Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.. _development_followthrough:
+
+Followthrough
+=============
+
+At this point, you have followed the guidelines given so far and, with the
+addition of your own engineering skills, have posted a perfect series of
+patches.  One of the biggest mistakes that even experienced kernel
+developers can make is to conclude that their work is now done.  In truth,
+posting patches indicates a transition into the next stage of the process,
+with, possibly, quite a bit of work yet to be done.
+
+It is a rare patch which is so good at its first posting that there is no
+room for improvement.  The kernel development process recognizes this fact,
+and, as a result, is heavily oriented toward the improvement of posted
+code.  You, as the author of that code, will be expected to work with the
+kernel community to ensure that your code is up to the kernel's quality
+standards.  A failure to participate in this process is quite likely to
+prevent the inclusion of your patches into the mainline.
+
+
+Working with reviewers
+----------------------
+
+A patch of any significance will result in a number of comments from other
+developers as they review the code.  Working with reviewers can be, for
+many developers, the most intimidating part of the kernel development
+process.  Life can be made much easier, though, if you keep a few things in
+mind:
+
+ - If you have explained your patch well, reviewers will understand its
+   value and why you went to the trouble of writing it.  But that value
+   will not keep them from asking a fundamental question: what will it be
+   like to maintain a kernel with this code in it five or ten years later?
+   Many of the changes you may be asked to make - from coding style tweaks
+   to substantial rewrites - come from the understanding that Linux will
+   still be around and under development a decade from now.
+
+ - Code review is hard work, and it is a relatively thankless occupation;
+   people remember who wrote kernel code, but there is little lasting fame
+   for those who reviewed it.  So reviewers can get grumpy, especially when
+   they see the same mistakes being made over and over again.  If you get a
+   review which seems angry, insulting, or outright offensive, resist the
+   impulse to respond in kind.  Code review is about the code, not about
+   the people, and code reviewers are not attacking you personally.
+
+ - Similarly, code reviewers are not trying to promote their employers'
+   agendas at the expense of your own.  Kernel developers often expect to
+   be working on the kernel years from now, but they understand that their
+   employer could change.  They truly are, almost without exception,
+   working toward the creation of the best kernel they can; they are not
+   trying to create discomfort for their employers' competitors.
+
+What all of this comes down to is that, when reviewers send you comments,
+you need to pay attention to the technical observations that they are
+making.  Do not let their form of expression or your own pride keep that
+from happening.  When you get review comments on a patch, take the time to
+understand what the reviewer is trying to say.  If possible, fix the things
+that the reviewer is asking you to fix.  And respond back to the reviewer:
+thank them, and describe how you will answer their questions.
+
+Note that you do not have to agree with every change suggested by
+reviewers.  If you believe that the reviewer has misunderstood your code,
+explain what is really going on.  If you have a technical objection to a
+suggested change, describe it and justify your solution to the problem.  If
+your explanations make sense, the reviewer will accept them.  Should your
+explanation not prove persuasive, though, especially if others start to
+agree with the reviewer, take some time to think things over again.  It can
+be easy to become blinded by your own solution to a problem to the point
+that you don't realize that something is fundamentally wrong or, perhaps,
+you're not even solving the right problem.
+
+Andrew Morton has suggested that every review comment which does not result
+in a code change should result in an additional code comment instead; that
+can help future reviewers avoid the questions which came up the first time
+around.
+
+One fatal mistake is to ignore review comments in the hope that they will
+go away.  They will not go away.  If you repost code without having
+responded to the comments you got the time before, you're likely to find
+that your patches go nowhere.
+
+Speaking of reposting code: please bear in mind that reviewers are not
+going to remember all the details of the code you posted the last time
+around.  So it is always a good idea to remind reviewers of previously
+raised issues and how you dealt with them; the patch changelog is a good
+place for this kind of information.  Reviewers should not have to search
+through list archives to familiarize themselves with what was said last
+time; if you help them get a running start, they will be in a better mood
+when they revisit your code.
+
+What if you've tried to do everything right and things still aren't going
+anywhere?  Most technical disagreements can be resolved through discussion,
+but there are times when somebody simply has to make a decision.  If you
+honestly believe that this decision is going against you wrongly, you can
+always try appealing to a higher power.  As of this writing, that higher
+power tends to be Andrew Morton.  Andrew has a great deal of respect in the
+kernel development community; he can often unjam a situation which seems to
+be hopelessly blocked.  Appealing to Andrew should not be done lightly,
+though, and not before all other alternatives have been explored.  And bear
+in mind, of course, that he may not agree with you either.
+
+
+What happens next
+-----------------
+
+If a patch is considered to be a good thing to add to the kernel, and once
+most of the review issues have been resolved, the next step is usually
+entry into a subsystem maintainer's tree.  How that works varies from one
+subsystem to the next; each maintainer has his or her own way of doing
+things.  In particular, there may be more than one tree - one, perhaps,
+dedicated to patches planned for the next merge window, and another for
+longer-term work.
