Re: [Libvir] Some doubts for OpenVZ

Shuveb Hussain wrote: > 1. The OpenVZ system has one config file per VM which contains all the > VM's parameters. So, during libvirt start-up, these files can be read, > or openvz utils can be popened() to get information regarding these VMs. It's not very well explained, but libvirt has a number of design concepts which are directly influenced by Xen, for better and sometimes for worse. I'll explain them here, since they seem to relate to your question. == "Defined" domains == In old versions of Xen (pre 3.0.4 I think?) you would have one config file in /etc/xen for each domain (eg. /etc/xen/database-config.sxp for a virtual machine called "database"). This config file would define amongst other things the memory to allocate to the domain, the disk image it uses and so on. Now, a domain can be shutdown, or it can be running. In Xen/libvirt terminology a domain which had a config file but which _isn't_ running is called "inactive" or a "defined domain". For older Xen, the file src/xm_internal.c contains the code which reads the config files and looks for defined domains, and more importantly _writes_ to the config files on certain actions. I think for OpenVZ you may want to start by looking at this file.

== UUIDs == You could also specify a UUID (either in the config file for old Xen, or Xen allocates one in new Xen), and the UUID persists across reboots, so it is supposed to uniquely, globally identify that domain for all time. (As a side note, in Xen 3.0.2 you didn't need to put the UUID in that config file, but Xen still somehow assigns UUIDs to domains). > Is there a necessity to have per-vm config files in libvirt for the > OpenVZ VMs? I would start by looking at src/xm_internal.c, since OpenVZ sounds a lot like the "old Xen" way of doing things. > I understand UUIDs are used to identify each of the running > VMs. Where will these values persist? Can I do away with UUIDs for > OpenVZ and avoid the libvirt specific config file? Libvirt relies on UUIDs, so you need to find a way to allocate a UUID for the full lifetime of an OpenVZ domain. That may be stored in the config file, if possible, or stored somewhere else.

> 2. In OpenVZ, there is just a VPS ID/Name. There is no temporary > reference like 'id'. For example QEMU is using the process PID. There is > no such notion for OpenVZ. In that case, can I make 'name' and 'id' same > for OpenVZ? What is VPS ID/Name? Is it a string? Number?

Again, libvirt conceptually needs a domain ID, which must be an integer. It's different from UUID in that domain IDs can be and are reused (they are a lot like PIDs).