diff --git a/Makefile b/Makefile
index 7cc7783..f954649 100644
--- a/Makefile
+++ b/Makefile
@@ -10,7 +10,7 @@ objects = ctree.o disk-io.o radix-tree.o extent-tree.o print-tree.o \
 	  root-tree.o dir-item.o file-item.o inode-item.o inode-map.o \
 	  extent-cache.o extent_io.o volumes.o utils.o repair.o \
 	  qgroup.o raid6.o free-space-cache.o list_sort.o props.o \
-	  ulist.o qgroup-verify.o
+	  ulist.o qgroup-verify.o backref.o
 cmds_objects = cmds-subvolume.o cmds-filesystem.o cmds-device.o cmds-scrub.o \
 	       cmds-inspect.o cmds-balance.o cmds-send.o cmds-receive.o \
 	       cmds-quota.o cmds-qgroup.o cmds-replace.o cmds-check.o \
diff --git a/backref.c b/backref.c
new file mode 100644
index 0000000..593f936
--- /dev/null
+++ b/backref.c
@@ -0,0 +1,1651 @@
+/*
+ * 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 "kerncompat.h"
+#include "ctree.h"
+#include "disk-io.h"
+#include "backref.h"
+#include "ulist.h"
+#include "transaction.h"
+
+#define pr_debug(...) do { } while (0)
+
+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;
+};
+
+/*
+ * 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 = kmalloc(sizeof(*ref), 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,
+			   u64 total_refs)
+{
+	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_leaf(root, path);
+
+	while (!ret && count < total_refs) {
+		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_item(root, path);
+	}
+
+	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, u64 total_refs)
+{
+	struct btrfs_root *root;
+	struct btrfs_key root_key;
+	struct extent_buffer *eb;
+	int ret = 0;
+	int root_level;
+	int level = ref->level;
+
+	root_key.objectid = ref->root_id;
+	root_key.type = BTRFS_ROOT_ITEM_KEY;
+	root_key.offset = (u64)-1;
+
+	root = btrfs_read_fs_root(fs_info, &root_key);
+	if (IS_ERR(root)) {
+		ret = PTR_ERR(root);
+		goto out;
+	}
+
+	root_level = btrfs_root_level(&root->root_item);
+
+	if (root_level + 1 == level)
+		goto out;
+
+	path->lowest_level = level;
+	ret = btrfs_search_slot(NULL, root, &ref->key_for_search, path, 0, 0);
+
+	pr_debug("search slot in root %llu (level %d, ref count %d) returned "
+		 "%d for key (%llu %u %llu)\n",
+		 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) {
+		WARN_ON(!level);
+		if (!level) {
+			ret = 1;
+			goto out;
+		}
+		level--;
+		eb = path->nodes[level];
+	}
+
+	ret = add_all_parents(root, path, parents, ref, level, time_seq,
+			      extent_item_pos, total_refs);
+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, u64 total_refs)
+{
+	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,
+					     total_refs);
+		/*
+		 * 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 = kmalloc(sizeof(*new_ref), 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;
+		}
+		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);
+		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);
+			kfree(ref2);
+		}
+
+	}
+}
+
+/*
+ * 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,
+			     u64 *total_refs)
+{
+	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);
+	*total_refs += btrfs_extent_refs(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;
+	int info_level = 0;
+	int ret;
+	struct list_head prefs;
+	struct __prelim_ref *ref;
+	struct extent_inode_elem *eie = NULL;
+	u64 total_refs = 0;
+
+	INIT_LIST_HEAD(&prefs);
+
+	key.objectid = bytenr;
+	key.offset = (u64)-1;
+	if (btrfs_fs_incompat(fs_info,
+			      BTRFS_FEATURE_INCOMPAT_SKINNY_METADATA))
+		key.type = BTRFS_METADATA_ITEM_KEY;
+	else
+		key.type = BTRFS_EXTENT_ITEM_KEY;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	ret = btrfs_search_slot(trans, fs_info->extent_root, &key, path, 0, 0);
+	if (ret < 0)
+		goto out;
+	BUG_ON(ret == 0);
+
+	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,
+						&total_refs);
+			if (ret)
+				goto out;
+			ret = __add_keyed_refs(fs_info, path, bytenr,
+					       info_level, &prefs);
+			if (ret)
+				goto out;
+		}
+	}
+	btrfs_release_path(path);
+
+	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, total_refs);
+	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 (roots && 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;
+				}
+				ret = find_extent_in_eb(eb, bytenr,
+							*extent_item_pos, &eie);
+				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);
+		kfree(ref);
+	}
+
+out:
+	btrfs_free_path(path);
+	while (!list_empty(&prefs)) {
+		ref = list_first_entry(&prefs, struct __prelim_ref, list);
+		list_del(&ref->list);
+		kfree(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)
+{
+	int ret;
+
+	*leafs = ulist_alloc(GFP_NOFS);
+	if (!*leafs)
+		return -ENOMEM;
+
+	ret = find_parent_nodes(trans, fs_info, bytenr,
+				time_seq, *leafs, NULL, extent_item_pos);
+	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.
+ */
+static 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;
+}
+
+int btrfs_find_all_roots(struct btrfs_trans_handle *trans,
+			 struct btrfs_fs_info *fs_info, u64 bytenr,
+			 u64 time_seq, struct ulist **roots)
+{
+	return __btrfs_find_all_roots(trans, fs_info, bytenr, time_seq, roots);
+}
+
+/*
+ * 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;
+	struct btrfs_inode_ref *iref;
+
+	if (bytes_left >= 0)
+		dest[bytes_left] = '\0';
+
+	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)
+			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)
+			eb->refs++;
+		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);
+
+	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,
+			      BTRFS_FEATURE_INCOMPAT_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;
+
+	ret = btrfs_previous_extent_item(fs_info->extent_root, path, 0);
+	if (ret) {
+		if (ret > 0)
+			ret = -ENOENT;
+		return ret;
+	}
+	btrfs_item_key_to_cpu(path->nodes[0], found_key, path->slots[0]);
+	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\n", 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\n",
+		 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\n", 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\n",
+				 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 ulist_iterator ref_uiter;
+	struct ulist_iterator root_uiter;
+
+	pr_debug("resolving all inodes for extent %llu\n",
+			extent_item_objectid);
+
+	ret = btrfs_find_all_leafs(trans, fs_info, extent_item_objectid,
+				   0, &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,
+					     0, &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\n", 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:
+	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 = 0;
+
+	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_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\n", 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);
+		}
+		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_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);
+		}
+		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);
+}
diff --git a/backref.h b/backref.h
new file mode 100644
index 0000000..fd22b99
--- /dev/null
+++ b/backref.h
@@ -0,0 +1,73 @@
+/*
+ * 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.
+ */
+
+#ifndef __BTRFS_BACKREF__
+#define __BTRFS_BACKREF__
+
+#include "ulist.h"
+#include "extent_io.h"
+
+struct inode_fs_paths {
+	struct btrfs_path		*btrfs_path;
+	struct btrfs_root		*fs_root;
+	struct btrfs_data_container	*fspath;
+};
+
+typedef int (iterate_extent_inodes_t)(u64 inum, u64 offset, u64 root,
+		void *ctx);
+
+int inode_item_info(u64 inum, u64 ioff, struct btrfs_root *fs_root,
+			struct btrfs_path *path);
+
+int extent_from_logical(struct btrfs_fs_info *fs_info, u64 logical,
+			struct btrfs_path *path, struct btrfs_key *found_key,
+			u64 *flags);
+
+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 iterate_extent_inodes(struct btrfs_fs_info *fs_info,
+				u64 extent_item_objectid,
+				u64 extent_offset, int search_commit_root,
+				iterate_extent_inodes_t *iterate, void *ctx);
+
+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 paths_from_inode(u64 inum, struct inode_fs_paths *ipath);
+
+int btrfs_find_all_roots(struct btrfs_trans_handle *trans,
+			 struct btrfs_fs_info *fs_info, u64 bytenr,
+			 u64 time_seq, struct ulist **roots);
+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);
+
+struct btrfs_data_container *init_data_container(u32 total_bytes);
+struct inode_fs_paths *init_ipath(s32 total_bytes, struct btrfs_root *fs_root,
+					struct btrfs_path *path);
+void free_ipath(struct inode_fs_paths *ipath);
+
+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);
+#endif
diff --git a/ctree.c b/ctree.c
index c085941..23399e2 100644
--- a/ctree.c
+++ b/ctree.c
@@ -1021,6 +1021,49 @@ void reada_for_search(struct btrfs_root *root, struct btrfs_path *path,
 	}
 }
 
