LXR linux/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
  11struct noop_data {
  12        struct list_head queue;
  13};
  14
  15static void noop_merged_requests(struct request_queue *q, struct request *rq,
  16                                 struct request *next)
  17{
  18        list_del_init(&next->queuelist);
  19}
  20
  21static int noop_dispatch(struct request_queue *q, int force)
  22{
  23        struct noop_data *nd = q->elevator->elevator_data;
  24        struct request *rq;
  25
  26        rq = list_first_entry_or_null(&nd->queue, struct request, queuelist);
  27        if (rq) {
  28                list_del_init(&rq->queuelist);
  29                elv_dispatch_sort(q, rq);
  30                return 1;
  31        }
  32        return 0;
  33}
  34
  35static 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
  42static struct request *
  43noop_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_prev_entry(rq, queuelist);
  50}
  51
  52static struct request *
  53noop_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_next_entry(rq, queuelist);
  60}
  61
  62static 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
  86static 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
  94static 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
 108static int __init noop_init(void)
 109{
 110        return elv_register(&elevator_noop);
 111}
 112
 113static void __exit noop_exit(void)
 114{
 115        elv_unregister(&elevator_noop);
 116}
 117
 118module_init(noop_init);
 119module_exit(noop_exit);
 120
 121
 122MODULE_AUTHOR("Jens Axboe");
 123MODULE_LICENSE("GPL");
 124MODULE_DESCRIPTION("No-op IO scheduler");
 125