On Sat, Dec 14, 2024 at 8:17 AM Martin KaFai Lau <martin.lau@xxxxxxxxx> 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@xxxxxxxxx> 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.
