/**

 * \file mixer/mixer.c

 * \brief Mixer Interface

 * \author Jaroslav Kysela <perex@perex.cz>

 * \author Abramo Bagnara <abramo@alsa-project.org>

 * \date 2001

 *

 * Mixer interface is designed to access mixer elements.

 * Callbacks may be used for event handling.

 */

/*

 *  Mixer Interface - main file

 *  Copyright (c) 1998/1999/2000 by Jaroslav Kysela <perex@perex.cz>

 *  Copyright (c) 2001 by Abramo Bagnara <abramo@alsa-project.org>

 *

 *

 *   This library is free software; you can redistribute it and/or modify

 *   it under the terms of the GNU Lesser General Public License as

 *   published by the Free Software Foundation; either version 2.1 of

 *   the License, or (at your option) any later version.

 *

 *   This program is distributed in the hope that it will be useful,

 *   but WITHOUT ANY WARRANTY; without even the implied warranty of

 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 *   GNU Lesser General Public License for more details.

 *

 *   You should have received a copy of the GNU Lesser General Public

 *   License along with this library; if not, write to the Free Software

 *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

 *

 */

/*! \page mixer Mixer interface

Mixer interface is designed to access the abstracted mixer controls.

This is an abstraction layer over the hcontrol layer.

\section mixer_general_overview General overview

*/

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <string.h>

#include <fcntl.h>

#include <sys/ioctl.h>

#include "mixer_local.h"

#ifndef DOC_HIDDEN

typedef struct _snd_mixer_slave {

	snd_hctl_t *hctl;

	struct list_head list;

} snd_mixer_slave_t;

#endif

static int snd_mixer_compare_default(const snd_mixer_elem_t *c1,

				     const snd_mixer_elem_t *c2);

/**

 * \brief Opens an empty mixer

 * \param mixerp Returned mixer handle

 * \param mode Open mode

 * \return 0 on success otherwise a negative error code

 */

int snd_mixer_open(snd_mixer_t **mixerp, int mode ATTRIBUTE_UNUSED)

{

	snd_mixer_t *mixer;

	assert(mixerp);

	mixer = calloc(1, sizeof(*mixer));

	if (mixer == NULL)

		return -ENOMEM;

	INIT_LIST_HEAD(&mixer->slaves);

	INIT_LIST_HEAD(&mixer->classes);

	INIT_LIST_HEAD(&mixer->elems);

	mixer->compare = snd_mixer_compare_default;

	*mixerp = mixer;

	return 0;

}

/**

 * \brief Attach an HCTL element to a mixer element

 * \param melem Mixer element

 * \param helem HCTL element

 * \return 0 on success otherwise a negative error code

 *

 * For use by mixer element class specific code.

 */

int snd_mixer_elem_attach(snd_mixer_elem_t *melem,

			  snd_hctl_elem_t *helem)

{

	bag_t *bag = snd_hctl_elem_get_callback_private(helem);

	int err;

	err = bag_add(bag, melem);

	if (err < 0)

		return err;

	return bag_add(&melem->helems, helem);

}

/**

 * \brief Detach an HCTL element from a mixer element

 * \param melem Mixer element

 * \param helem HCTL element

 * \return 0 on success otherwise a negative error code

 *

 * For use by mixer element class specific code.

 */

int snd_mixer_elem_detach(snd_mixer_elem_t *melem,

			  snd_hctl_elem_t *helem)

{

	bag_t *bag = snd_hctl_elem_get_callback_private(helem);

	int err;

	err = bag_del(bag, melem);

	assert(err >= 0);

	err = bag_del(&melem->helems, helem);

	assert(err >= 0);

	return 0;

}

/**

 * \brief Return true if a mixer element does not contain any HCTL elements

 * \param melem Mixer element

 * \return 0 if not empty, 1 if empty

 *

 * For use by mixer element class specific code.

