On Wed, May 21, 2025 at 03:44:56PM +0900, Alexandre Courbot wrote:
> These properties are very useful to have and should be accessible.
>
> Signed-off-by: Alexandre Courbot <acour...@nvidia.com>
> ---
> rust/kernel/dma.rs | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
> index
> 605e01e35715667f93297fd9ec49d8e7032e0910..2a60eefa47dfc1f836c30ee342e26c6ff3e9b13a
> 100644
> --- a/rust/kernel/dma.rs
> +++ b/rust/kernel/dma.rs
> @@ -129,6 +129,10 @@ pub mod attrs {
> //
> // Hence, find a way to revoke the device resources of a
> `CoherentAllocation`, but not the
> // entire `CoherentAllocation` including the allocated memory itself.
> +//
> +// # Invariants
> +//
> +// The size in bytes of the allocation is equal to `size_of::<T> * count()`.
I think this also needs an invariant comment whenever self.count is set.
> pub struct CoherentAllocation<T: AsBytes + FromBytes> {
> dev: ARef<Device>,
> dma_handle: bindings::dma_addr_t,
> @@ -201,6 +205,20 @@ 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 {
> + // As per the invariants of `CoherentAllocation`.
> + 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
>
