Adding upstream version 6.6.15.upstream/6.6.15

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

1 files changed, 8104 insertions, 0 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
new file mode 100644
index 0000000000..722a1dde75
--- /dev/null
+++ b/fs/btrfs/volumes.c
@@ -0,0 +1,8104 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2007 Oracle.  All rights reserved.
+ */
+
+#include <linux/sched.h>
+#include <linux/sched/mm.h>
+#include <linux/slab.h>
+#include <linux/ratelimit.h>
+#include <linux/kthread.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 "rcu-string.h"
+#include "dev-replace.h"
+#include "sysfs.h"
+#include "tree-checker.h"
+#include "space-info.h"
+#include "block-group.h"
+#include "discard.h"
+#include "zoned.h"
+#include "fs.h"
+#include "accessors.h"
+#include "uuid-tree.h"
+#include "ioctl.h"
+#include "relocation.h"
+#include "scrub.h"
+#include "super.h"
+
+#define BTRFS_BLOCK_GROUP_STRIPE_MASK	(BTRFS_BLOCK_GROUP_RAID0 | \
+					 BTRFS_BLOCK_GROUP_RAID10 | \
+					 BTRFS_BLOCK_GROUP_RAID56_MASK)
+
+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	= 2,
+		.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	= 1,
+		.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,
+	},
+};
+
+/*
+ * Convert block group flags (BTRFS_BLOCK_GROUP_*) to btrfs_raid_types, which
+ * can be used as index to access btrfs_raid_array[].
+ */
+enum btrfs_raid_types __attribute_const__ btrfs_bg_flags_to_raid_index(u64 flags)
+{
+	const u64 profile = (flags & BTRFS_BLOCK_GROUP_PROFILE_MASK);
+
+	if (!profile)
+		return BTRFS_RAID_SINGLE;
+
+	return BTRFS_BG_FLAG_TO_INDEX(profile);
+}
+
+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;
+}
+
+int btrfs_nr_parity_stripes(u64 type)
+{
+	enum btrfs_raid_types index = btrfs_bg_flags_to_raid_index(type);
+
+	return btrfs_raid_array[index].nparity;
+}
+
+/*
+ * 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_load(struct btrfs_device *device);
+
+/*
+ * 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;
+
+	ASSERT(fsid || !metadata_fsid);
+
+	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);
+		memcpy(fs_devs->metadata_uuid,
+		       metadata_fsid ?: fsid, BTRFS_FSID_SIZE);
+	}
+
+	return fs_devs;
+}
+
+static 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);
+	btrfs_destroy_dev_zone_info(device);
+	kfree(device);
+}
+
+static void free_fs_devices(struct btrfs_fs_devices *fs_devices)
+{
+	struct btrfs_device *device;
+
+	WARN_ON(fs_devices->opened);
+	while (!list_empty(&fs_devices->devices)) {
+		device = list_entry(fs_devices->devices.next,
+				    struct btrfs_device, dev_list);
+		list_del(&device->dev_list);
+		btrfs_free_device(device);
+	}
+	kfree(fs_devices);
+}
+
+void __exit btrfs_cleanup_fs_uuids(void)
+{
+	struct btrfs_fs_devices *fs_devices;
+
+	while (!list_empty(&fs_uuids)) {
+		fs_devices = list_entry(fs_uuids.next,
+					struct btrfs_fs_devices, fs_list);
+		list_del(&fs_devices->fs_list);
+		free_fs_devices(fs_devices);
+	}
+}
+
+static bool match_fsid_fs_devices(const struct btrfs_fs_devices *fs_devices,
+				  const u8 *fsid, const u8 *metadata_fsid)
+{
+	if (memcmp(fsid, fs_devices->fsid, BTRFS_FSID_SIZE) != 0)
+		return false;
+
+	if (!metadata_fsid)
+		return true;
+
+	if (memcmp(metadata_fsid, fs_devices->metadata_uuid, BTRFS_FSID_SIZE) != 0)
+		return false;
+
+	return true;
+}
+
+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 (match_fsid_fs_devices(fs_devices, fsid, metadata_fsid))
+			return fs_devices;
+	}
+	return NULL;
+}
+
+/*
+ * First check if the metadata_uuid is different from the fsid in the given
+ * fs_devices. Then check if the given fsid is the same as the metadata_uuid
+ * in the fs_devices. If it is, return true; otherwise, return false.
+ */
+static inline bool check_fsid_changed(const struct btrfs_fs_devices *fs_devices,
+				      const u8 *fsid)
+{
+	return memcmp(fs_devices->fsid, fs_devices->metadata_uuid,
+		      BTRFS_FSID_SIZE) != 0 &&
+	       memcmp(fs_devices->metadata_uuid, fsid, BTRFS_FSID_SIZE) == 0;
+}
+
+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)
+			continue;
+
+		if (match_fsid_fs_devices(fs_devices, disk_super->metadata_uuid,
+					  fs_devices->fsid))
+			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)
+			continue;
+
+		if (check_fsid_changed(fs_devices, disk_super->metadata_uuid))
+			return fs_devices;
+	}
+
+	return find_fsid(disk_super->fsid, disk_super->metadata_uuid);
+}
+
+
+static int
+btrfs_get_bdev_and_sb(const char *device_path, blk_mode_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, NULL);
+
+	if (IS_ERR(*bdev)) {
+		ret = PTR_ERR(*bdev);
+		goto error;
+	}
+
+	if (flush)
+		sync_blockdev(*bdev);
+	ret = set_blocksize(*bdev, BTRFS_BDEV_BLOCKSIZE);
+	if (ret) {
+		blkdev_put(*bdev, holder);
+		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, holder);
+		goto error;
+	}
+
+	return 0;
+
+error:
+	*bdev = NULL;
+	return ret;
+}
+
+/*
+ *  Search and remove all stale devices (which are not mounted).  When both
+ *  inputs are NULL, it will search and release all stale devices.
+ *
+ *  @devt:         Optional. When provided will it release all unmounted devices
+ *                 matching this devt only.
+ *  @skip_device:  Optional. Will skip this device when searching for the stale
+ *                 devices.
+ *
+ *  Return:	0 for success or if @devt is 0.
+ *		-EBUSY if @devt is a mounted device.
+ *		-ENOENT if @devt does not match any device in the list.
+ */
+static int btrfs_free_stale_devices(dev_t devt, 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 (devt)
+		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 (devt && devt != device->devt)
+				continue;
+			if (fs_devices->opened) {
+				/* for an already deleted device return 0 */
+				if (devt && 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, blk_mode_t flags,
+			void *holder)
+{
+	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);
+	}
+
+	if (!bdev_nonrot(bdev))
+		fs_devices->rotating = true;
+
+	if (bdev_max_discard_sectors(bdev))
+		fs_devices->discardable = true;
+
+	device->bdev = bdev;
+	clear_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
+	device->holder = holder;
+
+	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, holder);
+
+	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 (fs_devices->fsid_change)
+			continue;
+
+		if (check_fsid_changed(fs_devices,  disk_super->fsid))
+			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 currently 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 (check_fsid_changed(fs_devices, disk_super->metadata_uuid) &&
+		    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 constituent 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 (!fs_devices->fsid_change)
+			continue;
+
+		if (check_fsid_changed(fs_devices, disk_super->fsid))
+			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);
+	dev_t path_devt;
+	int error;
+	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);
+
+	error = lookup_bdev(path, &path_devt);
+	if (error) {
+		btrfs_err(NULL, "failed to lookup block device for path %s: %d",
+			  path, error);
+		return ERR_PTR(error);
+	}
+
+	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) {
+		fs_devices = alloc_fs_devices(disk_super->fsid,
+				has_metadata_uuid ? disk_super->metadata_uuid : 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 {
+		struct btrfs_dev_lookup_args args = {
+			.devid = devid,
+			.uuid = disk_super->dev_item.uuid,
+		};
+
+		mutex_lock(&fs_devices->device_list_mutex);
+		device = btrfs_find_device(fs_devices, &args);
+
+		/*
+		 * 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);
+			memcpy(fs_devices->metadata_uuid,
+			       btrfs_sb_fsid_ptr(disk_super), BTRFS_FSID_SIZE);
+			fs_devices->fsid_change = false;
+		}
+	}
+
+	if (!device) {
+		unsigned int nofs_flag;
+
+		if (fs_devices->opened) {
+			btrfs_err(NULL,
+"device %s belongs to fsid %pU, and the fs is already mounted, scanned by %s (%d)",
+				  path, fs_devices->fsid, current->comm,
+				  task_pid_nr(current));
+			mutex_unlock(&fs_devices->device_list_mutex);
+			return ERR_PTR(-EBUSY);
+		}
+
+		nofs_flag = memalloc_nofs_save();
+		device = btrfs_alloc_device(NULL, &devid,
+					    disk_super->dev_item.uuid, path);
+		memalloc_nofs_restore(nofs_flag);
+		if (IS_ERR(device)) {
+			mutex_unlock(&fs_devices->device_list_mutex);
+			/* we can safely leave the fs_devices entry around */
+			return device;
+		}
+
+		device->devt = path_devt;
+
+		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);
+			btrfs_err(NULL,
+"device %s already registered with a higher generation, found %llu expect %llu",
+				  path, found_transid, device->generation);
+			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
+		 *
+		 * NOTE: the device->fs_info may not be reliable here so pass
+		 * in a NULL to message helpers instead. This avoids a possible
+		 * use-after-free when the fs_info and fs_info->sb are already
+		 * torn down.
+		 */
+		if (device->bdev) {
+			if (device->devt != path_devt) {
+				mutex_unlock(&fs_devices->device_list_mutex);
+				btrfs_warn_in_rcu(NULL,
+	"duplicate device %s devid %llu generation %llu scanned by %s (%d)",
+						  path, devid, found_transid,
+						  current->comm,
+						  task_pid_nr(current));
+				return ERR_PTR(-EEXIST);
+			}
+			btrfs_info_in_rcu(NULL,
+	"devid %llu device path %s changed to %s scanned by %s (%d)",
+					  devid, btrfs_dev_name(device),
+					  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);
+		}
+		device->devt = path_devt;
+	}
+
+	/*
+	 * 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) {
+		const char *dev_path = NULL;
+
+		/*
+		 * 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)
+			dev_path = orig_dev->name->str;
+
+		device = btrfs_alloc_device(NULL, &orig_dev->devid,
+					    orig_dev->uuid, dev_path);
+		if (IS_ERR(device)) {
+			ret = PTR_ERR(device);
+			goto error;
+		}
+
+		if (orig_dev->zone_info) {
+			struct btrfs_zoned_device_info *zone_info;
+
+			zone_info = btrfs_clone_dev_zone_info(orig_dev);
+			if (!zone_info) {
+				btrfs_free_device(device);
+				ret = -ENOMEM;
+				goto error;
+			}
+			device->zone_info = zone_info;
+		}
+
+		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,
+				      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->holder);
+			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)
+{
+	struct btrfs_device *latest_dev = NULL;
+	struct btrfs_fs_devices *seed_dev;
+
+	mutex_lock(&uuid_mutex);
+	__btrfs_free_extra_devids(fs_devices, &latest_dev);
+
+	list_for_each_entry(seed_dev, &fs_devices->seed_list, seed_list)
+		__btrfs_free_extra_devids(seed_dev, &latest_dev);
+
+	fs_devices->latest_dev = latest_dev;
+
+	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->holder);
+}
+
+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);
+	btrfs_destroy_dev_zone_info(device);
+
+	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  */
+	WARN_ON(test_bit(BTRFS_DEV_STATE_FLUSH_SENT, &device->dev_state));
+	WARN_ON(test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state));
+	WARN_ON(!list_empty(&device->dev_alloc_list));
+	WARN_ON(!list_empty(&device->post_commit_list));
+}
+
+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,
+				blk_mode_t flags, void *holder)
+{
+	struct btrfs_device *device;
+	struct btrfs_device *latest_dev = NULL;
+	struct btrfs_device *tmp_device;
+
+	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_dev = latest_dev;
+	fs_devices->total_rw_bytes = 0;
+	fs_devices->chunk_alloc_policy = BTRFS_CHUNK_ALLOC_REGULAR;
+	fs_devices->read_policy = BTRFS_READ_POLICY_PID;
+
+	return 0;
+}
+
+static int devid_cmp(void *priv, const struct list_head *a,
+		     const struct list_head *b)
+{
+	const 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,
+		       blk_mode_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 open_mutex.
