/*
   * Copyright (C) 2016 Red Hat, Inc. All rights reserved.
   *
   * This file is released under the GPL.
   */
  
  #include "dm-core.h"
  #include "dm-rq.h"
  
  #include <linux/elevator.h> /* for rq_end_sector() */
  #include <linux/blk-mq.h>
  
  #define DM_MSG_PREFIX "core-rq"
  
  #define DM_MQ_NR_HW_QUEUES 1
  #define DM_MQ_QUEUE_DEPTH 2048
  static unsigned dm_mq_nr_hw_queues = DM_MQ_NR_HW_QUEUES;
  static unsigned dm_mq_queue_depth = DM_MQ_QUEUE_DEPTH;
  
  /*
   * Request-based DM's mempools' reserved IOs set by the user.
   */
  #define RESERVED_REQUEST_BASED_IOS	256
  static unsigned reserved_rq_based_ios = RESERVED_REQUEST_BASED_IOS;

  static bool use_blk_mq = IS_ENABLED(CONFIG_DM_MQ_DEFAULT);

  
  bool dm_use_blk_mq_default(void)
  {
  	return use_blk_mq;
  }
  
  bool dm_use_blk_mq(struct mapped_device *md)
  {
  	return md->use_blk_mq;
  }
  EXPORT_SYMBOL_GPL(dm_use_blk_mq);
  
  unsigned dm_get_reserved_rq_based_ios(void)
  {
  	return __dm_get_module_param(&reserved_rq_based_ios,
  				     RESERVED_REQUEST_BASED_IOS, DM_RESERVED_MAX_IOS);
  }
  EXPORT_SYMBOL_GPL(dm_get_reserved_rq_based_ios);
  
  static unsigned dm_get_blk_mq_nr_hw_queues(void)
  {
  	return __dm_get_module_param(&dm_mq_nr_hw_queues, 1, 32);
  }
  
  static unsigned dm_get_blk_mq_queue_depth(void)
  {
  	return __dm_get_module_param(&dm_mq_queue_depth,
  				     DM_MQ_QUEUE_DEPTH, BLK_MQ_MAX_DEPTH);
  }
  
  int dm_request_based(struct mapped_device *md)
  {
  	return blk_queue_stackable(md->queue);
  }
  
  static void dm_old_start_queue(struct request_queue *q)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(q->queue_lock, flags);
  	if (blk_queue_stopped(q))
  		blk_start_queue(q);
  	spin_unlock_irqrestore(q->queue_lock, flags);
  }

  static void dm_mq_start_queue(struct request_queue *q)
  {

  	blk_mq_unquiesce_queue(q);

  	blk_mq_kick_requeue_list(q);
  }

  void dm_start_queue(struct request_queue *q)
  {
  	if (!q->mq_ops)
  		dm_old_start_queue(q);

  	else
  		dm_mq_start_queue(q);

  }
  
  static void dm_old_stop_queue(struct request_queue *q)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(q->queue_lock, flags);

  	if (!blk_queue_stopped(q))
  		blk_stop_queue(q);

  	spin_unlock_irqrestore(q->queue_lock, flags);
  }

  static void dm_mq_stop_queue(struct request_queue *q)
  {

  	if (blk_mq_queue_stopped(q))

  		return;

  	blk_mq_quiesce_queue(q);

  }
  
  void dm_stop_queue(struct request_queue *q)
  {
  	if (!q->mq_ops)
  		dm_old_stop_queue(q);

  	else
  		dm_mq_stop_queue(q);

  }

  /*
   * Partial completion handling for request-based dm
   */
  static void end_clone_bio(struct bio *clone)
  {
  	struct dm_rq_clone_bio_info *info =
  		container_of(clone, struct dm_rq_clone_bio_info, clone);
  	struct dm_rq_target_io *tio = info->tio;

  	unsigned int nr_bytes = info->orig->bi_iter.bi_size;

  	blk_status_t error = clone->bi_status;

  	bool is_last = !clone->bi_next;

  
  	bio_put(clone);
  
  	if (tio->error)
  		/*
  		 * An error has already been detected on the request.
  		 * Once error occurred, just let clone->end_io() handle
  		 * the remainder.
  		 */
  		return;
  	else if (error) {
  		/*
  		 * Don't notice the error to the upper layer yet.
  		 * The error handling decision is made by the target driver,
  		 * when the request is completed.
  		 */
  		tio->error = error;

  		goto exit;

