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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
Jonathan Corbetd00c4552014-12-23 08:54:36 -070013This document contains a large number of suggestions in a relatively terse
14format. For detailed information on how the kernel development process
15works, see Documentation/development-process. Also, read
16Documentation/SubmitChecklist for a list of items to check before
17submitting code. If you are submitting a driver, also read
Jonathan Corbet082bd1c2014-12-23 09:27:04 -070018Documentation/SubmittingDrivers; for device tree binding patches, read
19Documentation/devicetree/bindings/submitting-patches.txt.
Linus Torvalds1da177e2005-04-16 15:20:36 -070020
Josh Triplett8e3072a2014-04-03 14:48:30 -070021Many of these steps describe the default behavior of the git version
22control system; if you use git to prepare your patches, you'll find much
23of the mechanical work done for you, though you'll still need to prepare
Jonathan Corbetd00c4552014-12-23 08:54:36 -070024and document a sensible set of patches. In general, use of git will make
25your life as a kernel developer easier.
Linus Torvalds1da177e2005-04-16 15:20:36 -070026
27--------------------------------------------
28SECTION 1 - CREATING AND SENDING YOUR CHANGE
29--------------------------------------------
30
31
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700320) Obtain a current source tree
33-------------------------------
34
35If you do not have a repository with the current kernel source handy, use
36git to obtain one. You'll want to start with the mainline repository,
37which can be grabbed with:
38
39 git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
40
41Note, however, that you may not want to develop against the mainline tree
42directly. Most subsystem maintainers run their own trees and want to see
43patches prepared against those trees. See the "T:" entry for the subsystem
44in the MAINTAINERS file to find that tree, or simply ask the maintainer if
45the tree is not listed there.
46
47It is still possible to download kernel releases via tarballs (as described
48in the next section), but that is the hard way to do kernel development.
Linus Torvalds1da177e2005-04-16 15:20:36 -070049
501) "diff -up"
51------------
52
Jonathan Corbet7994cc12014-12-23 08:43:41 -070053If you must generate your patches by hand, use "diff -up" or "diff -uprN"
54to create patches. Git generates patches in this form by default; if
55you're using git, you can skip this section entirely.
Linus Torvalds1da177e2005-04-16 15:20:36 -070056
57All changes to the Linux kernel occur in the form of patches, as
58generated by diff(1). When creating your patch, make sure to create it
59in "unified diff" format, as supplied by the '-u' argument to diff(1).
60Also, please use the '-p' argument which shows which C function each
61change is in - that makes the resultant diff a lot easier to read.
62Patches should be based in the root kernel source directory,
63not in any lower subdirectory.
64
65To create a patch for a single file, it is often sufficient to do:
66
Jonathan Corbetd00c4552014-12-23 08:54:36 -070067 SRCTREE= linux
Linus Torvalds1da177e2005-04-16 15:20:36 -070068 MYFILE= drivers/net/mydriver.c
69
70 cd $SRCTREE
71 cp $MYFILE $MYFILE.orig
72 vi $MYFILE # make your change
73 cd ..
74 diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
75
76To create a patch for multiple files, you should unpack a "vanilla",
77or unmodified kernel source tree, and generate a diff against your
78own source tree. For example:
79
Jonathan Corbetd00c4552014-12-23 08:54:36 -070080 MYSRC= /devel/linux
Linus Torvalds1da177e2005-04-16 15:20:36 -070081
Jonathan Corbetd00c4552014-12-23 08:54:36 -070082 tar xvfz linux-3.19.tar.gz
83 mv linux-3.19 linux-3.19-vanilla
84 diff -uprN -X linux-3.19-vanilla/Documentation/dontdiff \
85 linux-3.19-vanilla $MYSRC > /tmp/patch
Linus Torvalds1da177e2005-04-16 15:20:36 -070086
87"dontdiff" is a list of files which are generated by the kernel during
88the build process, and should be ignored in any diff(1)-generated
Jonathan Corbetd00c4552014-12-23 08:54:36 -070089patch.
Linus Torvalds1da177e2005-04-16 15:20:36 -070090
91Make sure your patch does not include any extra files which do not
92belong in a patch submission. Make sure to review your patch -after-
93generated it with diff(1), to ensure accuracy.
94
Josh Triplett8e3072a2014-04-03 14:48:30 -070095If your changes produce a lot of deltas, you need to split them into
96individual patches which modify things in logical stages; see section
97#3. This will facilitate easier reviewing by other kernel developers,
98very important if you want your patch accepted.
Linus Torvalds1da177e2005-04-16 15:20:36 -070099
Josh Triplett8e3072a2014-04-03 14:48:30 -0700100If you're using git, "git rebase -i" can help you with this process. If
101you're not using git, quilt <http://savannah.nongnu.org/projects/quilt>
102is another popular alternative.
Randy Dunlap84da7c02005-06-28 20:45:30 -0700103
104
Linus Torvalds1da177e2005-04-16 15:20:36 -0700105
1062) Describe your changes.
