1 =========
2 dm-linear
3 =========
4
5 Device-Mapper's "linear" target maps a linear range of the Device-Mapper
6 device onto a linear range of another device. This is the basic building
7 block of logical volume managers.
8
9 Parameters: <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
17 Example 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`;
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