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Based on kernel version 3.13. Page generated on 2014-01-20 22:04 EST.

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	If you want to refer to a specific commit, don't just refer to the
113	SHA-1 ID of the commit. Please also include the oneline summary of
114	the commit, to make it easier for reviewers to know what it is about.
115	Example:
116	
117		Commit e21d2170f36602ae2708 ("video: remove unnecessary
118		platform_set_drvdata()") removed the unnecessary
119		platform_set_drvdata(), but left the variable "dev" unused,
120		delete it.
121	
122	
123	3) Separate your changes.
124	
125	Separate _logical changes_ into a single patch file.
126	
127	For example, if your changes include both bug fixes and performance
128	enhancements for a single driver, separate those changes into two
129	or more patches.  If your changes include an API update, and a new
130	driver which uses that new API, separate those into two patches.
131	
132	On the other hand, if you make a single change to numerous files,
133	group those changes into a single patch.  Thus a single logical change
134	is contained within a single patch.
135	
136	If one patch depends on another patch in order for a change to be
137	complete, that is OK.  Simply note "this patch depends on patch X"
138	in your patch description.
139	
140	If you cannot condense your patch set into a smaller set of patches,
141	then only post say 15 or so at a time and wait for review and integration.
142	
143	
144	
145	4) Style check your changes.
146	
147	Check your patch for basic style violations, details of which can be
148	found in Documentation/CodingStyle.  Failure to do so simply wastes
149	the reviewers time and will get your patch rejected, probably
150	without even being read.
151	
152	At a minimum you should check your patches with the patch style
153	checker prior to submission (scripts/checkpatch.pl).  You should
154	be able to justify all violations that remain in your patch.
155	
156	
157	
158	5) Select e-mail destination.
159	
160	Look through the MAINTAINERS file and the source code, and determine
161	if your change applies to a specific subsystem of the kernel, with
162	an assigned maintainer.  If so, e-mail that person.  The script
163	scripts/get_maintainer.pl can be very useful at this step.
164	
165	If no maintainer is listed, or the maintainer does not respond, send
166	your patch to the primary Linux kernel developer's mailing list,
167	linux-kernel@vger.kernel.org.  Most kernel developers monitor this
168	e-mail list, and can comment on your changes.
169	
170	
171	Do not send more than 15 patches at once to the vger mailing lists!!!
172	
173	
174	Linus Torvalds is the final arbiter of all changes accepted into the
175	Linux kernel.  His e-mail address is <torvalds@linux-foundation.org>. 
176	He gets a lot of e-mail, so typically you should do your best to -avoid-
177	sending him e-mail. 
178	
179	Patches which are bug fixes, are "obvious" changes, or similarly
180	require little discussion should be sent or CC'd to Linus.  Patches
181	which require discussion or do not have a clear advantage should
182	usually be sent first to linux-kernel.  Only after the patch is
183	discussed should the patch then be submitted to Linus.
184	
185	
186	
187	6) Select your CC (e-mail carbon copy) list.
188	
189	Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
190	
191	Other kernel developers besides Linus need to be aware of your change,
192	so that they may comment on it and offer code review and suggestions.
193	linux-kernel is the primary Linux kernel developer mailing list.
194	Other mailing lists are available for specific subsystems, such as
195	USB, framebuffer devices, the VFS, the SCSI subsystem, etc.  See the
196	MAINTAINERS file for a mailing list that relates specifically to
197	your change.
198	
199	Majordomo lists of VGER.KERNEL.ORG at:
200		<http://vger.kernel.org/vger-lists.html>
201	
202	If changes affect userland-kernel interfaces, please send
203	the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
204	a man-pages patch, or at least a notification of the change,
205	so that some information makes its way into the manual pages.
206	
207	Even if the maintainer did not respond in step #5, make sure to ALWAYS
208	copy the maintainer when you change their code.
209	
210	For small patches you may want to CC the Trivial Patch Monkey
211	trivial@kernel.org which collects "trivial" patches. Have a look
212	into the MAINTAINERS file for its current manager.
