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Based on kernel version 4.8. Page generated on 2016-10-06 23:19 EST.

2		How to Get Your Change Into the Linux Kernel
3			or
4		Care And Operation Of Your Linus Torvalds
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.
13	This document contains a large number of suggestions in a relatively terse
14	format.  For detailed information on how the kernel development process
15	works, see Documentation/development-process.  Also, read
16	Documentation/SubmitChecklist for a list of items to check before
17	submitting code.  If you are submitting a driver, also read
18	Documentation/SubmittingDrivers; for device tree binding patches, read
19	Documentation/devicetree/bindings/submitting-patches.txt.
21	Many of these steps describe the default behavior of the git version
22	control system; if you use git to prepare your patches, you'll find much
23	of the mechanical work done for you, though you'll still need to prepare
24	and document a sensible set of patches.  In general, use of git will make
25	your life as a kernel developer easier.
27	--------------------------------------------
29	--------------------------------------------
32	0) Obtain a current source tree
33	-------------------------------
35	If you do not have a repository with the current kernel source handy, use
36	git to obtain one.  You'll want to start with the mainline repository,
37	which can be grabbed with:
39	  git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 
41	Note, however, that you may not want to develop against the mainline tree
42	directly.  Most subsystem maintainers run their own trees and want to see
43	patches prepared against those trees.  See the "T:" entry for the subsystem
44	in the MAINTAINERS file to find that tree, or simply ask the maintainer if
45	the tree is not listed there.
47	It is still possible to download kernel releases via tarballs (as described
48	in the next section), but that is the hard way to do kernel development.
50	1) "diff -up"
51	------------
53	If you must generate your patches by hand, use "diff -up" or "diff -uprN"
54	to create patches.  Git generates patches in this form by default; if
55	you're using git, you can skip this section entirely.
57	All changes to the Linux kernel occur in the form of patches, as
58	generated by diff(1).  When creating your patch, make sure to create it
59	in "unified diff" format, as supplied by the '-u' argument to diff(1).
60	Also, please use the '-p' argument which shows which C function each
61	change is in - that makes the resultant diff a lot easier to read.
62	Patches should be based in the root kernel source directory,
63	not in any lower subdirectory.
65	To create a patch for a single file, it is often sufficient to do:
67		SRCTREE= linux
68		MYFILE=  drivers/net/mydriver.c
70		cd $SRCTREE
71		cp $MYFILE $MYFILE.orig
72		vi $MYFILE	# make your change
73		cd ..
74		diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
76	To create a patch for multiple files, you should unpack a "vanilla",
77	or unmodified kernel source tree, and generate a diff against your
78	own source tree.  For example:
80		MYSRC= /devel/linux
82		tar xvfz linux-3.19.tar.gz
83		mv linux-3.19 linux-3.19-vanilla
84		diff -uprN -X linux-3.19-vanilla/Documentation/dontdiff \
85			linux-3.19-vanilla $MYSRC > /tmp/patch
87	"dontdiff" is a list of files which are generated by the kernel during
88	the build process, and should be ignored in any diff(1)-generated
89	patch.
91	Make sure your patch does not include any extra files which do not
92	belong in a patch submission.  Make sure to review your patch -after-
93	generating it with diff(1), to ensure accuracy.
95	If your changes produce a lot of deltas, you need to split them into
96	individual patches which modify things in logical stages; see section
97	#3.  This will facilitate review by other kernel developers,
98	very important if you want your patch accepted.
100	If you're using git, "git rebase -i" can help you with this process.  If
101	you're not using git, quilt <http://savannah.nongnu.org/projects/quilt>
102	is another popular alternative.
106	2) Describe your changes.
107	-------------------------
109	Describe your problem.  Whether your patch is a one-line bug fix or
110	5000 lines of a new feature, there must be an underlying problem that
111	motivated you to do this work.  Convince the reviewer that there is a
112	problem worth fixing and that it makes sense for them to read past the
113	first paragraph.
