linux-kernel - Re: [PATCH v2 1/5] rust: retain pointer mut-ness in `container

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Message-ID: <CAJ-ks9k_sq8CGxij6zFTkR9c75pDAGsHZ1B=aDew7FnbUz0uCg@mail.gmail.com>
Date: Wed, 12 Mar 2025 11:13:39 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas@...sle.eu>, 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>, Alice Ryhl <aliceryhl@...gle.com>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Brendan Higgins <brendan.higgins@...ux.dev>, David Gow <davidgow@...gle.com>, 
	Rae Moar <rmoar@...gle.com>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Luis Chamberlain <mcgrof@...nel.org>, Russ Weight <russ.weight@...ux.dev>, Rob Herring <robh@...nel.org>, 
	Saravana Kannan <saravanak@...gle.com>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com, 
	linux-pci@...r.kernel.org, linux-block@...r.kernel.org, 
	devicetree@...r.kernel.org
Subject: Re: [PATCH v2 1/5] rust: retain pointer mut-ness in `container_of!`

On Wed, Mar 12, 2025 at 10:22 AM Benno Lossin <benno.lossin@...ton.me> wrote:
>
> On Sun Mar 9, 2025 at 5:00 PM CET, Tamir Duberstein wrote:
> > Avoid casting the input pointer to `*const _`, allowing the output
> > pointer to be `*mut` if the input is `*mut`. This allows a number of
> > `*const` to `*mut` conversions to be removed at the cost of slightly
> > worse ergonomics when the macro is used with a reference rather than a
> > pointer; the only example of this was in the macro's own doctest.
> >
> > Signed-off-by: Tamir Duberstein <tamird@...il.com>
>
> One tiny nit below, but even without that:
>
> Reviewed-by: Benno Lossin <benno.lossin@...ton.me>
>
> > ---
> >  rust/kernel/lib.rs      |  5 ++---
> >  rust/kernel/pci.rs      |  2 +-
> >  rust/kernel/platform.rs |  2 +-
> >  rust/kernel/rbtree.rs   | 23 ++++++++++-------------
> >  4 files changed, 14 insertions(+), 18 deletions(-)
> >
> > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> > index 7697c60b2d1a..9cd6b6864739 100644
> > --- a/rust/kernel/lib.rs
> > +++ b/rust/kernel/lib.rs
> > @@ -187,7 +187,7 @@ fn panic(info: &core::panic::PanicInfo<'_>) -> ! {
> >  /// }
> >  ///
> >  /// let test = Test { a: 10, b: 20 };
> > -/// let b_ptr = &test.b;
> > +/// let b_ptr: *const _ = &test.b;
>
> You could also use `&raw test.b` to get a pointer instead of relying on
> the pointer coercion. That syntax is stable since 1.82.0, so older
> compilers would need to enable the `raw_ref_op` feature.
>
> I created an orthogonal good-first-issue for changing uses of
> `addr_of[_mut]!` to `&raw [mut]`, so maybe that can also be done there:
>
>     https://github.com/Rust-for-Linux/linux/issues/1148

Thanks for doing that! Yeah, I think moving to that syntax would be
good but as you say requires enabling the feature and/or bumping the
rust version, so it can't be done here directly.