On Tue Jul 7, 2026 at 6:14 PM BST, Daniel Almeida wrote: > Hi Gary, > > A bit late to the party here, but going through this series one by one :) > >> On 6 Jul 2026, at 09:44, Gary Guo <[email protected]> wrote: >> >> Currently many I/O related structs carry a `SIZE` parameter to denote the >> minimum size of the I/O region, while they also carry a field indicating >> the actual size. Proliferation of the pattern creates a lot of duplicated >> code, and makes it hard to create typed views of I/O. >> >> Introduce a `Region` type that carries the `SIZE` parameter. It is a >> wrapper of `[u8]`, which makes it dynamically sized with a metadata of >> `usize`. This way, pointers to `Region` naturally carry size information. >> This type is required to be 4-byte aligned. > > Why 4, specifically? i.e.: I wonder if this breaks u64 mmio accessors?
It does, but if the alignment is 8 then it breaks a lot of platform devices. 4 is the most common alignment needed so it is chosen. Different base types can be added subsequently when needs arise. There's some additional discussions here: https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/Generic.20I.2FO.20backends/with/601411822 and in earlier versions. Best, Gary >> >> Expose the minimum size information via `MIN_SIZE` constant of the >> `KnownSize` trait. Similarly, expose the minimum alignment information via >> `KnownSize::MIN_ALIGN`. >> >> With these changes, it is possible to add an associated type to `Io` trait >> to represent the type of I/O region. For untyped regions, this is the newly >> added `Region` type. Remove `IoKnownSize` as it is no longer necessary. Use >> the same mechanism to indicate minimum size of PCI config spaces. >> >> Reviewed-by: Alexandre Courbot <[email protected]> >> Signed-off-by: Gary Guo <[email protected]> > > If MIN_ALIGN = 4 is actually intentional: > > Reviewed-by: Daniel Almeida <[email protected]>
