GNU Linux-libre 5.10.219-gnu1

[releases.git] / fs / btrfs / volumes.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 */

#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/bio.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/ratelimit.h>
#include <linux/kthread.h>
#include <linux/raid/pq.h>
#include <linux/semaphore.h>
#include <linux/uuid.h>
#include <linux/list_sort.h>
#include <linux/namei.h>
#include "misc.h"
#include "ctree.h"
#include "extent_map.h"
#include "disk-io.h"
#include "transaction.h"
#include "print-tree.h"
#include "volumes.h"
#include "raid56.h"
#include "async-thread.h"
#include "check-integrity.h"
#include "rcu-string.h"
#include "dev-replace.h"
#include "sysfs.h"
#include "tree-checker.h"
#include "space-info.h"
#include "block-group.h"
#include "discard.h"

const struct btrfs_raid_attr btrfs_raid_array[BTRFS_NR_RAID_TYPES] = {
        [BTRFS_RAID_RAID10] = {
                .sub_stripes    = 2,
                .dev_stripes    = 1,
                .devs_max       = 0,    /* 0 == as many as possible */
                .devs_min       = 4,
                .tolerated_failures = 1,
                .devs_increment = 2,
                .ncopies        = 2,
                .nparity        = 0,
                .raid_name      = "raid10",
                .bg_flag        = BTRFS_BLOCK_GROUP_RAID10,
                .mindev_error   = BTRFS_ERROR_DEV_RAID10_MIN_NOT_MET,
        },
        [BTRFS_RAID_RAID1] = {
                .sub_stripes    = 1,
                .dev_stripes    = 1,
                .devs_max       = 2,
                .devs_min       = 2,
                .tolerated_failures = 1,
                .devs_increment = 2,
                .ncopies        = 2,
                .nparity        = 0,
                .raid_name      = "raid1",
                .bg_flag        = BTRFS_BLOCK_GROUP_RAID1,
                .mindev_error   = BTRFS_ERROR_DEV_RAID1_MIN_NOT_MET,
        },
        [BTRFS_RAID_RAID1C3] = {
                .sub_stripes    = 1,
                .dev_stripes    = 1,
                .devs_max       = 3,
                .devs_min       = 3,
                .tolerated_failures = 2,
                .devs_increment = 3,
                .ncopies        = 3,
                .nparity        = 0,
                .raid_name      = "raid1c3",
                .bg_flag        = BTRFS_BLOCK_GROUP_RAID1C3,
                .mindev_error   = BTRFS_ERROR_DEV_RAID1C3_MIN_NOT_MET,
        },
        [BTRFS_RAID_RAID1C4] = {
                .sub_stripes    = 1,
                .dev_stripes    = 1,
                .devs_max       = 4,
                .devs_min       = 4,
                .tolerated_failures = 3,
                .devs_increment = 4,
                .ncopies        = 4,
                .nparity        = 0,
                .raid_name      = "raid1c4",
                .bg_flag        = BTRFS_BLOCK_GROUP_RAID1C4,
                .mindev_error   = BTRFS_ERROR_DEV_RAID1C4_MIN_NOT_MET,
        },
        [BTRFS_RAID_DUP] = {
                .sub_stripes    = 1,
                .dev_stripes    = 2,
                .devs_max       = 1,
                .devs_min       = 1,
                .tolerated_failures = 0,
                .devs_increment = 1,
                .ncopies        = 2,
                .nparity        = 0,
                .raid_name      = "dup",
                .bg_flag        = BTRFS_BLOCK_GROUP_DUP,
                .mindev_error   = 0,
        },
        [BTRFS_RAID_RAID0] = {
                .sub_stripes    = 1,
                .dev_stripes    = 1,
                .devs_max       = 0,
                .devs_min       = 2,
                .tolerated_failures = 0,
                .devs_increment = 1,
                .ncopies        = 1,
                .nparity        = 0,
                .raid_name      = "raid0",
                .bg_flag        = BTRFS_BLOCK_GROUP_RAID0,
                .mindev_error   = 0,
        },
        [BTRFS_RAID_SINGLE] = {
                .sub_stripes    = 1,
                .dev_stripes    = 1,
                .devs_max       = 1,
                .devs_min       = 1,
                .tolerated_failures = 0,
                .devs_increment = 1,
                .ncopies        = 1,
                .nparity        = 0,
                .raid_name      = "single",
                .bg_flag        = 0,
                .mindev_error   = 0,
        },
        [BTRFS_RAID_RAID5] = {
                .sub_stripes    = 1,
                .dev_stripes    = 1,
                .devs_max       = 0,
                .devs_min       = 2,
                .tolerated_failures = 1,
                .devs_increment = 1,
                .ncopies        = 1,
                .nparity        = 1,
                .raid_name      = "raid5",
                .bg_flag        = BTRFS_BLOCK_GROUP_RAID5,
                .mindev_error   = BTRFS_ERROR_DEV_RAID5_MIN_NOT_MET,
        },
        [BTRFS_RAID_RAID6] = {
                .sub_stripes    = 1,
                .dev_stripes    = 1,
                .devs_max       = 0,
                .devs_min       = 3,
                .tolerated_failures = 2,
                .devs_increment = 1,
                .ncopies        = 1,
                .nparity        = 2,
                .raid_name      = "raid6",
                .bg_flag        = BTRFS_BLOCK_GROUP_RAID6,
                .mindev_error   = BTRFS_ERROR_DEV_RAID6_MIN_NOT_MET,
        },
};

const char *btrfs_bg_type_to_raid_name(u64 flags)
{
        const int index = btrfs_bg_flags_to_raid_index(flags);

        if (index >= BTRFS_NR_RAID_TYPES)
                return NULL;

        return btrfs_raid_array[index].raid_name;
}

/*
 * Fill @buf with textual description of @bg_flags, no more than @size_buf
 * bytes including terminating null byte.
 */
void btrfs_describe_block_groups(u64 bg_flags, char *buf, u32 size_buf)
{
        int i;
        int ret;
        char *bp = buf;
        u64 flags = bg_flags;
        u32 size_bp = size_buf;

        if (!flags) {
                strcpy(bp, "NONE");
                return;
        }

#define DESCRIBE_FLAG(flag, desc)                                               \
        do {                                                            \
                if (flags & (flag)) {                                   \
                        ret = snprintf(bp, size_bp, "%s|", (desc));     \
                        if (ret < 0 || ret >= size_bp)                  \
                                goto out_overflow;                      \
                        size_bp -= ret;                                 \
                        bp += ret;                                      \
                        flags &= ~(flag);                               \
                }                                                       \
        } while (0)

        DESCRIBE_FLAG(BTRFS_BLOCK_GROUP_DATA, "data");
        DESCRIBE_FLAG(BTRFS_BLOCK_GROUP_SYSTEM, "system");
        DESCRIBE_FLAG(BTRFS_BLOCK_GROUP_METADATA, "metadata");

        DESCRIBE_FLAG(BTRFS_AVAIL_ALLOC_BIT_SINGLE, "single");
        for (i = 0; i < BTRFS_NR_RAID_TYPES; i++)
                DESCRIBE_FLAG(btrfs_raid_array[i].bg_flag,
                              btrfs_raid_array[i].raid_name);
#undef DESCRIBE_FLAG

        if (flags) {
                ret = snprintf(bp, size_bp, "0x%llx|", flags);
                size_bp -= ret;
        }

        if (size_bp < size_buf)
                buf[size_buf - size_bp - 1] = '\0'; /* remove last | */

        /*
         * The text is trimmed, it's up to the caller to provide sufficiently
         * large buffer
         */
out_overflow:;
}

static int init_first_rw_device(struct btrfs_trans_handle *trans);
static int btrfs_relocate_sys_chunks(struct btrfs_fs_info *fs_info);
static void btrfs_dev_stat_print_on_error(struct btrfs_device *dev);
static void btrfs_dev_stat_print_on_load(struct btrfs_device *device);
static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
                             enum btrfs_map_op op,
                             u64 logical, u64 *length,
                             struct btrfs_bio **bbio_ret,
                             int mirror_num, int need_raid_map);

/*
 * Device locking
 * ==============
 *
 * There are several mutexes that protect manipulation of devices and low-level
 * structures like chunks but not block groups, extents or files
 *
 * uuid_mutex (global lock)
 * ------------------------
 * protects the fs_uuids list that tracks all per-fs fs_devices, resulting from
 * the SCAN_DEV ioctl registration or from mount either implicitly (the first
 * device) or requested by the device= mount option
 *
 * the mutex can be very coarse and can cover long-running operations
 *
 * protects: updates to fs_devices counters like missing devices, rw devices,
 * seeding, structure cloning, opening/closing devices at mount/umount time
 *
 * global::fs_devs - add, remove, updates to the global list
 *
 * does not protect: manipulation of the fs_devices::devices list in general
 * but in mount context it could be used to exclude list modifications by eg.
 * scan ioctl
 *
 * btrfs_device::name - renames (write side), read is RCU
 *
 * fs_devices::device_list_mutex (per-fs, with RCU)
 * ------------------------------------------------
 * protects updates to fs_devices::devices, ie. adding and deleting
 *
 * simple list traversal with read-only actions can be done with RCU protection
 *
 * may be used to exclude some operations from running concurrently without any
 * modifications to the list (see write_all_supers)
 *
 * Is not required at mount and close times, because our device list is
 * protected by the uuid_mutex at that point.
 *
 * balance_mutex
 * -------------
 * protects balance structures (status, state) and context accessed from
 * several places (internally, ioctl)
 *
 * chunk_mutex
 * -----------
 * protects chunks, adding or removing during allocation, trim or when a new
 * device is added/removed. Additionally it also protects post_commit_list of
 * individual devices, since they can be added to the transaction's
 * post_commit_list only with chunk_mutex held.
 *
 * cleaner_mutex
 * -------------
 * a big lock that is held by the cleaner thread and prevents running subvolume
 * cleaning together with relocation or delayed iputs
 *
 *
 * Lock nesting
 * ============
 *
 * uuid_mutex
 *   device_list_mutex
 *     chunk_mutex
 *   balance_mutex
 *
 *
 * Exclusive operations
 * ====================
 *
 * Maintains the exclusivity of the following operations that apply to the
 * whole filesystem and cannot run in parallel.
 *
 * - Balance (*)
 * - Device add
 * - Device remove
 * - Device replace (*)
 * - Resize
 *
 * The device operations (as above) can be in one of the following states:
 *
 * - Running state
 * - Paused state
 * - Completed state
 *
 * Only device operations marked with (*) can go into the Paused state for the
 * following reasons:
 *
 * - ioctl (only Balance can be Paused through ioctl)
 * - filesystem remounted as read-only
 * - filesystem unmounted and mounted as read-only
 * - system power-cycle and filesystem mounted as read-only
 * - filesystem or device errors leading to forced read-only
 *
 * The status of exclusive operation is set and cleared atomically.
 * During the course of Paused state, fs_info::exclusive_operation remains set.
 * A device operation in Paused or Running state can be canceled or resumed
 * either by ioctl (Balance only) or when remounted as read-write.
 * The exclusive status is cleared when the device operation is canceled or
 * completed.
 */

DEFINE_MUTEX(uuid_mutex);
static LIST_HEAD(fs_uuids);
struct list_head * __attribute_const__ btrfs_get_fs_uuids(void)
{
        return &fs_uuids;
}

/*
 * alloc_fs_devices - allocate struct btrfs_fs_devices
 * @fsid:               if not NULL, copy the UUID to fs_devices::fsid
 * @metadata_fsid:      if not NULL, copy the UUID to fs_devices::metadata_fsid
 *
 * Return a pointer to a new struct btrfs_fs_devices on success, or ERR_PTR().
 * The returned struct is not linked onto any lists and can be destroyed with
 * kfree() right away.
 */
static struct btrfs_fs_devices *alloc_fs_devices(const u8 *fsid,
                                                 const u8 *metadata_fsid)
{
        struct btrfs_fs_devices *fs_devs;

        fs_devs = kzalloc(sizeof(*fs_devs), GFP_KERNEL);
        if (!fs_devs)
                return ERR_PTR(-ENOMEM);

        mutex_init(&fs_devs->device_list_mutex);

        INIT_LIST_HEAD(&fs_devs->devices);
        INIT_LIST_HEAD(&fs_devs->alloc_list);
        INIT_LIST_HEAD(&fs_devs->fs_list);
        INIT_LIST_HEAD(&fs_devs->seed_list);
        if (fsid)
                memcpy(fs_devs->fsid, fsid, BTRFS_FSID_SIZE);

        if (metadata_fsid)
                memcpy(fs_devs->metadata_uuid, metadata_fsid, BTRFS_FSID_SIZE);
        else if (fsid)
                memcpy(fs_devs->metadata_uuid, fsid, BTRFS_FSID_SIZE);

        return fs_devs;
}

void btrfs_free_device(struct btrfs_device *device)
{
        WARN_ON(!list_empty(&device->post_commit_list));
        rcu_string_free(device->name);
        extent_io_tree_release(&device->alloc_state);
        bio_put(device->flush_bio);
        kfree(device);
}

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);
                btrfs_free_device(device);
        }
        kfree(fs_devices);
}

void __exit 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, fs_list);
                list_del(&fs_devices->fs_list);
                free_fs_devices(fs_devices);
        }
}

/*
 * Returns a pointer to a new btrfs_device on success; ERR_PTR() on error.
 * Returned struct is not linked onto any lists and must be destroyed using
 * btrfs_free_device.
 */
static struct btrfs_device *__alloc_device(struct btrfs_fs_info *fs_info)
{
        struct btrfs_device *dev;

        dev = kzalloc(sizeof(*dev), GFP_KERNEL);
        if (!dev)
                return ERR_PTR(-ENOMEM);

        /*
         * Preallocate a bio that's always going to be used for flushing device
         * barriers and matches the device lifespan
         */
        dev->flush_bio = bio_alloc_bioset(GFP_KERNEL, 0, NULL);
        if (!dev->flush_bio) {
                kfree(dev);
                return ERR_PTR(-ENOMEM);
        }

        INIT_LIST_HEAD(&dev->dev_list);
        INIT_LIST_HEAD(&dev->dev_alloc_list);
        INIT_LIST_HEAD(&dev->post_commit_list);

        atomic_set(&dev->reada_in_flight, 0);
        atomic_set(&dev->dev_stats_ccnt, 0);
        btrfs_device_data_ordered_init(dev);
        INIT_RADIX_TREE(&dev->reada_zones, GFP_NOFS & ~__GFP_DIRECT_RECLAIM);
        INIT_RADIX_TREE(&dev->reada_extents, GFP_NOFS & ~__GFP_DIRECT_RECLAIM);
        extent_io_tree_init(fs_info, &dev->alloc_state,
                            IO_TREE_DEVICE_ALLOC_STATE, NULL);

        return dev;
}

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

        ASSERT(fsid);

        /* Handle non-split brain cases */
        list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
                if (metadata_fsid) {
                        if (memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE) == 0
                            && memcmp(metadata_fsid, fs_devices->metadata_uuid,
                                      BTRFS_FSID_SIZE) == 0)
                                return fs_devices;
                } else {
                        if (memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE) == 0)
                                return fs_devices;
                }
        }
        return NULL;
}

static struct btrfs_fs_devices *find_fsid_with_metadata_uuid(
                                struct btrfs_super_block *disk_super)
{

        struct btrfs_fs_devices *fs_devices;

        /*
         * Handle scanned device having completed its fsid change but
         * belonging to a fs_devices that was created by first scanning
         * a device which didn't have its fsid/metadata_uuid changed
         * at all and the CHANGING_FSID_V2 flag set.
         */
        list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
                if (fs_devices->fsid_change &&
                    memcmp(disk_super->metadata_uuid, fs_devices->fsid,
                           BTRFS_FSID_SIZE) == 0 &&
                    memcmp(fs_devices->fsid, fs_devices->metadata_uuid,
                           BTRFS_FSID_SIZE) == 0) {
                        return fs_devices;
                }
        }
        /*
         * Handle scanned device having completed its fsid change but
         * belonging to a fs_devices that was created by a device that
         * has an outdated pair of fsid/metadata_uuid and
         * CHANGING_FSID_V2 flag set.
         */
        list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
                if (fs_devices->fsid_change &&
                    memcmp(fs_devices->metadata_uuid,
                           fs_devices->fsid, BTRFS_FSID_SIZE) != 0 &&
                    memcmp(disk_super->metadata_uuid, fs_devices->metadata_uuid,
                           BTRFS_FSID_SIZE) == 0) {
                        return fs_devices;
                }
        }

        return find_fsid(disk_super->fsid, disk_super->metadata_uuid);
}


static int
btrfs_get_bdev_and_sb(const char *device_path, fmode_t flags, void *holder,
                      int flush, struct block_device **bdev,
                      struct btrfs_super_block **disk_super)
{
        int ret;

        *bdev = blkdev_get_by_path(device_path, flags, holder);

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

        if (flush)
                filemap_write_and_wait((*bdev)->bd_inode->i_mapping);
        ret = set_blocksize(*bdev, BTRFS_BDEV_BLOCKSIZE);
        if (ret) {
                blkdev_put(*bdev, flags);
                goto error;
        }
        invalidate_bdev(*bdev);
        *disk_super = btrfs_read_dev_super(*bdev);
        if (IS_ERR(*disk_super)) {
                ret = PTR_ERR(*disk_super);
                blkdev_put(*bdev, flags);
                goto error;
        }

        return 0;

error:
        *bdev = NULL;
        return ret;
}

/*
 * Check if the device in the path matches the device in the given struct device.
 *
 * Returns:
 *   true  If it is the same device.
 *   false If it is not the same device or on error.
 */
static bool device_matched(const struct btrfs_device *device, const char *path)
{
        char *device_name;
        struct block_device *bdev_old;
        struct block_device *bdev_new;

        /*
         * If we are looking for a device with the matching dev_t, then skip
         * device without a name (a missing device).
         */
        if (!device->name)
                return false;

        device_name = kzalloc(BTRFS_PATH_NAME_MAX, GFP_KERNEL);
        if (!device_name)
                return false;

        rcu_read_lock();
        scnprintf(device_name, BTRFS_PATH_NAME_MAX, "%s", rcu_str_deref(device->name));
        rcu_read_unlock();

        bdev_old = lookup_bdev(device_name);
        kfree(device_name);
        if (IS_ERR(bdev_old))
                return false;

        bdev_new = lookup_bdev(path);
        if (IS_ERR(bdev_new))
                return false;

        if (bdev_old == bdev_new)
                return true;

        return false;
}

/*
 *  Search and remove all stale (devices which are not mounted) devices.
 *  When both inputs are NULL, it will search and release all stale devices.
 *  path:       Optional. When provided will it release all unmounted devices
 *              matching this path only.
 *  skip_dev:   Optional. Will skip this device when searching for the stale
 *              devices.
 *  Return:     0 for success or if @path is NULL.
 *              -EBUSY if @path is a mounted device.
 *              -ENOENT if @path does not match any device in the list.
 */
static int btrfs_free_stale_devices(const char *path,
                                     struct btrfs_device *skip_device)
{
        struct btrfs_fs_devices *fs_devices, *tmp_fs_devices;
        struct btrfs_device *device, *tmp_device;
        int ret = 0;

        lockdep_assert_held(&uuid_mutex);

        if (path)
                ret = -ENOENT;

        list_for_each_entry_safe(fs_devices, tmp_fs_devices, &fs_uuids, fs_list) {

                mutex_lock(&fs_devices->device_list_mutex);
                list_for_each_entry_safe(device, tmp_device,
                                         &fs_devices->devices, dev_list) {
                        if (skip_device && skip_device == device)
                                continue;
                        if (path && !device_matched(device, path))
                                continue;
                        if (fs_devices->opened) {
                                /* for an already deleted device return 0 */
                                if (path && ret != 0)
                                        ret = -EBUSY;
                                break;
                        }

                        /* delete the stale device */
                        fs_devices->num_devices--;
                        list_del(&device->dev_list);
                        btrfs_free_device(device);

                        ret = 0;
                }
                mutex_unlock(&fs_devices->device_list_mutex);

                if (fs_devices->num_devices == 0) {
                        btrfs_sysfs_remove_fsid(fs_devices);
                        list_del(&fs_devices->fs_list);
                        free_fs_devices(fs_devices);
                }
        }

        return ret;
}

/*
 * This is only used on mount, and we are protected from competing things
 * messing with our fs_devices by the uuid_mutex, thus we do not need the
 * fs_devices->device_list_mutex here.
 */
static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices,
                        struct btrfs_device *device, fmode_t flags,
                        void *holder)
{
        struct request_queue *q;
        struct block_device *bdev;
        struct btrfs_super_block *disk_super;
        u64 devid;
        int ret;

        if (device->bdev)
                return -EINVAL;
        if (!device->name)
                return -EINVAL;

        ret = btrfs_get_bdev_and_sb(device->name->str, flags, holder, 1,
                                    &bdev, &disk_super);
        if (ret)
                return ret;

        devid = btrfs_stack_device_id(&disk_super->dev_item);
        if (devid != device->devid)
                goto error_free_page;

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

        device->generation = btrfs_super_generation(disk_super);

        if (btrfs_super_flags(disk_super) & BTRFS_SUPER_FLAG_SEEDING) {
                if (btrfs_super_incompat_flags(disk_super) &
                    BTRFS_FEATURE_INCOMPAT_METADATA_UUID) {
                        pr_err(
                "BTRFS: Invalid seeding and uuid-changed device detected\n");
                        goto error_free_page;
                }

                clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
                fs_devices->seeding = true;
        } else {
                if (bdev_read_only(bdev))
                        clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
                else
                        set_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
        }

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

        device->bdev = bdev;
        clear_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
        device->mode = flags;

        fs_devices->open_devices++;
        if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
            device->devid != BTRFS_DEV_REPLACE_DEVID) {
                fs_devices->rw_devices++;
                list_add_tail(&device->dev_alloc_list, &fs_devices->alloc_list);
        }
        btrfs_release_disk_super(disk_super);

        return 0;

error_free_page:
        btrfs_release_disk_super(disk_super);
        blkdev_put(bdev, flags);

        return -EINVAL;
}

u8 *btrfs_sb_fsid_ptr(struct btrfs_super_block *sb)
{
        bool has_metadata_uuid = (btrfs_super_incompat_flags(sb) &
                                  BTRFS_FEATURE_INCOMPAT_METADATA_UUID);

        return has_metadata_uuid ? sb->metadata_uuid : sb->fsid;
}

/*
 * Handle scanned device having its CHANGING_FSID_V2 flag set and the fs_devices
 * being created with a disk that has already completed its fsid change. Such
 * disk can belong to an fs which has its FSID changed or to one which doesn't.
 * Handle both cases here.
 */
static struct btrfs_fs_devices *find_fsid_inprogress(
                                        struct btrfs_super_block *disk_super)
{
        struct btrfs_fs_devices *fs_devices;

        list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
                if (memcmp(fs_devices->metadata_uuid, fs_devices->fsid,
                           BTRFS_FSID_SIZE) != 0 &&
                    memcmp(fs_devices->metadata_uuid, disk_super->fsid,
                           BTRFS_FSID_SIZE) == 0 && !fs_devices->fsid_change) {
                        return fs_devices;
                }
        }

        return find_fsid(disk_super->fsid, NULL);
}


static struct btrfs_fs_devices *find_fsid_changed(
                                        struct btrfs_super_block *disk_super)
{
        struct btrfs_fs_devices *fs_devices;

        /*
         * Handles the case where scanned device is part of an fs that had
         * multiple successful changes of FSID but curently device didn't
         * observe it. Meaning our fsid will be different than theirs. We need
         * to handle two subcases :
         *  1 - The fs still continues to have different METADATA/FSID uuids.
         *  2 - The fs is switched back to its original FSID (METADATA/FSID
         *  are equal).
         */
        list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
                /* Changed UUIDs */
                if (memcmp(fs_devices->metadata_uuid, fs_devices->fsid,
                           BTRFS_FSID_SIZE) != 0 &&
                    memcmp(fs_devices->metadata_uuid, disk_super->metadata_uuid,
                           BTRFS_FSID_SIZE) == 0 &&
                    memcmp(fs_devices->fsid, disk_super->fsid,
                           BTRFS_FSID_SIZE) != 0)
                        return fs_devices;

                /* Unchanged UUIDs */
                if (memcmp(fs_devices->metadata_uuid, fs_devices->fsid,
                           BTRFS_FSID_SIZE) == 0 &&
                    memcmp(fs_devices->fsid, disk_super->metadata_uuid,
                           BTRFS_FSID_SIZE) == 0)
                        return fs_devices;
        }

        return NULL;
}

static struct btrfs_fs_devices *find_fsid_reverted_metadata(
                                struct btrfs_super_block *disk_super)
{
        struct btrfs_fs_devices *fs_devices;

