/*
   * Copyright (C) 2007 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/fs.h>

  #include <linux/slab.h>

  #include <linux/sched.h>

  #include <linux/writeback.h>

  #include <linux/pagemap.h>

  #include <linux/blkdev.h>

  #include <linux/uuid.h>

  #include "ctree.h"
  #include "disk-io.h"
  #include "transaction.h"

  #include "locking.h"

  #include "tree-log.h"

  #include "inode-map.h"

  #include "volumes.h"

  #include "dev-replace.h"

  #include "qgroup.h"

  #define BTRFS_ROOT_TRANS_TAG 0

  static const unsigned int btrfs_blocked_trans_types[TRANS_STATE_MAX] = {

  	[TRANS_STATE_RUNNING]		= 0U,
  	[TRANS_STATE_BLOCKED]		= (__TRANS_USERSPACE |
  					   __TRANS_START),
  	[TRANS_STATE_COMMIT_START]	= (__TRANS_USERSPACE |
  					   __TRANS_START |
  					   __TRANS_ATTACH),
  	[TRANS_STATE_COMMIT_DOING]	= (__TRANS_USERSPACE |
  					   __TRANS_START |
  					   __TRANS_ATTACH |
  					   __TRANS_JOIN),
  	[TRANS_STATE_UNBLOCKED]		= (__TRANS_USERSPACE |
  					   __TRANS_START |
  					   __TRANS_ATTACH |
  					   __TRANS_JOIN |
  					   __TRANS_JOIN_NOLOCK),
  	[TRANS_STATE_COMPLETED]		= (__TRANS_USERSPACE |
  					   __TRANS_START |
  					   __TRANS_ATTACH |
  					   __TRANS_JOIN |
  					   __TRANS_JOIN_NOLOCK),
  };

  void btrfs_put_transaction(struct btrfs_transaction *transaction)

  {

  	WARN_ON(atomic_read(&transaction->use_count) == 0);
  	if (atomic_dec_and_test(&transaction->use_count)) {

  		BUG_ON(!list_empty(&transaction->list));

  		WARN_ON(!RB_EMPTY_ROOT(&transaction->delayed_refs.href_root));

  		if (transaction->delayed_refs.pending_csums)

  			btrfs_err(transaction->fs_info,
  				  "pending csums is %llu",
  				  transaction->delayed_refs.pending_csums);

  		while (!list_empty(&transaction->pending_chunks)) {
  			struct extent_map *em;
  
  			em = list_first_entry(&transaction->pending_chunks,
  					      struct extent_map, list);
  			list_del_init(&em->list);
  			free_extent_map(em);
  		}

  		/*
  		 * If any block groups are found in ->deleted_bgs then it's
  		 * because the transaction was aborted and a commit did not
  		 * happen (things failed before writing the new superblock
  		 * and calling btrfs_finish_extent_commit()), so we can not
  		 * discard the physical locations of the block groups.
  		 */
  		while (!list_empty(&transaction->deleted_bgs)) {
  			struct btrfs_block_group_cache *cache;
  
  			cache = list_first_entry(&transaction->deleted_bgs,
  						 struct btrfs_block_group_cache,
  						 bg_list);
  			list_del_init(&cache->bg_list);
  			btrfs_put_block_group_trimming(cache);
  			btrfs_put_block_group(cache);
  		}

  		kmem_cache_free(btrfs_transaction_cachep, transaction);

  	}

  }

  static void clear_btree_io_tree(struct extent_io_tree *tree)
  {
  	spin_lock(&tree->lock);

  	/*
  	 * Do a single barrier for the waitqueue_active check here, the state
  	 * of the waitqueue should not change once clear_btree_io_tree is
  	 * called.
  	 */
  	smp_mb();

  	while (!RB_EMPTY_ROOT(&tree->state)) {
  		struct rb_node *node;
  		struct extent_state *state;
  
  		node = rb_first(&tree->state);
  		state = rb_entry(node, struct extent_state, rb_node);
  		rb_erase(&state->rb_node, &tree->state);
  		RB_CLEAR_NODE(&state->rb_node);
  		/*
  		 * btree io trees aren't supposed to have tasks waiting for
  		 * changes in the flags of extent states ever.
  		 */
  		ASSERT(!waitqueue_active(&state->wq));
  		free_extent_state(state);

  
  		cond_resched_lock(&tree->lock);

  	}
  	spin_unlock(&tree->lock);
  }

  static noinline void switch_commit_roots(struct btrfs_transaction *trans,
  					 struct btrfs_fs_info *fs_info)

  {

  	struct btrfs_root *root, *tmp;
  
  	down_write(&fs_info->commit_root_sem);
  	list_for_each_entry_safe(root, tmp, &trans->switch_commits,
  				 dirty_list) {
  		list_del_init(&root->dirty_list);
  		free_extent_buffer(root->commit_root);
  		root->commit_root = btrfs_root_node(root);
  		if (is_fstree(root->objectid))
  			btrfs_unpin_free_ino(root);

  		clear_btree_io_tree(&root->dirty_log_pages);

  	}

  
  	/* We can free old roots now. */
  	spin_lock(&trans->dropped_roots_lock);
  	while (!list_empty(&trans->dropped_roots)) {
  		root = list_first_entry(&trans->dropped_roots,
  					struct btrfs_root, root_list);
  		list_del_init(&root->root_list);
  		spin_unlock(&trans->dropped_roots_lock);
  		btrfs_drop_and_free_fs_root(fs_info, root);
  		spin_lock(&trans->dropped_roots_lock);
  	}
  	spin_unlock(&trans->dropped_roots_lock);

  	up_write(&fs_info->commit_root_sem);

  }

  static inline void extwriter_counter_inc(struct btrfs_transaction *trans,
  					 unsigned int type)
  {
  	if (type & TRANS_EXTWRITERS)
  		atomic_inc(&trans->num_extwriters);
  }
  
  static inline void extwriter_counter_dec(struct btrfs_transaction *trans,
  					 unsigned int type)
  {
  	if (type & TRANS_EXTWRITERS)
  		atomic_dec(&trans->num_extwriters);
  }
  
  static inline void extwriter_counter_init(struct btrfs_transaction *trans,
  					  unsigned int type)
  {
  	atomic_set(&trans->num_extwriters, ((type & TRANS_EXTWRITERS) ? 1 : 0));
  }
  
  static inline int extwriter_counter_read(struct btrfs_transaction *trans)
  {
  	return atomic_read(&trans->num_extwriters);

