os-autoinst architecture

This document gives an overview about the multi-process architecture of os-autoinst.

Process tree

Once everything is running, the process tree looks like this:

isotovideo: spawns further processes, IO-loop for passing commands (main occupation), cleanup
relevant files: isotovideo, needle.pm (initial needle scan)
- backend: spawns and handles backend (eg. qemu), receives commands from isotovideo IO-loop, handles the VNC connections, makes regular screenshots
  relevant files: baseclass.pm and derived, console.pm and derived, needle.pm (reloading, matching), cv.pm, ppmclibs/*
  - qemu (for instance)
  - videoencoder: encodes the Ogg Theora file
    relevant files: videoencoder.cpp
- autotest: determines test order, runs test code and thus testapi functions, sends commands to isotovideo IO-loop (via query_isotovideo)
  relevant files: autotest.pm, testapi.pm, console_proxy.pm, basetest.pm and derived, needle.pm (needles are instantiated here as well)
- command server: provides GET/POST HTTP routes and WS server, passes commands received via WS to isotovideo IO-loop
  relevant files: commands.pm, OpenQA/Commands.pm

The lists of relevant files has been reduced to the most important ones.
isotovideo starts everything and passes commands between the other processes.
All processes have an IO loop except autotest. The latter mainly executes the test code and everything else reacts to it.
The command server is accessed by the openQA worker and livehandler.