Function getsockopt 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn getsockopt(
    socket: c_int,
    level: c_int,
    option_name: c_int,
    option_value: *mut c_void,
    option_len: *mut socklen_t,
) -> c_int

See https://pubs.opengroup.org/onlinepubs/9799919799/functions/getsockopt.html.