/*
   * 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/slab.h>

  #include <linux/blkdev.h>

  #include <linux/writeback.h>
  #include <linux/pagevec.h>

  #include "ctree.h"
  #include "transaction.h"
  #include "btrfs_inode.h"

  #include "extent_io.h"

  static u64 entry_end(struct btrfs_ordered_extent *entry)

  {

  	if (entry->file_offset + entry->len < entry->file_offset)
  		return (u64)-1;
  	return entry->file_offset + entry->len;

  }

  /* returns NULL if the insertion worked, or it returns the node it did find
   * in the tree
   */

  static struct rb_node *tree_insert(struct rb_root *root, u64 file_offset,
  				   struct rb_node *node)

  {

  	struct rb_node **p = &root->rb_node;
  	struct rb_node *parent = NULL;

  	struct btrfs_ordered_extent *entry;

  	while (*p) {

  		parent = *p;

  		entry = rb_entry(parent, struct btrfs_ordered_extent, rb_node);

  		if (file_offset < entry->file_offset)

  			p = &(*p)->rb_left;

  		else if (file_offset >= entry_end(entry))

  			p = &(*p)->rb_right;
  		else
  			return parent;
  	}
  
  	rb_link_node(node, parent, p);
  	rb_insert_color(node, root);
  	return NULL;
  }

  /*
   * look for a given offset in the tree, and if it can't be found return the
   * first lesser offset
   */

  static struct rb_node *__tree_search(struct rb_root *root, u64 file_offset,
  				     struct rb_node **prev_ret)

  {

  	struct rb_node *n = root->rb_node;

  	struct rb_node *prev = NULL;

  	struct rb_node *test;
  	struct btrfs_ordered_extent *entry;
  	struct btrfs_ordered_extent *prev_entry = NULL;

  	while (n) {

  		entry = rb_entry(n, struct btrfs_ordered_extent, rb_node);

  		prev = n;
  		prev_entry = entry;

  		if (file_offset < entry->file_offset)

  			n = n->rb_left;

  		else if (file_offset >= entry_end(entry))

  			n = n->rb_right;
  		else
  			return n;
  	}
  	if (!prev_ret)
  		return NULL;

  	while (prev && file_offset >= entry_end(prev_entry)) {

  		test = rb_next(prev);
  		if (!test)
  			break;
  		prev_entry = rb_entry(test, struct btrfs_ordered_extent,
  				      rb_node);
  		if (file_offset < entry_end(prev_entry))
  			break;
  
  		prev = test;
  	}
  	if (prev)
  		prev_entry = rb_entry(prev, struct btrfs_ordered_extent,
  				      rb_node);

  	while (prev && file_offset < entry_end(prev_entry)) {

  		test = rb_prev(prev);
  		if (!test)
  			break;
  		prev_entry = rb_entry(test, struct btrfs_ordered_extent,
  				      rb_node);
  		prev = test;

  	}
  	*prev_ret = prev;
  	return NULL;
  }

  /*
   * helper to check if a given offset is inside a given entry
   */

  static int offset_in_entry(struct btrfs_ordered_extent *entry, u64 file_offset)
  {
  	if (file_offset < entry->file_offset ||
  	    entry->file_offset + entry->len <= file_offset)
  		return 0;
  	return 1;
  }

  static int range_overlaps(struct btrfs_ordered_extent *entry, u64 file_offset,
  			  u64 len)
  {
  	if (file_offset + len <= entry->file_offset ||
  	    entry->file_offset + entry->len <= file_offset)
  		return 0;
  	return 1;
  }

  /*
   * look find the first ordered struct that has this offset, otherwise
   * the first one less than this offset
   */

  static inline struct rb_node *tree_search(struct btrfs_ordered_inode_tree *tree,
  					  u64 file_offset)

