Kernel-4.18.0-80.el8_linear

dm-linear

Device-Mapper’s “linear” target maps a linear range of the Device-Mapper
device onto a linear range of another device. This is the basic building
block of logical volume managers.

Parameters:
: Full pathname to the underlying block-device, or a
“major:minor” device-number.
: Starting sector within the device.

Example scripts

[[
#!/bin/sh

Create an identity mapping for a device

echo “0 blockdev --getsz $1 linear $1 0” | dmsetup create identity
]]

[[
#!/bin/sh

Join 2 devices together

size1=blockdev --getsz $1
size2=blockdev --getsz $2
echo “0 $size1 linear $1 0
$size1 $size2 linear $2 0” | dmsetup create joined
]]

[[
#!/usr/bin/perl -w

Split a device into 4M chunks and then join them together in reverse order.

my $name = “reverse”;
my $extent_size = 4 * 1024 * 2;
my $dev = $ARGV[0];
my $table = “”;
my $count = 0;

if (!defined($dev)) {
die(“Please specify a device.\n”);
}

my $dev_size = blockdev --getsz $dev;
my $extents = int($dev_size / $extent_size) -
(($dev_size % $extent_size) ? 1 : 0);

while ($extents > 0) {
my $this_start = $count * $extent_size;
$extents–;
$count++;
my $this_offset = $extents * $extent_size;

    $table .= "$this_start $extent_size linear $dev $this_offset\n";

}

echo \"$table\" | dmsetup create $name;
]]