Re: [PATCH net-next] tcp: add tracepoint trace_tcp_retransmit_synack()

This tracepoint can be used to trace synack retransmits. It maintains
pointer to struct request_sock.

We cannot simply reuse trace_tcp_retransmit_skb() here, because the
sk here is the LISTEN socket. The IP addresses and ports should be
extracted from struct request_sock.

Signed-off-by: Song Liu <redacted>
---
 include/trace/events/tcp.h | 56 ++++++++++++++++++++++++++++++++++++++++++++++
 net/ipv4/tcp_output.c      |  1 +
 2 files changed, 57 insertions(+)

diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h
index 03699ba..07cccca 100644
--- a/include/trace/events/tcp.h
+++ b/include/trace/events/tcp.h

@@ -237,6 +237,62 @@ TRACE_EVENT(tcp_set_state,
                  show_tcp_state_name(__entry->newstate))
 );

+TRACE_EVENT(tcp_retransmit_synack,
+
+       TP_PROTO(const struct sock *sk, const struct request_sock *req),
+
+       TP_ARGS(sk, req),
+
+       TP_STRUCT__entry(
+               __field(const void *, skaddr)
+               __field(const void *, req)
+               __field(__u16, sport)
+               __field(__u16, dport)
+               __array(__u8, saddr, 4)
+               __array(__u8, daddr, 4)
+               __array(__u8, saddr_v6, 16)
+               __array(__u8, daddr_v6, 16)