// SPDX-License-Identifier: GPL-2.0

  /*
   * Copyright (C) STRATO AG 2012.  All rights reserved.

   */

  #include <linux/sched.h>
  #include <linux/bio.h>
  #include <linux/slab.h>

  #include <linux/blkdev.h>

  #include <linux/kthread.h>
  #include <linux/math64.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 "async-thread.h"
  #include "check-integrity.h"
  #include "rcu-string.h"
  #include "dev-replace.h"

  #include "sysfs.h"

  /*
   * Device replace overview
   *
   * [Objective]
   * To copy all extents (both new and on-disk) from source device to target
   * device, while still keeping the filesystem read-write.
   *
   * [Method]
   * There are two main methods involved:
   *
   * - Write duplication
   *
   *   All new writes will be written to both target and source devices, so even
   *   if replace gets canceled, sources device still contans up-to-date data.
   *
   *   Location:		handle_ops_on_dev_replace() from __btrfs_map_block()
   *   Start:		btrfs_dev_replace_start()
   *   End:		btrfs_dev_replace_finishing()
   *   Content:		Latest data/metadata
   *
   * - Copy existing extents
   *
   *   This happens by re-using scrub facility, as scrub also iterates through
   *   existing extents from commit root.
   *
   *   Location:		scrub_write_block_to_dev_replace() from
   *   			scrub_block_complete()
   *   Content:		Data/meta from commit root.
   *
   * Due to the content difference, we need to avoid nocow write when dev-replace
   * is happening.  This is done by marking the block group read-only and waiting
   * for NOCOW writes.
   *
   * After replace is done, the finishing part is done by swapping the target and
   * source devices.
   *
   *   Location:		btrfs_dev_replace_update_device_in_mapping_tree() from
   *   			btrfs_dev_replace_finishing()
   */

  static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info,
  				       int scrub_ret);

  static int btrfs_dev_replace_kthread(void *data);

  
  int btrfs_init_dev_replace(struct btrfs_fs_info *fs_info)
  {
  	struct btrfs_key key;
  	struct btrfs_root *dev_root = fs_info->dev_root;
  	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
  	struct extent_buffer *eb;
  	int slot;
  	int ret = 0;
  	struct btrfs_path *path = NULL;
  	int item_size;
  	struct btrfs_dev_replace_item *ptr;
  	u64 src_devid;
  
  	path = btrfs_alloc_path();
  	if (!path) {
  		ret = -ENOMEM;
  		goto out;
  	}
  
  	key.objectid = 0;
  	key.type = BTRFS_DEV_REPLACE_KEY;
  	key.offset = 0;
  	ret = btrfs_search_slot(NULL, dev_root, &key, path, 0, 0);
  	if (ret) {
  no_valid_dev_replace_entry_found:

  		/*
  		 * We don't have a replace item or it's corrupted.  If there is
  		 * a replace target, fail the mount.
  		 */
  		if (btrfs_find_device(fs_info->fs_devices,
  				      BTRFS_DEV_REPLACE_DEVID, NULL, NULL, false)) {
  			btrfs_err(fs_info,
  			"found replace target device without a valid replace item");
  			ret = -EUCLEAN;
  			goto out;
  		}

  		ret = 0;
  		dev_replace->replace_state =

  			BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED;

  		dev_replace->cont_reading_from_srcdev_mode =
  		    BTRFS_DEV_REPLACE_ITEM_CONT_READING_FROM_SRCDEV_MODE_ALWAYS;

  		dev_replace->time_started = 0;
  		dev_replace->time_stopped = 0;
  		atomic64_set(&dev_replace->num_write_errors, 0);
  		atomic64_set(&dev_replace->num_uncorrectable_read_errors, 0);
  		dev_replace->cursor_left = 0;
  		dev_replace->committed_cursor_left = 0;
  		dev_replace->cursor_left_last_write_of_item = 0;
  		dev_replace->cursor_right = 0;
  		dev_replace->srcdev = NULL;
  		dev_replace->tgtdev = NULL;
  		dev_replace->is_valid = 0;
  		dev_replace->item_needs_writeback = 0;
  		goto out;
  	}
  	slot = path->slots[0];
  	eb = path->nodes[0];
  	item_size = btrfs_item_size_nr(eb, slot);
  	ptr = btrfs_item_ptr(eb, slot, struct btrfs_dev_replace_item);
  
  	if (item_size != sizeof(struct btrfs_dev_replace_item)) {

  		btrfs_warn(fs_info,
  			"dev_replace entry found has unexpected size, ignore entry");

  		goto no_valid_dev_replace_entry_found;
  	}
  
  	src_devid = btrfs_dev_replace_src_devid(eb, ptr);
  	dev_replace->cont_reading_from_srcdev_mode =
  		btrfs_dev_replace_cont_reading_from_srcdev_mode(eb, ptr);
  	dev_replace->replace_state = btrfs_dev_replace_replace_state(eb, ptr);
  	dev_replace->time_started = btrfs_dev_replace_time_started(eb, ptr);
  	dev_replace->time_stopped =
  		btrfs_dev_replace_time_stopped(eb, ptr);
  	atomic64_set(&dev_replace->num_write_errors,
  		     btrfs_dev_replace_num_write_errors(eb, ptr));
  	atomic64_set(&dev_replace->num_uncorrectable_read_errors,
  		     btrfs_dev_replace_num_uncorrectable_read_errors(eb, ptr));
  	dev_replace->cursor_left = btrfs_dev_replace_cursor_left(eb, ptr);
  	dev_replace->committed_cursor_left = dev_replace->cursor_left;
  	dev_replace->cursor_left_last_write_of_item = dev_replace->cursor_left;
  	dev_replace->cursor_right = btrfs_dev_replace_cursor_right(eb, ptr);
  	dev_replace->is_valid = 1;
  
  	dev_replace->item_needs_writeback = 0;
  	switch (dev_replace->replace_state) {
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_FINISHED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_CANCELED:

  		/*
  		 * We don't have an active replace item but if there is a
  		 * replace target, fail the mount.
  		 */
  		if (btrfs_find_device(fs_info->fs_devices,
  				      BTRFS_DEV_REPLACE_DEVID, NULL, NULL, false)) {
  			btrfs_err(fs_info,
  			"replace devid present without an active replace item");
  			ret = -EUCLEAN;
  		} else {
  			dev_replace->srcdev = NULL;
  			dev_replace->tgtdev = NULL;
  		}

  		break;
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED:

  		dev_replace->srcdev = btrfs_find_device(fs_info->fs_devices,

  						src_devid, NULL, NULL, true);

  		dev_replace->tgtdev = btrfs_find_device(fs_info->fs_devices,

  							BTRFS_DEV_REPLACE_DEVID,

  							NULL, NULL, true);

  		/*
  		 * allow 'btrfs dev replace_cancel' if src/tgt device is
  		 * missing
  		 */
  		if (!dev_replace->srcdev &&

  		    !btrfs_test_opt(fs_info, DEGRADED)) {

  			ret = -EIO;

  			btrfs_warn(fs_info,
  			   "cannot mount because device replace operation is ongoing and");
  			btrfs_warn(fs_info,
  			   "srcdev (devid %llu) is missing, need to run 'btrfs dev scan'?",
  			   src_devid);

  		}
  		if (!dev_replace->tgtdev &&

  		    !btrfs_test_opt(fs_info, DEGRADED)) {

  			ret = -EIO;

  			btrfs_warn(fs_info,
  			   "cannot mount because device replace operation is ongoing and");
  			btrfs_warn(fs_info,
  			   "tgtdev (devid %llu) is missing, need to run 'btrfs dev scan'?",

  				BTRFS_DEV_REPLACE_DEVID);

  		}
  		if (dev_replace->tgtdev) {
  			if (dev_replace->srcdev) {
  				dev_replace->tgtdev->total_bytes =
  					dev_replace->srcdev->total_bytes;
  				dev_replace->tgtdev->disk_total_bytes =
  					dev_replace->srcdev->disk_total_bytes;

  				dev_replace->tgtdev->commit_total_bytes =
  					dev_replace->srcdev->commit_total_bytes;

  				dev_replace->tgtdev->bytes_used =
  					dev_replace->srcdev->bytes_used;

  				dev_replace->tgtdev->commit_bytes_used =
  					dev_replace->srcdev->commit_bytes_used;

  			}

  			set_bit(BTRFS_DEV_STATE_REPLACE_TGT,
  				&dev_replace->tgtdev->dev_state);

  
  			WARN_ON(fs_info->fs_devices->rw_devices == 0);
  			dev_replace->tgtdev->io_width = fs_info->sectorsize;
  			dev_replace->tgtdev->io_align = fs_info->sectorsize;
  			dev_replace->tgtdev->sector_size = fs_info->sectorsize;
  			dev_replace->tgtdev->fs_info = fs_info;
  			set_bit(BTRFS_DEV_STATE_IN_FS_METADATA,
  				&dev_replace->tgtdev->dev_state);

  		}
  		break;
  	}
  
  out:

  	btrfs_free_path(path);

  	return ret;
  }
  
  /*

   * Initialize a new device for device replace target from a given source dev
   * and path.
   *
   * Return 0 and new device in @device_out, otherwise return < 0
   */
  static int btrfs_init_dev_replace_tgtdev(struct btrfs_fs_info *fs_info,
  				  const char *device_path,
  				  struct btrfs_device *srcdev,
  				  struct btrfs_device **device_out)
  {
  	struct btrfs_device *device;
  	struct block_device *bdev;

  	struct rcu_string *name;
  	u64 devid = BTRFS_DEV_REPLACE_DEVID;
  	int ret = 0;
  
  	*device_out = NULL;

  	if (srcdev->fs_devices->seeding) {

  		btrfs_err(fs_info, "the filesystem is a seed filesystem!");
  		return -EINVAL;
  	}
  
  	bdev = blkdev_get_by_path(device_path, FMODE_WRITE | FMODE_EXCL,
  				  fs_info->bdev_holder);
  	if (IS_ERR(bdev)) {
  		btrfs_err(fs_info, "target device %s is invalid!", device_path);
  		return PTR_ERR(bdev);
  	}

  	sync_blockdev(bdev);

  	list_for_each_entry(device, &fs_info->fs_devices->devices, dev_list) {

  		if (device->bdev == bdev) {
  			btrfs_err(fs_info,
  				  "target device is in the filesystem!");
  			ret = -EEXIST;
  			goto error;
  		}
  	}
  
  
  	if (i_size_read(bdev->bd_inode) <
  	    btrfs_device_get_total_bytes(srcdev)) {
  		btrfs_err(fs_info,
  			  "target device is smaller than source device!");
  		ret = -EINVAL;
  		goto error;
  	}
  
