3 Submitting patches: the essential guide to getting your code into the kernel
4 ============================================================================
6 For a person or company who wishes to submit a change to the Linux
7 kernel, the process can sometimes be daunting if you're not familiar
8 with "the system." This text is a collection of suggestions which
9 can greatly increase the chances of your change being accepted.
11 This document contains a large number of suggestions in a relatively terse
12 format. For detailed information on how the kernel development process
13 works, see Documentation/process/development-process.rst. Also, read
14 Documentation/process/submit-checklist.rst
15 for a list of items to check before submitting code.
16 For device tree binding patches, read
17 Documentation/devicetree/bindings/submitting-patches.rst.
19 This documentation assumes that you're using ``git`` to prepare your patches.
20 If you're unfamiliar with ``git``, you would be well-advised to learn how to
21 use it, it will make your life as a kernel developer and in general much
24 Some subsystems and maintainer trees have additional information about
25 their workflow and expectations, see
26 :ref:`Documentation/process/maintainer-handbooks.rst <maintainer_handbooks_main>`.
28 Obtain a current source tree
29 ----------------------------
31 If you do not have a repository with the current kernel source handy, use
32 ``git`` to obtain one. You'll want to start with the mainline repository,
33 which can be grabbed with::
35 git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
37 Note, however, that you may not want to develop against the mainline tree
38 directly. Most subsystem maintainers run their own trees and want to see
39 patches prepared against those trees. See the **T:** entry for the subsystem
40 in the MAINTAINERS file to find that tree, or simply ask the maintainer if
41 the tree is not listed there.
48 Describe your problem. Whether your patch is a one-line bug fix or
49 5000 lines of a new feature, there must be an underlying problem that
50 motivated you to do this work. Convince the reviewer that there is a
51 problem worth fixing and that it makes sense for them to read past the
54 Describe user-visible impact. Straight up crashes and lockups are
55 pretty convincing, but not all bugs are that blatant. Even if the
56 problem was spotted during code review, describe the impact you think
57 it can have on users. Keep in mind that the majority of Linux
58 installations run kernels from secondary stable trees or
59 vendor/product-specific trees that cherry-pick only specific patches
60 from upstream, so include anything that could help route your change
61 downstream: provoking circumstances, excerpts from dmesg, crash
62 descriptions, performance regressions, latency spikes, lockups, etc.
64 Quantify optimizations and trade-offs. If you claim improvements in
65 performance, memory consumption, stack footprint, or binary size,
66 include numbers that back them up. But also describe non-obvious
67 costs. Optimizations usually aren't free but trade-offs between CPU,
68 memory, and readability; or, when it comes to heuristics, between
69 different workloads. Describe the expected downsides of your
70 optimization so that the reviewer can weigh costs against benefits.
72 Once the problem is established, describe what you are actually doing
73 about it in technical detail. It's important to describe the change
74 in plain English for the reviewer to verify that the code is behaving
77 The maintainer will thank you if you write your patch description in a
78 form which can be easily pulled into Linux's source code management
79 system, ``git``, as a "commit log". See :ref:`the_canonical_patch_format`.
81 Solve only one problem per patch. If your description starts to get
82 long, that's a sign that you probably need to split up your patch.
83 See :ref:`split_changes`.
85 When you submit or resubmit a patch or patch series, include the
86 complete patch description and justification for it. Don't just
87 say that this is version N of the patch (series). Don't expect the
88 subsystem maintainer to refer back to earlier patch versions or referenced
89 URLs to find the patch description and put that into the patch.
90 I.e., the patch (series) and its description should be self-contained.
91 This benefits both the maintainers and reviewers. Some reviewers
92 probably didn't even receive earlier versions of the patch.
94 Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
95 instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
96 to do frotz", as if you are giving orders to the codebase to change
99 If you want to refer to a specific commit, don't just refer to the
100 SHA-1 ID of the commit. Please also include the oneline summary of
101 the commit, to make it easier for reviewers to know what it is about.
