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         struct list_head *entry = &q->queue_head;
  17         struct request *__rq;
  18         int ret;
  19
  20         if ((ret = elv_try_last_merge(q, bio))) {
  21                 *req = q->last_merge;
  22                 return ret;
  23         }
  24
  25         while ((entry = entry->prev) != &q->queue_head) {
  26                 __rq = list_entry_rq(entry);
  27
  28                 if (__rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER))
  29                         break;
  30                 else if (__rq->flags & REQ_STARTED)
  31                         break;
  32
  33                 if (!blk_fs_request(__rq))
  34                         continue;
  35
  36                 if ((ret = elv_try_merge(__rq, bio))) {
  37                         *req = __rq;
  38                         q->last_merge = __rq;
  39                         return ret;
  40                 }
  41         }
  42
  43         return ELEVATOR_NO_MERGE;
  44 }
  45
  46 static void elevator_noop_merge_requests(request_queue_t *q, struct request *req,
  47                                          struct request *next)
  48 {
  49         list_del_init(&next->queuelist);
  50 }
  51
  52 static void elevator_noop_add_request(request_queue_t *q, struct request *rq,
  53                                       int where)
  54 {
  55         if (where == ELEVATOR_INSERT_FRONT)
  56                 list_add(&rq->queuelist, &q->queue_head);
  57         else
  58                 list_add_tail(&rq->queuelist, &q->queue_head);
  59
  60         /*
  61          * new merges must not precede this barrier
  62          */
  63         if (rq->flags & REQ_HARDBARRIER)
  64                 q->last_merge = NULL;
  65         else if (!q->last_merge)
  66                 q->last_merge = rq;
  67 }
  68
  69 static struct request *elevator_noop_next_request(request_queue_t *q)
  70 {
  71         if (!list_empty(&q->queue_head))
  72                 return list_entry_rq(q->queue_head.next);
  73
  74         return NULL;
  75 }
  76
  77 static struct elevator_type elevator_noop = {
  78         .ops = {
  79                 .elevator_merge_fn              = elevator_noop_merge,
  80                 .elevator_merge_req_fn          = elevator_noop_merge_requests,
  81                 .elevator_next_req_fn           = elevator_noop_next_request,
  82                 .elevator_add_req_fn            = elevator_noop_add_request,
  83         },
  84         .elevator_name = "noop",
  85         .elevator_owner = THIS_MODULE,
  86 };
  87
  88 static int __init noop_init(void)
  89 {
  90         return elv_register(&elevator_noop);
  91 }
  92
  93 static void __exit noop_exit(void)
  94 {
  95         elv_unregister(&elevator_noop);
  96 }
  97
  98 module_init(noop_init);
  99 module_exit(noop_exit);
 100
 101
 102 MODULE_AUTHOR("Jens Axboe");
 103 MODULE_LICENSE("GPL");
 104 MODULE_DESCRIPTION("No-op IO scheduler");