Subject: Build error on -next in rust/kernel/usb.rs:92:34 (was: Re: [PATCH 1/8] rust: device: narrow the generic of drvdata_obtain())

From: Thorsten Leemhuis <[email-masked]>
Date: Mon, 3 Nov 2025 07:43:56 +0100

On 10/21/25 00:34, Danilo Krummrich wrote:
> Let T be the actual private driver data type without the surrounding
> box, as it leaves less room for potential bugs.
> 
> Signed-off-by: Danilo Krummrich <[email-masked]>

This patch showed up in linux-next today and I wonder if that caused my
build to break on arm64 and x86:64. The error message looked like this
during "make bzimage":

"""
error[E0599]: no method named `data` found for struct `core::pin::Pin<kbox::Box<T, Kmalloc>>` in the current scope
  --> rust/kernel/usb.rs:92:34
   |
92 |         T::disconnect(intf, data.data());
   |                                  ^^^^ method not found in `core::pin::Pin<kbox::Box<T, Kmalloc>>`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0599`.
make[2]: *** [rust/Makefile:553: rust/kernel.o] Error 1
make[1]: *** [/builddir/build/BUILD/kernel-6.18.0-build/kernel-next-20251103/linux-6.18.0-0.0.next.20251103.436.vanilla.fc44.x86_64/Makefile:1316: prepare] Error 2
make: *** [Makefile:256: __sub-make] Error 2
"""

Full log:
https://download.copr.fedorainfracloud.org/results/@kernel-vanilla/next/fedora-rawhide-aarch64/09759703-next-next-all/builder-live.log.gz

A quick search for "T::disconnect(intf, data.data());" on lore
lead me here:

> diff --git a/rust/kernel/usb.rs b/rust/kernel/usb.rs
> index 9238b96c2185..05eed3f4f73e 100644
> --- a/rust/kernel/usb.rs
> +++ b/rust/kernel/usb.rs
> @@ -87,9 +87,9 @@ extern "C" fn disconnect_callback(intf: *mut bindings::usb_interface) {
>          // SAFETY: `disconnect_callback` is only ever called after a successful call to
>          // `probe_callback`, hence it's guaranteed that `Device::set_drvdata()` has been called
>          // and stored a `Pin<KBox<T>>`.
> -        let data = unsafe { dev.drvdata_obtain::<Pin<KBox<T>>>() };
> +        let data = unsafe { dev.drvdata_obtain::<T>() };
>  
> -        T::disconnect(intf, data.as_ref());
> +        T::disconnect(intf, data.data());
>      }
>  }

Ciao, Thorsten