packet: Add GSO/csum offload support.

This patch adds GSO/checksum offload to af_packet sockets using
virtio_net_hdr. Based on Rusty's patch to add this support to tun.
It allows GSO/checksum offload to be enabled when using raw socket
backend with virtio_net.
Adds PACKET_VNET_HDR socket option to prepend virtio_net_hdr in the
receive path and process/skip virtio_net_hdr in the send path. This
option is only allowed with SOCK_RAW sockets attached to ethernet
type devices.

v2 updates
----------
Michael's Comments
- Perform length check in packet_snd() when GSO is off even when
  vnet_hdr is present.
- Check for SKB_GSO_FCOE type and return -EINVAL
- don't allow tx/rx ring when vnet_hdr is enabled.
Herbert's Comments
- Removed ethernet specific code.
- protocol value is assumed to be passed in by the caller.

Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/if_packet.h b/include/linux/if_packet.h
index 4021d47cc437..aa57a5f993fc 100644
--- a/include/linux/if_packet.h
+++ b/include/linux/if_packet.h
@@ -46,6 +46,7 @@ struct sockaddr_ll {
 #define PACKET_RESERVE                  12
 #define PACKET_TX_RING                  13
 #define PACKET_LOSS                     14
+#define PACKET_VNET_HDR                 15
 
 struct tpacket_stats {
         unsigned int    tp_packets;