He is forceful in making his points, but respectful in the way he addressed Christoph's concerns.
This gives me great hope that the Linux maintainer community and contributers using Rust will be able to continue working together, find more common ground, and have more success.
According to the policy, rust folks should fix the rust binding when C changes breaks the binding. The C maintainer don't need to care rust, at all.
In practice, though, I would expect this needs lots of coordination. A PR with C only changes that breaks the whole building (because rust binding is broken) is unlikely to be merged to mainline.
Linus can reiterate his policy, but the issue can't be resolved without some rust developers keep on their persistent work and builds up their reputation.
I have never understood how that could work long-time. How do you release a kernel, where some parts are broken? Either you wait for Rust people to fix their side or you drop the C changes. Or your users suddenly find their driver doesn‘t work anymore after a kernel update.
As a preliminary measure when there isn‘t a substantial amount of Rust code, yet, sure. But the fears of some maintainers that the policy will change to "you either learn Rust and fix things or your code can be held up until someone else helps you out" are well-founded, IMO.
At least for Debian, all you need to do if you hit such a case is to simply go and choose the old kernel in the Grub screen. You don't even need to deal with installing an older package and dealing with version conflicts or other pains of downgrading.
What if Linus decided to go on a two month long vacation in the middle of the merge window?
> I don‘t claim that it can never work (or it cannot work in the common case), but as a hard rule it seems untenable.
There are quite a few rust developers already involved, if they cannot coordinate that at least some are available during a release critical two month period then none of them should be part of any professional project.
It is customary for maintainers to fix _all_ usage of their code themselves? That doesn't seem scalable.
quaff(something, 5, Q_DOOP) ... into ... quaff(something, 5, 0, Q_DEFAULT | (Q_DOOP << 4))
Then it's not beyond the wits of a C programmer to realise that the Rust binding
quaff(var1, n, maybe_doop) ... can be ... quaff(var1, n, 0, Q_DEFAULT | (maybe_doop << 4))
Probably the Rust maintainer will be horrified and emit a patch to do something more idiomatic for binding your new API but there's an excellent chance that meanwhile your minimal patch builds and works since now it has the right number and type of arguments.
Isn’t the point of Coccinelle that you don’t have to spend time walking through (C) driver code you’ve never heard of?
(I do have experience with this causing regressions: someone updates a set of drivers to a new API, and because of the differences and lack of a good way to test, breaks some detail of the driver)
Before features are merged to Linus' release branch, pretty much all changes are published and merged to linux-next first. It is exactly here that build issues and conflicts are first detected and worked out, giving maintainers early visibility into changes that are happening outside their subsystem. Problems with the rust bindings will probably show up here, and the Rust developers will have ample time to fix/realign their code before the merge window even starts. And it's not uncommon for larger features (e.g. when they require coordination across subsystems) to remain in linux-next for more than one cycle.
Then sure, some people who download a kernel release might enable a Rust driver, and that makes the build fail. But until Rust is considered a first-class, fully-supported language in the kernel, that's fine.
In practice, though, I would expect that the Rust maintainers would fix those sorts of things up before an actual release is cut, after the 2-week merge window, during the period when only fixes are accepted. Maybe not every single time, but most of the time; if no one is available to fix a particular bit of breakage, then it's broken for that release. And that's fine too, even if it might be annoying to some users.
> But until Rust is considered a first-class, fully-supported language in the kernel, that's fine
A first-class language whose kernel parts may always break does seem unreasonable. I still think policy will have to change by that point.
Which is currently the only way possible and it will stay that way for a long time because remember that clang support less targets than gcc and gcc cannot compile Rust.
Once gcc can /reliably/ compile Rust, then and only then Rust could be "upgraded" to a first class citizen in Linux. The "C-maintainers don't want to learn Rust" issue, will still be here of course, but there will already be many years of having a mixed code base..
C can break rust, and Debian/Ubuntu/Redhat/suse/etc can wait for it to be fixed before pushing a new kernel to end users.
"I respect you technically, and I like working with you[...] there needs to be people who just stand up to me and tell me I'm full of shit[...] But now I'm calling you out on YOURS."
...and (b) this is me recognizing that me taking charge of a conversation is a different thing than me taking control of your decisions:
"And no, I don't actually think it needs to be all that black-and-white."
(Of course Linus has changed over time for the better, he's recognized that, and I've learned a lot with him and have made amends with old colleagues.)
It's really cool to see someone temper their language and tone, but still keep their tell-it-like-it-is attitude. I probably wouldn't feel good if I were Christoph Hellwig reading that reply, but I also wouldn't feel like someone had personally attacked me and screamed at me far out of proportion to what I'd done.