// SPDX-License-Identifier: GPL-2.0

  /*
   *  MQ Deadline i/o scheduler - adaptation of the legacy deadline scheduler,
   *  for the blk-mq scheduling framework
   *
   *  Copyright (C) 2016 Jens Axboe <axboe@kernel.dk>
   */
  #include <linux/kernel.h>
  #include <linux/fs.h>
  #include <linux/blkdev.h>
  #include <linux/blk-mq.h>
  #include <linux/elevator.h>
  #include <linux/bio.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/compiler.h>
  #include <linux/rbtree.h>
  #include <linux/sbitmap.h>
  
  #include "blk.h"
  #include "blk-mq.h"

  #include "blk-mq-debugfs.h"

  #include "blk-mq-tag.h"
  #include "blk-mq-sched.h"
  
  /*

   * See Documentation/block/deadline-iosched.rst

   */
  static const int read_expire = HZ / 2;  /* max time before a read is submitted. */
  static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
  static const int writes_starved = 2;    /* max times reads can starve a write */
  static const int fifo_batch = 16;       /* # of sequential requests treated as one
  				     by the above parameters. For throughput. */
  
  struct deadline_data {
  	/*
  	 * run time data
  	 */
  
  	/*
  	 * requests (deadline_rq s) are present on both sort_list and fifo_list
  	 */
  	struct rb_root sort_list[2];
  	struct list_head fifo_list[2];
  
  	/*
  	 * next in sort order. read, write or both are NULL
  	 */
  	struct request *next_rq[2];
  	unsigned int batching;		/* number of sequential requests made */
  	unsigned int starved;		/* times reads have starved writes */
  
  	/*
  	 * settings that change how the i/o scheduler behaves
  	 */
  	int fifo_expire[2];
  	int fifo_batch;
  	int writes_starved;
  	int front_merges;
  
  	spinlock_t lock;

  	spinlock_t zone_lock;

  	struct list_head dispatch;
  };
  
  static inline struct rb_root *
  deadline_rb_root(struct deadline_data *dd, struct request *rq)
  {
  	return &dd->sort_list[rq_data_dir(rq)];
  }
  
  /*
   * get the request after `rq' in sector-sorted order
   */
  static inline struct request *
  deadline_latter_request(struct request *rq)
  {
  	struct rb_node *node = rb_next(&rq->rb_node);
  
  	if (node)
  		return rb_entry_rq(node);
  
  	return NULL;
  }
  
  static void
  deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
  {
  	struct rb_root *root = deadline_rb_root(dd, rq);
  
  	elv_rb_add(root, rq);
  }
  
  static inline void
  deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
  {
  	const int data_dir = rq_data_dir(rq);
  
  	if (dd->next_rq[data_dir] == rq)
  		dd->next_rq[data_dir] = deadline_latter_request(rq);
  
  	elv_rb_del(deadline_rb_root(dd, rq), rq);
  }
  
  /*
   * remove rq from rbtree and fifo.
   */
  static void deadline_remove_request(struct request_queue *q, struct request *rq)
  {
  	struct deadline_data *dd = q->elevator->elevator_data;
  
  	list_del_init(&rq->queuelist);
  
  	/*
  	 * We might not be on the rbtree, if we are doing an insert merge
  	 */
  	if (!RB_EMPTY_NODE(&rq->rb_node))
  		deadline_del_rq_rb(dd, rq);
  
  	elv_rqhash_del(q, rq);
  	if (q->last_merge == rq)
  		q->last_merge = NULL;
  }
  
  static void dd_request_merged(struct request_queue *q, struct request *req,

  			      enum elv_merge type)

  {
  	struct deadline_data *dd = q->elevator->elevator_data;
  
  	/*
  	 * if the merge was a front merge, we need to reposition request
  	 */
  	if (type == ELEVATOR_FRONT_MERGE) {
  		elv_rb_del(deadline_rb_root(dd, req), req);
  		deadline_add_rq_rb(dd, req);
  	}
  }
  
  static void dd_merged_requests(struct request_queue *q, struct request *req,
  			       struct request *next)
  {
  	/*
  	 * if next expires before rq, assign its expire time to rq
  	 * and move into next position (next will be deleted) in fifo
  	 */
  	if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
  		if (time_before((unsigned long)next->fifo_time,
  				(unsigned long)req->fifo_time)) {
  			list_move(&req->queuelist, &next->queuelist);
  			req->fifo_time = next->fifo_time;
  		}
  	}
  
