Re: [PATCH v9 2/2] img/app: Run PipeWire and WirePlumber in the VMs

[Demi Marie Obenour <demiobenour@gmail.com>]

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On 7/29/25 09:08, Alyssa Ross wrote:
> Demi Marie Obenour <demiobenour@gmail.com> writes:
> 
>> WirePlumber is completely overkill as a session manager here, and
>> ideally a trivial session manager would be used instead.  PipeWire is
>> configured to listen on the PulseAudio socket, so PulseAudio
>> compatibility works.  pw-record and pw-play both work, and if PulseAudio
>> is installed paplay and parecord also work.  This does install a lot of
>> unnecessary files into the VMs, which will hopefully be removed
>> later as part of a debloating effort.
>>
>> Only run-qemu has had a virtio-sound device added, as crosvm and Cloud
>> Hypervisor require a virtio-user sound device and that is more complex
>> to set up.
>>
>> Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
>> ---
>> Changes since v8:
>> - Add longer explanation for the priority.driver and priority.session
>>   values.
>> - Give credit to George Kiagiadakis.
>> - Fix spelling errors in comments.
>>
>> Changes since v7:
>> - Give the capture node a higher priority.session than the playback
>>   node, so WirePlumber links recording applications to the capture node
>>   instead of the monitor of the playback node.
>> - Give the capture node a higher priority.driver than the playback node,
>>   so PipeWire has the capture node drive the graph.  This is better
>>   because capture xruns lead to permanently corrupted data, whereas
>>   playback xruns do not.
>> - Re-enable monitor node creation in WirePlumber.
>>
>> Changes since v6:
>> - Fix spelling errors in commit messages.
>> - Sort lines in Makefile.
>> - Don't disable support.settings as a comment in wireplumber.conf says
>>   to not do that.  Instead, tell WirePlumber to not create monitor
>>   nodes.  This is a workaround for WirePlumber bug 829.
>> - Don't remove "-cpu host" from make run-qemu's QEMU command line.  This
>>   was needed for local testing with KVM disabled but should not have
>>   been submitted upstream.  Hardware with KVM support should be used
>>   instead.
>>
>> Changes since v5:
>>
>> - Use a drop-in configuration file for WirePlumber instead of overriding
>>   wireplumber.conf.  This should be more robust to future WirePlumber
>>   changes.
>> ---
>>  img/app/Makefile                              |  16 +-
>>  img/app/default.nix                           |   3 +
>>  img/app/etc/mdev.conf                         |   1 +
>>  img/app/etc/pipewire/pipewire.conf            | 229 ++++++++++++++++++
>>  .../etc/s6-rc/app/dependencies.d/wireplumber  |   0
>>  .../etc/s6-rc/pipewire/dependencies.d/dbus    |   0
>>  img/app/etc/s6-rc/pipewire/notification-fd    |   1 +
>>  .../s6-rc/pipewire/notification-fd.license    |   2 +
>>  img/app/etc/s6-rc/pipewire/run                |  23 ++
>>  img/app/etc/s6-rc/pipewire/type               |   1 +
>>  img/app/etc/s6-rc/pipewire/type.license       |   2 +
>>  .../etc/s6-rc/wireplumber/dependencies.d/dbus |   0
>>  .../s6-rc/wireplumber/dependencies.d/pipewire |   0
>>  img/app/etc/s6-rc/wireplumber/run             |   4 +
>>  img/app/etc/s6-rc/wireplumber/type            |   1 +
>>  img/app/etc/s6-rc/wireplumber/type.license    |   2 +
>>  .../wireplumber.conf.d/99_spectrum.conf       |  42 ++++
>>  17 files changed, 325 insertions(+), 2 deletions(-)
>>  create mode 100644 img/app/etc/pipewire/pipewire.conf
>>  create mode 100644 img/app/etc/s6-rc/app/dependencies.d/wireplumber
>>  create mode 100644 img/app/etc/s6-rc/pipewire/dependencies.d/dbus
>>  create mode 100644 img/app/etc/s6-rc/pipewire/notification-fd
>>  create mode 100644 img/app/etc/s6-rc/pipewire/notification-fd.license
>>  create mode 100644 img/app/etc/s6-rc/pipewire/run
>>  create mode 100644 img/app/etc/s6-rc/pipewire/type
>>  create mode 100644 img/app/etc/s6-rc/pipewire/type.license
>>  create mode 100644 img/app/etc/s6-rc/wireplumber/dependencies.d/dbus
>>  create mode 100644 img/app/etc/s6-rc/wireplumber/dependencies.d/pipewire
>>  create mode 100644 img/app/etc/s6-rc/wireplumber/run
>>  create mode 100644 img/app/etc/s6-rc/wireplumber/type
>>  create mode 100644 img/app/etc/s6-rc/wireplumber/type.license
>>  create mode 100644 img/app/etc/wireplumber/wireplumber.conf.d/99_spectrum.conf
> 
> We have app depending on wireplumber, but no notification-fd for
> wireplumber.  What's actually required here?  Does Wireplumber actually
> need to be running (for whatever definition thereof) by the time an
> application starts, or does it just need to start at some reasonable
> point?

The latter.  In systemd terms, this is WantedBy=.  I will fix this by
having ok-all depend on WirePlumber, while the app no longer does.

