netdev - Re: [PATCH net-next v2 09/12] net-timestamp: add tx OPT_ID

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Message-ID: <CAL+tcoDAGLXsqRb4c-hbtE3a38KQHz9jh-p1tKMkWPMKferQ6g@mail.gmail.com>
Date: Tue, 15 Oct 2024 10:25:28 +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 09/12] net-timestamp: add tx OPT_ID_TCP
 support for bpf case

On Tue, Oct 15, 2024 at 9:38 AM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> Jason Xing wrote:
> > From: Jason Xing <kernelxing@...cent.com>
> >
> > We can set OPT_ID|OPT_ID_TCP before we initialize the last skb
> > from each sendmsg. We only set the socket once like how we use
> > setsockopt() with OPT_ID|OPT_ID_TCP flags.
> >
> > Note: we will check if non-bpf _and_ bpf sk_tsflags have OPT_ID
> > flag. If either of them has been set before, we will not initialize
> > the key any more,
>
> Where and how is this achieved?

Please see this patch and you will find the following codes.
+       tsflags |= (sk->sk_tsflags[SOCKETOPT_TS_REQUESTOR] |
+                   sk->sk_tsflags[BPFPROG_TS_REQUESTOR]);

But the difference/problem is that the non-bpf feature only init it
when connect() is done, but the bpf feature could do it at the
beginning of connect(). If running txtimestamp -l 1000, the former
will generate 999 for turkey while the latter 1000.

>
> Also be aware of the subtle distinction between passing OPT_ID_TCP
> along with OPT_ID or not.
>
>