文件系统——Hash结构文件[zt]

https://blog.csdn.net/L_Jsword/article/details/15811723

实验四 文件系统——Hash结构文件   

一、实验目的

1、理解Linux文件系统的内部技术，掌握Linux与文件有关的系统调用命令，并在此基础上建立面向随机检索的hash结构文件。

2、Linux系统保持UNIX文件系统的风格，提供流式文件界面，这种结构具有简洁灵活的特点，但并不直接支持记录式文件和关键字检索。本实验是在Linux文件系统基础上，设计一组库函数，以提供对随机检索的支持。

 

二、实验内容

1、参考教材中hash文件构造算法，设计一组hash文件函数，包括hash文件创建、打开、关闭、读、写等。

2、编写一个测试程序，通过记录保存、查找、删除等操作，检查上述hash文件是否实现相关功能。

 

三、实验准备

1、教程Hash文件核心算法，包括记录保存、记录查找、记录删除等。

2、教程Linux系统有关文件的系统调用命令：creat，open，close，read，write，lseek。

 

四、实验设计

1、由于在Linux系统核心之外模拟实现hash文件，有关hash文件的说明信息不能保存 在inode中，而只能记录在文件的头部。这些信息包括hash文件标志、记录大小、文件 长度、记录数量等。

2、可以根据hash文件核心算法设计内部函数，包括记录的保存、查找、删除等，在此 基础上实现读、写等常规操作。

 

五、实验源码

//hashfile.h

 

#include<unistd.h>

#include<sys/stat.h>

#define COLLISIONFACTOR 0.5


struct HashFileHeader

{

int sig; //Hash文件印鉴

int reclen; //记录长度

int total_rec_num; //总记录数

int current_rec_num; //当前记录数

};

struct CFTag

{

char collision; //冲突计数

char free; //空闲标志

};


int hashfile_creat(const char *filename,mode_t mode,int reclen,int total_rec_num);

//int hashfile_open(const char *filename,int flags);

int hashfile_open(const char *filename,int flags,mode_t mode);

int hashfile_close(int fd);

int hashfile_read(int fd,int keyoffset,int keylen,void *buf);

int hashfile_write(int fd,int keyoffset,int keylen,void *buf);

int hashfile_delrec(int fd,int keyoffset,int keylen,void *buf);

int hashfile_findrec(int fd,int keyoffset,int keylen,void *buf);

int hashfile_saverec(int fd,int keyoffset,int keylen,void *buf);

int hash(int keyoffset,int keylen,void *buf,int total_rec_num);

int checkHashFileFull(int fd);

int readHashFileHeader(int fd,struct HashFileHeader *hfh);

//hashfile.c
#include<unistd.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<stdio.h>
#include<stdlib.h>
#include<memory.h>
#include"HashFile.h"

int hashfile_creat(const char *filename,mode_t mode,int reclen,int total_rec_num)
{
struct HashFileHeader hfh;
int fd;
int rtn;
char *buf;
int i=0;
hfh.sig = 31415926;
hfh.reclen = reclen;
hfh.total_rec_num = total_rec_num;
hfh.current_rec_num = 0;
//fd = open(filename,mode);
fd = creat(filename,mode);
if(fd != -1)
{
rtn = write(fd,&hfh,sizeof(struct HashFileHeader));
//lseek(fd,sizeof(struct HashFileHeader),SEEK_SET);
if(rtn != -1)
{
buf = (char*)malloc((reclen+sizeof(struct CFTag))*total_rec_num);
memset(buf,0,(reclen+sizeof(struct CFTag))*total_rec_num);   ////????
rtn = write(fd,buf,(reclen+sizeof(struct CFTag))*total_rec_num);
free(buf);
}
close(fd);
return rtn;
}
else{
close(fd);
return -1;
}
}

