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| -rw-r--r-- | Documentation/development-process/1.Intro | 68 | ||||
| -rw-r--r-- | Documentation/development-process/2.Process | 41 | ||||
| -rw-r--r-- | Documentation/development-process/3.Early-stage | 22 | ||||
| -rw-r--r-- | Documentation/development-process/4.Coding | 46 | ||||
| -rw-r--r-- | Documentation/development-process/5.Posting | 26 | ||||
| -rw-r--r-- | Documentation/development-process/6.Followthrough | 14 | ||||
| -rw-r--r-- | Documentation/development-process/7.AdvancedTopics | 13 | ||||
| -rw-r--r-- | Documentation/development-process/8.Conclusion | 8 | ||||
| -rw-r--r-- | Documentation/development-process/development-process.rst | 27 |
9 files changed, 179 insertions, 86 deletions
diff --git a/Documentation/development-process/1.Intro b/Documentation/development-process/1.Intro index 9b614480aa84..22642b3fe903 100644 --- a/Documentation/development-process/1.Intro +++ b/Documentation/development-process/1.Intro @@ -1,16 +1,8 @@ -1: A GUIDE TO THE KERNEL DEVELOPMENT PROCESS +Introdution +=========== -The purpose of this document is to help developers (and their managers) -work with the development community with a minimum of frustration. It is -an attempt to document how this community works in a way which is -accessible to those who are not intimately familiar with Linux kernel -development (or, indeed, free software development in general). While -there is some technical material here, this is very much a process-oriented -discussion which does not require a deep knowledge of kernel programming to -understand. - - -1.1: EXECUTIVE SUMMARY +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 @@ -20,41 +12,41 @@ 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. -Section 2 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 +: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. -Section 3 covers early-stage project planning, with an emphasis on -involving the development community as soon as possible. +:ref:`development_early_stage` covers early-stage project planning, with an +emphasis on involving the development community as soon as possible. -Section 4 is about the coding process; several pitfalls which have been -encountered by other developers are discussed. Some requirements for +: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. -Section 5 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. +: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. -Section 6 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 +: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. -Section 7 introduces a couple of "advanced" topics: managing patches with -git and reviewing patches posted by others. - -Section 8 concludes the document with pointers to sources for more -information on kernel development. +: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. -1.2: WHAT THIS DOCUMENT IS ABOUT +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 @@ -108,8 +100,8 @@ 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. - -1.3: CREDITS +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 @@ -120,8 +112,8 @@ 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. - -1.4: THE IMPORTANCE OF GETTING CODE INTO THE MAINLINE +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 @@ -233,8 +225,8 @@ 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. - -1.5: LICENSING +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 diff --git a/Documentation/development-process/2.Process b/Documentation/development-process/2.Process index c24e156a6118..ce5561bb3f8e 100644 --- a/Documentation/development-process/2.Process +++ b/Documentation/development-process/2.Process @@ -1,4 +1,7 @@ -2: HOW THE DEVELOPMENT PROCESS WORKS +.. _development_process: + +How the development process works +================================= Linux kernel development in the early 1990's was a pretty loose affair, with relatively small numbers of users and developers involved. With a @@ -7,19 +10,21 @@ course of one year, the kernel has since had to evolve a number of processes to keep development happening smoothly. A solid understanding of how the process works is required in order to be an effective part of it. - -2.1: THE BIG PICTURE +The big picture +--------------- The kernel developers use a loosely time-based release process, with a new major kernel release happening every two or three months. The recent release history looks like this: + ====== ================= 2.6.38 March 14, 2011 2.6.37 January 4, 2011 2.6.36 October 20, 2010 2.6.35 August 1, 2010 2.6.34 May 15, 2010 2.6.33 February 24, 2010 + ====== ================= Every 2.6.x release is a major kernel release with new features, internal API changes, and more. A typical 2.6 release can contain nearly 10,000 @@ -68,6 +73,7 @@ At that point the whole process starts over again. As an example, here is how the 2.6.38 development cycle went (all dates in 2011): + ============== =============================== January 4 2.6.37 stable release January 18 2.6.38-rc1, merge window closes January 21 2.6.38-rc2 @@ -78,6 +84,7 @@ As an example, here is how the 2.6.38 development cycle went (all dates in March 1 2.6.38-rc7 