Re: [PATCH v3 1/1] rust: introduce abstractions for fwctl

[Jason Gunthorpe]

On Tue, Feb 17, 2026 at 10:49:06PM +0200, Zhi Wang wrote:
> Introduce safe wrappers around `struct fwctl_device` and
> `struct fwctl_uctx`, allowing rust drivers to register fwctl devices and
> implement their control and RPC logic in safe rust.
> 
> Cc: Danilo Krummrich <dakr@xxxxxxxxxx>
> Cc: Gary Guo <gary@xxxxxxxxxxx>
> Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Cc: Joel Fernandes <joelagnelf@xxxxxxxxxx>
> Signed-off-by: Zhi Wang <zhiw@xxxxxxxxxx>
> ---
>  drivers/fwctl/Kconfig           |  12 +
>  rust/bindings/bindings_helper.h |   1 +
>  rust/helpers/fwctl.c            |  17 ++
>  rust/helpers/helpers.c          |   3 +-
>  rust/kernel/fwctl.rs            | 449 ++++++++++++++++++++++++++++++++

The binding is larger than the subystem file:

$ wc -l drivers/fwctl/main.c 
421 drivers/fwctl/main.c

:\

Anyhow is someone waiting for me to do something with it?

> +impl<T: Operations> Device<T> {
> +    /// Allocate a new fwctl device with embedded driver data.
> +    ///
> +    /// Returns an [`ARef`] that can be passed to [`Registration::new()`]
> +    /// to make the device visible to userspace. The caller may inspect or
> +    /// configure the device between allocation and registration.
> +    pub fn new(
> +        parent: &device::Device<device::Bound>,
> +        data: impl PinInit<T::DeviceData, Error>,
> +    ) -> Result<ARef<Self>> {
> +        let ops = core::ptr::from_ref::<bindings::fwctl_ops>(&VTable::<T>::VTABLE).cast_mut();
> +
> +        // SAFETY: `_fwctl_alloc_device` allocates `size` bytes via kzalloc and
> +        // initialises the embedded fwctl_device. `ops` points to a static vtable
> +        // that outlives the device. `parent` is bound.
> +        let raw = unsafe {
> +            bindings::_fwctl_alloc_device(parent.as_raw(), ops, core::mem::size_of::<Self>())
> +        };
> +
> +        if raw.is_null() {
> +            return Err(ENOMEM);
> +        }
> +
> +        // CAST: Device<T> is repr(C) with fwctl_device at offset 0.
> +        let this = raw as *mut Self;

Should this have some helper? It looks a bit fragile, in C we have a
static_assert on offsetof to prevent errors.

Jason