monitor: enable IO thread for (qmp & !mux) typed

Start to use dedicate IO thread for QMP monitors that are not using
MUXed chardev.
Reviewed-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NPeter Xu <peterx@redhat.com>
Message-Id: <20180309090006.10018-21-peterx@redhat.com>
Signed-off-by: NEric Blake <eblake@redhat.com>

monitor.c

@@ -36,6 +36,7 @@
 #include "net/slirp.h"
 #include "chardev/char-fe.h"
 #include "chardev/char-io.h"
+#include "chardev/char-mux.h"
 #include "ui/qemu-spice.h"
 #include "sysemu/numa.h"
 #include "monitor/monitor.h"
@@ -4536,8 +4537,10 @@ static void monitor_qmp_setup_handlers_bh(void *opaque)
 void monitor_init(Chardev *chr, int flags)
 {
     Monitor *mon = g_malloc(sizeof(*mon));
+    /* Enable IOThread for QMPs that are not using MUX chardev backends. */
+    bool use_io_thr = (!CHARDEV_IS_MUX(chr)) && (flags & MONITOR_USE_CONTROL);
 
-    monitor_data_init(mon, false, false);
+    monitor_data_init(mon, false, use_io_thr);
 
     qemu_chr_fe_init(&mon->chr, chr, &error_abort);
     mon->flags = flags;