btrfs_mark_buffer_dirty(parent);
        }

        /* update the path */
        if (left) {
                if (btrfs_header_nritems(left) > orig_slot) {
                        extent_buffer_get(left);
                        /* left was locked after cow */
                        path->nodes[level] = left;
                        path->slots[level + 1] -= 1;
                        path->slots[level] = orig_slot;
                        if (mid) {
                                btrfs_tree_unlock(mid);
                                free_extent_buffer(mid);
                        }
                } else {
                        orig_slot -= btrfs_header_nritems(left);
                        path->slots[level] = orig_slot;
                }
        }
        /* double check we haven't messed things up */
        if (orig_ptr !=
            btrfs_node_blockptr(path->nodes[level], path->slots[level]))
                BUG();
enospc:
        if (right) {
                btrfs_tree_unlock(right);
                free_extent_buffer(right);
        }
        if (left) {
                if (path->nodes[level] != left)
                        btrfs_tree_unlock(left);
                free_extent_buffer(left);
        }
        return ret;
}

/* Node balancing for insertion.  Here we only split or push nodes around
 * when they are completely full.  This is also done top down, so we
 * have to be pessimistic.
 */
static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
                                          struct btrfs_root *root,
                                          struct btrfs_path *path, int level)
{
        struct extent_buffer *right = NULL;
        struct extent_buffer *mid;
        struct extent_buffer *left = NULL;
        struct extent_buffer *parent = NULL;
        int ret = 0;
        int wret;
        int pslot;
        int orig_slot = path->slots[level];

        if (level == 0)
                return 1;

        mid = path->nodes[level];
        WARN_ON(btrfs_header_generation(mid) != trans->transid);

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

        if (!parent)
                return 1;

        left = read_node_slot(root, parent, pslot - 1);
        if (IS_ERR(left))
                left = NULL;

        /* first, try to make some room in the middle buffer */
        if (left) {
                u32 left_nr;

                btrfs_tree_lock(left);
                btrfs_set_lock_blocking(left);

                left_nr = btrfs_header_nritems(left);
                if (left_nr >= BTRFS_NODEPTRS_PER_BLOCK(root) - 1) {
                        wret = 1;
                } else {
                        ret = btrfs_cow_block(trans, root, left, parent,
                                              pslot - 1, &left);
                        if (ret)
                                wret = 1;
                        else {
                                wret = push_node_left(trans, root,
                                                      left, mid, 0);
                        }
                }
                if (wret < 0)
                        ret = wret;
                if (wret == 0) {
                        struct btrfs_disk_key disk_key;
                        orig_slot += left_nr;
                        btrfs_node_key(mid, &disk_key, 0);
                        tree_mod_log_set_node_key(root->fs_info, parent,
                                                  pslot, 0);
                        btrfs_set_node_key(parent, &disk_key, pslot);
                        btrfs_mark_buffer_dirty(parent);
                        if (btrfs_header_nritems(left) > orig_slot) {
                                path->nodes[level] = left;
                                path->slots[level + 1] -= 1;
                                path->slots[level] = orig_slot;
                                btrfs_tree_unlock(mid);
                                free_extent_buffer(mid);
                        } else {
                                orig_slot -=
                                        btrfs_header_nritems(left);
                                path->slots[level] = orig_slot;
                                btrfs_tree_unlock(left);
                                free_extent_buffer(left);
                        }
                        return 0;
                }
                btrfs_tree_unlock(left);
                free_extent_buffer(left);
        }
        right = read_node_slot(root, parent, pslot + 1);
        if (IS_ERR(right))
                right = NULL;

        /*
         * then try to empty the right most buffer into the middle
         */
        if (right) {
                u32 right_nr;

                btrfs_tree_lock(right);
                btrfs_set_lock_blocking(right);

                right_nr = btrfs_header_nritems(right);
                if (right_nr >= BTRFS_NODEPTRS_PER_BLOCK(root) - 1) {
                        wret = 1;
                } else {
                        ret = btrfs_cow_block(trans, root, right,
                                              parent, pslot + 1,
                                              &right);
                        if (ret)
                                wret = 1;
                        else {
                                wret = balance_node_right(trans, root,
                                                          right, mid);
                        }
                }
                if (wret < 0)
                        ret = wret;
                if (wret == 0) {
                        struct btrfs_disk_key disk_key;

                        btrfs_node_key(right, &disk_key, 0);
                        tree_mod_log_set_node_key(root->fs_info, parent,
                                                  pslot + 1, 0);
                        btrfs_set_node_key(parent, &disk_key, pslot + 1);
                        btrfs_mark_buffer_dirty(parent);

                        if (btrfs_header_nritems(mid) <= orig_slot) {
                                path->nodes[level] = right;
                                path->slots[level + 1] += 1;
                                path->slots[level] = orig_slot -
                                        btrfs_header_nritems(mid);
                                btrfs_tree_unlock(mid);
                                free_extent_buffer(mid);
                        } else {
                                btrfs_tree_unlock(right);
                                free_extent_buffer(right);
                        }
                        return 0;
                }
                btrfs_tree_unlock(right);
                free_extent_buffer(right);
        }
        return 1;
}

/*
 * readahead one full node of leaves, finding things that are close
 * to the block in 'slot', and triggering ra on them.
 */
static void reada_for_search(struct btrfs_root *root,
                             struct btrfs_path *path,
                             int level, int slot, u64 objectid)
{
        struct extent_buffer *node;
        struct btrfs_disk_key disk_key;
        u32 nritems;
        u64 search;
        u64 target;
        u64 nread = 0;
        u64 gen;
        struct extent_buffer *eb;
        u32 nr;
        u32 blocksize;
        u32 nscan = 0;

        if (level != 1)
                return;

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

        node = path->nodes[level];

        search = btrfs_node_blockptr(node, slot);
        blocksize = root->nodesize;
        eb = btrfs_find_tree_block(root->fs_info, search);
        if (eb) {
                free_extent_buffer(eb);
                return;
        }

        target = search;

        nritems = btrfs_header_nritems(node);
        nr = slot;

        while (1) {
                if (path->reada == READA_BACK) {
                        if (nr == 0)
                                break;
                        nr--;
                } else if (path->reada == READA_FORWARD) {
                        nr++;
                        if (nr >= nritems)
                                break;
                }
                if (path->reada == READA_BACK && objectid) {
                        btrfs_node_key(node, &disk_key, nr);
                        if (btrfs_disk_key_objectid(&disk_key) != objectid)
                                break;
                }
                search = btrfs_node_blockptr(node, nr);
                if ((search <= target && target - search <= 65536) ||
                    (search > target && search - target <= 65536)) {
                        gen = btrfs_node_ptr_generation(node, nr);
                        readahead_tree_block(root, search);
                        nread += blocksize;
                }
                nscan++;
                if ((nread > 65536 || nscan > 32))
                        break;
        }
}

static noinline void reada_for_balance(struct btrfs_root *root,
                                       struct btrfs_path *path, int level)
{
        int slot;
        int nritems;
        struct extent_buffer *parent;
        struct extent_buffer *eb;
        u64 gen;
        u64 block1 = 0;
        u64 block2 = 0;

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

        nritems = btrfs_header_nritems(parent);
        slot = path->slots[level + 1];

        if (slot > 0) {
                block1 = btrfs_node_blockptr(parent, slot - 1);
                gen = btrfs_node_ptr_generation(parent, slot - 1);
                eb = btrfs_find_tree_block(root->fs_info, block1);
                /*
                 * if we get -eagain from btrfs_buffer_uptodate, we
                 * don't want to return eagain here.  That will loop
                 * forever
                 */
                if (eb && btrfs_buffer_uptodate(eb, gen, 1) != 0)
                        block1 = 0;
                free_extent_buffer(eb);
        }
        if (slot + 1 < nritems) {
                block2 = btrfs_node_blockptr(parent, slot + 1);
                gen = btrfs_node_ptr_generation(parent, slot + 1);
                eb = btrfs_find_tree_block(root->fs_info, block2);
                if (eb && btrfs_buffer_uptodate(eb, gen, 1) != 0)
                        block2 = 0;
                free_extent_buffer(eb);
        }

        if (block1)
                readahead_tree_block(root, block1);
        if (block2)
                readahead_tree_block(root, block2);
}


/*
 * when we walk down the tree, it is usually safe to unlock the higher layers
 * in the tree.  The exceptions are when our path goes through slot 0, because
 * operations on the tree might require changing key pointers higher up in the
 * tree.
 *
 * callers might also have set path->keep_locks, which tells this code to keep
 * the lock if the path points to the last slot in the block.  This is part of
 * walking through the tree, and selecting the next slot in the higher block.
 *
 * lowest_unlock sets the lowest level in the tree we're allowed to unlock.  so
 * if lowest_unlock is 1, level 0 won't be unlocked
 */
static noinline void unlock_up(struct btrfs_path *path, int level,
                               int lowest_unlock, int min_write_lock_level,
                               int *write_lock_level)
{
        int i;
        int skip_level = level;
        int no_skips = 0;
        struct extent_buffer *t;

        for (i = level; i < BTRFS_MAX_LEVEL; i++) {
                if (!path->nodes[i])
                        break;
                if (!path->locks[i])
                        break;
                if (!no_skips && path->slots[i] == 0) {
                        skip_level = i + 1;
                        continue;
                }
                if (!no_skips && path->keep_locks) {
                        u32 nritems;
                        t = path->nodes[i];
                        nritems = btrfs_header_nritems(t);
                        if (nritems < 1 || path->slots[i] >= nritems - 1) {
                                skip_level = i + 1;
                                continue;
                        }
                }
                if (skip_level < i && i >= lowest_unlock)
                        no_skips = 1;

                t = path->nodes[i];
                if (i >= lowest_unlock && i > skip_level && path->locks[i]) {
                        btrfs_tree_unlock_rw(t, path->locks[i]);
                        path->locks[i] = 0;
                        if (write_lock_level &&
                            i > min_write_lock_level &&
                            i <= *write_lock_level) {
                                *write_lock_level = i - 1;
                        }
                }
        }
}

/*
 * This releases any locks held in the path starting at level and
 * going all the way up to the root.
 *
 * btrfs_search_slot will keep the lock held on higher nodes in a few
 * corner cases, such as COW of the block at slot zero in the node.  This
 * ignores those rules, and it should only be called when there are no
 * more updates to be done higher up in the tree.
 */
noinline void btrfs_unlock_up_safe(struct btrfs_path *path, int level)
{
        int i;

        if (path->keep_locks)
                return;

        for (i = level; i < BTRFS_MAX_LEVEL; i++) {
                if (!path->nodes[i])
                        continue;
                if (!path->locks[i])
                        continue;
                btrfs_tree_unlock_rw(path->nodes[i], path->locks[i]);
                path->locks[i] = 0;
        }
}

/*
 * helper function for btrfs_search_slot.  The goal is to find a block
 * in cache without setting the path to blocking.  If we find the block
 * we return zero and the path is unchanged.
 *
 * If we can't find the block, we set the path blocking and do some
 * reada.  -EAGAIN is returned and the search must be repeated.
 */
static int
read_block_for_search(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root, struct btrfs_path *p,
                       struct extent_buffer **eb_ret, int level, int slot,
                       struct btrfs_key *key, u64 time_seq)
{
        u64 blocknr;
        u64 gen;
        struct extent_buffer *b = *eb_ret;
        struct extent_buffer *tmp;
        int ret;

        blocknr = btrfs_node_blockptr(b, slot);
        gen = btrfs_node_ptr_generation(b, slot);

        tmp = btrfs_find_tree_block(root->fs_info, blocknr);
        if (tmp) {
                /* first we do an atomic uptodate check */
                if (btrfs_buffer_uptodate(tmp, gen, 1) > 0) {
                        *eb_ret = tmp;
                        return 0;
                }

                /* the pages were up to date, but we failed
                 * the generation number check.  Do a full
                 * read for the generation number that is correct.
                 * We must do this without dropping locks so
                 * we can trust our generation number
                 */
                btrfs_set_path_blocking(p);

                /* now we're allowed to do a blocking uptodate check */
                ret = btrfs_read_buffer(tmp, gen);
                if (!ret) {
                        *eb_ret = tmp;
                        return 0;
                }
                free_extent_buffer(tmp);
                btrfs_release_path(p);
                return -EIO;
        }

        /*
         * reduce lock contention at high levels
         * of the btree by dropping locks before
         * we read.  Don't release the lock on the current
         * level because we need to walk this node to figure
         * out which blocks to read.
         */
        btrfs_unlock_up_safe(p, level + 1);
        btrfs_set_path_blocking(p);

        free_extent_buffer(tmp);
        if (p->reada != READA_NONE)
                reada_for_search(root, p, level, slot, key->objectid);

        btrfs_release_path(p);

        ret = -EAGAIN;
        tmp = read_tree_block(root, blocknr, 0);
        if (!IS_ERR(tmp)) {
                /*
                 * If the read above didn't mark this buffer up to date,
                 * it will never end up being up to date.  Set ret to EIO now
                 * and give up so that our caller doesn't loop forever
                 * on our EAGAINs.
                 */
                if (!btrfs_buffer_uptodate(tmp, 0, 0))
                        ret = -EIO;
                free_extent_buffer(tmp);
        } else {
                ret = PTR_ERR(tmp);
        }
        return ret;
}

/*
 * helper function for btrfs_search_slot.  This does all of the checks
 * for node-level blocks and does any balancing required based on
 * the ins_len.
 *
 * If no extra work was required, zero is returned.  If we had to
 * drop the path, -EAGAIN is returned and btrfs_search_slot must
 * start over
 */
static int
setup_nodes_for_search(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root, struct btrfs_path *p,
                       struct extent_buffer *b, int level, int ins_len,
                       int *write_lock_level)
{
        int ret;
        if ((p->search_for_split || ins_len > 0) && btrfs_header_nritems(b) >=
            BTRFS_NODEPTRS_PER_BLOCK(root) - 3) {
                int sret;

                if (*write_lock_level < level + 1) {
                        *write_lock_level = level + 1;
                        btrfs_release_path(p);
                        goto again;
                }

                btrfs_set_path_blocking(p);
                reada_for_balance(root, p, level);
                sret = split_node(trans, root, p, level);
                btrfs_clear_path_blocking(p, NULL, 0);

