tracing: add __print_symbolic to trace events

This patch adds __print_symbolic which is similar to __print_flags but
works for an enumeration type instead. That is, there is only a one to one
mapping between the values and the symbols. When a match is made, then
it is printed, otherwise the hex value is outputed.

[ Impact: add interface for showing symbol names in events ]

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

include/linux/ftrace_event.h

@@ -20,6 +20,9 @@ const char *ftrace_print_flags_seq(struct trace_seq *p, const char *delim,
 				   unsigned long flags,
 				   const struct trace_print_flags *flag_array);
 
+const char *ftrace_print_symbols_seq(struct trace_seq *p, unsigned long val,
+				     const struct trace_print_flags *symbol_array);
+
 /*
  * The trace entry - the most basic unit of tracing. This is what
  * is printed in the end as a single line in the trace output, such as:

include/trace/ftrace.h

@@ -130,6 +130,14 @@
 		ftrace_print_flags_seq(p, delim, flag, flags);		\
 	})
 
+#undef __print_symbolic
+#define __print_symbolic(value, symbol_array...)			\
+	({								\
+		static const struct trace_print_flags symbols[] =	\
+			{ symbol_array, { -1, NULL }};			\
+		ftrace_print_symbols_seq(p, value, symbols);		\
+	})
+
 #undef TRACE_EVENT
 #define TRACE_EVENT(call, proto, args, tstruct, assign, print)		\
 enum print_line_t							\

kernel/trace/trace_output.c

@@ -251,6 +251,31 @@ ftrace_print_flags_seq(struct trace_seq *p, const char *delim,
 	return p->buffer;
 }
 
+const char *
+ftrace_print_symbols_seq(struct trace_seq *p, unsigned long val,
+			 const struct trace_print_flags *symbol_array)
+{
+	int i;
+
+	trace_seq_init(p);
+
+	for (i = 0;  symbol_array[i].name; i++) {
+
+		if (val != symbol_array[i].mask)
+			continue;
+
+		trace_seq_puts(p, symbol_array[i].name);
+		break;
+	}
+
+	if (!p->len)
+		trace_seq_printf(p, "0x%lx", val);
+
+	trace_seq_putc(p, 0);
+
+	return p->buffer;
+}
+
 #ifdef CONFIG_KRETPROBES
 static inline const char *kretprobed(const char *name)
 {