From: Mark McLoughlin <markmc@redhat.com>
Date: Wed, 1 Jul 2009 14:36:42 +0100
Subject: [misc] driver core: add root_device_register
Message-id: 1246455402.598.55.camel@blaa
O-Subject: [RHEL5.4 PATCH 1/3] [driver core] add root_device_register()
Bugzilla: 501468
RH-Acked-by: Prarit Bhargava <prarit@redhat.com>
RH-Acked-by: Don Dutile <ddutile@redhat.com>

https://bugzilla.redhat.com/501468

Root device objects should not be statically allocated, so this patch
adds an API for allocating them. Root devices appear in sysfs as
/sys/devices/{name}.

This allows us to avoid this warning from 'rmmod virtio_pci':

  Device 'virtio-pci' does not have a release() function, it is broken and must be fixed

The patch is a backport of this 2.6.29 commit:

  http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=0aa0dc41bf

Signed-off-by: Mark McLoughlin <markmc@redhat.com>

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 923ebef..aec061d 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -584,6 +584,93 @@ EXPORT_SYMBOL_GPL(put_device);
 EXPORT_SYMBOL_GPL(device_create_file);
 EXPORT_SYMBOL_GPL(device_remove_file);
 
+struct root_device
+{
+	struct device dev;
+	struct module *owner;
+};
+
+#define to_root_device(dev) container_of(dev, struct root_device, dev)
+
+static void root_device_release(struct device *dev)
+{
+	kfree(to_root_device(dev));
+}
+
+/**
+ * __root_device_register - allocate and register a root device
+ * @name: root device name
+ * @owner: owner module of the root device, usually THIS_MODULE
+ *
+ * This function allocates a root device and registers it
+ * using device_register(). In order to free the returned
+ * device, use root_device_unregister().
+ *
+ * Root devices are dummy devices which allow other devices
+ * to be grouped under /sys/devices. Use this function to
+ * allocate a root device and then use it as the parent of
+ * any device which should appear under /sys/devices/{name}
+ *
+ * The /sys/devices/{name} directory will also contain a
+ * 'module' symlink which points to the @owner directory
+ * in sysfs.
+ *
+ * Note: You probably want to use root_device_register().
+ */
+struct device *__root_device_register(const char *name, struct module *owner)
+{
+	struct root_device *root;
+	int err = -ENOMEM;
+
+	root = kzalloc(sizeof(struct root_device), GFP_KERNEL);
+	if (!root)
+		return ERR_PTR(err);
+
+	strlcpy(root->dev.bus_id, name, BUS_ID_SIZE);
+
+	root->dev.release = root_device_release;
+
+	err = device_register(&root->dev);
+	if (err) {
+		put_device(&root->dev);
+		return ERR_PTR(err);
+	}
+
+#ifdef CONFIG_MODULE	/* gotta find a "cleaner" way to do this */
+	if (owner) {
+		struct module_kobject *mk = &owner->mkobj;
+
+		err = sysfs_create_link(&root->dev.kobj, &mk->kobj, "module");
+		if (err) {
+			device_unregister(&root->dev);
+			return ERR_PTR(err);
+		}
+		root->owner = owner;
+	}
+#endif
+
+	return &root->dev;
+}
+EXPORT_SYMBOL_GPL(__root_device_register);
+
+/**
+ * root_device_unregister - unregister and free a root device
+ * @root: device going away.
+ *
+ * This function unregisters and cleans up a device that was created by
+ * root_device_register().
+ */
+void root_device_unregister(struct device *dev)
+{
+	struct root_device *root = to_root_device(dev);
+
+	if (root->owner)
+		sysfs_remove_link(&root->dev.kobj, "module");
+
+	device_unregister(dev);
+}
+EXPORT_SYMBOL_GPL(root_device_unregister);
+
 
 static void device_create_release(struct device *dev)
 {
diff --git a/include/linux/device.h b/include/linux/device.h
index d561172..9cd3442 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -429,6 +429,17 @@ extern int device_for_each_child(struct device *, void *,
 		     int (*fn)(struct device *, void *));
 
 /*
+ * Root device objects for grouping under /sys/devices
+ */
+extern struct device *__root_device_register(const char *name,
+					     struct module *owner);
+static inline struct device *root_device_register(const char *name)
+{
+	return __root_device_register(name, THIS_MODULE);
+}
+extern void root_device_unregister(struct device *root);
+
+/*
  * Manual binding of a device to driver. See drivers/base/bus.c
  * for information on use.
  */