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relocation.c

/*
 * Copyright (C) 2009 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include <linux/sched.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/rbtree.h>
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "volumes.h"
#include "locking.h"
#include "btrfs_inode.h"
#include "async-thread.h"

/*
 * backref_node, mapping_node and tree_block start with this
 */
struct tree_entry {
      struct rb_node rb_node;
      u64 bytenr;
};

/*
 * present a tree block in the backref cache
 */
00043 struct backref_node {
      struct rb_node rb_node;
      u64 bytenr;
      /* objectid tree block owner */
      u64 owner;
      /* list of upper level blocks reference this block */
      struct list_head upper;
      /* list of child blocks in the cache */
      struct list_head lower;
      /* NULL if this node is not tree root */
      struct btrfs_root *root;
      /* extent buffer got by COW the block */
      struct extent_buffer *eb;
      /* level of tree block */
      unsigned int level:8;
      /* 1 if the block is root of old snapshot */
      unsigned int old_root:1;
      /* 1 if no child blocks in the cache */
      unsigned int lowest:1;
      /* is the extent buffer locked */
      unsigned int locked:1;
      /* has the block been processed */
      unsigned int processed:1;
      /* have backrefs of this block been checked */
      unsigned int checked:1;
};

/*
 * present a block pointer in the backref cache
 */
00073 struct backref_edge {
      struct list_head list[2];
      struct backref_node *node[2];
      u64 blockptr;
};

#define LOWER     0
#define UPPER     1

00082 struct backref_cache {
      /* red black tree of all backref nodes in the cache */
      struct rb_root rb_root;
      /* list of backref nodes with no child block in the cache */
      struct list_head pending[BTRFS_MAX_LEVEL];
      spinlock_t lock;
};

/*
 * map address of tree root to tree
 */
00093 struct mapping_node {
      struct rb_node rb_node;
      u64 bytenr;
      void *data;
};

00099 struct mapping_tree {
      struct rb_root rb_root;
      spinlock_t lock;
};

/*
 * present a tree block to process
 */
00107 struct tree_block {
      struct rb_node rb_node;
      u64 bytenr;
      struct btrfs_key key;
      unsigned int level:8;
      unsigned int key_ready:1;
};

/* inode vector */
#define INODEVEC_SIZE 16

00118 struct inodevec {
      struct list_head list;
      struct inode *inode[INODEVEC_SIZE];
      int nr;
};

00124 struct reloc_control {
      /* block group to relocate */
      struct btrfs_block_group_cache *block_group;
      /* extent tree */
      struct btrfs_root *extent_root;
      /* inode for moving data */
      struct inode *data_inode;
      struct btrfs_workers workers;
      /* tree blocks have been processed */
      struct extent_io_tree processed_blocks;
      /* map start of tree root to corresponding reloc tree */
      struct mapping_tree reloc_root_tree;
      /* list of reloc trees */
      struct list_head reloc_roots;
      u64 search_start;
      u64 extents_found;
      u64 extents_skipped;
      int stage;
      int create_reloc_root;
      unsigned int found_file_extent:1;
      unsigned int found_old_snapshot:1;
};

/* stages of data relocation */
#define MOVE_DATA_EXTENTS     0
#define UPDATE_DATA_PTRS      1

/*
 * merge reloc tree to corresponding fs tree in worker threads
 */
00154 struct async_merge {
      struct btrfs_work work;
      struct reloc_control *rc;
      struct btrfs_root *root;
      struct completion *done;
      atomic_t *num_pending;
};

static void mapping_tree_init(struct mapping_tree *tree)
{
      tree->rb_root.rb_node = NULL;
      spin_lock_init(&tree->lock);
}

static void backref_cache_init(struct backref_cache *cache)
{
      int i;
      cache->rb_root.rb_node = NULL;
      for (i = 0; i < BTRFS_MAX_LEVEL; i++)
            INIT_LIST_HEAD(&cache->pending[i]);
      spin_lock_init(&cache->lock);
}

static void backref_node_init(struct backref_node *node)
{
      memset(node, 0, sizeof(*node));
      INIT_LIST_HEAD(&node->upper);
      INIT_LIST_HEAD(&node->lower);
      RB_CLEAR_NODE(&node->rb_node);
}

static struct rb_node *tree_insert(struct rb_root *root, u64 bytenr,
                           struct rb_node *node)
{
      struct rb_node **p = &root->rb_node;
      struct rb_node *parent = NULL;
      struct tree_entry *entry;

      while (*p) {
            parent = *p;
            entry = rb_entry(parent, struct tree_entry, rb_node);

            if (bytenr < entry->bytenr)
                  p = &(*p)->rb_left;
            else if (bytenr > entry->bytenr)
                  p = &(*p)->rb_right;
            else
                  return parent;
      }

      rb_link_node(node, parent, p);
      rb_insert_color(node, root);
      return NULL;
}

static struct rb_node *tree_search(struct rb_root *root, u64 bytenr)
{
      struct rb_node *n = root->rb_node;
      struct tree_entry *entry;

      while (n) {
            entry = rb_entry(n, struct tree_entry, rb_node);

            if (bytenr < entry->bytenr)
                  n = n->rb_left;
            else if (bytenr > entry->bytenr)
                  n = n->rb_right;
            else
                  return n;
      }
      return NULL;
}

/*
 * walk up backref nodes until reach node presents tree root
 */
static struct backref_node *walk_up_backref(struct backref_node *node,
                                  struct backref_edge *edges[],
                                  int *index)
{
      struct backref_edge *edge;
      int idx = *index;

      while (!list_empty(&node->upper)) {
            edge = list_entry(node->upper.next,
                          struct backref_edge, list[LOWER]);
            edges[idx++] = edge;
            node = edge->node[UPPER];
      }
      *index = idx;
      return node;
}

/*
 * walk down backref nodes to find start of next reference path
 */
static struct backref_node *walk_down_backref(struct backref_edge *edges[],
                                    int *index)
{
      struct backref_edge *edge;
      struct backref_node *lower;
      int idx = *index;

      while (idx > 0) {
            edge = edges[idx - 1];
            lower = edge->node[LOWER];
            if (list_is_last(&edge->list[LOWER], &lower->upper)) {
                  idx--;
                  continue;
            }
            edge = list_entry(edge->list[LOWER].next,
                          struct backref_edge, list[LOWER]);
            edges[idx - 1] = edge;
            *index = idx;
            return edge->node[UPPER];
      }
      *index = 0;
      return NULL;
}

static void drop_node_buffer(struct backref_node *node)
{
      if (node->eb) {
            if (node->locked) {
                  btrfs_tree_unlock(node->eb);
                  node->locked = 0;
            }
            free_extent_buffer(node->eb);
            node->eb = NULL;
      }
}

static void drop_backref_node(struct backref_cache *tree,
                        struct backref_node *node)
{
      BUG_ON(!node->lowest);
      BUG_ON(!list_empty(&node->upper));

      drop_node_buffer(node);
      list_del(&node->lower);

      rb_erase(&node->rb_node, &tree->rb_root);
      kfree(node);
}

/*
 * remove a backref node from the backref cache
 */
static void remove_backref_node(struct backref_cache *cache,
                        struct backref_node *node)
{
      struct backref_node *upper;
      struct backref_edge *edge;

      if (!node)
            return;

      BUG_ON(!node->lowest);
      while (!list_empty(&node->upper)) {
            edge = list_entry(node->upper.next, struct backref_edge,
                          list[LOWER]);
            upper = edge->node[UPPER];
            list_del(&edge->list[LOWER]);
            list_del(&edge->list[UPPER]);
            kfree(edge);
            /*
             * add the node to pending list if no other
             * child block cached.
             */
            if (list_empty(&upper->lower)) {
                  list_add_tail(&upper->lower,
                              &cache->pending[upper->level]);
                  upper->lowest = 1;
            }
      }
      drop_backref_node(cache, node);
}

/*
 * find reloc tree by address of tree root
 */
static struct btrfs_root *find_reloc_root(struct reloc_control *rc,
                                u64 bytenr)
{
      struct rb_node *rb_node;
      struct mapping_node *node;
      struct btrfs_root *root = NULL;

      spin_lock(&rc->reloc_root_tree.lock);
      rb_node = tree_search(&rc->reloc_root_tree.rb_root, bytenr);
      if (rb_node) {
            node = rb_entry(rb_node, struct mapping_node, rb_node);
            root = (struct btrfs_root *)node->data;
      }
      spin_unlock(&rc->reloc_root_tree.lock);
      return root;
}

static int is_cowonly_root(u64 root_objectid)
{
      if (root_objectid == BTRFS_ROOT_TREE_OBJECTID ||
          root_objectid == BTRFS_EXTENT_TREE_OBJECTID ||
          root_objectid == BTRFS_CHUNK_TREE_OBJECTID ||
          root_objectid == BTRFS_DEV_TREE_OBJECTID ||
          root_objectid == BTRFS_TREE_LOG_OBJECTID ||
          root_objectid == BTRFS_CSUM_TREE_OBJECTID)
            return 1;
      return 0;
}

static struct btrfs_root *read_fs_root(struct btrfs_fs_info *fs_info,
                              u64 root_objectid)
{
      struct btrfs_key key;

      key.objectid = root_objectid;
      key.type = BTRFS_ROOT_ITEM_KEY;
      if (is_cowonly_root(root_objectid))
            key.offset = 0;
      else
            key.offset = (u64)-1;

      return btrfs_read_fs_root_no_name(fs_info, &key);
}

#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
static noinline_for_stack
struct btrfs_root *find_tree_root(struct reloc_control *rc,
                          struct extent_buffer *leaf,
                          struct btrfs_extent_ref_v0 *ref0)
{
      struct btrfs_root *root;
      u64 root_objectid = btrfs_ref_root_v0(leaf, ref0);
      u64 generation = btrfs_ref_generation_v0(leaf, ref0);

      BUG_ON(root_objectid == BTRFS_TREE_RELOC_OBJECTID);

      root = read_fs_root(rc->extent_root->fs_info, root_objectid);
      BUG_ON(IS_ERR(root));

      if (root->ref_cows &&
          generation != btrfs_root_generation(&root->root_item))
            return NULL;

      return root;
}
#endif

static noinline_for_stack
int find_inline_backref(struct extent_buffer *leaf, int slot,
                  unsigned long *ptr, unsigned long *end)
{
      struct btrfs_extent_item *ei;
      struct btrfs_tree_block_info *bi;
      u32 item_size;

      item_size = btrfs_item_size_nr(leaf, slot);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
      if (item_size < sizeof(*ei)) {
            WARN_ON(item_size != sizeof(struct btrfs_extent_item_v0));
            return 1;
      }
#endif
      ei = btrfs_item_ptr(leaf, slot, struct btrfs_extent_item);
      WARN_ON(!(btrfs_extent_flags(leaf, ei) &
              BTRFS_EXTENT_FLAG_TREE_BLOCK));

      if (item_size <= sizeof(*ei) + sizeof(*bi)) {
            WARN_ON(item_size < sizeof(*ei) + sizeof(*bi));
            return 1;
      }

      bi = (struct btrfs_tree_block_info *)(ei + 1);
      *ptr = (unsigned long)(bi + 1);
      *end = (unsigned long)ei + item_size;
      return 0;
}

/*
 * build backref tree for a given tree block. root of the backref tree
 * corresponds the tree block, leaves of the backref tree correspond
 * roots of b-trees that reference the tree block.
 *
 * the basic idea of this function is check backrefs of a given block
 * to find upper level blocks that refernece the block, and then check
 * bakcrefs of these upper level blocks recursively. the recursion stop
 * when tree root is reached or backrefs for the block is cached.
 *
 * NOTE: if we find backrefs for a block are cached, we know backrefs
 * for all upper level blocks that directly/indirectly reference the
 * block are also cached.
 */
static struct backref_node *build_backref_tree(struct reloc_control *rc,
                                     struct backref_cache *cache,
                                     struct btrfs_key *node_key,
                                     int level, u64 bytenr)
{
      struct btrfs_path *path1;
      struct btrfs_path *path2;
      struct extent_buffer *eb;
      struct btrfs_root *root;
      struct backref_node *cur;
      struct backref_node *upper;
      struct backref_node *lower;
      struct backref_node *node = NULL;
      struct backref_node *exist = NULL;
      struct backref_edge *edge;
      struct rb_node *rb_node;
      struct btrfs_key key;
      unsigned long end;
      unsigned long ptr;
      LIST_HEAD(list);
      int ret;
      int err = 0;

      path1 = btrfs_alloc_path();
      path2 = btrfs_alloc_path();
      if (!path1 || !path2) {
            err = -ENOMEM;
            goto out;
      }

      node = kmalloc(sizeof(*node), GFP_NOFS);
      if (!node) {
            err = -ENOMEM;
            goto out;
      }

      backref_node_init(node);
      node->bytenr = bytenr;
      node->owner = 0;
      node->level = level;
      node->lowest = 1;
      cur = node;
again:
      end = 0;
      ptr = 0;
      key.objectid = cur->bytenr;
      key.type = BTRFS_EXTENT_ITEM_KEY;
      key.offset = (u64)-1;

      path1->search_commit_root = 1;
      path1->skip_locking = 1;
      ret = btrfs_search_slot(NULL, rc->extent_root, &key, path1,
                        0, 0);
      if (ret < 0) {
            err = ret;
            goto out;
      }
      BUG_ON(!ret || !path1->slots[0]);

      path1->slots[0]--;

