btrfs: clean_tree_block should panic on observed memory corruption and return void

[linux-2.6-block.git] / 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/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>
#include <linux/workqueue.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/crc32c.h>
#include <linux/slab.h>
#include <linux/migrate.h>
#include <linux/ratelimit.h>
#include <asm/unaligned.h>
#include "compat.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 "tree-log.h"
#include "free-space-cache.h"
#include "inode-map.h"
#include "check-integrity.h"

static struct extent_io_ops btree_extent_io_ops;
static void end_workqueue_fn(struct btrfs_work *work);
static void free_fs_root(struct btrfs_root *root);
static void btrfs_check_super_valid(struct btrfs_fs_info *fs_info,
                                    int read_only);
static int btrfs_destroy_ordered_operations(struct btrfs_root *root);
static int btrfs_destroy_ordered_extents(struct btrfs_root *root);
static int btrfs_destroy_delayed_refs(struct btrfs_transaction *trans,
                                      struct btrfs_root *root);
static int btrfs_destroy_pending_snapshots(struct btrfs_transaction *t);
static int btrfs_destroy_delalloc_inodes(struct btrfs_root *root);
static int btrfs_destroy_marked_extents(struct btrfs_root *root,
                                        struct extent_io_tree *dirty_pages,
                                        int mark);
static int btrfs_destroy_pinned_extent(struct btrfs_root *root,
                                       struct extent_io_tree *pinned_extents);
static int btrfs_cleanup_transaction(struct btrfs_root *root);

/*
 * 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;
        /*
         * bio_offset is optional, can be used if the pages in the bio
         * can't tell us where in the file the bio should go
         */
        u64 bio_offset;
        struct btrfs_work work;
};

/*
 * Lockdep class keys for extent_buffer->lock's in this root.  For a given
 * eb, the lockdep key is determined by the btrfs_root it belongs to and
 * the level the eb occupies in the tree.
 *
 * Different roots are used for different purposes and may nest inside each
 * other and they require separate keysets.  As lockdep keys should be
 * static, assign keysets according to the purpose of the root as indicated
 * by btrfs_root->objectid.  This ensures that all special purpose roots
 * have separate keysets.
 *
 * Lock-nesting across peer nodes is always done with the immediate parent
 * node locked thus preventing deadlock.  As lockdep doesn't know this, use
 * subclass to avoid triggering lockdep warning in such cases.
 *
 * The key is set by the readpage_end_io_hook after the buffer has passed
 * csum validation but before the pages are unlocked.  It is also set by
 * btrfs_init_new_buffer on freshly allocated blocks.
 *
 * We also add a check to make sure the highest level of the tree is the
 * same as our lockdep setup here.  If BTRFS_MAX_LEVEL changes, this code
 * needs update as well.
 */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
# if BTRFS_MAX_LEVEL != 8
#  error
# endif

static struct btrfs_lockdep_keyset {
        u64                     id;             /* root objectid */
        const char              *name_stem;     /* lock name stem */
        char                    names[BTRFS_MAX_LEVEL + 1][20];
        struct lock_class_key   keys[BTRFS_MAX_LEVEL + 1];
} btrfs_lockdep_keysets[] = {
        { .id = BTRFS_ROOT_TREE_OBJECTID,       .name_stem = "root"     },
        { .id = BTRFS_EXTENT_TREE_OBJECTID,     .name_stem = "extent"   },
        { .id = BTRFS_CHUNK_TREE_OBJECTID,      .name_stem = "chunk"    },
        { .id = BTRFS_DEV_TREE_OBJECTID,        .name_stem = "dev"      },
        { .id = BTRFS_FS_TREE_OBJECTID,         .name_stem = "fs"       },
        { .id = BTRFS_CSUM_TREE_OBJECTID,       .name_stem = "csum"     },
        { .id = BTRFS_ORPHAN_OBJECTID,          .name_stem = "orphan"   },
        { .id = BTRFS_TREE_LOG_OBJECTID,        .name_stem = "log"      },
        { .id = BTRFS_TREE_RELOC_OBJECTID,      .name_stem = "treloc"   },
        { .id = BTRFS_DATA_RELOC_TREE_OBJECTID, .name_stem = "dreloc"   },
        { .id = 0,                              .name_stem = "tree"     },
};

void __init btrfs_init_lockdep(void)
{
        int i, j;

        /* initialize lockdep class names */
        for (i = 0; i < ARRAY_SIZE(btrfs_lockdep_keysets); i++) {
                struct btrfs_lockdep_keyset *ks = &btrfs_lockdep_keysets[i];

                for (j = 0; j < ARRAY_SIZE(ks->names); j++)
                        snprintf(ks->names[j], sizeof(ks->names[j]),
                                 "btrfs-%s-%02d", ks->name_stem, j);
        }
}

void btrfs_set_buffer_lockdep_class(u64 objectid, struct extent_buffer *eb,
                                    int level)
{
        struct btrfs_lockdep_keyset *ks;

        BUG_ON(level >= ARRAY_SIZE(ks->keys));

        /* find the matching keyset, id 0 is the default entry */
        for (ks = btrfs_lockdep_keysets; ks->id; ks++)
                if (ks->id == objectid)
                        break;

        lockdep_set_class_and_name(&eb->lock,
                                   &ks->keys[level], ks->names[level]);
}

#endif

/*
 * 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 pg_offset, u64 start, u64 len,
                int create)
{
        struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
        struct extent_map *em;
        int ret;

        read_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;
                read_unlock(&em_tree->lock);
                goto out;
        }
        read_unlock(&em_tree->lock);

        em = alloc_extent_map();
        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;

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

                free_extent_map(em);
                em = lookup_extent_mapping(em_tree, start, len);
                if (em) {
                        ret = 0;
                } else {
                        em = lookup_extent_mapping(em_tree, failed_start,
                                                   failed_len);
                        ret = -EIO;
                }
        } else if (ret) {
                free_extent_map(em);
                em = NULL;
        }
        write_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 crc32c(seed, data, len);
}

void btrfs_csum_final(u32 crc, char *result)
{
        put_unaligned_le32(~crc, result);
}

/*
 * 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 *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,
                                        &kaddr, &map_start, &map_len);
                if (err)
                        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;
        }
        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) {
                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_ratelimited(KERN_INFO "btrfs: %s checksum verify "
                                       "failed on %llu wanted %X found %X "
                                       "level %d\n",
                                       root->fs_info->sb->s_id,
                                       (unsigned long long)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)
{
        struct extent_state *cached_state = NULL;
        int ret;

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

        lock_extent_bits(io_tree, eb->start, eb->start + eb->len - 1,
                         0, &cached_state, GFP_NOFS);
        if (extent_buffer_uptodate(io_tree, eb, cached_state) &&
            btrfs_header_generation(eb) == parent_transid) {
                ret = 0;
                goto out;
        }
        printk_ratelimited("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, &cached_state);
out:
        unlock_extent_cached(io_tree, eb->start, eb->start + eb->len - 1,
                             &cached_state, 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;

        clear_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags);
        io_tree = &BTRFS_I(root->fs_info->btree_inode)->io_tree;
        while (1) {
                ret = read_extent_buffer_pages(io_tree, eb, start,
                                               WAIT_COMPLETE,
                                               btree_get_extent, mirror_num);
                if (!ret &&
                    !verify_parent_transid(io_tree, eb, parent_transid))
                        return ret;

                /*
                 * This buffer's crc is fine, but its contents are corrupted, so
                 * there is no reason to read the other copies, they won't be
                 * any less wrong.
                 */
                if (test_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags))
                        return ret;

                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;
        unsigned long len;
        struct extent_buffer *eb;
        int ret;

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

        if (page->private == EXTENT_PAGE_PRIVATE) {
                WARN_ON(1);
                goto out;
        }
        if (!page->private) {
                WARN_ON(1);
                goto out;
        }
        len = page->private >> 2;
        WARN_ON(len == 0);

        eb = alloc_extent_buffer(tree, start, len, page);
        if (eb == NULL) {
                WARN_ON(1);
                goto out;
        }
        ret = btree_read_extent_buffer_pages(root, eb, start + PAGE_CACHE_SIZE,
                                             btrfs_header_generation(eb));
        BUG_ON(ret);
        WARN_ON(!btrfs_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN));

        found_start = btrfs_header_bytenr(eb);
        if (found_start != start) {
                WARN_ON(1);
                goto err;
        }
        if (eb->first_page != page) {
                WARN_ON(1);
                goto err;
        }
        if (!PageUptodate(page)) {
                WARN_ON(1);
                goto err;
        }
        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;
}

#define CORRUPT(reason, eb, root, slot)                         \
        printk(KERN_CRIT "btrfs: corrupt leaf, %s: block=%llu," \
               "root=%llu, slot=%d\n", reason,                  \
               (unsigned long long)btrfs_header_bytenr(eb),     \
               (unsigned long long)root->objectid, slot)

static noinline int check_leaf(struct btrfs_root *root,
                               struct extent_buffer *leaf)
{
        struct btrfs_key key;
        struct btrfs_key leaf_key;
        u32 nritems = btrfs_header_nritems(leaf);
        int slot;

        if (nritems == 0)
                return 0;

        /* Check the 0 item */
        if (btrfs_item_offset_nr(leaf, 0) + btrfs_item_size_nr(leaf, 0) !=
            BTRFS_LEAF_DATA_SIZE(root)) {
                CORRUPT("invalid item offset size pair", leaf, root, 0);
                return -EIO;
        }

        /*
         * Check to make sure each items keys are in the correct order and their
         * offsets make sense.  We only have to loop through nritems-1 because
         * we check the current slot against the next slot, which verifies the
         * next slot's offset+size makes sense and that the current's slot
         * offset is correct.
         */
        for (slot = 0; slot < nritems - 1; slot++) {
                btrfs_item_key_to_cpu(leaf, &leaf_key, slot);
                btrfs_item_key_to_cpu(leaf, &key, slot + 1);

                /* Make sure the keys are in the right order */
                if (btrfs_comp_cpu_keys(&leaf_key, &key) >= 0) {
                        CORRUPT("bad key order", leaf, root, slot);
                        return -EIO;
                }

                /*
                 * Make sure the offset and ends are right, remember that the
                 * item data starts at the end of the leaf and grows towards the
                 * front.
                 */
                if (btrfs_item_offset_nr(leaf, slot) !=
                        btrfs_item_end_nr(leaf, slot + 1)) {
                        CORRUPT("slot offset bad", leaf, root, slot);
                        return -EIO;
                }

