[BLOCK] Implement elv_drain_elevator for improved switch error detection

[safe/jmp/linux-2.6] / 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 <linux/delay.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);

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_type *e,
                           struct elevator_queue *eq)
{
        int ret = 0;

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

        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)
{
        struct elevator_type *e;

        /*
         * If default has not been set, use the compiled-in selection.
         */
        if (!chosen_elevator[0])
                strcpy(chosen_elevator, CONFIG_DEFAULT_IOSCHED);

        /*
         * If the given scheduler is not available, fall back to no-op.
         */
        if ((e = elevator_find(chosen_elevator)))
                elevator_put(e);
        else
                strcpy(chosen_elevator, "noop");
}

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;

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

        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);
                return -ENOMEM;
        }

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

        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);
}

/*
 * Insert rq into dispatch queue of q.  Queue lock must be held on
 * entry.  If sort != 0, rq is sort-inserted; otherwise, rq will be
 * appended to the dispatch queue.  To be used by specific elevators.
 */
void elv_dispatch_sort(request_queue_t *q, struct request *rq)
{
        sector_t boundary;
        struct list_head *entry;

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

        boundary = q->end_sector;

        list_for_each_prev(entry, &q->queue_head) {
                struct request *pos = list_entry_rq(entry);

                if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
                        break;
                if (rq->sector >= boundary) {
                        if (pos->sector < boundary)
                                continue;
                } else {
                        if (pos->sector >= boundary)
                                break;
                }
                if (rq->sector >= pos->sector)
                        break;
        }

        list_add(&rq->queuelist, entry);
}

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

        if (q->last_merge) {
                ret = elv_try_merge(q->last_merge, bio);
                if (ret != ELEVATOR_NO_MERGE) {
                        *req = q->last_merge;
                        return ret;
                }
        }

        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);

        q->last_merge = rq;
}

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

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

        q->last_merge = rq;
}

void elv_requeue_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--;
                if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
                        e->ops->elevator_deactivate_req_fn(q, rq);
        }

        rq->flags &= ~REQ_STARTED;

        /*
         * 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;
        }

        __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
}

static void elv_drain_elevator(request_queue_t *q)
{
        static int printed;
        while (q->elevator->ops->elevator_dispatch_fn(q, 1))
                ;
        if (q->nr_sorted == 0)
                return;
        if (printed++ < 10) {
                printk(KERN_ERR "%s: forced dispatching is broken "
                       "(nr_sorted=%u), please report this\n",
                       q->elevator->elevator_type->elevator_name, q->nr_sorted);
        }
}

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

                /*
                 * this request is scheduling boundary, update end_sector
                 */
                if (blk_fs_request(rq)) {
                        q->end_sector = rq_end_sector(rq);
                        q->boundary_rq = rq;
                }
        } else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
                where = ELEVATOR_INSERT_BACK;

        if (plug)
                blk_plug_device(q);

        rq->q = q;

        switch (where) {
        case ELEVATOR_INSERT_FRONT:
                rq->flags |= REQ_SOFTBARRIER;

                list_add(&rq->queuelist, &q->queue_head);
                break;

        case ELEVATOR_INSERT_BACK:
                rq->flags |= REQ_SOFTBARRIER;
                elv_drain_elevator(q);
                list_add_tail(&rq->queuelist, &q->queue_head);
                /*
                 * We kick the queue here for the following reasons.
                 * - The elevator might have returned NULL previously
                 *   to delay requests and returned them now.  As the
                 *   queue wasn't empty before this request, ll_rw_blk
                 *   won't run the queue on return, resulting in hang.
                 * - Usually, back inserted requests won't be merged
                 *   with anything.  There's no point in delaying queue
                 *   processing.
                 */
                blk_remove_plug(q);
                q->request_fn(q);
                break;

        case ELEVATOR_INSERT_SORT:
                BUG_ON(!blk_fs_request(rq));
                rq->flags |= REQ_SORTED;
                q->nr_sorted++;
                if (q->last_merge == NULL && rq_mergeable(rq))
                        q->last_merge = rq;
                /*
                 * Some ioscheds (cfq) run q->request_fn directly, so
                 * rq cannot be accessed after calling
                 * elevator_add_req_fn.
                 */
                q->elevator->ops->elevator_add_req_fn(q, rq);
                break;

        default:
                printk(KERN_ERR "%s: bad insertion point %d\n",
                       __FUNCTION__, where);
                BUG();
        }