      WARN_ON(cur->checked);
      if (!list_empty(&cur->upper)) {
            /*
             * the backref was added previously when processsing
             * backref of type BTRFS_TREE_BLOCK_REF_KEY
             */
            BUG_ON(!list_is_singular(&cur->upper));
            edge = list_entry(cur->upper.next, struct backref_edge,
                          list[LOWER]);
            BUG_ON(!list_empty(&edge->list[UPPER]));
            exist = edge->node[UPPER];
            /*
             * add the upper level block to pending list if we need
             * check its backrefs
             */
            if (!exist->checked)
                  list_add_tail(&edge->list[UPPER], &list);
      } else {
            exist = NULL;
      }

      while (1) {
            cond_resched();
            eb = path1->nodes[0];

            if (ptr >= end) {
                  if (path1->slots[0] >= btrfs_header_nritems(eb)) {
                        ret = btrfs_next_leaf(rc->extent_root, path1);
                        if (ret < 0) {
                              err = ret;
                              goto out;
                        }
                        if (ret > 0)
                              break;
                        eb = path1->nodes[0];
                  }

                  btrfs_item_key_to_cpu(eb, &key, path1->slots[0]);
                  if (key.objectid != cur->bytenr) {
                        WARN_ON(exist);
                        break;
                  }

                  if (key.type == BTRFS_EXTENT_ITEM_KEY) {
                        ret = find_inline_backref(eb, path1->slots[0],
                                            &ptr, &end);
                        if (ret)
                              goto next;
                  }
            }

            if (ptr < end) {
                  /* update key for inline back ref */
                  struct btrfs_extent_inline_ref *iref;
                  iref = (struct btrfs_extent_inline_ref *)ptr;
                  key.type = btrfs_extent_inline_ref_type(eb, iref);
                  key.offset = btrfs_extent_inline_ref_offset(eb, iref);
                  WARN_ON(key.type != BTRFS_TREE_BLOCK_REF_KEY &&
                        key.type != BTRFS_SHARED_BLOCK_REF_KEY);
            }

            if (exist &&
                ((key.type == BTRFS_TREE_BLOCK_REF_KEY &&
                  exist->owner == key.offset) ||
                 (key.type == BTRFS_SHARED_BLOCK_REF_KEY &&
                  exist->bytenr == key.offset))) {
                  exist = NULL;
                  goto next;
            }

#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
            if (key.type == BTRFS_SHARED_BLOCK_REF_KEY ||
                key.type == BTRFS_EXTENT_REF_V0_KEY) {
                  if (key.objectid == key.offset &&
                      key.type == BTRFS_EXTENT_REF_V0_KEY) {
                        struct btrfs_extent_ref_v0 *ref0;
                        ref0 = btrfs_item_ptr(eb, path1->slots[0],
                                    struct btrfs_extent_ref_v0);
                        root = find_tree_root(rc, eb, ref0);
                        if (root)
                              cur->root = root;
                        else
                              cur->old_root = 1;
                        break;
                  }
#else
            BUG_ON(key.type == BTRFS_EXTENT_REF_V0_KEY);
            if (key.type == BTRFS_SHARED_BLOCK_REF_KEY) {
#endif
                  if (key.objectid == key.offset) {
                        /*
                         * only root blocks of reloc trees use
                         * backref of this type.
                         */
                        root = find_reloc_root(rc, cur->bytenr);
                        BUG_ON(!root);
                        cur->root = root;
                        break;
                  }

                  edge = kzalloc(sizeof(*edge), GFP_NOFS);
                  if (!edge) {
                        err = -ENOMEM;
                        goto out;
                  }
                  rb_node = tree_search(&cache->rb_root, key.offset);
                  if (!rb_node) {
                        upper = kmalloc(sizeof(*upper), GFP_NOFS);
                        if (!upper) {
                              kfree(edge);
                              err = -ENOMEM;
                              goto out;
                        }
                        backref_node_init(upper);
                        upper->bytenr = key.offset;
                        upper->owner = 0;
                        upper->level = cur->level + 1;
                        /*
                         *  backrefs for the upper level block isn't
                         *  cached, add the block to pending list
                         */
                        list_add_tail(&edge->list[UPPER], &list);
                  } else {
                        upper = rb_entry(rb_node, struct backref_node,
                                     rb_node);
                        INIT_LIST_HEAD(&edge->list[UPPER]);
                  }
                  list_add(&edge->list[LOWER], &cur->upper);
                  edge->node[UPPER] = upper;
                  edge->node[LOWER] = cur;

                  goto next;
            } else if (key.type != BTRFS_TREE_BLOCK_REF_KEY) {
                  goto next;
            }

            /* key.type == BTRFS_TREE_BLOCK_REF_KEY */
            root = read_fs_root(rc->extent_root->fs_info, key.offset);
            if (IS_ERR(root)) {
                  err = PTR_ERR(root);
                  goto out;
            }

            if (btrfs_root_level(&root->root_item) == cur->level) {
                  /* tree root */
                  BUG_ON(btrfs_root_bytenr(&root->root_item) !=
                         cur->bytenr);
                  cur->root = root;
                  break;
            }

            level = cur->level + 1;

            /*
             * searching the tree to find upper level blocks
             * reference the block.
             */
            path2->search_commit_root = 1;
            path2->skip_locking = 1;
            path2->lowest_level = level;
            ret = btrfs_search_slot(NULL, root, node_key, path2, 0, 0);
            path2->lowest_level = 0;
            if (ret < 0) {
                  err = ret;
                  goto out;
            }
            if (ret > 0 && path2->slots[level] > 0)
                  path2->slots[level]--;

            eb = path2->nodes[level];
            WARN_ON(btrfs_node_blockptr(eb, path2->slots[level]) !=
                  cur->bytenr);

            lower = cur;
            for (; level < BTRFS_MAX_LEVEL; level++) {
                  if (!path2->nodes[level]) {
                        BUG_ON(btrfs_root_bytenr(&root->root_item) !=
                               lower->bytenr);
                        lower->root = root;
                        break;
                  }

                  edge = kzalloc(sizeof(*edge), GFP_NOFS);
                  if (!edge) {
                        err = -ENOMEM;
                        goto out;
                  }

                  eb = path2->nodes[level];
                  rb_node = tree_search(&cache->rb_root, eb->start);
                  if (!rb_node) {
                        upper = kmalloc(sizeof(*upper), GFP_NOFS);
                        if (!upper) {
                              kfree(edge);
                              err = -ENOMEM;
                              goto out;
                        }
                        backref_node_init(upper);
                        upper->bytenr = eb->start;
                        upper->owner = btrfs_header_owner(eb);
                        upper->level = lower->level + 1;

                        /*
                         * if we know the block isn't shared
                         * we can void checking its backrefs.
                         */
                        if (btrfs_block_can_be_shared(root, eb))
                              upper->checked = 0;
                        else
                              upper->checked = 1;

                        /*
                         * add the block to pending list if we
                         * need check its backrefs. only block
                         * at 'cur->level + 1' is added to the
                         * tail of pending list. this guarantees
                         * we check backrefs from lower level
                         * blocks to upper level blocks.
                         */
                        if (!upper->checked &&
                            level == cur->level + 1) {
                              list_add_tail(&edge->list[UPPER],
                                          &list);
                        } else
                              INIT_LIST_HEAD(&edge->list[UPPER]);
                  } else {
                        upper = rb_entry(rb_node, struct backref_node,
                                     rb_node);
                        BUG_ON(!upper->checked);
                        INIT_LIST_HEAD(&edge->list[UPPER]);
                  }
                  list_add_tail(&edge->list[LOWER], &lower->upper);
                  edge->node[UPPER] = upper;
                  edge->node[LOWER] = lower;

                  if (rb_node)
                        break;
                  lower = upper;
                  upper = NULL;
            }
            btrfs_release_path(root, path2);
next:
            if (ptr < end) {
                  ptr += btrfs_extent_inline_ref_size(key.type);
                  if (ptr >= end) {
                        WARN_ON(ptr > end);
                        ptr = 0;
                        end = 0;
                  }
            }
            if (ptr >= end)
                  path1->slots[0]++;
      }
      btrfs_release_path(rc->extent_root, path1);

      cur->checked = 1;
      WARN_ON(exist);

      /* the pending list isn't empty, take the first block to process */
      if (!list_empty(&list)) {
            edge = list_entry(list.next, struct backref_edge, list[UPPER]);
            list_del_init(&edge->list[UPPER]);
            cur = edge->node[UPPER];
            goto again;
      }

      /*
       * everything goes well, connect backref nodes and insert backref nodes
       * into the cache.
       */
      BUG_ON(!node->checked);
      rb_node = tree_insert(&cache->rb_root, node->bytenr, &node->rb_node);
      BUG_ON(rb_node);

      list_for_each_entry(edge, &node->upper, list[LOWER])
            list_add_tail(&edge->list[UPPER], &list);

      while (!list_empty(&list)) {
            edge = list_entry(list.next, struct backref_edge, list[UPPER]);
            list_del_init(&edge->list[UPPER]);
            upper = edge->node[UPPER];

            if (!RB_EMPTY_NODE(&upper->rb_node)) {
                  if (upper->lowest) {
                        list_del_init(&upper->lower);
                        upper->lowest = 0;
                  }

                  list_add_tail(&edge->list[UPPER], &upper->lower);
                  continue;
            }

            BUG_ON(!upper->checked);
            rb_node = tree_insert(&cache->rb_root, upper->bytenr,
                              &upper->rb_node);
            BUG_ON(rb_node);

            list_add_tail(&edge->list[UPPER], &upper->lower);

            list_for_each_entry(edge, &upper->upper, list[LOWER])
                  list_add_tail(&edge->list[UPPER], &list);
      }
out:
      btrfs_free_path(path1);
      btrfs_free_path(path2);
      if (err) {
            INIT_LIST_HEAD(&list);
            upper = node;
            while (upper) {
                  if (RB_EMPTY_NODE(&upper->rb_node)) {
                        list_splice_tail(&upper->upper, &list);
                        kfree(upper);
                  }

                  if (list_empty(&list))
                        break;

                  edge = list_entry(list.next, struct backref_edge,
                                list[LOWER]);
                  upper = edge->node[UPPER];
                  kfree(edge);
            }
            return ERR_PTR(err);
      }
      return node;
}

/*
 * helper to add 'address of tree root -> reloc tree' mapping
 */
static int __add_reloc_root(struct btrfs_root *root)
{
      struct rb_node *rb_node;
      struct mapping_node *node;
      struct reloc_control *rc = root->fs_info->reloc_ctl;

      node = kmalloc(sizeof(*node), GFP_NOFS);
      BUG_ON(!node);

      node->bytenr = root->node->start;
      node->data = root;

      spin_lock(&rc->reloc_root_tree.lock);
      rb_node = tree_insert(&rc->reloc_root_tree.rb_root,
                        node->bytenr, &node->rb_node);
      spin_unlock(&rc->reloc_root_tree.lock);
      BUG_ON(rb_node);

      list_add_tail(&root->root_list, &rc->reloc_roots);
      return 0;
}

/*
 * helper to update/delete the 'address of tree root -> reloc tree'
 * mapping
 */
static int __update_reloc_root(struct btrfs_root *root, int del)
{
      struct rb_node *rb_node;
      struct mapping_node *node = NULL;
      struct reloc_control *rc = root->fs_info->reloc_ctl;

      spin_lock(&rc->reloc_root_tree.lock);
      rb_node = tree_search(&rc->reloc_root_tree.rb_root,
                        root->commit_root->start);
      if (rb_node) {
            node = rb_entry(rb_node, struct mapping_node, rb_node);
            rb_erase(&node->rb_node, &rc->reloc_root_tree.rb_root);
      }
      spin_unlock(&rc->reloc_root_tree.lock);

      BUG_ON((struct btrfs_root *)node->data != root);

      if (!del) {
            spin_lock(&rc->reloc_root_tree.lock);
            node->bytenr = root->node->start;
            rb_node = tree_insert(&rc->reloc_root_tree.rb_root,
                              node->bytenr, &node->rb_node);
            spin_unlock(&rc->reloc_root_tree.lock);
            BUG_ON(rb_node);
      } else {
            list_del_init(&root->root_list);
            kfree(node);
      }
      return 0;
}

/*
 * create reloc tree for a given fs tree. reloc tree is just a
 * snapshot of the fs tree with special root objectid.
 */
int btrfs_init_reloc_root(struct btrfs_trans_handle *trans,
                    struct btrfs_root *root)
{
      struct btrfs_root *reloc_root;
      struct extent_buffer *eb;
      struct btrfs_root_item *root_item;
      struct btrfs_key root_key;
      int ret;

      if (root->reloc_root) {
            reloc_root = root->reloc_root;
            reloc_root->last_trans = trans->transid;
            return 0;
      }

      if (!root->fs_info->reloc_ctl ||
          !root->fs_info->reloc_ctl->create_reloc_root ||
          root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
            return 0;

      root_item = kmalloc(sizeof(*root_item), GFP_NOFS);
      BUG_ON(!root_item);

      root_key.objectid = BTRFS_TREE_RELOC_OBJECTID;
      root_key.type = BTRFS_ROOT_ITEM_KEY;
      root_key.offset = root->root_key.objectid;

      ret = btrfs_copy_root(trans, root, root->commit_root, &eb,
                        BTRFS_TREE_RELOC_OBJECTID);
      BUG_ON(ret);

      btrfs_set_root_last_snapshot(&root->root_item, trans->transid - 1);
      memcpy(root_item, &root->root_item, sizeof(*root_item));
      btrfs_set_root_refs(root_item, 1);
      btrfs_set_root_bytenr(root_item, eb->start);
      btrfs_set_root_level(root_item, btrfs_header_level(eb));
      btrfs_set_root_generation(root_item, trans->transid);
      memset(&root_item->drop_progress, 0, sizeof(struct btrfs_disk_key));
      root_item->drop_level = 0;

      btrfs_tree_unlock(eb);
      free_extent_buffer(eb);

      ret = btrfs_insert_root(trans, root->fs_info->tree_root,
                        &root_key, root_item);
      BUG_ON(ret);
      kfree(root_item);

      reloc_root = btrfs_read_fs_root_no_radix(root->fs_info->tree_root,
                                     &root_key);
      BUG_ON(IS_ERR(reloc_root));
      reloc_root->last_trans = trans->transid;

