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 .. _submittingpatches:
 
 Submitting patches: the essential guide to getting your code into the kernel
 ============================================================================
 
 For a person or company who wishes to submit a change to the Linux
 kernel, the process can sometimes be daunting if you're not familiar
 with "the system."  This text is a collection of suggestions which
 can greatly increase the chances of your change being accepted.
 
 This document contains a large number of suggestions in a relatively terse
 format.  For detailed information on how the kernel development process
 works, see Documentation/process/development-process.rst. Also, read
 Documentation/process/submit-checklist.rst
 for a list of items to check before submitting code.
 For device tree binding patches, read
 Documentation/devicetree/bindings/submitting-patches.rst.
 
 This documentation assumes that you're using ``git`` to prepare your patches.
 If you're unfamiliar with ``git``, you would be well-advised to learn how to
 use it, it will make your life as a kernel developer and in general much
 easier.
 
 Some subsystems and maintainer trees have additional information about
 their workflow and expectations, see
 :ref:`Documentation/process/maintainer-handbooks.rst <maintainer_handbooks_main>`.
 
 Obtain a current source tree
 ----------------------------
 
 If you do not have a repository with the current kernel source handy, use
 ``git`` to obtain one.  You'll want to start with the mainline repository,
 which can be grabbed with::
 
   git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
 
 Note, however, that you may not want to develop against the mainline tree
 directly.  Most subsystem maintainers run their own trees and want to see
 patches prepared against those trees.  See the **T:** entry for the subsystem
 in the MAINTAINERS file to find that tree, or simply ask the maintainer if
 the tree is not listed there.
 
 .. _describe_changes:
 
 Describe your changes
 ---------------------
 
 Describe your problem.  Whether your patch is a one-line bug fix or
 5000 lines of a new feature, there must be an underlying problem that
 motivated you to do this work.  Convince the reviewer that there is a
 problem worth fixing and that it makes sense for them to read past the
 first paragraph.
 
 Describe user-visible impact.  Straight up crashes and lockups are
 pretty convincing, but not all bugs are that blatant.  Even if the
 problem was spotted during code review, describe the impact you think
 it can have on users.  Keep in mind that the majority of Linux
 installations run kernels from secondary stable trees or
 vendor/product-specific trees that cherry-pick only specific patches
 from upstream, so include anything that could help route your change
 downstream: provoking circumstances, excerpts from dmesg, crash
 descriptions, performance regressions, latency spikes, lockups, etc.
 
 Quantify optimizations and trade-offs.  If you claim improvements in
 performance, memory consumption, stack footprint, or binary size,
 include numbers that back them up.  But also describe non-obvious
 costs.  Optimizations usually aren't free but trade-offs between CPU,
 memory, and readability; or, when it comes to heuristics, between
 different workloads.  Describe the expected downsides of your
 optimization so that the reviewer can weigh costs against benefits.
 
 Once the problem is established, describe what you are actually doing
 about it in technical detail.  It's important to describe the change
 in plain English for the reviewer to verify that the code is behaving
 as you intend it to.
 
 The maintainer will thank you if you write your patch description in a
 form which can be easily pulled into Linux's source code management
 system, ``git``, as a "commit log".  See :ref:`the_canonical_patch_format`.
 
 Solve only one problem per patch.  If your description starts to get
 long, that's a sign that you probably need to split up your patch.
 See :ref:`split_changes`.
 
 When you submit or resubmit a patch or patch series, include the
 complete patch description and justification for it.  Don't just
 say that this is version N of the patch (series).  Don't expect the
 subsystem maintainer to refer back to earlier patch versions or referenced
 URLs to find the patch description and put that into the patch.
 I.e., the patch (series) and its description should be self-contained.
 This benefits both the maintainers and reviewers.  Some reviewers
 probably didn't even receive earlier versions of the patch.
 
 Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
 instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
 to do frotz", as if you are giving orders to the codebase to change
 its behaviour.
 