        /*
         * Handle the case where the scanned device is part of an fs whose last
         * metadata UUID change reverted it to the original FSID. At the same
         * time * fs_devices was first created by another constitutent device
         * which didn't fully observe the operation. This results in an
         * btrfs_fs_devices created with metadata/fsid different AND
         * btrfs_fs_devices::fsid_change set AND the metadata_uuid of the
         * fs_devices equal to the FSID of the disk.
         */
        list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
                if (memcmp(fs_devices->fsid, fs_devices->metadata_uuid,
                           BTRFS_FSID_SIZE) != 0 &&
                    memcmp(fs_devices->metadata_uuid, disk_super->fsid,
                           BTRFS_FSID_SIZE) == 0 &&
                    fs_devices->fsid_change)
                        return fs_devices;
        }

        return NULL;
}
/*
 * Add new device to list of registered devices
 *
 * Returns:
 * device pointer which was just added or updated when successful
 * error pointer when failed
 */
static noinline struct btrfs_device *device_list_add(const char *path,
                           struct btrfs_super_block *disk_super,
                           bool *new_device_added)
{
        struct btrfs_device *device;
        struct btrfs_fs_devices *fs_devices = NULL;
        struct rcu_string *name;
        u64 found_transid = btrfs_super_generation(disk_super);
        u64 devid = btrfs_stack_device_id(&disk_super->dev_item);
        bool has_metadata_uuid = (btrfs_super_incompat_flags(disk_super) &
                BTRFS_FEATURE_INCOMPAT_METADATA_UUID);
        bool fsid_change_in_progress = (btrfs_super_flags(disk_super) &
                                        BTRFS_SUPER_FLAG_CHANGING_FSID_V2);

        if (fsid_change_in_progress) {
                if (!has_metadata_uuid)
                        fs_devices = find_fsid_inprogress(disk_super);
                else
                        fs_devices = find_fsid_changed(disk_super);
        } else if (has_metadata_uuid) {
                fs_devices = find_fsid_with_metadata_uuid(disk_super);
        } else {
                fs_devices = find_fsid_reverted_metadata(disk_super);
                if (!fs_devices)
                        fs_devices = find_fsid(disk_super->fsid, NULL);
        }


        if (!fs_devices) {
                if (has_metadata_uuid)
                        fs_devices = alloc_fs_devices(disk_super->fsid,
                                                      disk_super->metadata_uuid);
                else
                        fs_devices = alloc_fs_devices(disk_super->fsid, NULL);

                if (IS_ERR(fs_devices))
                        return ERR_CAST(fs_devices);

                fs_devices->fsid_change = fsid_change_in_progress;

                mutex_lock(&fs_devices->device_list_mutex);
                list_add(&fs_devices->fs_list, &fs_uuids);

                device = NULL;
        } else {
                mutex_lock(&fs_devices->device_list_mutex);
                device = btrfs_find_device(fs_devices, devid,
                                disk_super->dev_item.uuid, NULL, false);

                /*
                 * If this disk has been pulled into an fs devices created by
                 * a device which had the CHANGING_FSID_V2 flag then replace the
                 * metadata_uuid/fsid values of the fs_devices.
                 */
                if (fs_devices->fsid_change &&
                    found_transid > fs_devices->latest_generation) {
                        memcpy(fs_devices->fsid, disk_super->fsid,
                                        BTRFS_FSID_SIZE);

                        if (has_metadata_uuid)
                                memcpy(fs_devices->metadata_uuid,
                                       disk_super->metadata_uuid,
                                       BTRFS_FSID_SIZE);
                        else
                                memcpy(fs_devices->metadata_uuid,
                                       disk_super->fsid, BTRFS_FSID_SIZE);

                        fs_devices->fsid_change = false;
                }
        }

        if (!device) {
                if (fs_devices->opened) {
                        mutex_unlock(&fs_devices->device_list_mutex);
                        return ERR_PTR(-EBUSY);
                }

                device = btrfs_alloc_device(NULL, &devid,
                                            disk_super->dev_item.uuid);
                if (IS_ERR(device)) {
                        mutex_unlock(&fs_devices->device_list_mutex);
                        /* we can safely leave the fs_devices entry around */
                        return device;
                }

                name = rcu_string_strdup(path, GFP_NOFS);
                if (!name) {
                        btrfs_free_device(device);
                        mutex_unlock(&fs_devices->device_list_mutex);
                        return ERR_PTR(-ENOMEM);
                }
                rcu_assign_pointer(device->name, name);

                list_add_rcu(&device->dev_list, &fs_devices->devices);
                fs_devices->num_devices++;

                device->fs_devices = fs_devices;
                *new_device_added = true;

                if (disk_super->label[0])
                        pr_info(
        "BTRFS: device label %s devid %llu transid %llu %s scanned by %s (%d)\n",
                                disk_super->label, devid, found_transid, path,
                                current->comm, task_pid_nr(current));
                else
                        pr_info(
        "BTRFS: device fsid %pU devid %llu transid %llu %s scanned by %s (%d)\n",
                                disk_super->fsid, devid, found_transid, path,
                                current->comm, task_pid_nr(current));

        } else if (!device->name || strcmp(device->name->str, path)) {
                /*
                 * When FS is already mounted.
                 * 1. If you are here and if the device->name is NULL that
                 *    means this device was missing at time of FS mount.
                 * 2. If you are here and if the device->name is different
                 *    from 'path' that means either
                 *      a. The same device disappeared and reappeared with
                 *         different name. or
                 *      b. The missing-disk-which-was-replaced, has
                 *         reappeared now.
                 *
                 * We must allow 1 and 2a above. But 2b would be a spurious
                 * and unintentional.
                 *
                 * Further in case of 1 and 2a above, the disk at 'path'
                 * would have missed some transaction when it was away and
                 * in case of 2a the stale bdev has to be updated as well.
                 * 2b must not be allowed at all time.
                 */

                /*
                 * For now, we do allow update to btrfs_fs_device through the
                 * btrfs dev scan cli after FS has been mounted.  We're still
                 * tracking a problem where systems fail mount by subvolume id
                 * when we reject replacement on a mounted FS.
                 */
                if (!fs_devices->opened && found_transid < device->generation) {
                        /*
                         * That is if the FS is _not_ mounted and if you
                         * are here, that means there is more than one
                         * disk with same uuid and devid.We keep the one
                         * with larger generation number or the last-in if
                         * generation are equal.
                         */
                        mutex_unlock(&fs_devices->device_list_mutex);
                        return ERR_PTR(-EEXIST);
                }

                /*
                 * We are going to replace the device path for a given devid,
                 * make sure it's the same device if the device is mounted
                 */
                if (device->bdev) {
                        struct block_device *path_bdev;

                        path_bdev = lookup_bdev(path);
                        if (IS_ERR(path_bdev)) {
                                mutex_unlock(&fs_devices->device_list_mutex);
                                return ERR_CAST(path_bdev);
                        }

                        if (device->bdev != path_bdev) {
                                bdput(path_bdev);
                                mutex_unlock(&fs_devices->device_list_mutex);
                                /*
                                 * device->fs_info may not be reliable here, so
                                 * pass in a NULL instead. This avoids a
                                 * possible use-after-free when the fs_info and
                                 * fs_info->sb are already torn down.
                                 */
                                btrfs_warn_in_rcu(NULL,
        "duplicate device %s devid %llu generation %llu scanned by %s (%d)",
                                                  path, devid, found_transid,
                                                  current->comm,
                                                  task_pid_nr(current));
                                return ERR_PTR(-EEXIST);
                        }
                        bdput(path_bdev);
                        btrfs_info_in_rcu(device->fs_info,
        "devid %llu device path %s changed to %s scanned by %s (%d)",
                                          devid, rcu_str_deref(device->name),
                                          path, current->comm,
                                          task_pid_nr(current));
                }

                name = rcu_string_strdup(path, GFP_NOFS);
                if (!name) {
                        mutex_unlock(&fs_devices->device_list_mutex);
                        return ERR_PTR(-ENOMEM);
                }
                rcu_string_free(device->name);
                rcu_assign_pointer(device->name, name);
                if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) {
                        fs_devices->missing_devices--;
                        clear_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
                }
        }

        /*
         * Unmount does not free the btrfs_device struct but would zero
         * generation along with most of the other members. So just update
         * it back. We need it to pick the disk with largest generation
         * (as above).
         */
        if (!fs_devices->opened) {
                device->generation = found_transid;
                fs_devices->latest_generation = max_t(u64, found_transid,
                                                fs_devices->latest_generation);
        }

        fs_devices->total_devices = btrfs_super_num_devices(disk_super);

        mutex_unlock(&fs_devices->device_list_mutex);
        return device;
}

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;
        int ret = 0;

        lockdep_assert_held(&uuid_mutex);

        fs_devices = alloc_fs_devices(orig->fsid, NULL);
        if (IS_ERR(fs_devices))
                return fs_devices;

        fs_devices->total_devices = orig->total_devices;

        list_for_each_entry(orig_dev, &orig->devices, dev_list) {
                struct rcu_string *name;

                device = btrfs_alloc_device(NULL, &orig_dev->devid,
                                            orig_dev->uuid);
                if (IS_ERR(device)) {
                        ret = PTR_ERR(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.
                 */
                if (orig_dev->name) {
                        name = rcu_string_strdup(orig_dev->name->str,
                                        GFP_KERNEL);
                        if (!name) {
                                btrfs_free_device(device);
                                ret = -ENOMEM;
                                goto error;
                        }
                        rcu_assign_pointer(device->name, name);
                }

                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(ret);
}

static void __btrfs_free_extra_devids(struct btrfs_fs_devices *fs_devices,
                                      int step, struct btrfs_device **latest_dev)
{
        struct btrfs_device *device, *next;

        /* 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 (test_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state)) {
                        if (!test_bit(BTRFS_DEV_STATE_REPLACE_TGT,
                                      &device->dev_state) &&
                            !test_bit(BTRFS_DEV_STATE_MISSING,
                                      &device->dev_state) &&
                            (!*latest_dev ||
                             device->generation > (*latest_dev)->generation)) {
                                *latest_dev = device;
                        }
                        continue;
                }

                /*
                 * We have already validated the presence of BTRFS_DEV_REPLACE_DEVID,
                 * in btrfs_init_dev_replace() so just continue.
                 */
                if (device->devid == BTRFS_DEV_REPLACE_DEVID)
                        continue;

                if (device->bdev) {
                        blkdev_put(device->bdev, device->mode);
                        device->bdev = NULL;
                        fs_devices->open_devices--;
                }
                if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
                        list_del_init(&device->dev_alloc_list);
                        clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
                        fs_devices->rw_devices--;
                }
                list_del_init(&device->dev_list);
                fs_devices->num_devices--;
                btrfs_free_device(device);
        }

}

/*
 * After we have read the system tree and know devids belonging to this
 * filesystem, remove the device which does not belong there.
 */
void btrfs_free_extra_devids(struct btrfs_fs_devices *fs_devices, int step)
{
        struct btrfs_device *latest_dev = NULL;
        struct btrfs_fs_devices *seed_dev;

        mutex_lock(&uuid_mutex);
        __btrfs_free_extra_devids(fs_devices, step, &latest_dev);

        list_for_each_entry(seed_dev, &fs_devices->seed_list, seed_list)
                __btrfs_free_extra_devids(seed_dev, step, &latest_dev);

        fs_devices->latest_bdev = latest_dev->bdev;

        mutex_unlock(&uuid_mutex);
}

static void btrfs_close_bdev(struct btrfs_device *device)
{
        if (!device->bdev)
                return;

        if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
                sync_blockdev(device->bdev);
                invalidate_bdev(device->bdev);
        }

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

static void btrfs_close_one_device(struct btrfs_device *device)
{
        struct btrfs_fs_devices *fs_devices = device->fs_devices;

        if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
            device->devid != BTRFS_DEV_REPLACE_DEVID) {
                list_del_init(&device->dev_alloc_list);
                fs_devices->rw_devices--;
        }

        if (device->devid == BTRFS_DEV_REPLACE_DEVID)
                clear_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state);

        if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) {
                clear_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
                fs_devices->missing_devices--;
        }

        btrfs_close_bdev(device);
        if (device->bdev) {
                fs_devices->open_devices--;
                device->bdev = NULL;
        }
        clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);

        device->fs_info = NULL;
        atomic_set(&device->dev_stats_ccnt, 0);
        extent_io_tree_release(&device->alloc_state);

        /*
         * Reset the flush error record. We might have a transient flush error
         * in this mount, and if so we aborted the current transaction and set
         * the fs to an error state, guaranteeing no super blocks can be further
         * committed. However that error might be transient and if we unmount the
         * filesystem and mount it again, we should allow the mount to succeed
         * (btrfs_check_rw_degradable() should not fail) - if after mounting the
         * filesystem again we still get flush errors, then we will again abort
         * any transaction and set the error state, guaranteeing no commits of
         * unsafe super blocks.
         */
        device->last_flush_error = 0;

        /* Verify the device is back in a pristine state  */
        ASSERT(!test_bit(BTRFS_DEV_STATE_FLUSH_SENT, &device->dev_state));
        ASSERT(!test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state));
        ASSERT(list_empty(&device->dev_alloc_list));
        ASSERT(list_empty(&device->post_commit_list));
        ASSERT(atomic_read(&device->reada_in_flight) == 0);
}

static void close_fs_devices(struct btrfs_fs_devices *fs_devices)
{
        struct btrfs_device *device, *tmp;

        lockdep_assert_held(&uuid_mutex);

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

        list_for_each_entry_safe(device, tmp, &fs_devices->devices, dev_list)
                btrfs_close_one_device(device);

        WARN_ON(fs_devices->open_devices);
        WARN_ON(fs_devices->rw_devices);
        fs_devices->opened = 0;
        fs_devices->seeding = false;
        fs_devices->fs_info = NULL;
}

void btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
{
        LIST_HEAD(list);
        struct btrfs_fs_devices *tmp;

        mutex_lock(&uuid_mutex);
        close_fs_devices(fs_devices);
        if (!fs_devices->opened) {
                list_splice_init(&fs_devices->seed_list, &list);

                /*
                 * If the struct btrfs_fs_devices is not assembled with any
                 * other device, it can be re-initialized during the next mount
                 * without the needing device-scan step. Therefore, it can be
                 * fully freed.
                 */
                if (fs_devices->num_devices == 1) {
                        list_del(&fs_devices->fs_list);
                        free_fs_devices(fs_devices);
                }
        }


        list_for_each_entry_safe(fs_devices, tmp, &list, seed_list) {
                close_fs_devices(fs_devices);
                list_del(&fs_devices->seed_list);
                free_fs_devices(fs_devices);
        }
        mutex_unlock(&uuid_mutex);
}

static int open_fs_devices(struct btrfs_fs_devices *fs_devices,
                                fmode_t flags, void *holder)
{
        struct btrfs_device *device;
        struct btrfs_device *latest_dev = NULL;
        struct btrfs_device *tmp_device;
        int ret = 0;

        flags |= FMODE_EXCL;

        list_for_each_entry_safe(device, tmp_device, &fs_devices->devices,
                                 dev_list) {
                int ret2;

                ret2 = btrfs_open_one_device(fs_devices, device, flags, holder);
                if (ret2 == 0 &&
                    (!latest_dev || device->generation > latest_dev->generation)) {
                        latest_dev = device;
                } else if (ret2 == -ENODATA) {
                        fs_devices->num_devices--;
                        list_del(&device->dev_list);
                        btrfs_free_device(device);
                }
                if (ret == 0 && ret2 != 0)
                        ret = ret2;
        }

        if (fs_devices->open_devices == 0) {
                if (ret)
                        return ret;
                return -EINVAL;
        }

        fs_devices->opened = 1;
        fs_devices->latest_bdev = latest_dev->bdev;
        fs_devices->total_rw_bytes = 0;
        fs_devices->chunk_alloc_policy = BTRFS_CHUNK_ALLOC_REGULAR;

        return 0;
}

static int devid_cmp(void *priv, const struct list_head *a,
                     const struct list_head *b)
{
        struct btrfs_device *dev1, *dev2;

        dev1 = list_entry(a, struct btrfs_device, dev_list);
        dev2 = list_entry(b, struct btrfs_device, dev_list);

        if (dev1->devid < dev2->devid)
                return -1;
        else if (dev1->devid > dev2->devid)
                return 1;
        return 0;
}

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

        lockdep_assert_held(&uuid_mutex);
        /*
         * The device_list_mutex cannot be taken here in case opening the
         * underlying device takes further locks like bd_mutex.
         *
         * We also don't need the lock here as this is called during mount and
         * exclusion is provided by uuid_mutex
         */

        if (fs_devices->opened) {
                fs_devices->opened++;
                ret = 0;
        } else {
                list_sort(NULL, &fs_devices->devices, devid_cmp);
                ret = open_fs_devices(fs_devices, flags, holder);
        }

        return ret;
}

void btrfs_release_disk_super(struct btrfs_super_block *super)
{
        struct page *page = virt_to_page(super);

        put_page(page);
}

static struct btrfs_super_block *btrfs_read_disk_super(struct block_device *bdev,
                                                       u64 bytenr)
{
        struct btrfs_super_block *disk_super;
        struct page *page;
        void *p;
        pgoff_t index;

        /* make sure our super fits in the device */
        if (bytenr + PAGE_SIZE >= i_size_read(bdev->bd_inode))
                return ERR_PTR(-EINVAL);

        /* make sure our super fits in the page */
        if (sizeof(*disk_super) > PAGE_SIZE)
                return ERR_PTR(-EINVAL);

        /* make sure our super doesn't straddle pages on disk */
        index = bytenr >> PAGE_SHIFT;
        if ((bytenr + sizeof(*disk_super) - 1) >> PAGE_SHIFT != index)
                return ERR_PTR(-EINVAL);

        /* pull in the page with our super */
        page = read_cache_page_gfp(bdev->bd_inode->i_mapping, index, GFP_KERNEL);

        if (IS_ERR(page))
                return ERR_CAST(page);

        p = page_address(page);

        /* align our pointer to the offset of the super block */
        disk_super = p + offset_in_page(bytenr);

        if (btrfs_super_bytenr(disk_super) != bytenr ||
            btrfs_super_magic(disk_super) != BTRFS_MAGIC) {
                btrfs_release_disk_super(p);
                return ERR_PTR(-EINVAL);
        }

        if (disk_super->label[0] && disk_super->label[BTRFS_LABEL_SIZE - 1])
                disk_super->label[BTRFS_LABEL_SIZE - 1] = 0;

        return disk_super;
}

int btrfs_forget_devices(const char *path)
{
        int ret;

        mutex_lock(&uuid_mutex);
        ret = btrfs_free_stale_devices(strlen(path) ? path : NULL, NULL);
        mutex_unlock(&uuid_mutex);

        return ret;
}

/*
 * Look for a btrfs signature on a device. This may be called out of the mount path
 * and we are not allowed to call set_blocksize during the scan. The superblock
 * is read via pagecache
 */
struct btrfs_device *btrfs_scan_one_device(const char *path, fmode_t flags,
                                           void *holder)
{
        struct btrfs_super_block *disk_super;
        bool new_device_added = false;
        struct btrfs_device *device = NULL;
        struct block_device *bdev;
        u64 bytenr;

        lockdep_assert_held(&uuid_mutex);

        /*
         * we would like to check all the supers, but that would make
         * a btrfs mount succeed after a mkfs from a different FS.
         * So, we need to add a special mount option to scan for
         * later supers, using BTRFS_SUPER_MIRROR_MAX instead
         */
        bytenr = btrfs_sb_offset(0);

        /*
         * Avoid using flag |= FMODE_EXCL here, as the systemd-udev may
         * initiate the device scan which may race with the user's mount
         * or mkfs command, resulting in failure.
         * Since the device scan is solely for reading purposes, there is
         * no need for FMODE_EXCL. Additionally, the devices are read again
         * during the mount process. It is ok to get some inconsistent
         * values temporarily, as the device paths of the fsid are the only
         * required information for assembling the volume.
         */
        bdev = blkdev_get_by_path(path, flags, holder);
        if (IS_ERR(bdev))
                return ERR_CAST(bdev);

        disk_super = btrfs_read_disk_super(bdev, bytenr);
        if (IS_ERR(disk_super)) {
                device = ERR_CAST(disk_super);
                goto error_bdev_put;
        }

        device = device_list_add(path, disk_super, &new_device_added);
        if (!IS_ERR(device)) {
                if (new_device_added)
                        btrfs_free_stale_devices(path, device);
        }

        btrfs_release_disk_super(disk_super);

error_bdev_put:
        blkdev_put(bdev, flags);

        return device;
}

/*
 * Try to find a chunk that intersects [start, start + len] range and when one
 * such is found, record the end of it in *start
 */
static bool contains_pending_extent(struct btrfs_device *device, u64 *start,
                                    u64 len)
{
        u64 physical_start, physical_end;

        lockdep_assert_held(&device->fs_info->chunk_mutex);

        if (!find_first_extent_bit(&device->alloc_state, *start,
                                   &physical_start, &physical_end,
                                   CHUNK_ALLOCATED, NULL)) {

                if (in_range(physical_start, *start, len) ||
                    in_range(*start, physical_start,
                             physical_end + 1 - physical_start)) {
                        *start = physical_end + 1;
                        return true;
                }
        }
        return false;
}

static u64 dev_extent_search_start(struct btrfs_device *device, u64 start)
{
        switch (device->fs_devices->chunk_alloc_policy) {
        case BTRFS_CHUNK_ALLOC_REGULAR:
                /*
                 * We don't want to overwrite the superblock on the drive nor
                 * any area used by the boot loader (grub for example), so we
                 * make sure to start at an offset of at least 1MB.
                 */
                return max_t(u64, start, SZ_1M);
        default:
                BUG();
        }
}

/**
 * dev_extent_hole_check - check if specified hole is suitable for allocation
 * @device:     the device which we have the hole
 * @hole_start: starting position of the hole
 * @hole_size:  the size of the hole
 * @num_bytes:  the size of the free space that we need
 *
 * This function may modify @hole_start and @hole_end to reflect the suitable
 * position for allocation. Returns 1 if hole position is updated, 0 otherwise.
 */
static bool dev_extent_hole_check(struct btrfs_device *device, u64 *hole_start,
                                  u64 *hole_size, u64 num_bytes)
{
        bool changed = false;
        u64 hole_end = *hole_start + *hole_size;

        /*
         * Check before we set max_hole_start, otherwise we could end up
         * sending back this offset anyway.
         */
        if (contains_pending_extent(device, hole_start, *hole_size)) {
                if (hole_end >= *hole_start)
                        *hole_size = hole_end - *hole_start;
                else
                        *hole_size = 0;
                changed = true;
        }

        switch (device->fs_devices->chunk_alloc_policy) {
        case BTRFS_CHUNK_ALLOC_REGULAR:
                /* No extra check */
                break;
        default:
                BUG();
        }

        return changed;
}

/*
 * find_free_dev_extent_start - 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
 * @search_start: the position from which to begin the search
 * @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.
 *
 * NOTE: This function will search *commit* root of device tree, and does extra
 * check to ensure dev extents are not double allocated.
 * This makes the function safe to allocate dev extents but may not report
 * correct usable device space, as device extent freed in current transaction
 * is not reported as avaiable.
 */
static int find_free_dev_extent_start(struct btrfs_device *device,
                                u64 num_bytes, u64 search_start, u64 *start,
                                u64 *len)
{
        struct btrfs_fs_info *fs_info = device->fs_info;
        struct btrfs_root *root = fs_info->dev_root;
        struct btrfs_key key;
        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_end = device->total_bytes;
        int ret;
        int slot;
        struct extent_buffer *l;

        search_start = dev_extent_search_start(device, search_start);

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

        max_hole_start = search_start;
        max_hole_size = 0;

again:
        if (search_start >= search_end ||
                test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state)) {
                ret = -ENOSPC;
                goto out;
        }

        path->reada = READA_FORWARD;
        path->search_commit_root = 1;
        path->skip_locking = 1;

        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 (search_start < search_end) {
                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 (key.type != BTRFS_DEV_EXTENT_KEY)
                        goto next;

                if (key.offset > search_end)
                        break;

                if (key.offset > search_start) {
                        hole_size = key.offset - search_start;
                        dev_extent_hole_check(device, &search_start, &hole_size,
                                              num_bytes);

                        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 (dev_extent_hole_check(device, &search_start, &hole_size,
                                          num_bytes)) {
                        btrfs_release_path(path);
                        goto again;
                }

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

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

        ASSERT(max_hole_start + max_hole_size <= search_end);
out:
        btrfs_free_path(path);
        *start = max_hole_start;
        if (len)
                *len = max_hole_size;
        return ret;
}

int find_free_dev_extent(struct btrfs_device *device, u64 num_bytes,
                         u64 *start, u64 *len)
{
        /* FIXME use last free of some kind */
        return find_free_dev_extent_start(device, num_bytes, 0, start, len);
}

static int btrfs_free_dev_extent(struct btrfs_trans_handle *trans,
                          struct btrfs_device *device,
                          u64 start, u64 *dev_extent_len)
{
        struct btrfs_fs_info *fs_info = device->fs_info;
        struct btrfs_root *root = fs_info->dev_root;
        int ret;
        struct btrfs_path *path;
        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_handle_fs_error(fs_info, ret, "Slot search failed");
                goto out;
        }

        *dev_extent_len = btrfs_dev_extent_length(leaf, extent);

        ret = btrfs_del_item(trans, root, path);
        if (ret) {
                btrfs_handle_fs_error(fs_info, ret,
                                      "Failed to remove dev extent item");
        } else {
                set_bit(BTRFS_TRANS_HAVE_FREE_BGS, &trans->transaction->flags);
        }
out:
        btrfs_free_path(path);
        return ret;
}

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

        WARN_ON(!test_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state));
        WARN_ON(test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state));
        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,
                                        BTRFS_CHUNK_TREE_OBJECTID);
        btrfs_set_dev_extent_chunk_objectid(leaf, extent,
                                            BTRFS_FIRST_CHUNK_TREE_OBJECTID);
        btrfs_set_dev_extent_chunk_offset(leaf, extent, chunk_offset);