213	Trivial patches must qualify for one of the following rules:
214	 Spelling fixes in documentation
215	 Spelling fixes which could break grep(1)
216	 Warning fixes (cluttering with useless warnings is bad)
217	 Compilation fixes (only if they are actually correct)
218	 Runtime fixes (only if they actually fix things)
219	 Removing use of deprecated functions/macros (eg. check_region)
220	 Contact detail and documentation fixes
221	 Non-portable code replaced by portable code (even in arch-specific,
222	 since people copy, as long as it's trivial)
223	 Any fix by the author/maintainer of the file (ie. patch monkey
224	 in re-transmission mode)
225	
226	
227	
228	7) No MIME, no links, no compression, no attachments.  Just plain text.
229	
230	Linus and other kernel developers need to be able to read and comment
231	on the changes you are submitting.  It is important for a kernel
232	developer to be able to "quote" your changes, using standard e-mail
233	tools, so that they may comment on specific portions of your code.
234	
235	For this reason, all patches should be submitting e-mail "inline".
236	WARNING:  Be wary of your editor's word-wrap corrupting your patch,
237	if you choose to cut-n-paste your patch.
238	
239	Do not attach the patch as a MIME attachment, compressed or not.
240	Many popular e-mail applications will not always transmit a MIME
241	attachment as plain text, making it impossible to comment on your
242	code.  A MIME attachment also takes Linus a bit more time to process,
243	decreasing the likelihood of your MIME-attached change being accepted.
244	
245	Exception:  If your mailer is mangling patches then someone may ask
246	you to re-send them using MIME.
247	
248	See Documentation/email-clients.txt for hints about configuring
249	your e-mail client so that it sends your patches untouched.
250	
251	8) E-mail size.
252	
253	When sending patches to Linus, always follow step #7.
254	
255	Large changes are not appropriate for mailing lists, and some
256	maintainers.  If your patch, uncompressed, exceeds 300 kB in size,
257	it is preferred that you store your patch on an Internet-accessible
258	server, and provide instead a URL (link) pointing to your patch.
259	
260	
261	
262	9) Name your kernel version.
263	
264	It is important to note, either in the subject line or in the patch
265	description, the kernel version to which this patch applies.
266	
267	If the patch does not apply cleanly to the latest kernel version,
268	Linus will not apply it.
269	
270	
271	
272	10) Don't get discouraged.  Re-submit.
273	
274	After you have submitted your change, be patient and wait.  If Linus
275	likes your change and applies it, it will appear in the next version
276	of the kernel that he releases.
277	
278	However, if your change doesn't appear in the next version of the
279	kernel, there could be any number of reasons.  It's YOUR job to
280	narrow down those reasons, correct what was wrong, and submit your
281	updated change.
282	
283	It is quite common for Linus to "drop" your patch without comment.
284	That's the nature of the system.  If he drops your patch, it could be
285	due to
286	* Your patch did not apply cleanly to the latest kernel version.
287	* Your patch was not sufficiently discussed on linux-kernel.
288	* A style issue (see section 2).
289	* An e-mail formatting issue (re-read this section).
290	* A technical problem with your change.
291	* He gets tons of e-mail, and yours got lost in the shuffle.
292	* You are being annoying.
293	
294	When in doubt, solicit comments on linux-kernel mailing list.
295	
296	
297	
298	11) Include PATCH in the subject
299	
300	Due to high e-mail traffic to Linus, and to linux-kernel, it is common
301	convention to prefix your subject line with [PATCH].  This lets Linus
302	and other kernel developers more easily distinguish patches from other
303	e-mail discussions.
304	
305	
306	
307	12) Sign your work
308	
309	To improve tracking of who did what, especially with patches that can
310	percolate to their final resting place in the kernel through several
311	layers of maintainers, we've introduced a "sign-off" procedure on
312	patches that are being emailed around.
313	
314	The sign-off is a simple line at the end of the explanation for the
315	patch, which certifies that you wrote it or otherwise have the right to
316	pass it on as an open-source patch.  The rules are pretty simple: if you
317	can certify the below:
318	
319	        Developer's Certificate of Origin 1.1
320	
321	        By making a contribution to this project, I certify that:
322	
323	        (a) The contribution was created in whole or in part by me and I
324	            have the right to submit it under the open source license
325	            indicated in the file; or
326	
327	        (b) The contribution is based upon previous work that, to the best
328	            of my knowledge, is covered under an appropriate open source
329	            license and I have the right under that license to submit that
330	            work with modifications, whether created in whole or in part
331	            by me, under the same open source license (unless I am
332	            permitted to submit under a different license), as indicated
333	            in the file; or
334	
335	        (c) The contribution was provided directly to me by some other
336	            person who certified (a), (b) or (c) and I have not modified
337	            it.
