anchor.diff:    scanout
     width
     height
  +  framebuffer
     virgl-p
     virgl-data)
   
  
positive.code:            #:virtio-gpu-scanout
             #:virtio-gpu-width
             #:virtio-gpu-height
             #:virtio-gpu-virgl-p
             #:virtio-gpu-virgl-data
  
  
negative.code:               (return-from virtio::virtio-gpu-register nil)))
            (setf (virtio-gpu-scanout gpu) pmode
                  (virtio-gpu-width gpu) width
                  (virtio-gpu-height gpu) height
                  (virtio-gpu-framebuffer gpu) framebuffer-dma-buffer)
            (sup::video-set-framebuffer framebuffer-phys width height
                                        (* width 4) :x8r8g8b8
                                        :damage-fn
  