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

[lyude@redhat.com]

A thought that crossed my mind just now with this patch series while I
was working on converting iosys_map over to it: shouldn't we have some
unit tests for confirming runtime bounds checking works as well?

On Fri, 2026-02-06 at 15:00 +0900, 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@nvidia.com>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: Eliot Courtney <ecourtney@nvidia.com>
> 
> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
> ---
> 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,