control.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  Routines for driver control interface
 *  Copyright (c) by Jaroslav Kysela <perex@perex.cz>
 */

#include <linux/threads.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/time.h>
#include <linux/mm.h>
#include <linux/math64.h>
#include <linux/sched/signal.h>
#include <sound/core.h>
#include <sound/minors.h>
#include <sound/info.h>
#include <sound/control.h>

#ifdef CONFIG_SND_CTL_DEBUG
#define CREATE_TRACE_POINTS
#include "control_trace.h"
#else
#define trace_snd_ctl_put(card, kctl, iname, expected, actual)
#endif

// Max allocation size for user controls.
static int max_user_ctl_alloc_size = 8 * 1024 * 1024;
module_param_named(max_user_ctl_alloc_size, max_user_ctl_alloc_size, int, 0444);
MODULE_PARM_DESC(max_user_ctl_alloc_size, "Max allocation size for user controls");

#define MAX_CONTROL_COUNT	1028

struct snd_kctl_ioctl {
	struct list_head list;		/* list of all ioctls */
	snd_kctl_ioctl_func_t fioctl;
};

DECLARE_RWSEM(snd_ioctl_rwsem);
static DECLARE_RWSEM(snd_ctl_layer_rwsem);
static LIST_HEAD(snd_control_ioctls);
#ifdef CONFIG_COMPAT
static LIST_HEAD(snd_control_compat_ioctls);
#endif
static struct snd_ctl_layer_ops *snd_ctl_layer;

static int snd_ctl_remove_locked(struct snd_card *card,
				 struct snd_kcontrol *kcontrol);

static int snd_ctl_open(struct inode *inode, struct file *file)
{
	struct snd_card *card;
	struct snd_ctl_file *ctl;
	int i, err;

	stream_open(inode, file);

	card = snd_lookup_minor_data(iminor(inode), SNDRV_DEVICE_TYPE_CONTROL);
	if (!card) {
		err = -ENODEV;
		goto __error1;
	}
	err = snd_card_file_add(card, file);
	if (err < 0)
		goto __error1;
	if (!try_module_get(card->module)) {
		err = -ENODEV;
		goto __error2;
	}
	ctl = kzalloc_obj(*ctl);
	if (ctl == NULL) {
		err = -ENOMEM;
		goto __error;
	}
	INIT_LIST_HEAD(&ctl->events);
	init_waitqueue_head(&ctl->change_sleep);
	spin_lock_init(&ctl->read_lock);
	ctl->card = card;
	for (i = 0; i < SND_CTL_SUBDEV_ITEMS; i++)
		ctl->preferred_subdevice[i] = -1;
	ctl->pid = get_pid(task_pid(current));
	file->private_data = ctl;
	scoped_guard(write_lock_irqsave, &card->controls_rwlock)
		list_add_tail(&ctl->list, &card->ctl_files);
	snd_card_unref(card);
	return 0;

      __error:
	module_put(card->module);
      __error2:
	snd_card_file_remove(card, file);
      __error1:
	if (card)
		snd_card_unref(card);
      	return err;
}

static void snd_ctl_empty_read_queue(struct snd_ctl_file * ctl)
{
	struct snd_kctl_event *cread;

	guard(spinlock_irqsave)(&ctl->read_lock);
	while (!list_empty(&ctl->events)) {
		cread = snd_kctl_event(ctl->events.next);
		list_del(&cread->list);
		kfree(cread);
	}
}

static int snd_ctl_release(struct inode *inode, struct file *file)
{
	struct snd_card *card;
	struct snd_ctl_file *ctl;
	struct snd_kcontrol *control;
	unsigned int idx;

	ctl = file->private_data;
	file->private_data = NULL;
	card = ctl->card;

	scoped_guard(write_lock_irqsave, &card->controls_rwlock)
		list_del(&ctl->list);

	scoped_guard(rwsem_write, &card->controls_rwsem) {
		list_for_each_entry(control, &card->controls, list)
			for (idx = 0; idx < control->count; idx++)
				if (control->vd[idx].owner == ctl)
					control->vd[idx].owner = NULL;
	}

	snd_fasync_free(ctl->fasync);
	snd_ctl_empty_read_queue(ctl);
	put_pid(ctl->pid);
	kfree(ctl);
	module_put(card->module);
	snd_card_file_remove(card, file);
	return 0;
}

