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Based on kernel version 3.19. Page generated on 2015-02-13 21:22 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 your problem.  Whether your patch is a one-line bug fix or
88	5000 lines of a new feature, there must be an underlying problem that
89	motivated you to do this work.  Convince the reviewer that there is a
90	problem worth fixing and that it makes sense for them to read past the
91	first paragraph.
92	
93	Describe user-visible impact.  Straight up crashes and lockups are
94	pretty convincing, but not all bugs are that blatant.  Even if the
95	problem was spotted during code review, describe the impact you think
96	it can have on users.  Keep in mind that the majority of Linux
97	installations run kernels from secondary stable trees or
98	vendor/product-specific trees that cherry-pick only specific patches
99	from upstream, so include anything that could help route your change
100	downstream: provoking circumstances, excerpts from dmesg, crash
101	descriptions, performance regressions, latency spikes, lockups, etc.
102	
103	Quantify optimizations and trade-offs.  If you claim improvements in
104	performance, memory consumption, stack footprint, or binary size,
105	include numbers that back them up.  But also describe non-obvious
106	costs.  Optimizations usually aren't free but trade-offs between CPU,
107	memory, and readability; or, when it comes to heuristics, between
108	different workloads.  Describe the expected downsides of your
109	optimization so that the reviewer can weigh costs against benefits.
110	
111	Once the problem is established, describe what you are actually doing
112	about it in technical detail.  It's important to describe the change
113	in plain English for the reviewer to verify that the code is behaving
114	as you intend it to.
115	
116	The maintainer will thank you if you write your patch description in a
117	form which can be easily pulled into Linux's source code management
118	system, git, as a "commit log".  See #15, below.
119	
120	Solve only one problem per patch.  If your description starts to get
121	long, that's a sign that you probably need to split up your patch.
122	See #3, next.
123	
124	When you submit or resubmit a patch or patch series, include the
125	complete patch description and justification for it.  Don't just
126	say that this is version N of the patch (series).  Don't expect the
127	patch merger to refer back to earlier patch versions or referenced
128	URLs to find the patch description and put that into the patch.
129	I.e., the patch (series) and its description should be self-contained.
130	This benefits both the patch merger(s) and reviewers.  Some reviewers
131	probably didn't even receive earlier versions of the patch.
132	
133	Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
134	instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
135	to do frotz", as if you are giving orders to the codebase to change
136	its behaviour.
137	
138	If the patch fixes a logged bug entry, refer to that bug entry by
139	number and URL.  If the patch follows from a mailing list discussion,
140	give a URL to the mailing list archive; use the https://lkml.kernel.org/
141	redirector with a Message-Id, to ensure that the links cannot become
142	stale.
143	
144	However, try to make your explanation understandable without external
145	resources.  In addition to giving a URL to a mailing list archive or
146	bug, summarize the relevant points of the discussion that led to the
147	patch as submitted.
148	
149	If you want to refer to a specific commit, don't just refer to the
150	SHA-1 ID of the commit. Please also include the oneline summary of
151	the commit, to make it easier for reviewers to know what it is about.
152	Example:
153	
154		Commit e21d2170f36602ae2708 ("video: remove unnecessary
155		platform_set_drvdata()") removed the unnecessary
156		platform_set_drvdata(), but left the variable "dev" unused,
157		delete it.
158	
159	If your patch fixes a bug in a specific commit, e.g. you found an issue using
160	git-bisect, please use the 'Fixes:' tag with the first 12 characters of the
161	SHA-1 ID, and the one line summary.
162	Example:
163	
164		Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
165	
166	The following git-config settings can be used to add a pretty format for
167	outputting the above style in the git log or git show commands
168	
169		[core]
170			abbrev = 12
171		[pretty]
172			fixes = Fixes: %h (\"%s\")
173	
174	3) Separate your changes.
175	
176	Separate _logical changes_ into a single patch file.
177	
178	For example, if your changes include both bug fixes and performance
179	enhancements for a single driver, separate those changes into two
180	or more patches.  If your changes include an API update, and a new
181	driver which uses that new API, separate those into two patches.
