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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
Johannes Weiner7b9828d2014-08-05 23:32:56 -070087Describe your problem. Whether your patch is a one-line bug fix or
885000 lines of a new feature, there must be an underlying problem that
89motivated you to do this work. Convince the reviewer that there is a
90problem worth fixing and that it makes sense for them to read past the
91first paragraph.
Linus Torvalds1da177e2005-04-16 15:20:36 -070092
Johannes Weiner7b9828d2014-08-05 23:32:56 -070093Describe user-visible impact. Straight up crashes and lockups are
94pretty convincing, but not all bugs are that blatant. Even if the
95problem was spotted during code review, describe the impact you think
96it can have on users. Keep in mind that the majority of Linux
97installations run kernels from secondary stable trees or
98vendor/product-specific trees that cherry-pick only specific patches
99from upstream, so include anything that could help route your change
100downstream: provoking circumstances, excerpts from dmesg, crash
101descriptions, performance regressions, latency spikes, lockups, etc.
102
103Quantify optimizations and trade-offs. If you claim improvements in
104performance, memory consumption, stack footprint, or binary size,
105include numbers that back them up. But also describe non-obvious
106costs. Optimizations usually aren't free but trade-offs between CPU,
107memory, and readability; or, when it comes to heuristics, between
108different workloads. Describe the expected downsides of your
109optimization so that the reviewer can weigh costs against benefits.
110
111Once the problem is established, describe what you are actually doing
112about it in technical detail. It's important to describe the change
113in plain English for the reviewer to verify that the code is behaving
114as you intend it to.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700115
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400116The maintainer will thank you if you write your patch description in a
117form which can be easily pulled into Linux's source code management
118system, git, as a "commit log". See #15, below.
119
Johannes Weiner7b9828d2014-08-05 23:32:56 -0700120Solve only one problem per patch. If your description starts to get
121long, that's a sign that you probably need to split up your patch.
122See #3, next.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700123
Randy Dunlapd89b1942010-08-09 17:20:21 -0700124When you submit or resubmit a patch or patch series, include the
125complete patch description and justification for it. Don't just
126say that this is version N of the patch (series). Don't expect the
127patch merger to refer back to earlier patch versions or referenced
128URLs to find the patch description and put that into the patch.
129I.e., the patch (series) and its description should be self-contained.
130This benefits both the patch merger(s) and reviewers. Some reviewers
131probably didn't even receive earlier versions of the patch.
132
Josh Triplett74a475a2014-04-03 14:48:28 -0700133Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
134instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
135to do frotz", as if you are giving orders to the codebase to change
136its behaviour.
137
Randy Dunlapd89b1942010-08-09 17:20:21 -0700138If the patch fixes a logged bug entry, refer to that bug entry by
Josh Triplett9547c702014-04-03 14:48:29 -0700139number and URL. If the patch follows from a mailing list discussion,
140give a URL to the mailing list archive; use the https://lkml.kernel.org/
141redirector with a Message-Id, to ensure that the links cannot become
142stale.
143
144However, try to make your explanation understandable without external
145resources. In addition to giving a URL to a mailing list archive or
146bug, summarize the relevant points of the discussion that led to the
147patch as submitted.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700148
Geert Uytterhoeven0af52702013-07-31 14:59:38 -0700149If you want to refer to a specific commit, don't just refer to the
150SHA-1 ID of the commit. Please also include the oneline summary of
151the commit, to make it easier for reviewers to know what it is about.
152Example:
153
154 Commit e21d2170f36602ae2708 ("video: remove unnecessary
155 platform_set_drvdata()") removed the unnecessary
156 platform_set_drvdata(), but left the variable "dev" unused,
157 delete it.
158
Jacob Keller8401aa12014-06-06 14:36:39 -0700159If your patch fixes a bug in a specific commit, e.g. you found an issue using
160git-bisect, please use the 'Fixes:' tag with the first 12 characters of the
161SHA-1 ID, and the one line summary.
162Example:
163
164 Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
165
166The following git-config settings can be used to add a pretty format for
167outputting the above style in the git log or git show commands
168
169 [core]
170 abbrev = 12
171 [pretty]
172 fixes = Fixes: %h (\"%s\")
Linus Torvalds1da177e2005-04-16 15:20:36 -0700173
1743) Separate your changes.
