control: ucm: add ioctl to retrieve full card components

The fixed-size components field in SNDRV_CTL_IOCTL_CARD_INFO can be too
small on systems with many audio devices. The kernel [1] will provide a
new ioctl to read the full string while truncating the original in
card_info if it grows too big. Make sure the code falls back to original
if the new ioctl is not supported.

[1]: https://lore.kernel.org/all/20260122111249.67319-1-mstrozek@opensource.cirrus.com/
Signed-off-by: Maciej Strozek <mstrozek@opensource.cirrus.com>

aserver/aserver.c

@@ -647,6 +647,9 @@ static int ctl_shm_cmd(client_t *client)
 	case SNDRV_CTL_IOCTL_CARD_INFO:
 		ctrl->result = snd_ctl_card_info(ctl, &ctrl->u.card_info);
 		break;
+	case SNDRV_CTL_IOCTL_CARD_COMPONENTS:
+		ctrl->result = snd_ctl_card_components(ctl, &ctrl->u.card_components);
+		break;
 	case SNDRV_CTL_IOCTL_ELEM_LIST:
 	{
 		size_t maxsize = CTL_SHM_DATA_MAXLEN;

include/aserver.h

@@ -123,6 +123,7 @@ typedef struct {
 		int device;
 		int subscribe_events;
 		snd_ctl_card_info_t card_info;
+		snd_ctl_card_components_t card_components;
 		snd_ctl_elem_list_t element_list;
 		snd_ctl_elem_info_t element_info;
 		snd_ctl_elem_value_t element_read;

include/control.h

@@ -84,6 +84,11 @@ typedef struct snd_aes_iec958 {
  */
 typedef struct _snd_ctl_card_info snd_ctl_card_info_t;
 
+/**
+ * \brief CTL card components container.
+ */
+typedef struct _snd_ctl_card_components snd_ctl_card_components_t;
+
 /** CTL element identifier container */
 typedef struct _snd_ctl_elem_id snd_ctl_elem_id_t;
 
@@ -394,6 +399,7 @@ int snd_ctl_poll_descriptors(snd_ctl_t *ctl, struct pollfd *pfds, unsigned int s
 int snd_ctl_poll_descriptors_revents(snd_ctl_t *ctl, struct pollfd *pfds, unsigned int nfds, unsigned short *revents);
 int snd_ctl_subscribe_events(snd_ctl_t *ctl, int subscribe);
 int snd_ctl_card_info(snd_ctl_t *ctl, snd_ctl_card_info_t *info);
+int snd_ctl_card_components(snd_ctl_t *ctl, snd_ctl_card_components_t *components);
 int snd_ctl_elem_list(snd_ctl_t *ctl, snd_ctl_elem_list_t *list);
 int snd_ctl_elem_info(snd_ctl_t *ctl, snd_ctl_elem_info_t *info);
 int snd_ctl_elem_read(snd_ctl_t *ctl, snd_ctl_elem_value_t *data);
@@ -508,6 +514,22 @@ const char *snd_ctl_card_info_get_longname(const snd_ctl_card_info_t *obj);
 const char *snd_ctl_card_info_get_mixername(const snd_ctl_card_info_t *obj);
 const char *snd_ctl_card_info_get_components(const snd_ctl_card_info_t *obj);
 
+size_t snd_ctl_card_components_sizeof(void);
+/** \hideinitializer
+ * \brief allocate an invalid #snd_ctl_card_components_t using standard alloca
+ * \param ptr returned pointer
+ */
+#define snd_ctl_card_components_alloca(ptr) __snd_alloca(ptr, snd_ctl_card_components)
+int snd_ctl_card_components_malloc(snd_ctl_card_components_t **ptr);
+void snd_ctl_card_components_free(snd_ctl_card_components_t *obj);
+void snd_ctl_card_components_clear(snd_ctl_card_components_t *obj);
+void snd_ctl_card_components_copy(snd_ctl_card_components_t *dst, const snd_ctl_card_components_t *src);
+int snd_ctl_card_components_get_card(const snd_ctl_card_components_t *obj);
+unsigned int snd_ctl_card_components_get_length(const snd_ctl_card_components_t *obj);
+const char *snd_ctl_card_components_get_string(const snd_ctl_card_components_t *obj);
+
+size_t snd_ctl_elem_list_sizeof(void);
+
 size_t snd_ctl_event_sizeof(void);
 /** \hideinitializer
  * \brief allocate an invalid #snd_ctl_event_t using standard alloca

