Monday, April 20, 2009

How to Get Your Change Into the Linux Kernel ? / Submitting Patches

As title says ...


1
2 How to Get Your Change Into the Linux Kernel
3 or
4 Care And Operation Of Your Linus Torvalds
5
6
7
8For a person or company who wishes to submit a change to the Linux
9kernel, the process can sometimes be daunting if you're not familiar
10with "the system." This text is a collection of suggestions which
11can greatly increase the chances of your change being accepted.
12
13Read Documentation/SubmitChecklist for a list of items to check
14before submitting code. If you are submitting a driver, also read
15Documentation/SubmittingDrivers.
16
17
18
19--------------------------------------------
20SECTION 1 - CREATING AND SENDING YOUR CHANGE
21--------------------------------------------
22
23
24
251) "diff -up"
26------------
27
28Use "diff -up" or "diff -uprN" to create patches.
29
30All changes to the Linux kernel occur in the form of patches, as
31generated by diff(1). When creating your patch, make sure to create it
32in "unified diff" format, as supplied by the '-u' argument to diff(1).
33Also, please use the '-p' argument which shows which C function each
34change is in - that makes the resultant diff a lot easier to read.
35Patches should be based in the root kernel source directory,
36not in any lower subdirectory.
37
38To 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
49To create a patch for multiple files, you should unpack a "vanilla",
50or unmodified kernel source tree, and generate a diff against your
51own 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
61the build process, and should be ignored in any diff(1)-generated
62patch. The "dontdiff" file is included in the kernel tree in
632.6.12 and later. For earlier kernel versions, you can get it
64from <http://www.xenotime.net/linux/doc/dontdiff>.
65
66Make sure your patch does not include any extra files which do not
67belong in a patch submission. Make sure to review your patch -after-
68generated it with diff(1), to ensure accuracy.
69
70If your changes produce a lot of deltas, you may want to look into
71splitting them into individual patches which modify things in
72logical stages. This will facilitate easier reviewing by other
73kernel developers, very important if you want your patch accepted.
74There are a number of scripts which can aid in this:
75
76Quilt:
77http://savannah.nongnu.org/projects/quilt
78
79Andrew Morton's patch scripts:
80http://userweb.kernel.org/~akpm/stuff/patch-scripts.tar.gz
81Instead of these scripts, quilt is the recommended patch management
82tool (see above).
83
84
85
862) Describe your changes.
87
88Describe the technical detail of the change(s) your patch includes.
89
90Be as specific as possible. The WORST descriptions possible include
91things like "update driver X", "bug fix for driver X", or "this patch
92includes updates for subsystem X. Please apply."
93
94If your description starts to get long, that's a sign that you probably
95need to split up your patch. See #3, next.
96
97
98
993) Separate your changes.
100
101Separate _logical changes_ into a single patch file.
102
103For example, if your changes include both bug fixes and performance
104enhancements for a single driver, separate those changes into two
105or more patches. If your changes include an API update, and a new
106driver which uses that new API, separate those into two patches.
107
108On the other hand, if you make a single change to numerous files,
109group those changes into a single patch. Thus a single logical change
110is contained within a single patch.
111
112If one patch depends on another patch in order for a change to be
113complete, that is OK. Simply note "this patch depends on patch X"
114in your patch description.
115
116If you cannot condense your patch set into a smaller set of patches,
117then only post say 15 or so at a time and wait for review and integration.
118
119
120
1214) Style check your changes.
122
123Check your patch for basic style violations, details of which can be
124found in Documentation/CodingStyle. Failure to do so simply wastes
125the reviewers time and will get your patch rejected, probably
126without even being read.
127
128At a minimum you should check your patches with the patch style
129checker prior to submission (scripts/checkpatch.pl). You should
130be able to justify all violations that remain in your patch.
131
132
133
1345) Select e-mail destination.
