rxrpc: Use a tracepoint for skb accounting debugging

Use a tracepoint to log various skb accounting points to help in debugging
refcounting errors.

Signed-off-by: David Howells <dhowells@redhat.com>

include/trace/events/rxrpc.h

@@ -0,0 +1,56 @@
+/* AF_RXRPC tracepoints
+ *
+ * Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM rxrpc
+
+#if !defined(_TRACE_RXRPC_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_RXRPC_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(rxrpc_skb,
+	    TP_PROTO(struct sk_buff *skb, int op, int usage, int mod_count,
+		     const void *where),
+
+	    TP_ARGS(skb, op, usage, mod_count, where),
+
+	    TP_STRUCT__entry(
+		    __field(struct sk_buff *,		skb		)
+		    __field(int,			op		)
+		    __field(int,			usage		)
+		    __field(int,			mod_count	)
+		    __field(const void *,		where		)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->skb = skb;
+		    __entry->op = op;
+		    __entry->usage = usage;
+		    __entry->mod_count = mod_count;
+		    __entry->where = where;
+			   ),
+
+	    TP_printk("s=%p %s u=%d m=%d p=%pSR",
+		      __entry->skb,
+		      (__entry->op == 0 ? "NEW" :
+		       __entry->op == 1 ? "SEE" :
+		       __entry->op == 2 ? "GET" :
+		       __entry->op == 3 ? "FRE" :
+		       "PUR"),
+		      __entry->usage,
+		      __entry->mod_count,
+		      __entry->where)
+	    );
+
+#endif /* _TRACE_RXRPC_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>