  }

  /*
   * either allocate a new transaction or hop into the existing one
   */

  static noinline int join_transaction(struct btrfs_root *root, unsigned int type)

  {
  	struct btrfs_transaction *cur_trans;

  	struct btrfs_fs_info *fs_info = root->fs_info;

  	spin_lock(&fs_info->trans_lock);

  loop:

  	/* The file system has been taken offline. No new transactions. */

  	if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) {

  		spin_unlock(&fs_info->trans_lock);

  		return -EROFS;
  	}

  	cur_trans = fs_info->running_transaction;

  	if (cur_trans) {

  		if (cur_trans->aborted) {

  			spin_unlock(&fs_info->trans_lock);

  			return cur_trans->aborted;

  		}

  		if (btrfs_blocked_trans_types[cur_trans->state] & type) {

  			spin_unlock(&fs_info->trans_lock);
  			return -EBUSY;
  		}

  		atomic_inc(&cur_trans->use_count);

  		atomic_inc(&cur_trans->num_writers);

  		extwriter_counter_inc(cur_trans, type);

  		spin_unlock(&fs_info->trans_lock);

  		return 0;

  	}

  	spin_unlock(&fs_info->trans_lock);

  	/*
  	 * If we are ATTACH, we just want to catch the current transaction,
  	 * and commit it. If there is no transaction, just return ENOENT.
  	 */
  	if (type == TRANS_ATTACH)
  		return -ENOENT;

  	/*
  	 * JOIN_NOLOCK only happens during the transaction commit, so
  	 * it is impossible that ->running_transaction is NULL
  	 */
  	BUG_ON(type == TRANS_JOIN_NOLOCK);

  	cur_trans = kmem_cache_alloc(btrfs_transaction_cachep, GFP_NOFS);
  	if (!cur_trans)
  		return -ENOMEM;

  	spin_lock(&fs_info->trans_lock);
  	if (fs_info->running_transaction) {

  		/*
  		 * someone started a transaction after we unlocked.  Make sure

  		 * to redo the checks above

  		 */

  		kmem_cache_free(btrfs_transaction_cachep, cur_trans);

  		goto loop;

  	} else if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) {

  		spin_unlock(&fs_info->trans_lock);

  		kmem_cache_free(btrfs_transaction_cachep, cur_trans);
  		return -EROFS;

  	}

  	cur_trans->fs_info = fs_info;

  	atomic_set(&cur_trans->num_writers, 1);

  	extwriter_counter_init(cur_trans, type);

  	init_waitqueue_head(&cur_trans->writer_wait);
  	init_waitqueue_head(&cur_trans->commit_wait);

  	init_waitqueue_head(&cur_trans->pending_wait);

  	cur_trans->state = TRANS_STATE_RUNNING;

  	/*
  	 * One for this trans handle, one so it will live on until we
  	 * commit the transaction.
  	 */
  	atomic_set(&cur_trans->use_count, 2);

  	atomic_set(&cur_trans->pending_ordered, 0);

  	cur_trans->flags = 0;

  	cur_trans->start_time = get_seconds();

  	memset(&cur_trans->delayed_refs, 0, sizeof(cur_trans->delayed_refs));

  	cur_trans->delayed_refs.href_root = RB_ROOT;

  	cur_trans->delayed_refs.dirty_extent_root = RB_ROOT;

  	atomic_set(&cur_trans->delayed_refs.num_entries, 0);

  
  	/*
  	 * although the tree mod log is per file system and not per transaction,
  	 * the log must never go across transaction boundaries.
  	 */
  	smp_mb();

  	if (!list_empty(&fs_info->tree_mod_seq_list))

  		WARN(1, KERN_ERR "BTRFS: tree_mod_seq_list not empty when creating a fresh transaction
  ");

  	if (!RB_EMPTY_ROOT(&fs_info->tree_mod_log))

  		WARN(1, KERN_ERR "BTRFS: tree_mod_log rb tree not empty when creating a fresh transaction
  ");

  	atomic64_set(&fs_info->tree_mod_seq, 0);

  	spin_lock_init(&cur_trans->delayed_refs.lock);
  
  	INIT_LIST_HEAD(&cur_trans->pending_snapshots);

  	INIT_LIST_HEAD(&cur_trans->pending_chunks);

  	INIT_LIST_HEAD(&cur_trans->switch_commits);

  	INIT_LIST_HEAD(&cur_trans->dirty_bgs);

  	INIT_LIST_HEAD(&cur_trans->io_bgs);

  	INIT_LIST_HEAD(&cur_trans->dropped_roots);

  	mutex_init(&cur_trans->cache_write_mutex);

  	cur_trans->num_dirty_bgs = 0;

  	spin_lock_init(&cur_trans->dirty_bgs_lock);

  	INIT_LIST_HEAD(&cur_trans->deleted_bgs);

  	spin_lock_init(&cur_trans->dropped_roots_lock);

  	list_add_tail(&cur_trans->list, &fs_info->trans_list);

  	extent_io_tree_init(&cur_trans->dirty_pages,

  			     fs_info->btree_inode->i_mapping);
  	fs_info->generation++;
  	cur_trans->transid = fs_info->generation;
  	fs_info->running_transaction = cur_trans;

  	cur_trans->aborted = 0;

  	spin_unlock(&fs_info->trans_lock);

  	return 0;
  }

  /*

   * this does all the record keeping required to make sure that a reference
   * counted root is properly recorded in a given transaction.  This is required
   * to make sure the old root from before we joined the transaction is deleted
   * when the transaction commits

   */

  static int record_root_in_trans(struct btrfs_trans_handle *trans,

  			       struct btrfs_root *root,
  			       int force)

  {

  	if ((test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
  	    root->last_trans < trans->transid) || force) {

  		WARN_ON(root == root->fs_info->extent_root);

  		WARN_ON(root->commit_root != root->node);

  		/*

  		 * see below for IN_TRANS_SETUP usage rules

  		 * we have the reloc mutex held now, so there
  		 * is only one writer in this function
  		 */

  		set_bit(BTRFS_ROOT_IN_TRANS_SETUP, &root->state);

