Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 7855 insertions, 0 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
new file mode 100644
index 000000000..eaf5cd043
--- /dev/null
+++ b/fs/btrfs/volumes.c
@@ -0,0 +1,7855 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2007 Oracle.  All rights reserved.
+ */
+
+#include <linux/sched.h>
+#include <linux/sched/mm.h>
+#include <linux/bio.h>
+#include <linux/slab.h>
+#include <linux/blkdev.h>
+#include <linux/ratelimit.h>
+#include <linux/kthread.h>
+#include <linux/raid/pq.h>
+#include <linux/semaphore.h>
+#include <linux/uuid.h>
+#include <linux/list_sort.h>
+#include <linux/namei.h>
+#include "misc.h"
+#include "ctree.h"
+#include "extent_map.h"
+#include "disk-io.h"
+#include "transaction.h"
+#include "print-tree.h"
+#include "volumes.h"
+#include "raid56.h"
+#include "async-thread.h"
+#include "check-integrity.h"
+#include "rcu-string.h"
+#include "dev-replace.h"
+#include "sysfs.h"
+#include "tree-checker.h"
+#include "space-info.h"
+#include "block-group.h"
+#include "discard.h"
+
+const struct btrfs_raid_attr btrfs_raid_array[BTRFS_NR_RAID_TYPES] = {
+	[BTRFS_RAID_RAID10] = {
+		.sub_stripes	= 2,
+		.dev_stripes	= 1,
+		.devs_max	= 0,	/* 0 == as many as possible */
+		.devs_min	= 4,
+		.tolerated_failures = 1,
+		.devs_increment	= 2,
+		.ncopies	= 2,
+		.nparity        = 0,
+		.raid_name	= "raid10",
+		.bg_flag	= BTRFS_BLOCK_GROUP_RAID10,
+		.mindev_error	= BTRFS_ERROR_DEV_RAID10_MIN_NOT_MET,
+	},
+	[BTRFS_RAID_RAID1] = {
+		.sub_stripes	= 1,
+		.dev_stripes	= 1,
+		.devs_max	= 2,
+		.devs_min	= 2,
+		.tolerated_failures = 1,
+		.devs_increment	= 2,
+		.ncopies	= 2,
+		.nparity        = 0,
+		.raid_name	= "raid1",
+		.bg_flag	= BTRFS_BLOCK_GROUP_RAID1,
+		.mindev_error	= BTRFS_ERROR_DEV_RAID1_MIN_NOT_MET,
+	},
+	[BTRFS_RAID_RAID1C3] = {
+		.sub_stripes	= 1,
+		.dev_stripes	= 1,
+		.devs_max	= 3,
+		.devs_min	= 3,
+		.tolerated_failures = 2,
+		.devs_increment	= 3,
+		.ncopies	= 3,
+		.nparity        = 0,
+		.raid_name	= "raid1c3",
+		.bg_flag	= BTRFS_BLOCK_GROUP_RAID1C3,
+		.mindev_error	= BTRFS_ERROR_DEV_RAID1C3_MIN_NOT_MET,
+	},
+	[BTRFS_RAID_RAID1C4] = {
+		.sub_stripes	= 1,
+		.dev_stripes	= 1,
+		.devs_max	= 4,
+		.devs_min	= 4,
+		.tolerated_failures = 3,
+		.devs_increment	= 4,
+		.ncopies	= 4,
+		.nparity        = 0,
+		.raid_name	= "raid1c4",
+		.bg_flag	= BTRFS_BLOCK_GROUP_RAID1C4,
+		.mindev_error	= BTRFS_ERROR_DEV_RAID1C4_MIN_NOT_MET,
+	},
+	[BTRFS_RAID_DUP] = {
+		.sub_stripes	= 1,
+		.dev_stripes	= 2,
+		.devs_max	= 1,
+		.devs_min	= 1,
+		.tolerated_failures = 0,
+		.devs_increment	= 1,
+		.ncopies	= 2,
+		.nparity        = 0,
+		.raid_name	= "dup",
+		.bg_flag	= BTRFS_BLOCK_GROUP_DUP,
+		.mindev_error	= 0,
+	},
+	[BTRFS_RAID_RAID0] = {
+		.sub_stripes	= 1,
+		.dev_stripes	= 1,
+		.devs_max	= 0,
+		.devs_min	= 2,
+		.tolerated_failures = 0,
+		.devs_increment	= 1,
+		.ncopies	= 1,
+		.nparity        = 0,
+		.raid_name	= "raid0",
+		.bg_flag	= BTRFS_BLOCK_GROUP_RAID0,
+		.mindev_error	= 0,
+	},
+	[BTRFS_RAID_SINGLE] = {
+		.sub_stripes	= 1,
+		.dev_stripes	= 1,
+		.devs_max	= 1,
+		.devs_min	= 1,
+		.tolerated_failures = 0,
+		.devs_increment	= 1,
+		.ncopies	= 1,
+		.nparity        = 0,
+		.raid_name	= "single",
+		.bg_flag	= 0,
+		.mindev_error	= 0,
+	},
+	[BTRFS_RAID_RAID5] = {
+		.sub_stripes	= 1,
+		.dev_stripes	= 1,
+		.devs_max	= 0,
+		.devs_min	= 2,
+		.tolerated_failures = 1,
+		.devs_increment	= 1,
+		.ncopies	= 1,
+		.nparity        = 1,
+		.raid_name	= "raid5",
+		.bg_flag	= BTRFS_BLOCK_GROUP_RAID5,
+		.mindev_error	= BTRFS_ERROR_DEV_RAID5_MIN_NOT_MET,
+	},
+	[BTRFS_RAID_RAID6] = {
+		.sub_stripes	= 1,
+		.dev_stripes	= 1,
+		.devs_max	= 0,
+		.devs_min	= 3,
+		.tolerated_failures = 2,
+		.devs_increment	= 1,
+		.ncopies	= 1,
+		.nparity        = 2,
+		.raid_name	= "raid6",
+		.bg_flag	= BTRFS_BLOCK_GROUP_RAID6,
+		.mindev_error	= BTRFS_ERROR_DEV_RAID6_MIN_NOT_MET,
+	},
+};
+
+const char *btrfs_bg_type_to_raid_name(u64 flags)
+{
+	const int index = btrfs_bg_flags_to_raid_index(flags);
+
+	if (index >= BTRFS_NR_RAID_TYPES)
+		return NULL;
+
+	return btrfs_raid_array[index].raid_name;
+}
+
+/*
+ * Fill @buf with textual description of @bg_flags, no more than @size_buf
+ * bytes including terminating null byte.
+ */
+void btrfs_describe_block_groups(u64 bg_flags, char *buf, u32 size_buf)
+{
+	int i;
+	int ret;
+	char *bp = buf;
+	u64 flags = bg_flags;
+	u32 size_bp = size_buf;
+
+	if (!flags) {
+		strcpy(bp, "NONE");
+		return;
+	}
+
+#define DESCRIBE_FLAG(flag, desc)						\
+	do {								\
+		if (flags & (flag)) {					\
+			ret = snprintf(bp, size_bp, "%s|", (desc));	\
+			if (ret < 0 || ret >= size_bp)			\
+				goto out_overflow;			\
+			size_bp -= ret;					\
+			bp += ret;					\
+			flags &= ~(flag);				\
+		}							\
+	} while (0)
+
+	DESCRIBE_FLAG(BTRFS_BLOCK_GROUP_DATA, "data");
+	DESCRIBE_FLAG(BTRFS_BLOCK_GROUP_SYSTEM, "system");
+	DESCRIBE_FLAG(BTRFS_BLOCK_GROUP_METADATA, "metadata");
+
+	DESCRIBE_FLAG(BTRFS_AVAIL_ALLOC_BIT_SINGLE, "single");
+	for (i = 0; i < BTRFS_NR_RAID_TYPES; i++)
+		DESCRIBE_FLAG(btrfs_raid_array[i].bg_flag,
+			      btrfs_raid_array[i].raid_name);
+#undef DESCRIBE_FLAG
+
+	if (flags) {
+		ret = snprintf(bp, size_bp, "0x%llx|", flags);
+		size_bp -= ret;
+	}
+
+	if (size_bp < size_buf)
+		buf[size_buf - size_bp - 1] = '\0'; /* remove last | */
+
+	/*
+	 * The text is trimmed, it's up to the caller to provide sufficiently
+	 * large buffer
+	 */
+out_overflow:;
+}
+
+static int init_first_rw_device(struct btrfs_trans_handle *trans);
+static int btrfs_relocate_sys_chunks(struct btrfs_fs_info *fs_info);
+static void btrfs_dev_stat_print_on_error(struct btrfs_device *dev);
+static void btrfs_dev_stat_print_on_load(struct btrfs_device *device);
+static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
+			     enum btrfs_map_op op,
+			     u64 logical, u64 *length,
+			     struct btrfs_bio **bbio_ret,
+			     int mirror_num, int need_raid_map);
+
+/*
+ * Device locking
+ * ==============
+ *
+ * There are several mutexes that protect manipulation of devices and low-level
+ * structures like chunks but not block groups, extents or files
+ *
+ * uuid_mutex (global lock)
+ * ------------------------
+ * protects the fs_uuids list that tracks all per-fs fs_devices, resulting from
+ * the SCAN_DEV ioctl registration or from mount either implicitly (the first
+ * device) or requested by the device= mount option
+ *
+ * the mutex can be very coarse and can cover long-running operations
+ *
+ * protects: updates to fs_devices counters like missing devices, rw devices,
+ * seeding, structure cloning, opening/closing devices at mount/umount time
+ *
+ * global::fs_devs - add, remove, updates to the global list
+ *
+ * does not protect: manipulation of the fs_devices::devices list in general
+ * but in mount context it could be used to exclude list modifications by eg.
+ * scan ioctl
+ *
+ * btrfs_device::name - renames (write side), read is RCU
+ *
+ * fs_devices::device_list_mutex (per-fs, with RCU)
+ * ------------------------------------------------
+ * protects updates to fs_devices::devices, ie. adding and deleting
+ *
+ * simple list traversal with read-only actions can be done with RCU protection
+ *
+ * may be used to exclude some operations from running concurrently without any
+ * modifications to the list (see write_all_supers)
+ *
+ * Is not required at mount and close times, because our device list is
+ * protected by the uuid_mutex at that point.
+ *
+ * balance_mutex
+ * -------------
+ * protects balance structures (status, state) and context accessed from
+ * several places (internally, ioctl)
+ *
+ * chunk_mutex
+ * -----------
+ * protects chunks, adding or removing during allocation, trim or when a new
+ * device is added/removed. Additionally it also protects post_commit_list of
+ * individual devices, since they can be added to the transaction's
+ * post_commit_list only with chunk_mutex held.
+ *
+ * cleaner_mutex
+ * -------------
+ * a big lock that is held by the cleaner thread and prevents running subvolume
+ * cleaning together with relocation or delayed iputs
+ *
+ *
+ * Lock nesting
+ * ============
+ *
+ * uuid_mutex
+ *   device_list_mutex
+ *     chunk_mutex
+ *   balance_mutex
+ *
+ *
+ * Exclusive operations
+ * ====================
+ *
+ * Maintains the exclusivity of the following operations that apply to the
+ * whole filesystem and cannot run in parallel.
+ *
+ * - Balance (*)
+ * - Device add
+ * - Device remove
+ * - Device replace (*)
+ * - Resize
+ *
+ * The device operations (as above) can be in one of the following states:
+ *
+ * - Running state
+ * - Paused state
+ * - Completed state
+ *
+ * Only device operations marked with (*) can go into the Paused state for the
+ * following reasons:
+ *
+ * - ioctl (only Balance can be Paused through ioctl)
+ * - filesystem remounted as read-only
+ * - filesystem unmounted and mounted as read-only
+ * - system power-cycle and filesystem mounted as read-only
+ * - filesystem or device errors leading to forced read-only
+ *
+ * The status of exclusive operation is set and cleared atomically.
+ * During the course of Paused state, fs_info::exclusive_operation remains set.
+ * A device operation in Paused or Running state can be canceled or resumed
+ * either by ioctl (Balance only) or when remounted as read-write.
+ * The exclusive status is cleared when the device operation is canceled or
+ * completed.
+ */
+
+DEFINE_MUTEX(uuid_mutex);
+static LIST_HEAD(fs_uuids);
+struct list_head * __attribute_const__ btrfs_get_fs_uuids(void)
+{
+	return &fs_uuids;
+}
+
+/*
+ * alloc_fs_devices - allocate struct btrfs_fs_devices
+ * @fsid:		if not NULL, copy the UUID to fs_devices::fsid
+ * @metadata_fsid:	if not NULL, copy the UUID to fs_devices::metadata_fsid
+ *
+ * Return a pointer to a new struct btrfs_fs_devices on success, or ERR_PTR().
+ * The returned struct is not linked onto any lists and can be destroyed with
+ * kfree() right away.
+ */
+static struct btrfs_fs_devices *alloc_fs_devices(const u8 *fsid,
+						 const u8 *metadata_fsid)
+{
+	struct btrfs_fs_devices *fs_devs;
+
+	fs_devs = kzalloc(sizeof(*fs_devs), GFP_KERNEL);
+	if (!fs_devs)
+		return ERR_PTR(-ENOMEM);
+
+	mutex_init(&fs_devs->device_list_mutex);
+
+	INIT_LIST_HEAD(&fs_devs->devices);
+	INIT_LIST_HEAD(&fs_devs->alloc_list);
+	INIT_LIST_HEAD(&fs_devs->fs_list);
+	INIT_LIST_HEAD(&fs_devs->seed_list);
+	if (fsid)
+		memcpy(fs_devs->fsid, fsid, BTRFS_FSID_SIZE);
+
+	if (metadata_fsid)
+		memcpy(fs_devs->metadata_uuid, metadata_fsid, BTRFS_FSID_SIZE);
+	else if (fsid)
+		memcpy(fs_devs->metadata_uuid, fsid, BTRFS_FSID_SIZE);
+
+	return fs_devs;
+}
+
+void btrfs_free_device(struct btrfs_device *device)
+{
+	WARN_ON(!list_empty(&device->post_commit_list));
+	rcu_string_free(device->name);
+	extent_io_tree_release(&device->alloc_state);
+	bio_put(device->flush_bio);
+	kfree(device);
+}
+
+static void free_fs_devices(struct btrfs_fs_devices *fs_devices)
+{
+	struct btrfs_device *device;
+
+	WARN_ON(fs_devices->opened);
+	while (!list_empty(&fs_devices->devices)) {
+		device = list_entry(fs_devices->devices.next,
+				    struct btrfs_device, dev_list);
+		list_del(&device->dev_list);
+		btrfs_free_device(device);
+	}
+	kfree(fs_devices);
+}
+
+void __exit btrfs_cleanup_fs_uuids(void)
+{
+	struct btrfs_fs_devices *fs_devices;
+
+	while (!list_empty(&fs_uuids)) {
+		fs_devices = list_entry(fs_uuids.next,
+					struct btrfs_fs_devices, fs_list);
+		list_del(&fs_devices->fs_list);
+		free_fs_devices(fs_devices);
+	}
+}
+
+/*
+ * Returns a pointer to a new btrfs_device on success; ERR_PTR() on error.
+ * Returned struct is not linked onto any lists and must be destroyed using
+ * btrfs_free_device.
+ */
+static struct btrfs_device *__alloc_device(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_device *dev;
+
+	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+	if (!dev)
+		return ERR_PTR(-ENOMEM);
+
+	/*
+	 * Preallocate a bio that's always going to be used for flushing device
+	 * barriers and matches the device lifespan
+	 */
+	dev->flush_bio = bio_alloc_bioset(GFP_KERNEL, 0, NULL);
+	if (!dev->flush_bio) {
+		kfree(dev);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	INIT_LIST_HEAD(&dev->dev_list);
+	INIT_LIST_HEAD(&dev->dev_alloc_list);
+	INIT_LIST_HEAD(&dev->post_commit_list);
+
+	atomic_set(&dev->reada_in_flight, 0);
+	atomic_set(&dev->dev_stats_ccnt, 0);
+	btrfs_device_data_ordered_init(dev);
+	INIT_RADIX_TREE(&dev->reada_zones, GFP_NOFS & ~__GFP_DIRECT_RECLAIM);
+	INIT_RADIX_TREE(&dev->reada_extents, GFP_NOFS & ~__GFP_DIRECT_RECLAIM);
+	extent_io_tree_init(fs_info, &dev->alloc_state,
+			    IO_TREE_DEVICE_ALLOC_STATE, NULL);
+
+	return dev;
+}
+
+static noinline struct btrfs_fs_devices *find_fsid(
+		const u8 *fsid, const u8 *metadata_fsid)
+{
+	struct btrfs_fs_devices *fs_devices;
+
+	ASSERT(fsid);
+
+	/* Handle non-split brain cases */
+	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
+		if (metadata_fsid) {
+			if (memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE) == 0
+			    && memcmp(metadata_fsid, fs_devices->metadata_uuid,
+				      BTRFS_FSID_SIZE) == 0)
+				return fs_devices;
+		} else {
+			if (memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE) == 0)
+				return fs_devices;
+		}
+	}
+	return NULL;
+}
+
+static struct btrfs_fs_devices *find_fsid_with_metadata_uuid(
+				struct btrfs_super_block *disk_super)
+{
+
+	struct btrfs_fs_devices *fs_devices;
+
+	/*
+	 * Handle scanned device having completed its fsid change but
+	 * belonging to a fs_devices that was created by first scanning
+	 * a device which didn't have its fsid/metadata_uuid changed
+	 * at all and the CHANGING_FSID_V2 flag set.
+	 */
+	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
+		if (fs_devices->fsid_change &&
+		    memcmp(disk_super->metadata_uuid, fs_devices->fsid,
+			   BTRFS_FSID_SIZE) == 0 &&
+		    memcmp(fs_devices->fsid, fs_devices->metadata_uuid,
+			   BTRFS_FSID_SIZE) == 0) {
+			return fs_devices;
+		}
+	}
+	/*
+	 * Handle scanned device having completed its fsid change but
+	 * belonging to a fs_devices that was created by a device that
+	 * has an outdated pair of fsid/metadata_uuid and
+	 * CHANGING_FSID_V2 flag set.
+	 */
+	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
+		if (fs_devices->fsid_change &&
+		    memcmp(fs_devices->metadata_uuid,
+			   fs_devices->fsid, BTRFS_FSID_SIZE) != 0 &&
+		    memcmp(disk_super->metadata_uuid, fs_devices->metadata_uuid,
+			   BTRFS_FSID_SIZE) == 0) {
+			return fs_devices;
+		}
+	}
+
+	return find_fsid(disk_super->fsid, disk_super->metadata_uuid);
+}
+
+
+static int
+btrfs_get_bdev_and_sb(const char *device_path, fmode_t flags, void *holder,
+		      int flush, struct block_device **bdev,
+		      struct btrfs_super_block **disk_super)
+{
+	int ret;
+
+	*bdev = blkdev_get_by_path(device_path, flags, holder);
+
+	if (IS_ERR(*bdev)) {
+		ret = PTR_ERR(*bdev);
+		goto error;
+	}
+
+	if (flush)
+		filemap_write_and_wait((*bdev)->bd_inode->i_mapping);
+	ret = set_blocksize(*bdev, BTRFS_BDEV_BLOCKSIZE);
+	if (ret) {
+		blkdev_put(*bdev, flags);
+		goto error;
+	}
+	invalidate_bdev(*bdev);
+	*disk_super = btrfs_read_dev_super(*bdev);
+	if (IS_ERR(*disk_super)) {
+		ret = PTR_ERR(*disk_super);
+		blkdev_put(*bdev, flags);
+		goto error;
+	}
+
+	return 0;
+
+error:
+	*bdev = NULL;
+	return ret;
+}
+
+/*
+ * Check if the device in the path matches the device in the given struct device.
+ *
+ * Returns:
+ *   true  If it is the same device.
+ *   false If it is not the same device or on error.
+ */
+static bool device_matched(const struct btrfs_device *device, const char *path)
+{
+	char *device_name;
+	struct block_device *bdev_old;
+	struct block_device *bdev_new;
+
+	/*
+	 * If we are looking for a device with the matching dev_t, then skip
+	 * device without a name (a missing device).
+	 */
+	if (!device->name)
+		return false;
+
+	device_name = kzalloc(BTRFS_PATH_NAME_MAX, GFP_KERNEL);
+	if (!device_name)
+		return false;
+
+	rcu_read_lock();
+	scnprintf(device_name, BTRFS_PATH_NAME_MAX, "%s", rcu_str_deref(device->name));
+	rcu_read_unlock();
+
+	bdev_old = lookup_bdev(device_name);
+	kfree(device_name);
+	if (IS_ERR(bdev_old))
+		return false;
+
+	bdev_new = lookup_bdev(path);
+	if (IS_ERR(bdev_new))
+		return false;
+
+	if (bdev_old == bdev_new)
+		return true;
+
+	return false;
+}
+
+/*
+ *  Search and remove all stale (devices which are not mounted) devices.
+ *  When both inputs are NULL, it will search and release all stale devices.
+ *  path:	Optional. When provided will it release all unmounted devices
+ *		matching this path only.
+ *  skip_dev:	Optional. Will skip this device when searching for the stale
+ *		devices.
+ *  Return:	0 for success or if @path is NULL.
+ * 		-EBUSY if @path is a mounted device.
+ * 		-ENOENT if @path does not match any device in the list.
+ */
+static int btrfs_free_stale_devices(const char *path,
+				     struct btrfs_device *skip_device)
+{
+	struct btrfs_fs_devices *fs_devices, *tmp_fs_devices;
+	struct btrfs_device *device, *tmp_device;
+	int ret = 0;
+
+	lockdep_assert_held(&uuid_mutex);
+
+	if (path)
+		ret = -ENOENT;
+
+	list_for_each_entry_safe(fs_devices, tmp_fs_devices, &fs_uuids, fs_list) {
+
+		mutex_lock(&fs_devices->device_list_mutex);
+		list_for_each_entry_safe(device, tmp_device,
+					 &fs_devices->devices, dev_list) {
+			if (skip_device && skip_device == device)
+				continue;
+			if (path && !device_matched(device, path))
+				continue;
+			if (fs_devices->opened) {
+				/* for an already deleted device return 0 */
+				if (path && ret != 0)
+					ret = -EBUSY;
+				break;
+			}
+
+			/* delete the stale device */
+			fs_devices->num_devices--;
+			list_del(&device->dev_list);
+			btrfs_free_device(device);
+
+			ret = 0;
+		}
+		mutex_unlock(&fs_devices->device_list_mutex);
+
+		if (fs_devices->num_devices == 0) {
+			btrfs_sysfs_remove_fsid(fs_devices);
+			list_del(&fs_devices->fs_list);
+			free_fs_devices(fs_devices);
+		}
+	}
+
+	return ret;
+}
+
+/*
+ * This is only used on mount, and we are protected from competing things
+ * messing with our fs_devices by the uuid_mutex, thus we do not need the
+ * fs_devices->device_list_mutex here.
+ */
+static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices,
+			struct btrfs_device *device, fmode_t flags,
+			void *holder)
+{
+	struct request_queue *q;
+	struct block_device *bdev;
+	struct btrfs_super_block *disk_super;
+	u64 devid;
+	int ret;
+
+	if (device->bdev)
+		return -EINVAL;
+	if (!device->name)
+		return -EINVAL;
+
+	ret = btrfs_get_bdev_and_sb(device->name->str, flags, holder, 1,
+				    &bdev, &disk_super);
+	if (ret)
+		return ret;
+
+	devid = btrfs_stack_device_id(&disk_super->dev_item);
+	if (devid != device->devid)
+		goto error_free_page;
+
+	if (memcmp(device->uuid, disk_super->dev_item.uuid, BTRFS_UUID_SIZE))
+		goto error_free_page;
+
+	device->generation = btrfs_super_generation(disk_super);
+
+	if (btrfs_super_flags(disk_super) & BTRFS_SUPER_FLAG_SEEDING) {
+		if (btrfs_super_incompat_flags(disk_super) &
+		    BTRFS_FEATURE_INCOMPAT_METADATA_UUID) {
+			pr_err(
+		"BTRFS: Invalid seeding and uuid-changed device detected\n");
+			goto error_free_page;
+		}
+
+		clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
+		fs_devices->seeding = true;
+	} else {
+		if (bdev_read_only(bdev))
+			clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
+		else
+			set_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
+	}
+
+	q = bdev_get_queue(bdev);
+	if (!blk_queue_nonrot(q))
+		fs_devices->rotating = true;
+
+	device->bdev = bdev;
+	clear_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
+	device->mode = flags;
+
+	fs_devices->open_devices++;
+	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
+	    device->devid != BTRFS_DEV_REPLACE_DEVID) {
+		fs_devices->rw_devices++;
+		list_add_tail(&device->dev_alloc_list, &fs_devices->alloc_list);
+	}
+	btrfs_release_disk_super(disk_super);
+
+	return 0;
+
+error_free_page:
+	btrfs_release_disk_super(disk_super);
+	blkdev_put(bdev, flags);
+
+	return -EINVAL;
+}
+
+u8 *btrfs_sb_fsid_ptr(struct btrfs_super_block *sb)
+{
+	bool has_metadata_uuid = (btrfs_super_incompat_flags(sb) &
+				  BTRFS_FEATURE_INCOMPAT_METADATA_UUID);
+
+	return has_metadata_uuid ? sb->metadata_uuid : sb->fsid;
+}
+
+/*
+ * Handle scanned device having its CHANGING_FSID_V2 flag set and the fs_devices
+ * being created with a disk that has already completed its fsid change. Such
+ * disk can belong to an fs which has its FSID changed or to one which doesn't.
+ * Handle both cases here.
+ */
+static struct btrfs_fs_devices *find_fsid_inprogress(
+					struct btrfs_super_block *disk_super)
+{
+	struct btrfs_fs_devices *fs_devices;
+
+	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
+		if (memcmp(fs_devices->metadata_uuid, fs_devices->fsid,
+			   BTRFS_FSID_SIZE) != 0 &&
+		    memcmp(fs_devices->metadata_uuid, disk_super->fsid,
+			   BTRFS_FSID_SIZE) == 0 && !fs_devices->fsid_change) {
+			return fs_devices;
+		}
+	}
+
+	return find_fsid(disk_super->fsid, NULL);
+}
+
+
+static struct btrfs_fs_devices *find_fsid_changed(
+					struct btrfs_super_block *disk_super)
+{
+	struct btrfs_fs_devices *fs_devices;
+
+	/*
+	 * Handles the case where scanned device is part of an fs that had
+	 * multiple successful changes of FSID but curently device didn't
+	 * observe it. Meaning our fsid will be different than theirs. We need
+	 * to handle two subcases :
+	 *  1 - The fs still continues to have different METADATA/FSID uuids.
+	 *  2 - The fs is switched back to its original FSID (METADATA/FSID
+	 *  are equal).
+	 */
+	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
+		/* Changed UUIDs */
+		if (memcmp(fs_devices->metadata_uuid, fs_devices->fsid,
+			   BTRFS_FSID_SIZE) != 0 &&
+		    memcmp(fs_devices->metadata_uuid, disk_super->metadata_uuid,
+			   BTRFS_FSID_SIZE) == 0 &&
+		    memcmp(fs_devices->fsid, disk_super->fsid,
+			   BTRFS_FSID_SIZE) != 0)
+			return fs_devices;
+
+		/* Unchanged UUIDs */
+		if (memcmp(fs_devices->metadata_uuid, fs_devices->fsid,
+			   BTRFS_FSID_SIZE) == 0 &&
+		    memcmp(fs_devices->fsid, disk_super->metadata_uuid,
+			   BTRFS_FSID_SIZE) == 0)
+			return fs_devices;
+	}
+
+	return NULL;
+}
+
+static struct btrfs_fs_devices *find_fsid_reverted_metadata(
+				struct btrfs_super_block *disk_super)
+{
+	struct btrfs_fs_devices *fs_devices;
+
+	/*
+	 * Handle the case where the scanned device is part of an fs whose last
+	 * metadata UUID change reverted it to the original FSID. At the same
+	 * time * fs_devices was first created by another constitutent device
+	 * which didn't fully observe the operation. This results in an
+	 * btrfs_fs_devices created with metadata/fsid different AND
+	 * btrfs_fs_devices::fsid_change set AND the metadata_uuid of the
+	 * fs_devices equal to the FSID of the disk.
+	 */
+	list_for_each_entry(fs_devices, &fs_uuids, fs_list) {
+		if (memcmp(fs_devices->fsid, fs_devices->metadata_uuid,
+			   BTRFS_FSID_SIZE) != 0 &&
+		    memcmp(fs_devices->metadata_uuid, disk_super->fsid,
+			   BTRFS_FSID_SIZE) == 0 &&
+		    fs_devices->fsid_change)
+			return fs_devices;
+	}
+
+	return NULL;
+}
+/*
+ * Add new device to list of registered devices
+ *
+ * Returns:
+ * device pointer which was just added or updated when successful
+ * error pointer when failed
+ */
+static noinline struct btrfs_device *device_list_add(const char *path,
+			   struct btrfs_super_block *disk_super,
+			   bool *new_device_added)
+{
+	struct btrfs_device *device;
+	struct btrfs_fs_devices *fs_devices = NULL;
+	struct rcu_string *name;
+	u64 found_transid = btrfs_super_generation(disk_super);
+	u64 devid = btrfs_stack_device_id(&disk_super->dev_item);
+	bool has_metadata_uuid = (btrfs_super_incompat_flags(disk_super) &
+		BTRFS_FEATURE_INCOMPAT_METADATA_UUID);
+	bool fsid_change_in_progress = (btrfs_super_flags(disk_super) &
+					BTRFS_SUPER_FLAG_CHANGING_FSID_V2);
+
+	if (fsid_change_in_progress) {
+		if (!has_metadata_uuid)
+			fs_devices = find_fsid_inprogress(disk_super);
+		else
+			fs_devices = find_fsid_changed(disk_super);
+	} else if (has_metadata_uuid) {
+		fs_devices = find_fsid_with_metadata_uuid(disk_super);
+	} else {
+		fs_devices = find_fsid_reverted_metadata(disk_super);
+		if (!fs_devices)
+			fs_devices = find_fsid(disk_super->fsid, NULL);
+	}
+
+
+	if (!fs_devices) {
+		if (has_metadata_uuid)
+			fs_devices = alloc_fs_devices(disk_super->fsid,
+						      disk_super->metadata_uuid);
+		else
+			fs_devices = alloc_fs_devices(disk_super->fsid, NULL);
+
+		if (IS_ERR(fs_devices))
+			return ERR_CAST(fs_devices);
+
+		fs_devices->fsid_change = fsid_change_in_progress;
+
+		mutex_lock(&fs_devices->device_list_mutex);
+		list_add(&fs_devices->fs_list, &fs_uuids);
+
+		device = NULL;
+	} else {
+		mutex_lock(&fs_devices->device_list_mutex);
+		device = btrfs_find_device(fs_devices, devid,
+				disk_super->dev_item.uuid, NULL, false);
+
+		/*
+		 * If this disk has been pulled into an fs devices created by
+		 * a device which had the CHANGING_FSID_V2 flag then replace the
+		 * metadata_uuid/fsid values of the fs_devices.
+		 */
+		if (fs_devices->fsid_change &&
+		    found_transid > fs_devices->latest_generation) {
+			memcpy(fs_devices->fsid, disk_super->fsid,
+					BTRFS_FSID_SIZE);
+
+			if (has_metadata_uuid)
+				memcpy(fs_devices->metadata_uuid,
+				       disk_super->metadata_uuid,
+				       BTRFS_FSID_SIZE);
+			else
+				memcpy(fs_devices->metadata_uuid,
+				       disk_super->fsid, BTRFS_FSID_SIZE);
+
+			fs_devices->fsid_change = false;
+		}
+	}
+
+	if (!device) {
+		if (fs_devices->opened) {
+			mutex_unlock(&fs_devices->device_list_mutex);
+			return ERR_PTR(-EBUSY);
+		}
+
+		device = btrfs_alloc_device(NULL, &devid,
+					    disk_super->dev_item.uuid);
+		if (IS_ERR(device)) {
+			mutex_unlock(&fs_devices->device_list_mutex);
+			/* we can safely leave the fs_devices entry around */
+			return device;
+		}
+
+		name = rcu_string_strdup(path, GFP_NOFS);
+		if (!name) {
+			btrfs_free_device(device);
+			mutex_unlock(&fs_devices->device_list_mutex);
+			return ERR_PTR(-ENOMEM);
+		}
+		rcu_assign_pointer(device->name, name);
+
+		list_add_rcu(&device->dev_list, &fs_devices->devices);
+		fs_devices->num_devices++;
+
+		device->fs_devices = fs_devices;
+		*new_device_added = true;
+
+		if (disk_super->label[0])
+			pr_info(
+	"BTRFS: device label %s devid %llu transid %llu %s scanned by %s (%d)\n",
+				disk_super->label, devid, found_transid, path,
+				current->comm, task_pid_nr(current));
+		else
+			pr_info(
+	"BTRFS: device fsid %pU devid %llu transid %llu %s scanned by %s (%d)\n",
+				disk_super->fsid, devid, found_transid, path,
+				current->comm, task_pid_nr(current));
+
+	} else if (!device->name || strcmp(device->name->str, path)) {
+		/*
+		 * When FS is already mounted.
+		 * 1. If you are here and if the device->name is NULL that
+		 *    means this device was missing at time of FS mount.
+		 * 2. If you are here and if the device->name is different
+		 *    from 'path' that means either
+		 *      a. The same device disappeared and reappeared with
+		 *         different name. or
+		 *      b. The missing-disk-which-was-replaced, has
+		 *         reappeared now.
