net: L2TPv3 transport

This transport allows to connect a QEMU nic to a static Ethernet
over L2TPv3 tunnel. The transport supports all options present
in the Linux kernel implementation. It allows QEMU to connect
to any Linux host running kernel 3.3+, most routers and network
devices as well as other QEMU instances.

[Fixed up net_client_init1() switch statement to support -netdev
--Stefan]

Signed-off-by: Anton Ivanov <antivano@cisco.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

6 files changed, 908 insertions, 0 deletions

diff --git a/net/Makefile.objs b/net/Makefile.objs
index 301f6b6..a06ba59 100644
--- a/net/Makefile.objs
+++ b/net/Makefile.objs
@@ -2,6 +2,7 @@ common-obj-y = net.o queue.o checksum.o util.o hub.o
 common-obj-y += socket.o
 common-obj-y += dump.o
 common-obj-y += eth.o
+common-obj-$(CONFIG_LINUX) += l2tpv3.o
 common-obj-$(CONFIG_POSIX) += tap.o vhost-user.o
 common-obj-$(CONFIG_LINUX) += tap-linux.o
 common-obj-$(CONFIG_WIN32) += tap-win32.o
diff --git a/net/clients.h b/net/clients.h
index 7f3d4ae..2e8feda 100644
--- a/net/clients.h
+++ b/net/clients.h
@@ -47,6 +47,8 @@ int net_init_tap(const NetClientOptions *opts, const char *name,
 int net_init_bridge(const NetClientOptions *opts, const char *name,
                     NetClientState *peer);
 
+int net_init_l2tpv3(const NetClientOptions *opts, const char *name,
+                    NetClientState *peer);
 #ifdef CONFIG_VDE
 int net_init_vde(const NetClientOptions *opts, const char *name,
                  NetClientState *peer);
diff --git a/net/l2tpv3.c b/net/l2tpv3.c
new file mode 100644
index 0000000..528d95b
--- /dev/null
+++ b/net/l2tpv3.c
@@ -0,0 +1,757 @@
+/*
+ * QEMU System Emulator
+ *
+ * Copyright (c) 2003-2008 Fabrice Bellard
+ * Copyright (c) 2012-2014 Cisco Systems
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <linux/ip.h>
+#include <netdb.h>
+#include "config-host.h"
+#include "net/net.h"
+#include "clients.h"
+#include "monitor/monitor.h"
+#include "qemu-common.h"
+#include "qemu/error-report.h"
+#include "qemu/option.h"
+#include "qemu/sockets.h"
+#include "qemu/iov.h"
+#include "qemu/main-loop.h"
+
+
+/* The buffer size needs to be investigated for optimum numbers and
+ * optimum means of paging in on different systems. This size is
+ * chosen to be sufficient to accommodate one packet with some headers
+ */
+
+#define BUFFER_ALIGN sysconf(_SC_PAGESIZE)
+#define BUFFER_SIZE 2048
+#define IOVSIZE 2
+#define MAX_L2TPV3_MSGCNT 64
+#define MAX_L2TPV3_IOVCNT (MAX_L2TPV3_MSGCNT * IOVSIZE)
+
+/* Header set to 0x30000 signifies a data packet */
+
+#define L2TPV3_DATA_PACKET 0x30000
+
+/* IANA-assigned IP protocol ID for L2TPv3 */
+
+#ifndef IPPROTO_L2TP
+#define IPPROTO_L2TP 0x73
+#endif
+
+typedef struct NetL2TPV3State {
+    NetClientState nc;
+    int fd;
+
+    /*
+     * these are used for xmit - that happens packet a time
+     * and for first sign of life packet (easier to parse that once)
+     */
+
+    uint8_t *header_buf;
+    struct iovec *vec;
+
+    /*
+     * these are used for receive - try to "eat" up to 32 packets at a time
+     */
+
+    struct mmsghdr *msgvec;
+
+    /*
+     * peer address
+     */
+
+    struct sockaddr_storage *dgram_dst;
+    uint32_t dst_size;
+
+    /*
+     * L2TPv3 parameters
+     */
+
+    uint64_t rx_cookie;
+    uint64_t tx_cookie;
+    uint32_t rx_session;
+    uint32_t tx_session;
+    uint32_t header_size;
+    uint32_t counter;
+
+    /*
+    * DOS avoidance in error handling
+    */
+
+    bool header_mismatch;
+
+    /*
+     * Ring buffer handling
+     */
+
+    int queue_head;
+    int queue_tail;
+    int queue_depth;
+
+    /*
+     * Precomputed offsets
+     */
+
+    uint32_t offset;
+    uint32_t cookie_offset;
+    uint32_t counter_offset;
