Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---
 hw/net/virtio-net.c            | 100 ++++++++++++++++++++++++++++++++-
 include/hw/virtio/virtio-net.h |   2 +
 2 files changed, 101 insertions(+), 1 deletion(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 6b5b5dace3..874e349fee 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -38,6 +38,8 @@
 #include "qapi/qapi-events-migration.h"
 #include "hw/virtio/virtio-access.h"
 #include "migration/misc.h"
+#include "migration/migration.h"
+#include "migration/options.h"
 #include "standard-headers/linux/ethtool.h"
 #include "system/system.h"
 #include "system/replay.h"
@@ -2999,7 +3001,13 @@ static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue)
     n->multiqueue = multiqueue;
     virtio_net_change_num_queues(n, max * 2 + 1);
 
-    virtio_net_set_queue_pairs(n);
+    /*
+     * Called from set_features(0) on reset, when on target we
+     * doesn't have fds yet
+     */
+    if (!n->tap_wait_incoming) {
+        virtio_net_set_queue_pairs(n);
+    }
 }
 
 static int virtio_net_pre_load_queues(VirtIODevice *vdev, uint32_t n)
@@ -3009,6 +3017,19 @@ static int virtio_net_pre_load_queues(VirtIODevice *vdev, uint32_t n)
     return 0;
 }
 
+static int virtio_net_pre_save_device(void *opaque)
+{
+    VirtIONet *n = opaque;
+    int i, r;
+
+    for (i = 0; i < n->curr_queue_pairs; i++) {
+        r = peer_detach(n, i);
+        assert(!r);
+    }
+
+    return 0;
+}
+
 static uint64_t virtio_net_get_features(VirtIODevice *vdev, uint64_t features,
                                         Error **errp)
 {
@@ -3028,6 +3049,11 @@ static uint64_t virtio_net_get_features(VirtIODevice *vdev, uint64_t features,
 
     virtio_add_feature(&features, VIRTIO_NET_F_MAC);
 
+    if (n->tap_wait_incoming) {
+        /* Excessive feature set is OK for early initialization */
+        return features;
+    }
+
     if (!peer_has_vnet_hdr(n)) {
         virtio_clear_feature(&features, VIRTIO_NET_F_CSUM);
         virtio_clear_feature(&features, VIRTIO_NET_F_HOST_TSO4);
@@ -3494,11 +3520,69 @@ static const VMStateDescription vhost_user_net_backend_state = {
     }
 };
 
+static int virtio_net_tap_save(QEMUFile *f, void *pv, size_t size,
+                                     const VMStateField *field,
+                                     JSONWriter *vmdesc)
+{
+    VirtIONet *n = pv;
+    int i;
+
+    for (i = 0; i < n->max_queue_pairs; i++) {
+        NetClientState *nc = qemu_get_subqueue(n->nic, i);
+        assert(nc->peer->info->type == NET_CLIENT_DRIVER_TAP);
+
+        tap_save(nc->peer, f);
+    }
+
+    return 0;
+}
+
+static int virtio_net_tap_load(QEMUFile *f, void *pv, size_t size,
+                                     const VMStateField *field)
+{
+    VirtIONet *n = pv;
+    VirtIODevice *vdev = VIRTIO_DEVICE(n);
+    VirtioDeviceClass *vdc = VIRTIO_DEVICE_GET_CLASS(vdev);
+    Error *local_err = NULL;
+    int i;
+
+    for (i = 0; i < n->max_queue_pairs; i++) {
+        NetClientState *nc = qemu_get_subqueue(n->nic, i);
+        assert(nc->peer->info->type == NET_CLIENT_DRIVER_TAP);
+
+        tap_load(nc->peer, f);
+    }
+
+    peer_test_vnet_hdr(n);
+    n->tap_wait_incoming = false;
+
+    vdev->host_features = vdc->get_features(vdev, vdev->host_features,
+                                            &local_err);
+    if (local_err) {
+        error_report_err(local_err);
+        return -EINVAL;
+    }
+
+    return 0;
+}
+
+static bool virtio_net_is_tap_local(void *opaque, int version_id)
+{
+    VirtIONet *n = opaque;
+    NetClientState *nc;
+
+    nc = qemu_get_queue(n->nic);
+
+    return migrate_local_tap() && nc->peer &&
+        nc->peer->info->type == NET_CLIENT_DRIVER_TAP;
+}
+
 static const VMStateDescription vmstate_virtio_net_device = {
     .name = "virtio-net-device",
     .version_id = VIRTIO_NET_VM_VERSION,
     .minimum_version_id = VIRTIO_NET_VM_VERSION,
     .post_load = virtio_net_post_load_device,
+    .pre_save = virtio_net_pre_save_device,
     .fields = (const VMStateField[]) {
         VMSTATE_UINT8_ARRAY(mac, VirtIONet, ETH_ALEN),
         VMSTATE_STRUCT_POINTER(vqs, VirtIONet,
@@ -3525,6 +3609,15 @@ static const VMStateDescription vmstate_virtio_net_device = {
          * but based on the uint.
          */
         VMSTATE_BUFFER_POINTER_UNSAFE(vlans, VirtIONet, 0, MAX_VLAN >> 3),
+        {
+            .name = "tap",
+            .info = &(const VMStateInfo) {
+                .name = "virtio-net vhost-user backend state",
+                .get = virtio_net_tap_load,
+                .put = virtio_net_tap_save,
+            },
+            .field_exists = virtio_net_is_tap_local,
+        },
         VMSTATE_WITH_TMP(VirtIONet, struct VirtIONetMigTmp,
                          vmstate_virtio_net_has_vnet),
         VMSTATE_UINT8(mac_table.multi_overflow, VirtIONet),
@@ -3954,6 +4047,11 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
         vhost_net_set_config(get_vhost_net(nc->peer),
             (uint8_t *)&netcfg, 0, ETH_ALEN, VHOST_SET_CONFIG_TYPE_FRONTEND);
     }
+
+    if (nc->peer && nc->peer->info->type == NET_CLIENT_DRIVER_TAP) {
+        n->tap_wait_incoming = tap_local_incoming(nc->peer);
+    }
+
     QTAILQ_INIT(&n->rsc_chains);
     n->qdev = dev;
 
diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
index 73fdefc0dc..04ae0e4c06 100644
--- a/include/hw/virtio/virtio-net.h
+++ b/include/hw/virtio/virtio-net.h
@@ -231,6 +231,8 @@ struct VirtIONet {
     struct EBPFRSSContext ebpf_rss;
     uint32_t nr_ebpf_rss_fds;
     char **ebpf_rss_fds;
+
+    bool tap_wait_incoming;
 };
 
 size_t virtio_net_handle_ctrl_iov(VirtIODevice *vdev,
-- 
2.48.1