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_tGetSize();protected:struct Entry m_entry;FAT16 * m_fs;};