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. If the patch is a
117 result of some earlier mailing list discussions or something documented on the
120 When linking to mailing list archives, preferably use the lore.kernel.org
121 message archiver service. To create the link URL, use the contents of the
122 ``Message-Id`` header of the message without the surrounding angle brackets.
125 Link: https://lore.kernel.org/r/30th.anniversary.repost@klaava.Helsinki.FI/
127 Please check the link to make sure that it is actually working and points
128 to the relevant message.
130 However, try to make your explanation understandable without external
131 resources. In addition to giving a URL to a mailing list archive or bug,
132 summarize the relevant points of the discussion that led to the
135 In case your patch fixes a bug, use the 'Closes:' tag with a URL referencing
136 the report in the mailing list archives or a public bug tracker. For example::
138 Closes: https://example.com/issues/1234
140 Some bug trackers have the ability to close issues automatically when a
141 commit with such a tag is applied. Some bots monitoring mailing lists can
142 also track such tags and take certain actions. Private bug trackers and
143 invalid URLs are forbidden.
145 If your patch fixes a bug in a specific commit, e.g. you found an issue using
146 ``git bisect``, please use the 'Fixes:' tag with the first 12 characters of
147 the SHA-1 ID, and the one line summary. Do not split the tag across multiple
148 lines, tags are exempt from the "wrap at 75 columns" rule in order to simplify
149 parsing scripts. For example::
151 Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed")
153 The following ``git config`` settings can be used to add a pretty format for
154 outputting the above style in the ``git log`` or ``git show`` commands::
159 fixes = Fixes: %h (\"%s\")
163 $ git log -1 --pretty=fixes 54a4f0239f2e
164 Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed")
168 Separate your changes
169 ---------------------
171 Separate each **logical change** into a separate patch.
173 For example, if your changes include both bug fixes and performance
174 enhancements for a single driver, separate those changes into two
175 or more patches. If your changes include an API update, and a new
176 driver which uses that new API, separate those into two patches.
178 On the other hand, if you make a single change to numerous files,
179 group those changes into a single patch. Thus a single logical change
180 is contained within a single patch.
182 The point to remember is that each patch should make an easily understood
183 change that can be verified by reviewers. Each patch should be justifiable
186 If one patch depends on another patch in order for a change to be
187 complete, that is OK. Simply note **"this patch depends on patch X"**
188 in your patch description.
190 When dividing your change into a series of patches, take special care to
191 ensure that the kernel builds and runs properly after each patch in the
192 series. Developers using ``git bisect`` to track down a problem can end up
193 splitting your patch series at any point; they will not thank you if you
194 introduce bugs in the middle.
196 If you cannot condense your patch set into a smaller set of patches,
197 then only post say 15 or so at a time and wait for review and integration.
201 Style-check your changes
202 ------------------------
204 Check your patch for basic style violations, details of which can be
205 found in Documentation/process/coding-style.rst.
206 Failure to do so simply wastes
207 the reviewers time and will get your patch rejected, probably
208 without even being read.
210 One significant exception is when moving code from one file to
211 another -- in this case you should not modify the moved code at all in
212 the same patch which moves it. This clearly delineates the act of
213 moving the code and your changes. This greatly aids review of the
214 actual differences and allows tools to better track the history of
217 Check your patches with the patch style checker prior to submission
218 (scripts/checkpatch.pl). Note, though, that the style checker should be
219 viewed as a guide, not as a replacement for human judgment. If your code
220 looks better with a violation then its probably best left alone.
222 The checker reports at three levels:
223 - ERROR: things that are very likely to be wrong
224 - WARNING: things requiring careful review
225 - CHECK: things requiring thought
227 You should be able to justify all violations that remain in your
231 Select the recipients for your patch
232 ------------------------------------
234 You should always copy the appropriate subsystem maintainer(s) and list(s) on
235 any patch to code that they maintain; look through the MAINTAINERS file and the
236 source code revision history to see who those maintainers are. The script
237 scripts/get_maintainer.pl can be very useful at this step (pass paths to your
238 patches as arguments to scripts/get_maintainer.pl). If you cannot find a
239 maintainer for the subsystem you are working on, Andrew Morton
240 (akpm@linux-foundation.org) serves as a maintainer of last resort.
