devicemode: Implement driver_for_each_dev

- iterate over all devices a driver has, with proper locking on driver and refcounting on devices

drivers/base/driver.c

@@ -8,6 +8,39 @@
 #include <linux/errno.h>
 #include "base.h"
 
+
+int driver_for_each_dev(struct device_driver * drv, void * data, int (*callback)(struct device *, void * ))
+{
+	struct device * next;
+	struct device * dev = NULL;
+	struct list_head * node;
+	int error = 0;
+
+	get_driver(drv);
+	read_lock(&drv->lock);
+	node = drv->devices.next;
+	while (node != &drv->devices) {
+		next = list_entry(node,struct device,driver_list);
+		get_device(next);
+		read_unlock(&drv->lock);
+
+		if (dev)
+			put_device(dev);
+		dev = next;
+		if ((error = callback(dev,data))) {
+			put_device(dev);
+			break;
+		}
+		read_lock(&drv->lock);
+		node = dev->driver_list.next;
+	}
+	read_unlock(&drv->lock);
+	if (dev)
+		put_device(dev);
+	put_driver(drv);
+	return error;
+}
+
 /**
  * driver_make_dir - create a driverfs directory for a driver
  * @drv:	driver in question
@@ -68,5 +101,6 @@ void put_driver(struct device_driver * drv)
 		drv->release(drv);
 }
 
+EXPORT_SYMBOL(driver_for_each_dev);
 EXPORT_SYMBOL(driver_register);
 EXPORT_SYMBOL(put_driver);