rdma_cm: add rdma_reject_msg() helper function

rdma_reject_msg() returns a pointer to a string message associated with
the transport reject reason codes.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
index 36bf50e..877e4dc 100644
--- a/drivers/infiniband/core/cma.c
+++ b/drivers/infiniband/core/cma.c
@@ -101,6 +101,20 @@ const char *__attribute_const__ rdma_event_msg(enum rdma_cm_event_type event)
 }
 EXPORT_SYMBOL(rdma_event_msg);
 
+const char *__attribute_const__ rdma_reject_msg(struct rdma_cm_id *id,
+						int reason)
+{
+	if (rdma_ib_or_roce(id->device, id->port_num))
+		return ibcm_reject_msg(reason);
+
+	if (rdma_protocol_iwarp(id->device, id->port_num))
+		return iwcm_reject_msg(reason);
+
+	WARN_ON_ONCE(1);
+	return "unrecognized transport";
+}
+EXPORT_SYMBOL(rdma_reject_msg);
+
 static void cma_add_one(struct ib_device *device);
 static void cma_remove_one(struct ib_device *device, void *client_data);