diff options
author | Jeff Garzik <jgarzik@pobox.com> | 2005-11-18 19:54:12 -0500 |
---|---|---|
committer | Jeff Garzik <jgarzik@pobox.com> | 2005-11-18 19:54:12 -0500 |
commit | 625876f32ed63af262db3d0ac8178d2c0f510636 (patch) | |
tree | 93a0d2d5332fa679ecb99eee7b0955e444d6a41a /Documentation | |
parent | c902f981b79b512eb3d0c0410f8cae88c78beb57 (diff) | |
parent | b286e39207237e2f6929959372bf66d9a8d05a82 (diff) |
Merge branch 'master'
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/00-INDEX | 6 | ||||
-rw-r--r-- | Documentation/HOWTO | 618 |
2 files changed, 624 insertions, 0 deletions
diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX index 433cf5e9ae04..5f7f7d7f77d2 100644 --- a/Documentation/00-INDEX +++ b/Documentation/00-INDEX | |||
@@ -24,6 +24,8 @@ DMA-mapping.txt | |||
24 | - info for PCI drivers using DMA portably across all platforms. | 24 | - info for PCI drivers using DMA portably across all platforms. |
25 | DocBook/ | 25 | DocBook/ |
26 | - directory with DocBook templates etc. for kernel documentation. | 26 | - directory with DocBook templates etc. for kernel documentation. |
27 | HOWTO | ||
28 | - The process and procedures of how to do Linux kernel development. | ||
27 | IO-mapping.txt | 29 | IO-mapping.txt |
28 | - how to access I/O mapped memory from within device drivers. | 30 | - how to access I/O mapped memory from within device drivers. |
29 | IPMI.txt | 31 | IPMI.txt |
@@ -256,6 +258,10 @@ specialix.txt | |||
256 | - info on hardware/driver for specialix IO8+ multiport serial card. | 258 | - info on hardware/driver for specialix IO8+ multiport serial card. |
257 | spinlocks.txt | 259 | spinlocks.txt |
258 | - info on using spinlocks to provide exclusive access in kernel. | 260 | - info on using spinlocks to provide exclusive access in kernel. |
261 | stable_api_nonsense.txt | ||
262 | - info on why the kernel does not have a stable in-kernel api or abi. | ||
263 | stable_kernel_rules.txt | ||
264 | - rules and procedures for the -stable kernel releases. | ||
259 | stallion.txt | 265 | stallion.txt |
260 | - info on using the Stallion multiport serial driver. | 266 | - info on using the Stallion multiport serial driver. |
261 | svga.txt | 267 | svga.txt |
diff --git a/Documentation/HOWTO b/Documentation/HOWTO new file mode 100644 index 000000000000..6c9e746267da --- /dev/null +++ b/Documentation/HOWTO | |||
@@ -0,0 +1,618 @@ | |||
1 | HOWTO do Linux kernel development | ||
2 | --------------------------------- | ||
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: | ||
31 | - "The C Programming Language" by Kernighan and Ritchie [Prentice Hall] | ||
32 | - "Practical C Programming" by Steve Oualline [O'Reilly] | ||
33 | |||
34 | The kernel is written using GNU C and the GNU toolchain. While it | ||
35 | adheres to the ISO C89 standard, it uses a number of extensions that are | ||
36 | not featured in the standard. The kernel is a freestanding C | ||
37 | environment, with no reliance on the standard C library, so some | ||
38 | portions of the C standard are not supported. Arbitrary long long | ||
39 | divisions and floating point are not allowed. It can sometimes be | ||
40 | difficult to understand the assumptions the kernel has on the toolchain | ||
41 | and the extensions that it uses, and unfortunately there is no | ||
42 | definitive reference for them. Please check the gcc info pages (`info | ||
43 | gcc`) for some information on them. | ||
44 | |||
45 | Please remember that you are trying to learn how to work with the | ||
46 | existing development community. It is a diverse group of people, with | ||
47 | high standards for coding, style and procedure. These standards have | ||
48 | been created over time based on what they have found to work best for | ||
49 | such a large and geographically dispersed team. Try to learn as much as | ||
50 | possible about these standards ahead of time, as they are well | ||
51 | documented; do not expect people to adapt to you or your company's way | ||
52 | of doing things. | ||
53 | |||
54 | |||
55 | Legal Issues | ||
56 | ------------ | ||
57 | |||
58 | The Linux kernel source code is released under the GPL. Please see the | ||
59 | file, COPYING, in the main directory of the source tree, for details on | ||