  {

  	struct rb_root *root = &tree->tree;

  	struct rb_node *prev = NULL;

  	struct rb_node *ret;

  	struct btrfs_ordered_extent *entry;
  
  	if (tree->last) {
  		entry = rb_entry(tree->last, struct btrfs_ordered_extent,
  				 rb_node);
  		if (offset_in_entry(entry, file_offset))
  			return tree->last;
  	}
  	ret = __tree_search(root, file_offset, &prev);

  	if (!ret)

  		ret = prev;
  	if (ret)
  		tree->last = ret;

  	return ret;
  }

  /* allocate and add a new ordered_extent into the per-inode tree.
   * file_offset is the logical offset in the file
   *
   * start is the disk block number of an extent already reserved in the
   * extent allocation tree
   *
   * len is the length of the extent
   *

   * The tree is given a single reference on the ordered extent that was
   * inserted.
   */

  static int __btrfs_add_ordered_extent(struct inode *inode, u64 file_offset,
  				      u64 start, u64 len, u64 disk_len,

  				      int type, int dio, int compress_type)

  {

  	struct btrfs_ordered_inode_tree *tree;

  	struct rb_node *node;
  	struct btrfs_ordered_extent *entry;

  	tree = &BTRFS_I(inode)->ordered_tree;
  	entry = kzalloc(sizeof(*entry), GFP_NOFS);

  	if (!entry)
  		return -ENOMEM;

  	entry->file_offset = file_offset;
  	entry->start = start;
  	entry->len = len;

  	entry->disk_len = disk_len;

  	entry->bytes_left = len;

  	entry->inode = inode;

  	entry->compress_type = compress_type;

  	if (type != BTRFS_ORDERED_IO_DONE && type != BTRFS_ORDERED_COMPLETE)

  		set_bit(type, &entry->flags);

  	if (dio)
  		set_bit(BTRFS_ORDERED_DIRECT, &entry->flags);

  	/* one ref for the tree */
  	atomic_set(&entry->refs, 1);
  	init_waitqueue_head(&entry->wait);
  	INIT_LIST_HEAD(&entry->list);

  	INIT_LIST_HEAD(&entry->root_extent_list);

  	trace_btrfs_ordered_extent_add(inode, entry);

  	spin_lock(&tree->lock);

  	node = tree_insert(&tree->tree, file_offset,
  			   &entry->rb_node);

  	BUG_ON(node);

  	spin_unlock(&tree->lock);

  	spin_lock(&BTRFS_I(inode)->root->fs_info->ordered_extent_lock);
  	list_add_tail(&entry->root_extent_list,
  		      &BTRFS_I(inode)->root->fs_info->ordered_extents);
  	spin_unlock(&BTRFS_I(inode)->root->fs_info->ordered_extent_lock);

  	BUG_ON(node);

  	return 0;
  }

  int btrfs_add_ordered_extent(struct inode *inode, u64 file_offset,
  			     u64 start, u64 len, u64 disk_len, int type)
  {
  	return __btrfs_add_ordered_extent(inode, file_offset, start, len,

  					  disk_len, type, 0,
  					  BTRFS_COMPRESS_NONE);

  }
  
  int btrfs_add_ordered_extent_dio(struct inode *inode, u64 file_offset,
  				 u64 start, u64 len, u64 disk_len, int type)
  {
  	return __btrfs_add_ordered_extent(inode, file_offset, start, len,

  					  disk_len, type, 1,
  					  BTRFS_COMPRESS_NONE);
  }
  
  int btrfs_add_ordered_extent_compress(struct inode *inode, u64 file_offset,
  				      u64 start, u64 len, u64 disk_len,
  				      int type, int compress_type)
  {
  	return __btrfs_add_ordered_extent(inode, file_offset, start, len,
  					  disk_len, type, 0,
  					  compress_type);

  }

  /*
   * Add a struct btrfs_ordered_sum into the list of checksums to be inserted

   * when an ordered extent is finished.  If the list covers more than one
   * ordered extent, it is split across multiples.

