// 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/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 <linux/blk-cgroup.h>

  #include <trace/events/block.h>

  #include "blk.h"

  #include "blk-mq-sched.h"

  #include "blk-pm.h"

  #include "blk-wbt.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 is the elevator @e name matches @name and if @e provides all the
   * the feratures spcified 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)

  {

  	mutex_lock(&e->sysfs_lock);

  	if (e->type->ops.exit_sched)

  		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;
  		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
   */

  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,
  		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,
  };

  /*
   * elv_register_queue is called from either blk_register_queue or
   * elevator_switch, elevator switch is prevented from being happen
   * in the two paths, so it is safe to not hold q->sysfs_lock.
   */
  int elv_register_queue(struct request_queue *q, bool uevent)

  {

  	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++;

  			}
  		}

  		if (uevent)
  			kobject_uevent(&e->kobj, KOBJ_ADD);

  		e->registered = 1;

  	}
  	return error;

  }

  /*
   * elv_unregister_queue is called from either blk_unregister_queue or
   * elevator_switch, elevator switch is prevented from being happen
   * in the two paths, so it is safe to not hold q->sysfs_lock.
   */

  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;

  		/* Re-enable throttling in case elevator disabled it */
  		wbt_enable_default(q);

  	}

  }

  int elv_register(struct elevator_type *e)

  {

  	/* 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
  ", 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);

  int elevator_switch_mq(struct request_queue *q,

  			      struct elevator_type *new_e)
  {
  	int ret;

  	lockdep_assert_held(&q->sysfs_lock);

  	if (q->elevator) {

  		if (q->elevator->registered)

  			elv_unregister_queue(q);

  		ioc_clear_queue(q);
  		elevator_exit(q, q->elevator);
  	}
  
  	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, q->elevator);
  			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 (!q->mq_ops ||
  	    (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->nr_hw_queues != 1)
  		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(test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags));

  	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;

  	blk_mq_freeze_queue(q);
  	blk_mq_quiesce_queue(q);

  	err = blk_mq_init_sched(q, e);

  
  	blk_mq_unquiesce_queue(q);
  	blk_mq_unfreeze_queue(q);

  	if (err) {
  		pr_warn("\"%s\" elevator initialization failed, "
  			"falling back to \"none\"
  ", 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.

   */

  static 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 (!queue_is_mq(q) || !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
  ");

  	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, "
  ");
  	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);