libvirt users - May 2014 - Is there a way to get host uptime in remote libvirt

We manage hypervisors (VMWare ESXi/vCenter, KVM, XEN, Hyper-V) by remote Libvirt
API, in our case we need to get the host uptime via the same libvirt interface.
Is there a way get this info now for all the aforementioned hypervisor types?

The APIs virConnectGetSysinfo(), virNodeGetInfo() provide host info but it
doesn't include the system uptime.

The virNodeGetCPUStats() can returns CPU usage in nanosecond, can we add the
user + system + idle + iowait to calculate the system uptime? Looks like the sum
value has a huge gap with the real uptime value returned by "uptime"
CLI.

virsh # nodecpustats
user:               2985046540000000
system:             1368209710000000
idle:             388018933920000000

iowait:               43371960000000