source: bootcd/isolinux/syslinux-6.03/utils/mkdiskimage.in

#!/usr/bin/perl
## -----------------------------------------------------------------------
##
##   Copyright 2002-2008 H. Peter Anvin - All Rights Reserved
##   Copyright 2009-2010 Intel Corporation; author: H. Peter Anvin
##
##   This program is free software; you can redistribute it and/or modify
##   it under the terms of the GNU General Public License as published by
##   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
##   Boston MA 02111-1307, USA; either version 2 of the License, or
##   (at your option) any later version; incorporated herein by reference.
##
## -----------------------------------------------------------------------

#
# Creates a blank MS-DOS formatted hard disk image
#

use bytes;
use integer;
use Fcntl;
use Errno;
use Cwd;
use IO::Handle;                 # For flush()

sub absolute_path($) {
    my($f) = @_;
    my($c);

    return $f if ( $f =~ /^\// );
    $c = cwd();
    $c = '' if ( $c eq '/' );
    return $c.'/'.$f;
}

sub is_linux() {
    return !!eval '{ '.
        'use POSIX; '.
        '($sysname, $nodename, $release, $version, $machine) = POSIX::uname(); '.
        "return \$sysname eq \'Linux\'; }";
}

sub get_random() {
    # Get a 32-bit random number
    my $rfd, $rnd;
    my $rid;

    if (open($rfd, "< /dev/urandom\0") && read($rfd, $rnd, 4) == 4) {
        $rid = unpack("V", $rnd);
    }

    close($rfd) if (defined($rfd));
    return $rid if (defined($rid));

    # This sucks but is better than nothing...
    return ($$+time()) & 0xffffffff;
}

sub get_hex_data() {
    my $mbr = '';
    my $line, $byte;
    while ( $line = <DATA> ) {
        chomp $line;
        last if ($line eq '*');
        foreach $byte ( split(/\s+/, $line) ) {
            $mbr .= chr(hex($byte));
        }
    }
    return $mbr;
}

$is_linux = is_linux();
if ( $is_linux ) {
    # IOCTL numbers
    $BLKRRPART    = 0x125f;
    $BLKGETSIZE   = 0x1260;
}

%opt = ();
@args = ();

while (defined($a = shift(@ARGV))) {
    if ( $a =~ /^\-/ ) {
        foreach $o ( split(//, substr($a,1)) ) {
            $opt{$o} = 1;
            if ($o eq 'i') {
                $id = shift(@ARGV);
            }
        }
    } else {
        push(@args, $a);
    }
}

($file,$c,$h,$s) = @args;
$c += 0;  $h += 0;  $s += 0;

$pentry = 1;
$pentry = 2 if ( $opt{'2'} );
$pentry = 3 if ( $opt{'3'} );
$pentry = 4 if ( $opt{'4'} );

if ( $opt{'z'} ) {
    $h = $h || 64;
    $s = $s || 32;
}

if ( $opt{'M'} && $h && $s ) {
    # Specify size in megabytes, not in cylinders
    $c = ($c*1024*2)/($h*$s);
}

$is_open = 0;

if ( $c == 0 && $file ne '' ) {
    $len = 0;
    if ( sysopen(OUTPUT, $file, O_RDWR, 0666) ) {
        $is_open = 1;

        if ( (@filestat = stat(OUTPUT)) && S_ISREG($filestat[2]) ) {
            $len = $filestat[7] >> 9;
        } elsif ( $is_linux && S_ISBLK($filestat[2]) ) {
            $blksize = pack("L!", 0);
            if ( ioctl(OUTPUT, $BLKGETSIZE, $blksize) == 0 ) {
                $len = unpack("L!", $blksize); # In 512-byte sectors!
            }
        }
    }

    if ( !$len ) {
        print STDERR "$0: $file: don't know how to determine the size of this device\n";
        exit 1;
    }

    $c = $len/($h*$s);
}

if ( $file eq '' || $c < 1 || $h < 1 || $h > 256 || $s < 1 || $s > 63 ) {
    print STDERR "Usage: $0 [-doFMz4][-i id] file c h s (max: 1024 256 63)\n";
    print STDERR "    -d    add DOSEMU header\n";
    print STDERR "    -o    print filesystem offset to stdout\n";
    print STDERR "    -F    format partition as FAT32\n";
    print STDERR "    -M    \"c\" argument is megabytes, calculate cylinders\n";
    print STDERR "    -z    use zipdisk geometry (h=64 s=32)\n";
    print STDERR "    -4    use partition entry 4 (standard for zipdisks)\n";
    print STDERR "    -i    specify the MBR ID\n";
    print STDERR "    -s    output a sparse file (don't allocate all blocks)\n";
    exit 1;
}

if ($c > 1024) {
    print STDERR "Warning: more than 1024 cylinders ($c).\n";
    print STDERR "Not all BIOSes will be able to boot this device.\n";
    $cc = 1024;
} else {
    $cc = $c;
}

$cylsize = $h*$s*512;

if ( !$is_open ) {
    sysopen(OUTPUT, $file, O_CREAT|O_RDWR|O_TRUNC, 0666)
        or die "$0: Cannot open: $file\n";
}
binmode OUTPUT;