182	
183	On the other hand, if you make a single change to numerous files,
184	group those changes into a single patch.  Thus a single logical change
185	is contained within a single patch.
186	
187	If one patch depends on another patch in order for a change to be
188	complete, that is OK.  Simply note "this patch depends on patch X"
189	in your patch description.
190	
191	If you cannot condense your patch set into a smaller set of patches,
192	then only post say 15 or so at a time and wait for review and integration.
193	
194	
195	
196	4) Style check your changes.
197	
198	Check your patch for basic style violations, details of which can be
199	found in Documentation/CodingStyle.  Failure to do so simply wastes
200	the reviewers time and will get your patch rejected, probably
201	without even being read.
202	
203	At a minimum you should check your patches with the patch style
204	checker prior to submission (scripts/checkpatch.pl).  You should
205	be able to justify all violations that remain in your patch.
206	
207	
208	
209	5) Select e-mail destination.
210	
211	Look through the MAINTAINERS file and the source code, and determine
212	if your change applies to a specific subsystem of the kernel, with
213	an assigned maintainer.  If so, e-mail that person.  The script
214	scripts/get_maintainer.pl can be very useful at this step.
215	
216	If no maintainer is listed, or the maintainer does not respond, send
217	your patch to the primary Linux kernel developer's mailing list,
218	linux-kernel@vger.kernel.org.  Most kernel developers monitor this
219	e-mail list, and can comment on your changes.
220	
221	
222	Do not send more than 15 patches at once to the vger mailing lists!!!
223	
224	
225	Linus Torvalds is the final arbiter of all changes accepted into the
226	Linux kernel.  His e-mail address is <torvalds@linux-foundation.org>. 
227	He gets a lot of e-mail, so typically you should do your best to -avoid-
228	sending him e-mail. 
229	
230	Patches which are bug fixes, are "obvious" changes, or similarly
231	require little discussion should be sent or CC'd to Linus.  Patches
232	which require discussion or do not have a clear advantage should
233	usually be sent first to linux-kernel.  Only after the patch is
234	discussed should the patch then be submitted to Linus.
235	
236	
237	
238	6) Select your CC (e-mail carbon copy) list.
239	
240	Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
241	
242	Other kernel developers besides Linus need to be aware of your change,
243	so that they may comment on it and offer code review and suggestions.
244	linux-kernel is the primary Linux kernel developer mailing list.
245	Other mailing lists are available for specific subsystems, such as
246	USB, framebuffer devices, the VFS, the SCSI subsystem, etc.  See the
247	MAINTAINERS file for a mailing list that relates specifically to
248	your change.
249	
250	Majordomo lists of VGER.KERNEL.ORG at:
251		<http://vger.kernel.org/vger-lists.html>
252	
253	If changes affect userland-kernel interfaces, please send
254	the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
255	a man-pages patch, or at least a notification of the change,
256	so that some information makes its way into the manual pages.
257	
258	Even if the maintainer did not respond in step #5, make sure to ALWAYS
259	copy the maintainer when you change their code.
260	
261	For small patches you may want to CC the Trivial Patch Monkey
262	trivial@kernel.org which collects "trivial" patches. Have a look
263	into the MAINTAINERS file for its current manager.
264	Trivial patches must qualify for one of the following rules:
265	 Spelling fixes in documentation
266	 Spelling fixes which could break grep(1)
267	 Warning fixes (cluttering with useless warnings is bad)
268	 Compilation fixes (only if they are actually correct)
269	 Runtime fixes (only if they actually fix things)
270	 Removing use of deprecated functions/macros (eg. check_region)
271	 Contact detail and documentation fixes
272	 Non-portable code replaced by portable code (even in arch-specific,
273	 since people copy, as long as it's trivial)
274	 Any fix by the author/maintainer of the file (ie. patch monkey
275	 in re-transmission mode)
276	
277	
278	
279	7) No MIME, no links, no compression, no attachments.  Just plain text.
280	
281	Linus and other kernel developers need to be able to read and comment
282	on the changes you are submitting.  It is important for a kernel
283	developer to be able to "quote" your changes, using standard e-mail
284	tools, so that they may comment on specific portions of your code.
