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[linux-2.6.9-moxart.git] / drivers / block / elevator.c

/*
 *  linux/drivers/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 <asm/uaccess.h>

/*
 * 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;
}

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;
}

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;
}

/*
 * general block -> elevator interface starts here
 */
int elevator_init(request_queue_t *q, elevator_t *type)
{
        elevator_t *e = &q->elevator;

        memcpy(e, type, sizeof(*e));

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

        if (e->elevator_init_fn)
                return e->elevator_init_fn(q, e);

        return 0;
}

void elevator_exit(request_queue_t *q)
{
        elevator_t *e = &q->elevator;

        if (e->elevator_exit_fn)
                e->elevator_exit_fn(q, e);
}

int elevator_global_init(void)
{
        return 0;
}

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

        if (e->elevator_merge_fn)
                return e->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->elevator_merged_fn)
                e->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->elevator_merge_req_fn)
                e->elevator_merge_req_fn(q, rq, next);
}

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

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

}

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)
{
        return q->elevator.elevator_next_req_fn(q);
}

struct request *elv_next_request(request_queue_t *q)
{
        struct request *rq;
        int ret;

        while ((rq = __elv_next_request(q)) != NULL) {
                /*
                 * just mark as started even if we don't start it, a request
                 * that has been delayed should not be passed by new incoming
                 * requests
                 */
                rq->flags |= REQ_STARTED;

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

                if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
                        break;

                ret = q->prep_rq_fn(q, rq);
                if (ret == BLKPREP_OK) {
                        break;
                } else if (ret == BLKPREP_DEFER) {
                        rq = NULL;
                        break;
                } else if (ret == BLKPREP_KILL) {
                        int nr_bytes = rq->hard_nr_sectors << 9;

                        if (!nr_bytes)
                                nr_bytes = rq->data_len;

                        blkdev_dequeue_request(rq);
                        rq->flags |= REQ_QUIET;
                        end_that_request_chunk(rq, 0, nr_bytes);
                        end_that_request_last(rq);
                } else {
                        printk("%s: bad return=%d\n", __FUNCTION__, ret);
                        break;
                }
        }

        return rq;
}

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

        /*
         * the time frame between a request being removed from the lists
         * and to it is freed is accounted as io that is in progress at
         * the driver side. note that we only account requests that the
         * driver has seen (REQ_STARTED set), to avoid false accounting
         * for request-request merges
         */
        if (blk_account_rq(rq))
                q->in_flight++;

        /*
         * the main clearing point for q->last_merge is on retrieval of
         * request by driver (it calls elv_next_request()), but it _can_
         * also happen here if a request is added to the queue but later
         * deleted without ever being given to driver (merged with another
         * request).
         */
        if (rq == q->last_merge)
                q->last_merge = NULL;

        if (e->elevator_remove_req_fn)
                e->elevator_remove_req_fn(q, rq);
}

int elv_queue_empty(request_queue_t *q)
{
        elevator_t *e = &q->elevator;

        if (e->elevator_queue_empty_fn)
                return e->elevator_queue_empty_fn(q);

        return list_empty(&q->queue_head);
}

struct request *elv_latter_request(request_queue_t *q, struct request *rq)
{
        struct list_head *next;

        elevator_t *e = &q->elevator;

        if (e->elevator_latter_req_fn)
                return e->elevator_latter_req_fn(q, rq);

        next = rq->queuelist.next;
        if (next != &q->queue_head && next != &rq->queuelist)
                return list_entry_rq(next);

        return NULL;
}

struct request *elv_former_request(request_queue_t *q, struct request *rq)
{
        struct list_head *prev;

        elevator_t *e = &q->elevator;

        if (e->elevator_former_req_fn)
                return e->elevator_former_req_fn(q, rq);

        prev = rq->queuelist.prev;
        if (prev != &q->queue_head && prev != &rq->queuelist)
                return list_entry_rq(prev);

        return NULL;
}

int elv_set_request(request_queue_t *q, struct request *rq, int gfp_mask)
{
        elevator_t *e = &q->elevator;

        if (e->elevator_set_req_fn)
                return e->elevator_set_req_fn(q, rq, gfp_mask);

        rq->elevator_private = NULL;
        return 0;
}

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

        if (e->elevator_put_req_fn)
                e->elevator_put_req_fn(q, rq);
}

int elv_may_queue(request_queue_t *q, int rw)
{
        elevator_t *e = &q->elevator;

        if (e->elevator_may_queue_fn)
                return e->elevator_may_queue_fn(q, rw);

        return 0;
}

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

        /*
         * request is released from the driver, io must be done
         */
        if (blk_account_rq(rq))
                q->in_flight--;

        if (e->elevator_completed_req_fn)
                e->elevator_completed_req_fn(q, rq);
}

int elv_register_queue(struct request_queue *q)
{
        elevator_t *e;

        e = &q->elevator;

        e->kobj.parent = kobject_get(&q->kobj);
        if (!e->kobj.parent)
                return -EBUSY;

        snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
        e->kobj.ktype = e->elevator_ktype;

        return kobject_register(&e->kobj);
}

void elv_unregister_queue(struct request_queue *q)
{
        if (q) {
                elevator_t * e = &q->elevator;
                kobject_unregister(&e->kobj);
                kobject_put(&q->kobj);
        }
}

module_init(elevator_global_init);

EXPORT_SYMBOL(elv_add_request);
EXPORT_SYMBOL(__elv_add_request);
EXPORT_SYMBOL(elv_requeue_request);
EXPORT_SYMBOL(elv_next_request);
EXPORT_SYMBOL(elv_remove_request);
EXPORT_SYMBOL(elv_queue_empty);
EXPORT_SYMBOL(elv_completed_request);
EXPORT_SYMBOL(elevator_exit);
EXPORT_SYMBOL(elevator_init);