                BUG_ON(sret > 0);
                if (sret) {
                        ret = sret;
                        goto done;
                }
                b = p->nodes[level];
        } else if (ins_len < 0 && btrfs_header_nritems(b) <
                   BTRFS_NODEPTRS_PER_BLOCK(root) / 2) {
                int sret;

                if (*write_lock_level < level + 1) {
                        *write_lock_level = level + 1;
                        btrfs_release_path(p);
                        goto again;
                }

                btrfs_set_path_blocking(p);
                reada_for_balance(root, p, level);
                sret = balance_level(trans, root, p, level);
                btrfs_clear_path_blocking(p, NULL, 0);

                if (sret) {
                        ret = sret;
                        goto done;
                }
                b = p->nodes[level];
                if (!b) {
                        btrfs_release_path(p);
                        goto again;
                }
                BUG_ON(btrfs_header_nritems(b) == 1);
        }
        return 0;

again:
        ret = -EAGAIN;
done:
        return ret;
}

static void key_search_validate(struct extent_buffer *b,
                                struct btrfs_key *key,
                                int level)
{
#ifdef CONFIG_BTRFS_ASSERT
        struct btrfs_disk_key disk_key;

        btrfs_cpu_key_to_disk(&disk_key, key);

        if (level == 0)
                ASSERT(!memcmp_extent_buffer(b, &disk_key,
                    offsetof(struct btrfs_leaf, items[0].key),
                    sizeof(disk_key)));
        else
                ASSERT(!memcmp_extent_buffer(b, &disk_key,
                    offsetof(struct btrfs_node, ptrs[0].key),
                    sizeof(disk_key)));
#endif
}

static int key_search(struct extent_buffer *b, struct btrfs_key *key,
                      int level, int *prev_cmp, int *slot)
{
        if (*prev_cmp != 0) {
                *prev_cmp = bin_search(b, key, level, slot);
                return *prev_cmp;
        }

        key_search_validate(b, key, level);
        *slot = 0;

        return 0;
}

int btrfs_find_item(struct btrfs_root *fs_root, struct btrfs_path *path,
                u64 iobjectid, u64 ioff, u8 key_type,
                struct btrfs_key *found_key)
{
        int ret;
        struct btrfs_key key;
        struct extent_buffer *eb;

        ASSERT(path);
        ASSERT(found_key);

        key.type = key_type;
        key.objectid = iobjectid;
        key.offset = ioff;

        ret = btrfs_search_slot(NULL, fs_root, &key, path, 0, 0);
        if (ret < 0)
                return ret;

        eb = path->nodes[0];
        if (ret && path->slots[0] >= btrfs_header_nritems(eb)) {
                ret = btrfs_next_leaf(fs_root, path);
                if (ret)
                        return ret;
                eb = path->nodes[0];
        }

        btrfs_item_key_to_cpu(eb, found_key, path->slots[0]);
        if (found_key->type != key.type ||
                        found_key->objectid != key.objectid)
                return 1;

        return 0;
}

/*
 * 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 extent_buffer *b;
        int slot;
        int ret;
        int err;
        int level;
        int lowest_unlock = 1;
        int root_lock;
        /* everything at write_lock_level or lower must be write locked */
        int write_lock_level = 0;
        u8 lowest_level = 0;
        int min_write_lock_level;
        int prev_cmp;

        lowest_level = p->lowest_level;
        WARN_ON(lowest_level && ins_len > 0);
        WARN_ON(p->nodes[0] != NULL);
        BUG_ON(!cow && ins_len);

        if (ins_len < 0) {
                lowest_unlock = 2;

                /* when we are removing items, we might have to go up to level
                 * two as we update tree pointers  Make sure we keep write
                 * for those levels as well
                 */
                write_lock_level = 2;
        } else if (ins_len > 0) {
                /*
                 * for inserting items, make sure we have a write lock on
                 * level 1 so we can update keys
                 */
                write_lock_level = 1;
        }

        if (!cow)
                write_lock_level = -1;

        if (cow && (p->keep_locks || p->lowest_level))
                write_lock_level = BTRFS_MAX_LEVEL;

        min_write_lock_level = write_lock_level;

again:
        prev_cmp = -1;
        /*
         * we try very hard to do read locks on the root
         */
        root_lock = BTRFS_READ_LOCK;
        level = 0;
        if (p->search_commit_root) {
                /*
                 * the commit roots are read only
                 * so we always do read locks
                 */
                if (p->need_commit_sem)
                        down_read(&root->fs_info->commit_root_sem);
                b = root->commit_root;
                extent_buffer_get(b);
                level = btrfs_header_level(b);
                if (p->need_commit_sem)
                        up_read(&root->fs_info->commit_root_sem);
                if (!p->skip_locking)
                        btrfs_tree_read_lock(b);
        } else {
                if (p->skip_locking) {
                        b = btrfs_root_node(root);
                        level = btrfs_header_level(b);
                } else {
                        /* we don't know the level of the root node
                         * until we actually have it read locked
                         */
                        b = btrfs_read_lock_root_node(root);
                        level = btrfs_header_level(b);
                        if (level <= write_lock_level) {
                                /* whoops, must trade for write lock */
                                btrfs_tree_read_unlock(b);
                                free_extent_buffer(b);
                                b = btrfs_lock_root_node(root);
                                root_lock = BTRFS_WRITE_LOCK;

                                /* the level might have changed, check again */
                                level = btrfs_header_level(b);
                        }
                }
        }
        p->nodes[level] = b;
        if (!p->skip_locking)
                p->locks[level] = root_lock;

        while (b) {
                level = btrfs_header_level(b);

                /*
                 * setup the path here so we can release it under lock
                 * contention with the cow code
                 */
                if (cow) {
                        /*
                         * if we don't really need to cow this block
                         * then we don't want to set the path blocking,
                         * so we test it here
                         */
                        if (!should_cow_block(trans, root, b)) {
                                trans->dirty = true;
                                goto cow_done;
                        }

                        /*
                         * must have write locks on this node and the
                         * parent
                         */
                        if (level > write_lock_level ||
                            (level + 1 > write_lock_level &&
                            level + 1 < BTRFS_MAX_LEVEL &&
                            p->nodes[level + 1])) {
                                write_lock_level = level + 1;
                                btrfs_release_path(p);
                                goto again;
                        }

                        btrfs_set_path_blocking(p);
                        err = btrfs_cow_block(trans, root, b,
                                              p->nodes[level + 1],
                                              p->slots[level + 1], &b);
                        if (err) {
                                ret = err;
                                goto done;
                        }
                }
cow_done:
                p->nodes[level] = b;
                btrfs_clear_path_blocking(p, NULL, 0);

                /*
                 * we have a lock on b and as long as we aren't changing
                 * the tree, there is no way to for the items in b to change.
                 * It is safe to drop the lock on our parent before we
                 * go through the expensive btree search on b.
                 *
                 * If we're inserting or deleting (ins_len != 0), then we might
                 * be changing slot zero, which may require changing the parent.
                 * So, we can't drop the lock until after we know which slot
                 * we're operating on.
                 */
                if (!ins_len && !p->keep_locks) {
                        int u = level + 1;

                        if (u < BTRFS_MAX_LEVEL && p->locks[u]) {
                                btrfs_tree_unlock_rw(p->nodes[u], p->locks[u]);
                                p->locks[u] = 0;
                        }
                }

                ret = key_search(b, key, level, &prev_cmp, &slot);
                if (ret < 0)
                        goto done;

                if (level != 0) {
                        int dec = 0;
                        if (ret && slot > 0) {
                                dec = 1;
                                slot -= 1;
                        }
                        p->slots[level] = slot;
                        err = setup_nodes_for_search(trans, root, p, b, level,
                                             ins_len, &write_lock_level);
                        if (err == -EAGAIN)
                                goto again;
                        if (err) {
                                ret = err;
                                goto done;
                        }
                        b = p->nodes[level];
                        slot = p->slots[level];

                        /*
                         * slot 0 is special, if we change the key
                         * we have to update the parent pointer
                         * which means we must have a write lock
                         * on the parent
                         */
                        if (slot == 0 && ins_len &&
                            write_lock_level < level + 1) {
                                write_lock_level = level + 1;
                                btrfs_release_path(p);
                                goto again;
                        }

                        unlock_up(p, level, lowest_unlock,
                                  min_write_lock_level, &write_lock_level);

                        if (level == lowest_level) {
                                if (dec)
                                        p->slots[level]++;
                                goto done;
                        }

                        err = read_block_for_search(trans, root, p,
                                                    &b, level, slot, key, 0);
                        if (err == -EAGAIN)
                                goto again;
                        if (err) {
                                ret = err;
                                goto done;
                        }

                        if (!p->skip_locking) {
                                level = btrfs_header_level(b);
                                if (level <= write_lock_level) {
                                        err = btrfs_try_tree_write_lock(b);
                                        if (!err) {
                                                btrfs_set_path_blocking(p);
                                                btrfs_tree_lock(b);
                                                btrfs_clear_path_blocking(p, b,
                                                                  BTRFS_WRITE_LOCK);
                                        }
                                        p->locks[level] = BTRFS_WRITE_LOCK;
                                } else {
                                        err = btrfs_tree_read_lock_atomic(b);
                                        if (!err) {
                                                btrfs_set_path_blocking(p);
                                                btrfs_tree_read_lock(b);
                                                btrfs_clear_path_blocking(p, b,
                                                                  BTRFS_READ_LOCK);
                                        }
                                        p->locks[level] = BTRFS_READ_LOCK;
                                }
                                p->nodes[level] = b;
                        }
                } else {
                        p->slots[level] = slot;
                        if (ins_len > 0 &&
                            btrfs_leaf_free_space(root, b) < ins_len) {
                                if (write_lock_level < 1) {
                                        write_lock_level = 1;
                                        btrfs_release_path(p);
                                        goto again;
                                }

                                btrfs_set_path_blocking(p);
                                err = split_leaf(trans, root, key,
                                                 p, ins_len, ret == 0);
                                btrfs_clear_path_blocking(p, NULL, 0);

                                BUG_ON(err > 0);
                                if (err) {
                                        ret = err;
                                        goto done;
                                }
                        }
                        if (!p->search_for_split)
                                unlock_up(p, level, lowest_unlock,
                                          min_write_lock_level, &write_lock_level);
                        goto done;
                }
        }
        ret = 1;
done:
        /*
         * we don't really know what they plan on doing with the path
         * from here on, so for now just mark it as blocking
         */
        if (!p->leave_spinning)
                btrfs_set_path_blocking(p);
        if (ret < 0 && !p->skip_release_on_error)
                btrfs_release_path(p);
        return ret;
}

/*
 * Like btrfs_search_slot, this looks for a key in the given tree. It uses the
 * current state of the tree together with the operations recorded in the tree
 * modification log to search for the key in a previous version of this tree, as
 * denoted by the time_seq parameter.
 *
 * Naturally, there is no support for insert, delete or cow operations.
 *
 * The resulting path and return value will be set up as if we called
 * btrfs_search_slot at that point in time with ins_len and cow both set to 0.
 */
int btrfs_search_old_slot(struct btrfs_root *root, struct btrfs_key *key,
                          struct btrfs_path *p, u64 time_seq)
{
        struct extent_buffer *b;
        int slot;
        int ret;
        int err;
        int level;
        int lowest_unlock = 1;
        u8 lowest_level = 0;
        int prev_cmp = -1;

        lowest_level = p->lowest_level;
        WARN_ON(p->nodes[0] != NULL);

        if (p->search_commit_root) {
                BUG_ON(time_seq);
                return btrfs_search_slot(NULL, root, key, p, 0, 0);
        }

again:
        b = get_old_root(root, time_seq);
        level = btrfs_header_level(b);
        p->locks[level] = BTRFS_READ_LOCK;

        while (b) {
                level = btrfs_header_level(b);
                p->nodes[level] = b;
                btrfs_clear_path_blocking(p, NULL, 0);

                /*
                 * we have a lock on b and as long as we aren't changing
                 * the tree, there is no way to for the items in b to change.
                 * It is safe to drop the lock on our parent before we
                 * go through the expensive btree search on b.
                 */
                btrfs_unlock_up_safe(p, level + 1);

                /*
                 * Since we can unwind ebs we want to do a real search every
                 * time.
                 */
                prev_cmp = -1;
                ret = key_search(b, key, level, &prev_cmp, &slot);

                if (level != 0) {
                        int dec = 0;
                        if (ret && slot > 0) {
                                dec = 1;
                                slot -= 1;
                        }
                        p->slots[level] = slot;
                        unlock_up(p, level, lowest_unlock, 0, NULL);

                        if (level == lowest_level) {
                                if (dec)
                                        p->slots[level]++;
                                goto done;
                        }

                        err = read_block_for_search(NULL, root, p, &b, level,
                                                    slot, key, time_seq);
                        if (err == -EAGAIN)
                                goto again;
                        if (err) {
                                ret = err;
                                goto done;
                        }