  	}
  
  	/*
  	 * I/O for the bio successfully completed.
  	 * Notice the data completion to the upper layer.
  	 */

  	tio->completed += nr_bytes;

  
  	/*
  	 * Update the original request.
  	 * Do not use blk_end_request() here, because it may complete
  	 * the original request before the clone, and break the ordering.
  	 */

  	if (is_last)
   exit:
  		blk_update_request(tio->orig, BLK_STS_OK, tio->completed);

  }
  
  static struct dm_rq_target_io *tio_from_request(struct request *rq)
  {

  	return blk_mq_rq_to_pdu(rq);

  }
  
  static void rq_end_stats(struct mapped_device *md, struct request *orig)
  {
  	if (unlikely(dm_stats_used(&md->stats))) {
  		struct dm_rq_target_io *tio = tio_from_request(orig);
  		tio->duration_jiffies = jiffies - tio->duration_jiffies;
  		dm_stats_account_io(&md->stats, rq_data_dir(orig),
  				    blk_rq_pos(orig), tio->n_sectors, true,
  				    tio->duration_jiffies, &tio->stats_aux);
  	}
  }
  
  /*
   * Don't touch any member of the md after calling this function because
   * the md may be freed in dm_put() at the end of this function.
   * Or do dm_get() before calling this function and dm_put() later.
   */
  static void rq_completed(struct mapped_device *md, int rw, bool run_queue)
  {

  	struct request_queue *q = md->queue;
  	unsigned long flags;

  	atomic_dec(&md->pending[rw]);
  
  	/* nudge anyone waiting on suspend queue */
  	if (!md_in_flight(md))
  		wake_up(&md->wait);
  
  	/*
  	 * Run this off this callpath, as drivers could invoke end_io while
  	 * inside their request_fn (and holding the queue lock). Calling
  	 * back into ->request_fn() could deadlock attempting to grab the
  	 * queue lock again.
  	 */

  	if (!q->mq_ops && run_queue) {
  		spin_lock_irqsave(q->queue_lock, flags);
  		blk_run_queue_async(q);
  		spin_unlock_irqrestore(q->queue_lock, flags);
  	}

  
  	/*
  	 * dm_put() must be at the end of this function. See the comment above
  	 */
  	dm_put(md);
  }

  /*
   * Complete the clone and the original request.
   * Must be called without clone's queue lock held,
   * see end_clone_request() for more details.
   */

  static void dm_end_request(struct request *clone, blk_status_t error)

  {
  	int rw = rq_data_dir(clone);
  	struct dm_rq_target_io *tio = clone->end_io_data;
  	struct mapped_device *md = tio->md;
  	struct request *rq = tio->orig;

  	blk_rq_unprep_clone(clone);
  	tio->ti->type->release_clone_rq(clone);

  	rq_end_stats(md, rq);
  	if (!rq->q->mq_ops)
  		blk_end_request_all(rq, error);
  	else
  		blk_mq_end_request(rq, error);
  	rq_completed(md, rw, true);
  }

  /*
   * Requeue the original request of a clone.
   */

  static void dm_old_requeue_request(struct request *rq, unsigned long delay_ms)

  {
  	struct request_queue *q = rq->q;
  	unsigned long flags;
  
  	spin_lock_irqsave(q->queue_lock, flags);
  	blk_requeue_request(q, rq);

  	blk_delay_queue(q, delay_ms);

  	spin_unlock_irqrestore(q->queue_lock, flags);
  }

  static void __dm_mq_kick_requeue_list(struct request_queue *q, unsigned long msecs)

  {

  	blk_mq_delay_kick_requeue_list(q, msecs);

  }

  void dm_mq_kick_requeue_list(struct mapped_device *md)
  {
  	__dm_mq_kick_requeue_list(dm_get_md_queue(md), 0);
  }
  EXPORT_SYMBOL(dm_mq_kick_requeue_list);
  
  static void dm_mq_delay_requeue_request(struct request *rq, unsigned long msecs)
  {

  	blk_mq_requeue_request(rq, false);