+	 *
+	 * We also don't need the lock here as this is called during mount and
+	 * exclusion is provided by uuid_mutex
+	 */
+
+	if (fs_devices->opened) {
+		fs_devices->opened++;
+		ret = 0;
+	} else {
+		list_sort(NULL, &fs_devices->devices, devid_cmp);
+		ret = open_fs_devices(fs_devices, flags, holder);
+	}
+
+	return ret;
+}
+
+void btrfs_release_disk_super(struct btrfs_super_block *super)
+{
+	struct page *page = virt_to_page(super);
+
+	put_page(page);
+}
+
+static struct btrfs_super_block *btrfs_read_disk_super(struct block_device *bdev,
+						       u64 bytenr, u64 bytenr_orig)
+{
+	struct btrfs_super_block *disk_super;
+	struct page *page;
+	void *p;
+	pgoff_t index;
+
+	/* make sure our super fits in the device */
+	if (bytenr + PAGE_SIZE >= bdev_nr_bytes(bdev))
+		return ERR_PTR(-EINVAL);
+
+	/* make sure our super fits in the page */
+	if (sizeof(*disk_super) > PAGE_SIZE)
+		return ERR_PTR(-EINVAL);
+
+	/* make sure our super doesn't straddle pages on disk */
+	index = bytenr >> PAGE_SHIFT;
+	if ((bytenr + sizeof(*disk_super) - 1) >> PAGE_SHIFT != index)
+		return ERR_PTR(-EINVAL);
+
+	/* pull in the page with our super */
+	page = read_cache_page_gfp(bdev->bd_inode->i_mapping, index, GFP_KERNEL);
+
+	if (IS_ERR(page))
+		return ERR_CAST(page);
+
+	p = page_address(page);
+
+	/* align our pointer to the offset of the super block */
+	disk_super = p + offset_in_page(bytenr);
+
+	if (btrfs_super_bytenr(disk_super) != bytenr_orig ||
+	    btrfs_super_magic(disk_super) != BTRFS_MAGIC) {
+		btrfs_release_disk_super(p);
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (disk_super->label[0] && disk_super->label[BTRFS_LABEL_SIZE - 1])
+		disk_super->label[BTRFS_LABEL_SIZE - 1] = 0;
+
+	return disk_super;
+}
+
+int btrfs_forget_devices(dev_t devt)
+{
+	int ret;
+
+	mutex_lock(&uuid_mutex);
+	ret = btrfs_free_stale_devices(devt, 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, blk_mode_t flags)
+{
+	struct btrfs_super_block *disk_super;
+	bool new_device_added = false;
+	struct btrfs_device *device = NULL;
+	struct block_device *bdev;
+	u64 bytenr, bytenr_orig;
+	int ret;
+
+	lockdep_assert_held(&uuid_mutex);
+
+	/*
+	 * we would like to check all the supers, but that would make
+	 * a btrfs mount succeed after a mkfs from a different FS.
+	 * So, we need to add a special mount option to scan for
+	 * later supers, using BTRFS_SUPER_MIRROR_MAX instead
+	 */
+
+	/*
+	 * Avoid an exclusive open 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 an exclusive open. 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, NULL, NULL);
+	if (IS_ERR(bdev))
+		return ERR_CAST(bdev);
+
+	bytenr_orig = btrfs_sb_offset(0);
+	ret = btrfs_sb_log_location_bdev(bdev, 0, READ, &bytenr);
+	if (ret) {
+		device = ERR_PTR(ret);
+		goto error_bdev_put;
+	}
+
+	disk_super = btrfs_read_disk_super(bdev, bytenr, bytenr_orig);
+	if (IS_ERR(disk_super)) {
+		device = ERR_CAST(disk_super);
+		goto error_bdev_put;
+	}
+
+	device = device_list_add(path, disk_super, &new_device_added);
+	if (!IS_ERR(device) && new_device_added)
+		btrfs_free_stale_devices(device->devt, device);
+
+	btrfs_release_disk_super(disk_super);
+
+error_bdev_put:
+	blkdev_put(bdev, NULL);
+
+	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)
+{
+	switch (device->fs_devices->chunk_alloc_policy) {
+	case BTRFS_CHUNK_ALLOC_REGULAR:
+		return BTRFS_DEVICE_RANGE_RESERVED;
+	case BTRFS_CHUNK_ALLOC_ZONED:
+		/*
+		 * We don't care about the starting region like regular
+		 * allocator, because we anyway use/reserve the first two zones
+		 * for superblock logging.
+		 */
+		return 0;
+	default:
+		BUG();
+	}
+}
+
+static bool dev_extent_hole_check_zoned(struct btrfs_device *device,
+					u64 *hole_start, u64 *hole_size,
+					u64 num_bytes)
+{
+	u64 zone_size = device->zone_info->zone_size;
+	u64 pos;
+	int ret;
+	bool changed = false;
+
+	ASSERT(IS_ALIGNED(*hole_start, zone_size));
+
+	while (*hole_size > 0) {
+		pos = btrfs_find_allocatable_zones(device, *hole_start,
+						   *hole_start + *hole_size,
+						   num_bytes);
+		if (pos != *hole_start) {
+			*hole_size = *hole_start + *hole_size - pos;
+			*hole_start = pos;
+			changed = true;
+			if (*hole_size < num_bytes)
+				break;
+		}
+
+		ret = btrfs_ensure_empty_zones(device, pos, num_bytes);
+
+		/* Range is ensured to be empty */
+		if (!ret)
+			return changed;
+
+		/* Given hole range was invalid (outside of device) */
+		if (ret == -ERANGE) {
+			*hole_start += *hole_size;
+			*hole_size = 0;
+			return true;
+		}
+
+		*hole_start += zone_size;
+		*hole_size -= zone_size;
+		changed = true;
+	}
+
+	return changed;
+}
+
+/*
+ * Check if specified hole is suitable for allocation.
+ *
+ * @device:	the device which we have the hole
+ * @hole_start: starting position of the hole
+ * @hole_size:	the size of the hole
+ * @num_bytes:	the size of the free space that we need
+ *
+ * This function may modify @hole_start and @hole_size to reflect the suitable
+ * position for allocation. Returns 1 if hole position is updated, 0 otherwise.
+ */
+static bool dev_extent_hole_check(struct btrfs_device *device, u64 *hole_start,
+				  u64 *hole_size, u64 num_bytes)
+{
+	bool changed = false;
+	u64 hole_end = *hole_start + *hole_size;
+
+	for (;;) {
+		/*
+		 * Check before we set max_hole_start, otherwise we could end up
+		 * sending back this offset anyway.
+		 */
+		if (contains_pending_extent(device, hole_start, *hole_size)) {
+			if (hole_end >= *hole_start)
+				*hole_size = hole_end - *hole_start;
+			else
+				*hole_size = 0;
+			changed = true;
+		}
+
+		switch (device->fs_devices->chunk_alloc_policy) {
+		case BTRFS_CHUNK_ALLOC_REGULAR:
+			/* No extra check */
+			break;
+		case BTRFS_CHUNK_ALLOC_ZONED:
+			if (dev_extent_hole_check_zoned(device, hole_start,
+							hole_size, num_bytes)) {
+				changed = true;
+				/*
+				 * The changed hole can contain pending extent.
+				 * Loop again to check that.
+				 */
+				continue;
+			}
+			break;
+		default:
+			BUG();
+		}
+
+		break;
+	}
+
+	return changed;
+}
+
+/*
+ * Find free 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 does 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 available.
+ */
+static int find_free_dev_extent(struct btrfs_device *device, u64 num_bytes,
+				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 search_start;
+	u64 hole_size;
+	u64 max_hole_start;
+	u64 max_hole_size = 0;
+	u64 extent_end;
+	u64 search_end = device->total_bytes;
+	int ret;
+	int slot;
+	struct extent_buffer *l;
+
+	search_start = dev_extent_search_start(device);
+	max_hole_start = search_start;
+
+	WARN_ON(device->zone_info &&
+		!IS_ALIGNED(num_bytes, device->zone_info->zone_size));
+
+	path = btrfs_alloc_path();
+	if (!path) {
+		ret = -ENOMEM;
+		goto out;
+	}
+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_backwards(root, &key, path);
+	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;
+}
+
+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 {
+		goto out;
+	}
+
+	*dev_extent_len = btrfs_dev_extent_length(leaf, extent);
+
+	ret = btrfs_del_item(trans, root, path);
+	if (ret == 0)
+		set_bit(BTRFS_TRANS_HAVE_FREE_BGS, &trans->transaction->flags);
+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;
+
+	btrfs_reserve_chunk_metadata(trans, true);
+	ret = btrfs_insert_empty_item(trans, trans->fs_info->chunk_root, path,
+				      &key, sizeof(*dev_item));
+	btrfs_trans_release_chunk_metadata(trans);
+	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(trans, 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;
+	int ret;
+
+	ret = kern_path(device_path, LOOKUP_FOLLOW, &path);
+	if (ret)
+		return;
+
+	inode_update_time(d_inode(path.dentry), S_MTIME | S_CTIME | S_VERSION);
+	path_put(&path);
+}
+
+static int btrfs_rm_dev_item(struct btrfs_trans_handle *trans,
+			     struct btrfs_device *device)
+{
+	struct btrfs_root *root = device->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_DEV_ITEMS_OBJECTID;
+	key.type = BTRFS_DEV_ITEM_KEY;
+	key.offset = device->devid;
+
+	btrfs_reserve_chunk_metadata(trans, false);
+	ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
+	btrfs_trans_release_chunk_metadata(trans);
+	if (ret) {
+		if (ret > 0)
+			ret = -ENOENT;
+		goto out;
+	}
+
+	ret = btrfs_del_item(trans, root, path);
+out:
+	btrfs_free_path(path);
+	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)
+			return btrfs_raid_array[i].mindev_error;
+	}
+
+	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_dev
+ * 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_dev->bdev == device->bdev)
+		fs_info->fs_devices->latest_dev = next_device;
+}
+
+/*
+ * 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;
+}
+
+static void btrfs_scratch_superblock(struct btrfs_fs_info *fs_info,
+				     struct block_device *bdev, int copy_num)
+{
+	struct btrfs_super_block *disk_super;
+	const size_t len = sizeof(disk_super->magic);
+	const u64 bytenr = btrfs_sb_offset(copy_num);
+	int ret;
+
+	disk_super = btrfs_read_disk_super(bdev, bytenr, bytenr);
+	if (IS_ERR(disk_super))
+		return;
+
+	memset(&disk_super->magic, 0, len);
+	folio_mark_dirty(virt_to_folio(disk_super));
+	btrfs_release_disk_super(disk_super);
+
+	ret = sync_blockdev_range(bdev, bytenr, bytenr + len - 1);
+	if (ret)
+		btrfs_warn(fs_info, "error clearing superblock number %d (%d)",
+			copy_num, ret);
+}
+
+void btrfs_scratch_superblocks(struct btrfs_fs_info *fs_info,
+			       struct block_device *bdev,
+			       const char *device_path)
+{
+	int copy_num;
+
+	if (!bdev)
+		return;
+
+	for (copy_num = 0; copy_num < BTRFS_SUPER_MIRROR_MAX; copy_num++) {
+		if (bdev_is_zoned(bdev))
+			btrfs_reset_sb_log_zones(bdev, copy_num);
+		else
+			btrfs_scratch_superblock(fs_info, bdev, copy_num);
+	}
+
+	/* 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,
+		    struct btrfs_dev_lookup_args *args,
+		    struct block_device **bdev, void **holder)
+{
+	struct btrfs_trans_handle *trans;
+	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;
+
+	if (btrfs_fs_incompat(fs_info, EXTENT_TREE_V2)) {
+		btrfs_err(fs_info, "device remove not supported on extent tree v2 yet");
+		return -EINVAL;
+	}
+
+	/*
+	 * 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)
+		return ret;
+
+	device = btrfs_find_device(fs_info->fs_devices, args);
+	if (!device) {
+		if (args->missing)
+			ret = BTRFS_ERROR_DEV_MISSING_NOT_FOUND;
+		else
+			ret = -ENOENT;
+		return ret;
+	}
+
+	if (btrfs_pinned_by_swapfile(fs_info, device)) {
+		btrfs_warn_in_rcu(fs_info,
+		  "cannot remove device %s (devid %llu) due to active swapfile",
+				  btrfs_dev_name(device), device->devid);
+		return -ETXTBSY;
+	}
+
+	if (test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state))
+		return BTRFS_ERROR_DEV_TGT_REPLACE;
+
+	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
+	    fs_info->fs_devices->rw_devices == 1)
+		return BTRFS_ERROR_DEV_ONLY_WRITABLE;
+
+	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)
+		goto error_undo;
+
+	trans = btrfs_start_transaction(fs_info->chunk_root, 0);
+	if (IS_ERR(trans)) {
+		ret = PTR_ERR(trans);
+		goto error_undo;
+	}
+
+	ret = btrfs_rm_dev_item(trans, device);
+	if (ret) {
+		/* Any error in dev item removal is critical */
+		btrfs_crit(fs_info,
+			   "failed to remove device item for devid %llu: %d",
+			   device->devid, ret);
+		btrfs_abort_transaction(trans, ret);
+		btrfs_end_transaction(trans);
+		return ret;
+	}
+
+	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_list.