      __add_reloc_root(reloc_root);
      root->reloc_root = reloc_root;
      return 0;
}

/*
 * update root item of reloc tree
 */
int btrfs_update_reloc_root(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root)
{
      struct btrfs_root *reloc_root;
      struct btrfs_root_item *root_item;
      int del = 0;
      int ret;

      if (!root->reloc_root)
            return 0;

      reloc_root = root->reloc_root;
      root_item = &reloc_root->root_item;

      if (btrfs_root_refs(root_item) == 0) {
            root->reloc_root = NULL;
            del = 1;
      }

      __update_reloc_root(reloc_root, del);

      if (reloc_root->commit_root != reloc_root->node) {
            btrfs_set_root_node(root_item, reloc_root->node);
            free_extent_buffer(reloc_root->commit_root);
            reloc_root->commit_root = btrfs_root_node(reloc_root);
      }

      ret = btrfs_update_root(trans, root->fs_info->tree_root,
                        &reloc_root->root_key, root_item);
      BUG_ON(ret);
      return 0;
}

/*
 * helper to find first cached inode with inode number >= objectid
 * in a subvolume
 */
static struct inode *find_next_inode(struct btrfs_root *root, u64 objectid)
{
      struct rb_node *node;
      struct rb_node *prev;
      struct btrfs_inode *entry;
      struct inode *inode;

      spin_lock(&root->inode_lock);
again:
      node = root->inode_tree.rb_node;
      prev = NULL;
      while (node) {
            prev = node;
            entry = rb_entry(node, struct btrfs_inode, rb_node);

            if (objectid < entry->vfs_inode.i_ino)
                  node = node->rb_left;
            else if (objectid > entry->vfs_inode.i_ino)
                  node = node->rb_right;
            else
                  break;
      }
      if (!node) {
            while (prev) {
                  entry = rb_entry(prev, struct btrfs_inode, rb_node);
                  if (objectid <= entry->vfs_inode.i_ino) {
                        node = prev;
                        break;
                  }
                  prev = rb_next(prev);
            }
      }
      while (node) {
            entry = rb_entry(node, struct btrfs_inode, rb_node);
            inode = igrab(&entry->vfs_inode);
            if (inode) {
                  spin_unlock(&root->inode_lock);
                  return inode;
            }

            objectid = entry->vfs_inode.i_ino + 1;
            if (cond_resched_lock(&root->inode_lock))
                  goto again;

            node = rb_next(node);
      }
      spin_unlock(&root->inode_lock);
      return NULL;
}

static int in_block_group(u64 bytenr,
                    struct btrfs_block_group_cache *block_group)
{
      if (bytenr >= block_group->key.objectid &&
          bytenr < block_group->key.objectid + block_group->key.offset)
            return 1;
      return 0;
}

/*
 * get new location of data
 */
static int get_new_location(struct inode *reloc_inode, u64 *new_bytenr,
                      u64 bytenr, u64 num_bytes)
{
      struct btrfs_root *root = BTRFS_I(reloc_inode)->root;
      struct btrfs_path *path;
      struct btrfs_file_extent_item *fi;
      struct extent_buffer *leaf;
      int ret;

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

      bytenr -= BTRFS_I(reloc_inode)->index_cnt;
      ret = btrfs_lookup_file_extent(NULL, root, path, reloc_inode->i_ino,
                               bytenr, 0);
      if (ret < 0)
            goto out;
      if (ret > 0) {
            ret = -ENOENT;
            goto out;
      }

      leaf = path->nodes[0];
      fi = btrfs_item_ptr(leaf, path->slots[0],
                      struct btrfs_file_extent_item);

      BUG_ON(btrfs_file_extent_offset(leaf, fi) ||
             btrfs_file_extent_compression(leaf, fi) ||
             btrfs_file_extent_encryption(leaf, fi) ||
             btrfs_file_extent_other_encoding(leaf, fi));

      if (num_bytes != btrfs_file_extent_disk_num_bytes(leaf, fi)) {
            ret = 1;
            goto out;
      }

      if (new_bytenr)
            *new_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
      ret = 0;
out:
      btrfs_free_path(path);
      return ret;
}

/*
 * update file extent items in the tree leaf to point to
 * the new locations.
 */
static int replace_file_extents(struct btrfs_trans_handle *trans,
                        struct reloc_control *rc,
                        struct btrfs_root *root,
                        struct extent_buffer *leaf,
                        struct list_head *inode_list)
{
      struct btrfs_key key;
      struct btrfs_file_extent_item *fi;
      struct inode *inode = NULL;
      struct inodevec *ivec = NULL;
      u64 parent;
      u64 bytenr;
      u64 new_bytenr;
      u64 num_bytes;
      u64 end;
      u32 nritems;
      u32 i;
      int ret;
      int first = 1;
      int dirty = 0;

      if (rc->stage != UPDATE_DATA_PTRS)
            return 0;

      /* reloc trees always use full backref */
      if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
            parent = leaf->start;
      else
            parent = 0;

      nritems = btrfs_header_nritems(leaf);
      for (i = 0; i < nritems; i++) {
            cond_resched();
            btrfs_item_key_to_cpu(leaf, &key, i);
            if (key.type != BTRFS_EXTENT_DATA_KEY)
                  continue;
            fi = btrfs_item_ptr(leaf, i, struct btrfs_file_extent_item);
            if (btrfs_file_extent_type(leaf, fi) ==
                BTRFS_FILE_EXTENT_INLINE)
                  continue;
            bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
            num_bytes = btrfs_file_extent_disk_num_bytes(leaf, fi);
            if (bytenr == 0)
                  continue;
            if (!in_block_group(bytenr, rc->block_group))
                  continue;

            /*
             * if we are modifying block in fs tree, wait for readpage
             * to complete and drop the extent cache
             */
            if (root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID) {
                  if (!ivec || ivec->nr == INODEVEC_SIZE) {
                        ivec = kmalloc(sizeof(*ivec), GFP_NOFS);
                        BUG_ON(!ivec);
                        ivec->nr = 0;
                        list_add_tail(&ivec->list, inode_list);
                  }
                  if (first) {
                        inode = find_next_inode(root, key.objectid);
                        if (inode)
                              ivec->inode[ivec->nr++] = inode;
                        first = 0;
                  } else if (inode && inode->i_ino < key.objectid) {
                        inode = find_next_inode(root, key.objectid);
                        if (inode)
                              ivec->inode[ivec->nr++] = inode;
                  }
                  if (inode && inode->i_ino == key.objectid) {
                        end = key.offset +
                              btrfs_file_extent_num_bytes(leaf, fi);
                        WARN_ON(!IS_ALIGNED(key.offset,
                                        root->sectorsize));
                        WARN_ON(!IS_ALIGNED(end, root->sectorsize));
                        end--;
                        ret = try_lock_extent(&BTRFS_I(inode)->io_tree,
                                          key.offset, end,
                                          GFP_NOFS);
                        if (!ret)
                              continue;

                        btrfs_drop_extent_cache(inode, key.offset, end,
                                          1);
                        unlock_extent(&BTRFS_I(inode)->io_tree,
                                    key.offset, end, GFP_NOFS);
                  }
            }

            ret = get_new_location(rc->data_inode, &new_bytenr,
                               bytenr, num_bytes);
            if (ret > 0)
                  continue;
            BUG_ON(ret < 0);

            btrfs_set_file_extent_disk_bytenr(leaf, fi, new_bytenr);
            dirty = 1;

            key.offset -= btrfs_file_extent_offset(leaf, fi);
            ret = btrfs_inc_extent_ref(trans, root, new_bytenr,
                                 num_bytes, parent,
                                 btrfs_header_owner(leaf),
                                 key.objectid, key.offset);
            BUG_ON(ret);

            ret = btrfs_free_extent(trans, root, bytenr, num_bytes,
                              parent, btrfs_header_owner(leaf),
                              key.objectid, key.offset);
            BUG_ON(ret);
      }
      if (dirty)
            btrfs_mark_buffer_dirty(leaf);
      return 0;
}

static noinline_for_stack
int memcmp_node_keys(struct extent_buffer *eb, int slot,
                 struct btrfs_path *path, int level)
{
      struct btrfs_disk_key key1;
      struct btrfs_disk_key key2;
      btrfs_node_key(eb, &key1, slot);
      btrfs_node_key(path->nodes[level], &key2, path->slots[level]);
      return memcmp(&key1, &key2, sizeof(key1));
}

/*
 * try to replace tree blocks in fs tree with the new blocks
 * in reloc tree. tree blocks haven't been modified since the
 * reloc tree was create can be replaced.
 *
 * if a block was replaced, level of the block + 1 is returned.
 * if no block got replaced, 0 is returned. if there are other
 * errors, a negative error number is returned.
 */
static int replace_path(struct btrfs_trans_handle *trans,
                  struct btrfs_root *dest, struct btrfs_root *src,
                  struct btrfs_path *path, struct btrfs_key *next_key,
                  struct extent_buffer **leaf,
                  int lowest_level, int max_level)
{
      struct extent_buffer *eb;
      struct extent_buffer *parent;
      struct btrfs_key key;
      u64 old_bytenr;
      u64 new_bytenr;
      u64 old_ptr_gen;
      u64 new_ptr_gen;
      u64 last_snapshot;
      u32 blocksize;
      int level;
      int ret;
      int slot;

      BUG_ON(src->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID);
      BUG_ON(dest->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID);
      BUG_ON(lowest_level > 1 && leaf);

      last_snapshot = btrfs_root_last_snapshot(&src->root_item);

      slot = path->slots[lowest_level];
      btrfs_node_key_to_cpu(path->nodes[lowest_level], &key, slot);

      eb = btrfs_lock_root_node(dest);
      btrfs_set_lock_blocking(eb);
      level = btrfs_header_level(eb);

      if (level < lowest_level) {
            btrfs_tree_unlock(eb);
            free_extent_buffer(eb);
            return 0;
      }

      ret = btrfs_cow_block(trans, dest, eb, NULL, 0, &eb);
      BUG_ON(ret);
      btrfs_set_lock_blocking(eb);

      if (next_key) {
            next_key->objectid = (u64)-1;
            next_key->type = (u8)-1;
            next_key->offset = (u64)-1;
      }

      parent = eb;
      while (1) {
            level = btrfs_header_level(parent);
            BUG_ON(level < lowest_level);

            ret = btrfs_bin_search(parent, &key, level, &slot);
            if (ret && slot > 0)
                  slot--;

            if (next_key && slot + 1 < btrfs_header_nritems(parent))
                  btrfs_node_key_to_cpu(parent, next_key, slot + 1);

            old_bytenr = btrfs_node_blockptr(parent, slot);
            blocksize = btrfs_level_size(dest, level - 1);
            old_ptr_gen = btrfs_node_ptr_generation(parent, slot);

            if (level <= max_level) {
                  eb = path->nodes[level];
                  new_bytenr = btrfs_node_blockptr(eb,
                                          path->slots[level]);
                  new_ptr_gen = btrfs_node_ptr_generation(eb,
                                          path->slots[level]);
            } else {
                  new_bytenr = 0;
                  new_ptr_gen = 0;
            }

            if (new_bytenr > 0 && new_bytenr == old_bytenr) {
                  WARN_ON(1);
                  ret = level;
                  break;
            }

            if (new_bytenr == 0 || old_ptr_gen > last_snapshot ||
                memcmp_node_keys(parent, slot, path, level)) {
                  if (level <= lowest_level && !leaf) {
                        ret = 0;
                        break;
                  }

                  eb = read_tree_block(dest, old_bytenr, blocksize,
                                   old_ptr_gen);
                  btrfs_tree_lock(eb);
                  ret = btrfs_cow_block(trans, dest, eb, parent,
                                    slot, &eb);
                  BUG_ON(ret);
                  btrfs_set_lock_blocking(eb);

                  if (level <= lowest_level) {
                        *leaf = eb;
                        ret = 0;
                        break;
                  }

                  btrfs_tree_unlock(parent);
                  free_extent_buffer(parent);

                  parent = eb;
                  continue;
            }

            btrfs_node_key_to_cpu(path->nodes[level], &key,
                              path->slots[level]);
            btrfs_release_path(src, path);

            path->lowest_level = level;
            ret = btrfs_search_slot(trans, src, &key, path, 0, 1);
            path->lowest_level = 0;
            BUG_ON(ret);

            /*
             * swap blocks in fs tree and reloc tree.
             */
            btrfs_set_node_blockptr(parent, slot, new_bytenr);
            btrfs_set_node_ptr_generation(parent, slot, new_ptr_gen);
            btrfs_mark_buffer_dirty(parent);

            btrfs_set_node_blockptr(path->nodes[level],
                              path->slots[level], old_bytenr);
            btrfs_set_node_ptr_generation(path->nodes[level],
                                    path->slots[level], old_ptr_gen);
            btrfs_mark_buffer_dirty(path->nodes[level]);

            ret = btrfs_inc_extent_ref(trans, src, old_bytenr, blocksize,
                              path->nodes[level]->start,
                              src->root_key.objectid, level - 1, 0);
            BUG_ON(ret);
            ret = btrfs_inc_extent_ref(trans, dest, new_bytenr, blocksize,
                              0, dest->root_key.objectid, level - 1,
                              0);
            BUG_ON(ret);

            ret = btrfs_free_extent(trans, src, new_bytenr, blocksize,
                              path->nodes[level]->start,
                              src->root_key.objectid, level - 1, 0);
            BUG_ON(ret);

            ret = btrfs_free_extent(trans, dest, old_bytenr, blocksize,
                              0, dest->root_key.objectid, level - 1,
                              0);
            BUG_ON(ret);

            btrfs_unlock_up_safe(path, 0);

            ret = level;
            break;
      }
      btrfs_tree_unlock(parent);
      free_extent_buffer(parent);
      return ret;
}

/*
 * helper to find next relocated block in reloc tree
 */
static noinline_for_stack
int walk_up_reloc_tree(struct btrfs_root *root, struct btrfs_path *path,
                   int *level)
{
      struct extent_buffer *eb;
      int i;
      u64 last_snapshot;
      u32 nritems;

      last_snapshot = btrfs_root_last_snapshot(&root->root_item);

      for (i = 0; i < *level; i++) {
            free_extent_buffer(path->nodes[i]);
            path->nodes[i] = NULL;
      }

      for (i = *level; i < BTRFS_MAX_LEVEL && path->nodes[i]; i++) {
            eb = path->nodes[i];
            nritems = btrfs_header_nritems(eb);
            while (path->slots[i] + 1 < nritems) {
                  path->slots[i]++;
                  if (btrfs_node_ptr_generation(eb, path->slots[i]) <=
                      last_snapshot)
                        continue;

                  *level = i;
                  return 0;
            }
            free_extent_buffer(path->nodes[i]);
            path->nodes[i] = NULL;
      }
      return 1;
}

/*
 * walk down reloc tree to find relocated block of lowest level
 */
static noinline_for_stack
int walk_down_reloc_tree(struct btrfs_root *root, struct btrfs_path *path,
                   int *level)
{
      struct extent_buffer *eb = NULL;
      int i;
      u64 bytenr;
      u64 ptr_gen = 0;
      u64 last_snapshot;
      u32 blocksize;
      u32 nritems;

      last_snapshot = btrfs_root_last_snapshot(&root->root_item);

      for (i = *level; i > 0; i--) {
            eb = path->nodes[i];
            nritems = btrfs_header_nritems(eb);
            while (path->slots[i] < nritems) {
                  ptr_gen = btrfs_node_ptr_generation(eb, path->slots[i]);
                  if (ptr_gen > last_snapshot)
                        break;
                  path->slots[i]++;
            }
            if (path->slots[i] >= nritems) {
                  if (i == *level)
                        break;
                  *level = i + 1;
                  return 0;
            }
            if (i == 1) {
                  *level = i;
                  return 0;
            }

            bytenr = btrfs_node_blockptr(eb, path->slots[i]);
            blocksize = btrfs_level_size(root, i - 1);
            eb = read_tree_block(root, bytenr, blocksize, ptr_gen);
            BUG_ON(btrfs_header_level(eb) != i - 1);
            path->nodes[i - 1] = eb;
            path->slots[i - 1] = 0;
      }
      return 1;
}

/*
 * invalidate extent cache for file extents whose key in range of
 * [min_key, max_key)
 */
static int invalidate_extent_cache(struct btrfs_root *root,
                           struct btrfs_key *min_key,
                           struct btrfs_key *max_key)
{
      struct inode *inode = NULL;
      u64 objectid;
      u64 start, end;

      objectid = min_key->objectid;
      while (1) {
            cond_resched();
            iput(inode);

            if (objectid > max_key->objectid)
                  break;

            inode = find_next_inode(root, objectid);
            if (!inode)
                  break;

            if (inode->i_ino > max_key->objectid) {
                  iput(inode);
                  break;
            }

            objectid = inode->i_ino + 1;
            if (!S_ISREG(inode->i_mode))
                  continue;

            if (unlikely(min_key->objectid == inode->i_ino)) {
                  if (min_key->type > BTRFS_EXTENT_DATA_KEY)
                        continue;
                  if (min_key->type < BTRFS_EXTENT_DATA_KEY)
                        start = 0;
                  else {
                        start = min_key->offset;
                        WARN_ON(!IS_ALIGNED(start, root->sectorsize));
                  }
            } else {
                  start = 0;
            }

            if (unlikely(max_key->objectid == inode->i_ino)) {
                  if (max_key->type < BTRFS_EXTENT_DATA_KEY)
                        continue;
                  if (max_key->type > BTRFS_EXTENT_DATA_KEY) {
                        end = (u64)-1;
                  } else {
                        if (max_key->offset == 0)
                              continue;
                        end = max_key->offset;
                        WARN_ON(!IS_ALIGNED(end, root->sectorsize));
                        end--;
                  }
            } else {
                  end = (u64)-1;
            }

            /* the lock_extent waits for readpage to complete */
            lock_extent(&BTRFS_I(inode)->io_tree, start, end, GFP_NOFS);
            btrfs_drop_extent_cache(inode, start, end, 1);
            unlock_extent(&BTRFS_I(inode)->io_tree, start, end, GFP_NOFS);
      }
      return 0;
}

static int find_next_key(struct btrfs_path *path, int level,
                   struct btrfs_key *key)

{
      while (level < BTRFS_MAX_LEVEL) {
            if (!path->nodes[level])
                  break;
            if (path->slots[level] + 1 <
                btrfs_header_nritems(path->nodes[level])) {
                  btrfs_node_key_to_cpu(path->nodes[level], key,
                                    path->slots[level] + 1);
                  return 0;
            }
            level++;
      }
      return 1;
}

/*
 * merge the relocated tree blocks in reloc tree with corresponding
 * fs tree.
 */
static noinline_for_stack int merge_reloc_root(struct reloc_control *rc,
                                     struct btrfs_root *root)
{
      LIST_HEAD(inode_list);
      struct btrfs_key key;
      struct btrfs_key next_key;
      struct btrfs_trans_handle *trans;
      struct btrfs_root *reloc_root;
      struct btrfs_root_item *root_item;
      struct btrfs_path *path;
      struct extent_buffer *leaf = NULL;
      unsigned long nr;
      int level;
      int max_level;
      int replaced = 0;
      int ret;
      int err = 0;

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

      reloc_root = root->reloc_root;
      root_item = &reloc_root->root_item;

      if (btrfs_disk_key_objectid(&root_item->drop_progress) == 0) {
            level = btrfs_root_level(root_item);
            extent_buffer_get(reloc_root->node);
            path->nodes[level] = reloc_root->node;
            path->slots[level] = 0;
      } else {
            btrfs_disk_key_to_cpu(&key, &root_item->drop_progress);

            level = root_item->drop_level;
            BUG_ON(level == 0);
            path->lowest_level = level;
            ret = btrfs_search_slot(NULL, reloc_root, &key, path, 0, 0);
            path->lowest_level = 0;
            if (ret < 0) {
                  btrfs_free_path(path);
                  return ret;
            }

            btrfs_node_key_to_cpu(path->nodes[level], &next_key,
                              path->slots[level]);
            WARN_ON(memcmp(&key, &next_key, sizeof(key)));

            btrfs_unlock_up_safe(path, 0);
      }

      if (level == 0 && rc->stage == UPDATE_DATA_PTRS) {
            trans = btrfs_start_transaction(root, 1);

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

            ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
            if (ret < 0) {
                  err = ret;
                  goto out;
            }

            leaf = path->nodes[0];
            btrfs_unlock_up_safe(path, 1);
            ret = replace_file_extents(trans, rc, root, leaf,
                                 &inode_list);
            if (ret < 0)
                  err = ret;
            goto out;
      }

      memset(&next_key, 0, sizeof(next_key));

      while (1) {
            leaf = NULL;
            replaced = 0;
            trans = btrfs_start_transaction(root, 1);
            max_level = level;

            ret = walk_down_reloc_tree(reloc_root, path, &level);
            if (ret < 0) {
                  err = ret;
                  goto out;
            }
            if (ret > 0)
                  break;

            if (!find_next_key(path, level, &key) &&
                btrfs_comp_cpu_keys(&next_key, &key) >= 0) {
                  ret = 0;
            } else if (level == 1 && rc->stage == UPDATE_DATA_PTRS) {
                  ret = replace_path(trans, root, reloc_root,
                                 path, &next_key, &leaf,
                                 level, max_level);
            } else {
                  ret = replace_path(trans, root, reloc_root,
                                 path, &next_key, NULL,
                                 level, max_level);
            }
            if (ret < 0) {
                  err = ret;
                  goto out;
            }

            if (ret > 0) {
                  level = ret;
                  btrfs_node_key_to_cpu(path->nodes[level], &key,
                                    path->slots[level]);
                  replaced = 1;
            } else if (leaf) {
                  /*
                   * no block got replaced, try replacing file extents
                   */
                  btrfs_item_key_to_cpu(leaf, &key, 0);
                  ret = replace_file_extents(trans, rc, root, leaf,
                                       &inode_list);
                  btrfs_tree_unlock(leaf);
                  free_extent_buffer(leaf);
                  BUG_ON(ret < 0);
            }

            ret = walk_up_reloc_tree(reloc_root, path, &level);
            if (ret > 0)
                  break;

            BUG_ON(level == 0);
            /*
             * save the merging progress in the drop_progress.
             * this is OK since root refs == 1 in this case.
             */
            btrfs_node_key(path->nodes[level], &root_item->drop_progress,
                         path->slots[level]);
            root_item->drop_level = level;

            nr = trans->blocks_used;
            btrfs_end_transaction(trans, root);

            btrfs_btree_balance_dirty(root, nr);

            if (replaced && rc->stage == UPDATE_DATA_PTRS)
                  invalidate_extent_cache(root, &key, &next_key);
      }

      /*
       * handle the case only one block in the fs tree need to be
       * relocated and the block is tree root.
       */
      leaf = btrfs_lock_root_node(root);
      ret = btrfs_cow_block(trans, root, leaf, NULL, 0, &leaf);
      btrfs_tree_unlock(leaf);
      free_extent_buffer(leaf);
      if (ret < 0)
            err = ret;
out:
      btrfs_free_path(path);

      if (err == 0) {
            memset(&root_item->drop_progress, 0,
                   sizeof(root_item->drop_progress));
            root_item->drop_level = 0;
            btrfs_set_root_refs(root_item, 0);
      }

      nr = trans->blocks_used;
      btrfs_end_transaction(trans, root);

      btrfs_btree_balance_dirty(root, nr);

      /*
       * put inodes while we aren't holding the tree locks
       */
      while (!list_empty(&inode_list)) {
            struct inodevec *ivec;
            ivec = list_entry(inode_list.next, struct inodevec, list);
            list_del(&ivec->list);
            while (ivec->nr > 0) {
                  ivec->nr--;
                  iput(ivec->inode[ivec->nr]);
            }
            kfree(ivec);
      }

      if (replaced && rc->stage == UPDATE_DATA_PTRS)
            invalidate_extent_cache(root, &key, &next_key);

      return err;
}

/*
 * callback for the work threads.
 * this function merges reloc tree with corresponding fs tree,
 * and then drops the reloc tree.
 */
static void merge_func(struct btrfs_work *work)
{
      struct btrfs_trans_handle *trans;
      struct btrfs_root *root;
      struct btrfs_root *reloc_root;
      struct async_merge *async;

      async = container_of(work, struct async_merge, work);
      reloc_root = async->root;

      if (btrfs_root_refs(&reloc_root->root_item) > 0) {
            root = read_fs_root(reloc_root->fs_info,
                            reloc_root->root_key.offset);
            BUG_ON(IS_ERR(root));
            BUG_ON(root->reloc_root != reloc_root);

            merge_reloc_root(async->rc, root);

            trans = btrfs_start_transaction(root, 1);
            btrfs_update_reloc_root(trans, root);
            btrfs_end_transaction(trans, root);
      }

      btrfs_drop_snapshot(reloc_root, 0);

      if (atomic_dec_and_test(async->num_pending))
            complete(async->done);

      kfree(async);
}

static int merge_reloc_roots(struct reloc_control *rc)
{
      struct async_merge *async;
      struct btrfs_root *root;
      struct completion done;
      atomic_t num_pending;

      init_completion(&done);
      atomic_set(&num_pending, 1);

      while (!list_empty(&rc->reloc_roots)) {
            root = list_entry(rc->reloc_roots.next,
                          struct btrfs_root, root_list);
            list_del_init(&root->root_list);

            async = kmalloc(sizeof(*async), GFP_NOFS);
            BUG_ON(!async);
            async->work.func = merge_func;
            async->work.flags = 0;
            async->rc = rc;
            async->root = root;
            async->done = &done;
            async->num_pending = &num_pending;
            atomic_inc(&num_pending);
            btrfs_queue_worker(&rc->workers, &async->work);
      }

      if (!atomic_dec_and_test(&num_pending))
            wait_for_completion(&done);

      BUG_ON(!RB_EMPTY_ROOT(&rc->reloc_root_tree.rb_root));
      return 0;
}

static void free_block_list(struct rb_root *blocks)
{
      struct tree_block *block;
      struct rb_node *rb_node;
      while ((rb_node = rb_first(blocks))) {
            block = rb_entry(rb_node, struct tree_block, rb_node);
            rb_erase(rb_node, blocks);
            kfree(block);
      }
}

static int record_reloc_root_in_trans(struct btrfs_trans_handle *trans,
                              struct btrfs_root *reloc_root)
{
      struct btrfs_root *root;

      if (reloc_root->last_trans == trans->transid)
            return 0;

      root = read_fs_root(reloc_root->fs_info, reloc_root->root_key.offset);
      BUG_ON(IS_ERR(root));
      BUG_ON(root->reloc_root != reloc_root);

      return btrfs_record_root_in_trans(trans, root);
}

/*
 * select one tree from trees that references the block.
 * for blocks in refernce counted trees, we preper reloc tree.
 * if no reloc tree found and reloc_only is true, NULL is returned.
 */
static struct btrfs_root *__select_one_root(struct btrfs_trans_handle *trans,
                                  struct backref_node *node,
                                  struct backref_edge *edges[],
                                  int *nr, int reloc_only)
{
      struct backref_node *next;
      struct btrfs_root *root;
      int index;
      int loop = 0;
again:
      index = 0;
      next = node;
      while (1) {
            cond_resched();
            next = walk_up_backref(next, edges, &index);
            root = next->root;
            if (!root) {
                  BUG_ON(!node->old_root);
                  goto skip;
            }

