Btrfs: Replace the big fs_mutex with a collection of other locks

[linux-2.6-block.git] / fs / btrfs / volumes.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/sched.h>
#include <linux/bio.h>
#include <linux/buffer_head.h>
#include <linux/blkdev.h>
#include <linux/random.h>
#include <asm/div64.h>
#include "ctree.h"
#include "extent_map.h"
#include "disk-io.h"
#include "transaction.h"
#include "print-tree.h"
#include "volumes.h"
#include "async-thread.h"

struct map_lookup {
        u64 type;
        int io_align;
        int io_width;
        int stripe_len;
        int sector_size;
        int num_stripes;
        int sub_stripes;
        struct btrfs_bio_stripe stripes[];
};

#define map_lookup_size(n) (sizeof(struct map_lookup) + \
                            (sizeof(struct btrfs_bio_stripe) * (n)))

static DEFINE_MUTEX(uuid_mutex);
static LIST_HEAD(fs_uuids);

void btrfs_lock_volumes(void)
{
        mutex_lock(&uuid_mutex);
}

void btrfs_unlock_volumes(void)
{
        mutex_unlock(&uuid_mutex);
}

int btrfs_cleanup_fs_uuids(void)
{
        struct btrfs_fs_devices *fs_devices;
        struct list_head *uuid_cur;
        struct list_head *devices_cur;
        struct btrfs_device *dev;

        list_for_each(uuid_cur, &fs_uuids) {
                fs_devices = list_entry(uuid_cur, struct btrfs_fs_devices,
                                        list);
                while(!list_empty(&fs_devices->devices)) {
                        devices_cur = fs_devices->devices.next;
                        dev = list_entry(devices_cur, struct btrfs_device,
                                         dev_list);
                        if (dev->bdev) {
                                close_bdev_excl(dev->bdev);
                                fs_devices->open_devices--;
                        }
                        list_del(&dev->dev_list);
                        kfree(dev->name);
                        kfree(dev);
                }
        }
        return 0;
}

static struct btrfs_device *__find_device(struct list_head *head, u64 devid,
                                          u8 *uuid)
{
        struct btrfs_device *dev;
        struct list_head *cur;

        list_for_each(cur, head) {
                dev = list_entry(cur, struct btrfs_device, dev_list);
                if (dev->devid == devid &&
                    (!uuid || !memcmp(dev->uuid, uuid, BTRFS_UUID_SIZE))) {
                        return dev;
                }
        }
        return NULL;
}

static struct btrfs_fs_devices *find_fsid(u8 *fsid)
{
        struct list_head *cur;
        struct btrfs_fs_devices *fs_devices;

        list_for_each(cur, &fs_uuids) {
                fs_devices = list_entry(cur, struct btrfs_fs_devices, list);
                if (memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE) == 0)
                        return fs_devices;
        }
        return NULL;
}

/*
 * we try to collect pending bios for a device so we don't get a large
 * number of procs sending bios down to the same device.  This greatly
 * improves the schedulers ability to collect and merge the bios.
 *
 * But, it also turns into a long list of bios to process and that is sure
 * to eventually make the worker thread block.  The solution here is to
 * make some progress and then put this work struct back at the end of
 * the list if the block device is congested.  This way, multiple devices
 * can make progress from a single worker thread.
 */
int run_scheduled_bios(struct btrfs_device *device)
{
        struct bio *pending;
        struct backing_dev_info *bdi;
        struct bio *tail;
        struct bio *cur;
        int again = 0;
        unsigned long num_run = 0;

        bdi = device->bdev->bd_inode->i_mapping->backing_dev_info;
loop:
        spin_lock(&device->io_lock);

        /* take all the bios off the list at once and process them
         * later on (without the lock held).  But, remember the
         * tail and other pointers so the bios can be properly reinserted
         * into the list if we hit congestion
         */
        pending = device->pending_bios;
        tail = device->pending_bio_tail;
        WARN_ON(pending && !tail);
        device->pending_bios = NULL;
        device->pending_bio_tail = NULL;

        /*
         * if pending was null this time around, no bios need processing
         * at all and we can stop.  Otherwise it'll loop back up again
         * and do an additional check so no bios are missed.
         *
         * device->running_pending is used to synchronize with the
         * schedule_bio code.
         */
        if (pending) {
                again = 1;
                device->running_pending = 1;
        } else {
                again = 0;
                device->running_pending = 0;
        }
        spin_unlock(&device->io_lock);

        while(pending) {
                cur = pending;
                pending = pending->bi_next;
                cur->bi_next = NULL;
                atomic_dec(&device->dev_root->fs_info->nr_async_submits);
                submit_bio(cur->bi_rw, cur);
                num_run++;

                /*
                 * we made progress, there is more work to do and the bdi
                 * is now congested.  Back off and let other work structs
                 * run instead
                 */
                if (pending && num_run && bdi_write_congested(bdi)) {
                        struct bio *old_head;

                        spin_lock(&device->io_lock);
                        old_head = device->pending_bios;
                        device->pending_bios = pending;
                        if (device->pending_bio_tail)
                                tail->bi_next = old_head;
                        else
                                device->pending_bio_tail = tail;

                        spin_unlock(&device->io_lock);
                        btrfs_requeue_work(&device->work);
                        goto done;
                }
        }
        if (again)
                goto loop;
done:
        return 0;
}

void pending_bios_fn(struct btrfs_work *work)
{
        struct btrfs_device *device;

        device = container_of(work, struct btrfs_device, work);
        run_scheduled_bios(device);
}

static int device_list_add(const char *path,
                           struct btrfs_super_block *disk_super,
                           u64 devid, struct btrfs_fs_devices **fs_devices_ret)
{
        struct btrfs_device *device;
        struct btrfs_fs_devices *fs_devices;
        u64 found_transid = btrfs_super_generation(disk_super);

        fs_devices = find_fsid(disk_super->fsid);
        if (!fs_devices) {
                fs_devices = kzalloc(sizeof(*fs_devices), GFP_NOFS);
                if (!fs_devices)
                        return -ENOMEM;
                INIT_LIST_HEAD(&fs_devices->devices);
                INIT_LIST_HEAD(&fs_devices->alloc_list);
                list_add(&fs_devices->list, &fs_uuids);
                memcpy(fs_devices->fsid, disk_super->fsid, BTRFS_FSID_SIZE);
                fs_devices->latest_devid = devid;
                fs_devices->latest_trans = found_transid;
                device = NULL;
        } else {
                device = __find_device(&fs_devices->devices, devid,
                                       disk_super->dev_item.uuid);
        }
        if (!device) {
                device = kzalloc(sizeof(*device), GFP_NOFS);
                if (!device) {
                        /* we can safely leave the fs_devices entry around */
                        return -ENOMEM;
                }
                device->devid = devid;
                device->work.func = pending_bios_fn;
                memcpy(device->uuid, disk_super->dev_item.uuid,
                       BTRFS_UUID_SIZE);
                device->barriers = 1;
                spin_lock_init(&device->io_lock);
                device->name = kstrdup(path, GFP_NOFS);
                if (!device->name) {
                        kfree(device);
                        return -ENOMEM;
                }
                list_add(&device->dev_list, &fs_devices->devices);
                list_add(&device->dev_alloc_list, &fs_devices->alloc_list);
                fs_devices->num_devices++;
        }

        if (found_transid > fs_devices->latest_trans) {
                fs_devices->latest_devid = devid;
                fs_devices->latest_trans = found_transid;
        }
        *fs_devices_ret = fs_devices;
        return 0;
}

int btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices)
{
        struct list_head *head = &fs_devices->devices;
        struct list_head *cur;
        struct btrfs_device *device;

        mutex_lock(&uuid_mutex);
again:
        list_for_each(cur, head) {
                device = list_entry(cur, struct btrfs_device, dev_list);
                if (!device->in_fs_metadata) {
                        if (device->bdev) {
                                close_bdev_excl(device->bdev);
                                fs_devices->open_devices--;
                        }
                        list_del(&device->dev_list);
                        list_del(&device->dev_alloc_list);
                        fs_devices->num_devices--;
                        kfree(device->name);
                        kfree(device);
                        goto again;
                }
        }
        mutex_unlock(&uuid_mutex);
        return 0;
}

int btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
{
        struct list_head *head = &fs_devices->devices;
        struct list_head *cur;
        struct btrfs_device *device;

        mutex_lock(&uuid_mutex);
        list_for_each(cur, head) {
                device = list_entry(cur, struct btrfs_device, dev_list);
                if (device->bdev) {
                        close_bdev_excl(device->bdev);
                        fs_devices->open_devices--;
                }
                device->bdev = NULL;
                device->in_fs_metadata = 0;
        }
        fs_devices->mounted = 0;
        mutex_unlock(&uuid_mutex);
        return 0;
}

int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
                       int flags, void *holder)
{
        struct block_device *bdev;
        struct list_head *head = &fs_devices->devices;
        struct list_head *cur;
        struct btrfs_device *device;
        struct block_device *latest_bdev = NULL;
        struct buffer_head *bh;
        struct btrfs_super_block *disk_super;
        u64 latest_devid = 0;
        u64 latest_transid = 0;
        u64 transid;
        u64 devid;
        int ret = 0;

        mutex_lock(&uuid_mutex);
        if (fs_devices->mounted)
                goto out;

        list_for_each(cur, head) {
                device = list_entry(cur, struct btrfs_device, dev_list);
                if (device->bdev)
                        continue;

                if (!device->name)
                        continue;

                bdev = open_bdev_excl(device->name, flags, holder);

