virtio_gpu_cmd_resource_flush

It looks like the virtio-gpu flush should be fenced, but on the host side the received flush cmd doesn't have the fence flag set, and no fence_id.  So, I have to reply right away instead of waiting for scanout to complete.  Is that expected?  then what's the right way to vsync the guest?

At the moment, I'm queueing up the resources for scanout, but guest is flushing faster than host vsync.  I briefly looked at qemu implementation, but don't understand it yet.  A high level breakdown of what should be happening would be extremely helpful!

Thanks,
Josh