Sometimes one may want to obtain a DMA handle starting at a given
offset. This can be done by adding said offset to the result of
`dma_handle()`, but doing so on the client side carries the risk that
the operation will go outside the bounds of the allocation.
Thus, add a `dma_handle_with_offset` method that adds the desired offset
after checking that it is still valid.
Signed-off-by: Alexandre Courbot <acour...@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
15ff639b3067d0e4a39e181bbe709a9c372a591a..04546e58252d308e7a9f17bd2eae0aebfdc3c271
100644
--- a/rust/kernel/dma.rs
+++ b/rust/kernel/dma.rs
@@ -238,6 +238,20 @@ pub fn dma_handle(&self) -> bindings::dma_addr_t {
self.dma_handle
}
+ /// Returns a DMA handle starting at `offset` (in units of `T`) which may
be given to the
+ /// device as the DMA address base of the region.
+ ///
+ /// Returns `EINVAL` if `offset` is not within the bounds of the
allocation.
+ pub fn dma_handle_with_offset(&self, offset: usize) ->
Result<bindings::dma_addr_t> {
+ if offset >= self.count {
+ Err(EINVAL)
+ } else {
+ // INVARIANT: The type invariant of `Self` guarantees that
`size_of::<T> * count` fits
+ // into a `usize`, and `offset` is inferior to `count`.
+ Ok(self.dma_handle + (offset * core::mem::size_of::<T>()) as
bindings::dma_addr_t)
+ }
+ }
+
/// Returns a pointer to an element from the region with bounds checking.
`offset` is in
/// units of `T`, not the number of bytes.
///
--
2.49.0
