|  |  | 
|  | How to Get Your Change Into the Linux Kernel | 
|  | or | 
|  | Care And Operation Of Your Linus Torvalds | 
|  |  | 
|  |  | 
|  |  | 
|  | 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. | 
|  |  | 
|  | Read Documentation/SubmitChecklist for a list of items to check | 
|  | before submitting code.  If you are submitting a driver, also read | 
|  | Documentation/SubmittingDrivers. | 
|  |  | 
|  |  | 
|  |  | 
|  | -------------------------------------------- | 
|  | SECTION 1 - CREATING AND SENDING YOUR CHANGE | 
|  | -------------------------------------------- | 
|  |  | 
|  |  | 
|  |  | 
|  | 1) "diff -up" | 
|  | ------------ | 
|  |  | 
|  | Use "diff -up" or "diff -uprN" to create patches. | 
|  |  | 
|  | All changes to the Linux kernel occur in the form of patches, as | 
|  | generated by diff(1).  When creating your patch, make sure to create it | 
|  | in "unified diff" format, as supplied by the '-u' argument to 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-2.6 | 
|  | 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-2.6 | 
|  |  | 
|  | tar xvfz linux-2.6.12.tar.gz | 
|  | mv linux-2.6.12 linux-2.6.12-vanilla | 
|  | diff -uprN -X linux-2.6.12-vanilla/Documentation/dontdiff \ | 
|  | linux-2.6.12-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 diff(1)-generated | 
|  | patch.  The "dontdiff" file is included in the kernel tree in | 
|  | 2.6.12 and later. | 
|  |  | 
|  | 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- | 
|  | generated it with diff(1), to ensure accuracy. | 
|  |  | 
|  | If your changes produce a lot of deltas, you may want to look into | 
|  | splitting them into individual patches which modify things in | 
|  | logical stages.  This will facilitate easier reviewing by other | 
|  | kernel developers, very important if you want your patch accepted. | 
|  | There are a number of scripts which can aid in this: | 
|  |  | 
|  | Quilt: | 
|  | http://savannah.nongnu.org/projects/quilt | 
|  |  | 
|  | Andrew Morton's patch scripts: | 
|  | http://userweb.kernel.org/~akpm/stuff/patch-scripts.tar.gz | 
|  | Instead of these scripts, quilt is the recommended patch management | 
|  | tool (see above). | 
|  |  | 
|  |  | 
|  |  | 
|  | 2) Describe your changes. | 
|  |  | 
|  | Describe the technical detail of the change(s) your patch includes. | 
|  |  | 
|  | Be as specific as possible.  The WORST descriptions possible include | 
|  | things like "update driver X", "bug fix for driver X", or "this patch | 
|  | includes updates for subsystem X.  Please apply." | 
|  |  | 
|  | 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 #15, below. | 
|  |  | 
|  | If your description starts to get long, that's a sign that you probably | 
|  | need to split up your patch.  See #3, next. | 
|  |  | 
|  | 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 | 
|  | patch merger 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 patch merger(s) and reviewers.  Some reviewers | 
|  | probably didn't even receive earlier versions of the patch. | 
|  |  | 
|  | If the patch fixes a logged bug entry, refer to that bug entry by | 
|  | number and URL. | 
|  |  | 
|  |  | 
|  | 3) Separate your changes. | 
|  |  | 
|  | Separate _logical changes_ into a single patch file. | 
|  |  | 
|  | 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. | 
|  |  | 
|  | 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. | 
|  |  | 
|  | 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. | 
|  |  | 
|  |  | 
|  | 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. | 
|  | 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\") | 
|  |  | 
|  | 4) Style check your changes. | 
|  |  | 
|  | Check your patch for basic style violations, details of which can be | 
|  | found in Documentation/CodingStyle.  Failure to do so simply wastes | 
|  | the reviewers time and will get your patch rejected, probably | 
|  | without even being read. | 
|  |  | 
|  | At a minimum you should check your patches with the patch style | 
|  | checker prior to submission (scripts/checkpatch.pl).  You should | 
|  | be able to justify all violations that remain in your patch. | 
|  |  | 
|  |  | 
|  |  | 
|  | 5) Select e-mail destination. | 
|  |  | 
|  | Look through the MAINTAINERS file and the source code, and determine | 
|  | if your change applies to a specific subsystem of the kernel, with | 
|  | an assigned maintainer.  If so, e-mail that person.  The script | 
|  | scripts/get_maintainer.pl can be very useful at this step. | 
|  |  | 
|  | If no maintainer is listed, or the maintainer does not respond, send | 
|  | your patch to the primary Linux kernel developer's mailing list, | 
|  | linux-kernel@vger.kernel.org.  Most kernel developers monitor this | 
|  | e-mail list, and can comment on your changes. | 
|  |  | 
|  |  | 
|  | 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, so typically you should do your best to -avoid- | 
|  | sending him e-mail. | 
|  |  | 
|  | Patches which are bug fixes, are "obvious" changes, or similarly | 
|  | require little discussion should be sent or CC'd to Linus.  Patches | 
