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Date: Thu, 19 May 2022 17:34:37 +0000 From: Vladimir Oltean <vladimir.oltean@....com> To: Florian Fainelli <f.fainelli@...il.com> CC: Maxime Chevallier <maxime.chevallier@...tlin.com>, "davem@...emloft.net" <davem@...emloft.net>, Rob Herring <robh+dt@...nel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, "thomas.petazzoni@...tlin.com" <thomas.petazzoni@...tlin.com>, Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>, Russell King <linux@...linux.org.uk>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, Luka Perkov <luka.perkov@...tura.hr>, Robert Marko <robert.marko@...tura.hr> Subject: Re: [PATCH net-next v2 2/5] net: dsa: add out-of-band tagging protocol On Thu, May 19, 2022 at 10:11:13AM -0700, Florian Fainelli wrote: > unless we somehow manage to put it in the linear portion of > the SKB to avoid using any control buffer or extension. But how? Essentially the DSA master has to look at a packet and determine whether it came from DSA based on something which non-DSA code could not have done. In fact, I'm looking at the calls to skb_reset_mac_{header,len} from net/core/skbuff.c, specifically at VLAN and MPLS, and I believe (but haven't tested) that pushing such headers would also alter skb->mac_len to some value != ETH_HLEN. So simply having the DSA master check whether DSA was there by checking whether skb->mac_len is ETH_HLEN + DSA tag len could easily confuse DSA with some other protocol of same header size.
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