netdev - Re: [PATCH net-next v4 07/11] net-timestamp: support hwtstamp print for bpf extension

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Message-ID: <CAL+tcoCmUcRavWgjCpT73FfNM7c0Qoi3EYd30EwrOa_VVT5Rhw@mail.gmail.com>
Date: Sat, 14 Dec 2024 08:48:53 +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, bpf@...r.kernel.org, 
	netdev@...r.kernel.org, Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v4 07/11] net-timestamp: support hwtstamp print
 for bpf extension

On Sat, Dec 14, 2024 at 8:17 AM Martin KaFai Lau <martin.lau@...ux.dev> wrote:
>
> On 12/13/24 4:02 PM, Jason Xing wrote:
> > On Sat, Dec 14, 2024 at 7:15 AM Martin KaFai Lau <martin.lau@...ux.dev> wrote:
> >>
> >> On 12/13/24 7:13 AM, Jason Xing wrote:
> >>>>> -static void __skb_tstamp_tx_bpf(struct sock *sk, struct sk_buff *skb, int tstype)
> >>>>> +static void __skb_tstamp_tx_bpf(struct sock *sk, struct sk_buff *skb,
> >>>>> +                             struct skb_shared_hwtstamps *hwtstamps,
> >>>>> +                             int tstype)
> >>>>>     {
> >>>>> +     struct timespec64 tstamp;
> >>>>> +     u32 args[2] = {0, 0};
> >>>>>         int op;
> >>>>>
> >>>>>         if (!sk)
> >>>>> @@ -5552,6 +5556,11 @@ static void __skb_tstamp_tx_bpf(struct sock *sk, struct sk_buff *skb, int tstype
> >>>>>                 break;
> >>>>>         case SCM_TSTAMP_SND:
> >>>>>                 op = BPF_SOCK_OPS_TS_SW_OPT_CB;
> >>>>> +             if (hwtstamps) {
> >>>>> +                     tstamp = ktime_to_timespec64(hwtstamps->hwtstamp);
> >>>> Avoid this conversion which is likely not useful to the bpf prog. Directly pass
> >>>> hwtstamps->hwtstamp (in ns?) to the bpf prog. Put lower 32bits in args[0] and
> >>>> higher 32bits in args[1].
> >>> It makes sense.
> >>
> >> When replying the patch 2 thread, I noticed it may not even have to pass the
> >> hwtstamps in args here.
> >>
> >> Can "*skb_hwtstamps(skb) = *hwtstamps;" be done before calling the bpf prog?
> >> Then the bpf prog can directly get it from skb_shinfo(skb)->hwtstamps.
> >> It is like reading other fields in skb_shinfo(skb), e.g. the
> >> skb_shinfo(skb)->tskey discussed in patch 10. The bpf prog will have a more
> >> consistent experience in reading different fields of the skb_shinfo(skb).
> >> skb_shinfo(skb)->hwtstamps is a more intuitive place to obtain the hwtstamp than
> >> the broken up args[0] and args[1]. On top of that, there is also an older
> >> "skb_hwtstamp" field in "struct bpf_sock_ops".
> >
> > Right, right, last night, fortunately, I also spotted it. Let the bpf
> > prog parse the shared info from skb then. A new callback for hwtstamp
> > is needed, I suppose.
>
> Why a new callback is needed? "*skb_hwtstamps(skb) = *hwtstamps;" cannot be done
> in __skb_tstamp_tx_bpf?

Oh, I have no preference on this point. I will abort adding a new callback then.