[PATCH] driver core: add helper device_is_registered()

add the helper and use it instead of open coding the klist_node_attached() check
(which is a layering violation IMHO)

idea by Alan Stern.
Signed-off-by: Daniel Ritz <daniel.ritz@gmx.ch>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/s390/cio/ccwgroup.c

@@ -437,7 +437,7 @@ __ccwgroup_get_gdev_by_cdev(struct ccw_device *cdev)
 	if (cdev->dev.driver_data) {
 		gdev = (struct ccwgroup_device *)cdev->dev.driver_data;
 		if (get_device(&gdev->dev)) {
-			if (klist_node_attached(&gdev->dev.knode_bus))
+			if (device_is_registered(&gdev->dev))
 				return gdev;
 			put_device(&gdev->dev);
 		}

drivers/usb/core/message.c

@@ -987,7 +987,7 @@ void usb_disable_device(struct usb_device *dev, int skip_ep0)
 
 			/* remove this interface if it has been registered */
 			interface = dev->actconfig->interface[i];
-			if (!klist_node_attached(&interface->dev.knode_bus))
+			if (!device_is_registered(&interface->dev))
 				continue;
 			dev_dbg (&dev->dev, "unregistering interface %s\n",
 				interface->dev.bus_id);

drivers/usb/core/usb.c

@@ -303,7 +303,7 @@ int usb_driver_claim_interface(struct usb_driver *driver,
 	/* if interface was already added, bind now; else let
 	 * the future device_add() bind it, bypassing probe()
 	 */
-	if (klist_node_attached(&dev->knode_bus))
+	if (device_is_registered(dev))
 		device_bind_driver(dev);
 
 	return 0;
@@ -336,8 +336,8 @@ void usb_driver_release_interface(struct usb_driver *driver,
 	if (iface->condition != USB_INTERFACE_BOUND)
 		return;
 
-	/* release only after device_add() */
-	if (klist_node_attached(&dev->knode_bus)) {
+	/* don't release if the interface hasn't been added yet */
+	if (device_is_registered(dev)) {
 		iface->condition = USB_INTERFACE_UNBINDING;
 		device_release_driver(dev);
 	}

include/linux/device.h

@@ -317,6 +317,11 @@ dev_set_drvdata (struct device *dev, void *data)
 	dev->driver_data = data;
 }
 
+static inline int device_is_registered(struct device *dev)
+{
+	return klist_node_attached(&dev->knode_bus);
+}
+
 /*
  * High level routines for use by the bus drivers
  */