valid_gid
switch (valid_gid(gid, NULL)) {
extern int valid_gid(), add_group();
switch (valid_gid(gid, NULL)) {
extern int valid_gid(), mod_group();
extern int valid_gid(gid_t, struct group **);
if ((r = valid_gid((gid_t)l, &grp)) == NOTUNIQUE) {