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Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -08001HOWTO do Linux kernel development
2---------------------------------
3
4This is the be-all, end-all document on this topic. It contains
5instructions on how to become a Linux kernel developer and how to learn
6to work with the Linux kernel development community. It tries to not
7contain anything related to the technical aspects of kernel programming,
8but will help point you in the right direction for that.
9
10If anything in this document becomes out of date, please send in patches
11to the maintainer of this file, who is listed at the bottom of the
12document.
13
14
15Introduction
16------------
17
18So, you want to learn how to become a Linux kernel developer? Or you
19have been told by your manager, "Go write a Linux driver for this
20device." This document's goal is to teach you everything you need to
21know to achieve this by describing the process you need to go through,
22and hints on how to work with the community. It will also try to
23explain some of the reasons why the community works like it does.
24
25The kernel is written mostly in C, with some architecture-dependent
26parts written in assembly. A good understanding of C is required for
27kernel development. Assembly (any architecture) is not required unless
28you plan to do low-level development for that architecture. Though they
29are not a good substitute for a solid C education and/or years of
30experience, the following books are good for, if anything, reference:
31 - "The C Programming Language" by Kernighan and Ritchie [Prentice Hall]
32 - "Practical C Programming" by Steve Oualline [O'Reilly]
Robert P. J. Day4de0ca82007-01-17 04:54:07 -050033 - "C: A Reference Manual" by Harbison and Steele [Prentice Hall]
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -080034
35The kernel is written using GNU C and the GNU toolchain. While it
36adheres to the ISO C89 standard, it uses a number of extensions that are
37not featured in the standard. The kernel is a freestanding C
38environment, with no reliance on the standard C library, so some
39portions of the C standard are not supported. Arbitrary long long
40divisions and floating point are not allowed. It can sometimes be
41difficult to understand the assumptions the kernel has on the toolchain
42and the extensions that it uses, and unfortunately there is no
43definitive reference for them. Please check the gcc info pages (`info
44gcc`) for some information on them.
45
46Please remember that you are trying to learn how to work with the
47existing development community. It is a diverse group of people, with
48high standards for coding, style and procedure. These standards have
49been created over time based on what they have found to work best for
50such a large and geographically dispersed team. Try to learn as much as
51possible about these standards ahead of time, as they are well
52documented; do not expect people to adapt to you or your company's way
53of doing things.
54
55
56Legal Issues
57------------
58
59The Linux kernel source code is released under the GPL. Please see the
60file, COPYING, in the main directory of the source tree, for details on
61the license. If you have further questions about the license, please
62contact a lawyer, and do not ask on the Linux kernel mailing list. The
63people on the mailing lists are not lawyers, and you should not rely on
64their statements on legal matters.
65
66For common questions and answers about the GPL, please see:
67 http://www.gnu.org/licenses/gpl-faq.html
68
69
70Documentation
71------------
72
73The Linux kernel source tree has a large range of documents that are
74invaluable for learning how to interact with the kernel community. When
75new features are added to the kernel, it is recommended that new
76documentation files are also added which explain how to use the feature.
77When a kernel change causes the interface that the kernel exposes to
78userspace to change, it is recommended that you send the information or
79a patch to the manual pages explaining the change to the manual pages
Michael Kerrisk1d7f5022007-10-16 23:30:31 -070080maintainer at mtk.manpages@gmail.com.
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -080081
82Here is a list of files that are in the kernel source tree that are
83required reading:
84 README
85 This file gives a short background on the Linux kernel and describes
86 what is necessary to do to configure and build the kernel. People
87 who are new to the kernel should start here.
88
89 Documentation/Changes
90 This file gives a list of the minimum levels of various software
91 packages that are necessary to build and run the kernel
92 successfully.
93
94 Documentation/CodingStyle
95 This describes the Linux kernel coding style, and some of the
96 rationale behind it. All new code is expected to follow the
97 guidelines in this document. Most maintainers will only accept
98 patches if these rules are followed, and many people will only
99 review code if it is in the proper style.
