Re: [Bugme-new] [Bug 34322] New: No ECN marking in IPv6

[Eric Dumazet <eric.dumazet@gmail.com>]

Le jeudi 05 mai 2011 à 14:41 -0700, Andrew Morton a écrit :
> (switched to email.  Please respond via emailed reply-to-all, not via the
> bugzilla web interface).
> 
> On Tue, 3 May 2011 20:05:00 GMT
> bugzilla-daemon@bugzilla.kernel.org wrote:
> 
> > https://bugzilla.kernel.org/show_bug.cgi?id=34322
> > 
> >            Summary: No ECN marking in IPv6
> >            Product: Networking
> >            Version: 2.5
> >     Kernel Version: 2.6.38.4
> >           Platform: All
> >         OS/Version: Linux
> >               Tree: Mainline
> >             Status: NEW
> >           Severity: normal
> >           Priority: P1
> >          Component: IPV6
> >         AssignedTo: yoshfuji@linux-ipv6.org
> >         ReportedBy: sgunderson@bigfoot.com
> >         Regression: No
> > 
> > 
> > Hi,
> > 
> > I'm completely unable to get ECN to work for IPv6. /proc/sys/net/ipv4/tcp_ecn
> > is set to 1 on both sides, and ECN works just fine for IPv4 TCP connections,
> > but when I connect over IPv6 tclass just stays at 0x0, and as far as I'd
> > understood, there should be two bits here set to 10 (like in the diffserv field
> > of IPv4), right?
> > 
> > I do get ECN-echo bits in the TCP header, though (for the initial SYN and
> > SYN/ACK  packets).
> > 
> 
> and
> 
> > I looked at the code, and although I don't understand all of it, it
> > looks like e9df2e8fd8fbc95c57dbd1d33dada66c4627b44c (which also brought
> > ECN for IPv6 SCTP) might be the culprit.  It seems like TCP_ECN_send()
> > calls INET_ECN_xmit(), which only sets the ECN bit in the IPv4 ToS
> > field (inet_sk(sk)->tos), but after the patch, what's checked is
> > inet6_sk(sk)->tclass, which is a completely different field.
> > 
> > Is the analysis correct? Should the tclass be set as well?
> 
> and
> 
> > OK, as a quick hack, I did this:
> > 
> > --- a/linux-2.6.38.5/include/net/inet_ecn.h    2011-04-14 22:03:56.000000000+0200
> > +++ b/linux-2.6.38.5/include/net/inet_ecn.h    2011-05-04 00:36:52.803377902+0200
> > @@ -38,7 +38,7 @@
> >      return outer;
> >  }
> > 
> > -#define    INET_ECN_xmit(sk) do { inet_sk(sk)->tos |= INET_ECN_ECT_0; } while (0)
> > +#define    INET_ECN_xmit(sk) do { inet_sk(sk)->tos |= INET_ECN_ECT_0; if (inet6_sk(sk) != NULL) inet6_sk(sk)->tclass |= INET_ECN_ECT_0; } while (0)
> >  #define    INET_ECN_dontxmit(sk) \
> >      do { inet_sk(sk)->tos &= ~INET_ECN_MASK; } while (0)
> > 
> > and now my packets are properly marked with tclass 0x02 (ie.,
> > signalling ECN-capable transport, no congestion experienced yet).
> > 
> > I guess this isn't the right way of doing it, but at least it confirms
> > that the lack of setting tclass is part of the problem.
> 

Cc YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>

Hello Steinar

Analysis seems fine, but you also need to change INET_ECN_dontxmit() for
retransmitted packets.

Any chance you can refine your patch ?

Thanks !