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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 
 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         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 
 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_prev_entry(rq, 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_next_entry(rq, 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");
125 

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