+int btrfs_find_item(struct btrfs_root *fs_root, struct btrfs_path *found_path,
+		u64 iobjectid, u64 ioff, u8 key_type,
+		struct btrfs_key *found_key)
+{
+	int ret;
+	struct btrfs_key key;
+	struct extent_buffer *eb;
+	struct btrfs_path *path;
+
+	key.type = key_type;
+	key.objectid = iobjectid;
+	key.offset = ioff;
+
+	if (found_path == NULL) {
+		path = btrfs_alloc_path();
+		if (!path)
+			return -ENOMEM;
+	} else
+		path = found_path;
+
+	ret = btrfs_search_slot(NULL, fs_root, &key, path, 0, 0);
+	if ((ret < 0) || (found_key == NULL)) {
+		if (path != found_path)
+			btrfs_free_path(path);
+		return ret;
+	}
+
+	eb = path->nodes[0];
+	if (ret && path->slots[0] >= btrfs_header_nritems(eb)) {
+		ret = btrfs_next_leaf(fs_root, path);
+		if (ret)
+			return ret;
+		eb = path->nodes[0];
+	}
+
+	btrfs_item_key_to_cpu(eb, found_key, path->slots[0]);
+	if (found_key->type != key.type ||
+			found_key->objectid != key.objectid)
+		return 1;
+
+	return 0;
+}
+
 /*
  * look for key in the tree.  path is filled in with nodes along the way
  * if key is found, we return zero and you can find the item in the leaf
@@ -2813,3 +2856,44 @@ int btrfs_previous_item(struct btrfs_root *root,
 	return 1;
 }
 
