I'm trying to get virtual_oss set up as a loopback device so that I can record system audio, using the command: virtual_oss -S -C 2 -c 2 -r 48000 -b 16 -s 1024 -f /dev/dsp3 -l ldsp

but recording from /dev/ldsp then gives nothing but silence

maybe I'm not understanding what -f does. I thought it meant that the loopback device would route the sound being played back through /dev/dsp3

is it actually just forwarding the audio from the loopback to the main pcm device, while providing that for recording on the loopback?

-f /dev/dsp3 seems equivalent to -P /dev/dsp3 -R /dev/dsp3, so what exactly is happening with dsp3's recording stream?

ant-x: you can pass (a copy of) an open fd to another process using sendmsg()

over a Unix domain socket

and yes, httpd would be the client, blocklistd is the server

And there should be an interface pre-determined between the client and server, right?

re: httpd as a client -- understood that much from <obsessivecomputingdisorder.com/posts/blacklistd-guide> .

if you mean a protocol, yes, all IPC (or RPC) requires both sides agree on a protocol, or nothing could be communicated

Yes.

if I'm creating a virtual_oss loopback and not specifying playback-only, does that just make the loopback audio a separate recording source on the loopback device?

how do I configure a virtual_oss device using mixer?

Which is why blocklistd support has to be built into the client.