/*
   * Copyright (C) 2011 STRATO.  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/vmalloc.h>
  #include "ctree.h"
  #include "disk-io.h"
  #include "backref.h"
  #include "ulist.h"
  #include "transaction.h"
  #include "delayed-ref.h"
  #include "locking.h"
  
  struct extent_inode_elem {
  	u64 inum;
  	u64 offset;
  	struct extent_inode_elem *next;
  };
  
  static int check_extent_in_eb(struct btrfs_key *key, struct extent_buffer *eb,
  				struct btrfs_file_extent_item *fi,
  				u64 extent_item_pos,
  				struct extent_inode_elem **eie)
  {
  	u64 offset = 0;
  	struct extent_inode_elem *e;
  
  	if (!btrfs_file_extent_compression(eb, fi) &&
  	    !btrfs_file_extent_encryption(eb, fi) &&
  	    !btrfs_file_extent_other_encoding(eb, fi)) {
  		u64 data_offset;
  		u64 data_len;
  
  		data_offset = btrfs_file_extent_offset(eb, fi);
  		data_len = btrfs_file_extent_num_bytes(eb, fi);
  
  		if (extent_item_pos < data_offset ||
  		    extent_item_pos >= data_offset + data_len)
  			return 1;
  		offset = extent_item_pos - data_offset;
  	}
  
  	e = kmalloc(sizeof(*e), GFP_NOFS);
  	if (!e)
  		return -ENOMEM;
  
  	e->next = *eie;
  	e->inum = key->objectid;
  	e->offset = key->offset + offset;
  	*eie = e;
  
  	return 0;
  }
  
  static void free_inode_elem_list(struct extent_inode_elem *eie)
  {
  	struct extent_inode_elem *eie_next;
  
  	for (; eie; eie = eie_next) {
  		eie_next = eie->next;
  		kfree(eie);
  	}
  }
  
  static int find_extent_in_eb(struct extent_buffer *eb, u64 wanted_disk_byte,
  				u64 extent_item_pos,
  				struct extent_inode_elem **eie)
  {
  	u64 disk_byte;
  	struct btrfs_key key;
  	struct btrfs_file_extent_item *fi;
  	int slot;
  	int nritems;
  	int extent_type;
  	int ret;
  
  	/*
  	 * from the shared data ref, we only have the leaf but we need
  	 * the key. thus, we must look into all items and see that we
  	 * find one (some) with a reference to our extent item.
  	 */
  	nritems = btrfs_header_nritems(eb);
  	for (slot = 0; slot < nritems; ++slot) {
  		btrfs_item_key_to_cpu(eb, &key, slot);
  		if (key.type != BTRFS_EXTENT_DATA_KEY)
  			continue;
  		fi = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
  		extent_type = btrfs_file_extent_type(eb, fi);
  		if (extent_type == BTRFS_FILE_EXTENT_INLINE)
  			continue;
  		/* don't skip BTRFS_FILE_EXTENT_PREALLOC, we can handle that */
  		disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
  		if (disk_byte != wanted_disk_byte)
  			continue;
  
  		ret = check_extent_in_eb(&key, eb, fi, extent_item_pos, eie);
  		if (ret < 0)
  			return ret;
  	}
  
  	return 0;
  }
  
  /*
   * this structure records all encountered refs on the way up to the root
   */
  struct __prelim_ref {
  	struct list_head list;
  	u64 root_id;
  	struct btrfs_key key_for_search;
  	int level;
  	int count;
  	struct extent_inode_elem *inode_list;
  	u64 parent;
  	u64 wanted_disk_byte;
  };
  
  static struct kmem_cache *btrfs_prelim_ref_cache;
  
  int __init btrfs_prelim_ref_init(void)
  {
  	btrfs_prelim_ref_cache = kmem_cache_create("btrfs_prelim_ref",
  					sizeof(struct __prelim_ref),
  					0,
  					SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD,
  					NULL);
  	if (!btrfs_prelim_ref_cache)
  		return -ENOMEM;
  	return 0;
  }
  
  void btrfs_prelim_ref_exit(void)
  {
  	if (btrfs_prelim_ref_cache)
  		kmem_cache_destroy(btrfs_prelim_ref_cache);
  }
  
  /*
   * the rules for all callers of this function are:
   * - obtaining the parent is the goal
   * - if you add a key, you must know that it is a correct key
   * - if you cannot add the parent or a correct key, then we will look into the
   *   block later to set a correct key
   *
   * delayed refs
   * ============
   *        backref type | shared | indirect | shared | indirect
   * information         |   tree |     tree |   data |     data
   * --------------------+--------+----------+--------+----------
   *      parent logical |    y   |     -    |    -   |     -
   *      key to resolve |    -   |     y    |    y   |     y
   *  tree block logical |    -   |     -    |    -   |     -
   *  root for resolving |    y   |     y    |    y   |     y
   *
   * - column 1:       we've the parent -> done
   * - column 2, 3, 4: we use the key to find the parent
   *
   * on disk refs (inline or keyed)
   * ==============================
   *        backref type | shared | indirect | shared | indirect
   * information         |   tree |     tree |   data |     data
   * --------------------+--------+----------+--------+----------
   *      parent logical |    y   |     -    |    y   |     -
   *      key to resolve |    -   |     -    |    -   |     y
   *  tree block logical |    y   |     y    |    y   |     y
   *  root for resolving |    -   |     y    |    y   |     y
   *
   * - column 1, 3: we've the parent -> done
   * - column 2:    we take the first key from the block to find the parent
   *                (see __add_missing_keys)
   * - column 4:    we use the key to find the parent
   *
   * additional information that's available but not required to find the parent
   * block might help in merging entries to gain some speed.
   */
  
  static int __add_prelim_ref(struct list_head *head, u64 root_id,
  			    struct btrfs_key *key, int level,
  			    u64 parent, u64 wanted_disk_byte, int count,
  			    gfp_t gfp_mask)
  {
  	struct __prelim_ref *ref;
  
  	if (root_id == BTRFS_DATA_RELOC_TREE_OBJECTID)
  		return 0;
  
  	ref = kmem_cache_alloc(btrfs_prelim_ref_cache, gfp_mask);
  	if (!ref)
  		return -ENOMEM;
  
  	ref->root_id = root_id;
  	if (key)
  		ref->key_for_search = *key;
  	else
  		memset(&ref->key_for_search, 0, sizeof(ref->key_for_search));
  
  	ref->inode_list = NULL;
  	ref->level = level;
  	ref->count = count;
  	ref->parent = parent;
  	ref->wanted_disk_byte = wanted_disk_byte;
  	list_add_tail(&ref->list, head);
  
  	return 0;
  }
  
  static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path,
  			   struct ulist *parents, struct __prelim_ref *ref,
  			   int level, u64 time_seq, const u64 *extent_item_pos)
  {
  	int ret = 0;
  	int slot;
  	struct extent_buffer *eb;
  	struct btrfs_key key;
  	struct btrfs_key *key_for_search = &ref->key_for_search;
  	struct btrfs_file_extent_item *fi;
  	struct extent_inode_elem *eie = NULL, *old = NULL;
  	u64 disk_byte;
  	u64 wanted_disk_byte = ref->wanted_disk_byte;
  	u64 count = 0;
  
  	if (level != 0) {
  		eb = path->nodes[level];
  		ret = ulist_add(parents, eb->start, 0, GFP_NOFS);
  		if (ret < 0)
  			return ret;
  		return 0;
  	}
  