   */

  int btrfs_add_ordered_sum(struct inode *inode,
  			  struct btrfs_ordered_extent *entry,
  			  struct btrfs_ordered_sum *sum)

  {

  	struct btrfs_ordered_inode_tree *tree;

  	tree = &BTRFS_I(inode)->ordered_tree;

  	spin_lock(&tree->lock);

  	list_add_tail(&sum->list, &entry->list);

  	spin_unlock(&tree->lock);

  	return 0;

  }

  /*
   * this is used to account for finished IO across a given range

   * of the file.  The IO may span ordered extents.  If
   * a given ordered_extent is completely done, 1 is returned, otherwise
   * 0.
   *
   * test_and_set_bit on a flag in the struct btrfs_ordered_extent is used
   * to make sure this function only returns 1 once for a given ordered extent.
   *
   * file_offset is updated to one byte past the range that is recorded as
   * complete.  This allows you to walk forward in the file.
   */
  int btrfs_dec_test_first_ordered_pending(struct inode *inode,
  				   struct btrfs_ordered_extent **cached,
  				   u64 *file_offset, u64 io_size)
  {
  	struct btrfs_ordered_inode_tree *tree;
  	struct rb_node *node;
  	struct btrfs_ordered_extent *entry = NULL;
  	int ret;
  	u64 dec_end;
  	u64 dec_start;
  	u64 to_dec;
  
  	tree = &BTRFS_I(inode)->ordered_tree;
  	spin_lock(&tree->lock);
  	node = tree_search(tree, *file_offset);
  	if (!node) {
  		ret = 1;
  		goto out;
  	}
  
  	entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
  	if (!offset_in_entry(entry, *file_offset)) {
  		ret = 1;
  		goto out;
  	}
  
  	dec_start = max(*file_offset, entry->file_offset);
  	dec_end = min(*file_offset + io_size, entry->file_offset +
  		      entry->len);
  	*file_offset = dec_end;
  	if (dec_start > dec_end) {
  		printk(KERN_CRIT "bad ordering dec_start %llu end %llu
  ",
  		       (unsigned long long)dec_start,
  		       (unsigned long long)dec_end);
  	}
  	to_dec = dec_end - dec_start;
  	if (to_dec > entry->bytes_left) {
  		printk(KERN_CRIT "bad ordered accounting left %llu size %llu
  ",
  		       (unsigned long long)entry->bytes_left,
  		       (unsigned long long)to_dec);
  	}
  	entry->bytes_left -= to_dec;
  	if (entry->bytes_left == 0)
  		ret = test_and_set_bit(BTRFS_ORDERED_IO_DONE, &entry->flags);
  	else
  		ret = 1;
  out:
  	if (!ret && cached && entry) {
  		*cached = entry;
  		atomic_inc(&entry->refs);
  	}
  	spin_unlock(&tree->lock);
  	return ret == 0;
  }
  
  /*
   * this is used to account for finished IO across a given range

   * of the file.  The IO should not span ordered extents.  If
   * a given ordered_extent is completely done, 1 is returned, otherwise
   * 0.
   *
   * test_and_set_bit on a flag in the struct btrfs_ordered_extent is used
   * to make sure this function only returns 1 once for a given ordered extent.
   */

  int btrfs_dec_test_ordered_pending(struct inode *inode,

  				   struct btrfs_ordered_extent **cached,

  				   u64 file_offset, u64 io_size)

  {

  	struct btrfs_ordered_inode_tree *tree;

  	struct rb_node *node;

  	struct btrfs_ordered_extent *entry = NULL;

  	int ret;
  
  	tree = &BTRFS_I(inode)->ordered_tree;

  	spin_lock(&tree->lock);

  	node = tree_search(tree, file_offset);

  	if (!node) {

  		ret = 1;
  		goto out;

  	}

  	entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
  	if (!offset_in_entry(entry, file_offset)) {
  		ret = 1;
  		goto out;

