[systemd-devel] kdbus, udev and systemd in the initramfs

[Tom Gundersen]

On Wed, Jul 29, 2015 at 2:23 PM, Michael Biebl <mbiebl at gmail.com> wrote:
> 2015-07-29 5:40 GMT+02:00 Tom Gundersen <teg at jklm.no>:
>> On Wed, Jul 29, 2015 at 1:21 AM, Michael Biebl <mbiebl at gmail.com> wrote:
>>> something I was wondering regarding kdbus and udev.
>>> If udev wants to drop the netlink transport and instead rely on kdbus,
>>> would this mean, systemd becomes mandatory in the initramfs to setup
>>> kdbus before udev is run?
>>
>> _If_ udev drops netlink entirely, then yes someone would need to set
>> up kdbus. How this will all look has not been finally decided yet
>> though.
>
> Is this documented somewhere, what kind of setup needs to be done for
> kdbus?

Well, kdbus itself is extensively documented in the kernel man pages
[0], but I'm not aware of any step-by-step documentation for how to
make an alternative kdbus userspace implementation. Probably your best
bet is to look at the systemd code.

> How complicated is it, to get kdbus up and running with a
> minimal environment like the initramfs?

In principle, not hugely complicated. However, probably not worth the
effort unless you have a good reason to. Wouldn't it be simpler to
just use systemd (even if just as a wrapper around your current
scripts)?

Either way, I probably wouldn't put any serious amount of work into
this just for the sake of udev quite yet. We still don't know
precisely how it will shake out. In general though, I would expect
that one day you'll want kdbus in the initramfs for one reason or
another.

Cheers,

Tom

[0]: <http://www.freedesktop.org/software/systemd/kdbus/kdbus.html>