[RFC PATCH] rust: block: Use 32-bit atomics

[Alice Ryhl]

On Thu, Sep 5, 2024 at 8:12 AM David Gow <davidgow at google.com> wrote:
>
> Not all architectures have core::sync::atomic::AtomicU64 available. In
> particular, 32-bit x86 doesn't support it. AtomicU32 is available
> everywhere, so use that instead.
>
> Hopefully we can add AtomicU64 to Rust-for-Linux more broadly, so this
> won't be an issue, but it's not supported in core from upstream Rust:
> https://doc.rust-lang.org/std/sync/atomic/#portability
>
> This can be tested on 32-bit x86 UML via:
> ./tools/testing/kunit/kunit.py run --make_options LLVM=1 --kconfig_add CONFIG_RUST=y --kconfig_add CONFIG_64BIT=n --kconfig_add CONFIG_FORTIFY_SOURCE=n
>
> Fixes: 3253aba3408a ("rust: block: introduce `kernel::block::mq` module")
> Signed-off-by: David Gow <davidgow at google.com>
> ---
>
> Hi all,
>
> I encountered this build error with Rust/UML since the kernel::block::mq
> stuff landed. I'm not 100% sure just swapping AtomicU64 with AtomicU32
> is correct -- please correct me if not -- but this does at least get the
> Rust/UML/x86-32 builds here compiling and running again.
>
> (And gives me more encouragement to go to the Rust atomics talk at
> Plumbers.)

I would probably go with AtomicUsize over AtomicU32 in this case.

Alice