  	}

  	if (io_size > entry->bytes_left) {
  		printk(KERN_CRIT "bad ordered accounting left %llu size %llu
  ",
  		       (unsigned long long)entry->bytes_left,
  		       (unsigned long long)io_size);
  	}
  	entry->bytes_left -= io_size;
  	if (entry->bytes_left == 0)

  		ret = test_and_set_bit(BTRFS_ORDERED_IO_DONE, &entry->flags);

  	else
  		ret = 1;

  out:

  	if (!ret && cached && entry) {
  		*cached = entry;
  		atomic_inc(&entry->refs);
  	}

  	spin_unlock(&tree->lock);

  	return ret == 0;
  }

  /*
   * used to drop a reference on an ordered extent.  This will free
   * the extent if the last reference is dropped
   */

  int btrfs_put_ordered_extent(struct btrfs_ordered_extent *entry)
  {

  	struct list_head *cur;
  	struct btrfs_ordered_sum *sum;

  	trace_btrfs_ordered_extent_put(entry->inode, entry);

  	if (atomic_dec_and_test(&entry->refs)) {

  		while (!list_empty(&entry->list)) {

  			cur = entry->list.next;
  			sum = list_entry(cur, struct btrfs_ordered_sum, list);
  			list_del(&sum->list);
  			kfree(sum);
  		}

  		kfree(entry);

  	}

  	return 0;

  }

  /*
   * remove an ordered extent from the tree.  No references are dropped

   * and you must wake_up entry->wait.  You must hold the tree lock

   * while you call this function.

   */

  static int __btrfs_remove_ordered_extent(struct inode *inode,

  				struct btrfs_ordered_extent *entry)

  {

  	struct btrfs_ordered_inode_tree *tree;

  	struct btrfs_root *root = BTRFS_I(inode)->root;

  	struct rb_node *node;

  	tree = &BTRFS_I(inode)->ordered_tree;

  	node = &entry->rb_node;

  	rb_erase(node, &tree->tree);

  	tree->last = NULL;
  	set_bit(BTRFS_ORDERED_COMPLETE, &entry->flags);

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

  	list_del_init(&entry->root_extent_list);

  	trace_btrfs_ordered_extent_remove(inode, entry);

  	/*
  	 * we have no more ordered extents for this inode and
  	 * no dirty pages.  We can safely remove it from the
  	 * list of ordered extents
  	 */
  	if (RB_EMPTY_ROOT(&tree->tree) &&
  	    !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
  		list_del_init(&BTRFS_I(inode)->ordered_operations);
  	}

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

  	return 0;
  }
  
  /*
   * remove an ordered extent from the tree.  No references are dropped
   * but any waiters are woken.
   */
  int btrfs_remove_ordered_extent(struct inode *inode,
  				struct btrfs_ordered_extent *entry)
  {
  	struct btrfs_ordered_inode_tree *tree;
  	int ret;
  
  	tree = &BTRFS_I(inode)->ordered_tree;

  	spin_lock(&tree->lock);

  	ret = __btrfs_remove_ordered_extent(inode, entry);

  	spin_unlock(&tree->lock);

  	wake_up(&entry->wait);

  
  	return ret;

  }

  /*
   * wait for all the ordered extents in a root.  This is done when balancing
   * space between drives.
   */

  int btrfs_wait_ordered_extents(struct btrfs_root *root,
  			       int nocow_only, int delay_iput)

  {
  	struct list_head splice;
  	struct list_head *cur;
  	struct btrfs_ordered_extent *ordered;
  	struct inode *inode;
  
  	INIT_LIST_HEAD(&splice);
  
  	spin_lock(&root->fs_info->ordered_extent_lock);
  	list_splice_init(&root->fs_info->ordered_extents, &splice);

  	while (!list_empty(&splice)) {

  		cur = splice.next;
  		ordered = list_entry(cur, struct btrfs_ordered_extent,
  				     root_extent_list);

  		if (nocow_only &&

  		    !test_bit(BTRFS_ORDERED_NOCOW, &ordered->flags) &&
  		    !test_bit(BTRFS_ORDERED_PREALLOC, &ordered->flags)) {

  			list_move(&ordered->root_extent_list,
  				  &root->fs_info->ordered_extents);

  			cond_resched_lock(&root->fs_info->ordered_extent_lock);
  			continue;
  		}

  		list_del_init(&ordered->root_extent_list);
  		atomic_inc(&ordered->refs);

  
  		/*

  		 * the inode may be getting freed (in sys_unlink path).

