[SCSI] scsi_transport_sas: add expander backlink

This patch adds the ability to add a backlink to a particular port.  The
idea is to represent properly ports on expanders that are used
specifically for linking to the parent device in the topology.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
diff --git a/include/scsi/scsi_transport_sas.h b/include/scsi/scsi_transport_sas.h
index f5772ff..6cc2314 100644
--- a/include/scsi/scsi_transport_sas.h
+++ b/include/scsi/scsi_transport_sas.h
@@ -130,6 +130,8 @@
 
 	int			port_identifier;
 	int			num_phys;
+	/* port flags */
+	unsigned int		is_backlink:1;
 
 	/* the other end of the link */
 	struct sas_rphy		*rphy;
@@ -175,6 +177,7 @@
 void sas_port_delete(struct sas_port *);
 void sas_port_add_phy(struct sas_port *, struct sas_phy *);
 void sas_port_delete_phy(struct sas_port *, struct sas_phy *);
+void sas_port_mark_backlink(struct sas_port *);
 int scsi_is_sas_port(const struct device *);
 
 extern struct scsi_transport_template *