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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 | ||
38 | SRCTREE= linux-2.4 | |
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 | ||
51 | MYSRC= /devel/linux-2.4 | |
52 | ||
53 | tar xvfz linux-2.4.0-test11.tar.gz | |
54 | mv linux linux-vanilla | |
55 | wget http://www.moses.uklinux.net/patches/dontdiff | |
56 | diff -uprN -X dontdiff linux-vanilla $MYSRC > /tmp/patch | |
57 | rm -f dontdiff | |
58 | ||
59 | "dontdiff" is a list of files which are generated by the kernel during | |
60 | the build process, and should be ignored in any diff(1)-generated | |
61 | patch. dontdiff is maintained by Tigran Aivazian <tigran@veritas.com> | |
62 | ||
63 | Make sure your patch does not include any extra files which do not | |
64 | belong in a patch submission. Make sure to review your patch -after- | |
65 | generated it with diff(1), to ensure accuracy. | |
66 | ||
67 | If your changes produce a lot of deltas, you may want to look into | |
68 | splitting them into individual patches which modify things in | |
69 | logical stages, this will facilitate easier reviewing by other | |
70 | kernel developers, very important if you want your patch accepted. | |
71 | There are a number of scripts which can aid in this; | |
72 | ||
73 | Quilt: | |
74 | http://savannah.nongnu.org/projects/quilt | |
75 | ||
76 | Randy Dunlap's patch scripts: | |
77 | http://developer.osdl.org/rddunlap/scripts/patching-scripts.tgz | |
78 | ||
79 | Andrew Morton's patch scripts: | |
80 | http://www.zip.com.au/~akpm/linux/patches/patch-scripts-0.16 | |
81 | ||
82 | 2) Describe your changes. | |
83 | ||
84 | Describe the technical detail of the change(s) your patch includes. | |
85 | ||
86 | Be as specific as possible. The WORST descriptions possible include | |
87 | things like "update driver X", "bug fix for driver X", or "this patch | |
88 | includes updates for subsystem X. Please apply." | |
89 | ||
90 | If your description starts to get long, that's a sign that you probably | |
91 | need to split up your patch. See #3, next. | |
92 | ||
93 | ||
94 | ||
95 | 3) Separate your changes. | |
96 | ||
97 | Separate each logical change into its own patch. | |
98 | ||
99 | For example, if your changes include both bug fixes and performance | |
100 | enhancements for a single driver, separate those changes into two | |
101 | or more patches. If your changes include an API update, and a new | |
102 | driver which uses that new API, separate those into two patches. | |
103 | ||
104 | On the other hand, if you make a single change to numerous files, | |
105 | group those changes into a single patch. Thus a single logical change | |
106 | is contained within a single patch. | |
107 | ||
108 | If one patch depends on another patch in order for a change to be | |
109 | complete, that is OK. Simply note "this patch depends on patch X" | |
110 | in your patch description. | |
111 | ||
112 | ||
113 | 4) Select e-mail destination. | |
114 | ||
115 | Look through the MAINTAINERS file and the source code, and determine | |
116 | if your change applies to a specific subsystem of the kernel, with | |
117 | an assigned maintainer. If so, e-mail that person. | |
118 | ||
119 | If no maintainer is listed, or the maintainer does not respond, send | |
120 | your patch to the primary Linux kernel developer's mailing list, | |
121 | linux-kernel@vger.kernel.org. Most kernel developers monitor this | |
122 | e-mail list, and can comment on your changes. | |
123 | ||
124 | Linus Torvalds is the final arbiter of all changes accepted into the | |
125 | Linux kernel. His e-mail address is <torvalds@osdl.org>. He gets | |
126 | a lot of e-mail, so typically you should do your best to -avoid- sending | |
127 | him e-mail. | |
128 | ||
129 | Patches which are bug fixes, are "obvious" changes, or similarly | |
130 | require little discussion should be sent or CC'd to Linus. Patches | |
131 | which require discussion or do not have a clear advantage should | |
132 | usually be sent first to linux-kernel. Only after the patch is | |
133 | discussed should the patch then be submitted to Linus. | |
134 | ||
135 | For small patches you may want to CC the Trivial Patch Monkey | |
136 | trivial@rustcorp.com.au set up by Rusty Russell; which collects "trivial" | |
137 | patches. Trivial patches must qualify for one of the following rules: | |
138 | Spelling fixes in documentation | |
139 | Spelling fixes which could break grep(1). | |
140 | Warning fixes (cluttering with useless warnings is bad) | |
141 | Compilation fixes (only if they are actually correct) | |
142 | Runtime fixes (only if they actually fix things) | |
143 | Removing use of deprecated functions/macros (eg. check_region). | |
144 | Contact detail and documentation fixes | |
145 | Non-portable code replaced by portable code (even in arch-specific, | |
146 | since people copy, as long as it's trivial) | |
147 | Any fix by the author/maintainer of the file. (ie. patch monkey | |
148 | in re-transmission mode) | |
149 | ||
150 | ||
151 | ||
152 | 5) Select your CC (e-mail carbon copy) list. | |
153 | ||
154 | Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org. | |
155 | ||
156 | Other kernel developers besides Linus need to be aware of your change, | |
157 | so that they may comment on it and offer code review and suggestions. | |
158 | linux-kernel is the primary Linux kernel developer mailing list. | |
159 | Other mailing lists are available for specific subsystems, such as | |
160 | USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the | |
161 | MAINTAINERS file for a mailing list that relates specifically to | |
162 | your change. | |
163 | ||
164 | Even if the maintainer did not respond in step #4, make sure to ALWAYS | |
165 | copy the maintainer when you change their code. | |
166 | ||
167 | For small patches you may want to CC the Trivial Patch Monkey | |
168 | trivial@rustcorp.com.au set up by Rusty Russell; which collects "trivial" | |
169 | patches. Trivial patches must qualify for one of the following rules: | |
170 | Spelling fixes in documentation | |
171 | Spelling fixes which could break grep(1). | |
172 | Warning fixes (cluttering with useless warnings is bad) | |
173 | Compilation fixes (only if they are actually correct) | |
174 | Runtime fixes (only if they actually fix things) | |
175 | Removing use of deprecated functions/macros (eg. check_region). | |
176 | Contact detail and documentation fixes | |
177 | Non-portable code replaced by portable code (even in arch-specific, | |
178 | since people copy, as long as it's trivial) | |
179 | Any fix by the author/maintainer of the file. (ie. patch monkey | |
180 | in re-transmission mode) | |
181 | ||
182 | ||
183 | ||
184 | 6) No MIME, no links, no compression, no attachments. Just plain text. | |
185 | ||
186 | Linus and other kernel developers need to be able to read and comment | |
187 | on the changes you are submitting. It is important for a kernel | |
188 | developer to be able to "quote" your changes, using standard e-mail | |
189 | tools, so that they may comment on specific portions of your code. | |
190 | ||
191 | For this reason, all patches should be submitting e-mail "inline". | |
192 | WARNING: Be wary of your editor's word-wrap corrupting your patch, | |
193 | if you choose to cut-n-paste your patch. | |
194 | ||
195 | Do not attach the patch as a MIME attachment, compressed or not. | |
196 | Many popular e-mail applications will not always transmit a MIME | |
197 | attachment as plain text, making it impossible to comment on your | |
198 | code. A MIME attachment also takes Linus a bit more time to process, | |
199 | decreasing the likelihood of your MIME-attached change being accepted. | |
200 | ||
201 | Exception: If your mailer is mangling patches then someone may ask | |
202 | you to re-send them using MIME. | |
203 | ||
204 | ||
205 | ||
206 | 7) E-mail size. | |
207 | ||
208 | When sending patches to Linus, always follow step #6. | |
209 | ||
210 | Large changes are not appropriate for mailing lists, and some | |
211 | maintainers. If your patch, uncompressed, exceeds 40 kB in size, | |
212 | it is preferred that you store your patch on an Internet-accessible | |
213 | server, and provide instead a URL (link) pointing to your patch. | |
214 | ||
215 | ||
216 | ||
217 | 8) Name your kernel version. | |
218 | ||
219 | It is important to note, either in the subject line or in the patch | |
220 | description, the kernel version to which this patch applies. | |
221 | ||
222 | If the patch does not apply cleanly to the latest kernel version, | |
223 | Linus will not apply it. | |
224 | ||
225 | ||
226 | ||
227 | 9) Don't get discouraged. Re-submit. | |
228 | ||
229 | After you have submitted your change, be patient and wait. If Linus | |
230 | likes your change and applies it, it will appear in the next version | |
231 | of the kernel that he releases. | |
232 | ||
233 | However, if your change doesn't appear in the next version of the | |
234 | kernel, there could be any number of reasons. It's YOUR job to | |
235 | narrow down those reasons, correct what was wrong, and submit your | |
236 | updated change. | |
237 | ||
238 | It is quite common for Linus to "drop" your patch without comment. | |
239 | That's the nature of the system. If he drops your patch, it could be | |
240 | due to | |
241 | * Your patch did not apply cleanly to the latest kernel version | |
242 | * Your patch was not sufficiently discussed on linux-kernel. | |
243 | * A style issue (see section 2), | |
244 | * An e-mail formatting issue (re-read this section) | |
245 | * A technical problem with your change | |
246 | * He gets tons of e-mail, and yours got lost in the shuffle | |
247 | * You are being annoying (See Figure 1) | |
248 | ||
