Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 859 insertions, 0 deletions

diff --git a/block/elevator.c b/block/elevator.c
new file mode 100644
index 000000000..bd71f0fc4
--- /dev/null
+++ b/block/elevator.c
@@ -0,0 +1,859 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  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/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 "elevator.h"
+#include "blk.h"
+#include "blk-mq-sched.h"
+#include "blk-pm.h"
+#include "blk-wbt.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_bio_merge(struct request *rq, struct bio *bio)
+{
+	struct request_queue *q = rq->q;
+	struct elevator_queue *e = q->elevator;
+
+	if (e->type->ops.allow_merge)
+		return e->type->ops.allow_merge(q, rq, bio);
+
+	return 1;
+}
+
+/*
+ * can we safely merge with this request?
+ */
+bool elv_bio_merge_ok(struct request *rq, struct bio *bio)
+{
+	if (!blk_rq_merge_ok(rq, bio))
+		return false;
+
+	if (!elv_iosched_allow_bio_merge(rq, bio))
+		return false;
+
+	return true;
+}
+EXPORT_SYMBOL(elv_bio_merge_ok);
+
+static inline bool elv_support_features(unsigned int elv_features,
+					unsigned int required_features)
+{
+	return (required_features & elv_features) == required_features;
+}
+
+/**
+ * elevator_match - Test an elevator name and features
+ * @e: Scheduler to test
+ * @name: Elevator name to test
+ * @required_features: Features that the elevator must provide
+ *
+ * Return true if the elevator @e name matches @name and if @e provides all
+ * the features specified by @required_features.
+ */
+static bool elevator_match(const struct elevator_type *e, const char *name,
+			   unsigned int required_features)
+{
+	if (!elv_support_features(e->elevator_features, required_features))
+		return false;
+	if (!strcmp(e->elevator_name, name))
+		return true;
+	if (e->elevator_alias && !strcmp(e->elevator_alias, name))
+		return true;
+
+	return false;
+}
+
+/**
+ * elevator_find - Find an elevator
+ * @name: Name of the elevator to find
+ * @required_features: Features that the elevator must provide
+ *
+ * Return the first registered scheduler with name @name and supporting the
+ * features @required_features and NULL otherwise.
+ */
+static struct elevator_type *elevator_find(const char *name,
+					   unsigned int required_features)
+{
+	struct elevator_type *e;
+
+	list_for_each_entry(e, &elv_list, list) {
+		if (elevator_match(e, name, required_features))
+			return e;
+	}
+
+	return NULL;
+}
+
+static void elevator_put(struct elevator_type *e)
+{
+	module_put(e->elevator_owner);
+}
+
+static struct elevator_type *elevator_get(struct request_queue *q,
+					  const char *name, bool try_loading)
+{
+	struct elevator_type *e;
+
+	spin_lock(&elv_list_lock);
+
+	e = elevator_find(name, q->required_elevator_features);
+	if (!e && try_loading) {
+		spin_unlock(&elv_list_lock);
+		request_module("%s-iosched", name);
+		spin_lock(&elv_list_lock);
+		e = elevator_find(name, q->required_elevator_features);
+	}
+
+	if (e && !try_module_get(e->elevator_owner))
+		e = NULL;
+
+	spin_unlock(&elv_list_lock);
+	return e;
+}
+
+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);
+}
+
+void elevator_exit(struct request_queue *q)
+{
+	struct elevator_queue *e = q->elevator;
+
+	ioc_clear_queue(q);
+	blk_mq_sched_free_rqs(q);
+
+	mutex_lock(&e->sysfs_lock);
+	blk_mq_exit_sched(q, e);
+	mutex_unlock(&e->sysfs_lock);
+
+	kobject_put(&e->kobj);
+}
+
+static inline void __elv_rqhash_del(struct request *rq)
+{
+	hash_del(&rq->hash);
+	rq->rq_flags &= ~RQF_HASHED;
+}
+
+void elv_rqhash_del(struct request_queue *q, struct request *rq)
+{
+	if (ELV_ON_HASH(rq))
+		__elv_rqhash_del(rq);
+}
+EXPORT_SYMBOL_GPL(elv_rqhash_del);
+
+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->rq_flags |= RQF_HASHED;
+}
+EXPORT_SYMBOL_GPL(elv_rqhash_add);
+
+void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
+{
+	__elv_rqhash_del(rq);
+	elv_rqhash_add(q, rq);
+}
+
+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);
+
+enum elv_merge elv_merge(struct request_queue *q, struct request **req,
+		struct bio *bio)
+{
+	struct elevator_queue *e = q->elevator;
+	struct request *__rq;
+
+	/*
+	 * 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) || !bio_mergeable(bio))
+		return ELEVATOR_NO_MERGE;
+
+	/*
+	 * First try one-hit cache.
