test: add multipath helper functions

mpath_check_matching_ids() walks the list of scsi devices, and confirms
that all entries share one common device identification designator or
unit serial number.

Signed-off-by: David Disseldorp <ddiss@suse.de>

test-tool/iscsi-multipath.h

@@ -0,0 +1,31 @@
+/*
+   iscsi test-tool multipath support
+
+   Copyright (C) 2015 David Disseldorp
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef	_ISCSI_MULTIPATH_H_
+#define	_ISCSI_MULTIPATH_H_
+
+#define MPATH_MAX_DEVS 2
+extern int mp_num_sds;
+extern struct scsi_device *mp_sds[MPATH_MAX_DEVS];
+
+int
+mpath_check_matching_ids(int num_sds,
+			 struct scsi_device **sds);
+
+#endif	/* _ISCSI_MULTIPATH_H_ */