text: // SPDX-License-Identifier: GPL-2.0-only
  /*
   * Copyright (C) 2019 Arrikto, Inc. All Rights Reserved.
   */
  
  #include <linux/mm.h>
  #include <linux/bio.h>
  #include <linux/err.h>
  #include <linux/hash.h>
  #include <linux/list.h>
  #include <linux/log2.h>
  #include <linux/init.h>
  #include <linux/slab.h>
  #include <linux/wait.h>
  #include <linux/dm-io.h>
  #include <linux/mutex.h>
  #include <linux/atomic.h>
  #include <linux/bitops.h>
  #include <linux/blkdev.h>
  #include <linux/kdev_t.h>
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/jiffies.h>
  #include <linux/mempool.h>
  #include <linux/spinlock.h>
  #include <linux/blk_types.h>
  #include <linux/dm-kcopyd.h>
  #include <linux/workqueue.h>
  #include <linux/backing-dev.h>
  #include <linux/device-mapper.h>
  
  #include "dm.h"
  #include "dm-clone-metadata.h"
  
  #define DM_MSG_PREFIX "clone"
  
  /*
   * Minimum and maximum allowed region sizes
   */
  #define MIN_REGION_SIZE (1 << 3)  /* 4KB */
  #define MAX_REGION_SIZE (1 << 21) /* 1GB */
  
  #define MIN_HYDRATIONS 256 /* Size of hydration mempool */
  #define DEFAULT_HYDRATION_THRESHOLD 1 /* 1 region */
  #define DEFAULT_HYDRATION_BATCH_SIZE 1 /* Hydrate in batches of 1 region */
  
  #define COMMIT_PERIOD HZ /* 1 sec */
  
  /*
   * Hydration hash table size: 1 << HASH_TABLE_BITS
   */
  #define HASH_TABLE_BITS 15
  
  DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(clone_hydration_throttle,
  	"A percentage of time allocated for hydrating regions");
  
  /* Slab cache for struct dm_clone_region_hydration */
  static struct kmem_cache *_hydration_cache;
  
  /* dm-clone metadata modes */
  enum clone_metadata_mode {
  	CM_WRITE,		/* metadata may be changed */
  	CM_READ_ONLY,		/* metadata may not be changed */
  	CM_FAIL,		/* all metadata I/O fails */
  };
  
  struct hash_table_bucket;
  
  struct clone {
  	struct dm_target *ti;
  	struct dm_target_callbacks callbacks;
  
  	struct dm_dev *metadata_dev;
  	struct dm_dev *dest_dev;
  	struct dm_dev *source_dev;
  
  	unsigned long nr_regions;
  	sector_t region_size;
  	unsigned int region_shift;
  
  	/*
  	 * A metadata commit and the actions taken in case it fails should run
  	 * as a single atomic step.
  	 */
  	struct mutex commit_lock;
  
  	struct dm_clone_metadata *cmd;
  
  	/*
  	 * bio used to flush the destination device, before committing the
  	 * metadata.
  	 */
  	struct bio flush_bio;
  
  	/* Region hydration hash table */
  	struct hash_table_bucket *ht;
  
  	atomic_t ios_in_flight;
  
  	wait_queue_head_t hydration_stopped;
  
  	mempool_t hydration_pool;
  
  	unsigned long last_commit_jiffies;
  
  	/*
  	 * We defer incoming WRITE bios for regions that are not hydrated,
  	 * until after these regions have been hydrated.
  	 *
  	 * Also, we defer REQ_FUA and REQ_PREFLUSH bios, until after the
  	 * metadata have been committed.
  	 */
  	spinlock_t lock;
  	struct bio_list deferred_bios;
  	struct bio_list deferred_discard_bios;
  	struct bio_list deferred_flush_bios;
  	struct bio_list deferred_flush_completions;
  
  	/* Maximum number of regions being copied during background hydration. */
  	unsigned int hydration_threshold;
  
  	/* Number of regions to batch together during background hydration. */
  	unsigned int hydration_batch_size;
  
  	/* Which region to hydrate next */
  	unsigned long hydration_offset;
  
  	atomic_t hydrations_in_flight;
  
  	/*
  	 * Save a copy of the table line rather than reconstructing it for the
  	 * status.
  	 */
  	unsigned int nr_ctr_args;
  	const char **ctr_args;
  
  	struct workqueue_struct *wq;
  	struct work_struct worker;
  	struct delayed_work waker;
  
  	struct dm_kcopyd_client *kcopyd_client;
  
  	enum clone_metadata_mode mode;
  	unsigned long flags;
  };
  
  /*
   * dm-clone flags
   */
  #define DM_CLONE_DISCARD_PASSDOWN 0
  #define DM_CLONE_HYDRATION_ENABLED 1
  #define DM_CLONE_HYDRATION_SUSPENDED 2
  
  /*---------------------------------------------------------------------------*/
  
  /*
   * Metadata failure handling.
   */
  static enum clone_metadata_mode get_clone_mode(struct clone *clone)
  {
  	return READ_ONCE(clone->mode);
  }
  
  static const char *clone_device_name(struct clone *clone)
  {
  	return dm_table_device_name(clone->ti->table);
  }
  
  static void __set_clone_mode(struct clone *clone, enum clone_metadata_mode new_mode)
  {
  	const char *descs[] = {
  		"read-write",
  		"read-only",
  		"fail"
  	};
  
  	enum clone_metadata_mode old_mode = get_clone_mode(clone);
  
  	/* Never move out of fail mode */
  	if (old_mode == CM_FAIL)
  		new_mode = CM_FAIL;
  
  	switch (new_mode) {
  	case CM_FAIL:
  	case CM_READ_ONLY:
  		dm_clone_metadata_set_read_only(clone->cmd);
  		break;
  
  	case CM_WRITE:
  		dm_clone_metadata_set_read_write(clone->cmd);
  		break;
  	}
  
  	WRITE_ONCE(clone->mode, new_mode);
  
  	if (new_mode != old_mode) {
  		dm_table_event(clone->ti->table);
  		DMINFO("%s: Switching to %s mode", clone_device_name(clone),
  		       descs[(int)new_mode]);
  	}
  }
  
  static void __abort_transaction(struct clone *clone)
  {
  	const char *dev_name = clone_device_name(clone);
  
  	if (get_clone_mode(clone) >= CM_READ_ONLY)
  		return;
  
  	DMERR("%s: Aborting current metadata transaction", dev_name);
  	if (dm_clone_metadata_abort(clone->cmd)) {
  		DMERR("%s: Failed to abort metadata transaction", dev_name);
  		__set_clone_mode(clone, CM_FAIL);
  	}
  }
  
  static void __reload_in_core_bitset(struct clone *clone)
  {
  	const char *dev_name = clone_device_name(clone);
  
  	if (get_clone_mode(clone) == CM_FAIL)
  		return;
  
  	/* Reload the on-disk bitset */
  	DMINFO("%s: Reloading on-disk bitmap", dev_name);
  	if (dm_clone_reload_in_core_bitset(clone->cmd)) {
  		DMERR("%s: Failed to reload on-disk bitmap", dev_name);
  		__set_clone_mode(clone, CM_FAIL);
  	}
  }
  
  static void __metadata_operation_failed(struct clone *clone, const char *op, int r)
  {
  	DMERR("%s: Metadata operation `%s' failed: error = %d",
  	      clone_device_name(clone), op, r);
  
  	__abort_transaction(clone);
  	__set_clone_mode(clone, CM_READ_ONLY);
  
  	/*
  	 * dm_clone_reload_in_core_bitset() may run concurrently with either
  	 * dm_clone_set_region_hydrated() or dm_clone_cond_set_range(), but
  	 * it's safe as we have already set the metadata to read-only mode.
  	 */
  	__reload_in_core_bitset(clone);
  }
  
  /*---------------------------------------------------------------------------*/
  
  /* Wake up anyone waiting for region hydrations to stop */
  static inline void wakeup_hydration_waiters(struct clone *clone)
  {
  	wake_up_all(&clone->hydration_stopped);
  }
  
  static inline void wake_worker(struct clone *clone)
  {
  	queue_work(clone->wq, &clone->worker);
  }
  
  /*---------------------------------------------------------------------------*/
  
  /*
   * bio helper functions.
   */
  static inline void remap_to_source(struct clone *clone, struct bio *bio)
  {
  	bio_set_dev(bio, clone->source_dev->bdev);
  }
  
  static inline void remap_to_dest(struct clone *clone, struct bio *bio)
  {
  	bio_set_dev(bio, clone->dest_dev->bdev);
  }
  
  static bool bio_triggers_commit(struct clone *clone, struct bio *bio)
  {
  	return op_is_flush(bio->bi_opf) &&
  		dm_clone_changed_this_transaction(clone->cmd);
  }
  
