Getting access to checksums.

[Dan Carroll]

I'm currently working on a system that monitors file changes.
I'd like to calculate the checksums on each file both to see if a change 
has occured as well as looking for duplicate files.

I'm not sure what algorithm I'll end up using but I was wondering if it 
was possible to get access to ZFS' checksumming?
Does it happen on a file level or is it block level only?  And if it 
does, is there an easy way to obtain this information from the system?

-D