Re: [Libguestfs] [nbdkit PATCH] python: Let zero's may_trim parameter be optional

In preparation for adding other optional flag arguments to the python bindings, start by making the existing 'may_trim' flag to 'zero' be optional. That is, the plugin need not define the parameter if it does not make any semantic difference (ie. if the plugin ignores the hint and never trims); while if the parameter exists, we now pass it as a keyword argument rather than as a positional argument. This requires the plugin to give the parameter a specific name, and works whether or not the plugin provides a default for the parameter (although we do now recommend that plugins provide a default value, as it makes plugins built against newer nbdkit more likely to run even on older nbdkit). We can't see through a plugin that used '**kwargs', but that is less likely.

+/* Does a callback support the given keyword parameter? */ +static int +callback_has_parameter (PyObject *fn, const char *name) +{ + int r = 0; + PyObject *inspect, *pname, *spec, *args; + + assert (script != NULL); + assert (module != NULL); + + pname = PyString_FromString ("inspect");

+ if (!pname) + return -1; + inspect = PyImport_Import (pname); + Py_DECREF (pname); + + if (!inspect) + return -1; + +#if PY_MAJOR_VERSION >= 3 + pname = PyString_FromString ("getfullargspec");

+#else + pname = PyString_FromString ("getargspec"); +#endif + spec = PyObject_CallMethodObjArgs (inspect, pname, fn, NULL); + Py_DECREF (pname); + Py_DECREF (inspect); + if (!spec) + return -1; +

@@ -530,21 +594,31 @@ py_zero (void *handle, uint32_t count, uint64_t offset, int may_trim)

PyTuple_SetItem (args, 2, PyLong_FromUnsignedLongLong (offset)); - PyTuple_SetItem (args, 3, PyBool_FromLong (may_trim)); - r = PyObject_CallObject (fn, args); + if (zero_may_trim) + kwargs = Py_BuildValue("{s:i}", "may_trim", may_trim);