Re: network misbehaviour with gplpv and 2.6.30

[Paul Durrant <paul.durrant@citrix.com>]

James Harper wrote:
> With GPLPV under 2.6.30, GPLPV gets the following from the ring:
> 
> ring slot n (first buffer):
>  status (length) = 54 bytes
>  offset = 0
>  flags = NETRXF_extra_info (possibly csum too but not relevant)
> ring slot n + 1 (extra info)
>  gso.size (mss) = 1460
> 
> Because NETRXF_extra_info is not set, that's all I get for that packet.

I assume you mean NETRXF_more_data here? Are you saying that ring slot n 
has only NETRXF_extra_info and *not* NETRXF_more_data?

> In the IP header though, the total length is 1544 (which in itself is a
> little strange), but obviously I'm not getting a full packet, just the
> ETH+IP+TCP header.
> 
> According to Andrew Lyon it works fine in previous versions, so this
> problem only arises on 2.6.30. I don't know if netfront on Linux suffers
> from a similar problem.
> 
> I can't identify any changes that could cause this, but if the problem
> is in netback either the frags count isn't being set correctly, or
> skb->cb (which appears to be used temporarily to hold nr_frags) is
> becoming corrupt (set to 0) somehow, but the window where this could
> occur is very small and I can't see where it could happen.
> 
> Any suggestions as to where to start looking?
> 
> (one nice thing is that I have identified a crash that would occur when
> the IP header lied about its length!)
> 
> Thanks
> 
> James
> 
> 
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Paul Durrant, Software Engineer

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