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, struct elevator_type *e)
63{
64	struct noop_data *nd;
65	struct elevator_queue *eq;
66
67	eq = elevator_alloc(q, e);
68	if (!eq)
69		return -ENOMEM;
70
71	nd = kmalloc_node(sizeof(*nd), GFP_KERNEL, q->node);
72	if (!nd) {
73		kobject_put(&eq->kobj);
74		return -ENOMEM;
75	}
76	eq->elevator_data = nd;
77
78	INIT_LIST_HEAD(&nd->queue);
79
80	spin_lock_irq(q->queue_lock);
81	q->elevator = eq;
82	spin_unlock_irq(q->queue_lock);
83	return 0;
84}
85
86static void noop_exit_queue(struct elevator_queue *e)
87{
88	struct noop_data *nd = e->elevator_data;
89
90	BUG_ON(!list_empty(&nd->queue));
91	kfree(nd);
92}
93
94static struct elevator_type elevator_noop = {
95	.ops = {
96		.elevator_merge_req_fn		= noop_merged_requests,
97		.elevator_dispatch_fn		= noop_dispatch,
98		.elevator_add_req_fn		= noop_add_request,
99		.elevator_former_req_fn		= noop_former_request,
100		.elevator_latter_req_fn		= noop_latter_request,
101		.elevator_init_fn		= noop_init_queue,
102		.elevator_exit_fn		= noop_exit_queue,
103	},
104	.elevator_name = "noop",
105	.elevator_owner = THIS_MODULE,
106};
107
108static int __init noop_init(void)
109{
110	return elv_register(&elevator_noop);
111}
112
113static void __exit noop_exit(void)
114{
115	elv_unregister(&elevator_noop);
116}
117
118module_init(noop_init);
119module_exit(noop_exit);
120
121
122MODULE_AUTHOR("Jens Axboe");
123MODULE_LICENSE("GPL");
124MODULE_DESCRIPTION("No-op IO scheduler");
125