Almost every `xxxat()` function takes an optional `dirfd`, except [`fcntl::openat(2)`](https://docs.rs/nix/latest/nix/fcntl/fn.openat.html) and [`Dir::openat()`](https://docs.rs/nix/latest/nix/dir/struct.Dir.html#method.openat) ```rust pub fn openat<P: ?Sized + NixPath>( dirfd: RawFd, path: &P, oflag: OFlag, mode: Mode, ) -> Result<RawFd> ``` ```rust pub fn openat<P: ?Sized + NixPath>(dirfd: RawFd, path: &P, oflag: OFlag, mode: sys::stat::Mode) -> Result<Self> { let fd = fcntl::openat(dirfd, path, oflag, mode)?; Dir::from_fd(fd) } ``` Any reason why it does not take an `Option<RawFd>`?