/*
   * 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 <linux/slab.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"

  #include "free-space-cache.h"

  #include "inode-map.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
   */
  struct backref_node {
  	struct rb_node rb_node;
  	u64 bytenr;

  
  	u64 new_bytenr;
  	/* objectid of tree block owner, can be not uptodate */

  	u64 owner;

  	/* link to pending, changed or detached list */
  	struct list_head list;

  	/* 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;

  	/* is the block in non-reference counted tree */
  	unsigned int cowonly:1;
  	/* 1 if no child node 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;

  	/*
  	 * 1 if corresponding block has been cowed but some upper
  	 * level block pointers may not point to the new location
  	 */
  	unsigned int pending:1;
  	/*
  	 * 1 if the backref node isn't connected to any other
  	 * backref node.
  	 */
  	unsigned int detached:1;

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

  };
  
  #define LOWER	0
  #define UPPER	1
  
  struct backref_cache {
  	/* red black tree of all backref nodes in the cache */
  	struct rb_root rb_root;

  	/* for passing backref nodes to btrfs_reloc_cow_block */
  	struct backref_node *path[BTRFS_MAX_LEVEL];
  	/*
  	 * list of blocks that have been cowed but some block
  	 * pointers in upper level blocks may not reflect the
  	 * new location
  	 */

  	struct list_head pending[BTRFS_MAX_LEVEL];

  	/* list of backref nodes with no child node */
  	struct list_head leaves;
  	/* list of blocks that have been cowed in current transaction */
  	struct list_head changed;
  	/* list of detached backref node. */
  	struct list_head detached;
  
  	u64 last_trans;
  
  	int nr_nodes;
  	int nr_edges;

  };
  
  /*
   * map address of tree root to tree
   */
  struct mapping_node {
  	struct rb_node rb_node;
  	u64 bytenr;
  	void *data;
  };
  
  struct mapping_tree {
  	struct rb_root rb_root;
  	spinlock_t lock;
  };
  
  /*
   * present a tree block to process
   */
  struct tree_block {
  	struct rb_node rb_node;
  	u64 bytenr;
  	struct btrfs_key key;
  	unsigned int level:8;
  	unsigned int key_ready:1;
  };

  #define MAX_EXTENTS 128
  
  struct file_extent_cluster {
  	u64 start;
  	u64 end;
  	u64 boundary[MAX_EXTENTS];
  	unsigned int nr;
  };

  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_block_rsv *block_rsv;
  
  	struct backref_cache backref_cache;
  
  	struct file_extent_cluster cluster;

  	/* 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;

  	/* size of metadata reservation for merging reloc trees */
  	u64 merging_rsv_size;
  	/* size of relocated tree nodes */
  	u64 nodes_relocated;

  	u64 search_start;
  	u64 extents_found;

  	unsigned int stage:8;
  	unsigned int create_reloc_tree:1;
  	unsigned int merge_reloc_tree:1;

  	unsigned int found_file_extent:1;

  	unsigned int commit_transaction:1;

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

  static void remove_backref_node(struct backref_cache *cache,
  				struct backref_node *node);
  static void __mark_block_processed(struct reloc_control *rc,
  				   struct backref_node *node);

  
  static void mapping_tree_init(struct mapping_tree *tree)
  {

  	tree->rb_root = RB_ROOT;

  	spin_lock_init(&tree->lock);
  }
  
  static void backref_cache_init(struct backref_cache *cache)
  {
  	int i;

  	cache->rb_root = RB_ROOT;

  	for (i = 0; i < BTRFS_MAX_LEVEL; i++)
  		INIT_LIST_HEAD(&cache->pending[i]);

  	INIT_LIST_HEAD(&cache->changed);
  	INIT_LIST_HEAD(&cache->detached);
  	INIT_LIST_HEAD(&cache->leaves);
  }
  
  static void backref_cache_cleanup(struct backref_cache *cache)
  {
  	struct backref_node *node;
  	int i;
  
  	while (!list_empty(&cache->detached)) {
  		node = list_entry(cache->detached.next,
  				  struct backref_node, list);
  		remove_backref_node(cache, node);
  	}
  
  	while (!list_empty(&cache->leaves)) {
  		node = list_entry(cache->leaves.next,
  				  struct backref_node, lower);
  		remove_backref_node(cache, node);
  	}
  
  	cache->last_trans = 0;
  
  	for (i = 0; i < BTRFS_MAX_LEVEL; i++)
  		BUG_ON(!list_empty(&cache->pending[i]));
  	BUG_ON(!list_empty(&cache->changed));
  	BUG_ON(!list_empty(&cache->detached));
  	BUG_ON(!RB_EMPTY_ROOT(&cache->rb_root));
  	BUG_ON(cache->nr_nodes);
  	BUG_ON(cache->nr_edges);
  }
  
  static struct backref_node *alloc_backref_node(struct backref_cache *cache)
  {
  	struct backref_node *node;
  
  	node = kzalloc(sizeof(*node), GFP_NOFS);
  	if (node) {
  		INIT_LIST_HEAD(&node->list);
  		INIT_LIST_HEAD(&node->upper);
  		INIT_LIST_HEAD(&node->lower);
  		RB_CLEAR_NODE(&node->rb_node);
  		cache->nr_nodes++;
  	}
  	return node;
  }
  
  static void free_backref_node(struct backref_cache *cache,
  			      struct backref_node *node)
  {
  	if (node) {
  		cache->nr_nodes--;
  		kfree(node);
  	}
  }
  
  static struct backref_edge *alloc_backref_edge(struct backref_cache *cache)
  {
  	struct backref_edge *edge;
  
  	edge = kzalloc(sizeof(*edge), GFP_NOFS);
  	if (edge)
  		cache->nr_edges++;
  	return edge;

  }

  static void free_backref_edge(struct backref_cache *cache,
  			      struct backref_edge *edge)

  {

  	if (edge) {
  		cache->nr_edges--;
  		kfree(edge);
  	}

  }
  
  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];
  	}

  	BUG_ON(node->detached);

  	*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 unlock_node_buffer(struct backref_node *node)
  {
  	if (node->locked) {
  		btrfs_tree_unlock(node->eb);
  		node->locked = 0;
  	}
  }

  static void drop_node_buffer(struct backref_node *node)
  {
  	if (node->eb) {

  		unlock_node_buffer(node);

  		free_extent_buffer(node->eb);
  		node->eb = NULL;
  	}
  }
  
  static void drop_backref_node(struct backref_cache *tree,
  			      struct backref_node *node)
  {

  	BUG_ON(!list_empty(&node->upper));
  
  	drop_node_buffer(node);

  	list_del(&node->list);

  	list_del(&node->lower);

  	if (!RB_EMPTY_NODE(&node->rb_node))
  		rb_erase(&node->rb_node, &tree->rb_root);
  	free_backref_node(tree, 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 && !node->detached);

  	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]);

  		free_backref_edge(cache, edge);
  
  		if (RB_EMPTY_NODE(&upper->rb_node)) {
  			BUG_ON(!list_empty(&node->upper));
  			drop_backref_node(cache, node);
  			node = upper;
  			node->lowest = 1;
  			continue;
  		}

