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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
Josh Triplett8e3072a2014-04-03 14:48:30 -070017Many of these steps describe the default behavior of the git version
18control system; if you use git to prepare your patches, you'll find much
19of the mechanical work done for you, though you'll still need to prepare
20and document a sensible set of patches.
Linus Torvalds1da177e2005-04-16 15:20:36 -070021
22--------------------------------------------
23SECTION 1 - CREATING AND SENDING YOUR CHANGE
24--------------------------------------------
25
26
27
281) "diff -up"
29------------
30
Josh Triplett8e3072a2014-04-03 14:48:30 -070031Use "diff -up" or "diff -uprN" to create patches. git generates patches
32in this form by default; if you're using git, you can skip this section
33entirely.
Linus Torvalds1da177e2005-04-16 15:20:36 -070034
35All changes to the Linux kernel occur in the form of patches, as
36generated by diff(1). When creating your patch, make sure to create it
37in "unified diff" format, as supplied by the '-u' argument to diff(1).
38Also, please use the '-p' argument which shows which C function each
39change is in - that makes the resultant diff a lot easier to read.
40Patches should be based in the root kernel source directory,
41not in any lower subdirectory.
42
43To create a patch for a single file, it is often sufficient to do:
44
Randy Dunlap84da7c02005-06-28 20:45:30 -070045 SRCTREE= linux-2.6
Linus Torvalds1da177e2005-04-16 15:20:36 -070046 MYFILE= drivers/net/mydriver.c
47
48 cd $SRCTREE
49 cp $MYFILE $MYFILE.orig
50 vi $MYFILE # make your change
51 cd ..
52 diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
53
54To create a patch for multiple files, you should unpack a "vanilla",
55or unmodified kernel source tree, and generate a diff against your
56own source tree. For example:
57
Randy Dunlap84da7c02005-06-28 20:45:30 -070058 MYSRC= /devel/linux-2.6
Linus Torvalds1da177e2005-04-16 15:20:36 -070059
Randy Dunlap84da7c02005-06-28 20:45:30 -070060 tar xvfz linux-2.6.12.tar.gz
61 mv linux-2.6.12 linux-2.6.12-vanilla
62 diff -uprN -X linux-2.6.12-vanilla/Documentation/dontdiff \
63 linux-2.6.12-vanilla $MYSRC > /tmp/patch
Linus Torvalds1da177e2005-04-16 15:20:36 -070064
65"dontdiff" is a list of files which are generated by the kernel during
66the build process, and should be ignored in any diff(1)-generated
Randy Dunlap84da7c02005-06-28 20:45:30 -070067patch. The "dontdiff" file is included in the kernel tree in
Randy Dunlap755727b2013-03-08 12:43:35 -0800682.6.12 and later.
Linus Torvalds1da177e2005-04-16 15:20:36 -070069
70Make sure your patch does not include any extra files which do not
71belong in a patch submission. Make sure to review your patch -after-
72generated it with diff(1), to ensure accuracy.
73
Josh Triplett8e3072a2014-04-03 14:48:30 -070074If your changes produce a lot of deltas, you need to split them into
75individual patches which modify things in logical stages; see section
76#3. This will facilitate easier reviewing by other kernel developers,
77very important if you want your patch accepted.
Linus Torvalds1da177e2005-04-16 15:20:36 -070078
Josh Triplett8e3072a2014-04-03 14:48:30 -070079If you're using git, "git rebase -i" can help you with this process. If
80you're not using git, quilt <http://savannah.nongnu.org/projects/quilt>
81is another popular alternative.
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
Jacob Keller8401aa12014-06-06 14:36:39 -0700135If your patch fixes a bug in a specific commit, e.g. you found an issue using
136git-bisect, please use the 'Fixes:' tag with the first 12 characters of the
137SHA-1 ID, and the one line summary.
138Example:
139
140 Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
141
142The following git-config settings can be used to add a pretty format for
143outputting the above style in the git log or git show commands
144
145 [core]
146 abbrev = 12
147 [pretty]
148 fixes = Fixes: %h (\"%s\")
Linus Torvalds1da177e2005-04-16 15:20:36 -0700149
1503) Separate your changes.
