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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2011 STRATO.  All rights reserved.
  */
 
 #include <linux/mm.h>
 #include <linux/rbtree.h>
 #include <trace/events/btrfs.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "backref.h"
 #include "ulist.h"
 #include "transaction.h"
 #include "delayed-ref.h"
 #include "locking.h"
 #include "misc.h"
 #include "tree-mod-log.h"
 
 /* Just an arbitrary number so we can be sure this happened */
 #define BACKREF_FOUND_SHARED 6
 
 struct extent_inode_elem {
     u64 inum;
     u64 offset;
     struct extent_inode_elem *next;
 };
 
 static int check_extent_in_eb(const struct btrfs_key *key,
                   const struct extent_buffer *eb,
                   const struct btrfs_file_extent_item *fi,
                   u64 extent_item_pos,
                   struct extent_inode_elem **eie,
                   bool ignore_offset)
 {
     u64 offset = 0;
     struct extent_inode_elem *e;
 
     if (!ignore_offset &&
         !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(const struct extent_buffer *eb,
                  u64 wanted_disk_byte, u64 extent_item_pos,
                  struct extent_inode_elem **eie,
                  bool ignore_offset)
 {
     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, ignore_offset);
         if (ret < 0)
             return ret;
     }
 
     return 0;
 }
 
 struct preftree {
     struct rb_root_cached root;
     unsigned int count;
 };
 
 #define PREFTREE_INIT   { .root = RB_ROOT_CACHED, .count = 0 }
 
 struct preftrees {
     struct preftree direct;    /* BTRFS_SHARED_[DATA|BLOCK]_REF_KEY */
     struct preftree indirect;  /* BTRFS_[TREE_BLOCK|EXTENT_DATA]_REF_KEY */
     struct preftree indirect_missing_keys;
 };
 
 /*
  * Checks for a shared extent during backref search.
  *
  * The share_count tracks prelim_refs (direct and indirect) having a
  * ref->count >0:
  *  - incremented when a ref->count transitions to >0
  *  - decremented when a ref->count transitions to <1
  */
 struct share_check {
     u64 root_objectid;
     u64 inum;
     int share_count;
 };
 
 static inline int extent_is_shared(struct share_check *sc)
 {
     return (sc && sc->share_count > 1) ? BACKREF_FOUND_SHARED : 0;
 }
 
 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_MEM_SPREAD,
                     NULL);
     if (!btrfs_prelim_ref_cache)
         return -ENOMEM;
     return 0;
 }
 
 void __cold btrfs_prelim_ref_exit(void)
 {
     kmem_cache_destroy(btrfs_prelim_ref_cache);
 }
 
 static void free_pref(struct prelim_ref *ref)
 {
     kmem_cache_free(btrfs_prelim_ref_cache, ref);
 }
 
 /*
  * Return 0 when both refs are for the same block (and can be merged).
  * A -1 return indicates ref1 is a 'lower' block than ref2, while 1
  * indicates a 'higher' block.
  */
 static int prelim_ref_compare(struct prelim_ref *ref1,
                   struct prelim_ref *ref2)
 {
     if (ref1->level < ref2->level)
         return -1;
     if (ref1->level > ref2->level)
         return 1;
     if (ref1->root_id < ref2->root_id)
         return -1;
     if (ref1->root_id > ref2->root_id)
         return 1;
     if (ref1->key_for_search.type < ref2->key_for_search.type)
         return -1;
     if (ref1->key_for_search.type > ref2->key_for_search.type)
         return 1;
     if (ref1->key_for_search.objectid < ref2->key_for_search.objectid)
         return -1;
     if (ref1->key_for_search.objectid > ref2->key_for_search.objectid)
         return 1;
     if (ref1->key_for_search.offset < ref2->key_for_search.offset)
         return -1;
     if (ref1->key_for_search.offset > ref2->key_for_search.offset)
         return 1;
     if (ref1->parent < ref2->parent)
         return -1;
     if (ref1->parent > ref2->parent)
         return 1;
 
     return 0;
 }
 
 static void update_share_count(struct share_check *sc, int oldcount,
                    int newcount)
 {
     if ((!sc) || (oldcount == 0 && newcount < 1))
         return;
 
     if (oldcount > 0 && newcount < 1)
         sc->share_count--;
     else if (oldcount < 1 && newcount > 0)
         sc->share_count++;
 }
 
 /*
  * Add @newref to the @root rbtree, merging identical refs.
  *
  * Callers should assume that newref has been freed after calling.
  */
 static void prelim_ref_insert(const struct btrfs_fs_info *fs_info,
                   struct preftree *preftree,
                   struct prelim_ref *newref,
                   struct share_check *sc)
 {
     struct rb_root_cached *root;
     struct rb_node **p;
     struct rb_node *parent = NULL;
     struct prelim_ref *ref;
     int result;
     bool leftmost = true;
 
     root = &preftree->root;
     p = &root->rb_root.rb_node;
 
     while (*p) {
         parent = *p;
         ref = rb_entry(parent, struct prelim_ref, rbnode);
         result = prelim_ref_compare(ref, newref);
         if (result < 0) {
             p = &(*p)->rb_left;
         } else if (result > 0) {
             p = &(*p)->rb_right;
             leftmost = false;
         } else {
             /* Identical refs, merge them and free @newref */
             struct extent_inode_elem *eie = ref->inode_list;
 
             while (eie && eie->next)
                 eie = eie->next;
 
             if (!eie)
                 ref->inode_list = newref->inode_list;
             else
                 eie->next = newref->inode_list;
             trace_btrfs_prelim_ref_merge(fs_info, ref, newref,
                              preftree->count);
             /*
              * A delayed ref can have newref->count < 0.
              * The ref->count is updated to follow any
              * BTRFS_[ADD|DROP]_DELAYED_REF actions.
              */
             update_share_count(sc, ref->count,
                        ref->count + newref->count);
             ref->count += newref->count;
             free_pref(newref);
             return;
         }
     }
 
     update_share_count(sc, 0, newref->count);
     preftree->count++;
     trace_btrfs_prelim_ref_insert(fs_info, newref, NULL, preftree->count);
     rb_link_node(&newref->rbnode, parent, p);
     rb_insert_color_cached(&newref->rbnode, root, leftmost);
 }
 
 /*
  * Release the entire tree.  We don't care about internal consistency so
  * just free everything and then reset the tree root.
  */
 static void prelim_release(struct preftree *preftree)
 {
     struct prelim_ref *ref, *next_ref;
 
     rbtree_postorder_for_each_entry_safe(ref, next_ref,
                          &preftree->root.rb_root, rbnode)
         free_pref(ref);
 
     preftree->root = RB_ROOT_CACHED;
     preftree->count = 0;
 }
 
 /*
  * 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(const struct btrfs_fs_info *fs_info,
               struct preftree *preftree, u64 root_id,
               const struct btrfs_key *key, int level, u64 parent,
               u64 wanted_disk_byte, int count,
               struct share_check *sc, 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;
     prelim_ref_insert(fs_info, preftree, ref, sc);
     return extent_is_shared(sc);
 }
 
 /* direct refs use root == 0, key == NULL */
 static int add_direct_ref(const struct btrfs_fs_info *fs_info,
               struct preftrees *preftrees, int level, u64 parent,
               u64 wanted_disk_byte, int count,
               struct share_check *sc, gfp_t gfp_mask)
 {
     return add_prelim_ref(fs_info, &preftrees->direct, 0, NULL, level,
                   parent, wanted_disk_byte, count, sc, gfp_mask);
 }
 
 /* indirect refs use parent == 0 */
 static int add_indirect_ref(const struct btrfs_fs_info *fs_info,
                 struct preftrees *preftrees, u64 root_id,
                 const struct btrfs_key *key, int level,
                 u64 wanted_disk_byte, int count,
                 struct share_check *sc, gfp_t gfp_mask)
 {
     struct preftree *tree = &preftrees->indirect;
 
     if (!key)
         tree = &preftrees->indirect_missing_keys;
     return add_prelim_ref(fs_info, tree, root_id, key, level, 0,
                   wanted_disk_byte, count, sc, gfp_mask);
 }
 
 static int is_shared_data_backref(struct preftrees *preftrees, u64 bytenr)
 {
     struct rb_node **p = &preftrees->direct.root.rb_root.rb_node;
     struct rb_node *parent = NULL;
     struct prelim_ref *ref = NULL;
     struct prelim_ref target = {};
     int result;
 
     target.parent = bytenr;
 
     while (*p) {
         parent = *p;
         ref = rb_entry(parent, struct prelim_ref, rbnode);
         result = prelim_ref_compare(ref, &target);
 
         if (result < 0)
             p = &(*p)->rb_left;
         else if (result > 0)
             p = &(*p)->rb_right;
         else
             return 1;
     }
     return 0;
 }
 
 static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path,
                struct ulist *parents,
                struct preftrees *preftrees, struct prelim_ref *ref,
                int level, u64 time_seq, const u64 *extent_item_pos,
                bool ignore_offset)
 {
     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;
     u64 data_offset;
 
     if (level != 0) {
         eb = path->nodes[level];
         ret = ulist_add(parents, eb->start, 0, GFP_NOFS);
         if (ret < 0)
             return ret;
         return 0;
     }
 