  /* Get the address of the region in sectors */
  static inline sector_t region_to_sector(struct clone *clone, unsigned long region_nr)
  {
  	return (region_nr << clone->region_shift);
  }
  
  /* Get the region number of the bio */
  static inline unsigned long bio_to_region(struct clone *clone, struct bio *bio)
  {
  	return (bio->bi_iter.bi_sector >> clone->region_shift);
  }
  
  /* Get the region range covered by the bio */
  static void bio_region_range(struct clone *clone, struct bio *bio,
  			     unsigned long *rs, unsigned long *re)
  {
  	*rs = dm_sector_div_up(bio->bi_iter.bi_sector, clone->region_size);
  	*re = bio_end_sector(bio) >> clone->region_shift;
  }
  
  /* Check whether a bio overwrites a region */
  static inline bool is_overwrite_bio(struct clone *clone, struct bio *bio)
  {
  	return (bio_data_dir(bio) == WRITE && bio_sectors(bio) == clone->region_size);
  }
  
  static void fail_bios(struct bio_list *bios, blk_status_t status)
  {
  	struct bio *bio;
  
  	while ((bio = bio_list_pop(bios))) {
  		bio->bi_status = status;
  		bio_endio(bio);
  	}
  }
  
  static void submit_bios(struct bio_list *bios)
  {
  	struct bio *bio;
  	struct blk_plug plug;
  
  	blk_start_plug(&plug);
  
  	while ((bio = bio_list_pop(bios)))
  		generic_make_request(bio);
  
  	blk_finish_plug(&plug);
  }
  
  /*
   * Submit bio to the underlying device.
   *
   * If the bio triggers a commit, delay it, until after the metadata have been
   * committed.
   *
   * NOTE: The bio remapping must be performed by the caller.
   */
  static void issue_bio(struct clone *clone, struct bio *bio)
  {
  	if (!bio_triggers_commit(clone, bio)) {
  		generic_make_request(bio);
  		return;
  	}
  
  	/*
  	 * If the metadata mode is RO or FAIL we won't be able to commit the
  	 * metadata, so we complete the bio with an error.
  	 */
  	if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY)) {
  		bio_io_error(bio);
  		return;
  	}
  
  	/*
  	 * Batch together any bios that trigger commits and then issue a single
  	 * commit for them in process_deferred_flush_bios().
  	 */
  	spin_lock_irq(&clone->lock);
  	bio_list_add(&clone->deferred_flush_bios, bio);
  	spin_unlock_irq(&clone->lock);
  
  	wake_worker(clone);
  }
  
  /*
   * Remap bio to the destination device and submit it.
   *
   * If the bio triggers a commit, delay it, until after the metadata have been
   * committed.
   */
  static void remap_and_issue(struct clone *clone, struct bio *bio)
  {
  	remap_to_dest(clone, bio);
  	issue_bio(clone, bio);
  }
  
  /*
   * Issue bios that have been deferred until after their region has finished
   * hydrating.
   *
   * We delegate the bio submission to the worker thread, so this is safe to call
   * from interrupt context.
   */
  static void issue_deferred_bios(struct clone *clone, struct bio_list *bios)
  {
  	struct bio *bio;
  	unsigned long flags;
  	struct bio_list flush_bios = BIO_EMPTY_LIST;
  	struct bio_list normal_bios = BIO_EMPTY_LIST;
  
  	if (bio_list_empty(bios))
  		return;
  
  	while ((bio = bio_list_pop(bios))) {
  		if (bio_triggers_commit(clone, bio))
  			bio_list_add(&flush_bios, bio);
  		else
  			bio_list_add(&normal_bios, bio);
  	}
  
  	spin_lock_irqsave(&clone->lock, flags);
  	bio_list_merge(&clone->deferred_bios, &normal_bios);
  	bio_list_merge(&clone->deferred_flush_bios, &flush_bios);
  	spin_unlock_irqrestore(&clone->lock, flags);
  
  	wake_worker(clone);
  }
  
  static void complete_overwrite_bio(struct clone *clone, struct bio *bio)
  {
  	unsigned long flags;
  
  	/*
  	 * If the bio has the REQ_FUA flag set we must commit the metadata
  	 * before signaling its completion.
  	 *
  	 * complete_overwrite_bio() is only called by hydration_complete(),
  	 * after having successfully updated the metadata. This means we don't
  	 * need to call dm_clone_changed_this_transaction() to check if the
  	 * metadata has changed and thus we can avoid taking the metadata spin
  	 * lock.
  	 */
  	if (!(bio->bi_opf & REQ_FUA)) {
  		bio_endio(bio);
  		return;
  	}
  
  	/*
  	 * If the metadata mode is RO or FAIL we won't be able to commit the
  	 * metadata, so we complete the bio with an error.
  	 */
  	if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY)) {
  		bio_io_error(bio);
  		return;
  	}
  
  	/*
  	 * Batch together any bios that trigger commits and then issue a single
  	 * commit for them in process_deferred_flush_bios().
  	 */
  	spin_lock_irqsave(&clone->lock, flags);
  	bio_list_add(&clone->deferred_flush_completions, bio);
  	spin_unlock_irqrestore(&clone->lock, flags);
  
  	wake_worker(clone);
  }
  
  static void trim_bio(struct bio *bio, sector_t sector, unsigned int len)
  {
  	bio->bi_iter.bi_sector = sector;
  	bio->bi_iter.bi_size = to_bytes(len);
  }
  
  static void complete_discard_bio(struct clone *clone, struct bio *bio, bool success)
  {
  	unsigned long rs, re;
  
  	/*
  	 * If the destination device supports discards, remap and trim the
  	 * discard bio and pass it down. Otherwise complete the bio
  	 * immediately.
  	 */
  	if (test_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags) && success) {
  		remap_to_dest(clone, bio);
  		bio_region_range(clone, bio, &rs, &re);
  		trim_bio(bio, rs << clone->region_shift,
  			 (re - rs) << clone->region_shift);
  		generic_make_request(bio);
  	} else
  		bio_endio(bio);
  }
  
  static void process_discard_bio(struct clone *clone, struct bio *bio)
  {
  	unsigned long rs, re;
  
  	bio_region_range(clone, bio, &rs, &re);
  	BUG_ON(re > clone->nr_regions);
  
  	if (unlikely(rs == re)) {
  		bio_endio(bio);
  		return;
  	}
  
  	/*
  	 * The covered regions are already hydrated so we just need to pass
  	 * down the discard.
  	 */
  	if (dm_clone_is_range_hydrated(clone->cmd, rs, re - rs)) {
  		complete_discard_bio(clone, bio, true);
  		return;
  	}
  
  	/*
  	 * If the metadata mode is RO or FAIL we won't be able to update the
  	 * metadata for the regions covered by the discard so we just ignore
  	 * it.
  	 */
  	if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY)) {
  		bio_endio(bio);
  		return;
  	}
  
  	/*
  	 * Defer discard processing.
  	 */
  	spin_lock_irq(&clone->lock);
  	bio_list_add(&clone->deferred_discard_bios, bio);
  	spin_unlock_irq(&clone->lock);
  
  	wake_worker(clone);
  }
  
  /*---------------------------------------------------------------------------*/
  
  /*
   * dm-clone region hydrations.
   */
  struct dm_clone_region_hydration {
  	struct clone *clone;
  	unsigned long region_nr;
  
  	struct bio *overwrite_bio;
  	bio_end_io_t *overwrite_bio_end_io;
  
  	struct bio_list deferred_bios;
  
  	blk_status_t status;
  
  	/* Used by hydration batching */
  	struct list_head list;
  
  	/* Used by hydration hash table */
  	struct hlist_node h;
  };
  
  /*
   * Hydration hash table implementation.
   *
   * Ideally we would like to use list_bl, which uses bit spin locks and employs
   * the least significant bit of the list head to lock the corresponding bucket,
   * reducing the memory overhead for the locks. But, currently, list_bl and bit
   * spin locks don't support IRQ safe versions. Since we have to take the lock
   * in both process and interrupt context, we must fall back to using regular
   * spin locks; one per hash table bucket.
   */
  struct hash_table_bucket {
  	struct hlist_head head;
  
  	/* Spinlock protecting the bucket */
  	spinlock_t lock;
  };
  
  #define bucket_lock_irqsave(bucket, flags) \
  	spin_lock_irqsave(&(bucket)->lock, flags)
  
  #define bucket_unlock_irqrestore(bucket, flags) \
  	spin_unlock_irqrestore(&(bucket)->lock, flags)
  
  #define bucket_lock_irq(bucket) \
  	spin_lock_irq(&(bucket)->lock)
  
  #define bucket_unlock_irq(bucket) \
  	spin_unlock_irq(&(bucket)->lock)
  
  static int hash_table_init(struct clone *clone)
  {
  	unsigned int i, sz;
  	struct hash_table_bucket *bucket;
  
  	sz = 1 << HASH_TABLE_BITS;
  
  	clone->ht = kvmalloc(sz * sizeof(struct hash_table_bucket), GFP_KERNEL);
  	if (!clone->ht)
  		return -ENOMEM;
  
  	for (i = 0; i < sz; i++) {
  		bucket = clone->ht + i;
  
