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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
Randy Dunlapbc7455f2006-07-30 03:03:45 -070013Read Documentation/SubmitChecklist for a list of items to check
14before submitting code. If you are submitting a driver, also read
15Documentation/SubmittingDrivers.
Linus Torvalds1da177e2005-04-16 15:20:36 -070016
17
18
19--------------------------------------------
20SECTION 1 - CREATING AND SENDING YOUR CHANGE
21--------------------------------------------
22
23
24
251) "diff -up"
26------------
27
28Use "diff -up" or "diff -uprN" to create patches.
29
30All changes to the Linux kernel occur in the form of patches, as
31generated by diff(1). When creating your patch, make sure to create it
32in "unified diff" format, as supplied by the '-u' argument to diff(1).
33Also, please use the '-p' argument which shows which C function each
34change is in - that makes the resultant diff a lot easier to read.
35Patches should be based in the root kernel source directory,
36not in any lower subdirectory.
37
38To create a patch for a single file, it is often sufficient to do:
39
Randy Dunlap84da7c02005-06-28 20:45:30 -070040 SRCTREE= linux-2.6
Linus Torvalds1da177e2005-04-16 15:20:36 -070041 MYFILE= drivers/net/mydriver.c
42
43 cd $SRCTREE
44 cp $MYFILE $MYFILE.orig
45 vi $MYFILE # make your change
46 cd ..
47 diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
48
49To create a patch for multiple files, you should unpack a "vanilla",
50or unmodified kernel source tree, and generate a diff against your
51own source tree. For example:
52
Randy Dunlap84da7c02005-06-28 20:45:30 -070053 MYSRC= /devel/linux-2.6
Linus Torvalds1da177e2005-04-16 15:20:36 -070054
Randy Dunlap84da7c02005-06-28 20:45:30 -070055 tar xvfz linux-2.6.12.tar.gz
56 mv linux-2.6.12 linux-2.6.12-vanilla
57 diff -uprN -X linux-2.6.12-vanilla/Documentation/dontdiff \
58 linux-2.6.12-vanilla $MYSRC > /tmp/patch
Linus Torvalds1da177e2005-04-16 15:20:36 -070059
60"dontdiff" is a list of files which are generated by the kernel during
61the build process, and should be ignored in any diff(1)-generated
Randy Dunlap84da7c02005-06-28 20:45:30 -070062patch. The "dontdiff" file is included in the kernel tree in
Randy Dunlap755727b2013-03-08 12:43:35 -0800632.6.12 and later.
Linus Torvalds1da177e2005-04-16 15:20:36 -070064
65Make sure your patch does not include any extra files which do not
66belong in a patch submission. Make sure to review your patch -after-
67generated it with diff(1), to ensure accuracy.
68
69If your changes produce a lot of deltas, you may want to look into
70splitting them into individual patches which modify things in
Randy Dunlap84da7c02005-06-28 20:45:30 -070071logical stages. This will facilitate easier reviewing by other
Linus Torvalds1da177e2005-04-16 15:20:36 -070072kernel developers, very important if you want your patch accepted.
Randy Dunlap84da7c02005-06-28 20:45:30 -070073There are a number of scripts which can aid in this:
Linus Torvalds1da177e2005-04-16 15:20:36 -070074
75Quilt:
76http://savannah.nongnu.org/projects/quilt
77
Linus Torvalds1da177e2005-04-16 15:20:36 -070078Andrew Morton's patch scripts:
FD Cami2223c652008-10-15 22:02:00 -070079http://userweb.kernel.org/~akpm/stuff/patch-scripts.tar.gz
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -080080Instead of these scripts, quilt is the recommended patch management
81tool (see above).
Randy Dunlap84da7c02005-06-28 20:45:30 -070082
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
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -040093The maintainer will thank you if you write your patch description in a
94form which can be easily pulled into Linux's source code management
95system, git, as a "commit log". See #15, below.
96
Linus Torvalds1da177e2005-04-16 15:20:36 -070097If your description starts to get long, that's a sign that you probably
98need to split up your patch. See #3, next.
