Re: [PATCH bpf-next v8 08/12] bpf: support hw SCM_TSTAMP_SND of SO_TIMESTAMPING

[Martin KaFai Lau <martin.lau@linux.dev>]

On 2/5/25 8:03 AM, Jason Xing wrote:
>>> @@ -5574,9 +5575,9 @@ static void skb_tstamp_tx_bpf(struct sk_buff *skb, struct sock *sk,
>>>                op = BPF_SOCK_OPS_TS_SCHED_OPT_CB;
>>>                break;
>>>        case SCM_TSTAMP_SND:
>>> -             if (!sw)
>>> -                     return;
>>> -             op = BPF_SOCK_OPS_TS_SW_OPT_CB;
>>> +             op = sw ? BPF_SOCK_OPS_TS_SW_OPT_CB : BPF_SOCK_OPS_TS_HW_OPT_CB;
>>> +             if (!sw && hwtstamps)
>>> +                     *skb_hwtstamps(skb) = *hwtstamps;
>> Isn't this called by drivers that have actually set skb_hwtstamps?
> Oops, somehow my mind has gone blank 🙁 Will remove it. Thanks for
> correcting me!

I just noticed I missed this thread when reviewing v9.

I looked at a few drivers, e.g. the mlx5e_consume_skb(). It does not necessarily 
set the skb_hwtstamps(skb) before calling skb_tstamp_tx(). The __skb_tstamp_tx() 
is also setting skb_hwtstamps(skb) after testing "if (hwtstamps)", so I think 
this assignment is still needed here?