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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 Read Documentation/SubmitChecklist for a list of items to check
 14 before submitting code.  If you are submitting a driver, also read
 15 Documentation/SubmittingDrivers.
 16 
 17 Many of these steps describe the default behavior of the git version
 18 control system; if you use git to prepare your patches, you'll find much
 19 of the mechanical work done for you, though you'll still need to prepare
 20 and document a sensible set of patches.
 21 
 22 --------------------------------------------
 23 SECTION 1 - CREATING AND SENDING YOUR CHANGE
 24 --------------------------------------------
 25 
 26 
 27 
 28 1) "diff -up"
 29 ------------
 30 
 31 Use "diff -up" or "diff -uprN" to create patches.  git generates patches
 32 in this form by default; if you're using git, you can skip this section
 33 entirely.
 34 
 35 All changes to the Linux kernel occur in the form of patches, as
 36 generated by diff(1).  When creating your patch, make sure to create it
 37 in "unified diff" format, as supplied by the '-u' argument to diff(1).
 38 Also, please use the '-p' argument which shows which C function each
 39 change is in - that makes the resultant diff a lot easier to read.
 40 Patches should be based in the root kernel source directory,
 41 not in any lower subdirectory.
 42 
 43 To create a patch for a single file, it is often sufficient to do:
 44 
 45         SRCTREE= linux-2.6
 46         MYFILE=  drivers/net/mydriver.c
 47 
 48         cd $SRCTREE
 49         cp $MYFILE $MYFILE.orig
 50         vi $MYFILE      # make your change
 51         cd ..
 52         diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
 53 
 54 To create a patch for multiple files, you should unpack a "vanilla",
 55 or unmodified kernel source tree, and generate a diff against your
 56 own source tree.  For example:
 57 
 58         MYSRC= /devel/linux-2.6
 59 
 60         tar xvfz linux-2.6.12.tar.gz
 61         mv linux-2.6.12 linux-2.6.12-vanilla
 62         diff -uprN -X linux-2.6.12-vanilla/Documentation/dontdiff \
 63                 linux-2.6.12-vanilla $MYSRC > /tmp/patch
 64 
 65 "dontdiff" is a list of files which are generated by the kernel during
 66 the build process, and should be ignored in any diff(1)-generated
 67 patch.  The "dontdiff" file is included in the kernel tree in
 68 2.6.12 and later.
 69 
 70 Make sure your patch does not include any extra files which do not
 71 belong in a patch submission.  Make sure to review your patch -after-
 72 generated it with diff(1), to ensure accuracy.
 73 
 74 If your changes produce a lot of deltas, you need to split them into
 75 individual patches which modify things in logical stages; see section
 76 #3.  This will facilitate easier reviewing by other kernel developers,
 77 very important if you want your patch accepted.
 78 
 79 If you're using git, "git rebase -i" can help you with this process.  If
 80 you're not using git, quilt <http://savannah.nongnu.org/projects/quilt>
 81 is another popular alternative.
 82 
 83 
 84 
 85 2) Describe your changes.
 86 
 87 Describe the technical detail of the change(s) your patch includes.
 88 
 89 Be as specific as possible.  The WORST descriptions possible include
 90 things like "update driver X", "bug fix for driver X", or "this patch
 91 includes updates for subsystem X.  Please apply."
 92 
 93 The maintainer will thank you if you write your patch description in a
 94 form which can be easily pulled into Linux's source code management
 95 system, git, as a "commit log".  See #15, below.
 96 
 97 If your description starts to get long, that's a sign that you probably
 98 need to split up your patch.  See #3, next.
 99 
100 When you submit or resubmit a patch or patch series, include the
101 complete patch description and justification for it.  Don't just
102 say that this is version N of the patch (series).  Don't expect the
103 patch merger to refer back to earlier patch versions or referenced
104 URLs to find the patch description and put that into the patch.
105 I.e., the patch (series) and its description should be self-contained.
106 This benefits both the patch merger(s) and reviewers.  Some reviewers
107 probably didn't even receive earlier versions of the patch.
108 
109 Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
110 instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
111 to do frotz", as if you are giving orders to the codebase to change
112 its behaviour.
113 
114 If the patch fixes a logged bug entry, refer to that bug entry by
115 number and URL.  If the patch follows from a mailing list discussion,
116 give a URL to the mailing list archive; use the https://lkml.kernel.org/
117 redirector with a Message-Id, to ensure that the links cannot become
118 stale.
