fs/btrfs/volumes.c

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

#include <linux/sched.h>
#include <linux/bio.h>
#include <linux/slab.h>
#include <linux/buffer_head.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 "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 "math.h"
#include "dev-replace.h"
#include "sysfs.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,
		.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,
		.raid_name	= "raid1",
		.bg_flag	= BTRFS_BLOCK_GROUP_RAID1,
		.mindev_error	= BTRFS_ERROR_DEV_RAID1_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,
		.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,
		.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,
		.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,
		.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,
		.raid_name	= "raid6",
		.bg_flag	= BTRFS_BLOCK_GROUP_RAID6,
		.mindev_error	= BTRFS_ERROR_DEV_RAID6_MIN_NOT_MET,
	},
};

const char *get_raid_name(enum btrfs_raid_types type)
{
	if (type >= BTRFS_NR_RAID_TYPES)
		return NULL;

	return btrfs_raid_array[type].raid_name;
}

static int init_first_rw_device(struct btrfs_trans_handle *trans,
				struct btrfs_fs_info *fs_info);
static int btrfs_relocate_sys_chunks(struct btrfs_fs_info *fs_info);
static void __btrfs_reset_dev_stats(struct btrfs_device *dev);
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, openning/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!
 *
 * 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)
 *
 * 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
 *
 * 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
 *   volume_mutex
 *     device_list_mutex
 *       chunk_mutex
 *     balance_mutex
 *
 *
 * Exclusive operations, BTRFS_FS_EXCL_OP
 * ======================================
 *
 * 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
 *
 * BTRFS_FS_EXCL_OP flag is set and cleared using atomic operations.
 * During the course of Paused state, the BTRFS_FS_EXCL_OP 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.
 * BTRFS_FS_EXCL_OP flag is cleared when the device operation is canceled or
 * completed.
 */

DEFINE_MUTEX(uuid_mutex);
static LIST_HEAD(fs_uuids);
struct list_head *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
 *
 * 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)
{
	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->resized_devices);
	INIT_LIST_HEAD(&fs_devs->alloc_list);
	INIT_LIST_HEAD(&fs_devs->fs_list);
	if (fsid)
		memcpy(fs_devs->fsid, fsid, BTRFS_FSID_SIZE);

	return fs_devs;
}

void btrfs_free_device(struct btrfs_device *device)
{
	rcu_string_free(device->name);
	bio_put(device->flush_bio);
	kfree(device);
}

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

static void btrfs_kobject_uevent(struct block_device *bdev,
				 enum kobject_action action)
{
	int ret;

	ret = kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, action);
	if (ret)
		pr_warn("BTRFS: Sending event '%d' to kobject: '%s' (%p): failed\n",
			action,
			kobject_name(&disk_to_dev(bdev->bd_disk)->kobj),
			&disk_to_dev(bdev->bd_disk)->kobj);
}

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(void)
{
	struct btrfs_device *dev;

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

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

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

	spin_lock_init(&dev->io_lock);

	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);

	return dev;
}

/*
 * Find a device specified by @devid or @uuid in the list of @fs_devices, or
 * return NULL.
 *
 * If devid and uuid are both specified, the match must be exact, otherwise
 * only devid is used.
 */
static struct btrfs_device *find_device(struct btrfs_fs_devices *fs_devices,
		u64 devid, const u8 *uuid)
{
	struct btrfs_device *dev;

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

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

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

static int
btrfs_get_bdev_and_sb(const char *device_path, fmode_t flags, void *holder,
		      int flush, struct block_device **bdev,
		      struct buffer_head **bh)
{
	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);
	*bh = btrfs_read_dev_super(*bdev);
	if (IS_ERR(*bh)) {
		ret = PTR_ERR(*bh);
		blkdev_put(*bdev, flags);
		goto error;
	}

	return 0;

error:
	*bdev = NULL;
	*bh = NULL;
	return ret;
}

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

	struct bio *old_head;

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

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

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

	bdi = device->bdev->bd_bdi;

loop:
	spin_lock(&device->io_lock);

loop_lock:
	num_run = 0;

	/* take all the bios off the list at once and process them
	 * later on (without the lock held).  But, remember the
	 * tail and other pointers so the bios can be properly reinserted
	 * into the list if we hit congestion
	 */
	if (!force_reg && device->pending_sync_bios.head) {
		pending_bios = &device->pending_sync_bios;
		force_reg = 1;
	} else {
		pending_bios = &device->pending_bios;
		force_reg = 0;
	}

