Linux Cross Reference
Linux-2.6.17/Documentation/device-mapper/linear.txt

   dm-linear
   =========
   
   Device-Mapper's "linear" target maps a linear range of the Device-Mapper
   device onto a linear range of another device.  This is the basic building
   block of logical volume managers.
   
   Parameters: <dev path> <offset>
       <dev path>: Full pathname to the underlying block-device, or a
                  "major:minor" device-number.
      <offset>: Starting sector within the device.
  
  
  Example scripts
  ===============
  [[
  #!/bin/sh
  # Create an identity mapping for a device
  echo "0 `blockdev --getsize $1` linear $1 0" | dmsetup create identity
  ]]
  
  
  [[
  #!/bin/sh
  # Join 2 devices together
  size1=`blockdev --getsize $1`
  size2=`blockdev --getsize $2`
  echo "0 $size1 linear $1 0
  $size1 $size2 linear $2 0" | dmsetup create joined
  ]]
  
  
  [[
  #!/usr/bin/perl -w
  # Split a device into 4M chunks and then join them together in reverse order.
  
  my $name = "reverse";
  my $extent_size = 4 * 1024 * 2;
  my $dev = $ARGV[0];
  my $table = "";
  my $count = 0;
  
  if (!defined($dev)) {
          die("Please specify a device.\n");
  }
  
  my $dev_size = `blockdev --getsize $dev`;
  my $extents = int($dev_size / $extent_size) -
                (($dev_size % $extent_size) ? 1 : 0);
  
  while ($extents > 0) {
          my $this_start = $count * $extent_size;
          $extents--;
          $count++;
          my $this_offset = $extents * $extent_size;
  
          $table .= "$this_start $extent_size linear $dev $this_offset\n";
  }
  
  `echo \"$table\" | dmsetup create $name`;
  ]]