 */

int snd_mixer_elem_empty(snd_mixer_elem_t *melem)

{

	return bag_empty(&melem->helems);

}

static int hctl_elem_event_handler(snd_hctl_elem_t *helem,

				   unsigned int mask)

{

	bag_t *bag = snd_hctl_elem_get_callback_private(helem);

	if (mask == SND_CTL_EVENT_MASK_REMOVE) {

		int res = 0;

		int err;

		bag_iterator_t i, n;

		bag_for_each_safe(i, n, bag) {

			snd_mixer_elem_t *melem = bag_iterator_entry(i);

			snd_mixer_class_t *class = melem->class;

			err = class->event(class, mask, helem, melem);

			if (err < 0)

				res = err;

		}

		assert(bag_empty(bag));

		bag_free(bag);

		return res;

	}

	if (mask & (SND_CTL_EVENT_MASK_VALUE | SND_CTL_EVENT_MASK_INFO)) {

		int err = 0;

		bag_iterator_t i, n;

		bag_for_each_safe(i, n, bag) {

			snd_mixer_elem_t *melem = bag_iterator_entry(i);

			snd_mixer_class_t *class = melem->class;

			err = class->event(class, mask, helem, melem);

			if (err < 0)

				return err;

		}

	}

	return 0;

}

static int hctl_event_handler(snd_hctl_t *hctl, unsigned int mask,

			      snd_hctl_elem_t *elem)

{

	snd_mixer_t *mixer = snd_hctl_get_callback_private(hctl);

	int res = 0;

	if (mask & SND_CTL_EVENT_MASK_ADD) {

		struct list_head *pos;

		bag_t *bag;

		int err = bag_new(&bag;;

		if (err < 0)

			return err;

		snd_hctl_elem_set_callback(elem, hctl_elem_event_handler);

		snd_hctl_elem_set_callback_private(elem, bag);

		list_for_each(pos, &mixer->classes) {

			snd_mixer_class_t *c;

			c = list_entry(pos, snd_mixer_class_t, list);

			err = c->event(c, mask, elem, NULL);

			if (err < 0)

				res = err;

		}

	}

	return res;

}

/**

 * \brief Attach an HCTL specified with the CTL device name to an opened mixer

 * \param mixer Mixer handle

 * \param name HCTL name (see #snd_hctl_open)

 * \return 0 on success otherwise a negative error code

 */

int snd_mixer_attach(snd_mixer_t *mixer, const char *name)

{

	snd_hctl_t *hctl;

	int err;

	err = snd_hctl_open(&hctl, name, 0);

	if (err < 0)

		return err;

	err = snd_mixer_attach_hctl(mixer, hctl);

	if (err < 0)

		return err;

	return 0;

}

/**

 * \brief Attach an HCTL to an opened mixer

 * \param mixer Mixer handle

 * \param hctl the HCTL to be attached

 * \return 0 on success otherwise a negative error code

 *

 * Upon error, this function closes the given hctl handle automatically.

 */

int snd_mixer_attach_hctl(snd_mixer_t *mixer, snd_hctl_t *hctl)

{

	snd_mixer_slave_t *slave;

	int err;

	assert(hctl);

	slave = calloc(1, sizeof(*slave));

	if (slave == NULL) {

		snd_hctl_close(hctl);

		return -ENOMEM;

	}

	err = snd_hctl_nonblock(hctl, 1);

	if (err < 0) {

		snd_hctl_close(hctl);

		free(slave);

		return err;

	}

	snd_hctl_set_callback(hctl, hctl_event_handler);

	snd_hctl_set_callback_private(hctl, mixer);

	slave->hctl = hctl;

	list_add_tail(&slave->list, &mixer->slaves);

	return 0;

}

/**

 * \brief Detach a previously attached HCTL to an opened mixer freeing all related resources

 * \param mixer Mixer handle

 * \param name HCTL previously attached

 * \return 0 on success otherwise a negative error code

 */

int snd_mixer_detach(snd_mixer_t *mixer, const char *name)

{

	struct list_head *pos;

	list_for_each(pos, &mixer->slaves) {

		snd_mixer_slave_t *s;

		s = list_entry(pos, snd_mixer_slave_t, list);

		if (strcmp(name, snd_hctl_name(s->hctl)) == 0) {

			snd_hctl_close(s->hctl);

			list_del(pos);

			free(s);

			return 0;

		}

	}

	return -ENOENT;

}

/**

 * \brief Detach a previously attached HCTL to an opened mixer freeing all related resources

 * \param mixer Mixer handle

 * \param hctl HCTL previously attached

 * \return 0 on success otherwise a negative error code

 *

 * Note: The hctl handle is not closed!

