1 .. _process_howto: <<
2 <<
3 HOWTO do Linux kernel development 1 HOWTO do Linux kernel development
4 ================================= 2 =================================
5 3
6 This is the be-all, end-all document on this t 4 This is the be-all, end-all document on this topic. It contains
7 instructions on how to become a Linux kernel d 5 instructions on how to become a Linux kernel developer and how to learn
8 to work with the Linux kernel development comm 6 to work with the Linux kernel development community. It tries to not
9 contain anything related to the technical aspe 7 contain anything related to the technical aspects of kernel programming,
10 but will help point you in the right direction 8 but will help point you in the right direction for that.
11 9
12 If anything in this document becomes out of da 10 If anything in this document becomes out of date, please send in patches
13 to the maintainer of this file, who is listed 11 to the maintainer of this file, who is listed at the bottom of the
14 document. 12 document.
15 13
16 14
17 Introduction 15 Introduction
18 ------------ 16 ------------
19 17
20 So, you want to learn how to become a Linux ke 18 So, you want to learn how to become a Linux kernel developer? Or you
21 have been told by your manager, "Go write a Li 19 have been told by your manager, "Go write a Linux driver for this
22 device." This document's goal is to teach you 20 device." This document's goal is to teach you everything you need to
23 know to achieve this by describing the process 21 know to achieve this by describing the process you need to go through,
24 and hints on how to work with the community. 22 and hints on how to work with the community. It will also try to
25 explain some of the reasons why the community 23 explain some of the reasons why the community works like it does.
26 24
27 The kernel is written mostly in C, with some a 25 The kernel is written mostly in C, with some architecture-dependent
28 parts written in assembly. A good understandin 26 parts written in assembly. A good understanding of C is required for
29 kernel development. Assembly (any architectur 27 kernel development. Assembly (any architecture) is not required unless
30 you plan to do low-level development for that 28 you plan to do low-level development for that architecture. Though they
31 are not a good substitute for a solid C educat 29 are not a good substitute for a solid C education and/or years of
32 experience, the following books are good for, 30 experience, the following books are good for, if anything, reference:
33 31
34 - "The C Programming Language" by Kernighan a 32 - "The C Programming Language" by Kernighan and Ritchie [Prentice Hall]
35 - "Practical C Programming" by Steve Oualline 33 - "Practical C Programming" by Steve Oualline [O'Reilly]
36 - "C: A Reference Manual" by Harbison and St 34 - "C: A Reference Manual" by Harbison and Steele [Prentice Hall]
37 35
38 The kernel is written using GNU C and the GNU 36 The kernel is written using GNU C and the GNU toolchain. While it
39 adheres to the ISO C11 standard, it uses a num !! 37 adheres to the ISO C89 standard, it uses a number of extensions that are
40 not featured in the standard. The kernel is a 38 not featured in the standard. The kernel is a freestanding C
41 environment, with no reliance on the standard 39 environment, with no reliance on the standard C library, so some
42 portions of the C standard are not supported. 40 portions of the C standard are not supported. Arbitrary long long
43 divisions and floating point are not allowed. 41 divisions and floating point are not allowed. It can sometimes be
44 difficult to understand the assumptions the ke 42 difficult to understand the assumptions the kernel has on the toolchain
45 and the extensions that it uses, and unfortuna 43 and the extensions that it uses, and unfortunately there is no
46 definitive reference for them. Please check t 44 definitive reference for them. Please check the gcc info pages (`info
47 gcc`) for some information on them. 45 gcc`) for some information on them.
48 46
49 Please remember that you are trying to learn h 47 Please remember that you are trying to learn how to work with the
50 existing development community. It is a diver 48 existing development community. It is a diverse group of people, with
51 high standards for coding, style and procedure 49 high standards for coding, style and procedure. These standards have
52 been created over time based on what they have 50 been created over time based on what they have found to work best for
53 such a large and geographically dispersed team 51 such a large and geographically dispersed team. Try to learn as much as
54 possible about these standards ahead of time, 52 possible about these standards ahead of time, as they are well
55 documented; do not expect people to adapt to y 53 documented; do not expect people to adapt to you or your company's way
56 of doing things. 54 of doing things.
57 55
58 56
59 Legal Issues 57 Legal Issues
60 ------------ 58 ------------
61 59
62 The Linux kernel source code is released under !! 60 The Linux kernel source code is released under the GPL. Please see the
63 COPYING in the main directory of the source tr !! 61 file, COPYING, in the main directory of the source tree, for details on
64 rules and how to use `SPDX <https://spdx.org/> !! 62 the license. If you have further questions about the license, please
65 described in :ref:`Documentation/process/licen !! 63 contact a lawyer, and do not ask on the Linux kernel mailing list. The
66 If you have further questions about the licens !! 64 people on the mailing lists are not lawyers, and you should not rely on
67 not ask on the Linux kernel mailing list. The !! 65 their statements on legal matters.
68 not lawyers, and you should not rely on their <<
69 66
70 For common questions and answers about the GPL 67 For common questions and answers about the GPL, please see:
71 68
72 https://www.gnu.org/licenses/gpl-faq.h 69 https://www.gnu.org/licenses/gpl-faq.html
73 70
74 71
75 Documentation 72 Documentation
76 ------------- 73 -------------
77 74
78 The Linux kernel source tree has a large range 75 The Linux kernel source tree has a large range of documents that are
79 invaluable for learning how to interact with t 76 invaluable for learning how to interact with the kernel community. When
80 new features are added to the kernel, it is re 77 new features are added to the kernel, it is recommended that new
81 documentation files are also added which expla 78 documentation files are also added which explain how to use the feature.
