title: libGL error: failed to load driver swrast in docker container
body: <p>I have a docker container from which I am trying to run a pyqt app. Everything works well except a chunk of the GUI is not able to render. The docker logs throw this out:</p>
  
  <pre><code>libGL error: failed to load driver: swrast
  X Error: GLXBadContext 169
   Extension:    154 (Uknown extension)
   Minor opcode: 6 (Unknown request)
   Resource id:  0x6400003
  X Error: BadValue (integer parameter out of range for operation) 2
   Extension:    154 (Uknown extension)
   Minor opcode: 3 (Unknown request)
   Resource id:  0x0
  ...
  QGLContext::makeCurrent(): Failed.
  </code></pre>
  
  <p>In my Dockerfile, I tried installing pretty much all the packages I could find that might be related, including <code>mesa-utils</code>.</p>
  
  <p>In terms of the docker-compose file, here's what it looks like:</p>
  
  <pre><code>version: '2'
      services:
      gui:
          build: .
          volumes:
          - .:/usr/src
          - /tmp/.X11-unix:/tmp/.X11-unix
          command: /bin/bash -c "python start.py"
          environment:
          - DISPLAY=unix$DISPLAY
          - QT_X11_NO_MITSHM=1
          devices:
          - "/dev/snd:/dev/snd"
          - "/dev/dri:/dev/dri"
          privileged: true
  </code></pre>
  
  <p>Any ideas what I might be missing?</p>