ipmi_kcs: extract no_std core and add C ABI staticlib for shared us

[Manish Ranjan Mahanta (marma-dev)]

Summary

Refactors the IPMI KCS BMC device into a portable no_std core and wraps it in a C-ABI static library so the exact same emulator can be linked into the C++ Legacy HCL stack — eliminating a parallel C++ reimplementation of the KCS state machine and SEL handling.

This is PR 3 of 4 in the IPMI KCS stack (stacked on ipmi_kcs-sel):

• PR1 — the core ipmi_kcs device + resource handle.
• PR2 — host the device in OpenHCL/underhill with SEL forwarding.
• PR3 (this) — extract the no_std core + C-ABI staticlib for cross-language reuse.
• PR4 — package/publish the staticlib via the flowey pipeline.

What's included

New no_std core — vm/devices/ipmi_kcs_core/

The protocol/SEL/KCS logic is moved out of ipmi_kcs into a dependency-light, no_std + alloc crate:

• lib.rs — KcsDevice state machine (io_read/io_write/reset), KcsError, port range constants.
• protocol.rs — moved verbatim from ipmi_kcs.
• sel.rs — SEL record assembly (now no_std).
• sink.rs — SelSink / NullSelSink / BmcClock / SelDeps traits.
• Optional features: inspect (gated derive(Inspect)) and trace (gated tracelimit), both no-ops when off so the core stays portable.

New C-ABI library — vm/devices/ipmi_kcs_ffi/

A staticlib + rlib crate exposing a flat C interface over the core:

• src/lib.rs — ipmi_kcs_new / _free / _io_read / _io_write / _reset / _data_port / _status_port. SEL egress and the clock are supplied by the C++ caller via SelCallback / ClockCallback function pointers; CSelSink / CClock wrap the opaque context pointer.
• ipmi_kcs.h — hand-authored C header for the C++ consumer.
• Registered as a workspace leaf member (same model as the existing vmgs_lib staticlib).

ipmi_kcs device crate

Now a thin OpenVMM integration layer that re-exports the core and keeps only the OpenVMM-specific glue (ChipsetDevice, PortIoIntercept, save/restore, resolver). lib.rs shrinks ~600 lines; sink.rs is removed (moved to core).

Design notes

• Single source of truth — the KCS/IPMI/SEL behavior now lives in one Rust crate consumed by OpenVMM, OpenHCL, and C++ HCL. No divergence between hosts.
• C++ owns I/O policy — egress and time are injected across the FFI boundary via function pointers, mirroring the trait-injection pattern used in-tree (SelSink / BmcClock).
• Small footprint — the FFI surface measures ~4.7 KB of code (.text 4576 B + .rdata 128 B + .pdata 144 B); the CRT is already present in the host C++ binary.

Testing

• cargo test across the stack — 27 tests pass (core 22 + ipmi_kcs integration 3 + ffi 2).
• Builds clean for x86_64-unknown-linux-musl and x86_64-pc-windows-msvc.
• Fork validation pipeline produces the ipmi_kcs_ffi-x86_64-pc-windows-msvc staticlib artifact; dumpbin confirms the 7 exported C symbols.
• The artifact links cleanly into the Legacy HCL (hcl/fw) build with no unresolved symbols.

Risk

Low — pure refactor plus additive crates. The ipmi_kcs device's externally observable behavior is unchanged (verified by the moved-over tests); no existing configuration consumes the new FFI crate.

[github-actions]

⚠️ Unsafe Code Detected

This PR modifies files containing unsafe Rust code. Extra scrutiny is required during review.

For more on why we check whole files, instead of just diffs, check out the Rustonomicon

[Copilot]

Pull request overview

Refactors the IPMI KCS BMC device into a reusable no_std + alloc core crate and adds a C-ABI staticlib wrapper so the same KCS/SEL implementation can be linked from non-Rust hosts (e.g., Legacy HCL C++), while keeping ipmi_kcs as a thin OpenVMM integration layer.

Changes:

• Added ipmi_kcs_core (no_std + alloc) containing the KCS state machine, IPMI protocol types, and SEL handling with injectable sink/clock traits.
• Added ipmi_kcs_ffi staticlib exposing a flat C ABI plus a hand-authored ipmi_kcs.h header.
• Updated OpenVMM integration (ipmi_kcs, resources/resolver registration, workspace wiring) to consume the shared core.

Reviewed changes

Copilot reviewed 16 out of 17 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
vm/devices/ipmi_kcs/src/resolver.rs	Adds a chipset resource resolver for the OpenVMM IPMI KCS device.
vm/devices/ipmi_kcs/src/lib.rs	Implements the thin ChipsetDevice/PIO wrapper over ipmi_kcs_core + basic integration tests.
vm/devices/ipmi_kcs/Cargo.toml	New crate manifest wiring ipmi_kcs to ipmi_kcs_core (inspect/trace enabled).
vm/devices/ipmi_kcs_resources/src/lib.rs	Defines the resource handle (IpmiKcsHandle) for VM resource plumbing.
vm/devices/ipmi_kcs_resources/Cargo.toml	New crate manifest for the resource handle crate.
vm/devices/ipmi_kcs_ffi/src/lib.rs	Implements the C ABI wrapper over KcsDevice and includes ABI-driven unit tests.
vm/devices/ipmi_kcs_ffi/ipmi_kcs.h	Provides the C header for consuming the staticlib from C/C++.
vm/devices/ipmi_kcs_ffi/Cargo.toml	Declares staticlib + rlib crate types and depends on the core.
vm/devices/ipmi_kcs_core/src/sink.rs	Adds portable sink/clock traits (SelSink, BmcClock) and dependency bundle (SelDeps).
vm/devices/ipmi_kcs_core/src/sel.rs	Implements SEL storage + SEL IPMI command handling and tests.
vm/devices/ipmi_kcs_core/src/protocol.rs	Defines KCS/IPMI protocol constants and open enums + tests.
vm/devices/ipmi_kcs_core/src/lib.rs	Implements the core KCS state machine and integrates SEL + tests.
vm/devices/ipmi_kcs_core/Cargo.toml	New core crate manifest with inspect/trace features.
openvmm/openvmm_resources/src/lib.rs	Registers the IPMI KCS resolver under cfg(guest_arch = "x86_64").
openvmm/openvmm_resources/Cargo.toml	Adds ipmi_kcs dependency for openvmm_resources (currently host-arch gated).
Cargo.toml	Adds new workspace members and workspace dependency paths for the new crates.
Cargo.lock	Records the newly added workspace packages and dependency edges.

[Ben Hillis (benhillis)]

Manish Ranjan Mahanta (@marma-dev), active PR #4396 appears to replace this no_std/C-ABI direction, which also has unresolved input-safety issues. Could you close it, or revive only the distinct remaining work? Thanks.