  	/*
  	 * We normally enter this function with the path already pointing to
  	 * the first item to check. But sometimes, we may enter it with
  	 * slot==nritems. In that case, go to the next leaf before we continue.
  	 */
  	if (path->slots[0] >= btrfs_header_nritems(path->nodes[0]))
  		ret = btrfs_next_old_leaf(root, path, time_seq);
  
  	while (!ret && count < ref->count) {
  		eb = path->nodes[0];
  		slot = path->slots[0];
  
  		btrfs_item_key_to_cpu(eb, &key, slot);
  
  		if (key.objectid != key_for_search->objectid ||
  		    key.type != BTRFS_EXTENT_DATA_KEY)
  			break;
  
  		fi = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
  		disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
  
  		if (disk_byte == wanted_disk_byte) {
  			eie = NULL;
  			old = NULL;
  			count++;
  			if (extent_item_pos) {
  				ret = check_extent_in_eb(&key, eb, fi,
  						*extent_item_pos,
  						&eie);
  				if (ret < 0)
  					break;
  			}
  			if (ret > 0)
  				goto next;
  			ret = ulist_add_merge_ptr(parents, eb->start,
  						  eie, (void **)&old, GFP_NOFS);
  			if (ret < 0)
  				break;
  			if (!ret && extent_item_pos) {
  				while (old->next)
  					old = old->next;
  				old->next = eie;
  			}
  			eie = NULL;
  		}
  next:
  		ret = btrfs_next_old_item(root, path, time_seq);
  	}
  
  	if (ret > 0)
  		ret = 0;
  	else if (ret < 0)
  		free_inode_elem_list(eie);
  	return ret;
  }
  
  /*
   * resolve an indirect backref in the form (root_id, key, level)
   * to a logical address
   */
  static int __resolve_indirect_ref(struct btrfs_fs_info *fs_info,
  				  struct btrfs_path *path, u64 time_seq,
  				  struct __prelim_ref *ref,
  				  struct ulist *parents,
  				  const u64 *extent_item_pos)
  {
  	struct btrfs_root *root;
  	struct btrfs_key root_key;
  	struct extent_buffer *eb;
  	int ret = 0;
  	int root_level;
  	int level = ref->level;
  	int index;
  
  	root_key.objectid = ref->root_id;
  	root_key.type = BTRFS_ROOT_ITEM_KEY;
  	root_key.offset = (u64)-1;
  
  	index = srcu_read_lock(&fs_info->subvol_srcu);
  
  	root = btrfs_read_fs_root_no_name(fs_info, &root_key);
  	if (IS_ERR(root)) {
  		srcu_read_unlock(&fs_info->subvol_srcu, index);
  		ret = PTR_ERR(root);
  		goto out;
  	}
  
  	root_level = btrfs_old_root_level(root, time_seq);
  
  	if (root_level + 1 == level) {
  		srcu_read_unlock(&fs_info->subvol_srcu, index);
  		goto out;
  	}
  
  	path->lowest_level = level;
  	ret = btrfs_search_old_slot(root, &ref->key_for_search, path, time_seq);
  
  	/* root node has been locked, we can release @subvol_srcu safely here */
  	srcu_read_unlock(&fs_info->subvol_srcu, index);
  
  	pr_debug("search slot in root %llu (level %d, ref count %d) returned "
  		 "%d for key (%llu %u %llu)
  ",
  		 ref->root_id, level, ref->count, ret,
  		 ref->key_for_search.objectid, ref->key_for_search.type,
  		 ref->key_for_search.offset);
  	if (ret < 0)
  		goto out;
  
  	eb = path->nodes[level];
  	while (!eb) {
  		if (WARN_ON(!level)) {
  			ret = 1;
  			goto out;
  		}
  		level--;
  		eb = path->nodes[level];
  	}
  
  	ret = add_all_parents(root, path, parents, ref, level, time_seq,
  			      extent_item_pos);
  out:
  	path->lowest_level = 0;
  	btrfs_release_path(path);
  	return ret;
  }
  
  /*
   * resolve all indirect backrefs from the list
   */
  static int __resolve_indirect_refs(struct btrfs_fs_info *fs_info,
  				   struct btrfs_path *path, u64 time_seq,
  				   struct list_head *head,
  				   const u64 *extent_item_pos)
  {
  	int err;
  	int ret = 0;
  	struct __prelim_ref *ref;
  	struct __prelim_ref *ref_safe;
  	struct __prelim_ref *new_ref;
  	struct ulist *parents;
  	struct ulist_node *node;
  	struct ulist_iterator uiter;
  
  	parents = ulist_alloc(GFP_NOFS);
  	if (!parents)
  		return -ENOMEM;
  
  	/*
  	 * _safe allows us to insert directly after the current item without
  	 * iterating over the newly inserted items.
  	 * we're also allowed to re-assign ref during iteration.
  	 */
  	list_for_each_entry_safe(ref, ref_safe, head, list) {
  		if (ref->parent)	/* already direct */
  			continue;
  		if (ref->count == 0)
  			continue;
  		err = __resolve_indirect_ref(fs_info, path, time_seq, ref,
  					     parents, extent_item_pos);
  		/*
  		 * we can only tolerate ENOENT,otherwise,we should catch error
  		 * and return directly.
  		 */
  		if (err == -ENOENT) {
  			continue;
  		} else if (err) {
  			ret = err;
  			goto out;
  		}
  
  		/* we put the first parent into the ref at hand */
  		ULIST_ITER_INIT(&uiter);
  		node = ulist_next(parents, &uiter);
  		ref->parent = node ? node->val : 0;
  		ref->inode_list = node ?
  			(struct extent_inode_elem *)(uintptr_t)node->aux : NULL;
  
  		/* additional parents require new refs being added here */
  		while ((node = ulist_next(parents, &uiter))) {
  			new_ref = kmem_cache_alloc(btrfs_prelim_ref_cache,
  						   GFP_NOFS);
  			if (!new_ref) {
  				ret = -ENOMEM;
  				goto out;
  			}
  			memcpy(new_ref, ref, sizeof(*ref));
  			new_ref->parent = node->val;
  			new_ref->inode_list = (struct extent_inode_elem *)
  							(uintptr_t)node->aux;
  			list_add(&new_ref->list, &ref->list);
  		}
  		ulist_reinit(parents);
  	}
  out:
  	ulist_free(parents);
  	return ret;
  }
  
  static inline int ref_for_same_block(struct __prelim_ref *ref1,
  				     struct __prelim_ref *ref2)
  {
  	if (ref1->level != ref2->level)
  		return 0;
  	if (ref1->root_id != ref2->root_id)
  		return 0;
  	if (ref1->key_for_search.type != ref2->key_for_search.type)
  		return 0;
  	if (ref1->key_for_search.objectid != ref2->key_for_search.objectid)
  		return 0;
  	if (ref1->key_for_search.offset != ref2->key_for_search.offset)
  		return 0;
  	if (ref1->parent != ref2->parent)
  		return 0;
  
  	return 1;
  }
  
  /*
   * read tree blocks and add keys where required.
   */
  static int __add_missing_keys(struct btrfs_fs_info *fs_info,
  			      struct list_head *head)
  {
  	struct list_head *pos;
  	struct extent_buffer *eb;
  
  	list_for_each(pos, head) {
  		struct __prelim_ref *ref;
  		ref = list_entry(pos, struct __prelim_ref, list);
  
  		if (ref->parent)
  			continue;
  		if (ref->key_for_search.type)
  			continue;
  		BUG_ON(!ref->wanted_disk_byte);
  		eb = read_tree_block(fs_info->tree_root, ref->wanted_disk_byte,
  				     fs_info->tree_root->leafsize, 0);
  		if (!eb || !extent_buffer_uptodate(eb)) {
  			free_extent_buffer(eb);
  			return -EIO;
  		}
  		btrfs_tree_read_lock(eb);
  		if (btrfs_header_level(eb) == 0)
  			btrfs_item_key_to_cpu(eb, &ref->key_for_search, 0);
  		else
  			btrfs_node_key_to_cpu(eb, &ref->key_for_search, 0);
  		btrfs_tree_read_unlock(eb);
  		free_extent_buffer(eb);
  	}
  	return 0;
  }
  
