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[2604:1380:45e3:2400::1]) by mx.google.com with ESMTPS id n29-20020a63721d000000b005dc97d88896si1943437pgc.729.2024.02.17.13.15.40 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 17 Feb 2024 13:15:41 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel+bounces-70091-ouuuleilei=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1; Authentication-Results: mx.google.com; arc=pass (i=1 spf=pass spfdomain=bounce.ens-lyon.org); spf=pass (google.com: domain of linux-kernel+bounces-70091-ouuuleilei=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) smtp.mailfrom="linux-kernel+bounces-70091-ouuuleilei=gmail.com@vger.kernel.org" Received: from smtp.subspace.kernel.org (wormhole.subspace.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sv.mirrors.kernel.org (Postfix) with ESMTPS id D16B6280CBE for ; Sat, 17 Feb 2024 21:15:40 +0000 (UTC) Received: from localhost.localdomain (localhost.localdomain [127.0.0.1]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 449C47F7D4; Sat, 17 Feb 2024 21:14:39 +0000 (UTC) Received: from sonata.ens-lyon.org (sonata.ens-lyon.org [140.77.166.138]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F20DB7E0F1; Sat, 17 Feb 2024 21:14:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=140.77.166.138 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708204477; cv=none; b=XxY1I4+JDkLl72FZw4SS4pT6k9IjOTGL2spRE+9iOl2BigcyQR9AvKbLpimFlcYNYTun6GLbnHn2aqL3X6MVTXt4t1hPvRi+WhVPg7xQ9/DxyRYuSJR83jXn/S5L89UB0c7y9t8ta2CSE6aVaGEI4/BQbA8N2OIGew94T1sYEVE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708204477; c=relaxed/simple; bh=NtbqxagigOz/KVQq47nlYu3vg2cIX6Adg23k6043HVI=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition; b=DOvWjqr/BuMM7O7DH1ggzwSCCj2F1bOZEKjDp00nO3oaKRaKw/KYBnAhEIoegd1XnpTgGmP5mnVHCCCB8qxPDN8C2zoImTmJwWgvfQoo5vAg8JW7r/2KLmAJVULqxjlFaS4LNZ6cDz6fP0B6UZabFneM0NLm2V6cB/DDcCcLS/g= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ens-lyon.org; spf=pass smtp.mailfrom=bounce.ens-lyon.org; arc=none smtp.client-ip=140.77.166.138 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ens-lyon.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bounce.ens-lyon.org Received: from localhost (localhost [127.0.0.1]) by sonata.ens-lyon.org (Postfix) with ESMTP id 78F0CA029D; Sat, 17 Feb 2024 22:14:26 +0100 (CET) Received: from sonata.ens-lyon.org ([127.0.0.1]) by localhost (sonata.ens-lyon.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 4xRw_zWL_EC4; Sat, 17 Feb 2024 22:14:26 +0100 (CET) Received: from begin (dhcp-3.aquilenet.fr [185.233.100.123]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by sonata.ens-lyon.org (Postfix) with ESMTPSA id CE18BA025D; Sat, 17 Feb 2024 22:14:25 +0100 (CET) Received: from samy by begin with local (Exim 4.97) (envelope-from ) id 1rbS0v-00000000m4h-22Ur; Sat, 17 Feb 2024 22:14:25 +0100 Date: Sat, 17 Feb 2024 22:14:25 +0100 From: Samuel Thibault To: James Chapman , tparkin@katalix.com, edumazet@google.com, gnault@redhat.com Cc: davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, corbet@lwn.net, netdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCHv6] PPPoL2TP: Add more code snippets Message-ID: <20240217211425.qj576u3jmaa6yidf@begin> Mail-Followup-To: Samuel Thibault , James Chapman , tparkin@katalix.com, edumazet@google.com, gnault@redhat.com, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, corbet@lwn.net, netdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline User-Agent: NeoMutt/20170609 (1.8.3) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1791182284728891647 X-GMAIL-MSGID: 1791182284728891647 The existing documentation was not telling that one has to create a PPP channel and a PPP interface to get PPPoL2TP data offloading working. Also, tunnel switching was not mentioned, so that people were thinking it was not supported, while it actually is. Signed-off-by: Samuel Thibault Acked-by: Tom Parkin --- Difference from v1: - follow kernel coding style - check for failures - also mention netlink and ip for configuring the link - fix bridging channels Difference from v2: - fix text alignment Difference from v3: - fix some variables references - explicit inputs of the code snippets - explicit that bridging is supported for l2tp with PPP pseudowire type. - explicit that after bridging