OpenCloudOS-Kernel/fs/btrfs/free-space-cache.c

/*
 * Copyright (C) 2008 Red Hat.  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/pagemap.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/math64.h>
#include <linux/ratelimit.h>
#include "ctree.h"
#include "free-space-cache.h"
#include "transaction.h"
#include "disk-io.h"
#include "extent_io.h"
#include "inode-map.h"

#define BITS_PER_BITMAP		(PAGE_CACHE_SIZE * 8)
#define MAX_CACHE_BYTES_PER_GIG	(32 * 1024)

static int link_free_space(struct btrfs_free_space_ctl *ctl,
			   struct btrfs_free_space *info);

static struct inode *__lookup_free_space_inode(struct btrfs_root *root,
					       struct btrfs_path *path,
					       u64 offset)
{
	struct btrfs_key key;
	struct btrfs_key location;
	struct btrfs_disk_key disk_key;
	struct btrfs_free_space_header *header;
	struct extent_buffer *leaf;
	struct inode *inode = NULL;
	int ret;

	key.objectid = BTRFS_FREE_SPACE_OBJECTID;
	key.offset = offset;
	key.type = 0;

	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
	if (ret < 0)
		return ERR_PTR(ret);
	if (ret > 0) {
		btrfs_release_path(path);
		return ERR_PTR(-ENOENT);
	}

	leaf = path->nodes[0];
	header = btrfs_item_ptr(leaf, path->slots[0],
				struct btrfs_free_space_header);
	btrfs_free_space_key(leaf, header, &disk_key);
	btrfs_disk_key_to_cpu(&location, &disk_key);
	btrfs_release_path(path);

	inode = btrfs_iget(root->fs_info->sb, &location, root, NULL);
	if (!inode)
		return ERR_PTR(-ENOENT);
	if (IS_ERR(inode))
		return inode;
	if (is_bad_inode(inode)) {
		iput(inode);
		return ERR_PTR(-ENOENT);
	}

	inode->i_mapping->flags &= ~__GFP_FS;

	return inode;
}

struct inode *lookup_free_space_inode(struct btrfs_root *root,
				      struct btrfs_block_group_cache
				      *block_group, struct btrfs_path *path)
{
	struct inode *inode = NULL;
	u32 flags = BTRFS_INODE_NODATASUM | BTRFS_INODE_NODATACOW;

	spin_lock(&block_group->lock);
	if (block_group->inode)
		inode = igrab(block_group->inode);
	spin_unlock(&block_group->lock);
	if (inode)
		return inode;

	inode = __lookup_free_space_inode(root, path,
					  block_group->key.objectid);
	if (IS_ERR(inode))
		return inode;

	spin_lock(&block_group->lock);
	if (!((BTRFS_I(inode)->flags & flags) == flags)) {
		printk(KERN_INFO "Old style space inode found, converting.\n");
		BTRFS_I(inode)->flags |= BTRFS_INODE_NODATASUM |
			BTRFS_INODE_NODATACOW;
		block_group->disk_cache_state = BTRFS_DC_CLEAR;
	}

	if (!block_group->iref) {
		block_group->inode = igrab(inode);
		block_group->iref = 1;
	}
	spin_unlock(&block_group->lock);

	return inode;
}

int __create_free_space_inode(struct btrfs_root *root,
			      struct btrfs_trans_handle *trans,
			      struct btrfs_path *path, u64 ino, u64 offset)
{
	struct btrfs_key key;
	struct btrfs_disk_key disk_key;
	struct btrfs_free_space_header *header;
	struct btrfs_inode_item *inode_item;
	struct extent_buffer *leaf;
	u64 flags = BTRFS_INODE_NOCOMPRESS | BTRFS_INODE_PREALLOC;
	int ret;

	ret = btrfs_insert_empty_inode(trans, root, path, ino);
	if (ret)
		return ret;

	/* We inline crc's for the free disk space cache */
	if (ino != BTRFS_FREE_INO_OBJECTID)
		flags |= BTRFS_INODE_NODATASUM | BTRFS_INODE_NODATACOW;

	leaf = path->nodes[0];
	inode_item = btrfs_item_ptr(leaf, path->slots[0],
				    struct btrfs_inode_item);
	btrfs_item_key(leaf, &disk_key, path->slots[0]);
	memset_extent_buffer(leaf, 0, (unsigned long)inode_item,
			     sizeof(*inode_item));
	btrfs_set_inode_generation(leaf, inode_item, trans->transid);
	btrfs_set_inode_size(leaf, inode_item, 0);
	btrfs_set_inode_nbytes(leaf, inode_item, 0);
	btrfs_set_inode_uid(leaf, inode_item, 0);
	btrfs_set_inode_gid(leaf, inode_item, 0);
	btrfs_set_inode_mode(leaf, inode_item, S_IFREG | 0600);
	btrfs_set_inode_flags(leaf, inode_item, flags);
	btrfs_set_inode_nlink(leaf, inode_item, 1);
	btrfs_set_inode_transid(leaf, inode_item, trans->transid);
	btrfs_set_inode_block_group(leaf, inode_item, offset);
	btrfs_mark_buffer_dirty(leaf);
	btrfs_release_path(path);

	key.objectid = BTRFS_FREE_SPACE_OBJECTID;
	key.offset = offset;
	key.type = 0;

	ret = btrfs_insert_empty_item(trans, root, path, &key,
				      sizeof(struct btrfs_free_space_header));
	if (ret < 0) {
		btrfs_release_path(path);
		return ret;
	}
	leaf = path->nodes[0];
	header = btrfs_item_ptr(leaf, path->slots[0],
				struct btrfs_free_space_header);
	memset_extent_buffer(leaf, 0, (unsigned long)header, sizeof(*header));
	btrfs_set_free_space_key(leaf, header, &disk_key);
	btrfs_mark_buffer_dirty(leaf);
	btrfs_release_path(path);

	return 0;
}

int create_free_space_inode(struct btrfs_root *root,
			    struct btrfs_trans_handle *trans,
			    struct btrfs_block_group_cache *block_group,
			    struct btrfs_path *path)
{
	int ret;
	u64 ino;

	ret = btrfs_find_free_objectid(root, &ino);
	if (ret < 0)
		return ret;

	return __create_free_space_inode(root, trans, path, ino,
					 block_group->key.objectid);
}

int btrfs_truncate_free_space_cache(struct btrfs_root *root,
				    struct btrfs_trans_handle *trans,
				    struct btrfs_path *path,
				    struct inode *inode)
{
	struct btrfs_block_rsv *rsv;
	u64 needed_bytes;
	loff_t oldsize;
	int ret = 0;

	rsv = trans->block_rsv;
	trans->block_rsv = &root->fs_info->global_block_rsv;

	/* 1 for slack space, 1 for updating the inode */
	needed_bytes = btrfs_calc_trunc_metadata_size(root, 1) +
		btrfs_calc_trans_metadata_size(root, 1);

	spin_lock(&trans->block_rsv->lock);
	if (trans->block_rsv->reserved < needed_bytes) {
		spin_unlock(&trans->block_rsv->lock);
		trans->block_rsv = rsv;
		return -ENOSPC;
	}
	spin_unlock(&trans->block_rsv->lock);

	oldsize = i_size_read(inode);
	btrfs_i_size_write(inode, 0);
	truncate_pagecache(inode, oldsize, 0);

	/*
	 * We don't need an orphan item because truncating the free space cache
	 * will never be split across transactions.
	 */
	ret = btrfs_truncate_inode_items(trans, root, inode,
					 0, BTRFS_EXTENT_DATA_KEY);

	if (ret) {
		trans->block_rsv = rsv;
		WARN_ON(1);
		return ret;
	}

	ret = btrfs_update_inode(trans, root, inode);
	trans->block_rsv = rsv;

	return ret;
}

static int readahead_cache(struct inode *inode)
{
	struct file_ra_state *ra;
	unsigned long last_index;

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

	file_ra_state_init(ra, inode->i_mapping);
	last_index = (i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT;

	page_cache_sync_readahead(inode->i_mapping, ra, NULL, 0, last_index);

	kfree(ra);

	return 0;
}

struct io_ctl {
	void *cur, *orig;
	struct page *page;
	struct page **pages;
	struct btrfs_root *root;
	unsigned long size;
	int index;
	int num_pages;
	unsigned check_crcs:1;
};

static int io_ctl_init(struct io_ctl *io_ctl, struct inode *inode,
		       struct btrfs_root *root)
{
	memset(io_ctl, 0, sizeof(struct io_ctl));
	io_ctl->num_pages = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >>
		PAGE_CACHE_SHIFT;
	io_ctl->pages = kzalloc(sizeof(struct page *) * io_ctl->num_pages,
				GFP_NOFS);
	if (!io_ctl->pages)
		return -ENOMEM;
	io_ctl->root = root;
	if (btrfs_ino(inode) != BTRFS_FREE_INO_OBJECTID)
		io_ctl->check_crcs = 1;
	return 0;
}

static void io_ctl_free(struct io_ctl *io_ctl)
{
	kfree(io_ctl->pages);
}

static void io_ctl_unmap_page(struct io_ctl *io_ctl)
{
	if (io_ctl->cur) {
		kunmap(io_ctl->page);
		io_ctl->cur = NULL;
		io_ctl->orig = NULL;
	}
}

static void io_ctl_map_page(struct io_ctl *io_ctl, int clear)
{
	WARN_ON(io_ctl->cur);
	BUG_ON(io_ctl->index >= io_ctl->num_pages);
	io_ctl->page = io_ctl->pages[io_ctl->index++];
	io_ctl->cur = kmap(io_ctl->page);
	io_ctl->orig = io_ctl->cur;
	io_ctl->size = PAGE_CACHE_SIZE;
	if (clear)
		memset(io_ctl->cur, 0, PAGE_CACHE_SIZE);
}

static void io_ctl_drop_pages(struct io_ctl *io_ctl)
{
	int i;

	io_ctl_unmap_page(io_ctl);

	for (i = 0; i < io_ctl->num_pages; i++) {
		ClearPageChecked(io_ctl->pages[i]);
		unlock_page(io_ctl->pages[i]);
		page_cache_release(io_ctl->pages[i]);
	}
}

static int io_ctl_prepare_pages(struct io_ctl *io_ctl, struct inode *inode,
				int uptodate)
{
	struct page *page;
	gfp_t mask = btrfs_alloc_write_mask(inode->i_mapping);
	int i;

	for (i = 0; i < io_ctl->num_pages; i++) {
		page = find_or_create_page(inode->i_mapping, i, mask);
		if (!page) {
			io_ctl_drop_pages(io_ctl);
			return -ENOMEM;
		}
		io_ctl->pages[i] = page;
		if (uptodate && !PageUptodate(page)) {
			btrfs_readpage(NULL, page);
			lock_page(page);
			if (!PageUptodate(page)) {
				printk(KERN_ERR "btrfs: error reading free "
				       "space cache\n");
				io_ctl_drop_pages(io_ctl);
				return -EIO;
			}
		}
	}

	for (i = 0; i < io_ctl->num_pages; i++) {
		clear_page_dirty_for_io(io_ctl->pages[i]);
		set_page_extent_mapped(io_ctl->pages[i]);
	}

	return 0;
}

static void io_ctl_set_generation(struct io_ctl *io_ctl, u64 generation)
{
	u64 *val;

	io_ctl_map_page(io_ctl, 1);

