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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'o2ae19aca2009-04-16 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
112
1133) Separate your changes.
114
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800115Separate _logical changes_ into a single patch file.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700116
117For example, if your changes include both bug fixes and performance
118enhancements for a single driver, separate those changes into two
119or more patches. If your changes include an API update, and a new
120driver which uses that new API, separate those into two patches.
121
122On the other hand, if you make a single change to numerous files,
123group those changes into a single patch. Thus a single logical change
124is contained within a single patch.
125
126If one patch depends on another patch in order for a change to be
127complete, that is OK. Simply note "this patch depends on patch X"
128in your patch description.
129
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800130If you cannot condense your patch set into a smaller set of patches,
131then only post say 15 or so at a time and wait for review and integration.
132
133
Jacob Kellera5e309f2014-06-06 14:36:39 -0700134If your patch fixes a bug in a specific commit, e.g. you found an issue using
135git-bisect, please use the 'Fixes:' tag with the first 12 characters of the
136SHA-1 ID, and the one line summary.
137Example:
138
139 Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
140
141The following git-config settings can be used to add a pretty format for
142outputting the above style in the git log or git show commands
143
144 [core]
145 abbrev = 12
146 [pretty]
147 fixes = Fixes: %h (\"%s\")
Linus Torvalds1da177e2005-04-16 15:20:36 -0700148
Andy Whitcroft0a920b52007-06-01 00:46:48 -07001494) Style check your changes.
150
151Check your patch for basic style violations, details of which can be
152found in Documentation/CodingStyle. Failure to do so simply wastes
Linus Nilssonf56d35e2007-07-21 17:49:06 +0200153the reviewers time and will get your patch rejected, probably
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700154without even being read.
155
156At a minimum you should check your patches with the patch style
Andre Haupta570ab62007-09-11 15:23:47 -0700157checker prior to submission (scripts/checkpatch.pl). You should
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700158be able to justify all violations that remain in your patch.
159
160
161
1625) Select e-mail destination.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700163
164Look through the MAINTAINERS file and the source code, and determine
165if your change applies to a specific subsystem of the kernel, with
Michel Machadoe52d2e12012-04-02 22:10:53 -0400166an assigned maintainer. If so, e-mail that person. The script
167scripts/get_maintainer.pl can be very useful at this step.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700168
169If no maintainer is listed, or the maintainer does not respond, send
170your patch to the primary Linux kernel developer's mailing list,
171linux-kernel@vger.kernel.org. Most kernel developers monitor this
172e-mail list, and can comment on your changes.
173
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800174
175Do not send more than 15 patches at once to the vger mailing lists!!!
176
177
Linus Torvalds1da177e2005-04-16 15:20:36 -0700178Linus Torvalds is the final arbiter of all changes accepted into the
Linus Torvalds99ddcc72007-01-23 14:22:35 -0800179Linux kernel. His e-mail address is <torvalds@linux-foundation.org>.
180He gets a lot of e-mail, so typically you should do your best to -avoid-
181sending him e-mail.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700182
183Patches which are bug fixes, are "obvious" changes, or similarly
184require little discussion should be sent or CC'd to Linus. Patches
185which require discussion or do not have a clear advantage should
186usually be sent first to linux-kernel. Only after the patch is
187discussed should the patch then be submitted to Linus.
188
Linus Torvalds1da177e2005-04-16 15:20:36 -0700189
190
Andy Whitcroft0a920b52007-06-01 00:46:48 -07001916) Select your CC (e-mail carbon copy) list.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700192
193Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
194
195Other kernel developers besides Linus need to be aware of your change,
196so that they may comment on it and offer code review and suggestions.
197linux-kernel is the primary Linux kernel developer mailing list.
198Other mailing lists are available for specific subsystems, such as
199USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the
200MAINTAINERS file for a mailing list that relates specifically to
201your change.
202
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800203Majordomo lists of VGER.KERNEL.ORG at:
204 <http://vger.kernel.org/vger-lists.html>
205
Paul Jackson1caf1f02005-07-31 22:34:48 -0700206If changes affect userland-kernel interfaces, please send
207the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
208a man-pages patch, or at least a notification of the change,
209so that some information makes its way into the manual pages.