 */

int snd_mixer_detach_hctl(snd_mixer_t *mixer, snd_hctl_t *hctl)

{

	struct list_head *pos;

	list_for_each(pos, &mixer->slaves) {

		snd_mixer_slave_t *s;

		s = list_entry(pos, snd_mixer_slave_t, list);

		if (hctl == s->hctl) {

			list_del(pos);

			free(s);

			return 0;

		}

	}

	return -ENOENT;

}

/**

 * \brief Obtain a HCTL pointer associated to given name

 * \param mixer Mixer handle

 * \param name HCTL previously attached

 * \param hctl HCTL pointer

 * \return 0 on success otherwise a negative error code

 */

int snd_mixer_get_hctl(snd_mixer_t *mixer, const char *name, snd_hctl_t **hctl)

{

	struct list_head *pos;

	list_for_each(pos, &mixer->slaves) {

		snd_mixer_slave_t *s;

		s = list_entry(pos, snd_mixer_slave_t, list);

		if (strcmp(name, snd_hctl_name(s->hctl)) == 0) {

			*hctl = s->hctl;

			return 0;

		}

	}

	return -ENOENT;

}

static int snd_mixer_throw_event(snd_mixer_t *mixer, unsigned int mask,

			  snd_mixer_elem_t *elem)

{

	mixer->events++;

	if (mixer->callback)

		return mixer->callback(mixer, mask, elem);

	return 0;

}

static int snd_mixer_elem_throw_event(snd_mixer_elem_t *elem, unsigned int mask)

{

	elem->class->mixer->events++;

	if (elem->callback)

		return elem->callback(elem, mask);

	return 0;

}

static int _snd_mixer_find_elem(snd_mixer_t *mixer, snd_mixer_elem_t *elem, int *dir)

{

	unsigned int l, u;

	int c = 0;

	int idx = -1;

	assert(mixer && elem);

	assert(mixer->compare);

	l = 0;

	u = mixer->count;

	while (l < u) {

		idx = (l + u) / 2;

		c = mixer->compare(elem, mixer->pelems[idx]);

		if (c < 0)

			u = idx;

		else if (c > 0)

			l = idx + 1;

		else

			break;

	}

	*dir = c;

	return idx;

}

/**

 * \brief Get private data associated to give mixer element

 * \param elem Mixer element

 * \return private data

 *

 * For use by mixer element class specific code.

 */

void *snd_mixer_elem_get_private(const snd_mixer_elem_t *elem)

{

	return elem->private_data;

}

/**

 * \brief Allocate a new mixer element

 * \param elem Returned mixer element

 * \param type Mixer element type

 * \param compare_weight Mixer element compare weight

 * \param private_data Private data

 * \param private_free Private data free callback

 * \return 0 on success otherwise a negative error code

 *

 * For use by mixer element class specific code.

 */

int snd_mixer_elem_new(snd_mixer_elem_t **elem,

		       snd_mixer_elem_type_t type,

		       int compare_weight,

		       void *private_data,

		       void (*private_free)(snd_mixer_elem_t *elem))

{

	snd_mixer_elem_t *melem = calloc(1, sizeof(*melem));

	if (melem == NULL)

		return -ENOMEM;

	melem->type = type;

	melem->compare_weight = compare_weight;

	melem->private_data = private_data;

	melem->private_free = private_free;

	INIT_LIST_HEAD(&melem->helems);

	*elem = melem;

	return 0;

}

/**

 * \brief Add an element for a registered mixer element class

 * \param elem Mixer element

 * \param class Mixer element class

 * \return 0 on success otherwise a negative error code

 *

 * For use by mixer element class specific code.

 */

int snd_mixer_elem_add(snd_mixer_elem_t *elem, snd_mixer_class_t *class)

{

	int dir, idx;

	snd_mixer_t *mixer = class->mixer;

	elem->class = class;

	if (mixer->count == mixer->alloc) {

		snd_mixer_elem_t **m;

		mixer->alloc += 32;

		m = realloc(mixer->pelems, sizeof(*m) * mixer->alloc);

		if (!m) {

			mixer->alloc -= 32;

			return -ENOMEM;

		}

		mixer->pelems = m;

	}

	if (mixer->count == 0) {

		list_add_tail(&elem->list, &mixer->elems);

		mixer->pelems[0] = elem;

	} else {

		idx = _snd_mixer_find_elem(mixer, elem, &dir;;

		assert(dir != 0);

		if (dir > 0) {

			list_add(&elem->list, &mixer->pelems[idx]->list);

			idx++;

		} else {

			list_add_tail(&elem->list, &mixer->pelems[idx]->list);

		}

		memmove(mixer->pelems + idx + 1,

			mixer->pelems + idx,

			(mixer->count - idx) * sizeof(snd_mixer_elem_t *));

		mixer->pelems[idx] = elem;

	}

	mixer->count++;

	return snd_mixer_throw_event(mixer, SND_CTL_EVENT_MASK_ADD, elem);

}

/**

 * \brief Remove a mixer element

 * \param elem Mixer element

 * \return 0 on success otherwise a negative error code

 *

 * For use by mixer element class specific code.

