+/*
+ * Callback function which will check whether the given change for variable
+ * "name" from "oldval" to "newval" may be applied or not, and possibly apply
+ * such change.
+ * When (flag & H_FORCE) is set, it shall not print out any error message and
+ * shall force overwriting of write-once variables.
+.* Must return 0 for approval, 1 for denial.
+ */
+ int (*apply)(const char *name, const char *oldval,
+ const char *newval, int flag);