Re: [PATCH mptcp-net v5 5/5] selftests: mptcp: test transmission with small rcvbuf

[Matthieu Baerts <matttbe@kernel.org>]

Hi Geliang,

On 03/04/2026 03:17, Geliang Tang wrote:
> Hi Gang,
> 
> On Wed, 2026-04-01 at 16:54 +0800, Gang Yan wrote:
>> From: Gang Yan <yangang@kylinos.cn>
>>
>> This patch adds a test for transmission with a limited receive
>> buffer.
>>
>> Without the fixes in this set, this test fails with errors:
>>
>>  # 001 4 subflows with reduced rcvbuf
>>  # net.ipv4.tcp_rmem = 4096 4096 4096
>>  #       Info: Test file (size 1024 KB) for client
>>  #       Info: Test file (size 1024 KB) for server
>>  # copyfd_io_poll: poll timed out (events: POLLIN 1, POLLOUT 0)
>>  # copyfd_io_poll: poll timed out (events: POLLIN 0, POLLOUT 4)
>>  # [FAIL] client exit code 2, server 2
>>  # Server ns stats (ns2-qg1Hqo)
>>
>> Co-developed-by: Geliang Tang <geliang@kernel.org>
>> Signed-off-by: Geliang Tang <geliang@kernel.org>
>> Signed-off-by: Gang Yan <yangang@kylinos.cn>
>> ---
>> Notes:
>>
>> Changelog:
>> v5:
>>   - Drop the unnecessary tcp_rmem restore.
>>
>> ---
>>  tools/testing/selftests/net/mptcp/mptcp_join.sh | 17
>> +++++++++++++++++
>>  1 file changed, 17 insertions(+)
>>
>> diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh
>> b/tools/testing/selftests/net/mptcp/mptcp_join.sh
>> index beec41f6662a..a21333424085 100755
>> --- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
>> +++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
>> @@ -4417,6 +4417,22 @@ endpoint_tests()
>>  	fi
>>  }
>>  
>> +rcvbuf_tests()
>> +{
>> +	if reset "4 subflows with reduced rcvbuf"; then
>> +		ip netns exec $ns2 sysctl -w net.ipv4.tcp_rmem="4096
>> 4096 4096"
> 
> Instead of using reset() here, it's better to set this sysctl in a new
> helper - for example, reset_with_tcp_rmem() - as is done in other
> tests.

If there is only one test, I think it is fine to leave this here: at
least it is clear what is being done. A helper only used once just to
set one extra command might not be worth it.

But what you can do is to use 'sysctl -q', like every time 'sysctl' is used.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.