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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:04 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	Many of these steps describe the default behavior of the git version
18	control system; if you use git to prepare your patches, you'll find much
19	of the mechanical work done for you, though you'll still need to prepare
20	and document a sensible set of patches.
21	
22	--------------------------------------------
23	SECTION 1 - CREATING AND SENDING YOUR CHANGE
24	--------------------------------------------
25	
26	
27	
28	1) "diff -up"
29	------------
30	
31	Use "diff -up" or "diff -uprN" to create patches.  git generates patches
32	in this form by default; if you're using git, you can skip this section
33	entirely.
34	
35	All changes to the Linux kernel occur in the form of patches, as
36	generated by diff(1).  When creating your patch, make sure to create it
37	in "unified diff" format, as supplied by the '-u' argument to diff(1).
38	Also, please use the '-p' argument which shows which C function each
39	change is in - that makes the resultant diff a lot easier to read.
40	Patches should be based in the root kernel source directory,
41	not in any lower subdirectory.
42	
43	To create a patch for a single file, it is often sufficient to do:
44	
45		SRCTREE= linux-2.6
46		MYFILE=  drivers/net/mydriver.c
47	
48		cd $SRCTREE
49		cp $MYFILE $MYFILE.orig
50		vi $MYFILE	# make your change
51		cd ..
52		diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
53	
54	To create a patch for multiple files, you should unpack a "vanilla",
55	or unmodified kernel source tree, and generate a diff against your
56	own source tree.  For example:
57	
58		MYSRC= /devel/linux-2.6
59	
60		tar xvfz linux-2.6.12.tar.gz
61		mv linux-2.6.12 linux-2.6.12-vanilla
62		diff -uprN -X linux-2.6.12-vanilla/Documentation/dontdiff \
63			linux-2.6.12-vanilla $MYSRC > /tmp/patch
64	
65	"dontdiff" is a list of files which are generated by the kernel during
66	the build process, and should be ignored in any diff(1)-generated
67	patch.  The "dontdiff" file is included in the kernel tree in
68	2.6.12 and later.
69	
70	Make sure your patch does not include any extra files which do not
71	belong in a patch submission.  Make sure to review your patch -after-
72	generated it with diff(1), to ensure accuracy.
73	
74	If your changes produce a lot of deltas, you need to split them into
75	individual patches which modify things in logical stages; see section
76	#3.  This will facilitate easier reviewing by other kernel developers,
77	very important if you want your patch accepted.
78	
79	If you're using git, "git rebase -i" can help you with this process.  If
80	you're not using git, quilt <http://savannah.nongnu.org/projects/quilt>
81	is another popular alternative.
82	
83	
84	
85	2) Describe your changes.
86	
87	Describe the technical detail of the change(s) your patch includes.
88	
89	Be as specific as possible.  The WORST descriptions possible include
90	things like "update driver X", "bug fix for driver X", or "this patch
91	includes updates for subsystem X.  Please apply."
92	
93	The maintainer will thank you if you write your patch description in a
94	form which can be easily pulled into Linux's source code management
95	system, git, as a "commit log".  See #15, below.
96	
97	If your description starts to get long, that's a sign that you probably
98	need to split up your patch.  See #3, next.
99	
100	When you submit or resubmit a patch or patch series, include the
101	complete patch description and justification for it.  Don't just
102	say that this is version N of the patch (series).  Don't expect the
103	patch merger to refer back to earlier patch versions or referenced
104	URLs to find the patch description and put that into the patch.
105	I.e., the patch (series) and its description should be self-contained.
106	This benefits both the patch merger(s) and reviewers.  Some reviewers
107	probably didn't even receive earlier versions of the patch.
108	
109	Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
110	instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
111	to do frotz", as if you are giving orders to the codebase to change
112	its behaviour.
113	
114	If the patch fixes a logged bug entry, refer to that bug entry by
115	number and URL.  If the patch follows from a mailing list discussion,
116	give a URL to the mailing list archive; use the https://lkml.kernel.org/
117	redirector with a Message-Id, to ensure that the links cannot become
118	stale.
119	
120	However, try to make your explanation understandable without external
121	resources.  In addition to giving a URL to a mailing list archive or
122	bug, summarize the relevant points of the discussion that led to the
123	patch as submitted.
