XFRM_TRANS_SKB_CB
struct net *net = XFRM_TRANS_SKB_CB(skb)->net;
XFRM_TRANS_SKB_CB(skb)->finish(net, NULL, skb);
XFRM_TRANS_SKB_CB(skb)->finish = finish;
XFRM_TRANS_SKB_CB(skb)->net = hold_net;