[Discussion] About over-MTU-sized skb in virtualized env

Hi Florian

214 static int ip_finish_output_gso(struct sk_buff *skb)
 215 {
 216     netdev_features_t features;
 217     struct sk_buff *segs;
 218     int ret = 0;
 219
 220     /* common case: locally created skb or seglen is <= mtu */
 221     if (((IPCB(skb)->flags & IPSKB_FORWARDED) == 0) ||
 222           skb_gso_network_seglen(skb) <= ip_skb_dst_mtu(skb))
 223         return ip_finish_output2(skb);

Could you please state _concrete_ _reason_ why locally created skb length is ＿always＿ fitting into MTU size?
Especially in below scenario:
http://docs.openstack.org/admin-guide-cloud/content/figures/14/a/a/common/figures/under-the-hood-scenario-1-ovs-compute.png

As many people have discuss it in this thread:
http://marc.info/?t=141715669700004&r=1&w=2







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