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[Xen-users] Non-linear skbs apparently prevent NFQUEUE from working prop

To: Xen-users Mailing List <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-users] Non-linear skbs apparently prevent NFQUEUE from working properly
From: Jan Christoph Nordholz <hesso@xxxxxxxxxxxxxxxxxxxxxx>
Date: Mon, 19 Jan 2009 12:27:48 +0100
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Dear list members (especially Xen network wizards),

I'm using the netfilter_queue mechanism to modify packets on the wire that
are sent from one domU to another while they travel over the dom0 bridge.
This has worked fine as long as I was tinkering with UDP packets only -
but when I try to reinject TCP frames with an increased length, I run into
a BUG() because net/netfilter/nfnetlink_queue.c:nfqnl_mangle() calls
skb_put() which requires the skb to be aligned, which it apparently isn't
in a Xen environment.

I've ported my network scenario to a Usermode Linux setup and it's
working perfectly fine there, so I presume this has something to do with
Xen's network driver implementation.

It would be great if someone could point me into the right direction.
(This is 2.6.24 with Xen 3.2 - I'm reluctant to upgrade right now because
this is a production system. I'd prefer any option over upgrading.)


Thanks in advance,

Jan

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