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=ham 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 7131BC43381 for ; Thu, 28 Mar 2019 01:26:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 373D62082F for ; Thu, 28 Mar 2019 01:26:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="D5KoEZGX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727571AbfC1B0X (ORCPT ); Wed, 27 Mar 2019 21:26:23 -0400 Received: from mail-pg1-f193.google.com ([209.85.215.193]:36875 "EHLO mail-pg1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726108AbfC1B0X (ORCPT ); Wed, 27 Mar 2019 21:26:23 -0400 Received: by mail-pg1-f193.google.com with SMTP id q206so10794964pgq.4; Wed, 27 Mar 2019 18:26:22 -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=zAe9ICsvkGSLzshygvdVHxv+SbIQJKIZLHiGJATHM7Y=; b=D5KoEZGXW8i0DWOIGPv8mWfl14OqxCUO0DImJCtVC5SqT0sGmAUDWqCjz15JvH/U7Y ycScRLoAMyIMJfEwTkIHF3FxobUC/Myqvk1Ftq0xE6jE1ZLpH7fCw89UopJ4/Wa4MYkY L17/PBfWP76rr7VCxCZWpIoCzu8h0q+77hNMlTP1hPktLkvxUcXDK5olE5bIWcQcZJlY N97ZiCjiirrM/+/WRtpT11lw0mSBSZme1DJKpKC2QwJlNQbcOBfxPmtwfQy2recaLtZH WIF8/3RQIK65oh5HKzRSJpfW8JP5Nxt2S1iqeybLOD57f02h+2nTu3awDTGQGefIcDjv futA== 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=zAe9ICsvkGSLzshygvdVHxv+SbIQJKIZLHiGJATHM7Y=; b=smDGY9r5a215nVJ5hqzT2SpWN731Vgns/V2EcNqOEGTYgseXmx65URQQqTCcX0uxj/ e+IR++izB6OrUqOnFLfvkR2M9rOwGPiuda3avgZD+qG2Qk+qi9bq8dQ7tMLJ+aHWQv/t zHO5YRCbvddYKiaHAQjYODjAnc3+KTBklx5crylY9pZAJkOxpNyzJaOkwa6lrPxSZqmp X+CETYXtnXqmGuduITFtubgIQmAMwfEGQXDVlmoJYQF1B9r6IqlLnEyht887QLuo7U+O s0Q5jpuT107oAmV/oll2VspCdxPzs6s1I+ovLxo4MdOowp68Q+I2gyTIfy0mkqkG6VsT fhHw== X-Gm-Message-State: APjAAAWZhQUhRUPUly226g1Eb00lyvo98wQ66bfy2pwMiueRpEOMG++u V01hytib0J/UXJtzVS8vX7A= X-Google-Smtp-Source: APXvYqxJhYlA6FdxuhToFv0ITNHGhCeSIZH1hjDXSmfji4n6afdbF34g34nDt9wRRp8FNules7pc/A== X-Received: by 2002:a65:5303:: with SMTP id m3mr37030900pgq.292.1553736382400; Wed, 27 Mar 2019 18:26:22 -0700 (PDT) Received: from ast-mbp ([2620:10d:c090:180::27f1]) by smtp.gmail.com with ESMTPSA id j20sm29189608pfh.141.2019.03.27.18.26.20 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 27 Mar 2019 18:26:21 -0700 (PDT) Date: Wed, 27 Mar 2019 18:26:18 -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: <20190328012616.exa6q7brzxvcqvnz@ast-mbp> References: <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> <20190327175535.ewpc6a7gpfoxmxys@ast-mbp> <20190327195820.GF7431@mini-arch.hsd1.ca.comcast.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190327195820.GF7431@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 Wed, Mar 27, 2019 at 12:58:20PM -0700, Stanislav Fomichev wrote: > On 03/27, Alexei Starovoitov wrote: > > 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. > For with-skb, nhoff would be zero, and ctx->data would point to > TCI/L3. > For skb-less, ctx->data would point to L2 (DMAC), and nhoff would be > non-zero (TCI/L3 offset). > > If you want, for skb-less case, when calling BPF program we can do the math > ourselves and set ctx->data to data + nhoff, and pass nhoff = 0. > But I'm not sure whether we need to do that; flow dissector is supposed > to look at ctx->data + nhoff, it should not matter what each individual > value is, they only make sense together. My strong preference is to have data to point to L2 in all cases. Semantics of requiring bpf prog to start processing from a tuple (data + nhoff) where both point to random places is very confusing.