linux-kernel - Re: [PATCH] rust: transmute: implement FromBytes and AsBytes for ()

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Message-ID: <aToa5vxUu3PDv56i@google.com>
Date: Thu, 11 Dec 2025 01:14:14 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Alexandre Courbot <acourbot@...dia.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, John Hubbard <jhubbard@...dia.com>, 
	Alistair Popple <apopple@...dia.com>, Joel Fernandes <joelagnelf@...dia.com>, 
	Timur Tabi <ttabi@...dia.com>, Edwin Peer <epeer@...dia.com>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: transmute: implement FromBytes and AsBytes for ()

On Mon, Dec 08, 2025 at 01:15:13PM +0900, Alexandre Courbot wrote:
> This is useful when using types that may or may not be empty in generic
> code relying on these traits. It is also safe because technically a
> no-op.
> 
> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
> ---
> This is going to be useful in Nova's GSP message handling, as some
> messages are empty and we need to explicitly use an empty structure for
> them.
> 
> If accepted, I would like to merge it through `drm-rust-next` so Nova
> code can start using this feature quickly.
> ---
>  rust/kernel/transmute.rs | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/rust/kernel/transmute.rs b/rust/kernel/transmute.rs
> index be5dbf3829e2..8d78c81e3749 100644
> --- a/rust/kernel/transmute.rs
> +++ b/rust/kernel/transmute.rs
> @@ -170,6 +170,9 @@ macro_rules! impl_frombytes {
>  }
>  
>  impl_frombytes! {
> +    // SAFETY: This type is empty and thus does not consume any data.
> +    (),

This should mention that the type has no invariants.

>  impl_asbytes! {
> +    // SAFETY: This type is empty and thus returns an empty slice.
> +    (),

Ok.

Alice