  	/*
  	 * kill knowledge of next, this one is a goner
  	 */
  	deadline_remove_request(q, next);
  }
  
  /*
   * move an entry to dispatch queue
   */
  static void
  deadline_move_request(struct deadline_data *dd, struct request *rq)
  {
  	const int data_dir = rq_data_dir(rq);
  
  	dd->next_rq[READ] = NULL;
  	dd->next_rq[WRITE] = NULL;
  	dd->next_rq[data_dir] = deadline_latter_request(rq);
  
  	/*
  	 * take it off the sort and fifo list
  	 */
  	deadline_remove_request(rq->q, rq);
  }
  
  /*
   * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
   * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
   */
  static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
  {
  	struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
  
  	/*
  	 * rq is expired!
  	 */
  	if (time_after_eq(jiffies, (unsigned long)rq->fifo_time))
  		return 1;
  
  	return 0;
  }
  
  /*

   * For the specified data direction, return the next request to
   * dispatch using arrival ordered lists.
   */
  static struct request *
  deadline_fifo_request(struct deadline_data *dd, int data_dir)
  {

  	struct request *rq;
  	unsigned long flags;

  	if (WARN_ON_ONCE(data_dir != READ && data_dir != WRITE))
  		return NULL;
  
  	if (list_empty(&dd->fifo_list[data_dir]))
  		return NULL;

  	rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
  	if (data_dir == READ || !blk_queue_is_zoned(rq->q))
  		return rq;
  
  	/*
  	 * Look for a write request that can be dispatched, that is one with
  	 * an unlocked target zone.
  	 */
  	spin_lock_irqsave(&dd->zone_lock, flags);
  	list_for_each_entry(rq, &dd->fifo_list[WRITE], queuelist) {
  		if (blk_req_can_dispatch_to_zone(rq))
  			goto out;
  	}
  	rq = NULL;
  out:
  	spin_unlock_irqrestore(&dd->zone_lock, flags);
  
  	return rq;

  }
  
  /*
   * For the specified data direction, return the next request to
   * dispatch using sector position sorted lists.
   */
  static struct request *
  deadline_next_request(struct deadline_data *dd, int data_dir)
  {

  	struct request *rq;
  	unsigned long flags;

  	if (WARN_ON_ONCE(data_dir != READ && data_dir != WRITE))
  		return NULL;

  	rq = dd->next_rq[data_dir];
  	if (!rq)
  		return NULL;
  
  	if (data_dir == READ || !blk_queue_is_zoned(rq->q))
  		return rq;
  
  	/*
  	 * Look for a write request that can be dispatched, that is one with
  	 * an unlocked target zone.
  	 */
  	spin_lock_irqsave(&dd->zone_lock, flags);
  	while (rq) {
  		if (blk_req_can_dispatch_to_zone(rq))
  			break;
  		rq = deadline_latter_request(rq);
  	}
  	spin_unlock_irqrestore(&dd->zone_lock, flags);
  
  	return rq;

  }
  
  /*

   * deadline_dispatch_requests selects the best request according to
   * read/write expire, fifo_batch, etc
   */

  static struct request *__dd_dispatch_request(struct deadline_data *dd)

  {

  	struct request *rq, *next_rq;

  	bool reads, writes;
  	int data_dir;
  
  	if (!list_empty(&dd->dispatch)) {
  		rq = list_first_entry(&dd->dispatch, struct request, queuelist);
  		list_del_init(&rq->queuelist);
  		goto done;
  	}
  
  	reads = !list_empty(&dd->fifo_list[READ]);
  	writes = !list_empty(&dd->fifo_list[WRITE]);
  
  	/*
  	 * batches are currently reads XOR writes
  	 */

  	rq = deadline_next_request(dd, WRITE);
  	if (!rq)
  		rq = deadline_next_request(dd, READ);

  
  	if (rq && dd->batching < dd->fifo_batch)
  		/* we have a next request are still entitled to batch */
  		goto dispatch_request;
  