            /* no other choice for non-refernce counted tree */
            if (!root->ref_cows) {
                  BUG_ON(reloc_only);
                  break;
            }

            if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID) {
                  record_reloc_root_in_trans(trans, root);
                  break;
            }

            if (loop) {
                  btrfs_record_root_in_trans(trans, root);
                  break;
            }

            if (reloc_only || next != node) {
                  if (!root->reloc_root)
                        btrfs_record_root_in_trans(trans, root);
                  root = root->reloc_root;
                  /*
                   * if the reloc tree was created in current
                   * transation, there is no node in backref tree
                   * corresponds to the root of the reloc tree.
                   */
                  if (btrfs_root_last_snapshot(&root->root_item) ==
                      trans->transid - 1)
                        break;
            }
skip:
            root = NULL;
            next = walk_down_backref(edges, &index);
            if (!next || next->level <= node->level)
                  break;
      }

      if (!root && !loop && !reloc_only) {
            loop = 1;
            goto again;
      }

      if (root)
            *nr = index;
      else
            *nr = 0;

      return root;
}

static noinline_for_stack
struct btrfs_root *select_one_root(struct btrfs_trans_handle *trans,
                           struct backref_node *node)
{
      struct backref_edge *edges[BTRFS_MAX_LEVEL - 1];
      int nr;
      return __select_one_root(trans, node, edges, &nr, 0);
}

static noinline_for_stack
struct btrfs_root *select_reloc_root(struct btrfs_trans_handle *trans,
                             struct backref_node *node,
                             struct backref_edge *edges[], int *nr)
{
      return __select_one_root(trans, node, edges, nr, 1);
}

static void grab_path_buffers(struct btrfs_path *path,
                        struct backref_node *node,
                        struct backref_edge *edges[], int nr)
{
      int i = 0;
      while (1) {
            drop_node_buffer(node);
            node->eb = path->nodes[node->level];
            BUG_ON(!node->eb);
            if (path->locks[node->level])
                  node->locked = 1;
            path->nodes[node->level] = NULL;
            path->locks[node->level] = 0;

            if (i >= nr)
                  break;

            edges[i]->blockptr = node->eb->start;
            node = edges[i]->node[UPPER];
            i++;
      }
}

/*
 * relocate a block tree, and then update pointers in upper level
 * blocks that reference the block to point to the new location.
 *
 * if called by link_to_upper, the block has already been relocated.
 * in that case this function just updates pointers.
 */
static int do_relocation(struct btrfs_trans_handle *trans,
                   struct backref_node *node,
                   struct btrfs_key *key,
                   struct btrfs_path *path, int lowest)
{
      struct backref_node *upper;
      struct backref_edge *edge;
      struct backref_edge *edges[BTRFS_MAX_LEVEL - 1];
      struct btrfs_root *root;
      struct extent_buffer *eb;
      u32 blocksize;
      u64 bytenr;
      u64 generation;
      int nr;
      int slot;
      int ret;
      int err = 0;

      BUG_ON(lowest && node->eb);

      path->lowest_level = node->level + 1;
      list_for_each_entry(edge, &node->upper, list[LOWER]) {
            cond_resched();
            if (node->eb && node->eb->start == edge->blockptr)
                  continue;

            upper = edge->node[UPPER];
            root = select_reloc_root(trans, upper, edges, &nr);
            if (!root)
                  continue;

            if (upper->eb && !upper->locked)
                  drop_node_buffer(upper);

            if (!upper->eb) {
                  ret = btrfs_search_slot(trans, root, key, path, 0, 1);
                  if (ret < 0) {
                        err = ret;
                        break;
                  }
                  BUG_ON(ret > 0);

                  slot = path->slots[upper->level];

                  btrfs_unlock_up_safe(path, upper->level + 1);
                  grab_path_buffers(path, upper, edges, nr);

                  btrfs_release_path(NULL, path);
            } else {
                  ret = btrfs_bin_search(upper->eb, key, upper->level,
                                     &slot);
                  BUG_ON(ret);
            }

            bytenr = btrfs_node_blockptr(upper->eb, slot);
            if (!lowest) {
                  if (node->eb->start == bytenr) {
                        btrfs_tree_unlock(upper->eb);
                        upper->locked = 0;
                        continue;
                  }
            } else {
                  BUG_ON(node->bytenr != bytenr);
            }

            blocksize = btrfs_level_size(root, node->level);
            generation = btrfs_node_ptr_generation(upper->eb, slot);
            eb = read_tree_block(root, bytenr, blocksize, generation);
            btrfs_tree_lock(eb);
            btrfs_set_lock_blocking(eb);

            if (!node->eb) {
                  ret = btrfs_cow_block(trans, root, eb, upper->eb,
                                    slot, &eb);
                  if (ret < 0) {
                        err = ret;
                        break;
                  }
                  btrfs_set_lock_blocking(eb);
                  node->eb = eb;
                  node->locked = 1;
            } else {
                  btrfs_set_node_blockptr(upper->eb, slot,
                                    node->eb->start);
                  btrfs_set_node_ptr_generation(upper->eb, slot,
                                          trans->transid);
                  btrfs_mark_buffer_dirty(upper->eb);

                  ret = btrfs_inc_extent_ref(trans, root,
                                    node->eb->start, blocksize,
                                    upper->eb->start,
                                    btrfs_header_owner(upper->eb),
                                    node->level, 0);
                  BUG_ON(ret);

                  ret = btrfs_drop_subtree(trans, root, eb, upper->eb);
                  BUG_ON(ret);
            }
            if (!lowest) {
                  btrfs_tree_unlock(upper->eb);
                  upper->locked = 0;
            }
      }
      path->lowest_level = 0;
      return err;
}

static int link_to_upper(struct btrfs_trans_handle *trans,
                   struct backref_node *node,
                   struct btrfs_path *path)
{
      struct btrfs_key key;
      if (!node->eb || list_empty(&node->upper))
            return 0;

      btrfs_node_key_to_cpu(node->eb, &key, 0);
      return do_relocation(trans, node, &key, path, 0);
}

static int finish_pending_nodes(struct btrfs_trans_handle *trans,
                        struct backref_cache *cache,
                        struct btrfs_path *path)
{
      struct backref_node *node;
      int level;
      int ret;
      int err = 0;

      for (level = 0; level < BTRFS_MAX_LEVEL; level++) {
            while (!list_empty(&cache->pending[level])) {
                  node = list_entry(cache->pending[level].next,
                                struct backref_node, lower);
                  BUG_ON(node->level != level);

                  ret = link_to_upper(trans, node, path);
                  if (ret < 0)
                        err = ret;
                  /*
                   * this remove the node from the pending list and
                   * may add some other nodes to the level + 1
                   * pending list
                   */
                  remove_backref_node(cache, node);
            }
      }
      BUG_ON(!RB_EMPTY_ROOT(&cache->rb_root));
      return err;
}

static void mark_block_processed(struct reloc_control *rc,
                         struct backref_node *node)
{
      u32 blocksize;
      if (node->level == 0 ||
          in_block_group(node->bytenr, rc->block_group)) {
            blocksize = btrfs_level_size(rc->extent_root, node->level);
            set_extent_bits(&rc->processed_blocks, node->bytenr,
                        node->bytenr + blocksize - 1, EXTENT_DIRTY,
                        GFP_NOFS);
      }
      node->processed = 1;
}

/*
 * mark a block and all blocks directly/indirectly reference the block
 * as processed.
 */
static void update_processed_blocks(struct reloc_control *rc,
                            struct backref_node *node)
{
      struct backref_node *next = node;
      struct backref_edge *edge;
      struct backref_edge *edges[BTRFS_MAX_LEVEL - 1];
      int index = 0;

      while (next) {
            cond_resched();
            while (1) {
                  if (next->processed)
                        break;

                  mark_block_processed(rc, next);

                  if (list_empty(&next->upper))
                        break;

                  edge = list_entry(next->upper.next,
                                struct backref_edge, list[LOWER]);
                  edges[index++] = edge;
                  next = edge->node[UPPER];
            }
            next = walk_down_backref(edges, &index);
      }
}

static int tree_block_processed(u64 bytenr, u32 blocksize,
                        struct reloc_control *rc)
{
      if (test_range_bit(&rc->processed_blocks, bytenr,
                     bytenr + blocksize - 1, EXTENT_DIRTY, 1))
            return 1;
      return 0;
}

/*
 * check if there are any file extent pointers in the leaf point to
 * data require processing
 */
static int check_file_extents(struct reloc_control *rc,
                        u64 bytenr, u32 blocksize, u64 ptr_gen)
{
      struct btrfs_key found_key;
      struct btrfs_file_extent_item *fi;
      struct extent_buffer *leaf;
      u32 nritems;
      int i;
      int ret = 0;

      leaf = read_tree_block(rc->extent_root, bytenr, blocksize, ptr_gen);

      nritems = btrfs_header_nritems(leaf);
      for (i = 0; i < nritems; i++) {
            cond_resched();
            btrfs_item_key_to_cpu(leaf, &found_key, i);
            if (found_key.type != BTRFS_EXTENT_DATA_KEY)
                  continue;
            fi = btrfs_item_ptr(leaf, i, struct btrfs_file_extent_item);
            if (btrfs_file_extent_type(leaf, fi) ==
                BTRFS_FILE_EXTENT_INLINE)
                  continue;
            bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
            if (bytenr == 0)
                  continue;
            if (in_block_group(bytenr, rc->block_group)) {
                  ret = 1;
                  break;
            }
      }
      free_extent_buffer(leaf);
      return ret;
}

/*
 * scan child blocks of a given block to find blocks require processing
 */
static int add_child_blocks(struct btrfs_trans_handle *trans,
                      struct reloc_control *rc,
                      struct backref_node *node,
                      struct rb_root *blocks)
{
      struct tree_block *block;
      struct rb_node *rb_node;
      u64 bytenr;
      u64 ptr_gen;
      u32 blocksize;
      u32 nritems;
      int i;
      int err = 0;

      nritems = btrfs_header_nritems(node->eb);
      blocksize = btrfs_level_size(rc->extent_root, node->level - 1);
      for (i = 0; i < nritems; i++) {
            cond_resched();
            bytenr = btrfs_node_blockptr(node->eb, i);
            ptr_gen = btrfs_node_ptr_generation(node->eb, i);
            if (ptr_gen == trans->transid)
                  continue;
            if (!in_block_group(bytenr, rc->block_group) &&
                (node->level > 1 || rc->stage == MOVE_DATA_EXTENTS))
                  continue;
            if (tree_block_processed(bytenr, blocksize, rc))
                  continue;

            readahead_tree_block(rc->extent_root,
                             bytenr, blocksize, ptr_gen);
      }

      for (i = 0; i < nritems; i++) {
            cond_resched();
            bytenr = btrfs_node_blockptr(node->eb, i);
            ptr_gen = btrfs_node_ptr_generation(node->eb, i);
            if (ptr_gen == trans->transid)
                  continue;
            if (!in_block_group(bytenr, rc->block_group) &&
                (node->level > 1 || rc->stage == MOVE_DATA_EXTENTS))
                  continue;
            if (tree_block_processed(bytenr, blocksize, rc))
                  continue;
            if (!in_block_group(bytenr, rc->block_group) &&
                !check_file_extents(rc, bytenr, blocksize, ptr_gen))
                  continue;

            block = kmalloc(sizeof(*block), GFP_NOFS);
            if (!block) {
                  err = -ENOMEM;
                  break;
            }
            block->bytenr = bytenr;
            btrfs_node_key_to_cpu(node->eb, &block->key, i);
            block->level = node->level - 1;
            block->key_ready = 1;
            rb_node = tree_insert(blocks, block->bytenr, &block->rb_node);
            BUG_ON(rb_node);
      }
      if (err)
            free_block_list(blocks);
      return err;
}

/*
 * find adjacent blocks require processing
 */
static noinline_for_stack
int add_adjacent_blocks(struct btrfs_trans_handle *trans,
                  struct reloc_control *rc,
                  struct backref_cache *cache,
                  struct rb_root *blocks, int level,
                  struct backref_node **upper)
{
      struct backref_node *node;
      int ret = 0;

      WARN_ON(!list_empty(&cache->pending[level]));

      if (list_empty(&cache->pending[level + 1]))
            return 1;

      node = list_entry(cache->pending[level + 1].next,
                    struct backref_node, lower);
      if (node->eb)
            ret = add_child_blocks(trans, rc, node, blocks);

      *upper = node;
      return ret;
}

static int get_tree_block_key(struct reloc_control *rc,
                        struct tree_block *block)
{
      struct extent_buffer *eb;

      BUG_ON(block->key_ready);
      eb = read_tree_block(rc->extent_root, block->bytenr,
                       block->key.objectid, block->key.offset);
      WARN_ON(btrfs_header_level(eb) != block->level);
      if (block->level == 0)
            btrfs_item_key_to_cpu(eb, &block->key, 0);
      else
            btrfs_node_key_to_cpu(eb, &block->key, 0);
      free_extent_buffer(eb);
      block->key_ready = 1;
      return 0;
}

static int reada_tree_block(struct reloc_control *rc,
                      struct tree_block *block)
{
      BUG_ON(block->key_ready);
      readahead_tree_block(rc->extent_root, block->bytenr,
                       block->key.objectid, block->key.offset);
      return 0;
}

