1========= 2dm-linear 3========= 4 5Device-Mapper's "linear" target maps a linear range of the Device-Mapper 6device onto a linear range of another device. This is the basic building 7block of logical volume managers. 8 9Parameters: <dev path> <offset> 10 <dev path>: 11 Full pathname to the underlying block-device, or a 12 "major:minor" device-number. 13 <offset>: 14 Starting sector within the device. 15 16 17Example scripts 18=============== 19 20:: 21 22 #!/bin/sh 23 # Create an identity mapping for a device 24 echo "0 `blockdev --getsz $1` linear $1 0" | dmsetup create identity 25 26:: 27 28 #!/bin/sh 29 # Join 2 devices together 30 size1=`blockdev --getsz $1` 31 size2=`blockdev --getsz $2` 32 echo "0 $size1 linear $1 0 33 $size1 $size2 linear $2 0" | dmsetup create joined 34 35:: 36 37 #!/usr/bin/perl -w 38 # Split a device into 4M chunks and then join them together in reverse order. 39 40 my $name = "reverse"; 41 my $extent_size = 4 * 1024 * 2; 42 my $dev = $ARGV[0]; 43 my $table = ""; 44 my $count = 0; 45 46 if (!defined($dev)) { 47 die("Please specify a device.\n"); 48 } 49 50 my $dev_size = `blockdev --getsz $dev`; 51 my $extents = int($dev_size / $extent_size) - 52 (($dev_size % $extent_size) ? 1 : 0); 53 54 while ($extents > 0) { 55 my $this_start = $count * $extent_size; 56 $extents--; 57 $count++; 58 my $this_offset = $extents * $extent_size; 59 60 $table .= "$this_start $extent_size linear $dev $this_offset\n"; 61 } 62 63 `echo \"$table\" | dmsetup create $name`; 64