 If you want to refer to a specific commit, don't just refer to the
 SHA-1 ID of the commit. Please also include the oneline summary of
 the commit, to make it easier for reviewers to know what it is about.
 Example::
 
         Commit e21d2170f36602ae2708 ("video: remove unnecessary
         platform_set_drvdata()") removed the unnecessary
         platform_set_drvdata(), but left the variable "dev" unused,
         delete it.
 
 You should also be sure to use at least the first twelve characters of the
 SHA-1 ID.  The kernel repository holds a *lot* of objects, making
 collisions with shorter IDs a real possibility.  Bear in mind that, even if
 there is no collision with your six-character ID now, that condition may
 change five years from now.
 
 If related discussions or any other background information behind the change
 can be found on the web, add 'Link:' tags pointing to it. In case your patch
 fixes a bug, for example, add a tag with a URL referencing the report in the
 mailing list archives or a bug tracker; if the patch is a result of some
 earlier mailing list discussion or something documented on the web, point to
 it.
 
 When linking to mailing list archives, preferably use the lore.kernel.org
 message archiver service. To create the link URL, use the contents of the
 ``Message-Id`` header of the message without the surrounding angle brackets.
 For example::
 
     Link: https://lore.kernel.org/r/30th.anniversary.repost@klaava.Helsinki.FI/
 
 Please check the link to make sure that it is actually working and points
 to the relevant message.
 
 However, try to make your explanation understandable without external
 resources. In addition to giving a URL to a mailing list archive or bug,
 summarize the relevant points of the discussion that led to the
 patch as submitted.
 
 If your patch fixes a bug in a specific commit, e.g. you found an issue using
 ``git bisect``, please use the 'Fixes:' tag with the first 12 characters of
 the SHA-1 ID, and the one line summary.  Do not split the tag across multiple
 lines, tags are exempt from the "wrap at 75 columns" rule in order to simplify
 parsing scripts.  For example::
 
         Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed")
 
 The following ``git config`` settings can be used to add a pretty format for
 outputting the above style in the ``git log`` or ``git show`` commands::
 
         [core]
                 abbrev = 12
         [pretty]
                 fixes = Fixes: %h (\"%s\")
 
 An example call::
 
         $ git log -1 --pretty=fixes 54a4f0239f2e
         Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed")
 
 .. _split_changes:
 
 Separate your changes
 ---------------------
 
 Separate each **logical change** into a separate patch.
 
 For example, if your changes include both bug fixes and performance
 enhancements for a single driver, separate those changes into two
 or more patches.  If your changes include an API update, and a new
 driver which uses that new API, separate those into two patches.
 
 On the other hand, if you make a single change to numerous files,
 group those changes into a single patch.  Thus a single logical change
 is contained within a single patch.
 
 The point to remember is that each patch should make an easily understood
 change that can be verified by reviewers.  Each patch should be justifiable
 on its own merits.
 
 If one patch depends on another patch in order for a change to be
 complete, that is OK.  Simply note **"this patch depends on patch X"**
 in your patch description.
 
 When dividing your change into a series of patches, take special care to
 ensure that the kernel builds and runs properly after each patch in the
 series.  Developers using ``git bisect`` to track down a problem can end up
 splitting your patch series at any point; they will not thank you if you
 introduce bugs in the middle.
 
 If you cannot condense your patch set into a smaller set of patches,
 then only post say 15 or so at a time and wait for review and integration.
 
 
 
 Style-check your changes
 ------------------------
 
 Check your patch for basic style violations, details of which can be
 found in Documentation/process/coding-style.rst.
 Failure to do so simply wastes
 the reviewers time and will get your patch rejected, probably
 without even being read.
 
 One significant exception is when moving code from one file to
 another -- in this case you should not modify the moved code at all in
 the same patch which moves it.  This clearly delineates the act of
 moving the code and your changes.  This greatly aids review of the
 actual differences and allows tools to better track the history of
 the code itself.
 
 Check your patches with the patch style checker prior to submission
 (scripts/checkpatch.pl).  Note, though, that the style checker should be
 viewed as a guide, not as a replacement for human judgment.  If your code
 looks better with a violation then its probably best left alone.
 
