Play with VMFlexArray

I explained VMFlexArray in my last post, and went to some effort to get it approved as a topic for this years Google Summer of Code, kindly under the umbrella of the GNU Project, Classpath, and IcedTea.

Judging from the fact that only one Google Summer of Code student proposed to work on VMFlexArray, it seems as though the concepts might be difficult for students to conceptualize.

For that reason, I built a small VMWare image that anyone can freely download to experiment with VMFlexArray.

In the process of doing so, I also converted FB4J to use JNA instead of JNI, and I'm very glad I did. The average refresh rate has now gone up by a significant factor to above 40 fps, and I haven't even begun to optimize anything.

The way I would suggest someone begin experimenting with VMFlexArray is as follows:

1. Download and uncompress the VMWare image (there is a .vmdk inside the .vmwarevm folder for those who do not use Mac OS X / VMWare Fusion)
2. Run the VMFlexArrayLinux virtual machine
3. Log in with user 'root' and an empty password
4. Run 'ifconfig eth0' and write down the IP address
5. Open a terminal session on the host OS and ssh into the IP address from above (i.e. ssh root@[ip_addr])
6. run the demo ./fb4jdemo

You should see a white background and some colourful balls bouncing around on the VMWare's virtual SVGA II device.

I hope you're curious enough to begin to dissect the demo being run.

After some investigation, it should become obvious that JamVM and Classpath are being used under the hood for java. One might also notice that there is a java compiler (javac) in the image courtesy of Eclipse Compiler for Java (ecj). Some clever people will probably also notice /var/db/pkg.sqfs, which is a SquashFS version Gentoo's database of installed packages (tying all installed free software back to source repositories).

Then, please take note that there is a portage overlay located at /usr/local/portage/java_overlay, as well as a patch located in /usr/src. The portage overlay represents changes required to demonstrate VMFlexArray using jamvm and gnu classpath. The patch in /usr/src represents the one patch required to perform double-buffering using the VMWare frame buffer.

I went to some length to ensure that my patch set was easy to reproduce. Therefore, all required changes to JamVM are located in my feature/vmflexarray-demo branch, and all required Classpath changes are located in my feature/vmflexarray-demo branch. Also, all required changes to JNA-Posix are in my branch feature/ioctl.

My updated FB4J changes are currently in the feature/jna branch. These changes mean that FB4J does not require any of its own native components. They will be merged into master eventually, but I just need to a) clean up the README, and b) possibly machine-generate enums and constants from /usr/src/linux/fb.h

This is where it gets fun.

The next task in understanding VMFlexArray, for anyone who is curious, is to take the Fb4jDemo code and modify it to draw a different video effect. The good news is that there is a built-in java compiler (ecj) in the VMWare image, so that's rather easy.

Next, do something with FB4J that I haven't done yet - use it to read a Video 4 Linux device ;-) This will require you to roll your own kernel and add UVC, V4L, and other modules in.

Here's a screenshot of my latest run. Don't forget to download the compressed VMWare image to experiment with from here.

Happy frame buffer drawing!

In the mean time, I will continue to experiment on my end. Once I have some free time, I might attempt an OpenJDK port of the VMFlexArray changes.

Please note that the software is still very beta - e.g. I am currently getting an undiagnosed segfault after some time. I believe I ran into this problem before I did a major cleanup of the code, and will review it when I have some time.