151
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800152Separate _logical changes_ into a single patch file.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700153
154For example, if your changes include both bug fixes and performance
155enhancements for a single driver, separate those changes into two
156or more patches. If your changes include an API update, and a new
157driver which uses that new API, separate those into two patches.
158
159On the other hand, if you make a single change to numerous files,
160group those changes into a single patch. Thus a single logical change
161is contained within a single patch.
162
163If one patch depends on another patch in order for a change to be
164complete, that is OK. Simply note "this patch depends on patch X"
165in your patch description.
166
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800167If you cannot condense your patch set into a smaller set of patches,
168then only post say 15 or so at a time and wait for review and integration.
169
170
Linus Torvalds1da177e2005-04-16 15:20:36 -0700171
Andy Whitcroft0a920b52007-06-01 00:46:48 -07001724) Style check your changes.
173
174Check your patch for basic style violations, details of which can be
175found in Documentation/CodingStyle. Failure to do so simply wastes
Linus Nilssonf56d35e2007-07-21 17:49:06 +0200176the reviewers time and will get your patch rejected, probably
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700177without even being read.
178
179At a minimum you should check your patches with the patch style
Andre Haupta570ab62007-09-11 15:23:47 -0700180checker prior to submission (scripts/checkpatch.pl). You should
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700181be able to justify all violations that remain in your patch.
182
183
184
1855) Select e-mail destination.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700186
187Look through the MAINTAINERS file and the source code, and determine
188if your change applies to a specific subsystem of the kernel, with
Michel Machadoe52d2e12012-04-02 22:10:53 -0400189an assigned maintainer. If so, e-mail that person. The script
190scripts/get_maintainer.pl can be very useful at this step.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700191
192If no maintainer is listed, or the maintainer does not respond, send
193your patch to the primary Linux kernel developer's mailing list,
194linux-kernel@vger.kernel.org. Most kernel developers monitor this
195e-mail list, and can comment on your changes.
196
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800197
198Do not send more than 15 patches at once to the vger mailing lists!!!
199
200
Linus Torvalds1da177e2005-04-16 15:20:36 -0700201Linus Torvalds is the final arbiter of all changes accepted into the
Linus Torvalds99ddcc72007-01-23 14:22:35 -0800202Linux kernel. His e-mail address is <torvalds@linux-foundation.org>.
203He gets a lot of e-mail, so typically you should do your best to -avoid-
204sending him e-mail.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700205
206Patches which are bug fixes, are "obvious" changes, or similarly
207require little discussion should be sent or CC'd to Linus. Patches
208which require discussion or do not have a clear advantage should
209usually be sent first to linux-kernel. Only after the patch is
210discussed should the patch then be submitted to Linus.
211
Linus Torvalds1da177e2005-04-16 15:20:36 -0700212
213
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002146) Select your CC (e-mail carbon copy) list.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700215
216Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
217
218Other kernel developers besides Linus need to be aware of your change,
219so that they may comment on it and offer code review and suggestions.
220linux-kernel is the primary Linux kernel developer mailing list.
221Other mailing lists are available for specific subsystems, such as
222USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the
223MAINTAINERS file for a mailing list that relates specifically to
224your change.
225
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800226Majordomo lists of VGER.KERNEL.ORG at:
227 <http://vger.kernel.org/vger-lists.html>
228
Paul Jackson1caf1f02005-07-31 22:34:48 -0700229If changes affect userland-kernel interfaces, please send
230the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
231a man-pages patch, or at least a notification of the change,
232so that some information makes its way into the manual pages.
233
Michael Brunner8103b5c2009-08-04 00:41:11 +0200234Even if the maintainer did not respond in step #5, make sure to ALWAYS
Linus Torvalds1da177e2005-04-16 15:20:36 -0700235copy the maintainer when you change their code.
236
237For small patches you may want to CC the Trivial Patch Monkey
Markus Heidelberg82d27b22009-06-12 01:02:34 +0200238trivial@kernel.org which collects "trivial" patches. Have a look
239into the MAINTAINERS file for its current manager.
