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Based on kernel version 4.1. Page generated on 2015-06-28 12:14 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	generated 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 easier reviewing 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 your 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 distrbutors 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 your patch.
304	Note, however, that some subsystem maintainers want to come to their own
305	conclusions on which patches should go to the stable trees.  The networking
306	maintainer, in particular, would rather not see individual developers
307	adding lines like the above to their patches.
309	If changes affect userland-kernel interfaces, please send the MAN-PAGES
310	maintainer (as listed in the MAINTAINERS file) a man-pages patch, or at
311	least a notification of the change, so that some information makes its way
312	into the manual pages.  User-space API changes should also be copied to
313	linux-api@vger.kernel.org. 
315	For small patches you may want to CC the Trivial Patch Monkey
316	trivial@kernel.org which collects "trivial" patches. Have a look
317	into the MAINTAINERS file for its current manager.
318	Trivial patches must qualify for one of the following rules:
319	 Spelling fixes in documentation
320	 Spelling fixes for errors which could break grep(1)
321	 Warning fixes (cluttering with useless warnings is bad)
322	 Compilation fixes (only if they are actually correct)
323	 Runtime fixes (only if they actually fix things)
324	 Removing use of deprecated functions/macros
325	 Contact detail and documentation fixes
326	 Non-portable code replaced by portable code (even in arch-specific,
327	 since people copy, as long as it's trivial)
328	 Any fix by the author/maintainer of the file (ie. patch monkey
329	 in re-transmission mode)
333	6) No MIME, no links, no compression, no attachments.  Just plain text.
334	-----------------------------------------------------------------------
336	Linus and other kernel developers need to be able to read and comment
337	on the changes you are submitting.  It is important for a kernel
338	developer to be able to "quote" your changes, using standard e-mail
339	tools, so that they may comment on specific portions of your code.
341	For this reason, all patches should be submitting e-mail "inline".
342	WARNING:  Be wary of your editor's word-wrap corrupting your patch,
343	if you choose to cut-n-paste your patch.
345	Do not attach the patch as a MIME attachment, compressed or not.
346	Many popular e-mail applications will not always transmit a MIME
347	attachment as plain text, making it impossible to comment on your
348	code.  A MIME attachment also takes Linus a bit more time to process,
349	decreasing the likelihood of your MIME-attached change being accepted.
351	Exception:  If your mailer is mangling patches then someone may ask
352	you to re-send them using MIME.
354	See Documentation/email-clients.txt for hints about configuring
355	your e-mail client so that it sends your patches untouched.
357	7) E-mail size.
358	---------------
360	Large changes are not appropriate for mailing lists, and some
361	maintainers.  If your patch, uncompressed, exceeds 300 kB in size,
362	it is preferred that you store your patch on an Internet-accessible
363	server, and provide instead a URL (link) pointing to your patch.  But note
364	that if your patch exceeds 300 kB, it almost certainly needs to be broken up
365	anyway.
367	8) Respond to review comments.
368	------------------------------
370	Your patch will almost certainly get comments from reviewers on ways in
371	which the patch can be improved.  You must respond to those comments;
372	ignoring reviewers is a good way to get ignored in return.  Review comments
373	or questions that do not lead to a code change should almost certainly
374	bring about a comment or changelog entry so that the next reviewer better
375	understands what is going on.
377	Be sure to tell the reviewers what changes you are making and to thank them
378	for their time.  Code review is a tiring and time-consuming process, and
379	reviewers sometimes get grumpy.  Even in that case, though, respond
380	politely and address the problems they have pointed out.
383	9) Don't get discouraged - or impatient.
384	----------------------------------------
386	After you have submitted your change, be patient and wait.  Reviewers are
387	busy people and may not get to your patch right away.
389	Once upon a time, patches used to disappear into the void without comment,
390	but the development process works more smoothly than that now.  You should
391	receive comments within a week or so; if that does not happen, make sure
392	that you have sent your patches to the right place.  Wait for a minimum of
393	one week before resubmitting or pinging reviewers - possibly longer during
394	busy times like merge windows.
