|  | 
        In the table below, X denotes
        an I/O control command class, a
        denotes a value of X, and
        u denotes an identifier.
      
Table 16. IoControlCommand requirements
| expression | type | 
                  assertion/note | 
|---|---|---|
| 
                   | 
                   | 
                  Returns a value suitable for passing as the request
                  argument to POSIX  | 
| 
                   | 
                  a pointer, convertible to  |