[libvirt] Is possible that cpu_maps.xml changed during different releases?

Hi, all I have two questions to the cpu_maps.xml in different releases, hope someone can give me some hints: a) Will it be possible that the features defined in cpu_maps.xml for one specific CPU model (like Nehalem) will be different? For example, one feature is not listed for Nehalem in release x.y, and added in release x.y+1? 2) Is the format of the cpu_maps.xml fine defined or will be it changed during releases? I asked this because currently the features defined in the capabilities only list features not included in the definition in cpu_maps.xml for the corresponding model. So if I want to get the full features supported by the host, I have to parse the capabilities and the cpu_maps.xml. I didn't find the definition for cpu_maps.xml format, although the capabilities format is well defined in http://libvirt.org/guide/html/Application_Development_Guide-Connections-C.... Thanks --jyh