285	
286	For this reason, all patches should be submitting e-mail "inline".
287	WARNING:  Be wary of your editor's word-wrap corrupting your patch,
288	if you choose to cut-n-paste your patch.
289	
290	Do not attach the patch as a MIME attachment, compressed or not.
291	Many popular e-mail applications will not always transmit a MIME
292	attachment as plain text, making it impossible to comment on your
293	code.  A MIME attachment also takes Linus a bit more time to process,
294	decreasing the likelihood of your MIME-attached change being accepted.
295	
296	Exception:  If your mailer is mangling patches then someone may ask
297	you to re-send them using MIME.
298	
299	See Documentation/email-clients.txt for hints about configuring
300	your e-mail client so that it sends your patches untouched.
301	
302	8) E-mail size.
303	
304	When sending patches to Linus, always follow step #7.
305	
306	Large changes are not appropriate for mailing lists, and some
307	maintainers.  If your patch, uncompressed, exceeds 300 kB in size,
308	it is preferred that you store your patch on an Internet-accessible
309	server, and provide instead a URL (link) pointing to your patch.
310	
311	
312	
313	9) Name your kernel version.
314	
315	It is important to note, either in the subject line or in the patch
316	description, the kernel version to which this patch applies.
317	
318	If the patch does not apply cleanly to the latest kernel version,
319	Linus will not apply it.
320	
321	
322	
323	10) Don't get discouraged.  Re-submit.
324	
325	After you have submitted your change, be patient and wait.  If Linus
326	likes your change and applies it, it will appear in the next version
327	of the kernel that he releases.
328	
329	However, if your change doesn't appear in the next version of the
330	kernel, there could be any number of reasons.  It's YOUR job to
331	narrow down those reasons, correct what was wrong, and submit your
332	updated change.
333	
334	It is quite common for Linus to "drop" your patch without comment.
335	That's the nature of the system.  If he drops your patch, it could be
336	due to
337	* Your patch did not apply cleanly to the latest kernel version.
338	* Your patch was not sufficiently discussed on linux-kernel.
339	* A style issue (see section 2).
340	* An e-mail formatting issue (re-read this section).
341	* A technical problem with your change.
342	* He gets tons of e-mail, and yours got lost in the shuffle.
343	* You are being annoying.
344	
345	When in doubt, solicit comments on linux-kernel mailing list.
346	
347	
348	
349	11) Include PATCH in the subject
350	
351	Due to high e-mail traffic to Linus, and to linux-kernel, it is common
352	convention to prefix your subject line with [PATCH].  This lets Linus
353	and other kernel developers more easily distinguish patches from other
354	e-mail discussions.
355	
356	
357	
358	12) Sign your work
359	
360	To improve tracking of who did what, especially with patches that can
361	percolate to their final resting place in the kernel through several
362	layers of maintainers, we've introduced a "sign-off" procedure on
363	patches that are being emailed around.
364	
365	The sign-off is a simple line at the end of the explanation for the
366	patch, which certifies that you wrote it or otherwise have the right to
367	pass it on as an open-source patch.  The rules are pretty simple: if you
368	can certify the below:
369	
370	        Developer's Certificate of Origin 1.1
371	
372	        By making a contribution to this project, I certify that:
373	
374	        (a) The contribution was created in whole or in part by me and I
375	            have the right to submit it under the open source license
376	            indicated in the file; or
377	
378	        (b) The contribution is based upon previous work that, to the best
379	            of my knowledge, is covered under an appropriate open source
380	            license and I have the right under that license to submit that
381	            work with modifications, whether created in whole or in part
382	            by me, under the same open source license (unless I am
383	            permitted to submit under a different license), as indicated
384	            in the file; or
385	
386	        (c) The contribution was provided directly to me by some other
387	            person who certified (a), (b) or (c) and I have not modified
388	            it.
389	
390		(d) I understand and agree that this project and the contribution
391		    are public and that a record of the contribution (including all
392		    personal information I submit with it, including my sign-off) is
393		    maintained indefinitely and may be redistributed consistent with
394		    this project or the open source license(s) involved.
