In article [ref] (at Mon, 2 Aug 2004 19:09:14 -0700), "David S. Miller" [off-list ref] says:

An intesting solution would be to use stacked destinations, which
do no actual encapsulation (or perhaps do the routing header work)
and merely represent the hop-by-hop path.  Then the PMTU propagation
machinery can be used, and route lookups will go through a slower path
to find these special stacked hop-by-hop routes.

Well, I think it would probably be another rt6_info{} member 
rt6i_srcrt (or something like that).

--yoshfuji