                if (IS_ERR(bdev)) {
                        printk("open %s failed\n", device->name);
                        goto error;
                }
                set_blocksize(bdev, 4096);

                bh = __bread(bdev, BTRFS_SUPER_INFO_OFFSET / 4096, 4096);
                if (!bh)
                        goto error_close;

                disk_super = (struct btrfs_super_block *)bh->b_data;
                if (strncmp((char *)(&disk_super->magic), BTRFS_MAGIC,
                    sizeof(disk_super->magic)))
                        goto error_brelse;

                devid = le64_to_cpu(disk_super->dev_item.devid);
                if (devid != device->devid)
                        goto error_brelse;

                transid = btrfs_super_generation(disk_super);
                if (!latest_transid || transid > latest_transid) {
                        latest_devid = devid;
                        latest_transid = transid;
                        latest_bdev = bdev;
                }

                device->bdev = bdev;
                device->in_fs_metadata = 0;
                fs_devices->open_devices++;
                continue;

error_brelse:
                brelse(bh);
error_close:
                close_bdev_excl(bdev);
error:
                continue;
        }
        if (fs_devices->open_devices == 0) {
                ret = -EIO;
                goto out;
        }
        fs_devices->mounted = 1;
        fs_devices->latest_bdev = latest_bdev;
        fs_devices->latest_devid = latest_devid;
        fs_devices->latest_trans = latest_transid;
out:
        mutex_unlock(&uuid_mutex);
        return ret;
}

int btrfs_scan_one_device(const char *path, int flags, void *holder,
                          struct btrfs_fs_devices **fs_devices_ret)
{
        struct btrfs_super_block *disk_super;
        struct block_device *bdev;
        struct buffer_head *bh;
        int ret;
        u64 devid;
        u64 transid;

        mutex_lock(&uuid_mutex);

        bdev = open_bdev_excl(path, flags, holder);

        if (IS_ERR(bdev)) {
                ret = PTR_ERR(bdev);
                goto error;
        }

        ret = set_blocksize(bdev, 4096);
        if (ret)
                goto error_close;
        bh = __bread(bdev, BTRFS_SUPER_INFO_OFFSET / 4096, 4096);
        if (!bh) {
                ret = -EIO;
                goto error_close;
        }
        disk_super = (struct btrfs_super_block *)bh->b_data;
        if (strncmp((char *)(&disk_super->magic), BTRFS_MAGIC,
            sizeof(disk_super->magic))) {
                ret = -EINVAL;
                goto error_brelse;
        }
        devid = le64_to_cpu(disk_super->dev_item.devid);
        transid = btrfs_super_generation(disk_super);
        if (disk_super->label[0])
                printk("device label %s ", disk_super->label);
        else {
                /* FIXME, make a readl uuid parser */
                printk("device fsid %llx-%llx ",
                       *(unsigned long long *)disk_super->fsid,
                       *(unsigned long long *)(disk_super->fsid + 8));
        }
        printk("devid %Lu transid %Lu %s\n", devid, transid, path);
        ret = device_list_add(path, disk_super, devid, fs_devices_ret);

error_brelse:
        brelse(bh);
error_close:
        close_bdev_excl(bdev);
error:
        mutex_unlock(&uuid_mutex);
        return ret;
}

/*
 * this uses a pretty simple search, the expectation is that it is
 * called very infrequently and that a given device has a small number
 * of extents
 */
static int find_free_dev_extent(struct btrfs_trans_handle *trans,
                                struct btrfs_device *device,
                                struct btrfs_path *path,
                                u64 num_bytes, u64 *start)
{
        struct btrfs_key key;
        struct btrfs_root *root = device->dev_root;
        struct btrfs_dev_extent *dev_extent = NULL;
        u64 hole_size = 0;
        u64 last_byte = 0;
        u64 search_start = 0;
        u64 search_end = device->total_bytes;
        int ret;
        int slot = 0;
        int start_found;
        struct extent_buffer *l;

        start_found = 0;
        path->reada = 2;

        /* FIXME use last free of some kind */

        /* we don't want to overwrite the superblock on the drive,
         * so we make sure to start at an offset of at least 1MB
         */
        search_start = max((u64)1024 * 1024, search_start);

        if (root->fs_info->alloc_start + num_bytes <= device->total_bytes)
                search_start = max(root->fs_info->alloc_start, search_start);

        key.objectid = device->devid;
        key.offset = search_start;
        key.type = BTRFS_DEV_EXTENT_KEY;
        ret = btrfs_search_slot(trans, root, &key, path, 0, 0);
        if (ret < 0)
                goto error;
        ret = btrfs_previous_item(root, path, 0, key.type);
        if (ret < 0)
                goto error;
        l = path->nodes[0];
        btrfs_item_key_to_cpu(l, &key, path->slots[0]);
        while (1) {
                l = path->nodes[0];
                slot = path->slots[0];
                if (slot >= btrfs_header_nritems(l)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret == 0)
                                continue;
                        if (ret < 0)
                                goto error;
no_more_items:
                        if (!start_found) {
                                if (search_start >= search_end) {
                                        ret = -ENOSPC;
                                        goto error;
                                }
                                *start = search_start;
                                start_found = 1;
                                goto check_pending;
                        }
                        *start = last_byte > search_start ?
                                last_byte : search_start;
                        if (search_end <= *start) {
                                ret = -ENOSPC;
                                goto error;
                        }
                        goto check_pending;
                }
                btrfs_item_key_to_cpu(l, &key, slot);

                if (key.objectid < device->devid)
                        goto next;

                if (key.objectid > device->devid)
                        goto no_more_items;

                if (key.offset >= search_start && key.offset > last_byte &&
                    start_found) {
                        if (last_byte < search_start)
                                last_byte = search_start;
                        hole_size = key.offset - last_byte;
                        if (key.offset > last_byte &&
                            hole_size >= num_bytes) {
                                *start = last_byte;
                                goto check_pending;
                        }
                }
                if (btrfs_key_type(&key) != BTRFS_DEV_EXTENT_KEY) {
                        goto next;
                }

                start_found = 1;
                dev_extent = btrfs_item_ptr(l, slot, struct btrfs_dev_extent);
                last_byte = key.offset + btrfs_dev_extent_length(l, dev_extent);
next:
                path->slots[0]++;
                cond_resched();
        }
check_pending:
        /* we have to make sure we didn't find an extent that has already
         * been allocated by the map tree or the original allocation
         */
        btrfs_release_path(root, path);
        BUG_ON(*start < search_start);

        if (*start + num_bytes > search_end) {
                ret = -ENOSPC;
                goto error;
        }
        /* check for pending inserts here */
        return 0;

error:
        btrfs_release_path(root, path);
        return ret;
}

int btrfs_free_dev_extent(struct btrfs_trans_handle *trans,
                          struct btrfs_device *device,
                          u64 start)
{
        int ret;
        struct btrfs_path *path;
        struct btrfs_root *root = device->dev_root;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct extent_buffer *leaf = NULL;
        struct btrfs_dev_extent *extent = NULL;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        key.objectid = device->devid;
        key.offset = start;
        key.type = BTRFS_DEV_EXTENT_KEY;

        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        if (ret > 0) {
                ret = btrfs_previous_item(root, path, key.objectid,
                                          BTRFS_DEV_EXTENT_KEY);
                BUG_ON(ret);
                leaf = path->nodes[0];
                btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
                extent = btrfs_item_ptr(leaf, path->slots[0],
                                        struct btrfs_dev_extent);
                BUG_ON(found_key.offset > start || found_key.offset +
                       btrfs_dev_extent_length(leaf, extent) < start);
                ret = 0;
        } else if (ret == 0) {
                leaf = path->nodes[0];
                extent = btrfs_item_ptr(leaf, path->slots[0],
                                        struct btrfs_dev_extent);
        }
        BUG_ON(ret);

        if (device->bytes_used > 0)
                device->bytes_used -= btrfs_dev_extent_length(leaf, extent);
        ret = btrfs_del_item(trans, root, path);
        BUG_ON(ret);

        btrfs_free_path(path);
        return ret;
}

int btrfs_alloc_dev_extent(struct btrfs_trans_handle *trans,
                           struct btrfs_device *device,
                           u64 chunk_tree, u64 chunk_objectid,
                           u64 chunk_offset,
                           u64 num_bytes, u64 *start)
{
        int ret;
        struct btrfs_path *path;
        struct btrfs_root *root = device->dev_root;
        struct btrfs_dev_extent *extent;
        struct extent_buffer *leaf;
        struct btrfs_key key;

        WARN_ON(!device->in_fs_metadata);
        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        ret = find_free_dev_extent(trans, device, path, num_bytes, start);
        if (ret) {
                goto err;
        }

        key.objectid = device->devid;
        key.offset = *start;
        key.type = BTRFS_DEV_EXTENT_KEY;
        ret = btrfs_insert_empty_item(trans, root, path, &key,
                                      sizeof(*extent));
        BUG_ON(ret);

        leaf = path->nodes[0];
        extent = btrfs_item_ptr(leaf, path->slots[0],
                                struct btrfs_dev_extent);
        btrfs_set_dev_extent_chunk_tree(leaf, extent, chunk_tree);
        btrfs_set_dev_extent_chunk_objectid(leaf, extent, chunk_objectid);
        btrfs_set_dev_extent_chunk_offset(leaf, extent, chunk_offset);

        write_extent_buffer(leaf, root->fs_info->chunk_tree_uuid,
                    (unsigned long)btrfs_dev_extent_chunk_tree_uuid(extent),
                    BTRFS_UUID_SIZE);

        btrfs_set_dev_extent_length(leaf, extent, num_bytes);
        btrfs_mark_buffer_dirty(leaf);
err:
        btrfs_free_path(path);
        return ret;
}

static int find_next_chunk(struct btrfs_root *root, u64 objectid, u64 *offset)
{
        struct btrfs_path *path;
        int ret;
        struct btrfs_key key;
        struct btrfs_chunk *chunk;
        struct btrfs_key found_key;

        path = btrfs_alloc_path();
        BUG_ON(!path);

        key.objectid = objectid;
        key.offset = (u64)-1;
        key.type = BTRFS_CHUNK_ITEM_KEY;