210
Michael Brunner8103b5c2009-08-04 00:41:11 +0200211Even if the maintainer did not respond in step #5, make sure to ALWAYS
Linus Torvalds1da177e2005-04-16 15:20:36 -0700212copy the maintainer when you change their code.
213
214For small patches you may want to CC the Trivial Patch Monkey
Markus Heidelberg82d27b22009-06-12 01:02:34 +0200215trivial@kernel.org which collects "trivial" patches. Have a look
216into the MAINTAINERS file for its current manager.
217Trivial patches must qualify for one of the following rules:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700218 Spelling fixes in documentation
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700219 Spelling fixes which could break grep(1)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700220 Warning fixes (cluttering with useless warnings is bad)
221 Compilation fixes (only if they are actually correct)
222 Runtime fixes (only if they actually fix things)
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700223 Removing use of deprecated functions/macros (eg. check_region)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700224 Contact detail and documentation fixes
225 Non-portable code replaced by portable code (even in arch-specific,
226 since people copy, as long as it's trivial)
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700227 Any fix by the author/maintainer of the file (ie. patch monkey
Linus Torvalds1da177e2005-04-16 15:20:36 -0700228 in re-transmission mode)
Randy Dunlap84da7c02005-06-28 20:45:30 -0700229
Linus Torvalds1da177e2005-04-16 15:20:36 -0700230
231
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002327) No MIME, no links, no compression, no attachments. Just plain text.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700233
234Linus and other kernel developers need to be able to read and comment
235on the changes you are submitting. It is important for a kernel
236developer to be able to "quote" your changes, using standard e-mail
237tools, so that they may comment on specific portions of your code.
238
239For this reason, all patches should be submitting e-mail "inline".
240WARNING: Be wary of your editor's word-wrap corrupting your patch,
241if you choose to cut-n-paste your patch.
242
243Do not attach the patch as a MIME attachment, compressed or not.
244Many popular e-mail applications will not always transmit a MIME
245attachment as plain text, making it impossible to comment on your
246code. A MIME attachment also takes Linus a bit more time to process,
247decreasing the likelihood of your MIME-attached change being accepted.
248
249Exception: If your mailer is mangling patches then someone may ask
250you to re-send them using MIME.
251
Michael Opdenacker097091c2008-02-03 18:06:58 +0200252See Documentation/email-clients.txt for hints about configuring
253your e-mail client so that it sends your patches untouched.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700254
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002558) E-mail size.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700256
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700257When sending patches to Linus, always follow step #7.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700258
259Large changes are not appropriate for mailing lists, and some
Randy Dunlap4932be72009-10-01 15:44:06 -0700260maintainers. If your patch, uncompressed, exceeds 300 kB in size,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700261it is preferred that you store your patch on an Internet-accessible
262server, and provide instead a URL (link) pointing to your patch.
263
264
265
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002669) Name your kernel version.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700267
268It is important to note, either in the subject line or in the patch
269description, the kernel version to which this patch applies.
270
271If the patch does not apply cleanly to the latest kernel version,
272Linus will not apply it.
273
274
275
Andy Whitcroft0a920b52007-06-01 00:46:48 -070027610) Don't get discouraged. Re-submit.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700277
278After you have submitted your change, be patient and wait. If Linus
279likes your change and applies it, it will appear in the next version
280of the kernel that he releases.
281
282However, if your change doesn't appear in the next version of the
283kernel, there could be any number of reasons. It's YOUR job to
284narrow down those reasons, correct what was wrong, and submit your
285updated change.
286
287It is quite common for Linus to "drop" your patch without comment.
288That's the nature of the system. If he drops your patch, it could be
289due to
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700290* Your patch did not apply cleanly to the latest kernel version.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700291* Your patch was not sufficiently discussed on linux-kernel.
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700292* A style issue (see section 2).
293* An e-mail formatting issue (re-read this section).
294* A technical problem with your change.
295* He gets tons of e-mail, and yours got lost in the shuffle.
296* You are being annoying.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700297
298When in doubt, solicit comments on linux-kernel mailing list.