     /*
      * 1. 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.
      * 2. We are searching for normal backref but bytenr of this leaf
      *    matches shared data backref
      * 3. The leaf owner is not equal to the root we are searching
      *
      * For these cases, go to the next leaf before we continue.
      */
     eb = path->nodes[0];
     if (path->slots[0] >= btrfs_header_nritems(eb) ||
         is_shared_data_backref(preftrees, eb->start) ||
         ref->root_id != btrfs_header_owner(eb)) {
         if (time_seq == BTRFS_SEQ_LAST)
             ret = btrfs_next_leaf(root, path);
         else
             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;
 
         /*
          * We are searching for normal backref but bytenr of this leaf
          * matches shared data backref, OR
          * the leaf owner is not equal to the root we are searching for
          */
         if (slot == 0 &&
             (is_shared_data_backref(preftrees, eb->start) ||
              ref->root_id != btrfs_header_owner(eb))) {
             if (time_seq == BTRFS_SEQ_LAST)
                 ret = btrfs_next_leaf(root, path);
             else
                 ret = btrfs_next_old_leaf(root, path, time_seq);
             continue;
         }
         fi = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
         disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
         data_offset = btrfs_file_extent_offset(eb, fi);
 
         if (disk_byte == wanted_disk_byte) {
             eie = NULL;
             old = NULL;
             if (ref->key_for_search.offset == key.offset - data_offset)
                 count++;
             else
                 goto next;
             if (extent_item_pos) {
                 ret = check_extent_in_eb(&key, eb, fi,
                         *extent_item_pos,
                         &eie, ignore_offset);
                 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:
         if (time_seq == BTRFS_SEQ_LAST)
             ret = btrfs_next_item(root, path);
         else
             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 preftrees *preftrees,
                 struct prelim_ref *ref, struct ulist *parents,
                 const u64 *extent_item_pos, bool ignore_offset)
 {
     struct btrfs_root *root;
     struct extent_buffer *eb;
     int ret = 0;
     int root_level;
     int level = ref->level;
     struct btrfs_key search_key = ref->key_for_search;
 
     /*
      * If we're search_commit_root we could possibly be holding locks on
      * other tree nodes.  This happens when qgroups does backref walks when
      * adding new delayed refs.  To deal with this we need to look in cache
      * for the root, and if we don't find it then we need to search the
      * tree_root's commit root, thus the btrfs_get_fs_root_commit_root usage
      * here.
      */
     if (path->search_commit_root)
         root = btrfs_get_fs_root_commit_root(fs_info, path, ref->root_id);
     else
         root = btrfs_get_fs_root(fs_info, ref->root_id, false);
     if (IS_ERR(root)) {
         ret = PTR_ERR(root);
         goto out_free;
     }
 
     if (!path->search_commit_root &&
         test_bit(BTRFS_ROOT_DELETING, &root->state)) {
         ret = -ENOENT;
         goto out;
     }
 
     if (btrfs_is_testing(fs_info)) {
         ret = -ENOENT;
         goto out;
     }
 
     if (path->search_commit_root)
         root_level = btrfs_header_level(root->commit_root);
     else if (time_seq == BTRFS_SEQ_LAST)
         root_level = btrfs_header_level(root->node);
     else
         root_level = btrfs_old_root_level(root, time_seq);
 
     if (root_level + 1 == level)
         goto out;
 
     /*
      * We can often find data backrefs with an offset that is too large
      * (>= LLONG_MAX, maximum allowed file offset) due to underflows when
      * subtracting a file's offset with the data offset of its
      * corresponding extent data item. This can happen for example in the
      * clone ioctl.
      *
      * So if we detect such case we set the search key's offset to zero to
      * make sure we will find the matching file extent item at
      * add_all_parents(), otherwise we will miss it because the offset
      * taken form the backref is much larger then the offset of the file
      * extent item. This can make us scan a very large number of file
      * extent items, but at least it will not make us miss any.
      *
      * This is an ugly workaround for a behaviour that should have never
      * existed, but it does and a fix for the clone ioctl would touch a lot
      * of places, cause backwards incompatibility and would not fix the
      * problem for extents cloned with older kernels.
      */
     if (search_key.type == BTRFS_EXTENT_DATA_KEY &&
         search_key.offset >= LLONG_MAX)
         search_key.offset = 0;
     path->lowest_level = level;
     if (time_seq == BTRFS_SEQ_LAST)
         ret = btrfs_search_slot(NULL, root, &search_key, path, 0, 0);
     else
         ret = btrfs_search_old_slot(root, &search_key, path, time_seq);
 
     btrfs_debug(fs_info,
         "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, preftrees, ref, level,
                   time_seq, extent_item_pos, ignore_offset);
 out:
     btrfs_put_root(root);
 out_free:
     path->lowest_level = 0;
     btrfs_release_path(path);
     return ret;
 }
 
 static struct extent_inode_elem *
 unode_aux_to_inode_list(struct ulist_node *node)
 {
     if (!node)
         return NULL;
     return (struct extent_inode_elem *)(uintptr_t)node->aux;
 }
 
 /*
  * We maintain three separate rbtrees: one for direct refs, one for
  * indirect refs which have a key, and one for indirect refs which do not
  * have a key. Each tree does merge on insertion.
  *
  * Once all of the references are located, we iterate over the tree of
  * indirect refs with missing keys. An appropriate key is located and
  * the ref is moved onto the tree for indirect refs. After all missing
  * keys are thus located, we iterate over the indirect ref tree, resolve
  * each reference, and then insert the resolved reference onto the
  * direct tree (merging there too).
  *
  * New backrefs (i.e., for parent nodes) are added to the appropriate
  * rbtree as they are encountered. The new backrefs are subsequently
  * resolved as above.
  */
 static int resolve_indirect_refs(struct btrfs_fs_info *fs_info,
                  struct btrfs_path *path, u64 time_seq,
                  struct preftrees *preftrees,
                  const u64 *extent_item_pos,
                  struct share_check *sc, bool ignore_offset)
 {
     int err;
     int ret = 0;
     struct ulist *parents;
     struct ulist_node *node;
     struct ulist_iterator uiter;
     struct rb_node *rnode;
 
     parents = ulist_alloc(GFP_NOFS);
     if (!parents)
         return -ENOMEM;
 
     /*
      * We could trade memory usage for performance here by iterating
      * the tree, allocating new refs for each insertion, and then
      * freeing the entire indirect tree when we're done.  In some test
      * cases, the tree can grow quite large (~200k objects).
      */
     while ((rnode = rb_first_cached(&preftrees->indirect.root))) {
         struct prelim_ref *ref;
 
         ref = rb_entry(rnode, struct prelim_ref, rbnode);
         if (WARN(ref->parent,
              "BUG: direct ref found in indirect tree")) {
             ret = -EINVAL;
             goto out;
         }
 
         rb_erase_cached(&ref->rbnode, &preftrees->indirect.root);
         preftrees->indirect.count--;
 
         if (ref->count == 0) {
             free_pref(ref);
             continue;
         }
 
         if (sc && sc->root_objectid &&
             ref->root_id != sc->root_objectid) {
             free_pref(ref);
             ret = BACKREF_FOUND_SHARED;
             goto out;
         }
         err = resolve_indirect_ref(fs_info, path, time_seq, preftrees,
                        ref, parents, extent_item_pos,
                        ignore_offset);
         /*
          * we can only tolerate ENOENT,otherwise,we should catch error
          * and return directly.
          */
         if (err == -ENOENT) {
             prelim_ref_insert(fs_info, &preftrees->direct, ref,
                       NULL);
             continue;
         } else if (err) {
             free_pref(ref);
             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 = unode_aux_to_inode_list(node);
 
         /* Add a prelim_ref(s) for any other parent(s). */
         while ((node = ulist_next(parents, &uiter))) {
             struct prelim_ref *new_ref;
 
             new_ref = kmem_cache_alloc(btrfs_prelim_ref_cache,
                            GFP_NOFS);
             if (!new_ref) {
                 free_pref(ref);
                 ret = -ENOMEM;
                 goto out;
             }
             memcpy(new_ref, ref, sizeof(*ref));
             new_ref->parent = node->val;
             new_ref->inode_list = unode_aux_to_inode_list(node);
             prelim_ref_insert(fs_info, &preftrees->direct,
                       new_ref, NULL);
         }
 
         /*
          * Now it's a direct ref, put it in the direct tree. We must
          * do this last because the ref could be merged/freed here.
          */
         prelim_ref_insert(fs_info, &preftrees->direct, ref, NULL);
 
         ulist_reinit(parents);
         cond_resched();
     }
 out:
     ulist_free(parents);
     return ret;
 }
 
