Add guest offload setting in vhost lib.
Virtio 1.0 spec (5.1.6.4 Processing of Incoming Packets) says:
1. If the VIRTIO_NET_F_GUEST_CSUM feature was negotiated, the
VIRTIO_NET_HDR_F_NEEDS_CSUM bit in flags can be set: if so,
the packet checksum at offset csum_offset from csum_start
and any preceding checksums have been validated. The checksum
on the packet is incomplete and csum_start and csum_offset
indicate how to calculate it (see Packet Transmission point 1).
2. If the VIRTIO_NET_F_GUEST_TSO4, TSO6 or UFO options were
negotiated, then gso_type MAY be something other than
VIRTIO_NET_HDR_GSO_NONE, and gso_size field indicates the
desired MSS (see Packet Transmission point 2).
In order to support these features, the following changes are added,
1. Extend 'VHOST_SUPPORTED_FEATURES' macro to add the offload features negotiation.
2. Enqueue these offloads: convert some fields in mbuf to the fields in virtio_net_hdr.
There are more explanations for the implementation.
For VM2VM case, there is no need to do checksum, for we think the
data should be reliable enough, and setting VIRTIO_NET_HDR_F_NEEDS_CSUM
at RX side will let the TCP layer to bypass the checksum validation,
so that the RX side could receive the packet in the end.
In terms of us-vhost, at vhost RX side, the offload information is
inherited from mbuf, which is in turn inherited from TX side. If we
can still get those info at RX side, it means the packet is from
another VM at same host. So, it's safe to set the
VIRTIO_NET_HDR_F_NEEDS_CSUM, to skip checksum validation.
Signed-off-by: Jijiang Liu <jijiang.liu@intel.com>
Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
859b480d5a