Android文件系统日志记录

Question

ext3有3个日志记录选项:日志、已排序和回写。根据维基百科entry的说法，对于崩溃恢复，这些风险从最低风险到最高风险不等。由于某种原因，Android版本的Linux只支持后两个选项，默认为写回。(我正在运行Froyo)

有没有办法添加对日志模式的支持？我希望在ext3的/data分区上执行此操作，该分区也是大多数文件写入发生的位置。我的设备没有电池，所以我需要确保当有人断开电源时它是防崩溃的。

如果有人感兴趣，可以在kernel/fs/ext3/Kconfig中定义Linux选项。具体的选项是EXT3_DEFAULTS_TO_ORDERED。

Answer 1

解决方案是将以下内容添加到内核/fs/ext3/Kconfig中，并使用EXT3_DEFAULTS_TO_JOURNAL重新构建内核。

choice
    prompt "EXT3 default journal mode"
    default EXT3_DEFAULTS_TO_ORDERED
    help
      The journal mode options for ext3 have different tradeoffs
      between when data is guaranteed to be on disk and
      performance.  The use of "data=writeback" can cause
      unwritten data to appear in files after an system crash or
      power failure, which can be a security issue.  However,
      "data=ordered" mode can also result in major performance
      problems, including seconds-long delays before an fsync()
      call returns.  "data=journal" is the safest option but possibly
      the the great perfromance burden.  For details, see:

      http://ext4.wiki.kernel.org/index.php/Ext3_data_mode_tradeoffs

      If you have been historically happy with ext3's performance,
      data=ordered mode will be a safe choice.


config EXT3_DEFAULTS_TO_JOURNAL
    bool "Default to 'data=journal' in ext3"
    depends on EXT3_FS
    help
      Both data and metadata are journaled.  Should be safe
      against crashes, power failure, etc.


config EXT3_DEFAULTS_TO_ORDERED
    bool "Default to 'data=ordered' in ext3"
    depends on EXT3_FS
    help
      Only metadata are journaled. Data is written first and then
      metadata is update.  Mostly safe against crashes, power
      failures, etc., except if the anomally occurred while a file 
      is being overwritten.  Most of the time files are appended and
      not over written.

config EXT3_DEFAULTS_TO_WRITEBACK
    bool "Default to 'data=writeback' in ext3"
    depends on EXT3_FS
    help
      Ext2 with a fast ckfs.  Not always safe against crashes, 
      power failure, etc., but has the best preformance

endchoice