The first news is that it works! It is possible to use tc to setup QoS on IPv6 but the filter have to be updated.
When working on adding IPv6 support to lagfactory, I found out by reading tc sources and specifically ll_proto.c that the keyword to use for IPv6 was ipv6. Please read that file if you need to find the keyword for an other protocol.
So to send packet with Netfilter mark 5000 to a specific queue, one can use:
/sbin/tc filter add dev vboxnet0 protocol ipv6 parent 1:0 prio 3 handle 5000 fw flowid 1:3
All would have been simple, if I was not trying to have IPv6 and IPv4 support. My first try was to simply do:
${TC} filter add dev ${IIF} protocol ip parent 1:0 prio 3 handle 5000 fw flowid 1:3
${TC} filter add dev ${IIF} protocol ipv6 parent 1:0 prio 3 handle 5000 fw flowid 1:3
But the result was this beautiful message:
RTNETLINK answers: Invalid argument We have an error talking to the kernel
Please note the second message displayed that warn you you talk to rudely to kernel and that he just kick you out the room.
The fix is simple. In fact, you can not use twice the same prio. So it is successful to use:
${TC} filter add dev ${IIF} protocol ip parent 1:0 prio 3 handle 5000 fw flowid 1:3
${TC} filter add dev ${IIF} protocol ipv6 parent 1:0 prio 4 handle 5000 fw flowid 1:3