shm::shmget!

macro_rules! shmget {
    ($key: expr, $flag: expr, $size: expr) => ({
        extern crate shm;
        match unsafe {
            shm::ffi::shmget (
                $key as i32,
                $size as u64,
                $flag as i32
            )
        } {
            -1 => None,
            key => Some(key as i32),
        }
    });
}

The shmget macro returns the id of a memory segment.