  		/* make sure readers find IN_TRANS_SETUP before

  		 * they find our root->last_trans update
  		 */
  		smp_wmb();

  		spin_lock(&root->fs_info->fs_roots_radix_lock);

  		if (root->last_trans == trans->transid && !force) {

  			spin_unlock(&root->fs_info->fs_roots_radix_lock);
  			return 0;
  		}

  		radix_tree_tag_set(&root->fs_info->fs_roots_radix,
  			   (unsigned long)root->root_key.objectid,
  			   BTRFS_ROOT_TRANS_TAG);

  		spin_unlock(&root->fs_info->fs_roots_radix_lock);

  		root->last_trans = trans->transid;
  
  		/* this is pretty tricky.  We don't want to
  		 * take the relocation lock in btrfs_record_root_in_trans
  		 * unless we're really doing the first setup for this root in
  		 * this transaction.
  		 *
  		 * Normally we'd use root->last_trans as a flag to decide
  		 * if we want to take the expensive mutex.
  		 *
  		 * But, we have to set root->last_trans before we
  		 * init the relocation root, otherwise, we trip over warnings
  		 * in ctree.c.  The solution used here is to flag ourselves

  		 * with root IN_TRANS_SETUP.  When this is 1, we're still

  		 * fixing up the reloc trees and everyone must wait.
  		 *
  		 * When this is zero, they can trust root->last_trans and fly
  		 * through btrfs_record_root_in_trans without having to take the
  		 * lock.  smp_wmb() makes sure that all the writes above are
  		 * done before we pop in the zero below
  		 */

  		btrfs_init_reloc_root(trans, root);

  		smp_mb__before_atomic();

  		clear_bit(BTRFS_ROOT_IN_TRANS_SETUP, &root->state);

  	}
  	return 0;
  }

  void btrfs_add_dropped_root(struct btrfs_trans_handle *trans,
  			    struct btrfs_root *root)
  {
  	struct btrfs_transaction *cur_trans = trans->transaction;
  
  	/* Add ourselves to the transaction dropped list */
  	spin_lock(&cur_trans->dropped_roots_lock);
  	list_add_tail(&root->root_list, &cur_trans->dropped_roots);
  	spin_unlock(&cur_trans->dropped_roots_lock);
  
  	/* Make sure we don't try to update the root at commit time */
  	spin_lock(&root->fs_info->fs_roots_radix_lock);
  	radix_tree_tag_clear(&root->fs_info->fs_roots_radix,
  			     (unsigned long)root->root_key.objectid,
  			     BTRFS_ROOT_TRANS_TAG);
  	spin_unlock(&root->fs_info->fs_roots_radix_lock);
  }

  int btrfs_record_root_in_trans(struct btrfs_trans_handle *trans,
  			       struct btrfs_root *root)
  {

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

  		return 0;
  
  	/*

  	 * see record_root_in_trans for comments about IN_TRANS_SETUP usage

  	 * and barriers
  	 */
  	smp_rmb();
  	if (root->last_trans == trans->transid &&

  	    !test_bit(BTRFS_ROOT_IN_TRANS_SETUP, &root->state))

  		return 0;
  
  	mutex_lock(&root->fs_info->reloc_mutex);

  	record_root_in_trans(trans, root, 0);

  	mutex_unlock(&root->fs_info->reloc_mutex);
  
  	return 0;
  }

  static inline int is_transaction_blocked(struct btrfs_transaction *trans)
  {
  	return (trans->state >= TRANS_STATE_BLOCKED &&

  		trans->state < TRANS_STATE_UNBLOCKED &&
  		!trans->aborted);

  }

  /* wait for commit against the current transaction to become unblocked
   * when this is done, it is safe to start a new transaction, but the current
   * transaction might not be fully on disk.
   */

  static void wait_current_trans(struct btrfs_root *root)

  {

  	struct btrfs_transaction *cur_trans;

  	spin_lock(&root->fs_info->trans_lock);

  	cur_trans = root->fs_info->running_transaction;

  	if (cur_trans && is_transaction_blocked(cur_trans)) {

  		atomic_inc(&cur_trans->use_count);

  		spin_unlock(&root->fs_info->trans_lock);

  
  		wait_event(root->fs_info->transaction_wait,

  			   cur_trans->state >= TRANS_STATE_UNBLOCKED ||
  			   cur_trans->aborted);

  		btrfs_put_transaction(cur_trans);

  	} else {
  		spin_unlock(&root->fs_info->trans_lock);

  	}

  }

  static int may_wait_transaction(struct btrfs_root *root, int type)
  {

  	if (test_bit(BTRFS_FS_LOG_RECOVERING, &root->fs_info->flags))

  		return 0;
  
  	if (type == TRANS_USERSPACE)
  		return 1;
  
  	if (type == TRANS_START &&
  	    !atomic_read(&root->fs_info->open_ioctl_trans))

  		return 1;

  	return 0;
  }

  static inline bool need_reserve_reloc_root(struct btrfs_root *root)
  {
  	if (!root->fs_info->reloc_ctl ||

  	    !test_bit(BTRFS_ROOT_REF_COWS, &root->state) ||

  	    root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID ||
  	    root->reloc_root)
  		return false;
  
  	return true;
  }

  static struct btrfs_trans_handle *

  start_transaction(struct btrfs_root *root, unsigned int num_items,
  		  unsigned int type, enum btrfs_reserve_flush_enum flush)

  {

  	struct btrfs_trans_handle *h;
  	struct btrfs_transaction *cur_trans;

  	u64 num_bytes = 0;

  	u64 qgroup_reserved = 0;

  	bool reloc_reserved = false;
  	int ret;

  	/* Send isn't supposed to start transactions. */

  	ASSERT(current->journal_info != BTRFS_SEND_TRANS_STUB);

  	if (test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state))

  		return ERR_PTR(-EROFS);

  	if (current->journal_info) {

  		WARN_ON(type & TRANS_EXTWRITERS);

  		h = current->journal_info;
  		h->use_count++;

  		WARN_ON(h->use_count > 2);

  		h->orig_rsv = h->block_rsv;
  		h->block_rsv = NULL;
  		goto got_it;
  	}

  
  	/*
  	 * Do the reservation before we join the transaction so we can do all
  	 * the appropriate flushing if need be.
  	 */
  	if (num_items > 0 && root != root->fs_info->chunk_root) {

  		qgroup_reserved = num_items * root->nodesize;
  		ret = btrfs_qgroup_reserve_meta(root, qgroup_reserved);
  		if (ret)
  			return ERR_PTR(ret);

  		num_bytes = btrfs_calc_trans_metadata_size(root, num_items);

