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
94The maintainer will thank you if you write your patch description in a
95form which can be easily pulled into Linux's source code management
96system, git, as a "commit log".  See #15, below.
97
98If your description starts to get long, that's a sign that you probably
99need to split up your patch.  See #3, next.
100
101When you submit or resubmit a patch or patch series, include the
102complete patch description and justification for it.  Don't just
103say that this is version N of the patch (series).  Don't expect the
104patch merger to refer back to earlier patch versions or referenced
105URLs to find the patch description and put that into the patch.
106I.e., the patch (series) and its description should be self-contained.
107This benefits both the patch merger(s) and reviewers.  Some reviewers
108probably didn't even receive earlier versions of the patch.
109
110If the patch fixes a logged bug entry, refer to that bug entry by
111number and URL.
112
113
1143) Separate your changes.
115
116Separate _logical changes_ into a single patch file.
117
118For example, if your changes include both bug fixes and performance
119enhancements for a single driver, separate those changes into two
120or more patches.  If your changes include an API update, and a new
121driver which uses that new API, separate those into two patches.
122
123On the other hand, if you make a single change to numerous files,
124group those changes into a single patch.  Thus a single logical change
125is contained within a single patch.
126
127If one patch depends on another patch in order for a change to be
128complete, that is OK.  Simply note "this patch depends on patch X"
129in your patch description.
130
131If you cannot condense your patch set into a smaller set of patches,
132then only post say 15 or so at a time and wait for review and integration.
133
134
135
1364) Style check your changes.
137
138Check your patch for basic style violations, details of which can be
139found in Documentation/CodingStyle.  Failure to do so simply wastes
140the reviewers time and will get your patch rejected, probably
141without even being read.
142
143At a minimum you should check your patches with the patch style
144checker prior to submission (scripts/checkpatch.pl).  You should
145be able to justify all violations that remain in your patch.
146
147
148
1495) Select e-mail destination.
150
151Look through the MAINTAINERS file and the source code, and determine
152if your change applies to a specific subsystem of the kernel, with
153an assigned maintainer.  If so, e-mail that person.  The script
154scripts/get_maintainer.pl can be very useful at this step.
155
156If no maintainer is listed, or the maintainer does not respond, send
157your patch to the primary Linux kernel developer's mailing list,
158linux-kernel@vger.kernel.org.  Most kernel developers monitor this
159e-mail list, and can comment on your changes.
160
161
162Do not send more than 15 patches at once to the vger mailing lists!!!
163
164
165Linus Torvalds is the final arbiter of all changes accepted into the
166Linux kernel.  His e-mail address is <torvalds@linux-foundation.org>.
167He gets a lot of e-mail, so typically you should do your best to -avoid-
168sending him e-mail.
169
170Patches which are bug fixes, are "obvious" changes, or similarly
171require little discussion should be sent or CC'd to Linus.  Patches
172which require discussion or do not have a clear advantage should
173usually be sent first to linux-kernel.  Only after the patch is
174discussed should the patch then be submitted to Linus.
175
176
177
1786) Select your CC (e-mail carbon copy) list.
179
180Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
181
182Other kernel developers besides Linus need to be aware of your change,
183so that they may comment on it and offer code review and suggestions.
184linux-kernel is the primary Linux kernel developer mailing list.
185Other mailing lists are available for specific subsystems, such as
186USB, framebuffer devices, the VFS, the SCSI subsystem, etc.  See the
187MAINTAINERS file for a mailing list that relates specifically to
188your change.
189
190Majordomo lists of VGER.KERNEL.ORG at:
191	<http://vger.kernel.org/vger-lists.html>
192
193If changes affect userland-kernel interfaces, please send
194the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
195a man-pages patch, or at least a notification of the change,
196so that some information makes its way into the manual pages.
197
198Even if the maintainer did not respond in step #5, make sure to ALWAYS
199copy the maintainer when you change their code.
