What the Secret Sauce for Using Jumbo 9K Mbufs?

[David Christensen]

I was hoping to add Jumbo frame support in my Ethernet driver 
by using m_getjcl() to allocate MJUM9BYTES sized mbufs to my
receive ring but I'm getting the error EFBIG when I try to map
the mbuf into device memory with bus_dmamap_load_mbuf().  The
implementation is very similar to what's done in the myri10ge
driver so I'm not sure what's needed.  I tried adding 
kern.ipc.nmbjumbo9=1024 to my /etc/sysctl.conf but that didn't
make a difference either.  What am I missing?  If I do get it
working, how far back in time can I back port the driver using
9K mbufs?

I'm developing on FreeBSD 7.0-CURRENT with an amd64 system.

David Christensen

A quick link to the myri10ge example code:
http://fxr.watson.org/fxr/source/dev/myri10ge/if_myri10ge.c#L1255