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

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

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

	spin_unlock(&device->io_lock);

	while (pending) {

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

		cur = pending;
		pending = pending->bi_next;
		cur->bi_next = NULL;

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

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

		btrfsic_submit_bio(cur);
		num_run++;
		batch_run++;

		cond_resched();

		/*
		 * we made progress, there is more work to do and the bdi
		 * is now congested.  Back off and let other work structs
		 * run instead
		 */
		if (pending && bdi_write_congested(bdi) && batch_run > 8 &&
		    fs_info->fs_devices->open_devices > 1) {
			struct io_context *ioc;

			ioc = current->io_context;

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

			spin_unlock(&device->io_lock);
			btrfs_queue_work(fs_info->submit_workers,
					 &device->work);
			goto done;
		}
	}

	cond_resched();
	if (again)
		goto loop;

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

done:
	blk_finish_plug(&plug);
}

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

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

/*
 *  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.
 */
static void 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;

	list_for_each_entry_safe(fs_devices, tmp_fs_devices, &fs_uuids, fs_list) {
		mutex_lock(&fs_devices->device_list_mutex);
		if (fs_devices->opened) {
			mutex_unlock(&fs_devices->device_list_mutex);
			continue;
		}

		list_for_each_entry_safe(device, tmp_device,
					 &fs_devices->devices, dev_list) {
			int not_found = 0;

			if (skip_device && skip_device == device)
				continue;
			if (path && !device->name)
				continue;

			rcu_read_lock();
			if (path)
				not_found = strcmp(rcu_str_deref(device->name),
						   path);
			rcu_read_unlock();
			if (not_found)
				continue;

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

			if (fs_devices->num_devices == 0)
				break;
		}
		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);
		}
	}
}

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 buffer_head *bh;
	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, &bh);
	if (ret)
		return ret;

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

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

	device->generation = btrfs_super_generation(disk_super);

	if (btrfs_super_flags(disk_super) & BTRFS_SUPER_FLAG_SEEDING) {
		clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
		fs_devices->seeding = 1;
	} 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 = 1;

	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);
	}
	brelse(bh);

	return 0;

error_brelse:
	brelse(bh);
	blkdev_put(bdev, flags);

	return -EINVAL;
}

/*
 * 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;
	struct rcu_string *name;
	u64 found_transid = btrfs_super_generation(disk_super);
	u64 devid = btrfs_stack_device_id(&disk_super->dev_item);

	fs_devices = find_fsid(disk_super->fsid);
	if (!fs_devices) {
		fs_devices = alloc_fs_devices(disk_super->fsid);
		if (IS_ERR(fs_devices))
			return ERR_CAST(fs_devices);

		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 = find_device(fs_devices, devid,
				disk_super->dev_item.uuid);
	}

	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\n",
				disk_super->label, devid, found_transid, path);
		else
			pr_info("BTRFS: device fsid %pU devid %llu transid %llu %s\n",
				disk_super->fsid, devid, found_transid, path);

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

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

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

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

			if (device->bdev != path_bdev) {
				bdput(path_bdev);
				mutex_unlock(&fs_devices->device_list_mutex);
				btrfs_warn_in_rcu(device->fs_info,
			"duplicate device fsid:devid for %pU:%llu old:%s new:%s",
					disk_super->fsid, devid,
					rcu_str_deref(device->name), path);
				return ERR_PTR(-EEXIST);
			}
			bdput(path_bdev);
			btrfs_info_in_rcu(device->fs_info,
				"device fsid %pU devid %llu moved old:%s new:%s",
				disk_super->fsid, devid,
				rcu_str_deref(device->name), path);
		}

		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->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;

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

	mutex_lock(&orig->device_list_mutex);
	fs_devices->total_devices = orig->total_devices;

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

		device = btrfs_alloc_device(NULL, &orig_dev->devid,
					    orig_dev->uuid);
		if (IS_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);
				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(-ENOMEM);
}