 The checker reports at three levels:
  - ERROR: things that are very likely to be wrong
  - WARNING: things requiring careful review
  - CHECK: things requiring thought
 
 You should be able to justify all violations that remain in your
 patch.
 
 
 Select the recipients for your patch
 ------------------------------------
 
 You should always copy the appropriate subsystem maintainer(s) on any patch
 to code that they maintain; look through the MAINTAINERS file and the
 source code revision history to see who those maintainers are.  The
 script scripts/get_maintainer.pl can be very useful at this step (pass paths to
 your patches as arguments to scripts/get_maintainer.pl).  If you cannot find a
 maintainer for the subsystem you are working on, Andrew Morton
 (akpm@linux-foundation.org) serves as a maintainer of last resort.
 
 You should also normally choose at least one mailing list to receive a copy
 of your patch set.  linux-kernel@vger.kernel.org should be used by default
 for all patches, but the volume on that list has caused a number of
 developers to tune it out.  Look in the MAINTAINERS file for a
 subsystem-specific list; your patch will probably get more attention there.
 Please do not spam unrelated lists, though.
 
 Many kernel-related lists are hosted on vger.kernel.org; you can find a
 list of them at http://vger.kernel.org/vger-lists.html.  There are
 kernel-related lists hosted elsewhere as well, though.
 
 Do not send more than 15 patches at once to the vger mailing lists!!!
 
 Linus Torvalds is the final arbiter of all changes accepted into the
 Linux kernel.  His e-mail address is <torvalds@linux-foundation.org>.
 He gets a lot of e-mail, and, at this point, very few patches go through
 Linus directly, so typically you should do your best to -avoid-
 sending him e-mail.
 
 If you have a patch that fixes an exploitable security bug, send that patch
 to security@kernel.org.  For severe bugs, a short embargo may be considered
 to allow distributors to get the patch out to users; in such cases,
 obviously, the patch should not be sent to any public lists. See also
 Documentation/admin-guide/security-bugs.rst.
 
 Patches that fix a severe bug in a released kernel should be directed
 toward the stable maintainers by putting a line like this::
 
   Cc: stable@vger.kernel.org
 
 into the sign-off area of your patch (note, NOT an email recipient).  You
 should also read Documentation/process/stable-kernel-rules.rst
 in addition to this document.
 
 If changes affect userland-kernel interfaces, please send the MAN-PAGES
 maintainer (as listed in the MAINTAINERS file) a man-pages patch, or at
 least a notification of the change, so that some information makes its way
 into the manual pages.  User-space API changes should also be copied to
 linux-api@vger.kernel.org.
 
 
 No MIME, no links, no compression, no attachments.  Just plain text
 -------------------------------------------------------------------
 
 Linus and other kernel developers need to be able to read and comment
 on the changes you are submitting.  It is important for a kernel
 developer to be able to "quote" your changes, using standard e-mail
 tools, so that they may comment on specific portions of your code.
 
 For this reason, all patches should be submitted by e-mail "inline". The
 easiest way to do this is with ``git send-email``, which is strongly
 recommended.  An interactive tutorial for ``git send-email`` is available at
 https://git-send-email.io.
 
 If you choose not to use ``git send-email``:
 
 .. warning::
 
   Be wary of your editor's word-wrap corrupting your patch,
   if you choose to cut-n-paste your patch.
 
 Do not attach the patch as a MIME attachment, compressed or not.
 Many popular e-mail applications will not always transmit a MIME
 attachment as plain text, making it impossible to comment on your
 code.  A MIME attachment also takes Linus a bit more time to process,
 decreasing the likelihood of your MIME-attached change being accepted.
 
 Exception:  If your mailer is mangling patches then someone may ask
 you to re-send them using MIME.
 
 See Documentation/process/email-clients.rst for hints about configuring
 your e-mail client so that it sends your patches untouched.
 
 Respond to review comments
 --------------------------
 
 Your patch will almost certainly get comments from reviewers on ways in
 which the patch can be improved, in the form of a reply to your email. You must
 respond to those comments; ignoring reviewers is a good way to get ignored in
 return. You can simply reply to their emails to answer their comments. Review
 comments or questions that do not lead to a code change should almost certainly
 bring about a comment or changelog entry so that the next reviewer better
 understands what is going on.
 
