[PATCH v3 1/2] ALSA: control: tidy up whitespaces

[PATCH v3 1/2] ALSA: control: tidy up whitespaces

[Maciej Strozek]

Clean up trailing whitespaces by the way of changing card components array.

Signed-off-by: Maciej Strozek <mstrozek@opensource.cirrus.com>
---
 sound/core/control_compat.c | 2 +-
 sound/core/init.c           | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/sound/core/control_compat.c b/sound/core/control_compat.c
index 16bc80555f26..4ad571087ff5 100644
--- a/sound/core/control_compat.c
+++ b/sound/core/control_compat.c
@@ -417,7 +417,7 @@ 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),
diff --git a/sound/core/init.c b/sound/core/init.c
index 0c316189e947..593c05895e11 100644
--- a/sound/core/init.c
+++ b/sound/core/init.c
@@ -722,7 +722,7 @@ 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;

@@ -1031,7 +1031,7 @@ 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;
--
2.48.1

[PATCH v3 2/2] ALSA: control: add ioctl to retrieve full card components

[Maciej Strozek]

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
Suggested-by: Jaroslav Kysela <perex@perex.cz>
Suggested-by: Takashi Iwai <tiwai@suse.com>
Signed-off-by: Maciej Strozek <mstrozek@opensource.cirrus.com>
---
Changes for v3:
 - change components field to a dynamic array resizable in 32 byte increments
 - removed SNDRV_CTL_COMPONENTS_LEN define
 - sanity check if 'components' requests more than 512 bytes
 - added a commit to clean up trailing whitespaces
 - alsa-utils link no longer needed
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 | 14 ++++++++++++-
 sound/core/control.c        | 35 ++++++++++++++++++++++++++++++++-
 sound/core/control_compat.c |  2 ++
 sound/core/init.c           | 39 +++++++++++++++++++++++++++++--------
 5 files changed, 82 insertions(+), 12 deletions(-)

diff --git a/include/sound/core.h b/include/sound/core.h
index 4093ec82a0a1..2b58f79b524d 100644
--- a/include/sound/core.h
+++ b/include/sound/core.h
@@ -87,8 +87,8 @@ struct snd_card {
 	char longname[80];		/* name of this soundcard */
 	char irq_descr[32];		/* Interrupt description */
 	char mixername[80];		/* mixer name */
-	char components[128];		/* card components delimited with
-								space */
+	char *components_ptr;
+	unsigned int components_ptr_alloc_size; // current memory allocation components_ptr.
 	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..422b0b07613d 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 +1072,17 @@ 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;
+	unsigned int length;
+	unsigned char *components;
+};
+
 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 +1209,7 @@ 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 374e703d15a9..d793dbf85d15 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -876,9 +876,13 @@ static int snd_ctl_card_info(struct snd_card *card, struct snd_ctl_file * ctl,
 {
 	struct snd_ctl_card_info *info __free(kfree) =
 		kzalloc(sizeof(*info), GFP_KERNEL);
+	ssize_t n;

 	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));
@@ -886,13 +890,40 @@ 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_ptr, 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_components(struct snd_card *card,
+				  struct snd_ctl_card_components __user *_info)
+{
+	struct snd_ctl_card_components info;
+	unsigned int copy_len;
+
+	if (copy_from_user(&info, _info, sizeof(info)))
+		return -EFAULT;
+	if (!info.components)
+		return -EINVAL;
+
+	scoped_guard(rwsem_read, &snd_ioctl_rwsem) {
+		copy_len = strlen(card->components_ptr) + 1;
+		info.card = card->number;
+		info.length = copy_len;
+		if (copy_to_user(info.components, card->components_ptr, copy_len))
+			return -EFAULT;
+	}
+
+	if (copy_to_user(_info, &info, sizeof(info)))
+		return -EFAULT;
+
+	return 0;
+}
+
 static int snd_ctl_elem_list(struct snd_card *card,
 			     struct snd_ctl_elem_list *list)
 {
@@ -1988,6 +2019,8 @@ 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 4ad571087ff5..d325f9d0b8a1 100644
--- a/sound/core/control_compat.c
+++ b/sound/core/control_compat.c
@@ -456,6 +456,8 @@ static inline long snd_ctl_ioctl_compat(struct file *file, unsigned int cmd, uns
 	case SNDRV_CTL_IOCTL_TLV_WRITE:
 	case SNDRV_CTL_IOCTL_TLV_COMMAND:
 		return snd_ctl_ioctl(file, cmd, (unsigned long)argp);
+	case SNDRV_CTL_IOCTL_CARD_COMPONENTS:
+		return snd_ctl_card_components(ctl->card, argp);
 	case SNDRV_CTL_IOCTL_ELEM_LIST32:
 		return snd_ctl_elem_list_compat(ctl->card, argp);
 	case SNDRV_CTL_IOCTL_ELEM_INFO32:
diff --git a/sound/core/init.c b/sound/core/init.c
index 593c05895e11..426ed8916aa9 100644
--- a/sound/core/init.c
+++ b/sound/core/init.c
@@ -590,6 +590,8 @@ static int snd_card_do_free(struct snd_card *card)
 		snd_mixer_oss_notify_callback(card, SND_MIXER_OSS_NOTIFY_FREE);
 #endif
 	snd_device_free_all(card);
+	kfree(card->components_ptr);
+	card->components_ptr_alloc_size = 0;
 	if (card->private_free)
 		card->private_free(card);
 #ifdef CONFIG_SND_CTL_DEBUG
@@ -1036,19 +1038,40 @@ int snd_component_add(struct snd_card *card, const char *component)
 {
 	char *ptr;
 	int len = strlen(component);
+	unsigned int cur_len, need_len;

