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From:   Naresh Kamboju <naresh.kamboju@linaro.org>
Date:   Mon, 22 Jun 2020 14:21:38 +0530
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Subject: Re: [PATCH 1/2] selftests/lkdtm: Don't clear dmesg when running tests
To:     Michael Ellerman <mpe@ellerman.id.au>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
Cc:     Kees Cook <keescook@chromium.org>,
        Anders Roxell <anders.roxell@linaro.org>,
        =?UTF-8?B?RGFuaWVsIETDrWF6?= <daniel.diaz@linaro.org>,
        Justin Cook <justin.cook@linaro.org>,
        lkft-triage@lists.linaro.org, Miroslav Benes <mbenes@suse.cz>,
        Petr Mladek <pmladek@suse.com>, Shuah Khan <shuah@kernel.org>
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On Fri, 8 May 2020 at 12:23, Michael Ellerman <mpe@ellerman.id.au> wrote:
>
> It is Very Rude to clear dmesg in test scripts. That's because the
> script may be part of a larger test run, and clearing dmesg
> potentially destroys the output of other tests.
>
> We can avoid using dmesg -c by saving the content of dmesg before the
> test, and then using diff to compare that to the dmesg afterward,
> producing a log with just the added lines.
>
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
>  tools/testing/selftests/lkdtm/run.sh | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/lkdtm/run.sh b/tools/testing/selftests/lkdtm/run.sh
> index dadf819148a4..0b409e187c7b 100755
> --- a/tools/testing/selftests/lkdtm/run.sh
> +++ b/tools/testing/selftests/lkdtm/run.sh
> @@ -59,23 +59,25 @@ if [ -z "$expect" ]; then
>         expect="call trace:"
>  fi
>
> -# Clear out dmesg for output reporting
> -dmesg -c >/dev/null
> -
>  # Prepare log for report checking
> -LOG=$(mktemp --tmpdir -t lkdtm-XXXXXX)
> +LOG=$(mktemp --tmpdir -t lkdtm-log-XXXXXX)
> +DMESG=$(mktemp --tmpdir -t lkdtm-dmesg-XXXXXX)
>  cleanup() {
> -       rm -f "$LOG"
> +       rm -f "$LOG" "$DMESG"
>  }
>  trap cleanup EXIT
>
> +# Save existing dmesg so we can detect new content below
> +dmesg > "$DMESG"
> +
>  # Most shells yell about signals and we're expecting the "cat" process
>  # to usually be killed by the kernel. So we have to run it in a sub-shell
>  # and silence errors.
>  ($SHELL -c 'cat <(echo '"$test"') >'"$TRIGGER" 2>/dev/null) || true
>
>  # Record and dump the results
> -dmesg -c >"$LOG"
> +dmesg | diff --changed-group-format='%>' --unchanged-group-format='' "$DMESG" - > "$LOG" || true

We are facing problems with the diff `=%>` part of the option.
This report is from the OpenEmbedded environment.
We have the same problem from livepatch_testcases.

# selftests lkdtm BUG.sh
lkdtm: BUG.sh_ #
# diff unrecognized option '--changed-group-format=%>'
unrecognized: option_'--changed-group-format=%>' #
# BusyBox v1.27.2 (2020-03-30 164108 UTC) multi-call binary.
v1.27.2: (2020-03-30_164108 #
#
: _ #
# Usage diff [-abBdiNqrTstw] [-L LABEL] [-S FILE] [-U LINES] FILE1 FILE2
diff: [-abBdiNqrTstw]_[-L #
# BUG missing 'kernel BUG at' [FAIL]

Full test output log,
https://qa-reports.linaro.org/lkft/linux-next-oe/build/next-20200621/testrun/2850083/suite/kselftest/test/lkdtm_BUG.sh/log

-- 
Linaro LKFT
https://lkft.linaro.org