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1 | |
2 | How to Get Your Change Into the Linux Kernel | |
3 | or | |
4 | Care And Operation Of Your Linus Torvalds | |
5 | ||
6 | ||
7 | ||
8 | For a person or company who wishes to submit a change to the Linux | |
9 | kernel, the process can sometimes be daunting if you're not familiar | |
10 | with "the system." This text is a collection of suggestions which | |
11 | can greatly increase the chances of your change being accepted. | |
12 | ||
13 | If you are submitting a driver, also read Documentation/SubmittingDrivers. | |
14 | ||
15 | ||
16 | ||
17 | -------------------------------------------- | |
18 | SECTION 1 - CREATING AND SENDING YOUR CHANGE | |
19 | -------------------------------------------- | |
20 | ||
21 | ||
22 | ||
23 | 1) "diff -up" | |
24 | ------------ | |
25 | ||
26 | Use "diff -up" or "diff -uprN" to create patches. | |
27 | ||
28 | All changes to the Linux kernel occur in the form of patches, as | |
29 | generated by diff(1). When creating your patch, make sure to create it | |
30 | in "unified diff" format, as supplied by the '-u' argument to diff(1). | |
31 | Also, please use the '-p' argument which shows which C function each | |
32 | change is in - that makes the resultant diff a lot easier to read. | |
33 | Patches should be based in the root kernel source directory, | |
34 | not in any lower subdirectory. | |
35 | ||
36 | To create a patch for a single file, it is often sufficient to do: | |
37 | ||
84da7c08 | 38 | SRCTREE= linux-2.6 |
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39 | MYFILE= drivers/net/mydriver.c |
40 | ||
41 | cd $SRCTREE | |
42 | cp $MYFILE $MYFILE.orig | |
43 | vi $MYFILE # make your change | |
44 | cd .. | |
45 | diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch | |
46 | ||
47 | To create a patch for multiple files, you should unpack a "vanilla", | |
48 | or unmodified kernel source tree, and generate a diff against your | |
49 | own source tree. For example: | |
50 | ||
84da7c08 | 51 | MYSRC= /devel/linux-2.6 |
1da177e4 | 52 | |
84da7c08 RD |
53 | tar xvfz linux-2.6.12.tar.gz |
54 | mv linux-2.6.12 linux-2.6.12-vanilla | |
55 | diff -uprN -X linux-2.6.12-vanilla/Documentation/dontdiff \ | |
56 | linux-2.6.12-vanilla $MYSRC > /tmp/patch | |
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57 | |
58 | "dontdiff" is a list of files which are generated by the kernel during | |
59 | the build process, and should be ignored in any diff(1)-generated | |
84da7c08 RD |
60 | patch. The "dontdiff" file is included in the kernel tree in |
61 | 2.6.12 and later. For earlier kernel versions, you can get it | |
62 | from <http://www.xenotime.net/linux/doc/dontdiff>. | |
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63 | |
64 | Make sure your patch does not include any extra files which do not | |
65 | belong in a patch submission. Make sure to review your patch -after- | |
66 | generated it with diff(1), to ensure accuracy. | |
67 | ||
68 | If your changes produce a lot of deltas, you may want to look into | |
69 | splitting them into individual patches which modify things in | |
84da7c08 | 70 | logical stages. This will facilitate easier reviewing by other |
1da177e4 | 71 | kernel developers, very important if you want your patch accepted. |
84da7c08 | 72 | There are a number of scripts which can aid in this: |
1da177e4 LT |
73 | |
74 | Quilt: | |
75 | http://savannah.nongnu.org/projects/quilt | |
76 | ||
77 | Randy Dunlap's patch scripts: | |
84da7c08 | 78 | http://www.xenotime.net/linux/scripts/patching-scripts-002.tar.gz |
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79 | |
80 | Andrew Morton's patch scripts: | |
84da7c08 RD |
81 | http://www.zip.com.au/~akpm/linux/patches/patch-scripts-0.20 |
82 | ||
83 | ||
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84 | |
85 | 2) Describe your changes. | |
86 | ||
87 | Describe the technical detail of the change(s) your patch includes. | |
88 | ||
89 | Be as specific as possible. The WORST descriptions possible include | |
90 | things like "update driver X", "bug fix for driver X", or "this patch | |
91 | includes updates for subsystem X. Please apply." | |
92 | ||
93 | If your description starts to get long, that's a sign that you probably | |
94 | need to split up your patch. See #3, next. | |
95 | ||
96 | ||
97 | ||
