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Message-ID: <20260122111249.67319-1-mstrozek@opensource.cirrus.com>
Date: Thu, 22 Jan 2026 11:12:47 +0000
From: Maciej Strozek <mstrozek@...nsource.cirrus.com>
To: Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>
Cc: linux-kernel@...r.kernel.org, linux-sound@...r.kernel.org,
patches@...nsource.cirrus.com, alsa-devel@...a-project.org,
Maciej Strozek <mstrozek@...nsource.cirrus.com>
Subject: [PATCH v2] ALSA: control: 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.
Keep the existing struct snd_ctl_card_info ABI intact and add a new ioctl
to retrieve the full components string.
When the legacy components field is truncated, append '>' to indicate
that the full string is available via the new ioctl.
Link: https://github.com/alsa-project/alsa-lib/pull/494
Link: https://github.com/alsa-project/alsa-utils/pull/318
Suggested-by: Jaroslav Kysela <perex@...ex.cz>
Suggested-by: Takashi Iwai <tiwai@...e.com>
Signed-off-by: Maciej Strozek <mstrozek@...nsource.cirrus.com>
---
Changes for v2:
- do not modify existing card->components field
- add a new ioctl and struct to keep the full components string
- handle the split/trim in snd_ctl_card_info()
---
include/sound/core.h | 4 +++-
include/uapi/sound/asound.h | 15 ++++++++++++++-
sound/core/control.c | 34 +++++++++++++++++++++++++++++++++-
sound/core/control_compat.c | 3 ++-
sound/core/init.c | 14 +++++++-------
5 files changed, 59 insertions(+), 11 deletions(-)
diff --git a/include/sound/core.h b/include/sound/core.h
index 64327e971122..0b16e2cb3f53 100644
--- a/include/sound/core.h
+++ b/include/sound/core.h
@@ -15,6 +15,7 @@
#include <linux/stringify.h>
#include <linux/printk.h>
#include <linux/xarray.h>
+#include <uapi/sound/asound.h> /* SNDRV_CTL_COMPONENTS_LEN */
/* number of supported soundcards */
#ifdef CONFIG_SND_DYNAMIC_MINORS
@@ -88,7 +89,8 @@ struct snd_card {
char irq_descr[32]; /* Interrupt description */
char mixername[80]; /* mixer name */
char components[128]; /* card components delimited with
- space */
+ space, truncated to 127 chars */
+ char components_extended[SNDRV_CTL_COMPONENTS_LEN]; /* full card components string */
struct module *module; /* top-level module */
void *private_data; /* private data for soundcard */
diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
index d3ce75ba938a..5645ea8bb8a4 100644
--- a/include/uapi/sound/asound.h
+++ b/include/uapi/sound/asound.h
@@ -1058,7 +1058,7 @@ 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 */
@@ -1072,6 +1072,18 @@ 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 ((__force snd_ctl_elem_type_t) 0) /* invalid */
#define SNDRV_CTL_ELEM_TYPE_BOOLEAN ((__force snd_ctl_elem_type_t) 1) /* boolean type */
@@ -1198,6 +1210,7 @@ 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)
diff --git a/sound/core/control.c b/sound/core/control.c
index 9c3fd5113a61..0f0d9828aeb1 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -868,10 +868,14 @@ 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) = NULL;
+ ssize_t n;
info = kzalloc(sizeof(*info), GFP_KERNEL);
if (! info)
return -ENOMEM;
+
+ static_assert(sizeof(info->components) >= 2);
+
scoped_guard(rwsem_read, &snd_ioctl_rwsem) {
info->card = card->number;
strscpy(info->id, card->id, sizeof(info->id));
@@ -879,13 +883,39 @@ static int snd_ctl_card_info(struct snd_card *card, struct snd_ctl_file * ctl,
strscpy(info->name, card->shortname, sizeof(info->name));
strscpy(info->longname, card->longname, sizeof(info->longname));
