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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) 2009 Oracle.  All rights reserved.
  */
 
 #include <linux/sched.h>
 #include <linux/pagemap.h>
 #include <linux/writeback.h>
 #include <linux/blkdev.h>
 #include <linux/rbtree.h>
 #include <linux/slab.h>
 #include <linux/error-injection.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "transaction.h"
 #include "volumes.h"
 #include "locking.h"
 #include "btrfs_inode.h"
 #include "async-thread.h"
 #include "free-space-cache.h"
 #include "qgroup.h"
 #include "print-tree.h"
 #include "delalloc-space.h"
 #include "block-group.h"
 #include "backref.h"
 #include "misc.h"
 #include "subpage.h"
 #include "zoned.h"
 #include "inode-item.h"
 
 /*
  * Relocation overview
  *
  * [What does relocation do]
  *
  * The objective of relocation is to relocate all extents of the target block
  * group to other block groups.
  * This is utilized by resize (shrink only), profile converting, compacting
  * space, or balance routine to spread chunks over devices.
  *
  *      Before      |       After
  * ------------------------------------------------------------------
  *  BG A: 10 data extents   | BG A: deleted
  *  BG B:  2 data extents   | BG B: 10 data extents (2 old + 8 relocated)
  *  BG C:  1 extents        | BG C:  3 data extents (1 old + 2 relocated)
  *
  * [How does relocation work]
  *
  * 1.   Mark the target block group read-only
  *      New extents won't be allocated from the target block group.
  *
  * 2.1  Record each extent in the target block group
  *      To build a proper map of extents to be relocated.
  *
  * 2.2  Build data reloc tree and reloc trees
  *      Data reloc tree will contain an inode, recording all newly relocated
  *      data extents.
  *      There will be only one data reloc tree for one data block group.
  *
  *      Reloc tree will be a special snapshot of its source tree, containing
  *      relocated tree blocks.
  *      Each tree referring to a tree block in target block group will get its
  *      reloc tree built.
  *
  * 2.3  Swap source tree with its corresponding reloc tree
  *      Each involved tree only refers to new extents after swap.
  *
  * 3.   Cleanup reloc trees and data reloc tree.
  *      As old extents in the target block group are still referenced by reloc
  *      trees, we need to clean them up before really freeing the target block
  *      group.
  *
  * The main complexity is in steps 2.2 and 2.3.
  *
  * The entry point of relocation is relocate_block_group() function.
  */
 
 #define RELOCATION_RESERVED_NODES   256
 /*
  * map address of tree root to tree
  */
 struct mapping_node {
     struct {
         struct rb_node rb_node;
         u64 bytenr;
     }; /* Use rb_simle_node for search/insert */
     void *data;
 };
 
 struct mapping_tree {
     struct rb_root rb_root;
     spinlock_t lock;
 };
 
 /*
  * present a tree block to process
  */
 struct tree_block {
     struct {
         struct rb_node rb_node;
         u64 bytenr;
     }; /* Use rb_simple_node for search/insert */
     u64 owner;
     struct btrfs_key key;
     unsigned int level:8;
     unsigned int key_ready:1;
 };
 
 #define MAX_EXTENTS 128
 
 struct file_extent_cluster {
     u64 start;
     u64 end;
     u64 boundary[MAX_EXTENTS];
     unsigned int nr;
 };
 
 struct reloc_control {
     /* block group to relocate */
     struct btrfs_block_group *block_group;
     /* extent tree */
     struct btrfs_root *extent_root;
     /* inode for moving data */
     struct inode *data_inode;
 
     struct btrfs_block_rsv *block_rsv;
 
     struct btrfs_backref_cache backref_cache;
 
     struct file_extent_cluster cluster;
     /* tree blocks have been processed */
     struct extent_io_tree processed_blocks;
     /* map start of tree root to corresponding reloc tree */
     struct mapping_tree reloc_root_tree;
     /* list of reloc trees */
     struct list_head reloc_roots;
     /* list of subvolume trees that get relocated */
     struct list_head dirty_subvol_roots;
     /* size of metadata reservation for merging reloc trees */
     u64 merging_rsv_size;
     /* size of relocated tree nodes */
     u64 nodes_relocated;
     /* reserved size for block group relocation*/
     u64 reserved_bytes;
 
     u64 search_start;
     u64 extents_found;
 
     unsigned int stage:8;
     unsigned int create_reloc_tree:1;
     unsigned int merge_reloc_tree:1;
     unsigned int found_file_extent:1;
 };
 
 /* stages of data relocation */
 #define MOVE_DATA_EXTENTS   0
 #define UPDATE_DATA_PTRS    1
 
 static void mark_block_processed(struct reloc_control *rc,
                  struct btrfs_backref_node *node)
 {
     u32 blocksize;
 
     if (node->level == 0 ||
         in_range(node->bytenr, rc->block_group->start,
              rc->block_group->length)) {
         blocksize = rc->extent_root->fs_info->nodesize;
         set_extent_bits(&rc->processed_blocks, node->bytenr,
                 node->bytenr + blocksize - 1, EXTENT_DIRTY);
     }
     node->processed = 1;
 }
 
 
 static void mapping_tree_init(struct mapping_tree *tree)
 {
     tree->rb_root = RB_ROOT;
     spin_lock_init(&tree->lock);
 }
 
 /*
  * walk up backref nodes until reach node presents tree root
  */
 static struct btrfs_backref_node *walk_up_backref(
         struct btrfs_backref_node *node,
         struct btrfs_backref_edge *edges[], int *index)
 {
     struct btrfs_backref_edge *edge;
     int idx = *index;
 
     while (!list_empty(&node->upper)) {
         edge = list_entry(node->upper.next,
                   struct btrfs_backref_edge, list[LOWER]);
         edges[idx++] = edge;
         node = edge->node[UPPER];
     }
     BUG_ON(node->detached);
     *index = idx;
     return node;
 }
 
 /*
  * walk down backref nodes to find start of next reference path
  */
 static struct btrfs_backref_node *walk_down_backref(
         struct btrfs_backref_edge *edges[], int *index)
 {
     struct btrfs_backref_edge *edge;
     struct btrfs_backref_node *lower;
     int idx = *index;
 
     while (idx > 0) {
         edge = edges[idx - 1];
         lower = edge->node[LOWER];
         if (list_is_last(&edge->list[LOWER], &lower->upper)) {
             idx--;
             continue;
         }
         edge = list_entry(edge->list[LOWER].next,
                   struct btrfs_backref_edge, list[LOWER]);
         edges[idx - 1] = edge;
         *index = idx;
         return edge->node[UPPER];
     }
     *index = 0;
     return NULL;
 }
 
 static void update_backref_node(struct btrfs_backref_cache *cache,
                 struct btrfs_backref_node *node, u64 bytenr)
 {
     struct rb_node *rb_node;
     rb_erase(&node->rb_node, &cache->rb_root);
     node->bytenr = bytenr;
     rb_node = rb_simple_insert(&cache->rb_root, node->bytenr, &node->rb_node);
     if (rb_node)
         btrfs_backref_panic(cache->fs_info, bytenr, -EEXIST);
 }
 
 /*
  * update backref cache after a transaction commit
  */
 static int update_backref_cache(struct btrfs_trans_handle *trans,
                 struct btrfs_backref_cache *cache)
 {
     struct btrfs_backref_node *node;
     int level = 0;
 
     if (cache->last_trans == 0) {
         cache->last_trans = trans->transid;
         return 0;
     }
 
     if (cache->last_trans == trans->transid)
         return 0;
 
     /*
      * detached nodes are used to avoid unnecessary backref
      * lookup. transaction commit changes the extent tree.
      * so the detached nodes are no longer useful.
      */
     while (!list_empty(&cache->detached)) {
         node = list_entry(cache->detached.next,
                   struct btrfs_backref_node, list);
         btrfs_backref_cleanup_node(cache, node);
     }
 
     while (!list_empty(&cache->changed)) {
         node = list_entry(cache->changed.next,
                   struct btrfs_backref_node, list);
         list_del_init(&node->list);
         BUG_ON(node->pending);
         update_backref_node(cache, node, node->new_bytenr);
     }
 
     /*
      * some nodes can be left in the pending list if there were
      * errors during processing the pending nodes.
      */
     for (level = 0; level < BTRFS_MAX_LEVEL; level++) {
         list_for_each_entry(node, &cache->pending[level], list) {
             BUG_ON(!node->pending);
             if (node->bytenr == node->new_bytenr)
                 continue;
             update_backref_node(cache, node, node->new_bytenr);
         }
     }
 
     cache->last_trans = 0;
     return 1;
 }
 
 static bool reloc_root_is_dead(struct btrfs_root *root)
 {
     /*
      * Pair with set_bit/clear_bit in clean_dirty_subvols and
      * btrfs_update_reloc_root. We need to see the updated bit before
      * trying to access reloc_root
      */
     smp_rmb();
     if (test_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state))
         return true;
     return false;
 }
 
 /*
  * Check if this subvolume tree has valid reloc tree.
  *
  * Reloc tree after swap is considered dead, thus not considered as valid.
  * This is enough for most callers, as they don't distinguish dead reloc root
  * from no reloc root.  But btrfs_should_ignore_reloc_root() below is a
  * special case.
  */
 static bool have_reloc_root(struct btrfs_root *root)
 {
     if (reloc_root_is_dead(root))
         return false;
     if (!root->reloc_root)
         return false;
     return true;
 }
 
 int btrfs_should_ignore_reloc_root(struct btrfs_root *root)
 {
     struct btrfs_root *reloc_root;
 
     if (!test_bit(BTRFS_ROOT_SHAREABLE, &root->state))
         return 0;
 
     /* This root has been merged with its reloc tree, we can ignore it */
     if (reloc_root_is_dead(root))
         return 1;
 
     reloc_root = root->reloc_root;
     if (!reloc_root)
         return 0;
 
     if (btrfs_header_generation(reloc_root->commit_root) ==
         root->fs_info->running_transaction->transid)
         return 0;
     /*
      * if there is reloc tree and it was created in previous
      * transaction backref lookup can find the reloc tree,
      * so backref node for the fs tree root is useless for
      * relocation.
      */
     return 1;
 }
 
 /*
  * find reloc tree by address of tree root
  */
 struct btrfs_root *find_reloc_root(struct btrfs_fs_info *fs_info, u64 bytenr)
 {
     struct reloc_control *rc = fs_info->reloc_ctl;
     struct rb_node *rb_node;
     struct mapping_node *node;
     struct btrfs_root *root = NULL;
 
     ASSERT(rc);
     spin_lock(&rc->reloc_root_tree.lock);
     rb_node = rb_simple_search(&rc->reloc_root_tree.rb_root, bytenr);
     if (rb_node) {
         node = rb_entry(rb_node, struct mapping_node, rb_node);
         root = node->data;
     }
     spin_unlock(&rc->reloc_root_tree.lock);
     return btrfs_grab_root(root);
 }
 
 /*
  * For useless nodes, do two major clean ups:
  *
  * - Cleanup the children edges and nodes
  *   If child node is also orphan (no parent) during cleanup, then the child
  *   node will also be cleaned up.
  *
  * - Freeing up leaves (level 0), keeps nodes detached
  *   For nodes, the node is still cached as "detached"
  *
  * Return false if @node is not in the @useless_nodes list.
  * Return true if @node is in the @useless_nodes list.
  */
 static bool handle_useless_nodes(struct reloc_control *rc,
                  struct btrfs_backref_node *node)
 {
     struct btrfs_backref_cache *cache = &rc->backref_cache;
     struct list_head *useless_node = &cache->useless_node;
     bool ret = false;
 
     while (!list_empty(useless_node)) {
         struct btrfs_backref_node *cur;
 
         cur = list_first_entry(useless_node, struct btrfs_backref_node,
                  list);
         list_del_init(&cur->list);
 
         /* Only tree root nodes can be added to @useless_nodes */
         ASSERT(list_empty(&cur->upper));
 
         if (cur == node)
             ret = true;
 
         /* The node is the lowest node */
         if (cur->lowest) {
             list_del_init(&cur->lower);
             cur->lowest = 0;
         }
 
         /* Cleanup the lower edges */
         while (!list_empty(&cur->lower)) {
             struct btrfs_backref_edge *edge;
             struct btrfs_backref_node *lower;
 
             edge = list_entry(cur->lower.next,
                     struct btrfs_backref_edge, list[UPPER]);
             list_del(&edge->list[UPPER]);
             list_del(&edge->list[LOWER]);
             lower = edge->node[LOWER];
             btrfs_backref_free_edge(cache, edge);
 
             /* Child node is also orphan, queue for cleanup */
             if (list_empty(&lower->upper))
                 list_add(&lower->list, useless_node);
         }
         /* Mark this block processed for relocation */
         mark_block_processed(rc, cur);
 
         /*
          * Backref nodes for tree leaves are deleted from the cache.
          * Backref nodes for upper level tree blocks are left in the
          * cache to avoid unnecessary backref lookup.
          */
         if (cur->level > 0) {
             list_add(&cur->list, &cache->detached);
             cur->detached = 1;
         } else {
             rb_erase(&cur->rb_node, &cache->rb_root);
             btrfs_backref_free_node(cache, cur);
         }
     }
     return ret;
 }
 
 /*
  * Build backref tree for a given tree block. Root of the backref tree
  * corresponds the tree block, leaves of the backref tree correspond roots of
  * b-trees that reference the tree block.
  *
  * The basic idea of this function is check backrefs of a given block to find
  * upper level blocks that reference the block, and then check backrefs of
  * these upper level blocks recursively. The recursion stops when tree root is
  * reached or backrefs for the block is cached.
  *
  * NOTE: if we find that backrefs for a block are cached, we know backrefs for
  * all upper level blocks that directly/indirectly reference the block are also
  * cached.
  */
 static noinline_for_stack struct btrfs_backref_node *build_backref_tree(
             struct reloc_control *rc, struct btrfs_key *node_key,
             int level, u64 bytenr)
 {
     struct btrfs_backref_iter *iter;
     struct btrfs_backref_cache *cache = &rc->backref_cache;
     /* For searching parent of TREE_BLOCK_REF */
     struct btrfs_path *path;
     struct btrfs_backref_node *cur;
     struct btrfs_backref_node *node = NULL;
     struct btrfs_backref_edge *edge;
     int ret;
     int err = 0;
 
     iter = btrfs_backref_iter_alloc(rc->extent_root->fs_info, GFP_NOFS);
     if (!iter)
         return ERR_PTR(-ENOMEM);
     path = btrfs_alloc_path();
     if (!path) {
         err = -ENOMEM;
         goto out;
     }
 
     node = btrfs_backref_alloc_node(cache, bytenr, level);
     if (!node) {
         err = -ENOMEM;
         goto out;
     }
 
     node->lowest = 1;
     cur = node;
 
     /* Breadth-first search to build backref cache */
     do {
         ret = btrfs_backref_add_tree_node(cache, path, iter, node_key,
                           cur);
         if (ret < 0) {
             err = ret;
             goto out;
         }
         edge = list_first_entry_or_null(&cache->pending_edge,
                 struct btrfs_backref_edge, list[UPPER]);
         /*
          * The pending list isn't empty, take the first block to
          * process
          */
         if (edge) {
             list_del_init(&edge->list[UPPER]);
             cur = edge->node[UPPER];
         }
     } while (edge);
 
     /* Finish the upper linkage of newly added edges/nodes */
     ret = btrfs_backref_finish_upper_links(cache, node);
     if (ret < 0) {
         err = ret;
         goto out;
     }
 
     if (handle_useless_nodes(rc, node))
         node = NULL;
 out:
     btrfs_backref_iter_free(iter);
     btrfs_free_path(path);
     if (err) {
         btrfs_backref_error_cleanup(cache, node);
         return ERR_PTR(err);
     }
     ASSERT(!node || !node->detached);
     ASSERT(list_empty(&cache->useless_node) &&
            list_empty(&cache->pending_edge));
     return node;
 }
 
 /*
  * helper to add backref node for the newly created snapshot.
  * the backref node is created by cloning backref node that
  * corresponds to root of source tree
  */
 static int clone_backref_node(struct btrfs_trans_handle *trans,
                   struct reloc_control *rc,
                   struct btrfs_root *src,
                   struct btrfs_root *dest)
 {
     struct btrfs_root *reloc_root = src->reloc_root;
     struct btrfs_backref_cache *cache = &rc->backref_cache;
     struct btrfs_backref_node *node = NULL;
     struct btrfs_backref_node *new_node;
     struct btrfs_backref_edge *edge;
     struct btrfs_backref_edge *new_edge;
     struct rb_node *rb_node;
 
     if (cache->last_trans > 0)
         update_backref_cache(trans, cache);
 
     rb_node = rb_simple_search(&cache->rb_root, src->commit_root->start);
     if (rb_node) {
         node = rb_entry(rb_node, struct btrfs_backref_node, rb_node);
         if (node->detached)
             node = NULL;
         else
             BUG_ON(node->new_bytenr != reloc_root->node->start);
     }
 
     if (!node) {
         rb_node = rb_simple_search(&cache->rb_root,
                        reloc_root->commit_root->start);
         if (rb_node) {
             node = rb_entry(rb_node, struct btrfs_backref_node,
                     rb_node);
             BUG_ON(node->detached);
         }
     }
 
     if (!node)
         return 0;
 
     new_node = btrfs_backref_alloc_node(cache, dest->node->start,
                         node->level);
     if (!new_node)
         return -ENOMEM;
 
     new_node->lowest = node->lowest;
     new_node->checked = 1;
     new_node->root = btrfs_grab_root(dest);
     ASSERT(new_node->root);
 
     if (!node->lowest) {
         list_for_each_entry(edge, &node->lower, list[UPPER]) {
             new_edge = btrfs_backref_alloc_edge(cache);
             if (!new_edge)
                 goto fail;
 
             btrfs_backref_link_edge(new_edge, edge->node[LOWER],
                         new_node, LINK_UPPER);
         }
     } else {
         list_add_tail(&new_node->lower, &cache->leaves);
     }
 
     rb_node = rb_simple_insert(&cache->rb_root, new_node->bytenr,
                    &new_node->rb_node);
     if (rb_node)
         btrfs_backref_panic(trans->fs_info, new_node->bytenr, -EEXIST);
 
     if (!new_node->lowest) {
         list_for_each_entry(new_edge, &new_node->lower, list[UPPER]) {
             list_add_tail(&new_edge->list[LOWER],
                       &new_edge->node[LOWER]->upper);
         }
     }
     return 0;
 fail:
     while (!list_empty(&new_node->lower)) {
         new_edge = list_entry(new_node->lower.next,
                       struct btrfs_backref_edge, list[UPPER]);
         list_del(&new_edge->list[UPPER]);
         btrfs_backref_free_edge(cache, new_edge);
     }
     btrfs_backref_free_node(cache, new_node);
     return -ENOMEM;
 }
 