|  | which require discussion or do not have a clear advantage should | 
|  | usually be sent first to linux-kernel.  Only after the patch is | 
|  | discussed should the patch then be submitted to Linus. | 
|  |  | 
|  |  | 
|  |  | 
|  | 6) Select your CC (e-mail carbon copy) list. | 
|  |  | 
|  | Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org. | 
|  |  | 
|  | Other kernel developers besides Linus need to be aware of your change, | 
|  | so that they may comment on it and offer code review and suggestions. | 
|  | linux-kernel is the primary Linux kernel developer mailing list. | 
|  | Other mailing lists are available for specific subsystems, such as | 
|  | USB, framebuffer devices, the VFS, the SCSI subsystem, etc.  See the | 
|  | MAINTAINERS file for a mailing list that relates specifically to | 
|  | your change. | 
|  |  | 
|  | Majordomo lists of VGER.KERNEL.ORG at: | 
|  | <http://vger.kernel.org/vger-lists.html> | 
|  |  | 
|  | 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. | 
|  |  | 
|  | Even if the maintainer did not respond in step #5, make sure to ALWAYS | 
|  | copy the maintainer when you change their code. | 
|  |  | 
|  | 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 which could break 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 (eg. check_region) | 
|  | 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) | 
|  |  | 
|  |  | 
|  |  | 
|  | 7) 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 submitting 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 Documentation/email-clients.txt for hints about configuring | 
|  | your e-mail client so that it sends your patches untouched. | 
|  |  | 
|  | 8) E-mail size. | 
|  |  | 
|  | When sending patches to Linus, always follow step #7. | 
|  |  | 
|  | 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. | 
|  |  | 
|  |  | 
|  |  | 
|  | 9) Name your kernel version. | 
|  |  | 
|  | It is important to note, either in the subject line or in the patch | 
|  | description, the kernel version to which this patch applies. | 
|  |  | 
|  | If the patch does not apply cleanly to the latest kernel version, | 
|  | Linus will not apply it. | 
|  |  | 
|  |  | 
|  |  | 
|  | 10) Don't get discouraged.  Re-submit. | 
|  |  | 
|  | After you have submitted your change, be patient and wait.  If Linus | 
|  | likes your change and applies it, it will appear in the next version | 
|  | of the kernel that he releases. | 
|  |  | 
|  | However, if your change doesn't appear in the next version of the | 
|  | kernel, there could be any number of reasons.  It's YOUR job to | 
|  | narrow down those reasons, correct what was wrong, and submit your | 
|  | updated change. | 
|  |  | 
|  | It is quite common for Linus to "drop" your patch without comment. | 
|  | That's the nature of the system.  If he drops your patch, it could be | 
|  | due to | 
|  | * Your patch did not apply cleanly to the latest kernel version. | 
|  | * Your patch was not sufficiently discussed on linux-kernel. | 
|  | * A style issue (see section 2). | 
|  | * An e-mail formatting issue (re-read this section). | 
|  | * A technical problem with your change. | 
|  | * He gets tons of e-mail, and yours got lost in the shuffle. | 
|  | * You are being annoying. | 
|  |  | 
|  | When in doubt, solicit comments on linux-kernel mailing list. | 
|  |  | 
|  |  | 
|  |  | 
|  | 11) 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. | 
|  |  | 
|  |  | 
|  |  | 
|  | 12) Sign your work | 
|  |  | 
|  | 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 practise 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 practise | 
|  | 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 2.6-stable : | 
|  |  | 
|  | Date:   Tue May 13 19:10:30 2008 +0000 | 
|  |  | 
|  | SCSI: libiscsi regression in 2.6.25: fix nop timer handling | 
|  |  | 
|  | commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream | 
|  |  | 
|  | And here's what appears in 2.4 : | 
|  |  | 
|  | 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 trouble-shoot bugs in your | 
|  | tree. | 
|  |  | 
|  |  | 
|  | 13) When to use Acked-by: and Cc: | 
|  |  | 
|  | 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 | 
|  | arrange 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:. | 
|  |  | 
|  | 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.  This tag documents that potentially interested parties | 
|  | have been included in the discussion | 
|  |  | 
|  |  | 
|  | 14) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes: | 
|  |  | 
|  | If this patch fixes a problem reported by somebody else, consider adding a | 
|  | Reported-by: tag to credit the reporter for their contribution.  Please | 
|  | note that this tag should not be added without the reporter's permission, | 
|  | especially if the problem was not reported in a public forum.  That said, | 
|  | if we diligently credit our bug reporters, they will, hopefully, be | 
|  | inspired to help us again in the future. | 
|  |  | 
|  | 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 #2 above for more details. | 
