Handle a write reference for a vdev
#include <qvm/vio.h>
unsigned vio_write(struct vio_state *vsp, unsigned cookie, const struct qvm_state_block *vopnd, const struct qvm_state_block *oopnd, struct guest_cpu *gcp)
This function must be called by the vdev's vwrite() function, passing the parameters through.
(VIOREF_CLASS_*) indication of any further action that the reference requires the vdev to take.