	/*
	 * Skip the csum areas.  If we don't check crcs then we just have a
	 * 64bit chunk at the front of the first page.
	 */
	if (io_ctl->check_crcs) {
		io_ctl->cur += (sizeof(u32) * io_ctl->num_pages);
		io_ctl->size -= sizeof(u64) + (sizeof(u32) * io_ctl->num_pages);
	} else {
		io_ctl->cur += sizeof(u64);
		io_ctl->size -= sizeof(u64) * 2;
	}

	val = io_ctl->cur;
	*val = cpu_to_le64(generation);
	io_ctl->cur += sizeof(u64);
}

static int io_ctl_check_generation(struct io_ctl *io_ctl, u64 generation)
{
	u64 *gen;

	/*
	 * Skip the crc area.  If we don't check crcs then we just have a 64bit
	 * chunk at the front of the first page.
	 */
	if (io_ctl->check_crcs) {
		io_ctl->cur += sizeof(u32) * io_ctl->num_pages;
		io_ctl->size -= sizeof(u64) +
			(sizeof(u32) * io_ctl->num_pages);
	} else {
		io_ctl->cur += sizeof(u64);
		io_ctl->size -= sizeof(u64) * 2;
	}

	gen = io_ctl->cur;
	if (le64_to_cpu(*gen) != generation) {
		printk_ratelimited(KERN_ERR "btrfs: space cache generation "
				   "(%Lu) does not match inode (%Lu)\n", *gen,
				   generation);
		io_ctl_unmap_page(io_ctl);
		return -EIO;
	}
	io_ctl->cur += sizeof(u64);
	return 0;
}

static void io_ctl_set_crc(struct io_ctl *io_ctl, int index)
{
	u32 *tmp;
	u32 crc = ~(u32)0;
	unsigned offset = 0;

	if (!io_ctl->check_crcs) {
		io_ctl_unmap_page(io_ctl);
		return;
	}

	if (index == 0)
		offset = sizeof(u32) * io_ctl->num_pages;;

	crc = btrfs_csum_data(io_ctl->root, io_ctl->orig + offset, crc,
			      PAGE_CACHE_SIZE - offset);
	btrfs_csum_final(crc, (char *)&crc);
	io_ctl_unmap_page(io_ctl);
	tmp = kmap(io_ctl->pages[0]);
	tmp += index;
	*tmp = crc;
	kunmap(io_ctl->pages[0]);
}

static int io_ctl_check_crc(struct io_ctl *io_ctl, int index)
{
	u32 *tmp, val;
	u32 crc = ~(u32)0;
	unsigned offset = 0;

	if (!io_ctl->check_crcs) {
		io_ctl_map_page(io_ctl, 0);
		return 0;
	}

	if (index == 0)
		offset = sizeof(u32) * io_ctl->num_pages;

	tmp = kmap(io_ctl->pages[0]);
	tmp += index;
	val = *tmp;
	kunmap(io_ctl->pages[0]);

	io_ctl_map_page(io_ctl, 0);
	crc = btrfs_csum_data(io_ctl->root, io_ctl->orig + offset, crc,
			      PAGE_CACHE_SIZE - offset);
	btrfs_csum_final(crc, (char *)&crc);
	if (val != crc) {
		printk_ratelimited(KERN_ERR "btrfs: csum mismatch on free "
				   "space cache\n");
		io_ctl_unmap_page(io_ctl);
		return -EIO;
	}

	return 0;
}

static int io_ctl_add_entry(struct io_ctl *io_ctl, u64 offset, u64 bytes,
			    void *bitmap)
{
	struct btrfs_free_space_entry *entry;

	if (!io_ctl->cur)
		return -ENOSPC;

	entry = io_ctl->cur;
	entry->offset = cpu_to_le64(offset);
	entry->bytes = cpu_to_le64(bytes);
	entry->type = (bitmap) ? BTRFS_FREE_SPACE_BITMAP :
		BTRFS_FREE_SPACE_EXTENT;
	io_ctl->cur += sizeof(struct btrfs_free_space_entry);
	io_ctl->size -= sizeof(struct btrfs_free_space_entry);

	if (io_ctl->size >= sizeof(struct btrfs_free_space_entry))
		return 0;

	io_ctl_set_crc(io_ctl, io_ctl->index - 1);

	/* No more pages to map */
	if (io_ctl->index >= io_ctl->num_pages)
		return 0;

	/* map the next page */
	io_ctl_map_page(io_ctl, 1);
	return 0;
}

static int io_ctl_add_bitmap(struct io_ctl *io_ctl, void *bitmap)
{
	if (!io_ctl->cur)
		return -ENOSPC;

	/*
	 * If we aren't at the start of the current page, unmap this one and
	 * map the next one if there is any left.
	 */
	if (io_ctl->cur != io_ctl->orig) {
		io_ctl_set_crc(io_ctl, io_ctl->index - 1);
		if (io_ctl->index >= io_ctl->num_pages)
			return -ENOSPC;
		io_ctl_map_page(io_ctl, 0);
	}

	memcpy(io_ctl->cur, bitmap, PAGE_CACHE_SIZE);
	io_ctl_set_crc(io_ctl, io_ctl->index - 1);
	if (io_ctl->index < io_ctl->num_pages)
		io_ctl_map_page(io_ctl, 0);
	return 0;
}

static void io_ctl_zero_remaining_pages(struct io_ctl *io_ctl)
{
	/*
	 * If we're not on the boundary we know we've modified the page and we
	 * need to crc the page.
	 */
	if (io_ctl->cur != io_ctl->orig)
		io_ctl_set_crc(io_ctl, io_ctl->index - 1);
	else
		io_ctl_unmap_page(io_ctl);

	while (io_ctl->index < io_ctl->num_pages) {
		io_ctl_map_page(io_ctl, 1);
		io_ctl_set_crc(io_ctl, io_ctl->index - 1);
	}
}

static int io_ctl_read_entry(struct io_ctl *io_ctl,
			    struct btrfs_free_space *entry, u8 *type)
{
	struct btrfs_free_space_entry *e;
	int ret;

	if (!io_ctl->cur) {
		ret = io_ctl_check_crc(io_ctl, io_ctl->index);
		if (ret)
			return ret;
	}

	e = io_ctl->cur;
	entry->offset = le64_to_cpu(e->offset);
	entry->bytes = le64_to_cpu(e->bytes);
	*type = e->type;
	io_ctl->cur += sizeof(struct btrfs_free_space_entry);
	io_ctl->size -= sizeof(struct btrfs_free_space_entry);

	if (io_ctl->size >= sizeof(struct btrfs_free_space_entry))
		return 0;

	io_ctl_unmap_page(io_ctl);

	return 0;
}

static int io_ctl_read_bitmap(struct io_ctl *io_ctl,
			      struct btrfs_free_space *entry)
{
	int ret;

	ret = io_ctl_check_crc(io_ctl, io_ctl->index);
	if (ret)
		return ret;

	memcpy(entry->bitmap, io_ctl->cur, PAGE_CACHE_SIZE);
	io_ctl_unmap_page(io_ctl);

	return 0;
}

int __load_free_space_cache(struct btrfs_root *root, struct inode *inode,
			    struct btrfs_free_space_ctl *ctl,
			    struct btrfs_path *path, u64 offset)
{
	struct btrfs_free_space_header *header;
	struct extent_buffer *leaf;
	struct io_ctl io_ctl;
	struct btrfs_key key;
	struct btrfs_free_space *e, *n;
	struct list_head bitmaps;
	u64 num_entries;
	u64 num_bitmaps;
	u64 generation;
	u8 type;
	int ret = 0;

	INIT_LIST_HEAD(&bitmaps);

	/* Nothing in the space cache, goodbye */
	if (!i_size_read(inode))
		return 0;

	key.objectid = BTRFS_FREE_SPACE_OBJECTID;
	key.offset = offset;
	key.type = 0;

	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
	if (ret < 0)
		return 0;
	else if (ret > 0) {
		btrfs_release_path(path);
		return 0;
	}

	ret = -1;

	leaf = path->nodes[0];
	header = btrfs_item_ptr(leaf, path->slots[0],
				struct btrfs_free_space_header);
	num_entries = btrfs_free_space_entries(leaf, header);
	num_bitmaps = btrfs_free_space_bitmaps(leaf, header);
	generation = btrfs_free_space_generation(leaf, header);
	btrfs_release_path(path);

	if (BTRFS_I(inode)->generation != generation) {
		printk(KERN_ERR "btrfs: free space inode generation (%llu) did"
		       " not match free space cache generation (%llu)\n",
		       (unsigned long long)BTRFS_I(inode)->generation,
		       (unsigned long long)generation);
		return 0;
	}

	if (!num_entries)
		return 0;

	io_ctl_init(&io_ctl, inode, root);
	ret = readahead_cache(inode);
	if (ret)
		goto out;

	ret = io_ctl_prepare_pages(&io_ctl, inode, 1);
	if (ret)
		goto out;

	ret = io_ctl_check_crc(&io_ctl, 0);
	if (ret)
		goto free_cache;

	ret = io_ctl_check_generation(&io_ctl, generation);
	if (ret)
		goto free_cache;

	while (num_entries) {
		e = kmem_cache_zalloc(btrfs_free_space_cachep,
				      GFP_NOFS);
		if (!e)
			goto free_cache;

		ret = io_ctl_read_entry(&io_ctl, e, &type);
		if (ret) {
			kmem_cache_free(btrfs_free_space_cachep, e);
			goto free_cache;
		}

		if (!e->bytes) {
			kmem_cache_free(btrfs_free_space_cachep, e);
			goto free_cache;
		}

		if (type == BTRFS_FREE_SPACE_EXTENT) {
			spin_lock(&ctl->tree_lock);
			ret = link_free_space(ctl, e);
			spin_unlock(&ctl->tree_lock);
			if (ret) {
				printk(KERN_ERR "Duplicate entries in "
				       "free space cache, dumping\n");
				kmem_cache_free(btrfs_free_space_cachep, e);
				goto free_cache;
			}
		} else {
			BUG_ON(!num_bitmaps);
			num_bitmaps--;
			e->bitmap = kzalloc(PAGE_CACHE_SIZE, GFP_NOFS);
			if (!e->bitmap) {
				kmem_cache_free(
					btrfs_free_space_cachep, e);
				goto free_cache;
			}
			spin_lock(&ctl->tree_lock);
			ret = link_free_space(ctl, e);
			ctl->total_bitmaps++;
			ctl->op->recalc_thresholds(ctl);
			spin_unlock(&ctl->tree_lock);
			if (ret) {
				printk(KERN_ERR "Duplicate entries in "
				       "free space cache, dumping\n");
				kmem_cache_free(btrfs_free_space_cachep, e);
				goto free_cache;
			}
			list_add_tail(&e->list, &bitmaps);
		}

		num_entries--;
	}

	io_ctl_unmap_page(&io_ctl);

