Re: [PATCH v3 2/2] samples: rust: add sample code for scatterlist abstraction

[Andreas Hindborg <a.hindborg@kernel.org>]

"Abdiel Janulgue" <abdiel.janulgue@gmail.com> writes:

> Add simple excercises to test the scatterlist abstraction.
>
> Co-developed-by: Alexandre Courbot <acourbot@nvidia.com>
> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
> Signed-off-by: Abdiel Janulgue <abdiel.janulgue@gmail.com>
> ---
>  samples/rust/rust_dma.rs | 49 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 48 insertions(+), 1 deletion(-)
>
> diff --git a/samples/rust/rust_dma.rs b/samples/rust/rust_dma.rs
> index 9e05d5c0cdae..1fa278e8e29a 100644
> --- a/samples/rust/rust_dma.rs
> +++ b/samples/rust/rust_dma.rs
> @@ -4,11 +4,33 @@
>  //!
>  //! 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::*,
> +    sync::Arc, types::ARef,
> +};
>
>  struct DmaSampleDriver {
>      pdev: ARef<pci::Device>,
>      ca: CoherentAllocation<MyStruct>,
> +    _sgt: SGTable<OwnedSgt<PagesArray>, ManagedMapping>,
> +}
> +
> +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()
> +    }
> +}
> +
> +struct WrappedArc(Arc<kernel::bindings::sg_table>);
> +impl core::borrow::Borrow<kernel::bindings::sg_table> for WrappedArc {
> +    fn borrow(&self) -> &kernel::bindings::sg_table {
> +        &self.0
> +    }
>  }
>
>  const TEST_VALUES: [(u32, u32); 5] = [
> @@ -58,10 +80,35 @@ fn probe(pdev: &pci::Device<Core>, _info: &Self::IdInfo) -> Result<Pin<KBox<Self
>              kernel::dma_write!(ca[i] = MyStruct::new(value.0, value.1))?;
>          }
>
> +        let mut pages = KVec::new();
> +        for _ in TEST_VALUES.into_iter() {
> +            let _ = pages.push(Page::alloc_page(GFP_KERNEL)?, GFP_KERNEL);
> +        }
> +
> +        // Let's pretend this is valid...
> +        // SAFETY: `sg_table` is not a reference.
> +        let sg_table: bindings::sg_table = unsafe { core::mem::zeroed() };

I think this initialization can be safe with recent pin-init patches
[0]. Perhaps rebase on that, or add a todo?

Best regards,
Andreas Hindborg

[0] https://lore.kernel.org/r/20250523145125.523275-1-lossin@kernel.org