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- =========
- 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: <dev path> <offset>
- <dev path>:
- Full pathname to the underlying block-device, or a
- "major:minor" device-number.
- <offset>:
- 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`;
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