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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 "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 int del_ptr(struct btrfs_trans_handle *trans, struct btrfs_root *root,
               struct btrfs_path *path, int level, int slot);

struct btrfs_path *btrfs_alloc_path(void)
{
      struct btrfs_path *path;
      path = kmem_cache_zalloc(btrfs_path_cachep, GFP_NOFS);
      if (path)
            path->reada = 1;
      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])
                  btrfs_set_lock_blocking(p->nodes[i]);
      }
}

/*
 * 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 i;

#ifdef CONFIG_DEBUG_LOCK_ALLOC
      /* lockdep really cares that we take all of these spinlocks
       * in the right order.  If any of the locks in the path are not
       * currently blocking, it is going to complain.  So, make really
       * really sure by forcing the path to blocking before we clear
       * the path blocking.
       */
      if (held)
            btrfs_set_lock_blocking(held);
      btrfs_set_path_blocking(p);
#endif

      for (i = BTRFS_MAX_LEVEL - 1; i >= 0; i--) {
            if (p->nodes[i] && p->locks[i])
                  btrfs_clear_lock_blocking(p->nodes[i]);
      }

#ifdef CONFIG_DEBUG_LOCK_ALLOC
      if (held)
            btrfs_clear_lock_blocking(held);
#endif
}

/* this also releases the path */
void btrfs_free_path(struct btrfs_path *p)
{
      btrfs_release_path(NULL, 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_root *root, 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(p->nodes[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;
      spin_lock(&root->node_lock);
      eb = root->node;
      extent_buffer_get(eb);
      spin_unlock(&root->node_lock);
      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);

            spin_lock(&root->node_lock);
            if (eb == root->node) {
                  spin_unlock(&root->node_lock);
                  break;
            }
            spin_unlock(&root->node_lock);

            btrfs_tree_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 (root->track_dirty && list_empty(&root->dirty_list)) {
            list_add(&root->dirty_list,
                   &root->fs_info->dirty_cowonly_roots);
      }
}

/*
 * 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;
      u32 nritems;
      int ret = 0;
      int level;
      struct btrfs_disk_key disk_key;

      WARN_ON(root->ref_cows && trans->transid !=
            root->fs_info->running_transaction->transid);
      WARN_ON(root->ref_cows && trans->transid != root->last_trans);

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

      cow = btrfs_alloc_free_block(trans, root, buf->len, 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,
                      (unsigned long)btrfs_header_fsid(cow),
                      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;
}

/*
 * 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 refernece 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 (root->ref_cows &&
          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 (root->ref_cows &&
          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)
{
      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,
                                     buf->len, &refs, &flags);
            BUG_ON(ret);
            BUG_ON(refs == 0);
      } 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);

                  if (root->root_key.objectid ==
                      BTRFS_TREE_RELOC_OBJECTID) {
                        ret = btrfs_dec_ref(trans, root, buf, 0);
                        BUG_ON(ret);
                        ret = btrfs_inc_ref(trans, root, cow, 1);
                        BUG_ON(ret);
                  }
                  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);
            }
            if (new_flags != 0) {
                  ret = btrfs_set_disk_extent_flags(trans, root,
                                            buf->start,
                                            buf->len,
                                            new_flags, 0);
                  BUG_ON(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);
                  ret = btrfs_dec_ref(trans, root, buf, 1);
                  BUG_ON(ret);
            }
            clean_tree_block(trans, root, buf);
      }
      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;
      int unlock_orig = 0;
      u64 parent_start;

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

      btrfs_assert_tree_locked(buf);

      WARN_ON(root->ref_cows && trans->transid !=
            root->fs_info->running_transaction->transid);
      WARN_ON(root->ref_cows && 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_free_block(trans, root, buf->len, 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,
                      (unsigned long)btrfs_header_fsid(cow),
                      BTRFS_FSID_SIZE);

      update_ref_for_cow(trans, root, buf, cow);

      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;

            spin_lock(&root->node_lock);
            root->node = cow;
            extent_buffer_get(cow);
            spin_unlock(&root->node_lock);

            btrfs_free_extent(trans, root, buf->start, buf->len,
                          parent_start, root->root_key.objectid,
                          level, 0);
            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));
            btrfs_set_node_blockptr(parent, parent_slot,
                              cow->start);
            btrfs_set_node_ptr_generation(parent, parent_slot,
                                    trans->transid);
            btrfs_mark_buffer_dirty(parent);
            btrfs_free_extent(trans, root, buf->start, buf->len,
                          parent_start, root->root_key.objectid,
                          level, 0);
      }
      if (unlock_orig)
            btrfs_tree_unlock(buf);
      free_extent_buffer(buf);
      btrfs_mark_buffer_dirty(cow);
      *cow_ret = cow;
      return 0;
}

static inline int should_cow_block(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root,
                           struct extent_buffer *buf)
{
      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)))
            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 cow'd 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) {
            printk(KERN_CRIT "trans %llu running %llu\n",
                   (unsigned long long)trans->transid,
                   (unsigned long long)
                   root->fs_info->running_transaction->transid);
            WARN_ON(1);
      }
      if (trans->transid != root->fs_info->generation) {
            printk(KERN_CRIT "trans %llu running %llu\n",
                   (unsigned long long)trans->transid,
                   (unsigned long long)root->fs_info->generation);
            WARN_ON(1);
      }

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

      search_start = buf->start & ~((u64)(1024 * 1024 * 1024) - 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);
      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, int cache_only, 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);
      if (cache_only && parent_level != 1)
            return 0;

      if (trans->transaction != root->fs_info->running_transaction)
            WARN_ON(1);
      if (trans->transid != root->fs_info->generation)
            WARN_ON(1);

      parent_nritems = btrfs_header_nritems(parent);
      blocksize = btrfs_level_size(root, parent_level - 1);
      end_slot = parent_nritems;

      if (parent_nritems == 1)
            return 0;

      btrfs_set_lock_blocking(parent);

