linux-kernel - Re: [PATCH 2/5] tools lib api fs: Add tracefs mount helper functions

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Date:	Mon, 26 Jan 2015 10:02:55 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH 2/5] tools lib api fs: Add tracefs mount helper functions

On Sun, Jan 25, 2015 at 02:26:45PM -0500, Steven Rostedt wrote:
> On Sun, 25 Jan 2015 17:56:19 +0100
> Jiri Olsa <jolsa@...hat.com> wrote:
> 
> > On Sat, Jan 24, 2015 at 01:13:32PM -0500, Steven Rostedt wrote:
> > 
> > SNIP
> > 
> > > @@ -0,0 +1,29 @@
> > > +#ifndef __API_TRACEFS_H__
> > > +#define __API_TRACEFS_H__
> > > +
> > > +#define _STR(x) #x
> > > +#define STR(x) _STR(x)
> > > +
> > > +/*
> > > + * On most systems <limits.h> would have given us this, but  not on some systems
> > > + * (e.g. GNU/Hurd).
> > > + */
> > > +#ifndef PATH_MAX
> > > +#define PATH_MAX 4096
> > > +#endif
> > > +
> > > +#ifndef TRACEFS_MAGIC
> > > +#define TRACEFS_MAGIC          0x74726163
> > > +#endif
> > 
> > I missed the point when tracefs became actual standalone
> > filesystem.. I'll check ;-)
> > 
> > Is it mutualy exclusive to 'debugfs/tracing' or those 2 can live together?
> > 
> 
> I'm working on the patches right now. But when it happens perf should
> be aware of it. I already updated trace-cmd to be aware.
> 
> When tracefs is added, debugfs/tracing will automatically mount tracefs
> when debugfs is mounted. As debugfs currently has some issues with
> automounting, this part is being discussed currently as well.
> 
> Note, WTF is perf checking the magic number for debugfs?? If events
> move, even if its at the same path, this will break perf!

good question.. it's there since 2009:
  f6bdafef2ab9 perf_counter: Add tracepoint support to perf list, perf stat

I guess we didn't want anyone to trick us with fake tracepoints ;-)

jirka
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