Initial import

1 files changed, 1047 insertions, 0 deletions

diff --git a/block/elevator.c b/block/elevator.c
new file mode 100644
index 000000000..8985038f3
--- /dev/null
+++ b/block/elevator.c
@@ -0,0 +1,1047 @@
+/*
+ *  Block device elevator/IO-scheduler.
+ *
+ *  Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
+ *
+ * 30042000 Jens Axboe <axboe@kernel.dk> :
+ *
+ * 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/module.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/compiler.h>
+#include <linux/blktrace_api.h>
+#include <linux/hash.h>
+#include <linux/uaccess.h>
+#include <linux/pm_runtime.h>
+
+#include <trace/events/block.h>
+
+#include "blk.h"
+#include "blk-cgroup.h"
+
+static DEFINE_SPINLOCK(elv_list_lock);
+static LIST_HEAD(elv_list);
+
+/*
+ * Merge hash stuff.
+ */
+#define rq_hash_key(rq)		(blk_rq_pos(rq) + blk_rq_sectors(rq))
+
+/*
+ * Query io scheduler to see if the current process issuing bio may be
+ * merged with rq.
+ */
+static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
+{
+	struct request_queue *q = rq->q;
+	struct elevator_queue *e = q->elevator;
+
+	if (e->type->ops.elevator_allow_merge_fn)
+		return e->type->ops.elevator_allow_merge_fn(q, rq, bio);
+
+	return 1;
+}
+
+/*
+ * can we safely merge with this request?
+ */
+bool elv_rq_merge_ok(struct request *rq, struct bio *bio)
+{
+	if (!blk_rq_merge_ok(rq, bio))
+		return 0;
+
+	if (!elv_iosched_allow_merge(rq, bio))
+		return 0;
+
+	return 1;
+}
+EXPORT_SYMBOL(elv_rq_merge_ok);
+
+static struct elevator_type *elevator_find(const char *name)
+{
+	struct elevator_type *e;
+
+	list_for_each_entry(e, &elv_list, list) {
+		if (!strcmp(e->elevator_name, name))
+			return e;
+	}
+
+	return NULL;
+}
+
+static void elevator_put(struct elevator_type *e)
+{
+	module_put(e->elevator_owner);
+}
+
+static struct elevator_type *elevator_get(const char *name, bool try_loading)
+{
+	struct elevator_type *e;
+
+	spin_lock(&elv_list_lock);
+
+	e = elevator_find(name);
+	if (!e && try_loading) {
+		spin_unlock(&elv_list_lock);
+		request_module("%s-iosched", name);
+		spin_lock(&elv_list_lock);
+		e = elevator_find(name);
+	}
+
+	if (e && !try_module_get(e->elevator_owner))
+		e = NULL;
+
+	spin_unlock(&elv_list_lock);
+
+	return e;
+}
+
+static char chosen_elevator[ELV_NAME_MAX];
+
+static int __init elevator_setup(char *str)
+{
+	/*
+	 * Be backwards-compatible with previous kernels, so users
+	 * won't get the wrong elevator.
+	 */
+	strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
+	return 1;
+}
+
+__setup("elevator=", elevator_setup);
+
+/* called during boot to load the elevator chosen by the elevator param */
+void __init load_default_elevator_module(void)
+{
+	struct elevator_type *e;
+
+	if (!chosen_elevator[0])
+		return;
+
+	spin_lock(&elv_list_lock);
+	e = elevator_find(chosen_elevator);
+	spin_unlock(&elv_list_lock);
+
+	if (!e)
+		request_module("%s-iosched", chosen_elevator);
+}
+
+static struct kobj_type elv_ktype;
+
+struct elevator_queue *elevator_alloc(struct request_queue *q,
+				  struct elevator_type *e)
+{
+	struct elevator_queue *eq;
+
+	eq = kzalloc_node(sizeof(*eq), GFP_KERNEL, q->node);
+	if (unlikely(!eq))
+		return NULL;
+
+	eq->type = e;
+	kobject_init(&eq->kobj, &elv_ktype);
+	mutex_init(&eq->sysfs_lock);
+	hash_init(eq->hash);
+
+	return eq;
+}
+EXPORT_SYMBOL(elevator_alloc);
+
+static void elevator_release(struct kobject *kobj)
+{
+	struct elevator_queue *e;
+
+	e = container_of(kobj, struct elevator_queue, kobj);
+	elevator_put(e->type);
+	kfree(e);
+}
+
+int elevator_init(struct request_queue *q, char *name)
+{
+	struct elevator_type *e = NULL;
+	int err;
+
+	/*
+	 * q->sysfs_lock must be held to provide mutual exclusion between
+	 * elevator_switch() and here.
