linux-kernel - Re: [PATCH v2] rust: pin-init: add `#[bind]` attribute to access previously initialized fields

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Message-ID: <CAH5fLgg+-oz_cP9=ke+ukp9qYZAsD=hKqvvGfkJWRcCKdrTQ-g@mail.gmail.com>
Date: Wed, 10 Sep 2025 12:40:40 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Benno Lossin <lossin@...nel.org>, Danilo Krummrich <dakr@...nel.org>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, Fiona Behrens <me@...enk.dev>, 
	Alban Kurti <kurti@...icto.ai>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] rust: pin-init: add `#[bind]` attribute to access
 previously initialized fields

On Wed, Sep 10, 2025 at 12:36 PM Benno Lossin <lossin@...nel.org> wrote:
>
> On Wed Sep 10, 2025 at 12:17 PM CEST, Alice Ryhl wrote:
> > On Wed, Sep 10, 2025 at 12:07:53PM +0200, Benno Lossin wrote:
> >> Assigning a field a value in an initializer macro can be marked with the
> >> `#[bind]` attribute. Doing so creates a `let` binding with the same
> >> name. This `let` binding has the type `Pin<&mut T>` if the field is
> >> structurally pinned or `&mut T` otherwise (where `T` is the type of the
> >> field).
> >>
> >> Signed-off-by: Benno Lossin <lossin@...nel.org>
> >
> > Is there a reason we can't apply this to all fields and avoid the
> > attribute?
>
> Adding the attribute was due to Boqun's concern on v1 [1]. I think it
> might be surprising too, but I'm also happy with no attribute.
>
> [1]: https://lore.kernel.org/all/aLshd0_C-1rh3FAg@tardis-2.local

IMO the ideal is if it works without an attribute. Perhaps trying that
in the kernel is a reasonable experiment to find out whether that's
reasonable to do for the general language feature?

> > Do we have a place that might be able to use this?
>
> I didn't find one, but Danilo plans to base some changes on top this
> cycle that need this.

Danilo, what plans do you have?

Alice