todo

这是Linux系统下的对UDF文件系统新增的功能

FS:
    support extended attributes (in their own blocks/udf 2.0 streams)
    do delayed block assignments
    make sure reading works on big endian and/or 64 bit machines
    make sure block allocation failures (full disc) cannot mess up extents
    make any changes to support UDF 2.01
    handling bad block remapping (superblock data/metadata/data)
    handling writing VAT/sequential write media (CDR)
    add journaling support (?)
    WORM support

SUPPORT:
    rewrite mkudf (or at least, rework it)
    write a udffsck