242 linux-kernel@vger.kernel.org should be used by default for all patches, but the
243 volume on that list has caused a number of developers to tune it out. Please
244 do not spam unrelated lists and unrelated people, though.
246 Many kernel-related lists are hosted on vger.kernel.org; you can find a
247 list of them at http://vger.kernel.org/vger-lists.html. There are
248 kernel-related lists hosted elsewhere as well, though.
250 Do not send more than 15 patches at once to the vger mailing lists!!!
252 Linus Torvalds is the final arbiter of all changes accepted into the
253 Linux kernel. His e-mail address is <torvalds@linux-foundation.org>.
254 He gets a lot of e-mail, and, at this point, very few patches go through
255 Linus directly, so typically you should do your best to -avoid-
258 If you have a patch that fixes an exploitable security bug, send that patch
259 to security@kernel.org. For severe bugs, a short embargo may be considered
260 to allow distributors to get the patch out to users; in such cases,
261 obviously, the patch should not be sent to any public lists. See also
262 Documentation/process/security-bugs.rst.
264 Patches that fix a severe bug in a released kernel should be directed
265 toward the stable maintainers by putting a line like this::
267 Cc: stable@vger.kernel.org
269 into the sign-off area of your patch (note, NOT an email recipient). You
270 should also read Documentation/process/stable-kernel-rules.rst
271 in addition to this document.
273 If changes affect userland-kernel interfaces, please send the MAN-PAGES
274 maintainer (as listed in the MAINTAINERS file) a man-pages patch, or at
275 least a notification of the change, so that some information makes its way
276 into the manual pages. User-space API changes should also be copied to
277 linux-api@vger.kernel.org.
280 No MIME, no links, no compression, no attachments. Just plain text
281 -------------------------------------------------------------------
283 Linus and other kernel developers need to be able to read and comment
284 on the changes you are submitting. It is important for a kernel
285 developer to be able to "quote" your changes, using standard e-mail
286 tools, so that they may comment on specific portions of your code.
288 For this reason, all patches should be submitted by e-mail "inline". The
289 easiest way to do this is with ``git send-email``, which is strongly
290 recommended. An interactive tutorial for ``git send-email`` is available at
291 https://git-send-email.io.
293 If you choose not to use ``git send-email``:
297 Be wary of your editor's word-wrap corrupting your patch,
298 if you choose to cut-n-paste your patch.
300 Do not attach the patch as a MIME attachment, compressed or not.
301 Many popular e-mail applications will not always transmit a MIME
302 attachment as plain text, making it impossible to comment on your
303 code. A MIME attachment also takes Linus a bit more time to process,
304 decreasing the likelihood of your MIME-attached change being accepted.
306 Exception: If your mailer is mangling patches then someone may ask
307 you to re-send them using MIME.
309 See Documentation/process/email-clients.rst for hints about configuring
310 your e-mail client so that it sends your patches untouched.
312 Respond to review comments
313 --------------------------
315 Your patch will almost certainly get comments from reviewers on ways in
316 which the patch can be improved, in the form of a reply to your email. You must
317 respond to those comments; ignoring reviewers is a good way to get ignored in
318 return. You can simply reply to their emails to answer their comments. Review
319 comments or questions that do not lead to a code change should almost certainly
320 bring about a comment or changelog entry so that the next reviewer better
321 understands what is going on.
323 Be sure to tell the reviewers what changes you are making and to thank them
324 for their time. Code review is a tiring and time-consuming process, and
325 reviewers sometimes get grumpy. Even in that case, though, respond
326 politely and address the problems they have pointed out. When sending a next
327 version, add a ``patch changelog`` to the cover letter or to individual patches
328 explaining difference against previous submission (see
329 :ref:`the_canonical_patch_format`).