include/local.h

@@ -102,6 +102,7 @@
 #define _snd_pcm_status snd_pcm_status
 
 #define _snd_ctl_card_info snd_ctl_card_info
+#define _snd_ctl_card_components snd_ctl_card_components
 #define _snd_ctl_elem_id snd_ctl_elem_id
 #define _snd_ctl_elem_list snd_ctl_elem_list
 #define _snd_ctl_elem_info snd_ctl_elem_info

include/mixer_abst.h

@@ -75,6 +75,7 @@ typedef struct _sm_class_basic {
 	snd_ctl_t *ctl;
 	snd_hctl_t *hctl;
 	snd_ctl_card_info_t *info;
+	snd_ctl_card_components_t *card_components;
 } sm_class_basic_t;
 
 struct sm_elem_ops {

include/sound/uapi/asound.h

@@ -1044,7 +1044,7 @@ struct snd_timer_tread {
  *                                                                          *
  ****************************************************************************/
 
-#define SNDRV_CTL_VERSION		SNDRV_PROTOCOL_VERSION(2, 0, 9)
+#define SNDRV_CTL_VERSION		SNDRV_PROTOCOL_VERSION(2, 0, 10)
 
 struct snd_ctl_card_info {
 	int card;			/* card number */
@@ -1058,6 +1058,18 @@ struct snd_ctl_card_info {
 	unsigned char components[128];	/* card components / fine identification, delimited with one space (AC97 etc..) */
 };
 
+/*
+ * Card components can exceed the fixed 128 bytes in snd_ctl_card_info.
+ * Use SNDRV_CTL_IOCTL_CARD_COMPONENTS to retrieve the full string.
+ */
+#define SNDRV_CTL_COMPONENTS_LEN	512
+
+struct snd_ctl_card_components {
+	int card;			/* card number */
+	unsigned int length;		/* returned length of components string */
+	unsigned char components[SNDRV_CTL_COMPONENTS_LEN];
+};
+
 typedef int __bitwise snd_ctl_elem_type_t;
 #define	SNDRV_CTL_ELEM_TYPE_NONE	((snd_ctl_elem_type_t) 0) /* invalid */
 #define	SNDRV_CTL_ELEM_TYPE_BOOLEAN	((snd_ctl_elem_type_t) 1) /* boolean type */
@@ -1184,6 +1196,7 @@ struct snd_ctl_tlv {
 
 #define SNDRV_CTL_IOCTL_PVERSION	_IOR('U', 0x00, int)
 #define SNDRV_CTL_IOCTL_CARD_INFO	_IOR('U', 0x01, struct snd_ctl_card_info)
+#define SNDRV_CTL_IOCTL_CARD_COMPONENTS	_IOWR('U', 0x02, struct snd_ctl_card_components)
 #define SNDRV_CTL_IOCTL_ELEM_LIST	_IOWR('U', 0x10, struct snd_ctl_elem_list)
 #define SNDRV_CTL_IOCTL_ELEM_INFO	_IOWR('U', 0x11, struct snd_ctl_elem_info)
 #define SNDRV_CTL_IOCTL_ELEM_READ	_IOWR('U', 0x12, struct snd_ctl_elem_value)

src/control/control.c

@@ -388,6 +388,19 @@ int snd_ctl_card_info(snd_ctl_t *ctl, snd_ctl_card_info_t *info)
 	return ctl->ops->card_info(ctl, info);
 }
 
+/**
+ * \brief Get information about the card components.
+ * \param ctl The CTL handle.
+ * \param components The card components information is stored here.
+ * \return 0 on success, otherwise a negative error code.
+ */
+int snd_ctl_card_components(snd_ctl_t *ctl, snd_ctl_card_components_t *components)
+{
+	assert(ctl && components);
+	return ctl->ops->card_components(ctl, components);
+}
+
+
 /**
  * \brief Get a list of element identifiers
  *
@@ -2285,6 +2298,54 @@ const char *snd_ctl_card_info_get_components(const snd_ctl_card_info_t *obj)
 	return (const char *)obj->components;
 }
 
