if ret is None:raise libvirtError('virDomainCreateLinux() failed', conn=self)
libvirtError: virDomainCreateLinux() failed POST operation failed: <Fault 3: 'win2003'>
 
这一步怎么都解决不了，重装系统，升级xen
后来解决：
modprobe -a tun
echo "modprobe -a tun" >>/etc/rc.local