linux-kernel - Re: [PATCH 5/5] perf: Make perf aware of tracefs

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Date:	Mon, 26 Jan 2015 09:57:37 +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 5/5] perf: Make perf aware of tracefs

On Sun, Jan 25, 2015 at 02:31:51PM -0500, Steven Rostedt wrote:
> On Sun, 25 Jan 2015 18:34:33 +0100
> Jiri Olsa <jolsa@...hat.com> wrote:
> 
> > On Sat, Jan 24, 2015 at 01:13:35PM -0500, Steven Rostedt wrote:
> > 
> > SNIP
> > 
> > > @@ -351,11 +385,15 @@ const char *find_tracing_dir(void)
> > >  	if (tracing_found)
> > >  		return tracing;
> > >  
> > > -	debugfs = find_debugfs();
> > > -	if (!debugfs)
> > > -		return NULL;
> > > +	debugfs = find_tracefs();
> > > +	if (!debugfs) {
> > > +		tracing_dir = "/tracing";
> > > +		debugfs = find_debugfs();
> > > +		if (!debugfs)
> > > +			return NULL;
> > 
> > so this pattern 'try tracefs, if that does not work try debugfs'
> > is all over the patch.. how about we add new new 'virtual' fs to
> > encapsulate that, like:
> > 
> >   with followign interface:
> >     bool tpfs_configured(void);
> >     const char *tpfs_find_mountpoint(void);
> >     int tpfs_valid_mountpoint(const char *debugfs);
> >     char *tpfs_mount(const char *mountpoint);
> >     extern char tpfs_mountpoint[];
> > 
> > It does not neceserily needs to reside in tools/lib/api/fs/tpfs.[ch],
> > but I believe we need some form of encapsulation for this.
> 
> I did it this way because perf had no encapsulation for finding debugfs
> paths. I made the change in trace-cmd in one location. Perf does it a
> little different in each place. I have no idea why there was more than
> one location slapping on "/tracing".
> 
> I'd like to get tracefs into perf before doing any redesign of perf's
> infrastructure. That could come later as a cleanup.
> 
> This is not a fast path, it wont hurt performance. I agree it should be
> encapsulated, but that's going outside of the scope of this patch
> series, which is only to add awareness to tracefs, not to clean up
> perf's access to the debugfs/tracing directory.

sure, np.. it could be taken care of later

jirka
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