1.. _development_followthrough: 2 3Followthrough 4============= 5 6At this point, you have followed the guidelines given so far and, with the 7addition of your own engineering skills, have posted a perfect series of 8patches. One of the biggest mistakes that even experienced kernel 9developers can make is to conclude that their work is now done. In truth, 10posting patches indicates a transition into the next stage of the process, 11with, possibly, quite a bit of work yet to be done. 12 13It is a rare patch which is so good at its first posting that there is no 14room for improvement. The kernel development process recognizes this fact, 15and, as a result, is heavily oriented toward the improvement of posted 16code. You, as the author of that code, will be expected to work with the 17kernel community to ensure that your code is up to the kernel's quality 18standards. A failure to participate in this process is quite likely to 19prevent the inclusion of your patches into the mainline. 20 21 22Working with reviewers 23---------------------- 24 25A patch of any significance will result in a number of comments from other 26developers as they review the code. Working with reviewers can be, for 27many developers, the most intimidating part of the kernel development 28process. Life can be made much easier, though, if you keep a few things in 29mind: 30 31 - If you have explained your patch well, reviewers will understand its 32 value and why you went to the trouble of writing it. But that value 33 will not keep them from asking a fundamental question: what will it be 34 like to maintain a kernel with this code in it five or ten years later? 35 Many of the changes you may be asked to make - from coding style tweaks 36 to substantial rewrites - come from the understanding that Linux will 37 still be around and under development a decade from now. 38 39 - Code review is hard work, and it is a relatively thankless occupation; 40 people remember who wrote kernel code, but there is little lasting fame 41 for those who reviewed it. So reviewers can get grumpy, especially when 42 they see the same mistakes being made over and over again. If you get a 43 review which seems angry, insulting, or outright offensive, resist the 44 impulse to respond in kind. Code review is about the code, not about 45 the people, and code reviewers are not attacking you personally. 46 47 - Similarly, code reviewers are not trying to promote their employers' 48 agendas at the expense of your own. Kernel developers often expect to 49 be working on the kernel years from now, but they understand that their 50 employer could change. They truly are, almost without exception, 51 working toward the creation of the best kernel they can; they are not 52 trying to create discomfort for their employers' competitors. 53 54What all of this comes down to is that, when reviewers send you comments, 55you need to pay attention to the technical observations that they are 56making. Do not let their form of expression or your own pride keep that 57from happening. When you get review comments on a patch, take the time to 58understand what the reviewer is trying to say. If possible, fix the things 59that the reviewer is asking you to fix. And respond back to the reviewer: 60thank them, and describe how you will answer their questions. 61 62Note that you do not have to agree with every change suggested by 63reviewers. If you believe that the reviewer has misunderstood your code, 64explain what is really going on. If you have a technical objection to a 65suggested change, describe it and justify your solution to the problem. If 66your explanations make sense, the reviewer will accept them. Should your 67explanation not prove persuasive, though, especially if others start to 68agree with the reviewer, take some time to think things over again. It can 69be easy to become blinded by your own solution to a problem to the point 70that you don't realize that something is fundamentally wrong or, perhaps, 71you're not even solving the right problem. 72 73Andrew Morton has suggested that every review comment which does not result 74in a code change should result in an additional code comment instead; that 75can help future reviewers avoid the questions which came up the first time 76around. 77 78One fatal mistake is to ignore review comments in the hope that they will 79go away. They will not go away. If you repost code without having 80responded to the comments you got the time before, you're likely to find 81that your patches go nowhere. 82 83Speaking of reposting code: please bear in mind that reviewers are not 84going to remember all the details of the code you posted the last time 85around. So it is always a good idea to remind reviewers of previously 86raised issues and how you dealt with them; the patch changelog is a good 87place for this kind of information. Reviewers should not have to search 88through list archives to familiarize themselves with what was said last 89time; if you help them get a running start, they will be in a better mood 90when they revisit your code. 91 92What if you've tried to do everything right and things still aren't going 93anywhere? Most technical disagreements can be resolved through discussion, 94but there are times when somebody simply has to make a decision. If you 95honestly believe that this decision is going against you wrongly, you can 96always try appealing to a higher power. As of this writing, that higher 97power tends to be Andrew Morton. Andrew has a great deal of respect in the 98kernel development community; he can often unjam a situation which seems to 99be hopelessly blocked. Appealing to Andrew should not be done lightly, 100though, and not before all other alternatives have been explored. And bear 101in mind, of course, that he may not agree with you either. 