/*
 * 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 "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "volumes.h"
#include "locking.h"
#include "btrfs_inode.h"
#include "async-thread.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;
        /* objectid tree block owner */
        u64 owner;
        /* 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;
        /* 1 if the block is root of old snapshot */
        unsigned int old_root:1;
        /* 1 if no child blocks 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;
};

/*
 * present a block pointer in the backref cache
 */
struct backref_edge {
        struct list_head list[2];
        struct backref_node *node[2];
        u64 blockptr;
};

#define LOWER   0
#define UPPER   1

struct backref_cache {
        /* red black tree of all backref nodes in the cache */
        struct rb_root rb_root;
        /* list of backref nodes with no child block in the cache */
        struct list_head pending[BTRFS_MAX_LEVEL];
        spinlock_t lock;
};

/*
 * 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;
};

/* inode vector */
#define INODEVEC_SIZE 16

struct inodevec {
        struct list_head list;
        struct inode *inode[INODEVEC_SIZE];
        int nr;
};

#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_workers workers;
        /* 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;
        u64 search_start;
        u64 extents_found;
        u64 extents_skipped;
        int stage;
        int create_reloc_root;
        unsigned int found_file_extent:1;
        unsigned int found_old_snapshot:1;
};

/* stages of data relocation */
#define MOVE_DATA_EXTENTS       0
#define UPDATE_DATA_PTRS        1

/*
 * merge reloc tree to corresponding fs tree in worker threads
 */
struct async_merge {
        struct btrfs_work work;
        struct reloc_control *rc;
        struct btrfs_root *root;
        struct completion *done;
        atomic_t *num_pending;
};

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

static void backref_cache_init(struct backref_cache *cache)
{
        int i;
        cache->rb_root.rb_node = NULL;
        for (i = 0; i < BTRFS_MAX_LEVEL; i++)
                INIT_LIST_HEAD(&cache->pending[i]);
        spin_lock_init(&cache->lock);
}

static void backref_node_init(struct backref_node *node)
{
        memset(node, 0, sizeof(*node));
        INIT_LIST_HEAD(&node->upper);
        INIT_LIST_HEAD(&node->lower);
        RB_CLEAR_NODE(&node->rb_node);
}

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;
}

/*
 * 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];
        }
        *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 drop_node_buffer(struct backref_node *node)
{
        if (node->eb) {
                if (node->locked) {
                        btrfs_tree_unlock(node->eb);
                        node->locked = 0;
                }
                free_extent_buffer(node->eb);
                node->eb = NULL;
        }
}

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

        drop_node_buffer(node);
        list_del(&node->lower);

        rb_erase(&node->rb_node, &tree->rb_root);
        kfree(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);
        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]);
                kfree(edge);
                /*
                 * add the node to pending list if no other
                 * child block cached.
                 */
                if (list_empty(&upper->lower)) {
                        list_add_tail(&upper->lower,
                                      &cache->pending[upper->level]);
                        upper->lowest = 1;
                }
        }
        drop_backref_node(cache, node);
}

/*
 * 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)
                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_read_fs_root_no_name(fs_info, &key);
}

#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 (root->ref_cows &&
            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_extent_item *ei;
        struct btrfs_tree_block_info *bi;
        u32 item_size;

        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 (item_size <= sizeof(*ei) + sizeof(*bi)) {
                WARN_ON(item_size < sizeof(*ei) + sizeof(*bi));
                return 1;
        }

        bi = (struct btrfs_tree_block_info *)(ei + 1);
        *ptr = (unsigned long)(bi + 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 struct backref_node *build_backref_tree(struct reloc_control *rc,
                                               struct backref_cache *cache,
                                               struct btrfs_key *node_key,
                                               int level, u64 bytenr)
{
        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);
        int ret;
        int err = 0;

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

        node = kmalloc(sizeof(*node), GFP_NOFS);
        if (!node) {
                err = -ENOMEM;
                goto out;
        }

        backref_node_init(node);
        node->bytenr = bytenr;
        node->owner = 0;
        node->level = level;
        node->lowest = 1;
        cur = node;
again:
        end = 0;
        ptr = 0;
        key.objectid = cur->bytenr;
        key.type = BTRFS_EXTENT_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;
        }
        BUG_ON(!ret || !path1->slots[0]);

        path1->slots[0]--;

        WARN_ON(cur->checked);
        if (!list_empty(&cur->upper)) {
                /*
                 * the backref was added previously when processsing
                 * backref of type BTRFS_TREE_BLOCK_REF_KEY
                 */
                BUG_ON(!list_is_singular(&cur->upper));
                edge = list_entry(cur->upper.next, struct backref_edge,
                                  list[LOWER]);
                BUG_ON(!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) {
                                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.objectid == key.offset &&
                            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);
                                root = find_tree_root(rc, eb, ref0);
                                if (root)
                                        cur->root = root;
                                else
                                        cur->old_root = 1;
                                break;
                        }
#else
                BUG_ON(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);
                                BUG_ON(!root);
                                cur->root = root;
                                break;
                        }

                        edge = kzalloc(sizeof(*edge), GFP_NOFS);
                        if (!edge) {
                                err = -ENOMEM;
                                goto out;
                        }
                        rb_node = tree_search(&cache->rb_root, key.offset);
                        if (!rb_node) {
                                upper = kmalloc(sizeof(*upper), GFP_NOFS);
                                if (!upper) {
                                        kfree(edge);
                                        err = -ENOMEM;
                                        goto out;
                                }
                                backref_node_init(upper);
                                upper->bytenr = key.offset;
                                upper->owner = 0;
                                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);
                                INIT_LIST_HEAD(&edge->list[UPPER]);
                        }
                        list_add(&edge->list[LOWER], &cur->upper);
                        edge->node[UPPER] = upper;
                        edge->node[LOWER] = cur;

