netdev - Re: [PATCH net-next v4] net: Re-use and set mono_delivery

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Date: Wed, 13 Mar 2024 22:41:44 +0100
From: Daniel Borkmann <daniel@...earbox.net>
To: Martin KaFai Lau <martin.lau@...ux.dev>,
 "Abhishek Chauhan (ABC)" <quic_abchauha@...cinc.com>,
 Willem de Bruijn <willemdebruijn.kernel@...il.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>, bpf <bpf@...r.kernel.org>,
 Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>
Subject: Re: [PATCH net-next v4] net: Re-use and set mono_delivery_time bit
 for userspace tstamp packets

On 3/13/24 10:19 PM, Martin KaFai Lau wrote:
> On 3/13/24 1:59 PM, Abhishek Chauhan (ABC) wrote:
>>>> I think all this is crying for another bit in skb to mean user_delivery_time
>>>> (skb->tstamp depends on skb->sk->sk_clockid) while mono_delivery_time is the
>>>> mono time either set by kernel-tcp or bpf.
>>>
>>> It does sound like the approach with least side effects.
>>>
>> Martin and Willem , while we are discussing to use seperate bit per skb to check if its
>> SO_TXTIME from userspace or (rcv) timestamp . I came across two flags used in skbuff
>> called in filter framework
>> @tc_at_ingress: used within tc_classify to distinguish in/egress
>> @from_ingress: packet was redirected from the ingress path
>>
>> Since i believe the above testcase is based on redirecting from ingress to egress part
>> why cant we use these already existing flags ? Please advice
>>
>> I am not completely sure if we can use these flags to solve the bpf problem or not.
> 
> I don't see how they are related. It can tell where a skb is at. It cannot tell what is in skb->tstamp.

+1, if we go that route as per discussion, I'd also prefer clearly encoding delivery
time clock base in skb to avoid ambiguity.