 /*
  * helper to add 'address of tree root -> reloc tree' mapping
  */
 static int __must_check __add_reloc_root(struct btrfs_root *root)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct rb_node *rb_node;
     struct mapping_node *node;
     struct reloc_control *rc = fs_info->reloc_ctl;
 
     node = kmalloc(sizeof(*node), GFP_NOFS);
     if (!node)
         return -ENOMEM;
 
     node->bytenr = root->commit_root->start;
     node->data = root;
 
     spin_lock(&rc->reloc_root_tree.lock);
     rb_node = rb_simple_insert(&rc->reloc_root_tree.rb_root,
                    node->bytenr, &node->rb_node);
     spin_unlock(&rc->reloc_root_tree.lock);
     if (rb_node) {
         btrfs_err(fs_info,
                 "Duplicate root found for start=%llu while inserting into relocation tree",
                 node->bytenr);
         return -EEXIST;
     }
 
     list_add_tail(&root->root_list, &rc->reloc_roots);
     return 0;
 }
 
 /*
  * helper to delete the 'address of tree root -> reloc tree'
  * mapping
  */
 static void __del_reloc_root(struct btrfs_root *root)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct rb_node *rb_node;
     struct mapping_node *node = NULL;
     struct reloc_control *rc = fs_info->reloc_ctl;
     bool put_ref = false;
 
     if (rc && root->node) {
         spin_lock(&rc->reloc_root_tree.lock);
         rb_node = rb_simple_search(&rc->reloc_root_tree.rb_root,
                        root->commit_root->start);
         if (rb_node) {
             node = rb_entry(rb_node, struct mapping_node, rb_node);
             rb_erase(&node->rb_node, &rc->reloc_root_tree.rb_root);
             RB_CLEAR_NODE(&node->rb_node);
         }
         spin_unlock(&rc->reloc_root_tree.lock);
         ASSERT(!node || (struct btrfs_root *)node->data == root);
     }
 
     /*
      * We only put the reloc root here if it's on the list.  There's a lot
      * of places where the pattern is to splice the rc->reloc_roots, process
      * the reloc roots, and then add the reloc root back onto
      * rc->reloc_roots.  If we call __del_reloc_root while it's off of the
      * list we don't want the reference being dropped, because the guy
      * messing with the list is in charge of the reference.
      */
     spin_lock(&fs_info->trans_lock);
     if (!list_empty(&root->root_list)) {
         put_ref = true;
         list_del_init(&root->root_list);
     }
     spin_unlock(&fs_info->trans_lock);
     if (put_ref)
         btrfs_put_root(root);
     kfree(node);
 }
 
 /*
  * helper to update the 'address of tree root -> reloc tree'
  * mapping
  */
 static int __update_reloc_root(struct btrfs_root *root)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct rb_node *rb_node;
     struct mapping_node *node = NULL;
     struct reloc_control *rc = fs_info->reloc_ctl;
 
     spin_lock(&rc->reloc_root_tree.lock);
     rb_node = rb_simple_search(&rc->reloc_root_tree.rb_root,
                    root->commit_root->start);
     if (rb_node) {
         node = rb_entry(rb_node, struct mapping_node, rb_node);
         rb_erase(&node->rb_node, &rc->reloc_root_tree.rb_root);
     }
     spin_unlock(&rc->reloc_root_tree.lock);
 
     if (!node)
         return 0;
     BUG_ON((struct btrfs_root *)node->data != root);
 
     spin_lock(&rc->reloc_root_tree.lock);
     node->bytenr = root->node->start;
     rb_node = rb_simple_insert(&rc->reloc_root_tree.rb_root,
                    node->bytenr, &node->rb_node);
     spin_unlock(&rc->reloc_root_tree.lock);
     if (rb_node)
         btrfs_backref_panic(fs_info, node->bytenr, -EEXIST);
     return 0;
 }
 
 static struct btrfs_root *create_reloc_root(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root, u64 objectid)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct btrfs_root *reloc_root;
     struct extent_buffer *eb;
     struct btrfs_root_item *root_item;
     struct btrfs_key root_key;
     int ret = 0;
     bool must_abort = false;
 
     root_item = kmalloc(sizeof(*root_item), GFP_NOFS);
     if (!root_item)
         return ERR_PTR(-ENOMEM);
 
     root_key.objectid = BTRFS_TREE_RELOC_OBJECTID;
     root_key.type = BTRFS_ROOT_ITEM_KEY;
     root_key.offset = objectid;
 
     if (root->root_key.objectid == objectid) {
         u64 commit_root_gen;
 
         /* called by btrfs_init_reloc_root */
         ret = btrfs_copy_root(trans, root, root->commit_root, &eb,
                       BTRFS_TREE_RELOC_OBJECTID);
         if (ret)
             goto fail;
 
         /*
          * Set the last_snapshot field to the generation of the commit
          * root - like this ctree.c:btrfs_block_can_be_shared() behaves
          * correctly (returns true) when the relocation root is created
          * either inside the critical section of a transaction commit
          * (through transaction.c:qgroup_account_snapshot()) and when
          * it's created before the transaction commit is started.
          */
         commit_root_gen = btrfs_header_generation(root->commit_root);
         btrfs_set_root_last_snapshot(&root->root_item, commit_root_gen);
     } else {
         /*
          * called by btrfs_reloc_post_snapshot_hook.
          * the source tree is a reloc tree, all tree blocks
          * modified after it was created have RELOC flag
          * set in their headers. so it's OK to not update
          * the 'last_snapshot'.
          */
         ret = btrfs_copy_root(trans, root, root->node, &eb,
                       BTRFS_TREE_RELOC_OBJECTID);
         if (ret)
             goto fail;
     }
 
     /*
      * We have changed references at this point, we must abort the
      * transaction if anything fails.
      */
     must_abort = true;
 
     memcpy(root_item, &root->root_item, sizeof(*root_item));
     btrfs_set_root_bytenr(root_item, eb->start);
     btrfs_set_root_level(root_item, btrfs_header_level(eb));
     btrfs_set_root_generation(root_item, trans->transid);
 
     if (root->root_key.objectid == objectid) {
         btrfs_set_root_refs(root_item, 0);
         memset(&root_item->drop_progress, 0,
                sizeof(struct btrfs_disk_key));
         btrfs_set_root_drop_level(root_item, 0);
     }
 
     btrfs_tree_unlock(eb);
     free_extent_buffer(eb);
 
     ret = btrfs_insert_root(trans, fs_info->tree_root,
                 &root_key, root_item);
     if (ret)
         goto fail;
 
     kfree(root_item);
 
     reloc_root = btrfs_read_tree_root(fs_info->tree_root, &root_key);
     if (IS_ERR(reloc_root)) {
         ret = PTR_ERR(reloc_root);
         goto abort;
     }
     set_bit(BTRFS_ROOT_SHAREABLE, &reloc_root->state);
     reloc_root->last_trans = trans->transid;
     return reloc_root;
 fail:
     kfree(root_item);
 abort:
     if (must_abort)
         btrfs_abort_transaction(trans, ret);
     return ERR_PTR(ret);
 }
 
 /*
  * create reloc tree for a given fs tree. reloc tree is just a
  * snapshot of the fs tree with special root objectid.
  *
  * The reloc_root comes out of here with two references, one for
  * root->reloc_root, and another for being on the rc->reloc_roots list.
  */
 int btrfs_init_reloc_root(struct btrfs_trans_handle *trans,
               struct btrfs_root *root)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct btrfs_root *reloc_root;
     struct reloc_control *rc = fs_info->reloc_ctl;
     struct btrfs_block_rsv *rsv;
     int clear_rsv = 0;
     int ret;
 
     if (!rc)
         return 0;
 
     /*
      * The subvolume has reloc tree but the swap is finished, no need to
      * create/update the dead reloc tree
      */
     if (reloc_root_is_dead(root))
         return 0;
 
     /*
      * This is subtle but important.  We do not do
      * record_root_in_transaction for reloc roots, instead we record their
      * corresponding fs root, and then here we update the last trans for the
      * reloc root.  This means that we have to do this for the entire life
      * of the reloc root, regardless of which stage of the relocation we are
      * in.
      */
     if (root->reloc_root) {
         reloc_root = root->reloc_root;
         reloc_root->last_trans = trans->transid;
         return 0;
     }
 
     /*
      * We are merging reloc roots, we do not need new reloc trees.  Also
      * reloc trees never need their own reloc tree.
      */
     if (!rc->create_reloc_tree ||
         root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
         return 0;
 
     if (!trans->reloc_reserved) {
         rsv = trans->block_rsv;
         trans->block_rsv = rc->block_rsv;
         clear_rsv = 1;
     }
     reloc_root = create_reloc_root(trans, root, root->root_key.objectid);
     if (clear_rsv)
         trans->block_rsv = rsv;
     if (IS_ERR(reloc_root))
         return PTR_ERR(reloc_root);
 
     ret = __add_reloc_root(reloc_root);
     ASSERT(ret != -EEXIST);
     if (ret) {
         /* Pairs with create_reloc_root */
         btrfs_put_root(reloc_root);
         return ret;
     }
     root->reloc_root = btrfs_grab_root(reloc_root);
     return 0;
 }
 
 /*
  * update root item of reloc tree
  */
 int btrfs_update_reloc_root(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct btrfs_root *reloc_root;
     struct btrfs_root_item *root_item;
     int ret;
 
     if (!have_reloc_root(root))
         return 0;
 
     reloc_root = root->reloc_root;
     root_item = &reloc_root->root_item;
 
     /*
      * We are probably ok here, but __del_reloc_root() will drop its ref of
      * the root.  We have the ref for root->reloc_root, but just in case
      * hold it while we update the reloc root.
      */
     btrfs_grab_root(reloc_root);
 
     /* root->reloc_root will stay until current relocation finished */
     if (fs_info->reloc_ctl->merge_reloc_tree &&
         btrfs_root_refs(root_item) == 0) {
         set_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state);
         /*
          * Mark the tree as dead before we change reloc_root so
          * have_reloc_root will not touch it from now on.
          */
         smp_wmb();
         __del_reloc_root(reloc_root);
     }
 
     if (reloc_root->commit_root != reloc_root->node) {
         __update_reloc_root(reloc_root);
         btrfs_set_root_node(root_item, reloc_root->node);
         free_extent_buffer(reloc_root->commit_root);
         reloc_root->commit_root = btrfs_root_node(reloc_root);
     }
 
     ret = btrfs_update_root(trans, fs_info->tree_root,
                 &reloc_root->root_key, root_item);
     btrfs_put_root(reloc_root);
     return ret;
 }
 
 /*
  * helper to find first cached inode with inode number >= objectid
  * in a subvolume
  */
 static struct inode *find_next_inode(struct btrfs_root *root, u64 objectid)
 {
     struct rb_node *node;
     struct rb_node *prev;
     struct btrfs_inode *entry;
     struct inode *inode;
 
     spin_lock(&root->inode_lock);
 again:
     node = root->inode_tree.rb_node;
     prev = NULL;
     while (node) {
         prev = node;
         entry = rb_entry(node, struct btrfs_inode, rb_node);
 
         if (objectid < btrfs_ino(entry))
             node = node->rb_left;
         else if (objectid > btrfs_ino(entry))
             node = node->rb_right;
         else
             break;
     }
     if (!node) {
         while (prev) {
             entry = rb_entry(prev, struct btrfs_inode, rb_node);
             if (objectid <= btrfs_ino(entry)) {
                 node = prev;
                 break;
             }
             prev = rb_next(prev);
         }
     }
     while (node) {
         entry = rb_entry(node, struct btrfs_inode, rb_node);
         inode = igrab(&entry->vfs_inode);
         if (inode) {
             spin_unlock(&root->inode_lock);
             return inode;
         }
 
         objectid = btrfs_ino(entry) + 1;
         if (cond_resched_lock(&root->inode_lock))
             goto again;
 
         node = rb_next(node);
     }
     spin_unlock(&root->inode_lock);
     return NULL;
 }
 
 /*
  * get new location of data
  */
 static int get_new_location(struct inode *reloc_inode, u64 *new_bytenr,
                 u64 bytenr, u64 num_bytes)
 {
     struct btrfs_root *root = BTRFS_I(reloc_inode)->root;
     struct btrfs_path *path;
     struct btrfs_file_extent_item *fi;
     struct extent_buffer *leaf;
     int ret;
 
     path = btrfs_alloc_path();
     if (!path)
         return -ENOMEM;
 
     bytenr -= BTRFS_I(reloc_inode)->index_cnt;
     ret = btrfs_lookup_file_extent(NULL, root, path,
             btrfs_ino(BTRFS_I(reloc_inode)), bytenr, 0);
     if (ret < 0)
         goto out;
     if (ret > 0) {
         ret = -ENOENT;
         goto out;
     }
 
     leaf = path->nodes[0];
     fi = btrfs_item_ptr(leaf, path->slots[0],
                 struct btrfs_file_extent_item);
 
     BUG_ON(btrfs_file_extent_offset(leaf, fi) ||
            btrfs_file_extent_compression(leaf, fi) ||
            btrfs_file_extent_encryption(leaf, fi) ||
            btrfs_file_extent_other_encoding(leaf, fi));
 
     if (num_bytes != btrfs_file_extent_disk_num_bytes(leaf, fi)) {
         ret = -EINVAL;
         goto out;
     }
 
     *new_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
     ret = 0;
 out:
     btrfs_free_path(path);
     return ret;
 }
 
 /*
  * update file extent items in the tree leaf to point to
  * the new locations.
  */
 static noinline_for_stack
 int replace_file_extents(struct btrfs_trans_handle *trans,
              struct reloc_control *rc,
              struct btrfs_root *root,
              struct extent_buffer *leaf)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct btrfs_key key;
     struct btrfs_file_extent_item *fi;
     struct inode *inode = NULL;
     u64 parent;
     u64 bytenr;
     u64 new_bytenr = 0;
     u64 num_bytes;
     u64 end;
     u32 nritems;
     u32 i;
     int ret = 0;
     int first = 1;
     int dirty = 0;
 
     if (rc->stage != UPDATE_DATA_PTRS)
         return 0;
 
     /* reloc trees always use full backref */
     if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
         parent = leaf->start;
     else
         parent = 0;
 
     nritems = btrfs_header_nritems(leaf);
     for (i = 0; i < nritems; i++) {
         struct btrfs_ref ref = { 0 };
 
         cond_resched();
         btrfs_item_key_to_cpu(leaf, &key, i);
         if (key.type != BTRFS_EXTENT_DATA_KEY)
             continue;
         fi = btrfs_item_ptr(leaf, i, struct btrfs_file_extent_item);
         if (btrfs_file_extent_type(leaf, fi) ==
             BTRFS_FILE_EXTENT_INLINE)
             continue;
         bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
         num_bytes = btrfs_file_extent_disk_num_bytes(leaf, fi);
         if (bytenr == 0)
             continue;
         if (!in_range(bytenr, rc->block_group->start,
                   rc->block_group->length))
             continue;
 