                        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 (btrfs_root_level(&root->root_item) == cur->level) {
                        /* tree root */
                        BUG_ON(btrfs_root_bytenr(&root->root_item) !=
                               cur->bytenr);
                        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;
                for (; level < BTRFS_MAX_LEVEL; level++) {
                        if (!path2->nodes[level]) {
                                BUG_ON(btrfs_root_bytenr(&root->root_item) !=
                                       lower->bytenr);
                                lower->root = root;
                                break;
                        }

                        edge = kzalloc(sizeof(*edge), GFP_NOFS);
                        if (!edge) {
                                err = -ENOMEM;
                                goto out;
                        }

                        eb = path2->nodes[level];
                        rb_node = tree_search(&cache->rb_root, eb->start);
                        if (!rb_node) {
                                upper = kmalloc(sizeof(*upper), GFP_NOFS);
                                if (!upper) {
                                        kfree(edge);
                                        err = -ENOMEM;
                                        goto out;
                                }
                                backref_node_init(upper);
                                upper->bytenr = eb->start;
                                upper->owner = btrfs_header_owner(eb);
                                upper->level = lower->level + 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. only block
                                 * at 'cur->level + 1' is added to the
                                 * tail of pending list. this guarantees
                                 * we check backrefs from lower level
                                 * blocks to upper level blocks.
                                 */
                                if (!upper->checked &&
                                    level == cur->level + 1) {
                                        list_add_tail(&edge->list[UPPER],
                                                      &list);
                                } else
                                        INIT_LIST_HEAD(&edge->list[UPPER]);
                        } else {
                                upper = rb_entry(rb_node, struct backref_node,
                                                 rb_node);
                                BUG_ON(!upper->checked);
                                INIT_LIST_HEAD(&edge->list[UPPER]);
                        }
                        list_add_tail(&edge->list[LOWER], &lower->upper);
                        edge->node[UPPER] = upper;
                        edge->node[LOWER] = lower;

                        if (rb_node)
                                break;
                        lower = upper;
                        upper = NULL;
                }
                btrfs_release_path(root, 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(rc->extent_root, 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.
         */
        BUG_ON(!node->checked);
        rb_node = tree_insert(&cache->rb_root, node->bytenr, &node->rb_node);
        BUG_ON(rb_node);

        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 (!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;
                }

                BUG_ON(!upper->checked);
                rb_node = tree_insert(&cache->rb_root, upper->bytenr,
                                      &upper->rb_node);
                BUG_ON(rb_node);

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

                list_for_each_entry(edge, &upper->upper, list[LOWER])
                        list_add_tail(&edge->list[UPPER], &list);
        }
out:
        btrfs_free_path(path1);
        btrfs_free_path(path2);
        if (err) {
                INIT_LIST_HEAD(&list);
                upper = node;
                while (upper) {
                        if (RB_EMPTY_NODE(&upper->rb_node)) {
                                list_splice_tail(&upper->upper, &list);
                                kfree(upper);
                        }

                        if (list_empty(&list))
                                break;

                        edge = list_entry(list.next, struct backref_edge,
                                          list[LOWER]);
                        upper = edge->node[UPPER];
                        kfree(edge);
                }
                return ERR_PTR(err);
        }
        return node;
}

/*
 * helper to add 'address of tree root -> reloc tree' mapping
 */
static int __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);
        BUG_ON(!node);

        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);
        BUG_ON(rb_node);

        list_add_tail(&root->root_list, &rc->reloc_roots);
        return 0;
}

/*
 * helper to update/delete the 'address of tree root -> reloc tree'
 * mapping
 */
static int __update_reloc_root(struct btrfs_root *root, int del)
{
        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->commit_root->start);
        if (rb_node) {
                node = rb_entry(rb_node, struct mapping_node, rb_node);
                rb_erase(&node->rb_node, &rc->reloc_root_tree.rb_root);
        }
        spin_unlock(&rc->reloc_root_tree.lock);

        BUG_ON((struct btrfs_root *)node->data != root);

        if (!del) {
                spin_lock(&rc->reloc_root_tree.lock);
                node->bytenr = root->node->start;
                rb_node = tree_insert(&rc->reloc_root_tree.rb_root,
                                      node->bytenr, &node->rb_node);
                spin_unlock(&rc->reloc_root_tree.lock);
                BUG_ON(rb_node);
        } else {
                list_del_init(&root->root_list);
                kfree(node);
        }
        return 0;
}

/*
 * 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 extent_buffer *eb;
        struct btrfs_root_item *root_item;
        struct btrfs_key root_key;
        int ret;

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

        if (!root->fs_info->reloc_ctl ||
            !root->fs_info->reloc_ctl->create_reloc_root ||
            root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
                return 0;

        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 = root->root_key.objectid;

        ret = btrfs_copy_root(trans, root, root->commit_root, &eb,
                              BTRFS_TREE_RELOC_OBJECTID);
        BUG_ON(ret);

        btrfs_set_root_last_snapshot(&root->root_item, trans->transid - 1);
        memcpy(root_item, &root->root_item, sizeof(*root_item));
        btrfs_set_root_refs(root_item, 1);
        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);
        memset(&root_item->drop_progress, 0, sizeof(struct btrfs_disk_key));
        root_item->drop_level = 0;

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

        __add_reloc_root(reloc_root);
        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 del = 0;
        int ret;

        if (!root->reloc_root)
                return 0;

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

        if (btrfs_root_refs(root_item) == 0) {
                root->reloc_root = NULL;
                del = 1;
        }

