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Subject: Re: [PATCH net-next v4] net: Re-use and set mono_delivery_time bit
 for userspace tstamp packets
To: Martin KaFai Lau <martin.lau@linux.dev>,
 "Abhishek Chauhan (ABC)" <quic_abchauha@quicinc.com>,
 Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc: kernel@quicinc.com, "David S. Miller" <davem@davemloft.net>,
 Eric Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>,
 Paolo Abeni <pabeni@redhat.com>, netdev@vger.kernel.org,
 linux-kernel@vger.kernel.org, Andrew Halaney <ahalaney@redhat.com>,
 Martin KaFai Lau <martin.lau@kernel.org>, bpf <bpf@vger.kernel.org>,
 Alexei Starovoitov <ast@kernel.org>, Andrii Nakryiko <andrii@kernel.org>
References: <20240301201348.2815102-1-quic_abchauha@quicinc.com>
 <2a4cb416-5d95-459d-8c1c-3fb225240363@linux.dev>
 <65f16946cd33e_344ff1294fc@willemb.c.googlers.com.notmuch>
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 <02363fef-0b5e-4b6c-bad9-db924db230b9@quicinc.com>
 <0a0f948a-ca0e-4241-8a21-e7c7fc2ea471@linux.dev>
From: Daniel Borkmann <daniel@iogearbox.net>
Message-ID: <1e419a00-41cf-c760-7912-68b34b74f8d1@iogearbox.net>
Date: Wed, 13 Mar 2024 22:41:44 +0100
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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.