[Spice-devel] [vdagent-linux v2] systemd: Remove unneded virtio-port dependencies

[Frediano Ziglio]

> 
> On Tue, Dec 18, 2018 at 12:15:09PM -0500, Frediano Ziglio wrote:
> > > 
> > > The udev rule already adds SYSTEMD_WANTS=spice-vdagentd.socket
> > > to the relevant virtio devices, which automatically adds Wants=${device}
> > > to spice-vdagentd.socket (see 'systemctl show spice-vdagentd.socket').
> > > Adding a Requisite/After for these ports is at best redundant, and most
> > > likely wrong as this is causing boot time warnings:
> > > 
> > 
> > Lot of doubts, were you able to reproduce the issue?
> 
> Yes I was able to reproduce, and the message is gone with this patch.
> 
> > Looking at systemd documentation is not clear why the Requisite causes
> > an INFO message. Maybe something is attempting to launch the service?
> 
> Did not dig too deeply as to why that's causing an error. I'm not sure
> this is a valid unit name to be honest, which would explain a lot, but
> if that's the reason, then it would be easy to reproduce..
> 
> > What happen if Requisite is removed and service is enabled? Are we going
> > to have an error at every restart?
> 
> I don't understand your question. What kind of error do you think we
> will get? Note that we will still have a Wants= associated with the
> .socket file (automatically added by udev rule).
> 
> 
> Christophe
> 

Did some experiment, I think I got the full picture.

How to reproduce the bug: simply do a "systemctl start spice-vdagentd.socket" !
How did I get here is a bit more complicated.
The INFO/WARNING lines from the bug did not come from the activation from udev
but from sockets.target. The lines:

   [Install]
   WantedBy=sockets.target

tell systemd to activate the unit when sockets.target is activated (so when
network is configured). In the rpm you have (rpm -q --scripts spice-vdagentd):

    postinstall scriptlet (using /bin/sh):

    if [ $1 -eq 1 ] ; then 
          # Initial installation 
          systemctl preset spice-vdagentd.service spice-vdagentd.socket >/dev/null 2>&1 || : 
    fi

which will create a dependency from sockets.target to spice-vdagentd.socket
(like doing a "systemctl enable spice-vdagentd.socket").
To sum up the "[Install]" lines will enable the socket in all case. To test this
remove/comment the "Requisite" and "After", remove the com.redhat.spice.0 device
from the VM and start again the VM. Now with a "netstat -anop | grep spice" you
can see that the /var/run/spice-vdagentd/spice-vdagent-sock socket is in listen
mode (by systemd) even if there's no device. If you try to open the socket
(for instance with a "nc -U /var/run/spice-vdagentd/spice-vdagent-sock") systemd
will launch the SPICE service.

I think that a better solution, instead of removing the "Requisite", is to
remove the "[Install]" section. I tried it and correctly udev is activating
the socket if the device is detected. If the device is not detected the socket
won't be activated (you need also to preset the socket unit like in the rpm
script) which seems correct to me.

Frediano