[libvirt] RFC: what are the requirements to domain id

Hi, all. Domain id is somewhat required feature for hypervisors: virsh list prints them by default and active/inactive distinction is based on this id value analysys. But other than -1 is reserved for inactive domains there is no further requirements for it, one can happily keep them 0 for active domains. Looks like some drivers use process pids for this purpose. Qemu driver use its own incrementing counter and domain ids endure libvirtd restart. Vz do not provide a suitable value so the question arises can some simple id implementation be good enough? By simple I mean to keep counter as long as daemon lives and do not introduce any additional persistent state. As I said before there is basically no option to not to support it. A more profound question is what is this id for? How it is supposed to be used? Nikolay