The <tt>ddb</tt> directory holds routines used to debug the kernel.
The 4.3BSD Internals book by Leffler, McKusick, Karels and Quarterman
doesn't really cover this directory. However, some information has been
presented by Kirk KcKusick and Keith Bostic in their "UNIX Kernel Internals"
notes, which they have presented in many places in the past few years.
<p>