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+HOWTO do Linux kernel development
+---------------------------------
+
+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
+to work with the Linux kernel development community.  It tries to not
+contain anything related to the technical aspects of kernel programming,
+but will help point you in the right direction for that.
+
+If anything in this document becomes out of date, please send in patches
+to the maintainer of this file, who is listed at the bottom of the
+document.
+
+
+Introduction
+------------
+
+So, you want to learn how to become a Linux kernel developer?  Or you
+have been told by your manager, "Go write a Linux driver for this
+device."  This document's goal is to teach you everything you need to
+know to achieve this by describing the process you need to go through,
+and hints on how to work with the community.  It will also try to
+explain some of the reasons why the community works like it does.
+
+The kernel is written mostly in C, with some architecture-dependent
+parts written in assembly. A good understanding of C is required for
+kernel development.  Assembly (any architecture) is not required unless
+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]
+
+The kernel is written using GNU C and the GNU toolchain.  While it
+adheres to the ISO C89 standard, it uses a number of extensions that are
+not featured in the standard.  The kernel is a freestanding C
+environment, with no reliance on the standard C library, so some
+portions of the C standard are not supported.  Arbitrary long long
+divisions and floating point are not allowed.  It can sometimes be
+difficult to understand the assumptions the kernel has on the toolchain
+and the extensions that it uses, and unfortunately there is no
+definitive reference for them.  Please check the gcc info pages (`info
+gcc`) for some information on them.
+
+Please remember that you are trying to learn how to work with the
+existing development community.  It is a diverse group of people, with
+high standards for coding, style and procedure.  These standards have
+been created over time based on what they have found to work best for
+such a large and geographically dispersed team.  Try to learn as much as
+possible about these standards ahead of time, as they are well
+documented; do not expect people to adapt to you or your company's way
+of doing things.
+
+
+Legal Issues
+------------
+
+The Linux kernel source code is released under the GPL.  Please see the
+file, COPYING, in the main directory of the source tree, for details on
+the license.  If you have further questions about the license, please
+contact a lawyer, and do not ask on the Linux kernel mailing list.  The
+people on the mailing lists are not lawyers, and you should not rely on
+their statements on legal matters.
+
+For common questions and answers about the GPL, please see:
+        http://www.gnu.org/licenses/gpl-faq.html
+
+
+Documentation
+------------
+
+The Linux kernel source tree has a large range of documents that are
+invaluable for learning how to interact with the kernel community.  When
+new features are added to the kernel, it is recommended that new
+documentation files are also added which explain how to use the feature.
+When a kernel change causes the interface that the kernel exposes to
+userspace to change, it is recommended that you send the information or
+a patch to the manual pages explaining the change to the manual pages
+maintainer at mtk-manpages@gmx.net.
+
+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
+    who are new to the kernel should start here.
+
+  Documentation/Changes
+    This file gives a list of the minimum levels of various software
+    packages that are necessary to build and run the kernel
+    successfully.
+
+  Documentation/CodingStyle
+    This describes the Linux kernel coding style, and some of the
+    rationale behind it. All new code is expected to follow the
+    guidelines in this document. Most maintainers will only accept
+    patches if these rules are followed, and many people will only
+    review code if it is in the proper style.
+
+  Documentation/SubmittingPatches
+  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.zip.com.au/~akpm/linux/patches/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.
+
+  Documentation/SecurityBugs
+    If you feel you have found a security problem in the Linux kernel,
+    please follow the steps in this document to help notify the kernel
+    developers, and help solve the issue.
+
+  Documentation/ManagementStyle
+    This document describes how Linux kernel maintainers operate and the
+    shared ethos behind their methodologies.  This is important reading
+    for anyone new to kernel development (or anyone simply curious about
+    it), as it resolves a lot of common misconceptions and confusion
+    about the unique behavior of kernel maintainers.
+
+  Documentation/stable_kernel_rules.txt
+    This file describes the rules on how the stable kernel releases
+    happen, and what to do if you want to get a change into one of these
+    releases.
+
+  Documentation/kernel-docs.txt
+    A list of external documentation that pertains to kernel
+    development.  Please consult this list if you do not find what you
+    are looking for within the in-kernel documentation.
+
+  Documentation/applying-patches.txt
+    A good introduction describing exactly what a patch is and how to
+    apply it to the different development branches of the kernel.
+
+The kernel also has a large number of documents that can be
+automatically generated from the source code itself.  This includes a
+full description of the in-kernel API, and rules on how to handle
+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.
+
+
+Becoming A Kernel Developer
+---------------------------
+
+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
+past.)  It also has an IRC channel that you can use to ask questions in
+real-time, and a lot of helpful documentation that is useful for
+learning about Linux kernel development.