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

            if (!parent->map_token) {
                  map_extent_buffer(parent,
                              btrfs_node_key_ptr_offset(i),
                              sizeof(struct btrfs_key_ptr),
                              &parent->map_token, &parent->kaddr,
                              &parent->map_start, &parent->map_len,
                              KM_USER1);
            }
            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 - 2) {
                  other = btrfs_node_blockptr(parent, i + 1);
                  close = close_blocks(blocknr, other, blocksize);
            }
            if (close) {
                  last_block = blocknr;
                  continue;
            }
            if (parent->map_token) {
                  unmap_extent_buffer(parent, parent->map_token,
                                  KM_USER1);
                  parent->map_token = NULL;
            }

            cur = btrfs_find_tree_block(root, blocknr, blocksize);
            if (cur)
                  uptodate = btrfs_buffer_uptodate(cur, gen);
            else
                  uptodate = 0;
            if (!cur || !uptodate) {
                  if (cache_only) {
                        free_extent_buffer(cur);
                        continue;
                  }
                  if (!cur) {
                        cur = read_tree_block(root, blocknr,
                                           blocksize, gen);
                  } else if (!uptodate) {
                        btrfs_read_buffer(cur, gen);
                  }
            }
            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);
      }
      if (parent->map_token) {
            unmap_extent_buffer(parent, parent->map_token,
                            KM_USER1);
            parent->map_token = NULL;
      }
      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);
}

/*
 * extra debugging checks to make sure all the items in a key are
 * well formed and in the proper order
 */
static int check_node(struct btrfs_root *root, struct btrfs_path *path,
                  int level)
{
      struct extent_buffer *parent = NULL;
      struct extent_buffer *node = path->nodes[level];
      struct btrfs_disk_key parent_key;
      struct btrfs_disk_key node_key;
      int parent_slot;
      int slot;
      struct btrfs_key cpukey;
      u32 nritems = btrfs_header_nritems(node);

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

      slot = path->slots[level];
      BUG_ON(nritems == 0);
      if (parent) {
            parent_slot = path->slots[level + 1];
            btrfs_node_key(parent, &parent_key, parent_slot);
            btrfs_node_key(node, &node_key, 0);
            BUG_ON(memcmp(&parent_key, &node_key,
                        sizeof(struct btrfs_disk_key)));
            BUG_ON(btrfs_node_blockptr(parent, parent_slot) !=
                   btrfs_header_bytenr(node));
      }
      BUG_ON(nritems > BTRFS_NODEPTRS_PER_BLOCK(root));
      if (slot != 0) {
            btrfs_node_key_to_cpu(node, &cpukey, slot - 1);
            btrfs_node_key(node, &node_key, slot);
            BUG_ON(comp_keys(&node_key, &cpukey) <= 0);
      }
      if (slot < nritems - 1) {
            btrfs_node_key_to_cpu(node, &cpukey, slot + 1);
            btrfs_node_key(node, &node_key, slot);
            BUG_ON(comp_keys(&node_key, &cpukey) >= 0);
      }
      return 0;
}

/*
 * extra checking to make sure all the items in a leaf are
 * well formed and in the proper order
 */
static int check_leaf(struct btrfs_root *root, struct btrfs_path *path,
                  int level)
{
      struct extent_buffer *leaf = path->nodes[level];
      struct extent_buffer *parent = NULL;
      int parent_slot;
      struct btrfs_key cpukey;
      struct btrfs_disk_key parent_key;
      struct btrfs_disk_key leaf_key;
      int slot = path->slots[0];

      u32 nritems = btrfs_header_nritems(leaf);

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

      if (nritems == 0)
            return 0;

      if (parent) {
            parent_slot = path->slots[level + 1];
            btrfs_node_key(parent, &parent_key, parent_slot);
            btrfs_item_key(leaf, &leaf_key, 0);

            BUG_ON(memcmp(&parent_key, &leaf_key,
                   sizeof(struct btrfs_disk_key)));
            BUG_ON(btrfs_node_blockptr(parent, parent_slot) !=
                   btrfs_header_bytenr(leaf));
      }
      if (slot != 0 && slot < nritems - 1) {
            btrfs_item_key(leaf, &leaf_key, slot);
            btrfs_item_key_to_cpu(leaf, &cpukey, slot - 1);
            if (comp_keys(&leaf_key, &cpukey) <= 0) {
                  btrfs_print_leaf(root, leaf);
                  printk(KERN_CRIT "slot %d offset bad key\n", slot);
                  BUG_ON(1);
            }
            if (btrfs_item_offset_nr(leaf, slot - 1) !=
                   btrfs_item_end_nr(leaf, slot)) {
                  btrfs_print_leaf(root, leaf);
                  printk(KERN_CRIT "slot %d offset bad\n", slot);
                  BUG_ON(1);
            }
      }
      if (slot < nritems - 1) {
            btrfs_item_key(leaf, &leaf_key, slot);
            btrfs_item_key_to_cpu(leaf, &cpukey, slot + 1);
            BUG_ON(comp_keys(&leaf_key, &cpukey) >= 0);
            if (btrfs_item_offset_nr(leaf, slot) !=
                  btrfs_item_end_nr(leaf, slot + 1)) {
                  btrfs_print_leaf(root, leaf);
                  printk(KERN_CRIT "slot %d offset bad\n", slot);
                  BUG_ON(1);
            }
      }
      BUG_ON(btrfs_item_offset_nr(leaf, 0) +
             btrfs_item_size_nr(leaf, 0) != BTRFS_LEAF_DATA_SIZE(root));
      return 0;
}

static noinline int check_block(struct btrfs_root *root,
                        struct btrfs_path *path, int level)
{
      return 0;
      if (level == 0)
            return check_leaf(root, path, level);
      return check_node(root, path, level);
}

/*
 * 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 *map_token = NULL;
      char *kaddr = NULL;
      unsigned long map_start = 0;
      unsigned long map_len = 0;
      int err;

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

            if (!map_token || offset < map_start ||
                (offset + sizeof(struct btrfs_disk_key)) >
                map_start + map_len) {
                  if (map_token) {
                        unmap_extent_buffer(eb, map_token, KM_USER0);
                        map_token = NULL;
                  }

                  err = map_private_extent_buffer(eb, offset,
                                    sizeof(struct btrfs_disk_key),
                                    &map_token, &kaddr,
                                    &map_start, &map_len, KM_USER0);

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

            } 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;
                  if (map_token)
                        unmap_extent_buffer(eb, map_token, KM_USER0);
                  return 0;
            }
      }
      *slot = low;
      if (map_token)
            unmap_extent_buffer(eb, map_token, KM_USER0);
      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);
      }
      return -1;
}

