山东大学操作系统实验十实验报告

软件学院实验报告：10实验题目：具有二级索引的文件系统姓名：陶旭涛日期：2013-12-1 学号：201100300038Email：1595242630@实验目的：Nachos的文件系统中保存文件内容所在扇区索引的“文件头“目前只占用一个扇区，为了可以使Nachos文件系统创建较大的文件，将”文件头”扩大到两个扇区，也就是实现二级索引。

硬件环境：软件环境：Linux操作系统，Nachos操作系统实验步骤：1，通过实验5的扩展文件大小的实验，了解了nachos 系统的对文件系统的管理。

本次实验的目的主要是扩大Nachos系统可以创建的文件的大小，使用两个扇区来保存文件头的信息。

为了达到这个目的，首先了解nachos 自带的文件系统的文件头的结构：保存在一个扇区中，第一个int保存了文件的字节数（numBytes），第二个int保存了使用的扇区数（numSectors），第三个数据结构是文件所在的各个扇区号（dataSectors[NumDiresct]）。

也就是说，Nachos系统采用的是索引式的文件管理方式。

因而，要实现nachos文件系统的二级索引，可以使第一个索引节点（也就是原有的文件头那个扇区）的dataSectors数组的最后一个元素保留第二个索引节点（也就是第二个扇区）的引用（也就是扇区号）。