                        level = btrfs_header_level(b);
                        err = btrfs_tree_read_lock_atomic(b);
                        if (!err) {
                                btrfs_set_path_blocking(p);
                                btrfs_tree_read_lock(b);
                                btrfs_clear_path_blocking(p, b,
                                                          BTRFS_READ_LOCK);
                        }
                        b = tree_mod_log_rewind(root->fs_info, p, b, time_seq);
                        if (!b) {
                                ret = -ENOMEM;
                                goto done;
                        }
                        p->locks[level] = BTRFS_READ_LOCK;
                        p->nodes[level] = b;
                } else {
                        p->slots[level] = slot;
                        unlock_up(p, level, lowest_unlock, 0, NULL);
                        goto done;
                }
        }
        ret = 1;
done:
        if (!p->leave_spinning)
                btrfs_set_path_blocking(p);
        if (ret < 0)
                btrfs_release_path(p);

        return ret;
}

/*
 * helper to use instead of search slot if no exact match is needed but
 * instead the next or previous item should be returned.
 * When find_higher is true, the next higher item is returned, the next lower
 * otherwise.
 * When return_any and find_higher are both true, and no higher item is found,
 * return the next lower instead.
 * When return_any is true and find_higher is false, and no lower item is found,
 * return the next higher instead.
 * It returns 0 if any item is found, 1 if none is found (tree empty), and
 * < 0 on error
 */
int btrfs_search_slot_for_read(struct btrfs_root *root,
                               struct btrfs_key *key, struct btrfs_path *p,
                               int find_higher, int return_any)
{
        int ret;
        struct extent_buffer *leaf;

again:
        ret = btrfs_search_slot(NULL, root, key, p, 0, 0);
        if (ret <= 0)
                return ret;
        /*
         * a return value of 1 means the path is at the position where the
         * item should be inserted. Normally this is the next bigger item,
         * but in case the previous item is the last in a leaf, path points
         * to the first free slot in the previous leaf, i.e. at an invalid
         * item.
         */
        leaf = p->nodes[0];

        if (find_higher) {
                if (p->slots[0] >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(root, p);
                        if (ret <= 0)
                                return ret;
                        if (!return_any)
                                return 1;
                        /*
                         * no higher item found, return the next
                         * lower instead
                         */
                        return_any = 0;
                        find_higher = 0;
                        btrfs_release_path(p);
                        goto again;
                }
        } else {
                if (p->slots[0] == 0) {
                        ret = btrfs_prev_leaf(root, p);
                        if (ret < 0)
                                return ret;
                        if (!ret) {
                                leaf = p->nodes[0];
                                if (p->slots[0] == btrfs_header_nritems(leaf))
                                        p->slots[0]--;
                                return 0;
                        }
                        if (!return_any)
                                return 1;
                        /*
                         * no lower item found, return the next
                         * higher instead
                         */
                        return_any = 0;
                        find_higher = 1;
                        btrfs_release_path(p);
                        goto again;
                } else {
                        --p->slots[0];
                }
        }
        return 0;
}

/*
 * 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
 *
 */
static void fixup_low_keys(struct btrfs_fs_info *fs_info,
                           struct btrfs_path *path,
                           struct btrfs_disk_key *key, int level)
{
        int i;
        struct extent_buffer *t;

        for (i = level; i < BTRFS_MAX_LEVEL; i++) {
                int tslot = path->slots[i];
                if (!path->nodes[i])
                        break;
                t = path->nodes[i];
                tree_mod_log_set_node_key(fs_info, t, tslot, 1);
                btrfs_set_node_key(t, key, tslot);
                btrfs_mark_buffer_dirty(path->nodes[i]);
                if (tslot != 0)
                        break;
        }
}

/*
 * update item key.
 *
 * This function isn't completely safe. It's the caller's responsibility
 * that the new key won't break the order
 */
void btrfs_set_item_key_safe(struct btrfs_fs_info *fs_info,
                             struct btrfs_path *path,
                             struct btrfs_key *new_key)
{
        struct btrfs_disk_key disk_key;
        struct extent_buffer *eb;
        int slot;

        eb = path->nodes[0];
        slot = path->slots[0];
        if (slot > 0) {
                btrfs_item_key(eb, &disk_key, slot - 1);
                BUG_ON(comp_keys(&disk_key, new_key) >= 0);
        }
        if (slot < btrfs_header_nritems(eb) - 1) {
                btrfs_item_key(eb, &disk_key, slot + 1);
                BUG_ON(comp_keys(&disk_key, new_key) <= 0);
        }

        btrfs_cpu_key_to_disk(&disk_key, new_key);
        btrfs_set_item_key(eb, &disk_key, slot);
        btrfs_mark_buffer_dirty(eb);
        if (slot == 0)
                fixup_low_keys(fs_info, path, &disk_key, 1);
}

/*
 * 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 extent_buffer *dst,
                          struct extent_buffer *src, int empty)
{
        int push_items = 0;
        int src_nritems;
        int dst_nritems;
        int ret = 0;

        src_nritems = btrfs_header_nritems(src);
        dst_nritems = btrfs_header_nritems(dst);
        push_items = BTRFS_NODEPTRS_PER_BLOCK(root) - dst_nritems;
        WARN_ON(btrfs_header_generation(src) != trans->transid);
        WARN_ON(btrfs_header_generation(dst) != trans->transid);

        if (!empty && src_nritems <= 8)
                return 1;

        if (push_items <= 0)
                return 1;

        if (empty) {
                push_items = min(src_nritems, push_items);
                if (push_items < src_nritems) {
                        /* leave at least 8 pointers in the node if
                         * we aren't going to empty it
                         */
                        if (src_nritems - push_items < 8) {
                                if (push_items <= 8)
                                        return 1;
                                push_items -= 8;
                        }
                }
        } else
                push_items = min(src_nritems - 8, push_items);

        ret = tree_mod_log_eb_copy(root->fs_info, dst, src, dst_nritems, 0,
                                   push_items);
        if (ret) {
                btrfs_abort_transaction(trans, ret);
                return ret;
        }
        copy_extent_buffer(dst, src,
                           btrfs_node_key_ptr_offset(dst_nritems),
                           btrfs_node_key_ptr_offset(0),
                           push_items * sizeof(struct btrfs_key_ptr));

        if (push_items < src_nritems) {
                /*
                 * don't call tree_mod_log_eb_move here, key removal was already
                 * fully logged by tree_mod_log_eb_copy above.
                 */
                memmove_extent_buffer(src, btrfs_node_key_ptr_offset(0),
                                      btrfs_node_key_ptr_offset(push_items),
                                      (src_nritems - push_items) *
                                      sizeof(struct btrfs_key_ptr));
        }
        btrfs_set_header_nritems(src, src_nritems - push_items);
        btrfs_set_header_nritems(dst, dst_nritems + push_items);
        btrfs_mark_buffer_dirty(src);
        btrfs_mark_buffer_dirty(dst);

        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 extent_buffer *dst,
                              struct extent_buffer *src)
{
        int push_items = 0;
        int max_push;
        int src_nritems;
        int dst_nritems;
        int ret = 0;

        WARN_ON(btrfs_header_generation(src) != trans->transid);
        WARN_ON(btrfs_header_generation(dst) != trans->transid);

        src_nritems = btrfs_header_nritems(src);
        dst_nritems = btrfs_header_nritems(dst);
        push_items = BTRFS_NODEPTRS_PER_BLOCK(root) - dst_nritems;
        if (push_items <= 0)
                return 1;

        if (src_nritems < 4)
                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;

        tree_mod_log_eb_move(root->fs_info, dst, push_items, 0, dst_nritems);
        memmove_extent_buffer(dst, btrfs_node_key_ptr_offset(push_items),
                                      btrfs_node_key_ptr_offset(0),
                                      (dst_nritems) *
                                      sizeof(struct btrfs_key_ptr));

        ret = tree_mod_log_eb_copy(root->fs_info, dst, src, 0,
                                   src_nritems - push_items, push_items);
        if (ret) {
                btrfs_abort_transaction(trans, ret);
                return ret;
        }
        copy_extent_buffer(dst, src,
                           btrfs_node_key_ptr_offset(0),
                           btrfs_node_key_ptr_offset(src_nritems - push_items),
                           push_items * sizeof(struct btrfs_key_ptr));

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

        btrfs_mark_buffer_dirty(src);
        btrfs_mark_buffer_dirty(dst);

        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 noinline int insert_new_root(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root,
                           struct btrfs_path *path, int level)
{
        u64 lower_gen;
        struct extent_buffer *lower;
        struct extent_buffer *c;
        struct extent_buffer *old;
        struct btrfs_disk_key lower_key;

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

        lower = path->nodes[level-1];
        if (level == 1)
                btrfs_item_key(lower, &lower_key, 0);
        else
                btrfs_node_key(lower, &lower_key, 0);

        c = btrfs_alloc_tree_block(trans, root, 0, root->root_key.objectid,
                                   &lower_key, level, root->node->start, 0);
        if (IS_ERR(c))
                return PTR_ERR(c);

        root_add_used(root, root->nodesize);

        memset_extent_buffer(c, 0, 0, sizeof(struct btrfs_header));
        btrfs_set_header_nritems(c, 1);
        btrfs_set_header_level(c, level);
        btrfs_set_header_bytenr(c, c->start);
        btrfs_set_header_generation(c, trans->transid);
        btrfs_set_header_backref_rev(c, BTRFS_MIXED_BACKREF_REV);
        btrfs_set_header_owner(c, root->root_key.objectid);

        write_extent_buffer(c, root->fs_info->fsid, btrfs_header_fsid(),
                            BTRFS_FSID_SIZE);

        write_extent_buffer(c, root->fs_info->chunk_tree_uuid,
                            btrfs_header_chunk_tree_uuid(c), BTRFS_UUID_SIZE);

        btrfs_set_node_key(c, &lower_key, 0);
        btrfs_set_node_blockptr(c, 0, lower->start);
        lower_gen = btrfs_header_generation(lower);
        WARN_ON(lower_gen != trans->transid);

        btrfs_set_node_ptr_generation(c, 0, lower_gen);

        btrfs_mark_buffer_dirty(c);

        old = root->node;
        tree_mod_log_set_root_pointer(root, c, 0);
        rcu_assign_pointer(root->node, c);

        /* the super has an extra ref to root->node */
        free_extent_buffer(old);

        add_root_to_dirty_list(root);
        extent_buffer_get(c);
        path->nodes[level] = c;
        path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
        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.
 */
static void insert_ptr(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root, struct btrfs_path *path,
                       struct btrfs_disk_key *key, u64 bytenr,
                       int slot, int level)
{
        struct extent_buffer *lower;
        int nritems;
        int ret;

        BUG_ON(!path->nodes[level]);
        btrfs_assert_tree_locked(path->nodes[level]);
        lower = path->nodes[level];
        nritems = btrfs_header_nritems(lower);
        BUG_ON(slot > nritems);
        BUG_ON(nritems == BTRFS_NODEPTRS_PER_BLOCK(root));
        if (slot != nritems) {
                if (level)
                        tree_mod_log_eb_move(root->fs_info, lower, slot + 1,
                                             slot, nritems - slot);
                memmove_extent_buffer(lower,
                              btrfs_node_key_ptr_offset(slot + 1),
                              btrfs_node_key_ptr_offset(slot),
                              (nritems - slot) * sizeof(struct btrfs_key_ptr));
        }
        if (level) {
                ret = tree_mod_log_insert_key(root->fs_info, lower, slot,
                                              MOD_LOG_KEY_ADD, GFP_NOFS);
                BUG_ON(ret < 0);
        }
        btrfs_set_node_key(lower, key, slot);
        btrfs_set_node_blockptr(lower, slot, bytenr);
        WARN_ON(trans->transid == 0);
        btrfs_set_node_ptr_generation(lower, slot, trans->transid);
        btrfs_set_header_nritems(lower, nritems + 1);
        btrfs_mark_buffer_dirty(lower);
}

/*
 * 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 noinline int split_node(struct btrfs_trans_handle *trans,
                               struct btrfs_root *root,
                               struct btrfs_path *path, int level)
{
        struct extent_buffer *c;
        struct extent_buffer *split;
        struct btrfs_disk_key disk_key;
        int mid;
        int ret;
        u32 c_nritems;

        c = path->nodes[level];
        WARN_ON(btrfs_header_generation(c) != trans->transid);
        if (c == root->node) {
                /*
                 * trying to split the root, lets make a new one
                 *
                 * tree mod log: We don't log_removal old root in
                 * insert_new_root, because that root buffer will be kept as a
                 * normal node. We are going to log removal of half of the
                 * elements below with tree_mod_log_eb_copy. We're holding a
                 * tree lock on the buffer, which is why we cannot race with
                 * other tree_mod_log users.
                 */
                ret = insert_new_root(trans, root, path, level + 1);
                if (ret)
                        return ret;
        } else {
                ret = push_nodes_for_insert(trans, root, path, level);
                c = path->nodes[level];
                if (!ret && btrfs_header_nritems(c) <
                    BTRFS_NODEPTRS_PER_BLOCK(root) - 3)
                        return 0;
                if (ret < 0)
                        return ret;
        }

        c_nritems = btrfs_header_nritems(c);
        mid = (c_nritems + 1) / 2;
        btrfs_node_key(c, &disk_key, mid);

        split = btrfs_alloc_tree_block(trans, root, 0, root->root_key.objectid,
                        &disk_key, level, c->start, 0);
        if (IS_ERR(split))
                return PTR_ERR(split);

        root_add_used(root, root->nodesize);

        memset_extent_buffer(split, 0, 0, sizeof(struct btrfs_header));
        btrfs_set_header_level(split, btrfs_header_level(c));
        btrfs_set_header_bytenr(split, split->start);
        btrfs_set_header_generation(split, trans->transid);
        btrfs_set_header_backref_rev(split, BTRFS_MIXED_BACKREF_REV);
        btrfs_set_header_owner(split, root->root_key.objectid);
        write_extent_buffer(split, root->fs_info->fsid,
                            btrfs_header_fsid(), BTRFS_FSID_SIZE);
        write_extent_buffer(split, root->fs_info->chunk_tree_uuid,
                            btrfs_header_chunk_tree_uuid(split),
                            BTRFS_UUID_SIZE);

        ret = tree_mod_log_eb_copy(root->fs_info, split, c, 0,
                                   mid, c_nritems - mid);
        if (ret) {
                btrfs_abort_transaction(trans, ret);
                return ret;
        }
        copy_extent_buffer(split, c,
                           btrfs_node_key_ptr_offset(0),
                           btrfs_node_key_ptr_offset(mid),
                           (c_nritems - mid) * sizeof(struct btrfs_key_ptr));
        btrfs_set_header_nritems(split, c_nritems - mid);
        btrfs_set_header_nritems(c, mid);
        ret = 0;

        btrfs_mark_buffer_dirty(c);
        btrfs_mark_buffer_dirty(split);

        insert_ptr(trans, root, path, &disk_key, split->start,
                   path->slots[level + 1] + 1, level + 1);

        if (path->slots[level] >= mid) {
                path->slots[level] -= mid;
                btrfs_tree_unlock(c);
                free_extent_buffer(c);
                path->nodes[level] = split;
                path->slots[level + 1] += 1;
        } else {
                btrfs_tree_unlock(split);
                free_extent_buffer(split);
        }
        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 extent_buffer *l, int start, int nr)
{
        struct btrfs_item *start_item;
        struct btrfs_item *end_item;
        struct btrfs_map_token token;
        int data_len;
        int nritems = btrfs_header_nritems(l);
        int end = min(nritems, start + nr) - 1;

        if (!nr)
                return 0;
        btrfs_init_map_token(&token);
        start_item = btrfs_item_nr(start);
        end_item = btrfs_item_nr(end);
        data_len = btrfs_token_item_offset(l, start_item, &token) +
                btrfs_token_item_size(l, start_item, &token);
        data_len = data_len - btrfs_token_item_offset(l, end_item, &token);
        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
 */
noinline int btrfs_leaf_free_space(struct btrfs_root *root,
                                   struct extent_buffer *leaf)
{
        int nritems = btrfs_header_nritems(leaf);
        int ret;
        ret = BTRFS_LEAF_DATA_SIZE(root) - leaf_space_used(leaf, 0, nritems);
        if (ret < 0) {
                btrfs_crit(root->fs_info,
                        "leaf free space ret %d, leaf data size %lu, used %d nritems %d",
                       ret, (unsigned long) BTRFS_LEAF_DATA_SIZE(root),
                       leaf_space_used(leaf, 0, nritems), nritems);
        }
        return ret;
}

