[PATCH net-next v3 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[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 ++++++++++++++++++++++++
 kernel/bpf/btf.c           |  1 +
 net/ipv4/tcp.c             |  2 ++
 3 files changed, 27 insertions(+)

diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h
index 1a40c41ff8c30..75d3d53a3832c 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/kernel/bpf/btf.c b/kernel/bpf/btf.c
index eacb701bc2be2..475a1317ad275 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6518,6 +6518,7 @@ static const struct bpf_raw_tp_null_args raw_tp_null_args[] = {
 	{ "xprt_put_cong", 0x10 },
 	/* tcp */
 	{ "tcp_send_reset", 0x11 },
+	{ "tcp_sendmsg_locked", 0x100 },
 	/* tegra_apb_dma */
 	{ "tegra_dma_tx_status", 0x100 },
 	/* timer_migration */
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