snd_pcm_oss module not found

[jabranham]

Issue description

The snd_pcm_oss module is not found, resulting in this error on boot:

$ journalctl -b -p err
[...] systemd-modules-load[532]: Failed to find module 'snd_pcm_oss'

I think this is because sound.enableOSSEmulation defaults to True but the corresponding kernel modules don't seem to be compiled anywhere. Or at least not anywhere I could find.

Steps to reproduce

On nixos, set sound.enableOSSEmulation to True (the default), nixos-rebuild switch, reboot, then run journalctl -b -p err

Technical details

$ nix-shell -p nix-info --run "nix-info -m"`
 - system: `"x86_64-linux"`
 - host os: `Linux 4.14.93, NixOS, 18.09.1922.97e0d53d669 (Jellyfish)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.1.3`
 - channels(root): `"nixos-18.09.1922.97e0d53d669"`
 - channels(alex): `"nixos-19.03pre166308.626233eee6e"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

[ChengCat]

I run into this same issue.

[lheckemann]

I've made a change that should hopefully fix this (be38a70) but I have yet to test it.

[callahad]

Are we sure this is a complete fix?

I don't know much about sound daemons on Linux, but I did run across this statement in the Arch wiki (emphasis added):

To prevent applications from using ALSA's OSS emulation and bypassing PulseAudio (thereby preventing other applications from playing sound), make sure the module snd_pcm_oss is not being loaded

Perhaps we also need to check hardware.pulseaudio.enable before inserting snd_pcm_oss into boot.kernelModules at https://github.com/NixOS/nixpkgs/blob/release-18.09/nixos/modules/services/audio/alsa.nix#L100?

I don't know if this is necessary, or really how to test it, but if the Arch wiki is correct, it seems like inserting this module risks breaking pulseaudio.

[callahad]

(FWIW, snd_pcm_oss was added to boot.kernelModules six years ago in 0262475)

[lheckemann]

Good point. I'd say enableOSSEmulation should probably default to false regardless of pulseaudio — the OSS emulation hasn't actually been working for a while, and it can be done in a more versatile (e.g. not blocking other sound) way in user space using aoss.