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                                       int where)
  33 {
  34         if (where == ELEVATOR_INSERT_FRONT)
  35                 list_add(&rq->queuelist, &q->queue_head);
  36         else
  37                 list_add_tail(&rq->queuelist, &q->queue_head);
  38
  39         /*
  40          * new merges must not precede this barrier
  41          */
  42         if (rq->flags & REQ_HARDBARRIER)
  43                 q->last_merge = NULL;
  44         else if (!q->last_merge)
  45                 q->last_merge = rq;
  46 }
  47
  48 static struct request *elevator_noop_next_request(request_queue_t *q)
  49 {
  50         if (!list_empty(&q->queue_head))
  51                 return list_entry_rq(q->queue_head.next);
  52
  53         return NULL;
  54 }
  55
  56 static struct elevator_type elevator_noop = {
  57         .ops = {
  58                 .elevator_merge_fn              = elevator_noop_merge,
  59                 .elevator_merge_req_fn          = elevator_noop_merge_requests,
  60                 .elevator_next_req_fn           = elevator_noop_next_request,
  61                 .elevator_add_req_fn            = elevator_noop_add_request,
  62         },
  63         .elevator_name = "noop",
  64         .elevator_owner = THIS_MODULE,
  65 };
  66
  67 static int __init noop_init(void)
  68 {
  69         return elv_register(&elevator_noop);
  70 }
  71
  72 static void __exit noop_exit(void)
  73 {
  74         elv_unregister(&elevator_noop);
  75 }
  76
  77 module_init(noop_init);
  78 module_exit(noop_exit);
  79
  80
  81 MODULE_AUTHOR("Jens Axboe");
  82 MODULE_LICENSE("GPL");
  83 MODULE_DESCRIPTION("No-op IO scheduler");