On Fri, Jan 18, 2019 at 11:32:03AM +0800, Yongji Xie wrote: > On Thu, 17 Jan 2019 at 17:57, Jason Wang <jasow...@redhat.com> wrote: > > > > > > On 2019/1/15 下午10:51, Yongji Xie wrote: > > >> Well, this may work but here're my points: > > >> > > >> 1) The code want to recover from backed crash by introducing extra space > > >> to store inflight data, but it still depends on the backend to set/get > > >> the inflight state > > >> > > >> 2) Since the backend could be killed at any time, the backend must have > > >> the ability to recover from the partial inflight state > > >> > > >> So it looks to me 1) tends to be self-contradictory and 2) tends to be > > >> recursive. The above lines show how tricky could the code looks like. > > >> > > >> Solving this at vhost-user level through at backend is probably wrong. > > >> It's time to consider the support from virtio itself. > > >> > > > I agree that supporting this in virtio level may be better. For > > > example, resubmitting inflight I/O once DEVICE_NEEDS_RESET is set in > > > Stefan's proposal. But I still think QEMU should be able to provide > > > this ability too. Supposed that one vhost-user backend need to support > > > multiple VMs. We can't enable reconnect ability until all VMs' guest > > > driver support the new feature. It's limited. > > > > > > That's the way virtio evolves. > > > > > > > But if QEMU have the > > > ability to store inflight buffer, the backend could at least have a > > > chance to support this case. > > > > > > The problem is, you need a careful designed protocol described somewhere > > That's what we should discuss in detail in this series. > > > (is vhost-user.txt a good place for this?). And this work will be > > (partial) duplicated for the future support from virtio spec itself. > > > > I think the duplicated code is to maintain the inflight descriptor > list which should be in backend. That's not main work in this series. > And backend could choose to include it or not. > > Thanks, > Yongji
It would be if someone volunteered to rewrite the vhost user informal description that we have in qemu and make it a full spec. So far a text + implementation in contrib seems plenty to me. -- MST