240Trivial patches must qualify for one of the following rules:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700241 Spelling fixes in documentation
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700242 Spelling fixes which could break grep(1)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700243 Warning fixes (cluttering with useless warnings is bad)
244 Compilation fixes (only if they are actually correct)
245 Runtime fixes (only if they actually fix things)
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700246 Removing use of deprecated functions/macros (eg. check_region)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700247 Contact detail and documentation fixes
248 Non-portable code replaced by portable code (even in arch-specific,
249 since people copy, as long as it's trivial)
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700250 Any fix by the author/maintainer of the file (ie. patch monkey
Linus Torvalds1da177e2005-04-16 15:20:36 -0700251 in re-transmission mode)
Randy Dunlap84da7c02005-06-28 20:45:30 -0700252
Linus Torvalds1da177e2005-04-16 15:20:36 -0700253
254
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002557) No MIME, no links, no compression, no attachments. Just plain text.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700256
257Linus and other kernel developers need to be able to read and comment
258on the changes you are submitting. It is important for a kernel
259developer to be able to "quote" your changes, using standard e-mail
260tools, so that they may comment on specific portions of your code.
261
262For this reason, all patches should be submitting e-mail "inline".
263WARNING: Be wary of your editor's word-wrap corrupting your patch,
264if you choose to cut-n-paste your patch.
265
266Do not attach the patch as a MIME attachment, compressed or not.
267Many popular e-mail applications will not always transmit a MIME
268attachment as plain text, making it impossible to comment on your
269code. A MIME attachment also takes Linus a bit more time to process,
270decreasing the likelihood of your MIME-attached change being accepted.
271
272Exception: If your mailer is mangling patches then someone may ask
273you to re-send them using MIME.
274
Michael Opdenacker097091c2008-02-03 18:06:58 +0200275See Documentation/email-clients.txt for hints about configuring
276your e-mail client so that it sends your patches untouched.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700277
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002788) E-mail size.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700279
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700280When sending patches to Linus, always follow step #7.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700281
282Large changes are not appropriate for mailing lists, and some
Randy Dunlap4932be72009-10-01 15:44:06 -0700283maintainers. If your patch, uncompressed, exceeds 300 kB in size,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700284it is preferred that you store your patch on an Internet-accessible
285server, and provide instead a URL (link) pointing to your patch.
286
287
288
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002899) Name your kernel version.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700290
291It is important to note, either in the subject line or in the patch
292description, the kernel version to which this patch applies.
293
294If the patch does not apply cleanly to the latest kernel version,
295Linus will not apply it.
296
297
298
Andy Whitcroft0a920b52007-06-01 00:46:48 -070029910) Don't get discouraged. Re-submit.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700300
301After you have submitted your change, be patient and wait. If Linus
302likes your change and applies it, it will appear in the next version
303of the kernel that he releases.
304
305However, if your change doesn't appear in the next version of the
306kernel, there could be any number of reasons. It's YOUR job to
307narrow down those reasons, correct what was wrong, and submit your
308updated change.
309
310It is quite common for Linus to "drop" your patch without comment.
311That's the nature of the system. If he drops your patch, it could be
312due to
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700313* Your patch did not apply cleanly to the latest kernel version.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700314* Your patch was not sufficiently discussed on linux-kernel.
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700315* A style issue (see section 2).
316* An e-mail formatting issue (re-read this section).
317* A technical problem with your change.
318* He gets tons of e-mail, and yours got lost in the shuffle.
319* You are being annoying.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700320
321When in doubt, solicit comments on linux-kernel mailing list.
322
323
324
Andy Whitcroft0a920b52007-06-01 00:46:48 -070032511) Include PATCH in the subject
Linus Torvalds1da177e2005-04-16 15:20:36 -0700326
327Due to high e-mail traffic to Linus, and to linux-kernel, it is common
328convention to prefix your subject line with [PATCH]. This lets Linus
329and other kernel developers more easily distinguish patches from other
330e-mail discussions.