+    uint32_t session_offset;
+
+    /* Poll Control */
+
+    bool read_poll;
+    bool write_poll;
+
+    /* Flags */
+
+    bool ipv6;
+    bool udp;
+    bool has_counter;
+    bool pin_counter;
+    bool cookie;
+    bool cookie_is_64;
+
+} NetL2TPV3State;
+
+static int l2tpv3_can_send(void *opaque);
+static void net_l2tpv3_send(void *opaque);
+static void l2tpv3_writable(void *opaque);
+
+static void l2tpv3_update_fd_handler(NetL2TPV3State *s)
+{
+    qemu_set_fd_handler2(s->fd,
+                         s->read_poll ? l2tpv3_can_send : NULL,
+                         s->read_poll ? net_l2tpv3_send     : NULL,
+                         s->write_poll ? l2tpv3_writable : NULL,
+                         s);
+}
+
+static void l2tpv3_read_poll(NetL2TPV3State *s, bool enable)
+{
+    if (s->read_poll != enable) {
+        s->read_poll = enable;
+        l2tpv3_update_fd_handler(s);
+    }
+}
+
+static void l2tpv3_write_poll(NetL2TPV3State *s, bool enable)
+{
+    if (s->write_poll != enable) {
+        s->write_poll = enable;
+        l2tpv3_update_fd_handler(s);
+    }
+}
+
+static void l2tpv3_writable(void *opaque)
+{
+    NetL2TPV3State *s = opaque;
+    l2tpv3_write_poll(s, false);
+    qemu_flush_queued_packets(&s->nc);
+}
+
+static int l2tpv3_can_send(void *opaque)
+{
+    NetL2TPV3State *s = opaque;
+
+    return qemu_can_send_packet(&s->nc);
+}
+
+static void l2tpv3_send_completed(NetClientState *nc, ssize_t len)
+{
+    NetL2TPV3State *s = DO_UPCAST(NetL2TPV3State, nc, nc);
+    l2tpv3_read_poll(s, true);
+}
+
+static void l2tpv3_poll(NetClientState *nc, bool enable)
+{
+    NetL2TPV3State *s = DO_UPCAST(NetL2TPV3State, nc, nc);
+    l2tpv3_write_poll(s, enable);
+    l2tpv3_read_poll(s, enable);
+}
+
+static void l2tpv3_form_header(NetL2TPV3State *s)
+{
+    uint32_t *counter;
+
+    if (s->udp) {
+        stl_be_p((uint32_t *) s->header_buf, L2TPV3_DATA_PACKET);
+    }
+    stl_be_p(
+            (uint32_t *) (s->header_buf + s->session_offset),
+            s->tx_session
+        );
+    if (s->cookie) {
+        if (s->cookie_is_64) {
+            stq_be_p(
+                (uint64_t *)(s->header_buf + s->cookie_offset),
+                s->tx_cookie
+            );
+        } else {
+            stl_be_p(
+                (uint32_t *) (s->header_buf + s->cookie_offset),
+                s->tx_cookie
+            );
+        }
+    }
+    if (s->has_counter) {
+        counter = (uint32_t *)(s->header_buf + s->counter_offset);
+        if (s->pin_counter) {
+            *counter = 0;
+        } else {
+            stl_be_p(counter, ++s->counter);
+        }
+    }
+}
+
+static ssize_t net_l2tpv3_receive_dgram_iov(NetClientState *nc,
+                    const struct iovec *iov,
+                    int iovcnt)
+{
+    NetL2TPV3State *s = DO_UPCAST(NetL2TPV3State, nc, nc);
+
+    struct msghdr message;
+    int ret;
+
+    if (iovcnt > MAX_L2TPV3_IOVCNT - 1) {
+        error_report(
+            "iovec too long %d > %d, change l2tpv3.h",
+            iovcnt, MAX_L2TPV3_IOVCNT
+        );
+        return -1;
+    }
+    l2tpv3_form_header(s);
+    memcpy(s->vec + 1, iov, iovcnt * sizeof(struct iovec));
+    s->vec->iov_base = s->header_buf;
+    s->vec->iov_len = s->offset;
+    message.msg_name = s->dgram_dst;
+    message.msg_namelen = s->dst_size;
+    message.msg_iov = s->vec;
+    message.msg_iovlen = iovcnt + 1;
+    message.msg_control = NULL;
+    message.msg_controllen = 0;
+    message.msg_flags = 0;
+    do {
+        ret = sendmsg(s->fd, &message, 0);
+    } while ((ret == -1) && (errno == EINTR));
+    if (ret > 0) {
+        ret -= s->offset;
+    } else if (ret == 0) {
+        /* belt and braces - should not occur on DGRAM
+        * we should get an error and never a 0 send