  /*
   * merge two lists of backrefs and adjust counts accordingly
   *
   * mode = 1: merge identical keys, if key is set
   *    FIXME: if we add more keys in __add_prelim_ref, we can merge more here.
   *           additionally, we could even add a key range for the blocks we
   *           looked into to merge even more (-> replace unresolved refs by those
   *           having a parent).
   * mode = 2: merge identical parents
   */
  static void __merge_refs(struct list_head *head, int mode)
  {
  	struct list_head *pos1;
  
  	list_for_each(pos1, head) {
  		struct list_head *n2;
  		struct list_head *pos2;
  		struct __prelim_ref *ref1;
  
  		ref1 = list_entry(pos1, struct __prelim_ref, list);
  
  		for (pos2 = pos1->next, n2 = pos2->next; pos2 != head;
  		     pos2 = n2, n2 = pos2->next) {
  			struct __prelim_ref *ref2;
  			struct __prelim_ref *xchg;
  			struct extent_inode_elem *eie;
  
  			ref2 = list_entry(pos2, struct __prelim_ref, list);
  
  			if (mode == 1) {
  				if (!ref_for_same_block(ref1, ref2))
  					continue;
  				if (!ref1->parent && ref2->parent) {
  					xchg = ref1;
  					ref1 = ref2;
  					ref2 = xchg;
  				}
  			} else {
  				if (ref1->parent != ref2->parent)
  					continue;
  			}
  
  			eie = ref1->inode_list;
  			while (eie && eie->next)
  				eie = eie->next;
  			if (eie)
  				eie->next = ref2->inode_list;
  			else
  				ref1->inode_list = ref2->inode_list;
  			ref1->count += ref2->count;
  
  			list_del(&ref2->list);
  			kmem_cache_free(btrfs_prelim_ref_cache, ref2);
  		}
  
  	}
  }
  
  /*
   * add all currently queued delayed refs from this head whose seq nr is
   * smaller or equal that seq to the list
   */
  static int __add_delayed_refs(struct btrfs_delayed_ref_head *head, u64 seq,
  			      struct list_head *prefs)
  {
  	struct btrfs_delayed_extent_op *extent_op = head->extent_op;
  	struct rb_node *n = &head->node.rb_node;
  	struct btrfs_key key;
  	struct btrfs_key op_key = {0};
  	int sgn;
  	int ret = 0;
  
  	if (extent_op && extent_op->update_key)
  		btrfs_disk_key_to_cpu(&op_key, &extent_op->key);
  
  	spin_lock(&head->lock);
  	n = rb_first(&head->ref_root);
  	while (n) {
  		struct btrfs_delayed_ref_node *node;
  		node = rb_entry(n, struct btrfs_delayed_ref_node,
  				rb_node);
  		n = rb_next(n);
  		if (node->seq > seq)
  			continue;
  
  		switch (node->action) {
  		case BTRFS_ADD_DELAYED_EXTENT:
  		case BTRFS_UPDATE_DELAYED_HEAD:
  			WARN_ON(1);
  			continue;
  		case BTRFS_ADD_DELAYED_REF:
  			sgn = 1;
  			break;
  		case BTRFS_DROP_DELAYED_REF:
  			sgn = -1;
  			break;
  		default:
  			BUG_ON(1);
  		}
  		switch (node->type) {
  		case BTRFS_TREE_BLOCK_REF_KEY: {
  			struct btrfs_delayed_tree_ref *ref;
  
  			ref = btrfs_delayed_node_to_tree_ref(node);
  			ret = __add_prelim_ref(prefs, ref->root, &op_key,
  					       ref->level + 1, 0, node->bytenr,
  					       node->ref_mod * sgn, GFP_ATOMIC);
  			break;
  		}
  		case BTRFS_SHARED_BLOCK_REF_KEY: {
  			struct btrfs_delayed_tree_ref *ref;
  
  			ref = btrfs_delayed_node_to_tree_ref(node);
  			ret = __add_prelim_ref(prefs, ref->root, NULL,
  					       ref->level + 1, ref->parent,
  					       node->bytenr,
  					       node->ref_mod * sgn, GFP_ATOMIC);
  			break;
  		}
  		case BTRFS_EXTENT_DATA_REF_KEY: {
  			struct btrfs_delayed_data_ref *ref;
  			ref = btrfs_delayed_node_to_data_ref(node);
  
  			key.objectid = ref->objectid;
  			key.type = BTRFS_EXTENT_DATA_KEY;
  			key.offset = ref->offset;
  			ret = __add_prelim_ref(prefs, ref->root, &key, 0, 0,
  					       node->bytenr,
  					       node->ref_mod * sgn, GFP_ATOMIC);
  			break;
  		}
  		case BTRFS_SHARED_DATA_REF_KEY: {
  			struct btrfs_delayed_data_ref *ref;
  
  			ref = btrfs_delayed_node_to_data_ref(node);
  
  			key.objectid = ref->objectid;
  			key.type = BTRFS_EXTENT_DATA_KEY;
  			key.offset = ref->offset;
  			ret = __add_prelim_ref(prefs, ref->root, &key, 0,
  					       ref->parent, node->bytenr,
  					       node->ref_mod * sgn, GFP_ATOMIC);
  			break;
  		}
  		default:
  			WARN_ON(1);
  		}
  		if (ret)
  			break;
  	}
  	spin_unlock(&head->lock);
  	return ret;
  }
  
  /*
   * add all inline backrefs for bytenr to the list
   */
  static int __add_inline_refs(struct btrfs_fs_info *fs_info,
  			     struct btrfs_path *path, u64 bytenr,
  			     int *info_level, struct list_head *prefs)
  {
  	int ret = 0;
  	int slot;
  	struct extent_buffer *leaf;
  	struct btrfs_key key;
  	struct btrfs_key found_key;
  	unsigned long ptr;
  	unsigned long end;
  	struct btrfs_extent_item *ei;
  	u64 flags;
  	u64 item_size;
  
  	/*
  	 * enumerate all inline refs
  	 */
  	leaf = path->nodes[0];
  	slot = path->slots[0];
  
  	item_size = btrfs_item_size_nr(leaf, slot);
  	BUG_ON(item_size < sizeof(*ei));
  
  	ei = btrfs_item_ptr(leaf, slot, struct btrfs_extent_item);
  	flags = btrfs_extent_flags(leaf, ei);
  	btrfs_item_key_to_cpu(leaf, &found_key, slot);
  
  	ptr = (unsigned long)(ei + 1);
  	end = (unsigned long)ei + item_size;
  
  	if (found_key.type == BTRFS_EXTENT_ITEM_KEY &&
  	    flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
  		struct btrfs_tree_block_info *info;
  
  		info = (struct btrfs_tree_block_info *)ptr;
  		*info_level = btrfs_tree_block_level(leaf, info);
  		ptr += sizeof(struct btrfs_tree_block_info);
  		BUG_ON(ptr > end);
  	} else if (found_key.type == BTRFS_METADATA_ITEM_KEY) {
  		*info_level = found_key.offset;
  	} else {
  		BUG_ON(!(flags & BTRFS_EXTENT_FLAG_DATA));
  	}
  
  	while (ptr < end) {
  		struct btrfs_extent_inline_ref *iref;
  		u64 offset;
  		int type;
  
  		iref = (struct btrfs_extent_inline_ref *)ptr;
  		type = btrfs_extent_inline_ref_type(leaf, iref);
  		offset = btrfs_extent_inline_ref_offset(leaf, iref);
  
  		switch (type) {
  		case BTRFS_SHARED_BLOCK_REF_KEY:
  			ret = __add_prelim_ref(prefs, 0, NULL,
  						*info_level + 1, offset,
  						bytenr, 1, GFP_NOFS);
  			break;
  		case BTRFS_SHARED_DATA_REF_KEY: {
  			struct btrfs_shared_data_ref *sdref;
  			int count;
  
  			sdref = (struct btrfs_shared_data_ref *)(iref + 1);
  			count = btrfs_shared_data_ref_count(leaf, sdref);
  			ret = __add_prelim_ref(prefs, 0, NULL, 0, offset,
  					       bytenr, count, GFP_NOFS);
  			break;
  		}
  		case BTRFS_TREE_BLOCK_REF_KEY:
  			ret = __add_prelim_ref(prefs, offset, NULL,
  					       *info_level + 1, 0,
  					       bytenr, 1, GFP_NOFS);
  			break;
  		case BTRFS_EXTENT_DATA_REF_KEY: {
  			struct btrfs_extent_data_ref *dref;
  			int count;
  			u64 root;
  