  	__dm_mq_kick_requeue_list(rq->q, msecs);
  }

  static void dm_requeue_original_request(struct dm_rq_target_io *tio, bool delay_requeue)

  {

  	struct mapped_device *md = tio->md;
  	struct request *rq = tio->orig;

  	int rw = rq_data_dir(rq);

  	unsigned long delay_ms = delay_requeue ? 100 : 0;

  
  	rq_end_stats(md, rq);

  	if (tio->clone) {
  		blk_rq_unprep_clone(tio->clone);
  		tio->ti->type->release_clone_rq(tio->clone);
  	}

  
  	if (!rq->q->mq_ops)

  		dm_old_requeue_request(rq, delay_ms);

  	else

  		dm_mq_delay_requeue_request(rq, delay_ms);

  
  	rq_completed(md, rw, false);
  }

  static void dm_done(struct request *clone, blk_status_t error, bool mapped)

  {

  	int r = DM_ENDIO_DONE;

  	struct dm_rq_target_io *tio = clone->end_io_data;
  	dm_request_endio_fn rq_end_io = NULL;
  
  	if (tio->ti) {
  		rq_end_io = tio->ti->type->rq_end_io;
  
  		if (mapped && rq_end_io)
  			r = rq_end_io(tio->ti, clone, error, &tio->info);
  	}

  	if (unlikely(error == BLK_STS_TARGET)) {

  		if (req_op(clone) == REQ_OP_WRITE_SAME &&
  		    !clone->q->limits.max_write_same_sectors)
  			disable_write_same(tio->md);
  		if (req_op(clone) == REQ_OP_WRITE_ZEROES &&
  		    !clone->q->limits.max_write_zeroes_sectors)
  			disable_write_zeroes(tio->md);
  	}

  	switch (r) {
  	case DM_ENDIO_DONE:

  		/* The target wants to complete the I/O */

  		dm_end_request(clone, error);
  		break;
  	case DM_ENDIO_INCOMPLETE:

  		/* The target will handle the I/O */
  		return;

  	case DM_ENDIO_REQUEUE:

  		/* The target wants to requeue the I/O */

  		dm_requeue_original_request(tio, false);

  		break;
  	default:

  		DMWARN("unimplemented target endio return value: %d", r);
  		BUG();
  	}
  }
  
  /*
   * Request completion handler for request-based dm
   */
  static void dm_softirq_done(struct request *rq)
  {
  	bool mapped = true;
  	struct dm_rq_target_io *tio = tio_from_request(rq);
  	struct request *clone = tio->clone;
  	int rw;
  
  	if (!clone) {

  		struct mapped_device *md = tio->md;
  
  		rq_end_stats(md, rq);

  		rw = rq_data_dir(rq);

  		if (!rq->q->mq_ops)

  			blk_end_request_all(rq, tio->error);

  		else

  			blk_mq_end_request(rq, tio->error);

  		rq_completed(md, rw, false);

  		return;
  	}

  	if (rq->rq_flags & RQF_FAILED)

  		mapped = false;
  
  	dm_done(clone, tio->error, mapped);
  }
  
  /*
   * Complete the clone and the original request with the error status
   * through softirq context.
   */

  static void dm_complete_request(struct request *rq, blk_status_t error)

  {
  	struct dm_rq_target_io *tio = tio_from_request(rq);
  
  	tio->error = error;
  	if (!rq->q->mq_ops)
  		blk_complete_request(rq);
  	else

  		blk_mq_complete_request(rq);

  }
  
  /*
   * Complete the not-mapped clone and the original request with the error status
   * through softirq context.
   * Target's rq_end_io() function isn't called.
   * This may be used when the target's map_rq() or clone_and_map_rq() functions fail.
   */

  static void dm_kill_unmapped_request(struct request *rq, blk_status_t error)

  {

  	rq->rq_flags |= RQF_FAILED;

  	dm_complete_request(rq, error);
  }
  
  /*
   * Called with the clone's queue lock held (in the case of .request_fn)
   */

  static void end_clone_request(struct request *clone, blk_status_t error)

  {
  	struct dm_rq_target_io *tio = clone->end_io_data;

