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

[Takashi Iwai <tiwai@suse.de>]

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