  		/*

  		 * add the node to leaf node list if no other

  		 * child block cached.
  		 */
  		if (list_empty(&upper->lower)) {

  			list_add_tail(&upper->lower, &cache->leaves);

  			upper->lowest = 1;
  		}
  	}

  	drop_backref_node(cache, node);
  }

  static void update_backref_node(struct backref_cache *cache,
  				struct backref_node *node, u64 bytenr)
  {
  	struct rb_node *rb_node;
  	rb_erase(&node->rb_node, &cache->rb_root);
  	node->bytenr = bytenr;
  	rb_node = tree_insert(&cache->rb_root, node->bytenr, &node->rb_node);
  	BUG_ON(rb_node);
  }
  
  /*
   * update backref cache after a transaction commit
   */
  static int update_backref_cache(struct btrfs_trans_handle *trans,
  				struct backref_cache *cache)
  {
  	struct backref_node *node;
  	int level = 0;
  
  	if (cache->last_trans == 0) {
  		cache->last_trans = trans->transid;
  		return 0;
  	}
  
  	if (cache->last_trans == trans->transid)
  		return 0;
  
  	/*
  	 * detached nodes are used to avoid unnecessary backref
  	 * lookup. transaction commit changes the extent tree.
  	 * so the detached nodes are no longer useful.
  	 */
  	while (!list_empty(&cache->detached)) {
  		node = list_entry(cache->detached.next,
  				  struct backref_node, list);
  		remove_backref_node(cache, node);
  	}
  
  	while (!list_empty(&cache->changed)) {
  		node = list_entry(cache->changed.next,
  				  struct backref_node, list);
  		list_del_init(&node->list);
  		BUG_ON(node->pending);
  		update_backref_node(cache, node, node->new_bytenr);
  	}
  
  	/*
  	 * some nodes can be left in the pending list if there were
  	 * errors during processing the pending nodes.
  	 */
  	for (level = 0; level < BTRFS_MAX_LEVEL; level++) {
  		list_for_each_entry(node, &cache->pending[level], list) {
  			BUG_ON(!node->pending);
  			if (node->bytenr == node->new_bytenr)
  				continue;
  			update_backref_node(cache, node, node->new_bytenr);
  		}
  	}
  
  	cache->last_trans = 0;
  	return 1;
  }

  static int should_ignore_root(struct btrfs_root *root)
  {
  	struct btrfs_root *reloc_root;
  
  	if (!root->ref_cows)
  		return 0;
  
  	reloc_root = root->reloc_root;
  	if (!reloc_root)
  		return 0;
  
  	if (btrfs_root_last_snapshot(&reloc_root->root_item) ==
  	    root->fs_info->running_transaction->transid - 1)
  		return 0;
  	/*
  	 * if there is reloc tree and it was created in previous
  	 * transaction backref lookup can find the reloc tree,
  	 * so backref node for the fs tree root is useless for
  	 * relocation.
  	 */
  	return 1;
  }

  /*
   * 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 noinline_for_stack
  struct backref_node *build_backref_tree(struct reloc_control *rc,
  					struct btrfs_key *node_key,
  					int level, u64 bytenr)

  {

  	struct backref_cache *cache = &rc->backref_cache;

  	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);

  	LIST_HEAD(useless);
  	int cowonly;

  	int ret;
  	int err = 0;
  
  	path1 = btrfs_alloc_path();
  	path2 = btrfs_alloc_path();
  	if (!path1 || !path2) {
  		err = -ENOMEM;
  		goto out;
  	}

  	path1->reada = 1;
  	path2->reada = 2;

  	node = alloc_backref_node(cache);

  	if (!node) {
  		err = -ENOMEM;
  		goto out;
  	}

  	node->bytenr = bytenr;

  	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 processing

  		 * 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.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);

  				if (key.objectid == key.offset) {

  					root = find_tree_root(rc, eb, ref0);

  					if (root && !should_ignore_root(root))
  						cur->root = root;
  					else
  						list_add(&cur->list, &useless);
  					break;
  				}

  				if (is_cowonly_root(btrfs_ref_root_v0(eb,
  								      ref0)))
  					cur->cowonly = 1;

  			}
  #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 = alloc_backref_edge(cache);

  			if (!edge) {
  				err = -ENOMEM;
  				goto out;
  			}
  			rb_node = tree_search(&cache->rb_root, key.offset);
  			if (!rb_node) {

  				upper = alloc_backref_node(cache);

  				if (!upper) {

  					free_backref_edge(cache, edge);

  					err = -ENOMEM;
  					goto out;
  				}

  				upper->bytenr = key.offset;

  				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);

  				BUG_ON(!upper->checked);

  				INIT_LIST_HEAD(&edge->list[UPPER]);
  			}

  			list_add_tail(&edge->list[LOWER], &cur->upper);

  			edge->node[LOWER] = cur;

  			edge->node[UPPER] = upper;

  
  			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 (!root->ref_cows)
  			cur->cowonly = 1;

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

  			if (should_ignore_root(root))
  				list_add(&cur->list, &useless);
  			else
  				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);

  				if (should_ignore_root(root))
  					list_add(&lower->list, &useless);
  				else
  					lower->root = root;

  				break;
  			}

  			edge = alloc_backref_edge(cache);

  			if (!edge) {
  				err = -ENOMEM;
  				goto out;
  			}
  
  			eb = path2->nodes[level];
  			rb_node = tree_search(&cache->rb_root, eb->start);
  			if (!rb_node) {

  				upper = alloc_backref_node(cache);

  				if (!upper) {

  					free_backref_edge(cache, edge);

  					err = -ENOMEM;
  					goto out;
  				}

  				upper->bytenr = eb->start;
  				upper->owner = btrfs_header_owner(eb);
  				upper->level = lower->level + 1;

  				if (!root->ref_cows)
  					upper->cowonly = 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]);

  				if (!upper->owner)
  					upper->owner = btrfs_header_owner(eb);

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

  			edge->node[LOWER] = lower;

  			edge->node[UPPER] = upper;

  
  			if (rb_node)
  				break;
  			lower = upper;
  			upper = NULL;
  		}

  		btrfs_release_path(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(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);

  	cowonly = node->cowonly;
  	if (!cowonly) {
  		rb_node = tree_insert(&cache->rb_root, node->bytenr,
  				      &node->rb_node);
  		BUG_ON(rb_node);
  		list_add_tail(&node->lower, &cache->leaves);
  	}

  
  	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 (upper->detached) {
  			list_del(&edge->list[LOWER]);
  			lower = edge->node[LOWER];
  			free_backref_edge(cache, edge);
  			if (list_empty(&lower->upper))
  				list_add(&lower->list, &useless);
  			continue;
  		}

  
  		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);

  		BUG_ON(cowonly != upper->cowonly);
  		if (!cowonly) {
  			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);
  	}

