/*
   * Copyright (C) STRATO AG 2012.  All rights reserved.
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public
   * License v2 as published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * General Public License for more details.
   *
   * You should have received a copy of the GNU General Public
   * License along with this program; if not, write to the
   * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   * Boston, MA 021110-1307, USA.
   */
  #include <linux/sched.h>
  #include <linux/bio.h>
  #include <linux/slab.h>
  #include <linux/buffer_head.h>
  #include <linux/blkdev.h>
  #include <linux/random.h>
  #include <linux/iocontext.h>
  #include <linux/capability.h>
  #include <linux/kthread.h>
  #include <linux/math64.h>
  #include <asm/div64.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"

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

  static u64 __btrfs_dev_replace_cancel(struct btrfs_fs_info *fs_info);
  static int btrfs_dev_replace_kthread(void *data);
  static int btrfs_dev_replace_continue_on_mount(struct btrfs_fs_info *fs_info);
  
  
  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:
  		ret = 0;
  		dev_replace->replace_state =
  			BTRFS_DEV_REPLACE_ITEM_STATE_NEVER_STARTED;
  		dev_replace->cont_reading_from_srcdev_mode =
  		    BTRFS_DEV_REPLACE_ITEM_CONT_READING_FROM_SRCDEV_MODE_ALWAYS;
  		dev_replace->replace_state = 0;
  		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:
  		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, src_devid,
  							NULL, NULL);
  		dev_replace->tgtdev = btrfs_find_device(fs_info,
  							BTRFS_DEV_REPLACE_DEVID,
  							NULL, NULL);
  		/*
  		 * allow 'btrfs dev replace_cancel' if src/tgt device is
  		 * missing
  		 */
  		if (!dev_replace->srcdev &&

  		    !btrfs_test_opt(dev_root->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(dev_root->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;

  			}
  			dev_replace->tgtdev->is_tgtdev_for_dev_replace = 1;
  			btrfs_init_dev_replace_tgtdev_for_resume(fs_info,
  				dev_replace->tgtdev);
  		}
  		break;
  	}
  
  out:

  	btrfs_free_path(path);

  	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)
  {
  	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;

  	btrfs_dev_replace_lock(dev_replace, 0);

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

  		btrfs_dev_replace_unlock(dev_replace, 0);

  		return 0;
  	}

  	btrfs_dev_replace_unlock(dev_replace, 0);

  
  	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);

  	btrfs_dev_replace_lock(dev_replace, 1);

  	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;

  	btrfs_dev_replace_unlock(dev_replace, 1);

  
  	btrfs_mark_buffer_dirty(eb);
  
  out:
  	btrfs_free_path(path);
  
  	return ret;
  }
  
  void btrfs_after_dev_replace_commit(struct btrfs_fs_info *fs_info)
  {
  	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
  
  	dev_replace->committed_cursor_left =
  		dev_replace->cursor_left_last_write_of_item;
  }

  int btrfs_dev_replace_start(struct btrfs_root *root, char *tgtdev_name,
  				u64 srcdevid, char *srcdev_name, int read_src)

  {
  	struct btrfs_trans_handle *trans;
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
  	int ret;
  	struct btrfs_device *tgt_device = NULL;
  	struct btrfs_device *src_device = NULL;

  	/* the disk copy procedure reuses the scrub code */

  	mutex_lock(&fs_info->volume_mutex);

  	ret = btrfs_find_device_by_devspec(root, srcdevid,
  					    srcdev_name, &src_device);

  	if (ret) {

  		mutex_unlock(&fs_info->volume_mutex);
  		return ret;

  	}

  	ret = btrfs_init_dev_replace_tgtdev(root, tgtdev_name,

  					    src_device, &tgt_device);
  	mutex_unlock(&fs_info->volume_mutex);
  	if (ret)
  		return ret;

  	/*
  	 * 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, root);
  		if (ret)
  			return ret;
  	} else if (PTR_ERR(trans) != -ENOENT) {
  		return PTR_ERR(trans);
  	}

  	btrfs_dev_replace_lock(dev_replace, 1);

