From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_PASS,USER_AGENT_NEOMUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DD843C10F00 for ; Wed, 27 Mar 2019 17:55:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AE6492075C for ; Wed, 27 Mar 2019 17:55:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="bzFQxrPQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728546AbfC0Rzl (ORCPT ); Wed, 27 Mar 2019 13:55:41 -0400 Received: from mail-pf1-f194.google.com ([209.85.210.194]:44305 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727806AbfC0Rzk (ORCPT ); Wed, 27 Mar 2019 13:55:40 -0400 Received: by mail-pf1-f194.google.com with SMTP id y13so3936948pfm.11; Wed, 27 Mar 2019 10:55:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=0TxqlfD0mceKqEiSvYKpcG/DcF99ig5YsnMn2Knmhjc=; b=bzFQxrPQ6BJ0HHlenz2ObGdYaF+bFsOc+Wfj7Kiw6O1vmhpM3waPKac0rGdjnOIDBb fTyXGuMAlIDZTqpCWvz4yUqPM6pULwi9dMoDFv18CWhYYIjjAq4BqEYSC8RPvL6tjEIx epCR97byI+aJWb64zo/xIEad/XfpfVwAGqivuuMhRS3ChstA+t2FXUBBobuyEyCeoepy shaMoORFj0I2EsyuN1LHng+vkwf0OIZCU0sD+A7lWFUDt6WCFpvvp041AHXVP8e6s/aC yui722eBbtdyLBotwettslKw+o/NYS9kpzicLbE2er3vIfKET6VuWuXAlToUuJTEa7aB Kmzw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=0TxqlfD0mceKqEiSvYKpcG/DcF99ig5YsnMn2Knmhjc=; b=g5y/pClFll4gAr+l1NwkL8N22sZ8aDpnXgwEkS8nvuNF+C/z7n4Jhpen/d6opbeDlp XjMY13cYqkmoHrsdAQmj70+oa1+2nIeZO1G4YAHgV38uWSGTkau9MGeDSpvvq5jpSK2A 6b9RxYYK9XahSUCYBzOe7SPvlEf5ZuHRWfL7f5pbGS8cf6yJxzPhwYG6lVaYvtabeV67 3p4Xoy0sLSDhDWvVlxP9eNfGzvZZtPlxvELBYWNwoLvK1FJGVHQPXAAYS5i4SpylxBs5 CQuGWG39RFLymeU2JMBcOOAcAvRbfNqYyCqU6AOoL9yBOI2IHeLpFJh4gYGiIvn4LBcs yC6Q== X-Gm-Message-State: APjAAAW6n2ToDyuWMfnsLigGT59JJH5OZD/867Ka0FyWXpFdLiC+U0lm 0E91bnNZL7+jT+w7gfsQagc= X-Google-Smtp-Source: APXvYqy/WnTmsGukG0LbWnVmRx2lTraqg9DAzW4taNb6z87su9dhwtxAX8+RPGJAfBw6LBY7qND6XA== X-Received: by 2002:a65:5343:: with SMTP id w3mr18160428pgr.232.1553709339854; Wed, 27 Mar 2019 10:55:39 -0700 (PDT) Received: from ast-mbp ([2620:10d:c090:180::ca40]) by smtp.gmail.com with ESMTPSA id i16sm32673048pgk.51.2019.03.27.10.55.38 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 27 Mar 2019 10:55:38 -0700 (PDT) Date: Wed, 27 Mar 2019 10:55:37 -0700 From: Alexei Starovoitov To: Stanislav Fomichev Cc: Willem de Bruijn , Stanislav Fomichev , Network Development , bpf , David Miller , Alexei Starovoitov , Daniel Borkmann , Simon Horman , Willem de Bruijn , Petar Penkov Subject: Re: [RFC bpf-next v3 6/8] flow_dissector: handle no-skb use case Message-ID: <20190327175535.ewpc6a7gpfoxmxys@ast-mbp> References: <20190326003517.fuqb4mqsbqq4mtk5@ast-mbp> <20190326164529.GB7431@mini-arch.hsd1.ca.comcast.net> <20190326174802.jnhvtdephykfj6ku@ast-mbp> <20190326181719.GC7431@mini-arch.hsd1.ca.comcast.net> <20190326183011.jly4j3s332yohrj5@ast-mbp> <20190326185456.GD7431@mini-arch.hsd1.ca.comcast.net> <20190327014121.p45cblrgqgdyiu6z@ast-mbp> <20190327024421.GE7431@mini-arch.hsd1.ca.comcast.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190327024421.GE7431@mini-arch.hsd1.ca.comcast.net> User-Agent: NeoMutt/20180223 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Mar 26, 2019 at 07:44:21PM -0700, Stanislav Fomichev wrote: > On 03/26, Alexei Starovoitov wrote: > > On Tue, Mar 26, 2019 at 11:54:56AM -0700, Stanislav Fomichev wrote: > > > On 03/26, Alexei Starovoitov wrote: > > > > On Tue, Mar 26, 2019 at 11:17:19AM -0700, Stanislav Fomichev wrote: > > > > > On 03/26, Alexei Starovoitov wrote: > > > > > > On Tue, Mar 26, 2019 at 10:52 AM Willem de Bruijn > > > > > > wrote: > > > > > > > The BPF flow dissector should work the same. It is fine to pass the > > > > > > > data including ethernet header, but parsing can start at nhoff with > > > > > > > proto explicitly passed. > > > > > > > > > > > > > > We should not assume