        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto error;

        BUG_ON(ret == 0);

        ret = btrfs_previous_item(root, path, 0, BTRFS_CHUNK_ITEM_KEY);
        if (ret) {
                *offset = 0;
        } else {
                btrfs_item_key_to_cpu(path->nodes[0], &found_key,
                                      path->slots[0]);
                if (found_key.objectid != objectid)
                        *offset = 0;
                else {
                        chunk = btrfs_item_ptr(path->nodes[0], path->slots[0],
                                               struct btrfs_chunk);
                        *offset = found_key.offset +
                                btrfs_chunk_length(path->nodes[0], chunk);
                }
        }
        ret = 0;
error:
        btrfs_free_path(path);
        return ret;
}

static int find_next_devid(struct btrfs_root *root, struct btrfs_path *path,
                           u64 *objectid)
{
        int ret;
        struct btrfs_key key;
        struct btrfs_key found_key;

        key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
        key.type = BTRFS_DEV_ITEM_KEY;
        key.offset = (u64)-1;

        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto error;

        BUG_ON(ret == 0);

        ret = btrfs_previous_item(root, path, BTRFS_DEV_ITEMS_OBJECTID,
                                  BTRFS_DEV_ITEM_KEY);
        if (ret) {
                *objectid = 1;
        } else {
                btrfs_item_key_to_cpu(path->nodes[0], &found_key,
                                      path->slots[0]);
                *objectid = found_key.offset + 1;
        }
        ret = 0;
error:
        btrfs_release_path(root, path);
        return ret;
}

/*
 * the device information is stored in the chunk root
 * the btrfs_device struct should be fully filled in
 */
int btrfs_add_device(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root,
                     struct btrfs_device *device)
{
        int ret;
        struct btrfs_path *path;
        struct btrfs_dev_item *dev_item;
        struct extent_buffer *leaf;
        struct btrfs_key key;
        unsigned long ptr;
        u64 free_devid = 0;

        root = root->fs_info->chunk_root;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        ret = find_next_devid(root, path, &free_devid);
        if (ret)
                goto out;

        key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
        key.type = BTRFS_DEV_ITEM_KEY;
        key.offset = free_devid;

        ret = btrfs_insert_empty_item(trans, root, path, &key,
                                      sizeof(*dev_item));
        if (ret)
                goto out;

        leaf = path->nodes[0];
        dev_item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_dev_item);

        device->devid = free_devid;
        btrfs_set_device_id(leaf, dev_item, device->devid);
        btrfs_set_device_type(leaf, dev_item, device->type);
        btrfs_set_device_io_align(leaf, dev_item, device->io_align);
        btrfs_set_device_io_width(leaf, dev_item, device->io_width);
        btrfs_set_device_sector_size(leaf, dev_item, device->sector_size);
        btrfs_set_device_total_bytes(leaf, dev_item, device->total_bytes);
        btrfs_set_device_bytes_used(leaf, dev_item, device->bytes_used);
        btrfs_set_device_group(leaf, dev_item, 0);
        btrfs_set_device_seek_speed(leaf, dev_item, 0);
        btrfs_set_device_bandwidth(leaf, dev_item, 0);

        ptr = (unsigned long)btrfs_device_uuid(dev_item);
        write_extent_buffer(leaf, device->uuid, ptr, BTRFS_UUID_SIZE);
        btrfs_mark_buffer_dirty(leaf);
        ret = 0;

out:
        btrfs_free_path(path);
        return ret;
}

static int btrfs_rm_dev_item(struct btrfs_root *root,
                             struct btrfs_device *device)
{
        int ret;
        struct btrfs_path *path;
        struct block_device *bdev = device->bdev;
        struct btrfs_device *next_dev;
        struct btrfs_key key;
        u64 total_bytes;
        struct btrfs_fs_devices *fs_devices;
        struct btrfs_trans_handle *trans;

        root = root->fs_info->chunk_root;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        trans = btrfs_start_transaction(root, 1);
        key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
        key.type = BTRFS_DEV_ITEM_KEY;
        key.offset = device->devid;

        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        if (ret < 0)
                goto out;

        if (ret > 0) {
                ret = -ENOENT;
                goto out;
        }

        ret = btrfs_del_item(trans, root, path);
        if (ret)
                goto out;

        /*
         * at this point, the device is zero sized.  We want to
         * remove it from the devices list and zero out the old super
         */
        list_del_init(&device->dev_list);
        list_del_init(&device->dev_alloc_list);
        fs_devices = root->fs_info->fs_devices;

        next_dev = list_entry(fs_devices->devices.next, struct btrfs_device,
                              dev_list);
        if (bdev == root->fs_info->sb->s_bdev)
                root->fs_info->sb->s_bdev = next_dev->bdev;
        if (bdev == fs_devices->latest_bdev)
                fs_devices->latest_bdev = next_dev->bdev;

        total_bytes = btrfs_super_num_devices(&root->fs_info->super_copy);
        btrfs_set_super_num_devices(&root->fs_info->super_copy,
                                    total_bytes - 1);
out:
        btrfs_free_path(path);
        btrfs_commit_transaction(trans, root);
        return ret;
}

int btrfs_rm_device(struct btrfs_root *root, char *device_path)
{
        struct btrfs_device *device;
        struct block_device *bdev;
        struct buffer_head *bh = NULL;
        struct btrfs_super_block *disk_super;
        u64 all_avail;
        u64 devid;
        int ret = 0;

        mutex_lock(&root->fs_info->alloc_mutex);
        mutex_lock(&root->fs_info->chunk_mutex);
        mutex_lock(&uuid_mutex);

        all_avail = root->fs_info->avail_data_alloc_bits |
                root->fs_info->avail_system_alloc_bits |
                root->fs_info->avail_metadata_alloc_bits;

        if ((all_avail & BTRFS_BLOCK_GROUP_RAID10) &&
            btrfs_super_num_devices(&root->fs_info->super_copy) <= 4) {
                printk("btrfs: unable to go below four devices on raid10\n");
                ret = -EINVAL;
                goto out;
        }

        if ((all_avail & BTRFS_BLOCK_GROUP_RAID1) &&
            btrfs_super_num_devices(&root->fs_info->super_copy) <= 2) {
                printk("btrfs: unable to go below two devices on raid1\n");
                ret = -EINVAL;
                goto out;
        }

        if (strcmp(device_path, "missing") == 0) {
                struct list_head *cur;
                struct list_head *devices;
                struct btrfs_device *tmp;

                device = NULL;
                devices = &root->fs_info->fs_devices->devices;
                list_for_each(cur, devices) {
                        tmp = list_entry(cur, struct btrfs_device, dev_list);
                        if (tmp->in_fs_metadata && !tmp->bdev) {
                                device = tmp;
                                break;
                        }
                }
                bdev = NULL;
                bh = NULL;
                disk_super = NULL;
                if (!device) {
                        printk("btrfs: no missing devices found to remove\n");
                        goto out;
                }

        } else {
                bdev = open_bdev_excl(device_path, 0,
                                      root->fs_info->bdev_holder);
                if (IS_ERR(bdev)) {
                        ret = PTR_ERR(bdev);
                        goto out;
                }

                bh = __bread(bdev, BTRFS_SUPER_INFO_OFFSET / 4096, 4096);
                if (!bh) {
                        ret = -EIO;
                        goto error_close;
                }
                disk_super = (struct btrfs_super_block *)bh->b_data;
                if (strncmp((char *)(&disk_super->magic), BTRFS_MAGIC,
                    sizeof(disk_super->magic))) {
                        ret = -ENOENT;
                        goto error_brelse;
                }
                if (memcmp(disk_super->fsid, root->fs_info->fsid,
                           BTRFS_FSID_SIZE)) {
                        ret = -ENOENT;
                        goto error_brelse;
                }
                devid = le64_to_cpu(disk_super->dev_item.devid);
                device = btrfs_find_device(root, devid, NULL);
                if (!device) {
                        ret = -ENOENT;
                        goto error_brelse;
                }

