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[34.85.207.234]) by smtp.gmail.com with ESMTPSA id 00721157ae682-84ca527e9basm38426117b3.5.2026.08.24.11.35.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Aug 2026 11:35:19 -0700 (PDT) Date: Mon, 24 Aug 2026 14:35:18 -0400 From: Willem de Bruijn To: JR Lanteigne , Willem de Bruijn Cc: Eric Dumazet , Kuniyuki Iwashima , Paolo Abeni , Willem de Bruijn , "David S. Miller" , Jakub Kicinski , netdev@vger.kernel.org, Simon Horman , Miroslav Lichvar , richardcochran@gmail.com Message-ID: In-Reply-To: <178759055328.4181951.10346301845266420247@dnim.dev> References: <178746246095.3786864.2262454553798466512@dnim.dev> <178756707212.4073008.8425791726071449399@dnim.dev> <178759055328.4181951.10346301845266420247@dnim.dev> Subject: Re: [PATCH net] net: fall back to skb_iif for the timestamping pktinfo if_index Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit JR Lanteigne wrote: > Willem de Bruijn wrote: > > It may be possible to detect whether an skb_iif points to a physical > > or aggregate device (e.g., through lower_dev)? If so, then the value > > can still be used in most cases. > > That only guesses less often (tunnels register no lower adjacency). The lower_dev was only an example. There may be other ways to weed out non applicable devices. Like dev->type (ARPHRD_..). Though it may be hard to prove that all cases have been identified and skb_iif can be trusted to come from a physical NIC. Or inverse, iff dev->netdev_ops->ndo_hwtstamp_get is non-NULL. Also not foolproof. vlan_hwtstamp_get is one counterexample. I don't necessarily have an exact answer. But optionally an avenue to explore. > I agree with Miroslav: 0 when the physical interface is unknown. > > The userspace check fixes chrony only; every other consumer of > SCM_TIMESTAMPING_PKTINFO has to rediscover that if_index can be 0 > and grow its own IP_PKTINFO fallback. The kernel is the one place a > fix reaches all of them. > > The gap on cpsw: one napi serves both ports, the driver delivers > with netif_receive_skb() so the id is never set, and it would name > port 1 for every frame if it were. The driver knows the source port > per packet (CPDMA_RX_SOURCE_PORT) and needs a way to hand it to > put_ts_pktinfo(), e.g. via skb_shared_hwtstamps.