strscpy(info->mixername, card->mixername, sizeof(info->mixername));
- strscpy(info->components, card->components, sizeof(info->components));
+ n = strscpy(info->components, card->components_extended,
+ sizeof(info->components));
+ if (n < 0) {
+ info->components[sizeof(info->components) - 2] = '>';
+ info->components[sizeof(info->components) - 1] = '\0';
+ }
}
if (copy_to_user(arg, info, sizeof(struct snd_ctl_card_info)))
return -EFAULT;
return 0;
}
+static int snd_ctl_card_components(struct snd_card *card, void __user *arg)
+{
+ struct snd_ctl_card_components *info __free(kfree) = NULL;
+ int copied;
+
+ info = kzalloc(sizeof(*info), GFP_KERNEL);
+ if (!info)
+ return -ENOMEM;
+
+ scoped_guard(rwsem_read, &snd_ioctl_rwsem) {
+ info->card = card->number;
+ copied = strscpy(info->components, card->components_extended,
+ sizeof(info->components));
+ info->length = copied;
+ }
+
+ if (copy_to_user(arg, info, sizeof(*info)))
+ return -EFAULT;
+ return 0;
+}
+
static int snd_ctl_elem_list(struct snd_card *card,
struct snd_ctl_elem_list *list)
{
@@ -1914,6 +1944,8 @@ static long snd_ctl_ioctl(struct file *file, unsigned int cmd, unsigned long arg
return put_user(SNDRV_CTL_VERSION, ip) ? -EFAULT : 0;
case SNDRV_CTL_IOCTL_CARD_INFO:
return snd_ctl_card_info(card, ctl, cmd, argp);
+ case SNDRV_CTL_IOCTL_CARD_COMPONENTS:
+ return snd_ctl_card_components(card, argp);
case SNDRV_CTL_IOCTL_ELEM_LIST:
return snd_ctl_elem_list_user(card, argp);
case SNDRV_CTL_IOCTL_ELEM_INFO:
diff --git a/sound/core/control_compat.c b/sound/core/control_compat.c
index 6459809ed364..edb7b28d8177 100644
--- a/sound/core/control_compat.c
+++ b/sound/core/control_compat.c
@@ -416,7 +416,7 @@ static int snd_ctl_elem_add_compat(struct snd_ctl_file *file,
break;
}
return snd_ctl_elem_add(file, data, replace);
-}
+}
enum {
SNDRV_CTL_IOCTL_ELEM_LIST32 = _IOWR('U', 0x10, struct snd_ctl_elem_list32),
@@ -445,6 +445,7 @@ static inline long snd_ctl_ioctl_compat(struct file *file, unsigned int cmd, uns
switch (cmd) {
case SNDRV_CTL_IOCTL_PVERSION:
case SNDRV_CTL_IOCTL_CARD_INFO:
+ case SNDRV_CTL_IOCTL_CARD_COMPONENTS:
case SNDRV_CTL_IOCTL_SUBSCRIBE_EVENTS:
case SNDRV_CTL_IOCTL_POWER:
case SNDRV_CTL_IOCTL_POWER_STATE:
diff --git a/sound/core/init.c b/sound/core/init.c
index c372b3228785..3ec2f08ba765 100644
--- a/sound/core/init.c
+++ b/sound/core/init.c
@@ -714,7 +714,7 @@ static void snd_card_set_id_no_lock(struct snd_card *card, const char *src,
int len, loops;
bool is_default = false;
char *id;
-
+
copy_valid_id_string(card, src, nid);
id = card->id;
@@ -1023,24 +1023,24 @@ int __init snd_card_info_init(void)
*
* Return: Zero otherwise a negative error code.
*/
-
+
int snd_component_add(struct snd_card *card, const char *component)
{
char *ptr;
int len = strlen(component);
- ptr = strstr(card->components, component);
+ ptr = strstr(card->components_extended, component);
if (ptr != NULL) {
if (ptr[len] == '\0' || ptr[len] == ' ') /* already there */
return 1;
}
- if (strlen(card->components) + 1 + len + 1 > sizeof(card->components)) {
+ if (strlen(card->components_extended) + 1 + len + 1 > sizeof(card->components_extended)) {
snd_BUG();
return -ENOMEM;
}
- if (card->components[0] != '\0')
- strcat(card->components, " ");
- strcat(card->components, component);
+ if (card->components_extended[0] != '\0')
+ strcat(card->components_extended, " ");
+ strcat(card->components_extended, component);
return 0;
}
EXPORT_SYMBOL(snd_component_add);
--
2.48.1
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