[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: NJames Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/scsi_transport_sas.c

@@ -692,6 +692,13 @@ void sas_port_delete(struct sas_port *port)
 	}
 	mutex_unlock(&port->phy_list_mutex);
 
+	if (port->is_backlink) {
+		struct device *parent = port->dev.parent;
+
+		sysfs_remove_link(&port->dev.kobj, parent->bus_id);
+		port->is_backlink = 0;
+	}
+
 	transport_remove_device(dev);
 	device_del(dev);
 	transport_destroy_device(dev);
@@ -767,6 +774,19 @@ void sas_port_delete_phy(struct sas_port *port, struct sas_phy *phy)
 }
 EXPORT_SYMBOL(sas_port_delete_phy);
 
+void sas_port_mark_backlink(struct sas_port *port)
+{
+	struct device *parent = port->dev.parent->parent->parent;
+
+	if (port->is_backlink)
+		return;
+	port->is_backlink = 1;
+	sysfs_create_link(&port->dev.kobj, &parent->kobj,
+			  parent->bus_id);
+
+}
+EXPORT_SYMBOL(sas_port_mark_backlink);
+
 /*
  * SAS remote PHY attributes.
  */

include/scsi/scsi_transport_sas.h

@@ -130,6 +130,8 @@ struct sas_port {
 
 	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_free(struct sas_port *);
 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 *