 /*
  * read tree blocks and add keys where required.
  */
 static int add_missing_keys(struct btrfs_fs_info *fs_info,
                 struct preftrees *preftrees, bool lock)
 {
     struct prelim_ref *ref;
     struct extent_buffer *eb;
     struct preftree *tree = &preftrees->indirect_missing_keys;
     struct rb_node *node;
 
     while ((node = rb_first_cached(&tree->root))) {
         ref = rb_entry(node, struct prelim_ref, rbnode);
         rb_erase_cached(node, &tree->root);
 
         BUG_ON(ref->parent);    /* should not be a direct ref */
         BUG_ON(ref->key_for_search.type);
         BUG_ON(!ref->wanted_disk_byte);
 
         eb = read_tree_block(fs_info, ref->wanted_disk_byte,
                      ref->root_id, 0, ref->level - 1, NULL);
         if (IS_ERR(eb)) {
             free_pref(ref);
             return PTR_ERR(eb);
         }
         if (!extent_buffer_uptodate(eb)) {
             free_pref(ref);
             free_extent_buffer(eb);
             return -EIO;
         }
 
         if (lock)
             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);
         if (lock)
             btrfs_tree_read_unlock(eb);
         free_extent_buffer(eb);
         prelim_ref_insert(fs_info, &preftrees->indirect, ref, NULL);
         cond_resched();
     }
     return 0;
 }
 
 /*
  * 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(const struct btrfs_fs_info *fs_info,
                 struct btrfs_delayed_ref_head *head, u64 seq,
                 struct preftrees *preftrees, struct share_check *sc)
 {
     struct btrfs_delayed_ref_node *node;
     struct btrfs_delayed_extent_op *extent_op = head->extent_op;
     struct btrfs_key key;
     struct btrfs_key tmp_op_key;
     struct rb_node *n;
     int count;
     int ret = 0;
 
     if (extent_op && extent_op->update_key)
         btrfs_disk_key_to_cpu(&tmp_op_key, &extent_op->key);
 
     spin_lock(&head->lock);
     for (n = rb_first_cached(&head->ref_tree); n; n = rb_next(n)) {
         node = rb_entry(n, struct btrfs_delayed_ref_node,
                 ref_node);
         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:
             count = node->ref_mod;
             break;
         case BTRFS_DROP_DELAYED_REF:
             count = node->ref_mod * -1;
             break;
         default:
             BUG();
         }
         switch (node->type) {
         case BTRFS_TREE_BLOCK_REF_KEY: {
             /* NORMAL INDIRECT METADATA backref */
             struct btrfs_delayed_tree_ref *ref;
 
             ref = btrfs_delayed_node_to_tree_ref(node);
             ret = add_indirect_ref(fs_info, preftrees, ref->root,
                            &tmp_op_key, ref->level + 1,
                            node->bytenr, count, sc,
                            GFP_ATOMIC);
             break;
         }
         case BTRFS_SHARED_BLOCK_REF_KEY: {
             /* SHARED DIRECT METADATA backref */
             struct btrfs_delayed_tree_ref *ref;
 
             ref = btrfs_delayed_node_to_tree_ref(node);
 
             ret = add_direct_ref(fs_info, preftrees, ref->level + 1,
                          ref->parent, node->bytenr, count,
                          sc, GFP_ATOMIC);
             break;
         }
         case BTRFS_EXTENT_DATA_REF_KEY: {
             /* NORMAL INDIRECT DATA backref */
             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;
 
             /*
              * Found a inum that doesn't match our known inum, we
              * know it's shared.
              */
             if (sc && sc->inum && ref->objectid != sc->inum) {
                 ret = BACKREF_FOUND_SHARED;
                 goto out;
             }
 
             ret = add_indirect_ref(fs_info, preftrees, ref->root,
                            &key, 0, node->bytenr, count, sc,
                            GFP_ATOMIC);
             break;
         }
         case BTRFS_SHARED_DATA_REF_KEY: {
             /* SHARED DIRECT FULL backref */
             struct btrfs_delayed_data_ref *ref;
 
             ref = btrfs_delayed_node_to_data_ref(node);
 
             ret = add_direct_ref(fs_info, preftrees, 0, ref->parent,
                          node->bytenr, count, sc,
                          GFP_ATOMIC);
             break;
         }
         default:
             WARN_ON(1);
         }
         /*
          * We must ignore BACKREF_FOUND_SHARED until all delayed
          * refs have been checked.
          */
         if (ret && (ret != BACKREF_FOUND_SHARED))
             break;
     }
     if (!ret)
         ret = extent_is_shared(sc);
 out:
     spin_unlock(&head->lock);
     return ret;
 }
 
 /*
  * add all inline backrefs for bytenr to the list
  *
  * Returns 0 on success, <0 on error, or BACKREF_FOUND_SHARED.
  */
 static int add_inline_refs(const struct btrfs_fs_info *fs_info,
                struct btrfs_path *path, u64 bytenr,
                int *info_level, struct preftrees *preftrees,
                struct share_check *sc)
 {
     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(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_get_extent_inline_ref_type(leaf, iref,
                             BTRFS_REF_TYPE_ANY);
         if (type == BTRFS_REF_TYPE_INVALID)
             return -EUCLEAN;
 
         offset = btrfs_extent_inline_ref_offset(leaf, iref);
 
         switch (type) {
         case BTRFS_SHARED_BLOCK_REF_KEY:
             ret = add_direct_ref(fs_info, preftrees,
                          *info_level + 1, offset,
                          bytenr, 1, NULL, 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_direct_ref(fs_info, preftrees, 0, offset,
                          bytenr, count, sc, GFP_NOFS);
             break;
         }
         case BTRFS_TREE_BLOCK_REF_KEY:
             ret = add_indirect_ref(fs_info, preftrees, offset,
                            NULL, *info_level + 1,
                            bytenr, 1, NULL, 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);
 
             if (sc && sc->inum && key.objectid != sc->inum) {
                 ret = BACKREF_FOUND_SHARED;
                 break;
             }
 
             root = btrfs_extent_data_ref_root(leaf, dref);
 
             ret = add_indirect_ref(fs_info, preftrees, root,
                            &key, 0, bytenr, count,
                            sc, 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
  *
  * Returns 0 on success, <0 on error, or BACKREF_FOUND_SHARED.
  */
 static int add_keyed_refs(struct btrfs_root *extent_root,
               struct btrfs_path *path, u64 bytenr,
               int info_level, struct preftrees *preftrees,
               struct share_check *sc)
 {
     struct btrfs_fs_info *fs_info = extent_root->fs_info;
     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:
             /* SHARED DIRECT METADATA backref */
             ret = add_direct_ref(fs_info, preftrees,
                          info_level + 1, key.offset,
                          bytenr, 1, NULL, GFP_NOFS);
             break;
         case BTRFS_SHARED_DATA_REF_KEY: {
             /* SHARED DIRECT FULL backref */
             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_direct_ref(fs_info, preftrees, 0,
                          key.offset, bytenr, count,
                          sc, GFP_NOFS);
             break;
         }
         case BTRFS_TREE_BLOCK_REF_KEY:
             /* NORMAL INDIRECT METADATA backref */
             ret = add_indirect_ref(fs_info, preftrees, key.offset,
                            NULL, info_level + 1, bytenr,
                            1, NULL, GFP_NOFS);
             break;
         case BTRFS_EXTENT_DATA_REF_KEY: {
             /* NORMAL INDIRECT DATA backref */
             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);
 
             if (sc && sc->inum && key.objectid != sc->inum) {
                 ret = BACKREF_FOUND_SHARED;
                 break;
             }
 
             root = btrfs_extent_data_ref_root(leaf, dref);
             ret = add_indirect_ref(fs_info, preftrees, root,
                            &key, 0, bytenr, count,
                            sc, 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
  *
  * If time_seq is set to BTRFS_SEQ_LAST, it will not search delayed_refs, and
  * behave much like trans == NULL case, the difference only lies in it will not
  * commit root.
  * The special case is for qgroup to search roots in commit_transaction().
  *
  * @sc - if !NULL, then immediately return BACKREF_FOUND_SHARED when a
  * shared extent is detected.
  *
  * Otherwise this returns 0 for success and <0 for an error.
  *
  * If ignore_offset is set to false, only extent refs whose offsets match
  * extent_item_pos are returned.  If true, every extent ref is returned
  * and extent_item_pos is ignored.
  *
  * 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 share_check *sc, bool ignore_offset)
 {
     struct btrfs_root *root = btrfs_extent_root(fs_info, bytenr);
     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 prelim_ref *ref;
     struct rb_node *node;
     struct extent_inode_elem *eie = NULL;
     struct preftrees preftrees = {
         .direct = PREFTREE_INIT,
         .indirect = PREFTREE_INIT,
         .indirect_missing_keys = PREFTREE_INIT
     };
 