  	/*
  	 * Actual request completion is done in a softirq context which doesn't
  	 * hold the clone's queue lock.  Otherwise, deadlock could occur because:
  	 *     - another request may be submitted by the upper level driver
  	 *       of the stacking during the completion
  	 *     - the submission which requires queue lock may be done
  	 *       against this clone's queue
  	 */
  	dm_complete_request(tio->orig, error);
  }
  
  static void dm_dispatch_clone_request(struct request *clone, struct request *rq)
  {

  	blk_status_t r;

  
  	if (blk_queue_io_stat(clone->q))

  		clone->rq_flags |= RQF_IO_STAT;

  
  	clone->start_time = jiffies;
  	r = blk_insert_cloned_request(clone->q, clone);
  	if (r)
  		/* must complete clone in terms of original request */
  		dm_complete_request(rq, r);
  }
  
  static int dm_rq_bio_constructor(struct bio *bio, struct bio *bio_orig,
  				 void *data)
  {
  	struct dm_rq_target_io *tio = data;
  	struct dm_rq_clone_bio_info *info =
  		container_of(bio, struct dm_rq_clone_bio_info, clone);
  
  	info->orig = bio_orig;
  	info->tio = tio;
  	bio->bi_end_io = end_clone_bio;
  
  	return 0;
  }
  
  static int setup_clone(struct request *clone, struct request *rq,
  		       struct dm_rq_target_io *tio, gfp_t gfp_mask)
  {
  	int r;
  
  	r = blk_rq_prep_clone(clone, rq, tio->md->bs, gfp_mask,
  			      dm_rq_bio_constructor, tio);
  	if (r)
  		return r;

  	clone->end_io = end_clone_request;
  	clone->end_io_data = tio;
  
  	tio->clone = clone;
  
  	return 0;
  }

  static void map_tio_request(struct kthread_work *work);
  
  static void init_tio(struct dm_rq_target_io *tio, struct request *rq,
  		     struct mapped_device *md)
  {
  	tio->md = md;
  	tio->ti = NULL;
  	tio->clone = NULL;
  	tio->orig = rq;
  	tio->error = 0;

  	tio->completed = 0;

  	/*
  	 * Avoid initializing info for blk-mq; it passes
  	 * target-specific data through info.ptr
  	 * (see: dm_mq_init_request)
  	 */
  	if (!md->init_tio_pdu)
  		memset(&tio->info, 0, sizeof(tio->info));
  	if (md->kworker_task)

  		kthread_init_work(&tio->work, map_tio_request);

  }

  /*
   * Returns:

   * DM_MAPIO_*       : the request has been processed as indicated
   * DM_MAPIO_REQUEUE : the original request needs to be immediately requeued

   * < 0              : the request was completed due to failure
   */

  static int map_request(struct dm_rq_target_io *tio)

  {
  	int r;
  	struct dm_target *ti = tio->ti;

  	struct mapped_device *md = tio->md;
  	struct request *rq = tio->orig;

  	struct request *clone = NULL;

  	r = ti->type->clone_and_map_rq(ti, rq, &tio->info, &clone);

  	switch (r) {
  	case DM_MAPIO_SUBMITTED:
  		/* The target has taken the I/O to submit by itself later */
  		break;
  	case DM_MAPIO_REMAPPED:

  		if (setup_clone(clone, rq, tio, GFP_ATOMIC)) {
  			/* -ENOMEM */
  			ti->type->release_clone_rq(clone);
  			return DM_MAPIO_REQUEUE;
  		}

  		/* The target has remapped the I/O so dispatch it */
  		trace_block_rq_remap(clone->q, clone, disk_devt(dm_disk(md)),
  				     blk_rq_pos(rq));
  		dm_dispatch_clone_request(clone, rq);
  		break;
  	case DM_MAPIO_REQUEUE:
  		/* The target wants to requeue the I/O */

  		break;
  	case DM_MAPIO_DELAY_REQUEUE:
  		/* The target wants to requeue the I/O after a delay */

  		dm_requeue_original_request(tio, true);

  		break;

  	case DM_MAPIO_KILL:

  		/* The target wants to complete the I/O */

  		dm_kill_unmapped_request(rq, BLK_STS_IOERR);

  		break;

  	default:
  		DMWARN("unimplemented target map return value: %d", r);
  		BUG();

  	}

  	return r;