+	 */
+	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.
+	 *
+	 * We cannot call btrfs_close_bdev() here because we're holding the sb
+	 * write lock, and blkdev_put() will pull in the ->open_mutex on the
+	 * block device and it's dependencies.  Instead just flush the device
+	 * and let the caller do the final blkdev_put.
+	 */
+	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
+		btrfs_scratch_superblocks(fs_info, device->bdev,
+					  device->name->str);
+		if (device->bdev) {
+			sync_blockdev(device->bdev);
+			invalidate_bdev(device->bdev);
+		}
+	}
+
+	*bdev = device->bdev;
+	*holder = device->holder;
+	synchronize_rcu();
+	btrfs_free_device(device);
+
+	/*
+	 * This can happen if cur_devices is the private seed devices list.  We
+	 * cannot call close_fs_devices() here because it expects the uuid_mutex
+	 * to be held, but in fact we don't need that for the private
+	 * seed_devices, we can simply decrement cur_devices->opened and then
+	 * remove it from our list and free the fs_devices.
+	 */
+	if (cur_devices->num_devices == 0) {
+		list_del_init(&cur_devices->seed_list);
+		ASSERT(cur_devices->opened == 1);
+		cur_devices->opened--;
+		free_fs_devices(cur_devices);
+	}
+
+	ret = btrfs_commit_transaction(trans);
+
+	return ret;
+
+error_undo:
+	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
+		mutex_lock(&fs_info->chunk_mutex);
+		list_add(&device->dev_alloc_list,
+			 &fs_devices->alloc_list);
+		device->fs_devices->rw_devices++;
+		mutex_unlock(&fs_info->chunk_mutex);
+	}
+	return ret;
+}
+
+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);
+
+	btrfs_scratch_superblocks(tgtdev->fs_info, tgtdev->bdev,
+				  tgtdev->name->str);
+
+	btrfs_close_bdev(tgtdev);
+	synchronize_rcu();
+	btrfs_free_device(tgtdev);
+}
+
+/*
+ * Populate args from device at path.
+ *
+ * @fs_info:	the filesystem
+ * @args:	the args to populate
+ * @path:	the path to the device
+ *
+ * This will read the super block of the device at @path and populate @args with
+ * the devid, fsid, and uuid.  This is meant to be used for ioctls that need to
+ * lookup a device to operate on, but need to do it before we take any locks.
+ * This properly handles the special case of "missing" that a user may pass in,
+ * and does some basic sanity checks.  The caller must make sure that @path is
+ * properly NUL terminated before calling in, and must call
+ * btrfs_put_dev_args_from_path() in order to free up the temporary fsid and
+ * uuid buffers.
+ *
+ * Return: 0 for success, -errno for failure
+ */
+int btrfs_get_dev_args_from_path(struct btrfs_fs_info *fs_info,
+				 struct btrfs_dev_lookup_args *args,
+				 const char *path)
+{
+	struct btrfs_super_block *disk_super;
+	struct block_device *bdev;
+	int ret;
+
+	if (!path || !path[0])
+		return -EINVAL;
+	if (!strcmp(path, "missing")) {
+		args->missing = true;
+		return 0;
+	}
+
+	args->uuid = kzalloc(BTRFS_UUID_SIZE, GFP_KERNEL);
+	args->fsid = kzalloc(BTRFS_FSID_SIZE, GFP_KERNEL);
+	if (!args->uuid || !args->fsid) {
+		btrfs_put_dev_args_from_path(args);
+		return -ENOMEM;
+	}
+
+	ret = btrfs_get_bdev_and_sb(path, BLK_OPEN_READ, NULL, 0,
+				    &bdev, &disk_super);
+	if (ret) {
+		btrfs_put_dev_args_from_path(args);
+		return ret;
+	}
+
+	args->devid = btrfs_stack_device_id(&disk_super->dev_item);
+	memcpy(args->uuid, disk_super->dev_item.uuid, BTRFS_UUID_SIZE);
+	if (btrfs_fs_incompat(fs_info, METADATA_UUID))
+		memcpy(args->fsid, disk_super->metadata_uuid, BTRFS_FSID_SIZE);
+	else
+		memcpy(args->fsid, disk_super->fsid, BTRFS_FSID_SIZE);
+	btrfs_release_disk_super(disk_super);
+	blkdev_put(bdev, NULL);
+	return 0;
+}
+
+/*
+ * Only use this jointly with btrfs_get_dev_args_from_path() because we will
+ * allocate our ->uuid and ->fsid pointers, everybody else uses local variables
+ * that don't need to be freed.
+ */
+void btrfs_put_dev_args_from_path(struct btrfs_dev_lookup_args *args)
+{
+	kfree(args->uuid);
+	kfree(args->fsid);
+	args->uuid = NULL;
+	args->fsid = NULL;
+}
+
+struct btrfs_device *btrfs_find_device_by_devspec(
+		struct btrfs_fs_info *fs_info, u64 devid,
+		const char *device_path)
+{
+	BTRFS_DEV_LOOKUP_ARGS(args);
+	struct btrfs_device *device;
+	int ret;
+
+	if (devid) {
+		args.devid = devid;
+		device = btrfs_find_device(fs_info->fs_devices, &args);
+		if (!device)
+			return ERR_PTR(-ENOENT);
+		return device;
+	}
+
+	ret = btrfs_get_dev_args_from_path(fs_info, &args, device_path);
+	if (ret)
+		return ERR_PTR(ret);
+	device = btrfs_find_device(fs_info->fs_devices, &args);
+	btrfs_put_dev_args_from_path(&args);
+	if (!device)
+		return ERR_PTR(-ENOENT);
+	return device;
+}
+
+static struct btrfs_fs_devices *btrfs_init_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;
+
+	lockdep_assert_held(&uuid_mutex);
+	if (!fs_devices->seeding)
+		return ERR_PTR(-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 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 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);
+
+	return seed_devices;
+}
+
+/*
+ * Splice seed devices into the sprout fs_devices.
+ * Generate a new fsid for the sprouted read-write filesystem.
+ */
+static void btrfs_setup_sprout(struct btrfs_fs_info *fs_info,
+			       struct btrfs_fs_devices *seed_devices)
+{
+	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
+	struct btrfs_super_block *disk_super = fs_info->super_copy;
+	struct btrfs_device *device;
+	u64 super_flags;
+
+	/*
+	 * We are updating the fsid, the thread leading to device_list_add()
+	 * could race, so uuid_mutex is needed.
+	 */
+	lockdep_assert_held(&uuid_mutex);
+
+	/*
+	 * The threads listed below may traverse dev_list but can do that without
+	 * device_list_mutex:
+	 * - All device ops and balance - as we are in btrfs_exclop_start.
+	 * - Various dev_list readers - are using RCU.
+	 * - btrfs_ioctl_fitrim() - is using RCU.
+	 *
+	 * For-read threads as below are using device_list_mutex:
+	 * - Readonly scrub btrfs_scrub_dev()
+	 * - Readonly scrub btrfs_scrub_progress()
+	 * - btrfs_get_dev_stats()
+	 */
+	lockdep_assert_held(&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);
+
+	super_flags = btrfs_super_flags(disk_super) &
+		      ~BTRFS_SUPER_FLAG_SEEDING;
+	btrfs_set_super_flags(disk_super, super_flags);
+}
+
+/*
+ * Store the expected generation for seed devices in device items.
+ */
+static int btrfs_finish_sprout(struct btrfs_trans_handle *trans)
+{
+	BTRFS_DEV_LOOKUP_ARGS(args);
+	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];
+	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) {
+		btrfs_reserve_chunk_metadata(trans, false);
+		ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
+		btrfs_trans_release_chunk_metadata(trans);
+		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);
+		args.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);
+		args.uuid = dev_uuid;
+		args.fsid = fs_uuid;
+		device = btrfs_find_device(fs_info->fs_devices, &args);
+		BUG_ON(!device); /* Logic error */
+
+		if (device->fs_devices->seeding) {
+			btrfs_set_device_generation(leaf, dev_item,
+						    device->generation);
+			btrfs_mark_buffer_dirty(trans, 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 btrfs_trans_handle *trans;
+	struct btrfs_device *device;
+	struct block_device *bdev;
+	struct super_block *sb = fs_info->sb;
+	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
+	struct btrfs_fs_devices *seed_devices = NULL;
+	u64 orig_super_total_bytes;
+	u64 orig_super_num_devices;
+	int ret = 0;
+	bool seeding_dev = false;
+	bool locked = false;
+
+	if (sb_rdonly(sb) && !fs_devices->seeding)
+		return -EROFS;
+
+	bdev = blkdev_get_by_path(device_path, BLK_OPEN_WRITE,
+				  fs_info->bdev_holder, NULL);
+	if (IS_ERR(bdev))
+		return PTR_ERR(bdev);
+
+	if (!btrfs_check_device_zone_type(fs_info, bdev)) {
+		ret = -EINVAL;
+		goto error;
+	}
+
+	if (fs_devices->seeding) {
+		seeding_dev = true;
+		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, device_path);
+	if (IS_ERR(device)) {
+		/* we can safely leave the fs_devices entry around */
+		ret = PTR_ERR(device);
+		goto error;
+	}
+
+	device->fs_info = fs_info;
+	device->bdev = bdev;
+	ret = lookup_bdev(device_path, &device->devt);
+	if (ret)
+		goto error_free_device;
+
+	ret = btrfs_get_dev_zone_info(device, false);
+	if (ret)
+		goto error_free_device;
+
+	trans = btrfs_start_transaction(root, 0);
+	if (IS_ERR(trans)) {
+		ret = PTR_ERR(trans);
+		goto error_free_zone;
+	}
+
+	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(bdev_nr_bytes(bdev), fs_info->sectorsize);
+	device->disk_total_bytes = device->total_bytes;
+	device->commit_total_bytes = device->total_bytes;
+	set_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
+	clear_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state);
+	device->holder = fs_info->bdev_holder;
+	device->dev_stats_valid = 1;
+	set_blocksize(device->bdev, BTRFS_BDEV_BLOCKSIZE);
+
+	if (seeding_dev) {
+		btrfs_clear_sb_rdonly(sb);
+
+		/* GFP_KERNEL allocation must not be under device_list_mutex */
+		seed_devices = btrfs_init_sprout(fs_info);
+		if (IS_ERR(seed_devices)) {
+			ret = PTR_ERR(seed_devices);
+			btrfs_abort_transaction(trans, ret);
+			goto error_trans;
+		}
+	}
+
+	mutex_lock(&fs_devices->device_list_mutex);
+	if (seeding_dev) {
+		btrfs_setup_sprout(fs_info, seed_devices);
+		btrfs_assign_next_active_device(fs_info->fs_devices->latest_dev,
+						device);
+	}
+
+	device->fs_devices = fs_devices;
+
+	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 (!bdev_nonrot(bdev))
+		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_sprout_splice().