 */

int snd_mixer_elem_remove(snd_mixer_elem_t *elem)

{

	snd_mixer_t *mixer = elem->class->mixer;

	bag_iterator_t i, n;

	int err, idx, dir;

	unsigned int m;

	assert(elem);

	assert(mixer->count);

	idx = _snd_mixer_find_elem(mixer, elem, &dir;;

	if (dir != 0)

		return -EINVAL;

	bag_for_each_safe(i, n, &elem->helems) {

		snd_hctl_elem_t *helem = bag_iterator_entry(i);

		snd_mixer_elem_detach(elem, helem);

	}

	err = snd_mixer_elem_throw_event(elem, SND_CTL_EVENT_MASK_REMOVE);

	list_del(&elem->list);

	snd_mixer_elem_free(elem);

	mixer->count--;

	m = mixer->count - idx;

	if (m > 0)

		memmove(mixer->pelems + idx,

			mixer->pelems + idx + 1,

			m * sizeof(snd_mixer_elem_t *));

	return err;

}

/**

 * \brief Free a mixer element

 * \param elem Mixer element

 * \return 0 on success otherwise a negative error code

 *

 * For use by mixer element class specific code.

 */

void snd_mixer_elem_free(snd_mixer_elem_t *elem)

{

	if (elem->private_free)

		elem->private_free(elem);

	free(elem);

}

/**

 * \brief Mixer element informations are changed

 * \param elem Mixer element

 * \return 0 on success otherwise a negative error code

 *

 * For use by mixer element class specific code.

 */

int snd_mixer_elem_info(snd_mixer_elem_t *elem)

{

	return snd_mixer_elem_throw_event(elem, SND_CTL_EVENT_MASK_INFO);

}

/**

 * \brief Mixer element values is changed

 * \param elem Mixer element

 * \return 0 on success otherwise a negative error code

 *

 * For use by mixer element class specific code.

 */

int snd_mixer_elem_value(snd_mixer_elem_t *elem)

{

	return snd_mixer_elem_throw_event(elem, SND_CTL_EVENT_MASK_VALUE);

}

/**

 * \brief Register mixer element class

 * \param class Mixer element class

 * \param mixer Mixer handle

 * \return 0 on success otherwise a negative error code

 *

 * For use by mixer element class specific code.

 */

int snd_mixer_class_register(snd_mixer_class_t *class, snd_mixer_t *mixer)

{

	struct list_head *pos;

	class->mixer = mixer;

	list_add_tail(&class->list, &mixer->classes);

	if (!class->event)

		return 0;

	list_for_each(pos, &mixer->slaves) {

		int err;

		snd_mixer_slave_t *slave;

		snd_hctl_elem_t *elem;

		slave = list_entry(pos, snd_mixer_slave_t, list);

		elem = snd_hctl_first_elem(slave->hctl);

		while (elem) {

			err = class->event(class, SND_CTL_EVENT_MASK_ADD, elem, NULL);

			if (err < 0)

				return err;

			elem = snd_hctl_elem_next(elem);

		}

	}

	return 0;

}

/**

 * \brief Unregister mixer element class and remove all its elements

 * \param class Mixer element class

 * \return 0 on success otherwise a negative error code

 *

 * Note that the class structure is also deallocated!

 */

int snd_mixer_class_unregister(snd_mixer_class_t *class)

{

	unsigned int k;

	snd_mixer_elem_t *e;

	snd_mixer_t *mixer = class->mixer;

	for (k = mixer->count; k > 0; k--) {

		e = mixer->pelems[k-1];

		if (e->class == class)

			snd_mixer_elem_remove(e);

	}

	if (class->private_free)

		class->private_free(class);

	list_del(&class->list);

	free(class);

	return 0;

}

/**

 * \brief Load a mixer elements

 * \param mixer Mixer handle

 * \return 0 on success otherwise a negative error code

 */

int snd_mixer_load(snd_mixer_t *mixer)

{

	struct list_head *pos;

	list_for_each(pos, &mixer->slaves) {

		int err;

		snd_mixer_slave_t *s;

		s = list_entry(pos, snd_mixer_slave_t, list);

		err = snd_hctl_load(s->hctl);

		if (err < 0)

			return err;

	}

	return 0;

}

/**

 * \brief Unload all mixer elements and free all related resources

 * \param mixer Mixer handle

 */

void snd_mixer_free(snd_mixer_t *mixer)

