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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. 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 <acourbot@nvidia.com> Signed-off-by: Gary Guo <gary@garyguo.net> Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com> Link: https://patch.msgid.link/20260706-io_projection-v6-1-72cd5d055d54@garyguo.net [ Add brief explanation on MIN_ALIGN. - Danilo ] Signed-off-by: Danilo Krummrich <dakr@kernel.org>