1.. _submittingpatches:
2
3Submitting patches: the essential guide to getting your code into the kernel
4============================================================================
5
6For a person or company who wishes to submit a change to the Linux
7kernel, the process can sometimes be daunting if you're not familiar
8with "the system."  This text is a collection of suggestions which
9can greatly increase the chances of your change being accepted.
10
11This document contains a large number of suggestions in a relatively terse
12format.  For detailed information on how the kernel development process
13works, see :ref:`Documentation/process <development_process_main>`.
14Also, read :ref:`Documentation/process/submit-checklist.rst <submitchecklist>`
15for a list of items to check before
16submitting code.  If you are submitting a driver, also read
17:ref:`Documentation/process/submitting-drivers.rst <submittingdrivers>`;
18for device tree binding patches, read
19Documentation/devicetree/bindings/submitting-patches.txt.
20
21Many 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
24and document a sensible set of patches.  In general, use of ``git`` will make
25your life as a kernel developer easier.
26
270) Obtain a current source tree
28-------------------------------
29
30If you do not have a repository with the current kernel source handy, use
31``git`` to obtain one.  You'll want to start with the mainline repository,
32which can be grabbed with::
33
34  git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
35
36Note, however, that you may not want to develop against the mainline tree
37directly.  Most subsystem maintainers run their own trees and want to see
38patches prepared against those trees.  See the **T:** entry for the subsystem
39in the MAINTAINERS file to find that tree, or simply ask the maintainer if
40the tree is not listed there.
41
42It is still possible to download kernel releases via tarballs (as described
43in the next section), but that is the hard way to do kernel development.
44
451) ``diff -up``
46---------------
47
48If you must generate your patches by hand, use ``diff -up`` or ``diff -uprN``
49to create patches.  Git generates patches in this form by default; if
50you're using ``git``, you can skip this section entirely.
51
52All changes to the Linux kernel occur in the form of patches, as
53generated by :manpage:`diff(1)`.  When creating your patch, make sure to
54create it in "unified diff" format, as supplied by the ``-u`` argument
55to :manpage:`diff(1)`.
56Also, please use the ``-p`` argument which shows which C function each
57change is in - that makes the resultant ``diff`` a lot easier to read.
58Patches should be based in the root kernel source directory,
59not in any lower subdirectory.
60
61To create a patch for a single file, it is often sufficient to do::
62
63	SRCTREE= linux
64	MYFILE=  drivers/net/mydriver.c
65
66	cd $SRCTREE
67	cp $MYFILE $MYFILE.orig
68	vi $MYFILE	# make your change
69	cd ..
70	diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
71
72To create a patch for multiple files, you should unpack a "vanilla",
73or unmodified kernel source tree, and generate a ``diff`` against your
74own source tree.  For example::
75
76	MYSRC= /devel/linux
77
78	tar xvfz linux-3.19.tar.gz
79	mv linux-3.19 linux-3.19-vanilla
80	diff -uprN -X linux-3.19-vanilla/Documentation/dontdiff \
81		linux-3.19-vanilla $MYSRC > /tmp/patch
82
83``dontdiff`` is a list of files which are generated by the kernel during
84the build process, and should be ignored in any :manpage:`diff(1)`-generated
85patch.
86
87Make sure your patch does not include any extra files which do not
88belong in a patch submission.  Make sure to review your patch -after-
89generating it with :manpage:`diff(1)`, to ensure accuracy.
90
91If your changes produce a lot of deltas, you need to split them into
92individual patches which modify things in logical stages; see
93:ref:`split_changes`.  This will facilitate review by other kernel developers,
94very important if you want your patch accepted.
95
96If you're using ``git``, ``git rebase -i`` can help you with this process.  If
97you're not using ``git``, ``quilt`` <http://savannah.nongnu.org/projects/quilt>
98is another popular alternative.
