Where do I begin ?
A common question asked by a newbie is "I've just unpacked this huge tarball, and I want to help out, but I don't know where to start!"
It may seem daunting to be confronted with such a large amount of source code, but bear in mind, that very few kernel hackers understand every area of the kernel tree.
People specialise. If you're interested in TCP/IP, you'll not be needing to read the filesystem code. Figure out what it is you want to be working on, and focus on that.
Linux is a professional-quality kernel. This makes it difficult to come up with small "student projects" by which you can learn: often features are already implemented, and at a level that requires a good level of understanding before you can hack on them. However, there are several practical things and useful things you can do until you have learned enough to really start hacking :
Test and benchmark
- New code is constantly evolving, benchmark it. You will certainly notice some odd behaviours: there is your impetus to understand where the behaviour is coming from. Profile things, trace it (e.g. LTT), see if you can work out what might be causing problems. You'll learn the code by accident. Try out experimental patches posted to linux-kernel and trees like mjc's. Try and understand what a particular patch does, and how it does it.
Document
- Sounds boring ? Maybe, but you'll be doing everybody a favour, not least yourself. Forcing yourself to explain things crystalises your own understanding. Documentation of behaviour requires you to understand code. You'll find code a lot easier to read if you are directed to answering a specific question. Write articles for kernelnewbies and get them peer-reviewed in the IRC channel. Identify inaccuracies in the current man-pages, and fix them. Add source docs to the kernel source.
Kernel janitors
Kernel janitors is a project to fix mis-use of kernel APIs as the code mutates. This can quickly get pretty interesting. An educational talk on the project can be read [http://kerneljanitors.org/janitortalk.log here]