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d36cc9d0 | 1 | HOWTO do Linux kernel development |
022e04d6 | 2 | ================================= |
d36cc9d0 GKH |
3 | |
4 | This is the be-all, end-all document on this topic. It contains | |
5 | instructions on how to become a Linux kernel developer and how to learn | |
6 | to work with the Linux kernel development community. It tries to not | |
7 | contain anything related to the technical aspects of kernel programming, | |
8 | but will help point you in the right direction for that. | |
9 | ||
10 | If anything in this document becomes out of date, please send in patches | |
11 | to the maintainer of this file, who is listed at the bottom of the | |
12 | document. | |
13 | ||
14 | ||
15 | Introduction | |
16 | ------------ | |
17 | ||
18 | So, you want to learn how to become a Linux kernel developer? Or you | |
19 | have been told by your manager, "Go write a Linux driver for this | |
20 | device." This document's goal is to teach you everything you need to | |
21 | know to achieve this by describing the process you need to go through, | |
22 | and hints on how to work with the community. It will also try to | |
23 | explain some of the reasons why the community works like it does. | |
24 | ||
25 | The kernel is written mostly in C, with some architecture-dependent | |
26 | parts written in assembly. A good understanding of C is required for | |
27 | kernel development. Assembly (any architecture) is not required unless | |
28 | you plan to do low-level development for that architecture. Though they | |
29 | are not a good substitute for a solid C education and/or years of | |
30 | experience, the following books are good for, if anything, reference: | |
022e04d6 | 31 | |
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32 | - "The C Programming Language" by Kernighan and Ritchie [Prentice Hall] |
33 | - "Practical C Programming" by Steve Oualline [O'Reilly] | |
4de0ca81 | 34 | - "C: A Reference Manual" by Harbison and Steele [Prentice Hall] |
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35 | |
36 | The kernel is written using GNU C and the GNU toolchain. While it | |
37 | adheres to the ISO C89 standard, it uses a number of extensions that are | |
38 | not featured in the standard. The kernel is a freestanding C | |
39 | environment, with no reliance on the standard C library, so some | |
40 | portions of the C standard are not supported. Arbitrary long long | |
41 | divisions and floating point are not allowed. It can sometimes be | |
42 | difficult to understand the assumptions the kernel has on the toolchain | |
43 | and the extensions that it uses, and unfortunately there is no | |
44 | definitive reference for them. Please check the gcc info pages (`info | |
45 | gcc`) for some information on them. | |
46 | ||
47 | Please remember that you are trying to learn how to work with the | |
48 | existing development community. It is a diverse group of people, with | |
49 | high standards for coding, style and procedure. These standards have | |
50 | been created over time based on what they have found to work best for | |
51 | such a large and geographically dispersed team. Try to learn as much as | |
52 | possible about these standards ahead of time, as they are well | |
53 | documented; do not expect people to adapt to you or your company's way | |
54 | of doing things. | |
55 | ||
56 | ||
57 | Legal Issues | |
58 | ------------ | |
59 | ||
60 | The Linux kernel source code is released under the GPL. Please see the | |
61 | file, COPYING, in the main directory of the source tree, for details on | |
62 | the license. If you have further questions about the license, please | |
63 | contact a lawyer, and do not ask on the Linux kernel mailing list. The | |
64 | people on the mailing lists are not lawyers, and you should not rely on | |
65 | their statements on legal matters. | |
66 | ||
67 | For common questions and answers about the GPL, please see: | |
022e04d6 | 68 | |
f1eebe92 | 69 | https://www.gnu.org/licenses/gpl-faq.html |
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70 | |
71 | ||
72 | Documentation | |
ce655081 | 73 | ------------- |
d36cc9d0 GKH |
74 | |
75 | The Linux kernel source tree has a large range of documents that are | |
76 | invaluable for learning how to interact with the kernel community. When | |
77 | new features are added to the kernel, it is recommended that new | |