/**
 * snd_ctl_notify - Send notification to user-space for a control change
 * @card: the card to send notification
 * @mask: the event mask, SNDRV_CTL_EVENT_*
 * @id: the ctl element id to send notification
 *
 * This function adds an event record with the given id and mask, appends
 * to the list and wakes up the user-space for notification.  This can be
 * called in the atomic context.
 */
void snd_ctl_notify(struct snd_card *card, unsigned int mask,
		    struct snd_ctl_elem_id *id)
{
	struct snd_ctl_file *ctl;
	struct snd_kctl_event *ev;

	if (snd_BUG_ON(!card || !id))
		return;
	if (card->shutdown)
		return;

	guard(read_lock_irqsave)(&card->controls_rwlock);
#if IS_ENABLED(CONFIG_SND_MIXER_OSS)
	card->mixer_oss_change_count++;
#endif
	list_for_each_entry(ctl, &card->ctl_files, list) {
		if (!ctl->subscribed)
			continue;
		scoped_guard(spinlock, &ctl->read_lock) {
			list_for_each_entry(ev, &ctl->events, list) {
				if (ev->id.numid == id->numid) {
					ev->mask |= mask;
					goto _found;
				}
			}
			ev = kzalloc_obj(*ev, GFP_ATOMIC);
			if (ev) {
				ev->id = *id;
				ev->mask = mask;
				list_add_tail(&ev->list, &ctl->events);
			} else {
				dev_err(card->dev, "No memory available to allocate event\n");
			}
_found:
			wake_up(&ctl->change_sleep);
		}
		snd_kill_fasync(ctl->fasync, SIGIO, POLL_IN);
	}
}
EXPORT_SYMBOL(snd_ctl_notify);

/**
 * snd_ctl_notify_one - Send notification to user-space for a control change
 * @card: the card to send notification
 * @mask: the event mask, SNDRV_CTL_EVENT_*
 * @kctl: the pointer with the control instance
 * @ioff: the additional offset to the control index
 *
 * This function calls snd_ctl_notify() and does additional jobs
 * like LED state changes.
 */
void snd_ctl_notify_one(struct snd_card *card, unsigned int mask,
			struct snd_kcontrol *kctl, unsigned int ioff)
{
	struct snd_ctl_elem_id id = kctl->id;
	struct snd_ctl_layer_ops *lops;

	id.index += ioff;
	id.numid += ioff;
	snd_ctl_notify(card, mask, &id);
	guard(rwsem_read)(&snd_ctl_layer_rwsem);
	for (lops = snd_ctl_layer; lops; lops = lops->next)
		lops->lnotify(card, mask, kctl, ioff);
}
EXPORT_SYMBOL(snd_ctl_notify_one);

/**
 * snd_ctl_new - create a new control instance with some elements
 * @kctl: the pointer to store new control instance
 * @count: the number of elements in this control
 * @access: the default access flags for elements in this control
 * @file: given when locking these elements
 *
 * Allocates a memory object for a new control instance. The instance has
 * elements as many as the given number (@count). Each element has given
 * access permissions (@access). Each element is locked when @file is given.
 *
 * Return: 0 on success, error code on failure
 */
static int snd_ctl_new(struct snd_kcontrol **kctl, unsigned int count,
		       unsigned int access, struct snd_ctl_file *file)
{
	unsigned int idx;

	if (count == 0 || count > MAX_CONTROL_COUNT)
		return -EINVAL;

	*kctl = kzalloc_flex(**kctl, vd, count);
	if (!*kctl)
		return -ENOMEM;