  }
  
  static void dm_start_request(struct mapped_device *md, struct request *orig)
  {
  	if (!orig->q->mq_ops)
  		blk_start_request(orig);
  	else
  		blk_mq_start_request(orig);
  	atomic_inc(&md->pending[rq_data_dir(orig)]);
  
  	if (md->seq_rq_merge_deadline_usecs) {
  		md->last_rq_pos = rq_end_sector(orig);
  		md->last_rq_rw = rq_data_dir(orig);
  		md->last_rq_start_time = ktime_get();
  	}
  
  	if (unlikely(dm_stats_used(&md->stats))) {
  		struct dm_rq_target_io *tio = tio_from_request(orig);
  		tio->duration_jiffies = jiffies;
  		tio->n_sectors = blk_rq_sectors(orig);
  		dm_stats_account_io(&md->stats, rq_data_dir(orig),
  				    blk_rq_pos(orig), tio->n_sectors, false, 0,
  				    &tio->stats_aux);
  	}
  
  	/*
  	 * Hold the md reference here for the in-flight I/O.
  	 * We can't rely on the reference count by device opener,
  	 * because the device may be closed during the request completion
  	 * when all bios are completed.
  	 * See the comment in rq_completed() too.
  	 */
  	dm_get(md);
  }

  static int __dm_rq_init_rq(struct mapped_device *md, struct request *rq)
  {
  	struct dm_rq_target_io *tio = blk_mq_rq_to_pdu(rq);
  
  	/*
  	 * Must initialize md member of tio, otherwise it won't
  	 * be available in dm_mq_queue_rq.
  	 */
  	tio->md = md;
  
  	if (md->init_tio_pdu) {
  		/* target-specific per-io data is immediately after the tio */
  		tio->info.ptr = tio + 1;
  	}
  
  	return 0;
  }
  
  static int dm_rq_init_rq(struct request_queue *q, struct request *rq, gfp_t gfp)
  {
  	return __dm_rq_init_rq(q->rq_alloc_data, rq);
  }

  static void map_tio_request(struct kthread_work *work)
  {
  	struct dm_rq_target_io *tio = container_of(work, struct dm_rq_target_io, work);

  	if (map_request(tio) == DM_MAPIO_REQUEUE)
  		dm_requeue_original_request(tio, false);

  }
  
  ssize_t dm_attr_rq_based_seq_io_merge_deadline_show(struct mapped_device *md, char *buf)
  {
  	return sprintf(buf, "%u
  ", md->seq_rq_merge_deadline_usecs);
  }
  
  #define MAX_SEQ_RQ_MERGE_DEADLINE_USECS 100000
  
  ssize_t dm_attr_rq_based_seq_io_merge_deadline_store(struct mapped_device *md,
  						     const char *buf, size_t count)
  {
  	unsigned deadline;

  	if (dm_get_md_type(md) != DM_TYPE_REQUEST_BASED)

  		return count;
  
  	if (kstrtouint(buf, 10, &deadline))
  		return -EINVAL;
  
  	if (deadline > MAX_SEQ_RQ_MERGE_DEADLINE_USECS)
  		deadline = MAX_SEQ_RQ_MERGE_DEADLINE_USECS;
  
  	md->seq_rq_merge_deadline_usecs = deadline;
  
  	return count;
  }
  
  static bool dm_old_request_peeked_before_merge_deadline(struct mapped_device *md)
  {
  	ktime_t kt_deadline;
  
  	if (!md->seq_rq_merge_deadline_usecs)
  		return false;
  
  	kt_deadline = ns_to_ktime((u64)md->seq_rq_merge_deadline_usecs * NSEC_PER_USEC);
  	kt_deadline = ktime_add_safe(md->last_rq_start_time, kt_deadline);
  
  	return !ktime_after(ktime_get(), kt_deadline);
  }
  
  /*
   * q->request_fn for old request-based dm.
   * Called with the queue lock held.
   */
  static void dm_old_request_fn(struct request_queue *q)
  {
  	struct mapped_device *md = q->queuedata;
  	struct dm_target *ti = md->immutable_target;
  	struct request *rq;
  	struct dm_rq_target_io *tio;
  	sector_t pos = 0;
  
