drivers/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 /*
  11  * See if we can find a request that this buffer can be coalesced with.
  12  */
  13 static int elevator_noop_merge(request_queue_t *q, struct request **req,
  14                                struct bio *bio)
  15 {
  16         int ret;
  17
  18         ret = elv_try_last_merge(q, bio);
  19         if (ret != ELEVATOR_NO_MERGE)
  20                 *req = q->last_merge;
  21
  22         return ret;
  23 }
  24
  25 static void elevator_noop_merge_requests(request_queue_t *q, struct request *req,
  26                                          struct request *next)
  27 {
  28         list_del_init(&next->queuelist);
  29 }
  30
  31 static void elevator_noop_add_request(request_queue_t *q, struct request *rq)
  32 {
  33         elv_dispatch_add_tail(q, rq);
  34
  35         /*
  36          * new merges must not precede this barrier
  37          */
  38         if (rq->flags & REQ_HARDBARRIER)
  39                 q->last_merge = NULL;
  40         else if (!q->last_merge)
  41                 q->last_merge = rq;
  42 }
  43
  44 static int elevator_noop_dispatch(request_queue_t *q, int force)
  45 {
  46         return 0;
  47 }
  48
  49 static struct elevator_type elevator_noop = {
  50         .ops = {
  51                 .elevator_merge_fn              = elevator_noop_merge,
  52                 .elevator_merge_req_fn          = elevator_noop_merge_requests,
  53                 .elevator_dispatch_fn           = elevator_noop_dispatch,
  54                 .elevator_add_req_fn            = elevator_noop_add_request,
  55         },
  56         .elevator_name = "noop",
  57         .elevator_owner = THIS_MODULE,
  58 };
  59
  60 static int __init noop_init(void)
  61 {
  62         return elv_register(&elevator_noop);
  63 }
  64
  65 static void __exit noop_exit(void)
  66 {
  67         elv_unregister(&elevator_noop);
  68 }
  69
  70 module_init(noop_init);
  71 module_exit(noop_exit);
  72
  73
  74 MODULE_AUTHOR("Jens Axboe");
  75 MODULE_LICENSE("GPL");
  76 MODULE_DESCRIPTION("No-op IO scheduler");