F_DUPFD_CLOEXEC
nfd = fcntl(fd, F_DUPFD_CLOEXEC, FDBASE);
if ((tty_fd = fcntl(tfd, F_DUPFD_CLOEXEC, FDBASE)) == -1) {
case F_DUPFD_CLOEXEC:
case F_DUPFD_CLOEXEC:
if (SCARG(uap, cmd) == F_DUPFD_CLOEXEC)