Function libsystemd_sys::event::sd_event_add_signal

pub unsafe extern "C" fn sd_event_add_signal(
    e: *mut sd_event, 
    s: *mut *mut sd_event_source, 
    sig: c_int, 
    callback: sd_event_signal_handler_t, 
    userdata: *mut c_void
) -> c_int