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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
Josh Triplett74a475a2014-04-03 14:48:28 -0700109Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
110instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
111to do frotz", as if you are giving orders to the codebase to change
112its behaviour.
113
Randy Dunlapd89b1942010-08-09 17:20:21 -0700114If the patch fixes a logged bug entry, refer to that bug entry by
Josh Triplett9547c702014-04-03 14:48:29 -0700115number and URL. If the patch follows from a mailing list discussion,
116give a URL to the mailing list archive; use the https://lkml.kernel.org/
117redirector with a Message-Id, to ensure that the links cannot become
118stale.
119
120However, try to make your explanation understandable without external
121resources. In addition to giving a URL to a mailing list archive or
122bug, summarize the relevant points of the discussion that led to the
123patch as submitted.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700124
Geert Uytterhoeven0af52702013-07-31 14:59:38 -0700125If you want to refer to a specific commit, don't just refer to the
126SHA-1 ID of the commit. Please also include the oneline summary of
127the commit, to make it easier for reviewers to know what it is about.
128Example:
129
130 Commit e21d2170f36602ae2708 ("video: remove unnecessary
131 platform_set_drvdata()") removed the unnecessary
132 platform_set_drvdata(), but left the variable "dev" unused,
133 delete it.
134
Linus Torvalds1da177e2005-04-16 15:20:36 -0700135
1363) Separate your changes.
137
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800138Separate _logical changes_ into a single patch file.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700139
140For example, if your changes include both bug fixes and performance
141enhancements for a single driver, separate those changes into two
142or more patches. If your changes include an API update, and a new
143driver which uses that new API, separate those into two patches.
144
145On the other hand, if you make a single change to numerous files,
146group those changes into a single patch. Thus a single logical change
147is contained within a single patch.
148
149If one patch depends on another patch in order for a change to be
150complete, that is OK. Simply note "this patch depends on patch X"
151in your patch description.
152
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800153If you cannot condense your patch set into a smaller set of patches,
154then only post say 15 or so at a time and wait for review and integration.
155
156
Linus Torvalds1da177e2005-04-16 15:20:36 -0700157
Andy Whitcroft0a920b52007-06-01 00:46:48 -07001584) Style check your changes.
159
160Check your patch for basic style violations, details of which can be
161found in Documentation/CodingStyle. Failure to do so simply wastes
Linus Nilssonf56d35e2007-07-21 17:49:06 +0200162the reviewers time and will get your patch rejected, probably
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700163without even being read.
164
165At a minimum you should check your patches with the patch style
Andre Haupta570ab62007-09-11 15:23:47 -0700166checker prior to submission (scripts/checkpatch.pl). You should
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700167be able to justify all violations that remain in your patch.
168
169
170
1715) Select e-mail destination.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700172
173Look through the MAINTAINERS file and the source code, and determine
174if your change applies to a specific subsystem of the kernel, with
Michel Machadoe52d2e12012-04-02 22:10:53 -0400175an assigned maintainer. If so, e-mail that person. The script
176scripts/get_maintainer.pl can be very useful at this step.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700177
178If no maintainer is listed, or the maintainer does not respond, send
179your patch to the primary Linux kernel developer's mailing list,
180linux-kernel@vger.kernel.org. Most kernel developers monitor this
181e-mail list, and can comment on your changes.
182
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800183
184Do not send more than 15 patches at once to the vger mailing lists!!!
185
186
Linus Torvalds1da177e2005-04-16 15:20:36 -0700187Linus Torvalds is the final arbiter of all changes accepted into the
Linus Torvalds99ddcc72007-01-23 14:22:35 -0800188Linux kernel. His e-mail address is <torvalds@linux-foundation.org>.
189He gets a lot of e-mail, so typically you should do your best to -avoid-
190sending him e-mail.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700191
192Patches which are bug fixes, are "obvious" changes, or similarly
193require little discussion should be sent or CC'd to Linus. Patches
194which require discussion or do not have a clear advantage should
195usually be sent first to linux-kernel. Only after the patch is
196discussed should the patch then be submitted to Linus.
