path: root/block/elevator.c

/*
 *  Block device elevator/IO-scheduler.
 *
 *  Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
 *
 * 30042000 Jens Axboe <axboe@suse.de> :
 *
 * Split the elevator a bit so that it is possible to choose a different
 * one or even write a new "plug in". There are three pieces:
 * - elevator_fn, inserts a new request in the queue list
 * - elevator_merge_fn, decides whether a new buffer can be merged with
 *   an existing request
 * - elevator_dequeue_fn, called when a request is taken off the active list
 *
 * 20082000 Dave Jones <davej@suse.de> :
 * Removed tests for max-bomb-segments, which was breaking elvtune
 *  when run without -bN
 *
 * Jens:
 * - Rework again to work with bio instead of buffer_heads
 * - loose bi_dev comparisons, partition handling is right now
 * - completely modularize elevator setup and teardown
 *
 */
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/config.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/delay.h>
#include <linux/blktrace_api.h>

#include <asm/uaccess.h>

static DEFINE_SPINLOCK(elv_list_lock);
static LIST_HEAD(elv_list);

/*
 * can we safely merge with this request?
 */
inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
{
	if (!rq_mergeable(rq))
		return 0;

	/*
	 * different data direction or already started, don't merge
	 */
	if (bio_data_dir(bio) != rq_data_dir(rq))
		return 0;

	/*
	 * same device and no special stuff set, merge is ok
	 */
	if (rq->rq_disk == bio->bi_bdev->bd_disk &&
	    !rq->waiting && !rq->special)
		return 1;

	return 0;
}
EXPORT_SYMBOL(elv_rq_merge_ok);

static inline int elv_try_merge(struct request *__rq, struct bio *bio)
{
	int ret = ELEVATOR_NO_MERGE;

	/*
	 * we can merge and sequence is ok, check if it's possible
	 */
	if (elv_rq_merge_ok(__rq, bio)) {
		if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
			ret = ELEVATOR_BACK_MERGE;
		else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
			ret = ELEVATOR_FRONT_MERGE;
	}

	return ret;
}

static struct elevator_type *elevator_find(const char *name)
{
	struct elevator_type *e = NULL;
	struct list_head *entry;

	list_for_each(entry, &elv_list) {
		struct elevator_type *__e;

		__e = list_entry(entry, struct elevator_type, list);

		if (!strcmp(__e->elevator_name, name)) {
			e = __e;
			break;
		}
	}

	return e;
}

static void elevator_put(struct elevator_type *e)
{
	module_put(e->elevator_owner);
}

static struct elevator_type *elevator_get(const char *name)
{
	struct elevator_type *e;

	spin_lock_irq(&elv_list_lock);

	e = elevator_find(name);
	if (e && !try_module_get(e->elevator_owner))
		e = NULL;

	spin_unlock_irq(&elv_list_lock);

	return e;
}

static int elevator_attach(request_queue_t *q, struct elevator_queue *eq)
{
	int ret = 0;

	q->elevator = eq;

	if (eq->ops->elevator_init_fn)
		ret = eq->ops->elevator_init_fn(q, eq);

	return ret;
}

static char chosen_elevator[16];

static int __init elevator_setup(char *str)
{
	/*
	 * Be backwards-compatible with previous kernels, so users
	 * won't get the wrong elevator.
	 */
	if (!strcmp(str, "as"))
		strcpy(chosen_elevator, "anticipatory");
	else
		strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
	return 1;
}

__setup("elevator=", elevator_setup);

static struct kobj_type elv_ktype;

static elevator_t *elevator_alloc(struct elevator_type *e)
{
	elevator_t *eq = kmalloc(sizeof(elevator_t), GFP_KERNEL);
	if (eq) {
		memset(eq, 0, sizeof(*eq));
		eq->ops = &e->ops;
		eq->elevator_type = e;
		kobject_init(&eq->kobj);
		snprintf(eq->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
		eq->kobj.ktype = &elv_ktype;
		mutex_init(&eq->sysfs_lock);
	} else {
		elevator_put(e);
	}
	return eq;
}

static void elevator_release(struct kobject *kobj)
{
	elevator_t *e = container_of(kobj, elevator_t, kobj);
	elevator_put(e->elevator_type);
	kfree(e);
}

int elevator_init(request_queue_t *q, char *name)
{
	struct elevator_type *e = NULL;
	struct elevator_queue *eq;
	int ret = 0;

	INIT_LIST_HEAD(&q->queue_head);
	q->last_merge = NULL;
	q->end_sector = 0;
	q->boundary_rq = NULL;

	if (name && !(e = elevator_get(name)))