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700107-------------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700108
Johannes Weiner7b9828d2014-08-05 23:32:56 -0700109Describe your problem. Whether your patch is a one-line bug fix or
1105000 lines of a new feature, there must be an underlying problem that
111motivated you to do this work. Convince the reviewer that there is a
112problem worth fixing and that it makes sense for them to read past the
113first paragraph.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700114
Johannes Weiner7b9828d2014-08-05 23:32:56 -0700115Describe user-visible impact. Straight up crashes and lockups are
116pretty convincing, but not all bugs are that blatant. Even if the
117problem was spotted during code review, describe the impact you think
118it can have on users. Keep in mind that the majority of Linux
119installations run kernels from secondary stable trees or
120vendor/product-specific trees that cherry-pick only specific patches
121from upstream, so include anything that could help route your change
122downstream: provoking circumstances, excerpts from dmesg, crash
123descriptions, performance regressions, latency spikes, lockups, etc.
124
125Quantify optimizations and trade-offs. If you claim improvements in
126performance, memory consumption, stack footprint, or binary size,
127include numbers that back them up. But also describe non-obvious
128costs. Optimizations usually aren't free but trade-offs between CPU,
129memory, and readability; or, when it comes to heuristics, between
130different workloads. Describe the expected downsides of your
131optimization so that the reviewer can weigh costs against benefits.
132
133Once the problem is established, describe what you are actually doing
134about it in technical detail. It's important to describe the change
135in plain English for the reviewer to verify that the code is behaving
136as you intend it to.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700137
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400138The maintainer will thank you if you write your patch description in a
139form which can be easily pulled into Linux's source code management
140system, git, as a "commit log". See #15, below.
141
Johannes Weiner7b9828d2014-08-05 23:32:56 -0700142Solve only one problem per patch. If your description starts to get
143long, that's a sign that you probably need to split up your patch.
144See #3, next.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700145
Randy Dunlapd89b1942010-08-09 17:20:21 -0700146When you submit or resubmit a patch or patch series, include the
147complete patch description and justification for it. Don't just
148say that this is version N of the patch (series). Don't expect the
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700149subsystem maintainer to refer back to earlier patch versions or referenced
Randy Dunlapd89b1942010-08-09 17:20:21 -0700150URLs to find the patch description and put that into the patch.
151I.e., the patch (series) and its description should be self-contained.
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700152This benefits both the maintainers and reviewers. Some reviewers
Randy Dunlapd89b1942010-08-09 17:20:21 -0700153probably didn't even receive earlier versions of the patch.
154
Josh Triplett74a475a2014-04-03 14:48:28 -0700155Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
156instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
157to do frotz", as if you are giving orders to the codebase to change
158its behaviour.
159
Randy Dunlapd89b1942010-08-09 17:20:21 -0700160If the patch fixes a logged bug entry, refer to that bug entry by
Josh Triplett9547c702014-04-03 14:48:29 -0700161number and URL. If the patch follows from a mailing list discussion,
162give a URL to the mailing list archive; use the https://lkml.kernel.org/
163redirector with a Message-Id, to ensure that the links cannot become
164stale.
165
166However, try to make your explanation understandable without external
167resources. In addition to giving a URL to a mailing list archive or
168bug, summarize the relevant points of the discussion that led to the
169patch as submitted.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700170
Geert Uytterhoeven0af52702013-07-31 14:59:38 -0700171If you want to refer to a specific commit, don't just refer to the
172SHA-1 ID of the commit. Please also include the oneline summary of
173the commit, to make it easier for reviewers to know what it is about.
174Example:
175
176 Commit e21d2170f36602ae2708 ("video: remove unnecessary
177 platform_set_drvdata()") removed the unnecessary
178 platform_set_drvdata(), but left the variable "dev" unused,
179 delete it.
180
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700181You should also be sure to use at least the first twelve characters of the
182SHA-1 ID. The kernel repository holds a *lot* of objects, making
183collisions with shorter IDs a real possibility. Bear in mind that, even if
184there is no collision with your six-character ID now, that condition may
185change five years from now.
186
Jacob Keller8401aa12014-06-06 14:36:39 -0700187If your patch fixes a bug in a specific commit, e.g. you found an issue using
188git-bisect, please use the 'Fixes:' tag with the first 12 characters of the
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700189SHA-1 ID, and the one line summary. For example:
Jacob Keller8401aa12014-06-06 14:36:39 -0700190
191 Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
192
193The following git-config settings can be used to add a pretty format for
194outputting the above style in the git log or git show commands
195
196 [core]
197 abbrev = 12
198 [pretty]
199 fixes = Fixes: %h (\"%s\")
Linus Torvalds1da177e2005-04-16 15:20:36 -0700200
2013) Separate your changes.
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700202-------------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700203
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700204Separate each _logical change_ into a separate patch.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700205
206For example, if your changes include both bug fixes and performance
207enhancements for a single driver, separate those changes into two
208or more patches. If your changes include an API update, and a new
209driver which uses that new API, separate those into two patches.
210
211On the other hand, if you make a single change to numerous files,
212group those changes into a single patch. Thus a single logical change
213is contained within a single patch.
214
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700215The point to remember is that each patch should make an easily understood
216change that can be verified by reviewers. Each patch should be justifiable
217on its own merits.
218
Linus Torvalds1da177e2005-04-16 15:20:36 -0700219If one patch depends on another patch in order for a change to be
220complete, that is OK. Simply note "this patch depends on patch X"
221in your patch description.
