[libvirt] [PATCH] RFC: experimental libvirtd upstart job

[Serge E. Hallyn]

Quoting Daniel P. Berrange (berrange at redhat.com):
> On Fri, Feb 18, 2011 at 03:48:29PM -0600, Serge E. Hallyn wrote:
> > Quoting apevec at gmail.com (apevec at gmail.com):
> > > From: Alan Pevec <apevec at redhat.com>
> > =============================================
> > # libvirt-cgred-wait
> > start on starting libvirt-bin
> > stop on started cgred or stopped cgred
> > 
> > task
> > normal exit 2
> > script
> >   status cgred | grep -q "start/running" && exit 0
> >   start cgred || true
> >   sleep 3600
> > end script
> > =============================================
> 
> FYI, libvirt has no need for the  cgred to be present / running, and

Absolutely.  And so the above job ships with the libcgroup package,
not with libvirt.

> indeed if you're not careful with the rules you create for cgred it
> could really mess things up by moving VM proceses to a different
> cgroup behind libvirt's back.

Yes.  And with the default rules, if libcgroup is installed *and*
if libvirt does not wait until libcgroup is configured at boot, then
VMs won't start up.

So when just libvirt is installed, the above job is not needed (and
not installed on the machine).  When just libcgroup is installed, the
above job will be installed, but since it starts on 'starting libvirt',
it won't ever run if libvirt is not installed.

> For cgroups integration, libvirt merely requires that something has
> mounted the various cgroups controllers. The can be mounted in any
> location, and with any combination of controllers. libvirtd will
> detect what cgroups it is located in at startup, and create its
> own cgroups below these points in the hierarchy.

Yup, I definately don't want to suggest that there is anything wrong
with what libvirt does.

> On Fedora we do this with the 'cgconfig' init script which more or
> less just runs  'cgconfigparse -l /etc/cgconfig.conf' to mount the
> bits

Right, and the above job just makes sure that the above has finished
before libvirt starts.

thanks,
-serge