/*
 * 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/slab.h>
#include <linux/sort.h>
#include "ctree.h"
#include "delayed-ref.h"
#include "transaction.h"

/*
 * delayed back reference update tracking.  For subvolume trees
 * we queue up extent allocations and backref maintenance for
 * delayed processing.   This avoids deep call chains where we
 * add extents in the middle of btrfs_search_slot, and it allows
 * us to buffer up frequently modified backrefs in an rb tree instead
 * of hammering updates on the extent allocation tree.
 */

/*
 * compare two delayed tree backrefs with same bytenr and type
 */
static int comp_tree_refs(struct btrfs_delayed_tree_ref *ref2,
                          struct btrfs_delayed_tree_ref *ref1)
{
        if (ref1->node.type == BTRFS_TREE_BLOCK_REF_KEY) {
                if (ref1->root < ref2->root)
                        return -1;
                if (ref1->root > ref2->root)
                        return 1;
        } else {
                if (ref1->parent < ref2->parent)
                        return -1;
                if (ref1->parent > ref2->parent)
                        return 1;
        }
        return 0;
}

/*
 * compare two delayed data backrefs with same bytenr and type
 */
static int comp_data_refs(struct btrfs_delayed_data_ref *ref2,
                          struct btrfs_delayed_data_ref *ref1)
{
        if (ref1->node.type == BTRFS_EXTENT_DATA_REF_KEY) {
                if (ref1->root < ref2->root)
                        return -1;
                if (ref1->root > ref2->root)
                        return 1;
                if (ref1->objectid < ref2->objectid)
                        return -1;
                if (ref1->objectid > ref2->objectid)
                        return 1;
                if (ref1->offset < ref2->offset)
                        return -1;
                if (ref1->offset > ref2->offset)
                        return 1;
        } else {
                if (ref1->parent < ref2->parent)
                        return -1;
                if (ref1->parent > ref2->parent)
                        return 1;
        }
        return 0;
}

/*
 * entries in the rb tree are ordered by the byte number of the extent,
 * type of the delayed backrefs and content of delayed backrefs.
 */
static int comp_entry(struct btrfs_delayed_ref_node *ref2,
                      struct btrfs_delayed_ref_node *ref1)
{
        if (ref1->bytenr < ref2->bytenr)
                return -1;
        if (ref1->bytenr > ref2->bytenr)
                return 1;
        if (ref1->is_head && ref2->is_head)
                return 0;
        if (ref2->is_head)
                return -1;
        if (ref1->is_head)
                return 1;
        if (ref1->type < ref2->type)
                return -1;
        if (ref1->type > ref2->type)
                return 1;
        if (ref1->type == BTRFS_TREE_BLOCK_REF_KEY ||
            ref1->type == BTRFS_SHARED_BLOCK_REF_KEY) {
                return comp_tree_refs(btrfs_delayed_node_to_tree_ref(ref2),
                                      btrfs_delayed_node_to_tree_ref(ref1));
        } else if (ref1->type == BTRFS_EXTENT_DATA_REF_KEY ||
                   ref1->type == BTRFS_SHARED_DATA_REF_KEY) {
                return comp_data_refs(btrfs_delayed_node_to_data_ref(ref2),
                                      btrfs_delayed_node_to_data_ref(ref1));
        }
        BUG();
        return 0;
}

/*
 * insert a new ref into the rbtree.  This returns any existing refs
 * for the same (bytenr,parent) tuple, or NULL if the new node was properly
 * inserted.
 */
static struct btrfs_delayed_ref_node *tree_insert(struct rb_root *root,
                                                  struct rb_node *node)
{
        struct rb_node **p = &root->rb_node;
        struct rb_node *parent_node = NULL;
        struct btrfs_delayed_ref_node *entry;
        struct btrfs_delayed_ref_node *ins;
        int cmp;

        ins = rb_entry(node, struct btrfs_delayed_ref_node, rb_node);
        while (*p) {
                parent_node = *p;
                entry = rb_entry(parent_node, struct btrfs_delayed_ref_node,
                                 rb_node);

                cmp = comp_entry(entry, ins);
                if (cmp < 0)
                        p = &(*p)->rb_left;
                else if (cmp > 0)
                        p = &(*p)->rb_right;
                else
                        return entry;
        }