+	 */
+	lockdep_assert_held(&q->sysfs_lock);
+
+	if (unlikely(q->elevator))
+		return 0;
+
+	INIT_LIST_HEAD(&q->queue_head);
+	q->last_merge = NULL;
+	q->end_sector = 0;
+	q->boundary_rq = NULL;
+
+	if (name) {
+		e = elevator_get(name, true);
+		if (!e)
+			return -EINVAL;
+	}
+
+	/*
+	 * Use the default elevator specified by config boot param or
+	 * config option.  Don't try to load modules as we could be running
+	 * off async and request_module() isn't allowed from async.
+	 */
+	if (!e && *chosen_elevator) {
+		e = elevator_get(chosen_elevator, false);
+		if (!e)
+			printk(KERN_ERR "I/O scheduler %s not found\n",
+							chosen_elevator);
+	}
+
+	if (!e) {
+		e = elevator_get(CONFIG_DEFAULT_IOSCHED, false);
+		if (!e) {
+			printk(KERN_ERR
+				"Default I/O scheduler not found. " \
+				"Using noop.\n");
+			e = elevator_get("noop", false);
+		}
+	}
+
+	err = e->ops.elevator_init_fn(q, e);
+	if (err)
+		elevator_put(e);
+	return err;
+}
+EXPORT_SYMBOL(elevator_init);
+
+void elevator_exit(struct elevator_queue *e)
+{
+	mutex_lock(&e->sysfs_lock);
+	if (e->type->ops.elevator_exit_fn)
+		e->type->ops.elevator_exit_fn(e);
+	mutex_unlock(&e->sysfs_lock);
+
+	kobject_put(&e->kobj);
+}
+EXPORT_SYMBOL(elevator_exit);
+
+static inline void __elv_rqhash_del(struct request *rq)
+{
+	hash_del(&rq->hash);
+	rq->cmd_flags &= ~REQ_HASHED;
+}
+
+static void elv_rqhash_del(struct request_queue *q, struct request *rq)
+{
+	if (ELV_ON_HASH(rq))
+		__elv_rqhash_del(rq);
+}
+
+static void elv_rqhash_add(struct request_queue *q, struct request *rq)
+{
+	struct elevator_queue *e = q->elevator;
+
+	BUG_ON(ELV_ON_HASH(rq));
+	hash_add(e->hash, &rq->hash, rq_hash_key(rq));
+	rq->cmd_flags |= REQ_HASHED;
+}
+
+static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
+{
+	__elv_rqhash_del(rq);
+	elv_rqhash_add(q, rq);
+}
+
+static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
+{
+	struct elevator_queue *e = q->elevator;
+	struct hlist_node *next;
+	struct request *rq;
+
+	hash_for_each_possible_safe(e->hash, rq, next, hash, offset) {
+		BUG_ON(!ELV_ON_HASH(rq));
+
+		if (unlikely(!rq_mergeable(rq))) {
+			__elv_rqhash_del(rq);
+			continue;
+		}
+
+		if (rq_hash_key(rq) == offset)
+			return rq;
+	}
+
+	return NULL;
+}
+
+/*
+ * RB-tree support functions for inserting/lookup/removal of requests
+ * in a sorted RB tree.
