RE: OS throws away large packets

> >>> 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/freeb
sd-net/2007-September/015250.htm
l
> >   
> > 
>
http://lists.freebsd.org/pipermail/freeb
sd-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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RE: OS throws away large packets

Thread: RE: OS throws away large packets