119 
120 However, try to make your explanation understandable without external
121 resources.  In addition to giving a URL to a mailing list archive or
122 bug, summarize the relevant points of the discussion that led to the
123 patch as submitted.
124 
125 If you want to refer to a specific commit, don't just refer to the
126 SHA-1 ID of the commit. Please also include the oneline summary of
127 the commit, to make it easier for reviewers to know what it is about.
128 Example:
129 
130         Commit e21d2170f36602ae2708 ("video: remove unnecessary
131         platform_set_drvdata()") removed the unnecessary
132         platform_set_drvdata(), but left the variable "dev" unused,
133         delete it.
134 
135 If your patch fixes a bug in a specific commit, e.g. you found an issue using
136 git-bisect, please use the 'Fixes:' tag with the first 12 characters of the
137 SHA-1 ID, and the one line summary.
138 Example:
139 
140         Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
141 
142 The following git-config settings can be used to add a pretty format for
143 outputting the above style in the git log or git show commands
144 
145         [core]
146                 abbrev = 12
147         [pretty]
148                 fixes = Fixes: %h (\"%s\")
149 
150 3) Separate your changes.
151 
152 Separate _logical changes_ into a single patch file.
153 
154 For example, if your changes include both bug fixes and performance
155 enhancements for a single driver, separate those changes into two
156 or more patches.  If your changes include an API update, and a new
157 driver which uses that new API, separate those into two patches.
158 
159 On the other hand, if you make a single change to numerous files,
160 group those changes into a single patch.  Thus a single logical change
161 is contained within a single patch.
162 
163 If one patch depends on another patch in order for a change to be
164 complete, that is OK.  Simply note "this patch depends on patch X"
165 in your patch description.
166 
167 If you cannot condense your patch set into a smaller set of patches,
168 then only post say 15 or so at a time and wait for review and integration.
169 
170 
171 
172 4) Style check your changes.
173 
174 Check your patch for basic style violations, details of which can be
175 found in Documentation/CodingStyle.  Failure to do so simply wastes
176 the reviewers time and will get your patch rejected, probably
177 without even being read.
178 
179 At a minimum you should check your patches with the patch style
180 checker prior to submission (scripts/checkpatch.pl).  You should
181 be able to justify all violations that remain in your patch.
182 
183 
184 
185 5) Select e-mail destination.
186 
187 Look through the MAINTAINERS file and the source code, and determine
188 if your change applies to a specific subsystem of the kernel, with
189 an assigned maintainer.  If so, e-mail that person.  The script
190 scripts/get_maintainer.pl can be very useful at this step.
191 
192 If no maintainer is listed, or the maintainer does not respond, send
193 your patch to the primary Linux kernel developer's mailing list,
194 linux-kernel@vger.kernel.org.  Most kernel developers monitor this
195 e-mail list, and can comment on your changes.
196 
197 
198 Do not send more than 15 patches at once to the vger mailing lists!!!
199 
200 
201 Linus Torvalds is the final arbiter of all changes accepted into the
202 Linux kernel.  His e-mail address is <torvalds@linux-foundation.org>. 
203 He gets a lot of e-mail, so typically you should do your best to -avoid-
204 sending him e-mail. 
205 
206 Patches which are bug fixes, are "obvious" changes, or similarly
207 require little discussion should be sent or CC'd to Linus.  Patches
208 which require discussion or do not have a clear advantage should
209 usually be sent first to linux-kernel.  Only after the patch is
210 discussed should the patch then be submitted to Linus.
211 
212 
213 
214 6) Select your CC (e-mail carbon copy) list.
215 
216 Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
217 
218 Other kernel developers besides Linus need to be aware of your change,
219 so that they may comment on it and offer code review and suggestions.
220 linux-kernel is the primary Linux kernel developer mailing list.
221 Other mailing lists are available for specific subsystems, such as
222 USB, framebuffer devices, the VFS, the SCSI subsystem, etc.  See the
223 MAINTAINERS file for a mailing list that relates specifically to
224 your change.
225 
226 Majordomo lists of VGER.KERNEL.ORG at:
227         <http://vger.kernel.org/vger-lists.html>
228 
229 If changes affect userland-kernel interfaces, please send
230 the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
231 a man-pages patch, or at least a notification of the change,
232 so that some information makes its way into the manual pages.
