virtio-net: vhost-user: Implement internal migration

Add support of VHOST_USER_PROTOCOL_F_DEVICE_STATE in virtio-net
with vhost-user backend.

Cc: Hanna Czenczek <hreitz@redhat.com>
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Message-Id: <20250115135044.799698-3-lvivier@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/net/virtio-net.c

@@ -3337,6 +3337,117 @@ static const VMStateDescription vmstate_virtio_net_rss = {
     },
 };
 
+static struct vhost_dev *virtio_net_get_vhost(VirtIODevice *vdev)
+{
+    VirtIONet *n = VIRTIO_NET(vdev);
+    NetClientState *nc;
+    struct vhost_net *net;
+
+    if (!n->nic) {
+        return NULL;
+    }
+
+    nc = qemu_get_queue(n->nic);
+    if (!nc) {
+        return NULL;
+    }
+
+    net = get_vhost_net(nc->peer);
+    if (!net) {
+        return NULL;
+    }
+
+    return &net->dev;
+}
+
+static int vhost_user_net_save_state(QEMUFile *f, void *pv, size_t size,
+                                     const VMStateField *field,
+                                     JSONWriter *vmdesc)
+{
+    VirtIONet *n = pv;
+    VirtIODevice *vdev = VIRTIO_DEVICE(n);
+    struct vhost_dev *vhdev;
+    Error *local_error = NULL;
+    int ret;
+
+    vhdev = virtio_net_get_vhost(vdev);
+    if (vhdev == NULL) {
+        error_reportf_err(local_error,
+                          "Error getting vhost back-end of %s device %s: ",
+                          vdev->name, vdev->parent_obj.canonical_path);
+        return -1;
+    }
+
+    ret = vhost_save_backend_state(vhdev, f, &local_error);
+    if (ret < 0) {
+        error_reportf_err(local_error,
+                          "Error saving back-end state of %s device %s: ",
+                          vdev->name, vdev->parent_obj.canonical_path);
+        return ret;
+    }
+
+    return 0;
+}
+
+static int vhost_user_net_load_state(QEMUFile *f, void *pv, size_t size,
+                                     const VMStateField *field)
+{
+    VirtIONet *n = pv;
+    VirtIODevice *vdev = VIRTIO_DEVICE(n);
+    struct vhost_dev *vhdev;
+    Error *local_error = NULL;
+    int ret;
+
+    vhdev = virtio_net_get_vhost(vdev);
+    if (vhdev == NULL) {
+        error_reportf_err(local_error,
+                          "Error getting vhost back-end of %s device %s: ",
+                          vdev->name, vdev->parent_obj.canonical_path);
+        return -1;
+    }
+
+    ret = vhost_load_backend_state(vhdev, f, &local_error);
+    if (ret < 0) {
+        error_reportf_err(local_error,
+                          "Error loading  back-end state of %s device %s: ",
+                          vdev->name, vdev->parent_obj.canonical_path);
+        return ret;
+    }
+
+    return 0;
+}
+
+static bool vhost_user_net_is_internal_migration(void *opaque)
+{
+    VirtIONet *n = opaque;
+    VirtIODevice *vdev = VIRTIO_DEVICE(n);
+    struct vhost_dev *vhdev;
+
+    vhdev = virtio_net_get_vhost(vdev);
+    if (vhdev == NULL) {
+        return false;
+    }
+
+    return vhost_supports_device_state(vhdev);
+}
+
+static const VMStateDescription vhost_user_net_backend_state = {
+    .name = "virtio-net-device/backend",
+    .version_id = 0,
+    .needed = vhost_user_net_is_internal_migration,
+    .fields = (const VMStateField[]) {
+        {
+            .name = "backend",
+            .info = &(const VMStateInfo) {
+                .name = "virtio-net vhost-user backend state",
+                .get = vhost_user_net_load_state,
+                .put = vhost_user_net_save_state,
+            },
+         },
+         VMSTATE_END_OF_LIST()
+    }
+};
+
 static const VMStateDescription vmstate_virtio_net_device = {
     .name = "virtio-net-device",
     .version_id = VIRTIO_NET_VM_VERSION,
@@ -3389,6 +3500,7 @@ static const VMStateDescription vmstate_virtio_net_device = {
     },
     .subsections = (const VMStateDescription * const []) {
         &vmstate_virtio_net_rss,
+        &vhost_user_net_backend_state,
         NULL
     }
 };
@@ -3950,29 +4062,6 @@ static bool dev_unplug_pending(void *opaque)
     return vdc->primary_unplug_pending(dev);
 }
 
-static struct vhost_dev *virtio_net_get_vhost(VirtIODevice *vdev)
-{
-    VirtIONet *n = VIRTIO_NET(vdev);
-    NetClientState *nc;
-    struct vhost_net *net;
-
-    if (!n->nic) {
-        return NULL;
-    }
-
-    nc = qemu_get_queue(n->nic);
-    if (!nc) {
-        return NULL;
-    }
-
-    net = get_vhost_net(nc->peer);
-    if (!net) {
-        return NULL;
-    }
-
-    return &net->dev;
-}
-
 static const VMStateDescription vmstate_virtio_net = {
     .name = "virtio-net",
     .minimum_version_id = VIRTIO_NET_VM_VERSION,