  
  	device = btrfs_alloc_device(NULL, &devid, NULL);
  	if (IS_ERR(device)) {
  		ret = PTR_ERR(device);
  		goto error;
  	}
  
  	name = rcu_string_strdup(device_path, GFP_KERNEL);
  	if (!name) {
  		btrfs_free_device(device);
  		ret = -ENOMEM;
  		goto error;
  	}
  	rcu_assign_pointer(device->name, name);

  	set_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
  	device->generation = 0;
  	device->io_width = fs_info->sectorsize;
  	device->io_align = fs_info->sectorsize;
  	device->sector_size = fs_info->sectorsize;
  	device->total_bytes = btrfs_device_get_total_bytes(srcdev);
  	device->disk_total_bytes = btrfs_device_get_disk_total_bytes(srcdev);
  	device->bytes_used = btrfs_device_get_bytes_used(srcdev);
  	device->commit_total_bytes = srcdev->commit_total_bytes;
  	device->commit_bytes_used = device->bytes_used;
  	device->fs_info = fs_info;
  	device->bdev = bdev;
  	set_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
  	set_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state);
  	device->mode = FMODE_EXCL;
  	device->dev_stats_valid = 1;
  	set_blocksize(device->bdev, BTRFS_BDEV_BLOCKSIZE);
  	device->fs_devices = fs_info->fs_devices;

  
  	mutex_lock(&fs_info->fs_devices->device_list_mutex);

  	list_add(&device->dev_list, &fs_info->fs_devices->devices);
  	fs_info->fs_devices->num_devices++;
  	fs_info->fs_devices->open_devices++;
  	mutex_unlock(&fs_info->fs_devices->device_list_mutex);
  
  	*device_out = device;
  	return 0;
  
  error:
  	blkdev_put(bdev, FMODE_EXCL);
  	return ret;
  }
  
  /*

   * called from commit_transaction. Writes changed device replace state to
   * disk.
   */

  int btrfs_run_dev_replace(struct btrfs_trans_handle *trans)

  {

  	struct btrfs_fs_info *fs_info = trans->fs_info;

  	int ret;
  	struct btrfs_root *dev_root = fs_info->dev_root;
  	struct btrfs_path *path;
  	struct btrfs_key key;
  	struct extent_buffer *eb;
  	struct btrfs_dev_replace_item *ptr;
  	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;

  	down_read(&dev_replace->rwsem);

  	if (!dev_replace->is_valid ||
  	    !dev_replace->item_needs_writeback) {

  		up_read(&dev_replace->rwsem);

  		return 0;
  	}

  	up_read(&dev_replace->rwsem);

  
  	key.objectid = 0;
  	key.type = BTRFS_DEV_REPLACE_KEY;
  	key.offset = 0;
  
  	path = btrfs_alloc_path();
  	if (!path) {
  		ret = -ENOMEM;
  		goto out;
  	}
  	ret = btrfs_search_slot(trans, dev_root, &key, path, -1, 1);
  	if (ret < 0) {

  		btrfs_warn(fs_info,
  			   "error %d while searching for dev_replace item!",
  			   ret);

  		goto out;
  	}
  
  	if (ret == 0 &&
  	    btrfs_item_size_nr(path->nodes[0], path->slots[0]) < sizeof(*ptr)) {
  		/*
  		 * need to delete old one and insert a new one.
  		 * Since no attempt is made to recover any old state, if the
  		 * dev_replace state is 'running', the data on the target
  		 * drive is lost.
  		 * It would be possible to recover the state: just make sure
  		 * that the beginning of the item is never changed and always
  		 * contains all the essential information. Then read this
  		 * minimal set of information and use it as a base for the
  		 * new state.
  		 */
  		ret = btrfs_del_item(trans, dev_root, path);
  		if (ret != 0) {

  			btrfs_warn(fs_info,
  				   "delete too small dev_replace item failed %d!",
  				   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(fs_info,
  				   "insert dev_replace item failed %d!", ret);

  			goto out;
  		}
  	}
  
  	eb = path->nodes[0];
  	ptr = btrfs_item_ptr(eb, path->slots[0],
  			     struct btrfs_dev_replace_item);

  	down_write(&dev_replace->rwsem);

  	if (dev_replace->srcdev)
  		btrfs_set_dev_replace_src_devid(eb, ptr,
  			dev_replace->srcdev->devid);
  	else
  		btrfs_set_dev_replace_src_devid(eb, ptr, (u64)-1);
  	btrfs_set_dev_replace_cont_reading_from_srcdev_mode(eb, ptr,
  		dev_replace->cont_reading_from_srcdev_mode);
  	btrfs_set_dev_replace_replace_state(eb, ptr,
  		dev_replace->replace_state);
  	btrfs_set_dev_replace_time_started(eb, ptr, dev_replace->time_started);
  	btrfs_set_dev_replace_time_stopped(eb, ptr, dev_replace->time_stopped);
  	btrfs_set_dev_replace_num_write_errors(eb, ptr,
  		atomic64_read(&dev_replace->num_write_errors));
  	btrfs_set_dev_replace_num_uncorrectable_read_errors(eb, ptr,
  		atomic64_read(&dev_replace->num_uncorrectable_read_errors));
  	dev_replace->cursor_left_last_write_of_item =
  		dev_replace->cursor_left;
  	btrfs_set_dev_replace_cursor_left(eb, ptr,
  		dev_replace->cursor_left_last_write_of_item);
  	btrfs_set_dev_replace_cursor_right(eb, ptr,
  		dev_replace->cursor_right);
  	dev_replace->item_needs_writeback = 0;

  	up_write(&dev_replace->rwsem);

  
  	btrfs_mark_buffer_dirty(eb);
  
  out:
  	btrfs_free_path(path);
  
  	return ret;
  }

  static char* btrfs_dev_name(struct btrfs_device *device)
  {

  	if (!device || test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))

  		return "<missing disk>";
  	else
  		return rcu_str_deref(device->name);
  }

  static int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,

  		const char *tgtdev_name, u64 srcdevid, const char *srcdev_name,
  		int read_src)

