Root/Documentation/device-mapper/linear.txt

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

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