        }
        root->fs_info->fs_devices->num_devices--;
        root->fs_info->fs_devices->open_devices--;

        ret = btrfs_shrink_device(device, 0);
        if (ret)
                goto error_brelse;


        ret = btrfs_rm_dev_item(root->fs_info->chunk_root, device);
        if (ret)
                goto error_brelse;

        if (bh) {
                /* make sure this device isn't detected as part of
                 * the FS anymore
                 */
                memset(&disk_super->magic, 0, sizeof(disk_super->magic));
                set_buffer_dirty(bh);
                sync_dirty_buffer(bh);

                brelse(bh);
        }

        if (device->bdev) {
                /* one close for the device struct or super_block */
                close_bdev_excl(device->bdev);
        }
        if (bdev) {
                /* one close for us */
                close_bdev_excl(bdev);
        }
        kfree(device->name);
        kfree(device);
        ret = 0;
        goto out;

error_brelse:
        brelse(bh);
error_close:
        if (bdev)
                close_bdev_excl(bdev);
out:
        mutex_unlock(&uuid_mutex);
        mutex_unlock(&root->fs_info->chunk_mutex);
        mutex_unlock(&root->fs_info->alloc_mutex);
        return ret;
}

int btrfs_init_new_device(struct btrfs_root *root, char *device_path)
{
        struct btrfs_trans_handle *trans;
        struct btrfs_device *device;
        struct block_device *bdev;
        struct list_head *cur;
        struct list_head *devices;
        u64 total_bytes;
        int ret = 0;


        bdev = open_bdev_excl(device_path, 0, root->fs_info->bdev_holder);
        if (!bdev) {
                return -EIO;
        }

        mutex_lock(&root->fs_info->alloc_mutex);
        mutex_lock(&root->fs_info->chunk_mutex);

        trans = btrfs_start_transaction(root, 1);
        devices = &root->fs_info->fs_devices->devices;
        list_for_each(cur, devices) {
                device = list_entry(cur, struct btrfs_device, dev_list);
                if (device->bdev == bdev) {
                        ret = -EEXIST;
                        goto out;
                }
        }

        device = kzalloc(sizeof(*device), GFP_NOFS);
        if (!device) {
                /* we can safely leave the fs_devices entry around */
                ret = -ENOMEM;
                goto out_close_bdev;
        }

        device->barriers = 1;
        device->work.func = pending_bios_fn;
        generate_random_uuid(device->uuid);
        spin_lock_init(&device->io_lock);
        device->name = kstrdup(device_path, GFP_NOFS);
        if (!device->name) {
                kfree(device);
                goto out_close_bdev;
        }
        device->io_width = root->sectorsize;
        device->io_align = root->sectorsize;
        device->sector_size = root->sectorsize;
        device->total_bytes = i_size_read(bdev->bd_inode);
        device->dev_root = root->fs_info->dev_root;
        device->bdev = bdev;
        device->in_fs_metadata = 1;

        ret = btrfs_add_device(trans, root, device);
        if (ret)
                goto out_close_bdev;

        total_bytes = btrfs_super_total_bytes(&root->fs_info->super_copy);
        btrfs_set_super_total_bytes(&root->fs_info->super_copy,
                                    total_bytes + device->total_bytes);

        total_bytes = btrfs_super_num_devices(&root->fs_info->super_copy);
        btrfs_set_super_num_devices(&root->fs_info->super_copy,
                                    total_bytes + 1);

        list_add(&device->dev_list, &root->fs_info->fs_devices->devices);
        list_add(&device->dev_alloc_list,
                 &root->fs_info->fs_devices->alloc_list);
        root->fs_info->fs_devices->num_devices++;
        root->fs_info->fs_devices->open_devices++;
out:
        btrfs_end_transaction(trans, root);
        mutex_unlock(&root->fs_info->chunk_mutex);
        mutex_unlock(&root->fs_info->alloc_mutex);

        return ret;

out_close_bdev:
        close_bdev_excl(bdev);
        goto out;
}

int btrfs_update_device(struct btrfs_trans_handle *trans,
                        struct btrfs_device *device)
{
        int ret;
        struct btrfs_path *path;
        struct btrfs_root *root;
        struct btrfs_dev_item *dev_item;
        struct extent_buffer *leaf;
        struct btrfs_key key;

        root = device->dev_root->fs_info->chunk_root;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
        key.type = BTRFS_DEV_ITEM_KEY;
        key.offset = device->devid;

        ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
        if (ret < 0)
                goto out;

        if (ret > 0) {
                ret = -ENOENT;
                goto out;
        }

        leaf = path->nodes[0];
        dev_item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_dev_item);

        btrfs_set_device_id(leaf, dev_item, device->devid);
        btrfs_set_device_type(leaf, dev_item, device->type);
        btrfs_set_device_io_align(leaf, dev_item, device->io_align);
        btrfs_set_device_io_width(leaf, dev_item, device->io_width);
        btrfs_set_device_sector_size(leaf, dev_item, device->sector_size);
        btrfs_set_device_total_bytes(leaf, dev_item, device->total_bytes);
        btrfs_set_device_bytes_used(leaf, dev_item, device->bytes_used);
        btrfs_mark_buffer_dirty(leaf);

out:
        btrfs_free_path(path);
        return ret;
}

int btrfs_grow_device(struct btrfs_trans_handle *trans,
                      struct btrfs_device *device, u64 new_size)
{
        struct btrfs_super_block *super_copy =
                &device->dev_root->fs_info->super_copy;
        u64 old_total = btrfs_super_total_bytes(super_copy);
        u64 diff = new_size - device->total_bytes;

        btrfs_set_super_total_bytes(super_copy, old_total + diff);
        return btrfs_update_device(trans, device);
}

static int btrfs_free_chunk(struct btrfs_trans_handle *trans,
                            struct btrfs_root *root,
                            u64 chunk_tree, u64 chunk_objectid,
                            u64 chunk_offset)
{
        int ret;
        struct btrfs_path *path;
        struct btrfs_key key;

        root = root->fs_info->chunk_root;
        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        key.objectid = chunk_objectid;
        key.offset = chunk_offset;
        key.type = BTRFS_CHUNK_ITEM_KEY;

        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        BUG_ON(ret);

        ret = btrfs_del_item(trans, root, path);
        BUG_ON(ret);

        btrfs_free_path(path);
        return 0;
}

int btrfs_del_sys_chunk(struct btrfs_root *root, u64 chunk_objectid, u64
                        chunk_offset)
{
        struct btrfs_super_block *super_copy = &root->fs_info->super_copy;
        struct btrfs_disk_key *disk_key;
        struct btrfs_chunk *chunk;
        u8 *ptr;
        int ret = 0;
        u32 num_stripes;
        u32 array_size;
        u32 len = 0;
        u32 cur;
        struct btrfs_key key;

        array_size = btrfs_super_sys_array_size(super_copy);

        ptr = super_copy->sys_chunk_array;
        cur = 0;

        while (cur < array_size) {
                disk_key = (struct btrfs_disk_key *)ptr;
                btrfs_disk_key_to_cpu(&key, disk_key);

                len = sizeof(*disk_key);

                if (key.type == BTRFS_CHUNK_ITEM_KEY) {
                        chunk = (struct btrfs_chunk *)(ptr + len);
                        num_stripes = btrfs_stack_chunk_num_stripes(chunk);
                        len += btrfs_chunk_item_size(num_stripes);
                } else {
                        ret = -EIO;
                        break;
                }
                if (key.objectid == chunk_objectid &&
                    key.offset == chunk_offset) {
                        memmove(ptr, ptr + len, array_size - (cur + len));
                        array_size -= len;
                        btrfs_set_super_sys_array_size(super_copy, array_size);
                } else {
                        ptr += len;
                        cur += len;
                }
        }
        return ret;
}


int btrfs_relocate_chunk(struct btrfs_root *root,
                         u64 chunk_tree, u64 chunk_objectid,
                         u64 chunk_offset)
{
        struct extent_map_tree *em_tree;
        struct btrfs_root *extent_root;
        struct btrfs_trans_handle *trans;
        struct extent_map *em;
        struct map_lookup *map;
        int ret;
        int i;

        printk("btrfs relocating chunk %llu\n",
               (unsigned long long)chunk_offset);
        root = root->fs_info->chunk_root;
        extent_root = root->fs_info->extent_root;
        em_tree = &root->fs_info->mapping_tree.map_tree;

        /* step one, relocate all the extents inside this chunk */
        ret = btrfs_shrink_extent_tree(extent_root, chunk_offset);
        BUG_ON(ret);

        trans = btrfs_start_transaction(root, 1);
        BUG_ON(!trans);

        /*
         * step two, delete the device extents and the
         * chunk tree entries
         */
        spin_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, chunk_offset, 1);
        spin_unlock(&em_tree->lock);

        BUG_ON(em->start > chunk_offset ||
               em->start + em->len < chunk_offset);
        map = (struct map_lookup *)em->bdev;

        for (i = 0; i < map->num_stripes; i++) {
                ret = btrfs_free_dev_extent(trans, map->stripes[i].dev,
                                            map->stripes[i].physical);
                BUG_ON(ret);

                if (map->stripes[i].dev) {
                        ret = btrfs_update_device(trans, map->stripes[i].dev);
                        BUG_ON(ret);
                }
        }
        ret = btrfs_free_chunk(trans, root, chunk_tree, chunk_objectid,
                               chunk_offset);

        BUG_ON(ret);

        if (map->type & BTRFS_BLOCK_GROUP_SYSTEM) {
                ret = btrfs_del_sys_chunk(root, chunk_objectid, chunk_offset);
                BUG_ON(ret);
        }

        spin_lock(&em_tree->lock);
        remove_extent_mapping(em_tree, em);
        kfree(map);
        em->bdev = NULL;

        /* once for the tree */
        free_extent_map(em);
        spin_unlock(&em_tree->lock);

        /* once for us */
        free_extent_map(em);

        btrfs_end_transaction(trans, root);
        return 0;
}

static u64 div_factor(u64 num, int factor)
{
        if (factor == 10)
                return num;
        num *= factor;
        do_div(num, 10);
        return num;
}


int btrfs_balance(struct btrfs_root *dev_root)
{
        int ret;
        struct list_head *cur;
        struct list_head *devices = &dev_root->fs_info->fs_devices->devices;
        struct btrfs_device *device;
        u64 old_size;
        u64 size_to_free;
        struct btrfs_path *path;
        struct btrfs_key key;
        struct btrfs_chunk *chunk;
        struct btrfs_root *chunk_root = dev_root->fs_info->chunk_root;
        struct btrfs_trans_handle *trans;
        struct btrfs_key found_key;