int hashfile_open(const char *filename,int flags,mode_t mode)
{
int fd = open(filename,flags,mode);
struct HashFileHeader hfh;
if(read(fd,&hfh,sizeof(struct HashFileHeader))!= -1)
{
lseek(fd,0,SEEK_SET);
if(hfh.sig == 31415926)
return fd;
else
return -1;
}
else return -1;
}
int hashfile_close(int fd)
{
return close(fd);
}
int hashfile_read(int fd,int keyoffset,int keylen,void *buf)
{
struct HashFileHeader hfh;
readHashFileHeader(fd,&hfh);
int offset = hashfile_findrec(fd,keyoffset,keylen,buf);
if(offset != -1)
{
lseek(fd,offset+sizeof(struct CFTag),SEEK_SET);
return read(fd,buf,hfh.reclen);
}
else
{
return -1;
}
}
int hashfile_write(int fd,int keyoffset,int keylen,void *buf)
{
return hashfile_saverec(fd,keyoffset,keylen,buf);
//return -1;
}
int hashfile_delrec(int fd,int keyoffset,int keylen,void *buf)
{
int offset;
offset = hashfile_findrec(fd,keyoffset,keylen,buf);
if(offset != -1)
{
struct CFTag tag;
read(fd,&tag,sizeof(struct CFTag));
tag.free =0; //置空闲标志
lseek(fd,offset,SEEK_SET);
write(fd,&tag,sizeof(struct CFTag));
struct HashFileHeader hfh;
readHashFileHeader(fd,&hfh);
int addr = hash(keyoffset,keylen,buf,hfh.total_rec_num);
offset = sizeof(struct HashFileHeader)+addr*(hfh.reclen+sizeof(struct CFTag));
if(lseek(fd,offset,SEEK_SET)==-1)
return -1;
read(fd,&tag,sizeof(struct CFTag));
tag.collision--; //冲突计数减1
lseek(fd,offset,SEEK_SET);
write(fd,&tag,sizeof(struct CFTag));
hfh.current_rec_num--; //当前记录数减1
lseek(fd,0,SEEK_SET);
write(fd,&hfh,sizeof(struct HashFileHeader));
}
else{
return -1;
}
}

int hashfile_findrec(int fd,int keyoffset,int keylen,void *buf)
{
struct HashFileHeader hfh;
readHashFileHeader(fd,&hfh);
int addr = hash(keyoffset,keylen,buf,hfh.total_rec_num);
int offset = sizeof(struct HashFileHeader)+addr*(hfh.reclen+sizeof(struct CFTag));
if(lseek(fd,offset,SEEK_SET)==-1)
return -1;
struct CFTag tag;
read(fd,&tag,sizeof(struct CFTag));
char count = tag.collision;
if(count==0)
return -1; //不存在
recfree:
if(tag.free == 0)
{
offset += hfh.reclen+sizeof(struct CFTag);
if(lseek(fd,offset,SEEK_SET)==-1)
return -1;
read(fd,&tag,sizeof(struct CFTag));
goto recfree;
}
else{
char *p =(char*)malloc(hfh.reclen*sizeof(char));
read(fd,p,hfh.reclen);
//printf("Record is {%d , %s}\n",((struct jtRecord *)p)->key,((struct jtRecord *p)->other);
char *p1,*p2;
p1 = (char *)buf+keyoffset;
p2 = p + keyoffset;
int j=0;
while((*p1 == *p2)&&(j<keylen))
{
p1++;
p2++;
j++;
}
if(j==keylen)
{
free(p);
p = NULL;
return(offset);
}
else{
if(addr == hash(keyoffset,keylen,p,hfh.total_rec_num))
{
count--;
if(count == 0)
{
free(p);
p = NULL;
return -1;//不存在
}
}
free(p);
p = NULL;
offset += hfh.reclen+sizeof(struct CFTag);
if(lseek(fd,offset,SEEK_SET) == -1)
return -1;
read(fd,&tag,sizeof(struct CFTag));
goto recfree;
}
}
}
int hashfile_saverec(int fd,int keyoffset,int keylen,void *buf)
{
if(checkHashFileFull(fd))
{
return -1;
}
struct HashFileHeader hfh;
readHashFileHeader(fd,&hfh);
int addr = hash(keyoffset,keylen,buf,hfh.total_rec_num);
int offset = sizeof(struct HashFileHeader)+addr*(hfh.reclen+sizeof(struct CFTag));
if(lseek(fd,offset,SEEK_SET)==-1)
return -1;
struct CFTag tag;
read(fd,&tag,sizeof(struct CFTag));
tag.collision++;
lseek(fd,sizeof(struct CFTag)*(-1),SEEK_CUR);
write(fd,&tag,sizeof(struct CFTag));
while(tag.free!=0) //冲突，顺序探查
{
offset += hfh.reclen+sizeof(struct CFTag);
if(offset >= lseek(fd,0,SEEK_END))
offset = sizeof(struct HashFileHeader); //reach at and,then rewind
if(lseek(fd,offset,SEEK_SET)==-1)
return -1;
read(fd,&tag,sizeof(struct CFTag));
}
tag.free =-1;
lseek(fd,sizeof(struct CFTag)*(-1),SEEK_CUR);
write(fd,&tag,sizeof(struct CFTag));
write(fd,buf,hfh.reclen);
hfh.current_rec_num++;
lseek(fd,0,SEEK_SET);
return write(fd,&hfh,sizeof(struct HashFileHeader));  //存入记录
}

