drivers: power: report battery voltage in AOSP compatible format
[GitHub/mt8127/android_kernel_alcatel_ttab.git] / 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
18
19 --------------------------------------------
20 SECTION 1 - CREATING AND SENDING YOUR CHANGE
21 --------------------------------------------
22
23
24
25 1) "diff -up"
26 ------------
27
28 Use "diff -up" or "diff -uprN" to create patches.
29
30 All changes to the Linux kernel occur in the form of patches, as
31 generated by diff(1). When creating your patch, make sure to create it
32 in "unified diff" format, as supplied by the '-u' argument to diff(1).
33 Also, please use the '-p' argument which shows which C function each
34 change is in - that makes the resultant diff a lot easier to read.
35 Patches should be based in the root kernel source directory,
36 not in any lower subdirectory.
37
38 To create a patch for a single file, it is often sufficient to do:
39
40 SRCTREE= linux-2.6
41 MYFILE= drivers/net/mydriver.c
42
43 cd $SRCTREE
44 cp $MYFILE $MYFILE.orig
45 vi $MYFILE # make your change
46 cd ..
47 diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
48
49 To create a patch for multiple files, you should unpack a "vanilla",
50 or unmodified kernel source tree, and generate a diff against your
51 own source tree. For example:
52
53 MYSRC= /devel/linux-2.6
54
55 tar xvfz linux-2.6.12.tar.gz
56 mv linux-2.6.12 linux-2.6.12-vanilla
57 diff -uprN -X linux-2.6.12-vanilla/Documentation/dontdiff \
58 linux-2.6.12-vanilla $MYSRC > /tmp/patch
59
60 "dontdiff" is a list of files which are generated by the kernel during
61 the build process, and should be ignored in any diff(1)-generated
62 patch. The "dontdiff" file is included in the kernel tree in
63 2.6.12 and later.
64
65 Make sure your patch does not include any extra files which do not
66 belong in a patch submission. Make sure to review your patch -after-
67 generated it with diff(1), to ensure accuracy.
68
69 If your changes produce a lot of deltas, you may want to look into
70 splitting them into individual patches which modify things in
71 logical stages. This will facilitate easier reviewing by other
72 kernel developers, very important if you want your patch accepted.
73 There are a number of scripts which can aid in this:
74
75 Quilt:
76 http://savannah.nongnu.org/projects/quilt
77
78 Andrew Morton's patch scripts:
79 http://userweb.kernel.org/~akpm/stuff/patch-scripts.tar.gz
80 Instead of these scripts, quilt is the recommended patch management
81 tool (see above).
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 If the patch fixes a logged bug entry, refer to that bug entry by
110 number and URL.
111
112
113 3) Separate your changes.
114
115 Separate _logical changes_ into a single patch file.
116
117 For example, if your changes include both bug fixes and performance
118 enhancements for a single driver, separate those changes into two
119 or more patches. If your changes include an API update, and a new
120 driver which uses that new API, separate those into two patches.
121
122 On the other hand, if you make a single change to numerous files,
123 group those changes into a single patch. Thus a single logical change
124 is contained within a single patch.
125
126 If one patch depends on another patch in order for a change to be
127 complete, that is OK. Simply note "this patch depends on patch X"
128 in your patch description.
129
130 If you cannot condense your patch set into a smaller set of patches,
131 then only post say 15 or so at a time and wait for review and integration.
132
133
134 If your patch fixes a bug in a specific commit, e.g. you found an issue using
135 git-bisect, please use the 'Fixes:' tag with the first 12 characters of the
136 SHA-1 ID, and the one line summary.
137 Example:
138
139 Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
140
141 The following git-config settings can be used to add a pretty format for
142 outputting the above style in the git log or git show commands
143
144 [core]
145 abbrev = 12
146 [pretty]
147 fixes = Fixes: %h (\"%s\")
148
149 4) Style check your changes.
150
151 Check your patch for basic style violations, details of which can be
152 found in Documentation/CodingStyle. Failure to do so simply wastes
153 the reviewers time and will get your patch rejected, probably
154 without even being read.
155
156 At a minimum you should check your patches with the patch style
157 checker prior to submission (scripts/checkpatch.pl). You should
158 be able to justify all violations that remain in your patch.
159
160
161
162 5) Select e-mail destination.
163
164 Look through the MAINTAINERS file and the source code, and determine
165 if your change applies to a specific subsystem of the kernel, with
166 an assigned maintainer. If so, e-mail that person. The script
167 scripts/get_maintainer.pl can be very useful at this step.
