1=========
2dm-linear
3=========
4
5Device-Mapper's "linear" target maps a linear range of the Device-Mapper
6device onto a linear range of another device.  This is the basic building
7block of logical volume managers.
8
9Parameters: <dev path> <offset>
10    <dev path>:
11	Full pathname to the underlying block-device, or a
12        "major:minor" device-number.
13    <offset>:
14	Starting sector within the device.
15
16
17Example scripts
18===============
19
20::
21
22  #!/bin/sh
23  # Create an identity mapping for a device
24  echo "0 `blockdev --getsz $1` linear $1 0" | dmsetup create identity
25
26::
27
28  #!/bin/sh
29  # Join 2 devices together
30  size1=`blockdev --getsz $1`
31  size2=`blockdev --getsz $2`
32  echo "0 $size1 linear $1 0
33  $size1 $size2 linear $2 0" | dmsetup create joined
34
35::
36
37  #!/usr/bin/perl -w
38  # Split a device into 4M chunks and then join them together in reverse order.
39
40  my $name = "reverse";
41  my $extent_size = 4 * 1024 * 2;
42  my $dev = $ARGV[0];
43  my $table = "";
44  my $count = 0;
45
46  if (!defined($dev)) {
47          die("Please specify a device.\n");
48  }
49
50  my $dev_size = `blockdev --getsz $dev`;
51  my $extents = int($dev_size / $extent_size) -
52                (($dev_size % $extent_size) ? 1 : 0);
53
54  while ($extents > 0) {
55          my $this_start = $count * $extent_size;
56          $extents--;
57          $count++;
58          my $this_offset = $extents * $extent_size;
59
60          $table .= "$this_start $extent_size linear $dev $this_offset\n";
61  }
62
63  `echo \"$table\" | dmsetup create $name`;
64