2015-11-04 18:54, Jijiang Liu: > + /* if vhost TX checksum offload is required */ > + if (m->ol_flags & PKT_TX_IP_CKSUM) { > + hdr->csum_start = m->l2_len; > + hdr->csum_offset = offsetof(struct ipv4_hdr, hdr_checksum); > + } else if (m->ol_flags & PKT_TX_L4_MASK) { > + hdr->csum_start = m->l2_len + m->l3_len; > + switch (m->ol_flags & PKT_TX_L4_MASK) { > + case PKT_TX_TCP_CKSUM: > + hdr->csum_offset = offsetof(struct tcp_hdr, cksum); > + break; > + case PKT_TX_UDP_CKSUM: > + hdr->csum_offset = offsetof(struct udp_hdr, > + dgram_cksum); > + break; > + case PKT_TX_SCTP_CKSUM: > + hdr->csum_offset = offsetof(struct sctp_hdr, cksum); > + break; > + default: > + break; > + }
The header checksum to offload is deduced from csum_offset. Your vhost implementation do some parsing to deduce it: > + parse_ethernet(m, &l4_proto, &l4_hdr); > + if (hdr->flags == VIRTIO_NET_HDR_F_NEEDS_CSUM) { > + if ((hdr->csum_start == m->l2_len) && > + (hdr->csum_offset == offsetof(struct ipv4_hdr, > + hdr_checksum))) > + m->ol_flags |= PKT_TX_IP_CKSUM; > + else if (hdr->csum_start == (m->l2_len + m->l3_len)) { > + switch (hdr->csum_offset) { > + case (offsetof(struct tcp_hdr, cksum)): > + if (l4_proto == IPPROTO_TCP) > + m->ol_flags |= PKT_TX_TCP_CKSUM; > + break; > + case (offsetof(struct udp_hdr, dgram_cksum)): > + if (l4_proto == IPPROTO_UDP) > + m->ol_flags |= PKT_TX_UDP_CKSUM; > + break; > + case (offsetof(struct sctp_hdr, cksum)): > + if (l4_proto == IPPROTO_SCTP) > + m->ol_flags |= PKT_TX_SCTP_CKSUM; > + break; > + default: > + break; > + } > + } The kernel doesn't work this way. Please could you check that your virtio implementation works with a vanilla Linux with or without vhost? Thanks