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Architecture, community & Linus's role

Glyn Moody: What major architecture changes have there been to support new hardware?

Linus Torvalds: The USB stack has basically been re-written a couple of time just because some new use-case comes up and you realise that hey, the original USB stack just never took that into account, and it just doesn't work. So USB 3.0 needs new host controller support and it turns out it's different enough that you want to change the core stack so that it can work across different versions. And it's not just USB, it's PCI, and PCI becomes PCIe, and hotplug comes in.

That's another thing that's a huge difference between traditional Linux and traditional Unix. You have a [Unix] workstation and you boot it up, and it doesn't change afterwards – you don't add devices. Now people are taking adding a USB device for granted, but realistically that did not use to be the case. That whole being able to hotplug devices, we've had all these fundamental infrastructure changes that we've had to keep up with.

Glyn Moody: What about kernel community – how has that evolved?

Linus Torvalds: It used to be way flatter. I don't know when the change happened, but it used to be me and maybe 50 developers – it was not a deep hierarchy of people. These days, patches that reach me sometimes go through four levels of people. We do releases every three months; in every release we have like 1,000 people involved. And 500 of the 1,000 people basically send in a single line change for something really trivial – that's how some people work, and some of them never do anything else, and that's fine. But when you have a thousand people involved, especially when some of them are just these drive-by shooting people, you can't have me just taking patches from everybody individually. I wouldn't have time to interact with people.

Some people just specialise in drivers, they have other people who they know who specialise in that particular driver area, and they interact with the people who actually write the individual drivers or send patches. By the time I see the patch, it's gone through these layers, it's seldom four, but it's quite often two people in between.

Glyn Moody: So what impact does that have on your role?

Linus Torvalds: Well, the big thing is I don't read code any more. When a patch has already gone through two people, at that point, I can either look at the patch and say: no, all your work was wasted, and micromanage at that level – and quite frankly I don't want to do that, and I don't have the capacity to do that.

So most of the time, when it comes to the major subsystem maintainers, I trust them because I've been working with them for 5, 10, 15 years, so I don't even look at the code. They tell me these are the changes and they give me a very high-level overview. Depending on the person, it might be five lines of text saying this is roughly what has changed, and then they give me a diffstat, which just says 15 lines have changed in that file, and 25 lines have changed in that file and diffstat might be a few hundred lines because there's a few hundred files that have changed. But I don't even see the code itself, I just say: OK, the changes happen in these files, and by the way, I trust you to change those files, so that's fine. And then I just say: I'll take it.

Glyn Moody: So what's your role now?

Linus Torvalds: Largely I'm managing people. Not in the logistical sense – I obviously don't pay anybody, but I also don't have to worry about them having access to hardware and stuff like that. Largely what happens is I get involved when people start arguing and there's friction between people, or when bugs happen.

Bugs happen all the time, but quite often people don't know who to send the bug report to. So they will send the bug report to the Linux Kernel mailing list – nobody really is able to read it much. After people don't figure it out on the kernel mailing list, they often start bombarding me, saying: hey, this machine doesn't work for me any more. And since I didn't even read the code in the first place, but I know who is in charge, I end up being a connection point for bug reports and for the actual change requests. That's all I do, day in and day out, is I read email. And that's fine, I enjoy doing it, but it's very different from what I did.

Next: Another tool? Tablets and clouds.

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