/*
 * helper function to relocate a tree block
 */
static int relocate_tree_block(struct btrfs_trans_handle *trans,
                        struct reloc_control *rc,
                        struct backref_node *node,
                        struct btrfs_key *key,
                        struct btrfs_path *path)
{
      struct btrfs_root *root;
      int ret;

      root = select_one_root(trans, node);
      if (unlikely(!root)) {
            rc->found_old_snapshot = 1;
            update_processed_blocks(rc, node);
            return 0;
      }

      if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID) {
            ret = do_relocation(trans, node, key, path, 1);
            if (ret < 0)
                  goto out;
            if (node->level == 0 && rc->stage == UPDATE_DATA_PTRS) {
                  ret = replace_file_extents(trans, rc, root,
                                       node->eb, NULL);
                  if (ret < 0)
                        goto out;
            }
            drop_node_buffer(node);
      } else if (!root->ref_cows) {
            path->lowest_level = node->level;
            ret = btrfs_search_slot(trans, root, key, path, 0, 1);
            btrfs_release_path(root, path);
            if (ret < 0)
                  goto out;
      } else if (root != node->root) {
            WARN_ON(node->level > 0 || rc->stage != UPDATE_DATA_PTRS);
      }

      update_processed_blocks(rc, node);
      ret = 0;
out:
      drop_node_buffer(node);
      return ret;
}

/*
 * relocate a list of blocks
 */
static noinline_for_stack
int relocate_tree_blocks(struct btrfs_trans_handle *trans,
                   struct reloc_control *rc, struct rb_root *blocks)
{
      struct backref_cache *cache;
      struct backref_node *node;
      struct btrfs_path *path;
      struct tree_block *block;
      struct rb_node *rb_node;
      int level = -1;
      int ret;
      int err = 0;

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

      cache = kmalloc(sizeof(*cache), GFP_NOFS);
      if (!cache) {
            btrfs_free_path(path);
            return -ENOMEM;
      }

      backref_cache_init(cache);

      rb_node = rb_first(blocks);
      while (rb_node) {
            block = rb_entry(rb_node, struct tree_block, rb_node);
            if (level == -1)
                  level = block->level;
            else
                  BUG_ON(level != block->level);
            if (!block->key_ready)
                  reada_tree_block(rc, block);
            rb_node = rb_next(rb_node);
      }

      rb_node = rb_first(blocks);
      while (rb_node) {
            block = rb_entry(rb_node, struct tree_block, rb_node);
            if (!block->key_ready)
                  get_tree_block_key(rc, block);
            rb_node = rb_next(rb_node);
      }

      rb_node = rb_first(blocks);
      while (rb_node) {
            block = rb_entry(rb_node, struct tree_block, rb_node);

            node = build_backref_tree(rc, cache, &block->key,
                                block->level, block->bytenr);
            if (IS_ERR(node)) {
                  err = PTR_ERR(node);
                  goto out;
            }

            ret = relocate_tree_block(trans, rc, node, &block->key,
                                path);
            if (ret < 0) {
                  err = ret;
                  goto out;
            }
            remove_backref_node(cache, node);
            rb_node = rb_next(rb_node);
      }

      if (level > 0)
            goto out;

      free_block_list(blocks);

      /*
       * now backrefs of some upper level tree blocks have been cached,
       * try relocating blocks referenced by these upper level blocks.
       */
      while (1) {
            struct backref_node *upper = NULL;
            if (trans->transaction->in_commit ||
                trans->transaction->delayed_refs.flushing)
                  break;

            ret = add_adjacent_blocks(trans, rc, cache, blocks, level,
                                &upper);
            if (ret < 0)
                  err = ret;
            if (ret != 0)
                  break;

            rb_node = rb_first(blocks);
            while (rb_node) {
                  block = rb_entry(rb_node, struct tree_block, rb_node);
                  if (trans->transaction->in_commit ||
                      trans->transaction->delayed_refs.flushing)
                        goto out;
                  BUG_ON(!block->key_ready);
                  node = build_backref_tree(rc, cache, &block->key,
                                      level, block->bytenr);
                  if (IS_ERR(node)) {
                        err = PTR_ERR(node);
                        goto out;
                  }

                  ret = relocate_tree_block(trans, rc, node,
                                      &block->key, path);
                  if (ret < 0) {
                        err = ret;
                        goto out;
                  }
                  remove_backref_node(cache, node);
                  rb_node = rb_next(rb_node);
            }
            free_block_list(blocks);

            if (upper) {
                  ret = link_to_upper(trans, upper, path);
                  if (ret < 0) {
                        err = ret;
                        break;
                  }
                  remove_backref_node(cache, upper);
            }
      }
out:
      free_block_list(blocks);

      ret = finish_pending_nodes(trans, cache, path);
      if (ret < 0)
            err = ret;

      kfree(cache);
      btrfs_free_path(path);
      return err;
}

static noinline_for_stack
int relocate_inode_pages(struct inode *inode, u64 start, u64 len)
{
      u64 page_start;
      u64 page_end;
      unsigned long i;
      unsigned long first_index;
      unsigned long last_index;
      unsigned int total_read = 0;
      unsigned int total_dirty = 0;
      struct page *page;
      struct file_ra_state *ra;
      struct btrfs_ordered_extent *ordered;
      struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
      int ret = 0;

      ra = kzalloc(sizeof(*ra), GFP_NOFS);
      if (!ra)
            return -ENOMEM;

      mutex_lock(&inode->i_mutex);
      first_index = start >> PAGE_CACHE_SHIFT;
      last_index = (start + len - 1) >> PAGE_CACHE_SHIFT;

      /* make sure the dirty trick played by the caller work */
      while (1) {
            ret = invalidate_inode_pages2_range(inode->i_mapping,
                                        first_index, last_index);
            if (ret != -EBUSY)
                  break;
            schedule_timeout(HZ/10);
      }
      if (ret)
            goto out_unlock;

      file_ra_state_init(ra, inode->i_mapping);

      for (i = first_index ; i <= last_index; i++) {
            if (total_read % ra->ra_pages == 0) {
                  btrfs_force_ra(inode->i_mapping, ra, NULL, i,
                        min(last_index, ra->ra_pages + i - 1));
            }
            total_read++;
again:
            if (((u64)i << PAGE_CACHE_SHIFT) > i_size_read(inode))
                  BUG_ON(1);
            page = grab_cache_page(inode->i_mapping, i);
            if (!page) {
                  ret = -ENOMEM;
                  goto out_unlock;
            }
            if (!PageUptodate(page)) {
                  btrfs_readpage(NULL, page);
                  lock_page(page);
                  if (!PageUptodate(page)) {
                        unlock_page(page);
                        page_cache_release(page);
                        ret = -EIO;
                        goto out_unlock;
                  }
            }
            wait_on_page_writeback(page);

            page_start = (u64)page->index << PAGE_CACHE_SHIFT;
            page_end = page_start + PAGE_CACHE_SIZE - 1;
            lock_extent(io_tree, page_start, page_end, GFP_NOFS);

            ordered = btrfs_lookup_ordered_extent(inode, page_start);
            if (ordered) {
                  unlock_extent(io_tree, page_start, page_end, GFP_NOFS);
                  unlock_page(page);
                  page_cache_release(page);
                  btrfs_start_ordered_extent(inode, ordered, 1);
                  btrfs_put_ordered_extent(ordered);
                  goto again;
            }
            set_page_extent_mapped(page);

            if (i == first_index)
                  set_extent_bits(io_tree, page_start, page_end,
                              EXTENT_BOUNDARY, GFP_NOFS);
            btrfs_set_extent_delalloc(inode, page_start, page_end);

            set_page_dirty(page);
            total_dirty++;

            unlock_extent(io_tree, page_start, page_end, GFP_NOFS);
            unlock_page(page);
            page_cache_release(page);
      }
out_unlock:
      mutex_unlock(&inode->i_mutex);
      kfree(ra);
      balance_dirty_pages_ratelimited_nr(inode->i_mapping, total_dirty);
      return ret;
}

static noinline_for_stack
int relocate_data_extent(struct inode *inode, struct btrfs_key *extent_key)
{
      struct btrfs_root *root = BTRFS_I(inode)->root;
      struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
      struct extent_map *em;
      u64 start = extent_key->objectid - BTRFS_I(inode)->index_cnt;
      u64 end = start + extent_key->offset - 1;

      em = alloc_extent_map(GFP_NOFS);
      em->start = start;
      em->len = extent_key->offset;
      em->block_len = extent_key->offset;
      em->block_start = extent_key->objectid;
      em->bdev = root->fs_info->fs_devices->latest_bdev;
      set_bit(EXTENT_FLAG_PINNED, &em->flags);

      /* setup extent map to cheat btrfs_readpage */
      lock_extent(&BTRFS_I(inode)->io_tree, start, end, GFP_NOFS);
      while (1) {
            int ret;
            spin_lock(&em_tree->lock);
            ret = add_extent_mapping(em_tree, em);
            spin_unlock(&em_tree->lock);
            if (ret != -EEXIST) {
                  free_extent_map(em);
                  break;
            }
            btrfs_drop_extent_cache(inode, start, end, 0);
      }
      unlock_extent(&BTRFS_I(inode)->io_tree, start, end, GFP_NOFS);

      return relocate_inode_pages(inode, start, extent_key->offset);
}

#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
static int get_ref_objectid_v0(struct reloc_control *rc,
                         struct btrfs_path *path,
                         struct btrfs_key *extent_key,
                         u64 *ref_objectid, int *path_change)
{
      struct btrfs_key key;
      struct extent_buffer *leaf;
      struct btrfs_extent_ref_v0 *ref0;
      int ret;
      int slot;

      leaf = path->nodes[0];
      slot = path->slots[0];
      while (1) {
            if (slot >= btrfs_header_nritems(leaf)) {
                  ret = btrfs_next_leaf(rc->extent_root, path);
                  if (ret < 0)
                        return ret;
                  BUG_ON(ret > 0);
                  leaf = path->nodes[0];
                  slot = path->slots[0];
                  if (path_change)
                        *path_change = 1;
            }
            btrfs_item_key_to_cpu(leaf, &key, slot);
            if (key.objectid != extent_key->objectid)
                  return -ENOENT;

            if (key.type != BTRFS_EXTENT_REF_V0_KEY) {
                  slot++;
                  continue;
            }
            ref0 = btrfs_item_ptr(leaf, slot,
                        struct btrfs_extent_ref_v0);
            *ref_objectid = btrfs_ref_objectid_v0(leaf, ref0);
            break;
      }
      return 0;
}
#endif

/*
 * helper to add a tree block to the list.
 * the major work is getting the generation and level of the block
 */
static int add_tree_block(struct reloc_control *rc,
                    struct btrfs_key *extent_key,
                    struct btrfs_path *path,
                    struct rb_root *blocks)
{
      struct extent_buffer *eb;
      struct btrfs_extent_item *ei;
      struct btrfs_tree_block_info *bi;
      struct tree_block *block;
      struct rb_node *rb_node;
      u32 item_size;
      int level = -1;
      int generation;

      eb =  path->nodes[0];
      item_size = btrfs_item_size_nr(eb, path->slots[0]);

      if (item_size >= sizeof(*ei) + sizeof(*bi)) {
            ei = btrfs_item_ptr(eb, path->slots[0],
                        struct btrfs_extent_item);
            bi = (struct btrfs_tree_block_info *)(ei + 1);
            generation = btrfs_extent_generation(eb, ei);
            level = btrfs_tree_block_level(eb, bi);
      } else {
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
            u64 ref_owner;
            int ret;

            BUG_ON(item_size != sizeof(struct btrfs_extent_item_v0));
            ret = get_ref_objectid_v0(rc, path, extent_key,
                                &ref_owner, NULL);
            BUG_ON(ref_owner >= BTRFS_MAX_LEVEL);
            level = (int)ref_owner;
            /* FIXME: get real generation */
            generation = 0;
#else
            BUG();
#endif
      }

      btrfs_release_path(rc->extent_root, path);

      BUG_ON(level == -1);

      block = kmalloc(sizeof(*block), GFP_NOFS);
      if (!block)
            return -ENOMEM;

      block->bytenr = extent_key->objectid;
      block->key.objectid = extent_key->offset;
      block->key.offset = generation;
      block->level = level;
      block->key_ready = 0;

      rb_node = tree_insert(blocks, block->bytenr, &block->rb_node);
      BUG_ON(rb_node);

      return 0;
}

/*
 * helper to add tree blocks for backref of type BTRFS_SHARED_DATA_REF_KEY
 */
static int __add_tree_block(struct reloc_control *rc,
                      u64 bytenr, u32 blocksize,
                      struct rb_root *blocks)
{
      struct btrfs_path *path;
      struct btrfs_key key;
      int ret;

      if (tree_block_processed(bytenr, blocksize, rc))
            return 0;

      if (tree_search(blocks, bytenr))
            return 0;

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

      key.objectid = bytenr;
      key.type = BTRFS_EXTENT_ITEM_KEY;
      key.offset = blocksize;

      path->search_commit_root = 1;
      path->skip_locking = 1;
      ret = btrfs_search_slot(NULL, rc->extent_root, &key, path, 0, 0);
      if (ret < 0)
            goto out;
      BUG_ON(ret);

      btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
      ret = add_tree_block(rc, &key, path, blocks);
out:
      btrfs_free_path(path);
      return ret;
}