78 | documentation files are also added which explain how to use the feature. | |
79 | When a kernel change causes the interface that the kernel exposes to | |
80 | userspace to change, it is recommended that you send the information or | |
81 | a patch to the manual pages explaining the change to the manual pages | |
09b05f5e MK |
82 | maintainer at mtk.manpages@gmail.com, and CC the list |
83 | linux-api@vger.kernel.org. | |
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84 | |
85 | Here is a list of files that are in the kernel source tree that are | |
86 | required reading: | |
022e04d6 | 87 | |
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88 | README |
89 | This file gives a short background on the Linux kernel and describes | |
90 | what is necessary to do to configure and build the kernel. People | |
91 | who are new to the kernel should start here. | |
92 | ||
609d99a3 | 93 | :ref:`Documentation/Changes <changes>` |
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94 | This file gives a list of the minimum levels of various software |
95 | packages that are necessary to build and run the kernel | |
96 | successfully. | |
97 | ||
609d99a3 | 98 | :ref:`Documentation/CodingStyle <codingstyle>` |
d36cc9d0 GKH |
99 | This describes the Linux kernel coding style, and some of the |
100 | rationale behind it. All new code is expected to follow the | |
101 | guidelines in this document. Most maintainers will only accept | |
102 | patches if these rules are followed, and many people will only | |
103 | review code if it is in the proper style. | |
104 | ||
609d99a3 | 105 | :ref:`Documentation/SubmittingPatches <submittingpatches>` and :ref:`Documentation/SubmittingDrivers <submittingdrivers>` |
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106 | These files describe in explicit detail how to successfully create |
107 | and send a patch, including (but not limited to): | |
022e04d6 | 108 | |
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109 | - Email contents |
110 | - Email format | |
111 | - Who to send it to | |
022e04d6 | 112 | |
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113 | Following these rules will not guarantee success (as all patches are |
114 | subject to scrutiny for content and style), but not following them | |
115 | will almost always prevent it. | |
116 | ||
117 | Other excellent descriptions of how to create patches properly are: | |
022e04d6 | 118 | |
d36cc9d0 | 119 | "The Perfect Patch" |
f1eebe92 | 120 | https://www.ozlabs.org/~akpm/stuff/tpp.txt |
022e04d6 | 121 | |
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122 | "Linux kernel patch submission format" |
123 | http://linux.yyz.us/patch-format.html | |
124 | ||
609d99a3 | 125 | :ref:`Documentation/stable_api_nonsense.txt <stable_api_nonsense>` |
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126 | This file describes the rationale behind the conscious decision to |
127 | not have a stable API within the kernel, including things like: | |
022e04d6 | 128 | |
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129 | - Subsystem shim-layers (for compatibility?) |
130 | - Driver portability between Operating Systems. | |
131 | - Mitigating rapid change within the kernel source tree (or | |
132 | preventing rapid change) | |
022e04d6 | 133 | |
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134 | This document is crucial for understanding the Linux development |
135 | philosophy and is very important for people moving to Linux from | |
136 | development on other Operating Systems. | |
137 | ||
609d99a3 | 138 | :ref:`Documentation/SecurityBugs <securitybugs>` |
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139 | If you feel you have found a security problem in the Linux kernel, |
140 | please follow the steps in this document to help notify the kernel | |
141 | developers, and help solve the issue. | |
142 | ||
609d99a3 | 143 | :ref:`Documentation/ManagementStyle <managementstyle>` |
d36cc9d0 GKH |
144 | This document describes how Linux kernel maintainers operate and the |
145 | shared ethos behind their methodologies. This is important reading | |
146 | for anyone new to kernel development (or anyone simply curious about | |
147 | it), as it resolves a lot of common misconceptions and confusion | |
148 | about the unique behavior of kernel maintainers. | |
149 | ||