99
100.. _describe_changes:
101
1022) Describe your changes
103------------------------
104
105Describe your problem.  Whether your patch is a one-line bug fix or
1065000 lines of a new feature, there must be an underlying problem that
107motivated you to do this work.  Convince the reviewer that there is a
108problem worth fixing and that it makes sense for them to read past the
109first paragraph.
110
111Describe user-visible impact.  Straight up crashes and lockups are
112pretty convincing, but not all bugs are that blatant.  Even if the
113problem was spotted during code review, describe the impact you think
114it can have on users.  Keep in mind that the majority of Linux
115installations run kernels from secondary stable trees or
116vendor/product-specific trees that cherry-pick only specific patches
117from upstream, so include anything that could help route your change
118downstream: provoking circumstances, excerpts from dmesg, crash
119descriptions, performance regressions, latency spikes, lockups, etc.
120
121Quantify optimizations and trade-offs.  If you claim improvements in
122performance, memory consumption, stack footprint, or binary size,
123include numbers that back them up.  But also describe non-obvious
124costs.  Optimizations usually aren't free but trade-offs between CPU,
125memory, and readability; or, when it comes to heuristics, between
126different workloads.  Describe the expected downsides of your
127optimization so that the reviewer can weigh costs against benefits.
128
129Once the problem is established, describe what you are actually doing
130about it in technical detail.  It's important to describe the change
131in plain English for the reviewer to verify that the code is behaving
132as you intend it to.
133
134The maintainer will thank you if you write your patch description in a
135form which can be easily pulled into Linux's source code management
136system, ``git``, as a "commit log".  See :ref:`explicit_in_reply_to`.
137
138Solve only one problem per patch.  If your description starts to get
139long, that's a sign that you probably need to split up your patch.
140See :ref:`split_changes`.
141
142When you submit or resubmit a patch or patch series, include the
143complete patch description and justification for it.  Don't just
144say that this is version N of the patch (series).  Don't expect the
145subsystem maintainer to refer back to earlier patch versions or referenced
146URLs to find the patch description and put that into the patch.
147I.e., the patch (series) and its description should be self-contained.
148This benefits both the maintainers and reviewers.  Some reviewers
149probably didn't even receive earlier versions of the patch.
150
151Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
152instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
153to do frotz", as if you are giving orders to the codebase to change
154its behaviour.
155
156If the patch fixes a logged bug entry, refer to that bug entry by
157number and URL.  If the patch follows from a mailing list discussion,
158give a URL to the mailing list archive; use the https://lkml.kernel.org/
159redirector with a ``Message-Id``, to ensure that the links cannot become
160stale.
161
162However, try to make your explanation understandable without external
163resources.  In addition to giving a URL to a mailing list archive or
164bug, summarize the relevant points of the discussion that led to the
165patch as submitted.
166
167If you want to refer to a specific commit, don't just refer to the
168SHA-1 ID of the commit. Please also include the oneline summary of
169the commit, to make it easier for reviewers to know what it is about.
170Example::
171
172	Commit e21d2170f36602ae2708 ("video: remove unnecessary
173	platform_set_drvdata()") removed the unnecessary
174	platform_set_drvdata(), but left the variable "dev" unused,
175	delete it.
176
177You should also be sure to use at least the first twelve characters of the
178SHA-1 ID.  The kernel repository holds a *lot* of objects, making
179collisions with shorter IDs a real possibility.  Bear in mind that, even if
180there is no collision with your six-character ID now, that condition may
181change five years from now.
182
183If your patch fixes a bug in a specific commit, e.g. you found an issue using
184``git bisect``, please use the 'Fixes:' tag with the first 12 characters of
185the SHA-1 ID, and the one line summary.  For example::
186
187	Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
188
189The following ``git config`` settings can be used to add a pretty format for
190outputting the above style in the ``git log`` or ``git show`` commands::
191
192	[core]
193		abbrev = 12
194	[pretty]
195		fixes = Fixes: %h (\"%s\")
196
197.. _split_changes:
198
1993) Separate your changes
200------------------------
201
202Separate each **logical change** into a separate patch.
