Re: [PATCH v3 01/19] rust: dma: expose the count and size of CoherentAllocation

[Danilo Krummrich <dakr@kernel.org>]

On Wed, May 07, 2025 at 10:52:28PM +0900, Alexandre Courbot wrote:
> These properties are very useful to have and should be accessible.
> 
> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
> ---
>  rust/kernel/dma.rs | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
> index 605e01e35715667f93297fd9ec49d8e7032e0910..18602d771054fceb80c29278b1945254312ed7c6 100644
> --- a/rust/kernel/dma.rs
> +++ b/rust/kernel/dma.rs
> @@ -201,6 +201,20 @@ pub fn alloc_coherent(
>          CoherentAllocation::alloc_attrs(dev, count, gfp_flags, Attrs(0))
>      }
>  
> +    /// Returns the number of elements `T` in this allocation.
> +    ///
> +    /// Note that this is not the size of the allocation in bytes, which is provided by
> +    /// [`Self::size`].
> +    pub fn count(&self) -> usize {
> +        self.count
> +    }
> +
> +    /// Returns the size in bytes of this allocation.
> +    pub fn size(&self) -> usize {
> +        // This is guaranteed not to overflow as the same operation has been done in `alloc_attrs`.

Please make this an invariant of CoherentAllocation and refer to that instead.

> +        self.count * core::mem::size_of::<T>()
> +    }
> +
>      /// Returns the base address to the allocated region in the CPU's virtual address space.
>      pub fn start_ptr(&self) -> *const T {
>          self.cpu_addr
> 
> -- 
> 2.49.0
>