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

Eric Blake eblake at redhat.com
Tue Jul 20 14:59:29 UTC 2010

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 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.

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?

Eric Blake   eblake at redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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