168
169 If no maintainer is listed, or the maintainer does not respond, send
170 your patch to the primary Linux kernel developer's mailing list,
171 linux-kernel@vger.kernel.org. Most kernel developers monitor this
172 e-mail list, and can comment on your changes.
173
174
175 Do not send more than 15 patches at once to the vger mailing lists!!!
176
177
178 Linus Torvalds is the final arbiter of all changes accepted into the
179 Linux kernel. His e-mail address is <torvalds@linux-foundation.org>.
180 He gets a lot of e-mail, so typically you should do your best to -avoid-
181 sending him e-mail.
182
183 Patches which are bug fixes, are "obvious" changes, or similarly
184 require little discussion should be sent or CC'd to Linus. Patches
185 which require discussion or do not have a clear advantage should
186 usually be sent first to linux-kernel. Only after the patch is
187 discussed should the patch then be submitted to Linus.
188
189
190
191 6) Select your CC (e-mail carbon copy) list.
192
193 Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
194
195 Other kernel developers besides Linus need to be aware of your change,
196 so that they may comment on it and offer code review and suggestions.
197 linux-kernel is the primary Linux kernel developer mailing list.
198 Other mailing lists are available for specific subsystems, such as
199 USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the
200 MAINTAINERS file for a mailing list that relates specifically to
201 your change.
202
203 Majordomo lists of VGER.KERNEL.ORG at:
204 <http://vger.kernel.org/vger-lists.html>
205
206 If changes affect userland-kernel interfaces, please send
207 the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
208 a man-pages patch, or at least a notification of the change,
209 so that some information makes its way into the manual pages.
210
211 Even if the maintainer did not respond in step #5, make sure to ALWAYS
212 copy the maintainer when you change their code.
213
214 For small patches you may want to CC the Trivial Patch Monkey
215 trivial@kernel.org which collects "trivial" patches. Have a look
216 into the MAINTAINERS file for its current manager.
217 Trivial patches must qualify for one of the following rules:
218 Spelling fixes in documentation
219 Spelling fixes which could break grep(1)
220 Warning fixes (cluttering with useless warnings is bad)
221 Compilation fixes (only if they are actually correct)
222 Runtime fixes (only if they actually fix things)
223 Removing use of deprecated functions/macros (eg. check_region)
224 Contact detail and documentation fixes
225 Non-portable code replaced by portable code (even in arch-specific,
226 since people copy, as long as it's trivial)
227 Any fix by the author/maintainer of the file (ie. patch monkey
228 in re-transmission mode)
229
230
231
232 7) No MIME, no links, no compression, no attachments. Just plain text.
233
234 Linus and other kernel developers need to be able to read and comment
235 on the changes you are submitting. It is important for a kernel
236 developer to be able to "quote" your changes, using standard e-mail
237 tools, so that they may comment on specific portions of your code.
238
239 For this reason, all patches should be submitting e-mail "inline".
240 WARNING: Be wary of your editor's word-wrap corrupting your patch,
241 if you choose to cut-n-paste your patch.
242
243 Do not attach the patch as a MIME attachment, compressed or not.
244 Many popular e-mail applications will not always transmit a MIME
245 attachment as plain text, making it impossible to comment on your
246 code. A MIME attachment also takes Linus a bit more time to process,
247 decreasing the likelihood of your MIME-attached change being accepted.
248
249 Exception: If your mailer is mangling patches then someone may ask
250 you to re-send them using MIME.
251
252 See Documentation/email-clients.txt for hints about configuring
253 your e-mail client so that it sends your patches untouched.
254
255 8) E-mail size.
256
257 When sending patches to Linus, always follow step #7.
258
259 Large changes are not appropriate for mailing lists, and some
260 maintainers. If your patch, uncompressed, exceeds 300 kB in size,
261 it is preferred that you store your patch on an Internet-accessible
262 server, and provide instead a URL (link) pointing to your patch.
263
264
265
266 9) Name your kernel version.
267
268 It is important to note, either in the subject line or in the patch
269 description, the kernel version to which this patch applies.
270
271 If the patch does not apply cleanly to the latest kernel version,
272 Linus will not apply it.
273
274
275
276 10) Don't get discouraged. Re-submit.
277
278 After you have submitted your change, be patient and wait. If Linus
279 likes your change and applies it, it will appear in the next version
280 of the kernel that he releases.
281
282 However, if your change doesn't appear in the next version of the
283 kernel, there could be any number of reasons. It's YOUR job to
284 narrow down those reasons, correct what was wrong, and submit your
285 updated change.
