/*
 * Copyright (C) 2009 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include <linux/sched.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/rbtree.h>
#include <linux/slab.h>
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "volumes.h"
#include "locking.h"
#include "btrfs_inode.h"
#include "async-thread.h"
#include "free-space-cache.h"
#include "inode-map.h"

/*
 * backref_node, mapping_node and tree_block start with this
 */
struct tree_entry {
        struct rb_node rb_node;
        u64 bytenr;
};

/*
 * present a tree block in the backref cache
 */
struct backref_node {
        struct rb_node rb_node;
        u64 bytenr;

        u64 new_bytenr;
        /* objectid of tree block owner, can be not uptodate */
        u64 owner;
        /* link to pending, changed or detached list */
        struct list_head list;
        /* list of upper level blocks reference this block */
        struct list_head upper;
        /* list of child blocks in the cache */
        struct list_head lower;
        /* NULL if this node is not tree root */
        struct btrfs_root *root;
        /* extent buffer got by COW the block */
        struct extent_buffer *eb;
        /* level of tree block */
        unsigned int level:8;
        /* is the block in non-reference counted tree */
        unsigned int cowonly:1;
        /* 1 if no child node in the cache */
        unsigned int lowest:1;
        /* is the extent buffer locked */
        unsigned int locked:1;
        /* has the block been processed */
        unsigned int processed:1;
        /* have backrefs of this block been checked */
        unsigned int checked:1;
        /*
         * 1 if corresponding block has been cowed but some upper
         * level block pointers may not point to the new location
         */
        unsigned int pending:1;
        /*
         * 1 if the backref node isn't connected to any other
         * backref node.
         */
        unsigned int detached:1;
};

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

#define LOWER   0
#define UPPER   1
#define RELOCATION_RESERVED_NODES       256

struct backref_cache {
        /* red black tree of all backref nodes in the cache */
        struct rb_root rb_root;
        /* for passing backref nodes to btrfs_reloc_cow_block */
        struct backref_node *path[BTRFS_MAX_LEVEL];
        /*
         * list of blocks that have been cowed but some block
         * pointers in upper level blocks may not reflect the
         * new location
         */
        struct list_head pending[BTRFS_MAX_LEVEL];
        /* list of backref nodes with no child node */
        struct list_head leaves;
        /* list of blocks that have been cowed in current transaction */
        struct list_head changed;
        /* list of detached backref node. */
        struct list_head detached;

        u64 last_trans;

        int nr_nodes;
        int nr_edges;
};

/*
 * map address of tree root to tree
 */
struct mapping_node {
        struct rb_node rb_node;
        u64 bytenr;
        void *data;
};

struct mapping_tree {
        struct rb_root rb_root;
        spinlock_t lock;
};

/*
 * present a tree block to process
 */
struct tree_block {
        struct rb_node rb_node;
        u64 bytenr;
        struct btrfs_key key;
        unsigned int level:8;
        unsigned int key_ready:1;
};

#define MAX_EXTENTS 128

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

struct reloc_control {
        /* block group to relocate */
        struct btrfs_block_group_cache *block_group;
        /* extent tree */
        struct btrfs_root *extent_root;
        /* inode for moving data */
        struct inode *data_inode;

        struct btrfs_block_rsv *block_rsv;

        struct backref_cache backref_cache;

        struct file_extent_cluster cluster;
        /* tree blocks have been processed */
        struct extent_io_tree processed_blocks;
        /* map start of tree root to corresponding reloc tree */
        struct mapping_tree reloc_root_tree;
        /* list of reloc trees */
        struct list_head reloc_roots;
        /* size of metadata reservation for merging reloc trees */
        u64 merging_rsv_size;
        /* size of relocated tree nodes */
        u64 nodes_relocated;
        /* 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 remove_backref_node(struct backref_cache *cache,
                                struct backref_node *node);
static void __mark_block_processed(struct reloc_control *rc,
                                   struct backref_node *node);

static void mapping_tree_init(struct mapping_tree *tree)
{
        tree->rb_root = RB_ROOT;
        spin_lock_init(&tree->lock);
}

static void backref_cache_init(struct backref_cache *cache)
{
        int i;
        cache->rb_root = RB_ROOT;
        for (i = 0; i < BTRFS_MAX_LEVEL; i++)
                INIT_LIST_HEAD(&cache->pending[i]);
        INIT_LIST_HEAD(&cache->changed);
        INIT_LIST_HEAD(&cache->detached);
        INIT_LIST_HEAD(&cache->leaves);
}

static void backref_cache_cleanup(struct backref_cache *cache)
{
        struct backref_node *node;
        int i;

        while (!list_empty(&cache->detached)) {
                node = list_entry(cache->detached.next,
                                  struct backref_node, list);
                remove_backref_node(cache, node);
        }

        while (!list_empty(&cache->leaves)) {
                node = list_entry(cache->leaves.next,
                                  struct backref_node, lower);
                remove_backref_node(cache, node);
        }

        cache->last_trans = 0;

        for (i = 0; i < BTRFS_MAX_LEVEL; i++)
                BUG_ON(!list_empty(&cache->pending[i]));
        BUG_ON(!list_empty(&cache->changed));
        BUG_ON(!list_empty(&cache->detached));
        BUG_ON(!RB_EMPTY_ROOT(&cache->rb_root));
        BUG_ON(cache->nr_nodes);
        BUG_ON(cache->nr_edges);
}

static struct backref_node *alloc_backref_node(struct backref_cache *cache)
{
        struct backref_node *node;

        node = kzalloc(sizeof(*node), GFP_NOFS);
        if (node) {
                INIT_LIST_HEAD(&node->list);
                INIT_LIST_HEAD(&node->upper);
                INIT_LIST_HEAD(&node->lower);
                RB_CLEAR_NODE(&node->rb_node);
                cache->nr_nodes++;
        }
        return node;
}

static void free_backref_node(struct backref_cache *cache,
                              struct backref_node *node)
{
        if (node) {
                cache->nr_nodes--;
                kfree(node);
        }
}

static struct backref_edge *alloc_backref_edge(struct backref_cache *cache)
{
        struct backref_edge *edge;

        edge = kzalloc(sizeof(*edge), GFP_NOFS);
        if (edge)
                cache->nr_edges++;
        return edge;
}

static void free_backref_edge(struct backref_cache *cache,
                              struct backref_edge *edge)
{
        if (edge) {
                cache->nr_edges--;
                kfree(edge);
        }
}

static struct rb_node *tree_insert(struct rb_root *root, u64 bytenr,
                                   struct rb_node *node)
{
        struct rb_node **p = &root->rb_node;
        struct rb_node *parent = NULL;
        struct tree_entry *entry;

        while (*p) {
                parent = *p;
                entry = rb_entry(parent, struct tree_entry, rb_node);

                if (bytenr < entry->bytenr)
                        p = &(*p)->rb_left;
                else if (bytenr > entry->bytenr)
                        p = &(*p)->rb_right;
                else
                        return parent;
        }

        rb_link_node(node, parent, p);
        rb_insert_color(node, root);
        return NULL;
}

static struct rb_node *tree_search(struct rb_root *root, u64 bytenr)
{
        struct rb_node *n = root->rb_node;
        struct tree_entry *entry;

        while (n) {
                entry = rb_entry(n, struct tree_entry, rb_node);

                if (bytenr < entry->bytenr)
                        n = n->rb_left;
                else if (bytenr > entry->bytenr)
                        n = n->rb_right;
                else
                        return n;
        }
        return NULL;
}

static void backref_tree_panic(struct rb_node *rb_node, int errno, u64 bytenr)
{

        struct btrfs_fs_info *fs_info = NULL;
        struct backref_node *bnode = rb_entry(rb_node, struct backref_node,
                                              rb_node);
        if (bnode->root)
                fs_info = bnode->root->fs_info;
        btrfs_panic(fs_info, errno, "Inconsistency in backref cache "
                    "found at offset %llu", bytenr);
}

/*
 * walk up backref nodes until reach node presents tree root
 */
static struct backref_node *walk_up_backref(struct backref_node *node,
                                            struct backref_edge *edges[],
                                            int *index)
{
        struct backref_edge *edge;
        int idx = *index;

        while (!list_empty(&node->upper)) {
                edge = list_entry(node->upper.next,
                                  struct backref_edge, list[LOWER]);
                edges[idx++] = edge;
                node = edge->node[UPPER];
        }
        BUG_ON(node->detached);
        *index = idx;
        return node;
}

/*
 * walk down backref nodes to find start of next reference path
 */
static struct backref_node *walk_down_backref(struct backref_edge *edges[],
                                              int *index)
{
        struct backref_edge *edge;
        struct backref_node *lower;
        int idx = *index;

        while (idx > 0) {
                edge = edges[idx - 1];
                lower = edge->node[LOWER];
                if (list_is_last(&edge->list[LOWER], &lower->upper)) {
                        idx--;
                        continue;
                }
                edge = list_entry(edge->list[LOWER].next,
                                  struct backref_edge, list[LOWER]);
                edges[idx - 1] = edge;
                *index = idx;
                return edge->node[UPPER];
        }
        *index = 0;
        return NULL;
}

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

static void drop_node_buffer(struct backref_node *node)
{
        if (node->eb) {
                unlock_node_buffer(node);
                free_extent_buffer(node->eb);
                node->eb = NULL;
        }
}

static void drop_backref_node(struct backref_cache *tree,
                              struct backref_node *node)
{
        BUG_ON(!list_empty(&node->upper));

        drop_node_buffer(node);
        list_del(&node->list);
        list_del(&node->lower);
        if (!RB_EMPTY_NODE(&node->rb_node))
                rb_erase(&node->rb_node, &tree->rb_root);
        free_backref_node(tree, node);
}

