Nachos实验10设计并实现具有二级索引地文件资料系统

实验目的Nachos系统原有的文件系统只支持单级索引，最大能存取NumDirect * SectorSize的大小的文件，本次试验的目的：理解文件系统的组织结构扩展原有的文件系统，设计并实现具有二级索引的文件系统。

实验环境linux操作系统，Nachos操作系统实验分析已知在文件头的定义中描述了：#define NumDirect ((SectorSize - 2 * sizeof(int)) / sizeof(int))为了说明方便，经过实际计算，NumDirect = 30.二级索引的文件系统的filehdr首先，通过观察Nachos原有的filehdr（即上图左边的部分），可知Nachos的单级索引的文件系统最大只支持存取29个扇区大小的文件。

为了扩展二级索引，取数组的最后一个dataSectors[29]作为存取新的dataSectors数组块的索引，定义dataSectors[0] - dataSectors[28]存取数据所在的块号，dataSectors[29] == -1表示无二级索引块，为正值表示二级索引dataSectors2所在的索引块。

当文件超过原dataSectors数组所能能够存取的大小28的时候，通过bitmap为文件头的dataSectors2分配空间，返回的Sector号存在dataSectors[29]中。

fileSys每次读取filehdr的时候，仍然只读取原filehdr，如果想要访问和修改dataSectors2中的内容，则在filehdr中先通过dataSectors[29]获取到dataSectors2的扇区号，通过调用synchDisk -> ReadSector(dataSectors[lastIndex], (char *)dataSectors2)，读入dataSectors2的内容，然后再进行dataSectors数组29-62号所对应的数据块的读取。

因为本次实验是在实验5的基础上进行更改的，即支持文件的扩展，这就要求不仅要有读取dataSectors2数组的方法，还要可以重新写入dataSectors2的方法。

实现方法也就是首先如果需要访问dataSectors2，那么首先调用synchDisk -> ReadSector (dataSectors[lastIndex], (char *)dataSectors2)，读入dataSectors2的内容，然后进行各种应用程序的读写操作，最后调用synchDisk -> WriteSector (dataSectors[lastIndex], (char *)dataSectors2)，将更改后的结果写回。