-	ptr = strstr(card->components, component);
-	if (ptr != NULL) {
-		if (ptr[len] == '\0' || ptr[len] == ' ')	/* already there */
-			return 1;
+	if (card->components_ptr) {
+		ptr = strstr(card->components_ptr, component);
+		if (ptr) {
+			if (ptr[len] == '\0' || ptr[len] == ' ')	/* already there */
+				return 1;
+		}
+		cur_len = strlen(card->components_ptr) + 1;
+	} else {
+		cur_len = 0;
 	}
-	if (strlen(card->components) + 1 + len + 1 > sizeof(card->components)) {
+
+	need_len = cur_len + len + 1;
+	if (need_len > 512) {
 		snd_BUG();
 		return -ENOMEM;
 	}
-	if (card->components[0] != '\0')
-		strcat(card->components, " ");
-	strcat(card->components, component);
+
+	if (need_len > card->components_ptr_alloc_size) {
+		unsigned int new_alloc = roundup(need_len, 32);
+
+		ptr = krealloc(card->components_ptr, new_alloc, GFP_KERNEL);
+		if (!ptr)
+			return -ENOMEM;
+		if (!card->components_ptr)
+			ptr[0] = '\0';
+		card->components_ptr = ptr;
+		card->components_ptr_alloc_size = new_alloc;
+	}
+
+	if (card->components_ptr[0] != '\0')
+		strcat(card->components_ptr, " ");
+	strcat(card->components_ptr, component);
 	return 0;
 }
 EXPORT_SYMBOL(snd_component_add);
--
2.48.1

Re: [PATCH v3 2/2] ALSA: control: add ioctl to retrieve full card components

[Takashi Iwai]

On Tue, 03 Mar 2026 15:58:00 +0100,
Maciej Strozek wrote:
> 
> 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
> Suggested-by: Jaroslav Kysela <perex@perex.cz>
> Suggested-by: Takashi Iwai <tiwai@suse.com>
> Signed-off-by: Maciej Strozek <mstrozek@opensource.cirrus.com>
> ---
> Changes for v3:
>  - change components field to a dynamic array resizable in 32 byte increments
>  - removed SNDRV_CTL_COMPONENTS_LEN define
>  - sanity check if 'components' requests more than 512 bytes
>  - added a commit to clean up trailing whitespaces
>  - alsa-utils link no longer needed
> 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 | 14 ++++++++++++-
>  sound/core/control.c        | 35 ++++++++++++++++++++++++++++++++-
>  sound/core/control_compat.c |  2 ++
>  sound/core/init.c           | 39 +++++++++++++++++++++++++++++--------
>  5 files changed, 82 insertions(+), 12 deletions(-)
> 
> diff --git a/include/sound/core.h b/include/sound/core.h
> index 4093ec82a0a1..2b58f79b524d 100644
> --- a/include/sound/core.h
> +++ b/include/sound/core.h
> @@ -87,8 +87,8 @@ struct snd_card {
>  	char longname[80];		/* name of this soundcard */
>  	char irq_descr[32];		/* Interrupt description */
>  	char mixername[80];		/* mixer name */
> -	char components[128];		/* card components delimited with
> -								space */
> +	char *components_ptr;
> +	unsigned int components_ptr_alloc_size; // current memory allocation components_ptr.
>  	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..422b0b07613d 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 +1072,17 @@ 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;
> +	unsigned int length;
> +	unsigned char *components;
> +};

Embedding a pointer for ioctl is a nightmare for 32bit compatibility,
and you seem to have forgotten it, too ;)

IMO, in this case, it'd be easier to use a flex array instead, e.g.

struct snd_ctl_card_components {
	int card;
	unsigned int length;
	unsigned char components[];
};

And the ioctl can serve for two purposes:

- When length=0 is set, the kernel stores the current number of bytes
  and returns without copying.  User-space can use this mode for
  allocating the buffer.

