1 files changed, 802 insertions, 0 deletions

diff --git a/block/elevator.c b/block/elevator.c
new file mode 100644
index 000000000000..d4a49a3df829
--- /dev/null
+++ b/block/elevator.c
@@ -0,0 +1,802 @@
+/*
+ *  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)))
+                strcpy(chosen_elevator, "noop");
+        elevator_put(e);
+}
+
+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->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);
+}
+
+/*
+ * 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;
+
+        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->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);
+}
+
+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;
+
+                while (q->elevator->ops->elevator_dispatch_fn(q, 1))
+                        ;
+                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;
+                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);
+
+        while (q->elevator->ops->elevator_dispatch_fn(q, 1))
+                ;
+
+        while (q->rq.elvpriv) {
+                spin_unlock_irq(q->queue_lock);
+                msleep(10);
+                spin_lock_irq(q->queue_lock);
+        }
+
+        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);