From nobody Fri Dec 27 00:52:09 2024 Received: from sonata.ens-lyon.org (domu-toccata.ens-lyon.fr [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 F386C47A53; Mon, 12 Feb 2024 22:23:47 +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=1707776630; cv=none; b=q+YqUqQk3zsi9z0Hy23YVB7L3zgmemphmG8/W4A6Kun4gkOzg7NMKczWRwn7llYyxLlfxD5y970G3PnCHJcQNyzyayXgG5i7BtFo5o52kAJE0nLa2EmS/Tvzd1zmkBivNdpUC/UyOsrxWD6ssCl2e4Bf0PQ37TP8Wq30aR4v7WA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707776630; c=relaxed/simple; bh=rswK67lRPW2w2mGzLlf2hfF9gf8lba3HfNWGCdYFaro=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition; b=VmFEmJ/VtQZqv3d1CAmrUcMD9R4wWDR5T2pCSvBe23ENLZIxEXGcEBZjqN9KVG/faaUN21GmFE1YFZSm5P2x0cdx0G8qyVOwaewiQGCgOss7vc81u+cjyDBzT4Av2NQIYzFxebouu2ZRkp/2jhYg9zZGAj80cuivvnvsU2ZGkaI= 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 A84B0A02EA; Mon, 12 Feb 2024 23:23:45 +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 IUE8nl6jzjy6; Mon, 12 Feb 2024 23:23:45 +0100 (CET) Received: from begin (aamiens-653-1-111-57.w83-192.abo.wanadoo.fr [83.192.234.57]) (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 51E24A02E8; Mon, 12 Feb 2024 23:23:45 +0100 (CET) Received: from samy by begin with local (Exim 4.97) (envelope-from ) id 1rZeiG-0000000GUJD-3Vc3; Mon, 12 Feb 2024 23:23:44 +0100 Date: Mon, 12 Feb 2024 23:23:44 +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: [PATCHv4] PPPoL2TP: Add more code snippets Message-ID: <20240212222344.xtv233r5sixme32h@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 --- 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 --- a/Documentation/networking/l2tp.rst +++ b/Documentation/networking/l2tp.rst @@ -386,12 +386,17 @@ Sample userspace code: =20 - Create session PPPoX data socket:: =20 + /* Input: the L2TP tunnel UDP socket `tunnel_fd`, which needs to be + * bound already, otherwise it will not 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; @@ -406,11 +411,117 @@ 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 creat= ed as + * described above. */ + + int chindx; + int ppp_chan_fd; + + 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 describ= ed + * above */ + + int ppp_if_fd; + int ifunit =3D -1; + + 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 0; + + 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 session_f= d2 + * which were created as described further above. */ + + int chindx1; + int chindx2; + int ppp_chan_fd; + + 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; + +It can be noted that in this case no PPP interface is needed, and the PPP +channel does not need to be kept open. Only the session PPPoX data socket= s 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. =20 Old L2TPv2-only API -------------------