397	10) Include PATCH in the subject
398	--------------------------------
400	Due to high e-mail traffic to Linus, and to linux-kernel, it is common
401	convention to prefix your subject line with [PATCH].  This lets Linus
402	and other kernel developers more easily distinguish patches from other
403	e-mail discussions.
407	11) Sign your work
408	------------------
410	To improve tracking of who did what, especially with patches that can
411	percolate to their final resting place in the kernel through several
412	layers of maintainers, we've introduced a "sign-off" procedure on
413	patches that are being emailed around.
415	The sign-off is a simple line at the end of the explanation for the
416	patch, which certifies that you wrote it or otherwise have the right to
417	pass it on as an open-source patch.  The rules are pretty simple: if you
418	can certify the below:
420	        Developer's Certificate of Origin 1.1
422	        By making a contribution to this project, I certify that:
424	        (a) The contribution was created in whole or in part by me and I
425	            have the right to submit it under the open source license
426	            indicated in the file; or
428	        (b) The contribution is based upon previous work that, to the best
429	            of my knowledge, is covered under an appropriate open source
430	            license and I have the right under that license to submit that
431	            work with modifications, whether created in whole or in part
432	            by me, under the same open source license (unless I am
433	            permitted to submit under a different license), as indicated
434	            in the file; or
436	        (c) The contribution was provided directly to me by some other
437	            person who certified (a), (b) or (c) and I have not modified
438	            it.
440	        (d) I understand and agree that this project and the contribution
441	            are public and that a record of the contribution (including all
442	            personal information I submit with it, including my sign-off) is
443	            maintained indefinitely and may be redistributed consistent with
444	            this project or the open source license(s) involved.
446	then you just add a line saying
448		Signed-off-by: Random J Developer <random@developer.example.org>
450	using your real name (sorry, no pseudonyms or anonymous contributions.)
452	Some people also put extra tags at the end.  They'll just be ignored for
453	now, but you can do this to mark internal company procedures or just
454	point out some special detail about the sign-off.
456	If you are a subsystem or branch maintainer, sometimes you need to slightly
457	modify patches you receive in order to merge them, because the code is not
458	exactly the same in your tree and the submitters'. If you stick strictly to
459	rule (c), you should ask the submitter to rediff, but this is a totally
460	counter-productive waste of time and energy. Rule (b) allows you to adjust
461	the code, but then it is very impolite to change one submitter's code and
462	make him endorse your bugs. To solve this problem, it is recommended that
463	you add a line between the last Signed-off-by header and yours, indicating
464	the nature of your changes. While there is nothing mandatory about this, it
465	seems like prepending the description with your mail and/or name, all
466	enclosed in square brackets, is noticeable enough to make it obvious that
467	you are responsible for last-minute changes. Example :
469		Signed-off-by: Random J Developer <random@developer.example.org>
470		[lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
471		Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
473	This practice is particularly helpful if you maintain a stable branch and
474	want at the same time to credit the author, track changes, merge the fix,
475	and protect the submitter from complaints. Note that under no circumstances
476	can you change the author's identity (the From header), as it is the one
477	which appears in the changelog.
479	Special note to back-porters: It seems to be a common and useful practice
480	to insert an indication of the origin of a patch at the top of the commit
481	message (just after the subject line) to facilitate tracking. For instance,
482	here's what we see in a 3.x-stable release:
484	Date:   Tue Oct 7 07:26:38 2014 -0400
486	    libata: Un-break ATA blacklist
488	    commit 1c40279960bcd7d52dbdf1d466b20d24b99176c8 upstream.
490	And here's what might appear in an older kernel once a patch is backported:
492	    Date:   Tue May 13 22:12:27 2008 +0200
494	        wireless, airo: waitbusy() won't delay
496	        [backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]
498	Whatever the format, this information provides a valuable help to people
499	tracking your trees, and to people trying to troubleshoot bugs in your
500	tree.
503	12) When to use Acked-by: and Cc:
504	---------------------------------
506	The Signed-off-by: tag indicates that the signer was involved in the
507	development of the patch, or that he/she was in the patch's delivery path.
509	If a person was not directly involved in the preparation or handling of a
510	patch but wishes to signify and record their approval of it then they can
511	ask to have an Acked-by: line added to the patch's changelog.
513	Acked-by: is often used by the maintainer of the affected code when that
514	maintainer neither contributed to nor forwarded the patch.
516	Acked-by: is not as formal as Signed-off-by:.  It is a record that the acker
517	has at least reviewed the patch and has indicated acceptance.  Hence patch
518	mergers will sometimes manually convert an acker's "yep, looks good to me"
519	into an Acked-by: (but note that it is usually better to ask for an
520	explicit ack).
522	Acked-by: does not necessarily indicate acknowledgement of the entire patch.
523	For example, if a patch affects multiple subsystems and has an Acked-by: from
524	one subsystem maintainer then this usually indicates acknowledgement of just
525	the part which affects that maintainer's code.  Judgement should be used here.
526	When in doubt people should refer to the original discussion in the mailing
527	list archives.
529	If a person has had the opportunity to comment on a patch, but has not
530	provided such comments, you may optionally add a "Cc:" tag to the patch.
531	This is the only tag which might be added without an explicit action by the
532	person it names - but it should indicate that this person was copied on the
533	patch.  This tag documents that potentially interested parties
534	have been included in the discussion.
537	13) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
538	--------------------------------------------------------------------------
540	The Reported-by tag gives credit to people who find bugs and report them and it
541	hopefully inspires them to help us again in the future.  Please note that if
542	the bug was reported in private, then ask for permission first before using the
543	Reported-by tag.
545	A Tested-by: tag indicates that the patch has been successfully tested (in
546	some environment) by the person named.  This tag informs maintainers that
547	some testing has been performed, provides a means to locate testers for
548	future patches, and ensures credit for the testers.
550	Reviewed-by:, instead, indicates that the patch has been reviewed and found
551	acceptable according to the Reviewer's Statement:
553		Reviewer's statement of oversight
555		By offering my Reviewed-by: tag, I state that:
557	 	 (a) I have carried out a technical review of this patch to
558		     evaluate its appropriateness and readiness for inclusion into
559		     the mainline kernel.
561		 (b) Any problems, concerns, or questions relating to the patch
562		     have been communicated back to the submitter.  I am satisfied
563		     with the submitter's response to my comments.
565		 (c) While there may be things that could be improved with this
566		     submission, I believe that it is, at this time, (1) a
567		     worthwhile modification to the kernel, and (2) free of known
568		     issues which would argue against its inclusion.
570		 (d) While I have reviewed the patch and believe it to be sound, I
571		     do not (unless explicitly stated elsewhere) make any
572		     warranties or guarantees that it will achieve its stated
573		     purpose or function properly in any given situation.
575	A Reviewed-by tag is a statement of opinion that the patch is an
576	appropriate modification of the kernel without any remaining serious
577	technical issues.  Any interested reviewer (who has done the work) can
578	offer a Reviewed-by tag for a patch.  This tag serves to give credit to
579	reviewers and to inform maintainers of the degree of review which has been
580	done on the patch.  Reviewed-by: tags, when supplied by reviewers known to
581	understand the subject area and to perform thorough reviews, will normally
582	increase the likelihood of your patch getting into the kernel.
584	A Suggested-by: tag indicates that the patch idea is suggested by the person
585	named and ensures credit to the person for the idea. Please note that this
586	tag should not be added without the reporter's permission, especially if the
587	idea was not posted in a public forum. That said, if we diligently credit our
588	idea reporters, they will, hopefully, be inspired to help us again in the
589	future.
591	A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
592	is used to make it easy to determine where a bug originated, which can help
593	review a bug fix. This tag also assists the stable kernel team in determining
594	which stable kernel versions should receive your fix. This is the preferred
595	method for indicating a bug fixed by the patch. See #2 above for more details.
