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Linux/Documentation/SubmittingPatches

  1 
  2         How to Get Your Change Into the Linux Kernel
  3                 or
  4         Care And Operation Of Your Linus Torvalds
  5 
  6 
  7 
  8 For a person or company who wishes to submit a change to the Linux
  9 kernel, the process can sometimes be daunting if you're not familiar
 10 with "the system."  This text is a collection of suggestions which
 11 can greatly increase the chances of your change being accepted.
 12 
 13 This document contains a large number of suggestions in a relatively terse
 14 format.  For detailed information on how the kernel development process
 15 works, see Documentation/development-process.  Also, read
 16 Documentation/SubmitChecklist for a list of items to check before
 17 submitting code.  If you are submitting a driver, also read
 18 Documentation/SubmittingDrivers; for device tree binding patches, read
 19 Documentation/devicetree/bindings/submitting-patches.txt.
 20 
 21 Many of these steps describe the default behavior of the git version
 22 control system; if you use git to prepare your patches, you'll find much
 23 of the mechanical work done for you, though you'll still need to prepare
 24 and document a sensible set of patches.  In general, use of git will make
 25 your life as a kernel developer easier.
 26 
 27 --------------------------------------------
 28 SECTION 1 - CREATING AND SENDING YOUR CHANGE
 29 --------------------------------------------
 30 
 31 
 32 0) Obtain a current source tree
 33 -------------------------------
 34 
 35 If you do not have a repository with the current kernel source handy, use
 36 git to obtain one.  You'll want to start with the mainline repository,
 37 which can be grabbed with:
 38 
 39   git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 
 40 
 41 Note, however, that you may not want to develop against the mainline tree
 42 directly.  Most subsystem maintainers run their own trees and want to see
 43 patches prepared against those trees.  See the "T:" entry for the subsystem
 44 in the MAINTAINERS file to find that tree, or simply ask the maintainer if
 45 the tree is not listed there.
 46 
 47 It is still possible to download kernel releases via tarballs (as described
 48 in the next section), but that is the hard way to do kernel development.
 49 
 50 1) "diff -up"
 51 ------------
 52 
 53 If you must generate your patches by hand, use "diff -up" or "diff -uprN"
 54 to create patches.  Git generates patches in this form by default; if
 55 you're using git, you can skip this section entirely.
 56 
 57 All changes to the Linux kernel occur in the form of patches, as
 58 generated by diff(1).  When creating your patch, make sure to create it
 59 in "unified diff" format, as supplied by the '-u' argument to diff(1).
 60 Also, please use the '-p' argument which shows which C function each
 61 change is in - that makes the resultant diff a lot easier to read.
 62 Patches should be based in the root kernel source directory,
 63 not in any lower subdirectory.
 64 
 65 To create a patch for a single file, it is often sufficient to do:
 66 
 67         SRCTREE= linux
 68         MYFILE=  drivers/net/mydriver.c
 69 
 70         cd $SRCTREE
 71         cp $MYFILE $MYFILE.orig
 72         vi $MYFILE      # make your change
 73         cd ..
 74         diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
 75 
 76 To create a patch for multiple files, you should unpack a "vanilla",
 77 or unmodified kernel source tree, and generate a diff against your
 78 own source tree.  For example:
 79 
 80         MYSRC= /devel/linux
 81 
 82         tar xvfz linux-3.19.tar.gz
 83         mv linux-3.19 linux-3.19-vanilla
 84         diff -uprN -X linux-3.19-vanilla/Documentation/dontdiff \
 85                 linux-3.19-vanilla $MYSRC > /tmp/patch
 86 
 87 "dontdiff" is a list of files which are generated by the kernel during
 88 the build process, and should be ignored in any diff(1)-generated
 89 patch.
 90 
 91 Make sure your patch does not include any extra files which do not
 92 belong in a patch submission.  Make sure to review your patch -after-
 93 generated it with diff(1), to ensure accuracy.
 94 
 95 If your changes produce a lot of deltas, you need to split them into
 96 individual patches which modify things in logical stages; see section
 97 #3.  This will facilitate easier reviewing by other kernel developers,
 98 very important if you want your patch accepted.
