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Message-ID: <0a0f948a-ca0e-4241-8a21-e7c7fc2ea471@linux.dev>
Date: Wed, 13 Mar 2024 14:19:02 -0700
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Subject: Re: [PATCH net-next v4] net: Re-use and set mono_delivery_time bit
 for userspace tstamp packets
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To: "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>,
 Daniel Borkmann <daniel@iogearbox.net>, 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>
From: Martin KaFai Lau <martin.lau@linux.dev>
In-Reply-To: <02363fef-0b5e-4b6c-bad9-db924db230b9@quicinc.com>
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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.