299
300
301
Andy Whitcroft0a920b52007-06-01 00:46:48 -070030211) Include PATCH in the subject
Linus Torvalds1da177e2005-04-16 15:20:36 -0700303
304Due to high e-mail traffic to Linus, and to linux-kernel, it is common
305convention to prefix your subject line with [PATCH]. This lets Linus
306and other kernel developers more easily distinguish patches from other
307e-mail discussions.
308
309
310
Andy Whitcroft0a920b52007-06-01 00:46:48 -070031112) Sign your work
Linus Torvalds1da177e2005-04-16 15:20:36 -0700312
313To improve tracking of who did what, especially with patches that can
314percolate to their final resting place in the kernel through several
315layers of maintainers, we've introduced a "sign-off" procedure on
316patches that are being emailed around.
317
318The sign-off is a simple line at the end of the explanation for the
319patch, which certifies that you wrote it or otherwise have the right to
Zac Storerdb12fb82011-08-13 12:34:45 -0700320pass it on as an open-source patch. The rules are pretty simple: if you
Linus Torvalds1da177e2005-04-16 15:20:36 -0700321can certify the below:
322
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700323 Developer's Certificate of Origin 1.1
Linus Torvalds1da177e2005-04-16 15:20:36 -0700324
325 By making a contribution to this project, I certify that:
326
327 (a) The contribution was created in whole or in part by me and I
328 have the right to submit it under the open source license
329 indicated in the file; or
330
331 (b) The contribution is based upon previous work that, to the best
332 of my knowledge, is covered under an appropriate open source
333 license and I have the right under that license to submit that
334 work with modifications, whether created in whole or in part
335 by me, under the same open source license (unless I am
336 permitted to submit under a different license), as indicated
337 in the file; or
338
339 (c) The contribution was provided directly to me by some other
340 person who certified (a), (b) or (c) and I have not modified
341 it.
342
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700343 (d) I understand and agree that this project and the contribution
344 are public and that a record of the contribution (including all
345 personal information I submit with it, including my sign-off) is
346 maintained indefinitely and may be redistributed consistent with
347 this project or the open source license(s) involved.
348
Linus Torvalds1da177e2005-04-16 15:20:36 -0700349then you just add a line saying
350
Alexey Dobriyan9fd55592005-06-25 14:59:34 -0700351 Signed-off-by: Random J Developer <random@developer.example.org>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700352
Greg KHaf45f322006-09-12 20:35:52 -0700353using your real name (sorry, no pseudonyms or anonymous contributions.)
354
Linus Torvalds1da177e2005-04-16 15:20:36 -0700355Some people also put extra tags at the end. They'll just be ignored for
356now, but you can do this to mark internal company procedures or just
357point out some special detail about the sign-off.
358
Willy Tarreauadbd5882008-06-03 00:20:28 +0200359If you are a subsystem or branch maintainer, sometimes you need to slightly
360modify patches you receive in order to merge them, because the code is not
361exactly the same in your tree and the submitters'. If you stick strictly to
362rule (c), you should ask the submitter to rediff, but this is a totally
363counter-productive waste of time and energy. Rule (b) allows you to adjust
364the code, but then it is very impolite to change one submitter's code and
365make him endorse your bugs. To solve this problem, it is recommended that
366you add a line between the last Signed-off-by header and yours, indicating
367the nature of your changes. While there is nothing mandatory about this, it
368seems like prepending the description with your mail and/or name, all
369enclosed in square brackets, is noticeable enough to make it obvious that
370you are responsible for last-minute changes. Example :
371
372 Signed-off-by: Random J Developer <random@developer.example.org>
373 [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
374 Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
375
376This practise is particularly helpful if you maintain a stable branch and
377want at the same time to credit the author, track changes, merge the fix,
378and protect the submitter from complaints. Note that under no circumstances
379can you change the author's identity (the From header), as it is the one
380which appears in the changelog.
