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>

3 files changed, 36 insertions, 0 deletions

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 4b58cf1a11c2..bbf40f624fc8 100644
--- a/include/linux/ftrace_event.h
+++ b/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:
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 22c94719c569..87fc227c6fbe 100644
--- a/include/trace/ftrace.h
+++ b/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                                                       \
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index a4840c260c89..c12d95db2f56 100644
--- a/kernel/trace/trace_output.c
+++ b/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)
 {