200
201For small patches you may want to CC the Trivial Patch Monkey
202trivial@kernel.org which collects "trivial" patches. Have a look
203into the MAINTAINERS file for its current manager.
204Trivial patches must qualify for one of the following rules:
205 Spelling fixes in documentation
206 Spelling fixes which could break grep(1)
207 Warning fixes (cluttering with useless warnings is bad)
208 Compilation fixes (only if they are actually correct)
209 Runtime fixes (only if they actually fix things)
210 Removing use of deprecated functions/macros (eg. check_region)
211 Contact detail and documentation fixes
212 Non-portable code replaced by portable code (even in arch-specific,
213 since people copy, as long as it's trivial)
214 Any fix by the author/maintainer of the file (ie. patch monkey
215 in re-transmission mode)
216
217
218
2197) No MIME, no links, no compression, no attachments.  Just plain text.
220
221Linus and other kernel developers need to be able to read and comment
222on the changes you are submitting.  It is important for a kernel
223developer to be able to "quote" your changes, using standard e-mail
224tools, so that they may comment on specific portions of your code.
225
226For this reason, all patches should be submitting e-mail "inline".
227WARNING:  Be wary of your editor's word-wrap corrupting your patch,
228if you choose to cut-n-paste your patch.
229
230Do not attach the patch as a MIME attachment, compressed or not.
231Many popular e-mail applications will not always transmit a MIME
232attachment as plain text, making it impossible to comment on your
233code.  A MIME attachment also takes Linus a bit more time to process,
234decreasing the likelihood of your MIME-attached change being accepted.
235
236Exception:  If your mailer is mangling patches then someone may ask
237you to re-send them using MIME.
238
239See Documentation/email-clients.txt for hints about configuring
240your e-mail client so that it sends your patches untouched.
241
2428) E-mail size.
243
244When sending patches to Linus, always follow step #7.
245
246Large changes are not appropriate for mailing lists, and some
247maintainers.  If your patch, uncompressed, exceeds 300 kB in size,
248it is preferred that you store your patch on an Internet-accessible
249server, and provide instead a URL (link) pointing to your patch.
250
251
252
2539) Name your kernel version.
254
255It is important to note, either in the subject line or in the patch
256description, the kernel version to which this patch applies.
257
258If the patch does not apply cleanly to the latest kernel version,
259Linus will not apply it.
260
261
262
26310) Don't get discouraged.  Re-submit.
264
265After you have submitted your change, be patient and wait.  If Linus
266likes your change and applies it, it will appear in the next version
267of the kernel that he releases.
268
269However, if your change doesn't appear in the next version of the
270kernel, there could be any number of reasons.  It's YOUR job to
271narrow down those reasons, correct what was wrong, and submit your
272updated change.
273
274It is quite common for Linus to "drop" your patch without comment.
275That's the nature of the system.  If he drops your patch, it could be
276due to
277* Your patch did not apply cleanly to the latest kernel version.
278* Your patch was not sufficiently discussed on linux-kernel.
279* A style issue (see section 2).
280* An e-mail formatting issue (re-read this section).
281* A technical problem with your change.
282* He gets tons of e-mail, and yours got lost in the shuffle.
283* You are being annoying.
284
285When in doubt, solicit comments on linux-kernel mailing list.
286
287
288
28911) Include PATCH in the subject
290
291Due to high e-mail traffic to Linus, and to linux-kernel, it is common
292convention to prefix your subject line with [PATCH].  This lets Linus
293and other kernel developers more easily distinguish patches from other
294e-mail discussions.
295
296
297
29812) Sign your work
299
300To improve tracking of who did what, especially with patches that can
301percolate to their final resting place in the kernel through several
302layers of maintainers, we've introduced a "sign-off" procedure on
303patches that are being emailed around.
304
305The sign-off is a simple line at the end of the explanation for the
306patch, which certifies that you wrote it or otherwise have the right to
307pass it on as an open-source patch.  The rules are pretty simple: if you
308can certify the below:
309
310        Developer's Certificate of Origin 1.1
311
312        By making a contribution to this project, I certify that:
313
314        (a) The contribution was created in whole or in part by me and I
315            have the right to submit it under the open source license
316            indicated in the file; or
317
318        (b) The contribution is based upon previous work that, to the best
319            of my knowledge, is covered under an appropriate open source
320            license and I have the right under that license to submit that
321            work with modifications, whether created in whole or in part
322            by me, under the same open source license (unless I am
323            permitted to submit under a different license), as indicated
324            in the file; or
325
326        (c) The contribution was provided directly to me by some other
327            person who certified (a), (b) or (c) and I have not modified
328            it.
329
330	(d) I understand and agree that this project and the contribution
331	    are public and that a record of the contribution (including all
332	    personal information I submit with it, including my sign-off) is
333	    maintained indefinitely and may be redistributed consistent with
334	    this project or the open source license(s) involved.
335
336then you just add a line saying
337
338	Signed-off-by: Random J Developer <random@developer.example.org>
339
340using your real name (sorry, no pseudonyms or anonymous contributions.)
341
342Some people also put extra tags at the end.  They'll just be ignored for
343now, but you can do this to mark internal company procedures or just
344point out some special detail about the sign-off.
345
346If you are a subsystem or branch maintainer, sometimes you need to slightly
347modify patches you receive in order to merge them, because the code is not
348exactly the same in your tree and the submitters'. If you stick strictly to
349rule (c), you should ask the submitter to rediff, but this is a totally
350counter-productive waste of time and energy. Rule (b) allows you to adjust
351the code, but then it is very impolite to change one submitter's code and
352make him endorse your bugs. To solve this problem, it is recommended that
353you add a line between the last Signed-off-by header and yours, indicating
354the nature of your changes. While there is nothing mandatory about this, it
355seems like prepending the description with your mail and/or name, all
356enclosed in square brackets, is noticeable enough to make it obvious that
357you are responsible for last-minute changes. Example :
358
359	Signed-off-by: Random J Developer <random@developer.example.org>
360	[lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
361	Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
362
363This practise is particularly helpful if you maintain a stable branch and
364want at the same time to credit the author, track changes, merge the fix,
365and protect the submitter from complaints. Note that under no circumstances
366can you change the author's identity (the From header), as it is the one
367which appears in the changelog.
368
369Special note to back-porters: It seems to be a common and useful practise
370to insert an indication of the origin of a patch at the top of the commit
371message (just after the subject line) to facilitate tracking. For instance,
372here's what we see in 2.6-stable :
373
374    Date:   Tue May 13 19:10:30 2008 +0000
375
376        SCSI: libiscsi regression in 2.6.25: fix nop timer handling
377
378        commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
379
380And here's what appears in 2.4 :
381
382    Date:   Tue May 13 22:12:27 2008 +0200
383
384        wireless, airo: waitbusy() won't delay
385
386        [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
387
388Whatever the format, this information provides a valuable help to people
389tracking your trees, and to people trying to trouble-shoot bugs in your
390tree.
391
392
39313) When to use Acked-by: and Cc:
394
395The Signed-off-by: tag indicates that the signer was involved in the
396development of the patch, or that he/she was in the patch's delivery path.
397
398If a person was not directly involved in the preparation or handling of a
399patch but wishes to signify and record their approval of it then they can
400arrange to have an Acked-by: line added to the patch's changelog.
401
402Acked-by: is often used by the maintainer of the affected code when that
403maintainer neither contributed to nor forwarded the patch.
404
405Acked-by: is not as formal as Signed-off-by:.  It is a record that the acker
406has at least reviewed the patch and has indicated acceptance.  Hence patch
407mergers will sometimes manually convert an acker's "yep, looks good to me"
408into an Acked-by:.
409
410Acked-by: does not necessarily indicate acknowledgement of the entire patch.
411For example, if a patch affects multiple subsystems and has an Acked-by: from
412one subsystem maintainer then this usually indicates acknowledgement of just
413the part which affects that maintainer's code.  Judgement should be used here.
414When in doubt people should refer to the original discussion in the mailing
415list archives.
416
417If a person has had the opportunity to comment on a patch, but has not
418provided such comments, you may optionally add a "Cc:" tag to the patch.
419This is the only tag which might be added without an explicit action by the
420person it names.  This tag documents that potentially interested parties
421have been included in the discussion
422
423
42414) Using Reported-by:, Tested-by: and Reviewed-by:
425
426If this patch fixes a problem reported by somebody else, consider adding a
427Reported-by: tag to credit the reporter for their contribution.  Please
428note that this tag should not be added without the reporter's permission,
429especially if the problem was not reported in a public forum.  That said,
430if we diligently credit our bug reporters, they will, hopefully, be
431inspired to help us again in the future.
432
433A Tested-by: tag indicates that the patch has been successfully tested (in
434some environment) by the person named.  This tag informs maintainers that
435some testing has been performed, provides a means to locate testers for
436future patches, and ensures credit for the testers.
437
438Reviewed-by:, instead, indicates that the patch has been reviewed and found
439acceptable according to the Reviewer's Statement:
440
441	Reviewer's statement of oversight
442
443	By offering my Reviewed-by: tag, I state that:
444
445 	 (a) I have carried out a technical review of this patch to
446	     evaluate its appropriateness and readiness for inclusion into
447	     the mainline kernel.
448
449	 (b) Any problems, concerns, or questions relating to the patch
450	     have been communicated back to the submitter.  I am satisfied
451	     with the submitter's response to my comments.
452
453	 (c) While there may be things that could be improved with this
454	     submission, I believe that it is, at this time, (1) a
455	     worthwhile modification to the kernel, and (2) free of known
456	     issues which would argue against its inclusion.
457
458	 (d) While I have reviewed the patch and believe it to be sound, I
459	     do not (unless explicitly stated elsewhere) make any
460	     warranties or guarantees that it will achieve its stated
461	     purpose or function properly in any given situation.
462
463A Reviewed-by tag is a statement of opinion that the patch is an
464appropriate modification of the kernel without any remaining serious
465technical issues.  Any interested reviewer (who has done the work) can
466offer a Reviewed-by tag for a patch.  This tag serves to give credit to
467reviewers and to inform maintainers of the degree of review which has been
468done on the patch.  Reviewed-by: tags, when supplied by reviewers known to
469understand the subject area and to perform thorough reviews, will normally
470increase the likelihood of your patch getting into the kernel.
471
472
47315) The canonical patch format
474
475The canonical patch subject line is:
476
477    Subject: [PATCH 001/123] subsystem: summary phrase
478
479The canonical patch message body contains the following:
480
481  - A "from" line specifying the patch author.
482
483  - An empty line.
484
485  - The body of the explanation, which will be copied to the
486    permanent changelog to describe this patch.
487
488  - The "Signed-off-by:" lines, described above, which will
489    also go in the changelog.
490
491  - A marker line containing simply "---".
492
493  - Any additional comments not suitable for the changelog.
494
495  - The actual patch (diff output).
496
497The Subject line format makes it very easy to sort the emails
498alphabetically by subject line - pretty much any email reader will
499support that - since because the sequence number is zero-padded,
500the numerical and alphabetic sort is the same.
501
502The "subsystem" in the email's Subject should identify which
503area or subsystem of the kernel is being patched.
504
505The "summary phrase" in the email's Subject should concisely
506describe the patch which that email contains.  The "summary
507phrase" should not be a filename.  Do not use the same "summary
508phrase" for every patch in a whole patch series (where a "patch
509series" is an ordered sequence of multiple, related patches).
510
511Bear in mind that the "summary phrase" of your email becomes a
512globally-unique identifier for that patch.  It propagates all the way
513into the git changelog.  The "summary phrase" may later be used in
514developer discussions which refer to the patch.  People will want to
515google for the "summary phrase" to read discussion regarding that
516patch.  It will also be the only thing that people may quickly see
517when, two or three months later, they are going through perhaps
518thousands of patches using tools such as "gitk" or "git log
519--oneline".
520
521For these reasons, the "summary" must be no more than 70-75
522characters, and it must describe both what the patch changes, as well
523as why the patch might be necessary.  It is challenging to be both
524succinct and descriptive, but that is what a well-written summary
525should do.
526
527The "summary phrase" may be prefixed by tags enclosed in square
528brackets: "Subject: [PATCH tag] <summary phrase>".  The tags are not
529considered part of the summary phrase, but describe how the patch
530should be treated.  Common tags might include a version descriptor if
531the multiple versions of the patch have been sent out in response to
532comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
533comments.  If there are four patches in a patch series the individual
534patches may be numbered like this: 1/4, 2/4, 3/4, 4/4.  This assures
535that developers understand the order in which the patches should be
536applied and that they have reviewed or applied all of the patches in
537the patch series.
538
539A couple of example Subjects:
540
541    Subject: [patch 2/5] ext2: improve scalability of bitmap searching
542    Subject: [PATCHv2 001/207] x86: fix eflags tracking
543
544The "from" line must be the very first line in the message body,
545and has the form:
546
547        From: Original Author <author@example.com>
548
549The "from" line specifies who will be credited as the author of the
550patch in the permanent changelog.  If the "from" line is missing,
551then the "From:" line from the email header will be used to determine
552the patch author in the changelog.
553
554The explanation body will be committed to the permanent source
555changelog, so should make sense to a competent reader who has long
556since forgotten the immediate details of the discussion that might
557have led to this patch.  Including symptoms of the failure which the
558patch addresses (kernel log messages, oops messages, etc.) is
559especially useful for people who might be searching the commit logs
560looking for the applicable patch.  If a patch fixes a compile failure,
561it may not be necessary to include _all_ of the compile failures; just
562enough that it is likely that someone searching for the patch can find
563it.  As in the "summary phrase", it is important to be both succinct as
564well as descriptive.
565
566The "---" marker line serves the essential purpose of marking for patch
567handling tools where the changelog message ends.
568
569One good use for the additional comments after the "---" marker is for
570a diffstat, to show what files have changed, and the number of
571inserted and deleted lines per file.  A diffstat is especially useful
572on bigger patches.  Other comments relevant only to the moment or the
573maintainer, not suitable for the permanent changelog, should also go
574here.  A good example of such comments might be "patch changelogs"
575which describe what has changed between the v1 and v2 version of the
576patch.
577
578If you are going to include a diffstat after the "---" marker, please
579use diffstat options "-p 1 -w 70" so that filenames are listed from
580the top of the kernel source tree and don't use too much horizontal
581space (easily fit in 80 columns, maybe with some indentation).
582
583See more details on the proper patch format in the following
584references.
585
586
58716) Sending "git pull" requests  (from Linus emails)
588
589Please write the git repo address and branch name alone on the same line
590so that I can't even by mistake pull from the wrong branch, and so
591that a triple-click just selects the whole thing.
592
593So the proper format is something along the lines of:
594
595	"Please pull from
596
597		git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
598
599	 to get these changes:"
600
601so that I don't have to hunt-and-peck for the address and inevitably
602get it wrong (actually, I've only gotten it wrong a few times, and
603checking against the diffstat tells me when I get it wrong, but I'm
604just a lot more comfortable when I don't have to "look for" the right
605thing to pull, and double-check that I have the right branch-name).
606
607
608Please use "git diff -M --stat --summary" to generate the diffstat:
609the -M enables rename detection, and the summary enables a summary of
610new/deleted or renamed files.
611
612With rename detection, the statistics are rather different [...]
613because git will notice that a fair number of the changes are renames.