124	
125	If you want to refer to a specific commit, don't just refer to the
126	SHA-1 ID of the commit. Please also include the oneline summary of
127	the commit, to make it easier for reviewers to know what it is about.
128	Example:
129	
130		Commit e21d2170f36602ae2708 ("video: remove unnecessary
131		platform_set_drvdata()") removed the unnecessary
132		platform_set_drvdata(), but left the variable "dev" unused,
133		delete it.
134	
135	If your patch fixes a bug in a specific commit, e.g. you found an issue using
136	git-bisect, please use the 'Fixes:' tag with the first 12 characters of the
137	SHA-1 ID, and the one line summary.
138	Example:
139	
140		Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
141	
142	The following git-config settings can be used to add a pretty format for
143	outputting the above style in the git log or git show commands
144	
145		[core]
146			abbrev = 12
147		[pretty]
148			fixes = Fixes: %h (\"%s\")
149	
150	3) Separate your changes.
151	
152	Separate _logical changes_ into a single patch file.
153	
154	For example, if your changes include both bug fixes and performance
155	enhancements for a single driver, separate those changes into two
156	or more patches.  If your changes include an API update, and a new
157	driver which uses that new API, separate those into two patches.
158	
159	On the other hand, if you make a single change to numerous files,
160	group those changes into a single patch.  Thus a single logical change
161	is contained within a single patch.
162	
163	If one patch depends on another patch in order for a change to be
164	complete, that is OK.  Simply note "this patch depends on patch X"
165	in your patch description.
166	
167	If you cannot condense your patch set into a smaller set of patches,
168	then only post say 15 or so at a time and wait for review and integration.
169	
170	
171	
172	4) Style check your changes.
173	
174	Check your patch for basic style violations, details of which can be
175	found in Documentation/CodingStyle.  Failure to do so simply wastes
176	the reviewers time and will get your patch rejected, probably
177	without even being read.
178	
179	At a minimum you should check your patches with the patch style
180	checker prior to submission (scripts/checkpatch.pl).  You should
181	be able to justify all violations that remain in your patch.
182	
183	
184	
185	5) Select e-mail destination.
186	
187	Look through the MAINTAINERS file and the source code, and determine
188	if your change applies to a specific subsystem of the kernel, with
189	an assigned maintainer.  If so, e-mail that person.  The script
190	scripts/get_maintainer.pl can be very useful at this step.
191	
192	If no maintainer is listed, or the maintainer does not respond, send
193	your patch to the primary Linux kernel developer's mailing list,
194	linux-kernel@vger.kernel.org.  Most kernel developers monitor this
195	e-mail list, and can comment on your changes.
196	
197	
198	Do not send more than 15 patches at once to the vger mailing lists!!!
199	
200	
201	Linus Torvalds is the final arbiter of all changes accepted into the
202	Linux kernel.  His e-mail address is <torvalds@linux-foundation.org>. 
203	He gets a lot of e-mail, so typically you should do your best to -avoid-
204	sending him e-mail. 
205	
206	Patches which are bug fixes, are "obvious" changes, or similarly
207	require little discussion should be sent or CC'd to Linus.  Patches
208	which require discussion or do not have a clear advantage should
209	usually be sent first to linux-kernel.  Only after the patch is
210	discussed should the patch then be submitted to Linus.
211	
212	
213	
214	6) Select your CC (e-mail carbon copy) list.
215	
216	Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
217	
218	Other kernel developers besides Linus need to be aware of your change,
219	so that they may comment on it and offer code review and suggestions.
220	linux-kernel is the primary Linux kernel developer mailing list.
221	Other mailing lists are available for specific subsystems, such as
222	USB, framebuffer devices, the VFS, the SCSI subsystem, etc.  See the
223	MAINTAINERS file for a mailing list that relates specifically to
224	your change.
225	
226	Majordomo lists of VGER.KERNEL.ORG at:
227		<http://vger.kernel.org/vger-lists.html>
228	
229	If changes affect userland-kernel interfaces, please send
230	the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
231	a man-pages patch, or at least a notification of the change,
232	so that some information makes its way into the manual pages.
233	
234	Even if the maintainer did not respond in step #5, make sure to ALWAYS
235	copy the maintainer when you change their code.