         /*
          * if we are modifying block in fs tree, wait for read_folio
          * to complete and drop the extent cache
          */
         if (root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID) {
             if (first) {
                 inode = find_next_inode(root, key.objectid);
                 first = 0;
             } else if (inode && btrfs_ino(BTRFS_I(inode)) < key.objectid) {
                 btrfs_add_delayed_iput(inode);
                 inode = find_next_inode(root, key.objectid);
             }
             if (inode && btrfs_ino(BTRFS_I(inode)) == key.objectid) {
                 end = key.offset +
                       btrfs_file_extent_num_bytes(leaf, fi);
                 WARN_ON(!IS_ALIGNED(key.offset,
                             fs_info->sectorsize));
                 WARN_ON(!IS_ALIGNED(end, fs_info->sectorsize));
                 end--;
                 ret = try_lock_extent(&BTRFS_I(inode)->io_tree,
                               key.offset, end);
                 if (!ret)
                     continue;
 
                 btrfs_drop_extent_cache(BTRFS_I(inode),
                         key.offset, end, 1);
                 unlock_extent(&BTRFS_I(inode)->io_tree,
                           key.offset, end);
             }
         }
 
         ret = get_new_location(rc->data_inode, &new_bytenr,
                        bytenr, num_bytes);
         if (ret) {
             /*
              * Don't have to abort since we've not changed anything
              * in the file extent yet.
              */
             break;
         }
 
         btrfs_set_file_extent_disk_bytenr(leaf, fi, new_bytenr);
         dirty = 1;
 
         key.offset -= btrfs_file_extent_offset(leaf, fi);
         btrfs_init_generic_ref(&ref, BTRFS_ADD_DELAYED_REF, new_bytenr,
                        num_bytes, parent);
         btrfs_init_data_ref(&ref, btrfs_header_owner(leaf),
                     key.objectid, key.offset,
                     root->root_key.objectid, false);
         ret = btrfs_inc_extent_ref(trans, &ref);
         if (ret) {
             btrfs_abort_transaction(trans, ret);
             break;
         }
 
         btrfs_init_generic_ref(&ref, BTRFS_DROP_DELAYED_REF, bytenr,
                        num_bytes, parent);
         btrfs_init_data_ref(&ref, btrfs_header_owner(leaf),
                     key.objectid, key.offset,
                     root->root_key.objectid, false);
         ret = btrfs_free_extent(trans, &ref);
         if (ret) {
             btrfs_abort_transaction(trans, ret);
             break;
         }
     }
     if (dirty)
         btrfs_mark_buffer_dirty(leaf);
     if (inode)
         btrfs_add_delayed_iput(inode);
     return ret;
 }
 
 static noinline_for_stack
 int memcmp_node_keys(struct extent_buffer *eb, int slot,
              struct btrfs_path *path, int level)
 {
     struct btrfs_disk_key key1;
     struct btrfs_disk_key key2;
     btrfs_node_key(eb, &key1, slot);
     btrfs_node_key(path->nodes[level], &key2, path->slots[level]);
     return memcmp(&key1, &key2, sizeof(key1));
 }
 
 /*
  * try to replace tree blocks in fs tree with the new blocks
  * in reloc tree. tree blocks haven't been modified since the
  * reloc tree was create can be replaced.
  *
  * if a block was replaced, level of the block + 1 is returned.
  * if no block got replaced, 0 is returned. if there are other
  * errors, a negative error number is returned.
  */
 static noinline_for_stack
 int replace_path(struct btrfs_trans_handle *trans, struct reloc_control *rc,
          struct btrfs_root *dest, struct btrfs_root *src,
          struct btrfs_path *path, struct btrfs_key *next_key,
          int lowest_level, int max_level)
 {
     struct btrfs_fs_info *fs_info = dest->fs_info;
     struct extent_buffer *eb;
     struct extent_buffer *parent;
     struct btrfs_ref ref = { 0 };
     struct btrfs_key key;
     u64 old_bytenr;
     u64 new_bytenr;
     u64 old_ptr_gen;
     u64 new_ptr_gen;
     u64 last_snapshot;
     u32 blocksize;
     int cow = 0;
     int level;
     int ret;
     int slot;
 
     ASSERT(src->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID);
     ASSERT(dest->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID);
 
     last_snapshot = btrfs_root_last_snapshot(&src->root_item);
 again:
     slot = path->slots[lowest_level];
     btrfs_node_key_to_cpu(path->nodes[lowest_level], &key, slot);
 
     eb = btrfs_lock_root_node(dest);
     level = btrfs_header_level(eb);
 
     if (level < lowest_level) {
         btrfs_tree_unlock(eb);
         free_extent_buffer(eb);
         return 0;
     }
 
     if (cow) {
         ret = btrfs_cow_block(trans, dest, eb, NULL, 0, &eb,
                       BTRFS_NESTING_COW);
         if (ret) {
             btrfs_tree_unlock(eb);
             free_extent_buffer(eb);
             return ret;
         }
     }
 
     if (next_key) {
         next_key->objectid = (u64)-1;
         next_key->type = (u8)-1;
         next_key->offset = (u64)-1;
     }
 
     parent = eb;
     while (1) {
         level = btrfs_header_level(parent);
         ASSERT(level >= lowest_level);
 
         ret = btrfs_bin_search(parent, &key, &slot);
         if (ret < 0)
             break;
         if (ret && slot > 0)
             slot--;
 
         if (next_key && slot + 1 < btrfs_header_nritems(parent))
             btrfs_node_key_to_cpu(parent, next_key, slot + 1);
 
         old_bytenr = btrfs_node_blockptr(parent, slot);
         blocksize = fs_info->nodesize;
         old_ptr_gen = btrfs_node_ptr_generation(parent, slot);
 
         if (level <= max_level) {
             eb = path->nodes[level];
             new_bytenr = btrfs_node_blockptr(eb,
                             path->slots[level]);
             new_ptr_gen = btrfs_node_ptr_generation(eb,
                             path->slots[level]);
         } else {
             new_bytenr = 0;
             new_ptr_gen = 0;
         }
 
         if (WARN_ON(new_bytenr > 0 && new_bytenr == old_bytenr)) {
             ret = level;
             break;
         }
 
         if (new_bytenr == 0 || old_ptr_gen > last_snapshot ||
             memcmp_node_keys(parent, slot, path, level)) {
             if (level <= lowest_level) {
                 ret = 0;
                 break;
             }
 
             eb = btrfs_read_node_slot(parent, slot);
             if (IS_ERR(eb)) {
                 ret = PTR_ERR(eb);
                 break;
             }
             btrfs_tree_lock(eb);
             if (cow) {
                 ret = btrfs_cow_block(trans, dest, eb, parent,
                               slot, &eb,
                               BTRFS_NESTING_COW);
                 if (ret) {
                     btrfs_tree_unlock(eb);
                     free_extent_buffer(eb);
                     break;
                 }
             }
 
             btrfs_tree_unlock(parent);
             free_extent_buffer(parent);
 
             parent = eb;
             continue;
         }
 
         if (!cow) {
             btrfs_tree_unlock(parent);
             free_extent_buffer(parent);
             cow = 1;
             goto again;
         }
 
         btrfs_node_key_to_cpu(path->nodes[level], &key,
                       path->slots[level]);
         btrfs_release_path(path);
 
         path->lowest_level = level;
         set_bit(BTRFS_ROOT_RESET_LOCKDEP_CLASS, &src->state);
         ret = btrfs_search_slot(trans, src, &key, path, 0, 1);
         clear_bit(BTRFS_ROOT_RESET_LOCKDEP_CLASS, &src->state);
         path->lowest_level = 0;
         if (ret) {
             if (ret > 0)
                 ret = -ENOENT;
             break;
         }
 
         /*
          * Info qgroup to trace both subtrees.
          *
          * We must trace both trees.
          * 1) Tree reloc subtree
          *    If not traced, we will leak data numbers
          * 2) Fs subtree
          *    If not traced, we will double count old data
          *
          * We don't scan the subtree right now, but only record
          * the swapped tree blocks.
          * The real subtree rescan is delayed until we have new
          * CoW on the subtree root node before transaction commit.
          */
         ret = btrfs_qgroup_add_swapped_blocks(trans, dest,
                 rc->block_group, parent, slot,
                 path->nodes[level], path->slots[level],
                 last_snapshot);
         if (ret < 0)
             break;
         /*
          * swap blocks in fs tree and reloc tree.
          */
         btrfs_set_node_blockptr(parent, slot, new_bytenr);
         btrfs_set_node_ptr_generation(parent, slot, new_ptr_gen);
         btrfs_mark_buffer_dirty(parent);
 
         btrfs_set_node_blockptr(path->nodes[level],
                     path->slots[level], old_bytenr);
         btrfs_set_node_ptr_generation(path->nodes[level],
                           path->slots[level], old_ptr_gen);
         btrfs_mark_buffer_dirty(path->nodes[level]);
 
         btrfs_init_generic_ref(&ref, BTRFS_ADD_DELAYED_REF, old_bytenr,
                        blocksize, path->nodes[level]->start);
         btrfs_init_tree_ref(&ref, level - 1, src->root_key.objectid,
                     0, true);
         ret = btrfs_inc_extent_ref(trans, &ref);
         if (ret) {
             btrfs_abort_transaction(trans, ret);
             break;
         }
         btrfs_init_generic_ref(&ref, BTRFS_ADD_DELAYED_REF, new_bytenr,
                        blocksize, 0);
         btrfs_init_tree_ref(&ref, level - 1, dest->root_key.objectid, 0,
                     true);
         ret = btrfs_inc_extent_ref(trans, &ref);
         if (ret) {
             btrfs_abort_transaction(trans, ret);
             break;
         }
 
         btrfs_init_generic_ref(&ref, BTRFS_DROP_DELAYED_REF, new_bytenr,
                        blocksize, path->nodes[level]->start);
         btrfs_init_tree_ref(&ref, level - 1, src->root_key.objectid,
                     0, true);
         ret = btrfs_free_extent(trans, &ref);
         if (ret) {
             btrfs_abort_transaction(trans, ret);
             break;
         }
 
         btrfs_init_generic_ref(&ref, BTRFS_DROP_DELAYED_REF, old_bytenr,
                        blocksize, 0);
         btrfs_init_tree_ref(&ref, level - 1, dest->root_key.objectid,
                     0, true);
         ret = btrfs_free_extent(trans, &ref);
         if (ret) {
             btrfs_abort_transaction(trans, ret);
             break;
         }
 
         btrfs_unlock_up_safe(path, 0);
 
         ret = level;
         break;
     }
     btrfs_tree_unlock(parent);
     free_extent_buffer(parent);
     return ret;
 }
 
 /*
  * helper to find next relocated block in reloc tree
  */
 static noinline_for_stack
 int walk_up_reloc_tree(struct btrfs_root *root, struct btrfs_path *path,
                int *level)
 {
     struct extent_buffer *eb;
     int i;
     u64 last_snapshot;
     u32 nritems;
 
     last_snapshot = btrfs_root_last_snapshot(&root->root_item);
 
     for (i = 0; i < *level; i++) {
         free_extent_buffer(path->nodes[i]);
         path->nodes[i] = NULL;
     }
 
     for (i = *level; i < BTRFS_MAX_LEVEL && path->nodes[i]; i++) {
         eb = path->nodes[i];
         nritems = btrfs_header_nritems(eb);
         while (path->slots[i] + 1 < nritems) {
             path->slots[i]++;
             if (btrfs_node_ptr_generation(eb, path->slots[i]) <=
                 last_snapshot)
                 continue;
 
             *level = i;
             return 0;
         }
         free_extent_buffer(path->nodes[i]);
         path->nodes[i] = NULL;
     }
     return 1;
 }
 
 /*
  * walk down reloc tree to find relocated block of lowest level
  */
 static noinline_for_stack
 int walk_down_reloc_tree(struct btrfs_root *root, struct btrfs_path *path,
              int *level)
 {
     struct extent_buffer *eb = NULL;
     int i;
     u64 ptr_gen = 0;
     u64 last_snapshot;
     u32 nritems;
 
     last_snapshot = btrfs_root_last_snapshot(&root->root_item);
 
     for (i = *level; i > 0; i--) {
         eb = path->nodes[i];
         nritems = btrfs_header_nritems(eb);
         while (path->slots[i] < nritems) {
             ptr_gen = btrfs_node_ptr_generation(eb, path->slots[i]);
             if (ptr_gen > last_snapshot)
                 break;
             path->slots[i]++;
         }
         if (path->slots[i] >= nritems) {
             if (i == *level)
                 break;
             *level = i + 1;
             return 0;
         }
         if (i == 1) {
             *level = i;
             return 0;
         }
 
         eb = btrfs_read_node_slot(eb, path->slots[i]);
         if (IS_ERR(eb))
             return PTR_ERR(eb);
         BUG_ON(btrfs_header_level(eb) != i - 1);
         path->nodes[i - 1] = eb;
         path->slots[i - 1] = 0;
     }
     return 1;
 }
 
 /*
  * invalidate extent cache for file extents whose key in range of
  * [min_key, max_key)
  */
 static int invalidate_extent_cache(struct btrfs_root *root,
                    struct btrfs_key *min_key,
                    struct btrfs_key *max_key)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct inode *inode = NULL;
     u64 objectid;
     u64 start, end;
     u64 ino;
 
     objectid = min_key->objectid;
     while (1) {
         cond_resched();
         iput(inode);
 
         if (objectid > max_key->objectid)
             break;
 
         inode = find_next_inode(root, objectid);
         if (!inode)
             break;
         ino = btrfs_ino(BTRFS_I(inode));
 
         if (ino > max_key->objectid) {
             iput(inode);
             break;
         }
 
         objectid = ino + 1;
         if (!S_ISREG(inode->i_mode))
             continue;
 
         if (unlikely(min_key->objectid == ino)) {
             if (min_key->type > BTRFS_EXTENT_DATA_KEY)
                 continue;
             if (min_key->type < BTRFS_EXTENT_DATA_KEY)
                 start = 0;
             else {
                 start = min_key->offset;
                 WARN_ON(!IS_ALIGNED(start, fs_info->sectorsize));
             }
         } else {
             start = 0;
         }
 
         if (unlikely(max_key->objectid == ino)) {
             if (max_key->type < BTRFS_EXTENT_DATA_KEY)
                 continue;
             if (max_key->type > BTRFS_EXTENT_DATA_KEY) {
                 end = (u64)-1;
             } else {
                 if (max_key->offset == 0)
                     continue;
                 end = max_key->offset;
                 WARN_ON(!IS_ALIGNED(end, fs_info->sectorsize));
                 end--;
             }
         } else {
             end = (u64)-1;
         }
 
         /* the lock_extent waits for read_folio to complete */
         lock_extent(&BTRFS_I(inode)->io_tree, start, end);
         btrfs_drop_extent_cache(BTRFS_I(inode), start, end, 1);
         unlock_extent(&BTRFS_I(inode)->io_tree, start, end);
     }
     return 0;
 }
 
 static int find_next_key(struct btrfs_path *path, int level,
              struct btrfs_key *key)
 
 {
     while (level < BTRFS_MAX_LEVEL) {
         if (!path->nodes[level])
             break;
         if (path->slots[level] + 1 <
             btrfs_header_nritems(path->nodes[level])) {
             btrfs_node_key_to_cpu(path->nodes[level], key,
                           path->slots[level] + 1);
             return 0;
         }
         level++;
     }
     return 1;
 }
 
 /*
  * Insert current subvolume into reloc_control::dirty_subvol_roots
  */
 static int insert_dirty_subvol(struct btrfs_trans_handle *trans,
                    struct reloc_control *rc,
                    struct btrfs_root *root)
 {
     struct btrfs_root *reloc_root = root->reloc_root;
     struct btrfs_root_item *reloc_root_item;
     int ret;
 
     /* @root must be a subvolume tree root with a valid reloc tree */
     ASSERT(root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID);
     ASSERT(reloc_root);
 
     reloc_root_item = &reloc_root->root_item;
     memset(&reloc_root_item->drop_progress, 0,
         sizeof(reloc_root_item->drop_progress));
     btrfs_set_root_drop_level(reloc_root_item, 0);
     btrfs_set_root_refs(reloc_root_item, 0);
     ret = btrfs_update_reloc_root(trans, root);
     if (ret)
         return ret;
 
     if (list_empty(&root->reloc_dirty_list)) {
         btrfs_grab_root(root);
         list_add_tail(&root->reloc_dirty_list, &rc->dirty_subvol_roots);
     }
 
     return 0;
 }
 
 static int clean_dirty_subvols(struct reloc_control *rc)
 {
     struct btrfs_root *root;
     struct btrfs_root *next;
     int ret = 0;
     int ret2;
 
     list_for_each_entry_safe(root, next, &rc->dirty_subvol_roots,
                  reloc_dirty_list) {
         if (root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID) {
             /* Merged subvolume, cleanup its reloc root */
             struct btrfs_root *reloc_root = root->reloc_root;
 
             list_del_init(&root->reloc_dirty_list);
             root->reloc_root = NULL;
             /*
              * Need barrier to ensure clear_bit() only happens after
              * root->reloc_root = NULL. Pairs with have_reloc_root.
              */
             smp_wmb();
             clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state);
             if (reloc_root) {
                 /*
                  * btrfs_drop_snapshot drops our ref we hold for
                  * ->reloc_root.  If it fails however we must
                  * drop the ref ourselves.
                  */
                 ret2 = btrfs_drop_snapshot(reloc_root, 0, 1);
                 if (ret2 < 0) {
                     btrfs_put_root(reloc_root);
                     if (!ret)
                         ret = ret2;
                 }
             }
             btrfs_put_root(root);
         } else {
             /* Orphan reloc tree, just clean it up */
             ret2 = btrfs_drop_snapshot(root, 0, 1);
             if (ret2 < 0) {
                 btrfs_put_root(root);
                 if (!ret)
                     ret = ret2;
             }
         }
     }
     return ret;
 }
 