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

	mutex_lock(&uuid_mutex);
again:
	/* This is the initialized path, it is safe to release the devices. */
	list_for_each_entry_safe(device, next, &fs_devices->devices, dev_list) {
		if (test_bit(BTRFS_DEV_STATE_IN_FS_METADATA,
							&device->dev_state)) {
			if (!test_bit(BTRFS_DEV_STATE_REPLACE_TGT,
			     &device->dev_state) &&
			     (!latest_dev ||
			      device->generation > latest_dev->generation)) {
				latest_dev = device;
			}
			continue;
		}

		if (device->devid == BTRFS_DEV_REPLACE_DEVID) {
			/*
			 * In the first step, keep the device which has
			 * the correct fsid and the devid that is used
			 * for the dev_replace procedure.
			 * In the second step, the dev_replace state is
			 * read from the device tree and it is known
			 * whether the procedure is really active or
			 * not, which means whether this device is
			 * used or whether it should be removed.
			 */
			if (step == 0 || test_bit(BTRFS_DEV_STATE_REPLACE_TGT,
						  &device->dev_state)) {
				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);
			if (!test_bit(BTRFS_DEV_STATE_REPLACE_TGT,
				      &device->dev_state))
				fs_devices->rw_devices--;
		}
		list_del_init(&device->dev_list);
		fs_devices->num_devices--;
		btrfs_free_device(device);
	}

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

	fs_devices->latest_bdev = latest_dev->bdev;

	mutex_unlock(&uuid_mutex);
}

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

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

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;
	struct btrfs_device *new_device;
	struct rcu_string *name;

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

	new_device = btrfs_alloc_device(NULL, &device->devid,
					device->uuid);
	BUG_ON(IS_ERR(new_device)); /* -ENOMEM */

	/* Safe because we are under uuid_mutex */
	if (device->name) {
		name = rcu_string_strdup(device->name->str, GFP_NOFS);
		BUG_ON(!name); /* -ENOMEM */
		rcu_assign_pointer(new_device->name, name);
	}

	list_replace_rcu(&device->dev_list, &new_device->dev_list);
	new_device->fs_devices = device->fs_devices;

	call_rcu(&device->rcu, free_device_rcu);
}

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

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

	mutex_lock(&fs_devices->device_list_mutex);
	list_for_each_entry_safe(device, tmp, &fs_devices->devices, dev_list) {
		btrfs_close_one_device(device);
	}
	mutex_unlock(&fs_devices->device_list_mutex);

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

	return 0;
}

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

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

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

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;
	int ret = 0;

	flags |= FMODE_EXCL;

	list_for_each_entry(device, &fs_devices->devices, dev_list) {
		/* Just open everything we can; ignore failures here */
		if (btrfs_open_one_device(fs_devices, device, flags, holder))
			continue;

		if (!latest_dev ||
		    device->generation > latest_dev->generation)
			latest_dev = device;
	}
	if (fs_devices->open_devices == 0) {
		ret = -EINVAL;
		goto out;
	}
	fs_devices->opened = 1;
	fs_devices->latest_bdev = latest_dev->bdev;
	fs_devices->total_rw_bytes = 0;
out:
	return ret;
}

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);

	mutex_lock(&fs_devices->device_list_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);
	}
	mutex_unlock(&fs_devices->device_list_mutex);

	return ret;
}

static void btrfs_release_disk_super(struct page *page)
{
	kunmap(page);
	put_page(page);
}

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

	/* make sure our super fits in the device */
	if (bytenr + PAGE_SIZE >= i_size_read(bdev->bd_inode))
		return 1;

	/* make sure our super fits in the page */
	if (sizeof(**disk_super) > PAGE_SIZE)
		return 1;

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

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

	if (IS_ERR_OR_NULL(*page))
		return 1;

	p = kmap(*page);

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

	if (btrfs_super_bytenr(*disk_super) != bytenr ||
	    btrfs_super_magic(*disk_super) != BTRFS_MAGIC) {
		btrfs_release_disk_super(*page);
		return 1;
	}

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

	return 0;
}

/*
 * 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;
	struct page *page;
	u64 bytenr;

	lockdep_assert_held(&uuid_mutex);