197
Linus Torvalds1da177e2005-04-16 15:20:36 -0700198
199
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002006) Select your CC (e-mail carbon copy) list.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700201
202Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
203
204Other kernel developers besides Linus need to be aware of your change,
205so that they may comment on it and offer code review and suggestions.
206linux-kernel is the primary Linux kernel developer mailing list.
207Other mailing lists are available for specific subsystems, such as
208USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the
209MAINTAINERS file for a mailing list that relates specifically to
210your change.
211
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800212Majordomo lists of VGER.KERNEL.ORG at:
213 <http://vger.kernel.org/vger-lists.html>
214
Paul Jackson1caf1f02005-07-31 22:34:48 -0700215If changes affect userland-kernel interfaces, please send
216the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
217a man-pages patch, or at least a notification of the change,
218so that some information makes its way into the manual pages.
219
Michael Brunner8103b5c2009-08-04 00:41:11 +0200220Even if the maintainer did not respond in step #5, make sure to ALWAYS
Linus Torvalds1da177e2005-04-16 15:20:36 -0700221copy the maintainer when you change their code.
222
223For small patches you may want to CC the Trivial Patch Monkey
Markus Heidelberg82d27b22009-06-12 01:02:34 +0200224trivial@kernel.org which collects "trivial" patches. Have a look
225into the MAINTAINERS file for its current manager.
226Trivial patches must qualify for one of the following rules:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700227 Spelling fixes in documentation
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700228 Spelling fixes which could break grep(1)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700229 Warning fixes (cluttering with useless warnings is bad)
230 Compilation fixes (only if they are actually correct)
231 Runtime fixes (only if they actually fix things)
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700232 Removing use of deprecated functions/macros (eg. check_region)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700233 Contact detail and documentation fixes
234 Non-portable code replaced by portable code (even in arch-specific,
235 since people copy, as long as it's trivial)
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700236 Any fix by the author/maintainer of the file (ie. patch monkey
Linus Torvalds1da177e2005-04-16 15:20:36 -0700237 in re-transmission mode)
Randy Dunlap84da7c02005-06-28 20:45:30 -0700238
Linus Torvalds1da177e2005-04-16 15:20:36 -0700239
240
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002417) No MIME, no links, no compression, no attachments. Just plain text.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700242
243Linus and other kernel developers need to be able to read and comment
244on the changes you are submitting. It is important for a kernel
245developer to be able to "quote" your changes, using standard e-mail
246tools, so that they may comment on specific portions of your code.
247
248For this reason, all patches should be submitting e-mail "inline".
249WARNING: Be wary of your editor's word-wrap corrupting your patch,
250if you choose to cut-n-paste your patch.
251
252Do not attach the patch as a MIME attachment, compressed or not.
253Many popular e-mail applications will not always transmit a MIME
254attachment as plain text, making it impossible to comment on your
255code. A MIME attachment also takes Linus a bit more time to process,
256decreasing the likelihood of your MIME-attached change being accepted.
257
258Exception: If your mailer is mangling patches then someone may ask
259you to re-send them using MIME.
260
Michael Opdenacker097091c2008-02-03 18:06:58 +0200261See Documentation/email-clients.txt for hints about configuring
262your e-mail client so that it sends your patches untouched.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700263
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002648) E-mail size.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700265
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700266When sending patches to Linus, always follow step #7.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700267
268Large changes are not appropriate for mailing lists, and some
Randy Dunlap4932be72009-10-01 15:44:06 -0700269maintainers. If your patch, uncompressed, exceeds 300 kB in size,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700270it is preferred that you store your patch on an Internet-accessible
271server, and provide instead a URL (link) pointing to your patch.
272
273
274
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002759) Name your kernel version.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700276
277It is important to note, either in the subject line or in the patch
278description, the kernel version to which this patch applies.
279
280If the patch does not apply cleanly to the latest kernel version,
281Linus will not apply it.
282
283
284
Andy Whitcroft0a920b52007-06-01 00:46:48 -070028510) Don't get discouraged. Re-submit.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700286
287After you have submitted your change, be patient and wait. If Linus
288likes your change and applies it, it will appear in the next version
289of the kernel that he releases.
290
291However, if your change doesn't appear in the next version of the
292kernel, there could be any number of reasons. It's YOUR job to
293narrow down those reasons, correct what was wrong, and submit your
294updated change.