 99 
100 If you're using git, "git rebase -i" can help you with this process.  If
101 you're not using git, quilt <http://savannah.nongnu.org/projects/quilt>
102 is another popular alternative.
103 
104 
105 
106 2) Describe your changes.
107 -------------------------
108 
109 Describe your problem.  Whether your patch is a one-line bug fix or
110 5000 lines of a new feature, there must be an underlying problem that
111 motivated you to do this work.  Convince the reviewer that there is a
112 problem worth fixing and that it makes sense for them to read past the
113 first paragraph.
114 
115 Describe user-visible impact.  Straight up crashes and lockups are
116 pretty convincing, but not all bugs are that blatant.  Even if the
117 problem was spotted during code review, describe the impact you think
118 it can have on users.  Keep in mind that the majority of Linux
119 installations run kernels from secondary stable trees or
120 vendor/product-specific trees that cherry-pick only specific patches
121 from upstream, so include anything that could help route your change
122 downstream: provoking circumstances, excerpts from dmesg, crash
123 descriptions, performance regressions, latency spikes, lockups, etc.
124 
125 Quantify optimizations and trade-offs.  If you claim improvements in
126 performance, memory consumption, stack footprint, or binary size,
127 include numbers that back them up.  But also describe non-obvious
128 costs.  Optimizations usually aren't free but trade-offs between CPU,
129 memory, and readability; or, when it comes to heuristics, between
130 different workloads.  Describe the expected downsides of your
131 optimization so that the reviewer can weigh costs against benefits.
132 
133 Once the problem is established, describe what you are actually doing
134 about it in technical detail.  It's important to describe the change
135 in plain English for the reviewer to verify that the code is behaving
136 as you intend it to.
137 
138 The maintainer will thank you if you write your patch description in a
139 form which can be easily pulled into Linux's source code management
140 system, git, as a "commit log".  See #15, below.
141 
142 Solve only one problem per patch.  If your description starts to get
143 long, that's a sign that you probably need to split up your patch.
144 See #3, next.
145 
146 When you submit or resubmit a patch or patch series, include the
147 complete patch description and justification for it.  Don't just
148 say that this is version N of the patch (series).  Don't expect the
149 subsystem maintainer to refer back to earlier patch versions or referenced
150 URLs to find the patch description and put that into the patch.
151 I.e., the patch (series) and its description should be self-contained.
152 This benefits both the maintainers and reviewers.  Some reviewers
153 probably didn't even receive earlier versions of the patch.
154 
155 Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
156 instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
157 to do frotz", as if you are giving orders to the codebase to change
158 its behaviour.
159 
160 If the patch fixes a logged bug entry, refer to that bug entry by
161 number and URL.  If the patch follows from a mailing list discussion,
162 give a URL to the mailing list archive; use the https://lkml.kernel.org/
163 redirector with a Message-Id, to ensure that the links cannot become
164 stale.
165 
166 However, try to make your explanation understandable without external
167 resources.  In addition to giving a URL to a mailing list archive or
168 bug, summarize the relevant points of the discussion that led to the
169 patch as submitted.
170 
171 If you want to refer to a specific commit, don't just refer to the
172 SHA-1 ID of the commit. Please also include the oneline summary of
173 the commit, to make it easier for reviewers to know what it is about.
174 Example:
175 
176         Commit e21d2170f36602ae2708 ("video: remove unnecessary
177         platform_set_drvdata()") removed the unnecessary
178         platform_set_drvdata(), but left the variable "dev" unused,
179         delete it.
180 
181 You should also be sure to use at least the first twelve characters of the
182 SHA-1 ID.  The kernel repository holds a *lot* of objects, making
183 collisions with shorter IDs a real possibility.  Bear in mind that, even if
184 there is no collision with your six-character ID now, that condition may
185 change five years from now.
186 
187 If your patch fixes a bug in a specific commit, e.g. you found an issue using
188 git-bisect, please use the 'Fixes:' tag with the first 12 characters of the
189 SHA-1 ID, and the one line summary.  For example:
190 
191         Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
192 
193 The following git-config settings can be used to add a pretty format for
194 outputting the above style in the git log or git show commands
195 
196         [core]
197                 abbrev = 12
198         [pretty]
199                 fixes = Fixes: %h (\"%s\")
200 
201 3) Separate your changes.