  	/*
  	 * process useless backref nodes. backref nodes for tree leaves
  	 * are deleted from the cache. backref nodes for upper level
  	 * tree blocks are left in the cache to avoid unnecessary backref
  	 * lookup.
  	 */
  	while (!list_empty(&useless)) {
  		upper = list_entry(useless.next, struct backref_node, list);
  		list_del_init(&upper->list);
  		BUG_ON(!list_empty(&upper->upper));
  		if (upper == node)
  			node = NULL;
  		if (upper->lowest) {
  			list_del_init(&upper->lower);
  			upper->lowest = 0;
  		}
  		while (!list_empty(&upper->lower)) {
  			edge = list_entry(upper->lower.next,
  					  struct backref_edge, list[UPPER]);
  			list_del(&edge->list[UPPER]);
  			list_del(&edge->list[LOWER]);
  			lower = edge->node[LOWER];
  			free_backref_edge(cache, edge);
  
  			if (list_empty(&lower->upper))
  				list_add(&lower->list, &useless);
  		}
  		__mark_block_processed(rc, upper);
  		if (upper->level > 0) {
  			list_add(&upper->list, &cache->detached);
  			upper->detached = 1;
  		} else {
  			rb_erase(&upper->rb_node, &cache->rb_root);
  			free_backref_node(cache, upper);
  		}
  	}

  out:
  	btrfs_free_path(path1);
  	btrfs_free_path(path2);
  	if (err) {

  		while (!list_empty(&useless)) {
  			lower = list_entry(useless.next,
  					   struct backref_node, upper);
  			list_del_init(&lower->upper);
  		}

  		upper = node;

  		INIT_LIST_HEAD(&list);

  		while (upper) {
  			if (RB_EMPTY_NODE(&upper->rb_node)) {
  				list_splice_tail(&upper->upper, &list);

  				free_backref_node(cache, upper);

  			}
  
  			if (list_empty(&list))
  				break;
  
  			edge = list_entry(list.next, struct backref_edge,
  					  list[LOWER]);

  			list_del(&edge->list[LOWER]);

  			upper = edge->node[UPPER];

  			free_backref_edge(cache, edge);

  		}
  		return ERR_PTR(err);
  	}

  	BUG_ON(node && node->detached);

  	return node;
  }
  
  /*

   * helper to add backref node for the newly created snapshot.
   * the backref node is created by cloning backref node that
   * corresponds to root of source tree
   */
  static int clone_backref_node(struct btrfs_trans_handle *trans,
  			      struct reloc_control *rc,
  			      struct btrfs_root *src,
  			      struct btrfs_root *dest)
  {
  	struct btrfs_root *reloc_root = src->reloc_root;
  	struct backref_cache *cache = &rc->backref_cache;
  	struct backref_node *node = NULL;
  	struct backref_node *new_node;
  	struct backref_edge *edge;
  	struct backref_edge *new_edge;
  	struct rb_node *rb_node;
  
  	if (cache->last_trans > 0)
  		update_backref_cache(trans, cache);
  
  	rb_node = tree_search(&cache->rb_root, src->commit_root->start);
  	if (rb_node) {
  		node = rb_entry(rb_node, struct backref_node, rb_node);
  		if (node->detached)
  			node = NULL;
  		else
  			BUG_ON(node->new_bytenr != reloc_root->node->start);
  	}
  
  	if (!node) {
  		rb_node = tree_search(&cache->rb_root,
  				      reloc_root->commit_root->start);
  		if (rb_node) {
  			node = rb_entry(rb_node, struct backref_node,
  					rb_node);
  			BUG_ON(node->detached);
  		}
  	}
  
  	if (!node)
  		return 0;
  
  	new_node = alloc_backref_node(cache);
  	if (!new_node)
  		return -ENOMEM;
  
  	new_node->bytenr = dest->node->start;
  	new_node->level = node->level;
  	new_node->lowest = node->lowest;

  	new_node->checked = 1;

  	new_node->root = dest;
  
  	if (!node->lowest) {
  		list_for_each_entry(edge, &node->lower, list[UPPER]) {
  			new_edge = alloc_backref_edge(cache);
  			if (!new_edge)
  				goto fail;
  
  			new_edge->node[UPPER] = new_node;
  			new_edge->node[LOWER] = edge->node[LOWER];
  			list_add_tail(&new_edge->list[UPPER],
  				      &new_node->lower);
  		}

  	} else {
  		list_add_tail(&new_node->lower, &cache->leaves);

  	}
  
  	rb_node = tree_insert(&cache->rb_root, new_node->bytenr,
  			      &new_node->rb_node);
  	BUG_ON(rb_node);
  
  	if (!new_node->lowest) {
  		list_for_each_entry(new_edge, &new_node->lower, list[UPPER]) {
  			list_add_tail(&new_edge->list[LOWER],
  				      &new_edge->node[LOWER]->upper);
  		}
  	}
  	return 0;
  fail:
  	while (!list_empty(&new_node->lower)) {
  		new_edge = list_entry(new_node->lower.next,
  				      struct backref_edge, list[UPPER]);
  		list_del(&new_edge->list[UPPER]);
  		free_backref_edge(cache, new_edge);
  	}
  	free_backref_node(cache, new_node);
  	return -ENOMEM;
  }
  
  /*

   * 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;
  }

  static struct btrfs_root *create_reloc_root(struct btrfs_trans_handle *trans,
  					struct btrfs_root *root, u64 objectid)

  {
  	struct btrfs_root *reloc_root;
  	struct extent_buffer *eb;
  	struct btrfs_root_item *root_item;
  	struct btrfs_key root_key;
  	int ret;

  	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 = objectid;

  	if (root->root_key.objectid == objectid) {
  		/* called by btrfs_init_reloc_root */
  		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);
  	} else {
  		/*
  		 * called by btrfs_reloc_post_snapshot_hook.
  		 * the source tree is a reloc tree, all tree blocks
  		 * modified after it was created have RELOC flag
  		 * set in their headers. so it's OK to not update
  		 * the 'last_snapshot'.
  		 */
  		ret = btrfs_copy_root(trans, root, root->node, &eb,
  				      BTRFS_TREE_RELOC_OBJECTID);
  		BUG_ON(ret);
  	}

  	memcpy(root_item, &root->root_item, sizeof(*root_item));

  	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);

  
  	if (root->root_key.objectid == objectid) {
  		btrfs_set_root_refs(root_item, 0);
  		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;

  	return reloc_root;
  }
  
  /*
   * 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 reloc_control *rc = root->fs_info->reloc_ctl;
  	int clear_rsv = 0;
  
  	if (root->reloc_root) {
  		reloc_root = root->reloc_root;
  		reloc_root->last_trans = trans->transid;
  		return 0;
  	}
  
  	if (!rc || !rc->create_reloc_tree ||
  	    root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
  		return 0;
  
  	if (!trans->block_rsv) {
  		trans->block_rsv = rc->block_rsv;
  		clear_rsv = 1;
  	}
  	reloc_root = create_reloc_root(trans, root, root->root_key.objectid);
  	if (clear_rsv)
  		trans->block_rsv = NULL;