233 
234 Even if the maintainer did not respond in step #5, make sure to ALWAYS
235 copy the maintainer when you change their code.
236 
237 For small patches you may want to CC the Trivial Patch Monkey
238 trivial@kernel.org which collects "trivial" patches. Have a look
239 into the MAINTAINERS file for its current manager.
240 Trivial patches must qualify for one of the following rules:
241  Spelling fixes in documentation
242  Spelling fixes which could break grep(1)
243  Warning fixes (cluttering with useless warnings is bad)
244  Compilation fixes (only if they are actually correct)
245  Runtime fixes (only if they actually fix things)
246  Removing use of deprecated functions/macros (eg. check_region)
247  Contact detail and documentation fixes
248  Non-portable code replaced by portable code (even in arch-specific,
249  since people copy, as long as it's trivial)
250  Any fix by the author/maintainer of the file (ie. patch monkey
251  in re-transmission mode)
252 
253 
254 
255 7) No MIME, no links, no compression, no attachments.  Just plain text.
256 
257 Linus and other kernel developers need to be able to read and comment
258 on the changes you are submitting.  It is important for a kernel
259 developer to be able to "quote" your changes, using standard e-mail
260 tools, so that they may comment on specific portions of your code.
261 
262 For this reason, all patches should be submitting e-mail "inline".
263 WARNING:  Be wary of your editor's word-wrap corrupting your patch,
264 if you choose to cut-n-paste your patch.
265 
266 Do not attach the patch as a MIME attachment, compressed or not.
267 Many popular e-mail applications will not always transmit a MIME
268 attachment as plain text, making it impossible to comment on your
269 code.  A MIME attachment also takes Linus a bit more time to process,
270 decreasing the likelihood of your MIME-attached change being accepted.
271 
272 Exception:  If your mailer is mangling patches then someone may ask
273 you to re-send them using MIME.
274 
275 See Documentation/email-clients.txt for hints about configuring
276 your e-mail client so that it sends your patches untouched.
277 
278 8) E-mail size.
279 
280 When sending patches to Linus, always follow step #7.
281 
282 Large changes are not appropriate for mailing lists, and some
283 maintainers.  If your patch, uncompressed, exceeds 300 kB in size,
284 it is preferred that you store your patch on an Internet-accessible
285 server, and provide instead a URL (link) pointing to your patch.
286 
287 
288 
289 9) Name your kernel version.
290 
291 It is important to note, either in the subject line or in the patch
292 description, the kernel version to which this patch applies.
293 
294 If the patch does not apply cleanly to the latest kernel version,
295 Linus will not apply it.
296 
297 
298 
299 10) Don't get discouraged.  Re-submit.
300 
301 After you have submitted your change, be patient and wait.  If Linus
302 likes your change and applies it, it will appear in the next version
303 of the kernel that he releases.
304 
305 However, if your change doesn't appear in the next version of the
306 kernel, there could be any number of reasons.  It's YOUR job to
307 narrow down those reasons, correct what was wrong, and submit your
308 updated change.
309 
310 It is quite common for Linus to "drop" your patch without comment.
311 That's the nature of the system.  If he drops your patch, it could be
312 due to
313 * Your patch did not apply cleanly to the latest kernel version.
314 * Your patch was not sufficiently discussed on linux-kernel.
315 * A style issue (see section 2).
316 * An e-mail formatting issue (re-read this section).
317 * A technical problem with your change.
318 * He gets tons of e-mail, and yours got lost in the shuffle.
319 * You are being annoying.
320 
321 When in doubt, solicit comments on linux-kernel mailing list.
322 
323 
324 
325 11) Include PATCH in the subject
326 
327 Due to high e-mail traffic to Linus, and to linux-kernel, it is common
328 convention to prefix your subject line with [PATCH].  This lets Linus
329 and other kernel developers more easily distinguish patches from other
330 e-mail discussions.
331 
332 
333 
334 12) Sign your work
335 
336 To improve tracking of who did what, especially with patches that can
337 percolate to their final resting place in the kernel through several
338 layers of maintainers, we've introduced a "sign-off" procedure on
339 patches that are being emailed around.