  {

  	struct btrfs_root *root = fs_info->dev_root;

  	struct btrfs_trans_handle *trans;

  	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
  	int ret;
  	struct btrfs_device *tgt_device = NULL;
  	struct btrfs_device *src_device = NULL;

  	src_device = btrfs_find_device_by_devspec(fs_info, srcdevid,
  						  srcdev_name);
  	if (IS_ERR(src_device))
  		return PTR_ERR(src_device);

  	if (btrfs_pinned_by_swapfile(fs_info, src_device)) {
  		btrfs_warn_in_rcu(fs_info,
  	  "cannot replace device %s (devid %llu) due to active swapfile",
  			btrfs_dev_name(src_device), src_device->devid);
  		return -ETXTBSY;
  	}

  	/*
  	 * Here we commit the transaction to make sure commit_total_bytes
  	 * of all the devices are updated.
  	 */
  	trans = btrfs_attach_transaction(root);
  	if (!IS_ERR(trans)) {

  		ret = btrfs_commit_transaction(trans);

  		if (ret)
  			return ret;
  	} else if (PTR_ERR(trans) != -ENOENT) {
  		return PTR_ERR(trans);
  	}

  	ret = btrfs_init_dev_replace_tgtdev(fs_info, tgtdev_name,
  					    src_device, &tgt_device);
  	if (ret)
  		return ret;

  	down_write(&dev_replace->rwsem);

  	switch (dev_replace->replace_state) {
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_FINISHED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_CANCELED:
  		break;
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED:

  		ASSERT(0);

  		ret = BTRFS_IOCTL_DEV_REPLACE_RESULT_ALREADY_STARTED;

  		up_write(&dev_replace->rwsem);

  		goto leave;
  	}

  	dev_replace->cont_reading_from_srcdev_mode = read_src;

  	dev_replace->srcdev = src_device;

  	dev_replace->tgtdev = tgt_device;

  	btrfs_info_in_rcu(fs_info,

  		      "dev_replace from %s (devid %llu) to %s started",

  		      btrfs_dev_name(src_device),

  		      src_device->devid,
  		      rcu_str_deref(tgt_device->name));

  	/*
  	 * from now on, the writes to the srcdev are all duplicated to
  	 * go to the tgtdev as well (refer to btrfs_map_block()).
  	 */
  	dev_replace->replace_state = BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED;

  	dev_replace->time_started = ktime_get_real_seconds();

  	dev_replace->cursor_left = 0;
  	dev_replace->committed_cursor_left = 0;
  	dev_replace->cursor_left_last_write_of_item = 0;
  	dev_replace->cursor_right = 0;
  	dev_replace->is_valid = 1;
  	dev_replace->item_needs_writeback = 1;

  	atomic64_set(&dev_replace->num_write_errors, 0);
  	atomic64_set(&dev_replace->num_uncorrectable_read_errors, 0);

  	up_write(&dev_replace->rwsem);

  	ret = btrfs_sysfs_add_device(tgt_device);

  	if (ret)

  		btrfs_err(fs_info, "kobj add dev failed %d", ret);

  	btrfs_wait_ordered_roots(fs_info, U64_MAX, 0, (u64)-1);

  	/* Commit dev_replace state and reserve 1 item for it. */
  	trans = btrfs_start_transaction(root, 1);

  	if (IS_ERR(trans)) {
  		ret = PTR_ERR(trans);

  		down_write(&dev_replace->rwsem);

  		dev_replace->replace_state =
  			BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED;
  		dev_replace->srcdev = NULL;
  		dev_replace->tgtdev = NULL;

  		up_write(&dev_replace->rwsem);

  		goto leave;
  	}

  	ret = btrfs_commit_transaction(trans);

  	WARN_ON(ret);
  
  	/* the disk copy procedure reuses the scrub code */
  	ret = btrfs_scrub_dev(fs_info, src_device->devid, 0,

  			      btrfs_device_get_total_bytes(src_device),

  			      &dev_replace->scrub_progress, 0, 1);

  	ret = btrfs_dev_replace_finishing(fs_info, ret);

  	if (ret == -EINPROGRESS)

  		ret = BTRFS_IOCTL_DEV_REPLACE_RESULT_SCRUB_INPROGRESS;

  	return ret;

  
  leave:

  	btrfs_destroy_dev_replace_tgtdev(tgt_device);

  	return ret;
  }

  int btrfs_dev_replace_by_ioctl(struct btrfs_fs_info *fs_info,

  			    struct btrfs_ioctl_dev_replace_args *args)
  {
  	int ret;
  