202 -------------------------
203 
204 Separate each _logical change_ into a separate patch.
205 
206 For example, if your changes include both bug fixes and performance
207 enhancements for a single driver, separate those changes into two
208 or more patches.  If your changes include an API update, and a new
209 driver which uses that new API, separate those into two patches.
210 
211 On the other hand, if you make a single change to numerous files,
212 group those changes into a single patch.  Thus a single logical change
213 is contained within a single patch.
214 
215 The point to remember is that each patch should make an easily understood
216 change that can be verified by reviewers.  Each patch should be justifiable
217 on its own merits.
218 
219 If one patch depends on another patch in order for a change to be
220 complete, that is OK.  Simply note "this patch depends on patch X"
221 in your patch description.
222 
223 When dividing your change into a series of patches, take special care to
224 ensure that the kernel builds and runs properly after each patch in the
225 series.  Developers using "git bisect" to track down a problem can end up
226 splitting your patch series at any point; they will not thank you if you
227 introduce bugs in the middle.
228 
229 If you cannot condense your patch set into a smaller set of patches,
230 then only post say 15 or so at a time and wait for review and integration.
231 
232 
233 
234 4) Style-check your changes.
235 ----------------------------
236 
237 Check your patch for basic style violations, details of which can be
238 found in Documentation/CodingStyle.  Failure to do so simply wastes
239 the reviewers time and will get your patch rejected, probably
240 without even being read.
241 
242 One significant exception is when moving code from one file to
243 another -- in this case you should not modify the moved code at all in
244 the same patch which moves it.  This clearly delineates the act of
245 moving the code and your changes.  This greatly aids review of the
246 actual differences and allows tools to better track the history of
247 the code itself.
248 
249 Check your patches with the patch style checker prior to submission
250 (scripts/checkpatch.pl).  Note, though, that the style checker should be
251 viewed as a guide, not as a replacement for human judgment.  If your code
252 looks better with a violation then its probably best left alone.
253 
254 The checker reports at three levels:
255  - ERROR: things that are very likely to be wrong
256  - WARNING: things requiring careful review
257  - CHECK: things requiring thought
258 
259 You should be able to justify all violations that remain in your
260 patch.
261 
262 
263 5) Select the recipients for your patch.
264 ----------------------------------------
265 
266 You should always copy the appropriate subsystem maintainer(s) on any patch
267 to code that they maintain; look through the MAINTAINERS file and the
268 source code revision history to see who those maintainers are.  The
269 script scripts/get_maintainer.pl can be very useful at this step.  If you
270 cannot find a maintainer for the subsystem your are working on, Andrew
271 Morton (akpm@linux-foundation.org) serves as a maintainer of last resort.
272 
273 You should also normally choose at least one mailing list to receive a copy
274 of your patch set.  linux-kernel@vger.kernel.org functions as a list of
275 last resort, but the volume on that list has caused a number of developers
276 to tune it out.  Look in the MAINTAINERS file for a subsystem-specific
277 list; your patch will probably get more attention there.  Please do not
278 spam unrelated lists, though.
279 
280 Many kernel-related lists are hosted on vger.kernel.org; you can find a
281 list of them at http://vger.kernel.org/vger-lists.html.  There are
282 kernel-related lists hosted elsewhere as well, though.
283 
284 Do not send more than 15 patches at once to the vger mailing lists!!!
285 
286 Linus Torvalds is the final arbiter of all changes accepted into the
287 Linux kernel.  His e-mail address is <torvalds@linux-foundation.org>.
288 He gets a lot of e-mail, and, at this point, very few patches go through
289 Linus directly, so typically you should do your best to -avoid-
290 sending him e-mail.
291 
292 If you have a patch that fixes an exploitable security bug, send that patch
293 to security@kernel.org.  For severe bugs, a short embargo may be considered
294 to allow distrbutors to get the patch out to users; in such cases,
295 obviously, the patch should not be sent to any public lists.
