metadata.py 文件源码

def get_xattrs_as_blob(fs, filename):  # pragma: no cover
    tracing.trace('filename=%s' % filename)

    try:
        names = fs.llistxattr(filename)
    except (OSError, IOError), e:
        if e.errno in (errno.EOPNOTSUPP, errno.EACCES):
            return None
        raise
    tracing.trace('names=%s' % repr(names))
    if not names:
        return None

    values = []
    for name in names[:]:
        tracing.trace('trying name %s' % repr(name))
        try:
            value = fs.lgetxattr(filename, name)
        except OSError, e:
            # On btrfs, at least, this can happen: the filesystem returns
            # a list of attribute names, but then fails when looking up
            # the value for one or more of the names. We pretend that the
            # name was never returned in that case.
            #
            # Obviously this can happen due to race conditions as well.
            if e.errno == errno.ENODATA:
                names.remove(name)
                logging.warning(
                    '%s has extended attribute named %s without value, '
                    'ignoring attribute',
                    filename, name)
            else:
                raise
        else:
            tracing.trace('lgetxattr(%s)=%s' % (name, value))
            values.append(value)
    assert len(names) == len(values)

    name_blob = ''.join('%s\0' % name for name in names)

    lengths = [len(v) for v in values]
    fmt = '!' + 'Q' * len(values)
    value_blob = struct.pack(fmt, *lengths) + ''.join(values)

    return ('%s%s%s' %
            (struct.pack('!Q', len(name_blob)),
             name_blob,
             value_blob))