 /*
  * merge the relocated tree blocks in reloc tree with corresponding
  * fs tree.
  */
 static noinline_for_stack int merge_reloc_root(struct reloc_control *rc,
                            struct btrfs_root *root)
 {
     struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
     struct btrfs_key key;
     struct btrfs_key next_key;
     struct btrfs_trans_handle *trans = NULL;
     struct btrfs_root *reloc_root;
     struct btrfs_root_item *root_item;
     struct btrfs_path *path;
     struct extent_buffer *leaf;
     int reserve_level;
     int level;
     int max_level;
     int replaced = 0;
     int ret = 0;
     u32 min_reserved;
 
     path = btrfs_alloc_path();
     if (!path)
         return -ENOMEM;
     path->reada = READA_FORWARD;
 
     reloc_root = root->reloc_root;
     root_item = &reloc_root->root_item;
 
     if (btrfs_disk_key_objectid(&root_item->drop_progress) == 0) {
         level = btrfs_root_level(root_item);
         atomic_inc(&reloc_root->node->refs);
         path->nodes[level] = reloc_root->node;
         path->slots[level] = 0;
     } else {
         btrfs_disk_key_to_cpu(&key, &root_item->drop_progress);
 
         level = btrfs_root_drop_level(root_item);
         BUG_ON(level == 0);
         path->lowest_level = level;
         ret = btrfs_search_slot(NULL, reloc_root, &key, path, 0, 0);
         path->lowest_level = 0;
         if (ret < 0) {
             btrfs_free_path(path);
             return ret;
         }
 
         btrfs_node_key_to_cpu(path->nodes[level], &next_key,
                       path->slots[level]);
         WARN_ON(memcmp(&key, &next_key, sizeof(key)));
 
         btrfs_unlock_up_safe(path, 0);
     }
 
     /*
      * In merge_reloc_root(), we modify the upper level pointer to swap the
      * tree blocks between reloc tree and subvolume tree.  Thus for tree
      * block COW, we COW at most from level 1 to root level for each tree.
      *
      * Thus the needed metadata size is at most root_level * nodesize,
      * and * 2 since we have two trees to COW.
      */
     reserve_level = max_t(int, 1, btrfs_root_level(root_item));
     min_reserved = fs_info->nodesize * reserve_level * 2;
     memset(&next_key, 0, sizeof(next_key));
 
     while (1) {
         ret = btrfs_block_rsv_refill(fs_info, rc->block_rsv,
                          min_reserved,
                          BTRFS_RESERVE_FLUSH_LIMIT);
         if (ret)
             goto out;
         trans = btrfs_start_transaction(root, 0);
         if (IS_ERR(trans)) {
             ret = PTR_ERR(trans);
             trans = NULL;
             goto out;
         }
 
         /*
          * At this point we no longer have a reloc_control, so we can't
          * depend on btrfs_init_reloc_root to update our last_trans.
          *
          * But that's ok, we started the trans handle on our
          * corresponding fs_root, which means it's been added to the
          * dirty list.  At commit time we'll still call
          * btrfs_update_reloc_root() and update our root item
          * appropriately.
          */
         reloc_root->last_trans = trans->transid;
         trans->block_rsv = rc->block_rsv;
 
         replaced = 0;
         max_level = level;
 
         ret = walk_down_reloc_tree(reloc_root, path, &level);
         if (ret < 0)
             goto out;
         if (ret > 0)
             break;
 
         if (!find_next_key(path, level, &key) &&
             btrfs_comp_cpu_keys(&next_key, &key) >= 0) {
             ret = 0;
         } else {
             ret = replace_path(trans, rc, root, reloc_root, path,
                        &next_key, level, max_level);
         }
         if (ret < 0)
             goto out;
         if (ret > 0) {
             level = ret;
             btrfs_node_key_to_cpu(path->nodes[level], &key,
                           path->slots[level]);
             replaced = 1;
         }
 
         ret = walk_up_reloc_tree(reloc_root, path, &level);
         if (ret > 0)
             break;
 
         BUG_ON(level == 0);
         /*
          * save the merging progress in the drop_progress.
          * this is OK since root refs == 1 in this case.
          */
         btrfs_node_key(path->nodes[level], &root_item->drop_progress,
                    path->slots[level]);
         btrfs_set_root_drop_level(root_item, level);
 
         btrfs_end_transaction_throttle(trans);
         trans = NULL;
 
         btrfs_btree_balance_dirty(fs_info);
 
         if (replaced && rc->stage == UPDATE_DATA_PTRS)
             invalidate_extent_cache(root, &key, &next_key);
     }
 
     /*
      * handle the case only one block in the fs tree need to be
      * relocated and the block is tree root.
      */
     leaf = btrfs_lock_root_node(root);
     ret = btrfs_cow_block(trans, root, leaf, NULL, 0, &leaf,
                   BTRFS_NESTING_COW);
     btrfs_tree_unlock(leaf);
     free_extent_buffer(leaf);
 out:
     btrfs_free_path(path);
 
     if (ret == 0) {
         ret = insert_dirty_subvol(trans, rc, root);
         if (ret)
             btrfs_abort_transaction(trans, ret);
     }
 
     if (trans)
         btrfs_end_transaction_throttle(trans);
 
     btrfs_btree_balance_dirty(fs_info);
 
     if (replaced && rc->stage == UPDATE_DATA_PTRS)
         invalidate_extent_cache(root, &key, &next_key);
 
     return ret;
 }
 
 static noinline_for_stack
 int prepare_to_merge(struct reloc_control *rc, int err)
 {
     struct btrfs_root *root = rc->extent_root;
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct btrfs_root *reloc_root;
     struct btrfs_trans_handle *trans;
     LIST_HEAD(reloc_roots);
     u64 num_bytes = 0;
     int ret;
 
     mutex_lock(&fs_info->reloc_mutex);
     rc->merging_rsv_size += fs_info->nodesize * (BTRFS_MAX_LEVEL - 1) * 2;
     rc->merging_rsv_size += rc->nodes_relocated * 2;
     mutex_unlock(&fs_info->reloc_mutex);
 
 again:
     if (!err) {
         num_bytes = rc->merging_rsv_size;
         ret = btrfs_block_rsv_add(fs_info, rc->block_rsv, num_bytes,
                       BTRFS_RESERVE_FLUSH_ALL);
         if (ret)
             err = ret;
     }
 
     trans = btrfs_join_transaction(rc->extent_root);
     if (IS_ERR(trans)) {
         if (!err)
             btrfs_block_rsv_release(fs_info, rc->block_rsv,
                         num_bytes, NULL);
         return PTR_ERR(trans);
     }
 
     if (!err) {
         if (num_bytes != rc->merging_rsv_size) {
             btrfs_end_transaction(trans);
             btrfs_block_rsv_release(fs_info, rc->block_rsv,
                         num_bytes, NULL);
             goto again;
         }
     }
 
     rc->merge_reloc_tree = 1;
 
     while (!list_empty(&rc->reloc_roots)) {
         reloc_root = list_entry(rc->reloc_roots.next,
                     struct btrfs_root, root_list);
         list_del_init(&reloc_root->root_list);
 
         root = btrfs_get_fs_root(fs_info, reloc_root->root_key.offset,
                 false);
         if (IS_ERR(root)) {
             /*
              * Even if we have an error we need this reloc root
              * back on our list so we can clean up properly.
              */
             list_add(&reloc_root->root_list, &reloc_roots);
             btrfs_abort_transaction(trans, (int)PTR_ERR(root));
             if (!err)
                 err = PTR_ERR(root);
             break;
         }
         ASSERT(root->reloc_root == reloc_root);
 
         /*
          * set reference count to 1, so btrfs_recover_relocation
          * knows it should resumes merging
          */
         if (!err)
             btrfs_set_root_refs(&reloc_root->root_item, 1);
         ret = btrfs_update_reloc_root(trans, root);
 
         /*
          * Even if we have an error we need this reloc root back on our
          * list so we can clean up properly.
          */
         list_add(&reloc_root->root_list, &reloc_roots);
         btrfs_put_root(root);
 
         if (ret) {
             btrfs_abort_transaction(trans, ret);
             if (!err)
                 err = ret;
             break;
         }
     }
 
     list_splice(&reloc_roots, &rc->reloc_roots);
 
     if (!err)
         err = btrfs_commit_transaction(trans);
     else
         btrfs_end_transaction(trans);
     return err;
 }
 
 static noinline_for_stack
 void free_reloc_roots(struct list_head *list)
 {
     struct btrfs_root *reloc_root, *tmp;
 
     list_for_each_entry_safe(reloc_root, tmp, list, root_list)
         __del_reloc_root(reloc_root);
 }
 
 static noinline_for_stack
 void merge_reloc_roots(struct reloc_control *rc)
 {
     struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
     struct btrfs_root *root;
     struct btrfs_root *reloc_root;
     LIST_HEAD(reloc_roots);
     int found = 0;
     int ret = 0;
 again:
     root = rc->extent_root;
 
     /*
      * this serializes us with btrfs_record_root_in_transaction,
      * we have to make sure nobody is in the middle of
      * adding their roots to the list while we are
      * doing this splice
      */
     mutex_lock(&fs_info->reloc_mutex);
     list_splice_init(&rc->reloc_roots, &reloc_roots);
     mutex_unlock(&fs_info->reloc_mutex);
 
     while (!list_empty(&reloc_roots)) {
         found = 1;
         reloc_root = list_entry(reloc_roots.next,
                     struct btrfs_root, root_list);
 
         root = btrfs_get_fs_root(fs_info, reloc_root->root_key.offset,
                      false);
         if (btrfs_root_refs(&reloc_root->root_item) > 0) {
             if (IS_ERR(root)) {
                 /*
                  * For recovery we read the fs roots on mount,
                  * and if we didn't find the root then we marked
                  * the reloc root as a garbage root.  For normal
                  * relocation obviously the root should exist in
                  * memory.  However there's no reason we can't
                  * handle the error properly here just in case.
                  */
                 ASSERT(0);
                 ret = PTR_ERR(root);
                 goto out;
             }
             if (root->reloc_root != reloc_root) {
                 /*
                  * This is actually impossible without something
                  * going really wrong (like weird race condition
                  * or cosmic rays).
                  */
                 ASSERT(0);
                 ret = -EINVAL;
                 goto out;
             }
             ret = merge_reloc_root(rc, root);
             btrfs_put_root(root);
             if (ret) {
                 if (list_empty(&reloc_root->root_list))
                     list_add_tail(&reloc_root->root_list,
                               &reloc_roots);
                 goto out;
             }
         } else {
             if (!IS_ERR(root)) {
                 if (root->reloc_root == reloc_root) {
                     root->reloc_root = NULL;
                     btrfs_put_root(reloc_root);
                 }
                 clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE,
                       &root->state);
                 btrfs_put_root(root);
             }
 
             list_del_init(&reloc_root->root_list);
             /* Don't forget to queue this reloc root for cleanup */
             list_add_tail(&reloc_root->reloc_dirty_list,
                       &rc->dirty_subvol_roots);
         }
     }
 
     if (found) {
         found = 0;
         goto again;
     }
 out:
     if (ret) {
         btrfs_handle_fs_error(fs_info, ret, NULL);
         free_reloc_roots(&reloc_roots);
 
         /* new reloc root may be added */
         mutex_lock(&fs_info->reloc_mutex);
         list_splice_init(&rc->reloc_roots, &reloc_roots);
         mutex_unlock(&fs_info->reloc_mutex);
         free_reloc_roots(&reloc_roots);
     }
 
     /*
      * We used to have
      *
      * BUG_ON(!RB_EMPTY_ROOT(&rc->reloc_root_tree.rb_root));
      *
      * here, but it's wrong.  If we fail to start the transaction in
      * prepare_to_merge() we will have only 0 ref reloc roots, none of which
      * have actually been removed from the reloc_root_tree rb tree.  This is
      * fine because we're bailing here, and we hold a reference on the root
      * for the list that holds it, so these roots will be cleaned up when we
      * do the reloc_dirty_list afterwards.  Meanwhile the root->reloc_root
      * will be cleaned up on unmount.
      *
      * The remaining nodes will be cleaned up by free_reloc_control.
      */
 }
 
 static void free_block_list(struct rb_root *blocks)
 {
     struct tree_block *block;
     struct rb_node *rb_node;
     while ((rb_node = rb_first(blocks))) {
         block = rb_entry(rb_node, struct tree_block, rb_node);
         rb_erase(rb_node, blocks);
         kfree(block);
     }
 }
 
 static int record_reloc_root_in_trans(struct btrfs_trans_handle *trans,
                       struct btrfs_root *reloc_root)
 {
     struct btrfs_fs_info *fs_info = reloc_root->fs_info;
     struct btrfs_root *root;
     int ret;
 
     if (reloc_root->last_trans == trans->transid)
         return 0;
 
     root = btrfs_get_fs_root(fs_info, reloc_root->root_key.offset, false);
 
     /*
      * This should succeed, since we can't have a reloc root without having
      * already looked up the actual root and created the reloc root for this
      * root.
      *
      * However if there's some sort of corruption where we have a ref to a
      * reloc root without a corresponding root this could return ENOENT.
      */
     if (IS_ERR(root)) {
         ASSERT(0);
         return PTR_ERR(root);
     }
     if (root->reloc_root != reloc_root) {
         ASSERT(0);
         btrfs_err(fs_info,
               "root %llu has two reloc roots associated with it",
               reloc_root->root_key.offset);
         btrfs_put_root(root);
         return -EUCLEAN;
     }
     ret = btrfs_record_root_in_trans(trans, root);
     btrfs_put_root(root);
 
     return ret;
 }
 
 static noinline_for_stack
 struct btrfs_root *select_reloc_root(struct btrfs_trans_handle *trans,
                      struct reloc_control *rc,
                      struct btrfs_backref_node *node,
                      struct btrfs_backref_edge *edges[])
 {
     struct btrfs_backref_node *next;
     struct btrfs_root *root;
     int index = 0;
     int ret;
 
     next = node;
     while (1) {
         cond_resched();
         next = walk_up_backref(next, edges, &index);
         root = next->root;
 
         /*
          * If there is no root, then our references for this block are
          * incomplete, as we should be able to walk all the way up to a
          * block that is owned by a root.
          *
          * This path is only for SHAREABLE roots, so if we come upon a
          * non-SHAREABLE root then we have backrefs that resolve
          * improperly.
          *
          * Both of these cases indicate file system corruption, or a bug
          * in the backref walking code.
          */
         if (!root) {
             ASSERT(0);
             btrfs_err(trans->fs_info,
         "bytenr %llu doesn't have a backref path ending in a root",
                   node->bytenr);
             return ERR_PTR(-EUCLEAN);
         }
         if (!test_bit(BTRFS_ROOT_SHAREABLE, &root->state)) {
             ASSERT(0);
             btrfs_err(trans->fs_info,
     "bytenr %llu has multiple refs with one ending in a non-shareable root",
                   node->bytenr);
             return ERR_PTR(-EUCLEAN);
         }
 
         if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID) {
             ret = record_reloc_root_in_trans(trans, root);
             if (ret)
                 return ERR_PTR(ret);
             break;
         }
 
         ret = btrfs_record_root_in_trans(trans, root);
         if (ret)
             return ERR_PTR(ret);
         root = root->reloc_root;
 
         /*
          * We could have raced with another thread which failed, so
          * root->reloc_root may not be set, return ENOENT in this case.
          */
         if (!root)
             return ERR_PTR(-ENOENT);
 
         if (next->new_bytenr != root->node->start) {
             /*
              * We just created the reloc root, so we shouldn't have
              * ->new_bytenr set and this shouldn't be in the changed
              *  list.  If it is then we have multiple roots pointing
              *  at the same bytenr which indicates corruption, or
              *  we've made a mistake in the backref walking code.
              */
             ASSERT(next->new_bytenr == 0);
             ASSERT(list_empty(&next->list));
             if (next->new_bytenr || !list_empty(&next->list)) {
                 btrfs_err(trans->fs_info,
     "bytenr %llu possibly has multiple roots pointing at the same bytenr %llu",
                       node->bytenr, next->bytenr);
                 return ERR_PTR(-EUCLEAN);
             }
 
             next->new_bytenr = root->node->start;
             btrfs_put_root(next->root);
             next->root = btrfs_grab_root(root);
             ASSERT(next->root);
             list_add_tail(&next->list,
                       &rc->backref_cache.changed);
             mark_block_processed(rc, next);
             break;
         }
 
         WARN_ON(1);
         root = NULL;
         next = walk_down_backref(edges, &index);
         if (!next || next->level <= node->level)
             break;
     }
     if (!root) {
         /*
          * This can happen if there's fs corruption or if there's a bug
          * in the backref lookup code.
          */
         ASSERT(0);
         return ERR_PTR(-ENOENT);
     }
 
     next = node;
     /* setup backref node path for btrfs_reloc_cow_block */
     while (1) {
         rc->backref_cache.path[next->level] = next;
         if (--index < 0)
             break;
         next = edges[index]->node[UPPER];
     }
     return root;
 }
 
 /*
  * Select a tree root for relocation.
  *
  * Return NULL if the block is not shareable. We should use do_relocation() in
  * this case.
  *
  * Return a tree root pointer if the block is shareable.
  * Return -ENOENT if the block is root of reloc tree.
  */
 static noinline_for_stack
 struct btrfs_root *select_one_root(struct btrfs_backref_node *node)
 {
     struct btrfs_backref_node *next;
     struct btrfs_root *root;
     struct btrfs_root *fs_root = NULL;
     struct btrfs_backref_edge *edges[BTRFS_MAX_LEVEL - 1];
     int index = 0;
 
     next = node;
     while (1) {
         cond_resched();
         next = walk_up_backref(next, edges, &index);
         root = next->root;
 
         /*
          * This can occur if we have incomplete extent refs leading all
          * the way up a particular path, in this case return -EUCLEAN.
          */
         if (!root)
             return ERR_PTR(-EUCLEAN);
 
         /* No other choice for non-shareable tree */
         if (!test_bit(BTRFS_ROOT_SHAREABLE, &root->state))
             return root;
 
         if (root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID)
             fs_root = root;
 
         if (next != node)
             return NULL;
 
         next = walk_down_backref(edges, &index);
         if (!next || next->level <= node->level)
             break;
     }
 
     if (!fs_root)
         return ERR_PTR(-ENOENT);
     return fs_root;
 }
 
 static noinline_for_stack
 u64 calcu_metadata_size(struct reloc_control *rc,
             struct btrfs_backref_node *node, int reserve)
 {
     struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
     struct btrfs_backref_node *next = node;
     struct btrfs_backref_edge *edge;
     struct btrfs_backref_edge *edges[BTRFS_MAX_LEVEL - 1];
     u64 num_bytes = 0;
     int index = 0;
 
