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

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Message-ID: <e6f2c489-85a9-436e-8d05-4b3063c133fd@linux.dev>
Date: Mon, 10 Feb 2025 14:39:44 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Jason Xing <kerneljasonxing@...il.com>,
 Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, dsahern@...nel.org, 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, horms@...nel.org,
 bpf@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next v8 08/12] bpf: support hw SCM_TSTAMP_SND of
 SO_TIMESTAMPING

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?