82 When a kernel change causes the interface that 79 When a kernel change causes the interface that the kernel exposes to
83 userspace to change, it is recommended that yo 80 userspace to change, it is recommended that you send the information or
84 a patch to the manual pages explaining the cha 81 a patch to the manual pages explaining the change to the manual pages
85 maintainer at alx@kernel.org, and CC the list !! 82 maintainer at mtk.manpages@gmail.com, and CC the list
>> 83 linux-api@vger.kernel.org.
86 84
87 Here is a list of files that are in the kernel 85 Here is a list of files that are in the kernel source tree that are
88 required reading: 86 required reading:
89 87
90 :ref:`Documentation/admin-guide/README.rst < !! 88 README
91 This file gives a short background on the 89 This file gives a short background on the Linux kernel and describes
92 what is necessary to do to configure and b 90 what is necessary to do to configure and build the kernel. People
93 who are new to the kernel should start her 91 who are new to the kernel should start here.
94 92
95 :ref:`Documentation/process/changes.rst <cha 93 :ref:`Documentation/process/changes.rst <changes>`
96 This file gives a list of the minimum leve 94 This file gives a list of the minimum levels of various software
97 packages that are necessary to build and r 95 packages that are necessary to build and run the kernel
98 successfully. 96 successfully.
99 97
100 :ref:`Documentation/process/coding-style.rst 98 :ref:`Documentation/process/coding-style.rst <codingstyle>`
101 This describes the Linux kernel coding sty 99 This describes the Linux kernel coding style, and some of the
102 rationale behind it. All new code is expec 100 rationale behind it. All new code is expected to follow the
103 guidelines in this document. Most maintain 101 guidelines in this document. Most maintainers will only accept
104 patches if these rules are followed, and m 102 patches if these rules are followed, and many people will only
105 review code if it is in the proper style. 103 review code if it is in the proper style.
106 104
107 :ref:`Documentation/process/submitting-patch !! 105 :ref:`Documentation/process/submitting-patches.rst <submittingpatches>` and :ref:`Documentation/process/submitting-drivers.rst <submittingdrivers>`
108 This file describes in explicit detail how !! 106 These files describe in explicit detail how to successfully create
109 and send a patch, including (but not limit 107 and send a patch, including (but not limited to):
110 108
111 - Email contents 109 - Email contents
112 - Email format 110 - Email format
113 - Who to send it to 111 - Who to send it to
114 112
115 Following these rules will not guarantee s 113 Following these rules will not guarantee success (as all patches are
116 subject to scrutiny for content and style) 114 subject to scrutiny for content and style), but not following them
117 will almost always prevent it. 115 will almost always prevent it.
118 116
119 Other excellent descriptions of how to cre 117 Other excellent descriptions of how to create patches properly are:
120 118
121 "The Perfect Patch" 119 "The Perfect Patch"
122 https://www.ozlabs.org/~akpm/s 120 https://www.ozlabs.org/~akpm/stuff/tpp.txt
123 121
124 "Linux kernel patch submission format" 122 "Linux kernel patch submission format"
125 https://web.archive.org/web/20 !! 123 http://linux.yyz.us/patch-format.html
126 124
127 :ref:`Documentation/process/stable-api-nonse 125 :ref:`Documentation/process/stable-api-nonsense.rst <stable_api_nonsense>`
128 This file describes the rationale behind t 126 This file describes the rationale behind the conscious decision to
129 not have a stable API within the kernel, i 127 not have a stable API within the kernel, including things like:
130 128
131 - Subsystem shim-layers (for compatibili 129 - Subsystem shim-layers (for compatibility?)
132 - Driver portability between Operating S 130 - Driver portability between Operating Systems.
133 - Mitigating rapid change within the ker 131 - Mitigating rapid change within the kernel source tree (or
134 preventing rapid change) 132 preventing rapid change)
135 133
136 This document is crucial for understanding 134 This document is crucial for understanding the Linux development
137 philosophy and is very important for peopl 135 philosophy and is very important for people moving to Linux from
138 development on other Operating Systems. 136 development on other Operating Systems.
139 137
140 :ref:`Documentation/process/security-bugs.rs !! 138 :ref:`Documentation/admin-guide/security-bugs.rst <securitybugs>`
141 If you feel you have found a security prob 139 If you feel you have found a security problem in the Linux kernel,
142 please follow the steps in this document t 140 please follow the steps in this document to help notify the kernel
143 developers, and help solve the issue. 141 developers, and help solve the issue.
144 142
145 :ref:`Documentation/process/management-style 143 :ref:`Documentation/process/management-style.rst <managementstyle>`
146 This document describes how Linux kernel m 144 This document describes how Linux kernel maintainers operate and the
147 shared ethos behind their methodologies. 145 shared ethos behind their methodologies. This is important reading
148 for anyone new to kernel development (or a 146 for anyone new to kernel development (or anyone simply curious about
149 it), as it resolves a lot of common miscon 147 it), as it resolves a lot of common misconceptions and confusion
150 about the unique behavior of kernel mainta 148 about the unique behavior of kernel maintainers.
151 149
152 :ref:`Documentation/process/stable-kernel-ru 150 :ref:`Documentation/process/stable-kernel-rules.rst <stable_kernel_rules>`
153 This file describes the rules on how the s 151 This file describes the rules on how the stable kernel releases
154 happen, and what to do if you want to get 152 happen, and what to do if you want to get a change into one of these
155 releases. 153 releases.
156 154
157 :ref:`Documentation/process/kernel-docs.rst 155 :ref:`Documentation/process/kernel-docs.rst <kernel_docs>`
158 A list of external documentation that pert 156 A list of external documentation that pertains to kernel
159 development. Please consult this list if 157 development. Please consult this list if you do not find what you
160 are looking for within the in-kernel docum 158 are looking for within the in-kernel documentation.