/*
 * min slot controls the lowest index we're willing to push to the
 * right.  We'll push up to and including min_slot, but no lower
 */
static noinline int __push_leaf_right(struct btrfs_trans_handle *trans,
                                      struct btrfs_root *root,
                                      struct btrfs_path *path,
                                      int data_size, int empty,
                                      struct extent_buffer *right,
                                      int free_space, u32 left_nritems,
                                      u32 min_slot)
{
        struct extent_buffer *left = path->nodes[0];
        struct extent_buffer *upper = path->nodes[1];
        struct btrfs_map_token token;
        struct btrfs_disk_key disk_key;
        int slot;
        u32 i;
        int push_space = 0;
        int push_items = 0;
        struct btrfs_item *item;
        u32 nr;
        u32 right_nritems;
        u32 data_end;
        u32 this_item_size;

        btrfs_init_map_token(&token);

        if (empty)
                nr = 0;
        else
                nr = max_t(u32, 1, min_slot);

        if (path->slots[0] >= left_nritems)
                push_space += data_size;

        slot = path->slots[1];
        i = left_nritems - 1;
        while (i >= nr) {
                item = btrfs_item_nr(i);

                if (!empty && push_items > 0) {
                        if (path->slots[0] > i)
                                break;
                        if (path->slots[0] == i) {
                                int space = btrfs_leaf_free_space(root, left);
                                if (space + push_space * 2 > free_space)
                                        break;
                        }
                }

                if (path->slots[0] == i)
                        push_space += data_size;

                this_item_size = btrfs_item_size(left, item);
                if (this_item_size + sizeof(*item) + push_space > free_space)
                        break;

                push_items++;
                push_space += this_item_size + sizeof(*item);
                if (i == 0)
                        break;
                i--;
        }

        if (push_items == 0)
                goto out_unlock;

        WARN_ON(!empty && push_items == left_nritems);

        /* push left to right */
        right_nritems = btrfs_header_nritems(right);

        push_space = btrfs_item_end_nr(left, left_nritems - push_items);
        push_space -= leaf_data_end(root, left);

        /* make room in the right data area */
        data_end = leaf_data_end(root, right);
        memmove_extent_buffer(right,
                              btrfs_leaf_data(right) + data_end - push_space,
                              btrfs_leaf_data(right) + data_end,
                              BTRFS_LEAF_DATA_SIZE(root) - data_end);

        /* copy from the left data area */
        copy_extent_buffer(right, left, btrfs_leaf_data(right) +
                     BTRFS_LEAF_DATA_SIZE(root) - push_space,
                     btrfs_leaf_data(left) + leaf_data_end(root, left),
                     push_space);

        memmove_extent_buffer(right, btrfs_item_nr_offset(push_items),
                              btrfs_item_nr_offset(0),
                              right_nritems * sizeof(struct btrfs_item));

        /* copy the items from left to right */
        copy_extent_buffer(right, left, btrfs_item_nr_offset(0),
                   btrfs_item_nr_offset(left_nritems - push_items),
                   push_items * sizeof(struct btrfs_item));

        /* update the item pointers */
        right_nritems += push_items;
        btrfs_set_header_nritems(right, right_nritems);
        push_space = BTRFS_LEAF_DATA_SIZE(root);
        for (i = 0; i < right_nritems; i++) {
                item = btrfs_item_nr(i);
                push_space -= btrfs_token_item_size(right, item, &token);
                btrfs_set_token_item_offset(right, item, push_space, &token);
        }

        left_nritems -= push_items;
        btrfs_set_header_nritems(left, left_nritems);

        if (left_nritems)
                btrfs_mark_buffer_dirty(left);
        else
                clean_tree_block(trans, root->fs_info, left);

        btrfs_mark_buffer_dirty(right);

        btrfs_item_key(right, &disk_key, 0);
        btrfs_set_node_key(upper, &disk_key, slot + 1);
        btrfs_mark_buffer_dirty(upper);

        /* then fixup the leaf pointer in the path */
        if (path->slots[0] >= left_nritems) {
                path->slots[0] -= left_nritems;
                if (btrfs_header_nritems(path->nodes[0]) == 0)
                        clean_tree_block(trans, root->fs_info, path->nodes[0]);
                btrfs_tree_unlock(path->nodes[0]);
                free_extent_buffer(path->nodes[0]);
                path->nodes[0] = right;
                path->slots[1] += 1;
        } else {
                btrfs_tree_unlock(right);
                free_extent_buffer(right);
        }
        return 0;

out_unlock:
        btrfs_tree_unlock(right);
        free_extent_buffer(right);
        return 1;
}

/*
 * 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.
 *
 * this will push starting from min_slot to the end of the leaf.  It won't
 * push any slot lower than min_slot
 */
static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
                           *root, struct btrfs_path *path,
                           int min_data_size, int data_size,
                           int empty, u32 min_slot)
{
        struct extent_buffer *left = path->nodes[0];
        struct extent_buffer *right;
        struct extent_buffer *upper;
        int slot;
        int free_space;
        u32 left_nritems;
        int ret;

        if (!path->nodes[1])
                return 1;

        slot = path->slots[1];
        upper = path->nodes[1];
        if (slot >= btrfs_header_nritems(upper) - 1)
                return 1;

        btrfs_assert_tree_locked(path->nodes[1]);

        right = read_node_slot(root, upper, slot + 1);
        /*
         * slot + 1 is not valid or we fail to read the right node,
         * no big deal, just return.
         */
        if (IS_ERR(right))
                return 1;

        btrfs_tree_lock(right);
        btrfs_set_lock_blocking(right);

        free_space = btrfs_leaf_free_space(root, right);
        if (free_space < data_size)
                goto out_unlock;

        /* cow and double check */
        ret = btrfs_cow_block(trans, root, right, upper,
                              slot + 1, &right);
        if (ret)
                goto out_unlock;

        free_space = btrfs_leaf_free_space(root, right);
        if (free_space < data_size)
                goto out_unlock;

        left_nritems = btrfs_header_nritems(left);
        if (left_nritems == 0)
                goto out_unlock;

        if (path->slots[0] == left_nritems && !empty) {
                /* Key greater than all keys in the leaf, right neighbor has
                 * enough room for it and we're not emptying our leaf to delete
                 * it, therefore use right neighbor to insert the new item and
                 * no need to touch/dirty our left leaft. */
                btrfs_tree_unlock(left);
                free_extent_buffer(left);
                path->nodes[0] = right;
                path->slots[0] = 0;
                path->slots[1]++;
                return 0;
        }

        return __push_leaf_right(trans, root, path, min_data_size, empty,
                                right, free_space, left_nritems, min_slot);
out_unlock:
        btrfs_tree_unlock(right);
        free_extent_buffer(right);
        return 1;
}

/*
 * 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
 *
 * max_slot can put a limit on how far into the leaf we'll push items.  The
 * item at 'max_slot' won't be touched.  Use (u32)-1 to make us do all the
 * items
 */
static noinline int __push_leaf_left(struct btrfs_trans_handle *trans,
                                     struct btrfs_root *root,
                                     struct btrfs_path *path, int data_size,
                                     int empty, struct extent_buffer *left,
                                     int free_space, u32 right_nritems,
                                     u32 max_slot)
{
        struct btrfs_disk_key disk_key;
        struct extent_buffer *right = path->nodes[0];
        int i;
        int push_space = 0;
        int push_items = 0;
        struct btrfs_item *item;
        u32 old_left_nritems;
        u32 nr;
        int ret = 0;
        u32 this_item_size;
        u32 old_left_item_size;
        struct btrfs_map_token token;

        btrfs_init_map_token(&token);

        if (empty)
                nr = min(right_nritems, max_slot);
        else
                nr = min(right_nritems - 1, max_slot);

        for (i = 0; i < nr; i++) {
                item = btrfs_item_nr(i);

                if (!empty && push_items > 0) {
                        if (path->slots[0] < i)
                                break;
                        if (path->slots[0] == i) {
                                int space = btrfs_leaf_free_space(root, right);
                                if (space + push_space * 2 > free_space)
                                        break;
                        }
                }

                if (path->slots[0] == i)
                        push_space += data_size;

                this_item_size = btrfs_item_size(right, item);
                if (this_item_size + sizeof(*item) + push_space > free_space)
                        break;

                push_items++;
                push_space += this_item_size + sizeof(*item);
        }

        if (push_items == 0) {
                ret = 1;
                goto out;
        }
        WARN_ON(!empty && push_items == btrfs_header_nritems(right));

        /* push data from right to left */
        copy_extent_buffer(left, right,
                           btrfs_item_nr_offset(btrfs_header_nritems(left)),
                           btrfs_item_nr_offset(0),
                           push_items * sizeof(struct btrfs_item));

        push_space = BTRFS_LEAF_DATA_SIZE(root) -
                     btrfs_item_offset_nr(right, push_items - 1);

        copy_extent_buffer(left, right, btrfs_leaf_data(left) +
                     leaf_data_end(root, left) - push_space,
                     btrfs_leaf_data(right) +
                     btrfs_item_offset_nr(right, push_items - 1),
                     push_space);
        old_left_nritems = btrfs_header_nritems(left);
        BUG_ON(old_left_nritems <= 0);

        old_left_item_size = btrfs_item_offset_nr(left, old_left_nritems - 1);
        for (i = old_left_nritems; i < old_left_nritems + push_items; i++) {
                u32 ioff;

                item = btrfs_item_nr(i);

                ioff = btrfs_token_item_offset(left, item, &token);
                btrfs_set_token_item_offset(left, item,
                      ioff - (BTRFS_LEAF_DATA_SIZE(root) - old_left_item_size),
                      &token);
        }
        btrfs_set_header_nritems(left, old_left_nritems + push_items);

        /* fixup right node */
        if (push_items > right_nritems)
                WARN(1, KERN_CRIT "push items %d nr %u\n", push_items,
                       right_nritems);

        if (push_items < right_nritems) {
                push_space = btrfs_item_offset_nr(right, push_items - 1) -
                                                  leaf_data_end(root, right);
                memmove_extent_buffer(right, btrfs_leaf_data(right) +
                                      BTRFS_LEAF_DATA_SIZE(root) - push_space,
                                      btrfs_leaf_data(right) +
                                      leaf_data_end(root, right), push_space);

                memmove_extent_buffer(right, btrfs_item_nr_offset(0),
                              btrfs_item_nr_offset(push_items),
                             (btrfs_header_nritems(right) - push_items) *
                             sizeof(struct btrfs_item));
        }
        right_nritems -= push_items;
        btrfs_set_header_nritems(right, right_nritems);
        push_space = BTRFS_LEAF_DATA_SIZE(root);
        for (i = 0; i < right_nritems; i++) {
                item = btrfs_item_nr(i);

                push_space = push_space - btrfs_token_item_size(right,
                                                                item, &token);
                btrfs_set_token_item_offset(right, item, push_space, &token);
        }

        btrfs_mark_buffer_dirty(left);
        if (right_nritems)
                btrfs_mark_buffer_dirty(right);
        else
                clean_tree_block(trans, root->fs_info, right);

        btrfs_item_key(right, &disk_key, 0);
        fixup_low_keys(root->fs_info, path, &disk_key, 1);

        /* then fixup the leaf pointer in the path */
        if (path->slots[0] < push_items) {
                path->slots[0] += old_left_nritems;
                btrfs_tree_unlock(path->nodes[0]);
                free_extent_buffer(path->nodes[0]);
                path->nodes[0] = left;
                path->slots[1] -= 1;
        } else {
                btrfs_tree_unlock(left);
                free_extent_buffer(left);
                path->slots[0] -= push_items;
        }
        BUG_ON(path->slots[0] < 0);
        return ret;
out:
        btrfs_tree_unlock(left);
        free_extent_buffer(left);
        return ret;
}

/*
 * 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
 *
 * max_slot can put a limit on how far into the leaf we'll push items.  The
 * item at 'max_slot' won't be touched.  Use (u32)-1 to make us push all the
 * items
 */
static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
                          *root, struct btrfs_path *path, int min_data_size,
                          int data_size, int empty, u32 max_slot)
{
        struct extent_buffer *right = path->nodes[0];
        struct extent_buffer *left;
        int slot;
        int free_space;
        u32 right_nritems;
        int ret = 0;

        slot = path->slots[1];
        if (slot == 0)
                return 1;
        if (!path->nodes[1])
                return 1;

        right_nritems = btrfs_header_nritems(right);
        if (right_nritems == 0)
                return 1;

        btrfs_assert_tree_locked(path->nodes[1]);

        left = read_node_slot(root, path->nodes[1], slot - 1);
        /*
         * slot - 1 is not valid or we fail to read the left node,
         * no big deal, just return.
         */
        if (IS_ERR(left))
                return 1;

        btrfs_tree_lock(left);
        btrfs_set_lock_blocking(left);

        free_space = btrfs_leaf_free_space(root, left);
        if (free_space < data_size) {
                ret = 1;
                goto out;
        }

