/*
   * elevator noop
   */
  #include <linux/blkdev.h>
  #include <linux/elevator.h>
  #include <linux/bio.h>
  #include <linux/module.h>

  #include <linux/slab.h>

  #include <linux/init.h>

  struct noop_data {
  	struct list_head queue;
  };

  static void noop_merged_requests(struct request_queue *q, struct request *rq,

  				 struct request *next)
  {
  	list_del_init(&next->queuelist);
  }

  static int noop_dispatch(struct request_queue *q, int force)

  {
  	struct noop_data *nd = q->elevator->elevator_data;

  	struct request *rq;

  	rq = list_first_entry_or_null(&nd->queue, struct request, queuelist);
  	if (rq) {

  		list_del_init(&rq->queuelist);
  		elv_dispatch_sort(q, rq);
  		return 1;
  	}
  	return 0;
  }

  static void noop_add_request(struct request_queue *q, struct request *rq)

  {
  	struct noop_data *nd = q->elevator->elevator_data;
  
  	list_add_tail(&rq->queuelist, &nd->queue);
  }

  static struct request *

  noop_former_request(struct request_queue *q, struct request *rq)

  {
  	struct noop_data *nd = q->elevator->elevator_data;
  
  	if (rq->queuelist.prev == &nd->queue)
  		return NULL;

  	return list_prev_entry(rq, queuelist);

  }
  
  static struct request *

  noop_latter_request(struct request_queue *q, struct request *rq)

  {
  	struct noop_data *nd = q->elevator->elevator_data;
  
  	if (rq->queuelist.next == &nd->queue)
  		return NULL;

  	return list_next_entry(rq, queuelist);

  }

  static int noop_init_queue(struct request_queue *q, struct elevator_type *e)

  {

  	struct noop_data *nd;

  	struct elevator_queue *eq;
  
  	eq = elevator_alloc(q, e);
  	if (!eq)
  		return -ENOMEM;

  	nd = kmalloc_node(sizeof(*nd), GFP_KERNEL, q->node);

  	if (!nd) {
  		kobject_put(&eq->kobj);

  		return -ENOMEM;

  	}
  	eq->elevator_data = nd;

  	INIT_LIST_HEAD(&nd->queue);

  
  	spin_lock_irq(q->queue_lock);
  	q->elevator = eq;
  	spin_unlock_irq(q->queue_lock);

  	return 0;

  }

  static void noop_exit_queue(struct elevator_queue *e)

  {
  	struct noop_data *nd = e->elevator_data;
  
  	BUG_ON(!list_empty(&nd->queue));
  	kfree(nd);
  }

  static struct elevator_type elevator_noop = {

  	.ops.sq = {

  		.elevator_merge_req_fn		= noop_merged_requests,
  		.elevator_dispatch_fn		= noop_dispatch,
  		.elevator_add_req_fn		= noop_add_request,

  		.elevator_former_req_fn		= noop_former_request,
  		.elevator_latter_req_fn		= noop_latter_request,
  		.elevator_init_fn		= noop_init_queue,
  		.elevator_exit_fn		= noop_exit_queue,

  	},
  	.elevator_name = "noop",
  	.elevator_owner = THIS_MODULE,
  };
  
  static int __init noop_init(void)
  {

  	return elv_register(&elevator_noop);

  }
  
  static void __exit noop_exit(void)
  {
  	elv_unregister(&elevator_noop);
  }
  
  module_init(noop_init);
  module_exit(noop_exit);
  
  
  MODULE_AUTHOR("Jens Axboe");
  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION("No-op IO scheduler");