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

/*
 * find an head entry based on bytenr. This returns the delayed ref
 * head if it was able to find one, or NULL if nothing was in that spot
 */
static struct btrfs_delayed_ref_node *find_ref_head(struct rb_root *root,
                                  u64 bytenr,
                                  struct btrfs_delayed_ref_node **last)
{
        struct rb_node *n = root->rb_node;
        struct btrfs_delayed_ref_node *entry;
        int cmp;

        while (n) {
                entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
                WARN_ON(!entry->in_tree);
                if (last)
                        *last = entry;

                if (bytenr < entry->bytenr)
                        cmp = -1;
                else if (bytenr > entry->bytenr)
                        cmp = 1;
                else if (!btrfs_delayed_ref_is_head(entry))
                        cmp = 1;
                else
                        cmp = 0;

                if (cmp < 0)
                        n = n->rb_left;
                else if (cmp > 0)
                        n = n->rb_right;
                else
                        return entry;
        }
        return NULL;
}

int btrfs_delayed_ref_lock(struct btrfs_trans_handle *trans,
                           struct btrfs_delayed_ref_head *head)
{
        struct btrfs_delayed_ref_root *delayed_refs;

        delayed_refs = &trans->transaction->delayed_refs;
        assert_spin_locked(&delayed_refs->lock);
        if (mutex_trylock(&head->mutex))
                return 0;

        atomic_inc(&head->node.refs);
        spin_unlock(&delayed_refs->lock);

        mutex_lock(&head->mutex);
        spin_lock(&delayed_refs->lock);
        if (!head->node.in_tree) {
                mutex_unlock(&head->mutex);
                btrfs_put_delayed_ref(&head->node);
                return -EAGAIN;
        }
        btrfs_put_delayed_ref(&head->node);
        return 0;
}

int btrfs_find_ref_cluster(struct btrfs_trans_handle *trans,
                           struct list_head *cluster, u64 start)
{
        int count = 0;
        struct btrfs_delayed_ref_root *delayed_refs;
        struct rb_node *node;
        struct btrfs_delayed_ref_node *ref;
        struct btrfs_delayed_ref_head *head;

        delayed_refs = &trans->transaction->delayed_refs;
        if (start == 0) {
                node = rb_first(&delayed_refs->root);
        } else {
                ref = NULL;
                find_ref_head(&delayed_refs->root, start, &ref);
                if (ref) {
                        struct btrfs_delayed_ref_node *tmp;

                        node = rb_prev(&ref->rb_node);
                        while (node) {
                                tmp = rb_entry(node,
                                               struct btrfs_delayed_ref_node,
                                               rb_node);
                                if (tmp->bytenr < start)
                                        break;
                                ref = tmp;
                                node = rb_prev(&ref->rb_node);
                        }
                        node = &ref->rb_node;
                } else
                        node = rb_first(&delayed_refs->root);
        }
again:
        while (node && count < 32) {
                ref = rb_entry(node, struct btrfs_delayed_ref_node, rb_node);
                if (btrfs_delayed_ref_is_head(ref)) {
                        head = btrfs_delayed_node_to_head(ref);
                        if (list_empty(&head->cluster)) {
                                list_add_tail(&head->cluster, cluster);
                                delayed_refs->run_delayed_start =
                                        head->node.bytenr;
                                count++;

                                WARN_ON(delayed_refs->num_heads_ready == 0);
                                delayed_refs->num_heads_ready--;
                        } else if (count) {
                                /* the goal of the clustering is to find extents
                                 * that are likely to end up in the same extent
                                 * leaf on disk.  So, we don't want them spread
                                 * all over the tree.  Stop now if we've hit
                                 * a head that was already in use
                                 */
                                break;
                        }
                }
                node = rb_next(node);
        }
        if (count) {
                return 0;
        } else if (start) {
                /*
                 * we've gone to the end of the rbtree without finding any
                 * clusters.  start from the beginning and try again
                 */
                start = 0;
                node = rb_first(&delayed_refs->root);
                goto again;
        }
        return 1;
}