222
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700223When dividing your change into a series of patches, take special care to
224ensure that the kernel builds and runs properly after each patch in the
225series. Developers using "git bisect" to track down a problem can end up
226splitting your patch series at any point; they will not thank you if you
227introduce bugs in the middle.
228
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800229If you cannot condense your patch set into a smaller set of patches,
230then only post say 15 or so at a time and wait for review and integration.
231
232
Linus Torvalds1da177e2005-04-16 15:20:36 -0700233
Jonathan Corbet6de16eb2014-12-23 08:38:24 -07002344) Style-check your changes.
235----------------------------
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700236
237Check your patch for basic style violations, details of which can be
238found in Documentation/CodingStyle. Failure to do so simply wastes
Linus Nilssonf56d35e2007-07-21 17:49:06 +0200239the reviewers time and will get your patch rejected, probably
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700240without even being read.
241
Jonathan Corbet6de16eb2014-12-23 08:38:24 -0700242One significant exception is when moving code from one file to
243another -- in this case you should not modify the moved code at all in
244the same patch which moves it. This clearly delineates the act of
245moving the code and your changes. This greatly aids review of the
246actual differences and allows tools to better track the history of
247the code itself.
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700248
Jonathan Corbet6de16eb2014-12-23 08:38:24 -0700249Check your patches with the patch style checker prior to submission
250(scripts/checkpatch.pl). Note, though, that the style checker should be
251viewed as a guide, not as a replacement for human judgment. If your code
252looks better with a violation then its probably best left alone.
253
254The checker reports at three levels:
255 - ERROR: things that are very likely to be wrong
256 - WARNING: things requiring careful review
257 - CHECK: things requiring thought
258
259You should be able to justify all violations that remain in your
260patch.
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700261
262
Jonathan Corbetccae8612014-12-23 08:49:18 -07002635) Select the recipients for your patch.
264----------------------------------------
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700265
Jonathan Corbetccae8612014-12-23 08:49:18 -0700266You should always copy the appropriate subsystem maintainer(s) on any patch
267to code that they maintain; look through the MAINTAINERS file and the
268source code revision history to see who those maintainers are. The
269script scripts/get_maintainer.pl can be very useful at this step. If you
Sébastien Hindererd6eff072015-07-08 21:12:32 +0200270cannot find a maintainer for the subsystem you are working on, Andrew
Jonathan Corbetccae8612014-12-23 08:49:18 -0700271Morton (akpm@linux-foundation.org) serves as a maintainer of last resort.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700272
Jonathan Corbetccae8612014-12-23 08:49:18 -0700273You should also normally choose at least one mailing list to receive a copy
274of your patch set. linux-kernel@vger.kernel.org functions as a list of
275last resort, but the volume on that list has caused a number of developers
276to tune it out. Look in the MAINTAINERS file for a subsystem-specific
277list; your patch will probably get more attention there. Please do not
278spam unrelated lists, though.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700279
Jonathan Corbetccae8612014-12-23 08:49:18 -0700280Many kernel-related lists are hosted on vger.kernel.org; you can find a
281list of them at http://vger.kernel.org/vger-lists.html. There are
282kernel-related lists hosted elsewhere as well, though.
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800283
284Do not send more than 15 patches at once to the vger mailing lists!!!
285
Linus Torvalds1da177e2005-04-16 15:20:36 -0700286Linus Torvalds is the final arbiter of all changes accepted into the
Stefan Bellere00bfcb2014-12-17 17:13:56 -0800287Linux kernel. His e-mail address is <torvalds@linux-foundation.org>.
Jonathan Corbetccae8612014-12-23 08:49:18 -0700288He gets a lot of e-mail, and, at this point, very few patches go through
289Linus directly, so typically you should do your best to -avoid-
Stefan Bellere00bfcb2014-12-17 17:13:56 -0800290sending him e-mail.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700291
Jonathan Corbetccae8612014-12-23 08:49:18 -0700292If you have a patch that fixes an exploitable security bug, send that patch
293to security@kernel.org. For severe bugs, a short embargo may be considered
294to allow distrbutors to get the patch out to users; in such cases,
295obviously, the patch should not be sent to any public lists.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700296
Jonathan Corbetccae8612014-12-23 08:49:18 -0700297Patches that fix a severe bug in a released kernel should be directed
298toward the stable maintainers by putting a line like this:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700299
Jonathan Corbetccae8612014-12-23 08:49:18 -0700300 Cc: stable@vger.kernel.org
Linus Torvalds1da177e2005-04-16 15:20:36 -0700301
Luke Dashjr8cda4c32015-05-14 18:58:01 +0000302into the sign-off area of your patch (note, NOT an email recipient). You
303should also read Documentation/stable_kernel_rules.txt in addition to this
304file.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700305
Jonathan Corbetccae8612014-12-23 08:49:18 -0700306Note, however, that some subsystem maintainers want to come to their own
307conclusions on which patches should go to the stable trees. The networking
308maintainer, in particular, would rather not see individual developers
309adding lines like the above to their patches.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700310
Jonathan Corbetccae8612014-12-23 08:49:18 -0700311If changes affect userland-kernel interfaces, please send the MAN-PAGES
312maintainer (as listed in the MAINTAINERS file) a man-pages patch, or at
313least a notification of the change, so that some information makes its way
314into the manual pages. User-space API changes should also be copied to
315linux-api@vger.kernel.org.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700316
317For small patches you may want to CC the Trivial Patch Monkey
Markus Heidelberg82d27b22009-06-12 01:02:34 +0200318trivial@kernel.org which collects "trivial" patches. Have a look
319into the MAINTAINERS file for its current manager.