  	switch (args->start.cont_reading_from_srcdev_mode) {
  	case BTRFS_IOCTL_DEV_REPLACE_CONT_READING_FROM_SRCDEV_MODE_ALWAYS:
  	case BTRFS_IOCTL_DEV_REPLACE_CONT_READING_FROM_SRCDEV_MODE_AVOID:
  		break;
  	default:
  		return -EINVAL;
  	}
  
  	if ((args->start.srcdevid == 0 && args->start.srcdev_name[0] == '\0') ||
  	    args->start.tgtdev_name[0] == '\0')
  		return -EINVAL;

  	ret = btrfs_dev_replace_start(fs_info, args->start.tgtdev_name,

  					args->start.srcdevid,
  					args->start.srcdev_name,
  					args->start.cont_reading_from_srcdev_mode);
  	args->result = ret;
  	/* don't warn if EINPROGRESS, someone else might be running scrub */

  	if (ret == BTRFS_IOCTL_DEV_REPLACE_RESULT_SCRUB_INPROGRESS ||
  	    ret == BTRFS_IOCTL_DEV_REPLACE_RESULT_NO_ERROR)
  		return 0;

  
  	return ret;
  }

  /*

   * blocked until all in-flight bios operations are finished.

   */
  static void btrfs_rm_dev_replace_blocked(struct btrfs_fs_info *fs_info)
  {

  	set_bit(BTRFS_FS_STATE_DEV_REPLACING, &fs_info->fs_state);

  	wait_event(fs_info->dev_replace.replace_wait, !percpu_counter_sum(
  		   &fs_info->dev_replace.bio_counter));

  }
  
  /*
   * we have removed target device, it is safe to allow new bios request.
   */
  static void btrfs_rm_dev_replace_unblocked(struct btrfs_fs_info *fs_info)
  {
  	clear_bit(BTRFS_FS_STATE_DEV_REPLACING, &fs_info->fs_state);

  	wake_up(&fs_info->dev_replace.replace_wait);

  }

  /*
   * When finishing the device replace, before swapping the source device with the
   * target device we must update the chunk allocation state in the target device,
   * as it is empty because replace works by directly copying the chunks and not
   * through the normal chunk allocation path.
   */
  static int btrfs_set_target_alloc_state(struct btrfs_device *srcdev,
  					struct btrfs_device *tgtdev)
  {
  	struct extent_state *cached_state = NULL;
  	u64 start = 0;
  	u64 found_start;
  	u64 found_end;
  	int ret = 0;
  
  	lockdep_assert_held(&srcdev->fs_info->chunk_mutex);
  
  	while (!find_first_extent_bit(&srcdev->alloc_state, start,
  				      &found_start, &found_end,
  				      CHUNK_ALLOCATED, &cached_state)) {
  		ret = set_extent_bits(&tgtdev->alloc_state, found_start,
  				      found_end, CHUNK_ALLOCATED);
  		if (ret)
  			break;
  		start = found_end + 1;
  	}
  
  	free_extent_state(cached_state);
  	return ret;
  }

  static void btrfs_dev_replace_update_device_in_mapping_tree(
  						struct btrfs_fs_info *fs_info,
  						struct btrfs_device *srcdev,
  						struct btrfs_device *tgtdev)
  {
  	struct extent_map_tree *em_tree = &fs_info->mapping_tree;
  	struct extent_map *em;
  	struct map_lookup *map;
  	u64 start = 0;
  	int i;
  
  	write_lock(&em_tree->lock);
  	do {
  		em = lookup_extent_mapping(em_tree, start, (u64)-1);
  		if (!em)
  			break;
  		map = em->map_lookup;
  		for (i = 0; i < map->num_stripes; i++)
  			if (srcdev == map->stripes[i].dev)
  				map->stripes[i].dev = tgtdev;
  		start = em->start + em->len;
  		free_extent_map(em);
  	} while (start);
  	write_unlock(&em_tree->lock);
  }

  static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info,
  				       int scrub_ret)
  {
  	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
  	struct btrfs_device *tgt_device;
  	struct btrfs_device *src_device;
  	struct btrfs_root *root = fs_info->tree_root;
  	u8 uuid_tmp[BTRFS_UUID_SIZE];
  	struct btrfs_trans_handle *trans;
  	int ret = 0;
  
  	/* don't allow cancel or unmount to disturb the finishing procedure */
  	mutex_lock(&dev_replace->lock_finishing_cancel_unmount);

  	down_read(&dev_replace->rwsem);

  	/* was the operation canceled, or is it finished? */
  	if (dev_replace->replace_state !=
  	    BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED) {

  		up_read(&dev_replace->rwsem);

  		mutex_unlock(&dev_replace->lock_finishing_cancel_unmount);
  		return 0;
  	}
  
  	tgt_device = dev_replace->tgtdev;
  	src_device = dev_replace->srcdev;

  	up_read(&dev_replace->rwsem);

  	/*
  	 * flush all outstanding I/O and inode extent mappings before the
  	 * copy operation is declared as being finished
  	 */

  	ret = btrfs_start_delalloc_roots(fs_info, U64_MAX, false);

  	if (ret) {
  		mutex_unlock(&dev_replace->lock_finishing_cancel_unmount);
  		return ret;
  	}

  	btrfs_wait_ordered_roots(fs_info, U64_MAX, 0, (u64)-1);

  	if (!scrub_ret)
  		btrfs_reada_remove_dev(src_device);