+/*
+ * search in extent tree to find a previous Metadata/Data extent item with
+ * min objecitd.
+ *
+ * returns 0 if something is found, 1 if nothing was found and < 0 on error
+ */
+int btrfs_previous_extent_item(struct btrfs_root *root,
+			struct btrfs_path *path, u64 min_objectid)
+{
+	struct btrfs_key found_key;
+	struct extent_buffer *leaf;
+	u32 nritems;
+	int ret;
+
+	while (1) {
+		if (path->slots[0] == 0) {
+			ret = btrfs_prev_leaf(root, path);
+			if (ret != 0)
+				return ret;
+		} else {
+			path->slots[0]--;
+		}
+		leaf = path->nodes[0];
+		nritems = btrfs_header_nritems(leaf);
+		if (nritems == 0)
+			return 1;
+		if (path->slots[0] == nritems)
+			path->slots[0]--;
+
+		btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
+		if (found_key.objectid < min_objectid)
+			break;
+		if (found_key.type == BTRFS_EXTENT_ITEM_KEY ||
+		    found_key.type == BTRFS_METADATA_ITEM_KEY)
+			return 0;
+		if (found_key.objectid == min_objectid &&
+		    found_key.type < BTRFS_EXTENT_ITEM_KEY)
+			break;
+	}
+	return 1;
+}
diff --git a/ctree.h b/ctree.h
index 93b8585..eaab667 100644
--- a/ctree.h
+++ b/ctree.h
@@ -2253,6 +2253,8 @@ struct extent_buffer *read_node_slot(struct btrfs_root *root,
 int btrfs_previous_item(struct btrfs_root *root,
 			struct btrfs_path *path, u64 min_objectid,
 			int type);
+int btrfs_previous_extent_item(struct btrfs_root *root,
+			struct btrfs_path *path, u64 min_objectid);
 int btrfs_cow_block(struct btrfs_trans_handle *trans,
 		    struct btrfs_root *root, struct extent_buffer *buf,
 		    struct extent_buffer *parent, int parent_slot,
@@ -2281,6 +2283,9 @@ int btrfs_split_item(struct btrfs_trans_handle *trans,
 int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
 		      *root, struct btrfs_key *key, struct btrfs_path *p, int
 		      ins_len, int cow);
+int btrfs_find_item(struct btrfs_root *fs_root, struct btrfs_path *found_path,
+		u64 iobjectid, u64 ioff, u8 key_type,
+		struct btrfs_key *found_key);
 void btrfs_release_path(struct btrfs_path *p);
 void add_root_to_dirty_list(struct btrfs_root *root);
 struct btrfs_path *btrfs_alloc_path(void);
@@ -2313,6 +2318,15 @@ static inline int btrfs_insert_empty_item(struct btrfs_trans_handle *trans,
 }
 
