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

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Date:   Mon, 11 Dec 2023 15:34:26 +0000
From:   Alice Ryhl <aliceryhl@...gle.com>
To:     benno.lossin@...ton.me
Cc:     a.hindborg@...sung.com, alex.gaynor@...il.com,
        aliceryhl@...gle.com, arve@...roid.com, bjorn3_gh@...tonmail.com,
        boqun.feng@...il.com, brauner@...nel.org, cmllamas@...gle.com,
        dan.j.williams@...el.com, dxu@...uu.xyz, gary@...yguo.net,
        gregkh@...uxfoundation.org, joel@...lfernandes.org,
        keescook@...omium.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, maco@...roid.com, ojeda@...nel.org,
        peterz@...radead.org, rust-for-linux@...r.kernel.org,
        surenb@...gle.com, tglx@...utronix.de, tkjos@...roid.com,
        viro@...iv.linux.org.uk, wedsonaf@...il.com, willy@...radead.org
Subject: Re: [PATCH v2 2/7] rust: cred: add Rust abstraction for `struct cred`

Benno Lossin <benno.lossin@...ton.me> writes:
> 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)`?

Historical accident. It isn't needed anymore. I'll remove it.

> > +    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()`?

Will do.

Alice