OpenBSD pledge(2) Rust FFI bindings

// rustc --crate-type=lib pledge.rs
// rustc -L . main.rs

//
// pledge_ffi.rs
use std::os::raw::c_char;
use std::os::raw::c_int;

#[link(name = "c")]
extern {
    pub fn pledge(promises: *const c_char, paths: *const *const c_char) -> c_int;
}

//
// pledge.rs
#![crate_type = "lib"]

use std::ffi::CString;
mod pledge_ffi;

pub fn pledge(promises: &str) -> bool {
    if let Ok(c_str) = CString::new(promises) {
        unsafe {
            let result = pledge_ffi::pledge(c_str.as_ptr(), std::ptr::null());
            return result == 0;
        }
    }
    return false;
}

//
// main.rs
extern crate pledge;

use pledge::pledge;

use std::process::exit;
use std::fs::File;
use std::io::Write;

fn main() {
    let mut stderr = std::io::stderr();
    // example will crash
    // change to "stdio rpath"
    if !pledge("stdio") {
        writeln!(&mut stderr, "pledge").unwrap();
        exit(1);
    }

    println!("Now pledged.");

    // attempt elevation
    if !pledge("stdio rpath") {
        writeln!(&mut stderr, "pledge elevation fail").unwrap();
        //exit(1);
    }
    // .. promises were equal or reduced

    println!("Opening a file!");
    // kernel should abort here, unless promises changed
    let file = match File::open("/tmp/bogus/file") {
        Err(_) => exit(1),
        Ok(file) => file,
    };
}