Filesystem monitoring question

[Rools S]

I have a FreeBSD 6.0 box with a mounted filesystem that is accessible to a
number of clients via SMB and NFS.

I would like to monitor activity on this filesystem so that every time a
write to the mount is completed, my C program is run (which stats the file
and stores some info about it in a database etc.)

My question is: How do I construct a trigger for my code?

If anyone can point me in the right direction I would greatly appreciate it.

Thanks

Cornelis