[libvirt] [libvirt-guests] New feature ALWAYS_START

Daniel P. Berrange berrange at redhat.com
Wed Sep 23 13:21:34 UTC 2015

On Wed, Sep 23, 2015 at 03:16:04PM +0200, Martin Kletzander wrote:
> On Wed, Sep 23, 2015 at 12:50:57PM +0100, Daniel P. Berrange wrote:
> >On Wed, Sep 23, 2015 at 10:50:58AM +0200, Martin Kletzander wrote:
> >>On Tue, Sep 22, 2015 at 07:33:30AM +0200, Marek Lukács wrote:
> >>>Hi,
> >>>
> >>>It will be nice feature to have configuration option
> >>>ALWAYS_START="$uri:$name $uri:name ..." in libvirt-guests
> >>>configuration file.
> >>>
> >>>If ON_BOOT is "start" and if ALWAYS_START is not empty, it iterates
> >>>over the ALWAYS_START and starts guests with same conditions (delays
> >>>etc.) before it starts guests from LISTFILE.
> >>>
> >>
> >>To be honest, I don't think that's _exactly_ what you want _just_ from
> >>libvirt itself; let me explain.
> >>
> >>>Benefits:
> >>>- guests are started with delays
> >>
> >>Delays that are done due to the guests are not something we should
> >>handle.  Guests and mainly the applications inside them should handle
> >>this gracefully.  Just delaying the starts is still error-prone.
> >>
> >>>- guests are started after host failure
> >>
> >>That's what libvirt-guests does already.  And if you want some domains
> >>to be started on every start, there's the 'autostart' parameter for
> >>domains.
> >
> >Indeed, and I have a generall desire for libvirt-guests to go away
> >entirely and have all its functionality just built into libvirtd. So
> >I don't think taking functionality that already exist in libvirtd and
> >adding it to libvirt-guest is the right direction for us to take.
> >
> As Jirka pointed out, it's harder to do this in libvirtd because you
> want all the domains to be saved when shutting down, but not when
> stopping the service.  Another option would be that libvirt-guests
> would just tell libvirt over some other API, which is not
> hypervisor-specific (let's say admin api for example), that would call
> some function in all drivers that would do what libvirt-guests does
> now.

Yeah, I would anticipate adding a function in the admin API to trigger
"complete shutdown" of resources. It could be a useful admin task even
when a host is not shutting down.

When running in session mode, libvirtd listens for a dbus signal to
indicate that the desktop session is exiting, and does the save. I
wonder if system emits any kind of signal to indicate that a system
shutdown is taking place. If so we might be able to hook into that
instead of needing the admin AP

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