381
382Special note to back-porters: It seems to be a common and useful practise
383to insert an indication of the origin of a patch at the top of the commit
384message (just after the subject line) to facilitate tracking. For instance,
385here's what we see in 2.6-stable :
386
387 Date: Tue May 13 19:10:30 2008 +0000
388
389 SCSI: libiscsi regression in 2.6.25: fix nop timer handling
390
391 commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
392
393And here's what appears in 2.4 :
394
395 Date: Tue May 13 22:12:27 2008 +0200
396
397 wireless, airo: waitbusy() won't delay
398
399 [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
400
401Whatever the format, this information provides a valuable help to people
402tracking your trees, and to people trying to trouble-shoot bugs in your
403tree.
404
Linus Torvalds1da177e2005-04-16 15:20:36 -0700405
Jonathan Corbetef402032008-03-28 11:22:38 -060040613) When to use Acked-by: and Cc:
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700407
Andrew Morton0f44cd22007-06-08 13:46:45 -0700408The Signed-off-by: tag indicates that the signer was involved in the
409development of the patch, or that he/she was in the patch's delivery path.
410
411If a person was not directly involved in the preparation or handling of a
412patch but wishes to signify and record their approval of it then they can
413arrange to have an Acked-by: line added to the patch's changelog.
414
415Acked-by: is often used by the maintainer of the affected code when that
416maintainer neither contributed to nor forwarded the patch.
417
418Acked-by: is not as formal as Signed-off-by:. It is a record that the acker
419has at least reviewed the patch and has indicated acceptance. Hence patch
420mergers will sometimes manually convert an acker's "yep, looks good to me"
421into an Acked-by:.
422
423Acked-by: does not necessarily indicate acknowledgement of the entire patch.
424For example, if a patch affects multiple subsystems and has an Acked-by: from
425one subsystem maintainer then this usually indicates acknowledgement of just
426the part which affects that maintainer's code. Judgement should be used here.
Jonathan Corbetef402032008-03-28 11:22:38 -0600427When in doubt people should refer to the original discussion in the mailing
Andrew Morton0f44cd22007-06-08 13:46:45 -0700428list archives.
429
Jonathan Corbetef402032008-03-28 11:22:38 -0600430If a person has had the opportunity to comment on a patch, but has not
431provided such comments, you may optionally add a "Cc:" tag to the patch.
432This is the only tag which might be added without an explicit action by the
433person it names. This tag documents that potentially interested parties
434have been included in the discussion
Andrew Morton0f44cd22007-06-08 13:46:45 -0700435
Jonathan Corbetef402032008-03-28 11:22:38 -0600436
Jacob Kellera5e309f2014-06-06 14:36:39 -070043714) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
Jonathan Corbetbbb0a4242009-01-16 09:49:50 -0700438
439If this patch fixes a problem reported by somebody else, consider adding a
440Reported-by: tag to credit the reporter for their contribution. Please
441note that this tag should not be added without the reporter's permission,
442especially if the problem was not reported in a public forum. That said,
443if we diligently credit our bug reporters, they will, hopefully, be
444inspired to help us again in the future.
Jonathan Corbetef402032008-03-28 11:22:38 -0600445
446A Tested-by: tag indicates that the patch has been successfully tested (in
447some environment) by the person named. This tag informs maintainers that
448some testing has been performed, provides a means to locate testers for
449future patches, and ensures credit for the testers.
450
451Reviewed-by:, instead, indicates that the patch has been reviewed and found
452acceptable according to the Reviewer's Statement:
453
454 Reviewer's statement of oversight
455
456 By offering my Reviewed-by: tag, I state that:
457
458 (a) I have carried out a technical review of this patch to
459 evaluate its appropriateness and readiness for inclusion into
460 the mainline kernel.
461
462 (b) Any problems, concerns, or questions relating to the patch
463 have been communicated back to the submitter. I am satisfied
464 with the submitter's response to my comments.
465
466 (c) While there may be things that could be improved with this
467 submission, I believe that it is, at this time, (1) a
468 worthwhile modification to the kernel, and (2) free of known
469 issues which would argue against its inclusion.
470
471 (d) While I have reviewed the patch and believe it to be sound, I
472 do not (unless explicitly stated elsewhere) make any
473 warranties or guarantees that it will achieve its stated
474 purpose or function properly in any given situation.
