[PATCH net-next] trace: tcp: Add tracepoint for tcp_sendmsg()

[Breno Leitao <leitao@debian.org>]

Add a lightweight tracepoint to monitor TCP sendmsg operations, enabling
the tracing of TCP messages being sent.

Meta has been using BPF programs to monitor this function for years,
indicating significant interest in observing this important
functionality. Adding a proper tracepoint provides a stable API for all
users who need visibility into TCP message transmission.

The implementation uses DECLARE_TRACE instead of TRACE_EVENT to avoid
creating unnecessary trace event infrastructure and tracefs exports,
keeping the implementation minimal while stabilizing the API.

Given that this patch creates a rawtracepoint, you could hook into it
using regular tooling, like bpftrace, using regular rawtracepoint
infrastructure, such as:

	rawtracepoint:tcp_sendmsg_tp {
		....
	}

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 include/trace/events/tcp.h | 5 +++++
 net/ipv4/tcp.c             | 2 ++
 2 files changed, 7 insertions(+)

diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h
index 1a40c41ff8c30..7c0171d2dacdc 100644
--- a/include/trace/events/tcp.h
+++ b/include/trace/events/tcp.h
@@ -259,6 +259,11 @@ TRACE_EVENT(tcp_retransmit_synack,
 		  __entry->saddr_v6, __entry->daddr_v6)
 );
 
+DECLARE_TRACE(tcp_sendmsg_tp,
+	TP_PROTO(const struct sock *sk, const struct msghdr *msg, size_t size),
+	TP_ARGS(sk, msg, size)
+);
+
 DECLARE_TRACE(tcp_cwnd_reduction_tp,
 	TP_PROTO(const struct sock *sk, int newly_acked_sacked,
 		 int newly_lost, int flag),
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 08d73f17e8162..5ef86fbd8aa85 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1362,6 +1362,8 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 {
 	int ret;
 
+	trace_tcp_sendmsg_tp(sk, msg, size);
+
 	lock_sock(sk);
 	ret = tcp_sendmsg_locked(sk, msg, size);
 	release_sock(sk);

---
base-commit: e13b6da7045f997e1a5a5efd61d40e63c4fc20e8
change-id: 20250224-tcpsendmsg-4f0a236751d7

Best regards,
-- 
Breno Leitao <leitao@debian.org>