161 159
162 :ref:`Documentation/process/applying-patches 160 :ref:`Documentation/process/applying-patches.rst <applying_patches>`
163 A good introduction describing exactly wha 161 A good introduction describing exactly what a patch is and how to
164 apply it to the different development bran 162 apply it to the different development branches of the kernel.
165 163
166 The kernel also has a large number of document 164 The kernel also has a large number of documents that can be
167 automatically generated from the source code i 165 automatically generated from the source code itself or from
168 ReStructuredText markups (ReST), like this one 166 ReStructuredText markups (ReST), like this one. This includes a
169 full description of the in-kernel API, and rul 167 full description of the in-kernel API, and rules on how to handle
170 locking properly. 168 locking properly.
171 169
172 All such documents can be generated as PDF or 170 All such documents can be generated as PDF or HTML by running::
173 171
174 make pdfdocs 172 make pdfdocs
175 make htmldocs 173 make htmldocs
176 174
177 respectively from the main kernel source direc 175 respectively from the main kernel source directory.
178 176
179 The documents that uses ReST markup will be ge 177 The documents that uses ReST markup will be generated at Documentation/output.
180 They can also be generated on LaTeX and ePub f 178 They can also be generated on LaTeX and ePub formats with::
181 179
182 make latexdocs 180 make latexdocs
183 make epubdocs 181 make epubdocs
184 182
185 Becoming A Kernel Developer 183 Becoming A Kernel Developer
186 --------------------------- 184 ---------------------------
187 185
188 If you do not know anything about Linux kernel 186 If you do not know anything about Linux kernel development, you should
189 look at the Linux KernelNewbies project: 187 look at the Linux KernelNewbies project:
190 188
191 https://kernelnewbies.org 189 https://kernelnewbies.org
192 190
193 It consists of a helpful mailing list where yo 191 It consists of a helpful mailing list where you can ask almost any type
194 of basic kernel development question (make sur 192 of basic kernel development question (make sure to search the archives
195 first, before asking something that has alread 193 first, before asking something that has already been answered in the
196 past.) It also has an IRC channel that you ca 194 past.) It also has an IRC channel that you can use to ask questions in
197 real-time, and a lot of helpful documentation 195 real-time, and a lot of helpful documentation that is useful for
198 learning about Linux kernel development. 196 learning about Linux kernel development.
199 197
200 The website has basic information about code o 198 The website has basic information about code organization, subsystems,
201 and current projects (both in-tree and out-of- 199 and current projects (both in-tree and out-of-tree). It also describes
202 some basic logistical information, like how to 200 some basic logistical information, like how to compile a kernel and
203 apply a patch. 201 apply a patch.
204 202
205 If you do not know where you want to start, bu 203 If you do not know where you want to start, but you want to look for
206 some task to start doing to join into the kern 204 some task to start doing to join into the kernel development community,
207 go to the Linux Kernel Janitor's project: 205 go to the Linux Kernel Janitor's project:
208 206
209 https://kernelnewbies.org/KernelJanito 207 https://kernelnewbies.org/KernelJanitors
210 208
211 It is a great place to start. It describes a 209 It is a great place to start. It describes a list of relatively simple
212 problems that need to be cleaned up and fixed 210 problems that need to be cleaned up and fixed within the Linux kernel
213 source tree. Working with the developers in c 211 source tree. Working with the developers in charge of this project, you
214 will learn the basics of getting your patch in 212 will learn the basics of getting your patch into the Linux kernel tree,
215 and possibly be pointed in the direction of wh 213 and possibly be pointed in the direction of what to go work on next, if
216 you do not already have an idea. 214 you do not already have an idea.
217 215
>> 216 If you already have a chunk of code that you want to put into the kernel
>> 217 tree, but need some help getting it in the proper form, the
>> 218 kernel-mentors project was created to help you out with this. It is a
>> 219 mailing list, and can be found at:
>> 220
>> 221 https://selenic.com/mailman/listinfo/kernel-mentors
>> 222
218 Before making any actual modifications to the 223 Before making any actual modifications to the Linux kernel code, it is
219 imperative to understand how the code in quest 224 imperative to understand how the code in question works. For this
220 purpose, nothing is better than reading throug 225 purpose, nothing is better than reading through it directly (most tricky
221 bits are commented well), perhaps even with th 226 bits are commented well), perhaps even with the help of specialized
222 tools. One such tool that is particularly rec 227 tools. One such tool that is particularly recommended is the Linux
223 Cross-Reference project, which is able to pres 228 Cross-Reference project, which is able to present source code in a
224 self-referential, indexed webpage format. An e 229 self-referential, indexed webpage format. An excellent up-to-date
225 repository of the kernel code may be found at: 230 repository of the kernel code may be found at:
226 231
227 https://elixir.bootlin.com/ !! 232 http://lxr.free-electrons.com/
228 233
229 234
230 The development process 235 The development process
231 ----------------------- 236 -----------------------
232 237
233 Linux kernel development process currently con 238 Linux kernel development process currently consists of a few different
234 main kernel "branches" and lots of different s 239 main kernel "branches" and lots of different subsystem-specific kernel
235 branches. These different branches are: 240 branches. These different branches are:
236 241
237 - Linus's mainline tree !! 242 - main 4.x kernel tree
238 - Various stable trees with multiple major n !! 243 - 4.x.y -stable kernel tree
239 - Subsystem-specific trees !! 244 - 4.x -git kernel patches
240 - linux-next integration testing tree !! 245 - subsystem specific kernel trees and patches
241 !! 246 - the 4.x -next kernel tree for integration tests
242 Mainline tree !! 247
243 ~~~~~~~~~~~~~ !! 248 4.x kernel tree
244 !! 249 ~~~~~~~~~~~~~~~
245 The mainline tree is maintained by Linus Torva !! 250
246 https://kernel.org or in the repo. Its develo !! 251 4.x kernels are maintained by Linus Torvalds, and can be found on
>> 252 https://kernel.org in the pub/linux/kernel/v4.x/ directory. Its development
>> 253 process is as follows:
247 254
248 - As soon as a new kernel is released a two !! 255 - As soon as a new kernel is released a two weeks window is open,
249 during this period of time maintainers can 256 during this period of time maintainers can submit big diffs to
250 Linus, usually the patches that have alrea 257 Linus, usually the patches that have already been included in the
251 linux-next for a few weeks. The preferred !! 258 -next kernel for a few weeks. The preferred way to submit big changes
252 is using git (the kernel's source manageme 259 is using git (the kernel's source management tool, more information
253 can be found at https://git-scm.com/) but 260 can be found at https://git-scm.com/) but plain patches are also just
254 fine. 261 fine.