        /* cow and double check */
        ret = btrfs_cow_block(trans, root, left,
                              path->nodes[1], slot - 1, &left);
        if (ret) {
                /* we hit -ENOSPC, but it isn't fatal here */
                if (ret == -ENOSPC)
                        ret = 1;
                goto out;
        }

        free_space = btrfs_leaf_free_space(root, left);
        if (free_space < data_size) {
                ret = 1;
                goto out;
        }

        return __push_leaf_left(trans, root, path, min_data_size,
                               empty, left, free_space, right_nritems,
                               max_slot);
out:
        btrfs_tree_unlock(left);
        free_extent_buffer(left);
        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.
 */
static noinline void copy_for_split(struct btrfs_trans_handle *trans,
                                    struct btrfs_root *root,
                                    struct btrfs_path *path,
                                    struct extent_buffer *l,
                                    struct extent_buffer *right,
                                    int slot, int mid, int nritems)
{
        int data_copy_size;
        int rt_data_off;
        int i;
        struct btrfs_disk_key disk_key;
        struct btrfs_map_token token;

        btrfs_init_map_token(&token);

        nritems = nritems - mid;
        btrfs_set_header_nritems(right, nritems);
        data_copy_size = btrfs_item_end_nr(l, mid) - leaf_data_end(root, l);

        copy_extent_buffer(right, l, btrfs_item_nr_offset(0),
                           btrfs_item_nr_offset(mid),
                           nritems * sizeof(struct btrfs_item));

        copy_extent_buffer(right, l,
                     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_nr(l, mid);

        for (i = 0; i < nritems; i++) {
                struct btrfs_item *item = btrfs_item_nr(i);
                u32 ioff;

                ioff = btrfs_token_item_offset(right, item, &token);
                btrfs_set_token_item_offset(right, item,
                                            ioff + rt_data_off, &token);
        }

        btrfs_set_header_nritems(l, mid);
        btrfs_item_key(right, &disk_key, 0);
        insert_ptr(trans, root, path, &disk_key, right->start,
                   path->slots[1] + 1, 1);

        btrfs_mark_buffer_dirty(right);
        btrfs_mark_buffer_dirty(l);
        BUG_ON(path->slots[0] != slot);

        if (mid <= slot) {
                btrfs_tree_unlock(path->nodes[0]);
                free_extent_buffer(path->nodes[0]);
                path->nodes[0] = right;
                path->slots[0] -= mid;
                path->slots[1] += 1;
        } else {
                btrfs_tree_unlock(right);
                free_extent_buffer(right);
        }

        BUG_ON(path->slots[0] < 0);
}

/*
 * double splits happen when we need to insert a big item in the middle
 * of a leaf.  A double split can leave us with 3 mostly empty leaves:
 * leaf: [ slots 0 - N] [ our target ] [ N + 1 - total in leaf ]
 *          A                 B                 C
 *
 * We avoid this by trying to push the items on either side of our target
 * into the adjacent leaves.  If all goes well we can avoid the double split
 * completely.
 */
static noinline int push_for_double_split(struct btrfs_trans_handle *trans,
                                          struct btrfs_root *root,
                                          struct btrfs_path *path,
                                          int data_size)
{
        int ret;
        int progress = 0;
        int slot;
        u32 nritems;
        int space_needed = data_size;

        slot = path->slots[0];
        if (slot < btrfs_header_nritems(path->nodes[0]))
                space_needed -= btrfs_leaf_free_space(root, path->nodes[0]);

        /*
         * try to push all the items after our slot into the
         * right leaf
         */
        ret = push_leaf_right(trans, root, path, 1, space_needed, 0, slot);
        if (ret < 0)
                return ret;

        if (ret == 0)
                progress++;

        nritems = btrfs_header_nritems(path->nodes[0]);
        /*
         * our goal is to get our slot at the start or end of a leaf.  If
         * we've done so we're done
         */
        if (path->slots[0] == 0 || path->slots[0] == nritems)
                return 0;

        if (btrfs_leaf_free_space(root, path->nodes[0]) >= data_size)
                return 0;

        /* try to push all the items before our slot into the next leaf */
        slot = path->slots[0];
        ret = push_leaf_left(trans, root, path, 1, space_needed, 0, slot);
        if (ret < 0)
                return ret;

        if (ret == 0)
                progress++;

        if (progress)
                return 0;
        return 1;
}

/*
 * 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 noinline int split_leaf(struct btrfs_trans_handle *trans,
                               struct btrfs_root *root,
                               struct btrfs_key *ins_key,
                               struct btrfs_path *path, int data_size,
                               int extend)
{
        struct btrfs_disk_key disk_key;
        struct extent_buffer *l;
        u32 nritems;
        int mid;
        int slot;
        struct extent_buffer *right;
        struct btrfs_fs_info *fs_info = root->fs_info;
        int ret = 0;
        int wret;
        int split;
        int num_doubles = 0;
        int tried_avoid_double = 0;

        l = path->nodes[0];
        slot = path->slots[0];
        if (extend && data_size + btrfs_item_size_nr(l, slot) +
            sizeof(struct btrfs_item) > BTRFS_LEAF_DATA_SIZE(root))
                return -EOVERFLOW;

        /* first try to make some room by pushing left and right */
        if (data_size && path->nodes[1]) {
                int space_needed = data_size;

                if (slot < btrfs_header_nritems(l))
                        space_needed -= btrfs_leaf_free_space(root, l);

                wret = push_leaf_right(trans, root, path, space_needed,
                                       space_needed, 0, 0);
                if (wret < 0)
                        return wret;
                if (wret) {
                        wret = push_leaf_left(trans, root, path, space_needed,
                                              space_needed, 0, (u32)-1);
                        if (wret < 0)
                                return wret;
                }
                l = path->nodes[0];

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

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

        if (mid <= slot) {
                if (nritems == 1 ||
                    leaf_space_used(l, mid, nritems - mid) + data_size >
                        BTRFS_LEAF_DATA_SIZE(root)) {
                        if (slot >= nritems) {
                                split = 0;
                        } else {
                                mid = slot;
                                if (mid != nritems &&
                                    leaf_space_used(l, mid, nritems - mid) +
                                    data_size > BTRFS_LEAF_DATA_SIZE(root)) {
                                        if (data_size && !tried_avoid_double)
                                                goto push_for_double;
                                        split = 2;
                                }
                        }
                }
        } else {
                if (leaf_space_used(l, 0, mid) + data_size >
                        BTRFS_LEAF_DATA_SIZE(root)) {
                        if (!extend && data_size && slot == 0) {
                                split = 0;
                        } else if ((extend || !data_size) && slot == 0) {
                                mid = 1;
                        } else {
                                mid = slot;
                                if (mid != nritems &&
                                    leaf_space_used(l, mid, nritems - mid) +
                                    data_size > BTRFS_LEAF_DATA_SIZE(root)) {
                                        if (data_size && !tried_avoid_double)
                                                goto push_for_double;
                                        split = 2;
                                }
                        }
                }
        }

        if (split == 0)
                btrfs_cpu_key_to_disk(&disk_key, ins_key);
        else
                btrfs_item_key(l, &disk_key, mid);

        right = btrfs_alloc_tree_block(trans, root, 0, root->root_key.objectid,
                        &disk_key, 0, l->start, 0);
        if (IS_ERR(right))
                return PTR_ERR(right);

        root_add_used(root, root->nodesize);

        memset_extent_buffer(right, 0, 0, sizeof(struct btrfs_header));
        btrfs_set_header_bytenr(right, right->start);
        btrfs_set_header_generation(right, trans->transid);
        btrfs_set_header_backref_rev(right, BTRFS_MIXED_BACKREF_REV);
        btrfs_set_header_owner(right, root->root_key.objectid);
        btrfs_set_header_level(right, 0);
        write_extent_buffer(right, fs_info->fsid,
                            btrfs_header_fsid(), BTRFS_FSID_SIZE);

        write_extent_buffer(right, fs_info->chunk_tree_uuid,
                            btrfs_header_chunk_tree_uuid(right),
                            BTRFS_UUID_SIZE);

        if (split == 0) {
                if (mid <= slot) {
                        btrfs_set_header_nritems(right, 0);
                        insert_ptr(trans, root, path, &disk_key, right->start,
                                   path->slots[1] + 1, 1);
                        btrfs_tree_unlock(path->nodes[0]);
                        free_extent_buffer(path->nodes[0]);
                        path->nodes[0] = right;
                        path->slots[0] = 0;
                        path->slots[1] += 1;
                } else {
                        btrfs_set_header_nritems(right, 0);
                        insert_ptr(trans, root, path, &disk_key, right->start,
                                          path->slots[1], 1);
                        btrfs_tree_unlock(path->nodes[0]);
                        free_extent_buffer(path->nodes[0]);
                        path->nodes[0] = right;
                        path->slots[0] = 0;
                        if (path->slots[1] == 0)
                                fixup_low_keys(fs_info, path, &disk_key, 1);
                }
                btrfs_mark_buffer_dirty(right);
                return ret;
        }

        copy_for_split(trans, root, path, l, right, slot, mid, nritems);

        if (split == 2) {
                BUG_ON(num_doubles != 0);
                num_doubles++;
                goto again;
        }

        return 0;

push_for_double:
        push_for_double_split(trans, root, path, data_size);
        tried_avoid_double = 1;
        if (btrfs_leaf_free_space(root, path->nodes[0]) >= data_size)
                return 0;
        goto again;
}

static noinline int setup_leaf_for_split(struct btrfs_trans_handle *trans,
                                         struct btrfs_root *root,
                                         struct btrfs_path *path, int ins_len)
{
        struct btrfs_key key;
        struct extent_buffer *leaf;
        struct btrfs_file_extent_item *fi;
        u64 extent_len = 0;
        u32 item_size;
        int ret;

        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);

        BUG_ON(key.type != BTRFS_EXTENT_DATA_KEY &&
               key.type != BTRFS_EXTENT_CSUM_KEY);

        if (btrfs_leaf_free_space(root, leaf) >= ins_len)
                return 0;

        item_size = btrfs_item_size_nr(leaf, path->slots[0]);
        if (key.type == BTRFS_EXTENT_DATA_KEY) {
                fi = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);
                extent_len = btrfs_file_extent_num_bytes(leaf, fi);
        }
        btrfs_release_path(path);

        path->keep_locks = 1;
        path->search_for_split = 1;
        ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
        path->search_for_split = 0;
        if (ret > 0)
                ret = -EAGAIN;
        if (ret < 0)
                goto err;

        ret = -EAGAIN;
        leaf = path->nodes[0];
        /* if our item isn't there, return now */
        if (item_size != btrfs_item_size_nr(leaf, path->slots[0]))
                goto err;

        /* the leaf has  changed, it now has room.  return now */
        if (btrfs_leaf_free_space(root, path->nodes[0]) >= ins_len)
                goto err;

        if (key.type == BTRFS_EXTENT_DATA_KEY) {
                fi = btrfs_item_ptr(leaf, path->slots[0],
                                    struct btrfs_file_extent_item);
                if (extent_len != btrfs_file_extent_num_bytes(leaf, fi))
                        goto err;
        }

        btrfs_set_path_blocking(path);
        ret = split_leaf(trans, root, &key, path, ins_len, 1);
        if (ret)
                goto err;

        path->keep_locks = 0;
        btrfs_unlock_up_safe(path, 1);
        return 0;
err:
        path->keep_locks = 0;
        return ret;
}

static noinline int split_item(struct btrfs_trans_handle *trans,
                               struct btrfs_root *root,
                               struct btrfs_path *path,
                               struct btrfs_key *new_key,
                               unsigned long split_offset)
{
        struct extent_buffer *leaf;
        struct btrfs_item *item;
        struct btrfs_item *new_item;
        int slot;
        char *buf;
        u32 nritems;
        u32 item_size;
        u32 orig_offset;
        struct btrfs_disk_key disk_key;

        leaf = path->nodes[0];
        BUG_ON(btrfs_leaf_free_space(root, leaf) < sizeof(struct btrfs_item));

        btrfs_set_path_blocking(path);

        item = btrfs_item_nr(path->slots[0]);
        orig_offset = btrfs_item_offset(leaf, item);
        item_size = btrfs_item_size(leaf, item);

        buf = kmalloc(item_size, GFP_NOFS);
        if (!buf)
                return -ENOMEM;

        read_extent_buffer(leaf, buf, btrfs_item_ptr_offset(leaf,
                            path->slots[0]), item_size);

        slot = path->slots[0] + 1;
        nritems = btrfs_header_nritems(leaf);
        if (slot != nritems) {
                /* shift the items */
                memmove_extent_buffer(leaf, btrfs_item_nr_offset(slot + 1),
                                btrfs_item_nr_offset(slot),
                                (nritems - slot) * sizeof(struct btrfs_item));
        }

        btrfs_cpu_key_to_disk(&disk_key, new_key);
        btrfs_set_item_key(leaf, &disk_key, slot);

        new_item = btrfs_item_nr(slot);

        btrfs_set_item_offset(leaf, new_item, orig_offset);
        btrfs_set_item_size(leaf, new_item, item_size - split_offset);

        btrfs_set_item_offset(leaf, item,
                              orig_offset + item_size - split_offset);
        btrfs_set_item_size(leaf, item, split_offset);

        btrfs_set_header_nritems(leaf, nritems + 1);

        /* write the data for the start of the original item */
        write_extent_buffer(leaf, buf,
                            btrfs_item_ptr_offset(leaf, path->slots[0]),
                            split_offset);

        /* write the data for the new item */
        write_extent_buffer(leaf, buf + split_offset,
                            btrfs_item_ptr_offset(leaf, slot),
                            item_size - split_offset);
        btrfs_mark_buffer_dirty(leaf);

        BUG_ON(btrfs_leaf_free_space(root, leaf) < 0);
        kfree(buf);
        return 0;
}

/*
 * This function splits a single item into two items,
 * giving 'new_key' to the new item and splitting the
 * old one at split_offset (from the start of the item).
 *
 * The path may be released by this operation.  After
 * the split, the path is pointing to the old item.  The
 * new item is going to be in the same node as the old one.
 *
 * Note, the item being split must be smaller enough to live alone on
 * a tree block with room for one extra struct btrfs_item
 *
 * This allows us to split the item in place, keeping a lock on the
 * leaf the entire time.
 */
int btrfs_split_item(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root,
                     struct btrfs_path *path,
                     struct btrfs_key *new_key,
                     unsigned long split_offset)
{
        int ret;
        ret = setup_leaf_for_split(trans, root, path,
                                   sizeof(struct btrfs_item));
        if (ret)
                return ret;

        ret = split_item(trans, root, path, new_key, split_offset);
        return ret;
}