	/*
	 * We add the bitmaps at the end of the entries in order that
	 * the bitmap entries are added to the cache.
	 */
	list_for_each_entry_safe(e, n, &bitmaps, list) {
		list_del_init(&e->list);
		ret = io_ctl_read_bitmap(&io_ctl, e);
		if (ret)
			goto free_cache;
	}

	io_ctl_drop_pages(&io_ctl);
	ret = 1;
out:
	io_ctl_free(&io_ctl);
	return ret;
free_cache:
	io_ctl_drop_pages(&io_ctl);
	__btrfs_remove_free_space_cache(ctl);
	goto out;
}

int load_free_space_cache(struct btrfs_fs_info *fs_info,
			  struct btrfs_block_group_cache *block_group)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
	struct btrfs_root *root = fs_info->tree_root;
	struct inode *inode;
	struct btrfs_path *path;
	int ret = 0;
	bool matched;
	u64 used = btrfs_block_group_used(&block_group->item);

	/*
	 * If we're unmounting then just return, since this does a search on the
	 * normal root and not the commit root and we could deadlock.
	 */
	if (btrfs_fs_closing(fs_info))
		return 0;

	/*
	 * If this block group has been marked to be cleared for one reason or
	 * another then we can't trust the on disk cache, so just return.
	 */
	spin_lock(&block_group->lock);
	if (block_group->disk_cache_state != BTRFS_DC_WRITTEN) {
		spin_unlock(&block_group->lock);
		return 0;
	}
	spin_unlock(&block_group->lock);

	path = btrfs_alloc_path();
	if (!path)
		return 0;

	inode = lookup_free_space_inode(root, block_group, path);
	if (IS_ERR(inode)) {
		btrfs_free_path(path);
		return 0;
	}

	/* We may have converted the inode and made the cache invalid. */
	spin_lock(&block_group->lock);
	if (block_group->disk_cache_state != BTRFS_DC_WRITTEN) {
		spin_unlock(&block_group->lock);
		goto out;
	}
	spin_unlock(&block_group->lock);

	ret = __load_free_space_cache(fs_info->tree_root, inode, ctl,
				      path, block_group->key.objectid);
	btrfs_free_path(path);
	if (ret <= 0)
		goto out;

	spin_lock(&ctl->tree_lock);
	matched = (ctl->free_space == (block_group->key.offset - used -
				       block_group->bytes_super));
	spin_unlock(&ctl->tree_lock);

	if (!matched) {
		__btrfs_remove_free_space_cache(ctl);
		printk(KERN_ERR "block group %llu has an wrong amount of free "
		       "space\n", block_group->key.objectid);
		ret = -1;
	}
out:
	if (ret < 0) {
		/* This cache is bogus, make sure it gets cleared */
		spin_lock(&block_group->lock);
		block_group->disk_cache_state = BTRFS_DC_CLEAR;
		spin_unlock(&block_group->lock);
		ret = 0;

		printk(KERN_ERR "btrfs: failed to load free space cache "
		       "for block group %llu\n", block_group->key.objectid);
	}

	iput(inode);
	return ret;
}

/**
 * __btrfs_write_out_cache - write out cached info to an inode
 * @root - the root the inode belongs to
 * @ctl - the free space cache we are going to write out
 * @block_group - the block_group for this cache if it belongs to a block_group
 * @trans - the trans handle
 * @path - the path to use
 * @offset - the offset for the key we'll insert
 *
 * This function writes out a free space cache struct to disk for quick recovery
 * on mount.  This will return 0 if it was successfull in writing the cache out,
 * and -1 if it was not.
 */
int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
			    struct btrfs_free_space_ctl *ctl,
			    struct btrfs_block_group_cache *block_group,
			    struct btrfs_trans_handle *trans,
			    struct btrfs_path *path, u64 offset)
{
	struct btrfs_free_space_header *header;
	struct extent_buffer *leaf;
	struct rb_node *node;
	struct list_head *pos, *n;
	struct extent_state *cached_state = NULL;
	struct btrfs_free_cluster *cluster = NULL;
	struct extent_io_tree *unpin = NULL;
	struct io_ctl io_ctl;
	struct list_head bitmap_list;
	struct btrfs_key key;
	u64 start, end, len;
	int entries = 0;
	int bitmaps = 0;
	int ret;
	int err = -1;

	INIT_LIST_HEAD(&bitmap_list);

	if (!i_size_read(inode))
		return -1;

	io_ctl_init(&io_ctl, inode, root);

	/* Get the cluster for this block_group if it exists */
	if (block_group && !list_empty(&block_group->cluster_list))
		cluster = list_entry(block_group->cluster_list.next,
				     struct btrfs_free_cluster,
				     block_group_list);

	/*
	 * We shouldn't have switched the pinned extents yet so this is the
	 * right one
	 */
	unpin = root->fs_info->pinned_extents;

	/* Lock all pages first so we can lock the extent safely. */
	io_ctl_prepare_pages(&io_ctl, inode, 0);

	lock_extent_bits(&BTRFS_I(inode)->io_tree, 0, i_size_read(inode) - 1,
			 0, &cached_state, GFP_NOFS);

	/*
	 * When searching for pinned extents, we need to start at our start
	 * offset.
	 */
	if (block_group)
		start = block_group->key.objectid;

	node = rb_first(&ctl->free_space_offset);
	if (!node && cluster) {
		node = rb_first(&cluster->root);
		cluster = NULL;
	}

	/* Make sure we can fit our crcs into the first page */
	if (io_ctl.check_crcs &&
	    (io_ctl.num_pages * sizeof(u32)) >= PAGE_CACHE_SIZE) {
		WARN_ON(1);
		goto out_nospc;
	}

	io_ctl_set_generation(&io_ctl, trans->transid);

	/* Write out the extent entries */
	while (node) {
		struct btrfs_free_space *e;

		e = rb_entry(node, struct btrfs_free_space, offset_index);
		entries++;

		ret = io_ctl_add_entry(&io_ctl, e->offset, e->bytes,
				       e->bitmap);
		if (ret)
			goto out_nospc;

		if (e->bitmap) {
			list_add_tail(&e->list, &bitmap_list);
			bitmaps++;
		}
		node = rb_next(node);
		if (!node && cluster) {
			node = rb_first(&cluster->root);
			cluster = NULL;
		}
	}

	/*
	 * We want to add any pinned extents to our free space cache
	 * so we don't leak the space
	 */
	while (block_group && (start < block_group->key.objectid +
			       block_group->key.offset)) {
		ret = find_first_extent_bit(unpin, start, &start, &end,
					    EXTENT_DIRTY);
		if (ret) {
			ret = 0;
			break;
		}

		/* This pinned extent is out of our range */
		if (start >= block_group->key.objectid +
		    block_group->key.offset)
			break;

		len = block_group->key.objectid +
			block_group->key.offset - start;
		len = min(len, end + 1 - start);

		entries++;
		ret = io_ctl_add_entry(&io_ctl, start, len, NULL);
		if (ret)
			goto out_nospc;

		start = end + 1;
	}

	/* Write out the bitmaps */
	list_for_each_safe(pos, n, &bitmap_list) {
		struct btrfs_free_space *entry =
			list_entry(pos, struct btrfs_free_space, list);

		ret = io_ctl_add_bitmap(&io_ctl, entry->bitmap);
		if (ret)
			goto out_nospc;
		list_del_init(&entry->list);
	}

	/* Zero out the rest of the pages just to make sure */
	io_ctl_zero_remaining_pages(&io_ctl);

	ret = btrfs_dirty_pages(root, inode, io_ctl.pages, io_ctl.num_pages,
				0, i_size_read(inode), &cached_state);
	io_ctl_drop_pages(&io_ctl);
	unlock_extent_cached(&BTRFS_I(inode)->io_tree, 0,
			     i_size_read(inode) - 1, &cached_state, GFP_NOFS);

	if (ret)
		goto out;


	ret = filemap_write_and_wait(inode->i_mapping);
	if (ret)
		goto out;

	key.objectid = BTRFS_FREE_SPACE_OBJECTID;
	key.offset = offset;
	key.type = 0;

	ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
	if (ret < 0) {
		clear_extent_bit(&BTRFS_I(inode)->io_tree, 0, inode->i_size - 1,
				 EXTENT_DIRTY | EXTENT_DELALLOC, 0, 0, NULL,
				 GFP_NOFS);
		goto out;
	}
	leaf = path->nodes[0];
	if (ret > 0) {
		struct btrfs_key found_key;
		BUG_ON(!path->slots[0]);
		path->slots[0]--;
		btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
		if (found_key.objectid != BTRFS_FREE_SPACE_OBJECTID ||
		    found_key.offset != offset) {
			clear_extent_bit(&BTRFS_I(inode)->io_tree, 0,
					 inode->i_size - 1,
					 EXTENT_DIRTY | EXTENT_DELALLOC, 0, 0,
					 NULL, GFP_NOFS);
			btrfs_release_path(path);
			goto out;
		}
	}

