Add some comments

libc/Kconfig

@@ -74,6 +74,10 @@ config LIBC_IOCTL_VARIADIC
 		compatibility if you are porting code from other platforms that use
 		the variadic ioctl() function.
 
+		WARNING:  Use of this option could cause subtle system errors is
+		the third argument is omitted or if the sizeof the thread argument
+		is anything other than sizeof (unsigned long).
+
 config LIB_RAND_ORDER
 	int "Order of the random number generate"
 	default 1

libc/misc/lib_ioctl.c

@@ -87,7 +87,11 @@ int ioctl(int fd, int req, ...)
   va_list ap;
   unsigned long arg;
 
-  /* Get the unsigned long argument */
+  /* Get the unsigned long argument.
+   *
+   * REVISIT:  This could cause of the crash down the road if the actual size
+   * of the argument is anything other than sizeof(unsigned long);
+   */
 
   va_start(ap, req);
   arg = va_arg(ap, unsigned long);