  	/*
  	 * We have to use this loop approach because at this point src_device
  	 * has to be available for transaction commit to complete, yet new
  	 * chunks shouldn't be allocated on the device.
  	 */
  	while (1) {
  		trans = btrfs_start_transaction(root, 0);
  		if (IS_ERR(trans)) {

  			btrfs_reada_undo_remove_dev(src_device);

  			mutex_unlock(&dev_replace->lock_finishing_cancel_unmount);
  			return PTR_ERR(trans);
  		}
  		ret = btrfs_commit_transaction(trans);
  		WARN_ON(ret);
  
  		/* Prevent write_all_supers() during the finishing procedure */
  		mutex_lock(&fs_info->fs_devices->device_list_mutex);
  		/* Prevent new chunks being allocated on the source device */
  		mutex_lock(&fs_info->chunk_mutex);
  
  		if (!list_empty(&src_device->post_commit_list)) {
  			mutex_unlock(&fs_info->fs_devices->device_list_mutex);
  			mutex_unlock(&fs_info->chunk_mutex);
  		} else {
  			break;
  		}

  	}

  	down_write(&dev_replace->rwsem);

  	dev_replace->replace_state =
  		scrub_ret ? BTRFS_IOCTL_DEV_REPLACE_STATE_CANCELED
  			  : BTRFS_IOCTL_DEV_REPLACE_STATE_FINISHED;
  	dev_replace->tgtdev = NULL;
  	dev_replace->srcdev = NULL;

  	dev_replace->time_stopped = ktime_get_real_seconds();

  	dev_replace->item_needs_writeback = 1;

  	/*
  	 * Update allocation state in the new device and replace the old device
  	 * with the new one in the mapping tree.
  	 */

  	if (!scrub_ret) {

  		scrub_ret = btrfs_set_target_alloc_state(src_device, tgt_device);
  		if (scrub_ret)
  			goto error;

  		btrfs_dev_replace_update_device_in_mapping_tree(fs_info,
  								src_device,
  								tgt_device);
  	} else {

  		if (scrub_ret != -ECANCELED)
  			btrfs_err_in_rcu(fs_info,

  				 "btrfs_scrub_dev(%s, %llu, %s) failed %d",

  				 btrfs_dev_name(src_device),

  				 src_device->devid,
  				 rcu_str_deref(tgt_device->name), scrub_ret);

  error:

  		up_write(&dev_replace->rwsem);

  		mutex_unlock(&fs_info->chunk_mutex);
  		mutex_unlock(&fs_info->fs_devices->device_list_mutex);

  		btrfs_reada_undo_remove_dev(src_device);

  		btrfs_rm_dev_replace_blocked(fs_info);

  		if (tgt_device)

  			btrfs_destroy_dev_replace_tgtdev(tgt_device);

  		btrfs_rm_dev_replace_unblocked(fs_info);

  		mutex_unlock(&dev_replace->lock_finishing_cancel_unmount);

  		return scrub_ret;

  	}

  	btrfs_info_in_rcu(fs_info,
  			  "dev_replace from %s (devid %llu) to %s finished",

  			  btrfs_dev_name(src_device),

  			  src_device->devid,
  			  rcu_str_deref(tgt_device->name));

  	clear_bit(BTRFS_DEV_STATE_REPLACE_TGT, &tgt_device->dev_state);

  	tgt_device->devid = src_device->devid;
  	src_device->devid = BTRFS_DEV_REPLACE_DEVID;

  	memcpy(uuid_tmp, tgt_device->uuid, sizeof(uuid_tmp));
  	memcpy(tgt_device->uuid, src_device->uuid, sizeof(tgt_device->uuid));
  	memcpy(src_device->uuid, uuid_tmp, sizeof(src_device->uuid));

  	btrfs_device_set_total_bytes(tgt_device, src_device->total_bytes);
  	btrfs_device_set_disk_total_bytes(tgt_device,
  					  src_device->disk_total_bytes);
  	btrfs_device_set_bytes_used(tgt_device, src_device->bytes_used);

  	tgt_device->commit_bytes_used = src_device->bytes_used;

  	btrfs_assign_next_active_device(src_device, tgt_device);

  	list_add(&tgt_device->dev_alloc_list, &fs_info->fs_devices->alloc_list);

  	fs_info->fs_devices->rw_devices++;

  	up_write(&dev_replace->rwsem);

  	btrfs_rm_dev_replace_blocked(fs_info);

  	btrfs_rm_dev_replace_remove_srcdev(src_device);

  	btrfs_rm_dev_replace_unblocked(fs_info);

  	/*

  	 * Increment dev_stats_ccnt so that btrfs_run_dev_stats() will
  	 * update on-disk dev stats value during commit transaction
  	 */
  	atomic_inc(&tgt_device->dev_stats_ccnt);
  
  	/*

  	 * this is again a consistent state where no dev_replace procedure
  	 * is running, the target device is part of the filesystem, the
  	 * source device is not part of the filesystem anymore and its 1st
  	 * superblock is scratched out so that it is no longer marked to
  	 * belong to this filesystem.
  	 */

  	mutex_unlock(&fs_info->chunk_mutex);
  	mutex_unlock(&fs_info->fs_devices->device_list_mutex);

  	/* replace the sysfs entry */

  	btrfs_sysfs_remove_device(src_device);

  	btrfs_sysfs_update_devid(tgt_device);

  	if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &src_device->dev_state))
  		btrfs_scratch_superblocks(fs_info, src_device->bdev,
  					  src_device->name->str);