  		 */

  		inode = igrab(ordered->inode);

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

  		if (inode) {
  			btrfs_start_ordered_extent(inode, ordered, 1);
  			btrfs_put_ordered_extent(ordered);

  			if (delay_iput)
  				btrfs_add_delayed_iput(inode);
  			else
  				iput(inode);

  		} else {
  			btrfs_put_ordered_extent(ordered);
  		}

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

  /*

   * this is used during transaction commit to write all the inodes
   * added to the ordered operation list.  These files must be fully on
   * disk before the transaction commits.
   *
   * we have two modes here, one is to just start the IO via filemap_flush
   * and the other is to wait for all the io.  When we wait, we have an
   * extra check to make sure the ordered operation list really is empty
   * before we return
   */
  int btrfs_run_ordered_operations(struct btrfs_root *root, int wait)
  {
  	struct btrfs_inode *btrfs_inode;
  	struct inode *inode;
  	struct list_head splice;
  
  	INIT_LIST_HEAD(&splice);
  
  	mutex_lock(&root->fs_info->ordered_operations_mutex);
  	spin_lock(&root->fs_info->ordered_extent_lock);
  again:
  	list_splice_init(&root->fs_info->ordered_operations, &splice);
  
  	while (!list_empty(&splice)) {
  		btrfs_inode = list_entry(splice.next, struct btrfs_inode,
  				   ordered_operations);
  
  		inode = &btrfs_inode->vfs_inode;
  
  		list_del_init(&btrfs_inode->ordered_operations);
  
  		/*
  		 * the inode may be getting freed (in sys_unlink path).
  		 */
  		inode = igrab(inode);
  
  		if (!wait && inode) {
  			list_add_tail(&BTRFS_I(inode)->ordered_operations,
  			      &root->fs_info->ordered_operations);
  		}
  		spin_unlock(&root->fs_info->ordered_extent_lock);
  
  		if (inode) {
  			if (wait)
  				btrfs_wait_ordered_range(inode, 0, (u64)-1);
  			else
  				filemap_flush(inode->i_mapping);

  			btrfs_add_delayed_iput(inode);

  		}
  
  		cond_resched();
  		spin_lock(&root->fs_info->ordered_extent_lock);
  	}
  	if (wait && !list_empty(&root->fs_info->ordered_operations))
  		goto again;
  
  	spin_unlock(&root->fs_info->ordered_extent_lock);
  	mutex_unlock(&root->fs_info->ordered_operations_mutex);
  
  	return 0;
  }
  
  /*

   * Used to start IO or wait for a given ordered extent to finish.
   *
   * If wait is one, this effectively waits on page writeback for all the pages
   * in the extent, and it waits on the io completion code to insert
   * metadata into the btree corresponding to the extent
   */
  void btrfs_start_ordered_extent(struct inode *inode,
  				       struct btrfs_ordered_extent *entry,
  				       int wait)

  {
  	u64 start = entry->file_offset;
  	u64 end = start + entry->len - 1;

  	trace_btrfs_ordered_extent_start(inode, entry);

  	/*
  	 * pages in the range can be dirty, clean or writeback.  We
  	 * start IO on any dirty ones so the wait doesn't stall waiting
  	 * for pdflush to find them
  	 */

  	if (!test_bit(BTRFS_ORDERED_DIRECT, &entry->flags))
  		filemap_fdatawrite_range(inode->i_mapping, start, end);

  	if (wait) {

  		wait_event(entry->wait, test_bit(BTRFS_ORDERED_COMPLETE,
  						 &entry->flags));

  	}

  }

  /*
   * Used to wait on ordered extents across a large range of bytes.
   */

  int btrfs_wait_ordered_range(struct inode *inode, u64 start, u64 len)

  {
  	u64 end;

  	u64 orig_end;

  	struct btrfs_ordered_extent *ordered;

  	int found;

  
  	if (start + len < start) {

  		orig_end = INT_LIMIT(loff_t);