+	 */
+	if (q->last_merge && elv_bio_merge_ok(q->last_merge, bio)) {
+		enum elv_merge 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_bio_merge_ok(__rq, bio)) {
+		*req = __rq;
+
+		if (blk_discard_mergable(__rq))
+			return ELEVATOR_DISCARD_MERGE;
+		return ELEVATOR_BACK_MERGE;
+	}
+
+	if (e->type->ops.request_merge)
+		return e->type->ops.request_merge(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. 'free' will contain all
+ * requests that need to be freed.
+ */
+bool elv_attempt_insert_merge(struct request_queue *q, struct request *rq,
+			      struct list_head *free)
+{
+	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)) {
+		list_add(&rq->queuelist, free);
+		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;
+
+		list_add(&rq->queuelist, free);
+		/* 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,
+		enum elv_merge type)
+{
+	struct elevator_queue *e = q->elevator;
+
+	if (e->type->ops.request_merged)
+		e->type->ops.request_merged(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;
+
+	if (e->type->ops.requests_merged)
+		e->type->ops.requests_merged(q, rq, next);
+
+	elv_rqhash_reposition(q, rq);
+	q->last_merge = rq;
+}
+
+struct request *elv_latter_request(struct request_queue *q, struct request *rq)
+{
+	struct elevator_queue *e = q->elevator;
+
+	if (e->type->ops.next_request)
+		return e->type->ops.next_request(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.former_request)
+		return e->type->ops.former_request(q, rq);
+
+	return NULL;
+}
+
+#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, bool uevent)
+{
+	struct elevator_queue *e = q->elevator;
+	int error;
+
+	lockdep_assert_held(&q->sysfs_lock);
+
+	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++;
+			}
+		}
+		if (uevent)
+			kobject_uevent(&e->kobj, KOBJ_ADD);
+
+		e->registered = 1;
+	}
+	return error;
+}
+
+void elv_unregister_queue(struct request_queue *q)
+{
+	struct elevator_queue *e = q->elevator;
+
+	lockdep_assert_held(&q->sysfs_lock);
+
+	if (e && e->registered) {
+		struct elevator_queue *e = q->elevator;
+
+		kobject_uevent(&e->kobj, KOBJ_REMOVE);
+		kobject_del(&e->kobj);
+
+		e->registered = 0;
+	}
+}
+
+int elv_register(struct elevator_type *e)
+{
+	/* insert_requests and dispatch_request are mandatory */
+	if (WARN_ON_ONCE(!e->ops.insert_requests || !e->ops.dispatch_request))
+		return -EINVAL;
+
+	/* 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, 0)) {
+		spin_unlock(&elv_list_lock);
+		kmem_cache_destroy(e->icq_cache);
+		return -EBUSY;
+	}
+	list_add_tail(&e->list, &elv_list);
+	spin_unlock(&elv_list_lock);
+
+	printk(KERN_INFO "io scheduler %s registered\n", e->elevator_name);
+
+	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);
+
+static int elevator_switch_mq(struct request_queue *q,
+			      struct elevator_type *new_e)
+{
+	int ret;
+
+	lockdep_assert_held(&q->sysfs_lock);
+
+	if (q->elevator) {
+		elv_unregister_queue(q);
+		elevator_exit(q);
+	}
+
+	ret = blk_mq_init_sched(q, new_e);
+	if (ret)
+		goto out;
+
+	if (new_e) {
+		ret = elv_register_queue(q, true);
+		if (ret) {
+			elevator_exit(q);
+			goto out;
+		}
+	}
+
+	if (new_e)
+		blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
+	else
+		blk_add_trace_msg(q, "elv switch: none");
+
+out:
+	return ret;
+}
+
+static inline bool elv_support_iosched(struct request_queue *q)
+{
+	if (!queue_is_mq(q) ||
+	    (q->tag_set && (q->tag_set->flags & BLK_MQ_F_NO_SCHED)))
+		return false;
+	return true;
+}
+
+/*
+ * For single queue devices, default to using mq-deadline. If we have multiple
+ * queues or mq-deadline is not available, default to "none".
+ */
+static struct elevator_type *elevator_get_default(struct request_queue *q)
+{
+	if (q->tag_set && q->tag_set->flags & BLK_MQ_F_NO_SCHED_BY_DEFAULT)
+		return NULL;
+
+	if (q->nr_hw_queues != 1 &&
+	    !blk_mq_is_shared_tags(q->tag_set->flags))
+		return NULL;
+
+	return elevator_get(q, "mq-deadline", false);
+}
+
+/*
+ * Get the first elevator providing the features required by the request queue.
+ * Default to "none" if no matching elevator is found.
