Client/Server using an I/O manager

Now, what if the client that you're porting used an I/O manager? How would we convert that to QNX Neutrino? Answer: we already did. Once we establish a file-descriptor-based interface, we're using a resource manager. Under QNX Neutrino, you'd almost never use a "raw" message interface. Why not?

  1. You'd have to worry about the _IO_CONNECT message that came in with the client's open() call, or you'd have to figure out how to find the resource manager if you weren't going to use open().
  2. You'd have to figure out a way to associate a client with a particular context block inside of the resource manager. This isn't rocket science, but it does involve some amount of data management.
  3. You'd have to provide encapsulation of all your messages, instead of using the standard POSIX file-descriptor-based functions to do that for you.
  4. Your resource manager won't work with stdin/stdout-based applications. For the audio driver example, you couldn't just do mp3_decode spud.mp3 >/dev/audio; the open() would most likely fail (if not, then the write() would, and so on).