filesys.c

Linux下简单文件系统的操作 具体可以实现目录得建立删除等等功能

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <ctype.h>
#include "filesys.h"

#define DEBUG
#define RevByte(low,hight) ((hight)<<8|(low))
#define RevWord(lowest,lower,higher,highest) ((highest)<<24|(higher)<<16 |(lower)<<8|lowest)

struct BootDescriptor_t bdptor;
struct Entry *curdir=NULL; 
int fd;
unsigned char fatbuf[0x1200]; 

void ScanBootSector(){
unsigned char buf[SECTOR_SIZE];
int ret,i;

if((ret=read(fd,buf,SECTOR_SIZE))<0)
perror("read boot sector failed");

for(i=0;i<=10;i++) 
bdptor.Oem_name[i]=buf[i+0x03];
bdptor.Oem_name[i]='\0';

bdptor.BytesPerSector    =RevByte(buf[0x0b],buf[0x0c]);
bdptor.SectorsPerCluster =buf[0x0d];
bdptor.ReservedSectors    =RevByte(buf[0x0e],buf[0x0f]);
bdptor.FATs              =buf[0x10];
bdptor.RootDirEntries    =RevByte(buf[0x11],buf[0x12]);
bdptor.LogicSectors      =RevByte(buf[0x13],buf[0x14]);
bdptor.MediaType         =buf[0x15];
bdptor.SectorsPerFAT     =RevByte(buf[0x16],buf[0x17]);
bdptor.SectorsPerTrack   =RevByte(buf[0x18],buf[0x19]);
bdptor.Heads             =RevByte(buf[0x1a],buf[0x1b]);
bdptor.HiddenSectors     =RevByte(buf[0x1c],buf[0x1d]);

#ifdef  DEBUG 
printf("Oem_name \t\t%s\n"
"BytesPerSector \t\t%d\n"
"SectorsPerCluster \t%d\n"
"ReservedSectors \t%d\n"
"FATs \t\t\t%d\n"
"RootDirEntries \t\t%d\n"
"LogicSectors \t\t%d\n"
"MediaType \t\t%x\n"
"SectorsPerFAT \t\t%d\n"
"SectorsPerTrack \t%d\n"
"Heads \t\t\t%d\n"
"HiddenSectors \t\t%d\n",
bdptor.Oem_name,
bdptor.BytesPerSector,
bdptor.SectorsPerCluster,
bdptor.ReservedSectors,
bdptor.FATs,
bdptor.RootDirEntries,
bdptor.LogicSectors,
bdptor.MediaType,
bdptor.SectorsPerFAT,
bdptor.SectorsPerTrack,
bdptor.Heads,
bdptor.HiddenSectors);
#endif
}

void findDate(unsigned short *year,unsigned short *month,unsigned short *day,unsigned char info[2]){
int data;
data =RevByte(info[0],info[1]);
*year=((data & MASK_YEAR)>>9)+1980;
*month=(data & MASK_MONTH)>>5;
*day=(data &MASK_DAY);
}

void findTime(unsigned short *hour,unsigned short *min,unsigned short *sec,unsigned char info[2]){
int time; 
time=RevByte(info[0],info[1]);  
*hour=(time & MASK_HOUR)>>11;
*min=(time & MASK_MIN)>>5;
*sec=(time & MASK_SEC)*2;
}

/* bug for fix */
/*
void FileNameFormat_old(unsigned char *name){
unsigned char *q,*k,filename[12];
q=name;
k=name;
while (*q != '')  q++;
*q = '\0';
strcpy(filename,k);// name
*q = '';
strcat (filename,".");
while ( *q == '') q++;
k=q;
strcat(filename,k);// extension
strcpy(name,filename);
}
*/

void FileNameFormat(unsigned char *name){
unsigned char *p;
p=name+strlen(name)-1;/* stripp the traling space */
while(*p == ' ') p--;
p++;
*p='\0';
}

void ScanRootEntry(){
struct Entry entry;
int ret,offset;

if((ret=lseek(fd,ROOTDIR_OFFSET,SEEK_SET)) <0)
perror("lseek ROOTDIR_OFFSET failed");

offset=ROOTDIR_OFFSET;

printf("\nA:\\ls");
printf("\n\tname\tdate\t\t time\t\tsector\tsize\t\tattr\n");

while(offset < DATA_OFFSET){
ret=GetEntry(&entry); 
offset+=abs(ret);
if(ret>0){ 
printf("\t%12s"
"\t%d:%d:%d"
"\t%d:%d:%d"
"\t\t%d"
"\t%d"
"\t\t%s\n",
entry.short_name,
entry.year,entry.month,entry.day,
entry.hour,entry.min,entry.sec,
entry.size,
entry.FirstCluster, 
(entry.subdir)? "dir":"file");
}
}
printf("\n");
}