  		INIT_HLIST_HEAD(&bucket->head);
  		spin_lock_init(&bucket->lock);
  	}
  
  	return 0;
  }
  
  static void hash_table_exit(struct clone *clone)
  {
  	kvfree(clone->ht);
  }
  
  static struct hash_table_bucket *get_hash_table_bucket(struct clone *clone,
  						       unsigned long region_nr)
  {
  	return &clone->ht[hash_long(region_nr, HASH_TABLE_BITS)];
  }
  
  /*
   * Search hash table for a hydration with hd->region_nr == region_nr
   *
   * NOTE: Must be called with the bucket lock held
   */
  static struct dm_clone_region_hydration *__hash_find(struct hash_table_bucket *bucket,
  						     unsigned long region_nr)
  {
  	struct dm_clone_region_hydration *hd;
  
  	hlist_for_each_entry(hd, &bucket->head, h) {
  		if (hd->region_nr == region_nr)
  			return hd;
  	}
  
  	return NULL;
  }
  
  /*
   * Insert a hydration into the hash table.
   *
   * NOTE: Must be called with the bucket lock held.
   */
  static inline void __insert_region_hydration(struct hash_table_bucket *bucket,
  					     struct dm_clone_region_hydration *hd)
  {
  	hlist_add_head(&hd->h, &bucket->head);
  }
  
  /*
   * This function inserts a hydration into the hash table, unless someone else
   * managed to insert a hydration for the same region first. In the latter case
   * it returns the existing hydration descriptor for this region.
   *
   * NOTE: Must be called with the hydration hash table lock held.
   */
  static struct dm_clone_region_hydration *
  __find_or_insert_region_hydration(struct hash_table_bucket *bucket,
  				  struct dm_clone_region_hydration *hd)
  {
  	struct dm_clone_region_hydration *hd2;
  
  	hd2 = __hash_find(bucket, hd->region_nr);
  	if (hd2)
  		return hd2;
  
  	__insert_region_hydration(bucket, hd);
  
  	return hd;
  }
  
  /*---------------------------------------------------------------------------*/
  
  /* Allocate a hydration */
  static struct dm_clone_region_hydration *alloc_hydration(struct clone *clone)
  {
  	struct dm_clone_region_hydration *hd;
  
  	/*
  	 * Allocate a hydration from the hydration mempool.
  	 * This might block but it can't fail.
  	 */
  	hd = mempool_alloc(&clone->hydration_pool, GFP_NOIO);
  	hd->clone = clone;
  
  	return hd;
  }
  
  static inline void free_hydration(struct dm_clone_region_hydration *hd)
  {
  	mempool_free(hd, &hd->clone->hydration_pool);
  }
  
  /* Initialize a hydration */
  static void hydration_init(struct dm_clone_region_hydration *hd, unsigned long region_nr)
  {
  	hd->region_nr = region_nr;
  	hd->overwrite_bio = NULL;
  	bio_list_init(&hd->deferred_bios);
  	hd->status = 0;
  
  	INIT_LIST_HEAD(&hd->list);
  	INIT_HLIST_NODE(&hd->h);
  }
  
  /*---------------------------------------------------------------------------*/
  
  /*
   * Update dm-clone's metadata after a region has finished hydrating and remove
   * hydration from the hash table.
   */
  static int hydration_update_metadata(struct dm_clone_region_hydration *hd)
  {
  	int r = 0;
  	unsigned long flags;
  	struct hash_table_bucket *bucket;
  	struct clone *clone = hd->clone;
  
  	if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY))
  		r = -EPERM;
  
  	/* Update the metadata */
  	if (likely(!r) && hd->status == BLK_STS_OK)
  		r = dm_clone_set_region_hydrated(clone->cmd, hd->region_nr);
  
  	bucket = get_hash_table_bucket(clone, hd->region_nr);
  
  	/* Remove hydration from hash table */
  	bucket_lock_irqsave(bucket, flags);
  	hlist_del(&hd->h);
  	bucket_unlock_irqrestore(bucket, flags);
  
  	return r;
  }
  
  /*
   * Complete a region's hydration:
   *
   *	1. Update dm-clone's metadata.
   *	2. Remove hydration from hash table.
   *	3. Complete overwrite bio.
   *	4. Issue deferred bios.
   *	5. If this was the last hydration, wake up anyone waiting for
   *	   hydrations to finish.
   */
  static void hydration_complete(struct dm_clone_region_hydration *hd)
  {
  	int r;
  	blk_status_t status;
  	struct clone *clone = hd->clone;
  
  	r = hydration_update_metadata(hd);
  
  	if (hd->status == BLK_STS_OK && likely(!r)) {
  		if (hd->overwrite_bio)
  			complete_overwrite_bio(clone, hd->overwrite_bio);
  
  		issue_deferred_bios(clone, &hd->deferred_bios);
  	} else {
  		status = r ? BLK_STS_IOERR : hd->status;
  
  		if (hd->overwrite_bio)
  			bio_list_add(&hd->deferred_bios, hd->overwrite_bio);
  
  		fail_bios(&hd->deferred_bios, status);
  	}
  
  	free_hydration(hd);
  
  	if (atomic_dec_and_test(&clone->hydrations_in_flight))
  		wakeup_hydration_waiters(clone);
  }
  
  static void hydration_kcopyd_callback(int read_err, unsigned long write_err, void *context)
  {
  	blk_status_t status;
  
  	struct dm_clone_region_hydration *tmp, *hd = context;
  	struct clone *clone = hd->clone;
  
  	LIST_HEAD(batched_hydrations);
  
  	if (read_err || write_err) {
  		DMERR_LIMIT("%s: hydration failed", clone_device_name(clone));
  		status = BLK_STS_IOERR;
  	} else {
  		status = BLK_STS_OK;
  	}
  	list_splice_tail(&hd->list, &batched_hydrations);
  
  	hd->status = status;
  	hydration_complete(hd);
  
  	/* Complete batched hydrations */
  	list_for_each_entry_safe(hd, tmp, &batched_hydrations, list) {
  		hd->status = status;
  		hydration_complete(hd);
  	}
  
  	/* Continue background hydration, if there is no I/O in-flight */
  	if (test_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags) &&
  	    !atomic_read(&clone->ios_in_flight))
  		wake_worker(clone);
  }
  
  static void hydration_copy(struct dm_clone_region_hydration *hd, unsigned int nr_regions)
  {
  	unsigned long region_start, region_end;
  	sector_t tail_size, region_size, total_size;
  	struct dm_io_region from, to;
  	struct clone *clone = hd->clone;
  
  	region_size = clone->region_size;
  	region_start = hd->region_nr;
  	region_end = region_start + nr_regions - 1;
  
  	total_size = (nr_regions - 1) << clone->region_shift;
  
  	if (region_end == clone->nr_regions - 1) {
  		/*
  		 * The last region of the target might be smaller than
  		 * region_size.
  		 */
  		tail_size = clone->ti->len & (region_size - 1);
  		if (!tail_size)
  			tail_size = region_size;
  	} else {
  		tail_size = region_size;
  	}
  
  	total_size += tail_size;
  
  	from.bdev = clone->source_dev->bdev;
  	from.sector = region_to_sector(clone, region_start);
  	from.count = total_size;
  
  	to.bdev = clone->dest_dev->bdev;
  	to.sector = from.sector;
  	to.count = from.count;
  
  	/* Issue copy */
  	atomic_add(nr_regions, &clone->hydrations_in_flight);
  	dm_kcopyd_copy(clone->kcopyd_client, &from, 1, &to, 0,
  		       hydration_kcopyd_callback, hd);
  }
  
  static void overwrite_endio(struct bio *bio)
  {
  	struct dm_clone_region_hydration *hd = bio->bi_private;
  
  	bio->bi_end_io = hd->overwrite_bio_end_io;
  	hd->status = bio->bi_status;
  
  	hydration_complete(hd);
  }
  
  static void hydration_overwrite(struct dm_clone_region_hydration *hd, struct bio *bio)
  {
  	/*
  	 * We don't need to save and restore bio->bi_private because device
  	 * mapper core generates a new bio for us to use, with clean
  	 * bi_private.
  	 */
  	hd->overwrite_bio = bio;
  	hd->overwrite_bio_end_io = bio->bi_end_io;
  
  	bio->bi_end_io = overwrite_endio;
  	bio->bi_private = hd;
  
  	atomic_inc(&hd->clone->hydrations_in_flight);
  	generic_make_request(bio);
  }
  
  /*
   * Hydrate bio's region.
   *
   * This function starts the hydration of the bio's region and puts the bio in
   * the list of deferred bios for this region. In case, by the time this
   * function is called, the region has finished hydrating it's submitted to the
   * destination device.
   *
   * NOTE: The bio remapping must be performed by the caller.
   */
  static void hydrate_bio_region(struct clone *clone, struct bio *bio)
  {
  	unsigned long region_nr;
  	struct hash_table_bucket *bucket;
  	struct dm_clone_region_hydration *hd, *hd2;
  
  	region_nr = bio_to_region(clone, bio);
  	bucket = get_hash_table_bucket(clone, region_nr);
  
  	bucket_lock_irq(bucket);
  
  	hd = __hash_find(bucket, region_nr);
  	if (hd) {
  		/* Someone else is hydrating the region */
  		bio_list_add(&hd->deferred_bios, bio);
  		bucket_unlock_irq(bucket);
  		return;
  	}
  
  	if (dm_clone_is_region_hydrated(clone->cmd, region_nr)) {
  		/* The region has been hydrated */
  		bucket_unlock_irq(bucket);
  		issue_bio(clone, bio);
  		return;
  	}
  