331 See Documentation/process/email-clients.rst for recommendations on email
332 clients and mailing list etiquette.
334 .. _resend_reminders:
336 Don't get discouraged - or impatient
337 ------------------------------------
339 After you have submitted your change, be patient and wait. Reviewers are
340 busy people and may not get to your patch right away.
342 Once upon a time, patches used to disappear into the void without comment,
343 but the development process works more smoothly than that now. You should
344 receive comments within a week or so; if that does not happen, make sure
345 that you have sent your patches to the right place. Wait for a minimum of
346 one week before resubmitting or pinging reviewers - possibly longer during
347 busy times like merge windows.
349 It's also ok to resend the patch or the patch series after a couple of
350 weeks with the word "RESEND" added to the subject line::
352 [PATCH Vx RESEND] sub/sys: Condensed patch summary
354 Don't add "RESEND" when you are submitting a modified version of your
355 patch or patch series - "RESEND" only applies to resubmission of a
356 patch or patch series which have not been modified in any way from the
360 Include PATCH in the subject
361 -----------------------------
363 Due to high e-mail traffic to Linus, and to linux-kernel, it is common
364 convention to prefix your subject line with [PATCH]. This lets Linus
365 and other kernel developers more easily distinguish patches from other
368 ``git send-email`` will do this for you automatically.
371 Sign your work - the Developer's Certificate of Origin
372 ------------------------------------------------------
374 To improve tracking of who did what, especially with patches that can
375 percolate to their final resting place in the kernel through several
376 layers of maintainers, we've introduced a "sign-off" procedure on
377 patches that are being emailed around.
379 The sign-off is a simple line at the end of the explanation for the
380 patch, which certifies that you wrote it or otherwise have the right to
381 pass it on as an open-source patch. The rules are pretty simple: if you
382 can certify the below:
384 Developer's Certificate of Origin 1.1
385 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
387 By making a contribution to this project, I certify that:
389 (a) The contribution was created in whole or in part by me and I
390 have the right to submit it under the open source license
391 indicated in the file; or
393 (b) The contribution is based upon previous work that, to the best
394 of my knowledge, is covered under an appropriate open source
395 license and I have the right under that license to submit that
396 work with modifications, whether created in whole or in part
397 by me, under the same open source license (unless I am
398 permitted to submit under a different license), as indicated
401 (c) The contribution was provided directly to me by some other
402 person who certified (a), (b) or (c) and I have not modified
405 (d) I understand and agree that this project and the contribution
406 are public and that a record of the contribution (including all
407 personal information I submit with it, including my sign-off) is
408 maintained indefinitely and may be redistributed consistent with
409 this project or the open source license(s) involved.
411 then you just add a line saying::
413 Signed-off-by: Random J Developer <random@developer.example.org>
415 using a known identity (sorry, no anonymous contributions.)
416 This will be done for you automatically if you use ``git commit -s``.
417 Reverts should also include "Signed-off-by". ``git revert -s`` does that
420 Some people also put extra tags at the end. They'll just be ignored for
421 now, but you can do this to mark internal company procedures or just
422 point out some special detail about the sign-off.
424 Any further SoBs (Signed-off-by:'s) following the author's SoB are from
425 people handling and transporting the patch, but were not involved in its
426 development. SoB chains should reflect the **real** route a patch took
427 as it was propagated to the maintainers and ultimately to Linus, with
428 the first SoB entry signalling primary authorship of a single author.
431 When to use Acked-by:, Cc:, and Co-developed-by:
432 ------------------------------------------------
434 The Signed-off-by: tag indicates that the signer was involved in the
435 development of the patch, or that he/she was in the patch's delivery path.
437 If a person was not directly involved in the preparation or handling of a
438 patch but wishes to signify and record their approval of it then they can
439 ask to have an Acked-by: line added to the patch's changelog.
441 Acked-by: is often used by the maintainer of the affected code when that
442 maintainer neither contributed to nor forwarded the patch.