March 7 2.6.38-rc8 March 14 2.6.38 stable release + ============== =============================== How do the developers decide when to close the development cycle and create the stable release? The most significant metric used is the list of @@ -105,11 +112,13 @@ next development kernel. Kernels will typically receive stable updates for a little more than one development cycle past their initial release. So, for example, the 2.6.36 kernel's history looked like: + ============== =============================== October 10 2.6.36 stable release November 22 2.6.36.1 December 9 2.6.36.2 January 7 2.6.36.3 February 17 2.6.36.4 + ============== =============================== 2.6.36.4 was the final stable update for the 2.6.36 release. @@ -117,9 +126,11 @@ Some kernels are designated "long term" kernels; they will receive support for a longer period. As of this writing, the current long term kernels and their maintainers are: + ====== ====================== =========================== 2.6.27 Willy Tarreau (Deep-frozen stable kernel) 2.6.32 Greg Kroah-Hartman 2.6.35 Andi Kleen (Embedded flag kernel) + ====== ====================== =========================== The selection of a kernel for long-term support is purely a matter of a maintainer having the need and the time to maintain that release. There @@ -127,7 +138,8 @@ are no known plans for long-term support for any specific upcoming release. -2.2: THE LIFECYCLE OF A PATCH +The lifecycle of a patch +------------------------ Patches do not go directly from the developer's keyboard into the mainline kernel. There is, instead, a somewhat involved (if somewhat informal) @@ -195,8 +207,8 @@ is to try to cut the process down to a single "merging into the mainline" step. This approach invariably leads to frustration for everybody involved. - -2.3: HOW PATCHES GET INTO THE KERNEL +How patches get into the Kernel +------------------------------- There is exactly one person who can merge patches into the mainline kernel repository: Linus Torvalds. But, of the over 9,500 patches which went @@ -242,7 +254,8 @@ finding the right maintainer. Sending patches directly to Linus is not normally the right way to go. -2.4: NEXT TREES +Next trees +---------- The chain of subsystem trees guides the flow of patches into the kernel, but it also raises an interesting question: what if somebody wants to look @@ -294,7 +307,8 @@ all patches merged during a given merge window should really have found their way into linux-next some time before the merge window opens. -2.4.1: STAGING TREES +Staging trees +------------- The kernel source tree contains the drivers/staging/ directory, where many sub-directories for drivers or filesystems that are on their way to @@ -322,7 +336,8 @@ staging drivers. So staging is, at best, a stop on the way toward becoming a proper mainline driver. -2.5: TOOLS +Tools +----- As can be seen from the above text, the kernel development process depends heavily on the ability to herd collections of patches in various @@ -368,7 +383,8 @@ upstream. For the management of certain kinds of trees (-mm, for example), quilt is the best tool for the job. -2.6: MAILING LISTS +Mailing lists +------------- A great deal of Linux kernel development work is done by way of mailing lists. It is hard to be a fully-functioning member of the community @@ -436,7 +452,8 @@ filesystem, etc. subsystems. The best place to look for mailing lists is in the MAINTAINERS file packaged with the kernel source. -2.7: GETTING STARTED WITH KERNEL DEVELOPMENT +Getting started with Kernel development +--------------------------------------- Questions about how to get started with the kernel development process are common - from both individuals and companies. Equally common are missteps @@ -463,6 +480,8 @@ they wish for by these means. Andrew Morton gives this advice for aspiring kernel developers +:: + The #1 project for all kernel beginners should surely be "make sure that the kernel runs perfectly at all times on all machines which you can lay your hands on". Usually the way to do this is to work diff --git a/Documentation/development-process/3.Early-stage b/Documentation/development-process/3.Early-stage index f87ba7b3fbac..af2c0af931d6 100644 --- a/Documentation/development-process/3.Early-stage +++ b/Documentation/development-process/3.Early-stage @@ -1,4 +1,7 @@ -3: EARLY-STAGE PLANNING +.. _development_early_stage: + +Early-stage planning +==================== When contemplating a Linux kernel development project, it can be tempting to jump right in and start coding. As with any significant project, @@ -7,7 +10,8 @@ line of code is written. Some time spent in early planning and communication can save far more time later on. -3.1: SPECIFYING THE PROBLEM +Specifying the problem +---------------------- Like any engineering project, a successful kernel enhancement starts with a clear description of the problem to be solved. In some cases, this step is @@ -64,7 +68,8 @@ answers to a short set of questions: Only then does it make sense to start considering possible solutions. -3.2: EARLY DISCUSSION +Early discussion +---------------- When planning a kernel development project, it makes great sense to hold