Merge branch 'common/pfc' into sh-latest

[~andy/linux] / 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/slab.h>
#include <linux/buffer_head.h>
#include <linux/blkdev.h>
#include <linux/random.h>
#include <linux/iocontext.h>
#include <linux/capability.h>
#include <linux/ratelimit.h>
#include <linux/kthread.h>
#include <asm/div64.h>
#include "compat.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"
#include "check-integrity.h"
#include "rcu-string.h"

static int init_first_rw_device(struct btrfs_trans_handle *trans,
                                struct btrfs_root *root,
                                struct btrfs_device *device);
static int btrfs_relocate_sys_chunks(struct btrfs_root *root);
static void __btrfs_reset_dev_stats(struct btrfs_device *dev);
static void btrfs_dev_stat_print_on_load(struct btrfs_device *device);

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

static void lock_chunks(struct btrfs_root *root)
{
        mutex_lock(&root->fs_info->chunk_mutex);
}

static void unlock_chunks(struct btrfs_root *root)
{
        mutex_unlock(&root->fs_info->chunk_mutex);
}

static void free_fs_devices(struct btrfs_fs_devices *fs_devices)
{
        struct btrfs_device *device;
        WARN_ON(fs_devices->opened);
        while (!list_empty(&fs_devices->devices)) {
                device = list_entry(fs_devices->devices.next,
                                    struct btrfs_device, dev_list);
                list_del(&device->dev_list);
                rcu_string_free(device->name);
                kfree(device);
        }
        kfree(fs_devices);
}

void btrfs_cleanup_fs_uuids(void)
{
        struct btrfs_fs_devices *fs_devices;

        while (!list_empty(&fs_uuids)) {
                fs_devices = list_entry(fs_uuids.next,
                                        struct btrfs_fs_devices, list);
                list_del(&fs_devices->list);
                free_fs_devices(fs_devices);
        }
}

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

        list_for_each_entry(dev, head, dev_list) {
                if (dev->devid == devid &&
                    (!uuid || !memcmp(dev->uuid, uuid, BTRFS_UUID_SIZE))) {
                        return dev;
                }
        }
        return NULL;
}

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

        list_for_each_entry(fs_devices, &fs_uuids, list) {
                if (memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE) == 0)
                        return fs_devices;
        }
        return NULL;
}

static void requeue_list(struct btrfs_pending_bios *pending_bios,
                        struct bio *head, struct bio *tail)
{

        struct bio *old_head;

        old_head = pending_bios->head;
        pending_bios->head = head;
        if (pending_bios->tail)
                tail->bi_next = old_head;
        else
                pending_bios->tail = tail;
}

/*
 * 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.
 */
static noinline void run_scheduled_bios(struct btrfs_device *device)
{
        struct bio *pending;
        struct backing_dev_info *bdi;
        struct btrfs_fs_info *fs_info;
        struct btrfs_pending_bios *pending_bios;
        struct bio *tail;
        struct bio *cur;
        int again = 0;
        unsigned long num_run;
        unsigned long batch_run = 0;
        unsigned long limit;
        unsigned long last_waited = 0;
        int force_reg = 0;
        int sync_pending = 0;
        struct blk_plug plug;

        /*
         * this function runs all the bios we've collected for
         * a particular device.  We don't want to wander off to
         * another device without first sending all of these down.
         * So, setup a plug here and finish it off before we return
         */
        blk_start_plug(&plug);

        bdi = blk_get_backing_dev_info(device->bdev);
        fs_info = device->dev_root->fs_info;
        limit = btrfs_async_submit_limit(fs_info);
        limit = limit * 2 / 3;

loop:
        spin_lock(&device->io_lock);

loop_lock:
        num_run = 0;

        /* 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
         */
        if (!force_reg && device->pending_sync_bios.head) {
                pending_bios = &device->pending_sync_bios;
                force_reg = 1;
        } else {
                pending_bios = &device->pending_bios;
                force_reg = 0;
        }

        pending = pending_bios->head;
        tail = pending_bios->tail;
        WARN_ON(pending && !tail);

        /*
         * 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 (device->pending_sync_bios.head == NULL &&
            device->pending_bios.head == NULL) {
                again = 0;
                device->running_pending = 0;
        } else {
                again = 1;
                device->running_pending = 1;
        }

        pending_bios->head = NULL;
        pending_bios->tail = NULL;

        spin_unlock(&device->io_lock);

        while (pending) {

                rmb();
                /* we want to work on both lists, but do more bios on the
                 * sync list than the regular list
                 */
                if ((num_run > 32 &&
                    pending_bios != &device->pending_sync_bios &&
                    device->pending_sync_bios.head) ||
                   (num_run > 64 && pending_bios == &device->pending_sync_bios &&
                    device->pending_bios.head)) {
                        spin_lock(&device->io_lock);
                        requeue_list(pending_bios, pending, tail);
                        goto loop_lock;
                }

                cur = pending;
                pending = pending->bi_next;
                cur->bi_next = NULL;
                atomic_dec(&fs_info->nr_async_bios);

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

                BUG_ON(atomic_read(&cur->bi_cnt) == 0);

                /*
                 * if we're doing the sync list, record that our
                 * plug has some sync requests on it
                 *
                 * If we're doing the regular list and there are
                 * sync requests sitting around, unplug before
                 * we add more
                 */
                if (pending_bios == &device->pending_sync_bios) {
                        sync_pending = 1;
                } else if (sync_pending) {
                        blk_finish_plug(&plug);
                        blk_start_plug(&plug);
                        sync_pending = 0;
                }

                btrfsic_submit_bio(cur->bi_rw, cur);
                num_run++;
                batch_run++;
                if (need_resched())
                        cond_resched();

                /*
                 * 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 && bdi_write_congested(bdi) && batch_run > 8 &&
                    fs_info->fs_devices->open_devices > 1) {
                        struct io_context *ioc;

                        ioc = current->io_context;

                        /*
                         * the main goal here is that we don't want to
                         * block if we're going to be able to submit
                         * more requests without blocking.
                         *
                         * This code does two great things, it pokes into
                         * the elevator code from a filesystem _and_
                         * it makes assumptions about how batching works.
                         */
                        if (ioc && ioc->nr_batch_requests > 0 &&
                            time_before(jiffies, ioc->last_waited + HZ/50UL) &&
                            (last_waited == 0 ||
                             ioc->last_waited == last_waited)) {
                                /*
                                 * we want to go through our batch of
                                 * requests and stop.  So, we copy out
                                 * the ioc->last_waited time and test
                                 * against it before looping
                                 */
                                last_waited = ioc->last_waited;
                                if (need_resched())
                                        cond_resched();
                                continue;
                        }
                        spin_lock(&device->io_lock);
                        requeue_list(pending_bios, pending, tail);
                        device->running_pending = 1;

                        spin_unlock(&device->io_lock);
                        btrfs_requeue_work(&device->work);
                        goto done;
                }
                /* unplug every 64 requests just for good measure */
                if (batch_run % 64 == 0) {
                        blk_finish_plug(&plug);
                        blk_start_plug(&plug);
                        sync_pending = 0;
                }
        }

        cond_resched();
        if (again)
                goto loop;

        spin_lock(&device->io_lock);
        if (device->pending_bios.head || device->pending_sync_bios.head)
                goto loop_lock;
        spin_unlock(&device->io_lock);

done:
        blk_finish_plug(&plug);
}

static 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 noinline 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;
        struct rcu_string *name;
        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;
                mutex_init(&fs_devices->device_list_mutex);
                device = NULL;
        } else {
                device = __find_device(&fs_devices->devices, devid,
                                       disk_super->dev_item.uuid);
        }
        if (!device) {
                if (fs_devices->opened)
                        return -EBUSY;

                device = kzalloc(sizeof(*device), GFP_NOFS);
                if (!device) {
                        /* we can safely leave the fs_devices entry around */
                        return -ENOMEM;
                }
                device->devid = devid;
                device->dev_stats_valid = 0;
                device->work.func = pending_bios_fn;
                memcpy(device->uuid, disk_super->dev_item.uuid,
                       BTRFS_UUID_SIZE);
                spin_lock_init(&device->io_lock);

                name = rcu_string_strdup(path, GFP_NOFS);
                if (!name) {
                        kfree(device);
                        return -ENOMEM;
                }
                rcu_assign_pointer(device->name, name);
                INIT_LIST_HEAD(&device->dev_alloc_list);

                /* init readahead state */
                spin_lock_init(&device->reada_lock);
                device->reada_curr_zone = NULL;
                atomic_set(&device->reada_in_flight, 0);
                device->reada_next = 0;
                INIT_RADIX_TREE(&device->reada_zones, GFP_NOFS & ~__GFP_WAIT);
                INIT_RADIX_TREE(&device->reada_extents, GFP_NOFS & ~__GFP_WAIT);

                mutex_lock(&fs_devices->device_list_mutex);
                list_add_rcu(&device->dev_list, &fs_devices->devices);
                mutex_unlock(&fs_devices->device_list_mutex);

                device->fs_devices = fs_devices;
                fs_devices->num_devices++;
        } else if (!device->name || strcmp(device->name->str, path)) {
                name = rcu_string_strdup(path, GFP_NOFS);
                if (!name)
                        return -ENOMEM;
                rcu_string_free(device->name);
                rcu_assign_pointer(device->name, name);
                if (device->missing) {
                        fs_devices->missing_devices--;
                        device->missing = 0;
                }
        }

        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;
}

static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig)
{
        struct btrfs_fs_devices *fs_devices;
        struct btrfs_device *device;
        struct btrfs_device *orig_dev;

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

        INIT_LIST_HEAD(&fs_devices->devices);
        INIT_LIST_HEAD(&fs_devices->alloc_list);
        INIT_LIST_HEAD(&fs_devices->list);
        mutex_init(&fs_devices->device_list_mutex);
        fs_devices->latest_devid = orig->latest_devid;
        fs_devices->latest_trans = orig->latest_trans;
        memcpy(fs_devices->fsid, orig->fsid, sizeof(fs_devices->fsid));

        /* We have held the volume lock, it is safe to get the devices. */
        list_for_each_entry(orig_dev, &orig->devices, dev_list) {
                struct rcu_string *name;

                device = kzalloc(sizeof(*device), GFP_NOFS);
                if (!device)
                        goto error;

                /*
                 * This is ok to do without rcu read locked because we hold the
                 * uuid mutex so nothing we touch in here is going to disappear.
                 */
                name = rcu_string_strdup(orig_dev->name->str, GFP_NOFS);
                if (!name) {
                        kfree(device);
                        goto error;
                }
                rcu_assign_pointer(device->name, name);

                device->devid = orig_dev->devid;
                device->work.func = pending_bios_fn;
                memcpy(device->uuid, orig_dev->uuid, sizeof(device->uuid));
                spin_lock_init(&device->io_lock);
                INIT_LIST_HEAD(&device->dev_list);
                INIT_LIST_HEAD(&device->dev_alloc_list);

                list_add(&device->dev_list, &fs_devices->devices);
                device->fs_devices = fs_devices;
                fs_devices->num_devices++;
        }
        return fs_devices;
error:
        free_fs_devices(fs_devices);
        return ERR_PTR(-ENOMEM);
}

void btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices)
{
        struct btrfs_device *device, *next;

        struct block_device *latest_bdev = NULL;
        u64 latest_devid = 0;
        u64 latest_transid = 0;

        mutex_lock(&uuid_mutex);
again:
        /* This is the initialized path, it is safe to release the devices. */
        list_for_each_entry_safe(device, next, &fs_devices->devices, dev_list) {
                if (device->in_fs_metadata) {
                        if (!latest_transid ||
                            device->generation > latest_transid) {
                                latest_devid = device->devid;
                                latest_transid = device->generation;
                                latest_bdev = device->bdev;
                        }
                        continue;
                }

                if (device->bdev) {
                        blkdev_put(device->bdev, device->mode);
                        device->bdev = NULL;
                        fs_devices->open_devices--;
                }
                if (device->writeable) {
                        list_del_init(&device->dev_alloc_list);
                        device->writeable = 0;
                        fs_devices->rw_devices--;
                }
                list_del_init(&device->dev_list);
                fs_devices->num_devices--;
                rcu_string_free(device->name);
                kfree(device);
        }

        if (fs_devices->seed) {
                fs_devices = fs_devices->seed;
                goto again;
        }

        fs_devices->latest_bdev = latest_bdev;
        fs_devices->latest_devid = latest_devid;
        fs_devices->latest_trans = latest_transid;

        mutex_unlock(&uuid_mutex);
}

static void __free_device(struct work_struct *work)
{
        struct btrfs_device *device;

        device = container_of(work, struct btrfs_device, rcu_work);

        if (device->bdev)
                blkdev_put(device->bdev, device->mode);

        rcu_string_free(device->name);
        kfree(device);
}

static void free_device(struct rcu_head *head)
{
        struct btrfs_device *device;

        device = container_of(head, struct btrfs_device, rcu);

        INIT_WORK(&device->rcu_work, __free_device);
        schedule_work(&device->rcu_work);
}

static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
{
        struct btrfs_device *device;

        if (--fs_devices->opened > 0)
                return 0;

        mutex_lock(&fs_devices->device_list_mutex);
        list_for_each_entry(device, &fs_devices->devices, dev_list) {
                struct btrfs_device *new_device;
                struct rcu_string *name;

                if (device->bdev)
                        fs_devices->open_devices--;

                if (device->writeable) {
                        list_del_init(&device->dev_alloc_list);
                        fs_devices->rw_devices--;
                }

                if (device->can_discard)
                        fs_devices->num_can_discard--;

                new_device = kmalloc(sizeof(*new_device), GFP_NOFS);
                BUG_ON(!new_device); /* -ENOMEM */
                memcpy(new_device, device, sizeof(*new_device));

                /* Safe because we are under uuid_mutex */
                name = rcu_string_strdup(device->name->str, GFP_NOFS);
                BUG_ON(device->name && !name); /* -ENOMEM */
                rcu_assign_pointer(new_device->name, name);
                new_device->bdev = NULL;
                new_device->writeable = 0;
                new_device->in_fs_metadata = 0;
                new_device->can_discard = 0;
                list_replace_rcu(&device->dev_list, &new_device->dev_list);

                call_rcu(&device->rcu, free_device);
        }
        mutex_unlock(&fs_devices->device_list_mutex);

