tcp: introduce TCP_SKB_CB(skb)->tcp_tw_isn

TCP_SKB_CB(skb)->when has different meaning in output and input paths.

In output path, it contains a timestamp.
In input path, it contains an ISN, chosen by tcp_timewait_state_process()

Lets add a different name to ease code comprehension.

Note that 'when' field will disappear in following patch,
as skb_mstamp already contains timestamp, the anonymous
union will promptly disappear as well.

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

5 files changed, 11 insertions, 6 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 590e01a476ac..0cd7d2c65dc0 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -698,7 +698,12 @@ struct tcp_skb_cb {
         } header;       /* For incoming frames          */
         __u32           seq;            /* Starting sequence number     */
         __u32           end_seq;        /* SEQ + FIN + SYN + datalen    */
-        __u32           when;           /* used to compute rtt's        */
+        union {
+                /* used in output path */
+                __u32           when;   /* used to compute rtt's        */
+                /* used in input path */
+                __u32           tcp_tw_isn; /* isn chosen by tcp_timewait_state_process() */
+        };
         __u8            tcp_flags;      /* TCP header flags. (tcp[13])  */
 
         __u8            sacked;         /* State flags for SACK/FACK.   */
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index aba4926ca095..9c8b9f1dcf69 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5906,7 +5906,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
         struct request_sock *req;
         struct tcp_sock *tp = tcp_sk(sk);
         struct dst_entry *dst = NULL;
-        __u32 isn = TCP_SKB_CB(skb)->when;
+        __u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
         bool want_cookie = false, fastopen;
         struct flowi fl;
         struct tcp_fastopen_cookie foc = { .len = -1 };
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 487e2a41667f..02e6cd29ebf1 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1627,7 +1627,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
         TCP_SKB_CB(skb)->end_seq = (TCP_SKB_CB(skb)->seq + th->syn + th->fin +
                                     skb->len - th->doff * 4);
         TCP_SKB_CB(skb)->ack_seq = ntohl(th->ack_seq);
-        TCP_SKB_CB(skb)->when    = 0;
+        TCP_SKB_CB(skb)->tcp_tw_isn = 0;
         TCP_SKB_CB(skb)->ip_dsfield = ipv4_get_dsfield(iph);
         TCP_SKB_CB(skb)->sacked  = 0;
 
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 1649988bd1b6..a058f411d3a6 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -232,7 +232,7 @@ kill:
                 u32 isn = tcptw->tw_snd_nxt + 65535 + 2;
                 if (isn == 0)
                         isn++;
-                TCP_SKB_CB(skb)->when = isn;
+                TCP_SKB_CB(skb)->tcp_tw_isn = isn;
                 return TCP_TW_SYN;
         }
 
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 29964c3d363c..5b3c70ff7a72 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -738,7 +738,7 @@ static void tcp_v6_init_req(struct request_sock *req, struct sock *sk,
             ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
                 ireq->ir_iif = inet6_iif(skb);
 
-        if (!TCP_SKB_CB(skb)->when &&
+        if (!TCP_SKB_CB(skb)->tcp_tw_isn &&
             (ipv6_opt_accepted(sk, skb) || np->rxopt.bits.rxinfo ||
              np->rxopt.bits.rxoinfo || np->rxopt.bits.rxhlim ||
              np->rxopt.bits.rxohlim || np->repflow)) {
@@ -1412,7 +1412,7 @@ static int tcp_v6_rcv(struct sk_buff *skb)
         TCP_SKB_CB(skb)->end_seq = (TCP_SKB_CB(skb)->seq + th->syn + th->fin +
                                     skb->len - th->doff*4);
         TCP_SKB_CB(skb)->ack_seq = ntohl(th->ack_seq);
-        TCP_SKB_CB(skb)->when = 0;
+        TCP_SKB_CB(skb)->tcp_tw_isn = 0;
         TCP_SKB_CB(skb)->ip_dsfield = ipv6_get_dsfield(hdr);
         TCP_SKB_CB(skb)->sacked = 0;