|  |  | 
|  |  | 
|  | 15) The canonical patch format | 
|  |  | 
|  | 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. | 
|  |  | 
|  | - An empty line. | 
|  |  | 
|  | - The body of the explanation, which will be copied to the | 
|  | permanent changelog to describe this patch. | 
|  |  | 
|  | - 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: [PATCHv2 001/207] 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). | 
|  |  | 
|  | See more details on the proper patch format in the following | 
|  | references. | 
|  |  | 
|  |  | 
|  | 16) Sending "git pull" requests  (from Linus emails) | 
|  |  | 
|  | Please write the git repo address and branch name alone on the same line | 
|  | so that I can't even by mistake pull from the wrong branch, and so | 
|  | that a triple-click just selects the whole thing. | 
|  |  | 
|  | So the proper format is something along the lines of: | 
|  |  | 
|  | "Please pull from | 
|  |  | 
|  | git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus | 
|  |  | 
|  | to get these changes:" | 
|  |  | 
|  | so that I don't have to hunt-and-peck for the address and inevitably | 
|  | get it wrong (actually, I've only gotten it wrong a few times, and | 
|  | checking against the diffstat tells me when I get it wrong, but I'm | 
|  | just a lot more comfortable when I don't have to "look for" the right | 
|  | thing to pull, and double-check that I have the right branch-name). | 
|  |  | 
|  |  | 
|  | Please use "git diff -M --stat --summary" to generate the diffstat: | 
|  | the -M enables rename detection, and the summary enables a summary of | 
|  | new/deleted or renamed files. | 
|  |  | 
|  | With rename detection, the statistics are rather different [...] | 
|  | because git will notice that a fair number of the changes are renames. | 
|  |  | 
|  | ----------------------------------- | 
|  | SECTION 2 - HINTS, TIPS, AND TRICKS | 
|  | ----------------------------------- | 
|  |  | 
|  | This section lists many of the common "rules" associated with code | 
|  | submitted to the kernel.  There are always exceptions... but you must | 
|  | have a really good reason for doing so.  You could probably call this | 
|  | section Linus Computer Science 101. | 
|  |  | 
|  |  | 
|  |  | 
|  | 1) Read Documentation/CodingStyle | 
|  |  | 
|  | Nuff said.  If your code deviates too much from this, it is likely | 
|  | to be rejected without further review, and without comment. | 
|  |  | 
|  | 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).  The style checker should be viewed as | 
|  | a guide not as the final word.  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. | 
|  |  | 
|  |  | 
|  |  | 
|  | 2) #ifdefs are ugly | 
|  |  | 
|  | Code cluttered with ifdefs is difficult to read and maintain.  Don't do | 
|  | it.  Instead, put your ifdefs in a header, and conditionally define | 
|  | 'static inline' functions, or macros, which are used in the code. | 
|  | Let the compiler optimize away the "no-op" case. | 
|  |  | 
|  | Simple example, of poor code: | 
|  |  | 
|  | dev = alloc_etherdev (sizeof(struct funky_private)); | 
|  | if (!dev) | 
|  | return -ENODEV; | 
|  | #ifdef CONFIG_NET_FUNKINESS | 
|  | init_funky_net(dev); | 
|  | #endif | 
|  |  | 
|  | Cleaned-up example: | 
|  |  | 
|  | (in header) | 
|  | #ifndef CONFIG_NET_FUNKINESS | 
|  | static inline void init_funky_net (struct net_device *d) {} | 
|  | #endif | 
|  |  | 
|  | (in the code itself) | 
|  | dev = alloc_etherdev (sizeof(struct funky_private)); | 
|  | if (!dev) | 
|  | return -ENODEV; | 
|  | init_funky_net(dev); | 
|  |  | 
|  |  | 
|  |  | 
|  | 3) 'static inline' is better than a macro | 
|  |  | 
|  | Static inline functions are greatly preferred over macros. | 
|  | They provide type safety, have no length limitations, no formatting | 
|  | limitations, and under gcc they are as cheap as macros. | 
|  |  | 
|  | Macros should only be used for cases where a static inline is clearly | 
|  | suboptimal [there are a few, isolated cases of this in fast paths], | 
|  | or where it is impossible to use a static inline function [such as | 
|  | string-izing]. | 
|  |  | 
|  | 'static inline' is preferred over 'static __inline__', 'extern inline', | 
|  | and 'extern __inline__'. | 
|  |  | 
|  |  | 
|  |  | 
|  | 4) Don't over-design. | 
|  |  | 
|  | Don't try to anticipate nebulous future cases which may or may not | 
|  | be useful:  "Make it as simple as you can, and no simpler." | 
|  |  | 
|  |  | 
|  |  | 
|  | ---------------------- | 
|  | SECTION 3 - REFERENCES | 
|  | ---------------------- | 
|  |  | 
|  | Andrew Morton, "The perfect patch" (tpp). | 
|  | <http://userweb.kernel.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> | 
|  |  | 
|  | NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people! | 
|  | <http://marc.theaimsgroup.com/?l=linux-kernel&m=112112749912944&w=2> | 
|  |  | 
|  | Kernel Documentation/CodingStyle: | 
|  | <http://users.sosdg.org/~qiyong/lxr/source/Documentation/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 | 
|  |  | 
|  | -- |