135
136Look through the MAINTAINERS file and the source code, and determine
137if your change applies to a specific subsystem of the kernel, with
138an assigned maintainer. If so, e-mail that person.
139
140If no maintainer is listed, or the maintainer does not respond, send
141your patch to the primary Linux kernel developer's mailing list,
142linux-kernel@vger.kernel.org. Most kernel developers monitor this
143e-mail list, and can comment on your changes.
144
145
146Do not send more than 15 patches at once to the vger mailing lists!!!
147
148
149Linus Torvalds is the final arbiter of all changes accepted into the
150Linux kernel. His e-mail address is .
151He gets a lot of e-mail, so typically you should do your best to -avoid-
152sending him e-mail.
153
154Patches which are bug fixes, are "obvious" changes, or similarly
155require little discussion should be sent or CC'd to Linus. Patches
156which require discussion or do not have a clear advantage should
157usually be sent first to linux-kernel. Only after the patch is
158discussed should the patch then be submitted to Linus.
159
160
161
1626) Select your CC (e-mail carbon copy) list.
163
164Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
165
166Other kernel developers besides Linus need to be aware of your change,
167so that they may comment on it and offer code review and suggestions.
168linux-kernel is the primary Linux kernel developer mailing list.
169Other mailing lists are available for specific subsystems, such as
170USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the
171MAINTAINERS file for a mailing list that relates specifically to
172your change.
173
174Majordomo lists of VGER.KERNEL.ORG at:
175 <http://vger.kernel.org/vger-lists.html>
176
177If changes affect userland-kernel interfaces, please send
178the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
179a man-pages patch, or at least a notification of the change,
180so that some information makes its way into the manual pages.
181
182Even if the maintainer did not respond in step #4, make sure to ALWAYS
183copy the maintainer when you change their code.
184
185For small patches you may want to CC the Trivial Patch Monkey
186trivial@kernel.org managed by Jesper Juhl; which collects "trivial"
187patches. Trivial patches must qualify for one of the following rules:
188 Spelling fixes in documentation
189 Spelling fixes which could break grep(1)
190 Warning fixes (cluttering with useless warnings is bad)
191 Compilation fixes (only if they are actually correct)
192 Runtime fixes (only if they actually fix things)
193 Removing use of deprecated functions/macros (eg. check_region)
194 Contact detail and documentation fixes
195 Non-portable code replaced by portable code (even in arch-specific,
196 since people copy, as long as it's trivial)
197 Any fix by the author/maintainer of the file (ie. patch monkey
198 in re-transmission mode)
199URL: <http://www.kernel.org/pub/linux/kernel/people/juhl/trivial/>
200
201
202
2037) No MIME, no links, no compression, no attachments. Just plain text.
204
205Linus and other kernel developers need to be able to read and comment
206on the changes you are submitting. It is important for a kernel
207developer to be able to "quote" your changes, using standard e-mail
208tools, so that they may comment on specific portions of your code.
209
210For this reason, all patches should be submitting e-mail "inline".
211WARNING: Be wary of your editor's word-wrap corrupting your patch,
212if you choose to cut-n-paste your patch.
213
214Do not attach the patch as a MIME attachment, compressed or not.
215Many popular e-mail applications will not always transmit a MIME
216attachment as plain text, making it impossible to comment on your
217code. A MIME attachment also takes Linus a bit more time to process,
218decreasing the likelihood of your MIME-attached change being accepted.
219
220Exception: If your mailer is mangling patches then someone may ask
221you to re-send them using MIME.
222
223See Documentation/email-clients.txt for hints about configuring
224your e-mail client so that it sends your patches untouched.
225
2268) E-mail size.
227
228When sending patches to Linus, always follow step #7.
229
230Large changes are not appropriate for mailing lists, and some
231maintainers. If your patch, uncompressed, exceeds 40 kB in size,
232it is preferred that you store your patch on an Internet-accessible
233server, and provide instead a URL (link) pointing to your patch.
