[Libvir] Guest Identification

Hi, I'm trying to find a good way to correlate a domain to the machine it's running on. Can I use libvir or some other method on a domU to get some information that uniquely identifies it? Perhaps something that I can get from the XML running on dom0? I'm thinking of using the MAC address because I imagine that those things should be unique at least per hypervisor, but I'm not sure if that would work across physical boxes. The solution would be to use libvir to get the list of domains and then get the xml which includes the mac address. Then every domain on my network would hit a server and report its mac address, and then I could make a tree that links the dom0's to the domU's. I'm wondering if there's a better way to do this. Any suggestions would be greatly appreciated. Thanks for your help.