100
101 Documentation/SubmittingPatches
102 Documentation/SubmittingDrivers
103 These files describe in explicit detail how to successfully create
104 and send a patch, including (but not limited to):
105 - Email contents
106 - Email format
107 - Who to send it to
108 Following these rules will not guarantee success (as all patches are
109 subject to scrutiny for content and style), but not following them
110 will almost always prevent it.
111
112 Other excellent descriptions of how to create patches properly are:
113 "The Perfect Patch"
114 http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt
115 "Linux kernel patch submission format"
116 http://linux.yyz.us/patch-format.html
117
118 Documentation/stable_api_nonsense.txt
119 This file describes the rationale behind the conscious decision to
120 not have a stable API within the kernel, including things like:
121 - Subsystem shim-layers (for compatibility?)
122 - Driver portability between Operating Systems.
123 - Mitigating rapid change within the kernel source tree (or
124 preventing rapid change)
125 This document is crucial for understanding the Linux development
126 philosophy and is very important for people moving to Linux from
127 development on other Operating Systems.
128
129 Documentation/SecurityBugs
130 If you feel you have found a security problem in the Linux kernel,
131 please follow the steps in this document to help notify the kernel
132 developers, and help solve the issue.
133
134 Documentation/ManagementStyle
135 This document describes how Linux kernel maintainers operate and the
136 shared ethos behind their methodologies. This is important reading
137 for anyone new to kernel development (or anyone simply curious about
138 it), as it resolves a lot of common misconceptions and confusion
139 about the unique behavior of kernel maintainers.
140
141 Documentation/stable_kernel_rules.txt
142 This file describes the rules on how the stable kernel releases
143 happen, and what to do if you want to get a change into one of these
144 releases.
145
146 Documentation/kernel-docs.txt
147 A list of external documentation that pertains to kernel
148 development. Please consult this list if you do not find what you
149 are looking for within the in-kernel documentation.
150
151 Documentation/applying-patches.txt
152 A good introduction describing exactly what a patch is and how to
153 apply it to the different development branches of the kernel.
154
155The kernel also has a large number of documents that can be
156automatically generated from the source code itself. This includes a
157full description of the in-kernel API, and rules on how to handle
158locking properly. The documents will be created in the
159Documentation/DocBook/ directory and can be generated as PDF,
160Postscript, HTML, and man pages by running:
161 make pdfdocs
162 make psdocs
163 make htmldocs
164 make mandocs
165respectively from the main kernel source directory.
166
167
168Becoming A Kernel Developer
169---------------------------
170
171If you do not know anything about Linux kernel development, you should
172look at the Linux KernelNewbies project:
173 http://kernelnewbies.org
174It consists of a helpful mailing list where you can ask almost any type
175of basic kernel development question (make sure to search the archives
176first, before asking something that has already been answered in the
177past.) It also has an IRC channel that you can use to ask questions in
178real-time, and a lot of helpful documentation that is useful for
179learning about Linux kernel development.
180
181The website has basic information about code organization, subsystems,
182and current projects (both in-tree and out-of-tree). It also describes
183some basic logistical information, like how to compile a kernel and
184apply a patch.
185
186If you do not know where you want to start, but you want to look for
187some task to start doing to join into the kernel development community,
188go to the Linux Kernel Janitor's project:
189 http://janitor.kernelnewbies.org/
190It is a great place to start. It describes a list of relatively simple
191problems that need to be cleaned up and fixed within the Linux kernel
192source tree. Working with the developers in charge of this project, you
193will learn the basics of getting your patch into the Linux kernel tree,
194and possibly be pointed in the direction of what to go work on next, if
195you do not already have an idea.