296 
297 Patches that fix a severe bug in a released kernel should be directed
298 toward the stable maintainers by putting a line like this:
299 
300   Cc: stable@vger.kernel.org
301 
302 into your patch.
303 
304 Note, however, that some subsystem maintainers want to come to their own
305 conclusions on which patches should go to the stable trees.  The networking
306 maintainer, in particular, would rather not see individual developers
307 adding lines like the above to their patches.
308 
309 If changes affect userland-kernel interfaces, please send the MAN-PAGES
310 maintainer (as listed in the MAINTAINERS file) a man-pages patch, or at
311 least a notification of the change, so that some information makes its way
312 into the manual pages.  User-space API changes should also be copied to
313 linux-api@vger.kernel.org. 
314 
315 For small patches you may want to CC the Trivial Patch Monkey
316 trivial@kernel.org which collects "trivial" patches. Have a look
317 into the MAINTAINERS file for its current manager.
318 Trivial patches must qualify for one of the following rules:
319  Spelling fixes in documentation
320  Spelling fixes for errors which could break grep(1)
321  Warning fixes (cluttering with useless warnings is bad)
322  Compilation fixes (only if they are actually correct)
323  Runtime fixes (only if they actually fix things)
324  Removing use of deprecated functions/macros
325  Contact detail and documentation fixes
326  Non-portable code replaced by portable code (even in arch-specific,
327  since people copy, as long as it's trivial)
328  Any fix by the author/maintainer of the file (ie. patch monkey
329  in re-transmission mode)
330 
331 
332 
333 6) No MIME, no links, no compression, no attachments.  Just plain text.
334 -----------------------------------------------------------------------
335 
336 Linus and other kernel developers need to be able to read and comment
337 on the changes you are submitting.  It is important for a kernel
338 developer to be able to "quote" your changes, using standard e-mail
339 tools, so that they may comment on specific portions of your code.
340 
341 For this reason, all patches should be submitting e-mail "inline".
342 WARNING:  Be wary of your editor's word-wrap corrupting your patch,
343 if you choose to cut-n-paste your patch.
344 
345 Do not attach the patch as a MIME attachment, compressed or not.
346 Many popular e-mail applications will not always transmit a MIME
347 attachment as plain text, making it impossible to comment on your
348 code.  A MIME attachment also takes Linus a bit more time to process,
349 decreasing the likelihood of your MIME-attached change being accepted.
350 
351 Exception:  If your mailer is mangling patches then someone may ask
352 you to re-send them using MIME.
353 
354 See Documentation/email-clients.txt for hints about configuring
355 your e-mail client so that it sends your patches untouched.
356 
357 7) E-mail size.
358 ---------------
359 
360 Large changes are not appropriate for mailing lists, and some
361 maintainers.  If your patch, uncompressed, exceeds 300 kB in size,
362 it is preferred that you store your patch on an Internet-accessible
363 server, and provide instead a URL (link) pointing to your patch.  But note
364 that if your patch exceeds 300 kB, it almost certainly needs to be broken up
365 anyway.
366 
367 8) Respond to review comments.
368 ------------------------------
369 
370 Your patch will almost certainly get comments from reviewers on ways in
371 which the patch can be improved.  You must respond to those comments;
372 ignoring reviewers is a good way to get ignored in return.  Review comments
373 or questions that do not lead to a code change should almost certainly
374 bring about a comment or changelog entry so that the next reviewer better
375 understands what is going on.
376 
377 Be sure to tell the reviewers what changes you are making and to thank them
378 for their time.  Code review is a tiring and time-consuming process, and
379 reviewers sometimes get grumpy.  Even in that case, though, respond
380 politely and address the problems they have pointed out.
381 
382 
383 9) Don't get discouraged - or impatient.
384 ----------------------------------------
385 
386 After you have submitted your change, be patient and wait.  Reviewers are
387 busy people and may not get to your patch right away.
388 
389 Once upon a time, patches used to disappear into the void without comment,
390 but the development process works more smoothly than that now.  You should
391 receive comments within a week or so; if that does not happen, make sure
392 that you have sent your patches to the right place.  Wait for a minimum of
393 one week before resubmitting or pinging reviewers - possibly longer during
394 busy times like merge windows.
