[systemd-devel] Dependencies on DBus activated services during shutdown

[Michal Koutný]

Hello,
I'd like to ask your opinion on the following situation.

B.service exposes its API through D-Bus. A.service uses this API and
thus it has a dependency on B.service. This is implicit though -- and
we're happy we can rely on D-Bus activation and needn't to list all
dependencies explicitly.

As it comes, A.service needs B.service for proper termination. During
the shutdown transaction there is unspecified ordering of the two (since
the dependency is implicit only) and B.service is stopped before A.service.

A.service would attempt to D-Bus-activate B.service but that is rejected
because dbus-daemon will eventually stop too. Note this doesn't mean
dbus-daemon is already handling SIGTERM, it's because a dbus-daemon stop
job is pending [1]. A.service may thus cannot terminate properly.

I know this could be circumvented by explicitly specifying
After=b.service for the A.service but denies the elegance of the lazy
(implicit) activation.

Are there any better ways how to deal with this?

Thanks,
Michal Koutný

P.S. FTR, in my case A.service=libvirtd.service and
B.service=systemd-machined.service.

[1] https://github.com/systemd/systemd/blob/master/src/core/dbus.c#L169

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