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

static u64 find_next_chunk(struct btrfs_fs_info *fs_info)
{
        struct extent_map_tree *em_tree;
        struct extent_map *em;
        struct rb_node *n;
        u64 ret = 0;

        em_tree = &fs_info->mapping_tree;
        read_lock(&em_tree->lock);
        n = rb_last(&em_tree->map.rb_root);
        if (n) {
                em = rb_entry(n, struct extent_map, rb_node);
                ret = em->start + em->len;
        }
        read_unlock(&em_tree->lock);

        return ret;
}

static noinline int find_next_devid(struct btrfs_fs_info *fs_info,
                                    u64 *devid_ret)
{
        int ret;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct btrfs_path *path;

        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, fs_info->chunk_root, &key, path, 0, 0);
        if (ret < 0)
                goto error;

        if (ret == 0) {
                /* Corruption */
                btrfs_err(fs_info, "corrupted chunk tree devid -1 matched");
                ret = -EUCLEAN;
                goto error;
        }

        ret = btrfs_previous_item(fs_info->chunk_root, path,
                                  BTRFS_DEV_ITEMS_OBJECTID,
                                  BTRFS_DEV_ITEM_KEY);
        if (ret) {
                *devid_ret = 1;
        } else {
                btrfs_item_key_to_cpu(path->nodes[0], &found_key,
                                      path->slots[0]);
                *devid_ret = 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
 */
static int btrfs_add_dev_item(struct btrfs_trans_handle *trans,
                            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;

        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, trans->fs_info->chunk_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,
                                     btrfs_device_get_disk_total_bytes(device));
        btrfs_set_device_bytes_used(leaf, dev_item,
                                    btrfs_device_get_bytes_used(device));
        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 = btrfs_device_uuid(dev_item);
        write_extent_buffer(leaf, device->uuid, ptr, BTRFS_UUID_SIZE);
        ptr = btrfs_device_fsid(dev_item);
        write_extent_buffer(leaf, trans->fs_info->fs_devices->metadata_uuid,
                            ptr, BTRFS_FSID_SIZE);
        btrfs_mark_buffer_dirty(leaf);

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

/*
 * Function to update ctime/mtime for a given device path.
 * Mainly used for ctime/mtime based probe like libblkid.
 *
 * We don't care about errors here, this is just to be kind to userspace.
 */
static void update_dev_time(const char *device_path)
{
        struct path path;
        struct timespec64 now;
        int ret;

        ret = kern_path(device_path, LOOKUP_FOLLOW, &path);
        if (ret)
                return;

        now = current_time(d_inode(path.dentry));
        inode_update_time(d_inode(path.dentry), &now, S_MTIME | S_CTIME);
        path_put(&path);
}

static int btrfs_rm_dev_item(struct btrfs_device *device)
{
        struct btrfs_root *root = device->fs_info->chunk_root;
        int ret;
        struct btrfs_path *path;
        struct btrfs_key key;
        struct btrfs_trans_handle *trans;

        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;

        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        if (ret) {
                if (ret > 0)
                        ret = -ENOENT;
                btrfs_abort_transaction(trans, ret);
                btrfs_end_transaction(trans);
                goto out;
        }

        ret = btrfs_del_item(trans, root, path);
        if (ret) {
                btrfs_abort_transaction(trans, ret);
                btrfs_end_transaction(trans);
        }

out:
        btrfs_free_path(path);
        if (!ret)
                ret = btrfs_commit_transaction(trans);
        return ret;
}

/*
 * Verify that @num_devices satisfies the RAID profile constraints in the whole
 * filesystem. It's up to the caller to adjust that number regarding eg. device
 * replace.
 */
static int btrfs_check_raid_min_devices(struct btrfs_fs_info *fs_info,
                u64 num_devices)
{
        u64 all_avail;
        unsigned seq;
        int i;

        do {
                seq = read_seqbegin(&fs_info->profiles_lock);

                all_avail = fs_info->avail_data_alloc_bits |
                            fs_info->avail_system_alloc_bits |
                            fs_info->avail_metadata_alloc_bits;
        } while (read_seqretry(&fs_info->profiles_lock, seq));

        for (i = 0; i < BTRFS_NR_RAID_TYPES; i++) {
                if (!(all_avail & btrfs_raid_array[i].bg_flag))
                        continue;

                if (num_devices < btrfs_raid_array[i].devs_min) {
                        int ret = btrfs_raid_array[i].mindev_error;

                        if (ret)
                                return ret;
                }
        }

        return 0;
}

static struct btrfs_device * btrfs_find_next_active_device(
                struct btrfs_fs_devices *fs_devs, struct btrfs_device *device)
{
        struct btrfs_device *next_device;

        list_for_each_entry(next_device, &fs_devs->devices, dev_list) {
                if (next_device != device &&
                    !test_bit(BTRFS_DEV_STATE_MISSING, &next_device->dev_state)
                    && next_device->bdev)
                        return next_device;
        }

        return NULL;
}

/*
 * Helper function to check if the given device is part of s_bdev / latest_bdev
 * and replace it with the provided or the next active device, in the context
 * where this function called, there should be always be another device (or
 * this_dev) which is active.
 */
void __cold btrfs_assign_next_active_device(struct btrfs_device *device,
                                            struct btrfs_device *next_device)
{
        struct btrfs_fs_info *fs_info = device->fs_info;

        if (!next_device)
                next_device = btrfs_find_next_active_device(fs_info->fs_devices,
                                                            device);
        ASSERT(next_device);

        if (fs_info->sb->s_bdev &&
                        (fs_info->sb->s_bdev == device->bdev))
                fs_info->sb->s_bdev = next_device->bdev;

        if (fs_info->fs_devices->latest_bdev == device->bdev)
                fs_info->fs_devices->latest_bdev = next_device->bdev;
}

/*
 * Return btrfs_fs_devices::num_devices excluding the device that's being
 * currently replaced.
 */
static u64 btrfs_num_devices(struct btrfs_fs_info *fs_info)
{
        u64 num_devices = fs_info->fs_devices->num_devices;

        down_read(&fs_info->dev_replace.rwsem);
        if (btrfs_dev_replace_is_ongoing(&fs_info->dev_replace)) {
                ASSERT(num_devices > 1);
                num_devices--;
        }
        up_read(&fs_info->dev_replace.rwsem);

        return num_devices;
}

void btrfs_scratch_superblocks(struct btrfs_fs_info *fs_info,
                               struct block_device *bdev,
                               const char *device_path)
{
        struct btrfs_super_block *disk_super;
        int copy_num;

        if (!bdev)
                return;

        for (copy_num = 0; copy_num < BTRFS_SUPER_MIRROR_MAX; copy_num++) {
                struct page *page;
                int ret;

                disk_super = btrfs_read_dev_one_super(bdev, copy_num);
                if (IS_ERR(disk_super))
                        continue;

                memset(&disk_super->magic, 0, sizeof(disk_super->magic));

                page = virt_to_page(disk_super);
                set_page_dirty(page);
                lock_page(page);
                /* write_on_page() unlocks the page */
                ret = write_one_page(page);
                if (ret)
                        btrfs_warn(fs_info,
                                "error clearing superblock number %d (%d)",
                                copy_num, ret);
                btrfs_release_disk_super(disk_super);

        }

        /* Notify udev that device has changed */
        btrfs_kobject_uevent(bdev, KOBJ_CHANGE);

        /* Update ctime/mtime for device path for libblkid */
        update_dev_time(device_path);
}

int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
                    u64 devid)
{
        struct btrfs_device *device;
        struct btrfs_fs_devices *cur_devices;
        struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
        u64 num_devices;
        int ret = 0;

        /*
         * The device list in fs_devices is accessed without locks (neither
         * uuid_mutex nor device_list_mutex) as it won't change on a mounted
         * filesystem and another device rm cannot run.
         */
        num_devices = btrfs_num_devices(fs_info);

        ret = btrfs_check_raid_min_devices(fs_info, num_devices - 1);
        if (ret)
                goto out;

        device = btrfs_find_device_by_devspec(fs_info, devid, device_path);

        if (IS_ERR(device)) {
                if (PTR_ERR(device) == -ENOENT &&
                    device_path && strcmp(device_path, "missing") == 0)
                        ret = BTRFS_ERROR_DEV_MISSING_NOT_FOUND;
                else
                        ret = PTR_ERR(device);
                goto out;
        }

        if (btrfs_pinned_by_swapfile(fs_info, device)) {
                btrfs_warn_in_rcu(fs_info,
                  "cannot remove device %s (devid %llu) due to active swapfile",
                                  rcu_str_deref(device->name), device->devid);
                ret = -ETXTBSY;
                goto out;
        }

        if (test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state)) {
                ret = BTRFS_ERROR_DEV_TGT_REPLACE;
                goto out;
        }

        if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
            fs_info->fs_devices->rw_devices == 1) {
                ret = BTRFS_ERROR_DEV_ONLY_WRITABLE;
                goto out;
        }

        if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
                mutex_lock(&fs_info->chunk_mutex);
                list_del_init(&device->dev_alloc_list);
                device->fs_devices->rw_devices--;
                mutex_unlock(&fs_info->chunk_mutex);
        }

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

        /*
         * TODO: the superblock still includes this device in its num_devices
         * counter although write_all_supers() is not locked out. This
         * could give a filesystem state which requires a degraded mount.
         */
        ret = btrfs_rm_dev_item(device);
        if (ret)
                goto error_undo;

        clear_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
        btrfs_scrub_cancel_dev(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. Whoever is writing all supers, should
         * lock the device list mutex before getting the number of
         * devices in the super block (super_copy). Conversely,
         * whoever updates the number of devices in the super block
         * (super_copy) should hold the device list mutex.
         */

        /*
         * In normal cases the cur_devices == fs_devices. But in case
         * of deleting a seed device, the cur_devices should point to
         * its own fs_devices listed under the fs_devices->seed.
         */
        cur_devices = device->fs_devices;
        mutex_lock(&fs_devices->device_list_mutex);
        list_del_rcu(&device->dev_list);

        cur_devices->num_devices--;
        cur_devices->total_devices--;
        /* Update total_devices of the parent fs_devices if it's seed */
        if (cur_devices != fs_devices)
                fs_devices->total_devices--;

        if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))
                cur_devices->missing_devices--;

        btrfs_assign_next_active_device(device, NULL);

        if (device->bdev) {
                cur_devices->open_devices--;
                /* remove sysfs entry */
                btrfs_sysfs_remove_device(device);
        }

        num_devices = btrfs_super_num_devices(fs_info->super_copy) - 1;
        btrfs_set_super_num_devices(fs_info->super_copy, num_devices);
        mutex_unlock(&fs_devices->device_list_mutex);

        /*
         * at this point, the device is zero sized and detached from
         * the devices list.  All that's left is to zero out the old
         * supers and free the device.
         */
        if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state))
                btrfs_scratch_superblocks(fs_info, device->bdev,
                                          device->name->str);

        btrfs_close_bdev(device);
        synchronize_rcu();
        btrfs_free_device(device);

        if (cur_devices->open_devices == 0) {
                list_del_init(&cur_devices->seed_list);
                close_fs_devices(cur_devices);
                free_fs_devices(cur_devices);
        }

out:
        return ret;

error_undo:
        btrfs_reada_undo_remove_dev(device);
        if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
                mutex_lock(&fs_info->chunk_mutex);
                list_add(&device->dev_alloc_list,
                         &fs_devices->alloc_list);
                device->fs_devices->rw_devices++;
                mutex_unlock(&fs_info->chunk_mutex);
        }
        goto out;
}

void btrfs_rm_dev_replace_remove_srcdev(struct btrfs_device *srcdev)
{
        struct btrfs_fs_devices *fs_devices;

        lockdep_assert_held(&srcdev->fs_info->fs_devices->device_list_mutex);

        /*
         * in case of fs with no seed, srcdev->fs_devices will point
         * to fs_devices of fs_info. However when the dev being replaced is
         * a seed dev it will point to the seed's local fs_devices. In short
         * srcdev will have its correct fs_devices in both the cases.
         */
        fs_devices = srcdev->fs_devices;

        list_del_rcu(&srcdev->dev_list);
        list_del(&srcdev->dev_alloc_list);
        fs_devices->num_devices--;
        if (test_bit(BTRFS_DEV_STATE_MISSING, &srcdev->dev_state))
                fs_devices->missing_devices--;

        if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &srcdev->dev_state))
                fs_devices->rw_devices--;

        if (srcdev->bdev)
                fs_devices->open_devices--;
}

void btrfs_rm_dev_replace_free_srcdev(struct btrfs_device *srcdev)
{
        struct btrfs_fs_devices *fs_devices = srcdev->fs_devices;

        mutex_lock(&uuid_mutex);

        btrfs_close_bdev(srcdev);
        synchronize_rcu();
        btrfs_free_device(srcdev);

        /* if this is no devs we rather delete the fs_devices */
        if (!fs_devices->num_devices) {
                /*
                 * On a mounted FS, num_devices can't be zero unless it's a
                 * seed. In case of a seed device being replaced, the replace
                 * target added to the sprout FS, so there will be no more
                 * device left under the seed FS.
                 */
                ASSERT(fs_devices->seeding);

                list_del_init(&fs_devices->seed_list);
                close_fs_devices(fs_devices);
                free_fs_devices(fs_devices);
        }
        mutex_unlock(&uuid_mutex);
}

void btrfs_destroy_dev_replace_tgtdev(struct btrfs_device *tgtdev)
{
        struct btrfs_fs_devices *fs_devices = tgtdev->fs_info->fs_devices;

        mutex_lock(&fs_devices->device_list_mutex);

        btrfs_sysfs_remove_device(tgtdev);

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

        fs_devices->num_devices--;

        btrfs_assign_next_active_device(tgtdev, NULL);

        list_del_rcu(&tgtdev->dev_list);

        mutex_unlock(&fs_devices->device_list_mutex);

        /*
         * The update_dev_time() with in btrfs_scratch_superblocks()
         * may lead to a call to btrfs_show_devname() which will try
         * to hold device_list_mutex. And here this device
         * is already out of device list, so we don't have to hold
         * the device_list_mutex lock.
         */
        btrfs_scratch_superblocks(tgtdev->fs_info, tgtdev->bdev,
                                  tgtdev->name->str);

        btrfs_close_bdev(tgtdev);
        synchronize_rcu();
        btrfs_free_device(tgtdev);
}

static struct btrfs_device *btrfs_find_device_by_path(
                struct btrfs_fs_info *fs_info, const char *device_path)
{
        int ret = 0;
        struct btrfs_super_block *disk_super;
        u64 devid;
        u8 *dev_uuid;
        struct block_device *bdev;
        struct btrfs_device *device;

        ret = btrfs_get_bdev_and_sb(device_path, FMODE_READ,
                                    fs_info->bdev_holder, 0, &bdev, &disk_super);
        if (ret)
                return ERR_PTR(ret);

        devid = btrfs_stack_device_id(&disk_super->dev_item);
        dev_uuid = disk_super->dev_item.uuid;
        if (btrfs_fs_incompat(fs_info, METADATA_UUID))
                device = btrfs_find_device(fs_info->fs_devices, devid, dev_uuid,
                                           disk_super->metadata_uuid, true);
        else
                device = btrfs_find_device(fs_info->fs_devices, devid, dev_uuid,
                                           disk_super->fsid, true);

        btrfs_release_disk_super(disk_super);
        if (!device)
                device = ERR_PTR(-ENOENT);
        blkdev_put(bdev, FMODE_READ);
        return device;
}

/*
 * Lookup a device given by device id, or the path if the id is 0.
 */
struct btrfs_device *btrfs_find_device_by_devspec(
                struct btrfs_fs_info *fs_info, u64 devid,
                const char *device_path)
{
        struct btrfs_device *device;

        if (devid) {
                device = btrfs_find_device(fs_info->fs_devices, devid, NULL,
                                           NULL, true);
                if (!device)
                        return ERR_PTR(-ENOENT);
                return device;
        }

        if (!device_path || !device_path[0])
                return ERR_PTR(-EINVAL);

        if (strcmp(device_path, "missing") == 0) {
                /* Find first missing device */
                list_for_each_entry(device, &fs_info->fs_devices->devices,
                                    dev_list) {
                        if (test_bit(BTRFS_DEV_STATE_IN_FS_METADATA,
                                     &device->dev_state) && !device->bdev)
                                return device;
                }
                return ERR_PTR(-ENOENT);
        }

        return btrfs_find_device_by_path(fs_info, device_path);
}

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

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

        /*
         * Private copy of the seed devices, anchored at
         * fs_info->fs_devices->seed_list
         */
        seed_devices = alloc_fs_devices(NULL, NULL);
        if (IS_ERR(seed_devices))
                return PTR_ERR(seed_devices);

        /*
         * It's necessary to retain a copy of the original seed fs_devices in
         * fs_uuids so that filesystems which have been seeded can successfully
         * reference the seed device from open_seed_devices. This also supports
         * multiple fs seed.
         */
        old_devices = clone_fs_devices(fs_devices);
        if (IS_ERR(old_devices)) {
                kfree(seed_devices);
                return PTR_ERR(old_devices);
        }

        list_add(&old_devices->fs_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(&fs_devices->device_list_mutex);
        list_splice_init_rcu(&fs_devices->devices, &seed_devices->devices,
                              synchronize_rcu);
        list_for_each_entry(device, &seed_devices->devices, dev_list)
                device->fs_devices = seed_devices;

        fs_devices->seeding = false;
        fs_devices->num_devices = 0;
        fs_devices->open_devices = 0;
        fs_devices->missing_devices = 0;
        fs_devices->rotating = false;
        list_add(&seed_devices->seed_list, &fs_devices->seed_list);

        generate_random_uuid(fs_devices->fsid);
        memcpy(fs_devices->metadata_uuid, fs_devices->fsid, BTRFS_FSID_SIZE);
        memcpy(disk_super->fsid, fs_devices->fsid, BTRFS_FSID_SIZE);
        mutex_unlock(&fs_devices->device_list_mutex);

        super_flags = btrfs_super_flags(disk_super) &
                      ~BTRFS_SUPER_FLAG_SEEDING;
        btrfs_set_super_flags(disk_super, super_flags);

        return 0;
}

/*
 * Store the expected generation for seed devices in device items.
 */
static int btrfs_finish_sprout(struct btrfs_trans_handle *trans)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_root *root = fs_info->chunk_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_FSID_SIZE];
        u8 dev_uuid[BTRFS_UUID_SIZE];
        u64 devid;
        int ret;

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

        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, btrfs_device_uuid(dev_item),
                                   BTRFS_UUID_SIZE);
                read_extent_buffer(leaf, fs_uuid, btrfs_device_fsid(dev_item),
                                   BTRFS_FSID_SIZE);
                device = btrfs_find_device(fs_info->fs_devices, devid, dev_uuid,
                                           fs_uuid, true);
                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_fs_info *fs_info, const char *device_path)
{
        struct btrfs_root *root = fs_info->dev_root;
        struct request_queue *q;
        struct btrfs_trans_handle *trans;
        struct btrfs_device *device;
        struct block_device *bdev;
        struct super_block *sb = fs_info->sb;
        struct rcu_string *name;
        struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
        u64 orig_super_total_bytes;
        u64 orig_super_num_devices;
        int seeding_dev = 0;
        int ret = 0;
        bool locked = false;

        if (sb_rdonly(sb) && !fs_devices->seeding)
                return -EROFS;

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

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

        sync_blockdev(bdev);

        rcu_read_lock();
        list_for_each_entry_rcu(device, &fs_devices->devices, dev_list) {
                if (device->bdev == bdev) {
                        ret = -EEXIST;
                        rcu_read_unlock();
                        goto error;
                }
        }
        rcu_read_unlock();

        device = btrfs_alloc_device(fs_info, NULL, NULL);
        if (IS_ERR(device)) {
                /* we can safely leave the fs_devices entry around */
                ret = PTR_ERR(device);
                goto error;
        }

        name = rcu_string_strdup(device_path, GFP_KERNEL);
        if (!name) {
                ret = -ENOMEM;
                goto error_free_device;
        }
        rcu_assign_pointer(device->name, name);

        trans = btrfs_start_transaction(root, 0);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);
                goto error_free_device;
        }

        q = bdev_get_queue(bdev);
        set_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
        device->generation = trans->transid;
        device->io_width = fs_info->sectorsize;
        device->io_align = fs_info->sectorsize;
        device->sector_size = fs_info->sectorsize;
        device->total_bytes = round_down(i_size_read(bdev->bd_inode),
                                         fs_info->sectorsize);
        device->disk_total_bytes = device->total_bytes;
        device->commit_total_bytes = device->total_bytes;
        device->fs_info = fs_info;
        device->bdev = bdev;
        set_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
        clear_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state);
        device->mode = FMODE_EXCL;
        device->dev_stats_valid = 1;
        set_blocksize(device->bdev, BTRFS_BDEV_BLOCKSIZE);

        if (seeding_dev) {
                sb->s_flags &= ~SB_RDONLY;
                ret = btrfs_prepare_sprout(fs_info);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        goto error_trans;
                }
        }

        device->fs_devices = fs_devices;

        mutex_lock(&fs_devices->device_list_mutex);
        mutex_lock(&fs_info->chunk_mutex);
        list_add_rcu(&device->dev_list, &fs_devices->devices);
        list_add(&device->dev_alloc_list, &fs_devices->alloc_list);
        fs_devices->num_devices++;
        fs_devices->open_devices++;
        fs_devices->rw_devices++;
        fs_devices->total_devices++;
        fs_devices->total_rw_bytes += device->total_bytes;

        atomic64_add(device->total_bytes, &fs_info->free_chunk_space);

        if (!blk_queue_nonrot(q))
                fs_devices->rotating = true;

        orig_super_total_bytes = btrfs_super_total_bytes(fs_info->super_copy);
        btrfs_set_super_total_bytes(fs_info->super_copy,
                round_down(orig_super_total_bytes + device->total_bytes,
                           fs_info->sectorsize));

        orig_super_num_devices = btrfs_super_num_devices(fs_info->super_copy);
        btrfs_set_super_num_devices(fs_info->super_copy,
                                    orig_super_num_devices + 1);

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

        mutex_unlock(&fs_info->chunk_mutex);

        /* Add sysfs device entry */
        btrfs_sysfs_add_device(device);

        mutex_unlock(&fs_devices->device_list_mutex);

        if (seeding_dev) {
                mutex_lock(&fs_info->chunk_mutex);
                ret = init_first_rw_device(trans);
                mutex_unlock(&fs_info->chunk_mutex);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        goto error_sysfs;
                }
        }

        ret = btrfs_add_dev_item(trans, device);
        if (ret) {
                btrfs_abort_transaction(trans, ret);
                goto error_sysfs;
        }

        if (seeding_dev) {
                ret = btrfs_finish_sprout(trans);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        goto error_sysfs;
                }

                /*
                 * fs_devices now represents the newly sprouted filesystem and
                 * its fsid has been changed by btrfs_prepare_sprout
                 */
                btrfs_sysfs_update_sprout_fsid(fs_devices);
        }

        ret = btrfs_commit_transaction(trans);

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

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

                ret = btrfs_relocate_sys_chunks(fs_info);
                if (ret < 0)
                        btrfs_handle_fs_error(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;
                        ret = PTR_ERR(trans);
                        trans = NULL;
                        goto error_sysfs;
                }
                ret = btrfs_commit_transaction(trans);
        }

        /*
         * Now that we have written a new super block to this device, check all
         * other fs_devices list if device_path alienates any other scanned
         * device.
         * We can ignore the return value as it typically returns -EINVAL and
         * only succeeds if the device was an alien.
         */
        btrfs_forget_devices(device_path);

        /* Update ctime/mtime for blkid or udev */
        update_dev_time(device_path);

        return ret;

error_sysfs:
        btrfs_sysfs_remove_device(device);
        mutex_lock(&fs_info->fs_devices->device_list_mutex);
        mutex_lock(&fs_info->chunk_mutex);
        list_del_rcu(&device->dev_list);
        list_del(&device->dev_alloc_list);
        fs_info->fs_devices->num_devices--;
        fs_info->fs_devices->open_devices--;
        fs_info->fs_devices->rw_devices--;
        fs_info->fs_devices->total_devices--;
        fs_info->fs_devices->total_rw_bytes -= device->total_bytes;
        atomic64_sub(device->total_bytes, &fs_info->free_chunk_space);
        btrfs_set_super_total_bytes(fs_info->super_copy,
                                    orig_super_total_bytes);
        btrfs_set_super_num_devices(fs_info->super_copy,
                                    orig_super_num_devices);
        mutex_unlock(&fs_info->chunk_mutex);
        mutex_unlock(&fs_info->fs_devices->device_list_mutex);
error_trans:
        if (seeding_dev)
                sb->s_flags |= SB_RDONLY;
        if (trans)
                btrfs_end_transaction(trans);
error_free_device:
        btrfs_free_device(device);
error:
        blkdev_put(bdev, FMODE_EXCL);
        if (locked) {
                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 = device->fs_info->chunk_root;
        struct btrfs_dev_item *dev_item;
        struct extent_buffer *leaf;
        struct btrfs_key key;

        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,
                                     btrfs_device_get_disk_total_bytes(device));
        btrfs_set_device_bytes_used(leaf, dev_item,
                                    btrfs_device_get_bytes_used(device));
        btrfs_mark_buffer_dirty(leaf);

out:
        btrfs_free_path(path);
        return ret;
}

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

        if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state))
                return -EACCES;

        new_size = round_down(new_size, fs_info->sectorsize);

        mutex_lock(&fs_info->chunk_mutex);
        old_total = btrfs_super_total_bytes(super_copy);
        diff = round_down(new_size - device->total_bytes, fs_info->sectorsize);

        if (new_size <= device->total_bytes ||
            test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state)) {
                mutex_unlock(&fs_info->chunk_mutex);
                return -EINVAL;
        }