115	Describe user-visible impact.  Straight up crashes and lockups are
116	pretty convincing, but not all bugs are that blatant.  Even if the
117	problem was spotted during code review, describe the impact you think
118	it can have on users.  Keep in mind that the majority of Linux
119	installations run kernels from secondary stable trees or
120	vendor/product-specific trees that cherry-pick only specific patches
121	from upstream, so include anything that could help route your change
122	downstream: provoking circumstances, excerpts from dmesg, crash
123	descriptions, performance regressions, latency spikes, lockups, etc.
125	Quantify optimizations and trade-offs.  If you claim improvements in
126	performance, memory consumption, stack footprint, or binary size,
127	include numbers that back them up.  But also describe non-obvious
128	costs.  Optimizations usually aren't free but trade-offs between CPU,
129	memory, and readability; or, when it comes to heuristics, between
130	different workloads.  Describe the expected downsides of your
131	optimization so that the reviewer can weigh costs against benefits.
133	Once the problem is established, describe what you are actually doing
134	about it in technical detail.  It's important to describe the change
135	in plain English for the reviewer to verify that the code is behaving
136	as you intend it to.
138	The maintainer will thank you if you write your patch description in a
139	form which can be easily pulled into Linux's source code management
140	system, git, as a "commit log".  See #15, below.
142	Solve only one problem per patch.  If your description starts to get
143	long, that's a sign that you probably need to split up your patch.
144	See #3, next.
146	When you submit or resubmit a patch or patch series, include the
147	complete patch description and justification for it.  Don't just
148	say that this is version N of the patch (series).  Don't expect the
149	subsystem maintainer to refer back to earlier patch versions or referenced
150	URLs to find the patch description and put that into the patch.
151	I.e., the patch (series) and its description should be self-contained.
152	This benefits both the maintainers and reviewers.  Some reviewers
153	probably didn't even receive earlier versions of the patch.
155	Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
156	instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
157	to do frotz", as if you are giving orders to the codebase to change
158	its behaviour.
160	If the patch fixes a logged bug entry, refer to that bug entry by
161	number and URL.  If the patch follows from a mailing list discussion,
162	give a URL to the mailing list archive; use the https://lkml.kernel.org/
163	redirector with a Message-Id, to ensure that the links cannot become
164	stale.
166	However, try to make your explanation understandable without external
167	resources.  In addition to giving a URL to a mailing list archive or
168	bug, summarize the relevant points of the discussion that led to the
169	patch as submitted.
171	If you want to refer to a specific commit, don't just refer to the
172	SHA-1 ID of the commit. Please also include the oneline summary of
173	the commit, to make it easier for reviewers to know what it is about.
174	Example:
176		Commit e21d2170f36602ae2708 ("video: remove unnecessary
177		platform_set_drvdata()") removed the unnecessary
178		platform_set_drvdata(), but left the variable "dev" unused,
179		delete it.
181	You should also be sure to use at least the first twelve characters of the
182	SHA-1 ID.  The kernel repository holds a *lot* of objects, making
183	collisions with shorter IDs a real possibility.  Bear in mind that, even if
184	there is no collision with your six-character ID now, that condition may
185	change five years from now.
187	If your patch fixes a bug in a specific commit, e.g. you found an issue using
188	git-bisect, please use the 'Fixes:' tag with the first 12 characters of the
189	SHA-1 ID, and the one line summary.  For example:
191		Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
193	The following git-config settings can be used to add a pretty format for
194	outputting the above style in the git log or git show commands
196		[core]
197			abbrev = 12
198		[pretty]
199			fixes = Fixes: %h (\"%s\")
201	3) Separate your changes.
202	-------------------------
204	Separate each _logical change_ into a separate patch.
206	For example, if your changes include both bug fixes and performance
207	enhancements for a single driver, separate those changes into two
208	or more patches.  If your changes include an API update, and a new
209	driver which uses that new API, separate those into two patches.
211	On the other hand, if you make a single change to numerous files,
212	group those changes into a single patch.  Thus a single logical change
213	is contained within a single patch.