  			dref = (struct btrfs_extent_data_ref *)(&iref->offset);
  			count = btrfs_extent_data_ref_count(leaf, dref);
  			key.objectid = btrfs_extent_data_ref_objectid(leaf,
  								      dref);
  			key.type = BTRFS_EXTENT_DATA_KEY;
  			key.offset = btrfs_extent_data_ref_offset(leaf, dref);
  			root = btrfs_extent_data_ref_root(leaf, dref);
  			ret = __add_prelim_ref(prefs, root, &key, 0, 0,
  					       bytenr, count, GFP_NOFS);
  			break;
  		}
  		default:
  			WARN_ON(1);
  		}
  		if (ret)
  			return ret;
  		ptr += btrfs_extent_inline_ref_size(type);
  	}
  
  	return 0;
  }
  
  /*
   * add all non-inline backrefs for bytenr to the list
   */
  static int __add_keyed_refs(struct btrfs_fs_info *fs_info,
  			    struct btrfs_path *path, u64 bytenr,
  			    int info_level, struct list_head *prefs)
  {
  	struct btrfs_root *extent_root = fs_info->extent_root;
  	int ret;
  	int slot;
  	struct extent_buffer *leaf;
  	struct btrfs_key key;
  
  	while (1) {
  		ret = btrfs_next_item(extent_root, path);
  		if (ret < 0)
  			break;
  		if (ret) {
  			ret = 0;
  			break;
  		}
  
  		slot = path->slots[0];
  		leaf = path->nodes[0];
  		btrfs_item_key_to_cpu(leaf, &key, slot);
  
  		if (key.objectid != bytenr)
  			break;
  		if (key.type < BTRFS_TREE_BLOCK_REF_KEY)
  			continue;
  		if (key.type > BTRFS_SHARED_DATA_REF_KEY)
  			break;
  
  		switch (key.type) {
  		case BTRFS_SHARED_BLOCK_REF_KEY:
  			ret = __add_prelim_ref(prefs, 0, NULL,
  						info_level + 1, key.offset,
  						bytenr, 1, GFP_NOFS);
  			break;
  		case BTRFS_SHARED_DATA_REF_KEY: {
  			struct btrfs_shared_data_ref *sdref;
  			int count;
  
  			sdref = btrfs_item_ptr(leaf, slot,
  					      struct btrfs_shared_data_ref);
  			count = btrfs_shared_data_ref_count(leaf, sdref);
  			ret = __add_prelim_ref(prefs, 0, NULL, 0, key.offset,
  						bytenr, count, GFP_NOFS);
  			break;
  		}
  		case BTRFS_TREE_BLOCK_REF_KEY:
  			ret = __add_prelim_ref(prefs, key.offset, NULL,
  					       info_level + 1, 0,
  					       bytenr, 1, GFP_NOFS);
  			break;
  		case BTRFS_EXTENT_DATA_REF_KEY: {
  			struct btrfs_extent_data_ref *dref;
  			int count;
  			u64 root;
  
  			dref = btrfs_item_ptr(leaf, slot,
  					      struct btrfs_extent_data_ref);
  			count = btrfs_extent_data_ref_count(leaf, dref);
  			key.objectid = btrfs_extent_data_ref_objectid(leaf,
  								      dref);
  			key.type = BTRFS_EXTENT_DATA_KEY;
  			key.offset = btrfs_extent_data_ref_offset(leaf, dref);
  			root = btrfs_extent_data_ref_root(leaf, dref);
  			ret = __add_prelim_ref(prefs, root, &key, 0, 0,
  					       bytenr, count, GFP_NOFS);
  			break;
  		}
  		default:
  			WARN_ON(1);
  		}
  		if (ret)
  			return ret;
  
  	}
  
  	return ret;
  }
  
  /*
   * this adds all existing backrefs (inline backrefs, backrefs and delayed
   * refs) for the given bytenr to the refs list, merges duplicates and resolves
   * indirect refs to their parent bytenr.
   * When roots are found, they're added to the roots list
   *
   * FIXME some caching might speed things up
   */
  static int find_parent_nodes(struct btrfs_trans_handle *trans,
  			     struct btrfs_fs_info *fs_info, u64 bytenr,
  			     u64 time_seq, struct ulist *refs,
  			     struct ulist *roots, const u64 *extent_item_pos)
  {
  	struct btrfs_key key;
  	struct btrfs_path *path;
  	struct btrfs_delayed_ref_root *delayed_refs = NULL;
  	struct btrfs_delayed_ref_head *head;
  	int info_level = 0;
  	int ret;
  	struct list_head prefs_delayed;
  	struct list_head prefs;
  	struct __prelim_ref *ref;
  	struct extent_inode_elem *eie = NULL;
  
  	INIT_LIST_HEAD(&prefs);
  	INIT_LIST_HEAD(&prefs_delayed);
  
  	key.objectid = bytenr;
  	key.offset = (u64)-1;
  	if (btrfs_fs_incompat(fs_info, SKINNY_METADATA))
  		key.type = BTRFS_METADATA_ITEM_KEY;
  	else
  		key.type = BTRFS_EXTENT_ITEM_KEY;
  
  	path = btrfs_alloc_path();
  	if (!path)
  		return -ENOMEM;
  	if (!trans)
  		path->search_commit_root = 1;
  
  	/*
  	 * grab both a lock on the path and a lock on the delayed ref head.
  	 * We need both to get a consistent picture of how the refs look
  	 * at a specified point in time
  	 */
  again:
  	head = NULL;
  
  	ret = btrfs_search_slot(trans, fs_info->extent_root, &key, path, 0, 0);
  	if (ret < 0)
  		goto out;
  	BUG_ON(ret == 0);
  
  	if (trans) {
  		/*
  		 * look if there are updates for this ref queued and lock the
  		 * head
  		 */
  		delayed_refs = &trans->transaction->delayed_refs;
  		spin_lock(&delayed_refs->lock);
  		head = btrfs_find_delayed_ref_head(trans, bytenr);
  		if (head) {
  			if (!mutex_trylock(&head->mutex)) {
  				atomic_inc(&head->node.refs);
  				spin_unlock(&delayed_refs->lock);
  
  				btrfs_release_path(path);
  
  				/*
  				 * Mutex was contended, block until it's
  				 * released and try again
  				 */
  				mutex_lock(&head->mutex);
  				mutex_unlock(&head->mutex);
  				btrfs_put_delayed_ref(&head->node);
  				goto again;
  			}
  			spin_unlock(&delayed_refs->lock);
  			ret = __add_delayed_refs(head, time_seq,
  						 &prefs_delayed);
  			mutex_unlock(&head->mutex);
  			if (ret)
  				goto out;
  		} else {
  			spin_unlock(&delayed_refs->lock);
  		}
  	}
  
  	if (path->slots[0]) {
  		struct extent_buffer *leaf;
  		int slot;
  
  		path->slots[0]--;
  		leaf = path->nodes[0];
  		slot = path->slots[0];
  		btrfs_item_key_to_cpu(leaf, &key, slot);
  		if (key.objectid == bytenr &&
  		    (key.type == BTRFS_EXTENT_ITEM_KEY ||
  		     key.type == BTRFS_METADATA_ITEM_KEY)) {
  			ret = __add_inline_refs(fs_info, path, bytenr,
  						&info_level, &prefs);
  			if (ret)
  				goto out;
  			ret = __add_keyed_refs(fs_info, path, bytenr,
  					       info_level, &prefs);
  			if (ret)
  				goto out;
  		}
  	}
  	btrfs_release_path(path);
  
  	list_splice_init(&prefs_delayed, &prefs);
  
  	ret = __add_missing_keys(fs_info, &prefs);
  	if (ret)
  		goto out;
  
  	__merge_refs(&prefs, 1);
  
  	ret = __resolve_indirect_refs(fs_info, path, time_seq, &prefs,
  				      extent_item_pos);
  	if (ret)
  		goto out;
  
