RDF_SWAIT
if ((sc->sc_flags & RDF_SWAIT) == 0) {
sc->sc_flags |= RDF_SWAIT;
sc->sc_flags &= ~RDF_SWAIT;
if ((sc->sc_flags & RDF_SWAIT) == 0) {
sc->sc_flags |= RDF_SWAIT;
sc->sc_flags &= ~RDF_SWAIT;