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

        btrfs_device_set_total_bytes(device, new_size);
        btrfs_device_set_disk_total_bytes(device, new_size);
        btrfs_clear_space_info_full(device->fs_info);
        if (list_empty(&device->post_commit_list))
                list_add_tail(&device->post_commit_list,
                              &trans->transaction->dev_update_list);
        mutex_unlock(&fs_info->chunk_mutex);

        return btrfs_update_device(trans, device);
}

static int btrfs_free_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_root *root = fs_info->chunk_root;
        int ret;
        struct btrfs_path *path;
        struct btrfs_key key;

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

        key.objectid = BTRFS_FIRST_CHUNK_TREE_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_handle_fs_error(fs_info, -ENOENT,
                                      "Failed lookup while freeing chunk.");
                ret = -ENOENT;
                goto out;
        }

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

static int btrfs_del_sys_chunk(struct btrfs_fs_info *fs_info, u64 chunk_offset)
{
        struct btrfs_super_block *super_copy = 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;

        mutex_lock(&fs_info->chunk_mutex);
        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 == BTRFS_FIRST_CHUNK_TREE_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;
                }
        }
        mutex_unlock(&fs_info->chunk_mutex);
        return ret;
}

/*
 * btrfs_get_chunk_map() - Find the mapping containing the given logical extent.
 * @logical: Logical block offset in bytes.
 * @length: Length of extent in bytes.
 *
 * Return: Chunk mapping or ERR_PTR.
 */
struct extent_map *btrfs_get_chunk_map(struct btrfs_fs_info *fs_info,
                                       u64 logical, u64 length)
{
        struct extent_map_tree *em_tree;
        struct extent_map *em;

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

        if (!em) {
                btrfs_crit(fs_info,
                           "unable to find chunk map for logical %llu length %llu",
                           logical, length);
                return ERR_PTR(-EINVAL);
        }

        if (em->start > logical || em->start + em->len <= logical) {
                btrfs_crit(fs_info,
                           "found a bad chunk map, wanted %llu-%llu, found %llu-%llu",
                           logical, logical + length, em->start, em->start + em->len);
                free_extent_map(em);
                return ERR_PTR(-EINVAL);
        }

        /* callers are responsible for dropping em's ref. */
        return em;
}

int btrfs_remove_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct extent_map *em;
        struct map_lookup *map;
        u64 dev_extent_len = 0;
        int i, ret = 0;
        struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;

        em = btrfs_get_chunk_map(fs_info, chunk_offset, 1);
        if (IS_ERR(em)) {
                /*
                 * This is a logic error, but we don't want to just rely on the
                 * user having built with ASSERT enabled, so if ASSERT doesn't
                 * do anything we still error out.
                 */
                ASSERT(0);
                return PTR_ERR(em);
        }
        map = em->map_lookup;
        mutex_lock(&fs_info->chunk_mutex);
        check_system_chunk(trans, map->type);
        mutex_unlock(&fs_info->chunk_mutex);

        /*
         * Take the device list mutex to prevent races with the final phase of
         * a device replace operation that replaces the device object associated
         * with map stripes (dev-replace.c:btrfs_dev_replace_finishing()).
         */
        mutex_lock(&fs_devices->device_list_mutex);
        for (i = 0; i < map->num_stripes; i++) {
                struct btrfs_device *device = map->stripes[i].dev;
                ret = btrfs_free_dev_extent(trans, device,
                                            map->stripes[i].physical,
                                            &dev_extent_len);
                if (ret) {
                        mutex_unlock(&fs_devices->device_list_mutex);
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }

                if (device->bytes_used > 0) {
                        mutex_lock(&fs_info->chunk_mutex);
                        btrfs_device_set_bytes_used(device,
                                        device->bytes_used - dev_extent_len);
                        atomic64_add(dev_extent_len, &fs_info->free_chunk_space);
                        btrfs_clear_space_info_full(fs_info);
                        mutex_unlock(&fs_info->chunk_mutex);
                }

                ret = btrfs_update_device(trans, device);
                if (ret) {
                        mutex_unlock(&fs_devices->device_list_mutex);
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }
        }
        mutex_unlock(&fs_devices->device_list_mutex);

        ret = btrfs_free_chunk(trans, chunk_offset);
        if (ret) {
                btrfs_abort_transaction(trans, ret);
                goto out;
        }

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

        if (map->type & BTRFS_BLOCK_GROUP_SYSTEM) {
                ret = btrfs_del_sys_chunk(fs_info, chunk_offset);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }
        }

        ret = btrfs_remove_block_group(trans, chunk_offset, em);
        if (ret) {
                btrfs_abort_transaction(trans, ret);
                goto out;
        }

out:
        /* once for us */
        free_extent_map(em);
        return ret;
}

static int btrfs_relocate_chunk(struct btrfs_fs_info *fs_info, u64 chunk_offset)
{
        struct btrfs_root *root = fs_info->chunk_root;
        struct btrfs_trans_handle *trans;
        struct btrfs_block_group *block_group;
        int ret;

        /*
         * Prevent races with automatic removal of unused block groups.
         * After we relocate and before we remove the chunk with offset
         * chunk_offset, automatic removal of the block group can kick in,
         * resulting in a failure when calling btrfs_remove_chunk() below.
         *
         * Make sure to acquire this mutex before doing a tree search (dev
         * or chunk trees) to find chunks. Otherwise the cleaner kthread might
         * call btrfs_remove_chunk() (through btrfs_delete_unused_bgs()) after
         * we release the path used to search the chunk/dev tree and before
         * the current task acquires this mutex and calls us.
         */
        lockdep_assert_held(&fs_info->delete_unused_bgs_mutex);

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

        block_group = btrfs_lookup_block_group(fs_info, chunk_offset);
        if (!block_group)
                return -ENOENT;
        btrfs_discard_cancel_work(&fs_info->discard_ctl, block_group);
        btrfs_put_block_group(block_group);

        trans = btrfs_start_trans_remove_block_group(root->fs_info,
                                                     chunk_offset);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);
                btrfs_handle_fs_error(root->fs_info, ret, NULL);
                return ret;
        }

        /*
         * step two, delete the device extents and the
         * chunk tree entries
         */
        ret = btrfs_remove_chunk(trans, chunk_offset);
        btrfs_end_transaction(trans);
        return ret;
}

static int btrfs_relocate_sys_chunks(struct btrfs_fs_info *fs_info)
{
        struct btrfs_root *chunk_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_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) {
                mutex_lock(&fs_info->delete_unused_bgs_mutex);
                ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0);
                if (ret < 0) {
                        mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                        goto error;
                }
                if (ret == 0) {
                        /*
                         * On the first search we would find chunk tree with
                         * offset -1, which is not possible. On subsequent
                         * loops this would find an existing item on an invalid
                         * offset (one less than the previous one, wrong
                         * alignment and size).
                         */
                        ret = -EUCLEAN;
                        mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                        goto error;
                }

                ret = btrfs_previous_item(chunk_root, path, key.objectid,
                                          key.type);
                if (ret)
                        mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                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(fs_info, found_key.offset);
                        if (ret == -ENOSPC)
                                failed++;
                        else
                                BUG_ON(ret);
                }
                mutex_unlock(&fs_info->delete_unused_bgs_mutex);

                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 (WARN_ON(failed && retried)) {
                ret = -ENOSPC;
        }
error:
        btrfs_free_path(path);
        return ret;
}

/*
 * return 1 : allocate a data chunk successfully,
 * return <0: errors during allocating a data chunk,
 * return 0 : no need to allocate a data chunk.
 */
static int btrfs_may_alloc_data_chunk(struct btrfs_fs_info *fs_info,
                                      u64 chunk_offset)
{
        struct btrfs_block_group *cache;
        u64 bytes_used;
        u64 chunk_type;

        cache = btrfs_lookup_block_group(fs_info, chunk_offset);
        ASSERT(cache);
        chunk_type = cache->flags;
        btrfs_put_block_group(cache);

        if (!(chunk_type & BTRFS_BLOCK_GROUP_DATA))
                return 0;

        spin_lock(&fs_info->data_sinfo->lock);
        bytes_used = fs_info->data_sinfo->bytes_used;
        spin_unlock(&fs_info->data_sinfo->lock);

        if (!bytes_used) {
                struct btrfs_trans_handle *trans;
                int ret;

                trans = btrfs_join_transaction(fs_info->tree_root);
                if (IS_ERR(trans))
                        return PTR_ERR(trans);

                ret = btrfs_force_chunk_alloc(trans, BTRFS_BLOCK_GROUP_DATA);
                btrfs_end_transaction(trans);
                if (ret < 0)
                        return ret;
                return 1;
        }

        return 0;
}

static int insert_balance_item(struct btrfs_fs_info *fs_info,
                               struct btrfs_balance_control *bctl)
{
        struct btrfs_root *root = fs_info->tree_root;
        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_TEMPORARY_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);

        memzero_extent_buffer(leaf, (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);
        if (err && !ret)
                ret = err;
        return ret;
}

static int del_balance_item(struct btrfs_fs_info *fs_info)
{
        struct btrfs_root *root = fs_info->tree_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_fallback_global_rsv(root, 0);
        if (IS_ERR(trans)) {
                btrfs_free_path(path);
                return PTR_ERR(trans);
        }

        key.objectid = BTRFS_BALANCE_OBJECTID;
        key.type = BTRFS_TEMPORARY_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);
        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_USAGE_RANGE) &&
            !(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_USAGE_RANGE) &&
            !(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_USAGE_RANGE) &&
            !(bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT)) {
                bctl->meta.flags |= BTRFS_BALANCE_ARGS_USAGE;
                bctl->meta.usage = 90;
        }
}

/*
 * Clear the balance status in fs_info and delete the balance item from disk.
 */
static void reset_balance_state(struct btrfs_fs_info *fs_info)
{
        struct btrfs_balance_control *bctl = fs_info->balance_ctl;
        int ret;

        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);
        ret = del_balance_item(fs_info);
        if (ret)
                btrfs_handle_fs_error(fs_info, ret, NULL);
}

/*
 * 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 int chunk_usage_range_filter(struct btrfs_fs_info *fs_info, u64 chunk_offset,
                              struct btrfs_balance_args *bargs)
{
        struct btrfs_block_group *cache;
        u64 chunk_used;
        u64 user_thresh_min;
        u64 user_thresh_max;
        int ret = 1;

        cache = btrfs_lookup_block_group(fs_info, chunk_offset);
        chunk_used = cache->used;

        if (bargs->usage_min == 0)
                user_thresh_min = 0;
        else
                user_thresh_min = div_factor_fine(cache->length,
                                                  bargs->usage_min);

        if (bargs->usage_max == 0)
                user_thresh_max = 1;
        else if (bargs->usage_max > 100)
                user_thresh_max = cache->length;
        else
                user_thresh_max = div_factor_fine(cache->length,
                                                  bargs->usage_max);

        if (user_thresh_min <= chunk_used && chunk_used < user_thresh_max)
                ret = 0;

        btrfs_put_block_group(cache);
        return ret;
}

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

        cache = btrfs_lookup_block_group(fs_info, chunk_offset);
        chunk_used = cache->used;

        if (bargs->usage_min == 0)
                user_thresh = 1;
        else if (bargs->usage > 100)
                user_thresh = cache->length;
        else
                user_thresh = div_factor_fine(cache->length, 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;
}

static u64 calc_data_stripes(u64 type, int num_stripes)
{
        const int index = btrfs_bg_flags_to_raid_index(type);
        const int ncopies = btrfs_raid_array[index].ncopies;
        const int nparity = btrfs_raid_array[index].nparity;

        if (nparity)
                return num_stripes - nparity;
        else
                return num_stripes / ncopies;
}

/* [pstart, pend) */
static int chunk_drange_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);
        u64 stripe_offset;
        u64 stripe_length;
        u64 type;
        int factor;
        int i;

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

        type = btrfs_chunk_type(leaf, chunk);
        factor = calc_data_stripes(type, num_stripes);

        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);
                stripe_length = div_u64(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_stripes_range_filter(struct extent_buffer *leaf,
                               struct btrfs_chunk *chunk,
                               struct btrfs_balance_args *bargs)
{
        int num_stripes = btrfs_chunk_num_stripes(leaf, chunk);

        if (bargs->stripes_min <= num_stripes
                        && num_stripes <= bargs->stripes_max)
                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 extent_buffer *leaf,
                                struct btrfs_chunk *chunk, u64 chunk_offset)
{
        struct btrfs_fs_info *fs_info = leaf->fs_info;
        struct btrfs_balance_control *bctl = 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(fs_info, chunk_offset, bargs)) {
                return 0;
        } else if ((bargs->flags & BTRFS_BALANCE_ARGS_USAGE_RANGE) &&
            chunk_usage_range_filter(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, bargs)) {
                return 0;
        }

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

        /* stripes filter */
        if ((bargs->flags & BTRFS_BALANCE_ARGS_STRIPES_RANGE) &&
            chunk_stripes_range_filter(leaf, chunk, bargs)) {
                return 0;
        }

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

        /*
         * limited by count, must be the last filter
         */
        if ((bargs->flags & BTRFS_BALANCE_ARGS_LIMIT)) {
                if (bargs->limit == 0)
                        return 0;
                else
                        bargs->limit--;
        } else if ((bargs->flags & BTRFS_BALANCE_ARGS_LIMIT_RANGE)) {
                /*
                 * Same logic as the 'limit' filter; the minimum cannot be
                 * determined here because we do not have the global information
                 * about the count of all chunks that satisfy the filters.
                 */
                if (bargs->limit_max == 0)
                        return 0;
                else
                        bargs->limit_max--;
        }

        return 1;
}

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;
        u64 chunk_type;
        struct btrfs_chunk *chunk;
        struct btrfs_path *path = NULL;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct extent_buffer *leaf;
        int slot;
        int ret;
        int enospc_errors = 0;
        bool counting = true;
        /* The single value limit and min/max limits use the same bytes in the */
        u64 limit_data = bctl->data.limit;
        u64 limit_meta = bctl->meta.limit;
        u64 limit_sys = bctl->sys.limit;
        u32 count_data = 0;
        u32 count_meta = 0;
        u32 count_sys = 0;
        int chunk_reserved = 0;

        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:
        if (!counting) {
                /*
                 * The single value limit and min/max limits use the same bytes
                 * in the
                 */
                bctl->data.limit = limit_data;
                bctl->meta.limit = limit_meta;
                bctl->sys.limit = limit_sys;
        }
        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;
                }

                mutex_lock(&fs_info->delete_unused_bgs_mutex);
                ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0);
                if (ret < 0) {
                        mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                        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) {
                        mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                        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) {
                        mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                        break;
                }

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

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

                ret = should_balance_chunk(leaf, chunk, found_key.offset);

                btrfs_release_path(path);
                if (!ret) {
                        mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                        goto loop;
                }

                if (counting) {
                        mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                        spin_lock(&fs_info->balance_lock);
                        bctl->stat.expected++;
                        spin_unlock(&fs_info->balance_lock);

                        if (chunk_type & BTRFS_BLOCK_GROUP_DATA)
                                count_data++;
                        else if (chunk_type & BTRFS_BLOCK_GROUP_SYSTEM)
                                count_sys++;
                        else if (chunk_type & BTRFS_BLOCK_GROUP_METADATA)
                                count_meta++;

                        goto loop;
                }

                /*
                 * Apply limit_min filter, no need to check if the LIMITS
                 * filter is used, limit_min is 0 by default
                 */
                if (((chunk_type & BTRFS_BLOCK_GROUP_DATA) &&
                                        count_data < bctl->data.limit_min)
                                || ((chunk_type & BTRFS_BLOCK_GROUP_METADATA) &&
                                        count_meta < bctl->meta.limit_min)
                                || ((chunk_type & BTRFS_BLOCK_GROUP_SYSTEM) &&
                                        count_sys < bctl->sys.limit_min)) {
                        mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                        goto loop;
                }

                if (!chunk_reserved) {
                        /*
                         * We may be relocating the only data chunk we have,
                         * which could potentially end up with losing data's
                         * raid profile, so lets allocate an empty one in
                         * advance.
                         */
                        ret = btrfs_may_alloc_data_chunk(fs_info,
                                                         found_key.offset);
                        if (ret < 0) {
                                mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                                goto error;
                        } else if (ret == 1) {
                                chunk_reserved = 1;
                        }
                }

                ret = btrfs_relocate_chunk(fs_info, found_key.offset);
                mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                if (ret == -ENOSPC) {
                        enospc_errors++;
                } else if (ret == -ETXTBSY) {
                        btrfs_info(fs_info,
           "skipping relocation of block group %llu due to active swapfile",
                                   found_key.offset);
                        ret = 0;
                } else if (ret) {
                        goto error;
                } else {
                        spin_lock(&fs_info->balance_lock);
                        bctl->stat.completed++;
                        spin_unlock(&fs_info->balance_lock);
                }
loop:
                if (found_key.offset == 0)
                        break;
                key.offset = found_key.offset - 1;
        }

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

        return ret;
}

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

        flags &= ~BTRFS_BLOCK_GROUP_TYPE_MASK;

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

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

        return has_single_bit_set(flags);
}

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);
}

/*
 * Validate target profile against allowed profiles and return true if it's OK.
 * Otherwise print the error message and return false.
 */
static inline int validate_convert_profile(struct btrfs_fs_info *fs_info,
                const struct btrfs_balance_args *bargs,
                u64 allowed, const char *type)
{
        if (!(bargs->flags & BTRFS_BALANCE_ARGS_CONVERT))
                return true;

        /* Profile is valid and does not have bits outside of the allowed set */
        if (alloc_profile_is_valid(bargs->target, 1) &&
            (bargs->target & ~allowed) == 0)
                return true;

        btrfs_err(fs_info, "balance: invalid convert %s profile %s",
                        type, btrfs_bg_type_to_raid_name(bargs->target));
        return false;
}

/*
 * Fill @buf with textual description of balance filter flags @bargs, up to
 * @size_buf including the terminating null. The output may be trimmed if it
 * does not fit into the provided buffer.
 */
static void describe_balance_args(struct btrfs_balance_args *bargs, char *buf,
                                 u32 size_buf)
{
        int ret;
        u32 size_bp = size_buf;
        char *bp = buf;
        u64 flags = bargs->flags;
        char tmp_buf[128] = {'\0'};

        if (!flags)
                return;

#define CHECK_APPEND_NOARG(a)                                           \
        do {                                                            \
                ret = snprintf(bp, size_bp, (a));                       \
                if (ret < 0 || ret >= size_bp)                          \
                        goto out_overflow;                              \
                size_bp -= ret;                                         \
                bp += ret;                                              \
        } while (0)

#define CHECK_APPEND_1ARG(a, v1)                                        \
        do {                                                            \
                ret = snprintf(bp, size_bp, (a), (v1));                 \
                if (ret < 0 || ret >= size_bp)                          \
                        goto out_overflow;                              \
                size_bp -= ret;                                         \
                bp += ret;                                              \
        } while (0)

#define CHECK_APPEND_2ARG(a, v1, v2)                                    \
        do {                                                            \
                ret = snprintf(bp, size_bp, (a), (v1), (v2));           \
                if (ret < 0 || ret >= size_bp)                          \
                        goto out_overflow;                              \
                size_bp -= ret;                                         \
                bp += ret;                                              \
        } while (0)

        if (flags & BTRFS_BALANCE_ARGS_CONVERT)
                CHECK_APPEND_1ARG("convert=%s,",
                                  btrfs_bg_type_to_raid_name(bargs->target));

        if (flags & BTRFS_BALANCE_ARGS_SOFT)
                CHECK_APPEND_NOARG("soft,");

        if (flags & BTRFS_BALANCE_ARGS_PROFILES) {
                btrfs_describe_block_groups(bargs->profiles, tmp_buf,
                                            sizeof(tmp_buf));
                CHECK_APPEND_1ARG("profiles=%s,", tmp_buf);
        }

        if (flags & BTRFS_BALANCE_ARGS_USAGE)
                CHECK_APPEND_1ARG("usage=%llu,", bargs->usage);

        if (flags & BTRFS_BALANCE_ARGS_USAGE_RANGE)
                CHECK_APPEND_2ARG("usage=%u..%u,",
                                  bargs->usage_min, bargs->usage_max);

        if (flags & BTRFS_BALANCE_ARGS_DEVID)
                CHECK_APPEND_1ARG("devid=%llu,", bargs->devid);

        if (flags & BTRFS_BALANCE_ARGS_DRANGE)
                CHECK_APPEND_2ARG("drange=%llu..%llu,",
                                  bargs->pstart, bargs->pend);

        if (flags & BTRFS_BALANCE_ARGS_VRANGE)
                CHECK_APPEND_2ARG("vrange=%llu..%llu,",
                                  bargs->vstart, bargs->vend);

        if (flags & BTRFS_BALANCE_ARGS_LIMIT)
                CHECK_APPEND_1ARG("limit=%llu,", bargs->limit);

        if (flags & BTRFS_BALANCE_ARGS_LIMIT_RANGE)
                CHECK_APPEND_2ARG("limit=%u..%u,",
                                bargs->limit_min, bargs->limit_max);

        if (flags & BTRFS_BALANCE_ARGS_STRIPES_RANGE)
                CHECK_APPEND_2ARG("stripes=%u..%u,",
                                  bargs->stripes_min, bargs->stripes_max);

#undef CHECK_APPEND_2ARG
#undef CHECK_APPEND_1ARG
#undef CHECK_APPEND_NOARG

out_overflow:

        if (size_bp < size_buf)
                buf[size_buf - size_bp - 1] = '\0'; /* remove last , */
        else
                buf[0] = '\0';
}

static void describe_balance_start_or_resume(struct btrfs_fs_info *fs_info)
{
        u32 size_buf = 1024;
        char tmp_buf[192] = {'\0'};
        char *buf;
        char *bp;
        u32 size_bp = size_buf;
        int ret;
        struct btrfs_balance_control *bctl = fs_info->balance_ctl;

        buf = kzalloc(size_buf, GFP_KERNEL);
        if (!buf)
                return;

        bp = buf;

#define CHECK_APPEND_1ARG(a, v1)                                        \
        do {                                                            \
                ret = snprintf(bp, size_bp, (a), (v1));                 \
                if (ret < 0 || ret >= size_bp)                          \
                        goto out_overflow;                              \
                size_bp -= ret;                                         \
                bp += ret;                                              \
        } while (0)

        if (bctl->flags & BTRFS_BALANCE_FORCE)
                CHECK_APPEND_1ARG("%s", "-f ");

        if (bctl->flags & BTRFS_BALANCE_DATA) {
                describe_balance_args(&bctl->data, tmp_buf, sizeof(tmp_buf));
                CHECK_APPEND_1ARG("-d%s ", tmp_buf);
        }

        if (bctl->flags & BTRFS_BALANCE_METADATA) {
                describe_balance_args(&bctl->meta, tmp_buf, sizeof(tmp_buf));
                CHECK_APPEND_1ARG("-m%s ", tmp_buf);
        }

        if (bctl->flags & BTRFS_BALANCE_SYSTEM) {
                describe_balance_args(&bctl->sys, tmp_buf, sizeof(tmp_buf));
                CHECK_APPEND_1ARG("-s%s ", tmp_buf);
        }

#undef CHECK_APPEND_1ARG

out_overflow:

        if (size_bp < size_buf)
                buf[size_buf - size_bp - 1] = '\0'; /* remove last " " */
        btrfs_info(fs_info, "balance: %s %s",
                   (bctl->flags & BTRFS_BALANCE_RESUME) ?
                   "resume" : "start", buf);

        kfree(buf);
}

/*
 * Should be called with balance mutexe held
 */
int btrfs_balance(struct btrfs_fs_info *fs_info,
                  struct btrfs_balance_control *bctl,
                  struct btrfs_ioctl_balance_args *bargs)
{
        u64 meta_target, data_target;
        u64 allowed;
        int mixed = 0;
        int ret;
        u64 num_devices;
        unsigned seq;
        bool reducing_redundancy;
        int i;

        if (btrfs_fs_closing(fs_info) ||
            atomic_read(&fs_info->balance_pause_req) ||
            btrfs_should_cancel_balance(fs_info)) {
                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))) {
                        btrfs_err(fs_info,
          "balance: mixed groups data and metadata options must be the same");
                        ret = -EINVAL;
                        goto out;
                }
        }

        /*
         * rw_devices will not change at the moment, device add/delete/replace
         * are exclusive
         */
        num_devices = fs_info->fs_devices->rw_devices;

        /*
         * SINGLE profile on-disk has no profile bit, but in-memory we have a
         * special bit for it, to make it easier to distinguish.  Thus we need
         * to set it manually, or balance would refuse the profile.
         */
        allowed = BTRFS_AVAIL_ALLOC_BIT_SINGLE;
        for (i = 0; i < ARRAY_SIZE(btrfs_raid_array); i++)
                if (num_devices >= btrfs_raid_array[i].devs_min)
                        allowed |= btrfs_raid_array[i].bg_flag;

        if (!validate_convert_profile(fs_info, &bctl->data, allowed, "data") ||
            !validate_convert_profile(fs_info, &bctl->meta, allowed, "metadata") ||
            !validate_convert_profile(fs_info, &bctl->sys,  allowed, "system")) {
                ret = -EINVAL;
                goto out;
        }