320Trivial patches must qualify for one of the following rules:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700321 Spelling fixes in documentation
Jonathan Corbetccae8612014-12-23 08:49:18 -0700322 Spelling fixes for errors which could break grep(1)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700323 Warning fixes (cluttering with useless warnings is bad)
324 Compilation fixes (only if they are actually correct)
325 Runtime fixes (only if they actually fix things)
Jonathan Corbetccae8612014-12-23 08:49:18 -0700326 Removing use of deprecated functions/macros
Linus Torvalds1da177e2005-04-16 15:20:36 -0700327 Contact detail and documentation fixes
328 Non-portable code replaced by portable code (even in arch-specific,
329 since people copy, as long as it's trivial)
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700330 Any fix by the author/maintainer of the file (ie. patch monkey
Linus Torvalds1da177e2005-04-16 15:20:36 -0700331 in re-transmission mode)
Randy Dunlap84da7c02005-06-28 20:45:30 -0700332
Linus Torvalds1da177e2005-04-16 15:20:36 -0700333
334
Jonathan Corbetccae8612014-12-23 08:49:18 -07003356) No MIME, no links, no compression, no attachments. Just plain text.
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700336-----------------------------------------------------------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700337
338Linus and other kernel developers need to be able to read and comment
339on the changes you are submitting. It is important for a kernel
340developer to be able to "quote" your changes, using standard e-mail
341tools, so that they may comment on specific portions of your code.
342
Sébastien Hindererbdc89212015-07-12 17:44:15 +0200343For this reason, all patches should be submitted by e-mail "inline".
Linus Torvalds1da177e2005-04-16 15:20:36 -0700344WARNING: Be wary of your editor's word-wrap corrupting your patch,
345if you choose to cut-n-paste your patch.
346
347Do not attach the patch as a MIME attachment, compressed or not.
348Many popular e-mail applications will not always transmit a MIME
349attachment as plain text, making it impossible to comment on your
350code. A MIME attachment also takes Linus a bit more time to process,
351decreasing the likelihood of your MIME-attached change being accepted.
352
353Exception: If your mailer is mangling patches then someone may ask
354you to re-send them using MIME.
355
Michael Opdenacker097091c2008-02-03 18:06:58 +0200356See Documentation/email-clients.txt for hints about configuring
357your e-mail client so that it sends your patches untouched.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700358
Jonathan Corbetccae8612014-12-23 08:49:18 -07003597) E-mail size.
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700360---------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700361
362Large changes are not appropriate for mailing lists, and some
Randy Dunlap4932be72009-10-01 15:44:06 -0700363maintainers. If your patch, uncompressed, exceeds 300 kB in size,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700364it is preferred that you store your patch on an Internet-accessible
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700365server, and provide instead a URL (link) pointing to your patch. But note
366that if your patch exceeds 300 kB, it almost certainly needs to be broken up
367anyway.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700368
Jonathan Corbet0eea2312014-12-23 08:52:01 -07003698) Respond to review comments.
370------------------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700371
Jonathan Corbet0eea2312014-12-23 08:52:01 -0700372Your patch will almost certainly get comments from reviewers on ways in
373which the patch can be improved. You must respond to those comments;
374ignoring reviewers is a good way to get ignored in return. Review comments
375or questions that do not lead to a code change should almost certainly
376bring about a comment or changelog entry so that the next reviewer better
377understands what is going on.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700378
Jonathan Corbet0eea2312014-12-23 08:52:01 -0700379Be sure to tell the reviewers what changes you are making and to thank them
380for their time. Code review is a tiring and time-consuming process, and
381reviewers sometimes get grumpy. Even in that case, though, respond
382politely and address the problems they have pointed out.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700383
384
Jonathan Corbet0eea2312014-12-23 08:52:01 -07003859) Don't get discouraged - or impatient.
386----------------------------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700387
Jonathan Corbet0eea2312014-12-23 08:52:01 -0700388After you have submitted your change, be patient and wait. Reviewers are
389busy people and may not get to your patch right away.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700390
Jonathan Corbet0eea2312014-12-23 08:52:01 -0700391Once upon a time, patches used to disappear into the void without comment,
392but the development process works more smoothly than that now. You should
393receive comments within a week or so; if that does not happen, make sure
394that you have sent your patches to the right place. Wait for a minimum of
395one week before resubmitting or pinging reviewers - possibly longer during
396busy times like merge windows.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700397
398
Jonathan Corbetccae8612014-12-23 08:49:18 -070039910) Include PATCH in the subject
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700400--------------------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700401
402Due to high e-mail traffic to Linus, and to linux-kernel, it is common
403convention to prefix your subject line with [PATCH]. This lets Linus
404and other kernel developers more easily distinguish patches from other
405e-mail discussions.