395	
396	then you just add a line saying
397	
398		Signed-off-by: Random J Developer <random@developer.example.org>
399	
400	using your real name (sorry, no pseudonyms or anonymous contributions.)
401	
402	Some people also put extra tags at the end.  They'll just be ignored for
403	now, but you can do this to mark internal company procedures or just
404	point out some special detail about the sign-off. 
405	
406	If you are a subsystem or branch maintainer, sometimes you need to slightly
407	modify patches you receive in order to merge them, because the code is not
408	exactly the same in your tree and the submitters'. If you stick strictly to
409	rule (c), you should ask the submitter to rediff, but this is a totally
410	counter-productive waste of time and energy. Rule (b) allows you to adjust
411	the code, but then it is very impolite to change one submitter's code and
412	make him endorse your bugs. To solve this problem, it is recommended that
413	you add a line between the last Signed-off-by header and yours, indicating
414	the nature of your changes. While there is nothing mandatory about this, it
415	seems like prepending the description with your mail and/or name, all
416	enclosed in square brackets, is noticeable enough to make it obvious that
417	you are responsible for last-minute changes. Example :
418	
419		Signed-off-by: Random J Developer <random@developer.example.org>
420		[lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
421		Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
422	
423	This practice is particularly helpful if you maintain a stable branch and
424	want at the same time to credit the author, track changes, merge the fix,
425	and protect the submitter from complaints. Note that under no circumstances
426	can you change the author's identity (the From header), as it is the one
427	which appears in the changelog.
428	
429	Special note to back-porters: It seems to be a common and useful practice
430	to insert an indication of the origin of a patch at the top of the commit
431	message (just after the subject line) to facilitate tracking. For instance,
432	here's what we see in 2.6-stable :
433	
434	    Date:   Tue May 13 19:10:30 2008 +0000
435	
436	        SCSI: libiscsi regression in 2.6.25: fix nop timer handling
437	
438	        commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
439	
440	And here's what appears in 2.4 :
441	
442	    Date:   Tue May 13 22:12:27 2008 +0200
443	
444	        wireless, airo: waitbusy() won't delay
445	
446	        [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
447	
448	Whatever the format, this information provides a valuable help to people
449	tracking your trees, and to people trying to trouble-shoot bugs in your
450	tree.
451	
452	
453	13) When to use Acked-by: and Cc:
454	
455	The Signed-off-by: tag indicates that the signer was involved in the
456	development of the patch, or that he/she was in the patch's delivery path.
457	
458	If a person was not directly involved in the preparation or handling of a
459	patch but wishes to signify and record their approval of it then they can
460	arrange to have an Acked-by: line added to the patch's changelog.
461	
462	Acked-by: is often used by the maintainer of the affected code when that
463	maintainer neither contributed to nor forwarded the patch.
464	
465	Acked-by: is not as formal as Signed-off-by:.  It is a record that the acker
466	has at least reviewed the patch and has indicated acceptance.  Hence patch
467	mergers will sometimes manually convert an acker's "yep, looks good to me"
468	into an Acked-by:.
469	
470	Acked-by: does not necessarily indicate acknowledgement of the entire patch.
471	For example, if a patch affects multiple subsystems and has an Acked-by: from
472	one subsystem maintainer then this usually indicates acknowledgement of just
473	the part which affects that maintainer's code.  Judgement should be used here.
474	When in doubt people should refer to the original discussion in the mailing
475	list archives.
476	
477	If a person has had the opportunity to comment on a patch, but has not
478	provided such comments, you may optionally add a "Cc:" tag to the patch.
479	This is the only tag which might be added without an explicit action by the
480	person it names.  This tag documents that potentially interested parties
481	have been included in the discussion
482	
483	
484	14) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
485	
486	The Reported-by tag gives credit to people who find bugs and report them and it
487	hopefully inspires them to help us again in the future.  Please note that if
488	the bug was reported in private, then ask for permission first before using the
489	Reported-by tag.
490	
491	A Tested-by: tag indicates that the patch has been successfully tested (in
492	some environment) by the person named.  This tag informs maintainers that
493	some testing has been performed, provides a means to locate testers for
494	future patches, and ensures credit for the testers.
