Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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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 :ref:`Documentation/process <development_process_main>`.
+Also, read :ref:`Documentation/process/submit-checklist.rst <submitchecklist>`
+for a list of items to check before
+submitting code.  If you are submitting a driver, also read
+:ref:`Documentation/process/submitting-drivers.rst <submittingdrivers>`;
+for device tree binding patches, read
+Documentation/devicetree/bindings/submitting-patches.txt.
+
+Many of these steps describe the default behavior of the ``git`` version
+control system; if you use ``git`` to prepare your patches, you'll find much
+of the mechanical work done for you, though you'll still need to prepare
+and document a sensible set of patches.  In general, use of ``git`` will make
+your life as a kernel developer easier.
+
+0) 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.
+
+It is still possible to download kernel releases via tarballs (as described
+in the next section), but that is the hard way to do kernel development.
+
+1) ``diff -up``
+---------------
+
+If you must generate your patches by hand, use ``diff -up`` or ``diff -uprN``
+to create patches.  Git generates patches in this form by default; if
+you're using ``git``, you can skip this section entirely.
+
+All changes to the Linux kernel occur in the form of patches, as
+generated by :manpage:`diff(1)`.  When creating your patch, make sure to
+create it in "unified diff" format, as supplied by the ``-u`` argument
+to :manpage:`diff(1)`.
+Also, please use the ``-p`` argument which shows which C function each
+change is in - that makes the resultant ``diff`` a lot easier to read.
+Patches should be based in the root kernel source directory,
+not in any lower subdirectory.
+
+To create a patch for a single file, it is often sufficient to do::
+
+	SRCTREE= linux
+	MYFILE=  drivers/net/mydriver.c
+
+	cd $SRCTREE
+	cp $MYFILE $MYFILE.orig
+	vi $MYFILE	# make your change
+	cd ..
+	diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
+
+To create a patch for multiple files, you should unpack a "vanilla",
+or unmodified kernel source tree, and generate a ``diff`` against your
+own source tree.  For example::
+
+	MYSRC= /devel/linux
+
+	tar xvfz linux-3.19.tar.gz
+	mv linux-3.19 linux-3.19-vanilla
+	diff -uprN -X linux-3.19-vanilla/Documentation/dontdiff \
+		linux-3.19-vanilla $MYSRC > /tmp/patch
+
+``dontdiff`` is a list of files which are generated by the kernel during
+the build process, and should be ignored in any :manpage:`diff(1)`-generated
+patch.
+
+Make sure your patch does not include any extra files which do not
+belong in a patch submission.  Make sure to review your patch -after-
+generating it with :manpage:`diff(1)`, to ensure accuracy.
+
+If your changes produce a lot of deltas, you need to split them into
+individual patches which modify things in logical stages; see
+:ref:`split_changes`.  This will facilitate review by other kernel developers,
+very important if you want your patch accepted.
+
+If you're using ``git``, ``git rebase -i`` can help you with this process.  If
+you're not using ``git``, ``quilt`` <http://savannah.nongnu.org/projects/quilt>
+is another popular alternative.
+
+.. _describe_changes:
+
+2) 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 the patch fixes a logged bug entry, refer to that bug entry by
+number and URL.  If the patch follows from a mailing list discussion,
+give a URL to the mailing list archive; use the https://lkml.kernel.org/
+redirector with a ``Message-Id``, to ensure that the links cannot become
+stale.
+
+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 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 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.  For example::
+
+	Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
+
+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\")
+
+.. _split_changes:
+
+3) 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.
+
+
+
+4) Style-check your changes
+---------------------------
+
+Check your patch for basic style violations, details of which can be
+found in
+:ref:`Documentation/process/coding-style.rst <codingstyle>`.
+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.
+
+
+5) 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.  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 functions as a list of
+last resort, 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.
+
+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
+:ref:`Documentation/process/stable-kernel-rules.rst <stable_kernel_rules>`
+in addition to this file.
+
+Note, however, that some subsystem maintainers want to come to their own
+conclusions on which patches should go to the stable trees.  The networking
+maintainer, in particular, would rather not see individual developers
+adding lines like the above to their patches.
+
+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.
+
+For small patches you may want to CC the Trivial Patch Monkey
+trivial@kernel.org which collects "trivial" patches. Have a look
+into the MAINTAINERS file for its current manager.
+
+Trivial patches must qualify for one of the following rules:
+
+- Spelling fixes in documentation
+- Spelling fixes for errors which could break :manpage:`grep(1)`
+- Warning fixes (cluttering with useless warnings is bad)
+- Compilation fixes (only if they are actually correct)
+- Runtime fixes (only if they actually fix things)
+- Removing use of deprecated functions/macros
+- Contact detail and documentation fixes
+- Non-portable code replaced by portable code (even in arch-specific,
+  since people copy, as long as it's trivial)
+- Any fix by the author/maintainer of the file (ie. patch monkey
+  in re-transmission mode)
+
+
+
+6) 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".
+
+.. 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 :ref:`Documentation/process/email-clients.rst <email_clients>`
+for hints about configuring your e-mail client so that it sends your patches
+untouched.
+
+7) E-mail size
+--------------
+
+Large changes are not appropriate for mailing lists, and some
+maintainers.  If your patch, uncompressed, exceeds 300 kB in size,
+it is preferred that you store your patch on an Internet-accessible
+server, and provide instead a URL (link) pointing to your patch.  But note
+that if your patch exceeds 300 kB, it almost certainly needs to be broken up
+anyway.
+
+8) Respond to review comments
+-----------------------------
+
+Your patch will almost certainly get comments from reviewers on ways in
+which the patch can be improved.  You must respond to those comments;
+ignoring reviewers is a good way to get ignored in return.  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.
+
+
+9) 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.
+
+
+10) 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.