+size_t snd_ctl_card_components_sizeof()
+{
+	return sizeof(snd_ctl_card_components_t);
+}
+
+int snd_ctl_card_components_malloc(snd_ctl_card_components_t **ptr)
+{
+	assert(ptr);
+	*ptr = calloc(1, sizeof(snd_ctl_card_components_t));
+	if (!*ptr)
+		return -ENOMEM;
+	return 0;
+}
+
+void snd_ctl_card_components_free(snd_ctl_card_components_t *obj)
+{
+	free(obj);
+}
+
+void snd_ctl_card_components_clear(snd_ctl_card_components_t *obj)
+{
+	memset(obj, 0, sizeof(snd_ctl_card_components_t));
+}
+
+void snd_ctl_card_components_copy(snd_ctl_card_components_t *dst, const snd_ctl_card_components_t *src)
+{
+	assert(dst && src);
+	*dst = *src;
+}
+
+int snd_ctl_card_components_get_card(const snd_ctl_card_components_t *obj)
+{
+	assert(obj);
+	return obj->card;
+}
+
+unsigned int snd_ctl_card_components_get_length(const snd_ctl_card_components_t *obj)
+{
+	assert(obj);
+	return obj->length;
+}
+
+const char *snd_ctl_card_components_get_string(const snd_ctl_card_components_t *obj)
+{
+	assert(obj);
+	return (const char *)obj->components;
+}
+
 /**
  * \brief get size of #snd_ctl_event_t
  * \return size in bytes

src/control/control_ext.c

@@ -89,6 +89,15 @@ static int snd_ctl_ext_card_info(snd_ctl_t *handle, snd_ctl_card_info_t *info)
 	return 0;
 }
 
+static int snd_ctl_ext_card_components(snd_ctl_t *handle, snd_ctl_card_components_t *components)
+{
+	snd_ctl_ext_t *ext = handle->private_data;
+
+	memset(components, 0, sizeof(*components));
+	components->card = ext->card_idx;
+	return 0;
+}
+
 static int snd_ctl_ext_elem_list(snd_ctl_t *handle, snd_ctl_elem_list_t *list)
 {
 	snd_ctl_ext_t *ext = handle->private_data;
@@ -469,6 +478,7 @@ static const snd_ctl_ops_t snd_ctl_ext_ops = {
 	.async = snd_ctl_ext_async,
 	.subscribe_events = snd_ctl_ext_subscribe_events,
 	.card_info = snd_ctl_ext_card_info,
+	.card_components = snd_ctl_ext_card_components,
 	.element_list = snd_ctl_ext_elem_list,
 	.element_info = snd_ctl_ext_elem_info,
 	.element_add = snd_ctl_ext_elem_add,

src/control/control_hw.c

@@ -136,6 +136,16 @@ static int snd_ctl_hw_card_info(snd_ctl_t *handle, snd_ctl_card_info_t *info)
 	return 0;
 }
 
+static int snd_ctl_hw_card_components(snd_ctl_t *handle, snd_ctl_card_components_t *components)
+{
+	snd_ctl_hw_t *hw = handle->private_data;
+	if (hw->protocol < SNDRV_PROTOCOL_VERSION(2, 0, 10))
+		return -ENXIO;
+	if (ioctl(hw->fd, SNDRV_CTL_IOCTL_CARD_COMPONENTS, components) < 0)
+		return -errno;
+	return 0;
+}
+
 static int snd_ctl_hw_elem_list(snd_ctl_t *handle, snd_ctl_elem_list_t *list)
 {
 	snd_ctl_hw_t *hw = handle->private_data;
@@ -389,6 +399,7 @@ static const snd_ctl_ops_t snd_ctl_hw_ops = {
 	.async = snd_ctl_hw_async,
 	.subscribe_events = snd_ctl_hw_subscribe_events,
 	.card_info = snd_ctl_hw_card_info,
+	.card_components = snd_ctl_hw_card_components,
 	.element_list = snd_ctl_hw_elem_list,
 	.element_info = snd_ctl_hw_elem_info,
 	.element_add = snd_ctl_hw_elem_add,

src/control/control_local.h

@@ -28,6 +28,7 @@ typedef struct _snd_ctl_ops {
 	int (*async)(snd_ctl_t *handle, int sig, pid_t pid);
 	int (*subscribe_events)(snd_ctl_t *handle, int subscribe);
 	int (*card_info)(snd_ctl_t *handle, snd_ctl_card_info_t *info);
+	int (*card_components)(snd_ctl_t *handle, snd_ctl_card_components_t *components);
 	int (*element_list)(snd_ctl_t *handle, snd_ctl_elem_list_t *list);
 	int (*element_info)(snd_ctl_t *handle, snd_ctl_elem_info_t *info);
 	int (*element_add)(snd_ctl_t *handle, snd_ctl_elem_info_t *info);

src/control/control_remap.c

@@ -466,6 +466,12 @@ static int snd_ctl_remap_card_info(snd_ctl_t *ctl, snd_ctl_card_info_t *info)
 	return snd_ctl_card_info(priv->child, info);
 }
 
