linux-kernel - Re: [PATCH] rust: init: fix `Zeroable` implementation for `Option<NonNull<T>>` and `Option<KBox<T>>`

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Message-ID: <Z8hSXgC-ecXCEPiS@google.com>
Date: Wed, 5 Mar 2025 13:32:14 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Benno Lossin <benno.lossin@...ton.me>
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>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, stable@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: init: fix `Zeroable` implementation for
 `Option<NonNull<T>>` and `Option<KBox<T>>`

On Wed, Mar 05, 2025 at 01:29:01PM +0000, Benno Lossin wrote:
> According to [1], `NonNull<T>` and `#[repr(transparent)]` wrapper types
> such as our custom `KBox<T>` have the null pointer optimization only if
> `T: Sized`. Thus remove the `Zeroable` implementation for the unsized
> case.
> 
> Link: https://doc.rust-lang.org/stable/std/option/index.html#representation [1]
> Cc: stable@...r.kernel.org # v6.12+ (a custom patch will be needed for 6.6.y)
> Fixes: 38cde0bd7b67 ("rust: init: add `Zeroable` trait and `init::zeroed` function")
> Signed-off-by: Benno Lossin <benno.lossin@...ton.me>

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>