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<div class="moz-cite-prefix">On 18/09/2025 08:36, Geliang Tang
wrote:<span style="white-space: pre-wrap">
</span></div>
<blockquote type="cite" cite="mid:717920eaaa9d4d0da181d84dd11334dae2568f34.camel@kernel.org">
<pre wrap="" class="moz-quote-pre">
I have completed the implementation. Thanks to Xiang Gao and Gang Yan
for their help. I added a new option named TCP_MPTCPIFY in
jdk.net.ExtendedSocketOptions (the name was chosen to align with
'mptcpize' tool in mptcpd and 'mptcpify' in BCC). When this option is
set, it calls the JNI function mptcpify0.
Following your suggestion, mptcpify0 is implemented by referencing
Java_sun_net_sdp_SdpSupport_convert0. It creates a new MPTCP socket,
uses dup2 to duplicate it, and then closes the redundant socket.
I have added your tag in the patch:
Suggested-by: Alan Bateman <a class="moz-txt-link-rfc2396E" href="mailto:alan.bateman@oracle.com"><alan.bateman@oracle.com></a>
I also included a test example for this option. All modifications can
be found here:
<a class="moz-txt-link-freetext" href="https://github.com/openjdk/jdk/compare/master...geliangtang:jdk:master">https://github.com/openjdk/jdk/compare/master...geliangtang:jdk:master</a>
Please provide any feedback or suggestions. As for the next steps,
should I create a new issue for this feature and submit a proper pull
request?
</pre>
</blockquote>
<br>
Thanks for confirming that the direction suggested works. This at
least demonstrates a feasible direction that does not impact the
standard API.<br>
<br>
As regards next steps then I think start a thread on net-dev to try
to get input. I think it would be useful to show potential scenarios
where it would be useful and what performance benefits might come
from it. I think also useful to talk about whether this is something
that an application has to opt into, maybe there are other
configuration approaches that would not require application changes?<br>
<br>
I think it would be useful to discuss testing. If this feature were
integrated into the JDK then how would it be tested? Who would test
and maintain it? There is a JDK release every 6 months, is someone
going test it with each release?<br>
<br>
If it goes ahead then there the name of the extended socket option
and its API docs will need discussion. Details around state will
need to be specified, would it be supported to set TCP_MPTCP when
bound or connected, does it make sense to ever attempt to set it to
false after setting it to true (these are just examples of the
details that will need to be specified, they are not important right
now).<br>
<br>
-Alan.<br>
<br>
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