skb_rb_first
for (skb = skb_rb_first(root); skb != NULL; \
return skb_rb_first(&sk->tcp_rtx_queue);
struct sk_buff *fp, *head = skb_rb_first(&q->rb_fragments);
head = skb_rb_first(&q->rb_fragments);
skb = skb_rb_first(&tp->out_of_order_queue);
for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) {
skb = skb_rb_first(&tp->out_of_order_queue);
struct sk_buff *skb = skb_rb_first(&flow->t_root);
struct sk_buff *skb = skb_rb_first(&q->t_root);