tracing: Add trace_seq_has_overflowed() and trace_handle_return()

Adding a trace_seq_has_overflowed() which returns true if the trace_seq
had too much written into it allows us to simplify the code.

Instead of checking the return value of every call to trace_seq_printf()
and friends, they can all be called normally, and at the end we can
return !trace_seq_has_overflowed() instead.

Several functions also return TRACE_TYPE_PARTIAL_LINE when the trace_seq
overflowed and TRACE_TYPE_HANDLED otherwise. Another helper function
was created called trace_handle_return() which takes a trace_seq and
returns these enums. Using this helper function also simplifies the
code.

This change also makes it possible to remove the return values of
trace_seq_printf() and friends. They should instead just be
void functions.

Link: http://lkml.kernel.org/r/20141114011410.365183157@goodmis.org

Reviewed-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 26b4f2e..f13471b 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -280,11 +280,9 @@
 	if (ret)							\
 		return ret;						\
 									\
-	ret = trace_seq_printf(s, print);				\
-	if (!ret)							\
-		return TRACE_TYPE_PARTIAL_LINE;				\
+	trace_seq_printf(s, print);					\
 									\
-	return TRACE_TYPE_HANDLED;					\
+	return trace_handle_return(s);					\
 }									\
 static struct trace_event_functions ftrace_event_type_funcs_##call = {	\
 	.trace			= ftrace_raw_output_##call,		\