                /*
                 * Check to make sure that we don't point outside of the leaf,
                 * just incase all the items are consistent to eachother, but
                 * all point outside of the leaf.
                 */
                if (btrfs_item_end_nr(leaf, slot) >
                    BTRFS_LEAF_DATA_SIZE(root)) {
                        CORRUPT("slot end outside of leaf", leaf, root, slot);
                        return -EIO;
                }
        }

        return 0;
}

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;
        WARN_ON(len == 0);

        eb = alloc_extent_buffer(tree, start, len, page);
        if (eb == NULL) {
                ret = -EIO;
                goto out;
        }

        found_start = btrfs_header_bytenr(eb);
        if (found_start != start) {
                printk_ratelimited(KERN_INFO "btrfs 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(KERN_INFO "btrfs 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_ratelimited(KERN_INFO "btrfs bad fsid on block %llu\n",
                               (unsigned long long)eb->start);
                ret = -EIO;
                goto err;
        }
        found_level = btrfs_header_level(eb);

        btrfs_set_buffer_lockdep_class(btrfs_header_owner(eb),
                                       eb, found_level);

        ret = csum_tree_block(root, eb, 1);
        if (ret) {
                ret = -EIO;
                goto err;
        }

        /*
         * If this is a leaf block and it is corrupt, set the corrupt bit so
         * that we don't try and read the other copies of this block, just
         * return -EIO.
         */
        if (found_level == 0 && check_leaf(root, eb)) {
                set_bit(EXTENT_BUFFER_CORRUPT, &eb->bflags);
                ret = -EIO;
        }

        end = min_t(u64, eb->len, PAGE_CACHE_SIZE);
        end = eb->start + end - 1;
err:
        if (test_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags)) {
                clear_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags);
                btree_readahead_hook(root, eb, eb->start, ret);
        }

        free_extent_buffer(eb);
out:
        return ret;
}

static int btree_io_failed_hook(struct bio *failed_bio,
                         struct page *page, u64 start, u64 end,
                         int mirror_num, struct extent_state *state)
{
        struct extent_io_tree *tree;
        unsigned long len;
        struct extent_buffer *eb;
        struct btrfs_root *root = BTRFS_I(page->mapping->host)->root;

        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;
        WARN_ON(len == 0);

        eb = alloc_extent_buffer(tree, start, len, page);
        if (eb == NULL)
                goto out;

        if (test_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags)) {
                clear_bit(EXTENT_BUFFER_READAHEAD, &eb->bflags);
                btree_readahead_hook(root, eb, eb->start, -EIO);
        }
        free_extent_buffer(eb);

out:
        return -EIO;    /* we fixed nothing */
}

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 & REQ_WRITE) {
                if (end_io_wq->metadata == 1)
                        btrfs_queue_worker(&fs_info->endio_meta_write_workers,
                                           &end_io_wq->work);
                else if (end_io_wq->metadata == 2)
                        btrfs_queue_worker(&fs_info->endio_freespace_worker,
                                           &end_io_wq->work);
                else
                        btrfs_queue_worker(&fs_info->endio_write_workers,
                                           &end_io_wq->work);
        } else {
                if (end_io_wq->metadata)
                        btrfs_queue_worker(&fs_info->endio_meta_workers,
                                           &end_io_wq->work);
                else
                        btrfs_queue_worker(&fs_info->endio_workers,
                                           &end_io_wq->work);
        }
}

/*
 * For the metadata arg you want
 *
 * 0 - if data
 * 1 - if normal metadta
 * 2 - if writing to the free space cache area
 */
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;
}

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

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

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,
                               async->bio_offset);
}

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,
                        u64 bio_offset,
                        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;
        async->bio_offset = bio_offset;

        atomic_inc(&fs_info->nr_async_submits);

        if (rw & REQ_SYNC)
                btrfs_set_work_high_prio(&async->work);

        btrfs_queue_worker(&fs_info->workers, &async->work);

        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,
                                    u64 bio_offset)
{
        /*
         * 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,
                                 u64 bio_offset)
{
        /*
         * 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,
                                 u64 bio_offset)
{
        int ret;

        ret = btrfs_bio_wq_end_io(BTRFS_I(inode)->root->fs_info,
                                          bio, 1);
        BUG_ON(ret);

        if (!(rw & REQ_WRITE)) {
                /*
                 * called for a read, do the setup so that checksum validation
                 * can happen in the async kernel threads
                 */
                return btrfs_map_bio(BTRFS_I(inode)->root, rw, bio,
                                     mirror_num, 0);
        }

        /*
         * kthread helpers are used to submit writes so that checksumming
         * can happen in parallel across all CPUs
         */
        return btrfs_wq_submit_bio(BTRFS_I(inode)->root->fs_info,
                                   inode, rw, bio, mirror_num, 0,
                                   bio_offset,
                                   __btree_submit_bio_start,
                                   __btree_submit_bio_done);
}

#ifdef CONFIG_MIGRATION
static int btree_migratepage(struct address_space *mapping,
                        struct page *newpage, struct page *page,
                        enum migrate_mode mode)
{
        /*
         * we can't safely write a btree page from here,
         * we haven't done the locking hook
         */
        if (PageDirty(page))
                return -EAGAIN;
        /*
         * Buffers may be managed in a filesystem specific way.
         * We must have no buffers or drop them.
         */
        if (page_has_private(page) &&
            !try_to_release_page(page, GFP_KERNEL))
                return -EAGAIN;
        return migrate_page(mapping, newpage, page, mode);
}
#endif

static int btree_writepage(struct page *page, struct writeback_control *wbc)
{
        struct extent_io_tree *tree;
        struct btrfs_root *root = BTRFS_I(page->mapping->host)->root;
        struct extent_buffer *eb;
        int was_dirty;

        tree = &BTRFS_I(page->mapping->host)->io_tree;
        if (!(current->flags & PF_MEMALLOC)) {
                return extent_write_full_page(tree, page,
                                              btree_get_extent, wbc);
        }

        redirty_page_for_writepage(wbc, page);
        eb = btrfs_find_tree_block(root, page_offset(page), PAGE_CACHE_SIZE);
        WARN_ON(!eb);

        was_dirty = test_and_set_bit(EXTENT_BUFFER_DIRTY, &eb->bflags);
        if (!was_dirty) {
                spin_lock(&root->fs_info->delalloc_lock);
                root->fs_info->dirty_metadata_bytes += PAGE_CACHE_SIZE;
                spin_unlock(&root->fs_info->delalloc_lock);
        }
        free_extent_buffer(eb);

        unlock_page(page);
        return 0;
}

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) {
                struct btrfs_root *root = BTRFS_I(mapping->host)->root;
                u64 num_dirty;
                unsigned long thresh = 32 * 1024 * 1024;

                if (wbc->for_kupdate)
                        return 0;

                /* this is a bit racy, but that's ok */
                num_dirty = root->fs_info->dirty_metadata_bytes;
                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, 0);
}

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;

        /*
         * We need to mask out eg. __GFP_HIGHMEM and __GFP_DMA32 as we're doing
         * slab allocation from alloc_extent_state down the callchain where
         * it'd hit a BUG_ON as those flags are not allowed.
         */
        gfp_flags &= ~GFP_SLAB_BUG_MASK;

        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(KERN_WARNING "btrfs warning page private not zero "
                       "on page %llu\n", (unsigned long long)page_offset(page));
                ClearPagePrivate(page);
                set_page_private(page, 0);
                page_cache_release(page);
        }
}

static const struct address_space_operations btree_aops = {
        .readpage       = btree_readpage,
        .writepage      = btree_writepage,
        .writepages     = btree_writepages,
        .releasepage    = btree_releasepage,
        .invalidatepage = btree_invalidatepage,
#ifdef CONFIG_MIGRATION
        .migratepage    = btree_migratepage,
#endif
};

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, WAIT_NONE, btree_get_extent, 0);
        free_extent_buffer(buf);
        return ret;
}

int reada_tree_block_flagged(struct btrfs_root *root, u64 bytenr, u32 blocksize,
                         int mirror_num, struct extent_buffer **eb)
{
        struct extent_buffer *buf = NULL;
        struct inode *btree_inode = root->fs_info->btree_inode;
        struct extent_io_tree *io_tree = &BTRFS_I(btree_inode)->io_tree;
        int ret;

        buf = btrfs_find_create_tree_block(root, bytenr, blocksize);
        if (!buf)
                return 0;

        set_bit(EXTENT_BUFFER_READAHEAD, &buf->bflags);

        ret = read_extent_buffer_pages(io_tree, buf, 0, WAIT_PAGE_LOCK,
                                       btree_get_extent, mirror_num);
        if (ret) {
                free_extent_buffer(buf);
                return ret;
        }

        if (test_bit(EXTENT_BUFFER_CORRUPT, &buf->bflags)) {
                free_extent_buffer(buf);
                return -EIO;
        } else if (extent_buffer_uptodate(io_tree, buf, NULL)) {
                *eb = buf;
        } else {
                free_extent_buffer(buf);
        }
        return 0;
}

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);
        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);
        return eb;
}


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

int btrfs_wait_tree_block_writeback(struct extent_buffer *buf)
{
        return filemap_fdatawait_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;
        int ret;

        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)
                set_bit(EXTENT_BUFFER_UPTODATE, &buf->bflags);
        return buf;

}

void 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) {
                btrfs_assert_tree_locked(buf);

                if (test_and_clear_bit(EXTENT_BUFFER_DIRTY, &buf->bflags)) {
                        spin_lock(&root->fs_info->delalloc_lock);
                        if (root->fs_info->dirty_metadata_bytes >= buf->len)
                                root->fs_info->dirty_metadata_bytes -= buf->len;
                        else {
                                spin_unlock(&root->fs_info->delalloc_lock);
                                btrfs_panic(root->fs_info, -EOVERFLOW,
                                          "Can't clear %lu bytes from "
                                          " dirty_mdatadata_bytes (%lu)",
                                          buf->len,
                                          root->fs_info->dirty_metadata_bytes);
                        }
                        spin_unlock(&root->fs_info->delalloc_lock);
                }

                /* ugh, clear_extent_buffer_dirty needs to lock the page */
                btrfs_set_lock_blocking(buf);
                clear_extent_buffer_dirty(&BTRFS_I(btree_inode)->io_tree,
                                          buf);
        }
}

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->sectorsize = sectorsize;
        root->nodesize = nodesize;
        root->leafsize = leafsize;
        root->stripesize = stripesize;
        root->ref_cows = 0;
        root->track_dirty = 0;
        root->in_radix = 0;
        root->orphan_item_inserted = 0;
        root->orphan_cleanup_state = 0;

        root->objectid = objectid;
        root->last_trans = 0;
        root->highest_objectid = 0;
        root->name = NULL;
        root->inode_tree = RB_ROOT;
        INIT_RADIX_TREE(&root->delayed_nodes_tree, GFP_ATOMIC);
        root->block_rsv = NULL;
        root->orphan_block_rsv = NULL;