255 - After two weeks a -rc1 kernel is released 262 - After two weeks a -rc1 kernel is released and the focus is on making the
256 new kernel as rock solid as possible. Mos 263 new kernel as rock solid as possible. Most of the patches at this point
257 should fix a regression. Bugs that have a 264 should fix a regression. Bugs that have always existed are not
258 regressions, so only push these kinds of f 265 regressions, so only push these kinds of fixes if they are important.
259 Please note that a whole new driver (or fi 266 Please note that a whole new driver (or filesystem) might be accepted
260 after -rc1 because there is no risk of cau 267 after -rc1 because there is no risk of causing regressions with such a
261 change as long as the change is self-conta 268 change as long as the change is self-contained and does not affect areas
262 outside of the code that is being added. 269 outside of the code that is being added. git can be used to send
263 patches to Linus after -rc1 is released, b 270 patches to Linus after -rc1 is released, but the patches need to also be
264 sent to a public mailing list for review. 271 sent to a public mailing list for review.
265 - A new -rc is released whenever Linus deems 272 - A new -rc is released whenever Linus deems the current git tree to
266 be in a reasonably sane state adequate for 273 be in a reasonably sane state adequate for testing. The goal is to
267 release a new -rc kernel every week. 274 release a new -rc kernel every week.
268 - Process continues until the kernel is cons 275 - Process continues until the kernel is considered "ready", the
269 process should last around 6 weeks. 276 process should last around 6 weeks.
270 277
271 It is worth mentioning what Andrew Morton wrot 278 It is worth mentioning what Andrew Morton wrote on the linux-kernel
272 mailing list about kernel releases: 279 mailing list about kernel releases:
273 280
274 *"Nobody knows when a kernel will be r 281 *"Nobody knows when a kernel will be released, because it's
275 released according to perceived bug st 282 released according to perceived bug status, not according to a
276 preconceived timeline."* 283 preconceived timeline."*
277 284
278 Various stable trees with multiple major numbe !! 285 4.x.y -stable kernel tree
279 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ !! 286 ~~~~~~~~~~~~~~~~~~~~~~~~~
280 287
281 Kernels with 3-part versions are -stable kerne 288 Kernels with 3-part versions are -stable kernels. They contain
282 relatively small and critical fixes for securi 289 relatively small and critical fixes for security problems or significant
283 regressions discovered in a given major mainli !! 290 regressions discovered in a given 4.x kernel.
284 in a major stable series increments the third <<
285 number, keeping the first two parts the same. <<
286 291
287 This is the recommended branch for users who w 292 This is the recommended branch for users who want the most recent stable
288 kernel and are not interested in helping test 293 kernel and are not interested in helping test development/experimental
289 versions. 294 versions.
290 295
291 Stable trees are maintained by the "stable" te< !! 296 If no 4.x.y kernel is available, then the highest numbered 4.x
>> 297 kernel is the current stable kernel.
>> 298
>> 299 4.x.y are maintained by the "stable" team <stable@vger.kernel.org>, and
292 are released as needs dictate. The normal rel 300 are released as needs dictate. The normal release period is approximately
293 two weeks, but it can be longer if there are n 301 two weeks, but it can be longer if there are no pressing problems. A
294 security-related problem, instead, can cause a 302 security-related problem, instead, can cause a release to happen almost
295 instantly. 303 instantly.
296 304
297 The file :ref:`Documentation/process/stable-ke !! 305 The file Documentation/process/stable-kernel-rules.rst in the kernel tree
298 in the kernel tree documents what kinds of cha !! 306 documents what kinds of changes are acceptable for the -stable tree, and
299 the -stable tree, and how the release process !! 307 how the release process works.
>> 308
>> 309 4.x -git patches
>> 310 ~~~~~~~~~~~~~~~~
>> 311
>> 312 These are daily snapshots of Linus' kernel tree which are managed in a
>> 313 git repository (hence the name.) These patches are usually released
>> 314 daily and represent the current state of Linus' tree. They are more
>> 315 experimental than -rc kernels since they are generated automatically
>> 316 without even a cursory glance to see if they are sane.
