linux-kernel - Re: [PATCH v10 1/5] rust: types: Add Ownable/Owned types

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Message-ID: <aFKICIo8L958iFbz@mango>
Date: Wed, 18 Jun 2025 09:34:03 +0000
From: Oliver Mangold <oliver.mangold@...me>
To: Benno Lossin <lossin@...nel.org>
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>, Alice Ryhl <aliceryhl@...gle.com>, 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 1/5] rust: types: Add Ownable/Owned types

On 250514 1132, Benno Lossin wrote:
> On Fri May 2, 2025 at 11:02 AM CEST, Oliver Mangold wrote:
> 
> > +/// - That the C code follows the usual mutable reference requirements. That is, the kernel will
> > +///   never mutate the [`Ownable`] (excluding internal mutability that follows the usual rules)
> > +///   while Rust owns it.
> 
> I feel like this requirement is better put on the `Owned::from_raw`
> function.

Thinking about it some more, the problem I see here is that if the type
implements `OwnableMut` this requirement changes from "never mutate" to
"never access at all".

The safety requirements between `Ownable`, `OwnableMut`, `RefCounted`,
`OwnableRefCounted` and `AlwaysRefCounted` are interacting, but I agree
that, when looking at it a certain way, `Owned::from_raw()` is the place
where one would expect these to be. I'm not sure anymore what is best here
:/

> > +pub unsafe trait OwnableMut: Ownable {}
> 
> I don't like the name, but at the same time I also have no good
> suggestion :( I'll think some more about it.

There was already a bit of discussion about it. I had my own implementation of this
where I used the names `UniqueRefCounted` and `UniqueRef`, but after discovering
this version from Asahi Lina, I took it as it was, keeping the name.

No one else came up with different suggestions so far, so maybe we should just leave it
at `Owned`/`Ownable`?

Best,

Oliver