        BUG(); /* FIXME, needs locking */

        dev_root = dev_root->fs_info->dev_root;

        /* step one make some room on all the devices */
        list_for_each(cur, devices) {
                device = list_entry(cur, struct btrfs_device, dev_list);
                old_size = device->total_bytes;
                size_to_free = div_factor(old_size, 1);
                size_to_free = min(size_to_free, (u64)1 * 1024 * 1024);
                if (device->total_bytes - device->bytes_used > size_to_free)
                        continue;

                ret = btrfs_shrink_device(device, old_size - size_to_free);
                BUG_ON(ret);

                trans = btrfs_start_transaction(dev_root, 1);
                BUG_ON(!trans);

                ret = btrfs_grow_device(trans, device, old_size);
                BUG_ON(ret);

                btrfs_end_transaction(trans, dev_root);
        }

        /* step two, relocate all the chunks */
        path = btrfs_alloc_path();
        BUG_ON(!path);

        key.objectid = BTRFS_FIRST_CHUNK_TREE_OBJECTID;
        key.offset = (u64)-1;
        key.type = BTRFS_CHUNK_ITEM_KEY;

        while(1) {
                ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0);
                if (ret < 0)
                        goto error;

                /*
                 * this shouldn't happen, it means the last relocate
                 * failed
                 */
                if (ret == 0)
                        break;

                ret = btrfs_previous_item(chunk_root, path, 0,
                                          BTRFS_CHUNK_ITEM_KEY);
                if (ret) {
                        break;
                }
                btrfs_item_key_to_cpu(path->nodes[0], &found_key,
                                      path->slots[0]);
                if (found_key.objectid != key.objectid)
                        break;
                chunk = btrfs_item_ptr(path->nodes[0],
                                       path->slots[0],
                                       struct btrfs_chunk);
                key.offset = found_key.offset;
                /* chunk zero is special */
                if (key.offset == 0)
                        break;

                ret = btrfs_relocate_chunk(chunk_root,
                                           chunk_root->root_key.objectid,
                                           found_key.objectid,
                                           found_key.offset);
                BUG_ON(ret);
                btrfs_release_path(chunk_root, path);
        }
        ret = 0;
error:
        btrfs_free_path(path);
        return ret;
}

/*
 * shrinking a device means finding all of the device extents past
 * the new size, and then following the back refs to the chunks.
 * The chunk relocation code actually frees the device extent
 */
int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
{
        struct btrfs_trans_handle *trans;
        struct btrfs_root *root = device->dev_root;
        struct btrfs_dev_extent *dev_extent = NULL;
        struct btrfs_path *path;
        u64 length;
        u64 chunk_tree;
        u64 chunk_objectid;
        u64 chunk_offset;
        int ret;
        int slot;
        struct extent_buffer *l;
        struct btrfs_key key;
        struct btrfs_super_block *super_copy = &root->fs_info->super_copy;
        u64 old_total = btrfs_super_total_bytes(super_copy);
        u64 diff = device->total_bytes - new_size;


        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        trans = btrfs_start_transaction(root, 1);
        if (!trans) {
                ret = -ENOMEM;
                goto done;
        }

        path->reada = 2;

        device->total_bytes = new_size;
        ret = btrfs_update_device(trans, device);
        if (ret) {
                btrfs_end_transaction(trans, root);
                goto done;
        }
        WARN_ON(diff > old_total);
        btrfs_set_super_total_bytes(super_copy, old_total - diff);
        btrfs_end_transaction(trans, root);

        key.objectid = device->devid;
        key.offset = (u64)-1;
        key.type = BTRFS_DEV_EXTENT_KEY;

        while (1) {
                ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
                if (ret < 0)
                        goto done;

                ret = btrfs_previous_item(root, path, 0, key.type);
                if (ret < 0)
                        goto done;
                if (ret) {
                        ret = 0;
                        goto done;
                }

                l = path->nodes[0];
                slot = path->slots[0];
                btrfs_item_key_to_cpu(l, &key, path->slots[0]);

                if (key.objectid != device->devid)
                        goto done;

                dev_extent = btrfs_item_ptr(l, slot, struct btrfs_dev_extent);
                length = btrfs_dev_extent_length(l, dev_extent);

                if (key.offset + length <= new_size)
                        goto done;

                chunk_tree = btrfs_dev_extent_chunk_tree(l, dev_extent);
                chunk_objectid = btrfs_dev_extent_chunk_objectid(l, dev_extent);
                chunk_offset = btrfs_dev_extent_chunk_offset(l, dev_extent);
                btrfs_release_path(root, path);

                ret = btrfs_relocate_chunk(root, chunk_tree, chunk_objectid,
                                           chunk_offset);
                if (ret)
                        goto done;
        }

done:
        btrfs_free_path(path);
        return ret;
}

int btrfs_add_system_chunk(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root,
                           struct btrfs_key *key,
                           struct btrfs_chunk *chunk, int item_size)
{
        struct btrfs_super_block *super_copy = &root->fs_info->super_copy;
        struct btrfs_disk_key disk_key;
        u32 array_size;
        u8 *ptr;

        array_size = btrfs_super_sys_array_size(super_copy);
        if (array_size + item_size > BTRFS_SYSTEM_CHUNK_ARRAY_SIZE)
                return -EFBIG;

        ptr = super_copy->sys_chunk_array + array_size;
        btrfs_cpu_key_to_disk(&disk_key, key);
        memcpy(ptr, &disk_key, sizeof(disk_key));
        ptr += sizeof(disk_key);
        memcpy(ptr, chunk, item_size);
        item_size += sizeof(disk_key);
        btrfs_set_super_sys_array_size(super_copy, array_size + item_size);
        return 0;
}

static u64 chunk_bytes_by_type(u64 type, u64 calc_size, int num_stripes,
                               int sub_stripes)
{
        if (type & (BTRFS_BLOCK_GROUP_RAID1 | BTRFS_BLOCK_GROUP_DUP))
                return calc_size;
        else if (type & BTRFS_BLOCK_GROUP_RAID10)
                return calc_size * (num_stripes / sub_stripes);
        else
                return calc_size * num_stripes;
}


int btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
                      struct btrfs_root *extent_root, u64 *start,
                      u64 *num_bytes, u64 type)
{
        u64 dev_offset;
        struct btrfs_fs_info *info = extent_root->fs_info;
        struct btrfs_root *chunk_root = extent_root->fs_info->chunk_root;
        struct btrfs_path *path;
        struct btrfs_stripe *stripes;
        struct btrfs_device *device = NULL;
        struct btrfs_chunk *chunk;
        struct list_head private_devs;
        struct list_head *dev_list;
        struct list_head *cur;
        struct extent_map_tree *em_tree;
        struct map_lookup *map;
        struct extent_map *em;
        int min_stripe_size = 1 * 1024 * 1024;
        u64 physical;
        u64 calc_size = 1024 * 1024 * 1024;
        u64 max_chunk_size = calc_size;
        u64 min_free;
        u64 avail;
        u64 max_avail = 0;
        u64 percent_max;
        int num_stripes = 1;
        int min_stripes = 1;
        int sub_stripes = 0;
        int looped = 0;
        int ret;
        int index;
        int stripe_len = 64 * 1024;
        struct btrfs_key key;

        if ((type & BTRFS_BLOCK_GROUP_RAID1) &&
            (type & BTRFS_BLOCK_GROUP_DUP)) {
                WARN_ON(1);
                type &= ~BTRFS_BLOCK_GROUP_DUP;
        }
        dev_list = &extent_root->fs_info->fs_devices->alloc_list;
        if (list_empty(dev_list))
                return -ENOSPC;

        if (type & (BTRFS_BLOCK_GROUP_RAID0)) {
                num_stripes = extent_root->fs_info->fs_devices->open_devices;
                min_stripes = 2;
        }
        if (type & (BTRFS_BLOCK_GROUP_DUP)) {
                num_stripes = 2;
                min_stripes = 2;
        }
        if (type & (BTRFS_BLOCK_GROUP_RAID1)) {
                num_stripes = min_t(u64, 2,
                            extent_root->fs_info->fs_devices->open_devices);
                if (num_stripes < 2)
                        return -ENOSPC;
                min_stripes = 2;
        }
        if (type & (BTRFS_BLOCK_GROUP_RAID10)) {
                num_stripes = extent_root->fs_info->fs_devices->open_devices;
                if (num_stripes < 4)
                        return -ENOSPC;
                num_stripes &= ~(u32)1;
                sub_stripes = 2;
                min_stripes = 4;
        }

        if (type & BTRFS_BLOCK_GROUP_DATA) {
                max_chunk_size = 10 * calc_size;
                min_stripe_size = 64 * 1024 * 1024;
        } else if (type & BTRFS_BLOCK_GROUP_METADATA) {
                max_chunk_size = 4 * calc_size;
                min_stripe_size = 32 * 1024 * 1024;
        } else if (type & BTRFS_BLOCK_GROUP_SYSTEM) {
                calc_size = 8 * 1024 * 1024;
                max_chunk_size = calc_size * 2;
                min_stripe_size = 1 * 1024 * 1024;
        }

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        /* we don't want a chunk larger than 10% of the FS */
        percent_max = div_factor(btrfs_super_total_bytes(&info->super_copy), 1);
        max_chunk_size = min(percent_max, max_chunk_size);

again:
        if (calc_size * num_stripes > max_chunk_size) {
                calc_size = max_chunk_size;
                do_div(calc_size, num_stripes);
                do_div(calc_size, stripe_len);
                calc_size *= stripe_len;
        }
        /* we don't want tiny stripes */
        calc_size = max_t(u64, min_stripe_size, calc_size);

        do_div(calc_size, stripe_len);
        calc_size *= stripe_len;

