Hey @coolreader18 could you please let me know if my approach is right?

It doesn't look like libc has ctermid -- rust-lang/libc#1928. However, you can just define it inline, as:

extern "C" {
    fn ctermid(s: *mut libc::c_char) -> *mut libc::c_char;
}

Also, you have to pass std::ptr::null_mut() as the argument, and you should put the function at the end of the mod posix instead of the mod nt as you've done.

should I inline it within the function itself or is it ok as is?

I checked macos python 3.9 and linux 3.6 but cannot find os._ctermid
where is it expected to be defined?

where is it expected to be defined?

I dont really understand you comment :/ maybe please explain a little more? If you were referring to the function name, it was indeed named _ctermid now changed it back to ctermid with some refactoring

I expect this PR has just 1 commit. Any PR shouldn't contain a merge commit. Rebase or cherry-pick your work onto upstream/master please.
When I rebased your works, I made them into a single commit. You can attach your work onto that one.

Note for the reviewers: i saw another pr(#3017) for fcdir so removed the code here