60 | the license. If you have further questions about the license, please | ||
61 | contact a lawyer, and do not ask on the Linux kernel mailing list. The | ||
62 | people on the mailing lists are not lawyers, and you should not rely on | ||
63 | their statements on legal matters. | ||
64 | |||
65 | For common questions and answers about the GPL, please see: | ||
66 | http://www.gnu.org/licenses/gpl-faq.html | ||
67 | |||
68 | |||
69 | Documentation | ||
70 | ------------ | ||
71 | |||
72 | The Linux kernel source tree has a large range of documents that are | ||
73 | invaluable for learning how to interact with the kernel community. When | ||
74 | new features are added to the kernel, it is recommended that new | ||
75 | documentation files are also added which explain how to use the feature. | ||
76 | When a kernel change causes the interface that the kernel exposes to | ||
77 | userspace to change, it is recommended that you send the information or | ||
78 | a patch to the manual pages explaining the change to the manual pages | ||
79 | maintainer at mtk-manpages@gmx.net. | ||
80 | |||
81 | Here is a list of files that are in the kernel source tree that are | ||
82 | required reading: | ||
83 | README | ||
84 | This file gives a short background on the Linux kernel and describes | ||
85 | what is necessary to do to configure and build the kernel. People | ||
86 | who are new to the kernel should start here. | ||
87 | |||
88 | Documentation/Changes | ||
89 | This file gives a list of the minimum levels of various software | ||
90 | packages that are necessary to build and run the kernel | ||
91 | successfully. | ||
92 | |||
93 | Documentation/CodingStyle | ||
94 | This describes the Linux kernel coding style, and some of the | ||
95 | rationale behind it. All new code is expected to follow the | ||
96 | guidelines in this document. Most maintainers will only accept | ||
97 | patches if these rules are followed, and many people will only | ||
98 | review code if it is in the proper style. | ||
99 | |||
100 | Documentation/SubmittingPatches | ||
101 | Documentation/SubmittingDrivers | ||
102 | These files describe in explicit detail how to successfully create | ||
103 | and send a patch, including (but not limited to): | ||
104 | - Email contents | ||
105 | - Email format | ||
106 | - Who to send it to | ||
107 | Following these rules will not guarantee success (as all patches are | ||
108 | subject to scrutiny for content and style), but not following them | ||
109 | will almost always prevent it. | ||
110 | |||
111 | Other excellent descriptions of how to create patches properly are: | ||
112 | "The Perfect Patch" | ||
113 | http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt | ||
114 | "Linux kernel patch submission format" | ||
115 | http://linux.yyz.us/patch-format.html | ||
116 | |||
117 | Documentation/stable_api_nonsense.txt | ||
118 | This file describes the rationale behind the conscious decision to | ||
119 | not have a stable API within the kernel, including things like: | ||
120 | - Subsystem shim-layers (for compatibility?) | ||
121 | - Driver portability between Operating Systems. | ||
122 | - Mitigating rapid change within the kernel source tree (or | ||
123 | preventing rapid change) | ||
124 | This document is crucial for understanding the Linux development | ||
125 | philosophy and is very important for people moving to Linux from | ||
126 | development on other Operating Systems. | ||
127 | |||
128 | Documentation/SecurityBugs | ||
129 | If you feel you have found a security problem in the Linux kernel, | ||
130 | please follow the steps in this document to help notify the kernel | ||
131 | developers, and help solve the issue. | ||
132 | |||
133 | Documentation/ManagementStyle | ||
134 | This document describes how Linux kernel maintainers operate and the | ||
135 | shared ethos behind their methodologies. This is important reading | ||
136 | for anyone new to kernel development (or anyone simply curious about | ||
137 | it), as it resolves a lot of common misconceptions and confusion | ||
138 | about the unique behavior of kernel maintainers. | ||
139 | |||
140 | Documentation/stable_kernel_rules.txt | ||
141 | This file describes the rules on how the stable kernel releases | ||
