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

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Message-ID: <aMGE64_J5R8U_rk5@tardis-2.local>
Date: Wed, 10 Sep 2025 07:02:19 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Benno Lossin <lossin@...nel.org>
Cc: Alice Ryhl <aliceryhl@...gle.com>, Danilo Krummrich <dakr@...nel.org>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...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 02:19:00PM +0200, Benno Lossin wrote:
> On Wed Sep 10, 2025 at 12:40 PM CEST, Alice Ryhl wrote:
> > 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?
> 
> @Boqun what is your opinion on this?
> 

If we plan to make the in-place initializer language feature behave
similar, as I asked here [1], then dropping `#[bind]` seems good to me.

[1]: https://lore.kernel.org/rust-for-linux/aLshd0_C-1rh3FAg@tardis-2.local/

Thanks!

Regards,
Boqun

> I'm open to take v2 or v1, whatever you guys prefer.
> 
> ---
> Cheers,
> Benno