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diff --git a/Documentation/process/submitting-patches.rst b/Documentation/process/submitting-patches.rst new file mode 100644 index 000000000..3739c1ce6 --- /dev/null +++ b/Documentation/process/submitting-patches.rst @@ -0,0 +1,842 @@ +.. _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 |