215	The point to remember is that each patch should make an easily understood
216	change that can be verified by reviewers.  Each patch should be justifiable
217	on its own merits.
219	If one patch depends on another patch in order for a change to be
220	complete, that is OK.  Simply note "this patch depends on patch X"
221	in your patch description.
223	When dividing your change into a series of patches, take special care to
224	ensure that the kernel builds and runs properly after each patch in the
225	series.  Developers using "git bisect" to track down a problem can end up
226	splitting your patch series at any point; they will not thank you if you
227	introduce bugs in the middle.
229	If you cannot condense your patch set into a smaller set of patches,
230	then only post say 15 or so at a time and wait for review and integration.
234	4) Style-check your changes.
235	----------------------------
237	Check your patch for basic style violations, details of which can be
238	found in Documentation/CodingStyle.  Failure to do so simply wastes
239	the reviewers time and will get your patch rejected, probably
240	without even being read.
242	One significant exception is when moving code from one file to
243	another -- in this case you should not modify the moved code at all in
244	the same patch which moves it.  This clearly delineates the act of
245	moving the code and your changes.  This greatly aids review of the
246	actual differences and allows tools to better track the history of
247	the code itself.
249	Check your patches with the patch style checker prior to submission
250	(scripts/checkpatch.pl).  Note, though, that the style checker should be
251	viewed as a guide, not as a replacement for human judgment.  If your code
252	looks better with a violation then its probably best left alone.
254	The checker reports at three levels:
255	 - ERROR: things that are very likely to be wrong
256	 - WARNING: things requiring careful review
257	 - CHECK: things requiring thought
259	You should be able to justify all violations that remain in your
260	patch.
263	5) Select the recipients for your patch.
264	----------------------------------------
266	You should always copy the appropriate subsystem maintainer(s) on any patch
267	to code that they maintain; look through the MAINTAINERS file and the
268	source code revision history to see who those maintainers are.  The
269	script scripts/get_maintainer.pl can be very useful at this step.  If you
270	cannot find a maintainer for the subsystem you are working on, Andrew
271	Morton (akpm@linux-foundation.org) serves as a maintainer of last resort.
273	You should also normally choose at least one mailing list to receive a copy
274	of your patch set.  linux-kernel@vger.kernel.org functions as a list of
275	last resort, but the volume on that list has caused a number of developers
276	to tune it out.  Look in the MAINTAINERS file for a subsystem-specific
277	list; your patch will probably get more attention there.  Please do not
278	spam unrelated lists, though.
280	Many kernel-related lists are hosted on vger.kernel.org; you can find a
281	list of them at http://vger.kernel.org/vger-lists.html.  There are
282	kernel-related lists hosted elsewhere as well, though.
284	Do not send more than 15 patches at once to the vger mailing lists!!!
286	Linus Torvalds is the final arbiter of all changes accepted into the
287	Linux kernel.  His e-mail address is <torvalds@linux-foundation.org>.
288	He gets a lot of e-mail, and, at this point, very few patches go through
289	Linus directly, so typically you should do your best to -avoid-
290	sending him e-mail.
292	If you have a patch that fixes an exploitable security bug, send that patch
293	to security@kernel.org.  For severe bugs, a short embargo may be considered
294	to allow distributors to get the patch out to users; in such cases,
295	obviously, the patch should not be sent to any public lists.
297	Patches that fix a severe bug in a released kernel should be directed
298	toward the stable maintainers by putting a line like this:
300	  Cc: stable@vger.kernel.org
302	into the sign-off area of your patch (note, NOT an email recipient).  You
303	should also read Documentation/stable_kernel_rules.txt in addition to this
304	file.
306	Note, however, that some subsystem maintainers want to come to their own
307	conclusions on which patches should go to the stable trees.  The networking
308	maintainer, in particular, would rather not see individual developers
309	adding lines like the above to their patches.
311	If changes affect userland-kernel interfaces, please send the MAN-PAGES
312	maintainer (as listed in the MAINTAINERS file) a man-pages patch, or at
313	least a notification of the change, so that some information makes its way
314	into the manual pages.  User-space API changes should also be copied to
315	linux-api@vger.kernel.org. 
