Re: [PATCH net-next] gro: introduce gro_mac_header_len

From: Or Gerlitz <ogerlitz-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Date: Mon, 6 Feb 2012 18:44:03 +0200

As I wrote earlier on this thread, the reason is that in order to be
able to xmit skb's for which the stack doesn't provide a neighbour,
IPoIB makes sure to have extra INFINIBAND_ALEN bytes headroom on
skbs. Such that the ipoib hard_header functions writes a
"ipoib_pseudoheader" (= hw address) on the skb and the xmit function
grabs it from there and use that pseudoheader to search for the actual
IB L2 address handle kept for that dest. Example such skbs are unicast
ARP replies and multicast. see below some relevant code sections from
ipoib_main.c

Then IPoIB is broken and must be fixed, see my other reply.

We're not adding a bogus member to the netdevice just because IPoIB
tries to do path resolution and neighbour validation behind the
neighbour cache's back.
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