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Date: Tue, 17 Feb 2026 12:17:05 +0100
Message-Id: <DGH70XNPF9FI.2BRM4I81T6XLQ@kernel.org>
Subject: Re: [PATCH v2 1/6] rust: io: turn IoCapable into a functional trait
Cc: "Gary Guo" <gary@garyguo.net>, <lyude@redhat.com>, "Alice Ryhl"
 <aliceryhl@google.com>, "Daniel Almeida" <daniel.almeida@collabora.com>,
 "Miguel Ojeda" <ojeda@kernel.org>, "Boqun Feng" <boqun.feng@gmail.com>,
 =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>, "Benno Lossin"
 <lossin@kernel.org>, "Andreas Hindborg" <a.hindborg@kernel.org>, "Trevor
 Gross" <tmgross@umich.edu>, "Bjorn Helgaas" <bhelgaas@google.com>,
 =?utf-8?q?Krzysztof_Wilczy=C5=84ski?= <kwilczynski@kernel.org>,
 <driver-core@lists.linux.dev>, <rust-for-linux@vger.kernel.org>,
 <linux-kernel@vger.kernel.org>, <linux-pci@vger.kernel.org>, "Zhi Wang"
 <zhiw@nvidia.com>, "Eliot Courtney" <ecourtney@nvidia.com>
To: "Alexandre Courbot" <acourbot@nvidia.com>
From: "Danilo Krummrich" <dakr@kernel.org>
References: <20260206-io-v2-0-71dea20a06e6@nvidia.com>
 <20260206-io-v2-1-71dea20a06e6@nvidia.com>
 <97fc6c36933522eaf75f34f8fcd445715432fde4.camel@redhat.com>
 <DGCYWK1UF76I.A565AK23DZXS@nvidia.com>
 <DGD1LDCXJZR6.32S0Z7EHGYDUN@garyguo.net>
 <DGD2GXAFO99J.1Y3BA26PBVTAC@kernel.org>
 <DGGD4JTGJYXR.3THD2I3AA61PN@nvidia.com>
 <DGGDHY4582D1.1GZGZ7P98OKWO@kernel.org>
 <DGGF65JPF8S6.268LR7YDPTWMQ@nvidia.com>
 <DGGJSHVZB6U5.2V8OMF5N3KZNZ@kernel.org>
 <DGGUOQT5BJW2.14AK9GFZKC854@nvidia.com>
In-Reply-To: <DGGUOQT5BJW2.14AK9GFZKC854@nvidia.com>

On Tue Feb 17, 2026 at 2:36 AM CET, Alexandre Courbot wrote:
> Ah, I think I finally get it now. `Io` and `IoKnownSize` can piggyback
> on the `IoCapable` safety requirement, because all the unsafe code
> requires an `IoCapable` implementation anyway. I guess that's sound
> indeed.
>
> I don't think the same can apply to `io_read` and `io_write` though -
> `IoCapable` is public, and so anyone could call them with an arbitrary
> argument, e.g.
>
>    let mmio: &Mmio<0x100>;
>    ...
>    IoCapable::<u8>::io_read(mmio, usize::MAX);
>
> Here we have no way of making the callers enforce the internal safety
> requirement of these methods, thus we need to keep them unsafe.

Agreed.