+static int snd_ctl_remap_card_components(snd_ctl_t *ctl, snd_ctl_card_components_t *components)
+{
+	snd_ctl_remap_t *priv = ctl->private_data;
+	return snd_ctl_card_components(priv->child, components);
+}
+
 static int snd_ctl_remap_elem_list(snd_ctl_t *ctl, snd_ctl_elem_list_t *list)
 {
 	snd_ctl_remap_t *priv = ctl->private_data;
@@ -1185,6 +1191,7 @@ static const snd_ctl_ops_t snd_ctl_remap_ops = {
 	.async = snd_ctl_remap_async,
 	.subscribe_events = snd_ctl_remap_subscribe_events,
 	.card_info = snd_ctl_remap_card_info,
+	.card_components = snd_ctl_remap_card_components,
 	.element_list = snd_ctl_remap_elem_list,
 	.element_info = snd_ctl_remap_elem_info,
 	.element_read = snd_ctl_remap_elem_read,

src/control/control_shm.c

@@ -150,6 +150,15 @@ static int snd_ctl_shm_card_info(snd_ctl_t *ctl, snd_ctl_card_info_t *info)
 	return err;
 }
 
+static int snd_ctl_shm_card_components(snd_ctl_t *ctl, snd_ctl_card_components_t *components)
+{
+	snd_ctl_shm_t *shm = ctl->private_data;
+	volatile snd_ctl_shm_ctrl_t *ctrl = shm->ctrl;
+	ctrl->cmd = SNDRV_CTL_IOCTL_CARD_COMPONENTS;
+	ctrl->u.card_components = *components;
+	return snd_ctl_shm_action(ctl);
+}
+
 static int snd_ctl_shm_elem_list(snd_ctl_t *ctl, snd_ctl_elem_list_t *list)
 {
 	snd_ctl_shm_t *shm = ctl->private_data;
@@ -391,6 +400,7 @@ static const snd_ctl_ops_t snd_ctl_shm_ops = {
 	.async = snd_ctl_shm_async,
 	.subscribe_events = snd_ctl_shm_subscribe_events,
 	.card_info = snd_ctl_shm_card_info,
+	.card_components = snd_ctl_shm_card_components,
 	.element_list = snd_ctl_shm_elem_list,
 	.element_info = snd_ctl_shm_elem_info,
 	.element_read = snd_ctl_shm_elem_read,

src/mixer/simple_abst.c

@@ -48,6 +48,7 @@ typedef struct _class_priv {
 	snd_hctl_t *hctl;
 	int attach_flag;
 	snd_ctl_card_info_t *info;
+	snd_ctl_card_components_t *card_components;
 	void *dlhandle;
 	void *private_data;
 	void (*private_free)(snd_mixer_class_t *class);
@@ -161,7 +162,12 @@ static int match(snd_mixer_class_t *class, const char *lib, const char *searchl)
 