/*
 * remove a backref node from the backref cache
 */
static void remove_backref_node(struct backref_cache *cache,
                                struct backref_node *node)
{
        struct backref_node *upper;
        struct backref_edge *edge;

        if (!node)
                return;

        BUG_ON(!node->lowest && !node->detached);
        while (!list_empty(&node->upper)) {
                edge = list_entry(node->upper.next, struct backref_edge,
                                  list[LOWER]);
                upper = edge->node[UPPER];
                list_del(&edge->list[LOWER]);
                list_del(&edge->list[UPPER]);
                free_backref_edge(cache, edge);

                if (RB_EMPTY_NODE(&upper->rb_node)) {
                        BUG_ON(!list_empty(&node->upper));
                        drop_backref_node(cache, node);
                        node = upper;
                        node->lowest = 1;
                        continue;
                }
                /*
                 * add the node to leaf node list if no other
                 * child block cached.
                 */
                if (list_empty(&upper->lower)) {
                        list_add_tail(&upper->lower, &cache->leaves);
                        upper->lowest = 1;
                }
        }

        drop_backref_node(cache, node);
}

static void update_backref_node(struct backref_cache *cache,
                                struct backref_node *node, u64 bytenr)
{
        struct rb_node *rb_node;
        rb_erase(&node->rb_node, &cache->rb_root);
        node->bytenr = bytenr;
        rb_node = tree_insert(&cache->rb_root, node->bytenr, &node->rb_node);
        if (rb_node)
                backref_tree_panic(rb_node, -EEXIST, bytenr);
}

/*
 * update backref cache after a transaction commit
 */
static int update_backref_cache(struct btrfs_trans_handle *trans,
                                struct backref_cache *cache)
{
        struct backref_node *node;
        int level = 0;

        if (cache->last_trans == 0) {
                cache->last_trans = trans->transid;
                return 0;
        }

        if (cache->last_trans == trans->transid)
                return 0;

        /*
         * detached nodes are used to avoid unnecessary backref
         * lookup. transaction commit changes the extent tree.
         * so the detached nodes are no longer useful.
         */
        while (!list_empty(&cache->detached)) {
                node = list_entry(cache->detached.next,
                                  struct backref_node, list);
                remove_backref_node(cache, node);
        }

        while (!list_empty(&cache->changed)) {
                node = list_entry(cache->changed.next,
                                  struct backref_node, list);
                list_del_init(&node->list);
                BUG_ON(node->pending);
                update_backref_node(cache, node, node->new_bytenr);
        }

        /*
         * some nodes can be left in the pending list if there were
         * errors during processing the pending nodes.
         */
        for (level = 0; level < BTRFS_MAX_LEVEL; level++) {
                list_for_each_entry(node, &cache->pending[level], list) {
                        BUG_ON(!node->pending);
                        if (node->bytenr == node->new_bytenr)
                                continue;
                        update_backref_node(cache, node, node->new_bytenr);
                }
        }

        cache->last_trans = 0;
        return 1;
}


static int should_ignore_root(struct btrfs_root *root)
{
        struct btrfs_root *reloc_root;

        if (!test_bit(BTRFS_ROOT_REF_COWS, &root->state))
                return 0;

        reloc_root = root->reloc_root;
        if (!reloc_root)
                return 0;

        if (btrfs_root_last_snapshot(&reloc_root->root_item) ==
            root->fs_info->running_transaction->transid - 1)
                return 0;
        /*
         * if there is reloc tree and it was created in previous
         * transaction backref lookup can find the reloc tree,
         * so backref node for the fs tree root is useless for
         * relocation.
         */
        return 1;
}
/*
 * find reloc tree by address of tree root
 */
static struct btrfs_root *find_reloc_root(struct reloc_control *rc,
                                          u64 bytenr)
{
        struct rb_node *rb_node;
        struct mapping_node *node;
        struct btrfs_root *root = NULL;

        spin_lock(&rc->reloc_root_tree.lock);
        rb_node = tree_search(&rc->reloc_root_tree.rb_root, bytenr);
        if (rb_node) {
                node = rb_entry(rb_node, struct mapping_node, rb_node);
                root = (struct btrfs_root *)node->data;
        }
        spin_unlock(&rc->reloc_root_tree.lock);
        return root;
}

static int is_cowonly_root(u64 root_objectid)
{
        if (root_objectid == BTRFS_ROOT_TREE_OBJECTID ||
            root_objectid == BTRFS_EXTENT_TREE_OBJECTID ||
            root_objectid == BTRFS_CHUNK_TREE_OBJECTID ||
            root_objectid == BTRFS_DEV_TREE_OBJECTID ||
            root_objectid == BTRFS_TREE_LOG_OBJECTID ||
            root_objectid == BTRFS_CSUM_TREE_OBJECTID ||
            root_objectid == BTRFS_UUID_TREE_OBJECTID ||
            root_objectid == BTRFS_QUOTA_TREE_OBJECTID ||
            root_objectid == BTRFS_FREE_SPACE_TREE_OBJECTID)
                return 1;
        return 0;
}

static struct btrfs_root *read_fs_root(struct btrfs_fs_info *fs_info,
                                        u64 root_objectid)
{
        struct btrfs_key key;

        key.objectid = root_objectid;
        key.type = BTRFS_ROOT_ITEM_KEY;
        if (is_cowonly_root(root_objectid))
                key.offset = 0;
        else
                key.offset = (u64)-1;

        return btrfs_get_fs_root(fs_info, &key, false);
}

#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
static noinline_for_stack
struct btrfs_root *find_tree_root(struct reloc_control *rc,
                                  struct extent_buffer *leaf,
                                  struct btrfs_extent_ref_v0 *ref0)
{
        struct btrfs_root *root;
        u64 root_objectid = btrfs_ref_root_v0(leaf, ref0);
        u64 generation = btrfs_ref_generation_v0(leaf, ref0);

        BUG_ON(root_objectid == BTRFS_TREE_RELOC_OBJECTID);

        root = read_fs_root(rc->extent_root->fs_info, root_objectid);
        BUG_ON(IS_ERR(root));

        if (test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
            generation != btrfs_root_generation(&root->root_item))
                return NULL;

        return root;
}
#endif

static noinline_for_stack
int find_inline_backref(struct extent_buffer *leaf, int slot,
                        unsigned long *ptr, unsigned long *end)
{
        struct btrfs_key key;
        struct btrfs_extent_item *ei;
        struct btrfs_tree_block_info *bi;
        u32 item_size;

        btrfs_item_key_to_cpu(leaf, &key, slot);

        item_size = btrfs_item_size_nr(leaf, slot);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
        if (item_size < sizeof(*ei)) {
                WARN_ON(item_size != sizeof(struct btrfs_extent_item_v0));
                return 1;
        }
#endif
        ei = btrfs_item_ptr(leaf, slot, struct btrfs_extent_item);
        WARN_ON(!(btrfs_extent_flags(leaf, ei) &
                  BTRFS_EXTENT_FLAG_TREE_BLOCK));

        if (key.type == BTRFS_EXTENT_ITEM_KEY &&
            item_size <= sizeof(*ei) + sizeof(*bi)) {
                WARN_ON(item_size < sizeof(*ei) + sizeof(*bi));
                return 1;
        }
        if (key.type == BTRFS_METADATA_ITEM_KEY &&
            item_size <= sizeof(*ei)) {
                WARN_ON(item_size < sizeof(*ei));
                return 1;
        }

        if (key.type == BTRFS_EXTENT_ITEM_KEY) {
                bi = (struct btrfs_tree_block_info *)(ei + 1);
                *ptr = (unsigned long)(bi + 1);
        } else {
                *ptr = (unsigned long)(ei + 1);
        }
        *end = (unsigned long)ei + item_size;
        return 0;
}

/*
 * build backref tree for a given tree block. root of the backref tree
 * corresponds the tree block, leaves of the backref tree correspond
 * roots of b-trees that reference the tree block.
 *
 * the basic idea of this function is check backrefs of a given block
 * to find upper level blocks that refernece the block, and then check
 * bakcrefs of these upper level blocks recursively. the recursion stop
 * when tree root is reached or backrefs for the block is cached.
 *
 * NOTE: if we find backrefs for a block are cached, we know backrefs
 * for all upper level blocks that directly/indirectly reference the
 * block are also cached.
 */
static noinline_for_stack
struct backref_node *build_backref_tree(struct reloc_control *rc,
                                        struct btrfs_key *node_key,
                                        int level, u64 bytenr)
{
        struct backref_cache *cache = &rc->backref_cache;
        struct btrfs_path *path1;
        struct btrfs_path *path2;
        struct extent_buffer *eb;
        struct btrfs_root *root;
        struct backref_node *cur;
        struct backref_node *upper;
        struct backref_node *lower;
        struct backref_node *node = NULL;
        struct backref_node *exist = NULL;
        struct backref_edge *edge;
        struct rb_node *rb_node;
        struct btrfs_key key;
        unsigned long end;
        unsigned long ptr;
        LIST_HEAD(list);
        LIST_HEAD(useless);
        int cowonly;
        int ret;
        int err = 0;
        bool need_check = true;

        path1 = btrfs_alloc_path();
        path2 = btrfs_alloc_path();
        if (!path1 || !path2) {
                err = -ENOMEM;
                goto out;
        }
        path1->reada = READA_FORWARD;
        path2->reada = READA_FORWARD;