 Be sure to tell the reviewers what changes you are making and to thank them
 for their time.  Code review is a tiring and time-consuming process, and
 reviewers sometimes get grumpy.  Even in that case, though, respond
 politely and address the problems they have pointed out.  When sending a next
 version, add a ``patch changelog`` to the cover letter or to individual patches
 explaining difference aganst previous submission (see
 :ref:`the_canonical_patch_format`).
 
 See Documentation/process/email-clients.rst for recommendations on email
 clients and mailing list etiquette.
 
 .. _resend_reminders:
 
 Don't get discouraged - or impatient
 ------------------------------------
 
 After you have submitted your change, be patient and wait.  Reviewers are
 busy people and may not get to your patch right away.
 
 Once upon a time, patches used to disappear into the void without comment,
 but the development process works more smoothly than that now.  You should
 receive comments within a week or so; if that does not happen, make sure
 that you have sent your patches to the right place.  Wait for a minimum of
 one week before resubmitting or pinging reviewers - possibly longer during
 busy times like merge windows.
 
 It's also ok to resend the patch or the patch series after a couple of
 weeks with the word "RESEND" added to the subject line::
 
    [PATCH Vx RESEND] sub/sys: Condensed patch summary
 
 Don't add "RESEND" when you are submitting a modified version of your
 patch or patch series - "RESEND" only applies to resubmission of a
 patch or patch series which have not been modified in any way from the
 previous submission.
 
 
 Include PATCH in the subject
 -----------------------------
 
 Due to high e-mail traffic to Linus, and to linux-kernel, it is common
 convention to prefix your subject line with [PATCH].  This lets Linus
 and other kernel developers more easily distinguish patches from other
 e-mail discussions.
 
 ``git send-email`` will do this for you automatically.
 
 
 Sign your work - the Developer's Certificate of Origin
 ------------------------------------------------------
 
 To improve tracking of who did what, especially with patches that can
 percolate to their final resting place in the kernel through several
 layers of maintainers, we've introduced a "sign-off" procedure on
 patches that are being emailed around.
 
 The sign-off is a simple line at the end of the explanation for the
 patch, which certifies that you wrote it or otherwise have the right to
 pass it on as an open-source patch.  The rules are pretty simple: if you
 can certify the below:
 
 Developer's Certificate of Origin 1.1
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 By making a contribution to this project, I certify that:
 
         (a) The contribution was created in whole or in part by me and I
             have the right to submit it under the open source license
             indicated in the file; or
 
         (b) The contribution is based upon previous work that, to the best
             of my knowledge, is covered under an appropriate open source
             license and I have the right under that license to submit that
             work with modifications, whether created in whole or in part
             by me, under the same open source license (unless I am
             permitted to submit under a different license), as indicated
             in the file; or
 
         (c) The contribution was provided directly to me by some other
             person who certified (a), (b) or (c) and I have not modified
             it.
 
         (d) I understand and agree that this project and the contribution
             are public and that a record of the contribution (including all
             personal information I submit with it, including my sign-off) is
             maintained indefinitely and may be redistributed consistent with
             this project or the open source license(s) involved.
 
 then you just add a line saying::
 
         Signed-off-by: Random J Developer <random@developer.example.org>
 
 using your real name (sorry, no pseudonyms or anonymous contributions.)
 This will be done for you automatically if you use ``git commit -s``.
 Reverts should also include "Signed-off-by". ``git revert -s`` does that
 for you.
 
 Some people also put extra tags at the end.  They'll just be ignored for
 now, but you can do this to mark internal company procedures or just
 point out some special detail about the sign-off.
 
 Any further SoBs (Signed-off-by:'s) following the author's SoB are from
 people handling and transporting the patch, but were not involved in its
 development. SoB chains should reflect the **real** route a patch took
 as it was propagated to the maintainers and ultimately to Linus, with
 the first SoB entry signalling primary authorship of a single author.
 