331
332
333
Andy Whitcroft0a920b52007-06-01 00:46:48 -070033412) Sign your work
Linus Torvalds1da177e2005-04-16 15:20:36 -0700335
336To improve tracking of who did what, especially with patches that can
337percolate to their final resting place in the kernel through several
338layers of maintainers, we've introduced a "sign-off" procedure on
339patches that are being emailed around.
340
341The sign-off is a simple line at the end of the explanation for the
342patch, which certifies that you wrote it or otherwise have the right to
Zac Storerdb12fb82011-08-13 12:34:45 -0700343pass it on as an open-source patch. The rules are pretty simple: if you
Linus Torvalds1da177e2005-04-16 15:20:36 -0700344can certify the below:
345
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700346 Developer's Certificate of Origin 1.1
Linus Torvalds1da177e2005-04-16 15:20:36 -0700347
348 By making a contribution to this project, I certify that:
349
350 (a) The contribution was created in whole or in part by me and I
351 have the right to submit it under the open source license
352 indicated in the file; or
353
354 (b) The contribution is based upon previous work that, to the best
355 of my knowledge, is covered under an appropriate open source
356 license and I have the right under that license to submit that
357 work with modifications, whether created in whole or in part
358 by me, under the same open source license (unless I am
359 permitted to submit under a different license), as indicated
360 in the file; or
361
362 (c) The contribution was provided directly to me by some other
363 person who certified (a), (b) or (c) and I have not modified
364 it.
365
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700366 (d) I understand and agree that this project and the contribution
367 are public and that a record of the contribution (including all
368 personal information I submit with it, including my sign-off) is
369 maintained indefinitely and may be redistributed consistent with
370 this project or the open source license(s) involved.
371
Linus Torvalds1da177e2005-04-16 15:20:36 -0700372then you just add a line saying
373
Alexey Dobriyan9fd55592005-06-25 14:59:34 -0700374 Signed-off-by: Random J Developer <random@developer.example.org>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700375
Greg KHaf45f322006-09-12 20:35:52 -0700376using your real name (sorry, no pseudonyms or anonymous contributions.)
377
Linus Torvalds1da177e2005-04-16 15:20:36 -0700378Some people also put extra tags at the end. They'll just be ignored for
379now, but you can do this to mark internal company procedures or just
380point out some special detail about the sign-off.
381
Willy Tarreauadbd5882008-06-03 00:20:28 +0200382If you are a subsystem or branch maintainer, sometimes you need to slightly
383modify patches you receive in order to merge them, because the code is not
384exactly the same in your tree and the submitters'. If you stick strictly to
385rule (c), you should ask the submitter to rediff, but this is a totally
386counter-productive waste of time and energy. Rule (b) allows you to adjust
387the code, but then it is very impolite to change one submitter's code and
388make him endorse your bugs. To solve this problem, it is recommended that
389you add a line between the last Signed-off-by header and yours, indicating
390the nature of your changes. While there is nothing mandatory about this, it
391seems like prepending the description with your mail and/or name, all
392enclosed in square brackets, is noticeable enough to make it obvious that
393you are responsible for last-minute changes. Example :
394
395 Signed-off-by: Random J Developer <random@developer.example.org>
396 [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
397 Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
398
399This practise is particularly helpful if you maintain a stable branch and
400want at the same time to credit the author, track changes, merge the fix,
401and protect the submitter from complaints. Note that under no circumstances
402can you change the author's identity (the From header), as it is the one
403which appears in the changelog.
404
405Special note to back-porters: It seems to be a common and useful practise
406to insert an indication of the origin of a patch at the top of the commit
407message (just after the subject line) to facilitate tracking. For instance,
408here's what we see in 2.6-stable :
409
410 Date: Tue May 13 19:10:30 2008 +0000
411
412 SCSI: libiscsi regression in 2.6.25: fix nop timer handling
413
414 commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
415
416And here's what appears in 2.4 :
417
418 Date: Tue May 13 22:12:27 2008 +0200
419
420 wireless, airo: waitbusy() won't delay
421
422 [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
423
424Whatever the format, this information provides a valuable help to people
425tracking your trees, and to people trying to trouble-shoot bugs in your
426tree.
