Re: [PATCH v4 1/5] rust: implement `kernel::sync::Refcount`

["Benno Lossin" <lossin@kernel.org>]

On Sun Jun 22, 2025 at 2:57 PM CEST, Gary Guo wrote:
> +impl Refcount {
> +    /// Construct a new [`Refcount`] from an initial value.
> +    #[inline]
> +    pub fn new(value: i32) -> Self {

Should we really allow users to set a negative value from the get-go?
Here a `u31` might come in real handy...

> +        // SAFETY: There are no safety requirements for this FFI call.
> +        Self(Opaque::new(unsafe { bindings::REFCOUNT_INIT(value) }))
> +    }
> +
> +    #[inline]
> +    fn as_ptr(&self) -> *mut bindings::refcount_t {
> +        self.0.get()
> +    }
> +
> +    /// Set a refcount's value.
> +    #[inline]
> +    pub fn set(&self, value: i32) {

Same here. We should of course provide a `saturate` function, but I
don't see a reason to set it to another negative value.

---
Cheers,
Benno

> +        // SAFETY: `self.as_ptr()` is valid.
> +        unsafe { bindings::refcount_set(self.as_ptr(), value) }
> +    }