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Saturday, June 20, 2015

Linux Kernel: How to start contributing

Is really not that dificult to start contributing with a small patch to the Linux kernel, my first patch was to correct a missing space between binary operands (i==j) -> (i == j) that I found running a script available in the kernel code, I ran something like:
perl scripts/checkpatch.pl -f path_to_some_driver_folder/ | less
And I found the coding style problem. But first you need to download and compile the kernel.

This is going to be a short post with really useful links.

Things you will need to know to start:
* GIT
* C programing

1) Download, compile and install a kernel compiled by your self: follow these instructions
Note1: I takes a really long time: check my posts about CCache and Icecc to speed up compilation.
Note2: Consider to setup a virtual machine if you plan to develop something that can break your system.

2) Setup more tools, find a coding style problem and prepare a patch and submit it: follow these instructions
Note1: the above link tells you to not send the patch to the Linux list. You need to check who are the maintainers of the file you are modifying by running the script:
perl scripts/get_maintainer.pl <path_to_your_patch_generated_with_git_format.patch>
Or:
perl scripts/get_maintainer.pl -f <file_that_you_modified>
Or:
git show HEAD | perl scripts/get_maintainer.pl
This will get you a list of people and emails, so you can send your patch to all of them in CC.

Note2: Do interleaved/bottom-posting when replying emails. Don't put your reply before quoted original message as Gmail does by default.

3) Joing the #kernelnewbies irc channel on freenode, its a chat so you can make newbie questions.
If you don't know how to do it, download the HexChat irc client (sudo apt-get install hexchat), go to menu->Network List, look for freenode and click on connect. Then wait a window to show up asking you which channels you would like to connect and type #kernelnewbies, or type /join kernelnewbies in the freenode chat window.

How to start working in something more interesting then fixing coding style:

4) Start reading the Linux Device Drivers (LDD3) Book, its free and you can read online.
You will learn the basis in writing a driver. The book comes with some code to test the drivers it implement but most of it is not compatible with the last kernel version. If you are stuck and can not compile a driver provided by the LDD3, leave me a comment and I can help.

5) Be aware of the Documentation folder inside the Linux kernel tree, it has a lot of docs about the internal API and software architecture. Sometimes it is hard to find which file should you be reading (just ask in the #kernelnewbies).

6) Where to go now: Check the http://kernelnewbies.org/ site, it is meant for newbies :)

Check this ilustrated guide about Linux Kernel development from another Outreachy intern

I am working on a video4linux driver. If you are interested in learning how to write a driver for your camera, follow my posts :)

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