1 files changed, 44 insertions, 0 deletions
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 4a8ec457310f..8cdee120a50c 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1950,6 +1950,50 @@ void tcp_v4_early_demux(struct sk_buff *skb)
 	}
 }
 
+/* Packet is added to VJ-style prequeue for processing in process
+ * context, if a reader task is waiting. Apparently, this exciting
+ * idea (VJ's mail "Re: query about TCP header on tcp-ip" of 07 Sep 93)
+ * failed somewhere. Latency? Burstiness? Well, at least now we will
+ * see, why it failed. 8)8)				  --ANK
+ *
+ */
+bool tcp_prequeue(struct sock *sk, struct sk_buff *skb)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	if (sysctl_tcp_low_latency || !tp->ucopy.task)
+		return false;
+
+	if (skb->len <= tcp_hdrlen(skb) &&
+	    skb_queue_len(&tp->ucopy.prequeue) == 0)
+		return false;
+
+	__skb_queue_tail(&tp->ucopy.prequeue, skb);
+	tp->ucopy.memory += skb->truesize;
+	if (tp->ucopy.memory > sk->sk_rcvbuf) {
+		struct sk_buff *skb1;
+
+		BUG_ON(sock_owned_by_user(sk));
+
+		while ((skb1 = __skb_dequeue(&tp->ucopy.prequeue)) != NULL) {
+			sk_backlog_rcv(sk, skb1);
+			NET_INC_STATS_BH(sock_net(sk),
+					 LINUX_MIB_TCPPREQUEUEDROPPED);
+		}
+
+		tp->ucopy.memory = 0;
+	} else if (skb_queue_len(&tp->ucopy.prequeue) == 1) {
+		wake_up_interruptible_sync_poll(sk_sleep(sk),
+					   POLLIN | POLLRDNORM | POLLRDBAND);
+		if (!inet_csk_ack_scheduled(sk))
+			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
+						  (3 * tcp_rto_min(sk)) / 4,
+						  TCP_RTO_MAX);
+	}
+	return true;
+}
+EXPORT_SYMBOL(tcp_prequeue);
+
 /*
  *	From tcp_input.c
  */