        WARN_ON(fs_devices->open_devices);
        WARN_ON(fs_devices->rw_devices);
        fs_devices->opened = 0;
        fs_devices->seeding = 0;

        return 0;
}

int btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
{
        struct btrfs_fs_devices *seed_devices = NULL;
        int ret;

        mutex_lock(&uuid_mutex);
        ret = __btrfs_close_devices(fs_devices);
        if (!fs_devices->opened) {
                seed_devices = fs_devices->seed;
                fs_devices->seed = NULL;
        }
        mutex_unlock(&uuid_mutex);

        while (seed_devices) {
                fs_devices = seed_devices;
                seed_devices = fs_devices->seed;
                __btrfs_close_devices(fs_devices);
                free_fs_devices(fs_devices);
        }
        return ret;
}

static int __btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
                                fmode_t flags, void *holder)
{
        struct request_queue *q;
        struct block_device *bdev;
        struct list_head *head = &fs_devices->devices;
        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 devid;
        int seeding = 1;
        int ret = 0;

        flags |= FMODE_EXCL;

        list_for_each_entry(device, head, dev_list) {
                if (device->bdev)
                        continue;
                if (!device->name)
                        continue;

                bdev = blkdev_get_by_path(device->name->str, flags, holder);
                if (IS_ERR(bdev)) {
                        printk(KERN_INFO "open %s failed\n", device->name->str);
                        goto error;
                }
                filemap_write_and_wait(bdev->bd_inode->i_mapping);
                invalidate_bdev(bdev);
                set_blocksize(bdev, 4096);

                bh = btrfs_read_dev_super(bdev);
                if (!bh)
                        goto error_close;

                disk_super = (struct btrfs_super_block *)bh->b_data;
                devid = btrfs_stack_device_id(&disk_super->dev_item);
                if (devid != device->devid)
                        goto error_brelse;

                if (memcmp(device->uuid, disk_super->dev_item.uuid,
                           BTRFS_UUID_SIZE))
                        goto error_brelse;

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

                if (btrfs_super_flags(disk_super) & BTRFS_SUPER_FLAG_SEEDING) {
                        device->writeable = 0;
                } else {
                        device->writeable = !bdev_read_only(bdev);
                        seeding = 0;
                }

                q = bdev_get_queue(bdev);
                if (blk_queue_discard(q)) {
                        device->can_discard = 1;
                        fs_devices->num_can_discard++;
                }

                device->bdev = bdev;
                device->in_fs_metadata = 0;
                device->mode = flags;

                if (!blk_queue_nonrot(bdev_get_queue(bdev)))
                        fs_devices->rotating = 1;

                fs_devices->open_devices++;
                if (device->writeable) {
                        fs_devices->rw_devices++;
                        list_add(&device->dev_alloc_list,
                                 &fs_devices->alloc_list);
                }
                brelse(bh);
                continue;

error_brelse:
                brelse(bh);
error_close:
                blkdev_put(bdev, flags);
error:
                continue;
        }
        if (fs_devices->open_devices == 0) {
                ret = -EINVAL;
                goto out;
        }
        fs_devices->seeding = seeding;
        fs_devices->opened = 1;
        fs_devices->latest_bdev = latest_bdev;
        fs_devices->latest_devid = latest_devid;
        fs_devices->latest_trans = latest_transid;
        fs_devices->total_rw_bytes = 0;
out:
        return ret;
}

int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
                       fmode_t flags, void *holder)
{
        int ret;

        mutex_lock(&uuid_mutex);
        if (fs_devices->opened) {
                fs_devices->opened++;
                ret = 0;
        } else {
                ret = __btrfs_open_devices(fs_devices, flags, holder);
        }
        mutex_unlock(&uuid_mutex);
        return ret;
}

int btrfs_scan_one_device(const char *path, fmode_t 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;

        flags |= FMODE_EXCL;
        bdev = blkdev_get_by_path(path, flags, holder);

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

        mutex_lock(&uuid_mutex);
        ret = set_blocksize(bdev, 4096);
        if (ret)
                goto error_close;
        bh = btrfs_read_dev_super(bdev);
        if (!bh) {
                ret = -EINVAL;
                goto error_close;
        }
        disk_super = (struct btrfs_super_block *)bh->b_data;
        devid = btrfs_stack_device_id(&disk_super->dev_item);
        transid = btrfs_super_generation(disk_super);
        if (disk_super->label[0])
                printk(KERN_INFO "device label %s ", disk_super->label);
        else
                printk(KERN_INFO "device fsid %pU ", disk_super->fsid);
        printk(KERN_CONT "devid %llu transid %llu %s\n",
               (unsigned long long)devid, (unsigned long long)transid, path);
        ret = device_list_add(path, disk_super, devid, fs_devices_ret);

        brelse(bh);
error_close:
        mutex_unlock(&uuid_mutex);
        blkdev_put(bdev, flags);
error:
        return ret;
}

/* helper to account the used device space in the range */
int btrfs_account_dev_extents_size(struct btrfs_device *device, u64 start,
                                   u64 end, u64 *length)
{
        struct btrfs_key key;
        struct btrfs_root *root = device->dev_root;
        struct btrfs_dev_extent *dev_extent;
        struct btrfs_path *path;
        u64 extent_end;
        int ret;
        int slot;
        struct extent_buffer *l;

        *length = 0;

        if (start >= device->total_bytes)
                return 0;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
        path->reada = 2;

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

        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto out;
        if (ret > 0) {
                ret = btrfs_previous_item(root, path, key.objectid, key.type);
                if (ret < 0)
                        goto out;
        }

        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 out;

                        break;
                }
                btrfs_item_key_to_cpu(l, &key, slot);

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

                if (key.objectid > device->devid)
                        break;

                if (btrfs_key_type(&key) != BTRFS_DEV_EXTENT_KEY)
                        goto next;

                dev_extent = btrfs_item_ptr(l, slot, struct btrfs_dev_extent);
                extent_end = key.offset + btrfs_dev_extent_length(l,
                                                                  dev_extent);
                if (key.offset <= start && extent_end > end) {
                        *length = end - start + 1;
                        break;
                } else if (key.offset <= start && extent_end > start)
                        *length += extent_end - start;
                else if (key.offset > start && extent_end <= end)
                        *length += extent_end - key.offset;
                else if (key.offset > start && key.offset <= end) {
                        *length += end - key.offset + 1;
                        break;
                } else if (key.offset > end)
                        break;

next:
                path->slots[0]++;
        }
        ret = 0;
out:
        btrfs_free_path(path);
        return ret;
}

/*
 * find_free_dev_extent - find free space in the specified device
 * @device:     the device which we search the free space in
 * @num_bytes:  the size of the free space that we need
 * @start:      store the start of the free space.
 * @len:        the size of the free space. that we find, or the size of the max
 *              free space if we don't find suitable free space
 *
 * 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
 *
 * @start is used to store the start of the free space if we find. But if we
 * don't find suitable free space, it will be used to store the start position
 * of the max free space.
 *
 * @len is used to store the size of the free space that we find.
 * But if we don't find suitable free space, it is used to store the size of
 * the max free space.
 */
int find_free_dev_extent(struct btrfs_device *device, u64 num_bytes,
                         u64 *start, u64 *len)
{
        struct btrfs_key key;
        struct btrfs_root *root = device->dev_root;
        struct btrfs_dev_extent *dev_extent;
        struct btrfs_path *path;
        u64 hole_size;
        u64 max_hole_start;
        u64 max_hole_size;
        u64 extent_end;
        u64 search_start;
        u64 search_end = device->total_bytes;
        int ret;
        int slot;
        struct extent_buffer *l;

        /* 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(root->fs_info->alloc_start, 1024ull * 1024);

        max_hole_start = search_start;
        max_hole_size = 0;
        hole_size = 0;

        if (search_start >= search_end) {
                ret = -ENOSPC;
                goto error;
        }

        path = btrfs_alloc_path();
        if (!path) {
                ret = -ENOMEM;
                goto error;
        }
        path->reada = 2;

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

        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto out;
        if (ret > 0) {
                ret = btrfs_previous_item(root, path, key.objectid, key.type);
                if (ret < 0)
                        goto out;
        }

        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 out;

                        break;
                }
                btrfs_item_key_to_cpu(l, &key, slot);

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

                if (key.objectid > device->devid)
                        break;

                if (btrfs_key_type(&key) != BTRFS_DEV_EXTENT_KEY)
                        goto next;

                if (key.offset > search_start) {
                        hole_size = key.offset - search_start;

                        if (hole_size > max_hole_size) {
                                max_hole_start = search_start;
                                max_hole_size = hole_size;
                        }

                        /*
                         * If this free space is greater than which we need,
                         * it must be the max free space that we have found
                         * until now, so max_hole_start must point to the start
                         * of this free space and the length of this free space
                         * is stored in max_hole_size. Thus, we return
                         * max_hole_start and max_hole_size and go back to the
                         * caller.
                         */
                        if (hole_size >= num_bytes) {
                                ret = 0;
                                goto out;
                        }
                }

                dev_extent = btrfs_item_ptr(l, slot, struct btrfs_dev_extent);
                extent_end = key.offset + btrfs_dev_extent_length(l,
                                                                  dev_extent);
                if (extent_end > search_start)
                        search_start = extent_end;
next:
                path->slots[0]++;
                cond_resched();
        }

        /*
         * At this point, search_start should be the end of
         * allocated dev extents, and when shrinking the device,
         * search_end may be smaller than search_start.
         */
        if (search_end > search_start)
                hole_size = search_end - search_start;

        if (hole_size > max_hole_size) {
                max_hole_start = search_start;
                max_hole_size = hole_size;
        }

        /* See above. */
        if (hole_size < num_bytes)
                ret = -ENOSPC;
        else
                ret = 0;

out:
        btrfs_free_path(path);
error:
        *start = max_hole_start;
        if (len)
                *len = max_hole_size;
        return ret;
}

static 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;
again:
        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);
                if (ret)
                        goto out;
                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);
                key = found_key;
                btrfs_release_path(path);
                goto again;
        } else if (ret == 0) {
                leaf = path->nodes[0];
                extent = btrfs_item_ptr(leaf, path->slots[0],
                                        struct btrfs_dev_extent);
        } else {
                btrfs_error(root->fs_info, ret, "Slot search failed");
                goto out;
        }

        if (device->bytes_used > 0) {
                u64 len = btrfs_dev_extent_length(leaf, extent);
                device->bytes_used -= len;
                spin_lock(&root->fs_info->free_chunk_lock);
                root->fs_info->free_chunk_space += len;
                spin_unlock(&root->fs_info->free_chunk_lock);
        }
        ret = btrfs_del_item(trans, root, path);
        if (ret) {
                btrfs_error(root->fs_info, ret,
                            "Failed to remove dev extent item");
        }
out:
        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 start, u64 num_bytes)
{
        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;

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

        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);
out:
        btrfs_free_path(path);
        return ret;
}

static noinline 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();
        if (!path)
                return -ENOMEM;

        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); /* Corruption */

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

        root = 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 = (u64)-1;

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

        BUG_ON(ret == 0); /* Corruption */

        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_free_path(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;

        root = 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_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);

        btrfs_set_device_id(leaf, dev_item, device->devid);
        btrfs_set_device_generation(leaf, dev_item, 0);
        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);
        btrfs_set_device_start_offset(leaf, dev_item, 0);

        ptr = (unsigned long)btrfs_device_uuid(dev_item);
        write_extent_buffer(leaf, device->uuid, ptr, BTRFS_UUID_SIZE);
        ptr = (unsigned long)btrfs_device_fsid(dev_item);
        write_extent_buffer(leaf, root->fs_info->fsid, 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 btrfs_key key;
        struct btrfs_trans_handle *trans;

        root = root->fs_info->chunk_root;

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

        trans = btrfs_start_transaction(root, 0);
        if (IS_ERR(trans)) {
                btrfs_free_path(path);
                return PTR_ERR(trans);
        }
        key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
        key.type = BTRFS_DEV_ITEM_KEY;
        key.offset = device->devid;
        lock_chunks(root);

        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;
out:
        btrfs_free_path(path);
        unlock_chunks(root);
        btrfs_commit_transaction(trans, root);
        return ret;
}

int btrfs_rm_device(struct btrfs_root *root, char *device_path)
{
        struct btrfs_device *device;
        struct btrfs_device *next_device;
        struct block_device *bdev;
        struct buffer_head *bh = NULL;
        struct btrfs_super_block *disk_super;
        struct btrfs_fs_devices *cur_devices;
        u64 all_avail;
        u64 devid;
        u64 num_devices;
        u8 *dev_uuid;
        int ret = 0;
        bool clear_super = false;

        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) &&
            root->fs_info->fs_devices->num_devices <= 4) {
                printk(KERN_ERR "btrfs: unable to go below four devices "
                       "on raid10\n");
                ret = -EINVAL;
                goto out;
        }

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

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

                device = NULL;
                devices = &root->fs_info->fs_devices->devices;
                /*
                 * It is safe to read the devices since the volume_mutex
                 * is held.
                 */
                list_for_each_entry(tmp, devices, dev_list) {
                        if (tmp->in_fs_metadata && !tmp->bdev) {
                                device = tmp;
                                break;
                        }
                }
                bdev = NULL;
                bh = NULL;
                disk_super = NULL;
                if (!device) {
                        printk(KERN_ERR "btrfs: no missing devices found to "
                               "remove\n");
                        goto out;
                }
        } else {
                bdev = blkdev_get_by_path(device_path, FMODE_READ | FMODE_EXCL,
                                          root->fs_info->bdev_holder);
                if (IS_ERR(bdev)) {
                        ret = PTR_ERR(bdev);
                        goto out;
                }

                set_blocksize(bdev, 4096);
                invalidate_bdev(bdev);
                bh = btrfs_read_dev_super(bdev);
                if (!bh) {
                        ret = -EINVAL;
                        goto error_close;
                }
                disk_super = (struct btrfs_super_block *)bh->b_data;
                devid = btrfs_stack_device_id(&disk_super->dev_item);
                dev_uuid = disk_super->dev_item.uuid;
                device = btrfs_find_device(root, devid, dev_uuid,
                                           disk_super->fsid);
                if (!device) {
                        ret = -ENOENT;
                        goto error_brelse;
                }
        }

        if (device->writeable && root->fs_info->fs_devices->rw_devices == 1) {
                printk(KERN_ERR "btrfs: unable to remove the only writeable "
                       "device\n");
                ret = -EINVAL;
                goto error_brelse;
        }

        if (device->writeable) {
                lock_chunks(root);
                list_del_init(&device->dev_alloc_list);
                unlock_chunks(root);
                root->fs_info->fs_devices->rw_devices--;
                clear_super = true;
        }

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

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

        spin_lock(&root->fs_info->free_chunk_lock);
        root->fs_info->free_chunk_space = device->total_bytes -
                device->bytes_used;
        spin_unlock(&root->fs_info->free_chunk_lock);

        device->in_fs_metadata = 0;
        btrfs_scrub_cancel_dev(root, device);

        /*
         * the device list mutex makes sure that we don't change
         * the device list while someone else is writing out all
         * the device supers.
         */

        cur_devices = device->fs_devices;
        mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
        list_del_rcu(&device->dev_list);

        device->fs_devices->num_devices--;

        if (device->missing)
                root->fs_info->fs_devices->missing_devices--;

