USB: let both new_id and remove_id show dynamic id list

This enables the current list of dynamic IDs to be read out through
either new_id or remove_id.
Signed-off-by: NBjørn Mork <bjorn@mork.no>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-bus-usb

@@ -135,6 +135,17 @@ Description:
 		for the device and attempt to bind to it.  For example:
 		# echo "8086 10f5" > /sys/bus/usb/drivers/foo/new_id
 
+		Reading from this file will list all dynamically added
+		device IDs in the same format, with one entry per
+		line. For example:
+		# cat /sys/bus/usb/drivers/foo/new_id
+		8086 10f5
+		dead beef 06
+		f00d cafe
+
+		The list will be truncated at PAGE_SIZE bytes due to
+		sysfs restrictions.
+
 What:		/sys/bus/usb-serial/drivers/.../new_id
 Date:		October 2011
 Contact:	linux-usb@vger.kernel.org
@@ -157,6 +168,10 @@ Description:
 		match the driver to the device.  For example:
 		# echo "046d c315" > /sys/bus/usb/drivers/foo/remove_id
 
+		Reading from this file will list the dynamically added
+		device IDs, exactly like reading from the entry
+		"/sys/bus/usb/drivers/.../new_id"
+
 What:		/sys/bus/usb/device/.../avoid_reset_quirk
 Date:		December 2009
 Contact:	Oliver Neukum <oliver@neukum.org>

drivers/usb/core/driver.c

@@ -79,6 +79,23 @@ ssize_t usb_store_new_id(struct usb_dynids *dynids,
 }
 EXPORT_SYMBOL_GPL(usb_store_new_id);
 
+static ssize_t show_dynids(struct device_driver *driver, char *buf)
+{
+	struct usb_dynid *dynid;
+	struct usb_driver *usb_drv = to_usb_driver(driver);
+	size_t count = 0;
+
+	list_for_each_entry(dynid, &usb_drv->dynids.list, node)
+		if (dynid->id.bInterfaceClass != 0)
+			count += scnprintf(&buf[count], PAGE_SIZE - count, "%04x %04x %02x\n",
+					   dynid->id.idVendor, dynid->id.idProduct,
+					   dynid->id.bInterfaceClass);
+		else
+			count += scnprintf(&buf[count], PAGE_SIZE - count, "%04x %04x\n",
+					   dynid->id.idVendor, dynid->id.idProduct);
+	return count;
+}
+
 static ssize_t store_new_id(struct device_driver *driver,
 			    const char *buf, size_t count)
 {
@@ -86,7 +103,7 @@ static ssize_t store_new_id(struct device_driver *driver,
 
 	return usb_store_new_id(&usb_drv->dynids, driver, buf, count);
 }
-static DRIVER_ATTR(new_id, S_IWUSR, NULL, store_new_id);
+static DRIVER_ATTR(new_id, S_IRUGO | S_IWUSR, show_dynids, store_new_id);
 
 /**
  * store_remove_id - remove a USB device ID from this driver
@@ -127,7 +144,7 @@ store_remove_id(struct device_driver *driver, const char *buf, size_t count)
 		return retval;
 	return count;
 }
-static DRIVER_ATTR(remove_id, S_IWUSR, NULL, store_remove_id);
+static DRIVER_ATTR(remove_id, S_IRUGO | S_IWUSR, show_dynids, store_remove_id);
 
 static int usb_create_newid_files(struct usb_driver *usb_drv)
 {