shm::shmctl!

macro_rules! shmctl {
    ($id: expr, $cmd: expr) => ({
        extern crate std;
        shmctl!($id, $cmd, std::ptr::null_mut())
    });
    ($id: expr, $cmd: expr, $info: expr) => ({
        extern crate shm;
        match unsafe {
            shm::ffi::shmctl (
                $id,
                $cmd as i32,
                $info
            )
        } {
            -1 => false,
            _ => true,
        }
    });
}

The shmctl sets a information on the segment.