zero copy with PACKET_MMAP

Hi ,

The link

https://www.kernel.org/doc/Documentation/networking/packet_mmap.txt
talks about  achieving zero copy. But i find a deep  packet copy ( of
length snaplen= skb->len )  here
http://lxr.free-electrons.com/source/net/packet/af_packet.c#L1841.

Is there anything missing/wrong in my understanding ?


Thanks,
Ratheesh