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Subject: Re: [PATCH 5/7] rust: file: add `Kuid` wrapper
From:   comex <comexk@gmail.com>
In-Reply-To: <20231130-wohle-einfuhr-1708e9c3e596@brauner>
Date:   Thu, 7 Dec 2023 21:28:06 -0800
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Alice Ryhl <aliceryhl@google.com>,
        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>,
        Benno Lossin <benno.lossin@proton.me>,
        Andreas Hindborg <a.hindborg@samsung.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        =?utf-8?Q?Arve_Hj=C3=B8nnev=C3=A5g?= <arve@android.com>,
        Todd Kjos <tkjos@android.com>,
        Martijn Coenen <maco@android.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Carlos Llamas <cmllamas@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Kees Cook <keescook@chromium.org>,
        Matthew Wilcox <willy@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Daniel Xu <dxu@dxuuu.xyz>, linux-kernel@vger.kernel.org,
        rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org
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References: <20231129-alice-file-v1-0-f81afe8c7261@google.com>
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 <20231129-etappen-knapp-08e2e3af539f@brauner>
 <20231129164815.GI23596@noisy.programming.kicks-ass.net>
 <20231130-wohle-einfuhr-1708e9c3e596@brauner>
To:     Christian Brauner <brauner@kernel.org>
Precedence: bulk


> On Nov 30, 2023, at 4:46=E2=80=AFAM, Christian Brauner =
<brauner@kernel.org> wrote:
>=20
> I wouldn't even
> complain if it they were somehow auto-generated but as you say that
> might be out of scope.

FYI, rust-bindgen got an experimental feature of this nature earlier =
this year:

https://github.com/rust-lang/rust-bindgen/pull/2335

Though apparently it has significant limitations meriting it the =
=E2=80=9Cexperimental=E2=80=9D title.

Regarding the issue of wrappers not being inlined, it's possible to get =
LLVM to optimize C and Rust code together into an object file, with the =
help of a compatible Clang and LLD:

@ rustc -O --emit llvm-bc a.rs                                        =20=

@ clang --target=3Dx86_64-unknown-linux-gnu -O2 -c -emit-llvm -o b.bc =
b.c
@ ld.lld -r -o c.o a.bc b.bc

Basically LTO but within the scope of a single object file.  This would =
be redundant in cases where kernel-wide LTO is enabled.

Using this approach might slow down compilation a bit due to needing to =
pass the LLVM bitcode between multiple commands, but probably not very =
much.

Just chiming in as someone not involved in Rust for Linux but familiar =
with these tools.  Perhaps this has been considered before and rejected =
for some reason; I wouldn=E2=80=99t know.=