     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;
         path->skip_locking = 1;
     }
 
     if (time_seq == BTRFS_SEQ_LAST)
         path->skip_locking = 1;
 
 again:
     head = NULL;
 
     ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
     if (ret < 0)
         goto out;
     if (ret == 0) {
         /* This shouldn't happen, indicates a bug or fs corruption. */
         ASSERT(ret != 0);
         ret = -EUCLEAN;
         goto out;
     }
 
     if (trans && likely(trans->type != __TRANS_DUMMY) &&
         time_seq != BTRFS_SEQ_LAST) {
         /*
          * We have a specific time_seq we care about and trans which
          * means we have the path lock, we need to grab the ref head and
          * lock it so we have a consistent view of the refs at the given
          * time.
          */
         delayed_refs = &trans->transaction->delayed_refs;
         spin_lock(&delayed_refs->lock);
         head = btrfs_find_delayed_ref_head(delayed_refs, bytenr);
         if (head) {
             if (!mutex_trylock(&head->mutex)) {
                 refcount_inc(&head->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(head);
                 goto again;
             }
             spin_unlock(&delayed_refs->lock);
             ret = add_delayed_refs(fs_info, head, time_seq,
                            &preftrees, sc);
             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, &preftrees, sc);
             if (ret)
                 goto out;
             ret = add_keyed_refs(root, path, bytenr, info_level,
                          &preftrees, sc);
             if (ret)
                 goto out;
         }
     }
 
     btrfs_release_path(path);
 
     ret = add_missing_keys(fs_info, &preftrees, path->skip_locking == 0);
     if (ret)
         goto out;
 
     WARN_ON(!RB_EMPTY_ROOT(&preftrees.indirect_missing_keys.root.rb_root));
 
     ret = resolve_indirect_refs(fs_info, path, time_seq, &preftrees,
                     extent_item_pos, sc, ignore_offset);
     if (ret)
         goto out;
 
     WARN_ON(!RB_EMPTY_ROOT(&preftrees.indirect.root.rb_root));
 
     /*
      * This walks the tree of merged and resolved refs. Tree blocks are
      * read in as needed. Unique entries are added to the ulist, and
      * the list of found roots is updated.
      *
      * We release the entire tree in one go before returning.
      */
     node = rb_first_cached(&preftrees.direct.root);
     while (node) {
         ref = rb_entry(node, struct prelim_ref, rbnode);
         node = rb_next(&ref->rbnode);
         /*
          * ref->count < 0 can happen here if there are delayed
          * refs with a node->action of BTRFS_DROP_DELAYED_REF.
          * prelim_ref_insert() relies on this when merging
          * identical refs to keep the overall count correct.
          * prelim_ref_insert() will merge only those refs
          * which compare identically.  Any refs having
          * e.g. different offsets would not be merged,
          * and would retain their original ref->count < 0.
          */
         if (roots && ref->count && ref->root_id && ref->parent == 0) {
             if (sc && sc->root_objectid &&
                 ref->root_id != sc->root_objectid) {
                 ret = BACKREF_FOUND_SHARED;
                 goto out;
             }
 
             /* 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) {
                 struct extent_buffer *eb;
 
                 eb = read_tree_block(fs_info, ref->parent, 0,
                              0, ref->level, NULL);
                 if (IS_ERR(eb)) {
                     ret = PTR_ERR(eb);
                     goto out;
                 }
                 if (!extent_buffer_uptodate(eb)) {
                     free_extent_buffer(eb);
                     ret = -EIO;
                     goto out;
                 }
 
                 if (!path->skip_locking)
                     btrfs_tree_read_lock(eb);
                 ret = find_extent_in_eb(eb, bytenr,
                             *extent_item_pos, &eie, ignore_offset);
                 if (!path->skip_locking)
                     btrfs_tree_read_unlock(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.
                  *
                  * However if there was corruption we may not
                  * have found an eie, return an error in this
                  * case.
                  */
                 ASSERT(eie);
                 if (!eie) {
                     ret = -EUCLEAN;
                     goto out;
                 }
                 while (eie->next)
                     eie = eie->next;
                 eie->next = ref->inode_list;
             }
             eie = NULL;
         }
         cond_resched();
     }
 
 out:
     btrfs_free_path(path);
 
     prelim_release(&preftrees.direct);
     prelim_release(&preftrees.indirect);
     prelim_release(&preftrees.indirect_missing_keys);
 
     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 = unode_aux_to_inode_list(node);
         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
  */
 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, bool ignore_offset)
 {
     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, NULL, ignore_offset);
     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_safe(struct btrfs_trans_handle *trans,
                      struct btrfs_fs_info *fs_info, u64 bytenr,
                      u64 time_seq, struct ulist **roots,
                      bool ignore_offset)
 {
     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, NULL, ignore_offset);
         if (ret < 0 && ret != -ENOENT) {
             ulist_free(tmp);
             ulist_free(*roots);
             *roots = NULL;
             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,
              bool skip_commit_root_sem)
 {
     int ret;
 
     if (!trans && !skip_commit_root_sem)
         down_read(&fs_info->commit_root_sem);
     ret = btrfs_find_all_roots_safe(trans, fs_info, bytenr,
                     time_seq, roots, false);
     if (!trans && !skip_commit_root_sem)
         up_read(&fs_info->commit_root_sem);
     return ret;
 }
 
 /**
  * Check if an extent is shared or not
  *
  * @root:   root inode belongs to
  * @inum:   inode number of the inode whose extent we are checking
  * @bytenr: logical bytenr of the extent we are checking
  * @roots:  list of roots this extent is shared among
  * @tmp:    temporary list used for iteration
  *
  * btrfs_check_shared uses the backref walking code but will short
  * circuit as soon as it finds a root or inode that doesn't match the
  * one passed in. This provides a significant performance benefit for
  * callers (such as fiemap) which want to know whether the extent is
  * shared but do not need a ref count.
  *
  * This attempts to attach to the running transaction in order to account for
  * delayed refs, but continues on even when no running transaction exists.
  *
  * Return: 0 if extent is not shared, 1 if it is shared, < 0 on error.
  */
 int btrfs_check_shared(struct btrfs_root *root, u64 inum, u64 bytenr,
         struct ulist *roots, struct ulist *tmp)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct btrfs_trans_handle *trans;
     struct ulist_iterator uiter;
     struct ulist_node *node;
     struct btrfs_seq_list elem = BTRFS_SEQ_LIST_INIT(elem);
     int ret = 0;
     struct share_check shared = {
         .root_objectid = root->root_key.objectid,
         .inum = inum,
         .share_count = 0,
     };
 
     ulist_init(roots);
     ulist_init(tmp);
 
     trans = btrfs_join_transaction_nostart(root);
     if (IS_ERR(trans)) {
         if (PTR_ERR(trans) != -ENOENT && PTR_ERR(trans) != -EROFS) {
             ret = PTR_ERR(trans);
             goto out;
         }
         trans = NULL;
         down_read(&fs_info->commit_root_sem);
     } else {
         btrfs_get_tree_mod_seq(fs_info, &elem);
     }
 
     ULIST_ITER_INIT(&uiter);
     while (1) {
         ret = find_parent_nodes(trans, fs_info, bytenr, elem.seq, tmp,
                     roots, NULL, &shared, false);
         if (ret == BACKREF_FOUND_SHARED) {
             /* this is the only condition under which we return 1 */
             ret = 1;
             break;
         }
         if (ret < 0 && ret != -ENOENT)
             break;
         ret = 0;
         node = ulist_next(tmp, &uiter);
         if (!node)
             break;
         bytenr = node->val;
         shared.share_count = 0;
         cond_resched();
     }
 
     if (trans) {
         btrfs_put_tree_mod_seq(fs_info, &elem);
         btrfs_end_transaction(trans);
     } else {
         up_read(&fs_info->commit_root_sem);
     }
 out:
     ulist_release(roots);
     ulist_release(tmp);
     return ret;
 }
 
 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;
     const struct extent_buffer *leaf;
     unsigned long ptr;
 
     key.objectid = inode_objectid;
     key.type = 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 (found_key.type != 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) {
             if (!path->skip_locking)
                 btrfs_tree_read_unlock(eb);
             free_extent_buffer(eb);
         }
         ret = btrfs_find_item(fs_root, path, parent, 0,
                 BTRFS_INODE_REF_KEY, &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) {
             path->nodes[0] = NULL;
             path->locks[0] = 0;
         }
         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)
 {
     struct btrfs_root *extent_root = btrfs_extent_root(fs_info, logical);
     int ret;
     u64 flags;
     u64 size = 0;
     u32 item_size;
     const 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, extent_root, &key, path, 0, 0);
     if (ret < 0)
         return ret;
 
     ret = btrfs_previous_extent_item(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->nodesize;
     else if (found_key->type == BTRFS_EXTENT_ITEM_KEY)
         size = found_key->offset;
 
     if (found_key->objectid > logical ||
         found_key->objectid + size <= logical) {
         btrfs_debug(fs_info,
             "logical %llu is not within any extent", logical);
         return -ENOENT;
     }
 
     eb = path->nodes[0];
     item_size = btrfs_item_size(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);
 
     btrfs_debug(fs_info,
         "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();
         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,
                  const struct extent_buffer *eb,
                  const struct btrfs_key *key,
                  const 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_get_extent_inline_ref_type(eb, *out_eiref,
                              BTRFS_REF_TYPE_ANY);
     if (*out_type == BTRFS_REF_TYPE_INVALID)
         return -EUCLEAN;
 