discussions with the community before launching into implementation. Early @@ -117,7 +122,8 @@ In each of these cases, a great deal of pain and extra work could have been avoided with some early discussion with the kernel developers. -3.3: WHO DO YOU TALK TO? +Who do you talk to? +------------------- When developers decide to take their plans public, the next question will be: where do we start? The answer is to find the right mailing list(s) and @@ -141,6 +147,8 @@ development project. The task of finding the right maintainer is sometimes challenging enough that the kernel developers have added a script to ease the process: +:: + .../scripts/get_maintainer.pl This script will return the current maintainer(s) for a given file or @@ -155,7 +163,8 @@ If all else fails, talking to Andrew Morton can be an effective way to track down a maintainer for a specific piece of code. -3.4: WHEN TO POST? +When to post? +------------- If possible, posting your plans during the early stages can only be helpful. Describe the problem being solved and any plans that have been @@ -179,7 +188,8 @@ idea. The best thing to do in this situation is to proceed, keeping the community informed as you go. -3.5: GETTING OFFICIAL BUY-IN +Getting official buy-in +----------------------- If your work is being done in a corporate environment - as most Linux kernel work is - you must, obviously, have permission from suitably diff --git a/Documentation/development-process/4.Coding b/Documentation/development-process/4.Coding index 9a3ee77cefb1..9d5cef996f7f 100644 --- a/Documentation/development-process/4.Coding +++ b/Documentation/development-process/4.Coding @@ -1,4 +1,7 @@ -4: GETTING THE CODE RIGHT +.. _development_coding: + +Getting the code right +====================== While there is much to be said for a solid and community-oriented design process, the proof of any kernel development project is in the resulting @@ -12,9 +15,11 @@ will shift toward doing things right and the tools which can help in that quest. -4.1: PITFALLS +Pitfalls +--------- -* Coding style +Coding style +************ The kernel has long had a standard coding style, described in Documentation/CodingStyle. For much of that time, the policies described @@ -54,7 +59,8 @@ style (a line which becomes far less readable if split to fit within the 80-column limit, for example), just do it. -* Abstraction layers +Abstraction layers +****************** Computer Science professors teach students to make extensive use of abstraction layers in the name of flexibility and information hiding. @@ -87,7 +93,8 @@ implement that functionality at a higher level. There is no value in replicating the same code throughout the kernel. -* #ifdef and preprocessor use in general +#ifdef and preprocessor use in general +************************************** The C preprocessor seems to present a powerful temptation to some C programmers, who see it as a way to efficiently encode a great deal of @@ -113,7 +120,8 @@ easier to read, do not evaluate their arguments multiple times, and allow the compiler to perform type checking on the arguments and return value. -* Inline functions +Inline functions +**************** Inline functions present a hazard of their own, though. Programmers can become enamored of the perceived efficiency inherent in avoiding a function @@ -137,7 +145,8 @@ placement of "inline" keywords may not just be excessive; it could also be irrelevant. -* Locking +Locking +******* In May, 2006, the "Devicescape" networking stack was, with great fanfare, released under the GPL and made available for inclusion in the @@ -151,7 +160,7 @@ This code showed a number of signs of having been developed behind corporate doors. But one large problem in particular was that it was not designed to work on multiprocessor systems. Before this networking stack (now called mac80211) could be merged, a locking scheme needed to be -retrofitted onto it. +retrofitted onto it. Once upon a time, Linux kernel code could be developed without thinking about the concurrency issues presented by multiprocessor systems. Now, @@ -169,7 +178,8 @@ enough to pick the right tool for the job. Code which shows a lack of attention to concurrency will have a difficult path into the mainline. -* Regressions +Regressions +*********** One final hazard worth mentioning is this: it can be tempting to make a change (which may bring big improvements) which causes something to break @@ -185,6 +195,8 @@ change if it brings new functionality to ten systems for each one it breaks? The best answer to this question was expressed by Linus in July, 2007: +:: + So we don't fix bugs by introducing new problems. That way lies madness, and nobody ever knows if you actually make any real progress at all. Is it two steps forwards, one step back, or one @@ -201,8 +213,8 @@ reason, a great deal of thought, clear documentation, and wide review for user-space interfaces is always required. - -4.2: CODE CHECKING TOOLS +Code checking tools +------------------- For now, at least, the writing of error-free code remains an ideal that few of us can reach. What we can hope to do, though, is to catch and fix as @@ -250,7 +262,7 @@ testing purposes. In particular, you