6.Followthrough.rst 12 KB

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  1. .. _development_followthrough:
  2. Followthrough
  3. =============
  4. At this point, you have followed the guidelines given so far and, with the
  5. addition of your own engineering skills, have posted a perfect series of
  6. patches. One of the biggest mistakes that even experienced kernel
  7. developers can make is to conclude that their work is now done. In truth,
  8. posting patches indicates a transition into the next stage of the process,
  9. 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.
  17. Working with reviewers
  18. ----------------------
  19. A patch of any significance will result in a number of comments from other
  20. developers as they review the code. Working with reviewers can be, for
  21. many developers, the most intimidating part of the kernel development
  22. process. Life can be made much easier, though, if you keep a few things in
  23. mind:
  24. - If you have explained your patch well, reviewers will understand its
  25. value and why you went to the trouble of writing it. But that value
  26. will not keep them from asking a fundamental question: what will it be
  27. like to maintain a kernel with this code in it five or ten years later?
  28. Many of the changes you may be asked to make - from coding style tweaks
  29. to substantial rewrites - come from the understanding that Linux will
  30. still be around and under development a decade from now.
  31. - Code review is hard work, and it is a relatively thankless occupation;
  32. people remember who wrote kernel code, but there is little lasting fame
  33. for those who reviewed it. So reviewers can get grumpy, especially when
  34. they see the same mistakes being made over and over again. If you get a
  35. review which seems angry, insulting, or outright offensive, resist the
  36. impulse to respond in kind. Code review is about the code, not about
  37. the people, and code reviewers are not attacking you personally.
  38. - Similarly, code reviewers are not trying to promote their employers'
  39. agendas at the expense of your own. Kernel developers often expect to
  40. be working on the kernel years from now, but they understand that their
  41. employer could change. They truly are, almost without exception,
  42. working toward the creation of the best kernel they can; they are not
  43. trying to create discomfort for their employers' competitors.
  44. What all of this comes down to is that, when reviewers send you comments,
  45. you need to pay attention to the technical observations that they are
  46. making. Do not let their form of expression or your own pride keep that
  47. from happening. When you get review comments on a patch, take the time to
  48. understand what the reviewer is trying to say. If possible, fix the things
  49. that the reviewer is asking you to fix. And respond back to the reviewer:
  50. thank them, and describe how you will answer their questions.
  51. Note that you do not have to agree with every change suggested by
  52. reviewers. If you believe that the reviewer has misunderstood your code,
  53. explain what is really going on. If you have a technical objection to a
  54. suggested change, describe it and justify your solution to the problem. If
  55. your explanations make sense, the reviewer will accept them. Should your
  56. explanation not prove persuasive, though, especially if others start to
  57. agree with the reviewer, take some time to think things over again. It can
  58. be easy to become blinded by your own solution to a problem to the point
  59. that you don't realize that something is fundamentally wrong or, perhaps,
  60. you're not even solving the right problem.
  61. Andrew Morton has suggested that every review comment which does not result
  62. in a code change should result in an additional code comment instead; that
  63. can help future reviewers avoid the questions which came up the first time
  64. around.
  65. One fatal mistake is to ignore review comments in the hope that they will
  66. go away. They will not go away. If you repost code without having
  67. responded to the comments you got the time before, you're likely to find
  68. that your patches go nowhere.
  69. Speaking of reposting code: please bear in mind that reviewers are not
  70. going to remember all the details of the code you posted the last time
  71. around. So it is always a good idea to remind reviewers of previously
  72. raised issues and how you dealt with them; the patch changelog is a good
  73. place for this kind of information. Reviewers should not have to search
  74. through list archives to familiarize themselves with what was said last
  75. time; if you help them get a running start, they will be in a better mood
  76. when they revisit your code.
  77. What if you've tried to do everything right and things still aren't going
  78. anywhere? Most technical disagreements can be resolved through discussion,
  79. but there are times when somebody simply has to make a decision. If you
  80. honestly believe that this decision is going against you wrongly, you can
  81. always try appealing to a higher power. As of this writing, that higher
  82. power tends to be Andrew Morton. Andrew has a great deal of respect in the
  83. kernel development community; he can often unjam a situation which seems to
  84. be hopelessly blocked. Appealing to Andrew should not be done lightly,
  85. though, and not before all other alternatives have been explored. And bear
  86. in mind, of course, that he may not agree with you either.
  87. What happens next
  88. -----------------
  89. If a patch is considered to be a good thing to add to the kernel, and once
  90. most of the review issues have been resolved, the next step is usually
  91. entry into a subsystem maintainer's tree. How that works varies from one
  92. subsystem to the next; each maintainer has his or her own way of doing
  93. things. In particular, there may be more than one tree - one, perhaps,
  94. dedicated to patches planned for the next merge window, and another for
  95. longer-term work.
