How to build 9.0 from source?

[james]

I installed 9.0 without sources.

Now I'd like to try building the kernel (or specifically the mfi 
driver), so I've tried to get the sources.

The handbook says (in 9.55) to use sysinstall to get the source 
configuration - but that doesn't seem to work and what its trying to 
fetch seems more like an 8.x source set,

I fetched src.txz and unpacked it and sorted out the /usr/src/sys link, 
and 'make' in the root of that builds the boot code ok.

However, there is no /usr/src/UPDATING to check per 9.5, and 'cd 
/usr/src;make buildkernel' tells me:

make: don't know how t make buildkerel. Stop.

/usr/src was empty before I set up the 'sys' link (which in my case 
points to a zfs volume).

It seems wrong to m - how can I get sources etc installed so I can build 
the kernel? (And userspace if necessary - but its the mfi driver I want 
to fiddle with)

James