234
235
236
2379) Name your kernel version.
238
239It is important to note, either in the subject line or in the patch
240description, the kernel version to which this patch applies.
241
242If the patch does not apply cleanly to the latest kernel version,
243Linus will not apply it.
244
245
246
24710) Don't get discouraged. Re-submit.
248
249After you have submitted your change, be patient and wait. If Linus
250likes your change and applies it, it will appear in the next version
251of the kernel that he releases.
252
253However, if your change doesn't appear in the next version of the
254kernel, there could be any number of reasons. It's YOUR job to
255narrow down those reasons, correct what was wrong, and submit your
256updated change.
257
258It is quite common for Linus to "drop" your patch without comment.
259That's the nature of the system. If he drops your patch, it could be
260due to
261* Your patch did not apply cleanly to the latest kernel version.
262* Your patch was not sufficiently discussed on linux-kernel.
263* A style issue (see section 2).
264* An e-mail formatting issue (re-read this section).
265* A technical problem with your change.
266* He gets tons of e-mail, and yours got lost in the shuffle.
267* You are being annoying.
268
269When in doubt, solicit comments on linux-kernel mailing list.
270
271
272
27311) Include PATCH in the subject
274
275Due to high e-mail traffic to Linus, and to linux-kernel, it is common
276convention to prefix your subject line with [PATCH]. This lets Linus
277and other kernel developers more easily distinguish patches from other
278e-mail discussions.
279
280
281
28212) Sign your work
283
284To improve tracking of who did what, especially with patches that can
285percolate to their final resting place in the kernel through several
286layers of maintainers, we've introduced a "sign-off" procedure on
287patches that are being emailed around.
288
289The sign-off is a simple line at the end of the explanation for the
290patch, which certifies that you wrote it or otherwise have the right to
291pass it on as a open-source patch. The rules are pretty simple: if you
292can certify the below:
293
294 Developer's Certificate of Origin 1.1
295
296 By making a contribution to this project, I certify that:
297
298 (a) The contribution was created in whole or in part by me and I
299 have the right to submit it under the open source license
300 indicated in the file; or
301
302 (b) The contribution is based upon previous work that, to the best
303 of my knowledge, is covered under an appropriate open source
304 license and I have the right under that license to submit that
305 work with modifications, whether created in whole or in part
306 by me, under the same open source license (unless I am
307 permitted to submit under a different license), as indicated
308 in the file; or
309
310 (c) The contribution was provided directly to me by some other
311 person who certified (a), (b) or (c) and I have not modified
312 it.
313
314 (d) I understand and agree that this project and the contribution
315 are public and that a record of the contribution (including all
316 personal information I submit with it, including my sign-off) is
317 maintained indefinitely and may be redistributed consistent with
318 this project or the open source license(s) involved.
319
320then you just add a line saying
321
322 Signed-off-by: Random J Developer
323
324using your real name (sorry, no pseudonyms or anonymous contributions.)
325
326Some people also put extra tags at the end. They'll just be ignored for
327now, but you can do this to mark internal company procedures or just
328point out some special detail about the sign-off.
329
330If you are a subsystem or branch maintainer, sometimes you need to slightly
331modify patches you receive in order to merge them, because the code is not
332exactly the same in your tree and the submitters'. If you stick strictly to
333rule (c), you should ask the submitter to rediff, but this is a totally
334counter-productive waste of time and energy. Rule (b) allows you to adjust
335the code, but then it is very impolite to change one submitter's code and
336make him endorse your bugs. To solve this problem, it is recommended that
337you add a line between the last Signed-off-by header and yours, indicating
338the nature of your changes. While there is nothing mandatory about this, it
339seems like prepending the description with your mail and/or name, all
340enclosed in square brackets, is noticeable enough to make it obvious that
341you are responsible for last-minute changes. Example :
342
343 Signed-off-by: Random J Developer
344 [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
345 Signed-off-by: Lucky K Maintainer
346
347This practise is particularly helpful if you maintain a stable branch and
348want at the same time to credit the author, track changes, merge the fix,
349and protect the submitter from complaints. Note that under no circumstances
350can you change the author's identity (the From header), as it is the one
351which appears in the changelog.
352
353Special note to back-porters: It seems to be a common and useful practise
354to insert an indication of the origin of a patch at the top of the commit
355message (just after the subject line) to facilitate tracking. For instance,
356here's what we see in 2.6-stable :
357
358 Date: Tue May 13 19:10:30 2008 +0000
359
360 SCSI: libiscsi regression in 2.6.25: fix nop timer handling
361
362 commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
363
364And here's what appears in 2.4 :
365
366 Date: Tue May 13 22:12:27 2008 +0200
367
368 wireless, airo: waitbusy() won't delay
369
370 [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
371
372Whatever the format, this information provides a valuable help to people
373tracking your trees, and to people trying to trouble-shoot bugs in your
374tree.
375
376
37713) When to use Acked-by: and Cc:
378
379The Signed-off-by: tag indicates that the signer was involved in the
380development of the patch, or that he/she was in the patch's delivery path.
381
382If a person was not directly involved in the preparation or handling of a
383patch but wishes to signify and record their approval of it then they can
384arrange to have an Acked-by: line added to the patch's changelog.
385
386Acked-by: is often used by the maintainer of the affected code when that
387maintainer neither contributed to nor forwarded the patch.
388
389Acked-by: is not as formal as Signed-off-by:. It is a record that the acker
390has at least reviewed the patch and has indicated acceptance. Hence patch
391mergers will sometimes manually convert an acker's "yep, looks good to me"
392into an Acked-by:.
393
394Acked-by: does not necessarily indicate acknowledgement of the entire patch.
395For example, if a patch affects multiple subsystems and has an Acked-by: from
396one subsystem maintainer then this usually indicates acknowledgement of just
397the part which affects that maintainer's code. Judgement should be used here.
398When in doubt people should refer to the original discussion in the mailing
399list archives.
400
401If a person has had the opportunity to comment on a patch, but has not
402provided such comments, you may optionally add a "Cc:" tag to the patch.
403This is the only tag which might be added without an explicit action by the
404person it names. This tag documents that potentially interested parties
405have been included in the discussion
406
407
40814) Using Tested-by: and Reviewed-by:
409
410A Tested-by: tag indicates that the patch has been successfully tested (in
411some environment) by the person named. This tag informs maintainers that
412some testing has been performed, provides a means to locate testers for
413future patches, and ensures credit for the testers.
414
415Reviewed-by:, instead, indicates that the patch has been reviewed and found
416acceptable according to the Reviewer's Statement:
417
418 Reviewer's statement of oversight
419
420 By offering my Reviewed-by: tag, I state that:
421
422 (a) I have carried out a technical review of this patch to
423 evaluate its appropriateness and readiness for inclusion into
424 the mainline kernel.
425
426 (b) Any problems, concerns, or questions relating to the patch
427 have been communicated back to the submitter. I am satisfied
428 with the submitter's response to my comments.
429
430 (c) While there may be things that could be improved with this
431 submission, I believe that it is, at this time, (1) a
432 worthwhile modification to the kernel, and (2) free of known
433 issues which would argue against its inclusion.
434
435 (d) While I have reviewed the patch and believe it to be sound, I
436 do not (unless explicitly stated elsewhere) make any
437 warranties or guarantees that it will achieve its stated
438 purpose or function properly in any given situation.
439
440A Reviewed-by tag is a statement of opinion that the patch is an
441appropriate modification of the kernel without any remaining serious
442technical issues. Any interested reviewer (who has done the work) can
443offer a Reviewed-by tag for a patch. This tag serves to give credit to
444reviewers and to inform maintainers of the degree of review which has been
445done on the patch. Reviewed-by: tags, when supplied by reviewers known to
446understand the subject area and to perform thorough reviews, will normally
447increase the liklihood of your patch getting into the kernel.