300 317
301 Subsystem-specific trees !! 318 Subsystem Specific kernel trees and patches
302 ~~~~~~~~~~~~~~~~~~~~~~~~ !! 319 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
303 320
304 The maintainers of the various kernel subsyste 321 The maintainers of the various kernel subsystems --- and also many
305 kernel subsystem developers --- expose their c 322 kernel subsystem developers --- expose their current state of
306 development in source repositories. That way, 323 development in source repositories. That way, others can see what is
307 happening in the different areas of the kernel 324 happening in the different areas of the kernel. In areas where
308 development is rapid, a developer may be asked 325 development is rapid, a developer may be asked to base his submissions
309 onto such a subsystem kernel tree so that conf 326 onto such a subsystem kernel tree so that conflicts between the
310 submission and other already ongoing work are 327 submission and other already ongoing work are avoided.
311 328
312 Most of these repositories are git trees, but 329 Most of these repositories are git trees, but there are also other SCMs
313 in use, or patch queues being published as qui 330 in use, or patch queues being published as quilt series. Addresses of
314 these subsystem repositories are listed in the 331 these subsystem repositories are listed in the MAINTAINERS file. Many
315 of them can be browsed at https://git.kernel.o 332 of them can be browsed at https://git.kernel.org/.
316 333
317 Before a proposed patch is committed to such a 334 Before a proposed patch is committed to such a subsystem tree, it is
318 subject to review which primarily happens on m 335 subject to review which primarily happens on mailing lists (see the
319 respective section below). For several kernel 336 respective section below). For several kernel subsystems, this review
320 process is tracked with the tool patchwork. P 337 process is tracked with the tool patchwork. Patchwork offers a web
321 interface which shows patch postings, any comm 338 interface which shows patch postings, any comments on a patch or
322 revisions to it, and maintainers can mark patc 339 revisions to it, and maintainers can mark patches as under review,
323 accepted, or rejected. Most of these patchwor 340 accepted, or rejected. Most of these patchwork sites are listed at
324 https://patchwork.kernel.org/. 341 https://patchwork.kernel.org/.
325 342
326 linux-next integration testing tree !! 343 4.x -next kernel tree for integration tests
327 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ !! 344 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
328 345
329 Before updates from subsystem trees are merged !! 346 Before updates from subsystem trees are merged into the mainline 4.x
330 they need to be integration-tested. For this !! 347 tree, they need to be integration-tested. For this purpose, a special
331 testing repository exists into which virtually 348 testing repository exists into which virtually all subsystem trees are
332 pulled on an almost daily basis: 349 pulled on an almost daily basis:
333 350
334 https://git.kernel.org/pub/scm/linux/k !! 351 https://git.kernel.org/?p=linux/kernel/git/next/linux-next.git
335 352
336 This way, the linux-next gives a summary outlo !! 353 This way, the -next kernel gives a summary outlook onto what will be
337 expected to go into the mainline kernel at the 354 expected to go into the mainline kernel at the next merge period.
338 Adventurous testers are very welcome to runtim !! 355 Adventurous testers are very welcome to runtime-test the -next kernel.
339 356
340 357
341 Bug Reporting 358 Bug Reporting
342 ------------- 359 -------------
343 360
344 The file 'Documentation/admin-guide/reporting- !! 361 https://bugzilla.kernel.org is where the Linux kernel developers track kernel
345 source directory describes how to report a pos !! 362 bugs. Users are encouraged to report all bugs that they find in this
346 what kind of information is needed by the kern !! 363 tool. For details on how to use the kernel bugzilla, please see:
347 down the problem. !! 364
>> 365 https://bugzilla.kernel.org/page.cgi?id=faq.html
>> 366
>> 367 The file admin-guide/reporting-bugs.rst in the main kernel source directory has a good
>> 368 template for how to report a possible kernel bug, and details what kind
>> 369 of information is needed by the kernel developers to help track down the
>> 370 problem.
348 371
349 372
350 Managing bug reports 373 Managing bug reports
351 -------------------- 374 --------------------
352 375
353 One of the best ways to put into practice your 376 One of the best ways to put into practice your hacking skills is by fixing
354 bugs reported by other people. Not only will y !! 377 bugs reported by other people. Not only you will help to make the kernel
355 more stable, but you'll also learn to fix real !! 378 more stable, you'll learn to fix real world problems and you will improve
356 improve your skills, and other developers will !! 379 your skills, and other developers will be aware of your presence. Fixing
357 Fixing bugs is one of the best ways to get mer !! 380 bugs is one of the best ways to get merits among other developers, because
358 because not many people like wasting time fixi !! 381 not many people like wasting time fixing other people's bugs.
359 !! 382
360 To work on already reported bug reports, find !! 383 To work in the already reported bug reports, go to https://bugzilla.kernel.org.
361 Check the MAINTAINERS file where bugs for that !! 384 If you want to be advised of the future bug reports, you can subscribe to the
362 it will be a mailing list, rarely a bugtracker !! 385 bugme-new mailing list (only new bug reports are mailed here) or to the
363 place for recent reports and help where you se !! 386 bugme-janitor mailing list (every change in the bugzilla is mailed here)
364 https://bugzilla.kernel.org for bug reports; o !! 387
365 use it actively for reporting or tracking, nev !! 388 https://lists.linux-foundation.org/mailman/listinfo/bugme-new
366 kernel get filed there. !! 389
>> 390 https://lists.linux-foundation.org/mailman/listinfo/bugme-janitors
>> 391
367 392
368 393
369 Mailing lists 394 Mailing lists
370 ------------- 395 -------------
371 396
372 As some of the above documents describe, the m 397 As some of the above documents describe, the majority of the core kernel
373 developers participate on the Linux Kernel Mai 398 developers participate on the Linux Kernel Mailing list. Details on how
374 to subscribe and unsubscribe from the list can 399 to subscribe and unsubscribe from the list can be found at:
375 400
376 https://subspace.kernel.org/subscribin !! 401 http://vger.kernel.org/vger-lists.html#linux-kernel
377 402
378 There are archives of the mailing list on the 403 There are archives of the mailing list on the web in many different
379 places. Use a search engine to find these arc 404 places. Use a search engine to find these archives. For example:
380 405
381 https://lore.kernel.org/linux-kernel/ !! 406 http://dir.gmane.org/gmane.linux.kernel
382 407
383 It is highly recommended that you search the a 408 It is highly recommended that you search the archives about the topic
384 you want to bring up, before you post it to th 409 you want to bring up, before you post it to the list. A lot of things
385 already discussed in detail are only recorded 410 already discussed in detail are only recorded at the mailing list
386 archives. 411 archives.