	BTRFS_I(inode)->generation = trans->transid;
	header = btrfs_item_ptr(leaf, path->slots[0],
				struct btrfs_free_space_header);
	btrfs_set_free_space_entries(leaf, header, entries);
	btrfs_set_free_space_bitmaps(leaf, header, bitmaps);
	btrfs_set_free_space_generation(leaf, header, trans->transid);
	btrfs_mark_buffer_dirty(leaf);
	btrfs_release_path(path);

	err = 0;
out:
	io_ctl_free(&io_ctl);
	if (err) {
		invalidate_inode_pages2(inode->i_mapping);
		BTRFS_I(inode)->generation = 0;
	}
	btrfs_update_inode(trans, root, inode);
	return err;

out_nospc:
	list_for_each_safe(pos, n, &bitmap_list) {
		struct btrfs_free_space *entry =
			list_entry(pos, struct btrfs_free_space, list);
		list_del_init(&entry->list);
	}
	io_ctl_drop_pages(&io_ctl);
	unlock_extent_cached(&BTRFS_I(inode)->io_tree, 0,
			     i_size_read(inode) - 1, &cached_state, GFP_NOFS);
	goto out;
}

int btrfs_write_out_cache(struct btrfs_root *root,
			  struct btrfs_trans_handle *trans,
			  struct btrfs_block_group_cache *block_group,
			  struct btrfs_path *path)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
	struct inode *inode;
	int ret = 0;

	root = root->fs_info->tree_root;

	spin_lock(&block_group->lock);
	if (block_group->disk_cache_state < BTRFS_DC_SETUP) {
		spin_unlock(&block_group->lock);
		return 0;
	}
	spin_unlock(&block_group->lock);

	inode = lookup_free_space_inode(root, block_group, path);
	if (IS_ERR(inode))
		return 0;

	ret = __btrfs_write_out_cache(root, inode, ctl, block_group, trans,
				      path, block_group->key.objectid);
	if (ret) {
		spin_lock(&block_group->lock);
		block_group->disk_cache_state = BTRFS_DC_ERROR;
		spin_unlock(&block_group->lock);
		ret = 0;
#ifdef DEBUG
		printk(KERN_ERR "btrfs: failed to write free space cace "
		       "for block group %llu\n", block_group->key.objectid);
#endif
	}

	iput(inode);
	return ret;
}

static inline unsigned long offset_to_bit(u64 bitmap_start, u32 unit,
					  u64 offset)
{
	BUG_ON(offset < bitmap_start);
	offset -= bitmap_start;
	return (unsigned long)(div_u64(offset, unit));
}

static inline unsigned long bytes_to_bits(u64 bytes, u32 unit)
{
	return (unsigned long)(div_u64(bytes, unit));
}

static inline u64 offset_to_bitmap(struct btrfs_free_space_ctl *ctl,
				   u64 offset)
{
	u64 bitmap_start;
	u64 bytes_per_bitmap;

	bytes_per_bitmap = BITS_PER_BITMAP * ctl->unit;
	bitmap_start = offset - ctl->start;
	bitmap_start = div64_u64(bitmap_start, bytes_per_bitmap);
	bitmap_start *= bytes_per_bitmap;
	bitmap_start += ctl->start;

	return bitmap_start;
}

static int tree_insert_offset(struct rb_root *root, u64 offset,
			      struct rb_node *node, int bitmap)
{
	struct rb_node **p = &root->rb_node;
	struct rb_node *parent = NULL;
	struct btrfs_free_space *info;

	while (*p) {
		parent = *p;
		info = rb_entry(parent, struct btrfs_free_space, offset_index);

		if (offset < info->offset) {
			p = &(*p)->rb_left;
		} else if (offset > info->offset) {
			p = &(*p)->rb_right;
		} else {
			/*
			 * we could have a bitmap entry and an extent entry
			 * share the same offset.  If this is the case, we want
			 * the extent entry to always be found first if we do a
			 * linear search through the tree, since we want to have
			 * the quickest allocation time, and allocating from an
			 * extent is faster than allocating from a bitmap.  So
			 * if we're inserting a bitmap and we find an entry at
			 * this offset, we want to go right, or after this entry
			 * logically.  If we are inserting an extent and we've
			 * found a bitmap, we want to go left, or before
			 * logically.
			 */
			if (bitmap) {
				if (info->bitmap) {
					WARN_ON_ONCE(1);
					return -EEXIST;
				}
				p = &(*p)->rb_right;
			} else {
				if (!info->bitmap) {
					WARN_ON_ONCE(1);
					return -EEXIST;
				}
				p = &(*p)->rb_left;
			}
		}
	}

	rb_link_node(node, parent, p);
	rb_insert_color(node, root);

	return 0;
}

/*
 * searches the tree for the given offset.
 *
 * fuzzy - If this is set, then we are trying to make an allocation, and we just
 * want a section that has at least bytes size and comes at or after the given
 * offset.
 */
static struct btrfs_free_space *
tree_search_offset(struct btrfs_free_space_ctl *ctl,
		   u64 offset, int bitmap_only, int fuzzy)
{
	struct rb_node *n = ctl->free_space_offset.rb_node;
	struct btrfs_free_space *entry, *prev = NULL;

	/* find entry that is closest to the 'offset' */
	while (1) {
		if (!n) {
			entry = NULL;
			break;
		}

		entry = rb_entry(n, struct btrfs_free_space, offset_index);
		prev = entry;

		if (offset < entry->offset)
			n = n->rb_left;
		else if (offset > entry->offset)
			n = n->rb_right;
		else
			break;
	}

	if (bitmap_only) {
		if (!entry)
			return NULL;
		if (entry->bitmap)
			return entry;

		/*
		 * bitmap entry and extent entry may share same offset,
		 * in that case, bitmap entry comes after extent entry.
		 */
		n = rb_next(n);
		if (!n)
			return NULL;
		entry = rb_entry(n, struct btrfs_free_space, offset_index);
		if (entry->offset != offset)
			return NULL;

		WARN_ON(!entry->bitmap);
		return entry;
	} else if (entry) {
		if (entry->bitmap) {
			/*
			 * if previous extent entry covers the offset,
			 * we should return it instead of the bitmap entry
			 */
			n = &entry->offset_index;
			while (1) {
				n = rb_prev(n);
				if (!n)
					break;
				prev = rb_entry(n, struct btrfs_free_space,
						offset_index);
				if (!prev->bitmap) {
					if (prev->offset + prev->bytes > offset)
						entry = prev;
					break;
				}
			}
		}
		return entry;
	}

	if (!prev)
		return NULL;

	/* find last entry before the 'offset' */
	entry = prev;
	if (entry->offset > offset) {
		n = rb_prev(&entry->offset_index);
		if (n) {
			entry = rb_entry(n, struct btrfs_free_space,
					offset_index);
			BUG_ON(entry->offset > offset);
		} else {
			if (fuzzy)
				return entry;
			else
				return NULL;
		}
	}

	if (entry->bitmap) {
		n = &entry->offset_index;
		while (1) {
			n = rb_prev(n);
			if (!n)
				break;
			prev = rb_entry(n, struct btrfs_free_space,
					offset_index);
			if (!prev->bitmap) {
				if (prev->offset + prev->bytes > offset)
					return prev;
				break;
			}
		}
		if (entry->offset + BITS_PER_BITMAP * ctl->unit > offset)
			return entry;
	} else if (entry->offset + entry->bytes > offset)
		return entry;

	if (!fuzzy)
		return NULL;

	while (1) {
		if (entry->bitmap) {
			if (entry->offset + BITS_PER_BITMAP *
			    ctl->unit > offset)
				break;
		} else {
			if (entry->offset + entry->bytes > offset)
				break;
		}

		n = rb_next(&entry->offset_index);
		if (!n)
			return NULL;
		entry = rb_entry(n, struct btrfs_free_space, offset_index);
	}
	return entry;
}

static inline void
__unlink_free_space(struct btrfs_free_space_ctl *ctl,
		    struct btrfs_free_space *info)
{
	rb_erase(&info->offset_index, &ctl->free_space_offset);
	ctl->free_extents--;
}

static void unlink_free_space(struct btrfs_free_space_ctl *ctl,
			      struct btrfs_free_space *info)
{
	__unlink_free_space(ctl, info);
	ctl->free_space -= info->bytes;
}

static int link_free_space(struct btrfs_free_space_ctl *ctl,
			   struct btrfs_free_space *info)
{
	int ret = 0;

	BUG_ON(!info->bitmap && !info->bytes);
	ret = tree_insert_offset(&ctl->free_space_offset, info->offset,
				 &info->offset_index, (info->bitmap != NULL));
	if (ret)
		return ret;

	ctl->free_space += info->bytes;
	ctl->free_extents++;
	return ret;
}

static void recalculate_thresholds(struct btrfs_free_space_ctl *ctl)
{
	struct btrfs_block_group_cache *block_group = ctl->private;
	u64 max_bytes;
	u64 bitmap_bytes;
	u64 extent_bytes;
	u64 size = block_group->key.offset;
	u64 bytes_per_bg = BITS_PER_BITMAP * block_group->sectorsize;
	int max_bitmaps = div64_u64(size + bytes_per_bg - 1, bytes_per_bg);

	BUG_ON(ctl->total_bitmaps > max_bitmaps);

	/*
	 * The goal is to keep the total amount of memory used per 1gb of space
	 * at or below 32k, so we need to adjust how much memory we allow to be
	 * used by extent based free space tracking
	 */
	if (size < 1024 * 1024 * 1024)
		max_bytes = MAX_CACHE_BYTES_PER_GIG;
	else
		max_bytes = MAX_CACHE_BYTES_PER_GIG *
			div64_u64(size, 1024 * 1024 * 1024);

	/*
	 * we want to account for 1 more bitmap than what we have so we can make
	 * sure we don't go over our overall goal of MAX_CACHE_BYTES_PER_GIG as
	 * we add more bitmaps.
	 */
	bitmap_bytes = (ctl->total_bitmaps + 1) * PAGE_CACHE_SIZE;

	if (bitmap_bytes >= max_bytes) {
		ctl->extents_thresh = 0;
		return;
	}

	/*
	 * we want the extent entry threshold to always be at most 1/2 the maxw
	 * bytes we can have, or whatever is less than that.
	 */
	extent_bytes = max_bytes - bitmap_bytes;
	extent_bytes = min_t(u64, extent_bytes, div64_u64(max_bytes, 2));

	ctl->extents_thresh =
		div64_u64(extent_bytes, (sizeof(struct btrfs_free_space)));
}

static inline void __bitmap_clear_bits(struct btrfs_free_space_ctl *ctl,
				       struct btrfs_free_space *info,
				       u64 offset, u64 bytes)
{
	unsigned long start, count;

	start = offset_to_bit(info->offset, ctl->unit, offset);
	count = bytes_to_bits(bytes, ctl->unit);
	BUG_ON(start + count > BITS_PER_BITMAP);

	bitmap_clear(info->bitmap, start, count);

	info->bytes -= bytes;
}

static void bitmap_clear_bits(struct btrfs_free_space_ctl *ctl,
			      struct btrfs_free_space *info, u64 offset,
			      u64 bytes)
{
	__bitmap_clear_bits(ctl, info, offset, bytes);
	ctl->free_space -= bytes;
}

static void bitmap_set_bits(struct btrfs_free_space_ctl *ctl,
			    struct btrfs_free_space *info, u64 offset,
			    u64 bytes)
{
	unsigned long start, count;