  		/*
  		 * Do the reservation for the relocation root creation
  		 */

  		if (need_reserve_reloc_root(root)) {

  			num_bytes += root->nodesize;
  			reloc_reserved = true;
  		}

  		ret = btrfs_block_rsv_add(root,
  					  &root->fs_info->trans_block_rsv,
  					  num_bytes, flush);

  		if (ret)

  			goto reserve_fail;

  	}

  again:

  	h = kmem_cache_zalloc(btrfs_trans_handle_cachep, GFP_NOFS);

  	if (!h) {
  		ret = -ENOMEM;
  		goto alloc_fail;
  	}

  	/*
  	 * If we are JOIN_NOLOCK we're already committing a transaction and
  	 * waiting on this guy, so we don't need to do the sb_start_intwrite
  	 * because we're already holding a ref.  We need this because we could
  	 * have raced in and did an fsync() on a file which can kick a commit
  	 * and then we deadlock with somebody doing a freeze.

  	 *
  	 * If we are ATTACH, it means we just want to catch the current
  	 * transaction and commit it, so we needn't do sb_start_intwrite(). 

  	 */

  	if (type & __TRANS_FREEZABLE)

  		sb_start_intwrite(root->fs_info->sb);

  	if (may_wait_transaction(root, type))

  		wait_current_trans(root);

  	do {

  		ret = join_transaction(root, type);

  		if (ret == -EBUSY) {

  			wait_current_trans(root);

  			if (unlikely(type == TRANS_ATTACH))
  				ret = -ENOENT;
  		}

  	} while (ret == -EBUSY);

  	if (ret < 0)

  		goto join_fail;

  	cur_trans = root->fs_info->running_transaction;

  
  	h->transid = cur_trans->transid;
  	h->transaction = cur_trans;

  	h->root = root;

  	h->use_count = 1;

  	h->fs_info = root->fs_info;

  	h->type = type;

  	h->can_flush_pending_bgs = true;

  	INIT_LIST_HEAD(&h->qgroup_ref_list);

  	INIT_LIST_HEAD(&h->new_bgs);

  	smp_mb();

  	if (cur_trans->state >= TRANS_STATE_BLOCKED &&
  	    may_wait_transaction(root, type)) {

  		current->journal_info = h;

  		btrfs_commit_transaction(h, root);
  		goto again;
  	}

  	if (num_bytes) {

  		trace_btrfs_space_reservation(root->fs_info, "transaction",

  					      h->transid, num_bytes, 1);

  		h->block_rsv = &root->fs_info->trans_block_rsv;
  		h->bytes_reserved = num_bytes;

  		h->reloc_reserved = reloc_reserved;

  	}

  got_it:

  	btrfs_record_root_in_trans(h, root);

  
  	if (!current->journal_info && type != TRANS_USERSPACE)
  		current->journal_info = h;

  	return h;

  
  join_fail:

  	if (type & __TRANS_FREEZABLE)

  		sb_end_intwrite(root->fs_info->sb);
  	kmem_cache_free(btrfs_trans_handle_cachep, h);
  alloc_fail:
  	if (num_bytes)
  		btrfs_block_rsv_release(root, &root->fs_info->trans_block_rsv,
  					num_bytes);
  reserve_fail:

  	btrfs_qgroup_free_meta(root, qgroup_reserved);

  	return ERR_PTR(ret);

  }

  struct btrfs_trans_handle *btrfs_start_transaction(struct btrfs_root *root,

  						   unsigned int num_items)

  {

  	return start_transaction(root, num_items, TRANS_START,
  				 BTRFS_RESERVE_FLUSH_ALL);

  }

  struct btrfs_trans_handle *btrfs_start_transaction_fallback_global_rsv(
  					struct btrfs_root *root,
  					unsigned int num_items,
  					int min_factor)
  {
  	struct btrfs_trans_handle *trans;
  	u64 num_bytes;
  	int ret;
  
  	trans = btrfs_start_transaction(root, num_items);
  	if (!IS_ERR(trans) || PTR_ERR(trans) != -ENOSPC)
  		return trans;
  
  	trans = btrfs_start_transaction(root, 0);
  	if (IS_ERR(trans))
  		return trans;
  
  	num_bytes = btrfs_calc_trans_metadata_size(root, num_items);
  	ret = btrfs_cond_migrate_bytes(root->fs_info,
  				       &root->fs_info->trans_block_rsv,
  				       num_bytes,
  				       min_factor);
  	if (ret) {
  		btrfs_end_transaction(trans, root);
  		return ERR_PTR(ret);
  	}
  
  	trans->block_rsv = &root->fs_info->trans_block_rsv;
  	trans->bytes_reserved = num_bytes;

  	trace_btrfs_space_reservation(root->fs_info, "transaction",
  				      trans->transid, num_bytes, 1);

  
  	return trans;
  }

  struct btrfs_trans_handle *btrfs_start_transaction_lflush(

  					struct btrfs_root *root,
  					unsigned int num_items)

  {

  	return start_transaction(root, num_items, TRANS_START,
  				 BTRFS_RESERVE_FLUSH_LIMIT);

  }

  struct btrfs_trans_handle *btrfs_join_transaction(struct btrfs_root *root)

  {

  	return start_transaction(root, 0, TRANS_JOIN,
  				 BTRFS_RESERVE_NO_FLUSH);

  }

  struct btrfs_trans_handle *btrfs_join_transaction_nolock(struct btrfs_root *root)

  {

  	return start_transaction(root, 0, TRANS_JOIN_NOLOCK,
  				 BTRFS_RESERVE_NO_FLUSH);

  }

  struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root)

  {

  	return start_transaction(root, 0, TRANS_USERSPACE,
  				 BTRFS_RESERVE_NO_FLUSH);

  }

  /*
   * btrfs_attach_transaction() - catch the running transaction
   *
   * It is used when we want to commit the current the transaction, but
   * don't want to start a new one.
   *
   * Note: If this function return -ENOENT, it just means there is no
   * running transaction. But it is possible that the inactive transaction
   * is still in the memory, not fully on disk. If you hope there is no
   * inactive transaction in the fs when -ENOENT is returned, you should
   * invoke
   *     btrfs_attach_transaction_barrier()
   */

  struct btrfs_trans_handle *btrfs_attach_transaction(struct btrfs_root *root)