        INIT_LIST_HEAD(&root->dirty_list);
        INIT_LIST_HEAD(&root->orphan_list);
        INIT_LIST_HEAD(&root->root_list);
        spin_lock_init(&root->orphan_lock);
        spin_lock_init(&root->inode_lock);
        spin_lock_init(&root->accounting_lock);
        mutex_init(&root->objectid_mutex);
        mutex_init(&root->log_mutex);
        init_waitqueue_head(&root->log_writer_wait);
        init_waitqueue_head(&root->log_commit_wait[0]);
        init_waitqueue_head(&root->log_commit_wait[1]);
        atomic_set(&root->log_commit[0], 0);
        atomic_set(&root->log_commit[1], 0);
        atomic_set(&root->log_writers, 0);
        root->log_batch = 0;
        root->log_transid = 0;
        root->last_log_commit = 0;
        extent_io_tree_init(&root->dirty_log_pages,
                             fs_info->btree_inode->i_mapping);

        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->root_key.objectid = objectid;
        root->anon_dev = 0;
        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);
        if (ret > 0)
                return -ENOENT;
        BUG_ON(ret);

        generation = btrfs_root_generation(&root->root_item);
        blocksize = btrfs_level_size(root, btrfs_root_level(&root->root_item));
        root->commit_root = NULL;
        root->node = read_tree_block(root, btrfs_root_bytenr(&root->root_item),
                                     blocksize, generation);
        if (!root->node || !btrfs_buffer_uptodate(root->node, generation)) {
                free_extent_buffer(root->node);
                root->node = NULL;
                return -EIO;
        }
        root->commit_root = btrfs_root_node(root);
        return 0;
}

static struct btrfs_root *btrfs_alloc_root(struct btrfs_fs_info *fs_info)
{
        struct btrfs_root *root = kzalloc(sizeof(*root), GFP_NOFS);
        if (root)
                root->fs_info = fs_info;
        return root;
}

static struct btrfs_root *alloc_log_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;
        struct extent_buffer *leaf;

        root = btrfs_alloc_root(fs_info);
        if (!root)
                return ERR_PTR(-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;
        /*
         * log trees do not get reference counted because they go away
         * before a real commit is actually done.  They do store pointers
         * to file data extents, and those reference counts still get
         * updated (along with back refs to the log tree).
         */
        root->ref_cows = 0;

        leaf = btrfs_alloc_free_block(trans, root, root->leafsize, 0,
                                      BTRFS_TREE_LOG_OBJECTID, NULL,
                                      0, 0, 0, 0);
        if (IS_ERR(leaf)) {
                kfree(root);
                return ERR_CAST(leaf);
        }

        memset_extent_buffer(leaf, 0, 0, sizeof(struct btrfs_header));
        btrfs_set_header_bytenr(leaf, leaf->start);
        btrfs_set_header_generation(leaf, trans->transid);
        btrfs_set_header_backref_rev(leaf, BTRFS_MIXED_BACKREF_REV);
        btrfs_set_header_owner(leaf, BTRFS_TREE_LOG_OBJECTID);
        root->node = leaf;

        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);
        return root;
}

int btrfs_init_log_root_tree(struct btrfs_trans_handle *trans,
                             struct btrfs_fs_info *fs_info)
{
        struct btrfs_root *log_root;

        log_root = alloc_log_tree(trans, fs_info);
        if (IS_ERR(log_root))
                return PTR_ERR(log_root);
        WARN_ON(fs_info->log_root_tree);
        fs_info->log_root_tree = log_root;
        return 0;
}

int btrfs_add_log_tree(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root)
{
        struct btrfs_root *log_root;
        struct btrfs_inode_item *inode_item;

        log_root = alloc_log_tree(trans, root->fs_info);
        if (IS_ERR(log_root))
                return PTR_ERR(log_root);

        log_root->last_trans = trans->transid;
        log_root->root_key.offset = root->root_key.objectid;

        inode_item = &log_root->root_item.inode;
        inode_item->generation = cpu_to_le64(1);
        inode_item->size = cpu_to_le64(3);
        inode_item->nlink = cpu_to_le32(1);
        inode_item->nbytes = cpu_to_le64(root->leafsize);
        inode_item->mode = cpu_to_le32(S_IFDIR | 0755);

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

        WARN_ON(root->log_root);
        root->log_root = log_root;
        root->log_transid = 0;
        root->last_log_commit = 0;
        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 generation;
        u32 blocksize;
        int ret = 0;

        root = btrfs_alloc_root(fs_info);
        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 out;
        }

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

        path = btrfs_alloc_path();
        if (!path) {
                kfree(root);
                return ERR_PTR(-ENOMEM);
        }
        ret = btrfs_search_slot(NULL, tree_root, location, path, 0, 0);
        if (ret == 0) {
                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));
        }
        btrfs_free_path(path);
        if (ret) {
                kfree(root);
                if (ret > 0)
                        ret = -ENOENT;
                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);
        root->commit_root = btrfs_root_node(root);
        BUG_ON(!root->node);
out:
        if (location->objectid != BTRFS_TREE_LOG_OBJECTID) {
                root->ref_cows = 1;
                btrfs_check_and_init_root_item(&root->root_item);
        }

        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;
        if (location->objectid == BTRFS_CSUM_TREE_OBJECTID)
                return fs_info->csum_root;
again:
        spin_lock(&fs_info->fs_roots_radix_lock);
        root = radix_tree_lookup(&fs_info->fs_roots_radix,
                                 (unsigned long)location->objectid);
        spin_unlock(&fs_info->fs_roots_radix_lock);
        if (root)
                return root;

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

        root->free_ino_ctl = kzalloc(sizeof(*root->free_ino_ctl), GFP_NOFS);
        root->free_ino_pinned = kzalloc(sizeof(*root->free_ino_pinned),
                                        GFP_NOFS);
        if (!root->free_ino_pinned || !root->free_ino_ctl) {
                ret = -ENOMEM;
                goto fail;
        }

        btrfs_init_free_ino_ctl(root);
        mutex_init(&root->fs_commit_mutex);
        spin_lock_init(&root->cache_lock);
        init_waitqueue_head(&root->cache_wait);

        ret = get_anon_bdev(&root->anon_dev);
        if (ret)
                goto fail;

        if (btrfs_root_refs(&root->root_item) == 0) {
                ret = -ENOENT;
                goto fail;
        }

        ret = btrfs_find_orphan_item(fs_info->tree_root, location->objectid);
        if (ret < 0)
                goto fail;
        if (ret == 0)
                root->orphan_item_inserted = 1;

        ret = radix_tree_preload(GFP_NOFS & ~__GFP_HIGHMEM);
        if (ret)
                goto fail;

        spin_lock(&fs_info->fs_roots_radix_lock);
        ret = radix_tree_insert(&fs_info->fs_roots_radix,
                                (unsigned long)root->root_key.objectid,
                                root);
        if (ret == 0)
                root->in_radix = 1;

        spin_unlock(&fs_info->fs_roots_radix_lock);
        radix_tree_preload_end();
        if (ret) {
                if (ret == -EEXIST) {
                        free_fs_root(root);
                        goto again;
                }
                goto fail;
        }

        ret = btrfs_find_dead_roots(fs_info->tree_root,
                                    root->root_key.objectid);
        WARN_ON(ret);
        return root;
fail:
        free_fs_root(root);
        return ERR_PTR(ret);
}

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 btrfs_device *device;
        struct backing_dev_info *bdi;

        rcu_read_lock();
        list_for_each_entry_rcu(device, &info->fs_devices->devices, dev_list) {
                if (!device->bdev)
                        continue;
                bdi = blk_get_backing_dev_info(device->bdev);
                if (bdi && bdi_congested(bdi, bdi_bits)) {
                        ret = 1;
                        break;
                }
        }
        rcu_read_unlock();
        return ret;
}

/*
 * If this fails, caller must call bdi_destroy() to get rid of the
 * bdi again.
 */
static int setup_bdi(struct btrfs_fs_info *info, struct backing_dev_info *bdi)
{
        int err;

        bdi->capabilities = BDI_CAP_MAP_COPY;
        err = bdi_setup_and_register(bdi, "btrfs", BDI_CAP_MAP_COPY);
        if (err)
                return err;

        bdi->ra_pages   = default_backing_dev_info.ra_pages;
        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 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;
        }
        /* 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);
        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 bio reads 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 (!(bio->bi_rw & REQ_WRITE) && end_io_wq->metadata &&
            !bio_ready_for_csum(bio)) {
                btrfs_queue_worker(&fs_info->endio_meta_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 {
                vfs_check_frozen(root->fs_info->sb, SB_FREEZE_WRITE);

                if (!(root->fs_info->sb->s_flags & MS_RDONLY) &&
                    mutex_trylock(&root->fs_info->cleaner_mutex)) {
                        btrfs_run_delayed_iputs(root);
                        btrfs_clean_old_snapshots(root);
                        mutex_unlock(&root->fs_info->cleaner_mutex);
                        btrfs_run_defrag_inodes(root->fs_info);
                }

                if (!try_to_freeze()) {
                        set_current_state(TASK_INTERRUPTIBLE);
                        if (!kthread_should_stop())
                                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;
        u64 transid;
        unsigned long now;
        unsigned long delay;
        int ret;

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

                spin_lock(&root->fs_info->trans_lock);
                cur = root->fs_info->running_transaction;
                if (!cur) {
                        spin_unlock(&root->fs_info->trans_lock);
                        goto sleep;
                }

                now = get_seconds();
                if (!cur->blocked &&
                    (now < cur->start_time || now - cur->start_time < 30)) {
                        spin_unlock(&root->fs_info->trans_lock);
                        delay = HZ * 5;
                        goto sleep;
                }
                transid = cur->transid;
                spin_unlock(&root->fs_info->trans_lock);

                trans = btrfs_join_transaction(root);
                BUG_ON(IS_ERR(trans));
                if (transid == trans->transid) {
                        ret = btrfs_commit_transaction(trans, root);
                        BUG_ON(ret);
                } else {
                        btrfs_end_transaction(trans, root);
                }
sleep:
                wake_up_process(root->fs_info->cleaner_kthread);
                mutex_unlock(&root->fs_info->transaction_kthread_mutex);

                if (!try_to_freeze()) {
                        set_current_state(TASK_INTERRUPTIBLE);
                        if (!kthread_should_stop() &&
                            !btrfs_transaction_blocked(root->fs_info))
                                schedule_timeout(delay);
                        __set_current_state(TASK_RUNNING);
                }
        } while (!kthread_should_stop());
        return 0;
}