+ */
+void elv_rb_add(struct rb_root *root, struct request *rq)
+{
+	struct rb_node **p = &root->rb_node;
+	struct rb_node *parent = NULL;
+	struct request *__rq;
+
+	while (*p) {
+		parent = *p;
+		__rq = rb_entry(parent, struct request, rb_node);
+
+		if (blk_rq_pos(rq) < blk_rq_pos(__rq))
+			p = &(*p)->rb_left;
+		else if (blk_rq_pos(rq) >= blk_rq_pos(__rq))
+			p = &(*p)->rb_right;
+	}
+
+	rb_link_node(&rq->rb_node, parent, p);
+	rb_insert_color(&rq->rb_node, root);
+}
+EXPORT_SYMBOL(elv_rb_add);
+
+void elv_rb_del(struct rb_root *root, struct request *rq)
+{
+	BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
+	rb_erase(&rq->rb_node, root);
+	RB_CLEAR_NODE(&rq->rb_node);
+}
+EXPORT_SYMBOL(elv_rb_del);
+
+struct request *elv_rb_find(struct rb_root *root, sector_t sector)
+{
+	struct rb_node *n = root->rb_node;
+	struct request *rq;
+
+	while (n) {
+		rq = rb_entry(n, struct request, rb_node);
+
+		if (sector < blk_rq_pos(rq))
+			n = n->rb_left;
+		else if (sector > blk_rq_pos(rq))
+			n = n->rb_right;
+		else
+			return rq;
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL(elv_rb_find);
+
+/*
+ * Insert rq into dispatch queue of q.  Queue lock must be held on
+ * entry.  rq is sort instead into the dispatch queue. To be used by
+ * specific elevators.
+ */
+void elv_dispatch_sort(struct request_queue *q, struct request *rq)
+{
+	sector_t boundary;
+	struct list_head *entry;
+	int stop_flags;
+
+	if (q->last_merge == rq)
+		q->last_merge = NULL;
+
+	elv_rqhash_del(q, rq);
+
+	q->nr_sorted--;
+
+	boundary = q->end_sector;
+	stop_flags = REQ_SOFTBARRIER | REQ_STARTED;
+	list_for_each_prev(entry, &q->queue_head) {
+		struct request *pos = list_entry_rq(entry);
+
+		if ((rq->cmd_flags & REQ_DISCARD) !=
+		    (pos->cmd_flags & REQ_DISCARD))
+			break;
+		if (rq_data_dir(rq) != rq_data_dir(pos))
+			break;
+		if (pos->cmd_flags & stop_flags)
+			break;
+		if (blk_rq_pos(rq) >= boundary) {
+			if (blk_rq_pos(pos) < boundary)
+				continue;
+		} else {
+			if (blk_rq_pos(pos) >= boundary)
+				break;
+		}
+		if (blk_rq_pos(rq) >= blk_rq_pos(pos))
+			break;
+	}
+
+	list_add(&rq->queuelist, entry);
+}
+EXPORT_SYMBOL(elv_dispatch_sort);
+
+/*
+ * Insert rq into dispatch queue of q.  Queue lock must be held on
+ * entry.  rq is added to the back of the dispatch queue. To be used by
+ * specific elevators.
+ */
+void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
+{
+	if (q->last_merge == rq)
+		q->last_merge = NULL;
+
+	elv_rqhash_del(q, rq);
+
+	q->nr_sorted--;
+
+	q->end_sector = rq_end_sector(rq);
+	q->boundary_rq = rq;
+	list_add_tail(&rq->queuelist, &q->queue_head);
+}
+EXPORT_SYMBOL(elv_dispatch_add_tail);
+
+int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
+{
+	struct elevator_queue *e = q->elevator;
+	struct request *__rq;
+	int ret;
+
+	/*
+	 * Levels of merges:
+	 * 	nomerges:  No merges at all attempted
+	 * 	noxmerges: Only simple one-hit cache try
+	 * 	merges:	   All merge tries attempted
+	 */
+	if (blk_queue_nomerges(q))
+		return ELEVATOR_NO_MERGE;
+
+	/*
+	 * First try one-hit cache.
+	 */
+	if (q->last_merge && elv_rq_merge_ok(q->last_merge, bio)) {
+		ret = blk_try_merge(q->last_merge, bio);
+		if (ret != ELEVATOR_NO_MERGE) {
+			*req = q->last_merge;
+			return ret;
+		}
+	}
+
+	if (blk_queue_noxmerges(q))
+		return ELEVATOR_NO_MERGE;
+
+	/*
+	 * See if our hash lookup can find a potential backmerge.
+	 */
+	__rq = elv_rqhash_find(q, bio->bi_iter.bi_sector);
+	if (__rq && elv_rq_merge_ok(__rq, bio)) {
+		*req = __rq;
+		return ELEVATOR_BACK_MERGE;
+	}
+
+	if (e->type->ops.elevator_merge_fn)
+		return e->type->ops.elevator_merge_fn(q, req, bio);
+
+	return ELEVATOR_NO_MERGE;
+}
+
+/*
+ * Attempt to do an insertion back merge. Only check for the case where
+ * we can append 'rq' to an existing request, so we can throw 'rq' away
+ * afterwards.
