Btrfs: add support for multiple csum algorithms

[safe/jmp/linux-2.6] / fs / btrfs / disk-io.c

/*
 * 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/version.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/scatterlist.h>
#include <linux/swap.h>
#include <linux/radix-tree.h>
#include <linux/writeback.h>
#include <linux/buffer_head.h> // for block_sync_page
#include <linux/workqueue.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include "compat.h"
#include "crc32c.h"
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "btrfs_inode.h"
#include "volumes.h"
#include "print-tree.h"
#include "async-thread.h"
#include "locking.h"
#include "ref-cache.h"
#include "tree-log.h"

#if 0
static int check_tree_block(struct btrfs_root *root, struct extent_buffer *buf)
{
        if (extent_buffer_blocknr(buf) != btrfs_header_blocknr(buf)) {
                printk(KERN_CRIT "buf blocknr(buf) is %llu, header is %llu\n",
                       (unsigned long long)extent_buffer_blocknr(buf),
                       (unsigned long long)btrfs_header_blocknr(buf));
                return 1;
        }
        return 0;
}
#endif

static struct extent_io_ops btree_extent_io_ops;
static void end_workqueue_fn(struct btrfs_work *work);

/*
 * end_io_wq structs are used to do processing in task context when an IO is
 * complete.  This is used during reads to verify checksums, and it is used
 * by writes to insert metadata for new file extents after IO is complete.
 */
struct end_io_wq {
        struct bio *bio;
        bio_end_io_t *end_io;
        void *private;
        struct btrfs_fs_info *info;
        int error;
        int metadata;
        struct list_head list;
        struct btrfs_work work;
};

/*
 * async submit bios are used to offload expensive checksumming
 * onto the worker threads.  They checksum file and metadata bios
 * just before they are sent down the IO stack.
 */
struct async_submit_bio {
        struct inode *inode;
        struct bio *bio;
        struct list_head list;
        extent_submit_bio_hook_t *submit_bio_start;
        extent_submit_bio_hook_t *submit_bio_done;
        int rw;
        int mirror_num;
        unsigned long bio_flags;
        struct btrfs_work work;
};

/*
 * extents on the btree inode are pretty simple, there's one extent
 * that covers the entire device
 */
static struct extent_map *btree_get_extent(struct inode *inode,
                struct page *page, size_t page_offset, u64 start, u64 len,
                int create)
{
        struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
        struct extent_map *em;
        int ret;

        spin_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, start, len);
        if (em) {
                em->bdev =
                        BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
                spin_unlock(&em_tree->lock);
                goto out;
        }
        spin_unlock(&em_tree->lock);

        em = alloc_extent_map(GFP_NOFS);
        if (!em) {
                em = ERR_PTR(-ENOMEM);
                goto out;
        }
        em->start = 0;
        em->len = (u64)-1;
        em->block_len = (u64)-1;
        em->block_start = 0;
        em->bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;

        spin_lock(&em_tree->lock);
        ret = add_extent_mapping(em_tree, em);
        if (ret == -EEXIST) {
                u64 failed_start = em->start;
                u64 failed_len = em->len;

                printk("failed to insert %Lu %Lu -> %Lu into tree\n",
                       em->start, em->len, em->block_start);
                free_extent_map(em);
                em = lookup_extent_mapping(em_tree, start, len);
                if (em) {
                        printk("after failing, found %Lu %Lu %Lu\n",
                               em->start, em->len, em->block_start);
                        ret = 0;
                } else {
                        em = lookup_extent_mapping(em_tree, failed_start,
                                                   failed_len);
                        if (em) {
                                printk("double failure lookup gives us "
                                       "%Lu %Lu -> %Lu\n", em->start,
                                       em->len, em->block_start);
                                free_extent_map(em);
                        }
                        ret = -EIO;
                }
        } else if (ret) {
                free_extent_map(em);
                em = NULL;
        }
        spin_unlock(&em_tree->lock);

        if (ret)
                em = ERR_PTR(ret);
out:
        return em;
}

u32 btrfs_csum_data(struct btrfs_root *root, char *data, u32 seed, size_t len)
{
        return btrfs_crc32c(seed, data, len);
}

void btrfs_csum_final(u32 crc, char *result)
{
        *(__le32 *)result = ~cpu_to_le32(crc);
}

/*
 * compute the csum for a btree block, and either verify it or write it
 * into the csum field of the block.
 */
static int csum_tree_block(struct btrfs_root *root, struct extent_buffer *buf,
                           int verify)
{
        u16 csum_size =
                btrfs_super_csum_size(&root->fs_info->super_copy);
        char *result = NULL;
        unsigned long len;
        unsigned long cur_len;
        unsigned long offset = BTRFS_CSUM_SIZE;
        char *map_token = NULL;
        char *kaddr;
        unsigned long map_start;
        unsigned long map_len;
        int err;
        u32 crc = ~(u32)0;
        unsigned long inline_result;

        len = buf->len - offset;
        while(len > 0) {
                err = map_private_extent_buffer(buf, offset, 32,
                                        &map_token, &kaddr,
                                        &map_start, &map_len, KM_USER0);
                if (err) {
                        printk("failed to map extent buffer! %lu\n",
                               offset);
                        return 1;
                }
                cur_len = min(len, map_len - (offset - map_start));
                crc = btrfs_csum_data(root, kaddr + offset - map_start,
                                      crc, cur_len);
                len -= cur_len;
                offset += cur_len;
                unmap_extent_buffer(buf, map_token, KM_USER0);
        }
        if (csum_size > sizeof(inline_result)) {
                result = kzalloc(csum_size * sizeof(char), GFP_NOFS);
                if (!result)
                        return 1;
        } else {
                result = (char *)&inline_result;
        }

        btrfs_csum_final(crc, result);

        if (verify) {
                /* FIXME, this is not good */
                if (memcmp_extent_buffer(buf, result, 0, csum_size)) {
                        u32 val;
                        u32 found = 0;
                        memcpy(&found, result, csum_size);

                        read_extent_buffer(buf, &val, 0, csum_size);
                        printk("btrfs: %s checksum verify failed on %llu "
                               "wanted %X found %X level %d\n",
                               root->fs_info->sb->s_id,
                               buf->start, val, found, btrfs_header_level(buf));
                        if (result != (char *)&inline_result)
                                kfree(result);
                        return 1;
                }
        } else {
                write_extent_buffer(buf, result, 0, csum_size);
        }
        if (result != (char *)&inline_result)
                kfree(result);
        return 0;
}

/*
 * we can't consider a given block up to date unless the transid of the
 * block matches the transid in the parent node's pointer.  This is how we
 * detect blocks that either didn't get written at all or got written
 * in the wrong place.
 */
static int verify_parent_transid(struct extent_io_tree *io_tree,
                                 struct extent_buffer *eb, u64 parent_transid)
{
        int ret;

        if (!parent_transid || btrfs_header_generation(eb) == parent_transid)
                return 0;

        lock_extent(io_tree, eb->start, eb->start + eb->len - 1, GFP_NOFS);
        if (extent_buffer_uptodate(io_tree, eb) &&
            btrfs_header_generation(eb) == parent_transid) {
                ret = 0;
                goto out;
        }
        printk("parent transid verify failed on %llu wanted %llu found %llu\n",
               (unsigned long long)eb->start,
               (unsigned long long)parent_transid,
               (unsigned long long)btrfs_header_generation(eb));
        ret = 1;
        clear_extent_buffer_uptodate(io_tree, eb);
out:
        unlock_extent(io_tree, eb->start, eb->start + eb->len - 1,
                      GFP_NOFS);
        return ret;
}

/*
 * helper to read a given tree block, doing retries as required when
 * the checksums don't match and we have alternate mirrors to try.
 */
static int btree_read_extent_buffer_pages(struct btrfs_root *root,
                                          struct extent_buffer *eb,
                                          u64 start, u64 parent_transid)
{
        struct extent_io_tree *io_tree;
        int ret;
        int num_copies = 0;
        int mirror_num = 0;

        io_tree = &BTRFS_I(root->fs_info->btree_inode)->io_tree;
        while (1) {
                ret = read_extent_buffer_pages(io_tree, eb, start, 1,
                                               btree_get_extent, mirror_num);
                if (!ret &&
                    !verify_parent_transid(io_tree, eb, parent_transid))
                        return ret;
printk("read extent buffer pages failed with ret %d mirror no %d\n", ret, mirror_num);
                num_copies = btrfs_num_copies(&root->fs_info->mapping_tree,
                                              eb->start, eb->len);
                if (num_copies == 1)
                        return ret;

                mirror_num++;
                if (mirror_num > num_copies)
                        return ret;
        }
        return -EIO;
}