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

        node->bytenr = bytenr;
        node->level = level;
        node->lowest = 1;
        cur = node;
again:
        end = 0;
        ptr = 0;
        key.objectid = cur->bytenr;
        key.type = BTRFS_METADATA_ITEM_KEY;
        key.offset = (u64)-1;

        path1->search_commit_root = 1;
        path1->skip_locking = 1;
        ret = btrfs_search_slot(NULL, rc->extent_root, &key, path1,
                                0, 0);
        if (ret < 0) {
                err = ret;
                goto out;
        }
        ASSERT(ret);
        ASSERT(path1->slots[0]);

        path1->slots[0]--;

        WARN_ON(cur->checked);
        if (!list_empty(&cur->upper)) {
                /*
                 * the backref was added previously when processing
                 * backref of type BTRFS_TREE_BLOCK_REF_KEY
                 */
                ASSERT(list_is_singular(&cur->upper));
                edge = list_entry(cur->upper.next, struct backref_edge,
                                  list[LOWER]);
                ASSERT(list_empty(&edge->list[UPPER]));
                exist = edge->node[UPPER];
                /*
                 * add the upper level block to pending list if we need
                 * check its backrefs
                 */
                if (!exist->checked)
                        list_add_tail(&edge->list[UPPER], &list);
        } else {
                exist = NULL;
        }

        while (1) {
                cond_resched();
                eb = path1->nodes[0];

                if (ptr >= end) {
                        if (path1->slots[0] >= btrfs_header_nritems(eb)) {
                                ret = btrfs_next_leaf(rc->extent_root, path1);
                                if (ret < 0) {
                                        err = ret;
                                        goto out;
                                }
                                if (ret > 0)
                                        break;
                                eb = path1->nodes[0];
                        }

                        btrfs_item_key_to_cpu(eb, &key, path1->slots[0]);
                        if (key.objectid != cur->bytenr) {
                                WARN_ON(exist);
                                break;
                        }

                        if (key.type == BTRFS_EXTENT_ITEM_KEY ||
                            key.type == BTRFS_METADATA_ITEM_KEY) {
                                ret = find_inline_backref(eb, path1->slots[0],
                                                          &ptr, &end);
                                if (ret)
                                        goto next;
                        }
                }

                if (ptr < end) {
                        /* update key for inline back ref */
                        struct btrfs_extent_inline_ref *iref;
                        iref = (struct btrfs_extent_inline_ref *)ptr;
                        key.type = btrfs_extent_inline_ref_type(eb, iref);
                        key.offset = btrfs_extent_inline_ref_offset(eb, iref);
                        WARN_ON(key.type != BTRFS_TREE_BLOCK_REF_KEY &&
                                key.type != BTRFS_SHARED_BLOCK_REF_KEY);
                }

                if (exist &&
                    ((key.type == BTRFS_TREE_BLOCK_REF_KEY &&
                      exist->owner == key.offset) ||
                     (key.type == BTRFS_SHARED_BLOCK_REF_KEY &&
                      exist->bytenr == key.offset))) {
                        exist = NULL;
                        goto next;
                }

#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
                if (key.type == BTRFS_SHARED_BLOCK_REF_KEY ||
                    key.type == BTRFS_EXTENT_REF_V0_KEY) {
                        if (key.type == BTRFS_EXTENT_REF_V0_KEY) {
                                struct btrfs_extent_ref_v0 *ref0;
                                ref0 = btrfs_item_ptr(eb, path1->slots[0],
                                                struct btrfs_extent_ref_v0);
                                if (key.objectid == key.offset) {
                                        root = find_tree_root(rc, eb, ref0);
                                        if (root && !should_ignore_root(root))
                                                cur->root = root;
                                        else
                                                list_add(&cur->list, &useless);
                                        break;
                                }
                                if (is_cowonly_root(btrfs_ref_root_v0(eb,
                                                                      ref0)))
                                        cur->cowonly = 1;
                        }
#else
                ASSERT(key.type != BTRFS_EXTENT_REF_V0_KEY);
                if (key.type == BTRFS_SHARED_BLOCK_REF_KEY) {
#endif
                        if (key.objectid == key.offset) {
                                /*
                                 * only root blocks of reloc trees use
                                 * backref of this type.
                                 */
                                root = find_reloc_root(rc, cur->bytenr);
                                ASSERT(root);
                                cur->root = root;
                                break;
                        }

                        edge = alloc_backref_edge(cache);
                        if (!edge) {
                                err = -ENOMEM;
                                goto out;
                        }
                        rb_node = tree_search(&cache->rb_root, key.offset);
                        if (!rb_node) {
                                upper = alloc_backref_node(cache);
                                if (!upper) {
                                        free_backref_edge(cache, edge);
                                        err = -ENOMEM;
                                        goto out;
                                }
                                upper->bytenr = key.offset;
                                upper->level = cur->level + 1;
                                /*
                                 *  backrefs for the upper level block isn't
                                 *  cached, add the block to pending list
                                 */
                                list_add_tail(&edge->list[UPPER], &list);
                        } else {
                                upper = rb_entry(rb_node, struct backref_node,
                                                 rb_node);
                                ASSERT(upper->checked);
                                INIT_LIST_HEAD(&edge->list[UPPER]);
                        }
                        list_add_tail(&edge->list[LOWER], &cur->upper);
                        edge->node[LOWER] = cur;
                        edge->node[UPPER] = upper;

                        goto next;
                } else if (key.type != BTRFS_TREE_BLOCK_REF_KEY) {
                        goto next;
                }

                /* key.type == BTRFS_TREE_BLOCK_REF_KEY */
                root = read_fs_root(rc->extent_root->fs_info, key.offset);
                if (IS_ERR(root)) {
                        err = PTR_ERR(root);
                        goto out;
                }

                if (!test_bit(BTRFS_ROOT_REF_COWS, &root->state))
                        cur->cowonly = 1;

                if (btrfs_root_level(&root->root_item) == cur->level) {
                        /* tree root */
                        ASSERT(btrfs_root_bytenr(&root->root_item) ==
                               cur->bytenr);
                        if (should_ignore_root(root))
                                list_add(&cur->list, &useless);
                        else
                                cur->root = root;
                        break;
                }

                level = cur->level + 1;

                /*
                 * searching the tree to find upper level blocks
                 * reference the block.
                 */
                path2->search_commit_root = 1;
                path2->skip_locking = 1;
                path2->lowest_level = level;
                ret = btrfs_search_slot(NULL, root, node_key, path2, 0, 0);
                path2->lowest_level = 0;
                if (ret < 0) {
                        err = ret;
                        goto out;
                }
                if (ret > 0 && path2->slots[level] > 0)
                        path2->slots[level]--;

                eb = path2->nodes[level];
                WARN_ON(btrfs_node_blockptr(eb, path2->slots[level]) !=
                        cur->bytenr);

                lower = cur;
                need_check = true;
                for (; level < BTRFS_MAX_LEVEL; level++) {
                        if (!path2->nodes[level]) {
                                ASSERT(btrfs_root_bytenr(&root->root_item) ==
                                       lower->bytenr);
                                if (should_ignore_root(root))
                                        list_add(&lower->list, &useless);
                                else
                                        lower->root = root;
                                break;
                        }

                        edge = alloc_backref_edge(cache);
                        if (!edge) {
                                err = -ENOMEM;
                                goto out;
                        }

                        eb = path2->nodes[level];
                        rb_node = tree_search(&cache->rb_root, eb->start);
                        if (!rb_node) {
                                upper = alloc_backref_node(cache);
                                if (!upper) {
                                        free_backref_edge(cache, edge);
                                        err = -ENOMEM;
                                        goto out;
                                }
                                upper->bytenr = eb->start;
                                upper->owner = btrfs_header_owner(eb);
                                upper->level = lower->level + 1;
                                if (!test_bit(BTRFS_ROOT_REF_COWS,
                                              &root->state))
                                        upper->cowonly = 1;

                                /*
                                 * if we know the block isn't shared
                                 * we can void checking its backrefs.
                                 */
                                if (btrfs_block_can_be_shared(root, eb))
                                        upper->checked = 0;
                                else
                                        upper->checked = 1;

                                /*
                                 * add the block to pending list if we
                                 * need check its backrefs, we only do this once
                                 * while walking up a tree as we will catch
                                 * anything else later on.
                                 */
                                if (!upper->checked && need_check) {
                                        need_check = false;
                                        list_add_tail(&edge->list[UPPER],
                                                      &list);
                                } else {
                                        if (upper->checked)
                                                need_check = true;
                                        INIT_LIST_HEAD(&edge->list[UPPER]);
                                }
                        } else {
                                upper = rb_entry(rb_node, struct backref_node,
                                                 rb_node);
                                ASSERT(upper->checked);
                                INIT_LIST_HEAD(&edge->list[UPPER]);
                                if (!upper->owner)
                                        upper->owner = btrfs_header_owner(eb);
                        }
                        list_add_tail(&edge->list[LOWER], &lower->upper);
                        edge->node[LOWER] = lower;
                        edge->node[UPPER] = upper;

                        if (rb_node)
                                break;

