Developer's Handbook DDB instructions

[David Kirchner]

I'm trying to track down a background fsck deadlock bug. I've found a
thread on groups.google.com about another person having a similar
problem but with snapshots. The suggestion made there was to compile a
kernel with DDB, and the user was referred to the Developer's
Handbook.

http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/kerneldebug-online-ddb.html

The Handbook appears to be out of date -- it states that you have to
add "options DDB" to the kernel config to enable DDB. When you try
that, part way through the make depend process it informs you that you
also need KDB. Are there any other steps necessary to get DDB to work
on a newer version of FreeBSD (say 6.0-RELEASE)?

Since this particular deadlock test will probably take 12+ hours of
runtime to trigger, I'd like to get this right, so I can get as much
information as possible into a PR.