@@ -507,4 +507,16 @@ void visit_type_number(Visitor *v, const char *name, double *obj,
*/
void visit_type_any(Visitor *v, const char *name, QObject **obj, Error **errp);
+/*
+ * Visit a JSON null value.
+ *
+ * @name expresses the relationship of the null value to its parent
+ * container; see the general description of @name above.
+ *
+ * Unlike all other visit_type_* functions, no obj parameter is
+ * needed; rather, this is a witness that an explicit null value is
+ * expected rather than any other type.
+ */
+void visit_type_null(Visitor *v, const char *name, Error **errp);
+
#endif
@@ -86,6 +86,9 @@ struct Visitor
void (*type_any)(Visitor *v, const char *name, QObject **obj,
Error **errp);
+ /* Must be set to visit explicit null values. */
+ void (*type_null)(Visitor *v, const char *name, Error **errp);
+
/* Must be set for input visitors, optional otherwise. The core
* takes care of the return type in the public interface. */
void (*optional)(Visitor *v, const char *name, bool *present);
@@ -31,7 +31,7 @@ typedef struct OptsVisitor OptsVisitor;
* - values above INT64_MAX or LLONG_MAX are rejected.
*
* The Opts input visitor does not yet implement support for visiting
- * QAPI alternates, numbers (other than integers), or arbitrary
+ * QAPI alternates, numbers (other than integers), null, or arbitrary
* QTypes.
*/
OptsVisitor *opts_visitor_new(const QemuOpts *opts);
@@ -19,7 +19,7 @@ typedef struct StringInputVisitor StringInputVisitor;
/*
* The string input visitor does not yet implement support for
- * visiting QAPI structs, alternates, or arbitrary QTypes.
+ * visiting QAPI structs, alternates, null, or arbitrary QTypes.
*/
StringInputVisitor *string_input_visitor_new(const char *str);
void string_input_visitor_cleanup(StringInputVisitor *v);
@@ -19,7 +19,7 @@ typedef struct StringOutputVisitor StringOutputVisitor;
/*
* The string output visitor does not yet implement support for
- * visiting QAPI structs, alternates, or arbitrary QTypes.
+ * visiting QAPI structs, alternates, null, or arbitrary QTypes.
*/
StringOutputVisitor *string_output_visitor_new(bool human);
void string_output_visitor_cleanup(StringOutputVisitor *v);
@@ -218,6 +218,11 @@ void visit_type_any(Visitor *v, const char *name, QObject **obj, Error **errp)
v->type_any(v, name, obj, errp);
}
+void visit_type_null(Visitor *v, const char *name, Error **errp)
+{
+ v->type_null(v, name, errp);
+}
+
static void output_type_enum(Visitor *v, const char *name, int *obj,
const char *const strings[], Error **errp)
{
@@ -163,6 +163,10 @@ static void qapi_dealloc_type_anything(Visitor *v, const char *name,
}
}
+static void qapi_dealloc_type_null(Visitor *v, const char *name, Error **errp)
+{
+}
+
Visitor *qapi_dealloc_get_visitor(QapiDeallocVisitor *v)
{
return &v->visitor;
@@ -193,6 +197,7 @@ QapiDeallocVisitor *qapi_dealloc_visitor_new(void)
v->visitor.type_str = qapi_dealloc_type_str;
v->visitor.type_number = qapi_dealloc_type_number;
v->visitor.type_any = qapi_dealloc_type_anything;
+ v->visitor.type_null = qapi_dealloc_type_null;
QTAILQ_INIT(&v->stack);
Right now, qmp-output-visitor happens to produce a QNull result if nothing is actually visited between the creation of the visitor and the request for the resulting QObject. A stronger protocol would require that a QMP output visit MUST visit something. But to still be able to produce a JSON 'null' output, we need a new visitor function that states our intentions. Yes, we could say that such a visit must go through visit_type_any(), but that feels clunky. So this patch introduces the new visit_type_null() interface and its no-op interface in the dealloc visitor, and the next patch will then wire it up into the qmp visitors. For the visitors that will not implement the callback, document the situation. The code in qapi-visit-core unconditionally dereferences the callback pointer, so that a segfault will inform a developer if they need to implement the callback for their choice of visitor. If QAPI had a 'null' type, we'd also have to use visit_type_null() in the generated visitor functions (most likely, we'd use it via an alternate type that permits 'null' or an object); we'll create that usage when we need it. Signed-off-by: Eric Blake <eblake@redhat.com> --- v12: rebase to earlier changes, drop R-b due to better documentation [no v10, v11] v9: no change v8: rebase to 'name' motion v7: new patch, based on discussion about spapr_drc.c --- include/qapi/visitor.h | 12 ++++++++++++ include/qapi/visitor-impl.h | 3 +++ include/qapi/opts-visitor.h | 2 +- include/qapi/string-input-visitor.h | 2 +- include/qapi/string-output-visitor.h | 2 +- qapi/qapi-visit-core.c | 5 +++++ qapi/qapi-dealloc-visitor.c | 5 +++++ 7 files changed, 28 insertions(+), 3 deletions(-)