395 
396 
397 10) Include PATCH in the subject
398 --------------------------------
399 
400 Due to high e-mail traffic to Linus, and to linux-kernel, it is common
401 convention to prefix your subject line with [PATCH].  This lets Linus
402 and other kernel developers more easily distinguish patches from other
403 e-mail discussions.
404 
405 
406 
407 11) Sign your work
408 ------------------
409 
410 To improve tracking of who did what, especially with patches that can
411 percolate to their final resting place in the kernel through several
412 layers of maintainers, we've introduced a "sign-off" procedure on
413 patches that are being emailed around.
414 
415 The sign-off is a simple line at the end of the explanation for the
416 patch, which certifies that you wrote it or otherwise have the right to
417 pass it on as an open-source patch.  The rules are pretty simple: if you
418 can certify the below:
419 
420         Developer's Certificate of Origin 1.1
421 
422         By making a contribution to this project, I certify that:
423 
424         (a) The contribution was created in whole or in part by me and I
425             have the right to submit it under the open source license
426             indicated in the file; or
427 
428         (b) The contribution is based upon previous work that, to the best
429             of my knowledge, is covered under an appropriate open source
430             license and I have the right under that license to submit that
431             work with modifications, whether created in whole or in part
432             by me, under the same open source license (unless I am
433             permitted to submit under a different license), as indicated
434             in the file; or
435 
436         (c) The contribution was provided directly to me by some other
437             person who certified (a), (b) or (c) and I have not modified
438             it.
439 
440         (d) I understand and agree that this project and the contribution
441             are public and that a record of the contribution (including all
442             personal information I submit with it, including my sign-off) is
443             maintained indefinitely and may be redistributed consistent with
444             this project or the open source license(s) involved.
445 
446 then you just add a line saying
447 
448         Signed-off-by: Random J Developer <random@developer.example.org>
449 
450 using your real name (sorry, no pseudonyms or anonymous contributions.)
451 
452 Some people also put extra tags at the end.  They'll just be ignored for
453 now, but you can do this to mark internal company procedures or just
454 point out some special detail about the sign-off.
455 
456 If you are a subsystem or branch maintainer, sometimes you need to slightly
457 modify patches you receive in order to merge them, because the code is not
458 exactly the same in your tree and the submitters'. If you stick strictly to
459 rule (c), you should ask the submitter to rediff, but this is a totally
460 counter-productive waste of time and energy. Rule (b) allows you to adjust
461 the code, but then it is very impolite to change one submitter's code and
462 make him endorse your bugs. To solve this problem, it is recommended that
463 you add a line between the last Signed-off-by header and yours, indicating
464 the nature of your changes. While there is nothing mandatory about this, it
465 seems like prepending the description with your mail and/or name, all
466 enclosed in square brackets, is noticeable enough to make it obvious that
467 you are responsible for last-minute changes. Example :
468 
469         Signed-off-by: Random J Developer <random@developer.example.org>
470         [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
471         Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
472 
473 This practice is particularly helpful if you maintain a stable branch and
474 want at the same time to credit the author, track changes, merge the fix,
475 and protect the submitter from complaints. Note that under no circumstances
476 can you change the author's identity (the From header), as it is the one
477 which appears in the changelog.
478 
479 Special note to back-porters: It seems to be a common and useful practice
480 to insert an indication of the origin of a patch at the top of the commit
481 message (just after the subject line) to facilitate tracking. For instance,
482 here's what we see in a 3.x-stable release:
483 
484 Date:   Tue Oct 7 07:26:38 2014 -0400
485 
486     libata: Un-break ATA blacklist
487 
488     commit 1c40279960bcd7d52dbdf1d466b20d24b99176c8 upstream.
489 
490 And here's what might appear in an older kernel once a patch is backported:
491 
492     Date:   Tue May 13 22:12:27 2008 +0200
493 
494         wireless, airo: waitbusy() won't delay
495 
496         [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
497 
498 Whatever the format, this information provides a valuable help to people
499 tracking your trees, and to people trying to troubleshoot bugs in your
500 tree.
501 
502 
503 12) When to use Acked-by: and Cc:
504 ---------------------------------
505 
506 The Signed-off-by: tag indicates that the signer was involved in the
507 development of the patch, or that he/she was in the patch's delivery path.
