From 849369d6c66d3054688672f97d31fceb8e8230fb Mon Sep 17 00:00:00 2001
From: root <root@artemis.panaceas.org>
Date: Fri, 25 Dec 2015 04:40:36 +0000
Subject: initial_commit

---
 Documentation/device-mapper/linear.txt | 61 ++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)
 create mode 100644 Documentation/device-mapper/linear.txt

(limited to 'Documentation/device-mapper/linear.txt')

diff --git a/Documentation/device-mapper/linear.txt b/Documentation/device-mapper/linear.txt
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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 --getsize $1` linear $1 0" | dmsetup create identity
+]]
+
+
+[[
+#!/bin/sh
+# Join 2 devices together
+size1=`blockdev --getsize $1`
+size2=`blockdev --getsize $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 --getsize $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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