[arch-projects] [netcfg] [PATCH 3/3] systemd: Replace netcfg.service with a generator in order to get proper dependencies

[Jouke Witteveen]

On Thu, Oct 25, 2012 at 11:53 PM, Thomas Bächler <thomas at archlinux.org> wrote:
> Until now, netcfg might fail to start because it is started too early (this actually
> happened to me quite regularly). To fix this, we need to make systemd aware of the
> dependencies of a profile.
>
> This commit adds a systemd generator that creates profiles with the names
>    netcfg-profile-$PROFILE.service
> on boot. The ugly part: You cannot permanently enable such a profile, as it is
> generated during boot. To enable it, put it in NETWORKS=() - it will always be
> loaded, unless netcfg-profiles.target is masked. The old netcfg.service has
> been removed. This scheme does not support NETWORKS=(last) anymore, since we
> cannot determine which units were manually started or stopped before.
>
> If you add a new profile, you need to reload the systemd configuration so the
> service file shows up. We should encourage people to use systemctl to start
> and stop their profiles instead of netcfg.
>
> While this scheme is less intuitive than netcfg at profilename.service, it
> is the only way to provide proper dependencies during boot.
>
> A note on backgrounding: All netcfg profiles are now started in parallel,
> so backgrounding is unnecessary. However, due to the correct dependencies
> in the units, everything should work fine.
>
> Due to a bug in systemd's dependency resolution with devices, this patch
> requires systemd v195 to work.

This patch (and all the related ones) might be the end of netcfg.
There are a few reasons for which I don't like to merge them.

This will make it very difficult to maintain dual initscripts and
systemd compatibility. For instance, in the NETWORKS array, it is
possible to specify simple dependency relations between profiles. The
new approach introduces a new, systemd-specific DEPENDS array for
this. At the same time, systemd is basically a topological sorting
mechanism, ie a dependency resolver. We inherently duplicate stuff
here.

The proposed setup is quite complex. I feel it is likely possible to
do netcfg's job in a systemd empowered way and I also feel that the
proposed way is not the proper way of doing that. Therefore I suggest
to start a new project for profile based network management as we have
done with netcfg, but tailored to systemd. Let's call it netctl.

My goal for netctl would be to learn from netcfg experiences. No more
'menu' or 'last' on places where profile names are supposed to be put,
no more connection types without interfaces, no more incomprehensible
execution trails (there can be a lot of recursion, especially in calls
to the ethernet connection code). I would also like to use systemd's
power as much as possible. This might mean to hope for Lennarts
cooperation in at least two places:
1) write a proper ifplugd service (possibly ifplugd needs to be altered),
2) support variables from EnvironmentFile in the BindsTo/After part of
a unit (so that we can put our interfaces there).
There will be (at least) two types of service files: one for simple
wired/wireless connections with a fixed interface, one for connections
that generate an interface (for example: bond connections). The latter
will be the difficult kind. In any case, I would like the profile
files to be of the kind systemd accepts as environment files, but very
similar (in some cases even compatible) to those of netcfg.

In short, netctl should be a purified netcfg, depending on systemd.[1]
We might loose a few features of netcfg, but we would gain a lot of
simplicity and ease of use (for those used to systemd).

As for the problem addressed by the presented patch: we could put
After=udev-settle.service
in the services. A user can then prevent the case that netcfg is
started before there interfaces appear by enabling the udev-settle
service.

Any comments on this wild plan?

- Jouke

[1] and coreutils, iproute2, openresolv (let's do it right, this
time), and optionally also wpa_supplicant, wpa_actiond, ifplugd,
ifenslave, bridge-utils, dialog...