175
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800176Separate _logical changes_ into a single patch file.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700177
178For example, if your changes include both bug fixes and performance
179enhancements for a single driver, separate those changes into two
180or more patches. If your changes include an API update, and a new
181driver which uses that new API, separate those into two patches.
182
183On the other hand, if you make a single change to numerous files,
184group those changes into a single patch. Thus a single logical change
185is contained within a single patch.
186
187If one patch depends on another patch in order for a change to be
188complete, that is OK. Simply note "this patch depends on patch X"
189in your patch description.
190
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800191If you cannot condense your patch set into a smaller set of patches,
192then only post say 15 or so at a time and wait for review and integration.
193
194
Linus Torvalds1da177e2005-04-16 15:20:36 -0700195
Jonathan Corbet6de16eb2014-12-23 08:38:24 -07001964) Style-check your changes.
197----------------------------
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700198
199Check your patch for basic style violations, details of which can be
200found in Documentation/CodingStyle. Failure to do so simply wastes
Linus Nilssonf56d35e2007-07-21 17:49:06 +0200201the reviewers time and will get your patch rejected, probably
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700202without even being read.
203
Jonathan Corbet6de16eb2014-12-23 08:38:24 -0700204One significant exception is when moving code from one file to
205another -- in this case you should not modify the moved code at all in
206the same patch which moves it. This clearly delineates the act of
207moving the code and your changes. This greatly aids review of the
208actual differences and allows tools to better track the history of
209the code itself.
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700210
Jonathan Corbet6de16eb2014-12-23 08:38:24 -0700211Check your patches with the patch style checker prior to submission
212(scripts/checkpatch.pl). Note, though, that the style checker should be
213viewed as a guide, not as a replacement for human judgment. If your code
214looks better with a violation then its probably best left alone.
215
216The checker reports at three levels:
217 - ERROR: things that are very likely to be wrong
218 - WARNING: things requiring careful review
219 - CHECK: things requiring thought
220
221You should be able to justify all violations that remain in your
222patch.
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700223
224
2255) Select e-mail destination.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700226
227Look through the MAINTAINERS file and the source code, and determine
228if your change applies to a specific subsystem of the kernel, with
Michel Machadoe52d2e12012-04-02 22:10:53 -0400229an assigned maintainer. If so, e-mail that person. The script
230scripts/get_maintainer.pl can be very useful at this step.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700231
232If no maintainer is listed, or the maintainer does not respond, send
233your patch to the primary Linux kernel developer's mailing list,
234linux-kernel@vger.kernel.org. Most kernel developers monitor this
235e-mail list, and can comment on your changes.
236
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800237
238Do not send more than 15 patches at once to the vger mailing lists!!!
239
240
Linus Torvalds1da177e2005-04-16 15:20:36 -0700241Linus Torvalds is the final arbiter of all changes accepted into the
Linus Torvalds99ddcc72007-01-23 14:22:35 -0800242Linux kernel. His e-mail address is <torvalds@linux-foundation.org>.
243He gets a lot of e-mail, so typically you should do your best to -avoid-
244sending him e-mail.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700245
246Patches which are bug fixes, are "obvious" changes, or similarly
247require little discussion should be sent or CC'd to Linus. Patches
248which require discussion or do not have a clear advantage should
249usually be sent first to linux-kernel. Only after the patch is
250discussed should the patch then be submitted to Linus.
251
Linus Torvalds1da177e2005-04-16 15:20:36 -0700252
253
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002546) Select your CC (e-mail carbon copy) list.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700255
256Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
257
258Other kernel developers besides Linus need to be aware of your change,
259so that they may comment on it and offer code review and suggestions.
260linux-kernel is the primary Linux kernel developer mailing list.
261Other mailing lists are available for specific subsystems, such as
262USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the
263MAINTAINERS file for a mailing list that relates specifically to
264your change.
265
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800266Majordomo lists of VGER.KERNEL.ORG at:
267 <http://vger.kernel.org/vger-lists.html>
268
Paul Jackson1caf1f02005-07-31 22:34:48 -0700269If changes affect userland-kernel interfaces, please send
270the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
271a man-pages patch, or at least a notification of the change,
272so that some information makes its way into the manual pages.
273
Michael Brunner8103b5c2009-08-04 00:41:11 +0200274Even if the maintainer did not respond in step #5, make sure to ALWAYS
Linus Torvalds1da177e2005-04-16 15:20:36 -0700275copy the maintainer when you change their code.