  
  	__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)

  		goto out;

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

  	if (root->fs_info->reloc_ctl->merge_reloc_tree &&
  	    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);

  
  out:

  	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 < btrfs_ino(&entry->vfs_inode))

  			node = node->rb_left;

  		else if (objectid > btrfs_ino(&entry->vfs_inode))

  			node = node->rb_right;
  		else
  			break;
  	}
  	if (!node) {
  		while (prev) {
  			entry = rb_entry(prev, struct btrfs_inode, rb_node);

  			if (objectid <= btrfs_ino(&entry->vfs_inode)) {

  				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 = btrfs_ino(&entry->vfs_inode) + 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, btrfs_ino(reloc_inode),

  				       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;
  	}

  	*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 noinline_for_stack
  int replace_file_extents(struct btrfs_trans_handle *trans,
  			 struct reloc_control *rc,
  			 struct btrfs_root *root,
  			 struct extent_buffer *leaf)

  {
  	struct btrfs_key key;
  	struct btrfs_file_extent_item *fi;
  	struct inode *inode = NULL;

  	u64 parent;
  	u64 bytenr;

  	u64 new_bytenr = 0;

  	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 (first) {
  				inode = find_next_inode(root, key.objectid);

  				first = 0;

  			} else if (inode && btrfs_ino(inode) < key.objectid) {

  				btrfs_add_delayed_iput(inode);

  				inode = find_next_inode(root, key.objectid);

  			}

  			if (inode && btrfs_ino(inode) == 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) {
  			WARN_ON(1);

  			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);

  	if (inode)
  		btrfs_add_delayed_iput(inode);

  	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 noinline_for_stack
  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,
  		 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 cow = 0;

  	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);

  
  	last_snapshot = btrfs_root_last_snapshot(&src->root_item);

  again:

  	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;
  	}

  	if (cow) {
  		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) {

  				ret = 0;
  				break;
  			}
  
  			eb = read_tree_block(dest, old_bytenr, blocksize,
  					     old_ptr_gen);

  			BUG_ON(!eb);

  			btrfs_tree_lock(eb);

  			if (cow) {
  				ret = btrfs_cow_block(trans, dest, eb, parent,
  						      slot, &eb);
  				BUG_ON(ret);

  			}

  			btrfs_set_lock_blocking(eb);

  
  			btrfs_tree_unlock(parent);
  			free_extent_buffer(parent);
  
  			parent = eb;
  			continue;
  		}

  		if (!cow) {
  			btrfs_tree_unlock(parent);
  			free_extent_buffer(parent);
  			cow = 1;
  			goto again;
  		}

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

  		btrfs_release_path(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;

  	u64 ino;

  
  	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;

  		ino = btrfs_ino(inode);

  		if (ino > max_key->objectid) {

  			iput(inode);
  			break;
  		}

  		objectid = ino + 1;

  		if (!S_ISREG(inode->i_mode))
  			continue;

  		if (unlikely(min_key->objectid == 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 == 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;

  	unsigned long nr;
  	int level;
  	int max_level;
  	int replaced = 0;
  	int ret;
  	int err = 0;

  	u32 min_reserved;

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

  	path->reada = 1;

  
  	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);
  	}

  	min_reserved = root->nodesize * (BTRFS_MAX_LEVEL - 1) * 2;
  	memset(&next_key, 0, sizeof(next_key));

  	while (1) {
  		trans = btrfs_start_transaction(root, 0);

  		BUG_ON(IS_ERR(trans));

  		trans->block_rsv = rc->block_rsv;

  		ret = btrfs_block_rsv_refill(root, rc->block_rsv, min_reserved);

  		if (ret) {
  			BUG_ON(ret != -EAGAIN);
  			ret = btrfs_commit_transaction(trans, root);
  			BUG_ON(ret);
  			continue;

  		}

  		replaced = 0;

  		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 {

  			ret = replace_path(trans, root, reloc_root, path,
  					   &next_key, 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;

  		}
  
  		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_throttle(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);

  		btrfs_update_reloc_root(trans, root);

  	}
  
  	nr = trans->blocks_used;

  	btrfs_end_transaction_throttle(trans, root);

  
  	btrfs_btree_balance_dirty(root, nr);

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

  static noinline_for_stack
  int prepare_to_merge(struct reloc_control *rc, int err)

  {

  	struct btrfs_root *root = rc->extent_root;

  	struct btrfs_root *reloc_root;

  	struct btrfs_trans_handle *trans;
  	LIST_HEAD(reloc_roots);
  	u64 num_bytes = 0;
  	int ret;

  	mutex_lock(&root->fs_info->reloc_mutex);

  	rc->merging_rsv_size += root->nodesize * (BTRFS_MAX_LEVEL - 1) * 2;
  	rc->merging_rsv_size += rc->nodes_relocated * 2;

  	mutex_unlock(&root->fs_info->reloc_mutex);

  again:
  	if (!err) {
  		num_bytes = rc->merging_rsv_size;

  		ret = btrfs_block_rsv_add(root, rc->block_rsv, num_bytes);

  		if (ret)
  			err = ret;
  	}

  	trans = btrfs_join_transaction(rc->extent_root);

  	if (IS_ERR(trans)) {
  		if (!err)
  			btrfs_block_rsv_release(rc->extent_root,
  						rc->block_rsv, num_bytes);
  		return PTR_ERR(trans);
  	}

  
  	if (!err) {
  		if (num_bytes != rc->merging_rsv_size) {
  			btrfs_end_transaction(trans, rc->extent_root);
  			btrfs_block_rsv_release(rc->extent_root,
  						rc->block_rsv, num_bytes);

  			goto again;
  		}
  	}

  	rc->merge_reloc_tree = 1;
  
  	while (!list_empty(&rc->reloc_roots)) {
  		reloc_root = list_entry(rc->reloc_roots.next,
  					struct btrfs_root, root_list);
  		list_del_init(&reloc_root->root_list);

  		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);

  		/*
  		 * set reference count to 1, so btrfs_recover_relocation
  		 * knows it should resumes merging
  		 */
  		if (!err)
  			btrfs_set_root_refs(&reloc_root->root_item, 1);

  		btrfs_update_reloc_root(trans, root);

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

  	list_splice(&reloc_roots, &rc->reloc_roots);

  	if (!err)
  		btrfs_commit_transaction(trans, rc->extent_root);
  	else
  		btrfs_end_transaction(trans, rc->extent_root);
  	return err;

  }

  static noinline_for_stack
  int merge_reloc_roots(struct reloc_control *rc)

  {

  	struct btrfs_root *root;

  	struct btrfs_root *reloc_root;
  	LIST_HEAD(reloc_roots);
  	int found = 0;
  	int ret;
  again:
  	root = rc->extent_root;

