kobject: don't create directory for kobject/subsystem if name is NULL.

This allows subsystems to exist the hierarchy, but not be exported via
the filesystem. This fixes a minor flaw with partitions, as partition
objects are children of block devices, though they register with the 
partition subsystem. Really, the partition subsystem shouldn't have 
presence in the tree at all, yet still exist.

fs/partitions/check.c

@@ -355,7 +355,6 @@ static struct attribute * default_attrs[] = {
 extern struct subsystem block_subsys;
 
 static struct subsystem part_subsys = {
-	.kobj	= { .name = "part" },
 	.parent		= &block_subsys,
 	.default_attrs	= default_attrs,
 	.sysfs_ops	= &part_sysfs_ops,

lib/kobject.c

@@ -5,6 +5,7 @@
 #define DEBUG 0
 
 #include <linux/kobject.h>
+#include <linux/string.h>
 #include <linux/module.h>
 #include <linux/stat.h>
 
@@ -76,11 +77,13 @@ int kobject_register(struct kobject * kobj)
 		}
 		up_write(&s->rwsem);
 	}
-	error = sysfs_create_dir(kobj);
-	if (!error) {
-		error = kobject_populate_dir(kobj);
-		if (error)
-			sysfs_remove_dir(kobj);
+	if (strlen(kobj->name)) {
+		error = sysfs_create_dir(kobj);
+		if (!error) {
+			error = kobject_populate_dir(kobj);
+			if (error)
+				sysfs_remove_dir(kobj);
+		}
 	}
 	return error;
 }