  	/*
  	 * at this point we are not running a batch. select the appropriate
  	 * data direction (read / write)
  	 */
  
  	if (reads) {
  		BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));

  		if (deadline_fifo_request(dd, WRITE) &&
  		    (dd->starved++ >= dd->writes_starved))

  			goto dispatch_writes;
  
  		data_dir = READ;
  
  		goto dispatch_find_request;
  	}
  
  	/*
  	 * there are either no reads or writes have been starved
  	 */
  
  	if (writes) {
  dispatch_writes:
  		BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
  
  		dd->starved = 0;
  
  		data_dir = WRITE;
  
  		goto dispatch_find_request;
  	}
  
  	return NULL;
  
  dispatch_find_request:
  	/*
  	 * we are not running a batch, find best request for selected data_dir
  	 */

  	next_rq = deadline_next_request(dd, data_dir);
  	if (deadline_check_fifo(dd, data_dir) || !next_rq) {

  		/*
  		 * A deadline has expired, the last request was in the other
  		 * direction, or we have run out of higher-sectored requests.
  		 * Start again from the request with the earliest expiry time.
  		 */

  		rq = deadline_fifo_request(dd, data_dir);

  	} else {
  		/*
  		 * The last req was the same dir and we have a next request in
  		 * sort order. No expired requests so continue on from here.
  		 */

  		rq = next_rq;

  	}

  	/*
  	 * For a zoned block device, if we only have writes queued and none of
  	 * them can be dispatched, rq will be NULL.
  	 */
  	if (!rq)
  		return NULL;

  	dd->batching = 0;
  
  dispatch_request:
  	/*
  	 * rq is the selected appropriate request.
  	 */
  	dd->batching++;
  	deadline_move_request(dd, rq);
  done:

  	/*
  	 * If the request needs its target zone locked, do it.
  	 */
  	blk_req_zone_write_lock(rq);

  	rq->rq_flags |= RQF_STARTED;
  	return rq;
  }

  /*
   * One confusing aspect here is that we get called for a specific

   * hardware queue, but we may return a request that is for a

   * different hardware queue. This is because mq-deadline has shared
   * state for all hardware queues, in terms of sorting, FIFOs, etc.
   */

  static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx)

  {
  	struct deadline_data *dd = hctx->queue->elevator->elevator_data;

  	struct request *rq;

  
  	spin_lock(&dd->lock);

  	rq = __dd_dispatch_request(dd);

  	spin_unlock(&dd->lock);

  	if (rq)
  		atomic_dec(&rq->mq_hctx->elevator_queued);

  
  	return rq;

  }
  
  static void dd_exit_queue(struct elevator_queue *e)
  {
  	struct deadline_data *dd = e->elevator_data;
  
  	BUG_ON(!list_empty(&dd->fifo_list[READ]));
  	BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
  
  	kfree(dd);
  }
  
  /*
   * initialize elevator private data (deadline_data).
   */
  static int dd_init_queue(struct request_queue *q, struct elevator_type *e)
  {
  	struct deadline_data *dd;
  	struct elevator_queue *eq;
  
  	eq = elevator_alloc(q, e);
  	if (!eq)
  		return -ENOMEM;
  
  	dd = kzalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
  	if (!dd) {
  		kobject_put(&eq->kobj);
  		return -ENOMEM;
  	}
  	eq->elevator_data = dd;
  
  	INIT_LIST_HEAD(&dd->fifo_list[READ]);
  	INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
  	dd->sort_list[READ] = RB_ROOT;
  	dd->sort_list[WRITE] = RB_ROOT;
  	dd->fifo_expire[READ] = read_expire;
  	dd->fifo_expire[WRITE] = write_expire;
  	dd->writes_starved = writes_starved;
  	dd->front_merges = 1;
  	dd->fifo_batch = fifo_batch;
  	spin_lock_init(&dd->lock);

  	spin_lock_init(&dd->zone_lock);

  	INIT_LIST_HEAD(&dd->dispatch);
  
  	q->elevator = eq;
  	return 0;
  }
  
  static int dd_request_merge(struct request_queue *q, struct request **rq,
  			    struct bio *bio)
  {
  	struct deadline_data *dd = q->elevator->elevator_data;
  	sector_t sector = bio_end_sector(bio);
  	struct request *__rq;
  
  	if (!dd->front_merges)
  		return ELEVATOR_NO_MERGE;
  