	start = offset_to_bit(info->offset, ctl->unit, offset);
	count = bytes_to_bits(bytes, ctl->unit);
	BUG_ON(start + count > BITS_PER_BITMAP);

	bitmap_set(info->bitmap, start, count);

	info->bytes += bytes;
	ctl->free_space += bytes;
}

static int search_bitmap(struct btrfs_free_space_ctl *ctl,
			 struct btrfs_free_space *bitmap_info, u64 *offset,
			 u64 *bytes)
{
	unsigned long found_bits = 0;
	unsigned long bits, i;
	unsigned long next_zero;

	i = offset_to_bit(bitmap_info->offset, ctl->unit,
			  max_t(u64, *offset, bitmap_info->offset));
	bits = bytes_to_bits(*bytes, ctl->unit);

	for (i = find_next_bit(bitmap_info->bitmap, BITS_PER_BITMAP, i);
	     i < BITS_PER_BITMAP;
	     i = find_next_bit(bitmap_info->bitmap, BITS_PER_BITMAP, i + 1)) {
		next_zero = find_next_zero_bit(bitmap_info->bitmap,
					       BITS_PER_BITMAP, i);
		if ((next_zero - i) >= bits) {
			found_bits = next_zero - i;
			break;
		}
		i = next_zero;
	}

	if (found_bits) {
		*offset = (u64)(i * ctl->unit) + bitmap_info->offset;
		*bytes = (u64)(found_bits) * ctl->unit;
		return 0;
	}

	return -1;
}

static struct btrfs_free_space *
find_free_space(struct btrfs_free_space_ctl *ctl, u64 *offset, u64 *bytes)
{
	struct btrfs_free_space *entry;
	struct rb_node *node;
	int ret;

	if (!ctl->free_space_offset.rb_node)
		return NULL;

	entry = tree_search_offset(ctl, offset_to_bitmap(ctl, *offset), 0, 1);
	if (!entry)
		return NULL;

	for (node = &entry->offset_index; node; node = rb_next(node)) {
		entry = rb_entry(node, struct btrfs_free_space, offset_index);
		if (entry->bytes < *bytes)
			continue;

		if (entry->bitmap) {
			ret = search_bitmap(ctl, entry, offset, bytes);
			if (!ret)
				return entry;
			continue;
		}

		*offset = entry->offset;
		*bytes = entry->bytes;
		return entry;
	}

	return NULL;
}

static void add_new_bitmap(struct btrfs_free_space_ctl *ctl,
			   struct btrfs_free_space *info, u64 offset)
{
	info->offset = offset_to_bitmap(ctl, offset);
	info->bytes = 0;
	INIT_LIST_HEAD(&info->list);
	link_free_space(ctl, info);
	ctl->total_bitmaps++;

	ctl->op->recalc_thresholds(ctl);
}

static void free_bitmap(struct btrfs_free_space_ctl *ctl,
			struct btrfs_free_space *bitmap_info)
{
	unlink_free_space(ctl, bitmap_info);
	kfree(bitmap_info->bitmap);
	kmem_cache_free(btrfs_free_space_cachep, bitmap_info);
	ctl->total_bitmaps--;
	ctl->op->recalc_thresholds(ctl);
}

static noinline int remove_from_bitmap(struct btrfs_free_space_ctl *ctl,
			      struct btrfs_free_space *bitmap_info,
			      u64 *offset, u64 *bytes)
{
	u64 end;
	u64 search_start, search_bytes;
	int ret;

again:
	end = bitmap_info->offset + (u64)(BITS_PER_BITMAP * ctl->unit) - 1;

	/*
	 * XXX - this can go away after a few releases.
	 *
	 * since the only user of btrfs_remove_free_space is the tree logging
	 * stuff, and the only way to test that is under crash conditions, we
	 * want to have this debug stuff here just in case somethings not
	 * working.  Search the bitmap for the space we are trying to use to
	 * make sure its actually there.  If its not there then we need to stop
	 * because something has gone wrong.
	 */
	search_start = *offset;
	search_bytes = *bytes;
	search_bytes = min(search_bytes, end - search_start + 1);
	ret = search_bitmap(ctl, bitmap_info, &search_start, &search_bytes);
	BUG_ON(ret < 0 || search_start != *offset);

	if (*offset > bitmap_info->offset && *offset + *bytes > end) {
		bitmap_clear_bits(ctl, bitmap_info, *offset, end - *offset + 1);
		*bytes -= end - *offset + 1;
		*offset = end + 1;
	} else if (*offset >= bitmap_info->offset && *offset + *bytes <= end) {
		bitmap_clear_bits(ctl, bitmap_info, *offset, *bytes);
		*bytes = 0;
	}

	if (*bytes) {
		struct rb_node *next = rb_next(&bitmap_info->offset_index);
		if (!bitmap_info->bytes)
			free_bitmap(ctl, bitmap_info);

		/*
		 * no entry after this bitmap, but we still have bytes to
		 * remove, so something has gone wrong.
		 */
		if (!next)
			return -EINVAL;

		bitmap_info = rb_entry(next, struct btrfs_free_space,
				       offset_index);

		/*
		 * if the next entry isn't a bitmap we need to return to let the
		 * extent stuff do its work.
		 */
		if (!bitmap_info->bitmap)
			return -EAGAIN;

		/*
		 * Ok the next item is a bitmap, but it may not actually hold
		 * the information for the rest of this free space stuff, so
		 * look for it, and if we don't find it return so we can try
		 * everything over again.
		 */
		search_start = *offset;
		search_bytes = *bytes;
		ret = search_bitmap(ctl, bitmap_info, &search_start,
				    &search_bytes);
		if (ret < 0 || search_start != *offset)
			return -EAGAIN;

		goto again;
	} else if (!bitmap_info->bytes)
		free_bitmap(ctl, bitmap_info);

	return 0;
}

static u64 add_bytes_to_bitmap(struct btrfs_free_space_ctl *ctl,
			       struct btrfs_free_space *info, u64 offset,
			       u64 bytes)
{
	u64 bytes_to_set = 0;
	u64 end;

	end = info->offset + (u64)(BITS_PER_BITMAP * ctl->unit);

	bytes_to_set = min(end - offset, bytes);

	bitmap_set_bits(ctl, info, offset, bytes_to_set);

	return bytes_to_set;

}

static bool use_bitmap(struct btrfs_free_space_ctl *ctl,
		      struct btrfs_free_space *info)
{
	struct btrfs_block_group_cache *block_group = ctl->private;

	/*
	 * If we are below the extents threshold then we can add this as an
	 * extent, and don't have to deal with the bitmap
	 */
	if (ctl->free_extents < ctl->extents_thresh) {
		/*
		 * If this block group has some small extents we don't want to
		 * use up all of our free slots in the cache with them, we want
		 * to reserve them to larger extents, however if we have plent
		 * of cache left then go ahead an dadd them, no sense in adding
		 * the overhead of a bitmap if we don't have to.
		 */
		if (info->bytes <= block_group->sectorsize * 4) {
			if (ctl->free_extents * 2 <= ctl->extents_thresh)
				return false;
		} else {
			return false;
		}
	}

	/*
	 * some block groups are so tiny they can't be enveloped by a bitmap, so
	 * don't even bother to create a bitmap for this
	 */
	if (BITS_PER_BITMAP * block_group->sectorsize >
	    block_group->key.offset)
		return false;

	return true;
}

static struct btrfs_free_space_op free_space_op = {
	.recalc_thresholds	= recalculate_thresholds,
	.use_bitmap		= use_bitmap,
};

static int insert_into_bitmap(struct btrfs_free_space_ctl *ctl,
			      struct btrfs_free_space *info)
{
	struct btrfs_free_space *bitmap_info;
	struct btrfs_block_group_cache *block_group = NULL;
	int added = 0;
	u64 bytes, offset, bytes_added;
	int ret;

	bytes = info->bytes;
	offset = info->offset;

	if (!ctl->op->use_bitmap(ctl, info))
		return 0;

	if (ctl->op == &free_space_op)
		block_group = ctl->private;
again:
	/*
	 * Since we link bitmaps right into the cluster we need to see if we
	 * have a cluster here, and if so and it has our bitmap we need to add
	 * the free space to that bitmap.
	 */
	if (block_group && !list_empty(&block_group->cluster_list)) {
		struct btrfs_free_cluster *cluster;
		struct rb_node *node;
		struct btrfs_free_space *entry;

		cluster = list_entry(block_group->cluster_list.next,
				     struct btrfs_free_cluster,
				     block_group_list);
		spin_lock(&cluster->lock);
		node = rb_first(&cluster->root);
		if (!node) {
			spin_unlock(&cluster->lock);
			goto no_cluster_bitmap;
		}

		entry = rb_entry(node, struct btrfs_free_space, offset_index);
		if (!entry->bitmap) {
			spin_unlock(&cluster->lock);
			goto no_cluster_bitmap;
		}

		if (entry->offset == offset_to_bitmap(ctl, offset)) {
			bytes_added = add_bytes_to_bitmap(ctl, entry,
							  offset, bytes);
			bytes -= bytes_added;
			offset += bytes_added;
		}
		spin_unlock(&cluster->lock);
		if (!bytes) {
			ret = 1;
			goto out;
		}
	}

no_cluster_bitmap:
	bitmap_info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
					 1, 0);
	if (!bitmap_info) {
		BUG_ON(added);
		goto new_bitmap;
	}

	bytes_added = add_bytes_to_bitmap(ctl, bitmap_info, offset, bytes);
	bytes -= bytes_added;
	offset += bytes_added;
	added = 0;

	if (!bytes) {
		ret = 1;
		goto out;
	} else
		goto again;

new_bitmap:
	if (info && info->bitmap) {
		add_new_bitmap(ctl, info, offset);
		added = 1;
		info = NULL;
		goto again;
	} else {
		spin_unlock(&ctl->tree_lock);

		/* no pre-allocated info, allocate a new one */
		if (!info) {
			info = kmem_cache_zalloc(btrfs_free_space_cachep,
						 GFP_NOFS);
			if (!info) {
				spin_lock(&ctl->tree_lock);
				ret = -ENOMEM;
				goto out;
			}
		}

		/* allocate the bitmap */
		info->bitmap = kzalloc(PAGE_CACHE_SIZE, GFP_NOFS);
		spin_lock(&ctl->tree_lock);
		if (!info->bitmap) {
			ret = -ENOMEM;
			goto out;
		}
		goto again;
	}

out:
	if (info) {
		if (info->bitmap)
			kfree(info->bitmap);
		kmem_cache_free(btrfs_free_space_cachep, info);
	}

	return ret;
}

static bool try_merge_free_space(struct btrfs_free_space_ctl *ctl,
			  struct btrfs_free_space *info, bool update_stat)
{
	struct btrfs_free_space *left_info;
	struct btrfs_free_space *right_info;
	bool merged = false;
	u64 offset = info->offset;
	u64 bytes = info->bytes;