/*
 * This checks to see if there are any delayed refs in the
 * btree for a given bytenr.  It returns one if it finds any
 * and zero otherwise.
 *
 * If it only finds a head node, it returns 0.
 *
 * The idea is to use this when deciding if you can safely delete an
 * extent from the extent allocation tree.  There may be a pending
 * ref in the rbtree that adds or removes references, so as long as this
 * returns one you need to leave the BTRFS_EXTENT_ITEM in the extent
 * allocation tree.
 */
int btrfs_delayed_ref_pending(struct btrfs_trans_handle *trans, u64 bytenr)
{
        struct btrfs_delayed_ref_node *ref;
        struct btrfs_delayed_ref_root *delayed_refs;
        struct rb_node *prev_node;
        int ret = 0;

        delayed_refs = &trans->transaction->delayed_refs;
        spin_lock(&delayed_refs->lock);

        ref = find_ref_head(&delayed_refs->root, bytenr, NULL);
        if (ref) {
                prev_node = rb_prev(&ref->rb_node);
                if (!prev_node)
                        goto out;
                ref = rb_entry(prev_node, struct btrfs_delayed_ref_node,
                               rb_node);
                if (ref->bytenr == bytenr)
                        ret = 1;
        }
out:
        spin_unlock(&delayed_refs->lock);
        return ret;
}

/*
 * helper function to update an extent delayed ref in the
 * rbtree.  existing and update must both have the same
 * bytenr and parent
 *
 * This may free existing if the update cancels out whatever
 * operation it was doing.
 */
static noinline void
update_existing_ref(struct btrfs_trans_handle *trans,
                    struct btrfs_delayed_ref_root *delayed_refs,
                    struct btrfs_delayed_ref_node *existing,
                    struct btrfs_delayed_ref_node *update)
{
        if (update->action != existing->action) {
                /*
                 * this is effectively undoing either an add or a
                 * drop.  We decrement the ref_mod, and if it goes
                 * down to zero we just delete the entry without
                 * every changing the extent allocation tree.
                 */
                existing->ref_mod--;
                if (existing->ref_mod == 0) {
                        rb_erase(&existing->rb_node,
                                 &delayed_refs->root);
                        existing->in_tree = 0;
                        btrfs_put_delayed_ref(existing);
                        delayed_refs->num_entries--;
                        if (trans->delayed_ref_updates)
                                trans->delayed_ref_updates--;
                } else {
                        WARN_ON(existing->type == BTRFS_TREE_BLOCK_REF_KEY ||
                                existing->type == BTRFS_SHARED_BLOCK_REF_KEY);
                }
        } else {
                WARN_ON(existing->type == BTRFS_TREE_BLOCK_REF_KEY ||
                        existing->type == BTRFS_SHARED_BLOCK_REF_KEY);
                /*
                 * the action on the existing ref matches
                 * the action on the ref we're trying to add.
                 * Bump the ref_mod by one so the backref that
                 * is eventually added/removed has the correct
                 * reference count
                 */
                existing->ref_mod += update->ref_mod;
        }
}

/*
 * helper function to update the accounting in the head ref
 * existing and update must have the same bytenr
 */
static noinline void
update_existing_head_ref(struct btrfs_delayed_ref_node *existing,
                         struct btrfs_delayed_ref_node *update)
{
        struct btrfs_delayed_ref_head *existing_ref;
        struct btrfs_delayed_ref_head *ref;

        existing_ref = btrfs_delayed_node_to_head(existing);
        ref = btrfs_delayed_node_to_head(update);
        BUG_ON(existing_ref->is_data != ref->is_data);

        if (ref->must_insert_reserved) {
                /* if the extent was freed and then
                 * reallocated before the delayed ref
                 * entries were processed, we can end up
                 * with an existing head ref without
                 * the must_insert_reserved flag set.
                 * Set it again here
                 */
                existing_ref->must_insert_reserved = ref->must_insert_reserved;

                /*
                 * update the num_bytes so we make sure the accounting
                 * is done correctly
                 */
                existing->num_bytes = update->num_bytes;

        }

        if (ref->extent_op) {
                if (!existing_ref->extent_op) {
                        existing_ref->extent_op = ref->extent_op;
                } else {
                        if (ref->extent_op->update_key) {
                                memcpy(&existing_ref->extent_op->key,
                                       &ref->extent_op->key,
                                       sizeof(ref->extent_op->key));
                                existing_ref->extent_op->update_key = 1;
                        }
                        if (ref->extent_op->update_flags) {
                                existing_ref->extent_op->flags_to_set |=
                                        ref->extent_op->flags_to_set;
                                existing_ref->extent_op->update_flags = 1;
                        }
                        kfree(ref->extent_op);
                }
        }
        /*
         * update the reference mod on the head to reflect this new operation
         */
        existing->ref_mod += update->ref_mod;
}