     BUG_ON(reserve && node->processed);
 
     while (next) {
         cond_resched();
         while (1) {
             if (next->processed && (reserve || next != node))
                 break;
 
             num_bytes += fs_info->nodesize;
 
             if (list_empty(&next->upper))
                 break;
 
             edge = list_entry(next->upper.next,
                     struct btrfs_backref_edge, list[LOWER]);
             edges[index++] = edge;
             next = edge->node[UPPER];
         }
         next = walk_down_backref(edges, &index);
     }
     return num_bytes;
 }
 
 static int reserve_metadata_space(struct btrfs_trans_handle *trans,
                   struct reloc_control *rc,
                   struct btrfs_backref_node *node)
 {
     struct btrfs_root *root = rc->extent_root;
     struct btrfs_fs_info *fs_info = root->fs_info;
     u64 num_bytes;
     int ret;
     u64 tmp;
 
     num_bytes = calcu_metadata_size(rc, node, 1) * 2;
 
     trans->block_rsv = rc->block_rsv;
     rc->reserved_bytes += num_bytes;
 
     /*
      * We are under a transaction here so we can only do limited flushing.
      * If we get an enospc just kick back -EAGAIN so we know to drop the
      * transaction and try to refill when we can flush all the things.
      */
     ret = btrfs_block_rsv_refill(fs_info, rc->block_rsv, num_bytes,
                      BTRFS_RESERVE_FLUSH_LIMIT);
     if (ret) {
         tmp = fs_info->nodesize * RELOCATION_RESERVED_NODES;
         while (tmp <= rc->reserved_bytes)
             tmp <<= 1;
         /*
          * only one thread can access block_rsv at this point,
          * so we don't need hold lock to protect block_rsv.
          * we expand more reservation size here to allow enough
          * space for relocation and we will return earlier in
          * enospc case.
          */
         rc->block_rsv->size = tmp + fs_info->nodesize *
                       RELOCATION_RESERVED_NODES;
         return -EAGAIN;
     }
 
     return 0;
 }
 
 /*
  * relocate a block tree, and then update pointers in upper level
  * blocks that reference the block to point to the new location.
  *
  * if called by link_to_upper, the block has already been relocated.
  * in that case this function just updates pointers.
  */
 static int do_relocation(struct btrfs_trans_handle *trans,
              struct reloc_control *rc,
              struct btrfs_backref_node *node,
              struct btrfs_key *key,
              struct btrfs_path *path, int lowest)
 {
     struct btrfs_backref_node *upper;
     struct btrfs_backref_edge *edge;
     struct btrfs_backref_edge *edges[BTRFS_MAX_LEVEL - 1];
     struct btrfs_root *root;
     struct extent_buffer *eb;
     u32 blocksize;
     u64 bytenr;
     int slot;
     int ret = 0;
 
     /*
      * If we are lowest then this is the first time we're processing this
      * block, and thus shouldn't have an eb associated with it yet.
      */
     ASSERT(!lowest || !node->eb);
 
     path->lowest_level = node->level + 1;
     rc->backref_cache.path[node->level] = node;
     list_for_each_entry(edge, &node->upper, list[LOWER]) {
         struct btrfs_ref ref = { 0 };
 
         cond_resched();
 
         upper = edge->node[UPPER];
         root = select_reloc_root(trans, rc, upper, edges);
         if (IS_ERR(root)) {
             ret = PTR_ERR(root);
             goto next;
         }
 
         if (upper->eb && !upper->locked) {
             if (!lowest) {
                 ret = btrfs_bin_search(upper->eb, key, &slot);
                 if (ret < 0)
                     goto next;
                 BUG_ON(ret);
                 bytenr = btrfs_node_blockptr(upper->eb, slot);
                 if (node->eb->start == bytenr)
                     goto next;
             }
             btrfs_backref_drop_node_buffer(upper);
         }
 
         if (!upper->eb) {
             ret = btrfs_search_slot(trans, root, key, path, 0, 1);
             if (ret) {
                 if (ret > 0)
                     ret = -ENOENT;
 
                 btrfs_release_path(path);
                 break;
             }
 
             if (!upper->eb) {
                 upper->eb = path->nodes[upper->level];
                 path->nodes[upper->level] = NULL;
             } else {
                 BUG_ON(upper->eb != path->nodes[upper->level]);
             }
 
             upper->locked = 1;
             path->locks[upper->level] = 0;
 
             slot = path->slots[upper->level];
             btrfs_release_path(path);
         } else {
             ret = btrfs_bin_search(upper->eb, key, &slot);
             if (ret < 0)
                 goto next;
             BUG_ON(ret);
         }
 
         bytenr = btrfs_node_blockptr(upper->eb, slot);
         if (lowest) {
             if (bytenr != node->bytenr) {
                 btrfs_err(root->fs_info,
         "lowest leaf/node mismatch: bytenr %llu node->bytenr %llu slot %d upper %llu",
                       bytenr, node->bytenr, slot,
                       upper->eb->start);
                 ret = -EIO;
                 goto next;
             }
         } else {
             if (node->eb->start == bytenr)
                 goto next;
         }
 
         blocksize = root->fs_info->nodesize;
         eb = btrfs_read_node_slot(upper->eb, slot);
         if (IS_ERR(eb)) {
             ret = PTR_ERR(eb);
             goto next;
         }
         btrfs_tree_lock(eb);
 
         if (!node->eb) {
             ret = btrfs_cow_block(trans, root, eb, upper->eb,
                           slot, &eb, BTRFS_NESTING_COW);
             btrfs_tree_unlock(eb);
             free_extent_buffer(eb);
             if (ret < 0)
                 goto next;
             /*
              * We've just COWed this block, it should have updated
              * the correct backref node entry.
              */
             ASSERT(node->eb == eb);
         } else {
             btrfs_set_node_blockptr(upper->eb, slot,
                         node->eb->start);
             btrfs_set_node_ptr_generation(upper->eb, slot,
                               trans->transid);
             btrfs_mark_buffer_dirty(upper->eb);
 
             btrfs_init_generic_ref(&ref, BTRFS_ADD_DELAYED_REF,
                            node->eb->start, blocksize,
                            upper->eb->start);
             btrfs_init_tree_ref(&ref, node->level,
                         btrfs_header_owner(upper->eb),
                         root->root_key.objectid, false);
             ret = btrfs_inc_extent_ref(trans, &ref);
             if (!ret)
                 ret = btrfs_drop_subtree(trans, root, eb,
                              upper->eb);
             if (ret)
                 btrfs_abort_transaction(trans, ret);
         }
 next:
         if (!upper->pending)
             btrfs_backref_drop_node_buffer(upper);
         else
             btrfs_backref_unlock_node_buffer(upper);
         if (ret)
             break;
     }
 
     if (!ret && node->pending) {
         btrfs_backref_drop_node_buffer(node);
         list_move_tail(&node->list, &rc->backref_cache.changed);
         node->pending = 0;
     }
 
     path->lowest_level = 0;
 
     /*
      * We should have allocated all of our space in the block rsv and thus
      * shouldn't ENOSPC.
      */
     ASSERT(ret != -ENOSPC);
     return ret;
 }
 
 static int link_to_upper(struct btrfs_trans_handle *trans,
              struct reloc_control *rc,
              struct btrfs_backref_node *node,
              struct btrfs_path *path)
 {
     struct btrfs_key key;
 
     btrfs_node_key_to_cpu(node->eb, &key, 0);
     return do_relocation(trans, rc, node, &key, path, 0);
 }
 
 static int finish_pending_nodes(struct btrfs_trans_handle *trans,
                 struct reloc_control *rc,
                 struct btrfs_path *path, int err)
 {
     LIST_HEAD(list);
     struct btrfs_backref_cache *cache = &rc->backref_cache;
     struct btrfs_backref_node *node;
     int level;
     int ret;
 
     for (level = 0; level < BTRFS_MAX_LEVEL; level++) {
         while (!list_empty(&cache->pending[level])) {
             node = list_entry(cache->pending[level].next,
                       struct btrfs_backref_node, list);
             list_move_tail(&node->list, &list);
             BUG_ON(!node->pending);
 
             if (!err) {
                 ret = link_to_upper(trans, rc, node, path);
                 if (ret < 0)
                     err = ret;
             }
         }
         list_splice_init(&list, &cache->pending[level]);
     }
     return err;
 }
 
 /*
  * mark a block and all blocks directly/indirectly reference the block
  * as processed.
  */
 static void update_processed_blocks(struct reloc_control *rc,
                     struct btrfs_backref_node *node)
 {
     struct btrfs_backref_node *next = node;
     struct btrfs_backref_edge *edge;
     struct btrfs_backref_edge *edges[BTRFS_MAX_LEVEL - 1];
     int index = 0;
 
     while (next) {
         cond_resched();
         while (1) {
             if (next->processed)
                 break;
 
             mark_block_processed(rc, next);
 
             if (list_empty(&next->upper))
                 break;
 
             edge = list_entry(next->upper.next,
                     struct btrfs_backref_edge, list[LOWER]);
             edges[index++] = edge;
             next = edge->node[UPPER];
         }
         next = walk_down_backref(edges, &index);
     }
 }
 
 static int tree_block_processed(u64 bytenr, struct reloc_control *rc)
 {
     u32 blocksize = rc->extent_root->fs_info->nodesize;
 
     if (test_range_bit(&rc->processed_blocks, bytenr,
                bytenr + blocksize - 1, EXTENT_DIRTY, 1, NULL))
         return 1;
     return 0;
 }
 
 static int get_tree_block_key(struct btrfs_fs_info *fs_info,
                   struct tree_block *block)
 {
     struct extent_buffer *eb;
 
     eb = read_tree_block(fs_info, block->bytenr, block->owner,
                  block->key.offset, block->level, NULL);
     if (IS_ERR(eb))
         return PTR_ERR(eb);
     if (!extent_buffer_uptodate(eb)) {
         free_extent_buffer(eb);
         return -EIO;
     }
     if (block->level == 0)
         btrfs_item_key_to_cpu(eb, &block->key, 0);
     else
         btrfs_node_key_to_cpu(eb, &block->key, 0);
     free_extent_buffer(eb);
     block->key_ready = 1;
     return 0;
 }
 
 /*
  * helper function to relocate a tree block
  */
 static int relocate_tree_block(struct btrfs_trans_handle *trans,
                 struct reloc_control *rc,
                 struct btrfs_backref_node *node,
                 struct btrfs_key *key,
                 struct btrfs_path *path)
 {
     struct btrfs_root *root;
     int ret = 0;
 
     if (!node)
         return 0;
 
     /*
      * If we fail here we want to drop our backref_node because we are going
      * to start over and regenerate the tree for it.
      */
     ret = reserve_metadata_space(trans, rc, node);
     if (ret)
         goto out;
 
     BUG_ON(node->processed);
     root = select_one_root(node);
     if (IS_ERR(root)) {
         ret = PTR_ERR(root);
 
         /* See explanation in select_one_root for the -EUCLEAN case. */
         ASSERT(ret == -ENOENT);
         if (ret == -ENOENT) {
             ret = 0;
             update_processed_blocks(rc, node);
         }
         goto out;
     }
 
     if (root) {
         if (test_bit(BTRFS_ROOT_SHAREABLE, &root->state)) {
             /*
              * This block was the root block of a root, and this is
              * the first time we're processing the block and thus it
              * should not have had the ->new_bytenr modified and
              * should have not been included on the changed list.
              *
              * However in the case of corruption we could have
              * multiple refs pointing to the same block improperly,
              * and thus we would trip over these checks.  ASSERT()
              * for the developer case, because it could indicate a
              * bug in the backref code, however error out for a
              * normal user in the case of corruption.
              */
             ASSERT(node->new_bytenr == 0);
             ASSERT(list_empty(&node->list));
             if (node->new_bytenr || !list_empty(&node->list)) {
                 btrfs_err(root->fs_info,
                   "bytenr %llu has improper references to it",
                       node->bytenr);
                 ret = -EUCLEAN;
                 goto out;
             }
             ret = btrfs_record_root_in_trans(trans, root);
             if (ret)
                 goto out;
             /*
              * Another thread could have failed, need to check if we
              * have reloc_root actually set.
              */
             if (!root->reloc_root) {
                 ret = -ENOENT;
                 goto out;
             }
             root = root->reloc_root;
             node->new_bytenr = root->node->start;
             btrfs_put_root(node->root);
             node->root = btrfs_grab_root(root);
             ASSERT(node->root);
             list_add_tail(&node->list, &rc->backref_cache.changed);
         } else {
             path->lowest_level = node->level;
             if (root == root->fs_info->chunk_root)
                 btrfs_reserve_chunk_metadata(trans, false);
             ret = btrfs_search_slot(trans, root, key, path, 0, 1);
             btrfs_release_path(path);
             if (root == root->fs_info->chunk_root)
                 btrfs_trans_release_chunk_metadata(trans);
             if (ret > 0)
                 ret = 0;
         }
         if (!ret)
             update_processed_blocks(rc, node);
     } else {
         ret = do_relocation(trans, rc, node, key, path, 1);
     }
 out:
     if (ret || node->level == 0 || node->cowonly)
         btrfs_backref_cleanup_node(&rc->backref_cache, node);
     return ret;
 }
 
 /*
  * relocate a list of blocks
  */
 static noinline_for_stack
 int relocate_tree_blocks(struct btrfs_trans_handle *trans,
              struct reloc_control *rc, struct rb_root *blocks)
 {
     struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
     struct btrfs_backref_node *node;
     struct btrfs_path *path;
     struct tree_block *block;
     struct tree_block *next;
     int ret;
     int err = 0;
 
     path = btrfs_alloc_path();
     if (!path) {
         err = -ENOMEM;
         goto out_free_blocks;
     }
 
     /* Kick in readahead for tree blocks with missing keys */
     rbtree_postorder_for_each_entry_safe(block, next, blocks, rb_node) {
         if (!block->key_ready)
             btrfs_readahead_tree_block(fs_info, block->bytenr,
                            block->owner, 0,
                            block->level);
     }
 
     /* Get first keys */
     rbtree_postorder_for_each_entry_safe(block, next, blocks, rb_node) {
         if (!block->key_ready) {
             err = get_tree_block_key(fs_info, block);
             if (err)
                 goto out_free_path;
         }
     }
 
     /* Do tree relocation */
     rbtree_postorder_for_each_entry_safe(block, next, blocks, rb_node) {
         node = build_backref_tree(rc, &block->key,
                       block->level, block->bytenr);
         if (IS_ERR(node)) {
             err = PTR_ERR(node);
             goto out;
         }
 
         ret = relocate_tree_block(trans, rc, node, &block->key,
                       path);
         if (ret < 0) {
             err = ret;
             break;
         }
     }
 out:
     err = finish_pending_nodes(trans, rc, path, err);
 
 out_free_path:
     btrfs_free_path(path);
 out_free_blocks:
     free_block_list(blocks);
     return err;
 }
 
 static noinline_for_stack int prealloc_file_extent_cluster(
                 struct btrfs_inode *inode,
                 struct file_extent_cluster *cluster)
 {
     u64 alloc_hint = 0;
     u64 start;
     u64 end;
     u64 offset = inode->index_cnt;
     u64 num_bytes;
     int nr;
     int ret = 0;
     u64 i_size = i_size_read(&inode->vfs_inode);
     u64 prealloc_start = cluster->start - offset;
     u64 prealloc_end = cluster->end - offset;
     u64 cur_offset = prealloc_start;
 
     /*
      * For subpage case, previous i_size may not be aligned to PAGE_SIZE.
      * This means the range [i_size, PAGE_END + 1) is filled with zeros by
      * btrfs_do_readpage() call of previously relocated file cluster.
      *
      * If the current cluster starts in the above range, btrfs_do_readpage()
      * will skip the read, and relocate_one_page() will later writeback
      * the padding zeros as new data, causing data corruption.
      *
      * Here we have to manually invalidate the range (i_size, PAGE_END + 1).
      */
     if (!IS_ALIGNED(i_size, PAGE_SIZE)) {
         struct address_space *mapping = inode->vfs_inode.i_mapping;
         struct btrfs_fs_info *fs_info = inode->root->fs_info;
         const u32 sectorsize = fs_info->sectorsize;
         struct page *page;
 
         ASSERT(sectorsize < PAGE_SIZE);
         ASSERT(IS_ALIGNED(i_size, sectorsize));
 
         /*
          * Subpage can't handle page with DIRTY but without UPTODATE
          * bit as it can lead to the following deadlock:
          *
          * btrfs_read_folio()
          * | Page already *locked*
          * |- btrfs_lock_and_flush_ordered_range()
          *    |- btrfs_start_ordered_extent()
          *       |- extent_write_cache_pages()
          *          |- lock_page()
          *             We try to lock the page we already hold.
          *
          * Here we just writeback the whole data reloc inode, so that
          * we will be ensured to have no dirty range in the page, and
          * are safe to clear the uptodate bits.
          *
          * This shouldn't cause too much overhead, as we need to write
          * the data back anyway.
          */
         ret = filemap_write_and_wait(mapping);
         if (ret < 0)
             return ret;
 
         clear_extent_bits(&inode->io_tree, i_size,
                   round_up(i_size, PAGE_SIZE) - 1,
                   EXTENT_UPTODATE);
         page = find_lock_page(mapping, i_size >> PAGE_SHIFT);
         /*
          * If page is freed we don't need to do anything then, as we
          * will re-read the whole page anyway.
          */
         if (page) {
             btrfs_subpage_clear_uptodate(fs_info, page, i_size,
                     round_up(i_size, PAGE_SIZE) - i_size);
             unlock_page(page);
             put_page(page);
         }
     }
 
