netdev - Re: [RFC PATCH net-next v6 11/13] net-timestamp: add a new callback in tcp_tx

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Message-ID: <db1c1edc-f02f-4755-9b6d-b1c1e9b90564@linux.dev>
Date: Fri, 24 Jan 2025 16:50:09 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, dsahern@...nel.org, willemdebruijn.kernel@...il.com,
 willemb@...gle.com, ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
 eddyz87@...il.com, song@...nel.org, yonghong.song@...ux.dev,
 john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
 haoluo@...gle.com, jolsa@...nel.org, horms@...nel.org, bpf@...r.kernel.org,
 netdev@...r.kernel.org
Subject: Re: [RFC PATCH net-next v6 11/13] net-timestamp: add a new callback
 in tcp_tx_timestamp()

On 1/20/25 5:28 PM, Jason Xing wrote:
> 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@...il.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
> +					 */

I recall we agreed in v5 to adjust the "TCP_" naming part because it will be 
used in UDP also. Like completely remove the "TCP_" from the name?

>   };
>   
>   /* 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