On Wed, Apr 14, 2010 at 06:35:57PM +0200, Arnd Bergmann wrote: > On Wednesday 14 April 2010, Michael S. Tsirkin wrote: > > > > > > > > qemu needs the ability to inject raw packets into device > > > > from userspace, bypassing vhost/virtio (for live migration). > > > > > > Ok, but since there is only a write callback and no read, it won't > > > actually be able to do this with the current code, right? > > > > I think it'll work as is, with vhost qemu only ever writes, > > never reads from device. We'll also never need GSO etc > > which is a large part of what tap does (and macvtap will > > have to do). > > Ah, I see. I didn't realize that qemu needs to write to the > device even if vhost is used. But for the case of migration to > another machine without vhost, wouldn't qemu also need to read? Not that I know. Why? > > > Moreover, it seems weird to have a new type of interface here that > > > duplicates tap/macvtap with less functionality. Coming back > > > to your original comment, this means that while mpassthru is currently > > > not duplicating the actual code from macvtap, it would need to do > > > exactly that to get the qemu interface right! > > > > > I don't think so, see above. anyway, both can reuse tun.c :) > > There is one significant difference between macvtap/mpassthru and > tun/tap in that the directions are reversed. While macvtap and > mpassthru forward data from write into dev_queue_xmit and from > skb_receive into read, tun/tap forwards data from write into > skb_receive and from start_xmit into read. > > Also, I'm not really objecting to duplicating code between > macvtap and mpassthru, as the implementation can always be merged. > My main objection is instead to having two different _user_interfaces_ > for doing the same thing. > > Arnd They *could* do the same thing :) -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
