[PULL 06/11] monitor: Drop query-qmp-schema 'gen': false hack

[Markus Armbruster <armbru@redhat.com>]

QMP commands return their response as a generated QAPI type, which the
monitor core converts to JSON via QObject.

query-qmp-schema's response is the generated introspection data.  This
is a QLitObject since commit 7d0f982bfb "qapi: generate a literal
qobject for introspection", v2.12).  Before, it was a string.  Instead
of converting QLitObject / string -> QObject -> QAPI type
SchemaInfoList -> QObject -> JSON, we take a shortcut: the command is
'gen': false, so it can return the QObject instead of the QAPI type.
Slightly simpler and more efficient.

The next commit will filter the response for output policy, and this
is easier in the SchemaInfoList representation.  Drop the shortcut.

This replaces the manual command registration by a generated one.  The
manual registration makes the command available before the machine is
built by passing flag QCO_ALLOW_PRECONFIG.  To keep it available
there, we need need to add 'allow-preconfig': true to its definition
in the schema.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210312153210.2810514-6-armbru@redhat.com>
[Commit message typo fixed]
---
 qapi/introspect.json                 |  2 +-
 monitor/monitor-internal.h           |  3 ---
 monitor/misc.c                       |  2 --
 monitor/qmp-cmds-control.c           | 29 ++++++++++++++++------------
 storage-daemon/qemu-storage-daemon.c |  2 --
 5 files changed, 18 insertions(+), 20 deletions(-)

diff --git a/qapi/introspect.json b/qapi/introspect.json
index 944bb87a20..39bd303778 100644
--- a/qapi/introspect.json
+++ b/qapi/introspect.json
@@ -49,7 +49,7 @@
 ##
 { 'command': 'query-qmp-schema',
   'returns': [ 'SchemaInfo' ],
-  'gen': false }                # just to simplify qmp_query_json()
+  'allow-preconfig': true }
 
 ##
 # @SchemaMetaType:
diff --git a/monitor/monitor-internal.h b/monitor/monitor-internal.h
index 40903d6386..9c3a09cb01 100644
--- a/monitor/monitor-internal.h
+++ b/monitor/monitor-internal.h
@@ -183,7 +183,4 @@ void help_cmd(Monitor *mon, const char *name);
 void handle_hmp_command(MonitorHMP *mon, const char *cmdline);
 int hmp_compare_cmd(const char *name, const char *list);
 
-void qmp_query_qmp_schema(QDict *qdict, QObject **ret_data,
-                                 Error **errp);
-
 #endif
diff --git a/monitor/misc.c b/monitor/misc.c
index a7650ed747..0b46006e42 100644
--- a/monitor/misc.c
+++ b/monitor/misc.c
@@ -231,8 +231,6 @@ static void monitor_init_qmp_commands(void)
 
     qmp_init_marshal(&qmp_commands);
 
-    qmp_register_command(&qmp_commands, "query-qmp-schema",
-                         qmp_query_qmp_schema, QCO_ALLOW_PRECONFIG);
     qmp_register_command(&qmp_commands, "device_add", qmp_device_add,
                          QCO_NO_OPTIONS);
     qmp_register_command(&qmp_commands, "object-add", qmp_object_add,
diff --git a/monitor/qmp-cmds-control.c b/monitor/qmp-cmds-control.c
index 509ae870bd..25afd0867f 100644
--- a/monitor/qmp-cmds-control.c
+++ b/monitor/qmp-cmds-control.c
@@ -26,10 +26,14 @@
 
 #include "monitor-internal.h"
 #include "qemu-version.h"
+#include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qapi/qapi-commands-control.h"
+#include "qapi/qapi-commands-introspect.h"
 #include "qapi/qapi-emit-events.h"
 #include "qapi/qapi-introspect.h"
+#include "qapi/qapi-visit-introspect.h"
+#include "qapi/qobject-input-visitor.h"
 
 /*
  * Accept QMP capabilities in @list for @mon.
@@ -154,17 +158,18 @@ EventInfoList *qmp_query_events(Error **errp)
     return ev_list;
 }
 
-/*
- * Minor hack: generated marshalling suppressed for this command
- * ('gen': false in the schema) so we can parse the JSON string
- * directly into QObject instead of first parsing it with
- * visit_type_SchemaInfoList() into a SchemaInfoList, then marshal it
- * to QObject with generated output marshallers, every time.  Instead,
- * we do it in test-qobject-input-visitor.c, just to make sure
- * qapi-gen.py's output actually conforms to the schema.
- */
-void qmp_query_qmp_schema(QDict *qdict, QObject **ret_data,
-                                 Error **errp)
+SchemaInfoList *qmp_query_qmp_schema(Error **errp)
 {
-    *ret_data = qobject_from_qlit(&qmp_schema_qlit);
+    QObject *obj = qobject_from_qlit(&qmp_schema_qlit);
+    Visitor *v = qobject_input_visitor_new(obj);
+    SchemaInfoList *schema = NULL;
+
+    /* test_visitor_in_qmp_introspect() ensures this can't fail */
+    visit_type_SchemaInfoList(v, NULL, &schema, &error_abort);
+    g_assert(schema);
+
+    qobject_unref(obj);
+    visit_free(v);
+
+    return schema;
 }
diff --git a/storage-daemon/qemu-storage-daemon.c b/storage-daemon/qemu-storage-daemon.c
index 23756fc8e5..02afdbeafc 100644
--- a/storage-daemon/qemu-storage-daemon.c
+++ b/storage-daemon/qemu-storage-daemon.c
@@ -146,8 +146,6 @@ static QemuOptsList qemu_object_opts = {
 static void init_qmp_commands(void)
 {
     qmp_init_marshal(&qmp_commands);
-    qmp_register_command(&qmp_commands, "query-qmp-schema",
-                         qmp_query_qmp_schema, QCO_ALLOW_PRECONFIG);
     qmp_register_command(&qmp_commands, "object-add", qmp_object_add,
                          QCO_NO_OPTIONS);
 
-- 
2.26.2