- When length > 0 is set, the kernel copies the data on components[]
  up to the given length.  The length field is updated again to store
  the number of bytes (which would be copied).

What this length field specifies is another question: is it a string
length or a buffer length including NUL?

Also, we can keep the current string size, too, for returning in the
sequence in the above, instead of doing strlen() at each time.


thanks,

Takashi

Re: [PATCH v3 2/2] ALSA: control: add ioctl to retrieve full card components

[Jaroslav Kysela]

On 3/3/26 16:47, Takashi Iwai wrote:
> On Tue, 03 Mar 2026 15:58:00 +0100,
> Maciej Strozek wrote:
>>
>> 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
>> Suggested-by: Jaroslav Kysela <perex@perex.cz>
>> Suggested-by: Takashi Iwai <tiwai@suse.com>
>> Signed-off-by: Maciej Strozek <mstrozek@opensource.cirrus.com>
>> ---
>> Changes for v3:
>>   - change components field to a dynamic array resizable in 32 byte increments
>>   - removed SNDRV_CTL_COMPONENTS_LEN define
>>   - sanity check if 'components' requests more than 512 bytes
>>   - added a commit to clean up trailing whitespaces
>>   - alsa-utils link no longer needed
>> 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 | 14 ++++++++++++-
>>   sound/core/control.c        | 35 ++++++++++++++++++++++++++++++++-
>>   sound/core/control_compat.c |  2 ++
>>   sound/core/init.c           | 39 +++++++++++++++++++++++++++++--------
>>   5 files changed, 82 insertions(+), 12 deletions(-)
>>
>> diff --git a/include/sound/core.h b/include/sound/core.h
>> index 4093ec82a0a1..2b58f79b524d 100644
>> --- a/include/sound/core.h
>> +++ b/include/sound/core.h
>> @@ -87,8 +87,8 @@ struct snd_card {
>>   	char longname[80];		/* name of this soundcard */
>>   	char irq_descr[32];		/* Interrupt description */
>>   	char mixername[80];		/* mixer name */
>> -	char components[128];		/* card components delimited with
>> -								space */
>> +	char *components_ptr;
>> +	unsigned int components_ptr_alloc_size; // current memory allocation components_ptr.
>>   	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..422b0b07613d 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 +1072,17 @@ 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;
>> +	unsigned int length;
>> +	unsigned char *components;
>> +};
> 
> Embedding a pointer for ioctl is a nightmare for 32bit compatibility,
> and you seem to have forgotten it, too ;)

It's doable and we have other more important structures like struct snd_xferi 
using those pointers. But yes, the translation is missing in this patch set. I 
already gave hint that control_compat.c must be modified, too.

> IMO, in this case, it'd be easier to use a flex array instead, e.g.
> 
> struct snd_ctl_card_components {
> 	int card;
> 	unsigned int length;
> 	unsigned char components[];
> };

There is an issue that flex arrays will break _IOC_SIZE().

					Jaroslav

-- 
Jaroslav Kysela <perex@perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.

Re: [PATCH v3 2/2] ALSA: control: add ioctl to retrieve full card components

[Takashi Iwai]

