Re: [PATCH bpf-next v7 11/13] net-timestamp: add a new callback in tcp_tx_timestamp()

[Martin KaFai Lau <martin.lau@linux.dev>]

On 1/28/25 12:46 AM, Jason Xing wrote:
> Introduce the callback to correlate tcp_sendmsg timestamp with other
> points, like SND/SW/ACK. We can let bpf trace the beginning of
> tcp_sendmsg_locked() and fetch the socket addr, so that in

Instead of "fetch the socket addr...", should be "store the sendmsg timestamp at 
the bpf_sk_storage ...".

> 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.

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.

Do you have a chance to look at how this will work at UDP?