Root/block/noop-iosched.c

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 int noop_queue_empty(struct request_queue *q)
43{
44    struct noop_data *nd = q->elevator->elevator_data;
45
46    return list_empty(&nd->queue);
47}
48
49static struct request *
50noop_former_request(struct request_queue *q, struct request *rq)
51{
52    struct noop_data *nd = q->elevator->elevator_data;
53
54    if (rq->queuelist.prev == &nd->queue)
55        return NULL;
56    return list_entry(rq->queuelist.prev, struct request, queuelist);
57}
58
59static struct request *
60noop_latter_request(struct request_queue *q, struct request *rq)
61{
62    struct noop_data *nd = q->elevator->elevator_data;
63
64    if (rq->queuelist.next == &nd->queue)
65        return NULL;
66    return list_entry(rq->queuelist.next, struct request, queuelist);
67}
68
69static void *noop_init_queue(struct request_queue *q)
70{
71    struct noop_data *nd;
72
73    nd = kmalloc_node(sizeof(*nd), GFP_KERNEL, q->node);
74    if (!nd)
75        return NULL;
76    INIT_LIST_HEAD(&nd->queue);
77    return nd;
78}
79
80static void noop_exit_queue(struct elevator_queue *e)
81{
82    struct noop_data *nd = e->elevator_data;
83
84    BUG_ON(!list_empty(&nd->queue));
85    kfree(nd);
86}
87
88static struct elevator_type elevator_noop = {
89    .ops = {
90        .elevator_merge_req_fn = noop_merged_requests,
91        .elevator_dispatch_fn = noop_dispatch,
92        .elevator_add_req_fn = noop_add_request,
93        .elevator_queue_empty_fn = noop_queue_empty,
94        .elevator_former_req_fn = noop_former_request,
95        .elevator_latter_req_fn = noop_latter_request,
96        .elevator_init_fn = noop_init_queue,
97        .elevator_exit_fn = noop_exit_queue,
98    },
99    .elevator_name = "noop",
100    .elevator_owner = THIS_MODULE,
101};
102
103static int __init noop_init(void)
104{
105    elv_register(&elevator_noop);
106
107    return 0;
108}
109
110static void __exit noop_exit(void)
111{
112    elv_unregister(&elevator_noop);
113}
114
115module_init(noop_init);
116module_exit(noop_exit);
117
118
119MODULE_AUTHOR("Jens Axboe");
120MODULE_LICENSE("GPL");
121MODULE_DESCRIPTION("No-op IO scheduler");
122

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