linux-kernel - Re: [PATCH] perf tool: report user-friendly error from timechart

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Date:	Thu, 3 Oct 2013 15:09:55 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Ramkumar Ramachandra <artagnon@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH] perf tool: report user-friendly error from timechart


* Ramkumar Ramachandra <artagnon@...il.com> wrote:

> Ingo Molnar wrote:
> >> +     /* Perform a quick sanity check */
> >> +     if (!is_valid_tracepoint("power:cpu_frequency")) {
> >> +             fprintf(stderr, "Error:\tNo permissions to read $debugfs/tracing/events/power/cpu_frequency\n");
> >> +             fprintf(stderr, "Hint:\tChange the permissions of debugfs: /sys/kernel/debug\n");
> >> +             fprintf(stderr, "\tThe directory will be present if your kernel was compiled with debugfs support.\n");
> >
> > Is missing permissions the only way how is_valid_tracepoint() can fail?
> >
> > What if debugfs has the right permissions but CONFIG_TRACEPOINTS is
> > disabled in the kernel?
> 
> I'm thinking about all this in terms of files present in debugfs. Will 
> the cpu_frequecy file be present if tracepoints is disabled? (should I 
> quickly check using User-Mode Linux?). If it won't be present, then we 
> can just change the last line to "compiled with debugfs and tracepoints 
> support".

The debug/tracing/events directory won't be present if tracing is 
disabled.

Thanks,

	Ingo
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