svcrdma: Introduce infrastructure to support completion IDs

The goal is to replace CQE kernel memory addresses in completion-
related tracepoints.

Each completion ID matches an incoming Send or Receive completion
to a Completion Queue and to a previous ib_post_*(). The ID can
then be displayed in an error message or recorded in a trace
record.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

include/linux/sunrpc/rpc_rdma_cid.h

@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * * Copyright (c) 2020, Oracle and/or its affiliates.
+ */
+
+#ifndef RPC_RDMA_CID_H
+#define RPC_RDMA_CID_H
+
+/*
+ * The rpc_rdma_cid struct records completion ID information. A
+ * completion ID matches an incoming Send or Receive completion
+ * to a Completion Queue and to a previous ib_post_*(). The ID
+ * can then be displayed in an error message or recorded in a
+ * trace record.
+ *
+ * This struct is shared between the server and client RPC/RDMA
+ * transport implementations.
+ */
+struct rpc_rdma_cid {
+	u32			ci_queue_id;
+	int			ci_completion_id;
+};
+
+#endif	/* RPC_RDMA_CID_H */