摘要
对嵌入式系统来说,非正常断电随时可能发生,它会导致文件系统的不一致性,带来文件系统的破坏和数据信息的丢失。因此,在嵌入式存储设备上,设计和实现一种具有掉电安全特性的文件系统具有特别重要的意义,日志文件系统通过记录日志的方法来防止文件系统的异常破坏,这正是我们需要的防断电文件系统。
本文在介绍了几种不同类型的文件系统并比较了它们的优劣后,结合这些分析,我们分析了日志文件系统JFFS2的设计思想和层次结构,研究了JFFS2是如何满足掉电安全性的要求以及如何考虑闪存存储设备特殊属性的问题。接着,本文着重阐述了在嵌入式操作系统Nucleus上移植JFFS2的系统过程,整个系统移植过程包括:MTD物理接口层在Nucleus上的接口实现方案;通过分析对比Nucleus与Linux的系统差异,提出利用系统抽象层去解决JFFS2的系统依赖性问题;简化VFS及用户接口层使得JFFS2能够更为方便的为应用层所使用。
最后,文章展望了日志文件系统的应用前景,相信日志结构的闪存文件系统随着技术的成熟必然会凭其优势在嵌入式产品中得到越来越广泛地应用。
In embedded systems,unexpected power - off often occurs. For a normal kind of file system,unexpected power-off often causes the corruption of the file system and the lose of data。So fore,it is very important to design and implement a special kind of file system to prevent such corruption. Journaling File System is just such kind file system we need.
In this paper,we compare several kinds of file systems and point out the deference between them. On the base of analysis above,we analyse the design idea and architecure of JFFS2,a special journaling file system which considere the special read-write characters of Flash devices how to prevent corruption caused by unexpected power-off. At the last part of the paper,we put emphasis on the process that porting JFFS2 system to the Nucleus embedded system. The totally process focus on: the implementation of MTD driver on Nucleus to support Intel FLASH memory; through compare the operation system between Nucleus and Linux to get the system difference, then bring forward and implement an abstract operation system layer to make the JFFS2 porting little dependence; predigest the VFS layer and user interface to make the JFFS2 to be easy using without lot of effort.
Then we prospect the foreground of log-structure file system implementation,we think Journaling File System will be used far and wide in the embedded FLASH system with the technical improvement.
引文
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