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 alsa-lib can read the full
string if the original is truncated.

[1] https://lore.kernel.org/all/20260303145815.9930-1-mstrozek@opensource.cirrus.com/

Signed-off-by: Maciej Strozek <mstrozek@opensource.cirrus.com>

include/local.h

@@ -101,7 +101,6 @@
 #define _snd_pcm_sw_params snd_pcm_sw_params
 #define _snd_pcm_status snd_pcm_status
 
-#define _snd_ctl_card_info snd_ctl_card_info
 #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
@@ -226,6 +225,20 @@
 #include "seq_midi_event.h"
 #include "list.h"
 
+/* V2 structure - increased components string from 128 bytes to 512 bytes */
+struct _snd_ctl_card_info {
+       int card;                       /* card number */
+       int pad;                        /* reserved for future (was type) */
+       unsigned char id[16];           /* ID of card (user selectable) */
+       unsigned char driver[16];       /* Driver name */
+       unsigned char name[32];         /* Short name of soundcard */
+       unsigned char longname[80];     /* name + info text about soundcard */
+       unsigned char reserved_[16];    /* reserved for future (was ID of mixer) */
+       unsigned char mixername[80];    /* visual mixer identification */
+       char components[512];
+};
+
+
 struct _snd_async_handler {
 	enum {
 		SND_ASYNC_HANDLER_GENERIC,

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 +1058,17 @@ 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.
+ *
+ */
+struct snd_ctl_card_components {
+	int card;				/* card number */
+	unsigned int length;			/* returned length of components string for ioctl query */
+	unsigned char *components;		/* user buffer for components string */
+};
+
 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 +1195,7 @@ 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/cards.c

@@ -42,17 +42,17 @@
 static int snd_card_load2(const char *control)
 {
 	int open_dev;
-	snd_ctl_card_info_t info;
+	struct snd_ctl_card_info kinfo;
 
 	open_dev = snd_open_device(control, O_RDONLY);
 	if (open_dev >= 0) {
-		if (ioctl(open_dev, SNDRV_CTL_IOCTL_CARD_INFO, &info) < 0) {
+		if (ioctl(open_dev, SNDRV_CTL_IOCTL_CARD_INFO, &kinfo) < 0) {
 			int err = -errno;
 			close(open_dev);
 			return err;
 		}
 		close(open_dev);
-		return info.card;
+		return kinfo.card;
 	} else {
 		return -errno;
 	}

src/control/control_hw.c

@@ -129,10 +129,40 @@ static int snd_ctl_hw_subscribe_events(snd_ctl_t *handle, int subscribe)
 static int snd_ctl_hw_card_info(snd_ctl_t *handle, snd_ctl_card_info_t *info)
 {
 	snd_ctl_hw_t *hw = handle->private_data;
-	if (ioctl(hw->fd, SNDRV_CTL_IOCTL_CARD_INFO, info) < 0) {
+	struct snd_ctl_card_info kinfo;
+	struct snd_ctl_card_components comp;
+
+	if (ioctl(hw->fd, SNDRV_CTL_IOCTL_CARD_INFO, &kinfo) < 0) {
 		snd_errornum(CONTROL, "SNDRV_CTL_IOCTL_CARD_INFO failed");
 		return -errno;
 	}
+
+	snd_ctl_card_info_clear(info);
+	info->card = kinfo.card;
+	info->pad = kinfo.pad;
+	snd_strlcpy((char *)info->id, (char *)kinfo.id, sizeof(info->id));
+	snd_strlcpy((char *)info->driver, (char *)kinfo.driver, sizeof(info->driver));
+	snd_strlcpy((char *)info->name, (char *)kinfo.name, sizeof(info->name));
+	snd_strlcpy((char *)info->longname, (char *)kinfo.longname, sizeof(info->longname));
+	snd_strlcpy((char *)info->reserved_, (char *)kinfo.reserved_, sizeof(info->reserved_));
+	snd_strlcpy((char *)info->mixername, (char *)kinfo.mixername, sizeof(info->mixername));
+	if (strnlen((char *)kinfo.components, sizeof(kinfo.components)) == sizeof(kinfo.components) - 1 &&
+	    kinfo.components[sizeof(kinfo.components) - 2] == '>') {
+		comp.components = (unsigned char *)info->components;
+		comp.length = sizeof(info->components);
+		if (ioctl(hw->fd, SNDRV_CTL_IOCTL_CARD_COMPONENTS, &comp) < 0) {
+			snd_errornum(CONTROL, "SNDRV_CTL_IOCTL_CARD_COMPONENTS failed");
+			return -errno;
+		}
+		if (comp.length != strnlen((char *)comp.components, sizeof(info->components)) + 1 ) {
+			snd_error(CONTROL, "SNDRV_CTL_IOCTL_CARD_COMPONENTS unexpected length %u, should be %u",
+				     comp.length, strnlen((char *)comp.components, sizeof(info->components)) + 1);
+			return -errno;
+		}
+	} else {
+		snd_strlcpy(info->components, (char *)kinfo.components, sizeof(info->components));
+	}
+
 	return 0;
 }