98 | 3) Separate your changes. | |
99 | ||
100 | Separate each logical change into its own patch. | |
101 | ||
102 | For example, if your changes include both bug fixes and performance | |
103 | enhancements for a single driver, separate those changes into two | |
104 | or more patches. If your changes include an API update, and a new | |
105 | driver which uses that new API, separate those into two patches. | |
106 | ||
107 | On the other hand, if you make a single change to numerous files, | |
108 | group those changes into a single patch. Thus a single logical change | |
109 | is contained within a single patch. | |
110 | ||
111 | If one patch depends on another patch in order for a change to be | |
112 | complete, that is OK. Simply note "this patch depends on patch X" | |
113 | in your patch description. | |
114 | ||
115 | ||
116 | 4) Select e-mail destination. | |
117 | ||
118 | Look through the MAINTAINERS file and the source code, and determine | |
119 | if your change applies to a specific subsystem of the kernel, with | |
120 | an assigned maintainer. If so, e-mail that person. | |
121 | ||
122 | If no maintainer is listed, or the maintainer does not respond, send | |
123 | your patch to the primary Linux kernel developer's mailing list, | |
124 | linux-kernel@vger.kernel.org. Most kernel developers monitor this | |
125 | e-mail list, and can comment on your changes. | |
126 | ||
127 | Linus Torvalds is the final arbiter of all changes accepted into the | |
128 | Linux kernel. His e-mail address is <torvalds@osdl.org>. He gets | |
129 | a lot of e-mail, so typically you should do your best to -avoid- sending | |
130 | him e-mail. | |
131 | ||
132 | Patches which are bug fixes, are "obvious" changes, or similarly | |
133 | require little discussion should be sent or CC'd to Linus. Patches | |
134 | which require discussion or do not have a clear advantage should | |
135 | usually be sent first to linux-kernel. Only after the patch is | |
136 | discussed should the patch then be submitted to Linus. | |
137 | ||
1da177e4 LT |
138 | |
139 | ||
140 | 5) Select your CC (e-mail carbon copy) list. | |
141 | ||
142 | Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org. | |
143 | ||
144 | Other kernel developers besides Linus need to be aware of your change, | |
145 | so that they may comment on it and offer code review and suggestions. | |
146 | linux-kernel is the primary Linux kernel developer mailing list. | |
147 | Other mailing lists are available for specific subsystems, such as | |
148 | USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the | |
149 | MAINTAINERS file for a mailing list that relates specifically to | |
150 | your change. | |
151 | ||
1caf1f0f PJ |
152 | If changes affect userland-kernel interfaces, please send |
153 | the MAN-PAGES maintainer (as listed in the MAINTAINERS file) | |
154 | a man-pages patch, or at least a notification of the change, | |
155 | so that some information makes its way into the manual pages. | |
156 | ||
1da177e4 LT |
157 | Even if the maintainer did not respond in step #4, make sure to ALWAYS |
158 | copy the maintainer when you change their code. | |
159 | ||
160 | For small patches you may want to CC the Trivial Patch Monkey | |
161 | trivial@rustcorp.com.au set up by Rusty Russell; which collects "trivial" | |
162 | patches. Trivial patches must qualify for one of the following rules: | |
163 | Spelling fixes in documentation | |
164 | Spelling fixes which could break grep(1). | |
165 | Warning fixes (cluttering with useless warnings is bad) | |
166 | Compilation fixes (only if they are actually correct) | |
167 | Runtime fixes (only if they actually fix things) | |
168 | Removing use of deprecated functions/macros (eg. check_region). | |
169 | Contact detail and documentation fixes | |
170 | Non-portable code replaced by portable code (even in arch-specific, | |
171 | since people copy, as long as it's trivial) | |
172 | Any fix by the author/maintainer of the file. (ie. patch monkey | |
173 | in re-transmission mode) | |
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174 | URL: <http://www.kernel.org/pub/linux/kernel/people/rusty/trivial/> |
175 | ||
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176 | |
177 | ||
178 | ||
179 | 6) No MIME, no links, no compression, no attachments. Just plain text. | |
180 | ||
181 | Linus and other kernel developers need to be able to read and comment | |
