[PATCH v4 01/20] rust: dma: expose the count and size of CoherentAllocation

[Alexandre Courbot]

These properties are very useful to have and should be accessible.

Signed-off-by: Alexandre Courbot <acourbot at 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()`.
 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