Re: [PATCH v13 2/6] rust: introduce module_param module

[Andreas Hindborg <a.hindborg@kernel.org>]

"Benno Lossin" <lossin@kernel.org> writes:

> On Mon Jun 30, 2025 at 3:15 PM CEST, Andreas Hindborg wrote:
>> "Benno Lossin" <lossin@kernel.org> writes:
>>> On Mon Jun 30, 2025 at 1:18 PM CEST, Andreas Hindborg wrote:
>>>> "Benno Lossin" <lossin@kernel.org> writes:
>>>>> (no idea if the orderings are correct, I always have to think way to
>>>>> much about that... especially since our atomics seem to only take one
>>>>> ordering in compare_exchange?)
>>>>>
>>>>>> As far as I can tell, atomics may not land in v6.17, so this series
>>>>>> will probably not be ready for merge until v6.18 at the earliest.
>>>>>
>>>>> Yeah, sorry about that :(
>>>>
>>>> Actually, perhaps we could aim at merging this code without this
>>>> synchronization?
>>>
>>> I won't remember this issue in a few weeks and I fear that it will just
>>> get buried. In fact, I already had to re-read now what the actual issue
>>> was...
>>>
>>>> The lack of synchronization is only a problem if we
>>>> support custom parsing. This patch set does not allow custom parsing
>>>> code, so it does not suffer this issue.
>>>
>>> ... In doing that, I saw my original example of UB:
>>>
>>>     module! {
>>>         // ...
>>>         params: {
>>>             my_param: i64 {
>>>                 default: 0,
>>>                 description: "",
>>>             },
>>>         },
>>>     }
>>>
>>>     static BAD: &'static i64 = module_parameters::my_param.get();
>>>
>>> That can happen without custom parsing, so it's still a problem...
>>
>> Ah, got it. Thanks.
>
> On second thought, we *could* just make the accessor function `unsafe`.
> Of course with a pinky promise to make the implementation safe once
> atomics land. But I think if it helps you get your driver faster along,
> then we should do it.

No, I am OK for now with configfs.

But, progress is still great. How about if we add a copy accessor
instead for now, I think you proposed that a few million emails ago:

    pub fn get(&self) -> T;

or maybe rename:

    pub fn copy(&self) -> T;

Then we are fine safety wise for now, right? It is even sensible for
these `T: Copy` types.


Best regards,
Andreas Hindborg