How do you determine what physical device a file in on?

[Dror Matalon]

	I suspect that there are only machine dependent ways. Given 
two files x and y. I want to determine if they're on the same PHYSICAL devie.
(It's pretty easy to find out the logical device, you do an statfs on the 
file). Is there a portable or a semi-portable way to do this or do I need to 
go into every machine's disk drivers structures to find out. 


Thanks 

	Dror