/*
 * This function duplicate a item, giving 'new_key' to the new item.
 * It guarantees both items live in the same tree leaf and the new item
 * is contiguous with the original item.
 *
 * This allows us to split file extent in place, keeping a lock on the
 * leaf the entire time.
 */
int btrfs_duplicate_item(struct btrfs_trans_handle *trans,
                         struct btrfs_root *root,
                         struct btrfs_path *path,
                         struct btrfs_key *new_key)
{
        struct extent_buffer *leaf;
        int ret;
        u32 item_size;

        leaf = path->nodes[0];
        item_size = btrfs_item_size_nr(leaf, path->slots[0]);
        ret = setup_leaf_for_split(trans, root, path,
                                   item_size + sizeof(struct btrfs_item));
        if (ret)
                return ret;

        path->slots[0]++;
        setup_items_for_insert(root, path, new_key, &item_size,
                               item_size, item_size +
                               sizeof(struct btrfs_item), 1);
        leaf = path->nodes[0];
        memcpy_extent_buffer(leaf,
                             btrfs_item_ptr_offset(leaf, path->slots[0]),
                             btrfs_item_ptr_offset(leaf, path->slots[0] - 1),
                             item_size);
        return 0;
}

/*
 * make the item pointed to by the path smaller.  new_size indicates
 * how small to make it, and from_end tells us if we just chop bytes
 * off the end of the item or if we shift the item to chop bytes off
 * the front.
 */
void btrfs_truncate_item(struct btrfs_root *root, struct btrfs_path *path,
                         u32 new_size, int from_end)
{
        int slot;
        struct extent_buffer *leaf;
        struct btrfs_item *item;
        u32 nritems;
        unsigned int data_end;
        unsigned int old_data_start;
        unsigned int old_size;
        unsigned int size_diff;
        int i;
        struct btrfs_map_token token;

        btrfs_init_map_token(&token);

        leaf = path->nodes[0];
        slot = path->slots[0];

        old_size = btrfs_item_size_nr(leaf, slot);
        if (old_size == new_size)
                return;

        nritems = btrfs_header_nritems(leaf);
        data_end = leaf_data_end(root, leaf);

        old_data_start = btrfs_item_offset_nr(leaf, slot);

        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;
                item = btrfs_item_nr(i);

                ioff = btrfs_token_item_offset(leaf, item, &token);
                btrfs_set_token_item_offset(leaf, item,
                                            ioff + size_diff, &token);
        }

        /* shift the data */
        if (from_end) {
                memmove_extent_buffer(leaf, btrfs_leaf_data(leaf) +
                              data_end + size_diff, btrfs_leaf_data(leaf) +
                              data_end, old_data_start + new_size - data_end);
        } else {
                struct btrfs_disk_key disk_key;
                u64 offset;

                btrfs_item_key(leaf, &disk_key, slot);

                if (btrfs_disk_key_type(&disk_key) == BTRFS_EXTENT_DATA_KEY) {
                        unsigned long ptr;
                        struct btrfs_file_extent_item *fi;

                        fi = btrfs_item_ptr(leaf, slot,
                                            struct btrfs_file_extent_item);
                        fi = (struct btrfs_file_extent_item *)(
                             (unsigned long)fi - size_diff);

                        if (btrfs_file_extent_type(leaf, fi) ==
                            BTRFS_FILE_EXTENT_INLINE) {
                                ptr = btrfs_item_ptr_offset(leaf, slot);
                                memmove_extent_buffer(leaf, ptr,
                                      (unsigned long)fi,
                                      BTRFS_FILE_EXTENT_INLINE_DATA_START);
                        }
                }

                memmove_extent_buffer(leaf, btrfs_leaf_data(leaf) +
                              data_end + size_diff, btrfs_leaf_data(leaf) +
                              data_end, old_data_start - data_end);

                offset = btrfs_disk_key_offset(&disk_key);
                btrfs_set_disk_key_offset(&disk_key, offset + size_diff);
                btrfs_set_item_key(leaf, &disk_key, slot);
                if (slot == 0)
                        fixup_low_keys(root->fs_info, path, &disk_key, 1);
        }

        item = btrfs_item_nr(slot);
        btrfs_set_item_size(leaf, item, new_size);
        btrfs_mark_buffer_dirty(leaf);

        if (btrfs_leaf_free_space(root, leaf) < 0) {
                btrfs_print_leaf(root, leaf);
                BUG();
        }
}

/*
 * make the item pointed to by the path bigger, data_size is the added size.
 */
void btrfs_extend_item(struct btrfs_root *root, struct btrfs_path *path,
                       u32 data_size)
{
        int slot;
        struct extent_buffer *leaf;
        struct btrfs_item *item;
        u32 nritems;
        unsigned int data_end;
        unsigned int old_data;
        unsigned int old_size;
        int i;
        struct btrfs_map_token token;

        btrfs_init_map_token(&token);

        leaf = path->nodes[0];

        nritems = btrfs_header_nritems(leaf);
        data_end = leaf_data_end(root, leaf);

        if (btrfs_leaf_free_space(root, leaf) < data_size) {
                btrfs_print_leaf(root, leaf);
                BUG();
        }
        slot = path->slots[0];
        old_data = btrfs_item_end_nr(leaf, slot);

        BUG_ON(slot < 0);
        if (slot >= nritems) {
                btrfs_print_leaf(root, leaf);
                btrfs_crit(root->fs_info, "slot %d too large, nritems %d",
                       slot, nritems);
                BUG_ON(1);
        }

        /*
         * item0..itemN ... dataN.offset..dataN.size .. data0.size
         */
        /* first correct the data pointers */
        for (i = slot; i < nritems; i++) {
                u32 ioff;
                item = btrfs_item_nr(i);

                ioff = btrfs_token_item_offset(leaf, item, &token);
                btrfs_set_token_item_offset(leaf, item,
                                            ioff - data_size, &token);
        }

        /* shift the data */
        memmove_extent_buffer(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_nr(leaf, slot);
        item = btrfs_item_nr(slot);
        btrfs_set_item_size(leaf, item, old_size + data_size);
        btrfs_mark_buffer_dirty(leaf);

        if (btrfs_leaf_free_space(root, leaf) < 0) {
                btrfs_print_leaf(root, leaf);
                BUG();
        }
}

/*
 * this is a helper for btrfs_insert_empty_items, the main goal here is
 * to save stack depth by doing the bulk of the work in a function
 * that doesn't call btrfs_search_slot
 */
void setup_items_for_insert(struct btrfs_root *root, struct btrfs_path *path,
                            struct btrfs_key *cpu_key, u32 *data_size,
                            u32 total_data, u32 total_size, int nr)
{
        struct btrfs_item *item;
        int i;
        u32 nritems;
        unsigned int data_end;
        struct btrfs_disk_key disk_key;
        struct extent_buffer *leaf;
        int slot;
        struct btrfs_map_token token;

        if (path->slots[0] == 0) {
                btrfs_cpu_key_to_disk(&disk_key, cpu_key);
                fixup_low_keys(root->fs_info, path, &disk_key, 1);
        }
        btrfs_unlock_up_safe(path, 1);

        btrfs_init_map_token(&token);

        leaf = path->nodes[0];
        slot = path->slots[0];

        nritems = btrfs_header_nritems(leaf);
        data_end = leaf_data_end(root, leaf);

        if (btrfs_leaf_free_space(root, leaf) < total_size) {
                btrfs_print_leaf(root, leaf);
                btrfs_crit(root->fs_info, "not enough freespace need %u have %d",
                       total_size, btrfs_leaf_free_space(root, leaf));
                BUG();
        }

        if (slot != nritems) {
                unsigned int old_data = btrfs_item_end_nr(leaf, slot);

                if (old_data < data_end) {
                        btrfs_print_leaf(root, leaf);
                        btrfs_crit(root->fs_info, "slot %d old_data %d data_end %d",
                               slot, old_data, data_end);
                        BUG_ON(1);
                }
                /*
                 * item0..itemN ... dataN.offset..dataN.size .. data0.size
                 */
                /* first correct the data pointers */
                for (i = slot; i < nritems; i++) {
                        u32 ioff;

                        item = btrfs_item_nr( i);
                        ioff = btrfs_token_item_offset(leaf, item, &token);
                        btrfs_set_token_item_offset(leaf, item,
                                                    ioff - total_data, &token);
                }
                /* shift the items */
                memmove_extent_buffer(leaf, btrfs_item_nr_offset(slot + nr),
                              btrfs_item_nr_offset(slot),
                              (nritems - slot) * sizeof(struct btrfs_item));

                /* shift the data */
                memmove_extent_buffer(leaf, btrfs_leaf_data(leaf) +
                              data_end - total_data, btrfs_leaf_data(leaf) +
                              data_end, old_data - data_end);
                data_end = old_data;
        }

        /* setup the item for the new data */
        for (i = 0; i < nr; i++) {
                btrfs_cpu_key_to_disk(&disk_key, cpu_key + i);
                btrfs_set_item_key(leaf, &disk_key, slot + i);
                item = btrfs_item_nr(slot + i);
                btrfs_set_token_item_offset(leaf, item,
                                            data_end - data_size[i], &token);
                data_end -= data_size[i];
                btrfs_set_token_item_size(leaf, item, data_size[i], &token);
        }

        btrfs_set_header_nritems(leaf, nritems + nr);
        btrfs_mark_buffer_dirty(leaf);

        if (btrfs_leaf_free_space(root, leaf) < 0) {
                btrfs_print_leaf(root, leaf);
                BUG();
        }
}

/*
 * Given a key and some data, insert items into the tree.
 * This does all the path init required, making room in the tree if needed.
 */
int btrfs_insert_empty_items(struct btrfs_trans_handle *trans,
                            struct btrfs_root *root,
                            struct btrfs_path *path,
                            struct btrfs_key *cpu_key, u32 *data_size,
                            int nr)
{
        int ret = 0;
        int slot;
        int i;
        u32 total_size = 0;
        u32 total_data = 0;

        for (i = 0; i < nr; i++)
                total_data += data_size[i];

        total_size = total_data + (nr * sizeof(struct btrfs_item));
        ret = btrfs_search_slot(trans, root, cpu_key, path, total_size, 1);
        if (ret == 0)
                return -EEXIST;
        if (ret < 0)
                return ret;

        slot = path->slots[0];
        BUG_ON(slot < 0);

        setup_items_for_insert(root, path, cpu_key, data_size,
                               total_data, total_size, nr);
        return 0;
}

/*
 * 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;
        struct extent_buffer *leaf;
        unsigned long ptr;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
        ret = btrfs_insert_empty_item(trans, root, path, cpu_key, data_size);
        if (!ret) {
                leaf = path->nodes[0];
                ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
                write_extent_buffer(leaf, data, ptr, data_size);
                btrfs_mark_buffer_dirty(leaf);
        }
        btrfs_free_path(path);
        return ret;
}

/*
 * delete the pointer from a given node.
 *
 * the tree should have been previously balanced so the deletion does not
 * empty a node.
 */
static void del_ptr(struct btrfs_root *root, struct btrfs_path *path,
                    int level, int slot)
{
        struct extent_buffer *parent = path->nodes[level];
        u32 nritems;
        int ret;

        nritems = btrfs_header_nritems(parent);
        if (slot != nritems - 1) {
                if (level)
                        tree_mod_log_eb_move(root->fs_info, parent, slot,
                                             slot + 1, nritems - slot - 1);
                memmove_extent_buffer(parent,
                              btrfs_node_key_ptr_offset(slot),
                              btrfs_node_key_ptr_offset(slot + 1),
                              sizeof(struct btrfs_key_ptr) *
                              (nritems - slot - 1));
        } else if (level) {
                ret = tree_mod_log_insert_key(root->fs_info, parent, slot,
                                              MOD_LOG_KEY_REMOVE, GFP_NOFS);
                BUG_ON(ret < 0);
        }

        nritems--;
        btrfs_set_header_nritems(parent, nritems);
        if (nritems == 0 && parent == root->node) {
                BUG_ON(btrfs_header_level(root->node) != 1);
                /* just turn the root into a leaf and break */
                btrfs_set_header_level(root->node, 0);
        } else if (slot == 0) {
                struct btrfs_disk_key disk_key;

                btrfs_node_key(parent, &disk_key, 0);
                fixup_low_keys(root->fs_info, path, &disk_key, level + 1);
        }
        btrfs_mark_buffer_dirty(parent);
}

/*
 * a helper function to delete the leaf pointed to by path->slots[1] and
 * path->nodes[1].
 *
 * This deletes the pointer in path->nodes[1] and frees the leaf
 * block extent.  zero is returned if it all worked out, < 0 otherwise.
 *
 * The path must have already been setup for deleting the leaf, including
 * all the proper balancing.  path->nodes[1] must be locked.
 */
static noinline void btrfs_del_leaf(struct btrfs_trans_handle *trans,
                                    struct btrfs_root *root,
                                    struct btrfs_path *path,
                                    struct extent_buffer *leaf)
{
        WARN_ON(btrfs_header_generation(leaf) != trans->transid);
        del_ptr(root, path, 1, path->slots[1]);

        /*
         * btrfs_free_extent is expensive, we want to make sure we
         * aren't holding any locks when we call it
         */
        btrfs_unlock_up_safe(path, 0);

        root_sub_used(root, leaf->len);

        extent_buffer_get(leaf);
        btrfs_free_tree_block(trans, root, leaf, 0, 1);
        free_extent_buffer_stale(leaf);
}
/*
 * delete the item at the leaf level in path.  If that empties
 * the leaf, remove it from the tree
 */
int btrfs_del_items(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                    struct btrfs_path *path, int slot, int nr)
{
        struct extent_buffer *leaf;
        struct btrfs_item *item;
        u32 last_off;
        u32 dsize = 0;
        int ret = 0;
        int wret;
        int i;
        u32 nritems;
        struct btrfs_map_token token;

        btrfs_init_map_token(&token);

        leaf = path->nodes[0];
        last_off = btrfs_item_offset_nr(leaf, slot + nr - 1);

        for (i = 0; i < nr; i++)
                dsize += btrfs_item_size_nr(leaf, slot + i);

        nritems = btrfs_header_nritems(leaf);

        if (slot + nr != nritems) {
                int data_end = leaf_data_end(root, leaf);

                memmove_extent_buffer(leaf, btrfs_leaf_data(leaf) +
                              data_end + dsize,
                              btrfs_leaf_data(leaf) + data_end,
                              last_off - data_end);

                for (i = slot + nr; i < nritems; i++) {
                        u32 ioff;