196
197If you already have a chunk of code that you want to put into the kernel
198tree, but need some help getting it in the proper form, the
199kernel-mentors project was created to help you out with this. It is a
200mailing list, and can be found at:
201 http://selenic.com/mailman/listinfo/kernel-mentors
202
203Before making any actual modifications to the Linux kernel code, it is
204imperative to understand how the code in question works. For this
205purpose, nothing is better than reading through it directly (most tricky
206bits are commented well), perhaps even with the help of specialized
207tools. One such tool that is particularly recommended is the Linux
208Cross-Reference project, which is able to present source code in a
209self-referential, indexed webpage format. An excellent up-to-date
210repository of the kernel code may be found at:
Qi Yong4db29c12007-06-12 13:06:49 +0800211 http://users.sosdg.org/~qiyong/lxr/
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800212
213
214The development process
215-----------------------
216
217Linux kernel development process currently consists of a few different
218main kernel "branches" and lots of different subsystem-specific kernel
219branches. These different branches are:
220 - main 2.6.x kernel tree
221 - 2.6.x.y -stable kernel tree
222 - 2.6.x -git kernel patches
223 - 2.6.x -mm kernel patches
224 - subsystem specific kernel trees and patches
225
2262.6.x kernel tree
227-----------------
2282.6.x kernels are maintained by Linus Torvalds, and can be found on
229kernel.org in the pub/linux/kernel/v2.6/ directory. Its development
230process is as follows:
231 - As soon as a new kernel is released a two weeks window is open,
232 during this period of time maintainers can submit big diffs to
233 Linus, usually the patches that have already been included in the
234 -mm kernel for a few weeks. The preferred way to submit big changes
235 is using git (the kernel's source management tool, more information
236 can be found at http://git.or.cz/) but plain patches are also just
237 fine.
238 - After two weeks a -rc1 kernel is released it is now possible to push
239 only patches that do not include new features that could affect the
240 stability of the whole kernel. Please note that a whole new driver
241 (or filesystem) might be accepted after -rc1 because there is no
242 risk of causing regressions with such a change as long as the change
243 is self-contained and does not affect areas outside of the code that
244 is being added. git can be used to send patches to Linus after -rc1
245 is released, but the patches need to also be sent to a public
246 mailing list for review.
247 - A new -rc is released whenever Linus deems the current git tree to
248 be in a reasonably sane state adequate for testing. The goal is to
249 release a new -rc kernel every week.
250 - Process continues until the kernel is considered "ready", the
251 process should last around 6 weeks.
Jonathan Corbet0fe8a3c2008-04-25 11:23:56 -0600252 - Known regressions in each release are periodically posted to the
253 linux-kernel mailing list. The goal is to reduce the length of
254 that list to zero before declaring the kernel to be "ready," but, in
255 the real world, a small number of regressions often remain at
256 release time.
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800257
258It is worth mentioning what Andrew Morton wrote on the linux-kernel
259mailing list about kernel releases:
260 "Nobody knows when a kernel will be released, because it's
261 released according to perceived bug status, not according to a
262 preconceived timeline."
263
2642.6.x.y -stable kernel tree
265---------------------------
Jonathan Corbet0fe8a3c2008-04-25 11:23:56 -0600266Kernels with 4-part versions are -stable kernels. They contain
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800267relatively small and critical fixes for security problems or significant
268regressions discovered in a given 2.6.x kernel.
269
270This is the recommended branch for users who want the most recent stable
271kernel and are not interested in helping test development/experimental
272versions.
273
274If no 2.6.x.y kernel is available, then the highest numbered 2.6.x
275kernel is the current stable kernel.
276
2772.6.x.y are maintained by the "stable" team <stable@kernel.org>, and are
Jonathan Corbet0fe8a3c2008-04-25 11:23:56 -0600278released as needs dictate. The normal release period is approximately
279two weeks, but it can be longer if there are no pressing problems. A
280security-related problem, instead, can cause a release to happen almost
281instantly.
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800282
283The file Documentation/stable_kernel_rules.txt in the kernel tree
284documents what kinds of changes are acceptable for the -stable tree, and
285how the release process works.
286
2872.6.x -git patches
288------------------
289These are daily snapshots of Linus' kernel tree which are managed in a
290git repository (hence the name.) These patches are usually released
291daily and represent the current state of Linus' tree. They are more
292experimental than -rc kernels since they are generated automatically
293without even a cursory glance to see if they are sane.
