Re: [libvirt] how to assign an ip when assign a NIC or VF to the Virtual Machine?

> > 2011/5/8 Richard W.M. Jones <rjones(a)redhat.com > <mailto:rjones@redhat.com>> > > On Sun, May 08, 2011 at 10:56:54AM +0800, guan qin wrote: > > The second solution you mentioned may be difficult , because > when I assign > > the ethX to the VM, the X in the 'ethX' is random (the 'X' in > the host may > > be different in the VM),I don't know it before I boot the VM . > so maybe I > > couldn't edit the guest correctly before booting VM. > > AFAIK the guest should always see "eth0", so this shouldn't be any > problem. If not, write udev rule(s) in the guest to force the > name to > be stable. > > > The first solution : > > The network card's MAC address I can know and assign an fixed > IP in > > advance, but for the VFs , before I create the VF by "modprobe > > igb/ixgbe > > max_vfs=num1,num2" ,I couldn't know the MAC address before > either,the MAC > > address generated randomly too. > > So maybe I should edit the DHCP server configure file after > creating the > > VFs. > > It seems that for SR-IOV, MAC addresses are assigned to VFs randomly > by the kernel. It should be possible to read out the VF using (eg) > libvirt before the VM has booted (if not, it would be a bug). I > think > you can also assign fixed MAC addresses to VFs in advance if that > would be simpler. However I've not really used SR-IOV in anger so > this may be wrong. > On 05/08/2011 10:35 AM, guan qin wrote: > If I use SR-IOV, the guest may be always "eth0" , but when I use > the VT-d ,I often got an ethX with a random X in VM. > AFAIK, udev make the NIC name be stable by the MAC address. So when I > haven't assigned a VF or NetworkCard to the VM, > how can I force the name in the guest to 'eth0' ? (Please don't top-quote. It makes it hard to follow the discussion later). As I understand it (and I may have it wrong, as I don't actually have any SRIOV hardware to play with), an SRIOV VF gets a different random MAC address each time the host boots. However, udev on the host apparently ignores VFs when saving off its mac address <--> ethX mapping for reference on subsequent boots, so the VFs as seen from the host will have a stable name (but unstable mac address).

When you map that VF through to the guest, the guest probably doesn't know that it's a VF of an SRIOV card, it thinks it's a standard ethernet card, so the guest's udev saves that particular MAC address<->ethX mapping for subsequent boots; the problem is that the next time it boots, it will get *yet another* mac address, which will be mapped to *yet another* ethX name. The solution is to clear out the udev mapping on the guest before each boot, or otherwise teach it to not save the mapping. Alternately, use a different method of attaching your guest to the network (ie, instead of using PCI Passthrough, use <interface type='direct'> to attach a guest interface to one of the VFs, and give the guest a fixed MAC address of your own choosing.) -- libvir-list mailing list libvir-list(a)redhat.com https://www.redhat.com/mailman/listinfo/libvir-list