linux-kernel - Re: [RFC 1/2] rust: introduce abstractions for fwctl

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Message-Id: <DDYDVUFTJFVY.3U00QWH6LOF5D@kernel.org>
Date: Sun, 02 Nov 2025 18:26:58 +0100
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Zhi Wang" <zhiw@...dia.com>
Cc: <rust-for-linux@...r.kernel.org>, <bhelgaas@...gle.com>,
 <kwilczynski@...nel.org>, <ojeda@...nel.org>, <alex.gaynor@...il.com>,
 <boqun.feng@...il.com>, <gary@...yguo.net>, <bjorn3_gh@...tonmail.com>,
 <lossin@...nel.org>, <a.hindborg@...nel.org>, <aliceryhl@...gle.com>,
 <tmgross@...ch.edu>, <linux-kernel@...r.kernel.org>, <cjia@...dia.com>,
 <smitra@...dia.com>, <ankita@...dia.com>, <aniketa@...dia.com>,
 <kwankhede@...dia.com>, <targupta@...dia.com>, <zhiwang@...nel.org>,
 <alwilliamson@...dia.com>, <acourbot@...dia.com>, <joelagnelf@...dia.com>,
 <jhubbard@...dia.com>, <jgg@...dia.com>
Subject: Re: [RFC 1/2] rust: introduce abstractions for fwctl

Hi Zhi,

Additional to my other comments, some thoughts about naming.

On Thu Oct 30, 2025 at 5:03 PM CET, Zhi Wang wrote:
> +/// Trait implemented by each Rust driver that integrates with the fwctl subsystem.
> +///
> +/// Each implementation corresponds to a specific device type and provides
> +/// the vtable used by the core `fwctl` layer to manage per-FD user contexts
> +/// and handle RPC requests.
> +pub trait FwCtlOps: Sized {

Up to Jason, but I usually recommend to take the Rust module name into account,
i.e a user of the API can refer to this as fwctl::FwCtlOps.

Hence, I suggest to name this Ops or even Operations, such that users can refer
to this as fwctl::Ops or fwctl::Operations.

It would also be more consistent with existing code, e.g. pci::Device,
platform::Device, etc., but also the fwctl::Registration from this patch. :)

> +    /// Driver UCtx type.
> +    type UCtx;

I think we can affort to be a bit more verbose here, maybe just spell it out as
UserContext.

> +    /// fwctl device type, matching the C enum `fwctl_device_type`.
> +    const DEVICE_TYPE: u32;

I think it would make sense to have a new (Rust enum) type (fwctl::DeviceType)
for this, rather than using a raw u32, see [1] for reference.

[1] https://lore.kernel.org/all/20250828133323.53311-2-dakr@kernel.org/

> +/// Represents a per-FD user context (`struct fwctl_uctx`).
> +///
> +/// Each driver embeds `struct fwctl_uctx` as the first field of its own
> +/// context type and uses this wrapper to access driver-specific data.
> +#[repr(C)]
> +#[pin_data]
> +pub struct FwCtlUCtx<T> {

What about UserContext<T>? A driver would refer to this as fwctl::UserContext.