F_DUPFD
nfd = fcntl(fd, F_DUPFD, FDBASE);
case F_DUPFD:
CHECKe(s3 = fcntl(s, F_DUPFD, s));
CHECKe(s3 = fcntl(s, F_DUPFD, s));
CHECKe(s3 = fcntl(s, F_DUPFD, s));
CHECKe(s3 = fcntl(s, F_DUPFD, s));
if ((fd2 = fcntl(fd1, F_DUPFD, 0)) < 0)
case F_DUPFD: