linux-kernel - Re: [PATCH v11 4/4] rust: Add `OwnableRefCounted`

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Message-Id: <DB6R9YNA7TD5.FR3PSOX7SPI1@kernel.org>
Date: Tue, 08 Jul 2025 16:50:03 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Andreas Hindborg" <a.hindborg@...nel.org>
Cc: "Oliver Mangold" <oliver.mangold@...me>, "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>, "Alice Ryhl"
 <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>, "Asahi Lina"
 <lina+kernel@...hilina.net>, <rust-for-linux@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v11 4/4] rust: Add `OwnableRefCounted`

On Tue Jul 8, 2025 at 3:15 PM CEST, Andreas Hindborg wrote:
> "Benno Lossin" <lossin@...nel.org> writes:
>> On Mon Jul 7, 2025 at 3:21 PM CEST, Andreas Hindborg wrote:
>>> When a completion comes back from hardware, it carries the ID. We use
>>> the C block layer `tag_to_rq` machinery to turn this ID back into an
>>> `Owned<Request<_>>`. In that process, we check that `refcount == 1` and
>>> if so, we set refcount to 0 and invent an `Owned<Request<_>>`.
>>
>> (because if not, this would be wrong)
>
> I hope it is not wrong 😆 You can see the latest and greatest here [1].

Thanks for the pointer, the "implementation details" in the docs on
`Request` were very helpful! This is another argument for not having the
blanket impl for `Ownable` when `T: Refcount` I mentioned in the other
thread.

> [1] https://git.kernel.org/pub/scm/linux/kernel/git/a.hindborg/linux.git/tree/rust/kernel/block/mq/request.rs?h=rnull-v6.15#n398

The comment in line 424 looks wrong?

---
Cheers,
Benno