This right here. Rust only JUST got added to the kernel in 6.0 and I doubt that it will replace 30 years of C development any time soon.

> AFAIK Torvalds has also stipulated that any Rust code needs to be mirrored in C.

Do you have a cite for this? I hadn't heard this at all.

A significant amount of the lines of code in the kernel are for drivers (7 of 12 million lines?).

A potential strategy would be to set a date where any new drivers must be written in Rust. Deprecate every non-Rust driver on a date after that. Focus on rewriting only the drivers necessary for current hardware platforms (and some sensible/arbitrary cut-off going back x years). Then set a final deadline for a New Linux kernel release that removes all deprecated/C drivers.

I would blindly estimate that entire process to take 10-20 years (not including the time needed for debating the whole thing).

Then somebody "just" needs to rewrite the rest of the code.

So, uh, any volunteers?

They said a C-free build. For that you'd need to "just" rewrite the core kernel, which will be 150-200k lines, and the drivers + arch specific parts for one system. Still a tall order, but a decade isn't unrealistic if Rust proves itself.

Now, rewriting everything, including all the legacy drivers? Yeah, never happening even if Rust succeeds utterly.

I don't see such a feat taking place in the next decade, you need highly dedicated people. I can see new code being written in Rust but a C free build sounds like something that really won't be happening anytime soon.

I wish something like it could happen, but I am causyiously optimistic.

There are some open issues and features like inline assembly that aren't supported, but a moderately complete backend exists now:

https://github.com/bjorn3/rustc_codegen_cranelift

The compiler frontend is already written in Rust.

Honest question: what would the engineering rationale be behind dropping LLVM entirely and have rustc have its own code generation backend? There are two out there that might be interesting, one uses gcc and another is called cranelift, but it isn't the default and focuses exclusively on compilation speed for debug binaries.

If anything, it's more likely that the desirable choice is to shift LLVM to Rust.

By the time it's rewritten in Rust, old drivers will be dropped due to lack of demand for them.