475
476A Reviewed-by tag is a statement of opinion that the patch is an
477appropriate modification of the kernel without any remaining serious
478technical issues. Any interested reviewer (who has done the work) can
479offer a Reviewed-by tag for a patch. This tag serves to give credit to
480reviewers and to inform maintainers of the degree of review which has been
481done on the patch. Reviewed-by: tags, when supplied by reviewers known to
482understand the subject area and to perform thorough reviews, will normally
Pavel Machek5801da12009-06-04 16:26:50 +0200483increase the likelihood of your patch getting into the kernel.
Jonathan Corbetef402032008-03-28 11:22:38 -0600484
Mugunthan V N8543ae12013-04-29 16:18:17 -0700485A Suggested-by: tag indicates that the patch idea is suggested by the person
486named and ensures credit to the person for the idea. Please note that this
487tag should not be added without the reporter's permission, especially if the
488idea was not posted in a public forum. That said, if we diligently credit our
489idea reporters, they will, hopefully, be inspired to help us again in the
490future.
491
Jacob Kellera5e309f2014-06-06 14:36:39 -0700492A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
493is used to make it easy to determine where a bug originated, which can help
494review a bug fix. This tag also assists the stable kernel team in determining
495which stable kernel versions should receive your fix. This is the preferred
496method for indicating a bug fixed by the patch. See #2 above for more details.
497
Jonathan Corbetef402032008-03-28 11:22:38 -0600498
49915) The canonical patch format
Randy Dunlap84da7c02005-06-28 20:45:30 -0700500
Paul Jackson75f84262005-10-02 18:01:42 -0700501The canonical patch subject line is:
502
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700503 Subject: [PATCH 001/123] subsystem: summary phrase
Paul Jackson75f84262005-10-02 18:01:42 -0700504
505The canonical patch message body contains the following:
506
507 - A "from" line specifying the patch author.
508
509 - An empty line.
510
511 - The body of the explanation, which will be copied to the
512 permanent changelog to describe this patch.
513
514 - The "Signed-off-by:" lines, described above, which will
515 also go in the changelog.
516
517 - A marker line containing simply "---".
518
519 - Any additional comments not suitable for the changelog.
520
521 - The actual patch (diff output).
522
523The Subject line format makes it very easy to sort the emails
524alphabetically by subject line - pretty much any email reader will
525support that - since because the sequence number is zero-padded,
526the numerical and alphabetic sort is the same.
527
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700528The "subsystem" in the email's Subject should identify which
529area or subsystem of the kernel is being patched.
530
531The "summary phrase" in the email's Subject should concisely
532describe the patch which that email contains. The "summary
533phrase" should not be a filename. Do not use the same "summary
Randy Dunlap66effdc2007-05-09 02:33:42 -0700534phrase" for every patch in a whole patch series (where a "patch
535series" is an ordered sequence of multiple, related patches).
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700536
Theodore Ts'o2ae19aca2009-04-16 07:44:45 -0400537Bear in mind that the "summary phrase" of your email becomes a
538globally-unique identifier for that patch. It propagates all the way
539into the git changelog. The "summary phrase" may later be used in
540developer discussions which refer to the patch. People will want to
541google for the "summary phrase" to read discussion regarding that
542patch. It will also be the only thing that people may quickly see
543when, two or three months later, they are going through perhaps
544thousands of patches using tools such as "gitk" or "git log
545--oneline".
546
547For these reasons, the "summary" must be no more than 70-75
548characters, and it must describe both what the patch changes, as well
549as why the patch might be necessary. It is challenging to be both
550succinct and descriptive, but that is what a well-written summary
551should do.
552
553The "summary phrase" may be prefixed by tags enclosed in square
554brackets: "Subject: [PATCH tag] <summary phrase>". The tags are not
555considered part of the summary phrase, but describe how the patch
556should be treated. Common tags might include a version descriptor if
557the multiple versions of the patch have been sent out in response to
558comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
559comments. If there are four patches in a patch series the individual
560patches may be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures
561that developers understand the order in which the patches should be
562applied and that they have reviewed or applied all of the patches in
563the patch series.