        __update_reloc_root(reloc_root, del);

        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);
        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 < entry->vfs_inode.i_ino)
                        node = node->rb_left;
                else if (objectid > entry->vfs_inode.i_ino)
                        node = node->rb_right;
                else
                        break;
        }
        if (!node) {
                while (prev) {
                        entry = rb_entry(prev, struct btrfs_inode, rb_node);
                        if (objectid <= entry->vfs_inode.i_ino) {
                                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 = entry->vfs_inode.i_ino + 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, reloc_inode->i_ino,
                                       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 = 1;
                goto out;
        }

        if (new_bytenr)
                *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 int replace_file_extents(struct btrfs_trans_handle *trans,
                                struct reloc_control *rc,
                                struct btrfs_root *root,
                                struct extent_buffer *leaf,
                                struct list_head *inode_list)
{
        struct btrfs_key key;
        struct btrfs_file_extent_item *fi;
        struct inode *inode = NULL;
        struct inodevec *ivec = NULL;
        u64 parent;
        u64 bytenr;
        u64 new_bytenr;
        u64 num_bytes;
        u64 end;
        u32 nritems;
        u32 i;
        int ret;
        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 (!ivec || ivec->nr == INODEVEC_SIZE) {
                                ivec = kmalloc(sizeof(*ivec), GFP_NOFS);
                                BUG_ON(!ivec);
                                ivec->nr = 0;
                                list_add_tail(&ivec->list, inode_list);
                        }
                        if (first) {
                                inode = find_next_inode(root, key.objectid);
                                if (inode)
                                        ivec->inode[ivec->nr++] = inode;
                                first = 0;
                        } else if (inode && inode->i_ino < key.objectid) {
                                inode = find_next_inode(root, key.objectid);
                                if (inode)
                                        ivec->inode[ivec->nr++] = inode;
                        }
                        if (inode && inode->i_ino == 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,
                                                      GFP_NOFS);
                                if (!ret)
                                        continue;

                                btrfs_drop_extent_cache(inode, key.offset, end,
                                                        1);
                                unlock_extent(&BTRFS_I(inode)->io_tree,
                                              key.offset, end, GFP_NOFS);
                        }
                }

                ret = get_new_location(rc->data_inode, &new_bytenr,
                                       bytenr, num_bytes);
                if (ret > 0)
                        continue;
                BUG_ON(ret < 0);

                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);
                BUG_ON(ret);

                ret = btrfs_free_extent(trans, root, bytenr, num_bytes,
                                        parent, btrfs_header_owner(leaf),
                                        key.objectid, key.offset);
                BUG_ON(ret);
        }
        if (dirty)
                btrfs_mark_buffer_dirty(leaf);
        return 0;
}

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 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,
                        struct extent_buffer **leaf,
                        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 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);
        BUG_ON(lowest_level > 1 && leaf);

        last_snapshot = btrfs_root_last_snapshot(&src->root_item);

        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;
        }

        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 = btrfs_level_size(dest, level - 1);
                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 (new_bytenr > 0 && new_bytenr == old_bytenr) {
                        WARN_ON(1);
                        ret = level;
                        break;
                }

                if (new_bytenr == 0 || old_ptr_gen > last_snapshot ||
                    memcmp_node_keys(parent, slot, path, level)) {
                        if (level <= lowest_level && !leaf) {
                                ret = 0;
                                break;
                        }

                        eb = read_tree_block(dest, old_bytenr, blocksize,
                                             old_ptr_gen);
                        btrfs_tree_lock(eb);
                        ret = btrfs_cow_block(trans, dest, eb, parent,
                                              slot, &eb);
                        BUG_ON(ret);
                        btrfs_set_lock_blocking(eb);

                        if (level <= lowest_level) {
                                *leaf = eb;
                                ret = 0;
                                break;
                        }

                        btrfs_tree_unlock(parent);
                        free_extent_buffer(parent);

                        parent = eb;
                        continue;
                }

                btrfs_node_key_to_cpu(path->nodes[level], &key,
                                      path->slots[level]);
                btrfs_release_path(src, 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 blocksize;
        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]);
                blocksize = btrfs_level_size(root, i - 1);
                eb = read_tree_block(root, bytenr, blocksize, ptr_gen);
                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;

        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;

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

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

                if (unlikely(min_key->objectid == inode->i_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 == inode->i_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, GFP_NOFS);
                btrfs_drop_extent_cache(inode, start, end, 1);
                unlock_extent(&BTRFS_I(inode)->io_tree, start, end, GFP_NOFS);
        }
        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;
        struct btrfs_root *reloc_root;
        struct btrfs_root_item *root_item;
        struct btrfs_path *path;
        struct extent_buffer *leaf = NULL;
        unsigned long nr;
        int level;
        int max_level;
        int replaced = 0;
        int ret;
        int err = 0;

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

        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);
        }

        if (level == 0 && rc->stage == UPDATE_DATA_PTRS) {
                trans = btrfs_start_transaction(root, 1);

                leaf = path->nodes[0];
                btrfs_item_key_to_cpu(leaf, &key, 0);
                btrfs_release_path(reloc_root, path);

                ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
                if (ret < 0) {
                        err = ret;
                        goto out;
                }

                leaf = path->nodes[0];
                btrfs_unlock_up_safe(path, 1);
                ret = replace_file_extents(trans, rc, root, leaf,
                                           &inode_list);
                if (ret < 0)
                        err = ret;
                goto out;
        }

        memset(&next_key, 0, sizeof(next_key));

        while (1) {
                leaf = NULL;
                replaced = 0;
                trans = btrfs_start_transaction(root, 1);
                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 if (level == 1 && rc->stage == UPDATE_DATA_PTRS) {
                        ret = replace_path(trans, root, reloc_root,
                                           path, &next_key, &leaf,
                                           level, max_level);
                } else {
                        ret = replace_path(trans, root, reloc_root,
                                           path, &next_key, NULL,
                                           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;
                } else if (leaf) {
                        /*
                         * no block got replaced, try replacing file extents
                         */
                        btrfs_item_key_to_cpu(leaf, &key, 0);
                        ret = replace_file_extents(trans, rc, root, leaf,
                                                   &inode_list);
                        btrfs_tree_unlock(leaf);
                        free_extent_buffer(leaf);
                        BUG_ON(ret < 0);
                }

                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;

                nr = trans->blocks_used;
                btrfs_end_transaction(trans, root);

                btrfs_btree_balance_dirty(root, nr);