  	if (unlikely(!ti)) {
  		int srcu_idx;
  		struct dm_table *map = dm_get_live_table(md, &srcu_idx);

  		if (unlikely(!map)) {
  			dm_put_live_table(md, srcu_idx);
  			return;
  		}

  		ti = dm_table_find_target(map, pos);
  		dm_put_live_table(md, srcu_idx);
  	}
  
  	/*
  	 * For suspend, check blk_queue_stopped() and increment
  	 * ->pending within a single queue_lock not to increment the
  	 * number of in-flight I/Os after the queue is stopped in
  	 * dm_suspend().
  	 */
  	while (!blk_queue_stopped(q)) {
  		rq = blk_peek_request(q);
  		if (!rq)
  			return;
  
  		/* always use block 0 to find the target for flushes for now */
  		pos = 0;
  		if (req_op(rq) != REQ_OP_FLUSH)
  			pos = blk_rq_pos(rq);
  
  		if ((dm_old_request_peeked_before_merge_deadline(md) &&

  		     md_in_flight(md) && rq->bio && !bio_multiple_segments(rq->bio) &&

  		     md->last_rq_pos == pos && md->last_rq_rw == rq_data_dir(rq)) ||
  		    (ti->type->busy && ti->type->busy(ti))) {

  			blk_delay_queue(q, 10);

  			return;
  		}
  
  		dm_start_request(md, rq);
  
  		tio = tio_from_request(rq);

  		init_tio(tio, rq, md);

  		/* Establish tio->ti before queuing work (map_tio_request) */
  		tio->ti = ti;

  		kthread_queue_work(&md->kworker, &tio->work);

  		BUG_ON(!irqs_disabled());
  	}
  }
  
  /*
   * Fully initialize a .request_fn request-based queue.
   */

  int dm_old_init_request_queue(struct mapped_device *md, struct dm_table *t)

  {

  	struct dm_target *immutable_tgt;

  	/* Fully initialize the queue */

  	md->queue->cmd_size = sizeof(struct dm_rq_target_io);
  	md->queue->rq_alloc_data = md;

  	md->queue->request_fn = dm_old_request_fn;

  	md->queue->init_rq_fn = dm_rq_init_rq;
  
  	immutable_tgt = dm_table_get_immutable_target(t);
  	if (immutable_tgt && immutable_tgt->per_io_data_size) {
  		/* any target-specific per-io data is immediately after the tio */
  		md->queue->cmd_size += immutable_tgt->per_io_data_size;
  		md->init_tio_pdu = true;
  	}

  	if (blk_init_allocated_queue(md->queue) < 0)

  		return -EINVAL;
  
  	/* disable dm_old_request_fn's merge heuristic by default */
  	md->seq_rq_merge_deadline_usecs = 0;
  
  	dm_init_normal_md_queue(md);
  	blk_queue_softirq_done(md->queue, dm_softirq_done);

  
  	/* Initialize the request-based DM worker thread */

  	kthread_init_worker(&md->kworker);

  	md->kworker_task = kthread_run(kthread_worker_fn, &md->kworker,
  				       "kdmwork-%s", dm_device_name(md));

  	if (IS_ERR(md->kworker_task)) {
  		int error = PTR_ERR(md->kworker_task);
  		md->kworker_task = NULL;
  		return error;
  	}

  
  	elv_register_queue(md->queue);
  
  	return 0;
  }

  static int dm_mq_init_request(struct blk_mq_tag_set *set, struct request *rq,
  		unsigned int hctx_idx, unsigned int numa_node)

  {

  	return __dm_rq_init_rq(set->driver_data, rq);

  }

  static blk_status_t dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,

  			  const struct blk_mq_queue_data *bd)
  {
  	struct request *rq = bd->rq;
  	struct dm_rq_target_io *tio = blk_mq_rq_to_pdu(rq);
  	struct mapped_device *md = tio->md;
  	struct dm_target *ti = md->immutable_target;
  
  	if (unlikely(!ti)) {
  		int srcu_idx;
  		struct dm_table *map = dm_get_live_table(md, &srcu_idx);
  
  		ti = dm_table_find_target(map, 0);
  		dm_put_live_table(md, srcu_idx);
  	}
  
  	if (ti->type->busy && ti->type->busy(ti))

  		return BLK_STS_RESOURCE;

  
  	dm_start_request(md, rq);
  
