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

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Message-ID: <CALkWK0=KpwgTuUanH12dEQSJKmBNvxMJEO9T6FSjNcLNH+h6Cw@mail.gmail.com>
Date:	Thu, 3 Oct 2013 18:13:59 +0530
From:	Ramkumar Ramachandra <artagnon@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
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

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".
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