+        */
+        ret = iov_size(iov, iovcnt);
+    } else {
+        /* signal upper layer that socket buffer is full */
+        ret = -errno;
+        if (ret == -EAGAIN || ret == -ENOBUFS) {
+            l2tpv3_write_poll(s, true);
+            ret = 0;
+        }
+    }
+    return ret;
+}
+
+static ssize_t net_l2tpv3_receive_dgram(NetClientState *nc,
+                    const uint8_t *buf,
+                    size_t size)
+{
+    NetL2TPV3State *s = DO_UPCAST(NetL2TPV3State, nc, nc);
+
+    struct iovec *vec;
+    struct msghdr message;
+    ssize_t ret = 0;
+
+    l2tpv3_form_header(s);
+    vec = s->vec;
+    vec->iov_base = s->header_buf;
+    vec->iov_len = s->offset;
+    vec++;
+    vec->iov_base = (void *) buf;
+    vec->iov_len = size;
+    message.msg_name = s->dgram_dst;
+    message.msg_namelen = s->dst_size;
+    message.msg_iov = s->vec;
+    message.msg_iovlen = 2;
+    message.msg_control = NULL;
+    message.msg_controllen = 0;
+    message.msg_flags = 0;
+    do {
+        ret = sendmsg(s->fd, &message, 0);
+    } while ((ret == -1) && (errno == EINTR));
+    if (ret > 0) {
+        ret -= s->offset;
+    } else if (ret == 0) {
+        /* belt and braces - should not occur on DGRAM
+        * we should get an error and never a 0 send
+        */
+        ret = size;
+    } else {
+        ret = -errno;
+        if (ret == -EAGAIN || ret == -ENOBUFS) {
+            /* signal upper layer that socket buffer is full */
+            l2tpv3_write_poll(s, true);
+            ret = 0;
+        }
+    }
+    return ret;
+}
+
+static int l2tpv3_verify_header(NetL2TPV3State *s, uint8_t *buf)
+{
+
+    uint32_t *session;
+    uint64_t cookie;
+
+    if ((!s->udp) && (!s->ipv6)) {
+        buf += sizeof(struct iphdr) /* fix for ipv4 raw */;
+    }
+
+    /* we do not do a strict check for "data" packets as per
+    * the RFC spec because the pure IP spec does not have
+    * that anyway.
+    */
+
+    if (s->cookie) {
+        if (s->cookie_is_64) {
+            cookie = ldq_be_p(buf + s->cookie_offset);
+        } else {
+            cookie = ldl_be_p(buf + s->cookie_offset);
+        }
+        if (cookie != s->rx_cookie) {
+            if (!s->header_mismatch) {
+                error_report("unknown cookie id");
+            }
+            return -1;
+        }
+    }
+    session = (uint32_t *) (buf + s->session_offset);
+    if (ldl_be_p(session) != s->rx_session) {
+        if (!s->header_mismatch) {
+            error_report("session mismatch");
+        }
+        return -1;
+    }
+    return 0;
+}
+
+static void net_l2tpv3_process_queue(NetL2TPV3State *s)
+{
+    int size = 0;
+    struct iovec *vec;
+    bool bad_read;
+    int data_size;
+    struct mmsghdr *msgvec;
+
+    /* go into ring mode only if there is a "pending" tail */
+    if (s->queue_depth > 0) {
+        do {
+            msgvec = s->msgvec + s->queue_tail;
+            if (msgvec->msg_len > 0) {
+                data_size = msgvec->msg_len - s->header_size;
+                vec = msgvec->msg_hdr.msg_iov;
+                if ((data_size > 0) &&
+                    (l2tpv3_verify_header(s, vec->iov_base) == 0)) {
+                    vec++;
+                    /* Use the legacy delivery for now, we will
+                     * switch to using our own ring as a queueing mechanism
+                     * at a later date
+                     */
+                    size = qemu_send_packet_async(
+                            &s->nc,
+                            vec->iov_base,
+                            data_size,
+                            l2tpv3_send_completed
+                        );
+                    if (size == 0) {
+                        l2tpv3_read_poll(s, false);
+                    }