+		 */
+		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->devt);
+
+	/* Update ctime/mtime for blkid or udev */
+	update_dev_time(device_path);
+
+	return ret;
+
+error_sysfs:
+	btrfs_sysfs_remove_device(device);
+	mutex_lock(&fs_info->fs_devices->device_list_mutex);
+	mutex_lock(&fs_info->chunk_mutex);
+	list_del_rcu(&device->dev_list);
+	list_del(&device->dev_alloc_list);
+	fs_info->fs_devices->num_devices--;
+	fs_info->fs_devices->open_devices--;
+	fs_info->fs_devices->rw_devices--;
+	fs_info->fs_devices->total_devices--;
+	fs_info->fs_devices->total_rw_bytes -= device->total_bytes;
+	atomic64_sub(device->total_bytes, &fs_info->free_chunk_space);
+	btrfs_set_super_total_bytes(fs_info->super_copy,
+				    orig_super_total_bytes);
+	btrfs_set_super_num_devices(fs_info->super_copy,
+				    orig_super_num_devices);
+	mutex_unlock(&fs_info->chunk_mutex);
+	mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+error_trans:
+	if (seeding_dev)
+		btrfs_set_sb_rdonly(sb);
+	if (trans)
+		btrfs_end_transaction(trans);
+error_free_zone:
+	btrfs_destroy_dev_zone_info(device);
+error_free_device:
+	btrfs_free_device(device);
+error:
+	blkdev_put(bdev, fs_info->bdev_holder);
+	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(trans, 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;
+	int ret;
+
+	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);
+
+	btrfs_reserve_chunk_metadata(trans, false);
+	ret = btrfs_update_device(trans, device);
+	btrfs_trans_release_chunk_metadata(trans);
+
+	return ret;
+}
+
+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;
+
+	lockdep_assert_held(&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;
+		}
+	}
+	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;
+}
+
+static int remove_chunk_item(struct btrfs_trans_handle *trans,
+			     struct map_lookup *map, u64 chunk_offset)
+{
+	int i;
+
+	/*
+	 * Removing chunk items and updating the device items in the chunks btree
+	 * requires holding the chunk_mutex.
+	 * See the comment at btrfs_chunk_alloc() for the details.
+	 */
+	lockdep_assert_held(&trans->fs_info->chunk_mutex);
+
+	for (i = 0; i < map->num_stripes; i++) {
+		int ret;
+
+		ret = btrfs_update_device(trans, map->stripes[i].dev);
+		if (ret)
+			return ret;
+	}
+
+	return btrfs_free_chunk(trans, chunk_offset);
+}
+
+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;
+
+	/*
+	 * First delete the device extent items from the devices btree.
+	 * We take the device_list_mutex to avoid racing with the finishing phase
+	 * of a device replace operation. See the comment below before acquiring
+	 * fs_info->chunk_mutex. Note that here we do not acquire the chunk_mutex
+	 * because that can result in a deadlock when deleting the device extent
+	 * items from the devices btree - COWing an extent buffer from the btree
+	 * may result in allocating a new metadata chunk, which would attempt to
+	 * lock again fs_info->chunk_mutex.
+	 */
+	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);
+		}
+	}
+	mutex_unlock(&fs_devices->device_list_mutex);
+
+	/*
+	 * We acquire fs_info->chunk_mutex for 2 reasons:
+	 *
+	 * 1) Just like with the first phase of the chunk allocation, we must
+	 *    reserve system space, do all chunk btree updates and deletions, and
+	 *    update the system chunk array in the superblock while holding this
+	 *    mutex. This is for similar reasons as explained on the comment at
+	 *    the top of btrfs_chunk_alloc();
+	 *
+	 * 2) 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()), so we could grab the
+	 *    replaced device and then see it with an ID of
+	 *    BTRFS_DEV_REPLACE_DEVID, which would cause a failure when updating
+	 *    the device item, which does not exists on the chunk btree.
+	 *    The finishing phase of device replace acquires both the
+	 *    device_list_mutex and the chunk_mutex, in that order, so we are
+	 *    safe by just acquiring the chunk_mutex.
+	 */
+	trans->removing_chunk = true;
+	mutex_lock(&fs_info->chunk_mutex);
+
+	check_system_chunk(trans, map->type);
+
+	ret = remove_chunk_item(trans, map, chunk_offset);
+	/*
+	 * Normally we should not get -ENOSPC since we reserved space before
+	 * through the call to check_system_chunk().
+	 *
+	 * Despite our system space_info having enough free space, we may not
+	 * be able to allocate extents from its block groups, because all have
+	 * an incompatible profile, which will force us to allocate a new system
+	 * block group with the right profile, or right after we called
+	 * check_system_space() above, a scrub turned the only system block group
+	 * with enough free space into RO mode.
+	 * This is explained with more detail at do_chunk_alloc().
+	 *
+	 * So if we get -ENOSPC, allocate a new system chunk and retry once.
+	 */
+	if (ret == -ENOSPC) {
+		const u64 sys_flags = btrfs_system_alloc_profile(fs_info);
+		struct btrfs_block_group *sys_bg;
+
+		sys_bg = btrfs_create_chunk(trans, sys_flags);
+		if (IS_ERR(sys_bg)) {
+			ret = PTR_ERR(sys_bg);
+			btrfs_abort_transaction(trans, ret);
+			goto out;
+		}
+
+		ret = btrfs_chunk_alloc_add_chunk_item(trans, sys_bg);
+		if (ret) {
+			btrfs_abort_transaction(trans, ret);
+			goto out;
+		}
+
+		ret = remove_chunk_item(trans, map, chunk_offset);
+		if (ret) {
+			btrfs_abort_transaction(trans, ret);
+			goto out;
+		}
+	} else 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;
+		}
+	}
+
+	mutex_unlock(&fs_info->chunk_mutex);
+	trans->removing_chunk = false;
+
+	/*
+	 * We are done with chunk btree updates and deletions, so release the
+	 * system space we previously reserved (with check_system_chunk()).
+	 */
+	btrfs_trans_release_chunk_metadata(trans);
+
+	ret = btrfs_remove_block_group(trans, chunk_offset, em);
+	if (ret) {
+		btrfs_abort_transaction(trans, ret);
+		goto out;
+	}
+
+out:
+	if (trans->removing_chunk) {
+		mutex_unlock(&fs_info->chunk_mutex);
+		trans->removing_chunk = false;
+	}
+	/* once for us */
+	free_extent_map(em);
+	return ret;
+}
+
+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;
+	u64 length;
+	int ret;
+
+	if (btrfs_fs_incompat(fs_info, EXTENT_TREE_V2)) {
+		btrfs_err(fs_info,
+			  "relocate: not supported on extent tree v2 yet");
+		return -EINVAL;
+	}
+
+	/*
+	 * 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->reclaim_bgs_lock);
+
+	/* 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) {
+		/*
+		 * If we had a transaction abort, stop all running scrubs.
+		 * See transaction.c:cleanup_transaction() why we do it here.
+		 */
+		if (BTRFS_FS_ERROR(fs_info))
+			btrfs_scrub_cancel(fs_info);
+		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);
+	length = block_group->length;
+	btrfs_put_block_group(block_group);
+
+	/*
+	 * On a zoned file system, discard the whole block group, this will
+	 * trigger a REQ_OP_ZONE_RESET operation on the device zone. If
+	 * resetting the zone fails, don't treat it as a fatal problem from the
+	 * filesystem's point of view.
+	 */
+	if (btrfs_is_zoned(fs_info)) {
+		ret = btrfs_discard_extent(fs_info, chunk_offset, length, NULL);
+		if (ret)
+			btrfs_info(fs_info,
+				"failed to reset zone %llu after relocation",
+				chunk_offset);
+	}
+
+	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->reclaim_bgs_lock);
+		ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0);
+		if (ret < 0) {
+			mutex_unlock(&fs_info->reclaim_bgs_lock);
+			goto error;
+		}
+		BUG_ON(ret == 0); /* Corruption */
+
+		ret = btrfs_previous_item(chunk_root, path, key.objectid,
+					  key.type);
+		if (ret)
+			mutex_unlock(&fs_info->reclaim_bgs_lock);
+		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->reclaim_bgs_lock);
+
+		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(trans, 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 = mult_perc(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 = mult_perc(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 = mult_perc(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;
+
+	return (num_stripes - nparity) / 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->reclaim_bgs_lock);
+		ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0);
+		if (ret < 0) {
+			mutex_unlock(&fs_info->reclaim_bgs_lock);
+			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->reclaim_bgs_lock);
+			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->reclaim_bgs_lock);
+			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->reclaim_bgs_lock);
+			goto loop;
+		}
+
+		if (counting) {
+			mutex_unlock(&fs_info->reclaim_bgs_lock);
+			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->reclaim_bgs_lock);
+			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->reclaim_bgs_lock);
+				goto error;
+			} else if (ret == 1) {
+				chunk_reserved = 1;
+			}
+		}
+
+		ret = btrfs_relocate_chunk(fs_info, found_key.offset);
+		mutex_unlock(&fs_info->reclaim_bgs_lock);
+		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;
+}
+
+/*
+ * 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);
+}
+
+/*
+ * 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;
+	bool paused = false;
+	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));
+	}
+
+	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");
+		btrfs_exclop_balance(fs_info, BTRFS_EXCLOP_BALANCE_PAUSED);
+		paused = true;
+	}
+	/*
+	 * 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);
+	}
+
+	/* We didn't pause, we can clean everything up. */
+	if (!paused) {
+		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;
+	}
+
+	spin_lock(&fs_info->super_lock);
+	ASSERT(fs_info->exclusive_operation == BTRFS_EXCLOP_BALANCE_PAUSED);
+	fs_info->exclusive_operation = BTRFS_EXCLOP_BALANCE;
+	spin_unlock(&fs_info->super_lock);
+	/*
+	 * 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_PAUSED))
+		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(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->reclaim_bgs_lock);
+		ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+		if (ret < 0) {
+			mutex_unlock(&fs_info->reclaim_bgs_lock);
+			goto done;
+		}
+
+		ret = btrfs_previous_item(root, path, 0, key.type);
+		if (ret) {
+			mutex_unlock(&fs_info->reclaim_bgs_lock);
+			if (ret < 0)
+				goto done;
+			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->reclaim_bgs_lock);
+			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->reclaim_bgs_lock);
+			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->reclaim_bgs_lock);
+			goto done;
+		}
+
+		ret = btrfs_relocate_chunk(fs_info, chunk_offset);
+		mutex_unlock(&fs_info->reclaim_bgs_lock);
+		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);
+
+	btrfs_reserve_chunk_metadata(trans, false);
+	/* Now btrfs_update_device() will change the on-disk size. */
+	ret = btrfs_update_device(trans, device);
+	btrfs_trans_release_chunk_metadata(trans);
+	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;
+
+	lockdep_assert_held(&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)
+		return -EFBIG;
+
+	ptr = super_copy->sys_chunk_array + array_size;
+	btrfs_cpu_key_to_disk(&disk_key, key);
+	memcpy(ptr, &disk_key, sizeof(disk_key));
+	ptr += sizeof(disk_key);
+	memcpy(ptr, chunk, item_size);
+	item_size += sizeof(disk_key);
+	btrfs_set_super_sys_array_size(super_copy, array_size + item_size);
+
+	return 0;
+}
+
+/*
+ * sort the devices in descending order by max_avail, total_avail
+ */
+static int btrfs_cmp_device_info(const void *a, const void *b)
+{
+	const struct btrfs_device_info *di_a = a;
+	const struct btrfs_device_info *di_b = b;
+
+	if (di_a->max_avail > di_b->max_avail)
+		return -1;
+	if (di_a->max_avail < di_b->max_avail)
+		return 1;
+	if (di_a->total_avail > di_b->total_avail)
+		return -1;
+	if (di_a->total_avail < di_b->total_avail)
+		return 1;
+	return 0;
+}
+
+static 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_create_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)
+{
+	struct btrfs_space_info *space_info;
+
+	space_info = btrfs_find_space_info(fs_devices->fs_info, ctl->type);
+	ASSERT(space_info);
+
+	ctl->max_chunk_size = READ_ONCE(space_info->chunk_size);
+	ctl->max_stripe_size = min_t(u64, ctl->max_chunk_size, SZ_1G);