	(*kctl)->count = count;
	for (idx = 0; idx < count; idx++) {
		(*kctl)->vd[idx].access = access;
		(*kctl)->vd[idx].owner = file;
	}

	return 0;
}

/**
 * snd_ctl_new1 - create a control instance from the template
 * @ncontrol: the initialization record
 * @private_data: the private data to set
 *
 * Allocates a new struct snd_kcontrol instance and initialize from the given
 * template.  When the access field of ncontrol is 0, it's assumed as
 * READWRITE access. When the count field is 0, it's assumes as one.
 *
 * Return: The pointer of the newly generated instance, or %NULL on failure.
 */
struct snd_kcontrol *snd_ctl_new1(const struct snd_kcontrol_new *ncontrol,
				  void *private_data)
{
	struct snd_kcontrol *kctl;
	unsigned int count;
	unsigned int access;
	int err;

	if (snd_BUG_ON(!ncontrol || !ncontrol->info))
		return NULL;

	count = ncontrol->count;
	if (count == 0)
		count = 1;

	access = ncontrol->access;
	if (access == 0)
		access = SNDRV_CTL_ELEM_ACCESS_READWRITE;
	access &= (SNDRV_CTL_ELEM_ACCESS_READWRITE |
		   SNDRV_CTL_ELEM_ACCESS_VOLATILE |
		   SNDRV_CTL_ELEM_ACCESS_INACTIVE |
		   SNDRV_CTL_ELEM_ACCESS_TLV_READWRITE |
		   SNDRV_CTL_ELEM_ACCESS_TLV_COMMAND |
		   SNDRV_CTL_ELEM_ACCESS_TLV_CALLBACK |
		   SNDRV_CTL_ELEM_ACCESS_LED_MASK |
		   SNDRV_CTL_ELEM_ACCESS_SKIP_CHECK);

	err = snd_ctl_new(&kctl, count, access, NULL);
	if (err < 0)
		return NULL;

	/* The 'numid' member is decided when calling snd_ctl_add(). */
	kctl->id.iface = ncontrol->iface;
	kctl->id.device = ncontrol->device;
	kctl->id.subdevice = ncontrol->subdevice;
	if (ncontrol->name) {
		strscpy(kctl->id.name, ncontrol->name, sizeof(kctl->id.name));
		if (strcmp(ncontrol->name, kctl->id.name) != 0)
			pr_warn("ALSA: Control name '%s' truncated to '%s'\n",
				ncontrol->name, kctl->id.name);
	}
	kctl->id.index = ncontrol->index;

	kctl->info = ncontrol->info;
	kctl->get = ncontrol->get;
	kctl->put = ncontrol->put;
	kctl->tlv.p = ncontrol->tlv.p;

	kctl->private_value = ncontrol->private_value;
	kctl->private_data = private_data;

	return kctl;
}
EXPORT_SYMBOL(snd_ctl_new1);

/**
 * snd_ctl_free_one - release the control instance
 * @kcontrol: the control instance
 *
 * Releases the control instance created via snd_ctl_new()
 * or snd_ctl_new1().
 * Don't call this after the control was added to the card.
 */
void snd_ctl_free_one(struct snd_kcontrol *kcontrol)
{
	if (kcontrol) {
		if (kcontrol->private_free)
			kcontrol->private_free(kcontrol);
		kfree(kcontrol);
	}
}
EXPORT_SYMBOL(snd_ctl_free_one);

static bool snd_ctl_remove_numid_conflict(struct snd_card *card,
					  unsigned int count)
{
	struct snd_kcontrol *kctl;

	/* Make sure that the ids assigned to the control do not wrap around */
	if (card->last_numid >= UINT_MAX - count)
		card->last_numid = 0;

	list_for_each_entry(kctl, &card->controls, list) {
		if (kctl->id.numid < card->last_numid + 1 + count &&
		    kctl->id.numid + kctl->count > card->last_numid + 1) {
		    	card->last_numid = kctl->id.numid + kctl->count - 1;
			return true;
		}
	}
	return false;
}

static int snd_ctl_find_hole(struct snd_card *card, unsigned int count)
{
	unsigned int iter = 100000;

	while (snd_ctl_remove_numid_conflict(card, count)) {
		if (--iter == 0) {
			/* this situation is very unlikely */
			dev_err(card->dev, "unable to allocate new control numid\n");
			return -ENOMEM;
		}
	}
	return 0;
}