  	/* write back the superblocks */
  	trans = btrfs_start_transaction(root, 0);
  	if (!IS_ERR(trans))

  		btrfs_commit_transaction(trans);

  
  	mutex_unlock(&dev_replace->lock_finishing_cancel_unmount);

  	btrfs_rm_dev_replace_free_srcdev(src_device);

  	return 0;
  }

  /*
   * Read progress of device replace status according to the state and last
   * stored position. The value format is the same as for
   * btrfs_dev_replace::progress_1000
   */
  static u64 btrfs_dev_replace_progress(struct btrfs_fs_info *fs_info)
  {
  	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
  	u64 ret = 0;
  
  	switch (dev_replace->replace_state) {
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_CANCELED:
  		ret = 0;
  		break;
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_FINISHED:
  		ret = 1000;
  		break;
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED:
  		ret = div64_u64(dev_replace->cursor_left,
  				div_u64(btrfs_device_get_total_bytes(
  						dev_replace->srcdev), 1000));
  		break;
  	}
  
  	return ret;
  }

  void btrfs_dev_replace_status(struct btrfs_fs_info *fs_info,
  			      struct btrfs_ioctl_dev_replace_args *args)
  {
  	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;

  	down_read(&dev_replace->rwsem);

  	/* even if !dev_replace_is_valid, the values are good enough for
  	 * the replace_status ioctl */
  	args->result = BTRFS_IOCTL_DEV_REPLACE_RESULT_NO_ERROR;
  	args->status.replace_state = dev_replace->replace_state;
  	args->status.time_started = dev_replace->time_started;
  	args->status.time_stopped = dev_replace->time_stopped;
  	args->status.num_write_errors =
  		atomic64_read(&dev_replace->num_write_errors);
  	args->status.num_uncorrectable_read_errors =
  		atomic64_read(&dev_replace->num_uncorrectable_read_errors);

  	args->status.progress_1000 = btrfs_dev_replace_progress(fs_info);

  	up_read(&dev_replace->rwsem);

  }

  int btrfs_dev_replace_cancel(struct btrfs_fs_info *fs_info)

  {
  	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
  	struct btrfs_device *tgt_device = NULL;

  	struct btrfs_device *src_device = NULL;

  	struct btrfs_trans_handle *trans;
  	struct btrfs_root *root = fs_info->tree_root;

  	int result;

  	int ret;

  	if (sb_rdonly(fs_info->sb))

  		return -EROFS;

  	mutex_lock(&dev_replace->lock_finishing_cancel_unmount);

  	down_write(&dev_replace->rwsem);

  	switch (dev_replace->replace_state) {
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_FINISHED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_CANCELED:
  		result = BTRFS_IOCTL_DEV_REPLACE_RESULT_NOT_STARTED;

  		up_write(&dev_replace->rwsem);

  		break;

  	case BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED:

  		tgt_device = dev_replace->tgtdev;
  		src_device = dev_replace->srcdev;

  		up_write(&dev_replace->rwsem);

  		ret = btrfs_scrub_cancel(fs_info);
  		if (ret < 0) {
  			result = BTRFS_IOCTL_DEV_REPLACE_RESULT_NOT_STARTED;
  		} else {
  			result = BTRFS_IOCTL_DEV_REPLACE_RESULT_NO_ERROR;
  			/*
  			 * btrfs_dev_replace_finishing() will handle the
  			 * cleanup part
  			 */
  			btrfs_info_in_rcu(fs_info,
  				"dev_replace from %s (devid %llu) to %s canceled",
  				btrfs_dev_name(src_device), src_device->devid,
  				btrfs_dev_name(tgt_device));
  		}

  		break;

  	case BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED:

  		/*
  		 * Scrub doing the replace isn't running so we need to do the
  		 * cleanup step of btrfs_dev_replace_finishing() here
  		 */

  		result = BTRFS_IOCTL_DEV_REPLACE_RESULT_NO_ERROR;
  		tgt_device = dev_replace->tgtdev;

  		src_device = dev_replace->srcdev;

  		dev_replace->tgtdev = NULL;
  		dev_replace->srcdev = NULL;

  		dev_replace->replace_state =
  				BTRFS_IOCTL_DEV_REPLACE_STATE_CANCELED;
  		dev_replace->time_stopped = ktime_get_real_seconds();
  		dev_replace->item_needs_writeback = 1;

  		up_write(&dev_replace->rwsem);

  		/* Scrub for replace must not be running in suspended state */
  		ret = btrfs_scrub_cancel(fs_info);
  		ASSERT(ret != -ENOTCONN);

  
  		trans = btrfs_start_transaction(root, 0);
  		if (IS_ERR(trans)) {
  			mutex_unlock(&dev_replace->lock_finishing_cancel_unmount);
  			return PTR_ERR(trans);
  		}
  		ret = btrfs_commit_transaction(trans);
  		WARN_ON(ret);

  		btrfs_info_in_rcu(fs_info,
  		"suspended dev_replace from %s (devid %llu) to %s canceled",
  			btrfs_dev_name(src_device), src_device->devid,
  			btrfs_dev_name(tgt_device));
  
  		if (tgt_device)
  			btrfs_destroy_dev_replace_tgtdev(tgt_device);
  		break;
  	default:

  		up_write(&dev_replace->rwsem);