                        lower = upper;
                        upper = NULL;
                }
                btrfs_release_path(path2);
next:
                if (ptr < end) {
                        ptr += btrfs_extent_inline_ref_size(key.type);
                        if (ptr >= end) {
                                WARN_ON(ptr > end);
                                ptr = 0;
                                end = 0;
                        }
                }
                if (ptr >= end)
                        path1->slots[0]++;
        }
        btrfs_release_path(path1);

        cur->checked = 1;
        WARN_ON(exist);

        /* the pending list isn't empty, take the first block to process */
        if (!list_empty(&list)) {
                edge = list_entry(list.next, struct backref_edge, list[UPPER]);
                list_del_init(&edge->list[UPPER]);
                cur = edge->node[UPPER];
                goto again;
        }

        /*
         * everything goes well, connect backref nodes and insert backref nodes
         * into the cache.
         */
        ASSERT(node->checked);
        cowonly = node->cowonly;
        if (!cowonly) {
                rb_node = tree_insert(&cache->rb_root, node->bytenr,
                                      &node->rb_node);
                if (rb_node)
                        backref_tree_panic(rb_node, -EEXIST, node->bytenr);
                list_add_tail(&node->lower, &cache->leaves);
        }

        list_for_each_entry(edge, &node->upper, list[LOWER])
                list_add_tail(&edge->list[UPPER], &list);

        while (!list_empty(&list)) {
                edge = list_entry(list.next, struct backref_edge, list[UPPER]);
                list_del_init(&edge->list[UPPER]);
                upper = edge->node[UPPER];
                if (upper->detached) {
                        list_del(&edge->list[LOWER]);
                        lower = edge->node[LOWER];
                        free_backref_edge(cache, edge);
                        if (list_empty(&lower->upper))
                                list_add(&lower->list, &useless);
                        continue;
                }

                if (!RB_EMPTY_NODE(&upper->rb_node)) {
                        if (upper->lowest) {
                                list_del_init(&upper->lower);
                                upper->lowest = 0;
                        }

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

                if (!upper->checked) {
                        /*
                         * Still want to blow up for developers since this is a
                         * logic bug.
                         */
                        ASSERT(0);
                        err = -EINVAL;
                        goto out;
                }
                if (cowonly != upper->cowonly) {
                        ASSERT(0);
                        err = -EINVAL;
                        goto out;
                }

                if (!cowonly) {
                        rb_node = tree_insert(&cache->rb_root, upper->bytenr,
                                              &upper->rb_node);
                        if (rb_node)
                                backref_tree_panic(rb_node, -EEXIST,
                                                   upper->bytenr);
                }

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

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

                        if (list_empty(&lower->upper))
                                list_add(&lower->list, &useless);
                }
                __mark_block_processed(rc, upper);
                if (upper->level > 0) {
                        list_add(&upper->list, &cache->detached);
                        upper->detached = 1;
                } else {
                        rb_erase(&upper->rb_node, &cache->rb_root);
                        free_backref_node(cache, upper);
                }
        }
out:
        btrfs_free_path(path1);
        btrfs_free_path(path2);
        if (err) {
                while (!list_empty(&useless)) {
                        lower = list_entry(useless.next,
                                           struct backref_node, list);
                        list_del_init(&lower->list);
                }
                while (!list_empty(&list)) {
                        edge = list_first_entry(&list, struct backref_edge,
                                                list[UPPER]);
                        list_del(&edge->list[UPPER]);
                        list_del(&edge->list[LOWER]);
                        lower = edge->node[LOWER];
                        upper = edge->node[UPPER];
                        free_backref_edge(cache, edge);

                        /*
                         * Lower is no longer linked to any upper backref nodes
                         * and isn't in the cache, we can free it ourselves.
                         */
                        if (list_empty(&lower->upper) &&
                            RB_EMPTY_NODE(&lower->rb_node))
                                list_add(&lower->list, &useless);

                        if (!RB_EMPTY_NODE(&upper->rb_node))
                                continue;

                        /* Add this guy's upper edges to the list to proces */
                        list_for_each_entry(edge, &upper->upper, list[LOWER])
                                list_add_tail(&edge->list[UPPER], &list);
                        if (list_empty(&upper->upper))
                                list_add(&upper->list, &useless);
                }

                while (!list_empty(&useless)) {
                        lower = list_entry(useless.next,
                                           struct backref_node, list);
                        list_del_init(&lower->list);
                        free_backref_node(cache, lower);
                }
                return ERR_PTR(err);
        }
        ASSERT(!node || !node->detached);
        return node;
}

/*
 * helper to add backref node for the newly created snapshot.
 * the backref node is created by cloning backref node that
 * corresponds to root of source tree
 */
static int clone_backref_node(struct btrfs_trans_handle *trans,
                              struct reloc_control *rc,
                              struct btrfs_root *src,
                              struct btrfs_root *dest)
{
        struct btrfs_root *reloc_root = src->reloc_root;
        struct backref_cache *cache = &rc->backref_cache;
        struct backref_node *node = NULL;
        struct backref_node *new_node;
        struct backref_edge *edge;
        struct backref_edge *new_edge;
        struct rb_node *rb_node;

        if (cache->last_trans > 0)
                update_backref_cache(trans, cache);

        rb_node = tree_search(&cache->rb_root, src->commit_root->start);
        if (rb_node) {
                node = rb_entry(rb_node, struct backref_node, rb_node);
                if (node->detached)
                        node = NULL;
                else
                        BUG_ON(node->new_bytenr != reloc_root->node->start);
        }

        if (!node) {
                rb_node = tree_search(&cache->rb_root,
                                      reloc_root->commit_root->start);
                if (rb_node) {
                        node = rb_entry(rb_node, struct backref_node,
                                        rb_node);
                        BUG_ON(node->detached);
                }
        }

        if (!node)
                return 0;

        new_node = alloc_backref_node(cache);
        if (!new_node)
                return -ENOMEM;

        new_node->bytenr = dest->node->start;
        new_node->level = node->level;
        new_node->lowest = node->lowest;
        new_node->checked = 1;
        new_node->root = dest;

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

                        new_edge->node[UPPER] = new_node;
                        new_edge->node[LOWER] = edge->node[LOWER];
                        list_add_tail(&new_edge->list[UPPER],
                                      &new_node->lower);
                }
        } else {
                list_add_tail(&new_node->lower, &cache->leaves);
        }

        rb_node = tree_insert(&cache->rb_root, new_node->bytenr,
                              &new_node->rb_node);
        if (rb_node)
                backref_tree_panic(rb_node, -EEXIST, new_node->bytenr);

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

/*
 * helper to add 'address of tree root -> reloc tree' mapping
 */
static int __must_check __add_reloc_root(struct btrfs_root *root)
{
        struct rb_node *rb_node;
        struct mapping_node *node;
        struct reloc_control *rc = root->fs_info->reloc_ctl;

        node = kmalloc(sizeof(*node), GFP_NOFS);
        if (!node)
                return -ENOMEM;

        node->bytenr = root->node->start;
        node->data = root;

        spin_lock(&rc->reloc_root_tree.lock);
        rb_node = tree_insert(&rc->reloc_root_tree.rb_root,
                              node->bytenr, &node->rb_node);
        spin_unlock(&rc->reloc_root_tree.lock);
        if (rb_node) {
                btrfs_panic(root->fs_info, -EEXIST, "Duplicate root found "
                            "for start=%llu while inserting into relocation "
                            "tree", node->bytenr);
                kfree(node);
                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 rb_node *rb_node;
        struct mapping_node *node = NULL;
        struct reloc_control *rc = root->fs_info->reloc_ctl;

        spin_lock(&rc->reloc_root_tree.lock);
        rb_node = tree_search(&rc->reloc_root_tree.rb_root,
                              root->node->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;
        BUG_ON((struct btrfs_root *)node->data != root);

        spin_lock(&root->fs_info->trans_lock);
        list_del_init(&root->root_list);
        spin_unlock(&root->fs_info->trans_lock);
        kfree(node);
}

/*
 * helper to update the 'address of tree root -> reloc tree'
 * mapping
 */
static int __update_reloc_root(struct btrfs_root *root, u64 new_bytenr)
{
        struct rb_node *rb_node;
        struct mapping_node *node = NULL;
        struct reloc_control *rc = root->fs_info->reloc_ctl;

        spin_lock(&rc->reloc_root_tree.lock);
        rb_node = tree_search(&rc->reloc_root_tree.rb_root,
                              root->node->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 = new_bytenr;
        rb_node = tree_insert(&rc->reloc_root_tree.rb_root,
                              node->bytenr, &node->rb_node);
        spin_unlock(&rc->reloc_root_tree.lock);
        if (rb_node)
                backref_tree_panic(rb_node, -EEXIST, node->bytenr);
        return 0;
}

static struct btrfs_root *create_reloc_root(struct btrfs_trans_handle *trans,
                                        struct btrfs_root *root, u64 objectid)
{
        struct btrfs_root *reloc_root;
        struct extent_buffer *eb;
        struct btrfs_root_item *root_item;
        struct btrfs_key root_key;
        u64 last_snap = 0;
        int ret;

        root_item = kmalloc(sizeof(*root_item), GFP_NOFS);
        BUG_ON(!root_item);

        root_key.objectid = BTRFS_TREE_RELOC_OBJECTID;
        root_key.type = BTRFS_ROOT_ITEM_KEY;
        root_key.offset = objectid;

        if (root->root_key.objectid == objectid) {
                /* called by btrfs_init_reloc_root */
                ret = btrfs_copy_root(trans, root, root->commit_root, &eb,
                                      BTRFS_TREE_RELOC_OBJECTID);
                BUG_ON(ret);