317	For small patches you may want to CC the Trivial Patch Monkey
318	trivial@kernel.org which collects "trivial" patches. Have a look
319	into the MAINTAINERS file for its current manager.
320	Trivial patches must qualify for one of the following rules:
321	 Spelling fixes in documentation
322	 Spelling fixes for errors which could break grep(1)
323	 Warning fixes (cluttering with useless warnings is bad)
324	 Compilation fixes (only if they are actually correct)
325	 Runtime fixes (only if they actually fix things)
326	 Removing use of deprecated functions/macros
327	 Contact detail and documentation fixes
328	 Non-portable code replaced by portable code (even in arch-specific,
329	 since people copy, as long as it's trivial)
330	 Any fix by the author/maintainer of the file (ie. patch monkey
331	 in re-transmission mode)
335	6) No MIME, no links, no compression, no attachments.  Just plain text.
336	-----------------------------------------------------------------------
338	Linus and other kernel developers need to be able to read and comment
339	on the changes you are submitting.  It is important for a kernel
340	developer to be able to "quote" your changes, using standard e-mail
341	tools, so that they may comment on specific portions of your code.
343	For this reason, all patches should be submitted by e-mail "inline".
344	WARNING:  Be wary of your editor's word-wrap corrupting your patch,
345	if you choose to cut-n-paste your patch.
347	Do not attach the patch as a MIME attachment, compressed or not.
348	Many popular e-mail applications will not always transmit a MIME
349	attachment as plain text, making it impossible to comment on your
350	code.  A MIME attachment also takes Linus a bit more time to process,
351	decreasing the likelihood of your MIME-attached change being accepted.
353	Exception:  If your mailer is mangling patches then someone may ask
354	you to re-send them using MIME.
356	See Documentation/email-clients.txt for hints about configuring
357	your e-mail client so that it sends your patches untouched.
359	7) E-mail size.
360	---------------
362	Large changes are not appropriate for mailing lists, and some
363	maintainers.  If your patch, uncompressed, exceeds 300 kB in size,
364	it is preferred that you store your patch on an Internet-accessible
365	server, and provide instead a URL (link) pointing to your patch.  But note
366	that if your patch exceeds 300 kB, it almost certainly needs to be broken up
367	anyway.
369	8) Respond to review comments.
370	------------------------------
372	Your patch will almost certainly get comments from reviewers on ways in
373	which the patch can be improved.  You must respond to those comments;
374	ignoring reviewers is a good way to get ignored in return.  Review comments
375	or questions that do not lead to a code change should almost certainly
376	bring about a comment or changelog entry so that the next reviewer better
377	understands what is going on.
379	Be sure to tell the reviewers what changes you are making and to thank them
380	for their time.  Code review is a tiring and time-consuming process, and
381	reviewers sometimes get grumpy.  Even in that case, though, respond
382	politely and address the problems they have pointed out.
385	9) Don't get discouraged - or impatient.
386	----------------------------------------
388	After you have submitted your change, be patient and wait.  Reviewers are
389	busy people and may not get to your patch right away.
391	Once upon a time, patches used to disappear into the void without comment,
392	but the development process works more smoothly than that now.  You should
393	receive comments within a week or so; if that does not happen, make sure
394	that you have sent your patches to the right place.  Wait for a minimum of
395	one week before resubmitting or pinging reviewers - possibly longer during
396	busy times like merge windows.
399	10) Include PATCH in the subject
400	--------------------------------
402	Due to high e-mail traffic to Linus, and to linux-kernel, it is common
403	convention to prefix your subject line with [PATCH].  This lets Linus
404	and other kernel developers more easily distinguish patches from other
405	e-mail discussions.
409	11) Sign your work
410	------------------
412	To improve tracking of who did what, especially with patches that can
413	percolate to their final resting place in the kernel through several
414	layers of maintainers, we've introduced a "sign-off" procedure on
415	patches that are being emailed around.