  	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:

  		ret = BTRFS_IOCTL_DEV_REPLACE_RESULT_ALREADY_STARTED;

  		goto leave;
  	}

  	dev_replace->cont_reading_from_srcdev_mode = read_src;

  	WARN_ON(!src_device);
  	dev_replace->srcdev = src_device;
  	WARN_ON(!tgt_device);
  	dev_replace->tgtdev = tgt_device;

  	btrfs_info_in_rcu(fs_info,

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

  		      src_device->missing ? "<missing disk>" :
  		        rcu_str_deref(src_device->name),
  		      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 = get_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);

  	btrfs_dev_replace_unlock(dev_replace, 1);

  	ret = btrfs_sysfs_add_device_link(tgt_device->fs_devices, tgt_device);
  	if (ret)

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

  	btrfs_wait_ordered_roots(root->fs_info, -1, 0, (u64)-1);

  
  	/* force writing the updated state information to disk */
  	trans = btrfs_start_transaction(root, 0);
  	if (IS_ERR(trans)) {
  		ret = PTR_ERR(trans);

  		btrfs_dev_replace_lock(dev_replace, 1);

  		goto leave;
  	}
  
  	ret = btrfs_commit_transaction(trans, root);
  	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;

  	} else {
  		WARN_ON(ret);
  	}

  	return ret;

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

  	btrfs_dev_replace_unlock(dev_replace, 1);

  	btrfs_destroy_dev_replace_tgtdev(fs_info, tgt_device);

  	return ret;
  }

  int btrfs_dev_replace_by_ioctl(struct btrfs_root *root,
  			    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(root, 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 = 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->replace_wait, !percpu_counter_sum(
  		   &fs_info->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->replace_wait);

  }

  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);

  	btrfs_dev_replace_lock(dev_replace, 0);

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

  		btrfs_dev_replace_unlock(dev_replace, 0);

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

  	btrfs_dev_replace_unlock(dev_replace, 0);

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

  	ret = btrfs_start_delalloc_roots(root->fs_info, 0, -1);

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

  	btrfs_wait_ordered_roots(root->fs_info, -1, 0, (u64)-1);

  
  	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, root);
  	WARN_ON(ret);

  	mutex_lock(&uuid_mutex);

  	/* keep away write_all_supers() during the finishing procedure */
  	mutex_lock(&root->fs_info->fs_devices->device_list_mutex);

  	mutex_lock(&root->fs_info->chunk_mutex);

  	btrfs_dev_replace_lock(dev_replace, 1);

  	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 = get_seconds();

  	dev_replace->item_needs_writeback = 1;

  	/* replace old device with new one in mapping tree */
  	if (!scrub_ret) {
  		btrfs_dev_replace_update_device_in_mapping_tree(fs_info,
  								src_device,
  								tgt_device);
  	} else {

  		btrfs_err_in_rcu(root->fs_info,
  			      "btrfs_scrub_dev(%s, %llu, %s) failed %d",

  			      src_device->missing ? "<missing disk>" :
  			        rcu_str_deref(src_device->name),
  			      src_device->devid,
  			      rcu_str_deref(tgt_device->name), scrub_ret);

  		btrfs_dev_replace_unlock(dev_replace, 1);

  		mutex_unlock(&root->fs_info->chunk_mutex);

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

  		mutex_unlock(&uuid_mutex);

  		if (tgt_device)
  			btrfs_destroy_dev_replace_tgtdev(fs_info, tgt_device);
  		mutex_unlock(&dev_replace->lock_finishing_cancel_unmount);

  		return scrub_ret;

  	}

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

  		      src_device->missing ? "<missing disk>" :
  		        rcu_str_deref(src_device->name),
  		      src_device->devid,
  		      rcu_str_deref(tgt_device->name));
  	tgt_device->is_tgtdev_for_dev_replace = 0;
  	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);

  	ASSERT(list_empty(&src_device->resized_list));
  	tgt_device->commit_total_bytes = src_device->commit_total_bytes;

  	tgt_device->commit_bytes_used = src_device->bytes_used;

  
  	btrfs_assign_next_active_device(fs_info, src_device, tgt_device);