+
+	if (ctl->type & BTRFS_BLOCK_GROUP_SYSTEM)
+		ctl->devs_max = min_t(int, ctl->devs_max, BTRFS_MAX_DEVS_SYS_CHUNK);
+
+	/* We don't want a chunk larger than 10% of writable space */
+	ctl->max_chunk_size = min(mult_perc(fs_devices->total_rw_bytes, 10),
+				  ctl->max_chunk_size);
+	ctl->dev_extent_min = btrfs_stripe_nr_to_offset(ctl->dev_stripes);
+}
+
+static void init_alloc_chunk_ctl_policy_zoned(
+				      struct btrfs_fs_devices *fs_devices,
+				      struct alloc_chunk_ctl *ctl)
+{
+	u64 zone_size = fs_devices->fs_info->zone_size;
+	u64 limit;
+	int min_num_stripes = ctl->devs_min * ctl->dev_stripes;
+	int min_data_stripes = (min_num_stripes - ctl->nparity) / ctl->ncopies;
+	u64 min_chunk_size = min_data_stripes * zone_size;
+	u64 type = ctl->type;
+
+	ctl->max_stripe_size = zone_size;
+	if (type & BTRFS_BLOCK_GROUP_DATA) {
+		ctl->max_chunk_size = round_down(BTRFS_MAX_DATA_CHUNK_SIZE,
+						 zone_size);
+	} else if (type & BTRFS_BLOCK_GROUP_METADATA) {
+		ctl->max_chunk_size = ctl->max_stripe_size;
+	} else if (type & BTRFS_BLOCK_GROUP_SYSTEM) {
+		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 */
+	limit = max(round_down(mult_perc(fs_devices->total_rw_bytes, 10),
+			       zone_size),
+		    min_chunk_size);
+	ctl->max_chunk_size = min(limit, ctl->max_chunk_size);
+	ctl->dev_extent_min = zone_size * 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;
+	case BTRFS_CHUNK_ALLOC_ZONED:
+		init_alloc_chunk_ctl_policy_zoned(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);
+	}
+
+	/* Stripe size should not go beyond 1G. */
+	ctl->stripe_size = min_t(u64, ctl->stripe_size, SZ_1G);
+
+	/* 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_zoned(struct alloc_chunk_ctl *ctl,
+				    struct btrfs_device_info *devices_info)
+{
+	u64 zone_size = devices_info[0].dev->zone_info->zone_size;
+	/* Number of stripes that count for block group size */
+	int data_stripes;
+
+	/*
+	 * It should hold because:
+	 *    dev_extent_min == dev_extent_want == zone_size * dev_stripes
+	 */
+	ASSERT(devices_info[ctl->ndevs - 1].max_avail == ctl->dev_extent_min);
+
+	ctl->stripe_size = zone_size;
+	ctl->num_stripes = ctl->ndevs * ctl->dev_stripes;
+	data_stripes = (ctl->num_stripes - ctl->nparity) / ctl->ncopies;
+
+	/* stripe_size is fixed in zoned filesysmte. Reduce ndevs instead. */
+	if (ctl->stripe_size * data_stripes > ctl->max_chunk_size) {
+		ctl->ndevs = div_u64(div_u64(ctl->max_chunk_size * ctl->ncopies,
+					     ctl->stripe_size) + ctl->nparity,
+				     ctl->dev_stripes);
+		ctl->num_stripes = ctl->ndevs * ctl->dev_stripes;
+		data_stripes = (ctl->num_stripes - ctl->nparity) / ctl->ncopies;
+		ASSERT(ctl->stripe_size * data_stripes <= ctl->max_chunk_size);
+	}
+
+	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);
+	case BTRFS_CHUNK_ALLOC_ZONED:
+		return decide_stripe_size_zoned(ctl, devices_info);
+	default:
+		BUG();
+	}
+}
+
+static struct btrfs_block_group *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 btrfs_block_group *block_group;
+	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 ERR_PTR(-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->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 ERR_PTR(-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 ERR_PTR(ret);
+	}
+	write_unlock(&em_tree->lock);
+
+	block_group = btrfs_make_block_group(trans, type, start, ctl->chunk_size);
+	if (IS_ERR(block_group))
+		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 block_group;
+
+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 block_group;
+}
+
+struct btrfs_block_group *btrfs_create_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;
+	struct btrfs_block_group *block_group;
+	int ret;
+
+	lockdep_assert_held(&info->chunk_mutex);
+
+	if (!alloc_profile_is_valid(type, 0)) {
+		ASSERT(0);
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (list_empty(&fs_devices->alloc_list)) {
+		if (btrfs_test_opt(info, ENOSPC_DEBUG))
+			btrfs_debug(info, "%s: no writable device", __func__);
+		return ERR_PTR(-ENOSPC);
+	}
+
+	if (!(type & BTRFS_BLOCK_GROUP_TYPE_MASK)) {
+		btrfs_err(info, "invalid chunk type 0x%llx requested", type);
+		ASSERT(0);
+		return ERR_PTR(-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 ERR_PTR(-ENOMEM);
+
+	ret = gather_device_info(fs_devices, &ctl, devices_info);
+	if (ret < 0) {
+		block_group = ERR_PTR(ret);
+		goto out;
+	}
+
+	ret = decide_stripe_size(fs_devices, &ctl, devices_info);
+	if (ret < 0) {
+		block_group = ERR_PTR(ret);
+		goto out;
+	}
+
+	block_group = create_chunk(trans, &ctl, devices_info);
+
+out:
+	kfree(devices_info);
+	return block_group;
+}
+
+/*
+ * This function, btrfs_chunk_alloc_add_chunk_item(), typically belongs to the
+ * phase 1 of chunk allocation. It belongs to phase 2 only when allocating system
+ * chunks.
+ *
+ * See the comment at btrfs_chunk_alloc() for details about the chunk allocation
+ * phases.
+ */
+int btrfs_chunk_alloc_add_chunk_item(struct btrfs_trans_handle *trans,
+				     struct btrfs_block_group *bg)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_root *chunk_root = fs_info->chunk_root;
+	struct btrfs_key key;
+	struct btrfs_chunk *chunk;
+	struct btrfs_stripe *stripe;
+	struct extent_map *em;
+	struct map_lookup *map;
+	size_t item_size;
+	int i;
+	int ret;
+
+	/*
+	 * We take the chunk_mutex for 2 reasons:
+	 *
+	 * 1) Updates and insertions in the chunk btree must be done while holding
+	 *    the chunk_mutex, as well as updating the system chunk array in the
+	 *    superblock. See the comment on top of btrfs_chunk_alloc() for the
+	 *    details;
+	 *
+	 * 2) 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()), so we could grab the
+	 *    replaced device and then see it with an ID of BTRFS_DEV_REPLACE_DEVID,
+	 *    which would cause a failure when updating the device item, which does
+	 *    not exists, or persisting a stripe of the chunk item with such ID.
+	 *    Here we can't use the device_list_mutex because our caller already
+	 *    has locked the chunk_mutex, and the final phase of device replace
+	 *    acquires both mutexes - first the device_list_mutex and then the
+	 *    chunk_mutex. Using any of those two mutexes protects us from a
+	 *    concurrent device replace.
+	 */
+	lockdep_assert_held(&fs_info->chunk_mutex);
+
+	em = btrfs_get_chunk_map(fs_info, bg->start, bg->length);
+	if (IS_ERR(em)) {
+		ret = PTR_ERR(em);
+		btrfs_abort_transaction(trans, ret);
+		return ret;
+	}
+
+	map = em->map_lookup;
+	item_size = btrfs_chunk_item_size(map->num_stripes);
+
+	chunk = kzalloc(item_size, GFP_NOFS);
+	if (!chunk) {
+		ret = -ENOMEM;
+		btrfs_abort_transaction(trans, ret);
+		goto out;
+	}
+
+	for (i = 0; i < map->num_stripes; i++) {
+		struct btrfs_device *device = map->stripes[i].dev;
+
+		ret = btrfs_update_device(trans, device);
+		if (ret)
+			goto out;
+	}
+
+	stripe = &chunk->stripe;
+	for (i = 0; i < map->num_stripes; i++) {
+		struct btrfs_device *device = map->stripes[i].dev;
+		const u64 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++;
+	}
+
+	btrfs_set_stack_chunk_length(chunk, bg->length);
+	btrfs_set_stack_chunk_owner(chunk, BTRFS_EXTENT_TREE_OBJECTID);
+	btrfs_set_stack_chunk_stripe_len(chunk, BTRFS_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, BTRFS_STRIPE_LEN);
+	btrfs_set_stack_chunk_io_width(chunk, BTRFS_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 = bg->start;
+
+	ret = btrfs_insert_item(trans, chunk_root, &key, chunk, item_size);
+	if (ret)
+		goto out;
+
+	set_bit(BLOCK_GROUP_FLAG_CHUNK_ITEM_INSERTED, &bg->runtime_flags);
+
+	if (map->type & BTRFS_BLOCK_GROUP_SYSTEM) {
+		ret = btrfs_add_system_chunk(fs_info, &key, chunk, item_size);
+		if (ret)
+			goto out;
+	}
+
+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;
+	struct btrfs_block_group *meta_bg;
+	struct btrfs_block_group *sys_bg;
+
+	/*
+	 * When adding a new device for sprouting, the seed device is read-only
+	 * so we must first allocate a metadata and a system chunk. But before
+	 * adding the block group items to the extent, device and chunk btrees,
+	 * we must first:
+	 *
+	 * 1) Create both chunks without doing any changes to the btrees, as
+	 *    otherwise we would get -ENOSPC since the block groups from the
+	 *    seed device are read-only;
+	 *
+	 * 2) Add the device item for the new sprout device - finishing the setup
+	 *    of a new block group requires updating the device item in the chunk
+	 *    btree, so it must exist when we attempt to do it. The previous step
+	 *    ensures this does not fail with -ENOSPC.
+	 *
+	 * After that we can add the block group items to their btrees:
+	 * update existing device item in the chunk btree, add a new block group
+	 * item to the extent btree, add a new chunk item to the chunk btree and
+	 * finally add the new device extent items to the devices btree.
+	 */
+
+	alloc_profile = btrfs_metadata_alloc_profile(fs_info);
+	meta_bg = btrfs_create_chunk(trans, alloc_profile);
+	if (IS_ERR(meta_bg))
+		return PTR_ERR(meta_bg);
+
+	alloc_profile = btrfs_system_alloc_profile(fs_info);
+	sys_bg = btrfs_create_chunk(trans, alloc_profile);
+	if (IS_ERR(sys_bg))
+		return PTR_ERR(sys_bg);
+
+	return 0;
+}
+
+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;
+}
+
+bool btrfs_chunk_writeable(struct btrfs_fs_info *fs_info, u64 chunk_offset)
+{
+	struct extent_map *em;
+	struct map_lookup *map;
+	int miss_ndevs = 0;
+	int i;
+	bool ret = true;
+
+	em = btrfs_get_chunk_map(fs_info, chunk_offset, 1);
+	if (IS_ERR(em))
+		return false;
+
+	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)) {
+			ret = false;
+			goto end;
+		}
+	}
+
+	/*
+	 * If the number of missing devices is larger than max errors, we can
+	 * not write the data into that chunk successfully.
+	 */
+	if (miss_ndevs > btrfs_chunk_max_errors(map))
+		ret = false;
+end:
+	free_extent_map(em);
+	return ret;
+}
+
+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;
+	enum btrfs_raid_types index;
+	int ret = 1;
+
+	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;
+	index = btrfs_bg_flags_to_raid_index(map->type);
+
+	/* Non-RAID56, use their ncopies from btrfs_raid_array. */
+	if (!(map->type & BTRFS_BLOCK_GROUP_RAID56_MASK))
+		ret = btrfs_raid_array[index].ncopies;
+	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;
+	free_extent_map(em);
+	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;
+
+	if (!btrfs_fs_incompat(fs_info, RAID56))
+		return len;
+
+	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 = btrfs_stripe_nr_to_offset(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;
+
+	if (!btrfs_fs_incompat(fs_info, RAID56))
+		return 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;
+
+	switch (fs_info->fs_devices->read_policy) {
+	default:
+		/* Shouldn't happen, just warn and use pid instead of failing */
+		btrfs_warn_rl(fs_info,
+			      "unknown read_policy type %u, reset to pid",
+			      fs_info->fs_devices->read_policy);
+		fs_info->fs_devices->read_policy = BTRFS_READ_POLICY_PID;
+		fallthrough;
+	case BTRFS_READ_POLICY_PID:
+		preferred_mirror = first + (current->pid % num_stripes);
+		break;
+	}
+
+	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;
+}
+
+static struct btrfs_io_context *alloc_btrfs_io_context(struct btrfs_fs_info *fs_info,
+						       u16 total_stripes)
+{
+	struct btrfs_io_context *bioc;
+
+	bioc = kzalloc(
+		 /* The size of btrfs_io_context */
+		sizeof(struct btrfs_io_context) +
+		/* Plus the variable array for the stripes */
+		sizeof(struct btrfs_io_stripe) * (total_stripes),
+		GFP_NOFS);
+
+	if (!bioc)
+		return NULL;
+
+	refcount_set(&bioc->refs, 1);
+
+	bioc->fs_info = fs_info;
+	bioc->replace_stripe_src = -1;
+	bioc->full_stripe_logical = (u64)-1;
+
+	return bioc;
+}
+
+void btrfs_get_bioc(struct btrfs_io_context *bioc)
+{
+	WARN_ON(!refcount_read(&bioc->refs));
+	refcount_inc(&bioc->refs);
+}
+
+void btrfs_put_bioc(struct btrfs_io_context *bioc)
+{
+	if (!bioc)
+		return;
+	if (refcount_dec_and_test(&bioc->refs))
+		kfree(bioc);
+}
+
+/*
+ * Please note that, discard won't be sent to target device of device
+ * replace.
