usb-wwan: implement TIOCGSERIAL and TIOCSSERIAL to avoid blocking close(2)

Some devices (ex ZTE 2726) simply don't respond at all when data is sent
to some of their USB interfaces.  The data gets stuck in the TTYs queue
and sits there until close(2), which them blocks because closing_wait
defaults to 30 seconds (even though the fd is O_NONBLOCK).  This is
rarely desired.  Implement the standard mechanism to adjust closing_wait
and let applications handle it how they want to.
Signed-off-by: Dan Williams <dcbw@redhat.com>

drivers/usb/serial/option.c

@@ -989,6 +989,7 @@ static struct usb_serial_driver option_1port_device = {
 	.set_termios       = usb_wwan_set_termios,
 	.tiocmget          = usb_wwan_tiocmget,
 	.tiocmset          = usb_wwan_tiocmset,
+	.ioctl             = usb_wwan_ioctl,
 	.attach            = usb_wwan_startup,
 	.disconnect        = usb_wwan_disconnect,
 	.release           = usb_wwan_release,

drivers/usb/serial/usb-wwan.h

@@ -18,6 +18,8 @@ extern void usb_wwan_set_termios(struct tty_struct *tty,
 extern int usb_wwan_tiocmget(struct tty_struct *tty, struct file *file);
 extern int usb_wwan_tiocmset(struct tty_struct *tty, struct file *file,
 			     unsigned int set, unsigned int clear);
+extern int usb_wwan_ioctl(struct tty_struct *tty, struct file *file,
+			  unsigned int cmd, unsigned long arg);
 extern int usb_wwan_send_setup(struct usb_serial_port *port);
 extern int usb_wwan_write(struct tty_struct *tty, struct usb_serial_port *port,
 			  const unsigned char *buf, int count);

drivers/usb/serial/usb_wwan.c

@@ -33,6 +33,7 @@
 #include <linux/bitops.h>
 #include <linux/usb.h>
 #include <linux/usb/serial.h>
+#include <linux/serial.h>
 #include "usb-wwan.h"
 
 static int debug;
@@ -123,6 +124,83 @@ int usb_wwan_tiocmset(struct tty_struct *tty, struct file *file,
 }
 EXPORT_SYMBOL(usb_wwan_tiocmset);
 
+static int get_serial_info(struct usb_serial_port *port,
+			   struct serial_struct __user *retinfo)
+{
+	struct serial_struct tmp;
+
+	if (!retinfo)
+		return -EFAULT;
+
+	memset(&tmp, 0, sizeof(tmp));
+	tmp.line            = port->serial->minor;
+	tmp.port            = port->number;
+	tmp.baud_base       = tty_get_baud_rate(port->port.tty);
+	tmp.close_delay	    = port->port.close_delay / 10;
+	tmp.closing_wait    = port->port.closing_wait == ASYNC_CLOSING_WAIT_NONE ?
+				 ASYNC_CLOSING_WAIT_NONE :
+				 port->port.closing_wait / 10;
+
+	if (copy_to_user(retinfo, &tmp, sizeof(*retinfo)))
+		return -EFAULT;
+	return 0;
+}
+
+static int set_serial_info(struct usb_serial_port *port,
+			   struct serial_struct __user *newinfo)
+{
+	struct serial_struct new_serial;
+	unsigned int closing_wait, close_delay;
+	int retval = 0;
+
+	if (copy_from_user(&new_serial, newinfo, sizeof(new_serial)))
+		return -EFAULT;
+
+	close_delay = new_serial.close_delay * 10;
+	closing_wait = new_serial.closing_wait == ASYNC_CLOSING_WAIT_NONE ?
+			ASYNC_CLOSING_WAIT_NONE : new_serial.closing_wait * 10;
+
+	mutex_lock(&port->port.mutex);
+
+	if (!capable(CAP_SYS_ADMIN)) {
+		if ((close_delay != port->port.close_delay) ||
+		    (closing_wait != port->port.closing_wait))
+			retval = -EPERM;
+		else
+			retval = -EOPNOTSUPP;
+	} else {
+		port->port.close_delay  = close_delay;
+		port->port.closing_wait = closing_wait;
+	}
+
+	mutex_unlock(&port->port.mutex);
+	return retval;
+}
+
+int usb_wwan_ioctl(struct tty_struct *tty, struct file *file,
+		   unsigned int cmd, unsigned long arg)
+{
+	struct usb_serial_port *port = tty->driver_data;
+
+	dbg("%s cmd 0x%04x", __func__, cmd);
+
+	switch (cmd) {
+	case TIOCGSERIAL:
+		return get_serial_info(port,
+				       (struct serial_struct __user *) arg);
+	case TIOCSSERIAL:
+		return set_serial_info(port,
+				       (struct serial_struct __user *) arg);
+	default:
+		break;
+	}
+
+	dbg("%s arg not supported", __func__);
+
+	return -ENOIOCTLCMD;
+}
+EXPORT_SYMBOL(usb_wwan_ioctl);
+
 /* Write */
 int usb_wwan_write(struct tty_struct *tty, struct usb_serial_port *port,
 		   const unsigned char *buf, int count)