On Wed, Oct 31, 2012 at 03:51:08PM +0100, Stefan Hajnoczi wrote: > On Wed, Oct 31, 2012 at 10:57:24AM +0200, Michael S. Tsirkin wrote: > > On Wed, Oct 31, 2012 at 09:07:27AM +0100, Stefan Hajnoczi wrote: > > > On Tue, Oct 30, 2012 at 05:24:06PM +0200, Michael S. Tsirkin wrote: > > > > On Wed, Oct 24, 2012 at 02:49:21PM +0200, Stefan Hajnoczi wrote: > > > > > Allow netdev_del followed by netdev_add to re-peer a NIC and its > > > > > netdev: > > > > > > > > > > (qemu) info network > > > > > virtio-net-pci.0: > > > > > type=nic,model=virtio-net-pci,macaddr=52:54:00:12:34:56 > > > > > \ netdev0: type=user,net=10.0.2.0,restrict=off > > > > > > > > > > (qemu) netdev_del netdev0 > > > > > > > > > > (qemu) netdev_add socket,id=netdev0,listen=:1234 > > > > > > > > > > (qemu) info network > > > > > virtio-net-pci.0: > > > > > type=nic,model=virtio-net-pci,macaddr=52:54:00:12:34:56 > > > > > \ netdev0: type=socket, > > > > > > > > > > This makes it possible to switch netdev while the guest is running. > > > > > It > > > > > is not necessary to reset the NIC. > > > > > > > > > > Note that the NIC's link goes down in netdev_del and back up again in > > > > > netdev_add. Therefore the guest becomes aware that the network has > > > > > changed, although this depends on the emulated NIC model providing > > > > > link > > > > > status change interrupts. > > > > > > > > > > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com> > > > > > > > > I'd be surprised if this patch worked when one or both backends are tap. > > > > tap supports offloads but slirp doesn't, since guest > > > > probes offloads at startup, it assumes it can use offloads. > > > > We also program tap during device operation e.g. on set features. > > > > vhost operation could also be interesting, have not looked into it. > > > > > > Yes, I left a TODO in the RFC patch and described the issue below. > > > We'll have to reject incompatible netdevs. > > > > Ideally, we'd probe all backend capabilities at init time. > > However, looks like we allowed netdev and device creation in any order. > > Can we change this and require netdev always be there before device? > > I don't think the order is a problem. The relaxed order is only > relevant during startup from main() - but in that case we have no > constraints yet anyway. > The problem only occurs when netdev_add is used to create an > incompatible netdev after devices have initialized. We should be able > to check and error out in the code that my RFC patch modifies. If > constraints are violated then netdev_add can fail with an error (the new > netdev is not created and the QMP client needs to try again with a > compatible netdev configuration). > > Maybe I'm misunderstanding your point? > > Stefan
OK so if we basically require same type backend then I think it's mostly fine. I was trying to think of a way to allow changing backend type, this becomes messy very quickly. In partuclar macvtap probably shouldn't be swapped with tap even though they are the same type formally. -- MST
