[libvirt] [RFC] daemon: remove hardcode dep on libvirt-guests

[Daniel P. Berrange]

On Thu, Sep 29, 2016 at 01:00:15PM +0300, Nikolay Shirokovskiy wrote:
> 
> 
> On 29.09.2016 12:21, Jiri Denemark wrote:
> > On Thu, Sep 29, 2016 at 11:33:04 +0300, Nikolay Shirokovskiy wrote:
> >> Hi, all.
> >>
> >> In virtuozzo mgmt we do not use libvirt-guests service. First because
> >> we need do extra steps on domain start and second we want to decice
> >> whether to suspend or to shutdown a domain on per domain basis. Starting
> >> is not the problem but system shutdown is. As domain in systemd based
> >> systems is just another unit we need to set ordering dependency so
> >> that domain will not be killed before mgmt service as ba79e387 do for
> >> libvirt-guest service. So let's remove this hardcode. I see 2 options.
> > 
> > I don't see hard dependency anywhere in libvirtd.service, it just says
> > 
> > Before=libvirt-guests.service
> 
> Nope, I meant this code from mentioned commit:
> 
> @@ -243,8 +243,10 @@ int virSystemdCreateMachine(const char *name,
>                            iscontainer ? "container" : "vm",
>                            (unsigned int)pidleader,
>                            rootdir ? rootdir : "",
> -                          1, "Slice", "s",
> -                          slicename) < 0)
> +                          3,
> +                          "Slice", "s", slicename,
> +                          "After", "as", 1, "libvirtd.service",
> +                          "Before", "as", 1, "libvirt-guests.service") < 0)
> 
> This makes domain a special kind of unit (scope) and sets its ordering dependency.
> You can't do this with libvirtd.service itself because its different unit.

IIUC, the problem is that you want to replace 'libvirt-guests.service'
with a different impl ?

The way systemd tends to deal with things that must be a configurable
choice in this way is to define a target, and sysadmins can then make
arbitrary services dependancies of that target.

eg, we'd set 'Before: virt-guest-shutdown.target', and then make
libvirt-guests.service be a part of that target by default. You can
then have ability to turn off libvirt-guest.service and put your
own custom thing inside virt-guest-shutdown.taget

Regards,
Daniel
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