  	} else {
  		orig_end = start + len - 1;

  		if (orig_end > INT_LIMIT(loff_t))
  			orig_end = INT_LIMIT(loff_t);

  	}

  again:

  	/* start IO across the range first to instantiate any delalloc
  	 * extents
  	 */

  	filemap_fdatawrite_range(inode->i_mapping, start, orig_end);

  	/* The compression code will leave pages locked but return from
  	 * writepage without setting the page writeback.  Starting again
  	 * with WB_SYNC_ALL will end up waiting for the IO to actually start.
  	 */

  	filemap_fdatawrite_range(inode->i_mapping, start, orig_end);

  	filemap_fdatawait_range(inode->i_mapping, start, orig_end);

  	end = orig_end;

  	found = 0;

  	while (1) {

  		ordered = btrfs_lookup_first_ordered_extent(inode, end);

  		if (!ordered)

  			break;

  		if (ordered->file_offset > orig_end) {

  			btrfs_put_ordered_extent(ordered);
  			break;
  		}
  		if (ordered->file_offset + ordered->len < start) {
  			btrfs_put_ordered_extent(ordered);
  			break;
  		}

  		found++;

  		btrfs_start_ordered_extent(inode, ordered, 1);

  		end = ordered->file_offset;
  		btrfs_put_ordered_extent(ordered);

  		if (end == 0 || end == start)

  			break;
  		end--;
  	}

  	if (found || test_range_bit(&BTRFS_I(inode)->io_tree, start, orig_end,
  			   EXTENT_DELALLOC, 0, NULL)) {

  		schedule_timeout(1);

  		goto again;
  	}

  	return 0;

  }

  /*
   * find an ordered extent corresponding to file_offset.  return NULL if
   * nothing is found, otherwise take a reference on the extent and return it
   */

  struct btrfs_ordered_extent *btrfs_lookup_ordered_extent(struct inode *inode,
  							 u64 file_offset)
  {
  	struct btrfs_ordered_inode_tree *tree;
  	struct rb_node *node;
  	struct btrfs_ordered_extent *entry = NULL;
  
  	tree = &BTRFS_I(inode)->ordered_tree;

  	spin_lock(&tree->lock);

  	node = tree_search(tree, file_offset);
  	if (!node)
  		goto out;
  
  	entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
  	if (!offset_in_entry(entry, file_offset))
  		entry = NULL;
  	if (entry)
  		atomic_inc(&entry->refs);
  out:

  	spin_unlock(&tree->lock);

  	return entry;
  }

  /* Since the DIO code tries to lock a wide area we need to look for any ordered
   * extents that exist in the range, rather than just the start of the range.
   */
  struct btrfs_ordered_extent *btrfs_lookup_ordered_range(struct inode *inode,
  							u64 file_offset,
  							u64 len)
  {
  	struct btrfs_ordered_inode_tree *tree;
  	struct rb_node *node;
  	struct btrfs_ordered_extent *entry = NULL;
  
  	tree = &BTRFS_I(inode)->ordered_tree;
  	spin_lock(&tree->lock);
  	node = tree_search(tree, file_offset);
  	if (!node) {
  		node = tree_search(tree, file_offset + len);
  		if (!node)
  			goto out;
  	}
  
  	while (1) {
  		entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
  		if (range_overlaps(entry, file_offset, len))
  			break;
  
  		if (entry->file_offset >= file_offset + len) {
  			entry = NULL;
  			break;
  		}
  		entry = NULL;
  		node = rb_next(node);
  		if (!node)
  			break;
  	}
  out:
  	if (entry)
  		atomic_inc(&entry->refs);
  	spin_unlock(&tree->lock);
  	return entry;
  }

  /*
   * lookup and return any extent before 'file_offset'.  NULL is returned
   * if none is found
   */

  struct btrfs_ordered_extent *

  btrfs_lookup_first_ordered_extent(struct inode *inode, u64 file_offset)