/*
 * this will find the highest generation in the array of
 * root backups.  The index of the highest array is returned,
 * or -1 if we can't find anything.
 *
 * We check to make sure the array is valid by comparing the
 * generation of the latest  root in the array with the generation
 * in the super block.  If they don't match we pitch it.
 */
static int find_newest_super_backup(struct btrfs_fs_info *info, u64 newest_gen)
{
        u64 cur;
        int newest_index = -1;
        struct btrfs_root_backup *root_backup;
        int i;

        for (i = 0; i < BTRFS_NUM_BACKUP_ROOTS; i++) {
                root_backup = info->super_copy->super_roots + i;
                cur = btrfs_backup_tree_root_gen(root_backup);
                if (cur == newest_gen)
                        newest_index = i;
        }

        /* check to see if we actually wrapped around */
        if (newest_index == BTRFS_NUM_BACKUP_ROOTS - 1) {
                root_backup = info->super_copy->super_roots;
                cur = btrfs_backup_tree_root_gen(root_backup);
                if (cur == newest_gen)
                        newest_index = 0;
        }
        return newest_index;
}


/*
 * find the oldest backup so we know where to store new entries
 * in the backup array.  This will set the backup_root_index
 * field in the fs_info struct
 */
static void find_oldest_super_backup(struct btrfs_fs_info *info,
                                     u64 newest_gen)
{
        int newest_index = -1;

        newest_index = find_newest_super_backup(info, newest_gen);
        /* if there was garbage in there, just move along */
        if (newest_index == -1) {
                info->backup_root_index = 0;
        } else {
                info->backup_root_index = (newest_index + 1) % BTRFS_NUM_BACKUP_ROOTS;
        }
}

/*
 * copy all the root pointers into the super backup array.
 * this will bump the backup pointer by one when it is
 * done
 */
static void backup_super_roots(struct btrfs_fs_info *info)
{
        int next_backup;
        struct btrfs_root_backup *root_backup;
        int last_backup;

        next_backup = info->backup_root_index;
        last_backup = (next_backup + BTRFS_NUM_BACKUP_ROOTS - 1) %
                BTRFS_NUM_BACKUP_ROOTS;

        /*
         * just overwrite the last backup if we're at the same generation
         * this happens only at umount
         */
        root_backup = info->super_for_commit->super_roots + last_backup;
        if (btrfs_backup_tree_root_gen(root_backup) ==
            btrfs_header_generation(info->tree_root->node))
                next_backup = last_backup;

        root_backup = info->super_for_commit->super_roots + next_backup;

        /*
         * make sure all of our padding and empty slots get zero filled
         * regardless of which ones we use today
         */
        memset(root_backup, 0, sizeof(*root_backup));

        info->backup_root_index = (next_backup + 1) % BTRFS_NUM_BACKUP_ROOTS;

        btrfs_set_backup_tree_root(root_backup, info->tree_root->node->start);
        btrfs_set_backup_tree_root_gen(root_backup,
                               btrfs_header_generation(info->tree_root->node));

        btrfs_set_backup_tree_root_level(root_backup,
                               btrfs_header_level(info->tree_root->node));

        btrfs_set_backup_chunk_root(root_backup, info->chunk_root->node->start);
        btrfs_set_backup_chunk_root_gen(root_backup,
                               btrfs_header_generation(info->chunk_root->node));
        btrfs_set_backup_chunk_root_level(root_backup,
                               btrfs_header_level(info->chunk_root->node));

        btrfs_set_backup_extent_root(root_backup, info->extent_root->node->start);
        btrfs_set_backup_extent_root_gen(root_backup,
                               btrfs_header_generation(info->extent_root->node));
        btrfs_set_backup_extent_root_level(root_backup,
                               btrfs_header_level(info->extent_root->node));

        /*
         * we might commit during log recovery, which happens before we set
         * the fs_root.  Make sure it is valid before we fill it in.
         */
        if (info->fs_root && info->fs_root->node) {
                btrfs_set_backup_fs_root(root_backup,
                                         info->fs_root->node->start);
                btrfs_set_backup_fs_root_gen(root_backup,
                               btrfs_header_generation(info->fs_root->node));
                btrfs_set_backup_fs_root_level(root_backup,
                               btrfs_header_level(info->fs_root->node));
        }

        btrfs_set_backup_dev_root(root_backup, info->dev_root->node->start);
        btrfs_set_backup_dev_root_gen(root_backup,
                               btrfs_header_generation(info->dev_root->node));
        btrfs_set_backup_dev_root_level(root_backup,
                                       btrfs_header_level(info->dev_root->node));

        btrfs_set_backup_csum_root(root_backup, info->csum_root->node->start);
        btrfs_set_backup_csum_root_gen(root_backup,
                               btrfs_header_generation(info->csum_root->node));
        btrfs_set_backup_csum_root_level(root_backup,
                               btrfs_header_level(info->csum_root->node));

        btrfs_set_backup_total_bytes(root_backup,
                             btrfs_super_total_bytes(info->super_copy));
        btrfs_set_backup_bytes_used(root_backup,
                             btrfs_super_bytes_used(info->super_copy));
        btrfs_set_backup_num_devices(root_backup,
                             btrfs_super_num_devices(info->super_copy));

        /*
         * if we don't copy this out to the super_copy, it won't get remembered
         * for the next commit
         */
        memcpy(&info->super_copy->super_roots,
               &info->super_for_commit->super_roots,
               sizeof(*root_backup) * BTRFS_NUM_BACKUP_ROOTS);
}

/*
 * this copies info out of the root backup array and back into
 * the in-memory super block.  It is meant to help iterate through
 * the array, so you send it the number of backups you've already
 * tried and the last backup index you used.
 *
 * this returns -1 when it has tried all the backups
 */
static noinline int next_root_backup(struct btrfs_fs_info *info,
                                     struct btrfs_super_block *super,
                                     int *num_backups_tried, int *backup_index)
{
        struct btrfs_root_backup *root_backup;
        int newest = *backup_index;

        if (*num_backups_tried == 0) {
                u64 gen = btrfs_super_generation(super);

                newest = find_newest_super_backup(info, gen);
                if (newest == -1)
                        return -1;

                *backup_index = newest;
                *num_backups_tried = 1;
        } else if (*num_backups_tried == BTRFS_NUM_BACKUP_ROOTS) {
                /* we've tried all the backups, all done */
                return -1;
        } else {
                /* jump to the next oldest backup */
                newest = (*backup_index + BTRFS_NUM_BACKUP_ROOTS - 1) %
                        BTRFS_NUM_BACKUP_ROOTS;
                *backup_index = newest;
                *num_backups_tried += 1;
        }
        root_backup = super->super_roots + newest;

        btrfs_set_super_generation(super,
                                   btrfs_backup_tree_root_gen(root_backup));
        btrfs_set_super_root(super, btrfs_backup_tree_root(root_backup));
        btrfs_set_super_root_level(super,
                                   btrfs_backup_tree_root_level(root_backup));
        btrfs_set_super_bytes_used(super, btrfs_backup_bytes_used(root_backup));

        /*
         * fixme: the total bytes and num_devices need to match or we should
         * need a fsck
         */
        btrfs_set_super_total_bytes(super, btrfs_backup_total_bytes(root_backup));
        btrfs_set_super_num_devices(super, btrfs_backup_num_devices(root_backup));
        return 0;
}

/* helper to cleanup tree roots */
static void free_root_pointers(struct btrfs_fs_info *info, int chunk_root)
{
        free_extent_buffer(info->tree_root->node);
        free_extent_buffer(info->tree_root->commit_root);
        free_extent_buffer(info->dev_root->node);
        free_extent_buffer(info->dev_root->commit_root);
        free_extent_buffer(info->extent_root->node);
        free_extent_buffer(info->extent_root->commit_root);
        free_extent_buffer(info->csum_root->node);
        free_extent_buffer(info->csum_root->commit_root);

        info->tree_root->node = NULL;
        info->tree_root->commit_root = NULL;
        info->dev_root->node = NULL;
        info->dev_root->commit_root = NULL;
        info->extent_root->node = NULL;
        info->extent_root->commit_root = NULL;
        info->csum_root->node = NULL;
        info->csum_root->commit_root = NULL;

        if (chunk_root) {
                free_extent_buffer(info->chunk_root->node);
                free_extent_buffer(info->chunk_root->commit_root);
                info->chunk_root->node = NULL;
                info->chunk_root->commit_root = NULL;
        }
}


int 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_super_block *disk_super;
        struct btrfs_fs_info *fs_info = btrfs_sb(sb);
        struct btrfs_root *tree_root;
        struct btrfs_root *extent_root;
        struct btrfs_root *csum_root;
        struct btrfs_root *chunk_root;
        struct btrfs_root *dev_root;
        struct btrfs_root *log_tree_root;
        int ret;
        int err = -EINVAL;
        int num_backups_tried = 0;
        int backup_index = 0;

        tree_root = fs_info->tree_root = btrfs_alloc_root(fs_info);
        extent_root = fs_info->extent_root = btrfs_alloc_root(fs_info);
        csum_root = fs_info->csum_root = btrfs_alloc_root(fs_info);
        chunk_root = fs_info->chunk_root = btrfs_alloc_root(fs_info);
        dev_root = fs_info->dev_root = btrfs_alloc_root(fs_info);

        if (!tree_root || !extent_root || !csum_root ||
            !chunk_root || !dev_root) {
                err = -ENOMEM;
                goto fail;
        }

        ret = init_srcu_struct(&fs_info->subvol_srcu);
        if (ret) {
                err = ret;
                goto fail;
        }

        ret = setup_bdi(fs_info, &fs_info->bdi);
        if (ret) {
                err = ret;
                goto fail_srcu;
        }

        fs_info->btree_inode = new_inode(sb);
        if (!fs_info->btree_inode) {
                err = -ENOMEM;
                goto fail_bdi;
        }

        mapping_set_gfp_mask(fs_info->btree_inode->i_mapping, GFP_NOFS);

