gr_gidpolicy
gid_t next = gr_gidpolicy(cnf, -1);
static gid_t gr_gidpolicy(struct userconf * cnf, intmax_t id);
grp->gr_gid = gr_gidpolicy(cnf, id);
rc = groupadd(cnf, name, gr_gidpolicy(cnf, id), members, fd, dryrun,