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If you want the same type that s= upports >> both a fixed size and dynamic size, then a generic that is either array/= slice is >> the way to go. > > [...] > >> You still can use `io_project!(handle, [start..end]?)` to do the bounds >> checking. But as you said, the benefit might be minimal. > > I think we shouldn't overengineer this for now, and wait for actual use-c= ases > that require any of that. > > The only thing we need right now in practice is an API that takes the siz= e and > returns a handle to the buffer of this size exposing the DMA address that= is > subsequently passed to the device without further modification. > > So, if we want to re-use dma::Coherent, we can just do this > > pub struct CoherentHandle(Coherent<[u8]>); > =09 > impl CoherentHandle { > pub fn alloc_with_attrs( > dev: &device::Device, > size: usize, > gfp_flags: kernel::alloc::Flags, > dma_attrs: Attrs, > ) -> Result { > let dma_attrs =3D dma_attrs | Attrs(bindings::DMA_ATTR_NO_KERNEL= _MAPPING); > Coherent::::alloc_slice_with_attrs(dev, size, gfp_flags, dma= _attrs).map(Self) > } > =09 > #[inline] > pub fn alloc( > dev: &device::Device, > size: usize, > gfp_flags: kernel::alloc::Flags, > ) -> Result { > Self::alloc_with_attrs(dev, size, gfp_flags, Attrs(0)) > } > =09 > #[inline] > pub fn dma_handle(&self) -> DmaAddress { > self.0.dma_handle() > } > =09 > #[inline] > pub fn size(&self) -> usize { > self.0.size() > } > } > > and add a guarantee that Coherent::alloc_with_attrs() and Coherent::drop(= ) never > touch the cpu_ptr. Hmm, it sounds like we *could* actually have `Coherent` support `Drop` type= s and have `drop()` run the destructor for it. We don't need to for `FromBytes + AsBytes`, but I think we'd better not have that as a guarantee. So the original approach that you have is better. Best, Gary