Ethernet link layer. > > > > > > > > > > > > then skb-less dissector has to be different program type > > > > > > because semantics are different. > > > > > The semantics are the same as for c-based __skb_flow_dissect. > > > > > We just need to pass nhoff and proto that has been passed to > > > > > __skb_flow_dissect to the bpf program. In case of with-skb, > > > > > take this initial data from skb, like __skb_flow_dissect does (and don't > > > > > ask BPF program to do it essentially): > > > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/tree/net/core/flow_dissector.c#n763 > > > > > > > > > > I was thinking of passing proto as flow_keys->n_proto and we already > > > > > pass flow_keys->nhoff, so no need to do anything for it. With that, > > > > > BPF program doesn't need to look into skb and can parse optional vlan > > > > > and L3+ headers. The same way __skb_flow_dissect does that. > > > > > > > > makes sense. then I'd also prefer for proto to be in flow_keys to > > > > high light this difference. > > > Maybe rename existing flow_keys->n_proto to flow_keys->proto? > > > That would match __skb_flow_dissect and remove ambiguity with both proto > > > and n_proto in flow_keys. > > > > disabling useless fields in ctx is one thing, since probability of breaking users > > is low, but renaming n_proto is imo too much. > > > > > > may be add vlan_proto/present/tci there as well? > > > > At least on the kernel side ctx rewriter will be the same for w/ & w/o skb cases. > > > Why do you think we need them? My understanding was that when > > > skb_vlan_tag_present(skb) (or skb->vlan_present) returns true, that means > > > that vlan info has been already parsed out of the packet and stored in > > > the vlan_tci/vlan_proto (where vlan_proto is 8021Q/8021AD); skb data > > > points to proper L3 header. > > > > > > If that's correct, BPF flow dissector should not care about that. For > > > example, look at how C-based flow dissector does that: > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/tree/net/core/flow_dissector.c#n944 > > > > > > If skb_vlan_tag_present(skb) returns true, we set proto to skb->protocol > > > and move on. > > > > > > But, we would need vlan_proto/present/tci in the flow_keys in the future. > > > We don't currently return parsed vlan data from the BPF flow dissector. > > > But it feels like it's getting into bpf-next territory :-) > > > > Whether ctx->data points to L2 or L3 is uapi regardless whether > > progs/bpf_flow.c is relying on that or not. > > So far I think you're saying that in all three cases: > > no-skb, skb befor rfs, skb after rfs ctx->data points to L2, right? > > This has to be preserved. > It points to L3 (or vlan). And this will be preserved, I have no > intention to change that. > > Just to make sure, we are on the same page, here is what > __skb_flow_dissect (and BPF prog) is seeing in nhoff. > > NO-VLAN is always the same for both with-skb/no-skb: > +----+----+-----+--+ > |DMAC|SMAC|PROTO|L3| > +----+----+-----+--+ > ^ > +-- nhoff > proto = PROTO > > VLAN no-skb (eth_get_headlen): > +----+----+----+---+-----+--+ > |DMAC|SMAC|TPID|TCI|PROTO|L3| > +----+----+----+---+-----+--+ > ^ > +-- nhoff > proto = TPID where ctx->data will point to ? These nhoff differences are fine. I want to make sure that ctx->data is the same for all. > And in the last case, networking stack sets: > * skb->vlan_present to true > * skb->vlan_proto to TPID > * skb->vlan_tci to TCI > * skb->protocol to PROTO > * pulls vlan header, so skb->data points to L3 header then skb-less should point after L2 as well or point to L2 for all. I'm arguing about it because early on during tc-bpf days we had this discrepancy and it caused issues. Thankfully we addressed it before it became long term headache.