406
407
408
Jonathan Corbetccae8612014-12-23 08:49:18 -070040911) Sign your work
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700410------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700411
412To improve tracking of who did what, especially with patches that can
413percolate to their final resting place in the kernel through several
414layers of maintainers, we've introduced a "sign-off" procedure on
415patches that are being emailed around.
416
417The sign-off is a simple line at the end of the explanation for the
418patch, which certifies that you wrote it or otherwise have the right to
Zac Storerdb12fb82011-08-13 12:34:45 -0700419pass it on as an open-source patch. The rules are pretty simple: if you
Linus Torvalds1da177e2005-04-16 15:20:36 -0700420can certify the below:
421
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700422 Developer's Certificate of Origin 1.1
Linus Torvalds1da177e2005-04-16 15:20:36 -0700423
424 By making a contribution to this project, I certify that:
425
426 (a) The contribution was created in whole or in part by me and I
427 have the right to submit it under the open source license
428 indicated in the file; or
429
430 (b) The contribution is based upon previous work that, to the best
431 of my knowledge, is covered under an appropriate open source
432 license and I have the right under that license to submit that
433 work with modifications, whether created in whole or in part
434 by me, under the same open source license (unless I am
435 permitted to submit under a different license), as indicated
436 in the file; or
437
438 (c) The contribution was provided directly to me by some other
439 person who certified (a), (b) or (c) and I have not modified
440 it.
441
Stefan Bellere00bfcb2014-12-17 17:13:56 -0800442 (d) I understand and agree that this project and the contribution
443 are public and that a record of the contribution (including all
444 personal information I submit with it, including my sign-off) is
445 maintained indefinitely and may be redistributed consistent with
446 this project or the open source license(s) involved.
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700447
Linus Torvalds1da177e2005-04-16 15:20:36 -0700448then you just add a line saying
449
Alexey Dobriyan9fd55592005-06-25 14:59:34 -0700450 Signed-off-by: Random J Developer <random@developer.example.org>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700451
Greg KHaf45f322006-09-12 20:35:52 -0700452using your real name (sorry, no pseudonyms or anonymous contributions.)
453
Linus Torvalds1da177e2005-04-16 15:20:36 -0700454Some people also put extra tags at the end. They'll just be ignored for
455now, but you can do this to mark internal company procedures or just
Stefan Bellere00bfcb2014-12-17 17:13:56 -0800456point out some special detail about the sign-off.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700457
Willy Tarreauadbd5882008-06-03 00:20:28 +0200458If you are a subsystem or branch maintainer, sometimes you need to slightly
459modify patches you receive in order to merge them, because the code is not
460exactly the same in your tree and the submitters'. If you stick strictly to
461rule (c), you should ask the submitter to rediff, but this is a totally
462counter-productive waste of time and energy. Rule (b) allows you to adjust
463the code, but then it is very impolite to change one submitter's code and
464make him endorse your bugs. To solve this problem, it is recommended that
465you add a line between the last Signed-off-by header and yours, indicating
466the nature of your changes. While there is nothing mandatory about this, it
467seems like prepending the description with your mail and/or name, all
468enclosed in square brackets, is noticeable enough to make it obvious that
469you are responsible for last-minute changes. Example :
470
471 Signed-off-by: Random J Developer <random@developer.example.org>
472 [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
473 Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
474
Jeremiah Mahler305af082014-05-22 00:04:26 -0700475This practice is particularly helpful if you maintain a stable branch and
Willy Tarreauadbd5882008-06-03 00:20:28 +0200476want at the same time to credit the author, track changes, merge the fix,
477and protect the submitter from complaints. Note that under no circumstances
478can you change the author's identity (the From header), as it is the one
479which appears in the changelog.
480
Jeremiah Mahler305af082014-05-22 00:04:26 -0700481Special note to back-porters: It seems to be a common and useful practice
Willy Tarreauadbd5882008-06-03 00:20:28 +0200482to insert an indication of the origin of a patch at the top of the commit
483message (just after the subject line) to facilitate tracking. For instance,
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700484here's what we see in a 3.x-stable release:
Willy Tarreauadbd5882008-06-03 00:20:28 +0200485
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700486Date: Tue Oct 7 07:26:38 2014 -0400
Willy Tarreauadbd5882008-06-03 00:20:28 +0200487
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700488 libata: Un-break ATA blacklist
Willy Tarreauadbd5882008-06-03 00:20:28 +0200489
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700490 commit 1c40279960bcd7d52dbdf1d466b20d24b99176c8 upstream.
Willy Tarreauadbd5882008-06-03 00:20:28 +0200491
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700492And here's what might appear in an older kernel once a patch is backported:
Willy Tarreauadbd5882008-06-03 00:20:28 +0200493
494 Date: Tue May 13 22:12:27 2008 +0200
495
496 wireless, airo: waitbusy() won't delay
497
498 [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
499
500Whatever the format, this information provides a valuable help to people
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700501tracking your trees, and to people trying to troubleshoot bugs in your
Willy Tarreauadbd5882008-06-03 00:20:28 +0200502tree.
503
Linus Torvalds1da177e2005-04-16 15:20:36 -0700504
Jonathan Corbetccae8612014-12-23 08:49:18 -070050512) When to use Acked-by: and Cc:
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700506---------------------------------
Andy Whitcroft0a920b52007-06-01 00:46:48 -0700507
Andrew Morton0f44cd22007-06-08 13:46:45 -0700508The Signed-off-by: tag indicates that the signer was involved in the
509development of the patch, or that he/she was in the patch's delivery path.
