Re: [PATCH 1/2] rust: device: remove unused ref-to-ref transmute

["Onur Özkan" <work@onurozkan.dev>]

On Tue, 26 May 2026 10:39:31 -0400
Tamir Duberstein <tamird@kernel.org> wrote:

> The Ok return value of `read_array_from_fwnode_property` requires a
> reference-to-reference transmute to construct but is never read, thus
> remove it.
> 
> Signed-off-by: Tamir Duberstein <tamird@kernel.org>
> ---
>  rust/kernel/device/property.rs | 42 +++++++++++++++++-------------------------
>  1 file changed, 17 insertions(+), 25 deletions(-)
> 
> diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs
> index 5aead835fbbc..87be2784f7a7 100644
> --- a/rust/kernel/device/property.rs
> +++ b/rust/kernel/device/property.rs
> @@ -136,18 +136,15 @@ pub fn property_read_array_vec<'fwnode, 'name, T: PropertyInt>(
>          let mut val: KVec<T> = KVec::with_capacity(len, GFP_KERNEL)?;
>  
>          let res = T::read_array_from_fwnode_property(self, name, val.spare_capacity_mut());
> -        let res = match res {
> -            Ok(_) => {
> -                // SAFETY:
> -                // - `len` is equal to `val.capacity - val.len`, because
> -                //   `val.capacity` is `len` and `val.len` is zero.
> -                // - All elements within the interval [`0`, `len`) were initialized
> -                //   by `read_array_from_fwnode_property`.
> -                unsafe { val.inc_len(len) }
> -                Ok(val)
> -            }
> -            Err(e) => Err(e),
> -        };
> +        let res = res.map(|()| {
> +            // SAFETY:
> +            // - `len` is equal to `val.capacity - val.len`, because
> +            //   `val.capacity` is `len` and `val.len` is zero.
> +            // - All elements within the interval [`0`, `len`) were initialized
> +            //   by `read_array_from_fwnode_property`.
> +            unsafe { val.inc_len(len) }
> +            val
> +        });
>          Ok(PropertyGuard {
>              inner: res,
>              fwnode: self,
> @@ -474,12 +471,12 @@ fn read_from_fwnode_property(fwnode: &FwNode, name: &CStr) -> Result<Self> {
>  /// It must be public, because it appears in the signatures of other public
>  /// functions, but its methods shouldn't be used outside the kernel crate.
>  pub trait PropertyInt: Copy + Sealed {
> -    /// Reads a property array.
> -    fn read_array_from_fwnode_property<'a>(
> +    /// Reads a property array into `out`.
> +    fn read_array_from_fwnode_property(
>          fwnode: &FwNode,
>          name: &CStr,
> -        out: &'a mut [MaybeUninit<Self>],
> -    ) -> Result<&'a mut [Self]>;
> +        out: &mut [MaybeUninit<Self>],
> +    ) -> Result;
>  
>      /// Reads the length of a property array.
>      fn read_array_len_from_fwnode_property(fwnode: &FwNode, name: &CStr) -> Result<usize>;
> @@ -495,11 +492,11 @@ impl Sealed for $int {}
>          impl<const N: usize> Sealed for [$int; N] {}
>  
>          impl PropertyInt for $int {
> -            fn read_array_from_fwnode_property<'a>(
> +            fn read_array_from_fwnode_property(
>                  fwnode: &FwNode,
>                  name: &CStr,
> -                out: &'a mut [MaybeUninit<Self>],
> -            ) -> Result<&'a mut [Self]> {
> +                out: &mut [MaybeUninit<Self>],
> +            ) -> Result {
>                  // SAFETY:
>                  // - `fwnode`, `name` and `out` are all valid by their type
>                  //   invariants.
> @@ -515,12 +512,7 @@ fn read_array_from_fwnode_property<'a>(
>                          out.len(),
>                      )
>                  };
> -                to_result(ret)?;
> -                // SAFETY: Transmuting from `&'a mut [MaybeUninit<Self>]` to
> -                // `&'a mut [Self]` is sound, because the previous call to a
> -                // `fwnode_property_read_*_array` function (which didn't fail)
> -                // fully initialized the slice.
> -                Ok(unsafe { core::mem::transmute::<&mut [MaybeUninit<Self>], &mut [Self]>(out) })
> +                to_result(ret)
>              }
>  
>              fn read_array_len_from_fwnode_property(fwnode: &FwNode, name: &CStr) -> Result<usize> {
> 
> -- 
> 2.54.0
> 

Reviewed-by: Onur Özkan <work@onurozkan.dev>