test/multipath: add helper to obtain secondary sessions

A number of existing tests create a secondary iSCSI session by logging
into the target specified in the base sd during the test.

With multipath sessions now connected during iscsi-test-cu startup
(when launched with multiple URIs), secondary sessions can be
provided via multipath when available, rather than reconnecting.

This change adds a helper that conditionally returns the secondary
multipath device if available, or falls back to creating a new session
via the base sd target details.

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

test-tool/iscsi-multipath.h

@@ -30,6 +30,10 @@ mpath_check_matching_ids(int num_sds,
 int
 mpath_count_iscsi(int num_sds,
 		  struct scsi_device **sds);
+int
+mpath_sd2_get_or_clone(struct scsi_device *sd1, struct scsi_device **_sd2);
+void
+mpath_sd2_put(struct scsi_device *sd2);
 
 #define MPATH_SKIP_IF_UNAVAILABLE(_sds, _num_sds)			\
 do {									\