runsc: add a sandbox-only boot mode - #13986
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Add `runsc create/boot --sandbox-only`, which boots a sandbox from a spec describing only the sandbox: no Process and no Root. The kernel comes up empty and containers are added afterwards as subcontainers. This exists for the containerd Sandbox API, which lands separately. Under CRI with `sandboxer = "shim"` there is no pause container to stand in for the pod: containerd leaves Sandbox.Spec unset, so the sandbox bundle has no config.json, and there is neither a rootfs nor a process to run. runsc has so far required both. Limitations: - Checkpoint/restore is refused for a sandbox-only sandbox. The kernel state round-trips, but `runsc restore` cannot be told the spec describes a sandbox, so it either rejects it or dereferences the absent Process, and the loader would restore the sandbox as if it had a gofer. Lifting it is a --sandbox-only flag, a nil guard, and skipping the sandbox in the restorer's per-container loop; deferred rather than shipped untested. FUTURE_COPYBARA_INTEGRATE_REVIEW=#13981 from milantracy:sandbox-only 2defed0 PiperOrigin-RevId: 959101413
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August 4, 2026 18:05
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runsc: add a sandbox-only boot mode
Add
runsc create/boot --sandbox-only, which boots a sandbox from a spec describing only the sandbox: no Process and no Root. The kernel comes up empty and containers are added afterwards as subcontainers.This exists for the containerd Sandbox API, which lands separately. Under CRI with
sandboxer = "shim"there is no pause container to stand in for the pod: containerd leaves Sandbox.Spec unset, so the sandbox bundle has no config.json, and there is neither a rootfs nor a process to run. runsc has so far required both.Limitations:
runsc restorecannot be told the spec describes a sandbox, so it either rejects it or dereferences the absent Process, and the loader would restore the sandbox as if it had a gofer. Lifting it is a --sandbox-only flag, a nil guard, and skipping the sandbox in the restorer's per-container loop; deferred rather than shipped untested.FUTURE_COPYBARA_INTEGRATE_REVIEW=#13981 from milantracy:sandbox-only 2defed0