Messages in this thread | | | Date | Thu, 23 Nov 2023 19:05:57 -0500 | From | Willem de Bruijn <> | Subject | Re: [PATCH net-next] packet: Account for VLAN_HLEN in csum_start when virtio_net_hdr is enabled |
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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.
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