/*
 * checksum a dirty tree block before IO.  This has extra checks to make
 * sure we only fill in the checksum field in the first page of a multi-page block
 */
static int csum_dirty_buffer(struct btrfs_root *root, struct page *page)
{
        struct extent_io_tree *tree;
        u64 start = (u64)page->index << PAGE_CACHE_SHIFT;
        u64 found_start;
        int found_level;
        unsigned long len;
        struct extent_buffer *eb;
        int ret;

        tree = &BTRFS_I(page->mapping->host)->io_tree;

        if (page->private == EXTENT_PAGE_PRIVATE)
                goto out;
        if (!page->private)
                goto out;
        len = page->private >> 2;
        if (len == 0) {
                WARN_ON(1);
        }
        eb = alloc_extent_buffer(tree, start, len, page, GFP_NOFS);
        ret = btree_read_extent_buffer_pages(root, eb, start + PAGE_CACHE_SIZE,
                                             btrfs_header_generation(eb));
        BUG_ON(ret);
        found_start = btrfs_header_bytenr(eb);
        if (found_start != start) {
                printk("warning: eb start incorrect %Lu buffer %Lu len %lu\n",
                       start, found_start, len);
                WARN_ON(1);
                goto err;
        }
        if (eb->first_page != page) {
                printk("bad first page %lu %lu\n", eb->first_page->index,
                       page->index);
                WARN_ON(1);
                goto err;
        }
        if (!PageUptodate(page)) {
                printk("csum not up to date page %lu\n", page->index);
                WARN_ON(1);
                goto err;
        }
        found_level = btrfs_header_level(eb);

        csum_tree_block(root, eb, 0);
err:
        free_extent_buffer(eb);
out:
        return 0;
}

static int check_tree_block_fsid(struct btrfs_root *root,
                                 struct extent_buffer *eb)
{
        struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
        u8 fsid[BTRFS_UUID_SIZE];
        int ret = 1;

        read_extent_buffer(eb, fsid, (unsigned long)btrfs_header_fsid(eb),
                           BTRFS_FSID_SIZE);
        while (fs_devices) {
                if (!memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE)) {
                        ret = 0;
                        break;
                }
                fs_devices = fs_devices->seed;
        }
        return ret;
}

static int btree_readpage_end_io_hook(struct page *page, u64 start, u64 end,
                               struct extent_state *state)
{
        struct extent_io_tree *tree;
        u64 found_start;
        int found_level;
        unsigned long len;
        struct extent_buffer *eb;
        struct btrfs_root *root = BTRFS_I(page->mapping->host)->root;
        int ret = 0;

        tree = &BTRFS_I(page->mapping->host)->io_tree;
        if (page->private == EXTENT_PAGE_PRIVATE)
                goto out;
        if (!page->private)
                goto out;
        len = page->private >> 2;
        if (len == 0) {
                WARN_ON(1);
        }
        eb = alloc_extent_buffer(tree, start, len, page, GFP_NOFS);

        found_start = btrfs_header_bytenr(eb);
        if (found_start != start) {
                printk("bad tree block start %llu %llu\n",
                       (unsigned long long)found_start,
                       (unsigned long long)eb->start);
                ret = -EIO;
                goto err;
        }
        if (eb->first_page != page) {
                printk("bad first page %lu %lu\n", eb->first_page->index,
                       page->index);
                WARN_ON(1);
                ret = -EIO;
                goto err;
        }
        if (check_tree_block_fsid(root, eb)) {
                printk("bad fsid on block %Lu\n", eb->start);
                ret = -EIO;
                goto err;
        }
        found_level = btrfs_header_level(eb);

        ret = csum_tree_block(root, eb, 1);
        if (ret)
                ret = -EIO;

        end = min_t(u64, eb->len, PAGE_CACHE_SIZE);
        end = eb->start + end - 1;
err:
        free_extent_buffer(eb);
out:
        return ret;
}

static void end_workqueue_bio(struct bio *bio, int err)
{
        struct end_io_wq *end_io_wq = bio->bi_private;
        struct btrfs_fs_info *fs_info;

        fs_info = end_io_wq->info;
        end_io_wq->error = err;
        end_io_wq->work.func = end_workqueue_fn;
        end_io_wq->work.flags = 0;
        if (bio->bi_rw & (1 << BIO_RW))
                btrfs_queue_worker(&fs_info->endio_write_workers,
                                   &end_io_wq->work);
        else
                btrfs_queue_worker(&fs_info->endio_workers, &end_io_wq->work);
}

int btrfs_bio_wq_end_io(struct btrfs_fs_info *info, struct bio *bio,
                        int metadata)
{
        struct end_io_wq *end_io_wq;
        end_io_wq = kmalloc(sizeof(*end_io_wq), GFP_NOFS);
        if (!end_io_wq)
                return -ENOMEM;

        end_io_wq->private = bio->bi_private;
        end_io_wq->end_io = bio->bi_end_io;
        end_io_wq->info = info;
        end_io_wq->error = 0;
        end_io_wq->bio = bio;
        end_io_wq->metadata = metadata;

        bio->bi_private = end_io_wq;
        bio->bi_end_io = end_workqueue_bio;
        return 0;
}

unsigned long btrfs_async_submit_limit(struct btrfs_fs_info *info)
{
        unsigned long limit = min_t(unsigned long,
                                    info->workers.max_workers,
                                    info->fs_devices->open_devices);
        return 256 * limit;
}

int btrfs_congested_async(struct btrfs_fs_info *info, int iodone)
{
        return atomic_read(&info->nr_async_bios) >
                btrfs_async_submit_limit(info);
}

static void run_one_async_start(struct btrfs_work *work)
{
        struct btrfs_fs_info *fs_info;
        struct async_submit_bio *async;

        async = container_of(work, struct  async_submit_bio, work);
        fs_info = BTRFS_I(async->inode)->root->fs_info;
        async->submit_bio_start(async->inode, async->rw, async->bio,
                               async->mirror_num, async->bio_flags);
}

static void run_one_async_done(struct btrfs_work *work)
{
        struct btrfs_fs_info *fs_info;
        struct async_submit_bio *async;
        int limit;

        async = container_of(work, struct  async_submit_bio, work);
        fs_info = BTRFS_I(async->inode)->root->fs_info;

        limit = btrfs_async_submit_limit(fs_info);
        limit = limit * 2 / 3;

        atomic_dec(&fs_info->nr_async_submits);

        if (atomic_read(&fs_info->nr_async_submits) < limit &&
            waitqueue_active(&fs_info->async_submit_wait))
                wake_up(&fs_info->async_submit_wait);

        async->submit_bio_done(async->inode, async->rw, async->bio,
                               async->mirror_num, async->bio_flags);
}

static void run_one_async_free(struct btrfs_work *work)
{
        struct async_submit_bio *async;

        async = container_of(work, struct  async_submit_bio, work);
        kfree(async);
}

int btrfs_wq_submit_bio(struct btrfs_fs_info *fs_info, struct inode *inode,
                        int rw, struct bio *bio, int mirror_num,
                        unsigned long bio_flags,
                        extent_submit_bio_hook_t *submit_bio_start,
                        extent_submit_bio_hook_t *submit_bio_done)
{
        struct async_submit_bio *async;

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

        async->inode = inode;
        async->rw = rw;
        async->bio = bio;
        async->mirror_num = mirror_num;
        async->submit_bio_start = submit_bio_start;
        async->submit_bio_done = submit_bio_done;

        async->work.func = run_one_async_start;
        async->work.ordered_func = run_one_async_done;
        async->work.ordered_free = run_one_async_free;

        async->work.flags = 0;
        async->bio_flags = bio_flags;

        atomic_inc(&fs_info->nr_async_submits);
        btrfs_queue_worker(&fs_info->workers, &async->work);
#if 0
        int limit = btrfs_async_submit_limit(fs_info);
        if (atomic_read(&fs_info->nr_async_submits) > limit) {
                wait_event_timeout(fs_info->async_submit_wait,
                           (atomic_read(&fs_info->nr_async_submits) < limit),
                           HZ/10);

                wait_event_timeout(fs_info->async_submit_wait,
                           (atomic_read(&fs_info->nr_async_bios) < limit),
                           HZ/10);
        }
#endif
        while(atomic_read(&fs_info->async_submit_draining) &&
              atomic_read(&fs_info->nr_async_submits)) {
                wait_event(fs_info->async_submit_wait,
                           (atomic_read(&fs_info->nr_async_submits) == 0));
        }

        return 0;
}

static int btree_csum_one_bio(struct bio *bio)
{
        struct bio_vec *bvec = bio->bi_io_vec;
        int bio_index = 0;
        struct btrfs_root *root;

        WARN_ON(bio->bi_vcnt <= 0);
        while(bio_index < bio->bi_vcnt) {
                root = BTRFS_I(bvec->bv_page->mapping->host)->root;
                csum_dirty_buffer(root, bvec->bv_page);
                bio_index++;
                bvec++;
        }
        return 0;
}

static int __btree_submit_bio_start(struct inode *inode, int rw,
                                    struct bio *bio, int mirror_num,
                                    unsigned long bio_flags)
{
        /*
         * when we're called for a write, we're already in the async
         * submission context.  Just jump into btrfs_map_bio
         */
        btree_csum_one_bio(bio);
        return 0;
}

static int __btree_submit_bio_done(struct inode *inode, int rw, struct bio *bio,
                                 int mirror_num, unsigned long bio_flags)
{
        /*
         * when we're called for a write, we're already in the async
         * submission context.  Just jump into btrfs_map_bio
         */
        return btrfs_map_bio(BTRFS_I(inode)->root, rw, bio, mirror_num, 1);
}

static int btree_submit_bio_hook(struct inode *inode, int rw, struct bio *bio,
                                 int mirror_num, unsigned long bio_flags)
{
        /*
         * kthread helpers are used to submit writes so that checksumming
         * can happen in parallel across all CPUs
         */
        if (!(rw & (1 << BIO_RW))) {
                int ret;
                /*
                 * called for a read, do the setup so that checksum validation
                 * can happen in the async kernel threads
                 */
                ret = btrfs_bio_wq_end_io(BTRFS_I(inode)->root->fs_info,
                                          bio, 1);
                BUG_ON(ret);