/*
 * helper to check if the block use full backrefs for pointers in it
 */
static int block_use_full_backref(struct reloc_control *rc,
                          struct extent_buffer *eb)
{
      struct btrfs_path *path;
      struct btrfs_extent_item *ei;
      struct btrfs_key key;
      u64 flags;
      int ret;

      if (btrfs_header_flag(eb, BTRFS_HEADER_FLAG_RELOC) ||
          btrfs_header_backref_rev(eb) < BTRFS_MIXED_BACKREF_REV)
            return 1;

      path = btrfs_alloc_path();
      BUG_ON(!path);

      key.objectid = eb->start;
      key.type = BTRFS_EXTENT_ITEM_KEY;
      key.offset = eb->len;

      path->search_commit_root = 1;
      path->skip_locking = 1;
      ret = btrfs_search_slot(NULL, rc->extent_root,
                        &key, path, 0, 0);
      BUG_ON(ret);

      ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
                      struct btrfs_extent_item);
      flags = btrfs_extent_flags(path->nodes[0], ei);
      BUG_ON(!(flags & BTRFS_EXTENT_FLAG_TREE_BLOCK));
      if (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF)
            ret = 1;
      else
            ret = 0;
      btrfs_free_path(path);
      return ret;
}

/*
 * helper to add tree blocks for backref of type BTRFS_EXTENT_DATA_REF_KEY
 * this function scans fs tree to find blocks reference the data extent
 */
static int find_data_references(struct reloc_control *rc,
                        struct btrfs_key *extent_key,
                        struct extent_buffer *leaf,
                        struct btrfs_extent_data_ref *ref,
                        struct rb_root *blocks)
{
      struct btrfs_path *path;
      struct tree_block *block;
      struct btrfs_root *root;
      struct btrfs_file_extent_item *fi;
      struct rb_node *rb_node;
      struct btrfs_key key;
      u64 ref_root;
      u64 ref_objectid;
      u64 ref_offset;
      u32 ref_count;
      u32 nritems;
      int err = 0;
      int added = 0;
      int counted;
      int ret;

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

      ref_root = btrfs_extent_data_ref_root(leaf, ref);
      ref_objectid = btrfs_extent_data_ref_objectid(leaf, ref);
      ref_offset = btrfs_extent_data_ref_offset(leaf, ref);
      ref_count = btrfs_extent_data_ref_count(leaf, ref);

      root = read_fs_root(rc->extent_root->fs_info, ref_root);
      if (IS_ERR(root)) {
            err = PTR_ERR(root);
            goto out;
      }

      key.objectid = ref_objectid;
      key.offset = ref_offset;
      key.type = BTRFS_EXTENT_DATA_KEY;

      path->search_commit_root = 1;
      path->skip_locking = 1;
      ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
      if (ret < 0) {
            err = ret;
            goto out;
      }

      leaf = path->nodes[0];
      nritems = btrfs_header_nritems(leaf);
      /*
       * the references in tree blocks that use full backrefs
       * are not counted in
       */
      if (block_use_full_backref(rc, leaf))
            counted = 0;
      else
            counted = 1;
      rb_node = tree_search(blocks, leaf->start);
      if (rb_node) {
            if (counted)
                  added = 1;
            else
                  path->slots[0] = nritems;
      }

      while (ref_count > 0) {
            while (path->slots[0] >= nritems) {
                  ret = btrfs_next_leaf(root, path);
                  if (ret < 0) {
                        err = ret;
                        goto out;
                  }
                  if (ret > 0) {
                        WARN_ON(1);
                        goto out;
                  }

                  leaf = path->nodes[0];
                  nritems = btrfs_header_nritems(leaf);
                  added = 0;

                  if (block_use_full_backref(rc, leaf))
                        counted = 0;
                  else
                        counted = 1;
                  rb_node = tree_search(blocks, leaf->start);
                  if (rb_node) {
                        if (counted)
                              added = 1;
                        else
                              path->slots[0] = nritems;
                  }
            }

            btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
            if (key.objectid != ref_objectid ||
                key.type != BTRFS_EXTENT_DATA_KEY) {
                  WARN_ON(1);
                  break;
            }

            fi = btrfs_item_ptr(leaf, path->slots[0],
                            struct btrfs_file_extent_item);

            if (btrfs_file_extent_type(leaf, fi) ==
                BTRFS_FILE_EXTENT_INLINE)
                  goto next;

            if (btrfs_file_extent_disk_bytenr(leaf, fi) !=
                extent_key->objectid)
                  goto next;

            key.offset -= btrfs_file_extent_offset(leaf, fi);
            if (key.offset != ref_offset)
                  goto next;

            if (counted)
                  ref_count--;
            if (added)
                  goto next;

            if (!tree_block_processed(leaf->start, leaf->len, rc)) {
                  block = kmalloc(sizeof(*block), GFP_NOFS);
                  if (!block) {
                        err = -ENOMEM;
                        break;
                  }
                  block->bytenr = leaf->start;
                  btrfs_item_key_to_cpu(leaf, &block->key, 0);
                  block->level = 0;
                  block->key_ready = 1;
                  rb_node = tree_insert(blocks, block->bytenr,
                                    &block->rb_node);
                  BUG_ON(rb_node);
            }
            if (counted)
                  added = 1;
            else
                  path->slots[0] = nritems;
next:
            path->slots[0]++;

      }
out:
      btrfs_free_path(path);
      return err;
}

/*
 * hepler to find all tree blocks that reference a given data extent
 */
static noinline_for_stack
int add_data_references(struct reloc_control *rc,
                  struct btrfs_key *extent_key,
                  struct btrfs_path *path,
                  struct rb_root *blocks)
{
      struct btrfs_key key;
      struct extent_buffer *eb;
      struct btrfs_extent_data_ref *dref;
      struct btrfs_extent_inline_ref *iref;
      unsigned long ptr;
      unsigned long end;
      u32 blocksize;
      int ret;
      int err = 0;

      ret = get_new_location(rc->data_inode, NULL, extent_key->objectid,
                         extent_key->offset);
      BUG_ON(ret < 0);
      if (ret > 0) {
            /* the relocated data is fragmented */
            rc->extents_skipped++;
            btrfs_release_path(rc->extent_root, path);
            return 0;
      }

      blocksize = btrfs_level_size(rc->extent_root, 0);

      eb = path->nodes[0];
      ptr = btrfs_item_ptr_offset(eb, path->slots[0]);
      end = ptr + btrfs_item_size_nr(eb, path->slots[0]);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
      if (ptr + sizeof(struct btrfs_extent_item_v0) == end)
            ptr = end;
      else
#endif
            ptr += sizeof(struct btrfs_extent_item);

      while (ptr < end) {
            iref = (struct btrfs_extent_inline_ref *)ptr;
            key.type = btrfs_extent_inline_ref_type(eb, iref);
            if (key.type == BTRFS_SHARED_DATA_REF_KEY) {
                  key.offset = btrfs_extent_inline_ref_offset(eb, iref);
                  ret = __add_tree_block(rc, key.offset, blocksize,
                                     blocks);
            } else if (key.type == BTRFS_EXTENT_DATA_REF_KEY) {
                  dref = (struct btrfs_extent_data_ref *)(&iref->offset);
                  ret = find_data_references(rc, extent_key,
                                       eb, dref, blocks);
            } else {
                  BUG();
            }
            ptr += btrfs_extent_inline_ref_size(key.type);
      }
      WARN_ON(ptr > end);

      while (1) {
            cond_resched();
            eb = path->nodes[0];
            if (path->slots[0] >= btrfs_header_nritems(eb)) {
                  ret = btrfs_next_leaf(rc->extent_root, path);
                  if (ret < 0) {
                        err = ret;
                        break;
                  }
                  if (ret > 0)
                        break;
                  eb = path->nodes[0];
            }

            btrfs_item_key_to_cpu(eb, &key, path->slots[0]);
            if (key.objectid != extent_key->objectid)
                  break;

#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
            if (key.type == BTRFS_SHARED_DATA_REF_KEY ||
                key.type == BTRFS_EXTENT_REF_V0_KEY) {
#else
            BUG_ON(key.type == BTRFS_EXTENT_REF_V0_KEY);
            if (key.type == BTRFS_SHARED_DATA_REF_KEY) {
#endif
                  ret = __add_tree_block(rc, key.offset, blocksize,
                                     blocks);
            } else if (key.type == BTRFS_EXTENT_DATA_REF_KEY) {
                  dref = btrfs_item_ptr(eb, path->slots[0],
                                    struct btrfs_extent_data_ref);
                  ret = find_data_references(rc, extent_key,
                                       eb, dref, blocks);
            } else {
                  ret = 0;
            }
            if (ret) {
                  err = ret;
                  break;
            }
            path->slots[0]++;
      }
      btrfs_release_path(rc->extent_root, path);
      if (err)
            free_block_list(blocks);
      return err;
}

/*
 * hepler to find next unprocessed extent
 */
static noinline_for_stack
int find_next_extent(struct btrfs_trans_handle *trans,
                 struct reloc_control *rc, struct btrfs_path *path)
{
      struct btrfs_key key;
      struct extent_buffer *leaf;
      u64 start, end, last;
      int ret;

      last = rc->block_group->key.objectid + rc->block_group->key.offset;
      while (1) {
            cond_resched();
            if (rc->search_start >= last) {
                  ret = 1;
                  break;
            }

            key.objectid = rc->search_start;
            key.type = BTRFS_EXTENT_ITEM_KEY;
            key.offset = 0;

            path->search_commit_root = 1;
            path->skip_locking = 1;
            ret = btrfs_search_slot(NULL, rc->extent_root, &key, path,
                              0, 0);
            if (ret < 0)
                  break;
next:
            leaf = path->nodes[0];
            if (path->slots[0] >= btrfs_header_nritems(leaf)) {
                  ret = btrfs_next_leaf(rc->extent_root, path);
                  if (ret != 0)
                        break;
                  leaf = path->nodes[0];
            }

            btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
            if (key.objectid >= last) {
                  ret = 1;
                  break;
            }

            if (key.type != BTRFS_EXTENT_ITEM_KEY ||
                key.objectid + key.offset <= rc->search_start) {
                  path->slots[0]++;
                  goto next;
            }

            ret = find_first_extent_bit(&rc->processed_blocks,
                                  key.objectid, &start, &end,
                                  EXTENT_DIRTY);

            if (ret == 0 && start <= key.objectid) {
                  btrfs_release_path(rc->extent_root, path);
                  rc->search_start = end + 1;
            } else {
                  rc->search_start = key.objectid + key.offset;
                  return 0;
            }
      }
      btrfs_release_path(rc->extent_root, path);
      return ret;
}

static void set_reloc_control(struct reloc_control *rc)
{
      struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
      mutex_lock(&fs_info->trans_mutex);
      fs_info->reloc_ctl = rc;
      mutex_unlock(&fs_info->trans_mutex);
}

static void unset_reloc_control(struct reloc_control *rc)
{
      struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
      mutex_lock(&fs_info->trans_mutex);
      fs_info->reloc_ctl = NULL;
      mutex_unlock(&fs_info->trans_mutex);
}

static int check_extent_flags(u64 flags)
{
      if ((flags & BTRFS_EXTENT_FLAG_DATA) &&
          (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK))
            return 1;
      if (!(flags & BTRFS_EXTENT_FLAG_DATA) &&
          !(flags & BTRFS_EXTENT_FLAG_TREE_BLOCK))
            return 1;
      if ((flags & BTRFS_EXTENT_FLAG_DATA) &&
          (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF))
            return 1;
      return 0;
}

static noinline_for_stack int relocate_block_group(struct reloc_control *rc)
{
      struct rb_root blocks = RB_ROOT;
      struct btrfs_key key;
      struct btrfs_trans_handle *trans = NULL;
      struct btrfs_path *path;
      struct btrfs_extent_item *ei;
      unsigned long nr;
      u64 flags;
      u32 item_size;
      int ret;
      int err = 0;

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

      rc->search_start = rc->block_group->key.objectid;
      clear_extent_bits(&rc->processed_blocks, 0, (u64)-1, EXTENT_DIRTY,
                    GFP_NOFS);

      rc->create_reloc_root = 1;
      set_reloc_control(rc);

      trans = btrfs_start_transaction(rc->extent_root, 1);
      btrfs_commit_transaction(trans, rc->extent_root);

      while (1) {
            trans = btrfs_start_transaction(rc->extent_root, 1);

            ret = find_next_extent(trans, rc, path);
            if (ret < 0)
                  err = ret;
            if (ret != 0)
                  break;

            rc->extents_found++;

            ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
                            struct btrfs_extent_item);
            btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
            item_size = btrfs_item_size_nr(path->nodes[0],
                                     path->slots[0]);
            if (item_size >= sizeof(*ei)) {
                  flags = btrfs_extent_flags(path->nodes[0], ei);
                  ret = check_extent_flags(flags);
                  BUG_ON(ret);

            } else {
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
                  u64 ref_owner;
                  int path_change = 0;

                  BUG_ON(item_size !=
                         sizeof(struct btrfs_extent_item_v0));
                  ret = get_ref_objectid_v0(rc, path, &key, &ref_owner,
                                      &path_change);
                  if (ref_owner < BTRFS_FIRST_FREE_OBJECTID)
                        flags = BTRFS_EXTENT_FLAG_TREE_BLOCK;
                  else
                        flags = BTRFS_EXTENT_FLAG_DATA;

                  if (path_change) {
                        btrfs_release_path(rc->extent_root, path);

