[PATCH 3/3] Check num sacks in SACK fast path

[Baruch Even <baruch@ev-en.org>]

When we check for SACK fast path make sure that we also have the same number of
SACK blocks in the cache and in the new SACK data. This prevents us from
mistakenly taking the cache data if the old data in the SACK cache is the same
as the data in the SACK block.

Signed-Off-By: Baruch Even <baruch@ev-en.org>

Index: 2.6-rc6/include/linux/tcp.h
===================================================================
--- 2.6-rc6.orig/include/linux/tcp.h	2007-01-27 15:06:02.000000000 +0200
+++ 2.6-rc6/include/linux/tcp.h	2007-01-27 15:19:04.000000000 +0200
@@ -317,6 +317,7 @@
 	struct tcp_sack_block selective_acks[4]; /* The SACKS themselves*/
 
 	struct tcp_sack_block recv_sack_cache[4];
+	u32     recv_sack_cache_size;
 
 	/* from STCP, retrans queue hinting */
 	struct sk_buff* lost_skb_hint;
Index: 2.6-rc6/net/ipv4/tcp_input.c
===================================================================
--- 2.6-rc6.orig/net/ipv4/tcp_input.c	2007-01-27 15:18:30.000000000 +0200
+++ 2.6-rc6/net/ipv4/tcp_input.c	2007-01-27 15:30:09.000000000 +0200
@@ -979,7 +979,8 @@
 	 * if the only SACK change is the increase of the end_seq of
 	 * the first block then only apply that SACK block
 	 * and use retrans queue hinting otherwise slowpath */
-	flag = 1;
+	flag = num_sacks == tp->recv_sack_cache_size;
+	tp->recv_sack_cache_size = num_sacks;
 	for (i = 0; i < num_sacks; i++) {
 		__u32 start_seq = sp[i].start_seq;
 		__u32 end_seq = sp[i].end_seq;