                return btrfs_map_bio(BTRFS_I(inode)->root, rw, bio,
                                     mirror_num, 0);
        }
        return btrfs_wq_submit_bio(BTRFS_I(inode)->root->fs_info,
                                   inode, rw, bio, mirror_num, 0,
                                   __btree_submit_bio_start,
                                   __btree_submit_bio_done);
}

static int btree_writepage(struct page *page, struct writeback_control *wbc)
{
        struct extent_io_tree *tree;
        tree = &BTRFS_I(page->mapping->host)->io_tree;

        if (current->flags & PF_MEMALLOC) {
                redirty_page_for_writepage(wbc, page);
                unlock_page(page);
                return 0;
        }
        return extent_write_full_page(tree, page, btree_get_extent, wbc);
}

static int btree_writepages(struct address_space *mapping,
                            struct writeback_control *wbc)
{
        struct extent_io_tree *tree;
        tree = &BTRFS_I(mapping->host)->io_tree;
        if (wbc->sync_mode == WB_SYNC_NONE) {
                u64 num_dirty;
                u64 start = 0;
                unsigned long thresh = 32 * 1024 * 1024;

                if (wbc->for_kupdate)
                        return 0;

                num_dirty = count_range_bits(tree, &start, (u64)-1,
                                             thresh, EXTENT_DIRTY);
                if (num_dirty < thresh) {
                        return 0;
                }
        }
        return extent_writepages(tree, mapping, btree_get_extent, wbc);
}

static int btree_readpage(struct file *file, struct page *page)
{
        struct extent_io_tree *tree;
        tree = &BTRFS_I(page->mapping->host)->io_tree;
        return extent_read_full_page(tree, page, btree_get_extent);
}

static int btree_releasepage(struct page *page, gfp_t gfp_flags)
{
        struct extent_io_tree *tree;
        struct extent_map_tree *map;
        int ret;

        if (PageWriteback(page) || PageDirty(page))
            return 0;

        tree = &BTRFS_I(page->mapping->host)->io_tree;
        map = &BTRFS_I(page->mapping->host)->extent_tree;

        ret = try_release_extent_state(map, tree, page, gfp_flags);
        if (!ret) {
                return 0;
        }

        ret = try_release_extent_buffer(tree, page);
        if (ret == 1) {
                ClearPagePrivate(page);
                set_page_private(page, 0);
                page_cache_release(page);
        }

        return ret;
}

static void btree_invalidatepage(struct page *page, unsigned long offset)
{
        struct extent_io_tree *tree;
        tree = &BTRFS_I(page->mapping->host)->io_tree;
        extent_invalidatepage(tree, page, offset);
        btree_releasepage(page, GFP_NOFS);
        if (PagePrivate(page)) {
                printk("warning page private not zero on page %Lu\n",
                       page_offset(page));
                ClearPagePrivate(page);
                set_page_private(page, 0);
                page_cache_release(page);
        }
}

#if 0
static int btree_writepage(struct page *page, struct writeback_control *wbc)
{
        struct buffer_head *bh;
        struct btrfs_root *root = BTRFS_I(page->mapping->host)->root;
        struct buffer_head *head;
        if (!page_has_buffers(page)) {
                create_empty_buffers(page, root->fs_info->sb->s_blocksize,
                                        (1 << BH_Dirty)|(1 << BH_Uptodate));
        }
        head = page_buffers(page);
        bh = head;
        do {
                if (buffer_dirty(bh))
                        csum_tree_block(root, bh, 0);
                bh = bh->b_this_page;
        } while (bh != head);
        return block_write_full_page(page, btree_get_block, wbc);
}
#endif

static struct address_space_operations btree_aops = {
        .readpage       = btree_readpage,
        .writepage      = btree_writepage,
        .writepages     = btree_writepages,
        .releasepage    = btree_releasepage,
        .invalidatepage = btree_invalidatepage,
        .sync_page      = block_sync_page,
};

int readahead_tree_block(struct btrfs_root *root, u64 bytenr, u32 blocksize,
                         u64 parent_transid)
{
        struct extent_buffer *buf = NULL;
        struct inode *btree_inode = root->fs_info->btree_inode;
        int ret = 0;

        buf = btrfs_find_create_tree_block(root, bytenr, blocksize);
        if (!buf)
                return 0;
        read_extent_buffer_pages(&BTRFS_I(btree_inode)->io_tree,
                                 buf, 0, 0, btree_get_extent, 0);
        free_extent_buffer(buf);
        return ret;
}

struct extent_buffer *btrfs_find_tree_block(struct btrfs_root *root,
                                            u64 bytenr, u32 blocksize)
{
        struct inode *btree_inode = root->fs_info->btree_inode;
        struct extent_buffer *eb;
        eb = find_extent_buffer(&BTRFS_I(btree_inode)->io_tree,
                                bytenr, blocksize, GFP_NOFS);
        return eb;
}

struct extent_buffer *btrfs_find_create_tree_block(struct btrfs_root *root,
                                                 u64 bytenr, u32 blocksize)
{
        struct inode *btree_inode = root->fs_info->btree_inode;
        struct extent_buffer *eb;

        eb = alloc_extent_buffer(&BTRFS_I(btree_inode)->io_tree,
                                 bytenr, blocksize, NULL, GFP_NOFS);
        return eb;
}


int btrfs_write_tree_block(struct extent_buffer *buf)
{
        return btrfs_fdatawrite_range(buf->first_page->mapping, buf->start,
                                      buf->start + buf->len - 1, WB_SYNC_ALL);
}

int btrfs_wait_tree_block_writeback(struct extent_buffer *buf)
{
        return btrfs_wait_on_page_writeback_range(buf->first_page->mapping,
                                  buf->start, buf->start + buf->len -1);
}

struct extent_buffer *read_tree_block(struct btrfs_root *root, u64 bytenr,
                                      u32 blocksize, u64 parent_transid)
{
        struct extent_buffer *buf = NULL;
        struct inode *btree_inode = root->fs_info->btree_inode;
        struct extent_io_tree *io_tree;
        int ret;

        io_tree = &BTRFS_I(btree_inode)->io_tree;

        buf = btrfs_find_create_tree_block(root, bytenr, blocksize);
        if (!buf)
                return NULL;

        ret = btree_read_extent_buffer_pages(root, buf, 0, parent_transid);

        if (ret == 0) {
                buf->flags |= EXTENT_UPTODATE;
        } else {
                WARN_ON(1);
        }
        return buf;

}

int clean_tree_block(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                     struct extent_buffer *buf)
{
        struct inode *btree_inode = root->fs_info->btree_inode;
        if (btrfs_header_generation(buf) ==
            root->fs_info->running_transaction->transid) {
                WARN_ON(!btrfs_tree_locked(buf));
                clear_extent_buffer_dirty(&BTRFS_I(btree_inode)->io_tree,
                                          buf);
        }
        return 0;
}

static int __setup_root(u32 nodesize, u32 leafsize, u32 sectorsize,
                        u32 stripesize, struct btrfs_root *root,
                        struct btrfs_fs_info *fs_info,
                        u64 objectid)
{
        root->node = NULL;
        root->commit_root = NULL;
        root->ref_tree = NULL;
        root->sectorsize = sectorsize;
        root->nodesize = nodesize;
        root->leafsize = leafsize;
        root->stripesize = stripesize;
        root->ref_cows = 0;
        root->track_dirty = 0;

        root->fs_info = fs_info;
        root->objectid = objectid;
        root->last_trans = 0;
        root->highest_inode = 0;
        root->last_inode_alloc = 0;
        root->name = NULL;
        root->in_sysfs = 0;

        INIT_LIST_HEAD(&root->dirty_list);
        INIT_LIST_HEAD(&root->orphan_list);
        INIT_LIST_HEAD(&root->dead_list);
        spin_lock_init(&root->node_lock);
        spin_lock_init(&root->list_lock);
        mutex_init(&root->objectid_mutex);
        mutex_init(&root->log_mutex);
        extent_io_tree_init(&root->dirty_log_pages,
                             fs_info->btree_inode->i_mapping, GFP_NOFS);

        btrfs_leaf_ref_tree_init(&root->ref_tree_struct);
        root->ref_tree = &root->ref_tree_struct;

        memset(&root->root_key, 0, sizeof(root->root_key));
        memset(&root->root_item, 0, sizeof(root->root_item));
        memset(&root->defrag_progress, 0, sizeof(root->defrag_progress));
        memset(&root->root_kobj, 0, sizeof(root->root_kobj));
        root->defrag_trans_start = fs_info->generation;
        init_completion(&root->kobj_unregister);
        root->defrag_running = 0;
        root->defrag_level = 0;
        root->root_key.objectid = objectid;
        root->anon_super.s_root = NULL;
        root->anon_super.s_dev = 0;
        INIT_LIST_HEAD(&root->anon_super.s_list);
        INIT_LIST_HEAD(&root->anon_super.s_instances);
        init_rwsem(&root->anon_super.s_umount);

        return 0;
}

static int find_and_setup_root(struct btrfs_root *tree_root,
                               struct btrfs_fs_info *fs_info,
                               u64 objectid,
                               struct btrfs_root *root)
{
        int ret;
        u32 blocksize;
        u64 generation;