  	__merge_refs(&prefs, 2);
  
  	while (!list_empty(&prefs)) {
  		ref = list_first_entry(&prefs, struct __prelim_ref, list);
  		WARN_ON(ref->count < 0);
  		if (ref->count && ref->root_id && ref->parent == 0) {
  			/* no parent == root of tree */
  			ret = ulist_add(roots, ref->root_id, 0, GFP_NOFS);
  			if (ret < 0)
  				goto out;
  		}
  		if (ref->count && ref->parent) {
  			if (extent_item_pos && !ref->inode_list &&
  			    ref->level == 0) {
  				u32 bsz;
  				struct extent_buffer *eb;
  				bsz = btrfs_level_size(fs_info->extent_root,
  							ref->level);
  				eb = read_tree_block(fs_info->extent_root,
  							   ref->parent, bsz, 0);
  				if (!eb || !extent_buffer_uptodate(eb)) {
  					free_extent_buffer(eb);
  					ret = -EIO;
  					goto out;
  				}
  				btrfs_tree_read_lock(eb);
  				btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
  				ret = find_extent_in_eb(eb, bytenr,
  							*extent_item_pos, &eie);
  				btrfs_tree_read_unlock_blocking(eb);
  				free_extent_buffer(eb);
  				if (ret < 0)
  					goto out;
  				ref->inode_list = eie;
  			}
  			ret = ulist_add_merge_ptr(refs, ref->parent,
  						  ref->inode_list,
  						  (void **)&eie, GFP_NOFS);
  			if (ret < 0)
  				goto out;
  			if (!ret && extent_item_pos) {
  				/*
  				 * we've recorded that parent, so we must extend
  				 * its inode list here
  				 */
  				BUG_ON(!eie);
  				while (eie->next)
  					eie = eie->next;
  				eie->next = ref->inode_list;
  			}
  			eie = NULL;
  		}
  		list_del(&ref->list);
  		kmem_cache_free(btrfs_prelim_ref_cache, ref);
  	}
  
  out:
  	btrfs_free_path(path);
  	while (!list_empty(&prefs)) {
  		ref = list_first_entry(&prefs, struct __prelim_ref, list);
  		list_del(&ref->list);
  		kmem_cache_free(btrfs_prelim_ref_cache, ref);
  	}
  	while (!list_empty(&prefs_delayed)) {
  		ref = list_first_entry(&prefs_delayed, struct __prelim_ref,
  				       list);
  		list_del(&ref->list);
  		kmem_cache_free(btrfs_prelim_ref_cache, ref);
  	}
  	if (ret < 0)
  		free_inode_elem_list(eie);
  	return ret;
  }
  
  static void free_leaf_list(struct ulist *blocks)
  {
  	struct ulist_node *node = NULL;
  	struct extent_inode_elem *eie;
  	struct ulist_iterator uiter;
  
  	ULIST_ITER_INIT(&uiter);
  	while ((node = ulist_next(blocks, &uiter))) {
  		if (!node->aux)
  			continue;
  		eie = (struct extent_inode_elem *)(uintptr_t)node->aux;
  		free_inode_elem_list(eie);
  		node->aux = 0;
  	}
  
  	ulist_free(blocks);
  }
  
  /*
   * Finds all leafs with a reference to the specified combination of bytenr and
   * offset. key_list_head will point to a list of corresponding keys (caller must
   * free each list element). The leafs will be stored in the leafs ulist, which
   * must be freed with ulist_free.
   *
   * returns 0 on success, <0 on error
   */
  static int btrfs_find_all_leafs(struct btrfs_trans_handle *trans,
  				struct btrfs_fs_info *fs_info, u64 bytenr,
  				u64 time_seq, struct ulist **leafs,
  				const u64 *extent_item_pos)
  {
  	struct ulist *tmp;
  	int ret;
  
  	tmp = ulist_alloc(GFP_NOFS);
  	if (!tmp)
  		return -ENOMEM;
  	*leafs = ulist_alloc(GFP_NOFS);
  	if (!*leafs) {
  		ulist_free(tmp);
  		return -ENOMEM;
  	}
  
  	ret = find_parent_nodes(trans, fs_info, bytenr,
  				time_seq, *leafs, tmp, extent_item_pos);
  	ulist_free(tmp);
  
  	if (ret < 0 && ret != -ENOENT) {
  		free_leaf_list(*leafs);
  		return ret;
  	}
  
  	return 0;
  }
  
  /*
   * walk all backrefs for a given extent to find all roots that reference this
   * extent. Walking a backref means finding all extents that reference this
   * extent and in turn walk the backrefs of those, too. Naturally this is a
   * recursive process, but here it is implemented in an iterative fashion: We
   * find all referencing extents for the extent in question and put them on a
   * list. In turn, we find all referencing extents for those, further appending
   * to the list. The way we iterate the list allows adding more elements after
   * the current while iterating. The process stops when we reach the end of the
   * list. Found roots are added to the roots list.
   *
   * returns 0 on success, < 0 on error.
   */
  int btrfs_find_all_roots(struct btrfs_trans_handle *trans,
  				struct btrfs_fs_info *fs_info, u64 bytenr,
  				u64 time_seq, struct ulist **roots)
  {
  	struct ulist *tmp;
  	struct ulist_node *node = NULL;
  	struct ulist_iterator uiter;
  	int ret;
  
  	tmp = ulist_alloc(GFP_NOFS);
  	if (!tmp)
  		return -ENOMEM;
  	*roots = ulist_alloc(GFP_NOFS);
  	if (!*roots) {
  		ulist_free(tmp);
  		return -ENOMEM;
  	}
  
  	ULIST_ITER_INIT(&uiter);
  	while (1) {
  		ret = find_parent_nodes(trans, fs_info, bytenr,
  					time_seq, tmp, *roots, NULL);
  		if (ret < 0 && ret != -ENOENT) {
  			ulist_free(tmp);
  			ulist_free(*roots);
  			return ret;
  		}
  		node = ulist_next(tmp, &uiter);
  		if (!node)
  			break;
  		bytenr = node->val;
  		cond_resched();
  	}
  
  	ulist_free(tmp);
  	return 0;
  }
  
  /*
   * this makes the path point to (inum INODE_ITEM ioff)
   */
  int inode_item_info(u64 inum, u64 ioff, struct btrfs_root *fs_root,
  			struct btrfs_path *path)
  {
  	struct btrfs_key key;
  	return btrfs_find_item(fs_root, path, inum, ioff,
  			BTRFS_INODE_ITEM_KEY, &key);
  }
  
  static int inode_ref_info(u64 inum, u64 ioff, struct btrfs_root *fs_root,
  				struct btrfs_path *path,
  				struct btrfs_key *found_key)
  {
  	return btrfs_find_item(fs_root, path, inum, ioff,
  			BTRFS_INODE_REF_KEY, found_key);
  }
  
  int btrfs_find_one_extref(struct btrfs_root *root, u64 inode_objectid,
  			  u64 start_off, struct btrfs_path *path,
  			  struct btrfs_inode_extref **ret_extref,
  			  u64 *found_off)
  {
  	int ret, slot;
  	struct btrfs_key key;
  	struct btrfs_key found_key;
  	struct btrfs_inode_extref *extref;
  	struct extent_buffer *leaf;
  	unsigned long ptr;
  
  	key.objectid = inode_objectid;
  	btrfs_set_key_type(&key, BTRFS_INODE_EXTREF_KEY);
  	key.offset = start_off;
  
  	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
  	if (ret < 0)
  		return ret;
  
  	while (1) {
  		leaf = path->nodes[0];
  		slot = path->slots[0];
  		if (slot >= btrfs_header_nritems(leaf)) {
  			/*
  			 * If the item at offset is not found,
  			 * btrfs_search_slot will point us to the slot
  			 * where it should be inserted. In our case
  			 * that will be the slot directly before the
  			 * next INODE_REF_KEY_V2 item. In the case
  			 * that we're pointing to the last slot in a
  			 * leaf, we must move one leaf over.
  			 */
  			ret = btrfs_next_leaf(root, path);
  			if (ret) {
  				if (ret >= 1)
  					ret = -ENOENT;
  				break;
  			}
  			continue;
  		}
  
  		btrfs_item_key_to_cpu(leaf, &found_key, slot);
  
