/*
   * blk-mq scheduling framework
   *
   * Copyright (C) 2016 Jens Axboe
   */
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/blk-mq.h>
  
  #include <trace/events/block.h>
  
  #include "blk.h"
  #include "blk-mq.h"

  #include "blk-mq-debugfs.h"

  #include "blk-mq-sched.h"
  #include "blk-mq-tag.h"
  #include "blk-wbt.h"
  
  void blk_mq_sched_free_hctx_data(struct request_queue *q,
  				 void (*exit)(struct blk_mq_hw_ctx *))
  {
  	struct blk_mq_hw_ctx *hctx;
  	int i;
  
  	queue_for_each_hw_ctx(q, hctx, i) {
  		if (exit && hctx->sched_data)
  			exit(hctx);
  		kfree(hctx->sched_data);
  		hctx->sched_data = NULL;
  	}
  }
  EXPORT_SYMBOL_GPL(blk_mq_sched_free_hctx_data);

  void blk_mq_sched_assign_ioc(struct request *rq, struct bio *bio)

  {

  	struct request_queue *q = rq->q;
  	struct io_context *ioc = rq_ioc(bio);

  	struct io_cq *icq;
  
  	spin_lock_irq(q->queue_lock);
  	icq = ioc_lookup_icq(ioc, q);
  	spin_unlock_irq(q->queue_lock);
  
  	if (!icq) {
  		icq = ioc_create_icq(ioc, q, GFP_ATOMIC);
  		if (!icq)
  			return;
  	}

  	get_io_context(icq->ioc);

  	rq->elv.icq = icq;

  }

  /*
   * Mark a hardware queue as needing a restart. For shared queues, maintain
   * a count of how many hardware queues are marked for restart.
   */
  static void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
  {
  	if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
  		return;
  
  	if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
  		struct request_queue *q = hctx->queue;
  
  		if (!test_and_set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
  			atomic_inc(&q->shared_hctx_restart);
  	} else
  		set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
  }
  
  static bool blk_mq_sched_restart_hctx(struct blk_mq_hw_ctx *hctx)
  {
  	if (!test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
  		return false;
  
  	if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
  		struct request_queue *q = hctx->queue;
  
  		if (test_and_clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
  			atomic_dec(&q->shared_hctx_restart);
  	} else
  		clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
  
  	if (blk_mq_hctx_has_pending(hctx)) {
  		blk_mq_run_hw_queue(hctx, true);
  		return true;
  	}
  
  	return false;
  }

  void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
  {

  	struct request_queue *q = hctx->queue;
  	struct elevator_queue *e = q->elevator;

  	const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request;

  	bool do_sched_dispatch = true;

  	LIST_HEAD(rq_list);

  	/* RCU or SRCU read lock is needed before checking quiesced flag */
  	if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))

  		return;
  
  	hctx->run++;
  
  	/*
  	 * If we have previous entries on our dispatch list, grab them first for
  	 * more fair dispatch.
  	 */
  	if (!list_empty_careful(&hctx->dispatch)) {
  		spin_lock(&hctx->lock);
  		if (!list_empty(&hctx->dispatch))
  			list_splice_init(&hctx->dispatch, &rq_list);
  		spin_unlock(&hctx->lock);
  	}
  
  	/*
  	 * Only ask the scheduler for requests, if we didn't have residual
  	 * requests from the dispatch list. This is to avoid the case where
  	 * we only ever dispatch a fraction of the requests available because
  	 * of low device queue depth. Once we pull requests out of the IO
  	 * scheduler, we can no longer merge or sort them. So it's best to
  	 * leave them there for as long as we can. Mark the hw queue as
  	 * needing a restart in that case.
  	 */

  	if (!list_empty(&rq_list)) {

  		blk_mq_sched_mark_restart_hctx(hctx);

  		do_sched_dispatch = blk_mq_dispatch_rq_list(q, &rq_list);

  	} else if (!has_sched_dispatch) {

  		blk_mq_flush_busy_ctxs(hctx, &rq_list);

  		blk_mq_dispatch_rq_list(q, &rq_list);

  	}
  
  	/*

  	 * We want to dispatch from the scheduler if there was nothing
  	 * on the dispatch list or we were able to dispatch from the
  	 * dispatch list.

