zfsctl_snapshot_zname
err = zfsctl_snapshot_zname(sdvp, snm, sizeof (from), from);
err = zfsctl_snapshot_zname(tdvp, tnm, sizeof (to), to);
err = zfsctl_snapshot_zname(dvp, name, sizeof (snapname), snapname);
err = zfsctl_snapshot_zname(dvp, nm, sizeof (snapname), snapname);