stage1: add dbus and host systemd integration

[jonboulle]

This is a new tracker ticket to follow up #438 and #764:

• add dbus and other necessary dependencies to default (nspawn-based) stage1
• machinectl login integration
  • update documentation here
• systemd-run -M integration
  • update documentation here

[rlpowell]

Is there a version I can test this on yet?

[jonboulle]

I don't believe any work has been done on this yet

[jonboulle]

Can we access /run/systemd/private in the container instead of using dbus?

[jonboulle]

I'd like to find an owner for this for 1.7.0 as it's going to be a prerequisite for #2375

[alban]

Unfortunately the work has not been started for 1.7.0. Moving milestone.

[lucab]

#2375 has been de-prioritized and I'm not sure it will be followed further. I'm de-milestoning but I think I'm missing some background on the topic, @jonboulle can you please re-assess this later?

[alban]

kubernetes/kubernetes#25899

[jonboulle]

@tmrts is going to explore feasibility of this and make a go/no-go decision

[alban]

Can we access /run/systemd/private in the container instead of using dbus?

I would prefer to use that "private" socket if possible instead of adding dbus-daemon in stage1. It would be more lightweight. I did the following tests:

/run/systemd/private is not created in stage1 if we use the "coreos" flavor. But with the "src" flavor, it is created. systemd could be compiled with different ./configure options...

Then, I tried systemctl -M rkt-xxxx status ... but it connects to /var/run/dbus/system_bus_socket inside the container, which does not exist because stage1 does not have dbus-daemon. For testing, I added the following symlinks in stage1:

• /var/run -> ../run
• /var/run/dbus/system_bus_socket -> ../systemd/private

So with the previous symlinks, systemctl -M can connect to systemd's /run/systemd/private socket. It does not work though: strace reveals that systemctl calls the D-Bus Hello and strace on systemd reveals that it replies "Unknown object '/org/freedesktop/DBus'". The D-Bus Hello method should only be called when a client is connecting to a bus, not when it is connecting via p2p D-Bus. I don't know if systemd's private socket is supposed to handle a full D-Bus bus or only p2p D-Bus connections.

I am told on IRC that it should work, so we should report a bug on systemd.

[tmrts]

Bug report on systemd/systemd#3610

[iaguis]

This won't be ready for this release.

[tmrts]

We don't plan on adding the DBUS daemon either