From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [RFC PATCH net-next 0/4] switchdev: avoid duplicate packet forwarding Date: Mon, 15 Jun 2015 16:25:51 -0700 (PDT) Message-ID: <20150615.162551.805611215439524288.davem@davemloft.net> References: <1434218670-43821-1-git-send-email-sfeldma@gmail.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, jiri@resnulli.us, simon.horman@netronome.com, roopa@cumulusnetworks.com, ronen.arad@intel.com, john.r.fastabend@intel.com, andrew@lunn.ch, f.fainelli@gmail.com, linux@roeck-us.net, davidch@broadcom.com, stephen@networkplumber.org To: sfeldma@gmail.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:42449 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750835AbbFOXZx (ORCPT ); Mon, 15 Jun 2015 19:25:53 -0400 In-Reply-To: <1434218670-43821-1-git-send-email-sfeldma@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: From: sfeldma@gmail.com Date: Sat, 13 Jun 2015 11:04:26 -0700 > The switchdev port driver must do two things: > > 1) Generate a fwd_mark for each switch port, using some unique key of the > switch device (and optionally port). This is a one-time operation done > when port's netdev is setup. > > 2) On packet ingress from port, mark the skb with the ingress port's > fwd_mark. If the device supports it, it's useful to only mark skbs > which were already forwarded by the device. If the device does not > support such indication, all skbs can be marked, even if they're > local dst. > > Two new 32-bit fields are added to struct sk_buff and struct netdevice to > hold the fwd_mark. I've wrapped these with CONFIG_NET_SWITCHDEV for now. I > tried using skb->mark for this purpose, but ebtables can overwrite the > skb->mark before the bridge gets it, so that will not work. > > In general, this fwd_mark can be used for any case where a packet is > forwarded by the device and a copy is sent to the CPU, to avoid the kernel > re-forwarding the packet. sFlow is another use-case that comes to mind, > but I haven't explored the details. Generally I'm against adding new fields fo sk_buff but I'm trying to be open minded. :-) About the per-device fwd_mark, if the key attribute is uniqueness, let's just do it right and use something like lib/idr.c to generate truly unique indices at probe time for all devices using this facility. I like that better than having them be unique by a happy accident.