Interesting TCP issue

[Uwe Doering]

Steve Watt wrote:
> In <459AD141.5010502 at elischer.org>, Julian Elischer wrote:
> 
> [ Snip discussion of symptoms of window scaling broken when
> talking to at least the skype mail servers. ]
> 
>> we have seen this since 4.x
>> I think a fix may be in 7.0 but I'm not sure..
>> I thin kthere is a problem when the far end sets the window down to 1 
>> but scales it by a factor of 2^{big number}.
>>
>> Andre, can you check out this problem and MFC the correct fix
>> if it is indeed the same problem in 6.2?
> 
> It is the same problem; I took the (one-line) fix as indicated by
> 
>> http://cvs.ironport.com/cgi-bin/viewcvs.cgi/freebsd/src/sys/netinet/tcp_syncache.c.diff?r1=1.84&r2=1.85
> 
> (well, not cvs.ironport.com, which doesn't seem to exist at the moment),
> and applied the diff from 1.84 to
> 1.85 and to a 6.2-PRERELEASE box updated around 25 Dec 06.
> It works like a charm.
> 
> I would vote to MFC 1.85 now that 6.2 is out.
> 
> The diff, for those who are following along at home, is:
> 
> ===================================================================
> RCS file: /usr/local/www/cvsroot/FreeBSD/src/sys/netinet/tcp_syncache.c,v
> retrieving revision 1.84
> retrieving revision 1.85
> diff -u -p -r1.84 -r1.85
> --- src/sys/netinet/tcp_syncache.c	2006/02/09 21:29:02	1.84
> +++ src/sys/netinet/tcp_syncache.c	2006/02/28 23:05:59	1.85
> @@ -682,7 +682,7 @@ syncache_socket(sc, lso, m)
>  		tp->t_flags |= TF_NOOPT;
>  	if (sc->sc_flags & SCF_WINSCALE) {
>  		tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
> -		tp->requested_s_scale = sc->sc_requested_s_scale;
> +		tp->snd_scale = sc->sc_requested_s_scale;
>  		tp->request_r_scale = sc->sc_request_r_scale;
>  	}
>  	if (sc->sc_flags & SCF_TIMESTAMP) {

I wonder whether it is that easy.  As far as I can tell the commit to 
HEAD actually comprised changes to three files:

http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/netinet/tcp_input.c.diff?r1=1.290&r2=1.291
http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/netinet/tcp_syncache.c.diff?r1=1.84&r2=1.85
http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/netinet/tcp_var.h.diff?r1=1.127&r2=1.128

How about the modifications in 'tcp_input.c'?  Are they relevant to the 
problem this thread is about?  If so, assessing the correctness of an 
MFC might prove to be a little harder.

    Uwe
-- 
Uwe Doering         |  EscapeBox - Managed On-Demand UNIX Servers
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