294
2952.6.x -mm kernel patches
296------------------------
297These are experimental kernel patches released by Andrew Morton. Andrew
298takes all of the different subsystem kernel trees and patches and mushes
299them together, along with a lot of patches that have been plucked from
300the linux-kernel mailing list. This tree serves as a proving ground for
301new features and patches. Once a patch has proved its worth in -mm for
302a while Andrew or the subsystem maintainer pushes it on to Linus for
303inclusion in mainline.
304
305It is heavily encouraged that all new patches get tested in the -mm tree
Jonathan Corbet0fe8a3c2008-04-25 11:23:56 -0600306before they are sent to Linus for inclusion in the main kernel tree. Code
307which does not make an appearance in -mm before the opening of the merge
308window will prove hard to merge into the mainline.
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800309
310These kernels are not appropriate for use on systems that are supposed
311to be stable and they are more risky to run than any of the other
312branches.
313
314If you wish to help out with the kernel development process, please test
315and use these kernel releases and provide feedback to the linux-kernel
316mailing list if you have any problems, and if everything works properly.
317
318In addition to all the other experimental patches, these kernels usually
319also contain any changes in the mainline -git kernels available at the
320time of release.
321
322The -mm kernels are not released on a fixed schedule, but usually a few
323-mm kernels are released in between each -rc kernel (1 to 3 is common).
324
325Subsystem Specific kernel trees and patches
326-------------------------------------------
327A number of the different kernel subsystem developers expose their
328development trees so that others can see what is happening in the
329different areas of the kernel. These trees are pulled into the -mm
330kernel releases as described above.
331
332Here is a list of some of the different kernel trees available:
333 git trees:
334 - Kbuild development tree, Sam Ravnborg <sam@ravnborg.org>
Stefan Richter8a465c32007-06-27 14:10:01 -0700335 git.kernel.org:/pub/scm/linux/kernel/git/sam/kbuild.git
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800336
337 - ACPI development tree, Len Brown <len.brown@intel.com>
Stefan Richter8a465c32007-06-27 14:10:01 -0700338 git.kernel.org:/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6.git
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800339
Rob Landley26bbb292007-10-15 11:42:52 +0200340 - Block development tree, Jens Axboe <jens.axboe@oracle.com>
Stefan Richter8a465c32007-06-27 14:10:01 -0700341 git.kernel.org:/pub/scm/linux/kernel/git/axboe/linux-2.6-block.git
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800342
343 - DRM development tree, Dave Airlie <airlied@linux.ie>
Stefan Richter8a465c32007-06-27 14:10:01 -0700344 git.kernel.org:/pub/scm/linux/kernel/git/airlied/drm-2.6.git
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800345
346 - ia64 development tree, Tony Luck <tony.luck@intel.com>
Stefan Richter8a465c32007-06-27 14:10:01 -0700347 git.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800348
349 - infiniband, Roland Dreier <rolandd@cisco.com>
Stefan Richter8a465c32007-06-27 14:10:01 -0700350 git.kernel.org:/pub/scm/linux/kernel/git/roland/infiniband.git
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800351
352 - libata, Jeff Garzik <jgarzik@pobox.com>
Stefan Richter8a465c32007-06-27 14:10:01 -0700353 git.kernel.org:/pub/scm/linux/kernel/git/jgarzik/libata-dev.git
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800354
355 - network drivers, Jeff Garzik <jgarzik@pobox.com>
Stefan Richter8a465c32007-06-27 14:10:01 -0700356 git.kernel.org:/pub/scm/linux/kernel/git/jgarzik/netdev-2.6.git
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800357
358 - pcmcia, Dominik Brodowski <linux@dominikbrodowski.net>
Stefan Richter8a465c32007-06-27 14:10:01 -0700359 git.kernel.org:/pub/scm/linux/kernel/git/brodo/pcmcia-2.6.git
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800360
361 - SCSI, James Bottomley <James.Bottomley@SteelEye.com>
Stefan Richter8a465c32007-06-27 14:10:01 -0700362 git.kernel.org:/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6.git
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800363
Jonathan Corbet0fe8a3c2008-04-25 11:23:56 -0600364 - x86, Ingo Molnar <mingo@elte.hu>
365 git://git.kernel.org/pub/scm/linux/kernel/git/x86/linux-2.6-x86.git
366
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800367 quilt trees:
Jonathan Corbet0fe8a3c2008-04-25 11:23:56 -0600368 - USB, Driver Core, and I2C, Greg Kroah-Hartman <gregkh@suse.de>
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800369 kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800370
Stefan Richter8a465c32007-06-27 14:10:01 -0700371 Other kernel trees can be found listed at http://git.kernel.org/ and in
372 the MAINTAINERS file.