                last_snap = btrfs_root_last_snapshot(&root->root_item);
                btrfs_set_root_last_snapshot(&root->root_item,
                                             trans->transid - 1);
        } else {
                /*
                 * called by btrfs_reloc_post_snapshot_hook.
                 * the source tree is a reloc tree, all tree blocks
                 * modified after it was created have RELOC flag
                 * set in their headers. so it's OK to not update
                 * the 'last_snapshot'.
                 */
                ret = btrfs_copy_root(trans, root, root->node, &eb,
                                      BTRFS_TREE_RELOC_OBJECTID);
                BUG_ON(ret);
        }

        memcpy(root_item, &root->root_item, sizeof(*root_item));
        btrfs_set_root_bytenr(root_item, eb->start);
        btrfs_set_root_level(root_item, btrfs_header_level(eb));
        btrfs_set_root_generation(root_item, trans->transid);

        if (root->root_key.objectid == objectid) {
                btrfs_set_root_refs(root_item, 0);
                memset(&root_item->drop_progress, 0,
                       sizeof(struct btrfs_disk_key));
                root_item->drop_level = 0;
                /*
                 * abuse rtransid, it is safe because it is impossible to
                 * receive data into a relocation tree.
                 */
                btrfs_set_root_rtransid(root_item, last_snap);
                btrfs_set_root_otransid(root_item, trans->transid);
        }

        btrfs_tree_unlock(eb);
        free_extent_buffer(eb);

        ret = btrfs_insert_root(trans, root->fs_info->tree_root,
                                &root_key, root_item);
        BUG_ON(ret);
        kfree(root_item);

        reloc_root = btrfs_read_fs_root(root->fs_info->tree_root, &root_key);
        BUG_ON(IS_ERR(reloc_root));
        reloc_root->last_trans = trans->transid;
        return reloc_root;
}

/*
 * create reloc tree for a given fs tree. reloc tree is just a
 * snapshot of the fs tree with special root objectid.
 */
int btrfs_init_reloc_root(struct btrfs_trans_handle *trans,
                          struct btrfs_root *root)
{
        struct btrfs_root *reloc_root;
        struct reloc_control *rc = root->fs_info->reloc_ctl;
        struct btrfs_block_rsv *rsv;
        int clear_rsv = 0;
        int ret;

        if (root->reloc_root) {
                reloc_root = root->reloc_root;
                reloc_root->last_trans = trans->transid;
                return 0;
        }

        if (!rc || !rc->create_reloc_tree ||
            root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
                return 0;

        if (!trans->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;

        ret = __add_reloc_root(reloc_root);
        BUG_ON(ret < 0);
        root->reloc_root = reloc_root;
        return 0;
}

/*
 * update root item of reloc tree
 */
int btrfs_update_reloc_root(struct btrfs_trans_handle *trans,
                            struct btrfs_root *root)
{
        struct btrfs_root *reloc_root;
        struct btrfs_root_item *root_item;
        int ret;

        if (!root->reloc_root)
                goto out;

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

        if (root->fs_info->reloc_ctl->merge_reloc_tree &&
            btrfs_root_refs(root_item) == 0) {
                root->reloc_root = NULL;
                __del_reloc_root(reloc_root);
        }

        if (reloc_root->commit_root != reloc_root->node) {
                btrfs_set_root_node(root_item, reloc_root->node);
                free_extent_buffer(reloc_root->commit_root);
                reloc_root->commit_root = btrfs_root_node(reloc_root);
        }

        ret = btrfs_update_root(trans, root->fs_info->tree_root,
                                &reloc_root->root_key, root_item);
        BUG_ON(ret);

out:
        return 0;
}

/*
 * helper to find first cached inode with inode number >= objectid
 * in a subvolume
 */
static struct inode *find_next_inode(struct btrfs_root *root, u64 objectid)
{
        struct rb_node *node;
        struct rb_node *prev;
        struct btrfs_inode *entry;
        struct inode *inode;

        spin_lock(&root->inode_lock);
again:
        node = root->inode_tree.rb_node;
        prev = NULL;
        while (node) {
                prev = node;
                entry = rb_entry(node, struct btrfs_inode, rb_node);

                if (objectid < btrfs_ino(&entry->vfs_inode))
                        node = node->rb_left;
                else if (objectid > btrfs_ino(&entry->vfs_inode))
                        node = node->rb_right;
                else
                        break;
        }
        if (!node) {
                while (prev) {
                        entry = rb_entry(prev, struct btrfs_inode, rb_node);
                        if (objectid <= btrfs_ino(&entry->vfs_inode)) {
                                node = prev;
                                break;
                        }
                        prev = rb_next(prev);
                }
        }
        while (node) {
                entry = rb_entry(node, struct btrfs_inode, rb_node);
                inode = igrab(&entry->vfs_inode);
                if (inode) {
                        spin_unlock(&root->inode_lock);
                        return inode;
                }

                objectid = btrfs_ino(&entry->vfs_inode) + 1;
                if (cond_resched_lock(&root->inode_lock))
                        goto again;

                node = rb_next(node);
        }
        spin_unlock(&root->inode_lock);
        return NULL;
}

static int in_block_group(u64 bytenr,
                          struct btrfs_block_group_cache *block_group)
{
        if (bytenr >= block_group->key.objectid &&
            bytenr < block_group->key.objectid + block_group->key.offset)
                return 1;
        return 0;
}

/*
 * get new location of data
 */
static int get_new_location(struct inode *reloc_inode, u64 *new_bytenr,
                            u64 bytenr, u64 num_bytes)
{
        struct btrfs_root *root = BTRFS_I(reloc_inode)->root;
        struct btrfs_path *path;
        struct btrfs_file_extent_item *fi;
        struct extent_buffer *leaf;
        int ret;

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

        bytenr -= BTRFS_I(reloc_inode)->index_cnt;
        ret = btrfs_lookup_file_extent(NULL, root, path, btrfs_ino(reloc_inode),
                                       bytenr, 0);
        if (ret < 0)
                goto out;
        if (ret > 0) {
                ret = -ENOENT;
                goto out;
        }

        leaf = path->nodes[0];
        fi = btrfs_item_ptr(leaf, path->slots[0],
                            struct btrfs_file_extent_item);

        BUG_ON(btrfs_file_extent_offset(leaf, fi) ||
               btrfs_file_extent_compression(leaf, fi) ||
               btrfs_file_extent_encryption(leaf, fi) ||
               btrfs_file_extent_other_encoding(leaf, fi));

        if (num_bytes != btrfs_file_extent_disk_num_bytes(leaf, fi)) {
                ret = -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_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++) {
                cond_resched();
                btrfs_item_key_to_cpu(leaf, &key, i);
                if (key.type != BTRFS_EXTENT_DATA_KEY)
                        continue;
                fi = btrfs_item_ptr(leaf, i, struct btrfs_file_extent_item);
                if (btrfs_file_extent_type(leaf, fi) ==
                    BTRFS_FILE_EXTENT_INLINE)
                        continue;
                bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
                num_bytes = btrfs_file_extent_disk_num_bytes(leaf, fi);
                if (bytenr == 0)
                        continue;
                if (!in_block_group(bytenr, rc->block_group))
                        continue;

                /*
                 * if we are modifying block in fs tree, wait for readpage
                 * to complete and drop the extent cache
                 */
                if (root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID) {
                        if (first) {
                                inode = find_next_inode(root, key.objectid);
                                first = 0;
                        } else if (inode && btrfs_ino(inode) < key.objectid) {
                                btrfs_add_delayed_iput(inode);
                                inode = find_next_inode(root, key.objectid);
                        }
                        if (inode && btrfs_ino(inode) == key.objectid) {
                                end = key.offset +
                                      btrfs_file_extent_num_bytes(leaf, fi);
                                WARN_ON(!IS_ALIGNED(key.offset,
                                                    root->sectorsize));
                                WARN_ON(!IS_ALIGNED(end, root->sectorsize));
                                end--;
                                ret = try_lock_extent(&BTRFS_I(inode)->io_tree,
                                                      key.offset, end);
                                if (!ret)
                                        continue;

                                btrfs_drop_extent_cache(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);
                ret = btrfs_inc_extent_ref(trans, root, new_bytenr,
                                           num_bytes, parent,
                                           btrfs_header_owner(leaf),
                                           key.objectid, key.offset);
                if (ret) {
                        btrfs_abort_transaction(trans, root, ret);
                        break;
                }

                ret = btrfs_free_extent(trans, root, bytenr, num_bytes,
                                        parent, btrfs_header_owner(leaf),
                                        key.objectid, key.offset);
                if (ret) {
                        btrfs_abort_transaction(trans, root, 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 btrfs_root *dest, struct btrfs_root *src,
                 struct btrfs_path *path, struct btrfs_key *next_key,
                 int lowest_level, int max_level)
{
        struct extent_buffer *eb;
        struct extent_buffer *parent;
        struct btrfs_key key;
        u64 old_bytenr;
        u64 new_bytenr;
        u64 old_ptr_gen;
        u64 new_ptr_gen;
        u64 last_snapshot;
        u32 blocksize;
        int cow = 0;
        int level;
        int ret;
        int slot;