 
 When to use Acked-by:, Cc:, and Co-developed-by:
 ------------------------------------------------
 
 The Signed-off-by: tag indicates that the signer was involved in the
 development of the patch, or that he/she was in the patch's delivery path.
 
 If a person was not directly involved in the preparation or handling of a
 patch but wishes to signify and record their approval of it then they can
 ask to have an Acked-by: line added to the patch's changelog.
 
 Acked-by: is often used by the maintainer of the affected code when that
 maintainer neither contributed to nor forwarded the patch.
 
 Acked-by: is not as formal as Signed-off-by:.  It is a record that the acker
 has at least reviewed the patch and has indicated acceptance.  Hence patch
 mergers will sometimes manually convert an acker's "yep, looks good to me"
 into an Acked-by: (but note that it is usually better to ask for an
 explicit ack).
 
 Acked-by: does not necessarily indicate acknowledgement of the entire patch.
 For example, if a patch affects multiple subsystems and has an Acked-by: from
 one subsystem maintainer then this usually indicates acknowledgement of just
 the part which affects that maintainer's code.  Judgement should be used here.
 When in doubt people should refer to the original discussion in the mailing
 list archives.
 
 If a person has had the opportunity to comment on a patch, but has not
 provided such comments, you may optionally add a ``Cc:`` tag to the patch.
 This is the only tag which might be added without an explicit action by the
 person it names - but it should indicate that this person was copied on the
 patch.  This tag documents that potentially interested parties
 have been included in the discussion.
 
 Co-developed-by: states that the patch was co-created by multiple developers;
 it is used to give attribution to co-authors (in addition to the author
 attributed by the From: tag) when several people work on a single patch.  Since
 Co-developed-by: denotes authorship, every Co-developed-by: must be immediately
 followed by a Signed-off-by: of the associated co-author.  Standard sign-off
 procedure applies, i.e. the ordering of Signed-off-by: tags should reflect the
 chronological history of the patch insofar as possible, regardless of whether
 the author is attributed via From: or Co-developed-by:.  Notably, the last
 Signed-off-by: must always be that of the developer submitting the patch.
 
 Note, the From: tag is optional when the From: author is also the person (and
 email) listed in the From: line of the email header.
 
 Example of a patch submitted by the From: author::
 
         <changelog>
 
         Co-developed-by: First Co-Author <first@coauthor.example.org>
         Signed-off-by: First Co-Author <first@coauthor.example.org>
         Co-developed-by: Second Co-Author <second@coauthor.example.org>
         Signed-off-by: Second Co-Author <second@coauthor.example.org>
         Signed-off-by: From Author <from@author.example.org>
 
 Example of a patch submitted by a Co-developed-by: author::
 
         From: From Author <from@author.example.org>
 
         <changelog>
 
         Co-developed-by: Random Co-Author <random@coauthor.example.org>
         Signed-off-by: Random Co-Author <random@coauthor.example.org>
         Signed-off-by: From Author <from@author.example.org>
         Co-developed-by: Submitting Co-Author <sub@coauthor.example.org>
         Signed-off-by: Submitting Co-Author <sub@coauthor.example.org>
 
 
 Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
 ----------------------------------------------------------------------
 
 The Reported-by tag gives credit to people who find bugs and report them and it
 hopefully inspires them to help us again in the future.  Please note that if
 the bug was reported in private, then ask for permission first before using the
 Reported-by tag. The tag is intended for bugs; please do not use it to credit
 feature requests.
 
 A Tested-by: tag indicates that the patch has been successfully tested (in
 some environment) by the person named.  This tag informs maintainers that
 some testing has been performed, provides a means to locate testers for
 future patches, and ensures credit for the testers.
 
 Reviewed-by:, instead, indicates that the patch has been reviewed and found
 acceptable according to the Reviewer's Statement:
 
 Reviewer's statement of oversight
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 By offering my Reviewed-by: tag, I state that:
 
          (a) I have carried out a technical review of this patch to
              evaluate its appropriateness and readiness for inclusion into
              the mainline kernel.
 
          (b) Any problems, concerns, or questions relating to the patch
              have been communicated back to the submitter.  I am satisfied
              with the submitter's response to my comments.
 