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

/* given a node and slot number, this reads the blocks it points to.  The
 * extent buffer is returned with a reference taken (but unlocked).
 * NULL is returned on error.
 */
static noinline struct extent_buffer *read_node_slot(struct btrfs_root *root,
                           struct extent_buffer *parent, int slot)
{
      int level = btrfs_header_level(parent);
      if (slot < 0)
            return NULL;
      if (slot >= btrfs_header_nritems(parent))
            return NULL;

      BUG_ON(level == 0);

      return read_tree_block(root, btrfs_node_blockptr(parent, slot),
                   btrfs_level_size(root, level - 1),
                   btrfs_node_ptr_generation(parent, slot));
}

/*
 * 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];
      int err_on_enospc = 0;
      u64 orig_ptr;

      if (level == 0)
            return 0;

      mid = path->nodes[level];

      WARN_ON(!path->locks[level]);
      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);
            BUG_ON(!child);
            btrfs_tree_lock(child);
            btrfs_set_lock_blocking(child);
            ret = btrfs_cow_block(trans, root, child, mid, 0, &child);
            BUG_ON(ret);

            spin_lock(&root->node_lock);
            root->node = child;
            spin_unlock(&root->node_lock);

            add_root_to_dirty_list(root);
            btrfs_tree_unlock(child);

            path->locks[level] = 0;
            path->nodes[level] = NULL;
            clean_tree_block(trans, root, mid);
            btrfs_tree_unlock(mid);
            /* once for the path */
            free_extent_buffer(mid);
            ret = btrfs_free_extent(trans, root, mid->start, mid->len,
                              0, root->root_key.objectid, level, 1);
            /* once for the root ptr */
            free_extent_buffer(mid);
            return ret;
      }
      if (btrfs_header_nritems(mid) >
          BTRFS_NODEPTRS_PER_BLOCK(root) / 4)
            return 0;

      if (btrfs_header_nritems(mid) < 2)
            err_on_enospc = 1;

      left = read_node_slot(root, parent, pslot - 1);
      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 (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;
            if (btrfs_header_nritems(mid) < 2)
                  err_on_enospc = 1;
      }

      /*
       * 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) {
                  u64 bytenr = right->start;
                  u32 blocksize = right->len;

                  clean_tree_block(trans, root, right);
                  btrfs_tree_unlock(right);
                  free_extent_buffer(right);
                  right = NULL;
                  wret = del_ptr(trans, root, path, level + 1, pslot +
                               1);
                  if (wret)
                        ret = wret;
                  wret = btrfs_free_extent(trans, root, bytenr,
                                     blocksize, 0,
                                     root->root_key.objectid,
                                     level, 0);
                  if (wret)
                        ret = wret;
            } else {
                  struct btrfs_disk_key right_key;
                  btrfs_node_key(right, &right_key, 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
             */
            BUG_ON(!left);
            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) {
            /* we've managed to empty the middle node, drop it */
            u64 bytenr = mid->start;
            u32 blocksize = mid->len;

            clean_tree_block(trans, root, mid);
            btrfs_tree_unlock(mid);
            free_extent_buffer(mid);
            mid = NULL;
            wret = del_ptr(trans, root, path, level + 1, pslot);
            if (wret)
                  ret = wret;
            wret = btrfs_free_extent(trans, root, bytenr, blocksize,
                               0, root->root_key.objectid,
                               level, 0);
            if (wret)
                  ret = wret;
      } else {
            /* update the parent key to reflect our changes */
            struct btrfs_disk_key mid_key;
            btrfs_node_key(mid, &mid_key, 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 */
      check_block(root, path, level);
      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];
      u64 orig_ptr;

      if (level == 0)
            return 1;

      mid = path->nodes[level];
      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];

      if (!parent)
            return 1;

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

      /* 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);
                  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);

      /*
       * 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);
                  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;
      int direction = path->reada;
      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 = btrfs_level_size(root, level - 1);
      eb = btrfs_find_tree_block(root, search, blocksize);
      if (eb) {
            free_extent_buffer(eb);
            return;
      }

      target = search;

      nritems = btrfs_header_nritems(node);
      nr = slot;
      while (1) {
            if (direction < 0) {
                  if (nr == 0)
                        break;
                  nr--;
            } else if (direction > 0) {
                  nr++;
                  if (nr >= nritems)
                        break;
            }
            if (path->reada < 0 && 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)) {
                  readahead_tree_block(root, search, blocksize,
                             btrfs_node_ptr_generation(node, nr));
                  nread += blocksize;
            }
            nscan++;
            if ((nread > 65536 || nscan > 32))
                  break;
      }
}

/*
 * returns -EAGAIN if it had to drop the path, or zero if everything was in
 * cache
 */
static noinline int 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;
      int ret = 0;
      int blocksize;

      parent = path->nodes[level + 1];
      if (!parent)
            return 0;

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

      if (slot > 0) {
            block1 = btrfs_node_blockptr(parent, slot - 1);
            gen = btrfs_node_ptr_generation(parent, slot - 1);
            eb = btrfs_find_tree_block(root, block1, blocksize);
            if (eb && btrfs_buffer_uptodate(eb, gen))
                  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, block2, blocksize);
            if (eb && btrfs_buffer_uptodate(eb, gen))
                  block2 = 0;
            free_extent_buffer(eb);
      }
      if (block1 || block2) {
            ret = -EAGAIN;

            /* release the whole path */
            btrfs_release_path(root, path);

            /* read the blocks */
            if (block1)
                  readahead_tree_block(root, block1, blocksize, 0);
            if (block2)
                  readahead_tree_block(root, block2, blocksize, 0);

            if (block1) {
                  eb = read_tree_block(root, block1, blocksize, 0);
                  free_extent_buffer(eb);
            }
            if (block2) {
                  eb = read_tree_block(root, block2, blocksize, 0);
                  free_extent_buffer(eb);
            }
      }
      return ret;
}


/*
 * 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 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(t);
                  path->locks[i] = 0;
            }
      }
}

/*
 * 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(path->nodes[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 blocknr;
      u64 gen;
      u32 blocksize;
      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);
      blocksize = btrfs_level_size(root, level - 1);

      tmp = btrfs_find_tree_block(root, blocknr, blocksize);
      if (tmp && btrfs_buffer_uptodate(tmp, gen)) {
            /*
             * we found an up to date block without sleeping, return
             * right away
             */
            *eb_ret = tmp;
            return 0;
      }

