+ USER_HOST_LEVEL = xbt_lib_add_level(host_lib,NULL);
+}
+// ========== User data Layer ==========
+void *sg_host_user(sg_host_t host) {
+ return xbt_lib_get_level(host, USER_HOST_LEVEL);
+}
+void sg_host_user_set(sg_host_t host, void* userdata) {
+ xbt_lib_set(host_lib,host->key,USER_HOST_LEVEL,userdata);
+}
+void sg_host_user_destroy(sg_host_t host) {
+ xbt_lib_unset(host_lib,host->key,USER_HOST_LEVEL,1);