495	
496	Reviewed-by:, instead, indicates that the patch has been reviewed and found
497	acceptable according to the Reviewer's Statement:
498	
499		Reviewer's statement of oversight
500	
501		By offering my Reviewed-by: tag, I state that:
502	
503	 	 (a) I have carried out a technical review of this patch to
504		     evaluate its appropriateness and readiness for inclusion into
505		     the mainline kernel.
506	
507		 (b) Any problems, concerns, or questions relating to the patch
508		     have been communicated back to the submitter.  I am satisfied
509		     with the submitter's response to my comments.
510	
511		 (c) While there may be things that could be improved with this
512		     submission, I believe that it is, at this time, (1) a
513		     worthwhile modification to the kernel, and (2) free of known
514		     issues which would argue against its inclusion.
515	
516		 (d) While I have reviewed the patch and believe it to be sound, I
517		     do not (unless explicitly stated elsewhere) make any
518		     warranties or guarantees that it will achieve its stated
519		     purpose or function properly in any given situation.
520	
521	A Reviewed-by tag is a statement of opinion that the patch is an
522	appropriate modification of the kernel without any remaining serious
523	technical issues.  Any interested reviewer (who has done the work) can
524	offer a Reviewed-by tag for a patch.  This tag serves to give credit to
525	reviewers and to inform maintainers of the degree of review which has been
526	done on the patch.  Reviewed-by: tags, when supplied by reviewers known to
527	understand the subject area and to perform thorough reviews, will normally
528	increase the likelihood of your patch getting into the kernel.
529	
530	A Suggested-by: tag indicates that the patch idea is suggested by the person
531	named and ensures credit to the person for the idea. Please note that this
532	tag should not be added without the reporter's permission, especially if the
533	idea was not posted in a public forum. That said, if we diligently credit our
534	idea reporters, they will, hopefully, be inspired to help us again in the
535	future.
536	
537	A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
538	is used to make it easy to determine where a bug originated, which can help
539	review a bug fix. This tag also assists the stable kernel team in determining
540	which stable kernel versions should receive your fix. This is the preferred
541	method for indicating a bug fixed by the patch. See #2 above for more details.
542	
543	
544	15) The canonical patch format
545	
546	The canonical patch subject line is:
547	
548	    Subject: [PATCH 001/123] subsystem: summary phrase
549	
550	The canonical patch message body contains the following:
551	
552	  - A "from" line specifying the patch author.
553	
554	  - An empty line.
555	
556	  - The body of the explanation, which will be copied to the
557	    permanent changelog to describe this patch.
558	
559	  - The "Signed-off-by:" lines, described above, which will
560	    also go in the changelog.
561	
562	  - A marker line containing simply "---".
563	
564	  - Any additional comments not suitable for the changelog.
565	
566	  - The actual patch (diff output).
567	
568	The Subject line format makes it very easy to sort the emails
569	alphabetically by subject line - pretty much any email reader will
570	support that - since because the sequence number is zero-padded,
571	the numerical and alphabetic sort is the same.
572	
573	The "subsystem" in the email's Subject should identify which
574	area or subsystem of the kernel is being patched.
575	
576	The "summary phrase" in the email's Subject should concisely
577	describe the patch which that email contains.  The "summary
578	phrase" should not be a filename.  Do not use the same "summary
579	phrase" for every patch in a whole patch series (where a "patch
580	series" is an ordered sequence of multiple, related patches).
581	
582	Bear in mind that the "summary phrase" of your email becomes a
583	globally-unique identifier for that patch.  It propagates all the way
584	into the git changelog.  The "summary phrase" may later be used in
585	developer discussions which refer to the patch.  People will want to
586	google for the "summary phrase" to read discussion regarding that
587	patch.  It will also be the only thing that people may quickly see
588	when, two or three months later, they are going through perhaps
589	thousands of patches using tools such as "gitk" or "git log
590	--oneline".