295
296It is quite common for Linus to "drop" your patch without comment.
297That's the nature of the system. If he drops your patch, it could be
298due to
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700299* Your patch did not apply cleanly to the latest kernel version.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700300* Your patch was not sufficiently discussed on linux-kernel.
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700301* A style issue (see section 2).
302* An e-mail formatting issue (re-read this section).
303* A technical problem with your change.
304* He gets tons of e-mail, and yours got lost in the shuffle.
305* You are being annoying.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700306
307When in doubt, solicit comments on linux-kernel mailing list.
308
309
310
Andy Whitcroft0a920b52007-06-01 00:46:48 -070031111) Include PATCH in the subject
Linus Torvalds1da177e2005-04-16 15:20:36 -0700312
313Due to high e-mail traffic to Linus, and to linux-kernel, it is common
314convention to prefix your subject line with [PATCH]. This lets Linus
315and other kernel developers more easily distinguish patches from other
316e-mail discussions.
317
318
319
Andy Whitcroft0a920b52007-06-01 00:46:48 -070032012) Sign your work
Linus Torvalds1da177e2005-04-16 15:20:36 -0700321
322To improve tracking of who did what, especially with patches that can
323percolate to their final resting place in the kernel through several
324layers of maintainers, we've introduced a "sign-off" procedure on
325patches that are being emailed around.
326
327The sign-off is a simple line at the end of the explanation for the
328patch, which certifies that you wrote it or otherwise have the right to
Zac Storerdb12fb82011-08-13 12:34:45 -0700329pass it on as an open-source patch. The rules are pretty simple: if you
Linus Torvalds1da177e2005-04-16 15:20:36 -0700330can certify the below:
331
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700332 Developer's Certificate of Origin 1.1
Linus Torvalds1da177e2005-04-16 15:20:36 -0700333
334 By making a contribution to this project, I certify that:
335
336 (a) The contribution was created in whole or in part by me and I
337 have the right to submit it under the open source license
338 indicated in the file; or
339
340 (b) The contribution is based upon previous work that, to the best
341 of my knowledge, is covered under an appropriate open source
342 license and I have the right under that license to submit that
343 work with modifications, whether created in whole or in part
344 by me, under the same open source license (unless I am
345 permitted to submit under a different license), as indicated
346 in the file; or
347
348 (c) The contribution was provided directly to me by some other
349 person who certified (a), (b) or (c) and I have not modified
350 it.
351
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700352 (d) I understand and agree that this project and the contribution
353 are public and that a record of the contribution (including all
354 personal information I submit with it, including my sign-off) is
355 maintained indefinitely and may be redistributed consistent with
356 this project or the open source license(s) involved.
357
Linus Torvalds1da177e2005-04-16 15:20:36 -0700358then you just add a line saying
359
Alexey Dobriyan9fd55592005-06-25 14:59:34 -0700360 Signed-off-by: Random J Developer <random@developer.example.org>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700361
Greg KHaf45f322006-09-12 20:35:52 -0700362using your real name (sorry, no pseudonyms or anonymous contributions.)
363
Linus Torvalds1da177e2005-04-16 15:20:36 -0700364Some people also put extra tags at the end. They'll just be ignored for
365now, but you can do this to mark internal company procedures or just
366point out some special detail about the sign-off.
367
Willy Tarreauadbd5882008-06-03 00:20:28 +0200368If you are a subsystem or branch maintainer, sometimes you need to slightly
369modify patches you receive in order to merge them, because the code is not
370exactly the same in your tree and the submitters'. If you stick strictly to
371rule (c), you should ask the submitter to rediff, but this is a totally
372counter-productive waste of time and energy. Rule (b) allows you to adjust
373the code, but then it is very impolite to change one submitter's code and
374make him endorse your bugs. To solve this problem, it is recommended that
375you add a line between the last Signed-off-by header and yours, indicating
376the nature of your changes. While there is nothing mandatory about this, it
377seems like prepending the description with your mail and/or name, all
378enclosed in square brackets, is noticeable enough to make it obvious that
379you are responsible for last-minute changes. Example :
380
381 Signed-off-by: Random J Developer <random@developer.example.org>
382 [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
383 Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
384
385This practise is particularly helpful if you maintain a stable branch and
386want at the same time to credit the author, track changes, merge the fix,
387and protect the submitter from complaints. Note that under no circumstances
388can you change the author's identity (the From header), as it is the one
389which appears in the changelog.
