On Sat, Jun 1, 2019 at 9:22 PM Eli Britstein [off-list ref] wrote:

I think that's because QinQ, or VLAN is not an encapsulation. There is
no outer/inner packets, and if you want to mangle fields in the packet
you can do it and the result is well-defined.

Sort of, perhaps VLAN tags are too short to be called as an
encapsulation, my point is that it still needs some endpoints to push
or pop the tags, in a similar way we do encap/decap.

BTW, the motivation for my fix was a use case were 2 VGT VMs
communicating by OVS failed. Since OVS sees the same VLAN tag, it
doesn't add explicit VLAN pop/push actions (i.e pop, mangle, push). If
you force explicit pop/mangle/push you will break such applications.

From what you said, it seems act_csum is in the middle of packet
receive/transmit path. So, which is the one pops the VLAN tags in
this scenario? If the VM's are the endpoints, why not use act_csum
there?

Thanks.