99
Randy Dunlapd89b1942010-08-09 17:20:21 -0700100When you submit or resubmit a patch or patch series, include the
101complete patch description and justification for it. Don't just
102say that this is version N of the patch (series). Don't expect the
103patch merger to refer back to earlier patch versions or referenced
104URLs to find the patch description and put that into the patch.
105I.e., the patch (series) and its description should be self-contained.
106This benefits both the patch merger(s) and reviewers. Some reviewers
107probably didn't even receive earlier versions of the patch.
108
109If the patch fixes a logged bug entry, refer to that bug entry by
110number and URL.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700111
Geert Uytterhoeven0af52702013-07-31 14:59:38 -0700112If you want to refer to a specific commit, don't just refer to the
113SHA-1 ID of the commit. Please also include the oneline summary of
114the commit, to make it easier for reviewers to know what it is about.
115Example:
116
117 Commit e21d2170f36602ae2708 ("video: remove unnecessary
118 platform_set_drvdata()") removed the unnecessary
119 platform_set_drvdata(), but left the variable "dev" unused,
120 delete it.
121
Linus Torvalds1da177e2005-04-16 15:20:36 -0700122
1233) Separate your changes.
124
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800125Separate _logical changes_ into a single patch file.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700126
127For example, if your changes include both bug fixes and performance
128enhancements for a single driver, separate those changes into two
129or more patches. If your changes include an API update, and a new
130driver which uses that new API, separate those into two patches.
131
132On the other hand, if you make a single change to numerous files,
133group those changes into a single patch. Thus a single logical change
134is contained within a single patch.
135
136If one patch depends on another patch in order for a change to be
137complete, that is OK. Simply note "this patch depends on patch X"
138in your patch description.
139
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800140If you cannot condense your patch set into a smaller set of patches,
141then only post say 15 or so at a time and wait for review and integration.
142
143
Linus Torvalds1da177e2005-04-16 15:20:36 -0700144
Andy Whitcroft0a920b52007-06-01 00:46:48 -07001454) Style check your changes.
146
147Check your patch for basic style violations, details of which can be
148found in Documentation/CodingStyle. Failure to do so simply wastes
Linus Nilssonf56d35e2007-07-21 17:49:06 +0200149the reviewers time and will get your patch rejected, probably
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700150without even being read.
151
152At a minimum you should check your patches with the patch style
Andre Haupta570ab62007-09-11 15:23:47 -0700153checker prior to submission (scripts/checkpatch.pl). You should
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700154be able to justify all violations that remain in your patch.
155
156
157
1585) Select e-mail destination.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700159
160Look through the MAINTAINERS file and the source code, and determine
161if your change applies to a specific subsystem of the kernel, with
Michel Machadoe52d2e12012-04-02 22:10:53 -0400162an assigned maintainer. If so, e-mail that person. The script
163scripts/get_maintainer.pl can be very useful at this step.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700164
165If no maintainer is listed, or the maintainer does not respond, send
166your patch to the primary Linux kernel developer's mailing list,
167linux-kernel@vger.kernel.org. Most kernel developers monitor this
168e-mail list, and can comment on your changes.
169
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800170
171Do not send more than 15 patches at once to the vger mailing lists!!!
172
173
Linus Torvalds1da177e2005-04-16 15:20:36 -0700174Linus Torvalds is the final arbiter of all changes accepted into the
Linus Torvalds99ddcc72007-01-23 14:22:35 -0800175Linux kernel. His e-mail address is <torvalds@linux-foundation.org>.
176He gets a lot of e-mail, so typically you should do your best to -avoid-
177sending him e-mail.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700178
179Patches which are bug fixes, are "obvious" changes, or similarly
180require little discussion should be sent or CC'd to Linus. Patches
181which require discussion or do not have a clear advantage should
182usually be sent first to linux-kernel. Only after the patch is
183discussed should the patch then be submitted to Linus.
184
Linus Torvalds1da177e2005-04-16 15:20:36 -0700185
186
Andy Whitcroft0a920b52007-06-01 00:46:48 -07001876) Select your CC (e-mail carbon copy) list.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700188
189Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
190
191Other kernel developers besides Linus need to be aware of your change,
192so that they may comment on it and offer code review and suggestions.
193linux-kernel is the primary Linux kernel developer mailing list.
