Change FD_SETSIZE to c_int

[magicant]

FD_SETSIZE defines an upper bound for file descriptors that can be added to fd_set. It is common to check if a file descriptor is less than FD_SETSIZE before adding it to an fd_set. See the example below:

fn main() {
    let path = std::ffi::CStr::from_bytes_with_nul(b"/dev/null\0").unwrap();
    let fd = unsafe { libc::open(path.as_ptr(), libc::O_RDONLY) };
    if fd < 0 {
        eprint!("open failed\n");
        return;
    }

    let mut set = std::mem::MaybeUninit::<libc::fd_set>::uninit();
    unsafe { libc::FD_ZERO(set.as_mut_ptr()) }
    if fd < libc::FD_SETSIZE { // <- type mismatch!
        unsafe { libc::FD_SET(fd, set.as_mut_ptr()) }
    } else {
        eprint!("too large fd\n");
    }
}

Unfortunately, this example does not compile because of a type mismatch. fd is c_int while FD_SETSIZE is usize (or size_t).
Since FD_SETSIZE represents the max file descriptor + 1, I think it should have the same type as file descriptors. This pull request modifies the type to c_int and adds casts where needed.

[rustbot]

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[rustbot]

Some changes occurred in solarish module

cc @jclulow, @pfmooney

Some changes occurred in OpenBSD module

cc @semarie

[bors]

☔ The latest upstream changes (presumably #3348) made this pull request unmergeable. Please resolve the merge conflicts.

[sthibaul]

Please also update src/unix/hurd/mod.rs, introduced in the meanwhile, thanks!

[magicant]

Rebased and updated my commit.

I also changed _POSIX_OPEN_MAX as well as _POSIX_FD_SETSIZE to c_int since the latter is defined as an alias of the former.

[bors]

☔ The latest upstream changes (presumably #3428) made this pull request unmergeable. Please resolve the merge conflicts.

[sthibaul]

Ah, sorry, my commit indeed modified a lot, up to conflicting yours.

[magicant]

No problem, my diff is so small that the conflict can be easily resolved 🙂

[JohnTitor]

@bors r+

[bors]

📌 Commit 500365e has been approved by JohnTitor

It is now in the queue for this repository.

[bors]

⌛ Testing commit 500365e with merge 7412a8b...

[bors]

☀️ Test successful - checks-actions, checks-cirrus-freebsd-13, checks-cirrus-freebsd-14
Approved by: JohnTitor
Pushing 7412a8b to main...