609d99a3 | 150 | :ref:`Documentation/stable_kernel_rules.txt <stable_kernel_rules>` |
d36cc9d0 GKH |
151 | This file describes the rules on how the stable kernel releases |
152 | happen, and what to do if you want to get a change into one of these | |
153 | releases. | |
154 | ||
609d99a3 | 155 | :ref:`Documentation/kernel-docs.txt <kernel_docs>` |
d36cc9d0 GKH |
156 | A list of external documentation that pertains to kernel |
157 | development. Please consult this list if you do not find what you | |
158 | are looking for within the in-kernel documentation. | |
159 | ||
609d99a3 | 160 | :ref:`Documentation/applying-patches.txt <applying_patches>` |
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161 | A good introduction describing exactly what a patch is and how to |
162 | apply it to the different development branches of the kernel. | |
163 | ||
164 | The kernel also has a large number of documents that can be | |
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165 | automatically generated from the source code itself or from |
166 | ReStructuredText markups (ReST), like this one. This includes a | |
d36cc9d0 | 167 | full description of the in-kernel API, and rules on how to handle |
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168 | locking properly. |
169 | ||
1b49ecf2 | 170 | All such documents can be generated as PDF or HTML by running:: |
022e04d6 | 171 | |
d36cc9d0 | 172 | make pdfdocs |
d36cc9d0 | 173 | make htmldocs |
022e04d6 | 174 | |
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175 | respectively from the main kernel source directory. |
176 | ||
43fb67a5 | 177 | The documents that uses ReST markup will be generated at Documentation/output. |
1b49ecf2 | 178 | They can also be generated on LaTeX and ePub formats with:: |
43fb67a5 MCC |
179 | |
180 | make latexdocs | |
181 | make epubdocs | |
182 | ||
183 | Currently, there are some documents written on DocBook that are in | |
184 | the process of conversion to ReST. Such documents will be created in the | |
185 | Documentation/DocBook/ directory and can be generated also as | |
1b49ecf2 | 186 | Postscript or man pages by running:: |
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187 | |
188 | make psdocs | |
189 | make mandocs | |
d36cc9d0 GKH |
190 | |
191 | Becoming A Kernel Developer | |
192 | --------------------------- | |
193 | ||
194 | If you do not know anything about Linux kernel development, you should | |
195 | look at the Linux KernelNewbies project: | |
022e04d6 | 196 | |
f1eebe92 | 197 | https://kernelnewbies.org |
022e04d6 | 198 | |
d36cc9d0 GKH |
199 | It consists of a helpful mailing list where you can ask almost any type |
200 | of basic kernel development question (make sure to search the archives | |
201 | first, before asking something that has already been answered in the | |
202 | past.) It also has an IRC channel that you can use to ask questions in | |
203 | real-time, and a lot of helpful documentation that is useful for | |
204 | learning about Linux kernel development. | |
205 | ||
206 | The website has basic information about code organization, subsystems, | |
207 | and current projects (both in-tree and out-of-tree). It also describes | |
208 | some basic logistical information, like how to compile a kernel and | |
209 | apply a patch. | |
210 | ||
211 | If you do not know where you want to start, but you want to look for | |
212 | some task to start doing to join into the kernel development community, | |
213 | go to the Linux Kernel Janitor's project: | |
022e04d6 | 214 | |
f1eebe92 | 215 | https://kernelnewbies.org/KernelJanitors |
022e04d6 | 216 | |
d36cc9d0 GKH |
217 | It is a great place to start. It describes a list of relatively simple |
218 | problems that need to be cleaned up and fixed within the Linux kernel | |
219 | source tree. Working with the developers in charge of this project, you | |
220 | will learn the basics of getting your patch into the Linux kernel tree, | |
221 | and possibly be pointed in the direction of what to go work on next, if | |
222 | you do not already have an idea. | |
223 | ||
224 | If you already have a chunk of code that you want to put into the kernel | |
225 | tree, but need some help getting it in the proper form, the | |
226 | kernel-mentors project was created to help you out with this. It is a | |
227 | mailing list, and can be found at: | |
022e04d6 | 228 | |