  		/*
  		 * Check that we're still looking at an extended ref key for
  		 * this particular objectid. If we have different
  		 * objectid or type then there are no more to be found
  		 * in the tree and we can exit.
  		 */
  		ret = -ENOENT;
  		if (found_key.objectid != inode_objectid)
  			break;
  		if (btrfs_key_type(&found_key) != BTRFS_INODE_EXTREF_KEY)
  			break;
  
  		ret = 0;
  		ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
  		extref = (struct btrfs_inode_extref *)ptr;
  		*ret_extref = extref;
  		if (found_off)
  			*found_off = found_key.offset;
  		break;
  	}
  
  	return ret;
  }
  
  /*
   * this iterates to turn a name (from iref/extref) into a full filesystem path.
   * Elements of the path are separated by '/' and the path is guaranteed to be
   * 0-terminated. the path is only given within the current file system.
   * Therefore, it never starts with a '/'. the caller is responsible to provide
   * "size" bytes in "dest". the dest buffer will be filled backwards. finally,
   * the start point of the resulting string is returned. this pointer is within
   * dest, normally.
   * in case the path buffer would overflow, the pointer is decremented further
   * as if output was written to the buffer, though no more output is actually
   * generated. that way, the caller can determine how much space would be
   * required for the path to fit into the buffer. in that case, the returned
   * value will be smaller than dest. callers must check this!
   */
  char *btrfs_ref_to_path(struct btrfs_root *fs_root, struct btrfs_path *path,
  			u32 name_len, unsigned long name_off,
  			struct extent_buffer *eb_in, u64 parent,
  			char *dest, u32 size)
  {
  	int slot;
  	u64 next_inum;
  	int ret;
  	s64 bytes_left = ((s64)size) - 1;
  	struct extent_buffer *eb = eb_in;
  	struct btrfs_key found_key;
  	int leave_spinning = path->leave_spinning;
  	struct btrfs_inode_ref *iref;
  
  	if (bytes_left >= 0)
  		dest[bytes_left] = '\0';
  
  	path->leave_spinning = 1;
  	while (1) {
  		bytes_left -= name_len;
  		if (bytes_left >= 0)
  			read_extent_buffer(eb, dest + bytes_left,
  					   name_off, name_len);
  		if (eb != eb_in) {
  			btrfs_tree_read_unlock_blocking(eb);
  			free_extent_buffer(eb);
  		}
  		ret = inode_ref_info(parent, 0, fs_root, path, &found_key);
  		if (ret > 0)
  			ret = -ENOENT;
  		if (ret)
  			break;
  
  		next_inum = found_key.offset;
  
  		/* regular exit ahead */
  		if (parent == next_inum)
  			break;
  
  		slot = path->slots[0];
  		eb = path->nodes[0];
  		/* make sure we can use eb after releasing the path */
  		if (eb != eb_in) {
  			atomic_inc(&eb->refs);
  			btrfs_tree_read_lock(eb);
  			btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
  		}
  		btrfs_release_path(path);
  		iref = btrfs_item_ptr(eb, slot, struct btrfs_inode_ref);
  
  		name_len = btrfs_inode_ref_name_len(eb, iref);
  		name_off = (unsigned long)(iref + 1);
  
  		parent = next_inum;
  		--bytes_left;
  		if (bytes_left >= 0)
  			dest[bytes_left] = '/';
  	}
  
  	btrfs_release_path(path);
  	path->leave_spinning = leave_spinning;
  
  	if (ret)
  		return ERR_PTR(ret);
  
  	return dest + bytes_left;
  }
  
  /*
   * this makes the path point to (logical EXTENT_ITEM *)
   * returns BTRFS_EXTENT_FLAG_DATA for data, BTRFS_EXTENT_FLAG_TREE_BLOCK for
   * tree blocks and <0 on error.
   */
  int extent_from_logical(struct btrfs_fs_info *fs_info, u64 logical,
  			struct btrfs_path *path, struct btrfs_key *found_key,
  			u64 *flags_ret)
  {
  	int ret;
  	u64 flags;
  	u64 size = 0;
  	u32 item_size;
  	struct extent_buffer *eb;
  	struct btrfs_extent_item *ei;
  	struct btrfs_key key;
  
  	if (btrfs_fs_incompat(fs_info, SKINNY_METADATA))
  		key.type = BTRFS_METADATA_ITEM_KEY;
  	else
  		key.type = BTRFS_EXTENT_ITEM_KEY;
  	key.objectid = logical;
  	key.offset = (u64)-1;
  
  	ret = btrfs_search_slot(NULL, fs_info->extent_root, &key, path, 0, 0);
  	if (ret < 0)
  		return ret;
  
  	while (1) {
  		u32 nritems;
  		if (path->slots[0] == 0) {
  			btrfs_set_path_blocking(path);
  			ret = btrfs_prev_leaf(fs_info->extent_root, path);
  			if (ret != 0) {
  				if (ret > 0) {
  					pr_debug("logical %llu is not within "
  						 "any extent
  ", logical);
  					ret = -ENOENT;
  				}
  				return ret;
  			}
  		} else {
  			path->slots[0]--;
  		}
  		nritems = btrfs_header_nritems(path->nodes[0]);
  		if (nritems == 0) {
  			pr_debug("logical %llu is not within any extent
  ",
  				 logical);
  			return -ENOENT;
  		}
  		if (path->slots[0] == nritems)
  			path->slots[0]--;
  
  		btrfs_item_key_to_cpu(path->nodes[0], found_key,
  				      path->slots[0]);
  		if (found_key->type == BTRFS_EXTENT_ITEM_KEY ||
  		    found_key->type == BTRFS_METADATA_ITEM_KEY)
  			break;
  	}
  
  	if (found_key->type == BTRFS_METADATA_ITEM_KEY)
  		size = fs_info->extent_root->leafsize;
  	else if (found_key->type == BTRFS_EXTENT_ITEM_KEY)
  		size = found_key->offset;
  
  	if (found_key->objectid > logical ||
  	    found_key->objectid + size <= logical) {
  		pr_debug("logical %llu is not within any extent
  ", logical);
  		return -ENOENT;
  	}
  
  	eb = path->nodes[0];
  	item_size = btrfs_item_size_nr(eb, path->slots[0]);
  	BUG_ON(item_size < sizeof(*ei));
  
  	ei = btrfs_item_ptr(eb, path->slots[0], struct btrfs_extent_item);
  	flags = btrfs_extent_flags(eb, ei);
  
  	pr_debug("logical %llu is at position %llu within the extent (%llu "
  		 "EXTENT_ITEM %llu) flags %#llx size %u
  ",
  		 logical, logical - found_key->objectid, found_key->objectid,
  		 found_key->offset, flags, item_size);
  
  	WARN_ON(!flags_ret);
  	if (flags_ret) {
  		if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)
  			*flags_ret = BTRFS_EXTENT_FLAG_TREE_BLOCK;
  		else if (flags & BTRFS_EXTENT_FLAG_DATA)
  			*flags_ret = BTRFS_EXTENT_FLAG_DATA;
  		else
  			BUG_ON(1);
  		return 0;
  	}
  
  	return -EIO;
  }
  
  /*
   * helper function to iterate extent inline refs. ptr must point to a 0 value
   * for the first call and may be modified. it is used to track state.
   * if more refs exist, 0 is returned and the next call to
   * __get_extent_inline_ref must pass the modified ptr parameter to get the
   * next ref. after the last ref was processed, 1 is returned.
   * returns <0 on error
   */
  static int __get_extent_inline_ref(unsigned long *ptr, struct extent_buffer *eb,
  				   struct btrfs_key *key,
  				   struct btrfs_extent_item *ei, u32 item_size,
  				   struct btrfs_extent_inline_ref **out_eiref,
  				   int *out_type)
  {
  	unsigned long end;
  	u64 flags;
  	struct btrfs_tree_block_info *info;
  
  	if (!*ptr) {
  		/* first call */
  		flags = btrfs_extent_flags(eb, ei);
  		if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
  			if (key->type == BTRFS_METADATA_ITEM_KEY) {
  				/* a skinny metadata extent */
  				*out_eiref =
  				     (struct btrfs_extent_inline_ref *)(ei + 1);
  			} else {
  				WARN_ON(key->type != BTRFS_EXTENT_ITEM_KEY);
  				info = (struct btrfs_tree_block_info *)(ei + 1);
  				*out_eiref =
  				   (struct btrfs_extent_inline_ref *)(info + 1);
  			}
  		} else {
  			*out_eiref = (struct btrfs_extent_inline_ref *)(ei + 1);
  		}
  		*ptr = (unsigned long)*out_eiref;
  		if ((unsigned long)(*ptr) >= (unsigned long)ei + item_size)
  			return -ENOENT;
  	}
  
  	end = (unsigned long)ei + item_size;
  	*out_eiref = (struct btrfs_extent_inline_ref *)(*ptr);
  	*out_type = btrfs_extent_inline_ref_type(eb, *out_eiref);
  