427
Linus Torvalds1da177e2005-04-16 15:20:36 -0700428
Jonathan Corbetef402032008-03-28 11:22:38 -060042913) When to use Acked-by: and Cc:
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700430
Andrew Morton0f44cd22007-06-08 13:46:45 -0700431The Signed-off-by: tag indicates that the signer was involved in the
432development of the patch, or that he/she was in the patch's delivery path.
433
434If a person was not directly involved in the preparation or handling of a
435patch but wishes to signify and record their approval of it then they can
436arrange to have an Acked-by: line added to the patch's changelog.
437
438Acked-by: is often used by the maintainer of the affected code when that
439maintainer neither contributed to nor forwarded the patch.
440
441Acked-by: is not as formal as Signed-off-by:. It is a record that the acker
442has at least reviewed the patch and has indicated acceptance. Hence patch
443mergers will sometimes manually convert an acker's "yep, looks good to me"
444into an Acked-by:.
445
446Acked-by: does not necessarily indicate acknowledgement of the entire patch.
447For example, if a patch affects multiple subsystems and has an Acked-by: from
448one subsystem maintainer then this usually indicates acknowledgement of just
449the part which affects that maintainer's code. Judgement should be used here.
Jonathan Corbetef402032008-03-28 11:22:38 -0600450When in doubt people should refer to the original discussion in the mailing
Andrew Morton0f44cd22007-06-08 13:46:45 -0700451list archives.
452
Jonathan Corbetef402032008-03-28 11:22:38 -0600453If a person has had the opportunity to comment on a patch, but has not
454provided such comments, you may optionally add a "Cc:" tag to the patch.
455This is the only tag which might be added without an explicit action by the
456person it names. This tag documents that potentially interested parties
457have been included in the discussion
Andrew Morton0f44cd22007-06-08 13:46:45 -0700458
Jonathan Corbetef402032008-03-28 11:22:38 -0600459
Jacob Keller8401aa12014-06-06 14:36:39 -070046014) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
Jonathan Corbetbbb0a4242009-01-16 09:49:50 -0700461
462If this patch fixes a problem reported by somebody else, consider adding a
463Reported-by: tag to credit the reporter for their contribution. Please
464note that this tag should not be added without the reporter's permission,
465especially if the problem was not reported in a public forum. That said,
466if we diligently credit our bug reporters, they will, hopefully, be
467inspired to help us again in the future.
Jonathan Corbetef402032008-03-28 11:22:38 -0600468
469A Tested-by: tag indicates that the patch has been successfully tested (in
470some environment) by the person named. This tag informs maintainers that
471some testing has been performed, provides a means to locate testers for
472future patches, and ensures credit for the testers.
473
474Reviewed-by:, instead, indicates that the patch has been reviewed and found
475acceptable according to the Reviewer's Statement:
476
477 Reviewer's statement of oversight
478
479 By offering my Reviewed-by: tag, I state that:
480
481 (a) I have carried out a technical review of this patch to
482 evaluate its appropriateness and readiness for inclusion into
483 the mainline kernel.
484
485 (b) Any problems, concerns, or questions relating to the patch
486 have been communicated back to the submitter. I am satisfied
487 with the submitter's response to my comments.
488
489 (c) While there may be things that could be improved with this
490 submission, I believe that it is, at this time, (1) a
491 worthwhile modification to the kernel, and (2) free of known
492 issues which would argue against its inclusion.
493
494 (d) While I have reviewed the patch and believe it to be sound, I
495 do not (unless explicitly stated elsewhere) make any
496 warranties or guarantees that it will achieve its stated
497 purpose or function properly in any given situation.
498
499A Reviewed-by tag is a statement of opinion that the patch is an
500appropriate modification of the kernel without any remaining serious
501technical issues. Any interested reviewer (who has done the work) can
502offer a Reviewed-by tag for a patch. This tag serves to give credit to
503reviewers and to inform maintainers of the degree of review which has been
504done on the patch. Reviewed-by: tags, when supplied by reviewers known to
505understand the subject area and to perform thorough reviews, will normally
Pavel Machek5801da12009-06-04 16:26:50 +0200506increase the likelihood of your patch getting into the kernel.