276
277For small patches you may want to CC the Trivial Patch Monkey
Markus Heidelberg82d27b22009-06-12 01:02:34 +0200278trivial@kernel.org which collects "trivial" patches. Have a look
279into the MAINTAINERS file for its current manager.
280Trivial patches must qualify for one of the following rules:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700281 Spelling fixes in documentation
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700282 Spelling fixes which could break grep(1)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700283 Warning fixes (cluttering with useless warnings is bad)
284 Compilation fixes (only if they are actually correct)
285 Runtime fixes (only if they actually fix things)
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700286 Removing use of deprecated functions/macros (eg. check_region)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700287 Contact detail and documentation fixes
288 Non-portable code replaced by portable code (even in arch-specific,
289 since people copy, as long as it's trivial)
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700290 Any fix by the author/maintainer of the file (ie. patch monkey
Linus Torvalds1da177e2005-04-16 15:20:36 -0700291 in re-transmission mode)
Randy Dunlap84da7c02005-06-28 20:45:30 -0700292
Linus Torvalds1da177e2005-04-16 15:20:36 -0700293
294
Andy Whitcroft0a920b52007-06-01 00:46:48 -07002957) No MIME, no links, no compression, no attachments. Just plain text.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700296
297Linus and other kernel developers need to be able to read and comment
298on the changes you are submitting. It is important for a kernel
299developer to be able to "quote" your changes, using standard e-mail
300tools, so that they may comment on specific portions of your code.
301
302For this reason, all patches should be submitting e-mail "inline".
303WARNING: Be wary of your editor's word-wrap corrupting your patch,
304if you choose to cut-n-paste your patch.
305
306Do not attach the patch as a MIME attachment, compressed or not.
307Many popular e-mail applications will not always transmit a MIME
308attachment as plain text, making it impossible to comment on your
309code. A MIME attachment also takes Linus a bit more time to process,
310decreasing the likelihood of your MIME-attached change being accepted.
311
312Exception: If your mailer is mangling patches then someone may ask
313you to re-send them using MIME.
314
Michael Opdenacker097091c2008-02-03 18:06:58 +0200315See Documentation/email-clients.txt for hints about configuring
316your e-mail client so that it sends your patches untouched.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700317
Andy Whitcroft0a920b52007-06-01 00:46:48 -07003188) E-mail size.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700319
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700320When sending patches to Linus, always follow step #7.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700321
322Large changes are not appropriate for mailing lists, and some
Randy Dunlap4932be72009-10-01 15:44:06 -0700323maintainers. If your patch, uncompressed, exceeds 300 kB in size,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700324it is preferred that you store your patch on an Internet-accessible
325server, and provide instead a URL (link) pointing to your patch.
326
327
328
Andy Whitcroft0a920b52007-06-01 00:46:48 -07003299) Name your kernel version.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700330
331It is important to note, either in the subject line or in the patch
332description, the kernel version to which this patch applies.
333
334If the patch does not apply cleanly to the latest kernel version,
335Linus will not apply it.
336
337
338
Andy Whitcroft0a920b52007-06-01 00:46:48 -070033910) Don't get discouraged. Re-submit.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700340
341After you have submitted your change, be patient and wait. If Linus
342likes your change and applies it, it will appear in the next version
343of the kernel that he releases.
344
345However, if your change doesn't appear in the next version of the
346kernel, there could be any number of reasons. It's YOUR job to
347narrow down those reasons, correct what was wrong, and submit your
348updated change.
349
350It is quite common for Linus to "drop" your patch without comment.
351That's the nature of the system. If he drops your patch, it could be
352due to
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700353* Your patch did not apply cleanly to the latest kernel version.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700354* Your patch was not sufficiently discussed on linux-kernel.
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700355* A style issue (see section 2).
356* An e-mail formatting issue (re-read this section).
357* A technical problem with your change.
358* He gets tons of e-mail, and yours got lost in the shuffle.
359* You are being annoying.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700360
361When in doubt, solicit comments on linux-kernel mailing list.
362
363
364
Andy Whitcroft0a920b52007-06-01 00:46:48 -070036511) Include PATCH in the subject
Linus Torvalds1da177e2005-04-16 15:20:36 -0700366
367Due to high e-mail traffic to Linus, and to linux-kernel, it is common
368convention to prefix your subject line with [PATCH]. This lets Linus
369and other kernel developers more easily distinguish patches from other
370e-mail discussions.
