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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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22
qapi/string-output-visitor.c
View file

@ -58,6 +58,7 @@ struct StringOutputVisitor
Visitor visitor;
bool human;
GString *string;
char **result;
ListMode list_mode;
union {
int64_t s;
@ -305,16 +306,13 @@ static void end_list(Visitor *v, void **obj)
sov->list_mode = LM_NONE;
}
char *string_output_get_string(StringOutputVisitor *sov)
static void string_output_complete(Visitor *v, void *opaque)
{
char *string = g_string_free(sov->string, false);
sov->string = NULL;
return string;
}
StringOutputVisitor *sov = to_sov(v);
Visitor *string_output_get_visitor(StringOutputVisitor *sov)
{
return &sov->visitor;
assert(opaque == sov->result);
*sov->result = g_string_free(sov->string, false);
sov->string = NULL;
}
static void free_range(void *range, void *dummy)
@ -335,7 +333,7 @@ static void string_output_free(Visitor *v)
g_free(sov);
}
StringOutputVisitor *string_output_visitor_new(bool human)
Visitor *string_output_visitor_new(bool human, char **result)
{
StringOutputVisitor *v;
@ -343,6 +341,9 @@ StringOutputVisitor *string_output_visitor_new(bool human)
v->string = g_string_new(NULL);
v->human = human;
v->result = result;
*result = NULL;
v->visitor.type = VISITOR_OUTPUT;
v->visitor.type_int64 = print_type_int64;
v->visitor.type_uint64 = print_type_uint64;
@ -353,7 +354,8 @@ StringOutputVisitor *string_output_visitor_new(bool human)
v->visitor.start_list = start_list;
v->visitor.next_list = next_list;
v->visitor.end_list = end_list;
v->visitor.complete = string_output_complete;
v->visitor.free = string_output_free;
return v;
return &v->visitor;
}