142 | happen, and what to do if you want to get a change into one of these | ||
143 | releases. | ||
144 | |||
145 | Documentation/kernel-docs.txt | ||
146 | A list of external documentation that pertains to kernel | ||
147 | development. Please consult this list if you do not find what you | ||
148 | are looking for within the in-kernel documentation. | ||
149 | |||
150 | Documentation/applying-patches.txt | ||
151 | A good introduction describing exactly what a patch is and how to | ||
152 | apply it to the different development branches of the kernel. | ||
153 | |||
154 | The kernel also has a large number of documents that can be | ||
155 | automatically generated from the source code itself. This includes a | ||
156 | full description of the in-kernel API, and rules on how to handle | ||
157 | locking properly. The documents will be created in the | ||
158 | Documentation/DocBook/ directory and can be generated as PDF, | ||
159 | Postscript, HTML, and man pages by running: | ||
160 | make pdfdocs | ||
161 | make psdocs | ||
162 | make htmldocs | ||
163 | make mandocs | ||
164 | respectively from the main kernel source directory. | ||
165 | |||
166 | |||
167 | Becoming A Kernel Developer | ||
168 | --------------------------- | ||
169 | |||
170 | If you do not know anything about Linux kernel development, you should | ||
171 | look at the Linux KernelNewbies project: | ||
172 | http://kernelnewbies.org | ||
173 | It consists of a helpful mailing list where you can ask almost any type | ||
174 | of basic kernel development question (make sure to search the archives | ||
175 | first, before asking something that has already been answered in the | ||
176 | past.) It also has an IRC channel that you can use to ask questions in | ||
177 | real-time, and a lot of helpful documentation that is useful for | ||
178 | learning about Linux kernel development. | ||
179 | |||
180 | The website has basic information about code organization, subsystems, | ||
181 | and current projects (both in-tree and out-of-tree). It also describes | ||
182 | some basic logistical information, like how to compile a kernel and | ||
183 | apply a patch. | ||
184 | |||
185 | If you do not know where you want to start, but you want to look for | ||
186 | some task to start doing to join into the kernel development community, | ||
187 | go to the Linux Kernel Janitor's project: | ||
188 | http://janitor.kernelnewbies.org/ | ||
189 | It is a great place to start. It describes a list of relatively simple | ||
190 | problems that need to be cleaned up and fixed within the Linux kernel | ||
191 | source tree. Working with the developers in charge of this project, you | ||
192 | will learn the basics of getting your patch into the Linux kernel tree, | ||
193 | and possibly be pointed in the direction of what to go work on next, if | ||
194 | you do not already have an idea. | ||
195 | |||
196 | If you already have a chunk of code that you want to put into the kernel | ||
197 | tree, but need some help getting it in the proper form, the | ||
198 | kernel-mentors project was created to help you out with this. It is a | ||
199 | mailing list, and can be found at: | ||
200 | http://selenic.com/mailman/listinfo/kernel-mentors | ||
201 | |||
202 | Before making any actual modifications to the Linux kernel code, it is | ||
203 | imperative to understand how the code in question works. For this | ||
204 | purpose, nothing is better than reading through it directly (most tricky | ||
205 | bits are commented well), perhaps even with the help of specialized | ||
206 | tools. One such tool that is particularly recommended is the Linux | ||
207 | Cross-Reference project, which is able to present source code in a | ||
208 | self-referential, indexed webpage format. An excellent up-to-date | ||
209 | repository of the kernel code may be found at: | ||
210 | http://sosdg.org/~coywolf/lxr/ | ||
211 | |||
212 | |||
213 | The development process | ||
214 | ----------------------- | ||
215 | |||
216 | Linux kernel development process currently consists of a few different | ||
217 | main kernel "branches" and lots of different subsystem-specific kernel | ||
218 | branches. These different branches are: | ||
219 | - main 2.6.x kernel tree | ||
220 | - 2.6.x.y -stable kernel tree | ||