444 Acked-by: is not as formal as Signed-off-by:. It is a record that the acker
445 has at least reviewed the patch and has indicated acceptance. Hence patch
446 mergers will sometimes manually convert an acker's "yep, looks good to me"
447 into an Acked-by: (but note that it is usually better to ask for an
450 Acked-by: does not necessarily indicate acknowledgement of the entire patch.
451 For example, if a patch affects multiple subsystems and has an Acked-by: from
452 one subsystem maintainer then this usually indicates acknowledgement of just
453 the part which affects that maintainer's code. Judgement should be used here.
454 When in doubt people should refer to the original discussion in the mailing
457 If a person has had the opportunity to comment on a patch, but has not
458 provided such comments, you may optionally add a ``Cc:`` tag to the patch.
459 This is the only tag which might be added without an explicit action by the
460 person it names - but it should indicate that this person was copied on the
461 patch. This tag documents that potentially interested parties
462 have been included in the discussion.
464 Co-developed-by: states that the patch was co-created by multiple developers;
465 it is used to give attribution to co-authors (in addition to the author
466 attributed by the From: tag) when several people work on a single patch. Since
467 Co-developed-by: denotes authorship, every Co-developed-by: must be immediately
468 followed by a Signed-off-by: of the associated co-author. Standard sign-off
469 procedure applies, i.e. the ordering of Signed-off-by: tags should reflect the
470 chronological history of the patch insofar as possible, regardless of whether
471 the author is attributed via From: or Co-developed-by:. Notably, the last
472 Signed-off-by: must always be that of the developer submitting the patch.
474 Note, the From: tag is optional when the From: author is also the person (and
475 email) listed in the From: line of the email header.
477 Example of a patch submitted by the From: author::
481 Co-developed-by: First Co-Author <first@coauthor.example.org>
482 Signed-off-by: First Co-Author <first@coauthor.example.org>
483 Co-developed-by: Second Co-Author <second@coauthor.example.org>
484 Signed-off-by: Second Co-Author <second@coauthor.example.org>
485 Signed-off-by: From Author <from@author.example.org>
487 Example of a patch submitted by a Co-developed-by: author::
489 From: From Author <from@author.example.org>
493 Co-developed-by: Random Co-Author <random@coauthor.example.org>
494 Signed-off-by: Random Co-Author <random@coauthor.example.org>
495 Signed-off-by: From Author <from@author.example.org>
496 Co-developed-by: Submitting Co-Author <sub@coauthor.example.org>
497 Signed-off-by: Submitting Co-Author <sub@coauthor.example.org>
500 Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
501 ----------------------------------------------------------------------
503 The Reported-by tag gives credit to people who find bugs and report them and it
504 hopefully inspires them to help us again in the future. The tag is intended for
505 bugs; please do not use it to credit feature requests. The tag should be
506 followed by a Closes: tag pointing to the report, unless the report is not
507 available on the web. The Link: tag can be used instead of Closes: if the patch
508 fixes a part of the issue(s) being reported. Please note that if the bug was
509 reported in private, then ask for permission first before using the Reported-by
512 A Tested-by: tag indicates that the patch has been successfully tested (in
513 some environment) by the person named. This tag informs maintainers that
514 some testing has been performed, provides a means to locate testers for
515 future patches, and ensures credit for the testers.
517 Reviewed-by:, instead, indicates that the patch has been reviewed and found
518 acceptable according to the Reviewer's Statement:
520 Reviewer's statement of oversight
521 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
523 By offering my Reviewed-by: tag, I state that:
525 (a) I have carried out a technical review of this patch to
526 evaluate its appropriateness and readiness for inclusion into
529 (b) Any problems, concerns, or questions relating to the patch
530 have been communicated back to the submitter. I am satisfied
531 with the submitter's response to my comments.
533 (c) While there may be things that could be improved with this
534 submission, I believe that it is, at this time, (1) a
535 worthwhile modification to the kernel, and (2) free of known
536 issues which would argue against its inclusion.
