feat(kernel): kernel.cmdline and kernel.cmdline_extra in project config

[mobileoverlord]

What

Adds kernel.cmdline and kernel.cmdline_extra to project config, so the kernel command line is something a project sets rather than something baked into a BSP layer.

kernel:
  version: "6.18.37-rt*"
  cmdline_extra: "isolcpus=4-6 nohz_full=4-6"   # append
  # cmdline: "root=... console=..."             # replace outright

Both are resolved per-runtime with a global fallback and exported to the build and provision hooks as AVOCADO_KERNEL_CMDLINE / AVOCADO_KERNEL_CMDLINE_EXTRA.

Why

The command line was reachable only through the machine configuration (CONSOLE_CMDLINE, KERNEL_CMDLINE_EXTRA). Anything a project needs on it — isolcpus for a latency test, earlycon while bringing a board up — meant editing a BSP layer and rebuilding a feed. That is the wrong seam: those values are properties of the project, not of the machine, and two projects on the same target legitimately want different ones.

This came out of the rubikpi3 RT/KVM work, where tuning the command line per experiment otherwise required a full Yocto rebuild per iteration.

How

cmdline replaces, cmdline_extra appends. Append is the one to reach for; replace drops root= and console= unless restated, which on most boards means a device that flashes and boots to a dead console. They are rejected together at validate time rather than letting one silently win.

The platform hook is where these take effect — meta-avocado-qcom's avocado-build-rubikpi3 reads them when it rebuilds the UKI around the pinned kernel.

Results

• 3804 tests pass, including 5 new ones covering the resolver and the mutual exclusion
• clippy clean, cargo fmt clean
• exercised on hardware: cmdline_extra: "earlycon" reached the booted kernel's /proc/cmdline on a rubikpi3 via the UKI rebuild path

Note

Without this, references/rubikpi3-rt-kvm-ivshmem does not load — it sets cmdline_extra, and a CLI lacking the field reads it as an entry name in the kernel named-map form and refuses the file:

kernel: cannot mix singleton form (with config field keys like `package`,
`version`, `compile`, `install`, `image`) and named-map form

[Copilot]

🟢 Approval recommended

The functional changes are small, tested, and localized; the remaining feedback is a documentation correction.

Pull request overview

This PR makes kernel command-line configuration a first-class project setting by adding kernel.cmdline (replace) and kernel.cmdline_extra (append) to the YAML config, resolving them per-runtime with a top-level fallback, and exporting the resolved values to build/provision hooks via environment variables.

Changes:

• Extend KernelConfig with cmdline / cmdline_extra, including mutual-exclusion validation and singleton-vs-named-map deserialization support.
• Add Config::effective_kernel_cmdline() to resolve (replace, append) with runtime-over-top-level precedence.
• Export AVOCADO_KERNEL_CMDLINE / AVOCADO_KERNEL_CMDLINE_EXTRA to both runtime build and provision hook environments.

File summaries

File	Description
src/utils/config.rs	Adds config fields + validation, implements per-runtime cmdline resolver, and includes tests.
src/commands/runtime/build.rs	Exports resolved kernel cmdline vars for platform build hooks (e.g., UKI bake-in).
src/commands/runtime/provision.rs	Exports resolved kernel cmdline vars for provision-time image assembly hooks.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Lite

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