194Other mailing lists are available for specific subsystems, such as
195USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the
196MAINTAINERS file for a mailing list that relates specifically to
197your change.
198
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800199Majordomo lists of VGER.KERNEL.ORG at:
200 <http://vger.kernel.org/vger-lists.html>
201
Paul Jackson1caf1f02005-07-31 22:34:48 -0700202If changes affect userland-kernel interfaces, please send
203the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
204a man-pages patch, or at least a notification of the change,
205so that some information makes its way into the manual pages.
206
Michael Brunner8103b5c2009-08-04 00:41:11 +0200207Even if the maintainer did not respond in step #5, make sure to ALWAYS
Linus Torvalds1da177e2005-04-16 15:20:36 -0700208copy the maintainer when you change their code.
209
210For small patches you may want to CC the Trivial Patch Monkey
Markus Heidelberg82d27b22009-06-12 01:02:34 +0200211trivial@kernel.org which collects "trivial" patches. Have a look
212into the MAINTAINERS file for its current manager.
213Trivial patches must qualify for one of the following rules:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700214 Spelling fixes in documentation
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700215 Spelling fixes which could break grep(1)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700216 Warning fixes (cluttering with useless warnings is bad)
217 Compilation fixes (only if they are actually correct)
218 Runtime fixes (only if they actually fix things)
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700219 Removing use of deprecated functions/macros (eg. check_region)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700220 Contact detail and documentation fixes
221 Non-portable code replaced by portable code (even in arch-specific,
222 since people copy, as long as it's trivial)
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700223 Any fix by the author/maintainer of the file (ie. patch monkey
Linus Torvalds1da177e2005-04-16 15:20:36 -0700224 in re-transmission mode)
Randy Dunlap84da7c02005-06-28 20:45:30 -0700225
Linus Torvalds1da177e2005-04-16 15:20:36 -0700226
227
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002287) No MIME, no links, no compression, no attachments. Just plain text.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700229
230Linus and other kernel developers need to be able to read and comment
231on the changes you are submitting. It is important for a kernel
232developer to be able to "quote" your changes, using standard e-mail
233tools, so that they may comment on specific portions of your code.
234
235For this reason, all patches should be submitting e-mail "inline".
236WARNING: Be wary of your editor's word-wrap corrupting your patch,
237if you choose to cut-n-paste your patch.
238
239Do not attach the patch as a MIME attachment, compressed or not.
240Many popular e-mail applications will not always transmit a MIME
241attachment as plain text, making it impossible to comment on your
242code. A MIME attachment also takes Linus a bit more time to process,
243decreasing the likelihood of your MIME-attached change being accepted.
244
245Exception: If your mailer is mangling patches then someone may ask
246you to re-send them using MIME.
247
Michael Opdenacker097091c2008-02-03 18:06:58 +0200248See Documentation/email-clients.txt for hints about configuring
249your e-mail client so that it sends your patches untouched.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700250
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002518) E-mail size.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700252
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700253When sending patches to Linus, always follow step #7.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700254
255Large changes are not appropriate for mailing lists, and some
Randy Dunlap4932be72009-10-01 15:44:06 -0700256maintainers. If your patch, uncompressed, exceeds 300 kB in size,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700257it is preferred that you store your patch on an Internet-accessible
258server, and provide instead a URL (link) pointing to your patch.
259
260
261
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002629) Name your kernel version.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700263
264It is important to note, either in the subject line or in the patch
265description, the kernel version to which this patch applies.
266
267If the patch does not apply cleanly to the latest kernel version,
268Linus will not apply it.
269
270
271
Andy Whitcroft0a920b52007-06-01 00:46:48 -070027210) Don't get discouraged. Re-submit.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700273
274After you have submitted your change, be patient and wait. If Linus
275likes your change and applies it, it will appear in the next version
276of the kernel that he releases.
277
278However, if your change doesn't appear in the next version of the
279kernel, there could be any number of reasons. It's YOUR job to
280narrow down those reasons, correct what was wrong, and submit your
281updated change.
282
283It is quite common for Linus to "drop" your patch without comment.