591	
592	For these reasons, the "summary" must be no more than 70-75
593	characters, and it must describe both what the patch changes, as well
594	as why the patch might be necessary.  It is challenging to be both
595	succinct and descriptive, but that is what a well-written summary
596	should do.
597	
598	The "summary phrase" may be prefixed by tags enclosed in square
599	brackets: "Subject: [PATCH tag] <summary phrase>".  The tags are not
600	considered part of the summary phrase, but describe how the patch
601	should be treated.  Common tags might include a version descriptor if
602	the multiple versions of the patch have been sent out in response to
603	comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
604	comments.  If there are four patches in a patch series the individual
605	patches may be numbered like this: 1/4, 2/4, 3/4, 4/4.  This assures
606	that developers understand the order in which the patches should be
607	applied and that they have reviewed or applied all of the patches in
608	the patch series.
609	
610	A couple of example Subjects:
611	
612	    Subject: [patch 2/5] ext2: improve scalability of bitmap searching
613	    Subject: [PATCHv2 001/207] x86: fix eflags tracking
614	
615	The "from" line must be the very first line in the message body,
616	and has the form:
617	
618	        From: Original Author <author@example.com>
619	
620	The "from" line specifies who will be credited as the author of the
621	patch in the permanent changelog.  If the "from" line is missing,
622	then the "From:" line from the email header will be used to determine
623	the patch author in the changelog.
624	
625	The explanation body will be committed to the permanent source
626	changelog, so should make sense to a competent reader who has long
627	since forgotten the immediate details of the discussion that might
628	have led to this patch.  Including symptoms of the failure which the
629	patch addresses (kernel log messages, oops messages, etc.) is
630	especially useful for people who might be searching the commit logs
631	looking for the applicable patch.  If a patch fixes a compile failure,
632	it may not be necessary to include _all_ of the compile failures; just
633	enough that it is likely that someone searching for the patch can find
634	it.  As in the "summary phrase", it is important to be both succinct as
635	well as descriptive.
636	
637	The "---" marker line serves the essential purpose of marking for patch
638	handling tools where the changelog message ends.
639	
640	One good use for the additional comments after the "---" marker is for
641	a diffstat, to show what files have changed, and the number of
642	inserted and deleted lines per file.  A diffstat is especially useful
643	on bigger patches.  Other comments relevant only to the moment or the
644	maintainer, not suitable for the permanent changelog, should also go
645	here.  A good example of such comments might be "patch changelogs"
646	which describe what has changed between the v1 and v2 version of the
647	patch.
648	
649	If you are going to include a diffstat after the "---" marker, please
650	use diffstat options "-p 1 -w 70" so that filenames are listed from
651	the top of the kernel source tree and don't use too much horizontal
652	space (easily fit in 80 columns, maybe with some indentation).  (git
653	generates appropriate diffstats by default.)
654	
655	See more details on the proper patch format in the following
656	references.
657	
658	
659	16) Sending "git pull" requests  (from Linus emails)
660	
661	Please write the git repo address and branch name alone on the same line
662	so that I can't even by mistake pull from the wrong branch, and so
663	that a triple-click just selects the whole thing.
664	
665	So the proper format is something along the lines of:
666	
667		"Please pull from
668	
669			git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
670	
671		 to get these changes:"
672	
673	so that I don't have to hunt-and-peck for the address and inevitably
674	get it wrong (actually, I've only gotten it wrong a few times, and
675	checking against the diffstat tells me when I get it wrong, but I'm
676	just a lot more comfortable when I don't have to "look for" the right
677	thing to pull, and double-check that I have the right branch-name).
678	
679	
680	Please use "git diff -M --stat --summary" to generate the diffstat:
681	the -M enables rename detection, and the summary enables a summary of
682	new/deleted or renamed files.
683	
684	With rename detection, the statistics are rather different [...]
685	because git will notice that a fair number of the changes are renames.
686	
687	-----------------------------------
688	SECTION 2 - HINTS, TIPS, AND TRICKS
689	-----------------------------------
690	
691	This section lists many of the common "rules" associated with code
692	submitted to the kernel.  There are always exceptions... but you must
693	have a really good reason for doing so.  You could probably call this
694	section Linus Computer Science 101.