340 
341 The sign-off is a simple line at the end of the explanation for the
342 patch, which certifies that you wrote it or otherwise have the right to
343 pass it on as an open-source patch.  The rules are pretty simple: if you
344 can certify the below:
345 
346         Developer's Certificate of Origin 1.1
347 
348         By making a contribution to this project, I certify that:
349 
350         (a) The contribution was created in whole or in part by me and I
351             have the right to submit it under the open source license
352             indicated in the file; or
353 
354         (b) The contribution is based upon previous work that, to the best
355             of my knowledge, is covered under an appropriate open source
356             license and I have the right under that license to submit that
357             work with modifications, whether created in whole or in part
358             by me, under the same open source license (unless I am
359             permitted to submit under a different license), as indicated
360             in the file; or
361 
362         (c) The contribution was provided directly to me by some other
363             person who certified (a), (b) or (c) and I have not modified
364             it.
365 
366         (d) I understand and agree that this project and the contribution
367             are public and that a record of the contribution (including all
368             personal information I submit with it, including my sign-off) is
369             maintained indefinitely and may be redistributed consistent with
370             this project or the open source license(s) involved.
371 
372 then you just add a line saying
373 
374         Signed-off-by: Random J Developer <random@developer.example.org>
375 
376 using your real name (sorry, no pseudonyms or anonymous contributions.)
377 
378 Some people also put extra tags at the end.  They'll just be ignored for
379 now, but you can do this to mark internal company procedures or just
380 point out some special detail about the sign-off. 
381 
382 If you are a subsystem or branch maintainer, sometimes you need to slightly
383 modify patches you receive in order to merge them, because the code is not
384 exactly the same in your tree and the submitters'. If you stick strictly to
385 rule (c), you should ask the submitter to rediff, but this is a totally
386 counter-productive waste of time and energy. Rule (b) allows you to adjust
387 the code, but then it is very impolite to change one submitter's code and
388 make him endorse your bugs. To solve this problem, it is recommended that
389 you add a line between the last Signed-off-by header and yours, indicating
390 the nature of your changes. While there is nothing mandatory about this, it
391 seems like prepending the description with your mail and/or name, all
392 enclosed in square brackets, is noticeable enough to make it obvious that
393 you are responsible for last-minute changes. Example :
394 
395         Signed-off-by: Random J Developer <random@developer.example.org>
396         [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
397         Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
398 
399 This practise is particularly helpful if you maintain a stable branch and
400 want at the same time to credit the author, track changes, merge the fix,
401 and protect the submitter from complaints. Note that under no circumstances
402 can you change the author's identity (the From header), as it is the one
403 which appears in the changelog.
404 
405 Special note to back-porters: It seems to be a common and useful practise
406 to insert an indication of the origin of a patch at the top of the commit
407 message (just after the subject line) to facilitate tracking. For instance,
408 here's what we see in 2.6-stable :
409 
410     Date:   Tue May 13 19:10:30 2008 +0000
411 
412         SCSI: libiscsi regression in 2.6.25: fix nop timer handling
413 
414         commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
415 
416 And here's what appears in 2.4 :
417 
418     Date:   Tue May 13 22:12:27 2008 +0200
419 
420         wireless, airo: waitbusy() won't delay
421 
422         [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
423 
424 Whatever the format, this information provides a valuable help to people
425 tracking your trees, and to people trying to trouble-shoot bugs in your
426 tree.
427 
428 
429 13) When to use Acked-by: and Cc:
430 
431 The Signed-off-by: tag indicates that the signer was involved in the
432 development of the patch, or that he/she was in the patch's delivery path.
433 
434 If a person was not directly involved in the preparation or handling of a
435 patch but wishes to signify and record their approval of it then they can
436 arrange to have an Acked-by: line added to the patch's changelog.
437 
438 Acked-by: is often used by the maintainer of the affected code when that
439 maintainer neither contributed to nor forwarded the patch.
440 
441 Acked-by: is not as formal as Signed-off-by:.  It is a record that the acker
442 has at least reviewed the patch and has indicated acceptance.  Hence patch
443 mergers will sometimes manually convert an acker's "yep, looks good to me"
444 into an Acked-by:.
445 
446 Acked-by: does not necessarily indicate acknowledgement of the entire patch.
447 For example, if a patch affects multiple subsystems and has an Acked-by: from
448 one subsystem maintainer then this usually indicates acknowledgement of just
449 the part which affects that maintainer's code.  Judgement should be used here.
