device driver 공부중인 학생인데, ioctl 관련 질문입니다.

#define FND_CSX fnd 메모리주소
 
 
 
unsigned char disp[8] = {0};
 
int fnd_ioctl(struct inode *inode, struct file *file, unsigned int cmd, unsigned long arg)
{
char[8] a=arg;
    switch(cmd)
    {
        case 1:fnd_clear();
	case 2:fnd_write(a);  break;
        default: break;
    }
	return 0;
}
//static ssize_t fnd_write (struct file *filp, const char *buf, size_t count, loff_t *f_pos)
ssize_t fnd_write (const char *buf)
{
    int i;
 
    i=1;
    get_user(disp, (unsigned char*)buf);
    //copy_from_user(disp, buf, count);
    //printk( "write data %x \n", disp[5]);
 
    for(i =1; i <= MAX_FND; i++){	
    switch(i)
    {	
        case  1:    FND_CS7 = disp[0];  break;
        case  2:    FND_CS6 = disp[1];  break;
        case  3:    FND_CS5 = disp[2];  break;
        case  4:    FND_CS4 = disp[3];  break;
        case  5:    FND_CS3 = disp[4];  break;
        case  6:    FND_CS2 = disp[5];  break;
        case  7:    FND_CS1 = disp[6];  break;
        case  8:    FND_CS0 = disp[7];  break;
        default :   break;
    }
    }
    return 0;
}
 
static struct file_operations fnd_fops = {
	.open =fnd_open,
	//.write =fnd_write,
	.release =fnd_release,
	.ioctl =fnd_ioctl,
};

int main()
{
 
	int n=0; 
        int count=0;
        int dev=0;
	int len=0;
	int i=0;
	unsigned char		buf[MAXFND+1]="7\0";
	unsigned char	new_buf[MAXFND+1];
 
        dev = open( fnd_dev, O_RDWR);
 
while(1)
{
memset(buf, 0, sizeof(buf));
		memset(new_buf, 0, sizeof(new_buf));
		i=0;
		printf("##########################################\n");     
 
 
		printf("                        FND TEST\n");
		printf("                     press any numbers\n");
		printf("                                           'q' to exit \n");
		printf("#########################################\n");
 
                len=strlen(buf);
 
		for(n=MAXFND-len+1;n<MAXFND;n++) {
			new_buf[n]=asc_to_fnd( (buf[i]-48 ));
			i++; } 
 
 
                usleep(2000000)
                ioctl(dev, 2, new_buf);// 이부분에서 출력이 안됩니다. 혹시 몰라 2초의 딜레이 추가후 입력되도록 해보았는데 결과가 마찬가집니다.
 
 
 
 
}