util: don't skip error prefixes when QMP is active

The vreport() function will print to HMP if available, otherwise
to stderr. In the event that vreport() is called during execution
of a QMP command, it will print to stderr, but mistakenly omit the
message prefixes (timestamp, guest name, program name).

This new usage of monitor_is_cur_qmp() from vreport() requires that
we add a stub to satisfy linking of non-system emulator binaries.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

stubs/monitor-core.c

@@ -7,6 +7,11 @@ Monitor *monitor_cur(void)
     return NULL;
 }
 
+bool monitor_cur_is_qmp(void)
+{
+    return false;
+}
+
 Monitor *monitor_set_cur(Coroutine *co, Monitor *mon)
 {
     return NULL;

tests/unit/test-util-sockets.c

@@ -74,6 +74,7 @@ int monitor_get_fd(Monitor *mon, const char *fdname, Error **errp)
 Monitor *monitor_cur(void) { return cur_mon; }
 Monitor *monitor_set_cur(Coroutine *co, Monitor *mon) { abort(); }
 int monitor_vprintf(Monitor *mon, const char *fmt, va_list ap) { abort(); }
+bool monitor_cur_is_qmp(void) { abort(); };
 
 #ifndef _WIN32
 static void test_socket_fd_pass_name_good(void)

util/error-report.c

@@ -226,6 +226,14 @@ static void vreport(report_type type, const char *fmt, va_list ap)
     Monitor *cur = monitor_cur();
     gchar *timestr;
 
+    /*
+     * When current monitor is QMP, messages must go to stderr
+     * and have prefixes added
+     */
+    if (monitor_cur_is_qmp()) {
+        cur = NULL;
+    }
+
     if (message_with_timestamp && !cur) {
         timestr = real_time_iso8601();
         fprintf(stderr, "%s ", timestr);