448
449
45015) The canonical patch format
451
452The canonical patch subject line is:
453
454 Subject: [PATCH 001/123] subsystem: summary phrase
455
456The canonical patch message body contains the following:
457
458 - A "from" line specifying the patch author.
459
460 - An empty line.
461
462 - The body of the explanation, which will be copied to the
463 permanent changelog to describe this patch.
464
465 - The "Signed-off-by:" lines, described above, which will
466 also go in the changelog.
467
468 - A marker line containing simply "---".
469
470 - Any additional comments not suitable for the changelog.
471
472 - The actual patch (diff output).
473
474The Subject line format makes it very easy to sort the emails
475alphabetically by subject line - pretty much any email reader will
476support that - since because the sequence number is zero-padded,
477the numerical and alphabetic sort is the same.
478
479The "subsystem" in the email's Subject should identify which
480area or subsystem of the kernel is being patched.
481
482The "summary phrase" in the email's Subject should concisely
483describe the patch which that email contains. The "summary
484phrase" should not be a filename. Do not use the same "summary
485phrase" for every patch in a whole patch series (where a "patch
486series" is an ordered sequence of multiple, related patches).
487
488Bear in mind that the "summary phrase" of your email becomes
489a globally-unique identifier for that patch. It propagates
490all the way into the git changelog. The "summary phrase" may
491later be used in developer discussions which refer to the patch.
492People will want to google for the "summary phrase" to read
493discussion regarding that patch.
494
495A couple of example Subjects:
496
497 Subject: [patch 2/5] ext2: improve scalability of bitmap searching
498 Subject: [PATCHv2 001/207] x86: fix eflags tracking
499
500The "from" line must be the very first line in the message body,
501and has the form:
502
503 From: Original Author
504
505The "from" line specifies who will be credited as the author of the
506patch in the permanent changelog. If the "from" line is missing,
507then the "From:" line from the email header will be used to determine
508the patch author in the changelog.
509
510The explanation body will be committed to the permanent source
511changelog, so should make sense to a competent reader who has long
512since forgotten the immediate details of the discussion that might
513have led to this patch.
514
515The "---" marker line serves the essential purpose of marking for patch
516handling tools where the changelog message ends.
517
518One good use for the additional comments after the "---" marker is for
519a diffstat, to show what files have changed, and the number of inserted
520and deleted lines per file. A diffstat is especially useful on bigger
521patches. Other comments relevant only to the moment or the maintainer,
522not suitable for the permanent changelog, should also go here.
523Use diffstat options "-p 1 -w 70" so that filenames are listed from the
524top of the kernel source tree and don't use too much horizontal space
525(easily fit in 80 columns, maybe with some indentation).
526
527See more details on the proper patch format in the following
528references.
529
530
53116) Sending "git pull" requests (from Linus emails)
532
533Please write the git repo address and branch name alone on the same line
534so that I can't even by mistake pull from the wrong branch, and so
535that a triple-click just selects the whole thing.
536
537So the proper format is something along the lines of:
538
539 "Please pull from
540
541 git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
542
543 to get these changes:"
544
545so that I don't have to hunt-and-peck for the address and inevitably
546get it wrong (actually, I've only gotten it wrong a few times, and
547checking against the diffstat tells me when I get it wrong, but I'm
548just a lot more comfortable when I don't have to "look for" the right
549thing to pull, and double-check that I have the right branch-name).
550
551
552Please use "git diff -M --stat --summary" to generate the diffstat:
553the -M enables rename detection, and the summary enables a summary of
554new/deleted or renamed files.
555
556With rename detection, the statistics are rather different [...]
557because git will notice that a fair number of the changes are renames.