        __setup_root(tree_root->nodesize, tree_root->leafsize,
                     tree_root->sectorsize, tree_root->stripesize,
                     root, fs_info, objectid);
        ret = btrfs_find_last_root(tree_root, objectid,
                                   &root->root_item, &root->root_key);
        BUG_ON(ret);

        generation = btrfs_root_generation(&root->root_item);
        blocksize = btrfs_level_size(root, btrfs_root_level(&root->root_item));
        root->node = read_tree_block(root, btrfs_root_bytenr(&root->root_item),
                                     blocksize, generation);
        BUG_ON(!root->node);
        return 0;
}

int btrfs_free_log_root_tree(struct btrfs_trans_handle *trans,
                             struct btrfs_fs_info *fs_info)
{
        struct extent_buffer *eb;
        struct btrfs_root *log_root_tree = fs_info->log_root_tree;
        u64 start = 0;
        u64 end = 0;
        int ret;

        if (!log_root_tree)
                return 0;

        while(1) {
                ret = find_first_extent_bit(&log_root_tree->dirty_log_pages,
                                    0, &start, &end, EXTENT_DIRTY);
                if (ret)
                        break;

                clear_extent_dirty(&log_root_tree->dirty_log_pages,
                                   start, end, GFP_NOFS);
        }
        eb = fs_info->log_root_tree->node;

        WARN_ON(btrfs_header_level(eb) != 0);
        WARN_ON(btrfs_header_nritems(eb) != 0);

        ret = btrfs_free_reserved_extent(fs_info->tree_root,
                                eb->start, eb->len);
        BUG_ON(ret);

        free_extent_buffer(eb);
        kfree(fs_info->log_root_tree);
        fs_info->log_root_tree = NULL;
        return 0;
}

int btrfs_init_log_root_tree(struct btrfs_trans_handle *trans,
                             struct btrfs_fs_info *fs_info)
{
        struct btrfs_root *root;
        struct btrfs_root *tree_root = fs_info->tree_root;

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

        __setup_root(tree_root->nodesize, tree_root->leafsize,
                     tree_root->sectorsize, tree_root->stripesize,
                     root, fs_info, BTRFS_TREE_LOG_OBJECTID);

        root->root_key.objectid = BTRFS_TREE_LOG_OBJECTID;
        root->root_key.type = BTRFS_ROOT_ITEM_KEY;
        root->root_key.offset = BTRFS_TREE_LOG_OBJECTID;
        root->ref_cows = 0;

        root->node = btrfs_alloc_free_block(trans, root, root->leafsize,
                                            0, BTRFS_TREE_LOG_OBJECTID,
                                            trans->transid, 0, 0, 0);

        btrfs_set_header_nritems(root->node, 0);
        btrfs_set_header_level(root->node, 0);
        btrfs_set_header_bytenr(root->node, root->node->start);
        btrfs_set_header_generation(root->node, trans->transid);
        btrfs_set_header_owner(root->node, BTRFS_TREE_LOG_OBJECTID);

        write_extent_buffer(root->node, root->fs_info->fsid,
                            (unsigned long)btrfs_header_fsid(root->node),
                            BTRFS_FSID_SIZE);
        btrfs_mark_buffer_dirty(root->node);
        btrfs_tree_unlock(root->node);
        fs_info->log_root_tree = root;
        return 0;
}

struct btrfs_root *btrfs_read_fs_root_no_radix(struct btrfs_root *tree_root,
                                               struct btrfs_key *location)
{
        struct btrfs_root *root;
        struct btrfs_fs_info *fs_info = tree_root->fs_info;
        struct btrfs_path *path;
        struct extent_buffer *l;
        u64 highest_inode;
        u64 generation;
        u32 blocksize;
        int ret = 0;

        root = kzalloc(sizeof(*root), GFP_NOFS);
        if (!root)
                return ERR_PTR(-ENOMEM);
        if (location->offset == (u64)-1) {
                ret = find_and_setup_root(tree_root, fs_info,
                                          location->objectid, root);
                if (ret) {
                        kfree(root);
                        return ERR_PTR(ret);
                }
                goto insert;
        }

        __setup_root(tree_root->nodesize, tree_root->leafsize,
                     tree_root->sectorsize, tree_root->stripesize,
                     root, fs_info, location->objectid);

        path = btrfs_alloc_path();
        BUG_ON(!path);
        ret = btrfs_search_slot(NULL, tree_root, location, path, 0, 0);
        if (ret != 0) {
                if (ret > 0)
                        ret = -ENOENT;
                goto out;
        }
        l = path->nodes[0];
        read_extent_buffer(l, &root->root_item,
               btrfs_item_ptr_offset(l, path->slots[0]),
               sizeof(root->root_item));
        memcpy(&root->root_key, location, sizeof(*location));
        ret = 0;
out:
        btrfs_release_path(root, path);
        btrfs_free_path(path);
        if (ret) {
                kfree(root);
                return ERR_PTR(ret);
        }
        generation = btrfs_root_generation(&root->root_item);
        blocksize = btrfs_level_size(root, btrfs_root_level(&root->root_item));
        root->node = read_tree_block(root, btrfs_root_bytenr(&root->root_item),
                                     blocksize, generation);
        BUG_ON(!root->node);
insert:
        if (location->objectid != BTRFS_TREE_LOG_OBJECTID) {
                root->ref_cows = 1;
                ret = btrfs_find_highest_inode(root, &highest_inode);
                if (ret == 0) {
                        root->highest_inode = highest_inode;
                        root->last_inode_alloc = highest_inode;
                }
        }
        return root;
}

struct btrfs_root *btrfs_lookup_fs_root(struct btrfs_fs_info *fs_info,
                                        u64 root_objectid)
{
        struct btrfs_root *root;

        if (root_objectid == BTRFS_ROOT_TREE_OBJECTID)
                return fs_info->tree_root;
        if (root_objectid == BTRFS_EXTENT_TREE_OBJECTID)
                return fs_info->extent_root;

        root = radix_tree_lookup(&fs_info->fs_roots_radix,
                                 (unsigned long)root_objectid);
        return root;
}

struct btrfs_root *btrfs_read_fs_root_no_name(struct btrfs_fs_info *fs_info,
                                              struct btrfs_key *location)
{
        struct btrfs_root *root;
        int ret;

        if (location->objectid == BTRFS_ROOT_TREE_OBJECTID)
                return fs_info->tree_root;
        if (location->objectid == BTRFS_EXTENT_TREE_OBJECTID)
                return fs_info->extent_root;
        if (location->objectid == BTRFS_CHUNK_TREE_OBJECTID)
                return fs_info->chunk_root;
        if (location->objectid == BTRFS_DEV_TREE_OBJECTID)
                return fs_info->dev_root;

        root = radix_tree_lookup(&fs_info->fs_roots_radix,
                                 (unsigned long)location->objectid);
        if (root)
                return root;

        root = btrfs_read_fs_root_no_radix(fs_info->tree_root, location);
        if (IS_ERR(root))
                return root;

        set_anon_super(&root->anon_super, NULL);

        ret = radix_tree_insert(&fs_info->fs_roots_radix,
                                (unsigned long)root->root_key.objectid,
                                root);
        if (ret) {
                free_extent_buffer(root->node);
                kfree(root);
                return ERR_PTR(ret);
        }
        if (!(fs_info->sb->s_flags & MS_RDONLY)) {
                ret = btrfs_find_dead_roots(fs_info->tree_root,
                                            root->root_key.objectid, root);
                BUG_ON(ret);
                btrfs_orphan_cleanup(root);
        }
        return root;
}

struct btrfs_root *btrfs_read_fs_root(struct btrfs_fs_info *fs_info,
                                      struct btrfs_key *location,
                                      const char *name, int namelen)
{
        struct btrfs_root *root;
        int ret;

        root = btrfs_read_fs_root_no_name(fs_info, location);
        if (!root)
                return NULL;

        if (root->in_sysfs)
                return root;

        ret = btrfs_set_root_name(root, name, namelen);
        if (ret) {
                free_extent_buffer(root->node);
                kfree(root);
                return ERR_PTR(ret);
        }
#if 0
        ret = btrfs_sysfs_add_root(root);
        if (ret) {
                free_extent_buffer(root->node);
                kfree(root->name);
                kfree(root);
                return ERR_PTR(ret);
        }
#endif
        root->in_sysfs = 1;
        return root;
}
#if 0
static int add_hasher(struct btrfs_fs_info *info, char *type) {
        struct btrfs_hasher *hasher;

        hasher = kmalloc(sizeof(*hasher), GFP_NOFS);
        if (!hasher)
                return -ENOMEM;
        hasher->hash_tfm = crypto_alloc_hash(type, 0, CRYPTO_ALG_ASYNC);
        if (!hasher->hash_tfm) {
                kfree(hasher);
                return -EINVAL;
        }
        spin_lock(&info->hash_lock);
        list_add(&hasher->list, &info->hashers);
        spin_unlock(&info->hash_lock);
        return 0;
}
#endif

static int btrfs_congested_fn(void *congested_data, int bdi_bits)
{
        struct btrfs_fs_info *info = (struct btrfs_fs_info *)congested_data;
        int ret = 0;
        struct list_head *cur;
        struct btrfs_device *device;
        struct backing_dev_info *bdi;
#if 0
        if ((bdi_bits & (1 << BDI_write_congested)) &&
            btrfs_congested_async(info, 0))
                return 1;
#endif
        list_for_each(cur, &info->fs_devices->devices) {
                device = list_entry(cur, struct btrfs_device, dev_list);
                if (!device->bdev)
                        continue;
                bdi = blk_get_backing_dev_info(device->bdev);
                if (bdi && bdi_congested(bdi, bdi_bits)) {
                        ret = 1;
                        break;
                }
        }
        return ret;
}

