文件系统（四）

这一节中我们来看下FAT16目录的实现

 

首先自然是构造函数

FAT16Directory::FAT16Directory(System::Boot::FAT16 *fs, struct Entry *pEntry) { m_fs = fs; memcpy(&m_entry, pEntry, sizeof(struct Entry)); }

 

其中Struct Entry结构我们在前面已经提到过好多次了，这是FAT16目录表项数据结构。

#pragma pack(push) #pragma pack(1) struct BPB_Block { WORD BytesPerSector; BYTE SectorPerCluster; WORD ReservedSectors; BYTE NumberOfFATs; WORD NumberOfRootDirEntries; WORD TotalSectors; BYTE MediaDescriptor; WORD SectorsPerFAT; WORD SectorPerTrack; WORD Heads; DWORD HiddenSectors; DWORD TotalSectors32; BYTE PhysicalDriveNumber; BYTE Reserved; BYTE SignatureByte; DWORD SerialNumber; char Label[11]; // 11 Bytes char FSType[8]; // 8 Bytes }

 

 

Struct Entry的内容中包括目录的文件名。因此GetName方法就从这里取目录名。下面的代码中的两个循环分别取主文件名和扩展名。

wchar_t * FAT16Directory::GetName() { wchar_t * name = new wchar_t[13]; int i = 0; for(; i < 8; i++) { if(m_entry.filename[i] == 0 || m_entry.filename[i] == 0x20) break; name[i] = m_entry.filename[i]; } name[i++] = '.'; for(int j = 8; j < 11; j++) { if(m_entry.filename[j] == 0 || m_entry.filename[j] == 0x20) break; name[i ++] = m_entry.filename[j]; } name[i] = '/0'; return name; }

 

最后一个方法是GetSubDirectory方法。取子目录的代码比较复杂一些。但是我们可以用下面的流程图来表示

 

实现的代码如下所示：

Collection<IDirectory> FAT16Directory::GetSubDirectoryies() { IBlockDevice *pDevice = m_fs->GetDevice(); Collection<IDirectory> coll; // Get the boot sector char buffer[512]; pDevice->ReadBlock(0, buffer); struct BPB_Block * pBPB = (struct BPB_Block *)(buffer + 0x0b); int rootSize = (pBPB->NumberOfRootDirEntries * 32 + pBPB->BytesPerSector - 1) / pBPB->BytesPerSector; int firstsector = pBPB->NumberOfFATs * pBPB->SectorsPerFAT + 1 + rootSize; // count is the count of clusters the directory has int count = (m_entry.Size + pBPB->BytesPerSector * pBPB->SectorPerCluster- 1) / (pBPB->BytesPerSector * pBPB->SectorPerCluster); int bytesPerSector = pBPB->BytesPerSector; int SectorPerCluster = pBPB->SectorPerCluster; WORD cluster = m_entry.FirstClusterLow; // Read the cluster, we'll read it sector by sector while(count && cluster <= 0xFFF8) { for(int sector = 0; sector < SectorPerCluster; sector ++) { // Read a sector pDevice->ReadBlock(firstsector + (cluster - 2) * SectorPerCluster + 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 directory FAT16Directory * pDir = new FAT16Directory(m_fs, pEntry, m_pVga); coll.Add(pDir); } } } } count --; cluster = m_fs->NextCluster(cluster); } return coll; }

 

 

同样的方法可以实现GetFiles方法

Collection<IFile> FAT16Directory::GetFiles() { IBlockDevice *pDevice = m_fs->GetDevice(); Collection<IFile> coll; // Get the boot sector char buffer[512]; pDevice->ReadBlock(0, buffer); struct BPB_Block * pBPB = (struct BPB_Block *)(buffer + 0x0b); int rootSize = (pBPB->NumberOfRootDirEntries * 32 + pBPB->BytesPerSector - 1) / pBPB->BytesPerSector; int firstsector = pBPB->NumberOfFATs * pBPB->SectorsPerFAT + 1 + rootSize; // count is the count of clusters the directory has int count = (m_entry.Size + pBPB->BytesPerSector * pBPB->SectorPerCluster- 1) / (pBPB->BytesPerSector * pBPB->SectorPerCluster); int bytesPerSector = pBPB->BytesPerSector; int SectorPerCluster = pBPB->SectorPerCluster; WORD cluster = m_entry.FirstClusterLow; // Read the cluster, we'll read it sector by sector while(count && cluster <= 0xFFF8) { for(int sector = 0; sector < SectorPerCluster; sector ++) { // Read a sector pDevice->ReadBlock(firstsector + (cluster - 2) * SectorPerCluster + 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 directory FAT16File * pFile = new FAT16File(m_fs, pEntry, m_pVga); coll.Add(pFile); } } } } count --; cluster = m_fs->NextCluster(cluster); } return coll; }