linux-kernel - Re: [PATCH 2/2] rust: pin-init: add pin projections to `#[pin

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Message-ID: <20250910232027.332a840a.gary@garyguo.net>
Date: Wed, 10 Sep 2025 23:20:27 +0100
From: Gary Guo <gary@...yguo.net>
To: Benno Lossin <lossin@...nel.org>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, Andreas Hindborg <a.hindborg@...nel.org>, Alice
 Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, Danilo
 Krummrich <dakr@...nel.org>, Tejun Heo <tj@...nel.org>, Tamir Duberstein
 <tamird@...il.com>, Dirk Behme <dirk.behme@...il.com>, Alban Kurti
 <kurti@...icto.ai>, Fiona Behrens <me@...enk.dev>,
 rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] rust: pin-init: add pin projections to
 `#[pin_data]`

On Fri,  5 Sep 2025 19:12:07 +0200
Benno Lossin <lossin@...nel.org> wrote:

> Make the `#[pin_data]` macro generate a `*Projection` struct that holds
> either `Pin<&mut Field>` or `&mut Field` for every field of the original
> struct. Which version is chosen depends on weather there is a `#[pin]`
> or not respectively. Access to this projected version is enabled through
> generating `fn project(self: Pin<&mut Self>) -> SelfProjection<'_>`.
> 
> Link: https://github.com/Rust-for-Linux/pin-init/pull/75/commits/2d698367d646c7ede90e01aa22842c1002d017b3
> [ Adapt workqueue to use the new projection instead of its own, custom
>   one - Benno ]
> Signed-off-by: Benno Lossin <lossin@...nel.org>

LGTM, make sure to remove the spurious comment that Alice mentioned.

Reviewed-by: Gary Guo <gary@...yguo.net>

> ---
>  rust/kernel/workqueue.rs    | 10 ++-----
>  rust/pin-init/src/macros.rs | 60 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 62 insertions(+), 8 deletions(-)
> 
> diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
> index b9343d5bc00f..6ca14c629643 100644
> --- a/rust/kernel/workqueue.rs
> +++ b/rust/kernel/workqueue.rs
> @@ -356,18 +356,12 @@ struct ClosureWork<T> {
>      func: Option<T>,
>  }
>  
> -impl<T> ClosureWork<T> {
> -    fn project(self: Pin<&mut Self>) -> &mut Option<T> {
> -        // SAFETY: The `func` field is not structurally pinned.
> -        unsafe { &mut self.get_unchecked_mut().func }
> -    }
> -}
> -
>  impl<T: FnOnce()> WorkItem for ClosureWork<T> {
>      type Pointer = Pin<KBox<Self>>;
>  
>      fn run(mut this: Pin<KBox<Self>>) {
> -        if let Some(func) = this.as_mut().project().take() {
> +        if let Some(func) = this.as_mut().project().func.take() {
> +            // if let Some(func) = this.as_mut().project_func().take() {
>              (func)()
>          }
>      }