From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?ISO-8859-1?Q?S=E9bastien_Barr=E9?= Subject: increase in size for struct request_sock tolerable ? Date: Wed, 03 Mar 2010 10:35:37 +0100 Message-ID: <4B8E2D69.5070900@uclouvain.be> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: alan.p.smith@bt.com To: netdev@vger.kernel.org Return-path: Received: from smtp.sgsi.ucl.ac.be ([130.104.5.67]:43600 "EHLO smtp1.sgsi.ucl.ac.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755311Ab0CCJqK (ORCPT ); Wed, 3 Mar 2010 04:46:10 -0500 Sender: netdev-owner@vger.kernel.org List-ID: Hi, As part of the development of the MPTCP protocol=20 (http://inl.info.ucl.ac.be/mptcp), we are wondering whether it is=20 tolerable to extend the length of the struct request_sock. In the=20 current version of the protocol=20 (http://tools.ietf.org/id/draft-ford-mptcp-multiaddressed-02.txt), a=20 32bit token is exchanged as TCP options in the SYN and SYN/ACK segments= =2E=20 AFAIU, that requires that we store 8 bytes in the request sock for the=20 server side, so that it remembers the local and remote tokens until the= =20 real sock is created.Even worse, since the NULL token is not a reserved= =20 value, we need to store an additional bit (flag) to know that we=20 received that TCP option. Since there are no flags currently stored in=20 the request_sock, we need to directly increase the size by 8 additional= =20 bits. So with the current protocol design, I arrive to a struct request_sock=20 extension of 4 (local token)+4(remote token)+1(1bit flag+7free flags)=3D= 9=20 bytes. A minor protocol modification would allow reducing that constraint.=20 Basically, we would then differ the token exchange until the real sock=20 is created. The flag would still be needed, though, thus in that cas= e=20 we would arrive to 1 byte of extension only for the struct request_sock= =2E So my question is : Do you think there is a sufficient incentive here t= o=20 adapt our protocol draft ? Or is it tolerable to extend the struct=20 request_sock by 9 bytes ? Thanks in advance ! S=E9bastien. --=20 S=E9bastien Barr=E9 Researcher, CSE department, UCLouvain, Belgium http://inl.info.ucl.ac.be/sbarre