 int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path);
+static inline int btrfs_next_item(struct btrfs_root *root,
+				  struct btrfs_path *p)
+{
+	++p->slots[0];
+	if (p->slots[0] >= btrfs_header_nritems(p->nodes[0]))
+		return btrfs_next_leaf(root, p);
+	return 0;
+}
+
 int btrfs_prev_leaf(struct btrfs_root *root, struct btrfs_path *path);
 int btrfs_leaf_free_space(struct btrfs_root *root, struct extent_buffer *leaf);
 void btrfs_fixup_low_keys(struct btrfs_root *root, struct btrfs_path *path,
diff --git a/extent_io.c b/extent_io.c
index 1df377d..21ed72e 100644
--- a/extent_io.c
+++ b/extent_io.c
@@ -569,7 +569,6 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
 						   u64 bytenr, u32 blocksize)
 {
 	struct extent_buffer *eb;
-	int ret;
 
 	eb = malloc(sizeof(struct extent_buffer) + blocksize);
 	if (!eb) {
@@ -589,17 +588,23 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
 	eb->cache_node.size = blocksize;
 	INIT_LIST_HEAD(&eb->recow);
 
-	free_some_buffers(tree);
-	ret = insert_cache_extent(&tree->cache, &eb->cache_node);
-	if (ret) {
-		free(eb);
-		return NULL;
-	}
-	list_add_tail(&eb->lru, &tree->lru);
-	tree->cache_size += blocksize;
 	return eb;
 }
 
+struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer *src)
+{
+	struct extent_buffer *new;
+
+	new = __alloc_extent_buffer(NULL, src->start, src->len);
+	if (new == NULL)
+		return NULL;
+
+	copy_extent_buffer(new, src, 0, 0, src->len);
+	new->flags |= EXTENT_BUFFER_DUMMY;
+
+	return new;
+}
+
 void free_extent_buffer(struct extent_buffer *eb)
 {
 	if (!eb)
@@ -612,9 +617,11 @@ void free_extent_buffer(struct extent_buffer *eb)
 		BUG_ON(eb->flags & EXTENT_DIRTY);
 		list_del_init(&eb->lru);
 		list_del_init(&eb->recow);
-		remove_cache_extent(&tree->cache, &eb->cache_node);
-		BUG_ON(tree->cache_size < eb->len);
-		tree->cache_size -= eb->len;
+		if (!(eb->flags & EXTENT_BUFFER_DUMMY)) {
+			BUG_ON(tree->cache_size < eb->len);
+			remove_cache_extent(&tree->cache, &eb->cache_node);
+			tree->cache_size -= eb->len;
+		}
 		free(eb);
 	}
 }
@@ -663,12 +670,24 @@ struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
 		list_move_tail(&eb->lru, &tree->lru);
 		eb->refs++;
 	} else {
+		int ret;
+
 		if (cache) {
 			eb = container_of(cache, struct extent_buffer,
 					  cache_node);
 			free_extent_buffer(eb);
 		}
 		eb = __alloc_extent_buffer(tree, bytenr, blocksize);
+		if (!eb)
+			return NULL;
+		ret = insert_cache_extent(&tree->cache, &eb->cache_node);
+		if (ret) {
+			free(eb);
+			return NULL;
+		}
+		list_add_tail(&eb->lru, &tree->lru);
+		tree->cache_size += blocksize;
+		free_some_buffers(tree);
 	}
 	return eb;
 }
diff --git a/extent_io.h b/extent_io.h
index 68fb9ce..acc316e 100644
--- a/extent_io.h
+++ b/extent_io.h
@@ -40,6 +40,7 @@
 #define EXTENT_BUFFER_FILLED (1 << 8)
 #define EXTENT_CSUM (1 << 9)
 #define EXTENT_BAD_TRANSID (1 << 10)
+#define EXTENT_BUFFER_DUMMY (1 << 11)
 #define EXTENT_IOBITS (EXTENT_LOCKED | EXTENT_WRITEBACK)
 
