using page cache directly?

[Shaya Potter <spotter@cs.columbia.edu>]

I'm trying to write a stackable file system that supports branching 
(i.e. mount time options of old_branch and new_branch).  In order to do 
it, I need to version the directories as well, what I'd like to do is 
have a file act as the directory (basically ";branch" on the underlying 
fs inside the right dir) which will just map "Stacked Filename" to 
"underlying filename".  If I were doing it in user space, I'd just mmap 
the file, and deal with it directly like that, but as I understand it's 
not really appropriate to do that inside the kernel (and only possible 
w/ vmalloc'd pages).  The correct way (I was told) is to use the page 
cache.  As don't have a lot of experience with that, can someone point 
me in the right direction so I can learn to deal w/ it.

thanks,

shaya