+                    bad_read = false;
+                } else {
+                    bad_read = true;
+                    if (!s->header_mismatch) {
+                        /* report error only once */
+                        error_report("l2tpv3 header verification failed");
+                        s->header_mismatch = true;
+                    }
+                }
+            } else {
+                bad_read = true;
+            }
+            s->queue_tail = (s->queue_tail + 1) % MAX_L2TPV3_MSGCNT;
+            s->queue_depth--;
+        } while (
+                (s->queue_depth > 0) &&
+                 qemu_can_send_packet(&s->nc) &&
+                ((size > 0) || bad_read)
+            );
+    }
+}
+
+static void net_l2tpv3_send(void *opaque)
+{
+    NetL2TPV3State *s = opaque;
+    int target_count, count;
+    struct mmsghdr *msgvec;
+
+    /* go into ring mode only if there is a "pending" tail */
+
+    if (s->queue_depth) {
+
+        /* The ring buffer we use has variable intake
+         * count of how much we can read varies - adjust accordingly
+         */
+
+        target_count = MAX_L2TPV3_MSGCNT - s->queue_depth;
+
+        /* Ensure we do not overrun the ring when we have
+         * a lot of enqueued packets
+         */
+
+        if (s->queue_head + target_count > MAX_L2TPV3_MSGCNT) {
+            target_count = MAX_L2TPV3_MSGCNT - s->queue_head;
+        }
+    } else {
+
+        /* we do not have any pending packets - we can use
+        * the whole message vector linearly instead of using
+        * it as a ring
+        */
+
+        s->queue_head = 0;
+        s->queue_tail = 0;
+        target_count = MAX_L2TPV3_MSGCNT;
+    }
+
+    msgvec = s->msgvec + s->queue_head;
+    if (target_count > 0) {
+        do {
+            count = recvmmsg(
+                s->fd,
+                msgvec,
+                target_count, MSG_DONTWAIT, NULL);
+        } while ((count == -1) && (errno == EINTR));
+        if (count < 0) {
+            /* Recv error - we still need to flush packets here,
+             * (re)set queue head to current position
+             */
+            count = 0;
+        }
+        s->queue_head = (s->queue_head + count) % MAX_L2TPV3_MSGCNT;
+        s->queue_depth += count;
+    }
+    net_l2tpv3_process_queue(s);
+}
+
+static void destroy_vector(struct mmsghdr *msgvec, int count, int iovcount)
+{
+    int i, j;
+    struct iovec *iov;
+    struct mmsghdr *cleanup = msgvec;
+    if (cleanup) {
+        for (i = 0; i < count; i++) {
+            if (cleanup->msg_hdr.msg_iov) {
+                iov = cleanup->msg_hdr.msg_iov;
+                for (j = 0; j < iovcount; j++) {
+                    g_free(iov->iov_base);
+                    iov++;
+                }
+                g_free(cleanup->msg_hdr.msg_iov);
+            }
+            cleanup++;
+        }
+        g_free(msgvec);
+    }
+}
+
+static struct mmsghdr *build_l2tpv3_vector(NetL2TPV3State *s, int count)
+{
+    int i;
+    struct iovec *iov;
+    struct mmsghdr *msgvec, *result;
+
+    msgvec = g_malloc(sizeof(struct mmsghdr) * count);
+    result = msgvec;
+    for (i = 0; i < count ; i++) {
+        msgvec->msg_hdr.msg_name = NULL;
+        msgvec->msg_hdr.msg_namelen = 0;
+        iov =  g_malloc(sizeof(struct iovec) * IOVSIZE);
+        msgvec->msg_hdr.msg_iov = iov;
+        iov->iov_base = g_malloc(s->header_size);
+        iov->iov_len = s->header_size;
+        iov++ ;
+        iov->iov_base = qemu_memalign(BUFFER_ALIGN, BUFFER_SIZE);
+        iov->iov_len = BUFFER_SIZE;
+        msgvec->msg_hdr.msg_iovlen = 2;
+        msgvec->msg_hdr.msg_control = NULL;
+        msgvec->msg_hdr.msg_controllen = 0;
+        msgvec->msg_hdr.msg_flags = 0;
+        msgvec++;
+    }
+    return result;