     *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_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 */
     *out_root = btrfs_extent_inline_ref_offset(eb, eiref);
 
     if (key->type == BTRFS_EXTENT_ITEM_KEY) {
         struct btrfs_tree_block_info *info;
 
         info = (struct btrfs_tree_block_info *)(ei + 1);
         *out_level = btrfs_tree_block_level(eb, info);
     } else {
         ASSERT(key->type == BTRFS_METADATA_ITEM_KEY);
         *out_level = (u8)key->offset;
     }
 
     if (ret == 1)
         *ptr = (unsigned long)-1;
 
     return 0;
 }
 
 static int iterate_leaf_refs(struct btrfs_fs_info *fs_info,
                  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) {
         btrfs_debug(fs_info,
                 "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) {
             btrfs_debug(fs_info,
                     "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,
                 bool ignore_offset)
 {
     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 btrfs_seq_list seq_elem = BTRFS_SEQ_LIST_INIT(seq_elem);
     struct ulist_iterator ref_uiter;
     struct ulist_iterator root_uiter;
 
     btrfs_debug(fs_info, "resolving all inodes for extent %llu",
             extent_item_objectid);
 
     if (!search_commit_root) {
         trans = btrfs_attach_transaction(fs_info->tree_root);
         if (IS_ERR(trans)) {
             if (PTR_ERR(trans) != -ENOENT &&
                 PTR_ERR(trans) != -EROFS)
                 return PTR_ERR(trans);
             trans = NULL;
         }
     }
 
     if (trans)
         btrfs_get_tree_mod_seq(fs_info, &seq_elem);
     else
         down_read(&fs_info->commit_root_sem);
 
     ret = btrfs_find_all_leafs(trans, fs_info, extent_item_objectid,
                    seq_elem.seq, &refs,
                    &extent_item_pos, ignore_offset);
     if (ret)
         goto out;
 
     ULIST_ITER_INIT(&ref_uiter);
     while (!ret && (ref_node = ulist_next(refs, &ref_uiter))) {
         ret = btrfs_find_all_roots_safe(trans, fs_info, ref_node->val,
                         seq_elem.seq, &roots,
                         ignore_offset);
         if (ret)
             break;
         ULIST_ITER_INIT(&root_uiter);
         while (!ret && (root_node = ulist_next(roots, &root_uiter))) {
             btrfs_debug(fs_info,
                     "root %llu references leaf %llu, data list %#llx",
                     root_node->val, ref_node->val,
                     ref_node->aux);
             ret = iterate_leaf_refs(fs_info,
                         (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 (trans) {
         btrfs_put_tree_mod_seq(fs_info, &seq_elem);
         btrfs_end_transaction(trans);
     } else {
         up_read(&fs_info->commit_root_sem);
     }
 
     return ret;
 }
 
 static int build_ino_list(u64 inum, u64 offset, u64 root, void *ctx)
 {
     struct btrfs_data_container *inodes = ctx;
     const size_t c = 3 * sizeof(u64);
 
     if (inodes->bytes_left >= c) {
         inodes->bytes_left -= c;
         inodes->val[inodes->elem_cnt] = inum;
         inodes->val[inodes->elem_cnt + 1] = offset;
         inodes->val[inodes->elem_cnt + 2] = root;
         inodes->elem_cnt += 3;
     } else {
         inodes->bytes_missing += c - inodes->bytes_left;
         inodes->bytes_left = 0;
         inodes->elem_missed += 3;
     }
 
     return 0;
 }
 
 int iterate_inodes_from_logical(u64 logical, struct btrfs_fs_info *fs_info,
                 struct btrfs_path *path,
                 void *ctx, bool ignore_offset)
 {
     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,
                     build_ino_list, ctx, ignore_offset);
 
     return ret;
 }
 
 static int inode_to_path(u64 inum, u32 name_len, unsigned long name_off,
              struct extent_buffer *eb, struct inode_fs_paths *ipath);
 
 static int iterate_inode_refs(u64 inum, struct inode_fs_paths *ipath)
 {
     int ret = 0;
     int slot;
     u32 cur;
     u32 len;
     u32 name_len;
     u64 parent = 0;
     int found = 0;
     struct btrfs_root *fs_root = ipath->fs_root;
     struct btrfs_path *path = ipath->btrfs_path;
     struct extent_buffer *eb;
     struct btrfs_inode_ref *iref;
     struct btrfs_key found_key;
 
     while (!ret) {
         ret = btrfs_find_item(fs_root, path, inum,
                 parent ? parent + 1 : 0, BTRFS_INODE_REF_KEY,
                 &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;
         }
         btrfs_release_path(path);
 
         iref = btrfs_item_ptr(eb, slot, struct btrfs_inode_ref);
 
         for (cur = 0; cur < btrfs_item_size(eb, slot); cur += len) {
             name_len = btrfs_inode_ref_name_len(eb, iref);
             /* path must be released before calling iterate()! */
             btrfs_debug(fs_root->fs_info,
                 "following ref at offset %u for inode %llu in tree %llu",
                 cur, found_key.objectid,
                 fs_root->root_key.objectid);
             ret = inode_to_path(parent, name_len,
                       (unsigned long)(iref + 1), eb, ipath);
             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 inode_fs_paths *ipath)
 {
     int ret;
     int slot;
     u64 offset = 0;
     u64 parent;
     int found = 0;
     struct btrfs_root *fs_root = ipath->fs_root;
     struct btrfs_path *path = ipath->btrfs_path;
     struct extent_buffer *eb;
     struct btrfs_inode_extref *extref;
     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;
         }
         btrfs_release_path(path);
 
         item_size = btrfs_item_size(eb, slot);
         ptr = btrfs_item_ptr_offset(eb, 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 = inode_to_path(parent, name_len,
                       (unsigned long)&extref->name, eb, ipath);
             if (ret)
                 break;
 
             cur_offset += btrfs_inode_extref_name_len(eb, extref);
             cur_offset += sizeof(*extref);
         }
         free_extent_buffer(eb);
 
         offset++;
     }
 
     btrfs_release_path(path);
 
     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, struct inode_fs_paths *ipath)
 {
     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 is recorded 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)
 {
     int ret;
     int found_refs = 0;
 
     ret = iterate_inode_refs(inum, ipath);
     if (!ret)
         ++found_refs;
     else if (ret != -ENOENT)
         return ret;
 
     ret = iterate_inode_extrefs(inum, ipath);
     if (ret == -ENOENT && found_refs)
         return 0;
 
     return ret;
 }
 
 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 = kvmalloc(alloc_bytes, GFP_KERNEL);
     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 ERR_CAST(fspath);
 
     ifp = kmalloc(sizeof(*ifp), GFP_KERNEL);
     if (!ifp) {
         kvfree(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;
     kvfree(ipath->fspath);
     kfree(ipath);
 }
 
 struct btrfs_backref_iter *btrfs_backref_iter_alloc(
         struct btrfs_fs_info *fs_info, gfp_t gfp_flag)
 {
     struct btrfs_backref_iter *ret;
 
     ret = kzalloc(sizeof(*ret), gfp_flag);
     if (!ret)
         return NULL;
 
     ret->path = btrfs_alloc_path();
     if (!ret->path) {
         kfree(ret);
         return NULL;
     }
 
     /* Current backref iterator only supports iteration in commit root */
     ret->path->search_commit_root = 1;
     ret->path->skip_locking = 1;
     ret->fs_info = fs_info;
 
     return ret;
 }
 
 int btrfs_backref_iter_start(struct btrfs_backref_iter *iter, u64 bytenr)
 {
     struct btrfs_fs_info *fs_info = iter->fs_info;
     struct btrfs_root *extent_root = btrfs_extent_root(fs_info, bytenr);
     struct btrfs_path *path = iter->path;
     struct btrfs_extent_item *ei;
     struct btrfs_key key;
     int ret;
 
     key.objectid = bytenr;
     key.type = BTRFS_METADATA_ITEM_KEY;
     key.offset = (u64)-1;
     iter->bytenr = bytenr;
 
     ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
     if (ret < 0)
         return ret;
     if (ret == 0) {
         ret = -EUCLEAN;
         goto release;
     }
     if (path->slots[0] == 0) {
         WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG));
         ret = -EUCLEAN;
         goto release;
     }
     path->slots[0]--;
 
     btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
     if ((key.type != BTRFS_EXTENT_ITEM_KEY &&
          key.type != BTRFS_METADATA_ITEM_KEY) || key.objectid != bytenr) {
         ret = -ENOENT;
         goto release;
     }
     memcpy(&iter->cur_key, &key, sizeof(key));
     iter->item_ptr = (u32)btrfs_item_ptr_offset(path->nodes[0],
                             path->slots[0]);
     iter->end_ptr = (u32)(iter->item_ptr +
             btrfs_item_size(path->nodes[0], path->slots[0]));
     ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
                 struct btrfs_extent_item);
 
     /*
      * Only support iteration on tree backref yet.
      *
      * This is an extra precaution for non skinny-metadata, where
      * EXTENT_ITEM is also used for tree blocks, that we can only use
      * extent flags to determine if it's a tree block.
      */
     if (btrfs_extent_flags(path->nodes[0], ei) & BTRFS_EXTENT_FLAG_DATA) {
         ret = -ENOTSUPP;
         goto release;
     }
     iter->cur_ptr = (u32)(iter->item_ptr + sizeof(*ei));
 
     /* If there is no inline backref, go search for keyed backref */
     if (iter->cur_ptr >= iter->end_ptr) {
         ret = btrfs_next_item(extent_root, path);
 
         /* No inline nor keyed ref */
         if (ret > 0) {
             ret = -ENOENT;
             goto release;
         }
         if (ret < 0)
             goto release;
 
         btrfs_item_key_to_cpu(path->nodes[0], &iter->cur_key,
                 path->slots[0]);
         if (iter->cur_key.objectid != bytenr ||
             (iter->cur_key.type != BTRFS_SHARED_BLOCK_REF_KEY &&
              iter->cur_key.type != BTRFS_TREE_BLOCK_REF_KEY)) {
             ret = -ENOENT;
             goto release;
         }
         iter->cur_ptr = (u32)btrfs_item_ptr_offset(path->nodes[0],
                                path->slots[0]);
         iter->item_ptr = iter->cur_ptr;
         iter->end_ptr = (u32)(iter->item_ptr + btrfs_item_size(
                       path->nodes[0], path->slots[0]));
     }
 
     return 0;
 release:
     btrfs_backref_iter_release(iter);
     return ret;
 }
 
 /*
  * Go to the next backref item of current bytenr, can be either inlined or
  * keyed.
  *
  * Caller needs to check whether it's inline ref or not by iter->cur_key.
  *
  * Return 0 if we get next backref without problem.
  * Return >0 if there is no extra backref for this bytenr.
  * Return <0 if there is something wrong happened.
  */
 int btrfs_backref_iter_next(struct btrfs_backref_iter *iter)
 {
     struct extent_buffer *eb = btrfs_backref_get_eb(iter);
     struct btrfs_root *extent_root;
     struct btrfs_path *path = iter->path;
     struct btrfs_extent_inline_ref *iref;
     int ret;
     u32 size;
 
     if (btrfs_backref_iter_is_inline_ref(iter)) {
         /* We're still inside the inline refs */
         ASSERT(iter->cur_ptr < iter->end_ptr);
 
         if (btrfs_backref_has_tree_block_info(iter)) {
             /* First tree block info */
             size = sizeof(struct btrfs_tree_block_info);
         } else {
             /* Use inline ref type to determine the size */
             int type;
 
             iref = (struct btrfs_extent_inline_ref *)
                 ((unsigned long)iter->cur_ptr);
             type = btrfs_extent_inline_ref_type(eb, iref);
 
             size = btrfs_extent_inline_ref_size(type);
         }
         iter->cur_ptr += size;
         if (iter->cur_ptr < iter->end_ptr)
             return 0;
 
         /* All inline items iterated, fall through */
     }
 
     /* We're at keyed items, there is no inline item, go to the next one */
     extent_root = btrfs_extent_root(iter->fs_info, iter->bytenr);
     ret = btrfs_next_item(extent_root, iter->path);
     if (ret)
         return ret;
 
     btrfs_item_key_to_cpu(path->nodes[0], &iter->cur_key, path->slots[0]);
     if (iter->cur_key.objectid != iter->bytenr ||
         (iter->cur_key.type != BTRFS_TREE_BLOCK_REF_KEY &&
          iter->cur_key.type != BTRFS_SHARED_BLOCK_REF_KEY))
         return 1;
     iter->item_ptr = (u32)btrfs_item_ptr_offset(path->nodes[0],
                     path->slots[0]);
     iter->cur_ptr = iter->item_ptr;
     iter->end_ptr = iter->item_ptr + (u32)btrfs_item_size(path->nodes[0],
                         path->slots[0]);
     return 0;
 }
 
 void btrfs_backref_init_cache(struct btrfs_fs_info *fs_info,
                   struct btrfs_backref_cache *cache, int is_reloc)
 {
     int i;
 
     cache->rb_root = RB_ROOT;
     for (i = 0; i < BTRFS_MAX_LEVEL; i++)
         INIT_LIST_HEAD(&cache->pending[i]);
     INIT_LIST_HEAD(&cache->changed);
     INIT_LIST_HEAD(&cache->detached);
     INIT_LIST_HEAD(&cache->leaves);
     INIT_LIST_HEAD(&cache->pending_edge);
     INIT_LIST_HEAD(&cache->useless_node);
     cache->fs_info = fs_info;
     cache->is_reloc = is_reloc;
 }
 
 struct btrfs_backref_node *btrfs_backref_alloc_node(
         struct btrfs_backref_cache *cache, u64 bytenr, int level)
 {
     struct btrfs_backref_node *node;
 
     ASSERT(level >= 0 && level < BTRFS_MAX_LEVEL);
     node = kzalloc(sizeof(*node), GFP_NOFS);
     if (!node)
         return node;
 
     INIT_LIST_HEAD(&node->list);
     INIT_LIST_HEAD(&node->upper);
     INIT_LIST_HEAD(&node->lower);
     RB_CLEAR_NODE(&node->rb_node);
     cache->nr_nodes++;
     node->level = level;
     node->bytenr = bytenr;
 
     return node;
 }
 
 struct btrfs_backref_edge *btrfs_backref_alloc_edge(
         struct btrfs_backref_cache *cache)
 {
     struct btrfs_backref_edge *edge;
 
     edge = kzalloc(sizeof(*edge), GFP_NOFS);
     if (edge)
         cache->nr_edges++;
     return edge;
 }
 
 /*
  * Drop the backref node from cache, also cleaning up all its
  * upper edges and any uncached nodes in the path.
  *
  * This cleanup happens bottom up, thus the node should either
  * be the lowest node in the cache or a detached node.
  */
 void btrfs_backref_cleanup_node(struct btrfs_backref_cache *cache,
                 struct btrfs_backref_node *node)
 {
     struct btrfs_backref_node *upper;
     struct btrfs_backref_edge *edge;
 
     if (!node)
         return;
 
     BUG_ON(!node->lowest && !node->detached);
     while (!list_empty(&node->upper)) {
         edge = list_entry(node->upper.next, struct btrfs_backref_edge,
                   list[LOWER]);
         upper = edge->node[UPPER];
         list_del(&edge->list[LOWER]);
         list_del(&edge->list[UPPER]);
         btrfs_backref_free_edge(cache, edge);
 
         /*
          * Add the node to leaf node list if no other child block
          * cached.
          */
         if (list_empty(&upper->lower)) {
             list_add_tail(&upper->lower, &cache->leaves);
             upper->lowest = 1;
         }
     }
 
     btrfs_backref_drop_node(cache, node);
 }
 
 /*
  * Release all nodes/edges from current cache
  */
 void btrfs_backref_release_cache(struct btrfs_backref_cache *cache)
 {
     struct btrfs_backref_node *node;
     int i;
 
     while (!list_empty(&cache->detached)) {
         node = list_entry(cache->detached.next,
                   struct btrfs_backref_node, list);
         btrfs_backref_cleanup_node(cache, node);
     }
 
     while (!list_empty(&cache->leaves)) {
         node = list_entry(cache->leaves.next,
                   struct btrfs_backref_node, lower);
         btrfs_backref_cleanup_node(cache, node);
     }
 
     cache->last_trans = 0;
 
     for (i = 0; i < BTRFS_MAX_LEVEL; i++)
         ASSERT(list_empty(&cache->pending[i]));
     ASSERT(list_empty(&cache->pending_edge));
     ASSERT(list_empty(&cache->useless_node));
     ASSERT(list_empty(&cache->changed));
     ASSERT(list_empty(&cache->detached));
     ASSERT(RB_EMPTY_ROOT(&cache->rb_root));
     ASSERT(!cache->nr_nodes);
     ASSERT(!cache->nr_edges);
 }
 
