#!/usr/bin/perl

use strict;
use warnings;

use Fcntl qw(:DEFAULT O_ASYNC O_DIRECT);
use Sys::Mmap;

sysopen(my $FH,"./test.dat", 
        O_WRONLY | O_TRUNC | O_CREAT | O_ASYNC | O_DIRECT, 0666)
  or die "Couldn't open\n";

my $BUFSIZE = 1048576;
my $BUFFER;
mmap($BUFFER,$BUFSIZE,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON,
     STDOUT)
  or die "Couldn't mmap\n";

for (my $i = 0; $i < 20480; $i++) {
	my $written = syswrite($FH,$BUFFER,$BUFSIZE);
        die "System write error: $!\n" unless defined $written;
}