elevator.c

Linux块设备驱动源码

/*
 *  linux/drivers/block/elevator.c
 *
 *  Block device elevator/IO-scheduler.
 *
 *  Copyright (C) 2000 Andrea Arcangeli <[e-mail]> SuSE
 *
 * 30042000 Jens Axboe <[e-mail]> :
 *
 * 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 <[e-mail]> :
 * 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 <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);

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;
}
EXPORT_SYMBOL(elv_try_merge);

inline int elv_try_last_merge(request_queue_t *q, struct bio *bio)
{
	if (q->last_merge)
		return elv_try_merge(q->last_merge, bio);

	return ELEVATOR_NO_MERGE;
}
EXPORT_SYMBOL(elv_try_last_merge);

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

	spin_lock_irq(&elv_list_lock);
	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;
		}
	}
	spin_unlock_irq(&elv_list_lock);

	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 = elevator_find(name);

	if (!e)
		return NULL;
	if (!try_module_get(e->elevator_owner))
		return NULL;

	return e;
}

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

	memset(eq, 0, sizeof(*eq));
	eq->ops = &e->ops;
	eq->elevator_type = e;

	INIT_LIST_HEAD(&q->queue_head);
	q->last_merge = NULL;
	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 void elevator_setup_default(void)
{
	/*
	 * check if default is set and exists
	 */
	if (chosen_elevator[0] && elevator_find(chosen_elevator))
		return;

#if defined(CONFIG_IOSCHED_AS)
	strcpy(chosen_elevator, "anticipatory");
#elif defined(CONFIG_IOSCHED_DEADLINE)
	strcpy(chosen_elevator, "deadline");
#elif defined(CONFIG_IOSCHED_CFQ)
	strcpy(chosen_elevator, "cfq");
#elif defined(CONFIG_IOSCHED_NOOP)
	strcpy(chosen_elevator, "noop");
#else
#error "You must build at least 1 IO scheduler into the kernel"
#endif
}

static int __init elevator_setup(char *str)
{
	strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
	return 0;
}

__setup("elevator=", elevator_setup);

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

	elevator_setup_default();

	if (!name)
		name = chosen_elevator;

	e = elevator_get(name);
	if (!e)
		return -EINVAL;

	eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
	if (!eq) {
		elevator_put(e->elevator_type);
		return -ENOMEM;
	}

	ret = elevator_attach(q, e, eq);
	if (ret) {
		kfree(eq);
		elevator_put(e->elevator_type);
	}

	return ret;
}

void elevator_exit(elevator_t *e)
{
	if (e->ops->elevator_exit_fn)
		e->ops->elevator_exit_fn(e);

	elevator_put(e->elevator_type);
	e->elevator_type = NULL;
	kfree(e);
}

int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
{
	elevator_t *e = q->elevator;

	if (e->ops->elevator_merge_fn)
		return e->ops->elevator_merge_fn(q, req, bio);

	return ELEVATOR_NO_MERGE;
}

void elv_merged_request(request_queue_t *q, struct request *rq)
{
	elevator_t *e = q->elevator;

	if (e->ops->elevator_merged_fn)
		e->ops->elevator_merged_fn(q, rq);
}

void elv_merge_requests(request_queue_t *q, struct request *rq,
			     struct request *next)
{
	elevator_t *e = q->elevator;

	if (q->last_merge == next)
		q->last_merge = NULL;

	if (e->ops->elevator_merge_req_fn)
		e->ops->elevator_merge_req_fn(q, rq, next);
}

/*
 * For careful internal use by the block layer. Essentially the same as
 * a requeue in that it tells the io scheduler that this request is not
 * active in the driver or hardware anymore, but we don't want the request
 * added back to the scheduler. Function is not exported.
 */
void elv_deactivate_request(request_queue_t *q, struct request *rq)
{
	elevator_t *e = q->elevator;

	/*
	 * it already went through dequeue, we need to decrement the
	 * in_flight count again
	 */
	if (blk_account_rq(rq))
		q->in_flight--;

	rq->flags &= ~REQ_STARTED;

	if (e->ops->elevator_deactivate_req_fn)
		e->ops->elevator_deactivate_req_fn(q, rq);
}

void elv_requeue_request(request_queue_t *q, struct request *rq)
{
	elv_deactivate_request(q, rq);

	/*
	 * if this is the flush, requeue the original instead and drop the flush
	 */
	if (rq->flags & REQ_BAR_FLUSH) {
		clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
		rq = rq->end_io_data;
	}

	/*
	 * the request is prepped and may have some resources allocated.
	 * allowing unprepped requests to pass this one may cause resource
	 * deadlock.  turn on softbarrier.
	 */
	rq->flags |= REQ_SOFTBARRIER;

	/*
	 * if iosched has an explicit requeue hook, then use that. otherwise
	 * just put the request at the front of the queue
	 */
	if (q->elevator->ops->elevator_requeue_req_fn)
		q->elevator->ops->elevator_requeue_req_fn(q, rq);
	else
		__elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
}

void __elv_add_request(request_queue_t *q, struct request *rq, int where,
		       int plug)
{
	/*
	 * barriers implicitly indicate back insertion
	 */
	if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER) &&
	    where == ELEVATOR_INSERT_SORT)
		where = ELEVATOR_INSERT_BACK;

	if (plug)
		blk_plug_device(q);

	rq->q = q;

	if (!test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags)) {
		q->elevator->ops->elevator_add_req_fn(q, rq, where);

		if (blk_queue_plugged(q)) {
			int nrq = q->rq.count[READ] + q->rq.count[WRITE]
				  - q->in_flight;

			if (nrq >= q->unplug_thresh)
				__generic_unplug_device(q);
		}
	} else
		/*
		 * if drain is set, store the request "locally". when the drain
		 * is finished, the requests will be handed ordered to the io
		 * scheduler
		 */
		list_add_tail(&rq->queuelist, &q->drain_list);
}

void elv_add_request(request_queue_t *q, struct request *rq, int where,
		     int plug)
{
	unsigned long flags;

	spin_lock_irqsave(q->queue_lock, flags);
	__elv_add_request(q, rq, where, plug);
	spin_unlock_irqrestore(q->queue_lock, flags);
}

static inline struct request *__elv_next_request(request_queue_t *q)
{
	struct request *rq = q->elevator->ops->elevator_next_req_fn(q);

	/*
	 * if this is a barrier write and the device has to issue a
	 * flush sequence to support it, check how far we are
	 */
	if (rq && blk_fs_request(rq) && blk_barrier_rq(rq)) {