Trees

We have already used the term ''kernel tree'' for quite a few times and we have told you that it means ''the contents of the directory containing the kernel source code''. However, it also has another meaning which is ''a development branch of the kernel source code''. Usually, such a branch is equivalent to a patchset that can be applied on top of a specific version of the kernel sources and different branches are named differently, so that they can be easily distinguished from each other. The more popular branches, also referred to as ''trees'', are the following:

• The -mm tree (maintained by Andrew Morton), which is built from other trees (ie. development branches of the kernel) and from many individual, often experimental, patches.
• The -rt (real-time) tree (maintained by Ingo Molnar), which contains patches that turn Linux into a real time system.
• The -ck tree (maintained by Con Kolivas), focused on the improvements of the system's performance.

Many developers and the majority of kernel subsystems maintain their own trees used in the development process. After some time specific parts of these trees are included into the main kernel tree maintained by Linus Torvalds, called the mainline. The -git patches discussed in the previous sections represent the snapshots of the ever-evolving Linus' tree taken at various instants of time.