linux-kernel - Re: [PATCH v4 3/3] tracing: kdb: Allow ftdump to skip all but the last few entries

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Message-ID: <20190318095436.7f09a371@gandalf.local.home>
Date:   Mon, 18 Mar 2019 09:54:36 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Douglas Anderson <dianders@...omium.org>,
        Ingo Molnar <mingo@...hat.com>,
        Jason Wessel <jason.wessel@...driver.com>,
        kgdb-bugreport@...ts.sourceforge.net,
        Brian Norris <briannorris@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/3] tracing: kdb: Allow ftdump to skip all but the
 last few entries

On Mon, 18 Mar 2019 03:02:38 +0000
Daniel Thompson <daniel.thompson@...aro.org> wrote:

> > diff --git a/kernel/trace/trace_kdb.c b/kernel/trace/trace_kdb.c
> > index 4b666643d69f..996e1e9cd9a6 100644
> > --- a/kernel/trace/trace_kdb.c
> > +++ b/kernel/trace/trace_kdb.c
> > @@ -39,7 +39,8 @@ static void ftrace_dump_buf(int skip_entries, long cpu_file)
> >  	/* don't look at user memory in panic mode */
> >  	tr->trace_flags &= ~TRACE_ITER_SYM_USEROBJ;
> >  
> > -	kdb_printf("Dumping ftrace buffer:\n");
> > +	kdb_printf("Dumping ftrace buffer (skipping %d entries):\n",
> > +		   skip_entries);  
> 
> If someone *doesn't* need to skip any entries I'm not a fan of telling
> them we are "skipping 0 entries"; it is more unnerving than helpful
> ("huh? what does it need to tell me that no entried were skipped?
> what makes the tracer skip entries?... Doh... I get it").

I agree.

Probably best to have this:

	kdb_printf("Dumping ftrace buffer:\n");
	if (skip_entries)
		kdb_printf("(skipping %d entries)\n", skip_entries);

No reason to inject that skipping line in the first line.

-- Steve