     BUG_ON(cluster->start != cluster->boundary[0]);
     ret = btrfs_alloc_data_chunk_ondemand(inode,
                           prealloc_end + 1 - prealloc_start);
     if (ret)
         return ret;
 
     btrfs_inode_lock(&inode->vfs_inode, 0);
     for (nr = 0; nr < cluster->nr; nr++) {
         start = cluster->boundary[nr] - offset;
         if (nr + 1 < cluster->nr)
             end = cluster->boundary[nr + 1] - 1 - offset;
         else
             end = cluster->end - offset;
 
         lock_extent(&inode->io_tree, start, end);
         num_bytes = end + 1 - start;
         ret = btrfs_prealloc_file_range(&inode->vfs_inode, 0, start,
                         num_bytes, num_bytes,
                         end + 1, &alloc_hint);
         cur_offset = end + 1;
         unlock_extent(&inode->io_tree, start, end);
         if (ret)
             break;
     }
     btrfs_inode_unlock(&inode->vfs_inode, 0);
 
     if (cur_offset < prealloc_end)
         btrfs_free_reserved_data_space_noquota(inode->root->fs_info,
                            prealloc_end + 1 - cur_offset);
     return ret;
 }
 
 static noinline_for_stack int setup_relocation_extent_mapping(struct inode *inode,
                 u64 start, u64 end, u64 block_start)
 {
     struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
     struct extent_map *em;
     int ret = 0;
 
     em = alloc_extent_map();
     if (!em)
         return -ENOMEM;
 
     em->start = start;
     em->len = end + 1 - start;
     em->block_len = em->len;
     em->block_start = block_start;
     set_bit(EXTENT_FLAG_PINNED, &em->flags);
 
     lock_extent(&BTRFS_I(inode)->io_tree, start, end);
     while (1) {
         write_lock(&em_tree->lock);
         ret = add_extent_mapping(em_tree, em, 0);
         write_unlock(&em_tree->lock);
         if (ret != -EEXIST) {
             free_extent_map(em);
             break;
         }
         btrfs_drop_extent_cache(BTRFS_I(inode), start, end, 0);
     }
     unlock_extent(&BTRFS_I(inode)->io_tree, start, end);
     return ret;
 }
 
 /*
  * Allow error injection to test balance/relocation cancellation
  */
 noinline int btrfs_should_cancel_balance(struct btrfs_fs_info *fs_info)
 {
     return atomic_read(&fs_info->balance_cancel_req) ||
         atomic_read(&fs_info->reloc_cancel_req) ||
         fatal_signal_pending(current);
 }
 ALLOW_ERROR_INJECTION(btrfs_should_cancel_balance, TRUE);
 
 static u64 get_cluster_boundary_end(struct file_extent_cluster *cluster,
                     int cluster_nr)
 {
     /* Last extent, use cluster end directly */
     if (cluster_nr >= cluster->nr - 1)
         return cluster->end;
 
     /* Use next boundary start*/
     return cluster->boundary[cluster_nr + 1] - 1;
 }
 
 static int relocate_one_page(struct inode *inode, struct file_ra_state *ra,
                  struct file_extent_cluster *cluster,
                  int *cluster_nr, unsigned long page_index)
 {
     struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
     u64 offset = BTRFS_I(inode)->index_cnt;
     const unsigned long last_index = (cluster->end - offset) >> PAGE_SHIFT;
     gfp_t mask = btrfs_alloc_write_mask(inode->i_mapping);
     struct page *page;
     u64 page_start;
     u64 page_end;
     u64 cur;
     int ret;
 
     ASSERT(page_index <= last_index);
     page = find_lock_page(inode->i_mapping, page_index);
     if (!page) {
         page_cache_sync_readahead(inode->i_mapping, ra, NULL,
                 page_index, last_index + 1 - page_index);
         page = find_or_create_page(inode->i_mapping, page_index, mask);
         if (!page)
             return -ENOMEM;
     }
     ret = set_page_extent_mapped(page);
     if (ret < 0)
         goto release_page;
 
     if (PageReadahead(page))
         page_cache_async_readahead(inode->i_mapping, ra, NULL,
                 page_folio(page), page_index,
                 last_index + 1 - page_index);
 
     if (!PageUptodate(page)) {
         btrfs_read_folio(NULL, page_folio(page));
         lock_page(page);
         if (!PageUptodate(page)) {
             ret = -EIO;
             goto release_page;
         }
     }
 
     page_start = page_offset(page);
     page_end = page_start + PAGE_SIZE - 1;
 
     /*
      * Start from the cluster, as for subpage case, the cluster can start
      * inside the page.
      */
     cur = max(page_start, cluster->boundary[*cluster_nr] - offset);
     while (cur <= page_end) {
         u64 extent_start = cluster->boundary[*cluster_nr] - offset;
         u64 extent_end = get_cluster_boundary_end(cluster,
                         *cluster_nr) - offset;
         u64 clamped_start = max(page_start, extent_start);
         u64 clamped_end = min(page_end, extent_end);
         u32 clamped_len = clamped_end + 1 - clamped_start;
 
         /* Reserve metadata for this range */
         ret = btrfs_delalloc_reserve_metadata(BTRFS_I(inode),
                               clamped_len, clamped_len,
                               false);
         if (ret)
             goto release_page;
 
         /* Mark the range delalloc and dirty for later writeback */
         lock_extent(&BTRFS_I(inode)->io_tree, clamped_start, clamped_end);
         ret = btrfs_set_extent_delalloc(BTRFS_I(inode), clamped_start,
                         clamped_end, 0, NULL);
         if (ret) {
             clear_extent_bits(&BTRFS_I(inode)->io_tree,
                     clamped_start, clamped_end,
                     EXTENT_LOCKED | EXTENT_BOUNDARY);
             btrfs_delalloc_release_metadata(BTRFS_I(inode),
                             clamped_len, true);
             btrfs_delalloc_release_extents(BTRFS_I(inode),
                                clamped_len);
             goto release_page;
         }
         btrfs_page_set_dirty(fs_info, page, clamped_start, clamped_len);
 
         /*
          * Set the boundary if it's inside the page.
          * Data relocation requires the destination extents to have the
          * same size as the source.
          * EXTENT_BOUNDARY bit prevents current extent from being merged
          * with previous extent.
          */
         if (in_range(cluster->boundary[*cluster_nr] - offset,
                  page_start, PAGE_SIZE)) {
             u64 boundary_start = cluster->boundary[*cluster_nr] -
                         offset;
             u64 boundary_end = boundary_start +
                        fs_info->sectorsize - 1;
 
             set_extent_bits(&BTRFS_I(inode)->io_tree,
                     boundary_start, boundary_end,
                     EXTENT_BOUNDARY);
         }
         unlock_extent(&BTRFS_I(inode)->io_tree, clamped_start, clamped_end);
         btrfs_delalloc_release_extents(BTRFS_I(inode), clamped_len);
         cur += clamped_len;
 
         /* Crossed extent end, go to next extent */
         if (cur >= extent_end) {
             (*cluster_nr)++;
             /* Just finished the last extent of the cluster, exit. */
             if (*cluster_nr >= cluster->nr)
                 break;
         }
     }
     unlock_page(page);
     put_page(page);
 
     balance_dirty_pages_ratelimited(inode->i_mapping);
     btrfs_throttle(fs_info);
     if (btrfs_should_cancel_balance(fs_info))
         ret = -ECANCELED;
     return ret;
 
 release_page:
     unlock_page(page);
     put_page(page);
     return ret;
 }
 
 static int relocate_file_extent_cluster(struct inode *inode,
                     struct file_extent_cluster *cluster)
 {
     u64 offset = BTRFS_I(inode)->index_cnt;
     unsigned long index;
     unsigned long last_index;
     struct file_ra_state *ra;
     int cluster_nr = 0;
     int ret = 0;
 
     if (!cluster->nr)
         return 0;
 
     ra = kzalloc(sizeof(*ra), GFP_NOFS);
     if (!ra)
         return -ENOMEM;
 
     ret = prealloc_file_extent_cluster(BTRFS_I(inode), cluster);
     if (ret)
         goto out;
 
     file_ra_state_init(ra, inode->i_mapping);
 
     ret = setup_relocation_extent_mapping(inode, cluster->start - offset,
                    cluster->end - offset, cluster->start);
     if (ret)
         goto out;
 
     last_index = (cluster->end - offset) >> PAGE_SHIFT;
     for (index = (cluster->start - offset) >> PAGE_SHIFT;
          index <= last_index && !ret; index++)
         ret = relocate_one_page(inode, ra, cluster, &cluster_nr, index);
     if (ret == 0)
         WARN_ON(cluster_nr != cluster->nr);
 out:
     kfree(ra);
     return ret;
 }
 
 static noinline_for_stack
 int relocate_data_extent(struct inode *inode, struct btrfs_key *extent_key,
              struct file_extent_cluster *cluster)
 {
     int ret;
 
     if (cluster->nr > 0 && extent_key->objectid != cluster->end + 1) {
         ret = relocate_file_extent_cluster(inode, cluster);
         if (ret)
             return ret;
         cluster->nr = 0;
     }
 
     if (!cluster->nr)
         cluster->start = extent_key->objectid;
     else
         BUG_ON(cluster->nr >= MAX_EXTENTS);
     cluster->end = extent_key->objectid + extent_key->offset - 1;
     cluster->boundary[cluster->nr] = extent_key->objectid;
     cluster->nr++;
 
     if (cluster->nr >= MAX_EXTENTS) {
         ret = relocate_file_extent_cluster(inode, cluster);
         if (ret)
             return ret;
         cluster->nr = 0;
     }
     return 0;
 }
 
 /*
  * helper to add a tree block to the list.
  * the major work is getting the generation and level of the block
  */
 static int add_tree_block(struct reloc_control *rc,
               struct btrfs_key *extent_key,
               struct btrfs_path *path,
               struct rb_root *blocks)
 {
     struct extent_buffer *eb;
     struct btrfs_extent_item *ei;
     struct btrfs_tree_block_info *bi;
     struct tree_block *block;
     struct rb_node *rb_node;
     u32 item_size;
     int level = -1;
     u64 generation;
     u64 owner = 0;
 
     eb =  path->nodes[0];
     item_size = btrfs_item_size(eb, path->slots[0]);
 
     if (extent_key->type == BTRFS_METADATA_ITEM_KEY ||
         item_size >= sizeof(*ei) + sizeof(*bi)) {
         unsigned long ptr = 0, end;
 
         ei = btrfs_item_ptr(eb, path->slots[0],
                 struct btrfs_extent_item);
         end = (unsigned long)ei + item_size;
         if (extent_key->type == BTRFS_EXTENT_ITEM_KEY) {
             bi = (struct btrfs_tree_block_info *)(ei + 1);
             level = btrfs_tree_block_level(eb, bi);
             ptr = (unsigned long)(bi + 1);
         } else {
             level = (int)extent_key->offset;
             ptr = (unsigned long)(ei + 1);
         }
         generation = btrfs_extent_generation(eb, ei);
 
         /*
          * We're reading random blocks without knowing their owner ahead
          * of time.  This is ok most of the time, as all reloc roots and
          * fs roots have the same lock type.  However normal trees do
          * not, and the only way to know ahead of time is to read the
          * inline ref offset.  We know it's an fs root if
          *
          * 1. There's more than one ref.
          * 2. There's a SHARED_DATA_REF_KEY set.
          * 3. FULL_BACKREF is set on the flags.
          *
          * Otherwise it's safe to assume that the ref offset == the
          * owner of this block, so we can use that when calling
          * read_tree_block.
          */
         if (btrfs_extent_refs(eb, ei) == 1 &&
             !(btrfs_extent_flags(eb, ei) &
               BTRFS_BLOCK_FLAG_FULL_BACKREF) &&
             ptr < end) {
             struct btrfs_extent_inline_ref *iref;
             int type;
 
             iref = (struct btrfs_extent_inline_ref *)ptr;
             type = btrfs_get_extent_inline_ref_type(eb, iref,
                             BTRFS_REF_TYPE_BLOCK);
             if (type == BTRFS_REF_TYPE_INVALID)
                 return -EINVAL;
             if (type == BTRFS_TREE_BLOCK_REF_KEY)
                 owner = btrfs_extent_inline_ref_offset(eb, iref);
         }
     } else if (unlikely(item_size == sizeof(struct btrfs_extent_item_v0))) {
         btrfs_print_v0_err(eb->fs_info);
         btrfs_handle_fs_error(eb->fs_info, -EINVAL, NULL);
         return -EINVAL;
     } else {
         BUG();
     }
 
     btrfs_release_path(path);
 
     BUG_ON(level == -1);
 
     block = kmalloc(sizeof(*block), GFP_NOFS);
     if (!block)
         return -ENOMEM;
 
     block->bytenr = extent_key->objectid;
     block->key.objectid = rc->extent_root->fs_info->nodesize;
     block->key.offset = generation;
     block->level = level;
     block->key_ready = 0;
     block->owner = owner;
 
     rb_node = rb_simple_insert(blocks, block->bytenr, &block->rb_node);
     if (rb_node)
         btrfs_backref_panic(rc->extent_root->fs_info, block->bytenr,
                     -EEXIST);
 
     return 0;
 }
 
 /*
  * helper to add tree blocks for backref of type BTRFS_SHARED_DATA_REF_KEY
  */
 static int __add_tree_block(struct reloc_control *rc,
                 u64 bytenr, u32 blocksize,
                 struct rb_root *blocks)
 {
     struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
     struct btrfs_path *path;
     struct btrfs_key key;
     int ret;
     bool skinny = btrfs_fs_incompat(fs_info, SKINNY_METADATA);
 
     if (tree_block_processed(bytenr, rc))
         return 0;
 
     if (rb_simple_search(blocks, bytenr))
         return 0;
 
     path = btrfs_alloc_path();
     if (!path)
         return -ENOMEM;
 again:
     key.objectid = bytenr;
     if (skinny) {
         key.type = BTRFS_METADATA_ITEM_KEY;
         key.offset = (u64)-1;
     } else {
         key.type = BTRFS_EXTENT_ITEM_KEY;
         key.offset = blocksize;
     }
 
     path->search_commit_root = 1;
     path->skip_locking = 1;
     ret = btrfs_search_slot(NULL, rc->extent_root, &key, path, 0, 0);
     if (ret < 0)
         goto out;
 
     if (ret > 0 && skinny) {
         if (path->slots[0]) {
             path->slots[0]--;
             btrfs_item_key_to_cpu(path->nodes[0], &key,
                           path->slots[0]);
             if (key.objectid == bytenr &&
                 (key.type == BTRFS_METADATA_ITEM_KEY ||
                  (key.type == BTRFS_EXTENT_ITEM_KEY &&
                   key.offset == blocksize)))
                 ret = 0;
         }
 
         if (ret) {
             skinny = false;
             btrfs_release_path(path);
             goto again;
         }
     }
     if (ret) {
         ASSERT(ret == 1);
         btrfs_print_leaf(path->nodes[0]);
         btrfs_err(fs_info,
          "tree block extent item (%llu) is not found in extent tree",
              bytenr);
         WARN_ON(1);
         ret = -EINVAL;
         goto out;
     }
 
     ret = add_tree_block(rc, &key, path, blocks);
 out:
     btrfs_free_path(path);
     return ret;
 }
 
 static int delete_block_group_cache(struct btrfs_fs_info *fs_info,
                     struct btrfs_block_group *block_group,
                     struct inode *inode,
                     u64 ino)
 {
     struct btrfs_root *root = fs_info->tree_root;
     struct btrfs_trans_handle *trans;
     int ret = 0;
 
     if (inode)
         goto truncate;
 
     inode = btrfs_iget(fs_info->sb, ino, root);
     if (IS_ERR(inode))
         return -ENOENT;
 
 truncate:
     ret = btrfs_check_trunc_cache_free_space(fs_info,
                          &fs_info->global_block_rsv);
     if (ret)
         goto out;
 
     trans = btrfs_join_transaction(root);
     if (IS_ERR(trans)) {
         ret = PTR_ERR(trans);
         goto out;
     }
 
     ret = btrfs_truncate_free_space_cache(trans, block_group, inode);
 
     btrfs_end_transaction(trans);
     btrfs_btree_balance_dirty(fs_info);
 out:
     iput(inode);
     return ret;
 }
 
 /*
  * Locate the free space cache EXTENT_DATA in root tree leaf and delete the
  * cache inode, to avoid free space cache data extent blocking data relocation.
  */
 static int delete_v1_space_cache(struct extent_buffer *leaf,
                  struct btrfs_block_group *block_group,
                  u64 data_bytenr)
 {
     u64 space_cache_ino;
     struct btrfs_file_extent_item *ei;
     struct btrfs_key key;
     bool found = false;
     int i;
     int ret;
 
     if (btrfs_header_owner(leaf) != BTRFS_ROOT_TREE_OBJECTID)
         return 0;
 
     for (i = 0; i < btrfs_header_nritems(leaf); i++) {
         u8 type;
 
         btrfs_item_key_to_cpu(leaf, &key, i);
         if (key.type != BTRFS_EXTENT_DATA_KEY)
             continue;
         ei = btrfs_item_ptr(leaf, i, struct btrfs_file_extent_item);
         type = btrfs_file_extent_type(leaf, ei);
 
         if ((type == BTRFS_FILE_EXTENT_REG ||
              type == BTRFS_FILE_EXTENT_PREALLOC) &&
             btrfs_file_extent_disk_bytenr(leaf, ei) == data_bytenr) {
             found = true;
             space_cache_ino = key.objectid;
             break;
         }
     }
     if (!found)
         return -ENOENT;
     ret = delete_block_group_cache(leaf->fs_info, block_group, NULL,
                     space_cache_ino);
     return ret;
 }
 
