#!/usr/bin/perl -w
use strict;
use POSIX qw(pause sigaction SA_SIGINFO);

use constant {
    DN_ACCESS	=> 0x00000001,
    DN_MODIFY	=> 0x00000002,
    DN_CREATE	=> 0x00000004,
    DN_DELETE	=> 0x00000008,
    DN_RENAME	=> 0x00000010,
    DN_ATTRIB	=> 0x00000020,
    DN_MULTISHOT=> 0x80000000,

    F_SETSIG	=> 10,
    F_LINUX_SPECIFIC_BASE	=> 1024,
    SIGRTMIN	=> 32,
    SIGRTMAX	=> 64,
};
use constant F_NOTIFY	=> F_LINUX_SPECIFIC_BASE+2;

my $signum = SIGRTMIN+1;
my $dir = "/tmp";
 
my $new_action = 
    POSIX::SigAction->new(sub { print STDERR "Change in $dir"});
$new_action->safe(1);
sigaction($signum, $new_action) || 
    die "Could not sigaction signal $signum: $!";

open(my $fh, "<", "/tmp") || die "Could not open $dir: $!";
fcntl($fh, F_SETSIG, $signum) ||
    die "Could not set IO signal to $signum for $dir: $!";
fcntl($fh, F_NOTIFY, DN_MODIFY|DN_CREATE|DN_DELETE|DN_MULTISHOT) ||
    die "Could not set F_NOTIFY for $dir: $!";
pause while 1;