        INIT_RADIX_TREE(&fs_info->fs_roots_radix, GFP_ATOMIC);
        INIT_LIST_HEAD(&fs_info->trans_list);
        INIT_LIST_HEAD(&fs_info->dead_roots);
        INIT_LIST_HEAD(&fs_info->delayed_iputs);
        INIT_LIST_HEAD(&fs_info->hashers);
        INIT_LIST_HEAD(&fs_info->delalloc_inodes);
        INIT_LIST_HEAD(&fs_info->ordered_operations);
        INIT_LIST_HEAD(&fs_info->caching_block_groups);
        spin_lock_init(&fs_info->delalloc_lock);
        spin_lock_init(&fs_info->trans_lock);
        spin_lock_init(&fs_info->ref_cache_lock);
        spin_lock_init(&fs_info->fs_roots_radix_lock);
        spin_lock_init(&fs_info->delayed_iput_lock);
        spin_lock_init(&fs_info->defrag_inodes_lock);
        spin_lock_init(&fs_info->free_chunk_lock);
        mutex_init(&fs_info->reloc_mutex);

        init_completion(&fs_info->kobj_unregister);
        INIT_LIST_HEAD(&fs_info->dirty_cowonly_roots);
        INIT_LIST_HEAD(&fs_info->space_info);
        btrfs_mapping_init(&fs_info->mapping_tree);
        btrfs_init_block_rsv(&fs_info->global_block_rsv);
        btrfs_init_block_rsv(&fs_info->delalloc_block_rsv);
        btrfs_init_block_rsv(&fs_info->trans_block_rsv);
        btrfs_init_block_rsv(&fs_info->chunk_block_rsv);
        btrfs_init_block_rsv(&fs_info->empty_block_rsv);
        btrfs_init_block_rsv(&fs_info->delayed_block_rsv);
        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->defrag_running, 0);
        fs_info->sb = sb;
        fs_info->max_inline = 8192 * 1024;
        fs_info->metadata_ratio = 0;
        fs_info->defrag_inodes = RB_ROOT;
        fs_info->trans_no_join = 0;
        fs_info->free_chunk_space = 0;

        /* readahead state */
        INIT_RADIX_TREE(&fs_info->reada_tree, GFP_NOFS & ~__GFP_WAIT);
        spin_lock_init(&fs_info->reada_lock);

        fs_info->thread_pool_size = min_t(unsigned long,
                                          num_online_cpus() + 2, 8);

        INIT_LIST_HEAD(&fs_info->ordered_extents);
        spin_lock_init(&fs_info->ordered_extent_lock);
        fs_info->delayed_root = kmalloc(sizeof(struct btrfs_delayed_root),
                                        GFP_NOFS);
        if (!fs_info->delayed_root) {
                err = -ENOMEM;
                goto fail_iput;
        }
        btrfs_init_delayed_root(fs_info->delayed_root);

        mutex_init(&fs_info->scrub_lock);
        atomic_set(&fs_info->scrubs_running, 0);
        atomic_set(&fs_info->scrub_pause_req, 0);
        atomic_set(&fs_info->scrubs_paused, 0);
        atomic_set(&fs_info->scrub_cancel_req, 0);
        init_waitqueue_head(&fs_info->scrub_pause_wait);
        init_rwsem(&fs_info->scrub_super_lock);
        fs_info->scrub_workers_refcnt = 0;
#ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY
        fs_info->check_integrity_print_mask = 0;
#endif

        spin_lock_init(&fs_info->balance_lock);
        mutex_init(&fs_info->balance_mutex);
        atomic_set(&fs_info->balance_running, 0);
        atomic_set(&fs_info->balance_pause_req, 0);
        atomic_set(&fs_info->balance_cancel_req, 0);
        fs_info->balance_ctl = NULL;
        init_waitqueue_head(&fs_info->balance_wait_q);

        sb->s_blocksize = 4096;
        sb->s_blocksize_bits = blksize_bits(4096);
        sb->s_bdi = &fs_info->bdi;

        fs_info->btree_inode->i_ino = BTRFS_BTREE_INODE_OBJECTID;
        set_nlink(fs_info->btree_inode, 1);
        /*
         * 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;

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

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

        BTRFS_I(fs_info->btree_inode)->root = tree_root;
        memset(&BTRFS_I(fs_info->btree_inode)->location, 0,
               sizeof(struct btrfs_key));
        BTRFS_I(fs_info->btree_inode)->dummy_inode = 1;
        insert_inode_hash(fs_info->btree_inode);

        spin_lock_init(&fs_info->block_group_cache_lock);
        fs_info->block_group_cache_tree = RB_ROOT;

        extent_io_tree_init(&fs_info->freed_extents[0],
                             fs_info->btree_inode->i_mapping);
        extent_io_tree_init(&fs_info->freed_extents[1],
                             fs_info->btree_inode->i_mapping);
        fs_info->pinned_extents = &fs_info->freed_extents[0];
        fs_info->do_barriers = 1;


        mutex_init(&fs_info->ordered_operations_mutex);
        mutex_init(&fs_info->tree_log_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);
        init_rwsem(&fs_info->extent_commit_sem);
        init_rwsem(&fs_info->cleanup_work_sem);
        init_rwsem(&fs_info->subvol_sem);

        btrfs_init_free_cluster(&fs_info->meta_alloc_cluster);
        btrfs_init_free_cluster(&fs_info->data_alloc_cluster);

        init_waitqueue_head(&fs_info->transaction_throttle);
        init_waitqueue_head(&fs_info->transaction_wait);
        init_waitqueue_head(&fs_info->transaction_blocked_wait);
        init_waitqueue_head(&fs_info->async_submit_wait);

        __setup_root(4096, 4096, 4096, 4096, tree_root,
                     fs_info, BTRFS_ROOT_TREE_OBJECTID);

        bh = btrfs_read_dev_super(fs_devices->latest_bdev);
        if (!bh) {
                err = -EINVAL;
                goto fail_alloc;
        }

        memcpy(fs_info->super_copy, bh->b_data, sizeof(*fs_info->super_copy));
        memcpy(fs_info->super_for_commit, fs_info->super_copy,
               sizeof(*fs_info->super_for_commit));
        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_alloc;

        /* check FS state, whether FS is broken. */
        fs_info->fs_state |= btrfs_super_flags(disk_super);

        btrfs_check_super_valid(fs_info, sb->s_flags & MS_RDONLY);

        /*
         * run through our array of backup supers and setup
         * our ring pointer to the oldest one
         */
        generation = btrfs_super_generation(disk_super);
        find_oldest_super_backup(fs_info, generation);

        /*
         * In the long term, we'll store the compression type in the super
         * block, and it'll be used for per file compression control.
         */
        fs_info->compress_type = BTRFS_COMPRESS_ZLIB;

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

        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",
                       (unsigned long long)features);
                err = -EINVAL;
                goto fail_alloc;
        }

        features = btrfs_super_incompat_flags(disk_super);
        features |= BTRFS_FEATURE_INCOMPAT_MIXED_BACKREF;
        if (tree_root->fs_info->compress_type & BTRFS_COMPRESS_LZO)
                features |= BTRFS_FEATURE_INCOMPAT_COMPRESS_LZO;
        btrfs_set_super_incompat_flags(disk_super, features);

        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",
                       (unsigned long long)features);
                err = -EINVAL;
                goto fail_alloc;
        }

        btrfs_init_workers(&fs_info->generic_worker,
                           "genwork", 1, NULL);

        btrfs_init_workers(&fs_info->workers, "worker",
                           fs_info->thread_pool_size,
                           &fs_info->generic_worker);

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

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

        btrfs_init_workers(&fs_info->caching_workers, "cache",
                           2, &fs_info->generic_worker);

        /* 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,
                           &fs_info->generic_worker);
        btrfs_init_workers(&fs_info->endio_workers, "endio",
                           fs_info->thread_pool_size,
                           &fs_info->generic_worker);
        btrfs_init_workers(&fs_info->endio_meta_workers, "endio-meta",
                           fs_info->thread_pool_size,
                           &fs_info->generic_worker);
        btrfs_init_workers(&fs_info->endio_meta_write_workers,
                           "endio-meta-write", fs_info->thread_pool_size,
                           &fs_info->generic_worker);
        btrfs_init_workers(&fs_info->endio_write_workers, "endio-write",
                           fs_info->thread_pool_size,
                           &fs_info->generic_worker);
        btrfs_init_workers(&fs_info->endio_freespace_worker, "freespace-write",
                           1, &fs_info->generic_worker);
        btrfs_init_workers(&fs_info->delayed_workers, "delayed-meta",
                           fs_info->thread_pool_size,
                           &fs_info->generic_worker);
        btrfs_init_workers(&fs_info->readahead_workers, "readahead",
                           fs_info->thread_pool_size,
                           &fs_info->generic_worker);

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

        fs_info->endio_write_workers.idle_thresh = 2;
        fs_info->endio_meta_write_workers.idle_thresh = 2;
        fs_info->readahead_workers.idle_thresh = 2;

        /*
         * btrfs_start_workers can really only fail because of ENOMEM so just
         * return -ENOMEM if any of these fail.
         */
        ret = btrfs_start_workers(&fs_info->workers);
        ret |= btrfs_start_workers(&fs_info->generic_worker);
        ret |= btrfs_start_workers(&fs_info->submit_workers);
        ret |= btrfs_start_workers(&fs_info->delalloc_workers);
        ret |= btrfs_start_workers(&fs_info->fixup_workers);
        ret |= btrfs_start_workers(&fs_info->endio_workers);
        ret |= btrfs_start_workers(&fs_info->endio_meta_workers);
        ret |= btrfs_start_workers(&fs_info->endio_meta_write_workers);
        ret |= btrfs_start_workers(&fs_info->endio_write_workers);
        ret |= btrfs_start_workers(&fs_info->endio_freespace_worker);
        ret |= btrfs_start_workers(&fs_info->delayed_workers);
        ret |= btrfs_start_workers(&fs_info->caching_workers);
        ret |= btrfs_start_workers(&fs_info->readahead_workers);
        if (ret) {
                ret = -ENOMEM;
                goto fail_sb_buffer;
        }

        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(KERN_INFO "btrfs: valid FS not found on %s\n", sb->s_id);
                goto fail_sb_buffer;
        }

        if (sectorsize < PAGE_SIZE) {
                printk(KERN_WARNING "btrfs: Incompatible sector size "
                       "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(KERN_WARNING "btrfs: failed to read the system "
                       "array on %s\n", sb->s_id);
                goto fail_sb_buffer;
        }

        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);
        if (!test_bit(EXTENT_BUFFER_UPTODATE, &chunk_root->node->bflags)) {
                printk(KERN_WARNING "btrfs: failed to read chunk root on %s\n",
                       sb->s_id);
                goto fail_tree_roots;
        }
        btrfs_set_root_node(&chunk_root->root_item, chunk_root->node);
        chunk_root->commit_root = btrfs_root_node(chunk_root);