+}
+
+static void net_l2tpv3_cleanup(NetClientState *nc)
+{
+    NetL2TPV3State *s = DO_UPCAST(NetL2TPV3State, nc, nc);
+    qemu_purge_queued_packets(nc);
+    l2tpv3_read_poll(s, false);
+    l2tpv3_write_poll(s, false);
+    if (s->fd > 0) {
+        close(s->fd);
+    }
+    destroy_vector(s->msgvec, MAX_L2TPV3_MSGCNT, IOVSIZE);
+    g_free(s->vec);
+    g_free(s->header_buf);
+    g_free(s->dgram_dst);
+}
+
+static NetClientInfo net_l2tpv3_info = {
+    .type = NET_CLIENT_OPTIONS_KIND_L2TPV3,
+    .size = sizeof(NetL2TPV3State),
+    .receive = net_l2tpv3_receive_dgram,
+    .receive_iov = net_l2tpv3_receive_dgram_iov,
+    .poll = l2tpv3_poll,
+    .cleanup = net_l2tpv3_cleanup,
+};
+
+int net_init_l2tpv3(const NetClientOptions *opts,
+                    const char *name,
+                    NetClientState *peer)
+{
+
+
+    const NetdevL2TPv3Options *l2tpv3;
+    NetL2TPV3State *s;
+    NetClientState *nc;
+    int fd = -1, gairet;
+    struct addrinfo hints;
+    struct addrinfo *result = NULL;
+    char *srcport, *dstport;
+
+    nc = qemu_new_net_client(&net_l2tpv3_info, peer, "l2tpv3", name);
+
+    s = DO_UPCAST(NetL2TPV3State, nc, nc);
+
+    s->queue_head = 0;
+    s->queue_tail = 0;
+    s->header_mismatch = false;
+
+    assert(opts->kind == NET_CLIENT_OPTIONS_KIND_L2TPV3);
+    l2tpv3 = opts->l2tpv3;
+
+    if (l2tpv3->has_ipv6 && l2tpv3->ipv6) {
+        s->ipv6 = l2tpv3->ipv6;
+    } else {
+        s->ipv6 = false;
+    }
+
+    if ((l2tpv3->has_offset) && (l2tpv3->offset > 256)) {
+        error_report("l2tpv3_open : offset must be less than 256 bytes");
+        goto outerr;
+    }
+
+    if (l2tpv3->has_rxcookie || l2tpv3->has_txcookie) {
+        if (l2tpv3->has_rxcookie && l2tpv3->has_txcookie) {
+            s->cookie = true;
+        } else {
+            goto outerr;
+        }
+    } else {
+        s->cookie = false;
+    }
+
+    if (l2tpv3->has_cookie64 || l2tpv3->cookie64) {
+        s->cookie_is_64  = true;
+    } else {
+        s->cookie_is_64  = false;
+    }
+
+    if (l2tpv3->has_udp && l2tpv3->udp) {
+        s->udp = true;
+        if (!(l2tpv3->has_srcport && l2tpv3->has_dstport)) {
+            error_report("l2tpv3_open : need both src and dst port for udp");
+            goto outerr;
+        } else {
+            srcport = l2tpv3->srcport;
+            dstport = l2tpv3->dstport;
+        }
+    } else {
+        s->udp = false;
+        srcport = NULL;
+        dstport = NULL;
+    }
+
+
+    s->offset = 4;
+    s->session_offset = 0;
+    s->cookie_offset = 4;
+    s->counter_offset = 4;
+
+    s->tx_session = l2tpv3->txsession;
+    if (l2tpv3->has_rxsession) {
+        s->rx_session = l2tpv3->rxsession;
+    } else {
+        s->rx_session = s->tx_session;
+    }
+
+    if (s->cookie) {
+        s->rx_cookie = l2tpv3->rxcookie;
+        s->tx_cookie = l2tpv3->txcookie;
+        if (s->cookie_is_64 == true) {
+            /* 64 bit cookie */
+            s->offset += 8;
+            s->counter_offset += 8;
+        } else {
+            /* 32 bit cookie */
+            s->offset += 4;
+            s->counter_offset += 4;
+        }
+    }
+
+    memset(&hints, 0, sizeof(hints));
+
+    if (s->ipv6) {
+        hints.ai_family = AF_INET6;
+    } else {
+        hints.ai_family = AF_INET;
+    }
+    if (s->udp) {
+        hints.ai_socktype = SOCK_DGRAM;
+        hints.ai_protocol = 0;
+        s->offset += 4;
+        s->counter_offset += 4;
+        s->session_offset += 4;
+        s->cookie_offset += 4;
+    } else {
+        hints.ai_socktype = SOCK_RAW;
+        hints.ai_protocol = IPPROTO_L2TP;
+    }
+
+    gairet = getaddrinfo(l2tpv3->src, srcport, &hints, &result);
+
+    if ((gairet != 0) || (result == NULL)) {
+        error_report(