  	 */

  	if (do_sched_dispatch && has_sched_dispatch) {

  		do {
  			struct request *rq;
  
  			rq = e->type->ops.mq.dispatch_request(hctx);
  			if (!rq)
  				break;
  			list_add(&rq->queuelist, &rq_list);

  		} while (blk_mq_dispatch_rq_list(q, &rq_list));

  	}

  }

  bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
  			    struct request **merged_request)

  {
  	struct request *rq;

  	switch (elv_merge(q, &rq, bio)) {
  	case ELEVATOR_BACK_MERGE:

  		if (!blk_mq_sched_allow_merge(q, rq, bio))
  			return false;

  		if (!bio_attempt_back_merge(q, rq, bio))
  			return false;
  		*merged_request = attempt_back_merge(q, rq);
  		if (!*merged_request)
  			elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
  		return true;
  	case ELEVATOR_FRONT_MERGE:

  		if (!blk_mq_sched_allow_merge(q, rq, bio))
  			return false;

  		if (!bio_attempt_front_merge(q, rq, bio))
  			return false;
  		*merged_request = attempt_front_merge(q, rq);
  		if (!*merged_request)
  			elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
  		return true;
  	default:
  		return false;

  	}

  }
  EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);

  /*
   * Reverse check our software queue for entries that we could potentially
   * merge with. Currently includes a hand-wavy stop count of 8, to not spend
   * too much time checking for merges.
   */
  static bool blk_mq_attempt_merge(struct request_queue *q,
  				 struct blk_mq_ctx *ctx, struct bio *bio)
  {
  	struct request *rq;
  	int checked = 8;

  	lockdep_assert_held(&ctx->lock);

  	list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
  		bool merged = false;
  
  		if (!checked--)
  			break;
  
  		if (!blk_rq_merge_ok(rq, bio))
  			continue;
  
  		switch (blk_try_merge(rq, bio)) {
  		case ELEVATOR_BACK_MERGE:
  			if (blk_mq_sched_allow_merge(q, rq, bio))
  				merged = bio_attempt_back_merge(q, rq, bio);
  			break;
  		case ELEVATOR_FRONT_MERGE:
  			if (blk_mq_sched_allow_merge(q, rq, bio))
  				merged = bio_attempt_front_merge(q, rq, bio);
  			break;
  		case ELEVATOR_DISCARD_MERGE:
  			merged = bio_attempt_discard_merge(q, rq, bio);
  			break;
  		default:
  			continue;
  		}
  
  		if (merged)
  			ctx->rq_merged++;
  		return merged;
  	}
  
  	return false;
  }

  bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
  {
  	struct elevator_queue *e = q->elevator;

  	struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
  	struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
  	bool ret = false;

  	if (e && e->type->ops.mq.bio_merge) {

  		blk_mq_put_ctx(ctx);
  		return e->type->ops.mq.bio_merge(hctx, bio);
  	}

  	if ((hctx->flags & BLK_MQ_F_SHOULD_MERGE) &&
  			!list_empty_careful(&ctx->rq_list)) {

  		/* default per sw-queue merge */
  		spin_lock(&ctx->lock);
  		ret = blk_mq_attempt_merge(q, ctx, bio);
  		spin_unlock(&ctx->lock);
  	}
  
  	blk_mq_put_ctx(ctx);
  	return ret;

  }
  
  bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq)
  {
  	return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq);
  }
  EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
  
  void blk_mq_sched_request_inserted(struct request *rq)
  {
  	trace_block_rq_insert(rq->q, rq);
  }
  EXPORT_SYMBOL_GPL(blk_mq_sched_request_inserted);

  static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
  				       struct request *rq)

  {
  	if (rq->tag == -1) {
  		rq->rq_flags |= RQF_SORTED;
  		return false;
  	}
  
  	/*
  	 * If we already have a real request tag, send directly to
  	 * the dispatch list.
  	 */
  	spin_lock(&hctx->lock);
  	list_add(&rq->queuelist, &hctx->dispatch);
  	spin_unlock(&hctx->lock);
  	return true;
  }

  /**
   * list_for_each_entry_rcu_rr - iterate in a round-robin fashion over rcu list
   * @pos:    loop cursor.
   * @skip:   the list element that will not be examined. Iteration starts at
   *          @skip->next.
   * @head:   head of the list to examine. This list must have at least one
   *          element, namely @skip.
   * @member: name of the list_head structure within typeof(*pos).
   */
  #define list_for_each_entry_rcu_rr(pos, skip, head, member)		\
  	for ((pos) = (skip);						\
  	     (pos = (pos)->member.next != (head) ? list_entry_rcu(	\
  			(pos)->member.next, typeof(*pos), member) :	\
  	      list_entry_rcu((pos)->member.next->next, typeof(*pos), member)), \
  	     (pos) != (skip); )

  /*
   * Called after a driver tag has been freed to check whether a hctx needs to
   * be restarted. Restarts @hctx if its tag set is not shared. Restarts hardware
   * queues in a round-robin fashion if the tag set of @hctx is shared with other
   * hardware queues.
   */
  void blk_mq_sched_restart(struct blk_mq_hw_ctx *const hctx)
  {
  	struct blk_mq_tags *const tags = hctx->tags;
  	struct blk_mq_tag_set *const set = hctx->queue->tag_set;
  	struct request_queue *const queue = hctx->queue, *q;
  	struct blk_mq_hw_ctx *hctx2;
  	unsigned int i, j;
  
  	if (set->flags & BLK_MQ_F_TAG_SHARED) {

  		/*
  		 * If this is 0, then we know that no hardware queues
  		 * have RESTART marked. We're done.
  		 */
  		if (!atomic_read(&queue->shared_hctx_restart))
  			return;

  		rcu_read_lock();
  		list_for_each_entry_rcu_rr(q, queue, &set->tag_list,
  					   tag_set_list) {
  			queue_for_each_hw_ctx(q, hctx2, i)
  				if (hctx2->tags == tags &&
  				    blk_mq_sched_restart_hctx(hctx2))
  					goto done;
  		}
  		j = hctx->queue_num + 1;
  		for (i = 0; i < queue->nr_hw_queues; i++, j++) {
  			if (j == queue->nr_hw_queues)
  				j = 0;
  			hctx2 = queue->queue_hw_ctx[j];
  			if (hctx2->tags == tags &&
  			    blk_mq_sched_restart_hctx(hctx2))
  				break;

  		}

  done:
  		rcu_read_unlock();

  	} else {

  		blk_mq_sched_restart_hctx(hctx);

  	}
  }

  /*
   * Add flush/fua to the queue. If we fail getting a driver tag, then
   * punt to the requeue list. Requeue will re-invoke us from a context
   * that's safe to block from.
   */
  static void blk_mq_sched_insert_flush(struct blk_mq_hw_ctx *hctx,
  				      struct request *rq, bool can_block)
  {
  	if (blk_mq_get_driver_tag(rq, &hctx, can_block)) {
  		blk_insert_flush(rq);
  		blk_mq_run_hw_queue(hctx, true);
  	} else

  		blk_mq_add_to_requeue_list(rq, false, true);

  }
  
  void blk_mq_sched_insert_request(struct request *rq, bool at_head,
  				 bool run_queue, bool async, bool can_block)
  {
  	struct request_queue *q = rq->q;
  	struct elevator_queue *e = q->elevator;
  	struct blk_mq_ctx *ctx = rq->mq_ctx;
  	struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);

  	if (rq->tag == -1 && op_is_flush(rq->cmd_flags)) {

  		blk_mq_sched_insert_flush(hctx, rq, can_block);
  		return;
  	}

  	if (e && blk_mq_sched_bypass_insert(hctx, rq))
  		goto run;

  	if (e && e->type->ops.mq.insert_requests) {
  		LIST_HEAD(list);
  
  		list_add(&rq->queuelist, &list);
  		e->type->ops.mq.insert_requests(hctx, &list, at_head);
  	} else {
  		spin_lock(&ctx->lock);
  		__blk_mq_insert_request(hctx, rq, at_head);
  		spin_unlock(&ctx->lock);
  	}

  run:

  	if (run_queue)
  		blk_mq_run_hw_queue(hctx, async);
  }
  
  void blk_mq_sched_insert_requests(struct request_queue *q,
  				  struct blk_mq_ctx *ctx,
  				  struct list_head *list, bool run_queue_async)
  {
  	struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
  	struct elevator_queue *e = hctx->queue->elevator;

  	if (e) {
  		struct request *rq, *next;
  
  		/*
  		 * We bypass requests that already have a driver tag assigned,
  		 * which should only be flushes. Flushes are only ever inserted
  		 * as single requests, so we shouldn't ever hit the
  		 * WARN_ON_ONCE() below (but let's handle it just in case).
  		 */
  		list_for_each_entry_safe(rq, next, list, queuelist) {
  			if (WARN_ON_ONCE(rq->tag != -1)) {
  				list_del_init(&rq->queuelist);
  				blk_mq_sched_bypass_insert(hctx, rq);
  			}
  		}
  	}

  	if (e && e->type->ops.mq.insert_requests)
  		e->type->ops.mq.insert_requests(hctx, list, false);
  	else
  		blk_mq_insert_requests(hctx, ctx, list);
  
  	blk_mq_run_hw_queue(hctx, run_queue_async);
  }

  static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
  				   struct blk_mq_hw_ctx *hctx,
  				   unsigned int hctx_idx)
  {
  	if (hctx->sched_tags) {
  		blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx);
  		blk_mq_free_rq_map(hctx->sched_tags);
  		hctx->sched_tags = NULL;
  	}
  }

