NGF_INVALID
#define NG_INVALID NGF_INVALID /* compat for old code */
#define _NG_NODE_IS_VALID(node) (!((node)->nd_flags & NGF_INVALID))
#define _NG_NODE_NOT_VALID(node) ((node)->nd_flags & NGF_INVALID)
do{ node->nd_flags |= (NGF_REALLY_DIE|NGF_INVALID); }while (0)
do { node->nd_flags &= ~NGF_INVALID; } while (0)
NGF_INVALID,
node->nd_flags |= NGF_INVALID;
node->nd_flags |= NGF_INVALID|NGF_CLOSING;
node->nd_flags &= ~(NGF_INVALID|NGF_CLOSING);