Re: [PATCH v18 1/4] rust: drm: gem: shmem: Add DmaResvGuard helper

[Gary Guo]

On Thu Jun 4, 2026 at 8:24 PM BST, Lyude Paul wrote:
> Just a temporary holdover to make locking/unlocking the dma_resv lock much
> easier.
>
> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> Co-authored-by: Alexandre Courbot <acourbot@xxxxxxxxxx>
> Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxx>
>
> ---
> V17:
> * Fix format of commit message title
>
>  rust/kernel/drm/gem/shmem.rs | 31 ++++++++++++++++++++++++++++++-
>  1 file changed, 30 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/drm/gem/shmem.rs b/rust/kernel/drm/gem/shmem.rs
> index 084b798ce795b..650c34dd8b7a4 100644
> --- a/rust/kernel/drm/gem/shmem.rs
> +++ b/rust/kernel/drm/gem/shmem.rs
> @@ -30,7 +30,10 @@
>          Deref,
>          DerefMut, //
>      },
> -    ptr::NonNull, //
> +    ptr::{
> +        self,
> +        NonNull, //
> +    },
>  };
>  use gem::{
>      BaseObjectPrivate,
> @@ -244,3 +247,29 @@ impl<T: DriverObject, C: DeviceContext> driver::AllocImpl for Object<T, C> {
>          dumb_map_offset: None,
>      };
>  }
> +
> +/// Private helper-type for holding the `dma_resv` object for a GEM shmem object.
> +///
> +/// When this is dropped, the `dma_resv` lock is dropped as well.
> +///
> +// TODO: This should be replace with a WwMutex equivalent once we have such bindings in the kernel.
> +struct DmaResvGuard<'a, T: DriverObject, C: DeviceContext = Registered>(&'a Object<T, C>);
> +
> +impl<'a, T: DriverObject, C: DeviceContext> DmaResvGuard<'a, T, C> {
> +    #[inline(always)]

Why `always` here?

Best,
Gary

> +    #[expect(unused)]
> +    fn new(obj: &'a Object<T, C>) -> Self {
> +        // SAFETY: This lock is initialized throughout the lifetime of `object`.
> +        unsafe { bindings::dma_resv_lock(obj.raw_dma_resv(), ptr::null_mut()) };
> +
> +        Self(obj)
> +    }
> +}
> +
> +impl<'a, T: DriverObject, C: DeviceContext> Drop for DmaResvGuard<'a, T, C> {
> +    #[inline(always)]
> +    fn drop(&mut self) {
> +        // SAFETY: We are releasing the lock grabbed during the creation of this object.
> +        unsafe { bindings::dma_resv_unlock(self.0.raw_dma_resv()) };
> +    }
> +}