  {
  	struct btrfs_ordered_inode_tree *tree;
  	struct rb_node *node;
  	struct btrfs_ordered_extent *entry = NULL;
  
  	tree = &BTRFS_I(inode)->ordered_tree;

  	spin_lock(&tree->lock);

  	node = tree_search(tree, file_offset);
  	if (!node)
  		goto out;
  
  	entry = rb_entry(node, struct btrfs_ordered_extent, rb_node);
  	atomic_inc(&entry->refs);
  out:

  	spin_unlock(&tree->lock);

  	return entry;

  }

  /*
   * After an extent is done, call this to conditionally update the on disk
   * i_size.  i_size is updated to cover any fully written part of the file.
   */

  int btrfs_ordered_update_i_size(struct inode *inode, u64 offset,

  				struct btrfs_ordered_extent *ordered)
  {
  	struct btrfs_ordered_inode_tree *tree = &BTRFS_I(inode)->ordered_tree;
  	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
  	u64 disk_i_size;
  	u64 new_i_size;
  	u64 i_size_test;

  	u64 i_size = i_size_read(inode);

  	struct rb_node *node;

  	struct rb_node *prev = NULL;

  	struct btrfs_ordered_extent *test;

  	int ret = 1;
  
  	if (ordered)
  		offset = entry_end(ordered);

  	else
  		offset = ALIGN(offset, BTRFS_I(inode)->root->sectorsize);

  	spin_lock(&tree->lock);

  	disk_i_size = BTRFS_I(inode)->disk_i_size;

  	/* truncate file */
  	if (disk_i_size > i_size) {
  		BTRFS_I(inode)->disk_i_size = i_size;
  		ret = 0;
  		goto out;
  	}

  	/*
  	 * if the disk i_size is already at the inode->i_size, or
  	 * this ordered extent is inside the disk i_size, we're done
  	 */

  	if (disk_i_size == i_size || offset <= disk_i_size) {

  		goto out;
  	}
  
  	/*
  	 * we can't update the disk_isize if there are delalloc bytes
  	 * between disk_i_size and  this ordered extent
  	 */

  	if (test_range_bit(io_tree, disk_i_size, offset - 1,

  			   EXTENT_DELALLOC, 0, NULL)) {

  		goto out;
  	}
  	/*
  	 * walk backward from this ordered extent to disk_i_size.
  	 * if we find an ordered extent then we can't update disk i_size
  	 * yet
  	 */

  	if (ordered) {
  		node = rb_prev(&ordered->rb_node);
  	} else {
  		prev = tree_search(tree, offset);
  		/*
  		 * we insert file extents without involving ordered struct,
  		 * so there should be no ordered struct cover this offset
  		 */
  		if (prev) {
  			test = rb_entry(prev, struct btrfs_ordered_extent,
  					rb_node);
  			BUG_ON(offset_in_entry(test, offset));
  		}
  		node = prev;
  	}
  	while (node) {

  		test = rb_entry(node, struct btrfs_ordered_extent, rb_node);
  		if (test->file_offset + test->len <= disk_i_size)
  			break;

  		if (test->file_offset >= i_size)

  			break;
  		if (test->file_offset >= disk_i_size)
  			goto out;

  		node = rb_prev(node);

  	}

  	new_i_size = min_t(u64, offset, i_size);

  
  	/*
  	 * at this point, we know we can safely update i_size to at least
  	 * the offset from this ordered extent.  But, we need to
  	 * walk forward and see if ios from higher up in the file have
  	 * finished.
  	 */

  	if (ordered) {
  		node = rb_next(&ordered->rb_node);
  	} else {
  		if (prev)
  			node = rb_next(prev);
  		else
  			node = rb_first(&tree->tree);
  	}

  	i_size_test = 0;
  	if (node) {
  		/*
  		 * do we have an area where IO might have finished
  		 * between our ordered extent and the next one.
  		 */
  		test = rb_entry(node, struct btrfs_ordered_extent, rb_node);

  		if (test->file_offset > offset)

  			i_size_test = test->file_offset;

  	} else {

  		i_size_test = i_size;