+		 *
+		 * We must allow 1 and 2a above. But 2b would be a spurious
+		 * and unintentional.
+		 *
+		 * Further in case of 1 and 2a above, the disk at 'path'
+		 * would have missed some transaction when it was away and
+		 * in case of 2a the stale bdev has to be updated as well.
+		 * 2b must not be allowed at all time.
+		 */
+
+		/*
+		 * For now, we do allow update to btrfs_fs_device through the
+		 * btrfs dev scan cli after FS has been mounted.  We're still
+		 * tracking a problem where systems fail mount by subvolume id
+		 * when we reject replacement on a mounted FS.
+		 */
+		if (!fs_devices->opened && found_transid < device->generation) {
+			/*
+			 * That is if the FS is _not_ mounted and if you
+			 * are here, that means there is more than one
+			 * disk with same uuid and devid.We keep the one
+			 * with larger generation number or the last-in if
+			 * generation are equal.
+			 */
+			mutex_unlock(&fs_devices->device_list_mutex);
+			return ERR_PTR(-EEXIST);
+		}
+
+		/*
+		 * We are going to replace the device path for a given devid,
+		 * make sure it's the same device if the device is mounted
+		 */
+		if (device->bdev) {
+			struct block_device *path_bdev;
+
+			path_bdev = lookup_bdev(path);
+			if (IS_ERR(path_bdev)) {
+				mutex_unlock(&fs_devices->device_list_mutex);
+				return ERR_CAST(path_bdev);
+			}
+
+			if (device->bdev != path_bdev) {
+				bdput(path_bdev);
+				mutex_unlock(&fs_devices->device_list_mutex);
+				/*
+				 * device->fs_info may not be reliable here, so
+				 * pass in a NULL instead. This avoids a
+				 * possible use-after-free when the fs_info and
+				 * fs_info->sb are already torn down.
+				 */
+				btrfs_warn_in_rcu(NULL,
+	"duplicate device %s devid %llu generation %llu scanned by %s (%d)",
+						  path, devid, found_transid,
+						  current->comm,
+						  task_pid_nr(current));
+				return ERR_PTR(-EEXIST);
+			}
+			bdput(path_bdev);
+			btrfs_info_in_rcu(device->fs_info,
+	"devid %llu device path %s changed to %s scanned by %s (%d)",
+					  devid, rcu_str_deref(device->name),
+					  path, current->comm,
+					  task_pid_nr(current));
+		}
+
+		name = rcu_string_strdup(path, GFP_NOFS);
+		if (!name) {
+			mutex_unlock(&fs_devices->device_list_mutex);
+			return ERR_PTR(-ENOMEM);
+		}
+		rcu_string_free(device->name);
+		rcu_assign_pointer(device->name, name);
+		if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) {
+			fs_devices->missing_devices--;
+			clear_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
+		}
+	}
+
+	/*
+	 * Unmount does not free the btrfs_device struct but would zero
+	 * generation along with most of the other members. So just update
+	 * it back. We need it to pick the disk with largest generation
+	 * (as above).
+	 */
+	if (!fs_devices->opened) {
+		device->generation = found_transid;
+		fs_devices->latest_generation = max_t(u64, found_transid,
+						fs_devices->latest_generation);
+	}
+
+	fs_devices->total_devices = btrfs_super_num_devices(disk_super);
+
+	mutex_unlock(&fs_devices->device_list_mutex);
+	return device;
+}
+
+static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig)
+{
+	struct btrfs_fs_devices *fs_devices;
+	struct btrfs_device *device;
+	struct btrfs_device *orig_dev;
+	int ret = 0;
+
+	lockdep_assert_held(&uuid_mutex);
+
+	fs_devices = alloc_fs_devices(orig->fsid, NULL);
+	if (IS_ERR(fs_devices))
+		return fs_devices;
+
+	fs_devices->total_devices = orig->total_devices;
+
+	list_for_each_entry(orig_dev, &orig->devices, dev_list) {
+		struct rcu_string *name;
+
+		device = btrfs_alloc_device(NULL, &orig_dev->devid,
+					    orig_dev->uuid);
+		if (IS_ERR(device)) {
+			ret = PTR_ERR(device);
+			goto error;
+		}
+
+		/*
+		 * This is ok to do without rcu read locked because we hold the
+		 * uuid mutex so nothing we touch in here is going to disappear.
+		 */
+		if (orig_dev->name) {
+			name = rcu_string_strdup(orig_dev->name->str,
+					GFP_KERNEL);
+			if (!name) {
+				btrfs_free_device(device);
+				ret = -ENOMEM;
+				goto error;
+			}
+			rcu_assign_pointer(device->name, name);
+		}
+
+		list_add(&device->dev_list, &fs_devices->devices);
+		device->fs_devices = fs_devices;
+		fs_devices->num_devices++;
+	}
+	return fs_devices;
+error:
+	free_fs_devices(fs_devices);
+	return ERR_PTR(ret);
+}
+
+static void __btrfs_free_extra_devids(struct btrfs_fs_devices *fs_devices,
+				      int step, struct btrfs_device **latest_dev)
+{
+	struct btrfs_device *device, *next;
+
+	/* This is the initialized path, it is safe to release the devices. */
+	list_for_each_entry_safe(device, next, &fs_devices->devices, dev_list) {
+		if (test_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state)) {
+			if (!test_bit(BTRFS_DEV_STATE_REPLACE_TGT,
+				      &device->dev_state) &&
+			    !test_bit(BTRFS_DEV_STATE_MISSING,
+				      &device->dev_state) &&
+			    (!*latest_dev ||
+			     device->generation > (*latest_dev)->generation)) {
+				*latest_dev = device;
+			}
+			continue;
+		}
+
+		/*
+		 * We have already validated the presence of BTRFS_DEV_REPLACE_DEVID,
+		 * in btrfs_init_dev_replace() so just continue.
+		 */
+		if (device->devid == BTRFS_DEV_REPLACE_DEVID)
+			continue;
+
+		if (device->bdev) {
+			blkdev_put(device->bdev, device->mode);
+			device->bdev = NULL;
+			fs_devices->open_devices--;
+		}
+		if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
+			list_del_init(&device->dev_alloc_list);
+			clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
+			fs_devices->rw_devices--;
+		}
+		list_del_init(&device->dev_list);
+		fs_devices->num_devices--;
+		btrfs_free_device(device);
+	}
+
+}
+
+/*
+ * After we have read the system tree and know devids belonging to this
+ * filesystem, remove the device which does not belong there.
+ */
+void btrfs_free_extra_devids(struct btrfs_fs_devices *fs_devices, int step)
+{
+	struct btrfs_device *latest_dev = NULL;
+	struct btrfs_fs_devices *seed_dev;
+
+	mutex_lock(&uuid_mutex);
+	__btrfs_free_extra_devids(fs_devices, step, &latest_dev);
+
+	list_for_each_entry(seed_dev, &fs_devices->seed_list, seed_list)
+		__btrfs_free_extra_devids(seed_dev, step, &latest_dev);
+
+	fs_devices->latest_bdev = latest_dev->bdev;
+
+	mutex_unlock(&uuid_mutex);
+}
+
+static void btrfs_close_bdev(struct btrfs_device *device)
+{
+	if (!device->bdev)
+		return;
+
+	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
+		sync_blockdev(device->bdev);
+		invalidate_bdev(device->bdev);
+	}
+
+	blkdev_put(device->bdev, device->mode);
+}
+
+static void btrfs_close_one_device(struct btrfs_device *device)
+{
+	struct btrfs_fs_devices *fs_devices = device->fs_devices;
+
+	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
+	    device->devid != BTRFS_DEV_REPLACE_DEVID) {
+		list_del_init(&device->dev_alloc_list);
+		fs_devices->rw_devices--;
+	}
+
+	if (device->devid == BTRFS_DEV_REPLACE_DEVID)
+		clear_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state);
+
+	if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) {
+		clear_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
+		fs_devices->missing_devices--;
+	}
+
+	btrfs_close_bdev(device);
+	if (device->bdev) {
+		fs_devices->open_devices--;
+		device->bdev = NULL;
+	}
+	clear_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
+
+	device->fs_info = NULL;
+	atomic_set(&device->dev_stats_ccnt, 0);
+	extent_io_tree_release(&device->alloc_state);
+
+	/*
+	 * Reset the flush error record. We might have a transient flush error
+	 * in this mount, and if so we aborted the current transaction and set
+	 * the fs to an error state, guaranteeing no super blocks can be further
+	 * committed. However that error might be transient and if we unmount the
+	 * filesystem and mount it again, we should allow the mount to succeed
+	 * (btrfs_check_rw_degradable() should not fail) - if after mounting the
+	 * filesystem again we still get flush errors, then we will again abort
+	 * any transaction and set the error state, guaranteeing no commits of
+	 * unsafe super blocks.
+	 */
+	device->last_flush_error = 0;
+
+	/* Verify the device is back in a pristine state  */
+	ASSERT(!test_bit(BTRFS_DEV_STATE_FLUSH_SENT, &device->dev_state));
+	ASSERT(!test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state));
+	ASSERT(list_empty(&device->dev_alloc_list));
+	ASSERT(list_empty(&device->post_commit_list));
+	ASSERT(atomic_read(&device->reada_in_flight) == 0);
+}
+
+static void close_fs_devices(struct btrfs_fs_devices *fs_devices)
+{
+	struct btrfs_device *device, *tmp;
+
+	lockdep_assert_held(&uuid_mutex);
+
+	if (--fs_devices->opened > 0)
+		return;
+
+	list_for_each_entry_safe(device, tmp, &fs_devices->devices, dev_list)
+		btrfs_close_one_device(device);
+
+	WARN_ON(fs_devices->open_devices);
+	WARN_ON(fs_devices->rw_devices);
+	fs_devices->opened = 0;
+	fs_devices->seeding = false;
+	fs_devices->fs_info = NULL;
+}
+
+void btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
+{
+	LIST_HEAD(list);
+	struct btrfs_fs_devices *tmp;
+
+	mutex_lock(&uuid_mutex);
+	close_fs_devices(fs_devices);
+	if (!fs_devices->opened) {
+		list_splice_init(&fs_devices->seed_list, &list);
+
+		/*
+		 * If the struct btrfs_fs_devices is not assembled with any
+		 * other device, it can be re-initialized during the next mount
+		 * without the needing device-scan step. Therefore, it can be
+		 * fully freed.
+		 */
+		if (fs_devices->num_devices == 1) {
+			list_del(&fs_devices->fs_list);
+			free_fs_devices(fs_devices);
+		}
+	}
+
+
+	list_for_each_entry_safe(fs_devices, tmp, &list, seed_list) {
+		close_fs_devices(fs_devices);
+		list_del(&fs_devices->seed_list);
+		free_fs_devices(fs_devices);
+	}
+	mutex_unlock(&uuid_mutex);
+}
+
+static int open_fs_devices(struct btrfs_fs_devices *fs_devices,
+				fmode_t flags, void *holder)
+{
+	struct btrfs_device *device;
+	struct btrfs_device *latest_dev = NULL;
+	struct btrfs_device *tmp_device;
+
+	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;
+
+	return 0;
+}
+
+static int devid_cmp(void *priv, const struct list_head *a,
+		     const struct list_head *b)
+{
+	struct btrfs_device *dev1, *dev2;
+
+	dev1 = list_entry(a, struct btrfs_device, dev_list);
+	dev2 = list_entry(b, struct btrfs_device, dev_list);
+
+	if (dev1->devid < dev2->devid)
+		return -1;
+	else if (dev1->devid > dev2->devid)
+		return 1;
+	return 0;
+}
+
+int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
+		       fmode_t flags, void *holder)
+{
+	int ret;
+
+	lockdep_assert_held(&uuid_mutex);
+	/*
+	 * The device_list_mutex cannot be taken here in case opening the
+	 * underlying device takes further locks like bd_mutex.
+	 *
+	 * We also don't need the lock here as this is called during mount and
+	 * exclusion is provided by uuid_mutex
+	 */
+
+	if (fs_devices->opened) {
+		fs_devices->opened++;
+		ret = 0;
+	} else {
+		list_sort(NULL, &fs_devices->devices, devid_cmp);
+		ret = open_fs_devices(fs_devices, flags, holder);
+	}
+
+	return ret;
+}
+
+void btrfs_release_disk_super(struct btrfs_super_block *super)
+{
+	struct page *page = virt_to_page(super);
+
+	put_page(page);
+}
+
+static struct btrfs_super_block *btrfs_read_disk_super(struct block_device *bdev,
+						       u64 bytenr)
+{
+	struct btrfs_super_block *disk_super;
+	struct page *page;
+	void *p;
+	pgoff_t index;
+
+	/* make sure our super fits in the device */
+	if (bytenr + PAGE_SIZE >= i_size_read(bdev->bd_inode))
+		return ERR_PTR(-EINVAL);
+
+	/* make sure our super fits in the page */
+	if (sizeof(*disk_super) > PAGE_SIZE)
+		return ERR_PTR(-EINVAL);
+
+	/* make sure our super doesn't straddle pages on disk */
+	index = bytenr >> PAGE_SHIFT;
+	if ((bytenr + sizeof(*disk_super) - 1) >> PAGE_SHIFT != index)
+		return ERR_PTR(-EINVAL);
+
+	/* pull in the page with our super */
+	page = read_cache_page_gfp(bdev->bd_inode->i_mapping, index, GFP_KERNEL);
+
+	if (IS_ERR(page))
+		return ERR_CAST(page);
+
+	p = page_address(page);
+
+	/* align our pointer to the offset of the super block */
+	disk_super = p + offset_in_page(bytenr);
+
+	if (btrfs_super_bytenr(disk_super) != bytenr ||
+	    btrfs_super_magic(disk_super) != BTRFS_MAGIC) {
+		btrfs_release_disk_super(p);
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (disk_super->label[0] && disk_super->label[BTRFS_LABEL_SIZE - 1])
+		disk_super->label[BTRFS_LABEL_SIZE - 1] = 0;
+
+	return disk_super;
+}
+
+int btrfs_forget_devices(const char *path)
+{
+	int ret;
+
+	mutex_lock(&uuid_mutex);
+	ret = btrfs_free_stale_devices(strlen(path) ? path : NULL, NULL);
+	mutex_unlock(&uuid_mutex);
+
+	return ret;
+}
+
+/*
+ * Look for a btrfs signature on a device. This may be called out of the mount path
+ * and we are not allowed to call set_blocksize during the scan. The superblock
+ * is read via pagecache
+ */
+struct btrfs_device *btrfs_scan_one_device(const char *path, fmode_t flags,
+					   void *holder)
+{
+	struct btrfs_super_block *disk_super;
+	bool new_device_added = false;
+	struct btrfs_device *device = NULL;
+	struct block_device *bdev;
+	u64 bytenr;
+
+	lockdep_assert_held(&uuid_mutex);
+
+	/*
+	 * we would like to check all the supers, but that would make
+	 * a btrfs mount succeed after a mkfs from a different FS.
+	 * So, we need to add a special mount option to scan for
+	 * later supers, using BTRFS_SUPER_MIRROR_MAX instead
+	 */
+	bytenr = btrfs_sb_offset(0);
+
+	/*
+	 * Avoid using flag |= FMODE_EXCL here, as the systemd-udev may
+	 * initiate the device scan which may race with the user's mount
+	 * or mkfs command, resulting in failure.
+	 * Since the device scan is solely for reading purposes, there is
+	 * no need for FMODE_EXCL. Additionally, the devices are read again
+	 * during the mount process. It is ok to get some inconsistent
+	 * values temporarily, as the device paths of the fsid are the only
+	 * required information for assembling the volume.
+	 */
+	bdev = blkdev_get_by_path(path, flags, holder);
+	if (IS_ERR(bdev))
+		return ERR_CAST(bdev);
+
+	disk_super = btrfs_read_disk_super(bdev, bytenr);
+	if (IS_ERR(disk_super)) {
+		device = ERR_CAST(disk_super);
+		goto error_bdev_put;
+	}
+
+	device = device_list_add(path, disk_super, &new_device_added);
+	if (!IS_ERR(device)) {
+		if (new_device_added)
+			btrfs_free_stale_devices(path, device);
+	}
+
+	btrfs_release_disk_super(disk_super);
+
+error_bdev_put:
+	blkdev_put(bdev, flags);
+
+	return device;
+}
+
+/*
+ * Try to find a chunk that intersects [start, start + len] range and when one
+ * such is found, record the end of it in *start
+ */
+static bool contains_pending_extent(struct btrfs_device *device, u64 *start,
+				    u64 len)
+{
+	u64 physical_start, physical_end;
+
+	lockdep_assert_held(&device->fs_info->chunk_mutex);
+
+	if (!find_first_extent_bit(&device->alloc_state, *start,
+				   &physical_start, &physical_end,
+				   CHUNK_ALLOCATED, NULL)) {
+
+		if (in_range(physical_start, *start, len) ||
+		    in_range(*start, physical_start,
+			     physical_end - physical_start)) {
+			*start = physical_end + 1;
+			return true;
+		}
+	}
+	return false;
+}
+
+static u64 dev_extent_search_start(struct btrfs_device *device, u64 start)
+{
+	switch (device->fs_devices->chunk_alloc_policy) {
+	case BTRFS_CHUNK_ALLOC_REGULAR:
+		/*
+		 * We don't want to overwrite the superblock on the drive nor
+		 * any area used by the boot loader (grub for example), so we
+		 * make sure to start at an offset of at least 1MB.
+		 */
+		return max_t(u64, start, SZ_1M);
+	default:
+		BUG();
+	}
+}
+
+/**
+ * dev_extent_hole_check - check if specified hole is suitable for allocation
+ * @device:	the device which we have the hole
+ * @hole_start: starting position of the hole
+ * @hole_size:	the size of the hole
+ * @num_bytes:	the size of the free space that we need
+ *
+ * This function may modify @hole_start and @hole_end to reflect the suitable
+ * position for allocation. Returns 1 if hole position is updated, 0 otherwise.
+ */
+static bool dev_extent_hole_check(struct btrfs_device *device, u64 *hole_start,
+				  u64 *hole_size, u64 num_bytes)
+{
+	bool changed = false;
+	u64 hole_end = *hole_start + *hole_size;
+
+	/*
+	 * Check before we set max_hole_start, otherwise we could end up
+	 * sending back this offset anyway.
+	 */
+	if (contains_pending_extent(device, hole_start, *hole_size)) {
+		if (hole_end >= *hole_start)
+			*hole_size = hole_end - *hole_start;
+		else
+			*hole_size = 0;
+		changed = true;
+	}
+
+	switch (device->fs_devices->chunk_alloc_policy) {
+	case BTRFS_CHUNK_ALLOC_REGULAR:
+		/* No extra check */
+		break;
+	default:
+		BUG();
+	}
+
+	return changed;
+}
+
+/*
+ * find_free_dev_extent_start - find free space in the specified device
+ * @device:	  the device which we search the free space in
+ * @num_bytes:	  the size of the free space that we need
+ * @search_start: the position from which to begin the search
+ * @start:	  store the start of the free space.
+ * @len:	  the size of the free space. that we find, or the size
+ *		  of the max free space if we don't find suitable free space
+ *
+ * this uses a pretty simple search, the expectation is that it is
+ * called very infrequently and that a given device has a small number
+ * of extents
+ *
+ * @start is used to store the start of the free space if we find. But if we
+ * don't find suitable free space, it will be used to store the start position
+ * of the max free space.
+ *
+ * @len is used to store the size of the free space that we find.
+ * But if we don't find suitable free space, it is used to store the size of
+ * the max free space.
+ *
+ * NOTE: This function will search *commit* root of device tree, and does extra
+ * check to ensure dev extents are not double allocated.
+ * This makes the function safe to allocate dev extents but may not report
+ * correct usable device space, as device extent freed in current transaction
+ * is not reported as avaiable.
+ */
+static int find_free_dev_extent_start(struct btrfs_device *device,
+				u64 num_bytes, u64 search_start, u64 *start,
+				u64 *len)
+{
+	struct btrfs_fs_info *fs_info = device->fs_info;
+	struct btrfs_root *root = fs_info->dev_root;
+	struct btrfs_key key;
+	struct btrfs_dev_extent *dev_extent;
+	struct btrfs_path *path;
+	u64 hole_size;
+	u64 max_hole_start;
+	u64 max_hole_size;
+	u64 extent_end;
+	u64 search_end = device->total_bytes;
+	int ret;
+	int slot;
+	struct extent_buffer *l;
+
+	search_start = dev_extent_search_start(device, search_start);
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	max_hole_start = search_start;
+	max_hole_size = 0;
+
+again:
+	if (search_start >= search_end ||
+		test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state)) {
+		ret = -ENOSPC;
+		goto out;
+	}
+
+	path->reada = READA_FORWARD;
+	path->search_commit_root = 1;
+	path->skip_locking = 1;
+
+	key.objectid = device->devid;
+	key.offset = search_start;
+	key.type = BTRFS_DEV_EXTENT_KEY;
+
+	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+	if (ret < 0)
+		goto out;
+	if (ret > 0) {
+		ret = btrfs_previous_item(root, path, key.objectid, key.type);
+		if (ret < 0)
+			goto out;
+	}
+
+	while (search_start < search_end) {
+		l = path->nodes[0];
+		slot = path->slots[0];
+		if (slot >= btrfs_header_nritems(l)) {
+			ret = btrfs_next_leaf(root, path);
+			if (ret == 0)
+				continue;
+			if (ret < 0)
+				goto out;
+
+			break;
+		}
+		btrfs_item_key_to_cpu(l, &key, slot);
+
+		if (key.objectid < device->devid)
+			goto next;
+
+		if (key.objectid > device->devid)
+			break;
+
+		if (key.type != BTRFS_DEV_EXTENT_KEY)
+			goto next;
+
+		if (key.offset > search_end)
+			break;
+
+		if (key.offset > search_start) {
+			hole_size = key.offset - search_start;
+			dev_extent_hole_check(device, &search_start, &hole_size,
+					      num_bytes);
+
+			if (hole_size > max_hole_size) {
+				max_hole_start = search_start;
+				max_hole_size = hole_size;
+			}
+
+			/*
+			 * If this free space is greater than which we need,
+			 * it must be the max free space that we have found
+			 * until now, so max_hole_start must point to the start
+			 * of this free space and the length of this free space
+			 * is stored in max_hole_size. Thus, we return
+			 * max_hole_start and max_hole_size and go back to the
+			 * caller.
+			 */
+			if (hole_size >= num_bytes) {
+				ret = 0;
+				goto out;
+			}
+		}
+
+		dev_extent = btrfs_item_ptr(l, slot, struct btrfs_dev_extent);
+		extent_end = key.offset + btrfs_dev_extent_length(l,
+								  dev_extent);
+		if (extent_end > search_start)
+			search_start = extent_end;
+next:
+		path->slots[0]++;
+		cond_resched();
+	}
+
+	/*
+	 * At this point, search_start should be the end of
+	 * allocated dev extents, and when shrinking the device,
+	 * search_end may be smaller than search_start.
+	 */
+	if (search_end > search_start) {
+		hole_size = search_end - search_start;
+		if (dev_extent_hole_check(device, &search_start, &hole_size,
+					  num_bytes)) {
+			btrfs_release_path(path);
+			goto again;
+		}
+
+		if (hole_size > max_hole_size) {
+			max_hole_start = search_start;
+			max_hole_size = hole_size;
+		}
+	}
+
+	/* See above. */
+	if (max_hole_size < num_bytes)
+		ret = -ENOSPC;
+	else
+		ret = 0;
+
+	ASSERT(max_hole_start + max_hole_size <= search_end);
+out:
+	btrfs_free_path(path);
+	*start = max_hole_start;
+	if (len)
+		*len = max_hole_size;
+	return ret;
+}
+
+int find_free_dev_extent(struct btrfs_device *device, u64 num_bytes,
+			 u64 *start, u64 *len)
+{
+	/* FIXME use last free of some kind */
+	return find_free_dev_extent_start(device, num_bytes, 0, start, len);
+}
+
+static int btrfs_free_dev_extent(struct btrfs_trans_handle *trans,
+			  struct btrfs_device *device,
+			  u64 start, u64 *dev_extent_len)
+{
+	struct btrfs_fs_info *fs_info = device->fs_info;
+	struct btrfs_root *root = fs_info->dev_root;
+	int ret;
+	struct btrfs_path *path;
+	struct btrfs_key key;
+	struct btrfs_key found_key;
+	struct extent_buffer *leaf = NULL;
+	struct btrfs_dev_extent *extent = NULL;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	key.objectid = device->devid;
+	key.offset = start;
+	key.type = BTRFS_DEV_EXTENT_KEY;
+again:
+	ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
+	if (ret > 0) {
+		ret = btrfs_previous_item(root, path, key.objectid,
+					  BTRFS_DEV_EXTENT_KEY);
+		if (ret)
+			goto out;
+		leaf = path->nodes[0];
+		btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
+		extent = btrfs_item_ptr(leaf, path->slots[0],
+					struct btrfs_dev_extent);
+		BUG_ON(found_key.offset > start || found_key.offset +
+		       btrfs_dev_extent_length(leaf, extent) < start);
+		key = found_key;
+		btrfs_release_path(path);
+		goto again;
+	} else if (ret == 0) {
+		leaf = path->nodes[0];
+		extent = btrfs_item_ptr(leaf, path->slots[0],
+					struct btrfs_dev_extent);
+	} else {
+		btrfs_handle_fs_error(fs_info, ret, "Slot search failed");
+		goto out;
+	}
+
+	*dev_extent_len = btrfs_dev_extent_length(leaf, extent);
+
+	ret = btrfs_del_item(trans, root, path);
+	if (ret) {
+		btrfs_handle_fs_error(fs_info, ret,
+				      "Failed to remove dev extent item");
+	} else {
+		set_bit(BTRFS_TRANS_HAVE_FREE_BGS, &trans->transaction->flags);
+	}
+out:
+	btrfs_free_path(path);
+	return ret;
+}
+
+static int btrfs_alloc_dev_extent(struct btrfs_trans_handle *trans,
+				  struct btrfs_device *device,
+				  u64 chunk_offset, u64 start, u64 num_bytes)
+{
+	int ret;
+	struct btrfs_path *path;
+	struct btrfs_fs_info *fs_info = device->fs_info;
+	struct btrfs_root *root = fs_info->dev_root;
+	struct btrfs_dev_extent *extent;
+	struct extent_buffer *leaf;
+	struct btrfs_key key;
+
+	WARN_ON(!test_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state));
+	WARN_ON(test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state));
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	key.objectid = device->devid;
+	key.offset = start;
+	key.type = BTRFS_DEV_EXTENT_KEY;
+	ret = btrfs_insert_empty_item(trans, root, path, &key,
+				      sizeof(*extent));
+	if (ret)
+		goto out;
+
+	leaf = path->nodes[0];
+	extent = btrfs_item_ptr(leaf, path->slots[0],
+				struct btrfs_dev_extent);
+	btrfs_set_dev_extent_chunk_tree(leaf, extent,
+					BTRFS_CHUNK_TREE_OBJECTID);
+	btrfs_set_dev_extent_chunk_objectid(leaf, extent,
+					    BTRFS_FIRST_CHUNK_TREE_OBJECTID);
+	btrfs_set_dev_extent_chunk_offset(leaf, extent, chunk_offset);
+
+	btrfs_set_dev_extent_length(leaf, extent, num_bytes);
+	btrfs_mark_buffer_dirty(leaf);
+out:
+	btrfs_free_path(path);
+	return ret;
+}
+
+static u64 find_next_chunk(struct btrfs_fs_info *fs_info)
+{
+	struct extent_map_tree *em_tree;
+	struct extent_map *em;
+	struct rb_node *n;
+	u64 ret = 0;
+
+	em_tree = &fs_info->mapping_tree;
+	read_lock(&em_tree->lock);
+	n = rb_last(&em_tree->map.rb_root);
+	if (n) {
+		em = rb_entry(n, struct extent_map, rb_node);
+		ret = em->start + em->len;
+	}
+	read_unlock(&em_tree->lock);
+
+	return ret;
+}
+
+static noinline int find_next_devid(struct btrfs_fs_info *fs_info,
+				    u64 *devid_ret)
+{
+	int ret;
+	struct btrfs_key key;
+	struct btrfs_key found_key;
+	struct btrfs_path *path;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
+	key.type = BTRFS_DEV_ITEM_KEY;
+	key.offset = (u64)-1;
+
+	ret = btrfs_search_slot(NULL, fs_info->chunk_root, &key, path, 0, 0);
+	if (ret < 0)
+		goto error;
+
+	if (ret == 0) {
+		/* Corruption */
+		btrfs_err(fs_info, "corrupted chunk tree devid -1 matched");
+		ret = -EUCLEAN;
+		goto error;
+	}
+
+	ret = btrfs_previous_item(fs_info->chunk_root, path,
+				  BTRFS_DEV_ITEMS_OBJECTID,
+				  BTRFS_DEV_ITEM_KEY);
+	if (ret) {
+		*devid_ret = 1;
+	} else {
+		btrfs_item_key_to_cpu(path->nodes[0], &found_key,
+				      path->slots[0]);
+		*devid_ret = found_key.offset + 1;
+	}
+	ret = 0;
+error:
+	btrfs_free_path(path);
+	return ret;
+}
+
+/*
+ * the device information is stored in the chunk root
+ * the btrfs_device struct should be fully filled in
+ */
+static int btrfs_add_dev_item(struct btrfs_trans_handle *trans,
+			    struct btrfs_device *device)
+{
+	int ret;
+	struct btrfs_path *path;
+	struct btrfs_dev_item *dev_item;
+	struct extent_buffer *leaf;
+	struct btrfs_key key;
+	unsigned long ptr;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
+	key.type = BTRFS_DEV_ITEM_KEY;
+	key.offset = device->devid;
+
+	ret = btrfs_insert_empty_item(trans, trans->fs_info->chunk_root, path,
+				      &key, sizeof(*dev_item));
+	if (ret)
+		goto out;
+
+	leaf = path->nodes[0];
+	dev_item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_dev_item);
+
+	btrfs_set_device_id(leaf, dev_item, device->devid);
+	btrfs_set_device_generation(leaf, dev_item, 0);
+	btrfs_set_device_type(leaf, dev_item, device->type);
+	btrfs_set_device_io_align(leaf, dev_item, device->io_align);
+	btrfs_set_device_io_width(leaf, dev_item, device->io_width);
+	btrfs_set_device_sector_size(leaf, dev_item, device->sector_size);
+	btrfs_set_device_total_bytes(leaf, dev_item,
+				     btrfs_device_get_disk_total_bytes(device));
+	btrfs_set_device_bytes_used(leaf, dev_item,
+				    btrfs_device_get_bytes_used(device));
+	btrfs_set_device_group(leaf, dev_item, 0);
+	btrfs_set_device_seek_speed(leaf, dev_item, 0);
+	btrfs_set_device_bandwidth(leaf, dev_item, 0);
+	btrfs_set_device_start_offset(leaf, dev_item, 0);
+
+	ptr = btrfs_device_uuid(dev_item);
+	write_extent_buffer(leaf, device->uuid, ptr, BTRFS_UUID_SIZE);
+	ptr = btrfs_device_fsid(dev_item);
+	write_extent_buffer(leaf, trans->fs_info->fs_devices->metadata_uuid,
+			    ptr, BTRFS_FSID_SIZE);
+	btrfs_mark_buffer_dirty(leaf);
+
+	ret = 0;
+out:
+	btrfs_free_path(path);
+	return ret;
+}
+
+/*
+ * Function to update ctime/mtime for a given device path.
+ * Mainly used for ctime/mtime based probe like libblkid.
+ *
+ * We don't care about errors here, this is just to be kind to userspace.
+ */
+static void update_dev_time(const char *device_path)
+{
+	struct path path;
+	struct timespec64 now;
+	int ret;
+
+	ret = kern_path(device_path, LOOKUP_FOLLOW, &path);
+	if (ret)
+		return;
+
+	now = current_time(d_inode(path.dentry));
+	inode_update_time(d_inode(path.dentry), &now, S_MTIME | S_CTIME);
+	path_put(&path);
+}
+
+static int btrfs_rm_dev_item(struct btrfs_device *device)
+{
+	struct btrfs_root *root = device->fs_info->chunk_root;
+	int ret;
+	struct btrfs_path *path;
+	struct btrfs_key key;
+	struct btrfs_trans_handle *trans;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	trans = btrfs_start_transaction(root, 0);
+	if (IS_ERR(trans)) {
+		btrfs_free_path(path);
+		return PTR_ERR(trans);
+	}
+	key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
+	key.type = BTRFS_DEV_ITEM_KEY;
+	key.offset = device->devid;
+
+	ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
+	if (ret) {
+		if (ret > 0)
+			ret = -ENOENT;
+		btrfs_abort_transaction(trans, ret);
+		btrfs_end_transaction(trans);
+		goto out;
+	}
+
+	ret = btrfs_del_item(trans, root, path);
+	if (ret) {
+		btrfs_abort_transaction(trans, ret);
+		btrfs_end_transaction(trans);
+	}
+
+out:
+	btrfs_free_path(path);
+	if (!ret)
+		ret = btrfs_commit_transaction(trans);
+	return ret;
+}
+
+/*
+ * Verify that @num_devices satisfies the RAID profile constraints in the whole
+ * filesystem. It's up to the caller to adjust that number regarding eg. device
+ * replace.