f1eebe92 | 229 | https://selenic.com/mailman/listinfo/kernel-mentors |
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230 | |
231 | Before making any actual modifications to the Linux kernel code, it is | |
232 | imperative to understand how the code in question works. For this | |
233 | purpose, nothing is better than reading through it directly (most tricky | |
234 | bits are commented well), perhaps even with the help of specialized | |
235 | tools. One such tool that is particularly recommended is the Linux | |
236 | Cross-Reference project, which is able to present source code in a | |
237 | self-referential, indexed webpage format. An excellent up-to-date | |
238 | repository of the kernel code may be found at: | |
022e04d6 | 239 | |
1d12554f | 240 | http://lxr.free-electrons.com/ |
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241 | |
242 | ||
243 | The development process | |
244 | ----------------------- | |
245 | ||
246 | Linux kernel development process currently consists of a few different | |
247 | main kernel "branches" and lots of different subsystem-specific kernel | |
248 | branches. These different branches are: | |
022e04d6 | 249 | |
e4144fe5 MC |
250 | - main 4.x kernel tree |
251 | - 4.x.y -stable kernel tree | |
252 | - 4.x -git kernel patches | |
d36cc9d0 | 253 | - subsystem specific kernel trees and patches |
e4144fe5 | 254 | - the 4.x -next kernel tree for integration tests |
d36cc9d0 | 255 | |
e4144fe5 | 256 | 4.x kernel tree |
d36cc9d0 | 257 | ----------------- |
e4144fe5 | 258 | 4.x kernels are maintained by Linus Torvalds, and can be found on |
f1eebe92 | 259 | https://kernel.org in the pub/linux/kernel/v4.x/ directory. Its development |
d36cc9d0 | 260 | process is as follows: |
022e04d6 | 261 | |
d36cc9d0 GKH |
262 | - As soon as a new kernel is released a two weeks window is open, |
263 | during this period of time maintainers can submit big diffs to | |
264 | Linus, usually the patches that have already been included in the | |
c607cf0c | 265 | -next kernel for a few weeks. The preferred way to submit big changes |
d36cc9d0 | 266 | is using git (the kernel's source management tool, more information |
f1eebe92 | 267 | can be found at https://git-scm.com/) but plain patches are also just |
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268 | fine. |
269 | - After two weeks a -rc1 kernel is released it is now possible to push | |
270 | only patches that do not include new features that could affect the | |
271 | stability of the whole kernel. Please note that a whole new driver | |
272 | (or filesystem) might be accepted after -rc1 because there is no | |
273 | risk of causing regressions with such a change as long as the change | |
274 | is self-contained and does not affect areas outside of the code that | |
275 | is being added. git can be used to send patches to Linus after -rc1 | |
276 | is released, but the patches need to also be sent to a public | |
277 | mailing list for review. | |
278 | - A new -rc is released whenever Linus deems the current git tree to | |
279 | be in a reasonably sane state adequate for testing. The goal is to | |
280 | release a new -rc kernel every week. | |
281 | - Process continues until the kernel is considered "ready", the | |
282 | process should last around 6 weeks. | |
283 | ||
284 | It is worth mentioning what Andrew Morton wrote on the linux-kernel | |
285 | mailing list about kernel releases: | |
022e04d6 | 286 | |
34fed7e7 | 287 | *"Nobody knows when a kernel will be released, because it's |
d36cc9d0 | 288 | released according to perceived bug status, not according to a |
34fed7e7 | 289 | preconceived timeline."* |
d36cc9d0 | 290 | |
e4144fe5 | 291 | 4.x.y -stable kernel tree |
ce655081 | 292 | ------------------------- |
591bfc6b | 293 | Kernels with 3-part versions are -stable kernels. They contain |
d36cc9d0 | 294 | relatively small and critical fixes for security problems or significant |
e4144fe5 | 295 | regressions discovered in a given 4.x kernel. |
d36cc9d0 GKH |
296 | |
297 | This is the recommended branch for users who want the most recent stable | |
298 | kernel and are not interested in helping test development/experimental | |
299 | versions. | |
300 | ||
e4144fe5 | 301 | If no 4.x.y kernel is available, then the highest numbered 4.x |
d36cc9d0 GKH |
302 | kernel is the current stable kernel. |
303 | ||
e4144fe5 | 304 | 4.x.y are maintained by the "stable" team <stable@vger.kernel.org>, and |
