linux-kernel - Re: [PATCH 5/5] perf tools: Enhance parsing events tracepoint error output

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Date:	Fri, 11 Sep 2015 15:55:43 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Raphaël Beamonte <raphael.beamonte@...il.com>
Cc:	Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
	Jiri Olsa <jolsa@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH 5/5] perf tools: Enhance parsing events tracepoint error
 output

Em Fri, Sep 11, 2015 at 01:50:02PM -0400, Raphaël Beamonte escreveu:
> 2015-09-11 12:16 GMT-04:00 Jiri Olsa <jolsa@...hat.com>:
> > On Sat, Sep 12, 2015 at 01:09:31AM +0900, Namhyung Kim wrote:
> <SNIP>
> >> has a problem - if tracefs is mounted under debugfs, the access mode
> >> of debugfs also affects, so in this case I had to change it both for
> >> debugfs and tracefs..

> > hum, I wonder the error message needs to be that smart..
> 
> Hmm... If tracefs is mounted under debugfs, wouldn't remounting
> debugfs do the trick, as it was done before?

Not necessarily, we may be able to access /a/ but not /a/b/, so, before
we get to /a/b/ we need to solve access to /a/ to then realize that
/a/b/ also need permission change so that we can access it.

> If so, why couldn't we just check the paths with a basic strcmp to
> verify if tracefs starts by debugfs, and in that case offer to remount
> debugfs, else offer to remount tracefs?

say it is how it was before tracefs:

 /sys/kernel/debug/tracing/

If we can't access "/sys/kernel/debug/tracing/" because we can't access
"/sys/kernel/debug/" we need first to change (remount, chmod/grp/own,
whatever is best in each hypotetical use case) /sys/kernel/debug/ to
then do the same for /sys/kernel/debug/tracing/, no?

We could of course say something like "Something is wrong with tracefs
and/or debugfs, figure it out and try again", but we can do better,
right? 8-P

- Arnaldo
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