284That's the nature of the system. If he drops your patch, it could be
285due to
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700286* Your patch did not apply cleanly to the latest kernel version.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700287* Your patch was not sufficiently discussed on linux-kernel.
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700288* A style issue (see section 2).
289* An e-mail formatting issue (re-read this section).
290* A technical problem with your change.
291* He gets tons of e-mail, and yours got lost in the shuffle.
292* You are being annoying.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700293
294When in doubt, solicit comments on linux-kernel mailing list.
295
296
297
Andy Whitcroft0a920b52007-06-01 00:46:48 -070029811) Include PATCH in the subject
Linus Torvalds1da177e2005-04-16 15:20:36 -0700299
300Due to high e-mail traffic to Linus, and to linux-kernel, it is common
301convention to prefix your subject line with [PATCH]. This lets Linus
302and other kernel developers more easily distinguish patches from other
303e-mail discussions.
304
305
306
Andy Whitcroft0a920b52007-06-01 00:46:48 -070030712) Sign your work
Linus Torvalds1da177e2005-04-16 15:20:36 -0700308
309To improve tracking of who did what, especially with patches that can
310percolate to their final resting place in the kernel through several
311layers of maintainers, we've introduced a "sign-off" procedure on
312patches that are being emailed around.
313
314The sign-off is a simple line at the end of the explanation for the
315patch, which certifies that you wrote it or otherwise have the right to
Zac Storerdb12fb82011-08-13 12:34:45 -0700316pass it on as an open-source patch. The rules are pretty simple: if you
Linus Torvalds1da177e2005-04-16 15:20:36 -0700317can certify the below:
318
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700319 Developer's Certificate of Origin 1.1
Linus Torvalds1da177e2005-04-16 15:20:36 -0700320
321 By making a contribution to this project, I certify that:
322
323 (a) The contribution was created in whole or in part by me and I
324 have the right to submit it under the open source license
325 indicated in the file; or
326
327 (b) The contribution is based upon previous work that, to the best
328 of my knowledge, is covered under an appropriate open source
329 license and I have the right under that license to submit that
330 work with modifications, whether created in whole or in part
331 by me, under the same open source license (unless I am
332 permitted to submit under a different license), as indicated
333 in the file; or
334
335 (c) The contribution was provided directly to me by some other
336 person who certified (a), (b) or (c) and I have not modified
337 it.
338
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700339 (d) I understand and agree that this project and the contribution
340 are public and that a record of the contribution (including all
341 personal information I submit with it, including my sign-off) is
342 maintained indefinitely and may be redistributed consistent with
343 this project or the open source license(s) involved.
344
Linus Torvalds1da177e2005-04-16 15:20:36 -0700345then you just add a line saying
346
Alexey Dobriyan9fd55592005-06-25 14:59:34 -0700347 Signed-off-by: Random J Developer <random@developer.example.org>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700348
Greg KHaf45f322006-09-12 20:35:52 -0700349using your real name (sorry, no pseudonyms or anonymous contributions.)
350
Linus Torvalds1da177e2005-04-16 15:20:36 -0700351Some people also put extra tags at the end. They'll just be ignored for
352now, but you can do this to mark internal company procedures or just
353point out some special detail about the sign-off.
354
Willy Tarreauadbd5882008-06-03 00:20:28 +0200355If you are a subsystem or branch maintainer, sometimes you need to slightly
356modify patches you receive in order to merge them, because the code is not
357exactly the same in your tree and the submitters'. If you stick strictly to
358rule (c), you should ask the submitter to rediff, but this is a totally
359counter-productive waste of time and energy. Rule (b) allows you to adjust
360the code, but then it is very impolite to change one submitter's code and
361make him endorse your bugs. To solve this problem, it is recommended that
362you add a line between the last Signed-off-by header and yours, indicating
363the nature of your changes. While there is nothing mandatory about this, it
364seems like prepending the description with your mail and/or name, all
365enclosed in square brackets, is noticeable enough to make it obvious that
366you are responsible for last-minute changes. Example :
367
368 Signed-off-by: Random J Developer <random@developer.example.org>
369 [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
370 Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
371
372This practise is particularly helpful if you maintain a stable branch and
373want at the same time to credit the author, track changes, merge the fix,
374and protect the submitter from complaints. Note that under no circumstances
375can you change the author's identity (the From header), as it is the one
376which appears in the changelog.