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700564
565A couple of example Subjects:
566
567 Subject: [patch 2/5] ext2: improve scalability of bitmap searching
568 Subject: [PATCHv2 001/207] x86: fix eflags tracking
Paul Jackson75f84262005-10-02 18:01:42 -0700569
570The "from" line must be the very first line in the message body,
571and has the form:
572
573 From: Original Author <author@example.com>
574
575The "from" line specifies who will be credited as the author of the
576patch in the permanent changelog. If the "from" line is missing,
577then the "From:" line from the email header will be used to determine
578the patch author in the changelog.
579
580The explanation body will be committed to the permanent source
581changelog, so should make sense to a competent reader who has long
582since forgotten the immediate details of the discussion that might
Theodore Ts'o2ae19aca2009-04-16 07:44:45 -0400583have led to this patch. Including symptoms of the failure which the
584patch addresses (kernel log messages, oops messages, etc.) is
585especially useful for people who might be searching the commit logs
586looking for the applicable patch. If a patch fixes a compile failure,
587it may not be necessary to include _all_ of the compile failures; just
588enough that it is likely that someone searching for the patch can find
589it. As in the "summary phrase", it is important to be both succinct as
590well as descriptive.
Paul Jackson75f84262005-10-02 18:01:42 -0700591
592The "---" marker line serves the essential purpose of marking for patch
593handling tools where the changelog message ends.
594
595One good use for the additional comments after the "---" marker is for
Theodore Ts'o2ae19aca2009-04-16 07:44:45 -0400596a diffstat, to show what files have changed, and the number of
597inserted and deleted lines per file. A diffstat is especially useful
598on bigger patches. Other comments relevant only to the moment or the
599maintainer, not suitable for the permanent changelog, should also go
600here. A good example of such comments might be "patch changelogs"
601which describe what has changed between the v1 and v2 version of the
602patch.
603
604If you are going to include a diffstat after the "---" marker, please
605use diffstat options "-p 1 -w 70" so that filenames are listed from
606the top of the kernel source tree and don't use too much horizontal
607space (easily fit in 80 columns, maybe with some indentation).
Paul Jackson75f84262005-10-02 18:01:42 -0700608
609See more details on the proper patch format in the following
610references.
611
612
Randy Dunlap14863612008-07-27 20:44:24 -070061316) Sending "git pull" requests (from Linus emails)
Randy Dunlap84da7c02005-06-28 20:45:30 -0700614
Randy Dunlap14863612008-07-27 20:44:24 -0700615Please write the git repo address and branch name alone on the same line
616so that I can't even by mistake pull from the wrong branch, and so
617that a triple-click just selects the whole thing.
618
619So the proper format is something along the lines of:
620
621 "Please pull from
622
623 git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
624
625 to get these changes:"
626
627so that I don't have to hunt-and-peck for the address and inevitably
628get it wrong (actually, I've only gotten it wrong a few times, and
629checking against the diffstat tells me when I get it wrong, but I'm
630just a lot more comfortable when I don't have to "look for" the right
631thing to pull, and double-check that I have the right branch-name).
632
633
634Please use "git diff -M --stat --summary" to generate the diffstat:
635the -M enables rename detection, and the summary enables a summary of
636new/deleted or renamed files.
637
638With rename detection, the statistics are rather different [...]
639because git will notice that a fair number of the changes are renames.
Randy Dunlap84da7c02005-06-28 20:45:30 -0700640
Linus Torvalds1da177e2005-04-16 15:20:36 -0700641-----------------------------------
642SECTION 2 - HINTS, TIPS, AND TRICKS
643-----------------------------------
644
645This section lists many of the common "rules" associated with code
646submitted to the kernel. There are always exceptions... but you must
647have a really good reason for doing so. You could probably call this
648section Linus Computer Science 101.
649
650
651
6521) Read Documentation/CodingStyle
653
654Nuff said. If your code deviates too much from this, it is likely
655to be rejected without further review, and without comment.
656
Keiichi Kii5ab3bd52007-10-26 15:51:44 +0900657One significant exception is when moving code from one file to
658another -- in this case you should not modify the moved code at all in
Andy Whitcroftde7d4f02007-07-15 23:37:22 -0700659the same patch which moves it. This clearly delineates the act of
660moving the code and your changes. This greatly aids review of the
661actual differences and allows tools to better track the history of
662the code itself.
