Re: [PATCH 2/2] rust: scatterlist: honor the device's maximum segment size

On Mon Sep 7, 2026 at 11:43 AM JST, Alexandre Courbot wrote:

I guess what this last paragraph wants to state is that no user is
affected by this patch? There is another subtle user though: the Rust
DMA sample.

Yes, that's what I meant. I missed the sample, but it wouldn't make a
difference anyway. So I just removed the paragraph in v2.

nit: if we rename this variable, let's name it `max_mapping_size` for
consistency.

Agreed. Fixed. Let me know if everything is fixed in v2.

It also means that without patch 1, nova-core would split the firmware
into hundreds of 64KB SG entries, which is not breaking but still
something we want to avoid. The correct fix is to make sure that
`dma_set_max_seg_size` is called by the driver, and while we are at it
we also want every driver to call `dma_set_mask_and_coherent`. Ideally
we would use the type system to make sure that both functions are called
before any DMA operation can take place (using a safe interface), but
I'm not quite sure yet how we can do this.

This sounds sensible indeed. Should I open a thread regarding that on Zulip?