Jonathan Corbetef402032008-03-28 11:22:38 -0600507
Mugunthan V N8543ae12013-04-29 16:18:17 -0700508A Suggested-by: tag indicates that the patch idea is suggested by the person
509named and ensures credit to the person for the idea. Please note that this
510tag should not be added without the reporter's permission, especially if the
511idea was not posted in a public forum. That said, if we diligently credit our
512idea reporters, they will, hopefully, be inspired to help us again in the
513future.
514
Jacob Keller8401aa12014-06-06 14:36:39 -0700515A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
516is used to make it easy to determine where a bug originated, which can help
517review a bug fix. This tag also assists the stable kernel team in determining
518which stable kernel versions should receive your fix. This is the preferred
519method for indicating a bug fixed by the patch. See #2 above for more details.
520
Jonathan Corbetef402032008-03-28 11:22:38 -0600521
52215) The canonical patch format
Randy Dunlap84da7c02005-06-28 20:45:30 -0700523
Paul Jackson75f84262005-10-02 18:01:42 -0700524The canonical patch subject line is:
525
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700526 Subject: [PATCH 001/123] subsystem: summary phrase
Paul Jackson75f84262005-10-02 18:01:42 -0700527
528The canonical patch message body contains the following:
529
530 - A "from" line specifying the patch author.
531
532 - An empty line.
533
534 - The body of the explanation, which will be copied to the
535 permanent changelog to describe this patch.
536
537 - The "Signed-off-by:" lines, described above, which will
538 also go in the changelog.
539
540 - A marker line containing simply "---".
541
542 - Any additional comments not suitable for the changelog.
543
544 - The actual patch (diff output).
545
546The Subject line format makes it very easy to sort the emails
547alphabetically by subject line - pretty much any email reader will
548support that - since because the sequence number is zero-padded,
549the numerical and alphabetic sort is the same.
550
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700551The "subsystem" in the email's Subject should identify which
552area or subsystem of the kernel is being patched.
553
554The "summary phrase" in the email's Subject should concisely
555describe the patch which that email contains. The "summary
556phrase" should not be a filename. Do not use the same "summary
Randy Dunlap66effdc2007-05-09 02:33:42 -0700557phrase" for every patch in a whole patch series (where a "patch
558series" is an ordered sequence of multiple, related patches).
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700559
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400560Bear in mind that the "summary phrase" of your email becomes a
561globally-unique identifier for that patch. It propagates all the way
562into the git changelog. The "summary phrase" may later be used in
563developer discussions which refer to the patch. People will want to
564google for the "summary phrase" to read discussion regarding that
565patch. It will also be the only thing that people may quickly see
566when, two or three months later, they are going through perhaps
567thousands of patches using tools such as "gitk" or "git log
568--oneline".
569
570For these reasons, the "summary" must be no more than 70-75
571characters, and it must describe both what the patch changes, as well
572as why the patch might be necessary. It is challenging to be both
573succinct and descriptive, but that is what a well-written summary
574should do.
575
576The "summary phrase" may be prefixed by tags enclosed in square
577brackets: "Subject: [PATCH tag] <summary phrase>". The tags are not
578considered part of the summary phrase, but describe how the patch
579should be treated. Common tags might include a version descriptor if
580the multiple versions of the patch have been sent out in response to
581comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
582comments. If there are four patches in a patch series the individual
583patches may be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures
584that developers understand the order in which the patches should be
585applied and that they have reviewed or applied all of the patches in
586the patch series.
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700587
588A couple of example Subjects:
589
590 Subject: [patch 2/5] ext2: improve scalability of bitmap searching
591 Subject: [PATCHv2 001/207] x86: fix eflags tracking
Paul Jackson75f84262005-10-02 18:01:42 -0700592
593The "from" line must be the very first line in the message body,
594and has the form:
595
596 From: Original Author <author@example.com>
597
598The "from" line specifies who will be credited as the author of the
599patch in the permanent changelog. If the "from" line is missing,
600then the "From:" line from the email header will be used to determine
601the patch author in the changelog.