 /*
  * helper to find all tree blocks that reference a given data extent
  */
 static noinline_for_stack
 int add_data_references(struct reloc_control *rc,
             struct btrfs_key *extent_key,
             struct btrfs_path *path,
             struct rb_root *blocks)
 {
     struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
     struct ulist *leaves = NULL;
     struct ulist_iterator leaf_uiter;
     struct ulist_node *ref_node = NULL;
     const u32 blocksize = fs_info->nodesize;
     int ret = 0;
 
     btrfs_release_path(path);
     ret = btrfs_find_all_leafs(NULL, fs_info, extent_key->objectid,
                    0, &leaves, NULL, true);
     if (ret < 0)
         return ret;
 
     ULIST_ITER_INIT(&leaf_uiter);
     while ((ref_node = ulist_next(leaves, &leaf_uiter))) {
         struct extent_buffer *eb;
 
         eb = read_tree_block(fs_info, ref_node->val, 0, 0, 0, NULL);
         if (IS_ERR(eb)) {
             ret = PTR_ERR(eb);
             break;
         }
         ret = delete_v1_space_cache(eb, rc->block_group,
                         extent_key->objectid);
         free_extent_buffer(eb);
         if (ret < 0)
             break;
         ret = __add_tree_block(rc, ref_node->val, blocksize, blocks);
         if (ret < 0)
             break;
     }
     if (ret < 0)
         free_block_list(blocks);
     ulist_free(leaves);
     return ret;
 }
 
 /*
  * helper to find next unprocessed extent
  */
 static noinline_for_stack
 int find_next_extent(struct reloc_control *rc, struct btrfs_path *path,
              struct btrfs_key *extent_key)
 {
     struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
     struct btrfs_key key;
     struct extent_buffer *leaf;
     u64 start, end, last;
     int ret;
 
     last = rc->block_group->start + rc->block_group->length;
     while (1) {
         cond_resched();
         if (rc->search_start >= last) {
             ret = 1;
             break;
         }
 
         key.objectid = rc->search_start;
         key.type = BTRFS_EXTENT_ITEM_KEY;
         key.offset = 0;
 
         path->search_commit_root = 1;
         path->skip_locking = 1;
         ret = btrfs_search_slot(NULL, rc->extent_root, &key, path,
                     0, 0);
         if (ret < 0)
             break;
 next:
         leaf = path->nodes[0];
         if (path->slots[0] >= btrfs_header_nritems(leaf)) {
             ret = btrfs_next_leaf(rc->extent_root, path);
             if (ret != 0)
                 break;
             leaf = path->nodes[0];
         }
 
         btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
         if (key.objectid >= last) {
             ret = 1;
             break;
         }
 
         if (key.type != BTRFS_EXTENT_ITEM_KEY &&
             key.type != BTRFS_METADATA_ITEM_KEY) {
             path->slots[0]++;
             goto next;
         }
 
         if (key.type == BTRFS_EXTENT_ITEM_KEY &&
             key.objectid + key.offset <= rc->search_start) {
             path->slots[0]++;
             goto next;
         }
 
         if (key.type == BTRFS_METADATA_ITEM_KEY &&
             key.objectid + fs_info->nodesize <=
             rc->search_start) {
             path->slots[0]++;
             goto next;
         }
 
         ret = find_first_extent_bit(&rc->processed_blocks,
                         key.objectid, &start, &end,
                         EXTENT_DIRTY, NULL);
 
         if (ret == 0 && start <= key.objectid) {
             btrfs_release_path(path);
             rc->search_start = end + 1;
         } else {
             if (key.type == BTRFS_EXTENT_ITEM_KEY)
                 rc->search_start = key.objectid + key.offset;
             else
                 rc->search_start = key.objectid +
                     fs_info->nodesize;
             memcpy(extent_key, &key, sizeof(key));
             return 0;
         }
     }
     btrfs_release_path(path);
     return ret;
 }
 
 static void set_reloc_control(struct reloc_control *rc)
 {
     struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
 
     mutex_lock(&fs_info->reloc_mutex);
     fs_info->reloc_ctl = rc;
     mutex_unlock(&fs_info->reloc_mutex);
 }
 
 static void unset_reloc_control(struct reloc_control *rc)
 {
     struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
 
     mutex_lock(&fs_info->reloc_mutex);
     fs_info->reloc_ctl = NULL;
     mutex_unlock(&fs_info->reloc_mutex);
 }
 
 static noinline_for_stack
 int prepare_to_relocate(struct reloc_control *rc)
 {
     struct btrfs_trans_handle *trans;
     int ret;
 
     rc->block_rsv = btrfs_alloc_block_rsv(rc->extent_root->fs_info,
                           BTRFS_BLOCK_RSV_TEMP);
     if (!rc->block_rsv)
         return -ENOMEM;
 
     memset(&rc->cluster, 0, sizeof(rc->cluster));
     rc->search_start = rc->block_group->start;
     rc->extents_found = 0;
     rc->nodes_relocated = 0;
     rc->merging_rsv_size = 0;
     rc->reserved_bytes = 0;
     rc->block_rsv->size = rc->extent_root->fs_info->nodesize *
                   RELOCATION_RESERVED_NODES;
     ret = btrfs_block_rsv_refill(rc->extent_root->fs_info,
                      rc->block_rsv, rc->block_rsv->size,
                      BTRFS_RESERVE_FLUSH_ALL);
     if (ret)
         return ret;
 
     rc->create_reloc_tree = 1;
     set_reloc_control(rc);
 
     trans = btrfs_join_transaction(rc->extent_root);
     if (IS_ERR(trans)) {
         unset_reloc_control(rc);
         /*
          * extent tree is not a ref_cow tree and has no reloc_root to
          * cleanup.  And callers are responsible to free the above
          * block rsv.
          */
         return PTR_ERR(trans);
     }
 
     ret = btrfs_commit_transaction(trans);
     if (ret)
         unset_reloc_control(rc);
 
     return ret;
 }
 
 static noinline_for_stack int relocate_block_group(struct reloc_control *rc)
 {
     struct btrfs_fs_info *fs_info = rc->extent_root->fs_info;
     struct rb_root blocks = RB_ROOT;
     struct btrfs_key key;
     struct btrfs_trans_handle *trans = NULL;
     struct btrfs_path *path;
     struct btrfs_extent_item *ei;
     u64 flags;
     int ret;
     int err = 0;
     int progress = 0;
 
     path = btrfs_alloc_path();
     if (!path)
         return -ENOMEM;
     path->reada = READA_FORWARD;
 
     ret = prepare_to_relocate(rc);
     if (ret) {
         err = ret;
         goto out_free;
     }
 
     while (1) {
         rc->reserved_bytes = 0;
         ret = btrfs_block_rsv_refill(fs_info, rc->block_rsv,
                          rc->block_rsv->size,
                          BTRFS_RESERVE_FLUSH_ALL);
         if (ret) {
             err = ret;
             break;
         }
         progress++;
         trans = btrfs_start_transaction(rc->extent_root, 0);
         if (IS_ERR(trans)) {
             err = PTR_ERR(trans);
             trans = NULL;
             break;
         }
 restart:
         if (update_backref_cache(trans, &rc->backref_cache)) {
             btrfs_end_transaction(trans);
             trans = NULL;
             continue;
         }
 
         ret = find_next_extent(rc, path, &key);
         if (ret < 0)
             err = ret;
         if (ret != 0)
             break;
 
         rc->extents_found++;
 
         ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
                     struct btrfs_extent_item);
         flags = btrfs_extent_flags(path->nodes[0], ei);
 
         if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
             ret = add_tree_block(rc, &key, path, &blocks);
         } else if (rc->stage == UPDATE_DATA_PTRS &&
                (flags & BTRFS_EXTENT_FLAG_DATA)) {
             ret = add_data_references(rc, &key, path, &blocks);
         } else {
             btrfs_release_path(path);
             ret = 0;
         }
         if (ret < 0) {
             err = ret;
             break;
         }
 
         if (!RB_EMPTY_ROOT(&blocks)) {
             ret = relocate_tree_blocks(trans, rc, &blocks);
             if (ret < 0) {
                 if (ret != -EAGAIN) {
                     err = ret;
                     break;
                 }
                 rc->extents_found--;
                 rc->search_start = key.objectid;
             }
         }
 
         btrfs_end_transaction_throttle(trans);
         btrfs_btree_balance_dirty(fs_info);
         trans = NULL;
 
         if (rc->stage == MOVE_DATA_EXTENTS &&
             (flags & BTRFS_EXTENT_FLAG_DATA)) {
             rc->found_file_extent = 1;
             ret = relocate_data_extent(rc->data_inode,
                            &key, &rc->cluster);
             if (ret < 0) {
                 err = ret;
                 break;
             }
         }
         if (btrfs_should_cancel_balance(fs_info)) {
             err = -ECANCELED;
             break;
         }
     }
     if (trans && progress && err == -ENOSPC) {
         ret = btrfs_force_chunk_alloc(trans, rc->block_group->flags);
         if (ret == 1) {
             err = 0;
             progress = 0;
             goto restart;
         }
     }
 
     btrfs_release_path(path);
     clear_extent_bits(&rc->processed_blocks, 0, (u64)-1, EXTENT_DIRTY);
 
     if (trans) {
         btrfs_end_transaction_throttle(trans);
         btrfs_btree_balance_dirty(fs_info);
     }
 
     if (!err) {
         ret = relocate_file_extent_cluster(rc->data_inode,
                            &rc->cluster);
         if (ret < 0)
             err = ret;
     }
 
     rc->create_reloc_tree = 0;
     set_reloc_control(rc);
 
     btrfs_backref_release_cache(&rc->backref_cache);
     btrfs_block_rsv_release(fs_info, rc->block_rsv, (u64)-1, NULL);
 
     /*
      * Even in the case when the relocation is cancelled, we should all go
      * through prepare_to_merge() and merge_reloc_roots().
      *
      * For error (including cancelled balance), prepare_to_merge() will
      * mark all reloc trees orphan, then queue them for cleanup in
      * merge_reloc_roots()
      */
     err = prepare_to_merge(rc, err);
 
     merge_reloc_roots(rc);
 
     rc->merge_reloc_tree = 0;
     unset_reloc_control(rc);
     btrfs_block_rsv_release(fs_info, rc->block_rsv, (u64)-1, NULL);
 
     /* get rid of pinned extents */
     trans = btrfs_join_transaction(rc->extent_root);
     if (IS_ERR(trans)) {
         err = PTR_ERR(trans);
         goto out_free;
     }
     ret = btrfs_commit_transaction(trans);
     if (ret && !err)
         err = ret;
 out_free:
     ret = clean_dirty_subvols(rc);
     if (ret < 0 && !err)
         err = ret;
     btrfs_free_block_rsv(fs_info, rc->block_rsv);
     btrfs_free_path(path);
     return err;
 }
 
 static int __insert_orphan_inode(struct btrfs_trans_handle *trans,
                  struct btrfs_root *root, u64 objectid)
 {
     struct btrfs_path *path;
     struct btrfs_inode_item *item;
     struct extent_buffer *leaf;
     int ret;
 
     path = btrfs_alloc_path();
     if (!path)
         return -ENOMEM;
 
     ret = btrfs_insert_empty_inode(trans, root, path, objectid);
     if (ret)
         goto out;
 
     leaf = path->nodes[0];
     item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_inode_item);
     memzero_extent_buffer(leaf, (unsigned long)item, sizeof(*item));
     btrfs_set_inode_generation(leaf, item, 1);
     btrfs_set_inode_size(leaf, item, 0);
     btrfs_set_inode_mode(leaf, item, S_IFREG | 0600);
     btrfs_set_inode_flags(leaf, item, BTRFS_INODE_NOCOMPRESS |
                       BTRFS_INODE_PREALLOC);
     btrfs_mark_buffer_dirty(leaf);
 out:
     btrfs_free_path(path);
     return ret;
 }
 
 static void delete_orphan_inode(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root, u64 objectid)
 {
     struct btrfs_path *path;
     struct btrfs_key key;
     int ret = 0;
 
     path = btrfs_alloc_path();
     if (!path) {
         ret = -ENOMEM;
         goto out;
     }
 
     key.objectid = objectid;
     key.type = BTRFS_INODE_ITEM_KEY;
     key.offset = 0;
     ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
     if (ret) {
         if (ret > 0)
             ret = -ENOENT;
         goto out;
     }
     ret = btrfs_del_item(trans, root, path);
 out:
     if (ret)
         btrfs_abort_transaction(trans, ret);
     btrfs_free_path(path);
 }
 
 /*
  * helper to create inode for data relocation.
  * the inode is in data relocation tree and its link count is 0
  */
 static noinline_for_stack
 struct inode *create_reloc_inode(struct btrfs_fs_info *fs_info,
                  struct btrfs_block_group *group)
 {
     struct inode *inode = NULL;
     struct btrfs_trans_handle *trans;
     struct btrfs_root *root;
     u64 objectid;
     int err = 0;
 
     root = btrfs_grab_root(fs_info->data_reloc_root);
     trans = btrfs_start_transaction(root, 6);
     if (IS_ERR(trans)) {
         btrfs_put_root(root);
         return ERR_CAST(trans);
     }
 
     err = btrfs_get_free_objectid(root, &objectid);
     if (err)
         goto out;
 
     err = __insert_orphan_inode(trans, root, objectid);
     if (err)
         goto out;
 
     inode = btrfs_iget(fs_info->sb, objectid, root);
     if (IS_ERR(inode)) {
         delete_orphan_inode(trans, root, objectid);
         err = PTR_ERR(inode);
         inode = NULL;
         goto out;
     }
     BTRFS_I(inode)->index_cnt = group->start;
 
     err = btrfs_orphan_add(trans, BTRFS_I(inode));
 out:
     btrfs_put_root(root);
     btrfs_end_transaction(trans);
     btrfs_btree_balance_dirty(fs_info);
     if (err) {
         iput(inode);
         inode = ERR_PTR(err);
     }
     return inode;
 }
 
 /*
  * Mark start of chunk relocation that is cancellable. Check if the cancellation
  * has been requested meanwhile and don't start in that case.
  *
  * Return:
  *   0             success
  *   -EINPROGRESS  operation is already in progress, that's probably a bug
  *   -ECANCELED    cancellation request was set before the operation started
  */
 static int reloc_chunk_start(struct btrfs_fs_info *fs_info)
 {
     if (test_and_set_bit(BTRFS_FS_RELOC_RUNNING, &fs_info->flags)) {
         /* This should not happen */
         btrfs_err(fs_info, "reloc already running, cannot start");
         return -EINPROGRESS;
     }
 
     if (atomic_read(&fs_info->reloc_cancel_req) > 0) {
         btrfs_info(fs_info, "chunk relocation canceled on start");
         /*
          * On cancel, clear all requests but let the caller mark
          * the end after cleanup operations.
          */
         atomic_set(&fs_info->reloc_cancel_req, 0);
         return -ECANCELED;
     }
     return 0;
 }
 
 /*
  * Mark end of chunk relocation that is cancellable and wake any waiters.
  */
 static void reloc_chunk_end(struct btrfs_fs_info *fs_info)
 {
     /* Requested after start, clear bit first so any waiters can continue */
     if (atomic_read(&fs_info->reloc_cancel_req) > 0)
         btrfs_info(fs_info, "chunk relocation canceled during operation");
     clear_and_wake_up_bit(BTRFS_FS_RELOC_RUNNING, &fs_info->flags);
     atomic_set(&fs_info->reloc_cancel_req, 0);
 }
 
 static struct reloc_control *alloc_reloc_control(struct btrfs_fs_info *fs_info)
 {
     struct reloc_control *rc;
 
     rc = kzalloc(sizeof(*rc), GFP_NOFS);
     if (!rc)
         return NULL;
 
     INIT_LIST_HEAD(&rc->reloc_roots);
     INIT_LIST_HEAD(&rc->dirty_subvol_roots);
     btrfs_backref_init_cache(fs_info, &rc->backref_cache, 1);
     mapping_tree_init(&rc->reloc_root_tree);
     extent_io_tree_init(fs_info, &rc->processed_blocks,
                 IO_TREE_RELOC_BLOCKS, NULL);
     return rc;
 }
 
 static void free_reloc_control(struct reloc_control *rc)
 {
     struct mapping_node *node, *tmp;
 
     free_reloc_roots(&rc->reloc_roots);
     rbtree_postorder_for_each_entry_safe(node, tmp,
             &rc->reloc_root_tree.rb_root, rb_node)
         kfree(node);
 
     kfree(rc);
 }
 
 /*
  * Print the block group being relocated
  */
 static void describe_relocation(struct btrfs_fs_info *fs_info,
                 struct btrfs_block_group *block_group)
 {
     char buf[128] = {'\0'};
 
     btrfs_describe_block_groups(block_group->flags, buf, sizeof(buf));
 
     btrfs_info(fs_info,
            "relocating block group %llu flags %s",
            block_group->start, buf);
 }
 
 static const char *stage_to_string(int stage)
 {
     if (stage == MOVE_DATA_EXTENTS)
         return "move data extents";
     if (stage == UPDATE_DATA_PTRS)
         return "update data pointers";
     return "unknown";
 }
 
