[PATCH bpf-next v8 11/12] bpf: add a new callback in tcp_tx_timestamp()

[Jason Xing <kerneljasonxing@gmail.com>]

Introduce the callback to correlate tcp_sendmsg timestamp with other
points, like SND/SW/ACK. let bpf prog trace the beginning of
tcp_sendmsg_locked() and then store the sendmsg timestamp at
the bpf_sk_storage, so that in tcp_tx_timestamp() we can correlate
the timestamp with tskey which can be found in other sending points.

More details can be found in the selftest:
The selftest uses the bpf_sk_storage to store the sendmsg timestamp at
fentry/tcp_sendmsg_locked and retrieves it back at tcp_tx_timestamp
(i.e. BPF_SOCK_OPS_TS_SND_CB added in this patch).

Signed-off-by: Jason Xing <kerneljasonxing@gmail.com>
---
 include/uapi/linux/bpf.h       | 7 +++++++
 net/ipv4/tcp.c                 | 1 +
 tools/include/uapi/linux/bpf.h | 7 +++++++
 3 files changed, 15 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 800122a8abe5..accb3b314fff 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7052,6 +7052,13 @@ enum {
 					 * when SK_BPF_CB_TX_TIMESTAMPING
 					 * feature is on.
 					 */
+	BPF_SOCK_OPS_TS_SND_CB,		/* Called when every sendmsg syscall
+					 * is triggered. For TCP, it stays
+					 * in the last send process to
+					 * correlate with tcp_sendmsg timestamp
+					 * with other timestamping callbacks,
+					 * like SND/SW/ACK.
+					 */
 };
 
 /* 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 3df802410ebf..a2ac57543b6d 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -501,6 +501,7 @@ 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_SND_CB);
 	}
 }
 
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 06e68d772989..384502996cdd 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -7045,6 +7045,13 @@ enum {
 					 * when SK_BPF_CB_TX_TIMESTAMPING
 					 * feature is on.
 					 */
+	BPF_SOCK_OPS_TS_SND_CB,		/* Called when every sendmsg syscall
+					 * is triggered. For TCP, it stays
+					 * in the last send process to
+					 * correlate with tcp_sendmsg timestamp
+					 * with other timestamping callbacks,
+					 * like SND/SW/ACK.
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
-- 
2.43.5