  	/*
  	 * We must allocate a hydration descriptor and start the hydration of
  	 * the corresponding region.
  	 */
  	bucket_unlock_irq(bucket);
  
  	hd = alloc_hydration(clone);
  	hydration_init(hd, region_nr);
  
  	bucket_lock_irq(bucket);
  
  	/* Check if the region has been hydrated in the meantime. */
  	if (dm_clone_is_region_hydrated(clone->cmd, region_nr)) {
  		bucket_unlock_irq(bucket);
  		free_hydration(hd);
  		issue_bio(clone, bio);
  		return;
  	}
  
  	hd2 = __find_or_insert_region_hydration(bucket, hd);
  	if (hd2 != hd) {
  		/* Someone else started the region's hydration. */
  		bio_list_add(&hd2->deferred_bios, bio);
  		bucket_unlock_irq(bucket);
  		free_hydration(hd);
  		return;
  	}
  
  	/*
  	 * If the metadata mode is RO or FAIL then there is no point starting a
  	 * hydration, since we will not be able to update the metadata when the
  	 * hydration finishes.
  	 */
  	if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY)) {
  		hlist_del(&hd->h);
  		bucket_unlock_irq(bucket);
  		free_hydration(hd);
  		bio_io_error(bio);
  		return;
  	}
  
  	/*
  	 * Start region hydration.
  	 *
  	 * If a bio overwrites a region, i.e., its size is equal to the
  	 * region's size, then we don't need to copy the region from the source
  	 * to the destination device.
  	 */
  	if (is_overwrite_bio(clone, bio)) {
  		bucket_unlock_irq(bucket);
  		hydration_overwrite(hd, bio);
  	} else {
  		bio_list_add(&hd->deferred_bios, bio);
  		bucket_unlock_irq(bucket);
  		hydration_copy(hd, 1);
  	}
  }
  
  /*---------------------------------------------------------------------------*/
  
  /*
   * Background hydrations.
   */
  
  /*
   * Batch region hydrations.
   *
   * To better utilize device bandwidth we batch together the hydration of
   * adjacent regions. This allows us to use small region sizes, e.g., 4KB, which
   * is good for small, random write performance (because of the overwriting of
   * un-hydrated regions) and at the same time issue big copy requests to kcopyd
   * to achieve high hydration bandwidth.
   */
  struct batch_info {
  	struct dm_clone_region_hydration *head;
  	unsigned int nr_batched_regions;
  };
  
  static void __batch_hydration(struct batch_info *batch,
  			      struct dm_clone_region_hydration *hd)
  {
  	struct clone *clone = hd->clone;
  	unsigned int max_batch_size = READ_ONCE(clone->hydration_batch_size);
  
  	if (batch->head) {
  		/* Try to extend the current batch */
  		if (batch->nr_batched_regions < max_batch_size &&
  		    (batch->head->region_nr + batch->nr_batched_regions) == hd->region_nr) {
  			list_add_tail(&hd->list, &batch->head->list);
  			batch->nr_batched_regions++;
  			hd = NULL;
  		}
  
  		/* Check if we should issue the current batch */
  		if (batch->nr_batched_regions >= max_batch_size || hd) {
  			hydration_copy(batch->head, batch->nr_batched_regions);
  			batch->head = NULL;
  			batch->nr_batched_regions = 0;
  		}
  	}
  
  	if (!hd)
  		return;
  
  	/* We treat max batch sizes of zero and one equivalently */
  	if (max_batch_size <= 1) {
  		hydration_copy(hd, 1);
  		return;
  	}
  
  	/* Start a new batch */
  	BUG_ON(!list_empty(&hd->list));
  	batch->head = hd;
  	batch->nr_batched_regions = 1;
  }
  
  static unsigned long __start_next_hydration(struct clone *clone,
  					    unsigned long offset,
  					    struct batch_info *batch)
  {
  	struct hash_table_bucket *bucket;
  	struct dm_clone_region_hydration *hd;
  	unsigned long nr_regions = clone->nr_regions;
  
  	hd = alloc_hydration(clone);
  
  	/* Try to find a region to hydrate. */
  	do {
  		offset = dm_clone_find_next_unhydrated_region(clone->cmd, offset);
  		if (offset == nr_regions)
  			break;
  
  		bucket = get_hash_table_bucket(clone, offset);
  		bucket_lock_irq(bucket);
  
  		if (!dm_clone_is_region_hydrated(clone->cmd, offset) &&
  		    !__hash_find(bucket, offset)) {
  			hydration_init(hd, offset);
  			__insert_region_hydration(bucket, hd);
  			bucket_unlock_irq(bucket);
  
  			/* Batch hydration */
  			__batch_hydration(batch, hd);
  
  			return (offset + 1);
  		}
  
  		bucket_unlock_irq(bucket);
  
  	} while (++offset < nr_regions);
  
  	if (hd)
  		free_hydration(hd);
  
  	return offset;
  }
  
  /*
   * This function searches for regions that still reside in the source device
   * and starts their hydration.
   */
  static void do_hydration(struct clone *clone)
  {
  	unsigned int current_volume;
  	unsigned long offset, nr_regions = clone->nr_regions;
  
  	struct batch_info batch = {
  		.head = NULL,
  		.nr_batched_regions = 0,
  	};
  
  	if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY))
  		return;
  
  	if (dm_clone_is_hydration_done(clone->cmd))
  		return;
  
  	/*
  	 * Avoid race with device suspension.
  	 */
  	atomic_inc(&clone->hydrations_in_flight);
  
  	/*
  	 * Make sure atomic_inc() is ordered before test_bit(), otherwise we
  	 * might race with clone_postsuspend() and start a region hydration
  	 * after the target has been suspended.
  	 *
  	 * This is paired with the smp_mb__after_atomic() in
  	 * clone_postsuspend().
  	 */
  	smp_mb__after_atomic();
  
  	offset = clone->hydration_offset;
  	while (likely(!test_bit(DM_CLONE_HYDRATION_SUSPENDED, &clone->flags)) &&
  	       !atomic_read(&clone->ios_in_flight) &&
  	       test_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags) &&
  	       offset < nr_regions) {
  		current_volume = atomic_read(&clone->hydrations_in_flight);
  		current_volume += batch.nr_batched_regions;
  
  		if (current_volume > READ_ONCE(clone->hydration_threshold))
  			break;
  
  		offset = __start_next_hydration(clone, offset, &batch);
  	}
  
  	if (batch.head)
  		hydration_copy(batch.head, batch.nr_batched_regions);
  
  	if (offset >= nr_regions)
  		offset = 0;
  
  	clone->hydration_offset = offset;
  
  	if (atomic_dec_and_test(&clone->hydrations_in_flight))
  		wakeup_hydration_waiters(clone);
  }
  
  /*---------------------------------------------------------------------------*/
  
  static bool need_commit_due_to_time(struct clone *clone)
  {
  	return !time_in_range(jiffies, clone->last_commit_jiffies,
  			      clone->last_commit_jiffies + COMMIT_PERIOD);
  }
  
