[PATCH bpf-next v9 10/12] 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. For instance, 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.

Signed-off-by: Jason Xing <kerneljasonxing@gmail.com>
---
 include/uapi/linux/bpf.h       | 5 +++++
 net/ipv4/tcp.c                 | 4 ++++
 tools/include/uapi/linux/bpf.h | 5 +++++
 3 files changed, 14 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c04e788125a7..7b1a7dd68c0d 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7049,6 +7049,11 @@ enum {
 					 * when SK_BPF_CB_TX_TIMESTAMPING
 					 * feature is on.
 					 */
+	BPF_SOCK_OPS_TS_SND_CB,		/* Called when every sendmsg syscall
+					 * is triggered. It's used to correlate
+					 * sendmsg timestamp with corresponding
+					 * tskey.
+					 */
 };
 
 /* 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 0d704bda6c41..4895d7a6327b 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -492,6 +492,10 @@ static void tcp_tx_timestamp(struct sock *sk, struct sockcm_cookie *sockc)
 		if (tsflags & SOF_TIMESTAMPING_TX_RECORD_MASK)
 			shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1;
 	}
+
+	if (cgroup_bpf_enabled(CGROUP_SOCK_OPS) &&
+	    SK_BPF_CB_FLAG_TEST(sk, SK_BPF_CB_TX_TIMESTAMPING) && skb)
+		bpf_skops_tx_timestamping(sk, skb, BPF_SOCK_OPS_TS_SND_CB);
 }
 
 static bool tcp_stream_is_readable(struct sock *sk, int target)
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index d3e2988b3b4c..2739ee0154a0 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -7042,6 +7042,11 @@ enum {
 					 * when SK_BPF_CB_TX_TIMESTAMPING
 					 * feature is on.
 					 */
+	BPF_SOCK_OPS_TS_SND_CB,		/* Called when every sendmsg syscall
+					 * is triggered. It's used to correlate
+					 * sendmsg timestamp with corresponding
+					 * tskey.
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
-- 
2.43.5