        INIT_LIST_HEAD(&private_devs);
        cur = dev_list->next;
        index = 0;

        if (type & BTRFS_BLOCK_GROUP_DUP)
                min_free = calc_size * 2;
        else
                min_free = calc_size;

        /* we add 1MB because we never use the first 1MB of the device */
        min_free += 1024 * 1024;

        /* build a private list of devices we will allocate from */
        while(index < num_stripes) {
                device = list_entry(cur, struct btrfs_device, dev_alloc_list);

                if (device->total_bytes > device->bytes_used)
                        avail = device->total_bytes - device->bytes_used;
                else
                        avail = 0;
                cur = cur->next;

                if (device->in_fs_metadata && avail >= min_free) {
                        u64 ignored_start = 0;
                        ret = find_free_dev_extent(trans, device, path,
                                                   min_free,
                                                   &ignored_start);
                        if (ret == 0) {
                                list_move_tail(&device->dev_alloc_list,
                                               &private_devs);
                                index++;
                                if (type & BTRFS_BLOCK_GROUP_DUP)
                                        index++;
                        }
                } else if (device->in_fs_metadata && avail > max_avail)
                        max_avail = avail;
                if (cur == dev_list)
                        break;
        }
        if (index < num_stripes) {
                list_splice(&private_devs, dev_list);
                if (index >= min_stripes) {
                        num_stripes = index;
                        if (type & (BTRFS_BLOCK_GROUP_RAID10)) {
                                num_stripes /= sub_stripes;
                                num_stripes *= sub_stripes;
                        }
                        looped = 1;
                        goto again;
                }
                if (!looped && max_avail > 0) {
                        looped = 1;
                        calc_size = max_avail;
                        goto again;
                }
                btrfs_free_path(path);
                return -ENOSPC;
        }
        key.objectid = BTRFS_FIRST_CHUNK_TREE_OBJECTID;
        key.type = BTRFS_CHUNK_ITEM_KEY;
        ret = find_next_chunk(chunk_root, BTRFS_FIRST_CHUNK_TREE_OBJECTID,
                              &key.offset);
        if (ret) {
                btrfs_free_path(path);
                return ret;
        }

        chunk = kmalloc(btrfs_chunk_item_size(num_stripes), GFP_NOFS);
        if (!chunk) {
                btrfs_free_path(path);
                return -ENOMEM;
        }

        map = kmalloc(map_lookup_size(num_stripes), GFP_NOFS);
        if (!map) {
                kfree(chunk);
                btrfs_free_path(path);
                return -ENOMEM;
        }
        btrfs_free_path(path);
        path = NULL;

        stripes = &chunk->stripe;
        *num_bytes = chunk_bytes_by_type(type, calc_size,
                                         num_stripes, sub_stripes);

        index = 0;
        while(index < num_stripes) {
                struct btrfs_stripe *stripe;
                BUG_ON(list_empty(&private_devs));
                cur = private_devs.next;
                device = list_entry(cur, struct btrfs_device, dev_alloc_list);

                /* loop over this device again if we're doing a dup group */
                if (!(type & BTRFS_BLOCK_GROUP_DUP) ||
                    (index == num_stripes - 1))
                        list_move_tail(&device->dev_alloc_list, dev_list);

                ret = btrfs_alloc_dev_extent(trans, device,
                             info->chunk_root->root_key.objectid,
                             BTRFS_FIRST_CHUNK_TREE_OBJECTID, key.offset,
                             calc_size, &dev_offset);
                BUG_ON(ret);
                device->bytes_used += calc_size;
                ret = btrfs_update_device(trans, device);
                BUG_ON(ret);

                map->stripes[index].dev = device;
                map->stripes[index].physical = dev_offset;
                stripe = stripes + index;
                btrfs_set_stack_stripe_devid(stripe, device->devid);
                btrfs_set_stack_stripe_offset(stripe, dev_offset);
                memcpy(stripe->dev_uuid, device->uuid, BTRFS_UUID_SIZE);
                physical = dev_offset;
                index++;
        }
        BUG_ON(!list_empty(&private_devs));

        /* key was set above */
        btrfs_set_stack_chunk_length(chunk, *num_bytes);
        btrfs_set_stack_chunk_owner(chunk, extent_root->root_key.objectid);
        btrfs_set_stack_chunk_stripe_len(chunk, stripe_len);
        btrfs_set_stack_chunk_type(chunk, type);
        btrfs_set_stack_chunk_num_stripes(chunk, num_stripes);
        btrfs_set_stack_chunk_io_align(chunk, stripe_len);
        btrfs_set_stack_chunk_io_width(chunk, stripe_len);
        btrfs_set_stack_chunk_sector_size(chunk, extent_root->sectorsize);
        btrfs_set_stack_chunk_sub_stripes(chunk, sub_stripes);
        map->sector_size = extent_root->sectorsize;
        map->stripe_len = stripe_len;
        map->io_align = stripe_len;
        map->io_width = stripe_len;
        map->type = type;
        map->num_stripes = num_stripes;
        map->sub_stripes = sub_stripes;

        ret = btrfs_insert_item(trans, chunk_root, &key, chunk,
                                btrfs_chunk_item_size(num_stripes));
        BUG_ON(ret);
        *start = key.offset;;

        em = alloc_extent_map(GFP_NOFS);
        if (!em)
                return -ENOMEM;
        em->bdev = (struct block_device *)map;
        em->start = key.offset;
        em->len = *num_bytes;
        em->block_start = 0;

        if (type & BTRFS_BLOCK_GROUP_SYSTEM) {
                ret = btrfs_add_system_chunk(trans, chunk_root, &key,
                                    chunk, btrfs_chunk_item_size(num_stripes));
                BUG_ON(ret);
        }
        kfree(chunk);

        em_tree = &extent_root->fs_info->mapping_tree.map_tree;
        spin_lock(&em_tree->lock);
        ret = add_extent_mapping(em_tree, em);
        spin_unlock(&em_tree->lock);
        BUG_ON(ret);
        free_extent_map(em);
        return ret;
}

void btrfs_mapping_init(struct btrfs_mapping_tree *tree)
{
        extent_map_tree_init(&tree->map_tree, GFP_NOFS);
}

void btrfs_mapping_tree_free(struct btrfs_mapping_tree *tree)
{
        struct extent_map *em;

        while(1) {
                spin_lock(&tree->map_tree.lock);
                em = lookup_extent_mapping(&tree->map_tree, 0, (u64)-1);
                if (em)
                        remove_extent_mapping(&tree->map_tree, em);
                spin_unlock(&tree->map_tree.lock);
                if (!em)
                        break;
                kfree(em->bdev);
                /* once for us */
                free_extent_map(em);
                /* once for the tree */
                free_extent_map(em);
        }
}

int btrfs_num_copies(struct btrfs_mapping_tree *map_tree, u64 logical, u64 len)
{
        struct extent_map *em;
        struct map_lookup *map;
        struct extent_map_tree *em_tree = &map_tree->map_tree;
        int ret;

        spin_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, logical, len);
        spin_unlock(&em_tree->lock);
        BUG_ON(!em);

        BUG_ON(em->start > logical || em->start + em->len < logical);
        map = (struct map_lookup *)em->bdev;
        if (map->type & (BTRFS_BLOCK_GROUP_DUP | BTRFS_BLOCK_GROUP_RAID1))
                ret = map->num_stripes;
        else if (map->type & BTRFS_BLOCK_GROUP_RAID10)
                ret = map->sub_stripes;
        else
                ret = 1;
        free_extent_map(em);
        return ret;
}

static int find_live_mirror(struct map_lookup *map, int first, int num,
                            int optimal)
{
        int i;
        if (map->stripes[optimal].dev->bdev)
                return optimal;
        for (i = first; i < first + num; i++) {
                if (map->stripes[i].dev->bdev)
                        return i;
        }
        /* we couldn't find one that doesn't fail.  Just return something
         * and the io error handling code will clean up eventually
         */
        return optimal;
}

static int __btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,
                             u64 logical, u64 *length,
                             struct btrfs_multi_bio **multi_ret,
                             int mirror_num, struct page *unplug_page)
{
        struct extent_map *em;
        struct map_lookup *map;
        struct extent_map_tree *em_tree = &map_tree->map_tree;
        u64 offset;
        u64 stripe_offset;
        u64 stripe_nr;
        int stripes_allocated = 8;
        int stripes_required = 1;
        int stripe_index;
        int i;
        int num_stripes;
        int max_errors = 0;
        struct btrfs_multi_bio *multi = NULL;

        if (multi_ret && !(rw & (1 << BIO_RW))) {
                stripes_allocated = 1;
        }
again:
        if (multi_ret) {
                multi = kzalloc(btrfs_multi_bio_size(stripes_allocated),
                                GFP_NOFS);
                if (!multi)
                        return -ENOMEM;

                atomic_set(&multi->error, 0);
        }

        spin_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, logical, *length);
        spin_unlock(&em_tree->lock);

        if (!em && unplug_page)
                return 0;

        if (!em) {
                printk("unable to find logical %Lu len %Lu\n", logical, *length);
                BUG();
        }

        BUG_ON(em->start > logical || em->start + em->len < logical);
        map = (struct map_lookup *)em->bdev;
        offset = logical - em->start;

        if (mirror_num > map->num_stripes)
                mirror_num = 0;