>> +    # PipeWire chooses the node with the highest priority.driver value as
>> +    # graph driver, which is the node that decides when the processing graph
>> +    # is going to run.  If both the capture node and playback node are in
>> +    # the same graph, the capture node should be chosen as the driver.  This
>> +    # is because the driver gets to choose the rate of the graph and so is
>> +    # much less likely to xrun.  Since capture xruns result in corrupted
>> +    # audio recordings, while playback xruns just result in a glitch, it
>> +    # is more important to avoid capture xruns.
>> +    #
>> +    # When there are multiple sources or sinks that could be used,
>> +    # WirePlumber links application nodes to the one with the highest
>> +    # priority.session value.  In the configuration created here,
>> +    # there are two valid audio sources: the virtio sound card's
>> +    # capture stream and the monitor of its playback stream.  The
>> +    # capture stream is the correct choice, so its priority.session
>> +    # should be higher.
>> +    #
>> +    # The recommendation to give the capture device higher values
>> +    # for priority.driver and priority.session comes from George
>> +    # Kiagiadakis of Collabora, who also provided the values
>> +    # used (2000 and 1000) and why they must be different.
>> +    # The explanation for why it is more important to avoid
>> +    # capture xruns than playback xruns comes from past discussions
>> +    # that I (Demi Marie Obenour) had with Wim Taymans.
> 
> Just checking: they're okay with being credited, right?  (Important for
> me to be confident before mentioning anybody in an immutable log.)

That's actually not something I had checked.  I asked both if they are
okay with this.  Should I sent V10 without these, or should I wait
for a response from them?

>> diff --git a/img/app/etc/s6-rc/app/dependencies.d/wireplumber b/img/app/etc/s6-rc/app/dependencies.d/wireplumber
>> new file mode 100644
>> index 0000000000000000000000000000000000000000..e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
>> diff --git a/img/app/etc/s6-rc/pipewire/dependencies.d/dbus b/img/app/etc/s6-rc/pipewire/dependencies.d/dbus

This dependency wasn't needed and wasn't included in the VMs.
v10 will leave it out.

>> --- /dev/null
>> +++ b/img/app/etc/s6-rc/pipewire/run
>> @@ -0,0 +1,23 @@
>> +#!/bin/execlineb -P
>> +# SPDX-License-Identifier: EUPL-1.2+
>> +# SPDX-FileCopyrightText: 2023-2024 Alyssa Ross <hi@alyssa.is>
>> +# SPDX-FileCopyrightText: 2025 Demi Marie Obenour <demiobenour@gmail.com>
>> +
>> +s6-ipcserver-socketbinder -B /run/user/0/pipewire-0
>> +fdmove -c 3 0
>> +
>> +s6-ipcserver-socketbinder -B /run/user/0/pipewire-0-manager
>> +fdmove -c 4 0
>> +
>> +redirfd -r 0 /dev/null
>> +
>> +# Wait for sound devices to be available
>> +if { /etc/mdev/wait controlC0 }
>> +
>> +# Notify readiness.
>> +if { fdmove 1 5 echo }
>> +fdclose 5
> 
> We could move this earlier, right?  If things connect before the sound
> devices are available, PipeWire won't have been started yet so the
> connection will just not be accepted until they are.

That is indeed correct.  Will change in v10.

>> diff --git a/img/app/etc/wireplumber/wireplumber.conf.d/99_spectrum.conf b/img/app/etc/wireplumber/wireplumber.conf.d/99_spectrum.conf
>> new file mode 100644
>> index 0000000000000000000000000000000000000000..277e6019c46582afba12af9b1a27bb16ddd9e804
>> --- /dev/null
>> +++ b/img/app/etc/wireplumber/wireplumber.conf.d/99_spectrum.conf
>> @@ -0,0 +1,42 @@
>> +# SPDX-License-Identifier: MIT
>> +# SPDX-FileCopyrightText: 2019-2021 Collabora Ltd.
>> +# SPDX-FileCopyrightText: 2025 Demi Marie Obenour
>> +
>> +# Copyright © 2019-2021 Collabora Ltd.
> 
> Once again I'm surprised any of this is © Collabora…

It's out of an abundance of caution.  All of this is taken from
the wireplumber.conf files in Arch and Nixpkgs, which I believe
are just the upstream ones.  I suspect you are correct, but
it's much better to keep a copyright notice that is not needed
than to remove one that actually *is* needed.

>> +#
>> +# Permission is hereby granted, free of charge, to any person obtaining a
>> +# copy of this software and associated documentation files (the "Software"),
>> +# to deal in the Software without restriction, including without limitation
>> +# the rights to use, copy, modify, merge, publish, distribute, sublicense,
>> +# and/or sell copies of the Software, and to permit persons to whom the
>> +# Software is furnished to do so, subject to the following conditions:
>> +#
>> +# The above copyright notice and this permission notice (including the next
>> +# paragraph) shall be included in all copies or substantial portions of the
>> +# Software.
>> +#
>> +# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
>> +# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
>> +# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
>> +# THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
>> +# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
>> +# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
>> +# DEALINGS IN THE SOFTWARE.
>> +
>> +wireplumber.profiles = {
>> +  spectrum = {
>> +    # Spectrum VMs are essentially embedded systems, in that they are
>> +    # not at all general-purpose.
>> +    inherits = [ main-embedded ]
>> +    # Disable video and Bluetooth
>> +    hardware.video-capture = disabled
>> +    hardware.bluetooth = disabled
>> +    # Media Session is definitely not running
>> +    check.no-media-session = disabled
>> +  }
>> +}
>> +
>> +wireplumber.settings = {
>> +  # Default to 100% sink volume.  The host will adjust this as needed.
>> +  device.routes.default-sink-volume = 1.0
>> +}


-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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