smudge/clean filter needs filename

I'm using git-p4 to import and work with upstream p4 repositories. Some of the files are ktext, meaning they expect expansion of $Id$ and similar identifiers.

Using the filter driver for this file, I can do the "clean" part easily, but to calculate the "smudge" correctly, I need to know the filename inside the filter driver.

E.g., inside file foo/Makefile, the clean line:

    # $File$

should be smudged into:

    # $File: //depot/project/foo/Makefile $

I know the //depot/project location from context in the commit log message that git-p4 produces. But I don't know the pathname in the git repo that my smudge script is working on.

Would it make sense to pass that on the command line?  E.g.

    [filter "p4"]
    	clean  = git-p4smudge --clean %s
    	smudge = git-p4smudge --smudge %s

Or maybe put the path in an environment variable?

		-- Pete