tracing: increase size of number of possible events

With the new event tracing registration, we must increase the number
of events that can be registered. Currently the type field is only
one byte, which leaves us only 256 possible events.

Since we do not save the CPU number in the tracer anymore (it is determined
by the per cpu ring buffer that is used) we have an extra byte to use.

This patch increases the size of type from 1 byte (256 events) to
2 bytes (65,536 events).

It also adds a WARN_ON_ONCE if we exceed that limit.

[ Impact: allow more than 255 events ]
Signed-off-by: Steven Rostedt <srostedt@redhat.com>

include/linux/ftrace_event.h

@@ -16,13 +16,16 @@ struct dentry;
  *     bash-15816 [01]   235.197585: idle_cpu <- irq_enter
  */
 struct trace_entry {
-	int			type;
+	unsigned short		type;
 	unsigned char		flags;
 	unsigned char		preempt_count;
 	int			pid;
 	int			tgid;
 };
 
+#define FTRACE_MAX_EVENT						\
+	((1 << (sizeof(((struct trace_entry *)0)->type) * 8)) - 1)
+
 /*
  * Trace iterator - used by printout routines who present trace
  * results to users and which routines might sleep, etc:

kernel/trace/trace_events.c

@@ -398,7 +398,7 @@ static int trace_write_header(struct trace_seq *s)
 				"\tfield:%s %s;\toffset:%zu;\tsize:%zu;\n"
 				"\tfield:%s %s;\toffset:%zu;\tsize:%zu;\n"
 				"\n",
-				FIELD(int, type),
+				FIELD(unsigned short, type),
 				FIELD(unsigned char, flags),
 				FIELD(unsigned char, preempt_count),
 				FIELD(int, pid),

kernel/trace/trace_output.c

@@ -537,6 +537,8 @@ int register_ftrace_event(struct trace_event *event)
  out:
 	mutex_unlock(&trace_event_mutex);
 
+	WARN_ON_ONCE(next_event_type > FTRACE_MAX_EVENT);
+
 	return ret;
 }
 EXPORT_SYMBOL_GPL(register_ftrace_event);