USB: add read support to usb-serial/../new_id

Keep the usb-serial support for dynamic IDs in sync with the usb
support.  This enables readout of dynamic device IDs for
usb-serial drivers.  Common code is exported from the usb core
system and reused by the usb-serial bus driver.
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/driver.c

@@ -79,13 +79,12 @@ 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)
+ssize_t usb_show_dynids(struct usb_dynids *dynids, 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)
+	list_for_each_entry(dynid, &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,
@@ -95,6 +94,14 @@ static ssize_t show_dynids(struct device_driver *driver, char *buf)
 					   dynid->id.idVendor, dynid->id.idProduct);
 	return count;
 }
+EXPORT_SYMBOL_GPL(usb_show_dynids);
+
+static ssize_t show_dynids(struct device_driver *driver, char *buf)
+{
+	struct usb_driver *usb_drv = to_usb_driver(driver);
+
+	return usb_show_dynids(&usb_drv->dynids, buf);
+}
 
 static ssize_t store_new_id(struct device_driver *driver,
 			    const char *buf, size_t count)

drivers/usb/serial/bus.c

@@ -124,8 +124,15 @@ static ssize_t store_new_id(struct device_driver *driver,
 	return retval;
 }
 
+static ssize_t show_dynids(struct device_driver *driver, char *buf)
+{
+	struct usb_serial_driver *usb_drv = to_usb_serial_driver(driver);
+
+	return usb_show_dynids(&usb_drv->dynids, buf);
+}
+
 static struct driver_attribute drv_attrs[] = {
-	__ATTR(new_id, S_IWUSR, NULL, store_new_id),
+	__ATTR(new_id, S_IRUGO | S_IWUSR, show_dynids, store_new_id),
 	__ATTR_NULL,
 };
 

include/linux/usb.h

@@ -790,6 +790,8 @@ extern ssize_t usb_store_new_id(struct usb_dynids *dynids,
 				struct device_driver *driver,
 				const char *buf, size_t count);
 
+extern ssize_t usb_show_dynids(struct usb_dynids *dynids, char *buf);
+
 /**
  * struct usbdrv_wrap - wrapper for driver-model structure
  * @driver: The driver-model core driver structure.