type Opt struct {
	PipeFDEnvKey  string              // needs to be set
	TargetCmd     []string            // needs to be set
	NetworkDriver network.ChildDriver // nil for HostNetwork
	CopyUpDriver  copyup.ChildDriver  // cannot be nil if len(CopyUpDirs) != 0
	CopyUpDirs    []string
	PortDriver    port.ChildDriver
	MountProcfs   bool   // needs to be set if (and only if) parent.Opt.CreatePIDNS is set
	Propagation   string // mount propagation type
	Reaper        bool
}