        BUG_ON(src->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID);
        BUG_ON(dest->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID);

        last_snapshot = btrfs_root_last_snapshot(&src->root_item);
again:
        slot = path->slots[lowest_level];
        btrfs_node_key_to_cpu(path->nodes[lowest_level], &key, slot);

        eb = btrfs_lock_root_node(dest);
        btrfs_set_lock_blocking(eb);
        level = btrfs_header_level(eb);

        if (level < lowest_level) {
                btrfs_tree_unlock(eb);
                free_extent_buffer(eb);
                return 0;
        }

        if (cow) {
                ret = btrfs_cow_block(trans, dest, eb, NULL, 0, &eb);
                BUG_ON(ret);
        }
        btrfs_set_lock_blocking(eb);

        if (next_key) {
                next_key->objectid = (u64)-1;
                next_key->type = (u8)-1;
                next_key->offset = (u64)-1;
        }

        parent = eb;
        while (1) {
                level = btrfs_header_level(parent);
                BUG_ON(level < lowest_level);

                ret = btrfs_bin_search(parent, &key, level, &slot);
                if (ret && slot > 0)
                        slot--;

                if (next_key && slot + 1 < btrfs_header_nritems(parent))
                        btrfs_node_key_to_cpu(parent, next_key, slot + 1);

                old_bytenr = btrfs_node_blockptr(parent, slot);
                blocksize = dest->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 = read_tree_block(dest, old_bytenr, old_ptr_gen);
                        if (IS_ERR(eb)) {
                                ret = PTR_ERR(eb);
                                break;
                        } else if (!extent_buffer_uptodate(eb)) {
                                ret = -EIO;
                                free_extent_buffer(eb);
                                break;
                        }
                        btrfs_tree_lock(eb);
                        if (cow) {
                                ret = btrfs_cow_block(trans, dest, eb, parent,
                                                      slot, &eb);
                                BUG_ON(ret);
                        }
                        btrfs_set_lock_blocking(eb);

                        btrfs_tree_unlock(parent);
                        free_extent_buffer(parent);

                        parent = eb;
                        continue;
                }

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

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

                path->lowest_level = level;
                ret = btrfs_search_slot(trans, src, &key, path, 0, 1);
                path->lowest_level = 0;
                BUG_ON(ret);

                /*
                 * swap blocks in fs tree and reloc tree.
                 */
                btrfs_set_node_blockptr(parent, slot, new_bytenr);
                btrfs_set_node_ptr_generation(parent, slot, new_ptr_gen);
                btrfs_mark_buffer_dirty(parent);

                btrfs_set_node_blockptr(path->nodes[level],
                                        path->slots[level], old_bytenr);
                btrfs_set_node_ptr_generation(path->nodes[level],
                                              path->slots[level], old_ptr_gen);
                btrfs_mark_buffer_dirty(path->nodes[level]);

                ret = btrfs_inc_extent_ref(trans, src, old_bytenr, blocksize,
                                        path->nodes[level]->start,
                                        src->root_key.objectid, level - 1, 0);
                BUG_ON(ret);
                ret = btrfs_inc_extent_ref(trans, dest, new_bytenr, blocksize,
                                        0, dest->root_key.objectid, level - 1,
                                        0);
                BUG_ON(ret);

                ret = btrfs_free_extent(trans, src, new_bytenr, blocksize,
                                        path->nodes[level]->start,
                                        src->root_key.objectid, level - 1, 0);
                BUG_ON(ret);

                ret = btrfs_free_extent(trans, dest, old_bytenr, blocksize,
                                        0, dest->root_key.objectid, level - 1,
                                        0);
                BUG_ON(ret);

                btrfs_unlock_up_safe(path, 0);

                ret = level;
                break;
        }
        btrfs_tree_unlock(parent);
        free_extent_buffer(parent);
        return ret;
}

/*
 * helper to find next relocated block in reloc tree
 */
static noinline_for_stack
int walk_up_reloc_tree(struct btrfs_root *root, struct btrfs_path *path,
                       int *level)
{
        struct extent_buffer *eb;
        int i;
        u64 last_snapshot;
        u32 nritems;

        last_snapshot = btrfs_root_last_snapshot(&root->root_item);

        for (i = 0; i < *level; i++) {
                free_extent_buffer(path->nodes[i]);
                path->nodes[i] = NULL;
        }

        for (i = *level; i < BTRFS_MAX_LEVEL && path->nodes[i]; i++) {
                eb = path->nodes[i];
                nritems = btrfs_header_nritems(eb);
                while (path->slots[i] + 1 < nritems) {
                        path->slots[i]++;
                        if (btrfs_node_ptr_generation(eb, path->slots[i]) <=
                            last_snapshot)
                                continue;

                        *level = i;
                        return 0;
                }
                free_extent_buffer(path->nodes[i]);
                path->nodes[i] = NULL;
        }
        return 1;
}

/*
 * walk down reloc tree to find relocated block of lowest level
 */
static noinline_for_stack
int walk_down_reloc_tree(struct btrfs_root *root, struct btrfs_path *path,
                         int *level)
{
        struct extent_buffer *eb = NULL;
        int i;
        u64 bytenr;
        u64 ptr_gen = 0;
        u64 last_snapshot;
        u32 nritems;

        last_snapshot = btrfs_root_last_snapshot(&root->root_item);

        for (i = *level; i > 0; i--) {
                eb = path->nodes[i];
                nritems = btrfs_header_nritems(eb);
                while (path->slots[i] < nritems) {
                        ptr_gen = btrfs_node_ptr_generation(eb, path->slots[i]);
                        if (ptr_gen > last_snapshot)
                                break;
                        path->slots[i]++;
                }
                if (path->slots[i] >= nritems) {
                        if (i == *level)
                                break;
                        *level = i + 1;
                        return 0;
                }
                if (i == 1) {

                        *level = i;
                        return 0;
                }

                bytenr = btrfs_node_blockptr(eb, path->slots[i]);
                eb = read_tree_block(root, bytenr, ptr_gen);
                if (IS_ERR(eb)) {
                        return PTR_ERR(eb);
                } else if (!extent_buffer_uptodate(eb)) {
                        free_extent_buffer(eb);
                        return -EIO;
                }
                BUG_ON(btrfs_header_level(eb) != i - 1);
                path->nodes[i - 1] = eb;
                path->slots[i - 1] = 0;
        }
        return 1;
}

/*
 * invalidate extent cache for file extents whose key in range of
 * [min_key, max_key)
 */
static int invalidate_extent_cache(struct btrfs_root *root,
                                   struct btrfs_key *min_key,
                                   struct btrfs_key *max_key)
{
        struct inode *inode = NULL;
        u64 objectid;
        u64 start, end;
        u64 ino;

        objectid = min_key->objectid;
        while (1) {
                cond_resched();
                iput(inode);

                if (objectid > max_key->objectid)
                        break;

                inode = find_next_inode(root, objectid);
                if (!inode)
                        break;
                ino = btrfs_ino(inode);

                if (ino > max_key->objectid) {
                        iput(inode);
                        break;
                }

                objectid = ino + 1;
                if (!S_ISREG(inode->i_mode))
                        continue;

                if (unlikely(min_key->objectid == ino)) {
                        if (min_key->type > BTRFS_EXTENT_DATA_KEY)
                                continue;
                        if (min_key->type < BTRFS_EXTENT_DATA_KEY)
                                start = 0;
                        else {
                                start = min_key->offset;
                                WARN_ON(!IS_ALIGNED(start, root->sectorsize));
                        }
                } else {
                        start = 0;
                }

                if (unlikely(max_key->objectid == ino)) {
                        if (max_key->type < BTRFS_EXTENT_DATA_KEY)
                                continue;
                        if (max_key->type > BTRFS_EXTENT_DATA_KEY) {
                                end = (u64)-1;
                        } else {
                                if (max_key->offset == 0)
                                        continue;
                                end = max_key->offset;
                                WARN_ON(!IS_ALIGNED(end, root->sectorsize));
                                end--;
                        }
                } else {
                        end = (u64)-1;
                }

                /* the lock_extent waits for readpage to complete */
                lock_extent(&BTRFS_I(inode)->io_tree, start, end);
                btrfs_drop_extent_cache(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;
}

/*
 * merge the relocated tree blocks in reloc tree with corresponding
 * fs tree.
 */
static noinline_for_stack int merge_reloc_root(struct reloc_control *rc,
                                               struct btrfs_root *root)
{
        LIST_HEAD(inode_list);
        struct btrfs_key key;
        struct btrfs_key next_key;
        struct btrfs_trans_handle *trans = NULL;
        struct btrfs_root *reloc_root;
        struct btrfs_root_item *root_item;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        int level;
        int max_level;
        int replaced = 0;
        int ret;
        int err = 0;
        u32 min_reserved;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
        path->reada = 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);
                extent_buffer_get(reloc_root->node);
                path->nodes[level] = reloc_root->node;
                path->slots[level] = 0;
        } else {
                btrfs_disk_key_to_cpu(&key, &root_item->drop_progress);

                level = root_item->drop_level;
                BUG_ON(level == 0);
                path->lowest_level = level;
                ret = btrfs_search_slot(NULL, reloc_root, &key, path, 0, 0);
                path->lowest_level = 0;
                if (ret < 0) {
                        btrfs_free_path(path);
                        return ret;
                }

                btrfs_node_key_to_cpu(path->nodes[level], &next_key,
                                      path->slots[level]);
                WARN_ON(memcmp(&key, &next_key, sizeof(key)));

                btrfs_unlock_up_safe(path, 0);
        }

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

        while (1) {
                ret = btrfs_block_rsv_refill(root, rc->block_rsv, min_reserved,
                                             BTRFS_RESERVE_FLUSH_ALL);
                if (ret) {
                        err = ret;
                        goto out;
                }
                trans = btrfs_start_transaction(root, 0);
                if (IS_ERR(trans)) {
                        err = PTR_ERR(trans);
                        trans = NULL;
                        goto out;
                }
                trans->block_rsv = rc->block_rsv;

                replaced = 0;
                max_level = level;

                ret = walk_down_reloc_tree(reloc_root, path, &level);
                if (ret < 0) {
                        err = ret;
                        goto out;
                }
                if (ret > 0)
                        break;

                if (!find_next_key(path, level, &key) &&
                    btrfs_comp_cpu_keys(&next_key, &key) >= 0) {
                        ret = 0;
                } else {
                        ret = replace_path(trans, root, reloc_root, path,
                                           &next_key, level, max_level);
                }
                if (ret < 0) {
                        err = ret;
                        goto out;
                }

                if (ret > 0) {
                        level = ret;
                        btrfs_node_key_to_cpu(path->nodes[level], &key,
                                              path->slots[level]);
                        replaced = 1;
                }

                ret = walk_up_reloc_tree(reloc_root, path, &level);
                if (ret > 0)
                        break;

