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Comment by skydhash | Hacker News Reader

I’m not an OS programmer and have been dabbling with OpenBSD’s code for fun. But the fact is that Rust kinda lacks flexibility. Most of the OS is dedicated to building a beautiful lie for programs to run happily, and that’s where C shine.

I shudder to think about the amount of work that it would take to convince the rust compiler that everything is all right. Most hardware interactions is “parse, don’t validate” which means you’ll be pinky-swearing to the compiler.

And for my cursory glances at the code, most structures are handled well, that it’s mostly logic bug (from bad data) instead of bad memory access (which can happen).

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In practice you don't convince Rust that everything is right. You let it prove that most of the code is right and you promise it (via unsafe) that the rest is. Ideally these unsafe blocks would be carefully documented, reviewed and ideally enclosed in small modules that makes correctness easier to ascertain.

Rust is no panacea, but in my experience it is far easier to write memory safe code when the risky bits are discouraged and explicitly highlighted rather than every line of code being a possible risk. Humans are pretty bad at reviewing 100 lines of boring looking code (especially if this is one of dozens of patches this week) but much better (although by no means excellent at) reviewing 5 2-line unsafe blocks amongst 90 other lines of code.

Most data in the kernel are rather long lived or traversing too many layers. There are too many entry points (system calls, interrupts) into the kernel for guarantees to hold.

And OpenBSD development is rather slow. The tech mailing list average 300-400 mails a month.

I thought that parsing implied validation. Is this not the case?

Validation asserts what’s in the data type, while parsing just creates it. Especially in the context of C structures where you can just create it from a blob of bytes.

Ah, I suppose in my mind parsing precludes the idea of invalid data.

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