#![feature(unique)]
extern crate libc;
use std::os::unix::io::AsRawFd;
use std::ptr::Unique;
use std::io::Write;
const BUF_SIZE: usize = 1024;

mod ffi {
    use libc::{c_int, size_t, off_t};
    extern {
        pub fn mmap(addr: *mut u8, len: size_t, prot: c_int, flags: c_int, fd: c_int, offset: off_t) -> *mut u8;
        pub fn munmap(addr: *mut u8, len: size_t);
    }

}
fn mmap<T: AsRawFd>(file: T, len: usize) -> Option<Unique<u8>> {
    unsafe {
        let fd = file.as_raw_fd();
        let mmaped = ffi::mmap(std::ptr::null_mut(), len, libc::PROT_READ | libc::PROT_WRITE, libc::MAP_SHARED, fd, 0);
        Some(Unique::new(mmaped))
    }
}
fn munmap(buf: Unique<u8>, len: usize) {
    unsafe { ffi::munmap(*buf, len); }
}

fn main() {
    let mut file = std::fs::OpenOptions::new().read(true).write(true).create(true).open("/dev/shm/mmaped_file").unwrap();
    file.write(&[0; BUF_SIZE]);
    let len = file.metadata().unwrap().len() as usize;
    let mmaped = mmap(file, len);
    if let Some(buf) = mmaped {
        let buf = unsafe { std::slice::from_raw_parts_mut(*buf, len) };
        buf[0]='h' as u8;
    }
}