/* check whether the given id is contained in the given kctl */
static bool elem_id_matches(const struct snd_kcontrol *kctl,
			    const struct snd_ctl_elem_id *id)
{
	return kctl->id.iface == id->iface &&
		kctl->id.device == id->device &&
		kctl->id.subdevice == id->subdevice &&
		!strncmp(kctl->id.name, id->name, sizeof(kctl->id.name)) &&
		kctl->id.index <= id->index &&
		kctl->id.index + kctl->count > id->index;
}

#ifdef CONFIG_SND_CTL_FAST_LOOKUP
/* Compute a hash key for the corresponding ctl id
 * It's for the name lookup, hence the numid is excluded.
 * The hash key is bound in LONG_MAX to be used for Xarray key.
 */
#define MULTIPLIER	37
static unsigned long get_ctl_id_hash(const struct snd_ctl_elem_id *id)
{
	int i;
	unsigned long h;

	h = id->iface;
	h = MULTIPLIER * h + id->device;
	h = MULTIPLIER * h + id->subdevice;
	for (i = 0; i < SNDRV_CTL_ELEM_ID_NAME_MAXLEN && id->name[i]; i++)
		h = MULTIPLIER * h + id->name[i];
	h = MULTIPLIER * h + id->index;
	h &= LONG_MAX;
	return h;
}

/* add hash entries to numid and ctl xarray tables */
static void add_hash_entries(struct snd_card *card,
			     struct snd_kcontrol *kcontrol)
{
	struct snd_ctl_elem_id id = kcontrol->id;
	int i;

	xa_store_range(&card->ctl_numids, kcontrol->id.numid,
		       kcontrol->id.numid + kcontrol->count - 1,
		       kcontrol, GFP_KERNEL);

	for (i = 0; i < kcontrol->count; i++) {
		id.index = kcontrol->id.index + i;
		if (xa_insert(&card->ctl_hash, get_ctl_id_hash(&id),
			      kcontrol, GFP_KERNEL)) {
			/* skip hash for this entry, noting we had collision */
			card->ctl_hash_collision = true;
			dev_dbg(card->dev, "ctl_hash collision %d:%s:%d\n",
				id.iface, id.name, id.index);
		}
	}
}

/* remove hash entries that have been added */
static void remove_hash_entries(struct snd_card *card,
				struct snd_kcontrol *kcontrol)
{
	struct snd_ctl_elem_id id = kcontrol->id;
	struct snd_kcontrol *matched;
	unsigned long h;
	int i;

	for (i = 0; i < kcontrol->count; i++) {
		xa_erase(&card->ctl_numids, id.numid);
		h = get_ctl_id_hash(&id);
		matched = xa_load(&card->ctl_hash, h);
		if (matched && (matched == kcontrol ||
				elem_id_matches(matched, &id)))
			xa_erase(&card->ctl_hash, h);
		id.index++;
		id.numid++;
	}
}
#else /* CONFIG_SND_CTL_FAST_LOOKUP */
static inline void add_hash_entries(struct snd_card *card,
				    struct snd_kcontrol *kcontrol)
{
}
static inline void remove_hash_entries(struct snd_card *card,
				       struct snd_kcontrol *kcontrol)
{
}
#endif /* CONFIG_SND_CTL_FAST_LOOKUP */

enum snd_ctl_add_mode {
	CTL_ADD_EXCLUSIVE, CTL_REPLACE, CTL_ADD_ON_REPLACE,
};

/* add/replace a new kcontrol object; call with card->controls_rwsem locked */
static int __snd_ctl_add_replace(struct snd_card *card,
				 struct snd_kcontrol *kcontrol,
				 enum snd_ctl_add_mode mode)
{
	struct snd_ctl_elem_id id;
	unsigned int idx;
	struct snd_kcontrol *old;
	int err;

	lockdep_assert_held_write(&card->controls_rwsem);

	id = kcontrol->id;
	if (id.index > UINT_MAX - kcontrol->count)
		return -EINVAL;

	old = snd_ctl_find_id(card, &id);
	if (!old) {
		if (mode == CTL_REPLACE)
			return -EINVAL;
	} else {
		if (mode == CTL_ADD_EXCLUSIVE) {
			dev_err(card->dev,
				"control %i:%i:%i:%s:%i is already present\n",
				id.iface, id.device, id.subdevice, id.name,
				id.index);
			return -EBUSY;
		}