+ */
+struct btrfs_discard_stripe *btrfs_map_discard(struct btrfs_fs_info *fs_info,
+					       u64 logical, u64 *length_ret,
+					       u32 *num_stripes)
+{
+	struct extent_map *em;
+	struct map_lookup *map;
+	struct btrfs_discard_stripe *stripes;
+	u64 length = *length_ret;
+	u64 offset;
+	u32 stripe_nr;
+	u32 stripe_nr_end;
+	u32 stripe_cnt;
+	u64 stripe_end_offset;
+	u64 stripe_offset;
+	u32 stripe_index;
+	u32 factor = 0;
+	u32 sub_stripes = 0;
+	u32 stripes_per_dev = 0;
+	u32 remaining_stripes = 0;
+	u32 last_stripe = 0;
+	int ret;
+	int i;
+
+	em = btrfs_get_chunk_map(fs_info, logical, length);
+	if (IS_ERR(em))
+		return ERR_CAST(em);
+
+	map = em->map_lookup;
+
+	/* we don't discard raid56 yet */
+	if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
+		ret = -EOPNOTSUPP;
+		goto out_free_map;
+	}
+
+	offset = logical - em->start;
+	length = min_t(u64, em->start + em->len - logical, length);
+	*length_ret = length;
+
+	/*
+	 * stripe_nr counts the total number of stripes we have to stride
+	 * to get to this block
+	 */
+	stripe_nr = offset >> BTRFS_STRIPE_LEN_SHIFT;
+
+	/* stripe_offset is the offset of this block in its stripe */
+	stripe_offset = offset - btrfs_stripe_nr_to_offset(stripe_nr);
+
+	stripe_nr_end = round_up(offset + length, BTRFS_STRIPE_LEN) >>
+			BTRFS_STRIPE_LEN_SHIFT;
+	stripe_cnt = stripe_nr_end - stripe_nr;
+	stripe_end_offset = btrfs_stripe_nr_to_offset(stripe_nr_end) -
+			    (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_index = stripe_nr % factor;
+		stripe_nr /= factor;
+		stripe_index *= sub_stripes;
+
+		remaining_stripes = stripe_cnt % factor;
+		stripes_per_dev = stripe_cnt / factor;
+		last_stripe = ((stripe_nr_end - 1) % factor) * sub_stripes;
+	} else if (map->type & (BTRFS_BLOCK_GROUP_RAID1_MASK |
+				BTRFS_BLOCK_GROUP_DUP)) {
+		*num_stripes = map->num_stripes;
+	} else {
+		stripe_index = stripe_nr % map->num_stripes;
+		stripe_nr /= map->num_stripes;
+	}
+
+	stripes = kcalloc(*num_stripes, sizeof(*stripes), GFP_NOFS);
+	if (!stripes) {
+		ret = -ENOMEM;
+		goto out_free_map;
+	}
+
+	for (i = 0; i < *num_stripes; i++) {
+		stripes[i].physical =
+			map->stripes[stripe_index].physical +
+			stripe_offset + btrfs_stripe_nr_to_offset(stripe_nr);
+		stripes[i].dev = map->stripes[stripe_index].dev;
+
+		if (map->type & (BTRFS_BLOCK_GROUP_RAID0 |
+				 BTRFS_BLOCK_GROUP_RAID10)) {
+			stripes[i].length = btrfs_stripe_nr_to_offset(stripes_per_dev);
+
+			if (i / sub_stripes < remaining_stripes)
+				stripes[i].length += BTRFS_STRIPE_LEN;
+
+			/*
+			 * Special for the first stripe and
+			 * the last stripe:
+			 *
+			 * |-------|...|-------|
+			 *     |----------|
+			 *    off     end_off
+			 */
+			if (i < sub_stripes)
+				stripes[i].length -= stripe_offset;
+
+			if (stripe_index >= last_stripe &&
+			    stripe_index <= (last_stripe +
+					     sub_stripes - 1))
+				stripes[i].length -= stripe_end_offset;
+
+			if (i == sub_stripes - 1)
+				stripe_offset = 0;
+		} else {
+			stripes[i].length = length;
+		}
+
+		stripe_index++;
+		if (stripe_index == map->num_stripes) {
+			stripe_index = 0;
+			stripe_nr++;
+		}
+	}
+
+	free_extent_map(em);
+	return stripes;
+out_free_map:
+	free_extent_map(em);
+	return ERR_PTR(ret);
+}
+
+static bool is_block_group_to_copy(struct btrfs_fs_info *fs_info, u64 logical)
+{
+	struct btrfs_block_group *cache;
+	bool ret;
+
+	/* Non zoned filesystem does not use "to_copy" flag */
+	if (!btrfs_is_zoned(fs_info))
+		return false;
+
+	cache = btrfs_lookup_block_group(fs_info, logical);
+
+	ret = test_bit(BLOCK_GROUP_FLAG_TO_COPY, &cache->runtime_flags);
+
+	btrfs_put_block_group(cache);
+	return ret;
+}
+
+static void handle_ops_on_dev_replace(enum btrfs_map_op op,
+				      struct btrfs_io_context *bioc,
+				      struct btrfs_dev_replace *dev_replace,
+				      u64 logical,
+				      int *num_stripes_ret, int *max_errors_ret)
+{
+	u64 srcdev_devid = dev_replace->srcdev->devid;
+	/*
+	 * At this stage, num_stripes is still the real number of stripes,
+	 * excluding the duplicated stripes.
+	 */
+	int num_stripes = *num_stripes_ret;
+	int nr_extra_stripes = 0;
+	int max_errors = *max_errors_ret;
+	int i;
+
+	/*
+	 * A block group which has "to_copy" set will eventually be copied by
+	 * the dev-replace process. We can avoid cloning IO here.
+	 */
+	if (is_block_group_to_copy(dev_replace->srcdev->fs_info, logical))
+		return;
+
+	/*
+	 * 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.
+	 */
+	for (i = 0; i < num_stripes; i++) {
+		struct btrfs_io_stripe *old = &bioc->stripes[i];
+		struct btrfs_io_stripe *new = &bioc->stripes[num_stripes + nr_extra_stripes];
+
+		if (old->dev->devid != srcdev_devid)
+			continue;
+
+		new->physical = old->physical;
+		new->dev = dev_replace->tgtdev;
+		if (bioc->map_type & BTRFS_BLOCK_GROUP_RAID56_MASK)
+			bioc->replace_stripe_src = i;
+		nr_extra_stripes++;
+	}
+
+	/* We can only have at most 2 extra nr_stripes (for DUP). */
+	ASSERT(nr_extra_stripes <= 2);
+	/*
+	 * For GET_READ_MIRRORS, we can only return at most 1 extra stripe for
+	 * replace.
+	 * If we have 2 extra stripes, only choose the one with smaller physical.
+	 */
+	if (op == BTRFS_MAP_GET_READ_MIRRORS && nr_extra_stripes == 2) {
+		struct btrfs_io_stripe *first = &bioc->stripes[num_stripes];
+		struct btrfs_io_stripe *second = &bioc->stripes[num_stripes + 1];
+
+		/* Only DUP can have two extra stripes. */
+		ASSERT(bioc->map_type & BTRFS_BLOCK_GROUP_DUP);
+
+		/*
+		 * Swap the last stripe stripes and reduce @nr_extra_stripes.
+		 * The extra stripe would still be there, but won't be accessed.
+		 */
+		if (first->physical > second->physical) {
+			swap(second->physical, first->physical);
+			swap(second->dev, first->dev);
+			nr_extra_stripes--;
+		}
+	}
+
+	*num_stripes_ret = num_stripes + nr_extra_stripes;
+	*max_errors_ret = max_errors + nr_extra_stripes;
+	bioc->replace_nr_stripes = nr_extra_stripes;
+}
+
+static u64 btrfs_max_io_len(struct map_lookup *map, enum btrfs_map_op op,
+			    u64 offset, u32 *stripe_nr, u64 *stripe_offset,
+			    u64 *full_stripe_start)
+{
+	/*
+	 * Stripe_nr is the stripe where this block falls.  stripe_offset is
+	 * the offset of this block in its stripe.
+	 */
+	*stripe_offset = offset & BTRFS_STRIPE_LEN_MASK;
+	*stripe_nr = offset >> BTRFS_STRIPE_LEN_SHIFT;
+	ASSERT(*stripe_offset < U32_MAX);
+
+	if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
+		unsigned long full_stripe_len =
+			btrfs_stripe_nr_to_offset(nr_data_stripes(map));
+
+		/*
+		 * For full stripe start, we use previously calculated
+		 * @stripe_nr. Align it to nr_data_stripes, then multiply with
+		 * STRIPE_LEN.
+		 *
+		 * By this we can avoid u64 division completely.  And we have
+		 * to go rounddown(), not round_down(), as nr_data_stripes is
+		 * not ensured to be power of 2.
+		 */
+		*full_stripe_start =
+			btrfs_stripe_nr_to_offset(
+				rounddown(*stripe_nr, nr_data_stripes(map)));
+
+		ASSERT(*full_stripe_start + full_stripe_len > offset);
+		ASSERT(*full_stripe_start <= offset);
+		/*
+		 * For writes to RAID56, allow to write a full stripe set, but
+		 * no straddling of stripe sets.
+		 */
+		if (op == BTRFS_MAP_WRITE)
+			return full_stripe_len - (offset - *full_stripe_start);
+	}
+
+	/*
+	 * For other RAID types and for RAID56 reads, allow a single stripe (on
+	 * a single disk).
+	 */
+	if (map->type & BTRFS_BLOCK_GROUP_STRIPE_MASK)
+		return BTRFS_STRIPE_LEN - *stripe_offset;
+	return U64_MAX;
+}
+
+static void set_io_stripe(struct btrfs_io_stripe *dst, const struct map_lookup *map,
+			  u32 stripe_index, u64 stripe_offset, u32 stripe_nr)
+{
+	dst->dev = map->stripes[stripe_index].dev;
+	dst->physical = map->stripes[stripe_index].physical +
+			stripe_offset + btrfs_stripe_nr_to_offset(stripe_nr);
+}
+
+/*
+ * Map one logical range to one or more physical ranges.
+ *
+ * @length:		(Mandatory) mapped length of this run.
+ *			One logical range can be split into different segments
+ *			due to factors like zones and RAID0/5/6/10 stripe
+ *			boundaries.
+ *
+ * @bioc_ret:		(Mandatory) returned btrfs_io_context structure.
+ *			which has one or more physical ranges (btrfs_io_stripe)
+ *			recorded inside.
+ *			Caller should call btrfs_put_bioc() to free it after use.
+ *
+ * @smap:		(Optional) single physical range optimization.
+ *			If the map request can be fulfilled by one single
+ *			physical range, and this is parameter is not NULL,
+ *			then @bioc_ret would be NULL, and @smap would be
+ *			updated.
+ *
+ * @mirror_num_ret:	(Mandatory) returned mirror number if the original
+ *			value is 0.
+ *
+ *			Mirror number 0 means to choose any live mirrors.
+ *
+ *			For non-RAID56 profiles, non-zero mirror_num means
+ *			the Nth mirror. (e.g. mirror_num 1 means the first
+ *			copy).
+ *
+ *			For RAID56 profile, mirror 1 means rebuild from P and
+ *			the remaining data stripes.
+ *
+ *			For RAID6 profile, mirror > 2 means mark another
+ *			data/P stripe error and rebuild from the remaining
+ *			stripes..
+ *
+ * @need_raid_map:	(Used only for integrity checker) whether the map wants
+ *                      a full stripe map (including all data and P/Q stripes)
+ *                      for RAID56. Should always be 1 except integrity checker.
