Re: [PATCH] selftests/livepatch: fix and refactor new dmesg message code

From: Alexander Gordeev <agordeev@linux.ibm.com>
To: Joe Lawrence <joe.lawrence@redhat.com>
Cc: live-patching@vger.kernel.org, linux-kselftest@vger.kernel.org,
	linux-s390@vger.kernel.org, Petr Mladek <pmladek@suse.com>
Subject: Re: [PATCH] selftests/livepatch: fix and refactor new dmesg message code
Date: Wed, 20 Dec 2023 21:19:50 +0100	[thread overview]
Message-ID: <ZYNMZnRAgAXcvbqq@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com> (raw)
In-Reply-To: <20231220151151.267985-1-joe.lawrence@redhat.com>

On Wed, Dec 20, 2023 at 10:11:51AM -0500, Joe Lawrence wrote:
> The livepatching kselftests rely on comparing expected vs. observed
> dmesg output.  After each test, new dmesg entries are determined by the
> 'comm' utility comparing a saved, pre-test copy of dmesg to post-test
> dmesg output.
> 
> Alexander reports that the 'comm --nocheck-order -13' invocation used by
> the tests can be confused when dmesg entry timestamps vary in magnitude
> (ie, "[   98.820331]" vs. "[  100.031067]"), in which case, additional
> messages are reported as new.  The unexpected entries then spoil the
> test results.
> 
> Instead of relying on 'comm' or 'diff' to determine new testing dmesg
> entries, refactor the code:
> 
>   - pre-test  : log a unique canary dmesg entry
>   - test      : run tests, log messages
>   - post-test : filter dmesg starting from pre-test message
> 
> Reported-by: Alexander Gordeev <agordeev@linux.ibm.com>
> Closes: https://lore.kernel.org/live-patching/ZYAimyPYhxVA9wKg@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com/
> Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
> ---
>  .../testing/selftests/livepatch/functions.sh  | 37 +++++++++----------
>  1 file changed, 17 insertions(+), 20 deletions(-)

Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>