                        path->search_commit_root = 1;
                        path->skip_locking = 1;
                        ret = btrfs_search_slot(NULL, rc->extent_root,
                                          &key, path, 0, 0);
                        if (ret < 0) {
                              err = ret;
                              break;
                        }
                        BUG_ON(ret > 0);
                  }
#else
                  BUG();
#endif
            }

            if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
                  ret = add_tree_block(rc, &key, path, &blocks);
            } else if (rc->stage == UPDATE_DATA_PTRS &&
                   (flags & BTRFS_EXTENT_FLAG_DATA)) {
                  ret = add_data_references(rc, &key, path, &blocks);
            } else {
                  btrfs_release_path(rc->extent_root, path);
                  ret = 0;
            }
            if (ret < 0) {
                  err = 0;
                  break;
            }

            if (!RB_EMPTY_ROOT(&blocks)) {
                  ret = relocate_tree_blocks(trans, rc, &blocks);
                  if (ret < 0) {
                        err = ret;
                        break;
                  }
            }

            nr = trans->blocks_used;
            btrfs_end_transaction_throttle(trans, rc->extent_root);
            trans = NULL;
            btrfs_btree_balance_dirty(rc->extent_root, nr);

            if (rc->stage == MOVE_DATA_EXTENTS &&
                (flags & BTRFS_EXTENT_FLAG_DATA)) {
                  rc->found_file_extent = 1;
                  ret = relocate_data_extent(rc->data_inode, &key);
                  if (ret < 0) {
                        err = ret;
                        break;
                  }
            }
      }
      btrfs_free_path(path);

      if (trans) {
            nr = trans->blocks_used;
            btrfs_end_transaction(trans, rc->extent_root);
            btrfs_btree_balance_dirty(rc->extent_root, nr);
      }

      rc->create_reloc_root = 0;
      smp_mb();

      if (rc->extents_found > 0) {
            trans = btrfs_start_transaction(rc->extent_root, 1);
            btrfs_commit_transaction(trans, rc->extent_root);
      }

      merge_reloc_roots(rc);

      unset_reloc_control(rc);

      /* get rid of pinned extents */
      trans = btrfs_start_transaction(rc->extent_root, 1);
      btrfs_commit_transaction(trans, rc->extent_root);

      return err;
}

static int __insert_orphan_inode(struct btrfs_trans_handle *trans,
                         struct btrfs_root *root,
                         u64 objectid, u64 size)
{
      struct btrfs_path *path;
      struct btrfs_inode_item *item;
      struct extent_buffer *leaf;
      int ret;

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

      ret = btrfs_insert_empty_inode(trans, root, path, objectid);
      if (ret)
            goto out;

      leaf = path->nodes[0];
      item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_inode_item);
      memset_extent_buffer(leaf, 0, (unsigned long)item, sizeof(*item));
      btrfs_set_inode_generation(leaf, item, 1);
      btrfs_set_inode_size(leaf, item, size);
      btrfs_set_inode_mode(leaf, item, S_IFREG | 0600);
      btrfs_set_inode_flags(leaf, item, BTRFS_INODE_NOCOMPRESS);
      btrfs_mark_buffer_dirty(leaf);
      btrfs_release_path(root, path);
out:
      btrfs_free_path(path);
      return ret;
}

/*
 * helper to create inode for data relocation.
 * the inode is in data relocation tree and its link count is 0
 */
static struct inode *create_reloc_inode(struct btrfs_fs_info *fs_info,
                              struct btrfs_block_group_cache *group)
{
      struct inode *inode = NULL;
      struct btrfs_trans_handle *trans;
      struct btrfs_root *root;
      struct btrfs_key key;
      unsigned long nr;
      u64 objectid = BTRFS_FIRST_FREE_OBJECTID;
      int err = 0;

      root = read_fs_root(fs_info, BTRFS_DATA_RELOC_TREE_OBJECTID);
      if (IS_ERR(root))
            return ERR_CAST(root);

      trans = btrfs_start_transaction(root, 1);
      BUG_ON(!trans);

      err = btrfs_find_free_objectid(trans, root, objectid, &objectid);
      if (err)
            goto out;

      err = __insert_orphan_inode(trans, root, objectid, group->key.offset);
      BUG_ON(err);

      err = btrfs_insert_file_extent(trans, root, objectid, 0, 0, 0,
                               group->key.offset, 0, group->key.offset,
                               0, 0, 0);
      BUG_ON(err);

      key.objectid = objectid;
      key.type = BTRFS_INODE_ITEM_KEY;
      key.offset = 0;
      inode = btrfs_iget(root->fs_info->sb, &key, root);
      BUG_ON(IS_ERR(inode) || is_bad_inode(inode));
      BTRFS_I(inode)->index_cnt = group->key.objectid;

      err = btrfs_orphan_add(trans, inode);
out:
      nr = trans->blocks_used;
      btrfs_end_transaction(trans, root);

      btrfs_btree_balance_dirty(root, nr);
      if (err) {
            if (inode)
                  iput(inode);
            inode = ERR_PTR(err);
      }
      return inode;
}

/*
 * function to relocate all extents in a block group.
 */
int btrfs_relocate_block_group(struct btrfs_root *extent_root, u64 group_start)
{
      struct btrfs_fs_info *fs_info = extent_root->fs_info;
      struct reloc_control *rc;
      int ret;
      int err = 0;

      rc = kzalloc(sizeof(*rc), GFP_NOFS);
      if (!rc)
            return -ENOMEM;

      mapping_tree_init(&rc->reloc_root_tree);
      extent_io_tree_init(&rc->processed_blocks, NULL, GFP_NOFS);
      INIT_LIST_HEAD(&rc->reloc_roots);

      rc->block_group = btrfs_lookup_block_group(fs_info, group_start);
      BUG_ON(!rc->block_group);

      btrfs_init_workers(&rc->workers, "relocate",
                     fs_info->thread_pool_size);

      rc->extent_root = extent_root;
      btrfs_prepare_block_group_relocation(extent_root, rc->block_group);

      rc->data_inode = create_reloc_inode(fs_info, rc->block_group);
      if (IS_ERR(rc->data_inode)) {
            err = PTR_ERR(rc->data_inode);
            rc->data_inode = NULL;
            goto out;
      }

      printk(KERN_INFO "btrfs: relocating block group %llu flags %llu\n",
             (unsigned long long)rc->block_group->key.objectid,
             (unsigned long long)rc->block_group->flags);

      btrfs_start_delalloc_inodes(fs_info->tree_root);
      btrfs_wait_ordered_extents(fs_info->tree_root, 0);

      while (1) {
            mutex_lock(&fs_info->cleaner_mutex);
            btrfs_clean_old_snapshots(fs_info->tree_root);
            mutex_unlock(&fs_info->cleaner_mutex);

            rc->extents_found = 0;
            rc->extents_skipped = 0;

            ret = relocate_block_group(rc);
            if (ret < 0) {
                  err = ret;
                  break;
            }

            if (rc->extents_found == 0)
                  break;

            printk(KERN_INFO "btrfs: found %llu extents\n",
                  (unsigned long long)rc->extents_found);

            if (rc->stage == MOVE_DATA_EXTENTS && rc->found_file_extent) {
                  btrfs_wait_ordered_range(rc->data_inode, 0, (u64)-1);
                  invalidate_mapping_pages(rc->data_inode->i_mapping,
                                     0, -1);
                  rc->stage = UPDATE_DATA_PTRS;
            } else if (rc->stage == UPDATE_DATA_PTRS &&
                     rc->extents_skipped >= rc->extents_found) {
                  iput(rc->data_inode);
                  rc->data_inode = create_reloc_inode(fs_info,
                                              rc->block_group);
                  if (IS_ERR(rc->data_inode)) {
                        err = PTR_ERR(rc->data_inode);
                        rc->data_inode = NULL;
                        break;
                  }
                  rc->stage = MOVE_DATA_EXTENTS;
                  rc->found_file_extent = 0;
            }
      }

      filemap_fdatawrite_range(fs_info->btree_inode->i_mapping,
                         rc->block_group->key.objectid,
                         rc->block_group->key.objectid +
                         rc->block_group->key.offset - 1);

      WARN_ON(rc->block_group->pinned > 0);
      WARN_ON(rc->block_group->reserved > 0);
      WARN_ON(btrfs_block_group_used(&rc->block_group->item) > 0);
out:
      iput(rc->data_inode);
      btrfs_stop_workers(&rc->workers);
      btrfs_put_block_group(rc->block_group);
      kfree(rc);
      return err;
}

/*
 * recover relocation interrupted by system crash.
 *
 * this function resumes merging reloc trees with corresponding fs trees.
 * this is important for keeping the sharing of tree blocks
 */
int btrfs_recover_relocation(struct btrfs_root *root)
{
      LIST_HEAD(reloc_roots);
      struct btrfs_key key;
      struct btrfs_root *fs_root;
      struct btrfs_root *reloc_root;
      struct btrfs_path *path;
      struct extent_buffer *leaf;
      struct reloc_control *rc = NULL;
      struct btrfs_trans_handle *trans;
      int ret;
      int err = 0;

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

      key.objectid = BTRFS_TREE_RELOC_OBJECTID;
      key.type = BTRFS_ROOT_ITEM_KEY;
      key.offset = (u64)-1;

      while (1) {
            ret = btrfs_search_slot(NULL, root->fs_info->tree_root, &key,
                              path, 0, 0);
            if (ret < 0) {
                  err = ret;
                  goto out;
            }
            if (ret > 0) {
                  if (path->slots[0] == 0)
                        break;
                  path->slots[0]--;
            }
            leaf = path->nodes[0];
            btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
            btrfs_release_path(root->fs_info->tree_root, path);

            if (key.objectid != BTRFS_TREE_RELOC_OBJECTID ||
                key.type != BTRFS_ROOT_ITEM_KEY)
                  break;

            reloc_root = btrfs_read_fs_root_no_radix(root, &key);
            if (IS_ERR(reloc_root)) {
                  err = PTR_ERR(reloc_root);
                  goto out;
            }

            list_add(&reloc_root->root_list, &reloc_roots);

            if (btrfs_root_refs(&reloc_root->root_item) > 0) {
                  fs_root = read_fs_root(root->fs_info,
                                     reloc_root->root_key.offset);
                  if (IS_ERR(fs_root)) {
                        err = PTR_ERR(fs_root);
                        goto out;
                  }
            }

            if (key.offset == 0)
                  break;

            key.offset--;
      }
      btrfs_release_path(root->fs_info->tree_root, path);

      if (list_empty(&reloc_roots))
            goto out;

      rc = kzalloc(sizeof(*rc), GFP_NOFS);
      if (!rc) {
            err = -ENOMEM;
            goto out;
      }

      mapping_tree_init(&rc->reloc_root_tree);
      INIT_LIST_HEAD(&rc->reloc_roots);
      btrfs_init_workers(&rc->workers, "relocate",
                     root->fs_info->thread_pool_size);
      rc->extent_root = root->fs_info->extent_root;

      set_reloc_control(rc);

      while (!list_empty(&reloc_roots)) {
            reloc_root = list_entry(reloc_roots.next,
                              struct btrfs_root, root_list);
            list_del(&reloc_root->root_list);

            if (btrfs_root_refs(&reloc_root->root_item) == 0) {
                  list_add_tail(&reloc_root->root_list,
                              &rc->reloc_roots);
                  continue;
            }

            fs_root = read_fs_root(root->fs_info,
                               reloc_root->root_key.offset);
            BUG_ON(IS_ERR(fs_root));

            __add_reloc_root(reloc_root);
            fs_root->reloc_root = reloc_root;
      }

      trans = btrfs_start_transaction(rc->extent_root, 1);
      btrfs_commit_transaction(trans, rc->extent_root);

      merge_reloc_roots(rc);

      unset_reloc_control(rc);

      trans = btrfs_start_transaction(rc->extent_root, 1);
      btrfs_commit_transaction(trans, rc->extent_root);
out:
      if (rc) {
            btrfs_stop_workers(&rc->workers);
            kfree(rc);
      }
      while (!list_empty(&reloc_roots)) {
            reloc_root = list_entry(reloc_roots.next,
                              struct btrfs_root, root_list);
            list_del(&reloc_root->root_list);
            free_extent_buffer(reloc_root->node);
            free_extent_buffer(reloc_root->commit_root);
            kfree(reloc_root);
      }
      btrfs_free_path(path);

      if (err == 0) {
            /* cleanup orphan inode in data relocation tree */
            fs_root = read_fs_root(root->fs_info,
                               BTRFS_DATA_RELOC_TREE_OBJECTID);
            if (IS_ERR(fs_root))
                  err = PTR_ERR(fs_root);
      }
      return err;
}

/*
 * helper to add ordered checksum for data relocation.
 *
 * cloning checksum properly handles the nodatasum extents.
 * it also saves CPU time to re-calculate the checksum.
 */
int btrfs_reloc_clone_csums(struct inode *inode, u64 file_pos, u64 len)
{
      struct btrfs_ordered_sum *sums;
      struct btrfs_sector_sum *sector_sum;
      struct btrfs_ordered_extent *ordered;
      struct btrfs_root *root = BTRFS_I(inode)->root;
      size_t offset;
      int ret;
      u64 disk_bytenr;
      LIST_HEAD(list);

      ordered = btrfs_lookup_ordered_extent(inode, file_pos);
      BUG_ON(ordered->file_offset != file_pos || ordered->len != len);

      disk_bytenr = file_pos + BTRFS_I(inode)->index_cnt;
      ret = btrfs_lookup_csums_range(root->fs_info->csum_root, disk_bytenr,
                               disk_bytenr + len - 1, &list);

      while (!list_empty(&list)) {
            sums = list_entry(list.next, struct btrfs_ordered_sum, list);
            list_del_init(&sums->list);

            sector_sum = sums->sums;
            sums->bytenr = ordered->start;

            offset = 0;
            while (offset < sums->len) {
                  sector_sum->bytenr += ordered->start - disk_bytenr;
                  sector_sum++;
                  offset += root->sectorsize;
            }

            btrfs_add_ordered_sum(inode, ordered, sums);
      }
      btrfs_put_ordered_extent(ordered);
      return 0;
}

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