                BUG_ON(level == 0);
                /*
                 * save the merging progress in the drop_progress.
                 * this is OK since root refs == 1 in this case.
                 */
                btrfs_node_key(path->nodes[level], &root_item->drop_progress,
                               path->slots[level]);
                root_item->drop_level = level;

                btrfs_end_transaction_throttle(trans, root);
                trans = NULL;

                btrfs_btree_balance_dirty(root);

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

        /*
         * handle the case only one block in the fs tree need to be
         * relocated and the block is tree root.
         */
        leaf = btrfs_lock_root_node(root);
        ret = btrfs_cow_block(trans, root, leaf, NULL, 0, &leaf);
        btrfs_tree_unlock(leaf);
        free_extent_buffer(leaf);
        if (ret < 0)
                err = ret;
out:
        btrfs_free_path(path);

        if (err == 0) {
                memset(&root_item->drop_progress, 0,
                       sizeof(root_item->drop_progress));
                root_item->drop_level = 0;
                btrfs_set_root_refs(root_item, 0);
                btrfs_update_reloc_root(trans, root);
        }

        if (trans)
                btrfs_end_transaction_throttle(trans, root);

        btrfs_btree_balance_dirty(root);

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

        return err;
}

static noinline_for_stack
int prepare_to_merge(struct reloc_control *rc, int err)
{
        struct btrfs_root *root = rc->extent_root;
        struct btrfs_root *reloc_root;
        struct btrfs_trans_handle *trans;
        LIST_HEAD(reloc_roots);
        u64 num_bytes = 0;
        int ret;

        mutex_lock(&root->fs_info->reloc_mutex);
        rc->merging_rsv_size += root->nodesize * (BTRFS_MAX_LEVEL - 1) * 2;
        rc->merging_rsv_size += rc->nodes_relocated * 2;
        mutex_unlock(&root->fs_info->reloc_mutex);

again:
        if (!err) {
                num_bytes = rc->merging_rsv_size;
                ret = btrfs_block_rsv_add(root, rc->block_rsv, num_bytes,
                                          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(rc->extent_root,
                                                rc->block_rsv, num_bytes);
                return PTR_ERR(trans);
        }

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

        rc->merge_reloc_tree = 1;

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

                root = read_fs_root(reloc_root->fs_info,
                                    reloc_root->root_key.offset);
                BUG_ON(IS_ERR(root));
                BUG_ON(root->reloc_root != reloc_root);

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

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

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

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

static noinline_for_stack
void free_reloc_roots(struct list_head *list)
{
        struct btrfs_root *reloc_root;

        while (!list_empty(list)) {
                reloc_root = list_entry(list->next, struct btrfs_root,
                                        root_list);
                __del_reloc_root(reloc_root);
        }
}

static noinline_for_stack
void merge_reloc_roots(struct reloc_control *rc)
{
        struct btrfs_root *root;
        struct btrfs_root *reloc_root;
        u64 last_snap;
        u64 otransid;
        u64 objectid;
        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(&root->fs_info->reloc_mutex);
        list_splice_init(&rc->reloc_roots, &reloc_roots);
        mutex_unlock(&root->fs_info->reloc_mutex);

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

                if (btrfs_root_refs(&reloc_root->root_item) > 0) {
                        root = read_fs_root(reloc_root->fs_info,
                                            reloc_root->root_key.offset);
                        BUG_ON(IS_ERR(root));
                        BUG_ON(root->reloc_root != reloc_root);

                        ret = merge_reloc_root(rc, root);
                        if (ret) {
                                if (list_empty(&reloc_root->root_list))
                                        list_add_tail(&reloc_root->root_list,
                                                      &reloc_roots);
                                goto out;
                        }
                } else {
                        list_del_init(&reloc_root->root_list);
                }

                /*
                 * we keep the old last snapshod transid in rtranid when we
                 * created the relocation tree.
                 */
                last_snap = btrfs_root_rtransid(&reloc_root->root_item);
                otransid = btrfs_root_otransid(&reloc_root->root_item);
                objectid = reloc_root->root_key.offset;

                ret = btrfs_drop_snapshot(reloc_root, rc->block_rsv, 0, 1);
                if (ret < 0) {
                        if (list_empty(&reloc_root->root_list))
                                list_add_tail(&reloc_root->root_list,
                                              &reloc_roots);
                        goto out;
                }
        }

        if (found) {
                found = 0;
                goto again;
        }
out:
        if (ret) {
                btrfs_std_error(root->fs_info, ret, NULL);
                if (!list_empty(&reloc_roots))
                        free_reloc_roots(&reloc_roots);

                /* new reloc root may be added */
                mutex_lock(&root->fs_info->reloc_mutex);
                list_splice_init(&rc->reloc_roots, &reloc_roots);
                mutex_unlock(&root->fs_info->reloc_mutex);
                if (!list_empty(&reloc_roots))
                        free_reloc_roots(&reloc_roots);
        }

        BUG_ON(!RB_EMPTY_ROOT(&rc->reloc_root_tree.rb_root));
}

static void free_block_list(struct rb_root *blocks)
{
        struct tree_block *block;
        struct rb_node *rb_node;
        while ((rb_node = rb_first(blocks))) {
                block = rb_entry(rb_node, struct tree_block, rb_node);
                rb_erase(rb_node, blocks);
                kfree(block);
        }
}

static int record_reloc_root_in_trans(struct btrfs_trans_handle *trans,
                                      struct btrfs_root *reloc_root)
{
        struct btrfs_root *root;

        if (reloc_root->last_trans == trans->transid)
                return 0;

        root = read_fs_root(reloc_root->fs_info, reloc_root->root_key.offset);
        BUG_ON(IS_ERR(root));
        BUG_ON(root->reloc_root != reloc_root);

        return btrfs_record_root_in_trans(trans, root);
}

static noinline_for_stack
struct btrfs_root *select_reloc_root(struct btrfs_trans_handle *trans,
                                     struct reloc_control *rc,
                                     struct backref_node *node,
                                     struct backref_edge *edges[])
{
        struct backref_node *next;
        struct btrfs_root *root;
        int index = 0;

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

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

                btrfs_record_root_in_trans(trans, root);
                root = root->reloc_root;

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

                WARN_ON(1);
                root = NULL;
                next = walk_down_backref(edges, &index);
                if (!next || next->level <= node->level)
                        break;
        }
        if (!root)
                return NULL;

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

/*
 * select a tree root for relocation. return NULL if the block
 * is reference counted. we should use do_relocation() in this
 * case. return a tree root pointer if the block isn't reference
 * counted. return -ENOENT if the block is root of reloc tree.
 */
static noinline_for_stack
struct btrfs_root *select_one_root(struct backref_node *node)
{
        struct backref_node *next;
        struct btrfs_root *root;
        struct btrfs_root *fs_root = NULL;
        struct backref_edge *edges[BTRFS_MAX_LEVEL - 1];
        int index = 0;

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

                /* no other choice for non-references counted tree */
                if (!test_bit(BTRFS_ROOT_REF_COWS, &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 backref_node *node, int reserve)
{
        struct backref_node *next = node;
        struct backref_edge *edge;
        struct backref_edge *edges[BTRFS_MAX_LEVEL - 1];
        u64 num_bytes = 0;
        int index = 0;

        BUG_ON(reserve && node->processed);

        while (next) {
                cond_resched();
                while (1) {
                        if (next->processed && (reserve || next != node))
                                break;

                        num_bytes += rc->extent_root->nodesize;

                        if (list_empty(&next->upper))
                                break;

                        edge = list_entry(next->upper.next,
                                          struct backref_edge, list[LOWER]);
                        edges[index++] = edge;
                        next = edge->node[UPPER];
                }
                next = walk_down_backref(edges, &index);
        }
        return num_bytes;
}

static int reserve_metadata_space(struct btrfs_trans_handle *trans,
                                  struct reloc_control *rc,
                                  struct backref_node *node)
{
        struct btrfs_root *root = rc->extent_root;
        u64 num_bytes;
        int ret;
        u64 tmp;

        num_bytes = calcu_metadata_size(rc, node, 1) * 2;

        trans->block_rsv = rc->block_rsv;
        rc->reserved_bytes += num_bytes;
        ret = btrfs_block_rsv_refill(root, rc->block_rsv, num_bytes,
                                BTRFS_RESERVE_FLUSH_ALL);
        if (ret) {
                if (ret == -EAGAIN) {
                        tmp = rc->extent_root->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 eailer in
                         * enospc case.
                         */
                        rc->block_rsv->size = tmp + rc->extent_root->nodesize *
                                              RELOCATION_RESERVED_NODES;
                }
                return ret;
        }

