> >>> Hi all,
> >>>
> >>> I'm trying to implement Large Recieve Offload for an
> >>>
> >> Ethernet driver
> >>
> >>> on FreeBSD 6.3, but all my >MTU packets are being thrown
> by the OS.
> >>> I'm using mbuf chains in this imlpementation, each mbuf is
> >>>
> >> a cluster
> >>
> >>> of MCLBYTES bytes. They are linked by the m_next pointer.
> >>> The first packet being thrown away is 2945 bytes long.
> >>>
> >> Wireshark shows
> >>
> >>> the packet that is being passed to the OS is correct.
> >>>
> >>> Do I need to set some OS parameter to make it recieve mbuf chains?
> >>>
> >>> Please help.
> >>>
> >>>
> >> Hi Yony,
> >>
> >> I seem to remember some discussion about this list last
> year see the
> >> following threads:
> >>
> >>
> >>
> >
>
http://lists.freebsd.org/pipermail/freebsd-net/2007-September/015250.htm
l
> >
> >
>
http://lists.freebsd.org/pipermail/freebsd-net/2007-September/015350.htm
l
> >
> > >From my limited reading of these threads just now and possibly bad
> > memory. It would seem that the MRU to MTU relationship is
> defined in
> > the nic driver rather than
> >
> >> enforced further up the stack or at least that seamed to
> be the case
> >>
> > with the bce driver.
> >
> >> Hope this is helpful,
> >>
> >> Tom
> >>
> >
> > Hi Tom,
> >
> > >From what I understand these threads are referring to the bce
> > >hardware
> > configuration (bus configuration) and driver mbuf
> allocation size. Am
> > I correct?
> > In my case I'm not trying to receive packets >MTU from the
> HW, but to
> > chain mbuf clusters, each is MCLBYTES long, and pass the
> mbuf chain to
> > the OS.
> > Since tcpdump (analyzed by wireshark) catches the packets above the
> > driver and reports a good packet (and 2945 bytes long), I assume my
> > driver functionality is ok. From what I know tcpdump is supposed to
> > immitate the way the stack sees the packet, yet it is discarded.
> > My logic says there is an OS parameter handled by the
> driver (at net
> > device init time for example) that will set the OS to receive large
> > mbuf chains, or a kernel tcp parameter. Is the tcp stack
> submitted to
> > the mtu somehow?
> >
> >
> I don't see where you've identified what version of the os you're
> working with. There's a check in the 802.3 input path on earlier
> systems to discard frames >mtu. This was removed not too long ago
> with LRO in mind; check the history of sys/net/if_ethersubr.c.
>
> Sam
>
Hi Sam, I have mentioned working on 6.3.
FreeBSD 6.2 had this check in if_ethersubr.c / ether_input:
539 if (m->m_pkthdr.len >
540 ETHER_MAX_FRAME(ifp, etype, m->m_flags & M_HASFCS)) {
541 if_printf(ifp, "discard oversize frame "
542 "(ether type %x flags %x len %u >
max %lu)\n",
543 etype, m->m_flags, m->m_pkthdr.len,
544 ETHER_MAX_FRAME(ifp, etype,
545 m->m_flags &
M_HASFCS));
546 ifp->if_ierrors++;
547 m_freem(m);
548 return;
549 }
Patching it was explained by neterion in
http://trac.neterion.com/cgi-bin/trac.cgi/wiki/FreeBSD.
This check no longer exists in 6.3, nor any other oversize packet
handling (I couldn't find any so far).
I also get no error prints from the OS.
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