  /*
   * A non-zero return indicates read-only or fail mode.
   */
  static int commit_metadata(struct clone *clone, bool *dest_dev_flushed)
  {
  	int r = 0;
  
  	if (dest_dev_flushed)
  		*dest_dev_flushed = false;
  
  	mutex_lock(&clone->commit_lock);
  
  	if (!dm_clone_changed_this_transaction(clone->cmd))
  		goto out;
  
  	if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY)) {
  		r = -EPERM;
  		goto out;
  	}
  
  	r = dm_clone_metadata_pre_commit(clone->cmd);
  	if (unlikely(r)) {
  		__metadata_operation_failed(clone, "dm_clone_metadata_pre_commit", r);
  		goto out;
  	}
  
  	bio_reset(&clone->flush_bio);
  	bio_set_dev(&clone->flush_bio, clone->dest_dev->bdev);
  	clone->flush_bio.bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
  
  	r = submit_bio_wait(&clone->flush_bio);
  	if (unlikely(r)) {
  		__metadata_operation_failed(clone, "flush destination device", r);
  		goto out;
  	}
  
  	if (dest_dev_flushed)
  		*dest_dev_flushed = true;
  
  	r = dm_clone_metadata_commit(clone->cmd);
  	if (unlikely(r)) {
  		__metadata_operation_failed(clone, "dm_clone_metadata_commit", r);
  		goto out;
  	}
  
  	if (dm_clone_is_hydration_done(clone->cmd))
  		dm_table_event(clone->ti->table);
  out:
  	mutex_unlock(&clone->commit_lock);
  
  	return r;
  }
  
  static void process_deferred_discards(struct clone *clone)
  {
  	int r = -EPERM;
  	struct bio *bio;
  	struct blk_plug plug;
  	unsigned long rs, re;
  	struct bio_list discards = BIO_EMPTY_LIST;
  
  	spin_lock_irq(&clone->lock);
  	bio_list_merge(&discards, &clone->deferred_discard_bios);
  	bio_list_init(&clone->deferred_discard_bios);
  	spin_unlock_irq(&clone->lock);
  
  	if (bio_list_empty(&discards))
  		return;
  
  	if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY))
  		goto out;
  
  	/* Update the metadata */
  	bio_list_for_each(bio, &discards) {
  		bio_region_range(clone, bio, &rs, &re);
  		/*
  		 * A discard request might cover regions that have been already
  		 * hydrated. There is no need to update the metadata for these
  		 * regions.
  		 */
  		r = dm_clone_cond_set_range(clone->cmd, rs, re - rs);
  
  		if (unlikely(r))
  			break;
  	}
  out:
  	blk_start_plug(&plug);
  	while ((bio = bio_list_pop(&discards)))
  		complete_discard_bio(clone, bio, r == 0);
  	blk_finish_plug(&plug);
  }
  
  static void process_deferred_bios(struct clone *clone)
  {
  	struct bio_list bios = BIO_EMPTY_LIST;
  
  	spin_lock_irq(&clone->lock);
  	bio_list_merge(&bios, &clone->deferred_bios);
  	bio_list_init(&clone->deferred_bios);
  	spin_unlock_irq(&clone->lock);
  
  	if (bio_list_empty(&bios))
  		return;
  
  	submit_bios(&bios);
  }
  
  static void process_deferred_flush_bios(struct clone *clone)
  {
  	struct bio *bio;
  	bool dest_dev_flushed;
  	struct bio_list bios = BIO_EMPTY_LIST;
  	struct bio_list bio_completions = BIO_EMPTY_LIST;
  
  	/*
  	 * If there are any deferred flush bios, we must commit the metadata
  	 * before issuing them or signaling their completion.
  	 */
  	spin_lock_irq(&clone->lock);
  	bio_list_merge(&bios, &clone->deferred_flush_bios);
  	bio_list_init(&clone->deferred_flush_bios);
  
  	bio_list_merge(&bio_completions, &clone->deferred_flush_completions);
  	bio_list_init(&clone->deferred_flush_completions);
  	spin_unlock_irq(&clone->lock);
  
  	if (bio_list_empty(&bios) && bio_list_empty(&bio_completions) &&
  	    !(dm_clone_changed_this_transaction(clone->cmd) && need_commit_due_to_time(clone)))
  		return;
  
  	if (commit_metadata(clone, &dest_dev_flushed)) {
  		bio_list_merge(&bios, &bio_completions);
  
  		while ((bio = bio_list_pop(&bios)))
  			bio_io_error(bio);
  
  		return;
  	}
  
  	clone->last_commit_jiffies = jiffies;
  
  	while ((bio = bio_list_pop(&bio_completions)))
  		bio_endio(bio);
  
  	while ((bio = bio_list_pop(&bios))) {
  		if ((bio->bi_opf & REQ_PREFLUSH) && dest_dev_flushed) {
  			/* We just flushed the destination device as part of
  			 * the metadata commit, so there is no reason to send
  			 * another flush.
  			 */
  			bio_endio(bio);
  		} else {
  			generic_make_request(bio);
  		}
  	}
  }
  
  static void do_worker(struct work_struct *work)
  {
  	struct clone *clone = container_of(work, typeof(*clone), worker);
  
  	process_deferred_bios(clone);
  	process_deferred_discards(clone);
  
  	/*
  	 * process_deferred_flush_bios():
  	 *
  	 *   - Commit metadata
  	 *
  	 *   - Process deferred REQ_FUA completions
  	 *
  	 *   - Process deferred REQ_PREFLUSH bios
  	 */
  	process_deferred_flush_bios(clone);
  
  	/* Background hydration */
  	do_hydration(clone);
  }
  
  /*
   * Commit periodically so that not too much unwritten data builds up.
   *
   * Also, restart background hydration, if it has been stopped by in-flight I/O.
   */
  static void do_waker(struct work_struct *work)
  {
  	struct clone *clone = container_of(to_delayed_work(work), struct clone, waker);
  
  	wake_worker(clone);
  	queue_delayed_work(clone->wq, &clone->waker, COMMIT_PERIOD);
  }
  
  /*---------------------------------------------------------------------------*/
  
  /*
   * Target methods
   */
  static int clone_map(struct dm_target *ti, struct bio *bio)
  {
  	struct clone *clone = ti->private;
  	unsigned long region_nr;
  
  	atomic_inc(&clone->ios_in_flight);
  
  	if (unlikely(get_clone_mode(clone) == CM_FAIL))
  		return DM_MAPIO_KILL;
  
  	/*
  	 * REQ_PREFLUSH bios carry no data:
  	 *
  	 * - Commit metadata, if changed
  	 *
  	 * - Pass down to destination device
  	 */
  	if (bio->bi_opf & REQ_PREFLUSH) {
  		remap_and_issue(clone, bio);
  		return DM_MAPIO_SUBMITTED;
  	}
  
  	bio->bi_iter.bi_sector = dm_target_offset(ti, bio->bi_iter.bi_sector);
  
  	/*
  	 * dm-clone interprets discards and performs a fast hydration of the
  	 * discarded regions, i.e., we skip the copy from the source device and
  	 * just mark the regions as hydrated.
  	 */
  	if (bio_op(bio) == REQ_OP_DISCARD) {
  		process_discard_bio(clone, bio);
  		return DM_MAPIO_SUBMITTED;
  	}
  
  	/*
  	 * If the bio's region is hydrated, redirect it to the destination
  	 * device.
  	 *
  	 * If the region is not hydrated and the bio is a READ, redirect it to
  	 * the source device.
  	 *
  	 * Else, defer WRITE bio until after its region has been hydrated and
  	 * start the region's hydration immediately.
  	 */
  	region_nr = bio_to_region(clone, bio);
  	if (dm_clone_is_region_hydrated(clone->cmd, region_nr)) {
  		remap_and_issue(clone, bio);
  		return DM_MAPIO_SUBMITTED;
  	} else if (bio_data_dir(bio) == READ) {
  		remap_to_source(clone, bio);
  		return DM_MAPIO_REMAPPED;
  	}
  
  	remap_to_dest(clone, bio);
  	hydrate_bio_region(clone, bio);
  
  	return DM_MAPIO_SUBMITTED;
  }
  
  static int clone_endio(struct dm_target *ti, struct bio *bio, blk_status_t *error)
  {
  	struct clone *clone = ti->private;
  
  	atomic_dec(&clone->ios_in_flight);
  
  	return DM_ENDIO_DONE;
  }
  
  static void emit_flags(struct clone *clone, char *result, unsigned int maxlen,
  		       ssize_t *sz_ptr)
  {
  	ssize_t sz = *sz_ptr;
  	unsigned int count;
  
  	count = !test_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags);
  	count += !test_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags);
  
  	DMEMIT("%u ", count);
  
  	if (!test_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags))
  		DMEMIT("no_hydration ");
  
  	if (!test_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags))
  		DMEMIT("no_discard_passdown ");
  
  	*sz_ptr = sz;
  }
  
  static void emit_core_args(struct clone *clone, char *result,
  			   unsigned int maxlen, ssize_t *sz_ptr)
  {
  	ssize_t sz = *sz_ptr;
  	unsigned int count = 4;
  
  	DMEMIT("%u hydration_threshold %u hydration_batch_size %u ", count,
  	       READ_ONCE(clone->hydration_threshold),
  	       READ_ONCE(clone->hydration_batch_size));
  