+ *
+ * Returns true if we merged, false otherwise
+ */
+static bool elv_attempt_insert_merge(struct request_queue *q,
+				     struct request *rq)
+{
+	struct request *__rq;
+	bool ret;
+
+	if (blk_queue_nomerges(q))
+		return false;
+
+	/*
+	 * First try one-hit cache.
+	 */
+	if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq))
+		return true;
+
+	if (blk_queue_noxmerges(q))
+		return false;
+
+	ret = false;
+	/*
+	 * See if our hash lookup can find a potential backmerge.
+	 */
+	while (1) {
+		__rq = elv_rqhash_find(q, blk_rq_pos(rq));
+		if (!__rq || !blk_attempt_req_merge(q, __rq, rq))
+			break;
+
+		/* The merged request could be merged with others, try again */
+		ret = true;
+		rq = __rq;
+	}
+
+	return ret;
+}
+
+void elv_merged_request(struct request_queue *q, struct request *rq, int type)
+{
+	struct elevator_queue *e = q->elevator;
+
+	if (e->type->ops.elevator_merged_fn)
+		e->type->ops.elevator_merged_fn(q, rq, type);
+
+	if (type == ELEVATOR_BACK_MERGE)
+		elv_rqhash_reposition(q, rq);
+
+	q->last_merge = rq;
+}
+
+void elv_merge_requests(struct request_queue *q, struct request *rq,
+			     struct request *next)
+{
+	struct elevator_queue *e = q->elevator;
+	const int next_sorted = next->cmd_flags & REQ_SORTED;
+
+	if (next_sorted && e->type->ops.elevator_merge_req_fn)
+		e->type->ops.elevator_merge_req_fn(q, rq, next);
+
+	elv_rqhash_reposition(q, rq);
+
+	if (next_sorted) {
+		elv_rqhash_del(q, next);
+		q->nr_sorted--;
+	}
+
+	q->last_merge = rq;
+}
+
+void elv_bio_merged(struct request_queue *q, struct request *rq,
+			struct bio *bio)
+{
+	struct elevator_queue *e = q->elevator;
+
+	if (e->type->ops.elevator_bio_merged_fn)
+		e->type->ops.elevator_bio_merged_fn(q, rq, bio);
+}
+
+#ifdef CONFIG_PM
+static void blk_pm_requeue_request(struct request *rq)
+{
+	if (rq->q->dev && !(rq->cmd_flags & REQ_PM))
+		rq->q->nr_pending--;
+}
+
+static void blk_pm_add_request(struct request_queue *q, struct request *rq)
+{
+	if (q->dev && !(rq->cmd_flags & REQ_PM) && q->nr_pending++ == 0 &&
+	    (q->rpm_status == RPM_SUSPENDED || q->rpm_status == RPM_SUSPENDING))
+		pm_request_resume(q->dev);
+}
+#else
+static inline void blk_pm_requeue_request(struct request *rq) {}
+static inline void blk_pm_add_request(struct request_queue *q,
+				      struct request *rq)
+{
+}
+#endif
+
+void elv_requeue_request(struct request_queue *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[rq_is_sync(rq)]--;
+		if (rq->cmd_flags & REQ_SORTED)
+			elv_deactivate_rq(q, rq);
+	}
+
+	rq->cmd_flags &= ~REQ_STARTED;
+
+	blk_pm_requeue_request(rq);
+
+	__elv_add_request(q, rq, ELEVATOR_INSERT_REQUEUE);
+}
+
+void elv_drain_elevator(struct request_queue *q)
+{
+	static int printed;
+
+	lockdep_assert_held(q->queue_lock);
+
+	while (q->elevator->type->ops.elevator_dispatch_fn(q, 1))
+		;
+	if (q->nr_sorted && printed++ < 10) {
+		printk(KERN_ERR "%s: forced dispatching is broken "
+		       "(nr_sorted=%u), please report this\n",
+		       q->elevator->type->elevator_name, q->nr_sorted);
+	}
+}
+
+void __elv_add_request(struct request_queue *q, struct request *rq, int where)
+{
+	trace_block_rq_insert(q, rq);
+
+	blk_pm_add_request(q, rq);
+
+	rq->q = q;
+
+	if (rq->cmd_flags & REQ_SOFTBARRIER) {
+		/* barriers are scheduling boundary, update end_sector */