614
615-----------------------------------
616SECTION 2 - HINTS, TIPS, AND TRICKS
617-----------------------------------
618
619This section lists many of the common "rules" associated with code
620submitted to the kernel.  There are always exceptions... but you must
621have a really good reason for doing so.  You could probably call this
622section Linus Computer Science 101.
623
624
625
6261) Read Documentation/CodingStyle
627
628Nuff said.  If your code deviates too much from this, it is likely
629to be rejected without further review, and without comment.
630
631One significant exception is when moving code from one file to
632another -- in this case you should not modify the moved code at all in
633the same patch which moves it.  This clearly delineates the act of
634moving the code and your changes.  This greatly aids review of the
635actual differences and allows tools to better track the history of
636the code itself.
637
638Check your patches with the patch style checker prior to submission
639(scripts/checkpatch.pl).  The style checker should be viewed as
640a guide not as the final word.  If your code looks better with
641a violation then its probably best left alone.
642
643The checker reports at three levels:
644 - ERROR: things that are very likely to be wrong
645 - WARNING: things requiring careful review
646 - CHECK: things requiring thought
647
648You should be able to justify all violations that remain in your
649patch.
650
651
652
6532) #ifdefs are ugly
654
655Code cluttered with ifdefs is difficult to read and maintain.  Don't do
656it.  Instead, put your ifdefs in a header, and conditionally define
657'static inline' functions, or macros, which are used in the code.
658Let the compiler optimize away the "no-op" case.
659
660Simple example, of poor code:
661
662	dev = alloc_etherdev (sizeof(struct funky_private));
663	if (!dev)
664		return -ENODEV;
665	#ifdef CONFIG_NET_FUNKINESS
666	init_funky_net(dev);
667	#endif
668
669Cleaned-up example:
670
671(in header)
672	#ifndef CONFIG_NET_FUNKINESS
673	static inline void init_funky_net (struct net_device *d) {}
674	#endif
675
676(in the code itself)
677	dev = alloc_etherdev (sizeof(struct funky_private));
678	if (!dev)
679		return -ENODEV;
680	init_funky_net(dev);
681
682
683
6843) 'static inline' is better than a macro
685
686Static inline functions are greatly preferred over macros.
687They provide type safety, have no length limitations, no formatting
688limitations, and under gcc they are as cheap as macros.
689
690Macros should only be used for cases where a static inline is clearly
691suboptimal [there are a few, isolated cases of this in fast paths],
692or where it is impossible to use a static inline function [such as
693string-izing].
694
695'static inline' is preferred over 'static __inline__', 'extern inline',
696and 'extern __inline__'.
697
698
699
7004) Don't over-design.
701
702Don't try to anticipate nebulous future cases which may or may not
703be useful:  "Make it as simple as you can, and no simpler."
704
705
706
707----------------------
708SECTION 3 - REFERENCES
709----------------------
710
711Andrew Morton, "The perfect patch" (tpp).
712  <http://userweb.kernel.org/~akpm/stuff/tpp.txt>
713
714Jeff Garzik, "Linux kernel patch submission format".
715  <http://linux.yyz.us/patch-format.html>
716
717Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
718  <http://www.kroah.com/log/linux/maintainer.html>
719  <http://www.kroah.com/log/linux/maintainer-02.html>
720  <http://www.kroah.com/log/linux/maintainer-03.html>
721  <http://www.kroah.com/log/linux/maintainer-04.html>
722  <http://www.kroah.com/log/linux/maintainer-05.html>
723
724NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
725  <http://marc.theaimsgroup.com/?l=linux-kernel&m=112112749912944&w=2>
726
727Kernel Documentation/CodingStyle:
728  <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
729
730Linus Torvalds's mail on the canonical patch format:
731  <http://lkml.org/lkml/2005/4/7/183>
732
733Andi Kleen, "On submitting kernel patches"
734  Some strategies to get difficult or controversial changes in.
735  http://halobates.de/on-submitting-patches.pdf
736
737--
738