236	
237	For small patches you may want to CC the Trivial Patch Monkey
238	trivial@kernel.org which collects "trivial" patches. Have a look
239	into the MAINTAINERS file for its current manager.
240	Trivial patches must qualify for one of the following rules:
241	 Spelling fixes in documentation
242	 Spelling fixes which could break grep(1)
243	 Warning fixes (cluttering with useless warnings is bad)
244	 Compilation fixes (only if they are actually correct)
245	 Runtime fixes (only if they actually fix things)
246	 Removing use of deprecated functions/macros (eg. check_region)
247	 Contact detail and documentation fixes
248	 Non-portable code replaced by portable code (even in arch-specific,
249	 since people copy, as long as it's trivial)
250	 Any fix by the author/maintainer of the file (ie. patch monkey
251	 in re-transmission mode)
252	
253	
254	
255	7) No MIME, no links, no compression, no attachments.  Just plain text.
256	
257	Linus and other kernel developers need to be able to read and comment
258	on the changes you are submitting.  It is important for a kernel
259	developer to be able to "quote" your changes, using standard e-mail
260	tools, so that they may comment on specific portions of your code.
261	
262	For this reason, all patches should be submitting e-mail "inline".
263	WARNING:  Be wary of your editor's word-wrap corrupting your patch,
264	if you choose to cut-n-paste your patch.
265	
266	Do not attach the patch as a MIME attachment, compressed or not.
267	Many popular e-mail applications will not always transmit a MIME
268	attachment as plain text, making it impossible to comment on your
269	code.  A MIME attachment also takes Linus a bit more time to process,
270	decreasing the likelihood of your MIME-attached change being accepted.
271	
272	Exception:  If your mailer is mangling patches then someone may ask
273	you to re-send them using MIME.
274	
275	See Documentation/email-clients.txt for hints about configuring
276	your e-mail client so that it sends your patches untouched.
277	
278	8) E-mail size.
279	
280	When sending patches to Linus, always follow step #7.
281	
282	Large changes are not appropriate for mailing lists, and some
283	maintainers.  If your patch, uncompressed, exceeds 300 kB in size,
284	it is preferred that you store your patch on an Internet-accessible
285	server, and provide instead a URL (link) pointing to your patch.
286	
287	
288	
289	9) Name your kernel version.
290	
291	It is important to note, either in the subject line or in the patch
292	description, the kernel version to which this patch applies.
293	
294	If the patch does not apply cleanly to the latest kernel version,
295	Linus will not apply it.
296	
297	
298	
299	10) Don't get discouraged.  Re-submit.
300	
301	After you have submitted your change, be patient and wait.  If Linus
302	likes your change and applies it, it will appear in the next version
303	of the kernel that he releases.
304	
305	However, if your change doesn't appear in the next version of the
306	kernel, there could be any number of reasons.  It's YOUR job to
307	narrow down those reasons, correct what was wrong, and submit your
308	updated change.
309	
310	It is quite common for Linus to "drop" your patch without comment.
311	That's the nature of the system.  If he drops your patch, it could be
312	due to
313	* Your patch did not apply cleanly to the latest kernel version.
314	* Your patch was not sufficiently discussed on linux-kernel.
315	* A style issue (see section 2).
316	* An e-mail formatting issue (re-read this section).
317	* A technical problem with your change.
318	* He gets tons of e-mail, and yours got lost in the shuffle.
319	* You are being annoying.
320	
321	When in doubt, solicit comments on linux-kernel mailing list.
322	
323	
324	
325	11) Include PATCH in the subject
326	
327	Due to high e-mail traffic to Linus, and to linux-kernel, it is common
328	convention to prefix your subject line with [PATCH].  This lets Linus
329	and other kernel developers more easily distinguish patches from other
330	e-mail discussions.
331	
332	
333	
334	12) Sign your work
335	
336	To improve tracking of who did what, especially with patches that can
337	percolate to their final resting place in the kernel through several
338	layers of maintainers, we've introduced a "sign-off" procedure on
339	patches that are being emailed around.
