+++ /dev/null
-Introdution
-===========
-
-Executive summary
------------------
-
-The rest of this section covers the scope of the kernel development process
-and the kinds of frustrations that developers and their employers can
-encounter there. There are a great many reasons why kernel code should be
-merged into the official ("mainline") kernel, including automatic
-availability to users, community support in many forms, and the ability to
-influence the direction of kernel development. Code contributed to the
-Linux kernel must be made available under a GPL-compatible license.
-
-:ref:`development_process` introduces the development process, the kernel
-release cycle, and the mechanics of the merge window. The various phases in
-the patch development, review, and merging cycle are covered. There is some
-discussion of tools and mailing lists. Developers wanting to get started
-with kernel development are encouraged to track down and fix bugs as an
-initial exercise.
-
-:ref:`development_early_stage` covers early-stage project planning, with an
-emphasis on involving the development community as soon as possible.
-
-:ref:`development_coding` is about the coding process; several pitfalls which
-have been encountered by other developers are discussed. Some requirements for
-patches are covered, and there is an introduction to some of the tools
-which can help to ensure that kernel patches are correct.
-
-:ref:`development_posting` talks about the process of posting patches for
-review. To be taken seriously by the development community, patches must be
-properly formatted and described, and they must be sent to the right place.
-Following the advice in this section should help to ensure the best
-possible reception for your work.
-
-:ref:`development_followthrough` covers what happens after posting patches; the
-job is far from done at that point. Working with reviewers is a crucial part
-of the development process; this section offers a number of tips on how to
-avoid problems at this important stage. Developers are cautioned against
-assuming that the job is done when a patch is merged into the mainline.
-
-:ref:`development_advancedtopics` introduces a couple of "advanced" topics:
-managing patches with git and reviewing patches posted by others.
-
-:ref:`development_conclusion` concludes the document with pointers to sources
-for more information on kernel development.
-
-What this document is about
----------------------------
-
-The Linux kernel, at over 8 million lines of code and well over 1000
-contributors to each release, is one of the largest and most active free
-software projects in existence. Since its humble beginning in 1991, this
-kernel has evolved into a best-of-breed operating system component which
-runs on pocket-sized digital music players, desktop PCs, the largest
-supercomputers in existence, and all types of systems in between. It is a
-robust, efficient, and scalable solution for almost any situation.
-
-With the growth of Linux has come an increase in the number of developers
-(and companies) wishing to participate in its development. Hardware
-vendors want to ensure that Linux supports their products well, making
-those products attractive to Linux users. Embedded systems vendors, who
-use Linux as a component in an integrated product, want Linux to be as
-capable and well-suited to the task at hand as possible. Distributors and
-other software vendors who base their products on Linux have a clear
-interest in the capabilities, performance, and reliability of the Linux
-kernel. And end users, too, will often wish to change Linux to make it
-better suit their needs.
-
-One of the most compelling features of Linux is that it is accessible to
-these developers; anybody with the requisite skills can improve Linux and
-influence the direction of its development. Proprietary products cannot
-offer this kind of openness, which is a characteristic of the free software
-process. But, if anything, the kernel is even more open than most other
-free software projects. A typical three-month kernel development cycle can
-involve over 1000 developers working for more than 100 different companies
-(or for no company at all).
-
-Working with the kernel development community is not especially hard. But,
-that notwithstanding, many potential contributors have experienced
-difficulties when trying to do kernel work. The kernel community has
-evolved its own distinct ways of operating which allow it to function
-smoothly (and produce a high-quality product) in an environment where
-thousands of lines of code are being changed every day. So it is not
-surprising that Linux kernel development process differs greatly from
-proprietary development methods.
-
-The kernel's development process may come across as strange and
-intimidating to new developers, but there are good reasons and solid
-experience behind it. A developer who does not understand the kernel
-community's ways (or, worse, who tries to flout or circumvent them) will
-have a frustrating experience in store. The development community, while
-being helpful to those who are trying to learn, has little time for those
-who will not listen or who do not care about the development process.
-
-It is hoped that those who read this document will be able to avoid that
-frustrating experience. There is a lot of material here, but the effort
-involved in reading it will be repaid in short order. The development
-community is always in need of developers who will help to make the kernel
-better; the following text should help you - or those who work for you -
-join our community.
-
-Credits
--------
-
-This document was written by Jonathan Corbet, corbet@lwn.net. It has been
-improved by comments from Johannes Berg, James Berry, Alex Chiang, Roland
-Dreier, Randy Dunlap, Jake Edge, Jiri Kosina, Matt Mackall, Arthur Marsh,
-Amanda McPherson, Andrew Morton, Andrew Price, Tsugikazu Shibata, and
-Jochen Voß.
-
-This work was supported by the Linux Foundation; thanks especially to
-Amanda McPherson, who saw the value of this effort and made it all happen.
-
-The importance of getting code into the mainline
-------------------------------------------------
-
-Some companies and developers occasionally wonder why they should bother
-learning how to work with the kernel community and get their code into the
-mainline kernel (the "mainline" being the kernel maintained by Linus
-Torvalds and used as a base by Linux distributors). In the short term,
-contributing code can look like an avoidable expense; it seems easier to
-just keep the code separate and support users directly. The truth of the
-matter is that keeping code separate ("out of tree") is a false economy.
-
-As a way of illustrating the costs of out-of-tree code, here are a few
-relevant aspects of the kernel development process; most of these will be
-discussed in greater detail later in this document. Consider:
-
-- Code which has been merged into the mainline kernel is available to all
- Linux users. It will automatically be present on all distributions which
- enable it. There is no need for driver disks, downloads, or the hassles
- of supporting multiple versions of multiple distributions; it all just
- works, for the developer and for the user. Incorporation into the
- mainline solves a large number of distribution and support problems.
