linux-kernel - Re: [PATCH] selftests/lkdtm: Use "comm" instead of "diff" for dmesg

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Date:   Sat, 27 Jun 2020 08:52:50 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Shuah Khan <shuah@...nel.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/lkdtm: Use "comm" instead of "diff" for dmesg

On Sat, Jun 27, 2020 at 09:51:31PM +1000, Michael Ellerman wrote:
> Kees Cook <keescook@...omium.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?

No, it doesn't seem to. "comm" doesn't carry about the line prefixes.
AIUI, the only reason for a mention of "sort" is because of how "comm"
does its line pairing. i.e. as soon as it goes out of sync, it starts
accounting for the disjunction between files. But that's exactly what we
want it doing, and the prefix doesn't matter.

-- 
Kees Cook