  {

  	return start_transaction(root, 0, TRANS_ATTACH,
  				 BTRFS_RESERVE_NO_FLUSH);

  }

  /*

   * btrfs_attach_transaction_barrier() - catch the running transaction

   *
   * It is similar to the above function, the differentia is this one
   * will wait for all the inactive transactions until they fully
   * complete.
   */
  struct btrfs_trans_handle *
  btrfs_attach_transaction_barrier(struct btrfs_root *root)
  {
  	struct btrfs_trans_handle *trans;

  	trans = start_transaction(root, 0, TRANS_ATTACH,
  				  BTRFS_RESERVE_NO_FLUSH);

  	if (IS_ERR(trans) && PTR_ERR(trans) == -ENOENT)
  		btrfs_wait_for_commit(root, 0);
  
  	return trans;
  }

  /* wait for a transaction commit to be fully complete */

  static noinline void wait_for_commit(struct btrfs_root *root,

  				    struct btrfs_transaction *commit)
  {

  	wait_event(commit->commit_wait, commit->state == TRANS_STATE_COMPLETED);

  }

  int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid)
  {
  	struct btrfs_transaction *cur_trans = NULL, *t;

  	int ret = 0;

  	if (transid) {
  		if (transid <= root->fs_info->last_trans_committed)

  			goto out;

  
  		/* find specified transaction */

  		spin_lock(&root->fs_info->trans_lock);

  		list_for_each_entry(t, &root->fs_info->trans_list, list) {
  			if (t->transid == transid) {
  				cur_trans = t;

  				atomic_inc(&cur_trans->use_count);

  				ret = 0;

  				break;
  			}

  			if (t->transid > transid) {
  				ret = 0;

  				break;

  			}

  		}

  		spin_unlock(&root->fs_info->trans_lock);

  
  		/*
  		 * The specified transaction doesn't exist, or we
  		 * raced with btrfs_commit_transaction
  		 */
  		if (!cur_trans) {
  			if (transid > root->fs_info->last_trans_committed)
  				ret = -EINVAL;

  			goto out;

  		}

  	} else {
  		/* find newest transaction that is committing | committed */

  		spin_lock(&root->fs_info->trans_lock);

  		list_for_each_entry_reverse(t, &root->fs_info->trans_list,
  					    list) {

  			if (t->state >= TRANS_STATE_COMMIT_START) {
  				if (t->state == TRANS_STATE_COMPLETED)

  					break;

  				cur_trans = t;

  				atomic_inc(&cur_trans->use_count);

  				break;
  			}
  		}

  		spin_unlock(&root->fs_info->trans_lock);

  		if (!cur_trans)

  			goto out;  /* nothing committing|committed */

  	}

  	wait_for_commit(root, cur_trans);

  	btrfs_put_transaction(cur_trans);

  out:

  	return ret;
  }

  void btrfs_throttle(struct btrfs_root *root)
  {

  	if (!atomic_read(&root->fs_info->open_ioctl_trans))

  		wait_current_trans(root);

  }

  static int should_end_transaction(struct btrfs_trans_handle *trans,
  				  struct btrfs_root *root)
  {

  	if (root->fs_info->global_block_rsv.space_info->full &&

  	    btrfs_check_space_for_delayed_refs(trans, root))

  		return 1;

  	return !!btrfs_block_rsv_check(root, &root->fs_info->global_block_rsv, 5);

  }
  
  int btrfs_should_end_transaction(struct btrfs_trans_handle *trans,
  				 struct btrfs_root *root)
  {
  	struct btrfs_transaction *cur_trans = trans->transaction;
  	int updates;

  	int err;

  	smp_mb();

  	if (cur_trans->state >= TRANS_STATE_BLOCKED ||
  	    cur_trans->delayed_refs.flushing)

  		return 1;
  
  	updates = trans->delayed_ref_updates;
  	trans->delayed_ref_updates = 0;

  	if (updates) {

  		err = btrfs_run_delayed_refs(trans, root, updates * 2);

  		if (err) /* Error code will also eval true */
  			return err;
  	}

  
  	return should_end_transaction(trans, root);
  }

  static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,

  			  struct btrfs_root *root, int throttle)

  {

  	struct btrfs_transaction *cur_trans = trans->transaction;

  	struct btrfs_fs_info *info = root->fs_info;

  	u64 transid = trans->transid;

  	unsigned long cur = trans->delayed_ref_updates;

  	int lock = (trans->type != TRANS_JOIN_NOLOCK);

  	int err = 0;

  	int must_run_delayed_refs = 0;

  	if (trans->use_count > 1) {
  		trans->use_count--;

  		trans->block_rsv = trans->orig_rsv;
  		return 0;
  	}

  	btrfs_trans_release_metadata(trans, root);

  	trans->block_rsv = NULL;

  	if (!list_empty(&trans->new_bgs))
  		btrfs_create_pending_block_groups(trans, root);

  	trans->delayed_ref_updates = 0;

  	if (!trans->sync) {
  		must_run_delayed_refs =
  			btrfs_should_throttle_delayed_refs(trans, root);

  		cur = max_t(unsigned long, cur, 32);

  
  		/*
  		 * don't make the caller wait if they are from a NOLOCK
  		 * or ATTACH transaction, it will deadlock with commit
  		 */
  		if (must_run_delayed_refs == 1 &&
  		    (trans->type & (__TRANS_JOIN_NOLOCK | __TRANS_ATTACH)))
  			must_run_delayed_refs = 2;

  	}

  	btrfs_trans_release_metadata(trans, root);
  	trans->block_rsv = NULL;

  	if (!list_empty(&trans->new_bgs))
  		btrfs_create_pending_block_groups(trans, root);

  	btrfs_trans_release_chunk_metadata(trans);

  	if (lock && !atomic_read(&root->fs_info->open_ioctl_trans) &&

  	    should_end_transaction(trans, root) &&
  	    ACCESS_ONCE(cur_trans->state) == TRANS_STATE_RUNNING) {
  		spin_lock(&info->trans_lock);
  		if (cur_trans->state == TRANS_STATE_RUNNING)
  			cur_trans->state = TRANS_STATE_BLOCKED;
  		spin_unlock(&info->trans_lock);

