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(request_queue_t *q, struct request *rq,
  15                                  struct request *next)
  16 {
  17         list_del_init(&next->queuelist);
  18 }
  19
  20 static int noop_dispatch(request_queue_t *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(request_queue_t *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(request_queue_t *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(request_queue_t *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(request_queue_t *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 int noop_init_queue(request_queue_t *q, elevator_t *e)
  69 {
  70         struct noop_data *nd;
  71
  72         nd = kmalloc(sizeof(*nd), GFP_KERNEL);
  73         if (!nd)
  74                 return -ENOMEM;
  75         INIT_LIST_HEAD(&nd->queue);
  76         e->elevator_data = nd;
  77         return 0;
  78 }
  79
  80 static void noop_exit_queue(elevator_t *e)
  81 {
  82         struct noop_data *nd = e->elevator_data;
  83
  84         BUG_ON(!list_empty(&nd->queue));
  85         kfree(nd);
  86 }
  87
  88 static 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
 103 static int __init noop_init(void)
 104 {
 105         return elv_register(&elevator_noop);
 106 }
 107
 108 static void __exit noop_exit(void)
 109 {
 110         elv_unregister(&elevator_noop);
 111 }
 112
 113 module_init(noop_init);
 114 module_exit(noop_exit);
 115
 116
 117 MODULE_AUTHOR("Jens Axboe");
 118 MODULE_LICENSE("GPL");
 119 MODULE_DESCRIPTION("No-op IO scheduler");