alt Hacker NewsIt's important to note that the `unsafe` keyword is poorly named. What it does is unlock a few more capabilities at the cost of upholding the invariants the spec requires. It should really be called "assured" or something. The programmer is taking the wheel from the compiler and promising to drive safely.
As for why there is unsafe in the kernel? There are things, especially in a kernel, that cannot be expressed in safe Rust.
Still, having smaller sections of unsafe is a boon because you isolate these locations of elevated power, meaning they are auditable and obvious. Rust also excels at wrapping unsafe in safe abstractions that are impossible to misuse. A common comparison point is that in C your entire program is effectively unsafe, whereas in Rust it's a subset.
EDIT: Hacker News has limited my ability to respond. Please keep in mind that Rust has a large number of active fans, who may have biases for whatever reasons.
> Still, having smaller sections of unsafe is a boon because you isolate these locations of elevated power, meaning they are auditable and obvious.
The Rustonomicon makes it very clear that it is generally insufficient to only verify correctness of Rust-unsafe blocks. If the absence of UB in a Rust-unsafe block depends on Rust-not-unsafe code in the surrounding module, potentially the whole module has to be verified for correctness. And that assumes that the module has correct encapsulation, otherwise even more may have to be verified. And a single buggy change to Rust-not-unsafe code can cause UB, if a Rust-unsafe block somewhere depends on that code to be correct.