volumes.c

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/*
 * 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;

        if (atomic_dec_return(&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;
    fs_devices->total_devices = orig->total_devices;
    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 */
        if (device->name) {
            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 "btrfs: 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;
    u64 total_devices;

    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);
    total_devices = btrfs_super_num_devices(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);
    if (!ret && fs_devices_ret)
        (*fs_devices_ret)->total_devices = total_devices;
    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--;
    device->fs_devices->total_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);
    }

    root->fs_info->num_tolerated_disk_barrier_failures =
        btrfs_calc_num_tolerated_disk_barrier_failures(root->fs_info);

    /*
     * 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->total_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;

    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++;
    root->fs_info->fs_devices->total_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) {
            btrfs_abort_transaction(trans, root, ret);
            goto error_trans;
        }
        ret = btrfs_finish_sprout(trans, root);
        if (ret) {
            btrfs_abort_transaction(trans, root, ret);
            goto error_trans;
        }
    } else {
        ret = btrfs_add_device(trans, root, device);
        if (ret) {
            btrfs_abort_transaction(trans, root, 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);
    root->fs_info->num_tolerated_disk_barrier_failures =
        btrfs_calc_num_tolerated_disk_barrier_failures(root->fs_info);
    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.");
        trans = btrfs_attach_transaction(root);
        if (IS_ERR(trans)) {
            if (PTR_ERR(trans) == -ENOENT)
                return 0;
            return PTR_ERR(trans);
        }
        ret = btrfs_commit_transaction(trans, root);
    }

    return ret;

error_trans:
    unlock_chunks(root);
    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;
}

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;
        }
    }

    if (bctl->sys.flags & BTRFS_BALANCE_ARGS_CONVERT) {
        int num_tolerated_disk_barrier_failures;
        u64 target = bctl->sys.target;

        num_tolerated_disk_barrier_failures =
            btrfs_calc_num_tolerated_disk_barrier_failures(fs_info);
        if (num_tolerated_disk_barrier_failures > 0 &&
            (target &
             (BTRFS_BLOCK_GROUP_DUP | BTRFS_BLOCK_GROUP_RAID0 |
              BTRFS_AVAIL_ALLOC_BIT_SINGLE)))
            num_tolerated_disk_barrier_failures = 0;
        else if (num_tolerated_disk_barrier_failures > 1 &&
             (target &
              (BTRFS_BLOCK_GROUP_RAID1 | BTRFS_BLOCK_GROUP_RAID10)))
            num_tolerated_disk_barrier_failures = 1;

        fs_info->num_tolerated_disk_barrier_failures =
            num_tolerated_disk_barrier_failures;
    }

    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);
    }

    if (bctl->sys.flags & BTRFS_BALANCE_ARGS_CONVERT) {
        fs_info->num_tolerated_disk_barrier_failures =
            btrfs_calc_num_tolerated_disk_barrier_failures(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_fs_info *fs_info = data;
    int ret = 0;

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

    if (fs_info->balance_ctl) {
        printk(KERN_INFO "btrfs: continuing balance\n");
        ret = btrfs_balance(fs_info->balance_ctl, NULL);
    }

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

    return ret;
}

int btrfs_resume_balance_async(struct btrfs_fs_info *fs_info)
{
    struct task_struct *tsk;

    spin_lock(&fs_info->balance_lock);
    if (!fs_info->balance_ctl) {
        spin_unlock(&fs_info->balance_lock);
        return 0;
    }
    spin_unlock(&fs_info->balance_lock);

    if (btrfs_test_opt(fs_info->tree_root, SKIP_BALANCE)) {
        printk(KERN_INFO "btrfs: force skipping balance\n");
        return 0;
    }

    tsk = kthread_run(balance_kthread, fs_info, "btrfs-balance");
    if (IS_ERR(tsk))
        return PTR_ERR(tsk);

    return 0;
}

int btrfs_recover_balance(struct btrfs_fs_info *fs_info)
{
    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;

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

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

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

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

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

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

    set_balance_control(bctl);

    mutex_unlock(&fs_info->balance_mutex);
    mutex_unlock(&fs_info->volume_mutex);
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) {
        btrfs_abort_transaction(trans, root, ret);
        goto out;
    }

    ret = btrfs_add_device(trans, fs_info->chunk_root, device);
    if (ret) {
        btrfs_abort_transaction(trans, root, ret);
        goto out;
    }

    /*
     * 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) {
        btrfs_abort_transaction(trans, root, ret);
        goto out;
    }

    ret = __finish_chunk_alloc(trans, extent_root, sys_map,
                   sys_chunk_offset, sys_chunk_size,
                   sys_stripe_size);
    if (ret)
        btrfs_abort_transaction(trans, root, ret);

out:

    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 "btrfs: 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 (dev->bdev) {
                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 "btrfs: 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;
}

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) {
            __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)
{
    int i;

    for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++)
        if (btrfs_dev_stat_read(dev, i) != 0)
            break;
    if (i == BTRFS_DEV_STAT_VALUES_MAX)
        return; /* all values == 0, suppress message */

    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)
{
    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 (stats->flags & BTRFS_DEV_STATS_RESET) {
        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;
}