[systemd-devel] dependencies between instances

[Lennart Poettering]

On Mon, 28.01.13 07:39, Łukasz Stelmach (l.stelmach at samsung.com) wrote:

> Dear All,
> 
> I was trying to investigate this problem by my own eyeballs. After few
> hours I am almost sure (I'd be glad to hear it from someone of greater
> knowledge of systemd than me (which isn't that hard)) there is no link
> enabling dependencies between units from PID 1 and user session, is
> there?
> 
> On the other hand the user's instance shows devices and mounts on its
> units list (as far as I can tell it enumerates them by wandering around
> /sys and /proc/mounts).
> 
> I think it might be quite useful to enable cross instance dependencies
> like this. For example the network.target (whatever that
> means). Programmes started as services depending (After) on the
> network.target need not to implement network detection on their own as
> they won't be started before everything they expect (whatever that
> means) is in place.
> 
> What is your opinion? Is it worth implementing (if it is not there and I
> have missed something)?

I see the usefulness of this, but I am also a bit afraid of it, I must
say. It's kinda nice that these instances are currently so nicely
independent.

I have the suspicion that the different instances should probably track
the system state independently as far as that is possible... But I am
not sure if that's a complete solution.

Before we discuss this we relaly should be clear about the usecases
though. network.target is probably not a good idea, due to its weak
definition which makes is useful for very little beyond, let's say NFS
servers listed in /etc/fstab...

http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget

User code that relies on network.target sounds pretty wrong to me, since
we never had the concept of network.target there, and given how broken
it is  we really shouldn't introduce it now.

Can you suggest other usecases?

Lennart

-- 
Lennart Poettering - Red Hat, Inc.