On Tue, 03 Mar 2026 20:23:11 +0100,
Jaroslav Kysela wrote:
> 
> On 3/3/26 16:47, Takashi Iwai wrote:
> > On Tue, 03 Mar 2026 15:58:00 +0100,
> > Maciej Strozek wrote:
> >> 
> >> 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
> >> Suggested-by: Jaroslav Kysela <perex@perex.cz>
> >> Suggested-by: Takashi Iwai <tiwai@suse.com>
> >> Signed-off-by: Maciej Strozek <mstrozek@opensource.cirrus.com>
> >> ---
> >> Changes for v3:
> >>   - change components field to a dynamic array resizable in 32 byte increments
> >>   - removed SNDRV_CTL_COMPONENTS_LEN define
> >>   - sanity check if 'components' requests more than 512 bytes
> >>   - added a commit to clean up trailing whitespaces
> >>   - alsa-utils link no longer needed
> >> 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 | 14 ++++++++++++-
> >>   sound/core/control.c        | 35 ++++++++++++++++++++++++++++++++-
> >>   sound/core/control_compat.c |  2 ++
> >>   sound/core/init.c           | 39 +++++++++++++++++++++++++++++--------
> >>   5 files changed, 82 insertions(+), 12 deletions(-)
> >> 
> >> diff --git a/include/sound/core.h b/include/sound/core.h
> >> index 4093ec82a0a1..2b58f79b524d 100644
> >> --- a/include/sound/core.h
> >> +++ b/include/sound/core.h
> >> @@ -87,8 +87,8 @@ struct snd_card {
> >>   	char longname[80];		/* name of this soundcard */
> >>   	char irq_descr[32];		/* Interrupt description */
> >>   	char mixername[80];		/* mixer name */
> >> -	char components[128];		/* card components delimited with
> >> -								space */
> >> +	char *components_ptr;
> >> +	unsigned int components_ptr_alloc_size; // current memory allocation components_ptr.
> >>   	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..422b0b07613d 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 +1072,17 @@ 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;
> >> +	unsigned int length;
> >> +	unsigned char *components;
> >> +};
> > 
> > Embedding a pointer for ioctl is a nightmare for 32bit compatibility,
> > and you seem to have forgotten it, too ;)
> 
> It's doable and we have other more important structures like struct
> snd_xferi using those pointers. But yes, the translation is missing in
> this patch set. I already gave hint that control_compat.c must be
> modified, too.
> 
> > IMO, in this case, it'd be easier to use a flex array instead, e.g.
> > 
> > struct snd_ctl_card_components {
> > 	int card;
> > 	unsigned int length;
> > 	unsigned char components[];
> > };
> 
> There is an issue that flex arrays will break _IOC_SIZE().

That's true.  OTOH, having a pointer for the external data to be
copied means that _IOC_SIZE() doesn't cover the whole size but misses
the data, too.  So it's a question which implementation is uglier (or
easier to handle), after all.

BTW, it might be better to have both length and actual_length fields
in srtuct snd_ctl_card_components: the former specifies the allocated
buffer length while the latter is stored by kernel pointing to the
actual data size.  We can overwrite length field in return, but it
might be confusing when releasing a resource.


thanks,

Takashi

Re: [PATCH v3 2/2] ALSA: control: add ioctl to retrieve full card components

[Maciej Strozek]

W dniu wto, 03.03.2026 o godzinie 16∶47 +0100, użytkownik Takashi Iwai
napisał:
> > 
> > + */
> > +struct snd_ctl_card_components {
> > + int card;
> > + unsigned int length;
> > + unsigned char *components;
> > +};
> 
> And the ioctl can serve for two purposes:
> 
> - When length=0 is set, the kernel stores the current number of bytes
>   and returns without copying.  User-space can use this mode for
>   allocating the buffer.
> 
In alsa-lib all data must be allocated beforehand, so this length==0
query is not very useful there, it will just go into a [512] array
anyway. Are there any other users that may benefit from this?

-- 
Regards,
Maciej

Re: [PATCH v3 2/2] ALSA: control: add ioctl to retrieve full card components

[Takashi Iwai]

On Thu, 05 Mar 2026 10:54:35 +0100,
Maciej Strozek wrote:
> 
> W dniu wto, 03.03.2026 o godzinie 16∶47 +0100, użytkownik Takashi Iwai
> napisał:
> > > 
> > > + */
> > > +struct snd_ctl_card_components {
> > > + int card;
> > > + unsigned int length;
> > > + unsigned char *components;
> > > +};
> > 
> > And the ioctl can serve for two purposes:
> > 
> > - When length=0 is set, the kernel stores the current number of bytes
> >   and returns without copying.  User-space can use this mode for
> >   allocating the buffer.
> > 
> In alsa-lib all data must be allocated beforehand, so this length==0
> query is not very useful there, it will just go into a [512] array
> anyway. Are there any other users that may benefit from this?

My suggested API can work even with the fixed size 512, too, if 512 is
hight enough.  It's just more flexible.  And there is no restriction
about alsa-lib data allocation; the function can query the size then
allocate, too.