203
204For example, if your changes include both bug fixes and performance
205enhancements for a single driver, separate those changes into two
206or more patches.  If your changes include an API update, and a new
207driver which uses that new API, separate those into two patches.
208
209On the other hand, if you make a single change to numerous files,
210group those changes into a single patch.  Thus a single logical change
211is contained within a single patch.
212
213The point to remember is that each patch should make an easily understood
214change that can be verified by reviewers.  Each patch should be justifiable
215on its own merits.
216
217If one patch depends on another patch in order for a change to be
218complete, that is OK.  Simply note **"this patch depends on patch X"**
219in your patch description.
220
221When dividing your change into a series of patches, take special care to
222ensure that the kernel builds and runs properly after each patch in the
223series.  Developers using ``git bisect`` to track down a problem can end up
224splitting your patch series at any point; they will not thank you if you
225introduce bugs in the middle.
226
227If you cannot condense your patch set into a smaller set of patches,
228then only post say 15 or so at a time and wait for review and integration.
229
230
231
2324) Style-check your changes
233---------------------------
234
235Check your patch for basic style violations, details of which can be
236found in
237:ref:`Documentation/process/coding-style.rst <codingstyle>`.
238Failure to do so simply wastes
239the reviewers time and will get your patch rejected, probably
240without even being read.
241
242One 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.
248
249Check 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.
261
262
2635) Select the recipients for your patch
264---------------------------------------
265
266You 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
270cannot find a maintainer for the subsystem you are working on, Andrew
271Morton (akpm@linux-foundation.org) serves as a maintainer of last resort.
272
273You 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.
279
280Many 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.
283
284Do not send more than 15 patches at once to the vger mailing lists!!!
285
286Linus Torvalds is the final arbiter of all changes accepted into the
287Linux kernel.  His e-mail address is <torvalds@linux-foundation.org>.
288He 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-
290sending him e-mail.
291
292If 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 distributors to get the patch out to users; in such cases,
295obviously, the patch should not be sent to any public lists.
296
297Patches that fix a severe bug in a released kernel should be directed
298toward the stable maintainers by putting a line like this::
299
300  Cc: stable@vger.kernel.org
301
302into the sign-off area of your patch (note, NOT an email recipient).  You
303should also read
304:ref:`Documentation/process/stable-kernel-rules.rst <stable_kernel_rules>`
305in addition to this file.
306
307Note, however, that some subsystem maintainers want to come to their own
308conclusions on which patches should go to the stable trees.  The networking
309maintainer, in particular, would rather not see individual developers
310adding lines like the above to their patches.
311
312If changes affect userland-kernel interfaces, please send the MAN-PAGES
313maintainer (as listed in the MAINTAINERS file) a man-pages patch, or at
314least a notification of the change, so that some information makes its way
315into the manual pages.  User-space API changes should also be copied to
316linux-api@vger.kernel.org.
317
318For small patches you may want to CC the Trivial Patch Monkey
319trivial@kernel.org which collects "trivial" patches. Have a look
320into the MAINTAINERS file for its current manager.
321
322Trivial patches must qualify for one of the following rules:
323
324- Spelling fixes in documentation
325- Spelling fixes for errors which could break :manpage:`grep(1)`
326- Warning fixes (cluttering with useless warnings is bad)
327- Compilation fixes (only if they are actually correct)
328- Runtime fixes (only if they actually fix things)
329- Removing use of deprecated functions/macros
330- Contact detail and documentation fixes
331- Non-portable code replaced by portable code (even in arch-specific,
332  since people copy, as long as it's trivial)
333- Any fix by the author/maintainer of the file (ie. patch monkey
334  in re-transmission mode)
335
336
337
3386) No MIME, no links, no compression, no attachments.  Just plain text
339----------------------------------------------------------------------
340
341Linus and other kernel developers need to be able to read and comment
342on the changes you are submitting.  It is important for a kernel
343developer to be able to "quote" your changes, using standard e-mail
344tools, so that they may comment on specific portions of your code.