373
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800374Bug Reporting
375-------------
376
377bugzilla.kernel.org is where the Linux kernel developers track kernel
378bugs. Users are encouraged to report all bugs that they find in this
379tool. For details on how to use the kernel bugzilla, please see:
Jiri Pirko0302c012008-07-13 12:13:59 -0700380 http://bugzilla.kernel.org/page.cgi?id=faq.html
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800381
382The file REPORTING-BUGS in the main kernel source directory has a good
383template for how to report a possible kernel bug, and details what kind
384of information is needed by the kernel developers to help track down the
385problem.
386
387
Diego Calleja3f271002006-09-30 23:27:49 -0700388Managing bug reports
389--------------------
390
391One of the best ways to put into practice your hacking skills is by fixing
392bugs reported by other people. Not only you will help to make the kernel
393more stable, you'll learn to fix real world problems and you will improve
394your skills, and other developers will be aware of your presence. Fixing
Qi Yong4db29c12007-06-12 13:06:49 +0800395bugs is one of the best ways to get merits among other developers, because
Diego Calleja3f271002006-09-30 23:27:49 -0700396not many people like wasting time fixing other people's bugs.
397
398To work in the already reported bug reports, go to http://bugzilla.kernel.org.
399If you want to be advised of the future bug reports, you can subscribe to the
400bugme-new mailing list (only new bug reports are mailed here) or to the
401bugme-janitor mailing list (every change in the bugzilla is mailed here)
402
Jonathan Corbet0fe8a3c2008-04-25 11:23:56 -0600403 http://lists.linux-foundation.org/mailman/listinfo/bugme-new
404 http://lists.linux-foundation.org/mailman/listinfo/bugme-janitors
Diego Calleja3f271002006-09-30 23:27:49 -0700405
406
407
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800408Mailing lists
409-------------
410
411As some of the above documents describe, the majority of the core kernel
412developers participate on the Linux Kernel Mailing list. Details on how
413to subscribe and unsubscribe from the list can be found at:
414 http://vger.kernel.org/vger-lists.html#linux-kernel
415There are archives of the mailing list on the web in many different
416places. Use a search engine to find these archives. For example:
417 http://dir.gmane.org/gmane.linux.kernel
418It is highly recommended that you search the archives about the topic
419you want to bring up, before you post it to the list. A lot of things
420already discussed in detail are only recorded at the mailing list
421archives.
422
423Most of the individual kernel subsystems also have their own separate
424mailing list where they do their development efforts. See the
425MAINTAINERS file for a list of what these lists are for the different
426groups.
427
428Many of the lists are hosted on kernel.org. Information on them can be
429found at:
430 http://vger.kernel.org/vger-lists.html
431
432Please remember to follow good behavioral habits when using the lists.
433Though a bit cheesy, the following URL has some simple guidelines for
434interacting with the list (or any list):
435 http://www.albion.com/netiquette/
436
437If multiple people respond to your mail, the CC: list of recipients may
438get pretty large. Don't remove anybody from the CC: list without a good
439reason, or don't reply only to the list address. Get used to receiving the
440mail twice, one from the sender and the one from the list, and don't try
441to tune that by adding fancy mail-headers, people will not like it.
