Netgraph, meta and socket PF_NG

[Vincent Jardin]

With the regular data, I would like to send an opaque data from a netgraph 
node to a userland program that has a NG_DATA/PF_NETGRAPH socket. This opaque 
data is the meta.
How can it be performed ?

Then, from the userland program, how to send data with an opaque to a 
NG_DATA/PF_NG socket ? Then this opaque would be a netgraph's meta.

It seems that ng_socket does not support this feature, however I am not sure 
that I understand properly its source code. ;-(

Thanks,
  Vincent