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

        if (device->bdev)
                device->fs_devices->open_devices--;

        call_rcu(&device->rcu, free_device);
        mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);

        num_devices = btrfs_super_num_devices(root->fs_info->super_copy) - 1;
        btrfs_set_super_num_devices(root->fs_info->super_copy, num_devices);

        if (cur_devices->open_devices == 0) {
                struct btrfs_fs_devices *fs_devices;
                fs_devices = root->fs_info->fs_devices;
                while (fs_devices) {
                        if (fs_devices->seed == cur_devices)
                                break;
                        fs_devices = fs_devices->seed;
                }
                fs_devices->seed = cur_devices->seed;
                cur_devices->seed = NULL;
                lock_chunks(root);
                __btrfs_close_devices(cur_devices);
                unlock_chunks(root);
                free_fs_devices(cur_devices);
        }

        /*
         * at this point, the device is zero sized.  We want to
         * remove it from the devices list and zero out the old super
         */
        if (clear_super) {
                /* 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);
        }

        ret = 0;

error_brelse:
        brelse(bh);
error_close:
        if (bdev)
                blkdev_put(bdev, FMODE_READ | FMODE_EXCL);
out:
        mutex_unlock(&uuid_mutex);
        return ret;
error_undo:
        if (device->writeable) {
                lock_chunks(root);
                list_add(&device->dev_alloc_list,
                         &root->fs_info->fs_devices->alloc_list);
                unlock_chunks(root);
                root->fs_info->fs_devices->rw_devices++;
        }
        goto error_brelse;
}

/*
 * does all the dirty work required for changing file system's UUID.
 */
static int btrfs_prepare_sprout(struct btrfs_root *root)
{
        struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
        struct btrfs_fs_devices *old_devices;
        struct btrfs_fs_devices *seed_devices;
        struct btrfs_super_block *disk_super = root->fs_info->super_copy;
        struct btrfs_device *device;
        u64 super_flags;

        BUG_ON(!mutex_is_locked(&uuid_mutex));
        if (!fs_devices->seeding)
                return -EINVAL;

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

        old_devices = clone_fs_devices(fs_devices);
        if (IS_ERR(old_devices)) {
                kfree(seed_devices);
                return PTR_ERR(old_devices);
        }

        list_add(&old_devices->list, &fs_uuids);

        memcpy(seed_devices, fs_devices, sizeof(*seed_devices));
        seed_devices->opened = 1;
        INIT_LIST_HEAD(&seed_devices->devices);
        INIT_LIST_HEAD(&seed_devices->alloc_list);
        mutex_init(&seed_devices->device_list_mutex);

        mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
        list_splice_init_rcu(&fs_devices->devices, &seed_devices->devices,
                              synchronize_rcu);
        mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);

        list_splice_init(&fs_devices->alloc_list, &seed_devices->alloc_list);
        list_for_each_entry(device, &seed_devices->devices, dev_list) {
                device->fs_devices = seed_devices;
        }

        fs_devices->seeding = 0;
        fs_devices->num_devices = 0;
        fs_devices->open_devices = 0;
        fs_devices->seed = seed_devices;

        generate_random_uuid(fs_devices->fsid);
        memcpy(root->fs_info->fsid, fs_devices->fsid, BTRFS_FSID_SIZE);
        memcpy(disk_super->fsid, fs_devices->fsid, BTRFS_FSID_SIZE);
        super_flags = btrfs_super_flags(disk_super) &
                      ~BTRFS_SUPER_FLAG_SEEDING;
        btrfs_set_super_flags(disk_super, super_flags);

        return 0;
}

/*
 * strore the expected generation for seed devices in device items.
 */
static int btrfs_finish_sprout(struct btrfs_trans_handle *trans,
                               struct btrfs_root *root)
{
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_dev_item *dev_item;
        struct btrfs_device *device;
        struct btrfs_key key;
        u8 fs_uuid[BTRFS_UUID_SIZE];
        u8 dev_uuid[BTRFS_UUID_SIZE];
        u64 devid;
        int ret;

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

        root = root->fs_info->chunk_root;
        key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
        key.offset = 0;
        key.type = BTRFS_DEV_ITEM_KEY;

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

                leaf = path->nodes[0];
next_slot:
                if (path->slots[0] >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret > 0)
                                break;
                        if (ret < 0)
                                goto error;
                        leaf = path->nodes[0];
                        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
                        btrfs_release_path(path);
                        continue;
                }

                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
                if (key.objectid != BTRFS_DEV_ITEMS_OBJECTID ||
                    key.type != BTRFS_DEV_ITEM_KEY)
                        break;

                dev_item = btrfs_item_ptr(leaf, path->slots[0],
                                          struct btrfs_dev_item);
                devid = btrfs_device_id(leaf, dev_item);
                read_extent_buffer(leaf, dev_uuid,
                                   (unsigned long)btrfs_device_uuid(dev_item),
                                   BTRFS_UUID_SIZE);
                read_extent_buffer(leaf, fs_uuid,
                                   (unsigned long)btrfs_device_fsid(dev_item),
                                   BTRFS_UUID_SIZE);
                device = btrfs_find_device(root, devid, dev_uuid, fs_uuid);
                BUG_ON(!device); /* Logic error */

                if (device->fs_devices->seeding) {
                        btrfs_set_device_generation(leaf, dev_item,
                                                    device->generation);
                        btrfs_mark_buffer_dirty(leaf);
                }

                path->slots[0]++;
                goto next_slot;
        }
        ret = 0;
error:
        btrfs_free_path(path);
        return ret;
}

int btrfs_init_new_device(struct btrfs_root *root, char *device_path)
{
        struct request_queue *q;
        struct btrfs_trans_handle *trans;
        struct btrfs_device *device;
        struct block_device *bdev;
        struct list_head *devices;
        struct super_block *sb = root->fs_info->sb;
        struct rcu_string *name;
        u64 total_bytes;
        int seeding_dev = 0;
        int ret = 0;

        if ((sb->s_flags & MS_RDONLY) && !root->fs_info->fs_devices->seeding)
                return -EROFS;

        bdev = blkdev_get_by_path(device_path, FMODE_WRITE | FMODE_EXCL,
                                  root->fs_info->bdev_holder);
        if (IS_ERR(bdev))
                return PTR_ERR(bdev);

        if (root->fs_info->fs_devices->seeding) {
                seeding_dev = 1;
                down_write(&sb->s_umount);
                mutex_lock(&uuid_mutex);
        }

        filemap_write_and_wait(bdev->bd_inode->i_mapping);

        devices = &root->fs_info->fs_devices->devices;
        /*
         * we have the volume lock, so we don't need the extra
         * device list mutex while reading the list here.
         */
        list_for_each_entry(device, devices, dev_list) {
                if (device->bdev == bdev) {
                        ret = -EEXIST;
                        goto error;
                }
        }

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

        name = rcu_string_strdup(device_path, GFP_NOFS);
        if (!name) {
                kfree(device);
                ret = -ENOMEM;
                goto error;
        }
        rcu_assign_pointer(device->name, name);

        ret = find_next_devid(root, &device->devid);
        if (ret) {
                rcu_string_free(device->name);
                kfree(device);
                goto error;
        }

        trans = btrfs_start_transaction(root, 0);
        if (IS_ERR(trans)) {
                rcu_string_free(device->name);
                kfree(device);
                ret = PTR_ERR(trans);
                goto error;
        }

        lock_chunks(root);

        q = bdev_get_queue(bdev);
        if (blk_queue_discard(q))
                device->can_discard = 1;
        device->writeable = 1;
        device->work.func = pending_bios_fn;
        generate_random_uuid(device->uuid);
        spin_lock_init(&device->io_lock);
        device->generation = trans->transid;
        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->disk_total_bytes = device->total_bytes;
        device->dev_root = root->fs_info->dev_root;
        device->bdev = bdev;
        device->in_fs_metadata = 1;
        device->mode = FMODE_EXCL;
        set_blocksize(device->bdev, 4096);

        if (seeding_dev) {
                sb->s_flags &= ~MS_RDONLY;
                ret = btrfs_prepare_sprout(root);
                BUG_ON(ret); /* -ENOMEM */
        }

        device->fs_devices = root->fs_info->fs_devices;

        /*
         * we don't want write_supers to jump in here with our device
         * half setup
         */
        mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
        list_add_rcu(&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++;
        root->fs_info->fs_devices->rw_devices++;
        if (device->can_discard)
                root->fs_info->fs_devices->num_can_discard++;
        root->fs_info->fs_devices->total_rw_bytes += device->total_bytes;

        spin_lock(&root->fs_info->free_chunk_lock);
        root->fs_info->free_chunk_space += device->total_bytes;
        spin_unlock(&root->fs_info->free_chunk_lock);

        if (!blk_queue_nonrot(bdev_get_queue(bdev)))
                root->fs_info->fs_devices->rotating = 1;

        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);
        mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);

        if (seeding_dev) {
                ret = init_first_rw_device(trans, root, device);
                if (ret)
                        goto error_trans;
                ret = btrfs_finish_sprout(trans, root);
                if (ret)
                        goto error_trans;
        } else {
                ret = btrfs_add_device(trans, root, device);
                if (ret)
                        goto error_trans;
        }

        /*
         * we've got more storage, clear any full flags on the space
         * infos
         */
        btrfs_clear_space_info_full(root->fs_info);

        unlock_chunks(root);
        ret = btrfs_commit_transaction(trans, root);

        if (seeding_dev) {
                mutex_unlock(&uuid_mutex);
                up_write(&sb->s_umount);

                if (ret) /* transaction commit */
                        return ret;

                ret = btrfs_relocate_sys_chunks(root);
                if (ret < 0)
                        btrfs_error(root->fs_info, ret,
                                    "Failed to relocate sys chunks after "
                                    "device initialization. This can be fixed "
                                    "using the \"btrfs balance\" command.");
        }

        return ret;

error_trans:
        unlock_chunks(root);
        btrfs_abort_transaction(trans, root, ret);
        btrfs_end_transaction(trans, root);
        rcu_string_free(device->name);
        kfree(device);
error:
        blkdev_put(bdev, FMODE_EXCL);
        if (seeding_dev) {
                mutex_unlock(&uuid_mutex);
                up_write(&sb->s_umount);
        }
        return ret;
}

static noinline 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->disk_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;
}

static 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;

        if (!device->writeable)
                return -EACCES;
        if (new_size <= device->total_bytes)
                return -EINVAL;

        btrfs_set_super_total_bytes(super_copy, old_total + diff);
        device->fs_devices->total_rw_bytes += diff;

        device->total_bytes = new_size;
        device->disk_total_bytes = new_size;
        btrfs_clear_space_info_full(device->dev_root->fs_info);

        return btrfs_update_device(trans, device);
}

int btrfs_grow_device(struct btrfs_trans_handle *trans,
                      struct btrfs_device *device, u64 new_size)
{
        int ret;
        lock_chunks(device->dev_root);
        ret = __btrfs_grow_device(trans, device, new_size);
        unlock_chunks(device->dev_root);
        return ret;
}

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);
        if (ret < 0)
                goto out;
        else if (ret > 0) { /* Logic error or corruption */
                btrfs_error(root->fs_info, -ENOENT,
                            "Failed lookup while freeing chunk.");
                ret = -ENOENT;
                goto out;
        }

        ret = btrfs_del_item(trans, root, path);
        if (ret < 0)
                btrfs_error(root->fs_info, ret,
                            "Failed to delete chunk item.");
out:
        btrfs_free_path(path);
        return ret;
}

static 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;
}

static 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;

        root = root->fs_info->chunk_root;
        extent_root = root->fs_info->extent_root;
        em_tree = &root->fs_info->mapping_tree.map_tree;

        ret = btrfs_can_relocate(extent_root, chunk_offset);
        if (ret)
                return -ENOSPC;

        /* step one, relocate all the extents inside this chunk */
        ret = btrfs_relocate_block_group(extent_root, chunk_offset);
        if (ret)
                return ret;

        trans = btrfs_start_transaction(root, 0);
        BUG_ON(IS_ERR(trans));

        lock_chunks(root);

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

        BUG_ON(!em || 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);

        trace_btrfs_chunk_free(root, map, chunk_offset, em->len);

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

        ret = btrfs_remove_block_group(trans, extent_root, chunk_offset);
        BUG_ON(ret);

        write_lock(&em_tree->lock);
        remove_extent_mapping(em_tree, em);
        write_unlock(&em_tree->lock);

        kfree(map);
        em->bdev = NULL;

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

        unlock_chunks(root);
        btrfs_end_transaction(trans, root);
        return 0;
}

static int btrfs_relocate_sys_chunks(struct btrfs_root *root)
{
        struct btrfs_root *chunk_root = root->fs_info->chunk_root;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_chunk *chunk;
        struct btrfs_key key;
        struct btrfs_key found_key;
        u64 chunk_tree = chunk_root->root_key.objectid;
        u64 chunk_type;
        bool retried = false;
        int failed = 0;
        int ret;

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

again:
        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;
                BUG_ON(ret == 0); /* Corruption */

                ret = btrfs_previous_item(chunk_root, path, key.objectid,
                                          key.type);
                if (ret < 0)
                        goto error;
                if (ret > 0)
                        break;

                leaf = path->nodes[0];
                btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);

                chunk = btrfs_item_ptr(leaf, path->slots[0],
                                       struct btrfs_chunk);
                chunk_type = btrfs_chunk_type(leaf, chunk);
                btrfs_release_path(path);

                if (chunk_type & BTRFS_BLOCK_GROUP_SYSTEM) {
                        ret = btrfs_relocate_chunk(chunk_root, chunk_tree,
                                                   found_key.objectid,
                                                   found_key.offset);
                        if (ret == -ENOSPC)
                                failed++;
                        else if (ret)
                                BUG();
                }

                if (found_key.offset == 0)
                        break;
                key.offset = found_key.offset - 1;
        }
        ret = 0;
        if (failed && !retried) {
                failed = 0;
                retried = true;
                goto again;
        } else if (failed && retried) {
                WARN_ON(1);
                ret = -ENOSPC;
        }
error:
        btrfs_free_path(path);
        return ret;
}

static int insert_balance_item(struct btrfs_root *root,
                               struct btrfs_balance_control *bctl)
{
        struct btrfs_trans_handle *trans;
        struct btrfs_balance_item *item;
        struct btrfs_disk_balance_args disk_bargs;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_key key;
        int ret, err;

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

        trans = btrfs_start_transaction(root, 0);
        if (IS_ERR(trans)) {
                btrfs_free_path(path);
                return PTR_ERR(trans);
        }

        key.objectid = BTRFS_BALANCE_OBJECTID;
        key.type = BTRFS_BALANCE_ITEM_KEY;
        key.offset = 0;

