[libvirt] [PATCH] cpuCompare: Fix comparison of two host CPUs

[Dan Kenigsberg]

On Tue, Jul 13, 2010 at 11:14:13AM +0100, Daniel P. Berrange wrote:
> On Tue, Jul 13, 2010 at 12:03:43PM +0200, Jiri Denemark wrote:
> > Hi Dan,
> > 
> > > I do not compare CPUs for fun, but rather to know if a guest can be run
> > > on a specific host. However, this is not exactly what
> > > virConnectCompareCPU gives me: A vmx-enabled host cpu is a superset of
> > > itself, but it would not run itself as a guest since we do not have
> > > nested vxm yet. Similarly, if we ever have svm-emulation-by-kvm, we
> > > could be running svm guests on a vmx host.
> > > 
> > > Is it only me? Or should libvirt expose the more interesting meaning?
> > 
> > Absolutely, that would be just perfect. However, I believe libvirt does the
> > best it can. Only hypervisor itself knows that it can emulate some features
> > which are not present in host CPU or that some features cannot work in guests
> > even though host CPU provides them. For such advanced comparison, qemu would
> > need to provide a way for libvirt to ask for this stuff.
> 
> Yep, we would need a different API for this, because we would need to be
> able to pass in more data than we curently do. eg the machine type, the
> emulator binary path, virtualization type (kvm/qemu/xen) etc. It might be
> easiest to just have an API that takes the full domain XML instead of just
> the CPU XML snipoet

Would it make sense to implement this by a
VIR_DOMAIN_CHECK_COMPATIBILITY flag to virDomainCreateXML?