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

        ret = btrfs_read_chunk_tree(chunk_root);
        if (ret) {
                printk(KERN_WARNING "btrfs: failed to read chunk tree on %s\n",
                       sb->s_id);
                goto fail_tree_roots;
        }

        btrfs_close_extra_devices(fs_devices);

        if (!fs_devices->latest_bdev) {
                printk(KERN_CRIT "btrfs: failed to read devices on %s\n",
                       sb->s_id);
                goto fail_tree_roots;
        }

retry_root_backup:
        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 ||
            !test_bit(EXTENT_BUFFER_UPTODATE, &tree_root->node->bflags)) {
                printk(KERN_WARNING "btrfs: failed to read tree root on %s\n",
                       sb->s_id);

                goto recovery_tree_root;
        }

        btrfs_set_root_node(&tree_root->root_item, tree_root->node);
        tree_root->commit_root = btrfs_root_node(tree_root);

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

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

        ret = find_and_setup_root(tree_root, fs_info,
                                  BTRFS_CSUM_TREE_OBJECTID, csum_root);
        if (ret)
                goto recovery_tree_root;

        csum_root->track_dirty = 1;

        fs_info->generation = generation;
        fs_info->last_trans_committed = generation;

        ret = btrfs_init_space_info(fs_info);
        if (ret) {
                printk(KERN_ERR "Failed to initial space info: %d\n", ret);
                goto fail_block_groups;
        }

        ret = btrfs_read_block_groups(extent_root);
        if (ret) {
                printk(KERN_ERR "Failed to read block groups: %d\n", ret);
                goto fail_block_groups;
        }

        fs_info->cleaner_kthread = kthread_run(cleaner_kthread, tree_root,
                                               "btrfs-cleaner");
        if (IS_ERR(fs_info->cleaner_kthread))
                goto fail_block_groups;

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

        if (!btrfs_test_opt(tree_root, SSD) &&
            !btrfs_test_opt(tree_root, NOSSD) &&
            !fs_info->fs_devices->rotating) {
                printk(KERN_INFO "Btrfs detected SSD devices, enabling SSD "
                       "mode\n");
                btrfs_set_opt(fs_info->mount_opt, SSD);
        }

#ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY
        if (btrfs_test_opt(tree_root, CHECK_INTEGRITY)) {
                ret = btrfsic_mount(tree_root, fs_devices,
                                    btrfs_test_opt(tree_root,
                                        CHECK_INTEGRITY_INCLUDING_EXTENT_DATA) ?
                                    1 : 0,
                                    fs_info->check_integrity_print_mask);
                if (ret)
                        printk(KERN_WARNING "btrfs: failed to initialize"
                               " integrity check module %s\n", sb->s_id);
        }
#endif

        /* do not make disk changes in broken FS */
        if (btrfs_super_log_root(disk_super) != 0 &&
            !(fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR)) {
                u64 bytenr = btrfs_super_log_root(disk_super);

                if (fs_devices->rw_devices == 0) {
                        printk(KERN_WARNING "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 = btrfs_alloc_root(fs_info);
                if (!log_tree_root) {
                        err = -ENOMEM;
                        goto fail_trans_kthread;
                }

                __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);
                }
        }

        ret = btrfs_find_orphan_roots(tree_root);
        BUG_ON(ret);

        if (!(sb->s_flags & MS_RDONLY)) {
                ret = btrfs_cleanup_fs_roots(fs_info);
                BUG_ON(ret);

                ret = btrfs_recover_relocation(tree_root);
                if (ret < 0) {
                        printk(KERN_WARNING
                               "btrfs: failed to recover relocation\n");
                        err = -EINVAL;
                        goto fail_trans_kthread;
                }
        }

        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;
        if (IS_ERR(fs_info->fs_root)) {
                err = PTR_ERR(fs_info->fs_root);
                goto fail_trans_kthread;
        }

        if (!(sb->s_flags & MS_RDONLY)) {
                down_read(&fs_info->cleanup_work_sem);
                err = btrfs_orphan_cleanup(fs_info->fs_root);
                if (!err)
                        err = btrfs_orphan_cleanup(fs_info->tree_root);
                up_read(&fs_info->cleanup_work_sem);

                if (!err)
                        err = btrfs_recover_balance(fs_info->tree_root);

                if (err) {
                        close_ctree(tree_root);
                        return err;
                }
        }

        return 0;

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_block_groups:
        btrfs_free_block_groups(fs_info);

fail_tree_roots:
        free_root_pointers(fs_info, 1);

fail_sb_buffer:
        btrfs_stop_workers(&fs_info->generic_worker);
        btrfs_stop_workers(&fs_info->readahead_workers);
        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_meta_workers);
        btrfs_stop_workers(&fs_info->endio_meta_write_workers);
        btrfs_stop_workers(&fs_info->endio_write_workers);
        btrfs_stop_workers(&fs_info->endio_freespace_worker);
        btrfs_stop_workers(&fs_info->submit_workers);
        btrfs_stop_workers(&fs_info->delayed_workers);
        btrfs_stop_workers(&fs_info->caching_workers);
fail_alloc:
fail_iput:
        btrfs_mapping_tree_free(&fs_info->mapping_tree);

        invalidate_inode_pages2(fs_info->btree_inode->i_mapping);
        iput(fs_info->btree_inode);
fail_bdi:
        bdi_destroy(&fs_info->bdi);
fail_srcu:
        cleanup_srcu_struct(&fs_info->subvol_srcu);
fail:
        btrfs_close_devices(fs_info->fs_devices);
        return err;

recovery_tree_root:
        if (!btrfs_test_opt(tree_root, RECOVERY))
                goto fail_tree_roots;

        free_root_pointers(fs_info, 0);

        /* don't use the log in recovery mode, it won't be valid */
        btrfs_set_super_log_root(disk_super, 0);

        /* we can't trust the free space cache either */
        btrfs_set_opt(fs_info->mount_opt, CLEAR_CACHE);

        ret = next_root_backup(fs_info, fs_info->super_copy,
                               &num_backups_tried, &backup_index);
        if (ret == -1)
                goto fail_block_groups;
        goto retry_root_backup;
}

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

        if (uptodate) {
                set_buffer_uptodate(bh);
        } else {
                printk_ratelimited(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);
}

struct buffer_head *btrfs_read_dev_super(struct block_device *bdev)
{
        struct buffer_head *bh;
        struct buffer_head *latest = NULL;
        struct btrfs_super_block *super;
        int i;
        u64 transid = 0;
        u64 bytenr;

        /* we would like to check all the supers, but that would make
         * a btrfs mount succeed after a mkfs from a different FS.
         * So, we need to add a special mount option to scan for
         * later supers, using BTRFS_SUPER_MIRROR_MAX instead
         */
        for (i = 0; i < 1; i++) {
                bytenr = btrfs_sb_offset(i);
                if (bytenr + 4096 >= i_size_read(bdev->bd_inode))
                        break;
                bh = __bread(bdev, bytenr / 4096, 4096);
                if (!bh)
                        continue;

                super = (struct btrfs_super_block *)bh->b_data;
                if (btrfs_super_bytenr(super) != bytenr ||
                    strncmp((char *)(&super->magic), BTRFS_MAGIC,
                            sizeof(super->magic))) {
                        brelse(bh);
                        continue;
                }

                if (!latest || btrfs_super_generation(super) > transid) {
                        brelse(latest);
                        latest = bh;
                        transid = btrfs_super_generation(super);
                } else {
                        brelse(bh);
                }
        }
        return latest;
}

/*
 * this should be called twice, once with wait == 0 and
 * once with wait == 1.  When wait == 0 is done, all the buffer heads
 * we write are pinned.
 *
 * They are released when wait == 1 is done.
 * max_mirrors must be the same for both runs, and it indicates how
 * many supers on this one device should be written.
 *
 * max_mirrors == 0 means to write them all.
 */
static int write_dev_supers(struct btrfs_device *device,
                            struct btrfs_super_block *sb,
                            int do_barriers, int wait, int max_mirrors)
{
        struct buffer_head *bh;
        int i;
        int ret;
        int errors = 0;
        u32 crc;
        u64 bytenr;

        if (max_mirrors == 0)
                max_mirrors = BTRFS_SUPER_MIRROR_MAX;

        for (i = 0; i < max_mirrors; i++) {
                bytenr = btrfs_sb_offset(i);
                if (bytenr + BTRFS_SUPER_INFO_SIZE >= device->total_bytes)
                        break;

                if (wait) {
                        bh = __find_get_block(device->bdev, bytenr / 4096,
                                              BTRFS_SUPER_INFO_SIZE);
                        BUG_ON(!bh);
                        wait_on_buffer(bh);
                        if (!buffer_uptodate(bh))
                                errors++;

                        /* drop our reference */
                        brelse(bh);

                        /* drop the reference from the wait == 0 run */
                        brelse(bh);
                        continue;
                } else {
                        btrfs_set_super_bytenr(sb, bytenr);

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

                        /*
                         * one reference for us, and we leave it for the
                         * caller
                         */
                        bh = __getblk(device->bdev, bytenr / 4096,
                                      BTRFS_SUPER_INFO_SIZE);
                        memcpy(bh->b_data, sb, BTRFS_SUPER_INFO_SIZE);

                        /* one reference for submit_bh */
                        get_bh(bh);

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

                /*
                 * we fua the first super.  The others we allow
                 * to go down lazy.
                 */
                ret = btrfsic_submit_bh(WRITE_FUA, bh);
                if (ret)
                        errors++;
        }
        return errors < i ? 0 : -1;
}

/*
 * endio for the write_dev_flush, this will wake anyone waiting
 * for the barrier when it is done
 */
static void btrfs_end_empty_barrier(struct bio *bio, int err)
{
        if (err) {
                if (err == -EOPNOTSUPP)
                        set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
                clear_bit(BIO_UPTODATE, &bio->bi_flags);
        }
        if (bio->bi_private)
                complete(bio->bi_private);
        bio_put(bio);
}

/*
 * trigger flushes for one the devices.  If you pass wait == 0, the flushes are
 * sent down.  With wait == 1, it waits for the previous flush.
 *
 * any device where the flush fails with eopnotsupp are flagged as not-barrier
 * capable
 */
static int write_dev_flush(struct btrfs_device *device, int wait)
{
        struct bio *bio;
        int ret = 0;

        if (device->nobarriers)
                return 0;

        if (wait) {
                bio = device->flush_bio;
                if (!bio)
                        return 0;

                wait_for_completion(&device->flush_wait);

                if (bio_flagged(bio, BIO_EOPNOTSUPP)) {
                        printk("btrfs: disabling barriers on dev %s\n",
                               device->name);
                        device->nobarriers = 1;
                }
                if (!bio_flagged(bio, BIO_UPTODATE)) {
                        ret = -EIO;
                }

