netdev - Re: [PATCH net-next v3 10/14] net-timestamp: add basic support with tskey offset

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Message-ID: <CAL+tcoBNiZQr=yk_fb9eoKX1_Nr4LuDaa1kkLGbdnc=8JNKnNg@mail.gmail.com>
Date: Wed, 30 Oct 2024 14:50:03 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Martin KaFai Lau <martin.lau@...ux.dev>
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, shuah@...nel.org, ykolal@...com, 
	bpf@...r.kernel.org, netdev@...r.kernel.org, 
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v3 10/14] net-timestamp: add basic support with
 tskey offset

On Wed, Oct 30, 2024 at 1:42 PM Martin KaFai Lau <martin.lau@...ux.dev> wrote:
>
> On 10/28/24 4:05 AM, Jason Xing wrote:
> > +/* Used to track the tskey for bpf extension
> > + *
> > + * @sk_tskey: bpf extension can use it only when no application uses.
> > + *            Application can use it directly regardless of bpf extension.
> > + *
> > + * There are three strategies:
> > + * 1) If we've already set through setsockopt() and here we're going to set
> > + *    OPT_ID for bpf use, we will not re-initialize the @sk_tskey and will
> > + *    keep the record of delta between the current "key" and previous key.
> > + * 2) If we've already set through bpf_setsockopt() and here we're going to
> > + *    set for application use, we will record the delta first and then
> > + *    override/initialize the @sk_tskey.
> > + * 3) other cases, which means only either of them takes effect, so initialize
> > + *    everything simplely.
> > + */
> > +static long int sock_calculate_tskey_offset(struct sock *sk, int val, int bpf_type)
> > +{
> > +     u32 tskey;
> > +
> > +     if (sk_is_tcp(sk)) {
> > +             if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
> > +                     return -EINVAL;
> > +
> > +             if (val & SOF_TIMESTAMPING_OPT_ID_TCP)
> > +                     tskey = tcp_sk(sk)->write_seq;
> > +             else
> > +                     tskey = tcp_sk(sk)->snd_una;
> > +     } else {
> > +             tskey = 0;
> > +     }
> > +
> > +     if (bpf_type && (sk->sk_tsflags & SOF_TIMESTAMPING_OPT_ID)) {
> > +             sk->sk_tskey_bpf_offset = tskey - atomic_read(&sk->sk_tskey);
> > +             return 0;
> > +     } else if (!bpf_type && (sk->sk_tsflags_bpf & SOF_TIMESTAMPING_OPT_ID)) {
> > +             sk->sk_tskey_bpf_offset = atomic_read(&sk->sk_tskey) - tskey;
> > +     } else {
> > +             sk->sk_tskey_bpf_offset = 0;
> > +     }
> > +
> > +     return tskey;
> > +}
>
> Before diving into this route, the bpf prog can peek into the tcp seq no in the
> skb. It can also look at the sk->sk_tskey for UDP socket. Can you explain why
> those are not enough information for the bpf prog?

Well, it does make sense. It seems we don't need to implement tskey
for this bpf feature...

Due to lack of enough knowledge of bpf, could you provide more hints
that I can follow to write a bpf program to print more information
from the skb? Like in the last patch of this series, in
tools/testing/selftests/bpf/prog_tests/so_timestamping.c, do we have a
feasible way to do that?

Thanks,
Jason