                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);
        }

        nr = trans->blocks_used;
        btrfs_end_transaction(trans, root);

        btrfs_btree_balance_dirty(root, nr);

        /*
         * put inodes while we aren't holding the tree locks
         */
        while (!list_empty(&inode_list)) {
                struct inodevec *ivec;
                ivec = list_entry(inode_list.next, struct inodevec, list);
                list_del(&ivec->list);
                while (ivec->nr > 0) {
                        ivec->nr--;
                        iput(ivec->inode[ivec->nr]);
                }
                kfree(ivec);
        }

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

        return err;
}

/*
 * callback for the work threads.
 * this function merges reloc tree with corresponding fs tree,
 * and then drops the reloc tree.
 */
static void merge_func(struct btrfs_work *work)
{
        struct btrfs_trans_handle *trans;
        struct btrfs_root *root;
        struct btrfs_root *reloc_root;
        struct async_merge *async;

        async = container_of(work, struct async_merge, work);
        reloc_root = async->root;

        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);

                merge_reloc_root(async->rc, root);

                trans = btrfs_start_transaction(root, 1);
                btrfs_update_reloc_root(trans, root);
                btrfs_end_transaction(trans, root);
        }

        btrfs_drop_snapshot(reloc_root, 0);

        if (atomic_dec_and_test(async->num_pending))
                complete(async->done);

        kfree(async);
}

static int merge_reloc_roots(struct reloc_control *rc)
{
        struct async_merge *async;
        struct btrfs_root *root;
        struct completion done;
        atomic_t num_pending;

        init_completion(&done);
        atomic_set(&num_pending, 1);

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

                async = kmalloc(sizeof(*async), GFP_NOFS);
                BUG_ON(!async);
                async->work.func = merge_func;
                async->work.flags = 0;
                async->rc = rc;
                async->root = root;
                async->done = &done;
                async->num_pending = &num_pending;
                atomic_inc(&num_pending);
                btrfs_queue_worker(&rc->workers, &async->work);
        }

        if (!atomic_dec_and_test(&num_pending))
                wait_for_completion(&done);

        BUG_ON(!RB_EMPTY_ROOT(&rc->reloc_root_tree.rb_root));
        return 0;
}

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);
}

/*
 * select one tree from trees that references the block.
 * for blocks in refernce counted trees, we preper reloc tree.
 * if no reloc tree found and reloc_only is true, NULL is returned.
 */
static struct btrfs_root *__select_one_root(struct btrfs_trans_handle *trans,
                                            struct backref_node *node,
                                            struct backref_edge *edges[],
                                            int *nr, int reloc_only)
{
        struct backref_node *next;
        struct btrfs_root *root;
        int index;
        int loop = 0;
again:
        index = 0;
        next = node;
        while (1) {
                cond_resched();
                next = walk_up_backref(next, edges, &index);
                root = next->root;
                if (!root) {
                        BUG_ON(!node->old_root);
                        goto skip;
                }

                /* no other choice for non-refernce counted tree */
                if (!root->ref_cows) {
                        BUG_ON(reloc_only);
                        break;
                }

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

                if (loop) {
                        btrfs_record_root_in_trans(trans, root);
                        break;
                }

                if (reloc_only || next != node) {
                        if (!root->reloc_root)
                                btrfs_record_root_in_trans(trans, root);
                        root = root->reloc_root;
                        /*
                         * if the reloc tree was created in current
                         * transation, there is no node in backref tree
                         * corresponds to the root of the reloc tree.
                         */
                        if (btrfs_root_last_snapshot(&root->root_item) ==
                            trans->transid - 1)
                                break;
                }
skip:
                root = NULL;
                next = walk_down_backref(edges, &index);
                if (!next || next->level <= node->level)
                        break;
        }

        if (!root && !loop && !reloc_only) {
                loop = 1;
                goto again;
        }

        if (root)
                *nr = index;
        else
                *nr = 0;

        return root;
}

static noinline_for_stack
struct btrfs_root *select_one_root(struct btrfs_trans_handle *trans,
                                   struct backref_node *node)
{
        struct backref_edge *edges[BTRFS_MAX_LEVEL - 1];
        int nr;
        return __select_one_root(trans, node, edges, &nr, 0);
}

static noinline_for_stack
struct btrfs_root *select_reloc_root(struct btrfs_trans_handle *trans,
                                     struct backref_node *node,
                                     struct backref_edge *edges[], int *nr)
{
        return __select_one_root(trans, node, edges, nr, 1);
}

static void grab_path_buffers(struct btrfs_path *path,
                              struct backref_node *node,
                              struct backref_edge *edges[], int nr)
{
        int i = 0;
        while (1) {
                drop_node_buffer(node);
                node->eb = path->nodes[node->level];
                BUG_ON(!node->eb);
                if (path->locks[node->level])
                        node->locked = 1;
                path->nodes[node->level] = NULL;
                path->locks[node->level] = 0;

                if (i >= nr)
                        break;

                edges[i]->blockptr = node->eb->start;
                node = edges[i]->node[UPPER];
                i++;
        }
}

/*
 * 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 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 nr;
        int slot;
        int ret;
        int err = 0;

        BUG_ON(lowest && node->eb);

        path->lowest_level = node->level + 1;
        list_for_each_entry(edge, &node->upper, list[LOWER]) {
                cond_resched();
                if (node->eb && node->eb->start == edge->blockptr)
                        continue;

                upper = edge->node[UPPER];
                root = select_reloc_root(trans, upper, edges, &nr);
                if (!root)
                        continue;

                if (upper->eb && !upper->locked)
                        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);

                        slot = path->slots[upper->level];

                        btrfs_unlock_up_safe(path, upper->level + 1);
                        grab_path_buffers(path, upper, edges, nr);