104 Commit e21d2170f36602ae2708 ("video: remove unnecessary
105 platform_set_drvdata()") removed the unnecessary
106 platform_set_drvdata(), but left the variable "dev" unused,
109 You should also be sure to use at least the first twelve characters of the
110 SHA-1 ID. The kernel repository holds a *lot* of objects, making
111 collisions with shorter IDs a real possibility. Bear in mind that, even if
112 there is no collision with your six-character ID now, that condition may
113 change five years from now.
115 If related discussions or any other background information behind the change
116 can be found on the web, add 'Link:' tags pointing to it. In case your patch
117 fixes a bug, for example, add a tag with a URL referencing the report in the
118 mailing list archives or a bug tracker; if the patch is a result of some
119 earlier mailing list discussion or something documented on the web, point to
122 When linking to mailing list archives, preferably use the lore.kernel.org
123 message archiver service. To create the link URL, use the contents of the
124 ``Message-Id`` header of the message without the surrounding angle brackets.
127 Link: https://lore.kernel.org/r/30th.anniversary.repost@klaava.Helsinki.FI/
129 Please check the link to make sure that it is actually working and points
130 to the relevant message.
132 However, try to make your explanation understandable without external
133 resources. In addition to giving a URL to a mailing list archive or bug,
134 summarize the relevant points of the discussion that led to the
137 If your patch fixes a bug in a specific commit, e.g. you found an issue using
138 ``git bisect``, please use the 'Fixes:' tag with the first 12 characters of
139 the SHA-1 ID, and the one line summary. Do not split the tag across multiple
140 lines, tags are exempt from the "wrap at 75 columns" rule in order to simplify
141 parsing scripts. For example::
143 Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed")
145 The following ``git config`` settings can be used to add a pretty format for
146 outputting the above style in the ``git log`` or ``git show`` commands::
151 fixes = Fixes: %h (\"%s\")
155 $ git log -1 --pretty=fixes 54a4f0239f2e
156 Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed")
160 Separate your changes
161 ---------------------
163 Separate each **logical change** into a separate patch.
165 For example, if your changes include both bug fixes and performance
166 enhancements for a single driver, separate those changes into two
167 or more patches. If your changes include an API update, and a new
168 driver which uses that new API, separate those into two patches.
170 On the other hand, if you make a single change to numerous files,
171 group those changes into a single patch. Thus a single logical change
172 is contained within a single patch.
174 The point to remember is that each patch should make an easily understood
175 change that can be verified by reviewers. Each patch should be justifiable
178 If one patch depends on another patch in order for a change to be
179 complete, that is OK. Simply note **"this patch depends on patch X"**
180 in your patch description.
182 When dividing your change into a series of patches, take special care to
183 ensure that the kernel builds and runs properly after each patch in the
184 series. Developers using ``git bisect`` to track down a problem can end up
185 splitting your patch series at any point; they will not thank you if you
186 introduce bugs in the middle.
188 If you cannot condense your patch set into a smaller set of patches,
189 then only post say 15 or so at a time and wait for review and integration.
193 Style-check your changes
194 ------------------------
196 Check your patch for basic style violations, details of which can be
197 found in Documentation/process/coding-style.rst.
198 Failure to do so simply wastes
199 the reviewers time and will get your patch rejected, probably
200 without even being read.
202 One significant exception is when moving code from one file to
203 another -- in this case you should not modify the moved code at all in
204 the same patch which moves it. This clearly delineates the act of
205 moving the code and your changes. This greatly aids review of the
206 actual differences and allows tools to better track the history of
209 Check your patches with the patch style checker prior to submission
210 (scripts/checkpatch.pl). Note, though, that the style checker should be
211 viewed as a guide, not as a replacement for human judgment. If your code
212 looks better with a violation then its probably best left alone.
