Warn abou missing mutate flag to ioctl. Fixes #696535.

Doc/whatsnew/whatsnew24.tex

@@ -669,6 +669,8 @@ changes to your code:
   system ID in the wrong order.  This has been corrected; applications
   relying on the wrong order need to be fixed.
 
+\item \function{fcntl.ioctl} now warns if the mutate arg is omitted.
+
 \end{itemize}
 
 

Misc/NEWS

@@ -214,6 +214,8 @@ Core and builtins
 Extension modules
 -----------------
 
+- fcntl.ioctl now warns if the mutate flag is not specified.
+
 - nt now properly allows to refer to UNC roots, e.g. in nt.stat().
 
 - the weakref module now supports additional objects:  array.array,

Modules/fcntlmodule.c

@@ -108,7 +108,13 @@ fcntl_ioctl(PyObject *self, PyObject *args)
 		char *arg;
 
 		if (PyTuple_Size(args) == 3) {
-			/* warning goes here in 2.4 */
+#if (PY_MAJOR_VERSION>2) || (PY_MINOR_VERSION>=5)
+#error Remove the warning, change mutate_arg to 1
+#endif
+			if (PyErr_Warn(PyExc_FutureWarning,
+       "ioctl with mutable buffer will mutate the buffer by default in 2.5"
+				    ) < 0)
+				return NULL;
 			mutate_arg = 0;
 		}
 	       	if (mutate_arg) {