 /*
  * function to relocate all extents in a block group.
  */
 int btrfs_relocate_block_group(struct btrfs_fs_info *fs_info, u64 group_start)
 {
     struct btrfs_block_group *bg;
     struct btrfs_root *extent_root = btrfs_extent_root(fs_info, group_start);
     struct reloc_control *rc;
     struct inode *inode;
     struct btrfs_path *path;
     int ret;
     int rw = 0;
     int err = 0;
 
     /*
      * This only gets set if we had a half-deleted snapshot on mount.  We
      * cannot allow relocation to start while we're still trying to clean up
      * these pending deletions.
      */
     ret = wait_on_bit(&fs_info->flags, BTRFS_FS_UNFINISHED_DROPS, TASK_INTERRUPTIBLE);
     if (ret)
         return ret;
 
     /* We may have been woken up by close_ctree, so bail if we're closing. */
     if (btrfs_fs_closing(fs_info))
         return -EINTR;
 
     bg = btrfs_lookup_block_group(fs_info, group_start);
     if (!bg)
         return -ENOENT;
 
     /*
      * Relocation of a data block group creates ordered extents.  Without
      * sb_start_write(), we can freeze the filesystem while unfinished
      * ordered extents are left. Such ordered extents can cause a deadlock
      * e.g. when syncfs() is waiting for their completion but they can't
      * finish because they block when joining a transaction, due to the
      * fact that the freeze locks are being held in write mode.
      */
     if (bg->flags & BTRFS_BLOCK_GROUP_DATA)
         ASSERT(sb_write_started(fs_info->sb));
 
     if (btrfs_pinned_by_swapfile(fs_info, bg)) {
         btrfs_put_block_group(bg);
         return -ETXTBSY;
     }
 
     rc = alloc_reloc_control(fs_info);
     if (!rc) {
         btrfs_put_block_group(bg);
         return -ENOMEM;
     }
 
     ret = reloc_chunk_start(fs_info);
     if (ret < 0) {
         err = ret;
         goto out_put_bg;
     }
 
     rc->extent_root = extent_root;
     rc->block_group = bg;
 
     ret = btrfs_inc_block_group_ro(rc->block_group, true);
     if (ret) {
         err = ret;
         goto out;
     }
     rw = 1;
 
     path = btrfs_alloc_path();
     if (!path) {
         err = -ENOMEM;
         goto out;
     }
 
     inode = lookup_free_space_inode(rc->block_group, path);
     btrfs_free_path(path);
 
     if (!IS_ERR(inode))
         ret = delete_block_group_cache(fs_info, rc->block_group, inode, 0);
     else
         ret = PTR_ERR(inode);
 
     if (ret && ret != -ENOENT) {
         err = ret;
         goto out;
     }
 
     rc->data_inode = create_reloc_inode(fs_info, rc->block_group);
     if (IS_ERR(rc->data_inode)) {
         err = PTR_ERR(rc->data_inode);
         rc->data_inode = NULL;
         goto out;
     }
 
     describe_relocation(fs_info, rc->block_group);
 
     btrfs_wait_block_group_reservations(rc->block_group);
     btrfs_wait_nocow_writers(rc->block_group);
     btrfs_wait_ordered_roots(fs_info, U64_MAX,
                  rc->block_group->start,
                  rc->block_group->length);
 
     ret = btrfs_zone_finish(rc->block_group);
     WARN_ON(ret && ret != -EAGAIN);
 
     while (1) {
         int finishes_stage;
 
         mutex_lock(&fs_info->cleaner_mutex);
         ret = relocate_block_group(rc);
         mutex_unlock(&fs_info->cleaner_mutex);
         if (ret < 0)
             err = ret;
 
         finishes_stage = rc->stage;
         /*
          * We may have gotten ENOSPC after we already dirtied some
          * extents.  If writeout happens while we're relocating a
          * different block group we could end up hitting the
          * BUG_ON(rc->stage == UPDATE_DATA_PTRS) in
          * btrfs_reloc_cow_block.  Make sure we write everything out
          * properly so we don't trip over this problem, and then break
          * out of the loop if we hit an error.
          */
         if (rc->stage == MOVE_DATA_EXTENTS && rc->found_file_extent) {
             ret = btrfs_wait_ordered_range(rc->data_inode, 0,
                                (u64)-1);
             if (ret)
                 err = ret;
             invalidate_mapping_pages(rc->data_inode->i_mapping,
                          0, -1);
             rc->stage = UPDATE_DATA_PTRS;
         }
 
         if (err < 0)
             goto out;
 
         if (rc->extents_found == 0)
             break;
 
         btrfs_info(fs_info, "found %llu extents, stage: %s",
                rc->extents_found, stage_to_string(finishes_stage));
     }
 
     WARN_ON(rc->block_group->pinned > 0);
     WARN_ON(rc->block_group->reserved > 0);
     WARN_ON(rc->block_group->used > 0);
 out:
     if (err && rw)
         btrfs_dec_block_group_ro(rc->block_group);
     iput(rc->data_inode);
 out_put_bg:
     btrfs_put_block_group(bg);
     reloc_chunk_end(fs_info);
     free_reloc_control(rc);
     return err;
 }
 
 static noinline_for_stack int mark_garbage_root(struct btrfs_root *root)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct btrfs_trans_handle *trans;
     int ret, err;
 
     trans = btrfs_start_transaction(fs_info->tree_root, 0);
     if (IS_ERR(trans))
         return PTR_ERR(trans);
 
     memset(&root->root_item.drop_progress, 0,
         sizeof(root->root_item.drop_progress));
     btrfs_set_root_drop_level(&root->root_item, 0);
     btrfs_set_root_refs(&root->root_item, 0);
     ret = btrfs_update_root(trans, fs_info->tree_root,
                 &root->root_key, &root->root_item);
 
     err = btrfs_end_transaction(trans);
     if (err)
         return err;
     return ret;
 }
 
 /*
  * recover relocation interrupted by system crash.
  *
  * this function resumes merging reloc trees with corresponding fs trees.
  * this is important for keeping the sharing of tree blocks
  */
 int btrfs_recover_relocation(struct btrfs_fs_info *fs_info)
 {
     LIST_HEAD(reloc_roots);
     struct btrfs_key key;
     struct btrfs_root *fs_root;
     struct btrfs_root *reloc_root;
     struct btrfs_path *path;
     struct extent_buffer *leaf;
     struct reloc_control *rc = NULL;
     struct btrfs_trans_handle *trans;
     int ret;
     int err = 0;
 
     path = btrfs_alloc_path();
     if (!path)
         return -ENOMEM;
     path->reada = READA_BACK;
 
     key.objectid = BTRFS_TREE_RELOC_OBJECTID;
     key.type = BTRFS_ROOT_ITEM_KEY;
     key.offset = (u64)-1;
 
     while (1) {
         ret = btrfs_search_slot(NULL, fs_info->tree_root, &key,
                     path, 0, 0);
         if (ret < 0) {
             err = ret;
             goto out;
         }
         if (ret > 0) {
             if (path->slots[0] == 0)
                 break;
             path->slots[0]--;
         }
         leaf = path->nodes[0];
         btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
         btrfs_release_path(path);
 
         if (key.objectid != BTRFS_TREE_RELOC_OBJECTID ||
             key.type != BTRFS_ROOT_ITEM_KEY)
             break;
 
         reloc_root = btrfs_read_tree_root(fs_info->tree_root, &key);
         if (IS_ERR(reloc_root)) {
             err = PTR_ERR(reloc_root);
             goto out;
         }
 
         set_bit(BTRFS_ROOT_SHAREABLE, &reloc_root->state);
         list_add(&reloc_root->root_list, &reloc_roots);
 
         if (btrfs_root_refs(&reloc_root->root_item) > 0) {
             fs_root = btrfs_get_fs_root(fs_info,
                     reloc_root->root_key.offset, false);
             if (IS_ERR(fs_root)) {
                 ret = PTR_ERR(fs_root);
                 if (ret != -ENOENT) {
                     err = ret;
                     goto out;
                 }
                 ret = mark_garbage_root(reloc_root);
                 if (ret < 0) {
                     err = ret;
                     goto out;
                 }
             } else {
                 btrfs_put_root(fs_root);
             }
         }
 
         if (key.offset == 0)
             break;
 
         key.offset--;
     }
     btrfs_release_path(path);
 
     if (list_empty(&reloc_roots))
         goto out;
 
     rc = alloc_reloc_control(fs_info);
     if (!rc) {
         err = -ENOMEM;
         goto out;
     }
 
     ret = reloc_chunk_start(fs_info);
     if (ret < 0) {
         err = ret;
         goto out_end;
     }
 
     rc->extent_root = btrfs_extent_root(fs_info, 0);
 
     set_reloc_control(rc);
 
     trans = btrfs_join_transaction(rc->extent_root);
     if (IS_ERR(trans)) {
         err = PTR_ERR(trans);
         goto out_unset;
     }
 
     rc->merge_reloc_tree = 1;
 
     while (!list_empty(&reloc_roots)) {
         reloc_root = list_entry(reloc_roots.next,
                     struct btrfs_root, root_list);
         list_del(&reloc_root->root_list);
 
         if (btrfs_root_refs(&reloc_root->root_item) == 0) {
             list_add_tail(&reloc_root->root_list,
                       &rc->reloc_roots);
             continue;
         }
 
         fs_root = btrfs_get_fs_root(fs_info, reloc_root->root_key.offset,
                         false);
         if (IS_ERR(fs_root)) {
             err = PTR_ERR(fs_root);
             list_add_tail(&reloc_root->root_list, &reloc_roots);
             btrfs_end_transaction(trans);
             goto out_unset;
         }
 
         err = __add_reloc_root(reloc_root);
         ASSERT(err != -EEXIST);
         if (err) {
             list_add_tail(&reloc_root->root_list, &reloc_roots);
             btrfs_put_root(fs_root);
             btrfs_end_transaction(trans);
             goto out_unset;
         }
         fs_root->reloc_root = btrfs_grab_root(reloc_root);
         btrfs_put_root(fs_root);
     }
 
     err = btrfs_commit_transaction(trans);
     if (err)
         goto out_unset;
 
     merge_reloc_roots(rc);
 
     unset_reloc_control(rc);
 
     trans = btrfs_join_transaction(rc->extent_root);
     if (IS_ERR(trans)) {
         err = PTR_ERR(trans);
         goto out_clean;
     }
     err = btrfs_commit_transaction(trans);
 out_clean:
     ret = clean_dirty_subvols(rc);
     if (ret < 0 && !err)
         err = ret;
 out_unset:
     unset_reloc_control(rc);
 out_end:
     reloc_chunk_end(fs_info);
     free_reloc_control(rc);
 out:
     free_reloc_roots(&reloc_roots);
 
     btrfs_free_path(path);
 
     if (err == 0) {
         /* cleanup orphan inode in data relocation tree */
         fs_root = btrfs_grab_root(fs_info->data_reloc_root);
         ASSERT(fs_root);
         err = btrfs_orphan_cleanup(fs_root);
         btrfs_put_root(fs_root);
     }
     return err;
 }
 
 /*
  * helper to add ordered checksum for data relocation.
  *
  * cloning checksum properly handles the nodatasum extents.
  * it also saves CPU time to re-calculate the checksum.
  */
 int btrfs_reloc_clone_csums(struct btrfs_inode *inode, u64 file_pos, u64 len)
 {
     struct btrfs_fs_info *fs_info = inode->root->fs_info;
     struct btrfs_root *csum_root;
     struct btrfs_ordered_sum *sums;
     struct btrfs_ordered_extent *ordered;
     int ret;
     u64 disk_bytenr;
     u64 new_bytenr;
     LIST_HEAD(list);
 
     ordered = btrfs_lookup_ordered_extent(inode, file_pos);
     BUG_ON(ordered->file_offset != file_pos || ordered->num_bytes != len);
 
     disk_bytenr = file_pos + inode->index_cnt;
     csum_root = btrfs_csum_root(fs_info, disk_bytenr);
     ret = btrfs_lookup_csums_range(csum_root, disk_bytenr,
                        disk_bytenr + len - 1, &list, 0);
     if (ret)
         goto out;
 
     while (!list_empty(&list)) {
         sums = list_entry(list.next, struct btrfs_ordered_sum, list);
         list_del_init(&sums->list);
 
         /*
          * We need to offset the new_bytenr based on where the csum is.
          * We need to do this because we will read in entire prealloc
          * extents but we may have written to say the middle of the
          * prealloc extent, so we need to make sure the csum goes with
          * the right disk offset.
          *
          * We can do this because the data reloc inode refers strictly
          * to the on disk bytes, so we don't have to worry about
          * disk_len vs real len like with real inodes since it's all
          * disk length.
          */
         new_bytenr = ordered->disk_bytenr + sums->bytenr - disk_bytenr;
         sums->bytenr = new_bytenr;
 
         btrfs_add_ordered_sum(ordered, sums);
     }
 out:
     btrfs_put_ordered_extent(ordered);
     return ret;
 }
 
 int btrfs_reloc_cow_block(struct btrfs_trans_handle *trans,
               struct btrfs_root *root, struct extent_buffer *buf,
               struct extent_buffer *cow)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct reloc_control *rc;
     struct btrfs_backref_node *node;
     int first_cow = 0;
     int level;
     int ret = 0;
 
     rc = fs_info->reloc_ctl;
     if (!rc)
         return 0;
 
     BUG_ON(rc->stage == UPDATE_DATA_PTRS && btrfs_is_data_reloc_root(root));
 
     level = btrfs_header_level(buf);
     if (btrfs_header_generation(buf) <=
         btrfs_root_last_snapshot(&root->root_item))
         first_cow = 1;
 
     if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID &&
         rc->create_reloc_tree) {
         WARN_ON(!first_cow && level == 0);
 
         node = rc->backref_cache.path[level];
         BUG_ON(node->bytenr != buf->start &&
                node->new_bytenr != buf->start);
 
         btrfs_backref_drop_node_buffer(node);
         atomic_inc(&cow->refs);
         node->eb = cow;
         node->new_bytenr = cow->start;
 
         if (!node->pending) {
             list_move_tail(&node->list,
                        &rc->backref_cache.pending[level]);
             node->pending = 1;
         }
 
         if (first_cow)
             mark_block_processed(rc, node);
 
         if (first_cow && level > 0)
             rc->nodes_relocated += buf->len;
     }
 
     if (level == 0 && first_cow && rc->stage == UPDATE_DATA_PTRS)
         ret = replace_file_extents(trans, rc, root, cow);
     return ret;
 }
 
 /*
  * called before creating snapshot. it calculates metadata reservation
  * required for relocating tree blocks in the snapshot
  */
 void btrfs_reloc_pre_snapshot(struct btrfs_pending_snapshot *pending,
                   u64 *bytes_to_reserve)
 {
     struct btrfs_root *root = pending->root;
     struct reloc_control *rc = root->fs_info->reloc_ctl;
 
     if (!rc || !have_reloc_root(root))
         return;
 
     if (!rc->merge_reloc_tree)
         return;
 
     root = root->reloc_root;
     BUG_ON(btrfs_root_refs(&root->root_item) == 0);
     /*
      * relocation is in the stage of merging trees. the space
      * used by merging a reloc tree is twice the size of
      * relocated tree nodes in the worst case. half for cowing
      * the reloc tree, half for cowing the fs tree. the space
      * used by cowing the reloc tree will be freed after the
      * tree is dropped. if we create snapshot, cowing the fs
      * tree may use more space than it frees. so we need
      * reserve extra space.
      */
     *bytes_to_reserve += rc->nodes_relocated;
 }
 
 /*
  * called after snapshot is created. migrate block reservation
  * and create reloc root for the newly created snapshot
  *
  * This is similar to btrfs_init_reloc_root(), we come out of here with two
  * references held on the reloc_root, one for root->reloc_root and one for
  * rc->reloc_roots.
  */
 int btrfs_reloc_post_snapshot(struct btrfs_trans_handle *trans,
                    struct btrfs_pending_snapshot *pending)
 {
     struct btrfs_root *root = pending->root;
     struct btrfs_root *reloc_root;
     struct btrfs_root *new_root;
     struct reloc_control *rc = root->fs_info->reloc_ctl;
     int ret;
 
     if (!rc || !have_reloc_root(root))
         return 0;
 
     rc = root->fs_info->reloc_ctl;
     rc->merging_rsv_size += rc->nodes_relocated;
 
     if (rc->merge_reloc_tree) {
         ret = btrfs_block_rsv_migrate(&pending->block_rsv,
                           rc->block_rsv,
                           rc->nodes_relocated, true);
         if (ret)
             return ret;
     }
 
     new_root = pending->snap;
     reloc_root = create_reloc_root(trans, root->reloc_root,
                        new_root->root_key.objectid);
     if (IS_ERR(reloc_root))
         return PTR_ERR(reloc_root);
 
     ret = __add_reloc_root(reloc_root);
     ASSERT(ret != -EEXIST);
     if (ret) {
         /* Pairs with create_reloc_root */
         btrfs_put_root(reloc_root);
         return ret;
     }
     new_root->reloc_root = btrfs_grab_root(reloc_root);
 
     if (rc->create_reloc_tree)
         ret = clone_backref_node(trans, rc, root, reloc_root);
     return ret;
 }