508 
509 If a person was not directly involved in the preparation or handling of a
510 patch but wishes to signify and record their approval of it then they can
511 ask to have an Acked-by: line added to the patch's changelog.
512 
513 Acked-by: is often used by the maintainer of the affected code when that
514 maintainer neither contributed to nor forwarded the patch.
515 
516 Acked-by: is not as formal as Signed-off-by:.  It is a record that the acker
517 has at least reviewed the patch and has indicated acceptance.  Hence patch
518 mergers will sometimes manually convert an acker's "yep, looks good to me"
519 into an Acked-by: (but note that it is usually better to ask for an
520 explicit ack).
521 
522 Acked-by: does not necessarily indicate acknowledgement of the entire patch.
523 For example, if a patch affects multiple subsystems and has an Acked-by: from
524 one subsystem maintainer then this usually indicates acknowledgement of just
525 the part which affects that maintainer's code.  Judgement should be used here.
526 When in doubt people should refer to the original discussion in the mailing
527 list archives.
528 
529 If a person has had the opportunity to comment on a patch, but has not
530 provided such comments, you may optionally add a "Cc:" tag to the patch.
531 This is the only tag which might be added without an explicit action by the
532 person it names - but it should indicate that this person was copied on the
533 patch.  This tag documents that potentially interested parties
534 have been included in the discussion.
535 
536 
537 13) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
538 --------------------------------------------------------------------------
539 
540 The Reported-by tag gives credit to people who find bugs and report them and it
541 hopefully inspires them to help us again in the future.  Please note that if
542 the bug was reported in private, then ask for permission first before using the
543 Reported-by tag.
544 
545 A Tested-by: tag indicates that the patch has been successfully tested (in
546 some environment) by the person named.  This tag informs maintainers that
547 some testing has been performed, provides a means to locate testers for
548 future patches, and ensures credit for the testers.
549 
550 Reviewed-by:, instead, indicates that the patch has been reviewed and found
551 acceptable according to the Reviewer's Statement:
552 
553         Reviewer's statement of oversight
554 
555         By offering my Reviewed-by: tag, I state that:
556 
557          (a) I have carried out a technical review of this patch to
558              evaluate its appropriateness and readiness for inclusion into
559              the mainline kernel.
560 
561          (b) Any problems, concerns, or questions relating to the patch
562              have been communicated back to the submitter.  I am satisfied
563              with the submitter's response to my comments.
564 
565          (c) While there may be things that could be improved with this
566              submission, I believe that it is, at this time, (1) a
567              worthwhile modification to the kernel, and (2) free of known
568              issues which would argue against its inclusion.
569 
570          (d) While I have reviewed the patch and believe it to be sound, I
571              do not (unless explicitly stated elsewhere) make any
572              warranties or guarantees that it will achieve its stated
573              purpose or function properly in any given situation.
574 
575 A Reviewed-by tag is a statement of opinion that the patch is an
576 appropriate modification of the kernel without any remaining serious
577 technical issues.  Any interested reviewer (who has done the work) can
578 offer a Reviewed-by tag for a patch.  This tag serves to give credit to
579 reviewers and to inform maintainers of the degree of review which has been
580 done on the patch.  Reviewed-by: tags, when supplied by reviewers known to
581 understand the subject area and to perform thorough reviews, will normally
582 increase the likelihood of your patch getting into the kernel.
583 
584 A Suggested-by: tag indicates that the patch idea is suggested by the person
585 named and ensures credit to the person for the idea. Please note that this
586 tag should not be added without the reporter's permission, especially if the
587 idea was not posted in a public forum. That said, if we diligently credit our
588 idea reporters, they will, hopefully, be inspired to help us again in the
589 future.
590 
591 A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
592 is used to make it easy to determine where a bug originated, which can help
593 review a bug fix. This tag also assists the stable kernel team in determining
594 which stable kernel versions should receive your fix. This is the preferred
595 method for indicating a bug fixed by the patch. See #2 above for more details.
