[PATCH RFC net-next 7/9] tcp: propagate the start time onto every skb in the tx path

[Jason Xing <kerneljasonxing@gmail.com>]

Now that sendmsg() records a start time in sk->sk_start_time within
the socket lock protection, copy that value into the shared hwtstamps
of each skb.

The timing is tcp_skb_entail() runs once per newly allocated skb
in the sendmsg() loop, every segment produced by a single sendmsg()
carries the same start time.

Signed-off-by: Jason Xing <kerneljasonxing@gmail.com>
---
 net/ipv4/tcp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 28730a3e4473..85e3bae3569d 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -702,6 +702,9 @@ void tcp_skb_entail(struct sock *sk, struct sk_buff *skb)
 	tcb->tcp_flags = TCPHDR_ACK;
 	__skb_header_release(skb);
 	psp_enqueue_set_decrypted(sk, skb);
+	if (static_branch_unlikely(&bpfts_v2_needed_key) &&
+	    SK_BPF_CB_FLAG_TEST(sk, SK_BPF_CB_TIMESTAMPING_V2))
+		skb_hwtstamps(skb)->start_time = sk->sk_start_time;
 	tcp_add_write_queue_tail(sk, skb);
 	sk_wmem_queued_add(sk, skb->truesize);
 	sk_mem_charge(sk, skb->truesize);
-- 
2.43.7