text: /*
   * 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;
  	/* merging of sequenced refs is not allowed */
  	if (ref1->seq < ref2->seq)
  		return -1;
  	if (ref1->seq > ref2->seq)
  		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.
   * If return_bigger is given, the next bigger entry is returned if no exact
   * match is found.
   */
  static struct btrfs_delayed_ref_node *find_ref_head(struct rb_root *root,
  				  u64 bytenr,
  				  struct btrfs_delayed_ref_node **last,
  				  int return_bigger)
  {
  	struct rb_node *n;
  	struct btrfs_delayed_ref_node *entry;
  	int cmp = 0;
  
  again:
  	n = root->rb_node;
  	entry = NULL;
  	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;
  	}
  	if (entry && return_bigger) {
  		if (cmp > 0) {
  			n = rb_next(&entry->rb_node);
  			if (!n)
  				n = rb_first(root);
  			entry = rb_entry(n, struct btrfs_delayed_ref_node,
  					 rb_node);
  			bytenr = entry->bytenr;
  			return_bigger = 0;
  			goto again;
  		}
  		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_check_delayed_seq(struct btrfs_delayed_ref_root *delayed_refs,
  			    u64 seq)
  {
  	struct seq_list *elem;
  
  	assert_spin_locked(&delayed_refs->lock);
  	if (list_empty(&delayed_refs->seq_head))
  		return 0;
  
  	elem = list_first_entry(&delayed_refs->seq_head, struct seq_list, list);
  	if (seq >= elem->seq) {
  		pr_debug("holding back delayed_ref %llu, lowest is %llu (%p)\n",
  			 seq, elem->seq, delayed_refs);
  		return 1;
  	}
  	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 + 1, &ref, 1);
  		if (ref) {
  			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;
  }
  
  /*
   * 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_fs_info *fs_info,
  					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;
  	ref->seq = 0;
  
  	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);
  
  	trace_btrfs_delayed_ref_head(ref, head_ref, action);
  
  	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_fs_info *fs_info,
  					 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,
  					 int for_cow)
  {
  	struct btrfs_delayed_ref_node *existing;
  	struct btrfs_delayed_tree_ref *full_ref;
  	struct btrfs_delayed_ref_root *delayed_refs;
  	u64 seq = 0;
  
  	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;
  
  	if (need_ref_seq(for_cow, ref_root))
  		seq = inc_delayed_seq(delayed_refs);
  	ref->seq = seq;
  
  	full_ref = btrfs_delayed_node_to_tree_ref(ref);
  	full_ref->parent = parent;
  	full_ref->root = ref_root;
  	if (parent)
  		ref->type = BTRFS_SHARED_BLOCK_REF_KEY;
  	else
  		ref->type = BTRFS_TREE_BLOCK_REF_KEY;
  	full_ref->level = level;
  
  	trace_btrfs_delayed_tree_ref(ref, full_ref, action);
  
  	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_fs_info *fs_info,
  					 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, int for_cow)
  {
  	struct btrfs_delayed_ref_node *existing;
  	struct btrfs_delayed_data_ref *full_ref;
  	struct btrfs_delayed_ref_root *delayed_refs;
  	u64 seq = 0;
  
  	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;
  
  	if (need_ref_seq(for_cow, ref_root))
  		seq = inc_delayed_seq(delayed_refs);
  	ref->seq = seq;
  
  	full_ref = btrfs_delayed_node_to_data_ref(ref);
  	full_ref->parent = parent;
  	full_ref->root = ref_root;
  	if (parent)
  		ref->type = BTRFS_SHARED_DATA_REF_KEY;
  	else
  		ref->type = BTRFS_EXTENT_DATA_REF_KEY;
  
  	full_ref->objectid = owner;
  	full_ref->offset = offset;
  
  	trace_btrfs_delayed_data_ref(ref, full_ref, action);
  
  	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_fs_info *fs_info,
  			       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,
  			       int for_cow)
  {
  	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(fs_info, trans, &head_ref->node, bytenr,
  				   num_bytes, action, 0);
  	BUG_ON(ret);
  
  	ret = add_delayed_tree_ref(fs_info, trans, &ref->node, bytenr,
  				   num_bytes, parent, ref_root, level, action,
  				   for_cow);
  	BUG_ON(ret);
  	if (!need_ref_seq(for_cow, ref_root) &&
  	    waitqueue_active(&delayed_refs->seq_wait))
  		wake_up(&delayed_refs->seq_wait);
  	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_fs_info *fs_info,
  			       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,
  			       int for_cow)
  {
  	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(fs_info, trans, &head_ref->node, bytenr,
  				   num_bytes, action, 1);
  	BUG_ON(ret);
  
  	ret = add_delayed_data_ref(fs_info, trans, &ref->node, bytenr,
  				   num_bytes, parent, ref_root, owner, offset,
  				   action, for_cow);
  	BUG_ON(ret);
  	if (!need_ref_seq(for_cow, ref_root) &&
  	    waitqueue_active(&delayed_refs->seq_wait))
  		wake_up(&delayed_refs->seq_wait);
  	spin_unlock(&delayed_refs->lock);
  	return 0;
  }
  
  int btrfs_add_delayed_extent_op(struct btrfs_fs_info *fs_info,
  				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(fs_info, trans, &head_ref->node, bytenr,
  				   num_bytes, BTRFS_UPDATE_DELAYED_HEAD,
  				   extent_op->is_data);
  	BUG_ON(ret);
  
  	if (waitqueue_active(&delayed_refs->seq_wait))
  		wake_up(&delayed_refs->seq_wait);
  	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, 0);
  	if (ref)
  		return btrfs_delayed_node_to_head(ref);
  	return NULL;
  }
  