New API function sr_session_dev_list()

This exposes the list of devices added to the session. In the case of
loading a session from file, these struct sr_dev_inst are otherwise
not exposed to the frontend. See bug 145.

session.c

@@ -179,6 +179,31 @@ SR_API int sr_session_dev_add(const struct sr_dev_inst *sdi)
 	return SR_OK;
 }
 
+/**
+ * List all device instances attached to the current session.
+ *
+ * @param devlist A pointer where the device instance list will be
+ *                stored on return. If no devices are in the session,
+ *                this will be NULL. Each element in the list points
+ *                to a struct sr_dev_inst *.
+ *                The list must be freed by the caller, but not the
+ *                elements pointed to.
+ *
+ * @return SR_OK upon success, SR_ERR upon invalid arguments.
+ */
+SR_API int sr_session_dev_list(GSList **devlist)
+{
+
+	*devlist = NULL;
+
+	if (!session)
+		return SR_ERR;
+
+	*devlist = g_slist_copy(session->devs);
+
+	return SR_OK;
+}
+
 /**
  * Remove all datafeed callbacks in the current session.
  *