          (c) While there may be things that could be improved with this
              submission, I believe that it is, at this time, (1) a
              worthwhile modification to the kernel, and (2) free of known
              issues which would argue against its inclusion.
 
          (d) While I have reviewed the patch and believe it to be sound, I
              do not (unless explicitly stated elsewhere) make any
              warranties or guarantees that it will achieve its stated
              purpose or function properly in any given situation.
 
 A Reviewed-by tag is a statement of opinion that the patch is an
 appropriate modification of the kernel without any remaining serious
 technical issues.  Any interested reviewer (who has done the work) can
 offer a Reviewed-by tag for a patch.  This tag serves to give credit to
 reviewers and to inform maintainers of the degree of review which has been
 done on the patch.  Reviewed-by: tags, when supplied by reviewers known to
 understand the subject area and to perform thorough reviews, will normally
 increase the likelihood of your patch getting into the kernel.
 
 Both Tested-by and Reviewed-by tags, once received on mailing list from tester
 or reviewer, should be added by author to the applicable patches when sending
 next versions.  However if the patch has changed substantially in following
 version, these tags might not be applicable anymore and thus should be removed.
 Usually removal of someone's Tested-by or Reviewed-by tags should be mentioned
 in the patch changelog (after the '---' separator).
 
 A Suggested-by: tag indicates that the patch idea is suggested by the person
 named and ensures credit to the person for the idea. Please note that this
 tag should not be added without the reporter's permission, especially if the
 idea was not posted in a public forum. That said, if we diligently credit our
 idea reporters, they will, hopefully, be inspired to help us again in the
 future.
 
 A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
 is used to make it easy to determine where a bug originated, which can help
 review a bug fix. This tag also assists the stable kernel team in determining
 which stable kernel versions should receive your fix. This is the preferred
 method for indicating a bug fixed by the patch. See :ref:`describe_changes`
 for more details.
 
 Note: Attaching a Fixes: tag does not subvert the stable kernel rules
 process nor the requirement to Cc: stable@vger.kernel.org on all stable
 patch candidates. For more information, please read
 Documentation/process/stable-kernel-rules.rst.
 
 .. _the_canonical_patch_format:
 
 The canonical patch format
 --------------------------
 
 This section describes how the patch itself should be formatted.  Note
 that, if you have your patches stored in a ``git`` repository, proper patch
 formatting can be had with ``git format-patch``.  The tools cannot create
 the necessary text, though, so read the instructions below anyway.
 
 The canonical patch subject line is::
 
     Subject: [PATCH 001/123] subsystem: summary phrase
 
 The canonical patch message body contains the following:
 
   - A ``from`` line specifying the patch author, followed by an empty
     line (only needed if the person sending the patch is not the author).
 
   - The body of the explanation, line wrapped at 75 columns, which will
     be copied to the permanent changelog to describe this patch.
 
   - An empty line.
 
   - The ``Signed-off-by:`` lines, described above, which will
     also go in the changelog.
 
   - A marker line containing simply ``---``.
 
   - Any additional comments not suitable for the changelog.
 
   - The actual patch (``diff`` output).
 
 The Subject line format makes it very easy to sort the emails
 alphabetically by subject line - pretty much any email reader will
 support that - since because the sequence number is zero-padded,
 the numerical and alphabetic sort is the same.
 
 The ``subsystem`` in the email's Subject should identify which
 area or subsystem of the kernel is being patched.
 
 The ``summary phrase`` in the email's Subject should concisely
 describe the patch which that email contains.  The ``summary
 phrase`` should not be a filename.  Do not use the same ``summary
 phrase`` for every patch in a whole patch series (where a ``patch
 series`` is an ordered sequence of multiple, related patches).
 
 Bear in mind that the ``summary phrase`` of your email becomes a
 globally-unique identifier for that patch.  It propagates all the way
 into the ``git`` changelog.  The ``summary phrase`` may later be used in
 developer discussions which refer to the patch.  People will want to
 google for the ``summary phrase`` to read discussion regarding that
 patch.  It will also be the only thing that people may quickly see
 when, two or three months later, they are going through perhaps
 thousands of patches using tools such as ``gitk`` or ``git log
 --oneline``.
 