  	}

  	if (lock && ACCESS_ONCE(cur_trans->state) == TRANS_STATE_BLOCKED) {

  		if (throttle)

  			return btrfs_commit_transaction(trans, root);

  		else

  			wake_up_process(info->transaction_kthread);
  	}

  	if (trans->type & __TRANS_FREEZABLE)

  		sb_end_intwrite(root->fs_info->sb);

  	WARN_ON(cur_trans != info->running_transaction);

  	WARN_ON(atomic_read(&cur_trans->num_writers) < 1);
  	atomic_dec(&cur_trans->num_writers);

  	extwriter_counter_dec(cur_trans, trans->type);

  	/*
  	 * Make sure counter is updated before we wake up waiters.
  	 */

  	smp_mb();

  	if (waitqueue_active(&cur_trans->writer_wait))
  		wake_up(&cur_trans->writer_wait);

  	btrfs_put_transaction(cur_trans);

  
  	if (current->journal_info == trans)
  		current->journal_info = NULL;

  	if (throttle)
  		btrfs_run_delayed_iputs(root);

  	if (trans->aborted ||

  	    test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state)) {
  		wake_up_process(info->transaction_kthread);

  		err = -EIO;

  	}

  	assert_qgroups_uptodate(trans);

  	kmem_cache_free(btrfs_trans_handle_cachep, trans);

  	if (must_run_delayed_refs) {

  		btrfs_async_run_delayed_refs(root, cur, transid,

  					     must_run_delayed_refs == 1);
  	}

  	return err;

  }

  int btrfs_end_transaction(struct btrfs_trans_handle *trans,
  			  struct btrfs_root *root)
  {

  	return __btrfs_end_transaction(trans, root, 0);

  }
  
  int btrfs_end_transaction_throttle(struct btrfs_trans_handle *trans,
  				   struct btrfs_root *root)
  {

  	return __btrfs_end_transaction(trans, root, 1);

  }

  /*
   * when btree blocks are allocated, they have some corresponding bits set for
   * them in one of two extent_io trees.  This is used to make sure all of

   * those extents are sent to disk but does not wait on them

   */

  int btrfs_write_marked_extents(struct btrfs_root *root,

  			       struct extent_io_tree *dirty_pages, int mark)

  {

  	int err = 0;

  	int werr = 0;

  	struct address_space *mapping = root->fs_info->btree_inode->i_mapping;

  	struct extent_state *cached_state = NULL;

  	u64 start = 0;

  	u64 end;

  	while (!find_first_extent_bit(dirty_pages, start, &start, &end,

  				      mark, &cached_state)) {

  		bool wait_writeback = false;
  
  		err = convert_extent_bit(dirty_pages, start, end,
  					 EXTENT_NEED_WAIT,

  					 mark, &cached_state);

  		/*
  		 * convert_extent_bit can return -ENOMEM, which is most of the
  		 * time a temporary error. So when it happens, ignore the error
  		 * and wait for writeback of this range to finish - because we
  		 * failed to set the bit EXTENT_NEED_WAIT for the range, a call
  		 * to btrfs_wait_marked_extents() would not know that writeback
  		 * for this range started and therefore wouldn't wait for it to
  		 * finish - we don't want to commit a superblock that points to
  		 * btree nodes/leafs for which writeback hasn't finished yet
  		 * (and without errors).
  		 * We cleanup any entries left in the io tree when committing
  		 * the transaction (through clear_btree_io_tree()).
  		 */
  		if (err == -ENOMEM) {
  			err = 0;
  			wait_writeback = true;
  		}
  		if (!err)
  			err = filemap_fdatawrite_range(mapping, start, end);

  		if (err)
  			werr = err;

  		else if (wait_writeback)
  			werr = filemap_fdatawait_range(mapping, start, end);

  		free_extent_state(cached_state);

  		cached_state = NULL;

  		cond_resched();
  		start = end + 1;

  	}

  	return werr;
  }
  
  /*
   * when btree blocks are allocated, they have some corresponding bits set for
   * them in one of two extent_io trees.  This is used to make sure all of
   * those extents are on disk for transaction or log commit.  We wait
   * on all the pages and clear them from the dirty pages state tree
   */
  int btrfs_wait_marked_extents(struct btrfs_root *root,

  			      struct extent_io_tree *dirty_pages, int mark)

  {

  	int err = 0;
  	int werr = 0;

  	struct address_space *mapping = root->fs_info->btree_inode->i_mapping;

  	struct extent_state *cached_state = NULL;

  	u64 start = 0;
  	u64 end;

  	bool errors = false;

  	while (!find_first_extent_bit(dirty_pages, start, &start, &end,

  				      EXTENT_NEED_WAIT, &cached_state)) {

  		/*
  		 * Ignore -ENOMEM errors returned by clear_extent_bit().
  		 * When committing the transaction, we'll remove any entries
  		 * left in the io tree. For a log commit, we don't remove them
  		 * after committing the log because the tree can be accessed
  		 * concurrently - we do it only at transaction commit time when
  		 * it's safe to do it (through clear_btree_io_tree()).
  		 */
  		err = clear_extent_bit(dirty_pages, start, end,
  				       EXTENT_NEED_WAIT,
  				       0, 0, &cached_state, GFP_NOFS);
  		if (err == -ENOMEM)
  			err = 0;
  		if (!err)
  			err = filemap_fdatawait_range(mapping, start, end);

  		if (err)
  			werr = err;

  		free_extent_state(cached_state);
  		cached_state = NULL;

  		cond_resched();
  		start = end + 1;

  	}

  	if (err)
  		werr = err;

  
  	if (root->root_key.objectid == BTRFS_TREE_LOG_OBJECTID) {
  		if ((mark & EXTENT_DIRTY) &&

  		    test_and_clear_bit(BTRFS_FS_LOG1_ERR,
  				       &root->fs_info->flags))

  			errors = true;
  
  		if ((mark & EXTENT_NEW) &&

  		    test_and_clear_bit(BTRFS_FS_LOG2_ERR,
  				       &root->fs_info->flags))

  			errors = true;
  	} else {

  		if (test_and_clear_bit(BTRFS_FS_BTREE_ERR,
  				       &root->fs_info->flags))

  			errors = true;
  	}
  
  	if (errors && !werr)
  		werr = -EIO;

  	return werr;