695	
696	
697	
698	1) Read Documentation/CodingStyle
699	
700	Nuff said.  If your code deviates too much from this, it is likely
701	to be rejected without further review, and without comment.
702	
703	One significant exception is when moving code from one file to
704	another -- in this case you should not modify the moved code at all in
705	the same patch which moves it.  This clearly delineates the act of
706	moving the code and your changes.  This greatly aids review of the
707	actual differences and allows tools to better track the history of
708	the code itself.
709	
710	Check your patches with the patch style checker prior to submission
711	(scripts/checkpatch.pl).  The style checker should be viewed as
712	a guide not as the final word.  If your code looks better with
713	a violation then its probably best left alone.
714	
715	The checker reports at three levels:
716	 - ERROR: things that are very likely to be wrong
717	 - WARNING: things requiring careful review
718	 - CHECK: things requiring thought
719	
720	You should be able to justify all violations that remain in your
721	patch.
722	
723	
724	
725	2) #ifdefs are ugly
726	
727	Code cluttered with ifdefs is difficult to read and maintain.  Don't do
728	it.  Instead, put your ifdefs in a header, and conditionally define
729	'static inline' functions, or macros, which are used in the code.
730	Let the compiler optimize away the "no-op" case.
731	
732	Simple example, of poor code:
733	
734		dev = alloc_etherdev (sizeof(struct funky_private));
735		if (!dev)
736			return -ENODEV;
737		#ifdef CONFIG_NET_FUNKINESS
738		init_funky_net(dev);
739		#endif
740	
741	Cleaned-up example:
742	
743	(in header)
744		#ifndef CONFIG_NET_FUNKINESS
745		static inline void init_funky_net (struct net_device *d) {}
746		#endif
747	
748	(in the code itself)
749		dev = alloc_etherdev (sizeof(struct funky_private));
750		if (!dev)
751			return -ENODEV;
752		init_funky_net(dev);
753	
754	
755	
756	3) 'static inline' is better than a macro
757	
758	Static inline functions are greatly preferred over macros.
759	They provide type safety, have no length limitations, no formatting
760	limitations, and under gcc they are as cheap as macros.
761	
762	Macros should only be used for cases where a static inline is clearly
763	suboptimal [there are a few, isolated cases of this in fast paths],
764	or where it is impossible to use a static inline function [such as
765	string-izing].
766	
767	'static inline' is preferred over 'static __inline__', 'extern inline',
768	and 'extern __inline__'.
769	
770	
771	
772	4) Don't over-design.
773	
774	Don't try to anticipate nebulous future cases which may or may not
775	be useful:  "Make it as simple as you can, and no simpler."
776	
777	
778	
779	----------------------
780	SECTION 3 - REFERENCES
781	----------------------
782	
783	Andrew Morton, "The perfect patch" (tpp).
784	  <http://www.ozlabs.org/~akpm/stuff/tpp.txt>
785	
786	Jeff Garzik, "Linux kernel patch submission format".
787	  <http://linux.yyz.us/patch-format.html>
788	
789	Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
790	  <http://www.kroah.com/log/linux/maintainer.html>
791	  <http://www.kroah.com/log/linux/maintainer-02.html>
792	  <http://www.kroah.com/log/linux/maintainer-03.html>
793	  <http://www.kroah.com/log/linux/maintainer-04.html>
794	  <http://www.kroah.com/log/linux/maintainer-05.html>
795	  <http://www.kroah.com/log/linux/maintainer-06.html>
796	
797	NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
798	  <https://lkml.org/lkml/2005/7/11/336>
799	
800	Kernel Documentation/CodingStyle:
801	  <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
802	
803	Linus Torvalds's mail on the canonical patch format:
804	  <http://lkml.org/lkml/2005/4/7/183>
805	
806	Andi Kleen, "On submitting kernel patches"
807	  Some strategies to get difficult or controversial changes in.
808	  http://halobates.de/on-submitting-patches.pdf
809	
810	--
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