+ */
+static int btrfs_check_raid_min_devices(struct btrfs_fs_info *fs_info,
+		u64 num_devices)
+{
+	u64 all_avail;
+	unsigned seq;
+	int i;
+
+	do {
+		seq = read_seqbegin(&fs_info->profiles_lock);
+
+		all_avail = fs_info->avail_data_alloc_bits |
+			    fs_info->avail_system_alloc_bits |
+			    fs_info->avail_metadata_alloc_bits;
+	} while (read_seqretry(&fs_info->profiles_lock, seq));
+
+	for (i = 0; i < BTRFS_NR_RAID_TYPES; i++) {
+		if (!(all_avail & btrfs_raid_array[i].bg_flag))
+			continue;
+
+		if (num_devices < btrfs_raid_array[i].devs_min) {
+			int ret = btrfs_raid_array[i].mindev_error;
+
+			if (ret)
+				return ret;
+		}
+	}
+
+	return 0;
+}
+
+static struct btrfs_device * btrfs_find_next_active_device(
+		struct btrfs_fs_devices *fs_devs, struct btrfs_device *device)
+{
+	struct btrfs_device *next_device;
+
+	list_for_each_entry(next_device, &fs_devs->devices, dev_list) {
+		if (next_device != device &&
+		    !test_bit(BTRFS_DEV_STATE_MISSING, &next_device->dev_state)
+		    && next_device->bdev)
+			return next_device;
+	}
+
+	return NULL;
+}
+
+/*
+ * Helper function to check if the given device is part of s_bdev / latest_bdev
+ * and replace it with the provided or the next active device, in the context
+ * where this function called, there should be always be another device (or
+ * this_dev) which is active.
+ */
+void __cold btrfs_assign_next_active_device(struct btrfs_device *device,
+					    struct btrfs_device *next_device)
+{
+	struct btrfs_fs_info *fs_info = device->fs_info;
+
+	if (!next_device)
+		next_device = btrfs_find_next_active_device(fs_info->fs_devices,
+							    device);
+	ASSERT(next_device);
+
+	if (fs_info->sb->s_bdev &&
+			(fs_info->sb->s_bdev == device->bdev))
+		fs_info->sb->s_bdev = next_device->bdev;
+
+	if (fs_info->fs_devices->latest_bdev == device->bdev)
+		fs_info->fs_devices->latest_bdev = next_device->bdev;
+}
+
+/*
+ * Return btrfs_fs_devices::num_devices excluding the device that's being
+ * currently replaced.
+ */
+static u64 btrfs_num_devices(struct btrfs_fs_info *fs_info)
+{
+	u64 num_devices = fs_info->fs_devices->num_devices;
+
+	down_read(&fs_info->dev_replace.rwsem);
+	if (btrfs_dev_replace_is_ongoing(&fs_info->dev_replace)) {
+		ASSERT(num_devices > 1);
+		num_devices--;
+	}
+	up_read(&fs_info->dev_replace.rwsem);
+
+	return num_devices;
+}
+
+void btrfs_scratch_superblocks(struct btrfs_fs_info *fs_info,
+			       struct block_device *bdev,
+			       const char *device_path)
+{
+	struct btrfs_super_block *disk_super;
+	int copy_num;
+
+	if (!bdev)
+		return;
+
+	for (copy_num = 0; copy_num < BTRFS_SUPER_MIRROR_MAX; copy_num++) {
+		struct page *page;
+		int ret;
+
+		disk_super = btrfs_read_dev_one_super(bdev, copy_num);
+		if (IS_ERR(disk_super))
+			continue;
+
+		memset(&disk_super->magic, 0, sizeof(disk_super->magic));
+
+		page = virt_to_page(disk_super);
+		set_page_dirty(page);
+		lock_page(page);
+		/* write_on_page() unlocks the page */
+		ret = write_one_page(page);
+		if (ret)
+			btrfs_warn(fs_info,
+				"error clearing superblock number %d (%d)",
+				copy_num, ret);
+		btrfs_release_disk_super(disk_super);
+
+	}
+
+	/* Notify udev that device has changed */
+	btrfs_kobject_uevent(bdev, KOBJ_CHANGE);
+
+	/* Update ctime/mtime for device path for libblkid */
+	update_dev_time(device_path);
+}
+
+int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
+		    u64 devid)
+{
+	struct btrfs_device *device;
+	struct btrfs_fs_devices *cur_devices;
+	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
+	u64 num_devices;
+	int ret = 0;
+
+	/*
+	 * The device list in fs_devices is accessed without locks (neither
+	 * uuid_mutex nor device_list_mutex) as it won't change on a mounted
+	 * filesystem and another device rm cannot run.
+	 */
+	num_devices = btrfs_num_devices(fs_info);
+
+	ret = btrfs_check_raid_min_devices(fs_info, num_devices - 1);
+	if (ret)
+		goto out;
+
+	device = btrfs_find_device_by_devspec(fs_info, devid, device_path);
+
+	if (IS_ERR(device)) {
+		if (PTR_ERR(device) == -ENOENT &&
+		    device_path && strcmp(device_path, "missing") == 0)
+			ret = BTRFS_ERROR_DEV_MISSING_NOT_FOUND;
+		else
+			ret = PTR_ERR(device);
+		goto out;
+	}
+
+	if (btrfs_pinned_by_swapfile(fs_info, device)) {
+		btrfs_warn_in_rcu(fs_info,
+		  "cannot remove device %s (devid %llu) due to active swapfile",
+				  rcu_str_deref(device->name), device->devid);
+		ret = -ETXTBSY;
+		goto out;
+	}
+
+	if (test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state)) {
+		ret = BTRFS_ERROR_DEV_TGT_REPLACE;
+		goto out;
+	}
+
+	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
+	    fs_info->fs_devices->rw_devices == 1) {
+		ret = BTRFS_ERROR_DEV_ONLY_WRITABLE;
+		goto out;
+	}
+
+	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
+		mutex_lock(&fs_info->chunk_mutex);
+		list_del_init(&device->dev_alloc_list);
+		device->fs_devices->rw_devices--;
+		mutex_unlock(&fs_info->chunk_mutex);
+	}
+
+	ret = btrfs_shrink_device(device, 0);
+	if (!ret)
+		btrfs_reada_remove_dev(device);
+	if (ret)
+		goto error_undo;
+
+	/*
+	 * TODO: the superblock still includes this device in its num_devices
+	 * counter although write_all_supers() is not locked out. This
+	 * could give a filesystem state which requires a degraded mount.
+	 */
+	ret = btrfs_rm_dev_item(device);
+	if (ret)
+		goto error_undo;
+
+	clear_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
+	btrfs_scrub_cancel_dev(device);
+
+	/*
+	 * the device list mutex makes sure that we don't change
+	 * the device list while someone else is writing out all
+	 * the device supers. Whoever is writing all supers, should
+	 * lock the device list mutex before getting the number of
+	 * devices in the super block (super_copy). Conversely,
+	 * whoever updates the number of devices in the super block
+	 * (super_copy) should hold the device list mutex.
+	 */
+
+	/*
+	 * In normal cases the cur_devices == fs_devices. But in case
+	 * of deleting a seed device, the cur_devices should point to
+	 * its own fs_devices listed under the fs_devices->seed.
+	 */
+	cur_devices = device->fs_devices;
+	mutex_lock(&fs_devices->device_list_mutex);
+	list_del_rcu(&device->dev_list);
+
+	cur_devices->num_devices--;
+	cur_devices->total_devices--;
+	/* Update total_devices of the parent fs_devices if it's seed */
+	if (cur_devices != fs_devices)
+		fs_devices->total_devices--;
+
+	if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))
+		cur_devices->missing_devices--;
+
+	btrfs_assign_next_active_device(device, NULL);
+
+	if (device->bdev) {
+		cur_devices->open_devices--;
+		/* remove sysfs entry */
+		btrfs_sysfs_remove_device(device);
+	}
+
+	num_devices = btrfs_super_num_devices(fs_info->super_copy) - 1;
+	btrfs_set_super_num_devices(fs_info->super_copy, num_devices);
+	mutex_unlock(&fs_devices->device_list_mutex);
+
+	/*
+	 * at this point, the device is zero sized and detached from
+	 * the devices list.  All that's left is to zero out the old
+	 * supers and free the device.
+	 */
+	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state))
+		btrfs_scratch_superblocks(fs_info, device->bdev,
+					  device->name->str);
+
+	btrfs_close_bdev(device);
+	synchronize_rcu();
+	btrfs_free_device(device);
+
+	if (cur_devices->open_devices == 0) {
+		list_del_init(&cur_devices->seed_list);
+		close_fs_devices(cur_devices);
+		free_fs_devices(cur_devices);
+	}
+
+out:
+	return ret;
+
+error_undo:
+	btrfs_reada_undo_remove_dev(device);
+	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
+		mutex_lock(&fs_info->chunk_mutex);
+		list_add(&device->dev_alloc_list,
+			 &fs_devices->alloc_list);
+		device->fs_devices->rw_devices++;
+		mutex_unlock(&fs_info->chunk_mutex);
+	}
+	goto out;
+}
+
+void btrfs_rm_dev_replace_remove_srcdev(struct btrfs_device *srcdev)
+{
+	struct btrfs_fs_devices *fs_devices;
+
+	lockdep_assert_held(&srcdev->fs_info->fs_devices->device_list_mutex);
+
+	/*
+	 * in case of fs with no seed, srcdev->fs_devices will point
+	 * to fs_devices of fs_info. However when the dev being replaced is
+	 * a seed dev it will point to the seed's local fs_devices. In short
+	 * srcdev will have its correct fs_devices in both the cases.
+	 */
+	fs_devices = srcdev->fs_devices;
+
+	list_del_rcu(&srcdev->dev_list);
+	list_del(&srcdev->dev_alloc_list);
+	fs_devices->num_devices--;
+	if (test_bit(BTRFS_DEV_STATE_MISSING, &srcdev->dev_state))
+		fs_devices->missing_devices--;
+
+	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &srcdev->dev_state))
+		fs_devices->rw_devices--;
+
+	if (srcdev->bdev)
+		fs_devices->open_devices--;
+}
+
+void btrfs_rm_dev_replace_free_srcdev(struct btrfs_device *srcdev)
+{
+	struct btrfs_fs_devices *fs_devices = srcdev->fs_devices;
+
+	mutex_lock(&uuid_mutex);
+
+	btrfs_close_bdev(srcdev);
+	synchronize_rcu();
+	btrfs_free_device(srcdev);
+
+	/* if this is no devs we rather delete the fs_devices */
+	if (!fs_devices->num_devices) {
+		/*
+		 * On a mounted FS, num_devices can't be zero unless it's a
+		 * seed. In case of a seed device being replaced, the replace
+		 * target added to the sprout FS, so there will be no more
+		 * device left under the seed FS.
+		 */
+		ASSERT(fs_devices->seeding);
+
+		list_del_init(&fs_devices->seed_list);
+		close_fs_devices(fs_devices);
+		free_fs_devices(fs_devices);
+	}
+	mutex_unlock(&uuid_mutex);
+}
+
+void btrfs_destroy_dev_replace_tgtdev(struct btrfs_device *tgtdev)
+{
+	struct btrfs_fs_devices *fs_devices = tgtdev->fs_info->fs_devices;
+
+	mutex_lock(&fs_devices->device_list_mutex);
+
+	btrfs_sysfs_remove_device(tgtdev);
+
+	if (tgtdev->bdev)
+		fs_devices->open_devices--;
+
+	fs_devices->num_devices--;
+
+	btrfs_assign_next_active_device(tgtdev, NULL);
+
+	list_del_rcu(&tgtdev->dev_list);
+
+	mutex_unlock(&fs_devices->device_list_mutex);
+
+	/*
+	 * The update_dev_time() with in btrfs_scratch_superblocks()
+	 * may lead to a call to btrfs_show_devname() which will try
+	 * to hold device_list_mutex. And here this device
+	 * is already out of device list, so we don't have to hold
+	 * the device_list_mutex lock.
+	 */
+	btrfs_scratch_superblocks(tgtdev->fs_info, tgtdev->bdev,
+				  tgtdev->name->str);
+
+	btrfs_close_bdev(tgtdev);
+	synchronize_rcu();
+	btrfs_free_device(tgtdev);
+}
+
+static struct btrfs_device *btrfs_find_device_by_path(
+		struct btrfs_fs_info *fs_info, const char *device_path)
+{
+	int ret = 0;
+	struct btrfs_super_block *disk_super;
+	u64 devid;
+	u8 *dev_uuid;
+	struct block_device *bdev;
+	struct btrfs_device *device;
+
+	ret = btrfs_get_bdev_and_sb(device_path, FMODE_READ,
+				    fs_info->bdev_holder, 0, &bdev, &disk_super);
+	if (ret)
+		return ERR_PTR(ret);
+
+	devid = btrfs_stack_device_id(&disk_super->dev_item);
+	dev_uuid = disk_super->dev_item.uuid;
+	if (btrfs_fs_incompat(fs_info, METADATA_UUID))
+		device = btrfs_find_device(fs_info->fs_devices, devid, dev_uuid,
+					   disk_super->metadata_uuid, true);
+	else
+		device = btrfs_find_device(fs_info->fs_devices, devid, dev_uuid,
+					   disk_super->fsid, true);
+
+	btrfs_release_disk_super(disk_super);
+	if (!device)
+		device = ERR_PTR(-ENOENT);
+	blkdev_put(bdev, FMODE_READ);
+	return device;
+}
+
+/*
+ * Lookup a device given by device id, or the path if the id is 0.
+ */
+struct btrfs_device *btrfs_find_device_by_devspec(
+		struct btrfs_fs_info *fs_info, u64 devid,
+		const char *device_path)
+{
+	struct btrfs_device *device;
+
+	if (devid) {
+		device = btrfs_find_device(fs_info->fs_devices, devid, NULL,
+					   NULL, true);
+		if (!device)
+			return ERR_PTR(-ENOENT);
+		return device;
+	}
+
+	if (!device_path || !device_path[0])
+		return ERR_PTR(-EINVAL);
+
+	if (strcmp(device_path, "missing") == 0) {
+		/* Find first missing device */
+		list_for_each_entry(device, &fs_info->fs_devices->devices,
+				    dev_list) {
+			if (test_bit(BTRFS_DEV_STATE_IN_FS_METADATA,
+				     &device->dev_state) && !device->bdev)
+				return device;
+		}
+		return ERR_PTR(-ENOENT);
+	}
+
+	return btrfs_find_device_by_path(fs_info, device_path);
+}
+
+/*
+ * does all the dirty work required for changing file system's UUID.
+ */
+static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
+	struct btrfs_fs_devices *old_devices;
+	struct btrfs_fs_devices *seed_devices;
+	struct btrfs_super_block *disk_super = fs_info->super_copy;
+	struct btrfs_device *device;
+	u64 super_flags;
+
+	lockdep_assert_held(&uuid_mutex);
+	if (!fs_devices->seeding)
+		return -EINVAL;
+
+	/*
+	 * Private copy of the seed devices, anchored at
+	 * fs_info->fs_devices->seed_list
+	 */
+	seed_devices = alloc_fs_devices(NULL, NULL);
+	if (IS_ERR(seed_devices))
+		return PTR_ERR(seed_devices);
+
+	/*
+	 * It's necessary to retain a copy of the original seed fs_devices in
+	 * fs_uuids so that filesystems which have been seeded can successfully
+	 * reference the seed device from open_seed_devices. This also supports
+	 * multiple fs seed.
+	 */
+	old_devices = clone_fs_devices(fs_devices);
+	if (IS_ERR(old_devices)) {
+		kfree(seed_devices);
+		return PTR_ERR(old_devices);
+	}
+
+	list_add(&old_devices->fs_list, &fs_uuids);
+
+	memcpy(seed_devices, fs_devices, sizeof(*seed_devices));
+	seed_devices->opened = 1;
+	INIT_LIST_HEAD(&seed_devices->devices);
+	INIT_LIST_HEAD(&seed_devices->alloc_list);
+	mutex_init(&seed_devices->device_list_mutex);
+
+	mutex_lock(&fs_devices->device_list_mutex);
+	list_splice_init_rcu(&fs_devices->devices, &seed_devices->devices,
+			      synchronize_rcu);
+	list_for_each_entry(device, &seed_devices->devices, dev_list)
+		device->fs_devices = seed_devices;
+
+	fs_devices->seeding = false;
+	fs_devices->num_devices = 0;
+	fs_devices->open_devices = 0;
+	fs_devices->missing_devices = 0;
+	fs_devices->rotating = false;
+	list_add(&seed_devices->seed_list, &fs_devices->seed_list);
+
+	generate_random_uuid(fs_devices->fsid);
+	memcpy(fs_devices->metadata_uuid, fs_devices->fsid, BTRFS_FSID_SIZE);
+	memcpy(disk_super->fsid, fs_devices->fsid, BTRFS_FSID_SIZE);
+	mutex_unlock(&fs_devices->device_list_mutex);
+
+	super_flags = btrfs_super_flags(disk_super) &
+		      ~BTRFS_SUPER_FLAG_SEEDING;
+	btrfs_set_super_flags(disk_super, super_flags);
+
+	return 0;
+}
+
+/*
+ * Store the expected generation for seed devices in device items.
+ */
+static int btrfs_finish_sprout(struct btrfs_trans_handle *trans)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_root *root = fs_info->chunk_root;
+	struct btrfs_path *path;
+	struct extent_buffer *leaf;
+	struct btrfs_dev_item *dev_item;
+	struct btrfs_device *device;
+	struct btrfs_key key;
+	u8 fs_uuid[BTRFS_FSID_SIZE];
+	u8 dev_uuid[BTRFS_UUID_SIZE];
+	u64 devid;
+	int ret;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
+	key.offset = 0;
+	key.type = BTRFS_DEV_ITEM_KEY;
+
+	while (1) {
+		ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
+		if (ret < 0)
+			goto error;
+
+		leaf = path->nodes[0];
+next_slot:
+		if (path->slots[0] >= btrfs_header_nritems(leaf)) {
+			ret = btrfs_next_leaf(root, path);
+			if (ret > 0)
+				break;
+			if (ret < 0)
+				goto error;
+			leaf = path->nodes[0];
+			btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+			btrfs_release_path(path);
+			continue;
+		}
+
+		btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+		if (key.objectid != BTRFS_DEV_ITEMS_OBJECTID ||
+		    key.type != BTRFS_DEV_ITEM_KEY)
+			break;
+
+		dev_item = btrfs_item_ptr(leaf, path->slots[0],
+					  struct btrfs_dev_item);
+		devid = btrfs_device_id(leaf, dev_item);
+		read_extent_buffer(leaf, dev_uuid, btrfs_device_uuid(dev_item),
+				   BTRFS_UUID_SIZE);
+		read_extent_buffer(leaf, fs_uuid, btrfs_device_fsid(dev_item),
+				   BTRFS_FSID_SIZE);
+		device = btrfs_find_device(fs_info->fs_devices, devid, dev_uuid,
+					   fs_uuid, true);
+		BUG_ON(!device); /* Logic error */
+
+		if (device->fs_devices->seeding) {
+			btrfs_set_device_generation(leaf, dev_item,
+						    device->generation);
+			btrfs_mark_buffer_dirty(leaf);
+		}
+
+		path->slots[0]++;
+		goto next_slot;
+	}
+	ret = 0;
+error:
+	btrfs_free_path(path);
+	return ret;
+}
+
+int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path)
+{
+	struct btrfs_root *root = fs_info->dev_root;
+	struct request_queue *q;
+	struct btrfs_trans_handle *trans;
+	struct btrfs_device *device;
+	struct block_device *bdev;
+	struct super_block *sb = fs_info->sb;
+	struct rcu_string *name;
+	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
+	u64 orig_super_total_bytes;
+	u64 orig_super_num_devices;
+	int seeding_dev = 0;
+	int ret = 0;
+	bool locked = false;
+
+	if (sb_rdonly(sb) && !fs_devices->seeding)
+		return -EROFS;
+
+	bdev = blkdev_get_by_path(device_path, FMODE_WRITE | FMODE_EXCL,
+				  fs_info->bdev_holder);
+	if (IS_ERR(bdev))
+		return PTR_ERR(bdev);
+
+	if (fs_devices->seeding) {
+		seeding_dev = 1;
+		down_write(&sb->s_umount);
+		mutex_lock(&uuid_mutex);
+		locked = true;
+	}
+
+	sync_blockdev(bdev);
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(device, &fs_devices->devices, dev_list) {
+		if (device->bdev == bdev) {
+			ret = -EEXIST;
+			rcu_read_unlock();
+			goto error;
+		}
+	}
+	rcu_read_unlock();
+
+	device = btrfs_alloc_device(fs_info, NULL, NULL);
+	if (IS_ERR(device)) {
+		/* we can safely leave the fs_devices entry around */
+		ret = PTR_ERR(device);
+		goto error;
+	}
+
+	name = rcu_string_strdup(device_path, GFP_KERNEL);
+	if (!name) {
+		ret = -ENOMEM;
+		goto error_free_device;
+	}
+	rcu_assign_pointer(device->name, name);
+
+	trans = btrfs_start_transaction(root, 0);
+	if (IS_ERR(trans)) {
+		ret = PTR_ERR(trans);
+		goto error_free_device;
+	}
+
+	q = bdev_get_queue(bdev);
+	set_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
+	device->generation = trans->transid;
+	device->io_width = fs_info->sectorsize;
+	device->io_align = fs_info->sectorsize;
+	device->sector_size = fs_info->sectorsize;
+	device->total_bytes = round_down(i_size_read(bdev->bd_inode),
+					 fs_info->sectorsize);
+	device->disk_total_bytes = device->total_bytes;
+	device->commit_total_bytes = device->total_bytes;
+	device->fs_info = fs_info;
+	device->bdev = bdev;
+	set_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
+	clear_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state);
+	device->mode = FMODE_EXCL;
+	device->dev_stats_valid = 1;
+	set_blocksize(device->bdev, BTRFS_BDEV_BLOCKSIZE);
+
+	if (seeding_dev) {
+		sb->s_flags &= ~SB_RDONLY;
+		ret = btrfs_prepare_sprout(fs_info);
+		if (ret) {
+			btrfs_abort_transaction(trans, ret);
+			goto error_trans;
+		}
+	}
+
+	device->fs_devices = fs_devices;
+
+	mutex_lock(&fs_devices->device_list_mutex);
+	mutex_lock(&fs_info->chunk_mutex);
+	list_add_rcu(&device->dev_list, &fs_devices->devices);
+	list_add(&device->dev_alloc_list, &fs_devices->alloc_list);
+	fs_devices->num_devices++;
+	fs_devices->open_devices++;
+	fs_devices->rw_devices++;
+	fs_devices->total_devices++;
+	fs_devices->total_rw_bytes += device->total_bytes;
+
+	atomic64_add(device->total_bytes, &fs_info->free_chunk_space);
+
+	if (!blk_queue_nonrot(q))
+		fs_devices->rotating = true;
+
+	orig_super_total_bytes = btrfs_super_total_bytes(fs_info->super_copy);
+	btrfs_set_super_total_bytes(fs_info->super_copy,
+		round_down(orig_super_total_bytes + device->total_bytes,
+			   fs_info->sectorsize));
+
+	orig_super_num_devices = btrfs_super_num_devices(fs_info->super_copy);
+	btrfs_set_super_num_devices(fs_info->super_copy,
+				    orig_super_num_devices + 1);
+
+	/*
+	 * we've got more storage, clear any full flags on the space
+	 * infos
+	 */
+	btrfs_clear_space_info_full(fs_info);
+
+	mutex_unlock(&fs_info->chunk_mutex);
+
+	/* Add sysfs device entry */
+	btrfs_sysfs_add_device(device);
+
+	mutex_unlock(&fs_devices->device_list_mutex);
+
+	if (seeding_dev) {
+		mutex_lock(&fs_info->chunk_mutex);
+		ret = init_first_rw_device(trans);
+		mutex_unlock(&fs_info->chunk_mutex);
+		if (ret) {
+			btrfs_abort_transaction(trans, ret);
+			goto error_sysfs;
+		}
+	}
+
+	ret = btrfs_add_dev_item(trans, device);
+	if (ret) {
+		btrfs_abort_transaction(trans, ret);
+		goto error_sysfs;
+	}
+
+	if (seeding_dev) {
+		ret = btrfs_finish_sprout(trans);
+		if (ret) {
+			btrfs_abort_transaction(trans, ret);
+			goto error_sysfs;
+		}
+
+		/*
+		 * fs_devices now represents the newly sprouted filesystem and
+		 * its fsid has been changed by btrfs_prepare_sprout
+		 */
+		btrfs_sysfs_update_sprout_fsid(fs_devices);
+	}
+
+	ret = btrfs_commit_transaction(trans);
+
+	if (seeding_dev) {
+		mutex_unlock(&uuid_mutex);
+		up_write(&sb->s_umount);
+		locked = false;
+
+		if (ret) /* transaction commit */
+			return ret;
+
+		ret = btrfs_relocate_sys_chunks(fs_info);
+		if (ret < 0)
+			btrfs_handle_fs_error(fs_info, ret,
+				    "Failed to relocate sys chunks after device initialization. This can be fixed using the \"btrfs balance\" command.");
+		trans = btrfs_attach_transaction(root);
+		if (IS_ERR(trans)) {
+			if (PTR_ERR(trans) == -ENOENT)
+				return 0;
+			ret = PTR_ERR(trans);
+			trans = NULL;
+			goto error_sysfs;
+		}
+		ret = btrfs_commit_transaction(trans);
+	}
+
+	/*
+	 * Now that we have written a new super block to this device, check all
+	 * other fs_devices list if device_path alienates any other scanned
+	 * device.
+	 * We can ignore the return value as it typically returns -EINVAL and
+	 * only succeeds if the device was an alien.
+	 */
+	btrfs_forget_devices(device_path);
+
+	/* Update ctime/mtime for blkid or udev */
+	update_dev_time(device_path);
+
+	return ret;
+
+error_sysfs:
+	btrfs_sysfs_remove_device(device);
+	mutex_lock(&fs_info->fs_devices->device_list_mutex);
+	mutex_lock(&fs_info->chunk_mutex);
+	list_del_rcu(&device->dev_list);
+	list_del(&device->dev_alloc_list);
+	fs_info->fs_devices->num_devices--;
+	fs_info->fs_devices->open_devices--;
+	fs_info->fs_devices->rw_devices--;
+	fs_info->fs_devices->total_devices--;
+	fs_info->fs_devices->total_rw_bytes -= device->total_bytes;
+	atomic64_sub(device->total_bytes, &fs_info->free_chunk_space);
+	btrfs_set_super_total_bytes(fs_info->super_copy,
+				    orig_super_total_bytes);
+	btrfs_set_super_num_devices(fs_info->super_copy,
+				    orig_super_num_devices);
+	mutex_unlock(&fs_info->chunk_mutex);
+	mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+error_trans:
+	if (seeding_dev)
+		sb->s_flags |= SB_RDONLY;
+	if (trans)
+		btrfs_end_transaction(trans);
+error_free_device:
+	btrfs_free_device(device);
+error:
+	blkdev_put(bdev, FMODE_EXCL);
+	if (locked) {
+		mutex_unlock(&uuid_mutex);
+		up_write(&sb->s_umount);
+	}
+	return ret;
+}
+
+static noinline int btrfs_update_device(struct btrfs_trans_handle *trans,
+					struct btrfs_device *device)
+{
+	int ret;
+	struct btrfs_path *path;
+	struct btrfs_root *root = device->fs_info->chunk_root;
+	struct btrfs_dev_item *dev_item;
+	struct extent_buffer *leaf;
+	struct btrfs_key key;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
+	key.type = BTRFS_DEV_ITEM_KEY;
+	key.offset = device->devid;
+
+	ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
+	if (ret < 0)
+		goto out;
+
+	if (ret > 0) {
+		ret = -ENOENT;
+		goto out;
+	}
+
+	leaf = path->nodes[0];
+	dev_item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_dev_item);
+
+	btrfs_set_device_id(leaf, dev_item, device->devid);
+	btrfs_set_device_type(leaf, dev_item, device->type);
+	btrfs_set_device_io_align(leaf, dev_item, device->io_align);
+	btrfs_set_device_io_width(leaf, dev_item, device->io_width);
+	btrfs_set_device_sector_size(leaf, dev_item, device->sector_size);
+	btrfs_set_device_total_bytes(leaf, dev_item,
+				     btrfs_device_get_disk_total_bytes(device));
+	btrfs_set_device_bytes_used(leaf, dev_item,
+				    btrfs_device_get_bytes_used(device));
+	btrfs_mark_buffer_dirty(leaf);
+
+out:
+	btrfs_free_path(path);
+	return ret;
+}
+
+int btrfs_grow_device(struct btrfs_trans_handle *trans,
+		      struct btrfs_device *device, u64 new_size)
+{
+	struct btrfs_fs_info *fs_info = device->fs_info;
+	struct btrfs_super_block *super_copy = fs_info->super_copy;
+	u64 old_total;
+	u64 diff;
+
+	if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state))
+		return -EACCES;
+
+	new_size = round_down(new_size, fs_info->sectorsize);
+
+	mutex_lock(&fs_info->chunk_mutex);
+	old_total = btrfs_super_total_bytes(super_copy);
+	diff = round_down(new_size - device->total_bytes, fs_info->sectorsize);
+
+	if (new_size <= device->total_bytes ||
+	    test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state)) {
+		mutex_unlock(&fs_info->chunk_mutex);
+		return -EINVAL;
+	}
+
+	btrfs_set_super_total_bytes(super_copy,
+			round_down(old_total + diff, fs_info->sectorsize));
+	device->fs_devices->total_rw_bytes += diff;
+
+	btrfs_device_set_total_bytes(device, new_size);
+	btrfs_device_set_disk_total_bytes(device, new_size);
+	btrfs_clear_space_info_full(device->fs_info);
+	if (list_empty(&device->post_commit_list))
+		list_add_tail(&device->post_commit_list,
+			      &trans->transaction->dev_update_list);
+	mutex_unlock(&fs_info->chunk_mutex);
+
+	return btrfs_update_device(trans, device);
+}
+
+static int btrfs_free_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_root *root = fs_info->chunk_root;
+	int ret;
+	struct btrfs_path *path;
+	struct btrfs_key key;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	key.objectid = BTRFS_FIRST_CHUNK_TREE_OBJECTID;
+	key.offset = chunk_offset;
+	key.type = BTRFS_CHUNK_ITEM_KEY;
+
+	ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
+	if (ret < 0)
+		goto out;
+	else if (ret > 0) { /* Logic error or corruption */
+		btrfs_handle_fs_error(fs_info, -ENOENT,
+				      "Failed lookup while freeing chunk.");
+		ret = -ENOENT;
+		goto out;
+	}
+
+	ret = btrfs_del_item(trans, root, path);
+	if (ret < 0)
+		btrfs_handle_fs_error(fs_info, ret,
+				      "Failed to delete chunk item.");
+out:
+	btrfs_free_path(path);
+	return ret;
+}
+
+static int btrfs_del_sys_chunk(struct btrfs_fs_info *fs_info, u64 chunk_offset)
+{
+	struct btrfs_super_block *super_copy = fs_info->super_copy;
+	struct btrfs_disk_key *disk_key;
+	struct btrfs_chunk *chunk;
+	u8 *ptr;
+	int ret = 0;
+	u32 num_stripes;
+	u32 array_size;
+	u32 len = 0;
+	u32 cur;
+	struct btrfs_key key;
+
+	mutex_lock(&fs_info->chunk_mutex);
+	array_size = btrfs_super_sys_array_size(super_copy);
+
+	ptr = super_copy->sys_chunk_array;
+	cur = 0;
+
+	while (cur < array_size) {
+		disk_key = (struct btrfs_disk_key *)ptr;
+		btrfs_disk_key_to_cpu(&key, disk_key);
+
+		len = sizeof(*disk_key);
+
+		if (key.type == BTRFS_CHUNK_ITEM_KEY) {
+			chunk = (struct btrfs_chunk *)(ptr + len);
+			num_stripes = btrfs_stack_chunk_num_stripes(chunk);
+			len += btrfs_chunk_item_size(num_stripes);
+		} else {
+			ret = -EIO;
+			break;
+		}
+		if (key.objectid == BTRFS_FIRST_CHUNK_TREE_OBJECTID &&
+		    key.offset == chunk_offset) {
+			memmove(ptr, ptr + len, array_size - (cur + len));
+			array_size -= len;
+			btrfs_set_super_sys_array_size(super_copy, array_size);
+		} else {
+			ptr += len;
+			cur += len;
+		}
+	}
+	mutex_unlock(&fs_info->chunk_mutex);
+	return ret;
+}
+
+/*
+ * btrfs_get_chunk_map() - Find the mapping containing the given logical extent.
+ * @logical: Logical block offset in bytes.
+ * @length: Length of extent in bytes.
+ *
+ * Return: Chunk mapping or ERR_PTR.
+ */
+struct extent_map *btrfs_get_chunk_map(struct btrfs_fs_info *fs_info,
+				       u64 logical, u64 length)
+{
+	struct extent_map_tree *em_tree;
+	struct extent_map *em;
+
+	em_tree = &fs_info->mapping_tree;
+	read_lock(&em_tree->lock);
+	em = lookup_extent_mapping(em_tree, logical, length);
+	read_unlock(&em_tree->lock);
+
+	if (!em) {
+		btrfs_crit(fs_info,
+			   "unable to find chunk map for logical %llu length %llu",
+			   logical, length);
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (em->start > logical || em->start + em->len <= logical) {
+		btrfs_crit(fs_info,
+			   "found a bad chunk map, wanted %llu-%llu, found %llu-%llu",
+			   logical, logical + length, em->start, em->start + em->len);
+		free_extent_map(em);
+		return ERR_PTR(-EINVAL);
+	}
+
+	/* callers are responsible for dropping em's ref. */
+	return em;
+}
+
+int btrfs_remove_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct extent_map *em;
+	struct map_lookup *map;
+	u64 dev_extent_len = 0;
+	int i, ret = 0;
+	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
+
+	em = btrfs_get_chunk_map(fs_info, chunk_offset, 1);
+	if (IS_ERR(em)) {
+		/*
+		 * This is a logic error, but we don't want to just rely on the
+		 * user having built with ASSERT enabled, so if ASSERT doesn't
+		 * do anything we still error out.
