From nobody Fri Dec 27 17:39:46 2024 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) Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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: =20 - Create session PPPoX data socket:: =20 + /* Input: the L2TP tunnel UDP socket `tunnel_fd`, which needs to be + * bound already (both sockname and peername), otherwise it will n= ot be + * ready. + */ + struct sockaddr_pppol2tp sax; - int fd; + int session_fd; + int ret; + + session_fd =3D socket(AF_PPPOX, SOCK_DGRAM, PX_PROTO_OL2TP); + if (session_fd < 0) + return -errno; =20 - /* Note, the tunnel socket must be bound already, else it - * will not be ready - */ sax.sa_family =3D AF_PPPOX; sax.sa_protocol =3D PX_PROTO_OL2TP; sax.pppol2tp.fd =3D 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 =3D connect(session_fd, (struct sockaddr *)&sax, sizeof(sax)); - if (fd < 0 ) { + ret =3D 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 cre= ated + * as described above. + */ + + int ppp_chan_fd; + int chindx; + int ret; + + ret =3D ioctl(session_fd, PPPIOCGCHAN, &chindx); + if (ret < 0) + return -errno; + + ppp_chan_fd =3D open("/dev/ppp", O_RDWR); + if (ppp_chan_fd < 0) + return -errno; + + ret =3D 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 descr= ibed + * above. + */ + + int ifunit =3D -1; + int ppp_if_fd; + int ret; + + ppp_if_fd =3D open("/dev/ppp", O_RDWR); + if (ppp_if_fd < 0) + return -errno; + + ret =3D ioctl(ppp_if_fd, PPPIOCNEWUNIT, &ifunit); + if (ret < 0) { + close(ppp_if_fd); + return -errno; + } + + ret =3D 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 c= alled + L2TP tunnel switching or L2TP multihop) is supported by bridging the P= PP + channels of the two L2TP sessions to be bridged:: + + /* Input: the session PPPoX data sockets `session_fd1` and `sessio= n_fd2` + * which were created as described further above. + */ + + int ppp_chan_fd; + int chindx1; + int chindx2; + int ret; + + ret =3D ioctl(session_fd1, PPPIOCGCHAN, &chindx1); + if (ret < 0) + return -errno; + + ret =3D ioctl(session_fd2, PPPIOCGCHAN, &chindx2); + if (ret < 0) + return -errno; + + ppp_chan_fd =3D open("/dev/ppp", O_RDWR); + if (ppp_chan_fd < 0) + return -errno; + + ret =3D ioctl(ppp_chan_fd, PPPIOCATTCHAN, &chindx1); + if (ret < 0) { + close(ppp_chan_fd); + return -errno; + } + + ret =3D ioctl(ppp_chan_fd, PPPIOCBRIDGECHAN, &chindx2); + close(ppp_chan_fd); + if (ret < 0) + return -errno; + return 0; =20 +It can be noted that when bridging PPP channels, the PPP session is not lo= cally +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 PPPoL= 2TP +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 -------------------