+            "l2tpv3_open : could not resolve src, errno = %s",
+            gai_strerror(gairet)
+        );
+        goto outerr;
+    }
+    fd = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
+    if (fd == -1) {
+        fd = -errno;
+        error_report("l2tpv3_open : socket creation failed, errno = %d", -fd);
+        freeaddrinfo(result);
+        goto outerr;
+    }
+    if (bind(fd, (struct sockaddr *) result->ai_addr, result->ai_addrlen)) {
+        error_report("l2tpv3_open :  could not bind socket err=%i", errno);
+        goto outerr;
+    }
+    if (result) {
+        freeaddrinfo(result);
+    }
+
+    memset(&hints, 0, sizeof(hints));
+
+    if (s->ipv6) {
+        hints.ai_family = AF_INET6;
+    } else {
+        hints.ai_family = AF_INET;
+    }
+    if (s->udp) {
+        hints.ai_socktype = SOCK_DGRAM;
+        hints.ai_protocol = 0;
+    } else {
+        hints.ai_socktype = SOCK_RAW;
+        hints.ai_protocol = IPPROTO_L2TP;
+    }
+
+    result = NULL;
+    gairet = getaddrinfo(l2tpv3->dst, dstport, &hints, &result);
+    if ((gairet != 0) || (result == NULL)) {
+        error_report(
+            "l2tpv3_open : could not resolve dst, error = %s",
+            gai_strerror(gairet)
+        );
+        goto outerr;
+    }
+
+    s->dgram_dst = g_malloc(sizeof(struct sockaddr_storage));
+    memset(s->dgram_dst, '\0' , sizeof(struct sockaddr_storage));
+    memcpy(s->dgram_dst, result->ai_addr, result->ai_addrlen);
+    s->dst_size = result->ai_addrlen;
+
+    if (result) {
+        freeaddrinfo(result);
+    }
+
+    if (l2tpv3->has_counter && l2tpv3->counter) {
+        s->has_counter = true;
+        s->offset += 4;
+    } else {
+        s->has_counter = false;
+    }
+
+    if (l2tpv3->has_pincounter && l2tpv3->pincounter) {
+        s->has_counter = true;  /* pin counter implies that there is counter */
+        s->pin_counter = true;
+    } else {
+        s->pin_counter = false;
+    }
+
+    if (l2tpv3->has_offset) {
+        /* extra offset */
+        s->offset += l2tpv3->offset;
+    }
+
+    if ((s->ipv6) || (s->udp)) {
+        s->header_size = s->offset;
+    } else {
+        s->header_size = s->offset + sizeof(struct iphdr);
+    }
+
+    s->msgvec = build_l2tpv3_vector(s, MAX_L2TPV3_MSGCNT);
+    s->vec = g_malloc(sizeof(struct iovec) * MAX_L2TPV3_IOVCNT);
+    s->header_buf = g_malloc(s->header_size);
+
+    qemu_set_nonblock(fd);
+
+    s->fd = fd;
+    s->counter = 0;
+
+    l2tpv3_read_poll(s, true);
+
+    snprintf(s->nc.info_str, sizeof(s->nc.info_str),
+             "l2tpv3: connected");
+    return 0;
+outerr:
+    qemu_del_net_client(nc);
+    if (fd > 0) {
+        close(fd);
+    }
+    if (result) {
+        freeaddrinfo(result);
+    }
+    return -1;
+}
+
diff --git a/net/net.c b/net/net.c
index 3dac29b..e636071 100644
--- a/net/net.c
+++ b/net/net.c
@@ -806,6 +806,9 @@ static int (* const net_client_init_fun[NET_CLIENT_OPTIONS_KIND_MAX])(
 #ifdef CONFIG_VHOST_NET_USED
         [NET_CLIENT_OPTIONS_KIND_VHOST_USER] = net_init_vhost_user,
 #endif
+#ifdef CONFIG_LINUX
+        [NET_CLIENT_OPTIONS_KIND_L2TPV3]    = net_init_l2tpv3,
+#endif
 };
 
 
@@ -842,6 +845,9 @@ static int net_client_init1(const void *object, int is_netdev, Error **errp)
 #ifdef CONFIG_VHOST_NET_USED
         case NET_CLIENT_OPTIONS_KIND_VHOST_USER:
 #endif
+#ifdef CONFIG_LINUX
+        case NET_CLIENT_OPTIONS_KIND_L2TPV3:
+#endif
             break;
 
         default:
diff --git a/qapi-schema.json b/qapi-schema.json
index e7727a1..0000372 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -2040,6 +2040,62 @@
     '*udp':       'str' } }
 
 ##
+# @NetdevL2TPv3Options
+#
+# Connect the VLAN to Ethernet over L2TPv3 Static tunnel
+#
+# @src: source address
+#
+# @dst: destination address