 /*
  * Handle direct tree backref
  *
  * Direct tree backref means, the backref item shows its parent bytenr
  * directly. This is for SHARED_BLOCK_REF backref (keyed or inlined).
  *
  * @ref_key:    The converted backref key.
  *      For keyed backref, it's the item key.
  *      For inlined backref, objectid is the bytenr,
  *      type is btrfs_inline_ref_type, offset is
  *      btrfs_inline_ref_offset.
  */
 static int handle_direct_tree_backref(struct btrfs_backref_cache *cache,
                       struct btrfs_key *ref_key,
                       struct btrfs_backref_node *cur)
 {
     struct btrfs_backref_edge *edge;
     struct btrfs_backref_node *upper;
     struct rb_node *rb_node;
 
     ASSERT(ref_key->type == BTRFS_SHARED_BLOCK_REF_KEY);
 
     /* Only reloc root uses backref pointing to itself */
     if (ref_key->objectid == ref_key->offset) {
         struct btrfs_root *root;
 
         cur->is_reloc_root = 1;
         /* Only reloc backref cache cares about a specific root */
         if (cache->is_reloc) {
             root = find_reloc_root(cache->fs_info, cur->bytenr);
             if (!root)
                 return -ENOENT;
             cur->root = root;
         } else {
             /*
              * For generic purpose backref cache, reloc root node
              * is useless.
              */
             list_add(&cur->list, &cache->useless_node);
         }
         return 0;
     }
 
     edge = btrfs_backref_alloc_edge(cache);
     if (!edge)
         return -ENOMEM;
 
     rb_node = rb_simple_search(&cache->rb_root, ref_key->offset);
     if (!rb_node) {
         /* Parent node not yet cached */
         upper = btrfs_backref_alloc_node(cache, ref_key->offset,
                        cur->level + 1);
         if (!upper) {
             btrfs_backref_free_edge(cache, edge);
             return -ENOMEM;
         }
 
         /*
          *  Backrefs for the upper level block isn't cached, add the
          *  block to pending list
          */
         list_add_tail(&edge->list[UPPER], &cache->pending_edge);
     } else {
         /* Parent node already cached */
         upper = rb_entry(rb_node, struct btrfs_backref_node, rb_node);
         ASSERT(upper->checked);
         INIT_LIST_HEAD(&edge->list[UPPER]);
     }
     btrfs_backref_link_edge(edge, cur, upper, LINK_LOWER);
     return 0;
 }
 
 /*
  * Handle indirect tree backref
  *
  * Indirect tree backref means, we only know which tree the node belongs to.
  * We still need to do a tree search to find out the parents. This is for
  * TREE_BLOCK_REF backref (keyed or inlined).
  *
  * @ref_key:    The same as @ref_key in  handle_direct_tree_backref()
  * @tree_key:   The first key of this tree block.
  * @path:   A clean (released) path, to avoid allocating path every time
  *      the function get called.
  */
 static int handle_indirect_tree_backref(struct btrfs_backref_cache *cache,
                     struct btrfs_path *path,
                     struct btrfs_key *ref_key,
                     struct btrfs_key *tree_key,
                     struct btrfs_backref_node *cur)
 {
     struct btrfs_fs_info *fs_info = cache->fs_info;
     struct btrfs_backref_node *upper;
     struct btrfs_backref_node *lower;
     struct btrfs_backref_edge *edge;
     struct extent_buffer *eb;
     struct btrfs_root *root;
     struct rb_node *rb_node;
     int level;
     bool need_check = true;
     int ret;
 
     root = btrfs_get_fs_root(fs_info, ref_key->offset, false);
     if (IS_ERR(root))
         return PTR_ERR(root);
     if (!test_bit(BTRFS_ROOT_SHAREABLE, &root->state))
         cur->cowonly = 1;
 
     if (btrfs_root_level(&root->root_item) == cur->level) {
         /* Tree root */
         ASSERT(btrfs_root_bytenr(&root->root_item) == cur->bytenr);
         /*
          * For reloc backref cache, we may ignore reloc root.  But for
          * general purpose backref cache, we can't rely on
          * btrfs_should_ignore_reloc_root() as it may conflict with
          * current running relocation and lead to missing root.
          *
          * For general purpose backref cache, reloc root detection is
          * completely relying on direct backref (key->offset is parent
          * bytenr), thus only do such check for reloc cache.
          */
         if (btrfs_should_ignore_reloc_root(root) && cache->is_reloc) {
             btrfs_put_root(root);
             list_add(&cur->list, &cache->useless_node);
         } else {
             cur->root = root;
         }
         return 0;
     }
 
     level = cur->level + 1;
 
     /* Search the tree to find parent blocks referring to the block */
     path->search_commit_root = 1;
     path->skip_locking = 1;
     path->lowest_level = level;
     ret = btrfs_search_slot(NULL, root, tree_key, path, 0, 0);
     path->lowest_level = 0;
     if (ret < 0) {
         btrfs_put_root(root);
         return ret;
     }
     if (ret > 0 && path->slots[level] > 0)
         path->slots[level]--;
 
     eb = path->nodes[level];
     if (btrfs_node_blockptr(eb, path->slots[level]) != cur->bytenr) {
         btrfs_err(fs_info,
 "couldn't find block (%llu) (level %d) in tree (%llu) with key (%llu %u %llu)",
               cur->bytenr, level - 1, root->root_key.objectid,
               tree_key->objectid, tree_key->type, tree_key->offset);
         btrfs_put_root(root);
         ret = -ENOENT;
         goto out;
     }
     lower = cur;
 
     /* Add all nodes and edges in the path */
     for (; level < BTRFS_MAX_LEVEL; level++) {
         if (!path->nodes[level]) {
             ASSERT(btrfs_root_bytenr(&root->root_item) ==
                    lower->bytenr);
             /* Same as previous should_ignore_reloc_root() call */
             if (btrfs_should_ignore_reloc_root(root) &&
                 cache->is_reloc) {
                 btrfs_put_root(root);
                 list_add(&lower->list, &cache->useless_node);
             } else {
                 lower->root = root;
             }
             break;
         }
 
         edge = btrfs_backref_alloc_edge(cache);
         if (!edge) {
             btrfs_put_root(root);
             ret = -ENOMEM;
             goto out;
         }
 
         eb = path->nodes[level];
         rb_node = rb_simple_search(&cache->rb_root, eb->start);
         if (!rb_node) {
             upper = btrfs_backref_alloc_node(cache, eb->start,
                              lower->level + 1);
             if (!upper) {
                 btrfs_put_root(root);
                 btrfs_backref_free_edge(cache, edge);
                 ret = -ENOMEM;
                 goto out;
             }
             upper->owner = btrfs_header_owner(eb);
             if (!test_bit(BTRFS_ROOT_SHAREABLE, &root->state))
                 upper->cowonly = 1;
 
             /*
              * If we know the block isn't shared we can avoid
              * checking its backrefs.
              */
             if (btrfs_block_can_be_shared(root, eb))
                 upper->checked = 0;
             else
                 upper->checked = 1;
 
             /*
              * Add the block to pending list if we need to check its
              * backrefs, we only do this once while walking up a
              * tree as we will catch anything else later on.
              */
             if (!upper->checked && need_check) {
                 need_check = false;
                 list_add_tail(&edge->list[UPPER],
                           &cache->pending_edge);
             } else {
                 if (upper->checked)
                     need_check = true;
                 INIT_LIST_HEAD(&edge->list[UPPER]);
             }
         } else {
             upper = rb_entry(rb_node, struct btrfs_backref_node,
                      rb_node);
             ASSERT(upper->checked);
             INIT_LIST_HEAD(&edge->list[UPPER]);
             if (!upper->owner)
                 upper->owner = btrfs_header_owner(eb);
         }
         btrfs_backref_link_edge(edge, lower, upper, LINK_LOWER);
 
         if (rb_node) {
             btrfs_put_root(root);
             break;
         }
         lower = upper;
         upper = NULL;
     }
 out:
     btrfs_release_path(path);
     return ret;
 }
 
