4 #include <linux/blkdev.h>
5 #include <linux/elevator.h>
7 #include <linux/module.h>
8 #include <linux/init.h>
11 * See if we can find a request that this buffer can be coalesced with.
13 static int elevator_noop_merge(request_queue_t *q, struct request **req,
16 struct list_head *entry = &q->queue_head;
20 if ((ret = elv_try_last_merge(q, bio))) {
25 while ((entry = entry->prev) != &q->queue_head) {
26 __rq = list_entry_rq(entry);
28 if (__rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER))
30 else if (__rq->flags & REQ_STARTED)
33 if (!blk_fs_request(__rq))
36 if ((ret = elv_try_merge(__rq, bio))) {
43 return ELEVATOR_NO_MERGE;
46 static void elevator_noop_merge_requests(request_queue_t *q, struct request *req,
49 list_del_init(&next->queuelist);
52 static void elevator_noop_add_request(request_queue_t *q, struct request *rq,
55 if (where == ELEVATOR_INSERT_FRONT)
56 list_add(&rq->queuelist, &q->queue_head);
58 list_add_tail(&rq->queuelist, &q->queue_head);
61 * new merges must not precede this barrier
63 if (rq->flags & REQ_HARDBARRIER)
65 else if (!q->last_merge)
69 static struct request *elevator_noop_next_request(request_queue_t *q)
71 if (!list_empty(&q->queue_head))
72 return list_entry_rq(q->queue_head.next);
77 static struct elevator_type elevator_noop = {
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,
84 .elevator_name = "noop",
85 .elevator_owner = THIS_MODULE,
88 static int __init noop_init(void)
90 return elv_register(&elevator_noop);
93 static void __exit noop_exit(void)
95 elv_unregister(&elevator_noop);
98 module_init(noop_init);
99 module_exit(noop_exit);
102 MODULE_AUTHOR("Jens Axboe");
103 MODULE_LICENSE("GPL");
104 MODULE_DESCRIPTION("No-op IO scheduler");