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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 18:20:36 -0400
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 18:20:36 -0400
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/device-mapper/linear.txt
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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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]]