VOP_{READ,WRITE,LOCK}

Hi,

I remember I located the definition of VOP_{READ,WRITE}, etc, a couple 
of month back when I was playing with freebsd 4.4. However, I am now 
looking for the definition of VOP_{READ,WRITE,LOCK} in a freebsd 
current tree checkout. So far, I am not able to so far. Worse yet, I 
also lost track of my notes I had earlier.

So I think this must be a really common question to many newbies to 
freebsd. Instead of me spending more time digging into the tree, wonder 
if anybody in freebsd community could lend me a few hints?

Many thanks in advance,

Weikuan