On Mon, Apr 20, 2020 at 08:33:54PM +0800, Tiezhu Yang wrote: > If module name is empty, it is better to return directly at the beginning > of request_module() without doing the needless call_modprobe() operation. > > Call trace: > > request_module() > | > | > __request_module() > | > | > call_modprobe() > | > | > call_usermodehelper_exec() -- retval = sub_info->retval; > | > | > call_usermodehelper_exec_work() > | > | > call_usermodehelper_exec_sync() -- sub_info->retval = ret; > | > | --> call_usermodehelper_exec_async() --> do_execve() > | > kernel_wait4(pid, (int __user *)&ret, 0, NULL); > > sub_info->retval is 256 after call kernel_wait4(), the function > call_usermodehelper_exec() returns sub_info->retval which is 256, > then call_modprobe() and __request_module() returns 256. > > Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> Thanks for looking into this. I still cannot find where userspace it returns 256. Can you? If I run modprobe without an argument I see 1 returned. At least kmod [0] has a series of cmd helper structs, the one for modprobe seems to be kmod_cmd_compat_modprobe, and I can see -1 returned which can be converted to 255. It can also return EXIT_FAILURE or EXIT_SUCCESS and /usr/include/stdlib.h defines these as 1 and 0 respectively. https://git.kernel.org/pub/scm/utils/kernel/kmod/kmod.git/ Luis