345
346For this reason, all patches should be submitted by e-mail "inline".
347
348.. warning::
349
350  Be wary of your editor's word-wrap corrupting your patch,
351  if you choose to cut-n-paste your patch.
352
353Do not attach the patch as a MIME attachment, compressed or not.
354Many popular e-mail applications will not always transmit a MIME
355attachment as plain text, making it impossible to comment on your
356code.  A MIME attachment also takes Linus a bit more time to process,
357decreasing the likelihood of your MIME-attached change being accepted.
358
359Exception:  If your mailer is mangling patches then someone may ask
360you to re-send them using MIME.
361
362See :ref:`Documentation/process/email-clients.rst <email_clients>`
363for hints about configuring your e-mail client so that it sends your patches
364untouched.
365
3667) E-mail size
367--------------
368
369Large changes are not appropriate for mailing lists, and some
370maintainers.  If your patch, uncompressed, exceeds 300 kB in size,
371it is preferred that you store your patch on an Internet-accessible
372server, and provide instead a URL (link) pointing to your patch.  But note
373that if your patch exceeds 300 kB, it almost certainly needs to be broken up
374anyway.
375
3768) Respond to review comments
377-----------------------------
378
379Your patch will almost certainly get comments from reviewers on ways in
380which the patch can be improved.  You must respond to those comments;
381ignoring reviewers is a good way to get ignored in return.  Review comments
382or questions that do not lead to a code change should almost certainly
383bring about a comment or changelog entry so that the next reviewer better
384understands what is going on.
385
386Be sure to tell the reviewers what changes you are making and to thank them
387for their time.  Code review is a tiring and time-consuming process, and
388reviewers sometimes get grumpy.  Even in that case, though, respond
389politely and address the problems they have pointed out.
390
391
3929) Don't get discouraged - or impatient
393---------------------------------------
394
395After you have submitted your change, be patient and wait.  Reviewers are
396busy people and may not get to your patch right away.
397
398Once upon a time, patches used to disappear into the void without comment,
399but the development process works more smoothly than that now.  You should
400receive comments within a week or so; if that does not happen, make sure
401that you have sent your patches to the right place.  Wait for a minimum of
402one week before resubmitting or pinging reviewers - possibly longer during
403busy times like merge windows.
404
405
40610) Include PATCH in the subject
407--------------------------------
408
409Due to high e-mail traffic to Linus, and to linux-kernel, it is common
410convention to prefix your subject line with [PATCH].  This lets Linus
411and other kernel developers more easily distinguish patches from other
412e-mail discussions.
413
414
415
41611) Sign your work - the Developer's Certificate of Origin
417----------------------------------------------------------
418
419To improve tracking of who did what, especially with patches that can
420percolate to their final resting place in the kernel through several
421layers of maintainers, we've introduced a "sign-off" procedure on
422patches that are being emailed around.
423
424The sign-off is a simple line at the end of the explanation for the
425patch, which certifies that you wrote it or otherwise have the right to
426pass it on as an open-source patch.  The rules are pretty simple: if you
427can certify the below:
428
429Developer's Certificate of Origin 1.1
430^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
431
432By making a contribution to this project, I certify that:
433
434        (a) The contribution was created in whole or in part by me and I
435            have the right to submit it under the open source license
436            indicated in the file; or
437
438        (b) The contribution is based upon previous work that, to the best
439            of my knowledge, is covered under an appropriate open source
440            license and I have the right under that license to submit that
441            work with modifications, whether created in whole or in part
442            by me, under the same open source license (unless I am
443            permitted to submit under a different license), as indicated
444            in the file; or
445
446        (c) The contribution was provided directly to me by some other
447            person who certified (a), (b) or (c) and I have not modified
448            it.
