qapi: Add parameter to visit_end_*

Rather than making the dealloc visitor track of stack of pointers
remembered during visit_start_* in order to free them during
visit_end_*, it's a lot easier to just make all callers pass the
same pointer to visit_end_*.  The generated code has access to the
same pointer, while all other users are doing virtual walks and
can pass NULL.  The dealloc visitor is then greatly simplified.

All three visit_end_*() functions intentionally take a void**,
even though the visit_start_*() functions differ between void**,
GenericList**, and GenericAlternate**.  This is done for several
reasons: when doing a virtual walk, passing NULL doesn't care
what the type is, but when doing a generated walk, we already
have to cast the caller's specific FOO* to call visit_start,
while using void** lets us use visit_end without a cast. Also,
an upcoming patch will add a clone visitor that wants to use
the same implementation for all three visit_end callbacks,
which is made easier if all three share the same signature.

For visitors with already track per-object state (the QMP visitors
via a stack, and the string visitors which do not allow nesting),
add an assertion that the caller is indeed passing the same
pointer to paired calls.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1465490926-28625-4-git-send-email-eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 14 insertions, 9 deletions

diff --git a/qapi/qmp-output-visitor.c b/qapi/qmp-output-visitor.c
index 4d3cf78333..dca893584d 100644
--- a/qapi/qmp-output-visitor.c
+++ b/qapi/qmp-output-visitor.c
@@ -22,6 +22,7 @@
 typedef struct QStackEntry
 {
     QObject *value;
+    void *qapi; /* sanity check that caller uses same pointer */
     QTAILQ_ENTRY(QStackEntry) node;
 } QStackEntry;
 
@@ -36,7 +37,8 @@ struct QmpOutputVisitor
 
 #define qmp_output_add(qov, name, value) \
     qmp_output_add_obj(qov, name, QOBJECT(value))
-#define qmp_output_push(qov, value) qmp_output_push_obj(qov, QOBJECT(value))
+#define qmp_output_push(qov, value, qapi) \
+    qmp_output_push_obj(qov, QOBJECT(value), qapi)
 
 static QmpOutputVisitor *to_qov(Visitor *v)
 {
@@ -44,23 +46,26 @@ static QmpOutputVisitor *to_qov(Visitor *v)
 }
 
 /* Push @value onto the stack of current QObjects being built */
-static void qmp_output_push_obj(QmpOutputVisitor *qov, QObject *value)
+static void qmp_output_push_obj(QmpOutputVisitor *qov, QObject *value,
+                                void *qapi)
 {
     QStackEntry *e = g_malloc0(sizeof(*e));
 
     assert(qov->root);
     assert(value);
     e->value = value;
+    e->qapi = qapi;
     QTAILQ_INSERT_HEAD(&qov->stack, e, node);
 }
 
 /* Pop a value off the stack of QObjects being built, and return it. */
-static QObject *qmp_output_pop(QmpOutputVisitor *qov)
+static QObject *qmp_output_pop(QmpOutputVisitor *qov, void *qapi)
 {
     QStackEntry *e = QTAILQ_FIRST(&qov->stack);
     QObject *value;
 
     assert(e);
+    assert(e->qapi == qapi);
     QTAILQ_REMOVE(&qov->stack, e, node);
     value = e->value;
     assert(value);
@@ -104,13 +109,13 @@ static void qmp_output_start_struct(Visitor *v, const char *name, void **obj,
     QDict *dict = qdict_new();
 
     qmp_output_add(qov, name, dict);
-    qmp_output_push(qov, dict);
+    qmp_output_push(qov, dict, obj);
 }
 
-static void qmp_output_end_struct(Visitor *v)
+static void qmp_output_end_struct(Visitor *v, void **obj)
 {
     QmpOutputVisitor *qov = to_qov(v);
-    QObject *value = qmp_output_pop(qov);
+    QObject *value = qmp_output_pop(qov, obj);
     assert(qobject_type(value) == QTYPE_QDICT);
 }
 
@@ -122,7 +127,7 @@ static void qmp_output_start_list(Visitor *v, const char *name,
     QList *list = qlist_new();
 
     qmp_output_add(qov, name, list);
-    qmp_output_push(qov, list);
+    qmp_output_push(qov, list, listp);
 }
 
 static GenericList *qmp_output_next_list(Visitor *v, GenericList *tail,
@@ -131,10 +136,10 @@ static GenericList *qmp_output_next_list(Visitor *v, GenericList *tail,
     return tail->next;
 }
 
-static void qmp_output_end_list(Visitor *v)
+static void qmp_output_end_list(Visitor *v, void **obj)
 {
     QmpOutputVisitor *qov = to_qov(v);
-    QObject *value = qmp_output_pop(qov);
+    QObject *value = qmp_output_pop(qov, obj);
     assert(qobject_type(value) == QTYPE_QLIST);
 }