linux-kernel - Re: [PATCH 1/7] rust: types: support fallible PinInit types in Opaque::pin

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Message-Id: <DA9QST4SISFK.37NSCTH594NSF@kernel.org>
Date: Fri, 30 May 2025 21:29:40 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Danilo Krummrich" <dakr@...nel.org>, <gregkh@...uxfoundation.org>,
 <rafael@...nel.org>, <ojeda@...nel.org>, <alex.gaynor@...il.com>,
 <boqun.feng@...il.com>, <gary@...yguo.net>, <bjorn3_gh@...tonmail.com>,
 <benno.lossin@...ton.me>, <a.hindborg@...nel.org>, <aliceryhl@...gle.com>,
 <tmgross@...ch.edu>, <chrisi.schrefl@...il.com>
Cc: <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/7] rust: types: support fallible PinInit types in
 Opaque::pin_init

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@...nel.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)

Thanks!

---
Cheers,
Benno

>          })
>      }
>