linux-kernel - Re: [PATCH] selftests: ftrace: Use md5sum to take less time of checking logs

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Date:   Fri, 30 Jun 2017 15:03:13 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Denys Vlasenko <vda.linux@...glemail.com>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kselftest@...r.kernel.org, shuah@...nel.org,
        Ingo Molnar <mingo@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] selftests: ftrace: Use md5sum to take less time of
 checking logs

On Fri, 30 Jun 2017 20:50:45 +0200
Denys Vlasenko <vda.linux@...glemail.com> wrote:

> On Tue, Jun 27, 2017 at 12:28 PM, Masami Hiramatsu <mhiramat@...nel.org> wrote:
> > Use md5sum so that it takes less time of checking
> > trace logs update. Since busybox tail/cat takes too
> > long time to read the trace log, this uses md5sum
> > to check whether trace log is updated or not.
> >
> > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> > ---
> >  .../test.d/ftrace/func_traceonoff_triggers.tc      |    6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/testing/selftests/ftrace/test.d/ftrace/func_traceonoff_triggers.tc b/tools/testing/selftests/ftrace/test.d/ftrace/func_traceonoff_triggers.tc
> > index 9cf3852..7a9ab4f 100644
> > --- a/tools/testing/selftests/ftrace/test.d/ftrace/func_traceonoff_triggers.tc
> > +++ b/tools/testing/selftests/ftrace/test.d/ftrace/func_traceonoff_triggers.tc
> > @@ -103,11 +103,11 @@ if [ $on != "0" ]; then
> >      fail "Tracing is not off"
> >  fi
> >
> > -line1=`cat trace | tail -1`
> > +csum1=`md5sum trace`
> >  sleep $SLEEP_TIME
> > -line2=`cat trace | tail -1`
> > +csum2=`md5sum trace`  
> 
> If you replace that with "tail -1 <trace", this code
> in busybox will be used:
> 
>                         off_t current = lseek(fd, 0, SEEK_END);

The trace file is a kernel pseudo file that prevents lseek. Now what
you could do is:

 cat trace > tempfile
 csum1=`tail -1 <tempfile`

But then we need to make sure to clean up the files.

-- Steve