{

	struct list_head *pos;

	list_for_each(pos, &mixer->slaves) {

		snd_mixer_slave_t *s;

		s = list_entry(pos, snd_mixer_slave_t, list);

		snd_hctl_free(s->hctl);

	}

}

/**

 * \brief Close a mixer and free all related resources

 * \param mixer Mixer handle

 * \return 0 on success otherwise a negative error code

 */

int snd_mixer_close(snd_mixer_t *mixer)

{

	int res = 0;

	assert(mixer);

	while (!list_empty(&mixer->classes)) {

		snd_mixer_class_t *c;

		c = list_entry(mixer->classes.next, snd_mixer_class_t, list);

		snd_mixer_class_unregister(c);

	}

	assert(list_empty(&mixer->elems));

	assert(mixer->count == 0);

	free(mixer->pelems);

	mixer->pelems = NULL;

	while (!list_empty(&mixer->slaves)) {

		int err;

		snd_mixer_slave_t *s;

		s = list_entry(mixer->slaves.next, snd_mixer_slave_t, list);

		err = snd_hctl_close(s->hctl);

		if (err < 0)

			res = err;

		list_del(&s->list);

		free(s);

	}

	free(mixer);

	return res;

}

static int snd_mixer_compare_default(const snd_mixer_elem_t *c1,

				     const snd_mixer_elem_t *c2)

{

	int d = c1->compare_weight - c2->compare_weight;

	if (d)

		return d;

	assert(c1->class && c1->class->compare);

	assert(c2->class && c2->class->compare);

	assert(c1->class == c2->class);

	return c1->class->compare(c1, c2);

}

static int mixer_compare(const void *a, const void *b)

{

	snd_mixer_t *mixer;

	mixer = (*((const snd_mixer_elem_t * const *)a))->class->mixer;

	return mixer->compare(*(const snd_mixer_elem_t * const *)a, *(const snd_mixer_elem_t * const *)b);

}

static int snd_mixer_sort(snd_mixer_t *mixer)

{

	unsigned int k;

	assert(mixer);

	assert(mixer->compare);

	INIT_LIST_HEAD(&mixer->elems);

	qsort(mixer->pelems, mixer->count, sizeof(snd_mixer_elem_t *), mixer_compare);

	for (k = 0; k < mixer->count; k++)

		list_add_tail(&mixer->pelems[k]->list, &mixer->elems);

	return 0;

}

/**

 * \brief Change mixer compare function and reorder elements

 * \param mixer Mixer handle

 * \param compare Element compare function

 * \return 0 on success otherwise a negative error code

 */

int snd_mixer_set_compare(snd_mixer_t *mixer, snd_mixer_compare_t compare)

{

	snd_mixer_compare_t compare_old;

	int err;

	assert(mixer);

	compare_old = mixer->compare;

	mixer->compare = compare == NULL ? snd_mixer_compare_default : compare;

	if ((err = snd_mixer_sort(mixer)) < 0) {

		mixer->compare = compare_old;

		return err;

	}

	return 0;

}

/**

 * \brief get count of poll descriptors for mixer handle

 * \param mixer Mixer handle

 * \return count of poll descriptors

 */

int snd_mixer_poll_descriptors_count(snd_mixer_t *mixer)

{

	struct list_head *pos;

	unsigned int c = 0;

	assert(mixer);

	list_for_each(pos, &mixer->slaves) {

		snd_mixer_slave_t *s;

		int n;

		s = list_entry(pos, snd_mixer_slave_t, list);

		n = snd_hctl_poll_descriptors_count(s->hctl);

		if (n < 0)

			return n;

		c += n;

	}

	return c;

}

/**

 * \brief get poll descriptors

 * \param mixer Mixer handle

 * \param pfds array of poll descriptors

 * \param space space in the poll descriptor array

 * \return count of filled descriptors

 */

int snd_mixer_poll_descriptors(snd_mixer_t *mixer, struct pollfd *pfds, unsigned int space)

{

	struct list_head *pos;

	unsigned int count = 0;

	assert(mixer);

	list_for_each(pos, &mixer->slaves) {

		snd_mixer_slave_t *s;

		int n;

		s = list_entry(pos, snd_mixer_slave_t, list);

		n = snd_hctl_poll_descriptors(s->hctl, pfds, space);

		if (n < 0)

			return n;

		if (space >= (unsigned int) n) {

			count += n;

			space -= n;

			pfds += n;

		} else

			space = 0;

	}

	return count;