  	*sz_ptr = sz;
  }
  
  /*
   * Status format:
   *
   * <metadata block size> <#used metadata blocks>/<#total metadata blocks>
   * <clone region size> <#hydrated regions>/<#total regions> <#hydrating regions>
   * <#features> <features>* <#core args> <core args>* <clone metadata mode>
   */
  static void clone_status(struct dm_target *ti, status_type_t type,
  			 unsigned int status_flags, char *result,
  			 unsigned int maxlen)
  {
  	int r;
  	unsigned int i;
  	ssize_t sz = 0;
  	dm_block_t nr_free_metadata_blocks = 0;
  	dm_block_t nr_metadata_blocks = 0;
  	char buf[BDEVNAME_SIZE];
  	struct clone *clone = ti->private;
  
  	switch (type) {
  	case STATUSTYPE_INFO:
  		if (get_clone_mode(clone) == CM_FAIL) {
  			DMEMIT("Fail");
  			break;
  		}
  
  		/* Commit to ensure statistics aren't out-of-date */
  		if (!(status_flags & DM_STATUS_NOFLUSH_FLAG) && !dm_suspended(ti))
  			(void) commit_metadata(clone, NULL);
  
  		r = dm_clone_get_free_metadata_block_count(clone->cmd, &nr_free_metadata_blocks);
  
  		if (r) {
  			DMERR("%s: dm_clone_get_free_metadata_block_count returned %d",
  			      clone_device_name(clone), r);
  			goto error;
  		}
  
  		r = dm_clone_get_metadata_dev_size(clone->cmd, &nr_metadata_blocks);
  
  		if (r) {
  			DMERR("%s: dm_clone_get_metadata_dev_size returned %d",
  			      clone_device_name(clone), r);
  			goto error;
  		}
  
  		DMEMIT("%u %llu/%llu %llu %lu/%lu %u ",
  		       DM_CLONE_METADATA_BLOCK_SIZE,
  		       (unsigned long long)(nr_metadata_blocks - nr_free_metadata_blocks),
  		       (unsigned long long)nr_metadata_blocks,
  		       (unsigned long long)clone->region_size,
  		       dm_clone_nr_of_hydrated_regions(clone->cmd),
  		       clone->nr_regions,
  		       atomic_read(&clone->hydrations_in_flight));
  
  		emit_flags(clone, result, maxlen, &sz);
  		emit_core_args(clone, result, maxlen, &sz);
  
  		switch (get_clone_mode(clone)) {
  		case CM_WRITE:
  			DMEMIT("rw");
  			break;
  		case CM_READ_ONLY:
  			DMEMIT("ro");
  			break;
  		case CM_FAIL:
  			DMEMIT("Fail");
  		}
  
  		break;
  
  	case STATUSTYPE_TABLE:
  		format_dev_t(buf, clone->metadata_dev->bdev->bd_dev);
  		DMEMIT("%s ", buf);
  
  		format_dev_t(buf, clone->dest_dev->bdev->bd_dev);
  		DMEMIT("%s ", buf);
  
  		format_dev_t(buf, clone->source_dev->bdev->bd_dev);
  		DMEMIT("%s", buf);
  
  		for (i = 0; i < clone->nr_ctr_args; i++)
  			DMEMIT(" %s", clone->ctr_args[i]);
  	}
  
  	return;
  
  error:
  	DMEMIT("Error");
  }
  
  static int clone_is_congested(struct dm_target_callbacks *cb, int bdi_bits)
  {
  	struct request_queue *dest_q, *source_q;
  	struct clone *clone = container_of(cb, struct clone, callbacks);
  
  	source_q = bdev_get_queue(clone->source_dev->bdev);
  	dest_q = bdev_get_queue(clone->dest_dev->bdev);
  
  	return (bdi_congested(dest_q->backing_dev_info, bdi_bits) |
  		bdi_congested(source_q->backing_dev_info, bdi_bits));
  }
  
  static sector_t get_dev_size(struct dm_dev *dev)
  {
  	return i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT;
  }
  
  /*---------------------------------------------------------------------------*/
  
  /*
   * Construct a clone device mapping:
   *
   * clone <metadata dev> <destination dev> <source dev> <region size>
   *	[<#feature args> [<feature arg>]* [<#core args> [key value]*]]
   *
   * metadata dev: Fast device holding the persistent metadata
   * destination dev: The destination device, which will become a clone of the
   *                  source device
   * source dev: The read-only source device that gets cloned
   * region size: dm-clone unit size in sectors
   *
   * #feature args: Number of feature arguments passed
   * feature args: E.g. no_hydration, no_discard_passdown
   *
   * #core arguments: An even number of core arguments
   * core arguments: Key/value pairs for tuning the core
   *		   E.g. 'hydration_threshold 256'
   */
  static int parse_feature_args(struct dm_arg_set *as, struct clone *clone)
  {
  	int r;
  	unsigned int argc;
  	const char *arg_name;
  	struct dm_target *ti = clone->ti;
  
  	const struct dm_arg args = {
  		.min = 0,
  		.max = 2,
  		.error = "Invalid number of feature arguments"
  	};
  
  	/* No feature arguments supplied */
  	if (!as->argc)
  		return 0;
  
  	r = dm_read_arg_group(&args, as, &argc, &ti->error);
  	if (r)
  		return r;
  
  	while (argc) {
  		arg_name = dm_shift_arg(as);
  		argc--;
  
  		if (!strcasecmp(arg_name, "no_hydration")) {
  			__clear_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags);
  		} else if (!strcasecmp(arg_name, "no_discard_passdown")) {
  			__clear_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags);
  		} else {
  			ti->error = "Invalid feature argument";
  			return -EINVAL;
  		}
  	}
  
  	return 0;
  }
  
  static int parse_core_args(struct dm_arg_set *as, struct clone *clone)
  {
  	int r;
  	unsigned int argc;
  	unsigned int value;
  	const char *arg_name;
  	struct dm_target *ti = clone->ti;
  
  	const struct dm_arg args = {
  		.min = 0,
  		.max = 4,
  		.error = "Invalid number of core arguments"
  	};
  
  	/* Initialize core arguments */
  	clone->hydration_batch_size = DEFAULT_HYDRATION_BATCH_SIZE;
  	clone->hydration_threshold = DEFAULT_HYDRATION_THRESHOLD;
  
  	/* No core arguments supplied */
  	if (!as->argc)
  		return 0;
  
  	r = dm_read_arg_group(&args, as, &argc, &ti->error);
  	if (r)
  		return r;
  
  	if (argc & 1) {
  		ti->error = "Number of core arguments must be even";
  		return -EINVAL;
  	}
  
  	while (argc) {
  		arg_name = dm_shift_arg(as);
  		argc -= 2;
  
  		if (!strcasecmp(arg_name, "hydration_threshold")) {
  			if (kstrtouint(dm_shift_arg(as), 10, &value)) {
  				ti->error = "Invalid value for argument `hydration_threshold'";
  				return -EINVAL;
  			}
  			clone->hydration_threshold = value;
  		} else if (!strcasecmp(arg_name, "hydration_batch_size")) {
  			if (kstrtouint(dm_shift_arg(as), 10, &value)) {
  				ti->error = "Invalid value for argument `hydration_batch_size'";
  				return -EINVAL;
  			}
  			clone->hydration_batch_size = value;
  		} else {
  			ti->error = "Invalid core argument";
  			return -EINVAL;
  		}
  	}
  
  	return 0;
  }
  
  static int parse_region_size(struct clone *clone, struct dm_arg_set *as, char **error)
  {
  	int r;
  	unsigned int region_size;
  	struct dm_arg arg;
  
  	arg.min = MIN_REGION_SIZE;
  	arg.max = MAX_REGION_SIZE;
  	arg.error = "Invalid region size";
  
  	r = dm_read_arg(&arg, as, &region_size, error);
  	if (r)
  		return r;
  
  	/* Check region size is a power of 2 */
  	if (!is_power_of_2(region_size)) {
  		*error = "Region size is not a power of 2";
  		return -EINVAL;
  	}
  