  	*ptr += btrfs_extent_inline_ref_size(*out_type);
  	WARN_ON(*ptr > end);
  	if (*ptr == end)
  		return 1; /* last */
  
  	return 0;
  }
  
  /*
   * reads the tree block backref for an extent. tree level and root are returned
   * through out_level and out_root. ptr must point to a 0 value for the first
   * call and may be modified (see __get_extent_inline_ref comment).
   * returns 0 if data was provided, 1 if there was no more data to provide or
   * <0 on error.
   */
  int tree_backref_for_extent(unsigned long *ptr, struct extent_buffer *eb,
  			    struct btrfs_key *key, struct btrfs_extent_item *ei,
  			    u32 item_size, u64 *out_root, u8 *out_level)
  {
  	int ret;
  	int type;
  	struct btrfs_tree_block_info *info;
  	struct btrfs_extent_inline_ref *eiref;
  
  	if (*ptr == (unsigned long)-1)
  		return 1;
  
  	while (1) {
  		ret = __get_extent_inline_ref(ptr, eb, key, ei, item_size,
  					      &eiref, &type);
  		if (ret < 0)
  			return ret;
  
  		if (type == BTRFS_TREE_BLOCK_REF_KEY ||
  		    type == BTRFS_SHARED_BLOCK_REF_KEY)
  			break;
  
  		if (ret == 1)
  			return 1;
  	}
  
  	/* we can treat both ref types equally here */
  	info = (struct btrfs_tree_block_info *)(ei + 1);
  	*out_root = btrfs_extent_inline_ref_offset(eb, eiref);
  	*out_level = btrfs_tree_block_level(eb, info);
  
  	if (ret == 1)
  		*ptr = (unsigned long)-1;
  
  	return 0;
  }
  
  static int iterate_leaf_refs(struct extent_inode_elem *inode_list,
  				u64 root, u64 extent_item_objectid,
  				iterate_extent_inodes_t *iterate, void *ctx)
  {
  	struct extent_inode_elem *eie;
  	int ret = 0;
  
  	for (eie = inode_list; eie; eie = eie->next) {
  		pr_debug("ref for %llu resolved, key (%llu EXTEND_DATA %llu), "
  			 "root %llu
  ", extent_item_objectid,
  			 eie->inum, eie->offset, root);
  		ret = iterate(eie->inum, eie->offset, root, ctx);
  		if (ret) {
  			pr_debug("stopping iteration for %llu due to ret=%d
  ",
  				 extent_item_objectid, ret);
  			break;
  		}
  	}
  
  	return ret;
  }
  
  /*
   * calls iterate() for every inode that references the extent identified by
   * the given parameters.
   * when the iterator function returns a non-zero value, iteration stops.
   */
  int iterate_extent_inodes(struct btrfs_fs_info *fs_info,
  				u64 extent_item_objectid, u64 extent_item_pos,
  				int search_commit_root,
  				iterate_extent_inodes_t *iterate, void *ctx)
  {
  	int ret;
  	struct btrfs_trans_handle *trans = NULL;
  	struct ulist *refs = NULL;
  	struct ulist *roots = NULL;
  	struct ulist_node *ref_node = NULL;
  	struct ulist_node *root_node = NULL;
  	struct seq_list tree_mod_seq_elem = {};
  	struct ulist_iterator ref_uiter;
  	struct ulist_iterator root_uiter;
  
  	pr_debug("resolving all inodes for extent %llu
  ",
  			extent_item_objectid);
  
  	if (!search_commit_root) {
  		trans = btrfs_join_transaction(fs_info->extent_root);
  		if (IS_ERR(trans))
  			return PTR_ERR(trans);
  		btrfs_get_tree_mod_seq(fs_info, &tree_mod_seq_elem);
  	}
  
  	ret = btrfs_find_all_leafs(trans, fs_info, extent_item_objectid,
  				   tree_mod_seq_elem.seq, &refs,
  				   &extent_item_pos);
  	if (ret)
  		goto out;
  
  	ULIST_ITER_INIT(&ref_uiter);
  	while (!ret && (ref_node = ulist_next(refs, &ref_uiter))) {
  		ret = btrfs_find_all_roots(trans, fs_info, ref_node->val,
  					   tree_mod_seq_elem.seq, &roots);
  		if (ret)
  			break;
  		ULIST_ITER_INIT(&root_uiter);
  		while (!ret && (root_node = ulist_next(roots, &root_uiter))) {
  			pr_debug("root %llu references leaf %llu, data list "
  				 "%#llx
  ", root_node->val, ref_node->val,
  				 ref_node->aux);
  			ret = iterate_leaf_refs((struct extent_inode_elem *)
  						(uintptr_t)ref_node->aux,
  						root_node->val,
  						extent_item_objectid,
  						iterate, ctx);
  		}
  		ulist_free(roots);
  	}
  
  	free_leaf_list(refs);
  out:
  	if (!search_commit_root) {
  		btrfs_put_tree_mod_seq(fs_info, &tree_mod_seq_elem);
  		btrfs_end_transaction(trans, fs_info->extent_root);
  	}
  
  	return ret;
  }
  
  int iterate_inodes_from_logical(u64 logical, struct btrfs_fs_info *fs_info,
  				struct btrfs_path *path,
  				iterate_extent_inodes_t *iterate, void *ctx)
  {
  	int ret;
  	u64 extent_item_pos;
  	u64 flags = 0;
  	struct btrfs_key found_key;
  	int search_commit_root = path->search_commit_root;
  
  	ret = extent_from_logical(fs_info, logical, path, &found_key, &flags);
  	btrfs_release_path(path);
  	if (ret < 0)
  		return ret;
  	if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)
  		return -EINVAL;
  
  	extent_item_pos = logical - found_key.objectid;
  	ret = iterate_extent_inodes(fs_info, found_key.objectid,
  					extent_item_pos, search_commit_root,
  					iterate, ctx);
  
  	return ret;
  }
  
  typedef int (iterate_irefs_t)(u64 parent, u32 name_len, unsigned long name_off,
  			      struct extent_buffer *eb, void *ctx);
  
  static int iterate_inode_refs(u64 inum, struct btrfs_root *fs_root,
  			      struct btrfs_path *path,
  			      iterate_irefs_t *iterate, void *ctx)
  {
  	int ret = 0;
  	int slot;
  	u32 cur;
  	u32 len;
  	u32 name_len;
  	u64 parent = 0;
  	int found = 0;
  	struct extent_buffer *eb;
  	struct btrfs_item *item;
  	struct btrfs_inode_ref *iref;
  	struct btrfs_key found_key;
  
  	while (!ret) {
  		ret = inode_ref_info(inum, parent ? parent+1 : 0, fs_root, path,
  				     &found_key);
  		if (ret < 0)
  			break;
  		if (ret) {
  			ret = found ? 0 : -ENOENT;
  			break;
  		}
  		++found;
  