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

  	fs_info->fs_devices->rw_devices++;

  	btrfs_dev_replace_unlock(dev_replace, 1);

  	btrfs_rm_dev_replace_blocked(fs_info);

  	btrfs_rm_dev_replace_remove_srcdev(fs_info, src_device);

  	btrfs_rm_dev_replace_unblocked(fs_info);

  	/*
  	 * 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(&root->fs_info->chunk_mutex);

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

  	mutex_unlock(&uuid_mutex);

  	/* replace the sysfs entry */

  	btrfs_sysfs_rm_device_link(fs_info->fs_devices, src_device);

  	btrfs_rm_dev_replace_free_srcdev(fs_info, src_device);

  	/* write back the superblocks */
  	trans = btrfs_start_transaction(root, 0);
  	if (!IS_ERR(trans))
  		btrfs_commit_transaction(trans, root);
  
  	mutex_unlock(&dev_replace->lock_finishing_cancel_unmount);
  
  	return 0;
  }
  
  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.map_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);
  }

  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;

  	struct btrfs_device *srcdev;

  	btrfs_dev_replace_lock(dev_replace, 0);

  	/* 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);
  	switch (dev_replace->replace_state) {
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_CANCELED:
  		args->status.progress_1000 = 0;
  		break;
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_FINISHED:
  		args->status.progress_1000 = 1000;
  		break;
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED:

  		srcdev = dev_replace->srcdev;

  		args->status.progress_1000 = div_u64(dev_replace->cursor_left,
  			div_u64(btrfs_device_get_total_bytes(srcdev), 1000));

  		break;
  	}

  	btrfs_dev_replace_unlock(dev_replace, 0);

  }
  
  int btrfs_dev_replace_cancel(struct btrfs_fs_info *fs_info,
  			     struct btrfs_ioctl_dev_replace_args *args)
  {
  	args->result = __btrfs_dev_replace_cancel(fs_info);
  	return 0;
  }
  
  static u64 __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_trans_handle *trans;
  	struct btrfs_root *root = fs_info->tree_root;
  	u64 result;
  	int ret;

  	if (fs_info->sb->s_flags & MS_RDONLY)
  		return -EROFS;

  	mutex_lock(&dev_replace->lock_finishing_cancel_unmount);

  	btrfs_dev_replace_lock(dev_replace, 1);

  	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;

  		btrfs_dev_replace_unlock(dev_replace, 1);

  		goto leave;
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_STARTED:
  	case BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED:
  		result = BTRFS_IOCTL_DEV_REPLACE_RESULT_NO_ERROR;
  		tgt_device = dev_replace->tgtdev;
  		dev_replace->tgtdev = NULL;
  		dev_replace->srcdev = NULL;
  		break;
  	}
  	dev_replace->replace_state = BTRFS_IOCTL_DEV_REPLACE_STATE_CANCELED;

  	dev_replace->time_stopped = get_seconds();

  	dev_replace->item_needs_writeback = 1;

  	btrfs_dev_replace_unlock(dev_replace, 1);

  	btrfs_scrub_cancel(fs_info);
  
  	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, root);
  	WARN_ON(ret);
  	if (tgt_device)
  		btrfs_destroy_dev_replace_tgtdev(fs_info, tgt_device);
  
  leave:
  	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);

  	btrfs_dev_replace_lock(dev_replace, 1);

  	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 = get_seconds();

  		dev_replace->item_needs_writeback = 1;

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

  		break;
  	}

  	btrfs_dev_replace_unlock(dev_replace, 1);

  	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;

  	btrfs_dev_replace_lock(dev_replace, 1);

  	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:

  		btrfs_dev_replace_unlock(dev_replace, 1);

  		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'");

  		btrfs_dev_replace_unlock(dev_replace, 1);

  		return 0;
  	}

  	btrfs_dev_replace_unlock(dev_replace, 1);