        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)
{
        struct request *rq;

        if (unlikely(list_empty(&q->queue_head) &&
                     !q->elevator->ops->elevator_dispatch_fn(q, 0)))
                return NULL;

        rq = list_entry_rq(q->queue_head.next);

        /*
         * if this is a barrier write and the device has to issue a
         * flush sequence to support it, check how far we are
         */
        if (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) {
                if (!(rq->flags & REQ_STARTED)) {
                        elevator_t *e = q->elevator;

                        /*
                         * This is the first time the device driver
                         * sees this request (possibly after
                         * requeueing).  Notify IO scheduler.
                         */
                        if (blk_sorted_rq(rq) &&
                            e->ops->elevator_activate_req_fn)
                                e->ops->elevator_activate_req_fn(q, rq);

                        /*
                         * 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 (!q->boundary_rq || q->boundary_rq == rq) {
                        q->end_sector = rq_end_sector(rq);
                        q->boundary_rq = 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) {
                        /*
                         * the request may have been (partially) prepped.
                         * we need to keep this request in the front to
                         * avoid resource deadlock.  REQ_STARTED will
                         * prevent other fs requests from passing this one.
                         */
                        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_dequeue_request(request_queue_t *q, struct request *rq)
{
        BUG_ON(list_empty(&rq->queuelist));

        list_del_init(&rq->queuelist);

        /*
         * 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.
         */
        if (blk_account_rq(rq))
                q->in_flight++;
}

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

        if (!list_empty(&q->queue_head))
                return 0;

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

        return 1;
}

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, struct bio *bio,
                    gfp_t gfp_mask)
{
        elevator_t *e = q->elevator;

        if (e->ops->elevator_set_req_fn)
                return e->ops->elevator_set_req_fn(q, rq, bio, 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, struct bio *bio)
{
        elevator_t *e = q->elevator;

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

        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 (blk_sorted_rq(rq) && 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)
{
        spin_lock_irq(&elv_list_lock);
        if (elevator_find(e->elevator_name))
                BUG();
        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)
{
        struct task_struct *g, *p;

        /*
         * Iterate every thread in the process to remove the io contexts.
         */
        read_lock(&tasklist_lock);
        do_each_thread(g, p) {
                struct io_context *ioc = p->io_context;
                if (ioc && ioc->cic) {
                        ioc->cic->exit(ioc->cic);
                        ioc->cic->dtor(ioc->cic);
                        ioc->cic = NULL;
                }
                if (ioc && ioc->aic) {
                        ioc->aic->exit(ioc->aic);
                        ioc->aic->dtor(ioc->aic);
                        ioc->aic = NULL;
                }
        } while_each_thread(g, p);
        read_unlock(&tasklist_lock);

        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.
 */
static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
{
        elevator_t *old_elevator, *e;

        /*
         * Allocate new elevator
         */
        e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
        if (!e)
                goto error;

        /*
         * Turn on BYPASS and drain all requests w/ elevator private data
         */
        spin_lock_irq(q->queue_lock);

        set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);

        elv_drain_elevator(q);

        while (q->rq.elvpriv) {
                blk_remove_plug(q);
                q->request_fn(q);
                spin_unlock_irq(q->queue_lock);
                msleep(10);
                spin_lock_irq(q->queue_lock);
                elv_drain_elevator(q);
        }

        spin_unlock_irq(q->queue_lock);

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

        /*
         * 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 turn off BYPASS.
         */
        elevator_exit(old_elevator);
        clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
        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);
        e = NULL;
fail:
        q->elevator = old_elevator;
        elv_register_queue(q);
        clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
        kfree(e);
error:
        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)) {
                elevator_put(e);
                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;
}

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