pub fn capability_overlay_fallback(
has_cap_net_admin: bool,
tun_device_available: bool,
) -> Option<String>Expand description
Decide whether capability state forces a fallback from overlay to host networking. Pure and side-effect-free so it can be unit-tested without the host’s real capability state.
Returns Some(reason) when overlay networking cannot work and the daemon
must fall back to host networking (or hard-error if the operator passed
--require-overlay); returns None when overlay is viable.
Call this ONLY when the operator did not already request host networking —
an explicit --host-network is a deliberate choice, not a degraded state.