+		if (rq->cmd_type == REQ_TYPE_FS) {
+			q->end_sector = rq_end_sector(rq);
+			q->boundary_rq = rq;
+		}
+	} else if (!(rq->cmd_flags & REQ_ELVPRIV) &&
+		    (where == ELEVATOR_INSERT_SORT ||
+		     where == ELEVATOR_INSERT_SORT_MERGE))
+		where = ELEVATOR_INSERT_BACK;
+
+	switch (where) {
+	case ELEVATOR_INSERT_REQUEUE:
+	case ELEVATOR_INSERT_FRONT:
+		rq->cmd_flags |= REQ_SOFTBARRIER;
+		list_add(&rq->queuelist, &q->queue_head);
+		break;
+
+	case ELEVATOR_INSERT_BACK:
+		rq->cmd_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_run_queue(q);
+		break;
+
+	case ELEVATOR_INSERT_SORT_MERGE:
+		/*
+		 * If we succeed in merging this request with one in the
+		 * queue already, we are done - rq has now been freed,
+		 * so no need to do anything further.
+		 */
+		if (elv_attempt_insert_merge(q, rq))
+			break;
+	case ELEVATOR_INSERT_SORT:
+		BUG_ON(rq->cmd_type != REQ_TYPE_FS);
+		rq->cmd_flags |= REQ_SORTED;
+		q->nr_sorted++;
+		if (rq_mergeable(rq)) {
+			elv_rqhash_add(q, rq);
+			if (!q->last_merge)
+				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->type->ops.elevator_add_req_fn(q, rq);
+		break;
+
+	case ELEVATOR_INSERT_FLUSH:
+		rq->cmd_flags |= REQ_SOFTBARRIER;
+		blk_insert_flush(rq);
+		break;
+	default:
+		printk(KERN_ERR "%s: bad insertion point %d\n",
+		       __func__, where);
+		BUG();
+	}
+}
+EXPORT_SYMBOL(__elv_add_request);
+
+void elv_add_request(struct request_queue *q, struct request *rq, int where)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	__elv_add_request(q, rq, where);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+}
+EXPORT_SYMBOL(elv_add_request);
+
+struct request *elv_latter_request(struct request_queue *q, struct request *rq)
+{
+	struct elevator_queue *e = q->elevator;
+
+	if (e->type->ops.elevator_latter_req_fn)
+		return e->type->ops.elevator_latter_req_fn(q, rq);
+	return NULL;
+}
+
+struct request *elv_former_request(struct request_queue *q, struct request *rq)
+{
+	struct elevator_queue *e = q->elevator;
+
+	if (e->type->ops.elevator_former_req_fn)
+		return e->type->ops.elevator_former_req_fn(q, rq);
+	return NULL;
+}
+
+int elv_set_request(struct request_queue *q, struct request *rq,
+		    struct bio *bio, gfp_t gfp_mask)
+{
+	struct elevator_queue *e = q->elevator;
+
+	if (e->type->ops.elevator_set_req_fn)
+		return e->type->ops.elevator_set_req_fn(q, rq, bio, gfp_mask);
+	return 0;
+}
+
+void elv_put_request(struct request_queue *q, struct request *rq)
+{
+	struct elevator_queue *e = q->elevator;
+
+	if (e->type->ops.elevator_put_req_fn)
+		e->type->ops.elevator_put_req_fn(rq);
+}
+
+int elv_may_queue(struct request_queue *q, int rw)
+{
+	struct elevator_queue *e = q->elevator;
+
+	if (e->type->ops.elevator_may_queue_fn)
+		return e->type->ops.elevator_may_queue_fn(q, rw);
+
+	return ELV_MQUEUE_MAY;
+}
+
+void elv_completed_request(struct request_queue *q, struct request *rq)
+{
+	struct elevator_queue *e = q->elevator;
+
+	/*
+	 * request is released from the driver, io must be done
+	 */
+	if (blk_account_rq(rq)) {
+		q->in_flight[rq_is_sync(rq)]--;
+		if ((rq->cmd_flags & REQ_SORTED) &&
+		    e->type->ops.elevator_completed_req_fn)
+			e->type->ops.elevator_completed_req_fn(q, rq);
+	}
+}
+