390
391Special note to back-porters: It seems to be a common and useful practise
392to insert an indication of the origin of a patch at the top of the commit
393message (just after the subject line) to facilitate tracking. For instance,
394here's what we see in 2.6-stable :
395
396 Date: Tue May 13 19:10:30 2008 +0000
397
398 SCSI: libiscsi regression in 2.6.25: fix nop timer handling
399
400 commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
401
402And here's what appears in 2.4 :
403
404 Date: Tue May 13 22:12:27 2008 +0200
405
406 wireless, airo: waitbusy() won't delay
407
408 [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
409
410Whatever the format, this information provides a valuable help to people
411tracking your trees, and to people trying to trouble-shoot bugs in your
412tree.
413
Linus Torvalds1da177e2005-04-16 15:20:36 -0700414
Jonathan Corbetef402032008-03-28 11:22:38 -060041513) When to use Acked-by: and Cc:
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700416
Andrew Morton0f44cd22007-06-08 13:46:45 -0700417The Signed-off-by: tag indicates that the signer was involved in the
418development of the patch, or that he/she was in the patch's delivery path.
419
420If a person was not directly involved in the preparation or handling of a
421patch but wishes to signify and record their approval of it then they can
422arrange to have an Acked-by: line added to the patch's changelog.
423
424Acked-by: is often used by the maintainer of the affected code when that
425maintainer neither contributed to nor forwarded the patch.
426
427Acked-by: is not as formal as Signed-off-by:. It is a record that the acker
428has at least reviewed the patch and has indicated acceptance. Hence patch
429mergers will sometimes manually convert an acker's "yep, looks good to me"
430into an Acked-by:.
431
432Acked-by: does not necessarily indicate acknowledgement of the entire patch.
433For example, if a patch affects multiple subsystems and has an Acked-by: from
434one subsystem maintainer then this usually indicates acknowledgement of just
435the part which affects that maintainer's code. Judgement should be used here.
Jonathan Corbetef402032008-03-28 11:22:38 -0600436When in doubt people should refer to the original discussion in the mailing
Andrew Morton0f44cd22007-06-08 13:46:45 -0700437list archives.
438
Jonathan Corbetef402032008-03-28 11:22:38 -0600439If a person has had the opportunity to comment on a patch, but has not
440provided such comments, you may optionally add a "Cc:" tag to the patch.
441This is the only tag which might be added without an explicit action by the
442person it names. This tag documents that potentially interested parties
443have been included in the discussion
Andrew Morton0f44cd22007-06-08 13:46:45 -0700444
Jonathan Corbetef402032008-03-28 11:22:38 -0600445
Mugunthan V N8543ae12013-04-29 16:18:17 -070044614) Using Reported-by:, Tested-by:, Reviewed-by: and Suggested-by:
Jonathan Corbetbbb0a4242009-01-16 09:49:50 -0700447
448If this patch fixes a problem reported by somebody else, consider adding a
449Reported-by: tag to credit the reporter for their contribution. Please
450note that this tag should not be added without the reporter's permission,
451especially if the problem was not reported in a public forum. That said,
452if we diligently credit our bug reporters, they will, hopefully, be
453inspired to help us again in the future.
Jonathan Corbetef402032008-03-28 11:22:38 -0600454
455A Tested-by: tag indicates that the patch has been successfully tested (in
456some environment) by the person named. This tag informs maintainers that
457some testing has been performed, provides a means to locate testers for
458future patches, and ensures credit for the testers.
459
460Reviewed-by:, instead, indicates that the patch has been reviewed and found
461acceptable according to the Reviewer's Statement:
462
463 Reviewer's statement of oversight
464
465 By offering my Reviewed-by: tag, I state that:
466
467 (a) I have carried out a technical review of this patch to
468 evaluate its appropriateness and readiness for inclusion into
469 the mainline kernel.
470
471 (b) Any problems, concerns, or questions relating to the patch
472 have been communicated back to the submitter. I am satisfied
473 with the submitter's response to my comments.
