Q:

How can I get the source code for file utility in linux?

I need do find the timezone data file format. So i need file utility source code to port the executable file to our board.

A:

No, you don't. The file utility only knows about how to quickly identify a file -- that is, the minimum information needed to determine that this is a image, that is a text file, this is an ODT file etc (the 'magic' as it is called).  It's a mistake to think it knows anything more than that.
Instead, you should look at the 'tzfile' man page, as it is all about the timezone file format. It describes it quite precisely.

