Add simple excercises to test the scatterlist bindings.

Signed-off-by: Abdiel Janulgue <abdiel.janulgue@gmail.com>
---
 samples/rust/rust_dma.rs | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/samples/rust/rust_dma.rs b/samples/rust/rust_dma.rs
index 874c2c964afa..c4d44e5a45b8 100644
--- a/samples/rust/rust_dma.rs
+++ b/samples/rust/rust_dma.rs
@@ -4,11 +4,15 @@
 //!
 //! To make this driver probe, QEMU must be run with `-device pci-testdev`.
 
-use kernel::{bindings, device::Core, dma::CoherentAllocation, pci, prelude::*, types::ARef};
+use kernel::{
+    bindings, device::Core, dma::CoherentAllocation, page::*, pci, prelude::*, scatterlist::*,
+    types::ARef,
+};
 
 struct DmaSampleDriver {
     pdev: ARef<pci::Device>,
     ca: CoherentAllocation<MyStruct>,
+    sgt: DeviceSGTable<PagesArray>,
 }
 
 const TEST_VALUES: [(u32, u32); 5] = [
@@ -34,6 +38,18 @@ unsafe impl kernel::transmute::AsBytes for MyStruct {}
 // SAFETY: Instances of `MyStruct` have no uninitialized portions.
 unsafe impl kernel::transmute::FromBytes for MyStruct {}
 
+struct PagesArray(KVec<Page>);
+
+impl SGTablePages for PagesArray {
+    fn iter<'a>(&'a self) -> impl Iterator<Item = (&'a Page, usize, usize)> {
+        self.0.iter().map(|page| (page, kernel::page::PAGE_SIZE, 0))
+    }
+
+    fn entries(&self) -> usize {
+        self.0.len()
+    }
+}
+
 kernel::pci_device_table!(
     PCI_TABLE,
     MODULE_PCI_TABLE,
@@ -62,10 +78,20 @@ fn probe(pdev: &pci::Device<Core>, _info: &Self::IdInfo) -> Result<Pin<KBox<Self
             Ok(())
         }()?;
 
+        let mut pages = KVec::new();
+        for _ in TEST_VALUES.into_iter() {
+            let _ = pages.push(Page::alloc_page(GFP_KERNEL)?, GFP_KERNEL);
+        }
+
+        let sgt = SGTable::alloc_table(PagesArray(pages), GFP_KERNEL)?;
+        let sgt = sgt.dma_map(pdev.as_ref(), kernel::dma::DmaDataDirection::DmaToDevice)?;
+
         let drvdata = KBox::new(
             Self {
                 pdev: pdev.into(),
                 ca,
+                // Save object to excercise the destructor.
+                sgt,
             },
             GFP_KERNEL,
         )?;
@@ -77,6 +103,7 @@ fn probe(pdev: &pci::Device<Core>, _info: &Self::IdInfo) -> Result<Pin<KBox<Self
 impl Drop for DmaSampleDriver {
     fn drop(&mut self) {
         dev_info!(self.pdev.as_ref(), "Unload DMA test driver.\n");
+        assert_eq!(self.sgt.iter().count(), TEST_VALUES.len());
 
         let _ = || -> Result {
             for (i, value) in TEST_VALUES.into_iter().enumerate() {
-- 
2.43.0