#!/usr/bin/perl

use strict;
use File::Sync qw(fsync);
use Fcntl qw(:DEFAULT O_ASYNC O_DIRECT);

my $device = $ARGV[0];
my $logfn = $ARGV[1];
if (!$logfn)
{
    print "USAGE: perl r20.pl DEVICE LOGFILE\n";
    exit;
}

my $last = {};
my $logfd;
open $logfd, $logfn or die $!;
my $i = 0;
while (my $s = <$logfd>)
{
    $s =~ s/[\x0d\x0a]+$//;
    my ($pos, $hex) = split / /, $s, 2;
    $last->{$pos} = $i++;
}

my $fd;
sysopen $fd, $device, O_RDONLY or die $!;
my $buffer = " " x 4096;
my $fact;
$i = 0;
seek $logfd, 0, 0 or die $!;
while (my $s = <$logfd>)
{
    $s =~ s/[\x0d\x0a]+$//;
    my ($pos, $hex) = split / /, $s, 2;
    next if $last->{$pos} != $i; # only check last overwrite
    $hex = pack("H*", $hex);
    substr($buffer, 0, 4096, ($hex x 512));
    sysseek($fd, $pos*4096, 0) or die $!;
    sysread($fd, $fact, 4096) or die $!;
    if ($fact ne $buffer)
    {
        print "Mismatch at offset $pos*4096 (line $i): ".unpack("H*", substr($fact, 0, 8))." vs ".unpack("H*", $hex)."\n";
    }
    $i++;
}
close $fd;

close $logfd;