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 sector unsigned 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 sector pDevice->ReadBlock(sector, buffer); // For each entry, check if it exists for(struct Entry * pEntry = (struct Entry *)buffer; pEntry < (struct Entry *)(buffer + bytesPerSector); pEntry ++) { if(pEntry->filename[0] != '/0') { // this entry exists if(pEntry->attribute & 0x10) { // This is a file FAT16Directory* 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 sector unsigned 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 sector pDevice->ReadBlock(sector, buffer); // For each entry, check if it exists for(struct Entry * pEntry = (struct Entry *)buffer; pEntry < (struct Entry *)(buffer + bytesPerSector); pEntry ++) { if(pEntry->filename[0] != '/0') { // this entry exists if(pEntry->attribute & 0x20) { // This is a file FAT16File* pFile = new FAT16File(m_fs, pEntry); coll.Add(pFile); } } } count --; sector ++; } return coll; }