+ */
+static struct elevator_type *elevator_get_by_features(struct request_queue *q)
+{
+	struct elevator_type *e, *found = NULL;
+
+	spin_lock(&elv_list_lock);
+
+	list_for_each_entry(e, &elv_list, list) {
+		if (elv_support_features(e->elevator_features,
+					 q->required_elevator_features)) {
+			found = e;
+			break;
+		}
+	}
+
+	if (found && !try_module_get(found->elevator_owner))
+		found = NULL;
+
+	spin_unlock(&elv_list_lock);
+	return found;
+}
+
+/*
+ * For a device queue that has no required features, use the default elevator
+ * settings. Otherwise, use the first elevator available matching the required
+ * features. If no suitable elevator is find or if the chosen elevator
+ * initialization fails, fall back to the "none" elevator (no elevator).
+ */
+void elevator_init_mq(struct request_queue *q)
+{
+	struct elevator_type *e;
+	int err;
+
+	if (!elv_support_iosched(q))
+		return;
+
+	WARN_ON_ONCE(blk_queue_registered(q));
+
+	if (unlikely(q->elevator))
+		return;
+
+	if (!q->required_elevator_features)
+		e = elevator_get_default(q);
+	else
+		e = elevator_get_by_features(q);
+	if (!e)
+		return;
+
+	/*
+	 * We are called before adding disk, when there isn't any FS I/O,
+	 * so freezing queue plus canceling dispatch work is enough to
+	 * drain any dispatch activities originated from passthrough
+	 * requests, then no need to quiesce queue which may add long boot
+	 * latency, especially when lots of disks are involved.
+	 */
+	blk_mq_freeze_queue(q);
+	blk_mq_cancel_work_sync(q);
+
+	err = blk_mq_init_sched(q, e);
+
+	blk_mq_unfreeze_queue(q);
+
+	if (err) {
+		pr_warn("\"%s\" elevator initialization failed, "
+			"falling back to \"none\"\n", e->elevator_name);
+		elevator_put(e);
+	}
+}
+
+/*
+ * 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.
+ */
+int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
+{
+	int err;
+
+	lockdep_assert_held(&q->sysfs_lock);
+
+	blk_mq_freeze_queue(q);
+	blk_mq_quiesce_queue(q);
+
+	err = elevator_switch_mq(q, new_e);
+
+	blk_mq_unquiesce_queue(q);
+	blk_mq_unfreeze_queue(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;
+
+	/* Make sure queue is not in the middle of being removed */
+	if (!blk_queue_registered(q))
+		return -ENOENT;
+
+	/*
+	 * Special case for mq, turn off scheduling
+	 */
+	if (!strncmp(name, "none", 4)) {
+		if (!q->elevator)
+			return 0;
+		return elevator_switch(q, NULL);
+	}
+
+	strlcpy(elevator_name, name, sizeof(elevator_name));
+	e = elevator_get(q, strstrip(elevator_name), true);
+	if (!e)
+		return -EINVAL;
+
+	if (q->elevator &&
+	    elevator_match(q->elevator->type, elevator_name, 0)) {
+		elevator_put(e);
+		return 0;
+	}
+
+	return elevator_switch(q, e);
+}
+
+ssize_t elv_iosched_store(struct request_queue *q, const char *name,
+			  size_t count)
+{
+	int ret;
+
+	if (!elv_support_iosched(q))
+		return count;
+
+	ret = __elevator_change(q, name);
+	if (!ret)
+		return count;
+
+	return ret;
+}
+
+ssize_t elv_iosched_show(struct request_queue *q, char *name)
+{
+	struct elevator_queue *e = q->elevator;
+	struct elevator_type *elv = NULL;
+	struct elevator_type *__e;
+	int len = 0;
+
+	if (!queue_is_mq(q))
+		return sprintf(name, "none\n");
+
+	if (!q->elevator)
+		len += sprintf(name+len, "[none] ");
+	else
+		elv = e->type;
+
+	spin_lock(&elv_list_lock);
+	list_for_each_entry(__e, &elv_list, list) {
+		if (elv && elevator_match(elv, __e->elevator_name, 0)) {
+			len += sprintf(name+len, "[%s] ", elv->elevator_name);
+			continue;
+		}
+		if (elv_support_iosched(q) &&
+		    elevator_match(__e, __e->elevator_name,
+				   q->required_elevator_features))
+			len += sprintf(name+len, "%s ", __e->elevator_name);
+	}
+	spin_unlock(&elv_list_lock);
+
+	if (q->elevator)
+		len += sprintf(name+len, "none");
+
+	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);
+
+static int __init elevator_setup(char *str)
+{
+	pr_warn("Kernel parameter elevator= does not have any effect anymore.\n"
+		"Please use sysfs to set IO scheduler for individual devices.\n");
+	return 1;
+}
+
+__setup("elevator=", elevator_setup);