		err = snd_ctl_remove_locked(card, old);
		if (err < 0)
			return err;
	}

	if (snd_ctl_find_hole(card, kcontrol->count) < 0)
		return -ENOMEM;

	scoped_guard(write_lock_irq, &card->controls_rwlock) {
		list_add_tail(&kcontrol->list, &card->controls);
		card->controls_count += kcontrol->count;
		kcontrol->id.numid = card->last_numid + 1;
		card->last_numid += kcontrol->count;
	}

	add_hash_entries(card, kcontrol);

	for (idx = 0; idx < kcontrol->count; idx++)
		snd_ctl_notify_one(card, SNDRV_CTL_EVENT_MASK_ADD, kcontrol, idx);

	return 0;
}

static int snd_ctl_add_replace(struct snd_card *card,
			       struct snd_kcontrol *kcontrol,
			       enum snd_ctl_add_mode mode)
{
	int err = -EINVAL;

	if (! kcontrol)
		return err;
	if (snd_BUG_ON(!card || !kcontrol->info))
		goto error;

	scoped_guard(rwsem_write, &card->controls_rwsem)
		err = __snd_ctl_add_replace(card, kcontrol, mode);

	if (err < 0)
		goto error;
	return 0;

 error:
	snd_ctl_free_one(kcontrol);
	return err;
}

/**
 * snd_ctl_add - add the control instance to the card
 * @card: the card instance
 * @kcontrol: the control instance to add
 *
 * Adds the control instance created via snd_ctl_new() or
 * snd_ctl_new1() to the given card. Assigns also an unique
 * numid used for fast search.
 *
 * It frees automatically the control which cannot be added.
 *
 * Return: Zero if successful, or a negative error code on failure.
 *
 */
int snd_ctl_add(struct snd_card *card, struct snd_kcontrol *kcontrol)
{
	return snd_ctl_add_replace(card, kcontrol, CTL_ADD_EXCLUSIVE);
}
EXPORT_SYMBOL(snd_ctl_add);

/**
 * snd_ctl_replace - replace the control instance of the card
 * @card: the card instance
 * @kcontrol: the control instance to replace
 * @add_on_replace: add the control if not already added
 *
 * Replaces the given control.  If the given control does not exist
 * and the add_on_replace flag is set, the control is added.  If the
 * control exists, it is destroyed first.
 *
 * It frees automatically the control which cannot be added or replaced.
 *
 * Return: Zero if successful, or a negative error code on failure.
 */
int snd_ctl_replace(struct snd_card *card, struct snd_kcontrol *kcontrol,
		    bool add_on_replace)
{
	return snd_ctl_add_replace(card, kcontrol,
				   add_on_replace ? CTL_ADD_ON_REPLACE : CTL_REPLACE);
}
EXPORT_SYMBOL(snd_ctl_replace);

static int __snd_ctl_remove(struct snd_card *card,
			    struct snd_kcontrol *kcontrol,
			    bool remove_hash)
{
	unsigned int idx;

	lockdep_assert_held_write(&card->controls_rwsem);

	if (snd_BUG_ON(!card || !kcontrol))
		return -EINVAL;

	if (remove_hash)
		remove_hash_entries(card, kcontrol);

	scoped_guard(write_lock_irq, &card->controls_rwlock) {
		list_del(&kcontrol->list);
		card->controls_count -= kcontrol->count;
	}

	for (idx = 0; idx < kcontrol->count; idx++)
		snd_ctl_notify_one(card, SNDRV_CTL_EVENT_MASK_REMOVE, kcontrol, idx);
	snd_ctl_free_one(kcontrol);
	return 0;
}

static inline int snd_ctl_remove_locked(struct snd_card *card,
					struct snd_kcontrol *kcontrol)
{
	return __snd_ctl_remove(card, kcontrol, true);
}