474
475 (c) While there may be things that could be improved with this
476 submission, I believe that it is, at this time, (1) a
477 worthwhile modification to the kernel, and (2) free of known
478 issues which would argue against its inclusion.
479
480 (d) While I have reviewed the patch and believe it to be sound, I
481 do not (unless explicitly stated elsewhere) make any
482 warranties or guarantees that it will achieve its stated
483 purpose or function properly in any given situation.
484
485A Reviewed-by tag is a statement of opinion that the patch is an
486appropriate modification of the kernel without any remaining serious
487technical issues. Any interested reviewer (who has done the work) can
488offer a Reviewed-by tag for a patch. This tag serves to give credit to
489reviewers and to inform maintainers of the degree of review which has been
490done on the patch. Reviewed-by: tags, when supplied by reviewers known to
491understand the subject area and to perform thorough reviews, will normally
Pavel Machek5801da12009-06-04 16:26:50 +0200492increase the likelihood of your patch getting into the kernel.
Jonathan Corbetef402032008-03-28 11:22:38 -0600493
Mugunthan V N8543ae12013-04-29 16:18:17 -0700494A Suggested-by: tag indicates that the patch idea is suggested by the person
495named and ensures credit to the person for the idea. Please note that this
496tag should not be added without the reporter's permission, especially if the
497idea was not posted in a public forum. That said, if we diligently credit our
498idea reporters, they will, hopefully, be inspired to help us again in the
499future.
500
Jonathan Corbetef402032008-03-28 11:22:38 -0600501
50215) The canonical patch format
Randy Dunlap84da7c02005-06-28 20:45:30 -0700503
Paul Jackson75f84262005-10-02 18:01:42 -0700504The canonical patch subject line is:
505
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700506 Subject: [PATCH 001/123] subsystem: summary phrase
Paul Jackson75f84262005-10-02 18:01:42 -0700507
508The canonical patch message body contains the following:
509
510 - A "from" line specifying the patch author.
511
512 - An empty line.
513
514 - The body of the explanation, which will be copied to the
515 permanent changelog to describe this patch.
516
517 - The "Signed-off-by:" lines, described above, which will
518 also go in the changelog.
519
520 - A marker line containing simply "---".
521
522 - Any additional comments not suitable for the changelog.
523
524 - The actual patch (diff output).
525
526The Subject line format makes it very easy to sort the emails
527alphabetically by subject line - pretty much any email reader will
528support that - since because the sequence number is zero-padded,
529the numerical and alphabetic sort is the same.
530
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700531The "subsystem" in the email's Subject should identify which
532area or subsystem of the kernel is being patched.
533
534The "summary phrase" in the email's Subject should concisely
535describe the patch which that email contains. The "summary
536phrase" should not be a filename. Do not use the same "summary
Randy Dunlap66effdc2007-05-09 02:33:42 -0700537phrase" for every patch in a whole patch series (where a "patch
538series" is an ordered sequence of multiple, related patches).
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700539
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400540Bear in mind that the "summary phrase" of your email becomes a
541globally-unique identifier for that patch. It propagates all the way
542into the git changelog. The "summary phrase" may later be used in
543developer discussions which refer to the patch. People will want to
544google for the "summary phrase" to read discussion regarding that
545patch. It will also be the only thing that people may quickly see
546when, two or three months later, they are going through perhaps
547thousands of patches using tools such as "gitk" or "git log
548--oneline".
549
550For these reasons, the "summary" must be no more than 70-75
551characters, and it must describe both what the patch changes, as well
552as why the patch might be necessary. It is challenging to be both
553succinct and descriptive, but that is what a well-written summary
554should do.
555
556The "summary phrase" may be prefixed by tags enclosed in square
557brackets: "Subject: [PATCH tag] <summary phrase>". The tags are not
558considered part of the summary phrase, but describe how the patch
559should be treated. Common tags might include a version descriptor if
560the multiple versions of the patch have been sent out in response to
561comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
562comments. If there are four patches in a patch series the individual
563patches may be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures
564that developers understand the order in which the patches should be
565applied and that they have reviewed or applied all of the patches in
566the patch series.