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

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

        memset_extent_buffer(leaf, 0, (unsigned long)item, sizeof(*item));

        btrfs_cpu_balance_args_to_disk(&disk_bargs, &bctl->data);
        btrfs_set_balance_data(leaf, item, &disk_bargs);
        btrfs_cpu_balance_args_to_disk(&disk_bargs, &bctl->meta);
        btrfs_set_balance_meta(leaf, item, &disk_bargs);
        btrfs_cpu_balance_args_to_disk(&disk_bargs, &bctl->sys);
        btrfs_set_balance_sys(leaf, item, &disk_bargs);

        btrfs_set_balance_flags(leaf, item, bctl->flags);

        btrfs_mark_buffer_dirty(leaf);
out:
        btrfs_free_path(path);
        err = btrfs_commit_transaction(trans, root);
        if (err && !ret)
                ret = err;
        return ret;
}

static int del_balance_item(struct btrfs_root *root)
{
        struct btrfs_trans_handle *trans;
        struct btrfs_path *path;
        struct btrfs_key key;
        int ret, err;

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

        trans = btrfs_start_transaction(root, 0);
        if (IS_ERR(trans)) {
                btrfs_free_path(path);
                return PTR_ERR(trans);
        }

        key.objectid = BTRFS_BALANCE_OBJECTID;
        key.type = BTRFS_BALANCE_ITEM_KEY;
        key.offset = 0;

        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);
out:
        btrfs_free_path(path);
        err = btrfs_commit_transaction(trans, root);
        if (err && !ret)
                ret = err;
        return ret;
}

/*
 * This is a heuristic used to reduce the number of chunks balanced on
 * resume after balance was interrupted.
 */
static void update_balance_args(struct btrfs_balance_control *bctl)
{
        /*
         * Turn on soft mode for chunk types that were being converted.
         */
        if (bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT)
                bctl->data.flags |= BTRFS_BALANCE_ARGS_SOFT;
        if (bctl->sys.flags & BTRFS_BALANCE_ARGS_CONVERT)
                bctl->sys.flags |= BTRFS_BALANCE_ARGS_SOFT;
        if (bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT)
                bctl->meta.flags |= BTRFS_BALANCE_ARGS_SOFT;

        /*
         * Turn on usage filter if is not already used.  The idea is
         * that chunks that we have already balanced should be
         * reasonably full.  Don't do it for chunks that are being
         * converted - that will keep us from relocating unconverted
         * (albeit full) chunks.
         */
        if (!(bctl->data.flags & BTRFS_BALANCE_ARGS_USAGE) &&
            !(bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT)) {
                bctl->data.flags |= BTRFS_BALANCE_ARGS_USAGE;
                bctl->data.usage = 90;
        }
        if (!(bctl->sys.flags & BTRFS_BALANCE_ARGS_USAGE) &&
            !(bctl->sys.flags & BTRFS_BALANCE_ARGS_CONVERT)) {
                bctl->sys.flags |= BTRFS_BALANCE_ARGS_USAGE;
                bctl->sys.usage = 90;
        }
        if (!(bctl->meta.flags & BTRFS_BALANCE_ARGS_USAGE) &&
            !(bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT)) {
                bctl->meta.flags |= BTRFS_BALANCE_ARGS_USAGE;
                bctl->meta.usage = 90;
        }
}

/*
 * Should be called with both balance and volume mutexes held to
 * serialize other volume operations (add_dev/rm_dev/resize) with
 * restriper.  Same goes for unset_balance_control.
 */
static void set_balance_control(struct btrfs_balance_control *bctl)
{
        struct btrfs_fs_info *fs_info = bctl->fs_info;

        BUG_ON(fs_info->balance_ctl);

        spin_lock(&fs_info->balance_lock);
        fs_info->balance_ctl = bctl;
        spin_unlock(&fs_info->balance_lock);
}

static void unset_balance_control(struct btrfs_fs_info *fs_info)
{
        struct btrfs_balance_control *bctl = fs_info->balance_ctl;

        BUG_ON(!fs_info->balance_ctl);

        spin_lock(&fs_info->balance_lock);
        fs_info->balance_ctl = NULL;
        spin_unlock(&fs_info->balance_lock);

        kfree(bctl);
}

/*
 * Balance filters.  Return 1 if chunk should be filtered out
 * (should not be balanced).
 */
static int chunk_profiles_filter(u64 chunk_type,
                                 struct btrfs_balance_args *bargs)
{
        chunk_type = chunk_to_extended(chunk_type) &
                                BTRFS_EXTENDED_PROFILE_MASK;

        if (bargs->profiles & chunk_type)
                return 0;

        return 1;
}

static u64 div_factor_fine(u64 num, int factor)
{
        if (factor <= 0)
                return 0;
        if (factor >= 100)
                return num;

        num *= factor;
        do_div(num, 100);
        return num;
}

static int chunk_usage_filter(struct btrfs_fs_info *fs_info, u64 chunk_offset,
                              struct btrfs_balance_args *bargs)
{
        struct btrfs_block_group_cache *cache;
        u64 chunk_used, user_thresh;
        int ret = 1;

        cache = btrfs_lookup_block_group(fs_info, chunk_offset);
        chunk_used = btrfs_block_group_used(&cache->item);

        user_thresh = div_factor_fine(cache->key.offset, bargs->usage);
        if (chunk_used < user_thresh)
                ret = 0;

        btrfs_put_block_group(cache);
        return ret;
}

static int chunk_devid_filter(struct extent_buffer *leaf,
                              struct btrfs_chunk *chunk,
                              struct btrfs_balance_args *bargs)
{
        struct btrfs_stripe *stripe;
        int num_stripes = btrfs_chunk_num_stripes(leaf, chunk);
        int i;

        for (i = 0; i < num_stripes; i++) {
                stripe = btrfs_stripe_nr(chunk, i);
                if (btrfs_stripe_devid(leaf, stripe) == bargs->devid)
                        return 0;
        }

        return 1;
}

/* [pstart, pend) */
static int chunk_drange_filter(struct extent_buffer *leaf,
                               struct btrfs_chunk *chunk,
                               u64 chunk_offset,
                               struct btrfs_balance_args *bargs)
{
        struct btrfs_stripe *stripe;
        int num_stripes = btrfs_chunk_num_stripes(leaf, chunk);
        u64 stripe_offset;
        u64 stripe_length;
        int factor;
        int i;

        if (!(bargs->flags & BTRFS_BALANCE_ARGS_DEVID))
                return 0;

        if (btrfs_chunk_type(leaf, chunk) & (BTRFS_BLOCK_GROUP_DUP |
             BTRFS_BLOCK_GROUP_RAID1 | BTRFS_BLOCK_GROUP_RAID10))
                factor = 2;
        else
                factor = 1;
        factor = num_stripes / factor;

        for (i = 0; i < num_stripes; i++) {
                stripe = btrfs_stripe_nr(chunk, i);
                if (btrfs_stripe_devid(leaf, stripe) != bargs->devid)
                        continue;

                stripe_offset = btrfs_stripe_offset(leaf, stripe);
                stripe_length = btrfs_chunk_length(leaf, chunk);
                do_div(stripe_length, factor);

                if (stripe_offset < bargs->pend &&
                    stripe_offset + stripe_length > bargs->pstart)
                        return 0;
        }

        return 1;
}

/* [vstart, vend) */
static int chunk_vrange_filter(struct extent_buffer *leaf,
                               struct btrfs_chunk *chunk,
                               u64 chunk_offset,
                               struct btrfs_balance_args *bargs)
{
        if (chunk_offset < bargs->vend &&
            chunk_offset + btrfs_chunk_length(leaf, chunk) > bargs->vstart)
                /* at least part of the chunk is inside this vrange */
                return 0;

        return 1;
}

static int chunk_soft_convert_filter(u64 chunk_type,
                                     struct btrfs_balance_args *bargs)
{
        if (!(bargs->flags & BTRFS_BALANCE_ARGS_CONVERT))
                return 0;

        chunk_type = chunk_to_extended(chunk_type) &
                                BTRFS_EXTENDED_PROFILE_MASK;

        if (bargs->target == chunk_type)
                return 1;

        return 0;
}

static int should_balance_chunk(struct btrfs_root *root,
                                struct extent_buffer *leaf,
                                struct btrfs_chunk *chunk, u64 chunk_offset)
{
        struct btrfs_balance_control *bctl = root->fs_info->balance_ctl;
        struct btrfs_balance_args *bargs = NULL;
        u64 chunk_type = btrfs_chunk_type(leaf, chunk);

        /* type filter */
        if (!((chunk_type & BTRFS_BLOCK_GROUP_TYPE_MASK) &
              (bctl->flags & BTRFS_BALANCE_TYPE_MASK))) {
                return 0;
        }

        if (chunk_type & BTRFS_BLOCK_GROUP_DATA)
                bargs = &bctl->data;
        else if (chunk_type & BTRFS_BLOCK_GROUP_SYSTEM)
                bargs = &bctl->sys;
        else if (chunk_type & BTRFS_BLOCK_GROUP_METADATA)
                bargs = &bctl->meta;

        /* profiles filter */
        if ((bargs->flags & BTRFS_BALANCE_ARGS_PROFILES) &&
            chunk_profiles_filter(chunk_type, bargs)) {
                return 0;
        }

        /* usage filter */
        if ((bargs->flags & BTRFS_BALANCE_ARGS_USAGE) &&
            chunk_usage_filter(bctl->fs_info, chunk_offset, bargs)) {
                return 0;
        }

        /* devid filter */
        if ((bargs->flags & BTRFS_BALANCE_ARGS_DEVID) &&
            chunk_devid_filter(leaf, chunk, bargs)) {
                return 0;
        }

        /* drange filter, makes sense only with devid filter */
        if ((bargs->flags & BTRFS_BALANCE_ARGS_DRANGE) &&
            chunk_drange_filter(leaf, chunk, chunk_offset, bargs)) {
                return 0;
        }

        /* vrange filter */
        if ((bargs->flags & BTRFS_BALANCE_ARGS_VRANGE) &&
            chunk_vrange_filter(leaf, chunk, chunk_offset, bargs)) {
                return 0;
        }

        /* soft profile changing mode */
        if ((bargs->flags & BTRFS_BALANCE_ARGS_SOFT) &&
            chunk_soft_convert_filter(chunk_type, bargs)) {
                return 0;
        }

        return 1;
}

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

static int __btrfs_balance(struct btrfs_fs_info *fs_info)
{
        struct btrfs_balance_control *bctl = fs_info->balance_ctl;
        struct btrfs_root *chunk_root = fs_info->chunk_root;
        struct btrfs_root *dev_root = fs_info->dev_root;
        struct list_head *devices;
        struct btrfs_device *device;
        u64 old_size;
        u64 size_to_free;
        struct btrfs_chunk *chunk;
        struct btrfs_path *path;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct btrfs_trans_handle *trans;
        struct extent_buffer *leaf;
        int slot;
        int ret;
        int enospc_errors = 0;
        bool counting = true;

        /* step one make some room on all the devices */
        devices = &fs_info->fs_devices->devices;
        list_for_each_entry(device, devices, 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->writeable ||
                    device->total_bytes - device->bytes_used > size_to_free)
                        continue;

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

                trans = btrfs_start_transaction(dev_root, 0);
                BUG_ON(IS_ERR(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();
        if (!path) {
                ret = -ENOMEM;
                goto error;
        }

        /* zero out stat counters */
        spin_lock(&fs_info->balance_lock);
        memset(&bctl->stat, 0, sizeof(bctl->stat));
        spin_unlock(&fs_info->balance_lock);
again:
        key.objectid = BTRFS_FIRST_CHUNK_TREE_OBJECTID;
        key.offset = (u64)-1;
        key.type = BTRFS_CHUNK_ITEM_KEY;

        while (1) {
                if ((!counting && atomic_read(&fs_info->balance_pause_req)) ||
                    atomic_read(&fs_info->balance_cancel_req)) {
                        ret = -ECANCELED;
                        goto error;
                }

                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)
                        BUG(); /* FIXME break ? */

                ret = btrfs_previous_item(chunk_root, path, 0,
                                          BTRFS_CHUNK_ITEM_KEY);
                if (ret) {
                        ret = 0;
                        break;
                }

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

                if (found_key.objectid != key.objectid)
                        break;

                /* chunk zero is special */
                if (found_key.offset == 0)
                        break;

                chunk = btrfs_item_ptr(leaf, slot, struct btrfs_chunk);

                if (!counting) {
                        spin_lock(&fs_info->balance_lock);
                        bctl->stat.considered++;
                        spin_unlock(&fs_info->balance_lock);
                }

                ret = should_balance_chunk(chunk_root, leaf, chunk,
                                           found_key.offset);
                btrfs_release_path(path);
                if (!ret)
                        goto loop;

                if (counting) {
                        spin_lock(&fs_info->balance_lock);
                        bctl->stat.expected++;
                        spin_unlock(&fs_info->balance_lock);
                        goto loop;
                }

                ret = btrfs_relocate_chunk(chunk_root,
                                           chunk_root->root_key.objectid,
                                           found_key.objectid,
                                           found_key.offset);
                if (ret && ret != -ENOSPC)
                        goto error;
                if (ret == -ENOSPC) {
                        enospc_errors++;
                } else {
                        spin_lock(&fs_info->balance_lock);
                        bctl->stat.completed++;
                        spin_unlock(&fs_info->balance_lock);
                }
loop:
                key.offset = found_key.offset - 1;
        }

        if (counting) {
                btrfs_release_path(path);
                counting = false;
                goto again;
        }
error:
        btrfs_free_path(path);
        if (enospc_errors) {
                printk(KERN_INFO "btrfs: %d enospc errors during balance\n",
                       enospc_errors);
                if (!ret)
                        ret = -ENOSPC;
        }

        return ret;
}

/**
 * alloc_profile_is_valid - see if a given profile is valid and reduced
 * @flags: profile to validate
 * @extended: if true @flags is treated as an extended profile
 */
static int alloc_profile_is_valid(u64 flags, int extended)
{
        u64 mask = (extended ? BTRFS_EXTENDED_PROFILE_MASK :
                               BTRFS_BLOCK_GROUP_PROFILE_MASK);

        flags &= ~BTRFS_BLOCK_GROUP_TYPE_MASK;

        /* 1) check that all other bits are zeroed */
        if (flags & ~mask)
                return 0;

        /* 2) see if profile is reduced */
        if (flags == 0)
                return !extended; /* "0" is valid for usual profiles */

