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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
Download patch file Download diff file Expand all files Collapse all files

8
tests/test-string-output-visitor.c
View file

@ -20,7 +20,6 @@
#include "qapi/qmp/types.h"
typedef struct TestOutputVisitorData {
StringOutputVisitor *sov;
Visitor *ov;
char *str;
bool human;
@ -30,9 +29,7 @@ static void visitor_output_setup_internal(TestOutputVisitorData *data,
bool human)
{
data->human = human;
data->sov = string_output_visitor_new(human);
g_assert(data->sov);
data->ov = string_output_get_visitor(data->sov);
data->ov = string_output_visitor_new(human, &data->str);
g_assert(data->ov);
}
@ -52,7 +49,6 @@ static void visitor_output_teardown(TestOutputVisitorData *data,
const void *unused)
{
visit_free(data->ov);
data->sov = NULL;
data->ov = NULL;
g_free(data->str);
data->str = NULL;
@ -60,7 +56,7 @@ static void visitor_output_teardown(TestOutputVisitorData *data,
static char *visitor_get(TestOutputVisitorData *data)
{
data->str = string_output_get_string(data->sov);
visit_complete(data->ov, &data->str);
g_assert(data->str);
return data->str;
}