      /*
       * 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);

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

      btrfs_release_path(NULL, p);

      ret = -EAGAIN;
      tmp = read_tree_block(root, blocknr, blocksize, gen);
      if (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))
                  ret = -EIO;
            free_extent_buffer(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 ret;
      if ((p->search_for_split || ins_len > 0) && btrfs_header_nritems(b) >=
          BTRFS_NODEPTRS_PER_BLOCK(root) - 3) {
            int sret;

            sret = reada_for_balance(root, p, level);
            if (sret)
                  goto again;

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

            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;

            sret = reada_for_balance(root, p, level);
            if (sret)
                  goto again;

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

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

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

/*
 * 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;
      u8 lowest_level = 0;

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

      if (ins_len < 0)
            lowest_unlock = 2;

again:
      if (p->search_commit_root) {
            b = root->commit_root;
            extent_buffer_get(b);
            if (!p->skip_locking)
                  btrfs_tree_lock(b);
      } else {
            if (p->skip_locking)
                  b = btrfs_root_node(root);
            else
                  b = btrfs_lock_root_node(root);
      }

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

            /*
             * setup the path here so we can release it under lock
             * contention with the cow code
             */
            p->nodes[level] = b;
            if (!p->skip_locking)
                  p->locks[level] = 1;

            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))
                        goto cow_done;

                  btrfs_set_path_blocking(p);

                  err = btrfs_cow_block(trans, root, b,
                                    p->nodes[level + 1],
                                    p->slots[level + 1], &b);
                  if (err) {
                        free_extent_buffer(b);
                        ret = err;
                        goto done;
                  }
            }
cow_done:
            BUG_ON(!cow && ins_len);
            if (level != btrfs_header_level(b))
                  WARN_ON(1);
            level = btrfs_header_level(b);

            p->nodes[level] = b;
            if (!p->skip_locking)
                  p->locks[level] = 1;

            btrfs_clear_path_blocking(p, NULL);

            /*
             * 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 cow is true, 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 (!cow)
                  btrfs_unlock_up_safe(p, level + 1);

            ret = check_block(root, p, level);
            if (ret) {
                  ret = -1;
                  goto done;
            }

            ret = bin_search(b, key, level, &slot);

            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);
                  if (err == -EAGAIN)
                        goto again;
                  if (err) {
                        ret = err;
                        goto done;
                  }
                  b = p->nodes[level];
                  slot = p->slots[level];

                  unlock_up(p, level, lowest_unlock);

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

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

                  if (!p->skip_locking) {
                        btrfs_clear_path_blocking(p, NULL);
                        err = btrfs_try_spin_lock(b);

                        if (!err) {
                              btrfs_set_path_blocking(p);
                              btrfs_tree_lock(b);
                              btrfs_clear_path_blocking(p, b);
                        }
                  }
            } else {
                  p->slots[level] = slot;
                  if (ins_len > 0 &&
                      btrfs_leaf_free_space(root, b) < ins_len) {
                        btrfs_set_path_blocking(p);
                        err = split_leaf(trans, root, key,
                                     p, ins_len, ret == 0);
                        btrfs_clear_path_blocking(p, NULL);

                        BUG_ON(err > 0);
                        if (err) {
                              ret = err;
                              goto done;
                        }
                  }
                  if (!p->search_for_split)
                        unlock_up(p, level, lowest_unlock);
                  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)
            btrfs_release_path(root, p);
      return ret;
}

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

/*
 * update item key.
 *
 * This function isn't completely safe. It's the caller's responsibility
 * that the new key won't break the order
 */
int btrfs_set_item_key_safe(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root, 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);
            if (comp_keys(&disk_key, new_key) >= 0)
                  return -1;
      }
      if (slot < btrfs_header_nritems(eb) - 1) {
            btrfs_item_key(eb, &disk_key, slot + 1);
            if (comp_keys(&disk_key, new_key) <= 0)
                  return -1;
      }

      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(trans, root, path, &disk_key, 1);
      return 0;
}

/*
 * 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);

      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) {
            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;

      memmove_extent_buffer(dst, btrfs_node_key_ptr_offset(push_items),
                              btrfs_node_key_ptr_offset(0),
                              (dst_nritems) *
                              sizeof(struct btrfs_key_ptr));

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

      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,
                      (unsigned long)btrfs_header_fsid(c),
                      BTRFS_FSID_SIZE);

      write_extent_buffer(c, root->fs_info->chunk_tree_uuid,
                      (unsigned long)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);

      spin_lock(&root->node_lock);
      old = root->node;
      root->node = c;
      spin_unlock(&root->node_lock);

      /* 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] = 1;
      path->slots[level] = 0;
      return 0;
}

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

      BUG_ON(!path->nodes[level]);
      lower = path->nodes[level];
      nritems = btrfs_header_nritems(lower);
      BUG_ON(slot > nritems);
      if (nritems == BTRFS_NODEPTRS_PER_BLOCK(root))
            BUG();
      if (slot != nritems) {
            memmove_extent_buffer(lower,
                        btrfs_node_key_ptr_offset(slot + 1),
                        btrfs_node_key_ptr_offset(slot),
                        (nritems - slot) * sizeof(struct btrfs_key_ptr));
      }
      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);
      return 0;
}

/*
 * split the node at the specified level in path in two.
 * The path is corrected to point to the appropriate node after the split
 *
 * Before splitting this tries to make some room in the node by pushing
 * left and right, if either one works, it returns right away.
 *
 * returns 0 on success and < 0 on failure
 */
static 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;
      int wret;
      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 */
            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_free_block(trans, root, root->nodesize, 0,
                              root->root_key.objectid,
                              &disk_key, level, c->start, 0);
      if (IS_ERR(split))
            return PTR_ERR(split);

      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,
                      (unsigned long)btrfs_header_fsid(split),
                      BTRFS_FSID_SIZE);
      write_extent_buffer(split, root->fs_info->chunk_tree_uuid,
                      (unsigned long)btrfs_header_chunk_tree_uuid(split),
                      BTRFS_UUID_SIZE);


      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);

