configfs: accessing item hierarchy during rmdir(2)

Add a notification callback, ops->disconnect_notify(). It has the same
prototype as ->drop_item(), but it will be called just before the item
linkage is broken. This way, configfs users who want to do work while
the object is still in the heirarchy have a chance.

Client drivers will still need to config_item_put() in their
->drop_item(), if they implement it.  They need do nothing in
->disconnect_notify().  They don't have to provide it if they don't
care.  But someone who wants to be notified before ci_parent is set to
NULL can now be notified.


diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 8a3b6a1..aaff72f 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -715,6 +715,28 @@ static void configfs_detach_group(struct
 }
 
 /*
+ * After the item has been detached from the filesystem view, we are
+ * ready to tear it out of the hierarchy.  Notify the client before
+ * we do that so they can perform any cleanup that requires
+ * navigating the hierarchy.  A client does not need to provide this
+ * callback.  The subsystem semaphore MUST be held by the caller, and
+ * references must be valid for both items.  It also assumes the
+ * caller has validated ci_type.
+ */
+static void client_disconnect_notify(struct config_item *parent_item,
+				     struct config_item *item)
+{
+	struct config_item_type *type;
+
+	type = parent_item->ci_type;
+	BUG_ON(!type);
+
+	if (type->ct_group_ops && type->ct_group_ops->disconnect_notify)
+		type->ct_group_ops->disconnect_notify(to_config_group(parent_item),
+						      item);
+}
+
+/*
  * Drop the initial reference from make_item()/make_group()
  * This function assumes that reference is held on item
  * and that item holds a valid reference to the parent.  Also, it
@@ -734,7 +756,7 @@ static void client_drop_item(struct conf
 	 */
 	if (type->ct_group_ops && type->ct_group_ops->drop_item)
 		type->ct_group_ops->drop_item(to_config_group(parent_item),
-						item);
+					      item);
 	else
 		config_item_put(item);
 }
@@ -843,11 +865,14 @@ out_unlink:
 	if (ret) {
 		/* Tear down everything we built up */
 		down(&subsys->su_sem);
+
+		client_disconnect_notify(parent_item, item);
 		if (group)
 			unlink_group(group);
 		else
 			unlink_obj(item);
 		client_drop_item(parent_item, item);
+
 		up(&subsys->su_sem);
 
 		if (module_got)
@@ -912,11 +937,13 @@ static int configfs_rmdir(struct inode *
 		configfs_detach_group(item);
 
 		down(&subsys->su_sem);
+		client_disconnect_notify(parent_item, item);
 		unlink_group(to_config_group(item));
 	} else {
 		configfs_detach_item(item);
 
 		down(&subsys->su_sem);
+		client_disconnect_notify(parent_item, item);
 		unlink_obj(item);
 	}
 
diff --git a/include/linux/configfs.h b/include/linux/configfs.h
index a7f0150..11100ca 100644
--- a/include/linux/configfs.h
+++ b/include/linux/configfs.h
@@ -157,6 +157,7 @@ struct configfs_group_operations {
 	struct config_item *(*make_item)(struct config_group *group, const char *name);
 	struct config_group *(*make_group)(struct config_group *group, const char *name);
 	int (*commit_item)(struct config_item *item);
+	void (*disconnect_notify)(struct config_group *group, struct config_item *item);
 	void (*drop_item)(struct config_group *group, struct config_item *item);
 };