Read TIFF IFD structure and its tags from file.

        File cursor must be at storage position of IFD offset and is left at
        offset to next IFD.

        Raises StopIteration if offset (first bytes read) is 0.

def _fromfile(self):
        """Read TIFF IFD structure and its tags from file.

        File cursor must be at storage position of IFD offset and is left at
        offset to next IFD.

        Raises StopIteration if offset (first bytes read) is 0.

        """
        fd = self.parent._fd
        byte_order = self.parent.byte_order
        offset_size = self.parent.offset_size

        fmt = {4: 'I', 8: 'Q'}[offset_size]
        offset = struct.unpack(byte_order + fmt, fd.read(offset_size))[0]
        if not offset:
            raise StopIteration()

        # read standard tags
        tags = self.tags
        fd.seek(offset)
        fmt, size = {4: ('H', 2), 8: ('Q', 8)}[offset_size]
        try:
            numtags = struct.unpack(byte_order + fmt, fd.read(size))[0]
        except Exception:
            warnings.warn("corrupted page list")
            raise StopIteration()

        for _ in range(numtags):
            tag = TIFFtag(self.parent)
            tags[tag.name] = tag

        # read LSM info subrecords
        if self.is_lsm:
            pos = fd.tell()
            for name, reader in CZ_LSM_INFO_READERS.items():
                try:
                    offset = self.cz_lsm_info["offset_"+name]
                except KeyError:
                    continue
                if not offset:
                    continue
                fd.seek(offset)
                try:
                    setattr(self, "cz_lsm_"+name, reader(fd, byte_order))
                except ValueError:
                    pass
            fd.seek(pos)