214 The checker reports at three levels:
215 - ERROR: things that are very likely to be wrong
216 - WARNING: things requiring careful review
217 - CHECK: things requiring thought
219 You should be able to justify all violations that remain in your
223 Select the recipients for your patch
224 ------------------------------------
226 You should always copy the appropriate subsystem maintainer(s) on any patch
227 to code that they maintain; look through the MAINTAINERS file and the
228 source code revision history to see who those maintainers are. The
229 script scripts/get_maintainer.pl can be very useful at this step (pass paths to
230 your patches as arguments to scripts/get_maintainer.pl). If you cannot find a
231 maintainer for the subsystem you are working on, Andrew Morton
232 (akpm@linux-foundation.org) serves as a maintainer of last resort.
234 You should also normally choose at least one mailing list to receive a copy
235 of your patch set. linux-kernel@vger.kernel.org should be used by default
236 for all patches, but the volume on that list has caused a number of
237 developers to tune it out. Look in the MAINTAINERS file for a
238 subsystem-specific list; your patch will probably get more attention there.
239 Please do not spam unrelated lists, though.
241 Many kernel-related lists are hosted on vger.kernel.org; you can find a
242 list of them at http://vger.kernel.org/vger-lists.html. There are
243 kernel-related lists hosted elsewhere as well, though.
245 Do not send more than 15 patches at once to the vger mailing lists!!!
247 Linus Torvalds is the final arbiter of all changes accepted into the
248 Linux kernel. His e-mail address is <torvalds@linux-foundation.org>.
249 He gets a lot of e-mail, and, at this point, very few patches go through
250 Linus directly, so typically you should do your best to -avoid-
253 If you have a patch that fixes an exploitable security bug, send that patch
254 to security@kernel.org. For severe bugs, a short embargo may be considered
255 to allow distributors to get the patch out to users; in such cases,
256 obviously, the patch should not be sent to any public lists. See also
257 Documentation/admin-guide/security-bugs.rst.
259 Patches that fix a severe bug in a released kernel should be directed
260 toward the stable maintainers by putting a line like this::
262 Cc: stable@vger.kernel.org
264 into the sign-off area of your patch (note, NOT an email recipient). You
265 should also read Documentation/process/stable-kernel-rules.rst
266 in addition to this document.
268 If changes affect userland-kernel interfaces, please send the MAN-PAGES
269 maintainer (as listed in the MAINTAINERS file) a man-pages patch, or at
270 least a notification of the change, so that some information makes its way
271 into the manual pages. User-space API changes should also be copied to
272 linux-api@vger.kernel.org.
275 No MIME, no links, no compression, no attachments. Just plain text
276 -------------------------------------------------------------------
278 Linus and other kernel developers need to be able to read and comment
279 on the changes you are submitting. It is important for a kernel
280 developer to be able to "quote" your changes, using standard e-mail
281 tools, so that they may comment on specific portions of your code.
283 For this reason, all patches should be submitted by e-mail "inline". The
284 easiest way to do this is with ``git send-email``, which is strongly
285 recommended. An interactive tutorial for ``git send-email`` is available at
286 https://git-send-email.io.
288 If you choose not to use ``git send-email``:
292 Be wary of your editor's word-wrap corrupting your patch,
293 if you choose to cut-n-paste your patch.
295 Do not attach the patch as a MIME attachment, compressed or not.
296 Many popular e-mail applications will not always transmit a MIME
297 attachment as plain text, making it impossible to comment on your
298 code. A MIME attachment also takes Linus a bit more time to process,
299 decreasing the likelihood of your MIME-attached change being accepted.
301 Exception: If your mailer is mangling patches then someone may ask
302 you to re-send them using MIME.
304 See Documentation/process/email-clients.rst for hints about configuring
305 your e-mail client so that it sends your patches untouched.
307 Respond to review comments
308 --------------------------
310 Your patch will almost certainly get comments from reviewers on ways in
311 which the patch can be improved, in the form of a reply to your email. You must
312 respond to those comments; ignoring reviewers is a good way to get ignored in
313 return. You can simply reply to their emails to answer their comments. Review
314 comments or questions that do not lead to a code change should almost certainly
315 bring about a comment or changelog entry so that the next reviewer better
316 understands what is going on.