387 412
388 Most of the individual kernel subsystems also 413 Most of the individual kernel subsystems also have their own separate
389 mailing list where they do their development e 414 mailing list where they do their development efforts. See the
390 MAINTAINERS file for a list of what these list 415 MAINTAINERS file for a list of what these lists are for the different
391 groups. 416 groups.
392 417
393 Many of the lists are hosted on kernel.org. In 418 Many of the lists are hosted on kernel.org. Information on them can be
394 found at: 419 found at:
395 420
396 https://subspace.kernel.org !! 421 http://vger.kernel.org/vger-lists.html
397 422
398 Please remember to follow good behavioral habi 423 Please remember to follow good behavioral habits when using the lists.
399 Though a bit cheesy, the following URL has som 424 Though a bit cheesy, the following URL has some simple guidelines for
400 interacting with the list (or any list): 425 interacting with the list (or any list):
401 426
402 https://subspace.kernel.org/etiquette. !! 427 http://www.albion.com/netiquette/
403 428
404 If multiple people respond to your mail, the C 429 If multiple people respond to your mail, the CC: list of recipients may
405 get pretty large. Don't remove anybody from th 430 get pretty large. Don't remove anybody from the CC: list without a good
406 reason, or don't reply only to the list addres 431 reason, or don't reply only to the list address. Get used to receiving the
407 mail twice, one from the sender and the one fr 432 mail twice, one from the sender and the one from the list, and don't try
408 to tune that by adding fancy mail-headers, peo 433 to tune that by adding fancy mail-headers, people will not like it.
409 434
410 Remember to keep the context and the attributi 435 Remember to keep the context and the attribution of your replies intact,
411 keep the "John Kernelhacker wrote ...:" lines 436 keep the "John Kernelhacker wrote ...:" lines at the top of your reply, and
412 add your statements between the individual quo 437 add your statements between the individual quoted sections instead of
413 writing at the top of the mail. 438 writing at the top of the mail.
414 439
415 If you add patches to your mail, make sure the 440 If you add patches to your mail, make sure they are plain readable text
416 as stated in :ref:`Documentation/process/submi !! 441 as stated in Documentation/process/submitting-patches.rst.
417 Kernel developers don't want to deal with 442 Kernel developers don't want to deal with
418 attachments or compressed patches; they may wa 443 attachments or compressed patches; they may want to comment on
419 individual lines of your patch, which works on 444 individual lines of your patch, which works only that way. Make sure you
420 use a mail program that does not mangle spaces 445 use a mail program that does not mangle spaces and tab characters. A
421 good first test is to send the mail to yoursel 446 good first test is to send the mail to yourself and try to apply your
422 own patch by yourself. If that doesn't work, g 447 own patch by yourself. If that doesn't work, get your mail program fixed
423 or change it until it works. 448 or change it until it works.
424 449
425 Above all, please remember to show respect to 450 Above all, please remember to show respect to other subscribers.
426 451
427 452
428 Working with the community 453 Working with the community
429 -------------------------- 454 --------------------------
430 455
431 The goal of the kernel community is to provide 456 The goal of the kernel community is to provide the best possible kernel
432 there is. When you submit a patch for accepta 457 there is. When you submit a patch for acceptance, it will be reviewed
433 on its technical merits and those alone. So, 458 on its technical merits and those alone. So, what should you be
434 expecting? 459 expecting?
435 460
436 - criticism 461 - criticism
437 - comments 462 - comments
438 - requests for change 463 - requests for change
439 - requests for justification 464 - requests for justification
440 - silence 465 - silence
441 466
442 Remember, this is part of getting your patch i 467 Remember, this is part of getting your patch into the kernel. You have
443 to be able to take criticism and comments abou 468 to be able to take criticism and comments about your patches, evaluate
444 them at a technical level and either rework yo 469 them at a technical level and either rework your patches or provide
445 clear and concise reasoning as to why those ch 470 clear and concise reasoning as to why those changes should not be made.
446 If there are no responses to your posting, wai 471 If there are no responses to your posting, wait a few days and try
447 again, sometimes things get lost in the huge v 472 again, sometimes things get lost in the huge volume.
448 473
449 What should you not do? 474 What should you not do?
450 475
451 - expect your patch to be accepted without q 476 - expect your patch to be accepted without question
452 - become defensive 477 - become defensive
453 - ignore comments 478 - ignore comments
454 - resubmit the patch without making any of t 479 - resubmit the patch without making any of the requested changes
455 480
456 In a community that is looking for the best te 481 In a community that is looking for the best technical solution possible,
457 there will always be differing opinions on how 482 there will always be differing opinions on how beneficial a patch is.
458 You have to be cooperative, and willing to ada 483 You have to be cooperative, and willing to adapt your idea to fit within
459 the kernel. Or at least be willing to prove y 484 the kernel. Or at least be willing to prove your idea is worth it.
460 Remember, being wrong is acceptable as long as 485 Remember, being wrong is acceptable as long as you are willing to work
461 toward a solution that is right. 486 toward a solution that is right.
