block: don't init rq fields unnecessarily
[linux-2.6.git] / 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/init.h>
9
10 struct noop_data {
11         struct list_head queue;
12 };
13
14 static void noop_merged_requests(struct request_queue *q, struct request *rq,
15                                  struct request *next)
16 {
17         list_del_init(&next->queuelist);
18 }
19
20 static int noop_dispatch(struct request_queue *q, int force)
21 {
22         struct noop_data *nd = q->elevator->elevator_data;
23
24         if (!list_empty(&nd->queue)) {
25                 struct request *rq;
26                 rq = list_entry(nd->queue.next, struct request, queuelist);
27                 list_del_init(&rq->queuelist);
28                 elv_dispatch_sort(q, rq);
29                 return 1;
30         }
31         return 0;
32 }
33
34 static void noop_add_request(struct request_queue *q, struct request *rq)
35 {
36         struct noop_data *nd = q->elevator->elevator_data;
37
38         list_add_tail(&rq->queuelist, &nd->queue);
39 }
40
41 static int noop_queue_empty(struct request_queue *q)
42 {
43         struct noop_data *nd = q->elevator->elevator_data;
44
45         return list_empty(&nd->queue);
46 }
47
48 static struct request *
49 noop_former_request(struct request_queue *q, struct request *rq)
50 {
51         struct noop_data *nd = q->elevator->elevator_data;
52
53         if (rq->queuelist.prev == &nd->queue)
54                 return NULL;
55         return list_entry(rq->queuelist.prev, struct request, queuelist);
56 }
57
58 static struct request *
59 noop_latter_request(struct request_queue *q, struct request *rq)
60 {
61         struct noop_data *nd = q->elevator->elevator_data;
62
63         if (rq->queuelist.next == &nd->queue)
64                 return NULL;
65         return list_entry(rq->queuelist.next, struct request, queuelist);
66 }
67
68 static void *noop_init_queue(struct request_queue *q)
69 {
70         struct noop_data *nd;
71
72         nd = kmalloc_node(sizeof(*nd), GFP_KERNEL, q->node);
73         if (!nd)
74                 return NULL;
75         INIT_LIST_HEAD(&nd->queue);
76         return nd;
77 }
78
79 static void noop_exit_queue(struct elevator_queue *e)
80 {
81         struct noop_data *nd = e->elevator_data;
82
83         BUG_ON(!list_empty(&nd->queue));
84         kfree(nd);
85 }
86
87 static struct elevator_type elevator_noop = {
88         .ops = {
89                 .elevator_merge_req_fn          = noop_merged_requests,
90                 .elevator_dispatch_fn           = noop_dispatch,
91                 .elevator_add_req_fn            = noop_add_request,
92                 .elevator_queue_empty_fn        = noop_queue_empty,
93                 .elevator_former_req_fn         = noop_former_request,
94                 .elevator_latter_req_fn         = noop_latter_request,
95                 .elevator_init_fn               = noop_init_queue,
96                 .elevator_exit_fn               = noop_exit_queue,
97         },
98         .elevator_name = "noop",
99         .elevator_owner = THIS_MODULE,
100 };
101
102 static int __init noop_init(void)
103 {
104         elv_register(&elevator_noop);
105
106         return 0;
107 }
108
109 static void __exit noop_exit(void)
110 {
111         elv_unregister(&elevator_noop);
112 }
113
114 module_init(noop_init);
115 module_exit(noop_exit);
116
117
118 MODULE_AUTHOR("Jens Axboe");
119 MODULE_LICENSE("GPL");
120 MODULE_DESCRIPTION("No-op IO scheduler");