371
372
373
Andy Whitcroft0a920b52007-06-01 00:46:48 -070037412) Sign your work
Linus Torvalds1da177e2005-04-16 15:20:36 -0700375
376To improve tracking of who did what, especially with patches that can
377percolate to their final resting place in the kernel through several
378layers of maintainers, we've introduced a "sign-off" procedure on
379patches that are being emailed around.
380
381The sign-off is a simple line at the end of the explanation for the
382patch, which certifies that you wrote it or otherwise have the right to
Zac Storerdb12fb82011-08-13 12:34:45 -0700383pass it on as an open-source patch. The rules are pretty simple: if you
Linus Torvalds1da177e2005-04-16 15:20:36 -0700384can certify the below:
385
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700386 Developer's Certificate of Origin 1.1
Linus Torvalds1da177e2005-04-16 15:20:36 -0700387
388 By making a contribution to this project, I certify that:
389
390 (a) The contribution was created in whole or in part by me and I
391 have the right to submit it under the open source license
392 indicated in the file; or
393
394 (b) The contribution is based upon previous work that, to the best
395 of my knowledge, is covered under an appropriate open source
396 license and I have the right under that license to submit that
397 work with modifications, whether created in whole or in part
398 by me, under the same open source license (unless I am
399 permitted to submit under a different license), as indicated
400 in the file; or
401
402 (c) The contribution was provided directly to me by some other
403 person who certified (a), (b) or (c) and I have not modified
404 it.
405
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700406 (d) I understand and agree that this project and the contribution
407 are public and that a record of the contribution (including all
408 personal information I submit with it, including my sign-off) is
409 maintained indefinitely and may be redistributed consistent with
410 this project or the open source license(s) involved.
411
Linus Torvalds1da177e2005-04-16 15:20:36 -0700412then you just add a line saying
413
Alexey Dobriyan9fd55592005-06-25 14:59:34 -0700414 Signed-off-by: Random J Developer <random@developer.example.org>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700415
Greg KHaf45f322006-09-12 20:35:52 -0700416using your real name (sorry, no pseudonyms or anonymous contributions.)
417
Linus Torvalds1da177e2005-04-16 15:20:36 -0700418Some people also put extra tags at the end. They'll just be ignored for
419now, but you can do this to mark internal company procedures or just
420point out some special detail about the sign-off.
421
Willy Tarreauadbd5882008-06-03 00:20:28 +0200422If you are a subsystem or branch maintainer, sometimes you need to slightly
423modify patches you receive in order to merge them, because the code is not
424exactly the same in your tree and the submitters'. If you stick strictly to
425rule (c), you should ask the submitter to rediff, but this is a totally
426counter-productive waste of time and energy. Rule (b) allows you to adjust
427the code, but then it is very impolite to change one submitter's code and
428make him endorse your bugs. To solve this problem, it is recommended that
429you add a line between the last Signed-off-by header and yours, indicating
430the nature of your changes. While there is nothing mandatory about this, it
431seems like prepending the description with your mail and/or name, all
432enclosed in square brackets, is noticeable enough to make it obvious that
433you are responsible for last-minute changes. Example :
434
435 Signed-off-by: Random J Developer <random@developer.example.org>
436 [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
437 Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
438
Jeremiah Mahler305af082014-05-22 00:04:26 -0700439This practice is particularly helpful if you maintain a stable branch and
Willy Tarreauadbd5882008-06-03 00:20:28 +0200440want at the same time to credit the author, track changes, merge the fix,
441and protect the submitter from complaints. Note that under no circumstances
442can you change the author's identity (the From header), as it is the one
443which appears in the changelog.
444
Jeremiah Mahler305af082014-05-22 00:04:26 -0700445Special note to back-porters: It seems to be a common and useful practice
Willy Tarreauadbd5882008-06-03 00:20:28 +0200446to insert an indication of the origin of a patch at the top of the commit
447message (just after the subject line) to facilitate tracking. For instance,
448here's what we see in 2.6-stable :
449
450 Date: Tue May 13 19:10:30 2008 +0000
451
452 SCSI: libiscsi regression in 2.6.25: fix nop timer handling
453
454 commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
455
456And here's what appears in 2.4 :
457
458 Date: Tue May 13 22:12:27 2008 +0200
459
460 wireless, airo: waitbusy() won't delay
461
462 [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
463
464Whatever the format, this information provides a valuable help to people
465tracking your trees, and to people trying to trouble-shoot bugs in your
466tree.
