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

3	At this point, you have followed the guidelines given so far and, with the
4	addition of your own engineering skills, have posted a perfect series of
5	patches.  One of the biggest mistakes that even experienced kernel
6	developers can make is to conclude that their work is now done.  In truth,
7	posting patches indicates a transition into the next stage of the process,
8	with, possibly, quite a bit of work yet to be done.
10	It is a rare patch which is so good at its first posting that there is no
11	room for improvement.  The kernel development process recognizes this fact,
12	and, as a result, is heavily oriented toward the improvement of posted
13	code.  You, as the author of that code, will be expected to work with the
14	kernel community to ensure that your code is up to the kernel's quality
15	standards.  A failure to participate in this process is quite likely to
16	prevent the inclusion of your patches into the mainline.
21	A patch of any significance will result in a number of comments from other
22	developers as they review the code.  Working with reviewers can be, for
23	many developers, the most intimidating part of the kernel development
24	process.  Life can be made much easier, though, if you keep a few things in
25	mind:
27	 - If you have explained your patch well, reviewers will understand its
28	   value and why you went to the trouble of writing it.  But that value
29	   will not keep them from asking a fundamental question: what will it be
30	   like to maintain a kernel with this code in it five or ten years later?
31	   Many of the changes you may be asked to make - from coding style tweaks
32	   to substantial rewrites - come from the understanding that Linux will
33	   still be around and under development a decade from now.
35	 - Code review is hard work, and it is a relatively thankless occupation;
36	   people remember who wrote kernel code, but there is little lasting fame
37	   for those who reviewed it.  So reviewers can get grumpy, especially when
38	   they see the same mistakes being made over and over again.  If you get a
39	   review which seems angry, insulting, or outright offensive, resist the
40	   impulse to respond in kind.  Code review is about the code, not about
41	   the people, and code reviewers are not attacking you personally.
43	 - Similarly, code reviewers are not trying to promote their employers'
44	   agendas at the expense of your own.  Kernel developers often expect to
45	   be working on the kernel years from now, but they understand that their
46	   employer could change.  They truly are, almost without exception,
47	   working toward the creation of the best kernel they can; they are not
48	   trying to create discomfort for their employers' competitors.
50	What all of this comes down to is that, when reviewers send you comments,
51	you need to pay attention to the technical observations that they are
52	making.  Do not let their form of expression or your own pride keep that
53	from happening.  When you get review comments on a patch, take the time to
54	understand what the reviewer is trying to say.  If possible, fix the things
55	that the reviewer is asking you to fix.  And respond back to the reviewer:
56	thank them, and describe how you will answer their questions.
58	Note that you do not have to agree with every change suggested by
59	reviewers.  If you believe that the reviewer has misunderstood your code,
60	explain what is really going on.  If you have a technical objection to a
61	suggested change, describe it and justify your solution to the problem.  If
62	your explanations make sense, the reviewer will accept them.  Should your
63	explanation not prove persuasive, though, especially if others start to
64	agree with the reviewer, take some time to think things over again.  It can
65	be easy to become blinded by your own solution to a problem to the point
66	that you don't realize that something is fundamentally wrong or, perhaps,
67	you're not even solving the right problem.
69	Andrew Morton has suggested that every review comment which does not result
70	in a code change should result in an additional code comment instead; that
71	can help future reviewers avoid the questions which came up the first time
72	around.
74	One fatal mistake is to ignore review comments in the hope that they will
75	go away.  They will not go away.  If you repost code without having
76	responded to the comments you got the time before, you're likely to find
77	that your patches go nowhere.
79	Speaking of reposting code: please bear in mind that reviewers are not
80	going to remember all the details of the code you posted the last time
81	around.  So it is always a good idea to remind reviewers of previously
82	raised issues and how you dealt with them; the patch changelog is a good
83	place for this kind of information.  Reviewers should not have to search
84	through list archives to familiarize themselves with what was said last
85	time; if you help them get a running start, they will be in a better mood
86	when they revisit your code.
88	What if you've tried to do everything right and things still aren't going
89	anywhere?  Most technical disagreements can be resolved through discussion,
90	but there are times when somebody simply has to make a decision.  If you
91	honestly believe that this decision is going against you wrongly, you can
92	always try appealing to a higher power.  As of this writing, that higher
93	power tends to be Andrew Morton.  Andrew has a great deal of respect in the
94	kernel development community; he can often unjam a situation which seems to
95	be hopelessly blocked.  Appealing to Andrew should not be done lightly,
96	though, and not before all other alternatives have been explored.  And bear
97	in mind, of course, that he may not agree with you either.
102	If a patch is considered to be a good thing to add to the kernel, and once
103	most of the review issues have been resolved, the next step is usually
104	entry into a subsystem maintainer's tree.  How that works varies from one
105	subsystem to the next; each maintainer has his or her own way of doing
106	things.  In particular, there may be more than one tree - one, perhaps,
107	dedicated to patches planned for the next merge window, and another for
108	longer-term work.