  96. For patches applying to areas for which there is no obvious subsystem tree
  97. (memory management patches, for example), the default tree often ends up
  98. being -mm. Patches which affect multiple subsystems can also end up going
  99. through the -mm tree.
  100. Inclusion into a subsystem tree can bring a higher level of visibility to a
  101. patch. Now other developers working with that tree will get the patch by
  102. default. Subsystem trees typically feed linux-next as well, making their
  103. contents visible to the development community as a whole. At this point,
  104. there's a good chance that you will get more comments from a new set of
  105. reviewers; these comments need to be answered as in the previous round.
  106. What may also happen at this point, depending on the nature of your patch,
  107. is that conflicts with work being done by others turn up. In the worst
  108. case, heavy patch conflicts can result in some work being put on the back
  109. burner so that the remaining patches can be worked into shape and merged.
  110. Other times, conflict resolution will involve working with the other
  111. developers and, possibly, moving some patches between trees to ensure that
  112. everything applies cleanly. This work can be a pain, but count your
  113. blessings: before the advent of the linux-next tree, these conflicts often
  114. only turned up during the merge window and had to be addressed in a hurry.
  115. Now they can be resolved at leisure, before the merge window opens.
  116. Some day, if all goes well, you'll log on and see that your patch has been
  117. merged into the mainline kernel. Congratulations! Once the celebration is
  118. complete (and you have added yourself to the MAINTAINERS file), though, it
  119. is worth remembering an important little fact: the job still is not done.
  120. Merging into the mainline brings its own challenges.
  121. To begin with, the visibility of your patch has increased yet again. There
  122. may be a new round of comments from developers who had not been aware of
  123. the patch before. It may be tempting to ignore them, since there is no
  124. longer any question of your code being merged. Resist that temptation,
  125. though; you still need to be responsive to developers who have questions or
  126. suggestions.
  127. More importantly, though: inclusion into the mainline puts your code into
  128. the hands of a much larger group of testers. Even if you have contributed
  129. a driver for hardware which is not yet available, you will be surprised by
  130. how many people will build your code into their kernels. And, of course,
  131. where there are testers, there will be bug reports.
  132. The worst sort of bug reports are regressions. If your patch causes a
  133. regression, you'll find an uncomfortable number of eyes upon you;
  134. regressions need to be fixed as soon as possible. If you are unwilling or
  135. unable to fix the regression (and nobody else does it for you), your patch
  136. will almost certainly be removed during the stabilization period. Beyond
  137. negating all of the work you have done to get your patch into the mainline,
  138. having a patch pulled as the result of a failure to fix a regression could
  139. well make it harder for you to get work merged in the future.
  140. After any regressions have been dealt with, there may be other, ordinary
  141. bugs to deal with. The stabilization period is your best opportunity to
  142. fix these bugs and ensure that your code's debut in a mainline kernel
  143. release is as solid as possible. So, please, answer bug reports, and fix
  144. the problems if at all possible. That's what the stabilization period is
  145. for; you can start creating cool new patches once any problems with the old
  146. ones have been taken care of.
  147. And don't forget that there are other milestones which may also create bug
  148. reports: the next mainline stable release, when prominent distributors pick
  149. up a version of the kernel containing your patch, etc. Continuing to
  150. respond to these reports is a matter of basic pride in your work. If that
  151. is insufficient motivation, though, it's also worth considering that the
  152. development community remembers developers who lose interest in their code
  153. after it's merged. The next time you post a patch, they will be evaluating
  154. it with the assumption that you will not be around to maintain it
  155. afterward.
  156. Other things that can happen
  157. -----------------------------
  158. One day, you may open your mail client and see that somebody has mailed you
  159. a patch to your code. That is one of the advantages of having your code
  160. out there in the open, after all. If you agree with the patch, you can
  161. either forward it on to the subsystem maintainer (be sure to include a
  162. proper From: line so that the attribution is correct, and add a signoff of
  163. your own), or send an Acked-by: response back and let the original poster
  164. send it upward.
  165. If you disagree with the patch, send a polite response explaining why. If
  166. possible, tell the author what changes need to be made to make the patch
  167. acceptable to you. There is a certain resistance to merging patches which
  168. are opposed by the author and maintainer of the code, but it only goes so
  169. far. If you are seen as needlessly blocking good work, those patches will
  170. eventually flow around you and get into the mainline anyway. In the Linux
  171. kernel, nobody has absolute veto power over any code. Except maybe Linus.
  172. On very rare occasion, you may see something completely different: another
  173. developer posts a different solution to your problem. At that point,
  174. chances are that one of the two patches will not be merged, and "mine was
  175. here first" is not considered to be a compelling technical argument. If
  176. somebody else's patch displaces yours and gets into the mainline, there is
  177. really only one way to respond: be pleased that your problem got solved and
  178. get on with your work. Having one's work shoved aside in this manner can
  179. be hurtful and discouraging, but the community will remember your reaction
  180. long after they have forgotten whose patch actually got merged.