  static int blk_mq_sched_alloc_tags(struct request_queue *q,
  				   struct blk_mq_hw_ctx *hctx,
  				   unsigned int hctx_idx)
  {
  	struct blk_mq_tag_set *set = q->tag_set;
  	int ret;
  
  	hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests,
  					       set->reserved_tags);
  	if (!hctx->sched_tags)
  		return -ENOMEM;
  
  	ret = blk_mq_alloc_rqs(set, hctx->sched_tags, hctx_idx, q->nr_requests);
  	if (ret)
  		blk_mq_sched_free_tags(set, hctx, hctx_idx);
  
  	return ret;
  }

  static void blk_mq_sched_tags_teardown(struct request_queue *q)

  {
  	struct blk_mq_tag_set *set = q->tag_set;
  	struct blk_mq_hw_ctx *hctx;

  	int i;
  
  	queue_for_each_hw_ctx(q, hctx, i)
  		blk_mq_sched_free_tags(set, hctx, i);
  }

  int blk_mq_sched_init_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
  			   unsigned int hctx_idx)
  {
  	struct elevator_queue *e = q->elevator;

  	int ret;

  
  	if (!e)
  		return 0;

  	ret = blk_mq_sched_alloc_tags(q, hctx, hctx_idx);
  	if (ret)
  		return ret;
  
  	if (e->type->ops.mq.init_hctx) {
  		ret = e->type->ops.mq.init_hctx(hctx, hctx_idx);
  		if (ret) {
  			blk_mq_sched_free_tags(q->tag_set, hctx, hctx_idx);
  			return ret;
  		}
  	}

  	blk_mq_debugfs_register_sched_hctx(q, hctx);

  	return 0;

  }
  
  void blk_mq_sched_exit_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
  			    unsigned int hctx_idx)
  {
  	struct elevator_queue *e = q->elevator;
  
  	if (!e)
  		return;

  	blk_mq_debugfs_unregister_sched_hctx(hctx);

  	if (e->type->ops.mq.exit_hctx && hctx->sched_data) {
  		e->type->ops.mq.exit_hctx(hctx, hctx_idx);
  		hctx->sched_data = NULL;
  	}

  	blk_mq_sched_free_tags(q->tag_set, hctx, hctx_idx);
  }

  int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
  {
  	struct blk_mq_hw_ctx *hctx;

  	struct elevator_queue *eq;

  	unsigned int i;
  	int ret;
  
  	if (!e) {
  		q->elevator = NULL;
  		return 0;
  	}

  
  	/*

  	 * Default to double of smaller one between hw queue_depth and 128,
  	 * since we don't split into sync/async like the old code did.
  	 * Additionally, this is a per-hw queue depth.

  	 */

  	q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
  				   BLKDEV_MAX_RQ);

  	queue_for_each_hw_ctx(q, hctx, i) {

  		ret = blk_mq_sched_alloc_tags(q, hctx, i);

  		if (ret)

  			goto err;

  	}

  	ret = e->ops.mq.init_sched(q, e);
  	if (ret)
  		goto err;

  	blk_mq_debugfs_register_sched(q);
  
  	queue_for_each_hw_ctx(q, hctx, i) {
  		if (e->ops.mq.init_hctx) {

  			ret = e->ops.mq.init_hctx(hctx, i);
  			if (ret) {
  				eq = q->elevator;
  				blk_mq_exit_sched(q, eq);
  				kobject_put(&eq->kobj);
  				return ret;
  			}
  		}

  		blk_mq_debugfs_register_sched_hctx(q, hctx);

  	}

  	return 0;

  err:

  	blk_mq_sched_tags_teardown(q);
  	q->elevator = NULL;

  	return ret;

  }

  void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
  {

  	struct blk_mq_hw_ctx *hctx;
  	unsigned int i;

  	queue_for_each_hw_ctx(q, hctx, i) {
  		blk_mq_debugfs_unregister_sched_hctx(hctx);
  		if (e->type->ops.mq.exit_hctx && hctx->sched_data) {
  			e->type->ops.mq.exit_hctx(hctx, i);
  			hctx->sched_data = NULL;

  		}
  	}

  	blk_mq_debugfs_unregister_sched(q);

  	if (e->type->ops.mq.exit_sched)
  		e->type->ops.mq.exit_sched(e);
  	blk_mq_sched_tags_teardown(q);
  	q->elevator = NULL;
  }

  int blk_mq_sched_init(struct request_queue *q)
  {
  	int ret;

  	mutex_lock(&q->sysfs_lock);
  	ret = elevator_init(q, NULL);
  	mutex_unlock(&q->sysfs_lock);
  
  	return ret;
  }