// 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 bool 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 true;
}

/*
 * 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);

/**
 * elevator_match - Check whether @e's name or alias matches @name
 * @e: Scheduler to test
 * @name: Elevator name to test
 *
 * Return true if the elevator @e's name or alias matches @name.
 */
static bool elevator_match(const struct elevator_type *e, const char *name)
{
        return !strcmp(e->elevator_name, name) ||
                (e->elevator_alias && !strcmp(e->elevator_alias, name));
}

static struct elevator_type *__elevator_find(const char *name)
{
        struct elevator_type *e;

        list_for_each_entry(e, &elv_list, list)
                if (elevator_match(e, name))
                        return e;
        return NULL;
}

static struct elevator_type *elevator_find_get(const char *name)
{
        struct elevator_type *e;

        spin_lock(&elv_list_lock);
        e = __elevator_find(name);
        if (e && (!elevator_tryget(e)))
                e = NULL;
        spin_unlock(&elv_list_lock);
        return e;
}

static const struct kobj_type elv_ktype;

struct elevator_queue *elevator_alloc(struct request_queue *q,
                struct elevator_type *e, struct elevator_resources *res)
{
        struct elevator_queue *eq;

        eq = kzalloc_node(sizeof(*eq), GFP_KERNEL, q->node);
        if (unlikely(!eq))
                return NULL;

        __elevator_get(e);
        eq->type = e;
        kobject_init(&eq->kobj, &elv_ktype);
        mutex_init(&eq->sysfs_lock);
        hash_init(eq->hash);
        eq->et = res->et;
        eq->elevator_data = res->data;

        return eq;
}

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);
}

static void elevator_exit(struct request_queue *q)
{
        struct elevator_queue *e = q->elevator;

        lockdep_assert_held(&q->elevator_lock);

        ioc_clear_queue(q);

        mutex_lock(&e->sysfs_lock);
        blk_mq_exit_sched(q, e);
        mutex_unlock(&e->sysfs_lock);
}

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_const((atr), struct elv_fs_entry, attr)

static ssize_t
elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
{
        const struct elv_fs_entry *entry = to_elv(attr);
        struct elevator_queue *e;
        ssize_t error = -ENODEV;

        if (!entry->show)
                return -EIO;

        e = container_of(kobj, struct elevator_queue, kobj);
        mutex_lock(&e->sysfs_lock);
        if (!test_bit(ELEVATOR_FLAG_DYING, &e->flags))
                error = entry->show(e, page);
        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)
{
        const struct elv_fs_entry *entry = to_elv(attr);
        struct elevator_queue *e;
        ssize_t error = -ENODEV;

        if (!entry->store)
                return -EIO;

        e = container_of(kobj, struct elevator_queue, kobj);
        mutex_lock(&e->sysfs_lock);
        if (!test_bit(ELEVATOR_FLAG_DYING, &e->flags))
                error = entry->store(e, page, length);
        mutex_unlock(&e->sysfs_lock);
        return error;
}

static const struct sysfs_ops elv_sysfs_ops = {
        .show   = elv_attr_show,
        .store  = elv_attr_store,
};

static const struct kobj_type elv_ktype = {
        .sysfs_ops      = &elv_sysfs_ops,
        .release        = elevator_release,
};

static int elv_register_queue(struct request_queue *q,
                              struct elevator_queue *e,
                              bool uevent)
{
        int error;

        error = kobject_add(&e->kobj, &q->disk->queue_kobj, "iosched");
        if (!error) {
                const 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);

                /*
                 * Sched is initialized, it is ready to export it via
                 * debugfs
                 */
                blk_mq_sched_reg_debugfs(q);
                set_bit(ELEVATOR_FLAG_REGISTERED, &e->flags);
        }
        return error;
}

static void elv_unregister_queue(struct request_queue *q,
                                 struct elevator_queue *e)
{
        if (e && test_and_clear_bit(ELEVATOR_FLAG_REGISTERED, &e->flags)) {
                kobject_uevent(&e->kobj, KOBJ_REMOVE);
                kobject_del(&e->kobj);

                /* unexport via debugfs before exiting sched */
                blk_mq_sched_unreg_debugfs(q);
        }
}

int elv_register(struct elevator_type *e)
{
        /* finish request is mandatory */
        if (WARN_ON_ONCE(!e->ops.finish_request))
                return -EINVAL;
        /* 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)) {
                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);