318 Be sure to tell the reviewers what changes you are making and to thank them
319 for their time. Code review is a tiring and time-consuming process, and
320 reviewers sometimes get grumpy. Even in that case, though, respond
321 politely and address the problems they have pointed out. When sending a next
322 version, add a ``patch changelog`` to the cover letter or to individual patches
323 explaining difference aganst previous submission (see
324 :ref:`the_canonical_patch_format`).
326 See Documentation/process/email-clients.rst for recommendations on email
327 clients and mailing list etiquette.
329 .. _resend_reminders:
331 Don't get discouraged - or impatient
332 ------------------------------------
334 After you have submitted your change, be patient and wait. Reviewers are
335 busy people and may not get to your patch right away.
337 Once upon a time, patches used to disappear into the void without comment,
338 but the development process works more smoothly than that now. You should
339 receive comments within a week or so; if that does not happen, make sure
340 that you have sent your patches to the right place. Wait for a minimum of
341 one week before resubmitting or pinging reviewers - possibly longer during
342 busy times like merge windows.
344 It's also ok to resend the patch or the patch series after a couple of
345 weeks with the word "RESEND" added to the subject line::
347 [PATCH Vx RESEND] sub/sys: Condensed patch summary
349 Don't add "RESEND" when you are submitting a modified version of your
350 patch or patch series - "RESEND" only applies to resubmission of a
351 patch or patch series which have not been modified in any way from the
355 Include PATCH in the subject
356 -----------------------------
358 Due to high e-mail traffic to Linus, and to linux-kernel, it is common
359 convention to prefix your subject line with [PATCH]. This lets Linus
360 and other kernel developers more easily distinguish patches from other
363 ``git send-email`` will do this for you automatically.
366 Sign your work - the Developer's Certificate of Origin
367 ------------------------------------------------------
369 To improve tracking of who did what, especially with patches that can
370 percolate to their final resting place in the kernel through several
371 layers of maintainers, we've introduced a "sign-off" procedure on
372 patches that are being emailed around.
374 The sign-off is a simple line at the end of the explanation for the
375 patch, which certifies that you wrote it or otherwise have the right to
376 pass it on as an open-source patch. The rules are pretty simple: if you
377 can certify the below:
379 Developer's Certificate of Origin 1.1
380 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
382 By making a contribution to this project, I certify that:
384 (a) The contribution was created in whole or in part by me and I
385 have the right to submit it under the open source license
386 indicated in the file; or
388 (b) The contribution is based upon previous work that, to the best
389 of my knowledge, is covered under an appropriate open source
390 license and I have the right under that license to submit that
391 work with modifications, whether created in whole or in part
392 by me, under the same open source license (unless I am
393 permitted to submit under a different license), as indicated
396 (c) The contribution was provided directly to me by some other
397 person who certified (a), (b) or (c) and I have not modified
400 (d) I understand and agree that this project and the contribution
401 are public and that a record of the contribution (including all
402 personal information I submit with it, including my sign-off) is
403 maintained indefinitely and may be redistributed consistent with
404 this project or the open source license(s) involved.
406 then you just add a line saying::
408 Signed-off-by: Random J Developer <random@developer.example.org>
410 using your real name (sorry, no pseudonyms or anonymous contributions.)
411 This will be done for you automatically if you use ``git commit -s``.
412 Reverts should also include "Signed-off-by". ``git revert -s`` does that
415 Some people also put extra tags at the end. They'll just be ignored for
416 now, but you can do this to mark internal company procedures or just
417 point out some special detail about the sign-off.
419 Any further SoBs (Signed-off-by:'s) following the author's SoB are from
420 people handling and transporting the patch, but were not involved in its
421 development. SoB chains should reflect the **real** route a patch took
422 as it was propagated to the maintainers and ultimately to Linus, with
423 the first SoB entry signalling primary authorship of a single author.
426 When to use Acked-by:, Cc:, and Co-developed-by:
427 ------------------------------------------------
429 The Signed-off-by: tag indicates that the signer was involved in the
430 development of the patch, or that he/she was in the patch's delivery path.
