linux-kernel - Re: [PATCH] tools/testing/selftests/bpf/test_tc_tunnel.sh: Prevent client connect before server bind

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Date: Thu, 7 Mar 2024 17:03:43 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: "Alessandro Carminati (Red Hat)" <alessandro.carminati@...il.com>
Cc: Mykola Lysenko <mykolal@...com>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, bpf@...r.kernel.org,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
 Andrii Nakryiko <andrii@...nel.org>, Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH] tools/testing/selftests/bpf/test_tc_tunnel.sh: Prevent
 client connect before server bind

On 2/29/24 6:00 AM, Alessandro Carminati (Red Hat) wrote:
> In some systems, the netcat server can incur in delay to start listening.
> When this happens, the test can randomly fail in various points.
> This is an example error message:
>     # ip gre none gso
>     # encap 192.168.1.1 to 192.168.1.2, type gre, mac none len 2000
>     # test basic connectivity
>     # Ncat: Connection refused.

This explained what is the issue. Please also explain how the patch solves it.

> 
> Signed-off-by: Alessandro Carminati (Red Hat) <alessandro.carminati@...il.com>
> ---
>   tools/testing/selftests/bpf/test_tc_tunnel.sh | 19 ++++++++++++++++++-
>   1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/bpf/test_tc_tunnel.sh b/tools/testing/selftests/bpf/test_tc_tunnel.sh
> index 910044f08908..01c0f4b1a8c2 100755
> --- a/tools/testing/selftests/bpf/test_tc_tunnel.sh
> +++ b/tools/testing/selftests/bpf/test_tc_tunnel.sh
> @@ -72,7 +72,6 @@ cleanup() {
>   server_listen() {
>   	ip netns exec "${ns2}" nc "${netcat_opt}" -l "${port}" > "${outfile}" &
>   	server_pid=$!
> -	sleep 0.2
>   }
>   
>   client_connect() {
> @@ -93,6 +92,22 @@ verify_data() {
>   	fi
>   }
>   
> +wait_for_port() {
> +	local digits=8
> +	local port2check=$(printf ":%04X" $1)
> +	local prot=$([ "$2" == "-6" ] && echo 6 && digits=32)
> +
> +	for i in $(seq 20); do
> +		if ip netns exec "${ns2}" cat /proc/net/tcp${prot} | \
> +			sed -r 's/^[ \t]+[0-9]+: ([0-9A-F]{'${digits}'}:[0-9A-F]{4}) .*$/\1/' | \
> +			grep -q "${port2check}"; then

The idea is to check if there is socket listening on port 8888?

May be something simpler like "ss -OHtl src :$1" instead?

--
pw-bot: cr

The check-and-wait fix in this patch is fine to get your test environment going.

Eventually, it will be good to see the test_tc_tunnel.sh test moved to 
test_progs. The test_tc_tunnel.sh is not run by bpf CI and issue like this got 
unnoticed. Some other "*.sh" tests have already been moved to test_progs.