shm::ftok!

macro_rules! ftok {
    () => ({
        extern crate shm;
        ftok!(shm::ffi::TOK_PATHNAME)
    });
    ($pathname: expr) => ({
        extern crate shm;
        match unsafe {
            shm::ffi::ftok (
                $pathname.as_ptr() as *mut i8,
                shm::ffi::TOK_PROJ_ID as i32
            )
        } {
            -1 => None,
            key => Some(key as u64),
        }
    });
}

The ftok macro returns the System-V'IPC key from pathname.