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

                bytenr = btrfs_node_blockptr(upper->eb, slot);
                if (!lowest) {
                        if (node->eb->start == bytenr) {
                                btrfs_tree_unlock(upper->eb);
                                upper->locked = 0;
                                continue;
                        }
                } else {
                        BUG_ON(node->bytenr != bytenr);
                }

                blocksize = btrfs_level_size(root, node->level);
                generation = btrfs_node_ptr_generation(upper->eb, slot);
                eb = read_tree_block(root, bytenr, blocksize, generation);
                btrfs_tree_lock(eb);
                btrfs_set_lock_blocking(eb);

                if (!node->eb) {
                        ret = btrfs_cow_block(trans, root, eb, upper->eb,
                                              slot, &eb);
                        if (ret < 0) {
                                err = ret;
                                break;
                        }
                        btrfs_set_lock_blocking(eb);
                        node->eb = eb;
                        node->locked = 1;
                } 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);
                }
                if (!lowest) {
                        btrfs_tree_unlock(upper->eb);
                        upper->locked = 0;
                }
        }
        path->lowest_level = 0;
        return err;
}

static int link_to_upper(struct btrfs_trans_handle *trans,
                         struct backref_node *node,
                         struct btrfs_path *path)
{
        struct btrfs_key key;
        if (!node->eb || list_empty(&node->upper))
                return 0;

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

static int finish_pending_nodes(struct btrfs_trans_handle *trans,
                                struct backref_cache *cache,
                                struct btrfs_path *path)
{
        struct backref_node *node;
        int level;
        int ret;
        int err = 0;

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

                        ret = link_to_upper(trans, node, path);
                        if (ret < 0)
                                err = ret;
                        /*
                         * this remove the node from the pending list and
                         * may add some other nodes to the level + 1
                         * pending list
                         */
                        remove_backref_node(cache, node);
                }
        }
        BUG_ON(!RB_EMPTY_ROOT(&cache->rb_root));
        return err;
}

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 = btrfs_level_size(rc->extent_root, node->level);
                set_extent_bits(&rc->processed_blocks, node->bytenr,
                                node->bytenr + blocksize - 1, EXTENT_DIRTY,
                                GFP_NOFS);
        }
        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, u32 blocksize,
                                struct reloc_control *rc)
{
        if (test_range_bit(&rc->processed_blocks, bytenr,
                           bytenr + blocksize - 1, EXTENT_DIRTY, 1, NULL))
                return 1;
        return 0;
}

/*
 * check if there are any file extent pointers in the leaf point to
 * data require processing
 */
static int check_file_extents(struct reloc_control *rc,
                              u64 bytenr, u32 blocksize, u64 ptr_gen)
{
        struct btrfs_key found_key;
        struct btrfs_file_extent_item *fi;
        struct extent_buffer *leaf;
        u32 nritems;
        int i;
        int ret = 0;

        leaf = read_tree_block(rc->extent_root, bytenr, blocksize, ptr_gen);

        nritems = btrfs_header_nritems(leaf);
        for (i = 0; i < nritems; i++) {
                cond_resched();
                btrfs_item_key_to_cpu(leaf, &found_key, i);
                if (found_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);
                if (bytenr == 0)
                        continue;
                if (in_block_group(bytenr, rc->block_group)) {
                        ret = 1;
                        break;
                }
        }
        free_extent_buffer(leaf);
        return ret;
}

/*
 * scan child blocks of a given block to find blocks require processing
 */
static int add_child_blocks(struct btrfs_trans_handle *trans,
                            struct reloc_control *rc,
                            struct backref_node *node,
                            struct rb_root *blocks)
{
        struct tree_block *block;
        struct rb_node *rb_node;
        u64 bytenr;
        u64 ptr_gen;
        u32 blocksize;
        u32 nritems;
        int i;
        int err = 0;

        nritems = btrfs_header_nritems(node->eb);
        blocksize = btrfs_level_size(rc->extent_root, node->level - 1);
        for (i = 0; i < nritems; i++) {
                cond_resched();
                bytenr = btrfs_node_blockptr(node->eb, i);
                ptr_gen = btrfs_node_ptr_generation(node->eb, i);
                if (ptr_gen == trans->transid)
                        continue;
                if (!in_block_group(bytenr, rc->block_group) &&
                    (node->level > 1 || rc->stage == MOVE_DATA_EXTENTS))
                        continue;
                if (tree_block_processed(bytenr, blocksize, rc))
                        continue;

                readahead_tree_block(rc->extent_root,
                                     bytenr, blocksize, ptr_gen);
        }

        for (i = 0; i < nritems; i++) {
                cond_resched();
                bytenr = btrfs_node_blockptr(node->eb, i);
                ptr_gen = btrfs_node_ptr_generation(node->eb, i);
                if (ptr_gen == trans->transid)
                        continue;
                if (!in_block_group(bytenr, rc->block_group) &&
                    (node->level > 1 || rc->stage == MOVE_DATA_EXTENTS))
                        continue;
                if (tree_block_processed(bytenr, blocksize, rc))
                        continue;
                if (!in_block_group(bytenr, rc->block_group) &&
                    !check_file_extents(rc, bytenr, blocksize, ptr_gen))
                        continue;

                block = kmalloc(sizeof(*block), GFP_NOFS);
                if (!block) {
                        err = -ENOMEM;
                        break;
                }
                block->bytenr = bytenr;
                btrfs_node_key_to_cpu(node->eb, &block->key, i);
                block->level = node->level - 1;
                block->key_ready = 1;
                rb_node = tree_insert(blocks, block->bytenr, &block->rb_node);
                BUG_ON(rb_node);
        }
        if (err)
                free_block_list(blocks);
        return err;
}

/*
 * find adjacent blocks require processing
 */
static noinline_for_stack
int add_adjacent_blocks(struct btrfs_trans_handle *trans,
                        struct reloc_control *rc,
                        struct backref_cache *cache,
                        struct rb_root *blocks, int level,
                        struct backref_node **upper)
{
        struct backref_node *node;
        int ret = 0;