 /*
  * Add backref node @cur into @cache.
  *
  * NOTE: Even if the function returned 0, @cur is not yet cached as its upper
  *   links aren't yet bi-directional. Needs to finish such links.
  *   Use btrfs_backref_finish_upper_links() to finish such linkage.
  *
  * @path:   Released path for indirect tree backref lookup
  * @iter:   Released backref iter for extent tree search
  * @node_key:   The first key of the tree block
  */
 int btrfs_backref_add_tree_node(struct btrfs_backref_cache *cache,
                 struct btrfs_path *path,
                 struct btrfs_backref_iter *iter,
                 struct btrfs_key *node_key,
                 struct btrfs_backref_node *cur)
 {
     struct btrfs_fs_info *fs_info = cache->fs_info;
     struct btrfs_backref_edge *edge;
     struct btrfs_backref_node *exist;
     int ret;
 
     ret = btrfs_backref_iter_start(iter, cur->bytenr);
     if (ret < 0)
         return ret;
     /*
      * We skip the first btrfs_tree_block_info, as we don't use the key
      * stored in it, but fetch it from the tree block
      */
     if (btrfs_backref_has_tree_block_info(iter)) {
         ret = btrfs_backref_iter_next(iter);
         if (ret < 0)
             goto out;
         /* No extra backref? This means the tree block is corrupted */
         if (ret > 0) {
             ret = -EUCLEAN;
             goto out;
         }
     }
     WARN_ON(cur->checked);
     if (!list_empty(&cur->upper)) {
         /*
          * The backref was added previously when processing backref of
          * type BTRFS_TREE_BLOCK_REF_KEY
          */
         ASSERT(list_is_singular(&cur->upper));
         edge = list_entry(cur->upper.next, struct btrfs_backref_edge,
                   list[LOWER]);
         ASSERT(list_empty(&edge->list[UPPER]));
         exist = edge->node[UPPER];
         /*
          * Add the upper level block to pending list if we need check
          * its backrefs
          */
         if (!exist->checked)
             list_add_tail(&edge->list[UPPER], &cache->pending_edge);
     } else {
         exist = NULL;
     }
 
     for (; ret == 0; ret = btrfs_backref_iter_next(iter)) {
         struct extent_buffer *eb;
         struct btrfs_key key;
         int type;
 
         cond_resched();
         eb = btrfs_backref_get_eb(iter);
 
         key.objectid = iter->bytenr;
         if (btrfs_backref_iter_is_inline_ref(iter)) {
             struct btrfs_extent_inline_ref *iref;
 
             /* Update key for inline backref */
             iref = (struct btrfs_extent_inline_ref *)
                 ((unsigned long)iter->cur_ptr);
             type = btrfs_get_extent_inline_ref_type(eb, iref,
                             BTRFS_REF_TYPE_BLOCK);
             if (type == BTRFS_REF_TYPE_INVALID) {
                 ret = -EUCLEAN;
                 goto out;
             }
             key.type = type;
             key.offset = btrfs_extent_inline_ref_offset(eb, iref);
         } else {
             key.type = iter->cur_key.type;
             key.offset = iter->cur_key.offset;
         }
 
         /*
          * Parent node found and matches current inline ref, no need to
          * rebuild this node for this inline ref
          */
         if (exist &&
             ((key.type == BTRFS_TREE_BLOCK_REF_KEY &&
               exist->owner == key.offset) ||
              (key.type == BTRFS_SHARED_BLOCK_REF_KEY &&
               exist->bytenr == key.offset))) {
             exist = NULL;
             continue;
         }
 
         /* SHARED_BLOCK_REF means key.offset is the parent bytenr */
         if (key.type == BTRFS_SHARED_BLOCK_REF_KEY) {
             ret = handle_direct_tree_backref(cache, &key, cur);
             if (ret < 0)
                 goto out;
             continue;
         } else if (unlikely(key.type == BTRFS_EXTENT_REF_V0_KEY)) {
             ret = -EINVAL;
             btrfs_print_v0_err(fs_info);
             btrfs_handle_fs_error(fs_info, ret, NULL);
             goto out;
         } else if (key.type != BTRFS_TREE_BLOCK_REF_KEY) {
             continue;
         }
 
         /*
          * key.type == BTRFS_TREE_BLOCK_REF_KEY, inline ref offset
          * means the root objectid. We need to search the tree to get
          * its parent bytenr.
          */
         ret = handle_indirect_tree_backref(cache, path, &key, node_key,
                            cur);
         if (ret < 0)
             goto out;
     }
     ret = 0;
     cur->checked = 1;
     WARN_ON(exist);
 out:
     btrfs_backref_iter_release(iter);
     return ret;
 }
 
 /*
  * Finish the upwards linkage created by btrfs_backref_add_tree_node()
  */
 int btrfs_backref_finish_upper_links(struct btrfs_backref_cache *cache,
                      struct btrfs_backref_node *start)
 {
     struct list_head *useless_node = &cache->useless_node;
     struct btrfs_backref_edge *edge;
     struct rb_node *rb_node;
     LIST_HEAD(pending_edge);
 
     ASSERT(start->checked);
 
     /* Insert this node to cache if it's not COW-only */
     if (!start->cowonly) {
         rb_node = rb_simple_insert(&cache->rb_root, start->bytenr,
                        &start->rb_node);
         if (rb_node)
             btrfs_backref_panic(cache->fs_info, start->bytenr,
                         -EEXIST);
         list_add_tail(&start->lower, &cache->leaves);
     }
 
     /*
      * Use breadth first search to iterate all related edges.
      *
      * The starting points are all the edges of this node
      */
     list_for_each_entry(edge, &start->upper, list[LOWER])
         list_add_tail(&edge->list[UPPER], &pending_edge);
 
     while (!list_empty(&pending_edge)) {
         struct btrfs_backref_node *upper;
         struct btrfs_backref_node *lower;
 
         edge = list_first_entry(&pending_edge,
                 struct btrfs_backref_edge, list[UPPER]);
         list_del_init(&edge->list[UPPER]);
         upper = edge->node[UPPER];
         lower = edge->node[LOWER];
 
         /* Parent is detached, no need to keep any edges */
         if (upper->detached) {
             list_del(&edge->list[LOWER]);
             btrfs_backref_free_edge(cache, edge);
 
             /* Lower node is orphan, queue for cleanup */
             if (list_empty(&lower->upper))
                 list_add(&lower->list, useless_node);
             continue;
         }
 
         /*
          * All new nodes added in current build_backref_tree() haven't
          * been linked to the cache rb tree.
          * So if we have upper->rb_node populated, this means a cache
          * hit. We only need to link the edge, as @upper and all its
          * parents have already been linked.
          */
         if (!RB_EMPTY_NODE(&upper->rb_node)) {
             if (upper->lowest) {
                 list_del_init(&upper->lower);
                 upper->lowest = 0;
             }
 
             list_add_tail(&edge->list[UPPER], &upper->lower);
             continue;
         }
 
         /* Sanity check, we shouldn't have any unchecked nodes */
         if (!upper->checked) {
             ASSERT(0);
             return -EUCLEAN;
         }
 
         /* Sanity check, COW-only node has non-COW-only parent */
         if (start->cowonly != upper->cowonly) {
             ASSERT(0);
             return -EUCLEAN;
         }
 
         /* Only cache non-COW-only (subvolume trees) tree blocks */
         if (!upper->cowonly) {
             rb_node = rb_simple_insert(&cache->rb_root, upper->bytenr,
                            &upper->rb_node);
             if (rb_node) {
                 btrfs_backref_panic(cache->fs_info,
                         upper->bytenr, -EEXIST);
                 return -EUCLEAN;
             }
         }
 
         list_add_tail(&edge->list[UPPER], &upper->lower);
 
         /*
          * Also queue all the parent edges of this uncached node
          * to finish the upper linkage
          */
         list_for_each_entry(edge, &upper->upper, list[LOWER])
             list_add_tail(&edge->list[UPPER], &pending_edge);
     }
     return 0;
 }
 
 void btrfs_backref_error_cleanup(struct btrfs_backref_cache *cache,
                  struct btrfs_backref_node *node)
 {
     struct btrfs_backref_node *lower;
     struct btrfs_backref_node *upper;
     struct btrfs_backref_edge *edge;
 
     while (!list_empty(&cache->useless_node)) {
         lower = list_first_entry(&cache->useless_node,
                    struct btrfs_backref_node, list);
         list_del_init(&lower->list);
     }
     while (!list_empty(&cache->pending_edge)) {
         edge = list_first_entry(&cache->pending_edge,
                 struct btrfs_backref_edge, list[UPPER]);
         list_del(&edge->list[UPPER]);
         list_del(&edge->list[LOWER]);
         lower = edge->node[LOWER];
         upper = edge->node[UPPER];
         btrfs_backref_free_edge(cache, edge);
 
         /*
          * Lower is no longer linked to any upper backref nodes and
          * isn't in the cache, we can free it ourselves.
          */
         if (list_empty(&lower->upper) &&
             RB_EMPTY_NODE(&lower->rb_node))
             list_add(&lower->list, &cache->useless_node);
 
         if (!RB_EMPTY_NODE(&upper->rb_node))
             continue;
 
         /* Add this guy's upper edges to the list to process */
         list_for_each_entry(edge, &upper->upper, list[LOWER])
             list_add_tail(&edge->list[UPPER],
                       &cache->pending_edge);
         if (list_empty(&upper->upper))
             list_add(&upper->list, &cache->useless_node);
     }
 
     while (!list_empty(&cache->useless_node)) {
         lower = list_first_entry(&cache->useless_node,
                    struct btrfs_backref_node, list);
         list_del_init(&lower->list);
         if (lower == node)
             node = NULL;
         btrfs_backref_drop_node(cache, lower);
     }
 
     btrfs_backref_cleanup_node(cache, node);
     ASSERT(list_empty(&cache->useless_node) &&
            list_empty(&cache->pending_edge));
 }