        /* true if exactly one bit set */
        return (flags & (flags - 1)) == 0;
}

static inline int balance_need_close(struct btrfs_fs_info *fs_info)
{
        /* cancel requested || normal exit path */
        return atomic_read(&fs_info->balance_cancel_req) ||
                (atomic_read(&fs_info->balance_pause_req) == 0 &&
                 atomic_read(&fs_info->balance_cancel_req) == 0);
}

static void __cancel_balance(struct btrfs_fs_info *fs_info)
{
        int ret;

        unset_balance_control(fs_info);
        ret = del_balance_item(fs_info->tree_root);
        BUG_ON(ret);
}

void update_ioctl_balance_args(struct btrfs_fs_info *fs_info, int lock,
                               struct btrfs_ioctl_balance_args *bargs);

/*
 * Should be called with both balance and volume mutexes held
 */
int btrfs_balance(struct btrfs_balance_control *bctl,
                  struct btrfs_ioctl_balance_args *bargs)
{
        struct btrfs_fs_info *fs_info = bctl->fs_info;
        u64 allowed;
        int mixed = 0;
        int ret;

        if (btrfs_fs_closing(fs_info) ||
            atomic_read(&fs_info->balance_pause_req) ||
            atomic_read(&fs_info->balance_cancel_req)) {
                ret = -EINVAL;
                goto out;
        }

        allowed = btrfs_super_incompat_flags(fs_info->super_copy);
        if (allowed & BTRFS_FEATURE_INCOMPAT_MIXED_GROUPS)
                mixed = 1;

        /*
         * In case of mixed groups both data and meta should be picked,
         * and identical options should be given for both of them.
         */
        allowed = BTRFS_BALANCE_DATA | BTRFS_BALANCE_METADATA;
        if (mixed && (bctl->flags & allowed)) {
                if (!(bctl->flags & BTRFS_BALANCE_DATA) ||
                    !(bctl->flags & BTRFS_BALANCE_METADATA) ||
                    memcmp(&bctl->data, &bctl->meta, sizeof(bctl->data))) {
                        printk(KERN_ERR "btrfs: with mixed groups data and "
                               "metadata balance options must be the same\n");
                        ret = -EINVAL;
                        goto out;
                }
        }

        allowed = BTRFS_AVAIL_ALLOC_BIT_SINGLE;
        if (fs_info->fs_devices->num_devices == 1)
                allowed |= BTRFS_BLOCK_GROUP_DUP;
        else if (fs_info->fs_devices->num_devices < 4)
                allowed |= (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID1);
        else
                allowed |= (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID1 |
                                BTRFS_BLOCK_GROUP_RAID10);

        if ((bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT) &&
            (!alloc_profile_is_valid(bctl->data.target, 1) ||
             (bctl->data.target & ~allowed))) {
                printk(KERN_ERR "btrfs: unable to start balance with target "
                       "data profile %llu\n",
                       (unsigned long long)bctl->data.target);
                ret = -EINVAL;
                goto out;
        }
        if ((bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) &&
            (!alloc_profile_is_valid(bctl->meta.target, 1) ||
             (bctl->meta.target & ~allowed))) {
                printk(KERN_ERR "btrfs: unable to start balance with target "
                       "metadata profile %llu\n",
                       (unsigned long long)bctl->meta.target);
                ret = -EINVAL;
                goto out;
        }
        if ((bctl->sys.flags & BTRFS_BALANCE_ARGS_CONVERT) &&
            (!alloc_profile_is_valid(bctl->sys.target, 1) ||
             (bctl->sys.target & ~allowed))) {
                printk(KERN_ERR "btrfs: unable to start balance with target "
                       "system profile %llu\n",
                       (unsigned long long)bctl->sys.target);
                ret = -EINVAL;
                goto out;
        }

        /* allow dup'ed data chunks only in mixed mode */
        if (!mixed && (bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT) &&
            (bctl->data.target & BTRFS_BLOCK_GROUP_DUP)) {
                printk(KERN_ERR "btrfs: dup for data is not allowed\n");
                ret = -EINVAL;
                goto out;
        }

        /* allow to reduce meta or sys integrity only if force set */
        allowed = BTRFS_BLOCK_GROUP_DUP | BTRFS_BLOCK_GROUP_RAID1 |
                        BTRFS_BLOCK_GROUP_RAID10;
        if (((bctl->sys.flags & BTRFS_BALANCE_ARGS_CONVERT) &&
             (fs_info->avail_system_alloc_bits & allowed) &&
             !(bctl->sys.target & allowed)) ||
            ((bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) &&
             (fs_info->avail_metadata_alloc_bits & allowed) &&
             !(bctl->meta.target & allowed))) {
                if (bctl->flags & BTRFS_BALANCE_FORCE) {
                        printk(KERN_INFO "btrfs: force reducing metadata "
                               "integrity\n");
                } else {
                        printk(KERN_ERR "btrfs: balance will reduce metadata "
                               "integrity, use force if you want this\n");
                        ret = -EINVAL;
                        goto out;
                }
        }

        ret = insert_balance_item(fs_info->tree_root, bctl);
        if (ret && ret != -EEXIST)
                goto out;

        if (!(bctl->flags & BTRFS_BALANCE_RESUME)) {
                BUG_ON(ret == -EEXIST);
                set_balance_control(bctl);
        } else {
                BUG_ON(ret != -EEXIST);
                spin_lock(&fs_info->balance_lock);
                update_balance_args(bctl);
                spin_unlock(&fs_info->balance_lock);
        }

        atomic_inc(&fs_info->balance_running);
        mutex_unlock(&fs_info->balance_mutex);

        ret = __btrfs_balance(fs_info);

        mutex_lock(&fs_info->balance_mutex);
        atomic_dec(&fs_info->balance_running);

        if (bargs) {
                memset(bargs, 0, sizeof(*bargs));
                update_ioctl_balance_args(fs_info, 0, bargs);
        }

        if ((ret && ret != -ECANCELED && ret != -ENOSPC) ||
            balance_need_close(fs_info)) {
                __cancel_balance(fs_info);
        }

        wake_up(&fs_info->balance_wait_q);

        return ret;
out:
        if (bctl->flags & BTRFS_BALANCE_RESUME)
                __cancel_balance(fs_info);
        else
                kfree(bctl);
        return ret;
}

static int balance_kthread(void *data)
{
        struct btrfs_balance_control *bctl =
                        (struct btrfs_balance_control *)data;
        struct btrfs_fs_info *fs_info = bctl->fs_info;
        int ret = 0;

        mutex_lock(&fs_info->volume_mutex);
        mutex_lock(&fs_info->balance_mutex);

        set_balance_control(bctl);

        if (btrfs_test_opt(fs_info->tree_root, SKIP_BALANCE)) {
                printk(KERN_INFO "btrfs: force skipping balance\n");
        } else {
                printk(KERN_INFO "btrfs: continuing balance\n");
                ret = btrfs_balance(bctl, NULL);
        }

        mutex_unlock(&fs_info->balance_mutex);
        mutex_unlock(&fs_info->volume_mutex);
        return ret;
}

int btrfs_recover_balance(struct btrfs_root *tree_root)
{
        struct task_struct *tsk;
        struct btrfs_balance_control *bctl;
        struct btrfs_balance_item *item;
        struct btrfs_disk_balance_args disk_bargs;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_key key;
        int ret;

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

        bctl = kzalloc(sizeof(*bctl), GFP_NOFS);
        if (!bctl) {
                ret = -ENOMEM;
                goto out;
        }

        key.objectid = BTRFS_BALANCE_OBJECTID;
        key.type = BTRFS_BALANCE_ITEM_KEY;
        key.offset = 0;

        ret = btrfs_search_slot(NULL, tree_root, &key, path, 0, 0);
        if (ret < 0)
                goto out_bctl;
        if (ret > 0) { /* ret = -ENOENT; */
                ret = 0;
                goto out_bctl;
        }

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

        bctl->fs_info = tree_root->fs_info;
        bctl->flags = btrfs_balance_flags(leaf, item) | BTRFS_BALANCE_RESUME;

        btrfs_balance_data(leaf, item, &disk_bargs);
        btrfs_disk_balance_args_to_cpu(&bctl->data, &disk_bargs);
        btrfs_balance_meta(leaf, item, &disk_bargs);
        btrfs_disk_balance_args_to_cpu(&bctl->meta, &disk_bargs);
        btrfs_balance_sys(leaf, item, &disk_bargs);
        btrfs_disk_balance_args_to_cpu(&bctl->sys, &disk_bargs);

        tsk = kthread_run(balance_kthread, bctl, "btrfs-balance");
        if (IS_ERR(tsk))
                ret = PTR_ERR(tsk);
        else
                goto out;

out_bctl:
        kfree(bctl);
out:
        btrfs_free_path(path);
        return ret;
}

int btrfs_pause_balance(struct btrfs_fs_info *fs_info)
{
        int ret = 0;

        mutex_lock(&fs_info->balance_mutex);
        if (!fs_info->balance_ctl) {
                mutex_unlock(&fs_info->balance_mutex);
                return -ENOTCONN;
        }

        if (atomic_read(&fs_info->balance_running)) {
                atomic_inc(&fs_info->balance_pause_req);
                mutex_unlock(&fs_info->balance_mutex);

                wait_event(fs_info->balance_wait_q,
                           atomic_read(&fs_info->balance_running) == 0);

                mutex_lock(&fs_info->balance_mutex);
                /* we are good with balance_ctl ripped off from under us */
                BUG_ON(atomic_read(&fs_info->balance_running));
                atomic_dec(&fs_info->balance_pause_req);
        } else {
                ret = -ENOTCONN;
        }

        mutex_unlock(&fs_info->balance_mutex);
        return ret;
}

int btrfs_cancel_balance(struct btrfs_fs_info *fs_info)
{
        mutex_lock(&fs_info->balance_mutex);
        if (!fs_info->balance_ctl) {
                mutex_unlock(&fs_info->balance_mutex);
                return -ENOTCONN;
        }

        atomic_inc(&fs_info->balance_cancel_req);
        /*
         * if we are running just wait and return, balance item is
         * deleted in btrfs_balance in this case
         */
        if (atomic_read(&fs_info->balance_running)) {
                mutex_unlock(&fs_info->balance_mutex);
                wait_event(fs_info->balance_wait_q,
                           atomic_read(&fs_info->balance_running) == 0);
                mutex_lock(&fs_info->balance_mutex);
        } else {
                /* __cancel_balance needs volume_mutex */
                mutex_unlock(&fs_info->balance_mutex);
                mutex_lock(&fs_info->volume_mutex);
                mutex_lock(&fs_info->balance_mutex);

                if (fs_info->balance_ctl)
                        __cancel_balance(fs_info);

                mutex_unlock(&fs_info->volume_mutex);
        }

        BUG_ON(fs_info->balance_ctl || atomic_read(&fs_info->balance_running));
        atomic_dec(&fs_info->balance_cancel_req);
        mutex_unlock(&fs_info->balance_mutex);
        return 0;
}

/*
 * 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;
        int failed = 0;
        bool retried = false;
        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 old_size = device->total_bytes;
        u64 diff = device->total_bytes - new_size;

        if (new_size >= device->total_bytes)
                return -EINVAL;

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

        path->reada = 2;

        lock_chunks(root);

        device->total_bytes = new_size;
        if (device->writeable) {
                device->fs_devices->total_rw_bytes -= diff;
                spin_lock(&root->fs_info->free_chunk_lock);
                root->fs_info->free_chunk_space -= diff;
                spin_unlock(&root->fs_info->free_chunk_lock);
        }
        unlock_chunks(root);

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

        do {
                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;
                        btrfs_release_path(path);
                        break;
                }

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

                if (key.objectid != device->devid) {
                        btrfs_release_path(path);
                        break;
                }

                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) {
                        btrfs_release_path(path);
                        break;
                }

                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(path);

                ret = btrfs_relocate_chunk(root, chunk_tree, chunk_objectid,
                                           chunk_offset);
                if (ret && ret != -ENOSPC)
                        goto done;
                if (ret == -ENOSPC)
                        failed++;
        } while (key.offset-- > 0);

        if (failed && !retried) {
                failed = 0;
                retried = true;
                goto again;
        } else if (failed && retried) {
                ret = -ENOSPC;
                lock_chunks(root);

                device->total_bytes = old_size;
                if (device->writeable)
                        device->fs_devices->total_rw_bytes += diff;
                spin_lock(&root->fs_info->free_chunk_lock);
                root->fs_info->free_chunk_space += diff;
                spin_unlock(&root->fs_info->free_chunk_lock);
                unlock_chunks(root);
                goto done;
        }

        /* Shrinking succeeded, else we would be at "done". */
        trans = btrfs_start_transaction(root, 0);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);
                goto done;
        }

        lock_chunks(root);

        device->disk_total_bytes = new_size;
        /* Now btrfs_update_device() will change the on-disk size. */
        ret = btrfs_update_device(trans, device);
        if (ret) {
                unlock_chunks(root);
                btrfs_end_transaction(trans, root);
                goto done;
        }
        WARN_ON(diff > old_total);
        btrfs_set_super_total_bytes(super_copy, old_total - diff);
        unlock_chunks(root);
        btrfs_end_transaction(trans, root);
done:
        btrfs_free_path(path);
        return ret;
}

static int btrfs_add_system_chunk(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;
}

/*
 * sort the devices in descending order by max_avail, total_avail
 */
static int btrfs_cmp_device_info(const void *a, const void *b)
{
        const struct btrfs_device_info *di_a = a;
        const struct btrfs_device_info *di_b = b;

        if (di_a->max_avail > di_b->max_avail)
                return -1;
        if (di_a->max_avail < di_b->max_avail)
                return 1;
        if (di_a->total_avail > di_b->total_avail)
                return -1;
        if (di_a->total_avail < di_b->total_avail)
                return 1;
        return 0;
}

static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
                               struct btrfs_root *extent_root,
                               struct map_lookup **map_ret,
                               u64 *num_bytes_out, u64 *stripe_size_out,
                               u64 start, u64 type)
{
        struct btrfs_fs_info *info = extent_root->fs_info;
        struct btrfs_fs_devices *fs_devices = info->fs_devices;
        struct list_head *cur;
        struct map_lookup *map = NULL;
        struct extent_map_tree *em_tree;
        struct extent_map *em;
        struct btrfs_device_info *devices_info = NULL;
        u64 total_avail;
        int num_stripes;        /* total number of stripes to allocate */
        int sub_stripes;        /* sub_stripes info for map */
        int dev_stripes;        /* stripes per dev */
        int devs_max;           /* max devs to use */
        int devs_min;           /* min devs needed */
        int devs_increment;     /* ndevs has to be a multiple of this */
        int ncopies;            /* how many copies to data has */
        int ret;
        u64 max_stripe_size;
        u64 max_chunk_size;
        u64 stripe_size;
        u64 num_bytes;
        int ndevs;
        int i;
        int j;

