So The Register managed to incite a lot of discussion with a headline that plain-text e-mail is a barrier to entry for kernel development. While attention grabbing, this is actually not a new debate. Like a lot of tech arguments this one seems to come up on a cyclical basis. Maybe because maintainer summit didn’t happen this year it needed to come out elsewhere. I gave a few thoughts on twitter but this topic really deserves a longer look at the problem and what e-mail being a barrier really means.

Linux celebrated over one million commits recently. The Linux Foundation also came out with a report about the history of kernel development. All of this work was completed with development being done over e-mail. Clearly e-mail has been a successful method of development for the past 29 years by many metrics.

So if it’s so successful why consider changing? Part of the answer to this question lies in not what was accomplished by using e-mail but what was not accomplished because e-mail was the preferred method of development. I marked 10 years of being a full-time software professional a few weeks ago. This was a recent enough time span that I can still remember enough of what it was like to get started. There were a lot of steps to make sure your e-mail setup was correct (i.e. plain text and no weird footers). It was a little tricky but certainly doable. This is where the split comes in: what’s ‘a little tricky’ for one person may prevent someone else from contributing at all. I was fortunate to have enough general working knowledge of Linux to debug git-send-email when it didn’t work as well as having a corporate setup that could actually send plain text e-mail. Google around for how to set up git-send-email and you’ll see this is a step many people struggle with.

“But if you can’t even set up e-mail should you really be working on the kernel?” This is unfortunately a common refrain in this discussion. I’d turn the question on its head: why is setting up e-mail a core skill for working on the kernel? There’s a lot of value in learning and following community norms but what value does that particular norm bring? I’d argue that showing you can set up and use plain text e-mail does not make you a better kernel programmer. Supporting tooling for a project is important but there’s nothing inherent to e-mail that makes it a good indicator of anything. People can only handle keeping track of so many things at once. Having to figure out plain text e-mail is one more task on the stack. Reducing the overhead in mental load to participation lets people focus much more on the actual kernel work. We can maintain tools that take less work to run. Yes, the initial SMTP configuration is a one time setup but sending out a patch each time with git-send-email involves a lot of manual steps. Even if you get the manual steps right there’s always the chance that your e-mail will be rejected due to over zealous spam filtering. There was a three month period or so where all my e-mails to a particular maintainer were being rejected because my 3rd party SMTP server had ended up on a spam blocklist.

“But you can automate e-mail to do the manual parts” To some degree yes but this is hard to do across the entire tree. The kernel has very few unifying standards so for those who work across multiple areas you’re usually left making a best educated guess about where things should go. MAINTAINERS is a good start but it’s not always complete. And even if you can automate everything expecting every contributor to come up with their own automation is not a good use of time. “So provide everyone the automation” and there in lies the problem: the fact that everyone can use their own setup is seen as an advantage so it’s impossible to give something that works for everyone. Even trying to guess what would be the most common setup to give some baseline hasn’t been a fruitful conversation.

“So GitHub is the answer to our problems?” I’m not saying that either. “kids these days are using GitHub so we should switch too” is a very weak argument. Familiarity with a tool is a factor but it shouldn’t be the biggest factor. Everyone, new and experienced developers, can learn new tools. If I thought that e-mail was a suitable tool I would be promoting it as something newer developers should learn. Compare that with git which both new and experienced people will tell you can be difficult to use. It is worthwhile to learn git though and there’s been some improvement in UX recently (git switch). One objection to GitHub is the fact that it’s a proprietary platform. I’m not willing to entertain conspiracy theories about GitHub being owned by Microsoft and therefore wanting to destroy the Linux kernel but before committing to any cloud platform it’s important to do due diligence. Part of the concern about the ‘forge’ nature of GitHub is that it ends up being an single point of failure. Anyone who has tried to get work done when its down will know what a pain this is. The issue is that despite the fact that git is a distributed version control system you end up needing to host your repositories somewhere for pull requests to be useful. Anything that’s useful is going to end up being popular so you’re going to end up with more points of failure. “What if we all just hosted our own git trees” running infrastructure takes time, energy, and money, it’s really nice to not have to think about things like that.

“But e-mail is so much better for discussion and patch review” it’s hard to differentiate sometimes between “better because I’m more familiar with it” and “better because it has features I care about”. Is the experience of reviewing code in GitHub identical to reviewing code in e-mail? No. The steps are different. It’s never going to match 1-to-1. Do I think code review in GitHub is usable? Absolutely. Would I take GitHub review over e-mail? Unclear mostly because it’s hard for me to separate everything else I hate about e-mail patches from the review part. One nice advantage of GitHub is that it is incredibly easy to jump in on threads without having subscribed to the thread first. has improved the experience of replying via e-mail significantly by providing instructions and download links but it’s not as easy as point and click. has also improved the archiving experience significantly which was another area of concern with e-mail. Even with a proper archiving system, discussion is still disconnected from both bug reporting and the code review with e-mail. E-mail is really a lousy bug reporting system simply because it’s easy for things to get lost. “You can filter e-mail” yes, if you know what to filter on. Again, everyone having bespoke artisinal e-mail filters doesn’t actually solve the problem. Having a distinct separation between bug reports and new code is much easier to keep straight. I also grow weary of having to explain to new contributors that LKML is mostly just an archive and sending anything to LKML without another cc is probably not going to get a response (a great way to discourage contributors). Again, there is documentation out there to explain how to contribute but it doesn’t actually need to be this complicated.

“GitHub could never scale to the volume of the Linux Kernel” This is an interesting point. There was some discussion on twitter about monorepos. The kernel does appear to be unique in terms of number of contributors and volume of commits. Maybe GitHub can’t actually scale. That shouldn’t mean the only option ever is e-mail. Git itself came out of a need for a version control system that matched what the kernel needed (we’ll ignore other parts of the BitKeeper saga). The scaling issue often comes up when discussing CI. Those outside the kernel community are somewhat shocked and appalled about how much manual work happens. KernelCI has come a long way in integrating CI as part of the regular development process. It’s not clear if a traditional CI system like GitHub offers would even make sense. For one, testing kernels requires either physical machines to test on or a virtual environment, neither of which are particularly standard for setups like GitHub. The kernel is also (intentionally) designed to work on an incredibly wide variety of hardware. Testing every commit against all possible hardware is next to impossible. Even choosing a limited set of hardware can quickly create a bottleneck for getting anything merged. KernelCI has done a great job trying to balance coverage and speed. Part of the issue with the scaling argument is that it’s a bit of chicken and egg to determine if something like GitHub would actually scale. We can’t switch over because we are concerned it might not scale but we can’t really know if it scales until we switch over. The kernel likes small incremental changes but switching development workflows may be impossible to do incrementally.

Plain text e-mail may not be the biggest barrier for many people wanting to do kernel development but it can still be one. There are plenty of reasons to want something better than e-mail for development. There may be some reasons to stay on e-mail because no better tool exists but “lowering the bar” or other gatekeeping nonsense is not among the reasons. I personally eagerly await the day I don’t have to think about e-mailing patches.