+		 */
+		ASSERT(0);
+		return PTR_ERR(em);
+	}
+	map = em->map_lookup;
+	mutex_lock(&fs_info->chunk_mutex);
+	check_system_chunk(trans, map->type);
+	mutex_unlock(&fs_info->chunk_mutex);
+
+	/*
+	 * Take the device list mutex to prevent races with the final phase of
+	 * a device replace operation that replaces the device object associated
+	 * with map stripes (dev-replace.c:btrfs_dev_replace_finishing()).
+	 */
+	mutex_lock(&fs_devices->device_list_mutex);
+	for (i = 0; i < map->num_stripes; i++) {
+		struct btrfs_device *device = map->stripes[i].dev;
+		ret = btrfs_free_dev_extent(trans, device,
+					    map->stripes[i].physical,
+					    &dev_extent_len);
+		if (ret) {
+			mutex_unlock(&fs_devices->device_list_mutex);
+			btrfs_abort_transaction(trans, ret);
+			goto out;
+		}
+
+		if (device->bytes_used > 0) {
+			mutex_lock(&fs_info->chunk_mutex);
+			btrfs_device_set_bytes_used(device,
+					device->bytes_used - dev_extent_len);
+			atomic64_add(dev_extent_len, &fs_info->free_chunk_space);
+			btrfs_clear_space_info_full(fs_info);
+			mutex_unlock(&fs_info->chunk_mutex);
+		}
+
+		ret = btrfs_update_device(trans, device);
+		if (ret) {
+			mutex_unlock(&fs_devices->device_list_mutex);
+			btrfs_abort_transaction(trans, ret);
+			goto out;
+		}
+	}
+	mutex_unlock(&fs_devices->device_list_mutex);
+
+	ret = btrfs_free_chunk(trans, chunk_offset);
+	if (ret) {
+		btrfs_abort_transaction(trans, ret);
+		goto out;
+	}
+
+	trace_btrfs_chunk_free(fs_info, map, chunk_offset, em->len);
+
+	if (map->type & BTRFS_BLOCK_GROUP_SYSTEM) {
+		ret = btrfs_del_sys_chunk(fs_info, chunk_offset);
+		if (ret) {
+			btrfs_abort_transaction(trans, ret);
+			goto out;
+		}
+	}
+
+	ret = btrfs_remove_block_group(trans, chunk_offset, em);
+	if (ret) {
+		btrfs_abort_transaction(trans, ret);
+		goto out;
+	}
+
+out:
+	/* once for us */
+	free_extent_map(em);
+	return ret;
+}
+
+static int btrfs_relocate_chunk(struct btrfs_fs_info *fs_info, u64 chunk_offset)
+{
+	struct btrfs_root *root = fs_info->chunk_root;
+	struct btrfs_trans_handle *trans;
+	struct btrfs_block_group *block_group;
+	int ret;
+
+	/*
+	 * Prevent races with automatic removal of unused block groups.
+	 * After we relocate and before we remove the chunk with offset
+	 * chunk_offset, automatic removal of the block group can kick in,
+	 * resulting in a failure when calling btrfs_remove_chunk() below.
+	 *
+	 * Make sure to acquire this mutex before doing a tree search (dev
+	 * or chunk trees) to find chunks. Otherwise the cleaner kthread might
+	 * call btrfs_remove_chunk() (through btrfs_delete_unused_bgs()) after
+	 * we release the path used to search the chunk/dev tree and before
+	 * the current task acquires this mutex and calls us.
+	 */
+	lockdep_assert_held(&fs_info->delete_unused_bgs_mutex);
+
+	/* step one, relocate all the extents inside this chunk */
+	btrfs_scrub_pause(fs_info);
+	ret = btrfs_relocate_block_group(fs_info, chunk_offset);
+	btrfs_scrub_continue(fs_info);
+	if (ret)
+		return ret;
+
+	block_group = btrfs_lookup_block_group(fs_info, chunk_offset);
+	if (!block_group)
+		return -ENOENT;
+	btrfs_discard_cancel_work(&fs_info->discard_ctl, block_group);
+	btrfs_put_block_group(block_group);
+
+	trans = btrfs_start_trans_remove_block_group(root->fs_info,
+						     chunk_offset);
+	if (IS_ERR(trans)) {
+		ret = PTR_ERR(trans);
+		btrfs_handle_fs_error(root->fs_info, ret, NULL);
+		return ret;
+	}
+
+	/*
+	 * step two, delete the device extents and the
+	 * chunk tree entries
+	 */
+	ret = btrfs_remove_chunk(trans, chunk_offset);
+	btrfs_end_transaction(trans);
+	return ret;
+}
+
+static int btrfs_relocate_sys_chunks(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_root *chunk_root = fs_info->chunk_root;
+	struct btrfs_path *path;
+	struct extent_buffer *leaf;
+	struct btrfs_chunk *chunk;
+	struct btrfs_key key;
+	struct btrfs_key found_key;
+	u64 chunk_type;
+	bool retried = false;
+	int failed = 0;
+	int ret;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+again:
+	key.objectid = BTRFS_FIRST_CHUNK_TREE_OBJECTID;
+	key.offset = (u64)-1;
+	key.type = BTRFS_CHUNK_ITEM_KEY;
+
+	while (1) {
+		mutex_lock(&fs_info->delete_unused_bgs_mutex);
+		ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0);
+		if (ret < 0) {
+			mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+			goto error;
+		}
+		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;
+	u64 bytes_used;
+	u64 chunk_type;
+
+	cache = btrfs_lookup_block_group(fs_info, chunk_offset);
+	ASSERT(cache);
+	chunk_type = cache->flags;
+	btrfs_put_block_group(cache);
+
+	if (!(chunk_type & BTRFS_BLOCK_GROUP_DATA))
+		return 0;
+
+	spin_lock(&fs_info->data_sinfo->lock);
+	bytes_used = fs_info->data_sinfo->bytes_used;
+	spin_unlock(&fs_info->data_sinfo->lock);
+
+	if (!bytes_used) {
+		struct btrfs_trans_handle *trans;
+		int ret;
+
+		trans =	btrfs_join_transaction(fs_info->tree_root);
+		if (IS_ERR(trans))
+			return PTR_ERR(trans);
+
+		ret = btrfs_force_chunk_alloc(trans, BTRFS_BLOCK_GROUP_DATA);
+		btrfs_end_transaction(trans);
+		if (ret < 0)
+			return ret;
+		return 1;
+	}
+
+	return 0;
+}
+
+static int insert_balance_item(struct btrfs_fs_info *fs_info,
+			       struct btrfs_balance_control *bctl)
+{
+	struct btrfs_root *root = fs_info->tree_root;
+	struct btrfs_trans_handle *trans;
+	struct btrfs_balance_item *item;
+	struct btrfs_disk_balance_args disk_bargs;
+	struct btrfs_path *path;
+	struct extent_buffer *leaf;
+	struct btrfs_key key;
+	int ret, err;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	trans = btrfs_start_transaction(root, 0);
+	if (IS_ERR(trans)) {
+		btrfs_free_path(path);
+		return PTR_ERR(trans);
+	}
+
+	key.objectid = BTRFS_BALANCE_OBJECTID;
+	key.type = BTRFS_TEMPORARY_ITEM_KEY;
+	key.offset = 0;
+
+	ret = btrfs_insert_empty_item(trans, root, path, &key,
+				      sizeof(*item));
+	if (ret)
+		goto out;
+
+	leaf = path->nodes[0];
+	item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_balance_item);
+
+	memzero_extent_buffer(leaf, (unsigned long)item, sizeof(*item));
+
+	btrfs_cpu_balance_args_to_disk(&disk_bargs, &bctl->data);
+	btrfs_set_balance_data(leaf, item, &disk_bargs);
+	btrfs_cpu_balance_args_to_disk(&disk_bargs, &bctl->meta);
+	btrfs_set_balance_meta(leaf, item, &disk_bargs);
+	btrfs_cpu_balance_args_to_disk(&disk_bargs, &bctl->sys);
+	btrfs_set_balance_sys(leaf, item, &disk_bargs);
+
+	btrfs_set_balance_flags(leaf, item, bctl->flags);
+
+	btrfs_mark_buffer_dirty(leaf);
+out:
+	btrfs_free_path(path);
+	err = btrfs_commit_transaction(trans);
+	if (err && !ret)
+		ret = err;
+	return ret;
+}
+
+static int del_balance_item(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_root *root = fs_info->tree_root;
+	struct btrfs_trans_handle *trans;
+	struct btrfs_path *path;
+	struct btrfs_key key;
+	int ret, err;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	trans = btrfs_start_transaction_fallback_global_rsv(root, 0);
+	if (IS_ERR(trans)) {
+		btrfs_free_path(path);
+		return PTR_ERR(trans);
+	}
+
+	key.objectid = BTRFS_BALANCE_OBJECTID;
+	key.type = BTRFS_TEMPORARY_ITEM_KEY;
+	key.offset = 0;
+
+	ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
+	if (ret < 0)
+		goto out;
+	if (ret > 0) {
+		ret = -ENOENT;
+		goto out;
+	}
+
+	ret = btrfs_del_item(trans, root, path);
+out:
+	btrfs_free_path(path);
+	err = btrfs_commit_transaction(trans);
+	if (err && !ret)
+		ret = err;
+	return ret;
+}
+
+/*
+ * This is a heuristic used to reduce the number of chunks balanced on
+ * resume after balance was interrupted.
+ */
+static void update_balance_args(struct btrfs_balance_control *bctl)
+{
+	/*
+	 * Turn on soft mode for chunk types that were being converted.
+	 */
+	if (bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT)
+		bctl->data.flags |= BTRFS_BALANCE_ARGS_SOFT;
+	if (bctl->sys.flags & BTRFS_BALANCE_ARGS_CONVERT)
+		bctl->sys.flags |= BTRFS_BALANCE_ARGS_SOFT;
+	if (bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT)
+		bctl->meta.flags |= BTRFS_BALANCE_ARGS_SOFT;
+
+	/*
+	 * Turn on usage filter if is not already used.  The idea is
+	 * that chunks that we have already balanced should be
+	 * reasonably full.  Don't do it for chunks that are being
+	 * converted - that will keep us from relocating unconverted
+	 * (albeit full) chunks.
+	 */
+	if (!(bctl->data.flags & BTRFS_BALANCE_ARGS_USAGE) &&
+	    !(bctl->data.flags & BTRFS_BALANCE_ARGS_USAGE_RANGE) &&
+	    !(bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT)) {
+		bctl->data.flags |= BTRFS_BALANCE_ARGS_USAGE;
+		bctl->data.usage = 90;
+	}
+	if (!(bctl->sys.flags & BTRFS_BALANCE_ARGS_USAGE) &&
+	    !(bctl->sys.flags & BTRFS_BALANCE_ARGS_USAGE_RANGE) &&
+	    !(bctl->sys.flags & BTRFS_BALANCE_ARGS_CONVERT)) {
+		bctl->sys.flags |= BTRFS_BALANCE_ARGS_USAGE;
+		bctl->sys.usage = 90;
+	}
+	if (!(bctl->meta.flags & BTRFS_BALANCE_ARGS_USAGE) &&
+	    !(bctl->meta.flags & BTRFS_BALANCE_ARGS_USAGE_RANGE) &&
+	    !(bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT)) {
+		bctl->meta.flags |= BTRFS_BALANCE_ARGS_USAGE;
+		bctl->meta.usage = 90;
+	}
+}
+
+/*
+ * Clear the balance status in fs_info and delete the balance item from disk.
+ */
+static void reset_balance_state(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_balance_control *bctl = fs_info->balance_ctl;
+	int ret;
+
+	BUG_ON(!fs_info->balance_ctl);
+
+	spin_lock(&fs_info->balance_lock);
+	fs_info->balance_ctl = NULL;
+	spin_unlock(&fs_info->balance_lock);
+
+	kfree(bctl);
+	ret = del_balance_item(fs_info);
+	if (ret)
+		btrfs_handle_fs_error(fs_info, ret, NULL);
+}
+
+/*
+ * Balance filters.  Return 1 if chunk should be filtered out
+ * (should not be balanced).
+ */
+static int chunk_profiles_filter(u64 chunk_type,
+				 struct btrfs_balance_args *bargs)
+{
+	chunk_type = chunk_to_extended(chunk_type) &
+				BTRFS_EXTENDED_PROFILE_MASK;
+
+	if (bargs->profiles & chunk_type)
+		return 0;
+
+	return 1;
+}
+
+static int chunk_usage_range_filter(struct btrfs_fs_info *fs_info, u64 chunk_offset,
+			      struct btrfs_balance_args *bargs)
+{
+	struct btrfs_block_group *cache;
+	u64 chunk_used;
+	u64 user_thresh_min;
+	u64 user_thresh_max;
+	int ret = 1;
+
+	cache = btrfs_lookup_block_group(fs_info, chunk_offset);
+	chunk_used = cache->used;
+
+	if (bargs->usage_min == 0)
+		user_thresh_min = 0;
+	else
+		user_thresh_min = div_factor_fine(cache->length,
+						  bargs->usage_min);
+
+	if (bargs->usage_max == 0)
+		user_thresh_max = 1;
+	else if (bargs->usage_max > 100)
+		user_thresh_max = cache->length;
+	else
+		user_thresh_max = div_factor_fine(cache->length,
+						  bargs->usage_max);
+
+	if (user_thresh_min <= chunk_used && chunk_used < user_thresh_max)
+		ret = 0;
+
+	btrfs_put_block_group(cache);
+	return ret;
+}
+
+static int chunk_usage_filter(struct btrfs_fs_info *fs_info,
+		u64 chunk_offset, struct btrfs_balance_args *bargs)
+{
+	struct btrfs_block_group *cache;
+	u64 chunk_used, user_thresh;
+	int ret = 1;
+
+	cache = btrfs_lookup_block_group(fs_info, chunk_offset);
+	chunk_used = cache->used;
+
+	if (bargs->usage_min == 0)
+		user_thresh = 1;
+	else if (bargs->usage > 100)
+		user_thresh = cache->length;
+	else
+		user_thresh = div_factor_fine(cache->length, bargs->usage);
+
+	if (chunk_used < user_thresh)
+		ret = 0;
+
+	btrfs_put_block_group(cache);
+	return ret;
+}
+
+static int chunk_devid_filter(struct extent_buffer *leaf,
+			      struct btrfs_chunk *chunk,
+			      struct btrfs_balance_args *bargs)
+{
+	struct btrfs_stripe *stripe;
+	int num_stripes = btrfs_chunk_num_stripes(leaf, chunk);
+	int i;
+
+	for (i = 0; i < num_stripes; i++) {
+		stripe = btrfs_stripe_nr(chunk, i);
+		if (btrfs_stripe_devid(leaf, stripe) == bargs->devid)
+			return 0;
+	}
+
+	return 1;
+}
+
+static u64 calc_data_stripes(u64 type, int num_stripes)
+{
+	const int index = btrfs_bg_flags_to_raid_index(type);
+	const int ncopies = btrfs_raid_array[index].ncopies;
+	const int nparity = btrfs_raid_array[index].nparity;
+
+	if (nparity)
+		return num_stripes - nparity;
+	else
+		return num_stripes / ncopies;
+}
+
+/* [pstart, pend) */
+static int chunk_drange_filter(struct extent_buffer *leaf,
+			       struct btrfs_chunk *chunk,
+			       struct btrfs_balance_args *bargs)
+{
+	struct btrfs_stripe *stripe;
+	int num_stripes = btrfs_chunk_num_stripes(leaf, chunk);
+	u64 stripe_offset;
+	u64 stripe_length;
+	u64 type;
+	int factor;
+	int i;
+
+	if (!(bargs->flags & BTRFS_BALANCE_ARGS_DEVID))
+		return 0;
+
+	type = btrfs_chunk_type(leaf, chunk);
+	factor = calc_data_stripes(type, num_stripes);
+
+	for (i = 0; i < num_stripes; i++) {
+		stripe = btrfs_stripe_nr(chunk, i);
+		if (btrfs_stripe_devid(leaf, stripe) != bargs->devid)
+			continue;
+
+		stripe_offset = btrfs_stripe_offset(leaf, stripe);
+		stripe_length = btrfs_chunk_length(leaf, chunk);
+		stripe_length = div_u64(stripe_length, factor);
+
+		if (stripe_offset < bargs->pend &&
+		    stripe_offset + stripe_length > bargs->pstart)
+			return 0;
+	}
+
+	return 1;
+}
+
+/* [vstart, vend) */
+static int chunk_vrange_filter(struct extent_buffer *leaf,
+			       struct btrfs_chunk *chunk,
+			       u64 chunk_offset,
+			       struct btrfs_balance_args *bargs)
+{
+	if (chunk_offset < bargs->vend &&
+	    chunk_offset + btrfs_chunk_length(leaf, chunk) > bargs->vstart)
+		/* at least part of the chunk is inside this vrange */
+		return 0;
+
+	return 1;
+}
+
+static int chunk_stripes_range_filter(struct extent_buffer *leaf,
+			       struct btrfs_chunk *chunk,
+			       struct btrfs_balance_args *bargs)
+{
+	int num_stripes = btrfs_chunk_num_stripes(leaf, chunk);
+
+	if (bargs->stripes_min <= num_stripes
+			&& num_stripes <= bargs->stripes_max)
+		return 0;
+
+	return 1;
+}
+
+static int chunk_soft_convert_filter(u64 chunk_type,
+				     struct btrfs_balance_args *bargs)
+{
+	if (!(bargs->flags & BTRFS_BALANCE_ARGS_CONVERT))
+		return 0;
+
+	chunk_type = chunk_to_extended(chunk_type) &
+				BTRFS_EXTENDED_PROFILE_MASK;
+
+	if (bargs->target == chunk_type)
+		return 1;
+
+	return 0;
+}
+
+static int should_balance_chunk(struct extent_buffer *leaf,
+				struct btrfs_chunk *chunk, u64 chunk_offset)
+{
+	struct btrfs_fs_info *fs_info = leaf->fs_info;
+	struct btrfs_balance_control *bctl = fs_info->balance_ctl;
+	struct btrfs_balance_args *bargs = NULL;
+	u64 chunk_type = btrfs_chunk_type(leaf, chunk);
+
+	/* type filter */
+	if (!((chunk_type & BTRFS_BLOCK_GROUP_TYPE_MASK) &
+	      (bctl->flags & BTRFS_BALANCE_TYPE_MASK))) {
+		return 0;
+	}
+
+	if (chunk_type & BTRFS_BLOCK_GROUP_DATA)
+		bargs = &bctl->data;
+	else if (chunk_type & BTRFS_BLOCK_GROUP_SYSTEM)
+		bargs = &bctl->sys;
+	else if (chunk_type & BTRFS_BLOCK_GROUP_METADATA)
+		bargs = &bctl->meta;
+
+	/* profiles filter */
+	if ((bargs->flags & BTRFS_BALANCE_ARGS_PROFILES) &&
+	    chunk_profiles_filter(chunk_type, bargs)) {
+		return 0;
+	}
+
+	/* usage filter */
+	if ((bargs->flags & BTRFS_BALANCE_ARGS_USAGE) &&
+	    chunk_usage_filter(fs_info, chunk_offset, bargs)) {
+		return 0;
+	} else if ((bargs->flags & BTRFS_BALANCE_ARGS_USAGE_RANGE) &&
+	    chunk_usage_range_filter(fs_info, chunk_offset, bargs)) {
+		return 0;
+	}
+
+	/* devid filter */
+	if ((bargs->flags & BTRFS_BALANCE_ARGS_DEVID) &&
+	    chunk_devid_filter(leaf, chunk, bargs)) {
+		return 0;
+	}
+
+	/* drange filter, makes sense only with devid filter */
+	if ((bargs->flags & BTRFS_BALANCE_ARGS_DRANGE) &&
+	    chunk_drange_filter(leaf, chunk, bargs)) {
+		return 0;
+	}
+
+	/* vrange filter */
+	if ((bargs->flags & BTRFS_BALANCE_ARGS_VRANGE) &&
+	    chunk_vrange_filter(leaf, chunk, chunk_offset, bargs)) {
+		return 0;
+	}
+
+	/* stripes filter */
+	if ((bargs->flags & BTRFS_BALANCE_ARGS_STRIPES_RANGE) &&
+	    chunk_stripes_range_filter(leaf, chunk, bargs)) {
+		return 0;
+	}
+
+	/* soft profile changing mode */
+	if ((bargs->flags & BTRFS_BALANCE_ARGS_SOFT) &&
+	    chunk_soft_convert_filter(chunk_type, bargs)) {
+		return 0;
+	}
+
+	/*
+	 * limited by count, must be the last filter
+	 */
+	if ((bargs->flags & BTRFS_BALANCE_ARGS_LIMIT)) {
+		if (bargs->limit == 0)
+			return 0;
+		else
+			bargs->limit--;
+	} else if ((bargs->flags & BTRFS_BALANCE_ARGS_LIMIT_RANGE)) {
+		/*
+		 * Same logic as the 'limit' filter; the minimum cannot be
+		 * determined here because we do not have the global information
+		 * about the count of all chunks that satisfy the filters.
+		 */
+		if (bargs->limit_max == 0)
+			return 0;
+		else
+			bargs->limit_max--;
+	}
+
+	return 1;
+}
+
+static int __btrfs_balance(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_balance_control *bctl = fs_info->balance_ctl;
+	struct btrfs_root *chunk_root = fs_info->chunk_root;
+	u64 chunk_type;
+	struct btrfs_chunk *chunk;
+	struct btrfs_path *path = NULL;
+	struct btrfs_key key;
+	struct btrfs_key found_key;
+	struct extent_buffer *leaf;
+	int slot;
+	int ret;
+	int enospc_errors = 0;
+	bool counting = true;
+	/* The single value limit and min/max limits use the same bytes in the */
+	u64 limit_data = bctl->data.limit;
+	u64 limit_meta = bctl->meta.limit;
+	u64 limit_sys = bctl->sys.limit;
+	u32 count_data = 0;
+	u32 count_meta = 0;
+	u32 count_sys = 0;
+	int chunk_reserved = 0;
+
+	path = btrfs_alloc_path();
+	if (!path) {
+		ret = -ENOMEM;
+		goto error;
+	}
+
+	/* zero out stat counters */
+	spin_lock(&fs_info->balance_lock);
+	memset(&bctl->stat, 0, sizeof(bctl->stat));
+	spin_unlock(&fs_info->balance_lock);
+again:
+	if (!counting) {
+		/*
+		 * The single value limit and min/max limits use the same bytes
+		 * in the
+		 */
+		bctl->data.limit = limit_data;
+		bctl->meta.limit = limit_meta;
+		bctl->sys.limit = limit_sys;
+	}
+	key.objectid = BTRFS_FIRST_CHUNK_TREE_OBJECTID;
+	key.offset = (u64)-1;
+	key.type = BTRFS_CHUNK_ITEM_KEY;
+
+	while (1) {
+		if ((!counting && atomic_read(&fs_info->balance_pause_req)) ||
+		    atomic_read(&fs_info->balance_cancel_req)) {
+			ret = -ECANCELED;
+			goto error;
+		}
+
+		mutex_lock(&fs_info->delete_unused_bgs_mutex);
+		ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0);
+		if (ret < 0) {
+			mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+			goto error;
+		}
+
+		/*
+		 * this shouldn't happen, it means the last relocate
+		 * failed
+		 */
+		if (ret == 0)
+			BUG(); /* FIXME break ? */
+
+		ret = btrfs_previous_item(chunk_root, path, 0,
+					  BTRFS_CHUNK_ITEM_KEY);
+		if (ret) {
+			mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+			ret = 0;
+			break;
+		}
+
+		leaf = path->nodes[0];
+		slot = path->slots[0];
+		btrfs_item_key_to_cpu(leaf, &found_key, slot);
+
+		if (found_key.objectid != key.objectid) {
+			mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+			break;
+		}
+
+		chunk = btrfs_item_ptr(leaf, slot, struct btrfs_chunk);
+		chunk_type = btrfs_chunk_type(leaf, chunk);
+
+		if (!counting) {
+			spin_lock(&fs_info->balance_lock);
+			bctl->stat.considered++;
+			spin_unlock(&fs_info->balance_lock);
+		}
+
+		ret = should_balance_chunk(leaf, chunk, found_key.offset);
+
+		btrfs_release_path(path);
+		if (!ret) {
+			mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+			goto loop;
+		}
+
+		if (counting) {
+			mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+			spin_lock(&fs_info->balance_lock);
+			bctl->stat.expected++;
+			spin_unlock(&fs_info->balance_lock);
+
+			if (chunk_type & BTRFS_BLOCK_GROUP_DATA)
+				count_data++;
+			else if (chunk_type & BTRFS_BLOCK_GROUP_SYSTEM)
+				count_sys++;
+			else if (chunk_type & BTRFS_BLOCK_GROUP_METADATA)
+				count_meta++;
+
+			goto loop;
+		}
+
+		/*
+		 * Apply limit_min filter, no need to check if the LIMITS
+		 * filter is used, limit_min is 0 by default
+		 */
+		if (((chunk_type & BTRFS_BLOCK_GROUP_DATA) &&
+					count_data < bctl->data.limit_min)
+				|| ((chunk_type & BTRFS_BLOCK_GROUP_METADATA) &&
+					count_meta < bctl->meta.limit_min)
+				|| ((chunk_type & BTRFS_BLOCK_GROUP_SYSTEM) &&
+					count_sys < bctl->sys.limit_min)) {
+			mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+			goto loop;
+		}
+
+		if (!chunk_reserved) {
+			/*
+			 * We may be relocating the only data chunk we have,
+			 * which could potentially end up with losing data's
+			 * raid profile, so lets allocate an empty one in
+			 * advance.
+			 */
+			ret = btrfs_may_alloc_data_chunk(fs_info,
+							 found_key.offset);
+			if (ret < 0) {
+				mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+				goto error;
+			} else if (ret == 1) {
+				chunk_reserved = 1;
+			}
+		}
+
+		ret = btrfs_relocate_chunk(fs_info, found_key.offset);
+		mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+		if (ret == -ENOSPC) {
+			enospc_errors++;
+		} else if (ret == -ETXTBSY) {
+			btrfs_info(fs_info,
+	   "skipping relocation of block group %llu due to active swapfile",
+				   found_key.offset);
+			ret = 0;
+		} else if (ret) {
+			goto error;
+		} else {
+			spin_lock(&fs_info->balance_lock);
+			bctl->stat.completed++;
+			spin_unlock(&fs_info->balance_lock);
+		}
+loop:
+		if (found_key.offset == 0)
+			break;
+		key.offset = found_key.offset - 1;
+	}
+
+	if (counting) {
+		btrfs_release_path(path);
+		counting = false;
+		goto again;
+	}
+error:
+	btrfs_free_path(path);
+	if (enospc_errors) {
+		btrfs_info(fs_info, "%d enospc errors during balance",
+			   enospc_errors);
+		if (!ret)
+			ret = -ENOSPC;
+	}
+
+	return ret;
+}
+
+/**
+ * alloc_profile_is_valid - see if a given profile is valid and reduced
+ * @flags: profile to validate
+ * @extended: if true @flags is treated as an extended profile
+ */
+static int alloc_profile_is_valid(u64 flags, int extended)
+{
+	u64 mask = (extended ? BTRFS_EXTENDED_PROFILE_MASK :
+			       BTRFS_BLOCK_GROUP_PROFILE_MASK);
+
+	flags &= ~BTRFS_BLOCK_GROUP_TYPE_MASK;
+
+	/* 1) check that all other bits are zeroed */
+	if (flags & ~mask)
+		return 0;
+
+	/* 2) see if profile is reduced */
+	if (flags == 0)
+		return !extended; /* "0" is valid for usual profiles */
+
+	return has_single_bit_set(flags);
+}
+
+static inline int balance_need_close(struct btrfs_fs_info *fs_info)
+{
+	/* cancel requested || normal exit path */
+	return atomic_read(&fs_info->balance_cancel_req) ||
+		(atomic_read(&fs_info->balance_pause_req) == 0 &&
+		 atomic_read(&fs_info->balance_cancel_req) == 0);
+}
+
+/*
+ * Validate target profile against allowed profiles and return true if it's OK.
+ * Otherwise print the error message and return false.
+ */
+static inline int validate_convert_profile(struct btrfs_fs_info *fs_info,
+		const struct btrfs_balance_args *bargs,
+		u64 allowed, const char *type)
+{
+	if (!(bargs->flags & BTRFS_BALANCE_ARGS_CONVERT))
+		return true;
+
+	/* Profile is valid and does not have bits outside of the allowed set */
+	if (alloc_profile_is_valid(bargs->target, 1) &&
+	    (bargs->target & ~allowed) == 0)
+		return true;
+
+	btrfs_err(fs_info, "balance: invalid convert %s profile %s",
+			type, btrfs_bg_type_to_raid_name(bargs->target));
+	return false;
+}
+
+/*
+ * Fill @buf with textual description of balance filter flags @bargs, up to
+ * @size_buf including the terminating null. The output may be trimmed if it
+ * does not fit into the provided buffer.
+ */
+static void describe_balance_args(struct btrfs_balance_args *bargs, char *buf,
+				 u32 size_buf)
+{
+	int ret;
+	u32 size_bp = size_buf;
+	char *bp = buf;
+	u64 flags = bargs->flags;
+	char tmp_buf[128] = {'\0'};
+
+	if (!flags)
+		return;
+
+#define CHECK_APPEND_NOARG(a)						\
+	do {								\
+		ret = snprintf(bp, size_bp, (a));			\
+		if (ret < 0 || ret >= size_bp)				\
+			goto out_overflow;				\
+		size_bp -= ret;						\
+		bp += ret;						\
+	} while (0)
+
+#define CHECK_APPEND_1ARG(a, v1)					\
+	do {								\
+		ret = snprintf(bp, size_bp, (a), (v1));			\
+		if (ret < 0 || ret >= size_bp)				\
+			goto out_overflow;				\
+		size_bp -= ret;						\
+		bp += ret;						\
+	} while (0)
+
+#define CHECK_APPEND_2ARG(a, v1, v2)					\
+	do {								\
+		ret = snprintf(bp, size_bp, (a), (v1), (v2));		\
+		if (ret < 0 || ret >= size_bp)				\
+			goto out_overflow;				\
+		size_bp -= ret;						\
+		bp += ret;						\
+	} while (0)
+
+	if (flags & BTRFS_BALANCE_ARGS_CONVERT)
+		CHECK_APPEND_1ARG("convert=%s,",
+				  btrfs_bg_type_to_raid_name(bargs->target));
+
+	if (flags & BTRFS_BALANCE_ARGS_SOFT)
+		CHECK_APPEND_NOARG("soft,");
+
+	if (flags & BTRFS_BALANCE_ARGS_PROFILES) {
+		btrfs_describe_block_groups(bargs->profiles, tmp_buf,
+					    sizeof(tmp_buf));
+		CHECK_APPEND_1ARG("profiles=%s,", tmp_buf);
+	}
+
+	if (flags & BTRFS_BALANCE_ARGS_USAGE)
+		CHECK_APPEND_1ARG("usage=%llu,", bargs->usage);
+
+	if (flags & BTRFS_BALANCE_ARGS_USAGE_RANGE)
+		CHECK_APPEND_2ARG("usage=%u..%u,",
+				  bargs->usage_min, bargs->usage_max);
+
+	if (flags & BTRFS_BALANCE_ARGS_DEVID)
+		CHECK_APPEND_1ARG("devid=%llu,", bargs->devid);
+
+	if (flags & BTRFS_BALANCE_ARGS_DRANGE)
+		CHECK_APPEND_2ARG("drange=%llu..%llu,",
+				  bargs->pstart, bargs->pend);
+
+	if (flags & BTRFS_BALANCE_ARGS_VRANGE)
+		CHECK_APPEND_2ARG("vrange=%llu..%llu,",
+				  bargs->vstart, bargs->vend);
+
+	if (flags & BTRFS_BALANCE_ARGS_LIMIT)
+		CHECK_APPEND_1ARG("limit=%llu,", bargs->limit);
+
+	if (flags & BTRFS_BALANCE_ARGS_LIMIT_RANGE)
+		CHECK_APPEND_2ARG("limit=%u..%u,",
+				bargs->limit_min, bargs->limit_max);
+
+	if (flags & BTRFS_BALANCE_ARGS_STRIPES_RANGE)
+		CHECK_APPEND_2ARG("stripes=%u..%u,",
+				  bargs->stripes_min, bargs->stripes_max);
+
+#undef CHECK_APPEND_2ARG
+#undef CHECK_APPEND_1ARG
+#undef CHECK_APPEND_NOARG
+
+out_overflow:
+
+	if (size_bp < size_buf)
+		buf[size_buf - size_bp - 1] = '\0'; /* remove last , */
+	else
+		buf[0] = '\0';
+}
+
+static void describe_balance_start_or_resume(struct btrfs_fs_info *fs_info)
+{
+	u32 size_buf = 1024;
+	char tmp_buf[192] = {'\0'};
+	char *buf;
+	char *bp;
+	u32 size_bp = size_buf;
+	int ret;
+	struct btrfs_balance_control *bctl = fs_info->balance_ctl;
+
+	buf = kzalloc(size_buf, GFP_KERNEL);
+	if (!buf)
+		return;
+
+	bp = buf;
+
+#define CHECK_APPEND_1ARG(a, v1)					\
+	do {								\
+		ret = snprintf(bp, size_bp, (a), (v1));			\
+		if (ret < 0 || ret >= size_bp)				\
+			goto out_overflow;				\
+		size_bp -= ret;						\
+		bp += ret;						\
+	} while (0)
+
+	if (bctl->flags & BTRFS_BALANCE_FORCE)
+		CHECK_APPEND_1ARG("%s", "-f ");
+
+	if (bctl->flags & BTRFS_BALANCE_DATA) {
+		describe_balance_args(&bctl->data, tmp_buf, sizeof(tmp_buf));
+		CHECK_APPEND_1ARG("-d%s ", tmp_buf);
+	}
+
+	if (bctl->flags & BTRFS_BALANCE_METADATA) {
+		describe_balance_args(&bctl->meta, tmp_buf, sizeof(tmp_buf));
+		CHECK_APPEND_1ARG("-m%s ", tmp_buf);
+	}
+
+	if (bctl->flags & BTRFS_BALANCE_SYSTEM) {
+		describe_balance_args(&bctl->sys, tmp_buf, sizeof(tmp_buf));
+		CHECK_APPEND_1ARG("-s%s ", tmp_buf);
+	}
+
+#undef CHECK_APPEND_1ARG
+
+out_overflow:
+
+	if (size_bp < size_buf)
+		buf[size_buf - size_bp - 1] = '\0'; /* remove last " " */
+	btrfs_info(fs_info, "balance: %s %s",
+		   (bctl->flags & BTRFS_BALANCE_RESUME) ?
