Re: [PATCH] rust: module_param: return copy from value() for Copy types

["Gary Guo" <gary@garyguo.net>]

On Mon Mar 23, 2026 at 12:47 PM GMT, Andreas Hindborg wrote:
> Rename the existing `value()` method to `value_ref()` which returns a
> shared reference to the parameter value, and add a new `value()`
> method on `ModuleParamAccess<T>` where `T: Copy` that returns the
> value by copy.
>
> This provides a more ergonomic API for the common case where the
> parameter type implements `Copy`, avoiding the need to explicitly
> dereference the return value at call sites.
>
> Currently `value_ref()` has no in-tree callers, but it will be needed
> when support for non-`Copy` parameter types such as arrays and
> strings is added.
>
> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
> ---
> This change was suggested at [1].
>
> Link: https://lore.kernel.org/r/87cy13swpw.fsf@t14s.mail-host-address-is-not-set [1]
> ---
>  rust/kernel/module_param.rs  | 11 ++++++++++-
>  samples/rust/rust_minimal.rs |  2 +-
>  2 files changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/rust/kernel/module_param.rs b/rust/kernel/module_param.rs
> index 6a8a7a875643..5dcfe2ba87a1 100644
> --- a/rust/kernel/module_param.rs
> +++ b/rust/kernel/module_param.rs
> @@ -134,7 +134,7 @@ pub const fn new(default: T) -> Self {
>      /// Get a shared reference to the parameter value.
>      // Note: When sysfs access to parameters are enabled, we have to pass in a
>      // held lock guard here.
> -    pub fn value(&self) -> &T {
> +    pub fn value_ref(&self) -> &T {
>          self.value.as_ref().unwrap_or(&self.default)
>      }
>  
> @@ -146,6 +146,15 @@ pub const fn as_void_ptr(&self) -> *mut c_void {
>      }
>  }
>  
> +impl<T: Copy> ModuleParamAccess<T> {
> +    /// Get a copy of the parameter value.
> +    // Note: When sysfs access to parameters are enabled, we have to pass in a
> +    // held lock guard here.
> +    pub fn value(&self) -> T {

It's better to keep this close to `value_ref` in the same impl block. The `T:
Copy` bound doesn't need to be on the impl block, it can be on the item itself
with

    pub fn value(&self) -> T where T: Copy

Best,
Gary

> +        self.value.copy().unwrap_or(self.default)
> +    }
> +}
> +
>  #[doc(hidden)]
>  /// Generate a static [`kernel_param_ops`](srctree/include/linux/moduleparam.h) struct.
>  ///
> diff --git a/samples/rust/rust_minimal.rs b/samples/rust/rust_minimal.rs
> index 8eb9583571d7..60d03df6cd80 100644
> --- a/samples/rust/rust_minimal.rs
> +++ b/samples/rust/rust_minimal.rs
> @@ -28,7 +28,7 @@ fn init(_module: &'static ThisModule) -> Result<Self> {
>          pr_info!("Am I built-in? {}\n", !cfg!(MODULE));
>          pr_info!(
>              "test_parameter: {}\n",
> -            *module_parameters::test_parameter.value()
> +            module_parameters::test_parameter.value()
>          );
>  
>          let mut numbers = KVec::new();
>
> ---
> base-commit: c369299895a591d96745d6492d4888259b004a9e
> change-id: 20260323-module-value-ref-5884b5ae6b2a
>
> Best regards,