182 | on the changes you are submitting. It is important for a kernel | |
183 | developer to be able to "quote" your changes, using standard e-mail | |
184 | tools, so that they may comment on specific portions of your code. | |
185 | ||
186 | For this reason, all patches should be submitting e-mail "inline". | |
187 | WARNING: Be wary of your editor's word-wrap corrupting your patch, | |
188 | if you choose to cut-n-paste your patch. | |
189 | ||
190 | Do not attach the patch as a MIME attachment, compressed or not. | |
191 | Many popular e-mail applications will not always transmit a MIME | |
192 | attachment as plain text, making it impossible to comment on your | |
193 | code. A MIME attachment also takes Linus a bit more time to process, | |
194 | decreasing the likelihood of your MIME-attached change being accepted. | |
195 | ||
196 | Exception: If your mailer is mangling patches then someone may ask | |
197 | you to re-send them using MIME. | |
198 | ||
199 | ||
200 | ||
201 | 7) E-mail size. | |
202 | ||
203 | When sending patches to Linus, always follow step #6. | |
204 | ||
205 | Large changes are not appropriate for mailing lists, and some | |
206 | maintainers. If your patch, uncompressed, exceeds 40 kB in size, | |
207 | it is preferred that you store your patch on an Internet-accessible | |
208 | server, and provide instead a URL (link) pointing to your patch. | |
209 | ||
210 | ||
211 | ||
212 | 8) Name your kernel version. | |
213 | ||
214 | It is important to note, either in the subject line or in the patch | |
215 | description, the kernel version to which this patch applies. | |
216 | ||
217 | If the patch does not apply cleanly to the latest kernel version, | |
218 | Linus will not apply it. | |
219 | ||
220 | ||
221 | ||
222 | 9) Don't get discouraged. Re-submit. | |
223 | ||
224 | After you have submitted your change, be patient and wait. If Linus | |
225 | likes your change and applies it, it will appear in the next version | |
226 | of the kernel that he releases. | |
227 | ||
228 | However, if your change doesn't appear in the next version of the | |
229 | kernel, there could be any number of reasons. It's YOUR job to | |
230 | narrow down those reasons, correct what was wrong, and submit your | |
231 | updated change. | |
232 | ||
233 | It is quite common for Linus to "drop" your patch without comment. | |
234 | That's the nature of the system. If he drops your patch, it could be | |
235 | due to | |
236 | * Your patch did not apply cleanly to the latest kernel version | |
237 | * Your patch was not sufficiently discussed on linux-kernel. | |
238 | * A style issue (see section 2), | |
239 | * An e-mail formatting issue (re-read this section) | |
240 | * A technical problem with your change | |
241 | * He gets tons of e-mail, and yours got lost in the shuffle | |
242 | * You are being annoying (See Figure 1) | |
243 | ||
244 | When in doubt, solicit comments on linux-kernel mailing list. | |
245 | ||
246 | ||
247 | ||
248 | 10) Include PATCH in the subject | |
249 | ||
250 | Due to high e-mail traffic to Linus, and to linux-kernel, it is common | |
251 | convention to prefix your subject line with [PATCH]. This lets Linus | |
252 | and other kernel developers more easily distinguish patches from other | |
253 | e-mail discussions. | |
254 | ||
255 | ||
256 | ||
257 | 11) Sign your work | |
258 | ||
259 | To improve tracking of who did what, especially with patches that can | |
260 | percolate to their final resting place in the kernel through several | |
261 | layers of maintainers, we've introduced a "sign-off" procedure on | |
262 | patches that are being emailed around. | |
263 | ||
264 | The sign-off is a simple line at the end of the explanation for the | |
265 | patch, which certifies that you wrote it or otherwise have the right to | |
266 | pass it on as a open-source patch. The rules are pretty simple: if you | |
267 | can certify the below: | |
268 | ||
cbd83da8 | 269 | Developer's Certificate of Origin 1.1 |
1da177e4 LT |
270 | |
271 | By making a contribution to this project, I certify that: | |
272 | ||
273 | (a) The contribution was created in whole or in part by me and I | |
274 | have the right to submit it under the open source license | |
275 | indicated in the file; or | |
276 | ||
277 | (b) The contribution is based upon previous work that, to the best | |