377
378Special note to back-porters: It seems to be a common and useful practise
379to insert an indication of the origin of a patch at the top of the commit
380message (just after the subject line) to facilitate tracking. For instance,
381here's what we see in 2.6-stable :
382
383 Date: Tue May 13 19:10:30 2008 +0000
384
385 SCSI: libiscsi regression in 2.6.25: fix nop timer handling
386
387 commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
388
389And here's what appears in 2.4 :
390
391 Date: Tue May 13 22:12:27 2008 +0200
392
393 wireless, airo: waitbusy() won't delay
394
395 [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
396
397Whatever the format, this information provides a valuable help to people
398tracking your trees, and to people trying to trouble-shoot bugs in your
399tree.
400
Linus Torvalds1da177e2005-04-16 15:20:36 -0700401
Jonathan Corbetef402032008-03-28 11:22:38 -060040213) When to use Acked-by: and Cc:
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700403
Andrew Morton0f44cd22007-06-08 13:46:45 -0700404The Signed-off-by: tag indicates that the signer was involved in the
405development of the patch, or that he/she was in the patch's delivery path.
406
407If a person was not directly involved in the preparation or handling of a
408patch but wishes to signify and record their approval of it then they can
409arrange to have an Acked-by: line added to the patch's changelog.
410
411Acked-by: is often used by the maintainer of the affected code when that
412maintainer neither contributed to nor forwarded the patch.
413
414Acked-by: is not as formal as Signed-off-by:. It is a record that the acker
415has at least reviewed the patch and has indicated acceptance. Hence patch
416mergers will sometimes manually convert an acker's "yep, looks good to me"
417into an Acked-by:.
418
419Acked-by: does not necessarily indicate acknowledgement of the entire patch.
420For example, if a patch affects multiple subsystems and has an Acked-by: from
421one subsystem maintainer then this usually indicates acknowledgement of just
422the part which affects that maintainer's code. Judgement should be used here.
Jonathan Corbetef402032008-03-28 11:22:38 -0600423When in doubt people should refer to the original discussion in the mailing
Andrew Morton0f44cd22007-06-08 13:46:45 -0700424list archives.
425
Jonathan Corbetef402032008-03-28 11:22:38 -0600426If a person has had the opportunity to comment on a patch, but has not
427provided such comments, you may optionally add a "Cc:" tag to the patch.
428This is the only tag which might be added without an explicit action by the
429person it names. This tag documents that potentially interested parties
430have been included in the discussion
Andrew Morton0f44cd22007-06-08 13:46:45 -0700431
Jonathan Corbetef402032008-03-28 11:22:38 -0600432
Mugunthan V N8543ae12013-04-29 16:18:17 -070043314) Using Reported-by:, Tested-by:, Reviewed-by: and Suggested-by:
Jonathan Corbetbbb0a4242009-01-16 09:49:50 -0700434
435If this patch fixes a problem reported by somebody else, consider adding a
436Reported-by: tag to credit the reporter for their contribution. Please
437note that this tag should not be added without the reporter's permission,
438especially if the problem was not reported in a public forum. That said,
439if we diligently credit our bug reporters, they will, hopefully, be
440inspired to help us again in the future.
Jonathan Corbetef402032008-03-28 11:22:38 -0600441
442A Tested-by: tag indicates that the patch has been successfully tested (in
443some environment) by the person named. This tag informs maintainers that
444some testing has been performed, provides a means to locate testers for
445future patches, and ensures credit for the testers.
446
447Reviewed-by:, instead, indicates that the patch has been reviewed and found
448acceptable according to the Reviewer's Statement:
449
450 Reviewer's statement of oversight
451
452 By offering my Reviewed-by: tag, I state that:
453
454 (a) I have carried out a technical review of this patch to
455 evaluate its appropriateness and readiness for inclusion into
456 the mainline kernel.
457
458 (b) Any problems, concerns, or questions relating to the patch
459 have been communicated back to the submitter. I am satisfied
460 with the submitter's response to my comments.
