Re: [PATCH v2 1/3] rust: add UnsafePinned type

[Alice Ryhl <aliceryhl@google.com>]

On Wed, Apr 30, 2025 at 10:36:11AM +0200, Christian Schrefl wrote:
> `UnsafePinned<T>` is useful for cases where a value might be shared with
> C code but not directly used by it. In particular this is added for
> storing additional data in the `MiscDeviceRegistration` which will be
> shared between `fops->open` and the containing struct.
> 
> Similar to `Opaque` but guarantees that the value is always initialized
> and that the inner value is dropped when `UnsafePinned` is dropped.
> 
> This was originally proposed for the IRQ abstractions [0] and is also
> useful for other where the inner data may be aliased, but is always
> valid and automatic `Drop` is desired.
> 
> Since then the `UnsafePinned` type was added to upstream Rust [1] by Sky
> as a unstable feature, therefore this patch implements the subset of the
> upstream API for the `UnsafePinned` type required for additional data in
> `MiscDeviceRegistration` and in the implementation of the `Opaque` type.
> 
> Some differences to the upstream type definition are required in the
> kernel implementation, because upstream type uses some compiler changes
> to opt out of certain optimizations, this is documented in the
> documentation and a comment on the `UnsafePinned` type.
> 
> The documentation on is based on the upstream rust documentation with
> minor modifications for the kernel implementation.
> 
> Link: https://lore.kernel.org/rust-for-linux/CAH5fLgiOASgjoYKFz6kWwzLaH07DqP2ph+3YyCDh2+gYqGpABA@mail.gmail.com [0]
> Link: https://github.com/rust-lang/rust/pull/137043 [1]
> Suggested-by: Alice Ryhl <aliceryhl@google.com>
> Reviewed-by: Gerald Wisböck <gerald.wisboeck@feather.ink>
> Co-developed-by: Sky <sky@sky9.dev>
> Signed-off-by: Sky <sky@sky9.dev>
> Signed-off-by: Christian Schrefl <chrisi.schrefl@gmail.com>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>