linux-kernel - Re: [PATCH v3 4/4] rust: add parameter support to the `module!` macro

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Message-ID: <CAH5fLgjzf_C5KBd_UC4S=FS=SvR+GSO_t7NAkfRoYPAd9vZ2+g@mail.gmail.com>
Date: Wed, 8 Jan 2025 14:17:36 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Andreas Hindborg <a.hindborg@...nel.org>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>, 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>, 
	Benno Lossin <benno.lossin@...ton.me>, Masahiro Yamada <masahiroy@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, Trevor Gross <tmgross@...ch.edu>, 
	Adam Bratschi-Kaye <ark.email@...il.com>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH v3 4/4] rust: add parameter support to the `module!` macro

On Wed, Jan 8, 2025 at 1:45 PM Andreas Hindborg <a.hindborg@...nel.org> wrote:
>
> "Miguel Ojeda" <miguel.ojeda.sandonis@...il.com> writes:
>
> > On Fri, Dec 13, 2024 at 2:17 PM Andreas Hindborg <a.hindborg@...nel.org> wrote:
> >>
> >> scheduled for removal. Interior mutability via `SyncUnsafeCell` provides
> >> the same functionality and it is my understanding that this feature is
> >> on track to be stabilized.
> >
> > I am not sure about the last bit, but even if it is on track, we do
> > not want to start using new language features or APIs that could
> > potentially change.
> >
> > And even if it is a feature that we are sure will not change, we
> > should still let upstream Rust know before using it, since we are
> > actively discussing with them the remaining unstable items that the
> > kernel needs and they are putting the kernel in their roadmap.
> >
> > So I suggest we mention it next week in the Rust/Rust for Linux meeting.
>
> I don't think we ever discussed this?
>
> I was going to put this in the commit trailer for v4:
>
> ---
> Version 3 of this patch enabled the unstable feature `sync_unsafe_cell` [1] to
> avoid `static mut` variables as suggested by Trevor Tross and Benno Lossin [2].
>
> As we are moving closer to a new edition, it is now clear that `static mut` is
> not being deprecated in the 2024 edition as first anticipated [3].
>
> Still, `SyncUnsafeCell` allows us to use safe code when referring to the
> parameter value:
>
> ```
> {param_name}.as_mut_ptr().cast()
> ```
>
> rather than unsafe code:
>
> ```
> unsafe { addr_of_mut!(__{name}_{param_name}_value) }.cast()
> ```
>
> Thus, this version (4) keeps the feature enabled.
>
> [1] https://github.com/rust-lang/rust/issues/95439
> [2] https://lore.kernel.org/all/CALNs47sqt==o+hM5M1b0vTayKH177naybg_KurcirXszYAa22A@mail.gmail.com/
> [3] https://github.com/rust-lang/rust/issues/53639#issuecomment-2434023115
> ---
>
> What do you think?

It's pretty easy to avoid needing this feature, so I don't think we
should enable it.

Alice