title: who assigns event/interface id for handling in epoll_wait()
body: <p>This question bugs me from long time. 
  I want to know, in case of <code>event polling</code> mechanism. When I have a code in which I say I have 3 FDs to poll and I have assigned each <code>interface type</code> to each FD by which the event will be identified. The handling is also done using <code>epoll_create()</code>, then reception of events using <code>epoll_wait()</code>. </p>
  
  <pre><code>Say: 3 FDs. 
  1 Timer, 1 IPC, 1 MQTT -&gt; Creation using epoll_create
  </code></pre>
  
  <p>But my question is who assigns the event id or interface id to the external event as the category of events and their respective interface will always be internal.</p>
  
  <p>Please let me know if my question is clear or not.</p>