ui/vdagent: fix serial reset of guest agent

In order to reset the guest agent, we send CLOSED & OPENED events.

They are correctly received by the guest kernel. However, they might not
be noticed by the guest agent process, as the IO task (poll() for
example) might be wake up after both CLOSED & OPENED have been
processed.

Wait until the guest agent is disconnected to re-open our side.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20220912102455.111765-6-marcandre.lureau@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

ui/vdagent.c

@@ -471,7 +471,7 @@ static void vdagent_clipboard_reset_serial(VDAgentChardev *vd)
 
     /* reopen the agent connection to reset the serial state */
     qemu_chr_be_event(chr, CHR_EVENT_CLOSED);
-    qemu_chr_be_event(chr, CHR_EVENT_OPENED);
+    /* OPENED again after the guest disconnected, see set_fe_open */
 }
 
 static void vdagent_clipboard_notify(Notifier *notifier, void *data)
@@ -875,6 +875,9 @@ static void vdagent_chr_set_fe_open(struct Chardev *chr, int fe_open)
 {
     if (!fe_open) {
         trace_vdagent_close();
+        /* To reset_serial, we CLOSED our side. Make sure the other end knows we
+         * are ready again. */
+        qemu_chr_be_event(chr, CHR_EVENT_OPENED);
         return;
     }