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

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

	if (btrfs_read_disk_super(bdev, bytenr, &page, &disk_super)) {
		device = ERR_PTR(-EINVAL);
		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(page);

error_bdev_put:
	blkdev_put(bdev, flags);

	return device;
}

static int contains_pending_extent(struct btrfs_transaction *transaction,
				   struct btrfs_device *device,
				   u64 *start, u64 len)
{
	struct btrfs_fs_info *fs_info = device->fs_info;
	struct extent_map *em;
	struct list_head *search_list = &fs_info->pinned_chunks;
	int ret = 0;
	u64 physical_start = *start;

	if (transaction)
		search_list = &transaction->pending_chunks;
again:
	list_for_each_entry(em, search_list, list) {
		struct map_lookup *map;
		int i;

		map = em->map_lookup;
		for (i = 0; i < map->num_stripes; i++) {
			u64 end;

			if (map->stripes[i].dev != device)
				continue;
			if (map->stripes[i].physical >= physical_start + len ||
			    map->stripes[i].physical + em->orig_block_len <=
			    physical_start)
				continue;
			/*
			 * Make sure that while processing the pinned list we do
			 * not override our *start with a lower value, because
			 * we can have pinned chunks that fall within this
			 * device hole and that have lower physical addresses
			 * than the pending chunks we processed before. If we
			 * do not take this special care we can end up getting
			 * 2 pending chunks that start at the same physical
			 * device offsets because the end offset of a pinned
			 * chunk can be equal to the start offset of some
			 * pending chunk.
			 */
			end = map->stripes[i].physical + em->orig_block_len;
			if (end > *start) {
				*start = end;
				ret = 1;
			}
		}
	}
	if (search_list != &fs_info->pinned_chunks) {
		search_list = &fs_info->pinned_chunks;
		goto again;
	}

	return ret;
}


/*
 * 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.
 */
int find_free_dev_extent_start(struct btrfs_transaction *transaction,
			       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;

	/*
	 * 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.
	 */
	search_start = max_t(u64, search_start, SZ_1M);

	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;

			/*
			 * Have to check before we set max_hole_start, otherwise
			 * we could end up sending back this offset anyway.
			 */
			if (contains_pending_extent(transaction, device,
						    &search_start,
						    hole_size)) {
				if (key.offset >= search_start) {
					hole_size = key.offset - search_start;
				} else {
					WARN_ON_ONCE(1);
					hole_size = 0;
				}
			}

			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 (contains_pending_extent(transaction, device, &search_start,
					    hole_size)) {
			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_trans_handle *trans,
			 struct btrfs_device *device, u64 num_bytes,
			 u64 *start, u64 *len)
{
	/* FIXME use last free of some kind */
	return find_free_dev_extent_start(trans->transaction, 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.map_tree;
	read_lock(&em_tree->lock);
	n = rb_last(&em_tree->map);
	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;

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

	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->fsid, 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_fs_info *fs_info,
			     struct btrfs_device *device)
{
	struct btrfs_root *root = 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 btrfs_assign_next_active_device(struct btrfs_device *device,
				     struct btrfs_device *this_dev)
{
	struct btrfs_fs_info *fs_info = device->fs_info;
	struct btrfs_device *next_device;

	if (this_dev)
		next_device = this_dev;
	else
		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;
}

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 = fs_devices->num_devices;
	btrfs_dev_replace_read_lock(&fs_info->dev_replace);
	if (btrfs_dev_replace_is_ongoing(&fs_info->dev_replace)) {
		WARN_ON(num_devices < 1);
		num_devices--;
	}
	btrfs_dev_replace_read_unlock(&fs_info->dev_replace);

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

	ret = btrfs_find_device_by_devspec(fs_info, devid, device_path,
					   &device);
	if (ret)
		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);
	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(fs_info, device);
	if (ret)
		goto error_undo;

	clear_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
	btrfs_scrub_cancel_dev(fs_info, 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_rm_device_link(fs_devices, 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(device->bdev, device->name->str);

	btrfs_close_bdev(device);
	call_rcu(&device->rcu, free_device_rcu);

	if (cur_devices->open_devices == 0) {
		while (fs_devices) {
			if (fs_devices->seed == cur_devices) {
				fs_devices->seed = cur_devices->seed;
				break;
			}
			fs_devices = fs_devices->seed;
		}
		cur_devices->seed = NULL;
		close_fs_devices(cur_devices);
		free_fs_devices(cur_devices);
	}

out:
	mutex_unlock(&uuid_mutex);
	return ret;

error_undo:
	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_fs_info *fs_info,
				      struct btrfs_device *srcdev)
{
	struct btrfs_fs_devices *fs_devices = srcdev->fs_devices;

	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &srcdev->dev_state)) {
		/* zero out the old super if it is writable */
		btrfs_scratch_superblocks(srcdev->bdev, srcdev->name->str);
	}

	btrfs_close_bdev(srcdev);
	call_rcu(&srcdev->rcu, free_device_rcu);

