How can I add `snd-aloop` kernel module on public Debian 10(buster) image provided by GCP?

Question

Background

I am trying to enable snd-aloop module on a Compute Engine instance running public Debian 10 (buster) image provided by GCP.

Output of uname -a:

Linux *** 4.19.0-18-cloud-amd64 #1 SMP Debian 4.19.208-1 (2021-09-29) x86_64 GNU/Linux

Issues

I tried to install this module by running modprobe snd-aloop. However I got the following error:

modprobe: FATAL: Module snd-aloop not found in directory /lib/modules/4.19.0-18-cloud-amd64

It seems that said module is not present.

So I tried to find a suitable package. Prior to this I update package repos by running sudo apt-get update. Packages I tried to install:

• linux-modules-extra-gcp
• linux-image-generic
• linux-modules-extra-$(uname -r)

Unfortunately none of these packages can be found.

Also I am unable to find any relevant resource on the internet addressing this issue.

Questions

• How can I add snd-aloop kernel module on Debian 10(buster)?
• Is there a package which contains this module?

If possible I would like to avoid building and installing this module from source. If no other way is possible I will try this as a last option.

Answer 1

By default there's no sound support in Debian 10 image provided by GCP; when you run find /lib/modules/$(uname -r) -type f -name '*.ko' | grep snd to list all the loadable modules there are no sound modules whatsovewer.

Additionally when you install alsa-utils and run it you wil see:

wb@deb10:~$ sudo alsactl init
alsactl: init:1757: No soundcards found...

I tried to find a solution but after two hours I gave up in favor of finding a workaround.

If you're OK with Ubuntu 18.04 LTS - then you're in luck - this module is there:

wb@ubuntu18:~$ modinfo snd-aloop
filename:       /lib/modules/5.4.0-1063-gcp/kernel/sound/drivers/snd-aloop.ko
license:        GPL
description:    A loopback soundcard
author:         Jaroslav Kysela <perex@perex.cz>
srcversion:     9401A0B894527BA1238B364
depends:        snd-pcm,snd
retpoline:      Y
intree:         Y
name:           snd_aloop
vermagic:       5.4.0-1063-gcp SMP mod_unload modversions 
signat:         PKCS#7
signer:         
sig_key:        
sig_hashalgo:   md4
parm:           index:Index value for loopback soundcard. (array of int)
parm:           id:ID string for loopback soundcard. (array of charp)
parm:           enable:Enable this loopback soundcard. (array of bool)
parm:           pcm_substreams:PCM substreams # (1-8) for loopback driver. (array of int)
parm:           pcm_notify:Break capture when PCM format/rate/channels changes. (array of int)

and after modprobe snd-aloop we can see it loaded along with all dependencies:

wb@ubuntu18:~$ lsmod | grep snd
Module                  Size  Used by
snd_aloop              24576  0
snd_pcm               102400  1 snd_aloop
snd_timer              36864  1 snd_pcm
snd                    86016  3 snd_timer,snd_aloop,snd_pcm
soundcore              16384  1 snd

and if I run

wb@ubuntu18:~$ sudo alsactl init
Found hardware: "Loopback" "Loopback Mixer" "" "" ""
Hardware is initialized using a generic method

We can see that there's some audio "hardware" present.

Module in question is also present "out of the box" in Centos8.

It's missing on the other hand in:

• Debian 10
• Debian 11
• Ubuntu > 20