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Miller" , Jakub Kicinski , netdev@vger.kernel.org, Simon Horman , Miroslav Lichvar , richardcochran@gmail.com Subject: Re: [PATCH net] net: fall back to skb_iif for the timestamping pktinfo if_index Date: Mon, 24 Aug 2026 13:55:53 -0300 Message-ID: <178759055328.4181951.10346301845266420247@dnim.dev> In-Reply-To: References: <178746246095.3786864.2262454553798466512@dnim.dev> <178756707212.4073008.8425791726071449399@dnim.dev> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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). 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.