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

      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)
{
      int data_len;
      int nritems = btrfs_header_nritems(l);
      int end = min(nritems, start + nr) - 1;

      if (!nr)
            return 0;
      data_len = btrfs_item_end_nr(l, start);
      data_len = data_len - btrfs_item_offset_nr(l, end);
      data_len += sizeof(struct btrfs_item) * nr;
      WARN_ON(data_len < 0);
      return data_len;
}

/*
 * The space between the end of the leaf items and
 * the start of the leaf data.  IOW, how much room
 * the leaf has left for both items and data
 */
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) {
            printk(KERN_CRIT "leaf free space ret %d, leaf data size %lu, "
                   "used %d nritems %d\n",
                   ret, (unsigned long) BTRFS_LEAF_DATA_SIZE(root),
                   leaf_space_used(leaf, 0, nritems), nritems);
      }
      return ret;
}

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)
{
      struct extent_buffer *left = path->nodes[0];
      struct extent_buffer *upper = path->nodes[1];
      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;

      if (empty)
            nr = 0;
      else
            nr = 1;

      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(left, 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;

            if (!left->map_token) {
                  map_extent_buffer(left, (unsigned long)item,
                              sizeof(struct btrfs_item),
                              &left->map_token, &left->kaddr,
                              &left->map_start, &left->map_len,
                              KM_USER1);
            }

            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 (left->map_token) {
            unmap_extent_buffer(left, left->map_token, KM_USER1);
            left->map_token = NULL;
      }

      if (push_items == 0)
            goto out_unlock;

      if (!empty && push_items == left_nritems)
            WARN_ON(1);

      /* 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(right, i);
            if (!right->map_token) {
                  map_extent_buffer(right, (unsigned long)item,
                              sizeof(struct btrfs_item),
                              &right->map_token, &right->kaddr,
                              &right->map_start, &right->map_len,
                              KM_USER1);
            }
            push_space -= btrfs_item_size(right, item);
            btrfs_set_item_offset(right, item, push_space);
      }

      if (right->map_token) {
            unmap_extent_buffer(right, right->map_token, KM_USER1);
            right->map_token = NULL;
      }
      left_nritems -= push_items;
      btrfs_set_header_nritems(left, left_nritems);

      if (left_nritems)
            btrfs_mark_buffer_dirty(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, 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.
 */
static 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 *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);
      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;

      return __push_leaf_right(trans, root, path, data_size, empty,
                        right, free_space, left_nritems);
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
 */
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, int right_nritems)
{
      struct btrfs_disk_key disk_key;
      struct extent_buffer *right = path->nodes[0];
      int slot;
      int i;
      int push_space = 0;
      int push_items = 0;
      struct btrfs_item *item;
      u32 old_left_nritems;
      u32 nr;
      int ret = 0;
      int wret;
      u32 this_item_size;
      u32 old_left_item_size;

      slot = path->slots[1];

      if (empty)
            nr = right_nritems;
      else
            nr = right_nritems - 1;

      for (i = 0; i < nr; i++) {
            item = btrfs_item_nr(right, i);
            if (!right->map_token) {
                  map_extent_buffer(right, (unsigned long)item,
                              sizeof(struct btrfs_item),
                              &right->map_token, &right->kaddr,
                              &right->map_start, &right->map_len,
                              KM_USER1);
            }

            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 (right->map_token) {
            unmap_extent_buffer(right, right->map_token, KM_USER1);
            right->map_token = NULL;
      }

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

      /* 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(left, i);
            if (!left->map_token) {
                  map_extent_buffer(left, (unsigned long)item,
                              sizeof(struct btrfs_item),
                              &left->map_token, &left->kaddr,
                              &left->map_start, &left->map_len,
                              KM_USER1);
            }

            ioff = btrfs_item_offset(left, item);
            btrfs_set_item_offset(left, item,
                  ioff - (BTRFS_LEAF_DATA_SIZE(root) - old_left_item_size));
      }
      btrfs_set_header_nritems(left, old_left_nritems + push_items);
      if (left->map_token) {
            unmap_extent_buffer(left, left->map_token, KM_USER1);
            left->map_token = NULL;
      }

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

      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(right, i);

            if (!right->map_token) {
                  map_extent_buffer(right, (unsigned long)item,
                              sizeof(struct btrfs_item),
                              &right->map_token, &right->kaddr,
                              &right->map_start, &right->map_len,
                              KM_USER1);
            }

            push_space = push_space - btrfs_item_size(right, item);
            btrfs_set_item_offset(right, item, push_space);
      }
      if (right->map_token) {
            unmap_extent_buffer(right, right->map_token, KM_USER1);
            right->map_token = NULL;
      }

      btrfs_mark_buffer_dirty(left);
      if (right_nritems)
            btrfs_mark_buffer_dirty(right);

      btrfs_item_key(right, &disk_key, 0);
      wret = fixup_low_keys(trans, root, path, &disk_key, 1);
      if (wret)
            ret = wret;

      /* then fixup the leaf pointer in the path */
      if (path->slots[0] < push_items) {
            path->slots[0] += old_left_nritems;
            if (btrfs_header_nritems(path->nodes[0]) == 0)
                  clean_tree_block(trans, root, path->nodes[0]);
            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
 */
static 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 *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);
      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 */
            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, data_size,
                         empty, left, free_space, right_nritems);
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.
 *
 * returns 0 if all went well and < 0 on failure.
 */
static noinline int 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;
      int ret = 0;
      int wret;
      struct btrfs_disk_key disk_key;

      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(right, i);
            u32 ioff;

            if (!right->map_token) {
                  map_extent_buffer(right, (unsigned long)item,
                              sizeof(struct btrfs_item),
                              &right->map_token, &right->kaddr,
                              &right->map_start, &right->map_len,
                              KM_USER1);
            }

            ioff = btrfs_item_offset(right, item);
            btrfs_set_item_offset(right, item, ioff + rt_data_off);
      }

      if (right->map_token) {
            unmap_extent_buffer(right, right->map_token, KM_USER1);
            right->map_token = NULL;
      }

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

      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);

      return ret;
}

/*
 * split the path's leaf in two, making sure there is at least data_size
 * available for the resulting leaf level of the path.
 *
 * returns 0 if all went well and < 0 on failure.
 */
static 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;
      int ret = 0;
      int wret;
      int split;
      int num_doubles = 0;

