The Rust bindings for XArray include a build-time check to ensure that
you can only use the XArray with pointers that are 4-byte aligned.
Because of that, there is currently a build failure if you attempt to
create an XArray<KBox<T>> where T is a 1-byte or 2-byte aligned type.
However, this error is incorrect as KBox<_> is guaranteed to be a
pointer that comes from kmalloc, and kmalloc always produces pointers
that are at least 4-byte aligned.

To fix this, we augment the compile-time logic that computes the
alignment of KBox<_> to take the minimum alignment of its allocator into
account.

Intended to land through alloc-next under the RUST [ALLOC] entry.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
Changes in v2:
- Reword guarantee on `const MIN_ALIGN`.
- Change formatting of if/else in kbox.rs.
- Rebase on v6.17-rc1.
- Link to v1: https://lore.kernel.org/r/20250715-align-min-allocator-v1-0-3e1b2a5516c0@google.com (local)

---
Alice Ryhl (2):
      rust: alloc: specify the minimum alignment of each allocator
      rust: alloc: take the allocator into account for FOREIGN_ALIGN

 rust/kernel/alloc.rs           |  8 ++++++++
 rust/kernel/alloc/allocator.rs |  8 ++++++++
 rust/kernel/alloc/kbox.rs      | 13 +++++++++----
 rust/kernel/sync/arc.rs        |  6 +++---
 4 files changed, 28 insertions(+), 7 deletions(-)
---
base-commit: 062b3e4a1f880f104a8d4b90b767788786aa7b78
change-id: 20250715-align-min-allocator-b31aee53cbda

Best regards,
-- 
Alice Ryhl [off-list ref]