linux-kernel - Re: [PATCH v2 2/6] tracing: add flag to control different traces

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Date:   Tue, 28 Jul 2020 08:29:22 +0800
From:   Tingwei Zhang <tingweiz@...eaurora.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Tingwei Zhang <tingwei@...eaurora.org>,
        Ingo Molnar <mingo@...hat.com>, tsoni@...eaurora.org,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Mao Jinlong <jinlmao@...eaurora.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/6] tracing: add flag to control different traces

Hi Steve,
On Tue, Jul 28, 2020 at 02:45:50AM +0800, Steven Rostedt wrote:
> On Sun, 26 Jul 2020 10:59:27 +0800
> Tingwei Zhang <tingwei@...eaurora.org> wrote:
> 
> 
> > diff --git a/include/linux/trace.h b/include/linux/trace.h
> > index 7fd86d3c691f..d2fdf9be84b5 100644
> > --- a/include/linux/trace.h
> > +++ b/include/linux/trace.h
> > @@ -3,6 +3,9 @@
> >  #define _LINUX_TRACE_H
> >  
> >  #ifdef CONFIG_TRACING
> > +
> > +#define TRACE_EXPORT_FUNCTION	BIT_ULL(0)
> 
> All the flags variables below are defined as "int". Why the BIT_ULL()?
> BIT(0) should work just fine. The ULL makes one think these flags will
> be used for unsigned long variables, which it is not.
> 

That's my mistake.  Thanks for point that out. I'll fix it in next
revision.

> -- Steve
> 
> 
> > +
> 
> >  struct trace_export {
> >  	struct trace_export __rcu	*next;
> >  	void (*write)(struct trace_export *, const void *, unsigned int);
> > +	int flags;
> >  };
> >  
> >  int register_ftrace_export(struct trace_export *export);
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index bb62269724d5..8f1e66831e9e 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -2747,33 +2747,37 @@ trace_buffer_unlock_commit_nostack(struct
> trace_buffer *buffer,
> >  
> >  static void
> >  trace_process_export(struct trace_export *export,
> > -	       struct ring_buffer_event *event)
> > +	       struct ring_buffer_event *event, int flag)
> >  {
> >  	struct trace_entry *entry;
> >  	unsigned int size = 0;
> >  
> > -	entry = ring_buffer_event_data(event);
> > -	size = ring_buffer_event_length(event);
> > -	export->write(export, entry, size);
> > +	if (export->flags & flag) {
> > +		entry = ring_buffer_event_data(event);
> > +		size = ring_buffer_event_length(event);
> > +		export->write(export, entry, size);
> > +	}
> >  }