Re: [PATCH v10 00/10] Fix missing fops.owner in Rust DRM/misc abstractions

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

On Wed Aug 12, 2026 at 10:53 PM BST, Danilo Krummrich wrote:
> (Cc: Mark)
>
> On Wed Aug 12, 2026 at 6:33 PM CEST, Miguel Ojeda wrote:
>> On Tue, Aug 11, 2026 at 8:41 AM Alvin Sun <alvin.sun@linux.dev> wrote:
>>>
>>> The series moves `THIS_MODULE` into the `ModuleMetadata` as a const, threads it
>>> through `#[vtable]` to set `fops.owner` in DRM/miscdevice, and updates configfs
>>> and rnull to use `this_module::<LocalModule>()`.
>>
>> Applied to `rust-next` -- thanks everyone!
>
> This series has a semantic conflict with both the driver-core and the drm-rust
> tree:
>
> @Mark: When you merge driver-core-next after rust-next (which I think is the
> case) then you need to include the diff in [1] into the merge.
>
> In drm-rust-next the build fails with:
>
> 	error[E0425]: cannot find type `LocalModule` in the crate root
> 	   --> rust/kernel/drm/gem/shmem.rs:628:5
> 	    |
> 	628 |     #[vtable]
> 	    |     ^^^^^^^^^ not found in the crate root
> 	    |
> 	    = note: this error originates in the attribute macro `vtable` (in Nightly builds, run with -Z macro-backtrace for more info)
>
> which is because the kunit test in rust/kernel/drm/gem/shmem.rs uses the
> #[vtable] macro.
>
> This should be fixed up with a patch on top of this series in rust-next.
>
> I came up with to potential solutions [2] and [3]. I think with the new build
> system we want [3], but I'm not entirely sure this works correctly with the
> current build system in all cases (at least it did survive my tests).
>
> Alternatively, we could just open-code a dummy module as in [2] for now.
>
> [1] driver-core-next merge fixup
>
> diff --git a/rust/kernel/serdev.rs b/rust/kernel/serdev.rs
> index a4927452016e..17ca504b7f8d 100644
> --- a/rust/kernel/serdev.rs
> +++ b/rust/kernel/serdev.rs
> @@ -87,7 +87,7 @@ unsafe fn register(
>          }
>
>          // SAFETY: `sdrv` is guaranteed to be a valid `DriverType`.
> -        to_result(unsafe { bindings::__serdev_device_driver_register(sdrv.get(), module.0) })
> +        to_result(unsafe { bindings::__serdev_device_driver_register(sdrv.get(), module.as_ptr()) })

`module.0` shouldn't be used in the first place, it just happens to be visible
due to the unfortunate placement at crate root.

Perhaps you can update driver-core tree to use `as_ptr()`? It was already there
and not newly introduced in the series.

>      }
>
>      unsafe fn unregister(sdrv: &Opaque<Self::DriverType>) {
>
> [2] Open-coded dummy module
>
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index c04e6c5aa7e0..274924cfcc05 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -157,6 +157,15 @@
>  /// Prefix to appear before log messages printed from within the `kernel` crate.
>  const __LOG_PREFIX: &[u8] = b"rust_kernel\0";
>
> +/// Dummy module type for `#[vtable]` impl blocks within the kernel crate (e.g. kunit tests).
> +struct LocalModule;
> +
> +impl ModuleMetadata for LocalModule {
> +    const NAME: &'static str::CStr = c"rust_kernel";
> +    // SAFETY: `try_module_get`/`module_put` handle null module pointers gracefully.
> +    const THIS_MODULE: ThisModule = unsafe { ThisModule::from_ptr(core::ptr::null_mut()) };
> +}
> +
>  #[cfg(not(testlib))]
>  #[panic_handler]
>  fn panic(info: &core::panic::PanicInfo<'_>) -> ! {

IMO this is the correct way, also consistent with

https://lore.kernel.org/rust-for-linux/20260811-fix-fops-owner-v10-3-7e71776f9dbe@linux.dev/

It might make sense to add this to rust-next.

Best,
Gary