        /* if our multi bio struct is too small, back off and try again */
        if (rw & (1 << BIO_RW)) {
                if (map->type & (BTRFS_BLOCK_GROUP_RAID1 |
                                 BTRFS_BLOCK_GROUP_DUP)) {
                        stripes_required = map->num_stripes;
                        max_errors = 1;
                } else if (map->type & BTRFS_BLOCK_GROUP_RAID10) {
                        stripes_required = map->sub_stripes;
                        max_errors = 1;
                }
        }
        if (multi_ret && rw == WRITE &&
            stripes_allocated < stripes_required) {
                stripes_allocated = map->num_stripes;
                free_extent_map(em);
                kfree(multi);
                goto again;
        }
        stripe_nr = offset;
        /*
         * stripe_nr counts the total number of stripes we have to stride
         * to get to this block
         */
        do_div(stripe_nr, map->stripe_len);

        stripe_offset = stripe_nr * map->stripe_len;
        BUG_ON(offset < stripe_offset);

        /* stripe_offset is the offset of this block in its stripe*/
        stripe_offset = offset - stripe_offset;

        if (map->type & (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID1 |
                         BTRFS_BLOCK_GROUP_RAID10 |
                         BTRFS_BLOCK_GROUP_DUP)) {
                /* we limit the length of each bio to what fits in a stripe */
                *length = min_t(u64, em->len - offset,
                              map->stripe_len - stripe_offset);
        } else {
                *length = em->len - offset;
        }

        if (!multi_ret && !unplug_page)
                goto out;

        num_stripes = 1;
        stripe_index = 0;
        if (map->type & BTRFS_BLOCK_GROUP_RAID1) {
                if (unplug_page || (rw & (1 << BIO_RW)))
                        num_stripes = map->num_stripes;
                else if (mirror_num)
                        stripe_index = mirror_num - 1;
                else {
                        stripe_index = find_live_mirror(map, 0,
                                            map->num_stripes,
                                            current->pid % map->num_stripes);
                }

        } else if (map->type & BTRFS_BLOCK_GROUP_DUP) {
                if (rw & (1 << BIO_RW))
                        num_stripes = map->num_stripes;
                else if (mirror_num)
                        stripe_index = mirror_num - 1;

        } else if (map->type & BTRFS_BLOCK_GROUP_RAID10) {
                int factor = map->num_stripes / map->sub_stripes;

                stripe_index = do_div(stripe_nr, factor);
                stripe_index *= map->sub_stripes;

                if (unplug_page || (rw & (1 << BIO_RW)))
                        num_stripes = map->sub_stripes;
                else if (mirror_num)
                        stripe_index += mirror_num - 1;
                else {
                        stripe_index = find_live_mirror(map, stripe_index,
                                              map->sub_stripes, stripe_index +
                                              current->pid % map->sub_stripes);
                }
        } else {
                /*
                 * after this do_div call, stripe_nr is the number of stripes
                 * on this device we have to walk to find the data, and
                 * stripe_index is the number of our device in the stripe array
                 */
                stripe_index = do_div(stripe_nr, map->num_stripes);
        }
        BUG_ON(stripe_index >= map->num_stripes);

        for (i = 0; i < num_stripes; i++) {
                if (unplug_page) {
                        struct btrfs_device *device;
                        struct backing_dev_info *bdi;

                        device = map->stripes[stripe_index].dev;
                        if (device->bdev) {
                                bdi = blk_get_backing_dev_info(device->bdev);
                                if (bdi->unplug_io_fn) {
                                        bdi->unplug_io_fn(bdi, unplug_page);
                                }
                        }
                } else {
                        multi->stripes[i].physical =
                                map->stripes[stripe_index].physical +
                                stripe_offset + stripe_nr * map->stripe_len;
                        multi->stripes[i].dev = map->stripes[stripe_index].dev;
                }
                stripe_index++;
        }
        if (multi_ret) {
                *multi_ret = multi;
                multi->num_stripes = num_stripes;
                multi->max_errors = max_errors;
        }
out:
        free_extent_map(em);
        return 0;
}

int btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,
                      u64 logical, u64 *length,
                      struct btrfs_multi_bio **multi_ret, int mirror_num)
{
        return __btrfs_map_block(map_tree, rw, logical, length, multi_ret,
                                 mirror_num, NULL);
}

int btrfs_unplug_page(struct btrfs_mapping_tree *map_tree,
                      u64 logical, struct page *page)
{
        u64 length = PAGE_CACHE_SIZE;
        return __btrfs_map_block(map_tree, READ, logical, &length,
                                 NULL, 0, page);
}


#if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,23)
static void end_bio_multi_stripe(struct bio *bio, int err)
#else
static int end_bio_multi_stripe(struct bio *bio,
                                   unsigned int bytes_done, int err)
#endif
{
        struct btrfs_multi_bio *multi = bio->bi_private;

#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,23)
        if (bio->bi_size)
                return 1;
#endif
        if (err)
                atomic_inc(&multi->error);

        if (atomic_dec_and_test(&multi->stripes_pending)) {
                bio->bi_private = multi->private;
                bio->bi_end_io = multi->end_io;
                /* only send an error to the higher layers if it is
                 * beyond the tolerance of the multi-bio
                 */
                if (atomic_read(&multi->error) > multi->max_errors) {
                        err = -EIO;
                } else if (err) {
                        /*
                         * this bio is actually up to date, we didn't
                         * go over the max number of errors
                         */
                        set_bit(BIO_UPTODATE, &bio->bi_flags);
                        err = 0;
                }
                kfree(multi);

#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,23)
                bio_endio(bio, bio->bi_size, err);
#else
                bio_endio(bio, err);
#endif
        } else {
                bio_put(bio);
        }
#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,23)
        return 0;
#endif
}

struct async_sched {
        struct bio *bio;
        int rw;
        struct btrfs_fs_info *info;
        struct btrfs_work work;
};

/*
 * see run_scheduled_bios for a description of why bios are collected for
 * async submit.
 *
 * This will add one bio to the pending list for a device and make sure
 * the work struct is scheduled.
 */
int schedule_bio(struct btrfs_root *root, struct btrfs_device *device,
                 int rw, struct bio *bio)
{
        int should_queue = 1;

        /* don't bother with additional async steps for reads, right now */
        if (!(rw & (1 << BIO_RW))) {
                submit_bio(rw, bio);
                return 0;
        }

        /*
         * nr_async_sumbits allows us to reliably return congestion to the
         * higher layers.  Otherwise, the async bio makes it appear we have
         * made progress against dirty pages when we've really just put it
         * on a queue for later
         */
        atomic_inc(&root->fs_info->nr_async_submits);
        bio->bi_next = NULL;
        bio->bi_rw |= rw;

        spin_lock(&device->io_lock);

        if (device->pending_bio_tail)
                device->pending_bio_tail->bi_next = bio;

        device->pending_bio_tail = bio;
        if (!device->pending_bios)
                device->pending_bios = bio;
        if (device->running_pending)
                should_queue = 0;

        spin_unlock(&device->io_lock);

        if (should_queue)
                btrfs_queue_worker(&root->fs_info->submit_workers,
                                   &device->work);
        return 0;
}

int btrfs_map_bio(struct btrfs_root *root, int rw, struct bio *bio,
                  int mirror_num, int async_submit)
{
        struct btrfs_mapping_tree *map_tree;
        struct btrfs_device *dev;
        struct bio *first_bio = bio;
        u64 logical = bio->bi_sector << 9;
        u64 length = 0;
        u64 map_length;
        struct btrfs_multi_bio *multi = NULL;
        int ret;
        int dev_nr = 0;
        int total_devs = 1;

        length = bio->bi_size;
        map_tree = &root->fs_info->mapping_tree;
        map_length = length;

        ret = btrfs_map_block(map_tree, rw, logical, &map_length, &multi,
                              mirror_num);
        BUG_ON(ret);

        total_devs = multi->num_stripes;
        if (map_length < length) {
                printk("mapping failed logical %Lu bio len %Lu "
                       "len %Lu\n", logical, length, map_length);
                BUG();
        }
        multi->end_io = first_bio->bi_end_io;
        multi->private = first_bio->bi_private;
        atomic_set(&multi->stripes_pending, multi->num_stripes);

        while(dev_nr < total_devs) {
                if (total_devs > 1) {
                        if (dev_nr < total_devs - 1) {
                                bio = bio_clone(first_bio, GFP_NOFS);
                                BUG_ON(!bio);
                        } else {
                                bio = first_bio;
                        }
                        bio->bi_private = multi;
                        bio->bi_end_io = end_bio_multi_stripe;
                }
                bio->bi_sector = multi->stripes[dev_nr].physical >> 9;
                dev = multi->stripes[dev_nr].dev;
                if (dev && dev->bdev) {
                        bio->bi_bdev = dev->bdev;
                        if (async_submit)
                                schedule_bio(root, dev, rw, bio);
                        else
                                submit_bio(rw, bio);
                } else {
                        bio->bi_bdev = root->fs_info->fs_devices->latest_bdev;
                        bio->bi_sector = logical >> 9;
#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,23)
                        bio_endio(bio, bio->bi_size, -EIO);
#else
                        bio_endio(bio, -EIO);
#endif
                }
                dev_nr++;
        }
        if (total_devs == 1)
                kfree(multi);
        return 0;
}

struct btrfs_device *btrfs_find_device(struct btrfs_root *root, u64 devid,
                                       u8 *uuid)
{
        struct list_head *head = &root->fs_info->fs_devices->devices;

        return __find_device(head, devid, uuid);
}

static struct btrfs_device *add_missing_dev(struct btrfs_root *root,
                                            u64 devid, u8 *dev_uuid)
{
        struct btrfs_device *device;
        struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;

        device = kzalloc(sizeof(*device), GFP_NOFS);
        list_add(&device->dev_list,
                 &fs_devices->devices);
        list_add(&device->dev_alloc_list,
                 &fs_devices->alloc_list);
        device->barriers = 1;
        device->dev_root = root->fs_info->dev_root;
        device->devid = devid;
        device->work.func = pending_bios_fn;
        fs_devices->num_devices++;
        spin_lock_init(&device->io_lock);
        memcpy(device->uuid, dev_uuid, BTRFS_UUID_SIZE);
        return device;
}


static int read_one_chunk(struct btrfs_root *root, struct btrfs_key *key,
                          struct extent_buffer *leaf,
                          struct btrfs_chunk *chunk)
{
        struct btrfs_mapping_tree *map_tree = &root->fs_info->mapping_tree;
        struct map_lookup *map;
        struct extent_map *em;
        u64 logical;
        u64 length;
        u64 devid;
        u8 uuid[BTRFS_UUID_SIZE];
        int num_stripes;
        int ret;
        int i;

        logical = key->offset;
        length = btrfs_chunk_length(leaf, chunk);

        spin_lock(&map_tree->map_tree.lock);
        em = lookup_extent_mapping(&map_tree->map_tree, logical, 1);
        spin_unlock(&map_tree->map_tree.lock);

