Documentation/HOWTO: convert to ReST notation

HOWTO do Linux kernel development

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This is the be-all, end-all document on this topic.  It contains

instructions on how to become a Linux kernel developer and how to learn

you plan to do low-level development for that architecture.  Though they

are not a good substitute for a solid C education and/or years of

experience, the following books are good for, if anything, reference:

 - "The C Programming Language" by Kernighan and Ritchie [Prentice Hall]

 - "Practical C Programming" by Steve Oualline [O'Reilly]

 - "C:  A Reference Manual" by Harbison and Steele [Prentice Hall]

their statements on legal matters.

For common questions and answers about the GPL, please see:

	http://www.gnu.org/licenses/gpl-faq.html

Here is a list of files that are in the kernel source tree that are

required reading:

  README

    This file gives a short background on the Linux kernel and describes

    what is necessary to do to configure and build the kernel.  People

    patches if these rules are followed, and many people will only

    review code if it is in the proper style.

  Documentation/SubmittingPatches

  Documentation/SubmittingDrivers

  Documentation/SubmittingPatches and Documentation/SubmittingDrivers

    These files describe in explicit detail how to successfully create

    and send a patch, including (but not limited to):

       - Email contents

       - Email format

       - Who to send it to

    Following these rules will not guarantee success (as all patches are

    subject to scrutiny for content and style), but not following them

    will almost always prevent it.

    Other excellent descriptions of how to create patches properly are:

	"The Perfect Patch"

		http://www.ozlabs.org/~akpm/stuff/tpp.txt

	"Linux kernel patch submission format"

		http://linux.yyz.us/patch-format.html

  Documentation/stable_api_nonsense.txt

    This file describes the rationale behind the conscious decision to

    not have a stable API within the kernel, including things like:

      - Subsystem shim-layers (for compatibility?)

      - Driver portability between Operating Systems.

      - Mitigating rapid change within the kernel source tree (or

	preventing rapid change)

    This document is crucial for understanding the Linux development

    philosophy and is very important for people moving to Linux from

    development on other Operating Systems.

locking properly.  The documents will be created in the

Documentation/DocBook/ directory and can be generated as PDF,

Postscript, HTML, and man pages by running:

::

	make pdfdocs

	make psdocs

	make htmldocs

	make mandocs

respectively from the main kernel source directory.

If you do not know anything about Linux kernel development, you should

look at the Linux KernelNewbies project:

	http://kernelnewbies.org

It consists of a helpful mailing list where you can ask almost any type

of basic kernel development question (make sure to search the archives

first, before asking something that has already been answered in the

If you do not know where you want to start, but you want to look for

some task to start doing to join into the kernel development community,

go to the Linux Kernel Janitor's project:

	http://kernelnewbies.org/KernelJanitors

It is a great place to start.  It describes a list of relatively simple

problems that need to be cleaned up and fixed within the Linux kernel

source tree.  Working with the developers in charge of this project, you

tree, but need some help getting it in the proper form, the

kernel-mentors project was created to help you out with this.  It is a

mailing list, and can be found at:

	http://selenic.com/mailman/listinfo/kernel-mentors

Before making any actual modifications to the Linux kernel code, it is

Cross-Reference project, which is able to present source code in a

self-referential, indexed webpage format. An excellent up-to-date

repository of the kernel code may be found at:

	http://lxr.free-electrons.com/

Linux kernel development process currently consists of a few different

main kernel "branches" and lots of different subsystem-specific kernel

branches.  These different branches are:

  - main 4.x kernel tree

  - 4.x.y -stable kernel tree

  - 4.x -git kernel patches

4.x kernels are maintained by Linus Torvalds, and can be found on

kernel.org in the pub/linux/kernel/v4.x/ directory.  Its development

process is as follows:

  - As soon as a new kernel is released a two weeks window is open,

    during this period of time maintainers can submit big diffs to

    Linus, usually the patches that have already been included in the

It is worth mentioning what Andrew Morton wrote on the linux-kernel

mailing list about kernel releases:

::

	"Nobody knows when a kernel will be released, because it's

	released according to perceived bug status, not according to a

	preconceived timeline."

tree, they need to be integration-tested.  For this purpose, a special

testing repository exists into which virtually all subsystem trees are

pulled on an almost daily basis:

	http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git

This way, the -next kernel gives a summary outlook onto what will be

bugzilla.kernel.org is where the Linux kernel developers track kernel

bugs.  Users are encouraged to report all bugs that they find in this

tool.  For details on how to use the kernel bugzilla, please see:

	http://bugzilla.kernel.org/page.cgi?id=faq.html

The file REPORTING-BUGS in the main kernel source directory has a good

As some of the above documents describe, the majority of the core kernel

developers participate on the Linux Kernel Mailing list.  Details on how

to subscribe and unsubscribe from the list can be found at:

	http://vger.kernel.org/vger-lists.html#linux-kernel

There are archives of the mailing list on the web in many different

places.  Use a search engine to find these archives.  For example:

	http://dir.gmane.org/gmane.linux.kernel

It is highly recommended that you search the archives about the topic

you want to bring up, before you post it to the list. A lot of things

already discussed in detail are only recorded at the mailing list

Many of the lists are hosted on kernel.org. Information on them can be

found at:

	http://vger.kernel.org/vger-lists.html

Please remember to follow good behavioral habits when using the lists.

Though a bit cheesy, the following URL has some simple guidelines for

interacting with the list (or any list):

	http://www.albion.com/netiquette/

If multiple people respond to your mail, the CC: list of recipients may

there is.  When you submit a patch for acceptance, it will be reviewed

on its technical merits and those alone.  So, what should you be

expecting?

  - criticism

  - comments

  - requests for change

again, sometimes things get lost in the huge volume.

What should you not do?

  - expect your patch to be accepted without question

  - become defensive

  - ignore comments

The kernel community works differently than most traditional corporate

development environments.  Here are a list of things that you can try to

do to avoid problems:

  Good things to say regarding your proposed changes:

    - "This solves multiple problems."

    - "This deletes 2000 lines of code."

    - "Here is a patch that explains what I am trying to describe."

    - "This increases performance on typical machines..."

  Bad things you should avoid saying:

    - "We did it this way in AIX/ptx/Solaris, so therefore it must be

      good..."

    - "I've being doing this for 20 years, so..."

   and simplify (or simply re-order) patches before submitting them.

Here is an analogy from kernel developer Al Viro:

::

	"Think of a teacher grading homework from a math student.  The

	teacher does not want to see the student's trials and errors

	before they came up with the solution. They want to see the

	cleanest, most elegant answer.  A good student knows this, and

	would never submit her intermediate work before the final

	solution."

	solution.

	The same is true of kernel development. The maintainers and

	reviewers do not want to see the thought process behind the

the text in your email.  This information will become the ChangeLog

information for the patch, and will be preserved for everyone to see for

all time.  It should describe the patch completely, containing:

  - why the change is necessary

  - the overall design approach in the patch

  - implementation details

For more details on what this should all look like, please see the

ChangeLog section of the document:

  "The Perfect Patch"

      http://www.ozlabs.org/~akpm/stuff/tpp.txt

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Thanks to Paolo Ciarrocchi who allowed the "Development Process"

(http://lwn.net/Articles/94386/) section

to be based on text he had written, and to Randy Dunlap and Gerrit