Linus and Dirk on succession, Rust, and more

The "Linus and Dirk show" has been a fixture at Open Source Summit for as long as the conference has existed; it started back when the conference was called LinuxCon. Since Linus Torvalds famously does not like to give talks, as he said during this year's edition at Open Source Summit Europe (OSSEU) in Vienna, Austria, he and Dirk Hohndel have been sitting down for an informal chat on a wide range of topics as a keynote session. That way, Torvalds does not need to prepare, but also does not know what topics will be brought up, which makes it "so much more fun for one of us", Hohndel said with a grin. The topics this time ranged from the just-released 6.11 kernel and the upcoming Linux 6.12, through Rust for the kernel, to the recurring topic of succession and the graying of Linux maintainers.

After Torvalds suggested that they had been doing these talks for 20 years, though Hohndel pointed out that the tradition began in 2012, the conversation turned to the weather—a common topic after the surprisingly horrible weather in much of Europe due to Storm Boris. In a massive understatement, Hohndel said that it had been a "wee bit windy" the day before, which he and Torvalds had hoped to use as a sightseeing day, but the day before the conference started (September 15) was not a day to stray far from your hotel. It did give Torvalds plenty of time to do the 6.11 kernel release, which they discussed next.

6.11 and 6.12

Hohndel asked what was interesting in 6.11, but Torvalds replied that, like most every other kernel release over the last 15 years so, it was not particularly exciting, which is exactly how it is supposed to be. The release signals the opening of the two-week merge window, of course, which Torvalds chose to start while he was on the road for OSSEU (as well as the Maintainers Summit and Linux Plumbers Conference). The merge window is where "we're getting all the new code for the next release and that's the fun part" for him. Hohndel noted that Torvalds had been pulling patches on his laptop backstage while they were waiting for the session, "so it is just-in-time delivery of the Linux kernel".

Hohndel said that the bulk of what is being pulled these days seems to be drivers of various sorts, which Torvalds agreed is the case. More than half of the kernel is drivers, which has generally been true over the years, because that is "literally the point of a kernel" since it is meant to "abstract out all the hardware details". So, much of the code flowing in is meant to enable new hardware or to fix the hardware support already in the kernel.

For Torvalds, the surprise is that, after working on Linux for a third of a century now, there are still plenty of changes to the core kernel that are being made. Half of what he merged that day were low-level changes to the virtual filesystem (VFS) layer and there have been lots of discussions lately in the area of memory management. Those core changes are ultimately being driven by expansion in the hardware base, but also by new users, with new ways to use the kernel.

The extensible scheduler class (sched_ext), which allows scheduling decisions to be made by BPF programs, will be coming in 6.12, he said, in answer to a question from Hohndel. Torvalds had not yet merged it, but it was in his queue (and was merged later in the week). Some of the core kernel maintainers are at the conferences this week, so he got a lot of early pull requests the previous week, because they did not want to deal with them during their travel. "I'm stuck with that part", he said to laughter.

The conclusion of the 20-year project to get the realtime patches upstream was another thing that would be part of the next kernel, Torvalds confirmed. (In fact, he pulled the enablement patches on September 20, the day after receiving them in a rather different form.) People think that kernel development is rapid because of the pace of releases, but any given feature "may have been developed over months or years or, in some cases, decades". That development happens in the open on the mailing lists, but people typically do not see the background work that goes into a new feature that seems to just appear in the kernel. But, he agreed, the realtime patches are an outlier in terms of development time, in part because they "touched every single area in the kernel", so there is a lot of convincing and coordination that needed to be done; he knows of no other similar project out there.

Rust

Hohndel said that one of the topics that has been generating a lot of discussion in the community recently is "obviously Rust". He noted that one of the Rust-for-Linux maintainers stepped down citing "'non-technical nonsense' as the reason"; beyond that, there have been problems getting the Apple graphics driver written in Rust merged. He asked: "why is this so hard?"

"I actually enjoy it, I enjoy arguments", Torvalds said; one of the nice things about the Rust effort is that it "has livened up some of the discussions". Some of those arguments "get nasty" and people do "decide that this is not worth my time", but it is interesting and "kind of shows how much people care". He is not sure why Rust, in particular, has been so contentious, however.

The whole "Rust versus C discussion is taking almost religious overtones" that remind him of the vi versus Emacs fights from when he was young, which, Hohndel reminded, still go on. "C is, in the end, a very simple language", Torvalds said, which is why he and lots of other programmers enjoy it. The other side of that, though, is that it is also easy to make mistakes in C. Rust is quite different and there are those who do not like that difference; "that's OK".

There is no one who understands the entire kernel, he said; he relies heavily on the maintainers of various subsystems, since there are only a few areas that he gets personally involved in. There are C people who do not know Rust and the reverse is true as well, which is also fine. One of the nice things about the kernel is that people can specialize: some people care about drivers, others about specific architectures, or still others who like filesystems. "And that's how it should be."

There are, obviously, some people who do not like "the notion of Rust and having Rust encroach on their area". He finds it all interesting, however. People have "even talked about the Rust integration being a failure", which is way too early to determine. Even if that happens, "and I don't think it will, that's how you learn". He sees the Rust effort as a "positive, even if the arguments are not necessarily always".

Torvalds noted that kernel C is "not normal C"; there are a lot of rules on how the code can be written and there are tools to help detect when things go awry. There is memory-safety infrastructure within the kernel project that is not part of the C language, but it has been built up incrementally over the years, which allowed it to avoid any major outcry. The "Rust change is, obviously, a much bigger and a much more in-your-face" thing.