417	The sign-off is a simple line at the end of the explanation for the
418	patch, which certifies that you wrote it or otherwise have the right to
419	pass it on as an open-source patch.  The rules are pretty simple: if you
420	can certify the below:
422	        Developer's Certificate of Origin 1.1
424	        By making a contribution to this project, I certify that:
426	        (a) The contribution was created in whole or in part by me and I
427	            have the right to submit it under the open source license
428	            indicated in the file; or
430	        (b) The contribution is based upon previous work that, to the best
431	            of my knowledge, is covered under an appropriate open source
432	            license and I have the right under that license to submit that
433	            work with modifications, whether created in whole or in part
434	            by me, under the same open source license (unless I am
435	            permitted to submit under a different license), as indicated
436	            in the file; or
438	        (c) The contribution was provided directly to me by some other
439	            person who certified (a), (b) or (c) and I have not modified
440	            it.
442	        (d) I understand and agree that this project and the contribution
443	            are public and that a record of the contribution (including all
444	            personal information I submit with it, including my sign-off) is
445	            maintained indefinitely and may be redistributed consistent with
446	            this project or the open source license(s) involved.
448	then you just add a line saying
450		Signed-off-by: Random J Developer <random@developer.example.org>
452	using your real name (sorry, no pseudonyms or anonymous contributions.)
454	Some people also put extra tags at the end.  They'll just be ignored for
455	now, but you can do this to mark internal company procedures or just
456	point out some special detail about the sign-off.
458	If you are a subsystem or branch maintainer, sometimes you need to slightly
459	modify patches you receive in order to merge them, because the code is not
460	exactly the same in your tree and the submitters'. If you stick strictly to
461	rule (c), you should ask the submitter to rediff, but this is a totally
462	counter-productive waste of time and energy. Rule (b) allows you to adjust
463	the code, but then it is very impolite to change one submitter's code and
464	make him endorse your bugs. To solve this problem, it is recommended that
465	you add a line between the last Signed-off-by header and yours, indicating
466	the nature of your changes. While there is nothing mandatory about this, it
467	seems like prepending the description with your mail and/or name, all
468	enclosed in square brackets, is noticeable enough to make it obvious that
469	you are responsible for last-minute changes. Example :
471		Signed-off-by: Random J Developer <random@developer.example.org>
472		[lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
473		Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
475	This practice is particularly helpful if you maintain a stable branch and
476	want at the same time to credit the author, track changes, merge the fix,
477	and protect the submitter from complaints. Note that under no circumstances
478	can you change the author's identity (the From header), as it is the one
479	which appears in the changelog.
481	Special note to back-porters: It seems to be a common and useful practice
482	to insert an indication of the origin of a patch at the top of the commit
483	message (just after the subject line) to facilitate tracking. For instance,
484	here's what we see in a 3.x-stable release:
486	Date:   Tue Oct 7 07:26:38 2014 -0400
488	    libata: Un-break ATA blacklist
490	    commit 1c40279960bcd7d52dbdf1d466b20d24b99176c8 upstream.
492	And here's what might appear in an older kernel once a patch is backported:
494	    Date:   Tue May 13 22:12:27 2008 +0200
496	        wireless, airo: waitbusy() won't delay
498	        [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
500	Whatever the format, this information provides a valuable help to people
501	tracking your trees, and to people trying to troubleshoot bugs in your
502	tree.
505	12) When to use Acked-by: and Cc:
506	---------------------------------
508	The Signed-off-by: tag indicates that the signer was involved in the
509	development of the patch, or that he/she was in the patch's delivery path.
511	If a person was not directly involved in the preparation or handling of a
512	patch but wishes to signify and record their approval of it then they can
513	ask to have an Acked-by: line added to the patch's changelog.
515	Acked-by: is often used by the maintainer of the affected code when that
516	maintainer neither contributed to nor forwarded the patch.
518	Acked-by: is not as formal as Signed-off-by:.  It is a record that the acker
519	has at least reviewed the patch and has indicated acceptance.  Hence patch
520	mergers will sometimes manually convert an acker's "yep, looks good to me"
521	into an Acked-by: (but note that it is usually better to ask for an
522	explicit ack).
