Linux-2.6.12-rc2

[linux-2.6/next.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>

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);
}

static 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->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;
        }

        /*
         * 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)) {
                BUG_ON(q->ordered == QUEUE_ORDERED_NONE);

                if (q->ordered == QUEUE_ORDERED_FLUSH &&
                    !blk_barrier_preflush(rq))
                        rq = blk_start_pre_flush(q, rq);
        }

        return rq;
}

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(KERN_ERR "%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->ops->elevator_remove_req_fn)
                e->ops->elevator_remove_req_fn(q, rq);
}

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

        if (e->ops->elevator_queue_empty_fn)
                return e->ops->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->ops->elevator_latter_req_fn)
                return e->ops->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->ops->elevator_former_req_fn)
                return e->ops->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->ops->elevator_set_req_fn)
                return e->ops->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->ops->elevator_put_req_fn)
                e->ops->elevator_put_req_fn(q, rq);
}

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

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

        return ELV_MQUEUE_MAY;
}

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

int elv_register_queue(struct request_queue *q)
{
        elevator_t *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_type->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);
        }
}

int elv_register(struct elevator_type *e)
{
        if (elevator_find(e->elevator_name))
                BUG();

        spin_lock_irq(&elv_list_lock);
        list_add_tail(&e->list, &elv_list);
        spin_unlock_irq(&elv_list_lock);

        printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
        if (!strcmp(e->elevator_name, chosen_elevator))
                printk(" (default)");
        printk("\n");
        return 0;
}
EXPORT_SYMBOL_GPL(elv_register);

void elv_unregister(struct elevator_type *e)
{
        spin_lock_irq(&elv_list_lock);
        list_del_init(&e->list);
        spin_unlock_irq(&elv_list_lock);
}
EXPORT_SYMBOL_GPL(elv_unregister);

/*
 * switch to new_e io scheduler. be careful not to introduce deadlocks -
 * we don't free the old io scheduler, before we have allocated what we
 * need for the new one. this way we have a chance of going back to the old
 * one, if the new one fails init for some reason. we also do an intermediate
 * switch to noop to ensure safety with stack-allocated requests, since they
 * don't originate from the block layer allocator. noop is safe here, because
 * it never needs to touch the elevator itself for completion events. DRAIN
 * flags will make sure we don't touch it for additions either.
 */
static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
{
        elevator_t *e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
        struct elevator_type *noop_elevator = NULL;
        elevator_t *old_elevator;

        if (!e)
                goto error;

        /*
         * first step, drain requests from the block freelist
         */
        blk_wait_queue_drained(q, 0);

        /*
         * unregister old elevator data
         */
        elv_unregister_queue(q);
        old_elevator = q->elevator;

        /*
         * next step, switch to noop since it uses no private rq structures
         * and doesn't allocate any memory for anything. then wait for any
         * non-fs requests in-flight
         */
        noop_elevator = elevator_get("noop");
        spin_lock_irq(q->queue_lock);
        elevator_attach(q, noop_elevator, e);
        spin_unlock_irq(q->queue_lock);

        blk_wait_queue_drained(q, 1);

        /*
         * attach and start new elevator
         */
        if (elevator_attach(q, new_e, e))
                goto fail;

        if (elv_register_queue(q))
                goto fail_register;

        /*
         * finally exit old elevator and start queue again
         */
        elevator_exit(old_elevator);
        blk_finish_queue_drain(q);
        elevator_put(noop_elevator);
        return;

fail_register:
        /*
         * switch failed, exit the new io scheduler and reattach the old
         * one again (along with re-adding the sysfs dir)
         */
        elevator_exit(e);
fail:
        q->elevator = old_elevator;
        elv_register_queue(q);
        blk_finish_queue_drain(q);
error:
        if (noop_elevator)
                elevator_put(noop_elevator);
        elevator_put(new_e);
        printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
}

ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
{
        char elevator_name[ELV_NAME_MAX];
        struct elevator_type *e;

        memset(elevator_name, 0, sizeof(elevator_name));
        strncpy(elevator_name, name, sizeof(elevator_name));

        if (elevator_name[strlen(elevator_name) - 1] == '\n')
                elevator_name[strlen(elevator_name) - 1] = '\0';

        e = elevator_get(elevator_name);
        if (!e) {
                printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
                return -EINVAL;
        }

        if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name))
                return count;

        elevator_switch(q, e);
        return count;
}

ssize_t elv_iosched_show(request_queue_t *q, char *name)
{
        elevator_t *e = q->elevator;
        struct elevator_type *elv = e->elevator_type;
        struct list_head *entry;
        int len = 0;

        spin_lock_irq(q->queue_lock);
        list_for_each(entry, &elv_list) {
                struct elevator_type *__e;

                __e = list_entry(entry, struct elevator_type, list);
                if (!strcmp(elv->elevator_name, __e->elevator_name))
                        len += sprintf(name+len, "[%s] ", elv->elevator_name);
                else
                        len += sprintf(name+len, "%s ", __e->elevator_name);
        }
        spin_unlock_irq(q->queue_lock);

        len += sprintf(len+name, "\n");
        return len;
}

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);