Hohndel agreed that it was too early to say that Rust in the kernel was a failure, but that he had been hearing about efforts to build a Rust kernel from the bottom up as an alternative. He wondered if that was a potential outcome if there continues to be a struggle to get Rust into Linux; "an alternative universe" could perhaps arise from Redox, Maestro, or some other Rust kernel. In terms of languages for building a kernel, Torvalds said, there is not a lot of choice; unless you are going to write in assembly, you have to choose one of the C-like languages—or Rust. Linux is not everywhere, these days, in part because it has gotten "very big" over the last three decades; some developers are looking for something smaller, safer, and "not quite as fully-fledged", which is an area where Rust kernels could perhaps make an impact.

Hohndel disagreed somewhat with that, though he did agree that there are "deeply embedded" use cases where Linux is not used; but for general-purpose systems, "it is everywhere". He noted that most 5G modem chips have a complete Linux distribution running inside; "in your iPhone is a chip that runs, as its firmware, Linux". Torvalds reminded attendees of the old "joke" about "world domination", but "that joke became reality and isn't funny any more", he said to laughter.

Torvalds seemed optimistic that "some clueless young person will decide 'how hard can it be?'" and start their own operating system in Rust or some other language. If they keep at it "for many, many decades", they may get somewhere; "I am looking forward to seeing that". Hohndel clarified that by "clueless", Torvalds was referring to his younger self; "Oh, absolutely, yeah, you have to be all kinds of stupid to say 'I can do this'", he said to more laughter. He could not have done it without the "literally tens of thousands of other people"; the "only reason I ever started was that I didn't know how hard it would be, but that's what makes it fun".

Gray hair and burnout

The kernel Maintainers Summit was being held the next day, Hohndel said, and he expected the topic of burnout to come up. Maintainers are "an aging group", many with less or not "the right color of hair"—though Torvalds interjected: "gray is the right color". Meanwhile, kernel development is showing no signs of slowing down, Hohndel said; in fact, it is "accelerating in many ways, Rust being one of them". He wonders, as maintainers get older and burnout becomes more widespread, if there is a need to talk about "mini-Linus" who would be a successor.

"We have been talking about that forever", Torvalds replied, "some people are probably still disappointed that I'm still here". While it is definitely true that kernel maintainers are aging, the positive spin on that is that he does not know of many projects where maintainers—and not just him—have stuck around for more than three decades. The idea that people "burn out and go away" is true, but that is the norm for most projects; the fact that some stick around on the kernel project for decades is unusual, "and I think that's, to some degree, a good sign".

On the other hand, new developers may look at the project and not really see a place for themselves when they see people who have been with the project for a long time, he said. The kernel project is unlike other open-source projects, since the number of developers just seems to grow; there is a "fairly healthy developer subsystem" in the kernel. "The whole 'monkey dance' about 'developers, developers, developers'—we've got them"; he does not see the presence of some graying developers as a "huge problem".

Hohndel said that he was not claiming that the older maintainers were a problem, per se, just that it indicates things will have to change down the road. Torvalds has been doing Linux for 33 years, but Hohndel suggested that in another 33, he would not be—"possibly" was the reply. The current backup is Greg Kroah-Hartman, "who has even less hair than the two of us" and is around the same age as they are, Hohndel said. "How do we get the next generation to gain the experience" needed so that they can take over Torvalds's role in "10, 15, 20, 30 years", he wondered.

Since the kernel project has so many developers, it has always had a lot of competent people that could step up if needed, Torvalds said. Hohndel had mentioned Kroah-Hartman, but he has not always been the backup, Torvalds said. "Before Greg, there were Andrews [Morton] and Alans [Cox], and after Greg there will be Shannons and Steves, who knows?" It comes down to a matter of trust, he said; there will need to be a person or group of people that the community can trust.

Part of being trusted is having been around for "long enough that people know how you work", but that does not have to be 30 years. There are top-level maintainers for major subsystems who got there in just a few years, he said. In truth, being a maintainer is "not as glorious as it is sometimes conceived"; there are maintainers "who would be more than happy to get new people in to come and help".

Starting out

When they got their start in open source, that world was a smaller and simpler place, Hohndel said; these days, everything is "hype versus reality", and he was "not just talking about AI", with projects focused on making "the quick buck, about the quick exit, versus things that are making a difference". If Torvalds were starting today, did he think it "would be easy to find interesting, rewarding, long-term useful projects"?

Torvalds replied: "I don't think that has ever been easy". But setting up an open-source project is much easier these days; "do a few web clicks and you have a GitHub repository where you can start doing open source". In addition, you do not have to "explain why you are doing open source, because people take that for granted now". That means there are a lot of small projects out there "that you would never have seen 30 years ago".

That said, "it was never easy to find something meaningful that you could spend decades doing", which is still true today. You have to come up with an idea that you are interested in, Torvalds said, "but at the same time, you are not the only one interested in it". People often say "do what you love", but if that is "something that nobody else cares about, you are not going to create the next big, successful open-source project".

Finding something meaningful is particularly hard in the tech industry, where there is so much hype. "Everybody is following everybody else like lemmings off a cliff trying to chase the next big thing." Torvalds does not think that is a successful strategy; instead, "find something that isn't what everybody else does and excel at that". Hohndel interjected that they were out of time; he had hoped to end with something inspirational along the lines of "Linus telling the community where to go and make a difference", but, what he got was lemmings falling off a cliff, he said with a chuckle. That way, though, the session itself ended with laughter.

[ I would like to thank LWN's travel sponsor, the Linux Foundation, for travel assistance to Vienna for Open Source Summit Europe. ]