Function fdclosedir 

#[unsafe(no_mangle)]
pub extern "C" fn fdclosedir(dir: Box<DIR>) -> c_int

See https://man.freebsd.org/cgi/man.cgi?query=fdopendir&sektion=3

FreeBSD extension that transfers ownership of the directory file descriptor to the user.

It doesn’t matter if DIR was opened with opendir or fdopendir.