FDDUP_FLAG_CLOEXEC
((flags & FD_CLOEXEC) != 0 ? FDDUP_FLAG_CLOEXEC : 0) |
MPASS((flags & ~(FDDUP_FLAG_CLOEXEC | FDDUP_FLAG_CLOFORK)) == 0);
{ .f = FDDUP_FLAG_CLOEXEC, .t = UF_EXCLOSE },
error = kern_dup(td, FDDUP_FCNTL, FDDUP_FLAG_CLOEXEC, fd, tmp);
error = kern_dup(td, FDDUP_FIXED, FDDUP_FLAG_CLOEXEC, fd, tmp);