PFCB
NpFindRelativePrefix(
  IN  PDCB Dcb,
  IN  PUNICODE_STRING String,
  IN  BOOLEAN CaseInsensitive,
  OUT PUNICODE_STRING RemainingPart
  );

Routine Description:

    This routine searches the FCBs/DCBs of a volume and locates the
    FCB/DCB with longest matching prefix for the given input string.  The
    search is relative to a input DCB, and must not start with a leading "\"
    All searching is done case insensitive.

Arguments:

    Dcb - Supplies the Dcb to start searching from

    String - Supplies the input string to search for

    CaseInsensitive - Specifies if the search is to be done case sensitive
        (FALSE) or insensitive (TRUE)

    RemainingPart - Returns the index into the string when the prefix no
        longer matches.  For example, if the input string is "beta\gamma"
        and the input Dcb is for "\alpha" and we only match beta then
        the remaining string is "gamma".

Return Value:

    PFCB - Returns a pointer to either an FCB or a DCB whichever is the
        longest matching prefix.