sd_ioctl_cache
int sd_ioctl_cache(struct sd_softc *, long, struct dk_cache *);
if (sd_ioctl_cache(sc, DIOCGCACHE, &dkc) == 0 && dkc.wrcache == 0) {
sd_ioctl_cache(sc, DIOCSCACHE, &dkc);
error = sd_ioctl_cache(sc, cmd, (struct dk_cache *)addr);