/**
 * snd_ctl_remove - remove the control from the card and release it
 * @card: the card instance
 * @kcontrol: the control instance to remove
 *
 * Removes the control from the card and then releases the instance.
 * You don't need to call snd_ctl_free_one().
 * Passing NULL to @kcontrol argument is allowed as noop.
 *
 * Return: 0 if successful, or a negative error code on failure.
 *
 * Note that this function takes card->controls_rwsem lock internally.
 */
int snd_ctl_remove(struct snd_card *card, struct snd_kcontrol *kcontrol)
{
	if (!kcontrol)
		return 0;
	guard(rwsem_write)(&card->controls_rwsem);
	return snd_ctl_remove_locked(card, kcontrol);
}
EXPORT_SYMBOL(snd_ctl_remove);

/**
 * snd_ctl_remove_id - remove the control of the given id and release it
 * @card: the card instance
 * @id: the control id to remove
 *
 * Finds the control instance with the given id, removes it from the
 * card list and releases it.
 *
 * Return: 0 if successful, or a negative error code on failure.
 */
int snd_ctl_remove_id(struct snd_card *card, struct snd_ctl_elem_id *id)
{
	struct snd_kcontrol *kctl;

	guard(rwsem_write)(&card->controls_rwsem);
	kctl = snd_ctl_find_id(card, id);
	if (kctl == NULL)
		return -ENOENT;
	return snd_ctl_remove_locked(card, kctl);
}
EXPORT_SYMBOL(snd_ctl_remove_id);

/**
 * snd_ctl_remove_user_ctl - remove and release the unlocked user control
 * @file: active control handle
 * @id: the control id to remove
 *
 * Finds the control instance with the given id, removes it from the
 * card list and releases it.
 *
 * Return: 0 if successful, or a negative error code on failure.
 */
static int snd_ctl_remove_user_ctl(struct snd_ctl_file * file,
				   struct snd_ctl_elem_id *id)
{
	struct snd_card *card = file->card;
	struct snd_kcontrol *kctl;
	int idx;

	guard(rwsem_write)(&card->controls_rwsem);
	kctl = snd_ctl_find_id(card, id);
	if (kctl == NULL)
		return -ENOENT;
	if (!(kctl->vd[0].access & SNDRV_CTL_ELEM_ACCESS_USER))
		return -EINVAL;
	for (idx = 0; idx < kctl->count; idx++)
		if (kctl->vd[idx].owner != NULL && kctl->vd[idx].owner != file)
			return -EBUSY;
	return snd_ctl_remove_locked(card, kctl);
}

/**
 * snd_ctl_activate_id - activate/inactivate the control of the given id
 * @card: the card instance
 * @id: the control id to activate/inactivate
 * @active: non-zero to activate
 *
 * Finds the control instance with the given id, and activate or
 * inactivate the control together with notification, if changed.
 * The given ID data is filled with full information.
 *
 * Return: 0 if unchanged, 1 if changed, or a negative error code on failure.
 */
int snd_ctl_activate_id(struct snd_card *card, struct snd_ctl_elem_id *id,
			int active)
{
	struct snd_kcontrol *kctl;
	struct snd_kcontrol_volatile *vd;
	unsigned int index_offset;
	int ret;

	down_write(&card->controls_rwsem);
	kctl = snd_ctl_find_id(card, id);
	if (kctl == NULL) {
		ret = -ENOENT;
		goto unlock;
	}
	index_offset = snd_ctl_get_ioff(kctl, id);
	vd = &kctl->vd[index_offset];
	ret = 0;
	if (active) {
		if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_INACTIVE))
			goto unlock;
		vd->access &= ~SNDRV_CTL_ELEM_ACCESS_INACTIVE;
	} else {
		if (vd->access & SNDRV_CTL_ELEM_ACCESS_INACTIVE)
			goto unlock;
		vd->access |= SNDRV_CTL_ELEM_ACCESS_INACTIVE;
	}
	snd_ctl_build_ioff(id, kctl, index_offset);
	downgrade_write(&card->controls_rwsem);
	snd_ctl_notify_one(card, SNDRV_CTL_EVENT_MASK_INFO, kctl, index_offset);
	up_read(&card->controls_rwsem);
	return 1;

 unlock:
	up_write(&card->controls_rwsem);
	return ret;
}
EXPORT_SYMBOL_GPL(snd_ctl_activate_id);