Takashi

Re: [PATCH v3 2/2] ALSA: control: add ioctl to retrieve full card components

[Maciej Strozek]

W dniu czw, 05.03.2026 o godzinie 11∶04 +0100, użytkownik Takashi Iwai
napisał:
> On Thu, 05 Mar 2026 10:54:35 +0100,
> Maciej Strozek wrote:
> > 
> > W dniu wto, 03.03.2026 o godzinie 16∶47 +0100, użytkownik Takashi
> > Iwai
> > napisał:
> > > > 
> > > > + */
> > > > +struct snd_ctl_card_components {
> > > > + int card;
> > > > + unsigned int length;
> > > > + unsigned char *components;
> > > > +};
> > > 
> > > And the ioctl can serve for two purposes:
> > > 
> > > - When length=0 is set, the kernel stores the current number of
> > > bytes
> > >   and returns without copying.  User-space can use this mode for
> > >   allocating the buffer.
> > > 
> > In alsa-lib all data must be allocated beforehand, so this
> > length==0
> > query is not very useful there, it will just go into a [512] array
> > anyway. Are there any other users that may benefit from this?
> 
> My suggested API can work even with the fixed size 512, too, if 512
> is
> hight enough.  It's just more flexible.  And there is no restriction
> about alsa-lib data allocation; the function can query the size then
> allocate, too.
> 
> 
> Takashi

OK, will prepare v4 with this, thanks

-- 
Regards,
Maciej

Re: [PATCH v3 2/2] ALSA: control: add ioctl to retrieve full card components

[Takashi Iwai]

On Thu, 05 Mar 2026 11:11:40 +0100,
Maciej Strozek wrote:
> 
> W dniu czw, 05.03.2026 o godzinie 11∶04 +0100, użytkownik Takashi Iwai
> napisał:
> > On Thu, 05 Mar 2026 10:54:35 +0100,
> > Maciej Strozek wrote:
> > > 
> > > W dniu wto, 03.03.2026 o godzinie 16∶47 +0100, użytkownik Takashi
> > > Iwai
> > > napisał:
> > > > > 
> > > > > + */
> > > > > +struct snd_ctl_card_components {
> > > > > + int card;
> > > > > + unsigned int length;
> > > > > + unsigned char *components;
> > > > > +};
> > > > 
> > > > And the ioctl can serve for two purposes:
> > > > 
> > > > - When length=0 is set, the kernel stores the current number of
> > > > bytes
> > > >   and returns without copying.  User-space can use this mode for
> > > >   allocating the buffer.
> > > > 
> > > In alsa-lib all data must be allocated beforehand, so this
> > > length==0
> > > query is not very useful there, it will just go into a [512] array
> > > anyway. Are there any other users that may benefit from this?
> > 
> > My suggested API can work even with the fixed size 512, too, if 512
> > is
> > hight enough.  It's just more flexible.  And there is no restriction
> > about alsa-lib data allocation; the function can query the size then
> > allocate, too.
> > 
> > 
> > Takashi
> 
> OK, will prepare v4 with this, thanks

Well, let's see how others think, too.  The API design needs more
considerations because we can't change it any longer once after
defined.


thanks,

Takashi

Re: [PATCH v3 2/2] ALSA: control: add ioctl to retrieve full card components

[Jaroslav Kysela]

On 3/5/26 11:18, Takashi Iwai wrote:
> On Thu, 05 Mar 2026 11:11:40 +0100,
> Maciej Strozek wrote:
>>
>> W dniu czw, 05.03.2026 o godzinie 11∶04 +0100, użytkownik Takashi Iwai
>> napisał:
>>> On Thu, 05 Mar 2026 10:54:35 +0100,
>>> Maciej Strozek wrote:
>>>>
>>>> W dniu wto, 03.03.2026 o godzinie 16∶47 +0100, użytkownik Takashi
>>>> Iwai
>>>> napisał:
>>>>>>
>>>>>> + */
>>>>>> +struct snd_ctl_card_components {
>>>>>> + int card;
>>>>>> + unsigned int length;
>>>>>> + unsigned char *components;
>>>>>> +};
>>>>>
>>>>> And the ioctl can serve for two purposes:
>>>>>
>>>>> - When length=0 is set, the kernel stores the current number of
>>>>> bytes
>>>>>    and returns without copying.  User-space can use this mode for
>>>>>    allocating the buffer.
>>>>>
>>>> In alsa-lib all data must be allocated beforehand, so this
>>>> length==0
>>>> query is not very useful there, it will just go into a [512] array
>>>> anyway. Are there any other users that may benefit from this?
>>>
>>> My suggested API can work even with the fixed size 512, too, if 512
>>> is
>>> hight enough.  It's just more flexible.  And there is no restriction
>>> about alsa-lib data allocation; the function can query the size then
>>> allocate, too.
>>>
>>>
>>> Takashi
>>
>> OK, will prepare v4 with this, thanks
> 
> Well, let's see how others think, too.  The API design needs more
> considerations because we can't change it any longer once after
> defined.