432 If a person was not directly involved in the preparation or handling of a
433 patch but wishes to signify and record their approval of it then they can
434 ask to have an Acked-by: line added to the patch's changelog.
436 Acked-by: is often used by the maintainer of the affected code when that
437 maintainer neither contributed to nor forwarded the patch.
439 Acked-by: is not as formal as Signed-off-by:. It is a record that the acker
440 has at least reviewed the patch and has indicated acceptance. Hence patch
441 mergers will sometimes manually convert an acker's "yep, looks good to me"
442 into an Acked-by: (but note that it is usually better to ask for an
445 Acked-by: does not necessarily indicate acknowledgement of the entire patch.
446 For example, if a patch affects multiple subsystems and has an Acked-by: from
447 one subsystem maintainer then this usually indicates acknowledgement of just
448 the part which affects that maintainer's code. Judgement should be used here.
449 When in doubt people should refer to the original discussion in the mailing
452 If a person has had the opportunity to comment on a patch, but has not
453 provided such comments, you may optionally add a ``Cc:`` tag to the patch.
454 This is the only tag which might be added without an explicit action by the
455 person it names - but it should indicate that this person was copied on the
456 patch. This tag documents that potentially interested parties
457 have been included in the discussion.
459 Co-developed-by: states that the patch was co-created by multiple developers;
460 it is used to give attribution to co-authors (in addition to the author
461 attributed by the From: tag) when several people work on a single patch. Since
462 Co-developed-by: denotes authorship, every Co-developed-by: must be immediately
463 followed by a Signed-off-by: of the associated co-author. Standard sign-off
464 procedure applies, i.e. the ordering of Signed-off-by: tags should reflect the
465 chronological history of the patch insofar as possible, regardless of whether
466 the author is attributed via From: or Co-developed-by:. Notably, the last
467 Signed-off-by: must always be that of the developer submitting the patch.
469 Note, the From: tag is optional when the From: author is also the person (and
470 email) listed in the From: line of the email header.
472 Example of a patch submitted by the From: author::
476 Co-developed-by: First Co-Author <first@coauthor.example.org>
477 Signed-off-by: First Co-Author <first@coauthor.example.org>
478 Co-developed-by: Second Co-Author <second@coauthor.example.org>
479 Signed-off-by: Second Co-Author <second@coauthor.example.org>
480 Signed-off-by: From Author <from@author.example.org>
482 Example of a patch submitted by a Co-developed-by: author::
484 From: From Author <from@author.example.org>
488 Co-developed-by: Random Co-Author <random@coauthor.example.org>
489 Signed-off-by: Random Co-Author <random@coauthor.example.org>
490 Signed-off-by: From Author <from@author.example.org>
491 Co-developed-by: Submitting Co-Author <sub@coauthor.example.org>
492 Signed-off-by: Submitting Co-Author <sub@coauthor.example.org>
495 Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
496 ----------------------------------------------------------------------
498 The Reported-by tag gives credit to people who find bugs and report them and it
499 hopefully inspires them to help us again in the future. Please note that if
500 the bug was reported in private, then ask for permission first before using the
501 Reported-by tag. The tag is intended for bugs; please do not use it to credit
504 A Tested-by: tag indicates that the patch has been successfully tested (in
505 some environment) by the person named. This tag informs maintainers that
506 some testing has been performed, provides a means to locate testers for
507 future patches, and ensures credit for the testers.
509 Reviewed-by:, instead, indicates that the patch has been reviewed and found
510 acceptable according to the Reviewer's Statement:
512 Reviewer's statement of oversight
513 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
515 By offering my Reviewed-by: tag, I state that:
517 (a) I have carried out a technical review of this patch to
518 evaluate its appropriateness and readiness for inclusion into
521 (b) Any problems, concerns, or questions relating to the patch
522 have been communicated back to the submitter. I am satisfied
523 with the submitter's response to my comments.
