test_helpers.py 文件源码

def is_sparse(path):
    # LP: #1656371 - Looking at stat().st_blocks won't work on ZFS file
    # systems, since that seems to return 1, whereas on EXT4 it returns 0.
    # Rather than hard code the value based on file system type (which could
    # be different even on other file systems), a more reliable way seems to
    # be to use SEEK_DATA with an offset of 0 to find the first block of data
    # after position 0.  If there is no data, an ENXIO will get raised, at
    # least on any modern Linux kernels we care about.  See lseek(2) for
    # details.
    with open(path, 'r') as fp:
        try:
            os.lseek(fp.fileno(), 0, os.SEEK_DATA)
        except OSError as error:
            # There is no OSError subclass for ENXIO.
            if error.errno != errno.ENXIO:
                raise
            # The expected exception occurred, meaning, there is no data in
            # the file, so it's entirely sparse.
            return True
    # The expected exception did not occur, so there is data in the file.
    return False