+		   "resume" : "start", buf);
+
+	kfree(buf);
+}
+
+/*
+ * Should be called with balance mutexe held
+ */
+int btrfs_balance(struct btrfs_fs_info *fs_info,
+		  struct btrfs_balance_control *bctl,
+		  struct btrfs_ioctl_balance_args *bargs)
+{
+	u64 meta_target, data_target;
+	u64 allowed;
+	int mixed = 0;
+	int ret;
+	u64 num_devices;
+	unsigned seq;
+	bool reducing_redundancy;
+	int i;
+
+	if (btrfs_fs_closing(fs_info) ||
+	    atomic_read(&fs_info->balance_pause_req) ||
+	    btrfs_should_cancel_balance(fs_info)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	allowed = btrfs_super_incompat_flags(fs_info->super_copy);
+	if (allowed & BTRFS_FEATURE_INCOMPAT_MIXED_GROUPS)
+		mixed = 1;
+
+	/*
+	 * In case of mixed groups both data and meta should be picked,
+	 * and identical options should be given for both of them.
+	 */
+	allowed = BTRFS_BALANCE_DATA | BTRFS_BALANCE_METADATA;
+	if (mixed && (bctl->flags & allowed)) {
+		if (!(bctl->flags & BTRFS_BALANCE_DATA) ||
+		    !(bctl->flags & BTRFS_BALANCE_METADATA) ||
+		    memcmp(&bctl->data, &bctl->meta, sizeof(bctl->data))) {
+			btrfs_err(fs_info,
+	  "balance: mixed groups data and metadata options must be the same");
+			ret = -EINVAL;
+			goto out;
+		}
+	}
+
+	/*
+	 * rw_devices will not change at the moment, device add/delete/replace
+	 * are exclusive
+	 */
+	num_devices = fs_info->fs_devices->rw_devices;
+
+	/*
+	 * SINGLE profile on-disk has no profile bit, but in-memory we have a
+	 * special bit for it, to make it easier to distinguish.  Thus we need
+	 * to set it manually, or balance would refuse the profile.
+	 */
+	allowed = BTRFS_AVAIL_ALLOC_BIT_SINGLE;
+	for (i = 0; i < ARRAY_SIZE(btrfs_raid_array); i++)
+		if (num_devices >= btrfs_raid_array[i].devs_min)
+			allowed |= btrfs_raid_array[i].bg_flag;
+
+	if (!validate_convert_profile(fs_info, &bctl->data, allowed, "data") ||
+	    !validate_convert_profile(fs_info, &bctl->meta, allowed, "metadata") ||
+	    !validate_convert_profile(fs_info, &bctl->sys,  allowed, "system")) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/*
+	 * Allow to reduce metadata or system integrity only if force set for
+	 * profiles with redundancy (copies, parity)
+	 */
+	allowed = 0;
+	for (i = 0; i < ARRAY_SIZE(btrfs_raid_array); i++) {
+		if (btrfs_raid_array[i].ncopies >= 2 ||
+		    btrfs_raid_array[i].tolerated_failures >= 1)
+			allowed |= btrfs_raid_array[i].bg_flag;
+	}
+	do {
+		seq = read_seqbegin(&fs_info->profiles_lock);
+
+		if (((bctl->sys.flags & BTRFS_BALANCE_ARGS_CONVERT) &&
+		     (fs_info->avail_system_alloc_bits & allowed) &&
+		     !(bctl->sys.target & allowed)) ||
+		    ((bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) &&
+		     (fs_info->avail_metadata_alloc_bits & allowed) &&
+		     !(bctl->meta.target & allowed)))
+			reducing_redundancy = true;
+		else
+			reducing_redundancy = false;
+
+		/* if we're not converting, the target field is uninitialized */
+		meta_target = (bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) ?
+			bctl->meta.target : fs_info->avail_metadata_alloc_bits;
+		data_target = (bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT) ?
+			bctl->data.target : fs_info->avail_data_alloc_bits;
+	} while (read_seqretry(&fs_info->profiles_lock, seq));
+
+	if (reducing_redundancy) {
+		if (bctl->flags & BTRFS_BALANCE_FORCE) {
+			btrfs_info(fs_info,
+			   "balance: force reducing metadata redundancy");
+		} else {
+			btrfs_err(fs_info,
+	"balance: reduces metadata redundancy, use --force if you want this");
+			ret = -EINVAL;
+			goto out;
+		}
+	}
+
+	if (btrfs_get_num_tolerated_disk_barrier_failures(meta_target) <
+		btrfs_get_num_tolerated_disk_barrier_failures(data_target)) {
+		btrfs_warn(fs_info,
+	"balance: metadata profile %s has lower redundancy than data profile %s",
+				btrfs_bg_type_to_raid_name(meta_target),
+				btrfs_bg_type_to_raid_name(data_target));
+	}
+
+	if (fs_info->send_in_progress) {
+		btrfs_warn_rl(fs_info,
+"cannot run balance while send operations are in progress (%d in progress)",
+			      fs_info->send_in_progress);
+		ret = -EAGAIN;
+		goto out;
+	}
+
+	ret = insert_balance_item(fs_info, bctl);
+	if (ret && ret != -EEXIST)
+		goto out;
+
+	if (!(bctl->flags & BTRFS_BALANCE_RESUME)) {
+		BUG_ON(ret == -EEXIST);
+		BUG_ON(fs_info->balance_ctl);
+		spin_lock(&fs_info->balance_lock);
+		fs_info->balance_ctl = bctl;
+		spin_unlock(&fs_info->balance_lock);
+	} else {
+		BUG_ON(ret != -EEXIST);
+		spin_lock(&fs_info->balance_lock);
+		update_balance_args(bctl);
+		spin_unlock(&fs_info->balance_lock);
+	}
+
+	ASSERT(!test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
+	set_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags);
+	describe_balance_start_or_resume(fs_info);
+	mutex_unlock(&fs_info->balance_mutex);
+
+	ret = __btrfs_balance(fs_info);
+
+	mutex_lock(&fs_info->balance_mutex);
+	if (ret == -ECANCELED && atomic_read(&fs_info->balance_pause_req))
+		btrfs_info(fs_info, "balance: paused");
+	/*
+	 * Balance can be canceled by:
+	 *
+	 * - Regular cancel request
+	 *   Then ret == -ECANCELED and balance_cancel_req > 0
+	 *
+	 * - Fatal signal to "btrfs" process
+	 *   Either the signal caught by wait_reserve_ticket() and callers
+	 *   got -EINTR, or caught by btrfs_should_cancel_balance() and
+	 *   got -ECANCELED.
+	 *   Either way, in this case balance_cancel_req = 0, and
+	 *   ret == -EINTR or ret == -ECANCELED.
+	 *
+	 * So here we only check the return value to catch canceled balance.
+	 */
+	else if (ret == -ECANCELED || ret == -EINTR)
+		btrfs_info(fs_info, "balance: canceled");
+	else
+		btrfs_info(fs_info, "balance: ended with status: %d", ret);
+
+	clear_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags);
+
+	if (bargs) {
+		memset(bargs, 0, sizeof(*bargs));
+		btrfs_update_ioctl_balance_args(fs_info, bargs);
+	}
+
+	if ((ret && ret != -ECANCELED && ret != -ENOSPC) ||
+	    balance_need_close(fs_info)) {
+		reset_balance_state(fs_info);
+		btrfs_exclop_finish(fs_info);
+	}
+
+	wake_up(&fs_info->balance_wait_q);
+
+	return ret;
+out:
+	if (bctl->flags & BTRFS_BALANCE_RESUME)
+		reset_balance_state(fs_info);
+	else
+		kfree(bctl);
+	btrfs_exclop_finish(fs_info);
+
+	return ret;
+}
+
+static int balance_kthread(void *data)
+{
+	struct btrfs_fs_info *fs_info = data;
+	int ret = 0;
+
+	sb_start_write(fs_info->sb);
+	mutex_lock(&fs_info->balance_mutex);
+	if (fs_info->balance_ctl)
+		ret = btrfs_balance(fs_info, fs_info->balance_ctl, NULL);
+	mutex_unlock(&fs_info->balance_mutex);
+	sb_end_write(fs_info->sb);
+
+	return ret;
+}
+
+int btrfs_resume_balance_async(struct btrfs_fs_info *fs_info)
+{
+	struct task_struct *tsk;
+
+	mutex_lock(&fs_info->balance_mutex);
+	if (!fs_info->balance_ctl) {
+		mutex_unlock(&fs_info->balance_mutex);
+		return 0;
+	}
+	mutex_unlock(&fs_info->balance_mutex);
+
+	if (btrfs_test_opt(fs_info, SKIP_BALANCE)) {
+		btrfs_info(fs_info, "balance: resume skipped");
+		return 0;
+	}
+
+	/*
+	 * A ro->rw remount sequence should continue with the paused balance
+	 * regardless of who pauses it, system or the user as of now, so set
+	 * the resume flag.
+	 */
+	spin_lock(&fs_info->balance_lock);
+	fs_info->balance_ctl->flags |= BTRFS_BALANCE_RESUME;
+	spin_unlock(&fs_info->balance_lock);
+
+	tsk = kthread_run(balance_kthread, fs_info, "btrfs-balance");
+	return PTR_ERR_OR_ZERO(tsk);
+}
+
+int btrfs_recover_balance(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_balance_control *bctl;
+	struct btrfs_balance_item *item;
+	struct btrfs_disk_balance_args disk_bargs;
+	struct btrfs_path *path;
+	struct extent_buffer *leaf;
+	struct btrfs_key key;
+	int ret;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	key.objectid = BTRFS_BALANCE_OBJECTID;
+	key.type = BTRFS_TEMPORARY_ITEM_KEY;
+	key.offset = 0;
+
+	ret = btrfs_search_slot(NULL, fs_info->tree_root, &key, path, 0, 0);
+	if (ret < 0)
+		goto out;
+	if (ret > 0) { /* ret = -ENOENT; */
+		ret = 0;
+		goto out;
+	}
+
+	bctl = kzalloc(sizeof(*bctl), GFP_NOFS);
+	if (!bctl) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	leaf = path->nodes[0];
+	item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_balance_item);
+
+	bctl->flags = btrfs_balance_flags(leaf, item);
+	bctl->flags |= BTRFS_BALANCE_RESUME;
+
+	btrfs_balance_data(leaf, item, &disk_bargs);
+	btrfs_disk_balance_args_to_cpu(&bctl->data, &disk_bargs);
+	btrfs_balance_meta(leaf, item, &disk_bargs);
+	btrfs_disk_balance_args_to_cpu(&bctl->meta, &disk_bargs);
+	btrfs_balance_sys(leaf, item, &disk_bargs);
+	btrfs_disk_balance_args_to_cpu(&bctl->sys, &disk_bargs);
+
+	/*
+	 * This should never happen, as the paused balance state is recovered
+	 * during mount without any chance of other exclusive ops to collide.
+	 *
+	 * This gives the exclusive op status to balance and keeps in paused
+	 * state until user intervention (cancel or umount). If the ownership
+	 * cannot be assigned, show a message but do not fail. The balance
+	 * is in a paused state and must have fs_info::balance_ctl properly
+	 * set up.
+	 */
+	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE))
+		btrfs_warn(fs_info,
+	"balance: cannot set exclusive op status, resume manually");
+
+	btrfs_release_path(path);
+
+	mutex_lock(&fs_info->balance_mutex);
+	BUG_ON(fs_info->balance_ctl);
+	spin_lock(&fs_info->balance_lock);
+	fs_info->balance_ctl = bctl;
+	spin_unlock(&fs_info->balance_lock);
+	mutex_unlock(&fs_info->balance_mutex);
+out:
+	btrfs_free_path(path);
+	return ret;
+}
+
+int btrfs_pause_balance(struct btrfs_fs_info *fs_info)
+{
+	int ret = 0;
+
+	mutex_lock(&fs_info->balance_mutex);
+	if (!fs_info->balance_ctl) {
+		mutex_unlock(&fs_info->balance_mutex);
+		return -ENOTCONN;
+	}
+
+	if (test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags)) {
+		atomic_inc(&fs_info->balance_pause_req);
+		mutex_unlock(&fs_info->balance_mutex);
+
+		wait_event(fs_info->balance_wait_q,
+			   !test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
+
+		mutex_lock(&fs_info->balance_mutex);
+		/* we are good with balance_ctl ripped off from under us */
+		BUG_ON(test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
+		atomic_dec(&fs_info->balance_pause_req);
+	} else {
+		ret = -ENOTCONN;
+	}
+
+	mutex_unlock(&fs_info->balance_mutex);
+	return ret;
+}
+
+int btrfs_cancel_balance(struct btrfs_fs_info *fs_info)
+{
+	mutex_lock(&fs_info->balance_mutex);
+	if (!fs_info->balance_ctl) {
+		mutex_unlock(&fs_info->balance_mutex);
+		return -ENOTCONN;
+	}
+
+	/*
+	 * A paused balance with the item stored on disk can be resumed at
+	 * mount time if the mount is read-write. Otherwise it's still paused
+	 * and we must not allow cancelling as it deletes the item.
+	 */
+	if (sb_rdonly(fs_info->sb)) {
+		mutex_unlock(&fs_info->balance_mutex);
+		return -EROFS;
+	}
+
+	atomic_inc(&fs_info->balance_cancel_req);
+	/*
+	 * if we are running just wait and return, balance item is
+	 * deleted in btrfs_balance in this case
+	 */
+	if (test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags)) {
+		mutex_unlock(&fs_info->balance_mutex);
+		wait_event(fs_info->balance_wait_q,
+			   !test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
+		mutex_lock(&fs_info->balance_mutex);
+	} else {
+		mutex_unlock(&fs_info->balance_mutex);
+		/*
+		 * Lock released to allow other waiters to continue, we'll
+		 * reexamine the status again.
+		 */
+		mutex_lock(&fs_info->balance_mutex);
+
+		if (fs_info->balance_ctl) {
+			reset_balance_state(fs_info);
+			btrfs_exclop_finish(fs_info);
+			btrfs_info(fs_info, "balance: canceled");
+		}
+	}
+
+	ASSERT(!test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
+	atomic_dec(&fs_info->balance_cancel_req);
+	mutex_unlock(&fs_info->balance_mutex);
+	return 0;
+}
+
+int btrfs_uuid_scan_kthread(void *data)
+{
+	struct btrfs_fs_info *fs_info = data;
+	struct btrfs_root *root = fs_info->tree_root;
+	struct btrfs_key key;
+	struct btrfs_path *path = NULL;
+	int ret = 0;
+	struct extent_buffer *eb;
+	int slot;
+	struct btrfs_root_item root_item;
+	u32 item_size;
+	struct btrfs_trans_handle *trans = NULL;
+	bool closing = false;
+
+	path = btrfs_alloc_path();
+	if (!path) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	key.objectid = 0;
+	key.type = BTRFS_ROOT_ITEM_KEY;
+	key.offset = 0;
+
+	while (1) {
+		if (btrfs_fs_closing(fs_info)) {
+			closing = true;
+			break;
+		}
+		ret = btrfs_search_forward(root, &key, path,
+				BTRFS_OLDEST_GENERATION);
+		if (ret) {
+			if (ret > 0)
+				ret = 0;
+			break;
+		}
+
+		if (key.type != BTRFS_ROOT_ITEM_KEY ||
+		    (key.objectid < BTRFS_FIRST_FREE_OBJECTID &&
+		     key.objectid != BTRFS_FS_TREE_OBJECTID) ||
+		    key.objectid > BTRFS_LAST_FREE_OBJECTID)
+			goto skip;
+
+		eb = path->nodes[0];
+		slot = path->slots[0];
+		item_size = btrfs_item_size_nr(eb, slot);
+		if (item_size < sizeof(root_item))
+			goto skip;
+
+		read_extent_buffer(eb, &root_item,
+				   btrfs_item_ptr_offset(eb, slot),
+				   (int)sizeof(root_item));
+		if (btrfs_root_refs(&root_item) == 0)
+			goto skip;
+
+		if (!btrfs_is_empty_uuid(root_item.uuid) ||
+		    !btrfs_is_empty_uuid(root_item.received_uuid)) {
+			if (trans)
+				goto update_tree;
+
+			btrfs_release_path(path);
+			/*
+			 * 1 - subvol uuid item
+			 * 1 - received_subvol uuid item
+			 */
+			trans = btrfs_start_transaction(fs_info->uuid_root, 2);
+			if (IS_ERR(trans)) {
+				ret = PTR_ERR(trans);
+				break;
+			}
+			continue;
+		} else {
+			goto skip;
+		}
+update_tree:
+		btrfs_release_path(path);
+		if (!btrfs_is_empty_uuid(root_item.uuid)) {
+			ret = btrfs_uuid_tree_add(trans, root_item.uuid,
+						  BTRFS_UUID_KEY_SUBVOL,
+						  key.objectid);
+			if (ret < 0) {
+				btrfs_warn(fs_info, "uuid_tree_add failed %d",
+					ret);
+				break;
+			}
+		}
+
+		if (!btrfs_is_empty_uuid(root_item.received_uuid)) {
+			ret = btrfs_uuid_tree_add(trans,
+						  root_item.received_uuid,
+						 BTRFS_UUID_KEY_RECEIVED_SUBVOL,
+						  key.objectid);
+			if (ret < 0) {
+				btrfs_warn(fs_info, "uuid_tree_add failed %d",
+					ret);
+				break;
+			}
+		}
+
+skip:
+		btrfs_release_path(path);
+		if (trans) {
+			ret = btrfs_end_transaction(trans);
+			trans = NULL;
+			if (ret)
+				break;
+		}
+
+		if (key.offset < (u64)-1) {
+			key.offset++;
+		} else if (key.type < BTRFS_ROOT_ITEM_KEY) {
+			key.offset = 0;
+			key.type = BTRFS_ROOT_ITEM_KEY;
+		} else if (key.objectid < (u64)-1) {
+			key.offset = 0;
+			key.type = BTRFS_ROOT_ITEM_KEY;
+			key.objectid++;
+		} else {
+			break;
+		}
+		cond_resched();
+	}
+
+out:
+	btrfs_free_path(path);
+	if (trans && !IS_ERR(trans))
+		btrfs_end_transaction(trans);
+	if (ret)
+		btrfs_warn(fs_info, "btrfs_uuid_scan_kthread failed %d", ret);
+	else if (!closing)
+		set_bit(BTRFS_FS_UPDATE_UUID_TREE_GEN, &fs_info->flags);
+	up(&fs_info->uuid_tree_rescan_sem);
+	return 0;
+}
+
+int btrfs_create_uuid_tree(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_trans_handle *trans;
+	struct btrfs_root *tree_root = fs_info->tree_root;
+	struct btrfs_root *uuid_root;
+	struct task_struct *task;
+	int ret;
+
+	/*
+	 * 1 - root node
+	 * 1 - root item
+	 */
+	trans = btrfs_start_transaction(tree_root, 2);
+	if (IS_ERR(trans))
+		return PTR_ERR(trans);
+
+	uuid_root = btrfs_create_tree(trans, BTRFS_UUID_TREE_OBJECTID);
+	if (IS_ERR(uuid_root)) {
+		ret = PTR_ERR(uuid_root);
+		btrfs_abort_transaction(trans, ret);
+		btrfs_end_transaction(trans);
+		return ret;
+	}
+
+	fs_info->uuid_root = uuid_root;
+
+	ret = btrfs_commit_transaction(trans);
+	if (ret)
+		return ret;
+
+	down(&fs_info->uuid_tree_rescan_sem);
+	task = kthread_run(btrfs_uuid_scan_kthread, fs_info, "btrfs-uuid");
+	if (IS_ERR(task)) {
+		/* fs_info->update_uuid_tree_gen remains 0 in all error case */
+		btrfs_warn(fs_info, "failed to start uuid_scan task");
+		up(&fs_info->uuid_tree_rescan_sem);
+		return PTR_ERR(task);
+	}
+
+	return 0;
+}
+
+/*
+ * shrinking a device means finding all of the device extents past
+ * the new size, and then following the back refs to the chunks.
+ * The chunk relocation code actually frees the device extent
+ */
+int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
+{
+	struct btrfs_fs_info *fs_info = device->fs_info;
+	struct btrfs_root *root = fs_info->dev_root;
+	struct btrfs_trans_handle *trans;
+	struct btrfs_dev_extent *dev_extent = NULL;
+	struct btrfs_path *path;
+	u64 length;
+	u64 chunk_offset;
+	int ret;
+	int slot;
+	int failed = 0;
+	bool retried = false;
+	struct extent_buffer *l;
+	struct btrfs_key key;
+	struct btrfs_super_block *super_copy = fs_info->super_copy;
+	u64 old_total = btrfs_super_total_bytes(super_copy);
+	u64 old_size = btrfs_device_get_total_bytes(device);
+	u64 diff;
+	u64 start;
+
+	new_size = round_down(new_size, fs_info->sectorsize);
+	start = new_size;
+	diff = round_down(old_size - new_size, fs_info->sectorsize);
+
+	if (test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state))
+		return -EINVAL;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	path->reada = READA_BACK;
+
+	trans = btrfs_start_transaction(root, 0);
+	if (IS_ERR(trans)) {
+		btrfs_free_path(path);
+		return PTR_ERR(trans);
+	}
+
+	mutex_lock(&fs_info->chunk_mutex);
+
+	btrfs_device_set_total_bytes(device, new_size);
+	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
+		device->fs_devices->total_rw_bytes -= diff;
+		atomic64_sub(diff, &fs_info->free_chunk_space);
+	}
+
+	/*
+	 * Once the device's size has been set to the new size, ensure all
+	 * in-memory chunks are synced to disk so that the loop below sees them
+	 * and relocates them accordingly.
+	 */
+	if (contains_pending_extent(device, &start, diff)) {
+		mutex_unlock(&fs_info->chunk_mutex);
+		ret = btrfs_commit_transaction(trans);
+		if (ret)
+			goto done;
+	} else {
+		mutex_unlock(&fs_info->chunk_mutex);
+		btrfs_end_transaction(trans);
+	}
+
+again:
+	key.objectid = device->devid;
+	key.offset = (u64)-1;
+	key.type = BTRFS_DEV_EXTENT_KEY;
+
+	do {
+		mutex_lock(&fs_info->delete_unused_bgs_mutex);
+		ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+		if (ret < 0) {
+			mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+			goto done;
+		}
+
+		ret = btrfs_previous_item(root, path, 0, key.type);
+		if (ret)
+			mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+		if (ret < 0)
+			goto done;
+		if (ret) {
+			ret = 0;
+			btrfs_release_path(path);
+			break;
+		}
+
+		l = path->nodes[0];
+		slot = path->slots[0];
+		btrfs_item_key_to_cpu(l, &key, path->slots[0]);
+
+		if (key.objectid != device->devid) {
+			mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+			btrfs_release_path(path);
+			break;
+		}
+
+		dev_extent = btrfs_item_ptr(l, slot, struct btrfs_dev_extent);
+		length = btrfs_dev_extent_length(l, dev_extent);
+
+		if (key.offset + length <= new_size) {
+			mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+			btrfs_release_path(path);
+			break;
+		}
+
+		chunk_offset = btrfs_dev_extent_chunk_offset(l, dev_extent);
+		btrfs_release_path(path);
+
+		/*
+		 * We may be relocating the only data chunk we have,
+		 * which could potentially end up with losing data's
+		 * raid profile, so lets allocate an empty one in
+		 * advance.
+		 */
+		ret = btrfs_may_alloc_data_chunk(fs_info, chunk_offset);
+		if (ret < 0) {
+			mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+			goto done;
+		}
+
+		ret = btrfs_relocate_chunk(fs_info, chunk_offset);
+		mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+		if (ret == -ENOSPC) {
+			failed++;
+		} else if (ret) {
+			if (ret == -ETXTBSY) {
+				btrfs_warn(fs_info,
+		   "could not shrink block group %llu due to active swapfile",
+					   chunk_offset);
+			}
+			goto done;
+		}
+	} while (key.offset-- > 0);
+
+	if (failed && !retried) {
+		failed = 0;
+		retried = true;
+		goto again;
+	} else if (failed && retried) {
+		ret = -ENOSPC;
+		goto done;
+	}
+
+	/* Shrinking succeeded, else we would be at "done". */
+	trans = btrfs_start_transaction(root, 0);
+	if (IS_ERR(trans)) {
+		ret = PTR_ERR(trans);
+		goto done;
+	}
+
+	mutex_lock(&fs_info->chunk_mutex);
+	/* Clear all state bits beyond the shrunk device size */
+	clear_extent_bits(&device->alloc_state, new_size, (u64)-1,
+			  CHUNK_STATE_MASK);
+
+	btrfs_device_set_disk_total_bytes(device, new_size);
+	if (list_empty(&device->post_commit_list))
+		list_add_tail(&device->post_commit_list,
+			      &trans->transaction->dev_update_list);
+
+	WARN_ON(diff > old_total);
+	btrfs_set_super_total_bytes(super_copy,
+			round_down(old_total - diff, fs_info->sectorsize));
+	mutex_unlock(&fs_info->chunk_mutex);
+
+	/* Now btrfs_update_device() will change the on-disk size. */
+	ret = btrfs_update_device(trans, device);
+	if (ret < 0) {
+		btrfs_abort_transaction(trans, ret);
+		btrfs_end_transaction(trans);
+	} else {
+		ret = btrfs_commit_transaction(trans);
+	}
+done:
+	btrfs_free_path(path);
+	if (ret) {
+		mutex_lock(&fs_info->chunk_mutex);
+		btrfs_device_set_total_bytes(device, old_size);
+		if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state))
+			device->fs_devices->total_rw_bytes += diff;
+		atomic64_add(diff, &fs_info->free_chunk_space);
+		mutex_unlock(&fs_info->chunk_mutex);
+	}
+	return ret;
+}
+
+static int btrfs_add_system_chunk(struct btrfs_fs_info *fs_info,
+			   struct btrfs_key *key,
+			   struct btrfs_chunk *chunk, int item_size)
+{
+	struct btrfs_super_block *super_copy = fs_info->super_copy;
+	struct btrfs_disk_key disk_key;
+	u32 array_size;
+	u8 *ptr;
+
+	mutex_lock(&fs_info->chunk_mutex);
+	array_size = btrfs_super_sys_array_size(super_copy);
+	if (array_size + item_size + sizeof(disk_key)
+			> BTRFS_SYSTEM_CHUNK_ARRAY_SIZE) {
+		mutex_unlock(&fs_info->chunk_mutex);
+		return -EFBIG;
+	}
+
+	ptr = super_copy->sys_chunk_array + array_size;
+	btrfs_cpu_key_to_disk(&disk_key, key);
+	memcpy(ptr, &disk_key, sizeof(disk_key));
+	ptr += sizeof(disk_key);
+	memcpy(ptr, chunk, item_size);
+	item_size += sizeof(disk_key);
+	btrfs_set_super_sys_array_size(super_copy, array_size + item_size);
+	mutex_unlock(&fs_info->chunk_mutex);
+
+	return 0;
+}
+
+/*
+ * sort the devices in descending order by max_avail, total_avail
+ */
+static int btrfs_cmp_device_info(const void *a, const void *b)
+{
+	const struct btrfs_device_info *di_a = a;
+	const struct btrfs_device_info *di_b = b;
+
+	if (di_a->max_avail > di_b->max_avail)
+		return -1;
+	if (di_a->max_avail < di_b->max_avail)
+		return 1;
+	if (di_a->total_avail > di_b->total_avail)
+		return -1;
+	if (di_a->total_avail < di_b->total_avail)
+		return 1;
+	return 0;
+}
+
+static void check_raid56_incompat_flag(struct btrfs_fs_info *info, u64 type)
+{
+	if (!(type & BTRFS_BLOCK_GROUP_RAID56_MASK))
+		return;
+
+	btrfs_set_fs_incompat(info, RAID56);
+}
+
+static void check_raid1c34_incompat_flag(struct btrfs_fs_info *info, u64 type)
+{
+	if (!(type & (BTRFS_BLOCK_GROUP_RAID1C3 | BTRFS_BLOCK_GROUP_RAID1C4)))
+		return;
+
+	btrfs_set_fs_incompat(info, RAID1C34);
+}
+
+/*
+ * Structure used internally for __btrfs_alloc_chunk() function.
+ * Wraps needed parameters.
+ */
+struct alloc_chunk_ctl {
+	u64 start;
+	u64 type;
+	/* Total number of stripes to allocate */
+	int num_stripes;
+	/* sub_stripes info for map */
+	int sub_stripes;
+	/* Stripes per device */
+	int dev_stripes;
+	/* Maximum number of devices to use */
+	int devs_max;
+	/* Minimum number of devices to use */
+	int devs_min;
+	/* ndevs has to be a multiple of this */
+	int devs_increment;
+	/* Number of copies */
+	int ncopies;
+	/* Number of stripes worth of bytes to store parity information */
+	int nparity;
+	u64 max_stripe_size;
+	u64 max_chunk_size;
+	u64 dev_extent_min;
+	u64 stripe_size;
+	u64 chunk_size;
+	int ndevs;
+};
+
+static void init_alloc_chunk_ctl_policy_regular(
+				struct btrfs_fs_devices *fs_devices,
+				struct alloc_chunk_ctl *ctl)
+{
+	u64 type = ctl->type;
+
+	if (type & BTRFS_BLOCK_GROUP_DATA) {
+		ctl->max_stripe_size = SZ_1G;
+		ctl->max_chunk_size = BTRFS_MAX_DATA_CHUNK_SIZE;
+	} else if (type & BTRFS_BLOCK_GROUP_METADATA) {
+		/* For larger filesystems, use larger metadata chunks */
+		if (fs_devices->total_rw_bytes > 50ULL * SZ_1G)
+			ctl->max_stripe_size = SZ_1G;
+		else
+			ctl->max_stripe_size = SZ_256M;
+		ctl->max_chunk_size = ctl->max_stripe_size;
+	} else if (type & BTRFS_BLOCK_GROUP_SYSTEM) {
+		ctl->max_stripe_size = SZ_32M;
+		ctl->max_chunk_size = 2 * ctl->max_stripe_size;
+		ctl->devs_max = min_t(int, ctl->devs_max,
+				      BTRFS_MAX_DEVS_SYS_CHUNK);
+	} else {
+		BUG();
+	}
+
+	/* We don't want a chunk larger than 10% of writable space */
+	ctl->max_chunk_size = min(div_factor(fs_devices->total_rw_bytes, 1),
+				  ctl->max_chunk_size);
+	ctl->dev_extent_min = BTRFS_STRIPE_LEN * ctl->dev_stripes;
+}
+
+static void init_alloc_chunk_ctl(struct btrfs_fs_devices *fs_devices,
+				 struct alloc_chunk_ctl *ctl)
+{
+	int index = btrfs_bg_flags_to_raid_index(ctl->type);
+
+	ctl->sub_stripes = btrfs_raid_array[index].sub_stripes;
+	ctl->dev_stripes = btrfs_raid_array[index].dev_stripes;
+	ctl->devs_max = btrfs_raid_array[index].devs_max;
+	if (!ctl->devs_max)
+		ctl->devs_max = BTRFS_MAX_DEVS(fs_devices->fs_info);
+	ctl->devs_min = btrfs_raid_array[index].devs_min;
+	ctl->devs_increment = btrfs_raid_array[index].devs_increment;
+	ctl->ncopies = btrfs_raid_array[index].ncopies;
+	ctl->nparity = btrfs_raid_array[index].nparity;
+	ctl->ndevs = 0;
+
+	switch (fs_devices->chunk_alloc_policy) {
+	case BTRFS_CHUNK_ALLOC_REGULAR:
+		init_alloc_chunk_ctl_policy_regular(fs_devices, ctl);
+		break;
+	default:
+		BUG();
+	}
+}
+
+static int gather_device_info(struct btrfs_fs_devices *fs_devices,
+			      struct alloc_chunk_ctl *ctl,
+			      struct btrfs_device_info *devices_info)
+{
+	struct btrfs_fs_info *info = fs_devices->fs_info;
+	struct btrfs_device *device;
+	u64 total_avail;
+	u64 dev_extent_want = ctl->max_stripe_size * ctl->dev_stripes;
+	int ret;
+	int ndevs = 0;
+	u64 max_avail;
+	u64 dev_offset;
+
+	/*
+	 * in the first pass through the devices list, we gather information
+	 * about the available holes on each device.