        WARN_ON(!list_empty(&cache->pending[level]));

        if (list_empty(&cache->pending[level + 1]))
                return 1;

        node = list_entry(cache->pending[level + 1].next,
                          struct backref_node, lower);
        if (node->eb)
                ret = add_child_blocks(trans, rc, node, blocks);

        *upper = node;
        return ret;
}

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.objectid, block->key.offset);
        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;
}

static int reada_tree_block(struct reloc_control *rc,
                            struct tree_block *block)
{
        BUG_ON(block->key_ready);
        readahead_tree_block(rc->extent_root, block->bytenr,
                             block->key.objectid, block->key.offset);
        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;

        root = select_one_root(trans, node);
        if (unlikely(!root)) {
                rc->found_old_snapshot = 1;
                update_processed_blocks(rc, node);
                return 0;
        }

        if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID) {
                ret = do_relocation(trans, node, key, path, 1);
                if (ret < 0)
                        goto out;
                if (node->level == 0 && rc->stage == UPDATE_DATA_PTRS) {
                        ret = replace_file_extents(trans, rc, root,
                                                   node->eb, NULL);
                        if (ret < 0)
                                goto out;
                }
                drop_node_buffer(node);
        } else if (!root->ref_cows) {
                path->lowest_level = node->level;
                ret = btrfs_search_slot(trans, root, key, path, 0, 1);
                btrfs_release_path(root, path);
                if (ret < 0)
                        goto out;
        } else if (root != node->root) {
                WARN_ON(node->level > 0 || rc->stage != UPDATE_DATA_PTRS);
        }

        update_processed_blocks(rc, node);
        ret = 0;
out:
        drop_node_buffer(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_cache *cache;
        struct backref_node *node;
        struct btrfs_path *path;
        struct tree_block *block;
        struct rb_node *rb_node;
        int level = -1;
        int ret;
        int err = 0;

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

        cache = kmalloc(sizeof(*cache), GFP_NOFS);
        if (!cache) {
                btrfs_free_path(path);
                return -ENOMEM;
        }

        backref_cache_init(cache);

        rb_node = rb_first(blocks);
        while (rb_node) {
                block = rb_entry(rb_node, struct tree_block, rb_node);
                if (level == -1)
                        level = block->level;
                else
                        BUG_ON(level != block->level);
                if (!block->key_ready)
                        reada_tree_block(rc, block);
                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)
                        get_tree_block_key(rc, block);
                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, cache, &block->key,
                                          block->level, block->bytenr);
                if (IS_ERR(node)) {
                        err = PTR_ERR(node);
                        goto out;
                }

                ret = relocate_tree_block(trans, rc, node, &block->key,
                                          path);
                if (ret < 0) {
                        err = ret;
                        goto out;
                }
                remove_backref_node(cache, node);
                rb_node = rb_next(rb_node);
        }

        if (level > 0)
                goto out;

        free_block_list(blocks);

        /*
         * now backrefs of some upper level tree blocks have been cached,
         * try relocating blocks referenced by these upper level blocks.
         */
        while (1) {
                struct backref_node *upper = NULL;
                if (trans->transaction->in_commit ||
                    trans->transaction->delayed_refs.flushing)
                        break;

                ret = add_adjacent_blocks(trans, rc, cache, blocks, level,
                                          &upper);
                if (ret < 0)
                        err = ret;
                if (ret != 0)
                        break;

                rb_node = rb_first(blocks);
                while (rb_node) {
                        block = rb_entry(rb_node, struct tree_block, rb_node);
                        if (trans->transaction->in_commit ||
                            trans->transaction->delayed_refs.flushing)
                                goto out;
                        BUG_ON(!block->key_ready);
                        node = build_backref_tree(rc, cache, &block->key,
                                                  level, block->bytenr);
                        if (IS_ERR(node)) {
                                err = PTR_ERR(node);
                                goto out;
                        }

                        ret = relocate_tree_block(trans, rc, node,
                                                  &block->key, path);
                        if (ret < 0) {
                                err = ret;
                                goto out;
                        }
                        remove_backref_node(cache, node);
                        rb_node = rb_next(rb_node);
                }
                free_block_list(blocks);

                if (upper) {
                        ret = link_to_upper(trans, upper, path);
                        if (ret < 0) {
                                err = ret;
                                break;
                        }
                        remove_backref_node(cache, upper);
                }
        }
out:
        free_block_list(blocks);

        ret = finish_pending_nodes(trans, cache, path);
        if (ret < 0)
                err = ret;

        kfree(cache);
        btrfs_free_path(path);
        return err;
}

static noinline_for_stack
int setup_extent_mapping(struct inode *inode, u64 start, u64 end,
                         u64 block_start)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
        struct extent_map *em;
        int ret = 0;

        em = alloc_extent_map(GFP_NOFS);
        if (!em)
                return -ENOMEM;

        em->start = start;
        em->len = end + 1 - start;
        em->block_len = em->len;
        em->block_start = block_start;
        em->bdev = root->fs_info->fs_devices->latest_bdev;
        set_bit(EXTENT_FLAG_PINNED, &em->flags);

        lock_extent(&BTRFS_I(inode)->io_tree, start, end, GFP_NOFS);
        while (1) {
                write_lock(&em_tree->lock);
                ret = add_extent_mapping(em_tree, em);
                write_unlock(&em_tree->lock);
                if (ret != -EEXIST) {
                        free_extent_map(em);
                        break;
                }
                btrfs_drop_extent_cache(inode, start, end, 0);
        }
        unlock_extent(&BTRFS_I(inode)->io_tree, start, end, GFP_NOFS);
        return ret;
}

static int relocate_file_extent_cluster(struct inode *inode,
                                        struct file_extent_cluster *cluster)
{
        u64 page_start;
        u64 page_end;
        u64 offset = BTRFS_I(inode)->index_cnt;
        unsigned long index;
        unsigned long last_index;
        unsigned int dirty_page = 0;
        struct page *page;
        struct file_ra_state *ra;
        int nr = 0;
        int ret = 0;

        if (!cluster->nr)
                return 0;

        ra = kzalloc(sizeof(*ra), GFP_NOFS);
        if (!ra)
                return -ENOMEM;

        index = (cluster->start - offset) >> PAGE_CACHE_SHIFT;
        last_index = (cluster->end - offset) >> PAGE_CACHE_SHIFT;

        mutex_lock(&inode->i_mutex);

        i_size_write(inode, cluster->end + 1 - offset);
        ret = setup_extent_mapping(inode, cluster->start - offset,
                                   cluster->end - offset, cluster->start);
        if (ret)
                goto out_unlock;

        file_ra_state_init(ra, inode->i_mapping);

