[PATCH 2/3] USB: serial: make minor allocation dynamic

[Greg KH <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This moves the allocation of minor device numbers from a static array to
be dynamic, using the idr interface.  This means that you could
potentially get "gaps" in a minor number range for a single USB serial
device with multiple ports, but all should still work properly.

Note, we still have the limitation of 255 USB to serial devices in the
system, as that is all we are registering with the TTY layer at this
point in time.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/usb/serial/usb-serial.c |   97 ++++++++++++++++++++--------------------
 include/linux/usb/serial.h      |    4 -
 2 files changed, 51 insertions(+), 50 deletions(-)

--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -37,6 +37,7 @@
 #include <linux/usb.h>
 #include <linux/usb/serial.h>
 #include <linux/kfifo.h>
+#include <linux/idr.h>
 #include "pl2303.h"
 
 #define DRIVER_AUTHOR "Greg Kroah-Hartman <gregkh@linuxfoundation.org>"
@@ -49,7 +50,7 @@
    drivers depend on it.
 */
 
-static struct usb_serial *serial_table[SERIAL_TTY_MINORS];
+static DEFINE_IDR(serial_minors);
 static DEFINE_MUTEX(table_lock);
 static LIST_HEAD(usb_serial_driver_list);
 
@@ -60,61 +61,65 @@ static LIST_HEAD(usb_serial_driver_list)
  */
 struct usb_serial *usb_serial_get_by_index(unsigned index)
 {
-	struct usb_serial *serial;
+	struct usb_serial *serial = NULL;
+	struct usb_serial_port *port;
 
 	mutex_lock(&table_lock);
-	serial = serial_table[index];
+	port = idr_find(&serial_minors, index);
+	if (!port)
+		goto exit;
 
-	if (serial) {
-		mutex_lock(&serial->disc_mutex);
-		if (serial->disconnected) {
-			mutex_unlock(&serial->disc_mutex);
-			serial = NULL;
-		} else {
-			kref_get(&serial->kref);
-		}
+	serial = port->serial;
+	mutex_lock(&serial->disc_mutex);
+	if (serial->disconnected) {
+		mutex_unlock(&serial->disc_mutex);
+		serial = NULL;
+	} else {
+		kref_get(&serial->kref);
 	}
+exit:
 	mutex_unlock(&table_lock);
 	return serial;
 }
 
-static struct usb_serial *get_free_serial(struct usb_serial *serial,
-					int num_ports, unsigned int *minor)
+static int get_free_port(struct usb_serial_port *port)
 {
-	unsigned int i, j;
-	int good_spot;
-
-	dev_dbg(&serial->interface->dev, "%s %d\n", __func__, num_ports);
+	int i;
 
-	*minor = 0;
 	mutex_lock(&table_lock);
-	for (i = 0; i < SERIAL_TTY_MINORS; ++i) {
-		if (serial_table[i])
-			continue;
+	i = idr_alloc(&serial_minors, port, 0, 0, GFP_KERNEL);
+	if (i < 0)
+		goto exit;
+	port->minor = i;
+exit:
+	mutex_unlock(&table_lock);
+	return i;
+}
 
-		good_spot = 1;
-		for (j = 1; j <= num_ports-1; ++j)
-			if ((i+j >= SERIAL_TTY_MINORS) || (serial_table[i+j])) {
-				good_spot = 0;
-				i += j;
-				break;
-			}
-		if (good_spot == 0)
-			continue;
+static int get_free_serial(struct usb_serial *serial, int num_ports,
+			   unsigned int *minor)
+{
+	unsigned int i;
+	unsigned int j;
+	int x;
 
-		*minor = i;
-		j = 0;
-		dev_dbg(&serial->interface->dev, "%s - minor base = %d\n", __func__, *minor);
-		for (i = *minor; (i < (*minor + num_ports)) && (i < SERIAL_TTY_MINORS); ++i, ++j) {
-			serial_table[i] = serial;
-			serial->port[j]->minor = i;
-			serial->port[j]->port_number = i - *minor;
-		}
-		mutex_unlock(&table_lock);
-		return serial;
+	dev_dbg(&serial->interface->dev, "%s %d\n", __func__, num_ports);
+
+	*minor = 0xffffffff;
+	for (i = 0; i < num_ports; ++i) {
+		x = get_free_port(serial->port[i]);
+		if (x < 0)
+			goto error;
+		if (*minor == 0xffffffff)
+			*minor = x;
+		serial->port[i]->port_number = i;
 	}
-	mutex_unlock(&table_lock);
-	return NULL;
+	return 0;
+error:
+	/* unwind the already allocated minors */
+	for (j = 0; j < i; ++j)
+		idr_remove(&serial_minors, serial->port[j]->minor);
+	return x;
 }
 
 static void return_serial(struct usb_serial *serial)
@@ -123,7 +128,7 @@ static void return_serial(struct usb_ser
 
 	mutex_lock(&table_lock);
 	for (i = 0; i < serial->num_ports; ++i)
-		serial_table[serial->minor + i] = NULL;
+		idr_remove(&serial_minors, serial->port[i]->minor);
 	mutex_unlock(&table_lock);
 }
 
@@ -1040,7 +1045,7 @@ static int usb_serial_probe(struct usb_i
 	 */
 	serial->disconnected = 1;
 
-	if (get_free_serial(serial, num_ports, &minor) == NULL) {
+	if (get_free_serial(serial, num_ports, &minor)) {
 		dev_err(ddev, "No more free serial devices\n");
 		goto probe_error;
 	}
@@ -1224,7 +1229,6 @@ static struct usb_driver usb_serial_driv
 
 static int __init usb_serial_init(void)
 {
-	int i;
 	int result;
 
 	usb_serial_tty_driver = alloc_tty_driver(SERIAL_TTY_MINORS);
@@ -1232,9 +1236,6 @@ static int __init usb_serial_init(void)
 		return -ENOMEM;
 
 	/* Initialize our global data */
-	for (i = 0; i < SERIAL_TTY_MINORS; ++i)
-		serial_table[i] = NULL;
-
 	result = bus_register(&usb_serial_bus_type);
 	if (result) {
 		pr_err("%s - registering bus driver failed\n", __func__);
--- a/include/linux/usb/serial.h
+++ b/include/linux/usb/serial.h
@@ -21,7 +21,7 @@
 
 #define SERIAL_TTY_MAJOR	188	/* Nice legal number now */
 #define SERIAL_TTY_MINORS	254	/* loads of devices :) */
-#define SERIAL_TTY_NO_MINOR	255	/* No minor was assigned */
+#define SERIAL_TTY_NO_MINOR	0xffffffff	/* No minor was assigned */
 
 /* The maximum number of ports one device can grab at once */
 #define MAX_NUM_PORTS		8
@@ -161,13 +161,13 @@ struct usb_serial {
 	unsigned char			disconnected:1;
 	unsigned char			suspending:1;
 	unsigned char			attached:1;
-	unsigned char			minor;
 	unsigned char			num_ports;
 	unsigned char			num_port_pointers;
 	char				num_interrupt_in;
 	char				num_interrupt_out;
 	char				num_bulk_in;
 	char				num_bulk_out;
+	u32				minor;
 	struct usb_serial_port		*port[MAX_NUM_PORTS];
 	struct kref			kref;
 	struct mutex			disc_mutex;