  	__rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
  	if (__rq) {
  		BUG_ON(sector != blk_rq_pos(__rq));
  
  		if (elv_bio_merge_ok(__rq, bio)) {
  			*rq = __rq;
  			return ELEVATOR_FRONT_MERGE;
  		}
  	}
  
  	return ELEVATOR_NO_MERGE;
  }

  static bool dd_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio,
  		unsigned int nr_segs)

  {
  	struct request_queue *q = hctx->queue;
  	struct deadline_data *dd = q->elevator->elevator_data;

  	struct request *free = NULL;
  	bool ret;

  
  	spin_lock(&dd->lock);

  	ret = blk_mq_sched_try_merge(q, bio, nr_segs, &free);

  	spin_unlock(&dd->lock);

  	if (free)
  		blk_mq_free_request(free);

  	return ret;
  }
  
  /*
   * add rq to rbtree and fifo
   */
  static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
  			      bool at_head)
  {
  	struct request_queue *q = hctx->queue;
  	struct deadline_data *dd = q->elevator->elevator_data;
  	const int data_dir = rq_data_dir(rq);

  	/*
  	 * This may be a requeue of a write request that has locked its
  	 * target zone. If it is the case, this releases the zone lock.
  	 */
  	blk_req_zone_write_unlock(rq);

  	if (blk_mq_sched_try_insert_merge(q, rq))
  		return;
  
  	blk_mq_sched_request_inserted(rq);

  	if (at_head || blk_rq_is_passthrough(rq)) {

  		if (at_head)
  			list_add(&rq->queuelist, &dd->dispatch);
  		else
  			list_add_tail(&rq->queuelist, &dd->dispatch);
  	} else {
  		deadline_add_rq_rb(dd, rq);
  
  		if (rq_mergeable(rq)) {
  			elv_rqhash_add(q, rq);
  			if (!q->last_merge)
  				q->last_merge = rq;
  		}
  
  		/*
  		 * set expire time and add to fifo list
  		 */
  		rq->fifo_time = jiffies + dd->fifo_expire[data_dir];
  		list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
  	}
  }
  
  static void dd_insert_requests(struct blk_mq_hw_ctx *hctx,
  			       struct list_head *list, bool at_head)
  {
  	struct request_queue *q = hctx->queue;
  	struct deadline_data *dd = q->elevator->elevator_data;
  
  	spin_lock(&dd->lock);
  	while (!list_empty(list)) {
  		struct request *rq;
  
  		rq = list_first_entry(list, struct request, queuelist);
  		list_del_init(&rq->queuelist);
  		dd_insert_request(hctx, rq, at_head);

  		atomic_inc(&hctx->elevator_queued);

  	}
  	spin_unlock(&dd->lock);
  }

  /*

   * Nothing to do here. This is defined only to ensure that .finish_request
   * method is called upon request completion.
   */

  static void dd_prepare_request(struct request *rq)

  {
  }
  
  /*

   * For zoned block devices, write unlock the target zone of
   * completed write requests. Do this while holding the zone lock
   * spinlock so that the zone is never unlocked while deadline_fifo_request()

   * or deadline_next_request() are executing. This function is called for
   * all requests, whether or not these requests complete successfully.

   *
   * For a zoned block device, __dd_dispatch_request() may have stopped
   * dispatching requests if all the queued requests are write requests directed
   * at zones that are already locked due to on-going write requests. To ensure
   * write request dispatch progress in this case, mark the queue as needing a
   * restart to ensure that the queue is run again after completion of the
   * request and zones being unlocked.

   */

  static void dd_finish_request(struct request *rq)

  {
  	struct request_queue *q = rq->q;
  
  	if (blk_queue_is_zoned(q)) {
  		struct deadline_data *dd = q->elevator->elevator_data;
  		unsigned long flags;
  
  		spin_lock_irqsave(&dd->zone_lock, flags);
  		blk_req_zone_write_unlock(rq);

  		if (!list_empty(&dd->fifo_list[WRITE]))
  			blk_mq_sched_mark_restart_hctx(rq->mq_hctx);

  		spin_unlock_irqrestore(&dd->zone_lock, flags);
  	}
  }

  static bool dd_has_work(struct blk_mq_hw_ctx *hctx)
  {
  	struct deadline_data *dd = hctx->queue->elevator->elevator_data;

  	if (!atomic_read(&hctx->elevator_queued))
  		return false;

  	return !list_empty_careful(&dd->dispatch) ||
  		!list_empty_careful(&dd->fifo_list[0]) ||
  		!list_empty_careful(&dd->fifo_list[1]);
  }
  
