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

  struct noop_data {
  	struct list_head queue;
  };
  
  static void noop_merged_requests(request_queue_t *q, struct request *rq,
  				 struct request *next)
  {
  	list_del_init(&next->queuelist);
  }
  
  static int noop_dispatch(request_queue_t *q, int force)
  {
  	struct noop_data *nd = q->elevator->elevator_data;
  
  	if (!list_empty(&nd->queue)) {
  		struct request *rq;
  		rq = list_entry(nd->queue.next, struct request, queuelist);
  		list_del_init(&rq->queuelist);
  		elv_dispatch_sort(q, rq);
  		return 1;
  	}
  	return 0;
  }
  
  static void noop_add_request(request_queue_t *q, struct request *rq)
  {
  	struct noop_data *nd = q->elevator->elevator_data;
  
  	list_add_tail(&rq->queuelist, &nd->queue);
  }
  
  static int noop_queue_empty(request_queue_t *q)

  {

  	struct noop_data *nd = q->elevator->elevator_data;
  
  	return list_empty(&nd->queue);
  }
  
  static struct request *
  noop_former_request(request_queue_t *q, struct request *rq)
  {
  	struct noop_data *nd = q->elevator->elevator_data;
  
  	if (rq->queuelist.prev == &nd->queue)
  		return NULL;
  	return list_entry(rq->queuelist.prev, struct request, queuelist);
  }
  
  static struct request *
  noop_latter_request(request_queue_t *q, struct request *rq)
  {
  	struct noop_data *nd = q->elevator->elevator_data;
  
  	if (rq->queuelist.next == &nd->queue)
  		return NULL;
  	return list_entry(rq->queuelist.next, struct request, queuelist);

  }

  static void *noop_init_queue(request_queue_t *q, elevator_t *e)

  {

  	struct noop_data *nd;
  
  	nd = kmalloc(sizeof(*nd), GFP_KERNEL);
  	if (!nd)

  		return NULL;

  	INIT_LIST_HEAD(&nd->queue);

  	return nd;

  }

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

  static struct elevator_type elevator_noop = {
  	.ops = {

  		.elevator_merge_req_fn		= noop_merged_requests,
  		.elevator_dispatch_fn		= noop_dispatch,
  		.elevator_add_req_fn		= noop_add_request,
  		.elevator_queue_empty_fn	= noop_queue_empty,
  		.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");