On Sat, Mar 15, 2025 at 12:52:27PM -0400, Tamir Duberstein wrote: > On Thu, Dec 19, 2024 at 12:08 PM Danilo Krummrich <[email protected]> wrote: > > > > +/// Marker trait to indicate a Rust device ID type represents a > > corresponding C device ID type. > > +/// > > +/// This is meant to be implemented by buses/subsystems so that they can > > use [`IdTable`] to > > +/// guarantee (at compile-time) zero-termination of device id tables > > provided by drivers. > > +/// > > +/// # Safety > > +/// > > +/// Implementers must ensure that: > > +/// - `Self` is layout-compatible with [`RawDeviceId::RawType`]; i.e. > > it's safe to transmute to > > +/// `RawDeviceId`. > > +/// > > +/// This requirement is needed so `IdArray::new` can convert `Self` to > > `RawType` when building > > +/// the ID table. > > +/// > > +/// Ideally, this should be achieved using a const function that does > > conversion instead of > > +/// transmute; however, const trait functions relies on > > `const_trait_impl` unstable feature, > > +/// which is broken/gone in Rust 1.73. > > +/// > > +/// - `DRIVER_DATA_OFFSET` is the offset of context/data field of the > > device ID (usually named > > +/// `driver_data`) of the device ID, the field is suitable sized to > > write a `usize` value. > > +/// > > +/// Similar to the previous requirement, the data should ideally be > > added during `Self` to > > +/// `RawType` conversion, but there's currently no way to do it when > > using traits in const. > > +pub unsafe trait RawDeviceId { > > + /// The raw type that holds the device id. > > + /// > > + /// Id tables created from [`Self`] are going to hold this type in its > > zero-terminated array. > > + type RawType: Copy; > > + > > + /// The offset to the context/data field. > > + const DRIVER_DATA_OFFSET: usize; > > + > > + /// The index stored at `DRIVER_DATA_OFFSET` of the implementor of the > > [`RawDeviceId`] trait. > > + fn index(&self) -> usize; > > +} > > Very late to the game here, but have a question about the use of > OFFSET here. Why is this preferred to a method that returns a pointer > to the field?
We need it from const context, trait methods can't be const (yet).