  	/* Validate the region size against the device logical block size */
  	if (region_size % (bdev_logical_block_size(clone->source_dev->bdev) >> 9) ||
  	    region_size % (bdev_logical_block_size(clone->dest_dev->bdev) >> 9)) {
  		*error = "Region size is not a multiple of device logical block size";
  		return -EINVAL;
  	}
  
  	clone->region_size = region_size;
  
  	return 0;
  }
  
  static int validate_nr_regions(unsigned long n, char **error)
  {
  	/*
  	 * dm_bitset restricts us to 2^32 regions. test_bit & co. restrict us
  	 * further to 2^31 regions.
  	 */
  	if (n > (1UL << 31)) {
  		*error = "Too many regions. Consider increasing the region size";
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  static int parse_metadata_dev(struct clone *clone, struct dm_arg_set *as, char **error)
  {
  	int r;
  	sector_t metadata_dev_size;
  	char b[BDEVNAME_SIZE];
  
  	r = dm_get_device(clone->ti, dm_shift_arg(as), FMODE_READ | FMODE_WRITE,
  			  &clone->metadata_dev);
  	if (r) {
  		*error = "Error opening metadata device";
  		return r;
  	}
  
  	metadata_dev_size = get_dev_size(clone->metadata_dev);
  	if (metadata_dev_size > DM_CLONE_METADATA_MAX_SECTORS_WARNING)
  		DMWARN("Metadata device %s is larger than %u sectors: excess space will not be used.",
  		       bdevname(clone->metadata_dev->bdev, b), DM_CLONE_METADATA_MAX_SECTORS);
  
  	return 0;
  }
  
  static int parse_dest_dev(struct clone *clone, struct dm_arg_set *as, char **error)
  {
  	int r;
  	sector_t dest_dev_size;
  
  	r = dm_get_device(clone->ti, dm_shift_arg(as), FMODE_READ | FMODE_WRITE,
  			  &clone->dest_dev);
  	if (r) {
  		*error = "Error opening destination device";
  		return r;
  	}
  
  	dest_dev_size = get_dev_size(clone->dest_dev);
  	if (dest_dev_size < clone->ti->len) {
  		dm_put_device(clone->ti, clone->dest_dev);
  		*error = "Device size larger than destination device";
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  static int parse_source_dev(struct clone *clone, struct dm_arg_set *as, char **error)
  {
  	int r;
  	sector_t source_dev_size;
  
  	r = dm_get_device(clone->ti, dm_shift_arg(as), FMODE_READ,
  			  &clone->source_dev);
  	if (r) {
  		*error = "Error opening source device";
  		return r;
  	}
  
  	source_dev_size = get_dev_size(clone->source_dev);
  	if (source_dev_size < clone->ti->len) {
  		dm_put_device(clone->ti, clone->source_dev);
  		*error = "Device size larger than source device";
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  static int copy_ctr_args(struct clone *clone, int argc, const char **argv, char **error)
  {
  	unsigned int i;
  	const char **copy;
  
  	copy = kcalloc(argc, sizeof(*copy), GFP_KERNEL);
  	if (!copy)
  		goto error;
  
  	for (i = 0; i < argc; i++) {
  		copy[i] = kstrdup(argv[i], GFP_KERNEL);
  
  		if (!copy[i]) {
  			while (i--)
  				kfree(copy[i]);
  			kfree(copy);
  			goto error;
  		}
  	}
  
  	clone->nr_ctr_args = argc;
  	clone->ctr_args = copy;
  	return 0;
  
  error:
  	*error = "Failed to allocate memory for table line";
  	return -ENOMEM;
  }
  
  static int clone_ctr(struct dm_target *ti, unsigned int argc, char **argv)
  {
  	int r;
  	struct clone *clone;
  	struct dm_arg_set as;
  
  	if (argc < 4) {
  		ti->error = "Invalid number of arguments";
  		return -EINVAL;
  	}
  
  	as.argc = argc;
  	as.argv = argv;
  
  	clone = kzalloc(sizeof(*clone), GFP_KERNEL);
  	if (!clone) {
  		ti->error = "Failed to allocate clone structure";
  		return -ENOMEM;
  	}
  
  	clone->ti = ti;
  
  	/* Initialize dm-clone flags */
  	__set_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags);
  	__set_bit(DM_CLONE_HYDRATION_SUSPENDED, &clone->flags);
  	__set_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags);
  
  	r = parse_metadata_dev(clone, &as, &ti->error);
  	if (r)
  		goto out_with_clone;
  
  	r = parse_dest_dev(clone, &as, &ti->error);
  	if (r)
  		goto out_with_meta_dev;
  
  	r = parse_source_dev(clone, &as, &ti->error);
  	if (r)
  		goto out_with_dest_dev;
  
  	r = parse_region_size(clone, &as, &ti->error);
  	if (r)
  		goto out_with_source_dev;
  
  	clone->region_shift = __ffs(clone->region_size);
  	clone->nr_regions = dm_sector_div_up(ti->len, clone->region_size);
  
  	r = validate_nr_regions(clone->nr_regions, &ti->error);
  	if (r)
  		goto out_with_source_dev;
  
  	r = dm_set_target_max_io_len(ti, clone->region_size);
  	if (r) {
  		ti->error = "Failed to set max io len";
  		goto out_with_source_dev;
  	}
  
  	r = parse_feature_args(&as, clone);
  	if (r)
  		goto out_with_source_dev;
  
  	r = parse_core_args(&as, clone);
  	if (r)
  		goto out_with_source_dev;
  
  	/* Load metadata */
  	clone->cmd = dm_clone_metadata_open(clone->metadata_dev->bdev, ti->len,
  					    clone->region_size);
  	if (IS_ERR(clone->cmd)) {
  		ti->error = "Failed to load metadata";
  		r = PTR_ERR(clone->cmd);
  		goto out_with_source_dev;
  	}
  
  	__set_clone_mode(clone, CM_WRITE);
  
  	if (get_clone_mode(clone) != CM_WRITE) {
  		ti->error = "Unable to get write access to metadata, please check/repair metadata";
  		r = -EPERM;
  		goto out_with_metadata;
  	}
  
  	clone->last_commit_jiffies = jiffies;
  
  	/* Allocate hydration hash table */
  	r = hash_table_init(clone);
  	if (r) {
  		ti->error = "Failed to allocate hydration hash table";
  		goto out_with_metadata;
  	}
  
  	atomic_set(&clone->ios_in_flight, 0);
  	init_waitqueue_head(&clone->hydration_stopped);
  	spin_lock_init(&clone->lock);
  	bio_list_init(&clone->deferred_bios);
  	bio_list_init(&clone->deferred_discard_bios);
  	bio_list_init(&clone->deferred_flush_bios);
  	bio_list_init(&clone->deferred_flush_completions);
  	clone->hydration_offset = 0;
  	atomic_set(&clone->hydrations_in_flight, 0);
  	bio_init(&clone->flush_bio, NULL, 0);
  
  	clone->wq = alloc_workqueue("dm-" DM_MSG_PREFIX, WQ_MEM_RECLAIM, 0);
  	if (!clone->wq) {
  		ti->error = "Failed to allocate workqueue";
  		r = -ENOMEM;
  		goto out_with_ht;
  	}
  
  	INIT_WORK(&clone->worker, do_worker);
  	INIT_DELAYED_WORK(&clone->waker, do_waker);
  
  	clone->kcopyd_client = dm_kcopyd_client_create(&dm_kcopyd_throttle);
  	if (IS_ERR(clone->kcopyd_client)) {
  		r = PTR_ERR(clone->kcopyd_client);
  		goto out_with_wq;
  	}
  
  	r = mempool_init_slab_pool(&clone->hydration_pool, MIN_HYDRATIONS,
  				   _hydration_cache);
  	if (r) {
  		ti->error = "Failed to create dm_clone_region_hydration memory pool";
  		goto out_with_kcopyd;
  	}
  
  	/* Save a copy of the table line */
  	r = copy_ctr_args(clone, argc - 3, (const char **)argv + 3, &ti->error);
  	if (r)
  		goto out_with_mempool;
  
  	mutex_init(&clone->commit_lock);
  	clone->callbacks.congested_fn = clone_is_congested;
  	dm_table_add_target_callbacks(ti->table, &clone->callbacks);
  
  	/* Enable flushes */
  	ti->num_flush_bios = 1;
  	ti->flush_supported = true;
  
  	/* Enable discards */
  	ti->discards_supported = true;
  	ti->num_discard_bios = 1;
  
  	ti->private = clone;
  
  	return 0;
  
  out_with_mempool:
  	mempool_exit(&clone->hydration_pool);
  out_with_kcopyd:
  	dm_kcopyd_client_destroy(clone->kcopyd_client);
  out_with_wq:
  	destroy_workqueue(clone->wq);
  out_with_ht:
  	hash_table_exit(clone);
  out_with_metadata:
  	dm_clone_metadata_close(clone->cmd);
  out_with_source_dev:
  	dm_put_device(ti, clone->source_dev);
  out_with_dest_dev:
  	dm_put_device(ti, clone->dest_dev);
  out_with_meta_dev:
  	dm_put_device(ti, clone->metadata_dev);
  out_with_clone:
  	kfree(clone);
  
  	return r;
  }
  
  static void clone_dtr(struct dm_target *ti)
  {
  	unsigned int i;
  	struct clone *clone = ti->private;
  
  	mutex_destroy(&clone->commit_lock);
  	bio_uninit(&clone->flush_bio);
  
  	for (i = 0; i < clone->nr_ctr_args; i++)
  		kfree(clone->ctr_args[i]);
  	kfree(clone->ctr_args);
  
  	mempool_exit(&clone->hydration_pool);
  	dm_kcopyd_client_destroy(clone->kcopyd_client);
  	destroy_workqueue(clone->wq);
  	hash_table_exit(clone);
  	dm_clone_metadata_close(clone->cmd);
  	dm_put_device(ti, clone->source_dev);
  	dm_put_device(ti, clone->dest_dev);
  	dm_put_device(ti, clone->metadata_dev);
  
  	kfree(clone);
  }
  
  /*---------------------------------------------------------------------------*/
  
  static void clone_postsuspend(struct dm_target *ti)
  {
  	struct clone *clone = ti->private;
  