                        item = btrfs_item_nr(i);
                        ioff = btrfs_token_item_offset(leaf, item, &token);
                        btrfs_set_token_item_offset(leaf, item,
                                                    ioff + dsize, &token);
                }

                memmove_extent_buffer(leaf, btrfs_item_nr_offset(slot),
                              btrfs_item_nr_offset(slot + nr),
                              sizeof(struct btrfs_item) *
                              (nritems - slot - nr));
        }
        btrfs_set_header_nritems(leaf, nritems - nr);
        nritems -= nr;

        /* delete the leaf if we've emptied it */
        if (nritems == 0) {
                if (leaf == root->node) {
                        btrfs_set_header_level(leaf, 0);
                } else {
                        btrfs_set_path_blocking(path);
                        clean_tree_block(trans, root->fs_info, leaf);
                        btrfs_del_leaf(trans, root, path, leaf);
                }
        } else {
                int used = leaf_space_used(leaf, 0, nritems);
                if (slot == 0) {
                        struct btrfs_disk_key disk_key;

                        btrfs_item_key(leaf, &disk_key, 0);
                        fixup_low_keys(root->fs_info, path, &disk_key, 1);
                }

                /* 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];
                        extent_buffer_get(leaf);

                        btrfs_set_path_blocking(path);
                        wret = push_leaf_left(trans, root, path, 1, 1,
                                              1, (u32)-1);
                        if (wret < 0 && wret != -ENOSPC)
                                ret = wret;

                        if (path->nodes[0] == leaf &&
                            btrfs_header_nritems(leaf)) {
                                wret = push_leaf_right(trans, root, path, 1,
                                                       1, 1, 0);
                                if (wret < 0 && wret != -ENOSPC)
                                        ret = wret;
                        }

                        if (btrfs_header_nritems(leaf) == 0) {
                                path->slots[1] = slot;
                                btrfs_del_leaf(trans, root, path, leaf);
                                free_extent_buffer(leaf);
                                ret = 0;
                        } else {
                                /* if we're still in the path, make sure
                                 * we're dirty.  Otherwise, one of the
                                 * push_leaf functions must have already
                                 * dirtied this buffer
                                 */
                                if (path->nodes[0] == leaf)
                                        btrfs_mark_buffer_dirty(leaf);
                                free_extent_buffer(leaf);
                        }
                } else {
                        btrfs_mark_buffer_dirty(leaf);
                }
        }
        return ret;
}

/*
 * search the tree again to find a leaf with lesser keys
 * returns 0 if it found something or 1 if there are no lesser leaves.
 * returns < 0 on io errors.
 *
 * This may release the path, and so you may lose any locks held at the
 * time you call it.
 */
int btrfs_prev_leaf(struct btrfs_root *root, struct btrfs_path *path)
{
        struct btrfs_key key;
        struct btrfs_disk_key found_key;
        int ret;

        btrfs_item_key_to_cpu(path->nodes[0], &key, 0);

        if (key.offset > 0) {
                key.offset--;
        } else if (key.type > 0) {
                key.type--;
                key.offset = (u64)-1;
        } else if (key.objectid > 0) {
                key.objectid--;
                key.type = (u8)-1;
                key.offset = (u64)-1;
        } else {
                return 1;
        }

        btrfs_release_path(path);
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                return ret;
        btrfs_item_key(path->nodes[0], &found_key, 0);
        ret = comp_keys(&found_key, &key);
        /*
         * We might have had an item with the previous key in the tree right
         * before we released our path. And after we released our path, that
         * item might have been pushed to the first slot (0) of the leaf we
         * were holding due to a tree balance. Alternatively, an item with the
         * previous key can exist as the only element of a leaf (big fat item).
         * Therefore account for these 2 cases, so that our callers (like
         * btrfs_previous_item) don't miss an existing item with a key matching
         * the previous key we computed above.
         */
        if (ret <= 0)
                return 0;
        return 1;
}

/*
 * A helper function to walk down the tree starting at min_key, and looking
 * for nodes or leaves that are have a minimum transaction id.
 * This is used by the btree defrag code, and tree logging
 *
 * This does not cow, but it does stuff the starting key it finds back
 * into min_key, so you can call btrfs_search_slot with cow=1 on the
 * key and get a writable path.
 *
 * This does lock as it descends, and path->keep_locks should be set
 * to 1 by the caller.
 *
 * This honors path->lowest_level to prevent descent past a given level
 * of the tree.
 *
 * min_trans indicates the oldest transaction that you are interested
 * in walking through.  Any nodes or leaves older than min_trans are
 * skipped over (without reading them).
 *
 * returns zero if something useful was found, < 0 on error and 1 if there
 * was nothing in the tree that matched the search criteria.
 */
int btrfs_search_forward(struct btrfs_root *root, struct btrfs_key *min_key,
                         struct btrfs_path *path,
                         u64 min_trans)
{
        struct extent_buffer *cur;
        struct btrfs_key found_key;
        int slot;
        int sret;
        u32 nritems;
        int level;
        int ret = 1;
        int keep_locks = path->keep_locks;

        path->keep_locks = 1;
again:
        cur = btrfs_read_lock_root_node(root);
        level = btrfs_header_level(cur);
        WARN_ON(path->nodes[level]);
        path->nodes[level] = cur;
        path->locks[level] = BTRFS_READ_LOCK;

        if (btrfs_header_generation(cur) < min_trans) {
                ret = 1;
                goto out;
        }
        while (1) {
                nritems = btrfs_header_nritems(cur);
                level = btrfs_header_level(cur);
                sret = bin_search(cur, min_key, level, &slot);

                /* at the lowest level, we're done, setup the path and exit */
                if (level == path->lowest_level) {
                        if (slot >= nritems)
                                goto find_next_key;
                        ret = 0;
                        path->slots[level] = slot;
                        btrfs_item_key_to_cpu(cur, &found_key, slot);
                        goto out;
                }
                if (sret && slot > 0)
                        slot--;
                /*
                 * check this node pointer against the min_trans parameters.
                 * If it is too old, old, skip to the next one.
                 */
                while (slot < nritems) {
                        u64 gen;

                        gen = btrfs_node_ptr_generation(cur, slot);
                        if (gen < min_trans) {
                                slot++;
                                continue;
                        }
                        break;
                }
find_next_key:
                /*
                 * we didn't find a candidate key in this node, walk forward
                 * and find another one
                 */
                if (slot >= nritems) {
                        path->slots[level] = slot;
                        btrfs_set_path_blocking(path);
                        sret = btrfs_find_next_key(root, path, min_key, level,
                                                  min_trans);
                        if (sret == 0) {
                                btrfs_release_path(path);
                                goto again;
                        } else {
                                goto out;
                        }
                }
                /* save our key for returning back */
                btrfs_node_key_to_cpu(cur, &found_key, slot);
                path->slots[level] = slot;
                if (level == path->lowest_level) {
                        ret = 0;
                        goto out;
                }
                btrfs_set_path_blocking(path);
                cur = read_node_slot(root, cur, slot);
                if (IS_ERR(cur)) {
                        ret = PTR_ERR(cur);
                        goto out;
                }

                btrfs_tree_read_lock(cur);

                path->locks[level - 1] = BTRFS_READ_LOCK;
                path->nodes[level - 1] = cur;
                unlock_up(path, level, 1, 0, NULL);
                btrfs_clear_path_blocking(path, NULL, 0);
        }
out:
        path->keep_locks = keep_locks;
        if (ret == 0) {
                btrfs_unlock_up_safe(path, path->lowest_level + 1);
                btrfs_set_path_blocking(path);
                memcpy(min_key, &found_key, sizeof(found_key));
        }
        return ret;
}

static int tree_move_down(struct btrfs_root *root,
                           struct btrfs_path *path,
                           int *level, int root_level)
{
        struct extent_buffer *eb;

        BUG_ON(*level == 0);
        eb = read_node_slot(root, path->nodes[*level], path->slots[*level]);
        if (IS_ERR(eb))
                return PTR_ERR(eb);

        path->nodes[*level - 1] = eb;
        path->slots[*level - 1] = 0;
        (*level)--;
        return 0;
}

static int tree_move_next_or_upnext(struct btrfs_root *root,
                                    struct btrfs_path *path,
                                    int *level, int root_level)
{
        int ret = 0;
        int nritems;
        nritems = btrfs_header_nritems(path->nodes[*level]);

        path->slots[*level]++;

        while (path->slots[*level] >= nritems) {
                if (*level == root_level)
                        return -1;

                /* move upnext */
                path->slots[*level] = 0;
                free_extent_buffer(path->nodes[*level]);
                path->nodes[*level] = NULL;
                (*level)++;
                path->slots[*level]++;

                nritems = btrfs_header_nritems(path->nodes[*level]);
                ret = 1;
        }
        return ret;
}

/*
 * Returns 1 if it had to move up and next. 0 is returned if it moved only next
 * or down.
 */
static int tree_advance(struct btrfs_root *root,
                        struct btrfs_path *path,
                        int *level, int root_level,
                        int allow_down,
                        struct btrfs_key *key)
{
        int ret;

        if (*level == 0 || !allow_down) {
                ret = tree_move_next_or_upnext(root, path, level, root_level);
        } else {
                ret = tree_move_down(root, path, level, root_level);
        }
        if (ret >= 0) {
                if (*level == 0)
                        btrfs_item_key_to_cpu(path->nodes[*level], key,
                                        path->slots[*level]);
                else
                        btrfs_node_key_to_cpu(path->nodes[*level], key,
                                        path->slots[*level]);
        }
        return ret;
}

static int tree_compare_item(struct btrfs_root *left_root,
                             struct btrfs_path *left_path,
                             struct btrfs_path *right_path,
                             char *tmp_buf)
{
        int cmp;
        int len1, len2;
        unsigned long off1, off2;

        len1 = btrfs_item_size_nr(left_path->nodes[0], left_path->slots[0]);
        len2 = btrfs_item_size_nr(right_path->nodes[0], right_path->slots[0]);
        if (len1 != len2)
                return 1;

        off1 = btrfs_item_ptr_offset(left_path->nodes[0], left_path->slots[0]);
        off2 = btrfs_item_ptr_offset(right_path->nodes[0],
                                right_path->slots[0]);

        read_extent_buffer(left_path->nodes[0], tmp_buf, off1, len1);

        cmp = memcmp_extent_buffer(right_path->nodes[0], tmp_buf, off2, len1);
        if (cmp)
                return 1;
        return 0;
}

#define ADVANCE 1
#define ADVANCE_ONLY_NEXT -1

/*
 * This function compares two trees and calls the provided callback for
 * every changed/new/deleted item it finds.
 * If shared tree blocks are encountered, whole subtrees are skipped, making
 * the compare pretty fast on snapshotted subvolumes.
 *
 * This currently works on commit roots only. As commit roots are read only,
 * we don't do any locking. The commit roots are protected with transactions.
 * Transactions are ended and rejoined when a commit is tried in between.
 *
 * This function checks for modifications done to the trees while comparing.
 * If it detects a change, it aborts immediately.
 */
int btrfs_compare_trees(struct btrfs_root *left_root,
                        struct btrfs_root *right_root,
                        btrfs_changed_cb_t changed_cb, void *ctx)
{
        int ret;
        int cmp;
        struct btrfs_path *left_path = NULL;
        struct btrfs_path *right_path = NULL;
        struct btrfs_key left_key;
        struct btrfs_key right_key;
        char *tmp_buf = NULL;
        int left_root_level;
        int right_root_level;
        int left_level;
        int right_level;
        int left_end_reached;
        int right_end_reached;
        int advance_left;
        int advance_right;
        u64 left_blockptr;
        u64 right_blockptr;
        u64 left_gen;
        u64 right_gen;

        left_path = btrfs_alloc_path();
        if (!left_path) {
                ret = -ENOMEM;
                goto out;
        }
        right_path = btrfs_alloc_path();
        if (!right_path) {
                ret = -ENOMEM;
                goto out;
        }

        tmp_buf = kmalloc(left_root->nodesize, GFP_KERNEL | __GFP_NOWARN);
        if (!tmp_buf) {
                tmp_buf = vmalloc(left_root->nodesize);
                if (!tmp_buf) {
                        ret = -ENOMEM;
                        goto out;
                }
        }

        left_path->search_commit_root = 1;
        left_path->skip_locking = 1;
        right_path->search_commit_root = 1;
        right_path->skip_locking = 1;

