qapi: Anonymous unions

The discriminator for anonymous unions is the data type. This allows to
have a union type that allows both of these:

    { 'file': 'my_existing_block_device_id' }
    { 'file': { 'filename': '/tmp/mydisk.qcow2', 'read-only': true } }

Unions like this are specified in the schema with an empty dict as
discriminator. For this example you could take:

    { 'union': 'BlockRef',
      'discriminator': {},
      'data': { 'definition': 'BlockOptions',
                'reference': 'str' } }
    { 'type': 'ExampleObject',
      'data: { 'file': 'BlockRef' } }

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

2 files changed, 23 insertions, 0 deletions

diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index 9b4d51bc0a..d6a4012f78 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -12,6 +12,7 @@
  */
 
 #include "qemu-common.h"
+#include "qapi/qmp/qobject.h"
 #include "qapi/qmp/qerror.h"
 #include "qapi/visitor.h"
 #include "qapi/visitor-impl.h"
@@ -98,6 +99,14 @@ void visit_end_optional(Visitor *v, Error **errp)
     }
 }
 
+void visit_get_next_type(Visitor *v, int *obj, const int *qtypes,
+                         const char *name, Error **errp)
+{
+    if (!error_is_set(errp) && v->get_next_type) {
+        v->get_next_type(v, obj, qtypes, name, errp);
+    }
+}
+
 void visit_type_enum(Visitor *v, int *obj, const char *strings[],
                      const char *kind, const char *name, Error **errp)
 {
diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c
index 70864a1af2..bf42c04ea6 100644
--- a/qapi/qmp-input-visitor.c
+++ b/qapi/qmp-input-visitor.c
@@ -208,6 +208,19 @@ static void qmp_input_end_list(Visitor *v, Error **errp)
     qmp_input_pop(qiv, errp);
 }
 
+static void qmp_input_get_next_type(Visitor *v, int *kind, const int *qobjects,
+                                    const char *name, Error **errp)
+{
+    QmpInputVisitor *qiv = to_qiv(v);
+    QObject *qobj = qmp_input_get_object(qiv, name, false);
+
+    if (!qobj) {
+        error_set(errp, QERR_MISSING_PARAMETER, name ? name : "null");
+        return;
+    }
+    *kind = qobjects[qobject_type(qobj)];
+}
+
 static void qmp_input_type_int(Visitor *v, int64_t *obj, const char *name,
                                Error **errp)
 {
@@ -317,6 +330,7 @@ QmpInputVisitor *qmp_input_visitor_new(QObject *obj)
     v->visitor.type_str = qmp_input_type_str;
     v->visitor.type_number = qmp_input_type_number;
     v->visitor.start_optional = qmp_input_start_optional;
+    v->visitor.get_next_type = qmp_input_get_next_type;
 
     qmp_input_push(v, obj, NULL);
     qobject_incref(obj);