Re: C aggregate passing (Rust kernel policy)

Ralf Jung
2025-02-28T07:53:13Z

Hi,

On 27.02.25 20:15, Linus Torvalds wrote:
> On Thu, 27 Feb 2025 at 10:33, Ralf Jung <post@ralfj.de> wrote:
>>
>> The way you do global flags in Rust is like this:
>
> Note that I was really talking mainly about the unsafe cases, an din
> particular when interfacing with C code.

When Rust code and C code share memory that is concurrently accessed, all
accesses to that from the Rust side must be explicitly marked as atomic. A
pointer to such a memory should look like `&AtomicBool` in Rust, not `*mut
bool`. To my knowledge, the kernel already has appropriate APIs for that. That
will then ensure things behave like the AtomicBool example.

Kind regards,
Ralf

>
> Also, honestly:
>
>> FLAG.store(true, Ordering::SeqCst); // or release/acquire/relaxed
>
> I suspect in reality it would be hidden as accessor functions, or
> people just continue to write things in C.
>
> Yes, I know all about the C++ memory ordering. It's not only a
> standards mess, it's all very illegible code too.
>
> Linus