  
  	/*
  	 * this serializes us with btrfs_record_root_in_transaction,
  	 * we have to make sure nobody is in the middle of
  	 * adding their roots to the list while we are
  	 * doing this splice
  	 */
  	mutex_lock(&root->fs_info->reloc_mutex);

  	list_splice_init(&rc->reloc_roots, &reloc_roots);

  	mutex_unlock(&root->fs_info->reloc_mutex);

  	while (!list_empty(&reloc_roots)) {
  		found = 1;
  		reloc_root = list_entry(reloc_roots.next,
  					struct btrfs_root, root_list);

  		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);

  			ret = merge_reloc_root(rc, root);
  			BUG_ON(ret);
  		} else {
  			list_del_init(&reloc_root->root_list);
  		}
  		btrfs_drop_snapshot(reloc_root, rc->block_rsv, 0);

  	}

  	if (found) {
  		found = 0;
  		goto again;
  	}

  	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);
  }

  static noinline_for_stack
  struct btrfs_root *select_reloc_root(struct btrfs_trans_handle *trans,
  				     struct reloc_control *rc,
  				     struct backref_node *node,
  				     struct backref_edge *edges[], int *nr)

  {
  	struct backref_node *next;
  	struct btrfs_root *root;

  	int index = 0;

  	next = node;
  	while (1) {
  		cond_resched();
  		next = walk_up_backref(next, edges, &index);
  		root = next->root;

  		BUG_ON(!root);
  		BUG_ON(!root->ref_cows);

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

  		btrfs_record_root_in_trans(trans, root);
  		root = root->reloc_root;
  
  		if (next->new_bytenr != root->node->start) {
  			BUG_ON(next->new_bytenr);
  			BUG_ON(!list_empty(&next->list));
  			next->new_bytenr = root->node->start;
  			next->root = root;
  			list_add_tail(&next->list,
  				      &rc->backref_cache.changed);
  			__mark_block_processed(rc, next);

  			break;
  		}

  		WARN_ON(1);

  		root = NULL;
  		next = walk_down_backref(edges, &index);
  		if (!next || next->level <= node->level)
  			break;
  	}

  	if (!root)
  		return NULL;

  	*nr = index;
  	next = node;
  	/* setup backref node path for btrfs_reloc_cow_block */
  	while (1) {
  		rc->backref_cache.path[next->level] = next;
  		if (--index < 0)
  			break;
  		next = edges[index]->node[UPPER];

  	}

  	return root;
  }

  /*
   * select a tree root for relocation. return NULL if the block
   * is reference counted. we should use do_relocation() in this
   * case. return a tree root pointer if the block isn't reference
   * counted. return -ENOENT if the block is root of reloc tree.
   */

  static noinline_for_stack
  struct btrfs_root *select_one_root(struct btrfs_trans_handle *trans,
  				   struct backref_node *node)
  {

  	struct backref_node *next;
  	struct btrfs_root *root;
  	struct btrfs_root *fs_root = NULL;

  	struct backref_edge *edges[BTRFS_MAX_LEVEL - 1];

  	int index = 0;
  
  	next = node;
  	while (1) {
  		cond_resched();
  		next = walk_up_backref(next, edges, &index);
  		root = next->root;
  		BUG_ON(!root);

  		/* no other choice for non-references counted tree */

  		if (!root->ref_cows)
  			return root;
  
  		if (root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID)
  			fs_root = root;
  
  		if (next != node)
  			return NULL;
  
  		next = walk_down_backref(edges, &index);
  		if (!next || next->level <= node->level)
  			break;
  	}
  
  	if (!fs_root)
  		return ERR_PTR(-ENOENT);
  	return fs_root;

  }
  
  static noinline_for_stack

  u64 calcu_metadata_size(struct reloc_control *rc,
  			struct backref_node *node, int reserve)

  {

  	struct backref_node *next = node;
  	struct backref_edge *edge;
  	struct backref_edge *edges[BTRFS_MAX_LEVEL - 1];
  	u64 num_bytes = 0;
  	int index = 0;
  
  	BUG_ON(reserve && node->processed);
  
  	while (next) {
  		cond_resched();
  		while (1) {
  			if (next->processed && (reserve || next != node))
  				break;
  
  			num_bytes += btrfs_level_size(rc->extent_root,
  						      next->level);
  
  			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);
  	}
  	return num_bytes;

  }

  static int reserve_metadata_space(struct btrfs_trans_handle *trans,
  				  struct reloc_control *rc,
  				  struct backref_node *node)

  {

  	struct btrfs_root *root = rc->extent_root;
  	u64 num_bytes;
  	int ret;
  
  	num_bytes = calcu_metadata_size(rc, node, 1) * 2;

  	trans->block_rsv = rc->block_rsv;

  	ret = btrfs_block_rsv_add(root, rc->block_rsv, num_bytes);

  	if (ret) {
  		if (ret == -EAGAIN)
  			rc->commit_transaction = 1;
  		return ret;

  	}

  	return 0;
  }
  
  static void release_metadata_space(struct reloc_control *rc,
  				   struct backref_node *node)
  {
  	u64 num_bytes = calcu_metadata_size(rc, node, 0) * 2;
  	btrfs_block_rsv_release(rc->extent_root, rc->block_rsv, num_bytes);

  }
  
  /*
   * 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 reloc_control *rc,

  			 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;

  	rc->backref_cache.path[node->level] = node;

  	list_for_each_entry(edge, &node->upper, list[LOWER]) {
  		cond_resched();

  
  		upper = edge->node[UPPER];

  		root = select_reloc_root(trans, rc, upper, edges, &nr);
  		BUG_ON(!root);
  
  		if (upper->eb && !upper->locked) {
  			if (!lowest) {
  				ret = btrfs_bin_search(upper->eb, key,
  						       upper->level, &slot);
  				BUG_ON(ret);
  				bytenr = btrfs_node_blockptr(upper->eb, slot);
  				if (node->eb->start == bytenr)
  					goto next;
  			}

  			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);

  			if (!upper->eb) {
  				upper->eb = path->nodes[upper->level];
  				path->nodes[upper->level] = NULL;
  			} else {
  				BUG_ON(upper->eb != path->nodes[upper->level]);
  			}

  			upper->locked = 1;
  			path->locks[upper->level] = 0;

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

  			btrfs_release_path(path);

  		} else {
  			ret = btrfs_bin_search(upper->eb, key, upper->level,
  					       &slot);
  			BUG_ON(ret);
  		}
  
  		bytenr = btrfs_node_blockptr(upper->eb, slot);

  		if (lowest) {
  			BUG_ON(bytenr != node->bytenr);

  		} else {

  			if (node->eb->start == bytenr)
  				goto next;

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

  		if (!eb) {
  			err = -EIO;
  			goto next;
  		}

  		btrfs_tree_lock(eb);
  		btrfs_set_lock_blocking(eb);
  
  		if (!node->eb) {
  			ret = btrfs_cow_block(trans, root, eb, upper->eb,
  					      slot, &eb);

  			btrfs_tree_unlock(eb);
  			free_extent_buffer(eb);

  			if (ret < 0) {
  				err = ret;

  				goto next;

  			}

  			BUG_ON(node->eb != eb);

  		} 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);