286
287 It is quite common for Linus to "drop" your patch without comment.
288 That's the nature of the system. If he drops your patch, it could be
289 due to
290 * Your patch did not apply cleanly to the latest kernel version.
291 * Your patch was not sufficiently discussed on linux-kernel.
292 * A style issue (see section 2).
293 * An e-mail formatting issue (re-read this section).
294 * A technical problem with your change.
295 * He gets tons of e-mail, and yours got lost in the shuffle.
296 * You are being annoying.
297
298 When in doubt, solicit comments on linux-kernel mailing list.
299
300
301
302 11) Include PATCH in the subject
303
304 Due to high e-mail traffic to Linus, and to linux-kernel, it is common
305 convention to prefix your subject line with [PATCH]. This lets Linus
306 and other kernel developers more easily distinguish patches from other
307 e-mail discussions.
308
309
310
311 12) Sign your work
312
313 To improve tracking of who did what, especially with patches that can
314 percolate to their final resting place in the kernel through several
315 layers of maintainers, we've introduced a "sign-off" procedure on
316 patches that are being emailed around.
317
318 The sign-off is a simple line at the end of the explanation for the
319 patch, which certifies that you wrote it or otherwise have the right to
320 pass it on as an open-source patch. The rules are pretty simple: if you
321 can certify the below:
322
323 Developer's Certificate of Origin 1.1
324
325 By making a contribution to this project, I certify that:
326
327 (a) The contribution was created in whole or in part by me and I
328 have the right to submit it under the open source license
329 indicated in the file; or
330
331 (b) The contribution is based upon previous work that, to the best
332 of my knowledge, is covered under an appropriate open source
333 license and I have the right under that license to submit that
334 work with modifications, whether created in whole or in part
335 by me, under the same open source license (unless I am
336 permitted to submit under a different license), as indicated
337 in the file; or
338
339 (c) The contribution was provided directly to me by some other
340 person who certified (a), (b) or (c) and I have not modified
341 it.
342
343 (d) I understand and agree that this project and the contribution
344 are public and that a record of the contribution (including all
345 personal information I submit with it, including my sign-off) is
346 maintained indefinitely and may be redistributed consistent with
347 this project or the open source license(s) involved.
348
349 then you just add a line saying
350
351 Signed-off-by: Random J Developer <random@developer.example.org>
352
353 using your real name (sorry, no pseudonyms or anonymous contributions.)
354
355 Some people also put extra tags at the end. They'll just be ignored for
356 now, but you can do this to mark internal company procedures or just
357 point out some special detail about the sign-off.
358
359 If you are a subsystem or branch maintainer, sometimes you need to slightly
360 modify patches you receive in order to merge them, because the code is not
361 exactly the same in your tree and the submitters'. If you stick strictly to
362 rule (c), you should ask the submitter to rediff, but this is a totally
363 counter-productive waste of time and energy. Rule (b) allows you to adjust
364 the code, but then it is very impolite to change one submitter's code and
365 make him endorse your bugs. To solve this problem, it is recommended that
366 you add a line between the last Signed-off-by header and yours, indicating
367 the nature of your changes. While there is nothing mandatory about this, it
368 seems like prepending the description with your mail and/or name, all
369 enclosed in square brackets, is noticeable enough to make it obvious that
370 you are responsible for last-minute changes. Example :
371
372 Signed-off-by: Random J Developer <random@developer.example.org>
373 [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
374 Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
375
376 This practise is particularly helpful if you maintain a stable branch and
377 want at the same time to credit the author, track changes, merge the fix,
378 and protect the submitter from complaints. Note that under no circumstances
379 can you change the author's identity (the From header), as it is the one
380 which appears in the changelog.
381
382 Special note to back-porters: It seems to be a common and useful practise
383 to insert an indication of the origin of a patch at the top of the commit
384 message (just after the subject line) to facilitate tracking. For instance,
385 here's what we see in 2.6-stable :
386
387 Date: Tue May 13 19:10:30 2008 +0000
388
389 SCSI: libiscsi regression in 2.6.25: fix nop timer handling
390
391 commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
392
393 And here's what appears in 2.4 :
394
395 Date: Tue May 13 22:12:27 2008 +0200
396
397 wireless, airo: waitbusy() won't delay
398
399 [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
400
401 Whatever the format, this information provides a valuable help to people
402 tracking your trees, and to people trying to trouble-shoot bugs in your
403 tree.
