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 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");
114

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