  		}

  next:
  		if (!upper->pending)
  			drop_node_buffer(upper);
  		else
  			unlock_node_buffer(upper);
  		if (err)
  			break;

  	}

  
  	if (!err && node->pending) {
  		drop_node_buffer(node);
  		list_move_tail(&node->list, &rc->backref_cache.changed);
  		node->pending = 0;
  	}

  	path->lowest_level = 0;

  	BUG_ON(err == -ENOSPC);

  	return err;
  }
  
  static int link_to_upper(struct btrfs_trans_handle *trans,

  			 struct reloc_control *rc,

  			 struct backref_node *node,
  			 struct btrfs_path *path)
  {
  	struct btrfs_key key;

  
  	btrfs_node_key_to_cpu(node->eb, &key, 0);

  	return do_relocation(trans, rc, node, &key, path, 0);

  }
  
  static int finish_pending_nodes(struct btrfs_trans_handle *trans,

  				struct reloc_control *rc,
  				struct btrfs_path *path, int err)

  {

  	LIST_HEAD(list);
  	struct backref_cache *cache = &rc->backref_cache;

  	struct backref_node *node;
  	int level;
  	int ret;

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

  					  struct backref_node, list);
  			list_move_tail(&node->list, &list);
  			BUG_ON(!node->pending);

  			if (!err) {
  				ret = link_to_upper(trans, rc, node, path);
  				if (ret < 0)
  					err = ret;
  			}

  		}

  		list_splice_init(&list, &cache->pending[level]);

  	}

  	return err;
  }
  
  static void mark_block_processed(struct reloc_control *rc,

  				 u64 bytenr, u32 blocksize)
  {
  	set_extent_bits(&rc->processed_blocks, bytenr, bytenr + blocksize - 1,
  			EXTENT_DIRTY, GFP_NOFS);
  }
  
  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);

  		mark_block_processed(rc, node->bytenr, blocksize);

  	}
  	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, NULL))
  		return 1;
  	return 0;

  }
  
  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);

  	BUG_ON(!eb);

  	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 release = 0;
  	int ret = 0;
  
  	if (!node)
  		return 0;

  	BUG_ON(node->processed);

  	root = select_one_root(trans, node);

  	if (root == ERR_PTR(-ENOENT)) {

  		update_processed_blocks(rc, node);

  		goto out;

  	}

  	if (!root || root->ref_cows) {
  		ret = reserve_metadata_space(trans, rc, node);
  		if (ret)

  			goto out;

  		release = 1;

  	}

  	if (root) {
  		if (root->ref_cows) {
  			BUG_ON(node->new_bytenr);
  			BUG_ON(!list_empty(&node->list));
  			btrfs_record_root_in_trans(trans, root);
  			root = root->reloc_root;
  			node->new_bytenr = root->node->start;
  			node->root = root;
  			list_add_tail(&node->list, &rc->backref_cache.changed);
  		} else {
  			path->lowest_level = node->level;
  			ret = btrfs_search_slot(trans, root, key, path, 0, 1);

  			btrfs_release_path(path);

  			if (ret > 0)
  				ret = 0;
  		}
  		if (!ret)
  			update_processed_blocks(rc, node);
  	} else {
  		ret = do_relocation(trans, rc, node, key, path, 1);
  	}

  out:

  	if (ret || node->level == 0 || node->cowonly) {
  		if (release)
  			release_metadata_space(rc, node);
  		remove_backref_node(&rc->backref_cache, 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_node *node;
  	struct btrfs_path *path;
  	struct tree_block *block;
  	struct rb_node *rb_node;

  	int ret;
  	int err = 0;
  
  	path = btrfs_alloc_path();
  	if (!path)
  		return -ENOMEM;

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

  		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, &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) {

  			if (ret != -EAGAIN || rb_node == rb_first(blocks))
  				err = ret;

  			goto out;
  		}

  		rb_node = rb_next(rb_node);
  	}

  out:
  	free_block_list(blocks);

  	err = finish_pending_nodes(trans, rc, path, err);

  	btrfs_free_path(path);
  	return err;
  }
  
  static noinline_for_stack

  int prealloc_file_extent_cluster(struct inode *inode,
  				 struct file_extent_cluster *cluster)
  {
  	u64 alloc_hint = 0;
  	u64 start;
  	u64 end;
  	u64 offset = BTRFS_I(inode)->index_cnt;
  	u64 num_bytes;
  	int nr = 0;
  	int ret = 0;
  
  	BUG_ON(cluster->start != cluster->boundary[0]);
  	mutex_lock(&inode->i_mutex);
  
  	ret = btrfs_check_data_free_space(inode, cluster->end +
  					  1 - cluster->start);
  	if (ret)
  		goto out;
  
  	while (nr < cluster->nr) {
  		start = cluster->boundary[nr] - offset;
  		if (nr + 1 < cluster->nr)
  			end = cluster->boundary[nr + 1] - 1 - offset;
  		else
  			end = cluster->end - offset;
  
  		lock_extent(&BTRFS_I(inode)->io_tree, start, end, GFP_NOFS);
  		num_bytes = end + 1 - start;
  		ret = btrfs_prealloc_file_range(inode, 0, start,
  						num_bytes, num_bytes,
  						end + 1, &alloc_hint);
  		unlock_extent(&BTRFS_I(inode)->io_tree, start, end, GFP_NOFS);
  		if (ret)
  			break;
  		nr++;
  	}
  	btrfs_free_reserved_data_space(inode, cluster->end +
  				       1 - cluster->start);
  out:
  	mutex_unlock(&inode->i_mutex);
  	return ret;
  }
  
  static noinline_for_stack

  int setup_extent_mapping(struct inode *inode, u64 start, u64 end,
  			 u64 block_start)
  {
  	struct btrfs_root *root = BTRFS_I(inode)->root;
  	struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
  	struct extent_map *em;
  	int ret = 0;

  	em = alloc_extent_map();

  	if (!em)
  		return -ENOMEM;
  
  	em->start = start;
  	em->len = end + 1 - start;
  	em->block_len = em->len;
  	em->block_start = block_start;
  	em->bdev = root->fs_info->fs_devices->latest_bdev;
  	set_bit(EXTENT_FLAG_PINNED, &em->flags);
  
  	lock_extent(&BTRFS_I(inode)->io_tree, start, end, GFP_NOFS);
  	while (1) {
  		write_lock(&em_tree->lock);
  		ret = add_extent_mapping(em_tree, em);
  		write_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 ret;
  }
  
  static int relocate_file_extent_cluster(struct inode *inode,
  					struct file_extent_cluster *cluster)

  {
  	u64 page_start;
  	u64 page_end;

  	u64 offset = BTRFS_I(inode)->index_cnt;
  	unsigned long index;

  	unsigned long last_index;

  	struct page *page;
  	struct file_ra_state *ra;

  	gfp_t mask = btrfs_alloc_write_mask(inode->i_mapping);

  	int nr = 0;

  	int ret = 0;

  	if (!cluster->nr)
  		return 0;

