The Design And Implementation Of An Embedded File System

File system is one of the most primary sources in operating system, which is a collection of files and directories in a computer system. With the increasing of availability and lowering of price of embedded system hardware, and the expanding of application fields of embedded system, the embedded operating systems play a more important role and the development of embedded file system attract more attention. Due to the difference of system architecture and application requirement, there is a big difference between file system in embedded devices and that in desktop computers, such as: real-time response, transplantation, reducing and configuration, etc.The article describes a specified file system in embedded Linux, which is based on a standard Linux file system structure, and was transplanted to the hardware platform of a handed computing product after proper reducing and configuration.Firstly, the article gave a brief introduction to embedded system, Linux operating system, and their combination-embedded Linux operating system, and described its characters, advantages and the advance in the world; Secondly, the paper described the composition and structure of Linux file system, and gave detailed description about the primary and important files. Thirdly, the paper described the construction of one kind of embedded Linux file system in details, and discussed how to select and configure the needed files, and how to configure the authorities of users and groups to meet security requirement. At last, the paper summarized how to construct a development platform for further development of embedded system on the base of the constructed file system.The constructed file system inherited the tree directory structure in standard Linux file systems, while much reducing has been done according to the practical hardware limitation and the requirement of the final product, only the most fundamental files needed during the booting and running were reserved, even each of them were simplified as small as possible, to ensure the resulted system to be as small as possible. In addition, the physical arrangement of file system was optimized by placing the often modified files in the SDRAM and the less modified files in the Flash. Simplified configuration of system files and proper configuration of file properties and access mode provided security management for embedded system.The constructed embedded Linux file system has been successfully applied in the sPCC (secure Personal Computing Center), which is a trust mobile device produced by Shanghai Wellhope Information and Technology Co. Ltd.