510
511If a person was not directly involved in the preparation or handling of a
512patch but wishes to signify and record their approval of it then they can
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700513ask to have an Acked-by: line added to the patch's changelog.
Andrew Morton0f44cd22007-06-08 13:46:45 -0700514
515Acked-by: is often used by the maintainer of the affected code when that
516maintainer neither contributed to nor forwarded the patch.
517
518Acked-by: is not as formal as Signed-off-by:. It is a record that the acker
519has at least reviewed the patch and has indicated acceptance. Hence patch
520mergers will sometimes manually convert an acker's "yep, looks good to me"
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700521into an Acked-by: (but note that it is usually better to ask for an
522explicit ack).
Andrew Morton0f44cd22007-06-08 13:46:45 -0700523
524Acked-by: does not necessarily indicate acknowledgement of the entire patch.
525For example, if a patch affects multiple subsystems and has an Acked-by: from
526one subsystem maintainer then this usually indicates acknowledgement of just
527the part which affects that maintainer's code. Judgement should be used here.
Jonathan Corbetef402032008-03-28 11:22:38 -0600528When in doubt people should refer to the original discussion in the mailing
Andrew Morton0f44cd22007-06-08 13:46:45 -0700529list archives.
530
Jonathan Corbetef402032008-03-28 11:22:38 -0600531If a person has had the opportunity to comment on a patch, but has not
532provided such comments, you may optionally add a "Cc:" tag to the patch.
533This is the only tag which might be added without an explicit action by the
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700534person it names - but it should indicate that this person was copied on the
535patch. This tag documents that potentially interested parties
536have been included in the discussion.
Andrew Morton0f44cd22007-06-08 13:46:45 -0700537
Jonathan Corbetef402032008-03-28 11:22:38 -0600538
Jonathan Corbetccae8612014-12-23 08:49:18 -070053913) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
Jonathan Corbetd00c4552014-12-23 08:54:36 -0700540--------------------------------------------------------------------------
Jonathan Corbetbbb0a4242009-01-16 09:49:50 -0700541
Dan Carpenterd75ef702014-10-29 13:01:36 +0300542The Reported-by tag gives credit to people who find bugs and report them and it
543hopefully inspires them to help us again in the future. Please note that if
544the bug was reported in private, then ask for permission first before using the
545Reported-by tag.
Jonathan Corbetef402032008-03-28 11:22:38 -0600546
547A Tested-by: tag indicates that the patch has been successfully tested (in
548some environment) by the person named. This tag informs maintainers that
549some testing has been performed, provides a means to locate testers for
550future patches, and ensures credit for the testers.
551
552Reviewed-by:, instead, indicates that the patch has been reviewed and found
553acceptable according to the Reviewer's Statement:
554
555 Reviewer's statement of oversight
556
557 By offering my Reviewed-by: tag, I state that:
558
559 (a) I have carried out a technical review of this patch to
560 evaluate its appropriateness and readiness for inclusion into
561 the mainline kernel.
562
563 (b) Any problems, concerns, or questions relating to the patch
564 have been communicated back to the submitter. I am satisfied
565 with the submitter's response to my comments.
566
567 (c) While there may be things that could be improved with this
568 submission, I believe that it is, at this time, (1) a
569 worthwhile modification to the kernel, and (2) free of known
570 issues which would argue against its inclusion.
571
572 (d) While I have reviewed the patch and believe it to be sound, I
573 do not (unless explicitly stated elsewhere) make any
574 warranties or guarantees that it will achieve its stated
575 purpose or function properly in any given situation.
576
577A Reviewed-by tag is a statement of opinion that the patch is an
578appropriate modification of the kernel without any remaining serious
579technical issues. Any interested reviewer (who has done the work) can
580offer a Reviewed-by tag for a patch. This tag serves to give credit to
581reviewers and to inform maintainers of the degree of review which has been
582done on the patch. Reviewed-by: tags, when supplied by reviewers known to
583understand the subject area and to perform thorough reviews, will normally
Pavel Machek5801da12009-06-04 16:26:50 +0200584increase the likelihood of your patch getting into the kernel.
Jonathan Corbetef402032008-03-28 11:22:38 -0600585
Mugunthan V N8543ae12013-04-29 16:18:17 -0700586A Suggested-by: tag indicates that the patch idea is suggested by the person
587named and ensures credit to the person for the idea. Please note that this
588tag should not be added without the reporter's permission, especially if the
589idea was not posted in a public forum. That said, if we diligently credit our
590idea reporters, they will, hopefully, be inspired to help us again in the
591future.
592
Jacob Keller8401aa12014-06-06 14:36:39 -0700593A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
594is used to make it easy to determine where a bug originated, which can help
595review a bug fix. This tag also assists the stable kernel team in determining
596which stable kernel versions should receive your fix. This is the preferred
597method for indicating a bug fixed by the patch. See #2 above for more details.