+#define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)
+
+static ssize_t
+elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
+{
+	struct elv_fs_entry *entry = to_elv(attr);
+	struct elevator_queue *e;
+	ssize_t error;
+
+	if (!entry->show)
+		return -EIO;
+
+	e = container_of(kobj, struct elevator_queue, kobj);
+	mutex_lock(&e->sysfs_lock);
+	error = e->type ? entry->show(e, page) : -ENOENT;
+	mutex_unlock(&e->sysfs_lock);
+	return error;
+}
+
+static ssize_t
+elv_attr_store(struct kobject *kobj, struct attribute *attr,
+	       const char *page, size_t length)
+{
+	struct elv_fs_entry *entry = to_elv(attr);
+	struct elevator_queue *e;
+	ssize_t error;
+
+	if (!entry->store)
+		return -EIO;
+
+	e = container_of(kobj, struct elevator_queue, kobj);
+	mutex_lock(&e->sysfs_lock);
+	error = e->type ? entry->store(e, page, length) : -ENOENT;
+	mutex_unlock(&e->sysfs_lock);
+	return error;
+}
+
+static const struct sysfs_ops elv_sysfs_ops = {
+	.show	= elv_attr_show,
+	.store	= elv_attr_store,
+};
+
+static struct kobj_type elv_ktype = {
+	.sysfs_ops	= &elv_sysfs_ops,
+	.release	= elevator_release,
+};
+
+int elv_register_queue(struct request_queue *q)
+{
+	struct elevator_queue *e = q->elevator;
+	int error;
+
+	error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
+	if (!error) {
+		struct elv_fs_entry *attr = e->type->elevator_attrs;
+		if (attr) {
+			while (attr->attr.name) {
+				if (sysfs_create_file(&e->kobj, &attr->attr))
+					break;
+				attr++;
+			}
+		}
+		kobject_uevent(&e->kobj, KOBJ_ADD);
+		e->registered = 1;
+	}
+	return error;
+}
+EXPORT_SYMBOL(elv_register_queue);
+
+void elv_unregister_queue(struct request_queue *q)
+{
+	if (q) {
+		struct elevator_queue *e = q->elevator;
+
+		kobject_uevent(&e->kobj, KOBJ_REMOVE);
+		kobject_del(&e->kobj);
+		e->registered = 0;
+	}
+}
+EXPORT_SYMBOL(elv_unregister_queue);
+
+int elv_register(struct elevator_type *e)
+{
+	char *def = "";
+
+	/* create icq_cache if requested */
+	if (e->icq_size) {
+		if (WARN_ON(e->icq_size < sizeof(struct io_cq)) ||
+		    WARN_ON(e->icq_align < __alignof__(struct io_cq)))
+			return -EINVAL;
+
+		snprintf(e->icq_cache_name, sizeof(e->icq_cache_name),
+			 "%s_io_cq", e->elevator_name);
+		e->icq_cache = kmem_cache_create(e->icq_cache_name, e->icq_size,
+						 e->icq_align, 0, NULL);
+		if (!e->icq_cache)
+			return -ENOMEM;
+	}
+
+	/* register, don't allow duplicate names */
+	spin_lock(&elv_list_lock);
+	if (elevator_find(e->elevator_name)) {
+		spin_unlock(&elv_list_lock);
+		if (e->icq_cache)
+			kmem_cache_destroy(e->icq_cache);
+		return -EBUSY;
+	}
+	list_add_tail(&e->list, &elv_list);
+	spin_unlock(&elv_list_lock);
+
+	/* print pretty message */
+	if (!strcmp(e->elevator_name, chosen_elevator) ||
+			(!*chosen_elevator &&
+			 !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
+				def = " (default)";
+
+	printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name,
+								def);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(elv_register);
+
+void elv_unregister(struct elevator_type *e)
+{
+	/* unregister */
+	spin_lock(&elv_list_lock);
+	list_del_init(&e->list);
+	spin_unlock(&elv_list_lock);
+
+	/*
+	 * Destroy icq_cache if it exists.  icq's are RCU managed.  Make
+	 * sure all RCU operations are complete before proceeding.