602
603The explanation body will be committed to the permanent source
604changelog, so should make sense to a competent reader who has long
605since forgotten the immediate details of the discussion that might
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400606have led to this patch. Including symptoms of the failure which the
607patch addresses (kernel log messages, oops messages, etc.) is
608especially useful for people who might be searching the commit logs
609looking for the applicable patch. If a patch fixes a compile failure,
610it may not be necessary to include _all_ of the compile failures; just
611enough that it is likely that someone searching for the patch can find
612it. As in the "summary phrase", it is important to be both succinct as
613well as descriptive.
Paul Jackson75f84262005-10-02 18:01:42 -0700614
615The "---" marker line serves the essential purpose of marking for patch
616handling tools where the changelog message ends.
617
618One good use for the additional comments after the "---" marker is for
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400619a diffstat, to show what files have changed, and the number of
620inserted and deleted lines per file. A diffstat is especially useful
621on bigger patches. Other comments relevant only to the moment or the
622maintainer, not suitable for the permanent changelog, should also go
623here. A good example of such comments might be "patch changelogs"
624which describe what has changed between the v1 and v2 version of the
625patch.
626
627If you are going to include a diffstat after the "---" marker, please
628use diffstat options "-p 1 -w 70" so that filenames are listed from
629the top of the kernel source tree and don't use too much horizontal
Josh Triplett8e3072a2014-04-03 14:48:30 -0700630space (easily fit in 80 columns, maybe with some indentation). (git
631generates appropriate diffstats by default.)
Paul Jackson75f84262005-10-02 18:01:42 -0700632
633See more details on the proper patch format in the following
634references.
635
636
Randy Dunlap14863612008-07-27 20:44:24 -070063716) Sending "git pull" requests (from Linus emails)
Randy Dunlap84da7c02005-06-28 20:45:30 -0700638
Randy Dunlap14863612008-07-27 20:44:24 -0700639Please write the git repo address and branch name alone on the same line
640so that I can't even by mistake pull from the wrong branch, and so
641that a triple-click just selects the whole thing.
642
643So the proper format is something along the lines of:
644
645 "Please pull from
646
647 git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
648
649 to get these changes:"
650
651so that I don't have to hunt-and-peck for the address and inevitably
652get it wrong (actually, I've only gotten it wrong a few times, and
653checking against the diffstat tells me when I get it wrong, but I'm
654just a lot more comfortable when I don't have to "look for" the right
655thing to pull, and double-check that I have the right branch-name).
656
657
658Please use "git diff -M --stat --summary" to generate the diffstat:
659the -M enables rename detection, and the summary enables a summary of
660new/deleted or renamed files.
661
662With rename detection, the statistics are rather different [...]
663because git will notice that a fair number of the changes are renames.
Randy Dunlap84da7c02005-06-28 20:45:30 -0700664
Linus Torvalds1da177e2005-04-16 15:20:36 -0700665-----------------------------------
666SECTION 2 - HINTS, TIPS, AND TRICKS
667-----------------------------------
668
669This section lists many of the common "rules" associated with code
670submitted to the kernel. There are always exceptions... but you must
671have a really good reason for doing so. You could probably call this
672section Linus Computer Science 101.
673
674
675
6761) Read Documentation/CodingStyle
677
678Nuff said. If your code deviates too much from this, it is likely
679to be rejected without further review, and without comment.
680
Keiichi Kii5ab3bd52007-10-26 15:51:44 +0900681One significant exception is when moving code from one file to
682another -- in this case you should not modify the moved code at all in
Andy Whitcroftde7d4f02007-07-15 23:37:22 -0700683the same patch which moves it. This clearly delineates the act of
684moving the code and your changes. This greatly aids review of the
685actual differences and allows tools to better track the history of
686the code itself.
687
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700688Check your patches with the patch style checker prior to submission
Andy Whitcroftde7d4f02007-07-15 23:37:22 -0700689(scripts/checkpatch.pl). The style checker should be viewed as
690a guide not as the final word. If your code looks better with
691a violation then its probably best left alone.