        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 backref_node *node,
                         struct btrfs_key *key,
                         struct btrfs_path *path, int lowest)
{
        struct backref_node *upper;
        struct backref_edge *edge;
        struct backref_edge *edges[BTRFS_MAX_LEVEL - 1];
        struct btrfs_root *root;
        struct extent_buffer *eb;
        u32 blocksize;
        u64 bytenr;
        u64 generation;
        int slot;
        int ret;
        int err = 0;

        BUG_ON(lowest && node->eb);

        path->lowest_level = node->level + 1;
        rc->backref_cache.path[node->level] = node;
        list_for_each_entry(edge, &node->upper, list[LOWER]) {
                cond_resched();

                upper = edge->node[UPPER];
                root = select_reloc_root(trans, rc, upper, edges);
                BUG_ON(!root);

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

                if (!upper->eb) {
                        ret = btrfs_search_slot(trans, root, key, path, 0, 1);
                        if (ret < 0) {
                                err = ret;
                                break;
                        }
                        BUG_ON(ret > 0);

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

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

                        slot = path->slots[upper->level];
                        btrfs_release_path(path);
                } else {
                        ret = btrfs_bin_search(upper->eb, key, upper->level,
                                               &slot);
                        BUG_ON(ret);
                }

                bytenr = btrfs_node_blockptr(upper->eb, slot);
                if (lowest) {
                        BUG_ON(bytenr != node->bytenr);
                } else {
                        if (node->eb->start == bytenr)
                                goto next;
                }

                blocksize = root->nodesize;
                generation = btrfs_node_ptr_generation(upper->eb, slot);
                eb = read_tree_block(root, bytenr, generation);
                if (IS_ERR(eb)) {
                        err = PTR_ERR(eb);
                        goto next;
                } else if (!extent_buffer_uptodate(eb)) {
                        free_extent_buffer(eb);
                        err = -EIO;
                        goto next;
                }
                btrfs_tree_lock(eb);
                btrfs_set_lock_blocking(eb);

                if (!node->eb) {
                        ret = btrfs_cow_block(trans, root, eb, upper->eb,
                                              slot, &eb);
                        btrfs_tree_unlock(eb);
                        free_extent_buffer(eb);
                        if (ret < 0) {
                                err = ret;
                                goto next;
                        }
                        BUG_ON(node->eb != eb);
                } else {
                        btrfs_set_node_blockptr(upper->eb, slot,
                                                node->eb->start);
                        btrfs_set_node_ptr_generation(upper->eb, slot,
                                                      trans->transid);
                        btrfs_mark_buffer_dirty(upper->eb);

                        ret = btrfs_inc_extent_ref(trans, root,
                                                node->eb->start, blocksize,
                                                upper->eb->start,
                                                btrfs_header_owner(upper->eb),
                                                node->level, 0);
                        BUG_ON(ret);

                        ret = btrfs_drop_subtree(trans, root, eb, upper->eb);
                        BUG_ON(ret);
                }
next:
                if (!upper->pending)
                        drop_node_buffer(upper);
                else
                        unlock_node_buffer(upper);
                if (err)
                        break;
        }

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

        path->lowest_level = 0;
        BUG_ON(err == -ENOSPC);
        return err;
}

static int link_to_upper(struct btrfs_trans_handle *trans,
                         struct reloc_control *rc,
                         struct backref_node *node,
                         struct btrfs_path *path)
{
        struct btrfs_key key;

        btrfs_node_key_to_cpu(node->eb, &key, 0);
        return do_relocation(trans, rc, node, &key, path, 0);
}

static int finish_pending_nodes(struct btrfs_trans_handle *trans,
                                struct reloc_control *rc,
                                struct btrfs_path *path, int err)
{
        LIST_HEAD(list);
        struct backref_cache *cache = &rc->backref_cache;
        struct backref_node *node;
        int level;
        int ret;

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

                        if (!err) {
                                ret = link_to_upper(trans, rc, node, path);
                                if (ret < 0)
                                        err = ret;
                        }
                }
                list_splice_init(&list, &cache->pending[level]);
        }
        return err;
}

static void mark_block_processed(struct reloc_control *rc,
                                 u64 bytenr, u32 blocksize)
{
        set_extent_bits(&rc->processed_blocks, bytenr, bytenr + blocksize - 1,
                        EXTENT_DIRTY, GFP_NOFS);
}

static void __mark_block_processed(struct reloc_control *rc,
                                   struct backref_node *node)
{
        u32 blocksize;
        if (node->level == 0 ||
            in_block_group(node->bytenr, rc->block_group)) {
                blocksize = rc->extent_root->nodesize;
                mark_block_processed(rc, node->bytenr, blocksize);
        }
        node->processed = 1;
}

/*
 * mark a block and all blocks directly/indirectly reference the block
 * as processed.
 */
static void update_processed_blocks(struct reloc_control *rc,
                                    struct backref_node *node)
{
        struct backref_node *next = node;
        struct backref_edge *edge;
        struct backref_edge *edges[BTRFS_MAX_LEVEL - 1];
        int index = 0;

        while (next) {
                cond_resched();
                while (1) {
                        if (next->processed)
                                break;

                        __mark_block_processed(rc, next);

                        if (list_empty(&next->upper))
                                break;

                        edge = list_entry(next->upper.next,
                                          struct backref_edge, list[LOWER]);
                        edges[index++] = edge;
                        next = edge->node[UPPER];
                }
                next = walk_down_backref(edges, &index);
        }
}

static int tree_block_processed(u64 bytenr, struct reloc_control *rc)
{
        u32 blocksize = rc->extent_root->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 reloc_control *rc,
                              struct tree_block *block)
{
        struct extent_buffer *eb;

        BUG_ON(block->key_ready);
        eb = read_tree_block(rc->extent_root, block->bytenr,
                             block->key.offset);
        if (IS_ERR(eb)) {
                return PTR_ERR(eb);
        } else if (!extent_buffer_uptodate(eb)) {
                free_extent_buffer(eb);
                return -EIO;
        }
        WARN_ON(btrfs_header_level(eb) != block->level);
        if (block->level == 0)
                btrfs_item_key_to_cpu(eb, &block->key, 0);
        else
                btrfs_node_key_to_cpu(eb, &block->key, 0);
        free_extent_buffer(eb);
        block->key_ready = 1;
        return 0;
}

/*
 * helper function to relocate a tree block
 */
static int relocate_tree_block(struct btrfs_trans_handle *trans,
                                struct reloc_control *rc,
                                struct backref_node *node,
                                struct btrfs_key *key,
                                struct btrfs_path *path)
{
        struct btrfs_root *root;
        int ret = 0;

        if (!node)
                return 0;

        BUG_ON(node->processed);
        root = select_one_root(node);
        if (root == ERR_PTR(-ENOENT)) {
                update_processed_blocks(rc, node);
                goto out;
        }

        if (!root || test_bit(BTRFS_ROOT_REF_COWS, &root->state)) {
                ret = reserve_metadata_space(trans, rc, node);
                if (ret)
                        goto out;
        }

        if (root) {
                if (test_bit(BTRFS_ROOT_REF_COWS, &root->state)) {
                        BUG_ON(node->new_bytenr);
                        BUG_ON(!list_empty(&node->list));
                        btrfs_record_root_in_trans(trans, root);
                        root = root->reloc_root;
                        node->new_bytenr = root->node->start;
                        node->root = root;
                        list_add_tail(&node->list, &rc->backref_cache.changed);
                } else {
                        path->lowest_level = node->level;
                        ret = btrfs_search_slot(trans, root, key, path, 0, 1);
                        btrfs_release_path(path);
                        if (ret > 0)
                                ret = 0;
                }
                if (!ret)
                        update_processed_blocks(rc, node);
        } else {
                ret = do_relocation(trans, rc, node, key, path, 1);
        }
out:
        if (ret || node->level == 0 || node->cowonly)
                remove_backref_node(&rc->backref_cache, node);
        return ret;
}

/*
 * relocate a list of blocks
 */
static noinline_for_stack
int relocate_tree_blocks(struct btrfs_trans_handle *trans,
                         struct reloc_control *rc, struct rb_root *blocks)
{
        struct backref_node *node;
        struct btrfs_path *path;
        struct tree_block *block;
        struct rb_node *rb_node;
        int ret;
        int err = 0;

        path = btrfs_alloc_path();
        if (!path) {
                err = -ENOMEM;
                goto out_free_blocks;
        }

        rb_node = rb_first(blocks);
        while (rb_node) {
                block = rb_entry(rb_node, struct tree_block, rb_node);
                if (!block->key_ready)
                        readahead_tree_block(rc->extent_root, block->bytenr);
                rb_node = rb_next(rb_node);
        }

        rb_node = rb_first(blocks);
        while (rb_node) {
                block = rb_entry(rb_node, struct tree_block, rb_node);
                if (!block->key_ready) {
                        err = get_tree_block_key(rc, block);
                        if (err)
                                goto out_free_path;
                }
                rb_node = rb_next(rb_node);
        }

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

                node = build_backref_tree(rc, &block->key,
                                          block->level, block->bytenr);
                if (IS_ERR(node)) {
                        err = PTR_ERR(node);
                        goto out;