/*
 * this unplugs every device on the box, and it is only used when page
 * is null
 */
static void __unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
{
        struct list_head *cur;
        struct btrfs_device *device;
        struct btrfs_fs_info *info;

        info = (struct btrfs_fs_info *)bdi->unplug_io_data;
        list_for_each(cur, &info->fs_devices->devices) {
                device = list_entry(cur, struct btrfs_device, dev_list);
                bdi = blk_get_backing_dev_info(device->bdev);
                if (bdi->unplug_io_fn) {
                        bdi->unplug_io_fn(bdi, page);
                }
        }
}

static void btrfs_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
{
        struct inode *inode;
        struct extent_map_tree *em_tree;
        struct extent_map *em;
        struct address_space *mapping;
        u64 offset;

        /* the generic O_DIRECT read code does this */
        if (1 || !page) {
                __unplug_io_fn(bdi, page);
                return;
        }

        /*
         * page->mapping may change at any time.  Get a consistent copy
         * and use that for everything below
         */
        smp_mb();
        mapping = page->mapping;
        if (!mapping)
                return;

        inode = mapping->host;

        /*
         * don't do the expensive searching for a small number of
         * devices
         */
        if (BTRFS_I(inode)->root->fs_info->fs_devices->open_devices <= 2) {
                __unplug_io_fn(bdi, page);
                return;
        }

        offset = page_offset(page);

        em_tree = &BTRFS_I(inode)->extent_tree;
        spin_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, offset, PAGE_CACHE_SIZE);
        spin_unlock(&em_tree->lock);
        if (!em) {
                __unplug_io_fn(bdi, page);
                return;
        }

        if (em->block_start >= EXTENT_MAP_LAST_BYTE) {
                free_extent_map(em);
                __unplug_io_fn(bdi, page);
                return;
        }
        offset = offset - em->start;
        btrfs_unplug_page(&BTRFS_I(inode)->root->fs_info->mapping_tree,
                          em->block_start + offset, page);
        free_extent_map(em);
}

static int setup_bdi(struct btrfs_fs_info *info, struct backing_dev_info *bdi)
{
        bdi_init(bdi);
        bdi->ra_pages   = default_backing_dev_info.ra_pages;
        bdi->state              = 0;
        bdi->capabilities       = default_backing_dev_info.capabilities;
        bdi->unplug_io_fn       = btrfs_unplug_io_fn;
        bdi->unplug_io_data     = info;
        bdi->congested_fn       = btrfs_congested_fn;
        bdi->congested_data     = info;
        return 0;
}

static int bio_ready_for_csum(struct bio *bio)
{
        u64 length = 0;
        u64 buf_len = 0;
        u64 start = 0;
        struct page *page;
        struct extent_io_tree *io_tree = NULL;
        struct btrfs_fs_info *info = NULL;
        struct bio_vec *bvec;
        int i;
        int ret;

        bio_for_each_segment(bvec, bio, i) {
                page = bvec->bv_page;
                if (page->private == EXTENT_PAGE_PRIVATE) {
                        length += bvec->bv_len;
                        continue;
                }
                if (!page->private) {
                        length += bvec->bv_len;
                        continue;
                }
                length = bvec->bv_len;
                buf_len = page->private >> 2;
                start = page_offset(page) + bvec->bv_offset;
                io_tree = &BTRFS_I(page->mapping->host)->io_tree;
                info = BTRFS_I(page->mapping->host)->root->fs_info;
        }
        /* are we fully contained in this bio? */
        if (buf_len <= length)
                return 1;

        ret = extent_range_uptodate(io_tree, start + length,
                                    start + buf_len - 1);
        if (ret == 1)
                return ret;
        return ret;
}

/*
 * called by the kthread helper functions to finally call the bio end_io
 * functions.  This is where read checksum verification actually happens
 */
static void end_workqueue_fn(struct btrfs_work *work)
{
        struct bio *bio;
        struct end_io_wq *end_io_wq;
        struct btrfs_fs_info *fs_info;
        int error;

        end_io_wq = container_of(work, struct end_io_wq, work);
        bio = end_io_wq->bio;
        fs_info = end_io_wq->info;

        /* metadata bios are special because the whole tree block must
         * be checksummed at once.  This makes sure the entire block is in
         * ram and up to date before trying to verify things.  For
         * blocksize <= pagesize, it is basically a noop
         */
        if (end_io_wq->metadata && !bio_ready_for_csum(bio)) {
                btrfs_queue_worker(&fs_info->endio_workers,
                                   &end_io_wq->work);
                return;
        }
        error = end_io_wq->error;
        bio->bi_private = end_io_wq->private;
        bio->bi_end_io = end_io_wq->end_io;
        kfree(end_io_wq);
        bio_endio(bio, error);
}

static int cleaner_kthread(void *arg)
{
        struct btrfs_root *root = arg;

        do {
                smp_mb();
                if (root->fs_info->closing)
                        break;

                vfs_check_frozen(root->fs_info->sb, SB_FREEZE_WRITE);
                mutex_lock(&root->fs_info->cleaner_mutex);
                btrfs_clean_old_snapshots(root);
                mutex_unlock(&root->fs_info->cleaner_mutex);

                if (freezing(current)) {
                        refrigerator();
                } else {
                        smp_mb();
                        if (root->fs_info->closing)
                                break;
                        set_current_state(TASK_INTERRUPTIBLE);
                        schedule();
                        __set_current_state(TASK_RUNNING);
                }
        } while (!kthread_should_stop());
        return 0;
}

static int transaction_kthread(void *arg)
{
        struct btrfs_root *root = arg;
        struct btrfs_trans_handle *trans;
        struct btrfs_transaction *cur;
        unsigned long now;
        unsigned long delay;
        int ret;

        do {
                smp_mb();
                if (root->fs_info->closing)
                        break;

                delay = HZ * 30;
                vfs_check_frozen(root->fs_info->sb, SB_FREEZE_WRITE);
                mutex_lock(&root->fs_info->transaction_kthread_mutex);

                if (root->fs_info->total_ref_cache_size > 20 * 1024 * 1024) {
                        printk("btrfs: total reference cache size %Lu\n",
                                root->fs_info->total_ref_cache_size);
                }

                mutex_lock(&root->fs_info->trans_mutex);
                cur = root->fs_info->running_transaction;
                if (!cur) {
                        mutex_unlock(&root->fs_info->trans_mutex);
                        goto sleep;
                }

                now = get_seconds();
                if (now < cur->start_time || now - cur->start_time < 30) {
                        mutex_unlock(&root->fs_info->trans_mutex);
                        delay = HZ * 5;
                        goto sleep;
                }
                mutex_unlock(&root->fs_info->trans_mutex);
                trans = btrfs_start_transaction(root, 1);
                ret = btrfs_commit_transaction(trans, root);
sleep:
                wake_up_process(root->fs_info->cleaner_kthread);
                mutex_unlock(&root->fs_info->transaction_kthread_mutex);

                if (freezing(current)) {
                        refrigerator();
                } else {
                        if (root->fs_info->closing)
                                break;
                        set_current_state(TASK_INTERRUPTIBLE);
                        schedule_timeout(delay);
                        __set_current_state(TASK_RUNNING);
                }
        } while (!kthread_should_stop());
        return 0;
}

struct btrfs_root *open_ctree(struct super_block *sb,
                              struct btrfs_fs_devices *fs_devices,
                              char *options)
{
        u32 sectorsize;
        u32 nodesize;
        u32 leafsize;
        u32 blocksize;
        u32 stripesize;
        u64 generation;
        u64 features;
        struct btrfs_key location;
        struct buffer_head *bh;
        struct btrfs_root *extent_root = kzalloc(sizeof(struct btrfs_root),
                                                 GFP_NOFS);
        struct btrfs_root *tree_root = kzalloc(sizeof(struct btrfs_root),
                                               GFP_NOFS);
        struct btrfs_fs_info *fs_info = kzalloc(sizeof(*fs_info),
                                                GFP_NOFS);
        struct btrfs_root *chunk_root = kzalloc(sizeof(struct btrfs_root),
                                                GFP_NOFS);
        struct btrfs_root *dev_root = kzalloc(sizeof(struct btrfs_root),
                                              GFP_NOFS);
        struct btrfs_root *log_tree_root;

        int ret;
        int err = -EINVAL;

        struct btrfs_super_block *disk_super;

        if (!extent_root || !tree_root || !fs_info ||
            !chunk_root || !dev_root) {
                err = -ENOMEM;
                goto fail;
        }
        INIT_RADIX_TREE(&fs_info->fs_roots_radix, GFP_NOFS);
        INIT_LIST_HEAD(&fs_info->trans_list);
        INIT_LIST_HEAD(&fs_info->dead_roots);
        INIT_LIST_HEAD(&fs_info->hashers);
        INIT_LIST_HEAD(&fs_info->delalloc_inodes);
        spin_lock_init(&fs_info->hash_lock);
        spin_lock_init(&fs_info->delalloc_lock);
        spin_lock_init(&fs_info->new_trans_lock);
        spin_lock_init(&fs_info->ref_cache_lock);

        init_completion(&fs_info->kobj_unregister);
        fs_info->tree_root = tree_root;
        fs_info->extent_root = extent_root;
        fs_info->chunk_root = chunk_root;
        fs_info->dev_root = dev_root;
        fs_info->fs_devices = fs_devices;
        INIT_LIST_HEAD(&fs_info->dirty_cowonly_roots);
        INIT_LIST_HEAD(&fs_info->space_info);
        btrfs_mapping_init(&fs_info->mapping_tree);
        atomic_set(&fs_info->nr_async_submits, 0);
        atomic_set(&fs_info->async_delalloc_pages, 0);
        atomic_set(&fs_info->async_submit_draining, 0);
        atomic_set(&fs_info->nr_async_bios, 0);
        atomic_set(&fs_info->throttles, 0);
        atomic_set(&fs_info->throttle_gen, 0);
        fs_info->sb = sb;
        fs_info->max_extent = (u64)-1;
        fs_info->max_inline = 8192 * 1024;
        setup_bdi(fs_info, &fs_info->bdi);
        fs_info->btree_inode = new_inode(sb);
        fs_info->btree_inode->i_ino = 1;
        fs_info->btree_inode->i_nlink = 1;

        fs_info->thread_pool_size = min(num_online_cpus() + 2, 8);