/*
 * helper function to actually insert a head node into the rbtree.
 * this does all the dirty work in terms of maintaining the correct
 * overall modification count.
 */
static noinline int add_delayed_ref_head(struct btrfs_trans_handle *trans,
                                        struct btrfs_delayed_ref_node *ref,
                                        u64 bytenr, u64 num_bytes,
                                        int action, int is_data)
{
        struct btrfs_delayed_ref_node *existing;
        struct btrfs_delayed_ref_head *head_ref = NULL;
        struct btrfs_delayed_ref_root *delayed_refs;
        int count_mod = 1;
        int must_insert_reserved = 0;

        /*
         * the head node stores the sum of all the mods, so dropping a ref
         * should drop the sum in the head node by one.
         */
        if (action == BTRFS_UPDATE_DELAYED_HEAD)
                count_mod = 0;
        else if (action == BTRFS_DROP_DELAYED_REF)
                count_mod = -1;

        /*
         * BTRFS_ADD_DELAYED_EXTENT means that we need to update
         * the reserved accounting when the extent is finally added, or
         * if a later modification deletes the delayed ref without ever
         * inserting the extent into the extent allocation tree.
         * ref->must_insert_reserved is the flag used to record
         * that accounting mods are required.
         *
         * Once we record must_insert_reserved, switch the action to
         * BTRFS_ADD_DELAYED_REF because other special casing is not required.
         */
        if (action == BTRFS_ADD_DELAYED_EXTENT)
                must_insert_reserved = 1;
        else
                must_insert_reserved = 0;

        delayed_refs = &trans->transaction->delayed_refs;

        /* first set the basic ref node struct up */
        atomic_set(&ref->refs, 1);
        ref->bytenr = bytenr;
        ref->num_bytes = num_bytes;
        ref->ref_mod = count_mod;
        ref->type  = 0;
        ref->action  = 0;
        ref->is_head = 1;
        ref->in_tree = 1;

        head_ref = btrfs_delayed_node_to_head(ref);
        head_ref->must_insert_reserved = must_insert_reserved;
        head_ref->is_data = is_data;

        INIT_LIST_HEAD(&head_ref->cluster);
        mutex_init(&head_ref->mutex);

        existing = tree_insert(&delayed_refs->root, &ref->rb_node);

        if (existing) {
                update_existing_head_ref(existing, ref);
                /*
                 * we've updated the existing ref, free the newly
                 * allocated ref
                 */
                kfree(ref);
        } else {
                delayed_refs->num_heads++;
                delayed_refs->num_heads_ready++;
                delayed_refs->num_entries++;
                trans->delayed_ref_updates++;
        }
        return 0;
}

/*
 * helper to insert a delayed tree ref into the rbtree.
 */
static noinline int add_delayed_tree_ref(struct btrfs_trans_handle *trans,
                                         struct btrfs_delayed_ref_node *ref,
                                         u64 bytenr, u64 num_bytes, u64 parent,
                                         u64 ref_root, int level, int action)
{
        struct btrfs_delayed_ref_node *existing;
        struct btrfs_delayed_tree_ref *full_ref;
        struct btrfs_delayed_ref_root *delayed_refs;

        if (action == BTRFS_ADD_DELAYED_EXTENT)
                action = BTRFS_ADD_DELAYED_REF;

        delayed_refs = &trans->transaction->delayed_refs;

        /* first set the basic ref node struct up */
        atomic_set(&ref->refs, 1);
        ref->bytenr = bytenr;
        ref->num_bytes = num_bytes;
        ref->ref_mod = 1;
        ref->action = action;
        ref->is_head = 0;
        ref->in_tree = 1;

        full_ref = btrfs_delayed_node_to_tree_ref(ref);
        if (parent) {
                full_ref->parent = parent;
                ref->type = BTRFS_SHARED_BLOCK_REF_KEY;
        } else {
                full_ref->root = ref_root;
                ref->type = BTRFS_TREE_BLOCK_REF_KEY;
        }
        full_ref->level = level;

        existing = tree_insert(&delayed_refs->root, &ref->rb_node);

        if (existing) {
                update_existing_ref(trans, delayed_refs, existing, ref);
                /*
                 * we've updated the existing ref, free the newly
                 * allocated ref
                 */
                kfree(ref);
        } else {
                delayed_refs->num_entries++;
                trans->delayed_ref_updates++;
        }
        return 0;
}

