linux-kernel - Re: [PATCH v10 2/5] rust: Rename AlwaysRefCounted to RefCounted

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Message-ID: <aFAGeu5FwaEEUZD8@mango>
Date: Mon, 16 Jun 2025 11:56:47 +0000
From: Oliver Mangold <oliver.mangold@...me>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, Asahi Lina <lina@...hilina.net>, rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 2/5] rust: Rename AlwaysRefCounted to RefCounted

On 250502 1132, Alice Ryhl wrote:
> On Fri, May 02, 2025 at 09:02:37AM +0000, Oliver Mangold wrote:
> > AlwaysRefCounted will become a marker trait to indicate that it is allowed
> > to obtain an ARef<T> from a `&T`, which cannot be allowed for types which
> > are also Ownable.
> >
> > Signed-off-by: Oliver Mangold <oliver.mangold@...me>
> > Suggested-by: Alice Ryhl <aliceryhl@...gle.com>
> 
> >  // SAFETY: All instances of `Request<T>` are reference counted. This
> > -// implementation of `AlwaysRefCounted` ensure that increments to the ref count
> > +// implementation of `RefCounted` ensure that increments to the ref count
> >  // keeps the object alive in memory at least until a matching reference count
> >  // decrement is executed.
> 
> It looks like "keeps" now fits on the previous line. I would reflow all
> text in this patch.

Say, this means you have a tool to do that automatically for you? I'm doing
it by hand currently.

> > +/// An extension to RefCounted, which declares that it is allowed to convert
> > +/// from a shared reference `&T` to an owned reference [`ARef<T>`].
> > +///
> > +/// # Safety
> > +///
> > +/// Implementers must ensure that no safety invariants are violated by upgrading an `&T`
> > +/// to an [`ARef<T>`]. In particular that implies [`AlwaysRefCounted`] and [`Ownable`]
> > +/// cannot be implemented for the same type, as this would allow to violate the uniqueness
> > +/// guarantee of [`Owned<T>`] by derefencing it into an `&T` and obtaining an [`ARef`] from that.
> > +pub unsafe trait AlwaysRefCounted: RefCounted {}
> 
> Adding a new trait should not happen in a commit called "rename X to Y".
> Consider renaming this patch to "split AlwaysRefCounted into two traits"
> or similar.

Sure. Will do.

Oliver