        BUG_ON(!alloc_profile_is_valid(type, 0));

        if (list_empty(&fs_devices->alloc_list))
                return -ENOSPC;

        sub_stripes = 1;
        dev_stripes = 1;
        devs_increment = 1;
        ncopies = 1;
        devs_max = 0;   /* 0 == as many as possible */
        devs_min = 1;

        /*
         * define the properties of each RAID type.
         * FIXME: move this to a global table and use it in all RAID
         * calculation code
         */
        if (type & (BTRFS_BLOCK_GROUP_DUP)) {
                dev_stripes = 2;
                ncopies = 2;
                devs_max = 1;
        } else if (type & (BTRFS_BLOCK_GROUP_RAID0)) {
                devs_min = 2;
        } else if (type & (BTRFS_BLOCK_GROUP_RAID1)) {
                devs_increment = 2;
                ncopies = 2;
                devs_max = 2;
                devs_min = 2;
        } else if (type & (BTRFS_BLOCK_GROUP_RAID10)) {
                sub_stripes = 2;
                devs_increment = 2;
                ncopies = 2;
                devs_min = 4;
        } else {
                devs_max = 1;
        }

        if (type & BTRFS_BLOCK_GROUP_DATA) {
                max_stripe_size = 1024 * 1024 * 1024;
                max_chunk_size = 10 * max_stripe_size;
        } else if (type & BTRFS_BLOCK_GROUP_METADATA) {
                /* for larger filesystems, use larger metadata chunks */
                if (fs_devices->total_rw_bytes > 50ULL * 1024 * 1024 * 1024)
                        max_stripe_size = 1024 * 1024 * 1024;
                else
                        max_stripe_size = 256 * 1024 * 1024;
                max_chunk_size = max_stripe_size;
        } else if (type & BTRFS_BLOCK_GROUP_SYSTEM) {
                max_stripe_size = 32 * 1024 * 1024;
                max_chunk_size = 2 * max_stripe_size;
        } else {
                printk(KERN_ERR "btrfs: invalid chunk type 0x%llx requested\n",
                       type);
                BUG_ON(1);
        }

        /* we don't want a chunk larger than 10% of writeable space */
        max_chunk_size = min(div_factor(fs_devices->total_rw_bytes, 1),
                             max_chunk_size);

        devices_info = kzalloc(sizeof(*devices_info) * fs_devices->rw_devices,
                               GFP_NOFS);
        if (!devices_info)
                return -ENOMEM;

        cur = fs_devices->alloc_list.next;

        /*
         * in the first pass through the devices list, we gather information
         * about the available holes on each device.
         */
        ndevs = 0;
        while (cur != &fs_devices->alloc_list) {
                struct btrfs_device *device;
                u64 max_avail;
                u64 dev_offset;

                device = list_entry(cur, struct btrfs_device, dev_alloc_list);

                cur = cur->next;

                if (!device->writeable) {
                        printk(KERN_ERR
                               "btrfs: read-only device in alloc_list\n");
                        WARN_ON(1);
                        continue;
                }

                if (!device->in_fs_metadata)
                        continue;

                if (device->total_bytes > device->bytes_used)
                        total_avail = device->total_bytes - device->bytes_used;
                else
                        total_avail = 0;

                /* If there is no space on this device, skip it. */
                if (total_avail == 0)
                        continue;

                ret = find_free_dev_extent(device,
                                           max_stripe_size * dev_stripes,
                                           &dev_offset, &max_avail);
                if (ret && ret != -ENOSPC)
                        goto error;

                if (ret == 0)
                        max_avail = max_stripe_size * dev_stripes;

                if (max_avail < BTRFS_STRIPE_LEN * dev_stripes)
                        continue;

                devices_info[ndevs].dev_offset = dev_offset;
                devices_info[ndevs].max_avail = max_avail;
                devices_info[ndevs].total_avail = total_avail;
                devices_info[ndevs].dev = device;
                ++ndevs;
        }

        /*
         * now sort the devices by hole size / available space
         */
        sort(devices_info, ndevs, sizeof(struct btrfs_device_info),
             btrfs_cmp_device_info, NULL);

        /* round down to number of usable stripes */
        ndevs -= ndevs % devs_increment;

        if (ndevs < devs_increment * sub_stripes || ndevs < devs_min) {
                ret = -ENOSPC;
                goto error;
        }

        if (devs_max && ndevs > devs_max)
                ndevs = devs_max;
        /*
         * the primary goal is to maximize the number of stripes, so use as many
         * devices as possible, even if the stripes are not maximum sized.
         */
        stripe_size = devices_info[ndevs-1].max_avail;
        num_stripes = ndevs * dev_stripes;

        if (stripe_size * ndevs > max_chunk_size * ncopies) {
                stripe_size = max_chunk_size * ncopies;
                do_div(stripe_size, ndevs);
        }

        do_div(stripe_size, dev_stripes);

        /* align to BTRFS_STRIPE_LEN */
        do_div(stripe_size, BTRFS_STRIPE_LEN);
        stripe_size *= BTRFS_STRIPE_LEN;

        map = kmalloc(map_lookup_size(num_stripes), GFP_NOFS);
        if (!map) {
                ret = -ENOMEM;
                goto error;
        }
        map->num_stripes = num_stripes;

        for (i = 0; i < ndevs; ++i) {
                for (j = 0; j < dev_stripes; ++j) {
                        int s = i * dev_stripes + j;
                        map->stripes[s].dev = devices_info[i].dev;
                        map->stripes[s].physical = devices_info[i].dev_offset +
                                                   j * stripe_size;
                }
        }
        map->sector_size = extent_root->sectorsize;
        map->stripe_len = BTRFS_STRIPE_LEN;
        map->io_align = BTRFS_STRIPE_LEN;
        map->io_width = BTRFS_STRIPE_LEN;
        map->type = type;
        map->sub_stripes = sub_stripes;

        *map_ret = map;
        num_bytes = stripe_size * (num_stripes / ncopies);

        *stripe_size_out = stripe_size;
        *num_bytes_out = num_bytes;

        trace_btrfs_chunk_alloc(info->chunk_root, map, start, num_bytes);

        em = alloc_extent_map();
        if (!em) {
                ret = -ENOMEM;
                goto error;
        }
        em->bdev = (struct block_device *)map;
        em->start = start;
        em->len = num_bytes;
        em->block_start = 0;
        em->block_len = em->len;

        em_tree = &extent_root->fs_info->mapping_tree.map_tree;
        write_lock(&em_tree->lock);
        ret = add_extent_mapping(em_tree, em);
        write_unlock(&em_tree->lock);
        free_extent_map(em);
        if (ret)
                goto error;

        ret = btrfs_make_block_group(trans, extent_root, 0, type,
                                     BTRFS_FIRST_CHUNK_TREE_OBJECTID,
                                     start, num_bytes);
        if (ret)
                goto error;

        for (i = 0; i < map->num_stripes; ++i) {
                struct btrfs_device *device;
                u64 dev_offset;

                device = map->stripes[i].dev;
                dev_offset = map->stripes[i].physical;

                ret = btrfs_alloc_dev_extent(trans, device,
                                info->chunk_root->root_key.objectid,
                                BTRFS_FIRST_CHUNK_TREE_OBJECTID,
                                start, dev_offset, stripe_size);
                if (ret) {
                        btrfs_abort_transaction(trans, extent_root, ret);
                        goto error;
                }
        }

        kfree(devices_info);
        return 0;

error:
        kfree(map);
        kfree(devices_info);
        return ret;
}

static int __finish_chunk_alloc(struct btrfs_trans_handle *trans,
                                struct btrfs_root *extent_root,
                                struct map_lookup *map, u64 chunk_offset,
                                u64 chunk_size, u64 stripe_size)
{
        u64 dev_offset;
        struct btrfs_key key;
        struct btrfs_root *chunk_root = extent_root->fs_info->chunk_root;
        struct btrfs_device *device;
        struct btrfs_chunk *chunk;
        struct btrfs_stripe *stripe;
        size_t item_size = btrfs_chunk_item_size(map->num_stripes);
        int index = 0;
        int ret;

        chunk = kzalloc(item_size, GFP_NOFS);
        if (!chunk)
                return -ENOMEM;

        index = 0;
        while (index < map->num_stripes) {
                device = map->stripes[index].dev;
                device->bytes_used += stripe_size;
                ret = btrfs_update_device(trans, device);
                if (ret)
                        goto out_free;
                index++;
        }

        spin_lock(&extent_root->fs_info->free_chunk_lock);
        extent_root->fs_info->free_chunk_space -= (stripe_size *
                                                   map->num_stripes);
        spin_unlock(&extent_root->fs_info->free_chunk_lock);

        index = 0;
        stripe = &chunk->stripe;
        while (index < map->num_stripes) {
                device = map->stripes[index].dev;
                dev_offset = map->stripes[index].physical;

                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);
                stripe++;
                index++;
        }

        btrfs_set_stack_chunk_length(chunk, chunk_size);
        btrfs_set_stack_chunk_owner(chunk, extent_root->root_key.objectid);
        btrfs_set_stack_chunk_stripe_len(chunk, map->stripe_len);
        btrfs_set_stack_chunk_type(chunk, map->type);
        btrfs_set_stack_chunk_num_stripes(chunk, map->num_stripes);
        btrfs_set_stack_chunk_io_align(chunk, map->stripe_len);
        btrfs_set_stack_chunk_io_width(chunk, map->stripe_len);
        btrfs_set_stack_chunk_sector_size(chunk, extent_root->sectorsize);
        btrfs_set_stack_chunk_sub_stripes(chunk, map->sub_stripes);

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

        ret = btrfs_insert_item(trans, chunk_root, &key, chunk, item_size);

        if (ret == 0 && map->type & BTRFS_BLOCK_GROUP_SYSTEM) {
                /*
                 * TODO: Cleanup of inserted chunk root in case of
                 * failure.
                 */
                ret = btrfs_add_system_chunk(chunk_root, &key, chunk,
                                             item_size);
        }

out_free:
        kfree(chunk);
        return ret;
}

/*
 * Chunk allocation falls into two parts. The first part does works
 * that make the new allocated chunk useable, but not do any operation
 * that modifies the chunk tree. The second part does the works that
 * require modifying the chunk tree. This division is important for the
 * bootstrap process of adding storage to a seed btrfs.
 */
int btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
                      struct btrfs_root *extent_root, u64 type)
{
        u64 chunk_offset;
        u64 chunk_size;
        u64 stripe_size;
        struct map_lookup *map;
        struct btrfs_root *chunk_root = extent_root->fs_info->chunk_root;
        int ret;

        ret = find_next_chunk(chunk_root, BTRFS_FIRST_CHUNK_TREE_OBJECTID,
                              &chunk_offset);
        if (ret)
                return ret;

        ret = __btrfs_alloc_chunk(trans, extent_root, &map, &chunk_size,
                                  &stripe_size, chunk_offset, type);
        if (ret)
                return ret;

        ret = __finish_chunk_alloc(trans, extent_root, map, chunk_offset,
                                   chunk_size, stripe_size);
        if (ret)
                return ret;
        return 0;
}

static noinline int init_first_rw_device(struct btrfs_trans_handle *trans,
                                         struct btrfs_root *root,
                                         struct btrfs_device *device)
{
        u64 chunk_offset;
        u64 sys_chunk_offset;
        u64 chunk_size;
        u64 sys_chunk_size;
        u64 stripe_size;
        u64 sys_stripe_size;
        u64 alloc_profile;
        struct map_lookup *map;
        struct map_lookup *sys_map;
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_root *extent_root = fs_info->extent_root;
        int ret;

        ret = find_next_chunk(fs_info->chunk_root,
                              BTRFS_FIRST_CHUNK_TREE_OBJECTID, &chunk_offset);
        if (ret)
                return ret;

        alloc_profile = BTRFS_BLOCK_GROUP_METADATA |
                                fs_info->avail_metadata_alloc_bits;
        alloc_profile = btrfs_reduce_alloc_profile(root, alloc_profile);

        ret = __btrfs_alloc_chunk(trans, extent_root, &map, &chunk_size,
                                  &stripe_size, chunk_offset, alloc_profile);
        if (ret)
                return ret;

        sys_chunk_offset = chunk_offset + chunk_size;

        alloc_profile = BTRFS_BLOCK_GROUP_SYSTEM |
                                fs_info->avail_system_alloc_bits;
        alloc_profile = btrfs_reduce_alloc_profile(root, alloc_profile);

        ret = __btrfs_alloc_chunk(trans, extent_root, &sys_map,
                                  &sys_chunk_size, &sys_stripe_size,
                                  sys_chunk_offset, alloc_profile);
        if (ret)
                goto abort;

        ret = btrfs_add_device(trans, fs_info->chunk_root, device);
        if (ret)
                goto abort;

        /*
         * Modifying chunk tree needs allocating new blocks from both
         * system block group and metadata block group. So we only can
         * do operations require modifying the chunk tree after both
         * block groups were created.
         */
        ret = __finish_chunk_alloc(trans, extent_root, map, chunk_offset,
                                   chunk_size, stripe_size);
        if (ret)
                goto abort;

        ret = __finish_chunk_alloc(trans, extent_root, sys_map,
                                   sys_chunk_offset, sys_chunk_size,
                                   sys_stripe_size);
        if (ret)
                goto abort;

        return 0;

abort:
        btrfs_abort_transaction(trans, root, ret);
        return ret;
}

int btrfs_chunk_readonly(struct btrfs_root *root, u64 chunk_offset)
{
        struct extent_map *em;
        struct map_lookup *map;
        struct btrfs_mapping_tree *map_tree = &root->fs_info->mapping_tree;
        int readonly = 0;
        int i;

        read_lock(&map_tree->map_tree.lock);
        em = lookup_extent_mapping(&map_tree->map_tree, chunk_offset, 1);
        read_unlock(&map_tree->map_tree.lock);
        if (!em)
                return 1;

        if (btrfs_test_opt(root, DEGRADED)) {
                free_extent_map(em);
                return 0;
        }

        map = (struct map_lookup *)em->bdev;
        for (i = 0; i < map->num_stripes; i++) {
                if (!map->stripes[i].dev->writeable) {
                        readonly = 1;
                        break;
                }
        }
        free_extent_map(em);
        return readonly;
}

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

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

        while (1) {
                write_lock(&tree->map_tree.lock);
                em = lookup_extent_mapping(&tree->map_tree, 0, (u64)-1);
                if (em)
                        remove_extent_mapping(&tree->map_tree, em);
                write_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;

        read_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, logical, len);
        read_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_bio **bbio_ret,
                             int mirror_num)
{
        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_end_offset;
        u64 stripe_nr;
        u64 stripe_nr_orig;
        u64 stripe_nr_end;
        int stripe_index;
        int i;
        int ret = 0;
        int num_stripes;
        int max_errors = 0;
        struct btrfs_bio *bbio = NULL;

        read_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, logical, *length);
        read_unlock(&em_tree->lock);

        if (!em) {
                printk(KERN_CRIT "unable to find logical %llu len %llu\n",
                       (unsigned long long)logical,
                       (unsigned long long)*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;

