tcp: Remove redundant checks when setting eff_sacks

Remove redundant checks when setting eff_sacks and make the number of SACKs a
compile time constant. Now that the options code knows how many SACK blocks can
fit in the header, we don't need to have the SACK code guessing at it.

Signed-off-by: Adam Langley <agl@imperialviolet.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 16 insertions, 15 deletions

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 07e79bdb9cdf..2e2557388e36 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -224,6 +224,12 @@ struct tcp_options_received {
         u16     mss_clamp;      /* Maximal mss, negotiated at connection setup */
 };
 
+/* This is the max number of SACKS that we'll generate and process. It's safe
+ * to increse this, although since:
+ *   size = TCPOLEN_SACK_BASE_ALIGNED (4) + n * TCPOLEN_SACK_PERBLOCK (8)
+ * only four options will fit in a standard TCP header */
+#define TCP_NUM_SACKS 4
+
 struct tcp_request_sock {
         struct inet_request_sock        req;
 #ifdef CONFIG_TCP_MD5SIG
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 88810bc01370..1f5e6049883e 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1423,10 +1423,10 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb,
         unsigned char *ptr = (skb_transport_header(ack_skb) +
                               TCP_SKB_CB(ack_skb)->sacked);
         struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
-        struct tcp_sack_block sp[4];
+        struct tcp_sack_block sp[TCP_NUM_SACKS];
         struct tcp_sack_block *cache;
         struct sk_buff *skb;
-        int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE) >> 3;
+        int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
         int used_sacks;
         int reord = tp->packets_out;
         int flag = 0;
@@ -3735,8 +3735,7 @@ static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
                 tp->rx_opt.dsack = 1;
                 tp->duplicate_sack[0].start_seq = seq;
                 tp->duplicate_sack[0].end_seq = end_seq;
-                tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1,
-                                           4 - tp->rx_opt.tstamp_ok);
+                tp->rx_opt.eff_sacks = tp->rx_opt.num_sacks + 1;
         }
 }
 
@@ -3791,9 +3790,8 @@ static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
                          * Decrease num_sacks.
                          */
                         tp->rx_opt.num_sacks--;
-                        tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks +
-                                                   tp->rx_opt.dsack,
-                                                   4 - tp->rx_opt.tstamp_ok);
+                        tp->rx_opt.eff_sacks = tp->rx_opt.num_sacks +
+                                               tp->rx_opt.dsack;
                         for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
                                 sp[i] = sp[i + 1];
                         continue;
@@ -3843,7 +3841,7 @@ static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
          *
          * If the sack array is full, forget about the last one.
          */
-        if (this_sack >= 4) {
+        if (this_sack >= TCP_NUM_SACKS) {
                 this_sack--;
                 tp->rx_opt.num_sacks--;
                 sp--;
@@ -3856,8 +3854,7 @@ new_sack:
         sp->start_seq = seq;
         sp->end_seq = end_seq;
         tp->rx_opt.num_sacks++;
-        tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack,
-                                   4 - tp->rx_opt.tstamp_ok);
+        tp->rx_opt.eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
 }
 
 /* RCV.NXT advances, some SACKs should be eaten. */
@@ -3894,9 +3891,8 @@ static void tcp_sack_remove(struct tcp_sock *tp)
         }
         if (num_sacks != tp->rx_opt.num_sacks) {
                 tp->rx_opt.num_sacks = num_sacks;
-                tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks +
-                                           tp->rx_opt.dsack,
-                                           4 - tp->rx_opt.tstamp_ok);
+                tp->rx_opt.eff_sacks = tp->rx_opt.num_sacks +
+                                       tp->rx_opt.dsack;
         }
 }
 
@@ -3975,8 +3971,7 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
 
         if (tp->rx_opt.dsack) {
                 tp->rx_opt.dsack = 0;
-                tp->rx_opt.eff_sacks = min_t(unsigned int, tp->rx_opt.num_sacks,
-                                             4 - tp->rx_opt.tstamp_ok);
+                tp->rx_opt.eff_sacks = tp->rx_opt.num_sacks;
         }
 
         /*  Queue data for delivery to the user.