[TCP]: Extract tcp_match_queue_to_sack from sacktag code

This is necessary for upcoming DSACK bugfix. Reduces sacktag
length which is not very sad thing at all... :-)

Notice that there's a need to handle out-of-mem at caller's
place.

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

1 files changed, 35 insertions, 19 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 50047045df62..bd18c252dee4 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1181,6 +1181,38 @@ static int tcp_check_dsack(struct tcp_sock *tp, struct sk_buff *ack_skb,
         return dup_sack;
 }
 
+/* Check if skb is fully within the SACK block. In presence of GSO skbs,
+ * the incoming SACK may not exactly match but we can find smaller MSS
+ * aligned portion of it that matches. Therefore we might need to fragment
+ * which may fail and creates some hassle (caller must handle error case
+ * returns).
+ */
+int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
+                          u32 start_seq, u32 end_seq)
+{
+        int in_sack, err;
+        unsigned int pkt_len;
+
+        in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
+                  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
+
+        if (tcp_skb_pcount(skb) > 1 && !in_sack &&
+            after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
+
+                in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
+
+                if (!in_sack)
+                        pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
+                else
+                        pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
+                err = tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->gso_size);
+                if (err < 0)
+                        return err;
+        }
+
+        return in_sack;
+}
+
 static int
 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una)
 {
@@ -1333,25 +1365,9 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
                         if (!before(TCP_SKB_CB(skb)->seq, end_seq))
                                 break;
 
-                        in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
-                                !before(end_seq, TCP_SKB_CB(skb)->end_seq);
-
-                        if (tcp_skb_pcount(skb) > 1 && !in_sack &&
-                            after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
-                                unsigned int pkt_len;
-
-                                in_sack = !after(start_seq,
-                                                 TCP_SKB_CB(skb)->seq);
-
-                                if (!in_sack)
-                                        pkt_len = (start_seq -
-                                                   TCP_SKB_CB(skb)->seq);
-                                else
-                                        pkt_len = (end_seq -
-                                                   TCP_SKB_CB(skb)->seq);
-                                if (tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->gso_size))
-                                        break;
-                        }
+                        in_sack = tcp_match_skb_to_sack(sk, skb, start_seq, end_seq);
+                        if (in_sack < 0)
+                                break;
 
                         fack_count += tcp_skb_pcount(skb);