kobjects: add array of default attributes to subsystems, and create on registration.

struct subsystem may now contain a pointer to a NULL-terminated array of 
default attributes to be exported when an object is registered with the subsystem.
kobject registration will check the return values of the directory creation and 
the creation of each file, and handle it appropriately. 

The documentation has also been updated.

Documentation/kobject.txt

@@ -22,7 +22,7 @@ struct kobject {
 	struct list_head	entry;
 	struct kobject		* parent;
 	struct subsystem	* subsys;
-	struct sysfs_dir	dir;
+	struct dentry		* dentry;
 };
 
 void kobject_init(struct kobject *);
@@ -41,13 +41,15 @@ contain lists of kobjects that belong to that subsystem. Objects of a
 subsystem (the embedder objects in which kobjects live) are all of the
 same type. The interface looks like:
 
+
 struct subsystem {
 	struct kobject		kobj;
 	struct list_head	list;
 	struct rw_semaphore	rwsem;
 	struct subsystem	* parent;
-	struct sysfs_ops	* sysfs_ops;
 	void (*release)(struct kobject *);
+	struct sysfs_ops	* sysfs_ops;
+	struct attribute	** default_attrs;
 };
 
 void subsystem_init(struct subsystem *);
@@ -125,6 +127,14 @@ have been moved to reside in the subsystem, since they are common for
 all kobjects.
 
 
+Default Attributes
+
+Most subsystems have a set of default attributes associated with an
+object that registers with them. A subsystem definition may contain a
+NULL-terminated array of attributes that will be exported when an
+object is registered with the subsystem. 
+
+
 Reference Counting
 
 All objects contain reference counts. All functions accessing objects

include/linux/kobject.h

@@ -37,6 +37,7 @@ struct subsystem {
 	struct subsystem	* parent;
 	void (*release)(struct kobject *);
 	struct sysfs_ops	* sysfs_ops;
+	struct attribute	** default_attrs;
 };
 
 extern void subsystem_init(struct subsystem *);

lib/kobject.c

@@ -8,6 +8,34 @@
 #include <linux/module.h>
 #include <linux/stat.h>
 
+/**
+ *	kobject_populate_dir - populate directory with attributes.
+ *	@kobj:	object we're working on.
+ *
+ *	Most subsystems have a set of default attributes that 
+ *	are associated with an object that registers with them.
+ *	This is a helper called during object registration that 
+ *	loops through the default attributes of the subsystem 
+ *	and creates attributes files for them in sysfs.
+ *
+ */
+
+static int kobject_populate_dir(struct kobject * kobj)
+{
+	struct subsystem * s = kobj->subsys;
+	struct attribute * attr;
+	int error = 0;
+	int i;
+	
+	if (s && s->default_attrs) {
+		for (i = 0; (attr = s->default_attrs[i]); i++) {
+			if ((error = sysfs_create_file(kobj,attr)))
+				break;
+		}
+	}
+	return error;
+}
+
 /**
  *	kobject_init - initialize object.
  *	@kobj:	object in question.
@@ -31,10 +59,13 @@ void kobject_init(struct kobject * kobj)
 
 int kobject_register(struct kobject * kobj)
 {
+	int error = 0;
 	struct subsystem * s = subsys_get(kobj->subsys);
 	struct kobject * parent = kobject_get(kobj->parent);
 
 	pr_debug("kobject %s: registering\n",kobj->name);
+	if (parent)
+		pr_debug("  parent is %s\n",parent->name);
 	if (s) {
 		down_write(&s->rwsem);
 		if (parent) 
@@ -45,7 +76,13 @@ int kobject_register(struct kobject * kobj)
 		}
 		up_write(&s->rwsem);
 	}
-	return sysfs_create_dir(kobj);
+	error = sysfs_create_dir(kobj);
+	if (!error) {
+		error = kobject_populate_dir(kobj);
+		if (error)
+			sysfs_remove_dir(kobj);
+	}
+	return error;
 }
 
 /**
@@ -141,6 +178,8 @@ int subsystem_register(struct subsystem * s)
 	if (s->parent)
 		s->kobj.parent = &s->parent->kobj;
 	pr_debug("subsystem %s: registering\n",s->kobj.name);
+	if (s->parent)
+		pr_debug("  parent is %s\n",s->parent->kobj.name);
 	return kobject_register(&s->kobj);
 }