/*
 * helper to insert a delayed data ref into the rbtree.
 */
static noinline int add_delayed_data_ref(struct btrfs_trans_handle *trans,
                                         struct btrfs_delayed_ref_node *ref,
                                         u64 bytenr, u64 num_bytes, u64 parent,
                                         u64 ref_root, u64 owner, u64 offset,
                                         int action)
{
        struct btrfs_delayed_ref_node *existing;
        struct btrfs_delayed_data_ref *full_ref;
        struct btrfs_delayed_ref_root *delayed_refs;

        if (action == BTRFS_ADD_DELAYED_EXTENT)
                action = BTRFS_ADD_DELAYED_REF;

        delayed_refs = &trans->transaction->delayed_refs;

        /* first set the basic ref node struct up */
        atomic_set(&ref->refs, 1);
        ref->bytenr = bytenr;
        ref->num_bytes = num_bytes;
        ref->ref_mod = 1;
        ref->action = action;
        ref->is_head = 0;
        ref->in_tree = 1;

        full_ref = btrfs_delayed_node_to_data_ref(ref);
        if (parent) {
                full_ref->parent = parent;
                ref->type = BTRFS_SHARED_DATA_REF_KEY;
        } else {
                full_ref->root = ref_root;
                ref->type = BTRFS_EXTENT_DATA_REF_KEY;
        }
        full_ref->objectid = owner;
        full_ref->offset = offset;

        existing = tree_insert(&delayed_refs->root, &ref->rb_node);

        if (existing) {
                update_existing_ref(trans, delayed_refs, existing, ref);
                /*
                 * we've updated the existing ref, free the newly
                 * allocated ref
                 */
                kfree(ref);
        } else {
                delayed_refs->num_entries++;
                trans->delayed_ref_updates++;
        }
        return 0;
}

/*
 * add a delayed tree ref.  This does all of the accounting required
 * to make sure the delayed ref is eventually processed before this
 * transaction commits.
 */
int btrfs_add_delayed_tree_ref(struct btrfs_trans_handle *trans,
                               u64 bytenr, u64 num_bytes, u64 parent,
                               u64 ref_root,  int level, int action,
                               struct btrfs_delayed_extent_op *extent_op)
{
        struct btrfs_delayed_tree_ref *ref;
        struct btrfs_delayed_ref_head *head_ref;
        struct btrfs_delayed_ref_root *delayed_refs;
        int ret;

        BUG_ON(extent_op && extent_op->is_data);
        ref = kmalloc(sizeof(*ref), GFP_NOFS);
        if (!ref)
                return -ENOMEM;

        head_ref = kmalloc(sizeof(*head_ref), GFP_NOFS);
        if (!head_ref) {
                kfree(ref);
                return -ENOMEM;
        }

        head_ref->extent_op = extent_op;

        delayed_refs = &trans->transaction->delayed_refs;
        spin_lock(&delayed_refs->lock);

        /*
         * insert both the head node and the new ref without dropping
         * the spin lock
         */
        ret = add_delayed_ref_head(trans, &head_ref->node, bytenr, num_bytes,
                                   action, 0);
        BUG_ON(ret);

        ret = add_delayed_tree_ref(trans, &ref->node, bytenr, num_bytes,
                                   parent, ref_root, level, action);
        BUG_ON(ret);
        spin_unlock(&delayed_refs->lock);
        return 0;
}

/*
 * add a delayed data ref. it's similar to btrfs_add_delayed_tree_ref.
 */
int btrfs_add_delayed_data_ref(struct btrfs_trans_handle *trans,
                               u64 bytenr, u64 num_bytes,
                               u64 parent, u64 ref_root,
                               u64 owner, u64 offset, int action,
                               struct btrfs_delayed_extent_op *extent_op)
{
        struct btrfs_delayed_data_ref *ref;
        struct btrfs_delayed_ref_head *head_ref;
        struct btrfs_delayed_ref_root *delayed_refs;
        int ret;

        BUG_ON(extent_op && !extent_op->is_data);
        ref = kmalloc(sizeof(*ref), GFP_NOFS);
        if (!ref)
                return -ENOMEM;

        head_ref = kmalloc(sizeof(*head_ref), GFP_NOFS);
        if (!head_ref) {
                kfree(ref);
                return -ENOMEM;
        }

        head_ref->extent_op = extent_op;

        delayed_refs = &trans->transaction->delayed_refs;
        spin_lock(&delayed_refs->lock);