如果文件大小不超过一个索引节点可以保留的内容，则这个最后一个元素的值为-1。

2，通过分析可知，需要修改中的内容。

代码如下：boolFileHeader::Allocate(BitMap *freeMap, int fileSize){numBytes = fileSize;numSectors = divRoundUp(fileSize, SectorSize);if (freeMap->NumClear() < numSectors)return FALSE; // not enough space/*如果文件大小超过索引节点中保存扇区号的数目，则返回false*/else if(NumDirect + NumDirect2 <= numSectors)return FALSE;//the filesys cannot support such big file/*toNextNode 是保留第二个索引节点的扇区号*/int toNextNode=NumDirect-1; //toNextNode is the Sector number of the second node of the filehd//if the second node is not needed, then dataSector[toNextNode]=-1if(numSectors < toNextNode){for (int i = 0; i < numSectors; i++)dataSectors[i] = freeMap->Find();//为文件分配扇区dataSectors[toNextNode] = -1;}//If the numSectors excends the rage of dataSectors,else{for (int i = 0; i < toNextNode; i++)dataSectors[i] = freeMap->Find();dataSectors[toNextNode] = freeMap->Find();//找一个空闲的扇区，作为第二个扇区，索引节点//this is the content,i.e.filehdr of the allocated sectors, of the second nodeint dataSectors2[NumDirect2];for (int i = 0; i < numSectors - NumDirect; i++)dataSectors2[i] = freeMap->Find();//为文件分配扇区//the fefault synchDisk->WriteSector do not include the second node//so write back the new build nodesynchDisk->WriteSector(dataSectors[toNextNode], (char *)dataSectors2); }return TRUE;/*revised*/}voidFileHeader::Deallocate(BitMap *freeMap){/*toNextNode 是保留第二个索引节点的扇区号*/int toNextNode= NumDirect - 1;// test if has the second nodeif(dataSectors[toNextNode]==-1){for (int i = 0; i < numSectors; i++){ASSERT(freeMap->Test((int) dataSectors[i])); // ought to be marked!freeMap->Clear((int) dataSectors[i]);}}//has a second node, then find it, then clean the bitmap, thenelse{//clear the first n-1 bit,remain the toNextNodeint i=0;for ( ; i < toNextNode; i++){ASSERT(freeMap->Test((int) dataSectors[i])); // ought to be marked!freeMap->Clear((int) dataSectors[i]);}int dataSectors2[NumDirect2];synchDisk->ReadSector(dataSectors[toNextNode], (char *)dataSectors2);freeMap->Clear((int) dataSectors[toNextNode]);//clear the toNextNodefor( ; i < numSectors; i++)freeMap->Clear((int) dataSectors2[i-toNextNode]);//toNextNode==the number of filehdr item }}intFileHeader::ByteToSector(int offset){ASSERT(offset<=numBytes);/*toNextNode 是保留第二个索引节点的扇区号*/int toNextNode = NumDirect - 1; //test if offset excedes the first nodeif(offset / SectorSize < toNextNode)return(dataSectors[offset / SectorSize]);else{int dataSectors2[NumDirect2];synchDisk->ReadSector(dataSectors[toNextNode], (char *)dataSectors2);return (dataSectors2[offset / SectorSize - toNextNode]);}}voidFileHeader::Print(){/*revised*/int i, j, k;/*toNextNode 是保留第二个索引节点的扇区号*/int toNextNode = NumDirect - 1;char *data = new char[SectorSize];//test if there is a second nodeif(dataSectors[toNextNode] == -1){printf("FileHeader contents. File size: %d. File blocks:\n", numBytes); for (i = 0; i < numSectors; i++)printf("%d ", dataSectors[i]);printf("\nFile contents:\n");for (i = k = 0; i < numSectors; i++) {synchDisk->ReadSector(dataSectors[i], data);for (j = 0; (j < SectorSize) && (k < numBytes); j++, k++) {if ('\040' <= data[j] && data[j] <= '\176') // isprint(data[j])printf("%c", data[j]);elseprintf("\\%x", (unsigned char)data[j]);}printf("\n");}}// If there is a secondary index,// first read in the dataSectors2 from the Disk.// Then, deallocate the data blocks for this file.// At last, deallocate the block that dataSector2 locates.else{int dataSectors2[NumDirect2];synchDisk->ReadSector(dataSectors[toNextNode], (char *)dataSectors2);//1, print the filedre itemsprintf("FileHeader contents. File size: %d. File blocks:\n", numBytes);for (i = 0; i < toNextNode; i++)printf("%d ", dataSectors[i]);for(; i < numSectors; i++)printf("%d ", dataSectors2[i - toNextNode]);printf("\nFile contents:\n");//2,print the content of the first node pointedfor (i = k = 0; i < toNextNode; i++) {synchDisk->ReadSector(dataSectors[i], data);for (j = 0; (j < SectorSize) && (k < numBytes); j++, k++) {if ('\040' <= data[j] && data[j] <= '\176') // isprint(data[j])printf("%c", data[j]);elseprintf("\\%x", (unsigned char)data[j]);}printf("\n");}//3,print the content of the second node pointedfor( ; i < numSectors; i++) {synchDisk->ReadSector(dataSectors2[i - toNextNode], data);for (j = 0; (j < SectorSize) && (k < numBytes); j++, k++) {if ('\040' <= data[j] && data[j] <= '\176') // isprint(data[j])printf("%c", data[j]);elseprintf("\\%x", (unsigned char)data[j]);}printf("\n");}}delete [] data;/*revised*/}boolFileHeader::AppSectors(BitMap *freeMap, int appFileSize){/*revised*/if(appFileSize <= 0)return false;int restFileSize = SectorSize * numSectors - numBytes;if(restFileSize >= appFileSize){numBytes += appFileSize;return true;}else{int moreFileSize = appFileSize - restFileSize;if(freeMap->NumClear()< divRoundUp(moreFileSize, SectorSize))return FALSE;else if(NumDirect + NumDirect2 <= numSectors + divRoundUp(moreFileSize, SectorSize)) return FALSE;int i = numSectors;numBytes += appFileSize;numSectors += divRoundUp(moreFileSize, SectorSize);/*toNextNode 是保留第二个索引节点的扇区号*/int toNextNode = NumDirect-1; //test if has the second nodeif(dataSectors[toNextNode] == -1){//test if need the second nodeif(numSectors < toNextNode)for( ; i < numSectors; i++)dataSectors[i] = freeMap -> Find();//need the second nodeelse{for( ; i< toNextNode ; i++)dataSectors[i]= freeMap ->Find();dataSectors[toNextNode] = freeMap ->Find();int dataSectors2[NumDirect2];for ( ; i < numSectors ; i++)dataSectors2[i - toNextNode] = freeMap->Find();synchDisk->WriteSector(dataSectors[toNextNode], (char *)dataSectors2);}}/** If before appending, there is already a secondary index*///First read the dataSectors2 from the Disk.//Then, append the file size.//At last, write back the secondary index block into the sector,else{int dataSectors2[NumDirect2];synchDisk->ReadSector(dataSectors[toNextNode], (char *)dataSectors2);for( ; i < numSectors; i++)dataSectors2[i-toNextNode] = freeMap -> Find();//the var toNextNode==the number of int that synchDisk->WriteSector(dataSectors[toNextNode], (char *)dataSectors2);//the fefault synchDisk}}return TRUE;/*revised*/}运行结果：首先运行命令 ./nachos –f 格式化Nachos磁盘然后运行 ./nachos –ap test/big big 若干次，知道出现提示，文件太大不能再追究为止。