596 
597 
598 14) The canonical patch format
599 ------------------------------
600 
601 This section describes how the patch itself should be formatted.  Note
602 that, if you have your patches stored in a git repository, proper patch
603 formatting can be had with "git format-patch".  The tools cannot create
604 the necessary text, though, so read the instructions below anyway.
605 
606 The canonical patch subject line is:
607 
608     Subject: [PATCH 001/123] subsystem: summary phrase
609 
610 The canonical patch message body contains the following:
611 
612   - A "from" line specifying the patch author (only needed if the person
613     sending the patch is not the author).
614 
615   - An empty line.
616 
617   - The body of the explanation, which will be copied to the
618     permanent changelog to describe this patch.
619 
620   - The "Signed-off-by:" lines, described above, which will
621     also go in the changelog.
622 
623   - A marker line containing simply "---".
624 
625   - Any additional comments not suitable for the changelog.
626 
627   - The actual patch (diff output).
628 
629 The Subject line format makes it very easy to sort the emails
630 alphabetically by subject line - pretty much any email reader will
631 support that - since because the sequence number is zero-padded,
632 the numerical and alphabetic sort is the same.
633 
634 The "subsystem" in the email's Subject should identify which
635 area or subsystem of the kernel is being patched.
636 
637 The "summary phrase" in the email's Subject should concisely
638 describe the patch which that email contains.  The "summary
639 phrase" should not be a filename.  Do not use the same "summary
640 phrase" for every patch in a whole patch series (where a "patch
641 series" is an ordered sequence of multiple, related patches).
642 
643 Bear in mind that the "summary phrase" of your email becomes a
644 globally-unique identifier for that patch.  It propagates all the way
645 into the git changelog.  The "summary phrase" may later be used in
646 developer discussions which refer to the patch.  People will want to
647 google for the "summary phrase" to read discussion regarding that
648 patch.  It will also be the only thing that people may quickly see
649 when, two or three months later, they are going through perhaps
650 thousands of patches using tools such as "gitk" or "git log
651 --oneline".
652 
653 For these reasons, the "summary" must be no more than 70-75
654 characters, and it must describe both what the patch changes, as well
655 as why the patch might be necessary.  It is challenging to be both
656 succinct and descriptive, but that is what a well-written summary
657 should do.
658 
659 The "summary phrase" may be prefixed by tags enclosed in square
660 brackets: "Subject: [PATCH tag] <summary phrase>".  The tags are not
661 considered part of the summary phrase, but describe how the patch
662 should be treated.  Common tags might include a version descriptor if
663 the multiple versions of the patch have been sent out in response to
664 comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
665 comments.  If there are four patches in a patch series the individual
666 patches may be numbered like this: 1/4, 2/4, 3/4, 4/4.  This assures
667 that developers understand the order in which the patches should be
668 applied and that they have reviewed or applied all of the patches in
669 the patch series.
670 
671 A couple of example Subjects:
672 
673     Subject: [patch 2/5] ext2: improve scalability of bitmap searching
674     Subject: [PATCHv2 001/207] x86: fix eflags tracking
675 
676 The "from" line must be the very first line in the message body,
677 and has the form:
678 
679         From: Original Author <author@example.com>
680 
681 The "from" line specifies who will be credited as the author of the
682 patch in the permanent changelog.  If the "from" line is missing,
683 then the "From:" line from the email header will be used to determine
684 the patch author in the changelog.
685 
686 The explanation body will be committed to the permanent source
687 changelog, so should make sense to a competent reader who has long
688 since forgotten the immediate details of the discussion that might
689 have led to this patch.  Including symptoms of the failure which the
690 patch addresses (kernel log messages, oops messages, etc.) is
691 especially useful for people who might be searching the commit logs
692 looking for the applicable patch.  If a patch fixes a compile failure,
693 it may not be necessary to include _all_ of the compile failures; just
694 enough that it is likely that someone searching for the patch can find
695 it.  As in the "summary phrase", it is important to be both succinct as
696 well as descriptive.
697 
698 The "---" marker line serves the essential purpose of marking for patch
699 handling tools where the changelog message ends.
