Re: [PATCH 1/7] rust: types: support fallible PinInit types in Opaque::pin_init

[Danilo Krummrich <dakr@kernel.org>]

On Fri, May 30, 2025 at 10:11:00PM +0200, Christian Schrefl wrote:
> 
> 
> On 30.05.25 9:29 PM, Benno Lossin wrote:
> > On Fri May 30, 2025 at 4:24 PM CEST, Danilo Krummrich wrote:
> >> Currently, Opaque::pin_init only supports infallible PinInit
> >> implementations, i.e. impl PinInit<T, Infallible>.
> >>
> >> This has been sufficient so far, since users such as Revocable do not
> >> support fallibility.
> >>
> >> Since this is about to change, make Opaque::pin_init() generic over the
> >> error type E.
> >>
> >> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> >> ---
> >>  rust/kernel/types.rs | 8 ++++----
> >>  1 file changed, 4 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> >> index 22985b6f6982..75c99d6facf9 100644
> >> --- a/rust/kernel/types.rs
> >> +++ b/rust/kernel/types.rs
> >> @@ -354,13 +354,13 @@ pub const fn zeroed() -> Self {
> >>      }
> >>  
> >>      /// Create an opaque pin-initializer from the given pin-initializer.
> >> -    pub fn pin_init(slot: impl PinInit<T>) -> impl PinInit<Self> {
> >> -        Self::ffi_init(|ptr: *mut T| {
> >> +    pub fn pin_init<E>(slot: impl PinInit<T, E>) -> impl PinInit<Self, E> {
> >> +        Self::try_ffi_init(|ptr: *mut T| -> Result<(), E> {
> >>              // SAFETY:
> >>              //   - `ptr` is a valid pointer to uninitialized memory,
> >> -            //   - `slot` is not accessed on error; the call is infallible,
> >> +            //   - `slot` is not accessed on error,
> >>              //   - `slot` is pinned in memory.
> >> -            let _ = unsafe { PinInit::<T>::__pinned_init(slot, ptr) };
> >> +            unsafe { PinInit::<T, E>::__pinned_init(slot, ptr) }
> > 
> > Could you move this function into an `impl pin_init::Wrapper<T>` block?
> > (it's the same function, but in a trait that was recently added)
> 
> This is then basically this patch [0] from my `UnsafePinned` series.
> Just that I did not update the comment. :)

As mentioned in [0], I wasn't aware of this patch -- let's go with yours then.

> [0]: https://lore.kernel.org/rust-for-linux/20250511-rust_unsafe_pinned-v4-2-a86c32e47e3d@gmail.com/