locate-dominating-file

locate-dominating-file is a compiled Lisp function in `files.el'.

(locate-dominating-file FILE NAME)

Look up the directory hierarchy from FILE for a directory containing NAME.
Stop at the first parent directory containing a file NAME,
and return the directory. Return nil if not found.
Instead of a string, NAME can also be a predicate taking one argument
(a directory) and returning a non-nil value if that directory is the one for
which we're looking.