netdev - Re: [PATCH net-next v2] net: Modify mono_delivery_time with clockid_delivery

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Date: Wed, 28 Feb 2024 19:06:24 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 Abhishek Chauhan <quic_abchauha@...cinc.com>
Cc: kernel@...cinc.com, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, Andrew Halaney <ahalaney@...hat.com>,
 Martin KaFai Lau <martin.lau@...nel.org>
Subject: Re: [PATCH net-next v2] net: Modify mono_delivery_time with
 clockid_delivery_time

On 2/28/24 7:53 AM, Willem de Bruijn wrote:
> Sidenote: with sk_clockid, FQ could detect when skb->tstamp is not
> set in monotonic (i.e., set by SO_TXTIME) and drop the packet or
> ignore the embedded timestamp, warn, etc.

Thanks for cc-ing me. Sorry for the late reply. I just catch up to this thread 
and the v1.

I think it is needed to detect if skb->tstamp is monotonic or not in fq. The 
container (with the veth setup) may use sch_etf while the host usually uses fq 
at the physical NIC and expects monotonic skb->tstamp.

During forward (e.g. by bpf_redirect / ip[6]_forward from a veth to a physical 
NIC), skb_clear_tstamp() only forwards the monotonic skb->tstamp now. While 
sch_etf does check sk_clockid first before using skb->tstamp, fq does not check 
that now.
or fq_packet_beyond_horizon() is enough to catch this clock discrepancy?