449
450        (d) I understand and agree that this project and the contribution
451            are public and that a record of the contribution (including all
452            personal information I submit with it, including my sign-off) is
453            maintained indefinitely and may be redistributed consistent with
454            this project or the open source license(s) involved.
455
456then you just add a line saying::
457
458	Signed-off-by: Random J Developer <random@developer.example.org>
459
460using your real name (sorry, no pseudonyms or anonymous contributions.)
461
462Some people also put extra tags at the end.  They'll just be ignored for
463now, but you can do this to mark internal company procedures or just
464point out some special detail about the sign-off.
465
466If you are a subsystem or branch maintainer, sometimes you need to slightly
467modify patches you receive in order to merge them, because the code is not
468exactly the same in your tree and the submitters'. If you stick strictly to
469rule (c), you should ask the submitter to rediff, but this is a totally
470counter-productive waste of time and energy. Rule (b) allows you to adjust
471the code, but then it is very impolite to change one submitter's code and
472make him endorse your bugs. To solve this problem, it is recommended that
473you add a line between the last Signed-off-by header and yours, indicating
474the nature of your changes. While there is nothing mandatory about this, it
475seems like prepending the description with your mail and/or name, all
476enclosed in square brackets, is noticeable enough to make it obvious that
477you are responsible for last-minute changes. Example::
478
479	Signed-off-by: Random J Developer <random@developer.example.org>
480	[lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
481	Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
482
483This practice is particularly helpful if you maintain a stable branch and
484want at the same time to credit the author, track changes, merge the fix,
485and protect the submitter from complaints. Note that under no circumstances
486can you change the author's identity (the From header), as it is the one
487which appears in the changelog.
488
489Special note to back-porters: It seems to be a common and useful practice
490to insert an indication of the origin of a patch at the top of the commit
491message (just after the subject line) to facilitate tracking. For instance,
492here's what we see in a 3.x-stable release::
493
494  Date:   Tue Oct 7 07:26:38 2014 -0400
495
496    libata: Un-break ATA blacklist
497
498    commit 1c40279960bcd7d52dbdf1d466b20d24b99176c8 upstream.
499
500And here's what might appear in an older kernel once a patch is backported::
501
502    Date:   Tue May 13 22:12:27 2008 +0200
503
504        wireless, airo: waitbusy() won't delay
505
506        [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
507
508Whatever the format, this information provides a valuable help to people
509tracking your trees, and to people trying to troubleshoot bugs in your
510tree.
511
512
51312) When to use Acked-by:, Cc:, and Co-Developed-by:
514-------------------------------------------------------
515
516The Signed-off-by: tag indicates that the signer was involved in the
517development of the patch, or that he/she was in the patch's delivery path.
518
519If a person was not directly involved in the preparation or handling of a
520patch but wishes to signify and record their approval of it then they can
521ask to have an Acked-by: line added to the patch's changelog.
522
523Acked-by: is often used by the maintainer of the affected code when that
524maintainer neither contributed to nor forwarded the patch.
525
526Acked-by: is not as formal as Signed-off-by:.  It is a record that the acker
527has at least reviewed the patch and has indicated acceptance.  Hence patch
528mergers will sometimes manually convert an acker's "yep, looks good to me"
529into an Acked-by: (but note that it is usually better to ask for an
530explicit ack).
531
532Acked-by: does not necessarily indicate acknowledgement of the entire patch.
533For example, if a patch affects multiple subsystems and has an Acked-by: from
534one subsystem maintainer then this usually indicates acknowledgement of just
535the part which affects that maintainer's code.  Judgement should be used here.
536When in doubt people should refer to the original discussion in the mailing
537list archives.
538
539If a person has had the opportunity to comment on a patch, but has not
540provided such comments, you may optionally add a ``Cc:`` tag to the patch.
541This is the only tag which might be added without an explicit action by the
542person it names - but it should indicate that this person was copied on the
543patch.  This tag documents that potentially interested parties
544have been included in the discussion.