  /*
   * sysfs parts below
   */
  static ssize_t
  deadline_var_show(int var, char *page)
  {
  	return sprintf(page, "%d
  ", var);
  }

  static void
  deadline_var_store(int *var, const char *page)

  {
  	char *p = (char *) page;
  
  	*var = simple_strtol(p, &p, 10);

  }
  
  #define SHOW_FUNCTION(__FUNC, __VAR, __CONV)				\
  static ssize_t __FUNC(struct elevator_queue *e, char *page)		\
  {									\
  	struct deadline_data *dd = e->elevator_data;			\
  	int __data = __VAR;						\
  	if (__CONV)							\
  		__data = jiffies_to_msecs(__data);			\
  	return deadline_var_show(__data, (page));			\
  }
  SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
  SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
  SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
  SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
  SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
  #undef SHOW_FUNCTION
  
  #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)			\
  static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)	\
  {									\
  	struct deadline_data *dd = e->elevator_data;			\
  	int __data;							\

  	deadline_var_store(&__data, (page));				\

  	if (__data < (MIN))						\
  		__data = (MIN);						\
  	else if (__data > (MAX))					\
  		__data = (MAX);						\
  	if (__CONV)							\
  		*(__PTR) = msecs_to_jiffies(__data);			\
  	else								\
  		*(__PTR) = __data;					\

  	return count;							\

  }
  STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
  STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
  STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
  STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
  STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
  #undef STORE_FUNCTION
  
  #define DD_ATTR(name) \

  	__ATTR(name, 0644, deadline_##name##_show, deadline_##name##_store)

  
  static struct elv_fs_entry deadline_attrs[] = {
  	DD_ATTR(read_expire),
  	DD_ATTR(write_expire),
  	DD_ATTR(writes_starved),
  	DD_ATTR(front_merges),
  	DD_ATTR(fifo_batch),
  	__ATTR_NULL
  };

  #ifdef CONFIG_BLK_DEBUG_FS
  #define DEADLINE_DEBUGFS_DDIR_ATTRS(ddir, name)				\
  static void *deadline_##name##_fifo_start(struct seq_file *m,		\
  					  loff_t *pos)			\
  	__acquires(&dd->lock)						\
  {									\
  	struct request_queue *q = m->private;				\
  	struct deadline_data *dd = q->elevator->elevator_data;		\
  									\
  	spin_lock(&dd->lock);						\
  	return seq_list_start(&dd->fifo_list[ddir], *pos);		\
  }									\
  									\
  static void *deadline_##name##_fifo_next(struct seq_file *m, void *v,	\
  					 loff_t *pos)			\
  {									\
  	struct request_queue *q = m->private;				\
  	struct deadline_data *dd = q->elevator->elevator_data;		\
  									\
  	return seq_list_next(v, &dd->fifo_list[ddir], pos);		\
  }									\
  									\
  static void deadline_##name##_fifo_stop(struct seq_file *m, void *v)	\
  	__releases(&dd->lock)						\
  {									\
  	struct request_queue *q = m->private;				\
  	struct deadline_data *dd = q->elevator->elevator_data;		\
  									\
  	spin_unlock(&dd->lock);						\
  }									\
  									\
  static const struct seq_operations deadline_##name##_fifo_seq_ops = {	\
  	.start	= deadline_##name##_fifo_start,				\
  	.next	= deadline_##name##_fifo_next,				\
  	.stop	= deadline_##name##_fifo_stop,				\
  	.show	= blk_mq_debugfs_rq_show,				\
  };									\
  									\
  static int deadline_##name##_next_rq_show(void *data,			\
  					  struct seq_file *m)		\
  {									\
  	struct request_queue *q = data;					\
  	struct deadline_data *dd = q->elevator->elevator_data;		\
  	struct request *rq = dd->next_rq[ddir];				\
  									\
  	if (rq)								\
  		__blk_mq_debugfs_rq_show(m, rq);			\
  	return 0;							\
  }
  DEADLINE_DEBUGFS_DDIR_ATTRS(READ, read)
  DEADLINE_DEBUGFS_DDIR_ATTRS(WRITE, write)
  #undef DEADLINE_DEBUGFS_DDIR_ATTRS
  