        INIT_LIST_HEAD(&fs_info->ordered_extents);
        spin_lock_init(&fs_info->ordered_extent_lock);

        sb->s_blocksize = 4096;
        sb->s_blocksize_bits = blksize_bits(4096);

        /*
         * we set the i_size on the btree inode to the max possible int.
         * the real end of the address space is determined by all of
         * the devices in the system
         */
        fs_info->btree_inode->i_size = OFFSET_MAX;
        fs_info->btree_inode->i_mapping->a_ops = &btree_aops;
        fs_info->btree_inode->i_mapping->backing_dev_info = &fs_info->bdi;

        extent_io_tree_init(&BTRFS_I(fs_info->btree_inode)->io_tree,
                             fs_info->btree_inode->i_mapping,
                             GFP_NOFS);
        extent_map_tree_init(&BTRFS_I(fs_info->btree_inode)->extent_tree,
                             GFP_NOFS);

        BTRFS_I(fs_info->btree_inode)->io_tree.ops = &btree_extent_io_ops;

        spin_lock_init(&fs_info->block_group_cache_lock);
        fs_info->block_group_cache_tree.rb_node = NULL;

        extent_io_tree_init(&fs_info->pinned_extents,
                             fs_info->btree_inode->i_mapping, GFP_NOFS);
        extent_io_tree_init(&fs_info->pending_del,
                             fs_info->btree_inode->i_mapping, GFP_NOFS);
        extent_io_tree_init(&fs_info->extent_ins,
                             fs_info->btree_inode->i_mapping, GFP_NOFS);
        fs_info->do_barriers = 1;

        INIT_LIST_HEAD(&fs_info->dead_reloc_roots);
        btrfs_leaf_ref_tree_init(&fs_info->reloc_ref_tree);
        btrfs_leaf_ref_tree_init(&fs_info->shared_ref_tree);

        BTRFS_I(fs_info->btree_inode)->root = tree_root;
        memset(&BTRFS_I(fs_info->btree_inode)->location, 0,
               sizeof(struct btrfs_key));
        insert_inode_hash(fs_info->btree_inode);

        mutex_init(&fs_info->trans_mutex);
        mutex_init(&fs_info->tree_log_mutex);
        mutex_init(&fs_info->drop_mutex);
        mutex_init(&fs_info->extent_ins_mutex);
        mutex_init(&fs_info->pinned_mutex);
        mutex_init(&fs_info->chunk_mutex);
        mutex_init(&fs_info->transaction_kthread_mutex);
        mutex_init(&fs_info->cleaner_mutex);
        mutex_init(&fs_info->volume_mutex);
        mutex_init(&fs_info->tree_reloc_mutex);
        init_waitqueue_head(&fs_info->transaction_throttle);
        init_waitqueue_head(&fs_info->transaction_wait);
        init_waitqueue_head(&fs_info->async_submit_wait);
        init_waitqueue_head(&fs_info->tree_log_wait);
        atomic_set(&fs_info->tree_log_commit, 0);
        atomic_set(&fs_info->tree_log_writers, 0);
        fs_info->tree_log_transid = 0;

#if 0
        ret = add_hasher(fs_info, "crc32c");
        if (ret) {
                printk("btrfs: failed hash setup, modprobe cryptomgr?\n");
                err = -ENOMEM;
                goto fail_iput;
        }
#endif
        __setup_root(4096, 4096, 4096, 4096, tree_root,
                     fs_info, BTRFS_ROOT_TREE_OBJECTID);


        bh = __bread(fs_devices->latest_bdev,
                     BTRFS_SUPER_INFO_OFFSET / 4096, 4096);
        if (!bh)
                goto fail_iput;

        memcpy(&fs_info->super_copy, bh->b_data, sizeof(fs_info->super_copy));
        brelse(bh);

        memcpy(fs_info->fsid, fs_info->super_copy.fsid, BTRFS_FSID_SIZE);

        disk_super = &fs_info->super_copy;
        if (!btrfs_super_root(disk_super))
                goto fail_iput;

        ret = btrfs_parse_options(tree_root, options);
        if (ret) {
                err = ret;
                goto fail_iput;
        }

        features = btrfs_super_incompat_flags(disk_super) &
                ~BTRFS_FEATURE_INCOMPAT_SUPP;
        if (features) {
                printk(KERN_ERR "BTRFS: couldn't mount because of "
                       "unsupported optional features (%Lx).\n",
                       features);
                err = -EINVAL;
                goto fail_iput;
        }

        features = btrfs_super_compat_ro_flags(disk_super) &
                ~BTRFS_FEATURE_COMPAT_RO_SUPP;
        if (!(sb->s_flags & MS_RDONLY) && features) {
                printk(KERN_ERR "BTRFS: couldn't mount RDWR because of "
                       "unsupported option features (%Lx).\n",
                       features);
                err = -EINVAL;
                goto fail_iput;
        }

        /*
         * we need to start all the end_io workers up front because the
         * queue work function gets called at interrupt time, and so it
         * cannot dynamically grow.
         */
        btrfs_init_workers(&fs_info->workers, "worker",
                           fs_info->thread_pool_size);

        btrfs_init_workers(&fs_info->delalloc_workers, "delalloc",
                           fs_info->thread_pool_size);

        btrfs_init_workers(&fs_info->submit_workers, "submit",
                           min_t(u64, fs_devices->num_devices,
                           fs_info->thread_pool_size));

        /* a higher idle thresh on the submit workers makes it much more
         * likely that bios will be send down in a sane order to the
         * devices
         */
        fs_info->submit_workers.idle_thresh = 64;

        fs_info->workers.idle_thresh = 16;
        fs_info->workers.ordered = 1;

        fs_info->delalloc_workers.idle_thresh = 2;
        fs_info->delalloc_workers.ordered = 1;

        btrfs_init_workers(&fs_info->fixup_workers, "fixup", 1);
        btrfs_init_workers(&fs_info->endio_workers, "endio",
                           fs_info->thread_pool_size);
        btrfs_init_workers(&fs_info->endio_write_workers, "endio-write",
                           fs_info->thread_pool_size);

        /*
         * endios are largely parallel and should have a very
         * low idle thresh
         */
        fs_info->endio_workers.idle_thresh = 4;
        fs_info->endio_write_workers.idle_thresh = 64;

        btrfs_start_workers(&fs_info->workers, 1);
        btrfs_start_workers(&fs_info->submit_workers, 1);
        btrfs_start_workers(&fs_info->delalloc_workers, 1);
        btrfs_start_workers(&fs_info->fixup_workers, 1);
        btrfs_start_workers(&fs_info->endio_workers, fs_info->thread_pool_size);
        btrfs_start_workers(&fs_info->endio_write_workers,
                            fs_info->thread_pool_size);

        fs_info->bdi.ra_pages *= btrfs_super_num_devices(disk_super);
        fs_info->bdi.ra_pages = max(fs_info->bdi.ra_pages,
                                    4 * 1024 * 1024 / PAGE_CACHE_SIZE);

        nodesize = btrfs_super_nodesize(disk_super);
        leafsize = btrfs_super_leafsize(disk_super);
        sectorsize = btrfs_super_sectorsize(disk_super);
        stripesize = btrfs_super_stripesize(disk_super);
        tree_root->nodesize = nodesize;
        tree_root->leafsize = leafsize;
        tree_root->sectorsize = sectorsize;
        tree_root->stripesize = stripesize;

        sb->s_blocksize = sectorsize;
        sb->s_blocksize_bits = blksize_bits(sectorsize);

        if (strncmp((char *)(&disk_super->magic), BTRFS_MAGIC,
                    sizeof(disk_super->magic))) {
                printk("btrfs: valid FS not found on %s\n", sb->s_id);
                goto fail_sb_buffer;
        }

        mutex_lock(&fs_info->chunk_mutex);
        ret = btrfs_read_sys_array(tree_root);
        mutex_unlock(&fs_info->chunk_mutex);
        if (ret) {
                printk("btrfs: failed to read the system array on %s\n",
                       sb->s_id);
                goto fail_sys_array;
        }

        blocksize = btrfs_level_size(tree_root,
                                     btrfs_super_chunk_root_level(disk_super));
        generation = btrfs_super_chunk_root_generation(disk_super);

