Re: [PATCH v4 3/3] Run PipeWire and WirePlumber in the VMs

[Alyssa Ross <hi@alyssa.is>]

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Demi Marie Obenour <demiobenour@gmail.com> writes:

> On 7/18/25 07:27, 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.  I did build a
>>> Spectrum OS image and found that PipeWire and WirePlumber both
>>> successfully started.  PipeWire is configured to listen on the
>>> PulseAudio socket, so PulseAudio compatibility works.  This does inject
>>> a large number of completely unnecessary files into the VM, notably for
>>> libcamera and Bluetooth support.
>>>
>>> Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
>>> ---
>>>
>>> Notes:
>>>     I tested this with QEMU virtio-sound, but I am not sure if the paramters
>>>     are correct.  In particular, the sample rate might well be wrong.
>>>
>>>  img/app/Makefile                              |  28 +-
>>>  img/app/default.nix                           |  18 +
>>>  img/app/etc/pipewire/pipewire.conf            | 291 ++++++++
>>>  .../etc/s6-rc/app/dependencies.d/directories  |   0
>>>  .../app/dependencies.d/directories.license    |   2 +
>>>  .../etc/s6-rc/app/dependencies.d/wireplumber  |   0
>>>  .../app/dependencies.d/wireplumber.license    |   2 +
>>>  .../etc/s6-rc/dbus/dependencies.d/directories |   0
>>>  .../dbus/dependencies.d/directories.license   |   2 +
>>>  img/app/etc/s6-rc/directories/type            |   1 +
>>>  img/app/etc/s6-rc/directories/type.license    |   2 +
>>>  img/app/etc/s6-rc/directories/up              |  11 +
>>>  .../s6-rc/pipewire/dependencies.d/directories |   0
>>>  .../dependencies.d/directories.license        |   2 +
>>>  img/app/etc/s6-rc/pipewire/notification-fd    |   1 +
>>>  .../s6-rc/pipewire/notification-fd.license    |   2 +
>>>  img/app/etc/s6-rc/pipewire/run                |  20 +
>>>  img/app/etc/s6-rc/pipewire/type               |   1 +
>>>  img/app/etc/s6-rc/pipewire/type.license       |   2 +
>>>  .../dependencies.d/directories                |   0
>>>  .../dependencies.d/directories.license        |   2 +
>>>  img/app/etc/s6-rc/wayland-proxy-virtwl/run    |  11 -
>>>  .../etc/s6-rc/wireplumber/dependencies.d/dbus |   0
>>>  .../wireplumber/dependencies.d/dbus.license   |   2 +
>>>  .../s6-rc/wireplumber/dependencies.d/pipewire |   0
>>>  .../dependencies.d/pipewire.license           |   2 +
>>>  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 +
>>>  img/app/etc/wireplumber/wireplumber.conf      | 676 ++++++++++++++++++
>> 
>> The PipeWire and WirePlumber config files are still very big.  Is it
>> really not possible to make them smaller and rely on defaults where
>> possible?  With a whole big config like this, it's difficult to see what
>> Spectrum-specific stuff is going on.
>
> Both of these files are *smaller* than their upstream counterparts.
> The main Spectrum-specific stuff is:
>
> - Nodes are statically set up.  This is because PipeWire relies on
>   udev to enumerate device nodes, and Spectrum VMs don't have udev.
>
> - A lot of stuff in the upstream configuration files has been
>   removed.  Spectrum's configs should be *smaller* than their
>   upstream counterparts.
>
> Neither PipeWire nor WirePlumber has much in the way of a default
> configuration.  Without a configuration file, neither PipeWire nor
> WirePlumber does anything useful.  Overriding the defaults and
> using the upstream configuration file might be possible, but it
> seemed unlikely when I looked.  Spectrum VMs are more like
> embedded systems than the desktop systems the defaults are made
> for.

Okay, but there's still stuff that could definitely be trimmed.  The
comments explaining the syntax of the config file, and the default
values, for example.  I think they get in the way more than they help
because they make the actual non-default settings very sparse.
Similarly we probably don't need conditional overrides that are "only
applied when running in a VM".

> I recommend not including any of the upstream configuration
> files and only an allowlist of SPA plugins and PipeWire and
> WirePlumber modules.  Stuff like Bluetooth can also be excluded.
> Just because upstream nixpkgs pulls it in as a dependency does
> not mean the configuration in the VM actually needs it.
> Ideally, the various plugins and modules would all be separate
> build outputs with their own dependencies, and ‘pipewire’ and
> ‘wireplumber’ would be meta-packages that pull in all of them.

That's an interesting idea.  I think it would probably be feasible?  And
wouldn't share the same maintenance concerns as lots of overrides.

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