Sys-audio and (Windows) HVMs

Original forum link

https://forum.qubes-os.org/t/17735

Original poster

HSF3232

Editors

deeplow

Created at

2023-03-30 19:32:15

Last wiki edit

2023-09-07 05:25:28

Revisions

1 revision

Posts count

2

Likes count

2

So, after a while of having no audio in HVMs if using sys-audio, I decided to have a look into the issue. Using https://forum.qubes-os.org/t/using-sys-audio-for-windows-audio/10416/9 as a starting point, I created a patch file that can be applied to init in /usr/libexec/xen/boot/qemu-stubdom-linux-full-rootfs.

--- init    2023-03-30 17:15:27.389013186 +0100
+++ init    2023-03-30 17:17:35.048015003 +0100
@@ -29,6 +29,7 @@

 # add audiodev conf to cmdline and run pulseaudio 
 audio_model=$(echo "$dm_args" | sed -n '/^-soundhw/ {n;p}')
+audioid=$(xenstore-read "/global/qvm-hvm-audio-id" || echo "0")
 if [ -n "$audio_model" ] ; then
     model_args=
     if [ "$audio_model" == "ich6" ] ; then
@@ -38,7 +39,7 @@
     pa_args=$'-audiodev\npa,id=qemupa,server=unix:/tmp/pa.sock'$model_args;
     pulseaudio --use-pid-file=no --daemonize=no --exit-idle-time=-1 --disable-shm=yes -n \
    -L "module-native-protocol-unix auth-anonymous=1 socket=/tmp/pa.sock" \
-   -L "module-vchan-sink domid=0" &
+   -L "module-vchan-sink domid=$audioid" &
 fi

 # Extract network parameters and remove them from dm_args

Following @disp584's instructions, ensuring that commands are run as root...

1. If patch is not already installed... qubes-dom0-update patch
2. Make a working directory for the stubdom: mkdir /tmp/stubroot
3. Copy the stubdom into the directory: cp /usr/libexec/xen/boot/qemu-stubdom-linux-full-rootfs /tmp/stubroot/stubdom.gz
4. cd into the directory: cd /tmp/stubroot
5. Decompress: gzip -d stubdom.gz
6. Extract: cpio -i -d -H newc --no-absolute-filenames < stubdom ; rm stubdom
7. Patch init: patch < /path/to/downloaded/audioid.patch
8. Rebuild stubdom: find . -print0 | cpio --null -ov --format=newc | gzip -9 > ../new-stubdom
9. (Optional) Make a backup of the original stubdom: cp /usr/libexec/xen/boot/qemu-stubdom-linux-full-rootfs /usr/libexec/xen/boot/qemu-stubdom-linux-full-rootfs.BAK
10. Copy the new stubdom over the old one: mv ../new-stubdom /usr/libexec/xen/boot/qemu-stubdom-linux-full-rootfs
11. Save the following below to a script and execute said script to update the requisite xen variable:

    #!/bin/bash
    audiodomain=$(qubes-prefs default_audiovm)
    echo "Audio domain is $audiodomain"
    ADxid=$(qvm-prefs "$audiodomain" xid)
    echo "xid of audio domain is $ADxid"
    if [ "$ADxid" -gt -1 ]; then
      xenstore-write /global/qvm-hvm-audio-id "$ADxid"
      xenstore-chmod /global/qvm-hvm-audio-id "r*w0"
    else
      echo "Not updating, AudioVM not running!"
    fi
    
    echo "Wrote $ADxid to /global/qvm-hvm-audio-id and reset perms to r*w0"
    

This should now allow audio to work correctly within HVMs. Unfortunately, attempts to make the script above execute automatically as a libvirt hook only caused the system to hang upon reboot or upon starting up any HVM. Even executing the script above in background results in the system hanging. I suspect this is due to QubesDB or whatever qubes-prefs/qvm-prefs uses hanging while a VM starts up. Also, this script assumes that "default_audiovm" is set to something other than dom0 via qubes-prefs default_audiovm.

So, any additions to this solution is welcome!