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When dealing with a source base as large as the kernel, it certainly helps to have software tools to help understand how the pieces fit together. This page is meant to provide you with pointers to the most commonly used tools to make your first forrays in kernel-land as productive as possible.
Editing Kernel Sources
Perhaps the most important tool is a good programmers's text editor. Popular choices are [http://www.gnu.org/software/emacs/ emacs] and any vi clone, [http://www.vim.org vim] being the most widely used these days. Generally, text editors written for programmers are programable and have features such as syntax highlighting, text folding, brace matching, and easy integration with source management tools, such as make(1), cvs(1), text reformatting, man page lookups, and more.
Downloading
Once you're set on using a particular editor, you will need to download the kernel source tree you want to work with. Different possibilities are available.
Kernel source management with git
If you want to download the lastest kernel source, you need git. You can get it from [http://git.or.cz/index.html here].
There is a very good [http://linux.yyz.us/git-howto.html Kernel Hackers' Guide to git]
[http://www.wlug.org.nz/KernelDevelopmentWithGit Kernel Development With Git]
And some tips while using Git [#GitTips here]
Kernel tarballs
The alternative, more "classic", way to download a kernel source tree release is to pull it from http://kernel.org/ as a compressed archive file.
Navigation Aid
You're now ready to edit the kernel source code or browse it to learn. Where to start? As you read through the code, you'll need many times to lookup the declaration or definition of this or that particular data structure, macro or function. the most basic way to do so is to use a combination of the grep (or egrep) and find` commands;
find . --exec grep --with-filename myfunction '{}' \; Another way is,
find . -name '*.[chS] | xargs egrep -n "myregularexpression";
This searches the current directory [and all subdirectories] for files ending with .c, .h or .S, and runs egrep on each of them for the pattern myregularexpression. Substitute myregularexpression with more complex regular expressions.
Indexing tools for web browsing
While this approach works, other tools allow you to index the entire kernel source tree to faciliate its browsing. This makes learning to find your landmarks in the code a lot easier and allow you to quickly find the declarations / definitions of unknown data structures.
[http://lxr.linux.no/ LXR project] : Nice website to browse the kernel source, search for identifiers, and diff between kernel versions. Uses [http://sourceforge.net/projects/lxr/ lxr] as its backend.
Gonzui http://softice.lakeland.usf.edu/wiki/index.php/Setting_up_Gonzui
Some websites make it their duty to archive indexed kernel source trees:
[http://lxr.linux.no/source/ LXR Project]
[http://www.kernelhq.org/ KernelHQ] : Another website to browse/navigate the kernel source. Has all the kernel sources since 1.0.
[http://fxr.watson.org/ FXR watson] FreeBSD and Linux Kernel Cross-Reference
(An archive of all kernel versions was [http://www.memalpha.cx/Linux/Kernel/ here].)
Navigation Utilities
Eventually, you'll want to maybe incorporate such browsing capabilities in your favored editor;
[http://ctags.sourceforge.net/ ctags]
[http://cscope.sourceforge.net/ cscope]. Tutorials: [http://cscope.sourceforge.net/large_projects.html Using with large projects], [http://cscope.sourceforge.net/cscope_vim_tutorial.html Using Cscope with Vim].
Alternative tools include: freescope, etags, and idutils which build databases to use when searching for C symbols. Each has their own idiosyncrasies and features. Some integrate better with your text editor of choice. (Look especially for plugins to help with integration.) cgvg is another option, though it doesn't appear to use a database to speed searches.
Version Control
Navigate the changesets applied to: