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Linus Torvalds1da177e2005-04-16 15:20:36 -07001
2 How to Get Your Change Into the Linux Kernel
3 or
4 Care And Operation Of Your Linus Torvalds
5
6
7
8For a person or company who wishes to submit a change to the Linux
9kernel, the process can sometimes be daunting if you're not familiar
10with "the system." This text is a collection of suggestions which
11can greatly increase the chances of your change being accepted.
12
13If you are submitting a driver, also read Documentation/SubmittingDrivers.
14
15
16
17--------------------------------------------
18SECTION 1 - CREATING AND SENDING YOUR CHANGE
19--------------------------------------------
20
21
22
231) "diff -up"
24------------
25
26Use "diff -up" or "diff -uprN" to create patches.
27
28All changes to the Linux kernel occur in the form of patches, as
29generated by diff(1). When creating your patch, make sure to create it
30in "unified diff" format, as supplied by the '-u' argument to diff(1).
31Also, please use the '-p' argument which shows which C function each
32change is in - that makes the resultant diff a lot easier to read.
33Patches should be based in the root kernel source directory,
34not in any lower subdirectory.
35
36To create a patch for a single file, it is often sufficient to do:
37
Randy Dunlap84da7c02005-06-28 20:45:30 -070038 SRCTREE= linux-2.6
Linus Torvalds1da177e2005-04-16 15:20:36 -070039 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
47To create a patch for multiple files, you should unpack a "vanilla",
48or unmodified kernel source tree, and generate a diff against your
49own source tree. For example:
50
Randy Dunlap84da7c02005-06-28 20:45:30 -070051 MYSRC= /devel/linux-2.6
Linus Torvalds1da177e2005-04-16 15:20:36 -070052
Randy Dunlap84da7c02005-06-28 20:45:30 -070053 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
Linus Torvalds1da177e2005-04-16 15:20:36 -070057
58"dontdiff" is a list of files which are generated by the kernel during
59the build process, and should be ignored in any diff(1)-generated
Randy Dunlap84da7c02005-06-28 20:45:30 -070060patch. The "dontdiff" file is included in the kernel tree in
612.6.12 and later. For earlier kernel versions, you can get it
62from <http://www.xenotime.net/linux/doc/dontdiff>.
Linus Torvalds1da177e2005-04-16 15:20:36 -070063
64Make sure your patch does not include any extra files which do not
65belong in a patch submission. Make sure to review your patch -after-
66generated it with diff(1), to ensure accuracy.
67
68If your changes produce a lot of deltas, you may want to look into
69splitting them into individual patches which modify things in
Randy Dunlap84da7c02005-06-28 20:45:30 -070070logical stages. This will facilitate easier reviewing by other
Linus Torvalds1da177e2005-04-16 15:20:36 -070071kernel developers, very important if you want your patch accepted.
Randy Dunlap84da7c02005-06-28 20:45:30 -070072There are a number of scripts which can aid in this:
Linus Torvalds1da177e2005-04-16 15:20:36 -070073
74Quilt:
75http://savannah.nongnu.org/projects/quilt
76
77Randy Dunlap's patch scripts:
Randy Dunlap84da7c02005-06-28 20:45:30 -070078http://www.xenotime.net/linux/scripts/patching-scripts-002.tar.gz
Linus Torvalds1da177e2005-04-16 15:20:36 -070079
80Andrew Morton's patch scripts:
Randy Dunlap84da7c02005-06-28 20:45:30 -070081http://www.zip.com.au/~akpm/linux/patches/patch-scripts-0.20
82
83
Linus Torvalds1da177e2005-04-16 15:20:36 -070084
852) Describe your changes.
86
87Describe the technical detail of the change(s) your patch includes.
88
89Be as specific as possible. The WORST descriptions possible include
90things like "update driver X", "bug fix for driver X", or "this patch
91includes updates for subsystem X. Please apply."
92
93If your description starts to get long, that's a sign that you probably
94need to split up your patch. See #3, next.
95
96
97
983) Separate your changes.
99
100Separate each logical change into its own patch.
101
102For example, if your changes include both bug fixes and performance
103enhancements for a single driver, separate those changes into two
104or more patches. If your changes include an API update, and a new
105driver which uses that new API, separate those into two patches.
106
107On the other hand, if you make a single change to numerous files,
108group those changes into a single patch. Thus a single logical change
109is contained within a single patch.
110
111If one patch depends on another patch in order for a change to be
112complete, that is OK. Simply note "this patch depends on patch X"
113in your patch description.
114
115
1164) Select e-mail destination.
117
118Look through the MAINTAINERS file and the source code, and determine
119if your change applies to a specific subsystem of the kernel, with
120an assigned maintainer. If so, e-mail that person.
121
122If no maintainer is listed, or the maintainer does not respond, send
123your patch to the primary Linux kernel developer's mailing list,
124linux-kernel@vger.kernel.org. Most kernel developers monitor this
125e-mail list, and can comment on your changes.
126
127Linus Torvalds is the final arbiter of all changes accepted into the
128Linux kernel. His e-mail address is <torvalds@osdl.org>. He gets
129a lot of e-mail, so typically you should do your best to -avoid- sending
130him e-mail.
131
132Patches which are bug fixes, are "obvious" changes, or similarly
133require little discussion should be sent or CC'd to Linus. Patches
134which require discussion or do not have a clear advantage should
135usually be sent first to linux-kernel. Only after the patch is
136discussed should the patch then be submitted to Linus.
137
Linus Torvalds1da177e2005-04-16 15:20:36 -0700138
139
1405) Select your CC (e-mail carbon copy) list.
141
142Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
143
144Other kernel developers besides Linus need to be aware of your change,
145so that they may comment on it and offer code review and suggestions.
146linux-kernel is the primary Linux kernel developer mailing list.
147Other mailing lists are available for specific subsystems, such as
148USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the
149MAINTAINERS file for a mailing list that relates specifically to
150your change.
151
152Even if the maintainer did not respond in step #4, make sure to ALWAYS
153copy the maintainer when you change their code.
154
155For small patches you may want to CC the Trivial Patch Monkey
156trivial@rustcorp.com.au set up by Rusty Russell; which collects "trivial"
157patches. Trivial patches must qualify for one of the following rules:
158 Spelling fixes in documentation
159 Spelling fixes which could break grep(1).
160 Warning fixes (cluttering with useless warnings is bad)
161 Compilation fixes (only if they are actually correct)
162 Runtime fixes (only if they actually fix things)
163 Removing use of deprecated functions/macros (eg. check_region).
164 Contact detail and documentation fixes
165 Non-portable code replaced by portable code (even in arch-specific,
166 since people copy, as long as it's trivial)
167 Any fix by the author/maintainer of the file. (ie. patch monkey
168 in re-transmission mode)
Randy Dunlap84da7c02005-06-28 20:45:30 -0700169URL: <http://www.kernel.org/pub/linux/kernel/people/rusty/trivial/>
170
Linus Torvalds1da177e2005-04-16 15:20:36 -0700171
172
173
1746) No MIME, no links, no compression, no attachments. Just plain text.
175
176Linus and other kernel developers need to be able to read and comment
177on the changes you are submitting. It is important for a kernel
178developer to be able to "quote" your changes, using standard e-mail
179tools, so that they may comment on specific portions of your code.
180
181For this reason, all patches should be submitting e-mail "inline".
182WARNING: Be wary of your editor's word-wrap corrupting your patch,
183if you choose to cut-n-paste your patch.
184
185Do not attach the patch as a MIME attachment, compressed or not.
186Many popular e-mail applications will not always transmit a MIME
187attachment as plain text, making it impossible to comment on your
188code. A MIME attachment also takes Linus a bit more time to process,
189decreasing the likelihood of your MIME-attached change being accepted.
190
191Exception: If your mailer is mangling patches then someone may ask
192you to re-send them using MIME.
193
194
195
1967) E-mail size.
197
198When sending patches to Linus, always follow step #6.
199
200Large changes are not appropriate for mailing lists, and some
201maintainers. If your patch, uncompressed, exceeds 40 kB in size,
202it is preferred that you store your patch on an Internet-accessible
203server, and provide instead a URL (link) pointing to your patch.
204
205
206
2078) Name your kernel version.
208
209It is important to note, either in the subject line or in the patch
210description, the kernel version to which this patch applies.
211
212If the patch does not apply cleanly to the latest kernel version,
213Linus will not apply it.
214
215
216
2179) Don't get discouraged. Re-submit.
218
219After you have submitted your change, be patient and wait. If Linus
220likes your change and applies it, it will appear in the next version
221of the kernel that he releases.
222
223However, if your change doesn't appear in the next version of the
224kernel, there could be any number of reasons. It's YOUR job to
225narrow down those reasons, correct what was wrong, and submit your
226updated change.
227
228It is quite common for Linus to "drop" your patch without comment.
229That's the nature of the system. If he drops your patch, it could be
230due to
231* Your patch did not apply cleanly to the latest kernel version
232* Your patch was not sufficiently discussed on linux-kernel.
233* A style issue (see section 2),
234* An e-mail formatting issue (re-read this section)
235* A technical problem with your change
236* He gets tons of e-mail, and yours got lost in the shuffle
237* You are being annoying (See Figure 1)
238
239When in doubt, solicit comments on linux-kernel mailing list.
240
241
242
24310) Include PATCH in the subject
244
245Due to high e-mail traffic to Linus, and to linux-kernel, it is common
246convention to prefix your subject line with [PATCH]. This lets Linus
247and other kernel developers more easily distinguish patches from other
248e-mail discussions.
249
250
251
25211) Sign your work
253
254To improve tracking of who did what, especially with patches that can
255percolate to their final resting place in the kernel through several
256layers of maintainers, we've introduced a "sign-off" procedure on
257patches that are being emailed around.
258
259The sign-off is a simple line at the end of the explanation for the
260patch, which certifies that you wrote it or otherwise have the right to
261pass it on as a open-source patch. The rules are pretty simple: if you
262can certify the below:
263
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700264 Developer's Certificate of Origin 1.1
Linus Torvalds1da177e2005-04-16 15:20:36 -0700265
266 By making a contribution to this project, I certify that:
267
268 (a) The contribution was created in whole or in part by me and I
269 have the right to submit it under the open source license
270 indicated in the file; or
271
272 (b) The contribution is based upon previous work that, to the best
273 of my knowledge, is covered under an appropriate open source
274 license and I have the right under that license to submit that
275 work with modifications, whether created in whole or in part
276 by me, under the same open source license (unless I am
277 permitted to submit under a different license), as indicated
278 in the file; or
279
280 (c) The contribution was provided directly to me by some other
281 person who certified (a), (b) or (c) and I have not modified
282 it.
283
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700284 (d) I understand and agree that this project and the contribution
285 are public and that a record of the contribution (including all
286 personal information I submit with it, including my sign-off) is
287 maintained indefinitely and may be redistributed consistent with
288 this project or the open source license(s) involved.
289
Linus Torvalds1da177e2005-04-16 15:20:36 -0700290then you just add a line saying
291
Alexey Dobriyan9fd55592005-06-25 14:59:34 -0700292 Signed-off-by: Random J Developer <random@developer.example.org>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700293
294Some people also put extra tags at the end. They'll just be ignored for
295now, but you can do this to mark internal company procedures or just
296point out some special detail about the sign-off.
297
298
Randy Dunlap84da7c02005-06-28 20:45:30 -0700299
30012) More references for submitting patches
301
302Andrew Morton, "The perfect patch" (tpp).
303 <http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt>
304
305Jeff Garzik, "Linux kernel patch submission format."
306 <http://linux.yyz.us/patch-format.html>
307
308
309
Linus Torvalds1da177e2005-04-16 15:20:36 -0700310-----------------------------------
311SECTION 2 - HINTS, TIPS, AND TRICKS
312-----------------------------------
313
314This section lists many of the common "rules" associated with code
315submitted to the kernel. There are always exceptions... but you must
316have a really good reason for doing so. You could probably call this
317section Linus Computer Science 101.
318
319
320
3211) Read Documentation/CodingStyle
322
323Nuff said. If your code deviates too much from this, it is likely
324to be rejected without further review, and without comment.
325
326
327
3282) #ifdefs are ugly
329
330Code cluttered with ifdefs is difficult to read and maintain. Don't do
331it. Instead, put your ifdefs in a header, and conditionally define
332'static inline' functions, or macros, which are used in the code.
333Let the compiler optimize away the "no-op" case.
334
335Simple example, of poor code:
336
337 dev = alloc_etherdev (sizeof(struct funky_private));
338 if (!dev)
339 return -ENODEV;
340 #ifdef CONFIG_NET_FUNKINESS
341 init_funky_net(dev);
342 #endif
343
344Cleaned-up example:
345
346(in header)
347 #ifndef CONFIG_NET_FUNKINESS
348 static inline void init_funky_net (struct net_device *d) {}
349 #endif
350
351(in the code itself)
352 dev = alloc_etherdev (sizeof(struct funky_private));
353 if (!dev)
354 return -ENODEV;
355 init_funky_net(dev);
356
357
358
3593) 'static inline' is better than a macro
360
361Static inline functions are greatly preferred over macros.
362They provide type safety, have no length limitations, no formatting
363limitations, and under gcc they are as cheap as macros.
364
365Macros should only be used for cases where a static inline is clearly
366suboptimal [there a few, isolated cases of this in fast paths],
367or where it is impossible to use a static inline function [such as
368string-izing].
369
370'static inline' is preferred over 'static __inline__', 'extern inline',
371and 'extern __inline__'.
372
373
374
3754) Don't over-design.
376
377Don't try to anticipate nebulous future cases which may or may not
Randy Dunlap84da7c02005-06-28 20:45:30 -0700378be useful: "Make it as simple as you can, and no simpler."
Linus Torvalds1da177e2005-04-16 15:20:36 -0700379