598	14) The canonical patch format
599	------------------------------
601	This section describes how the patch itself should be formatted.  Note
602	that, if you have your patches stored in a git repository, proper patch
603	formatting can be had with "git format-patch".  The tools cannot create
604	the necessary text, though, so read the instructions below anyway.
606	The canonical patch subject line is:
608	    Subject: [PATCH 001/123] subsystem: summary phrase
610	The canonical patch message body contains the following:
612	  - A "from" line specifying the patch author (only needed if the person
613	    sending the patch is not the author).
615	  - An empty line.
617	  - The body of the explanation, line wrapped at 75 columns, which will
618	    be copied to the permanent changelog to describe this patch.
620	  - The "Signed-off-by:" lines, described above, which will
621	    also go in the changelog.
623	  - A marker line containing simply "---".
625	  - Any additional comments not suitable for the changelog.
627	  - The actual patch (diff output).
629	The Subject line format makes it very easy to sort the emails
630	alphabetically by subject line - pretty much any email reader will
631	support that - since because the sequence number is zero-padded,
632	the numerical and alphabetic sort is the same.
634	The "subsystem" in the email's Subject should identify which
635	area or subsystem of the kernel is being patched.
637	The "summary phrase" in the email's Subject should concisely
638	describe the patch which that email contains.  The "summary
639	phrase" should not be a filename.  Do not use the same "summary
640	phrase" for every patch in a whole patch series (where a "patch
641	series" is an ordered sequence of multiple, related patches).
643	Bear in mind that the "summary phrase" of your email becomes a
644	globally-unique identifier for that patch.  It propagates all the way
645	into the git changelog.  The "summary phrase" may later be used in
646	developer discussions which refer to the patch.  People will want to
647	google for the "summary phrase" to read discussion regarding that
648	patch.  It will also be the only thing that people may quickly see
649	when, two or three months later, they are going through perhaps
650	thousands of patches using tools such as "gitk" or "git log
651	--oneline".
653	For these reasons, the "summary" must be no more than 70-75
654	characters, and it must describe both what the patch changes, as well
655	as why the patch might be necessary.  It is challenging to be both
656	succinct and descriptive, but that is what a well-written summary
657	should do.
659	The "summary phrase" may be prefixed by tags enclosed in square
660	brackets: "Subject: [PATCH tag] <summary phrase>".  The tags are not
661	considered part of the summary phrase, but describe how the patch
662	should be treated.  Common tags might include a version descriptor if
663	the multiple versions of the patch have been sent out in response to
664	comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for
665	comments.  If there are four patches in a patch series the individual
666	patches may be numbered like this: 1/4, 2/4, 3/4, 4/4.  This assures
667	that developers understand the order in which the patches should be
668	applied and that they have reviewed or applied all of the patches in
669	the patch series.
671	A couple of example Subjects:
673	    Subject: [patch 2/5] ext2: improve scalability of bitmap searching
674	    Subject: [PATCHv2 001/207] x86: fix eflags tracking
676	The "from" line must be the very first line in the message body,
677	and has the form:
679	        From: Original Author <author@example.com>
681	The "from" line specifies who will be credited as the author of the
682	patch in the permanent changelog.  If the "from" line is missing,
683	then the "From:" line from the email header will be used to determine
684	the patch author in the changelog.
686	The explanation body will be committed to the permanent source
687	changelog, so should make sense to a competent reader who has long
688	since forgotten the immediate details of the discussion that might
689	have led to this patch.  Including symptoms of the failure which the
690	patch addresses (kernel log messages, oops messages, etc.) is
691	especially useful for people who might be searching the commit logs
692	looking for the applicable patch.  If a patch fixes a compile failure,
693	it may not be necessary to include _all_ of the compile failures; just
694	enough that it is likely that someone searching for the patch can find
695	it.  As in the "summary phrase", it is important to be both succinct as
696	well as descriptive.
698	The "---" marker line serves the essential purpose of marking for patch
699	handling tools where the changelog message ends.