340	
341	The sign-off is a simple line at the end of the explanation for the
342	patch, which certifies that you wrote it or otherwise have the right to
343	pass it on as an open-source patch.  The rules are pretty simple: if you
344	can certify the below:
345	
346	        Developer's Certificate of Origin 1.1
347	
348	        By making a contribution to this project, I certify that:
349	
350	        (a) The contribution was created in whole or in part by me and I
351	            have the right to submit it under the open source license
352	            indicated in the file; or
353	
354	        (b) The contribution is based upon previous work that, to the best
355	            of my knowledge, is covered under an appropriate open source
356	            license and I have the right under that license to submit that
357	            work with modifications, whether created in whole or in part
358	            by me, under the same open source license (unless I am
359	            permitted to submit under a different license), as indicated
360	            in the file; or
361	
362	        (c) The contribution was provided directly to me by some other
363	            person who certified (a), (b) or (c) and I have not modified
364	            it.
365	
366		(d) I understand and agree that this project and the contribution
367		    are public and that a record of the contribution (including all
368		    personal information I submit with it, including my sign-off) is
369		    maintained indefinitely and may be redistributed consistent with
370		    this project or the open source license(s) involved.
371	
372	then you just add a line saying
373	
374		Signed-off-by: Random J Developer <random@developer.example.org>
375	
376	using your real name (sorry, no pseudonyms or anonymous contributions.)
377	
378	Some people also put extra tags at the end.  They'll just be ignored for
379	now, but you can do this to mark internal company procedures or just
380	point out some special detail about the sign-off. 
381	
382	If you are a subsystem or branch maintainer, sometimes you need to slightly
383	modify patches you receive in order to merge them, because the code is not
384	exactly the same in your tree and the submitters'. If you stick strictly to
385	rule (c), you should ask the submitter to rediff, but this is a totally
386	counter-productive waste of time and energy. Rule (b) allows you to adjust
387	the code, but then it is very impolite to change one submitter's code and
388	make him endorse your bugs. To solve this problem, it is recommended that
389	you add a line between the last Signed-off-by header and yours, indicating
390	the nature of your changes. While there is nothing mandatory about this, it
391	seems like prepending the description with your mail and/or name, all
392	enclosed in square brackets, is noticeable enough to make it obvious that
393	you are responsible for last-minute changes. Example :
394	
395		Signed-off-by: Random J Developer <random@developer.example.org>
396		[lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
397		Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
398	
399	This practise is particularly helpful if you maintain a stable branch and
400	want at the same time to credit the author, track changes, merge the fix,
401	and protect the submitter from complaints. Note that under no circumstances
402	can you change the author's identity (the From header), as it is the one
403	which appears in the changelog.
404	
405	Special note to back-porters: It seems to be a common and useful practise
406	to insert an indication of the origin of a patch at the top of the commit
407	message (just after the subject line) to facilitate tracking. For instance,
408	here's what we see in 2.6-stable :
409	
410	    Date:   Tue May 13 19:10:30 2008 +0000
411	
412	        SCSI: libiscsi regression in 2.6.25: fix nop timer handling
413	
414	        commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
415	
416	And here's what appears in 2.4 :
417	
418	    Date:   Tue May 13 22:12:27 2008 +0200
419	
420	        wireless, airo: waitbusy() won't delay
421	
422	        [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
423	
424	Whatever the format, this information provides a valuable help to people
425	tracking your trees, and to people trying to trouble-shoot bugs in your
426	tree.
427	
428	
429	13) When to use Acked-by: and Cc:
430	
431	The Signed-off-by: tag indicates that the signer was involved in the
432	development of the patch, or that he/she was in the patch's delivery path.
433	
434	If a person was not directly involved in the preparation or handling of a
435	patch but wishes to signify and record their approval of it then they can
436	arrange to have an Acked-by: line added to the patch's changelog.
437	
438	Acked-by: is often used by the maintainer of the affected code when that
439	maintainer neither contributed to nor forwarded the patch.
440	
441	Acked-by: is not as formal as Signed-off-by:.  It is a record that the acker
442	has at least reviewed the patch and has indicated acceptance.  Hence patch
443	mergers will sometimes manually convert an acker's "yep, looks good to me"
444	into an Acked-by:.
445	
446	Acked-by: does not necessarily indicate acknowledgement of the entire patch.
447	For example, if a patch affects multiple subsystems and has an Acked-by: from
448	one subsystem maintainer then this usually indicates acknowledgement of just
449	the part which affects that maintainer's code.  Judgement should be used here.
450	When in doubt people should refer to the original discussion in the mailing
451	list archives.
