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, 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

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