---

前言

本章记录SPICE USBREDIR中关于USBREDIR Channel初始化的知识。

代码仓库取自：
https://github.com/freedesktop/spice-usbredir （tag: usbredir-0.7）
https://github.com/freedesktop/spice-gtk （tag: v0.30）

1. 客户端初始化

1.1 初始化USB Device Manager

Spice通过USB Device Manager来进行USB设备的管理。

客户端（例如VirtViewer）通过调用spice_usb_device_manager_get()来初始化DeviceManager。

该函数实现于spice-session.c:

SpiceUsbDeviceManager *spice_usb_device_manager_get(SpiceSession *session,
                                                    GError **err)
{
   
    
    SpiceUsbDeviceManager *self;
    static GStaticMutex mutex = G_STATIC_MUTEX_INIT;

    g_return_val_if_fail(SPICE_IS_SESSION(session), NULL);
    g_return_val_if_fail(err == NULL || *err == NULL, NULL);

    g_static_mutex_lock(&mutex);
    self = session->priv->usb_manager;
    if (self == NULL) {
   
    
        self = g_initable_new(SPICE_TYPE_USB_DEVICE_MANAGER, NULL, err,
                              "session", session, NULL);
        session->priv->usb_manager = self;
    }
    g_static_mutex_unlock(&mutex);

    return self;
}

可以看出USB Device Manger被实现为单体模式，每个session有且只有一个Manager对象。

接下来看看USB Device Manager的构造函数 (usb-device-manager.c)：

G_DEFINE_TYPE_WITH_CODE(SpiceUsbDeviceManager, spice_usb_device_manager, G_TYPE_OBJECT,
     G_IMPLEMENT_INTERFACE (G_TYPE_INITABLE, spice_usb_device_manager_initable_iface_init));
...
static void spice_usb_device_manager_initable_iface_init(GInitableIface *iface)
{
   
    
    iface->init = spice_usb_device_manager_initable_init;
}

在USB Device Manager的构造初始化函数spice_usb_device_manager_initable_init()中，注册USB设备热插拔回调函数，然后开始侦听USB设备热插拔事件。

static gboolean spice_usb_device_manager_initable_init(GInitable  *initable,
                                                       GCancellable  *cancellable,
                                                       GError        **err)
{
   
    
#ifdef USE_USBREDIR
    SpiceUsbDeviceManager *self = SPICE_USB_DEVICE_MANAGER(initable);
    SpiceUsbDeviceManagerPrivate *priv = self->priv;
    GList *list;
    GList *it;
    int rc;
#ifdef USE_GUDEV
    const gchar *const subsystems[] = {
   
    "usb", NULL};
#endif

#ifdef G_OS_WIN32
    priv->installer = spice_win_usb_driver_new(err);
    if (!priv->installer) {
   
    
        SPICE_DEBUG("failed to initialize winusb driver");
        return FALSE;
    }
#endif

    /* Initialize libusb */
    rc = libusb_init(&priv->context);
    if (rc < 0) {
   
    
        const char *desc = spice_usbutil_libusb_strerror(rc);
        g_warning("Error initializing USB support: %s [%i]", desc, rc);
        g_set_error(err, SPICE_CLIENT_ERROR, SPICE_CLIENT_ERROR_FAILED,
                    "Error initializing USB support: %s [%i]", desc, rc);
        return FALSE;
    }

    /* Start listening for usb devices plug / unplug */
#ifdef USE_GUDEV
    priv->udev = g_udev_client_new(subsystems);
    g_signal_connect(G_OBJECT(priv->udev), "uevent",
                     G_CALLBACK(spice_usb_device_manager_uevent_cb), self);
    /* Do coldplug (detection of already connected devices) */
    libusb_get_device_list(priv->context, &priv->coldplug_list);
    list = g_udev_client_query_by_subsystem(priv->udev, "usb");
    for (it = g_list_first(list); it; it = g_list_next(it)) {
   
    
        spice_usb_device_manager_add_udev(self, it->data);
        g_object_unref(it->data);
    }
    g_list_free(list);
    libusb_free_device_list(priv->coldplug_list, 1);
    priv->coldplug_list = NULL;
#else
    rc = libusb_hotplug_register_callback(priv->context,
        LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED | LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT,
        LIBUSB_HOTPLUG_ENUMERATE, LIBUSB_HOTPLUG_MATCH_ANY,
        LIBUSB_HOTPLUG_MATCH_ANY, LIBUSB_HOTPLUG_MATCH_ANY,
        spice_usb_device_manager_hotplug_cb, self, &priv->hp_handle);
    if (rc < 0) {
   
    
        const char *desc = spice_usbutil_libusb_strerror(rc);
        g_warning("Error initializing USB hotplug support: %s [%i]", desc, rc);
        g_set_error(err, SPICE_CLIENT_ERROR, SPICE_CLIENT_ERROR_FAILED,
                  "Error initializing USB hotplug support: %s [%i]", desc, rc);
        return FALSE;
    }
    spice_usb_device_manager_start_event_listening(self, NULL);
#endif

    /* Start listening for usb channels connect/disconnect */
    spice_g_signal_connect_object(priv->session, "channel-new", G_CALLBACK(channel_new), self, G_CONNECT_AFTER);
    g_signal_connect(priv->session, &#