pub fn ensure_host_container_parent() -> Option<String>Expand description
Ensure the top-level host container hierarchy exists and has controllers
delegated, returning the container parent path (/zlayer/containers,
relative to the cgroup-v2 mount) for libcontainer’s cgroupsPath.
Only meaningful when the daemon can write the cgroup-v2 root (root host
daemon — DaemonCapabilities::can_write_cgroup_root). Returns None on
non-Linux, or when the mkdir fails (e.g. a read-only /sys/fs/cgroup),
in which case callers fall back to in-scope placement.
Unlike ensure_daemon_leaf_and_container_parent, this does NOT migrate
the daemon PID: with containers rooted outside the unit cgroup, the unit
cgroup stays a clean leaf that systemd can always re-attach to on restart,
so no init leaf split is needed.