========= 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 --getsz $1 linear $1 0" | dmsetup create identity

::

#!/bin/sh

Join 2 devices together

size1=blockdev --getsz $1 size2=blockdev --getsz $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 --getsz $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;