| 1 | =========
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| 2 | dm-linear
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| 3 | =========
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| 4 |
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| 5 | Device-Mapper's "linear" target maps a linear range of the Device-Mapper
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| 6 | device onto a linear range of another device. This is the basic building
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| 7 | block of logical volume managers.
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| 8 |
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| 9 | Parameters: <dev path> <offset>
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| 10 | <dev path>:
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| 11 | Full pathname to the underlying block-device, or a
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| 12 | "major:minor" device-number.
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| 13 | <offset>:
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| 14 | Starting sector within the device.
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| 15 |
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| 16 |
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| 17 | Example scripts
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| 18 | ===============
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| 19 |
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| 20 | ::
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| 21 |
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| 22 | #!/bin/sh
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| 23 | # Create an identity mapping for a device
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| 24 | echo "0 `blockdev --getsz $1` linear $1 0" | dmsetup create identity
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| 25 |
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| 26 | ::
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| 27 |
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| 28 | #!/bin/sh
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| 29 | # Join 2 devices together
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| 30 | size1=`blockdev --getsz $1`
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| 31 | size2=`blockdev --getsz $2`
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| 32 | echo "0 $size1 linear $1 0
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| 33 | $size1 $size2 linear $2 0" | dmsetup create joined
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| 34 |
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| 35 | ::
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| 36 |
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| 37 | #!/usr/bin/perl -w
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| 38 | # Split a device into 4M chunks and then join them together in reverse order.
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| 39 |
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| 40 | my $name = "reverse";
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| 41 | my $extent_size = 4 * 1024 * 2;
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| 42 | my $dev = $ARGV[0];
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| 43 | my $table = "";
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| 44 | my $count = 0;
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| 45 |
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| 46 | if (!defined($dev)) {
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| 47 | die("Please specify a device.\n");
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| 48 | }
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| 49 |
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| 50 | my $dev_size = `blockdev --getsz $dev`;
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| 51 | my $extents = int($dev_size / $extent_size) -
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| 52 | (($dev_size % $extent_size) ? 1 : 0);
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| 53 |
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| 54 | while ($extents > 0) {
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| 55 | my $this_start = $count * $extent_size;
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| 56 | $extents--;
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| 57 | $count++;
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| 58 | my $this_offset = $extents * $extent_size;
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| 59 |
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| 60 | $table .= "$this_start $extent_size linear $dev $this_offset\n";
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| 61 | }
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| 62 |
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| 63 | `echo \"$table\" | dmsetup create $name`;
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