249 | When in doubt, solicit comments on linux-kernel mailing list. | |
250 | ||
251 | ||
252 | ||
253 | 10) Include PATCH in the subject | |
254 | ||
255 | Due to high e-mail traffic to Linus, and to linux-kernel, it is common | |
256 | convention to prefix your subject line with [PATCH]. This lets Linus | |
257 | and other kernel developers more easily distinguish patches from other | |
258 | e-mail discussions. | |
259 | ||
260 | ||
261 | ||
262 | 11) Sign your work | |
263 | ||
264 | To improve tracking of who did what, especially with patches that can | |
265 | percolate to their final resting place in the kernel through several | |
266 | layers of maintainers, we've introduced a "sign-off" procedure on | |
267 | patches that are being emailed around. | |
268 | ||
269 | The sign-off is a simple line at the end of the explanation for the | |
270 | patch, which certifies that you wrote it or otherwise have the right to | |
271 | pass it on as a open-source patch. The rules are pretty simple: if you | |
272 | can certify the below: | |
273 | ||
274 | Developer's Certificate of Origin 1.0 | |
275 | ||
276 | By making a contribution to this project, I certify that: | |
277 | ||
278 | (a) The contribution was created in whole or in part by me and I | |
279 | have the right to submit it under the open source license | |
280 | indicated in the file; or | |
281 | ||
282 | (b) The contribution is based upon previous work that, to the best | |
283 | of my knowledge, is covered under an appropriate open source | |
284 | license and I have the right under that license to submit that | |
285 | work with modifications, whether created in whole or in part | |
286 | by me, under the same open source license (unless I am | |
287 | permitted to submit under a different license), as indicated | |
288 | in the file; or | |
289 | ||
290 | (c) The contribution was provided directly to me by some other | |
291 | person who certified (a), (b) or (c) and I have not modified | |
292 | it. | |
293 | ||
294 | then you just add a line saying | |
295 | ||
296 | Signed-off-by: Random J Developer <random@developer.org> | |
297 | ||
298 | Some people also put extra tags at the end. They'll just be ignored for | |
299 | now, but you can do this to mark internal company procedures or just | |
300 | point out some special detail about the sign-off. | |
301 | ||
302 | ||
303 | ----------------------------------- | |
304 | SECTION 2 - HINTS, TIPS, AND TRICKS | |
305 | ----------------------------------- | |
306 | ||
307 | This section lists many of the common "rules" associated with code | |
308 | submitted to the kernel. There are always exceptions... but you must | |
309 | have a really good reason for doing so. You could probably call this | |
310 | section Linus Computer Science 101. | |
311 | ||
312 | ||
313 | ||
314 | 1) Read Documentation/CodingStyle | |
315 | ||
316 | Nuff said. If your code deviates too much from this, it is likely | |
317 | to be rejected without further review, and without comment. | |
318 | ||
319 | ||
320 | ||
321 | 2) #ifdefs are ugly | |
322 | ||
323 | Code cluttered with ifdefs is difficult to read and maintain. Don't do | |
324 | it. Instead, put your ifdefs in a header, and conditionally define | |
325 | 'static inline' functions, or macros, which are used in the code. | |
326 | Let the compiler optimize away the "no-op" case. | |
327 | ||
328 | Simple example, of poor code: | |
329 | ||
330 | dev = alloc_etherdev (sizeof(struct funky_private)); | |
331 | if (!dev) | |
332 | return -ENODEV; | |
333 | #ifdef CONFIG_NET_FUNKINESS | |
334 | init_funky_net(dev); | |
335 | #endif | |
336 | ||
337 | Cleaned-up example: | |
338 | ||
339 | (in header) | |
340 | #ifndef CONFIG_NET_FUNKINESS | |
341 | static inline void init_funky_net (struct net_device *d) {} | |
342 | #endif | |
343 | ||
344 | (in the code itself) | |
345 | dev = alloc_etherdev (sizeof(struct funky_private)); | |
346 | if (!dev) | |
347 | return -ENODEV; | |
348 | init_funky_net(dev); | |
349 | ||
350 | ||
351 | ||
352 | 3) 'static inline' is better than a macro | |
353 | ||
354 | Static inline functions are greatly preferred over macros. | |
355 | They provide type safety, have no length limitations, no formatting | |
356 | limitations, and under gcc they are as cheap as macros. | |
357 | ||
358 | Macros should only be used for cases where a static inline is clearly | |
359 | suboptimal [there a few, isolated cases of this in fast paths], | |
360 | or where it is impossible to use a static inline function [such as | |
361 | string-izing]. | |
362 | ||
363 | 'static inline' is preferred over 'static __inline__', 'extern inline', | |
364 | and 'extern __inline__'. | |
365 | ||
366 | ||
367 | ||
368 | 4) Don't over-design. | |
369 | ||
370 | Don't try to anticipate nebulous future cases which may or may not | |
371 | be useful: "Make it as simple as you can, and no simpler" | |
372 | ||
373 | ||
374 |