+	 */
+	list_for_each_entry(device, &fs_devices->alloc_list, dev_alloc_list) {
+		if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
+			WARN(1, KERN_ERR
+			       "BTRFS: read-only device in alloc_list\n");
+			continue;
+		}
+
+		if (!test_bit(BTRFS_DEV_STATE_IN_FS_METADATA,
+					&device->dev_state) ||
+		    test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state))
+			continue;
+
+		if (device->total_bytes > device->bytes_used)
+			total_avail = device->total_bytes - device->bytes_used;
+		else
+			total_avail = 0;
+
+		/* If there is no space on this device, skip it. */
+		if (total_avail < ctl->dev_extent_min)
+			continue;
+
+		ret = find_free_dev_extent(device, dev_extent_want, &dev_offset,
+					   &max_avail);
+		if (ret && ret != -ENOSPC)
+			return ret;
+
+		if (ret == 0)
+			max_avail = dev_extent_want;
+
+		if (max_avail < ctl->dev_extent_min) {
+			if (btrfs_test_opt(info, ENOSPC_DEBUG))
+				btrfs_debug(info,
+			"%s: devid %llu has no free space, have=%llu want=%llu",
+					    __func__, device->devid, max_avail,
+					    ctl->dev_extent_min);
+			continue;
+		}
+
+		if (ndevs == fs_devices->rw_devices) {
+			WARN(1, "%s: found more than %llu devices\n",
+			     __func__, fs_devices->rw_devices);
+			break;
+		}
+		devices_info[ndevs].dev_offset = dev_offset;
+		devices_info[ndevs].max_avail = max_avail;
+		devices_info[ndevs].total_avail = total_avail;
+		devices_info[ndevs].dev = device;
+		++ndevs;
+	}
+	ctl->ndevs = ndevs;
+
+	/*
+	 * now sort the devices by hole size / available space
+	 */
+	sort(devices_info, ndevs, sizeof(struct btrfs_device_info),
+	     btrfs_cmp_device_info, NULL);
+
+	return 0;
+}
+
+static int decide_stripe_size_regular(struct alloc_chunk_ctl *ctl,
+				      struct btrfs_device_info *devices_info)
+{
+	/* Number of stripes that count for block group size */
+	int data_stripes;
+
+	/*
+	 * The primary goal is to maximize the number of stripes, so use as
+	 * many devices as possible, even if the stripes are not maximum sized.
+	 *
+	 * The DUP profile stores more than one stripe per device, the
+	 * max_avail is the total size so we have to adjust.
+	 */
+	ctl->stripe_size = div_u64(devices_info[ctl->ndevs - 1].max_avail,
+				   ctl->dev_stripes);
+	ctl->num_stripes = ctl->ndevs * ctl->dev_stripes;
+
+	/* This will have to be fixed for RAID1 and RAID10 over more drives */
+	data_stripes = (ctl->num_stripes - ctl->nparity) / ctl->ncopies;
+
+	/*
+	 * Use the number of data stripes to figure out how big this chunk is
+	 * really going to be in terms of logical address space, and compare
+	 * that answer with the max chunk size. If it's higher, we try to
+	 * reduce stripe_size.
+	 */
+	if (ctl->stripe_size * data_stripes > ctl->max_chunk_size) {
+		/*
+		 * Reduce stripe_size, round it up to a 16MB boundary again and
+		 * then use it, unless it ends up being even bigger than the
+		 * previous value we had already.
+		 */
+		ctl->stripe_size = min(round_up(div_u64(ctl->max_chunk_size,
+							data_stripes), SZ_16M),
+				       ctl->stripe_size);
+	}
+
+	/* Align to BTRFS_STRIPE_LEN */
+	ctl->stripe_size = round_down(ctl->stripe_size, BTRFS_STRIPE_LEN);
+	ctl->chunk_size = ctl->stripe_size * data_stripes;
+
+	return 0;
+}
+
+static int decide_stripe_size(struct btrfs_fs_devices *fs_devices,
+			      struct alloc_chunk_ctl *ctl,
+			      struct btrfs_device_info *devices_info)
+{
+	struct btrfs_fs_info *info = fs_devices->fs_info;
+
+	/*
+	 * Round down to number of usable stripes, devs_increment can be any
+	 * number so we can't use round_down() that requires power of 2, while
+	 * rounddown is safe.
+	 */
+	ctl->ndevs = rounddown(ctl->ndevs, ctl->devs_increment);
+
+	if (ctl->ndevs < ctl->devs_min) {
+		if (btrfs_test_opt(info, ENOSPC_DEBUG)) {
+			btrfs_debug(info,
+	"%s: not enough devices with free space: have=%d minimum required=%d",
+				    __func__, ctl->ndevs, ctl->devs_min);
+		}
+		return -ENOSPC;
+	}
+
+	ctl->ndevs = min(ctl->ndevs, ctl->devs_max);
+
+	switch (fs_devices->chunk_alloc_policy) {
+	case BTRFS_CHUNK_ALLOC_REGULAR:
+		return decide_stripe_size_regular(ctl, devices_info);
+	default:
+		BUG();
+	}
+}
+
+static int create_chunk(struct btrfs_trans_handle *trans,
+			struct alloc_chunk_ctl *ctl,
+			struct btrfs_device_info *devices_info)
+{
+	struct btrfs_fs_info *info = trans->fs_info;
+	struct map_lookup *map = NULL;
+	struct extent_map_tree *em_tree;
+	struct extent_map *em;
+	u64 start = ctl->start;
+	u64 type = ctl->type;
+	int ret;
+	int i;
+	int j;
+
+	map = kmalloc(map_lookup_size(ctl->num_stripes), GFP_NOFS);
+	if (!map)
+		return -ENOMEM;
+	map->num_stripes = ctl->num_stripes;
+
+	for (i = 0; i < ctl->ndevs; ++i) {
+		for (j = 0; j < ctl->dev_stripes; ++j) {
+			int s = i * ctl->dev_stripes + j;
+			map->stripes[s].dev = devices_info[i].dev;
+			map->stripes[s].physical = devices_info[i].dev_offset +
+						   j * ctl->stripe_size;
+		}
+	}
+	map->stripe_len = BTRFS_STRIPE_LEN;
+	map->io_align = BTRFS_STRIPE_LEN;
+	map->io_width = BTRFS_STRIPE_LEN;
+	map->type = type;
+	map->sub_stripes = ctl->sub_stripes;
+
+	trace_btrfs_chunk_alloc(info, map, start, ctl->chunk_size);
+
+	em = alloc_extent_map();
+	if (!em) {
+		kfree(map);
+		return -ENOMEM;
+	}
+	set_bit(EXTENT_FLAG_FS_MAPPING, &em->flags);
+	em->map_lookup = map;
+	em->start = start;
+	em->len = ctl->chunk_size;
+	em->block_start = 0;
+	em->block_len = em->len;
+	em->orig_block_len = ctl->stripe_size;
+
+	em_tree = &info->mapping_tree;
+	write_lock(&em_tree->lock);
+	ret = add_extent_mapping(em_tree, em, 0);
+	if (ret) {
+		write_unlock(&em_tree->lock);
+		free_extent_map(em);
+		return ret;
+	}
+	write_unlock(&em_tree->lock);
+
+	ret = btrfs_make_block_group(trans, 0, type, start, ctl->chunk_size);
+	if (ret)
+		goto error_del_extent;
+
+	for (i = 0; i < map->num_stripes; i++) {
+		struct btrfs_device *dev = map->stripes[i].dev;
+
+		btrfs_device_set_bytes_used(dev,
+					    dev->bytes_used + ctl->stripe_size);
+		if (list_empty(&dev->post_commit_list))
+			list_add_tail(&dev->post_commit_list,
+				      &trans->transaction->dev_update_list);
+	}
+
+	atomic64_sub(ctl->stripe_size * map->num_stripes,
+		     &info->free_chunk_space);
+
+	free_extent_map(em);
+	check_raid56_incompat_flag(info, type);
+	check_raid1c34_incompat_flag(info, type);
+
+	return 0;
+
+error_del_extent:
+	write_lock(&em_tree->lock);
+	remove_extent_mapping(em_tree, em);
+	write_unlock(&em_tree->lock);
+
+	/* One for our allocation */
+	free_extent_map(em);
+	/* One for the tree reference */
+	free_extent_map(em);
+
+	return ret;
+}
+
+int btrfs_alloc_chunk(struct btrfs_trans_handle *trans, u64 type)
+{
+	struct btrfs_fs_info *info = trans->fs_info;
+	struct btrfs_fs_devices *fs_devices = info->fs_devices;
+	struct btrfs_device_info *devices_info = NULL;
+	struct alloc_chunk_ctl ctl;
+	int ret;
+
+	lockdep_assert_held(&info->chunk_mutex);
+
+	if (!alloc_profile_is_valid(type, 0)) {
+		ASSERT(0);
+		return -EINVAL;
+	}
+
+	if (list_empty(&fs_devices->alloc_list)) {
+		if (btrfs_test_opt(info, ENOSPC_DEBUG))
+			btrfs_debug(info, "%s: no writable device", __func__);
+		return -ENOSPC;
+	}
+
+	if (!(type & BTRFS_BLOCK_GROUP_TYPE_MASK)) {
+		btrfs_err(info, "invalid chunk type 0x%llx requested", type);
+		ASSERT(0);
+		return -EINVAL;
+	}
+
+	ctl.start = find_next_chunk(info);
+	ctl.type = type;
+	init_alloc_chunk_ctl(fs_devices, &ctl);
+
+	devices_info = kcalloc(fs_devices->rw_devices, sizeof(*devices_info),
+			       GFP_NOFS);
+	if (!devices_info)
+		return -ENOMEM;
+
+	ret = gather_device_info(fs_devices, &ctl, devices_info);
+	if (ret < 0)
+		goto out;
+
+	ret = decide_stripe_size(fs_devices, &ctl, devices_info);
+	if (ret < 0)
+		goto out;
+
+	ret = create_chunk(trans, &ctl, devices_info);
+
+out:
+	kfree(devices_info);
+	return ret;
+}
+
+/*
+ * Chunk allocation falls into two parts. The first part does work
+ * that makes the new allocated chunk usable, but does not do any operation
+ * that modifies the chunk tree. The second part does the work that
+ * requires modifying the chunk tree. This division is important for the
+ * bootstrap process of adding storage to a seed btrfs.
+ */
+int btrfs_finish_chunk_alloc(struct btrfs_trans_handle *trans,
+			     u64 chunk_offset, u64 chunk_size)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_root *extent_root = fs_info->extent_root;
+	struct btrfs_root *chunk_root = fs_info->chunk_root;
+	struct btrfs_key key;
+	struct btrfs_device *device;
+	struct btrfs_chunk *chunk;
+	struct btrfs_stripe *stripe;
+	struct extent_map *em;
+	struct map_lookup *map;
+	size_t item_size;
+	u64 dev_offset;
+	u64 stripe_size;
+	int i = 0;
+	int ret = 0;
+
+	em = btrfs_get_chunk_map(fs_info, chunk_offset, chunk_size);
+	if (IS_ERR(em))
+		return PTR_ERR(em);
+
+	map = em->map_lookup;
+	item_size = btrfs_chunk_item_size(map->num_stripes);
+	stripe_size = em->orig_block_len;
+
+	chunk = kzalloc(item_size, GFP_NOFS);
+	if (!chunk) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	/*
+	 * Take the device list mutex to prevent races with the final phase of
+	 * a device replace operation that replaces the device object associated
+	 * with the map's stripes, because the device object's id can change
+	 * at any time during that final phase of the device replace operation
+	 * (dev-replace.c:btrfs_dev_replace_finishing()).
+	 */
+	mutex_lock(&fs_info->fs_devices->device_list_mutex);
+	for (i = 0; i < map->num_stripes; i++) {
+		device = map->stripes[i].dev;
+		dev_offset = map->stripes[i].physical;
+
+		ret = btrfs_update_device(trans, device);
+		if (ret)
+			break;
+		ret = btrfs_alloc_dev_extent(trans, device, chunk_offset,
+					     dev_offset, stripe_size);
+		if (ret)
+			break;
+	}
+	if (ret) {
+		mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+		goto out;
+	}
+
+	stripe = &chunk->stripe;
+	for (i = 0; i < map->num_stripes; i++) {
+		device = map->stripes[i].dev;
+		dev_offset = map->stripes[i].physical;
+
+		btrfs_set_stack_stripe_devid(stripe, device->devid);
+		btrfs_set_stack_stripe_offset(stripe, dev_offset);
+		memcpy(stripe->dev_uuid, device->uuid, BTRFS_UUID_SIZE);
+		stripe++;
+	}
+	mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+
+	btrfs_set_stack_chunk_length(chunk, chunk_size);
+	btrfs_set_stack_chunk_owner(chunk, extent_root->root_key.objectid);
+	btrfs_set_stack_chunk_stripe_len(chunk, map->stripe_len);
+	btrfs_set_stack_chunk_type(chunk, map->type);
+	btrfs_set_stack_chunk_num_stripes(chunk, map->num_stripes);
+	btrfs_set_stack_chunk_io_align(chunk, map->stripe_len);
+	btrfs_set_stack_chunk_io_width(chunk, map->stripe_len);
+	btrfs_set_stack_chunk_sector_size(chunk, fs_info->sectorsize);
+	btrfs_set_stack_chunk_sub_stripes(chunk, map->sub_stripes);
+
+	key.objectid = BTRFS_FIRST_CHUNK_TREE_OBJECTID;
+	key.type = BTRFS_CHUNK_ITEM_KEY;
+	key.offset = chunk_offset;
+
+	ret = btrfs_insert_item(trans, chunk_root, &key, chunk, item_size);
+	if (ret == 0 && map->type & BTRFS_BLOCK_GROUP_SYSTEM) {
+		/*
+		 * TODO: Cleanup of inserted chunk root in case of
+		 * failure.
+		 */
+		ret = btrfs_add_system_chunk(fs_info, &key, chunk, item_size);
+	}
+
+out:
+	kfree(chunk);
+	free_extent_map(em);
+	return ret;
+}
+
+static noinline int init_first_rw_device(struct btrfs_trans_handle *trans)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	u64 alloc_profile;
+	int ret;
+
+	alloc_profile = btrfs_metadata_alloc_profile(fs_info);
+	ret = btrfs_alloc_chunk(trans, alloc_profile);
+	if (ret)
+		return ret;
+
+	alloc_profile = btrfs_system_alloc_profile(fs_info);
+	ret = btrfs_alloc_chunk(trans, alloc_profile);
+	return ret;
+}
+
+static inline int btrfs_chunk_max_errors(struct map_lookup *map)
+{
+	const int index = btrfs_bg_flags_to_raid_index(map->type);
+
+	return btrfs_raid_array[index].tolerated_failures;
+}
+
+int btrfs_chunk_readonly(struct btrfs_fs_info *fs_info, u64 chunk_offset)
+{
+	struct extent_map *em;
+	struct map_lookup *map;
+	int readonly = 0;
+	int miss_ndevs = 0;
+	int i;
+
+	em = btrfs_get_chunk_map(fs_info, chunk_offset, 1);
+	if (IS_ERR(em))
+		return 1;
+
+	map = em->map_lookup;
+	for (i = 0; i < map->num_stripes; i++) {
+		if (test_bit(BTRFS_DEV_STATE_MISSING,
+					&map->stripes[i].dev->dev_state)) {
+			miss_ndevs++;
+			continue;
+		}
+		if (!test_bit(BTRFS_DEV_STATE_WRITEABLE,
+					&map->stripes[i].dev->dev_state)) {
+			readonly = 1;
+			goto end;
+		}
+	}
+
+	/*
+	 * If the number of missing devices is larger than max errors,
+	 * we can not write the data into that chunk successfully, so
+	 * set it readonly.
+	 */
+	if (miss_ndevs > btrfs_chunk_max_errors(map))
+		readonly = 1;
+end:
+	free_extent_map(em);
+	return readonly;
+}
+
+void btrfs_mapping_tree_free(struct extent_map_tree *tree)
+{
+	struct extent_map *em;
+
+	while (1) {
+		write_lock(&tree->lock);
+		em = lookup_extent_mapping(tree, 0, (u64)-1);
+		if (em)
+			remove_extent_mapping(tree, em);
+		write_unlock(&tree->lock);
+		if (!em)
+			break;
+		/* once for us */
+		free_extent_map(em);
+		/* once for the tree */
+		free_extent_map(em);
+	}
+}
+
+int btrfs_num_copies(struct btrfs_fs_info *fs_info, u64 logical, u64 len)
+{
+	struct extent_map *em;
+	struct map_lookup *map;
+	int ret;
+
+	em = btrfs_get_chunk_map(fs_info, logical, len);
+	if (IS_ERR(em))
+		/*
+		 * We could return errors for these cases, but that could get
+		 * ugly and we'd probably do the same thing which is just not do
+		 * anything else and exit, so return 1 so the callers don't try
+		 * to use other copies.
+		 */
+		return 1;
+
+	map = em->map_lookup;
+	if (map->type & (BTRFS_BLOCK_GROUP_DUP | BTRFS_BLOCK_GROUP_RAID1_MASK))
+		ret = map->num_stripes;
+	else if (map->type & BTRFS_BLOCK_GROUP_RAID10)
+		ret = map->sub_stripes;
+	else if (map->type & BTRFS_BLOCK_GROUP_RAID5)
+		ret = 2;
+	else if (map->type & BTRFS_BLOCK_GROUP_RAID6)
+		/*
+		 * There could be two corrupted data stripes, we need
+		 * to loop retry in order to rebuild the correct data.
+		 *
+		 * Fail a stripe at a time on every retry except the
+		 * stripe under reconstruction.
+		 */
+		ret = map->num_stripes;
+	else
+		ret = 1;
+	free_extent_map(em);
+
+	down_read(&fs_info->dev_replace.rwsem);
+	if (btrfs_dev_replace_is_ongoing(&fs_info->dev_replace) &&
+	    fs_info->dev_replace.tgtdev)
+		ret++;
+	up_read(&fs_info->dev_replace.rwsem);
+
+	return ret;
+}
+
+unsigned long btrfs_full_stripe_len(struct btrfs_fs_info *fs_info,
+				    u64 logical)
+{
+	struct extent_map *em;
+	struct map_lookup *map;
+	unsigned long len = fs_info->sectorsize;
+
+	em = btrfs_get_chunk_map(fs_info, logical, len);
+
+	if (!WARN_ON(IS_ERR(em))) {
+		map = em->map_lookup;
+		if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK)
+			len = map->stripe_len * nr_data_stripes(map);
+		free_extent_map(em);
+	}
+	return len;
+}
+
+int btrfs_is_parity_mirror(struct btrfs_fs_info *fs_info, u64 logical, u64 len)
+{
+	struct extent_map *em;
+	struct map_lookup *map;
+	int ret = 0;
+
+	em = btrfs_get_chunk_map(fs_info, logical, len);
+
+	if(!WARN_ON(IS_ERR(em))) {
+		map = em->map_lookup;
+		if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK)
+			ret = 1;
+		free_extent_map(em);
+	}
+	return ret;
+}
+
+static int find_live_mirror(struct btrfs_fs_info *fs_info,
+			    struct map_lookup *map, int first,
+			    int dev_replace_is_ongoing)
+{
+	int i;
+	int num_stripes;
+	int preferred_mirror;
+	int tolerance;
+	struct btrfs_device *srcdev;
+
+	ASSERT((map->type &
+		 (BTRFS_BLOCK_GROUP_RAID1_MASK | BTRFS_BLOCK_GROUP_RAID10)));
+
+	if (map->type & BTRFS_BLOCK_GROUP_RAID10)
+		num_stripes = map->sub_stripes;
+	else
+		num_stripes = map->num_stripes;
+
+	preferred_mirror = first + current->pid % num_stripes;
+
+	if (dev_replace_is_ongoing &&
+	    fs_info->dev_replace.cont_reading_from_srcdev_mode ==
+	     BTRFS_DEV_REPLACE_ITEM_CONT_READING_FROM_SRCDEV_MODE_AVOID)
+		srcdev = fs_info->dev_replace.srcdev;
+	else
+		srcdev = NULL;
+
+	/*
+	 * try to avoid the drive that is the source drive for a
+	 * dev-replace procedure, only choose it if no other non-missing
+	 * mirror is available
+	 */
+	for (tolerance = 0; tolerance < 2; tolerance++) {
+		if (map->stripes[preferred_mirror].dev->bdev &&
+		    (tolerance || map->stripes[preferred_mirror].dev != srcdev))
+			return preferred_mirror;
+		for (i = first; i < first + num_stripes; i++) {
+			if (map->stripes[i].dev->bdev &&
+			    (tolerance || map->stripes[i].dev != srcdev))
+				return i;
+		}
+	}
+
+	/* we couldn't find one that doesn't fail.  Just return something
+	 * and the io error handling code will clean up eventually
+	 */
+	return preferred_mirror;
+}
+
+/* Bubble-sort the stripe set to put the parity/syndrome stripes last */
+static void sort_parity_stripes(struct btrfs_bio *bbio, int num_stripes)
+{
+	int i;
+	int again = 1;
+
+	while (again) {
+		again = 0;
+		for (i = 0; i < num_stripes - 1; i++) {
+			/* Swap if parity is on a smaller index */
+			if (bbio->raid_map[i] > bbio->raid_map[i + 1]) {
+				swap(bbio->stripes[i], bbio->stripes[i + 1]);
+				swap(bbio->raid_map[i], bbio->raid_map[i + 1]);
+				again = 1;
+			}
+		}
+	}
+}
+
+static struct btrfs_bio *alloc_btrfs_bio(int total_stripes, int real_stripes)
+{
+	struct btrfs_bio *bbio = kzalloc(
+		 /* the size of the btrfs_bio */
+		sizeof(struct btrfs_bio) +
+		/* plus the variable array for the stripes */
+		sizeof(struct btrfs_bio_stripe) * (total_stripes) +
+		/* plus the variable array for the tgt dev */
+		sizeof(int) * (real_stripes) +
+		/*
+		 * plus the raid_map, which includes both the tgt dev
+		 * and the stripes
+		 */
+		sizeof(u64) * (total_stripes),
+		GFP_NOFS|__GFP_NOFAIL);
+
+	atomic_set(&bbio->error, 0);
+	refcount_set(&bbio->refs, 1);
+
+	bbio->tgtdev_map = (int *)(bbio->stripes + total_stripes);
+	bbio->raid_map = (u64 *)(bbio->tgtdev_map + real_stripes);
+
+	return bbio;
+}
+
+void btrfs_get_bbio(struct btrfs_bio *bbio)
+{
+	WARN_ON(!refcount_read(&bbio->refs));
+	refcount_inc(&bbio->refs);
+}
+
+void btrfs_put_bbio(struct btrfs_bio *bbio)
+{
+	if (!bbio)
+		return;
+	if (refcount_dec_and_test(&bbio->refs))
+		kfree(bbio);
+}
+
+/* can REQ_OP_DISCARD be sent with other REQ like REQ_OP_WRITE? */
+/*
+ * Please note that, discard won't be sent to target device of device
+ * replace.
+ */
+static int __btrfs_map_block_for_discard(struct btrfs_fs_info *fs_info,
+					 u64 logical, u64 *length_ret,
+					 struct btrfs_bio **bbio_ret)
+{
+	struct extent_map *em;
+	struct map_lookup *map;
+	struct btrfs_bio *bbio;
+	u64 length = *length_ret;
+	u64 offset;
+	u64 stripe_nr;
+	u64 stripe_nr_end;
+	u64 stripe_end_offset;
+	u64 stripe_cnt;
+	u64 stripe_len;
+	u64 stripe_offset;
+	u64 num_stripes;
+	u32 stripe_index;
+	u32 factor = 0;
+	u32 sub_stripes = 0;
+	u64 stripes_per_dev = 0;
+	u32 remaining_stripes = 0;
+	u32 last_stripe = 0;
+	int ret = 0;
+	int i;
+
+	/* discard always return a bbio */
+	ASSERT(bbio_ret);
+
+	em = btrfs_get_chunk_map(fs_info, logical, length);
+	if (IS_ERR(em))
+		return PTR_ERR(em);
+
+	map = em->map_lookup;
+	/* we don't discard raid56 yet */
+	if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
+		ret = -EOPNOTSUPP;
+		goto out;
+	}
+
+	offset = logical - em->start;
+	length = min_t(u64, em->start + em->len - logical, length);
+	*length_ret = length;
+
+	stripe_len = map->stripe_len;
+	/*
+	 * stripe_nr counts the total number of stripes we have to stride
+	 * to get to this block
+	 */
+	stripe_nr = div64_u64(offset, stripe_len);
+
+	/* stripe_offset is the offset of this block in its stripe */
+	stripe_offset = offset - stripe_nr * stripe_len;
+
+	stripe_nr_end = round_up(offset + length, map->stripe_len);
+	stripe_nr_end = div64_u64(stripe_nr_end, map->stripe_len);
+	stripe_cnt = stripe_nr_end - stripe_nr;
+	stripe_end_offset = stripe_nr_end * map->stripe_len -
+			    (offset + length);
+	/*
+	 * after this, stripe_nr is the number of stripes on this
+	 * device we have to walk to find the data, and stripe_index is
+	 * the number of our device in the stripe array
+	 */
+	num_stripes = 1;
+	stripe_index = 0;
+	if (map->type & (BTRFS_BLOCK_GROUP_RAID0 |
+			 BTRFS_BLOCK_GROUP_RAID10)) {
+		if (map->type & BTRFS_BLOCK_GROUP_RAID0)
+			sub_stripes = 1;
+		else
+			sub_stripes = map->sub_stripes;
+
+		factor = map->num_stripes / sub_stripes;
+		num_stripes = min_t(u64, map->num_stripes,
+				    sub_stripes * stripe_cnt);
+		stripe_nr = div_u64_rem(stripe_nr, factor, &stripe_index);
+		stripe_index *= sub_stripes;
+		stripes_per_dev = div_u64_rem(stripe_cnt, factor,
+					      &remaining_stripes);
+		div_u64_rem(stripe_nr_end - 1, factor, &last_stripe);
+		last_stripe *= sub_stripes;
+	} else if (map->type & (BTRFS_BLOCK_GROUP_RAID1_MASK |
+				BTRFS_BLOCK_GROUP_DUP)) {
+		num_stripes = map->num_stripes;
+	} else {
+		stripe_nr = div_u64_rem(stripe_nr, map->num_stripes,
+					&stripe_index);
+	}
+
+	bbio = alloc_btrfs_bio(num_stripes, 0);
+	if (!bbio) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	for (i = 0; i < num_stripes; i++) {
+		bbio->stripes[i].physical =
+			map->stripes[stripe_index].physical +
+			stripe_offset + stripe_nr * map->stripe_len;
+		bbio->stripes[i].dev = map->stripes[stripe_index].dev;
+
+		if (map->type & (BTRFS_BLOCK_GROUP_RAID0 |
+				 BTRFS_BLOCK_GROUP_RAID10)) {
+			bbio->stripes[i].length = stripes_per_dev *
+				map->stripe_len;
+
+			if (i / sub_stripes < remaining_stripes)
+				bbio->stripes[i].length +=
+					map->stripe_len;
+
+			/*
+			 * Special for the first stripe and
+			 * the last stripe:
+			 *
+			 * |-------|...|-------|
+			 *     |----------|
+			 *    off     end_off
+			 */
+			if (i < sub_stripes)
+				bbio->stripes[i].length -=
+					stripe_offset;
+
+			if (stripe_index >= last_stripe &&
+			    stripe_index <= (last_stripe +
+					     sub_stripes - 1))
+				bbio->stripes[i].length -=
+					stripe_end_offset;
+
+			if (i == sub_stripes - 1)
+				stripe_offset = 0;
+		} else {
+			bbio->stripes[i].length = length;
+		}
+
+		stripe_index++;
+		if (stripe_index == map->num_stripes) {
+			stripe_index = 0;
+			stripe_nr++;
+		}
+	}
+
+	*bbio_ret = bbio;
+	bbio->map_type = map->type;
+	bbio->num_stripes = num_stripes;
+out:
+	free_extent_map(em);
+	return ret;
+}
+
+/*
+ * In dev-replace case, for repair case (that's the only case where the mirror
+ * is selected explicitly when calling btrfs_map_block), blocks left of the
+ * left cursor can also be read from the target drive.
+ *
+ * For REQ_GET_READ_MIRRORS, the target drive is added as the last one to the
+ * array of stripes.
+ * For READ, it also needs to be supported using the same mirror number.
+ *
+ * If the requested block is not left of the left cursor, EIO is returned. This
+ * can happen because btrfs_num_copies() returns one more in the dev-replace
+ * case.
+ */
+static int get_extra_mirror_from_replace(struct btrfs_fs_info *fs_info,
+					 u64 logical, u64 length,
+					 u64 srcdev_devid, int *mirror_num,
+					 u64 *physical)
+{
+	struct btrfs_bio *bbio = NULL;
+	int num_stripes;
+	int index_srcdev = 0;
+	int found = 0;
+	u64 physical_of_found = 0;
+	int i;
+	int ret = 0;
+
+	ret = __btrfs_map_block(fs_info, BTRFS_MAP_GET_READ_MIRRORS,
+				logical, &length, &bbio, 0, 0);
+	if (ret) {
+		ASSERT(bbio == NULL);
+		return ret;
+	}
+
+	num_stripes = bbio->num_stripes;
+	if (*mirror_num > num_stripes) {
+		/*
+		 * BTRFS_MAP_GET_READ_MIRRORS does not contain this mirror,
+		 * that means that the requested area is not left of the left
+		 * cursor
+		 */
+		btrfs_put_bbio(bbio);
+		return -EIO;
+	}
+
+	/*
+	 * process the rest of the function using the mirror_num of the source
+	 * drive. Therefore look it up first.  At the end, patch the device
+	 * pointer to the one of the target drive.
+	 */
+	for (i = 0; i < num_stripes; i++) {
+		if (bbio->stripes[i].dev->devid != srcdev_devid)
+			continue;
+
+		/*
+		 * In case of DUP, in order to keep it simple, only add the
+		 * mirror with the lowest physical address
+		 */
+		if (found &&
+		    physical_of_found <= bbio->stripes[i].physical)
+			continue;
+
+		index_srcdev = i;
+		found = 1;
+		physical_of_found = bbio->stripes[i].physical;
+	}
+
+	btrfs_put_bbio(bbio);
+
+	ASSERT(found);
+	if (!found)
+		return -EIO;
+
+	*mirror_num = index_srcdev + 1;
+	*physical = physical_of_found;
+	return ret;
+}
+
+static void handle_ops_on_dev_replace(enum btrfs_map_op op,
+				      struct btrfs_bio **bbio_ret,
+				      struct btrfs_dev_replace *dev_replace,
+				      int *num_stripes_ret, int *max_errors_ret)
+{
+	struct btrfs_bio *bbio = *bbio_ret;
+	u64 srcdev_devid = dev_replace->srcdev->devid;
+	int tgtdev_indexes = 0;
+	int num_stripes = *num_stripes_ret;
+	int max_errors = *max_errors_ret;
+	int i;
+
+	if (op == BTRFS_MAP_WRITE) {
+		int index_where_to_add;
+
+		/*
+		 * duplicate the write operations while the dev replace
+		 * procedure is running. Since the copying of the old disk to
+		 * the new disk takes place at run time while the filesystem is
+		 * mounted writable, the regular write operations to the old
+		 * disk have to be duplicated to go to the new disk as well.
+		 *
+		 * Note that device->missing is handled by the caller, and that
+		 * the write to the old disk is already set up in the stripes
+		 * array.
+		 */
+		index_where_to_add = num_stripes;
+		for (i = 0; i < num_stripes; i++) {
+			if (bbio->stripes[i].dev->devid == srcdev_devid) {
+				/* write to new disk, too */
+				struct btrfs_bio_stripe *new =
+					bbio->stripes + index_where_to_add;
+				struct btrfs_bio_stripe *old =
+					bbio->stripes + i;
+
+				new->physical = old->physical;
+				new->length = old->length;
+				new->dev = dev_replace->tgtdev;
+				bbio->tgtdev_map[i] = index_where_to_add;
+				index_where_to_add++;
+				max_errors++;
+				tgtdev_indexes++;
+			}
+		}
+		num_stripes = index_where_to_add;
+	} else if (op == BTRFS_MAP_GET_READ_MIRRORS) {
+		int index_srcdev = 0;
+		int found = 0;
+		u64 physical_of_found = 0;
+
+		/*
+		 * During the dev-replace procedure, the target drive can also
+		 * be used to read data in case it is needed to repair a corrupt
+		 * block elsewhere. This is possible if the requested area is
+		 * left of the left cursor. In this area, the target drive is a
+		 * full copy of the source drive.
