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qapi: Add new visit_complete() function

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Making each output visitor provide its own output collection
function was the only remaining reason for exposing visitor
sub-types to the rest of the code base.  Add a polymorphic
visit_complete() function which is a no-op for input visitors,
and which populates an opaque pointer for output visitors.  For
maximum type-safety, also add a parameter to the output visitor
constructors with a type-correct version of the output pointer,
and assert that the two uses match.

This approach was considered superior to either passing the
output parameter only during construction (action at a distance
during visit_free() feels awkward) or only during visit_complete()
(defeating type safety makes it easier to use incorrectly).

Most callers were function-local, and therefore a mechanical
conversion; the testsuite was a bit trickier, but the previous
cleanup patch minimized the churn here.

The visit_complete() function may be called at most once; doing
so lets us use transfer semantics rather than duplication or
ref-count semantics to get the just-built output back to the
caller, even though it means our behavior is not idempotent.

Generated code is simplified as follows for events:

|@@ -26,7 +26,7 @@ void qapi_event_send_acpi_device_ost(ACP
|     QDict *qmp;
|     Error *err = NULL;
|     QMPEventFuncEmit emit;
|-    QmpOutputVisitor *qov;
|+    QObject *obj;
|     Visitor *v;
|     q_obj_ACPI_DEVICE_OST_arg param = {
|         info
|@@ -39,8 +39,7 @@ void qapi_event_send_acpi_device_ost(ACP
|
|     qmp = qmp_event_build_dict("ACPI_DEVICE_OST");
|
|-    qov = qmp_output_visitor_new();
|-    v = qmp_output_get_visitor(qov);
|+    v = qmp_output_visitor_new(&obj);
|
|     visit_start_struct(v, "ACPI_DEVICE_OST", NULL, 0, &err);
|     if (err) {
|@@ -55,7 +54,8 @@ void qapi_event_send_acpi_device_ost(ACP
|         goto out;
|     }
|
|-    qdict_put_obj(qmp, "data", qmp_output_get_qobject(qov));
|+    visit_complete(v, &obj);
|+    qdict_put_obj(qmp, "data", obj);
|     emit(QAPI_EVENT_ACPI_DEVICE_OST, qmp, &err);

and for commands:

| {
|     Error *err = NULL;
|-    QmpOutputVisitor *qov = qmp_output_visitor_new();
|     Visitor *v;
|
|-    v = qmp_output_get_visitor(qov);
|+    v = qmp_output_visitor_new(ret_out);
|     visit_type_AddfdInfo(v, "unused", &ret_in, &err);
|-    if (err) {
|-        goto out;
|+    if (!err) {
|+        visit_complete(v, ret_out);
|     }
|-    *ret_out = qmp_output_get_qobject(qov);
|-
|-out:
|     error_propagate(errp, err);

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1465490926-28625-13-git-send-email-eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
This commit is contained in:
Eric Blake 2016-06-09 10:48:43 -06:00 • committed by Markus Armbruster
parent 23d1705f42
commit 3b098d5697
23 changed files with 166 additions and 160 deletions
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30
qemu-img.c
View file

@ -491,16 +491,16 @@ fail:
static void dump_json_image_check(ImageCheck *check, bool quiet)
{
QString *str;
QmpOutputVisitor *ov = qmp_output_visitor_new();
QObject *obj;
visit_type_ImageCheck(qmp_output_get_visitor(ov), NULL, &check,
&error_abort);
obj = qmp_output_get_qobject(ov);
Visitor *v = qmp_output_visitor_new(&obj);
visit_type_ImageCheck(v, NULL, &check, &error_abort);
visit_complete(v, &obj);
str = qobject_to_json_pretty(obj);
assert(str != NULL);
qprintf(quiet, "%s\n", qstring_get_str(str));
qobject_decref(obj);
visit_free(qmp_output_get_visitor(ov));
visit_free(v);
QDECREF(str);
}
@ -2181,32 +2181,32 @@ static void dump_snapshots(BlockDriverState *bs)
static void dump_json_image_info_list(ImageInfoList *list)
{
QString *str;
QmpOutputVisitor *ov = qmp_output_visitor_new();
QObject *obj;
visit_type_ImageInfoList(qmp_output_get_visitor(ov), NULL, &list,
&error_abort);
obj = qmp_output_get_qobject(ov);
Visitor *v = qmp_output_visitor_new(&obj);
visit_type_ImageInfoList(v, NULL, &list, &error_abort);
visit_complete(v, &obj);
str = qobject_to_json_pretty(obj);
assert(str != NULL);
printf("%s\n", qstring_get_str(str));
qobject_decref(obj);
visit_free(qmp_output_get_visitor(ov));
visit_free(v);
QDECREF(str);
}
static void dump_json_image_info(ImageInfo *info)
{
QString *str;
QmpOutputVisitor *ov = qmp_output_visitor_new();
QObject *obj;
visit_type_ImageInfo(qmp_output_get_visitor(ov), NULL, &info,
&error_abort);
obj = qmp_output_get_qobject(ov);
Visitor *v = qmp_output_visitor_new(&obj);
visit_type_ImageInfo(v, NULL, &info, &error_abort);
visit_complete(v, &obj);
str = qobject_to_json_pretty(obj);
assert(str != NULL);
printf("%s\n", qstring_get_str(str));
qobject_decref(obj);
visit_free(qmp_output_get_visitor(ov));
visit_free(v);
QDECREF(str);
}