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

[Daniel P. Berrange]

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.
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>


> P.S.: there is also a XEN type uspposedly for xen but I was unable to
>       find any baloon code in our current xen driver so no change there

Xen always has a balloon device, so we should make Xen driver always add
the <memballoon> device. 

Daniel
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