525 (c) While there may be things that could be improved with this
526 submission, I believe that it is, at this time, (1) a
527 worthwhile modification to the kernel, and (2) free of known
528 issues which would argue against its inclusion.
530 (d) While I have reviewed the patch and believe it to be sound, I
531 do not (unless explicitly stated elsewhere) make any
532 warranties or guarantees that it will achieve its stated
533 purpose or function properly in any given situation.
535 A Reviewed-by tag is a statement of opinion that the patch is an
536 appropriate modification of the kernel without any remaining serious
537 technical issues. Any interested reviewer (who has done the work) can
538 offer a Reviewed-by tag for a patch. This tag serves to give credit to
539 reviewers and to inform maintainers of the degree of review which has been
540 done on the patch. Reviewed-by: tags, when supplied by reviewers known to
541 understand the subject area and to perform thorough reviews, will normally
542 increase the likelihood of your patch getting into the kernel.
544 Both Tested-by and Reviewed-by tags, once received on mailing list from tester
545 or reviewer, should be added by author to the applicable patches when sending
546 next versions. However if the patch has changed substantially in following
547 version, these tags might not be applicable anymore and thus should be removed.
548 Usually removal of someone's Tested-by or Reviewed-by tags should be mentioned
549 in the patch changelog (after the '---' separator).
551 A Suggested-by: tag indicates that the patch idea is suggested by the person
552 named and ensures credit to the person for the idea. Please note that this
553 tag should not be added without the reporter's permission, especially if the
554 idea was not posted in a public forum. That said, if we diligently credit our
555 idea reporters, they will, hopefully, be inspired to help us again in the
558 A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
559 is used to make it easy to determine where a bug originated, which can help
560 review a bug fix. This tag also assists the stable kernel team in determining
561 which stable kernel versions should receive your fix. This is the preferred
562 method for indicating a bug fixed by the patch. See :ref:`describe_changes`
565 Note: Attaching a Fixes: tag does not subvert the stable kernel rules
566 process nor the requirement to Cc: stable@vger.kernel.org on all stable
567 patch candidates. For more information, please read
568 Documentation/process/stable-kernel-rules.rst.
570 .. _the_canonical_patch_format:
572 The canonical patch format
573 --------------------------
575 This section describes how the patch itself should be formatted. Note
576 that, if you have your patches stored in a ``git`` repository, proper patch
577 formatting can be had with ``git format-patch``. The tools cannot create
578 the necessary text, though, so read the instructions below anyway.
580 The canonical patch subject line is::
582 Subject: [PATCH 001/123] subsystem: summary phrase
584 The canonical patch message body contains the following:
586 - A ``from`` line specifying the patch author, followed by an empty
587 line (only needed if the person sending the patch is not the author).
589 - The body of the explanation, line wrapped at 75 columns, which will
590 be copied to the permanent changelog to describe this patch.
594 - The ``Signed-off-by:`` lines, described above, which will
595 also go in the changelog.
597 - A marker line containing simply ``---``.
599 - Any additional comments not suitable for the changelog.
601 - The actual patch (``diff`` output).
603 The Subject line format makes it very easy to sort the emails
604 alphabetically by subject line - pretty much any email reader will
605 support that - since because the sequence number is zero-padded,
606 the numerical and alphabetic sort is the same.
608 The ``subsystem`` in the email's Subject should identify which
609 area or subsystem of the kernel is being patched.
611 The ``summary phrase`` in the email's Subject should concisely
612 describe the patch which that email contains. The ``summary
613 phrase`` should not be a filename. Do not use the same ``summary
614 phrase`` for every patch in a whole patch series (where a ``patch
615 series`` is an ordered sequence of multiple, related patches).
