[RFC PATCH 0/2] rust block-mq TagSet flags plumbing and rnull blocking wiring

[Wenzhao Liao]

This RFC series fills a practical gap in the Rust block-mq abstraction by
exposing blk_mq_tag_set.flags safely, then wires one in-tree consumer
(`rnull`) via configfs as a reference.

Patch 1 introduces `TagSetFlags` and `TagSet::new_with_flags(...)` while
keeping `TagSet::new(...)` for compatibility.

Patch 2 adds a `blocking` configfs attribute to `rnull` and maps it to
`TagSetFlags::BLOCKING` when powering on a device.

Validation summary:
- Out-of-tree build on rust-next (LLVM=-15): defconfig, rustavailable.
- Enabled CONFIG_RUST=y, CONFIG_CONFIGFS_FS=y, CONFIG_BLK_DEV_RUST_NULL=m.
- Built vmlinux and drivers/block/rnull/rnull_mod.ko successfully.
- QEMU runtime test (initramfs automation) verifies:
  - `/sys/kernel/config/rnull/features` contains `blocking`;
  - writing `blocking` while powered on fails with busy semantics;
  - writing `blocking` after power off succeeds again.

Comments on API naming and any preferred follow-up scope are welcome.

Wenzhao Liao (2):
  rust: block: mq: safely expose TagSet flags
  block: rnull: support BLK_MQ_F_BLOCKING via configfs

 drivers/block/rnull/configfs.rs | 32 +++++++++++-
 drivers/block/rnull/rnull.rs    | 11 ++++-
 rust/kernel/block/mq.rs         |  2 +-
 rust/kernel/block/mq/tag_set.rs | 86 ++++++++++++++++++++++++++++++++-
 4 files changed, 126 insertions(+), 5 deletions(-)


base-commit: 3418d862679ac6da0b6bd681b18b3189c4fad20d
-- 
2.34.1