only the pppox sockets need to be kept - explicit that bridging can also be done with other types of ppp channels Difference from v4: - Fix coding style - Fix parameter of PPPIOCCONNECT ioctl. - Describe the ppp frame bridging. Difference from v5: - Fix coding style --- Documentation/networking/l2tp.rst | 135 ++++++++++++++++++++++++++++++++++++-- 1 file changed, 129 insertions(+), 6 deletions(-) --- a/Documentation/networking/l2tp.rst +++ b/Documentation/networking/l2tp.rst @@ -386,12 +386,19 @@ Sample userspace code: - Create session PPPoX data socket:: + /* Input: the L2TP tunnel UDP socket `tunnel_fd`, which needs to be + * bound already (both sockname and peername), otherwise it will not be + * ready. + */ + struct sockaddr_pppol2tp sax; - int fd; + int session_fd; + int ret; + + session_fd = socket(AF_PPPOX, SOCK_DGRAM, PX_PROTO_OL2TP); + if (session_fd < 0) + return -errno; - /* Note, the tunnel socket must be bound already, else it - * will not be ready - */ sax.sa_family = AF_PPPOX; sax.sa_protocol = PX_PROTO_OL2TP; sax.pppol2tp.fd = tunnel_fd; @@ -406,12 +413,128 @@ Sample userspace code: /* session_fd is the fd of the session's PPPoL2TP socket. * tunnel_fd is the fd of the tunnel UDP / L2TPIP socket. */ - fd = connect(session_fd, (struct sockaddr *)&sax, sizeof(sax)); - if (fd < 0 ) { + ret = connect(session_fd, (struct sockaddr *)&sax, sizeof(sax)); + if (ret < 0 ) { + close(session_fd); + return -errno; + } + + return session_fd; + +L2TP control packets will still be available for read on `tunnel_fd`. + + - Create PPP channel:: + + /* Input: the session PPPoX data socket `session_fd` which was created + * as described above. + */ + + int ppp_chan_fd; + int chindx; + int ret; + + ret = ioctl(session_fd, PPPIOCGCHAN, &chindx); + if (ret < 0) + return -errno; + + ppp_chan_fd = open("/dev/ppp", O_RDWR); + if (ppp_chan_fd < 0) + return -errno; + + ret = ioctl(ppp_chan_fd, PPPIOCATTCHAN, &chindx); + if (ret < 0) { + close(ppp_chan_fd); return -errno; } + + return ppp_chan_fd; + +LCP PPP frames will be available for read on `ppp_chan_fd`. + + - Create PPP interface:: + + /* Input: the PPP channel `ppp_chan_fd` which was created as described + * above. + */ + + int ifunit = -1; + int ppp_if_fd; + int ret; + + ppp_if_fd = open("/dev/ppp", O_RDWR); + if (ppp_if_fd < 0) + return -errno; + + ret = ioctl(ppp_if_fd, PPPIOCNEWUNIT, &ifunit); + if (ret < 0) { + close(ppp_if_fd); + return -errno; + } + + ret = ioctl(ppp_chan_fd, PPPIOCCONNECT, &ifunit); + if (ret < 0) { + close(ppp_if_fd); + return -errno; + } + + return ppp_if_fd; + +IPCP/IPv6CP PPP frames will be available for read on `ppp_if_fd`. + +The ppp interface can then be configured as usual with netlink's +RTM_NEWLINK, RTM_NEWADDR, RTM_NEWROUTE, or ioctl's SIOCSIFMTU, SIOCSIFADDR, +SIOCSIFDSTADDR, SIOCSIFNETMASK, SIOCSIFFLAGS, or with the `ip` command. + + - Bridging L2TP sessions which have PPP pseudowire types (this is also called + L2TP tunnel switching or L2TP multihop) is supported by bridging the PPP + channels of the two L2TP sessions to be bridged:: + + /* Input: the session PPPoX data sockets `session_fd1` and `session_fd2` + * which were created as described further above. + */ + + int ppp_chan_fd; + int chindx1; + int chindx2; + int ret; + + ret = ioctl(session_fd1, PPPIOCGCHAN, &chindx1); + if (ret < 0) + return -errno; + + ret = ioctl(session_fd2, PPPIOCGCHAN, &chindx2); + if (ret < 0) + return -errno; + + ppp_chan_fd = open("/dev/ppp", O_RDWR); + if (ppp_chan_fd < 0) + return -errno; + + ret = ioctl(ppp_chan_fd, PPPIOCATTCHAN, &chindx1); + if (ret < 0) { + close(ppp_chan_fd); + return -errno; + } + + ret = ioctl(ppp_chan_fd, PPPIOCBRIDGECHAN, &chindx2); + close(ppp_chan_fd); + if (ret < 0) + return -errno; + return 0; +It can be noted that when bridging PPP channels, the PPP session is not locally +terminated, and no local PPP interface is created. PPP frames arriving on one +channel are directly passed to the other channel, and vice versa. + +The PPP channel does not need to be kept open. Only the session PPPoX data +sockets need to be kept open. + +More generally, it is also possible in the same way to e.g. bridge a PPPoL2TP +PPP channel with other types of PPP channels, such as PPPoE. + +See more details for the PPP side in ppp_generic.rst. + Old L2TPv2-only API -------------------