[pulseaudio-discuss] Mixer connection when switching users

[David Henningsson]

On 2015-09-18 18:07, Tanu Kaskinen wrote:
> Hi,
>
> I noticed that my headphone volume wasn't getting restored properly
> when plugging in the headphones. The probable cause turned out to be
> that gdm's PulseAudio instance was messing with the mixer controls,
> causing mixer update events in my own PulseAudio instance.
>
> At the time I logged in, the gdm user lost access to the sound cards,
> but Linux doesn't revoke access to file descriptors that are already
> open. PulseAudio voluntarily closes the PCM device connections in that
> situation, but PulseAudio doesn't close the mixer connection, so gdm
> still had access to the mixer, and the jack detection events caused the
> gdm to fiddle with the mixer controls.
>
> I will fix this issue, but I'm not sure how I should do that. There
> might be some simple fix that would prevent mixer modifications when
> the sink suspend cause is PA_SUSPEND_SESSION, but I could also do a
> bigger change: close the mixer connection when udev changes the device
> permissions. I think it's a bug in itself that we keep the mixer
> connection open, even if in practice there's no harm from doing that.
> Do others think the same, or should I try to only make a minimal fix,
> adding a check somewhere that prevents writes to the mixer when
> PA_SUSPEND_SESSION is set?

Sorry for the late answer.

I tend to agree, we should close the mixer connection if we don't have 
any access rights to it anyway.

The fun thing happens when we have access again though - I think we 
first need to re-check jack detection stuff and update our current port 
(via module-switch-on-port-available), then we should probably 
synchronize volumes regardless of whether the port changed or not? And 
by that I mean always pushing our volume to the device, not the other 
way around.


-- 
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic