Re: [PATCH v6 2/2] ALSA: control: add ioctl to retrieve full card components

[Takashi Iwai <tiwai@suse.de>]

On Mon, 20 Jul 2026 12:35:05 +0200,
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 SNDRV_CTL_IOCTL_CARD_BYTES that carries a variable-length payload
> selected by a type discriminator. The first defined type
> SND_CTL_CARD_BTYPE_COMPONENTS returns the full components string. The
> ioctl is designed to be reused for other variable-length card payloads
> in the future.
> 
> The user-space caller may set data_allocated == 0 (or data == NULL) to
> query the required length; otherwise the kernel copies the payload into
> the user buffer and writes back the actual length in data_len.
> 
> When the legacy components field in struct snd_ctl_card_info is
> truncated, '>' is written just before the NUL terminator to signal to
> user-space that the full string is available via the new ioctl.
> 
> card->components is now dynamically allocated and grown in 32 byte
> increments via krealloc(), capped at 512 bytes.
> 
> 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 v6:
>  - take the snd_ioctl_rwsem write lock in snd_component_add()
> Changes for v5:
>  - use __u64 and u64_to_user_ptr() instead of 32bit compat layer
>  - handle a NULL card->components
> Changes for v4:
>  - replaced snd_ctl_card_components with snd_ctl_card_bytes for possible
>    future extensions
>  - support query mode (data_allocated == 0 or data == NULL)
>  - added compat 32-bit
>  - renamed card->components_ptr / components_ptr_alloc_size to
>    card->components / components_alloc_size
> 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()

Looks OK for me.  Jaroslav, could you review, too?
If nothing obvious is found, I'm going to take for 7.3.


thanks,

Takashi