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

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Message-ID: <CANiq72=XW1RtXuP4JRVEZzwBKtXOOkJCp3WBW-oEFWHQOf_kpg@mail.gmail.com>
Date: Wed, 8 Jan 2025 14:43:31 +0100
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Andreas Hindborg <a.hindborg@...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>, 
	Benno Lossin <benno.lossin@...ton.me>, Alice Ryhl <aliceryhl@...gle.com>, 
	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:
>
> I don't think we ever discussed this?

I don't think so -- we discussed other things related to 2025H1 the
last meeting. Perhaps you/we can bring it up in the next one?

> 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:

> What do you think?

The justification seems fairly weak... Unless we are fairly confident
the API will be stable (even if not stabilized right now), I am not
sure why we would want to do this right now.

Can we provide our own `SyncUnsafeCell` instead in the meantime, if
you want to keep the advantages?

> Returning an error and `pr_warn!` is doable. As far as I can tell, we do
> not have `WARN_ON_ONCE` yet?

Please see https://lore.kernel.org/rust-for-linux/20241126-pr_once_macros-v4-0-410b8ca9643e@tuta.io/
in case it helps.

> It turns out we can!

That is what I expected :)

Thanks!

Cheers,
Miguel