Extend object access hook framework to support arguments, and DROP.

This allows loadable modules to get control at drop time, perhaps for the
purpose of performing additional security checks or to log the event.
The initial purpose of this code is to support sepgsql, but other
applications should be possible as well.

KaiGai Kohei, reviewed by me.

src/backend/commands/tablespace.c

@@ -330,7 +330,7 @@ CreateTableSpace(CreateTableSpaceStmt *stmt)
 
 	/* Post creation hook for new tablespace */
 	InvokeObjectAccessHook(OAT_POST_CREATE,
-						   TableSpaceRelationId, tablespaceoid, 0);
+						   TableSpaceRelationId, tablespaceoid, 0, NULL);
 
 	create_tablespace_directories(location, tablespaceoid);
 
@@ -434,6 +434,15 @@ DropTableSpace(DropTableSpaceStmt *stmt)
 		aclcheck_error(ACLCHECK_NO_PRIV, ACL_KIND_TABLESPACE,
 					   tablespacename);
 
+	/* DROP hook for the tablespace being removed */
+	if (object_access_hook)
+	{
+		ObjectAccessDrop    drop_arg;
+		memset(&drop_arg, 0, sizeof(ObjectAccessDrop));
+		InvokeObjectAccessHook(OAT_DROP, TableSpaceRelationId,
+							   tablespaceoid, 0, &drop_arg);
+	}
+
 	/*
 	 * Remove the pg_tablespace tuple (this will roll back if we fail below)
 	 */