On Tue, Aug 12, 2008 at 01:55:26PM +0200, Stefan de Konink wrote: Sorry, I've only just noticed this question coming up. The size parameter is nothing to do with how many StatsPtr structures it can return. This function can only ever fill in the contents of 1 structure. Unfortunately to get stats structures for all interfaces, you have to parse the domain XML to get the interface names. This sucks greatly, but there it is. A while back I added an experimental call virConnectListAllDomains. I really need to get this in shape again and add other calls to avoid having to parse XML ... http://www.redhat.com/archives/libvir-list/2008-September/msg00077.html So what is 'size' for? It's to provide backwards and forwards ABI compatibility in case we decide to add new fields to the virDomainInterfaceStatStruct in future. Let's imagine that at some point in the future we decided to add an extra 8 byte field to this structure, taking it from the current 64 byte size to 72 bytes in size. We have to account for two possibilities: (1) A program is compiled against an older libvirt, but linked (dynamically) to a newer libvirt. (2) A program is compiled against a newer libvirt, but linked to an older libvirt. In each case, libvirt is able to do the Right Thing. In case (1), the program will pass size = 64. The newer libvirt will truncate the stats that it returns to 64 bytes, so it doesn't write garbage beyond the end of the structure. In case (2), the program will pass size = 72. The older (ie. current) libvirt understands this and will only write 64 bytes of data to the structure. (In this case, the program has the choice over whether it wishes to detect this situation -- which it can do by writing some canard value to the extra fields in the structure). Rich. -- Richard Jones, Emerging Technologies, Red Hat http://et.redhat.com/~rjones virt-top is 'top' for virtual machines. Tiny program with many powerful monitoring features, net stats, disk stats, logging, etc. http://et.redhat.com/~rjones/virt-top