Re: [PATCH v2 2/7] rust: cred: add Rust abstraction for `struct cred`

[Benno Lossin <benno.lossin@proton.me>]

On 12/6/23 12:59, Alice Ryhl wrote:
> +/// Wraps the kernel's `struct cred`.
> +///
> +/// # Invariants
> +///
> +/// Instances of this type are always ref-counted, that is, a call to `get_cred` ensures that the
> +/// allocation remains valid at least until the matching call to `put_cred`.
> +#[repr(transparent)]
> +pub struct Credential(pub(crate) Opaque<bindings::cred>);

Why is the field `pub(crate)`?

[...]

> +// SAFETY: The type invariants guarantee that `Credential` is always ref-counted.
> +unsafe impl AlwaysRefCounted for Credential {
> +    fn inc_ref(&self) {
> +        // SAFETY: The existence of a shared reference means that the refcount is nonzero.
> +        unsafe { bindings::get_cred(self.0.get()) };
> +    }
> +
> +    unsafe fn dec_ref(obj: core::ptr::NonNull<Self>) {
> +        // SAFETY: The safety requirements guarantee that the refcount is nonzero.

Can you also justify the `cast()`?

-- 
Cheers,
Benno

> +        unsafe { bindings::put_cred(obj.cast().as_ptr()) };
> +    }
> +}