[libvirt] [PATCH 3/4] Explicitly represent balloon device in XML and handle PCI address

Daniel P. Berrange berrange at redhat.com
Tue Jul 20 14:49:40 UTC 2010

On Tue, Jul 20, 2010 at 10:39:01AM -0400, Cole Robinson wrote:
> On 07/20/2010 09:09 AM, Daniel P. Berrange wrote:
> > From: Daniel P. Berrange <dan at berrange.com>
> > 
> > To allow compatability with older QEMU PCI device slot assignment
> > it is neccessary to explicitly track the balloon device in the
> > XML. This introduces a new device
> > 
> >    <memballoon model='virtio|xen'/>
> > 
> > It can also have a PCI address, auto-assigned if neccessary.
> > 
> > The memballoon will be automatically added to all Xen and QEMU
> > guests by default.
> > 
> Is there a way for users to remove/disable the balloon device? Certainly
> doesn't block this patch, but someone is going to ask for it eventually.

There isn't an easy way to allow for this without breaking back
compatability. We have always enabled the balloon driver, even 
though nothing was in the XML. Thus we can't simply leave out
the '<memballoon>' element and expect the balloon to go away
as that would break compat.

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