  	/* Init tio using md established in .init_request */
  	init_tio(tio, rq, md);
  
  	/*
  	 * Establish tio->ti before calling map_request().
  	 */
  	tio->ti = ti;
  
  	/* Direct call is fine since .queue_rq allows allocations */

  	if (map_request(tio) == DM_MAPIO_REQUEUE) {

  		/* Undo dm_start_request() before requeuing */
  		rq_end_stats(md, rq);
  		rq_completed(md, rq_data_dir(rq), false);

  		blk_mq_delay_run_hw_queue(hctx, 100/*ms*/);

  		return BLK_STS_RESOURCE;

  	}

  	return BLK_STS_OK;

  }

  static const struct blk_mq_ops dm_mq_ops = {

  	.queue_rq = dm_mq_queue_rq,

  	.complete = dm_softirq_done,
  	.init_request = dm_mq_init_request,
  };

  int dm_mq_init_request_queue(struct mapped_device *md, struct dm_table *t)

  {
  	struct request_queue *q;

  	struct dm_target *immutable_tgt;

  	int err;

  	if (!dm_table_all_blk_mq_devices(t)) {

  		DMERR("request-based dm-mq may only be stacked on blk-mq device(s)");
  		return -EINVAL;
  	}
  
  	md->tag_set = kzalloc_node(sizeof(struct blk_mq_tag_set), GFP_KERNEL, md->numa_node_id);
  	if (!md->tag_set)
  		return -ENOMEM;
  
  	md->tag_set->ops = &dm_mq_ops;
  	md->tag_set->queue_depth = dm_get_blk_mq_queue_depth();
  	md->tag_set->numa_node = md->numa_node_id;
  	md->tag_set->flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
  	md->tag_set->nr_hw_queues = dm_get_blk_mq_nr_hw_queues();
  	md->tag_set->driver_data = md;
  
  	md->tag_set->cmd_size = sizeof(struct dm_rq_target_io);

  	immutable_tgt = dm_table_get_immutable_target(t);

  	if (immutable_tgt && immutable_tgt->per_io_data_size) {
  		/* any target-specific per-io data is immediately after the tio */
  		md->tag_set->cmd_size += immutable_tgt->per_io_data_size;
  		md->init_tio_pdu = true;
  	}
  
  	err = blk_mq_alloc_tag_set(md->tag_set);
  	if (err)
  		goto out_kfree_tag_set;
  
  	q = blk_mq_init_allocated_queue(md->tag_set, md->queue);
  	if (IS_ERR(q)) {
  		err = PTR_ERR(q);
  		goto out_tag_set;
  	}
  	dm_init_md_queue(md);
  
  	/* backfill 'mq' sysfs registration normally done in blk_register_queue */

  	err = blk_mq_register_dev(disk_to_dev(md->disk), q);
  	if (err)
  		goto out_cleanup_queue;

  
  	return 0;

  out_cleanup_queue:
  	blk_cleanup_queue(q);

  out_tag_set:
  	blk_mq_free_tag_set(md->tag_set);
  out_kfree_tag_set:
  	kfree(md->tag_set);
  
  	return err;
  }
  
  void dm_mq_cleanup_mapped_device(struct mapped_device *md)
  {
  	if (md->tag_set) {
  		blk_mq_free_tag_set(md->tag_set);
  		kfree(md->tag_set);
  	}
  }
  
  module_param(reserved_rq_based_ios, uint, S_IRUGO | S_IWUSR);
  MODULE_PARM_DESC(reserved_rq_based_ios, "Reserved IOs in request-based mempools");
  
  module_param(use_blk_mq, bool, S_IRUGO | S_IWUSR);
  MODULE_PARM_DESC(use_blk_mq, "Use block multiqueue for request-based DM devices");
  
  module_param(dm_mq_nr_hw_queues, uint, S_IRUGO | S_IWUSR);
  MODULE_PARM_DESC(dm_mq_nr_hw_queues, "Number of hardware queues for request-based dm-mq devices");
  
  module_param(dm_mq_queue_depth, uint, S_IRUGO | S_IWUSR);
  MODULE_PARM_DESC(dm_mq_queue_depth, "Queue depth for request-based dm-mq devices");