461
462 (c) While there may be things that could be improved with this
463 submission, I believe that it is, at this time, (1) a
464 worthwhile modification to the kernel, and (2) free of known
465 issues which would argue against its inclusion.
466
467 (d) While I have reviewed the patch and believe it to be sound, I
468 do not (unless explicitly stated elsewhere) make any
469 warranties or guarantees that it will achieve its stated
470 purpose or function properly in any given situation.
471
472A Reviewed-by tag is a statement of opinion that the patch is an
473appropriate modification of the kernel without any remaining serious
474technical issues. Any interested reviewer (who has done the work) can
475offer a Reviewed-by tag for a patch. This tag serves to give credit to
476reviewers and to inform maintainers of the degree of review which has been
477done on the patch. Reviewed-by: tags, when supplied by reviewers known to
478understand the subject area and to perform thorough reviews, will normally
Pavel Machek5801da12009-06-04 16:26:50 +0200479increase the likelihood of your patch getting into the kernel.
Jonathan Corbetef402032008-03-28 11:22:38 -0600480
Mugunthan V N8543ae12013-04-29 16:18:17 -0700481A Suggested-by: tag indicates that the patch idea is suggested by the person
482named and ensures credit to the person for the idea. Please note that this
483tag should not be added without the reporter's permission, especially if the
484idea was not posted in a public forum. That said, if we diligently credit our
485idea reporters, they will, hopefully, be inspired to help us again in the
486future.
487
Jonathan Corbetef402032008-03-28 11:22:38 -0600488
48915) The canonical patch format
Randy Dunlap84da7c02005-06-28 20:45:30 -0700490
Paul Jackson75f84262005-10-02 18:01:42 -0700491The canonical patch subject line is:
492
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700493 Subject: [PATCH 001/123] subsystem: summary phrase
Paul Jackson75f84262005-10-02 18:01:42 -0700494
495The canonical patch message body contains the following:
496
497 - A "from" line specifying the patch author.
498
499 - An empty line.
500
501 - The body of the explanation, which will be copied to the
502 permanent changelog to describe this patch.
503
504 - The "Signed-off-by:" lines, described above, which will
505 also go in the changelog.
506
507 - A marker line containing simply "---".
508
509 - Any additional comments not suitable for the changelog.
510
511 - The actual patch (diff output).
512
513The Subject line format makes it very easy to sort the emails
514alphabetically by subject line - pretty much any email reader will
515support that - since because the sequence number is zero-padded,
516the numerical and alphabetic sort is the same.
517
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700518The "subsystem" in the email's Subject should identify which
519area or subsystem of the kernel is being patched.
520
521The "summary phrase" in the email's Subject should concisely
522describe the patch which that email contains. The "summary
523phrase" should not be a filename. Do not use the same "summary
Randy Dunlap66effdc2007-05-09 02:33:42 -0700524phrase" for every patch in a whole patch series (where a "patch
525series" is an ordered sequence of multiple, related patches).
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700526
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400527Bear in mind that the "summary phrase" of your email becomes a
528globally-unique identifier for that patch. It propagates all the way
529into the git changelog. The "summary phrase" may later be used in
530developer discussions which refer to the patch. People will want to
531google for the "summary phrase" to read discussion regarding that
532patch. It will also be the only thing that people may quickly see
533when, two or three months later, they are going through perhaps
534thousands of patches using tools such as "gitk" or "git log
535--oneline".
536
537For these reasons, the "summary" must be no more than 70-75
538characters, and it must describe both what the patch changes, as well
539as why the patch might be necessary. It is challenging to be both
540succinct and descriptive, but that is what a well-written summary
541should do.
542
543The "summary phrase" may be prefixed by tags enclosed in square
544brackets: "Subject: [PATCH tag] <summary phrase>". The tags are not
545considered part of the summary phrase, but describe how the patch
546should be treated. Common tags might include a version descriptor if
547the multiple versions of the patch have been sent out in response to
548comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
549comments. If there are four patches in a patch series the individual
550patches may be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures
551that developers understand the order in which the patches should be
552applied and that they have reviewed or applied all of the patches in
553the patch series.