+
+The website has basic information about code organization, subsystems,
+and current projects (both in-tree and out-of-tree). It also describes
+some basic logistical information, like how to compile a kernel and
+apply a patch.
+
+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://janitor.kernelnewbies.org/
+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
+will learn the basics of getting your patch into the Linux kernel tree,
+and possibly be pointed in the direction of what to go work on next, if
+you do not already have an idea.
+
+If you already have a chunk of code that you want to put into the kernel
+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
+imperative to understand how the code in question works.  For this
+purpose, nothing is better than reading through it directly (most tricky
+bits are commented well), perhaps even with the help of specialized
+tools.  One such tool that is particularly recommended is the Linux
+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://sosdg.org/~coywolf/lxr/
+
+
+The development process
+-----------------------
+
+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 2.6.x kernel tree
+  - 2.6.x.y -stable kernel tree
+  - 2.6.x -git kernel patches
+  - 2.6.x -mm kernel patches
+  - subsystem specific kernel trees and patches
+
+2.6.x kernel tree
+-----------------
+2.6.x kernels are maintained by Linus Torvalds, and can be found on
+kernel.org in the pub/linux/kernel/v2.6/ 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
+    -mm kernel for a few weeks.  The preferred way to submit big changes
+    is using git (the kernel's source management tool, more information
+    can be found at http://git.or.cz/) but plain patches are also just
+    fine.
+  - After two weeks a -rc1 kernel is released it is now possible to push
+    only patches that do not include new features that could affect the
+    stability of the whole kernel.  Please note that a whole new driver
+    (or filesystem) might be accepted after -rc1 because there is no
+    risk of causing regressions with such a change as long as the change
+    is self-contained and does not affect areas outside of the code that
+    is being added.  git can be used to send patches to Linus after -rc1
+    is released, but the patches need to also be sent to a public
+    mailing list for review.
+  - A new -rc is released whenever Linus deems the current git tree to
+    be in a reasonably sane state adequate for testing.  The goal is to
+    release a new -rc kernel every week.
+  - Process continues until the kernel is considered "ready", the
+    process should last around 6 weeks.
+
+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."
+
+2.6.x.y -stable kernel tree
+---------------------------
+Kernels with 4 digit versions are -stable kernels. They contain
+relatively small and critical fixes for security problems or significant
+regressions discovered in a given 2.6.x kernel.
+
+This is the recommended branch for users who want the most recent stable
+kernel and are not interested in helping test development/experimental
+versions.
+
+If no 2.6.x.y kernel is available, then the highest numbered 2.6.x
+kernel is the current stable kernel.
+
+2.6.x.y are maintained by the "stable" team <stable@kernel.org>, and are
+released almost every other week.
+
+The file Documentation/stable_kernel_rules.txt in the kernel tree
+documents what kinds of changes are acceptable for the -stable tree, and
+how the release process works.
+
+2.6.x -git patches
+------------------
+These are daily snapshots of Linus' kernel tree which are managed in a
+git repository (hence the name.) These patches are usually released
+daily and represent the current state of Linus' tree.  They are more
+experimental than -rc kernels since they are generated automatically
+without even a cursory glance to see if they are sane.
+
+2.6.x -mm kernel patches
+------------------------
+These are experimental kernel patches released by Andrew Morton.  Andrew
+takes all of the different subsystem kernel trees and patches and mushes
+them together, along with a lot of patches that have been plucked from
+the linux-kernel mailing list.  This tree serves as a proving ground for
+new features and patches.  Once a patch has proved its worth in -mm for
+a while Andrew or the subsystem maintainer pushes it on to Linus for
+inclusion in mainline.
+
+It is heavily encouraged that all new patches get tested in the -mm tree
+before they are sent to Linus for inclusion in the main kernel tree.
+
+These kernels are not appropriate for use on systems that are supposed
+to be stable and they are more risky to run than any of the other
+branches.
+
+If you wish to help out with the kernel development process, please test
+and use these kernel releases and provide feedback to the linux-kernel
+mailing list if you have any problems, and if everything works properly.
+
+In addition to all the other experimental patches, these kernels usually
+also contain any changes in the mainline -git kernels available at the
+time of release.
+
+The -mm kernels are not released on a fixed schedule, but usually a few
+-mm kernels are released in between each -rc kernel (1 to 3 is common).
+
+Subsystem Specific kernel trees and patches
+-------------------------------------------
+A number of the different kernel subsystem developers expose their
+development trees so that others can see what is happening in the
+different areas of the kernel.  These trees are pulled into the -mm
+kernel releases as described above.
