a file that acts like a tape loop?

[Ritchey Ruff]

What I need is a way to make a file act sort of like a tape loop
or a shift register.  I have a log file for a program that will
quickly grow to consume all of disk.  I really need the last
100k or so in case it dies or loops, but anything older than that
can be trashed.  Basically I need a file to act like a buffer
and I need reliability (if the machine or process dies I *need*
to have that last 100k--or whatever--but I don't need to 45M I
normally get now ;-).  Seems this would be usefull for things like
the /usr/adm/*log's, the sendmail log, the uucp log, etc.
That's why I'm asking before I go write it myself...anyone done it
already (I'm using 4.[2,3] BSD) ???

thanks in advance,
--ritchey ruff	ruffwork at cs.orst.edu -or- ...!tektronix!orstcs!ruffwork