/**
 * snd_ctl_rename_id - replace the id of a control on the card
 * @card: the card instance
 * @src_id: the old id
 * @dst_id: the new id
 *
 * Finds the control with the old id from the card, and replaces the
 * id with the new one.
 *
 * The function tries to keep the already assigned numid while replacing
 * the rest.
 *
 * Note that this function should be used only in the card initialization
 * phase.  Calling after the card instantiation may cause issues with
 * user-space expecting persistent numids.
 *
 * Return: Zero if successful, or a negative error code on failure.
 */
int snd_ctl_rename_id(struct snd_card *card, struct snd_ctl_elem_id *src_id,
		      struct snd_ctl_elem_id *dst_id)
{
	struct snd_kcontrol *kctl;
	int saved_numid;

	guard(rwsem_write)(&card->controls_rwsem);
	kctl = snd_ctl_find_id(card, src_id);
	if (kctl == NULL)
		return -ENOENT;
	saved_numid = kctl->id.numid;
	remove_hash_entries(card, kctl);
	kctl->id = *dst_id;
	kctl->id.numid = saved_numid;
	add_hash_entries(card, kctl);
	return 0;
}
EXPORT_SYMBOL(snd_ctl_rename_id);

/**
 * snd_ctl_rename - rename the control on the card
 * @card: the card instance
 * @kctl: the control to rename
 * @name: the new name
 *
 * Renames the specified control on the card to the new name.
 *
 * Note that this function takes card->controls_rwsem lock internally.
 */
void snd_ctl_rename(struct snd_card *card, struct snd_kcontrol *kctl,
		    const char *name)
{
	guard(rwsem_write)(&card->controls_rwsem);
	remove_hash_entries(card, kctl);

	if (strscpy(kctl->id.name, name, sizeof(kctl->id.name)) < 0)
		pr_warn("ALSA: Renamed control new name '%s' truncated to '%s'\n",
			name, kctl->id.name);

	add_hash_entries(card, kctl);
}
EXPORT_SYMBOL(snd_ctl_rename);

#ifndef CONFIG_SND_CTL_FAST_LOOKUP
static struct snd_kcontrol *
snd_ctl_find_numid_slow(struct snd_card *card, unsigned int numid)
{
	struct snd_kcontrol *kctl;

	guard(read_lock_irqsave)(&card->controls_rwlock);
	list_for_each_entry(kctl, &card->controls, list) {
		if (kctl->id.numid <= numid && kctl->id.numid + kctl->count > numid)
			return kctl;
	}
	return NULL;
}
#endif /* !CONFIG_SND_CTL_FAST_LOOKUP */

/**
 * snd_ctl_find_numid - find the control instance with the given number-id
 * @card: the card instance
 * @numid: the number-id to search
 *
 * Finds the control instance with the given number-id from the card.
 *
 * Return: The pointer of the instance if found, or %NULL if not.
 *
 * Note that this function takes card->controls_rwlock lock internally.
 */
struct snd_kcontrol *snd_ctl_find_numid(struct snd_card *card,
					unsigned int numid)
{
	if (snd_BUG_ON(!card || !numid))
		return NULL;

#ifdef CONFIG_SND_CTL_FAST_LOOKUP
	return xa_load(&card->ctl_numids, numid);
#else
	return snd_ctl_find_numid_slow(card, numid);
#endif
}
EXPORT_SYMBOL(snd_ctl_find_numid);

/**
 * snd_ctl_find_id - find the control instance with the given id
 * @card: the card instance
 * @id: the id to search
 *
 * Finds the control instance with the given id from the card.
 *
 * Return: The pointer of the instance if found, or %NULL if not.
 *
 * Note that this function takes card->controls_rwlock lock internally.
 */
struct snd_kcontrol *snd_ctl_find_id(struct snd_card *card,
				     const struct snd_ctl_elem_id *id)
{
	struct snd_kcontrol *kctl;

	if (snd_BUG_ON(!card || !id))
		return NULL;

	if (id->numid != 0)
		return snd_ctl_find_numid(card, id->numid);
#ifdef CONFIG_SND_CTL_FAST_LOOKUP
	kctl = xa_load(&card->ctl_hash, get_ctl_id_hash(id));
	if (kctl && elem_id_matches(kctl, id))
		return kctl;
	if (!card->ctl_hash_collision)
		return NULL; /* we can rely on only hash table */
#endif
	/* no matching in hash table - try all as the last resort */
	guard(read_lock_irqsave)(&card->controls_rwlock);
	list_for_each_entry(kctl, &card->controls, list)
		if (elem_id_matches(kctl, id))
			return kctl;