I think that the indirect pointer in ioctl structure is the best at the moment 
unless we decide to use the fixed char array. But (for discussion) we may try 
to be a bit clever and define universal bytes ioctl which may carry also other 
things in future like:

enum {
	SND_CTL_CARD_BTYPE_COMPONENTS = 1
};

struct snd_ctl_card_bytes {
	unsigned int card;		// this is duplication with info ioctl
					// to be removed?
	unsigned int type;		// e.g. SND_CTL_CARD_BTYPE_COMPONENTS
	unsigned int data_allocated;	// overall size of data
	unsigned int data_len;		// actual data len
	unsigned char *data;		// pointer to data array
};

Scenarios:

data_allocated = 0 or data == NULL -> driver just returns data_len
data_allocated < data_len -> driver returns -ENOMEM
data_allocated >= data_len -> driver will copy data

Note that data_len will be zero from the user space for read operations 
(driver knows it). But we can eventually use this ioctl to set some data in 
future, so data_len/data will be used for the write operation.

				Jaroslav

-- 
Jaroslav Kysela <perex@perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.

Re: [PATCH v3 2/2] ALSA: control: add ioctl to retrieve full card components

[Takashi Iwai]

On Fri, 06 Mar 2026 10:39:46 +0100,
Jaroslav Kysela wrote:
> 
> On 3/5/26 11:18, Takashi Iwai wrote:
> > On Thu, 05 Mar 2026 11:11:40 +0100,
> > Maciej Strozek wrote:
> >> 
> >> W dniu czw, 05.03.2026 o godzinie 11∶04 +0100, użytkownik Takashi Iwai
> >> napisał:
> >>> On Thu, 05 Mar 2026 10:54:35 +0100,
> >>> Maciej Strozek wrote:
> >>>> 
> >>>> W dniu wto, 03.03.2026 o godzinie 16∶47 +0100, użytkownik Takashi
> >>>> Iwai
> >>>> napisał:
> >>>>>> 
> >>>>>> + */
> >>>>>> +struct snd_ctl_card_components {
> >>>>>> + int card;
> >>>>>> + unsigned int length;
> >>>>>> + unsigned char *components;
> >>>>>> +};
> >>>>> 
> >>>>> And the ioctl can serve for two purposes:
> >>>>> 
> >>>>> - When length=0 is set, the kernel stores the current number of
> >>>>> bytes
> >>>>>    and returns without copying.  User-space can use this mode for
> >>>>>    allocating the buffer.
> >>>>> 
> >>>> In alsa-lib all data must be allocated beforehand, so this
> >>>> length==0
> >>>> query is not very useful there, it will just go into a [512] array
> >>>> anyway. Are there any other users that may benefit from this?
> >>> 
> >>> My suggested API can work even with the fixed size 512, too, if 512
> >>> is
> >>> hight enough.  It's just more flexible.  And there is no restriction
> >>> about alsa-lib data allocation; the function can query the size then
> >>> allocate, too.
> >>> 
> >>> 
> >>> Takashi
> >> 
> >> OK, will prepare v4 with this, thanks
> > 
> > Well, let's see how others think, too.  The API design needs more
> > considerations because we can't change it any longer once after
> > defined.
> 
> I think that the indirect pointer in ioctl structure is the best at
> the moment unless we decide to use the fixed char array.

OK, it might be indeed better if the user-space API is something like:

int snd_ctl_card_components(snd_ctl_t *ctl, unsigned char *buf, size_t len);

Then it's simpler to pass the pointer as is without copying.

> But (for
> discussion) we may try to be a bit clever and define universal bytes
> ioctl which may carry also other things in future like:
> 
> enum {
> 	SND_CTL_CARD_BTYPE_COMPONENTS = 1
> };

So this is for future extensions?

> struct snd_ctl_card_bytes {
> 	unsigned int card;		// this is duplication with info ioctl
> 					// to be removed?

Right, it sounds like superfluous.  I thought we were to allow
extracting a card info for a different card number, but it doesn't
look so.

> 	unsigned int type;		// e.g. SND_CTL_CARD_BTYPE_COMPONENTS
> 	unsigned int data_allocated;	// overall size of data
> 	unsigned int data_len;		// actual data len
> 	unsigned char *data;		// pointer to data array
> };
> 
> Scenarios:
> 
> data_allocated = 0 or data == NULL -> driver just returns data_len
> data_allocated < data_len -> driver returns -ENOMEM
> data_allocated >= data_len -> driver will copy data
> 
> Note that data_len will be zero from the user space for read
> operations (driver knows it). But we can eventually use this ioctl to
> set some data in future, so data_len/data will be used for the write
> operation.

