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

[Benno Lossin]

On 11/29/23 13:51, Alice Ryhl wrote:
> +    /// Returns the credentials of the task that originally opened the file.
> +    pub fn cred(&self) -> &Credential {
> +        // This `read_volatile` is intended to correspond to a READ_ONCE call.
> +        //
> +        // SAFETY: The file is valid because the shared reference guarantees a nonzero refcount.
> +        //
> +        // TODO: Replace with `read_once` when available on the Rust side.
> +        let ptr = unsafe { core::ptr::addr_of!((*self.0.get()).f_cred).read_volatile() };
> +
> +        // SAFETY: The signature of this function ensures that the caller will only access the
> +        // returned credential while the file is still valid, and the credential must stay valid
> +        // while the file is valid.

About the last part of this safety comment, is this a guarantee from the
C side? If yes, then I would phrase it that way:

    ... while the file is still valid, and the C side ensures that the
    credentials stay valid while the file is valid.

-- 
Cheers,
Benno

> +        unsafe { Credential::from_ptr(ptr) }
> +    }
> +