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

  	ret = prealloc_file_extent_cluster(inode, cluster);
  	if (ret)
  		goto out;

  	file_ra_state_init(ra, inode->i_mapping);

  	ret = setup_extent_mapping(inode, cluster->start - offset,
  				   cluster->end - offset, cluster->start);

  	if (ret)

  		goto out;

  	index = (cluster->start - offset) >> PAGE_CACHE_SHIFT;
  	last_index = (cluster->end - offset) >> PAGE_CACHE_SHIFT;

  	while (index <= last_index) {

  		mutex_lock(&inode->i_mutex);

  		ret = btrfs_delalloc_reserve_metadata(inode, PAGE_CACHE_SIZE);

  		mutex_unlock(&inode->i_mutex);

  		if (ret)
  			goto out;

  		page = find_lock_page(inode->i_mapping, index);

  		if (!page) {

  			page_cache_sync_readahead(inode->i_mapping,
  						  ra, NULL, index,
  						  last_index + 1 - index);

  			page = find_or_create_page(inode->i_mapping, index,

  						   mask);

  			if (!page) {

  				btrfs_delalloc_release_metadata(inode,
  							PAGE_CACHE_SIZE);

  				ret = -ENOMEM;

  				goto out;

  			}

  		}

  
  		if (PageReadahead(page)) {
  			page_cache_async_readahead(inode->i_mapping,
  						   ra, NULL, page, index,
  						   last_index + 1 - index);
  		}

  		if (!PageUptodate(page)) {
  			btrfs_readpage(NULL, page);
  			lock_page(page);
  			if (!PageUptodate(page)) {
  				unlock_page(page);
  				page_cache_release(page);

  				btrfs_delalloc_release_metadata(inode,
  							PAGE_CACHE_SIZE);

  				ret = -EIO;

  				goto out;

  			}
  		}

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

  
  		lock_extent(&BTRFS_I(inode)->io_tree,
  			    page_start, page_end, GFP_NOFS);

  		set_page_extent_mapped(page);

  		if (nr < cluster->nr &&
  		    page_start + offset == cluster->boundary[nr]) {
  			set_extent_bits(&BTRFS_I(inode)->io_tree,
  					page_start, page_end,

  					EXTENT_BOUNDARY, GFP_NOFS);

  			nr++;
  		}

  		btrfs_set_extent_delalloc(inode, page_start, page_end, NULL);

  		set_page_dirty(page);

  		unlock_extent(&BTRFS_I(inode)->io_tree,
  			      page_start, page_end, GFP_NOFS);

  		unlock_page(page);
  		page_cache_release(page);

  
  		index++;

  		balance_dirty_pages_ratelimited(inode->i_mapping);
  		btrfs_throttle(BTRFS_I(inode)->root);

  	}

  	WARN_ON(nr != cluster->nr);

  out:

  	kfree(ra);

  	return ret;
  }
  
  static noinline_for_stack

  int relocate_data_extent(struct inode *inode, struct btrfs_key *extent_key,
  			 struct file_extent_cluster *cluster)

  {

  	int ret;

  	if (cluster->nr > 0 && extent_key->objectid != cluster->end + 1) {
  		ret = relocate_file_extent_cluster(inode, cluster);
  		if (ret)
  			return ret;
  		cluster->nr = 0;

  	}

  	if (!cluster->nr)
  		cluster->start = extent_key->objectid;
  	else
  		BUG_ON(cluster->nr >= MAX_EXTENTS);
  	cluster->end = extent_key->objectid + extent_key->offset - 1;
  	cluster->boundary[cluster->nr] = extent_key->objectid;
  	cluster->nr++;
  
  	if (cluster->nr >= MAX_EXTENTS) {
  		ret = relocate_file_extent_cluster(inode, cluster);
  		if (ret)
  			return ret;
  		cluster->nr = 0;
  	}
  	return 0;

  }
  
  #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);

  		if (ret < 0)
  			return ret;

  		BUG_ON(ref_owner >= BTRFS_MAX_LEVEL);
  		level = (int)ref_owner;
  		/* FIXME: get real generation */
  		generation = 0;
  #else
  		BUG();
  #endif
  	}

  	btrfs_release_path(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)
  {

  	u64 flags;
  	int ret;
  
  	if (btrfs_header_flag(eb, BTRFS_HEADER_FLAG_RELOC) ||
  	    btrfs_header_backref_rev(eb) < BTRFS_MIXED_BACKREF_REV)
  		return 1;

  	ret = btrfs_lookup_extent_info(NULL, rc->extent_root,
  				       eb->start, eb->len, NULL, &flags);

  	BUG_ON(ret);

  	if (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF)
  		ret = 1;
  	else
  		ret = 0;

  	return ret;
  }

  static int delete_block_group_cache(struct btrfs_fs_info *fs_info,
  				    struct inode *inode, u64 ino)
  {
  	struct btrfs_key key;
  	struct btrfs_path *path;
  	struct btrfs_root *root = fs_info->tree_root;
  	struct btrfs_trans_handle *trans;
  	unsigned long nr;
  	int ret = 0;
  
  	if (inode)
  		goto truncate;
  
  	key.objectid = ino;
  	key.type = BTRFS_INODE_ITEM_KEY;
  	key.offset = 0;
  
  	inode = btrfs_iget(fs_info->sb, &key, root, NULL);

  	if (IS_ERR_OR_NULL(inode) || is_bad_inode(inode)) {

  		if (inode && !IS_ERR(inode))
  			iput(inode);
  		return -ENOENT;
  	}
  
  truncate:
  	path = btrfs_alloc_path();
  	if (!path) {
  		ret = -ENOMEM;
  		goto out;
  	}

  	trans = btrfs_join_transaction(root);

  	if (IS_ERR(trans)) {
  		btrfs_free_path(path);

  		ret = PTR_ERR(trans);

  		goto out;
  	}
  
  	ret = btrfs_truncate_free_space_cache(root, trans, path, inode);
  
  	btrfs_free_path(path);
  	nr = trans->blocks_used;
  	btrfs_end_transaction(trans, root);
  	btrfs_btree_balance_dirty(root, nr);
  out:
  	iput(inode);
  	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;

  	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);

  	/*
  	 * This is an extent belonging to the free space cache, lets just delete
  	 * it and redo the search.
  	 */
  	if (ref_root == BTRFS_ROOT_TREE_OBJECTID) {
  		ret = delete_block_group_cache(rc->extent_root->fs_info,
  					       NULL, ref_objectid);
  		if (ret != -ENOENT)
  			return ret;
  		ret = 0;
  	}
  
  	path = btrfs_alloc_path();
  	if (!path)
  		return -ENOMEM;

  	path->reada = 1;

  	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.type = BTRFS_EXTENT_DATA_KEY;

  	if (ref_offset > ((u64)-1 << 32))
  		key.offset = 0;
  	else
  		key.offset = ref_offset;

  
  	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 = btrfs_level_size(rc->extent_root, 0);

  	int ret;
  	int err = 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(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 *extent_key)