  static int deadline_batching_show(void *data, struct seq_file *m)
  {
  	struct request_queue *q = data;
  	struct deadline_data *dd = q->elevator->elevator_data;
  
  	seq_printf(m, "%u
  ", dd->batching);
  	return 0;
  }
  
  static int deadline_starved_show(void *data, struct seq_file *m)
  {
  	struct request_queue *q = data;
  	struct deadline_data *dd = q->elevator->elevator_data;
  
  	seq_printf(m, "%u
  ", dd->starved);
  	return 0;
  }
  
  static void *deadline_dispatch_start(struct seq_file *m, loff_t *pos)
  	__acquires(&dd->lock)
  {
  	struct request_queue *q = m->private;
  	struct deadline_data *dd = q->elevator->elevator_data;
  
  	spin_lock(&dd->lock);
  	return seq_list_start(&dd->dispatch, *pos);
  }
  
  static void *deadline_dispatch_next(struct seq_file *m, void *v, loff_t *pos)
  {
  	struct request_queue *q = m->private;
  	struct deadline_data *dd = q->elevator->elevator_data;
  
  	return seq_list_next(v, &dd->dispatch, pos);
  }
  
  static void deadline_dispatch_stop(struct seq_file *m, void *v)
  	__releases(&dd->lock)
  {
  	struct request_queue *q = m->private;
  	struct deadline_data *dd = q->elevator->elevator_data;
  
  	spin_unlock(&dd->lock);
  }
  
  static const struct seq_operations deadline_dispatch_seq_ops = {
  	.start	= deadline_dispatch_start,
  	.next	= deadline_dispatch_next,
  	.stop	= deadline_dispatch_stop,
  	.show	= blk_mq_debugfs_rq_show,
  };
  
  #define DEADLINE_QUEUE_DDIR_ATTRS(name)						\
  	{#name "_fifo_list", 0400, .seq_ops = &deadline_##name##_fifo_seq_ops},	\
  	{#name "_next_rq", 0400, deadline_##name##_next_rq_show}
  static const struct blk_mq_debugfs_attr deadline_queue_debugfs_attrs[] = {
  	DEADLINE_QUEUE_DDIR_ATTRS(read),
  	DEADLINE_QUEUE_DDIR_ATTRS(write),
  	{"batching", 0400, deadline_batching_show},
  	{"starved", 0400, deadline_starved_show},
  	{"dispatch", 0400, .seq_ops = &deadline_dispatch_seq_ops},
  	{},
  };
  #undef DEADLINE_QUEUE_DDIR_ATTRS
  #endif

  static struct elevator_type mq_deadline = {

  	.ops = {

  		.insert_requests	= dd_insert_requests,

  		.dispatch_request	= dd_dispatch_request,

  		.prepare_request	= dd_prepare_request,
  		.finish_request		= dd_finish_request,

  		.next_request		= elv_rb_latter_request,
  		.former_request		= elv_rb_former_request,
  		.bio_merge		= dd_bio_merge,
  		.request_merge		= dd_request_merge,
  		.requests_merged	= dd_merged_requests,
  		.request_merged		= dd_request_merged,
  		.has_work		= dd_has_work,
  		.init_sched		= dd_init_queue,
  		.exit_sched		= dd_exit_queue,
  	},

  #ifdef CONFIG_BLK_DEBUG_FS
  	.queue_debugfs_attrs = deadline_queue_debugfs_attrs,
  #endif

  	.elevator_attrs = deadline_attrs,
  	.elevator_name = "mq-deadline",

  	.elevator_alias = "deadline",

  	.elevator_features = ELEVATOR_F_ZBD_SEQ_WRITE,

  	.elevator_owner = THIS_MODULE,
  };

  MODULE_ALIAS("mq-deadline-iosched");

  
  static int __init deadline_init(void)
  {
  	return elv_register(&mq_deadline);
  }
  
  static void __exit deadline_exit(void)
  {
  	elv_unregister(&mq_deadline);
  }
  
  module_init(deadline_init);
  module_exit(deadline_exit);
  
  MODULE_AUTHOR("Jens Axboe");
  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION("MQ deadline IO scheduler");