  		parent = found_key.offset;
  		slot = path->slots[0];
  		eb = btrfs_clone_extent_buffer(path->nodes[0]);
  		if (!eb) {
  			ret = -ENOMEM;
  			break;
  		}
  		extent_buffer_get(eb);
  		btrfs_tree_read_lock(eb);
  		btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
  		btrfs_release_path(path);
  
  		item = btrfs_item_nr(slot);
  		iref = btrfs_item_ptr(eb, slot, struct btrfs_inode_ref);
  
  		for (cur = 0; cur < btrfs_item_size(eb, item); cur += len) {
  			name_len = btrfs_inode_ref_name_len(eb, iref);
  			/* path must be released before calling iterate()! */
  			pr_debug("following ref at offset %u for inode %llu in "
  				 "tree %llu
  ", cur, found_key.objectid,
  				 fs_root->objectid);
  			ret = iterate(parent, name_len,
  				      (unsigned long)(iref + 1), eb, ctx);
  			if (ret)
  				break;
  			len = sizeof(*iref) + name_len;
  			iref = (struct btrfs_inode_ref *)((char *)iref + len);
  		}
  		btrfs_tree_read_unlock_blocking(eb);
  		free_extent_buffer(eb);
  	}
  
  	btrfs_release_path(path);
  
  	return ret;
  }
  
  static int iterate_inode_extrefs(u64 inum, struct btrfs_root *fs_root,
  				 struct btrfs_path *path,
  				 iterate_irefs_t *iterate, void *ctx)
  {
  	int ret;
  	int slot;
  	u64 offset = 0;
  	u64 parent;
  	int found = 0;
  	struct extent_buffer *eb;
  	struct btrfs_inode_extref *extref;
  	struct extent_buffer *leaf;
  	u32 item_size;
  	u32 cur_offset;
  	unsigned long ptr;
  
  	while (1) {
  		ret = btrfs_find_one_extref(fs_root, inum, offset, path, &extref,
  					    &offset);
  		if (ret < 0)
  			break;
  		if (ret) {
  			ret = found ? 0 : -ENOENT;
  			break;
  		}
  		++found;
  
  		slot = path->slots[0];
  		eb = btrfs_clone_extent_buffer(path->nodes[0]);
  		if (!eb) {
  			ret = -ENOMEM;
  			break;
  		}
  		extent_buffer_get(eb);
  
  		btrfs_tree_read_lock(eb);
  		btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
  		btrfs_release_path(path);
  
  		leaf = path->nodes[0];
  		item_size = btrfs_item_size_nr(leaf, slot);
  		ptr = btrfs_item_ptr_offset(leaf, slot);
  		cur_offset = 0;
  
  		while (cur_offset < item_size) {
  			u32 name_len;
  
  			extref = (struct btrfs_inode_extref *)(ptr + cur_offset);
  			parent = btrfs_inode_extref_parent(eb, extref);
  			name_len = btrfs_inode_extref_name_len(eb, extref);
  			ret = iterate(parent, name_len,
  				      (unsigned long)&extref->name, eb, ctx);
  			if (ret)
  				break;
  
  			cur_offset += btrfs_inode_extref_name_len(leaf, extref);
  			cur_offset += sizeof(*extref);
  		}
  		btrfs_tree_read_unlock_blocking(eb);
  		free_extent_buffer(eb);
  
  		offset++;
  	}
  
  	btrfs_release_path(path);
  
  	return ret;
  }
  
  static int iterate_irefs(u64 inum, struct btrfs_root *fs_root,
  			 struct btrfs_path *path, iterate_irefs_t *iterate,
  			 void *ctx)
  {
  	int ret;
  	int found_refs = 0;
  
  	ret = iterate_inode_refs(inum, fs_root, path, iterate, ctx);
  	if (!ret)
  		++found_refs;
  	else if (ret != -ENOENT)
  		return ret;
  
  	ret = iterate_inode_extrefs(inum, fs_root, path, iterate, ctx);
  	if (ret == -ENOENT && found_refs)
  		return 0;
  
  	return ret;
  }
  
  /*
   * returns 0 if the path could be dumped (probably truncated)
   * returns <0 in case of an error
   */
  static int inode_to_path(u64 inum, u32 name_len, unsigned long name_off,
  			 struct extent_buffer *eb, void *ctx)
  {
  	struct inode_fs_paths *ipath = ctx;
  	char *fspath;
  	char *fspath_min;
  	int i = ipath->fspath->elem_cnt;
  	const int s_ptr = sizeof(char *);
  	u32 bytes_left;
  
  	bytes_left = ipath->fspath->bytes_left > s_ptr ?
  					ipath->fspath->bytes_left - s_ptr : 0;
  
  	fspath_min = (char *)ipath->fspath->val + (i + 1) * s_ptr;
  	fspath = btrfs_ref_to_path(ipath->fs_root, ipath->btrfs_path, name_len,
  				   name_off, eb, inum, fspath_min, bytes_left);
  	if (IS_ERR(fspath))
  		return PTR_ERR(fspath);
  
  	if (fspath > fspath_min) {
  		ipath->fspath->val[i] = (u64)(unsigned long)fspath;
  		++ipath->fspath->elem_cnt;
  		ipath->fspath->bytes_left = fspath - fspath_min;
  	} else {
  		++ipath->fspath->elem_missed;
  		ipath->fspath->bytes_missing += fspath_min - fspath;
  		ipath->fspath->bytes_left = 0;
  	}
  
  	return 0;
  }
  
  /*
   * this dumps all file system paths to the inode into the ipath struct, provided
   * is has been created large enough. each path is zero-terminated and accessed
   * from ipath->fspath->val[i].
   * when it returns, there are ipath->fspath->elem_cnt number of paths available
   * in ipath->fspath->val[]. when the allocated space wasn't sufficient, the
   * number of missed paths in recored in ipath->fspath->elem_missed, otherwise,
   * it's zero. ipath->fspath->bytes_missing holds the number of bytes that would
   * have been needed to return all paths.
   */
  int paths_from_inode(u64 inum, struct inode_fs_paths *ipath)
  {
  	return iterate_irefs(inum, ipath->fs_root, ipath->btrfs_path,
  			     inode_to_path, ipath);
  }
  
  struct btrfs_data_container *init_data_container(u32 total_bytes)
  {
  	struct btrfs_data_container *data;
  	size_t alloc_bytes;
  
  	alloc_bytes = max_t(size_t, total_bytes, sizeof(*data));
  	data = vmalloc(alloc_bytes);
  	if (!data)
  		return ERR_PTR(-ENOMEM);
  
  	if (total_bytes >= sizeof(*data)) {
  		data->bytes_left = total_bytes - sizeof(*data);
  		data->bytes_missing = 0;
  	} else {
  		data->bytes_missing = sizeof(*data) - total_bytes;
  		data->bytes_left = 0;
  	}
  
  	data->elem_cnt = 0;
  	data->elem_missed = 0;
  
  	return data;
  }
  
  /*
   * allocates space to return multiple file system paths for an inode.
   * total_bytes to allocate are passed, note that space usable for actual path
   * information will be total_bytes - sizeof(struct inode_fs_paths).
   * the returned pointer must be freed with free_ipath() in the end.
   */
  struct inode_fs_paths *init_ipath(s32 total_bytes, struct btrfs_root *fs_root,
  					struct btrfs_path *path)
  {
  	struct inode_fs_paths *ifp;
  	struct btrfs_data_container *fspath;
  
  	fspath = init_data_container(total_bytes);
  	if (IS_ERR(fspath))
  		return (void *)fspath;
  
  	ifp = kmalloc(sizeof(*ifp), GFP_NOFS);
  	if (!ifp) {
  		kfree(fspath);
  		return ERR_PTR(-ENOMEM);
  	}
  
  	ifp->btrfs_path = path;
  	ifp->fspath = fspath;
  	ifp->fs_root = fs_root;
  
  	return ifp;
  }
  
  void free_ipath(struct inode_fs_paths *ipath)
  {
  	if (!ipath)
  		return;
  	vfree(ipath->fspath);
  	kfree(ipath);
  }