        /*
         * Allow to reduce metadata or system integrity only if force set for
         * profiles with redundancy (copies, parity)
         */
        allowed = 0;
        for (i = 0; i < ARRAY_SIZE(btrfs_raid_array); i++) {
                if (btrfs_raid_array[i].ncopies >= 2 ||
                    btrfs_raid_array[i].tolerated_failures >= 1)
                        allowed |= btrfs_raid_array[i].bg_flag;
        }
        do {
                seq = read_seqbegin(&fs_info->profiles_lock);

                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)))
                        reducing_redundancy = true;
                else
                        reducing_redundancy = false;

                /* if we're not converting, the target field is uninitialized */
                meta_target = (bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) ?
                        bctl->meta.target : fs_info->avail_metadata_alloc_bits;
                data_target = (bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT) ?
                        bctl->data.target : fs_info->avail_data_alloc_bits;
        } while (read_seqretry(&fs_info->profiles_lock, seq));

        if (reducing_redundancy) {
                if (bctl->flags & BTRFS_BALANCE_FORCE) {
                        btrfs_info(fs_info,
                           "balance: force reducing metadata redundancy");
                } else {
                        btrfs_err(fs_info,
        "balance: reduces metadata redundancy, use --force if you want this");
                        ret = -EINVAL;
                        goto out;
                }
        }

        if (btrfs_get_num_tolerated_disk_barrier_failures(meta_target) <
                btrfs_get_num_tolerated_disk_barrier_failures(data_target)) {
                btrfs_warn(fs_info,
        "balance: metadata profile %s has lower redundancy than data profile %s",
                                btrfs_bg_type_to_raid_name(meta_target),
                                btrfs_bg_type_to_raid_name(data_target));
        }

        if (fs_info->send_in_progress) {
                btrfs_warn_rl(fs_info,
"cannot run balance while send operations are in progress (%d in progress)",
                              fs_info->send_in_progress);
                ret = -EAGAIN;
                goto out;
        }

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

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

        ASSERT(!test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
        set_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags);
        describe_balance_start_or_resume(fs_info);
        mutex_unlock(&fs_info->balance_mutex);

        ret = __btrfs_balance(fs_info);

        mutex_lock(&fs_info->balance_mutex);
        if (ret == -ECANCELED && atomic_read(&fs_info->balance_pause_req))
                btrfs_info(fs_info, "balance: paused");
        /*
         * Balance can be canceled by:
         *
         * - Regular cancel request
         *   Then ret == -ECANCELED and balance_cancel_req > 0
         *
         * - Fatal signal to "btrfs" process
         *   Either the signal caught by wait_reserve_ticket() and callers
         *   got -EINTR, or caught by btrfs_should_cancel_balance() and
         *   got -ECANCELED.
         *   Either way, in this case balance_cancel_req = 0, and
         *   ret == -EINTR or ret == -ECANCELED.
         *
         * So here we only check the return value to catch canceled balance.
         */
        else if (ret == -ECANCELED || ret == -EINTR)
                btrfs_info(fs_info, "balance: canceled");
        else
                btrfs_info(fs_info, "balance: ended with status: %d", ret);

        clear_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags);

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

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

        wake_up(&fs_info->balance_wait_q);

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

        return ret;
}

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

        sb_start_write(fs_info->sb);
        mutex_lock(&fs_info->balance_mutex);
        if (fs_info->balance_ctl)
                ret = btrfs_balance(fs_info, fs_info->balance_ctl, NULL);
        mutex_unlock(&fs_info->balance_mutex);
        sb_end_write(fs_info->sb);

        return ret;
}

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

        mutex_lock(&fs_info->balance_mutex);
        if (!fs_info->balance_ctl) {
                mutex_unlock(&fs_info->balance_mutex);
                return 0;
        }
        mutex_unlock(&fs_info->balance_mutex);

        if (btrfs_test_opt(fs_info, SKIP_BALANCE)) {
                btrfs_info(fs_info, "balance: resume skipped");
                return 0;
        }

        /*
         * A ro->rw remount sequence should continue with the paused balance
         * regardless of who pauses it, system or the user as of now, so set
         * the resume flag.
         */
        spin_lock(&fs_info->balance_lock);
        fs_info->balance_ctl->flags |= BTRFS_BALANCE_RESUME;
        spin_unlock(&fs_info->balance_lock);

        tsk = kthread_run(balance_kthread, fs_info, "btrfs-balance");
        return PTR_ERR_OR_ZERO(tsk);
}

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_TEMPORARY_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->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);

        /*
         * This should never happen, as the paused balance state is recovered
         * during mount without any chance of other exclusive ops to collide.
         *
         * This gives the exclusive op status to balance and keeps in paused
         * state until user intervention (cancel or umount). If the ownership
         * cannot be assigned, show a message but do not fail. The balance
         * is in a paused state and must have fs_info::balance_ctl properly
         * set up.
         */
        if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE))
                btrfs_warn(fs_info,
        "balance: cannot set exclusive op status, resume manually");

        btrfs_release_path(path);

        mutex_lock(&fs_info->balance_mutex);
        BUG_ON(fs_info->balance_ctl);
        spin_lock(&fs_info->balance_lock);
        fs_info->balance_ctl = bctl;
        spin_unlock(&fs_info->balance_lock);
        mutex_unlock(&fs_info->balance_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 (test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags)) {
                atomic_inc(&fs_info->balance_pause_req);
                mutex_unlock(&fs_info->balance_mutex);

                wait_event(fs_info->balance_wait_q,
                           !test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));

                mutex_lock(&fs_info->balance_mutex);
                /* we are good with balance_ctl ripped off from under us */
                BUG_ON(test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
                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;
        }

        /*
         * A paused balance with the item stored on disk can be resumed at
         * mount time if the mount is read-write. Otherwise it's still paused
         * and we must not allow cancelling as it deletes the item.
         */
        if (sb_rdonly(fs_info->sb)) {
                mutex_unlock(&fs_info->balance_mutex);
                return -EROFS;
        }

        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 (test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags)) {
                mutex_unlock(&fs_info->balance_mutex);
                wait_event(fs_info->balance_wait_q,
                           !test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
                mutex_lock(&fs_info->balance_mutex);
        } else {
                mutex_unlock(&fs_info->balance_mutex);
                /*
                 * Lock released to allow other waiters to continue, we'll
                 * reexamine the status again.
                 */
                mutex_lock(&fs_info->balance_mutex);

                if (fs_info->balance_ctl) {
                        reset_balance_state(fs_info);
                        btrfs_exclop_finish(fs_info);
                        btrfs_info(fs_info, "balance: canceled");
                }
        }

        ASSERT(!test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
        atomic_dec(&fs_info->balance_cancel_req);
        mutex_unlock(&fs_info->balance_mutex);
        return 0;
}

int btrfs_uuid_scan_kthread(void *data)
{
        struct btrfs_fs_info *fs_info = data;
        struct btrfs_root *root = fs_info->tree_root;
        struct btrfs_key key;
        struct btrfs_path *path = NULL;
        int ret = 0;
        struct extent_buffer *eb;
        int slot;
        struct btrfs_root_item root_item;
        u32 item_size;
        struct btrfs_trans_handle *trans = NULL;
        bool closing = false;

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

        key.objectid = 0;
        key.type = BTRFS_ROOT_ITEM_KEY;
        key.offset = 0;

        while (1) {
                if (btrfs_fs_closing(fs_info)) {
                        closing = true;
                        break;
                }
                ret = btrfs_search_forward(root, &key, path,
                                BTRFS_OLDEST_GENERATION);
                if (ret) {
                        if (ret > 0)
                                ret = 0;
                        break;
                }

                if (key.type != BTRFS_ROOT_ITEM_KEY ||
                    (key.objectid < BTRFS_FIRST_FREE_OBJECTID &&
                     key.objectid != BTRFS_FS_TREE_OBJECTID) ||
                    key.objectid > BTRFS_LAST_FREE_OBJECTID)
                        goto skip;

                eb = path->nodes[0];
                slot = path->slots[0];
                item_size = btrfs_item_size_nr(eb, slot);
                if (item_size < sizeof(root_item))
                        goto skip;

                read_extent_buffer(eb, &root_item,
                                   btrfs_item_ptr_offset(eb, slot),
                                   (int)sizeof(root_item));
                if (btrfs_root_refs(&root_item) == 0)
                        goto skip;

                if (!btrfs_is_empty_uuid(root_item.uuid) ||
                    !btrfs_is_empty_uuid(root_item.received_uuid)) {
                        if (trans)
                                goto update_tree;

                        btrfs_release_path(path);
                        /*
                         * 1 - subvol uuid item
                         * 1 - received_subvol uuid item
                         */
                        trans = btrfs_start_transaction(fs_info->uuid_root, 2);
                        if (IS_ERR(trans)) {
                                ret = PTR_ERR(trans);
                                break;
                        }
                        continue;
                } else {
                        goto skip;
                }
update_tree:
                btrfs_release_path(path);
                if (!btrfs_is_empty_uuid(root_item.uuid)) {
                        ret = btrfs_uuid_tree_add(trans, root_item.uuid,
                                                  BTRFS_UUID_KEY_SUBVOL,
                                                  key.objectid);
                        if (ret < 0) {
                                btrfs_warn(fs_info, "uuid_tree_add failed %d",
                                        ret);
                                break;
                        }
                }

                if (!btrfs_is_empty_uuid(root_item.received_uuid)) {
                        ret = btrfs_uuid_tree_add(trans,
                                                  root_item.received_uuid,
                                                 BTRFS_UUID_KEY_RECEIVED_SUBVOL,
                                                  key.objectid);
                        if (ret < 0) {
                                btrfs_warn(fs_info, "uuid_tree_add failed %d",
                                        ret);
                                break;
                        }
                }

skip:
                btrfs_release_path(path);
                if (trans) {
                        ret = btrfs_end_transaction(trans);
                        trans = NULL;
                        if (ret)
                                break;
                }

                if (key.offset < (u64)-1) {
                        key.offset++;
                } else if (key.type < BTRFS_ROOT_ITEM_KEY) {
                        key.offset = 0;
                        key.type = BTRFS_ROOT_ITEM_KEY;
                } else if (key.objectid < (u64)-1) {
                        key.offset = 0;
                        key.type = BTRFS_ROOT_ITEM_KEY;
                        key.objectid++;
                } else {
                        break;
                }
                cond_resched();
        }

out:
        btrfs_free_path(path);
        if (trans && !IS_ERR(trans))
                btrfs_end_transaction(trans);
        if (ret)
                btrfs_warn(fs_info, "btrfs_uuid_scan_kthread failed %d", ret);
        else if (!closing)
                set_bit(BTRFS_FS_UPDATE_UUID_TREE_GEN, &fs_info->flags);
        up(&fs_info->uuid_tree_rescan_sem);
        return 0;
}

int btrfs_create_uuid_tree(struct btrfs_fs_info *fs_info)
{
        struct btrfs_trans_handle *trans;
        struct btrfs_root *tree_root = fs_info->tree_root;
        struct btrfs_root *uuid_root;
        struct task_struct *task;
        int ret;

        /*
         * 1 - root node
         * 1 - root item
         */
        trans = btrfs_start_transaction(tree_root, 2);
        if (IS_ERR(trans))
                return PTR_ERR(trans);

        uuid_root = btrfs_create_tree(trans, BTRFS_UUID_TREE_OBJECTID);
        if (IS_ERR(uuid_root)) {
                ret = PTR_ERR(uuid_root);
                btrfs_abort_transaction(trans, ret);
                btrfs_end_transaction(trans);
                return ret;
        }

        fs_info->uuid_root = uuid_root;

        ret = btrfs_commit_transaction(trans);
        if (ret)
                return ret;

        down(&fs_info->uuid_tree_rescan_sem);
        task = kthread_run(btrfs_uuid_scan_kthread, fs_info, "btrfs-uuid");
        if (IS_ERR(task)) {
                /* fs_info->update_uuid_tree_gen remains 0 in all error case */
                btrfs_warn(fs_info, "failed to start uuid_scan task");
                up(&fs_info->uuid_tree_rescan_sem);
                return PTR_ERR(task);
        }

        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_fs_info *fs_info = device->fs_info;
        struct btrfs_root *root = fs_info->dev_root;
        struct btrfs_trans_handle *trans;
        struct btrfs_dev_extent *dev_extent = NULL;
        struct btrfs_path *path;
        u64 length;
        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 = fs_info->super_copy;
        u64 old_total = btrfs_super_total_bytes(super_copy);
        u64 old_size = btrfs_device_get_total_bytes(device);
        u64 diff;
        u64 start;

        new_size = round_down(new_size, fs_info->sectorsize);
        start = new_size;
        diff = round_down(old_size - new_size, fs_info->sectorsize);

        if (test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state))
                return -EINVAL;

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

        path->reada = READA_BACK;

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

        mutex_lock(&fs_info->chunk_mutex);

        btrfs_device_set_total_bytes(device, new_size);
        if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
                device->fs_devices->total_rw_bytes -= diff;
                atomic64_sub(diff, &fs_info->free_chunk_space);
        }

        /*
         * Once the device's size has been set to the new size, ensure all
         * in-memory chunks are synced to disk so that the loop below sees them
         * and relocates them accordingly.
         */
        if (contains_pending_extent(device, &start, diff)) {
                mutex_unlock(&fs_info->chunk_mutex);
                ret = btrfs_commit_transaction(trans);
                if (ret)
                        goto done;
        } else {
                mutex_unlock(&fs_info->chunk_mutex);
                btrfs_end_transaction(trans);
        }

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

        do {
                mutex_lock(&fs_info->delete_unused_bgs_mutex);
                ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
                if (ret < 0) {
                        mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                        goto done;
                }

                ret = btrfs_previous_item(root, path, 0, key.type);
                if (ret)
                        mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                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) {
                        mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                        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) {
                        mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                        btrfs_release_path(path);
                        break;
                }

                chunk_offset = btrfs_dev_extent_chunk_offset(l, dev_extent);
                btrfs_release_path(path);

                /*
                 * We may be relocating the only data chunk we have,
                 * which could potentially end up with losing data's
                 * raid profile, so lets allocate an empty one in
                 * advance.
                 */
                ret = btrfs_may_alloc_data_chunk(fs_info, chunk_offset);
                if (ret < 0) {
                        mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                        goto done;
                }

                ret = btrfs_relocate_chunk(fs_info, chunk_offset);
                mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                if (ret == -ENOSPC) {
                        failed++;
                } else if (ret) {
                        if (ret == -ETXTBSY) {
                                btrfs_warn(fs_info,
                   "could not shrink block group %llu due to active swapfile",
                                           chunk_offset);
                        }
                        goto done;
                }
        } while (key.offset-- > 0);

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

        mutex_lock(&fs_info->chunk_mutex);
        /* Clear all state bits beyond the shrunk device size */
        clear_extent_bits(&device->alloc_state, new_size, (u64)-1,
                          CHUNK_STATE_MASK);

        btrfs_device_set_disk_total_bytes(device, new_size);
        if (list_empty(&device->post_commit_list))
                list_add_tail(&device->post_commit_list,
                              &trans->transaction->dev_update_list);

        WARN_ON(diff > old_total);
        btrfs_set_super_total_bytes(super_copy,
                        round_down(old_total - diff, fs_info->sectorsize));
        mutex_unlock(&fs_info->chunk_mutex);

        /* Now btrfs_update_device() will change the on-disk size. */
        ret = btrfs_update_device(trans, device);
        if (ret < 0) {
                btrfs_abort_transaction(trans, ret);
                btrfs_end_transaction(trans);
        } else {
                ret = btrfs_commit_transaction(trans);
        }
done:
        btrfs_free_path(path);
        if (ret) {
                mutex_lock(&fs_info->chunk_mutex);
                btrfs_device_set_total_bytes(device, old_size);
                if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state))
                        device->fs_devices->total_rw_bytes += diff;
                atomic64_add(diff, &fs_info->free_chunk_space);
                mutex_unlock(&fs_info->chunk_mutex);
        }
        return ret;
}

static int btrfs_add_system_chunk(struct btrfs_fs_info *fs_info,
                           struct btrfs_key *key,
                           struct btrfs_chunk *chunk, int item_size)
{
        struct btrfs_super_block *super_copy = fs_info->super_copy;
        struct btrfs_disk_key disk_key;
        u32 array_size;
        u8 *ptr;

        mutex_lock(&fs_info->chunk_mutex);
        array_size = btrfs_super_sys_array_size(super_copy);
        if (array_size + item_size + sizeof(disk_key)
                        > BTRFS_SYSTEM_CHUNK_ARRAY_SIZE) {
                mutex_unlock(&fs_info->chunk_mutex);
                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);
        mutex_unlock(&fs_info->chunk_mutex);

        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 void check_raid56_incompat_flag(struct btrfs_fs_info *info, u64 type)
{
        if (!(type & BTRFS_BLOCK_GROUP_RAID56_MASK))
                return;

        btrfs_set_fs_incompat(info, RAID56);
}

static void check_raid1c34_incompat_flag(struct btrfs_fs_info *info, u64 type)
{
        if (!(type & (BTRFS_BLOCK_GROUP_RAID1C3 | BTRFS_BLOCK_GROUP_RAID1C4)))
                return;

        btrfs_set_fs_incompat(info, RAID1C34);
}

/*
 * Structure used internally for __btrfs_alloc_chunk() function.
 * Wraps needed parameters.
 */
struct alloc_chunk_ctl {
        u64 start;
        u64 type;
        /* Total number of stripes to allocate */
        int num_stripes;
        /* sub_stripes info for map */
        int sub_stripes;
        /* Stripes per device */
        int dev_stripes;
        /* Maximum number of devices to use */
        int devs_max;
        /* Minimum number of devices to use */
        int devs_min;
        /* ndevs has to be a multiple of this */
        int devs_increment;
        /* Number of copies */
        int ncopies;
        /* Number of stripes worth of bytes to store parity information */
        int nparity;
        u64 max_stripe_size;
        u64 max_chunk_size;
        u64 dev_extent_min;
        u64 stripe_size;
        u64 chunk_size;
        int ndevs;
};

static void init_alloc_chunk_ctl_policy_regular(
                                struct btrfs_fs_devices *fs_devices,
                                struct alloc_chunk_ctl *ctl)
{
        u64 type = ctl->type;

        if (type & BTRFS_BLOCK_GROUP_DATA) {
                ctl->max_stripe_size = SZ_1G;
                ctl->max_chunk_size = BTRFS_MAX_DATA_CHUNK_SIZE;
        } else if (type & BTRFS_BLOCK_GROUP_METADATA) {
                /* For larger filesystems, use larger metadata chunks */
                if (fs_devices->total_rw_bytes > 50ULL * SZ_1G)
                        ctl->max_stripe_size = SZ_1G;
                else
                        ctl->max_stripe_size = SZ_256M;
                ctl->max_chunk_size = ctl->max_stripe_size;
        } else if (type & BTRFS_BLOCK_GROUP_SYSTEM) {
                ctl->max_stripe_size = SZ_32M;
                ctl->max_chunk_size = 2 * ctl->max_stripe_size;
                ctl->devs_max = min_t(int, ctl->devs_max,
                                      BTRFS_MAX_DEVS_SYS_CHUNK);
        } else {
                BUG();
        }

        /* We don't want a chunk larger than 10% of writable space */
        ctl->max_chunk_size = min(div_factor(fs_devices->total_rw_bytes, 1),
                                  ctl->max_chunk_size);
        ctl->dev_extent_min = BTRFS_STRIPE_LEN * ctl->dev_stripes;
}

static void init_alloc_chunk_ctl(struct btrfs_fs_devices *fs_devices,
                                 struct alloc_chunk_ctl *ctl)
{
        int index = btrfs_bg_flags_to_raid_index(ctl->type);

        ctl->sub_stripes = btrfs_raid_array[index].sub_stripes;
        ctl->dev_stripes = btrfs_raid_array[index].dev_stripes;
        ctl->devs_max = btrfs_raid_array[index].devs_max;
        if (!ctl->devs_max)
                ctl->devs_max = BTRFS_MAX_DEVS(fs_devices->fs_info);
        ctl->devs_min = btrfs_raid_array[index].devs_min;
        ctl->devs_increment = btrfs_raid_array[index].devs_increment;
        ctl->ncopies = btrfs_raid_array[index].ncopies;
        ctl->nparity = btrfs_raid_array[index].nparity;
        ctl->ndevs = 0;

        switch (fs_devices->chunk_alloc_policy) {
        case BTRFS_CHUNK_ALLOC_REGULAR:
                init_alloc_chunk_ctl_policy_regular(fs_devices, ctl);
                break;
        default:
                BUG();
        }
}

static int gather_device_info(struct btrfs_fs_devices *fs_devices,
                              struct alloc_chunk_ctl *ctl,
                              struct btrfs_device_info *devices_info)
{
        struct btrfs_fs_info *info = fs_devices->fs_info;
        struct btrfs_device *device;
        u64 total_avail;
        u64 dev_extent_want = ctl->max_stripe_size * ctl->dev_stripes;
        int ret;
        int ndevs = 0;
        u64 max_avail;
        u64 dev_offset;

        /*
         * in the first pass through the devices list, we gather information
         * about the available holes on each device.
         */
        list_for_each_entry(device, &fs_devices->alloc_list, dev_alloc_list) {
                if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
                        WARN(1, KERN_ERR
                               "BTRFS: read-only device in alloc_list\n");
                        continue;
                }

                if (!test_bit(BTRFS_DEV_STATE_IN_FS_METADATA,
                                        &device->dev_state) ||
                    test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state))
                        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 < ctl->dev_extent_min)
                        continue;

                ret = find_free_dev_extent(device, dev_extent_want, &dev_offset,
                                           &max_avail);
                if (ret && ret != -ENOSPC)
                        return ret;

                if (ret == 0)
                        max_avail = dev_extent_want;

                if (max_avail < ctl->dev_extent_min) {
                        if (btrfs_test_opt(info, ENOSPC_DEBUG))
                                btrfs_debug(info,
                        "%s: devid %llu has no free space, have=%llu want=%llu",
                                            __func__, device->devid, max_avail,
                                            ctl->dev_extent_min);
                        continue;
                }

                if (ndevs == fs_devices->rw_devices) {
                        WARN(1, "%s: found more than %llu devices\n",
                             __func__, fs_devices->rw_devices);
                        break;
                }
                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;
        }
        ctl->ndevs = ndevs;

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

        return 0;
}

static int decide_stripe_size_regular(struct alloc_chunk_ctl *ctl,
                                      struct btrfs_device_info *devices_info)
{
        /* Number of stripes that count for block group size */
        int data_stripes;

        /*
         * 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.
         *
         * The DUP profile stores more than one stripe per device, the
         * max_avail is the total size so we have to adjust.
         */
        ctl->stripe_size = div_u64(devices_info[ctl->ndevs - 1].max_avail,
                                   ctl->dev_stripes);
        ctl->num_stripes = ctl->ndevs * ctl->dev_stripes;

        /* This will have to be fixed for RAID1 and RAID10 over more drives */
        data_stripes = (ctl->num_stripes - ctl->nparity) / ctl->ncopies;

        /*
         * Use the number of data stripes to figure out how big this chunk is
         * really going to be in terms of logical address space, and compare
         * that answer with the max chunk size. If it's higher, we try to
         * reduce stripe_size.
         */
        if (ctl->stripe_size * data_stripes > ctl->max_chunk_size) {
                /*
                 * Reduce stripe_size, round it up to a 16MB boundary again and
                 * then use it, unless it ends up being even bigger than the
                 * previous value we had already.
                 */
                ctl->stripe_size = min(round_up(div_u64(ctl->max_chunk_size,
                                                        data_stripes), SZ_16M),
                                       ctl->stripe_size);
        }

        /* Align to BTRFS_STRIPE_LEN */
        ctl->stripe_size = round_down(ctl->stripe_size, BTRFS_STRIPE_LEN);
        ctl->chunk_size = ctl->stripe_size * data_stripes;

        return 0;
}

static int decide_stripe_size(struct btrfs_fs_devices *fs_devices,
                              struct alloc_chunk_ctl *ctl,
                              struct btrfs_device_info *devices_info)
{
        struct btrfs_fs_info *info = fs_devices->fs_info;

        /*
         * Round down to number of usable stripes, devs_increment can be any
         * number so we can't use round_down() that requires power of 2, while
         * rounddown is safe.
         */
        ctl->ndevs = rounddown(ctl->ndevs, ctl->devs_increment);

        if (ctl->ndevs < ctl->devs_min) {
                if (btrfs_test_opt(info, ENOSPC_DEBUG)) {
                        btrfs_debug(info,
        "%s: not enough devices with free space: have=%d minimum required=%d",
                                    __func__, ctl->ndevs, ctl->devs_min);
                }
                return -ENOSPC;
        }

        ctl->ndevs = min(ctl->ndevs, ctl->devs_max);

        switch (fs_devices->chunk_alloc_policy) {
        case BTRFS_CHUNK_ALLOC_REGULAR:
                return decide_stripe_size_regular(ctl, devices_info);
        default:
                BUG();
        }
}

static int create_chunk(struct btrfs_trans_handle *trans,
                        struct alloc_chunk_ctl *ctl,
                        struct btrfs_device_info *devices_info)
{
        struct btrfs_fs_info *info = trans->fs_info;
        struct map_lookup *map = NULL;
        struct extent_map_tree *em_tree;
        struct extent_map *em;
        u64 start = ctl->start;
        u64 type = ctl->type;
        int ret;
        int i;
        int j;

        map = kmalloc(map_lookup_size(ctl->num_stripes), GFP_NOFS);
        if (!map)
                return -ENOMEM;
        map->num_stripes = ctl->num_stripes;