/*
*Argument:entry,Type:struct Entry*
*Return:offset for success,-count for fail or no entry
*Function:get entry fron form cluster or root dir
*Comment:One Entry maybe 32,64,96 Bytes
*/
int GetEntry(struct Entry *pentry){
int ret,i;
int count=0;
unsigned char buf[DIR_ENTRY_SIZE],info[2];

if((ret=read(fd,buf,DIR_ENTRY_SIZE))<0) 
 perror("read entry failed");
count+=ret;

if(buf[0]==0xe5 || buf[0]==0x00)
 return -1*count; 
else{
while(buf[11]==0x0f) { 
if((ret=read(fd,buf,DIR_ENTRY_SIZE))<0) 
perror("read root dir failed");
count+=ret;
}
for(i=0;i<=10;i++) 
pentry->short_name[i]=buf[i];
pentry->short_name[i]='\0';
}

FileNameFormat(pentry->short_name);

info[0]=buf[22];
info[1]=buf[23];
findTime(&(pentry->hour),&(pentry->min),&(pentry->sec),info);

info[0]=buf[24]; 
info[1]=buf[25];
findDate(&(pentry->year),&(pentry->month),&(pentry->day),info);

pentry->FirstCluster = RevByte (buf[26],buf[27]);
pentry->size = RevWord (buf[28],buf[29],buf[30],buf[31]);

pentry->readonly = (buf[11] &ATTR_READONLY) ? 1:0;
pentry->hidden   = (buf[11] &ATTR_HIDDEN)   ? 1:0;
pentry->system   = (buf[11] &ATTR_SYSTEM)   ? 1:0;
pentry->vlabel   = (buf[11] &ATTR_VLABEL)   ? 1:0;
pentry->subdir   = (buf[11] &ATTR_SUBDIR)   ? 1:0;
pentry->archive  = (buf[11] &ATTR_ARCHIVE)  ? 1:0;

return count;
}



int fd_ls(){
int ret,offset,cluster_addr;
struct Entry entry;

printf("\nA:\\ls\n");
/* printf("\tname\tdate\t\t time\t\tsector\tsize\t\tattr\n"); */

if (curdir == NULL) {ScanRootEntry(fd); }
else{ 
cluster_addr = DATA_OFFSET+(curdir->FirstCluster - 2) * SECTOR_SIZE;

if ((ret = lseek(fd,cluster_addr,SEEK_SET)) < 0)
perror("lseek cluster_addr failed");
offset = cluster_addr;

while (offset < cluster_addr +SECTOR_SIZE){
ret = GetEntry(&entry);
offset += abs(ret);
if (ret > 0){
printf( "%12s\t"
"%d:%d:%d\t"
"%d:%d:%d\t\t"
"%d\t"
"%d\t\t"
"%s\n",
entry.short_name,
entry.year,entry.month,entry.day,
entry.hour,entry.min,entry.sec,
entry.size,
entry.FirstCluster,
(entry.subdir)?"dir":"file");
}
}
}
return 0;
}



int ScanEntry(char *entryname,struct Entry *pentry,int mode){
int ret,offset,i;
int cluster_addr;
char uppername[80];

for (i = 0;i<strlen(entryname);i++)
uppername[i] = toupper(entryname[i]);

uppername[i] = '\0';

if (curdir == NULL){
if ((ret == lseek(fd,ROOTDIR_OFFSET,SEEK_SET)) < 0)
perror ("lseek ROOTDIR_OFFSET failed");
offset = ROOTDIR_OFFSET;
while (offset < DATA_OFFSET){
ret = GetEntry(pentry);
offset += abs(ret);
if (pentry->subdir == mode && !strcmp(pentry->short_name,uppername))
return offset;
}
return -1;
}else{
cluster_addr = DATA_OFFSET + (curdir->FirstCluster - 2) * SECTOR_SIZE;
if ((ret == lseek(fd,cluster_addr,SEEK_SET)) < 0)
perror ("lseek cluster_addr failed");
offset = cluster_addr;

while(offset < cluster_addr + SECTOR_SIZE){
ret = GetEntry(pentry);
offset += abs (ret);
if (pentry->subdir == mode && !strcmp(pentry->short_name,uppername))
return offset;
}
return -1;
}
}


