qapi: Add visitor for implicit structs

These can be used when an embedded struct is parsed and members not
belonging to the struct may be present in the input (e.g. parsing a
flat namespace QMP union, where fields from both the base and one
of the alternative types are mixed in the JSON object)

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

include/qapi/visitor-impl.h

@@ -22,6 +22,10 @@ struct Visitor
                          const char *name, size_t size, Error **errp);
     void (*end_struct)(Visitor *v, Error **errp);
 
+    void (*start_implicit_struct)(Visitor *v, void **obj, size_t size,
+                                  Error **errp);
+    void (*end_implicit_struct)(Visitor *v, Error **errp);
+
     void (*start_list)(Visitor *v, const char *name, Error **errp);
     GenericList *(*next_list)(Visitor *v, GenericList **list, Error **errp);
     void (*end_list)(Visitor *v, Error **errp);

include/qapi/visitor.h

@@ -33,6 +33,9 @@ void visit_end_handle(Visitor *v, Error **errp);
 void visit_start_struct(Visitor *v, void **obj, const char *kind,
                         const char *name, size_t size, Error **errp);
 void visit_end_struct(Visitor *v, Error **errp);
+void visit_start_implicit_struct(Visitor *v, void **obj, size_t size,
+                                 Error **errp);
+void visit_end_implicit_struct(Visitor *v, Error **errp);
 void visit_start_list(Visitor *v, const char *name, Error **errp);
 GenericList *visit_next_list(Visitor *v, GenericList **list, Error **errp);
 void visit_end_list(Visitor *v, Error **errp);

qapi/qapi-visit-core.c

@@ -45,6 +45,22 @@ void visit_end_struct(Visitor *v, Error **errp)
     v->end_struct(v, errp);
 }
 
+void visit_start_implicit_struct(Visitor *v, void **obj, size_t size,
+                                 Error **errp)
+{
+    if (!error_is_set(errp) && v->start_implicit_struct) {
+        v->start_implicit_struct(v, obj, size, errp);
+    }
+}
+
+void visit_end_implicit_struct(Visitor *v, Error **errp)
+{
+    assert(!error_is_set(errp));
+    if (v->end_implicit_struct) {
+        v->end_implicit_struct(v, errp);
+    }
+}
+
 void visit_start_list(Visitor *v, const char *name, Error **errp)
 {
     if (!error_is_set(errp)) {

qapi/qmp-input-visitor.c

@@ -144,6 +144,18 @@ static void qmp_input_end_struct(Visitor *v, Error **errp)
     qmp_input_pop(qiv, errp);
 }
 
+static void qmp_input_start_implicit_struct(Visitor *v, void **obj,
+                                            size_t size, Error **errp)
+{
+    if (obj) {
+        *obj = g_malloc0(size);
+    }
+}
+
+static void qmp_input_end_implicit_struct(Visitor *v, Error **errp)
+{
+}
+
 static void qmp_input_start_list(Visitor *v, const char *name, Error **errp)
 {
     QmpInputVisitor *qiv = to_qiv(v);
@@ -293,6 +305,8 @@ QmpInputVisitor *qmp_input_visitor_new(QObject *obj)
 
     v->visitor.start_struct = qmp_input_start_struct;
     v->visitor.end_struct = qmp_input_end_struct;
+    v->visitor.start_implicit_struct = qmp_input_start_implicit_struct;
+    v->visitor.end_implicit_struct = qmp_input_end_implicit_struct;
     v->visitor.start_list = qmp_input_start_list;
     v->visitor.next_list = qmp_input_next_list;
     v->visitor.end_list = qmp_input_end_list;