# Print out DOSEMU header, if requested
if ( $opt{'d'} ) {
    $emuhdr = "DOSEMU\0" . pack("VVVV", $h, $s, $c, 128);
    $emuhdr .= "\0" x (128 - length($emuhdr));
    print OUTPUT $emuhdr;
}

# Print the MBR and partition table
$mbr = get_hex_data();
if ( length($mbr) > 440 ) {
    die "$0: Bad MBR code\n";
}

$mbr .= "\0" x (440 - length($mbr));
if (defined($id)) {
    $id = to_int($id);
} else {
    $id = get_random();
}
$mbr .= pack("V", $id);         # Offset 440: MBR ID
$mbr .= "\0\0";                 # Offset 446: actual partition table

print OUTPUT $mbr;

# Print partition table
$psize = $c*$h*$s-$s;
$bhead   = ($h > 1) ? 1 : 0;
$bsect   = 1;
$bcyl    = ($h > 1) ? 0 : 1;
$ehead   = $h-1;
$esect   = $s + ((($cc-1) & 0x300) >> 2);
$ecyl    = ($cc-1) & 0xff;
if ( $c > 1024 ) {
    $fstype = 0x0e;
} elsif ( $psize > 65536 ) {
    $fstype = 0x06;
} else {
    $fstype = 0x04;
}
for ( $i = 1 ; $i <= 4 ; $i++ ) {
    if ( $i == $pentry ) {
        print OUTPUT pack("CCCCCCCCVV", 0x80, $bhead, $bsect, $bcyl, $fstype,
                          $ehead, $esect, $ecyl, $s, $psize);
    } else {
        print OUTPUT "\0" x 16;
    }
}
print OUTPUT "\x55\xaa";

# Output blank file
$totalsize = $c*$h*$s;
$tracks    = $c*$h;

# If -s is given, try to simply use truncate...
unless ($opt{'s'} && truncate(OUTPUT, $totalsize)) {
    $track = "\0" x (512*$s);

    # Print fractional track
    print OUTPUT "\0" x (512 * ($s-1));

    for ( $i = 1 ; $i < $tracks ; $i++ ) {
        print OUTPUT $track;
    }
}

# Print mtools temp file
$n = 0;
while ( !defined($tmpdir) ) {
    $tmpdir = "/tmp/mkdiskimage.$$.".($n++);
    if ( !mkdir($tmpdir, 0700) ) {
        die "$0: Failed to make temp directory: $tmpdir\n"
            if ( $! != EEXIST );
        undef $tmpdir;
    }
}

$cfgfile = $tmpdir.'/mtools.conf';
$imglink = $tmpdir.'/disk.img';
die "$0: Failed to create symlink $imglink\n"
    if ( !symlink(absolute_path($file), $imglink) );

$header_size = ($opt{'d'} ? 128 : 0);

# Start of filesystem
$offset = $s*512 + $header_size;

# Start of partition table entry
$pstart = $header_size + 446 + 16*($pentry-1);

open(MCONFIG, "> ${cfgfile}") or die "$0: Cannot make mtools config\n";
print MCONFIG "drive z:\n";
print MCONFIG "file=\"${imglink}\"\n";
print MCONFIG "cylinders=${c}\n";
print MCONFIG "heads=${h}\n";
print MCONFIG "sectors=${s}\n";
print MCONFIG "offset=${offset}\n";
print MCONFIG "mformat_only\n";
close(MCONFIG);

# Output the filesystem offset to stdout if appropriate
if ( $opt{'o'} ) {
    print $offset, "\n";
}

$ENV{'MTOOLSRC'} = $cfgfile;
if ( $opt{'F'} ) {
    system('mformat', '-F', 'z:');
} else {
    system('mformat', 'z:');
}

# Clean up in /tmp
unlink($cfgfile);
unlink($imglink);
rmdir($tmpdir);

# MTOOLS doesn't write the bsHiddenSecs field correctly
seek(OUTPUT, $offset + 0x1c, 0);
print OUTPUT pack("V", ($offset-$header_size)>>9);

# Set the partition type
if ( $opt{'F'} ) {
    if ( $c > 1024 ) {
        $fstype = 0x0c;         # FAT32 LBA
    } else {
        $fstype = 0x0b;
    }
} else {
    if ( $c > 1024 ) {
        $fstype = 0x0e;         # FAT16 LBA
    } elsif ( $psize > 65536 ) {
        $fstype = 0x06;         # FAT16 > 32MB
    } else {
        $fstype = 0x04;         # FAT16 <= 32MB
    }
    seek(OUTPUT, $offset + 0x36, 0);
    read(OUTPUT, $fsname, 8);

    # FAT12: adjust partition type
    if ( $fsname eq 'FAT12   ' ) {
        $fstype = 0x01;         # FAT12
    }
}
seek(OUTPUT, $pstart+4, 0);
print OUTPUT pack("C", $fstype);

flush OUTPUT;

# Just in case this is a block device, try to flush the partition table
if ( $is_linux ) {
    ioctl(OUTPUT, $BLKRRPART, 0);
};

exit 0;
__END__