442
443Remember to keep the context and the attribution of your replies intact,
444keep the "John Kernelhacker wrote ...:" lines at the top of your reply, and
445add your statements between the individual quoted sections instead of
446writing at the top of the mail.
447
448If you add patches to your mail, make sure they are plain readable text
449as stated in Documentation/SubmittingPatches. Kernel developers don't
450want to deal with attachments or compressed patches; they may want
451to comment on individual lines of your patch, which works only that way.
452Make sure you use a mail program that does not mangle spaces and tab
453characters. A good first test is to send the mail to yourself and try
454to apply your own patch by yourself. If that doesn't work, get your
455mail program fixed or change it until it works.
456
457Above all, please remember to show respect to other subscribers.
458
459
460Working with the community
461--------------------------
462
463The goal of the kernel community is to provide the best possible kernel
464there is. When you submit a patch for acceptance, it will be reviewed
465on its technical merits and those alone. So, what should you be
466expecting?
467 - criticism
468 - comments
469 - requests for change
470 - requests for justification
471 - silence
472
473Remember, this is part of getting your patch into the kernel. You have
474to be able to take criticism and comments about your patches, evaluate
475them at a technical level and either rework your patches or provide
476clear and concise reasoning as to why those changes should not be made.
477If there are no responses to your posting, wait a few days and try
478again, sometimes things get lost in the huge volume.
479
480What should you not do?
481 - expect your patch to be accepted without question
482 - become defensive
483 - ignore comments
484 - resubmit the patch without making any of the requested changes
485
486In a community that is looking for the best technical solution possible,
487there will always be differing opinions on how beneficial a patch is.
488You have to be cooperative, and willing to adapt your idea to fit within
489the kernel. Or at least be willing to prove your idea is worth it.
490Remember, being wrong is acceptable as long as you are willing to work
491toward a solution that is right.
492
493It is normal that the answers to your first patch might simply be a list
494of a dozen things you should correct. This does _not_ imply that your
495patch will not be accepted, and it is _not_ meant against you
496personally. Simply correct all issues raised against your patch and
497resend it.
498
499
500Differences between the kernel community and corporate structures
501-----------------------------------------------------------------
502
503The kernel community works differently than most traditional corporate
504development environments. Here are a list of things that you can try to
505do to try to avoid problems:
506 Good things to say regarding your proposed changes:
507 - "This solves multiple problems."
508 - "This deletes 2000 lines of code."
509 - "Here is a patch that explains what I am trying to describe."
510 - "I tested it on 5 different architectures..."
511 - "Here is a series of small patches that..."
512 - "This increases performance on typical machines..."
513
514 Bad things you should avoid saying:
515 - "We did it this way in AIX/ptx/Solaris, so therefore it must be
516 good..."
517 - "I've being doing this for 20 years, so..."
518 - "This is required for my company to make money"
519 - "This is for our Enterprise product line."
520 - "Here is my 1000 page design document that describes my idea"
521 - "I've been working on this for 6 months..."
522 - "Here's a 5000 line patch that..."
523 - "I rewrote all of the current mess, and here it is..."
524 - "I have a deadline, and this patch needs to be applied now."
525
526Another way the kernel community is different than most traditional
527software engineering work environments is the faceless nature of
528interaction. One benefit of using email and irc as the primary forms of
529communication is the lack of discrimination based on gender or race.
530The Linux kernel work environment is accepting of women and minorities
531because all you are is an email address. The international aspect also
532helps to level the playing field because you can't guess gender based on
533a person's name. A man may be named Andrea and a woman may be named Pat.
534Most women who have worked in the Linux kernel and have expressed an
535opinion have had positive experiences.
536
537The language barrier can cause problems for some people who are not
538comfortable with English. A good grasp of the language can be needed in
539order to get ideas across properly on mailing lists, so it is
540recommended that you check your emails to make sure they make sense in
541English before sending them.