524	Acked-by: does not necessarily indicate acknowledgement of the entire patch.
525	For example, if a patch affects multiple subsystems and has an Acked-by: from
526	one subsystem maintainer then this usually indicates acknowledgement of just
527	the part which affects that maintainer's code.  Judgement should be used here.
528	When in doubt people should refer to the original discussion in the mailing
529	list archives.
531	If a person has had the opportunity to comment on a patch, but has not
532	provided such comments, you may optionally add a "Cc:" tag to the patch.
533	This is the only tag which might be added without an explicit action by the
534	person it names - but it should indicate that this person was copied on the
535	patch.  This tag documents that potentially interested parties
536	have been included in the discussion.
539	13) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
540	--------------------------------------------------------------------------
542	The Reported-by tag gives credit to people who find bugs and report them and it
543	hopefully inspires them to help us again in the future.  Please note that if
544	the bug was reported in private, then ask for permission first before using the
545	Reported-by tag.
547	A Tested-by: tag indicates that the patch has been successfully tested (in
548	some environment) by the person named.  This tag informs maintainers that
549	some testing has been performed, provides a means to locate testers for
550	future patches, and ensures credit for the testers.
552	Reviewed-by:, instead, indicates that the patch has been reviewed and found
553	acceptable according to the Reviewer's Statement:
555		Reviewer's statement of oversight
557		By offering my Reviewed-by: tag, I state that:
559	 	 (a) I have carried out a technical review of this patch to
560		     evaluate its appropriateness and readiness for inclusion into
561		     the mainline kernel.
563		 (b) Any problems, concerns, or questions relating to the patch
564		     have been communicated back to the submitter.  I am satisfied
565		     with the submitter's response to my comments.
567		 (c) While there may be things that could be improved with this
568		     submission, I believe that it is, at this time, (1) a
569		     worthwhile modification to the kernel, and (2) free of known
570		     issues which would argue against its inclusion.
572		 (d) While I have reviewed the patch and believe it to be sound, I
573		     do not (unless explicitly stated elsewhere) make any
574		     warranties or guarantees that it will achieve its stated
575		     purpose or function properly in any given situation.
577	A Reviewed-by tag is a statement of opinion that the patch is an
578	appropriate modification of the kernel without any remaining serious
579	technical issues.  Any interested reviewer (who has done the work) can
580	offer a Reviewed-by tag for a patch.  This tag serves to give credit to
581	reviewers and to inform maintainers of the degree of review which has been
582	done on the patch.  Reviewed-by: tags, when supplied by reviewers known to
583	understand the subject area and to perform thorough reviews, will normally
584	increase the likelihood of your patch getting into the kernel.
586	A Suggested-by: tag indicates that the patch idea is suggested by the person
587	named and ensures credit to the person for the idea. Please note that this
588	tag should not be added without the reporter's permission, especially if the
589	idea was not posted in a public forum. That said, if we diligently credit our
590	idea reporters, they will, hopefully, be inspired to help us again in the
591	future.
593	A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
594	is used to make it easy to determine where a bug originated, which can help
595	review a bug fix. This tag also assists the stable kernel team in determining
596	which stable kernel versions should receive your fix. This is the preferred
597	method for indicating a bug fixed by the patch. See #2 above for more details.
600	14) The canonical patch format
601	------------------------------
603	This section describes how the patch itself should be formatted.  Note
604	that, if you have your patches stored in a git repository, proper patch
605	formatting can be had with "git format-patch".  The tools cannot create
606	the necessary text, though, so read the instructions below anyway.
608	The canonical patch subject line is:
610	    Subject: [PATCH 001/123] subsystem: summary phrase
612	The canonical patch message body contains the following:
614	  - A "from" line specifying the patch author (only needed if the person
615	    sending the patch is not the author).
617	  - An empty line.
619	  - The body of the explanation, line wrapped at 75 columns, which will
620	    be copied to the permanent changelog to describe this patch.