+ */
+int btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op,
+		    u64 logical, u64 *length,
+		    struct btrfs_io_context **bioc_ret,
+		    struct btrfs_io_stripe *smap, int *mirror_num_ret,
+		    int need_raid_map)
+{
+	struct extent_map *em;
+	struct map_lookup *map;
+	u64 map_offset;
+	u64 stripe_offset;
+	u32 stripe_nr;
+	u32 stripe_index;
+	int data_stripes;
+	int i;
+	int ret = 0;
+	int mirror_num = (mirror_num_ret ? *mirror_num_ret : 0);
+	int num_stripes;
+	int num_copies;
+	int max_errors = 0;
+	struct btrfs_io_context *bioc = NULL;
+	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
+	int dev_replace_is_ongoing = 0;
+	u16 num_alloc_stripes;
+	u64 raid56_full_stripe_start = (u64)-1;
+	u64 max_len;
+
+	ASSERT(bioc_ret);
+
+	num_copies = btrfs_num_copies(fs_info, logical, fs_info->sectorsize);
+	if (mirror_num > num_copies)
+		return -EINVAL;
+
+	em = btrfs_get_chunk_map(fs_info, logical, *length);
+	if (IS_ERR(em))
+		return PTR_ERR(em);
+
+	map = em->map_lookup;
+	data_stripes = nr_data_stripes(map);
+
+	map_offset = logical - em->start;
+	max_len = btrfs_max_io_len(map, op, map_offset, &stripe_nr,
+				   &stripe_offset, &raid56_full_stripe_start);
+	*length = min_t(u64, em->len - map_offset, max_len);
+
+	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);
+
+	num_stripes = 1;
+	stripe_index = 0;
+	if (map->type & BTRFS_BLOCK_GROUP_RAID0) {
+		stripe_index = stripe_nr % map->num_stripes;
+		stripe_nr /= map->num_stripes;
+		if (op == BTRFS_MAP_READ)
+			mirror_num = 1;
+	} else if (map->type & BTRFS_BLOCK_GROUP_RAID1_MASK) {
+		if (op != BTRFS_MAP_READ) {
+			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 (op != BTRFS_MAP_READ) {
+			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_index = (stripe_nr % factor) * map->sub_stripes;
+		stripe_nr /= factor;
+
+		if (op != BTRFS_MAP_READ)
+			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 && (op != BTRFS_MAP_READ || mirror_num > 1)) {
+			/*
+			 * Push stripe_nr back to the start of the full stripe
+			 * For those cases needing a full stripe, @stripe_nr
+			 * is the full stripe number.
+			 *
+			 * Originally we go raid56_full_stripe_start / full_stripe_len,
+			 * but that can be expensive.  Here we just divide
+			 * @stripe_nr with @data_stripes.
+			 */
+			stripe_nr /= data_stripes;
+
+			/* RAID[56] write or recovery. Return all stripes */
+			num_stripes = map->num_stripes;
+			max_errors = btrfs_chunk_max_errors(map);
+
+			/* Return the length to the full stripe end */
+			*length = min(logical + *length,
+				      raid56_full_stripe_start + em->start +
+				      btrfs_stripe_nr_to_offset(data_stripes)) -
+				  logical;
+			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_index = stripe_nr % data_stripes;
+			stripe_nr /= data_stripes;
+			if (mirror_num > 1)
+				stripe_index = data_stripes + mirror_num - 2;
+
+			/* We distribute the parity blocks across stripes */
+			stripe_index = (stripe_nr + stripe_index) % map->num_stripes;
+			if (op == BTRFS_MAP_READ && 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_index = stripe_nr % map->num_stripes;
+		stripe_nr /= map->num_stripes;
+		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 &&
+	    op != BTRFS_MAP_READ)
+		/*
+		 * For replace case, we need to add extra stripes for extra
+		 * duplicated stripes.
+		 *
+		 * For both WRITE and GET_READ_MIRRORS, we may have at most
+		 * 2 more stripes (DUP types, otherwise 1).
+		 */
+		num_alloc_stripes += 2;
+
+	/*
+	 * If this I/O maps to a single device, try to return the device and
+	 * physical block information on the stack instead of allocating an
+	 * I/O context structure.
+	 */
+	if (smap && num_alloc_stripes == 1 &&
+	    !((map->type & BTRFS_BLOCK_GROUP_RAID56_MASK) && mirror_num > 1)) {
+		set_io_stripe(smap, map, stripe_index, stripe_offset, stripe_nr);
+		if (mirror_num_ret)
+			*mirror_num_ret = mirror_num;
+		*bioc_ret = NULL;
+		ret = 0;
+		goto out;
+	}
+
+	bioc = alloc_btrfs_io_context(fs_info, num_alloc_stripes);
+	if (!bioc) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	bioc->map_type = map->type;
+
+	/*
+	 * For RAID56 full map, we need to make sure the stripes[] follows the
+	 * rule that data stripes are all ordered, then followed with P and Q
+	 * (if we have).
+	 *
+	 * It's still mostly the same as other profiles, just with extra rotation.
+	 */
+	if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK && need_raid_map &&
+	    (op != BTRFS_MAP_READ || mirror_num > 1)) {
+		/*
+		 * For RAID56 @stripe_nr is already the number of full stripes
+		 * before us, which is also the rotation value (needs to modulo
+		 * with num_stripes).
+		 *
+		 * In this case, we just add @stripe_nr with @i, then do the
+		 * modulo, to reduce one modulo call.
+		 */
+		bioc->full_stripe_logical = em->start +
+			btrfs_stripe_nr_to_offset(stripe_nr * data_stripes);
+		for (i = 0; i < num_stripes; i++)
+			set_io_stripe(&bioc->stripes[i], map,
+				      (i + stripe_nr) % num_stripes,
+				      stripe_offset, stripe_nr);
+	} else {
+		/*
+		 * For all other non-RAID56 profiles, just copy the target
+		 * stripe into the bioc.
+		 */
+		for (i = 0; i < num_stripes; i++) {
+			set_io_stripe(&bioc->stripes[i], map, stripe_index,
+				      stripe_offset, stripe_nr);
+			stripe_index++;
+		}
+	}
+
+	if (op != BTRFS_MAP_READ)
+		max_errors = btrfs_chunk_max_errors(map);
+
+	if (dev_replace_is_ongoing && dev_replace->tgtdev != NULL &&
+	    op != BTRFS_MAP_READ) {
+		handle_ops_on_dev_replace(op, bioc, dev_replace, logical,
+					  &num_stripes, &max_errors);
+	}
+
+	*bioc_ret = bioc;
+	bioc->num_stripes = num_stripes;
+	bioc->max_errors = max_errors;
+	bioc->mirror_num = mirror_num;
+
+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;
+}
+
+static bool dev_args_match_fs_devices(const struct btrfs_dev_lookup_args *args,
+				      const struct btrfs_fs_devices *fs_devices)
+{
+	if (args->fsid == NULL)
+		return true;
+	if (memcmp(fs_devices->metadata_uuid, args->fsid, BTRFS_FSID_SIZE) == 0)
+		return true;
+	return false;
+}
+
+static bool dev_args_match_device(const struct btrfs_dev_lookup_args *args,
+				  const struct btrfs_device *device)
+{
+	if (args->missing) {
+		if (test_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state) &&
+		    !device->bdev)
+			return true;
+		return false;
+	}
+
+	if (device->devid != args->devid)
+		return false;
+	if (args->uuid && memcmp(device->uuid, args->uuid, BTRFS_UUID_SIZE) != 0)
+		return false;
+	return true;
+}
+
+/*
+ * 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.
+ */
+struct btrfs_device *btrfs_find_device(const struct btrfs_fs_devices *fs_devices,
+				       const struct btrfs_dev_lookup_args *args)
+{
+	struct btrfs_device *device;
+	struct btrfs_fs_devices *seed_devs;
+
+	if (dev_args_match_fs_devices(args, fs_devices)) {
+		list_for_each_entry(device, &fs_devices->devices, dev_list) {
+			if (dev_args_match_device(args, device))
+				return device;
+		}
+	}
+
+	list_for_each_entry(seed_devs, &fs_devices->seed_list, seed_list) {
+		if (!dev_args_match_fs_devices(args, seed_devs))
+			continue;
+		list_for_each_entry(device, &seed_devs->devices, dev_list) {
+			if (dev_args_match_device(args, device))
+				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, NULL);
+	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;
+}
+
+/*
+ * Allocate new device struct, set up devid and UUID.
+ *
+ * @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.
+ * @path:	a pointer to device path if available, NULL otherwise.
+ *
+ * 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,
+					const char *path)
+{
+	struct btrfs_device *dev;
+	u64 tmp;
+
+	if (WARN_ON(!devid && !fs_info))
+		return ERR_PTR(-EINVAL);
+
+	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+	if (!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->dev_stats_ccnt, 0);
+	btrfs_device_data_ordered_init(dev);
+	extent_io_tree_init(fs_info, &dev->alloc_state, IO_TREE_DEVICE_ALLOC_STATE);
+
+	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);
+
+	if (path) {
+		struct rcu_string *name;
+
+		name = rcu_string_strdup(path, GFP_KERNEL);
+		if (!name) {
+			btrfs_free_device(dev);
+			return ERR_PTR(-ENOMEM);
+		}
+		rcu_assign_pointer(dev->name, name);
+	}
+
+	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);
+}
+
+u64 btrfs_calc_stripe_length(const struct extent_map *em)
+{
+	const struct map_lookup *map = em->map_lookup;
+	const int data_stripes = calc_data_stripes(map->type, map->num_stripes);
+
+	return div_u64(em->len, data_stripes);
+}
+
+#if BITS_PER_LONG == 32
+/*
+ * Due to page cache limit, metadata beyond BTRFS_32BIT_MAX_FILE_SIZE
+ * can't be accessed on 32bit systems.
+ *
+ * This function do mount time check to reject the fs if it already has
+ * metadata chunk beyond that limit.
+ */
+static int check_32bit_meta_chunk(struct btrfs_fs_info *fs_info,
+				  u64 logical, u64 length, u64 type)
+{
+	if (!(type & BTRFS_BLOCK_GROUP_METADATA))
+		return 0;
+
+	if (logical + length < MAX_LFS_FILESIZE)
+		return 0;
+
+	btrfs_err_32bit_limit(fs_info);
+	return -EOVERFLOW;
+}
+
+/*
+ * This is to give early warning for any metadata chunk reaching
+ * BTRFS_32BIT_EARLY_WARN_THRESHOLD.
+ * Although we can still access the metadata, it's not going to be possible
+ * once the limit is reached.
+ */
+static void warn_32bit_meta_chunk(struct btrfs_fs_info *fs_info,
+				  u64 logical, u64 length, u64 type)
+{
+	if (!(type & BTRFS_BLOCK_GROUP_METADATA))
+		return;
+
+	if (logical + length < BTRFS_32BIT_EARLY_WARN_THRESHOLD)
+		return;
+
+	btrfs_warn_32bit_limit(fs_info);
+}
+#endif
+
+static struct btrfs_device *handle_missing_device(struct btrfs_fs_info *fs_info,
+						  u64 devid, u8 *uuid)
+{
+	struct btrfs_device *dev;
+
+	if (!btrfs_test_opt(fs_info, DEGRADED)) {
+		btrfs_report_missing_device(fs_info, devid, uuid, true);
+		return ERR_PTR(-ENOENT);
+	}
+
+	dev = add_missing_dev(fs_info->fs_devices, devid, uuid);
+	if (IS_ERR(dev)) {
+		btrfs_err(fs_info, "failed to init missing device %llu: %ld",
+			  devid, PTR_ERR(dev));
+		return dev;
+	}
+	btrfs_report_missing_device(fs_info, devid, uuid, false);
+
+	return dev;
+}
+
+static int read_one_chunk(struct btrfs_key *key, struct extent_buffer *leaf,
+			  struct btrfs_chunk *chunk)
+{
+	BTRFS_DEV_LOOKUP_ARGS(args);
+	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;
+	u64 type;
+	u8 uuid[BTRFS_UUID_SIZE];
+	int index;
+	int num_stripes;
+	int ret;
+	int i;
+
+	logical = key->offset;
+	length = btrfs_chunk_length(leaf, chunk);
+	type = btrfs_chunk_type(leaf, chunk);
+	index = btrfs_bg_flags_to_raid_index(type);
+	num_stripes = btrfs_chunk_num_stripes(leaf, chunk);
+
+#if BITS_PER_LONG == 32
+	ret = check_32bit_meta_chunk(fs_info, logical, length, type);
+	if (ret < 0)
+		return ret;
+	warn_32bit_meta_chunk(fs_info, logical, length, type);
+#endif
+
+	/*
+	 * 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->type = type;
+	/*
+	 * We can't use the sub_stripes value, as for profiles other than
+	 * RAID10, they may have 0 as sub_stripes for filesystems created by
+	 * older mkfs (<v5.4).