467
Linus Torvalds1da177e2005-04-16 15:20:36 -0700468
Jonathan Corbetef402032008-03-28 11:22:38 -060046913) When to use Acked-by: and Cc:
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700470
Andrew Morton0f44cd22007-06-08 13:46:45 -0700471The Signed-off-by: tag indicates that the signer was involved in the
472development of the patch, or that he/she was in the patch's delivery path.
473
474If a person was not directly involved in the preparation or handling of a
475patch but wishes to signify and record their approval of it then they can
476arrange to have an Acked-by: line added to the patch's changelog.
477
478Acked-by: is often used by the maintainer of the affected code when that
479maintainer neither contributed to nor forwarded the patch.
480
481Acked-by: is not as formal as Signed-off-by:. It is a record that the acker
482has at least reviewed the patch and has indicated acceptance. Hence patch
483mergers will sometimes manually convert an acker's "yep, looks good to me"
484into an Acked-by:.
485
486Acked-by: does not necessarily indicate acknowledgement of the entire patch.
487For example, if a patch affects multiple subsystems and has an Acked-by: from
488one subsystem maintainer then this usually indicates acknowledgement of just
489the part which affects that maintainer's code. Judgement should be used here.
Jonathan Corbetef402032008-03-28 11:22:38 -0600490When in doubt people should refer to the original discussion in the mailing
Andrew Morton0f44cd22007-06-08 13:46:45 -0700491list archives.
492
Jonathan Corbetef402032008-03-28 11:22:38 -0600493If a person has had the opportunity to comment on a patch, but has not
494provided such comments, you may optionally add a "Cc:" tag to the patch.
495This is the only tag which might be added without an explicit action by the
496person it names. This tag documents that potentially interested parties
497have been included in the discussion
Andrew Morton0f44cd22007-06-08 13:46:45 -0700498
Jonathan Corbetef402032008-03-28 11:22:38 -0600499
Jacob Keller8401aa12014-06-06 14:36:39 -070050014) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
Jonathan Corbetbbb0a4242009-01-16 09:49:50 -0700501
Dan Carpenterd75ef702014-10-29 13:01:36 +0300502The Reported-by tag gives credit to people who find bugs and report them and it
503hopefully inspires them to help us again in the future. Please note that if
504the bug was reported in private, then ask for permission first before using the
505Reported-by tag.
Jonathan Corbetef402032008-03-28 11:22:38 -0600506
507A Tested-by: tag indicates that the patch has been successfully tested (in
508some environment) by the person named. This tag informs maintainers that
509some testing has been performed, provides a means to locate testers for
510future patches, and ensures credit for the testers.
511
512Reviewed-by:, instead, indicates that the patch has been reviewed and found
513acceptable according to the Reviewer's Statement:
514
515 Reviewer's statement of oversight
516
517 By offering my Reviewed-by: tag, I state that:
518
519 (a) I have carried out a technical review of this patch to
520 evaluate its appropriateness and readiness for inclusion into
521 the mainline kernel.
522
523 (b) Any problems, concerns, or questions relating to the patch
524 have been communicated back to the submitter. I am satisfied
525 with the submitter's response to my comments.
526
527 (c) While there may be things that could be improved with this
528 submission, I believe that it is, at this time, (1) a
529 worthwhile modification to the kernel, and (2) free of known
530 issues which would argue against its inclusion.
531
532 (d) While I have reviewed the patch and believe it to be sound, I
533 do not (unless explicitly stated elsewhere) make any
534 warranties or guarantees that it will achieve its stated
535 purpose or function properly in any given situation.
536
537A Reviewed-by tag is a statement of opinion that the patch is an
538appropriate modification of the kernel without any remaining serious
539technical issues. Any interested reviewer (who has done the work) can
540offer a Reviewed-by tag for a patch. This tag serves to give credit to
541reviewers and to inform maintainers of the degree of review which has been
542done on the patch. Reviewed-by: tags, when supplied by reviewers known to
543understand the subject area and to perform thorough reviews, will normally
Pavel Machek5801da12009-06-04 16:26:50 +0200544increase the likelihood of your patch getting into the kernel.