545
546A Co-Developed-by: states that the patch was also created by another developer
547along with the original author.  This is useful at times when multiple people
548work on a single patch.  Note, this person also needs to have a Signed-off-by:
549line in the patch as well.
550
551
55213) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
553--------------------------------------------------------------------------
554
555The Reported-by tag gives credit to people who find bugs and report them and it
556hopefully inspires them to help us again in the future.  Please note that if
557the bug was reported in private, then ask for permission first before using the
558Reported-by tag.
559
560A Tested-by: tag indicates that the patch has been successfully tested (in
561some environment) by the person named.  This tag informs maintainers that
562some testing has been performed, provides a means to locate testers for
563future patches, and ensures credit for the testers.
564
565Reviewed-by:, instead, indicates that the patch has been reviewed and found
566acceptable according to the Reviewer's Statement:
567
568Reviewer's statement of oversight
569^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
570
571By offering my Reviewed-by: tag, I state that:
572
573	 (a) I have carried out a technical review of this patch to
574	     evaluate its appropriateness and readiness for inclusion into
575	     the mainline kernel.
576
577	 (b) Any problems, concerns, or questions relating to the patch
578	     have been communicated back to the submitter.  I am satisfied
579	     with the submitter's response to my comments.
580
581	 (c) While there may be things that could be improved with this
582	     submission, I believe that it is, at this time, (1) a
583	     worthwhile modification to the kernel, and (2) free of known
584	     issues which would argue against its inclusion.
585
586	 (d) While I have reviewed the patch and believe it to be sound, I
587	     do not (unless explicitly stated elsewhere) make any
588	     warranties or guarantees that it will achieve its stated
589	     purpose or function properly in any given situation.
590
591A Reviewed-by tag is a statement of opinion that the patch is an
592appropriate modification of the kernel without any remaining serious
593technical issues.  Any interested reviewer (who has done the work) can
594offer a Reviewed-by tag for a patch.  This tag serves to give credit to
595reviewers and to inform maintainers of the degree of review which has been
596done on the patch.  Reviewed-by: tags, when supplied by reviewers known to
597understand the subject area and to perform thorough reviews, will normally
598increase the likelihood of your patch getting into the kernel.
599
600A Suggested-by: tag indicates that the patch idea is suggested by the person
601named and ensures credit to the person for the idea. Please note that this
602tag should not be added without the reporter's permission, especially if the
603idea was not posted in a public forum. That said, if we diligently credit our
604idea reporters, they will, hopefully, be inspired to help us again in the
605future.
606
607A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
608is used to make it easy to determine where a bug originated, which can help
609review a bug fix. This tag also assists the stable kernel team in determining
610which stable kernel versions should receive your fix. This is the preferred
611method for indicating a bug fixed by the patch. See :ref:`describe_changes`
612for more details.
613
614.. _the_canonical_patch_format:
615
61614) The canonical patch format
617------------------------------
618
619This section describes how the patch itself should be formatted.  Note
620that, if you have your patches stored in a ``git`` repository, proper patch
621formatting can be had with ``git format-patch``.  The tools cannot create
622the necessary text, though, so read the instructions below anyway.
623
624The canonical patch subject line is::
625
626    Subject: [PATCH 001/123] subsystem: summary phrase
627
628The canonical patch message body contains the following:
629
630  - A ``from`` line specifying the patch author, followed by an empty
631    line (only needed if the person sending the patch is not the author).
632
633  - The body of the explanation, line wrapped at 75 columns, which will
634    be copied to the permanent changelog to describe this patch.
635
636  - An empty line.
637
638  - The ``Signed-off-by:`` lines, described above, which will
639    also go in the changelog.
640
641  - A marker line containing simply ``---``.
642
643  - Any additional comments not suitable for the changelog.
644
645  - The actual patch (``diff`` output).
646
647The Subject line format makes it very easy to sort the emails
648alphabetically by subject line - pretty much any email reader will
649support that - since because the sequence number is zero-padded,
650the numerical and alphabetic sort is the same.