404
405
406 13) When to use Acked-by: and Cc:
407
408 The Signed-off-by: tag indicates that the signer was involved in the
409 development of the patch, or that he/she was in the patch's delivery path.
410
411 If a person was not directly involved in the preparation or handling of a
412 patch but wishes to signify and record their approval of it then they can
413 arrange to have an Acked-by: line added to the patch's changelog.
414
415 Acked-by: is often used by the maintainer of the affected code when that
416 maintainer neither contributed to nor forwarded the patch.
417
418 Acked-by: is not as formal as Signed-off-by:. It is a record that the acker
419 has at least reviewed the patch and has indicated acceptance. Hence patch
420 mergers will sometimes manually convert an acker's "yep, looks good to me"
421 into an Acked-by:.
422
423 Acked-by: does not necessarily indicate acknowledgement of the entire patch.
424 For example, if a patch affects multiple subsystems and has an Acked-by: from
425 one subsystem maintainer then this usually indicates acknowledgement of just
426 the part which affects that maintainer's code. Judgement should be used here.
427 When in doubt people should refer to the original discussion in the mailing
428 list archives.
429
430 If a person has had the opportunity to comment on a patch, but has not
431 provided such comments, you may optionally add a "Cc:" tag to the patch.
432 This is the only tag which might be added without an explicit action by the
433 person it names. This tag documents that potentially interested parties
434 have been included in the discussion
435
436
437 14) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
438
439 If this patch fixes a problem reported by somebody else, consider adding a
440 Reported-by: tag to credit the reporter for their contribution. Please
441 note that this tag should not be added without the reporter's permission,
442 especially if the problem was not reported in a public forum. That said,
443 if we diligently credit our bug reporters, they will, hopefully, be
444 inspired to help us again in the future.
445
446 A Tested-by: tag indicates that the patch has been successfully tested (in
447 some environment) by the person named. This tag informs maintainers that
448 some testing has been performed, provides a means to locate testers for
449 future patches, and ensures credit for the testers.
450
451 Reviewed-by:, instead, indicates that the patch has been reviewed and found
452 acceptable according to the Reviewer's Statement:
453
454 Reviewer's statement of oversight
455
456 By offering my Reviewed-by: tag, I state that:
457
458 (a) I have carried out a technical review of this patch to
459 evaluate its appropriateness and readiness for inclusion into
460 the mainline kernel.
461
462 (b) Any problems, concerns, or questions relating to the patch
463 have been communicated back to the submitter. I am satisfied
464 with the submitter's response to my comments.
465
466 (c) While there may be things that could be improved with this
467 submission, I believe that it is, at this time, (1) a
468 worthwhile modification to the kernel, and (2) free of known
469 issues which would argue against its inclusion.
470
471 (d) While I have reviewed the patch and believe it to be sound, I
472 do not (unless explicitly stated elsewhere) make any
473 warranties or guarantees that it will achieve its stated
474 purpose or function properly in any given situation.
475
476 A Reviewed-by tag is a statement of opinion that the patch is an
477 appropriate modification of the kernel without any remaining serious
478 technical issues. Any interested reviewer (who has done the work) can
479 offer a Reviewed-by tag for a patch. This tag serves to give credit to
480 reviewers and to inform maintainers of the degree of review which has been
481 done on the patch. Reviewed-by: tags, when supplied by reviewers known to
482 understand the subject area and to perform thorough reviews, will normally
483 increase the likelihood of your patch getting into the kernel.
484
485 A Suggested-by: tag indicates that the patch idea is suggested by the person
486 named and ensures credit to the person for the idea. Please note that this
487 tag should not be added without the reporter's permission, especially if the
488 idea was not posted in a public forum. That said, if we diligently credit our
489 idea reporters, they will, hopefully, be inspired to help us again in the
490 future.
491
492 A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
493 is used to make it easy to determine where a bug originated, which can help
494 review a bug fix. This tag also assists the stable kernel team in determining
495 which stable kernel versions should receive your fix. This is the preferred
496 method for indicating a bug fixed by the patch. See #2 above for more details.
497
498
499 15) The canonical patch format
500
501 The canonical patch subject line is:
502
503 Subject: [PATCH 001/123] subsystem: summary phrase
504
505 The canonical patch message body contains the following:
506
507 - A "from" line specifying the patch author.
508
509 - An empty line.
510
511 - The body of the explanation, which will be copied to the
512 permanent changelog to describe this patch.
513
514 - The "Signed-off-by:" lines, described above, which will
515 also go in the changelog.
