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File System Research and Design Based on Embedded Environment

Author: ChangLiang
Tutor: ZhaoHongWei
School: Jilin University
Course: Applied Computer Technology
Keywords: Filesystem B+tree Map NandFlash
CLC: TP316
Type: Master's thesis
Year: 2009
Downloads: 97
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Abstract


With the development of embedded technology and applications,embedded products have spread to all areas of people’s lives.Embedded products has many advantages,such as small size,low cost,short development cycle and can be carried easily and so on,can also be in strict accordance with the demand for tailor-made and save development costs,while meeting the the functions,working conditions and power requirements which general large-scale PC-should not be satisfied with.File system are the essential operating system component of the embedded devices,with limited resources,the file system should also has high efficiency,the data storage and access efficiency has a direct impact on the overall performance of the operating system.FAT file system as embedded file system is being used in large embedded firms,the traditional FAT file system in a manner stored by chain structure,a folder of all the directory from a cluster,the advantages of file storage structures has a clear architecture and high maintainability.As a result of this storage method,when searching a file we should according to traversal sequence,there’s no sort of structure,there is little influence to support smaller files in the directory,this store would not use much time to read,but with the rAPId growth of storage capacity,we can foresee that such storage can not satisfy people’s high efficiency requirements.In this paper,B+tree to solve the FAT file system directory storage,in fact B+ trees have been widely used for file storage areas,such as NTFS file system,for the FAT file system,has not been tried,but to solve the above-mentioned problem,that is,B+ tree is applied to the storage directory of them,but,as the index is stored in nonvolatile storage medium,so to avoid the boot set up after the index time and excessive memory overhead and so on.Fully consider the characteristics of embedded file system,in order to ensure that expansion and transplantation characteristics of the file system required to conduct a detailed stratification,file system can be divided into four levels generally,1.Driver layer;2.Middleware layer;3.the file system layer;4.a virtual file system layer.Driver layer are non-volatile storage devices sector operator interface,offered by the manufacturers of storage devices;middleware layer is the actual first level file system for embedded developers need to develop,this level of equipment required to initialize the physical block of management,file system access resume logic interface, and set up the bottom of the cache to speed up file system access,but also taking into account the physical storage units such as wear and tear,NandFlash is largely used in embedded memory field,and which has more and more large capacity in recent years,even more than the ordinary disk storage capacity,NAND Flash memory,by virtue of speed,capacity and other characteristics,occupy a larger proportion in the embedded storage device.NAND memory loss because of such issues as the depletion of this paper,the design of a balanced approach to resolve,at the same time in order to reduce the I/O overhead,part of the index information stored in Flash memory to speeded up the file system called and the speed of operation,at the same time,this article take full account of the file system’s secondary development,has a clear of hierarchy;File system layer,B+tree’s job is to initialize the index to read the situation,set up through the B+tree to operate the file system,while providing API access layer of the system,but also for equipment area initialization and file system initialization job;virtual file system layer(API layer) is for embedded device developers,and provide general file access the API,set up the mission file access mechanisms,optimizing the fileaverage waiting time of system access.Embedded application development ways are limited because of the development environment,and the limited means of debugging method is more cumbersome rough. But the lucky is the actual file system for the development,in fact,has less relation with the development board environment,only the first layer are connected to the storage medium,other levels are an independent existence from the development board, and so,in order to speed up the develop and test the speed of PC-use disk mirroring to create the method to simulate the NandFlash disk,create mirror strictly to the same format of the NandFlash,in essence,there is no difference.Provided with the same image access interface as the device driver,so that makes the operation of the document such as the development of debugging process easier,saving valuable time. Also check through with other instrument validation conveniently.Combinate uc/os real-time operating system and file system API layer,as a system simulation development,in the field of embedded applications uc/os used widely,it adopted the United States Aeronautics and Space Administration(FAA) security certification,is a complete,portable,can be curable,can be trimmed of preemptive multi-tasking real-time kernel.And fit in the embedded development platform,using MagicARM2200 as an experimental platform for the development of auxiliary,the use of ARM embedded processor is a high performance,low-power RISC chips and be selected as to support a more complex file system and applications of embedded file system operation processor is comfortable.In this paper,give full consideration to the process of developing the system file system compatibility,under the premise do not broken the format of the FAT file system and set up the index as ordinary file in the FAT file system,so it has downward compatibility,can be visited by ordinary FAT file system.At the same time,the file system layer can provide a variety of file system mount and system start with a better portability and scalability,when add a new system file system,just need to be combined with system kernel,and can achieve their visit easily.The upper class don not need to do any change.Fat file system has wide base of costomer,there will have a great demand in the future.In this pager,by comparing the test result,proved that the using B+ tree index mechanism on the file system can improve the performance of the file system.Reaching on the aim of the study.

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