usb: add usb_bus_release function

add global variables releasing logic when the usb buses
were removed or hot-unpluged.
Signed-off-by: NGonglei <arei.gonglei@huawei.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/usb/bus.c

@@ -87,6 +87,13 @@ void usb_bus_new(USBBus *bus, size_t bus_size,
     QTAILQ_INSERT_TAIL(&busses, bus, next);
 }
 
+void usb_bus_release(USBBus *bus)
+{
+    assert(next_usb_bus > 0);
+
+    QTAILQ_REMOVE(&busses, bus, next);
+}
+
 USBBus *usb_bus_find(int busnr)
 {
     USBBus *bus;

include/hw/usb.h

@@ -529,6 +529,7 @@ struct USBBusOps {
 
 void usb_bus_new(USBBus *bus, size_t bus_size,
                  USBBusOps *ops, DeviceState *host);
+void usb_bus_release(USBBus *bus);
 USBBus *usb_bus_find(int busnr);
 void usb_legacy_register(const char *typename, const char *usbdevice_name,
                          USBDevice *(*usbdevice_init)(USBBus *bus,