450 When in doubt people should refer to the original discussion in the mailing
451 list archives.
452 
453 If a person has had the opportunity to comment on a patch, but has not
454 provided such comments, you may optionally add a "Cc:" tag to the patch.
455 This is the only tag which might be added without an explicit action by the
456 person it names.  This tag documents that potentially interested parties
457 have been included in the discussion
458 
459 
460 14) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
461 
462 If this patch fixes a problem reported by somebody else, consider adding a
463 Reported-by: tag to credit the reporter for their contribution.  Please
464 note that this tag should not be added without the reporter's permission,
465 especially if the problem was not reported in a public forum.  That said,
466 if we diligently credit our bug reporters, they will, hopefully, be
467 inspired to help us again in the future.
468 
469 A Tested-by: tag indicates that the patch has been successfully tested (in
470 some environment) by the person named.  This tag informs maintainers that
471 some testing has been performed, provides a means to locate testers for
472 future patches, and ensures credit for the testers.
473 
474 Reviewed-by:, instead, indicates that the patch has been reviewed and found
475 acceptable according to the Reviewer's Statement:
476 
477         Reviewer's statement of oversight
478 
479         By offering my Reviewed-by: tag, I state that:
480 
481          (a) I have carried out a technical review of this patch to
482              evaluate its appropriateness and readiness for inclusion into
483              the mainline kernel.
484 
485          (b) Any problems, concerns, or questions relating to the patch
486              have been communicated back to the submitter.  I am satisfied
487              with the submitter's response to my comments.
488 
489          (c) While there may be things that could be improved with this
490              submission, I believe that it is, at this time, (1) a
491              worthwhile modification to the kernel, and (2) free of known
492              issues which would argue against its inclusion.
493 
494          (d) While I have reviewed the patch and believe it to be sound, I
495              do not (unless explicitly stated elsewhere) make any
496              warranties or guarantees that it will achieve its stated
497              purpose or function properly in any given situation.
498 
499 A Reviewed-by tag is a statement of opinion that the patch is an
500 appropriate modification of the kernel without any remaining serious
501 technical issues.  Any interested reviewer (who has done the work) can
502 offer a Reviewed-by tag for a patch.  This tag serves to give credit to
503 reviewers and to inform maintainers of the degree of review which has been
504 done on the patch.  Reviewed-by: tags, when supplied by reviewers known to
505 understand the subject area and to perform thorough reviews, will normally
506 increase the likelihood of your patch getting into the kernel.
507 
508 A Suggested-by: tag indicates that the patch idea is suggested by the person
509 named and ensures credit to the person for the idea. Please note that this
510 tag should not be added without the reporter's permission, especially if the
511 idea was not posted in a public forum. That said, if we diligently credit our
512 idea reporters, they will, hopefully, be inspired to help us again in the
513 future.
514 
515 A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
516 is used to make it easy to determine where a bug originated, which can help
517 review a bug fix. This tag also assists the stable kernel team in determining
518 which stable kernel versions should receive your fix. This is the preferred
519 method for indicating a bug fixed by the patch. See #2 above for more details.
520 
521 
522 15) The canonical patch format
523 
524 The canonical patch subject line is:
525 
526     Subject: [PATCH 001/123] subsystem: summary phrase
527 
528 The canonical patch message body contains the following:
529 
530   - A "from" line specifying the patch author.
531 
532   - An empty line.
533 
534   - The body of the explanation, which will be copied to the
535     permanent changelog to describe this patch.
536 
537   - The "Signed-off-by:" lines, described above, which will
538     also go in the changelog.
539 
540   - A marker line containing simply "---".
541 
542   - Any additional comments not suitable for the changelog.
543 
544   - The actual patch (diff output).
545 
546 The Subject line format makes it very easy to sort the emails
547 alphabetically by subject line - pretty much any email reader will
548 support that - since because the sequence number is zero-padded,
549 the numerical and alphabetic sort is the same.
550 
551 The "subsystem" in the email's Subject should identify which
552 area or subsystem of the kernel is being patched.
553 
554 The "summary phrase" in the email's Subject should concisely
555 describe the patch which that email contains.  The "summary
556 phrase" should not be a filename.  Do not use the same "summary
557 phrase" for every patch in a whole patch series (where a "patch
558 series" is an ordered sequence of multiple, related patches).