        __setup_root(nodesize, leafsize, sectorsize, stripesize,
                     chunk_root, fs_info, BTRFS_CHUNK_TREE_OBJECTID);

        chunk_root->node = read_tree_block(chunk_root,
                                           btrfs_super_chunk_root(disk_super),
                                           blocksize, generation);
        BUG_ON(!chunk_root->node);

        read_extent_buffer(chunk_root->node, fs_info->chunk_tree_uuid,
                 (unsigned long)btrfs_header_chunk_tree_uuid(chunk_root->node),
                 BTRFS_UUID_SIZE);

        mutex_lock(&fs_info->chunk_mutex);
        ret = btrfs_read_chunk_tree(chunk_root);
        mutex_unlock(&fs_info->chunk_mutex);
        if (ret) {
                printk("btrfs: failed to read chunk tree on %s\n", sb->s_id);
                goto fail_chunk_root;
        }

        btrfs_close_extra_devices(fs_devices);

        blocksize = btrfs_level_size(tree_root,
                                     btrfs_super_root_level(disk_super));
        generation = btrfs_super_generation(disk_super);

        tree_root->node = read_tree_block(tree_root,
                                          btrfs_super_root(disk_super),
                                          blocksize, generation);
        if (!tree_root->node)
                goto fail_chunk_root;


        ret = find_and_setup_root(tree_root, fs_info,
                                  BTRFS_EXTENT_TREE_OBJECTID, extent_root);
        if (ret)
                goto fail_tree_root;
        extent_root->track_dirty = 1;

        ret = find_and_setup_root(tree_root, fs_info,
                                  BTRFS_DEV_TREE_OBJECTID, dev_root);
        dev_root->track_dirty = 1;

        if (ret)
                goto fail_extent_root;

        btrfs_read_block_groups(extent_root);

        fs_info->generation = generation + 1;
        fs_info->last_trans_committed = generation;
        fs_info->data_alloc_profile = (u64)-1;
        fs_info->metadata_alloc_profile = (u64)-1;
        fs_info->system_alloc_profile = fs_info->metadata_alloc_profile;
        fs_info->cleaner_kthread = kthread_run(cleaner_kthread, tree_root,
                                               "btrfs-cleaner");
        if (!fs_info->cleaner_kthread)
                goto fail_extent_root;

        fs_info->transaction_kthread = kthread_run(transaction_kthread,
                                                   tree_root,
                                                   "btrfs-transaction");
        if (!fs_info->transaction_kthread)
                goto fail_cleaner;

        if (btrfs_super_log_root(disk_super) != 0) {
                u64 bytenr = btrfs_super_log_root(disk_super);

                if (fs_devices->rw_devices == 0) {
                        printk("Btrfs log replay required on RO media\n");
                        err = -EIO;
                        goto fail_trans_kthread;
                }
                blocksize =
                     btrfs_level_size(tree_root,
                                      btrfs_super_log_root_level(disk_super));

                log_tree_root = kzalloc(sizeof(struct btrfs_root),
                                                      GFP_NOFS);

                __setup_root(nodesize, leafsize, sectorsize, stripesize,
                             log_tree_root, fs_info, BTRFS_TREE_LOG_OBJECTID);

                log_tree_root->node = read_tree_block(tree_root, bytenr,
                                                      blocksize,
                                                      generation + 1);
                ret = btrfs_recover_log_trees(log_tree_root);
                BUG_ON(ret);

                if (sb->s_flags & MS_RDONLY) {
                        ret =  btrfs_commit_super(tree_root);
                        BUG_ON(ret);
                }
        }

        if (!(sb->s_flags & MS_RDONLY)) {
                ret = btrfs_cleanup_reloc_trees(tree_root);
                BUG_ON(ret);
        }

        location.objectid = BTRFS_FS_TREE_OBJECTID;
        location.type = BTRFS_ROOT_ITEM_KEY;
        location.offset = (u64)-1;

        fs_info->fs_root = btrfs_read_fs_root_no_name(fs_info, &location);
        if (!fs_info->fs_root)
                goto fail_trans_kthread;
        return tree_root;

fail_trans_kthread:
        kthread_stop(fs_info->transaction_kthread);
fail_cleaner:
        kthread_stop(fs_info->cleaner_kthread);

        /*
         * make sure we're done with the btree inode before we stop our
         * kthreads
         */
        filemap_write_and_wait(fs_info->btree_inode->i_mapping);
        invalidate_inode_pages2(fs_info->btree_inode->i_mapping);

fail_extent_root:
        free_extent_buffer(extent_root->node);
fail_tree_root:
        free_extent_buffer(tree_root->node);
fail_chunk_root:
        free_extent_buffer(chunk_root->node);
fail_sys_array:
        free_extent_buffer(dev_root->node);
fail_sb_buffer:
        btrfs_stop_workers(&fs_info->fixup_workers);
        btrfs_stop_workers(&fs_info->delalloc_workers);
        btrfs_stop_workers(&fs_info->workers);
        btrfs_stop_workers(&fs_info->endio_workers);
        btrfs_stop_workers(&fs_info->endio_write_workers);
        btrfs_stop_workers(&fs_info->submit_workers);
fail_iput:
        invalidate_inode_pages2(fs_info->btree_inode->i_mapping);
        iput(fs_info->btree_inode);
fail:
        btrfs_close_devices(fs_info->fs_devices);
        btrfs_mapping_tree_free(&fs_info->mapping_tree);

        kfree(extent_root);
        kfree(tree_root);
        bdi_destroy(&fs_info->bdi);
        kfree(fs_info);
        kfree(chunk_root);
        kfree(dev_root);
        return ERR_PTR(err);
}

static void btrfs_end_buffer_write_sync(struct buffer_head *bh, int uptodate)
{
        char b[BDEVNAME_SIZE];

        if (uptodate) {
                set_buffer_uptodate(bh);
        } else {
                if (!buffer_eopnotsupp(bh) && printk_ratelimit()) {
                        printk(KERN_WARNING "lost page write due to "
                                        "I/O error on %s\n",
                                       bdevname(bh->b_bdev, b));
                }
                /* note, we dont' set_buffer_write_io_error because we have
                 * our own ways of dealing with the IO errors
                 */
                clear_buffer_uptodate(bh);
        }
        unlock_buffer(bh);
        put_bh(bh);
}

static int write_all_supers(struct btrfs_root *root)
{
        struct list_head *cur;
        struct list_head *head = &root->fs_info->fs_devices->devices;
        struct btrfs_device *dev;
        struct btrfs_super_block *sb;
        struct btrfs_dev_item *dev_item;
        struct buffer_head *bh;
        int ret;
        int do_barriers;
        int max_errors;
        int total_errors = 0;
        u32 crc;
        u64 flags;

        max_errors = btrfs_super_num_devices(&root->fs_info->super_copy) - 1;
        do_barriers = !btrfs_test_opt(root, NOBARRIER);

        sb = &root->fs_info->super_for_commit;
        dev_item = &sb->dev_item;
        list_for_each(cur, head) {
                dev = list_entry(cur, struct btrfs_device, dev_list);
                if (!dev->bdev) {
                        total_errors++;
                        continue;
                }
                if (!dev->in_fs_metadata || !dev->writeable)
                        continue;

                btrfs_set_stack_device_generation(dev_item, 0);
                btrfs_set_stack_device_type(dev_item, dev->type);
                btrfs_set_stack_device_id(dev_item, dev->devid);
                btrfs_set_stack_device_total_bytes(dev_item, dev->total_bytes);
                btrfs_set_stack_device_bytes_used(dev_item, dev->bytes_used);
                btrfs_set_stack_device_io_align(dev_item, dev->io_align);
                btrfs_set_stack_device_io_width(dev_item, dev->io_width);
                btrfs_set_stack_device_sector_size(dev_item, dev->sector_size);
                memcpy(dev_item->uuid, dev->uuid, BTRFS_UUID_SIZE);
                memcpy(dev_item->fsid, dev->fs_devices->fsid, BTRFS_UUID_SIZE);
                flags = btrfs_super_flags(sb);
                btrfs_set_super_flags(sb, flags | BTRFS_HEADER_FLAG_WRITTEN);


                crc = ~(u32)0;
                crc = btrfs_csum_data(root, (char *)sb + BTRFS_CSUM_SIZE, crc,
                                      BTRFS_SUPER_INFO_SIZE - BTRFS_CSUM_SIZE);
                btrfs_csum_final(crc, sb->csum);

                bh = __getblk(dev->bdev, BTRFS_SUPER_INFO_OFFSET / 4096,
                              BTRFS_SUPER_INFO_SIZE);

                memcpy(bh->b_data, sb, BTRFS_SUPER_INFO_SIZE);
                dev->pending_io = bh;

                get_bh(bh);
                set_buffer_uptodate(bh);
                lock_buffer(bh);
                bh->b_end_io = btrfs_end_buffer_write_sync;

                if (do_barriers && dev->barriers) {
                        ret = submit_bh(WRITE_BARRIER, bh);
                        if (ret == -EOPNOTSUPP) {
                                printk("btrfs: disabling barriers on dev %s\n",
                                       dev->name);
                                set_buffer_uptodate(bh);
                                dev->barriers = 0;
                                get_bh(bh);
                                lock_buffer(bh);
                                ret = submit_bh(WRITE, bh);
                        }
                } else {
                        ret = submit_bh(WRITE, bh);
                }
                if (ret)
                        total_errors++;
        }
        if (total_errors > max_errors) {
                printk("btrfs: %d errors while writing supers\n", total_errors);
                BUG();
        }
        total_errors = 0;

        list_for_each(cur, head) {
                dev = list_entry(cur, struct btrfs_device, dev_list);
                if (!dev->bdev)
                        continue;
                if (!dev->in_fs_metadata || !dev->writeable)
                        continue;