-
-- While kernel developers strive to maintain a stable interface to user
- space, the internal kernel API is in constant flux. The lack of a stable
- internal interface is a deliberate design decision; it allows fundamental
- improvements to be made at any time and results in higher-quality code.
- But one result of that policy is that any out-of-tree code requires
- constant upkeep if it is to work with new kernels. Maintaining
- out-of-tree code requires significant amounts of work just to keep that
- code working.
-
- Code which is in the mainline, instead, does not require this work as the
- result of a simple rule requiring any developer who makes an API change
- to also fix any code that breaks as the result of that change. So code
- which has been merged into the mainline has significantly lower
- maintenance costs.
-
-- Beyond that, code which is in the kernel will often be improved by other
- developers. Surprising results can come from empowering your user
- community and customers to improve your product.
-
-- Kernel code is subjected to review, both before and after merging into
- the mainline. No matter how strong the original developer's skills are,
- this review process invariably finds ways in which the code can be
- improved. Often review finds severe bugs and security problems. This is
- especially true for code which has been developed in a closed
- environment; such code benefits strongly from review by outside
- developers. Out-of-tree code is lower-quality code.
-
-- Participation in the development process is your way to influence the
- direction of kernel development. Users who complain from the sidelines
- are heard, but active developers have a stronger voice - and the ability
- to implement changes which make the kernel work better for their needs.
-
-- When code is maintained separately, the possibility that a third party
- will contribute a different implementation of a similar feature always
- exists. Should that happen, getting your code merged will become much
- harder - to the point of impossibility. Then you will be faced with the
- unpleasant alternatives of either (1) maintaining a nonstandard feature
- out of tree indefinitely, or (2) abandoning your code and migrating your
- users over to the in-tree version.
-
-- Contribution of code is the fundamental action which makes the whole
- process work. By contributing your code you can add new functionality to
- the kernel and provide capabilities and examples which are of use to
- other kernel developers. If you have developed code for Linux (or are
- thinking about doing so), you clearly have an interest in the continued
- success of this platform; contributing code is one of the best ways to
- help ensure that success.
-
-All of the reasoning above applies to any out-of-tree kernel code,
-including code which is distributed in proprietary, binary-only form.
-There are, however, additional factors which should be taken into account
-before considering any sort of binary-only kernel code distribution. These
-include:
-
-- The legal issues around the distribution of proprietary kernel modules
- are cloudy at best; quite a few kernel copyright holders believe that
- most binary-only modules are derived products of the kernel and that, as
- a result, their distribution is a violation of the GNU General Public
- license (about which more will be said below). Your author is not a
- lawyer, and nothing in this document can possibly be considered to be
- legal advice. The true legal status of closed-source modules can only be
- determined by the courts. But the uncertainty which haunts those modules
- is there regardless.
-
-- Binary modules greatly increase the difficulty of debugging kernel
- problems, to the point that most kernel developers will not even try. So
- the distribution of binary-only modules will make it harder for your
- users to get support from the community.
-
-- Support is also harder for distributors of binary-only modules, who must
- provide a version of the module for every distribution and every kernel
- version they wish to support. Dozens of builds of a single module can
- be required to provide reasonably comprehensive coverage, and your users
- will have to upgrade your module separately every time they upgrade their
- kernel.
-
-- Everything that was said above about code review applies doubly to
- closed-source code. Since this code is not available at all, it cannot
- have been reviewed by the community and will, beyond doubt, have serious
- problems.
-
-Makers of embedded systems, in particular, may be tempted to disregard much
-of what has been said in this section in the belief that they are shipping
-a self-contained product which uses a frozen kernel version and requires no
-more development after its release. This argument misses the value of
-widespread code review and the value of allowing your users to add
-capabilities to your product. But these products, too, have a limited
-commercial life, after which a new version must be released. At that
-point, vendors whose code is in the mainline and well maintained will be
-much better positioned to get the new product ready for market quickly.
-
-Licensing
----------
-
-Code is contributed to the Linux kernel under a number of licenses, but all
-code must be compatible with version 2 of the GNU General Public License
-(GPLv2), which is the license covering the kernel distribution as a whole.
-In practice, that means that all code contributions are covered either by
-GPLv2 (with, optionally, language allowing distribution under later
-versions of the GPL) or the three-clause BSD license. Any contributions
-which are not covered by a compatible license will not be accepted into the
-kernel.
-
-Copyright assignments are not required (or requested) for code contributed
-to the kernel. All code merged into the mainline kernel retains its
-original ownership; as a result, the kernel now has thousands of owners.
-
-One implication of this ownership structure is that any attempt to change
-the licensing of the kernel is doomed to almost certain failure. There are
-few practical scenarios where the agreement of all copyright holders could
-be obtained (or their code removed from the kernel). So, in particular,
-there is no prospect of a migration to version 3 of the GPL in the
-foreseeable future.
-
-It is imperative that all code contributed to the kernel be legitimately
-free software. For that reason, code from anonymous (or pseudonymous)
-contributors will not be accepted. All contributors are required to "sign
-off" on their code, stating that the code can be distributed with the
-kernel under the GPL. Code which has not been licensed as free software by
-its owner, or which risks creating copyright-related problems for the
-kernel (such as code which derives from reverse-engineering efforts lacking
-proper safeguards) cannot be contributed.
-
-Questions about copyright-related issues are common on Linux development
-mailing lists. Such questions will normally receive no shortage of
-answers, but one should bear in mind that the people answering those
-questions are not lawyers and cannot provide legal advice. If you have
-legal questions relating to Linux source code, there is no substitute for
-talking with a lawyer who understands this field. Relying on answers
-obtained on technical mailing lists is a risky affair.
projects / cascardo / linux.git / blobdiff