2eb7f204 | 305 | are released as needs dictate. The normal release period is approximately |
0fe8a3ce JC |
306 | two weeks, but it can be longer if there are no pressing problems. A |
307 | security-related problem, instead, can cause a release to happen almost | |
308 | instantly. | |
d36cc9d0 GKH |
309 | |
310 | The file Documentation/stable_kernel_rules.txt in the kernel tree | |
311 | documents what kinds of changes are acceptable for the -stable tree, and | |
312 | how the release process works. | |
313 | ||
e4144fe5 | 314 | 4.x -git patches |
ce655081 | 315 | ---------------- |
d36cc9d0 GKH |
316 | These are daily snapshots of Linus' kernel tree which are managed in a |
317 | git repository (hence the name.) These patches are usually released | |
318 | daily and represent the current state of Linus' tree. They are more | |
319 | experimental than -rc kernels since they are generated automatically | |
320 | without even a cursory glance to see if they are sane. | |
321 | ||
d36cc9d0 GKH |
322 | Subsystem Specific kernel trees and patches |
323 | ------------------------------------------- | |
c607cf0c SR |
324 | The maintainers of the various kernel subsystems --- and also many |
325 | kernel subsystem developers --- expose their current state of | |
326 | development in source repositories. That way, others can see what is | |
327 | happening in the different areas of the kernel. In areas where | |
328 | development is rapid, a developer may be asked to base his submissions | |
329 | onto such a subsystem kernel tree so that conflicts between the | |
330 | submission and other already ongoing work are avoided. | |
331 | ||
332 | Most of these repositories are git trees, but there are also other SCMs | |
333 | in use, or patch queues being published as quilt series. Addresses of | |
334 | these subsystem repositories are listed in the MAINTAINERS file. Many | |
f1eebe92 | 335 | of them can be browsed at https://git.kernel.org/. |
c607cf0c SR |
336 | |
337 | Before a proposed patch is committed to such a subsystem tree, it is | |
338 | subject to review which primarily happens on mailing lists (see the | |
339 | respective section below). For several kernel subsystems, this review | |
340 | process is tracked with the tool patchwork. Patchwork offers a web | |
341 | interface which shows patch postings, any comments on a patch or | |
342 | revisions to it, and maintainers can mark patches as under review, | |
343 | accepted, or rejected. Most of these patchwork sites are listed at | |
f1eebe92 | 344 | https://patchwork.kernel.org/. |
c607cf0c | 345 | |
e4144fe5 | 346 | 4.x -next kernel tree for integration tests |
ce655081 | 347 | ------------------------------------------- |
e4144fe5 | 348 | Before updates from subsystem trees are merged into the mainline 4.x |
c607cf0c SR |
349 | tree, they need to be integration-tested. For this purpose, a special |
350 | testing repository exists into which virtually all subsystem trees are | |
351 | pulled on an almost daily basis: | |
022e04d6 | 352 | |
f1eebe92 | 353 | https://git.kernel.org/?p=linux/kernel/git/next/linux-next.git |
c607cf0c SR |
354 | |
355 | This way, the -next kernel gives a summary outlook onto what will be | |
356 | expected to go into the mainline kernel at the next merge period. | |
357 | Adventurous testers are very welcome to runtime-test the -next kernel. | |
d36cc9d0 | 358 | |
8a465c32 | 359 | |
d36cc9d0 GKH |
360 | Bug Reporting |
361 | ------------- | |
362 | ||
f1eebe92 | 363 | https://bugzilla.kernel.org is where the Linux kernel developers track kernel |
d36cc9d0 GKH |
364 | bugs. Users are encouraged to report all bugs that they find in this |
365 | tool. For details on how to use the kernel bugzilla, please see: | |
022e04d6 | 366 | |
f1eebe92 | 367 | https://bugzilla.kernel.org/page.cgi?id=faq.html |
d36cc9d0 GKH |
368 | |
369 | The file REPORTING-BUGS in the main kernel source directory has a good | |
370 | template for how to report a possible kernel bug, and details what kind | |
371 | of information is needed by the kernel developers to help track down the | |
372 | problem. | |
373 | ||
374 | ||
3f271008 DC |
375 | Managing bug reports |
376 | -------------------- | |
377 | ||
378 | One of the best ways to put into practice your hacking skills is by fixing | |
379 | bugs reported by other people. Not only you will help to make the kernel | |