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

        trace_btrfs_chunk_alloc(info, map, start, ctl->chunk_size);

        em = alloc_extent_map();
        if (!em) {
                kfree(map);
                return -ENOMEM;
        }
        set_bit(EXTENT_FLAG_FS_MAPPING, &em->flags);
        em->map_lookup = map;
        em->start = start;
        em->len = ctl->chunk_size;
        em->block_start = 0;
        em->block_len = em->len;
        em->orig_block_len = ctl->stripe_size;

        em_tree = &info->mapping_tree;
        write_lock(&em_tree->lock);
        ret = add_extent_mapping(em_tree, em, 0);
        if (ret) {
                write_unlock(&em_tree->lock);
                free_extent_map(em);
                return ret;
        }
        write_unlock(&em_tree->lock);

        ret = btrfs_make_block_group(trans, 0, type, start, ctl->chunk_size);
        if (ret)
                goto error_del_extent;

        for (i = 0; i < map->num_stripes; i++) {
                struct btrfs_device *dev = map->stripes[i].dev;

                btrfs_device_set_bytes_used(dev,
                                            dev->bytes_used + ctl->stripe_size);
                if (list_empty(&dev->post_commit_list))
                        list_add_tail(&dev->post_commit_list,
                                      &trans->transaction->dev_update_list);
        }

        atomic64_sub(ctl->stripe_size * map->num_stripes,
                     &info->free_chunk_space);

        free_extent_map(em);
        check_raid56_incompat_flag(info, type);
        check_raid1c34_incompat_flag(info, type);

        return 0;

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

        /* One for our allocation */
        free_extent_map(em);
        /* One for the tree reference */
        free_extent_map(em);

        return ret;
}

int btrfs_alloc_chunk(struct btrfs_trans_handle *trans, u64 type)
{
        struct btrfs_fs_info *info = trans->fs_info;
        struct btrfs_fs_devices *fs_devices = info->fs_devices;
        struct btrfs_device_info *devices_info = NULL;
        struct alloc_chunk_ctl ctl;
        int ret;

        lockdep_assert_held(&info->chunk_mutex);

        if (!alloc_profile_is_valid(type, 0)) {
                ASSERT(0);
                return -EINVAL;
        }

        if (list_empty(&fs_devices->alloc_list)) {
                if (btrfs_test_opt(info, ENOSPC_DEBUG))
                        btrfs_debug(info, "%s: no writable device", __func__);
                return -ENOSPC;
        }

        if (!(type & BTRFS_BLOCK_GROUP_TYPE_MASK)) {
                btrfs_err(info, "invalid chunk type 0x%llx requested", type);
                ASSERT(0);
                return -EINVAL;
        }

        ctl.start = find_next_chunk(info);
        ctl.type = type;
        init_alloc_chunk_ctl(fs_devices, &ctl);

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

        ret = gather_device_info(fs_devices, &ctl, devices_info);
        if (ret < 0)
                goto out;

        ret = decide_stripe_size(fs_devices, &ctl, devices_info);
        if (ret < 0)
                goto out;

        ret = create_chunk(trans, &ctl, devices_info);

out:
        kfree(devices_info);
        return ret;
}

/*
 * Chunk allocation falls into two parts. The first part does work
 * that makes the new allocated chunk usable, but does not do any operation
 * that modifies the chunk tree. The second part does the work that
 * requires modifying the chunk tree. This division is important for the
 * bootstrap process of adding storage to a seed btrfs.
 */
int btrfs_finish_chunk_alloc(struct btrfs_trans_handle *trans,
                             u64 chunk_offset, u64 chunk_size)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_root *extent_root = fs_info->extent_root;
        struct btrfs_root *chunk_root = fs_info->chunk_root;
        struct btrfs_key key;
        struct btrfs_device *device;
        struct btrfs_chunk *chunk;
        struct btrfs_stripe *stripe;
        struct extent_map *em;
        struct map_lookup *map;
        size_t item_size;
        u64 dev_offset;
        u64 stripe_size;
        int i = 0;
        int ret = 0;

        em = btrfs_get_chunk_map(fs_info, chunk_offset, chunk_size);
        if (IS_ERR(em))
                return PTR_ERR(em);

        map = em->map_lookup;
        item_size = btrfs_chunk_item_size(map->num_stripes);
        stripe_size = em->orig_block_len;

        chunk = kzalloc(item_size, GFP_NOFS);
        if (!chunk) {
                ret = -ENOMEM;
                goto out;
        }

        /*
         * Take the device list mutex to prevent races with the final phase of
         * a device replace operation that replaces the device object associated
         * with the map's stripes, because the device object's id can change
         * at any time during that final phase of the device replace operation
         * (dev-replace.c:btrfs_dev_replace_finishing()).
         */
        mutex_lock(&fs_info->fs_devices->device_list_mutex);
        for (i = 0; i < map->num_stripes; i++) {
                device = map->stripes[i].dev;
                dev_offset = map->stripes[i].physical;

                ret = btrfs_update_device(trans, device);
                if (ret)
                        break;
                ret = btrfs_alloc_dev_extent(trans, device, chunk_offset,
                                             dev_offset, stripe_size);
                if (ret)
                        break;
        }
        if (ret) {
                mutex_unlock(&fs_info->fs_devices->device_list_mutex);
                goto out;
        }

        stripe = &chunk->stripe;
        for (i = 0; i < map->num_stripes; i++) {
                device = map->stripes[i].dev;
                dev_offset = map->stripes[i].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++;
        }
        mutex_unlock(&fs_info->fs_devices->device_list_mutex);

        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, fs_info->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(fs_info, &key, chunk, item_size);
        }

out:
        kfree(chunk);
        free_extent_map(em);
        return ret;
}

static noinline int init_first_rw_device(struct btrfs_trans_handle *trans)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        u64 alloc_profile;
        int ret;

        alloc_profile = btrfs_metadata_alloc_profile(fs_info);
        ret = btrfs_alloc_chunk(trans, alloc_profile);
        if (ret)
                return ret;

        alloc_profile = btrfs_system_alloc_profile(fs_info);
        ret = btrfs_alloc_chunk(trans, alloc_profile);
        return ret;
}

static inline int btrfs_chunk_max_errors(struct map_lookup *map)
{
        const int index = btrfs_bg_flags_to_raid_index(map->type);

        return btrfs_raid_array[index].tolerated_failures;
}

int btrfs_chunk_readonly(struct btrfs_fs_info *fs_info, u64 chunk_offset)
{
        struct extent_map *em;
        struct map_lookup *map;
        int readonly = 0;
        int miss_ndevs = 0;
        int i;

        em = btrfs_get_chunk_map(fs_info, chunk_offset, 1);
        if (IS_ERR(em))
                return 1;

        map = em->map_lookup;
        for (i = 0; i < map->num_stripes; i++) {
                if (test_bit(BTRFS_DEV_STATE_MISSING,
                                        &map->stripes[i].dev->dev_state)) {
                        miss_ndevs++;
                        continue;
                }
                if (!test_bit(BTRFS_DEV_STATE_WRITEABLE,
                                        &map->stripes[i].dev->dev_state)) {
                        readonly = 1;
                        goto end;
                }
        }

        /*
         * If the number of missing devices is larger than max errors,
         * we can not write the data into that chunk successfully, so
         * set it readonly.
         */
        if (miss_ndevs > btrfs_chunk_max_errors(map))
                readonly = 1;
end:
        free_extent_map(em);
        return readonly;
}

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

        while (1) {
                write_lock(&tree->lock);
                em = lookup_extent_mapping(tree, 0, (u64)-1);
                if (em)
                        remove_extent_mapping(tree, em);
                write_unlock(&tree->lock);
                if (!em)
                        break;
                /* once for us */
                free_extent_map(em);
                /* once for the tree */
                free_extent_map(em);
        }
}

int btrfs_num_copies(struct btrfs_fs_info *fs_info, u64 logical, u64 len)
{
        struct extent_map *em;
        struct map_lookup *map;
        int ret;

        em = btrfs_get_chunk_map(fs_info, logical, len);
        if (IS_ERR(em))
                /*
                 * We could return errors for these cases, but that could get
                 * ugly and we'd probably do the same thing which is just not do
                 * anything else and exit, so return 1 so the callers don't try
                 * to use other copies.
                 */
                return 1;

        map = em->map_lookup;
        if (map->type & (BTRFS_BLOCK_GROUP_DUP | BTRFS_BLOCK_GROUP_RAID1_MASK))
                ret = map->num_stripes;
        else if (map->type & BTRFS_BLOCK_GROUP_RAID10)
                ret = map->sub_stripes;
        else if (map->type & BTRFS_BLOCK_GROUP_RAID5)
                ret = 2;
        else if (map->type & BTRFS_BLOCK_GROUP_RAID6)
                /*
                 * There could be two corrupted data stripes, we need
                 * to loop retry in order to rebuild the correct data.
                 *
                 * Fail a stripe at a time on every retry except the
                 * stripe under reconstruction.
                 */
                ret = map->num_stripes;
        else
                ret = 1;
        free_extent_map(em);

        down_read(&fs_info->dev_replace.rwsem);
        if (btrfs_dev_replace_is_ongoing(&fs_info->dev_replace) &&
            fs_info->dev_replace.tgtdev)
                ret++;
        up_read(&fs_info->dev_replace.rwsem);

        return ret;
}

unsigned long btrfs_full_stripe_len(struct btrfs_fs_info *fs_info,
                                    u64 logical)
{
        struct extent_map *em;
        struct map_lookup *map;
        unsigned long len = fs_info->sectorsize;

        em = btrfs_get_chunk_map(fs_info, logical, len);

        if (!WARN_ON(IS_ERR(em))) {
                map = em->map_lookup;
                if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK)
                        len = map->stripe_len * nr_data_stripes(map);
                free_extent_map(em);
        }
        return len;
}

int btrfs_is_parity_mirror(struct btrfs_fs_info *fs_info, u64 logical, u64 len)
{
        struct extent_map *em;
        struct map_lookup *map;
        int ret = 0;

        em = btrfs_get_chunk_map(fs_info, logical, len);

        if(!WARN_ON(IS_ERR(em))) {
                map = em->map_lookup;
                if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK)
                        ret = 1;
                free_extent_map(em);
        }
        return ret;
}

static int find_live_mirror(struct btrfs_fs_info *fs_info,
                            struct map_lookup *map, int first,
                            int dev_replace_is_ongoing)
{
        int i;
        int num_stripes;
        int preferred_mirror;
        int tolerance;
        struct btrfs_device *srcdev;

        ASSERT((map->type &
                 (BTRFS_BLOCK_GROUP_RAID1_MASK | BTRFS_BLOCK_GROUP_RAID10)));

        if (map->type & BTRFS_BLOCK_GROUP_RAID10)
                num_stripes = map->sub_stripes;
        else
                num_stripes = map->num_stripes;

        preferred_mirror = first + current->pid % num_stripes;

        if (dev_replace_is_ongoing &&
            fs_info->dev_replace.cont_reading_from_srcdev_mode ==
             BTRFS_DEV_REPLACE_ITEM_CONT_READING_FROM_SRCDEV_MODE_AVOID)
                srcdev = fs_info->dev_replace.srcdev;
        else
                srcdev = NULL;

        /*
         * try to avoid the drive that is the source drive for a
         * dev-replace procedure, only choose it if no other non-missing
         * mirror is available
         */
        for (tolerance = 0; tolerance < 2; tolerance++) {
                if (map->stripes[preferred_mirror].dev->bdev &&
                    (tolerance || map->stripes[preferred_mirror].dev != srcdev))
                        return preferred_mirror;
                for (i = first; i < first + num_stripes; i++) {
                        if (map->stripes[i].dev->bdev &&
                            (tolerance || map->stripes[i].dev != srcdev))
                                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 preferred_mirror;
}

/* Bubble-sort the stripe set to put the parity/syndrome stripes last */
static void sort_parity_stripes(struct btrfs_bio *bbio, int num_stripes)
{
        int i;
        int again = 1;

        while (again) {
                again = 0;
                for (i = 0; i < num_stripes - 1; i++) {
                        /* Swap if parity is on a smaller index */
                        if (bbio->raid_map[i] > bbio->raid_map[i + 1]) {
                                swap(bbio->stripes[i], bbio->stripes[i + 1]);
                                swap(bbio->raid_map[i], bbio->raid_map[i + 1]);
                                again = 1;
                        }
                }
        }
}

static struct btrfs_bio *alloc_btrfs_bio(int total_stripes, int real_stripes)
{
        struct btrfs_bio *bbio = kzalloc(
                 /* the size of the btrfs_bio */
                sizeof(struct btrfs_bio) +
                /* plus the variable array for the stripes */
                sizeof(struct btrfs_bio_stripe) * (total_stripes) +
                /* plus the variable array for the tgt dev */
                sizeof(int) * (real_stripes) +
                /*
                 * plus the raid_map, which includes both the tgt dev
                 * and the stripes
                 */
                sizeof(u64) * (total_stripes),
                GFP_NOFS|__GFP_NOFAIL);

        atomic_set(&bbio->error, 0);
        refcount_set(&bbio->refs, 1);

        bbio->tgtdev_map = (int *)(bbio->stripes + total_stripes);
        bbio->raid_map = (u64 *)(bbio->tgtdev_map + real_stripes);

        return bbio;
}

void btrfs_get_bbio(struct btrfs_bio *bbio)
{
        WARN_ON(!refcount_read(&bbio->refs));
        refcount_inc(&bbio->refs);
}

void btrfs_put_bbio(struct btrfs_bio *bbio)
{
        if (!bbio)
                return;
        if (refcount_dec_and_test(&bbio->refs))
                kfree(bbio);
}

/* can REQ_OP_DISCARD be sent with other REQ like REQ_OP_WRITE? */
/*
 * Please note that, discard won't be sent to target device of device
 * replace.
 */
static int __btrfs_map_block_for_discard(struct btrfs_fs_info *fs_info,
                                         u64 logical, u64 *length_ret,
                                         struct btrfs_bio **bbio_ret)
{
        struct extent_map *em;
        struct map_lookup *map;
        struct btrfs_bio *bbio;
        u64 length = *length_ret;
        u64 offset;
        u64 stripe_nr;
        u64 stripe_nr_end;
        u64 stripe_end_offset;
        u64 stripe_cnt;
        u64 stripe_len;
        u64 stripe_offset;
        u64 num_stripes;
        u32 stripe_index;
        u32 factor = 0;
        u32 sub_stripes = 0;
        u64 stripes_per_dev = 0;
        u32 remaining_stripes = 0;
        u32 last_stripe = 0;
        int ret = 0;
        int i;

        /* discard always return a bbio */
        ASSERT(bbio_ret);

        em = btrfs_get_chunk_map(fs_info, logical, length);
        if (IS_ERR(em))
                return PTR_ERR(em);

        map = em->map_lookup;
        /* we don't discard raid56 yet */
        if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
                ret = -EOPNOTSUPP;
                goto out;
        }

        offset = logical - em->start;
        length = min_t(u64, em->start + em->len - logical, length);
        *length_ret = length;

        stripe_len = map->stripe_len;
        /*
         * stripe_nr counts the total number of stripes we have to stride
         * to get to this block
         */
        stripe_nr = div64_u64(offset, stripe_len);

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

        stripe_nr_end = round_up(offset + length, map->stripe_len);
        stripe_nr_end = div64_u64(stripe_nr_end, map->stripe_len);
        stripe_cnt = stripe_nr_end - stripe_nr;
        stripe_end_offset = stripe_nr_end * map->stripe_len -
                            (offset + length);
        /*
         * after this, 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
         */
        num_stripes = 1;
        stripe_index = 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;
                num_stripes = min_t(u64, map->num_stripes,
                                    sub_stripes * stripe_cnt);
                stripe_nr = div_u64_rem(stripe_nr, factor, &stripe_index);
                stripe_index *= sub_stripes;
                stripes_per_dev = div_u64_rem(stripe_cnt, factor,
                                              &remaining_stripes);
                div_u64_rem(stripe_nr_end - 1, factor, &last_stripe);
                last_stripe *= sub_stripes;
        } else if (map->type & (BTRFS_BLOCK_GROUP_RAID1_MASK |
                                BTRFS_BLOCK_GROUP_DUP)) {
                num_stripes = map->num_stripes;
        } else {
                stripe_nr = div_u64_rem(stripe_nr, map->num_stripes,
                                        &stripe_index);
        }

        bbio = alloc_btrfs_bio(num_stripes, 0);
        if (!bbio) {
                ret = -ENOMEM;
                goto out;
        }

        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) {
                        stripe_index = 0;
                        stripe_nr++;
                }
        }

        *bbio_ret = bbio;
        bbio->map_type = map->type;
        bbio->num_stripes = num_stripes;
out:
        free_extent_map(em);
        return ret;
}

/*
 * In dev-replace case, for repair case (that's the only case where the mirror
 * is selected explicitly when calling btrfs_map_block), blocks left of the
 * left cursor can also be read from the target drive.
 *
 * For REQ_GET_READ_MIRRORS, the target drive is added as the last one to the
 * array of stripes.
 * For READ, it also needs to be supported using the same mirror number.
 *
 * If the requested block is not left of the left cursor, EIO is returned. This
 * can happen because btrfs_num_copies() returns one more in the dev-replace
 * case.
 */
static int get_extra_mirror_from_replace(struct btrfs_fs_info *fs_info,
                                         u64 logical, u64 length,
                                         u64 srcdev_devid, int *mirror_num,
                                         u64 *physical)
{
        struct btrfs_bio *bbio = NULL;
        int num_stripes;
        int index_srcdev = 0;
        int found = 0;
        u64 physical_of_found = 0;
        int i;
        int ret = 0;

        ret = __btrfs_map_block(fs_info, BTRFS_MAP_GET_READ_MIRRORS,
                                logical, &length, &bbio, 0, 0);
        if (ret) {
                ASSERT(bbio == NULL);
                return ret;
        }

        num_stripes = bbio->num_stripes;
        if (*mirror_num > num_stripes) {
                /*
                 * BTRFS_MAP_GET_READ_MIRRORS does not contain this mirror,
                 * that means that the requested area is not left of the left
                 * cursor
                 */
                btrfs_put_bbio(bbio);
                return -EIO;
        }

        /*
         * process the rest of the function using the mirror_num of the source
         * drive. Therefore look it up first.  At the end, patch the device
         * pointer to the one of the target drive.
         */
        for (i = 0; i < num_stripes; i++) {
                if (bbio->stripes[i].dev->devid != srcdev_devid)
                        continue;

                /*
                 * In case of DUP, in order to keep it simple, only add the
                 * mirror with the lowest physical address
                 */
                if (found &&
                    physical_of_found <= bbio->stripes[i].physical)
                        continue;

                index_srcdev = i;
                found = 1;
                physical_of_found = bbio->stripes[i].physical;
        }

        btrfs_put_bbio(bbio);

        ASSERT(found);
        if (!found)
                return -EIO;

        *mirror_num = index_srcdev + 1;
        *physical = physical_of_found;
        return ret;
}

static void handle_ops_on_dev_replace(enum btrfs_map_op op,
                                      struct btrfs_bio **bbio_ret,
                                      struct btrfs_dev_replace *dev_replace,
                                      int *num_stripes_ret, int *max_errors_ret)
{
        struct btrfs_bio *bbio = *bbio_ret;
        u64 srcdev_devid = dev_replace->srcdev->devid;
        int tgtdev_indexes = 0;
        int num_stripes = *num_stripes_ret;
        int max_errors = *max_errors_ret;
        int i;

        if (op == BTRFS_MAP_WRITE) {
                int index_where_to_add;

                /*
                 * duplicate the write operations while the dev replace
                 * procedure is running. Since the copying of the old disk to
                 * the new disk takes place at run time while the filesystem is
                 * mounted writable, the regular write operations to the old
                 * disk have to be duplicated to go to the new disk as well.
                 *
                 * Note that device->missing is handled by the caller, and that
                 * the write to the old disk is already set up in the stripes
                 * array.
                 */
                index_where_to_add = num_stripes;
                for (i = 0; i < num_stripes; i++) {
                        if (bbio->stripes[i].dev->devid == srcdev_devid) {
                                /* write to new disk, too */
                                struct btrfs_bio_stripe *new =
                                        bbio->stripes + index_where_to_add;
                                struct btrfs_bio_stripe *old =
                                        bbio->stripes + i;

                                new->physical = old->physical;
                                new->length = old->length;
                                new->dev = dev_replace->tgtdev;
                                bbio->tgtdev_map[i] = index_where_to_add;
                                index_where_to_add++;
                                max_errors++;
                                tgtdev_indexes++;
                        }
                }
                num_stripes = index_where_to_add;
        } else if (op == BTRFS_MAP_GET_READ_MIRRORS) {
                int index_srcdev = 0;
                int found = 0;
                u64 physical_of_found = 0;

                /*
                 * During the dev-replace procedure, the target drive can also
                 * be used to read data in case it is needed to repair a corrupt
                 * block elsewhere. This is possible if the requested area is
                 * left of the left cursor. In this area, the target drive is a
                 * full copy of the source drive.
                 */
                for (i = 0; i < num_stripes; i++) {
                        if (bbio->stripes[i].dev->devid == srcdev_devid) {
                                /*
                                 * In case of DUP, in order to keep it simple,
                                 * only add the mirror with the lowest physical
                                 * address
                                 */
                                if (found &&
                                    physical_of_found <=
                                     bbio->stripes[i].physical)
                                        continue;
                                index_srcdev = i;
                                found = 1;
                                physical_of_found = bbio->stripes[i].physical;
                        }
                }
                if (found) {
                        struct btrfs_bio_stripe *tgtdev_stripe =
                                bbio->stripes + num_stripes;

                        tgtdev_stripe->physical = physical_of_found;
                        tgtdev_stripe->length =
                                bbio->stripes[index_srcdev].length;
                        tgtdev_stripe->dev = dev_replace->tgtdev;
                        bbio->tgtdev_map[index_srcdev] = num_stripes;

                        tgtdev_indexes++;
                        num_stripes++;
                }
        }

        *num_stripes_ret = num_stripes;
        *max_errors_ret = max_errors;
        bbio->num_tgtdevs = tgtdev_indexes;
        *bbio_ret = bbio;
}

static bool need_full_stripe(enum btrfs_map_op op)
{
        return (op == BTRFS_MAP_WRITE || op == BTRFS_MAP_GET_READ_MIRRORS);
}

/*
 * btrfs_get_io_geometry - calculates the geomery of a particular (address, len)
 *                     tuple. This information is used to calculate how big a
 *                     particular bio can get before it straddles a stripe.
 *
 * @fs_info - the filesystem
 * @logical - address that we want to figure out the geometry of
 * @len     - the length of IO we are going to perform, starting at @logical
 * @op      - type of operation - write or read
 * @io_geom - pointer used to return values
 *
 * Returns < 0 in case a chunk for the given logical address cannot be found,
 * usually shouldn't happen unless @logical is corrupted, 0 otherwise.
 */
int btrfs_get_io_geometry(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
                        u64 logical, u64 len, struct btrfs_io_geometry *io_geom)
{
        struct extent_map *em;
        struct map_lookup *map;
        u64 offset;
        u64 stripe_offset;
        u64 stripe_nr;
        u64 stripe_len;
        u64 raid56_full_stripe_start = (u64)-1;
        int data_stripes;
        int ret = 0;

        ASSERT(op != BTRFS_MAP_DISCARD);

        em = btrfs_get_chunk_map(fs_info, logical, len);
        if (IS_ERR(em))
                return PTR_ERR(em);

        map = em->map_lookup;
        /* Offset of this logical address in the chunk */
        offset = logical - em->start;
        /* Len of a stripe in a chunk */
        stripe_len = map->stripe_len;
        /* Stripe wher this block falls in */
        stripe_nr = div64_u64(offset, stripe_len);
        /* Offset of stripe in the chunk */
        stripe_offset = stripe_nr * stripe_len;
        if (offset < stripe_offset) {
                btrfs_crit(fs_info,
"stripe math has gone wrong, stripe_offset=%llu offset=%llu start=%llu logical=%llu stripe_len=%llu",
                        stripe_offset, offset, em->start, logical, stripe_len);
                ret = -EINVAL;
                goto out;
        }

        /* stripe_offset is the offset of this block in its stripe */
        stripe_offset = offset - stripe_offset;
        data_stripes = nr_data_stripes(map);

        if (map->type & BTRFS_BLOCK_GROUP_PROFILE_MASK) {
                u64 max_len = stripe_len - stripe_offset;

                /*
                 * In case of raid56, we need to know the stripe aligned start
                 */
                if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
                        unsigned long full_stripe_len = stripe_len * data_stripes;
                        raid56_full_stripe_start = offset;

                        /*
                         * Allow a write of a full stripe, but make sure we
                         * don't allow straddling of stripes
                         */
                        raid56_full_stripe_start = div64_u64(raid56_full_stripe_start,
                                        full_stripe_len);
                        raid56_full_stripe_start *= full_stripe_len;

