linux-kernel - Re: [PATCH v2 09/12] rust: init: implement Zeroable for Opaque<T>

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Message-ID: <20230720133434.3546048-1-aliceryhl@google.com>
Date:   Thu, 20 Jul 2023 13:34:34 +0000
From:   Alice Ryhl <aliceryhl@...gle.com>
To:     benno.lossin@...ton.me
Cc:     alex.gaynor@...il.com, aliceryhl@...gle.com,
        bjorn3_gh@...tonmail.com, boqun.feng@...il.com, gary@...yguo.net,
        linux-kernel@...r.kernel.org, nmi@...aspace.dk, ojeda@...nel.org,
        rust-for-linux@...r.kernel.org, wedsonaf@...il.com
Subject: Re: [PATCH v2 09/12] rust: init: implement Zeroable for Opaque<T>

Benno Lossin <benno.lossin@...ton.me> writes:
> Since `Opaque<T>` contains a `MaybeUninit<T>`, all bytes zero is a valid
> bit pattern for that type.
> 
> Signed-off-by: Benno Lossin <benno.lossin@...ton.me>
> ---
>  ///
>  /// This is meant to be used with FFI objects that are never interpreted by Rust code.
>  #[repr(transparent)]
> +#[derive(Zeroable)]
>  pub struct Opaque<T> {
>      value: UnsafeCell<MaybeUninit<T>>,
>      _pin: PhantomPinned,
>  }

Does this actually work? I don't think we implement Zeroable for
UnsafeCell.

I suggest you instead add Opaque to the `impl_zeroable!` macro in
`rust/kernel/init.rs`.

Alice