clook-iosched.c

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

struct clook_data {
	struct list_head queue;
};

static void clook_merged_requests(struct request_queue *q, struct request *rq,
				 struct request *next)
{
	list_del_init(&next->queuelist);
}
/**
 * Instrumented to report activity.
 */
static int clook_dispatch(struct request_queue *q, int force)
{
	struct clook_data *nd = q->elevator->elevator_data;
	struct request *rq;

	rq = list_first_entry_or_null(&nd->queue, struct request, queuelist);
	if (rq) {
		list_del_init(&rq->queuelist);
		elv_dispatch_sort(q, rq);
		char direction = ((rq->cmd_flags & 1) ? 'W' : 'R');
		printk("[CLOOK] dsp %c %lu\n", direction, blk_rq_pos(rq));
		return 1;
	}
	return 0;
}

/**
 * Modified function
 * Notes:
 *   - The list we are inserting into is sorted,
 *     because new entries are only added by our function.
 *   - Adjacent requests should be merged.
 *   - Instrumented to report activity.
 */
static void clook_add_request(struct request_queue *q, struct request *rq)
{
	struct clook_data *nd = q->elevator->elevator_data;
	//cursor for selecting where to insert
	struct list_head *cur = NULL;

	//We can assume the array is already sorted, so insert as if inserting into a sorted array
	list_for_each(cur, &nd->queue) {
		if(rq_end_sector(list_entry(cur, struct request,queuelist)) > rq_end_sector(rq)) {
			break;
		}
	}

	list_add_tail(&rq->queuelist, &nd->queue);
	char direction = ((rq->cmd_flags & 1) ? 'W' : 'R');
	printk("[CLOOK] add %c %lu\n", direction, blk_rq_pos(rq));
}

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

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

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

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

static int clook_init_queue(struct request_queue *q, struct elevator_type *e)
{
	struct clook_data *nd;
	struct elevator_queue *eq;

	eq = elevator_alloc(q, e);
	if (!eq)
		return -ENOMEM;

	nd = kmalloc_node(sizeof(*nd), GFP_KERNEL, q->node);
	if (!nd) {
		kobject_put(&eq->kobj);
		return -ENOMEM;
	}
	eq->elevator_data = nd;

	INIT_LIST_HEAD(&nd->queue);

	spin_lock_irq(q->queue_lock);
	q->elevator = eq;
	spin_unlock_irq(q->queue_lock);
	return 0;
}

static void clook_exit_queue(struct elevator_queue *e)
{
	struct clook_data *nd = e->elevator_data;

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

static struct elevator_type elevator_clook = {
	.ops.sq = {
		.elevator_merge_req_fn		= clook_merged_requests,
		.elevator_dispatch_fn		= clook_dispatch,
		.elevator_add_req_fn		= clook_add_request,
		.elevator_former_req_fn		= clook_former_request,
		.elevator_latter_req_fn		= clook_latter_request,
		.elevator_init_fn		= clook_init_queue,
		.elevator_exit_fn		= clook_exit_queue,
	},
	.elevator_name = "clook",
	.elevator_owner = THIS_MODULE,
};

static int __init clook_init(void)
{
	return elv_register(&elevator_clook);
}

static void __exit clook_exit(void)
{
	elv_unregister(&elevator_clook);
}

module_init(clook_init);
module_exit(clook_exit);


MODULE_AUTHOR("David Ramirez");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("C-LOOK IO scheduler");