Re: [PATCH 3/3] host/rootfs: switch to systemd-udevd

[Alyssa Ross <hi@alyssa.is>]

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

> On 9/19/25 10:12, Alyssa Ross wrote:
>> I'm pleasantly surprised by how straightforward this is (mostly)!
>> 
>> Demi Marie Obenour <demiobenour@gmail.com> writes:
>> 
>>> The dependency on /dev/dri/card0 being present is eliminated, and
>>> whatever devices the user has are now picked up by the compositor.  New
>>> dependencies are added to ensure that udev coldplug has finished before
>>> any non-trivial services are started.  systemd-udev-trigger.service runs
>>> 'udevadm trigger' and has Before=sysinit.target, so anything that is not
>>> an early boot service can assume 'udevadm trigger' has run.
>> 
>> If software is expected to integrate with udev to discover new devices
>> at runtime, why do we need to introduce new dependencies?
>
> I believe 'udevadm trigger' is needed to process devices that are
> already plugged when systemd-udevd starts.  Otherwise, they will
> never appear.

Right, I get why we need to run it, but why do we need to block other
services on it?

>>> ---
>>>  host/rootfs/Makefile                               | 17 ++--
>>>  host/rootfs/default.nix                            | 94 ++++++----------------
>>>  host/rootfs/etc/init                               |  2 +-
>>>  host/rootfs/etc/mdev.conf                          |  7 --
>>>  host/rootfs/etc/mdev/listen                        |  2 +-
>>>  host/rootfs/etc/mdev/net/add                       |  1 +
>> 
>> We probably ought to rename /etc/mdev… is there an idiomatic place to
>> put these sorts of things with udev?
>
> /usr/lib/spectrum is the idiomatic place for this stuff.

Sounds good.

>> Can we remove our own static-nodes implementation?
>
> Yes, and I think it was never needed anyway as
> the kernel populates devtmpfs automatically.

It doesn't create static nodes though!  It's very annoying.

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