                /* drop the reference from the wait == 0 run */
                bio_put(bio);
                device->flush_bio = NULL;

                return ret;
        }

        /*
         * one reference for us, and we leave it for the
         * caller
         */
        device->flush_bio = NULL;;
        bio = bio_alloc(GFP_NOFS, 0);
        if (!bio)
                return -ENOMEM;

        bio->bi_end_io = btrfs_end_empty_barrier;
        bio->bi_bdev = device->bdev;
        init_completion(&device->flush_wait);
        bio->bi_private = &device->flush_wait;
        device->flush_bio = bio;

        bio_get(bio);
        btrfsic_submit_bio(WRITE_FLUSH, bio);

        return 0;
}

/*
 * send an empty flush down to each device in parallel,
 * then wait for them
 */
static int barrier_all_devices(struct btrfs_fs_info *info)
{
        struct list_head *head;
        struct btrfs_device *dev;
        int errors = 0;
        int ret;

        /* send down all the barriers */
        head = &info->fs_devices->devices;
        list_for_each_entry_rcu(dev, head, dev_list) {
                if (!dev->bdev) {
                        errors++;
                        continue;
                }
                if (!dev->in_fs_metadata || !dev->writeable)
                        continue;

                ret = write_dev_flush(dev, 0);
                if (ret)
                        errors++;
        }

        /* wait for all the barriers */
        list_for_each_entry_rcu(dev, head, dev_list) {
                if (!dev->bdev) {
                        errors++;
                        continue;
                }
                if (!dev->in_fs_metadata || !dev->writeable)
                        continue;

                ret = write_dev_flush(dev, 1);
                if (ret)
                        errors++;
        }
        if (errors)
                return -EIO;
        return 0;
}

int write_all_supers(struct btrfs_root *root, int max_mirrors)
{
        struct list_head *head;
        struct btrfs_device *dev;
        struct btrfs_super_block *sb;
        struct btrfs_dev_item *dev_item;
        int ret;
        int do_barriers;
        int max_errors;
        int total_errors = 0;
        u64 flags;

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

        sb = root->fs_info->super_for_commit;
        dev_item = &sb->dev_item;

        mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
        head = &root->fs_info->fs_devices->devices;

        if (do_barriers)
                barrier_all_devices(root->fs_info);

        list_for_each_entry_rcu(dev, head, 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);

                ret = write_dev_supers(dev, sb, do_barriers, 0, max_mirrors);
                if (ret)
                        total_errors++;
        }
        if (total_errors > max_errors) {
                printk(KERN_ERR "btrfs: %d errors while writing supers\n",
                       total_errors);
                BUG();
        }

        total_errors = 0;
        list_for_each_entry_rcu(dev, head, dev_list) {
                if (!dev->bdev)
                        continue;
                if (!dev->in_fs_metadata || !dev->writeable)
                        continue;

                ret = write_dev_supers(dev, sb, do_barriers, 1, max_mirrors);
                if (ret)
                        total_errors++;
        }
        mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
        if (total_errors > max_errors) {
                printk(KERN_ERR "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 max_mirrors)
{
        int ret;

        ret = write_all_supers(root, max_mirrors);
        return ret;
}

int btrfs_free_fs_root(struct btrfs_fs_info *fs_info, struct btrfs_root *root)
{
        spin_lock(&fs_info->fs_roots_radix_lock);
        radix_tree_delete(&fs_info->fs_roots_radix,
                          (unsigned long)root->root_key.objectid);
        spin_unlock(&fs_info->fs_roots_radix_lock);

        if (btrfs_root_refs(&root->root_item) == 0)
                synchronize_srcu(&fs_info->subvol_srcu);

        __btrfs_remove_free_space_cache(root->free_ino_pinned);
        __btrfs_remove_free_space_cache(root->free_ino_ctl);
        free_fs_root(root);
        return 0;
}

static void free_fs_root(struct btrfs_root *root)
{
        iput(root->cache_inode);
        WARN_ON(!RB_EMPTY_ROOT(&root->inode_tree));
        if (root->anon_dev)
                free_anon_bdev(root->anon_dev);
        free_extent_buffer(root->node);
        free_extent_buffer(root->commit_root);
        kfree(root->free_ino_ctl);
        kfree(root->free_ino_pinned);
        kfree(root->name);
        kfree(root);
}

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

        while (!list_empty(&fs_info->dead_roots)) {
                gang[0] = list_entry(fs_info->dead_roots.next,
                                     struct btrfs_root, root_list);
                list_del(&gang[0]->root_list);

                if (gang[0]->in_radix) {
                        btrfs_free_fs_root(fs_info, gang[0]);
                } else {
                        free_extent_buffer(gang[0]->node);
                        free_extent_buffer(gang[0]->commit_root);
                        kfree(gang[0]);
                }
        }

        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;

                root_objectid = gang[ret - 1]->root_key.objectid + 1;
                for (i = 0; i < ret; i++) {
                        int err;

                        root_objectid = gang[i]->root_key.objectid;
                        err = btrfs_orphan_cleanup(gang[i]);
                        if (err)
                                return err;
                }
                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_run_delayed_iputs(root);
        btrfs_clean_old_snapshots(root);
        mutex_unlock(&root->fs_info->cleaner_mutex);

        /* wait until ongoing cleanup work done */
        down_write(&root->fs_info->cleanup_work_sem);
        up_write(&root->fs_info->cleanup_work_sem);

        trans = btrfs_join_transaction(root);
        if (IS_ERR(trans))
                return PTR_ERR(trans);
        ret = btrfs_commit_transaction(trans, root);
        BUG_ON(ret);
        /* run commit again to drop the original snapshot */
        trans = btrfs_join_transaction(root);
        if (IS_ERR(trans))
                return PTR_ERR(trans);
        btrfs_commit_transaction(trans, root);
        ret = btrfs_write_and_wait_transaction(NULL, root);
        BUG_ON(ret);

        ret = write_ctree_super(NULL, root, 0);
        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();

        /* pause restriper - we want to resume on mount */
        btrfs_pause_balance(root->fs_info);

        btrfs_scrub_cancel(root);

        /* wait for any defraggers to finish */
        wait_event(fs_info->transaction_wait,
                   (atomic_read(&fs_info->defrag_running) == 0));

        /* clear out the rbtree of defraggable inodes */
        btrfs_run_defrag_inodes(fs_info);

        /*
         * Here come 2 situations when btrfs is broken to flip readonly:
         *
         * 1. when btrfs flips readonly somewhere else before
         * btrfs_commit_super, sb->s_flags has MS_RDONLY flag,
         * and btrfs will skip to write sb directly to keep
         * ERROR state on disk.
         *
         * 2. when btrfs flips readonly just in btrfs_commit_super,
         * and in such case, btrfs cannot write sb via btrfs_commit_super,
         * and since fs_state has been set BTRFS_SUPER_FLAG_ERROR flag,
         * btrfs will cleanup all FS resources first and write sb then.
         */
        if (!(fs_info->sb->s_flags & MS_RDONLY)) {
                ret = btrfs_commit_super(root);
                if (ret)
                        printk(KERN_ERR "btrfs: commit super ret %d\n", ret);
        }

        if (fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) {
                ret = btrfs_error_commit_super(root);
                if (ret)
                        printk(KERN_ERR "btrfs: commit super ret %d\n", ret);
        }

        btrfs_put_block_group_cache(fs_info);

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

        fs_info->closing = 2;
        smp_mb();

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

        free_extent_buffer(fs_info->extent_root->node);
        free_extent_buffer(fs_info->extent_root->commit_root);
        free_extent_buffer(fs_info->tree_root->node);
        free_extent_buffer(fs_info->tree_root->commit_root);
        free_extent_buffer(fs_info->chunk_root->node);
        free_extent_buffer(fs_info->chunk_root->commit_root);
        free_extent_buffer(fs_info->dev_root->node);
        free_extent_buffer(fs_info->dev_root->commit_root);
        free_extent_buffer(fs_info->csum_root->node);
        free_extent_buffer(fs_info->csum_root->commit_root);

        btrfs_free_block_groups(fs_info);

        del_fs_roots(fs_info);

        iput(fs_info->btree_inode);

        btrfs_stop_workers(&fs_info->generic_worker);
        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_meta_workers);
        btrfs_stop_workers(&fs_info->endio_meta_write_workers);
        btrfs_stop_workers(&fs_info->endio_write_workers);
        btrfs_stop_workers(&fs_info->endio_freespace_worker);
        btrfs_stop_workers(&fs_info->submit_workers);
        btrfs_stop_workers(&fs_info->delayed_workers);
        btrfs_stop_workers(&fs_info->caching_workers);
        btrfs_stop_workers(&fs_info->readahead_workers);

#ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY
        if (btrfs_test_opt(root, CHECK_INTEGRITY))
                btrfsic_unmount(root, fs_info->fs_devices);
#endif

        btrfs_close_devices(fs_info->fs_devices);
        btrfs_mapping_tree_free(&fs_info->mapping_tree);

        bdi_destroy(&fs_info->bdi);
        cleanup_srcu_struct(&fs_info->subvol_srcu);

        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,
                                     NULL);
        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;
        int was_dirty;

        btrfs_assert_tree_locked(buf);
        if (transid != root->fs_info->generation) {
                printk(KERN_CRIT "btrfs transid mismatch buffer %llu, "
                       "found %llu running %llu\n",
                        (unsigned long long)buf->start,
                        (unsigned long long)transid,
                        (unsigned long long)root->fs_info->generation);
                WARN_ON(1);
        }
        was_dirty = set_extent_buffer_dirty(&BTRFS_I(btree_inode)->io_tree,
                                            buf);
        if (!was_dirty) {
                spin_lock(&root->fs_info->delalloc_lock);
                root->fs_info->dirty_metadata_bytes += buf->len;
                spin_unlock(&root->fs_info->delalloc_lock);
        }
}

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
         */
        u64 num_dirty;
        unsigned long thresh = 32 * 1024 * 1024;

        if (current->flags & PF_MEMALLOC)
                return;

        btrfs_balance_delayed_items(root);

        num_dirty = root->fs_info->dirty_metadata_bytes;

        if (num_dirty > thresh) {
                balance_dirty_pages_ratelimited_nr(
                                   root->fs_info->btree_inode->i_mapping, 1);
        }
        return;
}

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
         */
        u64 num_dirty;
        unsigned long thresh = 32 * 1024 * 1024;

        if (current->flags & PF_MEMALLOC)
                return;

        num_dirty = root->fs_info->dirty_metadata_bytes;