  
  	WARN_ON(atomic_xchg(
  		&fs_info->mutually_exclusive_operation_running, 1));
  	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;
  	struct btrfs_ioctl_dev_replace_args *status_args;
  	u64 progress;

  	status_args = kzalloc(sizeof(*status_args), GFP_KERNEL);

  	if (status_args) {
  		btrfs_dev_replace_status(fs_info, status_args);
  		progress = status_args->status.progress_1000;
  		kfree(status_args);

  		progress = div_u64(progress, 10);

  		btrfs_info_in_rcu(fs_info,
  			"continuing dev_replace from %s (devid %llu) to %s @%u%%",

  			dev_replace->srcdev->missing ? "<missing disk>" :
  			rcu_str_deref(dev_replace->srcdev->name),
  			dev_replace->srcdev->devid,
  			dev_replace->tgtdev ?
  			rcu_str_deref(dev_replace->tgtdev->name) :
  			"<missing target disk>",
  			(unsigned int)progress);

  	}
  	btrfs_dev_replace_continue_on_mount(fs_info);
  	atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
  
  	return 0;
  }
  
  static int btrfs_dev_replace_continue_on_mount(struct btrfs_fs_info *fs_info)
  {
  	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
  	int ret;
  
  	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);
  	return 0;
  }
  
  int 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 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_dev_replace_lock(struct btrfs_dev_replace *dev_replace, int rw)

  {

  	if (rw == 1) {
  		/* write */
  again:
  		wait_event(dev_replace->read_lock_wq,
  			   atomic_read(&dev_replace->blocking_readers) == 0);
  		write_lock(&dev_replace->lock);
  		if (atomic_read(&dev_replace->blocking_readers)) {
  			write_unlock(&dev_replace->lock);
  			goto again;
  		}
  	} else {
  		read_lock(&dev_replace->lock);
  		atomic_inc(&dev_replace->read_locks);

  	}

  }

  void btrfs_dev_replace_unlock(struct btrfs_dev_replace *dev_replace, int rw)
  {
  	if (rw == 1) {
  		/* write */
  		ASSERT(atomic_read(&dev_replace->blocking_readers) == 0);
  		write_unlock(&dev_replace->lock);
  	} else {
  		ASSERT(atomic_read(&dev_replace->read_locks) > 0);
  		atomic_dec(&dev_replace->read_locks);
  		read_unlock(&dev_replace->lock);

  	}

  }

  /* inc blocking cnt and release read lock */
  void btrfs_dev_replace_set_lock_blocking(
  					struct btrfs_dev_replace *dev_replace)
  {
  	/* only set blocking for read lock */
  	ASSERT(atomic_read(&dev_replace->read_locks) > 0);
  	atomic_inc(&dev_replace->blocking_readers);
  	read_unlock(&dev_replace->lock);

  }

  /* acquire read lock and dec blocking cnt */
  void btrfs_dev_replace_clear_lock_blocking(
  					struct btrfs_dev_replace *dev_replace)

  {

  	/* only set blocking for read lock */
  	ASSERT(atomic_read(&dev_replace->read_locks) > 0);
  	ASSERT(atomic_read(&dev_replace->blocking_readers) > 0);
  	read_lock(&dev_replace->lock);
  	if (atomic_dec_and_test(&dev_replace->blocking_readers) &&
  	    waitqueue_active(&dev_replace->read_lock_wq))
  		wake_up(&dev_replace->read_lock_wq);

  }

  
  void btrfs_bio_counter_inc_noblocked(struct btrfs_fs_info *fs_info)
  {
  	percpu_counter_inc(&fs_info->bio_counter);
  }

  void btrfs_bio_counter_sub(struct btrfs_fs_info *fs_info, s64 amount)

  {

  	percpu_counter_sub(&fs_info->bio_counter, amount);

  
  	if (waitqueue_active(&fs_info->replace_wait))
  		wake_up(&fs_info->replace_wait);
  }
  
  void btrfs_bio_counter_inc_blocked(struct btrfs_fs_info *fs_info)
  {

  	while (1) {
  		percpu_counter_inc(&fs_info->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->replace_wait,
  			   !test_bit(BTRFS_FS_STATE_DEV_REPLACING,
  				     &fs_info->fs_state));

  	}

  }