701	One good use for the additional comments after the "---" marker is for
702	a diffstat, to show what files have changed, and the number of
703	inserted and deleted lines per file.  A diffstat is especially useful
704	on bigger patches.  Other comments relevant only to the moment or the
705	maintainer, not suitable for the permanent changelog, should also go
706	here.  A good example of such comments might be "patch changelogs"
707	which describe what has changed between the v1 and v2 version of the
708	patch.
710	If you are going to include a diffstat after the "---" marker, please
711	use diffstat options "-p 1 -w 70" so that filenames are listed from
712	the top of the kernel source tree and don't use too much horizontal
713	space (easily fit in 80 columns, maybe with some indentation).  (git
714	generates appropriate diffstats by default.)
716	See more details on the proper patch format in the following
717	references.
720	15) Sending "git pull" requests
721	-------------------------------
723	If you have a series of patches, it may be most convenient to have the
724	maintainer pull them directly into the subsystem repository with a
725	"git pull" operation.  Note, however, that pulling patches from a developer
726	requires a higher degree of trust than taking patches from a mailing list.
727	As a result, many subsystem maintainers are reluctant to take pull
728	requests, especially from new, unknown developers.  If in doubt you can use
729	the pull request as the cover letter for a normal posting of the patch
730	series, giving the maintainer the option of using either.
732	A pull request should have [GIT] or [PULL] in the subject line.  The
733	request itself should include the repository name and the branch of
734	interest on a single line; it should look something like:
736	  Please pull from
738	      git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
740	  to get these changes:"
742	A pull request should also include an overall message saying what will be
743	included in the request, a "git shortlog" listing of the patches
744	themselves, and a diffstat showing the overall effect of the patch series.
745	The easiest way to get all this information together is, of course, to let
746	git do it for you with the "git request-pull" command.
748	Some maintainers (including Linus) want to see pull requests from signed
749	commits; that increases their confidence that the request actually came
750	from you.  Linus, in particular, will not pull from public hosting sites
751	like GitHub in the absence of a signed tag.
753	The first step toward creating such tags is to make a GNUPG key and get it
754	signed by one or more core kernel developers.  This step can be hard for
755	new developers, but there is no way around it.  Attending conferences can
756	be a good way to find developers who can sign your key.
758	Once you have prepared a patch series in git that you wish to have somebody
759	pull, create a signed tag with "git tag -s".  This will create a new tag
760	identifying the last commit in the series and containing a signature
761	created with your private key.  You will also have the opportunity to add a
762	changelog-style message to the tag; this is an ideal place to describe the
763	effects of the pull request as a whole.
765	If the tree the maintainer will be pulling from is not the repository you
766	are working from, don't forget to push the signed tag explicitly to the
767	public tree.
769	When generating your pull request, use the signed tag as the target.  A
770	command like this will do the trick:
772	  git request-pull master git://my.public.tree/linux.git my-signed-tag
775	----------------------
777	----------------------
779	Andrew Morton, "The perfect patch" (tpp).
780	  <http://www.ozlabs.org/~akpm/stuff/tpp.txt>
782	Jeff Garzik, "Linux kernel patch submission format".
783	  <http://linux.yyz.us/patch-format.html>
785	Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
786	  <http://www.kroah.com/log/linux/maintainer.html>
787	  <http://www.kroah.com/log/linux/maintainer-02.html>
788	  <http://www.kroah.com/log/linux/maintainer-03.html>
789	  <http://www.kroah.com/log/linux/maintainer-04.html>
790	  <http://www.kroah.com/log/linux/maintainer-05.html>
791	  <http://www.kroah.com/log/linux/maintainer-06.html>
793	NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
794	  <https://lkml.org/lkml/2005/7/11/336>
796	Kernel Documentation/CodingStyle:
797	  <http://users.sosdg.org/~qiyong/lxr/source/Documentation/CodingStyle>
799	Linus Torvalds's mail on the canonical patch format:
800	  <http://lkml.org/lkml/2005/4/7/183>
802	Andi Kleen, "On submitting kernel patches"
803	  Some strategies to get difficult or controversial changes in.
804	  http://halobates.de/on-submitting-patches.pdf
806	--
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