fatgen.cpp

// Generador de Archivos FAT16
#define rechcast reinterpret_cast<const char *> 
#include <iostream>
#include <fstream>
using namespace std;

int main(int argc, char* argv[]){
    string fn;
    if(argc>1){
        fn = argv[1];
    }else{
        cout << "Input filename: ";
        cin >> fn;
    }
    fn = fn + ".FAT";
    cout << "Filename: " << fn << endl;
    ofstream FATfile(fn.c_str(), ios::binary | ios::out);
    if(!FATfile.is_open()){
        cout << "Can't open file!" << endl;
        return 1;
    }
    cout << "Writing Reserved Region... (512 Bytes)" << endl;
    char* buffer = new char[512]; // Empty sector
    for(int i = 0; i < 512;i++)
        buffer[i] = 0;
    /* BOOT START BLOCK */ 
    FATfile.write(buffer,3); // Bootstrap Jump Code, Unused here
    FATfile.write("MyFS PWN",8); // OEM Name, 8 char, Doesn't really matter
    /* BIOS PARAMETER BLOCK */
    int values = 512;
    FATfile.write(rechcast(&values),2); // Bytes Per Sector
    values = 8;
    FATfile.write(rechcast(&values),1); // Sectors Per Cluster, 8 Sectors * 512 Bytes/Sector = 4kB Clusters
    values = 1;
    FATfile.write(rechcast(&values),2); // # Reserved Sectors, FAT16 uses 1
    values = 2;
    FATfile.write(rechcast(&values),1); // # FAT Copies, Using 2
    values = 512;
    FATfile.write(rechcast(&values),2); // # Root Dir Entries, Using 512
    FATfile.write(buffer,2); // # Sectors in FS (Small), Unused here
    values = 0xF8;
    FATfile.write(rechcast(&values),1); // Media Descriptor, Using Fixed Disk
    values = 256;
    FATfile.write(rechcast(&values),2); // # Sectors per FAT, 256 Sectors/FAT * 512 Bytes/Sector = 128kB per FAT
    FATfile.write(buffer,2); // # Sectors per Track, Unused here
    FATfile.write(buffer,2); // # Heads, Unused here
    FATfile.write(buffer,4); // # Hidden Sectors, Unused here
    values = 524288;
    FATfile.write(rechcast(&values),4); // # Sectors in FS (Big), 524288 Sectors * 512 Bytes/Sector = 256MB FS
    /* EXTENDED BIOS PARAMETER BLOCK */
    FATfile.write(buffer,1); // Drive Number, Unused
    FATfile.write(buffer,1); // Reserved
    FATfile.write(buffer,1); // Extended Boot Signature, Unused
    FATfile.write(buffer,4); // Volume Serial Number, Unused
    FATfile.write("MyFATVolume",11); // Volume Label, Should be same as ROOT
    FATfile.write("'FAT16 '",8); // FS Type
    /* BOOTSTRAP CODE */
    FATfile.write(buffer,448); // Bootstrap Code, Unused
    values = 0xAA55;
    FATfile.write(rechcast(&values),2); // Boot Sector Signature
    cout << "Done writing Reserved Region." << endl;
    /* FAT REGION */
    cout << "Writing FAT Region..." << endl;
    for(int i=0; i<2; i++){// 2 FAT Total
        cout << "Writing file allocation table #" << i << endl;
        // First two FAT entries are special purpose. NOT empty.
        values = 0xFFF8; // 1st is 0xFFXX, where XX is Media Descriptor
        FATfile.write(rechcast(&values),2);
        values = 0xFFFF; // 2nd is EOF
        FATfile.write(rechcast(&values),2);
        FATfile.write(buffer,508); //Rest of sector remains empty.
        for(int j=0; j<255; j++){ // Other 255 Sectors of FAT
            FATfile.write(buffer,512); // 512 Bytes per Sector
        }
    }
    cout << "Done writing FAT Region." << endl;
    /* DATA REGION */
    cout << "Writing Data Region..." << endl;
    // 256MB = 524288 Sectors in Disk --> 524288 Total Sectors - 512 FAT Sectors - 1 Root Sector = 523775 Data Sectors
    for(int i=0; i<523775; i++){
        FATfile.write(buffer,512);
        if(i%50000==0){
            cout << i << "/523775 sectors written..." << endl;
        }
    }
    cout << "523775/523775 sectors written..." << endl;
    cout << "Done writing Data Region." << endl;
    cout << "Finished generating FAT file!" << endl;
    delete[] buffer;
    FATfile.close();
    return 0;
}