      /* first try to make some room by pushing left and right */
      if (data_size && ins_key->type != BTRFS_DIR_ITEM_KEY) {
            wret = push_leaf_right(trans, root, path, data_size, 0);
            if (wret < 0)
                  return wret;
            if (wret) {
                  wret = push_leaf_left(trans, root, path, data_size, 0);
                  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)) {
                              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)) {
                              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_free_block(trans, root, root->leafsize, 0,
                              root->root_key.objectid,
                              &disk_key, 0, l->start, 0);
      if (IS_ERR(right)) {
            BUG_ON(1);
            return PTR_ERR(right);
      }

      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, root->fs_info->fsid,
                      (unsigned long)btrfs_header_fsid(right),
                      BTRFS_FSID_SIZE);

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

      if (split == 0) {
            if (mid <= slot) {
                  btrfs_set_header_nritems(right, 0);
                  wret = insert_ptr(trans, root, path,
                                &disk_key, right->start,
                                path->slots[1] + 1, 1);
                  if (wret)
                        ret = wret;

                  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);
                  wret = insert_ptr(trans, root, path,
                                &disk_key,
                                right->start,
                                path->slots[1], 1);
                  if (wret)
                        ret = wret;
                  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) {
                        wret = fixup_low_keys(trans, root,
                                    path, &disk_key, 1);
                        if (wret)
                              ret = wret;
                  }
            }
            btrfs_mark_buffer_dirty(right);
            return ret;
      }

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

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

      return ret;
}

/*
 * 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)
{
      u32 item_size;
      struct extent_buffer *leaf;
      struct btrfs_key orig_key;
      struct btrfs_item *item;
      struct btrfs_item *new_item;
      int ret = 0;
      int slot;
      u32 nritems;
      u32 orig_offset;
      struct btrfs_disk_key disk_key;
      char *buf;

      leaf = path->nodes[0];
      btrfs_item_key_to_cpu(leaf, &orig_key, path->slots[0]);
      if (btrfs_leaf_free_space(root, leaf) >= sizeof(struct btrfs_item))
            goto split;

      item_size = btrfs_item_size_nr(leaf, path->slots[0]);
      btrfs_release_path(root, path);

      path->search_for_split = 1;
      path->keep_locks = 1;

      ret = btrfs_search_slot(trans, root, &orig_key, path, 0, 1);
      path->search_for_split = 0;

      /* if our item isn't there or got smaller, return now */
      if (ret != 0 || item_size != btrfs_item_size_nr(path->nodes[0],
                                          path->slots[0])) {
            path->keep_locks = 0;
            return -EAGAIN;
      }

      btrfs_set_path_blocking(path);
      ret = split_leaf(trans, root, &orig_key, path,
                   sizeof(struct btrfs_item), 1);
      path->keep_locks = 0;
      BUG_ON(ret);

      btrfs_unlock_up_safe(path, 1);
      leaf = path->nodes[0];
      BUG_ON(btrfs_leaf_free_space(root, leaf) < sizeof(struct btrfs_item));

split:
      /*
       * make sure any changes to the path from split_leaf leave it
       * in a blocking state
       */
      btrfs_set_path_blocking(path);

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

      buf = kmalloc(item_size, GFP_NOFS);
      read_extent_buffer(leaf, buf, btrfs_item_ptr_offset(leaf,
                      path->slots[0]), item_size);
      slot = path->slots[0] + 1;
      leaf = path->nodes[0];

      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(leaf, 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);

      ret = 0;
      if (btrfs_leaf_free_space(root, leaf) < 0) {
            btrfs_print_leaf(root, leaf);
            BUG();
      }
      kfree(buf);
      return ret;
}

/*
 * 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.
 */
int btrfs_truncate_item(struct btrfs_trans_handle *trans,
                  struct btrfs_root *root,
                  struct btrfs_path *path,
                  u32 new_size, int from_end)
{
      int ret = 0;
      int slot;
      int slot_orig;
      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;

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

      old_size = btrfs_item_size_nr(leaf, slot);
      if (old_size == new_size)
            return 0;

      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(leaf, i);

            if (!leaf->map_token) {
                  map_extent_buffer(leaf, (unsigned long)item,
                              sizeof(struct btrfs_item),
                              &leaf->map_token, &leaf->kaddr,
                              &leaf->map_start, &leaf->map_len,
                              KM_USER1);
            }

            ioff = btrfs_item_offset(leaf, item);
            btrfs_set_item_offset(leaf, item, ioff + size_diff);
      }

      if (leaf->map_token) {
            unmap_extent_buffer(leaf, leaf->map_token, KM_USER1);
            leaf->map_token = NULL;
      }

      /* 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,
                              offsetof(struct btrfs_file_extent_item,
                                     disk_bytenr));
                  }
            }

            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(trans, root, path, &disk_key, 1);
      }

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

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

/*
 * make the item pointed to by the path bigger, data_size is the new size.
 */
int btrfs_extend_item(struct btrfs_trans_handle *trans,
                  struct btrfs_root *root, struct btrfs_path *path,
                  u32 data_size)
{
      int ret = 0;
      int slot;
      int slot_orig;
      struct extent_buffer *leaf;
      struct btrfs_item *item;
      u32 nritems;
      unsigned int data_end;
      unsigned int old_data;
      unsigned int old_size;
      int i;

      slot_orig = path->slots[0];
      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);
            printk(KERN_CRIT "slot %d too large, nritems %d\n",
                   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(leaf, i);

            if (!leaf->map_token) {
                  map_extent_buffer(leaf, (unsigned long)item,
                              sizeof(struct btrfs_item),
                              &leaf->map_token, &leaf->kaddr,
                              &leaf->map_start, &leaf->map_len,
                              KM_USER1);
            }
            ioff = btrfs_item_offset(leaf, item);
            btrfs_set_item_offset(leaf, item, ioff - data_size);
      }

      if (leaf->map_token) {
            unmap_extent_buffer(leaf, leaf->map_token, KM_USER1);
            leaf->map_token = NULL;
      }

      /* 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(leaf, slot);
      btrfs_set_item_size(leaf, item, old_size + data_size);
      btrfs_mark_buffer_dirty(leaf);