542
543
544Break up your changes
545---------------------
546
547The Linux kernel community does not gladly accept large chunks of code
548dropped on it all at once. The changes need to be properly introduced,
549discussed, and broken up into tiny, individual portions. This is almost
550the exact opposite of what companies are used to doing. Your proposal
551should also be introduced very early in the development process, so that
552you can receive feedback on what you are doing. It also lets the
553community feel that you are working with them, and not simply using them
554as a dumping ground for your feature. However, don't send 50 emails at
555one time to a mailing list, your patch series should be smaller than
556that almost all of the time.
557
558The reasons for breaking things up are the following:
559
5601) Small patches increase the likelihood that your patches will be
561 applied, since they don't take much time or effort to verify for
562 correctness. A 5 line patch can be applied by a maintainer with
563 barely a second glance. However, a 500 line patch may take hours to
564 review for correctness (the time it takes is exponentially
565 proportional to the size of the patch, or something).
566
567 Small patches also make it very easy to debug when something goes
568 wrong. It's much easier to back out patches one by one than it is
569 to dissect a very large patch after it's been applied (and broken
570 something).
571
5722) It's important not only to send small patches, but also to rewrite
573 and simplify (or simply re-order) patches before submitting them.
574
575Here is an analogy from kernel developer Al Viro:
576 "Think of a teacher grading homework from a math student. The
577 teacher does not want to see the student's trials and errors
578 before they came up with the solution. They want to see the
579 cleanest, most elegant answer. A good student knows this, and
580 would never submit her intermediate work before the final
581 solution."
582
583 The same is true of kernel development. The maintainers and
584 reviewers do not want to see the thought process behind the
585 solution to the problem one is solving. They want to see a
586 simple and elegant solution."
587
588It may be challenging to keep the balance between presenting an elegant
589solution and working together with the community and discussing your
590unfinished work. Therefore it is good to get early in the process to
591get feedback to improve your work, but also keep your changes in small
592chunks that they may get already accepted, even when your whole task is
593not ready for inclusion now.
594
595Also realize that it is not acceptable to send patches for inclusion
596that are unfinished and will be "fixed up later."
597
598
599Justify your change
600-------------------
601
602Along with breaking up your patches, it is very important for you to let
603the Linux community know why they should add this change. New features
604must be justified as being needed and useful.
605
606
607Document your change
608--------------------
609
610When sending in your patches, pay special attention to what you say in
611the text in your email. This information will become the ChangeLog
612information for the patch, and will be preserved for everyone to see for
613all time. It should describe the patch completely, containing:
614 - why the change is necessary
615 - the overall design approach in the patch
616 - implementation details
617 - testing results
618
619For more details on what this should all look like, please see the
620ChangeLog section of the document:
621 "The Perfect Patch"
622 http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt
623
624
625
626
627All of these things are sometimes very hard to do. It can take years to
628perfect these practices (if at all). It's a continuous process of
629improvement that requires a lot of patience and determination. But
630don't give up, it's possible. Many have done it before, and each had to
631start exactly where you are now.
632
633
634
635
636----------
Paolo Ciarrocchi5bd982e2006-04-25 22:47:51 +0200637Thanks to Paolo Ciarrocchi who allowed the "Development Process"
638(http://linux.tar.bz/articles/2.6-development_process) section
Greg Kroah-Hartmand36cc9d2005-11-18 09:31:11 -0800639to be based on text he had written, and to Randy Dunlap and Gerrit
640Huizenga for some of the list of things you should and should not say.
641Also thanks to Pat Mochel, Hanna Linder, Randy Dunlap, Kay Sievers,
642Vojtech Pavlik, Jan Kara, Josh Boyer, Kees Cook, Andrew Morton, Andi
643Kleen, Vadim Lobanov, Jesper Juhl, Adrian Bunk, Keri Harris, Frans Pop,
644David A. Wheeler, Junio Hamano, Michael Kerrisk, and Alex Shepard for
645their review, comments, and contributions. Without their help, this
646document would not have been possible.
647
648
649
650Maintainer: Greg Kroah-Hartman <greg@kroah.com>