 For these reasons, the ``summary`` must be no more than 70-75
 characters, and it must describe both what the patch changes, as well
 as why the patch might be necessary.  It is challenging to be both
 succinct and descriptive, but that is what a well-written summary
 should do.
 
 The ``summary phrase`` may be prefixed by tags enclosed in square
 brackets: "Subject: [PATCH <tag>...] <summary phrase>".  The tags are
 not considered part of the summary phrase, but describe how the patch
 should be treated.  Common tags might include a version descriptor if
 the multiple versions of the patch have been sent out in response to
 comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
 comments.
 
 If there are four patches in a patch series the individual patches may
 be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures that developers
 understand the order in which the patches should be applied and that
 they have reviewed or applied all of the patches in the patch series.
 
 Here are some good example Subjects::
 
     Subject: [PATCH 2/5] ext2: improve scalability of bitmap searching
     Subject: [PATCH v2 01/27] x86: fix eflags tracking
     Subject: [PATCH v2] sub/sys: Condensed patch summary
     Subject: [PATCH v2 M/N] sub/sys: Condensed patch summary
 
 The ``from`` line must be the very first line in the message body,
 and has the form:
 
         From: Patch Author <author@example.com>
 
 The ``from`` line specifies who will be credited as the author of the
 patch in the permanent changelog.  If the ``from`` line is missing,
 then the ``From:`` line from the email header will be used to determine
 the patch author in the changelog.
 
 The explanation body will be committed to the permanent source
 changelog, so should make sense to a competent reader who has long since
 forgotten the immediate details of the discussion that might have led to
 this patch. Including symptoms of the failure which the patch addresses
 (kernel log messages, oops messages, etc.) are especially useful for
 people who might be searching the commit logs looking for the applicable
 patch. The text should be written in such detail so that when read
 weeks, months or even years later, it can give the reader the needed
 details to grasp the reasoning for **why** the patch was created.
 
 If a patch fixes a compile failure, it may not be necessary to include
 _all_ of the compile failures; just enough that it is likely that
 someone searching for the patch can find it. As in the ``summary
 phrase``, it is important to be both succinct as well as descriptive.
 
 The ``---`` marker line serves the essential purpose of marking for
 patch handling tools where the changelog message ends.
 
 One good use for the additional comments after the ``---`` marker is
 for a ``diffstat``, to show what files have changed, and the number of
 inserted and deleted lines per file. A ``diffstat`` is especially useful
 on bigger patches. If you are going to include a ``diffstat`` after the
 ``---`` marker, please use ``diffstat`` options ``-p 1 -w 70`` so that
 filenames are listed from the top of the kernel source tree and don't
 use too much horizontal space (easily fit in 80 columns, maybe with some
 indentation). (``git`` generates appropriate diffstats by default.)
 
 Other comments relevant only to the moment or the maintainer, not
 suitable for the permanent changelog, should also go here. A good
 example of such comments might be ``patch changelogs`` which describe
 what has changed between the v1 and v2 version of the patch.
 
 Please put this information **after** the ``---`` line which separates
 the changelog from the rest of the patch. The version information is
 not part of the changelog which gets committed to the git tree. It is
 additional information for the reviewers. If it's placed above the
 commit tags, it needs manual interaction to remove it. If it is below
 the separator line, it gets automatically stripped off when applying the
 patch::
 
   <commit message>
   ...
   Signed-off-by: Author <author@mail>
   ---
   V2 -> V3: Removed redundant helper function
   V1 -> V2: Cleaned up coding style and addressed review comments
 
   path/to/file | 5+++--
   ...
 
 See more details on the proper patch format in the following
 references.
 
 .. _backtraces:
 
 Backtraces in commit mesages
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Backtraces help document the call chain leading to a problem. However,
 not all backtraces are helpful. For example, early boot call chains are
 unique and obvious. Copying the full dmesg output verbatim, however,
 adds distracting information like timestamps, module lists, register and
 stack dumps.
 
