io: tls: Add qio_channel_tls_bye

Add a task dispatcher for gnutls_bye similar to the
qio_channel_tls_handshake_task(). The gnutls_bye() call might be
interrupted and so it needs to be rescheduled.

The migration code will make use of this to help the migration
destination identify a premature EOF. Once the session termination is
in place, any EOF that happens before the source issued gnutls_bye()
will be considered an error.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Acked-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>

include/io/channel-tls.h

@@ -49,8 +49,20 @@ struct QIOChannelTLS {
     QCryptoTLSSession *session;
     QIOChannelShutdown shutdown;
     guint hs_ioc_tag;
+    guint bye_ioc_tag;
 };
 
+/**
+ * qio_channel_tls_bye:
+ * @ioc: the TLS channel object
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Perform the TLS session termination. This method will return
+ * immediately and the termination will continue in the background,
+ * provided the main loop is running.
+ */
+void qio_channel_tls_bye(QIOChannelTLS *ioc, Error **errp);
+
 /**
  * qio_channel_tls_new_server:
  * @master: the underlying channel object