netdev - Re: [PATCH net-next v2 00/12] net-timestamp: bpf extension to equip applications transparently

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Message-ID: <CAL+tcoD-595iMJ79L7kVUsMgBfjnTQJgPaycOw2iP-nUDHCivA@mail.gmail.com>
Date: Sun, 13 Oct 2024 14:05:38 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: 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, martin.lau@...ux.dev, 
	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, bpf@...r.kernel.org, 
	netdev@...r.kernel.org, Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v2 00/12] net-timestamp: bpf extension to equip
 applications transparently

> I tested this by running "./txtimestamp -4 -L 127.0.0.1 -l 1000 -c 5"
> in the bpf attached directory and it can correctly print the
> timestamp. So it would not break users.
>
> And surprisingly I found the key is not that right (ERROR: key 1000,
> expected 999). I will investigate and fix it.

Ah, I think I know the reason. In this series, the BPF extension
allows setting before sending SYN packet in the beginning of
tcp_connect(), which is different from the original design that allows
setting after sending the SYN packet. It causes the unexpected key.
They are different. The reason why the failure is triggered is because
I reuse the tskey logic in the BPF extension...

====
Back to the question on how to solve the conflicts, if we finally
reckon that the original feature has the first priority, I can change
the order in the next version.

void __skb_tstamp_tx(struct sk_buff *orig_skb,
                     const struct sk_buff *ack_skb,
                     struct skb_shared_hwtstamps *hwtstamps,
                     struct sock *sk, int tstype)
{
        if (!sk)
                return;

       ret = skb_tstamp_tx_output(orig_skb, ack_skb, hwtstamps, sk, tstype);
       if (ret)
               /* Apps does set the SO_TIMESTAMPING flag, return directly */
               return;

       if (static_branch_unlikely(&bpf_tstamp_control))
                bpf_skb_tstamp_tx_output(sk, orig_skb, tstype, hwtstamps);
}

In this way, it will allow either of two features to work. Willem, do
you think it is fine with you?

Thanks,
Jason