        WARN_ON(cluster->start != cluster->boundary[0]);
        while (index <= last_index) {
                page = find_lock_page(inode->i_mapping, index);
                if (!page) {
                        page_cache_sync_readahead(inode->i_mapping,
                                                  ra, NULL, index,
                                                  last_index + 1 - index);
                        page = grab_cache_page(inode->i_mapping, index);
                        if (!page) {
                                ret = -ENOMEM;
                                goto out_unlock;
                        }
                }

                if (PageReadahead(page)) {
                        page_cache_async_readahead(inode->i_mapping,
                                                   ra, NULL, page, index,
                                                   last_index + 1 - index);
                }

                if (!PageUptodate(page)) {
                        btrfs_readpage(NULL, page);
                        lock_page(page);
                        if (!PageUptodate(page)) {
                                unlock_page(page);
                                page_cache_release(page);
                                ret = -EIO;
                                goto out_unlock;
                        }
                }

                page_start = (u64)page->index << PAGE_CACHE_SHIFT;
                page_end = page_start + PAGE_CACHE_SIZE - 1;

                lock_extent(&BTRFS_I(inode)->io_tree,
                            page_start, page_end, GFP_NOFS);

                set_page_extent_mapped(page);

                if (nr < cluster->nr &&
                    page_start + offset == cluster->boundary[nr]) {
                        set_extent_bits(&BTRFS_I(inode)->io_tree,
                                        page_start, page_end,
                                        EXTENT_BOUNDARY, GFP_NOFS);
                        nr++;
                }
                btrfs_set_extent_delalloc(inode, page_start, page_end);

                set_page_dirty(page);
                dirty_page++;

                unlock_extent(&BTRFS_I(inode)->io_tree,
                              page_start, page_end, GFP_NOFS);
                unlock_page(page);
                page_cache_release(page);

                index++;
                if (nr < cluster->nr &&
                    page_end + 1 + offset == cluster->boundary[nr]) {
                        balance_dirty_pages_ratelimited_nr(inode->i_mapping,
                                                           dirty_page);
                        dirty_page = 0;
                }
        }
        if (dirty_page) {
                balance_dirty_pages_ratelimited_nr(inode->i_mapping,
                                                   dirty_page);
        }
        WARN_ON(nr != cluster->nr);
out_unlock:
        mutex_unlock(&inode->i_mutex);
        kfree(ra);
        return ret;
}

static noinline_for_stack
int relocate_data_extent(struct inode *inode, struct btrfs_key *extent_key,
                         struct file_extent_cluster *cluster)
{
        int ret;

        if (cluster->nr > 0 && extent_key->objectid != cluster->end + 1) {
                ret = relocate_file_extent_cluster(inode, cluster);
                if (ret)
                        return ret;
                cluster->nr = 0;
        }

        if (!cluster->nr)
                cluster->start = extent_key->objectid;
        else
                BUG_ON(cluster->nr >= MAX_EXTENTS);
        cluster->end = extent_key->objectid + extent_key->offset - 1;
        cluster->boundary[cluster->nr] = extent_key->objectid;
        cluster->nr++;

        if (cluster->nr >= MAX_EXTENTS) {
                ret = relocate_file_extent_cluster(inode, cluster);
                if (ret)
                        return ret;
                cluster->nr = 0;
        }
        return 0;
}

#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
static int get_ref_objectid_v0(struct reloc_control *rc,
                               struct btrfs_path *path,
                               struct btrfs_key *extent_key,
                               u64 *ref_objectid, int *path_change)
{
        struct btrfs_key key;
        struct extent_buffer *leaf;
        struct btrfs_extent_ref_v0 *ref0;
        int ret;
        int slot;

        leaf = path->nodes[0];
        slot = path->slots[0];
        while (1) {
                if (slot >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(rc->extent_root, path);
                        if (ret < 0)
                                return ret;
                        BUG_ON(ret > 0);
                        leaf = path->nodes[0];
                        slot = path->slots[0];
                        if (path_change)
                                *path_change = 1;
                }
                btrfs_item_key_to_cpu(leaf, &key, slot);
                if (key.objectid != extent_key->objectid)
                        return -ENOENT;

                if (key.type != BTRFS_EXTENT_REF_V0_KEY) {
                        slot++;
                        continue;
                }
                ref0 = btrfs_item_ptr(leaf, slot,
                                struct btrfs_extent_ref_v0);
                *ref_objectid = btrfs_ref_objectid_v0(leaf, ref0);
                break;
        }
        return 0;
}
#endif

/*
 * helper to add a tree block to the list.
 * the major work is getting the generation and level of the block
 */
static int add_tree_block(struct reloc_control *rc,
                          struct btrfs_key *extent_key,
                          struct btrfs_path *path,
                          struct rb_root *blocks)
{
        struct extent_buffer *eb;
        struct btrfs_extent_item *ei;
        struct btrfs_tree_block_info *bi;
        struct tree_block *block;
        struct rb_node *rb_node;
        u32 item_size;
        int level = -1;
        int generation;

        eb =  path->nodes[0];
        item_size = btrfs_item_size_nr(eb, path->slots[0]);

        if (item_size >= sizeof(*ei) + sizeof(*bi)) {
                ei = btrfs_item_ptr(eb, path->slots[0],
                                struct btrfs_extent_item);
                bi = (struct btrfs_tree_block_info *)(ei + 1);
                generation = btrfs_extent_generation(eb, ei);
                level = btrfs_tree_block_level(eb, bi);
        } else {
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
                u64 ref_owner;
                int ret;

