user_mode_thread
extern pid_t user_mode_thread(int (*fn)(void *), void *arg, unsigned long flags);
pid = user_mode_thread(kernel_init, NULL, CLONE_FS);
pid = user_mode_thread(call_usermodehelper_exec_async, sub_info, SIGCHLD);
pid = user_mode_thread(call_usermodehelper_exec_async, sub_info,