 #define BLOCK_GROUP_DATA     EXTENT_WRITEBACK
@@ -111,6 +112,7 @@ struct extent_buffer *find_first_extent_buffer(struct extent_io_tree *tree,
 					       u64 start);
 struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
 					  u64 bytenr, u32 blocksize);
+struct extent_buffer *btrfs_clone_extent_buffer(struct extent_buffer *src);
 void free_extent_buffer(struct extent_buffer *eb);
 int read_extent_from_disk(struct extent_buffer *eb,
 			  unsigned long offset, unsigned long len);
diff --git a/kerncompat.h b/kerncompat.h
index 19c7fa5..ea34936 100644
--- a/kerncompat.h
+++ b/kerncompat.h
@@ -102,6 +102,9 @@ typedef __u32 u32;
 typedef __u64 u64;
 typedef __u16 u16;
 typedef __u8 u8;
+typedef __s64 s64;
+typedef __s32 s32;
+
 /*
  * Continuing to define __KERNEL__ breaks others parts of the code, so
  * we can just undefine it now that we have the correct headers...
@@ -113,6 +116,8 @@ typedef unsigned int __u32;
 typedef unsigned long long u64;
 typedef unsigned char u8;
 typedef unsigned short u16;
+typedef long long s64;
+typedef int s32
 #endif
 
 
@@ -263,6 +268,8 @@ static inline long IS_ERR(const void *ptr)
 #define kzalloc(x, y) calloc(1, x)
 #define kstrdup(x, y) strdup(x)
 #define kfree(x) free(x)
+#define vmalloc(x) malloc(x)
+#define vfree(x) free(x)
 
 #define BUG_ON(c) assert_trace(#c, __FILE__, __func__, __LINE__, !(c))
 
diff --git a/ulist.h b/ulist.h
index 2a0e948..9e0e4e0 100644
--- a/ulist.h
+++ b/ulist.h
@@ -58,6 +58,21 @@ void ulist_free(struct ulist *ulist);
 int ulist_add(struct ulist *ulist, u64 val, u64 aux, gfp_t gfp_mask);
 int ulist_add_merge(struct ulist *ulist, u64 val, u64 aux,
 		    u64 *old_aux, gfp_t gfp_mask);
+
+/* just like ulist_add_merge() but take a pointer for the aux data */
+static inline int ulist_add_merge_ptr(struct ulist *ulist, u64 val, void *aux,
+				      void **old_aux, gfp_t gfp_mask)
+{
+#if BITS_PER_LONG == 32
+	u64 old64 = (uintptr_t)*old_aux;
+	int ret = ulist_add_merge(ulist, val, (uintptr_t)aux, &old64, gfp_mask);
+	*old_aux = (void *)((uintptr_t)old64);
+	return ret;
+#else
+	return ulist_add_merge(ulist, val, (u64)aux, (u64 *)old_aux, gfp_mask);
+#endif
+}
+
 struct ulist_node *ulist_next(struct ulist *ulist,
 			      struct ulist_iterator *uiter);
 