559 
560 Bear in mind that the "summary phrase" of your email becomes a
561 globally-unique identifier for that patch.  It propagates all the way
562 into the git changelog.  The "summary phrase" may later be used in
563 developer discussions which refer to the patch.  People will want to
564 google for the "summary phrase" to read discussion regarding that
565 patch.  It will also be the only thing that people may quickly see
566 when, two or three months later, they are going through perhaps
567 thousands of patches using tools such as "gitk" or "git log
568 --oneline".
569 
570 For these reasons, the "summary" must be no more than 70-75
571 characters, and it must describe both what the patch changes, as well
572 as why the patch might be necessary.  It is challenging to be both
573 succinct and descriptive, but that is what a well-written summary
574 should do.
575 
576 The "summary phrase" may be prefixed by tags enclosed in square
577 brackets: "Subject: [PATCH tag] <summary phrase>".  The tags are not
578 considered part of the summary phrase, but describe how the patch
579 should be treated.  Common tags might include a version descriptor if
580 the multiple versions of the patch have been sent out in response to
581 comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
582 comments.  If there are four patches in a patch series the individual
583 patches may be numbered like this: 1/4, 2/4, 3/4, 4/4.  This assures
584 that developers understand the order in which the patches should be
585 applied and that they have reviewed or applied all of the patches in
586 the patch series.
587 
588 A couple of example Subjects:
589 
590     Subject: [patch 2/5] ext2: improve scalability of bitmap searching
591     Subject: [PATCHv2 001/207] x86: fix eflags tracking
592 
593 The "from" line must be the very first line in the message body,
594 and has the form:
595 
596         From: Original Author <author@example.com>
597 
598 The "from" line specifies who will be credited as the author of the
599 patch in the permanent changelog.  If the "from" line is missing,
600 then the "From:" line from the email header will be used to determine
601 the patch author in the changelog.
602 
603 The explanation body will be committed to the permanent source
604 changelog, so should make sense to a competent reader who has long
605 since forgotten the immediate details of the discussion that might
606 have led to this patch.  Including symptoms of the failure which the
607 patch addresses (kernel log messages, oops messages, etc.) is
608 especially useful for people who might be searching the commit logs
609 looking for the applicable patch.  If a patch fixes a compile failure,
610 it may not be necessary to include _all_ of the compile failures; just
611 enough that it is likely that someone searching for the patch can find
612 it.  As in the "summary phrase", it is important to be both succinct as
613 well as descriptive.
614 
615 The "---" marker line serves the essential purpose of marking for patch
616 handling tools where the changelog message ends.
617 
618 One good use for the additional comments after the "---" marker is for
619 a diffstat, to show what files have changed, and the number of
620 inserted and deleted lines per file.  A diffstat is especially useful
621 on bigger patches.  Other comments relevant only to the moment or the
622 maintainer, not suitable for the permanent changelog, should also go
623 here.  A good example of such comments might be "patch changelogs"
624 which describe what has changed between the v1 and v2 version of the
625 patch.
626 
627 If you are going to include a diffstat after the "---" marker, please
628 use diffstat options "-p 1 -w 70" so that filenames are listed from
629 the top of the kernel source tree and don't use too much horizontal
630 space (easily fit in 80 columns, maybe with some indentation).  (git
631 generates appropriate diffstats by default.)
632 
633 See more details on the proper patch format in the following
634 references.
635 
636 
637 16) Sending "git pull" requests  (from Linus emails)
638 
639 Please write the git repo address and branch name alone on the same line
640 so that I can't even by mistake pull from the wrong branch, and so
641 that a triple-click just selects the whole thing.
642 
643 So the proper format is something along the lines of:
644 
645         "Please pull from
646 
647                 git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
648 
649          to get these changes:"
650 
651 so that I don't have to hunt-and-peck for the address and inevitably
652 get it wrong (actually, I've only gotten it wrong a few times, and
653 checking against the diffstat tells me when I get it wrong, but I'm
654 just a lot more comfortable when I don't have to "look for" the right
655 thing to pull, and double-check that I have the right branch-name).
656 
657 
658 Please use "git diff -M --stat --summary" to generate the diffstat:
659 the -M enables rename detection, and the summary enables a summary of
660 new/deleted or renamed files.
