linux-kernel - Re: [PATCH 2/8] rust: device: add drvdata accessors

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Message-ID: <2025070159-perkiness-bullion-da76@gregkh>
Date: Tue, 1 Jul 2025 11:27:54 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Danilo Krummrich <dakr@...nel.org>
Cc: rafael@...nel.org, ojeda@...nel.org, alex.gaynor@...il.com,
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com,
	benno.lossin@...ton.me, a.hindborg@...nel.org, aliceryhl@...gle.com,
	tmgross@...ch.edu, david.m.ertman@...el.com, ira.weiny@...el.com,
	leon@...nel.org, kwilczynski@...nel.org, bhelgaas@...gle.com,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH 2/8] rust: device: add drvdata accessors

On Sat, Jun 21, 2025 at 09:43:28PM +0200, Danilo Krummrich wrote:
> Implement generic accessors for the private data of a driver bound to a
> device.
> 
> Those accessors should be used by bus abstractions from their
> corresponding core callbacks, such as probe(), remove(), etc.
> 
> Implementing them for device::Internal guarantees that driver's can't
> interfere with the logic implemented by the bus abstraction.
> 
> Signed-off-by: Danilo Krummrich <dakr@...nel.org>
> ---
>  rust/helpers/device.c | 10 ++++++++++
>  rust/kernel/device.rs | 43 ++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 52 insertions(+), 1 deletion(-)
> 
> diff --git a/rust/helpers/device.c b/rust/helpers/device.c
> index b2135c6686b0..9bf252649c75 100644
> --- a/rust/helpers/device.c
> +++ b/rust/helpers/device.c
> @@ -8,3 +8,13 @@ int rust_helper_devm_add_action(struct device *dev,
>  {
>  	return devm_add_action(dev, action, data);
>  }
> +
> +void *rust_helper_dev_get_drvdata(const struct device *dev)
> +{
> +	return dev_get_drvdata(dev);
> +}
> +
> +void rust_helper_dev_set_drvdata(struct device *dev, void *data)
> +{
> +	dev_set_drvdata(dev, data);
> +}
> diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
> index e9094d8322d5..146eba147d2f 100644
> --- a/rust/kernel/device.rs
> +++ b/rust/kernel/device.rs
> @@ -6,7 +6,7 @@
>  
>  use crate::{
>      bindings,
> -    types::{ARef, Opaque},
> +    types::{ARef, ForeignOwnable, Opaque},
>  };
>  use core::{fmt, marker::PhantomData, ptr};
>  
> @@ -62,6 +62,47 @@ pub unsafe fn get_device(ptr: *mut bindings::device) -> ARef<Self> {
>      }
>  }
>  
> +impl Device<Internal> {
> +    /// Store a pointer to the bound driver's private data.
> +    pub fn set_drvdata(&self, data: impl ForeignOwnable) {
> +        // SAFETY: By the type invariants, `self.as_raw()` is a valid pointer to a `struct device`.
> +        unsafe { bindings::dev_set_drvdata(self.as_raw(), data.into_foreign().cast()) }
> +    }

Ah, but a driver's private data in the device is NOT a bus-specific
thing, it's a driver-specific thing, so your previous patch about
Internal being there for busses feels odd.


> +
> +    /// Take ownership of the private data stored in this [`Device`].
> +    ///
> +    /// # Safety
> +    ///
> +    /// - Must only be called once after a preceding call to [`Device::set_drvdata`].
> +    /// - The type `T` must match the type of the `ForeignOwnable` previously stored by
> +    ///   [`Device::set_drvdata`].
> +    pub unsafe fn drvdata_obtain<T: ForeignOwnable>(&self) -> T {
> +        // SAFETY: By the type invariants, `self.as_raw()` is a valid pointer to a `struct device`.
> +        let ptr = unsafe { bindings::dev_get_drvdata(self.as_raw()) };
> +
> +        // SAFETY: By the safety requirements of this function, `ptr` comes from a previous call to
> +        // `into_foreign()`.
> +        unsafe { T::from_foreign(ptr.cast()) }
> +    }
> +
> +    /// Borrow the driver's private data bound to this [`Device`].
> +    ///
> +    /// # Safety
> +    ///
> +    /// - Must only be called after a preceding call to [`Device::set_drvdata`] and before
> +    ///   [`Device::drvdata_obtain`].
> +    /// - The type `T` must match the type of the `ForeignOwnable` previously stored by
> +    ///   [`Device::set_drvdata`].
> +    pub unsafe fn drvdata_borrow<T: ForeignOwnable>(&self) -> T::Borrowed<'_> {
> +        // SAFETY: By the type invariants, `self.as_raw()` is a valid pointer to a `struct device`.
> +        let ptr = unsafe { bindings::dev_get_drvdata(self.as_raw()) };
> +
> +        // SAFETY: By the safety requirements of this function, `ptr` comes from a previous call to
> +        // `into_foreign()`.
> +        unsafe { T::borrow(ptr.cast()) }
> +    }
> +}

Why can't this be part of Core?

thanks,

greg k-h