462 487
463 It is normal that the answers to your first pa 488 It is normal that the answers to your first patch might simply be a list
464 of a dozen things you should correct. This do 489 of a dozen things you should correct. This does **not** imply that your
465 patch will not be accepted, and it is **not** 490 patch will not be accepted, and it is **not** meant against you
466 personally. Simply correct all issues raised 491 personally. Simply correct all issues raised against your patch and
467 resend it. 492 resend it.
468 493
469 494
470 Differences between the kernel community and c 495 Differences between the kernel community and corporate structures
471 ---------------------------------------------- 496 -----------------------------------------------------------------
472 497
473 The kernel community works differently than mo 498 The kernel community works differently than most traditional corporate
474 development environments. Here are a list of 499 development environments. Here are a list of things that you can try to
475 do to avoid problems: 500 do to avoid problems:
476 501
477 Good things to say regarding your proposed c 502 Good things to say regarding your proposed changes:
478 503
479 - "This solves multiple problems." 504 - "This solves multiple problems."
480 - "This deletes 2000 lines of code." 505 - "This deletes 2000 lines of code."
481 - "Here is a patch that explains what I am 506 - "Here is a patch that explains what I am trying to describe."
482 - "I tested it on 5 different architecture 507 - "I tested it on 5 different architectures..."
483 - "Here is a series of small patches that. 508 - "Here is a series of small patches that..."
484 - "This increases performance on typical m 509 - "This increases performance on typical machines..."
485 510
486 Bad things you should avoid saying: 511 Bad things you should avoid saying:
487 512
488 - "We did it this way in AIX/ptx/Solaris, 513 - "We did it this way in AIX/ptx/Solaris, so therefore it must be
489 good..." 514 good..."
490 - "I've being doing this for 20 years, so. 515 - "I've being doing this for 20 years, so..."
491 - "This is required for my company to make 516 - "This is required for my company to make money"
492 - "This is for our Enterprise product line 517 - "This is for our Enterprise product line."
493 - "Here is my 1000 page design document th 518 - "Here is my 1000 page design document that describes my idea"
494 - "I've been working on this for 6 months. 519 - "I've been working on this for 6 months..."
495 - "Here's a 5000 line patch that..." 520 - "Here's a 5000 line patch that..."
496 - "I rewrote all of the current mess, and 521 - "I rewrote all of the current mess, and here it is..."
497 - "I have a deadline, and this patch needs 522 - "I have a deadline, and this patch needs to be applied now."
498 523
499 Another way the kernel community is different 524 Another way the kernel community is different than most traditional
500 software engineering work environments is the 525 software engineering work environments is the faceless nature of
501 interaction. One benefit of using email and i 526 interaction. One benefit of using email and irc as the primary forms of
502 communication is the lack of discrimination ba 527 communication is the lack of discrimination based on gender or race.
503 The Linux kernel work environment is accepting 528 The Linux kernel work environment is accepting of women and minorities
504 because all you are is an email address. The 529 because all you are is an email address. The international aspect also
505 helps to level the playing field because you c 530 helps to level the playing field because you can't guess gender based on
506 a person's name. A man may be named Andrea and 531 a person's name. A man may be named Andrea and a woman may be named Pat.
507 Most women who have worked in the Linux kernel 532 Most women who have worked in the Linux kernel and have expressed an
508 opinion have had positive experiences. 533 opinion have had positive experiences.
509 534
510 The language barrier can cause problems for so 535 The language barrier can cause problems for some people who are not
511 comfortable with English. A good grasp of the 536 comfortable with English. A good grasp of the language can be needed in
512 order to get ideas across properly on mailing 537 order to get ideas across properly on mailing lists, so it is
513 recommended that you check your emails to make 538 recommended that you check your emails to make sure they make sense in
514 English before sending them. 539 English before sending them.
515 540
516 541
517 Break up your changes 542 Break up your changes
518 --------------------- 543 ---------------------
519 544
520 The Linux kernel community does not gladly acc 545 The Linux kernel community does not gladly accept large chunks of code
521 dropped on it all at once. The changes need t 546 dropped on it all at once. The changes need to be properly introduced,
522 discussed, and broken up into tiny, individual 547 discussed, and broken up into tiny, individual portions. This is almost
523 the exact opposite of what companies are used 548 the exact opposite of what companies are used to doing. Your proposal
524 should also be introduced very early in the de 549 should also be introduced very early in the development process, so that
525 you can receive feedback on what you are doing 550 you can receive feedback on what you are doing. It also lets the
526 community feel that you are working with them, 551 community feel that you are working with them, and not simply using them
527 as a dumping ground for your feature. However 552 as a dumping ground for your feature. However, don't send 50 emails at
528 one time to a mailing list, your patch series 553 one time to a mailing list, your patch series should be smaller than
529 that almost all of the time. 554 that almost all of the time.
530 555
531 The reasons for breaking things up are the fol 556 The reasons for breaking things up are the following:
532 557
533 1) Small patches increase the likelihood that 558 1) Small patches increase the likelihood that your patches will be
534 applied, since they don't take much time or 559 applied, since they don't take much time or effort to verify for
535 correctness. A 5 line patch can be applied 560 correctness. A 5 line patch can be applied by a maintainer with
536 barely a second glance. However, a 500 line 561 barely a second glance. However, a 500 line patch may take hours to
537 review for correctness (the time it takes i 562 review for correctness (the time it takes is exponentially
538 proportional to the size of the patch, or s 563 proportional to the size of the patch, or something).
