Re: [PATCH v3 1/6] rust: module: add `THIS_MODULE` const to `ModuleMetadata` trait

[Alvin Sun <alvin.sun@linux.dev>]

On 6/22/26 18:50, Gary Guo wrote:
> On Mon Jun 22, 2026 at 3:44 AM BST, 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`.
>>
>> Move the `THIS_MODULE` static from the `module!` macro into the
>> `ModuleMetadata` impl, add a `this_module()` helper, and update `__init`
>> to use it.
>>
>> Signed-off-by: Alvin Sun <alvin.sun@linux.dev>
>> ---
>>   rust/kernel/lib.rs    |  8 ++++++++
>>   rust/macros/module.rs | 34 +++++++++++++++++-----------------
>>   2 files changed, 25 insertions(+), 17 deletions(-)
>>
>> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
>> index b72b2fbe046d6..50f5a7b5f028e 100644
>> --- a/rust/kernel/lib.rs
>> +++ b/rust/kernel/lib.rs
>> @@ -184,6 +184,14 @@ fn init(module: &'static ThisModule) -> impl pin_init::PinInit<Self, error::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.
>> +pub const fn this_module<M: ModuleMetadata>() -> &'static ThisModule {
>> +    &M::THIS_MODULE
>>   }
> Also, FWIW I think this should not put this in the crate root. Perhaps create a
> modules.rs?

Makes sense. I'll create a new `module.rs` and move the module-related items
(`ModuleMetadata`, `ThisModule`, `this_module()`) there, then re-export from
`lib.rs`.

Best regards,
Alvin Sun

>
> Best,
> Gary
>
>>   
>>   /// Equivalent to `THIS_MODULE` in the C API.
>> diff --git a/rust/macros/module.rs b/rust/macros/module.rs
>> index 06c18e2075083..b9fdee2f2af47 100644
>> --- a/rust/macros/module.rs
>> +++ b/rust/macros/module.rs
>> @@ -497,28 +497,28 @@ pub(crate) fn module(info: ModuleInfo) -> Result<TokenStream> {
>>           /// Used by the printing macros, e.g. [`info!`].
>>           const __LOG_PREFIX: &[u8] = #name_cstr.to_bytes_with_nul();
>>   
>> -        // SAFETY: `__this_module` is constructed by the kernel at load time and will not be
>> -        // freed until the module is unloaded.
>> -        #[cfg(MODULE)]
>> -        static THIS_MODULE: ::kernel::ThisModule = unsafe {
>> -            extern "C" {
>> -                static __this_module: ::kernel::types::Opaque<::kernel::bindings::module>;
>> -            };
>> -
>> -            ::kernel::ThisModule::from_ptr(__this_module.get())
>> -        };
>> -
>> -        #[cfg(not(MODULE))]
>> -        static THIS_MODULE: ::kernel::ThisModule = unsafe {
>> -            ::kernel::ThisModule::from_ptr(::core::ptr::null_mut())
>> -        };
>> -
>>           /// The `LocalModule` type is the type of the module created by `module!`,
>>           /// `module_pci_driver!`, `module_platform_driver!`, etc.
>>           type LocalModule = #type_;
>>   
>>           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 +616,7 @@ 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::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
>