Re: Re: Re: [Development report #7] Audio Stack Improvements

Mark Johnston wrote:
> On Fri, Mar 15, 2024 at 06:00:16PM +0100, Christos Margiolis wrote:
> > Applications are meant to open an audio device through /dev/dsp (if
> > hw.snd.basename_clone is enabled), or through /dev/dspX, so the vast
> > majority of applications should work with no problems.
> > 
> > Applications that open a device through /dev/dspX.[X]X will break with
> > this patch. However, opening a device like this is discouraged anyway,
> > according to the sound(4) man page (see FILES section):
> 
> To your knowledge, do any popular applications actually do this?  A
> comment in the man page isn't very important if applications end up
> ignoring it. :)

I don't really know of an application that does this.

Konstantin Belousov wrote:
> On Fri, Mar 15, 2024 at 10:38:01PM -0400, Mark Johnston wrote:
> > If needed, would it be a lot of work to provide backward compatibility?
> Should be rather trivial, to catch the case in the devfs lookup clone
> callback and instantiate fake nodes.

So, it is indeed trivial to catch it in the lookup loop, but currently
/dev/dsp%d.[p|r|vp|vr]%d will have no effect because with this patch you
cannot open a specific channel, so what we could do is simply dev_ref()
/dev/dsp%d.

Florian Walpen wrote:
> Is it even possible to open pcm devices through /dev/dspX.Y currently?
> I remember that I stumbled upon this when I developed the Jack backend
> and it wasn't possible to open /dev/dspX.Y, I had to use /dev/dspX.
> Just checked and that still seems to be the case on 14.0-RELEASE.
> Unless I missed something, I'd conclude that it's not used in ports
> :-)

I think you can, but because a specific channel can only be opened
exclusively, if say, /dev/dsp0.0 is already opened, an application
cannot re-open it, so maybe this is why you're getting errors. Also some
IOCTLs seem to not work on VCHANs:

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=246208
 
> Non-clone aliases like /dev/dsp_mmap seem to work though, never
> actually seen them in use but I think we should preserve them as part
> of OSSv4 compatibility.

Yeah, we can do this.

Christos