380 | more stable, you'll learn to fix real world problems and you will improve | |
381 | your skills, and other developers will be aware of your presence. Fixing | |
4db29c17 | 382 | bugs is one of the best ways to get merits among other developers, because |
3f271008 DC |
383 | not many people like wasting time fixing other people's bugs. |
384 | ||
f1eebe92 | 385 | To work in the already reported bug reports, go to https://bugzilla.kernel.org. |
3f271008 DC |
386 | If you want to be advised of the future bug reports, you can subscribe to the |
387 | bugme-new mailing list (only new bug reports are mailed here) or to the | |
388 | bugme-janitor mailing list (every change in the bugzilla is mailed here) | |
389 | ||
f1eebe92 MCC |
390 | https://lists.linux-foundation.org/mailman/listinfo/bugme-new |
391 | ||
392 | https://lists.linux-foundation.org/mailman/listinfo/bugme-janitors | |
3f271008 DC |
393 | |
394 | ||
395 | ||
d36cc9d0 GKH |
396 | Mailing lists |
397 | ------------- | |
398 | ||
399 | As some of the above documents describe, the majority of the core kernel | |
400 | developers participate on the Linux Kernel Mailing list. Details on how | |
401 | to subscribe and unsubscribe from the list can be found at: | |
022e04d6 | 402 | |
d36cc9d0 | 403 | http://vger.kernel.org/vger-lists.html#linux-kernel |
022e04d6 | 404 | |
d36cc9d0 GKH |
405 | There are archives of the mailing list on the web in many different |
406 | places. Use a search engine to find these archives. For example: | |
022e04d6 | 407 | |
d36cc9d0 | 408 | http://dir.gmane.org/gmane.linux.kernel |
022e04d6 | 409 | |
d36cc9d0 GKH |
410 | It is highly recommended that you search the archives about the topic |
411 | you want to bring up, before you post it to the list. A lot of things | |
412 | already discussed in detail are only recorded at the mailing list | |
413 | archives. | |
414 | ||
415 | Most of the individual kernel subsystems also have their own separate | |
416 | mailing list where they do their development efforts. See the | |
417 | MAINTAINERS file for a list of what these lists are for the different | |
418 | groups. | |
419 | ||
420 | Many of the lists are hosted on kernel.org. Information on them can be | |
421 | found at: | |
022e04d6 | 422 | |
d36cc9d0 GKH |
423 | http://vger.kernel.org/vger-lists.html |
424 | ||
425 | Please remember to follow good behavioral habits when using the lists. | |
426 | Though a bit cheesy, the following URL has some simple guidelines for | |
427 | interacting with the list (or any list): | |
022e04d6 | 428 | |
d36cc9d0 GKH |
429 | http://www.albion.com/netiquette/ |
430 | ||
431 | If multiple people respond to your mail, the CC: list of recipients may | |
432 | get pretty large. Don't remove anybody from the CC: list without a good | |
433 | reason, or don't reply only to the list address. Get used to receiving the | |
434 | mail twice, one from the sender and the one from the list, and don't try | |
435 | to tune that by adding fancy mail-headers, people will not like it. | |
436 | ||
437 | Remember to keep the context and the attribution of your replies intact, | |
438 | keep the "John Kernelhacker wrote ...:" lines at the top of your reply, and | |
439 | add your statements between the individual quoted sections instead of | |
440 | writing at the top of the mail. | |
441 | ||
442 | If you add patches to your mail, make sure they are plain readable text | |
34fed7e7 MCC |
443 | as stated in Documentation/SubmittingPatches. |
444 | Kernel developers don't want to deal with | |
445 | attachments or compressed patches; they may want to comment on | |
446 | individual lines of your patch, which works only that way. Make sure you | |
447 | use a mail program that does not mangle spaces and tab characters. A | |
448 | good first test is to send the mail to yourself and try to apply your | |
449 | own patch by yourself. If that doesn't work, get your mail program fixed | |
450 | or change it until it works. | |
d36cc9d0 GKH |
451 | |
452 | Above all, please remember to show respect to other subscribers. | |
453 | ||
454 | ||
455 | Working with the community | |
456 | -------------------------- | |
457 | ||
458 | The goal of the kernel community is to provide the best possible kernel | |
459 | there is. When you submit a patch for acceptance, it will be reviewed | |
460 | on its technical merits and those alone. So, what should you be | |