+	 * In that case, it can cause divide-by-zero errors later.
+	 * Since currently sub_stripes is fixed for each profile, let's
+	 * use the trusted value instead.
+	 */
+	map->sub_stripes = btrfs_raid_array[index].sub_stripes;
+	map->verified_stripes = 0;
+	em->orig_block_len = btrfs_calc_stripe_length(em);
+	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);
+		args.devid = devid;
+		read_extent_buffer(leaf, uuid, (unsigned long)
+				   btrfs_stripe_dev_uuid_nr(chunk, i),
+				   BTRFS_UUID_SIZE);
+		args.uuid = uuid;
+		map->stripes[i].dev = btrfs_find_device(fs_info->fs_devices, &args);
+		if (!map->stripes[i].dev) {
+			map->stripes[i].dev = handle_missing_device(fs_info,
+								    devid, uuid);
+			if (IS_ERR(map->stripes[i].dev)) {
+				ret = PTR_ERR(map->stripes[i].dev);
+				free_extent_map(em);
+				return ret;
+			}
+		}
+
+		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, BLK_OPEN_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)
+{
+	BTRFS_DEV_LOOKUP_ARGS(args);
+	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);
+	args.devid = devid;
+	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);
+	args.uuid = dev_uuid;
+	args.fsid = fs_uuid;
+
+	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, &args);
+	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);
+	if (device->bdev) {
+		u64 max_total_bytes = bdev_nr_bytes(device->bdev);
+
+		if (device->total_bytes > max_total_bytes) {
+			btrfs_err(fs_info,
+			"device total_bytes should be at most %llu but found %llu",
+				  max_total_bytes, device->total_bytes);
+			return -EINVAL;
+		}
+	}
+	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_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);
+
+	/*
+	 * We allocated a dummy extent, just to use extent buffer accessors.
+	 * There will be unused space after BTRFS_SUPER_INFO_SIZE, but
+	 * that's fine, we will not go beyond system chunk array anyway.
+	 */
+	sb = alloc_dummy_extent_buffer(fs_info, BTRFS_SUPER_INFO_OFFSET);
+	if (!sb)
+		return -ENOMEM;
+	set_extent_buffer_uptodate(sb);
+
+	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++)
+		btrfs_readahead_node_child(node, i);
+}
+
+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;
+	int iter_ret = 0;
+	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;
+
+	/*
+	 * Lockdep complains about possible circular locking dependency between
+	 * a disk's open_mutex (struct gendisk.open_mutex), the rw semaphores
+	 * used for freeze procection of a fs (struct super_block.s_writers),
+	 * which we take when starting a transaction, and extent buffers of the
+	 * chunk tree if we call read_one_dev() while holding a lock on an
+	 * extent buffer of the chunk tree. Since we are mounting the filesystem
+	 * and at this point there can't be any concurrent task modifying the
+	 * chunk tree, to keep it simple, just skip locking on the chunk tree.
+	 */
+	ASSERT(!test_bit(BTRFS_FS_OPEN, &fs_info->flags));
+	path->skip_locking = 1;
+
+	/*
+	 * 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;
+	btrfs_for_each_slot(root, &key, &found_key, path, iter_ret) {
+		struct extent_buffer *node = path->nodes[1];
+
+		leaf = path->nodes[0];
+		slot = path->slots[0];
+
+		if (node) {
+			if (last_ra_node != node->start) {
+				readahead_tree_node_children(node);
+				last_ra_node = node->start;
+			}
+		}
+		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;
+
+			/*
+			 * We are only called at mount time, so no need to take
+			 * fs_info->chunk_mutex. Plus, to avoid lockdep warnings,
+			 * we always lock first fs_info->chunk_mutex before
+			 * acquiring any locks on the chunk tree. This is a
+			 * requirement for chunk allocation, see the comment on
+			 * top of btrfs_chunk_alloc() for details.
+			 */
+			chunk = btrfs_item_ptr(leaf, slot, struct btrfs_chunk);
+			ret = read_one_chunk(&found_key, leaf, chunk);
+			if (ret)
+				goto error;
+		}
+	}
+	/* Catch error found during iteration */
+	if (iter_ret < 0) {
+		ret = iter_ret;
+		goto error;
+	}
+
+	/*
+	 * 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;
+}
+
+int 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;
+	int ret = 0;
+
+	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;
+			ret = btrfs_get_dev_zone_info(device, false);
+			if (ret)
+				break;
+		}
+
+		seed_devs->fs_info = fs_info;
+	}
+	mutex_unlock(&fs_devices->device_list_mutex);
+
+	return ret;
+}
+
+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;
+
+	if (!device->fs_info->dev_root)
+		return 0;
+
+	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(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, btrfs_dev_name(device));
+		goto out;
+	}
+
+	if (ret == 0 &&
+	    btrfs_item_size(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",
+					  btrfs_dev_name(device), 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",
+				btrfs_dev_name(device), 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(trans, 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);
+
+	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",
+			   btrfs_dev_name(dev),
+			   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",
+	       btrfs_dev_name(dev),
+	       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)
+{
+	BTRFS_DEV_LOOKUP_ARGS(args);
+	struct btrfs_device *dev;
+	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
+	int i;
+
+	mutex_lock(&fs_devices->device_list_mutex);
+	args.devid = stats->devid;
+	dev = btrfs_find_device(fs_info->fs_devices, &args);
+	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 btrfs_dev_lookup_args args = { .devid = devid };
+	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 = btrfs_calc_stripe_length(em);
+	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;
+	}
+
+	/*
+	 * Very old mkfs.btrfs (before v4.1) will not respect the reserved
+	 * space. Although kernel can handle it without problem, better to warn
+	 * the users.
+	 */
+	if (physical_offset < BTRFS_DEVICE_RANGE_RESERVED)
+		btrfs_warn(fs_info,
+		"devid %llu physical %llu len %llu inside the reserved space",
+			   devid, physical_offset, physical_len);
+
+	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 boundary */
+	dev = btrfs_find_device(fs_info->fs_devices, &args);
+	if (!dev) {
+		btrfs_err(fs_info, "failed to find 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;
+	}
+
+	if (dev->zone_info) {
+		u64 zone_size = dev->zone_info->zone_size;
+
+		if (!IS_ALIGNED(physical_offset, zone_size) ||
+		    !IS_ALIGNED(physical_len, zone_size)) {
+			btrfs_err(fs_info,
+"zoned: dev extent devid %llu physical offset %llu len %llu is not aligned to device zone",
+				  devid, physical_offset, physical_len);
+			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;
+
+	/*
+	 * We don't have a dev_root because we mounted with ignorebadroots and
+	 * failed to load the root, so we want to skip the verification in this
+	 * case for sure.
+	 *
+	 * However if the dev root is fine, but the tree itself is corrupted
+	 * we'd still fail to mount.  This verification is only to make sure
+	 * writes can happen safely, so instead just bypass this check
+	 * completely in the case of IGNOREBADROOTS.
+	 */
+	if (btrfs_test_opt(fs_info, IGNOREBADROOTS))
+		return 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_leaf(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;
+}
+
+static int relocating_repair_kthread(void *data)
+{
+	struct btrfs_block_group *cache = data;
+	struct btrfs_fs_info *fs_info = cache->fs_info;
+	u64 target;
+	int ret = 0;
+
+	target = cache->start;
+	btrfs_put_block_group(cache);
+
+	sb_start_write(fs_info->sb);
+	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE)) {
+		btrfs_info(fs_info,
+			   "zoned: skip relocating block group %llu to repair: EBUSY",
+			   target);
+		sb_end_write(fs_info->sb);
+		return -EBUSY;
+	}
+
+	mutex_lock(&fs_info->reclaim_bgs_lock);
+
+	/* Ensure block group still exists */
+	cache = btrfs_lookup_block_group(fs_info, target);
+	if (!cache)
+		goto out;
+
+	if (!test_bit(BLOCK_GROUP_FLAG_RELOCATING_REPAIR, &cache->runtime_flags))
+		goto out;
+
+	ret = btrfs_may_alloc_data_chunk(fs_info, target);
+	if (ret < 0)
+		goto out;
+
+	btrfs_info(fs_info,
+		   "zoned: relocating block group %llu to repair IO failure",
+		   target);
+	ret = btrfs_relocate_chunk(fs_info, target);
+
+out:
+	if (cache)
+		btrfs_put_block_group(cache);
+	mutex_unlock(&fs_info->reclaim_bgs_lock);
+	btrfs_exclop_finish(fs_info);
+	sb_end_write(fs_info->sb);
+
+	return ret;
+}
+
+bool btrfs_repair_one_zone(struct btrfs_fs_info *fs_info, u64 logical)
+{
+	struct btrfs_block_group *cache;
+
+	if (!btrfs_is_zoned(fs_info))
+		return false;
+
+	/* Do not attempt to repair in degraded state */
+	if (btrfs_test_opt(fs_info, DEGRADED))
+		return true;
+
+	cache = btrfs_lookup_block_group(fs_info, logical);
+	if (!cache)
+		return true;
+
+	if (test_and_set_bit(BLOCK_GROUP_FLAG_RELOCATING_REPAIR, &cache->runtime_flags)) {
+		btrfs_put_block_group(cache);
+		return true;
+	}
+
+	kthread_run(relocating_repair_kthread, cache,
+		    "btrfs-relocating-repair");
+
+	return true;
+}
+
+static void map_raid56_repair_block(struct btrfs_io_context *bioc,
+				    struct btrfs_io_stripe *smap,
+				    u64 logical)
+{
+	int data_stripes = nr_bioc_data_stripes(bioc);
+	int i;
+
+	for (i = 0; i < data_stripes; i++) {
+		u64 stripe_start = bioc->full_stripe_logical +
+				   btrfs_stripe_nr_to_offset(i);
+
+		if (logical >= stripe_start &&
+		    logical < stripe_start + BTRFS_STRIPE_LEN)
+			break;
+	}
+	ASSERT(i < data_stripes);
+	smap->dev = bioc->stripes[i].dev;
+	smap->physical = bioc->stripes[i].physical +
+			((logical - bioc->full_stripe_logical) &
+			 BTRFS_STRIPE_LEN_MASK);
+}
+
+/*
+ * Map a repair write into a single device.
+ *
+ * A repair write is triggered by read time repair or scrub, which would only
+ * update the contents of a single device.
+ * Not update any other mirrors nor go through RMW path.
+ *
+ * Callers should ensure:
+ *
+ * - Call btrfs_bio_counter_inc_blocked() first
+ * - The range does not cross stripe boundary
+ * - Has a valid @mirror_num passed in.
+ */
+int btrfs_map_repair_block(struct btrfs_fs_info *fs_info,
+			   struct btrfs_io_stripe *smap, u64 logical,
+			   u32 length, int mirror_num)
+{
+	struct btrfs_io_context *bioc = NULL;
+	u64 map_length = length;
+	int mirror_ret = mirror_num;
+	int ret;
+
+	ASSERT(mirror_num > 0);
+
+	ret = btrfs_map_block(fs_info, BTRFS_MAP_WRITE, logical, &map_length,
+			      &bioc, smap, &mirror_ret, true);
+	if (ret < 0)
+		return ret;
+
+	/* The map range should not cross stripe boundary. */
+	ASSERT(map_length >= length);
+
+	/* Already mapped to single stripe. */
+	if (!bioc)
+		goto out;
+
+	/* Map the RAID56 multi-stripe writes to a single one. */
+	if (bioc->map_type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
+		map_raid56_repair_block(bioc, smap, logical);
+		goto out;
+	}
+
+	ASSERT(mirror_num <= bioc->num_stripes);
+	smap->dev = bioc->stripes[mirror_num - 1].dev;
+	smap->physical = bioc->stripes[mirror_num - 1].physical;
+out:
+	btrfs_put_bioc(bioc);
+	ASSERT(smap->dev);
+	return 0;
+}