rust: io: add dynamically-sized `Region` type

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>

0 files changed, 0 insertions, 0 deletions