622	  - The "Signed-off-by:" lines, described above, which will
623	    also go in the changelog.
625	  - A marker line containing simply "---".
627	  - Any additional comments not suitable for the changelog.
629	  - The actual patch (diff output).
631	The Subject line format makes it very easy to sort the emails
632	alphabetically by subject line - pretty much any email reader will
633	support that - since because the sequence number is zero-padded,
634	the numerical and alphabetic sort is the same.
636	The "subsystem" in the email's Subject should identify which
637	area or subsystem of the kernel is being patched.
639	The "summary phrase" in the email's Subject should concisely
640	describe the patch which that email contains.  The "summary
641	phrase" should not be a filename.  Do not use the same "summary
642	phrase" for every patch in a whole patch series (where a "patch
643	series" is an ordered sequence of multiple, related patches).
645	Bear in mind that the "summary phrase" of your email becomes a
646	globally-unique identifier for that patch.  It propagates all the way
647	into the git changelog.  The "summary phrase" may later be used in
648	developer discussions which refer to the patch.  People will want to
649	google for the "summary phrase" to read discussion regarding that
650	patch.  It will also be the only thing that people may quickly see
651	when, two or three months later, they are going through perhaps
652	thousands of patches using tools such as "gitk" or "git log
653	--oneline".
655	For these reasons, the "summary" must be no more than 70-75
656	characters, and it must describe both what the patch changes, as well
657	as why the patch might be necessary.  It is challenging to be both
658	succinct and descriptive, but that is what a well-written summary
659	should do.
661	The "summary phrase" may be prefixed by tags enclosed in square
662	brackets: "Subject: [PATCH <tag>...] <summary phrase>".  The tags are
663	not considered part of the summary phrase, but describe how the patch
664	should be treated.  Common tags might include a version descriptor if
665	the multiple versions of the patch have been sent out in response to
666	comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
667	comments.  If there are four patches in a patch series the individual
668	patches may be numbered like this: 1/4, 2/4, 3/4, 4/4.  This assures
669	that developers understand the order in which the patches should be
670	applied and that they have reviewed or applied all of the patches in
671	the patch series.
673	A couple of example Subjects:
675	    Subject: [PATCH 2/5] ext2: improve scalability of bitmap searching
676	    Subject: [PATCH v2 01/27] x86: fix eflags tracking
678	The "from" line must be the very first line in the message body,
679	and has the form:
681	        From: Original Author <author@example.com>
683	The "from" line specifies who will be credited as the author of the
684	patch in the permanent changelog.  If the "from" line is missing,
685	then the "From:" line from the email header will be used to determine
686	the patch author in the changelog.
688	The explanation body will be committed to the permanent source
689	changelog, so should make sense to a competent reader who has long
690	since forgotten the immediate details of the discussion that might
691	have led to this patch.  Including symptoms of the failure which the
692	patch addresses (kernel log messages, oops messages, etc.) is
693	especially useful for people who might be searching the commit logs
694	looking for the applicable patch.  If a patch fixes a compile failure,
695	it may not be necessary to include _all_ of the compile failures; just
696	enough that it is likely that someone searching for the patch can find
697	it.  As in the "summary phrase", it is important to be both succinct as
698	well as descriptive.
700	The "---" marker line serves the essential purpose of marking for patch
701	handling tools where the changelog message ends.
703	One good use for the additional comments after the "---" marker is for
704	a diffstat, to show what files have changed, and the number of
705	inserted and deleted lines per file.  A diffstat is especially useful
706	on bigger patches.  Other comments relevant only to the moment or the
707	maintainer, not suitable for the permanent changelog, should also go
708	here.  A good example of such comments might be "patch changelogs"
709	which describe what has changed between the v1 and v2 version of the
710	patch.
712	If you are going to include a diffstat after the "---" marker, please
713	use diffstat options "-p 1 -w 70" so that filenames are listed from
714	the top of the kernel source tree and don't use too much horizontal
715	space (easily fit in 80 columns, maybe with some indentation).  (git
716	generates appropriate diffstats by default.)
