=========
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dm-linear
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=========
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Device-Mapper's "linear" target maps a linear range of the Device-Mapper
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device onto a linear range of another device. This is the basic building
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block of logical volume managers.
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Parameters: <dev path> <offset>
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<dev path>:
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Full pathname to the underlying block-device, or a
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"major:minor" device-number.
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<offset>:
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Starting sector within the device.
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Example scripts
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===============
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::
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#!/bin/sh
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# Create an identity mapping for a device
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echo "0 `blockdev --getsz $1` linear $1 0" | dmsetup create identity
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::
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#!/bin/sh
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# Join 2 devices together
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size1=`blockdev --getsz $1`
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size2=`blockdev --getsz $2`
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echo "0 $size1 linear $1 0
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$size1 $size2 linear $2 0" | dmsetup create joined
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::
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#!/usr/bin/perl -w
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# Split a device into 4M chunks and then join them together in reverse order.
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my $name = "reverse";
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my $extent_size = 4 * 1024 * 2;
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my $dev = $ARGV[0];
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my $table = "";
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my $count = 0;
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if (!defined($dev)) {
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die("Please specify a device.\n");
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}
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my $dev_size = `blockdev --getsz $dev`;
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my $extents = int($dev_size / $extent_size) -
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(($dev_size % $extent_size) ? 1 : 0);
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while ($extents > 0) {
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my $this_start = $count * $extent_size;
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$extents--;
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$count++;
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my $this_offset = $extents * $extent_size;
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$table .= "$this_start $extent_size linear $dev $this_offset\n";
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}
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`echo \"$table\" | dmsetup create $name`;
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