[PATCH v4 0/4] rust: DebugFS Bindings

[Matthew Maurer <mmaurer@google.com>]

This series provides safe DebugFS bindings for Rust, with a sample
driver using them.

This series currently only supports referencing `'static` lifetime
objects, because we need to know the objects outlive the DebugFS files.
A subsequent series may be able to relax this.

* Directories created in the root of debugfs are assumed to be owning,
  and will clean up after themselves when dropped.
* Subdirectories are assumed non-owning, remaining alive until their
  containing directory is cleaned up. They can be promoted to owning
  variants if needed.
* Files are non-owning, but can be manually removed by handle if needed.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
Changes in v4:
- Remove SubDir, replace with type-level constant.
- Add lifetime to Dir to prevent subdirectories and files from outliving
  their parents and triggering an Oops when accessed.
- Split unsafe blocks with two calls into two blocks
- Access `private` field through direct pointer dereference, avoiding
  creation of a reference to it.
- Notably not changed - owning/non-owning handle defaults. The best read
  I had from the thread was to continue with this mode, but I'm willing
  to change if need be.
- Comment changes
  - More comment markdown
  - Remove scopes from examples
  - Put `as_ptr` properties into a `# Guarantees` section.
- Link to v3: https://lore.kernel.org/r/20250501-debugfs-rust-v3-0-850869fab672@google.com

Changes in v3:
- Split `Dir` into `Dir`/`SubDir`/`File` to improve API.
- Add "." to end of all comments.
- Convert INVARIANT to # Invariants on types.
- Add backticks everywhere I found variables/types in my comments.
- Promoted invariant comment to doc comment.
- Extended sample commenting to make it clearer what is happening.
- Link to v2: https://lore.kernel.org/r/20250430-debugfs-rust-v2-0-2e8d3985812b@google.com

Changes in v2:
- Drop support for builder / pinned bindings in initial series
- Remove `ARef` usage to abstract the dentry nature of handles
- Remove error handling to discourage users from caring whether DebugFS
  is enabled.
- Support CONFIG_DEBUG_FS=n while leaving the API available
- Fixed mistaken decimal/octal mixup
- Doc/comment cleanup
- Link to v1: https://lore.kernel.org/r/20250429-debugfs-rust-v1-0-6b6e7cb7929f@google.com

---
Matthew Maurer (4):
      rust: debugfs: Bind DebugFS directory creation
      rust: debugfs: Bind file creation for long-lived Display
      rust: debugfs: Support format hooks
      rust: samples: Add debugfs sample

 MAINTAINERS                     |   2 +
 rust/bindings/bindings_helper.h |   1 +
 rust/kernel/debugfs.rs          | 418 ++++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs              |   1 +
 samples/rust/Kconfig            |  11 ++
 samples/rust/Makefile           |   1 +
 samples/rust/rust_debugfs.rs    |  56 ++++++
 7 files changed, 490 insertions(+)
---
base-commit: b6a7783d306baf3150ac54cd5124f6e85dd375b0
change-id: 20250428-debugfs-rust-3cd5c97eb7d1

Best regards,
-- 
Matthew Maurer <mmaurer@google.com>