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.
This patch introduces the new visit_type_null() interface, and later patches will then wire it up into the qmp visitors. Signed-off-by: Eric Blake <ebl...@redhat.com> Reviewed-by: Marc-André Lureau <marcandre.lur...@redhat.com> --- v9: no change v8: rebase to 'name' motion v7: new patch, based on discussion about spapr_drc.c --- include/qapi/visitor-impl.h | 3 +++ include/qapi/visitor.h | 8 ++++++++ qapi/qapi-dealloc-visitor.c | 5 +++++ qapi/qapi-visit-core.c | 5 +++++ 4 files changed, 21 insertions(+) diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h index aab46bc..8705136 100644 --- a/include/qapi/visitor-impl.h +++ b/include/qapi/visitor-impl.h @@ -75,6 +75,9 @@ struct Visitor * visitors do not currently visit arbitrary types). */ void (*type_any)(Visitor *v, const char *name, QObject **obj, Error **errp); + /* Must be provided to visit explicit null values (right now, only the + * dealloc visitor supports this). */ + void (*type_null)(Visitor *v, const char *name, Error **errp); /* May be NULL; most useful for input visitors. */ void (*optional)(Visitor *v, const char *name, bool *present); diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h index 5349a64..6e49b51 100644 --- a/include/qapi/visitor.h +++ b/include/qapi/visitor.h @@ -267,6 +267,14 @@ 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 tied to @name in the current object visit. + * @name will be NULL if this is visited as part of a list. + * 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); + +/** * Mark the start of visiting the branches of a union. Return true if * @data_present. * FIXME: Should not be needed diff --git a/qapi/qapi-dealloc-visitor.c b/qapi/qapi-dealloc-visitor.c index 560feb3..ede1703 100644 --- a/qapi/qapi-dealloc-visitor.c +++ b/qapi/qapi-dealloc-visitor.c @@ -162,6 +162,10 @@ static void qapi_dealloc_type_anything(Visitor *v, const char *name, } } +static void qapi_dealloc_type_null(Visitor *v, const char *name, Error **errp) +{ +} + static void qapi_dealloc_type_enum(Visitor *v, const char *name, int *obj, const char * const strings[], Error **errp) { @@ -222,6 +226,7 @@ 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; v->visitor.start_union = qapi_dealloc_start_union; QTAILQ_INIT(&v->stack); diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c index 1612d0d..399256b 100644 --- a/qapi/qapi-visit-core.c +++ b/qapi/qapi-visit-core.c @@ -262,6 +262,11 @@ 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); +} + void output_type_enum(Visitor *v, const char *name, int *obj, const char * const strings[], Error **errp) { -- 2.5.0