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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Kees Cook <keescook@chromium.org>, Shuah Khan <shuah@kernel.org>
Cc:     Naresh Kamboju <naresh.kamboju@linaro.org>,
        Petr Mladek <pmladek@suse.com>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] selftests/lkdtm: Use "comm" instead of "diff" for dmesg
In-Reply-To: <202006261358.3E8AA623A9@keescook>
References: <202006261358.3E8AA623A9@keescook>
Date:   Sat, 27 Jun 2020 21:51:31 +1000
Message-ID: <87k0zsbubg.fsf@mpe.ellerman.id.au>
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Kees Cook <keescook@chromium.org> writes:
> Instead of full GNU diff (which smaller boot environments may not have),
> use "comm" which is more available.

Although using "comm" requires CONFIG_PRINTK_TIME=y doesn't it?

Which is probably fine, but should be mentioned.

And I guess for completeness you could add:

diff --git a/tools/testing/selftests/lkdtm/config b/tools/testing/selftests/lkdtm/config
index d874990e442b..ae88bfb163ff 100644
--- a/tools/testing/selftests/lkdtm/config
+++ b/tools/testing/selftests/lkdtm/config
@@ -1 +1,2 @@
 CONFIG_LKDTM=y
+CONFIG_PRINTK_TIME=y


cheers

> Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
> Link: https://lore.kernel.org/lkml/CA+G9fYtHP+Gg+BrR_GkBMxu2oOi-_e9pATtpb6TVRswv1G1r1Q@mail.gmail.com
> Fixes: f131d9edc29d ("selftests/lkdtm: Don't clear dmesg when running tests")
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  tools/testing/selftests/lkdtm/run.sh | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/lkdtm/run.sh b/tools/testing/selftests/lkdtm/run.sh
> index 8383eb89d88a..5fe23009ae13 100755
> --- a/tools/testing/selftests/lkdtm/run.sh
> +++ b/tools/testing/selftests/lkdtm/run.sh
> @@ -82,7 +82,7 @@ dmesg > "$DMESG"
>  ($SHELL -c 'cat <(echo '"$test"') >'"$TRIGGER" 2>/dev/null) || true
>  
>  # Record and dump the results
> -dmesg | diff --changed-group-format='%>' --unchanged-group-format='' "$DMESG" - > "$LOG" || true
> +dmesg | comm -13 "$DMESG" - > "$LOG" || true
>  
>  cat "$LOG"
>  # Check for expected output
> -- 
> 2.25.1
>
>
> -- 
> Kees Cook