In all cases, data_len is filled with the expected data size in
return, right?


thanks,

Takashi

Re: [PATCH v3 2/2] ALSA: control: add ioctl to retrieve full card components

[Jaroslav Kysela]

On 3/6/26 11:43, Takashi Iwai wrote:
> On Fri, 06 Mar 2026 10:39:46 +0100,
> Jaroslav Kysela wrote:
>>
>> On 3/5/26 11:18, Takashi Iwai wrote:
>>> On Thu, 05 Mar 2026 11:11:40 +0100,
>>> Maciej Strozek wrote:
>>>>
>>>> W dniu czw, 05.03.2026 o godzinie 11∶04 +0100, użytkownik Takashi Iwai
>>>> napisał:
>>>>> On Thu, 05 Mar 2026 10:54:35 +0100,
>>>>> Maciej Strozek wrote:
>>>>>>
>>>>>> W dniu wto, 03.03.2026 o godzinie 16∶47 +0100, użytkownik Takashi
>>>>>> Iwai
>>>>>> napisał:
>>>>>>>>
>>>>>>>> + */
>>>>>>>> +struct snd_ctl_card_components {
>>>>>>>> + int card;
>>>>>>>> + unsigned int length;
>>>>>>>> + unsigned char *components;
>>>>>>>> +};
>>>>>>>
>>>>>>> And the ioctl can serve for two purposes:
>>>>>>>
>>>>>>> - When length=0 is set, the kernel stores the current number of
>>>>>>> bytes
>>>>>>>     and returns without copying.  User-space can use this mode for
>>>>>>>     allocating the buffer.
>>>>>>>
>>>>>> In alsa-lib all data must be allocated beforehand, so this
>>>>>> length==0
>>>>>> query is not very useful there, it will just go into a [512] array
>>>>>> anyway. Are there any other users that may benefit from this?
>>>>>
>>>>> My suggested API can work even with the fixed size 512, too, if 512
>>>>> is
>>>>> hight enough.  It's just more flexible.  And there is no restriction
>>>>> about alsa-lib data allocation; the function can query the size then
>>>>> allocate, too.
>>>>>
>>>>>
>>>>> Takashi
>>>>
>>>> OK, will prepare v4 with this, thanks
>>>
>>> Well, let's see how others think, too.  The API design needs more
>>> considerations because we can't change it any longer once after
>>> defined.
>>
>> I think that the indirect pointer in ioctl structure is the best at
>> the moment unless we decide to use the fixed char array.
> 
> OK, it might be indeed better if the user-space API is something like:
> 
> int snd_ctl_card_components(snd_ctl_t *ctl, unsigned char *buf, size_t len);
> 
> Then it's simpler to pass the pointer as is without copying.
> 
>> But (for
>> discussion) we may try to be a bit clever and define universal bytes
>> ioctl which may carry also other things in future like:
>>
>> enum {
>> 	SND_CTL_CARD_BTYPE_COMPONENTS = 1
>> };
> 
> So this is for future extensions?
> 
>> struct snd_ctl_card_bytes {
>> 	unsigned int card;		// this is duplication with info ioctl
>> 					// to be removed?
> 
> Right, it sounds like superfluous.  I thought we were to allow
> extracting a card info for a different card number, but it doesn't
> look so.
> 
>> 	unsigned int type;		// e.g. SND_CTL_CARD_BTYPE_COMPONENTS
>> 	unsigned int data_allocated;	// overall size of data
>> 	unsigned int data_len;		// actual data len
>> 	unsigned char *data;		// pointer to data array
>> };
>>
>> Scenarios:
>>
>> data_allocated = 0 or data == NULL -> driver just returns data_len
>> data_allocated < data_len -> driver returns -ENOMEM
>> data_allocated >= data_len -> driver will copy data
>>
>> Note that data_len will be zero from the user space for read
>> operations (driver knows it). But we can eventually use this ioctl to
>> set some data in future, so data_len/data will be used for the write
>> operation.
> 
> In all cases, data_len is filled with the expected data size in
> return, right?

I would return data_len only when data_allocated == 0 or when the user space 
array can hold complete data. When ioctl returns an error code (e.g. ENOMEM), 
the structure should not be modified IMHO.

Eventually, we can extend the structure to be even more universal and add 
'data_offset' and 'data_overall_len' to support fully partial transfers. In 
this case, data_len would mean filled/used chunk size and the "overflow" error 
won't exist.

						Jaroslav

-- 
Jaroslav Kysela <perex@perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.