617 Bear in mind that the ``summary phrase`` of your email becomes a
618 globally-unique identifier for that patch. It propagates all the way
619 into the ``git`` changelog. The ``summary phrase`` may later be used in
620 developer discussions which refer to the patch. People will want to
621 google for the ``summary phrase`` to read discussion regarding that
622 patch. It will also be the only thing that people may quickly see
623 when, two or three months later, they are going through perhaps
624 thousands of patches using tools such as ``gitk`` or ``git log
627 For these reasons, the ``summary`` must be no more than 70-75
628 characters, and it must describe both what the patch changes, as well
629 as why the patch might be necessary. It is challenging to be both
630 succinct and descriptive, but that is what a well-written summary
633 The ``summary phrase`` may be prefixed by tags enclosed in square
634 brackets: "Subject: [PATCH <tag>...] <summary phrase>". The tags are
635 not considered part of the summary phrase, but describe how the patch
636 should be treated. Common tags might include a version descriptor if
637 the multiple versions of the patch have been sent out in response to
638 comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
641 If there are four patches in a patch series the individual patches may
642 be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures that developers
643 understand the order in which the patches should be applied and that
644 they have reviewed or applied all of the patches in the patch series.
646 Here are some good example Subjects::
648 Subject: [PATCH 2/5] ext2: improve scalability of bitmap searching
649 Subject: [PATCH v2 01/27] x86: fix eflags tracking
650 Subject: [PATCH v2] sub/sys: Condensed patch summary
651 Subject: [PATCH v2 M/N] sub/sys: Condensed patch summary
653 The ``from`` line must be the very first line in the message body,
656 From: Patch Author <author@example.com>
658 The ``from`` line specifies who will be credited as the author of the
659 patch in the permanent changelog. If the ``from`` line is missing,
660 then the ``From:`` line from the email header will be used to determine
661 the patch author in the changelog.
663 The explanation body will be committed to the permanent source
664 changelog, so should make sense to a competent reader who has long since
665 forgotten the immediate details of the discussion that might have led to
666 this patch. Including symptoms of the failure which the patch addresses
667 (kernel log messages, oops messages, etc.) are especially useful for
668 people who might be searching the commit logs looking for the applicable
669 patch. The text should be written in such detail so that when read
670 weeks, months or even years later, it can give the reader the needed
671 details to grasp the reasoning for **why** the patch was created.
673 If a patch fixes a compile failure, it may not be necessary to include
674 _all_ of the compile failures; just enough that it is likely that
675 someone searching for the patch can find it. As in the ``summary
676 phrase``, it is important to be both succinct as well as descriptive.
678 The ``---`` marker line serves the essential purpose of marking for
679 patch handling tools where the changelog message ends.
681 One good use for the additional comments after the ``---`` marker is
682 for a ``diffstat``, to show what files have changed, and the number of
683 inserted and deleted lines per file. A ``diffstat`` is especially useful
684 on bigger patches. If you are going to include a ``diffstat`` after the
685 ``---`` marker, please use ``diffstat`` options ``-p 1 -w 70`` so that
686 filenames are listed from the top of the kernel source tree and don't
687 use too much horizontal space (easily fit in 80 columns, maybe with some
688 indentation). (``git`` generates appropriate diffstats by default.)
690 Other comments relevant only to the moment or the maintainer, not
691 suitable for the permanent changelog, should also go here. A good
692 example of such comments might be ``patch changelogs`` which describe
693 what has changed between the v1 and v2 version of the patch.