538 (d) While I have reviewed the patch and believe it to be sound, I
539 do not (unless explicitly stated elsewhere) make any
540 warranties or guarantees that it will achieve its stated
541 purpose or function properly in any given situation.
543 A Reviewed-by tag is a statement of opinion that the patch is an
544 appropriate modification of the kernel without any remaining serious
545 technical issues. Any interested reviewer (who has done the work) can
546 offer a Reviewed-by tag for a patch. This tag serves to give credit to
547 reviewers and to inform maintainers of the degree of review which has been
548 done on the patch. Reviewed-by: tags, when supplied by reviewers known to
549 understand the subject area and to perform thorough reviews, will normally
550 increase the likelihood of your patch getting into the kernel.
552 Both Tested-by and Reviewed-by tags, once received on mailing list from tester
553 or reviewer, should be added by author to the applicable patches when sending
554 next versions. However if the patch has changed substantially in following
555 version, these tags might not be applicable anymore and thus should be removed.
556 Usually removal of someone's Tested-by or Reviewed-by tags should be mentioned
557 in the patch changelog (after the '---' separator).
559 A Suggested-by: tag indicates that the patch idea is suggested by the person
560 named and ensures credit to the person for the idea. Please note that this
561 tag should not be added without the reporter's permission, especially if the
562 idea was not posted in a public forum. That said, if we diligently credit our
563 idea reporters, they will, hopefully, be inspired to help us again in the
566 A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
567 is used to make it easy to determine where a bug originated, which can help
568 review a bug fix. This tag also assists the stable kernel team in determining
569 which stable kernel versions should receive your fix. This is the preferred
570 method for indicating a bug fixed by the patch. See :ref:`describe_changes`
573 Note: Attaching a Fixes: tag does not subvert the stable kernel rules
574 process nor the requirement to Cc: stable@vger.kernel.org on all stable
575 patch candidates. For more information, please read
576 Documentation/process/stable-kernel-rules.rst.
578 .. _the_canonical_patch_format:
580 The canonical patch format
581 --------------------------
583 This section describes how the patch itself should be formatted. Note
584 that, if you have your patches stored in a ``git`` repository, proper patch
585 formatting can be had with ``git format-patch``. The tools cannot create
586 the necessary text, though, so read the instructions below anyway.
588 The canonical patch subject line is::
590 Subject: [PATCH 001/123] subsystem: summary phrase
592 The canonical patch message body contains the following:
594 - A ``from`` line specifying the patch author, followed by an empty
595 line (only needed if the person sending the patch is not the author).
597 - The body of the explanation, line wrapped at 75 columns, which will
598 be copied to the permanent changelog to describe this patch.
602 - The ``Signed-off-by:`` lines, described above, which will
603 also go in the changelog.
605 - A marker line containing simply ``---``.
607 - Any additional comments not suitable for the changelog.
609 - The actual patch (``diff`` output).
611 The Subject line format makes it very easy to sort the emails
612 alphabetically by subject line - pretty much any email reader will
613 support that - since because the sequence number is zero-padded,
614 the numerical and alphabetic sort is the same.
616 The ``subsystem`` in the email's Subject should identify which
617 area or subsystem of the kernel is being patched.
619 The ``summary phrase`` in the email's Subject should concisely
620 describe the patch which that email contains. The ``summary
621 phrase`` should not be a filename. Do not use the same ``summary
622 phrase`` for every patch in a whole patch series (where a ``patch
623 series`` is an ordered sequence of multiple, related patches).
