Messages in this thread | | | Date | Thu, 23 Nov 2023 19:19:52 -0500 | From | Willem de Bruijn <> | Subject | Re: [PATCH net-next] packet: Account for VLAN_HLEN in csum_start when virtio_net_hdr is enabled |
| |
Willem de Bruijn wrote: > Mike Pattrick wrote: > > On Thu, Nov 23, 2023 at 4:25 PM Willem de Bruijn > > <willemdebruijn.kernel@gmail.com> wrote: > > > > > > Mike Pattrick wrote: > > > > Af_packet provides checksum offload offsets to usermode applications > > > > through struct virtio_net_hdr when PACKET_VNET_HDR is enabled on the > > > > socket. For skbuffs with a vlan being sent to a SOCK_RAW socket, > > > > af_packet will include the link level header and so csum_start needs > > > > to be adjusted accordingly. > > > > > > Is this patch based on observing an incorrect offset in a workload, > > > or on code inspection? > > > > Based on an incorrect offset in a workload. The setup involved sending > > vxlan traffic though a veth interface configured with a vlan. The > > vnet_hdr's csum_start value was off by 4, and this problem went away > > when the vlan was removed. > > > > I'll take another look at this patch. > > This is a vlan device on top of a veth device? On which device and at > which point (ingress or egress) are you receiving the packet over the > packet socket? > > From a quick glance, in all cases that I see the VLAN tag is kept in > skb->vlan_tci, so is never part of the packet payload. > > But checksum offload with VXLAN can be non-trivial on its own. If > type & SKB_GSO_UDP_TUNNEL_CSUM | SKB_GSO_TUNNEL_REMCSUM, say. Then > csum_start will point to the checksum in vxlanhdr.
This last statement is incorrect. But SKB_GSO_UDP_TUNNEL_CSUM might be relevant to unexpected csum_start.
| |