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Re: [libvirt] [PATCH] allow memballoon type of none to desactivate it



On Mon, Aug 09, 2010 at 08:34:23PM +0200, Daniel Veillard wrote:
> On Mon, Aug 09, 2010 at 06:53:34PM +0100, Daniel P. Berrange wrote:
> > On Mon, Aug 09, 2010 at 06:38:27PM +0200, Daniel Veillard wrote:
> > >   The balloon device is automatically added to qemu guests if supported,
> > > but it may be useful to desactivate it. The simplest to not change the
> > > existing behaviour is to allow
> > >   <memballoon type="none"/>
> > > as an extra option to desactivate it (it is automatically added if the
> > > memballoon construct is missing for the domain).
> > > The following simple patch just adds the extra option and does not
> > > change the default behaviour but avoid creating a balloon device if
> > > type="none" is used.
> >  
> > I really don't like the idea of 'type=none' devices in general.
> 
> Since we automagically add the devices to describe an internal policy
> I think we're at fault here.
> 
> > I don't	think we should	have an	element	insides <devices> that
> > doesn't	actually represent a device.
> > 
> > If we want to disable the balloon, then	I think	we should aim
> > for an element or attribute elsewhere to toggle it.
> > 
> > eg, perhaps the	earlier <memory> element can indicate whether it
> > supports ballooning. eg
> > 
> >   <memory ballonable='yes|no'>2423423432</memory>
> > 
> > Thus if	ballooning is not enabled, the <memballoon> device would
> > never need to appear within <devices>
> 
>   Grumpf ... that mean at the internal stucture level we need to add an
> extra field, that is detected at a completely different time in parsing
> too ... more complex in general, but I can understand the purity POV.

I don't see this as a real problem. It is no  different from the way that
we automatically add <controller> devices at the end of parsing, if we saw
any <disk> or <channel> devices previously.

Regards,
Daniel
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