On 2026-06-29 at 17:17 +1000, Alexandre Courbot <[email protected]> wrote... > On Mon Jun 29, 2026 at 2:10 AM JST, SeungJong Ha via B4 Relay wrote: > > DMA-coherent allocations (CoherentAllocation/Coherent/dma::Pool) bound > > their element type on kernel::transmute::{AsBytes, FromBytes}. This RFC > > lets a type satisfy that bound by deriving zerocopy's byte-safety traits > > instead of a hand-written unsafe impl. > > > > The bound cannot be switched to zerocopy wholesale (some DMA structs are > > unions that IntoBytes cannot derive), and a blanket bridge impl is > > rejected by coherence. So the series bridges the two per type: > > > > 1. add the bridge macro impl_transmute_via_zerocopy!, which emits the > > transmute impls only for a zerocopy-derived type. > > 2. re-export zerocopy::Immutable from the prelude. > > 3-4. worked example: convert nova-core's GspMem and msgq POD types. > > Can you give more details about what the macro is for? My understanding > is that it is a temporary fix for the generated bindings; if so, I'd > prefer to apply a definitive solution (like using > `#[derive(zerocopy_derive::most_traits)]`, or updating the bindings > generator tool) rather than something that will be removed later.
I think the context is in the description for patch 1. It's not directly related to the bindings generator. Basically the problem is that these bindings are a little bit unique in that we access them using the dma_write/read macros. In other words we use these with Dma::Coherent which still requires the transmute rather than zerocopy trait bounds to be implemented. That said I think the correct long-term fix here would be to fix Dma::Coherent to make it work with the zerocopy traits. Not sure if anyone is looking at that or not. - Alistair > I also notice that the macro is in the Rust `transmute` module, but the > only user is Nova; so it should have been either be Nova-local, or used > by other Rust modules. > > But intuitively I'd say that we can (and should) probably do without > this intermediate step. But please let me know if there is something I > missed. >