598
Jonathan Corbetef402032008-03-28 11:22:38 -0600599
Jonathan Corbetccae8612014-12-23 08:49:18 -070060014) The canonical patch format
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700601------------------------------
602
603This section describes how the patch itself should be formatted. Note
604that, if you have your patches stored in a git repository, proper patch
605formatting can be had with "git format-patch". The tools cannot create
606the necessary text, though, so read the instructions below anyway.
Randy Dunlap84da7c02005-06-28 20:45:30 -0700607
Paul Jackson75f84262005-10-02 18:01:42 -0700608The canonical patch subject line is:
609
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700610 Subject: [PATCH 001/123] subsystem: summary phrase
Paul Jackson75f84262005-10-02 18:01:42 -0700611
612The canonical patch message body contains the following:
613
Jonathan Corbetccae8612014-12-23 08:49:18 -0700614 - A "from" line specifying the patch author (only needed if the person
615 sending the patch is not the author).
Paul Jackson75f84262005-10-02 18:01:42 -0700616
617 - An empty line.
618
Joe Perches2a076f42015-04-16 12:44:28 -0700619 - The body of the explanation, line wrapped at 75 columns, which will
620 be copied to the permanent changelog to describe this patch.
Paul Jackson75f84262005-10-02 18:01:42 -0700621
622 - The "Signed-off-by:" lines, described above, which will
623 also go in the changelog.
624
625 - A marker line containing simply "---".
626
627 - Any additional comments not suitable for the changelog.
628
629 - The actual patch (diff output).
630
631The Subject line format makes it very easy to sort the emails
632alphabetically by subject line - pretty much any email reader will
633support that - since because the sequence number is zero-padded,
634the numerical and alphabetic sort is the same.
635
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700636The "subsystem" in the email's Subject should identify which
637area or subsystem of the kernel is being patched.
638
639The "summary phrase" in the email's Subject should concisely
640describe the patch which that email contains. The "summary
641phrase" should not be a filename. Do not use the same "summary
Randy Dunlap66effdc2007-05-09 02:33:42 -0700642phrase" for every patch in a whole patch series (where a "patch
643series" is an ordered sequence of multiple, related patches).
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700644
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400645Bear in mind that the "summary phrase" of your email becomes a
646globally-unique identifier for that patch. It propagates all the way
647into the git changelog. The "summary phrase" may later be used in
648developer discussions which refer to the patch. People will want to
649google for the "summary phrase" to read discussion regarding that
650patch. It will also be the only thing that people may quickly see
651when, two or three months later, they are going through perhaps
652thousands of patches using tools such as "gitk" or "git log
653--oneline".
654
655For these reasons, the "summary" must be no more than 70-75
656characters, and it must describe both what the patch changes, as well
657as why the patch might be necessary. It is challenging to be both
658succinct and descriptive, but that is what a well-written summary
659should do.
660
661The "summary phrase" may be prefixed by tags enclosed in square
662brackets: "Subject: [PATCH tag] <summary phrase>". The tags are not
663considered part of the summary phrase, but describe how the patch
664should be treated. Common tags might include a version descriptor if
665the multiple versions of the patch have been sent out in response to
666comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
667comments. If there are four patches in a patch series the individual
668patches may be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures
669that developers understand the order in which the patches should be
670applied and that they have reviewed or applied all of the patches in
671the patch series.
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700672
673A couple of example Subjects:
674
675 Subject: [patch 2/5] ext2: improve scalability of bitmap searching
676 Subject: [PATCHv2 001/207] x86: fix eflags tracking
Paul Jackson75f84262005-10-02 18:01:42 -0700677
678The "from" line must be the very first line in the message body,
679and has the form:
680
681 From: Original Author <author@example.com>
682
683The "from" line specifies who will be credited as the author of the
684patch in the permanent changelog. If the "from" line is missing,
685then the "From:" line from the email header will be used to determine
686the patch author in the changelog.
687
688The explanation body will be committed to the permanent source
689changelog, so should make sense to a competent reader who has long
690since forgotten the immediate details of the discussion that might
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400691have led to this patch. Including symptoms of the failure which the
692patch addresses (kernel log messages, oops messages, etc.) is
693especially useful for people who might be searching the commit logs
694looking for the applicable patch. If a patch fixes a compile failure,
695it may not be necessary to include _all_ of the compile failures; just
696enough that it is likely that someone searching for the patch can find
697it. As in the "summary phrase", it is important to be both succinct as
698well as descriptive.
Paul Jackson75f84262005-10-02 18:01:42 -0700699
700The "---" marker line serves the essential purpose of marking for patch
701handling tools where the changelog message ends.
702
703One good use for the additional comments after the "---" marker is for
Theodore Ts'o2ae19ac2009-04-16 07:44:45 -0400704a diffstat, to show what files have changed, and the number of
705inserted and deleted lines per file. A diffstat is especially useful
706on bigger patches. Other comments relevant only to the moment or the
707maintainer, not suitable for the permanent changelog, should also go
708here. A good example of such comments might be "patch changelogs"
709which describe what has changed between the v1 and v2 version of the
710patch.
711
712If you are going to include a diffstat after the "---" marker, please
713use diffstat options "-p 1 -w 70" so that filenames are listed from
714the top of the kernel source tree and don't use too much horizontal
Josh Triplett8e3072a2014-04-03 14:48:30 -0700715space (easily fit in 80 columns, maybe with some indentation). (git
716generates appropriate diffstats by default.)