+	 */
+	if (e->icq_cache) {
+		rcu_barrier();
+		kmem_cache_destroy(e->icq_cache);
+		e->icq_cache = NULL;
+	}
+}
+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 int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
+{
+	struct elevator_queue *old = q->elevator;
+	bool registered = old->registered;
+	int err;
+
+	/*
+	 * Turn on BYPASS and drain all requests w/ elevator private data.
+	 * Block layer doesn't call into a quiesced elevator - all requests
+	 * are directly put on the dispatch list without elevator data
+	 * using INSERT_BACK.  All requests have SOFTBARRIER set and no
+	 * merge happens either.
+	 */
+	blk_queue_bypass_start(q);
+
+	/* unregister and clear all auxiliary data of the old elevator */
+	if (registered)
+		elv_unregister_queue(q);
+
+	spin_lock_irq(q->queue_lock);
+	ioc_clear_queue(q);
+	spin_unlock_irq(q->queue_lock);
+
+	/* allocate, init and register new elevator */
+	err = new_e->ops.elevator_init_fn(q, new_e);
+	if (err)
+		goto fail_init;
+
+	if (registered) {
+		err = elv_register_queue(q);
+		if (err)
+			goto fail_register;
+	}
+
+	/* done, kill the old one and finish */
+	elevator_exit(old);
+	blk_queue_bypass_end(q);
+
+	blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
+
+	return 0;
+
+fail_register:
+	elevator_exit(q->elevator);
+fail_init:
+	/* switch failed, restore and re-register old elevator */
+	q->elevator = old;
+	elv_register_queue(q);
+	blk_queue_bypass_end(q);
+
+	return err;
+}
+
+/*
+ * Switch this queue to the given IO scheduler.
+ */
+static int __elevator_change(struct request_queue *q, const char *name)
+{
+	char elevator_name[ELV_NAME_MAX];
+	struct elevator_type *e;
+
+	if (!q->elevator)
+		return -ENXIO;
+
+	strlcpy(elevator_name, name, sizeof(elevator_name));
+	e = elevator_get(strstrip(elevator_name), true);
+	if (!e) {
+		printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
+		return -EINVAL;
+	}
+
+	if (!strcmp(elevator_name, q->elevator->type->elevator_name)) {
+		elevator_put(e);
+		return 0;
+	}
+
+	return elevator_switch(q, e);
+}
+
+int elevator_change(struct request_queue *q, const char *name)
+{
+	int ret;
+
+	/* Protect q->elevator from elevator_init() */
+	mutex_lock(&q->sysfs_lock);
+	ret = __elevator_change(q, name);
+	mutex_unlock(&q->sysfs_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL(elevator_change);
+
+ssize_t elv_iosched_store(struct request_queue *q, const char *name,
+			  size_t count)
+{
+	int ret;
+
+	if (!q->elevator)
+		return count;
+
+	ret = __elevator_change(q, name);
+	if (!ret)
+		return count;
+
+	printk(KERN_ERR "elevator: switch to %s failed\n", name);
+	return ret;
+}
+
+ssize_t elv_iosched_show(struct request_queue *q, char *name)
+{
+	struct elevator_queue *e = q->elevator;
+	struct elevator_type *elv;
+	struct elevator_type *__e;
+	int len = 0;
+
+	if (!q->elevator || !blk_queue_stackable(q))
+		return sprintf(name, "none\n");
+
+	elv = e->type;
+
+	spin_lock(&elv_list_lock);
+	list_for_each_entry(__e, &elv_list, 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(&elv_list_lock);
+
+	len += sprintf(len+name, "\n");
+	return len;
+}
+
+struct request *elv_rb_former_request(struct request_queue *q,
+				      struct request *rq)
+{
+	struct rb_node *rbprev = rb_prev(&rq->rb_node);
+
+	if (rbprev)
+		return rb_entry_rq(rbprev);
+
+	return NULL;
+}
+EXPORT_SYMBOL(elv_rb_former_request);
+
+struct request *elv_rb_latter_request(struct request_queue *q,
+				      struct request *rq)
+{
+	struct rb_node *rbnext = rb_next(&rq->rb_node);
+
+	if (rbnext)
+		return rb_entry_rq(rbnext);
+
+	return NULL;
+}
+EXPORT_SYMBOL(elv_rb_latter_request);