  		result = -EINVAL;
  	}

  	mutex_unlock(&dev_replace->lock_finishing_cancel_unmount);
  	return result;
  }
  
  void btrfs_dev_replace_suspend_for_unmount(struct btrfs_fs_info *fs_info)
  {
  	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
  
  	mutex_lock(&dev_replace->lock_finishing_cancel_unmount);

  	down_write(&dev_replace->rwsem);

  	switch (dev_replace->replace_state) {
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_FINISHED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_CANCELED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED:
  		break;
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED:
  		dev_replace->replace_state =
  			BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED;

  		dev_replace->time_stopped = ktime_get_real_seconds();

  		dev_replace->item_needs_writeback = 1;

  		btrfs_info(fs_info, "suspending dev_replace for unmount");

  		break;
  	}

  	up_write(&dev_replace->rwsem);

  	mutex_unlock(&dev_replace->lock_finishing_cancel_unmount);
  }
  
  /* resume dev_replace procedure that was interrupted by unmount */
  int btrfs_resume_dev_replace_async(struct btrfs_fs_info *fs_info)
  {
  	struct task_struct *task;
  	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;

  	down_write(&dev_replace->rwsem);

  	switch (dev_replace->replace_state) {
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_FINISHED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_CANCELED:

  		up_write(&dev_replace->rwsem);

  		return 0;
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED:
  		break;
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED:
  		dev_replace->replace_state =
  			BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED;
  		break;
  	}
  	if (!dev_replace->tgtdev || !dev_replace->tgtdev->bdev) {

  		btrfs_info(fs_info,

  			   "cannot continue dev_replace, tgtdev is missing");
  		btrfs_info(fs_info,
  			   "you may cancel the operation after 'mount -o degraded'");

  		dev_replace->replace_state =
  					BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED;

  		up_write(&dev_replace->rwsem);

  		return 0;
  	}

  	up_write(&dev_replace->rwsem);

  	/*
  	 * This could collide with a paused balance, but the exclusive op logic
  	 * should never allow both to start and pause. We don't want to allow
  	 * dev-replace to start anyway.
  	 */

  	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_DEV_REPLACE)) {

  		down_write(&dev_replace->rwsem);

  		dev_replace->replace_state =
  					BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED;

  		up_write(&dev_replace->rwsem);

  		btrfs_info(fs_info,
  		"cannot resume dev-replace, other exclusive operation running");
  		return 0;
  	}

  	task = kthread_run(btrfs_dev_replace_kthread, fs_info, "btrfs-devrepl");

  	return PTR_ERR_OR_ZERO(task);

  }
  
  static int btrfs_dev_replace_kthread(void *data)
  {
  	struct btrfs_fs_info *fs_info = data;
  	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;

  	u64 progress;

  	int ret;

  	progress = btrfs_dev_replace_progress(fs_info);
  	progress = div_u64(progress, 10);
  	btrfs_info_in_rcu(fs_info,

  		"continuing dev_replace from %s (devid %llu) to target %s @%u%%",
  		btrfs_dev_name(dev_replace->srcdev),

  		dev_replace->srcdev->devid,

  		btrfs_dev_name(dev_replace->tgtdev),

  		(unsigned int)progress);

  	ret = btrfs_scrub_dev(fs_info, dev_replace->srcdev->devid,
  			      dev_replace->committed_cursor_left,

  			      btrfs_device_get_total_bytes(dev_replace->srcdev),

  			      &dev_replace->scrub_progress, 0, 1);
  	ret = btrfs_dev_replace_finishing(fs_info, ret);

  	WARN_ON(ret && ret != -ECANCELED);

  	btrfs_exclop_finish(fs_info);

  	return 0;
  }

  int __pure btrfs_dev_replace_is_ongoing(struct btrfs_dev_replace *dev_replace)

  {
  	if (!dev_replace->is_valid)
  		return 0;
  
  	switch (dev_replace->replace_state) {
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_FINISHED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_CANCELED:
  		return 0;
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED:
  		/*
  		 * return true even if tgtdev is missing (this is
  		 * something that can happen if the dev_replace
  		 * procedure is suspended by an umount and then
  		 * the tgtdev is missing (or "btrfs dev scan") was

  		 * not called and the filesystem is remounted

  		 * in degraded state. This does not stop the
  		 * dev_replace procedure. It needs to be canceled

  		 * manually if the cancellation is wanted.

  		 */
  		break;
  	}
  	return 1;
  }

  void btrfs_bio_counter_inc_noblocked(struct btrfs_fs_info *fs_info)
  {

  	percpu_counter_inc(&fs_info->dev_replace.bio_counter);

  }

  void btrfs_bio_counter_sub(struct btrfs_fs_info *fs_info, s64 amount)

  {

  	percpu_counter_sub(&fs_info->dev_replace.bio_counter, amount);
  	cond_wake_up_nomb(&fs_info->dev_replace.replace_wait);

  }
  
  void btrfs_bio_counter_inc_blocked(struct btrfs_fs_info *fs_info)
  {

  	while (1) {

  		percpu_counter_inc(&fs_info->dev_replace.bio_counter);

  		if (likely(!test_bit(BTRFS_FS_STATE_DEV_REPLACING,
  				     &fs_info->fs_state)))
  			break;

  		btrfs_bio_counter_dec(fs_info);

  		wait_event(fs_info->dev_replace.replace_wait,

  			   !test_bit(BTRFS_FS_STATE_DEV_REPLACING,
  				     &fs_info->fs_state));

  	}

  }