221 | - 2.6.x -git kernel patches | ||
222 | - 2.6.x -mm kernel patches | ||
223 | - subsystem specific kernel trees and patches | ||
224 | |||
225 | 2.6.x kernel tree | ||
226 | ----------------- | ||
227 | 2.6.x kernels are maintained by Linus Torvalds, and can be found on | ||
228 | kernel.org in the pub/linux/kernel/v2.6/ directory. Its development | ||
229 | process is as follows: | ||
230 | - As soon as a new kernel is released a two weeks window is open, | ||
231 | during this period of time maintainers can submit big diffs to | ||
232 | Linus, usually the patches that have already been included in the | ||
233 | -mm kernel for a few weeks. The preferred way to submit big changes | ||
234 | is using git (the kernel's source management tool, more information | ||
235 | can be found at http://git.or.cz/) but plain patches are also just | ||
236 | fine. | ||
237 | - After two weeks a -rc1 kernel is released it is now possible to push | ||
238 | only patches that do not include new features that could affect the | ||
239 | stability of the whole kernel. Please note that a whole new driver | ||
240 | (or filesystem) might be accepted after -rc1 because there is no | ||
241 | risk of causing regressions with such a change as long as the change | ||
242 | is self-contained and does not affect areas outside of the code that | ||
243 | is being added. git can be used to send patches to Linus after -rc1 | ||
244 | is released, but the patches need to also be sent to a public | ||
245 | mailing list for review. | ||
246 | - A new -rc is released whenever Linus deems the current git tree to | ||
247 | be in a reasonably sane state adequate for testing. The goal is to | ||
248 | release a new -rc kernel every week. | ||
249 | - Process continues until the kernel is considered "ready", the | ||
250 | process should last around 6 weeks. | ||
251 | |||
252 | It is worth mentioning what Andrew Morton wrote on the linux-kernel | ||
253 | mailing list about kernel releases: | ||
254 | "Nobody knows when a kernel will be released, because it's | ||
255 | released according to perceived bug status, not according to a | ||
256 | preconceived timeline." | ||
257 | |||
258 | 2.6.x.y -stable kernel tree | ||
259 | --------------------------- | ||
260 | Kernels with 4 digit versions are -stable kernels. They contain | ||
261 | relatively small and critical fixes for security problems or significant | ||
262 | regressions discovered in a given 2.6.x kernel. | ||
263 | |||
264 | This is the recommended branch for users who want the most recent stable | ||
265 | kernel and are not interested in helping test development/experimental | ||
266 | versions. | ||
267 | |||
268 | If no 2.6.x.y kernel is available, then the highest numbered 2.6.x | ||
269 | kernel is the current stable kernel. | ||
270 | |||
271 | 2.6.x.y are maintained by the "stable" team <stable@kernel.org>, and are | ||
272 | released almost every other week. | ||
273 | |||
274 | The file Documentation/stable_kernel_rules.txt in the kernel tree | ||
275 | documents what kinds of changes are acceptable for the -stable tree, and | ||
276 | how the release process works. | ||
277 | |||
278 | 2.6.x -git patches | ||
279 | ------------------ | ||
280 | These are daily snapshots of Linus' kernel tree which are managed in a | ||
281 | git repository (hence the name.) These patches are usually released | ||
282 | daily and represent the current state of Linus' tree. They are more | ||
283 | experimental than -rc kernels since they are generated automatically | ||
284 | without even a cursory glance to see if they are sane. | ||
285 | |||
286 | 2.6.x -mm kernel patches | ||
287 | ------------------------ | ||
288 | These are experimental kernel patches released by Andrew Morton. Andrew | ||
289 | takes all of the different subsystem kernel trees and patches and mushes | ||
290 | them together, along with a lot of patches that have been plucked from | ||
291 | the linux-kernel mailing list. This tree serves as a proving ground for | ||
292 | new features and patches. Once a patch has proved its worth in -mm for | ||
293 | a while Andrew or the subsystem maintainer pushes it on to Linus for | ||
294 | inclusion in mainline. | ||
295 | |||