692
693The checker reports at three levels:
694 - ERROR: things that are very likely to be wrong
695 - WARNING: things requiring careful review
696 - CHECK: things requiring thought
697
698You should be able to justify all violations that remain in your
699patch.
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700700
Linus Torvalds1da177e2005-04-16 15:20:36 -0700701
702
7032) #ifdefs are ugly
704
705Code cluttered with ifdefs is difficult to read and maintain. Don't do
706it. Instead, put your ifdefs in a header, and conditionally define
707'static inline' functions, or macros, which are used in the code.
708Let the compiler optimize away the "no-op" case.
709
710Simple example, of poor code:
711
712 dev = alloc_etherdev (sizeof(struct funky_private));
713 if (!dev)
714 return -ENODEV;
715 #ifdef CONFIG_NET_FUNKINESS
716 init_funky_net(dev);
717 #endif
718
719Cleaned-up example:
720
721(in header)
722 #ifndef CONFIG_NET_FUNKINESS
723 static inline void init_funky_net (struct net_device *d) {}
724 #endif
725
726(in the code itself)
727 dev = alloc_etherdev (sizeof(struct funky_private));
728 if (!dev)
729 return -ENODEV;
730 init_funky_net(dev);
731
732
733
7343) 'static inline' is better than a macro
735
736Static inline functions are greatly preferred over macros.
737They provide type safety, have no length limitations, no formatting
738limitations, and under gcc they are as cheap as macros.
739
740Macros should only be used for cases where a static inline is clearly
Jim Meyeringf2b2ea62008-04-02 13:04:46 -0700741suboptimal [there are a few, isolated cases of this in fast paths],
Linus Torvalds1da177e2005-04-16 15:20:36 -0700742or where it is impossible to use a static inline function [such as
743string-izing].
744
745'static inline' is preferred over 'static __inline__', 'extern inline',
746and 'extern __inline__'.
747
748
749
7504) Don't over-design.
751
752Don't try to anticipate nebulous future cases which may or may not
Randy Dunlap84da7c02005-06-28 20:45:30 -0700753be useful: "Make it as simple as you can, and no simpler."
Linus Torvalds1da177e2005-04-16 15:20:36 -0700754
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800755
756
757----------------------
758SECTION 3 - REFERENCES
759----------------------
760
761Andrew Morton, "The perfect patch" (tpp).
Mitchel Humpherys37c703f2014-04-03 14:50:40 -0700762 <http://www.ozlabs.org/~akpm/stuff/tpp.txt>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800763
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700764Jeff Garzik, "Linux kernel patch submission format".
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800765 <http://linux.yyz.us/patch-format.html>
766
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700767Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
Vikram Narayananf5039932011-05-23 12:01:25 -0700768 <http://www.kroah.com/log/linux/maintainer.html>
769 <http://www.kroah.com/log/linux/maintainer-02.html>
770 <http://www.kroah.com/log/linux/maintainer-03.html>
771 <http://www.kroah.com/log/linux/maintainer-04.html>
772 <http://www.kroah.com/log/linux/maintainer-05.html>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800773
Randy Dunlapbc7455f2006-07-30 03:03:45 -0700774NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
Mitchel Humpherys37c703f2014-04-03 14:50:40 -0700775 <https://lkml.org/lkml/2005/7/11/336>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800776
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700777Kernel Documentation/CodingStyle:
Qi Yong4db29c12007-06-12 13:06:49 +0800778 <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800779
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700780Linus Torvalds's mail on the canonical patch format:
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800781 <http://lkml.org/lkml/2005/4/7/183>
Andi Kleen95367272008-10-15 22:02:02 -0700782
783Andi Kleen, "On submitting kernel patches"
Lucas De Marchi25985ed2011-03-30 22:57:33 -0300784 Some strategies to get difficult or controversial changes in.
Andi Kleen95367272008-10-15 22:02:02 -0700785 http://halobates.de/on-submitting-patches.pdf
786
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800787--