625 Bear in mind that the ``summary phrase`` of your email becomes a
626 globally-unique identifier for that patch. It propagates all the way
627 into the ``git`` changelog. The ``summary phrase`` may later be used in
628 developer discussions which refer to the patch. People will want to
629 google for the ``summary phrase`` to read discussion regarding that
630 patch. It will also be the only thing that people may quickly see
631 when, two or three months later, they are going through perhaps
632 thousands of patches using tools such as ``gitk`` or ``git log
635 For these reasons, the ``summary`` must be no more than 70-75
636 characters, and it must describe both what the patch changes, as well
637 as why the patch might be necessary. It is challenging to be both
638 succinct and descriptive, but that is what a well-written summary
641 The ``summary phrase`` may be prefixed by tags enclosed in square
642 brackets: "Subject: [PATCH <tag>...] <summary phrase>". The tags are
643 not considered part of the summary phrase, but describe how the patch
644 should be treated. Common tags might include a version descriptor if
645 the multiple versions of the patch have been sent out in response to
646 comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
649 If there are four patches in a patch series the individual patches may
650 be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures that developers
651 understand the order in which the patches should be applied and that
652 they have reviewed or applied all of the patches in the patch series.
654 Here are some good example Subjects::
656 Subject: [PATCH 2/5] ext2: improve scalability of bitmap searching
657 Subject: [PATCH v2 01/27] x86: fix eflags tracking
658 Subject: [PATCH v2] sub/sys: Condensed patch summary
659 Subject: [PATCH v2 M/N] sub/sys: Condensed patch summary
661 The ``from`` line must be the very first line in the message body,
664 From: Patch Author <author@example.com>
666 The ``from`` line specifies who will be credited as the author of the
667 patch in the permanent changelog. If the ``from`` line is missing,
668 then the ``From:`` line from the email header will be used to determine
669 the patch author in the changelog.
671 The explanation body will be committed to the permanent source
672 changelog, so should make sense to a competent reader who has long since
673 forgotten the immediate details of the discussion that might have led to
674 this patch. Including symptoms of the failure which the patch addresses
675 (kernel log messages, oops messages, etc.) are especially useful for
676 people who might be searching the commit logs looking for the applicable
677 patch. The text should be written in such detail so that when read
678 weeks, months or even years later, it can give the reader the needed
679 details to grasp the reasoning for **why** the patch was created.
681 If a patch fixes a compile failure, it may not be necessary to include
682 _all_ of the compile failures; just enough that it is likely that
683 someone searching for the patch can find it. As in the ``summary
684 phrase``, it is important to be both succinct as well as descriptive.
686 The ``---`` marker line serves the essential purpose of marking for
687 patch handling tools where the changelog message ends.
689 One good use for the additional comments after the ``---`` marker is
690 for a ``diffstat``, to show what files have changed, and the number of
691 inserted and deleted lines per file. A ``diffstat`` is especially useful
692 on bigger patches. If you are going to include a ``diffstat`` after the
693 ``---`` marker, please use ``diffstat`` options ``-p 1 -w 70`` so that
694 filenames are listed from the top of the kernel source tree and don't
695 use too much horizontal space (easily fit in 80 columns, maybe with some
696 indentation). (``git`` generates appropriate diffstats by default.)
698 Other comments relevant only to the moment or the maintainer, not
699 suitable for the permanent changelog, should also go here. A good
700 example of such comments might be ``patch changelogs`` which describe
701 what has changed between the v1 and v2 version of the patch.