461 | expecting? | |
022e04d6 | 462 | |
d36cc9d0 GKH |
463 | - criticism |
464 | - comments | |
465 | - requests for change | |
466 | - requests for justification | |
467 | - silence | |
468 | ||
469 | Remember, this is part of getting your patch into the kernel. You have | |
470 | to be able to take criticism and comments about your patches, evaluate | |
471 | them at a technical level and either rework your patches or provide | |
472 | clear and concise reasoning as to why those changes should not be made. | |
473 | If there are no responses to your posting, wait a few days and try | |
474 | again, sometimes things get lost in the huge volume. | |
475 | ||
476 | What should you not do? | |
022e04d6 | 477 | |
d36cc9d0 GKH |
478 | - expect your patch to be accepted without question |
479 | - become defensive | |
480 | - ignore comments | |
481 | - resubmit the patch without making any of the requested changes | |
482 | ||
483 | In a community that is looking for the best technical solution possible, | |
484 | there will always be differing opinions on how beneficial a patch is. | |
485 | You have to be cooperative, and willing to adapt your idea to fit within | |
486 | the kernel. Or at least be willing to prove your idea is worth it. | |
487 | Remember, being wrong is acceptable as long as you are willing to work | |
488 | toward a solution that is right. | |
489 | ||
490 | It is normal that the answers to your first patch might simply be a list | |
34fed7e7 MCC |
491 | of a dozen things you should correct. This does **not** imply that your |
492 | patch will not be accepted, and it is **not** meant against you | |
d36cc9d0 GKH |
493 | personally. Simply correct all issues raised against your patch and |
494 | resend it. | |
495 | ||
496 | ||
497 | Differences between the kernel community and corporate structures | |
498 | ----------------------------------------------------------------- | |
499 | ||
500 | The kernel community works differently than most traditional corporate | |
501 | development environments. Here are a list of things that you can try to | |
106f9d93 | 502 | do to avoid problems: |
022e04d6 | 503 | |
d36cc9d0 | 504 | Good things to say regarding your proposed changes: |
022e04d6 | 505 | |
d36cc9d0 GKH |
506 | - "This solves multiple problems." |
507 | - "This deletes 2000 lines of code." | |
508 | - "Here is a patch that explains what I am trying to describe." | |
509 | - "I tested it on 5 different architectures..." | |
510 | - "Here is a series of small patches that..." | |
511 | - "This increases performance on typical machines..." | |
512 | ||
513 | Bad things you should avoid saying: | |
022e04d6 | 514 | |
d36cc9d0 GKH |
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 | ||
526 | Another way the kernel community is different than most traditional | |
527 | software engineering work environments is the faceless nature of | |
528 | interaction. One benefit of using email and irc as the primary forms of | |
529 | communication is the lack of discrimination based on gender or race. | |
530 | The Linux kernel work environment is accepting of women and minorities | |
531 | because all you are is an email address. The international aspect also | |
532 | helps to level the playing field because you can't guess gender based on | |
533 | a person's name. A man may be named Andrea and a woman may be named Pat. | |
534 | Most women who have worked in the Linux kernel and have expressed an | |
535 | opinion have had positive experiences. | |
536 | ||
537 | The language barrier can cause problems for some people who are not | |
538 | comfortable with English. A good grasp of the language can be needed in | |
539 | order to get ideas across properly on mailing lists, so it is | |
540 | recommended that you check your emails to make sure they make sense in | |
541 | English before sending them. | |
542 | ||
543 | ||
544 | Break up your changes | |
545 | --------------------- | |
546 | ||
547 | The Linux kernel community does not gladly accept large chunks of code | |
548 | dropped on it all at once. The changes need to be properly introduced, | |
549 | discussed, and broken up into tiny, individual portions. This is almost | |
550 | the exact opposite of what companies are used to doing. Your proposal | |
551 | should also be introduced very early in the development process, so that | |
