When the inner packet checksum is offloaded, the outer UDP checksum is easy to calculate as it doesn't depend on the payload (because the inner checksum cancels out everything from the inner packet except the pseudo header). Thus, transmit checksums for VXLAN (and in principle other encapsulations, but I haven't enabled it for / tested with those) can be offloaded on any device supporting NETIF_F_HW_CSUM. Only the innermost checksum has to be offloaded, the rest are filled in by the stack. Tested by hacking a driver to report NETIF_F_HW_CSUM, call skb_checksum_help before transmitting a packet, and not actually offload anything to the hw. In principle it should also be possible to apply this technique when the inner packet has been checksummed by software, but only if skb->csum_start and skb->csum_offset have been filled in to describe the inner checksum. However in this case it is easier to use skb->csum and skb->csum_start, as gso_make_checksum() already does - a similar but simpler technique. It's not clear to me where else this should be done, so this is out of scope for this patch series.
Edward Cree (2): net: udp: local checksum offload for encapsulation net: vxlan: enable local checksum offload on HW_CSUM devices drivers/net/vxlan.c | 5 ++++- net/ipv4/udp.c | 34 +++++++++++++++++++++++++++++----- 2 files changed, 33 insertions(+), 6 deletions(-) -- 2.4.3 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
