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>

1 files changed, 6 insertions, 1 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.   */