On Thu, Jan 16, 2025 at 9:18 AM Martin KaFai Lau <martin.lau@xxxxxxxxx> wrote:
>
> On 1/15/25 4:41 PM, Jason Xing wrote:
> >>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> >>> index a0aff1b4eb61..87420c0f2235 100644
> >>> --- a/include/uapi/linux/bpf.h
> >>> +++ b/include/uapi/linux/bpf.h
> >>> @@ -7037,6 +7037,9 @@ enum {
> >>> * feature is on. It indicates the
> >>> * recorded timestamp.
> >>> */
> >>> + BPF_SOCK_OPS_TS_TCP_SND_CB, /* Called when every tcp_sendmsg
> >>> + * syscall is triggered
> >>> + */
> >>
> >> UDP will need this also?
> >
> > Yep.
>
> Then the TCP naming will need to be adjusted.
Right, right!
>
> While on UDP, how the UDP bpf callback will look like during sendmsg?
>
> >>> @@ -1067,10 +1068,15 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
> >>> int flags, err, copied = 0;
> >>> int mss_now = 0, size_goal, copied_syn = 0;
> >>> int process_backlog = 0;
> >>> + u32 first_write_seq = 0;
> >>> int zc = 0;
> >>> long timeo;
> >>>
> >>> flags = msg->msg_flags;
> >>> + if (SK_BPF_CB_FLAG_TEST(sk, SK_BPF_CB_TX_TIMESTAMPING)) {
> >>> + first_write_seq = tp->write_seq;
> >>> + bpf_skops_tx_timestamping(sk, NULL, BPF_SOCK_OPS_TS_TCP_SND_CB);
> >>
> >> My preference is to skip this bpf callout for now and depends on a bpf trace
> >> program if it is really needed.
> >
> > I have no idea if the bpf program wants to record the timestamp here
> > without the above three lines? Please enlighten me more. Thanks in
> > advance.
> >
> > I guess there is one way which I don't know yet to monitor at the
> > beginning of tcp_sendmsg_locked().
>
> The tracing bpf program (fentry in particular here). Give the one-liner bpftrace
> script a try.
>
> Take a look at trace_tcp_connect in test_sk_storage_tracing.c. It uses fentry
> and also bpf_sk_storage_get.
Thanks for the reference!
>
> If tcp_sendmsg_locked is inline-d, it can go up to the tcp_sendmsg(). It would
> be nice to have a stable bpf callback if it is really useful but I suspect this
> can be revisited later with the UDP support.
Got it!
>
> [ I will followup other replies later. ]
>
Thank you!