	/* if this is no devs we rather delete the fs_devices */
	if (!fs_devices->num_devices) {
		struct btrfs_fs_devices *tmp_fs_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);

		tmp_fs_devices = fs_info->fs_devices;
		while (tmp_fs_devices) {
			if (tmp_fs_devices->seed == fs_devices) {
				tmp_fs_devices->seed = fs_devices->seed;
				break;
			}
			tmp_fs_devices = tmp_fs_devices->seed;
		}
		fs_devices->seed = NULL;
		close_fs_devices(fs_devices);
		free_fs_devices(fs_devices);
	}
}

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

	WARN_ON(!tgtdev);
	mutex_lock(&fs_devices->device_list_mutex);

	btrfs_sysfs_rm_device_link(fs_devices, 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->bdev, tgtdev->name->str);

	btrfs_close_bdev(tgtdev);
	call_rcu(&tgtdev->rcu, free_device_rcu);
}

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

	*device = NULL;
	ret = btrfs_get_bdev_and_sb(device_path, FMODE_READ,
				    fs_info->bdev_holder, 0, &bdev, &bh);
	if (ret)
		return ret;
	disk_super = (struct btrfs_super_block *)bh->b_data;
	devid = btrfs_stack_device_id(&disk_super->dev_item);
	dev_uuid = disk_super->dev_item.uuid;
	*device = btrfs_find_device(fs_info, devid, dev_uuid, disk_super->fsid);
	brelse(bh);
	if (!*device)
		ret = -ENOENT;
	blkdev_put(bdev, FMODE_READ);
	return ret;
}

int btrfs_find_device_missing_or_by_path(struct btrfs_fs_info *fs_info,
					 const char *device_path,
					 struct btrfs_device **device)
{
	*device = NULL;
	if (strcmp(device_path, "missing") == 0) {
		struct list_head *devices;
		struct btrfs_device *tmp;

		devices = &fs_info->fs_devices->devices;
		list_for_each_entry(tmp, devices, dev_list) {
			if (test_bit(BTRFS_DEV_STATE_IN_FS_METADATA,
					&tmp->dev_state) && !tmp->bdev) {
				*device = tmp;
				break;
			}
		}

		if (!*device)
			return BTRFS_ERROR_DEV_MISSING_NOT_FOUND;

		return 0;
	} else {
		return btrfs_find_device_by_path(fs_info, device_path, device);
	}
}

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

	if (devid) {
		ret = 0;
		*device = btrfs_find_device(fs_info, devid, NULL, NULL);
		if (!*device)
			ret = -ENOENT;
	} else {
		if (!devpath || !devpath[0])
			return -EINVAL;

		ret = btrfs_find_device_missing_or_by_path(fs_info, devpath,
							   device);
	}
	return ret;
}

/*
 * 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;

	seed_devices = alloc_fs_devices(NULL);
	if (IS_ERR(seed_devices))
		return PTR_ERR(seed_devices);

	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;

	mutex_lock(&fs_info->chunk_mutex);
	list_splice_init(&fs_devices->alloc_list, &seed_devices->alloc_list);
	mutex_unlock(&fs_info->chunk_mutex);

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

	generate_random_uuid(fs_devices->fsid);
	memcpy(fs_info->fsid, 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)
{
	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, 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 unlocked = false;

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

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

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

	filemap_write_and_wait(bdev->bd_inode->i_mapping);

	mutex_lock(&fs_devices->device_list_mutex);
	list_for_each_entry(device, &fs_devices->devices, dev_list) {
		if (device->bdev == bdev) {
			ret = -EEXIST;
			mutex_unlock(
				&fs_devices->device_list_mutex);
			goto error;
		}
	}
	mutex_unlock(&fs_devices->device_list_mutex);

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

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

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

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

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

	device->fs_devices = fs_devices;

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

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

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

	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);

	/* add sysfs device entry */
	btrfs_sysfs_add_device_link(fs_devices, device);

	/*
	 * 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);
	mutex_unlock(&fs_devices->device_list_mutex);

	if (seeding_dev) {
		mutex_lock(&fs_info->chunk_mutex);
		ret = init_first_rw_device(trans, fs_info);
		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) {
		char fsid_buf[BTRFS_UUID_UNPARSED_SIZE];

