Merge branch 'block-dir' of git://brick.kernel.dk/data/git/linux-2.6-block

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);