	/*
	 * first we want to see if there is free space adjacent to the range we
	 * are adding, if there is remove that struct and add a new one to
	 * cover the entire range
	 */
	right_info = tree_search_offset(ctl, offset + bytes, 0, 0);
	if (right_info && rb_prev(&right_info->offset_index))
		left_info = rb_entry(rb_prev(&right_info->offset_index),
				     struct btrfs_free_space, offset_index);
	else
		left_info = tree_search_offset(ctl, offset - 1, 0, 0);

	if (right_info && !right_info->bitmap) {
		if (update_stat)
			unlink_free_space(ctl, right_info);
		else
			__unlink_free_space(ctl, right_info);
		info->bytes += right_info->bytes;
		kmem_cache_free(btrfs_free_space_cachep, right_info);
		merged = true;
	}

	if (left_info && !left_info->bitmap &&
	    left_info->offset + left_info->bytes == offset) {
		if (update_stat)
			unlink_free_space(ctl, left_info);
		else
			__unlink_free_space(ctl, left_info);
		info->offset = left_info->offset;
		info->bytes += left_info->bytes;
		kmem_cache_free(btrfs_free_space_cachep, left_info);
		merged = true;
	}

	return merged;
}

int __btrfs_add_free_space(struct btrfs_free_space_ctl *ctl,
			   u64 offset, u64 bytes)
{
	struct btrfs_free_space *info;
	int ret = 0;

	info = kmem_cache_zalloc(btrfs_free_space_cachep, GFP_NOFS);
	if (!info)
		return -ENOMEM;

	info->offset = offset;
	info->bytes = bytes;

	spin_lock(&ctl->tree_lock);

	if (try_merge_free_space(ctl, info, true))
		goto link;

	/*
	 * There was no extent directly to the left or right of this new
	 * extent then we know we're going to have to allocate a new extent, so
	 * before we do that see if we need to drop this into a bitmap
	 */
	ret = insert_into_bitmap(ctl, info);
	if (ret < 0) {
		goto out;
	} else if (ret) {
		ret = 0;
		goto out;
	}
link:
	ret = link_free_space(ctl, info);
	if (ret)
		kmem_cache_free(btrfs_free_space_cachep, info);
out:
	spin_unlock(&ctl->tree_lock);

	if (ret) {
		printk(KERN_CRIT "btrfs: unable to add free space :%d\n", ret);
		BUG_ON(ret == -EEXIST);
	}

	return ret;
}

int btrfs_remove_free_space(struct btrfs_block_group_cache *block_group,
			    u64 offset, u64 bytes)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
	struct btrfs_free_space *info;
	struct btrfs_free_space *next_info = NULL;
	int ret = 0;

	spin_lock(&ctl->tree_lock);

again:
	info = tree_search_offset(ctl, offset, 0, 0);
	if (!info) {
		/*
		 * oops didn't find an extent that matched the space we wanted
		 * to remove, look for a bitmap instead
		 */
		info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
					  1, 0);
		if (!info) {
			/* the tree logging code might be calling us before we
			 * have fully loaded the free space rbtree for this
			 * block group.  So it is possible the entry won't
			 * be in the rbtree yet at all.  The caching code
			 * will make sure not to put it in the rbtree if
			 * the logging code has pinned it.
			 */
			goto out_lock;
		}
	}

	if (info->bytes < bytes && rb_next(&info->offset_index)) {
		u64 end;
		next_info = rb_entry(rb_next(&info->offset_index),
					     struct btrfs_free_space,
					     offset_index);

		if (next_info->bitmap)
			end = next_info->offset +
			      BITS_PER_BITMAP * ctl->unit - 1;
		else
			end = next_info->offset + next_info->bytes;

		if (next_info->bytes < bytes ||
		    next_info->offset > offset || offset > end) {
			printk(KERN_CRIT "Found free space at %llu, size %llu,"
			      " trying to use %llu\n",
			      (unsigned long long)info->offset,
			      (unsigned long long)info->bytes,
			      (unsigned long long)bytes);
			WARN_ON(1);
			ret = -EINVAL;
			goto out_lock;
		}

		info = next_info;
	}

	if (info->bytes == bytes) {
		unlink_free_space(ctl, info);
		if (info->bitmap) {
			kfree(info->bitmap);
			ctl->total_bitmaps--;
		}
		kmem_cache_free(btrfs_free_space_cachep, info);
		ret = 0;
		goto out_lock;
	}

	if (!info->bitmap && info->offset == offset) {
		unlink_free_space(ctl, info);
		info->offset += bytes;
		info->bytes -= bytes;
		ret = link_free_space(ctl, info);
		WARN_ON(ret);
		goto out_lock;
	}

	if (!info->bitmap && info->offset <= offset &&
	    info->offset + info->bytes >= offset + bytes) {
		u64 old_start = info->offset;
		/*
		 * we're freeing space in the middle of the info,
		 * this can happen during tree log replay
		 *
		 * first unlink the old info and then
		 * insert it again after the hole we're creating
		 */
		unlink_free_space(ctl, info);
		if (offset + bytes < info->offset + info->bytes) {
			u64 old_end = info->offset + info->bytes;

			info->offset = offset + bytes;
			info->bytes = old_end - info->offset;
			ret = link_free_space(ctl, info);
			WARN_ON(ret);
			if (ret)
				goto out_lock;
		} else {
			/* the hole we're creating ends at the end
			 * of the info struct, just free the info
			 */
			kmem_cache_free(btrfs_free_space_cachep, info);
		}
		spin_unlock(&ctl->tree_lock);

		/* step two, insert a new info struct to cover
		 * anything before the hole
		 */
		ret = btrfs_add_free_space(block_group, old_start,
					   offset - old_start);
		WARN_ON(ret);
		goto out;
	}

	ret = remove_from_bitmap(ctl, info, &offset, &bytes);
	if (ret == -EAGAIN)
		goto again;
	BUG_ON(ret);
out_lock:
	spin_unlock(&ctl->tree_lock);
out:
	return ret;
}

void btrfs_dump_free_space(struct btrfs_block_group_cache *block_group,
			   u64 bytes)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
	struct btrfs_free_space *info;
	struct rb_node *n;
	int count = 0;

	for (n = rb_first(&ctl->free_space_offset); n; n = rb_next(n)) {
		info = rb_entry(n, struct btrfs_free_space, offset_index);
		if (info->bytes >= bytes)
			count++;
		printk(KERN_CRIT "entry offset %llu, bytes %llu, bitmap %s\n",
		       (unsigned long long)info->offset,
		       (unsigned long long)info->bytes,
		       (info->bitmap) ? "yes" : "no");
	}
	printk(KERN_INFO "block group has cluster?: %s\n",
	       list_empty(&block_group->cluster_list) ? "no" : "yes");
	printk(KERN_INFO "%d blocks of free space at or bigger than bytes is"
	       "\n", count);
}

void btrfs_init_free_space_ctl(struct btrfs_block_group_cache *block_group)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;

	spin_lock_init(&ctl->tree_lock);
	ctl->unit = block_group->sectorsize;
	ctl->start = block_group->key.objectid;
	ctl->private = block_group;
	ctl->op = &free_space_op;

	/*
	 * we only want to have 32k of ram per block group for keeping
	 * track of free space, and if we pass 1/2 of that we want to
	 * start converting things over to using bitmaps
	 */
	ctl->extents_thresh = ((1024 * 32) / 2) /
				sizeof(struct btrfs_free_space);
}

/*
 * for a given cluster, put all of its extents back into the free
 * space cache.  If the block group passed doesn't match the block group
 * pointed to by the cluster, someone else raced in and freed the
 * cluster already.  In that case, we just return without changing anything
 */
static int
__btrfs_return_cluster_to_free_space(
			     struct btrfs_block_group_cache *block_group,
			     struct btrfs_free_cluster *cluster)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
	struct btrfs_free_space *entry;
	struct rb_node *node;

	spin_lock(&cluster->lock);
	if (cluster->block_group != block_group)
		goto out;

	cluster->block_group = NULL;
	cluster->window_start = 0;
	list_del_init(&cluster->block_group_list);

	node = rb_first(&cluster->root);
	while (node) {
		bool bitmap;

		entry = rb_entry(node, struct btrfs_free_space, offset_index);
		node = rb_next(&entry->offset_index);
		rb_erase(&entry->offset_index, &cluster->root);

		bitmap = (entry->bitmap != NULL);
		if (!bitmap)
			try_merge_free_space(ctl, entry, false);
		tree_insert_offset(&ctl->free_space_offset,
				   entry->offset, &entry->offset_index, bitmap);
	}
	cluster->root = RB_ROOT;

out:
	spin_unlock(&cluster->lock);
	btrfs_put_block_group(block_group);
	return 0;
}

void __btrfs_remove_free_space_cache_locked(struct btrfs_free_space_ctl *ctl)
{
	struct btrfs_free_space *info;
	struct rb_node *node;

	while ((node = rb_last(&ctl->free_space_offset)) != NULL) {
		info = rb_entry(node, struct btrfs_free_space, offset_index);
		if (!info->bitmap) {
			unlink_free_space(ctl, info);
			kmem_cache_free(btrfs_free_space_cachep, info);
		} else {
			free_bitmap(ctl, info);
		}
		if (need_resched()) {
			spin_unlock(&ctl->tree_lock);
			cond_resched();
			spin_lock(&ctl->tree_lock);
		}
	}
}

void __btrfs_remove_free_space_cache(struct btrfs_free_space_ctl *ctl)
{
	spin_lock(&ctl->tree_lock);
	__btrfs_remove_free_space_cache_locked(ctl);
	spin_unlock(&ctl->tree_lock);
}

void btrfs_remove_free_space_cache(struct btrfs_block_group_cache *block_group)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
	struct btrfs_free_cluster *cluster;
	struct list_head *head;

	spin_lock(&ctl->tree_lock);
	while ((head = block_group->cluster_list.next) !=
	       &block_group->cluster_list) {
		cluster = list_entry(head, struct btrfs_free_cluster,
				     block_group_list);

		WARN_ON(cluster->block_group != block_group);
		__btrfs_return_cluster_to_free_space(block_group, cluster);
		if (need_resched()) {
			spin_unlock(&ctl->tree_lock);
			cond_resched();
			spin_lock(&ctl->tree_lock);
		}
	}
	__btrfs_remove_free_space_cache_locked(ctl);
	spin_unlock(&ctl->tree_lock);