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700554
555A couple of example Subjects:
556
557 Subject: [patch 2/5] ext2: improve scalability of bitmap searching
558 Subject: [PATCHv2 001/207] x86: fix eflags tracking
Paul Jackson75f84262005-10-02 18:01:42 -0700559
560The "from" line must be the very first line in the message body,
561and has the form:
562
563 From: Original Author <author@example.com>
564
565The "from" line specifies who will be credited as the author of the
566patch in the permanent changelog. If the "from" line is missing,
567then the "From:" line from the email header will be used to determine
568the patch author in the changelog.
569
570The explanation body will be committed to the permanent source
571changelog, so should make sense to a competent reader who has long
572since forgotten the immediate details of the discussion that might
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400573have led to this patch. Including symptoms of the failure which the
574patch addresses (kernel log messages, oops messages, etc.) is
575especially useful for people who might be searching the commit logs
576looking for the applicable patch. If a patch fixes a compile failure,
577it may not be necessary to include _all_ of the compile failures; just
578enough that it is likely that someone searching for the patch can find
579it. As in the "summary phrase", it is important to be both succinct as
580well as descriptive.
Paul Jackson75f84262005-10-02 18:01:42 -0700581
582The "---" marker line serves the essential purpose of marking for patch
583handling tools where the changelog message ends.
584
585One good use for the additional comments after the "---" marker is for
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400586a diffstat, to show what files have changed, and the number of
587inserted and deleted lines per file. A diffstat is especially useful
588on bigger patches. Other comments relevant only to the moment or the
589maintainer, not suitable for the permanent changelog, should also go
590here. A good example of such comments might be "patch changelogs"
591which describe what has changed between the v1 and v2 version of the
592patch.
593
594If you are going to include a diffstat after the "---" marker, please
595use diffstat options "-p 1 -w 70" so that filenames are listed from
596the top of the kernel source tree and don't use too much horizontal
597space (easily fit in 80 columns, maybe with some indentation).
Paul Jackson75f84262005-10-02 18:01:42 -0700598
599See more details on the proper patch format in the following
600references.
601
602
Randy Dunlap14863612008-07-27 20:44:24 -070060316) Sending "git pull" requests (from Linus emails)
Randy Dunlap84da7c02005-06-28 20:45:30 -0700604
Randy Dunlap14863612008-07-27 20:44:24 -0700605Please write the git repo address and branch name alone on the same line
606so that I can't even by mistake pull from the wrong branch, and so
607that a triple-click just selects the whole thing.
608
609So the proper format is something along the lines of:
610
611 "Please pull from
612
613 git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
614
615 to get these changes:"
616
617so that I don't have to hunt-and-peck for the address and inevitably
618get it wrong (actually, I've only gotten it wrong a few times, and
619checking against the diffstat tells me when I get it wrong, but I'm
620just a lot more comfortable when I don't have to "look for" the right
621thing to pull, and double-check that I have the right branch-name).
622
623
624Please use "git diff -M --stat --summary" to generate the diffstat:
625the -M enables rename detection, and the summary enables a summary of
626new/deleted or renamed files.
627
628With rename detection, the statistics are rather different [...]
629because git will notice that a fair number of the changes are renames.
Randy Dunlap84da7c02005-06-28 20:45:30 -0700630
Linus Torvalds1da177e2005-04-16 15:20:36 -0700631-----------------------------------
632SECTION 2 - HINTS, TIPS, AND TRICKS
633-----------------------------------
634
635This section lists many of the common "rules" associated with code
636submitted to the kernel. There are always exceptions... but you must
637have a really good reason for doing so. You could probably call this
638section Linus Computer Science 101.
639
640
641
6421) Read Documentation/CodingStyle
643
644Nuff said. If your code deviates too much from this, it is likely
645to be rejected without further review, and without comment.
646
Keiichi Kii5ab3bd52007-10-26 15:51:44 +0900647One significant exception is when moving code from one file to
648another -- in this case you should not modify the moved code at all in
Andy Whitcroftde7d4f02007-07-15 23:37:22 -0700649the same patch which moves it. This clearly delineates the act of
650moving the code and your changes. This greatly aids review of the
651actual differences and allows tools to better track the history of
652the code itself.
