[RFC PATCH net-next v6 11/13] net-timestamp: add a new callback in tcp_tx_timestamp()

[Jason Xing <kerneljasonxing@gmail.com>]

Introduce the callback to correlate tcp_sendmsg timestamp with other
three points (SND/SW/ACK). We can let bpf trace the beginning of
tcp_sendmsg_locked() and fetch the socket addr, so that in
tcp_tx_timestamp() we can correlate the tskey with the socket addr.
It is accurate since they are under the protect of socket lock.
More details can be found in the selftest.

Signed-off-by: Jason Xing <kerneljasonxing@gmail.com>
---
 include/uapi/linux/bpf.h       | 3 +++
 net/ipv4/tcp.c                 | 1 +
 tools/include/uapi/linux/bpf.h | 3 +++
 3 files changed, 7 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 3b9bfc88345c..55c74fa18163 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7042,6 +7042,9 @@ enum {
 					 * feature is on. It indicates the
 					 * recorded timestamp.
 					 */
+	BPF_SOCK_OPS_TS_TCP_SND_CB,	/* Called when every tcp_sendmsg
+					 * syscall is triggered
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 0a41006b10d1..49e489c346ea 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -500,6 +500,7 @@ static void tcp_tx_timestamp(struct sock *sk, struct sockcm_cookie *sockc)
 		tcb->txstamp_ack_bpf = 1;
 		shinfo->tx_flags |= SKBTX_BPF;
 		shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1;
+		bpf_skops_tx_timestamping(sk, skb, BPF_SOCK_OPS_TS_TCP_SND_CB);
 	}
 }
 
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index b463aa9c27da..38fc04a7ac20 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -7035,6 +7035,9 @@ enum {
 					 * feature is on. It indicates the
 					 * recorded timestamp.
 					 */
+	BPF_SOCK_OPS_TS_TCP_SND_CB,	/* Called when every tcp_sendmsg
+					 * syscall is triggered
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
-- 
2.43.5