netdev - Re: [PATCH net-next v5 08/15] net-timestamp: support sw SCM_TSTAMP

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Message-ID: <fc4dd0d9-d4ae-4601-be01-5fad7c74e585@linux.dev>
Date: Fri, 17 Jan 2025 16:46:56 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Jason Xing <kerneljasonxing@...il.com>
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, horms@...nel.org, bpf@...r.kernel.org,
 netdev@...r.kernel.org
Subject: Re: [PATCH net-next v5 08/15] net-timestamp: support sw
 SCM_TSTAMP_SND for bpf extension

On 1/15/25 3:56 PM, Jason Xing wrote:
> On Thu, Jan 16, 2025 at 6:48 AM Martin KaFai Lau <martin.lau@...ux.dev> wrote:
>>
>> On 1/12/25 3:37 AM, Jason Xing wrote:
>>> Support SCM_TSTAMP_SND case. Then we will get the software
>>> timestamp when the driver is about to send the skb. Later, I
>>> will support the hardware timestamp.
>>
>>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
>>> index 169c6d03d698..0fb31df4ed95 100644
>>> --- a/net/core/skbuff.c
>>> +++ b/net/core/skbuff.c
>>> @@ -5578,6 +5578,9 @@ static void __skb_tstamp_tx_bpf(struct sk_buff *skb, struct sock *sk, int tstype
>>>        case SCM_TSTAMP_SCHED:
>>>                op = BPF_SOCK_OPS_TS_SCHED_OPT_CB;
>>>                break;
>>> +     case SCM_TSTAMP_SND:
>>> +             op = BPF_SOCK_OPS_TS_SW_OPT_CB;
>>
>> For the hwtstamps case, is skb_hwtstamps(skb) set? From looking at a few
>> drivers, it does not look like it. I don't see the hwtstamps support in patch 10
>> either. What did I miss ?
> 
> Sorry, I missed adding a new flag, namely, BPF_SOCK_OPS_TS_HW_OPT_CB.
> I can also skip adding that new one and rename
> BPF_SOCK_OPS_TS_SW_OPT_CB accordingly for sw and hw cases if we
> finally decide to use hwtstamps parameter to distinguish two different
> cases.

I think having a separate BPF_SOCK_OPS_TS_HW_OPT_CB is better considering your 
earlier hwtstamps may be NULL comment. I don't see the drivers I looked at 
passing NULL though but the comment of skb_tstamp_tx did say it may be NULL :/

Regardless, afaict, skb_hwtstamps(skb) is still not set to the hwtstamps passed 
by the driver here. The bpf prog is supposed to directly get the hwtstamps from 
the skops->skb pointer.