  	}
  
  	/*
  	 * i_size_test is the end of a region after this ordered
  	 * extent where there are no ordered extents.  As long as there
  	 * are no delalloc bytes in this area, it is safe to update
  	 * disk_i_size to the end of the region.
  	 */

  	if (i_size_test > offset &&
  	    !test_range_bit(io_tree, offset, i_size_test - 1,
  			    EXTENT_DELALLOC, 0, NULL)) {
  		new_i_size = min_t(u64, i_size_test, i_size);

  	}
  	BTRFS_I(inode)->disk_i_size = new_i_size;

  	ret = 0;

  out:

  	/*
  	 * we need to remove the ordered extent with the tree lock held
  	 * so that other people calling this function don't find our fully
  	 * processed ordered entry and skip updating the i_size
  	 */
  	if (ordered)
  		__btrfs_remove_ordered_extent(inode, ordered);

  	spin_unlock(&tree->lock);

  	if (ordered)
  		wake_up(&ordered->wait);
  	return ret;

  }

  /*
   * search the ordered extents for one corresponding to 'offset' and
   * try to find a checksum.  This is used because we allow pages to
   * be reclaimed before their checksum is actually put into the btree
   */

  int btrfs_find_ordered_sum(struct inode *inode, u64 offset, u64 disk_bytenr,
  			   u32 *sum)

  {
  	struct btrfs_ordered_sum *ordered_sum;
  	struct btrfs_sector_sum *sector_sums;
  	struct btrfs_ordered_extent *ordered;
  	struct btrfs_ordered_inode_tree *tree = &BTRFS_I(inode)->ordered_tree;

  	unsigned long num_sectors;
  	unsigned long i;
  	u32 sectorsize = BTRFS_I(inode)->root->sectorsize;

  	int ret = 1;

  
  	ordered = btrfs_lookup_ordered_extent(inode, offset);
  	if (!ordered)
  		return 1;

  	spin_lock(&tree->lock);

  	list_for_each_entry_reverse(ordered_sum, &ordered->list, list) {

  		if (disk_bytenr >= ordered_sum->bytenr) {

  			num_sectors = ordered_sum->len / sectorsize;

  			sector_sums = ordered_sum->sums;

  			for (i = 0; i < num_sectors; i++) {

  				if (sector_sums[i].bytenr == disk_bytenr) {

  					*sum = sector_sums[i].sum;
  					ret = 0;
  					goto out;
  				}
  			}

  		}
  	}
  out:

  	spin_unlock(&tree->lock);

  	btrfs_put_ordered_extent(ordered);

  	return ret;
  }

  /*
   * add a given inode to the list of inodes that must be fully on
   * disk before a transaction commit finishes.
   *
   * This basically gives us the ext3 style data=ordered mode, and it is mostly
   * used to make sure renamed files are fully on disk.
   *
   * It is a noop if the inode is already fully on disk.
   *
   * If trans is not null, we'll do a friendly check for a transaction that
   * is already flushing things and force the IO down ourselves.
   */
  int btrfs_add_ordered_operation(struct btrfs_trans_handle *trans,
  				struct btrfs_root *root,
  				struct inode *inode)
  {
  	u64 last_mod;
  
  	last_mod = max(BTRFS_I(inode)->generation, BTRFS_I(inode)->last_trans);
  
  	/*
  	 * if this file hasn't been changed since the last transaction
  	 * commit, we can safely return without doing anything
  	 */
  	if (last_mod < root->fs_info->last_trans_committed)
  		return 0;
  
  	/*
  	 * the transaction is already committing.  Just start the IO and
  	 * don't bother with all of this list nonsense
  	 */
  	if (trans && root->fs_info->running_transaction->blocked) {
  		btrfs_wait_ordered_range(inode, 0, (u64)-1);
  		return 0;
  	}
  
  	spin_lock(&root->fs_info->ordered_extent_lock);
  	if (list_empty(&BTRFS_I(inode)->ordered_operations)) {
  		list_add_tail(&BTRFS_I(inode)->ordered_operations,
  			      &root->fs_info->ordered_operations);
  	}
  	spin_unlock(&root->fs_info->ordered_extent_lock);
  
  	return 0;
  }