On Tue, 9 Mar 2021 at 09:01, Bin Meng <bmeng...@gmail.com> wrote: > > Hi Jason, > > On Tue, Mar 9, 2021 at 5:00 PM Bin Meng <bmeng...@gmail.com> wrote: > > > > Hi Jason, > > > > On Tue, Mar 9, 2021 at 4:57 PM Jason Wang <jasow...@redhat.com> wrote: > > > > > > > > > On 2021/3/9 4:35 下午, Bin Meng wrote: > > > > Hi Jason, > > > > > > > > On Tue, Mar 9, 2021 at 4:23 PM Jason Wang <jasow...@redhat.com> wrote: > > > >> > > > >> On 2021/3/8 6:22 下午, Peter Maydell wrote: > > > >>> I think the key thing we need to do here is make a decision > > > >>> and be clear about what we're doing. There are three options > > > >>> I can see: > > > >>> > > > >>> (1) we say that the net API demands that backends pad > > > >>> packets they emit to the minimum ethernet frame length > > > >>> unless they specifically are intending to emit a short frame, > > > >>> and we fix any backends that don't comply (or equivalently, > > > >>> add support in the core code for a backend to mark itself > > > >>> as "I don't pad; please do it for me"). > > > >>> > > > >>> (2) we say that the networking subsystem doesn't support > > > >>> short packets, and just have the common code always enforce > > > >>> padding short frames to the minimum length somewhere between > > > >>> when it receives a packet from a backend and passes it to > > > >>> a NIC model. > > > >>> > > > >>> (3) we say that it's the job of the NIC models to pad > > > >>> short frames as they see them coming in.
> > > >> I'm not sure how much value we can gain from (1). So (2) looks better > > > >> to me. > > > >> > > > >> Bin or Philippe, want to send a new version? > > > >> > > > > I think this series does what (2) asks for. Or am I missing anything? > > > > > > > > > It only did the padding for user/TAP. > > > > (hit send too soon ...) > > Ah, so we want this: > > if (sender->info->type != NET_CLIENT_DRIVER_NIC) > > correct? No, option (2) is "always pad short packets regardless of sender->info->type". Even if a NIC driver sends out a short packet, we want to pad it, because we might be feeding it to something that assumes it does not see short packets. thanks -- PMM
