[libvirt-users] API for retrieving resource metrics from VMs?

Hello. I'm a new getting started to learn the libvirt API. I've tried to find APIs which retrieve resource metrics such as cpu, disk, memory, and network I/O usages, but I could find few related thing; I was intended to use libvirt-Java binding first, it seems I'd be better to use the others like Python binding or C API though. The Java binding API is likely to provide very limited API list comparing with the above APIs so far. So, I'd like to know which APIs can retrieve that resources from VMs. I don't care about the language, but I really want to know whether such APIs even exists or not. As far as I know, cpu, memory, and network I/O seems being provided, but I'm not sure disk usage per VMs can be obtained via libvirt API. Thanks in advance. Best regards bgkim