        /* already mapped? */
        if (em && em->start <= logical && em->start + em->len > logical) {
                free_extent_map(em);
                return 0;
        } else if (em) {
                free_extent_map(em);
        }

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

        em = alloc_extent_map(GFP_NOFS);
        if (!em)
                return -ENOMEM;
        num_stripes = btrfs_chunk_num_stripes(leaf, chunk);
        map = kmalloc(map_lookup_size(num_stripes), GFP_NOFS);
        if (!map) {
                free_extent_map(em);
                return -ENOMEM;
        }

        em->bdev = (struct block_device *)map;
        em->start = logical;
        em->len = length;
        em->block_start = 0;

        map->num_stripes = num_stripes;
        map->io_width = btrfs_chunk_io_width(leaf, chunk);
        map->io_align = btrfs_chunk_io_align(leaf, chunk);
        map->sector_size = btrfs_chunk_sector_size(leaf, chunk);
        map->stripe_len = btrfs_chunk_stripe_len(leaf, chunk);
        map->type = btrfs_chunk_type(leaf, chunk);
        map->sub_stripes = btrfs_chunk_sub_stripes(leaf, chunk);
        for (i = 0; i < num_stripes; i++) {
                map->stripes[i].physical =
                        btrfs_stripe_offset_nr(leaf, chunk, i);
                devid = btrfs_stripe_devid_nr(leaf, chunk, i);
                read_extent_buffer(leaf, uuid, (unsigned long)
                                   btrfs_stripe_dev_uuid_nr(chunk, i),
                                   BTRFS_UUID_SIZE);
                map->stripes[i].dev = btrfs_find_device(root, devid, uuid);

                if (!map->stripes[i].dev && !btrfs_test_opt(root, DEGRADED)) {
                        kfree(map);
                        free_extent_map(em);
                        return -EIO;
                }
                if (!map->stripes[i].dev) {
                        map->stripes[i].dev =
                                add_missing_dev(root, devid, uuid);
                        if (!map->stripes[i].dev) {
                                kfree(map);
                                free_extent_map(em);
                                return -EIO;
                        }
                }
                map->stripes[i].dev->in_fs_metadata = 1;
        }

        spin_lock(&map_tree->map_tree.lock);
        ret = add_extent_mapping(&map_tree->map_tree, em);
        spin_unlock(&map_tree->map_tree.lock);
        BUG_ON(ret);
        free_extent_map(em);

        return 0;
}

static int fill_device_from_item(struct extent_buffer *leaf,
                                 struct btrfs_dev_item *dev_item,
                                 struct btrfs_device *device)
{
        unsigned long ptr;

        device->devid = btrfs_device_id(leaf, dev_item);
        device->total_bytes = btrfs_device_total_bytes(leaf, dev_item);
        device->bytes_used = btrfs_device_bytes_used(leaf, dev_item);
        device->type = btrfs_device_type(leaf, dev_item);
        device->io_align = btrfs_device_io_align(leaf, dev_item);
        device->io_width = btrfs_device_io_width(leaf, dev_item);
        device->sector_size = btrfs_device_sector_size(leaf, dev_item);

        ptr = (unsigned long)btrfs_device_uuid(dev_item);
        read_extent_buffer(leaf, device->uuid, ptr, BTRFS_UUID_SIZE);

        return 0;
}

static int read_one_dev(struct btrfs_root *root,
                        struct extent_buffer *leaf,
                        struct btrfs_dev_item *dev_item)
{
        struct btrfs_device *device;
        u64 devid;
        int ret;
        u8 dev_uuid[BTRFS_UUID_SIZE];

        devid = btrfs_device_id(leaf, dev_item);
        read_extent_buffer(leaf, dev_uuid,
                           (unsigned long)btrfs_device_uuid(dev_item),
                           BTRFS_UUID_SIZE);
        device = btrfs_find_device(root, devid, dev_uuid);
        if (!device) {
                printk("warning devid %Lu missing\n", devid);
                device = add_missing_dev(root, devid, dev_uuid);
                if (!device)
                        return -ENOMEM;
        }

        fill_device_from_item(leaf, dev_item, device);
        device->dev_root = root->fs_info->dev_root;
        device->in_fs_metadata = 1;
        ret = 0;
#if 0
        ret = btrfs_open_device(device);
        if (ret) {
                kfree(device);
        }
#endif
        return ret;
}

int btrfs_read_super_device(struct btrfs_root *root, struct extent_buffer *buf)
{
        struct btrfs_dev_item *dev_item;

        dev_item = (struct btrfs_dev_item *)offsetof(struct btrfs_super_block,
                                                     dev_item);
        return read_one_dev(root, buf, dev_item);
}

int btrfs_read_sys_array(struct btrfs_root *root)
{
        struct btrfs_super_block *super_copy = &root->fs_info->super_copy;
        struct extent_buffer *sb;
        struct btrfs_disk_key *disk_key;
        struct btrfs_chunk *chunk;
        u8 *ptr;
        unsigned long sb_ptr;
        int ret = 0;
        u32 num_stripes;
        u32 array_size;
        u32 len = 0;
        u32 cur;
        struct btrfs_key key;

        sb = btrfs_find_create_tree_block(root, BTRFS_SUPER_INFO_OFFSET,
                                          BTRFS_SUPER_INFO_SIZE);
        if (!sb)
                return -ENOMEM;
        btrfs_set_buffer_uptodate(sb);
        write_extent_buffer(sb, super_copy, 0, BTRFS_SUPER_INFO_SIZE);
        array_size = btrfs_super_sys_array_size(super_copy);

        ptr = super_copy->sys_chunk_array;
        sb_ptr = offsetof(struct btrfs_super_block, sys_chunk_array);
        cur = 0;

        while (cur < array_size) {
                disk_key = (struct btrfs_disk_key *)ptr;
                btrfs_disk_key_to_cpu(&key, disk_key);

                len = sizeof(*disk_key); ptr += len;
                sb_ptr += len;
                cur += len;

                if (key.type == BTRFS_CHUNK_ITEM_KEY) {
                        chunk = (struct btrfs_chunk *)sb_ptr;
                        ret = read_one_chunk(root, &key, sb, chunk);
                        if (ret)
                                break;
                        num_stripes = btrfs_chunk_num_stripes(sb, chunk);
                        len = btrfs_chunk_item_size(num_stripes);
                } else {
                        ret = -EIO;
                        break;
                }
                ptr += len;
                sb_ptr += len;
                cur += len;
        }
        free_extent_buffer(sb);
        return ret;
}

int btrfs_read_chunk_tree(struct btrfs_root *root)
{
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_key key;
        struct btrfs_key found_key;
        int ret;
        int slot;

        root = root->fs_info->chunk_root;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        /* first we search for all of the device items, and then we
         * read in all of the chunk items.  This way we can create chunk
         * mappings that reference all of the devices that are afound
         */
        key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
        key.offset = 0;
        key.type = 0;
again:
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        while(1) {
                leaf = path->nodes[0];
                slot = path->slots[0];
                if (slot >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret == 0)
                                continue;
                        if (ret < 0)
                                goto error;
                        break;
                }
                btrfs_item_key_to_cpu(leaf, &found_key, slot);
                if (key.objectid == BTRFS_DEV_ITEMS_OBJECTID) {
                        if (found_key.objectid != BTRFS_DEV_ITEMS_OBJECTID)
                                break;
                        if (found_key.type == BTRFS_DEV_ITEM_KEY) {
                                struct btrfs_dev_item *dev_item;
                                dev_item = btrfs_item_ptr(leaf, slot,
                                                  struct btrfs_dev_item);
                                ret = read_one_dev(root, leaf, dev_item);
                                BUG_ON(ret);
                        }
                } else if (found_key.type == BTRFS_CHUNK_ITEM_KEY) {
                        struct btrfs_chunk *chunk;
                        chunk = btrfs_item_ptr(leaf, slot, struct btrfs_chunk);
                        ret = read_one_chunk(root, &found_key, leaf, chunk);
                }
                path->slots[0]++;
        }
        if (key.objectid == BTRFS_DEV_ITEMS_OBJECTID) {
                key.objectid = 0;
                btrfs_release_path(root, path);
                goto again;
        }

        btrfs_free_path(path);
        ret = 0;
error:
        return ret;
}