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

On 07/20/2010 08:49 AM, Daniel P. Berrange wrote: > 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(a)berrange.com&gt; >>> >>> 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. You are correct that we can't remove XML to remove the feature, but we can add some. What about using <memballoon model='none'/> as a way to explicitly request that it be excluded?