}

/**

 * \brief get returned events from poll descriptors

 * \param mixer Mixer handle

 * \param pfds array of poll descriptors

 * \param nfds count of poll descriptors

 * \param revents returned events

 * \return zero if success, otherwise a negative error code

 */

int snd_mixer_poll_descriptors_revents(snd_mixer_t *mixer, struct pollfd *pfds, unsigned int nfds, unsigned short *revents)

{

	unsigned int idx;

	unsigned short res;

        assert(mixer && pfds && revents);

	if (nfds == 0)

		return -EINVAL;

	res = 0;

	for (idx = 0; idx < nfds; idx++, pfds++)

		res |= pfds->revents & (POLLIN|POLLERR|POLLNVAL);

	*revents = res;

	return 0;

}

/**

 * \brief Wait for a mixer to become ready (i.e. at least one event pending)

 * \param mixer Mixer handle

 * \param timeout maximum time in milliseconds to wait

 * \return 0 otherwise a negative error code on failure

 */

int snd_mixer_wait(snd_mixer_t *mixer, int timeout)

{

	struct pollfd spfds[16];

	struct pollfd *pfds = spfds;

	int err;

	int count;

	count = snd_mixer_poll_descriptors(mixer, pfds, sizeof(spfds) / sizeof(spfds[0]));

	if (count < 0)

		return count;

	if ((unsigned int) count > sizeof(spfds) / sizeof(spfds[0])) {

		pfds = malloc(count * sizeof(*pfds));

		if (!pfds)

			return -ENOMEM;

		err = snd_mixer_poll_descriptors(mixer, pfds, 

						 (unsigned int) count);

		assert(err == count);

	}

	err = poll(pfds, (unsigned int) count, timeout);

	if (err < 0)

		return -errno;

	return 0;

}

/**

 * \brief get first element for a mixer

 * \param mixer Mixer handle

 * \return pointer to first element

 */

snd_mixer_elem_t *snd_mixer_first_elem(snd_mixer_t *mixer)

{

	assert(mixer);

	if (list_empty(&mixer->elems))

		return NULL;

	return list_entry(mixer->elems.next, snd_mixer_elem_t, list);

}

/**

 * \brief get last element for a mixer

 * \param mixer Mixer handle

 * \return pointer to last element

 */

snd_mixer_elem_t *snd_mixer_last_elem(snd_mixer_t *mixer)

{

	assert(mixer);

	if (list_empty(&mixer->elems))

		return NULL;

	return list_entry(mixer->elems.prev, snd_mixer_elem_t, list);

}

/**

 * \brief get next mixer element

 * \param elem mixer element

 * \return pointer to next element

 */

snd_mixer_elem_t *snd_mixer_elem_next(snd_mixer_elem_t *elem)

{

	assert(elem);

	if (elem->list.next == &elem->class->mixer->elems)

		return NULL;

	return list_entry(elem->list.next, snd_mixer_elem_t, list);

}

/**

 * \brief get previous mixer element

 * \param elem mixer element

 * \return pointer to previous element

 */

snd_mixer_elem_t *snd_mixer_elem_prev(snd_mixer_elem_t *elem)

{

	assert(elem);

	if (elem->list.prev == &elem->class->mixer->elems)

		return NULL;

	return list_entry(elem->list.prev, snd_mixer_elem_t, list);

}

/**

 * \brief Handle pending mixer events invoking callbacks

 * \param mixer Mixer handle

 * \return Number of events that occured on success, otherwise a negative error code on failure

 */

int snd_mixer_handle_events(snd_mixer_t *mixer)

{

	struct list_head *pos;

	assert(mixer);

	mixer->events = 0;

	list_for_each(pos, &mixer->slaves) {

		int err;

		snd_mixer_slave_t *s;

		s = list_entry(pos, snd_mixer_slave_t, list);

		err = snd_hctl_handle_events(s->hctl);

		if (err < 0)

			return err;

	}

	return mixer->events;

}

/**

 * \brief Set callback function for a mixer

 * \param obj mixer handle

 * \param val callback function

 */

void snd_mixer_set_callback(snd_mixer_t *obj, snd_mixer_callback_t val)

{

	assert(obj);

	obj->callback = val;

}

/**

 * \brief Set callback private value for a mixer

 * \param mixer mixer handle

 * \param val callback private value

 */

void snd_mixer_set_callback_private(snd_mixer_t *mixer, void * val)

{

	assert(mixer);

	mixer->callback_private = val;

}

/**

 * \brief Get callback private value for a mixer