title: ALSA Callback When New Card/Device is Added
body: <p>I'm working with the ALSA C API, and I need to be able to detect when a card is plugged in (example: adding a USB device with sound capabilities). I know that you can subscribe to events for a particular card, but I want to generically subscribe saying "When a new card is added, tell me."</p>
  
  <p>Is this possible with the ALSA API? Or do I just need to launch a thread and continuously query for changes.</p>