651
652The ``subsystem`` in the email's Subject should identify which
653area or subsystem of the kernel is being patched.
654
655The ``summary phrase`` in the email's Subject should concisely
656describe the patch which that email contains.  The ``summary
657phrase`` should not be a filename.  Do not use the same ``summary
658phrase`` for every patch in a whole patch series (where a ``patch
659series`` is an ordered sequence of multiple, related patches).
660
661Bear in mind that the ``summary phrase`` of your email becomes a
662globally-unique identifier for that patch.  It propagates all the way
663into the ``git`` changelog.  The ``summary phrase`` may later be used in
664developer discussions which refer to the patch.  People will want to
665google for the ``summary phrase`` to read discussion regarding that
666patch.  It will also be the only thing that people may quickly see
667when, two or three months later, they are going through perhaps
668thousands of patches using tools such as ``gitk`` or ``git log
669--oneline``.
670
671For these reasons, the ``summary`` must be no more than 70-75
672characters, and it must describe both what the patch changes, as well
673as why the patch might be necessary.  It is challenging to be both
674succinct and descriptive, but that is what a well-written summary
675should do.
676
677The ``summary phrase`` may be prefixed by tags enclosed in square
678brackets: "Subject: [PATCH <tag>...] <summary phrase>".  The tags are
679not considered part of the summary phrase, but describe how the patch
680should be treated.  Common tags might include a version descriptor if
681the multiple versions of the patch have been sent out in response to
682comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
683comments.  If there are four patches in a patch series the individual
684patches may be numbered like this: 1/4, 2/4, 3/4, 4/4.  This assures
685that developers understand the order in which the patches should be
686applied and that they have reviewed or applied all of the patches in
687the patch series.
688
689A couple of example Subjects::
690
691    Subject: [PATCH 2/5] ext2: improve scalability of bitmap searching
692    Subject: [PATCH v2 01/27] x86: fix eflags tracking
693
694The ``from`` line must be the very first line in the message body,
695and has the form:
696
697        From: Original Author <author@example.com>
698
699The ``from`` line specifies who will be credited as the author of the
700patch in the permanent changelog.  If the ``from`` line is missing,
701then the ``From:`` line from the email header will be used to determine
702the patch author in the changelog.
703
704The explanation body will be committed to the permanent source
705changelog, so should make sense to a competent reader who has long
706since forgotten the immediate details of the discussion that might
707have led to this patch.  Including symptoms of the failure which the
708patch addresses (kernel log messages, oops messages, etc.) is
709especially useful for people who might be searching the commit logs
710looking for the applicable patch.  If a patch fixes a compile failure,
711it may not be necessary to include _all_ of the compile failures; just
712enough that it is likely that someone searching for the patch can find
713it.  As in the ``summary phrase``, it is important to be both succinct as
714well as descriptive.
715
716The ``---`` marker line serves the essential purpose of marking for patch
717handling tools where the changelog message ends.
718
719One good use for the additional comments after the ``---`` marker is for
720a ``diffstat``, to show what files have changed, and the number of
721inserted and deleted lines per file.  A ``diffstat`` is especially useful
722on bigger patches.  Other comments relevant only to the moment or the
723maintainer, not suitable for the permanent changelog, should also go
724here.  A good example of such comments might be ``patch changelogs``
725which describe what has changed between the v1 and v2 version of the
726patch.
727
728If you are going to include a ``diffstat`` after the ``---`` marker, please
729use ``diffstat`` options ``-p 1 -w 70`` so that filenames are listed from
730the top of the kernel source tree and don't use too much horizontal
731space (easily fit in 80 columns, maybe with some indentation).  (``git``
732generates appropriate diffstats by default.)
733
734See more details on the proper patch format in the following
735references.
