local memory contexts to avoid a discard_const_p()

[Andrew Bartlett]

On Sun, 2010-12-12 at 21:11 +0100, Jelmer Vernooij wrote:
> Hi Matthias,
> 
> As discussed earlier, can you please send this kind of patch to the list
> for review first? 
> 
> I have my doubts about the usefulness of these changes in general
> compared to the benefit. Eliminating talloc contexts doesn't really gain
> us much. The overhead of creating an extra talloc context compared to
> the overhead of using Python in the first place is negligible.

> > @@ -248,27 +253,19 @@ static PyObject *py_dsdb_get_oid_from_attid(PyObject *self, PyObject *args)
> >  
> >  	PyErr_LDB_OR_RAISE(py_ldb, ldb);
> >  
> > -	mem_ctx = talloc_new(NULL);
> > -	if (mem_ctx == NULL) {
> > -	   PyErr_NoMemory();
> > -	   return NULL;
> > -	}
> > -
> >  	schema = dsdb_get_schema(ldb, NULL);
> >  
> >  	if (!schema) {
> >  		PyErr_SetString(PyExc_RuntimeError, "Failed to find a schema from ldb \n");
> > -		talloc_free(mem_ctx);
> >  		return NULL;
> >  	}
> >  	
> >  	status = dsdb_schema_pfm_oid_from_attid(schema->prefixmap, attid,
> > -	                                        mem_ctx, &oid);
> > +	                                        NULL, &oid);
> >  	PyErr_WERROR_IS_ERR_RAISE(status);
> >  
> >  	ret = PyString_FromString(oid);
> > -
> > -	talloc_free(mem_ctx);
> > +	talloc_free(discard_const_p(char, oid));
> ^^ Is this really necessary? I'd rather have the extra memory context
> than add an extra discard_const_p.

I agree, it's really useful to be able to avoid the const issues by
using a new memory context here.  Every discard_const_p() hides a
potentially serious bug, and so should be avoided where other reasonable
alternatives exist).  The local memory context seems a very reasonable
alternative, and so it seems a backwards step to eliminate it.

Andrew Bartlett

-- 
Andrew Bartlett                                http://samba.org/~abartlet/
Authentication Developer, Samba Team           http://samba.org
Samba Developer, Cisco Inc.
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