Filemap.py 文件源码

def _lseek(file_obj, offset, whence):
    """This is a helper function which invokes 'os.lseek' for file object
    'file_obj' and with specified 'offset' and 'whence'. The 'whence'
    argument is supposed to be either '_SEEK_DATA' or '_SEEK_HOLE'. When
    there is no more data or hole starting from 'offset', this function
    returns '-1'.  Otherwise the data or hole position is returned."""

    try:
        return os.lseek(file_obj.fileno(), offset, whence)
    except OSError as err:
        # The 'lseek' system call returns the ENXIO if there is no data or
        # hole starting from the specified offset.
        if err.errno == os.errno.ENXIO:
            return -1
        elif err.errno == os.errno.EINVAL:
            raise ErrorNotSupp("the kernel or file-system does not support "
                               "\"SEEK_HOLE\" and \"SEEK_DATA\"")
        else:
            raise