文件系统（二）

为了实现读取FAT16文件系统，我们需要为FAT16实现上节提到的那些接口，先看 IFileSystem接口

 

/** * This Class is a read-only FAT-16 file system. A file system can be created on a * block device */ class FAT16 : public IFileSystem { public: FAT16(IBlockDevice * pDevice); ~FAT16(); public: virtual IDirectory * GetRootDirectory(); IBlockDevice * GetDevice(){return m_pDevice;} WORD NextCluster(WORD cluster); protected: IBlockDevice * m_pDevice; };

 

其中需要一提的是NextCluster方法。 由于FAT16采取链式分配，这个方法将返回某一簇的下一簇。

 

接下来是FAT16的目录项结构定义

#pragma pack(push) #pragma pack(1) struct Entry { char filename[11]; BYTE attribute; BYTE Reserved; BYTE CreationTimeTenth; WORD CreationTime; WORD CreationDate; WORD LastAccessDate; WORD FirstClusterHigh; WORD LastWriteTime; WORD LastWriteDate; WORD FirstClusterLow; DWORD Size; }; #pragma pack(pop)

 

 

再下来是FAT16的目录类和文件类

class FAT16Directory: public IDirectory { public: FAT16Directory(FAT16 * fs, struct Entry * pEntry); public: virtual wchar_t * GetName(); virtual Collection<IDirectory> GetSubDirectoryies(); virtual Collection<IFile> GetFiles(); protected: struct Entry m_entry; FAT16 * m_fs; }; class FAT16RootDirctory : public IDirectory { public: FAT16RootDirctory(FAT16 * fs): m_fs(fs), m_pVga(pVga){} public: virtual wchar_t * GetName() {return NULL;}; virtual Collection<IDirectory> GetSubDirectoryies(); virtual Collection<IFile> GetFiles(); protected: FAT16 * m_fs; }; class FAT16File : public IFile { public: FAT16File(FAT16 * fs, struct Entry * pEntry); public: virtual wchar_t * GetName(); virtual void Read(void * buffer); virtual size_t GetSize(); protected: struct Entry m_entry; FAT16 * m_fs; };