}

u64 btrfs_find_space_for_alloc(struct btrfs_block_group_cache *block_group,
			       u64 offset, u64 bytes, u64 empty_size)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
	struct btrfs_free_space *entry = NULL;
	u64 bytes_search = bytes + empty_size;
	u64 ret = 0;

	spin_lock(&ctl->tree_lock);
	entry = find_free_space(ctl, &offset, &bytes_search);
	if (!entry)
		goto out;

	ret = offset;
	if (entry->bitmap) {
		bitmap_clear_bits(ctl, entry, offset, bytes);
		if (!entry->bytes)
			free_bitmap(ctl, entry);
	} else {
		unlink_free_space(ctl, entry);
		entry->offset += bytes;
		entry->bytes -= bytes;
		if (!entry->bytes)
			kmem_cache_free(btrfs_free_space_cachep, entry);
		else
			link_free_space(ctl, entry);
	}

out:
	spin_unlock(&ctl->tree_lock);

	return ret;
}

/*
 * given a cluster, put all of its extents back into the free space
 * cache.  If a block group is passed, this function will only free
 * a cluster that belongs to the passed block group.
 *
 * Otherwise, it'll get a reference on the block group pointed to by the
 * cluster and remove the cluster from it.
 */
int btrfs_return_cluster_to_free_space(
			       struct btrfs_block_group_cache *block_group,
			       struct btrfs_free_cluster *cluster)
{
	struct btrfs_free_space_ctl *ctl;
	int ret;

	/* first, get a safe pointer to the block group */
	spin_lock(&cluster->lock);
	if (!block_group) {
		block_group = cluster->block_group;
		if (!block_group) {
			spin_unlock(&cluster->lock);
			return 0;
		}
	} else if (cluster->block_group != block_group) {
		/* someone else has already freed it don't redo their work */
		spin_unlock(&cluster->lock);
		return 0;
	}
	atomic_inc(&block_group->count);
	spin_unlock(&cluster->lock);

	ctl = block_group->free_space_ctl;

	/* now return any extents the cluster had on it */
	spin_lock(&ctl->tree_lock);
	ret = __btrfs_return_cluster_to_free_space(block_group, cluster);
	spin_unlock(&ctl->tree_lock);

	/* finally drop our ref */
	btrfs_put_block_group(block_group);
	return ret;
}

static u64 btrfs_alloc_from_bitmap(struct btrfs_block_group_cache *block_group,
				   struct btrfs_free_cluster *cluster,
				   struct btrfs_free_space *entry,
				   u64 bytes, u64 min_start)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
	int err;
	u64 search_start = cluster->window_start;
	u64 search_bytes = bytes;
	u64 ret = 0;

	search_start = min_start;
	search_bytes = bytes;

	err = search_bitmap(ctl, entry, &search_start, &search_bytes);
	if (err)
		return 0;

	ret = search_start;
	__bitmap_clear_bits(ctl, entry, ret, bytes);

	return ret;
}

/*
 * given a cluster, try to allocate 'bytes' from it, returns 0
 * if it couldn't find anything suitably large, or a logical disk offset
 * if things worked out
 */
u64 btrfs_alloc_from_cluster(struct btrfs_block_group_cache *block_group,
			     struct btrfs_free_cluster *cluster, u64 bytes,
			     u64 min_start)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
	struct btrfs_free_space *entry = NULL;
	struct rb_node *node;
	u64 ret = 0;

	spin_lock(&cluster->lock);
	if (bytes > cluster->max_size)
		goto out;

	if (cluster->block_group != block_group)
		goto out;

	node = rb_first(&cluster->root);
	if (!node)
		goto out;

	entry = rb_entry(node, struct btrfs_free_space, offset_index);
	while(1) {
		if (entry->bytes < bytes ||
		    (!entry->bitmap && entry->offset < min_start)) {
			node = rb_next(&entry->offset_index);
			if (!node)
				break;
			entry = rb_entry(node, struct btrfs_free_space,
					 offset_index);
			continue;
		}

		if (entry->bitmap) {
			ret = btrfs_alloc_from_bitmap(block_group,
						      cluster, entry, bytes,
						      min_start);
			if (ret == 0) {
				node = rb_next(&entry->offset_index);
				if (!node)
					break;
				entry = rb_entry(node, struct btrfs_free_space,
						 offset_index);
				continue;
			}
		} else {
			ret = entry->offset;

			entry->offset += bytes;
			entry->bytes -= bytes;
		}

		if (entry->bytes == 0)
			rb_erase(&entry->offset_index, &cluster->root);
		break;
	}
out:
	spin_unlock(&cluster->lock);

	if (!ret)
		return 0;

	spin_lock(&ctl->tree_lock);

	ctl->free_space -= bytes;
	if (entry->bytes == 0) {
		ctl->free_extents--;
		if (entry->bitmap) {
			kfree(entry->bitmap);
			ctl->total_bitmaps--;
			ctl->op->recalc_thresholds(ctl);
		}
		kmem_cache_free(btrfs_free_space_cachep, entry);
	}

	spin_unlock(&ctl->tree_lock);

	return ret;
}

static int btrfs_bitmap_cluster(struct btrfs_block_group_cache *block_group,
				struct btrfs_free_space *entry,
				struct btrfs_free_cluster *cluster,
				u64 offset, u64 bytes, u64 min_bytes)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
	unsigned long next_zero;
	unsigned long i;
	unsigned long search_bits;
	unsigned long total_bits;
	unsigned long found_bits;
	unsigned long start = 0;
	unsigned long total_found = 0;
	int ret;
	bool found = false;

	i = offset_to_bit(entry->offset, block_group->sectorsize,
			  max_t(u64, offset, entry->offset));
	search_bits = bytes_to_bits(bytes, block_group->sectorsize);
	total_bits = bytes_to_bits(min_bytes, block_group->sectorsize);

again:
	found_bits = 0;
	for (i = find_next_bit(entry->bitmap, BITS_PER_BITMAP, i);
	     i < BITS_PER_BITMAP;
	     i = find_next_bit(entry->bitmap, BITS_PER_BITMAP, i + 1)) {
		next_zero = find_next_zero_bit(entry->bitmap,
					       BITS_PER_BITMAP, i);
		if (next_zero - i >= search_bits) {
			found_bits = next_zero - i;
			break;
		}
		i = next_zero;
	}

	if (!found_bits)
		return -ENOSPC;

	if (!found) {
		start = i;
		cluster->max_size = 0;
		found = true;
	}

	total_found += found_bits;

	if (cluster->max_size < found_bits * block_group->sectorsize)
		cluster->max_size = found_bits * block_group->sectorsize;

	if (total_found < total_bits) {
		i = find_next_bit(entry->bitmap, BITS_PER_BITMAP, next_zero);
		if (i - start > total_bits * 2) {
			total_found = 0;
			cluster->max_size = 0;
			found = false;
		}
		goto again;
	}

	cluster->window_start = start * block_group->sectorsize +
		entry->offset;
	rb_erase(&entry->offset_index, &ctl->free_space_offset);
	ret = tree_insert_offset(&cluster->root, entry->offset,
				 &entry->offset_index, 1);
	BUG_ON(ret);

	return 0;
}

/*
 * This searches the block group for just extents to fill the cluster with.
 */
static noinline int
setup_cluster_no_bitmap(struct btrfs_block_group_cache *block_group,
			struct btrfs_free_cluster *cluster,
			struct list_head *bitmaps, u64 offset, u64 bytes,
			u64 min_bytes)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
	struct btrfs_free_space *first = NULL;
	struct btrfs_free_space *entry = NULL;
	struct btrfs_free_space *prev = NULL;
	struct btrfs_free_space *last;
	struct rb_node *node;
	u64 window_start;
	u64 window_free;
	u64 max_extent;
	u64 max_gap = 128 * 1024;

	entry = tree_search_offset(ctl, offset, 0, 1);
	if (!entry)
		return -ENOSPC;

	/*
	 * We don't want bitmaps, so just move along until we find a normal
	 * extent entry.
	 */
	while (entry->bitmap) {
		if (list_empty(&entry->list))
			list_add_tail(&entry->list, bitmaps);
		node = rb_next(&entry->offset_index);
		if (!node)
			return -ENOSPC;
		entry = rb_entry(node, struct btrfs_free_space, offset_index);
	}

	window_start = entry->offset;
	window_free = entry->bytes;
	max_extent = entry->bytes;
	first = entry;
	last = entry;
	prev = entry;

	while (window_free <= min_bytes) {
		node = rb_next(&entry->offset_index);
		if (!node)
			return -ENOSPC;
		entry = rb_entry(node, struct btrfs_free_space, offset_index);

		if (entry->bitmap) {
			if (list_empty(&entry->list))
				list_add_tail(&entry->list, bitmaps);
			continue;
		}

		/*
		 * we haven't filled the empty size and the window is
		 * very large.  reset and try again
		 */
		if (entry->offset - (prev->offset + prev->bytes) > max_gap ||
		    entry->offset - window_start > (min_bytes * 2)) {
			first = entry;
			window_start = entry->offset;
			window_free = entry->bytes;
			last = entry;
			max_extent = entry->bytes;
		} else {
			last = entry;
			window_free += entry->bytes;
			if (entry->bytes > max_extent)
				max_extent = entry->bytes;
		}
		prev = entry;
	}

	cluster->window_start = first->offset;

	node = &first->offset_index;

	/*
	 * now we've found our entries, pull them out of the free space
	 * cache and put them into the cluster rbtree
	 */
	do {
		int ret;

		entry = rb_entry(node, struct btrfs_free_space, offset_index);
		node = rb_next(&entry->offset_index);
		if (entry->bitmap)
			continue;

		rb_erase(&entry->offset_index, &ctl->free_space_offset);
		ret = tree_insert_offset(&cluster->root, entry->offset,
					 &entry->offset_index, 0);
		BUG_ON(ret);
	} while (node && entry != last);

	cluster->max_size = max_extent;

	return 0;
}

/*
 * This specifically looks for bitmaps that may work in the cluster, we assume
 * that we have already failed to find extents that will work.
 */
static noinline int
setup_cluster_bitmap(struct btrfs_block_group_cache *block_group,
		     struct btrfs_free_cluster *cluster,
		     struct list_head *bitmaps, u64 offset, u64 bytes,
		     u64 min_bytes)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
	struct btrfs_free_space *entry;
	int ret = -ENOSPC;
	u64 bitmap_offset = offset_to_bitmap(ctl, offset);

	if (ctl->total_bitmaps == 0)
		return -ENOSPC;

