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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 6B111C32751 for ; Wed, 7 Aug 2019 12:36:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4B0D8218FD for ; Wed, 7 Aug 2019 12:36:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387690AbfHGMgb (ORCPT ); Wed, 7 Aug 2019 08:36:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54022 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387598AbfHGMg3 (ORCPT ); Wed, 7 Aug 2019 08:36:29 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 617843174654; Wed, 7 Aug 2019 12:36:29 +0000 (UTC) Received: from firesoul.localdomain (ovpn-200-48.brq.redhat.com [10.40.200.48]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0BCE15C258; Wed, 7 Aug 2019 12:36:29 +0000 (UTC) Received: from [10.10.10.1] (localhost [IPv6:::1]) by firesoul.localdomain (Postfix) with ESMTP id 3A6DC3002D560; Wed, 7 Aug 2019 14:36:28 +0200 (CEST) Subject: [bpf-next PATCH 3/3] samples/bpf: xdp_fwd explain bpf_fib_lookup return codes From: Jesper Dangaard Brouer To: netdev@vger.kernel.org, Daniel Borkmann , Alexei Starovoitov Cc: xdp-newbies@vger.kernel.org, a.s.protopopov@gmail.com, dsahern@gmail.com, Jesper Dangaard Brouer Date: Wed, 07 Aug 2019 14:36:28 +0200 Message-ID: <156518138817.5636.3626699603179533211.stgit@firesoul> In-Reply-To: <156518133219.5636.728822418668658886.stgit@firesoul> References: <156518133219.5636.728822418668658886.stgit@firesoul> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Wed, 07 Aug 2019 12:36:29 +0000 (UTC) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Make it clear that this XDP program depend on the network stack to do the ARP resolution. This is connected with the BPF_FIB_LKUP_RET_NO_NEIGH return code from bpf_fib_lookup(). Another common mistake (seen via XDP-tutorial) is that users don't realize that sysctl net.ipv{4,6}.conf.all.forwarding setting is honored by bpf_fib_lookup. Reported-by: Anton Protopopov Signed-off-by: Jesper Dangaard Brouer --- samples/bpf/xdp_fwd_kern.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/samples/bpf/xdp_fwd_kern.c b/samples/bpf/xdp_fwd_kern.c index 4a5ad381ed2a..df11163454e7 100644 --- a/samples/bpf/xdp_fwd_kern.c +++ b/samples/bpf/xdp_fwd_kern.c @@ -103,8 +103,23 @@ static __always_inline int xdp_fwd_flags(struct xdp_md *ctx, u32 flags) fib_params.ifindex = ctx->ingress_ifindex; rc = bpf_fib_lookup(ctx, &fib_params, sizeof(fib_params), flags); - - if (rc == 0) { + /* + * Some rc (return codes) from bpf_fib_lookup() are important, + * to understand how this XDP-prog interacts with network stack. + * + * BPF_FIB_LKUP_RET_NO_NEIGH: + * Even if route lookup was a success, then the MAC-addresses are also + * needed. This is obtained from arp/neighbour table, but if table is + * (still) empty then BPF_FIB_LKUP_RET_NO_NEIGH is returned. To avoid + * doing ARP lookup directly from XDP, then send packet to normal + * network stack via XDP_PASS and expect it will do ARP resolution. + * + * BPF_FIB_LKUP_RET_FWD_DISABLED: + * The bpf_fib_lookup respect sysctl net.ipv{4,6}.conf.all.forwarding + * setting, and will return BPF_FIB_LKUP_RET_FWD_DISABLED if not + * enabled this on ingress device. + */ + if (rc == BPF_FIB_LKUP_RET_SUCCESS) { int *val; /* Verify egress index has been configured as TX-port.