516
517 - A marker line containing simply "---".
518
519 - Any additional comments not suitable for the changelog.
520
521 - The actual patch (diff output).
522
523 The Subject line format makes it very easy to sort the emails
524 alphabetically by subject line - pretty much any email reader will
525 support that - since because the sequence number is zero-padded,
526 the numerical and alphabetic sort is the same.
527
528 The "subsystem" in the email's Subject should identify which
529 area or subsystem of the kernel is being patched.
530
531 The "summary phrase" in the email's Subject should concisely
532 describe the patch which that email contains. The "summary
533 phrase" should not be a filename. Do not use the same "summary
534 phrase" for every patch in a whole patch series (where a "patch
535 series" is an ordered sequence of multiple, related patches).
536
537 Bear in mind that the "summary phrase" of your email becomes a
538 globally-unique identifier for that patch. It propagates all the way
539 into the git changelog. The "summary phrase" may later be used in
540 developer discussions which refer to the patch. People will want to
541 google for the "summary phrase" to read discussion regarding that
542 patch. It will also be the only thing that people may quickly see
543 when, two or three months later, they are going through perhaps
544 thousands of patches using tools such as "gitk" or "git log
545 --oneline".
546
547 For these reasons, the "summary" must be no more than 70-75
548 characters, and it must describe both what the patch changes, as well
549 as why the patch might be necessary. It is challenging to be both
550 succinct and descriptive, but that is what a well-written summary
551 should do.
552
553 The "summary phrase" may be prefixed by tags enclosed in square
554 brackets: "Subject: [PATCH tag] <summary phrase>". The tags are not
555 considered part of the summary phrase, but describe how the patch
556 should be treated. Common tags might include a version descriptor if
557 the multiple versions of the patch have been sent out in response to
558 comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
559 comments. If there are four patches in a patch series the individual
560 patches may be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures
561 that developers understand the order in which the patches should be
562 applied and that they have reviewed or applied all of the patches in
563 the patch series.
564
565 A couple of example Subjects:
566
567 Subject: [patch 2/5] ext2: improve scalability of bitmap searching
568 Subject: [PATCHv2 001/207] x86: fix eflags tracking
569
570 The "from" line must be the very first line in the message body,
571 and has the form:
572
573 From: Original Author <author@example.com>
574
575 The "from" line specifies who will be credited as the author of the
576 patch in the permanent changelog. If the "from" line is missing,
577 then the "From:" line from the email header will be used to determine
578 the patch author in the changelog.
579
580 The explanation body will be committed to the permanent source
581 changelog, so should make sense to a competent reader who has long
582 since forgotten the immediate details of the discussion that might
583 have led to this patch. Including symptoms of the failure which the
584 patch addresses (kernel log messages, oops messages, etc.) is
585 especially useful for people who might be searching the commit logs
586 looking for the applicable patch. If a patch fixes a compile failure,
587 it may not be necessary to include _all_ of the compile failures; just
588 enough that it is likely that someone searching for the patch can find
589 it. As in the "summary phrase", it is important to be both succinct as
590 well as descriptive.
591
592 The "---" marker line serves the essential purpose of marking for patch
593 handling tools where the changelog message ends.
594
595 One good use for the additional comments after the "---" marker is for
596 a diffstat, to show what files have changed, and the number of
597 inserted and deleted lines per file. A diffstat is especially useful
598 on bigger patches. Other comments relevant only to the moment or the
599 maintainer, not suitable for the permanent changelog, should also go
600 here. A good example of such comments might be "patch changelogs"
601 which describe what has changed between the v1 and v2 version of the
602 patch.
603
604 If you are going to include a diffstat after the "---" marker, please
605 use diffstat options "-p 1 -w 70" so that filenames are listed from
606 the top of the kernel source tree and don't use too much horizontal
607 space (easily fit in 80 columns, maybe with some indentation).
608
609 See more details on the proper patch format in the following
610 references.
611
612
613 16) Sending "git pull" requests (from Linus emails)
614
615 Please write the git repo address and branch name alone on the same line
616 so that I can't even by mistake pull from the wrong branch, and so
617 that a triple-click just selects the whole thing.
618
619 So the proper format is something along the lines of:
620
621 "Please pull from
622
623 git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
624
625 to get these changes:"
626
627 so that I don't have to hunt-and-peck for the address and inevitably
628 get it wrong (actually, I've only gotten it wrong a few times, and
629 checking against the diffstat tells me when I get it wrong, but I'm
630 just a lot more comfortable when I don't have to "look for" the right
631 thing to pull, and double-check that I have the right branch-name).
