usb-bot: hotplug support

This patch marks usb-bot as hot-pluggable device, makes attached
property settable and turns off auto-attach in case the device
was hotplugged.

Hot-plugging a usb-bot device with one or more scsi devices can be
done this way now:

  (1) device-add usb-bot,id=foo
  (2) device-add scsi-{hd,cd},bus=foo.0,lun=0
  (2b) optionally add more devices (luns 0 ... 15).
  (3) qom-set foo.attached = true

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-id: 1465984019-28963-5-git-send-email-kraxel@redhat.com

hw/usb/dev-storage.c

@@ -634,9 +634,14 @@ static void usb_msd_realize_storage(USBDevice *dev, Error **errp)
 static void usb_msd_realize_bot(USBDevice *dev, Error **errp)
 {
     MSDState *s = USB_STORAGE_DEV(dev);
+    DeviceState *d = DEVICE(dev);
 
     usb_desc_create_serial(dev);
     usb_desc_init(dev);
+    if (d->hotplugged) {
+        s->dev.auto_attach = 0;
+    }
+
     scsi_bus_new(&s->bus, sizeof(s->bus), DEVICE(dev),
                  &usb_msd_scsi_info_bot, NULL);
     usb_msd_handle_reset(dev);
@@ -806,10 +811,9 @@ static void usb_msd_instance_init(Object *obj)
 static void usb_msd_class_initfn_bot(ObjectClass *klass, void *data)
 {
     USBDeviceClass *uc = USB_DEVICE_CLASS(klass);
-    DeviceClass *dc = DEVICE_CLASS(klass);
 
     uc->realize = usb_msd_realize_bot;
-    dc->hotpluggable = false;
+    uc->attached_settable = true;
 }
 
 static const TypeInfo msd_info = {