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Thinking about Rust in the kernel again, does Rust have some kind of generic version of the idea of unsafe/safe code, as an attribute? Often in kernel land you're allowed to call functions only in certain contexts (process, atomic, etc.) and locking has to follow an order.

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Daniel Micay

@DanielMicay

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@marcan42

It can be represented this in the type system with ownership similar to managing resources, lock scopes, etc. Those functions can require a reference to the type of object representing the required state and then it's not possible to call them outside of the lifetime of it.

7:54 AM · May 16, 2022Twitter Web App

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That's not practical because it would mean *every* function has to take such a reference, since the default is "may sleep". The problem isn't functions requiring a special context, it's functions forbidding *all but* a special context.

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It's not able to represent the inverse of that. If there's any way to use a function in a type or memory unsafe way it has to be marked unsafe. Safe code doesn't have non-atomic data races, etc. Most of this is already covered by safe vs. unsafe. You have to make safe primitives.

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You can implement transitions between different states by taking that type by value (consuming it) and returning another type representing another state. What you can't do is enforce the destructor is called since safe code allows making reference cycles or otherwise leaking.