cdc-acm: add TIOCGICOUNT

Simple straightforward implementation. Just returning the statistics
gathered for TIOCMIWAIT
Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/cdc-acm.c

@@ -853,6 +853,27 @@ static int wait_serial_change(struct acm *acm, unsigned long arg)
 	return rv;
 }
 
+static int get_serial_usage(struct acm *acm,
+			    struct serial_icounter_struct __user *count)
+{
+	struct serial_icounter_struct icount;
+	int rv = 0;
+
+	memset(&icount, 0, sizeof(icount));
+	icount.dsr = acm->iocount.dsr;
+	icount.rng = acm->iocount.rng;
+	icount.dcd = acm->iocount.dcd;
+	icount.frame = acm->iocount.frame;
+	icount.overrun = acm->iocount.overrun;
+	icount.parity = acm->iocount.parity;
+	icount.brk = acm->iocount.brk;
+
+	if (copy_to_user(count, &icount, sizeof(icount)) > 0)
+		rv = -EFAULT;
+
+	return rv;
+}
+
 static int acm_tty_ioctl(struct tty_struct *tty,
 					unsigned int cmd, unsigned long arg)
 {
@@ -869,6 +890,9 @@ static int acm_tty_ioctl(struct tty_struct *tty,
 	case TIOCMIWAIT:
 		rv = wait_serial_change(acm, arg);
 		break;
+	case TIOCGICOUNT:
+		rv = get_serial_usage(acm, (struct serial_icounter_struct __user *) arg);
+		break;
 	}
 
 	return rv;