+		 */
+		for (i = 0; i < num_stripes; i++) {
+			if (bbio->stripes[i].dev->devid == srcdev_devid) {
+				/*
+				 * In case of DUP, in order to keep it simple,
+				 * only add the mirror with the lowest physical
+				 * address
+				 */
+				if (found &&
+				    physical_of_found <=
+				     bbio->stripes[i].physical)
+					continue;
+				index_srcdev = i;
+				found = 1;
+				physical_of_found = bbio->stripes[i].physical;
+			}
+		}
+		if (found) {
+			struct btrfs_bio_stripe *tgtdev_stripe =
+				bbio->stripes + num_stripes;
+
+			tgtdev_stripe->physical = physical_of_found;
+			tgtdev_stripe->length =
+				bbio->stripes[index_srcdev].length;
+			tgtdev_stripe->dev = dev_replace->tgtdev;
+			bbio->tgtdev_map[index_srcdev] = num_stripes;
+
+			tgtdev_indexes++;
+			num_stripes++;
+		}
+	}
+
+	*num_stripes_ret = num_stripes;
+	*max_errors_ret = max_errors;
+	bbio->num_tgtdevs = tgtdev_indexes;
+	*bbio_ret = bbio;
+}
+
+static bool need_full_stripe(enum btrfs_map_op op)
+{
+	return (op == BTRFS_MAP_WRITE || op == BTRFS_MAP_GET_READ_MIRRORS);
+}
+
+/*
+ * btrfs_get_io_geometry - calculates the geomery of a particular (address, len)
+ *		       tuple. This information is used to calculate how big a
+ *		       particular bio can get before it straddles a stripe.
+ *
+ * @fs_info - the filesystem
+ * @logical - address that we want to figure out the geometry of
+ * @len	    - the length of IO we are going to perform, starting at @logical
+ * @op      - type of operation - write or read
+ * @io_geom - pointer used to return values
+ *
+ * Returns < 0 in case a chunk for the given logical address cannot be found,
+ * usually shouldn't happen unless @logical is corrupted, 0 otherwise.
+ */
+int btrfs_get_io_geometry(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
+			u64 logical, u64 len, struct btrfs_io_geometry *io_geom)
+{
+	struct extent_map *em;
+	struct map_lookup *map;
+	u64 offset;
+	u64 stripe_offset;
+	u64 stripe_nr;
+	u64 stripe_len;
+	u64 raid56_full_stripe_start = (u64)-1;
+	int data_stripes;
+	int ret = 0;
+
+	ASSERT(op != BTRFS_MAP_DISCARD);
+
+	em = btrfs_get_chunk_map(fs_info, logical, len);
+	if (IS_ERR(em))
+		return PTR_ERR(em);
+
+	map = em->map_lookup;
+	/* Offset of this logical address in the chunk */
+	offset = logical - em->start;
+	/* Len of a stripe in a chunk */
+	stripe_len = map->stripe_len;
+	/* Stripe wher this block falls in */
+	stripe_nr = div64_u64(offset, stripe_len);
+	/* Offset of stripe in the chunk */
+	stripe_offset = stripe_nr * stripe_len;
+	if (offset < stripe_offset) {
+		btrfs_crit(fs_info,
+"stripe math has gone wrong, stripe_offset=%llu offset=%llu start=%llu logical=%llu stripe_len=%llu",
+			stripe_offset, offset, em->start, logical, stripe_len);
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/* stripe_offset is the offset of this block in its stripe */
+	stripe_offset = offset - stripe_offset;
+	data_stripes = nr_data_stripes(map);
+
+	if (map->type & BTRFS_BLOCK_GROUP_PROFILE_MASK) {
+		u64 max_len = stripe_len - stripe_offset;
+
+		/*
+		 * In case of raid56, we need to know the stripe aligned start
+		 */
+		if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
+			unsigned long full_stripe_len = stripe_len * data_stripes;
+			raid56_full_stripe_start = offset;
+
+			/*
+			 * Allow a write of a full stripe, but make sure we
+			 * don't allow straddling of stripes
+			 */
+			raid56_full_stripe_start = div64_u64(raid56_full_stripe_start,
+					full_stripe_len);
+			raid56_full_stripe_start *= full_stripe_len;
+
+			/*
+			 * For writes to RAID[56], allow a full stripeset across
+			 * all disks. For other RAID types and for RAID[56]
+			 * reads, just allow a single stripe (on a single disk).
+			 */
+			if (op == BTRFS_MAP_WRITE) {
+				max_len = stripe_len * data_stripes -
+					  (offset - raid56_full_stripe_start);
+			}
+		}
+		len = min_t(u64, em->len - offset, max_len);
+	} else {
+		len = em->len - offset;
+	}
+
+	io_geom->len = len;
+	io_geom->offset = offset;
+	io_geom->stripe_len = stripe_len;
+	io_geom->stripe_nr = stripe_nr;
+	io_geom->stripe_offset = stripe_offset;
+	io_geom->raid56_stripe_offset = raid56_full_stripe_start;
+
+out:
+	/* once for us */
+	free_extent_map(em);
+	return ret;
+}
+
+static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
+			     enum btrfs_map_op op,
+			     u64 logical, u64 *length,
+			     struct btrfs_bio **bbio_ret,
+			     int mirror_num, int need_raid_map)
+{
+	struct extent_map *em;
+	struct map_lookup *map;
+	u64 stripe_offset;
+	u64 stripe_nr;
+	u64 stripe_len;
+	u32 stripe_index;
+	int data_stripes;
+	int i;
+	int ret = 0;
+	int num_stripes;
+	int max_errors = 0;
+	int tgtdev_indexes = 0;
+	struct btrfs_bio *bbio = NULL;
+	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
+	int dev_replace_is_ongoing = 0;
+	int num_alloc_stripes;
+	int patch_the_first_stripe_for_dev_replace = 0;
+	u64 physical_to_patch_in_first_stripe = 0;
+	u64 raid56_full_stripe_start = (u64)-1;
+	struct btrfs_io_geometry geom;
+
+	ASSERT(bbio_ret);
+	ASSERT(op != BTRFS_MAP_DISCARD);
+
+	ret = btrfs_get_io_geometry(fs_info, op, logical, *length, &geom);
+	if (ret < 0)
+		return ret;
+
+	em = btrfs_get_chunk_map(fs_info, logical, *length);
+	ASSERT(!IS_ERR(em));
+	map = em->map_lookup;
+
+	*length = geom.len;
+	stripe_len = geom.stripe_len;
+	stripe_nr = geom.stripe_nr;
+	stripe_offset = geom.stripe_offset;
+	raid56_full_stripe_start = geom.raid56_stripe_offset;
+	data_stripes = nr_data_stripes(map);
+
+	down_read(&dev_replace->rwsem);
+	dev_replace_is_ongoing = btrfs_dev_replace_is_ongoing(dev_replace);
+	/*
+	 * Hold the semaphore for read during the whole operation, write is
+	 * requested at commit time but must wait.
+	 */
+	if (!dev_replace_is_ongoing)
+		up_read(&dev_replace->rwsem);
+
+	if (dev_replace_is_ongoing && mirror_num == map->num_stripes + 1 &&
+	    !need_full_stripe(op) && dev_replace->tgtdev != NULL) {
+		ret = get_extra_mirror_from_replace(fs_info, logical, *length,
+						    dev_replace->srcdev->devid,
+						    &mirror_num,
+					    &physical_to_patch_in_first_stripe);
+		if (ret)
+			goto out;
+		else
+			patch_the_first_stripe_for_dev_replace = 1;
+	} else if (mirror_num > map->num_stripes) {
+		mirror_num = 0;
+	}
+
+	num_stripes = 1;
+	stripe_index = 0;
+	if (map->type & BTRFS_BLOCK_GROUP_RAID0) {
+		stripe_nr = div_u64_rem(stripe_nr, map->num_stripes,
+				&stripe_index);
+		if (!need_full_stripe(op))
+			mirror_num = 1;
+	} else if (map->type & BTRFS_BLOCK_GROUP_RAID1_MASK) {
+		if (need_full_stripe(op))
+			num_stripes = map->num_stripes;
+		else if (mirror_num)
+			stripe_index = mirror_num - 1;
+		else {
+			stripe_index = find_live_mirror(fs_info, map, 0,
+					    dev_replace_is_ongoing);
+			mirror_num = stripe_index + 1;
+		}
+
+	} else if (map->type & BTRFS_BLOCK_GROUP_DUP) {
+		if (need_full_stripe(op)) {
+			num_stripes = map->num_stripes;
+		} else if (mirror_num) {
+			stripe_index = mirror_num - 1;
+		} else {
+			mirror_num = 1;
+		}
+
+	} else if (map->type & BTRFS_BLOCK_GROUP_RAID10) {
+		u32 factor = map->num_stripes / map->sub_stripes;
+
+		stripe_nr = div_u64_rem(stripe_nr, factor, &stripe_index);
+		stripe_index *= map->sub_stripes;
+
+		if (need_full_stripe(op))
+			num_stripes = map->sub_stripes;
+		else if (mirror_num)
+			stripe_index += mirror_num - 1;
+		else {
+			int old_stripe_index = stripe_index;
+			stripe_index = find_live_mirror(fs_info, map,
+					      stripe_index,
+					      dev_replace_is_ongoing);
+			mirror_num = stripe_index - old_stripe_index + 1;
+		}
+
+	} else if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
+		if (need_raid_map && (need_full_stripe(op) || mirror_num > 1)) {
+			/* push stripe_nr back to the start of the full stripe */
+			stripe_nr = div64_u64(raid56_full_stripe_start,
+					stripe_len * data_stripes);
+
+			/* RAID[56] write or recovery. Return all stripes */
+			num_stripes = map->num_stripes;
+			max_errors = nr_parity_stripes(map);
+
+			*length = map->stripe_len;
+			stripe_index = 0;
+			stripe_offset = 0;
+		} else {
+			/*
+			 * Mirror #0 or #1 means the original data block.
+			 * Mirror #2 is RAID5 parity block.
+			 * Mirror #3 is RAID6 Q block.
+			 */
+			stripe_nr = div_u64_rem(stripe_nr,
+					data_stripes, &stripe_index);
+			if (mirror_num > 1)
+				stripe_index = data_stripes + mirror_num - 2;
+
+			/* We distribute the parity blocks across stripes */
+			div_u64_rem(stripe_nr + stripe_index, map->num_stripes,
+					&stripe_index);
+			if (!need_full_stripe(op) && mirror_num <= 1)
+				mirror_num = 1;
+		}
+	} else {
+		/*
+		 * after this, stripe_nr is the number of stripes on this
+		 * device we have to walk to find the data, and stripe_index is
+		 * the number of our device in the stripe array
+		 */
+		stripe_nr = div_u64_rem(stripe_nr, map->num_stripes,
+				&stripe_index);
+		mirror_num = stripe_index + 1;
+	}
+	if (stripe_index >= map->num_stripes) {
+		btrfs_crit(fs_info,
+			   "stripe index math went horribly wrong, got stripe_index=%u, num_stripes=%u",
+			   stripe_index, map->num_stripes);
+		ret = -EINVAL;
+		goto out;
+	}
+
+	num_alloc_stripes = num_stripes;
+	if (dev_replace_is_ongoing && dev_replace->tgtdev != NULL) {
+		if (op == BTRFS_MAP_WRITE)
+			num_alloc_stripes <<= 1;
+		if (op == BTRFS_MAP_GET_READ_MIRRORS)
+			num_alloc_stripes++;
+		tgtdev_indexes = num_stripes;
+	}
+
+	bbio = alloc_btrfs_bio(num_alloc_stripes, tgtdev_indexes);
+	if (!bbio) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	for (i = 0; i < num_stripes; i++) {
+		bbio->stripes[i].physical = map->stripes[stripe_index].physical +
+			stripe_offset + stripe_nr * map->stripe_len;
+		bbio->stripes[i].dev = map->stripes[stripe_index].dev;
+		stripe_index++;
+	}
+
+	/* build raid_map */
+	if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK && need_raid_map &&
+	    (need_full_stripe(op) || mirror_num > 1)) {
+		u64 tmp;
+		unsigned rot;
+
+		/* Work out the disk rotation on this stripe-set */
+		div_u64_rem(stripe_nr, num_stripes, &rot);
+
+		/* Fill in the logical address of each stripe */
+		tmp = stripe_nr * data_stripes;
+		for (i = 0; i < data_stripes; i++)
+			bbio->raid_map[(i+rot) % num_stripes] =
+				em->start + (tmp + i) * map->stripe_len;
+
+		bbio->raid_map[(i+rot) % map->num_stripes] = RAID5_P_STRIPE;
+		if (map->type & BTRFS_BLOCK_GROUP_RAID6)
+			bbio->raid_map[(i+rot+1) % num_stripes] =
+				RAID6_Q_STRIPE;
+
+		sort_parity_stripes(bbio, num_stripes);
+	}
+
+	if (need_full_stripe(op))
+		max_errors = btrfs_chunk_max_errors(map);
+
+	if (dev_replace_is_ongoing && dev_replace->tgtdev != NULL &&
+	    need_full_stripe(op)) {
+		handle_ops_on_dev_replace(op, &bbio, dev_replace, &num_stripes,
+					  &max_errors);
+	}
+
+	*bbio_ret = bbio;
+	bbio->map_type = map->type;
+	bbio->num_stripes = num_stripes;
+	bbio->max_errors = max_errors;
+	bbio->mirror_num = mirror_num;
+
+	/*
+	 * this is the case that REQ_READ && dev_replace_is_ongoing &&
+	 * mirror_num == num_stripes + 1 && dev_replace target drive is
+	 * available as a mirror
+	 */
+	if (patch_the_first_stripe_for_dev_replace && num_stripes > 0) {
+		WARN_ON(num_stripes > 1);
+		bbio->stripes[0].dev = dev_replace->tgtdev;
+		bbio->stripes[0].physical = physical_to_patch_in_first_stripe;
+		bbio->mirror_num = map->num_stripes + 1;
+	}
+out:
+	if (dev_replace_is_ongoing) {
+		lockdep_assert_held(&dev_replace->rwsem);
+		/* Unlock and let waiting writers proceed */
+		up_read(&dev_replace->rwsem);
+	}
+	free_extent_map(em);
+	return ret;
+}
+
+int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
+		      u64 logical, u64 *length,
+		      struct btrfs_bio **bbio_ret, int mirror_num)
+{
+	if (op == BTRFS_MAP_DISCARD)
+		return __btrfs_map_block_for_discard(fs_info, logical,
+						     length, bbio_ret);
+
+	return __btrfs_map_block(fs_info, op, logical, length, bbio_ret,
+				 mirror_num, 0);
+}
+
+/* For Scrub/replace */
+int btrfs_map_sblock(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
+		     u64 logical, u64 *length,
+		     struct btrfs_bio **bbio_ret)
+{
+	return __btrfs_map_block(fs_info, op, logical, length, bbio_ret, 0, 1);
+}
+
+static inline void btrfs_end_bbio(struct btrfs_bio *bbio, struct bio *bio)
+{
+	bio->bi_private = bbio->private;
+	bio->bi_end_io = bbio->end_io;
+	bio_endio(bio);
+
+	btrfs_put_bbio(bbio);
+}
+
+static void btrfs_end_bio(struct bio *bio)
+{
+	struct btrfs_bio *bbio = bio->bi_private;
+	int is_orig_bio = 0;
+
+	if (bio->bi_status) {
+		atomic_inc(&bbio->error);
+		if (bio->bi_status == BLK_STS_IOERR ||
+		    bio->bi_status == BLK_STS_TARGET) {
+			struct btrfs_device *dev = btrfs_io_bio(bio)->device;
+
+			ASSERT(dev->bdev);
+			if (bio_op(bio) == REQ_OP_WRITE)
+				btrfs_dev_stat_inc_and_print(dev,
+						BTRFS_DEV_STAT_WRITE_ERRS);
+			else if (!(bio->bi_opf & REQ_RAHEAD))
+				btrfs_dev_stat_inc_and_print(dev,
+						BTRFS_DEV_STAT_READ_ERRS);
+			if (bio->bi_opf & REQ_PREFLUSH)
+				btrfs_dev_stat_inc_and_print(dev,
+						BTRFS_DEV_STAT_FLUSH_ERRS);
+		}
+	}
+
+	if (bio == bbio->orig_bio)
+		is_orig_bio = 1;
+
+	btrfs_bio_counter_dec(bbio->fs_info);
+
+	if (atomic_dec_and_test(&bbio->stripes_pending)) {
+		if (!is_orig_bio) {
+			bio_put(bio);
+			bio = bbio->orig_bio;
+		}
+
+		btrfs_io_bio(bio)->mirror_num = bbio->mirror_num;
+		/* only send an error to the higher layers if it is
+		 * beyond the tolerance of the btrfs bio
+		 */
+		if (atomic_read(&bbio->error) > bbio->max_errors) {
+			bio->bi_status = BLK_STS_IOERR;
+		} else {
+			/*
+			 * this bio is actually up to date, we didn't
+			 * go over the max number of errors
+			 */
+			bio->bi_status = BLK_STS_OK;
+		}
+
+		btrfs_end_bbio(bbio, bio);
+	} else if (!is_orig_bio) {
+		bio_put(bio);
+	}
+}
+
+static void submit_stripe_bio(struct btrfs_bio *bbio, struct bio *bio,
+			      u64 physical, struct btrfs_device *dev)
+{
+	struct btrfs_fs_info *fs_info = bbio->fs_info;
+
+	bio->bi_private = bbio;
+	btrfs_io_bio(bio)->device = dev;
+	bio->bi_end_io = btrfs_end_bio;
+	bio->bi_iter.bi_sector = physical >> 9;
+	btrfs_debug_in_rcu(fs_info,
+	"btrfs_map_bio: rw %d 0x%x, sector=%llu, dev=%lu (%s id %llu), size=%u",
+		bio_op(bio), bio->bi_opf, (u64)bio->bi_iter.bi_sector,
+		(unsigned long)dev->bdev->bd_dev, rcu_str_deref(dev->name),
+		dev->devid, bio->bi_iter.bi_size);
+	bio_set_dev(bio, dev->bdev);
+
+	btrfs_bio_counter_inc_noblocked(fs_info);
+
+	btrfsic_submit_bio(bio);
+}
+
+static void bbio_error(struct btrfs_bio *bbio, struct bio *bio, u64 logical)
+{
+	atomic_inc(&bbio->error);
+	if (atomic_dec_and_test(&bbio->stripes_pending)) {
+		/* Should be the original bio. */
+		WARN_ON(bio != bbio->orig_bio);
+
+		btrfs_io_bio(bio)->mirror_num = bbio->mirror_num;
+		bio->bi_iter.bi_sector = logical >> 9;
+		if (atomic_read(&bbio->error) > bbio->max_errors)
+			bio->bi_status = BLK_STS_IOERR;
+		else
+			bio->bi_status = BLK_STS_OK;
+		btrfs_end_bbio(bbio, bio);
+	}
+}
+
+blk_status_t btrfs_map_bio(struct btrfs_fs_info *fs_info, struct bio *bio,
+			   int mirror_num)
+{
+	struct btrfs_device *dev;
+	struct bio *first_bio = bio;
+	u64 logical = (u64)bio->bi_iter.bi_sector << 9;
+	u64 length = 0;
+	u64 map_length;
+	int ret;
+	int dev_nr;
+	int total_devs;
+	struct btrfs_bio *bbio = NULL;
+
+	length = bio->bi_iter.bi_size;
+	map_length = length;
+
+	btrfs_bio_counter_inc_blocked(fs_info);
+	ret = __btrfs_map_block(fs_info, btrfs_op(bio), logical,
+				&map_length, &bbio, mirror_num, 1);
+	if (ret) {
+		btrfs_bio_counter_dec(fs_info);
+		return errno_to_blk_status(ret);
+	}
+
+	total_devs = bbio->num_stripes;
+	bbio->orig_bio = first_bio;
+	bbio->private = first_bio->bi_private;
+	bbio->end_io = first_bio->bi_end_io;
+	bbio->fs_info = fs_info;
+	atomic_set(&bbio->stripes_pending, bbio->num_stripes);
+
+	if ((bbio->map_type & BTRFS_BLOCK_GROUP_RAID56_MASK) &&
+	    ((bio_op(bio) == REQ_OP_WRITE) || (mirror_num > 1))) {
+		/* In this case, map_length has been set to the length of
+		   a single stripe; not the whole write */
+		if (bio_op(bio) == REQ_OP_WRITE) {
+			ret = raid56_parity_write(fs_info, bio, bbio,
+						  map_length);
+		} else {
+			ret = raid56_parity_recover(fs_info, bio, bbio,
+						    map_length, mirror_num, 1);
+		}
+
+		btrfs_bio_counter_dec(fs_info);
+		return errno_to_blk_status(ret);
+	}
+
+	if (map_length < length) {
+		btrfs_crit(fs_info,
+			   "mapping failed logical %llu bio len %llu len %llu",
+			   logical, length, map_length);
+		BUG();
+	}
+
+	for (dev_nr = 0; dev_nr < total_devs; dev_nr++) {
+		dev = bbio->stripes[dev_nr].dev;
+		if (!dev || !dev->bdev || test_bit(BTRFS_DEV_STATE_MISSING,
+						   &dev->dev_state) ||
+		    (bio_op(first_bio) == REQ_OP_WRITE &&
+		    !test_bit(BTRFS_DEV_STATE_WRITEABLE, &dev->dev_state))) {
+			bbio_error(bbio, first_bio, logical);
+			continue;
+		}
+
+		if (dev_nr < total_devs - 1)
+			bio = btrfs_bio_clone(first_bio);
+		else
+			bio = first_bio;
+
+		submit_stripe_bio(bbio, bio, bbio->stripes[dev_nr].physical, dev);
+	}
+	btrfs_bio_counter_dec(fs_info);
+	return BLK_STS_OK;
+}
+
+/*
+ * Find a device specified by @devid or @uuid in the list of @fs_devices, or
+ * return NULL.
+ *
+ * If devid and uuid are both specified, the match must be exact, otherwise
+ * only devid is used.
+ *
+ * If @seed is true, traverse through the seed devices.
+ */
+struct btrfs_device *btrfs_find_device(struct btrfs_fs_devices *fs_devices,
+				       u64 devid, u8 *uuid, u8 *fsid,
+				       bool seed)
+{
+	struct btrfs_device *device;
+	struct btrfs_fs_devices *seed_devs;
+
+	if (!fsid || !memcmp(fs_devices->metadata_uuid, fsid, BTRFS_FSID_SIZE)) {
+		list_for_each_entry(device, &fs_devices->devices, dev_list) {
+			if (device->devid == devid &&
+			    (!uuid || memcmp(device->uuid, uuid,
+					     BTRFS_UUID_SIZE) == 0))
+				return device;
+		}
+	}
+
+	list_for_each_entry(seed_devs, &fs_devices->seed_list, seed_list) {
+		if (!fsid ||
+		    !memcmp(seed_devs->metadata_uuid, fsid, BTRFS_FSID_SIZE)) {
+			list_for_each_entry(device, &seed_devs->devices,
+					    dev_list) {
+				if (device->devid == devid &&
+				    (!uuid || memcmp(device->uuid, uuid,
+						     BTRFS_UUID_SIZE) == 0))
+					return device;
+			}
+		}
+	}
+
+	return NULL;
+}
+
+static struct btrfs_device *add_missing_dev(struct btrfs_fs_devices *fs_devices,
+					    u64 devid, u8 *dev_uuid)
+{
+	struct btrfs_device *device;
+	unsigned int nofs_flag;
+
+	/*
+	 * We call this under the chunk_mutex, so we want to use NOFS for this
+	 * allocation, however we don't want to change btrfs_alloc_device() to
+	 * always do NOFS because we use it in a lot of other GFP_KERNEL safe
+	 * places.
+	 */
+	nofs_flag = memalloc_nofs_save();
+	device = btrfs_alloc_device(NULL, &devid, dev_uuid);
+	memalloc_nofs_restore(nofs_flag);
+	if (IS_ERR(device))
+		return device;
+
+	list_add(&device->dev_list, &fs_devices->devices);
+	device->fs_devices = fs_devices;
+	fs_devices->num_devices++;
+
+	set_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
+	fs_devices->missing_devices++;
+
+	return device;
+}
+
+/**
+ * btrfs_alloc_device - allocate struct btrfs_device
+ * @fs_info:	used only for generating a new devid, can be NULL if
+ *		devid is provided (i.e. @devid != NULL).
+ * @devid:	a pointer to devid for this device.  If NULL a new devid
+ *		is generated.
+ * @uuid:	a pointer to UUID for this device.  If NULL a new UUID
+ *		is generated.
+ *
+ * Return: a pointer to a new &struct btrfs_device on success; ERR_PTR()
+ * on error.  Returned struct is not linked onto any lists and must be
+ * destroyed with btrfs_free_device.
+ */
+struct btrfs_device *btrfs_alloc_device(struct btrfs_fs_info *fs_info,
+					const u64 *devid,
+					const u8 *uuid)
+{
+	struct btrfs_device *dev;
+	u64 tmp;
+
+	if (WARN_ON(!devid && !fs_info))
+		return ERR_PTR(-EINVAL);
+
+	dev = __alloc_device(fs_info);
+	if (IS_ERR(dev))
+		return dev;
+
+	if (devid)
+		tmp = *devid;
+	else {
+		int ret;
+
+		ret = find_next_devid(fs_info, &tmp);
+		if (ret) {
+			btrfs_free_device(dev);
+			return ERR_PTR(ret);
+		}
+	}
+	dev->devid = tmp;
+
+	if (uuid)
+		memcpy(dev->uuid, uuid, BTRFS_UUID_SIZE);
+	else
+		generate_random_uuid(dev->uuid);
+
+	return dev;
+}
+
+static void btrfs_report_missing_device(struct btrfs_fs_info *fs_info,
+					u64 devid, u8 *uuid, bool error)
+{
+	if (error)
+		btrfs_err_rl(fs_info, "devid %llu uuid %pU is missing",
+			      devid, uuid);
+	else
+		btrfs_warn_rl(fs_info, "devid %llu uuid %pU is missing",
+			      devid, uuid);
+}
+
+static u64 calc_stripe_length(u64 type, u64 chunk_len, int num_stripes)
+{
+	int index = btrfs_bg_flags_to_raid_index(type);
+	int ncopies = btrfs_raid_array[index].ncopies;
+	const int nparity = btrfs_raid_array[index].nparity;
+	int data_stripes;
+
+	if (nparity)
+		data_stripes = num_stripes - nparity;
+	else
+		data_stripes = num_stripes / ncopies;
+
+	return div_u64(chunk_len, data_stripes);
+}
+
+static int read_one_chunk(struct btrfs_key *key, struct extent_buffer *leaf,
+			  struct btrfs_chunk *chunk)
+{
+	struct btrfs_fs_info *fs_info = leaf->fs_info;
+	struct extent_map_tree *map_tree = &fs_info->mapping_tree;
+	struct map_lookup *map;
+	struct extent_map *em;
+	u64 logical;
+	u64 length;
+	u64 devid;
+	u8 uuid[BTRFS_UUID_SIZE];
+	int num_stripes;
+	int ret;
+	int i;
+
+	logical = key->offset;
+	length = btrfs_chunk_length(leaf, chunk);
+	num_stripes = btrfs_chunk_num_stripes(leaf, chunk);
+
+	/*
+	 * Only need to verify chunk item if we're reading from sys chunk array,
+	 * as chunk item in tree block is already verified by tree-checker.
+	 */
+	if (leaf->start == BTRFS_SUPER_INFO_OFFSET) {
+		ret = btrfs_check_chunk_valid(leaf, chunk, logical);
+		if (ret)
+			return ret;
+	}
+
+	read_lock(&map_tree->lock);
+	em = lookup_extent_mapping(map_tree, logical, 1);
+	read_unlock(&map_tree->lock);
+
+	/* already mapped? */
+	if (em && em->start <= logical && em->start + em->len > logical) {
+		free_extent_map(em);
+		return 0;
+	} else if (em) {
+		free_extent_map(em);
+	}
+
+	em = alloc_extent_map();
+	if (!em)
+		return -ENOMEM;
+	map = kmalloc(map_lookup_size(num_stripes), GFP_NOFS);
+	if (!map) {
+		free_extent_map(em);
+		return -ENOMEM;
+	}
+
+	set_bit(EXTENT_FLAG_FS_MAPPING, &em->flags);
+	em->map_lookup = map;
+	em->start = logical;
+	em->len = length;
+	em->orig_start = 0;
+	em->block_start = 0;
+	em->block_len = em->len;
+
+	map->num_stripes = num_stripes;
+	map->io_width = btrfs_chunk_io_width(leaf, chunk);
+	map->io_align = btrfs_chunk_io_align(leaf, chunk);
+	map->stripe_len = btrfs_chunk_stripe_len(leaf, chunk);
+	map->type = btrfs_chunk_type(leaf, chunk);
+	map->sub_stripes = btrfs_chunk_sub_stripes(leaf, chunk);
+	map->verified_stripes = 0;
+	em->orig_block_len = calc_stripe_length(map->type, em->len,
+						map->num_stripes);
+	for (i = 0; i < num_stripes; i++) {
+		map->stripes[i].physical =
+			btrfs_stripe_offset_nr(leaf, chunk, i);
+		devid = btrfs_stripe_devid_nr(leaf, chunk, i);
+		read_extent_buffer(leaf, uuid, (unsigned long)
+				   btrfs_stripe_dev_uuid_nr(chunk, i),
+				   BTRFS_UUID_SIZE);
+		map->stripes[i].dev = btrfs_find_device(fs_info->fs_devices,
+							devid, uuid, NULL, true);
+		if (!map->stripes[i].dev &&
+		    !btrfs_test_opt(fs_info, DEGRADED)) {
+			free_extent_map(em);
+			btrfs_report_missing_device(fs_info, devid, uuid, true);
+			return -ENOENT;
+		}
+		if (!map->stripes[i].dev) {
+			map->stripes[i].dev =
+				add_missing_dev(fs_info->fs_devices, devid,
+						uuid);
+			if (IS_ERR(map->stripes[i].dev)) {
+				free_extent_map(em);
+				btrfs_err(fs_info,
+					"failed to init missing dev %llu: %ld",
+					devid, PTR_ERR(map->stripes[i].dev));
+				return PTR_ERR(map->stripes[i].dev);
+			}
+			btrfs_report_missing_device(fs_info, devid, uuid, false);
+		}
+		set_bit(BTRFS_DEV_STATE_IN_FS_METADATA,
+				&(map->stripes[i].dev->dev_state));
+
+	}
+
+	write_lock(&map_tree->lock);
+	ret = add_extent_mapping(map_tree, em, 0);
+	write_unlock(&map_tree->lock);
+	if (ret < 0) {
+		btrfs_err(fs_info,
+			  "failed to add chunk map, start=%llu len=%llu: %d",
+			  em->start, em->len, ret);
+	}
+	free_extent_map(em);
+
+	return ret;
+}
+
+static void fill_device_from_item(struct extent_buffer *leaf,
+				 struct btrfs_dev_item *dev_item,
+				 struct btrfs_device *device)
+{
+	unsigned long ptr;
+
+	device->devid = btrfs_device_id(leaf, dev_item);
+	device->disk_total_bytes = btrfs_device_total_bytes(leaf, dev_item);
+	device->total_bytes = device->disk_total_bytes;
+	device->commit_total_bytes = device->disk_total_bytes;
+	device->bytes_used = btrfs_device_bytes_used(leaf, dev_item);
+	device->commit_bytes_used = device->bytes_used;
+	device->type = btrfs_device_type(leaf, dev_item);
+	device->io_align = btrfs_device_io_align(leaf, dev_item);
+	device->io_width = btrfs_device_io_width(leaf, dev_item);
+	device->sector_size = btrfs_device_sector_size(leaf, dev_item);
+	WARN_ON(device->devid == BTRFS_DEV_REPLACE_DEVID);
+	clear_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state);
+
+	ptr = btrfs_device_uuid(dev_item);
+	read_extent_buffer(leaf, device->uuid, ptr, BTRFS_UUID_SIZE);
+}
+
+static struct btrfs_fs_devices *open_seed_devices(struct btrfs_fs_info *fs_info,
+						  u8 *fsid)
+{
+	struct btrfs_fs_devices *fs_devices;
+	int ret;
+
+	lockdep_assert_held(&uuid_mutex);
+	ASSERT(fsid);
+
+	/* This will match only for multi-device seed fs */
+	list_for_each_entry(fs_devices, &fs_info->fs_devices->seed_list, seed_list)
+		if (!memcmp(fs_devices->fsid, fsid, BTRFS_FSID_SIZE))
+			return fs_devices;
+
+
+	fs_devices = find_fsid(fsid, NULL);
+	if (!fs_devices) {
+		if (!btrfs_test_opt(fs_info, DEGRADED))
+			return ERR_PTR(-ENOENT);
+
+		fs_devices = alloc_fs_devices(fsid, NULL);
+		if (IS_ERR(fs_devices))
+			return fs_devices;
+
+		fs_devices->seeding = true;
+		fs_devices->opened = 1;
+		return fs_devices;
+	}
+
+	/*
+	 * Upon first call for a seed fs fsid, just create a private copy of the
+	 * respective fs_devices and anchor it at fs_info->fs_devices->seed_list
+	 */
+	fs_devices = clone_fs_devices(fs_devices);
+	if (IS_ERR(fs_devices))
+		return fs_devices;
+
+	ret = open_fs_devices(fs_devices, FMODE_READ, fs_info->bdev_holder);
+	if (ret) {
+		free_fs_devices(fs_devices);
+		return ERR_PTR(ret);
+	}
+
+	if (!fs_devices->seeding) {
+		close_fs_devices(fs_devices);
+		free_fs_devices(fs_devices);
+		return ERR_PTR(-EINVAL);
+	}
+
+	list_add(&fs_devices->seed_list, &fs_info->fs_devices->seed_list);
+
+	return fs_devices;
+}
+
+static int read_one_dev(struct extent_buffer *leaf,
+			struct btrfs_dev_item *dev_item)
+{
+	struct btrfs_fs_info *fs_info = leaf->fs_info;
+	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
+	struct btrfs_device *device;
+	u64 devid;
+	int ret;
+	u8 fs_uuid[BTRFS_FSID_SIZE];
+	u8 dev_uuid[BTRFS_UUID_SIZE];
+
+	devid = btrfs_device_id(leaf, dev_item);
+	read_extent_buffer(leaf, dev_uuid, btrfs_device_uuid(dev_item),
+			   BTRFS_UUID_SIZE);
+	read_extent_buffer(leaf, fs_uuid, btrfs_device_fsid(dev_item),
+			   BTRFS_FSID_SIZE);
+
+	if (memcmp(fs_uuid, fs_devices->metadata_uuid, BTRFS_FSID_SIZE)) {
+		fs_devices = open_seed_devices(fs_info, fs_uuid);
+		if (IS_ERR(fs_devices))
+			return PTR_ERR(fs_devices);
+	}
+
+	device = btrfs_find_device(fs_info->fs_devices, devid, dev_uuid,
+				   fs_uuid, true);
+	if (!device) {
+		if (!btrfs_test_opt(fs_info, DEGRADED)) {
+			btrfs_report_missing_device(fs_info, devid,
+							dev_uuid, true);
+			return -ENOENT;
+		}
+
+		device = add_missing_dev(fs_devices, devid, dev_uuid);
+		if (IS_ERR(device)) {
+			btrfs_err(fs_info,
+				"failed to add missing dev %llu: %ld",
+				devid, PTR_ERR(device));
+			return PTR_ERR(device);
+		}
+		btrfs_report_missing_device(fs_info, devid, dev_uuid, false);
+	} else {
+		if (!device->bdev) {
+			if (!btrfs_test_opt(fs_info, DEGRADED)) {
+				btrfs_report_missing_device(fs_info,
+						devid, dev_uuid, true);
+				return -ENOENT;
+			}
+			btrfs_report_missing_device(fs_info, devid,
+							dev_uuid, false);
+		}
+
+		if (!device->bdev &&
+		    !test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) {
+			/*
+			 * this happens when a device that was properly setup
+			 * in the device info lists suddenly goes bad.