+
+
+
+11) 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.)
+
+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.
+
+If you are a subsystem or branch maintainer, sometimes you need to slightly
+modify patches you receive in order to merge them, because the code is not
+exactly the same in your tree and the submitters'. If you stick strictly to
+rule (c), you should ask the submitter to rediff, but this is a totally
+counter-productive waste of time and energy. Rule (b) allows you to adjust
+the code, but then it is very impolite to change one submitter's code and
+make him endorse your bugs. To solve this problem, it is recommended that
+you add a line between the last Signed-off-by header and yours, indicating
+the nature of your changes. While there is nothing mandatory about this, it
+seems like prepending the description with your mail and/or name, all
+enclosed in square brackets, is noticeable enough to make it obvious that
+you are responsible for last-minute changes. Example::
+
+	Signed-off-by: Random J Developer <random@developer.example.org>
+	[lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
+	Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
+
+This practice is particularly helpful if you maintain a stable branch and
+want at the same time to credit the author, track changes, merge the fix,
+and protect the submitter from complaints. Note that under no circumstances
+can you change the author's identity (the From header), as it is the one
+which appears in the changelog.
+
+Special note to back-porters: It seems to be a common and useful practice
+to insert an indication of the origin of a patch at the top of the commit
+message (just after the subject line) to facilitate tracking. For instance,
+here's what we see in a 3.x-stable release::
+
+  Date:   Tue Oct 7 07:26:38 2014 -0400
+
+    libata: Un-break ATA blacklist
+
+    commit 1c40279960bcd7d52dbdf1d466b20d24b99176c8 upstream.
+
+And here's what might appear in an older kernel once a patch is backported::
+
+    Date:   Tue May 13 22:12:27 2008 +0200
+
+        wireless, airo: waitbusy() won't delay
+
+        [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
+
+Whatever the format, this information provides a valuable help to people
+tracking your trees, and to people trying to troubleshoot bugs in your
+tree.
+
+
+12) 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.
+
+A Co-Developed-by: states that the patch was also created by another developer
+along with the original author.  This is useful at times when multiple people
+work on a single patch.  Note, this person also needs to have a Signed-off-by:
+line in the patch as well.
+
+
+13) 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.
+
+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.
+
+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.
+
+.. _the_canonical_patch_format:
+
+14) 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.
+
+A couple of example Subjects::
+
+    Subject: [PATCH 2/5] ext2: improve scalability of bitmap searching
+    Subject: [PATCH v2 01/27] x86: fix eflags tracking
+
+The ``from`` line must be the very first line in the message body,
+and has the form:
+
+        From: Original 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.) is
+especially useful for people who might be searching the commit logs
+looking for the applicable patch.  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.  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.
+
+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.)
+
+See more details on the proper patch format in the following
+references.
+
+.. _explicit_in_reply_to:
+
+15) 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://lkml.kernel.org/ redirector (e.g., in
+the cover email text) to link to an earlier version of the patch series.
+
+
+16) Sending ``git pull`` requests
+---------------------------------
+
+If you have a series of patches, it may be most convenient to have the
+maintainer pull them directly into the subsystem repository with a
+``git pull`` operation.  Note, however, that pulling patches from a developer
+requires a higher degree of trust than taking patches from a mailing list.
+As a result, many subsystem maintainers are reluctant to take pull
+requests, especially from new, unknown developers.  If in doubt you can use
+the pull request as the cover letter for a normal posting of the patch
+series, giving the maintainer the option of using either.
+
+A pull request should have [GIT PULL] in the subject line.  The
+request itself should include the repository name and the branch of
+interest on a single line; it should look something like::
+
+  Please pull from
+
+      git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
+
+  to get these changes:
+
+A pull request should also include an overall message saying what will be
+included in the request, a ``git shortlog`` listing of the patches
+themselves, and a ``diffstat`` showing the overall effect of the patch series.
+The easiest way to get all this information together is, of course, to let
+``git`` do it for you with the ``git request-pull`` command.
+
+Some maintainers (including Linus) want to see pull requests from signed
+commits; that increases their confidence that the request actually came
+from you.  Linus, in particular, will not pull from public hosting sites
+like GitHub in the absence of a signed tag.
+
+The first step toward creating such tags is to make a GNUPG key and get it
+signed by one or more core kernel developers.  This step can be hard for
+new developers, but there is no way around it.  Attending conferences can
+be a good way to find developers who can sign your key.
+
+Once you have prepared a patch series in ``git`` that you wish to have somebody
+pull, create a signed tag with ``git tag -s``.  This will create a new tag
+identifying the last commit in the series and containing a signature
+created with your private key.  You will also have the opportunity to add a
+changelog-style message to the tag; this is an ideal place to describe the
+effects of the pull request as a whole.
+
+If the tree the maintainer will be pulling from is not the repository you
+are working from, don't forget to push the signed tag explicitly to the
+public tree.
+
+When generating your pull request, use the signed tag as the target.  A
+command like this will do the trick::
+
+  git request-pull master git://my.public.tree/linux.git my-signed-tag
+
+
+References
+----------
+
+Andrew Morton, "The perfect patch" (tpp).
+  <http://www.ozlabs.org/~akpm/stuff/tpp.txt>
+
+Jeff Garzik, "Linux kernel patch submission format".
+  <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://lkml.org/lkml/2005/7/11/336>
+
+Kernel Documentation/process/coding-style.rst:
+  :ref:`Documentation/process/coding-style.rst <codingstyle>`
+
+Linus Torvalds's mail on the canonical patch format:
+  <http://lkml.org/lkml/2005/4/7/183>
+
+Andi Kleen, "On submitting kernel patches"
+  Some strategies to get difficult or controversial changes in.
+
+  http://halobates.de/on-submitting-patches.pdf