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

		/* Sprouting would change fsid of the mounted root,
		 * so rename the fsid on the sysfs
		 */
		snprintf(fsid_buf, BTRFS_UUID_UNPARSED_SIZE, "%pU",
						fs_info->fsid);
		if (kobject_rename(&fs_devices->fsid_kobj, fsid_buf))
			btrfs_warn(fs_info,
				   "sysfs: failed to create fsid for sprout");
	}

	ret = btrfs_commit_transaction(trans);

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

		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);
	}

	/* Update ctime/mtime for libblkid */
	update_dev_time(device_path);
	return ret;

error_sysfs:
	btrfs_sysfs_rm_device_link(fs_devices, device);
	mutex_lock(&fs_info->fs_devices->device_list_mutex);
	mutex_lock(&fs_info->chunk_mutex);
	list_del_rcu(&device->dev_list);
	list_del(&device->dev_alloc_list);
	fs_info->fs_devices->num_devices--;
	fs_info->fs_devices->open_devices--;
	fs_info->fs_devices->rw_devices--;
	fs_info->fs_devices->total_devices--;
	fs_info->fs_devices->total_rw_bytes -= device->total_bytes;
	atomic64_sub(device->total_bytes, &fs_info->free_chunk_space);
	btrfs_set_super_total_bytes(fs_info->super_copy,
				    orig_super_total_bytes);
	btrfs_set_super_num_devices(fs_info->super_copy,
				    orig_super_num_devices);
	mutex_unlock(&fs_info->chunk_mutex);
	mutex_unlock(&fs_info->fs_devices->device_list_mutex);
error_trans:
	if (seeding_dev)
		sb->s_flags |= SB_RDONLY;
	if (trans)
		btrfs_end_transaction(trans);
error_free_device:
	btrfs_free_device(device);
error:
	blkdev_put(bdev, FMODE_EXCL);
	if (seeding_dev && !unlocked) {
		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;
	struct btrfs_fs_devices *fs_devices;
	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;
	}

	fs_devices = fs_info->fs_devices;

	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->resized_list))
		list_add_tail(&device->resized_list,
			      &fs_devices->resized_devices);
	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;
}

static struct extent_map *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.map_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);
	}

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

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

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

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

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

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

		if (map->stripes[i].dev) {
			ret = btrfs_update_device(trans, map->stripes[i].dev);
			if (ret) {
				mutex_unlock(&fs_devices->device_list_mutex);
				btrfs_abort_transaction(trans, ret);
				goto out;
			}
		}
	}
	mutex_unlock(&fs_devices->device_list_mutex);

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

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

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

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

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

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

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

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

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

	/*
	 * We add the kobjects here (and after forcing data chunk creation)
	 * since relocation is the only place we'll create chunks of a new
	 * type at runtime.  The only place where we'll remove the last
	 * chunk of a type is the call immediately below this one.  Even
	 * so, we're protected against races with the cleaner thread since
	 * we're covered by the delete_unused_bgs_mutex.
	 */
	btrfs_add_raid_kobjects(fs_info);

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

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

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

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

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

	while (1) {
		mutex_lock(&fs_info->delete_unused_bgs_mutex);
		ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0);
		if (ret < 0) {
			mutex_unlock(&fs_info->delete_unused_bgs_mutex);
			goto error;
		}
		BUG_ON(ret == 0); /* Corruption */

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

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

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

		if (chunk_type & BTRFS_BLOCK_GROUP_SYSTEM) {
			ret = btrfs_relocate_chunk(fs_info, found_key.offset);
			if (ret == -ENOSPC)
				failed++;
			else
				BUG_ON(ret);
		}
		mutex_unlock(&fs_info->delete_unused_bgs_mutex);

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

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

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

	if (chunk_type & BTRFS_BLOCK_GROUP_DATA) {
		spin_lock(&fs_info->data_sinfo->lock);
		bytes_used = fs_info->data_sinfo->bytes_used;
		spin_unlock(&fs_info->data_sinfo->lock);

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

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

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

			btrfs_add_raid_kobjects(fs_info);

			return 1;
		}
	}
	return 0;
}

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

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

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

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

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

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

	memzero_extent_buffer(leaf, (unsigned long)item, sizeof(*item));

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

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

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

static int del_balance_item(struct btrfs_fs_info *fs_info)
{
	struct btrfs_root *root = fs_info->tree_root;
	struct btrfs_trans_handle *trans;
	struct btrfs_path *path;
	struct btrfs_key key;
	int ret, err;

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

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

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

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

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

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

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