736
737.. _explicit_in_reply_to:
738
73915) Explicit In-Reply-To headers
740--------------------------------
741
742It can be helpful to manually add In-Reply-To: headers to a patch
743(e.g., when using ``git send-email``) to associate the patch with
744previous relevant discussion, e.g. to link a bug fix to the email with
745the bug report.  However, for a multi-patch series, it is generally
746best to avoid using In-Reply-To: to link to older versions of the
747series.  This way multiple versions of the patch don't become an
748unmanageable forest of references in email clients.  If a link is
749helpful, you can use the https://lkml.kernel.org/ redirector (e.g., in
750the cover email text) to link to an earlier version of the patch series.
751
752
75316) Sending ``git pull`` requests
754---------------------------------
755
756If you have a series of patches, it may be most convenient to have the
757maintainer pull them directly into the subsystem repository with a
758``git pull`` operation.  Note, however, that pulling patches from a developer
759requires a higher degree of trust than taking patches from a mailing list.
760As a result, many subsystem maintainers are reluctant to take pull
761requests, especially from new, unknown developers.  If in doubt you can use
762the pull request as the cover letter for a normal posting of the patch
763series, giving the maintainer the option of using either.
764
765A pull request should have [GIT PULL] in the subject line.  The
766request itself should include the repository name and the branch of
767interest on a single line; it should look something like::
768
769  Please pull from
770
771      git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
772
773  to get these changes:
774
775A pull request should also include an overall message saying what will be
776included in the request, a ``git shortlog`` listing of the patches
777themselves, and a ``diffstat`` showing the overall effect of the patch series.
778The easiest way to get all this information together is, of course, to let
779``git`` do it for you with the ``git request-pull`` command.
780
781Some maintainers (including Linus) want to see pull requests from signed
782commits; that increases their confidence that the request actually came
783from you.  Linus, in particular, will not pull from public hosting sites
784like GitHub in the absence of a signed tag.
785
786The first step toward creating such tags is to make a GNUPG key and get it
787signed by one or more core kernel developers.  This step can be hard for
788new developers, but there is no way around it.  Attending conferences can
789be a good way to find developers who can sign your key.
790
791Once you have prepared a patch series in ``git`` that you wish to have somebody
792pull, create a signed tag with ``git tag -s``.  This will create a new tag
793identifying the last commit in the series and containing a signature
794created with your private key.  You will also have the opportunity to add a
795changelog-style message to the tag; this is an ideal place to describe the
796effects of the pull request as a whole.
797
798If the tree the maintainer will be pulling from is not the repository you
799are working from, don't forget to push the signed tag explicitly to the
800public tree.
801
802When generating your pull request, use the signed tag as the target.  A
803command like this will do the trick::
804
805  git request-pull master git://my.public.tree/linux.git my-signed-tag
806
807
808References
809----------
810
811Andrew Morton, "The perfect patch" (tpp).
812  <http://www.ozlabs.org/~akpm/stuff/tpp.txt>
813
814Jeff Garzik, "Linux kernel patch submission format".
815  <http://linux.yyz.us/patch-format.html>
816
817Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
818  <http://www.kroah.com/log/linux/maintainer.html>
819
820  <http://www.kroah.com/log/linux/maintainer-02.html>
821
822  <http://www.kroah.com/log/linux/maintainer-03.html>
823
824  <http://www.kroah.com/log/linux/maintainer-04.html>
825
826  <http://www.kroah.com/log/linux/maintainer-05.html>
827
828  <http://www.kroah.com/log/linux/maintainer-06.html>
829
830NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
831  <https://lkml.org/lkml/2005/7/11/336>
832
833Kernel Documentation/process/coding-style.rst:
834  :ref:`Documentation/process/coding-style.rst <codingstyle>`
835
836Linus Torvalds's mail on the canonical patch format:
837  <http://lkml.org/lkml/2005/4/7/183>
838
839Andi Kleen, "On submitting kernel patches"
840  Some strategies to get difficult or controversial changes in.
841
842  http://halobates.de/on-submitting-patches.pdf
843