由分析可知，文件系统的二级索引功能的扩展只针对filehdr，所有的修改的都只在中进行，连头文件filehdr.h也不涉及。

关键源代码及注释——在头文件中添加dataSectors2的大小定义：#define NumDirect2 (SectorSize / sizeof(int))更改MaxFileSize：#define MaxFileSize ((NumDirect + NumDirect2)* SectorSize)转向进行说明，所有函数体中绿色部分均为本次实验的注释（建议看Allocate和Deallocate 就好了，其他的原理类似，appSectors涉及实验5的部分）：// //省略无数责任声明//// @LiZhen 17/11/09//// Extends the file system to double the max file size that// Nachos can store#include "copyright.h"#include "system.h"#include "filehdr.h"Allocate//----------------------------------------------------------------------// FileHeader::Allocate// Initialize a fresh file header for a newly created file.// Allocate data blocks for the file out of the map of free disk blocks.// Return FALSE if there are not enough free blocks to accomodate// the new file.//// "freeMap" is the bit map of free disk sectors// "fileSize" is the bit map of free disk sectors//// @LiZhen 17/11/09//// Extends the file system to double the max file size that// Nachos can store// Current max file size of Nachos file system is// (NumDirect + NumDirect2) * SectorSize//// If the dataSectors[NumDirect - 1] == -1, no secondary index. // otherwise, use the dataSecotrs[NumDirect - 1] to stroe the// pointer to the secondary index block -- dataSectors2[].//----------------------------------------------------------------------boolFileHeader::Allocate(BitMap *freeMap, int fileSize){numBytes = fileSize;numSectors = divRoundUp(fileSize, SectorSize);if (freeMap->NumClear() < numSectors)return FALSE; // not enough spaceelse if(NumDirect + NumDirect2 <= numSectors)return FALSE;//not enough pointer space//First figure out the current length of dataSectors//dataSectors array index ranges from 0 to lastIndex-1int lastIndex=NumDirect-1;//If do not need the secondary index,//do not change the original code except//assign dataSectors[lastIndex] = -1if(numSectors < lastIndex){for (int i = 0; i < numSectors; i++)dataSectors[i] = freeMap->Find();dataSectors[lastIndex] = -1;}//If the numSectors excends the rage of dataSectors,//first handle the first 0--lastIndex-1 as before.//Then, ask bitmap to allocate a new sector to stroe//the Secondary index block -- dataSectors2.//At last, write back the secondary index block into the sector.else{for (int i = 0; i < lastIndex; i++)dataSectors[i] = freeMap->Find();dataSectors[lastIndex] = freeMap->Find();int dataSectors2[NumDirect2];//secondary index blockfor (int i = 0; i < numSectors - NumDirect; i++)dataSectors2[i] = freeMap->Find();synchDisk->WriteSector(dataSectors[lastIndex], (char *)dataSectors2); }return TRUE;}AppSectors//---------------------------------------------------------//FileHeader::AppSectors//@LiZhen 10/31/2009// In lab5// add appFileSize more bytes in the current file// refresh the bitmap to show the allocating changes.//@LiZhen 17/11/09// In lab10// Handle the reading and writing of the dataSectors2// if needed.//---------------------------------------------------------boolFileHeader::AppSectors(BitMap *freeMap, int appFileSize){if(appFileSize <= 0)return false;int restFileSize = SectorSize * numSectors - numBytes;// printf("the moreFileSize is %d\n",moreFileSize);// printf("the appFileSize is %d\n",appFileSize);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);/*** In lab10**///First figure out the current length of dataSectors//dataSectors array index ranges from 0 to lastIndex-1int lastIndex = NumDirect-1;/** If before appending, there is no secondary index*/if(dataSectors[lastIndex] == -1){//If after being appended, new dataSecoters do NOT need the secondary index,//do not change the original code.if(numSectors < lastIndex)for( ; i < numSectors; i++)dataSectors[i] = freeMap -> Find();//If after being appended, new dataSecoters DO need the secondary index, //first handle the first 0--lastIndex-1 as before.//Then, ask bitmap to allocate a new sector to stroe//the Secondary index block -- dataSectors2.//At last, write back the secondary index block into the sector.else{for( ; i< lastIndex ; i++)dataSectors[i]= freeMap ->Find();dataSectors[lastIndex] = freeMap ->Find();int dataSectors2[NumDirect2];for ( ; i < numSectors ; i++)dataSectors2[i - lastIndex] = freeMap->Find();synchDisk->WriteSector(dataSectors[lastIndex], (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[lastIndex], (char *)dataSectors2);for( ; i < numSectors; i++)dataSectors2[i-lastIndex] = freeMap -> Find();synchDisk->WriteSector(dataSectors[lastIndex], (char *)dataSectors2);}return TRUE;}Deallocate//----------------------------------------------------------------------// FileHeader::Deallocate// De-allocate all the space allocated for data blocks for this file.//// "freeMap" is the bit map of free disk sectors//// @LiZhen 17/11/09// Deallocate the dataSectors2 if needed.