netdev - Re: [PATCH net-next v3 10/14] net-timestamp: add basic support with tskey offset

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Message-ID: <CAL+tcoBHNbHu0i+oLA5inZg=sYXUb4+va0qd-c1TZCQFunk7Dg@mail.gmail.com>
Date: Thu, 31 Oct 2024 14:16:38 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Martin KaFai Lau <martin.lau@...ux.dev>
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, shuah@...nel.org, ykolal@...com, 
	bpf@...r.kernel.org, netdev@...r.kernel.org, 
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v3 10/14] net-timestamp: add basic support with
 tskey offset

On Thu, Oct 31, 2024 at 1:52 PM Martin KaFai Lau <martin.lau@...ux.dev> wrote:
>
> On 10/30/24 7:41 PM, Jason Xing wrote:
>
> >> All that said, while looking at tcp_tx_timestamp() again, there is always
> >> "shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1;". shinfo->tskey can be
> >> used directly as-is by the bpf prog. I think now I am missing why the bpf prog
> >> needs the sk_tskey in the sk?
> >
> > As you said, tcp seqno could be treated as the key, but it leaks the
> > information in TCP layer to users. Please see the commit:
>
> I don't think it is a concern for bpf prog running in the kernel. The sockops
> bpf prog can already read the sk, the skb (which has seqno), and many others.
>
> The bpf prog is not a print-only logic. Only using bpf prog to do raw data
> dumping is not fully utilizing its capability, e.g. data aggregation. The bpf
> prog should aggregate the data first which is to calculate the delay here.

Agree, I forgot BPF is only for admin, so it's a feasible solution. It
saves a lot of energy :)

It looks like the thing is getting simpler and simpler, which could be
mostly taken over by bpf itself at last. Good news!

Thanks,
Jason