+#
+# @srcport: #optional source port - mandatory for udp, optional for ip
+#
+# @dstport: #optional destination port - mandatory for udp, optional for ip
+#
+# @ipv6: #optional - force the use of ipv6
+#
+# @udp: #optional - use the udp version of l2tpv3 encapsulation
+#
+# @cookie64: #optional - use 64 bit coookies
+#
+# @counter: #optional have sequence counter
+#
+# @pincounter: #optional pin sequence counter to zero -
+#              workaround for buggy implementations or
+#              networks with packet reorder
+#
+# @txcookie: #optional 32 or 64 bit transmit cookie
+#
+# @rxcookie: #optional 32 or 64 bit receive cookie
+#
+# @txsession: 32 bit transmit session
+#
+# @rxsession: #optional 32 bit receive session - if not specified
+#             set to the same value as transmit
+#
+# @offset: #optional additional offset - allows the insertion of
+#          additional application-specific data before the packet payload
+#
+# Since 2.1
+##
+{ 'type': 'NetdevL2TPv3Options',
+  'data': {
+    'src':          'str',
+    'dst':          'str',
+    '*srcport':     'str',
+    '*dstport':     'str',
+    '*ipv6':        'bool',
+    '*udp':         'bool',
+    '*cookie64':    'bool',
+    '*counter':     'bool',
+    '*pincounter':  'bool',
+    '*txcookie':    'uint64',
+    '*rxcookie':    'uint64',
+    'txsession':    'uint32',
+    '*rxsession':   'uint32',
+    '*offset':      'uint32' } }
+
+##
 # @NetdevVdeOptions
 #
 # Connect the VLAN to a vde switch running on the host.
@@ -2150,6 +2206,9 @@
 # A discriminated record of network device traits.
 #
 # Since 1.2
+#
+# 'l2tpv3' - since 2.1
+#
 ##
 { 'union': 'NetClientOptions',
   'data': {
@@ -2157,6 +2216,7 @@
     'nic':      'NetLegacyNicOptions',
     'user':     'NetdevUserOptions',
     'tap':      'NetdevTapOptions',
+    'l2tpv3':   'NetdevL2TPv3Options',
     'socket':   'NetdevSocketOptions',
     'vde':      'NetdevVdeOptions',
     'dump':     'NetdevDumpOptions',
diff --git a/qemu-options.hx b/qemu-options.hx
index ff76ad4..9e54686 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1433,6 +1433,29 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
     "                (default=" DEFAULT_BRIDGE_INTERFACE ") using the program 'helper'\n"
     "                (default=" DEFAULT_BRIDGE_HELPER ")\n"
 #endif
+#ifdef __linux__
+    "-net l2tpv3[,vlan=n][,name=str],src=srcaddr,dst=dstaddr[,srcport=srcport][,dstport=dstport],txsession=txsession[,rxsession=rxsession][,ipv6=on/off][,udp=on/off][,cookie64=on/off][,counter][,pincounter][,txcookie=txcookie][,rxcookie=rxcookie][,offset=offset]\n"
+    "                connect the VLAN to an Ethernet over L2TPv3 pseudowire\n"
+    "                Linux kernel 3.3+ as well as most routers can talk\n"
+    "                L2TPv3. This transport allows to connect a VM to a VM,\n"
+    "                VM to a router and even VM to Host. It is a nearly-universal\n"
+    "                standard (RFC3391). Note - this implementation uses static\n"
+    "                pre-configured tunnels (same as the Linux kernel).\n"
+    "                use 'src=' to specify source address\n"
+    "                use 'dst=' to specify destination address\n"
+    "                use 'udp=on' to specify udp encapsulation\n"
+    "                use 'dstport=' to specify destination udp port\n"
+    "                use 'dstport=' to specify destination udp port\n"
+    "                use 'ipv6=on' to force v6\n"
+    "                L2TPv3 uses cookies to prevent misconfiguration as\n"
+    "                well as a weak security measure\n"
+    "                use 'rxcookie=0x012345678' to specify a rxcookie\n"
+    "                use 'txcookie=0x012345678' to specify a txcookie\n"