296 | It is heavily encouraged that all new patches get tested in the -mm tree | ||
297 | before they are sent to Linus for inclusion in the main kernel tree. | ||
298 | |||
299 | These kernels are not appropriate for use on systems that are supposed | ||
300 | to be stable and they are more risky to run than any of the other | ||
301 | branches. | ||
302 | |||
303 | If you wish to help out with the kernel development process, please test | ||
304 | and use these kernel releases and provide feedback to the linux-kernel | ||
305 | mailing list if you have any problems, and if everything works properly. | ||
306 | |||
307 | In addition to all the other experimental patches, these kernels usually | ||
308 | also contain any changes in the mainline -git kernels available at the | ||
309 | time of release. | ||
310 | |||
311 | The -mm kernels are not released on a fixed schedule, but usually a few | ||
312 | -mm kernels are released in between each -rc kernel (1 to 3 is common). | ||
313 | |||
314 | Subsystem Specific kernel trees and patches | ||
315 | ------------------------------------------- | ||
316 | A number of the different kernel subsystem developers expose their | ||
317 | development trees so that others can see what is happening in the | ||
318 | different areas of the kernel. These trees are pulled into the -mm | ||
319 | kernel releases as described above. | ||
320 | |||
321 | Here is a list of some of the different kernel trees available: | ||
322 | git trees: | ||
323 | - Kbuild development tree, Sam Ravnborg <sam@ravnborg.org> | ||
324 | kernel.org:/pub/scm/linux/kernel/git/sam/kbuild.git | ||
325 | |||
326 | - ACPI development tree, Len Brown <len.brown@intel.com> | ||
327 | kernel.org:/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6.git | ||
328 | |||
329 | - Block development tree, Jens Axboe <axboe@suse.de> | ||
330 | kernel.org:/pub/scm/linux/kernel/git/axboe/linux-2.6-block.git | ||
331 | |||
332 | - DRM development tree, Dave Airlie <airlied@linux.ie> | ||
333 | kernel.org:/pub/scm/linux/kernel/git/airlied/drm-2.6.git | ||
334 | |||
335 | - ia64 development tree, Tony Luck <tony.luck@intel.com> | ||
336 | kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git | ||
337 | |||
338 | - ieee1394 development tree, Jody McIntyre <scjody@modernduck.com> | ||
339 | kernel.org:/pub/scm/linux/kernel/git/scjody/ieee1394.git | ||
340 | |||
341 | - infiniband, Roland Dreier <rolandd@cisco.com> | ||
342 | kernel.org:/pub/scm/linux/kernel/git/roland/infiniband.git | ||
343 | |||
344 | - libata, Jeff Garzik <jgarzik@pobox.com> | ||
345 | kernel.org:/pub/scm/linux/kernel/git/jgarzik/libata-dev.git | ||
346 | |||
347 | - network drivers, Jeff Garzik <jgarzik@pobox.com> | ||
348 | kernel.org:/pub/scm/linux/kernel/git/jgarzik/netdev-2.6.git | ||
349 | |||
350 | - pcmcia, Dominik Brodowski <linux@dominikbrodowski.net> | ||
351 | kernel.org:/pub/scm/linux/kernel/git/brodo/pcmcia-2.6.git | ||
352 | |||
353 | - SCSI, James Bottomley <James.Bottomley@SteelEye.com> | ||
354 | kernel.org:/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6.git | ||
355 | |||
356 | Other git kernel trees can be found listed at http://kernel.org/git | ||
357 | |||
358 | quilt trees: | ||
359 | - USB, PCI, Driver Core, and I2C, Greg Kroah-Hartman <gregkh@suse.de> | ||
360 | kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/ | ||
361 | |||
362 | |||
363 | Bug Reporting | ||
364 | ------------- | ||
365 | |||
366 | bugzilla.kernel.org is where the Linux kernel developers track kernel | ||
367 | bugs. Users are encouraged to report all bugs that they find in this | ||
368 | tool. For details on how to use the kernel bugzilla, please see: | ||
369 | http://test.kernel.org/bugzilla/faq.html | ||
370 | |||
371 | The file REPORTING-BUGS in the main kernel source directory has a good | ||
372 | template for how to report a possible kernel bug, and details what kind | ||
373 | of information is needed by the kernel developers to help track down the | ||
374 | problem. | ||
375 | |||
376 | |||
377 | Mailing lists | ||
378 | ------------- | ||
379 | |||
380 | As some of the above documents describe, the majority of the core kernel | ||
381 | developers participate on the Linux Kernel Mailing list. Details on how | ||
382 | to subscribe and unsubscribe from the list can be found at: | ||
