linux/drivers/block/noop-iosched.c
Linus Torvalds 1da177e4c3 Linux-2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!
2005-04-16 15:20:36 -07:00

105 lines
2.2 KiB
C

/*
* elevator noop
*/
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/module.h>
#include <linux/init.h>
/*
* See if we can find a request that this buffer can be coalesced with.
*/
static int elevator_noop_merge(request_queue_t *q, struct request **req,
struct bio *bio)
{
struct list_head *entry = &q->queue_head;
struct request *__rq;
int ret;
if ((ret = elv_try_last_merge(q, bio))) {
*req = q->last_merge;
return ret;
}
while ((entry = entry->prev) != &q->queue_head) {
__rq = list_entry_rq(entry);
if (__rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER))
break;
else if (__rq->flags & REQ_STARTED)
break;
if (!blk_fs_request(__rq))
continue;
if ((ret = elv_try_merge(__rq, bio))) {
*req = __rq;
q->last_merge = __rq;
return ret;
}
}
return ELEVATOR_NO_MERGE;
}
static void elevator_noop_merge_requests(request_queue_t *q, struct request *req,
struct request *next)
{
list_del_init(&next->queuelist);
}
static void elevator_noop_add_request(request_queue_t *q, struct request *rq,
int where)
{
if (where == ELEVATOR_INSERT_FRONT)
list_add(&rq->queuelist, &q->queue_head);
else
list_add_tail(&rq->queuelist, &q->queue_head);
/*
* new merges must not precede this barrier
*/
if (rq->flags & REQ_HARDBARRIER)
q->last_merge = NULL;
else if (!q->last_merge)
q->last_merge = rq;
}
static struct request *elevator_noop_next_request(request_queue_t *q)
{
if (!list_empty(&q->queue_head))
return list_entry_rq(q->queue_head.next);
return NULL;
}
static struct elevator_type elevator_noop = {
.ops = {
.elevator_merge_fn = elevator_noop_merge,
.elevator_merge_req_fn = elevator_noop_merge_requests,
.elevator_next_req_fn = elevator_noop_next_request,
.elevator_add_req_fn = elevator_noop_add_request,
},
.elevator_name = "noop",
.elevator_owner = THIS_MODULE,
};
static int __init noop_init(void)
{
return elv_register(&elevator_noop);
}
static void __exit noop_exit(void)
{
elv_unregister(&elevator_noop);
}
module_init(noop_init);
module_exit(noop_exit);
MODULE_AUTHOR("Jens Axboe");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("No-op IO scheduler");