Based on kernel version 4.1. Page generated on 2015-06-28 12:08 EST.
1 6: FOLLOWTHROUGH 2 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. 9 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 18 19 6.1: WORKING WITH REVIEWERS 20 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: 26 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. 34 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. 42 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. 49 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. 57 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. 68 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. 73 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. 78 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. 87 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. 98 99 100 6.2: WHAT HAPPENS NEXT 101 102 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. 109 110 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. 114 115 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. 121 122 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. 132 133 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. 138 139 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. 145 146 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. 151 152 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. 160 161 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. 168 169 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. 178 179 180 6.3: OTHER THINGS THAT CAN HAPPEN 181 182 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. 189 190 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. 197 198 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.