ldb:pyldb: reorder structs for possible type-punning

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

diff --git a/lib/ldb/pyldb.h b/lib/ldb/pyldb.h
index 5487def58a03005d43061571ccd8041c7b02210b..27d5fe3b4411311fe6f2b894320100c71aa32277 100644 (file)
--- a/lib/ldb/pyldb.h
+++ b/lib/ldb/pyldb.h
@@ -51,15 +51,51 @@ typedef struct {
                return NULL; \
        }
 
+/*
+ * A note about PyLdbObject back-references and struct member ordering.
+ *
+ * PyLdbDnObject, PyLdbMessageObject, and PyLdbResultObject all
+ * contain pointers to the PyLdbObject that was used to create them.
+ * This is used to check that the ldb pointer in the underlying ldb
+ * struct is still valid -- that is, it points to the same ldb as the
+ * PyLdbObject.
+ *
+ * We keep these pointers in third place in the structs, like this
+ *  {
+ *     PyObject_HEAD
+ *      TALLOC_CTX *mem_ctx;
+ *     PyLdbObject *pyldb;
+ *      ...
+ *  }
+ *
+ * so that, if we feel like it in future, we can do type-punning in
+ * the way Python does. For example:
+ *
+ * typedef struct {
+ *        PyObject_HEAD
+ *        TALLOC_CTX *mem_ctx;
+ *        PyLdbObject *pyldb;
+ * } PyLdbChildObject;
+ *
+ * #define pyldb_child_get_pyldb(pyobj) ((PyLdbChildObject *)pyobj)->pyldb
+ *
+ * #define PY_LDB_OWNS_THIS_CHILD(pyldb, child) \
+ *     (((PyLdbObject *)ldb) == ((PyLdbChildObject *)child)->ldb)
+ *
+ * At present we don't do this, because there are not a whole lot of
+ * cases where we want to do the same things with dNs, messages, and
+ * results.
+ */
+
 typedef struct {
        PyObject_HEAD
        TALLOC_CTX *mem_ctx;
-       struct ldb_dn *dn;
        /*
         * We use this to keep a reference to the ldb context within
         * the struct ldb_dn and to know if it is still valid
         */
        PyLdbObject *pyldb;
+       struct ldb_dn *dn;
 } PyLdbDnObject;
 
 PyObject *pyldb_Dn_FromDn(struct ldb_dn *dn, PyLdbObject *pyldb);
@@ -97,14 +133,15 @@ bool pyldb_check_type(PyObject *obj, const char *type_name);
 typedef struct {
        PyObject_HEAD
        TALLOC_CTX *mem_ctx;
-       struct ldb_message *msg;
        /*
         * We use this to keep a reference to the ldb context within
         * the struct ldb_dn (under struct ldb_message) and to know if
         * it is still valid
         */
        PyLdbObject *pyldb;
+       struct ldb_message *msg;
 } PyLdbMessageObject;
+
 #define pyldb_Message_AsMessage(pyobj) ((PyLdbMessageObject *)pyobj)->msg
 
 /*
@@ -131,10 +168,10 @@ typedef struct {
 typedef struct {
        PyObject_HEAD
        TALLOC_CTX *mem_ctx;
+       PyLdbObject *pyldb;
        PyObject *msgs;
        PyObject *referals;
        PyObject *controls;
-       PyLdbObject *pyldb;
 } PyLdbResultObject;
 
 typedef struct {