[$] The "rnull" Rust block driver

The null block driver (null_blk) is a small driver that is mostly useful for benchmarking block-layer implementations.

It accepts all requests and marks them complete as quickly as possible, doing as little work as possible.

In June 2026, Andreas Hindborg shared a patch set implementing the same functionality in Rust, in order to show that a simple block driver is now possible to write using the kernel's Rust APIs and to enable comparisons between the C and Rust implementations. A minimal version of the "rnull" driver is already present in the mainline kernel, but Hindborg's patch set brings it up to feature parity with the C version.