tcp: add tcp_mss_clamp() helper

Small cleanup factorizing code doing the TCP_MAXSEG clamping.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 10 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 6d5bab8a3ea6..956bea9a5394 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3062,7 +3062,6 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
         struct sk_buff *skb;
         int tcp_header_size;
         struct tcphdr *th;
-        u16 user_mss;
         int mss;
 
         skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
@@ -3092,10 +3091,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
         }
         skb_dst_set(skb, dst);
 
-        mss = dst_metric_advmss(dst);
-        user_mss = READ_ONCE(tp->rx_opt.user_mss);
-        if (user_mss && user_mss < mss)
-                mss = user_mss;
+        mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
 
         memset(&opts, 0, sizeof(opts));
 #ifdef CONFIG_SYN_COOKIES
@@ -3201,9 +3197,7 @@ static void tcp_connect_init(struct sock *sk)
 
         if (!tp->window_clamp)
                 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
-        tp->advmss = dst_metric_advmss(dst);
-        if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
-                tp->advmss = tp->rx_opt.user_mss;
+        tp->advmss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
 
         tcp_initialize_rcv_mss(sk);
 
@@ -3280,8 +3274,8 @@ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
          * user-MSS. Reserve maximum option space for middleboxes that add
          * private TCP options. The cost is reduced data space in SYN :(
          */
-        if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
-                tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
+        tp->rx_opt.mss_clamp = tcp_mss_clamp(tp, tp->rx_opt.mss_clamp);
+
         space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
                 MAX_TCP_OPTION_SPACE;