1/*
  2 * elevator noop
  3 */
  4#include <linux/blkdev.h>
  5#include <linux/elevator.h>
  6#include <linux/bio.h>
  7#include <linux/module.h>
  8#include <linux/slab.h>
  9#include <linux/init.h>
 10
 11struct noop_data {
 12	struct list_head queue;
 13};
 14
 15static void noop_merged_requests(struct request_queue *q, struct request *rq,
 16				 struct request *next)
 17{
 18	list_del_init(&next->queuelist);
 19}
 20
 21static int noop_dispatch(struct request_queue *q, int force)
 22{
 23	struct noop_data *nd = q->elevator->elevator_data;
 24
 25	if (!list_empty(&nd->queue)) {
 26		struct request *rq;
 27		rq = list_entry(nd->queue.next, struct request, queuelist);
 28		list_del_init(&rq->queuelist);
 29		elv_dispatch_sort(q, rq);
 30		return 1;
 31	}
 32	return 0;
 33}
 34
 35static void noop_add_request(struct request_queue *q, struct request *rq)
 36{
 37	struct noop_data *nd = q->elevator->elevator_data;
 38
 39	list_add_tail(&rq->queuelist, &nd->queue);
 40}
 41
 42static struct request *
 43noop_former_request(struct request_queue *q, struct request *rq)
 44{
 45	struct noop_data *nd = q->elevator->elevator_data;
 46
 47	if (rq->queuelist.prev == &nd->queue)
 48		return NULL;
 49	return list_entry(rq->queuelist.prev, struct request, queuelist);
 50}
 51
 52static struct request *
 53noop_latter_request(struct request_queue *q, struct request *rq)
 54{
 55	struct noop_data *nd = q->elevator->elevator_data;
 56
 57	if (rq->queuelist.next == &nd->queue)
 58		return NULL;
 59	return list_entry(rq->queuelist.next, struct request, queuelist);
 60}
 61
 62static int noop_init_queue(struct request_queue *q)
 63{
 64	struct noop_data *nd;
 65
 66	nd = kmalloc_node(sizeof(*nd), GFP_KERNEL, q->node);
 67	if (!nd)
 68		return -ENOMEM;
 69
 70	INIT_LIST_HEAD(&nd->queue);
 71	q->elevator->elevator_data = nd;
 72	return 0;
 73}
 74
 75static void noop_exit_queue(struct elevator_queue *e)
 76{
 77	struct noop_data *nd = e->elevator_data;
 78
 79	BUG_ON(!list_empty(&nd->queue));
 80	kfree(nd);
 81}
 82
 83static struct elevator_type elevator_noop = {
 84	.ops = {
 85		.elevator_merge_req_fn		= noop_merged_requests,
 86		.elevator_dispatch_fn		= noop_dispatch,
 87		.elevator_add_req_fn		= noop_add_request,
 88		.elevator_former_req_fn		= noop_former_request,
 89		.elevator_latter_req_fn		= noop_latter_request,
 90		.elevator_init_fn		= noop_init_queue,
 91		.elevator_exit_fn		= noop_exit_queue,
 92	},
 93	.elevator_name = "noop",
 94	.elevator_owner = THIS_MODULE,
 95};
 96
 97static int __init noop_init(void)
 98{
 99	return elv_register(&elevator_noop);
100}
101
102static void __exit noop_exit(void)
103{
104	elv_unregister(&elevator_noop);
105}
106
107module_init(noop_init);
108module_exit(noop_exit);
109
110
111MODULE_AUTHOR("Jens Axboe");
112MODULE_LICENSE("GPL");
113MODULE_DESCRIPTION("No-op IO scheduler");