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 struct request *
  43 noop_former_request(struct request_queue *q, struct request *rq)
  44 {
  45         struct noop_data *nd = q->elevator->elevator_data;
  46
  47         if (rq->queuelist.prev == &nd->queue)
  48                 return NULL;
  49         return list_entry(rq->queuelist.prev, struct request, queuelist);
  50 }
  51
  52 static struct request *
  53 noop_latter_request(struct request_queue *q, struct request *rq)
  54 {
  55         struct noop_data *nd = q->elevator->elevator_data;
  56
  57         if (rq->queuelist.next == &nd->queue)
  58                 return NULL;
  59         return list_entry(rq->queuelist.next, struct request, queuelist);
  60 }
  61
  62 static int noop_init_queue(struct request_queue *q, struct elevator_type *e)
  63 {
  64         struct noop_data *nd;
  65         struct elevator_queue *eq;
  66
  67         eq = elevator_alloc(q, e);
  68         if (!eq)
  69                 return -ENOMEM;
  70
  71         nd = kmalloc_node(sizeof(*nd), GFP_KERNEL, q->node);
  72         if (!nd) {
  73                 kobject_put(&eq->kobj);
  74                 return -ENOMEM;
  75         }
  76         eq->elevator_data = nd;
  77
  78         INIT_LIST_HEAD(&nd->queue);
  79
  80         spin_lock_irq(q->queue_lock);
  81         q->elevator = eq;
  82         spin_unlock_irq(q->queue_lock);
  83         return 0;
  84 }
  85
  86 static void noop_exit_queue(struct elevator_queue *e)
  87 {
  88         struct noop_data *nd = e->elevator_data;
  89
  90         BUG_ON(!list_empty(&nd->queue));
  91         kfree(nd);
  92 }
  93
  94 static struct elevator_type elevator_noop = {
  95         .ops = {
  96                 .elevator_merge_req_fn          = noop_merged_requests,
  97                 .elevator_dispatch_fn           = noop_dispatch,
  98                 .elevator_add_req_fn            = noop_add_request,
  99                 .elevator_former_req_fn         = noop_former_request,
 100                 .elevator_latter_req_fn         = noop_latter_request,
 101                 .elevator_init_fn               = noop_init_queue,
 102                 .elevator_exit_fn               = noop_exit_queue,
 103         },
 104         .elevator_name = "noop",
 105         .elevator_owner = THIS_MODULE,
 106 };
 107
 108 static int __init noop_init(void)
 109 {
 110         return elv_register(&elevator_noop);
 111 }
 112
 113 static void __exit noop_exit(void)
 114 {
 115         elv_unregister(&elevator_noop);
 116 }
 117
 118 module_init(noop_init);
 119 module_exit(noop_exit);
 120
 121
 122 MODULE_AUTHOR("Jens Axboe");
 123 MODULE_LICENSE("GPL");
 124 MODULE_DESCRIPTION("No-op IO scheduler");