Jonathan Corbetef402032008-03-28 11:22:38 -0600545
Mugunthan V N8543ae12013-04-29 16:18:17 -0700546A Suggested-by: tag indicates that the patch idea is suggested by the person
547named and ensures credit to the person for the idea. Please note that this
548tag should not be added without the reporter's permission, especially if the
549idea was not posted in a public forum. That said, if we diligently credit our
550idea reporters, they will, hopefully, be inspired to help us again in the
551future.
552
Jacob Keller8401aa12014-06-06 14:36:39 -0700553A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
554is used to make it easy to determine where a bug originated, which can help
555review a bug fix. This tag also assists the stable kernel team in determining
556which stable kernel versions should receive your fix. This is the preferred
557method for indicating a bug fixed by the patch. See #2 above for more details.
558
Jonathan Corbetef402032008-03-28 11:22:38 -0600559
56015) The canonical patch format
Randy Dunlap84da7c02005-06-28 20:45:30 -0700561
Paul Jackson75f84262005-10-02 18:01:42 -0700562The canonical patch subject line is:
563
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700564 Subject: [PATCH 001/123] subsystem: summary phrase
Paul Jackson75f84262005-10-02 18:01:42 -0700565
566The canonical patch message body contains the following:
567
568 - A "from" line specifying the patch author.
569
570 - An empty line.
571
572 - The body of the explanation, which will be copied to the
573 permanent changelog to describe this patch.
574
575 - The "Signed-off-by:" lines, described above, which will
576 also go in the changelog.
577
578 - A marker line containing simply "---".
579
580 - Any additional comments not suitable for the changelog.
581
582 - The actual patch (diff output).
583
584The Subject line format makes it very easy to sort the emails
585alphabetically by subject line - pretty much any email reader will
586support that - since because the sequence number is zero-padded,
587the numerical and alphabetic sort is the same.
588
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700589The "subsystem" in the email's Subject should identify which
590area or subsystem of the kernel is being patched.
591
592The "summary phrase" in the email's Subject should concisely
593describe the patch which that email contains. The "summary
594phrase" should not be a filename. Do not use the same "summary
Randy Dunlap66effdc2007-05-09 02:33:42 -0700595phrase" for every patch in a whole patch series (where a "patch
596series" is an ordered sequence of multiple, related patches).
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700597
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400598Bear in mind that the "summary phrase" of your email becomes a
599globally-unique identifier for that patch. It propagates all the way
600into the git changelog. The "summary phrase" may later be used in
601developer discussions which refer to the patch. People will want to
602google for the "summary phrase" to read discussion regarding that
603patch. It will also be the only thing that people may quickly see
604when, two or three months later, they are going through perhaps
605thousands of patches using tools such as "gitk" or "git log
606--oneline".
607
608For these reasons, the "summary" must be no more than 70-75
609characters, and it must describe both what the patch changes, as well
610as why the patch might be necessary. It is challenging to be both
611succinct and descriptive, but that is what a well-written summary
612should do.
613
614The "summary phrase" may be prefixed by tags enclosed in square
615brackets: "Subject: [PATCH tag] <summary phrase>". The tags are not
616considered part of the summary phrase, but describe how the patch
617should be treated. Common tags might include a version descriptor if
618the multiple versions of the patch have been sent out in response to
619comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
620comments. If there are four patches in a patch series the individual
621patches may be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures
622that developers understand the order in which the patches should be
623applied and that they have reviewed or applied all of the patches in
624the patch series.
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700625
626A couple of example Subjects:
627
628 Subject: [patch 2/5] ext2: improve scalability of bitmap searching
629 Subject: [PATCHv2 001/207] x86: fix eflags tracking
Paul Jackson75f84262005-10-02 18:01:42 -0700630
631The "from" line must be the very first line in the message body,
632and has the form:
633
634 From: Original Author <author@example.com>
635
636The "from" line specifies who will be credited as the author of the
637patch in the permanent changelog. If the "from" line is missing,
638then the "From:" line from the email header will be used to determine
639the patch author in the changelog.
640
641The explanation body will be committed to the permanent source
642changelog, so should make sense to a competent reader who has long
643since forgotten the immediate details of the discussion that might
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400644have led to this patch. Including symptoms of the failure which the
645patch addresses (kernel log messages, oops messages, etc.) is
646especially useful for people who might be searching the commit logs
647looking for the applicable patch. If a patch fixes a compile failure,
648it may not be necessary to include _all_ of the compile failures; just
649enough that it is likely that someone searching for the patch can find
650it. As in the "summary phrase", it is important to be both succinct as
651well as descriptive.