/*
 * Switch to new_e io scheduler.
 *
 * If switching fails, we are most likely running out of memory and not able
 * to restore the old io scheduler, so leaving the io scheduler being none.
 */
static int elevator_switch(struct request_queue *q, struct elv_change_ctx *ctx)
{
        struct elevator_type *new_e = NULL;
        int ret = 0;

        WARN_ON_ONCE(q->mq_freeze_depth == 0);
        lockdep_assert_held(&q->elevator_lock);

        if (strncmp(ctx->name, "none", 4)) {
                new_e = elevator_find_get(ctx->name);
                if (!new_e)
                        return -EINVAL;
        }

        blk_mq_quiesce_queue(q);

        if (q->elevator) {
                ctx->old = q->elevator;
                elevator_exit(q);
        }

        if (new_e) {
                ret = blk_mq_init_sched(q, new_e, &ctx->res);
                if (ret)
                        goto out_unfreeze;
                ctx->new = q->elevator;
        } else {
                blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
                q->elevator = NULL;
                q->nr_requests = q->tag_set->queue_depth;
                q->async_depth = q->tag_set->queue_depth;
        }
        blk_add_trace_msg(q, "elv switch: %s", ctx->name);

out_unfreeze:
        blk_mq_unquiesce_queue(q);

        if (ret) {
                pr_warn("elv: switch to \"%s\" failed, falling back to \"none\"\n",
                        new_e->elevator_name);
        }

        if (new_e)
                elevator_put(new_e);
        return ret;
}

static void elv_exit_and_release(struct elv_change_ctx *ctx,
                struct request_queue *q)
{
        struct elevator_queue *e;
        unsigned memflags;

        memflags = blk_mq_freeze_queue(q);
        mutex_lock(&q->elevator_lock);
        e = q->elevator;
        elevator_exit(q);
        mutex_unlock(&q->elevator_lock);
        blk_mq_unfreeze_queue(q, memflags);
        if (e) {
                blk_mq_free_sched_res(&ctx->res, ctx->type, q->tag_set);
                kobject_put(&e->kobj);
        }
}

static int elevator_change_done(struct request_queue *q,
                                struct elv_change_ctx *ctx)
{
        int ret = 0;

        if (ctx->old) {
                struct elevator_resources res = {
                        .et = ctx->old->et,
                        .data = ctx->old->elevator_data
                };

                elv_unregister_queue(q, ctx->old);
                blk_mq_free_sched_res(&res, ctx->old->type, q->tag_set);
                kobject_put(&ctx->old->kobj);
        }
        if (ctx->new) {
                ret = elv_register_queue(q, ctx->new, !ctx->no_uevent);
                if (ret)
                        elv_exit_and_release(ctx, q);
        }
        return ret;
}

/*
 * Switch this queue to the given IO scheduler.
 */
static int elevator_change(struct request_queue *q, struct elv_change_ctx *ctx)
{
        unsigned int memflags;
        struct blk_mq_tag_set *set = q->tag_set;
        int ret = 0;

        lockdep_assert_held(&set->update_nr_hwq_lock);

        if (strncmp(ctx->name, "none", 4)) {
                ret = blk_mq_alloc_sched_res(q, ctx->type, &ctx->res,
                                set->nr_hw_queues);
                if (ret)
                        return ret;
        }

        memflags = blk_mq_freeze_queue(q);
        /*
         * May be 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.
         *
         * Disk isn't added yet, so verifying queue lock only manually.
         */
        blk_mq_cancel_work_sync(q);
        mutex_lock(&q->elevator_lock);
        if (!(q->elevator && elevator_match(q->elevator->type, ctx->name)))
                ret = elevator_switch(q, ctx);
        mutex_unlock(&q->elevator_lock);
        blk_mq_unfreeze_queue(q, memflags);
        if (!ret)
                ret = elevator_change_done(q, ctx);

        /*
         * Free sched resource if it's allocated but we couldn't switch elevator.
         */
        if (!ctx->new)
                blk_mq_free_sched_res(&ctx->res, ctx->type, set);

        return ret;
}

/*
 * The I/O scheduler depends on the number of hardware queues, this forces a
 * reattachment when nr_hw_queues changes.
 */
void elv_update_nr_hw_queues(struct request_queue *q,
                struct elv_change_ctx *ctx)
{
        struct blk_mq_tag_set *set = q->tag_set;
        int ret = -ENODEV;

        WARN_ON_ONCE(q->mq_freeze_depth == 0);

        if (ctx->type && !blk_queue_dying(q) && blk_queue_registered(q)) {
                mutex_lock(&q->elevator_lock);
                /* force to reattach elevator after nr_hw_queue is updated */
                ret = elevator_switch(q, ctx);
                mutex_unlock(&q->elevator_lock);
        }
        blk_mq_unfreeze_queue_nomemrestore(q);
        if (!ret)
                WARN_ON_ONCE(elevator_change_done(q, ctx));

