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/slab.h>
   9 #include <linux/init.h>
  10
  11 struct noop_data {
  12         struct list_head queue;
  13 };
  14
  15 static void noop_merged_requests(struct request_queue *q, struct request *rq,
  16                                  struct request *next)
  17 {
  18         list_del_init(&next->queuelist);
  19 }
  20
  21 static int noop_dispatch(struct request_queue *q, int force)
  22 {
  23         struct noop_data *nd = q->elevator->elevator_data;
  24
  25         if (!list_empty(&nd->queue)) {
  26                 struct request *rq;
  27                 rq = list_entry(nd->queue.next, struct request, queuelist);
  28                 list_del_init(&rq->queuelist);
  29                 elv_dispatch_sort(q, rq);
  30                 return 1;
  31         }
  32         return 0;
  33 }
  34
  35 static void noop_add_request(struct request_queue *q, struct request *rq)
  36 {
  37         struct noop_data *nd = q->elevator->elevator_data;
  38
  39         list_add_tail(&rq->queuelist, &nd->queue);
  40 }
  41
  42 static int noop_queue_empty(struct request_queue *q)
  43 {
  44         struct noop_data *nd = q->elevator->elevator_data;
  45
  46         return list_empty(&nd->queue);
  47 }
  48
  49 static struct request *
  50 noop_former_request(struct request_queue *q, struct request *rq)
  51 {
  52         struct noop_data *nd = q->elevator->elevator_data;
  53
  54         if (rq->queuelist.prev == &nd->queue)
  55                 return NULL;
  56         return list_entry(rq->queuelist.prev, struct request, queuelist);
  57 }
  58
  59 static struct request *
  60 noop_latter_request(struct request_queue *q, struct request *rq)
  61 {
  62         struct noop_data *nd = q->elevator->elevator_data;
  63
  64         if (rq->queuelist.next == &nd->queue)
  65                 return NULL;
  66         return list_entry(rq->queuelist.next, struct request, queuelist);
  67 }
  68
  69 static void *noop_init_queue(struct request_queue *q)
  70 {
  71         struct noop_data *nd;
  72
  73         nd = kmalloc_node(sizeof(*nd), GFP_KERNEL, q->node);
  74         if (!nd)
  75                 return NULL;
  76         INIT_LIST_HEAD(&nd->queue);
  77         return nd;
  78 }
  79
  80 static void noop_exit_queue(struct elevator_queue *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         elv_register(&elevator_noop);
 106
 107         return 0;
 108 }
 109
 110 static void __exit noop_exit(void)
 111 {
 112         elv_unregister(&elevator_noop);
 113 }
 114
 115 module_init(noop_init);
 116 module_exit(noop_exit);
 117
 118
 119 MODULE_AUTHOR("Jens Axboe");
 120 MODULE_LICENSE("GPL");
 121 MODULE_DESCRIPTION("No-op IO scheduler");