  	/*
  	 * To successfully suspend the device:
  	 *
  	 *	- We cancel the delayed work for periodic commits and wait for
  	 *	  it to finish.
  	 *
  	 *	- We stop the background hydration, i.e. we prevent new region
  	 *	  hydrations from starting.
  	 *
  	 *	- We wait for any in-flight hydrations to finish.
  	 *
  	 *	- We flush the workqueue.
  	 *
  	 *	- We commit the metadata.
  	 */
  	cancel_delayed_work_sync(&clone->waker);
  
  	set_bit(DM_CLONE_HYDRATION_SUSPENDED, &clone->flags);
  
  	/*
  	 * Make sure set_bit() is ordered before atomic_read(), otherwise we
  	 * might race with do_hydration() and miss some started region
  	 * hydrations.
  	 *
  	 * This is paired with smp_mb__after_atomic() in do_hydration().
  	 */
  	smp_mb__after_atomic();
  
  	wait_event(clone->hydration_stopped, !atomic_read(&clone->hydrations_in_flight));
  	flush_workqueue(clone->wq);
  
  	(void) commit_metadata(clone, NULL);
  }
  
  static void clone_resume(struct dm_target *ti)
  {
  	struct clone *clone = ti->private;
  
  	clear_bit(DM_CLONE_HYDRATION_SUSPENDED, &clone->flags);
  	do_waker(&clone->waker.work);
  }
  
  static bool bdev_supports_discards(struct block_device *bdev)
  {
  	struct request_queue *q = bdev_get_queue(bdev);
  
  	return (q && blk_queue_discard(q));
  }
  
  /*
   * If discard_passdown was enabled verify that the destination device supports
   * discards. Disable discard_passdown if not.
   */
  static void disable_passdown_if_not_supported(struct clone *clone)
  {
  	struct block_device *dest_dev = clone->dest_dev->bdev;
  	struct queue_limits *dest_limits = &bdev_get_queue(dest_dev)->limits;
  	const char *reason = NULL;
  	char buf[BDEVNAME_SIZE];
  
  	if (!test_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags))
  		return;
  
  	if (!bdev_supports_discards(dest_dev))
  		reason = "discard unsupported";
  	else if (dest_limits->max_discard_sectors < clone->region_size)
  		reason = "max discard sectors smaller than a region";
  
  	if (reason) {
  		DMWARN("Destination device (%s) %s: Disabling discard passdown.",
  		       bdevname(dest_dev, buf), reason);
  		clear_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags);
  	}
  }
  
  static void set_discard_limits(struct clone *clone, struct queue_limits *limits)
  {
  	struct block_device *dest_bdev = clone->dest_dev->bdev;
  	struct queue_limits *dest_limits = &bdev_get_queue(dest_bdev)->limits;
  
  	if (!test_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags)) {
  		/* No passdown is done so we set our own virtual limits */
  		limits->discard_granularity = clone->region_size << SECTOR_SHIFT;
  		limits->max_discard_sectors = round_down(UINT_MAX >> SECTOR_SHIFT, clone->region_size);
  		return;
  	}
  
  	/*
  	 * clone_iterate_devices() is stacking both the source and destination
  	 * device limits but discards aren't passed to the source device, so
  	 * inherit destination's limits.
  	 */
  	limits->max_discard_sectors = dest_limits->max_discard_sectors;
  	limits->max_hw_discard_sectors = dest_limits->max_hw_discard_sectors;
  	limits->discard_granularity = dest_limits->discard_granularity;
  	limits->discard_alignment = dest_limits->discard_alignment;
  	limits->discard_misaligned = dest_limits->discard_misaligned;
  	limits->max_discard_segments = dest_limits->max_discard_segments;
  }
  
  static void clone_io_hints(struct dm_target *ti, struct queue_limits *limits)
  {
  	struct clone *clone = ti->private;
  	u64 io_opt_sectors = limits->io_opt >> SECTOR_SHIFT;
  
  	/*
  	 * If the system-determined stacked limits are compatible with
  	 * dm-clone's region size (io_opt is a factor) do not override them.
  	 */
  	if (io_opt_sectors < clone->region_size ||
  	    do_div(io_opt_sectors, clone->region_size)) {
  		blk_limits_io_min(limits, clone->region_size << SECTOR_SHIFT);
  		blk_limits_io_opt(limits, clone->region_size << SECTOR_SHIFT);
  	}
  
  	disable_passdown_if_not_supported(clone);
  	set_discard_limits(clone, limits);
  }
  
  static int clone_iterate_devices(struct dm_target *ti,
  				 iterate_devices_callout_fn fn, void *data)
  {
  	int ret;
  	struct clone *clone = ti->private;
  	struct dm_dev *dest_dev = clone->dest_dev;
  	struct dm_dev *source_dev = clone->source_dev;
  
  	ret = fn(ti, source_dev, 0, ti->len, data);
  	if (!ret)
  		ret = fn(ti, dest_dev, 0, ti->len, data);
  	return ret;
  }
  
  /*
   * dm-clone message functions.
   */
  static void set_hydration_threshold(struct clone *clone, unsigned int nr_regions)
  {
  	WRITE_ONCE(clone->hydration_threshold, nr_regions);
  
  	/*
  	 * If user space sets hydration_threshold to zero then the hydration
  	 * will stop. If at a later time the hydration_threshold is increased
  	 * we must restart the hydration process by waking up the worker.
  	 */
  	wake_worker(clone);
  }
  
  static void set_hydration_batch_size(struct clone *clone, unsigned int nr_regions)
  {
  	WRITE_ONCE(clone->hydration_batch_size, nr_regions);
  }
  
  static void enable_hydration(struct clone *clone)
  {
  	if (!test_and_set_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags))
  		wake_worker(clone);
  }
  
  static void disable_hydration(struct clone *clone)
  {
  	clear_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags);
  }
  
  static int clone_message(struct dm_target *ti, unsigned int argc, char **argv,
  			 char *result, unsigned int maxlen)
  {
  	struct clone *clone = ti->private;
  	unsigned int value;
  
  	if (!argc)
  		return -EINVAL;
  
  	if (!strcasecmp(argv[0], "enable_hydration")) {
  		enable_hydration(clone);
  		return 0;
  	}
  
  	if (!strcasecmp(argv[0], "disable_hydration")) {
  		disable_hydration(clone);
  		return 0;
  	}
  
  	if (argc != 2)
  		return -EINVAL;
  
  	if (!strcasecmp(argv[0], "hydration_threshold")) {
  		if (kstrtouint(argv[1], 10, &value))
  			return -EINVAL;
  
  		set_hydration_threshold(clone, value);
  
  		return 0;
  	}
  
  	if (!strcasecmp(argv[0], "hydration_batch_size")) {
  		if (kstrtouint(argv[1], 10, &value))
  			return -EINVAL;
  
  		set_hydration_batch_size(clone, value);
  
  		return 0;
  	}
  
  	DMERR("%s: Unsupported message `%s'", clone_device_name(clone), argv[0]);
  	return -EINVAL;
  }
  
  static struct target_type clone_target = {
  	.name = "clone",
  	.version = {1, 0, 0},
  	.module = THIS_MODULE,
  	.ctr = clone_ctr,
  	.dtr =  clone_dtr,
  	.map = clone_map,
  	.end_io = clone_endio,
  	.postsuspend = clone_postsuspend,
  	.resume = clone_resume,
  	.status = clone_status,
  	.message = clone_message,
  	.io_hints = clone_io_hints,
  	.iterate_devices = clone_iterate_devices,
  };
  
  /*---------------------------------------------------------------------------*/
  
  /* Module functions */
  static int __init dm_clone_init(void)
  {
  	int r;
  
  	_hydration_cache = KMEM_CACHE(dm_clone_region_hydration, 0);
  	if (!_hydration_cache)
  		return -ENOMEM;
  
  	r = dm_register_target(&clone_target);
  	if (r < 0) {
  		DMERR("Failed to register clone target");
  		return r;
  	}
  
  	return 0;
  }
  
  static void __exit dm_clone_exit(void)
  {
  	dm_unregister_target(&clone_target);
  
  	kmem_cache_destroy(_hydration_cache);
  	_hydration_cache = NULL;
  }
  
  /* Module hooks */
  module_init(dm_clone_init);
  module_exit(dm_clone_exit);
  
  MODULE_DESCRIPTION(DM_NAME " clone target");
  MODULE_AUTHOR("Nikos Tsironis <ntsironis@arrikto.com>");
  MODULE_LICENSE("GPL");
  