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

/*
 * 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.
 * Returns the number of keys that were inserted.
 */
int btrfs_insert_some_items(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root,
                      struct btrfs_path *path,
                      struct btrfs_key *cpu_key, u32 *data_size,
                      int nr)
{
      struct extent_buffer *leaf;
      struct btrfs_item *item;
      int ret = 0;
      int slot;
      int i;
      u32 nritems;
      u32 total_data = 0;
      u32 total_size = 0;
      unsigned int data_end;
      struct btrfs_disk_key disk_key;
      struct btrfs_key found_key;

      for (i = 0; i < nr; i++) {
            if (total_size + data_size[i] + sizeof(struct btrfs_item) >
                BTRFS_LEAF_DATA_SIZE(root)) {
                  break;
                  nr = i;
            }
            total_data += data_size[i];
            total_size += data_size[i] + sizeof(struct btrfs_item);
      }
      BUG_ON(nr == 0);

      ret = btrfs_search_slot(trans, root, cpu_key, path, total_size, 1);
      if (ret == 0)
            return -EEXIST;
      if (ret < 0)
            goto out;

      leaf = path->nodes[0];

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

      if (btrfs_leaf_free_space(root, leaf) < total_size) {
            for (i = nr; i >= 0; i--) {
                  total_data -= data_size[i];
                  total_size -= data_size[i] + sizeof(struct btrfs_item);
                  if (total_size < btrfs_leaf_free_space(root, leaf))
                        break;
            }
            nr = i;
      }

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

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

            item = btrfs_item_nr(leaf, slot);
            btrfs_item_key_to_cpu(leaf, &found_key, slot);

            /* figure out how many keys we can insert in here */
            total_data = data_size[0];
            for (i = 1; i < nr; i++) {
                  if (btrfs_comp_cpu_keys(&found_key, cpu_key + i) <= 0)
                        break;
                  total_data += data_size[i];
            }
            nr = i;

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

                  item = btrfs_item_nr(leaf, i);
                  if (!leaf->map_token) {
                        map_extent_buffer(leaf, (unsigned long)item,
                              sizeof(struct btrfs_item),
                              &leaf->map_token, &leaf->kaddr,
                              &leaf->map_start, &leaf->map_len,
                              KM_USER1);
                  }

                  ioff = btrfs_item_offset(leaf, item);
                  btrfs_set_item_offset(leaf, item, ioff - total_data);
            }
            if (leaf->map_token) {
                  unmap_extent_buffer(leaf, leaf->map_token, KM_USER1);
                  leaf->map_token = NULL;
            }

            /* 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;
      } else {
            /*
             * this sucks but it has to be done, if we are inserting at
             * the end of the leaf only insert 1 of the items, since we
             * have no way of knowing whats on the next leaf and we'd have
             * to drop our current locks to figure it out
             */
            nr = 1;
      }

      /* 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(leaf, slot + i);
            btrfs_set_item_offset(leaf, item, data_end - data_size[i]);
            data_end -= data_size[i];
            btrfs_set_item_size(leaf, item, data_size[i]);
      }
      btrfs_set_header_nritems(leaf, nritems + nr);
      btrfs_mark_buffer_dirty(leaf);

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

      if (btrfs_leaf_free_space(root, leaf) < 0) {
            btrfs_print_leaf(root, leaf);
            BUG();
      }
out:
      if (!ret)
            ret = nr;
      return ret;
}

/*
 * 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
 */
static noinline_for_stack int
setup_items_for_insert(struct btrfs_trans_handle *trans,
                  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;
      int ret;
      struct extent_buffer *leaf;
      int slot;

      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);
            printk(KERN_CRIT "not enough freespace need %u have %d\n",
                   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);
                  printk(KERN_CRIT "slot %d old_data %d data_end %d\n",
                         slot, old_data, data_end);
                  BUG_ON(1);
            }
            /*
             * item0..itemN ... dataN.offset..dataN.size .. data0.size
             */
            /* first correct the data pointers */
            WARN_ON(leaf->map_token);
            for (i = slot; i < nritems; i++) {
                  u32 ioff;

                  item = btrfs_item_nr(leaf, i);
                  if (!leaf->map_token) {
                        map_extent_buffer(leaf, (unsigned long)item,
                              sizeof(struct btrfs_item),
                              &leaf->map_token, &leaf->kaddr,
                              &leaf->map_start, &leaf->map_len,
                              KM_USER1);
                  }

                  ioff = btrfs_item_offset(leaf, item);
                  btrfs_set_item_offset(leaf, item, ioff - total_data);
            }
            if (leaf->map_token) {
                  unmap_extent_buffer(leaf, leaf->map_token, KM_USER1);
                  leaf->map_token = NULL;
            }

            /* 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(leaf, slot + i);
            btrfs_set_item_offset(leaf, item, data_end - data_size[i]);
            data_end -= data_size[i];
            btrfs_set_item_size(leaf, item, data_size[i]);
      }

      btrfs_set_header_nritems(leaf, nritems + nr);

      ret = 0;
      if (slot == 0) {
            struct btrfs_disk_key disk_key;
            btrfs_cpu_key_to_disk(&disk_key, cpu_key);
            ret = fixup_low_keys(trans, root, path, &disk_key, 1);
      }
      btrfs_unlock_up_safe(path, 1);
      btrfs_mark_buffer_dirty(leaf);

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

/*
 * 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)
{
      struct extent_buffer *leaf;
      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)
            goto out;

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

      ret = setup_items_for_insert(trans, root, path, cpu_key, data_size,
                         total_data, total_size, nr);

out:
      return ret;
}

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

      path = btrfs_alloc_path();
      BUG_ON(!path);
      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 int del_ptr(struct btrfs_trans_handle *trans, struct btrfs_root *root,
               struct btrfs_path *path, int level, int slot)
{
      struct extent_buffer *parent = path->nodes[level];
      u32 nritems;
      int ret = 0;
      int wret;

      nritems = btrfs_header_nritems(parent);
      if (slot != nritems - 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));
      }
      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);
            wret = fixup_low_keys(trans, root, path, &disk_key, level + 1);
            if (wret)
                  ret = wret;
      }
      btrfs_mark_buffer_dirty(parent);
      return ret;
}

/*
 * 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 int btrfs_del_leaf(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root,
                           struct btrfs_path *path,
                           struct extent_buffer *leaf)
{
      int ret;

      WARN_ON(btrfs_header_generation(leaf) != trans->transid);
      ret = del_ptr(trans, root, path, 1, path->slots[1]);
      if (ret)
            return ret;

