linux-kernel - Re: [PATCH v2] rust/kernel: Add faux device bindings

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Message-ID: <Z6ZOMD__u4VbH8ME@pollux>
Date: Fri, 7 Feb 2025 19:17:20 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Lyude Paul <lyude@...hat.com>
Cc: rust-for-linux@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Maíra Canal <mairacanal@...eup.net>,
	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>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Xiangfei Ding <dingxiangfei2009@...il.com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] rust/kernel: Add faux device bindings

On Thu, Feb 06, 2025 at 07:40:45PM -0500, Lyude Paul wrote:
>
> +/// The registration of a faux device.
> +///
> +/// This type represents the registration of a [`struct faux_device`]. When an instance of this type
> +/// is dropped, its respective faux device will be unregistered from the system.
> +///
> +/// # Invariants
> +///
> +/// `self.0` always holds a valid pointer to an initialized and registered [`struct faux_device`].
> +///
> +/// [`struct faux_device`]: srctree/include/linux/device/faux.h
> +#[repr(transparent)]
> +pub struct Registration(NonNull<bindings::faux_device>);
> +
> +impl Registration {
> +    /// Create and register a new faux device with the given name.
> +    pub fn new(name: &CStr) -> Result<Self> {
> +        // SAFETY:
> +        // - `name` is copied by this function into its own storage
> +        // - `faux_ops` is safe to leave NULL according to the C API
> +        let dev = unsafe { bindings::faux_device_create(name.as_char_ptr(), null()) };
> +
> +        // The above function will return either a valid device, or NULL on failure
> +        Ok(Self(NonNull::new(dev).ok_or(ENOMEM)?))

Since the type has an "Invariants" section, you need to add "INVARIANT:" to this
comment.

> +    }

...

> diff --git a/samples/rust/rust_driver_faux.rs b/samples/rust/rust_driver_faux.rs
> new file mode 100644
> index 0000000000000..81ec465d52651
> --- /dev/null
> +++ b/samples/rust/rust_driver_faux.rs
> @@ -0,0 +1,29 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Rust faux device sample.
> +
> +use kernel::{c_str, faux::*, prelude::*, Module};
> +
> +module! {
> +    type: SampleModule,
> +    name: "rust_faux_driver",
> +    author: "Lyude Paul",
> +    description: "Rust faux device sample",
> +    license: "GPL",
> +}
> +
> +struct SampleModule {
> +    _dev: Registration,

Probably forgot to change this to "_reg" or similar.

Also, maybe faux::Registration here and below, personally I tend to find it a
bit more obvious. But of course totally up to you.

> +}
> +
> +impl Module for SampleModule {
> +    fn init(_module: &'static ThisModule) -> Result<Self> {
> +        pr_info!("Initialising Rust Faux Device Sample\n");
> +
> +        let dev = Registration::new(c_str!("rust-faux-sample-device"))?;
> +
> +        dev_info!(dev.as_ref(), "Hello from faux device!");
> +
> +        Ok(Self { _dev: dev })
> +    }
> +}