[TCP]: Add highest_sack seqno, points to globally highest SACK

It is guaranteed to be valid only when !tp->sacked_out. In most
cases this seqno is available in the last ACK but there is no
guarantee for that. The new fast recovery loss marking algorithm
needs this as entry point.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 9 insertions, 1 deletions

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index c6b9f92e8289..c072f88afb97 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -333,6 +333,8 @@ struct tcp_sock {
 
         struct tcp_sack_block_wire recv_sack_cache[4];
 
+        u32     highest_sack;   /* Start seq of globally highest revd SACK (valid only in slowpath) */
+
         /* from STCP, retrans queue hinting */
         struct sk_buff* lost_skb_hint;
 
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index f893e90061eb..813f2049b85d 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -979,8 +979,10 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
         int i;
         int first_sack_index;
 
-        if (!tp->sacked_out)
+        if (!tp->sacked_out) {
                 tp->fackets_out = 0;
+                tp->highest_sack = tp->snd_una;
+        }
         prior_fackets = tp->fackets_out;
 
         /* Check for D-SACK. */
@@ -1217,6 +1219,10 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
 
                                 if (fack_count > tp->fackets_out)
                                         tp->fackets_out = fack_count;
+
+                                if (after(TCP_SKB_CB(skb)->seq,
+                                    tp->highest_sack))
+                                        tp->highest_sack = TCP_SKB_CB(skb)->seq;
                         } else {
                                 if (dup_sack && (sacked&TCPCB_RETRANS))
                                         reord = min(fack_count, reord);