338	
339		(d) I understand and agree that this project and the contribution
340		    are public and that a record of the contribution (including all
341		    personal information I submit with it, including my sign-off) is
342		    maintained indefinitely and may be redistributed consistent with
343		    this project or the open source license(s) involved.
344	
345	then you just add a line saying
346	
347		Signed-off-by: Random J Developer <random@developer.example.org>
348	
349	using your real name (sorry, no pseudonyms or anonymous contributions.)
350	
351	Some people also put extra tags at the end.  They'll just be ignored for
352	now, but you can do this to mark internal company procedures or just
353	point out some special detail about the sign-off. 
354	
355	If you are a subsystem or branch maintainer, sometimes you need to slightly
356	modify patches you receive in order to merge them, because the code is not
357	exactly the same in your tree and the submitters'. If you stick strictly to
358	rule (c), you should ask the submitter to rediff, but this is a totally
359	counter-productive waste of time and energy. Rule (b) allows you to adjust
360	the code, but then it is very impolite to change one submitter's code and
361	make him endorse your bugs. To solve this problem, it is recommended that
362	you add a line between the last Signed-off-by header and yours, indicating
363	the nature of your changes. While there is nothing mandatory about this, it
364	seems like prepending the description with your mail and/or name, all
365	enclosed in square brackets, is noticeable enough to make it obvious that
366	you are responsible for last-minute changes. Example :
367	
368		Signed-off-by: Random J Developer <random@developer.example.org>
369		[lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
370		Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
371	
372	This practise is particularly helpful if you maintain a stable branch and
373	want at the same time to credit the author, track changes, merge the fix,
374	and protect the submitter from complaints. Note that under no circumstances
375	can you change the author's identity (the From header), as it is the one
376	which appears in the changelog.
377	
378	Special note to back-porters: It seems to be a common and useful practise
379	to insert an indication of the origin of a patch at the top of the commit
380	message (just after the subject line) to facilitate tracking. For instance,
381	here's what we see in 2.6-stable :
382	
383	    Date:   Tue May 13 19:10:30 2008 +0000
384	
385	        SCSI: libiscsi regression in 2.6.25: fix nop timer handling
386	
387	        commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
388	
389	And here's what appears in 2.4 :
390	
391	    Date:   Tue May 13 22:12:27 2008 +0200
392	
393	        wireless, airo: waitbusy() won't delay
394	
395	        [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
396	
397	Whatever the format, this information provides a valuable help to people
398	tracking your trees, and to people trying to trouble-shoot bugs in your
399	tree.
400	
401	
402	13) When to use Acked-by: and Cc:
403	
404	The Signed-off-by: tag indicates that the signer was involved in the
405	development of the patch, or that he/she was in the patch's delivery path.
406	
407	If a person was not directly involved in the preparation or handling of a
408	patch but wishes to signify and record their approval of it then they can
409	arrange to have an Acked-by: line added to the patch's changelog.
410	
411	Acked-by: is often used by the maintainer of the affected code when that
412	maintainer neither contributed to nor forwarded the patch.
413	
414	Acked-by: is not as formal as Signed-off-by:.  It is a record that the acker
415	has at least reviewed the patch and has indicated acceptance.  Hence patch
416	mergers will sometimes manually convert an acker's "yep, looks good to me"
417	into an Acked-by:.
418	
419	Acked-by: does not necessarily indicate acknowledgement of the entire patch.
420	For example, if a patch affects multiple subsystems and has an Acked-by: from
421	one subsystem maintainer then this usually indicates acknowledgement of just
422	the part which affects that maintainer's code.  Judgement should be used here.
423	When in doubt people should refer to the original discussion in the mailing
424	list archives.
425	
426	If a person has had the opportunity to comment on a patch, but has not
427	provided such comments, you may optionally add a "Cc:" tag to the patch.
