From c0a3065d5def59a894afc8cf5e988396cd0c2f5e Mon Sep 17 00:00:00 2001 From: Alexandre Courbot Date: Thu, 19 Jun 2025 22:23:46 +0900 Subject: [PATCH] rust: dma: expose the count and size of CoherentAllocation These properties are very useful to have (and to be used by nova-core) and should be accessible, hence add them. Additionally, add type invariants for the size of an allocation. Signed-off-by: Alexandre Courbot Link: https://lore.kernel.org/r/20250619-nova-frts-v6-2-ecf41ef99252@nvidia.com [ Slightly extend the commit message. - Danilo ] Signed-off-by: Danilo Krummrich --- rust/kernel/dma.rs | 32 ++++++++++++++++++++++++++------ 1 file changed, 26 insertions(+), 6 deletions(-) diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs index 038e68c5a293a..34a406a0602e3 100644 --- a/rust/kernel/dma.rs +++ b/rust/kernel/dma.rs @@ -114,9 +114,11 @@ pub mod attrs { /// /// # Invariants /// -/// For the lifetime of an instance of [`CoherentAllocation`], the `cpu_addr` is a valid pointer -/// to an allocated region of coherent memory and `dma_handle` is the DMA address base of -/// the region. +/// - For the lifetime of an instance of [`CoherentAllocation`], the `cpu_addr` is a valid pointer +/// to an allocated region of coherent memory and `dma_handle` is the DMA address base of the +/// region. +/// - The size in bytes of the allocation is equal to `size_of:: * count`. +/// - `size_of:: * count` fits into a `usize`. // TODO // // DMA allocations potentially carry device resources (e.g.IOMMU mappings), hence for soundness @@ -179,9 +181,12 @@ impl CoherentAllocation { if ret.is_null() { return Err(ENOMEM); } - // INVARIANT: We just successfully allocated a coherent region which is accessible for - // `count` elements, hence the cpu address is valid. We also hold a refcounted reference - // to the device. + // INVARIANT: + // - We just successfully allocated a coherent region which is accessible for + // `count` elements, hence the cpu address is valid. We also hold a refcounted reference + // to the device. + // - The allocated `size` is equal to `size_of:: * count`. + // - The allocated `size` fits into a `usize`. Ok(Self { dev: dev.into(), dma_handle, @@ -201,6 +206,21 @@ impl CoherentAllocation { 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 { + // INVARIANT: The type invariant of `Self` guarantees that `size_of:: * count` fits into + // a `usize`. + self.count * core::mem::size_of::() + } + /// 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 -- 2.47.2