663
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700664Check your patches with the patch style checker prior to submission
Andy Whitcroftde7d4f02007-07-15 23:37:22 -0700665(scripts/checkpatch.pl). The style checker should be viewed as
666a guide not as the final word. If your code looks better with
667a violation then its probably best left alone.
668
669The checker reports at three levels:
670 - ERROR: things that are very likely to be wrong
671 - WARNING: things requiring careful review
672 - CHECK: things requiring thought
673
674You should be able to justify all violations that remain in your
675patch.
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700676
Linus Torvalds1da177e2005-04-16 15:20:36 -0700677
678
6792) #ifdefs are ugly
680
681Code cluttered with ifdefs is difficult to read and maintain. Don't do
682it. Instead, put your ifdefs in a header, and conditionally define
683'static inline' functions, or macros, which are used in the code.
684Let the compiler optimize away the "no-op" case.
685
686Simple example, of poor code:
687
688 dev = alloc_etherdev (sizeof(struct funky_private));
689 if (!dev)
690 return -ENODEV;
691 #ifdef CONFIG_NET_FUNKINESS
692 init_funky_net(dev);
693 #endif
694
695Cleaned-up example:
696
697(in header)
698 #ifndef CONFIG_NET_FUNKINESS
699 static inline void init_funky_net (struct net_device *d) {}
700 #endif
701
702(in the code itself)
703 dev = alloc_etherdev (sizeof(struct funky_private));
704 if (!dev)
705 return -ENODEV;
706 init_funky_net(dev);
707
708
709
7103) 'static inline' is better than a macro
711
712Static inline functions are greatly preferred over macros.
713They provide type safety, have no length limitations, no formatting
714limitations, and under gcc they are as cheap as macros.
715
716Macros should only be used for cases where a static inline is clearly
Jim Meyeringf2b2ea62008-04-02 13:04:46 -0700717suboptimal [there are a few, isolated cases of this in fast paths],
Linus Torvalds1da177e2005-04-16 15:20:36 -0700718or where it is impossible to use a static inline function [such as
719string-izing].
720
721'static inline' is preferred over 'static __inline__', 'extern inline',
722and 'extern __inline__'.
723
724
725
7264) Don't over-design.
727
728Don't try to anticipate nebulous future cases which may or may not
Randy Dunlap84da7c02005-06-28 20:45:30 -0700729be useful: "Make it as simple as you can, and no simpler."
Linus Torvalds1da177e2005-04-16 15:20:36 -0700730
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800731
732
733----------------------
734SECTION 3 - REFERENCES
735----------------------
736
737Andrew Morton, "The perfect patch" (tpp).
FD Cami2223c652008-10-15 22:02:00 -0700738 <http://userweb.kernel.org/~akpm/stuff/tpp.txt>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800739
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700740Jeff Garzik, "Linux kernel patch submission format".
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800741 <http://linux.yyz.us/patch-format.html>
742
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700743Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
Vikram Narayananf5039932011-05-23 12:01:25 -0700744 <http://www.kroah.com/log/linux/maintainer.html>
745 <http://www.kroah.com/log/linux/maintainer-02.html>
746 <http://www.kroah.com/log/linux/maintainer-03.html>
747 <http://www.kroah.com/log/linux/maintainer-04.html>
748 <http://www.kroah.com/log/linux/maintainer-05.html>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800749
Randy Dunlapbc7455f2006-07-30 03:03:45 -0700750NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800751 <http://marc.theaimsgroup.com/?l=linux-kernel&m=112112749912944&w=2>
752
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700753Kernel Documentation/CodingStyle:
Qi Yong4db29c12007-06-12 13:06:49 +0800754 <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800755
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700756Linus Torvalds's mail on the canonical patch format:
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800757 <http://lkml.org/lkml/2005/4/7/183>
Andi Kleen95367272008-10-15 22:02:02 -0700758
759Andi Kleen, "On submitting kernel patches"
Lucas De Marchi25985ed2011-03-30 22:57:33 -0300760 Some strategies to get difficult or controversial changes in.
Andi Kleen95367272008-10-15 22:02:02 -0700761 http://halobates.de/on-submitting-patches.pdf
762
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800763--