  {
  	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(path);

  			rc->search_start = end + 1;
  		} else {
  			rc->search_start = key.objectid + key.offset;

  			memcpy(extent_key, &key, sizeof(key));

  			return 0;
  		}
  	}

  	btrfs_release_path(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->reloc_mutex);

  	fs_info->reloc_ctl = rc;

  	mutex_unlock(&fs_info->reloc_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->reloc_mutex);

  	fs_info->reloc_ctl = NULL;

  	mutex_unlock(&fs_info->reloc_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 prepare_to_relocate(struct reloc_control *rc)
  {
  	struct btrfs_trans_handle *trans;
  	int ret;
  
  	rc->block_rsv = btrfs_alloc_block_rsv(rc->extent_root);
  	if (!rc->block_rsv)
  		return -ENOMEM;
  
  	/*
  	 * reserve some space for creating reloc trees.
  	 * btrfs_init_reloc_root will use them when there
  	 * is no reservation in transaction handle.
  	 */

  	ret = btrfs_block_rsv_add(rc->extent_root, rc->block_rsv,

  				  rc->extent_root->nodesize * 256);

  	if (ret)
  		return ret;

  	memset(&rc->cluster, 0, sizeof(rc->cluster));
  	rc->search_start = rc->block_group->key.objectid;
  	rc->extents_found = 0;
  	rc->nodes_relocated = 0;
  	rc->merging_rsv_size = 0;

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

  	trans = btrfs_join_transaction(rc->extent_root);

  	BUG_ON(IS_ERR(trans));

  	btrfs_commit_transaction(trans, rc->extent_root);
  	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;

  	int progress = 0;

  
  	path = btrfs_alloc_path();

  	if (!path)

  		return -ENOMEM;

  	path->reada = 1;

  	ret = prepare_to_relocate(rc);
  	if (ret) {
  		err = ret;
  		goto out_free;
  	}

  
  	while (1) {

  		progress++;

  		trans = btrfs_start_transaction(rc->extent_root, 0);

  		BUG_ON(IS_ERR(trans));

  restart:

  		if (update_backref_cache(trans, &rc->backref_cache)) {
  			btrfs_end_transaction(trans, rc->extent_root);
  			continue;
  		}
  
  		ret = find_next_extent(trans, rc, path, &key);

  		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);

  		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(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(path);

  			ret = 0;
  		}
  		if (ret < 0) {

  			err = ret;

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

  				if (ret != -EAGAIN) {
  					err = ret;
  					break;
  				}
  				rc->extents_found--;
  				rc->search_start = key.objectid;
  			}
  		}

  		ret = btrfs_block_rsv_check(rc->extent_root, rc->block_rsv, 5);

  		if (ret < 0) {
  			if (ret != -EAGAIN) {

  				err = ret;

  				WARN_ON(1);

  				break;
  			}

  			rc->commit_transaction = 1;

  		}

  		if (rc->commit_transaction) {
  			rc->commit_transaction = 0;
  			ret = btrfs_commit_transaction(trans, rc->extent_root);
  			BUG_ON(ret);
  		} else {
  			nr = trans->blocks_used;
  			btrfs_end_transaction_throttle(trans, rc->extent_root);
  			btrfs_btree_balance_dirty(rc->extent_root, nr);
  		}

  		trans = NULL;

  
  		if (rc->stage == MOVE_DATA_EXTENTS &&
  		    (flags & BTRFS_EXTENT_FLAG_DATA)) {
  			rc->found_file_extent = 1;

  			ret = relocate_data_extent(rc->data_inode,

  						   &key, &rc->cluster);

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

  	if (trans && progress && err == -ENOSPC) {
  		ret = btrfs_force_chunk_alloc(trans, rc->extent_root,
  					      rc->block_group->flags);
  		if (ret == 0) {
  			err = 0;
  			progress = 0;
  			goto restart;
  		}
  	}

  	btrfs_release_path(path);

  	clear_extent_bits(&rc->processed_blocks, 0, (u64)-1, EXTENT_DIRTY,
  			  GFP_NOFS);

  
  	if (trans) {
  		nr = trans->blocks_used;

  		btrfs_end_transaction_throttle(trans, rc->extent_root);

  		btrfs_btree_balance_dirty(rc->extent_root, nr);
  	}

  	if (!err) {

  		ret = relocate_file_extent_cluster(rc->data_inode,
  						   &rc->cluster);

  		if (ret < 0)
  			err = ret;
  	}

  	rc->create_reloc_tree = 0;
  	set_reloc_control(rc);

  	backref_cache_cleanup(&rc->backref_cache);
  	btrfs_block_rsv_release(rc->extent_root, rc->block_rsv, (u64)-1);

  	err = prepare_to_merge(rc, err);

  
  	merge_reloc_roots(rc);

  	rc->merge_reloc_tree = 0;

  	unset_reloc_control(rc);

  	btrfs_block_rsv_release(rc->extent_root, rc->block_rsv, (u64)-1);

  
  	/* get rid of pinned extents */

  	trans = btrfs_join_transaction(rc->extent_root);

  	if (IS_ERR(trans))
  		err = PTR_ERR(trans);
  	else
  		btrfs_commit_transaction(trans, rc->extent_root);

  out_free:
  	btrfs_free_block_rsv(rc->extent_root, rc->block_rsv);
  	btrfs_free_path(path);

  	return err;
  }
  
  static int __insert_orphan_inode(struct btrfs_trans_handle *trans,

  				 struct btrfs_root *root, u64 objectid)

  {
  	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, 0);

  	btrfs_set_inode_mode(leaf, item, S_IFREG | 0600);

  	btrfs_set_inode_flags(leaf, item, BTRFS_INODE_NOCOMPRESS |
  					  BTRFS_INODE_PREALLOC);

  	btrfs_mark_buffer_dirty(leaf);

  	btrfs_release_path(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 noinline_for_stack
  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, 6);

  	if (IS_ERR(trans))
  		return ERR_CAST(trans);

  	err = btrfs_find_free_objectid(root, &objectid);

  	if (err)
  		goto out;

  	err = __insert_orphan_inode(trans, root, objectid);

  	BUG_ON(err);
  
  	key.objectid = objectid;
  	key.type = BTRFS_INODE_ITEM_KEY;
  	key.offset = 0;

  	inode = btrfs_iget(root->fs_info->sb, &key, root, NULL);

  	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;
  }

  static struct reloc_control *alloc_reloc_control(void)
  {
  	struct reloc_control *rc;
  
  	rc = kzalloc(sizeof(*rc), GFP_NOFS);
  	if (!rc)
  		return NULL;
  
  	INIT_LIST_HEAD(&rc->reloc_roots);
  	backref_cache_init(&rc->backref_cache);
  	mapping_tree_init(&rc->reloc_root_tree);

  	extent_io_tree_init(&rc->processed_blocks, NULL);

  	return rc;
  }

  /*
   * 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;

  	struct inode *inode;
  	struct btrfs_path *path;

  	int ret;

  	int rw = 0;

  	int err = 0;

  	rc = alloc_reloc_control();