[Click] Strange buffer_length() value for packets of more than 1500 bytes

[Roman Chertov]

Bobby,

I believe the jumbo frame problem was fixed.  See 
http://www.mail-archive.com/click@amsterdam.lcs.mit.edu/msg03800.html

Roman

On Fri, 17 Dec 2010 11:35:16 -0800 (PST) Bobby Longpocket
<bobbylongpocket at yahoo.com> wrote

> Hi Manel,
> 
> My guess is that it is related to the Ethernet driver on the receive side. 
> When you set the MTU higher (into jumbogram territory), it probably changes
> the receive mechanism to store only the first part of the packet in the
> 'data' part of the buffer and sticks the rest off in the 'frags' area of the
> buffer.  Probably your version of Click doesn't support packets that are
> stored this way (and, for all I know, none do).
> 
> Bobby
> 
> 
> > Hi all,
> >
> > I am using linuxmodule click-1.7 over linux-2.6.24.7 (but
> > this is also 
> > the case with linux-2.6.18.2)
> > If I send packets of 1480 bytes and with the default mtu of
> > 1500, the 
> > the buffer size allocated at the receiver is of 1664, 
> >
> > (p->buffer_length()= 1664 ) which is fine.
> > However, when I send large packets of more than 1500 bytes,
> > and set 
> > the mtu to a value > 1500,  the buffer allocated at
> > the reception is 
> > always of 256 ((p->buffer_length()= 256)) whatever the
> > packet size is.
> > So, if I want to access to the data stored beyond the 256
> > bytes in 
> > that packet, the data I get is erroneous.
> > So i am wondering if there is a limitation on the maximum
> > buffers 
> > size? where this limitation is hard-coded? and why does it
> > change with 
> > the mtu?
> >
> > Thanks for helping
> >
> >
> > Ps: Click scripts are roughly :
> >
> > Sender :
> > RatedSource ->UDPIPEncap -> EtherEncap ->
> > ToDevice(eth0)
> > Receiver:
> > FromDevice(eth0) -> Myelement -> Discard
> >
> > In Myelement, I only get p->buffer_length() and p->
> > data() and p->end_data()
> >
> >
> > Manel BOURGUIBA
> > PhD Candidate
> > PHARE - LIP6 - UPMC - Sorbonne Universit?s
> > BC169 - Office 25/26-319
> > 4 place Jussieu
> > 75252 PARIS cedex 05
> > +33 1 44 27 61 88
> 
> 
> 
> 
> 
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