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.