        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)
                set_bit(EXTENT_BUFFER_UPTODATE, &buf->bflags);
        return ret;
}

static int btree_lock_page_hook(struct page *page, void *data,
                                void (*flush_fn)(void *))
{
        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);
        if (!eb)
                goto out;

        if (!btrfs_try_tree_write_lock(eb)) {
                flush_fn(data);
                btrfs_tree_lock(eb);
        }
        btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);

        if (test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) {
                spin_lock(&root->fs_info->delalloc_lock);
                if (root->fs_info->dirty_metadata_bytes >= eb->len)
                        root->fs_info->dirty_metadata_bytes -= eb->len;
                else
                        WARN_ON(1);
                spin_unlock(&root->fs_info->delalloc_lock);
        }

        btrfs_tree_unlock(eb);
        free_extent_buffer(eb);
out:
        if (!trylock_page(page)) {
                flush_fn(data);
                lock_page(page);
        }
        return 0;
}

static void btrfs_check_super_valid(struct btrfs_fs_info *fs_info,
                              int read_only)
{
        if (read_only)
                return;

        if (fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR)
                printk(KERN_WARNING "warning: mount fs with errors, "
                       "running btrfsck is recommended\n");
}

int btrfs_error_commit_super(struct btrfs_root *root)
{
        int ret;

        mutex_lock(&root->fs_info->cleaner_mutex);
        btrfs_run_delayed_iputs(root);
        mutex_unlock(&root->fs_info->cleaner_mutex);

        down_write(&root->fs_info->cleanup_work_sem);
        up_write(&root->fs_info->cleanup_work_sem);

        /* cleanup FS via transaction */
        btrfs_cleanup_transaction(root);

        ret = write_ctree_super(NULL, root, 0);

        return ret;
}

static int btrfs_destroy_ordered_operations(struct btrfs_root *root)
{
        struct btrfs_inode *btrfs_inode;
        struct list_head splice;

        INIT_LIST_HEAD(&splice);

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

        list_splice_init(&root->fs_info->ordered_operations, &splice);
        while (!list_empty(&splice)) {
                btrfs_inode = list_entry(splice.next, struct btrfs_inode,
                                         ordered_operations);

                list_del_init(&btrfs_inode->ordered_operations);

                btrfs_invalidate_inodes(btrfs_inode->root);
        }

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

        return 0;
}

static int btrfs_destroy_ordered_extents(struct btrfs_root *root)
{
        struct list_head splice;
        struct btrfs_ordered_extent *ordered;
        struct inode *inode;

        INIT_LIST_HEAD(&splice);

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

        list_splice_init(&root->fs_info->ordered_extents, &splice);
        while (!list_empty(&splice)) {
                ordered = list_entry(splice.next, struct btrfs_ordered_extent,
                                     root_extent_list);

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

                /* the inode may be getting freed (in sys_unlink path). */
                inode = igrab(ordered->inode);

                spin_unlock(&root->fs_info->ordered_extent_lock);
                if (inode)
                        iput(inode);

                atomic_set(&ordered->refs, 1);
                btrfs_put_ordered_extent(ordered);

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

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

        return 0;
}

static int btrfs_destroy_delayed_refs(struct btrfs_transaction *trans,
                                      struct btrfs_root *root)
{
        struct rb_node *node;
        struct btrfs_delayed_ref_root *delayed_refs;
        struct btrfs_delayed_ref_node *ref;
        int ret = 0;

        delayed_refs = &trans->delayed_refs;

        spin_lock(&delayed_refs->lock);
        if (delayed_refs->num_entries == 0) {
                spin_unlock(&delayed_refs->lock);
                printk(KERN_INFO "delayed_refs has NO entry\n");
                return ret;
        }

        node = rb_first(&delayed_refs->root);
        while (node) {
                ref = rb_entry(node, struct btrfs_delayed_ref_node, rb_node);
                node = rb_next(node);

                ref->in_tree = 0;
                rb_erase(&ref->rb_node, &delayed_refs->root);
                delayed_refs->num_entries--;

                atomic_set(&ref->refs, 1);
                if (btrfs_delayed_ref_is_head(ref)) {
                        struct btrfs_delayed_ref_head *head;

                        head = btrfs_delayed_node_to_head(ref);
                        mutex_lock(&head->mutex);
                        kfree(head->extent_op);
                        delayed_refs->num_heads--;
                        if (list_empty(&head->cluster))
                                delayed_refs->num_heads_ready--;
                        list_del_init(&head->cluster);
                        mutex_unlock(&head->mutex);
                }

                spin_unlock(&delayed_refs->lock);
                btrfs_put_delayed_ref(ref);

                cond_resched();
                spin_lock(&delayed_refs->lock);
        }

        spin_unlock(&delayed_refs->lock);

        return ret;
}

static int btrfs_destroy_pending_snapshots(struct btrfs_transaction *t)
{
        struct btrfs_pending_snapshot *snapshot;
        struct list_head splice;

        INIT_LIST_HEAD(&splice);

        list_splice_init(&t->pending_snapshots, &splice);

        while (!list_empty(&splice)) {
                snapshot = list_entry(splice.next,
                                      struct btrfs_pending_snapshot,
                                      list);

                list_del_init(&snapshot->list);

                kfree(snapshot);
        }

        return 0;
}

static int btrfs_destroy_delalloc_inodes(struct btrfs_root *root)
{
        struct btrfs_inode *btrfs_inode;
        struct list_head splice;

        INIT_LIST_HEAD(&splice);

        spin_lock(&root->fs_info->delalloc_lock);
        list_splice_init(&root->fs_info->delalloc_inodes, &splice);

        while (!list_empty(&splice)) {
                btrfs_inode = list_entry(splice.next, struct btrfs_inode,
                                    delalloc_inodes);

                list_del_init(&btrfs_inode->delalloc_inodes);

                btrfs_invalidate_inodes(btrfs_inode->root);
        }

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

        return 0;
}

static int btrfs_destroy_marked_extents(struct btrfs_root *root,
                                        struct extent_io_tree *dirty_pages,
                                        int mark)
{
        int ret;
        struct page *page;
        struct inode *btree_inode = root->fs_info->btree_inode;
        struct extent_buffer *eb;
        u64 start = 0;
        u64 end;
        u64 offset;
        unsigned long index;

        while (1) {
                ret = find_first_extent_bit(dirty_pages, start, &start, &end,
                                            mark);
                if (ret)
                        break;

                clear_extent_bits(dirty_pages, start, end, mark, GFP_NOFS);
                while (start <= end) {
                        index = start >> PAGE_CACHE_SHIFT;
                        start = (u64)(index + 1) << PAGE_CACHE_SHIFT;
                        page = find_get_page(btree_inode->i_mapping, index);
                        if (!page)
                                continue;
                        offset = page_offset(page);

                        spin_lock(&dirty_pages->buffer_lock);
                        eb = radix_tree_lookup(
                             &(&BTRFS_I(page->mapping->host)->io_tree)->buffer,
                                               offset >> PAGE_CACHE_SHIFT);
                        spin_unlock(&dirty_pages->buffer_lock);
                        if (eb) {
                                ret = test_and_clear_bit(EXTENT_BUFFER_DIRTY,
                                                         &eb->bflags);
                                atomic_set(&eb->refs, 1);
                        }
                        if (PageWriteback(page))
                                end_page_writeback(page);

                        lock_page(page);
                        if (PageDirty(page)) {
                                clear_page_dirty_for_io(page);
                                spin_lock_irq(&page->mapping->tree_lock);
                                radix_tree_tag_clear(&page->mapping->page_tree,
                                                        page_index(page),
                                                        PAGECACHE_TAG_DIRTY);
                                spin_unlock_irq(&page->mapping->tree_lock);
                        }

                        page->mapping->a_ops->invalidatepage(page, 0);
                        unlock_page(page);
                }
        }

        return ret;
}

static int btrfs_destroy_pinned_extent(struct btrfs_root *root,
                                       struct extent_io_tree *pinned_extents)
{
        struct extent_io_tree *unpin;
        u64 start;
        u64 end;
        int ret;

        unpin = pinned_extents;
        while (1) {
                ret = find_first_extent_bit(unpin, 0, &start, &end,
                                            EXTENT_DIRTY);
                if (ret)
                        break;

                /* opt_discard */
                if (btrfs_test_opt(root, DISCARD))
                        ret = btrfs_error_discard_extent(root, start,
                                                         end + 1 - start,
                                                         NULL);

                clear_extent_dirty(unpin, start, end, GFP_NOFS);
                btrfs_error_unpin_extent_range(root, start, end);
                cond_resched();
        }

        return 0;
}

static int btrfs_cleanup_transaction(struct btrfs_root *root)
{
        struct btrfs_transaction *t;
        LIST_HEAD(list);

        WARN_ON(1);

        mutex_lock(&root->fs_info->transaction_kthread_mutex);

        spin_lock(&root->fs_info->trans_lock);
        list_splice_init(&root->fs_info->trans_list, &list);
        root->fs_info->trans_no_join = 1;
        spin_unlock(&root->fs_info->trans_lock);

        while (!list_empty(&list)) {
                t = list_entry(list.next, struct btrfs_transaction, list);
                if (!t)
                        break;

                btrfs_destroy_ordered_operations(root);

                btrfs_destroy_ordered_extents(root);

                btrfs_destroy_delayed_refs(t, root);

                btrfs_block_rsv_release(root,
                                        &root->fs_info->trans_block_rsv,
                                        t->dirty_pages.dirty_bytes);

                /* FIXME: cleanup wait for commit */
                t->in_commit = 1;
                t->blocked = 1;
                if (waitqueue_active(&root->fs_info->transaction_blocked_wait))
                        wake_up(&root->fs_info->transaction_blocked_wait);

                t->blocked = 0;
                if (waitqueue_active(&root->fs_info->transaction_wait))
                        wake_up(&root->fs_info->transaction_wait);

                t->commit_done = 1;
                if (waitqueue_active(&t->commit_wait))
                        wake_up(&t->commit_wait);

                btrfs_destroy_pending_snapshots(t);

                btrfs_destroy_delalloc_inodes(root);

                spin_lock(&root->fs_info->trans_lock);
                root->fs_info->running_transaction = NULL;
                spin_unlock(&root->fs_info->trans_lock);

                btrfs_destroy_marked_extents(root, &t->dirty_pages,
                                             EXTENT_DIRTY);

                btrfs_destroy_pinned_extent(root,
                                            root->fs_info->pinned_extents);

                atomic_set(&t->use_count, 0);
                list_del_init(&t->list);
                memset(t, 0, sizeof(*t));
                kmem_cache_free(btrfs_transaction_cachep, t);
        }

        spin_lock(&root->fs_info->trans_lock);
        root->fs_info->trans_no_join = 0;
        spin_unlock(&root->fs_info->trans_lock);
        mutex_unlock(&root->fs_info->transaction_kthread_mutex);

        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,
        .readpage_io_failed_hook = btree_io_failed_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,
};