278 | of my knowledge, is covered under an appropriate open source | |
279 | license and I have the right under that license to submit that | |
280 | work with modifications, whether created in whole or in part | |
281 | by me, under the same open source license (unless I am | |
282 | permitted to submit under a different license), as indicated | |
283 | in the file; or | |
284 | ||
285 | (c) The contribution was provided directly to me by some other | |
286 | person who certified (a), (b) or (c) and I have not modified | |
287 | it. | |
288 | ||
cbd83da8 LT |
289 | (d) I understand and agree that this project and the contribution |
290 | are public and that a record of the contribution (including all | |
291 | personal information I submit with it, including my sign-off) is | |
292 | maintained indefinitely and may be redistributed consistent with | |
293 | this project or the open source license(s) involved. | |
294 | ||
1da177e4 LT |
295 | then you just add a line saying |
296 | ||
9fd5559c | 297 | Signed-off-by: Random J Developer <random@developer.example.org> |
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298 | |
299 | Some people also put extra tags at the end. They'll just be ignored for | |
300 | now, but you can do this to mark internal company procedures or just | |
301 | point out some special detail about the sign-off. | |
302 | ||
303 | ||
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304 | |
305 | 12) More references for submitting patches | |
306 | ||
307 | Andrew Morton, "The perfect patch" (tpp). | |
308 | <http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt> | |
309 | ||
310 | Jeff Garzik, "Linux kernel patch submission format." | |
311 | <http://linux.yyz.us/patch-format.html> | |
312 | ||
313 | ||
314 | ||
1da177e4 LT |
315 | ----------------------------------- |
316 | SECTION 2 - HINTS, TIPS, AND TRICKS | |
317 | ----------------------------------- | |
318 | ||
319 | This section lists many of the common "rules" associated with code | |
320 | submitted to the kernel. There are always exceptions... but you must | |
321 | have a really good reason for doing so. You could probably call this | |
322 | section Linus Computer Science 101. | |
323 | ||
324 | ||
325 | ||
326 | 1) Read Documentation/CodingStyle | |
327 | ||
328 | Nuff said. If your code deviates too much from this, it is likely | |
329 | to be rejected without further review, and without comment. | |
330 | ||
331 | ||
332 | ||
333 | 2) #ifdefs are ugly | |
334 | ||
335 | Code cluttered with ifdefs is difficult to read and maintain. Don't do | |
336 | it. Instead, put your ifdefs in a header, and conditionally define | |
337 | 'static inline' functions, or macros, which are used in the code. | |
338 | Let the compiler optimize away the "no-op" case. | |
339 | ||
340 | Simple example, of poor code: | |
341 | ||
342 | dev = alloc_etherdev (sizeof(struct funky_private)); | |
343 | if (!dev) | |
344 | return -ENODEV; | |
345 | #ifdef CONFIG_NET_FUNKINESS | |
346 | init_funky_net(dev); | |
347 | #endif | |
348 | ||
349 | Cleaned-up example: | |
350 | ||
351 | (in header) | |
352 | #ifndef CONFIG_NET_FUNKINESS | |
353 | static inline void init_funky_net (struct net_device *d) {} | |
354 | #endif | |
355 | ||
356 | (in the code itself) | |
357 | dev = alloc_etherdev (sizeof(struct funky_private)); | |
358 | if (!dev) | |
359 | return -ENODEV; | |
360 | init_funky_net(dev); | |
361 | ||
362 | ||
363 | ||
364 | 3) 'static inline' is better than a macro | |
365 | ||
366 | Static inline functions are greatly preferred over macros. | |
367 | They provide type safety, have no length limitations, no formatting | |
368 | limitations, and under gcc they are as cheap as macros. | |
369 | ||
370 | Macros should only be used for cases where a static inline is clearly | |
371 | suboptimal [there a few, isolated cases of this in fast paths], | |
372 | or where it is impossible to use a static inline function [such as | |
373 | string-izing]. | |
374 | ||
375 | 'static inline' is preferred over 'static __inline__', 'extern inline', | |
376 | and 'extern __inline__'. | |
377 | ||
378 | ||
379 | ||
380 | 4) Don't over-design. | |
381 | ||
382 | Don't try to anticipate nebulous future cases which may or may not | |
84da7c08 | 383 | be useful: "Make it as simple as you can, and no simpler." |
1da177e4 | 384 |