+
+Here is a list of some of the different kernel trees available:
+  git trees:
+    - Kbuild development tree, Sam Ravnborg <sam@ravnborg.org>
+        kernel.org:/pub/scm/linux/kernel/git/sam/kbuild.git
+
+    - ACPI development tree, Len Brown <len.brown@intel.com>
+        kernel.org:/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6.git
+
+    - Block development tree, Jens Axboe <axboe@suse.de>
+        kernel.org:/pub/scm/linux/kernel/git/axboe/linux-2.6-block.git
+
+    - DRM development tree, Dave Airlie <airlied@linux.ie>
+        kernel.org:/pub/scm/linux/kernel/git/airlied/drm-2.6.git
+
+    - ia64 development tree, Tony Luck <tony.luck@intel.com>
+        kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git
+
+    - ieee1394 development tree, Jody McIntyre <scjody@modernduck.com>
+        kernel.org:/pub/scm/linux/kernel/git/scjody/ieee1394.git
+
+    - infiniband, Roland Dreier <rolandd@cisco.com>
+        kernel.org:/pub/scm/linux/kernel/git/roland/infiniband.git
+
+    - libata, Jeff Garzik <jgarzik@pobox.com>
+        kernel.org:/pub/scm/linux/kernel/git/jgarzik/libata-dev.git
+
+    - network drivers, Jeff Garzik <jgarzik@pobox.com>
+        kernel.org:/pub/scm/linux/kernel/git/jgarzik/netdev-2.6.git
+
+    - pcmcia, Dominik Brodowski <linux@dominikbrodowski.net>
+        kernel.org:/pub/scm/linux/kernel/git/brodo/pcmcia-2.6.git
+
+    - SCSI, James Bottomley <James.Bottomley@SteelEye.com>
+        kernel.org:/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6.git
+
+  Other git kernel trees can be found listed at http://kernel.org/git
+
+  quilt trees:
+    - USB, PCI, Driver Core, and I2C, Greg Kroah-Hartman <gregkh@suse.de>
+        kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/
+
+
+Bug Reporting
+-------------
+
+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://test.kernel.org/bugzilla/faq.html
+
+The file REPORTING-BUGS in the main kernel source directory has a good
+template for how to report a possible kernel bug, and details what kind
+of information is needed by the kernel developers to help track down the
+problem.
+
+
+Mailing lists
+-------------
+
+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
+archives.
+
+Most of the individual kernel subsystems also have their own separate
+mailing list where they do their development efforts.  See the
+MAINTAINERS file for a list of what these lists are for the different
+groups.
+
+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
+get pretty large. Don't remove anybody from the CC: list without a good
+reason, or don't reply only to the list address. Get used to receiving the
+mail twice, one from the sender and the one from the list, and don't try
+to tune that by adding fancy mail-headers, people will not like it.
+
+Remember to keep the context and the attribution of your replies intact,
+keep the "John Kernelhacker wrote ...:" lines at the top of your reply, and
+add your statements between the individual quoted sections instead of
+writing at the top of the mail.
+
+If you add patches to your mail, make sure they are plain readable text
+as stated in Documentation/SubmittingPatches. Kernel developers don't
+want to deal with attachments or compressed patches; they may want
+to comment on individual lines of your patch, which works only that way.
+Make sure you use a mail program that does not mangle spaces and tab
+characters. A good first test is to send the mail to yourself and try
+to apply your own patch by yourself. If that doesn't work, get your
+mail program fixed or change it until it works.
+
+Above all, please remember to show respect to other subscribers.
+
+
+Working with the community
+--------------------------
+
+The goal of the kernel community is to provide the best possible kernel
+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
+  - requests for justification
+  - silence
+
+Remember, this is part of getting your patch into the kernel.  You have
+to be able to take criticism and comments about your patches, evaluate
+them at a technical level and either rework your patches or provide
+clear and concise reasoning as to why those changes should not be made.
+If there are no responses to your posting, wait a few days and try
+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
+  - resubmit the patch without making any of the requested changes
+
+In a community that is looking for the best technical solution possible,
+there will always be differing opinions on how beneficial a patch is.
+You have to be cooperative, and willing to adapt your idea to fit within
+the kernel.  Or at least be willing to prove your idea is worth it.
+Remember, being wrong is acceptable as long as you are willing to work
+toward a solution that is right.
+
+It is normal that the answers to your first patch might simply be a list
+of a dozen things you should correct.  This does _not_ imply that your
+patch will not be accepted, and it is _not_ meant against you
+personally.  Simply correct all issues raised against your patch and
+resend it.