539 564
540 Small patches also make it very easy to deb 565 Small patches also make it very easy to debug when something goes
541 wrong. It's much easier to back out patche 566 wrong. It's much easier to back out patches one by one than it is
542 to dissect a very large patch after it's be 567 to dissect a very large patch after it's been applied (and broken
543 something). 568 something).
544 569
545 2) It's important not only to send small patch 570 2) It's important not only to send small patches, but also to rewrite
546 and simplify (or simply re-order) patches b 571 and simplify (or simply re-order) patches before submitting them.
547 572
548 Here is an analogy from kernel developer Al Vi 573 Here is an analogy from kernel developer Al Viro:
549 574
550 *"Think of a teacher grading homework 575 *"Think of a teacher grading homework from a math student. The
551 teacher does not want to see the stude 576 teacher does not want to see the student's trials and errors
552 before they came up with the solution. 577 before they came up with the solution. They want to see the
553 cleanest, most elegant answer. A good 578 cleanest, most elegant answer. A good student knows this, and
554 would never submit her intermediate wo 579 would never submit her intermediate work before the final
555 solution.* 580 solution.*
556 581
557 *The same is true of kernel developmen 582 *The same is true of kernel development. The maintainers and
558 reviewers do not want to see the thoug 583 reviewers do not want to see the thought process behind the
559 solution to the problem one is solving 584 solution to the problem one is solving. They want to see a
560 simple and elegant solution."* 585 simple and elegant solution."*
561 586
562 It may be challenging to keep the balance betw 587 It may be challenging to keep the balance between presenting an elegant
563 solution and working together with the communi 588 solution and working together with the community and discussing your
564 unfinished work. Therefore it is good to get e 589 unfinished work. Therefore it is good to get early in the process to
565 get feedback to improve your work, but also ke 590 get feedback to improve your work, but also keep your changes in small
566 chunks that they may get already accepted, eve 591 chunks that they may get already accepted, even when your whole task is
567 not ready for inclusion now. 592 not ready for inclusion now.
568 593
569 Also realize that it is not acceptable to send 594 Also realize that it is not acceptable to send patches for inclusion
570 that are unfinished and will be "fixed up late 595 that are unfinished and will be "fixed up later."
571 596
572 597
573 Justify your change 598 Justify your change
574 ------------------- 599 -------------------
575 600
576 Along with breaking up your patches, it is ver 601 Along with breaking up your patches, it is very important for you to let
577 the Linux community know why they should add t 602 the Linux community know why they should add this change. New features
578 must be justified as being needed and useful. 603 must be justified as being needed and useful.
579 604
580 605
581 Document your change 606 Document your change
582 -------------------- 607 --------------------
583 608
584 When sending in your patches, pay special atte 609 When sending in your patches, pay special attention to what you say in
585 the text in your email. This information will 610 the text in your email. This information will become the ChangeLog
586 information for the patch, and will be preserv 611 information for the patch, and will be preserved for everyone to see for
587 all time. It should describe the patch comple 612 all time. It should describe the patch completely, containing:
588 613
589 - why the change is necessary 614 - why the change is necessary
590 - the overall design approach in the patch 615 - the overall design approach in the patch
591 - implementation details 616 - implementation details
592 - testing results 617 - testing results
593 618
594 For more details on what this should all look 619 For more details on what this should all look like, please see the
595 ChangeLog section of the document: 620 ChangeLog section of the document:
596 621
597 "The Perfect Patch" 622 "The Perfect Patch"
598 https://www.ozlabs.org/~akpm/stuff/tpp.t !! 623 http://www.ozlabs.org/~akpm/stuff/tpp.txt
599 624
600 625
601 All of these things are sometimes very hard to 626 All of these things are sometimes very hard to do. It can take years to
602 perfect these practices (if at all). It's a co 627 perfect these practices (if at all). It's a continuous process of
603 improvement that requires a lot of patience an 628 improvement that requires a lot of patience and determination. But
604 don't give up, it's possible. Many have done i 629 don't give up, it's possible. Many have done it before, and each had to
605 start exactly where you are now. 630 start exactly where you are now.
606 631
607 632
608 633
609 634
610 ---------- 635 ----------
611 636
612 Thanks to Paolo Ciarrocchi who allowed the "De 637 Thanks to Paolo Ciarrocchi who allowed the "Development Process"
613 (https://lwn.net/Articles/94386/) section 638 (https://lwn.net/Articles/94386/) section
614 to be based on text he had written, and to Ran 639 to be based on text he had written, and to Randy Dunlap and Gerrit
615 Huizenga for some of the list of things you sh 640 Huizenga for some of the list of things you should and should not say.
616 Also thanks to Pat Mochel, Hanna Linder, Randy 641 Also thanks to Pat Mochel, Hanna Linder, Randy Dunlap, Kay Sievers,
617 Vojtech Pavlik, Jan Kara, Josh Boyer, Kees Coo 642 Vojtech Pavlik, Jan Kara, Josh Boyer, Kees Cook, Andrew Morton, Andi
618 Kleen, Vadim Lobanov, Jesper Juhl, Adrian Bunk 643 Kleen, Vadim Lobanov, Jesper Juhl, Adrian Bunk, Keri Harris, Frans Pop,
619 David A. Wheeler, Junio Hamano, Michael Kerris 644 David A. Wheeler, Junio Hamano, Michael Kerrisk, and Alex Shepard for
620 their review, comments, and contributions. Wi 645 their review, comments, and contributions. Without their help, this
621 document would not have been possible. 646 document would not have been possible.
622 647
623 648
624 649
625 Maintainer: Greg Kroah-Hartman <greg@kroah.com> 650 Maintainer: Greg Kroah-Hartman <greg@kroah.com>
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