      /*
       * 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);

      ret = btrfs_free_extent(trans, root, leaf->start, leaf->len,
                        0, root->root_key.objectid, 0, 0);
      return ret;
}
/*
 * 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;
      int last_off;
      int dsize = 0;
      int ret = 0;
      int wret;
      int i;
      u32 nritems;

      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(leaf, i);
                  if (!leaf->map_token) {
                        map_extent_buffer(leaf, (unsigned long)item,
                              sizeof(struct btrfs_item),
                              &leaf->map_token, &leaf->kaddr,
                              &leaf->map_start, &leaf->map_len,
                              KM_USER1);
                  }
                  ioff = btrfs_item_offset(leaf, item);
                  btrfs_set_item_offset(leaf, item, ioff + dsize);
            }

            if (leaf->map_token) {
                  unmap_extent_buffer(leaf, leaf->map_token, KM_USER1);
                  leaf->map_token = NULL;
            }

            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 {
                  ret = btrfs_del_leaf(trans, root, path, leaf);
                  BUG_ON(ret);
            }
      } 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);
                  wret = fixup_low_keys(trans, root, path,
                                    &disk_key, 1);
                  if (wret)
                        ret = wret;
            }

            /* delete the leaf if it is mostly empty */
            if (used < BTRFS_LEAF_DATA_SIZE(root) / 3) {
                  /* push_leaf_left fixes the path.
                   * make sure the path still points to our leaf
                   * for possible call to del_ptr below
                   */
                  slot = path->slots[1];
                  extent_buffer_get(leaf);

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

                  if (btrfs_header_nritems(leaf) == 0) {
                        path->slots[1] = slot;
                        ret = btrfs_del_leaf(trans, root, path, leaf);
                        BUG_ON(ret);
                        free_extent_buffer(leaf);
                  } 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--;
      else if (key.objectid > 0)
            key.objectid--;
      else
            return 1;

      btrfs_release_path(root, 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);
      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 either in cache or 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_key *max_key,
                   struct btrfs_path *path, int cache_only,
                   u64 min_trans)
{
      struct extent_buffer *cur;
      struct btrfs_key found_key;
      int slot;
      int sret;
      u32 nritems;
      int level;
      int ret = 1;

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

      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 cache_only and
             * min_trans parameters.  If it isn't in cache or is too
             * old, skip to the next one.
             */
            while (slot < nritems) {
                  u64 blockptr;
                  u64 gen;
                  struct extent_buffer *tmp;
                  struct btrfs_disk_key disk_key;

                  blockptr = btrfs_node_blockptr(cur, slot);
                  gen = btrfs_node_ptr_generation(cur, slot);
                  if (gen < min_trans) {
                        slot++;
                        continue;
                  }
                  if (!cache_only)
                        break;

                  if (max_key) {
                        btrfs_node_key(cur, &disk_key, slot);
                        if (comp_keys(&disk_key, max_key) >= 0) {
                              ret = 1;
                              goto out;
                        }
                  }

                  tmp = btrfs_find_tree_block(root, blockptr,
                                  btrfs_level_size(root, level - 1));

                  if (tmp && btrfs_buffer_uptodate(tmp, gen)) {
                        free_extent_buffer(tmp);
                        break;
                  }
                  if (tmp)
                        free_extent_buffer(tmp);
                  slot++;
            }
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,
                                      cache_only, min_trans);
                  if (sret == 0) {
                        btrfs_release_path(root, 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;
                  unlock_up(path, level, 1);
                  goto out;
            }
            btrfs_set_path_blocking(path);
            cur = read_node_slot(root, cur, slot);

            btrfs_tree_lock(cur);

            path->locks[level - 1] = 1;
            path->nodes[level - 1] = cur;
            unlock_up(path, level, 1);
            btrfs_clear_path_blocking(path, NULL);
      }
out:
      if (ret == 0)
            memcpy(min_key, &found_key, sizeof(found_key));
      btrfs_set_path_blocking(path);
      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 cache_only and 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,
                  int cache_only, 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(root, 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 blockptr = btrfs_node_blockptr(c, slot);
                  u64 gen = btrfs_node_ptr_generation(c, slot);

                  if (cache_only) {
                        struct extent_buffer *cur;
                        cur = btrfs_find_tree_block(root, blockptr,
                                  btrfs_level_size(root, level - 1));
                        if (!cur || !btrfs_buffer_uptodate(cur, gen)) {
                              slot++;
                              if (cur)
                                    free_extent_buffer(cur);
                              goto next;
                        }
                        free_extent_buffer(cur);
                  }
                  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)
{
      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 force_blocking = 0;

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

      /*
       * we take the blocks in an order that upsets lockdep.  Using
       * blocking mode is the only way around it.
       */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
      force_blocking = 1;
#endif

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

      path->keep_locks = 1;

      if (!force_blocking)
            path->leave_spinning = 1;

      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;
      }

      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(next);
                  free_extent_buffer(next);
            }

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

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

            if (!path->skip_locking) {
                  ret = btrfs_try_spin_lock(next);
                  if (!ret) {
                        btrfs_set_path_blocking(path);
                        btrfs_tree_lock(next);
                        if (!force_blocking)
                              btrfs_clear_path_blocking(path, next);
                  }
                  if (force_blocking)
                        btrfs_set_lock_blocking(next);
            }
            break;
      }
      path->slots[level] = slot;
      while (1) {
            level--;
            c = path->nodes[level];
            if (path->locks[level])
                  btrfs_tree_unlock(c);

            free_extent_buffer(c);
            path->nodes[level] = next;
            path->slots[level] = 0;
            if (!path->skip_locking)
                  path->locks[level] = 1;

            if (!level)
                  break;

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

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

            if (!path->skip_locking) {
                  btrfs_assert_tree_locked(path->nodes[level]);
                  ret = btrfs_try_spin_lock(next);
                  if (!ret) {
                        btrfs_set_path_blocking(path);
                        btrfs_tree_lock(next);
                        if (!force_blocking)
                              btrfs_clear_path_blocking(path, next);
                  }
                  if (force_blocking)
                        btrfs_set_lock_blocking(next);
            }
      }
      ret = 0;
done:
      unlock_up(path, 0, 1);
      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;
}

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