title: how to use epoll with data->ptr, instead of data.fd?
body: <p>I'm writing an application using epoll and large amount of fd's.
  in order to improve the searches of fd to application relevant DB, I want to pass to epoll application info, such as index in DB array.
  I thought of using the data->ptr (epoll_data_t --> *ptr), as far as I understood, I can give pointer that holds the fd and private information from the application layer, but couldn't found any documents or examples.</p>
  
  <p>I found this post, which seems to be relevant, but there is no implementation example...
  <a href="https://stackoverflow.com/questions/11916707/how-to-use-epoll-event-data-ptr">How to use epoll_event data.ptr</a></p>
  
  <p>Thanks</p>