PPPoL2TP: Add more code snippets
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 <samuel.thibault@ens-lyon.org> Acked-by: Tom Parkin <tparkin@katalix.com> Link: https://lore.kernel.org/r/20240217211425.qj576u3jmaa6yidf@begin Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Samuel Thibault
Jakub Kicinski
parent
f796feabb9
commit
6d5c36565c
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@ -386,12 +386,19 @@ Sample userspace code:
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- Create session PPPoX data socket::
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struct sockaddr_pppol2tp sax;
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int fd;
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/* Note, the tunnel socket must be bound already, else it
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* will not be ready
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/* Input: the L2TP tunnel UDP socket `tunnel_fd`, which needs to be
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* bound already (both sockname and peername), otherwise it will not be
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* ready.
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*/
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struct sockaddr_pppol2tp sax;
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int session_fd;
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int ret;
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session_fd = socket(AF_PPPOX, SOCK_DGRAM, PX_PROTO_OL2TP);
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if (session_fd < 0)
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return -errno;
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sax.sa_family = AF_PPPOX;
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sax.sa_protocol = PX_PROTO_OL2TP;
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sax.pppol2tp.fd = tunnel_fd;
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@ -406,12 +413,128 @@ Sample userspace code:
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/* session_fd is the fd of the session's PPPoL2TP socket.
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* tunnel_fd is the fd of the tunnel UDP / L2TPIP socket.
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*/
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fd = connect(session_fd, (struct sockaddr *)&sax, sizeof(sax));
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if (fd < 0 ) {
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ret = connect(session_fd, (struct sockaddr *)&sax, sizeof(sax));
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if (ret < 0 ) {
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close(session_fd);
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return -errno;
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}
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return session_fd;
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L2TP control packets will still be available for read on `tunnel_fd`.
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- Create PPP channel::
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/* Input: the session PPPoX data socket `session_fd` which was created
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* as described above.
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*/
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int ppp_chan_fd;
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int chindx;
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int ret;
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ret = ioctl(session_fd, PPPIOCGCHAN, &chindx);
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if (ret < 0)
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return -errno;
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ppp_chan_fd = open("/dev/ppp", O_RDWR);
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if (ppp_chan_fd < 0)
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return -errno;
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ret = ioctl(ppp_chan_fd, PPPIOCATTCHAN, &chindx);
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if (ret < 0) {
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close(ppp_chan_fd);
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return -errno;
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}
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return ppp_chan_fd;
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LCP PPP frames will be available for read on `ppp_chan_fd`.
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- Create PPP interface::
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/* Input: the PPP channel `ppp_chan_fd` which was created as described
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* above.
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*/
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int ifunit = -1;
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int ppp_if_fd;
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int ret;
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ppp_if_fd = open("/dev/ppp", O_RDWR);
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if (ppp_if_fd < 0)
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return -errno;
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ret = ioctl(ppp_if_fd, PPPIOCNEWUNIT, &ifunit);
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if (ret < 0) {
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close(ppp_if_fd);
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return -errno;
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}
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ret = ioctl(ppp_chan_fd, PPPIOCCONNECT, &ifunit);
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if (ret < 0) {
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close(ppp_if_fd);
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return -errno;
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}
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return ppp_if_fd;
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IPCP/IPv6CP PPP frames will be available for read on `ppp_if_fd`.
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The ppp<ifunit> interface can then be configured as usual with netlink's
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RTM_NEWLINK, RTM_NEWADDR, RTM_NEWROUTE, or ioctl's SIOCSIFMTU, SIOCSIFADDR,
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SIOCSIFDSTADDR, SIOCSIFNETMASK, SIOCSIFFLAGS, or with the `ip` command.
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- Bridging L2TP sessions which have PPP pseudowire types (this is also called
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L2TP tunnel switching or L2TP multihop) is supported by bridging the PPP
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channels of the two L2TP sessions to be bridged::
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/* Input: the session PPPoX data sockets `session_fd1` and `session_fd2`
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* which were created as described further above.
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*/
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int ppp_chan_fd;
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int chindx1;
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int chindx2;
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int ret;
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ret = ioctl(session_fd1, PPPIOCGCHAN, &chindx1);
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if (ret < 0)
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return -errno;
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ret = ioctl(session_fd2, PPPIOCGCHAN, &chindx2);
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if (ret < 0)
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return -errno;
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ppp_chan_fd = open("/dev/ppp", O_RDWR);
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if (ppp_chan_fd < 0)
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return -errno;
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ret = ioctl(ppp_chan_fd, PPPIOCATTCHAN, &chindx1);
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if (ret < 0) {
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close(ppp_chan_fd);
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return -errno;
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}
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ret = ioctl(ppp_chan_fd, PPPIOCBRIDGECHAN, &chindx2);
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close(ppp_chan_fd);
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if (ret < 0)
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return -errno;
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return 0;
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It can be noted that when bridging PPP channels, the PPP session is not locally
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terminated, and no local PPP interface is created. PPP frames arriving on one
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channel are directly passed to the other channel, and vice versa.
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The PPP channel does not need to be kept open. Only the session PPPoX data
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sockets need to be kept open.
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More generally, it is also possible in the same way to e.g. bridge a PPPoL2TP
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PPP channel with other types of PPP channels, such as PPPoE.
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See more details for the PPP side in ppp_generic.rst.
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Old L2TPv2-only API
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-------------------
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