int hash(int keyoffset,int keylen,void *buf,int total_rec_num)
{
int i=0;
char *p =(char*)buf+keyoffset;
int addr =0;
for(i=0;i<keylen;i++)
{
addr += (int)(*p);
p++;
}
return addr%(int)(total_rec_num*COLLISIONFACTOR);
}

int checkHashFileFull(int fd)
{
struct HashFileHeader hfh;
readHashFileHeader(fd,&hfh);
if(hfh.current_rec_num<hfh.total_rec_num)
return 0;
else
return 1;
}
int readHashFileHeader(int fd,struct HashFileHeader *hfh)
{
lseek(fd,0,SEEK_SET);
return read(fd,hfh,sizeof(struct HashFileHeader));
}
//jtRecord.h
#define RECORDLEN 32

struct jtRecord
{
int key;
char other[RECORDLEN-sizeof(int)];
};

#ifdef HAVE_CONFIG_H
#include<config.h>
#endif

//jtRecord.c
#ifdef HAVE_CONFIG_H
#include<config.h>
#endif

#include<stdio.h>
#include<stdlib.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<string.h>

#include"HashFile.h"
#include"jtRecord.h"
#define KEYOFFSET 0
#define KEYLEN sizeof(int)
#define FileNAME "jing.hash"

void showHashFile();

int main(int argc,char *argv[])
{
struct jtRecord rec[6] = {
{1,"jing"},{2,"wang"},{3,"li"},
{4,"zhang"},{5,"qing"},{6,"yuan"}
};
int j=0;
for(j=0;j<6;j++)
{
printf("<%d,%d>\t",rec[j].key,hash(KEYOFFSET,KEYLEN,&rec[j],6));
}
int fd = hashfile_creat(FileNAME,O_RDWR|O_CREAT,RECORDLEN,6);
int i=0;
printf("\nOpen and Save Record...\n");
fd = hashfile_open(FileNAME,O_RDWR,0);
for(i=0;i<6;i++)
{
hashfile_saverec(fd,KEYOFFSET,KEYLEN,&rec[i]);
}
hashfile_close(fd);
showHashFile();
//Demo find Rec
printf("\nFind Record...");
fd = hashfile_open(FileNAME,O_RDWR,0);
int offset = hashfile_findrec(fd,KEYOFFSET,KEYLEN,&rec[4]);
printf("\noffset is %d\n",offset);
hashfile_close(fd);
struct jtRecord jt;
struct CFTag tag;
fd = open(FileNAME,O_RDWR);
lseek(fd,offset,SEEK_SET);
read(fd,&tag,sizeof(struct CFTag));
printf("Tag is <%d,%d>\t",tag.collision,tag.free);
read(fd,&jt,sizeof(struct jtRecord));
printf("Record is {%d,%s}\n",jt.key,jt.other);
//Demo Delete Rec
printf("\nDelete Record...");
fd = hashfile_open(FileNAME,O_RDWR,0);
hashfile_delrec(fd,KEYOFFSET,KEYLEN,&rec[2]);
hashfile_close(fd);
showHashFile();
//Demo Read
fd = hashfile_open(FileNAME,O_RDWR,0);
char buf[32];
memcpy(buf,&rec[1],KEYLEN);
hashfile_read(fd,KEYOFFSET,KEYLEN,buf);
printf("\nRead Record is {%d,%s}\n",
((struct jtRecord *)buf)->key,((struct jtRecord *)buf)->other);
hashfile_close(fd);
//Demo Write
printf("\nWrite Record...");
fd = hashfile_open(FileNAME,O_RDWR,0);
hashfile_write(fd,KEYOFFSET,KEYLEN,&rec[3]);
hashfile_close(fd);
showHashFile();
return 0;
}

void showHashFile()
{
int fd;
printf("\n");
fd = open(FileNAME,O_RDWR);
lseek(fd,sizeof(struct HashFileHeader),SEEK_SET);
struct jtRecord jt;
struct CFTag tag;
while(1)
{
if(read(fd,&tag,sizeof(struct CFTag))<=0)
break;
printf("Tag is <%d,%d>\t",tag.collision,tag.free);
if(read(fd,&jt,sizeof(struct jtRecord))<=0)
break;
printf("Record is {%d,%s}\n",jt.key,jt.other);
}
close(fd);
}

六、实验结果

文件系统鈥斺擧ash结构文件

七、实验小结

编译成功后，要在管理员权限下运行，因为程序要运行文件的系统调用（create、write等）