695 Please put this information **after** the ``---`` line which separates
696 the changelog from the rest of the patch. The version information is
697 not part of the changelog which gets committed to the git tree. It is
698 additional information for the reviewers. If it's placed above the
699 commit tags, it needs manual interaction to remove it. If it is below
700 the separator line, it gets automatically stripped off when applying the
705 Signed-off-by: Author <author@mail>
707 V2 -> V3: Removed redundant helper function
708 V1 -> V2: Cleaned up coding style and addressed review comments
710 path/to/file | 5+++--
713 See more details on the proper patch format in the following
718 Backtraces in commit messages
719 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
721 Backtraces help document the call chain leading to a problem. However,
722 not all backtraces are helpful. For example, early boot call chains are
723 unique and obvious. Copying the full dmesg output verbatim, however,
724 adds distracting information like timestamps, module lists, register and
727 Therefore, the most useful backtraces should distill the relevant
728 information from the dump, which makes it easier to focus on the real
729 issue. Here is an example of a well-trimmed backtrace::
731 unchecked MSR access error: WRMSR to 0xd51 (tried to write 0x0000000000000064)
732 at rIP: 0xffffffffae059994 (native_write_msr+0x4/0x20)
738 .. _explicit_in_reply_to:
740 Explicit In-Reply-To headers
741 ----------------------------
743 It can be helpful to manually add In-Reply-To: headers to a patch
744 (e.g., when using ``git send-email``) to associate the patch with
745 previous relevant discussion, e.g. to link a bug fix to the email with
746 the bug report. However, for a multi-patch series, it is generally
747 best to avoid using In-Reply-To: to link to older versions of the
748 series. This way multiple versions of the patch don't become an
749 unmanageable forest of references in email clients. If a link is
750 helpful, you can use the https://lore.kernel.org/ redirector (e.g., in
751 the cover email text) to link to an earlier version of the patch series.
754 Providing base tree information
755 -------------------------------
757 When other developers receive your patches and start the review process,
758 it is often useful for them to know where in the tree history they
759 should place your work. This is particularly useful for automated CI
760 processes that attempt to run a series of tests in order to establish
761 the quality of your submission before the maintainer starts the review.
763 If you are using ``git format-patch`` to generate your patches, you can
764 automatically include the base tree information in your submission by
765 using the ``--base`` flag. The easiest and most convenient way to use
766 this option is with topical branches::
768 $ git checkout -t -b my-topical-branch master
769 Branch 'my-topical-branch' set up to track local branch 'master'.
770 Switched to a new branch 'my-topical-branch'
772 [perform your edits and commits]
774 $ git format-patch --base=auto --cover-letter -o outgoing/ master
775 outgoing/0000-cover-letter.patch
776 outgoing/0001-First-Commit.patch
779 When you open ``outgoing/0000-cover-letter.patch`` for editing, you will
780 notice that it will have the ``base-commit:`` trailer at the very
781 bottom, which provides the reviewer and the CI tools enough information
782 to properly perform ``git am`` without worrying about conflicts::
784 $ git checkout -b patch-review [base-commit-id]
785 Switched to a new branch 'patch-review'
786 $ git am patches.mbox
787 Applying: First Commit
790 Please see ``man git-format-patch`` for more information about this
795 The ``--base`` feature was introduced in git version 2.9.0.
797 If you are not using git to format your patches, you can still include
798 the same ``base-commit`` trailer to indicate the commit hash of the tree
799 on which your work is based. You should add it either in the cover
800 letter or in the first patch of the series and it should be placed
801 either below the ``---`` line or at the very bottom of all other
802 content, right before your email signature.
808 Andrew Morton, "The perfect patch" (tpp).
809 <https://www.ozlabs.org/~akpm/stuff/tpp.txt>
811 Jeff Garzik, "Linux kernel patch submission format".
812 <https://web.archive.org/web/20180829112450/http://linux.yyz.us/patch-format.html>
814 Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
815 <http://www.kroah.com/log/linux/maintainer.html>
817 <http://www.kroah.com/log/linux/maintainer-02.html>
819 <http://www.kroah.com/log/linux/maintainer-03.html>
821 <http://www.kroah.com/log/linux/maintainer-04.html>
823 <http://www.kroah.com/log/linux/maintainer-05.html>
825 <http://www.kroah.com/log/linux/maintainer-06.html>
827 NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
828 <https://lore.kernel.org/r/20050711.125305.08322243.davem@davemloft.net>
830 Kernel Documentation/process/coding-style.rst
832 Linus Torvalds's mail on the canonical patch format:
833 <https://lore.kernel.org/r/Pine.LNX.4.58.0504071023190.28951@ppc970.osdl.org>
835 Andi Kleen, "On submitting kernel patches"
836 Some strategies to get difficult or controversial changes in.
838 http://halobates.de/on-submitting-patches.pdf