                BUG_ON(!dev->pending_io);
                bh = dev->pending_io;
                wait_on_buffer(bh);
                if (!buffer_uptodate(dev->pending_io)) {
                        if (do_barriers && dev->barriers) {
                                printk("btrfs: disabling barriers on dev %s\n",
                                       dev->name);
                                set_buffer_uptodate(bh);
                                get_bh(bh);
                                lock_buffer(bh);
                                dev->barriers = 0;
                                ret = submit_bh(WRITE, bh);
                                BUG_ON(ret);
                                wait_on_buffer(bh);
                                if (!buffer_uptodate(bh))
                                        total_errors++;
                        } else {
                                total_errors++;
                        }

                }
                dev->pending_io = NULL;
                brelse(bh);
        }
        if (total_errors > max_errors) {
                printk("btrfs: %d errors while writing supers\n", total_errors);
                BUG();
        }
        return 0;
}

int write_ctree_super(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root)
{
        int ret;

        ret = write_all_supers(root);
        return ret;
}

int btrfs_free_fs_root(struct btrfs_fs_info *fs_info, struct btrfs_root *root)
{
        radix_tree_delete(&fs_info->fs_roots_radix,
                          (unsigned long)root->root_key.objectid);
        if (root->anon_super.s_dev) {
                down_write(&root->anon_super.s_umount);
                kill_anon_super(&root->anon_super);
        }
#if 0
        if (root->in_sysfs)
                btrfs_sysfs_del_root(root);
#endif
        if (root->node)
                free_extent_buffer(root->node);
        if (root->commit_root)
                free_extent_buffer(root->commit_root);
        if (root->name)
                kfree(root->name);
        kfree(root);
        return 0;
}

static int del_fs_roots(struct btrfs_fs_info *fs_info)
{
        int ret;
        struct btrfs_root *gang[8];
        int i;

        while(1) {
                ret = radix_tree_gang_lookup(&fs_info->fs_roots_radix,
                                             (void **)gang, 0,
                                             ARRAY_SIZE(gang));
                if (!ret)
                        break;
                for (i = 0; i < ret; i++)
                        btrfs_free_fs_root(fs_info, gang[i]);
        }
        return 0;
}

int btrfs_cleanup_fs_roots(struct btrfs_fs_info *fs_info)
{
        u64 root_objectid = 0;
        struct btrfs_root *gang[8];
        int i;
        int ret;

        while (1) {
                ret = radix_tree_gang_lookup(&fs_info->fs_roots_radix,
                                             (void **)gang, root_objectid,
                                             ARRAY_SIZE(gang));
                if (!ret)
                        break;
                for (i = 0; i < ret; i++) {
                        root_objectid = gang[i]->root_key.objectid;
                        ret = btrfs_find_dead_roots(fs_info->tree_root,
                                                    root_objectid, gang[i]);
                        BUG_ON(ret);
                        btrfs_orphan_cleanup(gang[i]);
                }
                root_objectid++;
        }
        return 0;
}

int btrfs_commit_super(struct btrfs_root *root)
{
        struct btrfs_trans_handle *trans;
        int ret;

        mutex_lock(&root->fs_info->cleaner_mutex);
        btrfs_clean_old_snapshots(root);
        mutex_unlock(&root->fs_info->cleaner_mutex);
        trans = btrfs_start_transaction(root, 1);
        ret = btrfs_commit_transaction(trans, root);
        BUG_ON(ret);
        /* run commit again to drop the original snapshot */
        trans = btrfs_start_transaction(root, 1);
        btrfs_commit_transaction(trans, root);
        ret = btrfs_write_and_wait_transaction(NULL, root);
        BUG_ON(ret);

        ret = write_ctree_super(NULL, root);
        return ret;
}

int close_ctree(struct btrfs_root *root)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        int ret;

        fs_info->closing = 1;
        smp_mb();

        kthread_stop(root->fs_info->transaction_kthread);
        kthread_stop(root->fs_info->cleaner_kthread);

        if (!(fs_info->sb->s_flags & MS_RDONLY)) {
                ret =  btrfs_commit_super(root);
                if (ret) {
                        printk("btrfs: commit super returns %d\n", ret);
                }
        }

        if (fs_info->delalloc_bytes) {
                printk("btrfs: at unmount delalloc count %Lu\n",
                       fs_info->delalloc_bytes);
        }
        if (fs_info->total_ref_cache_size) {
                printk("btrfs: at umount reference cache size %Lu\n",
                        fs_info->total_ref_cache_size);
        }

        if (fs_info->extent_root->node)
                free_extent_buffer(fs_info->extent_root->node);

        if (fs_info->tree_root->node)
                free_extent_buffer(fs_info->tree_root->node);

        if (root->fs_info->chunk_root->node);
                free_extent_buffer(root->fs_info->chunk_root->node);

        if (root->fs_info->dev_root->node);
                free_extent_buffer(root->fs_info->dev_root->node);

        btrfs_free_block_groups(root->fs_info);

        del_fs_roots(fs_info);

        iput(fs_info->btree_inode);

        btrfs_stop_workers(&fs_info->fixup_workers);
        btrfs_stop_workers(&fs_info->delalloc_workers);
        btrfs_stop_workers(&fs_info->workers);
        btrfs_stop_workers(&fs_info->endio_workers);
        btrfs_stop_workers(&fs_info->endio_write_workers);
        btrfs_stop_workers(&fs_info->submit_workers);

#if 0
        while(!list_empty(&fs_info->hashers)) {
                struct btrfs_hasher *hasher;
                hasher = list_entry(fs_info->hashers.next, struct btrfs_hasher,
                                    hashers);
                list_del(&hasher->hashers);
                crypto_free_hash(&fs_info->hash_tfm);
                kfree(hasher);
        }
#endif
        btrfs_close_devices(fs_info->fs_devices);
        btrfs_mapping_tree_free(&fs_info->mapping_tree);

        bdi_destroy(&fs_info->bdi);

        kfree(fs_info->extent_root);
        kfree(fs_info->tree_root);
        kfree(fs_info->chunk_root);
        kfree(fs_info->dev_root);
        return 0;
}

int btrfs_buffer_uptodate(struct extent_buffer *buf, u64 parent_transid)
{
        int ret;
        struct inode *btree_inode = buf->first_page->mapping->host;

        ret = extent_buffer_uptodate(&BTRFS_I(btree_inode)->io_tree, buf);
        if (!ret)
                return ret;

        ret = verify_parent_transid(&BTRFS_I(btree_inode)->io_tree, buf,
                                    parent_transid);
        return !ret;
}

int btrfs_set_buffer_uptodate(struct extent_buffer *buf)
{
        struct inode *btree_inode = buf->first_page->mapping->host;
        return set_extent_buffer_uptodate(&BTRFS_I(btree_inode)->io_tree,
                                          buf);
}

void btrfs_mark_buffer_dirty(struct extent_buffer *buf)
{
        struct btrfs_root *root = BTRFS_I(buf->first_page->mapping->host)->root;
        u64 transid = btrfs_header_generation(buf);
        struct inode *btree_inode = root->fs_info->btree_inode;

        WARN_ON(!btrfs_tree_locked(buf));
        if (transid != root->fs_info->generation) {
                printk(KERN_CRIT "transid mismatch buffer %llu, found %Lu running %Lu\n",
                        (unsigned long long)buf->start,
                        transid, root->fs_info->generation);
                WARN_ON(1);
        }
        set_extent_buffer_dirty(&BTRFS_I(btree_inode)->io_tree, buf);
}

void btrfs_btree_balance_dirty(struct btrfs_root *root, unsigned long nr)
{
        /*
         * looks as though older kernels can get into trouble with
         * this code, they end up stuck in balance_dirty_pages forever
         */
        struct extent_io_tree *tree;
        u64 num_dirty;
        u64 start = 0;
        unsigned long thresh = 32 * 1024 * 1024;
        tree = &BTRFS_I(root->fs_info->btree_inode)->io_tree;

        if (current_is_pdflush() || current->flags & PF_MEMALLOC)
                return;

        num_dirty = count_range_bits(tree, &start, (u64)-1,
                                     thresh, EXTENT_DIRTY);
        if (num_dirty > thresh) {
                balance_dirty_pages_ratelimited_nr(
                                   root->fs_info->btree_inode->i_mapping, 1);
        }
        return;
}

int btrfs_read_buffer(struct extent_buffer *buf, u64 parent_transid)
{
        struct btrfs_root *root = BTRFS_I(buf->first_page->mapping->host)->root;
        int ret;
        ret = btree_read_extent_buffer_pages(root, buf, 0, parent_transid);
        if (ret == 0) {
                buf->flags |= EXTENT_UPTODATE;
        }
        return ret;
}

int btree_lock_page_hook(struct page *page)
{
        struct inode *inode = page->mapping->host;
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
        struct extent_buffer *eb;
        unsigned long len;
        u64 bytenr = page_offset(page);

        if (page->private == EXTENT_PAGE_PRIVATE)
                goto out;

        len = page->private >> 2;
        eb = find_extent_buffer(io_tree, bytenr, len, GFP_NOFS);
        if (!eb)
                goto out;

        btrfs_tree_lock(eb);
        spin_lock(&root->fs_info->hash_lock);
        btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);
        spin_unlock(&root->fs_info->hash_lock);
        btrfs_tree_unlock(eb);
        free_extent_buffer(eb);
out:
        lock_page(page);
        return 0;
}

static struct extent_io_ops btree_extent_io_ops = {
        .write_cache_pages_lock_hook = btree_lock_page_hook,
        .readpage_end_io_hook = btree_readpage_end_io_hook,
        .submit_bio_hook = btree_submit_bio_hook,
        /* note we're sharing with inode.c for the merge bio hook */
        .merge_bio_hook = btrfs_merge_bio_hook,
};