 Therefore, the most useful backtraces should distill the relevant
 information from the dump, which makes it easier to focus on the real
 issue. Here is an example of a well-trimmed backtrace::
 
   unchecked MSR access error: WRMSR to 0xd51 (tried to write 0x0000000000000064)
   at rIP: 0xffffffffae059994 (native_write_msr+0x4/0x20)
   Call Trace:
   mba_wrmsr
   update_domains
   rdtgroup_mkdir
 
 .. _explicit_in_reply_to:
 
 Explicit In-Reply-To headers
 ----------------------------
 
 It can be helpful to manually add In-Reply-To: headers to a patch
 (e.g., when using ``git send-email``) to associate the patch with
 previous relevant discussion, e.g. to link a bug fix to the email with
 the bug report.  However, for a multi-patch series, it is generally
 best to avoid using In-Reply-To: to link to older versions of the
 series.  This way multiple versions of the patch don't become an
 unmanageable forest of references in email clients.  If a link is
 helpful, you can use the https://lore.kernel.org/ redirector (e.g., in
 the cover email text) to link to an earlier version of the patch series.
 
 
 Providing base tree information
 -------------------------------
 
 When other developers receive your patches and start the review process,
 it is often useful for them to know where in the tree history they
 should place your work. This is particularly useful for automated CI
 processes that attempt to run a series of tests in order to establish
 the quality of your submission before the maintainer starts the review.
 
 If you are using ``git format-patch`` to generate your patches, you can
 automatically include the base tree information in your submission by
 using the ``--base`` flag. The easiest and most convenient way to use
 this option is with topical branches::
 
     $ git checkout -t -b my-topical-branch master
     Branch 'my-topical-branch' set up to track local branch 'master'.
     Switched to a new branch 'my-topical-branch'
 
     [perform your edits and commits]
 
     $ git format-patch --base=auto --cover-letter -o outgoing/ master
     outgoing/0000-cover-letter.patch
     outgoing/0001-First-Commit.patch
     outgoing/...
 
 When you open ``outgoing/0000-cover-letter.patch`` for editing, you will
 notice that it will have the ``base-commit:`` trailer at the very
 bottom, which provides the reviewer and the CI tools enough information
 to properly perform ``git am`` without worrying about conflicts::
 
     $ git checkout -b patch-review [base-commit-id]
     Switched to a new branch 'patch-review'
     $ git am patches.mbox
     Applying: First Commit
     Applying: ...
 
 Please see ``man git-format-patch`` for more information about this
 option.
 
 .. note::
 
     The ``--base`` feature was introduced in git version 2.9.0.
 
 If you are not using git to format your patches, you can still include
 the same ``base-commit`` trailer to indicate the commit hash of the tree
 on which your work is based. You should add it either in the cover
 letter or in the first patch of the series and it should be placed
 either below the ``---`` line or at the very bottom of all other
 content, right before your email signature.
 
 
 References
 ----------
 
 Andrew Morton, "The perfect patch" (tpp).
   <https://www.ozlabs.org/~akpm/stuff/tpp.txt>
 
 Jeff Garzik, "Linux kernel patch submission format".
   <https://web.archive.org/web/20180829112450/http://linux.yyz.us/patch-format.html>
 
 Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
   <http://www.kroah.com/log/linux/maintainer.html>
 
   <http://www.kroah.com/log/linux/maintainer-02.html>
 
   <http://www.kroah.com/log/linux/maintainer-03.html>
 
   <http://www.kroah.com/log/linux/maintainer-04.html>
 
   <http://www.kroah.com/log/linux/maintainer-05.html>
 
   <http://www.kroah.com/log/linux/maintainer-06.html>
 
 NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
   <https://lore.kernel.org/r/20050711.125305.08322243.davem@davemloft.net>
 
 Kernel Documentation/process/coding-style.rst
 
 Linus Torvalds's mail on the canonical patch format:
   <https://lore.kernel.org/r/Pine.LNX.4.58.0504071023190.28951@ppc970.osdl.org>
 
 Andi Kleen, "On submitting kernel patches"
   Some strategies to get difficult or controversial changes in.
 
   http://halobates.de/on-submitting-patches.pdf

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