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[Qemu-devel] [PATCH v8] net: L2TPv3 transport


From: anton . ivanov
Subject: [Qemu-devel] [PATCH v8] net: L2TPv3 transport
Date: Sun, 6 Apr 2014 15:22:16 +0100

From: Anton Ivanov <address@hidden>

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.

Signed-off-by: Anton Ivanov <address@hidden>
---
Comments address in this patch:

1. Fixed packet re-xmit on full queue and lack of read_poll
handling noticed by Stephan (mea culpa - when moving back to 
QEMU buffering I forgot to adjust the code for the changed
"drop responsibility"). Performance is now back to where it should
be. 116% of tap+bridge for VM to VM witout TSO/GRO, measured with
iperf and mtu 1500. 

2. Added "belt and braces" cleanup after addrinfo though it probably
is not needed as addrinfo will return NULL on errors so there should be
nothing to dispose off.

 net/Makefile.objs |    1 +
 net/clients.h     |    2 +
 net/l2tpv3.c      |  753 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 net/net.c         |    3 +
 qapi-schema.json  |   60 +++++
 qemu-options.hx   |   82 ++++++
 6 files changed, 901 insertions(+)
 create mode 100644 net/l2tpv3.c

diff --git a/net/Makefile.objs b/net/Makefile.objs
index 4854a14..160214e 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
 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 7793294..bbf177c 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..3a41161
--- /dev/null
+++ b/net/l2tpv3.c
@@ -0,0 +1,753 @@
+/*
+ * 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;
+    }
+
+    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;
+    }
+
+    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;
+
+    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 0a88e68..749d34c 100644
--- a/net/net.c
+++ b/net/net.c
@@ -731,6 +731,9 @@ static int (* const 
net_client_init_fun[NET_CLIENT_OPTIONS_KIND_MAX])(
         [NET_CLIENT_OPTIONS_KIND_BRIDGE]    = net_init_bridge,
 #endif
         [NET_CLIENT_OPTIONS_KIND_HUBPORT]   = net_init_hubport,
+#ifdef CONFIG_LINUX
+        [NET_CLIENT_OPTIONS_KIND_L2TPV3]    = net_init_l2tpv3,
+#endif
 };
 
 
diff --git a/qapi-schema.json b/qapi-schema.json
index 83fa485..aefc478 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -2941,6 +2941,62 @@
     '*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.
@@ -3014,6 +3070,9 @@
 # A discriminated record of network device traits.
 #
 # Since 1.2
+#
+# 'l2tpv3' - since 2.1
+#
 ##
 { 'union': 'NetClientOptions',
   'data': {
@@ -3021,6 +3080,7 @@
     '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 8b94264..e1caf6f 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1395,6 +1395,29 @@ 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"
@@ -1730,6 +1753,65 @@ qemu-system-i386 linux.img \
                  -net socket,mcast=239.192.168.1:1102,localaddr=1.2.3.4
 @end example
 
address@hidden -netdev 
l2tpv3,address@hidden,address@hidden,address@hidden,address@hidden,address@hidden,address@hidden,address@hidden,ipv6][,udp][,cookie64][,counter][,pincounter][,address@hidden,address@hidden,address@hidden
address@hidden -net 
l2tpv3[,address@hidden,address@hidden,address@hidden,address@hidden,address@hidden,address@hidden,address@hidden,address@hidden,ipv6][,udp][,cookie64][,counter][,pincounter][,address@hidden,address@hidden,address@hidden
+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.
+
address@hidden address@hidden
+    source address (mandatory)
address@hidden address@hidden
+    destination address (mandatory)
address@hidden udp
+    select udp encapsulation (default is ip).
address@hidden address@hidden
+    source udp port.
address@hidden address@hidden
+    destination udp port.
address@hidden ipv6
+    force v6, otherwise defaults to v4.
address@hidden address@hidden
address@hidden address@hidden
+    Cookies are a weak form of security in the l2tpv3 specification.
+Their function is mostly to prevent misconfiguration. By default they are 32
+bit.
address@hidden cookie64
+    Set cookie size to 64 bit instead of the default 32
address@hidden counter=off
+    Force a 'cut-down' L2TPv3 with no counter as in
+draft-mkonstan-l2tpext-keyed-ipv6-tunnel-00
address@hidden pincounter=on
+    Work around broken counter handling in peer. This may also help on
+networks which have packet reorder.
address@hidden address@hidden
+    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:
address@hidden
+# 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
+
+
address@hidden example
+
 @item -netdev 
vde,address@hidden,address@hidden,address@hidden,address@hidden,address@hidden
 @item -net vde[,address@hidden,address@hidden,address@hidden 
[,address@hidden,address@hidden,address@hidden
 Connect VLAN @var{n} to PORT @var{n} of a vde switch running on host and
-- 
1.7.10.4




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