The Linux Foundation’s Rust for Linux: Code Documentation & Tests is an archived LF Live webinar from April 20, 2022—not a current mentorship opening. It is useful for kernel contributors because it separates the safety contract an API publishes from the justification required at each local unsafe operation.
Session details and archive links
| Item | Details |
|---|---|
| Session | Rust for Linux: Code Documentation & Tests |
| Date and time | Recorded April 20, 2022, at 09:00 AM, according to the Linux Foundation webinar archive |
| Presenter and mentor | Miguel Ojeda, identified as Rust for Linux maintainer and LF Live mentor |
| Format | Virtual, free-to-attend LF Live webinar |
| Materials | Official LF Live series page with recording and slides; Linux Foundation webinar archive |
The primary slide deck is available as “Rust for Linux: Code Documentation & Tests” (April 20, 2022).
The central rule: document the contract, then justify each unsafe block
Rust for Linux documentation has two different audiences and two different jobs:
- API documentation tells callers what must be true before they invoke an unsafe function.
- A local
// SAFETY:comment explains why one particular unsafe block is sound in its surrounding code.
Confusing these layers produces documentation that is either unusably vague for callers or disconnected from the code that actually relies on the guarantee.
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Public functions, types, and modules should be documented. For an unsafe function, add a # Safety section that states every precondition a caller must uphold. If an API dereferences a raw pointer, the contract should make the required validity, alignment, and initialization conditions explicit, along with any lifetime, aliasing, ownership, locking, or kernel-state assumptions that the operation depends on.
The section is not a claim that the function is harmless. It is the boundary of responsibility: callers can rely on the implementation to work when the listed conditions hold, and they must not call it when they do not.
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Put the implementation reasoning beside unsafe
Immediately before an unsafe block, write a // SAFETY: comment that connects the operation to facts established by the surrounding code. For example, if a raw pointer is dereferenced, the comment should identify where validity and alignment came from, why the pointed-to memory is initialized, and why no conflicting access can occur at that point.
This comment is local evidence, not a replacement for the public contract. If the same unsafe API is called in three places, each block needs its own explanation because each context establishes the preconditions differently.
“The # Safety sections are critical for users to understand the preconditions.”
— Miguel Ojeda, Rust for Linux: Code Documentation & Tests
Document type invariants as part of the abstraction
A type that promises a property for every valid value should state that property in an # Invariants section. Examples include a non-null pointer wrapper, a range whose bounds are ordered, or a kernel handle that is valid only while a particular resource remains held.
What an invariant section should answer
- What must always be true of every value of the type?
- Which fields, ownership rules, states, or external kernel conditions participate in that property?
- What operations could break it?
Explain preservation in constructors and mutations
Code that creates or mutates the type should explain why the invariant remains true after the operation. A constructor can show how it validates inputs; a mutating method can identify the check or ordering rule that prevents an invalid state. This makes later review more mechanical: a reviewer can compare each state transition with the invariant instead of reconstructing the abstraction from scattered unsafe code.
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Use documentation examples as executable specifications
Examples serve two purposes: they teach the normal call pattern and, when enabled as documentation tests, they can be compiled and run. That makes them an early warning when an API, trait bound, import, or safety requirement changes while the prose remains untouched.
What to include in an example
- A short, realistic use of the public API.
- Any setup needed to establish the documented preconditions.
- The expected result or observable effect.
- A warning about a common misuse when that misuse is easy to make.
An example should not silently bypass an unsafe requirement. If callers must uphold a condition, show where that condition is established or state clearly that the snippet is illustrative and cannot be copied without the required guarantees.
Testing categories discussed in the 2022 presentation
The deck groups Rust testing into three familiar categories:
| Category | Purpose |
|---|---|
| Unit tests | Exercise focused components and internal behavior close to the code under test. |
| Documentation tests | Compile and, when configured to do so, run examples embedded in API documentation. |
| Integration tests | Check behavior through the public interface and across component boundaries. |
The slides also describe work underway in 2022 to integrate Rust tests with KUnit and say Rust-for-Linux continuous integration ran tests before merges while covering only a few configurations at that time. Those statements describe the project’s status when the presentation was made; they are not a claim about current kernel or CI coverage. Verify present-day support in current Rust-for-Linux and kernel documentation before designing a workflow around it.
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A practical review checklist for Rust kernel code
- Document every public function, type, and module that users of the API need to understand.
- For each unsafe function, list caller obligations under
# Safety; include pointer validity, alignment, initialization, aliasing, lifetime, and relevant kernel-state requirements where applicable. - For every unsafe block, place a
// SAFETY:comment immediately before it and cite the local facts that establish those obligations. - Write an
# Invariantssection for types whose validity depends on a maintained property. - Explain invariant preservation in constructors, setters, state transitions, and other mutating code.
- Add documentation examples for the common path and notable pitfalls.
- Run the project’s available unit, documentation, and integration tests, and check current Rust-for-Linux/KUnit integration guidance rather than relying on the 2022 presentation’s status.
What this archived webinar can—and cannot—tell you
The session remains a focused guide to documenting unsafe Rust and structuring tests around kernel-facing APIs. It does not establish a current mentorship application window, current CI configuration matrix, or today’s exact KUnit integration status. Treat its principles as durable guidance, but confirm implementation details against current project documentation.
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