718	See more details on the proper patch format in the following
719	references.
721	15) Explicit In-Reply-To headers
722	--------------------------------
724	It can be helpful to manually add In-Reply-To: headers to a patch
725	(e.g., when using "git send-email") to associate the patch with
726	previous relevant discussion, e.g. to link a bug fix to the email with
727	the bug report.  However, for a multi-patch series, it is generally
728	best to avoid using In-Reply-To: to link to older versions of the
729	series.  This way multiple versions of the patch don't become an
730	unmanageable forest of references in email clients.  If a link is
731	helpful, you can use the https://lkml.kernel.org/ redirector (e.g., in
732	the cover email text) to link to an earlier version of the patch series.
735	16) Sending "git pull" requests
736	-------------------------------
738	If you have a series of patches, it may be most convenient to have the
739	maintainer pull them directly into the subsystem repository with a
740	"git pull" operation.  Note, however, that pulling patches from a developer
741	requires a higher degree of trust than taking patches from a mailing list.
742	As a result, many subsystem maintainers are reluctant to take pull
743	requests, especially from new, unknown developers.  If in doubt you can use
744	the pull request as the cover letter for a normal posting of the patch
745	series, giving the maintainer the option of using either.
747	A pull request should have [GIT] or [PULL] in the subject line.  The
748	request itself should include the repository name and the branch of
749	interest on a single line; it should look something like:
751	  Please pull from
753	      git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
755	  to get these changes:
757	A pull request should also include an overall message saying what will be
758	included in the request, a "git shortlog" listing of the patches
759	themselves, and a diffstat showing the overall effect of the patch series.
760	The easiest way to get all this information together is, of course, to let
761	git do it for you with the "git request-pull" command.
763	Some maintainers (including Linus) want to see pull requests from signed
764	commits; that increases their confidence that the request actually came
765	from you.  Linus, in particular, will not pull from public hosting sites
766	like GitHub in the absence of a signed tag.
768	The first step toward creating such tags is to make a GNUPG key and get it
769	signed by one or more core kernel developers.  This step can be hard for
770	new developers, but there is no way around it.  Attending conferences can
771	be a good way to find developers who can sign your key.
773	Once you have prepared a patch series in git that you wish to have somebody
774	pull, create a signed tag with "git tag -s".  This will create a new tag
775	identifying the last commit in the series and containing a signature
776	created with your private key.  You will also have the opportunity to add a
777	changelog-style message to the tag; this is an ideal place to describe the
778	effects of the pull request as a whole.
780	If the tree the maintainer will be pulling from is not the repository you
781	are working from, don't forget to push the signed tag explicitly to the
782	public tree.
784	When generating your pull request, use the signed tag as the target.  A
785	command like this will do the trick:
787	  git request-pull master git://my.public.tree/linux.git my-signed-tag
790	----------------------
792	----------------------
794	Andrew Morton, "The perfect patch" (tpp).
795	  <http://www.ozlabs.org/~akpm/stuff/tpp.txt>
797	Jeff Garzik, "Linux kernel patch submission format".
798	  <http://linux.yyz.us/patch-format.html>
800	Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
801	  <http://www.kroah.com/log/linux/maintainer.html>
802	  <http://www.kroah.com/log/linux/maintainer-02.html>
803	  <http://www.kroah.com/log/linux/maintainer-03.html>
804	  <http://www.kroah.com/log/linux/maintainer-04.html>
805	  <http://www.kroah.com/log/linux/maintainer-05.html>
806	  <http://www.kroah.com/log/linux/maintainer-06.html>
808	NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
809	  <https://lkml.org/lkml/2005/7/11/336>
811	Kernel Documentation/CodingStyle:
812	  <Documentation/CodingStyle>
814	Linus Torvalds's mail on the canonical patch format:
815	  <http://lkml.org/lkml/2005/4/7/183>
817	Andi Kleen, "On submitting kernel patches"
818	  Some strategies to get difficult or controversial changes in.
819	  http://halobates.de/on-submitting-patches.pdf
821	--
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