console: add dpy_ui_info_supported

Allow ui code to check whenever the emulated
display supports display change notifications.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

include/ui/console.h

@@ -228,6 +228,7 @@ void update_displaychangelistener(DisplayChangeListener *dcl,
                                   uint64_t interval);
 void unregister_displaychangelistener(DisplayChangeListener *dcl);
 
+bool dpy_ui_info_supported(QemuConsole *con);
 int dpy_set_ui_info(QemuConsole *con, QemuUIInfo *info);
 
 void dpy_gfx_update(QemuConsole *con, int x, int y, int w, int h);

ui/console.c

@@ -1391,11 +1391,16 @@ static void dpy_set_ui_info_timer(void *opaque)
     con->hw_ops->ui_info(con->hw, con->head, &con->ui_info);
 }
 
+bool dpy_ui_info_supported(QemuConsole *con)
+{
+    return con->hw_ops->ui_info != NULL;
+}
+
 int dpy_set_ui_info(QemuConsole *con, QemuUIInfo *info)
 {
     assert(con != NULL);
     con->ui_info = *info;
-    if (!con->hw_ops->ui_info) {
+    if (!dpy_ui_info_supported(con)) {
         return -1;
     }