From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sowmini Varadhan Subject: Re: [PATCH RFC 0/3] kcm: Kernel Connection Multiplexor (KCM) Date: Mon, 21 Sep 2015 17:26:24 -0400 Message-ID: <20150921212624.GD3861@oracle.com> References: <1442788161-2626305-1-git-send-email-tom@herbertland.com> <20150921122422.GA31092@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "David S. Miller" , Linux Kernel Network Developers , Kernel Team To: Tom Herbert Return-path: Received: from userp1040.oracle.com ([156.151.31.81]:33065 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756836AbbIUV0a (ORCPT ); Mon, 21 Sep 2015 17:26:30 -0400 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On (09/21/15 10:33), Tom Herbert wrote: > > > > Some things that were not clear to me from the patch-set: > > > > The doc statses that we re-assemble packets the "stated length" - > > but how will the receiver know the "stated length"? > > BPF program returns the length of the next message. In my testing so > far I've been using HTTP/2 which defines a frame format with first 3 > bytes being header length field . The BPF program (using LLVM/Clang-- > thanks Alexei!) is just: Maybe I dont see something about the mux/demux here (I have to take a closer look at reserve_psock/unreserve_psock), but will every tcp segment have a 3 byte length in the payload? Not every TCP segment in the RDS-TCP case will have a RDS header, thus the comments before rds_send_xmit(), thus applying the bpf filter to a TCP segment holding some "from-the-middle" piece of the RDS dgram may not be possible > > the notes say one can "accept()" over a kcm socket- but "accept()" > > is itself a connection-oriented concept- one does not accept() on : > The accept method is overloaded on KCM sockets to do the socket > cloning operation. This is unrelated to TCP semantics, connection > management is performed on TCP sockets (i.e. before being attached to > a KCM multiplexor). If possible,it might be better to use some other glibc-func/name/syscall/sockopt/whatever for this, rather than overloading accept().. feels like that would keep the semantics cleaner, and probably less likely to trip up on accept code in the kernel.. --Sowmini