/*Argument:dir Type char*
*Return:1 if success,or -1 if filed
*Function:change dir to parent dir or subdir
eg"cd.."or"cd subdir",full path not support
*/
int fd_cd(char *dir){
struct Entry *pentry;
int ret;

printf("\nA:\\cd %s\n",dir);
if (!strcmp(dir,"."))
return 1;

if (!strcmp(dir,"..") && curdir == NULL)
return 1;/* ??? */

pentry = (struct Entry*)malloc(sizeof(struct Entry));


ret = ScanEntry(dir,pentry,1);
if (ret < 0){
printf ("no such dir\n");
free(pentry);
return -1;
}
free (curdir);
curdir = pentry;

#ifdef DEBUG
/*printf("%12s\t"*/
/*"%d:%d:%d\t"*/
/*"%d:%d:%d\t"*/
/*"%d\t"*/
/*"%d\t\t"*/
/*"%s\n",*/
/*prntry->short_name,*/
/*pentry->year,pentry->month,pentry->day,*/
/*pentry->hour,pentry->min,pentry->sec,*/
/*pentry->size,*/
/*pentry->FirstCluster*/
/*(pentry->subdir)?"dir":"file"*/
#endif

return 1;
}

unsigned short GetFatCluster(unsigned short prev){
unsigned short next,fatentry;
int index;

index = prev *1.5;
fatentry = RevByte (fatbuf[index],fatbuf[index+1]);

if (prev % 2 ==1) next = fatentry >> 4;
else next = fatentry & 0x0fff;

return next;
}



void ClearFatCluster(unsigned short cluster){
int index;

index = (int)cluster * 1.5;

if (cluster % 2 == 1){
fatbuf[index] &= 0x0f;
fatbuf[index+1] &= 0x00;
}else{
fatbuf[index] &= 0x00;
fatbuf[index+1] &= 0xf0;
}
}


int fd_rm(char *filename){
struct Entry *pentry;
int ret;
unsigned char c;
unsigned short seed,next;

printf("\nA:\\rm %s\n",filename);

pentry = (struct Entry*)malloc(sizeof(struct Entry));
ret = ScanEntry(filename,pentry,0);
if(ret < 0){
printf("no such file\n");
free(pentry);
return -1;
}

seed = pentry->FirstCluster;
while ((next = GetFatCluster(seed)) != 0x0fff){
seed = next;
ClearFatCluster(next);
}
ClearFatCluster(pentry->FirstCluster);
c = 0xe5;
if (lseek(fd,ret-0x40,SEEK_SET) < 0)
perror("lseek fd_rm failed");
if (write(fd,&c,1) < 0)
perror("write failed");
if(lseek(fd,ret-0x20,SEEK_SET) < 0)
perror("lseek fd_rm failed");
if(write(fd,&c,1) <  0)
perror("write failed");
free(pentry);
if (WriteFat()<0)
exit(1);
printf("file rm OK!\n");
return 1;
}

int WriteFat(){
if(lseek(fd,FAT_ONE_OFFSET,SEEK_SET) < 0){
perror("lseek failed");
return -1;
}
if(write(fd,fatbuf,0x1200) < 0){
perror("read failed");
return -1;
}
if(lseek(fd,FAT_TWO_OFFSET,SEEK_SET) < 0){
perror("lseek failed");
return -1;
}
if(write(fd,fatbuf,0x1200) < 0){
perror("read failed");
return -1;
}
return 1;
}


int ReadFat(){ 
if(lseek(fd,FAT_ONE_OFFSET,SEEK_SET)<0){ 
perror("lseek failed");
return -1;
}
if(read(fd,fatbuf,0x1200)<0){  
perror("read failed");
return -1;
}
}


int main(){
if((fd=open(DEVNAME,O_RDWR))<0) perror("open failed"); 

if (ReadFat()<0)  exit(1); 
ScanBootSector();
ScanRootEntry();

/*test one*/
fd_cd("testdir");

/*test two */
fd_ls();

/*test three*/
 fd_rm("testfile"); 

close(fd);
free(curdir);
return 0;
}