Re: [PATCH v8 1/1] rust: introduce abstractions for fwctl

[Alexandre Courbot]

On Fri Aug 14, 2026 at 12:23 AM JST, Zhi Wang wrote:
> Introduce safe Rust wrappers around struct fwctl_device and
> struct fwctl_uctx. This lets Rust drivers register fwctl devices and
> implement firmware RPC callbacks through a typed trait interface.
>
> The abstraction keeps lifetime and reference-count handling inside the
> wrapper, exposes pinned per-FD user contexts to drivers, and validates the
> layout assumptions required by the C fwctl allocation model. Allocation
> sizes are padded so the kmalloc-backed C allocations also satisfy Rust
> alignment requirements.
>
> Registration owns driver private data with a lifetime tied to the bound
> parent device and verifies the parent identity before registration.
> Callbacks access that data through a higher-ranked closure, preventing its
> erased lifetime from escaping, while Device remains only the refcounted
> fwctl object. This avoids requiring Rust drop glue from the fwctl_device
> release path after unregister or module teardown.
>
> RPC callbacks receive typed scope information, a mutable request/response
> buffer, and the userspace output-buffer size. Response pointer conversion,
> length validation, and raw output-length handling remain inside the
> abstraction.
>
> Add the Rust sources to the FWCTL MAINTAINERS entry and add myself as the
> maintainer for the Rust abstractions.
>
> Co-developed-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> Link: https://lore.kernel.org/r/DJJW7X4ESDSM.QCVYK2FC7ZR3@xxxxxxxxxx
> Signed-off-by: Zhi Wang <zhiw@xxxxxxxxxx>

Reviewed-by: Alexandre Courbot <acourbot@xxxxxxxxxx>

Thanks for this great work!