Re: [PATCH v9 02/10] rust: module: add `THIS_MODULE` const to `ModuleMetadata` trait

[Petr Pavlu <petr.pavlu@suse.com>]

On 7/23/26 4:10 AM, Alvin Sun wrote:
> Since `const_refs_to_static` has been stable as of the MSRV bump, a
> `ThisModule` pointer can now be used in const contexts.
> 
> Add a `THIS_MODULE` const to the `ModuleMetadata` trait so that modules
> can provide their `ThisModule` pointer in const contexts such as static
> `file_operations`.
> 
> Add a `this_module()` helper to retrieve the `THIS_MODULE` pointer of a
> given module type, and update `__init` to use it instead of the
> `THIS_MODULE` static generated by the `module!` macro.
> 
> The `static THIS_MODULE` generated by the `module!` macro is retained
> for backwards compatibility with existing users and removed in a later
> patch once all references have been migrated.
> 
> Assisted-by: opencode:glm-5.2
> Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
> Reviewed-by: Gary Guo <gary@garyguo.net>
> Acked-by: Danilo Krummrich <dakr@kernel.org>
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: Alvin Sun <alvin.sun@linux.dev>

Acked-by: Petr Pavlu <petr.pavlu@suse.com>

> ---
>  rust/kernel/module.rs |  9 +++++++++
>  rust/macros/module.rs | 18 +++++++++++++++++-
>  2 files changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/rust/kernel/module.rs b/rust/kernel/module.rs
> index be242a82e86d2..d713705984477 100644
> --- a/rust/kernel/module.rs
> +++ b/rust/kernel/module.rs
> @@ -42,6 +42,15 @@ fn init(module: &'static ThisModule) -> impl pin_init::PinInit<Self, crate::erro
>  pub trait ModuleMetadata {
>      /// The name of the module as specified in the `module!` macro.
>      const NAME: &'static crate::str::CStr;
> +
> +    /// The module's `THIS_MODULE` pointer.
> +    const THIS_MODULE: ThisModule;
> +}
> +
> +/// Returns a reference to the `THIS_MODULE` of the given module type.
> +#[inline]
> +pub const fn this_module<M: ModuleMetadata>() -> &'static ThisModule {
> +    &M::THIS_MODULE
>  }
>  
>  /// Equivalent to `THIS_MODULE` in the C API.
> diff --git a/rust/macros/module.rs b/rust/macros/module.rs
> index 06c18e2075083..aa9a618d5d19e 100644
> --- a/rust/macros/module.rs
> +++ b/rust/macros/module.rs
> @@ -519,6 +519,22 @@ pub(crate) fn module(info: ModuleInfo) -> Result<TokenStream> {
>  
>          impl ::kernel::ModuleMetadata for #type_ {
>              const NAME: &'static ::kernel::str::CStr = #name_cstr;
> +
> +            #[cfg(MODULE)]
> +            const THIS_MODULE: ::kernel::ThisModule = {
> +                extern "C" {
> +                    static __this_module: ::kernel::types::Opaque<::kernel::bindings::module>;
> +                }
> +
> +                // SAFETY: `__this_module` is constructed by the kernel at load time
> +                // and lives until the module is unloaded.
> +                unsafe { ::kernel::ThisModule::from_ptr(__this_module.get()) }
> +            };
> +
> +            #[cfg(not(MODULE))]
> +            const THIS_MODULE: ::kernel::ThisModule = unsafe {
> +                ::kernel::ThisModule::from_ptr(::core::ptr::null_mut())
> +            };
>          }
>  
>          // Double nested modules, since then nobody can access the public items inside.
> @@ -616,7 +632,7 @@ pub extern "C" fn #ident_exit() {
>                  /// This function must only be called once.
>                  unsafe fn __init() -> ::kernel::ffi::c_int {
>                      let initer = <super::super::LocalModule as ::kernel::InPlaceModule>::init(
> -                        &super::super::THIS_MODULE
> +                        ::kernel::module::this_module::<super::super::LocalModule>()
>                      );
>                      // SAFETY: No data race, since `__MOD` can only be accessed by this module
>                      // and there only `__init` and `__exit` access it. These functions are only
>