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
  */