+    "                use 'cookie64=on' to set cookie size to 64 bit, otherwise 32\n"
+    "                use 'counter=off' to force a 'cut-down' L2TPv3 with no counter\n"
+    "                use 'pincounter=on' to work around broken counter handling in peer\n"
+    "                use 'offset=X' to add an extra offset between header and data\n"
+#endif
     "-net socket[,vlan=n][,name=str][,fd=h][,listen=[host]:port][,connect=host:port]\n"
     "                connect the vlan 'n' to another VLAN using a socket connection\n"
     "-net socket[,vlan=n][,name=str][,fd=h][,mcast=maddr:port[,localaddr=addr]]\n"
@@ -1778,6 +1801,65 @@ qemu-system-i386 linux.img \
                  -net socket,mcast=239.192.168.1:1102,localaddr=1.2.3.4
 @end example
 
+@item -netdev l2tpv3,id=@var{id},src=@var{srcaddr},dst=@var{dstaddr}[,srcport=@var{srcport}][,dstport=@var{dstport}],txsession=@var{txsession}[,rxsession=@var{rxsession}][,ipv6][,udp][,cookie64][,counter][,pincounter][,txcookie=@var{txcookie}][,rxcookie=@var{rxcookie}][,offset=@var{offset}]
+@item -net l2tpv3[,vlan=@var{n}][,name=@var{name}],src=@var{srcaddr},dst=@var{dstaddr}[,srcport=@var{srcport}][,dstport=@var{dstport}],txsession=@var{txsession}[,rxsession=@var{rxsession}][,ipv6][,udp][,cookie64][,counter][,pincounter][,txcookie=@var{txcookie}][,rxcookie=@var{rxcookie}][,offset=@var{offset}]
+Connect VLAN @var{n} to L2TPv3 pseudowire. L2TPv3 (RFC3391) is a popular
+protocol to transport Ethernet (and other Layer 2) data frames between
+two systems. It is present in routers, firewalls and the Linux kernel
+(from version 3.3 onwards).
+
+This transport allows a VM to communicate to another VM, router or firewall directly.
+
+@item src=@var{srcaddr}
+    source address (mandatory)
+@item dst=@var{dstaddr}
+    destination address (mandatory)
+@item udp
+    select udp encapsulation (default is ip).
+@item srcport=@var{srcport}
+    source udp port.
+@item dstport=@var{dstport}
+    destination udp port.
+@item ipv6
+    force v6, otherwise defaults to v4.
+@item rxcookie=@var{rxcookie}
+@item txcookie=@var{txcookie}
+    Cookies are a weak form of security in the l2tpv3 specification.
+Their function is mostly to prevent misconfiguration. By default they are 32
+bit.
+@item cookie64
+    Set cookie size to 64 bit instead of the default 32
+@item counter=off
+    Force a 'cut-down' L2TPv3 with no counter as in
+draft-mkonstan-l2tpext-keyed-ipv6-tunnel-00
+@item pincounter=on
+    Work around broken counter handling in peer. This may also help on
+networks which have packet reorder.
+@item offset=@var{offset}
+    Add an extra offset between header and data
+
+For example, to attach a VM running on host 4.3.2.1 via L2TPv3 to the bridge br-lan
+on the remote Linux host 1.2.3.4:
+@example
+# Setup tunnel on linux host using raw ip as encapsulation
+# on 1.2.3.4
+ip l2tp add tunnel remote 4.3.2.1 local 1.2.3.4 tunnel_id 1 peer_tunnel_id 1 \
+    encap udp udp_sport 16384 udp_dport 16384
+ip l2tp add session tunnel_id 1 name vmtunnel0 session_id \
+    0xFFFFFFFF peer_session_id 0xFFFFFFFF
+ifconfig vmtunnel0 mtu 1500
+ifconfig vmtunnel0 up
+brctl addif br-lan vmtunnel0
+
+
+# on 4.3.2.1
+# launch QEMU instance - if your network has reorder or is very lossy add ,pincounter
+
+qemu-system-i386 linux.img -net nic -net l2tpv3,src=4.2.3.1,dst=1.2.3.4,udp,srcport=16384,dstport=16384,rxsession=0xffffffff,txsession=0xffffffff,counter
+
+
+@end example
+
 @item -netdev vde,id=@var{id}[,sock=@var{socketpath}][,port=@var{n}][,group=@var{groupname}][,mode=@var{octalmode}]
 @item -net vde[,vlan=@var{n}][,name=@var{name}][,sock=@var{socketpath}] [,port=@var{n}][,group=@var{groupname}][,mode=@var{octalmode}]
 Connect VLAN @var{n} to PORT @var{n} of a vde switch running on host and