110	For patches applying to areas for which there is no obvious subsystem tree
111	(memory management patches, for example), the default tree often ends up
112	being -mm.  Patches which affect multiple subsystems can also end up going
113	through the -mm tree.
115	Inclusion into a subsystem tree can bring a higher level of visibility to a
116	patch.  Now other developers working with that tree will get the patch by
117	default.  Subsystem trees typically feed linux-next as well, making their
118	contents visible to the development community as a whole.  At this point,
119	there's a good chance that you will get more comments from a new set of
120	reviewers; these comments need to be answered as in the previous round.
122	What may also happen at this point, depending on the nature of your patch,
123	is that conflicts with work being done by others turn up.  In the worst
124	case, heavy patch conflicts can result in some work being put on the back
125	burner so that the remaining patches can be worked into shape and merged.
126	Other times, conflict resolution will involve working with the other
127	developers and, possibly, moving some patches between trees to ensure that
128	everything applies cleanly.  This work can be a pain, but count your
129	blessings: before the advent of the linux-next tree, these conflicts often
130	only turned up during the merge window and had to be addressed in a hurry.
131	Now they can be resolved at leisure, before the merge window opens.
133	Some day, if all goes well, you'll log on and see that your patch has been
134	merged into the mainline kernel.  Congratulations!  Once the celebration is
135	complete (and you have added yourself to the MAINTAINERS file), though, it
136	is worth remembering an important little fact: the job still is not done.
137	Merging into the mainline brings its own challenges.
139	To begin with, the visibility of your patch has increased yet again.  There
140	may be a new round of comments from developers who had not been aware of
141	the patch before.  It may be tempting to ignore them, since there is no
142	longer any question of your code being merged.  Resist that temptation,
143	though; you still need to be responsive to developers who have questions or
144	suggestions.
146	More importantly, though: inclusion into the mainline puts your code into
147	the hands of a much larger group of testers.  Even if you have contributed
148	a driver for hardware which is not yet available, you will be surprised by
149	how many people will build your code into their kernels.  And, of course,
150	where there are testers, there will be bug reports.
152	The worst sort of bug reports are regressions.  If your patch causes a
153	regression, you'll find an uncomfortable number of eyes upon you;
154	regressions need to be fixed as soon as possible.  If you are unwilling or
155	unable to fix the regression (and nobody else does it for you), your patch
156	will almost certainly be removed during the stabilization period.  Beyond
157	negating all of the work you have done to get your patch into the mainline,
158	having a patch pulled as the result of a failure to fix a regression could
159	well make it harder for you to get work merged in the future.
161	After any regressions have been dealt with, there may be other, ordinary
162	bugs to deal with.  The stabilization period is your best opportunity to
163	fix these bugs and ensure that your code's debut in a mainline kernel
164	release is as solid as possible.  So, please, answer bug reports, and fix
165	the problems if at all possible.  That's what the stabilization period is
166	for; you can start creating cool new patches once any problems with the old
167	ones have been taken care of.
169	And don't forget that there are other milestones which may also create bug
170	reports: the next mainline stable release, when prominent distributors pick
171	up a version of the kernel containing your patch, etc.  Continuing to
172	respond to these reports is a matter of basic pride in your work.  If that
173	is insufficient motivation, though, it's also worth considering that the
174	development community remembers developers who lose interest in their code
175	after it's merged.  The next time you post a patch, they will be evaluating
176	it with the assumption that you will not be around to maintain it
177	afterward.
182	One day, you may open your mail client and see that somebody has mailed you
183	a patch to your code.  That is one of the advantages of having your code
184	out there in the open, after all.  If you agree with the patch, you can
185	either forward it on to the subsystem maintainer (be sure to include a
186	proper From: line so that the attribution is correct, and add a signoff of
187	your own), or send an Acked-by: response back and let the original poster
188	send it upward.
190	If you disagree with the patch, send a polite response explaining why.  If
191	possible, tell the author what changes need to be made to make the patch
192	acceptable to you.  There is a certain resistance to merging patches which
193	are opposed by the author and maintainer of the code, but it only goes so
194	far.  If you are seen as needlessly blocking good work, those patches will
195	eventually flow around you and get into the mainline anyway.  In the Linux
196	kernel, nobody has absolute veto power over any code.  Except maybe Linus.
198	On very rare occasion, you may see something completely different: another
199	developer posts a different solution to your problem.  At that point,
200	chances are that one of the two patches will not be merged, and "mine was
201	here first" is not considered to be a compelling technical argument.  If
202	somebody else's patch displaces yours and gets into the mainline, there is
203	really only one way to respond: be pleased that your problem got solved and
204	get on with your work.  Having one's work shoved aside in this manner can
205	be hurtful and discouraging, but the community will remember your reaction
206	long after they have forgotten whose patch actually got merged.
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