s390: Add a mechanism to get the subchannel id.

This will be needed by the new virtio-ccw transport.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/cio/device_ops.c

@@ -763,6 +763,18 @@ _ccw_device_get_subchannel_number(struct ccw_device *cdev)
 	return cdev->private->schid.sch_no;
 }
 
+/**
+ * ccw_device_get_schid - obtain a subchannel id
+ * @cdev: device to obtain the id for
+ * @schid: where to fill in the values
+ */
+void ccw_device_get_schid(struct ccw_device *cdev, struct subchannel_id *schid)
+{
+	struct subchannel *sch = to_subchannel(cdev->dev.parent);
+
+	*schid = sch->schid;
+}
+EXPORT_SYMBOL_GPL(ccw_device_get_schid);
 
 MODULE_LICENSE("GPL");
 EXPORT_SYMBOL(ccw_device_set_options_mask);