703 Please put this information **after** the ``---`` line which separates
704 the changelog from the rest of the patch. The version information is
705 not part of the changelog which gets committed to the git tree. It is
706 additional information for the reviewers. If it's placed above the
707 commit tags, it needs manual interaction to remove it. If it is below
708 the separator line, it gets automatically stripped off when applying the
713 Signed-off-by: Author <author@mail>
715 V2 -> V3: Removed redundant helper function
716 V1 -> V2: Cleaned up coding style and addressed review comments
718 path/to/file | 5+++--
721 See more details on the proper patch format in the following
726 Backtraces in commit messages
727 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
729 Backtraces help document the call chain leading to a problem. However,
730 not all backtraces are helpful. For example, early boot call chains are
731 unique and obvious. Copying the full dmesg output verbatim, however,
732 adds distracting information like timestamps, module lists, register and
735 Therefore, the most useful backtraces should distill the relevant
736 information from the dump, which makes it easier to focus on the real
737 issue. Here is an example of a well-trimmed backtrace::
739 unchecked MSR access error: WRMSR to 0xd51 (tried to write 0x0000000000000064)
740 at rIP: 0xffffffffae059994 (native_write_msr+0x4/0x20)
746 .. _explicit_in_reply_to:
748 Explicit In-Reply-To headers
749 ----------------------------
751 It can be helpful to manually add In-Reply-To: headers to a patch
752 (e.g., when using ``git send-email``) to associate the patch with
753 previous relevant discussion, e.g. to link a bug fix to the email with
754 the bug report. However, for a multi-patch series, it is generally
755 best to avoid using In-Reply-To: to link to older versions of the
756 series. This way multiple versions of the patch don't become an
757 unmanageable forest of references in email clients. If a link is
758 helpful, you can use the https://lore.kernel.org/ redirector (e.g., in
759 the cover email text) to link to an earlier version of the patch series.
762 Providing base tree information
763 -------------------------------
765 When other developers receive your patches and start the review process,
766 it is often useful for them to know where in the tree history they
767 should place your work. This is particularly useful for automated CI
768 processes that attempt to run a series of tests in order to establish
769 the quality of your submission before the maintainer starts the review.
771 If you are using ``git format-patch`` to generate your patches, you can
772 automatically include the base tree information in your submission by
773 using the ``--base`` flag. The easiest and most convenient way to use
774 this option is with topical branches::
776 $ git checkout -t -b my-topical-branch master
777 Branch 'my-topical-branch' set up to track local branch 'master'.
778 Switched to a new branch 'my-topical-branch'
780 [perform your edits and commits]
782 $ git format-patch --base=auto --cover-letter -o outgoing/ master
783 outgoing/0000-cover-letter.patch
784 outgoing/0001-First-Commit.patch
787 When you open ``outgoing/0000-cover-letter.patch`` for editing, you will
788 notice that it will have the ``base-commit:`` trailer at the very
789 bottom, which provides the reviewer and the CI tools enough information
790 to properly perform ``git am`` without worrying about conflicts::
792 $ git checkout -b patch-review [base-commit-id]
793 Switched to a new branch 'patch-review'
794 $ git am patches.mbox
795 Applying: First Commit
798 Please see ``man git-format-patch`` for more information about this
803 The ``--base`` feature was introduced in git version 2.9.0.
805 If you are not using git to format your patches, you can still include
806 the same ``base-commit`` trailer to indicate the commit hash of the tree
807 on which your work is based. You should add it either in the cover
808 letter or in the first patch of the series and it should be placed
809 either below the ``---`` line or at the very bottom of all other
810 content, right before your email signature.
816 Andrew Morton, "The perfect patch" (tpp).
817 <https://www.ozlabs.org/~akpm/stuff/tpp.txt>
819 Jeff Garzik, "Linux kernel patch submission format".
820 <https://web.archive.org/web/20180829112450/http://linux.yyz.us/patch-format.html>
822 Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
823 <http://www.kroah.com/log/linux/maintainer.html>
825 <http://www.kroah.com/log/linux/maintainer-02.html>
827 <http://www.kroah.com/log/linux/maintainer-03.html>
829 <http://www.kroah.com/log/linux/maintainer-04.html>
831 <http://www.kroah.com/log/linux/maintainer-05.html>
833 <http://www.kroah.com/log/linux/maintainer-06.html>
835 NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
836 <https://lore.kernel.org/r/20050711.125305.08322243.davem@davemloft.net>
838 Kernel Documentation/process/coding-style.rst
840 Linus Torvalds's mail on the canonical patch format:
841 <https://lore.kernel.org/r/Pine.LNX.4.58.0504071023190.28951@ppc970.osdl.org>
843 Andi Kleen, "On submitting kernel patches"
844 Some strategies to get difficult or controversial changes in.
846 http://halobates.de/on-submitting-patches.pdf