tracing: make trace pipe recognize latency format flag

The trace_pipe did not recognize the latency format flag and would produce
different output than the trace file. The problem was partly due that
the trace flags in the iterator was not set as well as the trace_pipe
zeros out part of the iterator (including the flags) to be able to use
the same routines as the trace file. trace_flags of the iterator should
not cause any problems when not zeroed out by for trace_pipe.
Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

include/linux/ftrace_event.h

@@ -51,6 +51,7 @@ struct trace_iterator {
 	int			cpu_file;
 	struct mutex		mutex;
 	struct ring_buffer_iter	*buffer_iter[NR_CPUS];
+	unsigned long		iter_flags;
 
 	/* The below is zeroed out in pipe_read */
 	struct trace_seq	seq;
@@ -58,7 +59,6 @@ struct trace_iterator {
 	int			cpu;
 	u64			ts;
 
-	unsigned long		iter_flags;
 	loff_t			pos;
 	long			idx;
 

kernel/trace/trace.c

@@ -2826,6 +2826,9 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
 	/* trace pipe does not show start of buffer */
 	cpumask_setall(iter->started);
 
+	if (trace_flags & TRACE_ITER_LATENCY_FMT)
+		iter->iter_flags |= TRACE_FILE_LAT_FMT;
+
 	iter->cpu_file = cpu_file;
 	iter->tr = &global_trace;
 	mutex_init(&iter->mutex);