文件系统（五）

FAT16文件系统的根目录处理方式和其他目录有点不同。区别在于根目录的空间不是由文件分配表管理的，而是格式化时预留的。我们可以从BPB数据中计算出根目录的各个扇区的位置。因此取GetSubDirectory方法的实现如下。

/* * Get a list of all directories in root * We will get the boot sector of device and use the parameters to * find the root directory */Collection<IDirectory>FAT16RootDirctory::GetSubDirectoryies(){IBlockDevice *pDevice = m_fs->GetDevice();Collection<IDirectory> coll;MainPartition * pPartition = (MainPartition*)pDevice;// Get the boot sectorunsigned char buffer[512];pDevice->ReadBlock(0, buffer);struct BPB_Block * pBPB = (struct BPB_Block *)(buffer + 0x0b);int sector = pBPB->NumberOfFATs * pBPB->SectorsPerFAT + 1;int count = (pBPB->NumberOfRootDirEntries * 32 + pBPB->BytesPerSector - 1) / pBPB->BytesPerSector;int bytesPerSector = pBPB->BytesPerSector;while(count){// Read a sectorpDevice->ReadBlock(sector, buffer);// For each entry, check if it existsfor(struct Entry * pEntry = (struct Entry *)buffer; pEntry < (struct Entry *)(buffer + bytesPerSector); pEntry ++){if(pEntry->filename[0] != '/0'){// this entry existsif(pEntry->attribute & 0x10){// This is a fileFAT16Directory* pDir = new FAT16Directory(m_fs, pEntry);coll.Add(pDir);}}}count --;sector ++;}return coll;}

 

类似的，我们可以写出GetFiles方法：

/* * Get a list of all files in root * We will get the boot sector of device and use the parameters to * find the root directory */Collection<IFile>FAT16RootDirctory::GetFiles(){IBlockDevice *pDevice = m_fs->GetDevice();Collection<IFile> coll;MainPartition * pPartition = (MainPartition*)pDevice;// Get the boot sectorunsigned char buffer[512];pDevice->ReadBlock(0, buffer);struct BPB_Block * pBPB = (struct BPB_Block *)(buffer + 0x0b);int sector = pBPB->NumberOfFATs * pBPB->SectorsPerFAT + 1;int count = (pBPB->NumberOfRootDirEntries * 32 + pBPB->BytesPerSector - 1) / pBPB->BytesPerSector;int bytesPerSector = pBPB->BytesPerSector;while(count){// Read a sectorpDevice->ReadBlock(sector, buffer);// For each entry, check if it existsfor(struct Entry * pEntry = (struct Entry *)buffer; pEntry < (struct Entry *)(buffer + bytesPerSector); pEntry ++){if(pEntry->filename[0] != '/0'){// this entry existsif(pEntry->attribute & 0x20){// This is a fileFAT16File* pFile = new FAT16File(m_fs, pEntry);coll.Add(pFile);}}}count --;sector ++;}return coll;}