383 | http://vger.kernel.org/vger-lists.html#linux-kernel | ||
384 | There are archives of the mailing list on the web in many different | ||
385 | places. Use a search engine to find these archives. For example: | ||
386 | http://dir.gmane.org/gmane.linux.kernel | ||
387 | It is highly recommended that you search the archives about the topic | ||
388 | you want to bring up, before you post it to the list. A lot of things | ||
389 | already discussed in detail are only recorded at the mailing list | ||
390 | archives. | ||
391 | |||
392 | Most of the individual kernel subsystems also have their own separate | ||
393 | mailing list where they do their development efforts. See the | ||
394 | MAINTAINERS file for a list of what these lists are for the different | ||
395 | groups. | ||
396 | |||
397 | Many of the lists are hosted on kernel.org. Information on them can be | ||
398 | found at: | ||
399 | http://vger.kernel.org/vger-lists.html | ||
400 | |||
401 | Please remember to follow good behavioral habits when using the lists. | ||
402 | Though a bit cheesy, the following URL has some simple guidelines for | ||
403 | interacting with the list (or any list): | ||
404 | http://www.albion.com/netiquette/ | ||
405 | |||
406 | If multiple people respond to your mail, the CC: list of recipients may | ||
407 | get pretty large. Don't remove anybody from the CC: list without a good | ||
408 | reason, or don't reply only to the list address. Get used to receiving the | ||
409 | mail twice, one from the sender and the one from the list, and don't try | ||
410 | to tune that by adding fancy mail-headers, people will not like it. | ||
411 | |||
412 | Remember to keep the context and the attribution of your replies intact, | ||
413 | keep the "John Kernelhacker wrote ...:" lines at the top of your reply, and | ||
414 | add your statements between the individual quoted sections instead of | ||
415 | writing at the top of the mail. | ||
416 | |||
417 | If you add patches to your mail, make sure they are plain readable text | ||
418 | as stated in Documentation/SubmittingPatches. Kernel developers don't | ||
419 | want to deal with attachments or compressed patches; they may want | ||
420 | to comment on individual lines of your patch, which works only that way. | ||
421 | Make sure you use a mail program that does not mangle spaces and tab | ||
422 | characters. A good first test is to send the mail to yourself and try | ||
423 | to apply your own patch by yourself. If that doesn't work, get your | ||
424 | mail program fixed or change it until it works. | ||
425 | |||
426 | Above all, please remember to show respect to other subscribers. | ||
427 | |||
428 | |||
429 | Working with the community | ||
430 | -------------------------- | ||
431 | |||
432 | The goal of the kernel community is to provide the best possible kernel | ||
433 | there is. When you submit a patch for acceptance, it will be reviewed | ||
434 | on its technical merits and those alone. So, what should you be | ||
435 | expecting? | ||
436 | - criticism | ||
437 | - comments | ||
438 | - requests for change | ||
439 | - requests for justification | ||
440 | - silence | ||
441 | |||
442 | Remember, this is part of getting your patch into the kernel. You have | ||
443 | to be able to take criticism and comments about your patches, evaluate | ||
444 | them at a technical level and either rework your patches or provide | ||
445 | clear and concise reasoning as to why those changes should not be made. | ||
446 | If there are no responses to your posting, wait a few days and try | ||
447 | again, sometimes things get lost in the huge volume. | ||
448 | |||
449 | What should you not do? | ||
450 | - expect your patch to be accepted without question | ||
451 | - become defensive | ||
452 | - ignore comments | ||
453 | - resubmit the patch without making any of the requested changes | ||
454 | |||
455 | In a community that is looking for the best technical solution possible, | ||
456 | there will always be differing opinions on how beneficial a patch is. | ||
457 | You have to be cooperative, and willing to adapt your idea to fit within | ||
458 | the kernel. Or at least be willing to prove your idea is worth it. | ||
