Sound on multi-user system
It's been some time I've been annoyed by a problem that google reveals
is not so uncommon, but for which a solution seems to be quite hard to
find: letting the user currently active on a seat to use the sound
card, as long as no other really uses it. I also vaguely recall that
this used not to be a problem - in the old pre-alsa days, maybe ?
The basic problem seems to be that any program playing sound directly
though alsa wants to open /dev/snd/pcmC0D0p, but that only one is
allowed at any time. If only those apps released the device when they
don't need it any more, that would be all fine, but it appears not.
Those sound daemons around (had a quick look at jack and pulseaudio,
which seemed to me good choices) suffer from the same problem, since
(at least in their default setup) they run as the user wanting to play
sound, and open the alsa device for their exclusive use.
Pulseaudio apparently has an option to run as a system daemon: that
looks like a way to solve the problem... except that mode is not the
recommended one, and that (as a result ?) no obvious doc in the
package explain how to use it at all.
So the question is: is there any current method for solving this
problem with the software we have ?
I suppose the problem is that the client apps don't ask the alsa lib
to release the device - if they do, then that would simply be a but in
the alsa lib not to free the hw resource, and thus probably a simple
fix.
Then it would be quite painful to fix all those apps to behave
properly - although we could want to set this as a release goal for
squeeze+1. An easier solution, since daemons like jackd see to be in
widespread use, to just make them behave properly and release the alsa
device when they have no use for it (maybe after some timeout). As
long as all clients first try to connect to jackd before trying to
open the alsa device directly, it looks like that would work as expected.
How does that sound ?
Best regards,
--
Yann
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