        /*
         * insert both the head node and the new ref without dropping
         * the spin lock
         */
        ret = add_delayed_ref_head(trans, &head_ref->node, bytenr, num_bytes,
                                   action, 1);
        BUG_ON(ret);

        ret = add_delayed_data_ref(trans, &ref->node, bytenr, num_bytes,
                                   parent, ref_root, owner, offset, action);
        BUG_ON(ret);
        spin_unlock(&delayed_refs->lock);
        return 0;
}

int btrfs_add_delayed_extent_op(struct btrfs_trans_handle *trans,
                                u64 bytenr, u64 num_bytes,
                                struct btrfs_delayed_extent_op *extent_op)
{
        struct btrfs_delayed_ref_head *head_ref;
        struct btrfs_delayed_ref_root *delayed_refs;
        int ret;

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

        head_ref->extent_op = extent_op;

        delayed_refs = &trans->transaction->delayed_refs;
        spin_lock(&delayed_refs->lock);

        ret = add_delayed_ref_head(trans, &head_ref->node, bytenr,
                                   num_bytes, BTRFS_UPDATE_DELAYED_HEAD,
                                   extent_op->is_data);
        BUG_ON(ret);

        spin_unlock(&delayed_refs->lock);
        return 0;
}

/*
 * this does a simple search for the head node for a given extent.
 * It must be called with the delayed ref spinlock held, and it returns
 * the head node if any where found, or NULL if not.
 */
struct btrfs_delayed_ref_head *
btrfs_find_delayed_ref_head(struct btrfs_trans_handle *trans, u64 bytenr)
{
        struct btrfs_delayed_ref_node *ref;
        struct btrfs_delayed_ref_root *delayed_refs;

        delayed_refs = &trans->transaction->delayed_refs;
        ref = find_ref_head(&delayed_refs->root, bytenr, NULL);
        if (ref)
                return btrfs_delayed_node_to_head(ref);
        return NULL;
}

/*
 * add a delayed ref to the tree.  This does all of the accounting required
 * to make sure the delayed ref is eventually processed before this
 * transaction commits.
 *
 * The main point of this call is to add and remove a backreference in a single
 * shot, taking the lock only once, and only searching for the head node once.
 *
 * It is the same as doing a ref add and delete in two separate calls.
 */
#if 0
int btrfs_update_delayed_ref(struct btrfs_trans_handle *trans,
                          u64 bytenr, u64 num_bytes, u64 orig_parent,
                          u64 parent, u64 orig_ref_root, u64 ref_root,
                          u64 orig_ref_generation, u64 ref_generation,
                          u64 owner_objectid, int pin)
{
        struct btrfs_delayed_ref *ref;
        struct btrfs_delayed_ref *old_ref;
        struct btrfs_delayed_ref_head *head_ref;
        struct btrfs_delayed_ref_root *delayed_refs;
        int ret;

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

        old_ref = kmalloc(sizeof(*old_ref), GFP_NOFS);
        if (!old_ref) {
                kfree(ref);
                return -ENOMEM;
        }

        /*
         * the parent = 0 case comes from cases where we don't actually
         * know the parent yet.  It will get updated later via a add/drop
         * pair.
         */
        if (parent == 0)
                parent = bytenr;
        if (orig_parent == 0)
                orig_parent = bytenr;

        head_ref = kmalloc(sizeof(*head_ref), GFP_NOFS);
        if (!head_ref) {
                kfree(ref);
                kfree(old_ref);
                return -ENOMEM;
        }
        delayed_refs = &trans->transaction->delayed_refs;
        spin_lock(&delayed_refs->lock);

        /*
         * insert both the head node and the new ref without dropping
         * the spin lock
         */
        ret = __btrfs_add_delayed_ref(trans, &head_ref->node, bytenr, num_bytes,
                                      (u64)-1, 0, 0, 0,
                                      BTRFS_UPDATE_DELAYED_HEAD, 0);
        BUG_ON(ret);

        ret = __btrfs_add_delayed_ref(trans, &ref->node, bytenr, num_bytes,
                                      parent, ref_root, ref_generation,
                                      owner_objectid, BTRFS_ADD_DELAYED_REF, 0);
        BUG_ON(ret);

        ret = __btrfs_add_delayed_ref(trans, &old_ref->node, bytenr, num_bytes,
                                      orig_parent, orig_ref_root,
                                      orig_ref_generation, owner_objectid,
                                      BTRFS_DROP_DELAYED_REF, pin);
        BUG_ON(ret);
        spin_unlock(&delayed_refs->lock);
        return 0;
}
#endif