  }

  /*
   * when btree blocks are allocated, they have some corresponding bits set for
   * them in one of two extent_io trees.  This is used to make sure all of
   * those extents are on disk for transaction or log commit
   */

  static int btrfs_write_and_wait_marked_extents(struct btrfs_root *root,

  				struct extent_io_tree *dirty_pages, int mark)

  {
  	int ret;
  	int ret2;

  	struct blk_plug plug;

  	blk_start_plug(&plug);

  	ret = btrfs_write_marked_extents(root, dirty_pages, mark);

  	blk_finish_plug(&plug);

  	ret2 = btrfs_wait_marked_extents(root, dirty_pages, mark);

  
  	if (ret)
  		return ret;
  	if (ret2)
  		return ret2;
  	return 0;

  }

  static int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,

  				     struct btrfs_root *root)
  {

  	int ret;
  
  	ret = btrfs_write_and_wait_marked_extents(root,

  					   &trans->transaction->dirty_pages,
  					   EXTENT_DIRTY);

  	clear_btree_io_tree(&trans->transaction->dirty_pages);
  
  	return ret;

  }

  /*
   * this is used to update the root pointer in the tree of tree roots.
   *
   * But, in the case of the extent allocation tree, updating the root
   * pointer may allocate blocks which may change the root of the extent
   * allocation tree.
   *
   * So, this loops and repeats and makes sure the cowonly root didn't
   * change while the root pointer was being updated in the metadata.
   */

  static int update_cowonly_root(struct btrfs_trans_handle *trans,
  			       struct btrfs_root *root)

  {
  	int ret;

  	u64 old_root_bytenr;

  	u64 old_root_used;

  	struct btrfs_root *tree_root = root->fs_info->tree_root;

  	old_root_used = btrfs_root_used(&root->root_item);

  	while (1) {

  		old_root_bytenr = btrfs_root_bytenr(&root->root_item);

  		if (old_root_bytenr == root->node->start &&

  		    old_root_used == btrfs_root_used(&root->root_item))

  			break;

  		btrfs_set_root_node(&root->root_item, root->node);

  		ret = btrfs_update_root(trans, tree_root,

  					&root->root_key,
  					&root->root_item);

  		if (ret)
  			return ret;

  		old_root_used = btrfs_root_used(&root->root_item);

  	}

  	return 0;
  }

  /*
   * update all the cowonly tree roots on disk

   *
   * The error handling in this function may not be obvious. Any of the
   * failures will cause the file system to go offline. We still need
   * to clean up the delayed refs.

   */

  static noinline int commit_cowonly_roots(struct btrfs_trans_handle *trans,
  					 struct btrfs_root *root)

  {
  	struct btrfs_fs_info *fs_info = root->fs_info;

  	struct list_head *dirty_bgs = &trans->transaction->dirty_bgs;

  	struct list_head *io_bgs = &trans->transaction->io_bgs;

  	struct list_head *next;

  	struct extent_buffer *eb;

  	int ret;

  
  	eb = btrfs_lock_root_node(fs_info->tree_root);

  	ret = btrfs_cow_block(trans, fs_info->tree_root, eb, NULL,
  			      0, &eb);

  	btrfs_tree_unlock(eb);
  	free_extent_buffer(eb);

  	if (ret)
  		return ret;

  	ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);

  	if (ret)
  		return ret;

  	ret = btrfs_run_dev_stats(trans, root->fs_info);

  	if (ret)
  		return ret;

  	ret = btrfs_run_dev_replace(trans, root->fs_info);

  	if (ret)
  		return ret;

  	ret = btrfs_run_qgroups(trans, root->fs_info);

  	if (ret)
  		return ret;

  	ret = btrfs_setup_space_cache(trans, root);
  	if (ret)
  		return ret;

  	/* run_qgroups might have added some more refs */
  	ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);

  	if (ret)
  		return ret;

  again:

  	while (!list_empty(&fs_info->dirty_cowonly_roots)) {

  		next = fs_info->dirty_cowonly_roots.next;
  		list_del_init(next);
  		root = list_entry(next, struct btrfs_root, dirty_list);

  		clear_bit(BTRFS_ROOT_DIRTY, &root->state);

  		if (root != fs_info->extent_root)
  			list_add_tail(&root->dirty_list,
  				      &trans->transaction->switch_commits);

  		ret = update_cowonly_root(trans, root);
  		if (ret)
  			return ret;

  		ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
  		if (ret)
  			return ret;

  	}

  	while (!list_empty(dirty_bgs) || !list_empty(io_bgs)) {

  		ret = btrfs_write_dirty_block_groups(trans, root);
  		if (ret)
  			return ret;
  		ret = btrfs_run_delayed_refs(trans, root, (unsigned long)-1);
  		if (ret)
  			return ret;
  	}
  
  	if (!list_empty(&fs_info->dirty_cowonly_roots))
  		goto again;

  	list_add_tail(&fs_info->extent_root->dirty_list,
  		      &trans->transaction->switch_commits);

  	btrfs_after_dev_replace_commit(fs_info);

  	return 0;
  }

  /*
   * dead roots are old snapshots that need to be deleted.  This allocates
   * a dirty root struct and adds it into the list of dead roots that need to
   * be deleted
   */

  void btrfs_add_dead_root(struct btrfs_root *root)

  {

  	spin_lock(&root->fs_info->trans_lock);

  	if (list_empty(&root->root_list))
  		list_add_tail(&root->root_list, &root->fs_info->dead_roots);

  	spin_unlock(&root->fs_info->trans_lock);

  }

  /*

   * update all the cowonly tree roots on disk

   */

  static noinline int commit_fs_roots(struct btrfs_trans_handle *trans,
  				    struct btrfs_root *root)

  {

  	struct btrfs_root *gang[8];

  	struct btrfs_fs_info *fs_info = root->fs_info;

  	int i;
  	int ret;

  	int err = 0;

  	spin_lock(&fs_info->fs_roots_radix_lock);

  	while (1) {

  		ret = radix_tree_gang_lookup_tag(&fs_info->fs_roots_radix,
  						 (void **)gang, 0,

