virtio-serial: save/load: Ensure nr_ports on src and dest are same.

The number of ports on the source as well as the destination machines
should match. If they don't, it means some ports that got hotplugged on
the source aren't instantiated on the destination. Or that ports that
were hot-unplugged on the source are created on the destination.
Signed-off-by: NAmit Shah <amit.shah@redhat.com>
Reported-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/virtio-serial-bus.c

@@ -402,7 +402,7 @@ static int virtio_serial_load(QEMUFile *f, void *opaque, int version_id)
 {
     VirtIOSerial *s = opaque;
     VirtIOSerialPort *port;
-    uint32_t max_nr_ports, nr_active_ports;
+    uint32_t max_nr_ports, nr_active_ports, nr_ports;
     unsigned int i;
 
     if (version_id > 2) {
@@ -419,7 +419,21 @@ static int virtio_serial_load(QEMUFile *f, void *opaque, int version_id)
     /* The config space */
     qemu_get_be16s(f, &s->config.cols);
     qemu_get_be16s(f, &s->config.rows);
-    s->config.nr_ports = qemu_get_be32(f);
+    nr_ports = qemu_get_be32(f);
+
+    if (nr_ports != s->config.nr_ports) {
+        /*
+         * Source hot-plugged/unplugged ports and we don't have all of
+         * them here.
+         *
+         * Note: This condition cannot check for all hotplug/unplug
+         * events: eg, if one port was hot-plugged and one was
+         * unplugged, the nr_ports remains the same but the port id's
+         * would have changed and we won't catch it here. A later
+         * check for !find_port_by_id() will confirm if this happened.
+         */
+        return -EINVAL;
+    }
 
     /* Items in struct VirtIOSerial */