int foreach_type (const char *host, const char *plugin,
callback_type_t, void *user_data);
int foreach_plugin (const char *host, callback_plugin_t, void *user_data);
int foreach_type (const char *host, const char *plugin,
callback_type_t, void *user_data);
int foreach_plugin (const char *host, callback_plugin_t, void *user_data);