                        /*
                         * For writes to RAID[56], allow a full stripeset across
                         * all disks. For other RAID types and for RAID[56]
                         * reads, just allow a single stripe (on a single disk).
                         */
                        if (op == BTRFS_MAP_WRITE) {
                                max_len = stripe_len * data_stripes -
                                          (offset - raid56_full_stripe_start);
                        }
                }
                len = min_t(u64, em->len - offset, max_len);
        } else {
                len = em->len - offset;
        }

        io_geom->len = len;
        io_geom->offset = offset;
        io_geom->stripe_len = stripe_len;
        io_geom->stripe_nr = stripe_nr;
        io_geom->stripe_offset = stripe_offset;
        io_geom->raid56_stripe_offset = raid56_full_stripe_start;

out:
        /* once for us */
        free_extent_map(em);
        return ret;
}

static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
                             enum btrfs_map_op op,
                             u64 logical, u64 *length,
                             struct btrfs_bio **bbio_ret,
                             int mirror_num, int need_raid_map)
{
        struct extent_map *em;
        struct map_lookup *map;
        u64 stripe_offset;
        u64 stripe_nr;
        u64 stripe_len;
        u32 stripe_index;
        int data_stripes;
        int i;
        int ret = 0;
        int num_stripes;
        int max_errors = 0;
        int tgtdev_indexes = 0;
        struct btrfs_bio *bbio = NULL;
        struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
        int dev_replace_is_ongoing = 0;
        int num_alloc_stripes;
        int patch_the_first_stripe_for_dev_replace = 0;
        u64 physical_to_patch_in_first_stripe = 0;
        u64 raid56_full_stripe_start = (u64)-1;
        struct btrfs_io_geometry geom;

        ASSERT(bbio_ret);
        ASSERT(op != BTRFS_MAP_DISCARD);

        ret = btrfs_get_io_geometry(fs_info, op, logical, *length, &geom);
        if (ret < 0)
                return ret;

        em = btrfs_get_chunk_map(fs_info, logical, *length);
        ASSERT(!IS_ERR(em));
        map = em->map_lookup;

        *length = geom.len;
        stripe_len = geom.stripe_len;
        stripe_nr = geom.stripe_nr;
        stripe_offset = geom.stripe_offset;
        raid56_full_stripe_start = geom.raid56_stripe_offset;
        data_stripes = nr_data_stripes(map);

        down_read(&dev_replace->rwsem);
        dev_replace_is_ongoing = btrfs_dev_replace_is_ongoing(dev_replace);
        /*
         * Hold the semaphore for read during the whole operation, write is
         * requested at commit time but must wait.
         */
        if (!dev_replace_is_ongoing)
                up_read(&dev_replace->rwsem);

        if (dev_replace_is_ongoing && mirror_num == map->num_stripes + 1 &&
            !need_full_stripe(op) && dev_replace->tgtdev != NULL) {
                ret = get_extra_mirror_from_replace(fs_info, logical, *length,
                                                    dev_replace->srcdev->devid,
                                                    &mirror_num,
                                            &physical_to_patch_in_first_stripe);
                if (ret)
                        goto out;
                else
                        patch_the_first_stripe_for_dev_replace = 1;
        } else if (mirror_num > map->num_stripes) {
                mirror_num = 0;
        }

        num_stripes = 1;
        stripe_index = 0;
        if (map->type & BTRFS_BLOCK_GROUP_RAID0) {
                stripe_nr = div_u64_rem(stripe_nr, map->num_stripes,
                                &stripe_index);
                if (!need_full_stripe(op))
                        mirror_num = 1;
        } else if (map->type & BTRFS_BLOCK_GROUP_RAID1_MASK) {
                if (need_full_stripe(op))
                        num_stripes = map->num_stripes;
                else if (mirror_num)
                        stripe_index = mirror_num - 1;
                else {
                        stripe_index = find_live_mirror(fs_info, map, 0,
                                            dev_replace_is_ongoing);
                        mirror_num = stripe_index + 1;
                }

        } else if (map->type & BTRFS_BLOCK_GROUP_DUP) {
                if (need_full_stripe(op)) {
                        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) {
                u32 factor = map->num_stripes / map->sub_stripes;

                stripe_nr = div_u64_rem(stripe_nr, factor, &stripe_index);
                stripe_index *= map->sub_stripes;

                if (need_full_stripe(op))
                        num_stripes = map->sub_stripes;
                else if (mirror_num)
                        stripe_index += mirror_num - 1;
                else {
                        int old_stripe_index = stripe_index;
                        stripe_index = find_live_mirror(fs_info, map,
                                              stripe_index,
                                              dev_replace_is_ongoing);
                        mirror_num = stripe_index - old_stripe_index + 1;
                }

        } else if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
                if (need_raid_map && (need_full_stripe(op) || mirror_num > 1)) {
                        /* push stripe_nr back to the start of the full stripe */
                        stripe_nr = div64_u64(raid56_full_stripe_start,
                                        stripe_len * data_stripes);

                        /* RAID[56] write or recovery. Return all stripes */
                        num_stripes = map->num_stripes;
                        max_errors = nr_parity_stripes(map);

                        *length = map->stripe_len;
                        stripe_index = 0;
                        stripe_offset = 0;
                } else {
                        /*
                         * Mirror #0 or #1 means the original data block.
                         * Mirror #2 is RAID5 parity block.
                         * Mirror #3 is RAID6 Q block.
                         */
                        stripe_nr = div_u64_rem(stripe_nr,
                                        data_stripes, &stripe_index);
                        if (mirror_num > 1)
                                stripe_index = data_stripes + mirror_num - 2;

                        /* We distribute the parity blocks across stripes */
                        div_u64_rem(stripe_nr + stripe_index, map->num_stripes,
                                        &stripe_index);
                        if (!need_full_stripe(op) && mirror_num <= 1)
                                mirror_num = 1;
                }
        } else {
                /*
                 * after this, 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_nr = div_u64_rem(stripe_nr, map->num_stripes,
                                &stripe_index);
                mirror_num = stripe_index + 1;
        }
        if (stripe_index >= map->num_stripes) {
                btrfs_crit(fs_info,
                           "stripe index math went horribly wrong, got stripe_index=%u, num_stripes=%u",
                           stripe_index, map->num_stripes);
                ret = -EINVAL;
                goto out;
        }

        num_alloc_stripes = num_stripes;
        if (dev_replace_is_ongoing && dev_replace->tgtdev != NULL) {
                if (op == BTRFS_MAP_WRITE)
                        num_alloc_stripes <<= 1;
                if (op == BTRFS_MAP_GET_READ_MIRRORS)
                        num_alloc_stripes++;
                tgtdev_indexes = num_stripes;
        }

        bbio = alloc_btrfs_bio(num_alloc_stripes, tgtdev_indexes);
        if (!bbio) {
                ret = -ENOMEM;
                goto out;
        }

        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++;
        }

        /* build raid_map */
        if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK && need_raid_map &&
            (need_full_stripe(op) || mirror_num > 1)) {
                u64 tmp;
                unsigned rot;

                /* Work out the disk rotation on this stripe-set */
                div_u64_rem(stripe_nr, num_stripes, &rot);

                /* Fill in the logical address of each stripe */
                tmp = stripe_nr * data_stripes;
                for (i = 0; i < data_stripes; i++)
                        bbio->raid_map[(i+rot) % num_stripes] =
                                em->start + (tmp + i) * map->stripe_len;

                bbio->raid_map[(i+rot) % map->num_stripes] = RAID5_P_STRIPE;
                if (map->type & BTRFS_BLOCK_GROUP_RAID6)
                        bbio->raid_map[(i+rot+1) % num_stripes] =
                                RAID6_Q_STRIPE;

                sort_parity_stripes(bbio, num_stripes);
        }

        if (need_full_stripe(op))
                max_errors = btrfs_chunk_max_errors(map);

        if (dev_replace_is_ongoing && dev_replace->tgtdev != NULL &&
            need_full_stripe(op)) {
                handle_ops_on_dev_replace(op, &bbio, dev_replace, &num_stripes,
                                          &max_errors);
        }

        *bbio_ret = bbio;
        bbio->map_type = map->type;
        bbio->num_stripes = num_stripes;
        bbio->max_errors = max_errors;
        bbio->mirror_num = mirror_num;

        /*
         * this is the case that REQ_READ && dev_replace_is_ongoing &&
         * mirror_num == num_stripes + 1 && dev_replace target drive is
         * available as a mirror
         */
        if (patch_the_first_stripe_for_dev_replace && num_stripes > 0) {
                WARN_ON(num_stripes > 1);
                bbio->stripes[0].dev = dev_replace->tgtdev;
                bbio->stripes[0].physical = physical_to_patch_in_first_stripe;
                bbio->mirror_num = map->num_stripes + 1;
        }
out:
        if (dev_replace_is_ongoing) {
                lockdep_assert_held(&dev_replace->rwsem);
                /* Unlock and let waiting writers proceed */
                up_read(&dev_replace->rwsem);
        }
        free_extent_map(em);
        return ret;
}

int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
                      u64 logical, u64 *length,
                      struct btrfs_bio **bbio_ret, int mirror_num)
{
        if (op == BTRFS_MAP_DISCARD)
                return __btrfs_map_block_for_discard(fs_info, logical,
                                                     length, bbio_ret);

        return __btrfs_map_block(fs_info, op, logical, length, bbio_ret,
                                 mirror_num, 0);
}

/* For Scrub/replace */
int btrfs_map_sblock(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
                     u64 logical, u64 *length,
                     struct btrfs_bio **bbio_ret)
{
        return __btrfs_map_block(fs_info, op, logical, length, bbio_ret, 0, 1);
}

static inline void btrfs_end_bbio(struct btrfs_bio *bbio, struct bio *bio)
{
        bio->bi_private = bbio->private;
        bio->bi_end_io = bbio->end_io;
        bio_endio(bio);

        btrfs_put_bbio(bbio);
}

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

        if (bio->bi_status) {
                atomic_inc(&bbio->error);
                if (bio->bi_status == BLK_STS_IOERR ||
                    bio->bi_status == BLK_STS_TARGET) {
                        struct btrfs_device *dev = btrfs_io_bio(bio)->device;

                        ASSERT(dev->bdev);
                        if (bio_op(bio) == REQ_OP_WRITE)
                                btrfs_dev_stat_inc_and_print(dev,
                                                BTRFS_DEV_STAT_WRITE_ERRS);
                        else if (!(bio->bi_opf & REQ_RAHEAD))
                                btrfs_dev_stat_inc_and_print(dev,
                                                BTRFS_DEV_STAT_READ_ERRS);
                        if (bio->bi_opf & REQ_PREFLUSH)
                                btrfs_dev_stat_inc_and_print(dev,
                                                BTRFS_DEV_STAT_FLUSH_ERRS);
                }
        }

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

        btrfs_bio_counter_dec(bbio->fs_info);

        if (atomic_dec_and_test(&bbio->stripes_pending)) {
                if (!is_orig_bio) {
                        bio_put(bio);
                        bio = bbio->orig_bio;
                }

                btrfs_io_bio(bio)->mirror_num = bbio->mirror_num;
                /* only send an error to the higher layers if it is
                 * beyond the tolerance of the btrfs bio
                 */
                if (atomic_read(&bbio->error) > bbio->max_errors) {
                        bio->bi_status = BLK_STS_IOERR;
                } else {
                        /*
                         * this bio is actually up to date, we didn't
                         * go over the max number of errors
                         */
                        bio->bi_status = BLK_STS_OK;
                }

                btrfs_end_bbio(bbio, bio);
        } else if (!is_orig_bio) {
                bio_put(bio);
        }
}

static void submit_stripe_bio(struct btrfs_bio *bbio, struct bio *bio,
                              u64 physical, struct btrfs_device *dev)
{
        struct btrfs_fs_info *fs_info = bbio->fs_info;

        bio->bi_private = bbio;
        btrfs_io_bio(bio)->device = dev;
        bio->bi_end_io = btrfs_end_bio;
        bio->bi_iter.bi_sector = physical >> 9;
        btrfs_debug_in_rcu(fs_info,
        "btrfs_map_bio: rw %d 0x%x, sector=%llu, dev=%lu (%s id %llu), size=%u",
                bio_op(bio), bio->bi_opf, (u64)bio->bi_iter.bi_sector,
                (unsigned long)dev->bdev->bd_dev, rcu_str_deref(dev->name),
                dev->devid, bio->bi_iter.bi_size);
        bio_set_dev(bio, dev->bdev);

        btrfs_bio_counter_inc_noblocked(fs_info);

        btrfsic_submit_bio(bio);
}

static void bbio_error(struct btrfs_bio *bbio, struct bio *bio, u64 logical)
{
        atomic_inc(&bbio->error);
        if (atomic_dec_and_test(&bbio->stripes_pending)) {
                /* Should be the original bio. */
                WARN_ON(bio != bbio->orig_bio);

                btrfs_io_bio(bio)->mirror_num = bbio->mirror_num;
                bio->bi_iter.bi_sector = logical >> 9;
                if (atomic_read(&bbio->error) > bbio->max_errors)
                        bio->bi_status = BLK_STS_IOERR;
                else
                        bio->bi_status = BLK_STS_OK;
                btrfs_end_bbio(bbio, bio);
        }
}

blk_status_t btrfs_map_bio(struct btrfs_fs_info *fs_info, struct bio *bio,
                           int mirror_num)
{
        struct btrfs_device *dev;
        struct bio *first_bio = bio;
        u64 logical = (u64)bio->bi_iter.bi_sector << 9;
        u64 length = 0;
        u64 map_length;
        int ret;
        int dev_nr;
        int total_devs;
        struct btrfs_bio *bbio = NULL;

        length = bio->bi_iter.bi_size;
        map_length = length;

        btrfs_bio_counter_inc_blocked(fs_info);
        ret = __btrfs_map_block(fs_info, btrfs_op(bio), logical,
                                &map_length, &bbio, mirror_num, 1);
        if (ret) {
                btrfs_bio_counter_dec(fs_info);
                return errno_to_blk_status(ret);
        }

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

        if ((bbio->map_type & BTRFS_BLOCK_GROUP_RAID56_MASK) &&
            ((bio_op(bio) == REQ_OP_WRITE) || (mirror_num > 1))) {
                /* In this case, map_length has been set to the length of
                   a single stripe; not the whole write */
                if (bio_op(bio) == REQ_OP_WRITE) {
                        ret = raid56_parity_write(fs_info, bio, bbio,
                                                  map_length);
                } else {
                        ret = raid56_parity_recover(fs_info, bio, bbio,
                                                    map_length, mirror_num, 1);
                }

                btrfs_bio_counter_dec(fs_info);
                return errno_to_blk_status(ret);
        }

        if (map_length < length) {
                btrfs_crit(fs_info,
                           "mapping failed logical %llu bio len %llu len %llu",
                           logical, length, map_length);
                BUG();
        }

        for (dev_nr = 0; dev_nr < total_devs; dev_nr++) {
                dev = bbio->stripes[dev_nr].dev;
                if (!dev || !dev->bdev || test_bit(BTRFS_DEV_STATE_MISSING,
                                                   &dev->dev_state) ||
                    (bio_op(first_bio) == REQ_OP_WRITE &&
                    !test_bit(BTRFS_DEV_STATE_WRITEABLE, &dev->dev_state))) {
                        bbio_error(bbio, first_bio, logical);
                        continue;
                }

                if (dev_nr < total_devs - 1)
                        bio = btrfs_bio_clone(first_bio);
                else
                        bio = first_bio;

                submit_stripe_bio(bbio, bio, bbio->stripes[dev_nr].physical, dev);
        }
        btrfs_bio_counter_dec(fs_info);
        return BLK_STS_OK;
}

/*
 * Find a device specified by @devid or @uuid in the list of @fs_devices, or
 * return NULL.
 *
 * If devid and uuid are both specified, the match must be exact, otherwise
 * only devid is used.
 *
 * If @seed is true, traverse through the seed devices.
 */
struct btrfs_device *btrfs_find_device(struct btrfs_fs_devices *fs_devices,
                                       u64 devid, u8 *uuid, u8 *fsid,
                                       bool seed)
{
        struct btrfs_device *device;
        struct btrfs_fs_devices *seed_devs;

        if (!fsid || !memcmp(fs_devices->metadata_uuid, fsid, BTRFS_FSID_SIZE)) {
                list_for_each_entry(device, &fs_devices->devices, dev_list) {
                        if (device->devid == devid &&
                            (!uuid || memcmp(device->uuid, uuid,
                                             BTRFS_UUID_SIZE) == 0))
                                return device;
                }
        }

        list_for_each_entry(seed_devs, &fs_devices->seed_list, seed_list) {
                if (!fsid ||
                    !memcmp(seed_devs->metadata_uuid, fsid, BTRFS_FSID_SIZE)) {
                        list_for_each_entry(device, &seed_devs->devices,
                                            dev_list) {
                                if (device->devid == devid &&
                                    (!uuid || memcmp(device->uuid, uuid,
                                                     BTRFS_UUID_SIZE) == 0))
                                        return device;
                        }
                }
        }

        return NULL;
}

static struct btrfs_device *add_missing_dev(struct btrfs_fs_devices *fs_devices,
                                            u64 devid, u8 *dev_uuid)
{
        struct btrfs_device *device;
        unsigned int nofs_flag;

        /*
         * We call this under the chunk_mutex, so we want to use NOFS for this
         * allocation, however we don't want to change btrfs_alloc_device() to
         * always do NOFS because we use it in a lot of other GFP_KERNEL safe
         * places.
         */
        nofs_flag = memalloc_nofs_save();
        device = btrfs_alloc_device(NULL, &devid, dev_uuid);
        memalloc_nofs_restore(nofs_flag);
        if (IS_ERR(device))
                return device;

        list_add(&device->dev_list, &fs_devices->devices);
        device->fs_devices = fs_devices;
        fs_devices->num_devices++;

        set_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
        fs_devices->missing_devices++;

        return device;
}

/**
 * btrfs_alloc_device - allocate struct btrfs_device
 * @fs_info:    used only for generating a new devid, can be NULL if
 *              devid is provided (i.e. @devid != NULL).
 * @devid:      a pointer to devid for this device.  If NULL a new devid
 *              is generated.
 * @uuid:       a pointer to UUID for this device.  If NULL a new UUID
 *              is generated.
 *
 * Return: a pointer to a new &struct btrfs_device on success; ERR_PTR()
 * on error.  Returned struct is not linked onto any lists and must be
 * destroyed with btrfs_free_device.
 */
struct btrfs_device *btrfs_alloc_device(struct btrfs_fs_info *fs_info,
                                        const u64 *devid,
                                        const u8 *uuid)
{
        struct btrfs_device *dev;
        u64 tmp;

        if (WARN_ON(!devid && !fs_info))
                return ERR_PTR(-EINVAL);

        dev = __alloc_device(fs_info);
        if (IS_ERR(dev))
                return dev;

        if (devid)
                tmp = *devid;
        else {
                int ret;

                ret = find_next_devid(fs_info, &tmp);
                if (ret) {
                        btrfs_free_device(dev);
                        return ERR_PTR(ret);
                }
        }
        dev->devid = tmp;

        if (uuid)
                memcpy(dev->uuid, uuid, BTRFS_UUID_SIZE);
        else
                generate_random_uuid(dev->uuid);

        return dev;
}

static void btrfs_report_missing_device(struct btrfs_fs_info *fs_info,
                                        u64 devid, u8 *uuid, bool error)
{
        if (error)
                btrfs_err_rl(fs_info, "devid %llu uuid %pU is missing",
                              devid, uuid);
        else
                btrfs_warn_rl(fs_info, "devid %llu uuid %pU is missing",
                              devid, uuid);
}

static u64 calc_stripe_length(u64 type, u64 chunk_len, int num_stripes)
{
        int index = btrfs_bg_flags_to_raid_index(type);
        int ncopies = btrfs_raid_array[index].ncopies;
        const int nparity = btrfs_raid_array[index].nparity;
        int data_stripes;

        if (nparity)
                data_stripes = num_stripes - nparity;
        else
                data_stripes = num_stripes / ncopies;

        return div_u64(chunk_len, data_stripes);
}

static int read_one_chunk(struct btrfs_key *key, struct extent_buffer *leaf,
                          struct btrfs_chunk *chunk)
{
        struct btrfs_fs_info *fs_info = leaf->fs_info;
        struct extent_map_tree *map_tree = &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);
        num_stripes = btrfs_chunk_num_stripes(leaf, chunk);

        /*
         * Only need to verify chunk item if we're reading from sys chunk array,
         * as chunk item in tree block is already verified by tree-checker.
         */
        if (leaf->start == BTRFS_SUPER_INFO_OFFSET) {
                ret = btrfs_check_chunk_valid(leaf, chunk, logical);
                if (ret)
                        return ret;
        }

        read_lock(&map_tree->lock);
        em = lookup_extent_mapping(map_tree, logical, 1);
        read_unlock(&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;
        map = kmalloc(map_lookup_size(num_stripes), GFP_NOFS);
        if (!map) {
                free_extent_map(em);
                return -ENOMEM;
        }

        set_bit(EXTENT_FLAG_FS_MAPPING, &em->flags);
        em->map_lookup = map;
        em->start = logical;
        em->len = length;
        em->orig_start = 0;
        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->stripe_len = btrfs_chunk_stripe_len(leaf, chunk);
        map->type = btrfs_chunk_type(leaf, chunk);
        map->sub_stripes = btrfs_chunk_sub_stripes(leaf, chunk);
        map->verified_stripes = 0;
        em->orig_block_len = calc_stripe_length(map->type, em->len,
                                                map->num_stripes);
        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(fs_info->fs_devices,
                                                        devid, uuid, NULL, true);
                if (!map->stripes[i].dev &&
                    !btrfs_test_opt(fs_info, DEGRADED)) {
                        free_extent_map(em);
                        btrfs_report_missing_device(fs_info, devid, uuid, true);
                        return -ENOENT;
                }
                if (!map->stripes[i].dev) {
                        map->stripes[i].dev =
                                add_missing_dev(fs_info->fs_devices, devid,
                                                uuid);
                        if (IS_ERR(map->stripes[i].dev)) {
                                free_extent_map(em);
                                btrfs_err(fs_info,
                                        "failed to init missing dev %llu: %ld",
                                        devid, PTR_ERR(map->stripes[i].dev));
                                return PTR_ERR(map->stripes[i].dev);
                        }
                        btrfs_report_missing_device(fs_info, devid, uuid, false);
                }
                set_bit(BTRFS_DEV_STATE_IN_FS_METADATA,
                                &(map->stripes[i].dev->dev_state));

        }

        write_lock(&map_tree->lock);
        ret = add_extent_mapping(map_tree, em, 0);
        write_unlock(&map_tree->lock);
        if (ret < 0) {
                btrfs_err(fs_info,
                          "failed to add chunk map, start=%llu len=%llu: %d",
                          em->start, em->len, ret);
        }
        free_extent_map(em);

        return ret;
}

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->commit_total_bytes = device->disk_total_bytes;
        device->bytes_used = btrfs_device_bytes_used(leaf, dev_item);
        device->commit_bytes_used = device->bytes_used;
        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);
        WARN_ON(device->devid == BTRFS_DEV_REPLACE_DEVID);
        clear_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state);

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

static struct btrfs_fs_devices *open_seed_devices(struct btrfs_fs_info *fs_info,
                                                  u8 *fsid)
{
        struct btrfs_fs_devices *fs_devices;
        int ret;

        lockdep_assert_held(&uuid_mutex);
        ASSERT(fsid);

        /* This will match only for multi-device seed fs */
        list_for_each_entry(fs_devices, &fs_info->fs_devices->seed_list, seed_list)
                if (!memcmp(fs_devices->fsid, fsid, BTRFS_FSID_SIZE))
                        return fs_devices;


        fs_devices = find_fsid(fsid, NULL);
        if (!fs_devices) {
                if (!btrfs_test_opt(fs_info, DEGRADED))
                        return ERR_PTR(-ENOENT);

                fs_devices = alloc_fs_devices(fsid, NULL);
                if (IS_ERR(fs_devices))
                        return fs_devices;

                fs_devices->seeding = true;
                fs_devices->opened = 1;
                return fs_devices;
        }

        /*
         * Upon first call for a seed fs fsid, just create a private copy of the
         * respective fs_devices and anchor it at fs_info->fs_devices->seed_list
         */
        fs_devices = clone_fs_devices(fs_devices);
        if (IS_ERR(fs_devices))
                return fs_devices;

        ret = open_fs_devices(fs_devices, FMODE_READ, fs_info->bdev_holder);
        if (ret) {
                free_fs_devices(fs_devices);
                return ERR_PTR(ret);
        }

        if (!fs_devices->seeding) {
                close_fs_devices(fs_devices);
                free_fs_devices(fs_devices);
                return ERR_PTR(-EINVAL);
        }

        list_add(&fs_devices->seed_list, &fs_info->fs_devices->seed_list);

        return fs_devices;
}

static int read_one_dev(struct extent_buffer *leaf,
                        struct btrfs_dev_item *dev_item)
{
        struct btrfs_fs_info *fs_info = leaf->fs_info;
        struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
        struct btrfs_device *device;
        u64 devid;
        int ret;
        u8 fs_uuid[BTRFS_FSID_SIZE];
        u8 dev_uuid[BTRFS_UUID_SIZE];

        devid = btrfs_device_id(leaf, dev_item);
        read_extent_buffer(leaf, dev_uuid, btrfs_device_uuid(dev_item),
                           BTRFS_UUID_SIZE);
        read_extent_buffer(leaf, fs_uuid, btrfs_device_fsid(dev_item),
                           BTRFS_FSID_SIZE);

        if (memcmp(fs_uuid, fs_devices->metadata_uuid, BTRFS_FSID_SIZE)) {
                fs_devices = open_seed_devices(fs_info, fs_uuid);
                if (IS_ERR(fs_devices))
                        return PTR_ERR(fs_devices);
        }

        device = btrfs_find_device(fs_info->fs_devices, devid, dev_uuid,
                                   fs_uuid, true);
        if (!device) {
                if (!btrfs_test_opt(fs_info, DEGRADED)) {
                        btrfs_report_missing_device(fs_info, devid,
                                                        dev_uuid, true);
                        return -ENOENT;
                }

                device = add_missing_dev(fs_devices, devid, dev_uuid);
                if (IS_ERR(device)) {
                        btrfs_err(fs_info,
                                "failed to add missing dev %llu: %ld",
                                devid, PTR_ERR(device));
                        return PTR_ERR(device);
                }
                btrfs_report_missing_device(fs_info, devid, dev_uuid, false);
        } else {
                if (!device->bdev) {
                        if (!btrfs_test_opt(fs_info, DEGRADED)) {
                                btrfs_report_missing_device(fs_info,
                                                devid, dev_uuid, true);
                                return -ENOENT;
                        }
                        btrfs_report_missing_device(fs_info, devid,
                                                        dev_uuid, false);
                }

                if (!device->bdev &&
                    !test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) {
                        /*
                         * 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
                         */
                        device->fs_devices->missing_devices++;
                        set_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
                }

