[alsa-devel] Detect when sound card is in use

[Takashi Iwai]

At Tue, 28 Apr 2009 21:16:26 +0200,
Claus Ilginnis wrote:
> 
> 
> Hi everyone,
> 
> I have a problem and I dont't know where to ask my questions anymore, so
> I hope this mailing list can help me make progress with my problem....
> 
> I have a speaker set connected to an USB-Power-Plug (by which I can turn
> the speakers on and off )
> 
> Now I want to detect, when the soundcard is in use and when not.
> (to turn the speakers on when needed...)
> (I am a C++ programmer so I can mess some things up)
> 
> So my question is:
> Which way is best to detect wheather my sound card is in use or not ?
> Is there a general overview/documentation of the sound kernel modules
> which describes the general relationship between them ?
> What would you do ?

The easiest way would be to check the status of device files, such as
/dev/snd/*, whether any process opens it, e.g. via lsof command.
But, this doesn't cover the case like an app such as a mixer applet
which keeps opening the device but access only occasionally.


Takashi