428	This is the only tag which might be added without an explicit action by the
429	person it names.  This tag documents that potentially interested parties
430	have been included in the discussion
431	
432	
433	14) Using Reported-by:, Tested-by:, Reviewed-by: and Suggested-by:
434	
435	If this patch fixes a problem reported by somebody else, consider adding a
436	Reported-by: tag to credit the reporter for their contribution.  Please
437	note that this tag should not be added without the reporter's permission,
438	especially if the problem was not reported in a public forum.  That said,
439	if we diligently credit our bug reporters, they will, hopefully, be
440	inspired to help us again in the future.
441	
442	A Tested-by: tag indicates that the patch has been successfully tested (in
443	some environment) by the person named.  This tag informs maintainers that
444	some testing has been performed, provides a means to locate testers for
445	future patches, and ensures credit for the testers.
446	
447	Reviewed-by:, instead, indicates that the patch has been reviewed and found
448	acceptable according to the Reviewer's Statement:
449	
450		Reviewer's statement of oversight
451	
452		By offering my Reviewed-by: tag, I state that:
453	
454	 	 (a) I have carried out a technical review of this patch to
455		     evaluate its appropriateness and readiness for inclusion into
456		     the mainline kernel.
457	
458		 (b) Any problems, concerns, or questions relating to the patch
459		     have been communicated back to the submitter.  I am satisfied
460		     with the submitter's response to my comments.
461	
462		 (c) While there may be things that could be improved with this
463		     submission, I believe that it is, at this time, (1) a
464		     worthwhile modification to the kernel, and (2) free of known
465		     issues which would argue against its inclusion.
466	
467		 (d) While I have reviewed the patch and believe it to be sound, I
468		     do not (unless explicitly stated elsewhere) make any
469		     warranties or guarantees that it will achieve its stated
470		     purpose or function properly in any given situation.
471	
472	A Reviewed-by tag is a statement of opinion that the patch is an
473	appropriate modification of the kernel without any remaining serious
474	technical issues.  Any interested reviewer (who has done the work) can
475	offer a Reviewed-by tag for a patch.  This tag serves to give credit to
476	reviewers and to inform maintainers of the degree of review which has been
477	done on the patch.  Reviewed-by: tags, when supplied by reviewers known to
478	understand the subject area and to perform thorough reviews, will normally
479	increase the likelihood of your patch getting into the kernel.
480	
481	A Suggested-by: tag indicates that the patch idea is suggested by the person
482	named and ensures credit to the person for the idea. Please note that this
483	tag should not be added without the reporter's permission, especially if the
484	idea was not posted in a public forum. That said, if we diligently credit our
485	idea reporters, they will, hopefully, be inspired to help us again in the
486	future.
487	
488	
489	15) The canonical patch format
490	
491	The canonical patch subject line is:
492	
493	    Subject: [PATCH 001/123] subsystem: summary phrase
494	
495	The canonical patch message body contains the following:
496	
497	  - A "from" line specifying the patch author.
498	
499	  - An empty line.
500	
501	  - The body of the explanation, which will be copied to the
502	    permanent changelog to describe this patch.
503	
504	  - The "Signed-off-by:" lines, described above, which will
505	    also go in the changelog.
506	
507	  - A marker line containing simply "---".
508	
509	  - Any additional comments not suitable for the changelog.
510	
511	  - The actual patch (diff output).
512	
513	The Subject line format makes it very easy to sort the emails
514	alphabetically by subject line - pretty much any email reader will
515	support that - since because the sequence number is zero-padded,
516	the numerical and alphabetic sort is the same.
517	
518	The "subsystem" in the email's Subject should identify which
519	area or subsystem of the kernel is being patched.
520	
521	The "summary phrase" in the email's Subject should concisely
522	describe the patch which that email contains.  The "summary
523	phrase" should not be a filename.  Do not use the same "summary
524	phrase" for every patch in a whole patch series (where a "patch
525	series" is an ordered sequence of multiple, related patches).
526	
527	Bear in mind that the "summary phrase" of your email becomes a
528	globally-unique identifier for that patch.  It propagates all the way
529	into the git changelog.  The "summary phrase" may later be used in
530	developer discussions which refer to the patch.  People will want to
531	google for the "summary phrase" to read discussion regarding that
532	patch.  It will also be the only thing that people may quickly see
533	when, two or three months later, they are going through perhaps
534	thousands of patches using tools such as "gitk" or "git log
535	--oneline".
536	
537	For these reasons, the "summary" must be no more than 70-75
538	characters, and it must describe both what the patch changes, as well
539	as why the patch might be necessary.  It is challenging to be both
540	succinct and descriptive, but that is what a well-written summary
541	should do.
542	
543	The "summary phrase" may be prefixed by tags enclosed in square
544	brackets: "Subject: [PATCH tag] <summary phrase>".  The tags are not
545	considered part of the summary phrase, but describe how the patch
546	should be treated.  Common tags might include a version descriptor if
547	the multiple versions of the patch have been sent out in response to
548	comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
549	comments.  If there are four patches in a patch series the individual
550	patches may be numbered like this: 1/4, 2/4, 3/4, 4/4.  This assures
551	that developers understand the order in which the patches should be
552	applied and that they have reviewed or applied all of the patches in
553	the patch series.
554	
555	A couple of example Subjects:
556	
557	    Subject: [patch 2/5] ext2: improve scalability of bitmap searching
558	    Subject: [PATCHv2 001/207] x86: fix eflags tracking
559	
560	The "from" line must be the very first line in the message body,
561	and has the form:
562	
563	        From: Original Author <author@example.com>
564	
565	The "from" line specifies who will be credited as the author of the
566	patch in the permanent changelog.  If the "from" line is missing,
567	then the "From:" line from the email header will be used to determine
568	the patch author in the changelog.
569	
570	The explanation body will be committed to the permanent source
571	changelog, so should make sense to a competent reader who has long
572	since forgotten the immediate details of the discussion that might
573	have led to this patch.  Including symptoms of the failure which the
574	patch addresses (kernel log messages, oops messages, etc.) is
575	especially useful for people who might be searching the commit logs
576	looking for the applicable patch.  If a patch fixes a compile failure,
577	it may not be necessary to include _all_ of the compile failures; just
578	enough that it is likely that someone searching for the patch can find
579	it.  As in the "summary phrase", it is important to be both succinct as
580	well as descriptive.
581	
582	The "---" marker line serves the essential purpose of marking for patch
583	handling tools where the changelog message ends.
584	
585	One good use for the additional comments after the "---" marker is for
586	a diffstat, to show what files have changed, and the number of
587	inserted and deleted lines per file.  A diffstat is especially useful
588	on bigger patches.  Other comments relevant only to the moment or the
589	maintainer, not suitable for the permanent changelog, should also go
590	here.  A good example of such comments might be "patch changelogs"
591	which describe what has changed between the v1 and v2 version of the
592	patch.
593	
594	If you are going to include a diffstat after the "---" marker, please
595	use diffstat options "-p 1 -w 70" so that filenames are listed from
596	the top of the kernel source tree and don't use too much horizontal
597	space (easily fit in 80 columns, maybe with some indentation).
598	
599	See more details on the proper patch format in the following
600	references.
601	
602	
603	16) Sending "git pull" requests  (from Linus emails)
604	
605	Please write the git repo address and branch name alone on the same line
606	so that I can't even by mistake pull from the wrong branch, and so
607	that a triple-click just selects the whole thing.
608	
609	So the proper format is something along the lines of:
610	
611		"Please pull from
612	
613			git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
614	
615		 to get these changes:"
616	
617	so that I don't have to hunt-and-peck for the address and inevitably
618	get it wrong (actually, I've only gotten it wrong a few times, and
619	checking against the diffstat tells me when I get it wrong, but I'm
620	just a lot more comfortable when I don't have to "look for" the right
621	thing to pull, and double-check that I have the right branch-name).
622	
623	
624	Please use "git diff -M --stat --summary" to generate the diffstat:
625	the -M enables rename detection, and the summary enables a summary of
626	new/deleted or renamed files.
627	
628	With rename detection, the statistics are rather different [...]
629	because git will notice that a fair number of the changes are renames.