+
+
+Differences between the kernel community and corporate structures
+-----------------------------------------------------------------
+
+The kernel community works differently than most traditional corporate
+development environments.  Here are a list of things that you can try to
+do to try 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."
+    - "I tested it on 5 different architectures..."
+    - "Here is a series of small patches that..."
+    - "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..."
+    - "This is required for my company to make money"
+    - "This is for our Enterprise product line."
+    - "Here is my 1000 page design document that describes my idea"
+    - "I've been working on this for 6 months..."
+    - "Here's a 5000 line patch that..."
+    - "I rewrote all of the current mess, and here it is..."
+    - "I have a deadline, and this patch needs to be applied now."
+
+Another way the kernel community is different than most traditional
+software engineering work environments is the faceless nature of
+interaction.  One benefit of using email and irc as the primary forms of
+communication is the lack of discrimination based on gender or race.
+The Linux kernel work environment is accepting of women and minorities
+because all you are is an email address.  The international aspect also
+helps to level the playing field because you can't guess gender based on
+a person's name. A man may be named Andrea and a woman may be named Pat.
+Most women who have worked in the Linux kernel and have expressed an
+opinion have had positive experiences.
+
+The language barrier can cause problems for some people who are not
+comfortable with English.  A good grasp of the language can be needed in
+order to get ideas across properly on mailing lists, so it is
+recommended that you check your emails to make sure they make sense in
+English before sending them.
+
+
+Break up your changes
+---------------------
+
+The Linux kernel community does not gladly accept large chunks of code
+dropped on it all at once.  The changes need to be properly introduced,
+discussed, and broken up into tiny, individual portions.  This is almost
+the exact opposite of what companies are used to doing.  Your proposal
+should also be introduced very early in the development process, so that
+you can receive feedback on what you are doing.  It also lets the
+community feel that you are working with them, and not simply using them
+as a dumping ground for your feature.  However, don't send 50 emails at
+one time to a mailing list, your patch series should be smaller than
+that almost all of the time.
+
+The reasons for breaking things up are the following:
+
+1) Small patches increase the likelihood that your patches will be
+   applied, since they don't take much time or effort to verify for
+   correctness.  A 5 line patch can be applied by a maintainer with
+   barely a second glance. However, a 500 line patch may take hours to
+   review for correctness (the time it takes is exponentially
+   proportional to the size of the patch, or something).
+
+   Small patches also make it very easy to debug when something goes
+   wrong.  It's much easier to back out patches one by one than it is
+   to dissect a very large patch after it's been applied (and broken
+   something).
+
+2) It's important not only to send small patches, but also to rewrite
+   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."
+
+        The same is true of kernel development. The maintainers and
+        reviewers do not want to see the thought process behind the
+        solution to the problem one is solving. They want to see a
+        simple and elegant solution."
+
+It may be challenging to keep the balance between presenting an elegant
+solution and working together with the community and discussing your
+unfinished work. Therefore it is good to get early in the process to
+get feedback to improve your work, but also keep your changes in small
+chunks that they may get already accepted, even when your whole task is
+not ready for inclusion now.
+
+Also realize that it is not acceptable to send patches for inclusion
+that are unfinished and will be "fixed up later."
+
+
+Justify your change
+-------------------
+
+Along with breaking up your patches, it is very important for you to let
+the Linux community know why they should add this change.  New features
+must be justified as being needed and useful.
+
+
+Document your change
+--------------------
+
+When sending in your patches, pay special attention to what you say in
+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
+  - testing results
+
+For more details on what this should all look like, please see the
+ChangeLog section of the document:
+  "The Perfect Patch"
+      http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt
+
+
+
+
+All of these things are sometimes very hard to do. It can take years to
+perfect these practices (if at all). It's a continuous process of
+improvement that requires a lot of patience and determination. But
+don't give up, it's possible. Many have done it before, and each had to
+start exactly where you are now.
+
+
+
+
+----------
+Thanks to Paolo Ciarrocchi who allowed the "Development Process" section
+to be based on text he had written, and to Randy Dunlap and Gerrit
+Huizenga for some of the list of things you should and should not say.
+Also thanks to Pat Mochel, Hanna Linder, Randy Dunlap, Kay Sievers,
+Vojtech Pavlik, Jan Kara, Josh Boyer, Kees Cook, Andrew Morton, Andi
+Kleen, Vadim Lobanov, Jesper Juhl, Adrian Bunk, Keri Harris, Frans Pop,
+David A. Wheeler, Junio Hamano, Michael Kerrisk, and Alex Shepard for
+their review, comments, and contributions.  Without their help, this
+document would not have been possible.
+
+
+
+Maintainer: Greg Kroah-Hartman <greg@kroah.com>