linux-kernel - Re: [PATCH] rust: Enable the new_uninit feature for kernel and driver crates

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Date:   Mon, 27 Feb 2023 14:09:37 +0100
From:   Andreas Hindborg <nmi@...aspace.dk>
To:     Asahi Lina <lina@...hilina.net>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kbuild@...r.kernel.org, asahi@...ts.linux.dev
Subject: Re: [PATCH] rust: Enable the new_uninit feature for kernel and
 driver crates


Asahi Lina <lina@...hilina.net> writes:

> The unstable new_uninit feature enables various library APIs to create
> uninitialized containers, such as `Box::assume_init()`. This is
> necessary to build abstractions that directly initialize memory at the
> target location, instead of doing copies through the stack.
>
> Will be used by the DRM scheduler abstraction in the kernel crate, and
> by field-wise initialization (e.g. using `place!()` or a future
> replacement macro which may itself live in `kernel`) in driver crates.
>
> See [1] [2] [3] for background information.
>
> [1] https://github.com/Rust-for-Linux/linux/issues/879
> [2] https://github.com/Rust-for-Linux/linux/issues/2
> [3] https://github.com/rust-lang/rust/issues/63291
>
> Signed-off-by: Asahi Lina <lina@...hilina.net>
> ---
>  rust/kernel/lib.rs     | 1 +
>  scripts/Makefile.build | 2 +-
>  2 files changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index 223564f9f0cc..1118cd3e0b5f 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -17,6 +17,7 @@
>  #![feature(core_ffi_c)]
>  #![feature(dispatch_from_dyn)]
>  #![feature(generic_associated_types)]
> +#![feature(new_uninit)]
>  #![feature(receiver_trait)]
>  #![feature(unsize)]
>  
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index a0d5c6cca76d..0f637e1ca8dc 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -277,7 +277,7 @@ $(obj)/%.lst: $(src)/%.c FORCE
>  # Compile Rust sources (.rs)
>  # ---------------------------------------------------------------------------
>  
> -rust_allowed_features := core_ffi_c
> +rust_allowed_features := core_ffi_c,new_uninit

What is the purpose of adding the feature here? The kernel crate seems
to compile fine without this.

BR Andreas