Re: [PATCH v3 2/2] ALSA: control: add ioctl to retrieve full card components

[Takashi Iwai]

On Mon, 09 Mar 2026 10:44:25 +0100,
Jaroslav Kysela wrote:
> 
> On 3/6/26 11:43, Takashi Iwai wrote:
> > On Fri, 06 Mar 2026 10:39:46 +0100,
> > Jaroslav Kysela wrote:
> >> 
> >> On 3/5/26 11:18, Takashi Iwai wrote:
> >>> On Thu, 05 Mar 2026 11:11:40 +0100,
> >>> Maciej Strozek wrote:
> >>>> 
> >>>> W dniu czw, 05.03.2026 o godzinie 11∶04 +0100, użytkownik Takashi Iwai
> >>>> napisał:
> >>>>> On Thu, 05 Mar 2026 10:54:35 +0100,
> >>>>> Maciej Strozek wrote:
> >>>>>> 
> >>>>>> W dniu wto, 03.03.2026 o godzinie 16∶47 +0100, użytkownik Takashi
> >>>>>> Iwai
> >>>>>> napisał:
> >>>>>>>> 
> >>>>>>>> + */
> >>>>>>>> +struct snd_ctl_card_components {
> >>>>>>>> + int card;
> >>>>>>>> + unsigned int length;
> >>>>>>>> + unsigned char *components;
> >>>>>>>> +};
> >>>>>>> 
> >>>>>>> And the ioctl can serve for two purposes:
> >>>>>>> 
> >>>>>>> - When length=0 is set, the kernel stores the current number of
> >>>>>>> bytes
> >>>>>>>     and returns without copying.  User-space can use this mode for
> >>>>>>>     allocating the buffer.
> >>>>>>> 
> >>>>>> In alsa-lib all data must be allocated beforehand, so this
> >>>>>> length==0
> >>>>>> query is not very useful there, it will just go into a [512] array
> >>>>>> anyway. Are there any other users that may benefit from this?
> >>>>> 
> >>>>> My suggested API can work even with the fixed size 512, too, if 512
> >>>>> is
> >>>>> hight enough.  It's just more flexible.  And there is no restriction
> >>>>> about alsa-lib data allocation; the function can query the size then
> >>>>> allocate, too.
> >>>>> 
> >>>>> 
> >>>>> Takashi
> >>>> 
> >>>> OK, will prepare v4 with this, thanks
> >>> 
> >>> Well, let's see how others think, too.  The API design needs more
> >>> considerations because we can't change it any longer once after
> >>> defined.
> >> 
> >> I think that the indirect pointer in ioctl structure is the best at
> >> the moment unless we decide to use the fixed char array.
> > 
> > OK, it might be indeed better if the user-space API is something like:
> > 
> > int snd_ctl_card_components(snd_ctl_t *ctl, unsigned char *buf, size_t len);
> > 
> > Then it's simpler to pass the pointer as is without copying.
> > 
> >> But (for
> >> discussion) we may try to be a bit clever and define universal bytes
> >> ioctl which may carry also other things in future like:
> >> 
> >> enum {
> >> 	SND_CTL_CARD_BTYPE_COMPONENTS = 1
> >> };
> > 
> > So this is for future extensions?
> > 
> >> struct snd_ctl_card_bytes {
> >> 	unsigned int card;		// this is duplication with info ioctl
> >> 					// to be removed?
> > 
> > Right, it sounds like superfluous.  I thought we were to allow
> > extracting a card info for a different card number, but it doesn't
> > look so.
> > 
> >> 	unsigned int type;		// e.g. SND_CTL_CARD_BTYPE_COMPONENTS
> >> 	unsigned int data_allocated;	// overall size of data
> >> 	unsigned int data_len;		// actual data len
> >> 	unsigned char *data;		// pointer to data array
> >> };
> >> 
> >> Scenarios:
> >> 
> >> data_allocated = 0 or data == NULL -> driver just returns data_len
> >> data_allocated < data_len -> driver returns -ENOMEM
> >> data_allocated >= data_len -> driver will copy data
> >> 
> >> Note that data_len will be zero from the user space for read
> >> operations (driver knows it). But we can eventually use this ioctl to
> >> set some data in future, so data_len/data will be used for the write
> >> operation.
> > 
> > In all cases, data_len is filled with the expected data size in
> > return, right?
> 
> I would return data_len only when data_allocated == 0 or when the user
> space array can hold complete data. When ioctl returns an error code
> (e.g. ENOMEM), the structure should not be modified IMHO.

I find it OK, otherwise you'd need one more ioctl, but it's a kind of
bike-shedding topic, and I don't mind much whether it should be so or
not.

> Eventually, we can extend the structure to be even more universal and
> add 'data_offset' and 'data_overall_len' to support fully partial
> transfers. In this case, data_len would mean filled/used chunk size
> and the "overflow" error won't exist.

Yeah, we can, and I had that in mind, too.  But it makes things
complex, so let's not step into it yet.


thanks,

Takashi