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

[Tamir Duberstein]

On Sat, May 30, 2026 at 7:07 AM Gary Guo <gary@xxxxxxxxxxx> wrote:
>
> On Tue May 26, 2026 at 3:39 PM BST, Tamir Duberstein 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@xxxxxxxxxx>
> > ---
> >  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;
>
> I think the old signature is quite reasonable. You provide storage and the
> buffer is filled and that the return value is the proof of initialization.
>
> If you're concerned with `transmute` it should just be replaced with
> `assume_init_mut()`.

The signature is reasonable, but it is dead code. This is a private
function; I see no benefit in keeping dead code around. If it is
needed in the future, it can be easily restored.