632
633
634 Please use "git diff -M --stat --summary" to generate the diffstat:
635 the -M enables rename detection, and the summary enables a summary of
636 new/deleted or renamed files.
637
638 With rename detection, the statistics are rather different [...]
639 because git will notice that a fair number of the changes are renames.
640
641 -----------------------------------
642 SECTION 2 - HINTS, TIPS, AND TRICKS
643 -----------------------------------
644
645 This section lists many of the common "rules" associated with code
646 submitted to the kernel. There are always exceptions... but you must
647 have a really good reason for doing so. You could probably call this
648 section Linus Computer Science 101.
649
650
651
652 1) Read Documentation/CodingStyle
653
654 Nuff said. If your code deviates too much from this, it is likely
655 to be rejected without further review, and without comment.
656
657 One significant exception is when moving code from one file to
658 another -- in this case you should not modify the moved code at all in
659 the same patch which moves it. This clearly delineates the act of
660 moving the code and your changes. This greatly aids review of the
661 actual differences and allows tools to better track the history of
662 the code itself.
663
664 Check your patches with the patch style checker prior to submission
665 (scripts/checkpatch.pl). The style checker should be viewed as
666 a guide not as the final word. If your code looks better with
667 a violation then its probably best left alone.
668
669 The checker reports at three levels:
670 - ERROR: things that are very likely to be wrong
671 - WARNING: things requiring careful review
672 - CHECK: things requiring thought
673
674 You should be able to justify all violations that remain in your
675 patch.
676
677
678
679 2) #ifdefs are ugly
680
681 Code cluttered with ifdefs is difficult to read and maintain. Don't do
682 it. Instead, put your ifdefs in a header, and conditionally define
683 'static inline' functions, or macros, which are used in the code.
684 Let the compiler optimize away the "no-op" case.
685
686 Simple example, of poor code:
687
688 dev = alloc_etherdev (sizeof(struct funky_private));
689 if (!dev)
690 return -ENODEV;
691 #ifdef CONFIG_NET_FUNKINESS
692 init_funky_net(dev);
693 #endif
694
695 Cleaned-up example:
696
697 (in header)
698 #ifndef CONFIG_NET_FUNKINESS
699 static inline void init_funky_net (struct net_device *d) {}
700 #endif
701
702 (in the code itself)
703 dev = alloc_etherdev (sizeof(struct funky_private));
704 if (!dev)
705 return -ENODEV;
706 init_funky_net(dev);
707
708
709
710 3) 'static inline' is better than a macro
711
712 Static inline functions are greatly preferred over macros.
713 They provide type safety, have no length limitations, no formatting
714 limitations, and under gcc they are as cheap as macros.
715
716 Macros should only be used for cases where a static inline is clearly
717 suboptimal [there are a few, isolated cases of this in fast paths],
718 or where it is impossible to use a static inline function [such as
719 string-izing].
720
721 'static inline' is preferred over 'static __inline__', 'extern inline',
722 and 'extern __inline__'.
723
724
725
726 4) Don't over-design.
727
728 Don't try to anticipate nebulous future cases which may or may not
729 be useful: "Make it as simple as you can, and no simpler."
730
731
732
733 ----------------------
734 SECTION 3 - REFERENCES
735 ----------------------
736
737 Andrew Morton, "The perfect patch" (tpp).
738 <http://userweb.kernel.org/~akpm/stuff/tpp.txt>
739
740 Jeff Garzik, "Linux kernel patch submission format".
741 <http://linux.yyz.us/patch-format.html>
742
743 Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
744 <http://www.kroah.com/log/linux/maintainer.html>
745 <http://www.kroah.com/log/linux/maintainer-02.html>
746 <http://www.kroah.com/log/linux/maintainer-03.html>
747 <http://www.kroah.com/log/linux/maintainer-04.html>
748 <http://www.kroah.com/log/linux/maintainer-05.html>
749
750 NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
751 <http://marc.theaimsgroup.com/?l=linux-kernel&m=112112749912944&w=2>
752
753 Kernel Documentation/CodingStyle:
754 <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
755
756 Linus Torvalds's mail on the canonical patch format:
757 <http://lkml.org/lkml/2005/4/7/183>
758
759 Andi Kleen, "On submitting kernel patches"
760 Some strategies to get difficult or controversial changes in.
761 http://halobates.de/on-submitting-patches.pdf
762
763 --