459 | Remember, being wrong is acceptable as long as you are willing to work | ||
460 | toward a solution that is right. | ||
461 | |||
462 | It is normal that the answers to your first patch might simply be a list | ||
463 | of a dozen things you should correct. This does _not_ imply that your | ||
464 | patch will not be accepted, and it is _not_ meant against you | ||
465 | personally. Simply correct all issues raised against your patch and | ||
466 | resend it. | ||
467 | |||
468 | |||
469 | Differences between the kernel community and corporate structures | ||
470 | ----------------------------------------------------------------- | ||
471 | |||
472 | The kernel community works differently than most traditional corporate | ||
473 | development environments. Here are a list of things that you can try to | ||
474 | do to try to avoid problems: | ||
475 | Good things to say regarding your proposed changes: | ||
476 | - "This solves multiple problems." | ||
477 | - "This deletes 2000 lines of code." | ||
478 | - "Here is a patch that explains what I am trying to describe." | ||
479 | - "I tested it on 5 different architectures..." | ||
480 | - "Here is a series of small patches that..." | ||
481 | - "This increases performance on typical machines..." | ||
482 | |||
483 | Bad things you should avoid saying: | ||
484 | - "We did it this way in AIX/ptx/Solaris, so therefore it must be | ||
485 | good..." | ||
486 | - "I've being doing this for 20 years, so..." | ||
487 | - "This is required for my company to make money" | ||
488 | - "This is for our Enterprise product line." | ||
489 | - "Here is my 1000 page design document that describes my idea" | ||
490 | - "I've been working on this for 6 months..." | ||
491 | - "Here's a 5000 line patch that..." | ||
492 | - "I rewrote all of the current mess, and here it is..." | ||
493 | - "I have a deadline, and this patch needs to be applied now." | ||
494 | |||
495 | Another way the kernel community is different than most traditional | ||
496 | software engineering work environments is the faceless nature of | ||
497 | interaction. One benefit of using email and irc as the primary forms of | ||
498 | communication is the lack of discrimination based on gender or race. | ||
499 | The Linux kernel work environment is accepting of women and minorities | ||
500 | because all you are is an email address. The international aspect also | ||
501 | helps to level the playing field because you can't guess gender based on | ||
502 | a person's name. A man may be named Andrea and a woman may be named Pat. | ||
503 | Most women who have worked in the Linux kernel and have expressed an | ||
504 | opinion have had positive experiences. | ||
505 | |||
506 | The language barrier can cause problems for some people who are not | ||
507 | comfortable with English. A good grasp of the language can be needed in | ||
508 | order to get ideas across properly on mailing lists, so it is | ||
509 | recommended that you check your emails to make sure they make sense in | ||
510 | English before sending them. | ||
511 | |||
512 | |||
513 | Break up your changes | ||
514 | --------------------- | ||
515 | |||
516 | The Linux kernel community does not gladly accept large chunks of code | ||
517 | dropped on it all at once. The changes need to be properly introduced, | ||
518 | discussed, and broken up into tiny, individual portions. This is almost | ||
519 | the exact opposite of what companies are used to doing. Your proposal | ||
520 | should also be introduced very early in the development process, so that | ||
521 | you can receive feedback on what you are doing. It also lets the | ||
522 | community feel that you are working with them, and not simply using them | ||
523 | as a dumping ground for your feature. However, don't send 50 emails at | ||
524 | one time to a mailing list, your patch series should be smaller than | ||
525 | that almost all of the time. | ||
526 | |||
527 | The reasons for breaking things up are the following: | ||
528 | |||
529 | 1) Small patches increase the likelihood that your patches will be | ||
530 | applied, since they don't take much time or effort to verify for | ||
531 | correctness. A 5 line patch can be applied by a maintainer with | ||
532 | barely a second glance. However, a 500 line patch may take hours to | ||
