netdev - skb_is_gso() in ip

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Message-ID: <CAF0Lin26AEdtz+Ui=LQ-T285OpbgfnsN3ofdmvbwavM9eQjBCw@mail.gmail.com>
Date:	Wed, 12 Jun 2013 16:48:03 +0300
From:	Andy Johnson <johnsonzjo@...il.com>
To:	netdev@...r.kernel.org
Subject: skb_is_gso() in ip_forward.c

Hi,

I would appreciate if someone can explain the following :

We have this in net/ipv4/ip_forward():
...
 if (unlikely(skb->len > dst_mtu(&rt->dst) && !skb_is_gso(skb) &&
  ...
  icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
                            htonl(dst_mtu(&rt->dst)));
                  goto drop;
          }
...

As I understand, it the traffic is GSO and the length of the skb is
larger than the MTU, we don't send destination unreachable ICMP and
we continue with forwarding the packet. My qustion is: why is it so ?
is it because when working with GSO the size of skb->len is not the
size of the packet which is sent on the wire ? The what does it
represent when the traffic is GSO ?
I would appreaicate if someone can elaborate on this.

Best
Andy
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