Paul Jackson75f84262005-10-02 18:01:42 -0700652
653The "---" marker line serves the essential purpose of marking for patch
654handling tools where the changelog message ends.
655
656One good use for the additional comments after the "---" marker is for
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400657a diffstat, to show what files have changed, and the number of
658inserted and deleted lines per file. A diffstat is especially useful
659on bigger patches. Other comments relevant only to the moment or the
660maintainer, not suitable for the permanent changelog, should also go
661here. A good example of such comments might be "patch changelogs"
662which describe what has changed between the v1 and v2 version of the
663patch.
664
665If you are going to include a diffstat after the "---" marker, please
666use diffstat options "-p 1 -w 70" so that filenames are listed from
667the top of the kernel source tree and don't use too much horizontal
Josh Triplett8e3072a2014-04-03 14:48:30 -0700668space (easily fit in 80 columns, maybe with some indentation). (git
669generates appropriate diffstats by default.)
Paul Jackson75f84262005-10-02 18:01:42 -0700670
671See more details on the proper patch format in the following
672references.
673
674
Randy Dunlap14863612008-07-27 20:44:24 -070067516) Sending "git pull" requests (from Linus emails)
Randy Dunlap84da7c02005-06-28 20:45:30 -0700676
Randy Dunlap14863612008-07-27 20:44:24 -0700677Please write the git repo address and branch name alone on the same line
678so that I can't even by mistake pull from the wrong branch, and so
679that a triple-click just selects the whole thing.
680
681So the proper format is something along the lines of:
682
683 "Please pull from
684
685 git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
686
687 to get these changes:"
688
689so that I don't have to hunt-and-peck for the address and inevitably
690get it wrong (actually, I've only gotten it wrong a few times, and
691checking against the diffstat tells me when I get it wrong, but I'm
692just a lot more comfortable when I don't have to "look for" the right
693thing to pull, and double-check that I have the right branch-name).
694
695
696Please use "git diff -M --stat --summary" to generate the diffstat:
697the -M enables rename detection, and the summary enables a summary of
698new/deleted or renamed files.
699
700With rename detection, the statistics are rather different [...]
701because git will notice that a fair number of the changes are renames.
Randy Dunlap84da7c02005-06-28 20:45:30 -0700702
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800703
704----------------------
Jonathan Corbet6de16eb2014-12-23 08:38:24 -0700705SECTION 2 - REFERENCES
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800706----------------------
707
708Andrew Morton, "The perfect patch" (tpp).
Mitchel Humpherys37c703f2014-04-03 14:50:40 -0700709 <http://www.ozlabs.org/~akpm/stuff/tpp.txt>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800710
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700711Jeff Garzik, "Linux kernel patch submission format".
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800712 <http://linux.yyz.us/patch-format.html>
713
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700714Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
Vikram Narayananf5039932011-05-23 12:01:25 -0700715 <http://www.kroah.com/log/linux/maintainer.html>
716 <http://www.kroah.com/log/linux/maintainer-02.html>
717 <http://www.kroah.com/log/linux/maintainer-03.html>
718 <http://www.kroah.com/log/linux/maintainer-04.html>
719 <http://www.kroah.com/log/linux/maintainer-05.html>
Sudip Mukherjee7e0dae62014-09-07 11:26:12 -0700720 <http://www.kroah.com/log/linux/maintainer-06.html>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800721
Randy Dunlapbc7455f2006-07-30 03:03:45 -0700722NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
Mitchel Humpherys37c703f2014-04-03 14:50:40 -0700723 <https://lkml.org/lkml/2005/7/11/336>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800724
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700725Kernel Documentation/CodingStyle:
Qi Yong4db29c12007-06-12 13:06:49 +0800726 <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800727
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700728Linus Torvalds's mail on the canonical patch format:
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800729 <http://lkml.org/lkml/2005/4/7/183>
Andi Kleen95367272008-10-15 22:02:02 -0700730
731Andi Kleen, "On submitting kernel patches"
Lucas De Marchi25985ed2011-03-30 22:57:33 -0300732 Some strategies to get difficult or controversial changes in.
Andi Kleen95367272008-10-15 22:02:02 -0700733 http://halobates.de/on-submitting-patches.pdf
734
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800735--