102 103 104What happens next 105----------------- 106 107If a patch is considered to be a good thing to add to the kernel, and once 108most of the review issues have been resolved, the next step is usually 109entry into a subsystem maintainer's tree. How that works varies from one 110subsystem to the next; each maintainer has his or her own way of doing 111things. In particular, there may be more than one tree - one, perhaps, 112dedicated to patches planned for the next merge window, and another for 113longer-term work. 114 115For patches applying to areas for which there is no obvious subsystem tree 116(memory management patches, for example), the default tree often ends up 117being -mm. Patches which affect multiple subsystems can also end up going 118through the -mm tree. 119 120Inclusion into a subsystem tree can bring a higher level of visibility to a 121patch. Now other developers working with that tree will get the patch by 122default. Subsystem trees typically feed linux-next as well, making their 123contents visible to the development community as a whole. At this point, 124there's a good chance that you will get more comments from a new set of 125reviewers; these comments need to be answered as in the previous round. 126 127What may also happen at this point, depending on the nature of your patch, 128is that conflicts with work being done by others turn up. In the worst 129case, heavy patch conflicts can result in some work being put on the back 130burner so that the remaining patches can be worked into shape and merged. 131Other times, conflict resolution will involve working with the other 132developers and, possibly, moving some patches between trees to ensure that 133everything applies cleanly. This work can be a pain, but count your 134blessings: before the advent of the linux-next tree, these conflicts often 135only turned up during the merge window and had to be addressed in a hurry. 136Now they can be resolved at leisure, before the merge window opens. 137 138Some day, if all goes well, you'll log on and see that your patch has been 139merged into the mainline kernel. Congratulations! Once the celebration is 140complete (and you have added yourself to the MAINTAINERS file), though, it 141is worth remembering an important little fact: the job still is not done. 142Merging into the mainline brings its own challenges. 143 144To begin with, the visibility of your patch has increased yet again. There 145may be a new round of comments from developers who had not been aware of 146the patch before. It may be tempting to ignore them, since there is no 147longer any question of your code being merged. Resist that temptation, 148though; you still need to be responsive to developers who have questions or 149suggestions. 150 151More importantly, though: inclusion into the mainline puts your code into 152the hands of a much larger group of testers. Even if you have contributed 153a driver for hardware which is not yet available, you will be surprised by 154how many people will build your code into their kernels. And, of course, 155where there are testers, there will be bug reports. 156 157The worst sort of bug reports are regressions. If your patch causes a 158regression, you'll find an uncomfortable number of eyes upon you; 159regressions need to be fixed as soon as possible. If you are unwilling or 160unable to fix the regression (and nobody else does it for you), your patch 161will almost certainly be removed during the stabilization period. Beyond 162negating all of the work you have done to get your patch into the mainline, 163having a patch pulled as the result of a failure to fix a regression could 164well make it harder for you to get work merged in the future. 165 166After any regressions have been dealt with, there may be other, ordinary 167bugs to deal with. The stabilization period is your best opportunity to 168fix these bugs and ensure that your code's debut in a mainline kernel 169release is as solid as possible. So, please, answer bug reports, and fix 170the problems if at all possible. That's what the stabilization period is 171for; you can start creating cool new patches once any problems with the old 172ones have been taken care of. 173 174And don't forget that there are other milestones which may also create bug 175reports: the next mainline stable release, when prominent distributors pick 176up a version of the kernel containing your patch, etc. Continuing to 177respond to these reports is a matter of basic pride in your work. If that 178is insufficient motivation, though, it's also worth considering that the 179development community remembers developers who lose interest in their code 180after it's merged. The next time you post a patch, they will be evaluating 181it with the assumption that you will not be around to maintain it 182afterward. 183 184 185Other things that can happen 186----------------------------- 187 188One day, you may open your mail client and see that somebody has mailed you 189a patch to your code. That is one of the advantages of having your code 190out there in the open, after all. If you agree with the patch, you can 191either forward it on to the subsystem maintainer (be sure to include a 192proper From: line so that the attribution is correct, and add a signoff of 193your own), or send an Acked-by: response back and let the original poster 194send it upward. 195 196If you disagree with the patch, send a polite response explaining why. If 197possible, tell the author what changes need to be made to make the patch 198acceptable to you. There is a certain resistance to merging patches which 199are opposed by the author and maintainer of the code, but it only goes so 200far. If you are seen as needlessly blocking good work, those patches will 201eventually flow around you and get into the mainline anyway. In the Linux 202kernel, nobody has absolute veto power over any code. Except maybe Linus. 203 204On very rare occasion, you may see something completely different: another 205developer posts a different solution to your problem. At that point, 206chances are that one of the two patches will not be merged, and "mine was 207here first" is not considered to be a compelling technical argument. If 208somebody else's patch displaces yours and gets into the mainline, there is 209really only one way to respond: be pleased that your problem got solved and 210get on with your work. Having one's work shoved aside in this manner can 211be hurtful and discouraging, but the community will remember your reaction 212long after they have forgotten whose patch actually got merged. 213