        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 (rw & REQ_DISCARD)
                *length = min_t(u64, em->len - offset, *length);
        else if (map->type & BTRFS_BLOCK_GROUP_PROFILE_MASK) {
                /* 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 (!bbio_ret)
                goto out;

        num_stripes = 1;
        stripe_index = 0;
        stripe_nr_orig = stripe_nr;
        stripe_nr_end = (offset + *length + map->stripe_len - 1) &
                        (~(map->stripe_len - 1));
        do_div(stripe_nr_end, map->stripe_len);
        stripe_end_offset = stripe_nr_end * map->stripe_len -
                            (offset + *length);
        if (map->type & BTRFS_BLOCK_GROUP_RAID0) {
                if (rw & REQ_DISCARD)
                        num_stripes = min_t(u64, map->num_stripes,
                                            stripe_nr_end - stripe_nr_orig);
                stripe_index = do_div(stripe_nr, map->num_stripes);
        } else if (map->type & BTRFS_BLOCK_GROUP_RAID1) {
                if (rw & (REQ_WRITE | REQ_DISCARD))
                        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);
                        mirror_num = stripe_index + 1;
                }

        } else if (map->type & BTRFS_BLOCK_GROUP_DUP) {
                if (rw & (REQ_WRITE | REQ_DISCARD)) {
                        num_stripes = map->num_stripes;
                } else if (mirror_num) {
                        stripe_index = mirror_num - 1;
                } else {
                        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 (rw & REQ_WRITE)
                        num_stripes = map->sub_stripes;
                else if (rw & REQ_DISCARD)
                        num_stripes = min_t(u64, map->sub_stripes *
                                            (stripe_nr_end - stripe_nr_orig),
                                            map->num_stripes);
                else if (mirror_num)
                        stripe_index += mirror_num - 1;
                else {
                        int old_stripe_index = stripe_index;
                        stripe_index = find_live_mirror(map, stripe_index,
                                              map->sub_stripes, stripe_index +
                                              current->pid % map->sub_stripes);
                        mirror_num = stripe_index - old_stripe_index + 1;
                }
        } 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);
                mirror_num = stripe_index + 1;
        }
        BUG_ON(stripe_index >= map->num_stripes);

        bbio = kzalloc(btrfs_bio_size(num_stripes), GFP_NOFS);
        if (!bbio) {
                ret = -ENOMEM;
                goto out;
        }
        atomic_set(&bbio->error, 0);

        if (rw & REQ_DISCARD) {
                int factor = 0;
                int sub_stripes = 0;
                u64 stripes_per_dev = 0;
                u32 remaining_stripes = 0;
                u32 last_stripe = 0;

                if (map->type &
                    (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID10)) {
                        if (map->type & BTRFS_BLOCK_GROUP_RAID0)
                                sub_stripes = 1;
                        else
                                sub_stripes = map->sub_stripes;

                        factor = map->num_stripes / sub_stripes;
                        stripes_per_dev = div_u64_rem(stripe_nr_end -
                                                      stripe_nr_orig,
                                                      factor,
                                                      &remaining_stripes);
                        div_u64_rem(stripe_nr_end - 1, factor, &last_stripe);
                        last_stripe *= sub_stripes;
                }

                for (i = 0; i < num_stripes; i++) {
                        bbio->stripes[i].physical =
                                map->stripes[stripe_index].physical +
                                stripe_offset + stripe_nr * map->stripe_len;
                        bbio->stripes[i].dev = map->stripes[stripe_index].dev;

                        if (map->type & (BTRFS_BLOCK_GROUP_RAID0 |
                                         BTRFS_BLOCK_GROUP_RAID10)) {
                                bbio->stripes[i].length = stripes_per_dev *
                                                          map->stripe_len;

                                if (i / sub_stripes < remaining_stripes)
                                        bbio->stripes[i].length +=
                                                map->stripe_len;

                                /*
                                 * Special for the first stripe and
                                 * the last stripe:
                                 *
                                 * |-------|...|-------|
                                 *     |----------|
                                 *    off     end_off
                                 */
                                if (i < sub_stripes)
                                        bbio->stripes[i].length -=
                                                stripe_offset;

                                if (stripe_index >= last_stripe &&
                                    stripe_index <= (last_stripe +
                                                     sub_stripes - 1))
                                        bbio->stripes[i].length -=
                                                stripe_end_offset;

                                if (i == sub_stripes - 1)
                                        stripe_offset = 0;
                        } else
                                bbio->stripes[i].length = *length;

                        stripe_index++;
                        if (stripe_index == map->num_stripes) {
                                /* This could only happen for RAID0/10 */
                                stripe_index = 0;
                                stripe_nr++;
                        }
                }
        } else {
                for (i = 0; i < num_stripes; i++) {
                        bbio->stripes[i].physical =
                                map->stripes[stripe_index].physical +
                                stripe_offset +
                                stripe_nr * map->stripe_len;
                        bbio->stripes[i].dev =
                                map->stripes[stripe_index].dev;
                        stripe_index++;
                }
        }

        if (rw & REQ_WRITE) {
                if (map->type & (BTRFS_BLOCK_GROUP_RAID1 |
                                 BTRFS_BLOCK_GROUP_RAID10 |
                                 BTRFS_BLOCK_GROUP_DUP)) {
                        max_errors = 1;
                }
        }

        *bbio_ret = bbio;
        bbio->num_stripes = num_stripes;
        bbio->max_errors = max_errors;
        bbio->mirror_num = mirror_num;
out:
        free_extent_map(em);
        return ret;
}

int btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,
                      u64 logical, u64 *length,
                      struct btrfs_bio **bbio_ret, int mirror_num)
{
        return __btrfs_map_block(map_tree, rw, logical, length, bbio_ret,
                                 mirror_num);
}

int btrfs_rmap_block(struct btrfs_mapping_tree *map_tree,
                     u64 chunk_start, u64 physical, u64 devid,
                     u64 **logical, int *naddrs, int *stripe_len)
{
        struct extent_map_tree *em_tree = &map_tree->map_tree;
        struct extent_map *em;
        struct map_lookup *map;
        u64 *buf;
        u64 bytenr;
        u64 length;
        u64 stripe_nr;
        int i, j, nr = 0;

        read_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, chunk_start, 1);
        read_unlock(&em_tree->lock);

        BUG_ON(!em || em->start != chunk_start);
        map = (struct map_lookup *)em->bdev;

        length = em->len;
        if (map->type & BTRFS_BLOCK_GROUP_RAID10)
                do_div(length, map->num_stripes / map->sub_stripes);
        else if (map->type & BTRFS_BLOCK_GROUP_RAID0)
                do_div(length, map->num_stripes);

        buf = kzalloc(sizeof(u64) * map->num_stripes, GFP_NOFS);
        BUG_ON(!buf); /* -ENOMEM */

        for (i = 0; i < map->num_stripes; i++) {
                if (devid && map->stripes[i].dev->devid != devid)
                        continue;
                if (map->stripes[i].physical > physical ||
                    map->stripes[i].physical + length <= physical)
                        continue;

                stripe_nr = physical - map->stripes[i].physical;
                do_div(stripe_nr, map->stripe_len);

                if (map->type & BTRFS_BLOCK_GROUP_RAID10) {
                        stripe_nr = stripe_nr * map->num_stripes + i;
                        do_div(stripe_nr, map->sub_stripes);
                } else if (map->type & BTRFS_BLOCK_GROUP_RAID0) {
                        stripe_nr = stripe_nr * map->num_stripes + i;
                }
                bytenr = chunk_start + stripe_nr * map->stripe_len;
                WARN_ON(nr >= map->num_stripes);
                for (j = 0; j < nr; j++) {
                        if (buf[j] == bytenr)
                                break;
                }
                if (j == nr) {
                        WARN_ON(nr >= map->num_stripes);
                        buf[nr++] = bytenr;
                }
        }

        *logical = buf;
        *naddrs = nr;
        *stripe_len = map->stripe_len;

        free_extent_map(em);
        return 0;
}

static void *merge_stripe_index_into_bio_private(void *bi_private,
                                                 unsigned int stripe_index)
{
        /*
         * with single, dup, RAID0, RAID1 and RAID10, stripe_index is
         * at most 1.
         * The alternative solution (instead of stealing bits from the
         * pointer) would be to allocate an intermediate structure
         * that contains the old private pointer plus the stripe_index.
         */
        BUG_ON((((uintptr_t)bi_private) & 3) != 0);
        BUG_ON(stripe_index > 3);
        return (void *)(((uintptr_t)bi_private) | stripe_index);
}

static struct btrfs_bio *extract_bbio_from_bio_private(void *bi_private)
{
        return (struct btrfs_bio *)(((uintptr_t)bi_private) & ~((uintptr_t)3));
}

static unsigned int extract_stripe_index_from_bio_private(void *bi_private)
{
        return (unsigned int)((uintptr_t)bi_private) & 3;
}

static void btrfs_end_bio(struct bio *bio, int err)
{
        struct btrfs_bio *bbio = extract_bbio_from_bio_private(bio->bi_private);
        int is_orig_bio = 0;

        if (err) {
                atomic_inc(&bbio->error);
                if (err == -EIO || err == -EREMOTEIO) {
                        unsigned int stripe_index =
                                extract_stripe_index_from_bio_private(
                                        bio->bi_private);
                        struct btrfs_device *dev;

                        BUG_ON(stripe_index >= bbio->num_stripes);
                        dev = bbio->stripes[stripe_index].dev;
                        if (bio->bi_rw & WRITE)
                                btrfs_dev_stat_inc(dev,
                                                   BTRFS_DEV_STAT_WRITE_ERRS);
                        else
                                btrfs_dev_stat_inc(dev,
                                                   BTRFS_DEV_STAT_READ_ERRS);
                        if ((bio->bi_rw & WRITE_FLUSH) == WRITE_FLUSH)
                                btrfs_dev_stat_inc(dev,
                                                   BTRFS_DEV_STAT_FLUSH_ERRS);
                        btrfs_dev_stat_print_on_error(dev);
                }
        }

        if (bio == bbio->orig_bio)
                is_orig_bio = 1;

        if (atomic_dec_and_test(&bbio->stripes_pending)) {
                if (!is_orig_bio) {
                        bio_put(bio);
                        bio = bbio->orig_bio;
                }
                bio->bi_private = bbio->private;
                bio->bi_end_io = bbio->end_io;
                bio->bi_bdev = (struct block_device *)
                                        (unsigned long)bbio->mirror_num;
                /* only send an error to the higher layers if it is
                 * beyond the tolerance of the multi-bio
                 */
                if (atomic_read(&bbio->error) > bbio->max_errors) {
                        err = -EIO;
                } else {
                        /*
                         * 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(bbio);

                bio_endio(bio, err);
        } else if (!is_orig_bio) {
                bio_put(bio);
        }
}

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.
 */
static noinline void schedule_bio(struct btrfs_root *root,
                                 struct btrfs_device *device,
                                 int rw, struct bio *bio)
{
        int should_queue = 1;
        struct btrfs_pending_bios *pending_bios;

        /* don't bother with additional async steps for reads, right now */
        if (!(rw & REQ_WRITE)) {
                bio_get(bio);
                btrfsic_submit_bio(rw, bio);
                bio_put(bio);
                return;
        }

        /*
         * nr_async_bios 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_bios);
        WARN_ON(bio->bi_next);
        bio->bi_next = NULL;
        bio->bi_rw |= rw;

        spin_lock(&device->io_lock);
        if (bio->bi_rw & REQ_SYNC)
                pending_bios = &device->pending_sync_bios;
        else
                pending_bios = &device->pending_bios;

        if (pending_bios->tail)
                pending_bios->tail->bi_next = bio;

        pending_bios->tail = bio;
        if (!pending_bios->head)
                pending_bios->head = 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);
}

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 = (u64)bio->bi_sector << 9;
        u64 length = 0;
        u64 map_length;
        int ret;
        int dev_nr = 0;
        int total_devs = 1;
        struct btrfs_bio *bbio = NULL;

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

        ret = btrfs_map_block(map_tree, rw, logical, &map_length, &bbio,
                              mirror_num);
        if (ret) /* -ENOMEM */
                return ret;

        total_devs = bbio->num_stripes;
        if (map_length < length) {
                printk(KERN_CRIT "mapping failed logical %llu bio len %llu "
                       "len %llu\n", (unsigned long long)logical,
                       (unsigned long long)length,
                       (unsigned long long)map_length);
                BUG();
        }

        bbio->orig_bio = first_bio;
        bbio->private = first_bio->bi_private;
        bbio->end_io = first_bio->bi_end_io;
        atomic_set(&bbio->stripes_pending, bbio->num_stripes);

        while (dev_nr < total_devs) {
                if (dev_nr < total_devs - 1) {
                        bio = bio_clone(first_bio, GFP_NOFS);
                        BUG_ON(!bio); /* -ENOMEM */
                } else {
                        bio = first_bio;
                }
                bio->bi_private = bbio;
                bio->bi_private = merge_stripe_index_into_bio_private(
                                bio->bi_private, (unsigned int)dev_nr);
                bio->bi_end_io = btrfs_end_bio;
                bio->bi_sector = bbio->stripes[dev_nr].physical >> 9;
                dev = bbio->stripes[dev_nr].dev;
                if (dev && dev->bdev && (rw != WRITE || dev->writeable)) {
#ifdef DEBUG
                        struct rcu_string *name;

                        rcu_read_lock();
                        name = rcu_dereference(dev->name);
                        pr_debug("btrfs_map_bio: rw %d, secor=%llu, dev=%lu "
                                 "(%s id %llu), size=%u\n", rw,
                                 (u64)bio->bi_sector, (u_long)dev->bdev->bd_dev,
                                 name->str, dev->devid, bio->bi_size);
                        rcu_read_unlock();
#endif
                        bio->bi_bdev = dev->bdev;
                        if (async_submit)
                                schedule_bio(root, dev, rw, bio);
                        else
                                btrfsic_submit_bio(rw, bio);
                } else {
                        bio->bi_bdev = root->fs_info->fs_devices->latest_bdev;
                        bio->bi_sector = logical >> 9;
                        bio_endio(bio, -EIO);
                }
                dev_nr++;
        }
        return 0;
}

struct btrfs_device *btrfs_find_device(struct btrfs_root *root, u64 devid,
                                       u8 *uuid, u8 *fsid)
{
        struct btrfs_device *device;
        struct btrfs_fs_devices *cur_devices;

        cur_devices = root->fs_info->fs_devices;
        while (cur_devices) {
                if (!fsid ||
                    !memcmp(cur_devices->fsid, fsid, BTRFS_UUID_SIZE)) {
                        device = __find_device(&cur_devices->devices,
                                               devid, uuid);
                        if (device)
                                return device;
                }
                cur_devices = cur_devices->seed;
        }
        return NULL;
}