should turn on: There are quite a few other debugging options, some of which will be discussed below. Some of them have a significant performance impact and should not be used all of the time. But some time spent learning the -available options will likely be paid back many times over in short order. +available options will likely be paid back many times over in short order. One of the heavier debugging tools is the locking checker, or "lockdep." This tool will track the acquisition and release of every lock (spinlock or @@ -263,7 +275,7 @@ occasion, deadlock. This kind of problem can be painful (for both developers and users) in a deployed system; lockdep allows them to be found in an automated manner ahead of time. Code with any sort of non-trivial locking should be run with lockdep enabled before being submitted for -inclusion. +inclusion. As a diligent kernel programmer, you will, beyond doubt, check the return status of any operation (such as a memory allocation) which can fail. The @@ -300,7 +312,7 @@ Documentation/coccinelle.txt for more information. Other kinds of portability errors are best found by compiling your code for other architectures. If you do not happen to have an S/390 system or a Blackfin development board handy, you can still perform the compilation -step. A large set of cross compilers for x86 systems can be found at +step. A large set of cross compilers for x86 systems can be found at http://www.kernel.org/pub/tools/crosstool/ @@ -308,7 +320,8 @@ Some time spent installing and using these compilers will help avoid embarrassment later. -4.3: DOCUMENTATION +Documentation +------------- Documentation has often been more the exception than the rule with kernel development. Even so, adequate documentation will help to ease the merging @@ -364,7 +377,8 @@ out. Anything which might tempt a code janitor to make an incorrect "cleanup" needs a comment saying why it is done the way it is. And so on. -4.4: INTERNAL API CHANGES +Internal API changes +-------------------- The binary interface provided by the kernel to user space cannot be broken except under the most severe circumstances. The kernel's internal diff --git a/Documentation/development-process/5.Posting b/Documentation/development-process/5.Posting index 8a48c9b62864..b511ddf7e82a 100644 --- a/Documentation/development-process/5.Posting +++ b/Documentation/development-process/5.Posting @@ -1,4 +1,7 @@ -5: POSTING PATCHES +.. _development_posting: + +Posting patches +=============== Sooner or later, the time comes when your work is ready to be presented to the community for review and, eventually, inclusion into the mainline @@ -11,7 +14,8 @@ SubmittingDrivers, and SubmitChecklist in the kernel documentation directory. -5.1: WHEN TO POST +When to post +------------ There is a constant temptation to avoid posting patches before they are completely "ready." For simple patches, that is not a problem. If the @@ -27,7 +31,8 @@ patches which are known to be half-baked, but those who do will come in with the idea that they can help you drive the work in the right direction. -5.2: BEFORE CREATING PATCHES +Before creating patches +----------------------- There are a number of things which should be done before you consider sending patches to the development community. These include: @@ -52,7 +57,8 @@ As a general rule, putting in some extra thought before posting code almost always pays back the effort in short order. -5.3: PATCH PREPARATION +Patch preparation +----------------- The preparation of patches for posting can be a surprising amount of work, but, once again, attempting to save time here is not generally advisable @@ -122,7 +128,8 @@ which takes quite a bit of time and thought after the "real work" has been done. When done properly, though, it is time well spent. -5.4: PATCH FORMATTING AND CHANGELOGS +Patch formatting and changelogs +------------------------------- So now you have a perfect series of patches for posting, but the work is not done quite yet. Each patch needs to be formatted into a message which @@ -140,6 +147,8 @@ that end, each patch will be composed of the following: subsystem name first, followed by the purpose of the patch. For example: + :: + gpio: fix build on CONFIG_GPIO_SYSFS=n - A blank line followed by a detailed description of the contents of the @@ -192,6 +201,8 @@ been associated with the development of this patch. They are described in detail in the SubmittingPatches document; what follows here is a brief summary. Each of these lines has the format: +:: + tag: Full Name <email address> optional-other-stuff The tags in common use are: @@ -225,7 +236,8 @@ Be careful in the addition of tags to your patches: only Cc: is appropriate for addition without the explicit permission of the person named. -5.5: SENDING THE PATCH +Sending the patch +----------------- Before you mail your patches, there are a couple of other things you should take care of: @@ -287,6 +299,8 @@ obvious maintainer, Andrew Morton is often the patch target of last resort. Patches need good subject lines. The canonical format for a patch line is something like: +:: + [PATCH nn/mm] subsys: one-line description of the patch where "nn" is the