Per-jail private loopback

[Garrett Wollman]

I'm a bit new to managing jails, and one of the things I'm finding I
need is a way for jails to have their own private loopback interfaces
-- so that things like sendmail and local DNS resolvers actually work
right without explicit configuration.  Is there any way of making this
work short of going all the way to full VIMAGE?  (I'm reluctant to do
the latter because it then means I have to carry two separate kernels,
one for performance and one for jail hosts.)  Or is VIMAGE cheap
enough that I won't notice the performance hit?  Does that even get me
to where I need to be (with each jail having its own 127.0.0.1)?

-GAWollman