653
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700654Check your patches with the patch style checker prior to submission
Andy Whitcroftde7d4f02007-07-15 23:37:22 -0700655(scripts/checkpatch.pl). The style checker should be viewed as
656a guide not as the final word. If your code looks better with
657a violation then its probably best left alone.
658
659The checker reports at three levels:
660 - ERROR: things that are very likely to be wrong
661 - WARNING: things requiring careful review
662 - CHECK: things requiring thought
663
664You should be able to justify all violations that remain in your
665patch.
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700666
Linus Torvalds1da177e2005-04-16 15:20:36 -0700667
668
6692) #ifdefs are ugly
670
671Code cluttered with ifdefs is difficult to read and maintain. Don't do
672it. Instead, put your ifdefs in a header, and conditionally define
673'static inline' functions, or macros, which are used in the code.
674Let the compiler optimize away the "no-op" case.
675
676Simple example, of poor code:
677
678 dev = alloc_etherdev (sizeof(struct funky_private));
679 if (!dev)
680 return -ENODEV;
681 #ifdef CONFIG_NET_FUNKINESS
682 init_funky_net(dev);
683 #endif
684
685Cleaned-up example:
686
687(in header)
688 #ifndef CONFIG_NET_FUNKINESS
689 static inline void init_funky_net (struct net_device *d) {}
690 #endif
691
692(in the code itself)
693 dev = alloc_etherdev (sizeof(struct funky_private));
694 if (!dev)
695 return -ENODEV;
696 init_funky_net(dev);
697
698
699
7003) 'static inline' is better than a macro
701
702Static inline functions are greatly preferred over macros.
703They provide type safety, have no length limitations, no formatting
704limitations, and under gcc they are as cheap as macros.
705
706Macros should only be used for cases where a static inline is clearly
Jim Meyeringf2b2ea62008-04-02 13:04:46 -0700707suboptimal [there are a few, isolated cases of this in fast paths],
Linus Torvalds1da177e2005-04-16 15:20:36 -0700708or where it is impossible to use a static inline function [such as
709string-izing].
710
711'static inline' is preferred over 'static __inline__', 'extern inline',
712and 'extern __inline__'.
713
714
715
7164) Don't over-design.
717
718Don't try to anticipate nebulous future cases which may or may not
Randy Dunlap84da7c02005-06-28 20:45:30 -0700719be useful: "Make it as simple as you can, and no simpler."
Linus Torvalds1da177e2005-04-16 15:20:36 -0700720
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800721
722
723----------------------
724SECTION 3 - REFERENCES
725----------------------
726
727Andrew Morton, "The perfect patch" (tpp).
FD Cami2223c652008-10-15 22:02:00 -0700728 <http://userweb.kernel.org/~akpm/stuff/tpp.txt>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800729
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700730Jeff Garzik, "Linux kernel patch submission format".
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800731 <http://linux.yyz.us/patch-format.html>
732
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700733Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
Vikram Narayananf5039932011-05-23 12:01:25 -0700734 <http://www.kroah.com/log/linux/maintainer.html>
735 <http://www.kroah.com/log/linux/maintainer-02.html>
736 <http://www.kroah.com/log/linux/maintainer-03.html>
737 <http://www.kroah.com/log/linux/maintainer-04.html>
738 <http://www.kroah.com/log/linux/maintainer-05.html>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800739
Randy Dunlapbc7455f2006-07-30 03:03:45 -0700740NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800741 <http://marc.theaimsgroup.com/?l=linux-kernel&m=112112749912944&w=2>
742
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700743Kernel Documentation/CodingStyle:
Qi Yong4db29c12007-06-12 13:06:49 +0800744 <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800745
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700746Linus Torvalds's mail on the canonical patch format:
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800747 <http://lkml.org/lkml/2005/4/7/183>
Andi Kleen95367272008-10-15 22:02:02 -0700748
749Andi Kleen, "On submitting kernel patches"
Lucas De Marchi25985ed2011-03-30 22:57:33 -0300750 Some strategies to get difficult or controversial changes in.
Andi Kleen95367272008-10-15 22:02:02 -0700751 http://halobates.de/on-submitting-patches.pdf
752
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800753--