커널레벨 파일 건드리기 예제 에러좀 봐주세요....

    struct file * fd;
    char * filename="/tmp/rambo.txt";
    char *buff=NULL;
    printk("read function...\n");
    fd=sfile_open(filename,O_RDONLY,0);
    if (fd != NULL) {
        printk("OK.....\n");
        count=10;
        offset=0;
        sfile_read(fd,offset,buff,count);
        printk(" buff %s\n",buff);
    }else{
        printk("not ok\n");
    }

#if 1
struct file* sfile_open(const char* path, int flags, int rights) {
    struct file* filp = NULL;
    mm_segment_t oldfs;
    int err = 0;
 
    oldfs = get_fs();
    set_fs(get_ds());
    filp = filp_open(path, flags, rights);
    set_fs(oldfs);
    if(IS_ERR(filp)) {
        err = PTR_ERR(filp);
        return NULL;
    }
    return filp;
}
void file_close(struct file* file) {
    filp_close(file, NULL);
}
 
int sfile_read(struct file* file, unsigned long long offset, unsigned char* data, unsigned int size) {
    mm_segment_t oldfs;
    int ret;
 
    printk("file_read...=\n");
    oldfs = get_fs();
    set_fs(get_ds());
 
    ret = vfs_read(file, data, size, &offset);
    printk("data is %s,ret is %d\n",data,ret);
 
    set_fs(oldfs);
    return ret;
}