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700567
568A couple of example Subjects:
569
570 Subject: [patch 2/5] ext2: improve scalability of bitmap searching
571 Subject: [PATCHv2 001/207] x86: fix eflags tracking
Paul Jackson75f84262005-10-02 18:01:42 -0700572
573The "from" line must be the very first line in the message body,
574and has the form:
575
576 From: Original Author <author@example.com>
577
578The "from" line specifies who will be credited as the author of the
579patch in the permanent changelog. If the "from" line is missing,
580then the "From:" line from the email header will be used to determine
581the patch author in the changelog.
582
583The explanation body will be committed to the permanent source
584changelog, so should make sense to a competent reader who has long
585since forgotten the immediate details of the discussion that might
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400586have led to this patch. Including symptoms of the failure which the
587patch addresses (kernel log messages, oops messages, etc.) is
588especially useful for people who might be searching the commit logs
589looking for the applicable patch. If a patch fixes a compile failure,
590it may not be necessary to include _all_ of the compile failures; just
591enough that it is likely that someone searching for the patch can find
592it. As in the "summary phrase", it is important to be both succinct as
593well as descriptive.
Paul Jackson75f84262005-10-02 18:01:42 -0700594
595The "---" marker line serves the essential purpose of marking for patch
596handling tools where the changelog message ends.
597
598One good use for the additional comments after the "---" marker is for
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400599a diffstat, to show what files have changed, and the number of
600inserted and deleted lines per file. A diffstat is especially useful
601on bigger patches. Other comments relevant only to the moment or the
602maintainer, not suitable for the permanent changelog, should also go
603here. A good example of such comments might be "patch changelogs"
604which describe what has changed between the v1 and v2 version of the
605patch.
606
607If you are going to include a diffstat after the "---" marker, please
608use diffstat options "-p 1 -w 70" so that filenames are listed from
609the top of the kernel source tree and don't use too much horizontal
610space (easily fit in 80 columns, maybe with some indentation).
Paul Jackson75f84262005-10-02 18:01:42 -0700611
612See more details on the proper patch format in the following
613references.
614
615
Randy Dunlap14863612008-07-27 20:44:24 -070061616) Sending "git pull" requests (from Linus emails)
Randy Dunlap84da7c02005-06-28 20:45:30 -0700617
Randy Dunlap14863612008-07-27 20:44:24 -0700618Please write the git repo address and branch name alone on the same line
619so that I can't even by mistake pull from the wrong branch, and so
620that a triple-click just selects the whole thing.
621
622So the proper format is something along the lines of:
623
624 "Please pull from
625
626 git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
627
628 to get these changes:"
629
630so that I don't have to hunt-and-peck for the address and inevitably
631get it wrong (actually, I've only gotten it wrong a few times, and
632checking against the diffstat tells me when I get it wrong, but I'm
633just a lot more comfortable when I don't have to "look for" the right
634thing to pull, and double-check that I have the right branch-name).
635
636
637Please use "git diff -M --stat --summary" to generate the diffstat:
638the -M enables rename detection, and the summary enables a summary of
639new/deleted or renamed files.
640
641With rename detection, the statistics are rather different [...]
642because git will notice that a fair number of the changes are renames.
Randy Dunlap84da7c02005-06-28 20:45:30 -0700643
Linus Torvalds1da177e2005-04-16 15:20:36 -0700644-----------------------------------
645SECTION 2 - HINTS, TIPS, AND TRICKS
646-----------------------------------
647
648This section lists many of the common "rules" associated with code
649submitted to the kernel. There are always exceptions... but you must
650have a really good reason for doing so. You could probably call this
651section Linus Computer Science 101.
652
653
654
6551) Read Documentation/CodingStyle
656
657Nuff said. If your code deviates too much from this, it is likely
658to be rejected without further review, and without comment.
659
Keiichi Kii5ab3bd52007-10-26 15:51:44 +0900660One significant exception is when moving code from one file to
661another -- in this case you should not modify the moved code at all in
Andy Whitcroftde7d4f02007-07-15 23:37:22 -0700662the same patch which moves it. This clearly delineates the act of
663moving the code and your changes. This greatly aids review of the
664actual differences and allows tools to better track the history of
665the code itself.