ordinal number of the patch, "mm" is the total number of diff --git a/Documentation/development-process/6.Followthrough b/Documentation/development-process/6.Followthrough index 41d324a9420d..a173cd5f93d2 100644 --- a/Documentation/development-process/6.Followthrough +++ b/Documentation/development-process/6.Followthrough @@ -1,4 +1,7 @@ -6: FOLLOWTHROUGH +.. _development_followthrough: + +Followthrough +============= At this point, you have followed the guidelines given so far and, with the addition of your own engineering skills, have posted a perfect series of @@ -16,7 +19,8 @@ standards. A failure to participate in this process is quite likely to prevent the inclusion of your patches into the mainline. -6.1: WORKING WITH REVIEWERS +Working with reviewers +---------------------- A patch of any significance will result in a number of comments from other developers as they review the code. Working with reviewers can be, for @@ -97,7 +101,8 @@ though, and not before all other alternatives have been explored. And bear in mind, of course, that he may not agree with you either. -6.2: WHAT HAPPENS NEXT +What happens next +----------------- If a patch is considered to be a good thing to add to the kernel, and once most of the review issues have been resolved, the next step is usually @@ -177,7 +182,8 @@ it with the assumption that you will not be around to maintain it afterward. -6.3: OTHER THINGS THAT CAN HAPPEN +Other things that can happen +----------------------------- One day, you may open your mail client and see that somebody has mailed you a patch to your code. That is one of the advantages of having your code diff --git a/Documentation/development-process/7.AdvancedTopics b/Documentation/development-process/7.AdvancedTopics index 26dc3fa196e4..81d61c5d62dd 100644 --- a/Documentation/development-process/7.AdvancedTopics +++ b/Documentation/development-process/7.AdvancedTopics @@ -1,11 +1,15 @@ -7: ADVANCED TOPICS +.. _development_advancedtopics: + +Advanced topics +=============== At this point, hopefully, you have a handle on how the development process works. There is still more to learn, however! This section will cover a number of topics which can be helpful for developers wanting to become a regular part of the Linux kernel development process. -7.1: MANAGING PATCHES WITH GIT +Managing patches with git +------------------------- The use of distributed version control for the kernel began in early 2002, when Linus first started playing with the proprietary BitKeeper @@ -114,6 +118,8 @@ radar. Kernel developers tend to get unhappy when they see that kind of thing happening; putting up a git tree with unreviewed or off-topic patches can affect your ability to get trees pulled in the future. Quoting Linus: +:: + You can send me patches, but for me to pull a git patch from you, I need to know that you know what you're doing, and I need to be able to trust things *without* then having to go and check every @@ -141,7 +147,8 @@ format the request as other developers expect, and will also check to be sure that you have remembered to push those changes to the public server. -7.2: REVIEWING PATCHES +Reviewing patches +----------------- Some readers will certainly object to putting this section with "advanced topics" on the grounds that even beginning kernel developers should be diff --git a/Documentation/development-process/8.Conclusion b/Documentation/development-process/8.Conclusion index caef69022e9c..23ec7cbc2d2b 100644 --- a/Documentation/development-process/8.Conclusion +++ b/Documentation/development-process/8.Conclusion @@ -1,4 +1,7 @@ -8: FOR MORE INFORMATION +.. _development_conclusion: + +For more information +==================== There are numerous sources of information on Linux kernel development and related topics. First among those will always be the Documentation @@ -47,7 +50,8 @@ Documentation for git can be found at: http://www.kernel.org/pub/software/scm/git/docs/user-manual.html -9: CONCLUSION +Conclusion +========== Congratulations to anybody who has made it through this long-winded document. Hopefully it has provided a helpful understanding of how the diff --git a/Documentation/development-process/development-process.rst b/Documentation/development-process/development-process.rst new file mode 100644 index 000000000000..d431a1098875 --- /dev/null +++ b/Documentation/development-process/development-process.rst @@ -0,0 +1,27 @@ +A guide to the Kernel Development Process +========================================= + +Contents: + +.. toctree:: + :numbered: + :maxdepth: 2 + + 1.Intro + 2.Process + 3.Early-stage + 4.Coding + 5.Posting + 6.Followthrough + 7.AdvancedTopics + 8.Conclusion + +The purpose of this document is to help developers (and their managers) +work with the development community with a minimum of frustration. It is +an attempt to document how this community works in a way which is +accessible to those who are not intimately familiar with Linux kernel +development (or, indeed, free software development in general). While +there is some technical material here, this is very much a process-oriented +discussion which does not require a deep knowledge of kernel programming to +understand. + |