General Information

This document contains useful information to know when working with the Rust support in the kernel.

Code documentation

Rust kernel code is documented using rustdoc, its built-in documentation generator.

The generated HTML docs include integrated search, linked items (e.g. types, functions, constants), source code, etc. They may be read at (TODO: link when in mainline and generated alongside the rest of the documentation):

The docs can also be easily generated and read locally. This is quite fast (same order as compiling the code itself) and no special tools or environment are needed. This has the added advantage that they will be tailored to the particular kernel configuration used. To generate them, use the rustdoc target with the same invocation used for compilation, e.g.:

make LLVM=1 rustdoc

To read the docs locally in your web browser, run e.g.:

xdg-open Documentation/output/rust/rustdoc/kernel/index.html

To learn about how to write the documentation, please see Coding Guidelines.

Extra lints

While rustc is a very helpful compiler, some extra lints and analyses are available via clippy, a Rust linter. To enable it, pass CLIPPY=1 to the same invocation used for compilation, e.g.:

make LLVM=1 CLIPPY=1

Please note that Clippy may change code generation, thus it should not be enabled while building a production kernel.

Abstractions vs. bindings

Abstractions are Rust code wrapping kernel functionality from the C side.

In order to use functions and types from the C side, bindings are created. Bindings are the declarations for Rust of those functions and types from the C side.

For instance, one may write a Mutex abstraction in Rust which wraps a struct mutex from the C side and calls its functions through the bindings.

Abstractions are not available for all the kernel internal APIs and concepts, but it is intended that coverage is expanded as time goes on. "Leaf" modules (e.g. drivers) should not use the C bindings directly. Instead, subsystems should provide as-safe-as-possible abstractions as needed.

Conditional compilation

Rust code has access to conditional compilation based on the kernel configuration:

#[cfg(CONFIG_X)]       // Enabled               (`y` or `m`)
#[cfg(CONFIG_X="y")]   // Enabled as a built-in (`y`)
#[cfg(CONFIG_X="m")]   // Enabled as a module   (`m`)
#[cfg(not(CONFIG_X))]  // Disabled