666
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700667Check your patches with the patch style checker prior to submission
Andy Whitcroftde7d4f02007-07-15 23:37:22 -0700668(scripts/checkpatch.pl). The style checker should be viewed as
669a guide not as the final word. If your code looks better with
670a violation then its probably best left alone.
671
672The checker reports at three levels:
673 - ERROR: things that are very likely to be wrong
674 - WARNING: things requiring careful review
675 - CHECK: things requiring thought
676
677You should be able to justify all violations that remain in your
678patch.
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700679
Linus Torvalds1da177e2005-04-16 15:20:36 -0700680
681
6822) #ifdefs are ugly
683
684Code cluttered with ifdefs is difficult to read and maintain. Don't do
685it. Instead, put your ifdefs in a header, and conditionally define
686'static inline' functions, or macros, which are used in the code.
687Let the compiler optimize away the "no-op" case.
688
689Simple example, of poor code:
690
691 dev = alloc_etherdev (sizeof(struct funky_private));
692 if (!dev)
693 return -ENODEV;
694 #ifdef CONFIG_NET_FUNKINESS
695 init_funky_net(dev);
696 #endif
697
698Cleaned-up example:
699
700(in header)
701 #ifndef CONFIG_NET_FUNKINESS
702 static inline void init_funky_net (struct net_device *d) {}
703 #endif
704
705(in the code itself)
706 dev = alloc_etherdev (sizeof(struct funky_private));
707 if (!dev)
708 return -ENODEV;
709 init_funky_net(dev);
710
711
712
7133) 'static inline' is better than a macro
714
715Static inline functions are greatly preferred over macros.
716They provide type safety, have no length limitations, no formatting
717limitations, and under gcc they are as cheap as macros.
718
719Macros should only be used for cases where a static inline is clearly
Jim Meyeringf2b2ea62008-04-02 13:04:46 -0700720suboptimal [there are a few, isolated cases of this in fast paths],
Linus Torvalds1da177e2005-04-16 15:20:36 -0700721or where it is impossible to use a static inline function [such as
722string-izing].
723
724'static inline' is preferred over 'static __inline__', 'extern inline',
725and 'extern __inline__'.
726
727
728
7294) Don't over-design.
730
731Don't try to anticipate nebulous future cases which may or may not
Randy Dunlap84da7c02005-06-28 20:45:30 -0700732be useful: "Make it as simple as you can, and no simpler."
Linus Torvalds1da177e2005-04-16 15:20:36 -0700733
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800734
735
736----------------------
737SECTION 3 - REFERENCES
738----------------------
739
740Andrew Morton, "The perfect patch" (tpp).
FD Cami2223c652008-10-15 22:02:00 -0700741 <http://userweb.kernel.org/~akpm/stuff/tpp.txt>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800742
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700743Jeff Garzik, "Linux kernel patch submission format".
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800744 <http://linux.yyz.us/patch-format.html>
745
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700746Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
Vikram Narayananf5039932011-05-23 12:01:25 -0700747 <http://www.kroah.com/log/linux/maintainer.html>
748 <http://www.kroah.com/log/linux/maintainer-02.html>
749 <http://www.kroah.com/log/linux/maintainer-03.html>
750 <http://www.kroah.com/log/linux/maintainer-04.html>
751 <http://www.kroah.com/log/linux/maintainer-05.html>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800752
Randy Dunlapbc7455f2006-07-30 03:03:45 -0700753NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800754 <http://marc.theaimsgroup.com/?l=linux-kernel&m=112112749912944&w=2>
755
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700756Kernel Documentation/CodingStyle:
Qi Yong4db29c12007-06-12 13:06:49 +0800757 <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800758
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700759Linus Torvalds's mail on the canonical patch format:
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800760 <http://lkml.org/lkml/2005/4/7/183>
Andi Kleen95367272008-10-15 22:02:02 -0700761
762Andi Kleen, "On submitting kernel patches"
Lucas De Marchi25985ed2011-03-30 22:57:33 -0300763 Some strategies to get difficult or controversial changes in.
Andi Kleen95367272008-10-15 22:02:02 -0700764 http://halobates.de/on-submitting-patches.pdf
765
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800766--