        /*
         * Free sched resource if it's allocated but we couldn't switch elevator.
         */
        if (!ctx->new)
                blk_mq_free_sched_res(&ctx->res, ctx->type, set);
}

/*
 * Use the default elevator settings. If the chosen elevator initialization
 * fails, fall back to the "none" elevator (no elevator).
 */
void elevator_set_default(struct request_queue *q)
{
        struct elv_change_ctx ctx = {
                .name = "mq-deadline",
                .no_uevent = true,
        };
        int err;

        /* now we allow to switch elevator */
        blk_queue_flag_clear(QUEUE_FLAG_NO_ELV_SWITCH, q);

        if (q->tag_set->flags & BLK_MQ_F_NO_SCHED_BY_DEFAULT)
                return;

        /*
         * For single queue devices, default to using mq-deadline. If we
         * have multiple queues or mq-deadline is not available, default
         * to "none".
         */
        ctx.type = elevator_find_get(ctx.name);
        if (!ctx.type)
                return;

        if ((q->nr_hw_queues == 1 ||
                        blk_mq_is_shared_tags(q->tag_set->flags))) {
                err = elevator_change(q, &ctx);
                if (err < 0)
                        pr_warn("\"%s\" elevator initialization, failed %d, falling back to \"none\"\n",
                                        ctx.name, err);
        }
        elevator_put(ctx.type);
}

void elevator_set_none(struct request_queue *q)
{
        struct elv_change_ctx ctx = {
                .name   = "none",
        };
        int err;

        err = elevator_change(q, &ctx);
        if (err < 0)
                pr_warn("%s: set none elevator failed %d\n", __func__, err);
}

static void elv_iosched_load_module(const char *elevator_name)
{
        struct elevator_type *found;

        spin_lock(&elv_list_lock);
        found = __elevator_find(elevator_name);
        spin_unlock(&elv_list_lock);

        if (!found)
                request_module("%s-iosched", elevator_name);
}

ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
                          size_t count)
{
        char elevator_name[ELV_NAME_MAX];
        struct elv_change_ctx ctx = {};
        int ret;
        struct request_queue *q = disk->queue;
        struct blk_mq_tag_set *set = q->tag_set;

        /* Make sure queue is not in the middle of being removed */
        if (!blk_queue_registered(q))
                return -ENOENT;

        /*
         * If the attribute needs to load a module, do it before freezing the
         * queue to ensure that the module file can be read when the request
         * queue is the one for the device storing the module file.
         */
        strscpy(elevator_name, buf, sizeof(elevator_name));
        ctx.name = strstrip(elevator_name);

        elv_iosched_load_module(ctx.name);
        ctx.type = elevator_find_get(ctx.name);

        /*
         * Use trylock to avoid circular lock dependency with kernfs active
         * reference during concurrent disk deletion:
         *   update_nr_hwq_lock -> kn->active (via del_gendisk -> kobject_del)
         *   kn->active -> update_nr_hwq_lock (via this sysfs write path)
         */
        if (!down_read_trylock(&set->update_nr_hwq_lock)) {
                ret = -EBUSY;
                goto out;
        }
        if (!blk_queue_no_elv_switch(q)) {
                ret = elevator_change(q, &ctx);
                if (!ret)
                        ret = count;
        } else {
                ret = -ENOENT;
        }
        up_read(&set->update_nr_hwq_lock);

out:
        if (ctx.type)
                elevator_put(ctx.type);
        return ret;
}

ssize_t elv_iosched_show(struct gendisk *disk, char *name)
{
        struct request_queue *q = disk->queue;
        struct elevator_type *cur = NULL, *e;
        int len = 0;

        mutex_lock(&q->elevator_lock);
        if (!q->elevator) {
                len += sprintf(name+len, "[none] ");
        } else {
                len += sprintf(name+len, "none ");
                cur = q->elevator->type;
        }

        spin_lock(&elv_list_lock);
        list_for_each_entry(e, &elv_list, list) {
                if (e == cur)
                        len += sprintf(name+len, "[%s] ", e->elevator_name);
                else
                        len += sprintf(name+len, "%s ", e->elevator_name);
        }
        spin_unlock(&elv_list_lock);

        len += sprintf(name+len, "\n");
        mutex_unlock(&q->elevator_lock);

        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);