diff --git a/lib/Linux/ExtentsMap.pm b/lib/Linux/ExtentsMap.pm
new file mode 100644
index 0000000..8827ec4
--- /dev/null
+++ b/lib/Linux/ExtentsMap.pm
@@ -0,0 +1,149 @@
+#!/usr/bin/perl
+#
+# Linux::ExtentsMap - Read and Manipulate List of Extents
+#
+# Copyright (C) 2014-2019 Axel Burri
+#
+# 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, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# ---------------------------------------------------------------------
+# The official btrbk website is located at:
+# https://digint.ch/btrbk/
+#
+# Author:
+# Axel Burri <axel@tty0.ch>
+# ---------------------------------------------------------------------
+#
+# Based on work from:
+# Graham Cobb: https://github.com/GrahamCobb/extents-lists
+# ---------------------------------------------------------------------
+
+package Linux::ExtentsMap;
+
+our $blocksize = 4096; # default blocksize
+
+sub new
+{
+  my $class = shift;
+  my $file = shift;
+
+  my $self = {
+    map => defined($file) ? filefrag_extentmap($file) : [],
+  };
+  bless $self, ref($class) || $class;
+  return $self->merge;
+}
+
+
+# returns extents range (unsorted array of [start,end], inclusive) from FIEMAP ioctl
+sub filefrag_extentmap($)
+{
+  my $file = shift || die;
+
+  # NOTE: this returns exitstatus=0 if file is not found, or no files found
+  my $ret = `find '$file' -xdev -type f -print0 | xargs -0 -r filefrag -vs`;
+  return undef unless(defined($ret));
+  return undef if($?);
+
+  my @range;
+  foreach (split(/\n/, $ret))
+  {
+    # get extents start / end
+    push @range, [ $1, $2 ] if(/^\s*[0-9]+:\s*[0-9]+\.\.\s*[0-9]+:\s*([0-9]+)\.\.\s*([0-9]+):/);
+    if(/block of ([0-9]+) bytes/) {
+      die "filefrag reports blocksize=$1 (expected $blocksize) in: $file" if($1 ne $blocksize);
+    }
+  }
+  return \@range;
+}
+
+
+sub total_blocks()
+{
+  my $self = shift;
+  my $count = 0;
+  foreach(@{$self->{map}}) {
+    $count += ($_->[1] - $_->[0] + 1);
+  }
+  return $count;
+}
+
+
+sub size()
+{
+  my $self = shift;
+  my $total_blocks = $self->total_blocks();
+  return $total_blocks * $blocksize;
+}
+
+
+# merge sorted map
+sub merge($)
+{
+  my $self = shift;
+  my @merged;
+  my $start = -1;
+  my $end = -2;
+  foreach (sort { $a->[0] <=> $b->[0] } @{$self->{map}})
+  {
+    if($_->[0] <= $end + 1) {
+      # range overlaps the preceeding one, or is adjacent to it
+      $end = $_->[1] if($_->[1] > $end);
+    }
+    else {
+      push @merged, [ $start, $end ] if($start >= 0);
+      $start = $_->[0];
+      $end = $_->[1];
+    }
+  }
+  push @merged, [ $start, $end ] if($start >= 0);
+  $self->{map} = \@merged;
+  return $self;
+}
+
+
+sub diff($)
+{
+  my $self = shift;
+  my $l = $self->{map};
+  my $r = (shift)->{map};
+  my $i = 0;
+  my $rn = scalar(@$r);
+  my @diff;
+
+  foreach(@$l) {
+    my $l_start = $_->[0];
+    my $l_end   = $_->[1];
+    while(($i < $rn) && ($r->[$i][1] < $l_start)) { # r_end < l_start
+      # advance r to next overlapping
+      $i++;
+    }
+    while(($i < $rn) && ($r->[$i][0] <= $l_end)) { # r_start <= l_end
+      # while overlapping, advance l_start
+      my $r_start = $r->[$i][0];
+      my $r_end   = $r->[$i][1];
+
+      push @diff, [ $l_start, $r_start - 1 ] if($l_start < $r_start);
+      $l_start = $r_end + 1;
+      last if($l_start > $l_end);
+      $i++;
+    }
+    push @diff, [ $l_start, $l_end ] if($l_start <= $l_end);
+  }
+  my $ret = { map => \@diff };
+  bless $ret, ref($self);
+  return $ret;
+}
+
+1;