Paul Jackson75f84262005-10-02 18:01:42 -0700717
718See more details on the proper patch format in the following
719references.
720
721
Jonathan Corbetccae8612014-12-23 08:49:18 -070072215) Sending "git pull" requests
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700723-------------------------------
Randy Dunlap84da7c02005-06-28 20:45:30 -0700724
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700725If you have a series of patches, it may be most convenient to have the
726maintainer pull them directly into the subsystem repository with a
727"git pull" operation. Note, however, that pulling patches from a developer
728requires a higher degree of trust than taking patches from a mailing list.
729As a result, many subsystem maintainers are reluctant to take pull
Jonathan Corbetb792ffe2014-12-23 09:28:40 -0700730requests, especially from new, unknown developers. If in doubt you can use
731the pull request as the cover letter for a normal posting of the patch
732series, giving the maintainer the option of using either.
Randy Dunlap14863612008-07-27 20:44:24 -0700733
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700734A pull request should have [GIT] or [PULL] in the subject line. The
735request itself should include the repository name and the branch of
736interest on a single line; it should look something like:
Randy Dunlap14863612008-07-27 20:44:24 -0700737
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700738 Please pull from
Randy Dunlap14863612008-07-27 20:44:24 -0700739
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700740 git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
Randy Dunlap14863612008-07-27 20:44:24 -0700741
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700742 to get these changes:"
Randy Dunlap14863612008-07-27 20:44:24 -0700743
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700744A pull request should also include an overall message saying what will be
745included in the request, a "git shortlog" listing of the patches
746themselves, and a diffstat showing the overall effect of the patch series.
747The easiest way to get all this information together is, of course, to let
748git do it for you with the "git request-pull" command.
Randy Dunlap14863612008-07-27 20:44:24 -0700749
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700750Some maintainers (including Linus) want to see pull requests from signed
751commits; that increases their confidence that the request actually came
752from you. Linus, in particular, will not pull from public hosting sites
753like GitHub in the absence of a signed tag.
Randy Dunlap14863612008-07-27 20:44:24 -0700754
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700755The first step toward creating such tags is to make a GNUPG key and get it
756signed by one or more core kernel developers. This step can be hard for
757new developers, but there is no way around it. Attending conferences can
758be a good way to find developers who can sign your key.
Randy Dunlap14863612008-07-27 20:44:24 -0700759
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700760Once you have prepared a patch series in git that you wish to have somebody
761pull, create a signed tag with "git tag -s". This will create a new tag
762identifying the last commit in the series and containing a signature
763created with your private key. You will also have the opportunity to add a
764changelog-style message to the tag; this is an ideal place to describe the
765effects of the pull request as a whole.
Randy Dunlap84da7c02005-06-28 20:45:30 -0700766
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700767If the tree the maintainer will be pulling from is not the repository you
768are working from, don't forget to push the signed tag explicitly to the
769public tree.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700770
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700771When generating your pull request, use the signed tag as the target. A
772command like this will do the trick:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700773
Jonathan Corbet7994cc12014-12-23 08:43:41 -0700774 git request-pull master git://my.public.tree/linux.git my-signed-tag
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800775
776
777----------------------
Jonathan Corbet6de16eb2014-12-23 08:38:24 -0700778SECTION 2 - REFERENCES
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800779----------------------
780
781Andrew Morton, "The perfect patch" (tpp).
Mitchel Humpherys37c703f2014-04-03 14:50:40 -0700782 <http://www.ozlabs.org/~akpm/stuff/tpp.txt>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800783
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700784Jeff Garzik, "Linux kernel patch submission format".
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800785 <http://linux.yyz.us/patch-format.html>
786
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700787Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
Vikram Narayananf5039932011-05-23 12:01:25 -0700788 <http://www.kroah.com/log/linux/maintainer.html>
789 <http://www.kroah.com/log/linux/maintainer-02.html>
790 <http://www.kroah.com/log/linux/maintainer-03.html>
791 <http://www.kroah.com/log/linux/maintainer-04.html>
792 <http://www.kroah.com/log/linux/maintainer-05.html>
Sudip Mukherjee7e0dae62014-09-07 11:26:12 -0700793 <http://www.kroah.com/log/linux/maintainer-06.html>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800794
Randy Dunlapbc7455f2006-07-30 03:03:45 -0700795NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
Mitchel Humpherys37c703f2014-04-03 14:50:40 -0700796 <https://lkml.org/lkml/2005/7/11/336>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800797
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700798Kernel Documentation/CodingStyle:
Luis de Bethencourt60498bb2015-07-03 16:22:11 +0100799 <Documentation/CodingStyle>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800800
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700801Linus Torvalds's mail on the canonical patch format:
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800802 <http://lkml.org/lkml/2005/4/7/183>
Andi Kleen95367272008-10-15 22:02:02 -0700803
804Andi Kleen, "On submitting kernel patches"
Lucas De Marchi25985ed2011-03-30 22:57:33 -0300805 Some strategies to get difficult or controversial changes in.
Andi Kleen95367272008-10-15 22:02:02 -0700806 http://halobates.de/on-submitting-patches.pdf
807
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800808--