Re: [PATCH mptcp-next] selftests: mptcp: print stats before socket closure

Hi Paolo,

On 14/08/2026 18:44, Paolo Abeni wrote:
> On 8/14/26 4:07 PM, Matthieu Baerts (NGI0) wrote:
>> In case of poll timeout, it might be too late to print the stats after
>> the socket closure.
>>
>> Now, in case of poll timeout, 'ss' and 'nstat' are invoked from
>> mptcp_connect to print the stats before exiting. This should help
>> debugging poll timeout issues.
>>
>> Note: for this "workaround", system() is used for debugging purposes
>> only. The returned result can then be safely ignored.
>>
>> Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>
>> ---
>>  tools/testing/selftests/net/mptcp/mptcp_connect.c | 15 +++++++++++++++
>>  1 file changed, 15 insertions(+)
>>
>> diff --git a/tools/testing/selftests/net/mptcp/mptcp_connect.c b/tools/testing/selftests/net/mptcp/mptcp_connect.c
>> index ea4cb6c1bd5e..842c0eb99aa9 100644
>> --- a/tools/testing/selftests/net/mptcp/mptcp_connect.c
>> +++ b/tools/testing/selftests/net/mptcp/mptcp_connect.c
>> @@ -210,6 +210,19 @@ static void xgetaddrinfo(const char *node, const char *service,
>>  	}
>>  }
>>  
>> +static void print_err_stats(void)
>> +{
>> +	char cmd[128];
>> +
>> +	snprintf(cmd, sizeof(cmd), "ss -Menitam -o '%cport = :%s' >&2",
>> +		 listen_mode ? 's' : 'd', cfg_port);
>> +
>> +	fprintf(stderr, "socket stats before socket closure:\n");
>> +	(void)!system(cmd);
>> +	(void)!system("NSTAT_HISTORY='/tmp/$(ip netns id).nstat' nstat -s | "
>> +		      "grep Tcp >&2");
> 
> Overall LGTM. I tried something similar in the past, but the correct
> redirection always fouled me. A couple of questions:

Thank you for having checked!

> - Is the '!' operator needed?

Yes, to avoid a warning because the results are unused. Only using
(void) is not enough from what I saw.

> - Can we avoid the pipe? with something alike the following:
> 	(void)system("NSTAT_HISTORY='/tmp/$(ip netns id).nstat' nstat -s *Tcp*

Oh nice, I didn't think about that. Yes it works except it keeps the
header (#kernel). Maybe fine here, but we don't change that in the .sh
scripts?

I can send a v2 with that and an extra explanation.

Cheers,
Matt
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