Message-ID: <96cb824e-8251-a329-11e5-3618a4e59bc8@asahilina.net>
Date:   Mon, 27 Feb 2023 22:47:37 +0900
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Subject: Re: [PATCH] rust: Enable the new_uninit feature for kernel and driver
 crates
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To:     Andreas Hindborg <nmi@metaspace.dk>
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?UTF-8?Q?Bj=c3=b6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nicolas Schier <nicolas@fjasle.eu>,
        rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-kbuild@vger.kernel.org, asahi@lists.linux.dev
References: <20230224-rust-new_uninit-v1-1-c951443d9e26@asahilina.net>
 <87pm9v9rmg.fsf@metaspace.dk>
From:   Asahi Lina <lina@asahilina.net>
In-Reply-To: <87pm9v9rmg.fsf@metaspace.dk>
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On 27/02/2023 22.09, Andreas Hindborg wrote:
> 
> Asahi Lina <lina@asahilina.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@asahilina.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.

It's for the upcoming DRM abstractions, as I mentioned in the commit
message. There's so many dependencies that I'm trying to get as much as
I can early to avoid having to review very big patchsets down the line ^^

~~ Lina