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noop-iosched.c

/*
 * elevator noop
 */
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/module.h>
#include <linux/init.h>

struct noop_data {
      struct list_head queue;
};

static void noop_merged_requests(struct request_queue *q, struct request *rq,
                         struct request *next)
{
      list_del_init(&next->queuelist);
}

static int noop_dispatch(struct request_queue *q, int force)
{
      struct noop_data *nd = q->elevator->elevator_data;

      if (!list_empty(&nd->queue)) {
            struct request *rq;
            rq = list_entry(nd->queue.next, struct request, queuelist);
            list_del_init(&rq->queuelist);
            elv_dispatch_sort(q, rq);
            return 1;
      }
      return 0;
}

static void noop_add_request(struct request_queue *q, struct request *rq)
{
      struct noop_data *nd = q->elevator->elevator_data;

      list_add_tail(&rq->queuelist, &nd->queue);
}

static int noop_queue_empty(struct request_queue *q)
{
      struct noop_data *nd = q->elevator->elevator_data;

      return list_empty(&nd->queue);
}

static struct request *
noop_former_request(struct request_queue *q, struct request *rq)
{
      struct noop_data *nd = q->elevator->elevator_data;

      if (rq->queuelist.prev == &nd->queue)
            return NULL;
      return list_entry(rq->queuelist.prev, struct request, queuelist);
}

static struct request *
noop_latter_request(struct request_queue *q, struct request *rq)
{
      struct noop_data *nd = q->elevator->elevator_data;

      if (rq->queuelist.next == &nd->queue)
            return NULL;
      return list_entry(rq->queuelist.next, struct request, queuelist);
}

static void *noop_init_queue(struct request_queue *q)
{
      struct noop_data *nd;

      nd = kmalloc_node(sizeof(*nd), GFP_KERNEL, q->node);
      if (!nd)
            return NULL;
      INIT_LIST_HEAD(&nd->queue);
      return nd;
}

static void noop_exit_queue(elevator_t *e)
{
      struct noop_data *nd = e->elevator_data;

      BUG_ON(!list_empty(&nd->queue));
      kfree(nd);
}

static struct elevator_type elevator_noop = {
      .ops = {
            .elevator_merge_req_fn        = noop_merged_requests,
            .elevator_dispatch_fn         = noop_dispatch,
            .elevator_add_req_fn          = noop_add_request,
            .elevator_queue_empty_fn      = noop_queue_empty,
            .elevator_former_req_fn       = noop_former_request,
            .elevator_latter_req_fn       = noop_latter_request,
            .elevator_init_fn       = noop_init_queue,
            .elevator_exit_fn       = noop_exit_queue,
      },
      .elevator_name = "noop",
      .elevator_owner = THIS_MODULE,
};

static int __init noop_init(void)
{
      elv_register(&elevator_noop);

      return 0;
}

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");

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