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);
        if (!device)
                return NULL;
        list_add(&device->dev_list,
                 &fs_devices->devices);
        device->dev_root = root->fs_info->dev_root;
        device->devid = devid;
        device->work.func = pending_bios_fn;
        device->fs_devices = fs_devices;
        device->missing = 1;
        fs_devices->num_devices++;
        fs_devices->missing_devices++;
        spin_lock_init(&device->io_lock);
        INIT_LIST_HEAD(&device->dev_alloc_list);
        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);

        read_lock(&map_tree->map_tree.lock);
        em = lookup_extent_mapping(&map_tree->map_tree, logical, 1);
        read_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);
        }

        em = alloc_extent_map();
        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;
        em->block_len = em->len;

        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,
                                                        NULL);
                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;
        }

        write_lock(&map_tree->map_tree.lock);
        ret = add_extent_mapping(&map_tree->map_tree, em);
        write_unlock(&map_tree->map_tree.lock);
        BUG_ON(ret); /* Tree corruption */
        free_extent_map(em);

        return 0;
}

static void 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->disk_total_bytes = btrfs_device_total_bytes(leaf, dev_item);
        device->total_bytes = device->disk_total_bytes;
        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);
}

static int open_seed_devices(struct btrfs_root *root, u8 *fsid)
{
        struct btrfs_fs_devices *fs_devices;
        int ret;

        BUG_ON(!mutex_is_locked(&uuid_mutex));

        fs_devices = root->fs_info->fs_devices->seed;
        while (fs_devices) {
                if (!memcmp(fs_devices->fsid, fsid, BTRFS_UUID_SIZE)) {
                        ret = 0;
                        goto out;
                }
                fs_devices = fs_devices->seed;
        }

        fs_devices = find_fsid(fsid);
        if (!fs_devices) {
                ret = -ENOENT;
                goto out;
        }

        fs_devices = clone_fs_devices(fs_devices);
        if (IS_ERR(fs_devices)) {
                ret = PTR_ERR(fs_devices);
                goto out;
        }

        ret = __btrfs_open_devices(fs_devices, FMODE_READ,
                                   root->fs_info->bdev_holder);
        if (ret) {
                free_fs_devices(fs_devices);
                goto out;
        }

        if (!fs_devices->seeding) {
                __btrfs_close_devices(fs_devices);
                free_fs_devices(fs_devices);
                ret = -EINVAL;
                goto out;
        }

        fs_devices->seed = root->fs_info->fs_devices->seed;
        root->fs_info->fs_devices->seed = fs_devices;
out:
        return ret;
}

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 fs_uuid[BTRFS_UUID_SIZE];
        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);
        read_extent_buffer(leaf, fs_uuid,
                           (unsigned long)btrfs_device_fsid(dev_item),
                           BTRFS_UUID_SIZE);

        if (memcmp(fs_uuid, root->fs_info->fsid, BTRFS_UUID_SIZE)) {
                ret = open_seed_devices(root, fs_uuid);
                if (ret && !btrfs_test_opt(root, DEGRADED))
                        return ret;
        }

        device = btrfs_find_device(root, devid, dev_uuid, fs_uuid);
        if (!device || !device->bdev) {
                if (!btrfs_test_opt(root, DEGRADED))
                        return -EIO;

                if (!device) {
                        printk(KERN_WARNING "warning devid %llu missing\n",
                               (unsigned long long)devid);
                        device = add_missing_dev(root, devid, dev_uuid);
                        if (!device)
                                return -ENOMEM;
                } else if (!device->missing) {
                        /*
                         * this happens when a device that was properly setup
                         * in the device info lists suddenly goes bad.
                         * device->bdev is NULL, and so we have to set
                         * device->missing to one here
                         */
                        root->fs_info->fs_devices->missing_devices++;
                        device->missing = 1;
                }
        }

        if (device->fs_devices != root->fs_info->fs_devices) {
                BUG_ON(device->writeable);
                if (device->generation !=
                    btrfs_device_generation(leaf, dev_item))
                        return -EINVAL;
        }

        fill_device_from_item(leaf, dev_item, device);
        device->dev_root = root->fs_info->dev_root;
        device->in_fs_metadata = 1;
        if (device->writeable) {
                device->fs_devices->total_rw_bytes += device->total_bytes;
                spin_lock(&root->fs_info->free_chunk_lock);
                root->fs_info->free_chunk_space += device->total_bytes -
                        device->bytes_used;
                spin_unlock(&root->fs_info->free_chunk_lock);
        }
        ret = 0;
        return ret;
}

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);
        btrfs_set_buffer_lockdep_class(root->root_key.objectid, sb, 0);
        /*
         * The sb extent buffer is artifical and just used to read the system array.
         * btrfs_set_buffer_uptodate() call does not properly mark all it's
         * pages up-to-date when the page is larger: extent does not cover the
         * whole page and consequently check_page_uptodate does not find all
         * the page's extents up-to-date (the hole beyond sb),
         * write_extent_buffer then triggers a WARN_ON.
         *
         * Regular short extents go through mark_extent_buffer_dirty/writeback cycle,
         * but sb spans only this function. Add an explicit SetPageUptodate call
         * to silence the warning eg. on PowerPC 64.
         */
        if (PAGE_CACHE_SIZE > BTRFS_SUPER_INFO_SIZE)
                SetPageUptodate(sb->pages[0]);

        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;
}

struct btrfs_device *btrfs_find_device_for_logical(struct btrfs_root *root,
                                                   u64 logical, int mirror_num)
{
        struct btrfs_mapping_tree *map_tree = &root->fs_info->mapping_tree;
        int ret;
        u64 map_length = 0;
        struct btrfs_bio *bbio = NULL;
        struct btrfs_device *device;

        BUG_ON(mirror_num == 0);
        ret = btrfs_map_block(map_tree, WRITE, logical, &map_length, &bbio,
                              mirror_num);
        if (ret) {
                BUG_ON(bbio != NULL);
                return NULL;
        }
        BUG_ON(mirror_num != bbio->mirror_num);
        device = bbio->stripes[mirror_num - 1].dev;
        kfree(bbio);
        return device;
}

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;

        mutex_lock(&uuid_mutex);
        lock_chunks(root);

        /* 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);
        if (ret < 0)
                goto error;
        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);
                                if (ret)
                                        goto error;
                        }
                } 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);
                        if (ret)
                                goto error;
                }
                path->slots[0]++;
        }
        if (key.objectid == BTRFS_DEV_ITEMS_OBJECTID) {
                key.objectid = 0;
                btrfs_release_path(path);
                goto again;
        }
        ret = 0;
error:
        unlock_chunks(root);
        mutex_unlock(&uuid_mutex);

        btrfs_free_path(path);
        return ret;
}

static void __btrfs_reset_dev_stats(struct btrfs_device *dev)
{
        int i;

        for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++)
                btrfs_dev_stat_reset(dev, i);
}

int btrfs_init_dev_stats(struct btrfs_fs_info *fs_info)
{
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct btrfs_root *dev_root = fs_info->dev_root;
        struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
        struct extent_buffer *eb;
        int slot;
        int ret = 0;
        struct btrfs_device *device;
        struct btrfs_path *path = NULL;
        int i;

        path = btrfs_alloc_path();
        if (!path) {
                ret = -ENOMEM;
                goto out;
        }

        mutex_lock(&fs_devices->device_list_mutex);
        list_for_each_entry(device, &fs_devices->devices, dev_list) {
                int item_size;
                struct btrfs_dev_stats_item *ptr;

                key.objectid = 0;
                key.type = BTRFS_DEV_STATS_KEY;
                key.offset = device->devid;
                ret = btrfs_search_slot(NULL, dev_root, &key, path, 0, 0);
                if (ret) {
                        printk_in_rcu(KERN_WARNING "btrfs: no dev_stats entry found for device %s (devid %llu) (OK on first mount after mkfs)\n",
                                      rcu_str_deref(device->name),
                                      (unsigned long long)device->devid);
                        __btrfs_reset_dev_stats(device);
                        device->dev_stats_valid = 1;
                        btrfs_release_path(path);
                        continue;
                }
                slot = path->slots[0];
                eb = path->nodes[0];
                btrfs_item_key_to_cpu(eb, &found_key, slot);
                item_size = btrfs_item_size_nr(eb, slot);

                ptr = btrfs_item_ptr(eb, slot,
                                     struct btrfs_dev_stats_item);

                for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++) {
                        if (item_size >= (1 + i) * sizeof(__le64))
                                btrfs_dev_stat_set(device, i,
                                        btrfs_dev_stats_value(eb, ptr, i));
                        else
                                btrfs_dev_stat_reset(device, i);
                }

                device->dev_stats_valid = 1;
                btrfs_dev_stat_print_on_load(device);
                btrfs_release_path(path);
        }
        mutex_unlock(&fs_devices->device_list_mutex);

out:
        btrfs_free_path(path);
        return ret < 0 ? ret : 0;
}

static int update_dev_stat_item(struct btrfs_trans_handle *trans,
                                struct btrfs_root *dev_root,
                                struct btrfs_device *device)
{
        struct btrfs_path *path;
        struct btrfs_key key;
        struct extent_buffer *eb;
        struct btrfs_dev_stats_item *ptr;
        int ret;
        int i;

        key.objectid = 0;
        key.type = BTRFS_DEV_STATS_KEY;
        key.offset = device->devid;

        path = btrfs_alloc_path();
        BUG_ON(!path);
        ret = btrfs_search_slot(trans, dev_root, &key, path, -1, 1);
        if (ret < 0) {
                printk_in_rcu(KERN_WARNING "btrfs: error %d while searching for dev_stats item for device %s!\n",
                              ret, rcu_str_deref(device->name));
                goto out;
        }

        if (ret == 0 &&
            btrfs_item_size_nr(path->nodes[0], path->slots[0]) < sizeof(*ptr)) {
                /* need to delete old one and insert a new one */
                ret = btrfs_del_item(trans, dev_root, path);
                if (ret != 0) {
                        printk_in_rcu(KERN_WARNING "btrfs: delete too small dev_stats item for device %s failed %d!\n",
                                      rcu_str_deref(device->name), ret);
                        goto out;
                }
                ret = 1;
        }

        if (ret == 1) {
                /* need to insert a new item */
                btrfs_release_path(path);
                ret = btrfs_insert_empty_item(trans, dev_root, path,
                                              &key, sizeof(*ptr));
                if (ret < 0) {
                        printk_in_rcu(KERN_WARNING "btrfs: insert dev_stats item for device %s failed %d!\n",
                                      rcu_str_deref(device->name), ret);
                        goto out;
                }
        }

        eb = path->nodes[0];
        ptr = btrfs_item_ptr(eb, path->slots[0], struct btrfs_dev_stats_item);
        for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++)
                btrfs_set_dev_stats_value(eb, ptr, i,
                                          btrfs_dev_stat_read(device, i));
        btrfs_mark_buffer_dirty(eb);

out:
        btrfs_free_path(path);
        return ret;
}

/*
 * called from commit_transaction. Writes all changed device stats to disk.
 */
int btrfs_run_dev_stats(struct btrfs_trans_handle *trans,
                        struct btrfs_fs_info *fs_info)
{
        struct btrfs_root *dev_root = fs_info->dev_root;
        struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
        struct btrfs_device *device;
        int ret = 0;

        mutex_lock(&fs_devices->device_list_mutex);
        list_for_each_entry(device, &fs_devices->devices, dev_list) {
                if (!device->dev_stats_valid || !device->dev_stats_dirty)
                        continue;

                ret = update_dev_stat_item(trans, dev_root, device);
                if (!ret)
                        device->dev_stats_dirty = 0;
        }
        mutex_unlock(&fs_devices->device_list_mutex);

        return ret;
}

void btrfs_dev_stat_inc_and_print(struct btrfs_device *dev, int index)
{
        btrfs_dev_stat_inc(dev, index);
        btrfs_dev_stat_print_on_error(dev);
}

void btrfs_dev_stat_print_on_error(struct btrfs_device *dev)
{
        if (!dev->dev_stats_valid)
                return;
        printk_ratelimited_in_rcu(KERN_ERR
                           "btrfs: bdev %s errs: wr %u, rd %u, flush %u, corrupt %u, gen %u\n",
                           rcu_str_deref(dev->name),
                           btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_WRITE_ERRS),
                           btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_READ_ERRS),
                           btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_FLUSH_ERRS),
                           btrfs_dev_stat_read(dev,
                                               BTRFS_DEV_STAT_CORRUPTION_ERRS),
                           btrfs_dev_stat_read(dev,
                                               BTRFS_DEV_STAT_GENERATION_ERRS));
}

static void btrfs_dev_stat_print_on_load(struct btrfs_device *dev)
{
        printk_in_rcu(KERN_INFO "btrfs: bdev %s errs: wr %u, rd %u, flush %u, corrupt %u, gen %u\n",
               rcu_str_deref(dev->name),
               btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_WRITE_ERRS),
               btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_READ_ERRS),
               btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_FLUSH_ERRS),
               btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_CORRUPTION_ERRS),
               btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_GENERATION_ERRS));
}

int btrfs_get_dev_stats(struct btrfs_root *root,
                        struct btrfs_ioctl_get_dev_stats *stats,
                        int reset_after_read)
{
        struct btrfs_device *dev;
        struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
        int i;

        mutex_lock(&fs_devices->device_list_mutex);
        dev = btrfs_find_device(root, stats->devid, NULL, NULL);
        mutex_unlock(&fs_devices->device_list_mutex);

        if (!dev) {
                printk(KERN_WARNING
                       "btrfs: get dev_stats failed, device not found\n");
                return -ENODEV;
        } else if (!dev->dev_stats_valid) {
                printk(KERN_WARNING
                       "btrfs: get dev_stats failed, not yet valid\n");
                return -ENODEV;
        } else if (reset_after_read) {
                for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++) {
                        if (stats->nr_items > i)
                                stats->values[i] =
                                        btrfs_dev_stat_read_and_reset(dev, i);
                        else
                                btrfs_dev_stat_reset(dev, i);
                }
        } else {
                for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++)
                        if (stats->nr_items > i)
                                stats->values[i] = btrfs_dev_stat_read(dev, i);
        }
        if (stats->nr_items > BTRFS_DEV_STAT_VALUES_MAX)
                stats->nr_items = BTRFS_DEV_STAT_VALUES_MAX;
        return 0;
}