//----------------------------------------------------------------------voidFileHeader::Deallocate(BitMap *freeMap){int lastIndex = NumDirect - 1;// If there is no secondary index,// handle it as original.if(dataSectors[lastIndex]==-1){for (int i = 0; i < numSectors; i++){ASSERT(freeMap->Test((int) dataSectors[i])); // ought to be marked!freeMap->Clear((int) dataSectors[i]);}}// 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.elseint i=0;for ( ; i < lastIndex; i++){ASSERT(freeMap->Test((int) dataSectors[i])); // ought to be marked!freeMap->Clear((int) dataSectors[i]);}int dataSectors2[NumDirect2];synchDisk->ReadSector(dataSectors[lastIndex], (char *)dataSectors2); freeMap->Clear((int) dataSectors[lastIndex]);for( ; i < numSectors; i++)freeMap->Clear((int) dataSectors2[i-lastIndex]);}}ByteToSectors//----------------------------------------------------------------------// FileHeader::ByteToSector// Return which disk sector is storing a particular byte within the file. // This is essentially a translation from a virtual address (the// offset in the file) to a physical address (the sector where the// data at the offset is stored).//// "offset" is the location within the file of the byte in question//// @LiZhen 17/11/09// Handle the reading and writing of the dataSectors2// if needed.//----------------------------------------------------------------------intFileHeader::ByteToSector(int offset){int lastIndex = NumDirect - 1;if(offset / SectorSize < lastIndex)return(dataSectors[offset / SectorSize]);{int dataSectors2[NumDirect2];synchDisk->ReadSector(dataSectors[lastIndex], (char *)dataSectors2); return (dataSectors2[offset / SectorSize - lastIndex]);}}Print//----------------------------------------------------------------------// FileHeader::Print// Print the contents of the file header, and the contents of all// the data blocks pointed to by the file header.//// @LiZhen 17/11/09// Handle the reading and writing of the dataSectors2// if needed.//----------------------------------------------------------------------voidFileHeader::Print(){int i, j, k;int lastIndex = NumDirect - 1;char *data = new char[SectorSize];// If there is no secondary index,// handle it as original.if(dataSectors[lastIndex] == -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[lastIndex], (char *)dataSectors2);printf("FileHeader contents. File size: %d. File blocks:\n", numBytes);for (i = 0; i < lastIndex; i++)printf("%d ", dataSectors[i]);for(; i < numSectors; i++)printf("%d ", dataSectors2[i - lastIndex]);printf("\nFile contents:\n");for (i = k = 0; i < lastIndex; 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");}for( ; i < numSectors; i++) {synchDisk->ReadSector(dataSectors2[i - lastIndex], 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;}没有进行任何更改的函数void FileHeader::FetchFrom(int sector)void FileHeader::WriteBack(int sector)int FileHeader::FileLength()调试记录编译好Nachos之后，在终端敲入一下命令：[student@localhost lab10]$ ./nachos –D得到运行结果（请一扫而过）：Bit map file header:FileHeader contents. File size: 128. File blocks:2File contents:\1f\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\ 0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\ 0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0Directory file header:FileHeader contents. File size: 200. File blocks:3 4File contents:\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0 \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0 \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0 \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0Bitmap set:0, 1, 2, 3, 4,Directory contents:No threads ready or runnable, and no pending interrupts.Assuming the program completed.Machine halting!Ticks: total 5400, idle 5060, system 340, user 0Disk I/O: reads 10, writes 0Console I/O: reads 0, writes 0Paging: faults 0Network I/O: packets received 0, sent 0Cleaning up...然后在终端中敲入如下代码，将big文件复制到Nachos中：[student@localhost lab10]$ ./nachos -cp test/big big并执行append命令13次左右：[student@localhost lab10]$ ./nachos -ap test/big big最后显示结果（关键部分加粗显示，其余部分一扫而过）：[student@localhost lab10]$ ./nachos -DBit map file header:FileHeader contents. File size: 128. File blocks:2File contents:\ff\ff\ff\ff\ff\1f\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0 \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0Directory file header:FileHeader contents. File size: 200. File blocks:3 4File contents:\1\0\0\0\5\0\0\0big\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\ 0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\ 0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0 \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0Bitmap set:0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44,Directory contents:Name: big, Sector: 5FileHeader contents. File size: 4760. File blocks:6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 36 37 38 39 40 41 42 43 44File contents:big file big file big file big file big file \abig file big file big file big file big file \abig file big file big file big filebig file \abig file big file big file big file big file \abig file big file big file big file big file \abig file big file big file******省略无数big file*****file big file big file big file big file \abig file big file big file big file big file \abig file big file big file big file bigfile \a***end of file***\aNo threads ready or runnable, and no pending interrupts.Assuming the program completed.Machine halting!Ticks: total 54400, idle 52750, system 1650, user 0Disk I/O: reads 50, writes 0Console I/O: reads 0, writes 0Paging: faults 0Network I/O: packets received 0, sent 0Cleaning up...运行分析Bitmap set:0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44,首先看bitmap，它应该显示出当前那些扇区号被占用了。