[PATCH net-next v2 2/2] trace: tcp: Add tracepoint for tcp_sendmsg_locked()

[Breno Leitao <leitao@debian.org>]

Add a tracepoint to monitor TCP send operations, enabling detailed
visibility into TCP message transmission.

Create a new tracepoint within the tcp_sendmsg_locked function,
capturing traditional fields along with size_goal, which indicates the
optimal data size for a single TCP segment. Additionally, a reference to
the struct sock sk is passed, allowing direct access for BPF programs.
The implementation is largely based on David's patch and suggestions.

The implementation is largely based on David's patch[1] and suggestions.

Link: https://lore.kernel.org/all/70168c8f-bf52-4279-b4c4-be64527aa1ac@kernel.org/ [1]
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 include/trace/events/tcp.h | 24 ++++++++++++++++++++++++
 net/ipv4/tcp.c             |  2 ++
 2 files changed, 26 insertions(+)

diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h
index 1a40c41ff8c30..cab25504c4f9d 100644
--- a/include/trace/events/tcp.h
+++ b/include/trace/events/tcp.h
@@ -259,6 +259,30 @@ TRACE_EVENT(tcp_retransmit_synack,
 		  __entry->saddr_v6, __entry->daddr_v6)
 );
 
+TRACE_EVENT(tcp_sendmsg_locked,
+	TP_PROTO(const struct sock *sk, const struct msghdr *msg,
+		 const struct sk_buff *skb, int size_goal),
+
+	TP_ARGS(sk, msg, skb, size_goal),
+
+	TP_STRUCT__entry(
+		__field(const void *, skb_addr)
+		__field(int, skb_len)
+		__field(int, msg_left)
+		__field(int, size_goal)
+	),
+
+	TP_fast_assign(
+		__entry->skb_addr = skb;
+		__entry->skb_len = skb ? skb->len : 0;
+		__entry->msg_left = msg_data_left(msg);
+		__entry->size_goal = size_goal;
+	),
+
+	TP_printk("skb_addr %p skb_len %d msg_left %d size_goal %d",
+		__entry->skb_addr, __entry->skb_len, __entry->msg_left,
+		__entry->size_goal));
+
 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 ea8de00f669d0..270ce2c8c2d54 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1160,6 +1160,8 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 		if (skb)
 			copy = size_goal - skb->len;
 
+		trace_tcp_sendmsg_locked(sk, msg, skb, size_goal);
+
 		if (copy <= 0 || !tcp_skb_can_collapse_to(skb)) {
 			bool first_skb;
 

-- 
2.47.1