Date: Sat, 4 Apr 2009 10:21:38 -0300 From: "Luiz Otavio O Souza" <lists.br@gmail.com> To: "Julian Elischer" <julian@elischer.org> Cc: Lawrence Stewart <lstewart@freebsd.org>, freebsd-net@freebsd.org Subject: Re: Setting the mss for socket Message-ID: <3F89BC6021844DC58B956E5433650445@adnote989> References: <3FD46C21A487490FB15B89E890790121@adnote989> <49d5c0de.E5bkeKr%2Bp%2Bfg4K00%perryh@pluto.rain.com> <64D5D9E633734200A603D067ED5A81E9@adnote989> <49D63315.6050108@elischer.org>
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[-- Attachment #1 --] > Luiz Otavio O Souza wrote: >>>> Is there a way to set the mss for a socket ? Like you can do >>>> in linux with setsockopt(TCP_MAXSEG) ? >>>> >>>> So i can set the maximum size of packets (or sort of) from a >>>> simple userland program. >>> >>> Depending on exactly what you need to accomplish, you may >>> find something useful in this thread from last August in >>> freebsd-questions@ >>> >>> setting the other end's TCP segment size >> >> Very informative thread, thanks. >> >> This thread show me that TCP_MAXSEG is implemented in freebsd but don't >> work. You can set the setsockopt(IPPROTO_TCP, TCP_MAXSEG), wich will set >> the >> tp->t_maxseg, but this value is recalculated at tcp_input, so in short, >> you >> cannot set the max segment size for a socket. >> >> I've posted a completly wrong patch (from style point-of-view - and using >> SOL_SOCKET instead of IPPROTO_TCP), but with that patch i'm able to set >> the >> mss in iperf. > > this thread shoud be in FreeBSD-net@ so tha the right people see it > many developers do not read hackers every day as it tends to overload > them. The above patch is a better fix for this, it fix the setsockopt(IPPROTO_TCP, TCP_MAXSEG), so iperf (and other userland programs) works by default. It's clear on code that tp->t_maxseg should not be changed, at least in this situation (it keeps the maximum mss for connection and it is used to calculate the tcp window scaling). tp->t_maxseg is also reseted to maxmtu (or rmx_mtu) at tcp_mss_update(). So here is the patch: http://loos.no-ip.org/downloads/mss-patch Thanks Luiz [-- Attachment #2 --] --- netinet/socketvar.h.orig 2009-04-03 22:29:34.000000000 -0300 +++ netinet/socketvar.h 2009-04-03 22:29:44.000000000 -0300 @@ -115,6 +115,7 @@ char *so_accept_filter_str; /* saved user args */ } *so_accf; int so_fibnum; /* routing domain for this socket */ + int so_maxseg; /* maxseg this socket */ }; /* --- netinet/tcp_usrreq.c.orig 2009-04-03 22:24:53.000000000 -0300 +++ netinet/tcp_usrreq.c 2009-04-03 23:26:35.000000000 -0300 @@ -1352,9 +1352,8 @@ return (error); INP_WLOCK_RECHECK(inp); - if (optval > 0 && optval <= tp->t_maxseg && - optval + 40 >= V_tcp_minmss) - tp->t_maxseg = optval; + if (optval >= 40 && optval <= tp->t_maxseg) + so->so_maxseg = optval; else error = EINVAL; INP_WUNLOCK(inp); @@ -1389,7 +1388,10 @@ error = sooptcopyout(sopt, &optval, sizeof optval); break; case TCP_MAXSEG: - optval = tp->t_maxseg; + if (so->so_maxseg) + optval = so->so_maxseg; + else + optval = tp->t_maxseg; INP_WUNLOCK(inp); error = sooptcopyout(sopt, &optval, sizeof optval); break; --- netinet/tcp_output.c.orig 2009-04-02 22:48:04.000000000 -0300 +++ netinet/tcp_output.c 2009-04-03 23:28:07.000000000 -0300 @@ -493,6 +493,11 @@ } } + if (so->so_maxseg && len > so->so_maxseg) { + len = so->so_maxseg; + sendalot = 1; + } + if (sack_rxmit) { if (SEQ_LT(p->rxmit + len, tp->snd_una + so->so_snd.sb_cc)) flags &= ~TH_FIN; @@ -518,6 +523,8 @@ if (len) { if (len >= tp->t_maxseg) goto send; + if (so->so_maxseg && len >= so->so_maxseg) + goto send; /* * NOTE! on localhost connections an 'ack' from the remote * end may occur synchronously with the output and cause
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