	return NULL;
}
EXPORT_SYMBOL(snd_ctl_find_id);

static int snd_ctl_card_info(struct snd_card *card, struct snd_ctl_file * ctl,
			     unsigned int cmd, void __user *arg)
{
	struct snd_ctl_card_info *info __free(kfree) =
		kzalloc_obj(*info);
	ssize_t n;

	if (! info)
		return -ENOMEM;

	static_assert(sizeof(info->components) >= 2);

	scoped_guard(rwsem_read, &snd_ioctl_rwsem) {
		const char *components = card->components;

		if (!components)
			components = "";

		info->card = card->number;
		strscpy(info->id, card->id, sizeof(info->id));
		strscpy(info->driver, card->driver, sizeof(info->driver));
		strscpy(info->name, card->shortname, sizeof(info->name));
		strscpy(info->longname, card->longname, sizeof(info->longname));
		strscpy(info->mixername, card->mixername, sizeof(info->mixername));
		n = strscpy(info->components, components, sizeof(info->components));
		if (n < 0) // mark the truncation with '>' before NULL terminator
			info->components[sizeof(info->components) - 2] = '>';
	}
	if (copy_to_user(arg, info, sizeof(struct snd_ctl_card_info)))
		return -EFAULT;
	return 0;
}

static int snd_ctl_card_bytes(struct snd_card *card,
			      struct snd_ctl_card_bytes *info,
			      unsigned int __user *data_len_out)
{
	unsigned int data_len;

	switch (info->type) {
	case SND_CTL_CARD_BTYPE_COMPONENTS:
		scoped_guard(rwsem_read, &snd_ioctl_rwsem) {
			const char *components = card->components;

			if (!components)
				components = "";

			data_len = strlen(components) + 1;

			if (!info->data || info->data_allocated == 0)
				break;

			if (info->data_allocated < data_len)
				return -ENOMEM;

			if (copy_to_user(u64_to_user_ptr(info->data), components, data_len))
				return -EFAULT;
		}
		break;
	default:
		return -EINVAL;
	}

	if (put_user(data_len, data_len_out))
		return -EFAULT;

	return 0;
}

static int snd_ctl_card_bytes_user(struct snd_card *card,
				   struct snd_ctl_card_bytes __user *_info)
{
	struct snd_ctl_card_bytes info;

	if (copy_from_user(&info, _info, sizeof(info)))
		return -EFAULT;

	return snd_ctl_card_bytes(card, &info, &_info->data_len);
}

static int snd_ctl_elem_list(struct snd_card *card,
			     struct snd_ctl_elem_list *list)
{
	struct snd_kcontrol *kctl;
	struct snd_ctl_elem_id id;
	unsigned int offset, space, jidx;

	offset = list->offset;
	space = list->space;

	guard(rwsem_read)(&card->controls_rwsem);
	list->count = card->controls_count;
	list->used = 0;
	if (!space)
		return 0;
	list_for_each_entry(kctl, &card->controls, list) {
		if (offset >= kctl->count) {
			offset -= kctl->count;
			continue;
		}
		for (jidx = offset; jidx < kctl->count; jidx++) {
			snd_ctl_build_ioff(&id, kctl, jidx);
			if (copy_to_user(list->pids + list->used, &id, sizeof(id)))
				return -EFAULT;
			list->used++;
			if (!--space)
				return 0;
		}
		offset = 0;
	}
	return 0;
}

static int snd_ctl_elem_list_user(struct snd_card *card,
				  struct snd_ctl_elem_list __user *_list)
{
	struct snd_ctl_elem_list list;
	int err;

	if (copy_from_user(&list, _list, sizeof(list)))
		return -EFAULT;
	err = snd_ctl_elem_list(card, &list);
	if (err)
		return err;
	if (copy_to_user(_list, &list, sizeof(list)))
		return -EFAULT;

	return 0;
}

/* Check whether the given kctl info is valid */