Re: [PATCH 1/3] rust: types: add Opaque::try_ffi_init

[Fiona Behrens]

On 26 Sep 2024, at 16:58, Alice Ryhl wrote:

> This will be used by the miscdevice abstractions, as the C function
> `misc_register` is fallible.
>
> Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> ---

Reviewed-by: Fiona Behrens <me@xxxxxxxxxx>


>  rust/kernel/types.rs | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> index 3238ffaab031..dd9c606c515c 100644
> --- a/rust/kernel/types.rs
> +++ b/rust/kernel/types.rs
> @@ -299,6 +299,22 @@ pub fn ffi_init(init_func: impl FnOnce(*mut T)) -> impl PinInit<Self> {
>          }
>      }
>
> +    /// Creates a fallible pin-initializer from the given initializer closure.
> +    ///
> +    /// The returned initializer calls the given closure with the pointer to the inner `T` of this
> +    /// `Opaque`. Since this memory is uninitialized, the closure is not allowed to read from it.
> +    ///
> +    /// This function is safe, because the `T` inside of an `Opaque` is allowed to be
> +    /// uninitialized. Additionally, access to the inner `T` requires `unsafe`, so the caller needs
> +    /// to verify at that point that the inner value is valid.
> +    pub fn try_ffi_init<E>(
> +        init_func: impl FnOnce(*mut T) -> Result<(), E>,
> +    ) -> impl PinInit<Self, E> {
> +        // SAFETY: We contain a `MaybeUninit`, so it is OK for the `init_func` to not fully
> +        // initialize the `T`.
> +        unsafe { init::pin_init_from_closure::<_, E>(move |slot| init_func(Self::raw_get(slot))) }
> +    }
> +
>      /// Returns a raw pointer to the opaque data.
>      pub const fn get(&self) -> *mut T {
>          UnsafeCell::get(&self.value).cast::<T>()
>
> -- 
> 2.46.0.792.g87dc391469-goog