vm_device_pipe
if (vm_device_pipe(&dev, dev_dispatch_vm, NULL)) {
if (vm_device_pipe(&dev, dev_dispatch_vm, ev_base_main)) {
if (vm_device_pipe(&dev, dev_dispatch_vm, NULL)) {
vm_device_pipe(dev, virtio_dispatch_dev, NULL);
int vm_device_pipe(struct virtio_dev *, void (*)(int, short, void *),