452	
453	If a person has had the opportunity to comment on a patch, but has not
454	provided such comments, you may optionally add a "Cc:" tag to the patch.
455	This is the only tag which might be added without an explicit action by the
456	person it names.  This tag documents that potentially interested parties
457	have been included in the discussion
458	
459	
460	14) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
461	
462	If this patch fixes a problem reported by somebody else, consider adding a
463	Reported-by: tag to credit the reporter for their contribution.  Please
464	note that this tag should not be added without the reporter's permission,
465	especially if the problem was not reported in a public forum.  That said,
466	if we diligently credit our bug reporters, they will, hopefully, be
467	inspired to help us again in the future.
468	
469	A Tested-by: tag indicates that the patch has been successfully tested (in
470	some environment) by the person named.  This tag informs maintainers that
471	some testing has been performed, provides a means to locate testers for
472	future patches, and ensures credit for the testers.
473	
474	Reviewed-by:, instead, indicates that the patch has been reviewed and found
475	acceptable according to the Reviewer's Statement:
476	
477		Reviewer's statement of oversight
478	
479		By offering my Reviewed-by: tag, I state that:
480	
481	 	 (a) I have carried out a technical review of this patch to
482		     evaluate its appropriateness and readiness for inclusion into
483		     the mainline kernel.
484	
485		 (b) Any problems, concerns, or questions relating to the patch
486		     have been communicated back to the submitter.  I am satisfied
487		     with the submitter's response to my comments.
488	
489		 (c) While there may be things that could be improved with this
490		     submission, I believe that it is, at this time, (1) a
491		     worthwhile modification to the kernel, and (2) free of known
492		     issues which would argue against its inclusion.
493	
494		 (d) While I have reviewed the patch and believe it to be sound, I
495		     do not (unless explicitly stated elsewhere) make any
496		     warranties or guarantees that it will achieve its stated
497		     purpose or function properly in any given situation.
498	
499	A Reviewed-by tag is a statement of opinion that the patch is an
500	appropriate modification of the kernel without any remaining serious
501	technical issues.  Any interested reviewer (who has done the work) can
502	offer a Reviewed-by tag for a patch.  This tag serves to give credit to
503	reviewers and to inform maintainers of the degree of review which has been
504	done on the patch.  Reviewed-by: tags, when supplied by reviewers known to
505	understand the subject area and to perform thorough reviews, will normally
506	increase the likelihood of your patch getting into the kernel.
507	
508	A Suggested-by: tag indicates that the patch idea is suggested by the person
509	named and ensures credit to the person for the idea. Please note that this
510	tag should not be added without the reporter's permission, especially if the
511	idea was not posted in a public forum. That said, if we diligently credit our
512	idea reporters, they will, hopefully, be inspired to help us again in the
513	future.
514	
515	A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
516	is used to make it easy to determine where a bug originated, which can help
517	review a bug fix. This tag also assists the stable kernel team in determining
518	which stable kernel versions should receive your fix. This is the preferred
519	method for indicating a bug fixed by the patch. See #2 above for more details.
520	
521	
522	15) The canonical patch format
523	
524	The canonical patch subject line is:
525	
526	    Subject: [PATCH 001/123] subsystem: summary phrase
527	
528	The canonical patch message body contains the following:
529	
530	  - A "from" line specifying the patch author.
531	
532	  - An empty line.
533	
534	  - The body of the explanation, which will be copied to the
535	    permanent changelog to describe this patch.
536	
537	  - The "Signed-off-by:" lines, described above, which will
538	    also go in the changelog.
539	
540	  - A marker line containing simply "---".
541	
542	  - Any additional comments not suitable for the changelog.
543	
544	  - The actual patch (diff output).
545	
546	The Subject line format makes it very easy to sort the emails
547	alphabetically by subject line - pretty much any email reader will
548	support that - since because the sequence number is zero-padded,
549	the numerical and alphabetic sort is the same.
550	
551	The "subsystem" in the email's Subject should identify which
552	area or subsystem of the kernel is being patched.
553	
554	The "summary phrase" in the email's Subject should concisely
555	describe the patch which that email contains.  The "summary
556	phrase" should not be a filename.  Do not use the same "summary
557	phrase" for every patch in a whole patch series (where a "patch
558	series" is an ordered sequence of multiple, related patches).
