linux-kernel - Re: [PATCH] rust: driver: let probe() return impl PinInit<Self, Error>

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Message-ID: <aPI-9GoI7ZsNCpQr@google.com>
Date: Fri, 17 Oct 2025 13:04:52 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: gregkh@...uxfoundation.org, rafael@...nel.org, viresh.kumar@...aro.org, 
	acourbot@...dia.com, ira.weiny@...el.com, leon@...nel.org, 
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	bjorn3_gh@...tonmail.com, lossin@...nel.org, a.hindborg@...nel.org, 
	tmgross@...ch.edu, rust-for-linux@...r.kernel.org, linux-pci@...r.kernel.org, 
	linux-pm@...r.kernel.org, nouveau@...ts.freedesktop.org, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: driver: let probe() return impl PinInit<Self, Error>

On Thu, Oct 16, 2025 at 02:55:28PM +0200, Danilo Krummrich wrote:
> The driver model defines the lifetime of the private data stored in (and
> owned by) a bus device to be valid from when the driver is bound to a
> device (i.e. from successful probe()) until the driver is unbound from
> the device.
> 
> This is already taken care of by the Rust implementation of the driver
> model. However, we still ask drivers to return a Result<Pin<KBox<Self>>>
> from probe().
> 
> Unlike in C, where we do not have the concept of initializers, but
> rather deal with uninitialized memory, drivers can just return an
> impl PinInit<Self, Error> instead.
> 
> This contributed to more clarity to the fact that a driver returns it's
> device private data in probe() and the Rust driver model owns the data,
> manages the lifetime and - considering the lifetime - provides (safe)
> accessors for the driver.
> 
> Hence, let probe() functions return an impl PinInit<Self, Error> instead
> of Result<Pin<KBox<Self>>>.
> 
> Signed-off-by: Danilo Krummrich <dakr@...nel.org>
> ---
> Depends on a minor pin-init patch [1] (Benno will send it to the list
> soon). A branch with this patch and the pin-init dependency is available
> in [2].
> 
> [1] https://github.com/Rust-for-Linux/pin-init/pull/86/commits
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/log/?h=probe_return

Overall LGTM.
Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>

>  impl Device<CoreInternal> {
>      /// Store a pointer to the bound driver's private data.
> -    pub fn set_drvdata(&self, data: impl ForeignOwnable) {
> +    pub fn set_drvdata<T: 'static>(&self, data: impl PinInit<T, Error>) -> Result {
> +        let data = KBox::pin_init(data, GFP_KERNEL)?;

Perhaps the gfp flags should be an argument set_drvdata?

Alice