 	if (searchl == NULL)
 		return try_open(class, lib);
-	components = snd_ctl_card_info_get_components(priv->info);
+
+	if (priv->card_components)
+		components = snd_ctl_card_components_get_string(priv->card_components);
+	else
+		components = snd_ctl_card_info_get_components(priv->info);
+
 	while (*components != '\0') {
 		if (!strncmp(components, searchl, strlen(searchl)))
 			return try_open(class, lib);
@@ -248,6 +254,8 @@ static void private_free(snd_mixer_class_t *class)
 		priv->private_free(class);
 	if (priv->dlhandle)
 		snd_dlclose(priv->dlhandle);
+	if (priv->card_components)
+		snd_ctl_card_components_free(priv->card_components);
 	if (priv->info)
 		snd_ctl_card_info_free(priv->info);
 	if (priv->hctl) {
@@ -335,8 +343,15 @@ int snd_mixer_simple_basic_register(snd_mixer_t *mixer,
 	err = snd_ctl_card_info(priv->ctl, priv->info);
 	if (err < 0)
 		goto __error;
-	if (err >= 0)
-		err = find_module(class, top);
+	err = snd_ctl_card_components_malloc(&priv->card_components);
+	if (err >= 0) {
+		err = snd_ctl_card_components(priv->ctl, priv->card_components);
+		if (err < 0) {
+			snd_ctl_card_components_free(priv->card_components);
+			priv->card_components = NULL;
+		}
+	}
+	err = find_module(class, top);
 	if (err >= 0)
 		err = snd_mixer_attach_hctl(mixer, priv->hctl);
 	if (err >= 0) {
@@ -374,6 +389,7 @@ int snd_mixer_sbasic_info(const snd_mixer_class_t *class, sm_class_basic_t *info
 	info->ctl = priv->ctl;
 	info->hctl = priv->hctl;
 	info->info = priv->info;
+	info->card_components = priv->card_components;
 	return 0;
 }
 

src/ucm/ucm_local.h

@@ -121,6 +121,7 @@ struct ctl_list {
 	struct list_head dev_list;
 	snd_ctl_t *ctl;
 	snd_ctl_card_info_t *ctl_info;
+	snd_ctl_card_components_t *ctl_components;
 	int slave;
 	int ucm_group;
 };

src/ucm/ucm_subs.c

@@ -156,6 +156,8 @@ static char *rval_card_components(snd_use_case_mgr_t *uc_mgr)
 	ctl_list = uc_mgr_get_master_ctl(uc_mgr);
 	if (ctl_list == NULL)
 		return NULL;
+	if (ctl_list->ctl_components)
+		return strdup(snd_ctl_card_components_get_string(ctl_list->ctl_components));
 	return strdup(snd_ctl_card_info_get_components(ctl_list->ctl_info));
 }
 

src/ucm/utils.c

@@ -152,6 +152,8 @@ static void uc_mgr_free_ctl(struct ctl_list *ctl_list)
 		free(ctl_dev->device);
 		free(ctl_dev);
 	}
+	if (ctl_list->ctl_components)
+		snd_ctl_card_components_free(ctl_list->ctl_components);
 	snd_ctl_card_info_free(ctl_list->ctl_info);
 	free(ctl_list);
 }
@@ -219,6 +221,14 @@ static int uc_mgr_ctl_add(snd_use_case_mgr_t *uc_mgr,
 			return -ENOMEM;
 		}
 		snd_ctl_card_info_copy(cl->ctl_info, info);
+		if (snd_ctl_card_components_malloc(&cl->ctl_components) >= 0) {
+			if (snd_ctl_card_components(ctl, cl->ctl_components) < 0) {
+				snd_ctl_card_components_free(cl->ctl_components);
+				cl->ctl_components = NULL;
+			}
+		} else {
+			cl->ctl_components = NULL;
+		}
 		cl->slave = slave;
 		*ctl_list = cl;
 	} else {

test/control.c

@@ -8,11 +8,13 @@ int main(void)
 	int idx, dev, err;
 	snd_ctl_t *handle;
 	snd_ctl_card_info_t *info;
+	snd_ctl_card_components_t *components;
 	snd_pcm_info_t *pcminfo;
 	snd_rawmidi_info_t *rawmidiinfo;
 	char str[128];
 
 	snd_ctl_card_info_alloca(&info);
+	snd_ctl_card_components_alloca(&components);
 	snd_pcm_info_alloca(&pcminfo);
 	snd_rawmidi_info_alloca(&rawmidiinfo);
 
@@ -40,7 +42,10 @@ int main(void)
 		printf("  name - '%s'\n", snd_ctl_card_info_get_name(info));
 		printf("  longname - '%s'\n", snd_ctl_card_info_get_longname(info));
 		printf("  mixername - '%s'\n", snd_ctl_card_info_get_mixername(info));
-		printf("  components - '%s'\n", snd_ctl_card_info_get_components(info));
+		if (snd_ctl_card_components(handle, components) >= 0)
+			printf("  components - '%s'\n", snd_ctl_card_components_get_string(components));
+		else
+			printf("  components - '%s'\n", snd_ctl_card_info_get_components(info));
 		dev = -1;
 		while (1) {
 			snd_pcm_sync_id_t sync;