Rust in the Linux kernel: part 2

Summary

Welcome to LWN.net The following subscription-only content has been made available to you by an LWN subscriber. Thousands of subscribers depend on LWN for the best news from the Linux and free software communities. If you enjoy this article, please consider subscribing to LWN. Thank you for visiting LWN.net! In 2023, Fujita Tomonori wrote a Rust version of the existing driver for the Asix AX88796B embedded Ethernet controller. At slightly more than 100 lines, it's about as simple as a driver can be, and therefore is a useful touchstone for the differences between writing Rust and C in the kernel. Looking at the Rust syntax, types, and APIs used by the driver and contrasting them with the C version will help illustrate those differences. Readers who are already conversant with Rust may find this article retreads some basics, but it is my hope that it can still serve as a useful reference for implementing simple drivers in Rust. The C version and the Rust version of the AX88796B driver are remarkably similar, but there are still some important differences that could trip up a developer performing a naive rewrite from one to the other. The setup The least-different thing between the two versions is the legalities. The Rust driver starts with an SPDX comment asserting that the file is covered by the GPL, as many files in the kernel do. Below that is a documentation comment: //! Rust Asix PHYs driver //! //! C version of this driver: [`drivers/net/phy/ax88796b.c`](./ax88796b.c) As mentioned in the previous article, comments starting with //! contain documentation that applies to the entire file. The next few lines are a use statement, the Rust analogue of #include: use kernel::{ c_str, net::phy::{self, reg::C22, DeviceId, Driver}, prelude::*, uapi, }; Like C, Rust modules are located starting from a search path and then continuing down a directory tree. Unlike C, a use statement can selectively import only some items defined in a module. For example, DeviceId is not a se...