533 | review for correctness (the time it takes is exponentially | ||
534 | proportional to the size of the patch, or something). | ||
535 | |||
536 | Small patches also make it very easy to debug when something goes | ||
537 | wrong. It's much easier to back out patches one by one than it is | ||
538 | to dissect a very large patch after it's been applied (and broken | ||
539 | something). | ||
540 | |||
541 | 2) It's important not only to send small patches, but also to rewrite | ||
542 | and simplify (or simply re-order) patches before submitting them. | ||
543 | |||
544 | Here is an analogy from kernel developer Al Viro: | ||
545 | "Think of a teacher grading homework from a math student. The | ||
546 | teacher does not want to see the student's trials and errors | ||
547 | before they came up with the solution. They want to see the | ||
548 | cleanest, most elegant answer. A good student knows this, and | ||
549 | would never submit her intermediate work before the final | ||
550 | solution." | ||
551 | |||
552 | The same is true of kernel development. The maintainers and | ||
553 | reviewers do not want to see the thought process behind the | ||
554 | solution to the problem one is solving. They want to see a | ||
555 | simple and elegant solution." | ||
556 | |||
557 | It may be challenging to keep the balance between presenting an elegant | ||
558 | solution and working together with the community and discussing your | ||
559 | unfinished work. Therefore it is good to get early in the process to | ||
560 | get feedback to improve your work, but also keep your changes in small | ||
561 | chunks that they may get already accepted, even when your whole task is | ||
562 | not ready for inclusion now. | ||
563 | |||
564 | Also realize that it is not acceptable to send patches for inclusion | ||
565 | that are unfinished and will be "fixed up later." | ||
566 | |||
567 | |||
568 | Justify your change | ||
569 | ------------------- | ||
570 | |||
571 | Along with breaking up your patches, it is very important for you to let | ||
572 | the Linux community know why they should add this change. New features | ||
573 | must be justified as being needed and useful. | ||
574 | |||
575 | |||
576 | Document your change | ||
577 | -------------------- | ||
578 | |||
579 | When sending in your patches, pay special attention to what you say in | ||
580 | the text in your email. This information will become the ChangeLog | ||
581 | information for the patch, and will be preserved for everyone to see for | ||
582 | all time. It should describe the patch completely, containing: | ||
583 | - why the change is necessary | ||
584 | - the overall design approach in the patch | ||
585 | - implementation details | ||
586 | - testing results | ||
587 | |||
588 | For more details on what this should all look like, please see the | ||
589 | ChangeLog section of the document: | ||
590 | "The Perfect Patch" | ||
591 | http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt | ||
592 | |||
593 | |||
594 | |||
595 | |||
596 | All of these things are sometimes very hard to do. It can take years to | ||
597 | perfect these practices (if at all). It's a continuous process of | ||
598 | improvement that requires a lot of patience and determination. But | ||
599 | don't give up, it's possible. Many have done it before, and each had to | ||
600 | start exactly where you are now. | ||
601 | |||
602 | |||
603 | |||
604 | |||
605 | ---------- | ||
606 | Thanks to Paolo Ciarrocchi who allowed the "Development Process" section | ||
607 | to be based on text he had written, and to Randy Dunlap and Gerrit | ||
608 | Huizenga for some of the list of things you should and should not say. | ||
609 | Also thanks to Pat Mochel, Hanna Linder, Randy Dunlap, Kay Sievers, | ||
610 | Vojtech Pavlik, Jan Kara, Josh Boyer, Kees Cook, Andrew Morton, Andi | ||
611 | Kleen, Vadim Lobanov, Jesper Juhl, Adrian Bunk, Keri Harris, Frans Pop, | ||
612 | David A. Wheeler, Junio Hamano, Michael Kerrisk, and Alex Shepard for | ||
613 | their review, comments, and contributions. Without their help, this | ||
614 | document would not have been possible. | ||
615 | |||
616 | |||
617 | |||
618 | Maintainer: Greg Kroah-Hartman <greg@kroah.com> | ||