[PATCH v3 0/2] rust: impl_flags: add convenience functions

[Andreas Hindborg <a.hindborg@kernel.org>]

Add a few convenience functions that makes it easier to work with the
`impl_flags` module and C APIs.

These conversion functions are useful when assigning flags to C structs in
Rust abstractions:

  let mut lim = bindings::queue_limits::zeroed();

  if self.rotational {
      lim.features = Feature::Rotational.into();
  }

  if self.write_cache {
      lim.features |= Feature::WriteCache;
  }

Or when providing flags from C to Rust:

  impl<T: Operations> RequestInner<T> {
      pub fn flags(&self) -> Flags {
          // SAFETY: By C API contract and type invariant, `cmd_flags` is valid for read
          let flags = unsafe { (*self.0.get()).cmd_flags & !((1 << bindings::REQ_OP_BITS) - 1) };
          Flags::try_from(flags).expect("Request should have valid flags")
      }
  }

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
Changes in v3:
- Use `Self` instead of `$flags` in the `TryFrom` implementation (Miguel).
- Drop the hand-written `TryFrom<u32> for VmMapFlags` in
`drivers/gpu/drm/tyr`, which is equivalent to, and now conflicts with, the
implementation generated by the macro. Without this, tyr fails to build
with E0119.
- Expand the commit message of patch 2 with a before-and-after
  comparison of the `gen_disk` call site, the alternatives considered
  (`as` cast, explicit `From`, container temporary), and the trade-off
  of offering operators on the underlying type (Miguel, Gary).
- Use `pin_init::zeroed()` instead of `core::mem::zeroed()` in the
  patch 2 commit message example (Miguel).
- Rebase on v7.4-rc1 and on v3 of the `bits()` prerequisite patch.
- Link to v2: https://msgid.link/20260605-impl-flags-additions-v2-0-0d27242f460b@kernel.org

Changes in v2:
- Use an `as` cast instead of `core::mem::transmute` in
  `From<$flag> for $ty` (Miguel).
- Replace the `match` in `TryFrom::try_from` with an early-return
  `if` (Miguel)
- Construct the result directly instead of via `transmute` in `try_from`
  (Miguel).
- Use `Self` in the new conversion impls (Miguel).
- Mark `TryFrom::try_from` `#[inline]`.
- Extend the rustdoc example to demonstrate both new conversion
  impls (Miguel).
- Link to v1: https://msgid.link/20260215-impl-flags-additions-v1-0-6538c8fb841c@kernel.org

---
Andreas Hindborg (2):
      rust: impl_flags: add conversion functions
      rust: impl_flags: add bitwise operations with the underlying type

 drivers/gpu/drm/tyr/vm.rs | 13 -------------
 rust/kernel/impl_flags.rs | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+), 13 deletions(-)
---
base-commit: bc71431221f5ba8bb33918399552636e059c2c45
change-id: 20260215-impl-flags-additions-0340ffcba5b9
prerequisite-change-id: 20260212-impl-flags-inner-c61974b27b18:v3
prerequisite-patch-id: 4f477e1886497d4ba3898867e2765c7324b62ba4

Best regards,
--  
Andreas Hindborg <a.hindborg@kernel.org>