558
559-----------------------------------
560SECTION 2 - HINTS, TIPS, AND TRICKS
561-----------------------------------
562
563This section lists many of the common "rules" associated with code
564submitted to the kernel. There are always exceptions... but you must
565have a really good reason for doing so. You could probably call this
566section Linus Computer Science 101.
567
568
569
5701) Read Documentation/CodingStyle
571
572Nuff said. If your code deviates too much from this, it is likely
573to be rejected without further review, and without comment.
574
575One significant exception is when moving code from one file to
576another -- in this case you should not modify the moved code at all in
577the same patch which moves it. This clearly delineates the act of
578moving the code and your changes. This greatly aids review of the
579actual differences and allows tools to better track the history of
580the code itself.
581
582Check your patches with the patch style checker prior to submission
583(scripts/checkpatch.pl). The style checker should be viewed as
584a guide not as the final word. If your code looks better with
585a violation then its probably best left alone.
586
587The checker reports at three levels:
588 - ERROR: things that are very likely to be wrong
589 - WARNING: things requiring careful review
590 - CHECK: things requiring thought
591
592You should be able to justify all violations that remain in your
593patch.
594
595
596
5972) #ifdefs are ugly
598
599Code cluttered with ifdefs is difficult to read and maintain. Don't do
600it. Instead, put your ifdefs in a header, and conditionally define
601'static inline' functions, or macros, which are used in the code.
602Let the compiler optimize away the "no-op" case.
603
604Simple example, of poor code:
605
606 dev = alloc_etherdev (sizeof(struct funky_private));
607 if (!dev)
608 return -ENODEV;
609 #ifdef CONFIG_NET_FUNKINESS
610 init_funky_net(dev);
611 #endif
612
613Cleaned-up example:
614
615(in header)
616 #ifndef CONFIG_NET_FUNKINESS
617 static inline void init_funky_net (struct net_device *d) {}
618 #endif
619
620(in the code itself)
621 dev = alloc_etherdev (sizeof(struct funky_private));
622 if (!dev)
623 return -ENODEV;
624 init_funky_net(dev);
625
626
627
6283) 'static inline' is better than a macro
629
630Static inline functions are greatly preferred over macros.
631They provide type safety, have no length limitations, no formatting
632limitations, and under gcc they are as cheap as macros.
633
634Macros should only be used for cases where a static inline is clearly
635suboptimal [there are a few, isolated cases of this in fast paths],
636or where it is impossible to use a static inline function [such as
637string-izing].
638
639'static inline' is preferred over 'static __inline__', 'extern inline',
640and 'extern __inline__'.
641
642
643
6444) Don't over-design.
645
646Don't try to anticipate nebulous future cases which may or may not
647be useful: "Make it as simple as you can, and no simpler."
648
649
650
651----------------------
652SECTION 3 - REFERENCES
653----------------------
654
655Andrew Morton, "The perfect patch" (tpp).
656 <http://userweb.kernel.org/~akpm/stuff/tpp.txt>
657
658Jeff Garzik, "Linux kernel patch submission format".
659 <http://linux.yyz.us/patch-format.html>
660
661Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
662 <http://www.kroah.com/log/2005/03/31/>
663 <http://www.kroah.com/log/2005/07/08/>
664 <http://www.kroah.com/log/2005/10/19/>
665 <http://www.kroah.com/log/2006/01/11/>
666
667NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
668 <http://marc.theaimsgroup.com/?l=linux-kernel&m=112112749912944&w=2>
669
670Kernel Documentation/CodingStyle:
671 <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
672
673Linus Torvalds's mail on the canonical patch format:
674 <http://lkml.org/lkml/2005/4/7/183>
675
676Andi Kleen, "On submitting kernel patches"
677 Some strategies to get difficult or controversal changes in.
678 http://halobates.de/on-submitting-patches.pdf
679
680--
681


Reference : http://lxr.linux.no/linux/Documentation/SubmittingPatches

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