661 
662 With rename detection, the statistics are rather different [...]
663 because git will notice that a fair number of the changes are renames.
664 
665 -----------------------------------
666 SECTION 2 - HINTS, TIPS, AND TRICKS
667 -----------------------------------
668 
669 This section lists many of the common "rules" associated with code
670 submitted to the kernel.  There are always exceptions... but you must
671 have a really good reason for doing so.  You could probably call this
672 section Linus Computer Science 101.
673 
674 
675 
676 1) Read Documentation/CodingStyle
677 
678 Nuff said.  If your code deviates too much from this, it is likely
679 to be rejected without further review, and without comment.
680 
681 One significant exception is when moving code from one file to
682 another -- in this case you should not modify the moved code at all in
683 the same patch which moves it.  This clearly delineates the act of
684 moving the code and your changes.  This greatly aids review of the
685 actual differences and allows tools to better track the history of
686 the code itself.
687 
688 Check your patches with the patch style checker prior to submission
689 (scripts/checkpatch.pl).  The style checker should be viewed as
690 a guide not as the final word.  If your code looks better with
691 a violation then its probably best left alone.
692 
693 The checker reports at three levels:
694  - ERROR: things that are very likely to be wrong
695  - WARNING: things requiring careful review
696  - CHECK: things requiring thought
697 
698 You should be able to justify all violations that remain in your
699 patch.
700 
701 
702 
703 2) #ifdefs are ugly
704 
705 Code cluttered with ifdefs is difficult to read and maintain.  Don't do
706 it.  Instead, put your ifdefs in a header, and conditionally define
707 'static inline' functions, or macros, which are used in the code.
708 Let the compiler optimize away the "no-op" case.
709 
710 Simple example, of poor code:
711 
712         dev = alloc_etherdev (sizeof(struct funky_private));
713         if (!dev)
714                 return -ENODEV;
715         #ifdef CONFIG_NET_FUNKINESS
716         init_funky_net(dev);
717         #endif
718 
719 Cleaned-up example:
720 
721 (in header)
722         #ifndef CONFIG_NET_FUNKINESS
723         static inline void init_funky_net (struct net_device *d) {}
724         #endif
725 
726 (in the code itself)
727         dev = alloc_etherdev (sizeof(struct funky_private));
728         if (!dev)
729                 return -ENODEV;
730         init_funky_net(dev);
731 
732 
733 
734 3) 'static inline' is better than a macro
735 
736 Static inline functions are greatly preferred over macros.
737 They provide type safety, have no length limitations, no formatting
738 limitations, and under gcc they are as cheap as macros.
739 
740 Macros should only be used for cases where a static inline is clearly
741 suboptimal [there are a few, isolated cases of this in fast paths],
742 or where it is impossible to use a static inline function [such as
743 string-izing].
744 
745 'static inline' is preferred over 'static __inline__', 'extern inline',
746 and 'extern __inline__'.
747 
748 
749 
750 4) Don't over-design.
751 
752 Don't try to anticipate nebulous future cases which may or may not
753 be useful:  "Make it as simple as you can, and no simpler."
754 
755 
756 
757 ----------------------
758 SECTION 3 - REFERENCES
759 ----------------------
760 
761 Andrew Morton, "The perfect patch" (tpp).
762   <http://www.ozlabs.org/~akpm/stuff/tpp.txt>
763 
764 Jeff Garzik, "Linux kernel patch submission format".
765   <http://linux.yyz.us/patch-format.html>
766 
767 Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
768   <http://www.kroah.com/log/linux/maintainer.html>
769   <http://www.kroah.com/log/linux/maintainer-02.html>
770   <http://www.kroah.com/log/linux/maintainer-03.html>
771   <http://www.kroah.com/log/linux/maintainer-04.html>
772   <http://www.kroah.com/log/linux/maintainer-05.html>
773 
774 NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
775   <https://lkml.org/lkml/2005/7/11/336>
776 
777 Kernel Documentation/CodingStyle:
778   <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
779 
780 Linus Torvalds's mail on the canonical patch format:
781   <http://lkml.org/lkml/2005/4/7/183>
782 
783 Andi Kleen, "On submitting kernel patches"
784   Some strategies to get difficult or controversial changes in.
785   http://halobates.de/on-submitting-patches.pdf
786 
787 --

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