                /* Move the device to its own fs_devices */
                if (device->fs_devices != fs_devices) {
                        ASSERT(test_bit(BTRFS_DEV_STATE_MISSING,
                                                        &device->dev_state));

                        list_move(&device->dev_list, &fs_devices->devices);
                        device->fs_devices->num_devices--;
                        fs_devices->num_devices++;

                        device->fs_devices->missing_devices--;
                        fs_devices->missing_devices++;

                        device->fs_devices = fs_devices;
                }
        }

        if (device->fs_devices != fs_info->fs_devices) {
                BUG_ON(test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state));
                if (device->generation !=
                    btrfs_device_generation(leaf, dev_item))
                        return -EINVAL;
        }

        fill_device_from_item(leaf, dev_item, device);
        set_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
        if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
           !test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state)) {
                device->fs_devices->total_rw_bytes += device->total_bytes;
                atomic64_add(device->total_bytes - device->bytes_used,
                                &fs_info->free_chunk_space);
        }
        ret = 0;
        return ret;
}

int btrfs_read_sys_array(struct btrfs_fs_info *fs_info)
{
        struct btrfs_root *root = fs_info->tree_root;
        struct btrfs_super_block *super_copy = fs_info->super_copy;
        struct extent_buffer *sb;
        struct btrfs_disk_key *disk_key;
        struct btrfs_chunk *chunk;
        u8 *array_ptr;
        unsigned long sb_array_offset;
        int ret = 0;
        u32 num_stripes;
        u32 array_size;
        u32 len = 0;
        u32 cur_offset;
        u64 type;
        struct btrfs_key key;

        ASSERT(BTRFS_SUPER_INFO_SIZE <= fs_info->nodesize);
        /*
         * This will create extent buffer of nodesize, superblock size is
         * fixed to BTRFS_SUPER_INFO_SIZE. If nodesize > sb size, this will
         * overallocate but we can keep it as-is, only the first page is used.
         */
        sb = btrfs_find_create_tree_block(fs_info, BTRFS_SUPER_INFO_OFFSET);
        if (IS_ERR(sb))
                return PTR_ERR(sb);
        set_extent_buffer_uptodate(sb);
        btrfs_set_buffer_lockdep_class(root->root_key.objectid, sb, 0);
        /*
         * The sb extent buffer is artificial and just used to read the system array.
         * set_extent_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_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);

        array_ptr = super_copy->sys_chunk_array;
        sb_array_offset = offsetof(struct btrfs_super_block, sys_chunk_array);
        cur_offset = 0;

        while (cur_offset < array_size) {
                disk_key = (struct btrfs_disk_key *)array_ptr;
                len = sizeof(*disk_key);
                if (cur_offset + len > array_size)
                        goto out_short_read;

                btrfs_disk_key_to_cpu(&key, disk_key);

                array_ptr += len;
                sb_array_offset += len;
                cur_offset += len;

                if (key.type != BTRFS_CHUNK_ITEM_KEY) {
                        btrfs_err(fs_info,
                            "unexpected item type %u in sys_array at offset %u",
                                  (u32)key.type, cur_offset);
                        ret = -EIO;
                        break;
                }

                chunk = (struct btrfs_chunk *)sb_array_offset;
                /*
                 * At least one btrfs_chunk with one stripe must be present,
                 * exact stripe count check comes afterwards
                 */
                len = btrfs_chunk_item_size(1);
                if (cur_offset + len > array_size)
                        goto out_short_read;

                num_stripes = btrfs_chunk_num_stripes(sb, chunk);
                if (!num_stripes) {
                        btrfs_err(fs_info,
                        "invalid number of stripes %u in sys_array at offset %u",
                                  num_stripes, cur_offset);
                        ret = -EIO;
                        break;
                }

                type = btrfs_chunk_type(sb, chunk);
                if ((type & BTRFS_BLOCK_GROUP_SYSTEM) == 0) {
                        btrfs_err(fs_info,
                        "invalid chunk type %llu in sys_array at offset %u",
                                  type, cur_offset);
                        ret = -EIO;
                        break;
                }

                len = btrfs_chunk_item_size(num_stripes);
                if (cur_offset + len > array_size)
                        goto out_short_read;

                ret = read_one_chunk(&key, sb, chunk);
                if (ret)
                        break;

                array_ptr += len;
                sb_array_offset += len;
                cur_offset += len;
        }
        clear_extent_buffer_uptodate(sb);
        free_extent_buffer_stale(sb);
        return ret;

out_short_read:
        btrfs_err(fs_info, "sys_array too short to read %u bytes at offset %u",
                        len, cur_offset);
        clear_extent_buffer_uptodate(sb);
        free_extent_buffer_stale(sb);
        return -EIO;
}

/*
 * Check if all chunks in the fs are OK for read-write degraded mount
 *
 * If the @failing_dev is specified, it's accounted as missing.
 *
 * Return true if all chunks meet the minimal RW mount requirements.
 * Return false if any chunk doesn't meet the minimal RW mount requirements.
 */
bool btrfs_check_rw_degradable(struct btrfs_fs_info *fs_info,
                                        struct btrfs_device *failing_dev)
{
        struct extent_map_tree *map_tree = &fs_info->mapping_tree;
        struct extent_map *em;
        u64 next_start = 0;
        bool ret = true;

        read_lock(&map_tree->lock);
        em = lookup_extent_mapping(map_tree, 0, (u64)-1);
        read_unlock(&map_tree->lock);
        /* No chunk at all? Return false anyway */
        if (!em) {
                ret = false;
                goto out;
        }
        while (em) {
                struct map_lookup *map;
                int missing = 0;
                int max_tolerated;
                int i;

                map = em->map_lookup;
                max_tolerated =
                        btrfs_get_num_tolerated_disk_barrier_failures(
                                        map->type);
                for (i = 0; i < map->num_stripes; i++) {
                        struct btrfs_device *dev = map->stripes[i].dev;

                        if (!dev || !dev->bdev ||
                            test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state) ||
                            dev->last_flush_error)
                                missing++;
                        else if (failing_dev && failing_dev == dev)
                                missing++;
                }
                if (missing > max_tolerated) {
                        if (!failing_dev)
                                btrfs_warn(fs_info,
        "chunk %llu missing %d devices, max tolerance is %d for writable mount",
                                   em->start, missing, max_tolerated);
                        free_extent_map(em);
                        ret = false;
                        goto out;
                }
                next_start = extent_map_end(em);
                free_extent_map(em);

                read_lock(&map_tree->lock);
                em = lookup_extent_mapping(map_tree, next_start,
                                           (u64)(-1) - next_start);
                read_unlock(&map_tree->lock);
        }
out:
        return ret;
}

static void readahead_tree_node_children(struct extent_buffer *node)
{
        int i;
        const int nr_items = btrfs_header_nritems(node);

        for (i = 0; i < nr_items; i++) {
                u64 start;

                start = btrfs_node_blockptr(node, i);
                readahead_tree_block(node->fs_info, start);
        }
}

int btrfs_read_chunk_tree(struct btrfs_fs_info *fs_info)
{
        struct btrfs_root *root = fs_info->chunk_root;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_key key;
        struct btrfs_key found_key;
        int ret;
        int slot;
        u64 total_dev = 0;
        u64 last_ra_node = 0;

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

        /*
         * uuid_mutex is needed only if we are mounting a sprout FS
         * otherwise we don't need it.
         */
        mutex_lock(&uuid_mutex);

        /*
         * It is possible for mount and umount to race in such a way that
         * we execute this code path, but open_fs_devices failed to clear
         * total_rw_bytes. We certainly want it cleared before reading the
         * device items, so clear it here.
         */
        fs_info->fs_devices->total_rw_bytes = 0;

        /*
         * Read all device items, and then all the chunk items. All
         * device items are found before any chunk item (their object id
         * is smaller than the lowest possible object id for a chunk
         * item - BTRFS_FIRST_CHUNK_TREE_OBJECTID).
         */
        key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
        key.offset = 0;
        key.type = 0;
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto error;
        while (1) {
                struct extent_buffer *node;

                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;
                }
                /*
                 * The nodes on level 1 are not locked but we don't need to do
                 * that during mount time as nothing else can access the tree
                 */
                node = path->nodes[1];
                if (node) {
                        if (last_ra_node != node->start) {
                                readahead_tree_node_children(node);
                                last_ra_node = node->start;
                        }
                }
                btrfs_item_key_to_cpu(leaf, &found_key, slot);
                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(leaf, dev_item);
                        if (ret)
                                goto error;
                        total_dev++;
                } else if (found_key.type == BTRFS_CHUNK_ITEM_KEY) {
                        struct btrfs_chunk *chunk;
                        chunk = btrfs_item_ptr(leaf, slot, struct btrfs_chunk);
                        mutex_lock(&fs_info->chunk_mutex);
                        ret = read_one_chunk(&found_key, leaf, chunk);
                        mutex_unlock(&fs_info->chunk_mutex);
                        if (ret)
                                goto error;
                }
                path->slots[0]++;
        }

        /*
         * After loading chunk tree, we've got all device information,
         * do another round of validation checks.
         */
        if (total_dev != fs_info->fs_devices->total_devices) {
                btrfs_warn(fs_info,
"super block num_devices %llu mismatch with DEV_ITEM count %llu, will be repaired on next transaction commit",
                          btrfs_super_num_devices(fs_info->super_copy),
                          total_dev);
                fs_info->fs_devices->total_devices = total_dev;
                btrfs_set_super_num_devices(fs_info->super_copy, total_dev);
        }
        if (btrfs_super_total_bytes(fs_info->super_copy) <
            fs_info->fs_devices->total_rw_bytes) {
                btrfs_err(fs_info,
        "super_total_bytes %llu mismatch with fs_devices total_rw_bytes %llu",
                          btrfs_super_total_bytes(fs_info->super_copy),
                          fs_info->fs_devices->total_rw_bytes);
                ret = -EINVAL;
                goto error;
        }
        ret = 0;
error:
        mutex_unlock(&uuid_mutex);

        btrfs_free_path(path);
        return ret;
}

void btrfs_init_devices_late(struct btrfs_fs_info *fs_info)
{
        struct btrfs_fs_devices *fs_devices = fs_info->fs_devices, *seed_devs;
        struct btrfs_device *device;

        fs_devices->fs_info = fs_info;

        mutex_lock(&fs_devices->device_list_mutex);
        list_for_each_entry(device, &fs_devices->devices, dev_list)
                device->fs_info = fs_info;

        list_for_each_entry(seed_devs, &fs_devices->seed_list, seed_list) {
                list_for_each_entry(device, &seed_devs->devices, dev_list)
                        device->fs_info = fs_info;

                seed_devs->fs_info = fs_info;
        }
        mutex_unlock(&fs_devices->device_list_mutex);
}

static u64 btrfs_dev_stats_value(const struct extent_buffer *eb,
                                 const struct btrfs_dev_stats_item *ptr,
                                 int index)
{
        u64 val;

        read_extent_buffer(eb, &val,
                           offsetof(struct btrfs_dev_stats_item, values) +
                            ((unsigned long)ptr) + (index * sizeof(u64)),
                           sizeof(val));
        return val;
}

static void btrfs_set_dev_stats_value(struct extent_buffer *eb,
                                      struct btrfs_dev_stats_item *ptr,
                                      int index, u64 val)
{
        write_extent_buffer(eb, &val,
                            offsetof(struct btrfs_dev_stats_item, values) +
                             ((unsigned long)ptr) + (index * sizeof(u64)),
                            sizeof(val));
}

static int btrfs_device_init_dev_stats(struct btrfs_device *device,
                                       struct btrfs_path *path)
{
        struct btrfs_dev_stats_item *ptr;
        struct extent_buffer *eb;
        struct btrfs_key key;
        int item_size;
        int i, ret, slot;

        key.objectid = BTRFS_DEV_STATS_OBJECTID;
        key.type = BTRFS_PERSISTENT_ITEM_KEY;
        key.offset = device->devid;
        ret = btrfs_search_slot(NULL, device->fs_info->dev_root, &key, path, 0, 0);
        if (ret) {
                for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++)
                        btrfs_dev_stat_set(device, i, 0);
                device->dev_stats_valid = 1;
                btrfs_release_path(path);
                return ret < 0 ? ret : 0;
        }
        slot = path->slots[0];
        eb = path->nodes[0];
        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_set(device, i, 0);
        }

        device->dev_stats_valid = 1;
        btrfs_dev_stat_print_on_load(device);
        btrfs_release_path(path);

        return 0;
}

int btrfs_init_dev_stats(struct btrfs_fs_info *fs_info)
{
        struct btrfs_fs_devices *fs_devices = fs_info->fs_devices, *seed_devs;
        struct btrfs_device *device;
        struct btrfs_path *path = NULL;
        int ret = 0;

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

        mutex_lock(&fs_devices->device_list_mutex);
        list_for_each_entry(device, &fs_devices->devices, dev_list) {
                ret = btrfs_device_init_dev_stats(device, path);
                if (ret)
                        goto out;
        }
        list_for_each_entry(seed_devs, &fs_devices->seed_list, seed_list) {
                list_for_each_entry(device, &seed_devs->devices, dev_list) {
                        ret = btrfs_device_init_dev_stats(device, path);
                        if (ret)
                                goto out;
                }
        }
out:
        mutex_unlock(&fs_devices->device_list_mutex);

        btrfs_free_path(path);
        return ret;
}

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

        key.objectid = BTRFS_DEV_STATS_OBJECTID;
        key.type = BTRFS_PERSISTENT_ITEM_KEY;
        key.offset = device->devid;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
        ret = btrfs_search_slot(trans, dev_root, &key, path, -1, 1);
        if (ret < 0) {
                btrfs_warn_in_rcu(fs_info,
                        "error %d while searching for dev_stats item for device %s",
                              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) {
                        btrfs_warn_in_rcu(fs_info,
                                "delete too small dev_stats item for device %s failed %d",
                                      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) {
                        btrfs_warn_in_rcu(fs_info,
                                "insert dev_stats item for device %s failed %d",
                                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 = trans->fs_info;
        struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
        struct btrfs_device *device;
        int stats_cnt;
        int ret = 0;

        mutex_lock(&fs_devices->device_list_mutex);
        list_for_each_entry(device, &fs_devices->devices, dev_list) {
                stats_cnt = atomic_read(&device->dev_stats_ccnt);
                if (!device->dev_stats_valid || stats_cnt == 0)
                        continue;


                /*
                 * There is a LOAD-LOAD control dependency between the value of
                 * dev_stats_ccnt and updating the on-disk values which requires
                 * reading the in-memory counters. Such control dependencies
                 * require explicit read memory barriers.
                 *
                 * This memory barriers pairs with smp_mb__before_atomic in
                 * btrfs_dev_stat_inc/btrfs_dev_stat_set and with the full
                 * barrier implied by atomic_xchg in
                 * btrfs_dev_stats_read_and_reset
                 */
                smp_rmb();

                ret = update_dev_stat_item(trans, device);
                if (!ret)
                        atomic_sub(stats_cnt, &device->dev_stats_ccnt);
        }
        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);
}

static void btrfs_dev_stat_print_on_error(struct btrfs_device *dev)
{
        if (!dev->dev_stats_valid)
                return;
        btrfs_err_rl_in_rcu(dev->fs_info,
                "bdev %s errs: wr %u, rd %u, flush %u, corrupt %u, gen %u",
                           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 */

        btrfs_info_in_rcu(dev->fs_info,
                "bdev %s errs: wr %u, rd %u, flush %u, corrupt %u, gen %u",
               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_fs_info *fs_info,
                        struct btrfs_ioctl_get_dev_stats *stats)
{
        struct btrfs_device *dev;
        struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
        int i;

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

        if (!dev) {
                btrfs_warn(fs_info, "get dev_stats failed, device not found");
                return -ENODEV;
        } else if (!dev->dev_stats_valid) {
                btrfs_warn(fs_info, "get dev_stats failed, not yet valid");
                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_set(dev, i, 0);
                }
                btrfs_info(fs_info, "device stats zeroed by %s (%d)",
                           current->comm, task_pid_nr(current));
        } 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;
}

/*
 * Update the size and bytes used for each device where it changed.  This is
 * delayed since we would otherwise get errors while writing out the
 * superblocks.
 *
 * Must be invoked during transaction commit.
 */
void btrfs_commit_device_sizes(struct btrfs_transaction *trans)
{
        struct btrfs_device *curr, *next;

        ASSERT(trans->state == TRANS_STATE_COMMIT_DOING);

        if (list_empty(&trans->dev_update_list))
                return;

        /*
         * We don't need the device_list_mutex here.  This list is owned by the
         * transaction and the transaction must complete before the device is
         * released.
         */
        mutex_lock(&trans->fs_info->chunk_mutex);
        list_for_each_entry_safe(curr, next, &trans->dev_update_list,
                                 post_commit_list) {
                list_del_init(&curr->post_commit_list);
                curr->commit_total_bytes = curr->disk_total_bytes;
                curr->commit_bytes_used = curr->bytes_used;
        }
        mutex_unlock(&trans->fs_info->chunk_mutex);
}

/*
 * Multiplicity factor for simple profiles: DUP, RAID1-like and RAID10.
 */
int btrfs_bg_type_to_factor(u64 flags)
{
        const int index = btrfs_bg_flags_to_raid_index(flags);

        return btrfs_raid_array[index].ncopies;
}



static int verify_one_dev_extent(struct btrfs_fs_info *fs_info,
                                 u64 chunk_offset, u64 devid,
                                 u64 physical_offset, u64 physical_len)
{
        struct extent_map_tree *em_tree = &fs_info->mapping_tree;
        struct extent_map *em;
        struct map_lookup *map;
        struct btrfs_device *dev;
        u64 stripe_len;
        bool found = false;
        int ret = 0;
        int i;

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

        if (!em) {
                btrfs_err(fs_info,
"dev extent physical offset %llu on devid %llu doesn't have corresponding chunk",
                          physical_offset, devid);
                ret = -EUCLEAN;
                goto out;
        }

        map = em->map_lookup;
        stripe_len = calc_stripe_length(map->type, em->len, map->num_stripes);
        if (physical_len != stripe_len) {
                btrfs_err(fs_info,
"dev extent physical offset %llu on devid %llu length doesn't match chunk %llu, have %llu expect %llu",
                          physical_offset, devid, em->start, physical_len,
                          stripe_len);
                ret = -EUCLEAN;
                goto out;
        }

        for (i = 0; i < map->num_stripes; i++) {
                if (map->stripes[i].dev->devid == devid &&
                    map->stripes[i].physical == physical_offset) {
                        found = true;
                        if (map->verified_stripes >= map->num_stripes) {
                                btrfs_err(fs_info,
                                "too many dev extents for chunk %llu found",
                                          em->start);
                                ret = -EUCLEAN;
                                goto out;
                        }
                        map->verified_stripes++;
                        break;
                }
        }
        if (!found) {
                btrfs_err(fs_info,
        "dev extent physical offset %llu devid %llu has no corresponding chunk",
                        physical_offset, devid);
                ret = -EUCLEAN;
        }

        /* Make sure no dev extent is beyond device bondary */
        dev = btrfs_find_device(fs_info->fs_devices, devid, NULL, NULL, true);
        if (!dev) {
                btrfs_err(fs_info, "failed to find devid %llu", devid);
                ret = -EUCLEAN;
                goto out;
        }

        /* It's possible this device is a dummy for seed device */
        if (dev->disk_total_bytes == 0) {
                struct btrfs_fs_devices *devs;

                devs = list_first_entry(&fs_info->fs_devices->seed_list,
                                        struct btrfs_fs_devices, seed_list);
                dev = btrfs_find_device(devs, devid, NULL, NULL, false);
                if (!dev) {
                        btrfs_err(fs_info, "failed to find seed devid %llu",
                                  devid);
                        ret = -EUCLEAN;
                        goto out;
                }
        }

        if (physical_offset + physical_len > dev->disk_total_bytes) {
                btrfs_err(fs_info,
"dev extent devid %llu physical offset %llu len %llu is beyond device boundary %llu",
                          devid, physical_offset, physical_len,
                          dev->disk_total_bytes);
                ret = -EUCLEAN;
                goto out;
        }
out:
        free_extent_map(em);
        return ret;
}

static int verify_chunk_dev_extent_mapping(struct btrfs_fs_info *fs_info)
{
        struct extent_map_tree *em_tree = &fs_info->mapping_tree;
        struct extent_map *em;
        struct rb_node *node;
        int ret = 0;

        read_lock(&em_tree->lock);
        for (node = rb_first_cached(&em_tree->map); node; node = rb_next(node)) {
                em = rb_entry(node, struct extent_map, rb_node);
                if (em->map_lookup->num_stripes !=
                    em->map_lookup->verified_stripes) {
                        btrfs_err(fs_info,
                        "chunk %llu has missing dev extent, have %d expect %d",
                                  em->start, em->map_lookup->verified_stripes,
                                  em->map_lookup->num_stripes);
                        ret = -EUCLEAN;
                        goto out;
                }
        }
out:
        read_unlock(&em_tree->lock);
        return ret;
}

/*
 * Ensure that all dev extents are mapped to correct chunk, otherwise
 * later chunk allocation/free would cause unexpected behavior.
 *
 * NOTE: This will iterate through the whole device tree, which should be of
 * the same size level as the chunk tree.  This slightly increases mount time.
 */
int btrfs_verify_dev_extents(struct btrfs_fs_info *fs_info)
{
        struct btrfs_path *path;
        struct btrfs_root *root = fs_info->dev_root;
        struct btrfs_key key;
        u64 prev_devid = 0;
        u64 prev_dev_ext_end = 0;
        int ret = 0;

        key.objectid = 1;
        key.type = BTRFS_DEV_EXTENT_KEY;
        key.offset = 0;

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

        path->reada = READA_FORWARD;
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto out;

        if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
                ret = btrfs_next_item(root, path);
                if (ret < 0)
                        goto out;
                /* No dev extents at all? Not good */
                if (ret > 0) {
                        ret = -EUCLEAN;
                        goto out;
                }
        }
        while (1) {
                struct extent_buffer *leaf = path->nodes[0];
                struct btrfs_dev_extent *dext;
                int slot = path->slots[0];
                u64 chunk_offset;
                u64 physical_offset;
                u64 physical_len;
                u64 devid;

                btrfs_item_key_to_cpu(leaf, &key, slot);
                if (key.type != BTRFS_DEV_EXTENT_KEY)
                        break;
                devid = key.objectid;
                physical_offset = key.offset;

                dext = btrfs_item_ptr(leaf, slot, struct btrfs_dev_extent);
                chunk_offset = btrfs_dev_extent_chunk_offset(leaf, dext);
                physical_len = btrfs_dev_extent_length(leaf, dext);

                /* Check if this dev extent overlaps with the previous one */
                if (devid == prev_devid && physical_offset < prev_dev_ext_end) {
                        btrfs_err(fs_info,
"dev extent devid %llu physical offset %llu overlap with previous dev extent end %llu",
                                  devid, physical_offset, prev_dev_ext_end);
                        ret = -EUCLEAN;
                        goto out;
                }

                ret = verify_one_dev_extent(fs_info, chunk_offset, devid,
                                            physical_offset, physical_len);
                if (ret < 0)
                        goto out;
                prev_devid = devid;
                prev_dev_ext_end = physical_offset + physical_len;

                ret = btrfs_next_item(root, path);
                if (ret < 0)
                        goto out;
                if (ret > 0) {
                        ret = 0;
                        break;
                }
        }

        /* Ensure all chunks have corresponding dev extents */
        ret = verify_chunk_dev_extent_mapping(fs_info);
out:
        btrfs_free_path(path);
        return ret;
}

/*
 * Check whether the given block group or device is pinned by any inode being
 * used as a swapfile.
 */
bool btrfs_pinned_by_swapfile(struct btrfs_fs_info *fs_info, void *ptr)
{
        struct btrfs_swapfile_pin *sp;
        struct rb_node *node;

        spin_lock(&fs_info->swapfile_pins_lock);
        node = fs_info->swapfile_pins.rb_node;
        while (node) {
                sp = rb_entry(node, struct btrfs_swapfile_pin, node);
                if (ptr < sp->ptr)
                        node = node->rb_left;
                else if (ptr > sp->ptr)
                        node = node->rb_right;
                else
                        break;
        }
        spin_unlock(&fs_info->swapfile_pins_lock);
        return node != NULL;
}