qdev: fix get_fw_dev_path to support to add nothing to fw_dev_path

Recent virtio refactoring in QEMU made virtio-bus become the parent bus
of scsi-bus, and virtio-bus doesn't have get_fw_dev_path implementation,
typename will be added to fw_dev_path by default, the new fw_dev_path
could not be identified by seabios. It causes that bootindex parameter
of scsi device doesn't work.

This patch implements get_fw_dev_path() in BusClass, it will be called
if bus doesn't implement the method, tyename will be added to
fw_dev_path. If the implemented method returns NULL, nothing will be
added to fw_dev_path.

It also implements virtio_bus_get_fw_dev_path() to return NULL. Then
QEMU will still pass original style of fw_dev_path to seabios.

Signed-off-by: Amos Kong <akong@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Message-id: 1369814202-10346-1-git-send-email-akong@redhat.com
--
v2: only add nothing to fw_dev_path when get_fw_dev_path() is
    implemented and returns NULL. then it will not effect other devices
    don't have get_fw_dev_path() implementation.
v3: implement default get_fw_dev_path() in BusClass
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

hw/core/qdev.c

@@ -515,7 +515,7 @@ static int qdev_get_fw_dev_path_helper(DeviceState *dev, char *p, int size)
             l += snprintf(p + l, size - l, "%s", d);
             g_free(d);
         } else {
-            l += snprintf(p + l, size - l, "%s", object_get_typename(OBJECT(dev)));
+            return l;
         }
     }
     l += snprintf(p + l , size - l, "/");
@@ -867,9 +867,17 @@ static void qbus_initfn(Object *obj)
     QTAILQ_INIT(&bus->children);
 }
 
+static char *default_bus_get_fw_dev_path(DeviceState *dev)
+{
+    return g_strdup(object_get_typename(OBJECT(dev)));
+}
+
 static void bus_class_init(ObjectClass *class, void *data)
 {
+    BusClass *bc = BUS_CLASS(class);
+
     class->unparent = bus_unparent;
+    bc->get_fw_dev_path = default_bus_get_fw_dev_path;
 }
 
 static void qbus_finalize(Object *obj)

hw/virtio/virtio-bus.c

@@ -161,10 +161,16 @@ static char *virtio_bus_get_dev_path(DeviceState *dev)
     return qdev_get_dev_path(proxy);
 }
 
+static char *virtio_bus_get_fw_dev_path(DeviceState *dev)
+{
+    return NULL;
+}
+
 static void virtio_bus_class_init(ObjectClass *klass, void *data)
 {
     BusClass *bus_class = BUS_CLASS(klass);
     bus_class->get_dev_path = virtio_bus_get_dev_path;
+    bus_class->get_fw_dev_path = virtio_bus_get_fw_dev_path;
 }
 
 static const TypeInfo virtio_bus_info = {