  						 ARRAY_SIZE(gang),
  						 BTRFS_ROOT_TRANS_TAG);
  		if (ret == 0)
  			break;
  		for (i = 0; i < ret; i++) {
  			root = gang[i];

  			radix_tree_tag_clear(&fs_info->fs_roots_radix,
  					(unsigned long)root->root_key.objectid,
  					BTRFS_ROOT_TRANS_TAG);

  			spin_unlock(&fs_info->fs_roots_radix_lock);

  			btrfs_free_log(trans, root);

  			btrfs_update_reloc_root(trans, root);

  			btrfs_orphan_commit_root(trans, root);

  			btrfs_save_ino_cache(root, trans);

  			/* see comments in should_cow_block() */

  			clear_bit(BTRFS_ROOT_FORCE_COW, &root->state);

  			smp_mb__after_atomic();

  			if (root->commit_root != root->node) {

  				list_add_tail(&root->dirty_list,
  					&trans->transaction->switch_commits);

  				btrfs_set_root_node(&root->root_item,
  						    root->node);
  			}

  			err = btrfs_update_root(trans, fs_info->tree_root,

  						&root->root_key,
  						&root->root_item);

  			spin_lock(&fs_info->fs_roots_radix_lock);

  			if (err)
  				break;

  			btrfs_qgroup_free_meta_all(root);

  		}
  	}

  	spin_unlock(&fs_info->fs_roots_radix_lock);

  	return err;

  }

  /*

   * defrag a given btree.
   * Every leaf in the btree is read and defragged.

   */

  int btrfs_defrag_root(struct btrfs_root *root)

  {
  	struct btrfs_fs_info *info = root->fs_info;

  	struct btrfs_trans_handle *trans;

  	int ret;

  	if (test_and_set_bit(BTRFS_ROOT_DEFRAG_RUNNING, &root->state))

  		return 0;

  	while (1) {

  		trans = btrfs_start_transaction(root, 0);
  		if (IS_ERR(trans))
  			return PTR_ERR(trans);

  		ret = btrfs_defrag_leaves(trans, root);

  		btrfs_end_transaction(trans, root);

  		btrfs_btree_balance_dirty(info->tree_root);

  		cond_resched();

  		if (btrfs_fs_closing(info) || ret != -EAGAIN)

  			break;

  		if (btrfs_defrag_cancelled(info)) {
  			btrfs_debug(info, "defrag_root cancelled");

  			ret = -EAGAIN;
  			break;
  		}

  	}

  	clear_bit(BTRFS_ROOT_DEFRAG_RUNNING, &root->state);

  	return ret;

  }

  /*

   * Do all special snapshot related qgroup dirty hack.
   *
   * Will do all needed qgroup inherit and dirty hack like switch commit
   * roots inside one transaction and write all btree into disk, to make
   * qgroup works.
   */
  static int qgroup_account_snapshot(struct btrfs_trans_handle *trans,
  				   struct btrfs_root *src,
  				   struct btrfs_root *parent,
  				   struct btrfs_qgroup_inherit *inherit,
  				   u64 dst_objectid)
  {
  	struct btrfs_fs_info *fs_info = src->fs_info;
  	int ret;
  
  	/*
  	 * Save some performance in the case that qgroups are not
  	 * enabled. If this check races with the ioctl, rescan will
  	 * kick in anyway.
  	 */
  	mutex_lock(&fs_info->qgroup_ioctl_lock);

  	if (!test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags)) {

  		mutex_unlock(&fs_info->qgroup_ioctl_lock);
  		return 0;
  	}
  	mutex_unlock(&fs_info->qgroup_ioctl_lock);
  
  	/*
  	 * We are going to commit transaction, see btrfs_commit_transaction()
  	 * comment for reason locking tree_log_mutex
  	 */
  	mutex_lock(&fs_info->tree_log_mutex);
  
  	ret = commit_fs_roots(trans, src);
  	if (ret)
  		goto out;
  	ret = btrfs_qgroup_prepare_account_extents(trans, fs_info);
  	if (ret < 0)
  		goto out;
  	ret = btrfs_qgroup_account_extents(trans, fs_info);
  	if (ret < 0)
  		goto out;
  
  	/* Now qgroup are all updated, we can inherit it to new qgroups */
  	ret = btrfs_qgroup_inherit(trans, fs_info,
  				   src->root_key.objectid, dst_objectid,
  				   inherit);
  	if (ret < 0)
  		goto out;
  
  	/*
  	 * Now we do a simplified commit transaction, which will:
  	 * 1) commit all subvolume and extent tree
  	 *    To ensure all subvolume and extent tree have a valid
  	 *    commit_root to accounting later insert_dir_item()
  	 * 2) write all btree blocks onto disk
  	 *    This is to make sure later btree modification will be cowed
  	 *    Or commit_root can be populated and cause wrong qgroup numbers
  	 * In this simplified commit, we don't really care about other trees
  	 * like chunk and root tree, as they won't affect qgroup.
  	 * And we don't write super to avoid half committed status.
  	 */
  	ret = commit_cowonly_roots(trans, src);
  	if (ret)
  		goto out;
  	switch_commit_roots(trans->transaction, fs_info);
  	ret = btrfs_write_and_wait_transaction(trans, src);
  	if (ret)

  		btrfs_handle_fs_error(fs_info, ret,

  			"Error while writing out transaction for qgroup");
  
  out:
  	mutex_unlock(&fs_info->tree_log_mutex);
  
  	/*
  	 * Force parent root to be updated, as we recorded it before so its
  	 * last_trans == cur_transid.
  	 * Or it won't be committed again onto disk after later
  	 * insert_dir_item()
  	 */
  	if (!ret)
  		record_root_in_trans(trans, parent, 1);
  	return ret;
  }
  
  /*

   * new snapshots need to be created at a very specific time in the

   * transaction commit.  This does the actual creation.
   *
   * Note:
   * If the error which may affect the commitment of the current transaction
   * happens, we should return the error number. If the error which just affect
   * the creation of the pending snapshots, just return 0.

   */

  static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,

  				   struct btrfs_fs_info *fs_info,
  				   struct btrfs_pending_snapshot *pending)
  {
  	struct btrfs_key key;

  	struct btrfs_root_item *new_root_item;

  	struct btrfs_root *tree_root = fs_info->tree_root;
  	struct btrfs_root *root = pending->root;

  	struct btrfs_root *parent_root;