[TCP] MIB: Add counters for discarded SACK blocks

In DSACK case, some events are not extraordinary, such as packet
duplication generated DSACK. They can arrive easily below
snd_una when undo_marker is not set (TCP being in CA_Open),
counting such DSACKs amoung SACK discards will likely just
mislead if they occur in some scenario when there are other
problems as well. Similarly, excessively delayed packets could
cause "normal" DSACKs. Therefore, separate counters are
allocated for DSACK events.

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

1 files changed, 9 insertions, 1 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a2364ebf8585..f9e4d7ad68b7 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1240,8 +1240,16 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
                 int fack_count;
                 int dup_sack = (found_dup_sack && (i == first_sack_index));
 
-                if (!tcp_is_sackblock_valid(tp, dup_sack, start_seq, end_seq))
+                if (!tcp_is_sackblock_valid(tp, dup_sack, start_seq, end_seq)) {
+                        if (dup_sack) {
+                                if (!tp->undo_marker)
+                                        NET_INC_STATS_BH(LINUX_MIB_TCPDSACKIGNOREDNOUNDO);
+                                else
+                                        NET_INC_STATS_BH(LINUX_MIB_TCPDSACKIGNOREDOLD);
+                        } else
+                                NET_INC_STATS_BH(LINUX_MIB_TCPSACKDISCARD);
                         continue;
+                }
 
                 skb = cached_skb;
                 fack_count = cached_fack_count;