It's not clear from your question whether you are trying to write a user mode application, or trying to write kernel code. Parts of your question imply that you're writing user-mode code, but iget() is a kernel routine which isn't available to user-mode programs.
Why don't you be a bit more specific about what you're trying to do, and perhaps we can help you out. Assuming that you're writing a user-mode application, are you trying to read the filesystem directly using the device file, and using direct I/O to the device? Or are you trying to get some information from a filesystem that is already mounted?
Why do you need to read an inode? What are you trying to do with it?