VIO_DESC_FREE
sc->sc_vd->vd_desc[desc].hdr.dstate = VIO_DESC_FREE;
vd->vd_desc[i].hdr.dstate = VIO_DESC_FREE;
while (sc->sc_vd->vd_desc[prod].hdr.dstate == VIO_DESC_FREE) {
vd->vd_desc[i].hdr.dstate = VIO_DESC_FREE;
sc->sc_vd->vd_desc[cons].hdr.dstate = VIO_DESC_FREE;
sc->sc_vd->vd_desc[i].hdr.dstate = VIO_DESC_FREE;