	/*
	 * The bitmap that covers offset won't be in the list unless offset
	 * is just its start offset.
	 */
	entry = list_first_entry(bitmaps, struct btrfs_free_space, list);
	if (entry->offset != bitmap_offset) {
		entry = tree_search_offset(ctl, bitmap_offset, 1, 0);
		if (entry && list_empty(&entry->list))
			list_add(&entry->list, bitmaps);
	}

	list_for_each_entry(entry, bitmaps, list) {
		if (entry->bytes < min_bytes)
			continue;
		ret = btrfs_bitmap_cluster(block_group, entry, cluster, offset,
					   bytes, min_bytes);
		if (!ret)
			return 0;
	}

	/*
	 * The bitmaps list has all the bitmaps that record free space
	 * starting after offset, so no more search is required.
	 */
	return -ENOSPC;
}

/*
 * here we try to find a cluster of blocks in a block group.  The goal
 * is to find at least bytes free and up to empty_size + bytes free.
 * We might not find them all in one contiguous area.
 *
 * returns zero and sets up cluster if things worked out, otherwise
 * it returns -enospc
 */
int btrfs_find_space_cluster(struct btrfs_trans_handle *trans,
			     struct btrfs_root *root,
			     struct btrfs_block_group_cache *block_group,
			     struct btrfs_free_cluster *cluster,
			     u64 offset, u64 bytes, u64 empty_size)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
	struct btrfs_free_space *entry, *tmp;
	LIST_HEAD(bitmaps);
	u64 min_bytes;
	int ret;

	/* for metadata, allow allocates with more holes */
	if (btrfs_test_opt(root, SSD_SPREAD)) {
		min_bytes = bytes + empty_size;
	} else if (block_group->flags & BTRFS_BLOCK_GROUP_METADATA) {
		/*
		 * we want to do larger allocations when we are
		 * flushing out the delayed refs, it helps prevent
		 * making more work as we go along.
		 */
		if (trans->transaction->delayed_refs.flushing)
			min_bytes = max(bytes, (bytes + empty_size) >> 1);
		else
			min_bytes = max(bytes, (bytes + empty_size) >> 4);
	} else
		min_bytes = max(bytes, (bytes + empty_size) >> 2);

	spin_lock(&ctl->tree_lock);

	/*
	 * If we know we don't have enough space to make a cluster don't even
	 * bother doing all the work to try and find one.
	 */
	if (ctl->free_space < min_bytes) {
		spin_unlock(&ctl->tree_lock);
		return -ENOSPC;
	}

	spin_lock(&cluster->lock);

	/* someone already found a cluster, hooray */
	if (cluster->block_group) {
		ret = 0;
		goto out;
	}

	ret = setup_cluster_no_bitmap(block_group, cluster, &bitmaps, offset,
				      bytes, min_bytes);
	if (ret)
		ret = setup_cluster_bitmap(block_group, cluster, &bitmaps,
					   offset, bytes, min_bytes);

	/* Clear our temporary list */
	list_for_each_entry_safe(entry, tmp, &bitmaps, list)
		list_del_init(&entry->list);

	if (!ret) {
		atomic_inc(&block_group->count);
		list_add_tail(&cluster->block_group_list,
			      &block_group->cluster_list);
		cluster->block_group = block_group;
	}
out:
	spin_unlock(&cluster->lock);
	spin_unlock(&ctl->tree_lock);

	return ret;
}

/*
 * simple code to zero out a cluster
 */
void btrfs_init_free_cluster(struct btrfs_free_cluster *cluster)
{
	spin_lock_init(&cluster->lock);
	spin_lock_init(&cluster->refill_lock);
	cluster->root = RB_ROOT;
	cluster->max_size = 0;
	INIT_LIST_HEAD(&cluster->block_group_list);
	cluster->block_group = NULL;
}

int btrfs_trim_block_group(struct btrfs_block_group_cache *block_group,
			   u64 *trimmed, u64 start, u64 end, u64 minlen)
{
	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
	struct btrfs_free_space *entry = NULL;
	struct btrfs_fs_info *fs_info = block_group->fs_info;
	u64 bytes = 0;
	u64 actually_trimmed;
	int ret = 0;

	*trimmed = 0;

	while (start < end) {
		spin_lock(&ctl->tree_lock);

		if (ctl->free_space < minlen) {
			spin_unlock(&ctl->tree_lock);
			break;
		}

		entry = tree_search_offset(ctl, start, 0, 1);
		if (!entry)
			entry = tree_search_offset(ctl,
						   offset_to_bitmap(ctl, start),
						   1, 1);

		if (!entry || entry->offset >= end) {
			spin_unlock(&ctl->tree_lock);
			break;
		}

		if (entry->bitmap) {
			ret = search_bitmap(ctl, entry, &start, &bytes);
			if (!ret) {
				if (start >= end) {
					spin_unlock(&ctl->tree_lock);
					break;
				}
				bytes = min(bytes, end - start);
				bitmap_clear_bits(ctl, entry, start, bytes);
				if (entry->bytes == 0)
					free_bitmap(ctl, entry);
			} else {
				start = entry->offset + BITS_PER_BITMAP *
					block_group->sectorsize;
				spin_unlock(&ctl->tree_lock);
				ret = 0;
				continue;
			}
		} else {
			start = entry->offset;
			bytes = min(entry->bytes, end - start);
			unlink_free_space(ctl, entry);
			kmem_cache_free(btrfs_free_space_cachep, entry);
		}

		spin_unlock(&ctl->tree_lock);

		if (bytes >= minlen) {
			struct btrfs_space_info *space_info;
			int update = 0;

			space_info = block_group->space_info;
			spin_lock(&space_info->lock);
			spin_lock(&block_group->lock);
			if (!block_group->ro) {
				block_group->reserved += bytes;
				space_info->bytes_reserved += bytes;
				update = 1;
			}
			spin_unlock(&block_group->lock);
			spin_unlock(&space_info->lock);

			ret = btrfs_error_discard_extent(fs_info->extent_root,
							 start,
							 bytes,
							 &actually_trimmed);

			btrfs_add_free_space(block_group, start, bytes);
			if (update) {
				spin_lock(&space_info->lock);
				spin_lock(&block_group->lock);
				if (block_group->ro)
					space_info->bytes_readonly += bytes;
				block_group->reserved -= bytes;
				space_info->bytes_reserved -= bytes;
				spin_unlock(&space_info->lock);
				spin_unlock(&block_group->lock);
			}

			if (ret)
				break;
			*trimmed += actually_trimmed;
		}
		start += bytes;
		bytes = 0;

		if (fatal_signal_pending(current)) {
			ret = -ERESTARTSYS;
			break;
		}

		cond_resched();
	}

	return ret;
}

/*
 * Find the left-most item in the cache tree, and then return the
 * smallest inode number in the item.
 *
 * Note: the returned inode number may not be the smallest one in
 * the tree, if the left-most item is a bitmap.
 */
u64 btrfs_find_ino_for_alloc(struct btrfs_root *fs_root)
{
	struct btrfs_free_space_ctl *ctl = fs_root->free_ino_ctl;
	struct btrfs_free_space *entry = NULL;
	u64 ino = 0;

	spin_lock(&ctl->tree_lock);

	if (RB_EMPTY_ROOT(&ctl->free_space_offset))
		goto out;

	entry = rb_entry(rb_first(&ctl->free_space_offset),
			 struct btrfs_free_space, offset_index);

	if (!entry->bitmap) {
		ino = entry->offset;

		unlink_free_space(ctl, entry);
		entry->offset++;
		entry->bytes--;
		if (!entry->bytes)
			kmem_cache_free(btrfs_free_space_cachep, entry);
		else
			link_free_space(ctl, entry);
	} else {
		u64 offset = 0;
		u64 count = 1;
		int ret;

		ret = search_bitmap(ctl, entry, &offset, &count);
		BUG_ON(ret);

		ino = offset;
		bitmap_clear_bits(ctl, entry, offset, 1);
		if (entry->bytes == 0)
			free_bitmap(ctl, entry);
	}
out:
	spin_unlock(&ctl->tree_lock);

	return ino;
}

struct inode *lookup_free_ino_inode(struct btrfs_root *root,
				    struct btrfs_path *path)
{
	struct inode *inode = NULL;

	spin_lock(&root->cache_lock);
	if (root->cache_inode)
		inode = igrab(root->cache_inode);
	spin_unlock(&root->cache_lock);
	if (inode)
		return inode;

	inode = __lookup_free_space_inode(root, path, 0);
	if (IS_ERR(inode))
		return inode;

	spin_lock(&root->cache_lock);
	if (!btrfs_fs_closing(root->fs_info))
		root->cache_inode = igrab(inode);
	spin_unlock(&root->cache_lock);

	return inode;
}

int create_free_ino_inode(struct btrfs_root *root,
			  struct btrfs_trans_handle *trans,
			  struct btrfs_path *path)
{
	return __create_free_space_inode(root, trans, path,
					 BTRFS_FREE_INO_OBJECTID, 0);
}

int load_free_ino_cache(struct btrfs_fs_info *fs_info, struct btrfs_root *root)
{
	struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
	struct btrfs_path *path;
	struct inode *inode;
	int ret = 0;
	u64 root_gen = btrfs_root_generation(&root->root_item);

	if (!btrfs_test_opt(root, INODE_MAP_CACHE))
		return 0;

	/*
	 * If we're unmounting then just return, since this does a search on the
	 * normal root and not the commit root and we could deadlock.
	 */
	if (btrfs_fs_closing(fs_info))
		return 0;

	path = btrfs_alloc_path();
	if (!path)
		return 0;

	inode = lookup_free_ino_inode(root, path);
	if (IS_ERR(inode))
		goto out;

	if (root_gen != BTRFS_I(inode)->generation)
		goto out_put;

	ret = __load_free_space_cache(root, inode, ctl, path, 0);

	if (ret < 0)
		printk(KERN_ERR "btrfs: failed to load free ino cache for "
		       "root %llu\n", root->root_key.objectid);
out_put:
	iput(inode);
out:
	btrfs_free_path(path);
	return ret;
}

int btrfs_write_out_ino_cache(struct btrfs_root *root,
			      struct btrfs_trans_handle *trans,
			      struct btrfs_path *path)
{
	struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
	struct inode *inode;
	int ret;

	if (!btrfs_test_opt(root, INODE_MAP_CACHE))
		return 0;

	inode = lookup_free_ino_inode(root, path);
	if (IS_ERR(inode))
		return 0;

	ret = __btrfs_write_out_cache(root, inode, ctl, NULL, trans, path, 0);
	if (ret) {
		btrfs_delalloc_release_metadata(inode, inode->i_size);
#ifdef DEBUG
		printk(KERN_ERR "btrfs: failed to write free ino cache "
		       "for root %llu\n", root->root_key.objectid);
#endif
	}

	iput(inode);
	return ret;
}