700 
701 One good use for the additional comments after the "---" marker is for
702 a diffstat, to show what files have changed, and the number of
703 inserted and deleted lines per file.  A diffstat is especially useful
704 on bigger patches.  Other comments relevant only to the moment or the
705 maintainer, not suitable for the permanent changelog, should also go
706 here.  A good example of such comments might be "patch changelogs"
707 which describe what has changed between the v1 and v2 version of the
708 patch.
709 
710 If you are going to include a diffstat after the "---" marker, please
711 use diffstat options "-p 1 -w 70" so that filenames are listed from
712 the top of the kernel source tree and don't use too much horizontal
713 space (easily fit in 80 columns, maybe with some indentation).  (git
714 generates appropriate diffstats by default.)
715 
716 See more details on the proper patch format in the following
717 references.
718 
719 
720 15) Sending "git pull" requests
721 -------------------------------
722 
723 If you have a series of patches, it may be most convenient to have the
724 maintainer pull them directly into the subsystem repository with a
725 "git pull" operation.  Note, however, that pulling patches from a developer
726 requires a higher degree of trust than taking patches from a mailing list.
727 As a result, many subsystem maintainers are reluctant to take pull
728 requests, especially from new, unknown developers.  If in doubt you can use
729 the pull request as the cover letter for a normal posting of the patch
730 series, giving the maintainer the option of using either.
731 
732 A pull request should have [GIT] or [PULL] in the subject line.  The
733 request itself should include the repository name and the branch of
734 interest on a single line; it should look something like:
735 
736   Please pull from
737 
738       git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
739 
740   to get these changes:"
741 
742 A pull request should also include an overall message saying what will be
743 included in the request, a "git shortlog" listing of the patches
744 themselves, and a diffstat showing the overall effect of the patch series.
745 The easiest way to get all this information together is, of course, to let
746 git do it for you with the "git request-pull" command.
747 
748 Some maintainers (including Linus) want to see pull requests from signed
749 commits; that increases their confidence that the request actually came
750 from you.  Linus, in particular, will not pull from public hosting sites
751 like GitHub in the absence of a signed tag.
752 
753 The first step toward creating such tags is to make a GNUPG key and get it
754 signed by one or more core kernel developers.  This step can be hard for
755 new developers, but there is no way around it.  Attending conferences can
756 be a good way to find developers who can sign your key.
757 
758 Once you have prepared a patch series in git that you wish to have somebody
759 pull, create a signed tag with "git tag -s".  This will create a new tag
760 identifying the last commit in the series and containing a signature
761 created with your private key.  You will also have the opportunity to add a
762 changelog-style message to the tag; this is an ideal place to describe the
763 effects of the pull request as a whole.
764 
765 If the tree the maintainer will be pulling from is not the repository you
766 are working from, don't forget to push the signed tag explicitly to the
767 public tree.
768 
769 When generating your pull request, use the signed tag as the target.  A
770 command like this will do the trick:
771 
772   git request-pull master git://my.public.tree/linux.git my-signed-tag
773 
774 
775 ----------------------
776 SECTION 2 - REFERENCES
777 ----------------------
778 
779 Andrew Morton, "The perfect patch" (tpp).
780   <http://www.ozlabs.org/~akpm/stuff/tpp.txt>
781 
782 Jeff Garzik, "Linux kernel patch submission format".
783   <http://linux.yyz.us/patch-format.html>
784 
785 Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
786   <http://www.kroah.com/log/linux/maintainer.html>
787   <http://www.kroah.com/log/linux/maintainer-02.html>
788   <http://www.kroah.com/log/linux/maintainer-03.html>
789   <http://www.kroah.com/log/linux/maintainer-04.html>
790   <http://www.kroah.com/log/linux/maintainer-05.html>
791   <http://www.kroah.com/log/linux/maintainer-06.html>
792 
793 NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
794   <https://lkml.org/lkml/2005/7/11/336>
795 
796 Kernel Documentation/CodingStyle:
797   <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
798 
799 Linus Torvalds's mail on the canonical patch format:
800   <http://lkml.org/lkml/2005/4/7/183>
801 
802 Andi Kleen, "On submitting kernel patches"
803   Some strategies to get difficult or controversial changes in.
804   http://halobates.de/on-submitting-patches.pdf
805 
806 --

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