netdev - Re: [PATCH RFC net-next 05/13] selftests: forwarding: add TCPDUMP_EXTRA

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Message-ID: <20220411172042.prh3hy7ehpc5o34f@skbuf>
Date:   Mon, 11 Apr 2022 17:20:42 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Joachim Wiberg <troglobit@...il.com>
CC:     Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bridge@...ts.linux-foundation.org" 
        <bridge@...ts.linux-foundation.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Tobias Waldekranz <tobias@...dekranz.com>
Subject: Re: [PATCH RFC net-next 05/13] selftests: forwarding: add
 TCPDUMP_EXTRA_FLAGS to lib.sh

On Mon, Apr 11, 2022 at 03:38:29PM +0200, Joachim Wiberg wrote:
> For some use-cases we may want to change the tcpdump flags used in
> tcpdump_start().  For instance, observing interfaces without the PROMISC
> flag, e.g. to see what's really being forwarded to the bridge interface.
> 
> Signed-off-by: Joachim Wiberg <troglobit@...il.com>
> ---
>  tools/testing/selftests/net/forwarding/lib.sh | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>  mode change 100644 => 100755 tools/testing/selftests/net/forwarding/lib.sh
> 
> diff --git a/tools/testing/selftests/net/forwarding/lib.sh b/tools/testing/selftests/net/forwarding/lib.sh
> old mode 100644
> new mode 100755
> index 664b9ecaf228..00cdcab7accf
> --- a/tools/testing/selftests/net/forwarding/lib.sh
> +++ b/tools/testing/selftests/net/forwarding/lib.sh
> @@ -1369,7 +1369,13 @@ tcpdump_start()
>  		capuser="-Z $SUDO_USER"
>  	fi
>  
> -	$ns_cmd tcpdump -e -n -Q in -i $if_name \
> +	if [ -z $TCPDUMP_EXTRA_FLAGS ]; then
> +		extra_flags=""
> +	else
> +		extra_flags="$TCPDUMP_EXTRA_FLAGS"
> +	fi
> +
> +	$ns_cmd tcpdump $extra_flags -e -n -Q in -i $if_name \

Could you call directly "$ns_cmd tcpdump $TCPDUMP_EXTRA_FLAGS ..." here,
without an intermediary "extra_flags" global variable which holds the
same content?

You could initialize it just like the way other variables are
initialized, at the beginning of lib.sh:

TCPDUMP_EXTRA_FLAGS=${TCPDUMP_EXTRA_FLAGS:=}

>  		-s 65535 -B 32768 $capuser -w $capfile > "$capout" 2>&1 &
>  	cappid=$!
>  
> -- 
> 2.25.1
>