sys_ functions in syscalls.h are undefined

I’m just making a kernel module. And I meet this warnings:

WARNING: "sys_getpid" [/PATH/NAME.ko] undefined!
WARNING: "sys_stat" [/PATH/NAME.ko] undefined!
WARNING: "sys_rmdir" [/PATH/NAME.ko] undefined!
WARNING: "sys_mremap" [/PATH/NAME.ko] undefined!
WARNING: "sys_fchmod" [/PATH/NAME.ko] undefined!
WARNING: "sys_gettimeofday" [/PATH/NAME.ko] undefined!
WARNING: "sys_utimes" [/PATH/NAME.ko] undefined!
WARNING: "sys_fcntl" [/PATH/NAME.ko] undefined!
WARNING: "sys_getcwd" [/PATH/NAME.ko] undefined!
WARNING: "sys_unlink" [/PATH/NAME.ko] undefined!
WARNING: "localtime" [/PATH/NAME.ko] undefined!
WARNING: "sys_write" [/PATH/NAME.ko] undefined!
WARNING: "sys_fsync" [/PATH/NAME.ko] undefined!
WARNING: "sys_fchown" [/PATH/NAME.ko] undefined!
WARNING: "sys_ftruncate" [/PATH/NAME.ko] undefined!
WARNING: "sys_fstat" [/PATH/NAME.ko] undefined!
WARNING: "sys_munmap" [/PATH/NAME.ko] undefined!
WARNING: "sys_geteuid" [/PATH/NAME.ko] undefined!
WARNING: "sys_read" [/PATH/NAME.ko] undefined!
WARNING: "sys_access" [/PATH/NAME.ko] undefined!
WARNING: "sys_old_mmap" [/PATH/NAME.ko] undefined!
WARNING: "errno" [/PATH/NAME.ko] undefined!
WARNING: "getenv" [/PATH/NAME.ko] undefined!
WARNING: "sys_mkdir" [/PATH/NAME.ko] undefined!
WARNING: "sys_time" [/PATH/NAME.ko] undefined!
WARNING: "sys_lseek" [/PATH/NAME.ko] undefined!
WARNING: "sysconf" [/PATH/NAME.ko] undefined!

How can I fix this problem?

This is my codes:

#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/syscalls.h>
#include <linux/fs.h>
#include <linux/delay.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/stat.h>
#include <linux/fcntl.h>
#include <asm-generic/unistd.h>
#include <uapi/asm-generic/fcntl.h>
#include <linux/time.h>
#include <linux/errno.h>
#include <linux/mman.h>

// And use functions(sys_open, sys_write, ...)

And my workspace is Ubuntu 3.13.0-66-generic.

I need to use file descriptor. So, I can’t use filp_ functions(like filp_open).

Edit1:

My Makefile: obj-m += NAME.o

NAME-objs := FILE1.o FILE2.o FILE3.o FILE4.o

ccflags-y := -mhard-float -msse -mpreferred-stack-boundary=4 -w -I/usr/include -I/usr/include/x86_64-linux-gnu/
ldflags-y += -lpthread -ldl


KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)

default:
    $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules 

clean:
    rm -rf *.ko *.mod *.cmd *.o *.mod.c *.order *.symvers  .tmp_versions

Answer

Calling system calls(sys_* functions) from the kernel code is not a good idea. Actually, many of system calls can be expressed in functions, available for kernel modules.

I need to use file descriptor. So, I can’t use filp_ functions(like filp_open).

File descriptor can be easy transformed into file pointer using fdget. See, e.g., implementation of fallocate system call (SYSCALL_DEFINE4(fallocate...) in fs/open.h).

As for errno, this variable is user space only. System calls return error using -E convention, it is libc who stores this value into errno.