// 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 "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"
#include "zoned.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);
        btrfs_destroy_dev_zone_info(device);
        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_kmalloc(GFP_KERNEL, 0);
        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;
}

static bool device_path_matched(const char *path, struct btrfs_device *device)
{
        int found;

        rcu_read_lock();
        found = strcmp(rcu_str_deref(device->name), path);
        rcu_read_unlock();

        return found == 0;
}

/*
 *  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;

        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->name)
                                continue;
                        if (path && !device_path_matched(path, device))
                                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;
}

/*
 * 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);

                /*
                 * 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) {
                        int error;
                        dev_t path_dev;

                        error = lookup_bdev(path, &path_dev);
                        if (error) {
                                mutex_unlock(&fs_devices->device_list_mutex);
                                return ERR_PTR(error);
                        }

                        if (device->bdev->bd_dev != path_dev) {
                                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);
                        }
                        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;

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

        mutex_lock(&orig->device_list_mutex);
        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++;
        }
        mutex_unlock(&orig->device_list_mutex);
        return fs_devices;
error:
        mutex_unlock(&orig->device_list_mutex);
        free_fs_devices(fs_devices);
        return ERR_PTR(ret);
}

static void __btrfs_free_extra_devids(struct btrfs_fs_devices *fs_devices,
                                      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);
                }
                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)
{
        struct btrfs_device *latest_dev = NULL;
        struct btrfs_fs_devices *seed_dev;

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

        list_for_each_entry(seed_dev, &fs_devices->seed_list, seed_list)
                __btrfs_free_extra_devids(seed_dev, &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 (test_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);
        btrfs_destroy_dev_zone_info(device);

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

        /* 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);

        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;

        flags |= FMODE_EXCL;

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

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

        return 0;
}

static int devid_cmp(void *priv, struct list_head *a, 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, u64 bytenr_orig)
{
        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_orig ||
            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, bytenr_orig;
        int ret;

        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
         */
        flags |= FMODE_EXCL;

        bdev = blkdev_get_by_path(path, flags, holder);
        if (IS_ERR(bdev))
                return ERR_CAST(bdev);

        bytenr_orig = btrfs_sb_offset(0);
        ret = btrfs_sb_log_location_bdev(bdev, 0, READ, &bytenr);
        if (ret)
                return ERR_PTR(ret);

        disk_super = btrfs_read_disk_super(bdev, bytenr, bytenr_orig);
        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 - 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);
        case BTRFS_CHUNK_ALLOC_ZONED:
                /*
                 * We don't care about the starting region like regular
                 * allocator, because we anyway use/reserve the first two zones
                 * for superblock logging.
                 */
                return ALIGN(start, device->zone_info->zone_size);
        default:
                BUG();
        }
}

static bool dev_extent_hole_check_zoned(struct btrfs_device *device,
                                        u64 *hole_start, u64 *hole_size,
                                        u64 num_bytes)
{
        u64 zone_size = device->zone_info->zone_size;
        u64 pos;
        int ret;
        bool changed = false;

        ASSERT(IS_ALIGNED(*hole_start, zone_size));

        while (*hole_size > 0) {
                pos = btrfs_find_allocatable_zones(device, *hole_start,
                                                   *hole_start + *hole_size,
                                                   num_bytes);
                if (pos != *hole_start) {
                        *hole_size = *hole_start + *hole_size - pos;
                        *hole_start = pos;
                        changed = true;
                        if (*hole_size < num_bytes)
                                break;
                }

                ret = btrfs_ensure_empty_zones(device, pos, num_bytes);

                /* Range is ensured to be empty */
                if (!ret)
                        return changed;

                /* Given hole range was invalid (outside of device) */
                if (ret == -ERANGE) {
                        *hole_start += *hole_size;
                        *hole_size = 0;
                        return 1;
                }

                *hole_start += zone_size;
                *hole_size -= zone_size;
                changed = true;
        }

        return changed;
}

/**
 * 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_size 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;

        for (;;) {
                /*
                 * 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;
                case BTRFS_CHUNK_ALLOC_ZONED:
                        if (dev_extent_hole_check_zoned(device, hole_start,
                                                        hole_size, num_bytes)) {
                                changed = true;
                                /*
                                 * The changed hole can contain pending extent.
                                 * Loop again to check that.
                                 */
                                continue;
                        }
                        break;
                default:
                        BUG();
                }

                break;
        }

        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);

        WARN_ON(device->zone_info &&
                !IS_ALIGNED(num_bytes, device->zone_info->zone_size));

        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 (1) {
                l = path->nodes[0];
                slot = path->slots[0];
                if (slot >= btrfs_header_nritems(l)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret == 0)
                                continue;
                        if (ret < 0)
                                goto out;

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

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

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

                if (key.type != BTRFS_DEV_EXTENT_KEY)
                        goto next;

                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;

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.
 */
static void update_dev_time(const char *path_name)
{
        struct file *filp;

        filp = filp_open(path_name, O_RDWR, 0);
        if (IS_ERR(filp))
                return;
        file_update_time(filp);
        filp_close(filp, NULL);
}

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;

                if (bdev_is_zoned(bdev)) {
                        btrfs_reset_sb_log_zones(bdev, copy_num);
                        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;

        mutex_lock(&uuid_mutex);

        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 &&
                    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);
        }

        mutex_unlock(&uuid_mutex);
        ret = btrfs_shrink_device(device, 0);
        if (!ret)
                btrfs_reada_remove_dev(device);
        mutex_lock(&uuid_mutex);
        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:
        mutex_unlock(&uuid_mutex);
        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);
        else
                device = btrfs_find_device(fs_info->fs_devices, devid, dev_uuid,
                                           disk_super->fsid);

        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);
                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);
                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 (!btrfs_check_device_zone_type(fs_info, bdev)) {
                ret = -EINVAL;
                goto error;
        }

        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);

        device->fs_info = fs_info;
        device->bdev = bdev;

        ret = btrfs_get_dev_zone_info(device);
        if (ret)
                goto error_free_device;

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

        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;
        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) {
                btrfs_clear_sb_rdonly(sb);
                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)
                btrfs_set_sb_rdonly(sb);
        if (trans)
                btrfs_end_transaction(trans);
error_free_zone:
        btrfs_destroy_dev_zone_info(device);
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 logical %llu length %llu",
                           logical, length);
                return ERR_PTR(-EINVAL);
        }