qemu-ga: switch to the new error format on the wire

IMPORTANT: this BREAKS qemu-ga compatibility for the error response.

Instead of returning something like:

{ "error": { "class": "InvalidParameterValue",
             "data": {"name": "mode", "expected": "halt|powerdown|reboot" } } }

qemu-ga now returns:

 { "error": { "class": "GenericError",
              "desc": "Parameter 'mode' expects halt|powerdown|reboot" } }

Notice that this is also a bug fix, as qemu-ga wasn't returning the
human message.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>

Makefile.objs

@@ -211,6 +211,7 @@ common-obj-$(CONFIG_SMARTCARD_NSS) += $(libcacard-y)
 # qapi
 
 qapi-obj-y = qapi/
+qapi-obj-y += qapi-types.o qapi-visit.o
 
 common-obj-y += qmp-marshal.o qapi-visit.o qapi-types.o
 common-obj-y += qmp.o hmp.o

qapi/qmp-core.h

@@ -49,6 +49,7 @@ void qmp_disable_command(const char *name);
 void qmp_enable_command(const char *name);
 bool qmp_command_is_enabled(const char *name);
 char **qmp_get_command_list(void);
+QObject *qmp_build_error_object(Error *errp);
 
 #endif
 

qapi/qmp-dispatch.c

@@ -14,6 +14,7 @@
 #include "qemu-objects.h"
 #include "qapi/qmp-core.h"
 #include "json-parser.h"
+#include "qapi-types.h"
 #include "error.h"
 #include "error_int.h"
 #include "qerror.h"
@@ -109,6 +110,13 @@ static QObject *do_qmp_dispatch(QObject *request, Error **errp)
     return ret;
 }
 
+QObject *qmp_build_error_object(Error *errp)
+{
+    return qobject_from_jsonf("{ 'class': %s, 'desc': %s }",
+                              ErrorClass_lookup[error_get_class(errp)],
+                              error_get_pretty(errp));
+}
+
 QObject *qmp_dispatch(QObject *request)
 {
     Error *err = NULL;
@@ -119,7 +127,7 @@ QObject *qmp_dispatch(QObject *request)
 
     rsp = qdict_new();
     if (err) {
-        qdict_put_obj(rsp, "error", error_get_qobject(err));
+        qdict_put_obj(rsp, "error", qmp_build_error_object(err));
         error_free(err);
     } else if (ret) {
         qdict_put_obj(rsp, "return", ret);

qemu-ga.c

@@ -515,7 +515,7 @@ static void process_event(JSONMessageParser *parser, QList *tokens)
         } else {
             g_warning("failed to parse event: %s", error_get_pretty(err));
         }
-        qdict_put_obj(qdict, "error", error_get_qobject(err));
+        qdict_put_obj(qdict, "error", qmp_build_error_object(err));
         error_free(err);
     } else {
         qdict = qobject_to_qdict(obj);
@@ -532,7 +532,7 @@ static void process_event(JSONMessageParser *parser, QList *tokens)
             qdict = qdict_new();
             g_warning("unrecognized payload format");
             error_set(&err, QERR_UNSUPPORTED);
-            qdict_put_obj(qdict, "error", error_get_qobject(err));
+            qdict_put_obj(qdict, "error", qmp_build_error_object(err));
             error_free(err);
         }
         ret = send_response(s, QOBJECT(qdict));