tty: Make tiocgicount a handler

Dan Rosenberg noted that various drivers return the struct with uncleared
fields. Instead of spending forever trying to stomp all the drivers that
get it wrong (and every new driver) do the job in one place.

This first patch adds the needed operations and hooks them up, including
the needed USB midlayer and serial core plumbing.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/char/tty_io.c

@@ -96,6 +96,7 @@
 #include <linux/bitops.h>
 #include <linux/delay.h>
 #include <linux/seq_file.h>
+#include <linux/serial.h>
 
 #include <linux/uaccess.h>
 #include <asm/system.h>
@@ -2511,6 +2512,20 @@ static int tty_tiocmset(struct tty_struct *tty, struct file *file, unsigned int
 	return tty->ops->tiocmset(tty, file, set, clear);
 }
 
+static int tty_tiocgicount(struct tty_struct *tty, void __user *arg)
+{
+	int retval = -EINVAL;
+	struct serial_icounter_struct icount;
+	memset(&icount, 0, sizeof(icount));
+	if (tty->ops->get_icount)
+		retval = tty->ops->get_icount(tty, &icount);
+	if (retval != 0)
+		return retval;
+	if (copy_to_user(arg, &icount, sizeof(icount)))
+		return -EFAULT;
+	return 0;
+}
+
 struct tty_struct *tty_pair_get_tty(struct tty_struct *tty)
 {
 	if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
@@ -2631,6 +2646,12 @@ long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case TIOCMBIC:
 	case TIOCMBIS:
 		return tty_tiocmset(tty, file, cmd, p);
+	case TIOCGICOUNT:
+		retval = tty_tiocgicount(tty, p);
+		/* For the moment allow fall through to the old method */
+        	if (retval != -EINVAL)
+			return retval;
+		break;
 	case TCFLSH:
 		switch (arg) {
 		case TCIFLUSH: