netdev - Re: [PATCH net] selftests: mirror_gre_changes: Tighten up the TTL test match

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Date: Sat, 12 Aug 2023 19:47:38 +0200
From: Simon Horman <horms@...nel.org>
To: Petr Machata <petrm@...dia.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, mlxsw@...dia.com,
	Ido Schimmel <idosch@...dia.com>, Jiri Pirko <jiri@...nulli.us>,
	Mirsad Todorovac <mirsad.todorovac@....unizg.hr>,
	Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net] selftests: mirror_gre_changes: Tighten up the TTL
 test match

On Fri, Aug 11, 2023 at 05:59:27PM +0200, Petr Machata wrote:

+ Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org

> This test verifies whether the encapsulated packets have the correct
> configured TTL. It does so by sending ICMP packets through the test
> topology and mirroring them to a gretap netdevice. On a busy host
> however, more than just the test ICMP packets may end up flowing
> through the topology, get mirrored, and counted. This leads to
> potential spurious failures as the test observes much more mirrored
> packets than the sent test packets, and assumes a bug.
> 
> Fix this by tightening up the mirror action match. Change it from
> matchall to a flower classifier matching on ICMP packets specifically.
> 
> Fixes: 45315673e0c5 ("selftests: forwarding: Test changes in mirror-to-gretap")
> Signed-off-by: Petr Machata <petrm@...dia.com>
> Tested-by: Mirsad Todorovac <mirsad.todorovac@....unizg.hr>
> Reviewed-by: Ido Schimmel <idosch@...dia.com>

Reviewed-by: Simon Horman <horms@...nel.org>

> ---
>  tools/testing/selftests/net/forwarding/mirror_gre_changes.sh | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/net/forwarding/mirror_gre_changes.sh b/tools/testing/selftests/net/forwarding/mirror_gre_changes.sh
> index aff88f78e339..5ea9d63915f7 100755
> --- a/tools/testing/selftests/net/forwarding/mirror_gre_changes.sh
> +++ b/tools/testing/selftests/net/forwarding/mirror_gre_changes.sh
> @@ -72,7 +72,8 @@ test_span_gre_ttl()
>  
>  	RET=0
>  
> -	mirror_install $swp1 ingress $tundev "matchall $tcflags"
> +	mirror_install $swp1 ingress $tundev \
> +		"prot ip flower $tcflags ip_prot icmp"
>  	tc filter add dev $h3 ingress pref 77 prot $prot \
>  		flower skip_hw ip_ttl 50 action pass
>  
> -- 
> 2.41.0
> 
>