                BUG_ON(item_size != sizeof(struct btrfs_extent_item_v0));
                ret = get_ref_objectid_v0(rc, path, extent_key,
                                          &ref_owner, NULL);
                BUG_ON(ref_owner >= BTRFS_MAX_LEVEL);
                level = (int)ref_owner;
                /* FIXME: get real generation */
                generation = 0;
#else
                BUG();
#endif
        }

        btrfs_release_path(rc->extent_root, path);

        BUG_ON(level == -1);

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

        block->bytenr = extent_key->objectid;
        block->key.objectid = extent_key->offset;
        block->key.offset = generation;
        block->level = level;
        block->key_ready = 0;

        rb_node = tree_insert(blocks, block->bytenr, &block->rb_node);
        BUG_ON(rb_node);

        return 0;
}

/*
 * helper to add tree blocks for backref of type BTRFS_SHARED_DATA_REF_KEY
 */
static int __add_tree_block(struct reloc_control *rc,
                            u64 bytenr, u32 blocksize,
                            struct rb_root *blocks)
{
        struct btrfs_path *path;
        struct btrfs_key key;
        int ret;

        if (tree_block_processed(bytenr, blocksize, rc))
                return 0;

        if (tree_search(blocks, bytenr))
                return 0;

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

        key.objectid = bytenr;
        key.type = BTRFS_EXTENT_ITEM_KEY;
        key.offset = blocksize;

        path->search_commit_root = 1;
        path->skip_locking = 1;
        ret = btrfs_search_slot(NULL, rc->extent_root, &key, path, 0, 0);
        if (ret < 0)
                goto out;
        BUG_ON(ret);

        btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
        ret = add_tree_block(rc, &key, path, blocks);
out:
        btrfs_free_path(path);
        return ret;
}

/*
 * helper to check if the block use full backrefs for pointers in it
 */
static int block_use_full_backref(struct reloc_control *rc,
                                  struct extent_buffer *eb)
{
        struct btrfs_path *path;
        struct btrfs_extent_item *ei;
        struct btrfs_key key;
        u64 flags;
        int ret;

        if (btrfs_header_flag(eb, BTRFS_HEADER_FLAG_RELOC) ||
            btrfs_header_backref_rev(eb) < BTRFS_MIXED_BACKREF_REV)
                return 1;

        path = btrfs_alloc_path();
        BUG_ON(!path);

        key.objectid = eb->start;
        key.type = BTRFS_EXTENT_ITEM_KEY;
        key.offset = eb->len;

        path->search_commit_root = 1;
        path->skip_locking = 1;
        ret = btrfs_search_slot(NULL, rc->extent_root,
                                &key, path, 0, 0);
        BUG_ON(ret);

        ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
                            struct btrfs_extent_item);
        flags = btrfs_extent_flags(path->nodes[0], ei);
        BUG_ON(!(flags & BTRFS_EXTENT_FLAG_TREE_BLOCK));
        if (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF)
                ret = 1;
        else
                ret = 0;
        btrfs_free_path(path);
        return ret;
}

/*
 * helper to add tree blocks for backref of type BTRFS_EXTENT_DATA_REF_KEY
 * this function scans fs tree to find blocks reference the data extent
 */
static int find_data_references(struct reloc_control *rc,
                                struct btrfs_key *extent_key,
                                struct extent_buffer *leaf,
                                struct btrfs_extent_data_ref *ref,
                                struct rb_root *blocks)
{
        struct btrfs_path *path;
        struct tree_block *block;
        struct btrfs_root *root;
        struct btrfs_file_extent_item *fi;
        struct rb_node *rb_node;
        struct btrfs_key key;
        u64 ref_root;
        u64 ref_objectid;
        u64 ref_offset;
        u32 ref_count;
        u32 nritems;
        int err = 0;
        int added = 0;
        int counted;
        int ret;

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

        ref_root = btrfs_extent_data_ref_root(leaf, ref);
        ref_objectid = btrfs_extent_data_ref_objectid(leaf, ref);
        ref_offset = btrfs_extent_data_ref_offset(leaf, ref);
        ref_count = btrfs_extent_data_ref_count(leaf, ref);

        root = read_fs_root(rc->extent_root->fs_info, ref_root);
        if (IS_ERR(root)) {
                err = PTR_ERR(root);
                goto out;
        }

        key.objectid = ref_objectid;
        key.offset = ref_offset;
        key.type = BTRFS_EXTENT_DATA_KEY;

        path->search_commit_root = 1;
        path->skip_locking = 1;
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0) {
                err = ret;
                goto out;
        }

        leaf = path->nodes[0];
        nritems = btrfs_header_nritems(leaf);
        /*
         * the references in tree blocks that use full backrefs
         * are not counted in
         */
        if (block_use_full_backref(rc, leaf))
                counted = 0;
        else
                counted = 1;
        rb_node = tree_search(blocks, leaf->start);
        if (rb_node) {
                if (counted)
                        added = 1;
                else
                        path->slots[0] = nritems;
        }

        while (ref_count > 0) {
                while (path->slots[0] >= nritems) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0) {
                                err = ret;
                                goto out;
                        }
                        if (ret > 0) {
                                WARN_ON(1);
                                goto out;
                        }

                        leaf = path->nodes[0];
                        nritems = btrfs_header_nritems(leaf);
                        added = 0;

                        if (block_use_full_backref(rc, leaf))
                                counted = 0;
                        else
                                counted = 1;
                        rb_node = tree_search(blocks, leaf->start);
                        if (rb_node) {
                                if (counted)
                                        added = 1;
                                else
                                        path->slots[0] = nritems;
                        }
                }

                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);