630	
631	-----------------------------------
632	SECTION 2 - HINTS, TIPS, AND TRICKS
633	-----------------------------------
634	
635	This section lists many of the common "rules" associated with code
636	submitted to the kernel.  There are always exceptions... but you must
637	have a really good reason for doing so.  You could probably call this
638	section Linus Computer Science 101.
639	
640	
641	
642	1) Read Documentation/CodingStyle
643	
644	Nuff said.  If your code deviates too much from this, it is likely
645	to be rejected without further review, and without comment.
646	
647	One significant exception is when moving code from one file to
648	another -- in this case you should not modify the moved code at all in
649	the same patch which moves it.  This clearly delineates the act of
650	moving the code and your changes.  This greatly aids review of the
651	actual differences and allows tools to better track the history of
652	the code itself.
653	
654	Check your patches with the patch style checker prior to submission
655	(scripts/checkpatch.pl).  The style checker should be viewed as
656	a guide not as the final word.  If your code looks better with
657	a violation then its probably best left alone.
658	
659	The checker reports at three levels:
660	 - ERROR: things that are very likely to be wrong
661	 - WARNING: things requiring careful review
662	 - CHECK: things requiring thought
663	
664	You should be able to justify all violations that remain in your
665	patch.
666	
667	
668	
669	2) #ifdefs are ugly
670	
671	Code cluttered with ifdefs is difficult to read and maintain.  Don't do
672	it.  Instead, put your ifdefs in a header, and conditionally define
673	'static inline' functions, or macros, which are used in the code.
674	Let the compiler optimize away the "no-op" case.
675	
676	Simple example, of poor code:
677	
678		dev = alloc_etherdev (sizeof(struct funky_private));
679		if (!dev)
680			return -ENODEV;
681		#ifdef CONFIG_NET_FUNKINESS
682		init_funky_net(dev);
683		#endif
684	
685	Cleaned-up example:
686	
687	(in header)
688		#ifndef CONFIG_NET_FUNKINESS
689		static inline void init_funky_net (struct net_device *d) {}
690		#endif
691	
692	(in the code itself)
693		dev = alloc_etherdev (sizeof(struct funky_private));
694		if (!dev)
695			return -ENODEV;
696		init_funky_net(dev);
697	
698	
699	
700	3) 'static inline' is better than a macro
701	
702	Static inline functions are greatly preferred over macros.
703	They provide type safety, have no length limitations, no formatting
704	limitations, and under gcc they are as cheap as macros.
705	
706	Macros should only be used for cases where a static inline is clearly
707	suboptimal [there are a few, isolated cases of this in fast paths],
708	or where it is impossible to use a static inline function [such as
709	string-izing].
710	
711	'static inline' is preferred over 'static __inline__', 'extern inline',
712	and 'extern __inline__'.
713	
714	
715	
716	4) Don't over-design.
717	
718	Don't try to anticipate nebulous future cases which may or may not
719	be useful:  "Make it as simple as you can, and no simpler."
720	
721	
722	
723	----------------------
724	SECTION 3 - REFERENCES
725	----------------------
726	
727	Andrew Morton, "The perfect patch" (tpp).
728	  <http://userweb.kernel.org/~akpm/stuff/tpp.txt>
729	
730	Jeff Garzik, "Linux kernel patch submission format".
731	  <http://linux.yyz.us/patch-format.html>
732	
733	Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
734	  <http://www.kroah.com/log/linux/maintainer.html>
735	  <http://www.kroah.com/log/linux/maintainer-02.html>
736	  <http://www.kroah.com/log/linux/maintainer-03.html>
737	  <http://www.kroah.com/log/linux/maintainer-04.html>
738	  <http://www.kroah.com/log/linux/maintainer-05.html>
739	
740	NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
741	  <http://marc.theaimsgroup.com/?l=linux-kernel&m=112112749912944&w=2>
742	
743	Kernel Documentation/CodingStyle:
744	  <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
745	
746	Linus Torvalds's mail on the canonical patch format:
747	  <http://lkml.org/lkml/2005/4/7/183>
748	
749	Andi Kleen, "On submitting kernel patches"
750	  Some strategies to get difficult or controversial changes in.
751	  http://halobates.de/on-submitting-patches.pdf
752	
753	--
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