+
+For patches applying to areas for which there is no obvious subsystem tree
+(memory management patches, for example), the default tree often ends up
+being -mm.  Patches which affect multiple subsystems can also end up going
+through the -mm tree.
+
+Inclusion into a subsystem tree can bring a higher level of visibility to a
+patch.  Now other developers working with that tree will get the patch by
+default.  Subsystem trees typically feed linux-next as well, making their
+contents visible to the development community as a whole.  At this point,
+there's a good chance that you will get more comments from a new set of
+reviewers; these comments need to be answered as in the previous round.
+
+What may also happen at this point, depending on the nature of your patch,
+is that conflicts with work being done by others turn up.  In the worst
+case, heavy patch conflicts can result in some work being put on the back
+burner so that the remaining patches can be worked into shape and merged.
+Other times, conflict resolution will involve working with the other
+developers and, possibly, moving some patches between trees to ensure that
+everything applies cleanly.  This work can be a pain, but count your
+blessings: before the advent of the linux-next tree, these conflicts often
+only turned up during the merge window and had to be addressed in a hurry.
+Now they can be resolved at leisure, before the merge window opens.
+
+Some day, if all goes well, you'll log on and see that your patch has been
+merged into the mainline kernel.  Congratulations!  Once the celebration is
+complete (and you have added yourself to the MAINTAINERS file), though, it
+is worth remembering an important little fact: the job still is not done.
+Merging into the mainline brings its own challenges.
+
+To begin with, the visibility of your patch has increased yet again.  There
+may be a new round of comments from developers who had not been aware of
+the patch before.  It may be tempting to ignore them, since there is no
+longer any question of your code being merged.  Resist that temptation,
+though; you still need to be responsive to developers who have questions or
+suggestions.
+
+More importantly, though: inclusion into the mainline puts your code into
+the hands of a much larger group of testers.  Even if you have contributed
+a driver for hardware which is not yet available, you will be surprised by
+how many people will build your code into their kernels.  And, of course,
+where there are testers, there will be bug reports.
+
+The worst sort of bug reports are regressions.  If your patch causes a
+regression, you'll find an uncomfortable number of eyes upon you;
+regressions need to be fixed as soon as possible.  If you are unwilling or
+unable to fix the regression (and nobody else does it for you), your patch
+will almost certainly be removed during the stabilization period.  Beyond
+negating all of the work you have done to get your patch into the mainline,
+having a patch pulled as the result of a failure to fix a regression could
+well make it harder for you to get work merged in the future.
+
+After any regressions have been dealt with, there may be other, ordinary
+bugs to deal with.  The stabilization period is your best opportunity to
+fix these bugs and ensure that your code's debut in a mainline kernel
+release is as solid as possible.  So, please, answer bug reports, and fix
+the problems if at all possible.  That's what the stabilization period is
+for; you can start creating cool new patches once any problems with the old
+ones have been taken care of.
+
+And don't forget that there are other milestones which may also create bug
+reports: the next mainline stable release, when prominent distributors pick
+up a version of the kernel containing your patch, etc.  Continuing to
+respond to these reports is a matter of basic pride in your work.  If that
+is insufficient motivation, though, it's also worth considering that the
+development community remembers developers who lose interest in their code
+after it's merged.  The next time you post a patch, they will be evaluating
+it with the assumption that you will not be around to maintain it
+afterward.
+
+
+Other things that can happen
+-----------------------------
+
+One day, you may open your mail client and see that somebody has mailed you
+a patch to your code.  That is one of the advantages of having your code
+out there in the open, after all.  If you agree with the patch, you can
+either forward it on to the subsystem maintainer (be sure to include a
+proper From: line so that the attribution is correct, and add a signoff of
+your own), or send an Acked-by: response back and let the original poster
+send it upward.
+
+If you disagree with the patch, send a polite response explaining why.  If
+possible, tell the author what changes need to be made to make the patch
+acceptable to you.  There is a certain resistance to merging patches which
+are opposed by the author and maintainer of the code, but it only goes so
+far.  If you are seen as needlessly blocking good work, those patches will
+eventually flow around you and get into the mainline anyway.  In the Linux
+kernel, nobody has absolute veto power over any code.  Except maybe Linus.
+
+On very rare occasion, you may see something completely different: another
+developer posts a different solution to your problem.  At that point,
+chances are that one of the two patches will not be merged, and "mine was
+here first" is not considered to be a compelling technical argument.  If
+somebody else's patch displaces yours and gets into the mainline, there is
+really only one way to respond: be pleased that your problem got solved and
+get on with your work.  Having one's work shoved aside in this manner can
+be hurtful and discouraging, but the community will remember your reaction
+long after they have forgotten whose patch actually got merged.