linux-kernel - Re: [PATCH v2 0/6] rust: io: turn IoCapable into a functional trait

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Message-Id: <DG7YXVIJHEWY.BFPZCOIAK1UR@garyguo.net>
Date: Fri, 06 Feb 2026 15:02:57 +0000
From: "Gary Guo" <gary@...yguo.net>
To: "Alexandre Courbot" <acourbot@...dia.com>, "Danilo Krummrich"
 <dakr@...nel.org>, "Alice Ryhl" <aliceryhl@...gle.com>, "Daniel Almeida"
 <daniel.almeida@...labora.com>, "Miguel Ojeda" <ojeda@...nel.org>, "Boqun
 Feng" <boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, "Benno Lossin"
 <lossin@...nel.org>, "Andreas Hindborg" <a.hindborg@...nel.org>, "Trevor
 Gross" <tmgross@...ch.edu>, "Bjorn Helgaas" <bhelgaas@...gle.com>,
 Krzysztof Wilczyński <kwilczynski@...nel.org>
Cc: <driver-core@...ts.linux.dev>, <rust-for-linux@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>, "Zhi Wang"
 <zhiw@...dia.com>, "Lyude Paul" <lyude@...hat.com>, "Eliot Courtney"
 <ecourtney@...dia.com>
Subject: Re: [PATCH v2 0/6] rust: io: turn IoCapable into a functional trait

On Fri Feb 6, 2026 at 6:00 AM GMT, Alexandre Courbot wrote:
> `IoCapable<T>` is currently used as a marker trait to signal that the
> methods of the `Io` trait corresponding to `T` have been overridden by
> the implementor (the default implementations triggering a build-time
> error).
>
> This goes against the DRY principle and separates the signaling of the
> capability from its implementation, making it possible to forget a step
> while implementing a new `Io`.
>
> Another undesirable side-effect is that it makes the implementation of
> I/O backends boilerplate-y and convoluted: currently this is done using
> two levels of imbricated macros that generate unsafe code.
>
> This patchset fixes these issues by turning `IoCapable` into a
> functional trait including the raw implementation of the I/O
> accessors for `T` using unsafe methods that work with an arbitrary
> address, and making the default methods of `Io` call into these
> implementations after checking the bounds.
>
> This makes overriding these accessors on all I/O backends unneeded,
> resulting in a net -90 LoCs while avoiding a violation of the DRY
> principle and reducing (and simplifying) the use of macros generating
> unsafe code.
>
> Patch 1 adds the `io_read` and `io_write` unsafe methods to `IoCapable`,
> provides the required implementations for `Mmio` and `pci::ConfigSpace`,
> and make the default I/O accessors of `Io` call into them instead of
> failing.
>
> Patches 2 to 4 get rid of the `_relaxed` variants we had in `Mmio`,
> since these are not usable in code generic against `Io` and makes use of
> the macros we want to remove. They are replaced by a `RelaxedMmio`
> wrapper type that implements the required `IoCapable`s and is thus
> usable in generic code.
>
> Patches 5 and 6 remove the overloaded implementations of the `Io`
> methods for `pci::ConfigSpace` and `Mmio`, respectively, while also
> deleting the macros that have become unused.
>
> There is more work coming on top of this patchset (notably the
> `register!` macro with proper I/O), but I wanted to send this work first
> as it stands on its own IMHO and is more digestible from a review
> perspective.
>
> The base for this patchset is `driver-core-testing`.
>
> Cc: Zhi Wang <zhiw@...dia.com>
> Cc: Lyude Paul <lyude@...hat.com>
> Cc: Eliot Courtney <ecourtney@...dia.com>
>
> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>

For the whole series:

Reviewed-by: Gary Guo <gary@...yguo.net>

> ---
> Changes in v2:
> - Turn `RelaxedMmio` into an actual wrapper type and make it available
>   through a `Mmio::relaxed()` method.
> - Link to v1: https://patch.msgid.link/20260202-io-v1-0-9bb2177d23be@nvidia.com
>
> ---
> Alexandre Courbot (6):
>       rust: io: turn IoCapable into a functional trait
>       rust: io: mem: use non-relaxed I/O ops in examples
>       rust: io: provide Mmio relaxed ops through a wrapper type
>       rust: io: remove legacy relaxed accessors of Mmio
>       rust: pci: io: remove overloaded Io methods of ConfigSpace
>       rust: io: remove overloaded Io methods of Mmio
>
>  rust/kernel/io.rs     | 435 ++++++++++++++++++++++----------------------------
>  rust/kernel/io/mem.rs |  10 +-
>  rust/kernel/pci/io.rs |  99 ++++--------
>  3 files changed, 227 insertions(+), 317 deletions(-)
> ---
> base-commit: f55ae0bfa00e446ea751d09f468daeafc303e03f
> change-id: 20260202-io-81fd368f7565
>
> Best regards,