system call problem

From: Peter (coscpp_at_gmail.com)
Date: 09/21/05 

Date: 21 Sep 2005 07:43:31 -0700

what's the relationship between system calls and functions in
device driver? Is system call defined just as interface between
user and device?? When we invoke the certain system call for the
specifical _FILE_ ? that's, we, actually, invoke an implementation by
the corresponding device driver? But obviously the functions in
file_operations in device driver just a subset of the system calls!??
Is my thought right? if not, what's wrong here?