tcp: add mss_clamp to tcp_request_sock_ops

Add mss_clamp member to tcp_request_sock_ops so that we can later
unify tcp_v4_conn_request and tcp_v6_conn_request.
Signed-off-by: NOctavian Purdila <octavian.purdila@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -1592,6 +1592,7 @@ struct tcp_sock_af_ops {
 };
 
 struct tcp_request_sock_ops {
+	u16 mss_clamp;
 #ifdef CONFIG_TCP_MD5SIG
 	struct tcp_md5sig_key	*(*md5_lookup) (struct sock *sk,
 						struct request_sock *req);

net/ipv4/tcp_ipv4.c

@@ -1265,6 +1265,7 @@ struct request_sock_ops tcp_request_sock_ops __read_mostly = {
 };
 
 static const struct tcp_request_sock_ops tcp_request_sock_ipv4_ops = {
+	.mss_clamp	=	TCP_MSS_DEFAULT,
 #ifdef CONFIG_TCP_MD5SIG
 	.md5_lookup	=	tcp_v4_reqsk_md5_lookup,
 	.calc_md5_hash	=	tcp_v4_md5_hash_skb,
@@ -1324,7 +1325,7 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 	af_ops = tcp_rsk(req)->af_specific = &tcp_request_sock_ipv4_ops;
 
 	tcp_clear_options(&tmp_opt);
-	tmp_opt.mss_clamp = TCP_MSS_DEFAULT;
+	tmp_opt.mss_clamp = af_ops->mss_clamp;
 	tmp_opt.user_mss  = tp->rx_opt.user_mss;
 	tcp_parse_options(skb, &tmp_opt, 0, want_cookie ? NULL : &foc);
 

net/ipv6/tcp_ipv6.c

@@ -754,6 +754,8 @@ struct request_sock_ops tcp6_request_sock_ops __read_mostly = {
 };
 
 static const struct tcp_request_sock_ops tcp_request_sock_ipv6_ops = {
+	.mss_clamp	=	IPV6_MIN_MTU - sizeof(struct tcphdr) -
+				sizeof(struct ipv6hdr),
 #ifdef CONFIG_TCP_MD5SIG
 	.md5_lookup	=	tcp_v6_reqsk_md5_lookup,
 	.calc_md5_hash	=	tcp_v6_md5_hash_skb,
@@ -1047,7 +1049,7 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
 	af_ops = tcp_rsk(req)->af_specific = &tcp_request_sock_ipv6_ops;
 
 	tcp_clear_options(&tmp_opt);
-	tmp_opt.mss_clamp = IPV6_MIN_MTU - sizeof(struct tcphdr) - sizeof(struct ipv6hdr);
+	tmp_opt.mss_clamp = af_ops->mss_clamp;
 	tmp_opt.user_mss = tp->rx_opt.user_mss;
 	tcp_parse_options(skb, &tmp_opt, 0, want_cookie ? NULL : &foc);