+static int tcp_can_collapse(struct sock *sk, struct sk_buff *skb)
+{
+ if (tcp_skb_pcount(skb) > 1)
+ return 0;
+ /* TODO: SACK collapsing could be used to remove this condition */
+ if (skb_shinfo(skb)->nr_frags != 0)
+ return 0;
+ if (skb_cloned(skb))
+ return 0;
+ if (skb == tcp_send_head(sk))
+ return 0;
+ /* Some heurestics for collapsing over SACK'd could be invented */
+ if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
+ return 0;
+
+ return 1;
+}
+
+static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
+ int space)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb = to, *tmp;
+ int first = 1;
+
+ if (!sysctl_tcp_retrans_collapse)
+ return;
+ if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN)
+ return;
+
+ tcp_for_write_queue_from_safe(skb, tmp, sk) {
+ if (!tcp_can_collapse(sk, skb))
+ break;
+
+ space -= skb->len;
+
+ if (first) {
+ first = 0;
+ continue;
+ }
+
+ if (space < 0)
+ break;
+ /* Punt if not enough space exists in the first SKB for
+ * the data in the second
+ */
+ if (skb->len > skb_tailroom(to))
+ break;
+
+ if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
+ break;
+
+ tcp_collapse_retrans(sk, to);
+ }
+}
+