+			 * device->bdev is NULL, and so we have to set
+			 * device->missing to one here
+			 */
+			device->fs_devices->missing_devices++;
+			set_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
+		}
+
+		/* Move the device to its own fs_devices */
+		if (device->fs_devices != fs_devices) {
+			ASSERT(test_bit(BTRFS_DEV_STATE_MISSING,
+							&device->dev_state));
+
+			list_move(&device->dev_list, &fs_devices->devices);
+			device->fs_devices->num_devices--;
+			fs_devices->num_devices++;
+
+			device->fs_devices->missing_devices--;
+			fs_devices->missing_devices++;
+
+			device->fs_devices = fs_devices;
+		}
+	}
+
+	if (device->fs_devices != fs_info->fs_devices) {
+		BUG_ON(test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state));
+		if (device->generation !=
+		    btrfs_device_generation(leaf, dev_item))
+			return -EINVAL;
+	}
+
+	fill_device_from_item(leaf, dev_item, device);
+	set_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
+	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
+	   !test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state)) {
+		device->fs_devices->total_rw_bytes += device->total_bytes;
+		atomic64_add(device->total_bytes - device->bytes_used,
+				&fs_info->free_chunk_space);
+	}
+	ret = 0;
+	return ret;
+}
+
+int btrfs_read_sys_array(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_root *root = fs_info->tree_root;
+	struct btrfs_super_block *super_copy = fs_info->super_copy;
+	struct extent_buffer *sb;
+	struct btrfs_disk_key *disk_key;
+	struct btrfs_chunk *chunk;
+	u8 *array_ptr;
+	unsigned long sb_array_offset;
+	int ret = 0;
+	u32 num_stripes;
+	u32 array_size;
+	u32 len = 0;
+	u32 cur_offset;
+	u64 type;
+	struct btrfs_key key;
+
+	ASSERT(BTRFS_SUPER_INFO_SIZE <= fs_info->nodesize);
+	/*
+	 * This will create extent buffer of nodesize, superblock size is
+	 * fixed to BTRFS_SUPER_INFO_SIZE. If nodesize > sb size, this will
+	 * overallocate but we can keep it as-is, only the first page is used.
+	 */
+	sb = btrfs_find_create_tree_block(fs_info, BTRFS_SUPER_INFO_OFFSET);
+	if (IS_ERR(sb))
+		return PTR_ERR(sb);
+	set_extent_buffer_uptodate(sb);
+	btrfs_set_buffer_lockdep_class(root->root_key.objectid, sb, 0);
+	/*
+	 * The sb extent buffer is artificial and just used to read the system array.
+	 * set_extent_buffer_uptodate() call does not properly mark all it's
+	 * pages up-to-date when the page is larger: extent does not cover the
+	 * whole page and consequently check_page_uptodate does not find all
+	 * the page's extents up-to-date (the hole beyond sb),
+	 * write_extent_buffer then triggers a WARN_ON.
+	 *
+	 * Regular short extents go through mark_extent_buffer_dirty/writeback cycle,
+	 * but sb spans only this function. Add an explicit SetPageUptodate call
+	 * to silence the warning eg. on PowerPC 64.
+	 */
+	if (PAGE_SIZE > BTRFS_SUPER_INFO_SIZE)
+		SetPageUptodate(sb->pages[0]);
+
+	write_extent_buffer(sb, super_copy, 0, BTRFS_SUPER_INFO_SIZE);
+	array_size = btrfs_super_sys_array_size(super_copy);
+
+	array_ptr = super_copy->sys_chunk_array;
+	sb_array_offset = offsetof(struct btrfs_super_block, sys_chunk_array);
+	cur_offset = 0;
+
+	while (cur_offset < array_size) {
+		disk_key = (struct btrfs_disk_key *)array_ptr;
+		len = sizeof(*disk_key);
+		if (cur_offset + len > array_size)
+			goto out_short_read;
+
+		btrfs_disk_key_to_cpu(&key, disk_key);
+
+		array_ptr += len;
+		sb_array_offset += len;
+		cur_offset += len;
+
+		if (key.type != BTRFS_CHUNK_ITEM_KEY) {
+			btrfs_err(fs_info,
+			    "unexpected item type %u in sys_array at offset %u",
+				  (u32)key.type, cur_offset);
+			ret = -EIO;
+			break;
+		}
+
+		chunk = (struct btrfs_chunk *)sb_array_offset;
+		/*
+		 * At least one btrfs_chunk with one stripe must be present,
+		 * exact stripe count check comes afterwards
+		 */
+		len = btrfs_chunk_item_size(1);
+		if (cur_offset + len > array_size)
+			goto out_short_read;
+
+		num_stripes = btrfs_chunk_num_stripes(sb, chunk);
+		if (!num_stripes) {
+			btrfs_err(fs_info,
+			"invalid number of stripes %u in sys_array at offset %u",
+				  num_stripes, cur_offset);
+			ret = -EIO;
+			break;
+		}
+
+		type = btrfs_chunk_type(sb, chunk);
+		if ((type & BTRFS_BLOCK_GROUP_SYSTEM) == 0) {
+			btrfs_err(fs_info,
+			"invalid chunk type %llu in sys_array at offset %u",
+				  type, cur_offset);
+			ret = -EIO;
+			break;
+		}
+
+		len = btrfs_chunk_item_size(num_stripes);
+		if (cur_offset + len > array_size)
+			goto out_short_read;
+
+		ret = read_one_chunk(&key, sb, chunk);
+		if (ret)
+			break;
+
+		array_ptr += len;
+		sb_array_offset += len;
+		cur_offset += len;
+	}
+	clear_extent_buffer_uptodate(sb);
+	free_extent_buffer_stale(sb);
+	return ret;
+
+out_short_read:
+	btrfs_err(fs_info, "sys_array too short to read %u bytes at offset %u",
+			len, cur_offset);
+	clear_extent_buffer_uptodate(sb);
+	free_extent_buffer_stale(sb);
+	return -EIO;
+}
+
+/*
+ * Check if all chunks in the fs are OK for read-write degraded mount
+ *
+ * If the @failing_dev is specified, it's accounted as missing.
+ *
+ * Return true if all chunks meet the minimal RW mount requirements.
+ * Return false if any chunk doesn't meet the minimal RW mount requirements.
+ */
+bool btrfs_check_rw_degradable(struct btrfs_fs_info *fs_info,
+					struct btrfs_device *failing_dev)
+{
+	struct extent_map_tree *map_tree = &fs_info->mapping_tree;
+	struct extent_map *em;
+	u64 next_start = 0;
+	bool ret = true;
+
+	read_lock(&map_tree->lock);
+	em = lookup_extent_mapping(map_tree, 0, (u64)-1);
+	read_unlock(&map_tree->lock);
+	/* No chunk at all? Return false anyway */
+	if (!em) {
+		ret = false;
+		goto out;
+	}
+	while (em) {
+		struct map_lookup *map;
+		int missing = 0;
+		int max_tolerated;
+		int i;
+
+		map = em->map_lookup;
+		max_tolerated =
+			btrfs_get_num_tolerated_disk_barrier_failures(
+					map->type);
+		for (i = 0; i < map->num_stripes; i++) {
+			struct btrfs_device *dev = map->stripes[i].dev;
+
+			if (!dev || !dev->bdev ||
+			    test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state) ||
+			    dev->last_flush_error)
+				missing++;
+			else if (failing_dev && failing_dev == dev)
+				missing++;
+		}
+		if (missing > max_tolerated) {
+			if (!failing_dev)
+				btrfs_warn(fs_info,
+	"chunk %llu missing %d devices, max tolerance is %d for writable mount",
+				   em->start, missing, max_tolerated);
+			free_extent_map(em);
+			ret = false;
+			goto out;
+		}
+		next_start = extent_map_end(em);
+		free_extent_map(em);
+
+		read_lock(&map_tree->lock);
+		em = lookup_extent_mapping(map_tree, next_start,
+					   (u64)(-1) - next_start);
+		read_unlock(&map_tree->lock);
+	}
+out:
+	return ret;
+}
+
+static void readahead_tree_node_children(struct extent_buffer *node)
+{
+	int i;
+	const int nr_items = btrfs_header_nritems(node);
+
+	for (i = 0; i < nr_items; i++) {
+		u64 start;
+
+		start = btrfs_node_blockptr(node, i);
+		readahead_tree_block(node->fs_info, start);
+	}
+}
+
+int btrfs_read_chunk_tree(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_root *root = fs_info->chunk_root;
+	struct btrfs_path *path;
+	struct extent_buffer *leaf;
+	struct btrfs_key key;
+	struct btrfs_key found_key;
+	int ret;
+	int slot;
+	u64 total_dev = 0;
+	u64 last_ra_node = 0;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	/*
+	 * uuid_mutex is needed only if we are mounting a sprout FS
+	 * otherwise we don't need it.
+	 */
+	mutex_lock(&uuid_mutex);
+
+	/*
+	 * It is possible for mount and umount to race in such a way that
+	 * we execute this code path, but open_fs_devices failed to clear
+	 * total_rw_bytes. We certainly want it cleared before reading the
+	 * device items, so clear it here.
+	 */
+	fs_info->fs_devices->total_rw_bytes = 0;
+
+	/*
+	 * Read all device items, and then all the chunk items. All
+	 * device items are found before any chunk item (their object id
+	 * is smaller than the lowest possible object id for a chunk
+	 * item - BTRFS_FIRST_CHUNK_TREE_OBJECTID).
+	 */
+	key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
+	key.offset = 0;
+	key.type = 0;
+	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+	if (ret < 0)
+		goto error;
+	while (1) {
+		struct extent_buffer *node;
+
+		leaf = path->nodes[0];
+		slot = path->slots[0];
+		if (slot >= btrfs_header_nritems(leaf)) {
+			ret = btrfs_next_leaf(root, path);
+			if (ret == 0)
+				continue;
+			if (ret < 0)
+				goto error;
+			break;
+		}
+		/*
+		 * The nodes on level 1 are not locked but we don't need to do
+		 * that during mount time as nothing else can access the tree
+		 */
+		node = path->nodes[1];
+		if (node) {
+			if (last_ra_node != node->start) {
+				readahead_tree_node_children(node);
+				last_ra_node = node->start;
+			}
+		}
+		btrfs_item_key_to_cpu(leaf, &found_key, slot);
+		if (found_key.type == BTRFS_DEV_ITEM_KEY) {
+			struct btrfs_dev_item *dev_item;
+			dev_item = btrfs_item_ptr(leaf, slot,
+						  struct btrfs_dev_item);
+			ret = read_one_dev(leaf, dev_item);
+			if (ret)
+				goto error;
+			total_dev++;
+		} else if (found_key.type == BTRFS_CHUNK_ITEM_KEY) {
+			struct btrfs_chunk *chunk;
+			chunk = btrfs_item_ptr(leaf, slot, struct btrfs_chunk);
+			mutex_lock(&fs_info->chunk_mutex);
+			ret = read_one_chunk(&found_key, leaf, chunk);
+			mutex_unlock(&fs_info->chunk_mutex);
+			if (ret)
+				goto error;
+		}
+		path->slots[0]++;
+	}
+
+	/*
+	 * After loading chunk tree, we've got all device information,
+	 * do another round of validation checks.
+	 */
+	if (total_dev != fs_info->fs_devices->total_devices) {
+		btrfs_warn(fs_info,
+"super block num_devices %llu mismatch with DEV_ITEM count %llu, will be repaired on next transaction commit",
+			  btrfs_super_num_devices(fs_info->super_copy),
+			  total_dev);
+		fs_info->fs_devices->total_devices = total_dev;
+		btrfs_set_super_num_devices(fs_info->super_copy, total_dev);
+	}
+	if (btrfs_super_total_bytes(fs_info->super_copy) <
+	    fs_info->fs_devices->total_rw_bytes) {
+		btrfs_err(fs_info,
+	"super_total_bytes %llu mismatch with fs_devices total_rw_bytes %llu",
+			  btrfs_super_total_bytes(fs_info->super_copy),
+			  fs_info->fs_devices->total_rw_bytes);
+		ret = -EINVAL;
+		goto error;
+	}
+	ret = 0;
+error:
+	mutex_unlock(&uuid_mutex);
+
+	btrfs_free_path(path);
+	return ret;
+}
+
+void btrfs_init_devices_late(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices, *seed_devs;
+	struct btrfs_device *device;
+
+	fs_devices->fs_info = fs_info;
+
+	mutex_lock(&fs_devices->device_list_mutex);
+	list_for_each_entry(device, &fs_devices->devices, dev_list)
+		device->fs_info = fs_info;
+
+	list_for_each_entry(seed_devs, &fs_devices->seed_list, seed_list) {
+		list_for_each_entry(device, &seed_devs->devices, dev_list)
+			device->fs_info = fs_info;
+
+		seed_devs->fs_info = fs_info;
+	}
+	mutex_unlock(&fs_devices->device_list_mutex);
+}
+
+static u64 btrfs_dev_stats_value(const struct extent_buffer *eb,
+				 const struct btrfs_dev_stats_item *ptr,
+				 int index)
+{
+	u64 val;
+
+	read_extent_buffer(eb, &val,
+			   offsetof(struct btrfs_dev_stats_item, values) +
+			    ((unsigned long)ptr) + (index * sizeof(u64)),
+			   sizeof(val));
+	return val;
+}
+
+static void btrfs_set_dev_stats_value(struct extent_buffer *eb,
+				      struct btrfs_dev_stats_item *ptr,
+				      int index, u64 val)
+{
+	write_extent_buffer(eb, &val,
+			    offsetof(struct btrfs_dev_stats_item, values) +
+			     ((unsigned long)ptr) + (index * sizeof(u64)),
+			    sizeof(val));
+}
+
+static int btrfs_device_init_dev_stats(struct btrfs_device *device,
+				       struct btrfs_path *path)
+{
+	struct btrfs_dev_stats_item *ptr;
+	struct extent_buffer *eb;
+	struct btrfs_key key;
+	int item_size;
+	int i, ret, slot;
+
+	key.objectid = BTRFS_DEV_STATS_OBJECTID;
+	key.type = BTRFS_PERSISTENT_ITEM_KEY;
+	key.offset = device->devid;
+	ret = btrfs_search_slot(NULL, device->fs_info->dev_root, &key, path, 0, 0);
+	if (ret) {
+		for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++)
+			btrfs_dev_stat_set(device, i, 0);
+		device->dev_stats_valid = 1;
+		btrfs_release_path(path);
+		return ret < 0 ? ret : 0;
+	}
+	slot = path->slots[0];
+	eb = path->nodes[0];
+	item_size = btrfs_item_size_nr(eb, slot);
+
+	ptr = btrfs_item_ptr(eb, slot, struct btrfs_dev_stats_item);
+
+	for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++) {
+		if (item_size >= (1 + i) * sizeof(__le64))
+			btrfs_dev_stat_set(device, i,
+					   btrfs_dev_stats_value(eb, ptr, i));
+		else
+			btrfs_dev_stat_set(device, i, 0);
+	}
+
+	device->dev_stats_valid = 1;
+	btrfs_dev_stat_print_on_load(device);
+	btrfs_release_path(path);
+
+	return 0;
+}
+
+int btrfs_init_dev_stats(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices, *seed_devs;
+	struct btrfs_device *device;
+	struct btrfs_path *path = NULL;
+	int ret = 0;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	mutex_lock(&fs_devices->device_list_mutex);
+	list_for_each_entry(device, &fs_devices->devices, dev_list) {
+		ret = btrfs_device_init_dev_stats(device, path);
+		if (ret)
+			goto out;
+	}
+	list_for_each_entry(seed_devs, &fs_devices->seed_list, seed_list) {
+		list_for_each_entry(device, &seed_devs->devices, dev_list) {
+			ret = btrfs_device_init_dev_stats(device, path);
+			if (ret)
+				goto out;
+		}
+	}
+out:
+	mutex_unlock(&fs_devices->device_list_mutex);
+
+	btrfs_free_path(path);
+	return ret;
+}
+
+static int update_dev_stat_item(struct btrfs_trans_handle *trans,
+				struct btrfs_device *device)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_root *dev_root = fs_info->dev_root;
+	struct btrfs_path *path;
+	struct btrfs_key key;
+	struct extent_buffer *eb;
+	struct btrfs_dev_stats_item *ptr;
+	int ret;
+	int i;
+
+	key.objectid = BTRFS_DEV_STATS_OBJECTID;
+	key.type = BTRFS_PERSISTENT_ITEM_KEY;
+	key.offset = device->devid;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+	ret = btrfs_search_slot(trans, dev_root, &key, path, -1, 1);
+	if (ret < 0) {
+		btrfs_warn_in_rcu(fs_info,
+			"error %d while searching for dev_stats item for device %s",
+			      ret, rcu_str_deref(device->name));
+		goto out;
+	}
+
+	if (ret == 0 &&
+	    btrfs_item_size_nr(path->nodes[0], path->slots[0]) < sizeof(*ptr)) {
+		/* need to delete old one and insert a new one */
+		ret = btrfs_del_item(trans, dev_root, path);
+		if (ret != 0) {
+			btrfs_warn_in_rcu(fs_info,
+				"delete too small dev_stats item for device %s failed %d",
+				      rcu_str_deref(device->name), ret);
+			goto out;
+		}
+		ret = 1;
+	}
+
+	if (ret == 1) {
+		/* need to insert a new item */
+		btrfs_release_path(path);
+		ret = btrfs_insert_empty_item(trans, dev_root, path,
+					      &key, sizeof(*ptr));
+		if (ret < 0) {
+			btrfs_warn_in_rcu(fs_info,
+				"insert dev_stats item for device %s failed %d",
+				rcu_str_deref(device->name), ret);
+			goto out;
+		}
+	}
+
+	eb = path->nodes[0];
+	ptr = btrfs_item_ptr(eb, path->slots[0], struct btrfs_dev_stats_item);
+	for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++)
+		btrfs_set_dev_stats_value(eb, ptr, i,
+					  btrfs_dev_stat_read(device, i));
+	btrfs_mark_buffer_dirty(eb);
+
+out:
+	btrfs_free_path(path);
+	return ret;
+}
+
+/*
+ * called from commit_transaction. Writes all changed device stats to disk.
+ */
+int btrfs_run_dev_stats(struct btrfs_trans_handle *trans)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
+	struct btrfs_device *device;
+	int stats_cnt;
+	int ret = 0;
+
+	mutex_lock(&fs_devices->device_list_mutex);
+	list_for_each_entry(device, &fs_devices->devices, dev_list) {
+		stats_cnt = atomic_read(&device->dev_stats_ccnt);
+		if (!device->dev_stats_valid || stats_cnt == 0)
+			continue;
+
+
+		/*
+		 * There is a LOAD-LOAD control dependency between the value of
+		 * dev_stats_ccnt and updating the on-disk values which requires
+		 * reading the in-memory counters. Such control dependencies
+		 * require explicit read memory barriers.
+		 *
+		 * This memory barriers pairs with smp_mb__before_atomic in
+		 * btrfs_dev_stat_inc/btrfs_dev_stat_set and with the full
+		 * barrier implied by atomic_xchg in
+		 * btrfs_dev_stats_read_and_reset
+		 */
+		smp_rmb();
+
+		ret = update_dev_stat_item(trans, device);
+		if (!ret)
+			atomic_sub(stats_cnt, &device->dev_stats_ccnt);
+	}
+	mutex_unlock(&fs_devices->device_list_mutex);
+
+	return ret;
+}
+
+void btrfs_dev_stat_inc_and_print(struct btrfs_device *dev, int index)
+{
+	btrfs_dev_stat_inc(dev, index);
+	btrfs_dev_stat_print_on_error(dev);
+}
+
+static void btrfs_dev_stat_print_on_error(struct btrfs_device *dev)
+{
+	if (!dev->dev_stats_valid)
+		return;
+	btrfs_err_rl_in_rcu(dev->fs_info,
+		"bdev %s errs: wr %u, rd %u, flush %u, corrupt %u, gen %u",
+			   rcu_str_deref(dev->name),
+			   btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_WRITE_ERRS),
+			   btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_READ_ERRS),
+			   btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_FLUSH_ERRS),
+			   btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_CORRUPTION_ERRS),
+			   btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_GENERATION_ERRS));
+}
+
+static void btrfs_dev_stat_print_on_load(struct btrfs_device *dev)
+{
+	int i;
+
+	for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++)
+		if (btrfs_dev_stat_read(dev, i) != 0)
+			break;
+	if (i == BTRFS_DEV_STAT_VALUES_MAX)
+		return; /* all values == 0, suppress message */
+
+	btrfs_info_in_rcu(dev->fs_info,
+		"bdev %s errs: wr %u, rd %u, flush %u, corrupt %u, gen %u",
+	       rcu_str_deref(dev->name),
+	       btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_WRITE_ERRS),
+	       btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_READ_ERRS),
+	       btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_FLUSH_ERRS),
+	       btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_CORRUPTION_ERRS),
+	       btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_GENERATION_ERRS));
+}
+
+int btrfs_get_dev_stats(struct btrfs_fs_info *fs_info,
+			struct btrfs_ioctl_get_dev_stats *stats)
+{
+	struct btrfs_device *dev;
+	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
+	int i;
+
+	mutex_lock(&fs_devices->device_list_mutex);
+	dev = btrfs_find_device(fs_info->fs_devices, stats->devid, NULL, NULL,
+				true);
+	mutex_unlock(&fs_devices->device_list_mutex);
+
+	if (!dev) {
+		btrfs_warn(fs_info, "get dev_stats failed, device not found");
+		return -ENODEV;
+	} else if (!dev->dev_stats_valid) {
+		btrfs_warn(fs_info, "get dev_stats failed, not yet valid");
+		return -ENODEV;
+	} else if (stats->flags & BTRFS_DEV_STATS_RESET) {
+		for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++) {
+			if (stats->nr_items > i)
+				stats->values[i] =
+					btrfs_dev_stat_read_and_reset(dev, i);
+			else
+				btrfs_dev_stat_set(dev, i, 0);
+		}
+		btrfs_info(fs_info, "device stats zeroed by %s (%d)",
+			   current->comm, task_pid_nr(current));
+	} else {
+		for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++)
+			if (stats->nr_items > i)
+				stats->values[i] = btrfs_dev_stat_read(dev, i);
+	}
+	if (stats->nr_items > BTRFS_DEV_STAT_VALUES_MAX)
+		stats->nr_items = BTRFS_DEV_STAT_VALUES_MAX;
+	return 0;
+}
+
+/*
+ * Update the size and bytes used for each device where it changed.  This is
+ * delayed since we would otherwise get errors while writing out the
+ * superblocks.
+ *
+ * Must be invoked during transaction commit.
+ */
+void btrfs_commit_device_sizes(struct btrfs_transaction *trans)
+{
+	struct btrfs_device *curr, *next;
+
+	ASSERT(trans->state == TRANS_STATE_COMMIT_DOING);
+
+	if (list_empty(&trans->dev_update_list))
+		return;
+
+	/*
+	 * We don't need the device_list_mutex here.  This list is owned by the
+	 * transaction and the transaction must complete before the device is
+	 * released.
+	 */
+	mutex_lock(&trans->fs_info->chunk_mutex);
+	list_for_each_entry_safe(curr, next, &trans->dev_update_list,
+				 post_commit_list) {
+		list_del_init(&curr->post_commit_list);
+		curr->commit_total_bytes = curr->disk_total_bytes;
+		curr->commit_bytes_used = curr->bytes_used;
+	}
+	mutex_unlock(&trans->fs_info->chunk_mutex);
+}
+
+/*
+ * Multiplicity factor for simple profiles: DUP, RAID1-like and RAID10.
+ */
+int btrfs_bg_type_to_factor(u64 flags)
+{
+	const int index = btrfs_bg_flags_to_raid_index(flags);
+
+	return btrfs_raid_array[index].ncopies;
+}
+
+
+
+static int verify_one_dev_extent(struct btrfs_fs_info *fs_info,
+				 u64 chunk_offset, u64 devid,
+				 u64 physical_offset, u64 physical_len)
+{
+	struct extent_map_tree *em_tree = &fs_info->mapping_tree;
+	struct extent_map *em;
+	struct map_lookup *map;
+	struct btrfs_device *dev;
+	u64 stripe_len;
+	bool found = false;
+	int ret = 0;
+	int i;
+
+	read_lock(&em_tree->lock);
+	em = lookup_extent_mapping(em_tree, chunk_offset, 1);
+	read_unlock(&em_tree->lock);
+
+	if (!em) {
+		btrfs_err(fs_info,
+"dev extent physical offset %llu on devid %llu doesn't have corresponding chunk",
+			  physical_offset, devid);
+		ret = -EUCLEAN;
+		goto out;
+	}
+
+	map = em->map_lookup;
+	stripe_len = calc_stripe_length(map->type, em->len, map->num_stripes);
+	if (physical_len != stripe_len) {
+		btrfs_err(fs_info,
+"dev extent physical offset %llu on devid %llu length doesn't match chunk %llu, have %llu expect %llu",
+			  physical_offset, devid, em->start, physical_len,
+			  stripe_len);
+		ret = -EUCLEAN;
+		goto out;
+	}
+
+	for (i = 0; i < map->num_stripes; i++) {
+		if (map->stripes[i].dev->devid == devid &&
+		    map->stripes[i].physical == physical_offset) {
+			found = true;
+			if (map->verified_stripes >= map->num_stripes) {
+				btrfs_err(fs_info,
+				"too many dev extents for chunk %llu found",
+					  em->start);
+				ret = -EUCLEAN;
+				goto out;
+			}
+			map->verified_stripes++;
+			break;
+		}
+	}
+	if (!found) {
+		btrfs_err(fs_info,
+	"dev extent physical offset %llu devid %llu has no corresponding chunk",
+			physical_offset, devid);
+		ret = -EUCLEAN;
+	}
+
+	/* Make sure no dev extent is beyond device bondary */
+	dev = btrfs_find_device(fs_info->fs_devices, devid, NULL, NULL, true);
+	if (!dev) {
+		btrfs_err(fs_info, "failed to find devid %llu", devid);
+		ret = -EUCLEAN;
+		goto out;
+	}
+
+	/* It's possible this device is a dummy for seed device */
+	if (dev->disk_total_bytes == 0) {
+		struct btrfs_fs_devices *devs;
+
+		devs = list_first_entry(&fs_info->fs_devices->seed_list,
+					struct btrfs_fs_devices, seed_list);
+		dev = btrfs_find_device(devs, devid, NULL, NULL, false);
+		if (!dev) {
+			btrfs_err(fs_info, "failed to find seed devid %llu",
+				  devid);
+			ret = -EUCLEAN;
+			goto out;
+		}
+	}
+
+	if (physical_offset + physical_len > dev->disk_total_bytes) {
+		btrfs_err(fs_info,
+"dev extent devid %llu physical offset %llu len %llu is beyond device boundary %llu",
+			  devid, physical_offset, physical_len,
+			  dev->disk_total_bytes);
+		ret = -EUCLEAN;
+		goto out;
+	}
+out:
+	free_extent_map(em);
+	return ret;
+}
+
+static int verify_chunk_dev_extent_mapping(struct btrfs_fs_info *fs_info)
+{
+	struct extent_map_tree *em_tree = &fs_info->mapping_tree;
+	struct extent_map *em;
+	struct rb_node *node;
+	int ret = 0;
+
+	read_lock(&em_tree->lock);
+	for (node = rb_first_cached(&em_tree->map); node; node = rb_next(node)) {
+		em = rb_entry(node, struct extent_map, rb_node);
+		if (em->map_lookup->num_stripes !=
+		    em->map_lookup->verified_stripes) {
+			btrfs_err(fs_info,
+			"chunk %llu has missing dev extent, have %d expect %d",
+				  em->start, em->map_lookup->verified_stripes,
+				  em->map_lookup->num_stripes);
+			ret = -EUCLEAN;
+			goto out;
+		}
+	}
+out:
+	read_unlock(&em_tree->lock);
+	return ret;
+}
+
+/*
+ * Ensure that all dev extents are mapped to correct chunk, otherwise
+ * later chunk allocation/free would cause unexpected behavior.
+ *
+ * NOTE: This will iterate through the whole device tree, which should be of
+ * the same size level as the chunk tree.  This slightly increases mount time.
+ */
+int btrfs_verify_dev_extents(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_path *path;
+	struct btrfs_root *root = fs_info->dev_root;
+	struct btrfs_key key;
+	u64 prev_devid = 0;
+	u64 prev_dev_ext_end = 0;
+	int ret = 0;
+
+	key.objectid = 1;
+	key.type = BTRFS_DEV_EXTENT_KEY;
+	key.offset = 0;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	path->reada = READA_FORWARD;
+	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+	if (ret < 0)
+		goto out;
+
+	if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
+		ret = btrfs_next_item(root, path);
+		if (ret < 0)
+			goto out;
+		/* No dev extents at all? Not good */
+		if (ret > 0) {
+			ret = -EUCLEAN;
+			goto out;
+		}
+	}
+	while (1) {
+		struct extent_buffer *leaf = path->nodes[0];
+		struct btrfs_dev_extent *dext;
+		int slot = path->slots[0];
+		u64 chunk_offset;
+		u64 physical_offset;
+		u64 physical_len;
+		u64 devid;
+
+		btrfs_item_key_to_cpu(leaf, &key, slot);
+		if (key.type != BTRFS_DEV_EXTENT_KEY)
+			break;
+		devid = key.objectid;
+		physical_offset = key.offset;
+
+		dext = btrfs_item_ptr(leaf, slot, struct btrfs_dev_extent);
+		chunk_offset = btrfs_dev_extent_chunk_offset(leaf, dext);
+		physical_len = btrfs_dev_extent_length(leaf, dext);
+
+		/* Check if this dev extent overlaps with the previous one */
+		if (devid == prev_devid && physical_offset < prev_dev_ext_end) {
+			btrfs_err(fs_info,
+"dev extent devid %llu physical offset %llu overlap with previous dev extent end %llu",
+				  devid, physical_offset, prev_dev_ext_end);
+			ret = -EUCLEAN;
+			goto out;
+		}
+
+		ret = verify_one_dev_extent(fs_info, chunk_offset, devid,
+					    physical_offset, physical_len);
+		if (ret < 0)
+			goto out;
+		prev_devid = devid;
+		prev_dev_ext_end = physical_offset + physical_len;
+
+		ret = btrfs_next_item(root, path);
+		if (ret < 0)
+			goto out;
+		if (ret > 0) {
+			ret = 0;
+			break;
+		}
+	}
+
+	/* Ensure all chunks have corresponding dev extents */
+	ret = verify_chunk_dev_extent_mapping(fs_info);
+out:
+	btrfs_free_path(path);
+	return ret;
+}
+
+/*
+ * Check whether the given block group or device is pinned by any inode being
+ * used as a swapfile.
+ */
+bool btrfs_pinned_by_swapfile(struct btrfs_fs_info *fs_info, void *ptr)
+{
+	struct btrfs_swapfile_pin *sp;
+	struct rb_node *node;
+
+	spin_lock(&fs_info->swapfile_pins_lock);
+	node = fs_info->swapfile_pins.rb_node;
+	while (node) {
+		sp = rb_entry(node, struct btrfs_swapfile_pin, node);
+		if (ptr < sp->ptr)
+			node = node->rb_left;
+		else if (ptr > sp->ptr)
+			node = node->rb_right;
+		else
+			break;
+	}
+	spin_unlock(&fs_info->swapfile_pins_lock);
+	return node != NULL;
+}