[CopperWing]

The DMA subsystem maintainer has some reasons: at this time you can disable all rust drivers when building the Linux kernel but you cannot disable rust wrappers to C language APIs. So if you need to change for example the DMA APIs, you also need to fix the rust wrapper before submitting the C patches otherwise you cannot even build a C only kernel.

[Zollerboy1]

A C only kernel build without CONFIG_RUST will not build a single line of Rust code nor will it touch anything in the rust subdirectory. If you don’t want to deal with rust, you don’t have to at all.

[WesolyKubeczek]

It’s a little bit more nuanced than this. Your parent commenter is wrong, by the way.

Suppose you want Rust, just not a single Rust driver using PCI. But CONFIG_PCI and CONFIG_RUST both selected will cause the PCI abstractions to get built anyway, even if not a single driver using them is selected. Then if the PCI subsystem introduces a change but the Rust counterpart fails to follow it fast enough, the build will break for the kernel as a whole.

This was illustrated with an example in that email thread.

I have some sad experience with polyglot projects. Unless you enjoy pain and drudgery, it’s an extremely unrewarding thing requiring very careful treading.

[paholg]

I don't think that's true. I have seen R4L folks reiterate time and again that C changes are allowed to break Rust code, and they will be the ones to fix it.