[alsa-devel] [PATCH - alsa-lib 1/1] Change card/pid get functions to return -ENOSYS if the kernel is too old

[Adam Goode]

On Mon, Apr 4, 2016 at 10:54 AM, Takashi Iwai <tiwai at suse.de> wrote:

> On Fri, 01 Apr 2016 23:15:58 +0200,
> Martin Koegler wrote:
> >
> > On Fri, Apr 01, 2016 at 01:33:50PM -0400, Adam Goode wrote:
> > > When trying to get the pid or card of a client, the get functions will
> > > return -1 if there is no pid or card for a client. Clients have zero or
> > > one of these, so -1 is correct for these cases. But we also need to
> detect
> > > the case where the kernel cannot tell us if there is a card or pid, so
> > > that userspace can fallback to probing this information in the old way.
> >
> > Its a pity, that alsa-lib 1.1.1 has just been released, which just
> returns -1.
> > If the time between releases is really about 2 kernel releases, you will
> very likely
> > have to cope with the old API for some time.
>
> Strictly speaking, for the function behavior change, we'd need a new
> API function and deprecated the old one eventually.  But, this case is
> in a gray zone; the function definition doesn't prohibit to return an
> error value yet, but the change like this is incompatible with the
> current aconnect code, which is likely regarded as a template for
> other programs.
>
> OTOH, this is a pretty new API function, and it might be not too bad
> to fix the usage in the early stage, especially when it's a good
> improvement of the function behavior.
>
> So, for now, I'm inclined to take this change with a slight risk of
> breakage.  But I'm open for more arguments, and would like to hear any
> objections.
>
>
Thanks for reviewing this. As an alternative, we could introduce a
completely new function that either returns the kernel interface version
(which means client code would have to keep a mapping of versions ->
implemented features) or returns the implementation state of this
particular feature. In some ways that would be slightly more
straightforward for Chromium, since I could probe ALSA once for the kernel
state using a function specifically for that purpose. But it doesn't matter
to me either way.


Thanks,

Adam



>
> thanks,
>
> Takashi
>