552 | you can receive feedback on what you are doing. It also lets the | |
553 | community feel that you are working with them, and not simply using them | |
554 | as a dumping ground for your feature. However, don't send 50 emails at | |
555 | one time to a mailing list, your patch series should be smaller than | |
556 | that almost all of the time. | |
557 | ||
558 | The reasons for breaking things up are the following: | |
559 | ||
560 | 1) 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 | ||
572 | 2) 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 | ||
575 | Here is an analogy from kernel developer Al Viro: | |
022e04d6 | 576 | |
34fed7e7 | 577 | *"Think of a teacher grading homework from a math student. The |
d36cc9d0 GKH |
578 | teacher does not want to see the student's trials and errors |
579 | before they came up with the solution. They want to see the | |
580 | cleanest, most elegant answer. A good student knows this, and | |
581 | would never submit her intermediate work before the final | |
34fed7e7 | 582 | solution.* |
d36cc9d0 | 583 | |
34fed7e7 | 584 | *The same is true of kernel development. The maintainers and |
d36cc9d0 GKH |
585 | reviewers do not want to see the thought process behind the |
586 | solution to the problem one is solving. They want to see a | |
34fed7e7 | 587 | simple and elegant solution."* |
d36cc9d0 GKH |
588 | |
589 | It may be challenging to keep the balance between presenting an elegant | |
590 | solution and working together with the community and discussing your | |
591 | unfinished work. Therefore it is good to get early in the process to | |
592 | get feedback to improve your work, but also keep your changes in small | |
593 | chunks that they may get already accepted, even when your whole task is | |
594 | not ready for inclusion now. | |
595 | ||
596 | Also realize that it is not acceptable to send patches for inclusion | |
597 | that are unfinished and will be "fixed up later." | |
598 | ||
599 | ||
600 | Justify your change | |
601 | ------------------- | |
602 | ||
603 | Along with breaking up your patches, it is very important for you to let | |
604 | the Linux community know why they should add this change. New features | |
605 | must be justified as being needed and useful. | |
606 | ||
607 | ||
608 | Document your change | |
609 | -------------------- | |
610 | ||
611 | When sending in your patches, pay special attention to what you say in | |
612 | the text in your email. This information will become the ChangeLog | |
613 | information for the patch, and will be preserved for everyone to see for | |
614 | all time. It should describe the patch completely, containing: | |
022e04d6 | 615 | |
d36cc9d0 GKH |
616 | - why the change is necessary |
617 | - the overall design approach in the patch | |
618 | - implementation details | |
619 | - testing results | |
620 | ||
621 | For more details on what this should all look like, please see the | |
622 | ChangeLog section of the document: | |
022e04d6 | 623 | |
d36cc9d0 | 624 | "The Perfect Patch" |
937d9f55 | 625 | http://www.ozlabs.org/~akpm/stuff/tpp.txt |
d36cc9d0 GKH |
626 | |
627 | ||
d36cc9d0 GKH |
628 | All of these things are sometimes very hard to do. It can take years to |
629 | perfect these practices (if at all). It's a continuous process of | |
630 | improvement that requires a lot of patience and determination. But | |
631 | don't give up, it's possible. Many have done it before, and each had to | |
632 | start exactly where you are now. | |
633 | ||
634 | ||
635 | ||
636 | ||
637 | ---------- | |
022e04d6 | 638 | |
5bd982ed | 639 | Thanks to Paolo Ciarrocchi who allowed the "Development Process" |
f1eebe92 | 640 | (https://lwn.net/Articles/94386/) section |
d36cc9d0 GKH |
641 | to be based on text he had written, and to Randy Dunlap and Gerrit |
642 | Huizenga for some of the list of things you should and should not say. | |
643 | Also thanks to Pat Mochel, Hanna Linder, Randy Dunlap, Kay Sievers, | |
644 | Vojtech Pavlik, Jan Kara, Josh Boyer, Kees Cook, Andrew Morton, Andi | |
645 | Kleen, Vadim Lobanov, Jesper Juhl, Adrian Bunk, Keri Harris, Frans Pop, | |
646 | David A. Wheeler, Junio Hamano, Michael Kerrisk, and Alex Shepard for | |
647 | their review, comments, and contributions. Without their help, this | |
648 | document would not have been possible. | |
649 | ||
650 | ||
651 | ||
652 | Maintainer: Greg Kroah-Hartman <greg@kroah.com> |