        /*
         * Strategy: Go to the first items of both trees. Then do
         *
         * If both trees are at level 0
         *   Compare keys of current items
         *     If left < right treat left item as new, advance left tree
         *       and repeat
         *     If left > right treat right item as deleted, advance right tree
         *       and repeat
         *     If left == right do deep compare of items, treat as changed if
         *       needed, advance both trees and repeat
         * If both trees are at the same level but not at level 0
         *   Compare keys of current nodes/leafs
         *     If left < right advance left tree and repeat
         *     If left > right advance right tree and repeat
         *     If left == right compare blockptrs of the next nodes/leafs
         *       If they match advance both trees but stay at the same level
         *         and repeat
         *       If they don't match advance both trees while allowing to go
         *         deeper and repeat
         * If tree levels are different
         *   Advance the tree that needs it and repeat
         *
         * Advancing a tree means:
         *   If we are at level 0, try to go to the next slot. If that's not
         *   possible, go one level up and repeat. Stop when we found a level
         *   where we could go to the next slot. We may at this point be on a
         *   node or a leaf.
         *
         *   If we are not at level 0 and not on shared tree blocks, go one
         *   level deeper.
         *
         *   If we are not at level 0 and on shared tree blocks, go one slot to
         *   the right if possible or go up and right.
         */

        down_read(&left_root->fs_info->commit_root_sem);
        left_level = btrfs_header_level(left_root->commit_root);
        left_root_level = left_level;
        left_path->nodes[left_level] = left_root->commit_root;
        extent_buffer_get(left_path->nodes[left_level]);

        right_level = btrfs_header_level(right_root->commit_root);
        right_root_level = right_level;
        right_path->nodes[right_level] = right_root->commit_root;
        extent_buffer_get(right_path->nodes[right_level]);
        up_read(&left_root->fs_info->commit_root_sem);

        if (left_level == 0)
                btrfs_item_key_to_cpu(left_path->nodes[left_level],
                                &left_key, left_path->slots[left_level]);
        else
                btrfs_node_key_to_cpu(left_path->nodes[left_level],
                                &left_key, left_path->slots[left_level]);
        if (right_level == 0)
                btrfs_item_key_to_cpu(right_path->nodes[right_level],
                                &right_key, right_path->slots[right_level]);
        else
                btrfs_node_key_to_cpu(right_path->nodes[right_level],
                                &right_key, right_path->slots[right_level]);

        left_end_reached = right_end_reached = 0;
        advance_left = advance_right = 0;

        while (1) {
                if (advance_left && !left_end_reached) {
                        ret = tree_advance(left_root, left_path, &left_level,
                                        left_root_level,
                                        advance_left != ADVANCE_ONLY_NEXT,
                                        &left_key);
                        if (ret == -1)
                                left_end_reached = ADVANCE;
                        else if (ret < 0)
                                goto out;
                        advance_left = 0;
                }
                if (advance_right && !right_end_reached) {
                        ret = tree_advance(right_root, right_path, &right_level,
                                        right_root_level,
                                        advance_right != ADVANCE_ONLY_NEXT,
                                        &right_key);
                        if (ret == -1)
                                right_end_reached = ADVANCE;
                        else if (ret < 0)
                                goto out;
                        advance_right = 0;
                }

                if (left_end_reached && right_end_reached) {
                        ret = 0;
                        goto out;
                } else if (left_end_reached) {
                        if (right_level == 0) {
                                ret = changed_cb(left_root, right_root,
                                                left_path, right_path,
                                                &right_key,
                                                BTRFS_COMPARE_TREE_DELETED,
                                                ctx);
                                if (ret < 0)
                                        goto out;
                        }
                        advance_right = ADVANCE;
                        continue;
                } else if (right_end_reached) {
                        if (left_level == 0) {
                                ret = changed_cb(left_root, right_root,
                                                left_path, right_path,
                                                &left_key,
                                                BTRFS_COMPARE_TREE_NEW,
                                                ctx);
                                if (ret < 0)
                                        goto out;
                        }
                        advance_left = ADVANCE;
                        continue;
                }

                if (left_level == 0 && right_level == 0) {
                        cmp = btrfs_comp_cpu_keys(&left_key, &right_key);
                        if (cmp < 0) {
                                ret = changed_cb(left_root, right_root,
                                                left_path, right_path,
                                                &left_key,
                                                BTRFS_COMPARE_TREE_NEW,
                                                ctx);
                                if (ret < 0)
                                        goto out;
                                advance_left = ADVANCE;
                        } else if (cmp > 0) {
                                ret = changed_cb(left_root, right_root,
                                                left_path, right_path,
                                                &right_key,
                                                BTRFS_COMPARE_TREE_DELETED,
                                                ctx);
                                if (ret < 0)
                                        goto out;
                                advance_right = ADVANCE;
                        } else {
                                enum btrfs_compare_tree_result result;

                                WARN_ON(!extent_buffer_uptodate(left_path->nodes[0]));
                                ret = tree_compare_item(left_root, left_path,
                                                right_path, tmp_buf);
                                if (ret)
                                        result = BTRFS_COMPARE_TREE_CHANGED;
                                else
                                        result = BTRFS_COMPARE_TREE_SAME;
                                ret = changed_cb(left_root, right_root,
                                                 left_path, right_path,
                                                 &left_key, result, ctx);
                                if (ret < 0)
                                        goto out;
                                advance_left = ADVANCE;
                                advance_right = ADVANCE;
                        }
                } else if (left_level == right_level) {
                        cmp = btrfs_comp_cpu_keys(&left_key, &right_key);
                        if (cmp < 0) {
                                advance_left = ADVANCE;
                        } else if (cmp > 0) {
                                advance_right = ADVANCE;
                        } else {
                                left_blockptr = btrfs_node_blockptr(
                                                left_path->nodes[left_level],
                                                left_path->slots[left_level]);
                                right_blockptr = btrfs_node_blockptr(
                                                right_path->nodes[right_level],
                                                right_path->slots[right_level]);
                                left_gen = btrfs_node_ptr_generation(
                                                left_path->nodes[left_level],
                                                left_path->slots[left_level]);
                                right_gen = btrfs_node_ptr_generation(
                                                right_path->nodes[right_level],
                                                right_path->slots[right_level]);
                                if (left_blockptr == right_blockptr &&
                                    left_gen == right_gen) {
                                        /*
                                         * As we're on a shared block, don't
                                         * allow to go deeper.
                                         */
                                        advance_left = ADVANCE_ONLY_NEXT;
                                        advance_right = ADVANCE_ONLY_NEXT;
                                } else {
                                        advance_left = ADVANCE;
                                        advance_right = ADVANCE;
                                }
                        }
                } else if (left_level < right_level) {
                        advance_right = ADVANCE;
                } else {
                        advance_left = ADVANCE;
                }
        }

out:
        btrfs_free_path(left_path);
        btrfs_free_path(right_path);
        kvfree(tmp_buf);
        return ret;
}

/*
 * this is similar to btrfs_next_leaf, but does not try to preserve
 * and fixup the path.  It looks for and returns the next key in the
 * tree based on the current path and the min_trans parameters.
 *
 * 0 is returned if another key is found, < 0 if there are any errors
 * and 1 is returned if there are no higher keys in the tree
 *
 * path->keep_locks should be set to 1 on the search made before
 * calling this function.
 */
int btrfs_find_next_key(struct btrfs_root *root, struct btrfs_path *path,
                        struct btrfs_key *key, int level, u64 min_trans)
{
        int slot;
        struct extent_buffer *c;

        WARN_ON(!path->keep_locks);
        while (level < BTRFS_MAX_LEVEL) {
                if (!path->nodes[level])
                        return 1;

                slot = path->slots[level] + 1;
                c = path->nodes[level];
next:
                if (slot >= btrfs_header_nritems(c)) {
                        int ret;
                        int orig_lowest;
                        struct btrfs_key cur_key;
                        if (level + 1 >= BTRFS_MAX_LEVEL ||
                            !path->nodes[level + 1])
                                return 1;

                        if (path->locks[level + 1]) {
                                level++;
                                continue;
                        }

                        slot = btrfs_header_nritems(c) - 1;
                        if (level == 0)
                                btrfs_item_key_to_cpu(c, &cur_key, slot);
                        else
                                btrfs_node_key_to_cpu(c, &cur_key, slot);

                        orig_lowest = path->lowest_level;
                        btrfs_release_path(path);
                        path->lowest_level = level;
                        ret = btrfs_search_slot(NULL, root, &cur_key, path,
                                                0, 0);
                        path->lowest_level = orig_lowest;
                        if (ret < 0)
                                return ret;

                        c = path->nodes[level];
                        slot = path->slots[level];
                        if (ret == 0)
                                slot++;
                        goto next;
                }

                if (level == 0)
                        btrfs_item_key_to_cpu(c, key, slot);
                else {
                        u64 gen = btrfs_node_ptr_generation(c, slot);

                        if (gen < min_trans) {
                                slot++;
                                goto next;
                        }
                        btrfs_node_key_to_cpu(c, key, slot);
                }
                return 0;
        }
        return 1;
}

/*
 * search the tree again to find a leaf with greater keys
 * 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)
{
        return btrfs_next_old_leaf(root, path, 0);
}

int btrfs_next_old_leaf(struct btrfs_root *root, struct btrfs_path *path,
                        u64 time_seq)
{
        int slot;
        int level;
        struct extent_buffer *c;
        struct extent_buffer *next;
        struct btrfs_key key;
        u32 nritems;
        int ret;
        int old_spinning = path->leave_spinning;
        int next_rw_lock = 0;

        nritems = btrfs_header_nritems(path->nodes[0]);
        if (nritems == 0)
                return 1;

        btrfs_item_key_to_cpu(path->nodes[0], &key, nritems - 1);
again:
        level = 1;
        next = NULL;
        next_rw_lock = 0;
        btrfs_release_path(path);

        path->keep_locks = 1;
        path->leave_spinning = 1;

        if (time_seq)
                ret = btrfs_search_old_slot(root, &key, path, time_seq);
        else
                ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        path->keep_locks = 0;

        if (ret < 0)
                return ret;

        nritems = btrfs_header_nritems(path->nodes[0]);
        /*
         * by releasing the path above we dropped all our locks.  A balance
         * could have added more items next to the key that used to be
         * at the very end of the block.  So, check again here and
         * advance the path if there are now more items available.
         */
        if (nritems > 0 && path->slots[0] < nritems - 1) {
                if (ret == 0)
                        path->slots[0]++;
                ret = 0;
                goto done;
        }
        /*
         * So the above check misses one case:
         * - after releasing the path above, someone has removed the item that
         *   used to be at the very end of the block, and balance between leafs
         *   gets another one with bigger key.offset to replace it.
         *
         * This one should be returned as well, or we can get leaf corruption
         * later(esp. in __btrfs_drop_extents()).
         *
         * And a bit more explanation about this check,
         * with ret > 0, the key isn't found, the path points to the slot
         * where it should be inserted, so the path->slots[0] item must be the
         * bigger one.
         */
        if (nritems > 0 && ret > 0 && path->slots[0] == nritems - 1) {
                ret = 0;
                goto done;
        }

        while (level < BTRFS_MAX_LEVEL) {
                if (!path->nodes[level]) {
                        ret = 1;
                        goto done;
                }

                slot = path->slots[level] + 1;
                c = path->nodes[level];
                if (slot >= btrfs_header_nritems(c)) {
                        level++;
                        if (level == BTRFS_MAX_LEVEL) {
                                ret = 1;
                                goto done;
                        }
                        continue;
                }

                if (next) {
                        btrfs_tree_unlock_rw(next, next_rw_lock);
                        free_extent_buffer(next);
                }

                next = c;
                next_rw_lock = path->locks[level];
                ret = read_block_for_search(NULL, root, path, &next, level,
                                            slot, &key, 0);
                if (ret == -EAGAIN)
                        goto again;

                if (ret < 0) {
                        btrfs_release_path(path);
                        goto done;
                }

                if (!path->skip_locking) {
                        ret = btrfs_try_tree_read_lock(next);
                        if (!ret && time_seq) {
                                /*
                                 * If we don't get the lock, we may be racing
                                 * with push_leaf_left, holding that lock while
                                 * itself waiting for the leaf we've currently
                                 * locked. To solve this situation, we give up
                                 * on our lock and cycle.
                                 */
                                free_extent_buffer(next);
                                btrfs_release_path(path);
                                cond_resched();
                                goto again;
                        }
                        if (!ret) {
                                btrfs_set_path_blocking(path);
                                btrfs_tree_read_lock(next);
                                btrfs_clear_path_blocking(path, next,
                                                          BTRFS_READ_LOCK);
                        }
                        next_rw_lock = BTRFS_READ_LOCK;
                }
                break;
        }
        path->slots[level] = slot;
        while (1) {
                level--;
                c = path->nodes[level];
                if (path->locks[level])
                        btrfs_tree_unlock_rw(c, path->locks[level]);

                free_extent_buffer(c);
                path->nodes[level] = next;
                path->slots[level] = 0;
                if (!path->skip_locking)
                        path->locks[level] = next_rw_lock;
                if (!level)
                        break;

                ret = read_block_for_search(NULL, root, path, &next, level,
                                            0, &key, 0);
                if (ret == -EAGAIN)
                        goto again;

                if (ret < 0) {
                        btrfs_release_path(path);
                        goto done;
                }

                if (!path->skip_locking) {
                        ret = btrfs_try_tree_read_lock(next);
                        if (!ret) {
                                btrfs_set_path_blocking(path);
                                btrfs_tree_read_lock(next);
                                btrfs_clear_path_blocking(path, next,
                                                          BTRFS_READ_LOCK);
                        }
                        next_rw_lock = BTRFS_READ_LOCK;
                }
        }
        ret = 0;
done:
        unlock_up(path, 0, 1, 0, NULL);
        path->leave_spinning = old_spinning;
        if (!old_spinning)
                btrfs_set_path_blocking(path);

        return ret;
}

/*
 * this uses btrfs_prev_leaf to walk backwards in the tree, and keeps
 * searching until it gets past min_objectid or finds an item of 'type'
 *
 * returns 0 if something is found, 1 if nothing was found and < 0 on error
 */
int btrfs_previous_item(struct btrfs_root *root,
                        struct btrfs_path *path, u64 min_objectid,
                        int type)
{
        struct btrfs_key found_key;
        struct extent_buffer *leaf;
        u32 nritems;
        int ret;

        while (1) {
                if (path->slots[0] == 0) {
                        btrfs_set_path_blocking(path);
                        ret = btrfs_prev_leaf(root, path);
                        if (ret != 0)
                                return ret;
                } else {
                        path->slots[0]--;
                }
                leaf = path->nodes[0];
                nritems = btrfs_header_nritems(leaf);
                if (nritems == 0)
                        return 1;
                if (path->slots[0] == nritems)
                        path->slots[0]--;

                btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
                if (found_key.objectid < min_objectid)
                        break;
                if (found_key.type == type)
                        return 0;
                if (found_key.objectid == min_objectid &&
                    found_key.type < type)
                        break;
        }
        return 1;
}

/*
 * search in extent tree to find a previous Metadata/Data extent item with
 * min objecitd.
 *
 * returns 0 if something is found, 1 if nothing was found and < 0 on error
 */
int btrfs_previous_extent_item(struct btrfs_root *root,
                        struct btrfs_path *path, u64 min_objectid)
{
        struct btrfs_key found_key;
        struct extent_buffer *leaf;
        u32 nritems;
        int ret;

        while (1) {
                if (path->slots[0] == 0) {
                        btrfs_set_path_blocking(path);
                        ret = btrfs_prev_leaf(root, path);
                        if (ret != 0)
                                return ret;
                } else {
                        path->slots[0]--;
                }
                leaf = path->nodes[0];
                nritems = btrfs_header_nritems(leaf);
                if (nritems == 0)
                        return 1;
                if (path->slots[0] == nritems)
                        path->slots[0]--;

                btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
                if (found_key.objectid < min_objectid)
                        break;
                if (found_key.type == BTRFS_EXTENT_ITEM_KEY ||
                    found_key.type == BTRFS_METADATA_ITEM_KEY)
                        return 0;
                if (found_key.objectid == min_objectid &&
                    found_key.type < BTRFS_EXTENT_ITEM_KEY)
                        break;
        }
        return 1;
}