559	
560	Bear in mind that the "summary phrase" of your email becomes a
561	globally-unique identifier for that patch.  It propagates all the way
562	into the git changelog.  The "summary phrase" may later be used in
563	developer discussions which refer to the patch.  People will want to
564	google for the "summary phrase" to read discussion regarding that
565	patch.  It will also be the only thing that people may quickly see
566	when, two or three months later, they are going through perhaps
567	thousands of patches using tools such as "gitk" or "git log
568	--oneline".
569	
570	For these reasons, the "summary" must be no more than 70-75
571	characters, and it must describe both what the patch changes, as well
572	as why the patch might be necessary.  It is challenging to be both
573	succinct and descriptive, but that is what a well-written summary
574	should do.
575	
576	The "summary phrase" may be prefixed by tags enclosed in square
577	brackets: "Subject: [PATCH tag] <summary phrase>".  The tags are not
578	considered part of the summary phrase, but describe how the patch
579	should be treated.  Common tags might include a version descriptor if
580	the multiple versions of the patch have been sent out in response to
581	comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
582	comments.  If there are four patches in a patch series the individual
583	patches may be numbered like this: 1/4, 2/4, 3/4, 4/4.  This assures
584	that developers understand the order in which the patches should be
585	applied and that they have reviewed or applied all of the patches in
586	the patch series.
587	
588	A couple of example Subjects:
589	
590	    Subject: [patch 2/5] ext2: improve scalability of bitmap searching
591	    Subject: [PATCHv2 001/207] x86: fix eflags tracking
592	
593	The "from" line must be the very first line in the message body,
594	and has the form:
595	
596	        From: Original Author <author@example.com>
597	
598	The "from" line specifies who will be credited as the author of the
599	patch in the permanent changelog.  If the "from" line is missing,
600	then the "From:" line from the email header will be used to determine
601	the patch author in the changelog.
602	
603	The explanation body will be committed to the permanent source
604	changelog, so should make sense to a competent reader who has long
605	since forgotten the immediate details of the discussion that might
606	have led to this patch.  Including symptoms of the failure which the
607	patch addresses (kernel log messages, oops messages, etc.) is
608	especially useful for people who might be searching the commit logs
609	looking for the applicable patch.  If a patch fixes a compile failure,
610	it may not be necessary to include _all_ of the compile failures; just
611	enough that it is likely that someone searching for the patch can find
612	it.  As in the "summary phrase", it is important to be both succinct as
613	well as descriptive.
614	
615	The "---" marker line serves the essential purpose of marking for patch
616	handling tools where the changelog message ends.
617	
618	One good use for the additional comments after the "---" marker is for
619	a diffstat, to show what files have changed, and the number of
620	inserted and deleted lines per file.  A diffstat is especially useful
621	on bigger patches.  Other comments relevant only to the moment or the
622	maintainer, not suitable for the permanent changelog, should also go
623	here.  A good example of such comments might be "patch changelogs"
624	which describe what has changed between the v1 and v2 version of the
625	patch.
626	
627	If you are going to include a diffstat after the "---" marker, please
628	use diffstat options "-p 1 -w 70" so that filenames are listed from
629	the top of the kernel source tree and don't use too much horizontal
630	space (easily fit in 80 columns, maybe with some indentation).  (git
631	generates appropriate diffstats by default.)
632	
633	See more details on the proper patch format in the following
634	references.
635	
636	
637	16) Sending "git pull" requests  (from Linus emails)
638	
639	Please write the git repo address and branch name alone on the same line
640	so that I can't even by mistake pull from the wrong branch, and so
641	that a triple-click just selects the whole thing.
642	
643	So the proper format is something along the lines of:
644	
645		"Please pull from
646	
647			git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
648	
649		 to get these changes:"
650	
651	so that I don't have to hunt-and-peck for the address and inevitably
652	get it wrong (actually, I've only gotten it wrong a few times, and
653	checking against the diffstat tells me when I get it wrong, but I'm
654	just a lot more comfortable when I don't have to "look for" the right
655	thing to pull, and double-check that I have the right branch-name).
656	
657	
658	Please use "git diff -M --stat --summary" to generate the diffstat:
659	the -M enables rename detection, and the summary enables a summary of
660	new/deleted or renamed files.
