error: Let converted handlers print in human monitor

While fully converted handlers are not supposed to print anything when
running in a QMP monitor, they are free to print in a human monitor.
For instance, device_add (not yet converted) prints help, and will
continue to do so after conversion.

Moreover, utility functions converted to QError should remain usable
from unconverted handlers.

Two problems:

* handler_audit() complains when a converted handler prints.  Limit
  that to QMP monitors.

* With QMP, handlers need to pass the error object by way of
  monitor_set_error().  However, we do that both for QMP and for the
  human monitor.  The human monitor prints the error object after the
  handler returns.  If the handler prints anything else, that output
  "overtakes" the error message.

  Limit use of monitor_set_error() to QMP monitors.  Update
  handler_audit() accordingly.

monitor.c

@@ -3876,13 +3876,6 @@ void monitor_set_error(Monitor *mon, QError *qerror)
     }
 }
 
-static void monitor_print_error(Monitor *mon)
-{
-    qerror_print(mon->error);
-    QDECREF(mon->error);
-    mon->error = NULL;
-}
-
 static int is_async_return(const QObject *data)
 {
     if (data && qobject_type(data) == QTYPE_QDICT) {
@@ -3894,45 +3887,49 @@ static int is_async_return(const QObject *data)
 
 static void handler_audit(Monitor *mon, const mon_cmd_t *cmd, int ret)
 {
-    if (ret && !monitor_has_error(mon)) {
-        /*
-         * If it returns failure, it must have passed on error.
-         *
-         * Action: Report an internal error to the client if in QMP.
-         */
-        if (monitor_ctrl_mode(mon)) {
+    if (monitor_ctrl_mode(mon)) {
+        if (ret && !monitor_has_error(mon)) {
+            /*
+             * If it returns failure, it must have passed on error.
+             *
+             * Action: Report an internal error to the client if in QMP.
+             */
             qerror_report(QERR_UNDEFINED_ERROR);
+            MON_DEBUG("command '%s' returned failure but did not pass an error\n",
+                      cmd->name);
         }
-        MON_DEBUG("command '%s' returned failure but did not pass an error\n",
-                  cmd->name);
-    }
 
 #ifdef CONFIG_DEBUG_MONITOR
-    if (!ret && monitor_has_error(mon)) {
-        /*
-         * If it returns success, it must not have passed an error.
-         *
-         * Action: Report the passed error to the client.
-         */
-        MON_DEBUG("command '%s' returned success but passed an error\n",
-                  cmd->name);
-    }
+        if (!ret && monitor_has_error(mon)) {
+            /*
+             * If it returns success, it must not have passed an error.
+             *
+             * Action: Report the passed error to the client.
+             */
+            MON_DEBUG("command '%s' returned success but passed an error\n",
+                      cmd->name);
+        }
 
-    if (mon_print_count_get(mon) > 0 && strcmp(cmd->name, "info") != 0) {
-        /*
-         * Handlers should not call Monitor print functions.
-         *
-         * Action: Ignore them in QMP.
-         *
-         * (XXX: we don't check any 'info' or 'query' command here
-         * because the user print function _is_ called by do_info(), hence
-         * we will trigger this check. This problem will go away when we
-         * make 'query' commands real and kill do_info())
-         */
-        MON_DEBUG("command '%s' called print functions %d time(s)\n",
-                  cmd->name, mon_print_count_get(mon));
-    }
+        if (mon_print_count_get(mon) > 0 && strcmp(cmd->name, "info") != 0) {
+            /*
+             * Handlers should not call Monitor print functions.
+             *
+             * Action: Ignore them in QMP.
+             *
+             * (XXX: we don't check any 'info' or 'query' command here
+             * because the user print function _is_ called by do_info(), hence
+             * we will trigger this check. This problem will go away when we
+             * make 'query' commands real and kill do_info())
+             */
+            MON_DEBUG("command '%s' called print functions %d time(s)\n",
+                      cmd->name, mon_print_count_get(mon));
+        }
 #endif
+    } else {
+        assert(!monitor_has_error(mon));
+        QDECREF(mon->error);
+        mon->error = NULL;
+    }
 }
 
 static void monitor_call_handler(Monitor *mon, const mon_cmd_t *cmd,
@@ -3985,9 +3982,6 @@ static void handle_user_command(Monitor *mon, const char *cmdline)
         cmd->mhandler.cmd(mon, qdict);
     }
 
-    if (monitor_has_error(mon))
-        monitor_print_error(mon);
-
 out:
     QDECREF(qdict);
 }

qemu-error.c

@@ -207,7 +207,7 @@ void qerror_report_internal(const char *file, int linenr, const char *func,
     qerror = qerror_from_info(file, linenr, func, fmt, &va);
     va_end(va);
 
-    if (cur_mon) {
+    if (monitor_cur_is_qmp()) {
         monitor_set_error(cur_mon, qerror);
     } else {
         qerror_print(qerror);