661	
662	With rename detection, the statistics are rather different [...]
663	because git will notice that a fair number of the changes are renames.
664	
665	-----------------------------------
666	SECTION 2 - HINTS, TIPS, AND TRICKS
667	-----------------------------------
668	
669	This section lists many of the common "rules" associated with code
670	submitted to the kernel.  There are always exceptions... but you must
671	have a really good reason for doing so.  You could probably call this
672	section Linus Computer Science 101.
673	
674	
675	
676	1) Read Documentation/CodingStyle
677	
678	Nuff said.  If your code deviates too much from this, it is likely
679	to be rejected without further review, and without comment.
680	
681	One significant exception is when moving code from one file to
682	another -- in this case you should not modify the moved code at all in
683	the same patch which moves it.  This clearly delineates the act of
684	moving the code and your changes.  This greatly aids review of the
685	actual differences and allows tools to better track the history of
686	the code itself.
687	
688	Check your patches with the patch style checker prior to submission
689	(scripts/checkpatch.pl).  The style checker should be viewed as
690	a guide not as the final word.  If your code looks better with
691	a violation then its probably best left alone.
692	
693	The checker reports at three levels:
694	 - ERROR: things that are very likely to be wrong
695	 - WARNING: things requiring careful review
696	 - CHECK: things requiring thought
697	
698	You should be able to justify all violations that remain in your
699	patch.
700	
701	
702	
703	2) #ifdefs are ugly
704	
705	Code cluttered with ifdefs is difficult to read and maintain.  Don't do
706	it.  Instead, put your ifdefs in a header, and conditionally define
707	'static inline' functions, or macros, which are used in the code.
708	Let the compiler optimize away the "no-op" case.
709	
710	Simple example, of poor code:
711	
712		dev = alloc_etherdev (sizeof(struct funky_private));
713		if (!dev)
714			return -ENODEV;
715		#ifdef CONFIG_NET_FUNKINESS
716		init_funky_net(dev);
717		#endif
718	
719	Cleaned-up example:
720	
721	(in header)
722		#ifndef CONFIG_NET_FUNKINESS
723		static inline void init_funky_net (struct net_device *d) {}
724		#endif
725	
726	(in the code itself)
727		dev = alloc_etherdev (sizeof(struct funky_private));
728		if (!dev)
729			return -ENODEV;
730		init_funky_net(dev);
731	
732	
733	
734	3) 'static inline' is better than a macro
735	
736	Static inline functions are greatly preferred over macros.
737	They provide type safety, have no length limitations, no formatting
738	limitations, and under gcc they are as cheap as macros.
739	
740	Macros should only be used for cases where a static inline is clearly
741	suboptimal [there are a few, isolated cases of this in fast paths],
742	or where it is impossible to use a static inline function [such as
743	string-izing].
744	
745	'static inline' is preferred over 'static __inline__', 'extern inline',
746	and 'extern __inline__'.
747	
748	
749	
750	4) Don't over-design.
751	
752	Don't try to anticipate nebulous future cases which may or may not
753	be useful:  "Make it as simple as you can, and no simpler."
754	
755	
756	
757	----------------------
758	SECTION 3 - REFERENCES
759	----------------------
760	
761	Andrew Morton, "The perfect patch" (tpp).
762	  <http://www.ozlabs.org/~akpm/stuff/tpp.txt>
763	
764	Jeff Garzik, "Linux kernel patch submission format".
765	  <http://linux.yyz.us/patch-format.html>
766	
767	Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
768	  <http://www.kroah.com/log/linux/maintainer.html>
769	  <http://www.kroah.com/log/linux/maintainer-02.html>
770	  <http://www.kroah.com/log/linux/maintainer-03.html>
771	  <http://www.kroah.com/log/linux/maintainer-04.html>
772	  <http://www.kroah.com/log/linux/maintainer-05.html>
773	
774	NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
775	  <https://lkml.org/lkml/2005/7/11/336>
776	
777	Kernel Documentation/CodingStyle:
778	  <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
779	
780	Linus Torvalds's mail on the canonical patch format:
781	  <http://lkml.org/lkml/2005/4/7/183>
782	
783	Andi Kleen, "On submitting kernel patches"
784	  Some strategies to get difficult or controversial changes in.
785	  http://halobates.de/on-submitting-patches.pdf
786	
787	--
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